[dpdk-dev] [PATCH v4 0/4] doc: changes to abi policy introducing major abi versions

[dpdk-dev] [PATCH v4 0/4] doc: changes to abi policy introducing major abi versions

[Ray Kinsella]

TL;DR abbreviation:
A major ABI version that all DPDK releases during a one year period
support. ABI versioning is managed at a project-level, in place of library-level
management. ABI changes to add new features are permitted, as long as ABI
compatibility with the major ABI version is maintained.

Detail:
This patch introduces major ABI versions, supported for one year and released
aligned with the LTS release. This ABI version is then supported by all
subsequent releases within that one year period. The intention is that the one
year support period, will then be reviewed after the initial year with the
intention of lengthing the support period for the next ABI version.

ABI changes that preserve ABI compatibility with the major ABI version are
permitted in subsequent releases. ABI changes, follow similar approval rules as
before with the additional gate of now requiring technical board approval. The
merging and release of ABI breaking changes would now be pushed to the
declaration of the next major ABI version.

This change encourages developers to maintain ABI compatibility with the major
ABI version, by promoting a permissive culture around those changes that
preserve ABI compatibility. This approach begins to align DPDK with those
projects that declare major ABI versions (e.g. version 2.x, 3.x) and support
those versions for some period, typically two years or more.

To provide an example of how this might work in practice:

 * DPDK v20 is declared as the supported ABI version for one year, aligned with
   the DPDK v19.11 (LTS) release. All library sonames are updated to reflect the
   new ABI version, e.g. librte_eal.so.20, librte_acl.so.20...
 * DPDK v20.02 .. v20.08 releases are ABI compatible with the DPDK v20 ABI. ABI
   changes are permitted from DPDK v20.02 onwards, with the condition that ABI
   compatibility with DPDK v20 is preserved.
 * DPDK v21 is declared as the new supported ABI version for two years, aligned
   with the DPDK v20.11 (LTS) release. The DPDK v20 ABI is now depreciated,
   library sonames are updated to v21 and ABI compatibility breaking changes may
   be introduced.

v4
 * Removed changes to stable.rst, fixed typos and clarified the ABI policy
   "warning".

v3
 * Added myself as the maintainer of the ABI policy.
 * Updated the policy and versioning guides to use the year of the LTS+1 (e.g.
   v20), as the abi major version number.

v2
 * Restructured the patch into 3 patches:
   1. Splits the original versioning document into an ABI policy document
     and ABI versioning document.
   2. Add changes to the policy document introducing major ABI versions.
   3. Fixes up the versioning document in light of major ABI versioning. 
 * Reduces the initial ABI stability from two years to one year, with a review
   after the first year.
 * Adds detail around ABI version handling for experimental libraries.
 * Adds detail around chain of responsility for removing deprecated symbols.

Ray Kinsella (4):
  doc: separate versioning.rst into version and policy
  doc: changes to abi policy introducing major abi versions
  doc: updates to versioning guide for abi versions
  doc: add maintainer for abi policy

 MAINTAINERS                                |   4 +
 doc/guides/contributing/abi_policy.rst     | 308 +++++++++++++++
 doc/guides/contributing/abi_versioning.rst | 515 +++++++++++++++++++++++++
 doc/guides/contributing/index.rst          |   3 +-
 doc/guides/contributing/patches.rst        |   6 +-
 doc/guides/contributing/stable.rst         |  12 +-
 doc/guides/contributing/versioning.rst     | 591 -----------------------------
 doc/guides/rel_notes/deprecation.rst       |   2 +-
 8 files changed, 837 insertions(+), 604 deletions(-)
 create mode 100644 doc/guides/contributing/abi_policy.rst
 create mode 100644 doc/guides/contributing/abi_versioning.rst
 delete mode 100644 doc/guides/contributing/versioning.rst

-- 
2.7.4

[dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Ray Kinsella]

Separate versioning.rst into abi versioning and abi policy guidance, in
preparation for adding more detail to the abi policy.

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
---
 doc/guides/contributing/abi_policy.rst     | 169 +++++++++
 doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
 doc/guides/contributing/index.rst          |   3 +-
 doc/guides/contributing/versioning.rst     | 591 -----------------------------
 4 files changed, 598 insertions(+), 592 deletions(-)
 create mode 100644 doc/guides/contributing/abi_policy.rst
 create mode 100644 doc/guides/contributing/abi_versioning.rst
 delete mode 100644 doc/guides/contributing/versioning.rst

diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
new file mode 100644
index 0000000..55bacb4
--- /dev/null
+++ b/doc/guides/contributing/abi_policy.rst
@@ -0,0 +1,169 @@
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright 2018 The DPDK contributors
+
+.. abi_api_policy:
+
+DPDK ABI/API policy
+===================
+
+Description
+-----------
+
+This document details some methods for handling ABI management in the DPDK.
+
+General Guidelines
+------------------
+
+#. Whenever possible, ABI should be preserved
+#. ABI/API may be changed with a deprecation process
+#. The modification of symbols can generally be managed with versioning
+#. Libraries or APIs marked in ``experimental`` state may change without constraint
+#. New APIs will be marked as ``experimental`` for at least one release to allow
+   any issues found by users of the new API to be fixed quickly
+#. The addition of symbols is generally not problematic
+#. The removal of symbols generally is an ABI break and requires bumping of the
+   LIBABIVER macro
+#. Updates to the minimum hardware requirements, which drop support for hardware which
+   was previously supported, should be treated as an ABI change.
+
+What is an ABI
+~~~~~~~~~~~~~~
+
+An ABI (Application Binary Interface) is the set of runtime interfaces exposed
+by a library. It is similar to an API (Application Programming Interface) but
+is the result of compilation.  It is also effectively cloned when applications
+link to dynamic libraries.  That is to say when an application is compiled to
+link against dynamic libraries, it is assumed that the ABI remains constant
+between the time the application is compiled/linked, and the time that it runs.
+Therefore, in the case of dynamic linking, it is critical that an ABI is
+preserved, or (when modified), done in such a way that the application is unable
+to behave improperly or in an unexpected fashion.
+
+
+ABI/API Deprecation
+-------------------
+
+The DPDK ABI policy
+~~~~~~~~~~~~~~~~~~~
+
+ABI versions are set at the time of major release labeling, and the ABI may
+change multiple times, without warning, between the last release label and the
+HEAD label of the git tree.
+
+ABI versions, once released, are available until such time as their
+deprecation has been noted in the Release Notes for at least one major release
+cycle. For example consider the case where the ABI for DPDK 2.0 has been
+shipped and then a decision is made to modify it during the development of
+DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
+release and the modification will be made available in the DPDK 2.2 release.
+
+ABI versions may be deprecated in whole or in part as needed by a given
+update.
+
+Some ABI changes may be too significant to reasonably maintain multiple
+versions. In those cases ABI's may be updated without backward compatibility
+being provided. The requirements for doing so are:
+
+#. At least 3 acknowledgments of the need to do so must be made on the
+   dpdk.org mailing list.
+
+   - The acknowledgment of the maintainer of the component is mandatory, or if
+     no maintainer is available for the component, the tree/sub-tree maintainer
+     for that component must acknowledge the ABI change instead.
+
+   - It is also recommended that acknowledgments from different "areas of
+     interest" be sought for each deprecation, for example: from NIC vendors,
+     CPU vendors, end-users, etc.
+
+#. The changes (including an alternative map file) can be included with
+   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
+   to provide more details about oncoming changes.
+   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
+   More preferred way to provide this information is sending the feature
+   as a separate patch and reference it in deprecation notice.
+
+#. A full deprecation cycle, as explained above, must be made to offer
+   downstream consumers sufficient warning of the change.
+
+Note that the above process for ABI deprecation should not be undertaken
+lightly. ABI stability is extremely important for downstream consumers of the
+DPDK, especially when distributed in shared object form. Every effort should
+be made to preserve the ABI whenever possible. The ABI should only be changed
+for significant reasons, such as performance enhancements. ABI breakage due to
+changes such as reorganizing public structure fields for aesthetic or
+readability purposes should be avoided.
+
+.. note::
+
+   Updates to the minimum hardware requirements, which drop support for hardware
+   which was previously supported, should be treated as an ABI change, and
+   follow the relevant deprecation policy procedures as above: 3 acks and
+   announcement at least one release in advance.
+
+Examples of Deprecation Notices
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The following are some examples of ABI deprecation notices which would be
+added to the Release Notes:
+
+* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
+  to be replaced with the inline function ``rte_foo()``.
+
+* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
+  in version 2.0. Backwards compatibility will be maintained for this function
+  until the release of version 2.1
+
+* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
+  performance reasons. Existing binary applications will have backwards
+  compatibility in release 2.0, while newly built binaries will need to
+  reference the new structure variant ``struct rte_foo2``. Compatibility will
+  be removed in release 2.2, and all applications will require updating and
+  rebuilding to the new structure at that time, which will be renamed to the
+  original ``struct rte_foo``.
+
+* Significant ABI changes are planned for the ``librte_dostuff`` library. The
+  upcoming release 2.0 will not contain these changes, but release 2.1 will,
+  and no backwards compatibility is planned due to the extensive nature of
+  these changes. Binaries using this library built prior to version 2.1 will
+  require updating and recompilation.
+
+New API replacing previous one
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If a new API proposed functionally replaces an existing one, when the new API
+becomes non-experimental then the old one is marked with ``__rte_deprecated``.
+Deprecated APIs are removed completely just after the next LTS.
+
+Reminder that old API should follow deprecation process to be removed.
+
+
+Experimental APIs
+-----------------
+
+APIs marked as ``experimental`` are not considered part of the ABI and may
+change without warning at any time.  Since changes to APIs are most likely
+immediately after their introduction, as users begin to take advantage of
+those new APIs and start finding issues with them, new DPDK APIs will be
+automatically marked as ``experimental`` to allow for a period of stabilization
+before they become part of a tracked ABI.
+
+Note that marking an API as experimental is a multi step process.
+To mark an API as experimental, the symbols which are desired to be exported
+must be placed in an EXPERIMENTAL version block in the corresponding libraries'
+version map script.
+Secondly, the corresponding prototypes of those exported functions (in the
+development header files), must be marked with the ``__rte_experimental`` tag
+(see ``rte_compat.h``).
+The DPDK build makefiles perform a check to ensure that the map file and the
+C code reflect the same list of symbols.
+This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
+during compilation in the corresponding library Makefile.
+
+In addition to tagging the code with ``__rte_experimental``,
+the doxygen markup must also contain the EXPERIMENTAL string,
+and the MAINTAINERS file should note the EXPERIMENTAL libraries.
+
+For removing the experimental tag associated with an API, deprecation notice
+is not required. Though, an API should remain in experimental state for at least
+one release. Thereafter, normal process of posting patch for review to mailing
+list can be followed.
diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
new file mode 100644
index 0000000..53e6ac0
--- /dev/null
+++ b/doc/guides/contributing/abi_versioning.rst
@@ -0,0 +1,427 @@
+..  SPDX-License-Identifier: BSD-3-Clause
+    Copyright 2018 The DPDK contributors
+
+.. library_versioning:
+
+Library versioning
+------------------
+
+Downstreams might want to provide different DPDK releases at the same time to
+support multiple consumers of DPDK linked against older and newer sonames.
+
+Also due to the interdependencies that DPDK libraries can have applications
+might end up with an executable space in which multiple versions of a library
+are mapped by ld.so.
+
+Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
+depending on LibA.
+
+.. note::
+
+    Application
+    \-> LibA.old
+    \-> LibB.new -> LibA.new
+
+That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
+If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
+library - versions defined in the libraries ``LIBABIVER``.
+An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
+``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
+
+
+ABI versioning
+--------------
+
+Versioning Macros
+~~~~~~~~~~~~~~~~~
+
+When a symbol is exported from a library to provide an API, it also provides a
+calling convention (ABI) that is embodied in its name, return type and
+arguments. Occasionally that function may need to change to accommodate new
+functionality or behavior. When that occurs, it is desirable to allow for
+backward compatibility for a time with older binaries that are dynamically
+linked to the DPDK.
+
+To support backward compatibility the ``rte_compat.h``
+header file provides macros to use when updating exported functions. These
+macros are used in conjunction with the ``rte_<library>_version.map`` file for
+a given library to allow multiple versions of a symbol to exist in a shared
+library so that older binaries need not be immediately recompiled.
+
+The macros exported are:
+
+* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
+  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
+
+* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
+  the linker to bind references to symbol ``b`` to the internal symbol
+  ``b_e``.
+
+* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
+  fully qualified function ``p``, so that if a symbol becomes versioned, it
+  can still be mapped back to the public symbol name.
+
+Examples of ABI Macro use
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Updating a public API
+_____________________
+
+Assume we have a function as follows
+
+.. code-block:: c
+
+ /*
+  * Create an acl context object for apps to
+  * manipulate
+  */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param)
+ {
+        ...
+ }
+
+
+Assume that struct rte_acl_ctx is a private structure, and that a developer
+wishes to enhance the acl api so that a debugging flag can be enabled on a
+per-context basis.  This requires an addition to the structure (which, being
+private, is safe), but it also requires modifying the code as follows
+
+.. code-block:: c
+
+ /*
+  * Create an acl context object for apps to
+  * manipulate
+  */
+ struct rte_acl_ctx *
+ rte_acl_create(const struct rte_acl_param *param, int debug)
+ {
+        ...
+ }
+
+
+Note also that, being a public function, the header file prototype must also be
+changed, as must all the call sites, to reflect the new ABI footprint.  We will
+maintain previous ABI versions that are accessible only to previously compiled
+binaries
+
+The addition of a parameter to the function is ABI breaking as the function is
+public, and existing application may use it in its current form.  However, the
+compatibility macros in DPDK allow a developer to use symbol versioning so that
+multiple functions can be mapped to the same public symbol based on when an
+application was linked to it.  To see how this is done, we start with the
+requisite libraries version map file.  Initially the version map file for the
+acl library looks like this
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_create;
+        rte_acl_dump;
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+This file needs to be modified as follows
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_create;
+        rte_acl_dump;
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+   DPDK_2.1 {
+        global:
+        rte_acl_create;
+
+   } DPDK_2.0;
+
+The addition of the new block tells the linker that a new version node is
+available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
+symbols from the DPDK_2.0 node.  This list is directly translated into a list of
+exported symbols when DPDK is compiled as a shared library
+
+Next, we need to specify in the code which function map to the rte_acl_create
+symbol at which versions.  First, at the site of the initial symbol definition,
+we need to update the function so that it is uniquely named, and not in conflict
+with the public symbol name
+
+.. code-block:: c
+
+  struct rte_acl_ctx *
+ -rte_acl_create(const struct rte_acl_param *param)
+ +rte_acl_create_v20(const struct rte_acl_param *param)
+ {
+        size_t sz;
+        struct rte_acl_ctx *ctx;
+        ...
+
+Note that the base name of the symbol was kept intact, as this is conducive to
+the macros used for versioning symbols.  That is our next step, mapping this new
+symbol name to the initial symbol name at version node 2.0.  Immediately after
+the function, we add this line of code
+
+.. code-block:: c
+
+   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+
+Remembering to also add the rte_compat.h header to the requisite c file where
+these changes are being made.  The above macro instructs the linker to create a
+new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
+builds, but now points to the above newly named function.  We have now mapped
+the original rte_acl_create symbol to the original function (but with a new
+name)
+
+Next, we need to create the 2.1 version of the symbol.  We create a new function
+name, with a different suffix, and  implement it appropriately
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
+   {
+        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
+
+        ctx->debug = debug;
+
+        return ctx;
+   }
+
+This code serves as our new API call.  Its the same as our old call, but adds
+the new parameter in place.  Next we need to map this function to the symbol
+``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
+in the header file, adding the macro there to inform all including applications,
+that on re-link, the default rte_acl_create symbol should point to this
+function.  Note that we could do this by simply naming the function above
+rte_acl_create, and the linker would chose the most recent version tag to apply
+in the version script, but we can also do this in the header file
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   -rte_acl_create(const struct rte_acl_param *param);
+   +rte_acl_create(const struct rte_acl_param *param, int debug);
+   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+
+The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
+header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
+version node to it.  This method is more explicit and flexible than just
+re-implementing the exact symbol name, and allows for other features (such as
+linking to the old symbol version by default, when the new ABI is to be opt-in
+for a period.
+
+One last thing we need to do.  Note that we've taken what was a public symbol,
+and duplicated it into two uniquely and differently named symbols.  We've then
+mapped each of those back to the public symbol ``rte_acl_create`` with different
+version tags.  This only applies to dynamic linking, as static linking has no
+notion of versioning.  That leaves this code in a position of no longer having a
+symbol simply named ``rte_acl_create`` and a static build will fail on that
+missing symbol.
+
+To correct this, we can simply map a function of our choosing back to the public
+symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
+assumption is that the most recent version of the symbol is the one you want to
+map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
+defined, we add this
+
+.. code-block:: c
+
+   struct rte_acl_ctx *
+   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
+   {
+        ...
+   }
+   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
+
+That tells the compiler that, when building a static library, any calls to the
+symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
+
+That's it, on the next shared library rebuild, there will be two versions of
+rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
+and a new DPDK_2.1 version, used by future built applications.
+
+
+Deprecating part of a public API
+________________________________
+
+Lets assume that you've done the above update, and after a few releases have
+passed you decide you would like to retire the old version of the function.
+After having gone through the ABI deprecation announcement process, removal is
+easy.  Start by removing the symbol from the requisite version map file:
+
+.. code-block:: none
+
+   DPDK_2.0 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_dump;
+ -      rte_acl_create
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+   };
+
+   DPDK_2.1 {
+        global:
+        rte_acl_create;
+   } DPDK_2.0;
+
+
+Next remove the corresponding versioned export.
+
+.. code-block:: c
+
+ -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+
+
+Note that the internal function definition could also be removed, but its used
+in our example by the newer version _v21, so we leave it in place.  This is a
+coding style choice.
+
+Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
+indicate to applications doing dynamic linking that this is a later, and
+possibly incompatible library version:
+
+.. code-block:: c
+
+   -LIBABIVER := 1
+   +LIBABIVER := 2
+
+Deprecating an entire ABI version
+_________________________________
+
+While removing a symbol from and ABI may be useful, it is often more practical
+to remove an entire version node at once.  If a version node completely
+specifies an API, then removing part of it, typically makes it incomplete.  In
+those cases it is better to remove the entire node
+
+To do this, start by modifying the version map file, such that all symbols from
+the node to be removed are merged into the next node in the map
+
+In the case of our map above, it would transform to look as follows
+
+.. code-block:: none
+
+   DPDK_2.1 {
+        global:
+
+        rte_acl_add_rules;
+        rte_acl_build;
+        rte_acl_classify;
+        rte_acl_classify_alg;
+        rte_acl_classify_scalar;
+        rte_acl_dump;
+        rte_acl_create
+        rte_acl_find_existing;
+        rte_acl_free;
+        rte_acl_ipv4vlan_add_rules;
+        rte_acl_ipv4vlan_build;
+        rte_acl_list_dump;
+        rte_acl_reset;
+        rte_acl_reset_rules;
+        rte_acl_set_ctx_classify;
+
+        local: *;
+ };
+
+Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
+updated to point to the new version node in any header files for all affected
+symbols.
+
+.. code-block:: c
+
+ -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
+ +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+
+Lastly, any VERSION_SYMBOL macros that point to the old version node should be
+removed, taking care to keep, where need old code in place to support newer
+versions of the symbol.
+
+
+Running the ABI Validator
+-------------------------
+
+The ``devtools`` directory in the DPDK source tree contains a utility program,
+``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
+Compliance Checker
+<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
+
+This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
+utilities which can be installed via a package manager. For example::
+
+   sudo yum install abi-compliance-checker
+   sudo yum install abi-dumper
+
+The syntax of the ``validate-abi.sh`` utility is::
+
+   ./devtools/validate-abi.sh <REV1> <REV2>
+
+Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
+https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
+on the local repo.
+
+For example::
+
+   # Check between the previous and latest commit:
+   ./devtools/validate-abi.sh HEAD~1 HEAD
+
+   # Check on a specific compilation target:
+   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
+
+   # Check between two tags:
+   ./devtools/validate-abi.sh v2.0.0 v2.1.0
+
+   # Check between git master and local topic-branch "vhost-hacking":
+   ./devtools/validate-abi.sh master vhost-hacking
+
+After the validation script completes (it can take a while since it need to
+compile both tags) it will create compatibility reports in the
+``./abi-check/compat_report`` directory. Listed incompatibilities can be found
+as follows::
+
+  grep -lr Incompatible abi-check/compat_reports/
diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
index e2608d3..2fefd91 100644
--- a/doc/guides/contributing/index.rst
+++ b/doc/guides/contributing/index.rst
@@ -10,7 +10,8 @@ Contributor's Guidelines
 
     coding_style
     design
-    versioning
+    abi_policy
+    abi_versioning
     documentation
     patches
     vulnerability
diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
deleted file mode 100644
index 3ab2c43..0000000
--- a/doc/guides/contributing/versioning.rst
+++ /dev/null
@@ -1,591 +0,0 @@
-..  SPDX-License-Identifier: BSD-3-Clause
-    Copyright 2018 The DPDK contributors
-
-DPDK ABI/API policy
-===================
-
-Description
------------
-
-This document details some methods for handling ABI management in the DPDK.
-
-General Guidelines
-------------------
-
-#. Whenever possible, ABI should be preserved
-#. ABI/API may be changed with a deprecation process
-#. The modification of symbols can generally be managed with versioning
-#. Libraries or APIs marked in ``experimental`` state may change without constraint
-#. New APIs will be marked as ``experimental`` for at least one release to allow
-   any issues found by users of the new API to be fixed quickly
-#. The addition of symbols is generally not problematic
-#. The removal of symbols generally is an ABI break and requires bumping of the
-   LIBABIVER macro
-#. Updates to the minimum hardware requirements, which drop support for hardware which
-   was previously supported, should be treated as an ABI change.
-
-What is an ABI
-~~~~~~~~~~~~~~
-
-An ABI (Application Binary Interface) is the set of runtime interfaces exposed
-by a library. It is similar to an API (Application Programming Interface) but
-is the result of compilation.  It is also effectively cloned when applications
-link to dynamic libraries.  That is to say when an application is compiled to
-link against dynamic libraries, it is assumed that the ABI remains constant
-between the time the application is compiled/linked, and the time that it runs.
-Therefore, in the case of dynamic linking, it is critical that an ABI is
-preserved, or (when modified), done in such a way that the application is unable
-to behave improperly or in an unexpected fashion.
-
-
-ABI/API Deprecation
--------------------
-
-The DPDK ABI policy
-~~~~~~~~~~~~~~~~~~~
-
-ABI versions are set at the time of major release labeling, and the ABI may
-change multiple times, without warning, between the last release label and the
-HEAD label of the git tree.
-
-ABI versions, once released, are available until such time as their
-deprecation has been noted in the Release Notes for at least one major release
-cycle. For example consider the case where the ABI for DPDK 2.0 has been
-shipped and then a decision is made to modify it during the development of
-DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
-release and the modification will be made available in the DPDK 2.2 release.
-
-ABI versions may be deprecated in whole or in part as needed by a given
-update.
-
-Some ABI changes may be too significant to reasonably maintain multiple
-versions. In those cases ABI's may be updated without backward compatibility
-being provided. The requirements for doing so are:
-
-#. At least 3 acknowledgments of the need to do so must be made on the
-   dpdk.org mailing list.
-
-   - The acknowledgment of the maintainer of the component is mandatory, or if
-     no maintainer is available for the component, the tree/sub-tree maintainer
-     for that component must acknowledge the ABI change instead.
-
-   - It is also recommended that acknowledgments from different "areas of
-     interest" be sought for each deprecation, for example: from NIC vendors,
-     CPU vendors, end-users, etc.
-
-#. The changes (including an alternative map file) can be included with
-   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
-   to provide more details about oncoming changes.
-   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
-   More preferred way to provide this information is sending the feature
-   as a separate patch and reference it in deprecation notice.
-
-#. A full deprecation cycle, as explained above, must be made to offer
-   downstream consumers sufficient warning of the change.
-
-Note that the above process for ABI deprecation should not be undertaken
-lightly. ABI stability is extremely important for downstream consumers of the
-DPDK, especially when distributed in shared object form. Every effort should
-be made to preserve the ABI whenever possible. The ABI should only be changed
-for significant reasons, such as performance enhancements. ABI breakage due to
-changes such as reorganizing public structure fields for aesthetic or
-readability purposes should be avoided.
-
-.. note::
-
-   Updates to the minimum hardware requirements, which drop support for hardware
-   which was previously supported, should be treated as an ABI change, and
-   follow the relevant deprecation policy procedures as above: 3 acks and
-   announcement at least one release in advance.
-
-Examples of Deprecation Notices
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-The following are some examples of ABI deprecation notices which would be
-added to the Release Notes:
-
-* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
-  to be replaced with the inline function ``rte_foo()``.
-
-* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
-  in version 2.0. Backwards compatibility will be maintained for this function
-  until the release of version 2.1
-
-* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
-  performance reasons. Existing binary applications will have backwards
-  compatibility in release 2.0, while newly built binaries will need to
-  reference the new structure variant ``struct rte_foo2``. Compatibility will
-  be removed in release 2.2, and all applications will require updating and
-  rebuilding to the new structure at that time, which will be renamed to the
-  original ``struct rte_foo``.
-
-* Significant ABI changes are planned for the ``librte_dostuff`` library. The
-  upcoming release 2.0 will not contain these changes, but release 2.1 will,
-  and no backwards compatibility is planned due to the extensive nature of
-  these changes. Binaries using this library built prior to version 2.1 will
-  require updating and recompilation.
-
-New API replacing previous one
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If a new API proposed functionally replaces an existing one, when the new API
-becomes non-experimental then the old one is marked with ``__rte_deprecated``.
-Deprecated APIs are removed completely just after the next LTS.
-
-Reminder that old API should follow deprecation process to be removed.
-
-
-Experimental APIs
------------------
-
-APIs marked as ``experimental`` are not considered part of the ABI and may
-change without warning at any time.  Since changes to APIs are most likely
-immediately after their introduction, as users begin to take advantage of
-those new APIs and start finding issues with them, new DPDK APIs will be
-automatically marked as ``experimental`` to allow for a period of stabilization
-before they become part of a tracked ABI.
-
-Note that marking an API as experimental is a multi step process.
-To mark an API as experimental, the symbols which are desired to be exported
-must be placed in an EXPERIMENTAL version block in the corresponding libraries'
-version map script.
-Secondly, the corresponding prototypes of those exported functions (in the
-development header files), must be marked with the ``__rte_experimental`` tag
-(see ``rte_compat.h``).
-The DPDK build makefiles perform a check to ensure that the map file and the
-C code reflect the same list of symbols.
-This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
-during compilation in the corresponding library Makefile.
-
-In addition to tagging the code with ``__rte_experimental``,
-the doxygen markup must also contain the EXPERIMENTAL string,
-and the MAINTAINERS file should note the EXPERIMENTAL libraries.
-
-For removing the experimental tag associated with an API, deprecation notice
-is not required. Though, an API should remain in experimental state for at least
-one release. Thereafter, normal process of posting patch for review to mailing
-list can be followed.
-
-
-Library versioning
-------------------
-
-Downstreams might want to provide different DPDK releases at the same time to
-support multiple consumers of DPDK linked against older and newer sonames.
-
-Also due to the interdependencies that DPDK libraries can have applications
-might end up with an executable space in which multiple versions of a library
-are mapped by ld.so.
-
-Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
-depending on LibA.
-
-.. note::
-
-    Application
-    \-> LibA.old
-    \-> LibB.new -> LibA.new
-
-That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
-If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
-library - versions defined in the libraries ``LIBABIVER``.
-An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
-``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
-
-
-ABI versioning
---------------
-
-Versioning Macros
-~~~~~~~~~~~~~~~~~
-
-When a symbol is exported from a library to provide an API, it also provides a
-calling convention (ABI) that is embodied in its name, return type and
-arguments. Occasionally that function may need to change to accommodate new
-functionality or behavior. When that occurs, it is desirable to allow for
-backward compatibility for a time with older binaries that are dynamically
-linked to the DPDK.
-
-To support backward compatibility the ``rte_compat.h``
-header file provides macros to use when updating exported functions. These
-macros are used in conjunction with the ``rte_<library>_version.map`` file for
-a given library to allow multiple versions of a symbol to exist in a shared
-library so that older binaries need not be immediately recompiled.
-
-The macros exported are:
-
-* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
-  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
-
-* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
-  the linker to bind references to symbol ``b`` to the internal symbol
-  ``b_e``.
-
-* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
-  fully qualified function ``p``, so that if a symbol becomes versioned, it
-  can still be mapped back to the public symbol name.
-
-Examples of ABI Macro use
-^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Updating a public API
-_____________________
-
-Assume we have a function as follows
-
-.. code-block:: c
-
- /*
-  * Create an acl context object for apps to
-  * manipulate
-  */
- struct rte_acl_ctx *
- rte_acl_create(const struct rte_acl_param *param)
- {
-        ...
- }
-
-
-Assume that struct rte_acl_ctx is a private structure, and that a developer
-wishes to enhance the acl api so that a debugging flag can be enabled on a
-per-context basis.  This requires an addition to the structure (which, being
-private, is safe), but it also requires modifying the code as follows
-
-.. code-block:: c
-
- /*
-  * Create an acl context object for apps to
-  * manipulate
-  */
- struct rte_acl_ctx *
- rte_acl_create(const struct rte_acl_param *param, int debug)
- {
-        ...
- }
-
-
-Note also that, being a public function, the header file prototype must also be
-changed, as must all the call sites, to reflect the new ABI footprint.  We will
-maintain previous ABI versions that are accessible only to previously compiled
-binaries
-
-The addition of a parameter to the function is ABI breaking as the function is
-public, and existing application may use it in its current form.  However, the
-compatibility macros in DPDK allow a developer to use symbol versioning so that
-multiple functions can be mapped to the same public symbol based on when an
-application was linked to it.  To see how this is done, we start with the
-requisite libraries version map file.  Initially the version map file for the
-acl library looks like this
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_create;
-        rte_acl_dump;
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-This file needs to be modified as follows
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_create;
-        rte_acl_dump;
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-   DPDK_2.1 {
-        global:
-        rte_acl_create;
-
-   } DPDK_2.0;
-
-The addition of the new block tells the linker that a new version node is
-available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
-symbols from the DPDK_2.0 node.  This list is directly translated into a list of
-exported symbols when DPDK is compiled as a shared library
-
-Next, we need to specify in the code which function map to the rte_acl_create
-symbol at which versions.  First, at the site of the initial symbol definition,
-we need to update the function so that it is uniquely named, and not in conflict
-with the public symbol name
-
-.. code-block:: c
-
-  struct rte_acl_ctx *
- -rte_acl_create(const struct rte_acl_param *param)
- +rte_acl_create_v20(const struct rte_acl_param *param)
- {
-        size_t sz;
-        struct rte_acl_ctx *ctx;
-        ...
-
-Note that the base name of the symbol was kept intact, as this is conducive to
-the macros used for versioning symbols.  That is our next step, mapping this new
-symbol name to the initial symbol name at version node 2.0.  Immediately after
-the function, we add this line of code
-
-.. code-block:: c
-
-   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
-
-Remembering to also add the rte_compat.h header to the requisite c file where
-these changes are being made.  The above macro instructs the linker to create a
-new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
-builds, but now points to the above newly named function.  We have now mapped
-the original rte_acl_create symbol to the original function (but with a new
-name)
-
-Next, we need to create the 2.1 version of the symbol.  We create a new function
-name, with a different suffix, and  implement it appropriately
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
-   {
-        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
-
-        ctx->debug = debug;
-
-        return ctx;
-   }
-
-This code serves as our new API call.  Its the same as our old call, but adds
-the new parameter in place.  Next we need to map this function to the symbol
-``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
-in the header file, adding the macro there to inform all including applications,
-that on re-link, the default rte_acl_create symbol should point to this
-function.  Note that we could do this by simply naming the function above
-rte_acl_create, and the linker would chose the most recent version tag to apply
-in the version script, but we can also do this in the header file
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   -rte_acl_create(const struct rte_acl_param *param);
-   +rte_acl_create(const struct rte_acl_param *param, int debug);
-   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
-
-The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
-header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
-version node to it.  This method is more explicit and flexible than just
-re-implementing the exact symbol name, and allows for other features (such as
-linking to the old symbol version by default, when the new ABI is to be opt-in
-for a period.
-
-One last thing we need to do.  Note that we've taken what was a public symbol,
-and duplicated it into two uniquely and differently named symbols.  We've then
-mapped each of those back to the public symbol ``rte_acl_create`` with different
-version tags.  This only applies to dynamic linking, as static linking has no
-notion of versioning.  That leaves this code in a position of no longer having a
-symbol simply named ``rte_acl_create`` and a static build will fail on that
-missing symbol.
-
-To correct this, we can simply map a function of our choosing back to the public
-symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
-assumption is that the most recent version of the symbol is the one you want to
-map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
-defined, we add this
-
-.. code-block:: c
-
-   struct rte_acl_ctx *
-   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
-   {
-        ...
-   }
-   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
-
-That tells the compiler that, when building a static library, any calls to the
-symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
-
-That's it, on the next shared library rebuild, there will be two versions of
-rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
-and a new DPDK_2.1 version, used by future built applications.
-
-
-Deprecating part of a public API
-________________________________
-
-Lets assume that you've done the above update, and after a few releases have
-passed you decide you would like to retire the old version of the function.
-After having gone through the ABI deprecation announcement process, removal is
-easy.  Start by removing the symbol from the requisite version map file:
-
-.. code-block:: none
-
-   DPDK_2.0 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_dump;
- -      rte_acl_create
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
-   };
-
-   DPDK_2.1 {
-        global:
-        rte_acl_create;
-   } DPDK_2.0;
-
-
-Next remove the corresponding versioned export.
-
-.. code-block:: c
-
- -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
-
-
-Note that the internal function definition could also be removed, but its used
-in our example by the newer version _v21, so we leave it in place.  This is a
-coding style choice.
-
-Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
-indicate to applications doing dynamic linking that this is a later, and
-possibly incompatible library version:
-
-.. code-block:: c
-
-   -LIBABIVER := 1
-   +LIBABIVER := 2
-
-Deprecating an entire ABI version
-_________________________________
-
-While removing a symbol from and ABI may be useful, it is often more practical
-to remove an entire version node at once.  If a version node completely
-specifies an API, then removing part of it, typically makes it incomplete.  In
-those cases it is better to remove the entire node
-
-To do this, start by modifying the version map file, such that all symbols from
-the node to be removed are merged into the next node in the map
-
-In the case of our map above, it would transform to look as follows
-
-.. code-block:: none
-
-   DPDK_2.1 {
-        global:
-
-        rte_acl_add_rules;
-        rte_acl_build;
-        rte_acl_classify;
-        rte_acl_classify_alg;
-        rte_acl_classify_scalar;
-        rte_acl_dump;
-        rte_acl_create
-        rte_acl_find_existing;
-        rte_acl_free;
-        rte_acl_ipv4vlan_add_rules;
-        rte_acl_ipv4vlan_build;
-        rte_acl_list_dump;
-        rte_acl_reset;
-        rte_acl_reset_rules;
-        rte_acl_set_ctx_classify;
-
-        local: *;
- };
-
-Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
-updated to point to the new version node in any header files for all affected
-symbols.
-
-.. code-block:: c
-
- -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
- +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
-
-Lastly, any VERSION_SYMBOL macros that point to the old version node should be
-removed, taking care to keep, where need old code in place to support newer
-versions of the symbol.
-
-
-Running the ABI Validator
--------------------------
-
-The ``devtools`` directory in the DPDK source tree contains a utility program,
-``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
-Compliance Checker
-<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
-
-This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
-utilities which can be installed via a package manager. For example::
-
-   sudo yum install abi-compliance-checker
-   sudo yum install abi-dumper
-
-The syntax of the ``validate-abi.sh`` utility is::
-
-   ./devtools/validate-abi.sh <REV1> <REV2>
-
-Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
-https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
-on the local repo.
-
-For example::
-
-   # Check between the previous and latest commit:
-   ./devtools/validate-abi.sh HEAD~1 HEAD
-
-   # Check on a specific compilation target:
-   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
-
-   # Check between two tags:
-   ./devtools/validate-abi.sh v2.0.0 v2.1.0
-
-   # Check between git master and local topic-branch "vhost-hacking":
-   ./devtools/validate-abi.sh master vhost-hacking
-
-After the validation script completes (it can take a while since it need to
-compile both tags) it will create compatibility reports in the
-``./abi-check/compat_report`` directory. Listed incompatibilities can be found
-as follows::
-
-  grep -lr Incompatible abi-check/compat_reports/
-- 
2.7.4

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Neil Horman]

On Wed, Sep 25, 2019 at 11:23:53AM +0100, Ray Kinsella wrote:
> Separate versioning.rst into abi versioning and abi policy guidance, in
> preparation for adding more detail to the abi policy.
> 
> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
> ---
>  doc/guides/contributing/abi_policy.rst     | 169 +++++++++
>  doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
>  doc/guides/contributing/index.rst          |   3 +-
>  doc/guides/contributing/versioning.rst     | 591 -----------------------------
>  4 files changed, 598 insertions(+), 592 deletions(-)
>  create mode 100644 doc/guides/contributing/abi_policy.rst
>  create mode 100644 doc/guides/contributing/abi_versioning.rst
>  delete mode 100644 doc/guides/contributing/versioning.rst
> 
> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
> new file mode 100644
> index 0000000..55bacb4
> --- /dev/null
> +++ b/doc/guides/contributing/abi_policy.rst
> @@ -0,0 +1,169 @@
> +..  SPDX-License-Identifier: BSD-3-Clause
> +    Copyright 2018 The DPDK contributors
> +
> +.. abi_api_policy:
> +
> +DPDK ABI/API policy
> +===================
> +
> +Description
> +-----------
> +
> +This document details some methods for handling ABI management in the DPDK.
> +
> +General Guidelines
> +------------------
> +
> +#. Whenever possible, ABI should be preserved
> +#. ABI/API may be changed with a deprecation process
> +#. The modification of symbols can generally be managed with versioning
> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
> +#. New APIs will be marked as ``experimental`` for at least one release to allow
> +   any issues found by users of the new API to be fixed quickly
> +#. The addition of symbols is generally not problematic
> +#. The removal of symbols generally is an ABI break and requires bumping of the
> +   LIBABIVER macro
> +#. Updates to the minimum hardware requirements, which drop support for hardware which
> +   was previously supported, should be treated as an ABI change.
> +
> +What is an ABI
> +~~~~~~~~~~~~~~
> +
> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
> +by a library. It is similar to an API (Application Programming Interface) but
> +is the result of compilation.  It is also effectively cloned when applications
> +link to dynamic libraries.  That is to say when an application is compiled to
> +link against dynamic libraries, it is assumed that the ABI remains constant
> +between the time the application is compiled/linked, and the time that it runs.
> +Therefore, in the case of dynamic linking, it is critical that an ABI is
> +preserved, or (when modified), done in such a way that the application is unable
> +to behave improperly or in an unexpected fashion.
> +
> +
> +ABI/API Deprecation
> +-------------------
> +
> +The DPDK ABI policy
> +~~~~~~~~~~~~~~~~~~~
> +
> +ABI versions are set at the time of major release labeling, and the ABI may
> +change multiple times, without warning, between the last release label and the
> +HEAD label of the git tree.
> +
> +ABI versions, once released, are available until such time as their
> +deprecation has been noted in the Release Notes for at least one major release
> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
> +shipped and then a decision is made to modify it during the development of
> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
> +release and the modification will be made available in the DPDK 2.2 release.
> +
This seems..confusing.  In patch 0:
=================================================================
* DPDK v20 is declared as the supported ABI version for one year, aligned with
   the DPDK v19.11 (LTS) release. All library sonames are updated to reflect the
   new ABI version, e.g. librte_eal.so.20, librte_acl.so.20...
 * DPDK v20.02 .. v20.08 releases are ABI compatible with the DPDK v20 ABI. ABI
   changes are permitted from DPDK v20.02 onwards, with the condition that ABI
   compatibility with DPDK v20 is preserved.
 * DPDK v21 is declared as the new supported ABI version for two years, aligned
   with the DPDK v20.11 (LTS) release. The DPDK v20 ABI is now depreciated,
   library sonames are updated to v21 and ABI compatibility breaking changes may
   be introduced.
===================================================================

Issues I see:
1) We have lots of version numbers floating around here: v20 (referencing an ABI
version I think), DPDK 19.11 (an LTS release that maps to ABI v20), dpdk 20.02..
dpdk 20.08 which can modify the ABI as long as they maintain backwards
compatibility (I think), dpdk v21 (referecing a new ABI that will be supported
at a later release), dpdk 20.11 which guarantees ABI v21, dpdk 2.0 which maps to
abi v20, dpdk 2.1 (a minor release which decides to break ABI), and dpdk 2.2
(a subsequent minor release which adheres to a new abi)

2) Conflicts as to when ABI can be modified in breaking and compatible ways.
Are we allowed to break abi after 1 year, or only in a new major release

I think you need a taxonomy, to clearly deliniate your syntax for noting abi
versions, vs dpdk release major versions, and minor versions, so we are more
clear as to what the docs are referring to, as well as perhaps a timeline to
more clearly illustrate when compatible and incompatible ABI changes are
allowed.

 
> +ABI versions may be deprecated in whole or in part as needed by a given
> +update.
> +
> +Some ABI changes may be too significant to reasonably maintain multiple
> +versions. In those cases ABI's may be updated without backward compatibility
> +being provided. The requirements for doing so are:
> +
> +#. At least 3 acknowledgments of the need to do so must be made on the
> +   dpdk.org mailing list.
> +
> +   - The acknowledgment of the maintainer of the component is mandatory, or if
> +     no maintainer is available for the component, the tree/sub-tree maintainer
> +     for that component must acknowledge the ABI change instead.
> +
> +   - It is also recommended that acknowledgments from different "areas of
> +     interest" be sought for each deprecation, for example: from NIC vendors,
> +     CPU vendors, end-users, etc.
> +
> +#. The changes (including an alternative map file) can be included with
> +   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
> +   to provide more details about oncoming changes.
> +   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
> +   More preferred way to provide this information is sending the feature
> +   as a separate patch and reference it in deprecation notice.
> +
> +#. A full deprecation cycle, as explained above, must be made to offer
> +   downstream consumers sufficient warning of the change.
> +
> +Note that the above process for ABI deprecation should not be undertaken
> +lightly. ABI stability is extremely important for downstream consumers of the
> +DPDK, especially when distributed in shared object form. Every effort should
> +be made to preserve the ABI whenever possible. The ABI should only be changed
> +for significant reasons, such as performance enhancements. ABI breakage due to
> +changes such as reorganizing public structure fields for aesthetic or
> +readability purposes should be avoided.
> +
> +.. note::
> +
> +   Updates to the minimum hardware requirements, which drop support for hardware
> +   which was previously supported, should be treated as an ABI change, and
> +   follow the relevant deprecation policy procedures as above: 3 acks and
> +   announcement at least one release in advance.
> +
> +Examples of Deprecation Notices
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +The following are some examples of ABI deprecation notices which would be
> +added to the Release Notes:
> +
> +* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
> +  to be replaced with the inline function ``rte_foo()``.
> +
> +* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
> +  in version 2.0. Backwards compatibility will be maintained for this function
> +  until the release of version 2.1
> +
> +* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
> +  performance reasons. Existing binary applications will have backwards
> +  compatibility in release 2.0, while newly built binaries will need to
> +  reference the new structure variant ``struct rte_foo2``. Compatibility will
> +  be removed in release 2.2, and all applications will require updating and
> +  rebuilding to the new structure at that time, which will be renamed to the
> +  original ``struct rte_foo``.
> +
> +* Significant ABI changes are planned for the ``librte_dostuff`` library. The
> +  upcoming release 2.0 will not contain these changes, but release 2.1 will,
> +  and no backwards compatibility is planned due to the extensive nature of
> +  these changes. Binaries using this library built prior to version 2.1 will
> +  require updating and recompilation.
> +
> +New API replacing previous one
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +If a new API proposed functionally replaces an existing one, when the new API
> +becomes non-experimental then the old one is marked with ``__rte_deprecated``.
> +Deprecated APIs are removed completely just after the next LTS.
> +
> +Reminder that old API should follow deprecation process to be removed.
> +
> +
> +Experimental APIs
> +-----------------
> +
> +APIs marked as ``experimental`` are not considered part of the ABI and may
> +change without warning at any time.  Since changes to APIs are most likely
> +immediately after their introduction, as users begin to take advantage of
> +those new APIs and start finding issues with them, new DPDK APIs will be
> +automatically marked as ``experimental`` to allow for a period of stabilization
> +before they become part of a tracked ABI.
> +
> +Note that marking an API as experimental is a multi step process.
> +To mark an API as experimental, the symbols which are desired to be exported
> +must be placed in an EXPERIMENTAL version block in the corresponding libraries'
> +version map script.
> +Secondly, the corresponding prototypes of those exported functions (in the
> +development header files), must be marked with the ``__rte_experimental`` tag
> +(see ``rte_compat.h``).
> +The DPDK build makefiles perform a check to ensure that the map file and the
> +C code reflect the same list of symbols.
> +This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
> +during compilation in the corresponding library Makefile.
> +
> +In addition to tagging the code with ``__rte_experimental``,
> +the doxygen markup must also contain the EXPERIMENTAL string,
> +and the MAINTAINERS file should note the EXPERIMENTAL libraries.
> +
> +For removing the experimental tag associated with an API, deprecation notice
> +is not required. Though, an API should remain in experimental state for at least
> +one release. Thereafter, normal process of posting patch for review to mailing
> +list can be followed.
> diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
> new file mode 100644
> index 0000000..53e6ac0
> --- /dev/null
> +++ b/doc/guides/contributing/abi_versioning.rst
> @@ -0,0 +1,427 @@
> +..  SPDX-License-Identifier: BSD-3-Clause
> +    Copyright 2018 The DPDK contributors
> +
> +.. library_versioning:
> +
> +Library versioning
> +------------------
> +
> +Downstreams might want to provide different DPDK releases at the same time to
> +support multiple consumers of DPDK linked against older and newer sonames.
> +
> +Also due to the interdependencies that DPDK libraries can have applications
> +might end up with an executable space in which multiple versions of a library
> +are mapped by ld.so.
> +
> +Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
> +depending on LibA.
> +
> +.. note::
> +
> +    Application
> +    \-> LibA.old
> +    \-> LibB.new -> LibA.new
> +
> +That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
> +If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
> +library - versions defined in the libraries ``LIBABIVER``.
> +An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
> +``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
> +
> +
> +ABI versioning
> +--------------
> +
> +Versioning Macros
> +~~~~~~~~~~~~~~~~~
> +
> +When a symbol is exported from a library to provide an API, it also provides a
> +calling convention (ABI) that is embodied in its name, return type and
> +arguments. Occasionally that function may need to change to accommodate new
> +functionality or behavior. When that occurs, it is desirable to allow for
> +backward compatibility for a time with older binaries that are dynamically
> +linked to the DPDK.
> +
> +To support backward compatibility the ``rte_compat.h``
> +header file provides macros to use when updating exported functions. These
> +macros are used in conjunction with the ``rte_<library>_version.map`` file for
> +a given library to allow multiple versions of a symbol to exist in a shared
> +library so that older binaries need not be immediately recompiled.
> +
> +The macros exported are:
> +
> +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
> +  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
> +
> +* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
> +  the linker to bind references to symbol ``b`` to the internal symbol
> +  ``b_e``.
> +
> +* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
> +  fully qualified function ``p``, so that if a symbol becomes versioned, it
> +  can still be mapped back to the public symbol name.
> +
> +Examples of ABI Macro use
> +^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Updating a public API
> +_____________________
> +
> +Assume we have a function as follows
> +
> +.. code-block:: c
> +
> + /*
> +  * Create an acl context object for apps to
> +  * manipulate
> +  */
> + struct rte_acl_ctx *
> + rte_acl_create(const struct rte_acl_param *param)
> + {
> +        ...
> + }
> +
> +
> +Assume that struct rte_acl_ctx is a private structure, and that a developer
> +wishes to enhance the acl api so that a debugging flag can be enabled on a
> +per-context basis.  This requires an addition to the structure (which, being
> +private, is safe), but it also requires modifying the code as follows
> +
> +.. code-block:: c
> +
> + /*
> +  * Create an acl context object for apps to
> +  * manipulate
> +  */
> + struct rte_acl_ctx *
> + rte_acl_create(const struct rte_acl_param *param, int debug)
> + {
> +        ...
> + }
> +
> +
> +Note also that, being a public function, the header file prototype must also be
> +changed, as must all the call sites, to reflect the new ABI footprint.  We will
> +maintain previous ABI versions that are accessible only to previously compiled
> +binaries
> +
> +The addition of a parameter to the function is ABI breaking as the function is
> +public, and existing application may use it in its current form.  However, the
> +compatibility macros in DPDK allow a developer to use symbol versioning so that
> +multiple functions can be mapped to the same public symbol based on when an
> +application was linked to it.  To see how this is done, we start with the
> +requisite libraries version map file.  Initially the version map file for the
> +acl library looks like this
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_create;
> +        rte_acl_dump;
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +This file needs to be modified as follows
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_create;
> +        rte_acl_dump;
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +   DPDK_2.1 {
> +        global:
> +        rte_acl_create;
> +
> +   } DPDK_2.0;
> +
> +The addition of the new block tells the linker that a new version node is
> +available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
> +symbols from the DPDK_2.0 node.  This list is directly translated into a list of
> +exported symbols when DPDK is compiled as a shared library
> +
> +Next, we need to specify in the code which function map to the rte_acl_create
> +symbol at which versions.  First, at the site of the initial symbol definition,
> +we need to update the function so that it is uniquely named, and not in conflict
> +with the public symbol name
> +
> +.. code-block:: c
> +
> +  struct rte_acl_ctx *
> + -rte_acl_create(const struct rte_acl_param *param)
> + +rte_acl_create_v20(const struct rte_acl_param *param)
> + {
> +        size_t sz;
> +        struct rte_acl_ctx *ctx;
> +        ...
> +
> +Note that the base name of the symbol was kept intact, as this is conducive to
> +the macros used for versioning symbols.  That is our next step, mapping this new
> +symbol name to the initial symbol name at version node 2.0.  Immediately after
> +the function, we add this line of code
> +
> +.. code-block:: c
> +
> +   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> +
> +Remembering to also add the rte_compat.h header to the requisite c file where
> +these changes are being made.  The above macro instructs the linker to create a
> +new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
> +builds, but now points to the above newly named function.  We have now mapped
> +the original rte_acl_create symbol to the original function (but with a new
> +name)
> +
> +Next, we need to create the 2.1 version of the symbol.  We create a new function
> +name, with a different suffix, and  implement it appropriately
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
> +   {
> +        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
> +
> +        ctx->debug = debug;
> +
> +        return ctx;
> +   }
> +
> +This code serves as our new API call.  Its the same as our old call, but adds
> +the new parameter in place.  Next we need to map this function to the symbol
> +``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
> +in the header file, adding the macro there to inform all including applications,
> +that on re-link, the default rte_acl_create symbol should point to this
> +function.  Note that we could do this by simply naming the function above
> +rte_acl_create, and the linker would chose the most recent version tag to apply
> +in the version script, but we can also do this in the header file
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   -rte_acl_create(const struct rte_acl_param *param);
> +   +rte_acl_create(const struct rte_acl_param *param, int debug);
> +   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> +
> +The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
> +header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
> +version node to it.  This method is more explicit and flexible than just
> +re-implementing the exact symbol name, and allows for other features (such as
> +linking to the old symbol version by default, when the new ABI is to be opt-in
> +for a period.
> +
> +One last thing we need to do.  Note that we've taken what was a public symbol,
> +and duplicated it into two uniquely and differently named symbols.  We've then
> +mapped each of those back to the public symbol ``rte_acl_create`` with different
> +version tags.  This only applies to dynamic linking, as static linking has no
> +notion of versioning.  That leaves this code in a position of no longer having a
> +symbol simply named ``rte_acl_create`` and a static build will fail on that
> +missing symbol.
> +
> +To correct this, we can simply map a function of our choosing back to the public
> +symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
> +assumption is that the most recent version of the symbol is the one you want to
> +map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
> +defined, we add this
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
> +   {
> +        ...
> +   }
> +   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
> +
> +That tells the compiler that, when building a static library, any calls to the
> +symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
> +
> +That's it, on the next shared library rebuild, there will be two versions of
> +rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
> +and a new DPDK_2.1 version, used by future built applications.
> +
> +
> +Deprecating part of a public API
> +________________________________
> +
> +Lets assume that you've done the above update, and after a few releases have
> +passed you decide you would like to retire the old version of the function.
> +After having gone through the ABI deprecation announcement process, removal is
> +easy.  Start by removing the symbol from the requisite version map file:
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_dump;
> + -      rte_acl_create
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +   DPDK_2.1 {
> +        global:
> +        rte_acl_create;
> +   } DPDK_2.0;
> +
> +
> +Next remove the corresponding versioned export.
> +
> +.. code-block:: c
> +
> + -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> +
> +
> +Note that the internal function definition could also be removed, but its used
> +in our example by the newer version _v21, so we leave it in place.  This is a
> +coding style choice.
> +
> +Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
> +indicate to applications doing dynamic linking that this is a later, and
> +possibly incompatible library version:
> +
> +.. code-block:: c
> +
> +   -LIBABIVER := 1
> +   +LIBABIVER := 2
> +
> +Deprecating an entire ABI version
> +_________________________________
> +
> +While removing a symbol from and ABI may be useful, it is often more practical
> +to remove an entire version node at once.  If a version node completely
> +specifies an API, then removing part of it, typically makes it incomplete.  In
> +those cases it is better to remove the entire node
> +
> +To do this, start by modifying the version map file, such that all symbols from
> +the node to be removed are merged into the next node in the map
> +
> +In the case of our map above, it would transform to look as follows
> +
> +.. code-block:: none
> +
> +   DPDK_2.1 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_dump;
> +        rte_acl_create
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> + };
> +
> +Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
> +updated to point to the new version node in any header files for all affected
> +symbols.
> +
> +.. code-block:: c
> +
> + -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> +
> +Lastly, any VERSION_SYMBOL macros that point to the old version node should be
> +removed, taking care to keep, where need old code in place to support newer
> +versions of the symbol.
> +
> +
> +Running the ABI Validator
> +-------------------------
> +
> +The ``devtools`` directory in the DPDK source tree contains a utility program,
> +``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
> +Compliance Checker
> +<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
> +
> +This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
> +utilities which can be installed via a package manager. For example::
> +
> +   sudo yum install abi-compliance-checker
> +   sudo yum install abi-dumper
> +
> +The syntax of the ``validate-abi.sh`` utility is::
> +
> +   ./devtools/validate-abi.sh <REV1> <REV2>
> +
> +Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
> +https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
> +on the local repo.
> +
> +For example::
> +
> +   # Check between the previous and latest commit:
> +   ./devtools/validate-abi.sh HEAD~1 HEAD
> +
> +   # Check on a specific compilation target:
> +   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
> +
> +   # Check between two tags:
> +   ./devtools/validate-abi.sh v2.0.0 v2.1.0
> +
> +   # Check between git master and local topic-branch "vhost-hacking":
> +   ./devtools/validate-abi.sh master vhost-hacking
> +
> +After the validation script completes (it can take a while since it need to
> +compile both tags) it will create compatibility reports in the
> +``./abi-check/compat_report`` directory. Listed incompatibilities can be found
> +as follows::
> +
> +  grep -lr Incompatible abi-check/compat_reports/
> diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
> index e2608d3..2fefd91 100644
> --- a/doc/guides/contributing/index.rst
> +++ b/doc/guides/contributing/index.rst
> @@ -10,7 +10,8 @@ Contributor's Guidelines
>  
>      coding_style
>      design
> -    versioning
> +    abi_policy
> +    abi_versioning
>      documentation
>      patches
>      vulnerability
> diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
> deleted file mode 100644
> index 3ab2c43..0000000
> --- a/doc/guides/contributing/versioning.rst
> +++ /dev/null
> @@ -1,591 +0,0 @@
> -..  SPDX-License-Identifier: BSD-3-Clause
> -    Copyright 2018 The DPDK contributors
> -
> -DPDK ABI/API policy
> -===================
> -
> -Description
> ------------
> -
> -This document details some methods for handling ABI management in the DPDK.
> -
> -General Guidelines
> -------------------
> -
> -#. Whenever possible, ABI should be preserved
> -#. ABI/API may be changed with a deprecation process
> -#. The modification of symbols can generally be managed with versioning
> -#. Libraries or APIs marked in ``experimental`` state may change without constraint
> -#. New APIs will be marked as ``experimental`` for at least one release to allow
> -   any issues found by users of the new API to be fixed quickly
> -#. The addition of symbols is generally not problematic
> -#. The removal of symbols generally is an ABI break and requires bumping of the
> -   LIBABIVER macro
> -#. Updates to the minimum hardware requirements, which drop support for hardware which
> -   was previously supported, should be treated as an ABI change.
> -
> -What is an ABI
> -~~~~~~~~~~~~~~
> -
> -An ABI (Application Binary Interface) is the set of runtime interfaces exposed
> -by a library. It is similar to an API (Application Programming Interface) but
> -is the result of compilation.  It is also effectively cloned when applications
> -link to dynamic libraries.  That is to say when an application is compiled to
> -link against dynamic libraries, it is assumed that the ABI remains constant
> -between the time the application is compiled/linked, and the time that it runs.
> -Therefore, in the case of dynamic linking, it is critical that an ABI is
> -preserved, or (when modified), done in such a way that the application is unable
> -to behave improperly or in an unexpected fashion.
> -
> -
> -ABI/API Deprecation
> --------------------
> -
> -The DPDK ABI policy
> -~~~~~~~~~~~~~~~~~~~
> -
> -ABI versions are set at the time of major release labeling, and the ABI may
> -change multiple times, without warning, between the last release label and the
> -HEAD label of the git tree.
> -
> -ABI versions, once released, are available until such time as their
> -deprecation has been noted in the Release Notes for at least one major release
> -cycle. For example consider the case where the ABI for DPDK 2.0 has been
> -shipped and then a decision is made to modify it during the development of
> -DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
> -release and the modification will be made available in the DPDK 2.2 release.
> -
> -ABI versions may be deprecated in whole or in part as needed by a given
> -update.
> -
> -Some ABI changes may be too significant to reasonably maintain multiple
> -versions. In those cases ABI's may be updated without backward compatibility
> -being provided. The requirements for doing so are:
> -
> -#. At least 3 acknowledgments of the need to do so must be made on the
> -   dpdk.org mailing list.
> -
> -   - The acknowledgment of the maintainer of the component is mandatory, or if
> -     no maintainer is available for the component, the tree/sub-tree maintainer
> -     for that component must acknowledge the ABI change instead.
> -
> -   - It is also recommended that acknowledgments from different "areas of
> -     interest" be sought for each deprecation, for example: from NIC vendors,
> -     CPU vendors, end-users, etc.
> -
> -#. The changes (including an alternative map file) can be included with
> -   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
> -   to provide more details about oncoming changes.
> -   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
> -   More preferred way to provide this information is sending the feature
> -   as a separate patch and reference it in deprecation notice.
> -
> -#. A full deprecation cycle, as explained above, must be made to offer
> -   downstream consumers sufficient warning of the change.
> -
> -Note that the above process for ABI deprecation should not be undertaken
> -lightly. ABI stability is extremely important for downstream consumers of the
> -DPDK, especially when distributed in shared object form. Every effort should
> -be made to preserve the ABI whenever possible. The ABI should only be changed
> -for significant reasons, such as performance enhancements. ABI breakage due to
> -changes such as reorganizing public structure fields for aesthetic or
> -readability purposes should be avoided.
> -
> -.. note::
> -
> -   Updates to the minimum hardware requirements, which drop support for hardware
> -   which was previously supported, should be treated as an ABI change, and
> -   follow the relevant deprecation policy procedures as above: 3 acks and
> -   announcement at least one release in advance.
> -
> -Examples of Deprecation Notices
> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -
> -The following are some examples of ABI deprecation notices which would be
> -added to the Release Notes:
> -
> -* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
> -  to be replaced with the inline function ``rte_foo()``.
> -
> -* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
> -  in version 2.0. Backwards compatibility will be maintained for this function
> -  until the release of version 2.1
> -
> -* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
> -  performance reasons. Existing binary applications will have backwards
> -  compatibility in release 2.0, while newly built binaries will need to
> -  reference the new structure variant ``struct rte_foo2``. Compatibility will
> -  be removed in release 2.2, and all applications will require updating and
> -  rebuilding to the new structure at that time, which will be renamed to the
> -  original ``struct rte_foo``.
> -
> -* Significant ABI changes are planned for the ``librte_dostuff`` library. The
> -  upcoming release 2.0 will not contain these changes, but release 2.1 will,
> -  and no backwards compatibility is planned due to the extensive nature of
> -  these changes. Binaries using this library built prior to version 2.1 will
> -  require updating and recompilation.
> -
> -New API replacing previous one
> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -
> -If a new API proposed functionally replaces an existing one, when the new API
> -becomes non-experimental then the old one is marked with ``__rte_deprecated``.
> -Deprecated APIs are removed completely just after the next LTS.
> -
> -Reminder that old API should follow deprecation process to be removed.
> -
> -
> -Experimental APIs
> ------------------
> -
> -APIs marked as ``experimental`` are not considered part of the ABI and may
> -change without warning at any time.  Since changes to APIs are most likely
> -immediately after their introduction, as users begin to take advantage of
> -those new APIs and start finding issues with them, new DPDK APIs will be
> -automatically marked as ``experimental`` to allow for a period of stabilization
> -before they become part of a tracked ABI.
> -
> -Note that marking an API as experimental is a multi step process.
> -To mark an API as experimental, the symbols which are desired to be exported
> -must be placed in an EXPERIMENTAL version block in the corresponding libraries'
> -version map script.
> -Secondly, the corresponding prototypes of those exported functions (in the
> -development header files), must be marked with the ``__rte_experimental`` tag
> -(see ``rte_compat.h``).
> -The DPDK build makefiles perform a check to ensure that the map file and the
> -C code reflect the same list of symbols.
> -This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
> -during compilation in the corresponding library Makefile.
> -
> -In addition to tagging the code with ``__rte_experimental``,
> -the doxygen markup must also contain the EXPERIMENTAL string,
> -and the MAINTAINERS file should note the EXPERIMENTAL libraries.
> -
> -For removing the experimental tag associated with an API, deprecation notice
> -is not required. Though, an API should remain in experimental state for at least
> -one release. Thereafter, normal process of posting patch for review to mailing
> -list can be followed.
> -
> -
> -Library versioning
> -------------------
> -
> -Downstreams might want to provide different DPDK releases at the same time to
> -support multiple consumers of DPDK linked against older and newer sonames.
> -
> -Also due to the interdependencies that DPDK libraries can have applications
> -might end up with an executable space in which multiple versions of a library
> -are mapped by ld.so.
> -
> -Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
> -depending on LibA.
> -
> -.. note::
> -
> -    Application
> -    \-> LibA.old
> -    \-> LibB.new -> LibA.new
> -
> -That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
> -If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
> -library - versions defined in the libraries ``LIBABIVER``.
> -An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
> -``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
> -
> -
> -ABI versioning
> ---------------
> -
> -Versioning Macros
> -~~~~~~~~~~~~~~~~~
> -
> -When a symbol is exported from a library to provide an API, it also provides a
> -calling convention (ABI) that is embodied in its name, return type and
> -arguments. Occasionally that function may need to change to accommodate new
> -functionality or behavior. When that occurs, it is desirable to allow for
> -backward compatibility for a time with older binaries that are dynamically
> -linked to the DPDK.
> -
> -To support backward compatibility the ``rte_compat.h``
> -header file provides macros to use when updating exported functions. These
> -macros are used in conjunction with the ``rte_<library>_version.map`` file for
> -a given library to allow multiple versions of a symbol to exist in a shared
> -library so that older binaries need not be immediately recompiled.
> -
> -The macros exported are:
> -
> -* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
> -  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
> -
> -* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
> -  the linker to bind references to symbol ``b`` to the internal symbol
> -  ``b_e``.
> -
> -* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
> -  fully qualified function ``p``, so that if a symbol becomes versioned, it
> -  can still be mapped back to the public symbol name.
> -
> -Examples of ABI Macro use
> -^^^^^^^^^^^^^^^^^^^^^^^^^
> -
> -Updating a public API
> -_____________________
> -
> -Assume we have a function as follows
> -
> -.. code-block:: c
> -
> - /*
> -  * Create an acl context object for apps to
> -  * manipulate
> -  */
> - struct rte_acl_ctx *
> - rte_acl_create(const struct rte_acl_param *param)
> - {
> -        ...
> - }
> -
> -
> -Assume that struct rte_acl_ctx is a private structure, and that a developer
> -wishes to enhance the acl api so that a debugging flag can be enabled on a
> -per-context basis.  This requires an addition to the structure (which, being
> -private, is safe), but it also requires modifying the code as follows
> -
> -.. code-block:: c
> -
> - /*
> -  * Create an acl context object for apps to
> -  * manipulate
> -  */
> - struct rte_acl_ctx *
> - rte_acl_create(const struct rte_acl_param *param, int debug)
> - {
> -        ...
> - }
> -
> -
> -Note also that, being a public function, the header file prototype must also be
> -changed, as must all the call sites, to reflect the new ABI footprint.  We will
> -maintain previous ABI versions that are accessible only to previously compiled
> -binaries
> -
> -The addition of a parameter to the function is ABI breaking as the function is
> -public, and existing application may use it in its current form.  However, the
> -compatibility macros in DPDK allow a developer to use symbol versioning so that
> -multiple functions can be mapped to the same public symbol based on when an
> -application was linked to it.  To see how this is done, we start with the
> -requisite libraries version map file.  Initially the version map file for the
> -acl library looks like this
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_create;
> -        rte_acl_dump;
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -This file needs to be modified as follows
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_create;
> -        rte_acl_dump;
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -   DPDK_2.1 {
> -        global:
> -        rte_acl_create;
> -
> -   } DPDK_2.0;
> -
> -The addition of the new block tells the linker that a new version node is
> -available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
> -symbols from the DPDK_2.0 node.  This list is directly translated into a list of
> -exported symbols when DPDK is compiled as a shared library
> -
> -Next, we need to specify in the code which function map to the rte_acl_create
> -symbol at which versions.  First, at the site of the initial symbol definition,
> -we need to update the function so that it is uniquely named, and not in conflict
> -with the public symbol name
> -
> -.. code-block:: c
> -
> -  struct rte_acl_ctx *
> - -rte_acl_create(const struct rte_acl_param *param)
> - +rte_acl_create_v20(const struct rte_acl_param *param)
> - {
> -        size_t sz;
> -        struct rte_acl_ctx *ctx;
> -        ...
> -
> -Note that the base name of the symbol was kept intact, as this is conducive to
> -the macros used for versioning symbols.  That is our next step, mapping this new
> -symbol name to the initial symbol name at version node 2.0.  Immediately after
> -the function, we add this line of code
> -
> -.. code-block:: c
> -
> -   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> -
> -Remembering to also add the rte_compat.h header to the requisite c file where
> -these changes are being made.  The above macro instructs the linker to create a
> -new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
> -builds, but now points to the above newly named function.  We have now mapped
> -the original rte_acl_create symbol to the original function (but with a new
> -name)
> -
> -Next, we need to create the 2.1 version of the symbol.  We create a new function
> -name, with a different suffix, and  implement it appropriately
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
> -   {
> -        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
> -
> -        ctx->debug = debug;
> -
> -        return ctx;
> -   }
> -
> -This code serves as our new API call.  Its the same as our old call, but adds
> -the new parameter in place.  Next we need to map this function to the symbol
> -``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
> -in the header file, adding the macro there to inform all including applications,
> -that on re-link, the default rte_acl_create symbol should point to this
> -function.  Note that we could do this by simply naming the function above
> -rte_acl_create, and the linker would chose the most recent version tag to apply
> -in the version script, but we can also do this in the header file
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   -rte_acl_create(const struct rte_acl_param *param);
> -   +rte_acl_create(const struct rte_acl_param *param, int debug);
> -   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> -
> -The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
> -header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
> -version node to it.  This method is more explicit and flexible than just
> -re-implementing the exact symbol name, and allows for other features (such as
> -linking to the old symbol version by default, when the new ABI is to be opt-in
> -for a period.
> -
> -One last thing we need to do.  Note that we've taken what was a public symbol,
> -and duplicated it into two uniquely and differently named symbols.  We've then
> -mapped each of those back to the public symbol ``rte_acl_create`` with different
> -version tags.  This only applies to dynamic linking, as static linking has no
> -notion of versioning.  That leaves this code in a position of no longer having a
> -symbol simply named ``rte_acl_create`` and a static build will fail on that
> -missing symbol.
> -
> -To correct this, we can simply map a function of our choosing back to the public
> -symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
> -assumption is that the most recent version of the symbol is the one you want to
> -map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
> -defined, we add this
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
> -   {
> -        ...
> -   }
> -   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
> -
> -That tells the compiler that, when building a static library, any calls to the
> -symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
> -
> -That's it, on the next shared library rebuild, there will be two versions of
> -rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
> -and a new DPDK_2.1 version, used by future built applications.
> -
> -
> -Deprecating part of a public API
> -________________________________
> -
> -Lets assume that you've done the above update, and after a few releases have
> -passed you decide you would like to retire the old version of the function.
> -After having gone through the ABI deprecation announcement process, removal is
> -easy.  Start by removing the symbol from the requisite version map file:
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_dump;
> - -      rte_acl_create
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -   DPDK_2.1 {
> -        global:
> -        rte_acl_create;
> -   } DPDK_2.0;
> -
> -
> -Next remove the corresponding versioned export.
> -
> -.. code-block:: c
> -
> - -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> -
> -
> -Note that the internal function definition could also be removed, but its used
> -in our example by the newer version _v21, so we leave it in place.  This is a
> -coding style choice.
> -
> -Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
> -indicate to applications doing dynamic linking that this is a later, and
> -possibly incompatible library version:
> -
> -.. code-block:: c
> -
> -   -LIBABIVER := 1
> -   +LIBABIVER := 2
> -
> -Deprecating an entire ABI version
> -_________________________________
> -
> -While removing a symbol from and ABI may be useful, it is often more practical
> -to remove an entire version node at once.  If a version node completely
> -specifies an API, then removing part of it, typically makes it incomplete.  In
> -those cases it is better to remove the entire node
> -
> -To do this, start by modifying the version map file, such that all symbols from
> -the node to be removed are merged into the next node in the map
> -
> -In the case of our map above, it would transform to look as follows
> -
> -.. code-block:: none
> -
> -   DPDK_2.1 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_dump;
> -        rte_acl_create
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> - };
> -
> -Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
> -updated to point to the new version node in any header files for all affected
> -symbols.
> -
> -.. code-block:: c
> -
> - -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> -
> -Lastly, any VERSION_SYMBOL macros that point to the old version node should be
> -removed, taking care to keep, where need old code in place to support newer
> -versions of the symbol.
> -
> -
> -Running the ABI Validator
> --------------------------
> -
> -The ``devtools`` directory in the DPDK source tree contains a utility program,
> -``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
> -Compliance Checker
> -<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
> -
> -This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
> -utilities which can be installed via a package manager. For example::
> -
> -   sudo yum install abi-compliance-checker
> -   sudo yum install abi-dumper
> -
> -The syntax of the ``validate-abi.sh`` utility is::
> -
> -   ./devtools/validate-abi.sh <REV1> <REV2>
> -
> -Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
> -https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
> -on the local repo.
> -
> -For example::
> -
> -   # Check between the previous and latest commit:
> -   ./devtools/validate-abi.sh HEAD~1 HEAD
> -
> -   # Check on a specific compilation target:
> -   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
> -
> -   # Check between two tags:
> -   ./devtools/validate-abi.sh v2.0.0 v2.1.0
> -
> -   # Check between git master and local topic-branch "vhost-hacking":
> -   ./devtools/validate-abi.sh master vhost-hacking
> -
> -After the validation script completes (it can take a while since it need to
> -compile both tags) it will create compatibility reports in the
> -``./abi-check/compat_report`` directory. Listed incompatibilities can be found
> -as follows::
> -
> -  grep -lr Incompatible abi-check/compat_reports/
> -- 
> 2.7.4
> 
> 

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Ray Kinsella]

Hi Neil,

Thanks for the feedback, other comment below.

On 25/09/2019 13:24, Neil Horman wrote:
> On Wed, Sep 25, 2019 at 11:23:53AM +0100, Ray Kinsella wrote:
>> Separate versioning.rst into abi versioning and abi policy guidance, in
>> preparation for adding more detail to the abi policy.
>>
>> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
>> ---
>>  doc/guides/contributing/abi_policy.rst     | 169 +++++++++
>>  doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
>>  doc/guides/contributing/index.rst          |   3 +-
>>  doc/guides/contributing/versioning.rst     | 591 -----------------------------
>>  4 files changed, 598 insertions(+), 592 deletions(-)
>>  create mode 100644 doc/guides/contributing/abi_policy.rst
>>  create mode 100644 doc/guides/contributing/abi_versioning.rst
>>  delete mode 100644 doc/guides/contributing/versioning.rst
>>
>> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
>> new file mode 100644
>> index 0000000..55bacb4
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_policy.rst
>> @@ -0,0 +1,169 @@
>> +..  SPDX-License-Identifier: BSD-3-Clause
>> +    Copyright 2018 The DPDK contributors
>> +
>> +.. abi_api_policy:
>> +
>> +DPDK ABI/API policy
>> +===================
>> +
>> +Description
>> +-----------
>> +
>> +This document details some methods for handling ABI management in the DPDK.
>> +
>> +General Guidelines
>> +------------------
>> +
>> +#. Whenever possible, ABI should be preserved
>> +#. ABI/API may be changed with a deprecation process
>> +#. The modification of symbols can generally be managed with versioning
>> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> +#. New APIs will be marked as ``experimental`` for at least one release to allow
>> +   any issues found by users of the new API to be fixed quickly
>> +#. The addition of symbols is generally not problematic
>> +#. The removal of symbols generally is an ABI break and requires bumping of the
>> +   LIBABIVER macro
>> +#. Updates to the minimum hardware requirements, which drop support for hardware which
>> +   was previously supported, should be treated as an ABI change.
>> +
>> +What is an ABI
>> +~~~~~~~~~~~~~~
>> +
>> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> +by a library. It is similar to an API (Application Programming Interface) but
>> +is the result of compilation.  It is also effectively cloned when applications
>> +link to dynamic libraries.  That is to say when an application is compiled to
>> +link against dynamic libraries, it is assumed that the ABI remains constant
>> +between the time the application is compiled/linked, and the time that it runs.
>> +Therefore, in the case of dynamic linking, it is critical that an ABI is
>> +preserved, or (when modified), done in such a way that the application is unable
>> +to behave improperly or in an unexpected fashion.
>> +
>> +
>> +ABI/API Deprecation
>> +-------------------
>> +
>> +The DPDK ABI policy
>> +~~~~~~~~~~~~~~~~~~~
>> +
>> +ABI versions are set at the time of major release labeling, and the ABI may
>> +change multiple times, without warning, between the last release label and the
>> +HEAD label of the git tree.
>> +
>> +ABI versions, once released, are available until such time as their
>> +deprecation has been noted in the Release Notes for at least one major release
>> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> +shipped and then a decision is made to modify it during the development of
>> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> +release and the modification will be made available in the DPDK 2.2 release.
>> +
> This seems..confusing.  

Agreed, this is from the original policy. I updated all the references
to DPDK 2.0 in the abi_versioning document. Clearly missed these ones,
thanks for that, the text is confusing I will update it.

> In patch 0:
> =================================================================
> * DPDK v20 is declared as the supported ABI version for one year, aligned with
>    the DPDK v19.11 (LTS) release. All library sonames are updated to reflect the
>    new ABI version, e.g. librte_eal.so.20, librte_acl.so.20...
>  * DPDK v20.02 .. v20.08 releases are ABI compatible with the DPDK v20 ABI. ABI
>    changes are permitted from DPDK v20.02 onwards, with the condition that ABI
>    compatibility with DPDK v20 is preserved.
>  * DPDK v21 is declared as the new supported ABI version for two years, aligned
>    with the DPDK v20.11 (LTS) release. The DPDK v20 ABI is now depreciated,
>    library sonames are updated to v21 and ABI compatibility breaking changes may
>    be introduced.
> ===================================================================
> 
> Issues I see:
> 1) We have lots of version numbers floating around here: 

> v20 (referencing an ABI version I think), 
yes

> DPDK 19.11 (an LTS release that maps to ABI v20), dpdk 20.02..
yes

> dpdk 20.08 which can modify the ABI as long as they maintain backwards compatibility (I think)
yes

> dpdk v21 (referecing a new ABI that will be supported at a later release), 
yes

> dpdk 20.11 which guarantees ABI v21, 

yes, and depreciates v20

> dpdk 2.0 which maps to
> abi v20, dpdk 2.1 (a minor release which decides to break ABI), and dpdk 2.2
> (a subsequent minor release which adheres to a new abi)

references to 2.x should be removed.

> 2) Conflicts as to when ABI can be modified in breaking and compatible ways.
> Are we allowed to break abi after 1 year, or only in a new major release

ABI breaking is permitted at the declaration of a new major release, at
the moment, aligned with the LTS. Other than, aligned with the quarterly
releases, only in compatible ways.

> 
> I think you need a taxonomy, to clearly deliniate your syntax for noting abi
> versions, vs dpdk release major versions, and minor versions, so we are more
> clear as to what the docs are referring to, as well as perhaps a timeline to
> more clearly illustrate when compatible and incompatible ABI changes are
> allowed.

I agree - I think a diagram would even better.
I have a good starting point for this.

> 
>  
>> +ABI versions may be deprecated in whole or in part as needed by a given
>> +update.
>> +
>> +Some ABI changes may be too significant to reasonably maintain multiple
>> +versions. In those cases ABI's may be updated without backward compatibility
>> +being provided. The requirements for doing so are:
>> +
>> +#. At least 3 acknowledgments of the need to do so must be made on the
>> +   dpdk.org mailing list.
>> +
>> +   - The acknowledgment of the maintainer of the component is mandatory, or if
>> +     no maintainer is available for the component, the tree/sub-tree maintainer
>> +     for that component must acknowledge the ABI change instead.
>> +
>> +   - It is also recommended that acknowledgments from different "areas of
>> +     interest" be sought for each deprecation, for example: from NIC vendors,
>> +     CPU vendors, end-users, etc.
>> +
>> +#. The changes (including an alternative map file) can be included with
>> +   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> +   to provide more details about oncoming changes.
>> +   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> +   More preferred way to provide this information is sending the feature
>> +   as a separate patch and reference it in deprecation notice.
>> +
>> +#. A full deprecation cycle, as explained above, must be made to offer
>> +   downstream consumers sufficient warning of the change.
>> +
>> +Note that the above process for ABI deprecation should not be undertaken
>> +lightly. ABI stability is extremely important for downstream consumers of the
>> +DPDK, especially when distributed in shared object form. Every effort should
>> +be made to preserve the ABI whenever possible. The ABI should only be changed
>> +for significant reasons, such as performance enhancements. ABI breakage due to
>> +changes such as reorganizing public structure fields for aesthetic or
>> +readability purposes should be avoided.
>> +
>> +.. note::
>> +
>> +   Updates to the minimum hardware requirements, which drop support for hardware
>> +   which was previously supported, should be treated as an ABI change, and
>> +   follow the relevant deprecation policy procedures as above: 3 acks and
>> +   announcement at least one release in advance.
>> +
>> +Examples of Deprecation Notices
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +The following are some examples of ABI deprecation notices which would be
>> +added to the Release Notes:
>> +
>> +* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> +  to be replaced with the inline function ``rte_foo()``.
>> +
>> +* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> +  in version 2.0. Backwards compatibility will be maintained for this function
>> +  until the release of version 2.1
>> +
>> +* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> +  performance reasons. Existing binary applications will have backwards
>> +  compatibility in release 2.0, while newly built binaries will need to
>> +  reference the new structure variant ``struct rte_foo2``. Compatibility will
>> +  be removed in release 2.2, and all applications will require updating and
>> +  rebuilding to the new structure at that time, which will be renamed to the
>> +  original ``struct rte_foo``.
>> +
>> +* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> +  upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> +  and no backwards compatibility is planned due to the extensive nature of
>> +  these changes. Binaries using this library built prior to version 2.1 will
>> +  require updating and recompilation.
>> +
>> +New API replacing previous one
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +If a new API proposed functionally replaces an existing one, when the new API
>> +becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> +Deprecated APIs are removed completely just after the next LTS.
>> +
>> +Reminder that old API should follow deprecation process to be removed.
>> +
>> +
>> +Experimental APIs
>> +-----------------
>> +
>> +APIs marked as ``experimental`` are not considered part of the ABI and may
>> +change without warning at any time.  Since changes to APIs are most likely
>> +immediately after their introduction, as users begin to take advantage of
>> +those new APIs and start finding issues with them, new DPDK APIs will be
>> +automatically marked as ``experimental`` to allow for a period of stabilization
>> +before they become part of a tracked ABI.
>> +
>> +Note that marking an API as experimental is a multi step process.
>> +To mark an API as experimental, the symbols which are desired to be exported
>> +must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> +version map script.
>> +Secondly, the corresponding prototypes of those exported functions (in the
>> +development header files), must be marked with the ``__rte_experimental`` tag
>> +(see ``rte_compat.h``).
>> +The DPDK build makefiles perform a check to ensure that the map file and the
>> +C code reflect the same list of symbols.
>> +This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> +during compilation in the corresponding library Makefile.
>> +
>> +In addition to tagging the code with ``__rte_experimental``,
>> +the doxygen markup must also contain the EXPERIMENTAL string,
>> +and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> +
>> +For removing the experimental tag associated with an API, deprecation notice
>> +is not required. Though, an API should remain in experimental state for at least
>> +one release. Thereafter, normal process of posting patch for review to mailing
>> +list can be followed.
>> diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
>> new file mode 100644
>> index 0000000..53e6ac0
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_versioning.rst
>> @@ -0,0 +1,427 @@
>> +..  SPDX-License-Identifier: BSD-3-Clause
>> +    Copyright 2018 The DPDK contributors
>> +
>> +.. library_versioning:
>> +
>> +Library versioning
>> +------------------
>> +
>> +Downstreams might want to provide different DPDK releases at the same time to
>> +support multiple consumers of DPDK linked against older and newer sonames.
>> +
>> +Also due to the interdependencies that DPDK libraries can have applications
>> +might end up with an executable space in which multiple versions of a library
>> +are mapped by ld.so.
>> +
>> +Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> +depending on LibA.
>> +
>> +.. note::
>> +
>> +    Application
>> +    \-> LibA.old
>> +    \-> LibB.new -> LibA.new
>> +
>> +That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> +If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> +library - versions defined in the libraries ``LIBABIVER``.
>> +An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> +``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> +
>> +
>> +ABI versioning
>> +--------------
>> +
>> +Versioning Macros
>> +~~~~~~~~~~~~~~~~~
>> +
>> +When a symbol is exported from a library to provide an API, it also provides a
>> +calling convention (ABI) that is embodied in its name, return type and
>> +arguments. Occasionally that function may need to change to accommodate new
>> +functionality or behavior. When that occurs, it is desirable to allow for
>> +backward compatibility for a time with older binaries that are dynamically
>> +linked to the DPDK.
>> +
>> +To support backward compatibility the ``rte_compat.h``
>> +header file provides macros to use when updating exported functions. These
>> +macros are used in conjunction with the ``rte_<library>_version.map`` file for
>> +a given library to allow multiple versions of a symbol to exist in a shared
>> +library so that older binaries need not be immediately recompiled.
>> +
>> +The macros exported are:
>> +
>> +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> +  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
>> +
>> +* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> +  the linker to bind references to symbol ``b`` to the internal symbol
>> +  ``b_e``.
>> +
>> +* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> +  fully qualified function ``p``, so that if a symbol becomes versioned, it
>> +  can still be mapped back to the public symbol name.
>> +
>> +Examples of ABI Macro use
>> +^^^^^^^^^^^^^^^^^^^^^^^^^
>> +
>> +Updating a public API
>> +_____________________
>> +
>> +Assume we have a function as follows
>> +
>> +.. code-block:: c
>> +
>> + /*
>> +  * Create an acl context object for apps to
>> +  * manipulate
>> +  */
>> + struct rte_acl_ctx *
>> + rte_acl_create(const struct rte_acl_param *param)
>> + {
>> +        ...
>> + }
>> +
>> +
>> +Assume that struct rte_acl_ctx is a private structure, and that a developer
>> +wishes to enhance the acl api so that a debugging flag can be enabled on a
>> +per-context basis.  This requires an addition to the structure (which, being
>> +private, is safe), but it also requires modifying the code as follows
>> +
>> +.. code-block:: c
>> +
>> + /*
>> +  * Create an acl context object for apps to
>> +  * manipulate
>> +  */
>> + struct rte_acl_ctx *
>> + rte_acl_create(const struct rte_acl_param *param, int debug)
>> + {
>> +        ...
>> + }
>> +
>> +
>> +Note also that, being a public function, the header file prototype must also be
>> +changed, as must all the call sites, to reflect the new ABI footprint.  We will
>> +maintain previous ABI versions that are accessible only to previously compiled
>> +binaries
>> +
>> +The addition of a parameter to the function is ABI breaking as the function is
>> +public, and existing application may use it in its current form.  However, the
>> +compatibility macros in DPDK allow a developer to use symbol versioning so that
>> +multiple functions can be mapped to the same public symbol based on when an
>> +application was linked to it.  To see how this is done, we start with the
>> +requisite libraries version map file.  Initially the version map file for the
>> +acl library looks like this
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_create;
>> +        rte_acl_dump;
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +This file needs to be modified as follows
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_create;
>> +        rte_acl_dump;
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +        rte_acl_create;
>> +
>> +   } DPDK_2.0;
>> +
>> +The addition of the new block tells the linker that a new version node is
>> +available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> +symbols from the DPDK_2.0 node.  This list is directly translated into a list of
>> +exported symbols when DPDK is compiled as a shared library
>> +
>> +Next, we need to specify in the code which function map to the rte_acl_create
>> +symbol at which versions.  First, at the site of the initial symbol definition,
>> +we need to update the function so that it is uniquely named, and not in conflict
>> +with the public symbol name
>> +
>> +.. code-block:: c
>> +
>> +  struct rte_acl_ctx *
>> + -rte_acl_create(const struct rte_acl_param *param)
>> + +rte_acl_create_v20(const struct rte_acl_param *param)
>> + {
>> +        size_t sz;
>> +        struct rte_acl_ctx *ctx;
>> +        ...
>> +
>> +Note that the base name of the symbol was kept intact, as this is conducive to
>> +the macros used for versioning symbols.  That is our next step, mapping this new
>> +symbol name to the initial symbol name at version node 2.0.  Immediately after
>> +the function, we add this line of code
>> +
>> +.. code-block:: c
>> +
>> +   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +Remembering to also add the rte_compat.h header to the requisite c file where
>> +these changes are being made.  The above macro instructs the linker to create a
>> +new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
>> +builds, but now points to the above newly named function.  We have now mapped
>> +the original rte_acl_create symbol to the original function (but with a new
>> +name)
>> +
>> +Next, we need to create the 2.1 version of the symbol.  We create a new function
>> +name, with a different suffix, and  implement it appropriately
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> +   {
>> +        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> +
>> +        ctx->debug = debug;
>> +
>> +        return ctx;
>> +   }
>> +
>> +This code serves as our new API call.  Its the same as our old call, but adds
>> +the new parameter in place.  Next we need to map this function to the symbol
>> +``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
>> +in the header file, adding the macro there to inform all including applications,
>> +that on re-link, the default rte_acl_create symbol should point to this
>> +function.  Note that we could do this by simply naming the function above
>> +rte_acl_create, and the linker would chose the most recent version tag to apply
>> +in the version script, but we can also do this in the header file
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   -rte_acl_create(const struct rte_acl_param *param);
>> +   +rte_acl_create(const struct rte_acl_param *param, int debug);
>> +   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
>> +header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
>> +version node to it.  This method is more explicit and flexible than just
>> +re-implementing the exact symbol name, and allows for other features (such as
>> +linking to the old symbol version by default, when the new ABI is to be opt-in
>> +for a period.
>> +
>> +One last thing we need to do.  Note that we've taken what was a public symbol,
>> +and duplicated it into two uniquely and differently named symbols.  We've then
>> +mapped each of those back to the public symbol ``rte_acl_create`` with different
>> +version tags.  This only applies to dynamic linking, as static linking has no
>> +notion of versioning.  That leaves this code in a position of no longer having a
>> +symbol simply named ``rte_acl_create`` and a static build will fail on that
>> +missing symbol.
>> +
>> +To correct this, we can simply map a function of our choosing back to the public
>> +symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
>> +assumption is that the most recent version of the symbol is the one you want to
>> +map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
>> +defined, we add this
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
>> +   {
>> +        ...
>> +   }
>> +   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
>> +
>> +That tells the compiler that, when building a static library, any calls to the
>> +symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
>> +
>> +That's it, on the next shared library rebuild, there will be two versions of
>> +rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> +and a new DPDK_2.1 version, used by future built applications.
>> +
>> +
>> +Deprecating part of a public API
>> +________________________________
>> +
>> +Lets assume that you've done the above update, and after a few releases have
>> +passed you decide you would like to retire the old version of the function.
>> +After having gone through the ABI deprecation announcement process, removal is
>> +easy.  Start by removing the symbol from the requisite version map file:
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_dump;
>> + -      rte_acl_create
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +        rte_acl_create;
>> +   } DPDK_2.0;
>> +
>> +
>> +Next remove the corresponding versioned export.
>> +
>> +.. code-block:: c
>> +
>> + -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +
>> +Note that the internal function definition could also be removed, but its used
>> +in our example by the newer version _v21, so we leave it in place.  This is a
>> +coding style choice.
>> +
>> +Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> +indicate to applications doing dynamic linking that this is a later, and
>> +possibly incompatible library version:
>> +
>> +.. code-block:: c
>> +
>> +   -LIBABIVER := 1
>> +   +LIBABIVER := 2
>> +
>> +Deprecating an entire ABI version
>> +_________________________________
>> +
>> +While removing a symbol from and ABI may be useful, it is often more practical
>> +to remove an entire version node at once.  If a version node completely
>> +specifies an API, then removing part of it, typically makes it incomplete.  In
>> +those cases it is better to remove the entire node
>> +
>> +To do this, start by modifying the version map file, such that all symbols from
>> +the node to be removed are merged into the next node in the map
>> +
>> +In the case of our map above, it would transform to look as follows
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_dump;
>> +        rte_acl_create
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> + };
>> +
>> +Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> +updated to point to the new version node in any header files for all affected
>> +symbols.
>> +
>> +.. code-block:: c
>> +
>> + -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +Lastly, any VERSION_SYMBOL macros that point to the old version node should be
>> +removed, taking care to keep, where need old code in place to support newer
>> +versions of the symbol.
>> +
>> +
>> +Running the ABI Validator
>> +-------------------------
>> +
>> +The ``devtools`` directory in the DPDK source tree contains a utility program,
>> +``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
>> +Compliance Checker
>> +<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
>> +
>> +This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
>> +utilities which can be installed via a package manager. For example::
>> +
>> +   sudo yum install abi-compliance-checker
>> +   sudo yum install abi-dumper
>> +
>> +The syntax of the ``validate-abi.sh`` utility is::
>> +
>> +   ./devtools/validate-abi.sh <REV1> <REV2>
>> +
>> +Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
>> +https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
>> +on the local repo.
>> +
>> +For example::
>> +
>> +   # Check between the previous and latest commit:
>> +   ./devtools/validate-abi.sh HEAD~1 HEAD
>> +
>> +   # Check on a specific compilation target:
>> +   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
>> +
>> +   # Check between two tags:
>> +   ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> +
>> +   # Check between git master and local topic-branch "vhost-hacking":
>> +   ./devtools/validate-abi.sh master vhost-hacking
>> +
>> +After the validation script completes (it can take a while since it need to
>> +compile both tags) it will create compatibility reports in the
>> +``./abi-check/compat_report`` directory. Listed incompatibilities can be found
>> +as follows::
>> +
>> +  grep -lr Incompatible abi-check/compat_reports/
>> diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
>> index e2608d3..2fefd91 100644
>> --- a/doc/guides/contributing/index.rst
>> +++ b/doc/guides/contributing/index.rst
>> @@ -10,7 +10,8 @@ Contributor's Guidelines
>>  
>>      coding_style
>>      design
>> -    versioning
>> +    abi_policy
>> +    abi_versioning
>>      documentation
>>      patches
>>      vulnerability
>> diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
>> deleted file mode 100644
>> index 3ab2c43..0000000
>> --- a/doc/guides/contributing/versioning.rst
>> +++ /dev/null
>> @@ -1,591 +0,0 @@
>> -..  SPDX-License-Identifier: BSD-3-Clause
>> -    Copyright 2018 The DPDK contributors
>> -
>> -DPDK ABI/API policy
>> -===================
>> -
>> -Description
>> ------------
>> -
>> -This document details some methods for handling ABI management in the DPDK.
>> -
>> -General Guidelines
>> -------------------
>> -
>> -#. Whenever possible, ABI should be preserved
>> -#. ABI/API may be changed with a deprecation process
>> -#. The modification of symbols can generally be managed with versioning
>> -#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> -#. New APIs will be marked as ``experimental`` for at least one release to allow
>> -   any issues found by users of the new API to be fixed quickly
>> -#. The addition of symbols is generally not problematic
>> -#. The removal of symbols generally is an ABI break and requires bumping of the
>> -   LIBABIVER macro
>> -#. Updates to the minimum hardware requirements, which drop support for hardware which
>> -   was previously supported, should be treated as an ABI change.
>> -
>> -What is an ABI
>> -~~~~~~~~~~~~~~
>> -
>> -An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> -by a library. It is similar to an API (Application Programming Interface) but
>> -is the result of compilation.  It is also effectively cloned when applications
>> -link to dynamic libraries.  That is to say when an application is compiled to
>> -link against dynamic libraries, it is assumed that the ABI remains constant
>> -between the time the application is compiled/linked, and the time that it runs.
>> -Therefore, in the case of dynamic linking, it is critical that an ABI is
>> -preserved, or (when modified), done in such a way that the application is unable
>> -to behave improperly or in an unexpected fashion.
>> -
>> -
>> -ABI/API Deprecation
>> --------------------
>> -
>> -The DPDK ABI policy
>> -~~~~~~~~~~~~~~~~~~~
>> -
>> -ABI versions are set at the time of major release labeling, and the ABI may
>> -change multiple times, without warning, between the last release label and the
>> -HEAD label of the git tree.
>> -
>> -ABI versions, once released, are available until such time as their
>> -deprecation has been noted in the Release Notes for at least one major release
>> -cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> -shipped and then a decision is made to modify it during the development of
>> -DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> -release and the modification will be made available in the DPDK 2.2 release.
>> -
>> -ABI versions may be deprecated in whole or in part as needed by a given
>> -update.
>> -
>> -Some ABI changes may be too significant to reasonably maintain multiple
>> -versions. In those cases ABI's may be updated without backward compatibility
>> -being provided. The requirements for doing so are:
>> -
>> -#. At least 3 acknowledgments of the need to do so must be made on the
>> -   dpdk.org mailing list.
>> -
>> -   - The acknowledgment of the maintainer of the component is mandatory, or if
>> -     no maintainer is available for the component, the tree/sub-tree maintainer
>> -     for that component must acknowledge the ABI change instead.
>> -
>> -   - It is also recommended that acknowledgments from different "areas of
>> -     interest" be sought for each deprecation, for example: from NIC vendors,
>> -     CPU vendors, end-users, etc.
>> -
>> -#. The changes (including an alternative map file) can be included with
>> -   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> -   to provide more details about oncoming changes.
>> -   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> -   More preferred way to provide this information is sending the feature
>> -   as a separate patch and reference it in deprecation notice.
>> -
>> -#. A full deprecation cycle, as explained above, must be made to offer
>> -   downstream consumers sufficient warning of the change.
>> -
>> -Note that the above process for ABI deprecation should not be undertaken
>> -lightly. ABI stability is extremely important for downstream consumers of the
>> -DPDK, especially when distributed in shared object form. Every effort should
>> -be made to preserve the ABI whenever possible. The ABI should only be changed
>> -for significant reasons, such as performance enhancements. ABI breakage due to
>> -changes such as reorganizing public structure fields for aesthetic or
>> -readability purposes should be avoided.
>> -
>> -.. note::
>> -
>> -   Updates to the minimum hardware requirements, which drop support for hardware
>> -   which was previously supported, should be treated as an ABI change, and
>> -   follow the relevant deprecation policy procedures as above: 3 acks and
>> -   announcement at least one release in advance.
>> -
>> -Examples of Deprecation Notices
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -The following are some examples of ABI deprecation notices which would be
>> -added to the Release Notes:
>> -
>> -* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> -  to be replaced with the inline function ``rte_foo()``.
>> -
>> -* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> -  in version 2.0. Backwards compatibility will be maintained for this function
>> -  until the release of version 2.1
>> -
>> -* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> -  performance reasons. Existing binary applications will have backwards
>> -  compatibility in release 2.0, while newly built binaries will need to
>> -  reference the new structure variant ``struct rte_foo2``. Compatibility will
>> -  be removed in release 2.2, and all applications will require updating and
>> -  rebuilding to the new structure at that time, which will be renamed to the
>> -  original ``struct rte_foo``.
>> -
>> -* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> -  upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> -  and no backwards compatibility is planned due to the extensive nature of
>> -  these changes. Binaries using this library built prior to version 2.1 will
>> -  require updating and recompilation.
>> -
>> -New API replacing previous one
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -If a new API proposed functionally replaces an existing one, when the new API
>> -becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> -Deprecated APIs are removed completely just after the next LTS.
>> -
>> -Reminder that old API should follow deprecation process to be removed.
>> -
>> -
>> -Experimental APIs
>> ------------------
>> -
>> -APIs marked as ``experimental`` are not considered part of the ABI and may
>> -change without warning at any time.  Since changes to APIs are most likely
>> -immediately after their introduction, as users begin to take advantage of
>> -those new APIs and start finding issues with them, new DPDK APIs will be
>> -automatically marked as ``experimental`` to allow for a period of stabilization
>> -before they become part of a tracked ABI.
>> -
>> -Note that marking an API as experimental is a multi step process.
>> -To mark an API as experimental, the symbols which are desired to be exported
>> -must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> -version map script.
>> -Secondly, the corresponding prototypes of those exported functions (in the
>> -development header files), must be marked with the ``__rte_experimental`` tag
>> -(see ``rte_compat.h``).
>> -The DPDK build makefiles perform a check to ensure that the map file and the
>> -C code reflect the same list of symbols.
>> -This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> -during compilation in the corresponding library Makefile.
>> -
>> -In addition to tagging the code with ``__rte_experimental``,
>> -the doxygen markup must also contain the EXPERIMENTAL string,
>> -and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> -
>> -For removing the experimental tag associated with an API, deprecation notice
>> -is not required. Though, an API should remain in experimental state for at least
>> -one release. Thereafter, normal process of posting patch for review to mailing
>> -list can be followed.
>> -
>> -
>> -Library versioning
>> -------------------
>> -
>> -Downstreams might want to provide different DPDK releases at the same time to
>> -support multiple consumers of DPDK linked against older and newer sonames.
>> -
>> -Also due to the interdependencies that DPDK libraries can have applications
>> -might end up with an executable space in which multiple versions of a library
>> -are mapped by ld.so.
>> -
>> -Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> -depending on LibA.
>> -
>> -.. note::
>> -
>> -    Application
>> -    \-> LibA.old
>> -    \-> LibB.new -> LibA.new
>> -
>> -That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> -If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> -library - versions defined in the libraries ``LIBABIVER``.
>> -An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> -``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> -
>> -
>> -ABI versioning
>> ---------------
>> -
>> -Versioning Macros
>> -~~~~~~~~~~~~~~~~~
>> -
>> -When a symbol is exported from a library to provide an API, it also provides a
>> -calling convention (ABI) that is embodied in its name, return type and
>> -arguments. Occasionally that function may need to change to accommodate new
>> -functionality or behavior. When that occurs, it is desirable to allow for
>> -backward compatibility for a time with older binaries that are dynamically
>> -linked to the DPDK.
>> -
>> -To support backward compatibility the ``rte_compat.h``
>> -header file provides macros to use when updating exported functions. These
>> -macros are used in conjunction with the ``rte_<library>_version.map`` file for
>> -a given library to allow multiple versions of a symbol to exist in a shared
>> -library so that older binaries need not be immediately recompiled.
>> -
>> -The macros exported are:
>> -
>> -* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> -  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
>> -
>> -* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> -  the linker to bind references to symbol ``b`` to the internal symbol
>> -  ``b_e``.
>> -
>> -* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> -  fully qualified function ``p``, so that if a symbol becomes versioned, it
>> -  can still be mapped back to the public symbol name.
>> -
>> -Examples of ABI Macro use
>> -^^^^^^^^^^^^^^^^^^^^^^^^^
>> -
>> -Updating a public API
>> -_____________________
>> -
>> -Assume we have a function as follows
>> -
>> -.. code-block:: c
>> -
>> - /*
>> -  * Create an acl context object for apps to
>> -  * manipulate
>> -  */
>> - struct rte_acl_ctx *
>> - rte_acl_create(const struct rte_acl_param *param)
>> - {
>> -        ...
>> - }
>> -
>> -
>> -Assume that struct rte_acl_ctx is a private structure, and that a developer
>> -wishes to enhance the acl api so that a debugging flag can be enabled on a
>> -per-context basis.  This requires an addition to the structure (which, being
>> -private, is safe), but it also requires modifying the code as follows
>> -
>> -.. code-block:: c
>> -
>> - /*
>> -  * Create an acl context object for apps to
>> -  * manipulate
>> -  */
>> - struct rte_acl_ctx *
>> - rte_acl_create(const struct rte_acl_param *param, int debug)
>> - {
>> -        ...
>> - }
>> -
>> -
>> -Note also that, being a public function, the header file prototype must also be
>> -changed, as must all the call sites, to reflect the new ABI footprint.  We will
>> -maintain previous ABI versions that are accessible only to previously compiled
>> -binaries
>> -
>> -The addition of a parameter to the function is ABI breaking as the function is
>> -public, and existing application may use it in its current form.  However, the
>> -compatibility macros in DPDK allow a developer to use symbol versioning so that
>> -multiple functions can be mapped to the same public symbol based on when an
>> -application was linked to it.  To see how this is done, we start with the
>> -requisite libraries version map file.  Initially the version map file for the
>> -acl library looks like this
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_create;
>> -        rte_acl_dump;
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -This file needs to be modified as follows
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_create;
>> -        rte_acl_dump;
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -        rte_acl_create;
>> -
>> -   } DPDK_2.0;
>> -
>> -The addition of the new block tells the linker that a new version node is
>> -available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> -symbols from the DPDK_2.0 node.  This list is directly translated into a list of
>> -exported symbols when DPDK is compiled as a shared library
>> -
>> -Next, we need to specify in the code which function map to the rte_acl_create
>> -symbol at which versions.  First, at the site of the initial symbol definition,
>> -we need to update the function so that it is uniquely named, and not in conflict
>> -with the public symbol name
>> -
>> -.. code-block:: c
>> -
>> -  struct rte_acl_ctx *
>> - -rte_acl_create(const struct rte_acl_param *param)
>> - +rte_acl_create_v20(const struct rte_acl_param *param)
>> - {
>> -        size_t sz;
>> -        struct rte_acl_ctx *ctx;
>> -        ...
>> -
>> -Note that the base name of the symbol was kept intact, as this is conducive to
>> -the macros used for versioning symbols.  That is our next step, mapping this new
>> -symbol name to the initial symbol name at version node 2.0.  Immediately after
>> -the function, we add this line of code
>> -
>> -.. code-block:: c
>> -
>> -   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -Remembering to also add the rte_compat.h header to the requisite c file where
>> -these changes are being made.  The above macro instructs the linker to create a
>> -new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
>> -builds, but now points to the above newly named function.  We have now mapped
>> -the original rte_acl_create symbol to the original function (but with a new
>> -name)
>> -
>> -Next, we need to create the 2.1 version of the symbol.  We create a new function
>> -name, with a different suffix, and  implement it appropriately
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> -   {
>> -        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> -
>> -        ctx->debug = debug;
>> -
>> -        return ctx;
>> -   }
>> -
>> -This code serves as our new API call.  Its the same as our old call, but adds
>> -the new parameter in place.  Next we need to map this function to the symbol
>> -``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
>> -in the header file, adding the macro there to inform all including applications,
>> -that on re-link, the default rte_acl_create symbol should point to this
>> -function.  Note that we could do this by simply naming the function above
>> -rte_acl_create, and the linker would chose the most recent version tag to apply
>> -in the version script, but we can also do this in the header file
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   -rte_acl_create(const struct rte_acl_param *param);
>> -   +rte_acl_create(const struct rte_acl_param *param, int debug);
>> -   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
>> -header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
>> -version node to it.  This method is more explicit and flexible than just
>> -re-implementing the exact symbol name, and allows for other features (such as
>> -linking to the old symbol version by default, when the new ABI is to be opt-in
>> -for a period.
>> -
>> -One last thing we need to do.  Note that we've taken what was a public symbol,
>> -and duplicated it into two uniquely and differently named symbols.  We've then
>> -mapped each of those back to the public symbol ``rte_acl_create`` with different
>> -version tags.  This only applies to dynamic linking, as static linking has no
>> -notion of versioning.  That leaves this code in a position of no longer having a
>> -symbol simply named ``rte_acl_create`` and a static build will fail on that
>> -missing symbol.
>> -
>> -To correct this, we can simply map a function of our choosing back to the public
>> -symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
>> -assumption is that the most recent version of the symbol is the one you want to
>> -map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
>> -defined, we add this
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
>> -   {
>> -        ...
>> -   }
>> -   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
>> -
>> -That tells the compiler that, when building a static library, any calls to the
>> -symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
>> -
>> -That's it, on the next shared library rebuild, there will be two versions of
>> -rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> -and a new DPDK_2.1 version, used by future built applications.
>> -
>> -
>> -Deprecating part of a public API
>> -________________________________
>> -
>> -Lets assume that you've done the above update, and after a few releases have
>> -passed you decide you would like to retire the old version of the function.
>> -After having gone through the ABI deprecation announcement process, removal is
>> -easy.  Start by removing the symbol from the requisite version map file:
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_dump;
>> - -      rte_acl_create
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -        rte_acl_create;
>> -   } DPDK_2.0;
>> -
>> -
>> -Next remove the corresponding versioned export.
>> -
>> -.. code-block:: c
>> -
>> - -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -
>> -Note that the internal function definition could also be removed, but its used
>> -in our example by the newer version _v21, so we leave it in place.  This is a
>> -coding style choice.
>> -
>> -Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> -indicate to applications doing dynamic linking that this is a later, and
>> -possibly incompatible library version:
>> -
>> -.. code-block:: c
>> -
>> -   -LIBABIVER := 1
>> -   +LIBABIVER := 2
>> -
>> -Deprecating an entire ABI version
>> -_________________________________
>> -
>> -While removing a symbol from and ABI may be useful, it is often more practical
>> -to remove an entire version node at once.  If a version node completely
>> -specifies an API, then removing part of it, typically makes it incomplete.  In
>> -those cases it is better to remove the entire node
>> -
>> -To do this, start by modifying the version map file, such that all symbols from
>> -the node to be removed are merged into the next node in the map
>> -
>> -In the case of our map above, it would transform to look as follows
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_dump;
>> -        rte_acl_create
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> - };
>> -
>> -Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> -updated to point to the new version node in any header files for all affected
>> -symbols.
>> -
>> -.. code-block:: c
>> -
>> - -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -Lastly, any VERSION_SYMBOL macros that point to the old version node should be
>> -removed, taking care to keep, where need old code in place to support newer
>> -versions of the symbol.
>> -
>> -
>> -Running the ABI Validator
>> --------------------------
>> -
>> -The ``devtools`` directory in the DPDK source tree contains a utility program,
>> -``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
>> -Compliance Checker
>> -<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
>> -
>> -This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
>> -utilities which can be installed via a package manager. For example::
>> -
>> -   sudo yum install abi-compliance-checker
>> -   sudo yum install abi-dumper
>> -
>> -The syntax of the ``validate-abi.sh`` utility is::
>> -
>> -   ./devtools/validate-abi.sh <REV1> <REV2>
>> -
>> -Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
>> -https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
>> -on the local repo.
>> -
>> -For example::
>> -
>> -   # Check between the previous and latest commit:
>> -   ./devtools/validate-abi.sh HEAD~1 HEAD
>> -
>> -   # Check on a specific compilation target:
>> -   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
>> -
>> -   # Check between two tags:
>> -   ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> -
>> -   # Check between git master and local topic-branch "vhost-hacking":
>> -   ./devtools/validate-abi.sh master vhost-hacking
>> -
>> -After the validation script completes (it can take a while since it need to
>> -compile both tags) it will create compatibility reports in the
>> -``./abi-check/compat_report`` directory. Listed incompatibilities can be found
>> -as follows::
>> -
>> -  grep -lr Incompatible abi-check/compat_reports/
>> -- 
>> 2.7.4
>>
>>

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Neil Horman]

On Wed, Sep 25, 2019 at 02:01:01PM +0100, Ray Kinsella wrote:
> Hi Neil,
> 
> Thanks for the feedback, other comment below.
> 
> On 25/09/2019 13:24, Neil Horman wrote:
> > On Wed, Sep 25, 2019 at 11:23:53AM +0100, Ray Kinsella wrote:
> >> Separate versioning.rst into abi versioning and abi policy guidance, in
> >> preparation for adding more detail to the abi policy.
> >>
> >> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
> >> ---
> >>  doc/guides/contributing/abi_policy.rst     | 169 +++++++++
> >>  doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
> >>  doc/guides/contributing/index.rst          |   3 +-
> >>  doc/guides/contributing/versioning.rst     | 591 -----------------------------
> >>  4 files changed, 598 insertions(+), 592 deletions(-)
> >>  create mode 100644 doc/guides/contributing/abi_policy.rst
> >>  create mode 100644 doc/guides/contributing/abi_versioning.rst
> >>  delete mode 100644 doc/guides/contributing/versioning.rst
> >>
> >> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
> >> new file mode 100644
> >> index 0000000..55bacb4
> >> --- /dev/null
> >> +++ b/doc/guides/contributing/abi_policy.rst
> >> @@ -0,0 +1,169 @@
> >> +..  SPDX-License-Identifier: BSD-3-Clause
> >> +    Copyright 2018 The DPDK contributors
> >> +
> >> +.. abi_api_policy:
> >> +
> >> +DPDK ABI/API policy
> >> +===================
> >> +
> >> +Description
> >> +-----------
> >> +
> >> +This document details some methods for handling ABI management in the DPDK.
> >> +
> >> +General Guidelines
> >> +------------------
> >> +
> >> +#. Whenever possible, ABI should be preserved
> >> +#. ABI/API may be changed with a deprecation process
> >> +#. The modification of symbols can generally be managed with versioning
> >> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
> >> +#. New APIs will be marked as ``experimental`` for at least one release to allow
> >> +   any issues found by users of the new API to be fixed quickly
> >> +#. The addition of symbols is generally not problematic
> >> +#. The removal of symbols generally is an ABI break and requires bumping of the
> >> +   LIBABIVER macro
> >> +#. Updates to the minimum hardware requirements, which drop support for hardware which
> >> +   was previously supported, should be treated as an ABI change.
> >> +
> >> +What is an ABI
> >> +~~~~~~~~~~~~~~
> >> +
> >> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
> >> +by a library. It is similar to an API (Application Programming Interface) but
> >> +is the result of compilation.  It is also effectively cloned when applications
> >> +link to dynamic libraries.  That is to say when an application is compiled to
> >> +link against dynamic libraries, it is assumed that the ABI remains constant
> >> +between the time the application is compiled/linked, and the time that it runs.
> >> +Therefore, in the case of dynamic linking, it is critical that an ABI is
> >> +preserved, or (when modified), done in such a way that the application is unable
> >> +to behave improperly or in an unexpected fashion.
> >> +
> >> +
> >> +ABI/API Deprecation
> >> +-------------------
> >> +
> >> +The DPDK ABI policy
> >> +~~~~~~~~~~~~~~~~~~~
> >> +
> >> +ABI versions are set at the time of major release labeling, and the ABI may
> >> +change multiple times, without warning, between the last release label and the
> >> +HEAD label of the git tree.
> >> +
> >> +ABI versions, once released, are available until such time as their
> >> +deprecation has been noted in the Release Notes for at least one major release
> >> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
> >> +shipped and then a decision is made to modify it during the development of
> >> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
> >> +release and the modification will be made available in the DPDK 2.2 release.
> >> +
> > This seems..confusing.  
> 
> Agreed, this is from the original policy. I updated all the references
> to DPDK 2.0 in the abi_versioning document. Clearly missed these ones,
> thanks for that, the text is confusing I will update it.
> 
Thank you!

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Ray Kinsella]

On 25/09/2019 13:24, Neil Horman wrote:
> On Wed, Sep 25, 2019 at 11:23:53AM +0100, Ray Kinsella wrote:
> This seems..confusing.  In patch 0:
> =================================================================
> * DPDK v20 is declared as the supported ABI version for one year, aligned with
>    the DPDK v19.11 (LTS) release. All library sonames are updated to reflect the
>    new ABI version, e.g. librte_eal.so.20, librte_acl.so.20...
>  * DPDK v20.02 .. v20.08 releases are ABI compatible with the DPDK v20 ABI. ABI
>    changes are permitted from DPDK v20.02 onwards, with the condition that ABI
>    compatibility with DPDK v20 is preserved.
>  * DPDK v21 is declared as the new supported ABI version for two years, aligned
>    with the DPDK v20.11 (LTS) release. The DPDK v20 ABI is now depreciated,
>    library sonames are updated to v21 and ABI compatibility breaking changes may
>    be introduced.
> ===================================================================

Actually Neil,

Apologies now I am taking a closer look at your email.
I understand what is going on.

Patch 1/4 separates the ABI Policy from the detail of ABI Version
management, but it is still old policy that your where reading at this
point, hence all the references to DPDK 2.0 and why it doesn't

Patch 2/4 is the _new policy_, where you will see that all references to
2.0 have been removed.

You other points around the needing a taxonomy still are 100% valid
though and I am working on adding a diagram.

Ray K

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Aaron Conole]

Ray Kinsella <mdr@ashroe.eu> writes:

> Separate versioning.rst into abi versioning and abi policy guidance, in
> preparation for adding more detail to the abi policy.
>
> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
> ---
>  doc/guides/contributing/abi_policy.rst     | 169 +++++++++
>  doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
>  doc/guides/contributing/index.rst          |   3 +-
>  doc/guides/contributing/versioning.rst     | 591 -----------------------------
>  4 files changed, 598 insertions(+), 592 deletions(-)
>  create mode 100644 doc/guides/contributing/abi_policy.rst
>  create mode 100644 doc/guides/contributing/abi_versioning.rst
>  delete mode 100644 doc/guides/contributing/versioning.rst
>
> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
> new file mode 100644
> index 0000000..55bacb4
> --- /dev/null
> +++ b/doc/guides/contributing/abi_policy.rst
> @@ -0,0 +1,169 @@
> +..  SPDX-License-Identifier: BSD-3-Clause
> +    Copyright 2018 The DPDK contributors
> +
> +.. abi_api_policy:
> +
> +DPDK ABI/API policy
> +===================
> +
> +Description
> +-----------
> +
> +This document details some methods for handling ABI management in the DPDK.
> +
> +General Guidelines
> +------------------
> +
> +#. Whenever possible, ABI should be preserved
> +#. ABI/API may be changed with a deprecation process
> +#. The modification of symbols can generally be managed with versioning
> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
> +#. New APIs will be marked as ``experimental`` for at least one release to allow
> +   any issues found by users of the new API to be fixed quickly
> +#. The addition of symbols is generally not problematic
> +#. The removal of symbols generally is an ABI break and requires bumping of the
> +   LIBABIVER macro
> +#. Updates to the minimum hardware requirements, which drop support for hardware which
> +   was previously supported, should be treated as an ABI change.
> +
> +What is an ABI
> +~~~~~~~~~~~~~~
> +
> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
> +by a library. It is similar to an API (Application Programming Interface) but
> +is the result of compilation.  It is also effectively cloned when applications
> +link to dynamic libraries.  That is to say when an application is compiled to
> +link against dynamic libraries, it is assumed that the ABI remains constant
> +between the time the application is compiled/linked, and the time that it runs.
> +Therefore, in the case of dynamic linking, it is critical that an ABI is
> +preserved, or (when modified), done in such a way that the application is unable
> +to behave improperly or in an unexpected fashion.
> +

This section probably needs a bit more details.  People still are
confused what exactly constitutes ABI vs. API (see
http://mails.dpdk.org/archives/dev/2018-January/085209.html for a
confusing example).

It's important that people know not just function signatures, but also
return codes, and even data structure layouts are all part of the ABI.

> +
> +ABI/API Deprecation
> +-------------------
> +
> +The DPDK ABI policy
> +~~~~~~~~~~~~~~~~~~~
> +
> +ABI versions are set at the time of major release labeling, and the ABI may
> +change multiple times, without warning, between the last release label and the
> +HEAD label of the git tree.
> +
> +ABI versions, once released, are available until such time as their
> +deprecation has been noted in the Release Notes for at least one major release
> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
> +shipped and then a decision is made to modify it during the development of
> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
> +release and the modification will be made available in the DPDK 2.2 release.
> +
> +ABI versions may be deprecated in whole or in part as needed by a given
> +update.
> +
> +Some ABI changes may be too significant to reasonably maintain multiple
> +versions. In those cases ABI's may be updated without backward compatibility
> +being provided. The requirements for doing so are:
> +
> +#. At least 3 acknowledgments of the need to do so must be made on the
> +   dpdk.org mailing list.
> +
> +   - The acknowledgment of the maintainer of the component is mandatory, or if
> +     no maintainer is available for the component, the tree/sub-tree maintainer
> +     for that component must acknowledge the ABI change instead.
> +
> +   - It is also recommended that acknowledgments from different "areas of
> +     interest" be sought for each deprecation, for example: from NIC vendors,
> +     CPU vendors, end-users, etc.
> +
> +#. The changes (including an alternative map file) can be included with
> +   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
> +   to provide more details about oncoming changes.
> +   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
> +   More preferred way to provide this information is sending the feature
> +   as a separate patch and reference it in deprecation notice.
> +
> +#. A full deprecation cycle, as explained above, must be made to offer
> +   downstream consumers sufficient warning of the change.
> +
> +Note that the above process for ABI deprecation should not be undertaken
> +lightly. ABI stability is extremely important for downstream consumers of the
> +DPDK, especially when distributed in shared object form. Every effort should
> +be made to preserve the ABI whenever possible. The ABI should only be changed
> +for significant reasons, such as performance enhancements. ABI breakage due to
> +changes such as reorganizing public structure fields for aesthetic or
> +readability purposes should be avoided.
> +
> +.. note::
> +
> +   Updates to the minimum hardware requirements, which drop support for hardware
> +   which was previously supported, should be treated as an ABI change, and
> +   follow the relevant deprecation policy procedures as above: 3 acks and
> +   announcement at least one release in advance.
> +
> +Examples of Deprecation Notices
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +The following are some examples of ABI deprecation notices which would be
> +added to the Release Notes:
> +
> +* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
> +  to be replaced with the inline function ``rte_foo()``.
> +
> +* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
> +  in version 2.0. Backwards compatibility will be maintained for this function
> +  until the release of version 2.1
> +
> +* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
> +  performance reasons. Existing binary applications will have backwards
> +  compatibility in release 2.0, while newly built binaries will need to
> +  reference the new structure variant ``struct rte_foo2``. Compatibility will
> +  be removed in release 2.2, and all applications will require updating and
> +  rebuilding to the new structure at that time, which will be renamed to the
> +  original ``struct rte_foo``.
> +
> +* Significant ABI changes are planned for the ``librte_dostuff`` library. The
> +  upcoming release 2.0 will not contain these changes, but release 2.1 will,
> +  and no backwards compatibility is planned due to the extensive nature of
> +  these changes. Binaries using this library built prior to version 2.1 will
> +  require updating and recompilation.
> +
> +New API replacing previous one
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +If a new API proposed functionally replaces an existing one, when the new API
> +becomes non-experimental then the old one is marked with ``__rte_deprecated``.
> +Deprecated APIs are removed completely just after the next LTS.
> +
> +Reminder that old API should follow deprecation process to be removed.
> +
> +
> +Experimental APIs
> +-----------------
> +
> +APIs marked as ``experimental`` are not considered part of the ABI and may
> +change without warning at any time.  Since changes to APIs are most likely
> +immediately after their introduction, as users begin to take advantage of
> +those new APIs and start finding issues with them, new DPDK APIs will be
> +automatically marked as ``experimental`` to allow for a period of stabilization
> +before they become part of a tracked ABI.
> +
> +Note that marking an API as experimental is a multi step process.
> +To mark an API as experimental, the symbols which are desired to be exported
> +must be placed in an EXPERIMENTAL version block in the corresponding libraries'
> +version map script.
> +Secondly, the corresponding prototypes of those exported functions (in the
> +development header files), must be marked with the ``__rte_experimental`` tag
> +(see ``rte_compat.h``).
> +The DPDK build makefiles perform a check to ensure that the map file and the
> +C code reflect the same list of symbols.
> +This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
> +during compilation in the corresponding library Makefile.
> +
> +In addition to tagging the code with ``__rte_experimental``,
> +the doxygen markup must also contain the EXPERIMENTAL string,
> +and the MAINTAINERS file should note the EXPERIMENTAL libraries.
> +
> +For removing the experimental tag associated with an API, deprecation notice
> +is not required. Though, an API should remain in experimental state for at least
> +one release. Thereafter, normal process of posting patch for review to mailing
> +list can be followed.
> diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
> new file mode 100644
> index 0000000..53e6ac0
> --- /dev/null
> +++ b/doc/guides/contributing/abi_versioning.rst
> @@ -0,0 +1,427 @@
> +..  SPDX-License-Identifier: BSD-3-Clause
> +    Copyright 2018 The DPDK contributors
> +
> +.. library_versioning:
> +
> +Library versioning
> +------------------
> +
> +Downstreams might want to provide different DPDK releases at the same time to
> +support multiple consumers of DPDK linked against older and newer sonames.
> +
> +Also due to the interdependencies that DPDK libraries can have applications
> +might end up with an executable space in which multiple versions of a library
> +are mapped by ld.so.
> +
> +Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
> +depending on LibA.
> +
> +.. note::
> +
> +    Application
> +    \-> LibA.old
> +    \-> LibB.new -> LibA.new
> +
> +That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
> +If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
> +library - versions defined in the libraries ``LIBABIVER``.
> +An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
> +``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
> +
> +
> +ABI versioning
> +--------------
> +
> +Versioning Macros
> +~~~~~~~~~~~~~~~~~
> +
> +When a symbol is exported from a library to provide an API, it also provides a
> +calling convention (ABI) that is embodied in its name, return type and
> +arguments. Occasionally that function may need to change to accommodate new
> +functionality or behavior. When that occurs, it is desirable to allow for
> +backward compatibility for a time with older binaries that are dynamically
> +linked to the DPDK.
> +
> +To support backward compatibility the ``rte_compat.h``
> +header file provides macros to use when updating exported functions. These
> +macros are used in conjunction with the ``rte_<library>_version.map`` file for
> +a given library to allow multiple versions of a symbol to exist in a shared
> +library so that older binaries need not be immediately recompiled.
> +
> +The macros exported are:
> +
> +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
> +  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
> +
> +* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
> +  the linker to bind references to symbol ``b`` to the internal symbol
> +  ``b_e``.
> +
> +* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
> +  fully qualified function ``p``, so that if a symbol becomes versioned, it
> +  can still be mapped back to the public symbol name.
> +
> +Examples of ABI Macro use
> +^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +Updating a public API
> +_____________________
> +
> +Assume we have a function as follows
> +
> +.. code-block:: c
> +
> + /*
> +  * Create an acl context object for apps to
> +  * manipulate
> +  */
> + struct rte_acl_ctx *
> + rte_acl_create(const struct rte_acl_param *param)
> + {
> +        ...
> + }
> +
> +
> +Assume that struct rte_acl_ctx is a private structure, and that a developer
> +wishes to enhance the acl api so that a debugging flag can be enabled on a
> +per-context basis.  This requires an addition to the structure (which, being
> +private, is safe), but it also requires modifying the code as follows
> +
> +.. code-block:: c
> +
> + /*
> +  * Create an acl context object for apps to
> +  * manipulate
> +  */
> + struct rte_acl_ctx *
> + rte_acl_create(const struct rte_acl_param *param, int debug)
> + {
> +        ...
> + }
> +
> +
> +Note also that, being a public function, the header file prototype must also be
> +changed, as must all the call sites, to reflect the new ABI footprint.  We will
> +maintain previous ABI versions that are accessible only to previously compiled
> +binaries
> +
> +The addition of a parameter to the function is ABI breaking as the function is
> +public, and existing application may use it in its current form.  However, the
> +compatibility macros in DPDK allow a developer to use symbol versioning so that
> +multiple functions can be mapped to the same public symbol based on when an
> +application was linked to it.  To see how this is done, we start with the
> +requisite libraries version map file.  Initially the version map file for the
> +acl library looks like this
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_create;
> +        rte_acl_dump;
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +This file needs to be modified as follows
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_create;
> +        rte_acl_dump;
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +   DPDK_2.1 {
> +        global:
> +        rte_acl_create;
> +
> +   } DPDK_2.0;
> +
> +The addition of the new block tells the linker that a new version node is
> +available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
> +symbols from the DPDK_2.0 node.  This list is directly translated into a list of
> +exported symbols when DPDK is compiled as a shared library
> +
> +Next, we need to specify in the code which function map to the rte_acl_create
> +symbol at which versions.  First, at the site of the initial symbol definition,
> +we need to update the function so that it is uniquely named, and not in conflict
> +with the public symbol name
> +
> +.. code-block:: c
> +
> +  struct rte_acl_ctx *
> + -rte_acl_create(const struct rte_acl_param *param)
> + +rte_acl_create_v20(const struct rte_acl_param *param)
> + {
> +        size_t sz;
> +        struct rte_acl_ctx *ctx;
> +        ...
> +
> +Note that the base name of the symbol was kept intact, as this is conducive to
> +the macros used for versioning symbols.  That is our next step, mapping this new
> +symbol name to the initial symbol name at version node 2.0.  Immediately after
> +the function, we add this line of code
> +
> +.. code-block:: c
> +
> +   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> +
> +Remembering to also add the rte_compat.h header to the requisite c file where
> +these changes are being made.  The above macro instructs the linker to create a
> +new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
> +builds, but now points to the above newly named function.  We have now mapped
> +the original rte_acl_create symbol to the original function (but with a new
> +name)
> +
> +Next, we need to create the 2.1 version of the symbol.  We create a new function
> +name, with a different suffix, and  implement it appropriately
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
> +   {
> +        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
> +
> +        ctx->debug = debug;
> +
> +        return ctx;
> +   }
> +
> +This code serves as our new API call.  Its the same as our old call, but adds
> +the new parameter in place.  Next we need to map this function to the symbol
> +``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
> +in the header file, adding the macro there to inform all including applications,
> +that on re-link, the default rte_acl_create symbol should point to this
> +function.  Note that we could do this by simply naming the function above
> +rte_acl_create, and the linker would chose the most recent version tag to apply
> +in the version script, but we can also do this in the header file
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   -rte_acl_create(const struct rte_acl_param *param);
> +   +rte_acl_create(const struct rte_acl_param *param, int debug);
> +   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> +
> +The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
> +header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
> +version node to it.  This method is more explicit and flexible than just
> +re-implementing the exact symbol name, and allows for other features (such as
> +linking to the old symbol version by default, when the new ABI is to be opt-in
> +for a period.
> +
> +One last thing we need to do.  Note that we've taken what was a public symbol,
> +and duplicated it into two uniquely and differently named symbols.  We've then
> +mapped each of those back to the public symbol ``rte_acl_create`` with different
> +version tags.  This only applies to dynamic linking, as static linking has no
> +notion of versioning.  That leaves this code in a position of no longer having a
> +symbol simply named ``rte_acl_create`` and a static build will fail on that
> +missing symbol.
> +
> +To correct this, we can simply map a function of our choosing back to the public
> +symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
> +assumption is that the most recent version of the symbol is the one you want to
> +map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
> +defined, we add this
> +
> +.. code-block:: c
> +
> +   struct rte_acl_ctx *
> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
> +   {
> +        ...
> +   }
> +   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
> +
> +That tells the compiler that, when building a static library, any calls to the
> +symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
> +
> +That's it, on the next shared library rebuild, there will be two versions of
> +rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
> +and a new DPDK_2.1 version, used by future built applications.
> +
> +
> +Deprecating part of a public API
> +________________________________
> +
> +Lets assume that you've done the above update, and after a few releases have
> +passed you decide you would like to retire the old version of the function.
> +After having gone through the ABI deprecation announcement process, removal is
> +easy.  Start by removing the symbol from the requisite version map file:
> +
> +.. code-block:: none
> +
> +   DPDK_2.0 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_dump;
> + -      rte_acl_create
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> +   };
> +
> +   DPDK_2.1 {
> +        global:
> +        rte_acl_create;
> +   } DPDK_2.0;
> +
> +
> +Next remove the corresponding versioned export.
> +
> +.. code-block:: c
> +
> + -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> +
> +
> +Note that the internal function definition could also be removed, but its used
> +in our example by the newer version _v21, so we leave it in place.  This is a
> +coding style choice.
> +
> +Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
> +indicate to applications doing dynamic linking that this is a later, and
> +possibly incompatible library version:
> +
> +.. code-block:: c
> +
> +   -LIBABIVER := 1
> +   +LIBABIVER := 2
> +
> +Deprecating an entire ABI version
> +_________________________________
> +
> +While removing a symbol from and ABI may be useful, it is often more practical
> +to remove an entire version node at once.  If a version node completely
> +specifies an API, then removing part of it, typically makes it incomplete.  In
> +those cases it is better to remove the entire node
> +
> +To do this, start by modifying the version map file, such that all symbols from
> +the node to be removed are merged into the next node in the map
> +
> +In the case of our map above, it would transform to look as follows
> +
> +.. code-block:: none
> +
> +   DPDK_2.1 {
> +        global:
> +
> +        rte_acl_add_rules;
> +        rte_acl_build;
> +        rte_acl_classify;
> +        rte_acl_classify_alg;
> +        rte_acl_classify_scalar;
> +        rte_acl_dump;
> +        rte_acl_create
> +        rte_acl_find_existing;
> +        rte_acl_free;
> +        rte_acl_ipv4vlan_add_rules;
> +        rte_acl_ipv4vlan_build;
> +        rte_acl_list_dump;
> +        rte_acl_reset;
> +        rte_acl_reset_rules;
> +        rte_acl_set_ctx_classify;
> +
> +        local: *;
> + };
> +
> +Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
> +updated to point to the new version node in any header files for all affected
> +symbols.
> +
> +.. code-block:: c
> +
> + -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> +
> +Lastly, any VERSION_SYMBOL macros that point to the old version node should be
> +removed, taking care to keep, where need old code in place to support newer
> +versions of the symbol.
> +
> +
> +Running the ABI Validator
> +-------------------------
> +
> +The ``devtools`` directory in the DPDK source tree contains a utility program,
> +``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
> +Compliance Checker
> +<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
> +
> +This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
> +utilities which can be installed via a package manager. For example::
> +
> +   sudo yum install abi-compliance-checker
> +   sudo yum install abi-dumper
> +
> +The syntax of the ``validate-abi.sh`` utility is::
> +
> +   ./devtools/validate-abi.sh <REV1> <REV2>
> +
> +Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
> +https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
> +on the local repo.
> +
> +For example::
> +
> +   # Check between the previous and latest commit:
> +   ./devtools/validate-abi.sh HEAD~1 HEAD
> +
> +   # Check on a specific compilation target:
> +   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
> +
> +   # Check between two tags:
> +   ./devtools/validate-abi.sh v2.0.0 v2.1.0
> +
> +   # Check between git master and local topic-branch "vhost-hacking":
> +   ./devtools/validate-abi.sh master vhost-hacking
> +
> +After the validation script completes (it can take a while since it need to
> +compile both tags) it will create compatibility reports in the
> +``./abi-check/compat_report`` directory. Listed incompatibilities can be found
> +as follows::
> +
> +  grep -lr Incompatible abi-check/compat_reports/
> diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
> index e2608d3..2fefd91 100644
> --- a/doc/guides/contributing/index.rst
> +++ b/doc/guides/contributing/index.rst
> @@ -10,7 +10,8 @@ Contributor's Guidelines
>  
>      coding_style
>      design
> -    versioning
> +    abi_policy
> +    abi_versioning
>      documentation
>      patches
>      vulnerability
> diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
> deleted file mode 100644
> index 3ab2c43..0000000
> --- a/doc/guides/contributing/versioning.rst
> +++ /dev/null
> @@ -1,591 +0,0 @@
> -..  SPDX-License-Identifier: BSD-3-Clause
> -    Copyright 2018 The DPDK contributors
> -
> -DPDK ABI/API policy
> -===================
> -
> -Description
> ------------
> -
> -This document details some methods for handling ABI management in the DPDK.
> -
> -General Guidelines
> -------------------
> -
> -#. Whenever possible, ABI should be preserved
> -#. ABI/API may be changed with a deprecation process
> -#. The modification of symbols can generally be managed with versioning
> -#. Libraries or APIs marked in ``experimental`` state may change without constraint
> -#. New APIs will be marked as ``experimental`` for at least one release to allow
> -   any issues found by users of the new API to be fixed quickly
> -#. The addition of symbols is generally not problematic
> -#. The removal of symbols generally is an ABI break and requires bumping of the
> -   LIBABIVER macro
> -#. Updates to the minimum hardware requirements, which drop support for hardware which
> -   was previously supported, should be treated as an ABI change.
> -
> -What is an ABI
> -~~~~~~~~~~~~~~
> -
> -An ABI (Application Binary Interface) is the set of runtime interfaces exposed
> -by a library. It is similar to an API (Application Programming Interface) but
> -is the result of compilation.  It is also effectively cloned when applications
> -link to dynamic libraries.  That is to say when an application is compiled to
> -link against dynamic libraries, it is assumed that the ABI remains constant
> -between the time the application is compiled/linked, and the time that it runs.
> -Therefore, in the case of dynamic linking, it is critical that an ABI is
> -preserved, or (when modified), done in such a way that the application is unable
> -to behave improperly or in an unexpected fashion.
> -
> -
> -ABI/API Deprecation
> --------------------
> -
> -The DPDK ABI policy
> -~~~~~~~~~~~~~~~~~~~
> -
> -ABI versions are set at the time of major release labeling, and the ABI may
> -change multiple times, without warning, between the last release label and the
> -HEAD label of the git tree.
> -
> -ABI versions, once released, are available until such time as their
> -deprecation has been noted in the Release Notes for at least one major release
> -cycle. For example consider the case where the ABI for DPDK 2.0 has been
> -shipped and then a decision is made to modify it during the development of
> -DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
> -release and the modification will be made available in the DPDK 2.2 release.
> -
> -ABI versions may be deprecated in whole or in part as needed by a given
> -update.
> -
> -Some ABI changes may be too significant to reasonably maintain multiple
> -versions. In those cases ABI's may be updated without backward compatibility
> -being provided. The requirements for doing so are:
> -
> -#. At least 3 acknowledgments of the need to do so must be made on the
> -   dpdk.org mailing list.
> -
> -   - The acknowledgment of the maintainer of the component is mandatory, or if
> -     no maintainer is available for the component, the tree/sub-tree maintainer
> -     for that component must acknowledge the ABI change instead.
> -
> -   - It is also recommended that acknowledgments from different "areas of
> -     interest" be sought for each deprecation, for example: from NIC vendors,
> -     CPU vendors, end-users, etc.
> -
> -#. The changes (including an alternative map file) can be included with
> -   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
> -   to provide more details about oncoming changes.
> -   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
> -   More preferred way to provide this information is sending the feature
> -   as a separate patch and reference it in deprecation notice.
> -
> -#. A full deprecation cycle, as explained above, must be made to offer
> -   downstream consumers sufficient warning of the change.
> -
> -Note that the above process for ABI deprecation should not be undertaken
> -lightly. ABI stability is extremely important for downstream consumers of the
> -DPDK, especially when distributed in shared object form. Every effort should
> -be made to preserve the ABI whenever possible. The ABI should only be changed
> -for significant reasons, such as performance enhancements. ABI breakage due to
> -changes such as reorganizing public structure fields for aesthetic or
> -readability purposes should be avoided.
> -
> -.. note::
> -
> -   Updates to the minimum hardware requirements, which drop support for hardware
> -   which was previously supported, should be treated as an ABI change, and
> -   follow the relevant deprecation policy procedures as above: 3 acks and
> -   announcement at least one release in advance.
> -
> -Examples of Deprecation Notices
> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -
> -The following are some examples of ABI deprecation notices which would be
> -added to the Release Notes:
> -
> -* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
> -  to be replaced with the inline function ``rte_foo()``.
> -
> -* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
> -  in version 2.0. Backwards compatibility will be maintained for this function
> -  until the release of version 2.1
> -
> -* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
> -  performance reasons. Existing binary applications will have backwards
> -  compatibility in release 2.0, while newly built binaries will need to
> -  reference the new structure variant ``struct rte_foo2``. Compatibility will
> -  be removed in release 2.2, and all applications will require updating and
> -  rebuilding to the new structure at that time, which will be renamed to the
> -  original ``struct rte_foo``.
> -
> -* Significant ABI changes are planned for the ``librte_dostuff`` library. The
> -  upcoming release 2.0 will not contain these changes, but release 2.1 will,
> -  and no backwards compatibility is planned due to the extensive nature of
> -  these changes. Binaries using this library built prior to version 2.1 will
> -  require updating and recompilation.
> -
> -New API replacing previous one
> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> -
> -If a new API proposed functionally replaces an existing one, when the new API
> -becomes non-experimental then the old one is marked with ``__rte_deprecated``.
> -Deprecated APIs are removed completely just after the next LTS.
> -
> -Reminder that old API should follow deprecation process to be removed.
> -
> -
> -Experimental APIs
> ------------------
> -
> -APIs marked as ``experimental`` are not considered part of the ABI and may
> -change without warning at any time.  Since changes to APIs are most likely
> -immediately after their introduction, as users begin to take advantage of
> -those new APIs and start finding issues with them, new DPDK APIs will be
> -automatically marked as ``experimental`` to allow for a period of stabilization
> -before they become part of a tracked ABI.
> -
> -Note that marking an API as experimental is a multi step process.
> -To mark an API as experimental, the symbols which are desired to be exported
> -must be placed in an EXPERIMENTAL version block in the corresponding libraries'
> -version map script.
> -Secondly, the corresponding prototypes of those exported functions (in the
> -development header files), must be marked with the ``__rte_experimental`` tag
> -(see ``rte_compat.h``).
> -The DPDK build makefiles perform a check to ensure that the map file and the
> -C code reflect the same list of symbols.
> -This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
> -during compilation in the corresponding library Makefile.
> -
> -In addition to tagging the code with ``__rte_experimental``,
> -the doxygen markup must also contain the EXPERIMENTAL string,
> -and the MAINTAINERS file should note the EXPERIMENTAL libraries.
> -
> -For removing the experimental tag associated with an API, deprecation notice
> -is not required. Though, an API should remain in experimental state for at least
> -one release. Thereafter, normal process of posting patch for review to mailing
> -list can be followed.
> -
> -
> -Library versioning
> -------------------
> -
> -Downstreams might want to provide different DPDK releases at the same time to
> -support multiple consumers of DPDK linked against older and newer sonames.
> -
> -Also due to the interdependencies that DPDK libraries can have applications
> -might end up with an executable space in which multiple versions of a library
> -are mapped by ld.so.
> -
> -Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
> -depending on LibA.
> -
> -.. note::
> -
> -    Application
> -    \-> LibA.old
> -    \-> LibB.new -> LibA.new
> -
> -That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
> -If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
> -library - versions defined in the libraries ``LIBABIVER``.
> -An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
> -``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
> -
> -
> -ABI versioning
> ---------------
> -
> -Versioning Macros
> -~~~~~~~~~~~~~~~~~
> -
> -When a symbol is exported from a library to provide an API, it also provides a
> -calling convention (ABI) that is embodied in its name, return type and
> -arguments. Occasionally that function may need to change to accommodate new
> -functionality or behavior. When that occurs, it is desirable to allow for
> -backward compatibility for a time with older binaries that are dynamically
> -linked to the DPDK.
> -
> -To support backward compatibility the ``rte_compat.h``
> -header file provides macros to use when updating exported functions. These
> -macros are used in conjunction with the ``rte_<library>_version.map`` file for
> -a given library to allow multiple versions of a symbol to exist in a shared
> -library so that older binaries need not be immediately recompiled.
> -
> -The macros exported are:
> -
> -* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
> -  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
> -
> -* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
> -  the linker to bind references to symbol ``b`` to the internal symbol
> -  ``b_e``.
> -
> -* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
> -  fully qualified function ``p``, so that if a symbol becomes versioned, it
> -  can still be mapped back to the public symbol name.
> -
> -Examples of ABI Macro use
> -^^^^^^^^^^^^^^^^^^^^^^^^^
> -
> -Updating a public API
> -_____________________
> -
> -Assume we have a function as follows
> -
> -.. code-block:: c
> -
> - /*
> -  * Create an acl context object for apps to
> -  * manipulate
> -  */
> - struct rte_acl_ctx *
> - rte_acl_create(const struct rte_acl_param *param)
> - {
> -        ...
> - }
> -
> -
> -Assume that struct rte_acl_ctx is a private structure, and that a developer
> -wishes to enhance the acl api so that a debugging flag can be enabled on a
> -per-context basis.  This requires an addition to the structure (which, being
> -private, is safe), but it also requires modifying the code as follows
> -
> -.. code-block:: c
> -
> - /*
> -  * Create an acl context object for apps to
> -  * manipulate
> -  */
> - struct rte_acl_ctx *
> - rte_acl_create(const struct rte_acl_param *param, int debug)
> - {
> -        ...
> - }
> -
> -
> -Note also that, being a public function, the header file prototype must also be
> -changed, as must all the call sites, to reflect the new ABI footprint.  We will
> -maintain previous ABI versions that are accessible only to previously compiled
> -binaries
> -
> -The addition of a parameter to the function is ABI breaking as the function is
> -public, and existing application may use it in its current form.  However, the
> -compatibility macros in DPDK allow a developer to use symbol versioning so that
> -multiple functions can be mapped to the same public symbol based on when an
> -application was linked to it.  To see how this is done, we start with the
> -requisite libraries version map file.  Initially the version map file for the
> -acl library looks like this
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_create;
> -        rte_acl_dump;
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -This file needs to be modified as follows
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_create;
> -        rte_acl_dump;
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -   DPDK_2.1 {
> -        global:
> -        rte_acl_create;
> -
> -   } DPDK_2.0;
> -
> -The addition of the new block tells the linker that a new version node is
> -available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
> -symbols from the DPDK_2.0 node.  This list is directly translated into a list of
> -exported symbols when DPDK is compiled as a shared library
> -
> -Next, we need to specify in the code which function map to the rte_acl_create
> -symbol at which versions.  First, at the site of the initial symbol definition,
> -we need to update the function so that it is uniquely named, and not in conflict
> -with the public symbol name
> -
> -.. code-block:: c
> -
> -  struct rte_acl_ctx *
> - -rte_acl_create(const struct rte_acl_param *param)
> - +rte_acl_create_v20(const struct rte_acl_param *param)
> - {
> -        size_t sz;
> -        struct rte_acl_ctx *ctx;
> -        ...
> -
> -Note that the base name of the symbol was kept intact, as this is conducive to
> -the macros used for versioning symbols.  That is our next step, mapping this new
> -symbol name to the initial symbol name at version node 2.0.  Immediately after
> -the function, we add this line of code
> -
> -.. code-block:: c
> -
> -   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> -
> -Remembering to also add the rte_compat.h header to the requisite c file where
> -these changes are being made.  The above macro instructs the linker to create a
> -new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
> -builds, but now points to the above newly named function.  We have now mapped
> -the original rte_acl_create symbol to the original function (but with a new
> -name)
> -
> -Next, we need to create the 2.1 version of the symbol.  We create a new function
> -name, with a different suffix, and  implement it appropriately
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
> -   {
> -        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
> -
> -        ctx->debug = debug;
> -
> -        return ctx;
> -   }
> -
> -This code serves as our new API call.  Its the same as our old call, but adds
> -the new parameter in place.  Next we need to map this function to the symbol
> -``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
> -in the header file, adding the macro there to inform all including applications,
> -that on re-link, the default rte_acl_create symbol should point to this
> -function.  Note that we could do this by simply naming the function above
> -rte_acl_create, and the linker would chose the most recent version tag to apply
> -in the version script, but we can also do this in the header file
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   -rte_acl_create(const struct rte_acl_param *param);
> -   +rte_acl_create(const struct rte_acl_param *param, int debug);
> -   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> -
> -The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
> -header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
> -version node to it.  This method is more explicit and flexible than just
> -re-implementing the exact symbol name, and allows for other features (such as
> -linking to the old symbol version by default, when the new ABI is to be opt-in
> -for a period.
> -
> -One last thing we need to do.  Note that we've taken what was a public symbol,
> -and duplicated it into two uniquely and differently named symbols.  We've then
> -mapped each of those back to the public symbol ``rte_acl_create`` with different
> -version tags.  This only applies to dynamic linking, as static linking has no
> -notion of versioning.  That leaves this code in a position of no longer having a
> -symbol simply named ``rte_acl_create`` and a static build will fail on that
> -missing symbol.
> -
> -To correct this, we can simply map a function of our choosing back to the public
> -symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
> -assumption is that the most recent version of the symbol is the one you want to
> -map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
> -defined, we add this
> -
> -.. code-block:: c
> -
> -   struct rte_acl_ctx *
> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
> -   {
> -        ...
> -   }
> -   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
> -
> -That tells the compiler that, when building a static library, any calls to the
> -symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
> -
> -That's it, on the next shared library rebuild, there will be two versions of
> -rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
> -and a new DPDK_2.1 version, used by future built applications.
> -
> -
> -Deprecating part of a public API
> -________________________________
> -
> -Lets assume that you've done the above update, and after a few releases have
> -passed you decide you would like to retire the old version of the function.
> -After having gone through the ABI deprecation announcement process, removal is
> -easy.  Start by removing the symbol from the requisite version map file:
> -
> -.. code-block:: none
> -
> -   DPDK_2.0 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_dump;
> - -      rte_acl_create
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> -   };
> -
> -   DPDK_2.1 {
> -        global:
> -        rte_acl_create;
> -   } DPDK_2.0;
> -
> -
> -Next remove the corresponding versioned export.
> -
> -.. code-block:: c
> -
> - -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
> -
> -
> -Note that the internal function definition could also be removed, but its used
> -in our example by the newer version _v21, so we leave it in place.  This is a
> -coding style choice.
> -
> -Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
> -indicate to applications doing dynamic linking that this is a later, and
> -possibly incompatible library version:
> -
> -.. code-block:: c
> -
> -   -LIBABIVER := 1
> -   +LIBABIVER := 2
> -
> -Deprecating an entire ABI version
> -_________________________________
> -
> -While removing a symbol from and ABI may be useful, it is often more practical
> -to remove an entire version node at once.  If a version node completely
> -specifies an API, then removing part of it, typically makes it incomplete.  In
> -those cases it is better to remove the entire node
> -
> -To do this, start by modifying the version map file, such that all symbols from
> -the node to be removed are merged into the next node in the map
> -
> -In the case of our map above, it would transform to look as follows
> -
> -.. code-block:: none
> -
> -   DPDK_2.1 {
> -        global:
> -
> -        rte_acl_add_rules;
> -        rte_acl_build;
> -        rte_acl_classify;
> -        rte_acl_classify_alg;
> -        rte_acl_classify_scalar;
> -        rte_acl_dump;
> -        rte_acl_create
> -        rte_acl_find_existing;
> -        rte_acl_free;
> -        rte_acl_ipv4vlan_add_rules;
> -        rte_acl_ipv4vlan_build;
> -        rte_acl_list_dump;
> -        rte_acl_reset;
> -        rte_acl_reset_rules;
> -        rte_acl_set_ctx_classify;
> -
> -        local: *;
> - };
> -
> -Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
> -updated to point to the new version node in any header files for all affected
> -symbols.
> -
> -.. code-block:: c
> -
> - -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
> -
> -Lastly, any VERSION_SYMBOL macros that point to the old version node should be
> -removed, taking care to keep, where need old code in place to support newer
> -versions of the symbol.
> -
> -
> -Running the ABI Validator
> --------------------------
> -
> -The ``devtools`` directory in the DPDK source tree contains a utility program,
> -``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
> -Compliance Checker
> -<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
> -
> -This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
> -utilities which can be installed via a package manager. For example::
> -
> -   sudo yum install abi-compliance-checker
> -   sudo yum install abi-dumper
> -
> -The syntax of the ``validate-abi.sh`` utility is::
> -
> -   ./devtools/validate-abi.sh <REV1> <REV2>
> -
> -Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
> -https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
> -on the local repo.
> -
> -For example::
> -
> -   # Check between the previous and latest commit:
> -   ./devtools/validate-abi.sh HEAD~1 HEAD
> -
> -   # Check on a specific compilation target:
> -   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
> -
> -   # Check between two tags:
> -   ./devtools/validate-abi.sh v2.0.0 v2.1.0
> -
> -   # Check between git master and local topic-branch "vhost-hacking":
> -   ./devtools/validate-abi.sh master vhost-hacking
> -
> -After the validation script completes (it can take a while since it need to
> -compile both tags) it will create compatibility reports in the
> -``./abi-check/compat_report`` directory. Listed incompatibilities can be found
> -as follows::
> -
> -  grep -lr Incompatible abi-check/compat_reports/

Re: [dpdk-dev] [PATCH v4 1/4] doc: separate versioning.rst into version and policy

[Ray Kinsella]

On 27/09/2019 16:43, Aaron Conole wrote:
> Ray Kinsella <mdr@ashroe.eu> writes:
> 
>> Separate versioning.rst into abi versioning and abi policy guidance, in
>> preparation for adding more detail to the abi policy.
>>
>> Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
>> ---
>>  doc/guides/contributing/abi_policy.rst     | 169 +++++++++
>>  doc/guides/contributing/abi_versioning.rst | 427 +++++++++++++++++++++
>>  doc/guides/contributing/index.rst          |   3 +-
>>  doc/guides/contributing/versioning.rst     | 591 -----------------------------
>>  4 files changed, 598 insertions(+), 592 deletions(-)
>>  create mode 100644 doc/guides/contributing/abi_policy.rst
>>  create mode 100644 doc/guides/contributing/abi_versioning.rst
>>  delete mode 100644 doc/guides/contributing/versioning.rst
>>
>> diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
>> new file mode 100644
>> index 0000000..55bacb4
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_policy.rst
>> @@ -0,0 +1,169 @@
>> +..  SPDX-License-Identifier: BSD-3-Clause
>> +    Copyright 2018 The DPDK contributors
>> +
>> +.. abi_api_policy:
>> +
>> +DPDK ABI/API policy
>> +===================
>> +
>> +Description
>> +-----------
>> +
>> +This document details some methods for handling ABI management in the DPDK.
>> +
>> +General Guidelines
>> +------------------
>> +
>> +#. Whenever possible, ABI should be preserved
>> +#. ABI/API may be changed with a deprecation process
>> +#. The modification of symbols can generally be managed with versioning
>> +#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> +#. New APIs will be marked as ``experimental`` for at least one release to allow
>> +   any issues found by users of the new API to be fixed quickly
>> +#. The addition of symbols is generally not problematic
>> +#. The removal of symbols generally is an ABI break and requires bumping of the
>> +   LIBABIVER macro
>> +#. Updates to the minimum hardware requirements, which drop support for hardware which
>> +   was previously supported, should be treated as an ABI change.
>> +
>> +What is an ABI
>> +~~~~~~~~~~~~~~
>> +
>> +An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> +by a library. It is similar to an API (Application Programming Interface) but
>> +is the result of compilation.  It is also effectively cloned when applications
>> +link to dynamic libraries.  That is to say when an application is compiled to
>> +link against dynamic libraries, it is assumed that the ABI remains constant
>> +between the time the application is compiled/linked, and the time that it runs.
>> +Therefore, in the case of dynamic linking, it is critical that an ABI is
>> +preserved, or (when modified), done in such a way that the application is unable
>> +to behave improperly or in an unexpected fashion.
>> +
> 
> This section probably needs a bit more details.  People still are
> confused what exactly constitutes ABI vs. API (see
> http://mails.dpdk.org/archives/dev/2018-January/085209.html for a
> confusing example).
> 
> It's important that people know not just function signatures, but also
> return codes, and even data structure layouts are all part of the ABI.

Hi Aaron, just saw this now after I sent the v5.
This text is actually from the original policy, this patch is just
separating the abi policy from the abi versioning.

That said, I think another diagram would also be helpful here.
I have one we can use.

> 
>> +
>> +ABI/API Deprecation
>> +-------------------
>> +
>> +The DPDK ABI policy
>> +~~~~~~~~~~~~~~~~~~~
>> +
>> +ABI versions are set at the time of major release labeling, and the ABI may
>> +change multiple times, without warning, between the last release label and the
>> +HEAD label of the git tree.
>> +
>> +ABI versions, once released, are available until such time as their
>> +deprecation has been noted in the Release Notes for at least one major release
>> +cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> +shipped and then a decision is made to modify it during the development of
>> +DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> +release and the modification will be made available in the DPDK 2.2 release.
>> +
>> +ABI versions may be deprecated in whole or in part as needed by a given
>> +update.
>> +
>> +Some ABI changes may be too significant to reasonably maintain multiple
>> +versions. In those cases ABI's may be updated without backward compatibility
>> +being provided. The requirements for doing so are:
>> +
>> +#. At least 3 acknowledgments of the need to do so must be made on the
>> +   dpdk.org mailing list.
>> +
>> +   - The acknowledgment of the maintainer of the component is mandatory, or if
>> +     no maintainer is available for the component, the tree/sub-tree maintainer
>> +     for that component must acknowledge the ABI change instead.
>> +
>> +   - It is also recommended that acknowledgments from different "areas of
>> +     interest" be sought for each deprecation, for example: from NIC vendors,
>> +     CPU vendors, end-users, etc.
>> +
>> +#. The changes (including an alternative map file) can be included with
>> +   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> +   to provide more details about oncoming changes.
>> +   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> +   More preferred way to provide this information is sending the feature
>> +   as a separate patch and reference it in deprecation notice.
>> +
>> +#. A full deprecation cycle, as explained above, must be made to offer
>> +   downstream consumers sufficient warning of the change.
>> +
>> +Note that the above process for ABI deprecation should not be undertaken
>> +lightly. ABI stability is extremely important for downstream consumers of the
>> +DPDK, especially when distributed in shared object form. Every effort should
>> +be made to preserve the ABI whenever possible. The ABI should only be changed
>> +for significant reasons, such as performance enhancements. ABI breakage due to
>> +changes such as reorganizing public structure fields for aesthetic or
>> +readability purposes should be avoided.
>> +
>> +.. note::
>> +
>> +   Updates to the minimum hardware requirements, which drop support for hardware
>> +   which was previously supported, should be treated as an ABI change, and
>> +   follow the relevant deprecation policy procedures as above: 3 acks and
>> +   announcement at least one release in advance.
>> +
>> +Examples of Deprecation Notices
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +The following are some examples of ABI deprecation notices which would be
>> +added to the Release Notes:
>> +
>> +* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> +  to be replaced with the inline function ``rte_foo()``.
>> +
>> +* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> +  in version 2.0. Backwards compatibility will be maintained for this function
>> +  until the release of version 2.1
>> +
>> +* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> +  performance reasons. Existing binary applications will have backwards
>> +  compatibility in release 2.0, while newly built binaries will need to
>> +  reference the new structure variant ``struct rte_foo2``. Compatibility will
>> +  be removed in release 2.2, and all applications will require updating and
>> +  rebuilding to the new structure at that time, which will be renamed to the
>> +  original ``struct rte_foo``.
>> +
>> +* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> +  upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> +  and no backwards compatibility is planned due to the extensive nature of
>> +  these changes. Binaries using this library built prior to version 2.1 will
>> +  require updating and recompilation.
>> +
>> +New API replacing previous one
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +If a new API proposed functionally replaces an existing one, when the new API
>> +becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> +Deprecated APIs are removed completely just after the next LTS.
>> +
>> +Reminder that old API should follow deprecation process to be removed.
>> +
>> +
>> +Experimental APIs
>> +-----------------
>> +
>> +APIs marked as ``experimental`` are not considered part of the ABI and may
>> +change without warning at any time.  Since changes to APIs are most likely
>> +immediately after their introduction, as users begin to take advantage of
>> +those new APIs and start finding issues with them, new DPDK APIs will be
>> +automatically marked as ``experimental`` to allow for a period of stabilization
>> +before they become part of a tracked ABI.
>> +
>> +Note that marking an API as experimental is a multi step process.
>> +To mark an API as experimental, the symbols which are desired to be exported
>> +must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> +version map script.
>> +Secondly, the corresponding prototypes of those exported functions (in the
>> +development header files), must be marked with the ``__rte_experimental`` tag
>> +(see ``rte_compat.h``).
>> +The DPDK build makefiles perform a check to ensure that the map file and the
>> +C code reflect the same list of symbols.
>> +This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> +during compilation in the corresponding library Makefile.
>> +
>> +In addition to tagging the code with ``__rte_experimental``,
>> +the doxygen markup must also contain the EXPERIMENTAL string,
>> +and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> +
>> +For removing the experimental tag associated with an API, deprecation notice
>> +is not required. Though, an API should remain in experimental state for at least
>> +one release. Thereafter, normal process of posting patch for review to mailing
>> +list can be followed.
>> diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
>> new file mode 100644
>> index 0000000..53e6ac0
>> --- /dev/null
>> +++ b/doc/guides/contributing/abi_versioning.rst
>> @@ -0,0 +1,427 @@
>> +..  SPDX-License-Identifier: BSD-3-Clause
>> +    Copyright 2018 The DPDK contributors
>> +
>> +.. library_versioning:
>> +
>> +Library versioning
>> +------------------
>> +
>> +Downstreams might want to provide different DPDK releases at the same time to
>> +support multiple consumers of DPDK linked against older and newer sonames.
>> +
>> +Also due to the interdependencies that DPDK libraries can have applications
>> +might end up with an executable space in which multiple versions of a library
>> +are mapped by ld.so.
>> +
>> +Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> +depending on LibA.
>> +
>> +.. note::
>> +
>> +    Application
>> +    \-> LibA.old
>> +    \-> LibB.new -> LibA.new
>> +
>> +That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> +If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> +library - versions defined in the libraries ``LIBABIVER``.
>> +An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> +``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> +
>> +
>> +ABI versioning
>> +--------------
>> +
>> +Versioning Macros
>> +~~~~~~~~~~~~~~~~~
>> +
>> +When a symbol is exported from a library to provide an API, it also provides a
>> +calling convention (ABI) that is embodied in its name, return type and
>> +arguments. Occasionally that function may need to change to accommodate new
>> +functionality or behavior. When that occurs, it is desirable to allow for
>> +backward compatibility for a time with older binaries that are dynamically
>> +linked to the DPDK.
>> +
>> +To support backward compatibility the ``rte_compat.h``
>> +header file provides macros to use when updating exported functions. These
>> +macros are used in conjunction with the ``rte_<library>_version.map`` file for
>> +a given library to allow multiple versions of a symbol to exist in a shared
>> +library so that older binaries need not be immediately recompiled.
>> +
>> +The macros exported are:
>> +
>> +* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> +  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
>> +
>> +* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> +  the linker to bind references to symbol ``b`` to the internal symbol
>> +  ``b_e``.
>> +
>> +* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> +  fully qualified function ``p``, so that if a symbol becomes versioned, it
>> +  can still be mapped back to the public symbol name.
>> +
>> +Examples of ABI Macro use
>> +^^^^^^^^^^^^^^^^^^^^^^^^^
>> +
>> +Updating a public API
>> +_____________________
>> +
>> +Assume we have a function as follows
>> +
>> +.. code-block:: c
>> +
>> + /*
>> +  * Create an acl context object for apps to
>> +  * manipulate
>> +  */
>> + struct rte_acl_ctx *
>> + rte_acl_create(const struct rte_acl_param *param)
>> + {
>> +        ...
>> + }
>> +
>> +
>> +Assume that struct rte_acl_ctx is a private structure, and that a developer
>> +wishes to enhance the acl api so that a debugging flag can be enabled on a
>> +per-context basis.  This requires an addition to the structure (which, being
>> +private, is safe), but it also requires modifying the code as follows
>> +
>> +.. code-block:: c
>> +
>> + /*
>> +  * Create an acl context object for apps to
>> +  * manipulate
>> +  */
>> + struct rte_acl_ctx *
>> + rte_acl_create(const struct rte_acl_param *param, int debug)
>> + {
>> +        ...
>> + }
>> +
>> +
>> +Note also that, being a public function, the header file prototype must also be
>> +changed, as must all the call sites, to reflect the new ABI footprint.  We will
>> +maintain previous ABI versions that are accessible only to previously compiled
>> +binaries
>> +
>> +The addition of a parameter to the function is ABI breaking as the function is
>> +public, and existing application may use it in its current form.  However, the
>> +compatibility macros in DPDK allow a developer to use symbol versioning so that
>> +multiple functions can be mapped to the same public symbol based on when an
>> +application was linked to it.  To see how this is done, we start with the
>> +requisite libraries version map file.  Initially the version map file for the
>> +acl library looks like this
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_create;
>> +        rte_acl_dump;
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +This file needs to be modified as follows
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_create;
>> +        rte_acl_dump;
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +        rte_acl_create;
>> +
>> +   } DPDK_2.0;
>> +
>> +The addition of the new block tells the linker that a new version node is
>> +available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> +symbols from the DPDK_2.0 node.  This list is directly translated into a list of
>> +exported symbols when DPDK is compiled as a shared library
>> +
>> +Next, we need to specify in the code which function map to the rte_acl_create
>> +symbol at which versions.  First, at the site of the initial symbol definition,
>> +we need to update the function so that it is uniquely named, and not in conflict
>> +with the public symbol name
>> +
>> +.. code-block:: c
>> +
>> +  struct rte_acl_ctx *
>> + -rte_acl_create(const struct rte_acl_param *param)
>> + +rte_acl_create_v20(const struct rte_acl_param *param)
>> + {
>> +        size_t sz;
>> +        struct rte_acl_ctx *ctx;
>> +        ...
>> +
>> +Note that the base name of the symbol was kept intact, as this is conducive to
>> +the macros used for versioning symbols.  That is our next step, mapping this new
>> +symbol name to the initial symbol name at version node 2.0.  Immediately after
>> +the function, we add this line of code
>> +
>> +.. code-block:: c
>> +
>> +   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +Remembering to also add the rte_compat.h header to the requisite c file where
>> +these changes are being made.  The above macro instructs the linker to create a
>> +new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
>> +builds, but now points to the above newly named function.  We have now mapped
>> +the original rte_acl_create symbol to the original function (but with a new
>> +name)
>> +
>> +Next, we need to create the 2.1 version of the symbol.  We create a new function
>> +name, with a different suffix, and  implement it appropriately
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> +   {
>> +        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> +
>> +        ctx->debug = debug;
>> +
>> +        return ctx;
>> +   }
>> +
>> +This code serves as our new API call.  Its the same as our old call, but adds
>> +the new parameter in place.  Next we need to map this function to the symbol
>> +``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
>> +in the header file, adding the macro there to inform all including applications,
>> +that on re-link, the default rte_acl_create symbol should point to this
>> +function.  Note that we could do this by simply naming the function above
>> +rte_acl_create, and the linker would chose the most recent version tag to apply
>> +in the version script, but we can also do this in the header file
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   -rte_acl_create(const struct rte_acl_param *param);
>> +   +rte_acl_create(const struct rte_acl_param *param, int debug);
>> +   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
>> +header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
>> +version node to it.  This method is more explicit and flexible than just
>> +re-implementing the exact symbol name, and allows for other features (such as
>> +linking to the old symbol version by default, when the new ABI is to be opt-in
>> +for a period.
>> +
>> +One last thing we need to do.  Note that we've taken what was a public symbol,
>> +and duplicated it into two uniquely and differently named symbols.  We've then
>> +mapped each of those back to the public symbol ``rte_acl_create`` with different
>> +version tags.  This only applies to dynamic linking, as static linking has no
>> +notion of versioning.  That leaves this code in a position of no longer having a
>> +symbol simply named ``rte_acl_create`` and a static build will fail on that
>> +missing symbol.
>> +
>> +To correct this, we can simply map a function of our choosing back to the public
>> +symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
>> +assumption is that the most recent version of the symbol is the one you want to
>> +map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
>> +defined, we add this
>> +
>> +.. code-block:: c
>> +
>> +   struct rte_acl_ctx *
>> +   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
>> +   {
>> +        ...
>> +   }
>> +   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
>> +
>> +That tells the compiler that, when building a static library, any calls to the
>> +symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
>> +
>> +That's it, on the next shared library rebuild, there will be two versions of
>> +rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> +and a new DPDK_2.1 version, used by future built applications.
>> +
>> +
>> +Deprecating part of a public API
>> +________________________________
>> +
>> +Lets assume that you've done the above update, and after a few releases have
>> +passed you decide you would like to retire the old version of the function.
>> +After having gone through the ABI deprecation announcement process, removal is
>> +easy.  Start by removing the symbol from the requisite version map file:
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.0 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_dump;
>> + -      rte_acl_create
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> +   };
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +        rte_acl_create;
>> +   } DPDK_2.0;
>> +
>> +
>> +Next remove the corresponding versioned export.
>> +
>> +.. code-block:: c
>> +
>> + -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> +
>> +
>> +Note that the internal function definition could also be removed, but its used
>> +in our example by the newer version _v21, so we leave it in place.  This is a
>> +coding style choice.
>> +
>> +Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> +indicate to applications doing dynamic linking that this is a later, and
>> +possibly incompatible library version:
>> +
>> +.. code-block:: c
>> +
>> +   -LIBABIVER := 1
>> +   +LIBABIVER := 2
>> +
>> +Deprecating an entire ABI version
>> +_________________________________
>> +
>> +While removing a symbol from and ABI may be useful, it is often more practical
>> +to remove an entire version node at once.  If a version node completely
>> +specifies an API, then removing part of it, typically makes it incomplete.  In
>> +those cases it is better to remove the entire node
>> +
>> +To do this, start by modifying the version map file, such that all symbols from
>> +the node to be removed are merged into the next node in the map
>> +
>> +In the case of our map above, it would transform to look as follows
>> +
>> +.. code-block:: none
>> +
>> +   DPDK_2.1 {
>> +        global:
>> +
>> +        rte_acl_add_rules;
>> +        rte_acl_build;
>> +        rte_acl_classify;
>> +        rte_acl_classify_alg;
>> +        rte_acl_classify_scalar;
>> +        rte_acl_dump;
>> +        rte_acl_create
>> +        rte_acl_find_existing;
>> +        rte_acl_free;
>> +        rte_acl_ipv4vlan_add_rules;
>> +        rte_acl_ipv4vlan_build;
>> +        rte_acl_list_dump;
>> +        rte_acl_reset;
>> +        rte_acl_reset_rules;
>> +        rte_acl_set_ctx_classify;
>> +
>> +        local: *;
>> + };
>> +
>> +Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> +updated to point to the new version node in any header files for all affected
>> +symbols.
>> +
>> +.. code-block:: c
>> +
>> + -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> + +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> +
>> +Lastly, any VERSION_SYMBOL macros that point to the old version node should be
>> +removed, taking care to keep, where need old code in place to support newer
>> +versions of the symbol.
>> +
>> +
>> +Running the ABI Validator
>> +-------------------------
>> +
>> +The ``devtools`` directory in the DPDK source tree contains a utility program,
>> +``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
>> +Compliance Checker
>> +<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
>> +
>> +This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
>> +utilities which can be installed via a package manager. For example::
>> +
>> +   sudo yum install abi-compliance-checker
>> +   sudo yum install abi-dumper
>> +
>> +The syntax of the ``validate-abi.sh`` utility is::
>> +
>> +   ./devtools/validate-abi.sh <REV1> <REV2>
>> +
>> +Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
>> +https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
>> +on the local repo.
>> +
>> +For example::
>> +
>> +   # Check between the previous and latest commit:
>> +   ./devtools/validate-abi.sh HEAD~1 HEAD
>> +
>> +   # Check on a specific compilation target:
>> +   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
>> +
>> +   # Check between two tags:
>> +   ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> +
>> +   # Check between git master and local topic-branch "vhost-hacking":
>> +   ./devtools/validate-abi.sh master vhost-hacking
>> +
>> +After the validation script completes (it can take a while since it need to
>> +compile both tags) it will create compatibility reports in the
>> +``./abi-check/compat_report`` directory. Listed incompatibilities can be found
>> +as follows::
>> +
>> +  grep -lr Incompatible abi-check/compat_reports/
>> diff --git a/doc/guides/contributing/index.rst b/doc/guides/contributing/index.rst
>> index e2608d3..2fefd91 100644
>> --- a/doc/guides/contributing/index.rst
>> +++ b/doc/guides/contributing/index.rst
>> @@ -10,7 +10,8 @@ Contributor's Guidelines
>>  
>>      coding_style
>>      design
>> -    versioning
>> +    abi_policy
>> +    abi_versioning
>>      documentation
>>      patches
>>      vulnerability
>> diff --git a/doc/guides/contributing/versioning.rst b/doc/guides/contributing/versioning.rst
>> deleted file mode 100644
>> index 3ab2c43..0000000
>> --- a/doc/guides/contributing/versioning.rst
>> +++ /dev/null
>> @@ -1,591 +0,0 @@
>> -..  SPDX-License-Identifier: BSD-3-Clause
>> -    Copyright 2018 The DPDK contributors
>> -
>> -DPDK ABI/API policy
>> -===================
>> -
>> -Description
>> ------------
>> -
>> -This document details some methods for handling ABI management in the DPDK.
>> -
>> -General Guidelines
>> -------------------
>> -
>> -#. Whenever possible, ABI should be preserved
>> -#. ABI/API may be changed with a deprecation process
>> -#. The modification of symbols can generally be managed with versioning
>> -#. Libraries or APIs marked in ``experimental`` state may change without constraint
>> -#. New APIs will be marked as ``experimental`` for at least one release to allow
>> -   any issues found by users of the new API to be fixed quickly
>> -#. The addition of symbols is generally not problematic
>> -#. The removal of symbols generally is an ABI break and requires bumping of the
>> -   LIBABIVER macro
>> -#. Updates to the minimum hardware requirements, which drop support for hardware which
>> -   was previously supported, should be treated as an ABI change.
>> -
>> -What is an ABI
>> -~~~~~~~~~~~~~~
>> -
>> -An ABI (Application Binary Interface) is the set of runtime interfaces exposed
>> -by a library. It is similar to an API (Application Programming Interface) but
>> -is the result of compilation.  It is also effectively cloned when applications
>> -link to dynamic libraries.  That is to say when an application is compiled to
>> -link against dynamic libraries, it is assumed that the ABI remains constant
>> -between the time the application is compiled/linked, and the time that it runs.
>> -Therefore, in the case of dynamic linking, it is critical that an ABI is
>> -preserved, or (when modified), done in such a way that the application is unable
>> -to behave improperly or in an unexpected fashion.
>> -
>> -
>> -ABI/API Deprecation
>> --------------------
>> -
>> -The DPDK ABI policy
>> -~~~~~~~~~~~~~~~~~~~
>> -
>> -ABI versions are set at the time of major release labeling, and the ABI may
>> -change multiple times, without warning, between the last release label and the
>> -HEAD label of the git tree.
>> -
>> -ABI versions, once released, are available until such time as their
>> -deprecation has been noted in the Release Notes for at least one major release
>> -cycle. For example consider the case where the ABI for DPDK 2.0 has been
>> -shipped and then a decision is made to modify it during the development of
>> -DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
>> -release and the modification will be made available in the DPDK 2.2 release.
>> -
>> -ABI versions may be deprecated in whole or in part as needed by a given
>> -update.
>> -
>> -Some ABI changes may be too significant to reasonably maintain multiple
>> -versions. In those cases ABI's may be updated without backward compatibility
>> -being provided. The requirements for doing so are:
>> -
>> -#. At least 3 acknowledgments of the need to do so must be made on the
>> -   dpdk.org mailing list.
>> -
>> -   - The acknowledgment of the maintainer of the component is mandatory, or if
>> -     no maintainer is available for the component, the tree/sub-tree maintainer
>> -     for that component must acknowledge the ABI change instead.
>> -
>> -   - It is also recommended that acknowledgments from different "areas of
>> -     interest" be sought for each deprecation, for example: from NIC vendors,
>> -     CPU vendors, end-users, etc.
>> -
>> -#. The changes (including an alternative map file) can be included with
>> -   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
>> -   to provide more details about oncoming changes.
>> -   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
>> -   More preferred way to provide this information is sending the feature
>> -   as a separate patch and reference it in deprecation notice.
>> -
>> -#. A full deprecation cycle, as explained above, must be made to offer
>> -   downstream consumers sufficient warning of the change.
>> -
>> -Note that the above process for ABI deprecation should not be undertaken
>> -lightly. ABI stability is extremely important for downstream consumers of the
>> -DPDK, especially when distributed in shared object form. Every effort should
>> -be made to preserve the ABI whenever possible. The ABI should only be changed
>> -for significant reasons, such as performance enhancements. ABI breakage due to
>> -changes such as reorganizing public structure fields for aesthetic or
>> -readability purposes should be avoided.
>> -
>> -.. note::
>> -
>> -   Updates to the minimum hardware requirements, which drop support for hardware
>> -   which was previously supported, should be treated as an ABI change, and
>> -   follow the relevant deprecation policy procedures as above: 3 acks and
>> -   announcement at least one release in advance.
>> -
>> -Examples of Deprecation Notices
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -The following are some examples of ABI deprecation notices which would be
>> -added to the Release Notes:
>> -
>> -* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
>> -  to be replaced with the inline function ``rte_foo()``.
>> -
>> -* The function ``rte_mbuf_grok()`` has been updated to include a new parameter
>> -  in version 2.0. Backwards compatibility will be maintained for this function
>> -  until the release of version 2.1
>> -
>> -* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
>> -  performance reasons. Existing binary applications will have backwards
>> -  compatibility in release 2.0, while newly built binaries will need to
>> -  reference the new structure variant ``struct rte_foo2``. Compatibility will
>> -  be removed in release 2.2, and all applications will require updating and
>> -  rebuilding to the new structure at that time, which will be renamed to the
>> -  original ``struct rte_foo``.
>> -
>> -* Significant ABI changes are planned for the ``librte_dostuff`` library. The
>> -  upcoming release 2.0 will not contain these changes, but release 2.1 will,
>> -  and no backwards compatibility is planned due to the extensive nature of
>> -  these changes. Binaries using this library built prior to version 2.1 will
>> -  require updating and recompilation.
>> -
>> -New API replacing previous one
>> -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> -
>> -If a new API proposed functionally replaces an existing one, when the new API
>> -becomes non-experimental then the old one is marked with ``__rte_deprecated``.
>> -Deprecated APIs are removed completely just after the next LTS.
>> -
>> -Reminder that old API should follow deprecation process to be removed.
>> -
>> -
>> -Experimental APIs
>> ------------------
>> -
>> -APIs marked as ``experimental`` are not considered part of the ABI and may
>> -change without warning at any time.  Since changes to APIs are most likely
>> -immediately after their introduction, as users begin to take advantage of
>> -those new APIs and start finding issues with them, new DPDK APIs will be
>> -automatically marked as ``experimental`` to allow for a period of stabilization
>> -before they become part of a tracked ABI.
>> -
>> -Note that marking an API as experimental is a multi step process.
>> -To mark an API as experimental, the symbols which are desired to be exported
>> -must be placed in an EXPERIMENTAL version block in the corresponding libraries'
>> -version map script.
>> -Secondly, the corresponding prototypes of those exported functions (in the
>> -development header files), must be marked with the ``__rte_experimental`` tag
>> -(see ``rte_compat.h``).
>> -The DPDK build makefiles perform a check to ensure that the map file and the
>> -C code reflect the same list of symbols.
>> -This check can be circumvented by defining ``ALLOW_EXPERIMENTAL_API``
>> -during compilation in the corresponding library Makefile.
>> -
>> -In addition to tagging the code with ``__rte_experimental``,
>> -the doxygen markup must also contain the EXPERIMENTAL string,
>> -and the MAINTAINERS file should note the EXPERIMENTAL libraries.
>> -
>> -For removing the experimental tag associated with an API, deprecation notice
>> -is not required. Though, an API should remain in experimental state for at least
>> -one release. Thereafter, normal process of posting patch for review to mailing
>> -list can be followed.
>> -
>> -
>> -Library versioning
>> -------------------
>> -
>> -Downstreams might want to provide different DPDK releases at the same time to
>> -support multiple consumers of DPDK linked against older and newer sonames.
>> -
>> -Also due to the interdependencies that DPDK libraries can have applications
>> -might end up with an executable space in which multiple versions of a library
>> -are mapped by ld.so.
>> -
>> -Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
>> -depending on LibA.
>> -
>> -.. note::
>> -
>> -    Application
>> -    \-> LibA.old
>> -    \-> LibB.new -> LibA.new
>> -
>> -That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
>> -If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
>> -library - versions defined in the libraries ``LIBABIVER``.
>> -An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
>> -``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
>> -
>> -
>> -ABI versioning
>> ---------------
>> -
>> -Versioning Macros
>> -~~~~~~~~~~~~~~~~~
>> -
>> -When a symbol is exported from a library to provide an API, it also provides a
>> -calling convention (ABI) that is embodied in its name, return type and
>> -arguments. Occasionally that function may need to change to accommodate new
>> -functionality or behavior. When that occurs, it is desirable to allow for
>> -backward compatibility for a time with older binaries that are dynamically
>> -linked to the DPDK.
>> -
>> -To support backward compatibility the ``rte_compat.h``
>> -header file provides macros to use when updating exported functions. These
>> -macros are used in conjunction with the ``rte_<library>_version.map`` file for
>> -a given library to allow multiple versions of a symbol to exist in a shared
>> -library so that older binaries need not be immediately recompiled.
>> -
>> -The macros exported are:
>> -
>> -* ``VERSION_SYMBOL(b, e, n)``: Creates a symbol version table entry binding
>> -  versioned symbol ``b@DPDK_n`` to the internal function ``b_e``.
>> -
>> -* ``BIND_DEFAULT_SYMBOL(b, e, n)``: Creates a symbol version entry instructing
>> -  the linker to bind references to symbol ``b`` to the internal symbol
>> -  ``b_e``.
>> -
>> -* ``MAP_STATIC_SYMBOL(f, p)``: Declare the prototype ``f``, and map it to the
>> -  fully qualified function ``p``, so that if a symbol becomes versioned, it
>> -  can still be mapped back to the public symbol name.
>> -
>> -Examples of ABI Macro use
>> -^^^^^^^^^^^^^^^^^^^^^^^^^
>> -
>> -Updating a public API
>> -_____________________
>> -
>> -Assume we have a function as follows
>> -
>> -.. code-block:: c
>> -
>> - /*
>> -  * Create an acl context object for apps to
>> -  * manipulate
>> -  */
>> - struct rte_acl_ctx *
>> - rte_acl_create(const struct rte_acl_param *param)
>> - {
>> -        ...
>> - }
>> -
>> -
>> -Assume that struct rte_acl_ctx is a private structure, and that a developer
>> -wishes to enhance the acl api so that a debugging flag can be enabled on a
>> -per-context basis.  This requires an addition to the structure (which, being
>> -private, is safe), but it also requires modifying the code as follows
>> -
>> -.. code-block:: c
>> -
>> - /*
>> -  * Create an acl context object for apps to
>> -  * manipulate
>> -  */
>> - struct rte_acl_ctx *
>> - rte_acl_create(const struct rte_acl_param *param, int debug)
>> - {
>> -        ...
>> - }
>> -
>> -
>> -Note also that, being a public function, the header file prototype must also be
>> -changed, as must all the call sites, to reflect the new ABI footprint.  We will
>> -maintain previous ABI versions that are accessible only to previously compiled
>> -binaries
>> -
>> -The addition of a parameter to the function is ABI breaking as the function is
>> -public, and existing application may use it in its current form.  However, the
>> -compatibility macros in DPDK allow a developer to use symbol versioning so that
>> -multiple functions can be mapped to the same public symbol based on when an
>> -application was linked to it.  To see how this is done, we start with the
>> -requisite libraries version map file.  Initially the version map file for the
>> -acl library looks like this
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_create;
>> -        rte_acl_dump;
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -This file needs to be modified as follows
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_create;
>> -        rte_acl_dump;
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -        rte_acl_create;
>> -
>> -   } DPDK_2.0;
>> -
>> -The addition of the new block tells the linker that a new version node is
>> -available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
>> -symbols from the DPDK_2.0 node.  This list is directly translated into a list of
>> -exported symbols when DPDK is compiled as a shared library
>> -
>> -Next, we need to specify in the code which function map to the rte_acl_create
>> -symbol at which versions.  First, at the site of the initial symbol definition,
>> -we need to update the function so that it is uniquely named, and not in conflict
>> -with the public symbol name
>> -
>> -.. code-block:: c
>> -
>> -  struct rte_acl_ctx *
>> - -rte_acl_create(const struct rte_acl_param *param)
>> - +rte_acl_create_v20(const struct rte_acl_param *param)
>> - {
>> -        size_t sz;
>> -        struct rte_acl_ctx *ctx;
>> -        ...
>> -
>> -Note that the base name of the symbol was kept intact, as this is conducive to
>> -the macros used for versioning symbols.  That is our next step, mapping this new
>> -symbol name to the initial symbol name at version node 2.0.  Immediately after
>> -the function, we add this line of code
>> -
>> -.. code-block:: c
>> -
>> -   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -Remembering to also add the rte_compat.h header to the requisite c file where
>> -these changes are being made.  The above macro instructs the linker to create a
>> -new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
>> -builds, but now points to the above newly named function.  We have now mapped
>> -the original rte_acl_create symbol to the original function (but with a new
>> -name)
>> -
>> -Next, we need to create the 2.1 version of the symbol.  We create a new function
>> -name, with a different suffix, and  implement it appropriately
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug);
>> -   {
>> -        struct rte_acl_ctx *ctx = rte_acl_create_v20(param);
>> -
>> -        ctx->debug = debug;
>> -
>> -        return ctx;
>> -   }
>> -
>> -This code serves as our new API call.  Its the same as our old call, but adds
>> -the new parameter in place.  Next we need to map this function to the symbol
>> -``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
>> -in the header file, adding the macro there to inform all including applications,
>> -that on re-link, the default rte_acl_create symbol should point to this
>> -function.  Note that we could do this by simply naming the function above
>> -rte_acl_create, and the linker would chose the most recent version tag to apply
>> -in the version script, but we can also do this in the header file
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   -rte_acl_create(const struct rte_acl_param *param);
>> -   +rte_acl_create(const struct rte_acl_param *param, int debug);
>> -   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
>> -header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
>> -version node to it.  This method is more explicit and flexible than just
>> -re-implementing the exact symbol name, and allows for other features (such as
>> -linking to the old symbol version by default, when the new ABI is to be opt-in
>> -for a period.
>> -
>> -One last thing we need to do.  Note that we've taken what was a public symbol,
>> -and duplicated it into two uniquely and differently named symbols.  We've then
>> -mapped each of those back to the public symbol ``rte_acl_create`` with different
>> -version tags.  This only applies to dynamic linking, as static linking has no
>> -notion of versioning.  That leaves this code in a position of no longer having a
>> -symbol simply named ``rte_acl_create`` and a static build will fail on that
>> -missing symbol.
>> -
>> -To correct this, we can simply map a function of our choosing back to the public
>> -symbol in the static build with the ``MAP_STATIC_SYMBOL`` macro.  Generally the
>> -assumption is that the most recent version of the symbol is the one you want to
>> -map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
>> -defined, we add this
>> -
>> -.. code-block:: c
>> -
>> -   struct rte_acl_ctx *
>> -   rte_acl_create_v21(const struct rte_acl_param *param, int debug)
>> -   {
>> -        ...
>> -   }
>> -   MAP_STATIC_SYMBOL(struct rte_acl_ctx *rte_acl_create(const struct rte_acl_param *param, int debug), rte_acl_create_v21);
>> -
>> -That tells the compiler that, when building a static library, any calls to the
>> -symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
>> -
>> -That's it, on the next shared library rebuild, there will be two versions of
>> -rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
>> -and a new DPDK_2.1 version, used by future built applications.
>> -
>> -
>> -Deprecating part of a public API
>> -________________________________
>> -
>> -Lets assume that you've done the above update, and after a few releases have
>> -passed you decide you would like to retire the old version of the function.
>> -After having gone through the ABI deprecation announcement process, removal is
>> -easy.  Start by removing the symbol from the requisite version map file:
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.0 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_dump;
>> - -      rte_acl_create
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> -   };
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -        rte_acl_create;
>> -   } DPDK_2.0;
>> -
>> -
>> -Next remove the corresponding versioned export.
>> -
>> -.. code-block:: c
>> -
>> - -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
>> -
>> -
>> -Note that the internal function definition could also be removed, but its used
>> -in our example by the newer version _v21, so we leave it in place.  This is a
>> -coding style choice.
>> -
>> -Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
>> -indicate to applications doing dynamic linking that this is a later, and
>> -possibly incompatible library version:
>> -
>> -.. code-block:: c
>> -
>> -   -LIBABIVER := 1
>> -   +LIBABIVER := 2
>> -
>> -Deprecating an entire ABI version
>> -_________________________________
>> -
>> -While removing a symbol from and ABI may be useful, it is often more practical
>> -to remove an entire version node at once.  If a version node completely
>> -specifies an API, then removing part of it, typically makes it incomplete.  In
>> -those cases it is better to remove the entire node
>> -
>> -To do this, start by modifying the version map file, such that all symbols from
>> -the node to be removed are merged into the next node in the map
>> -
>> -In the case of our map above, it would transform to look as follows
>> -
>> -.. code-block:: none
>> -
>> -   DPDK_2.1 {
>> -        global:
>> -
>> -        rte_acl_add_rules;
>> -        rte_acl_build;
>> -        rte_acl_classify;
>> -        rte_acl_classify_alg;
>> -        rte_acl_classify_scalar;
>> -        rte_acl_dump;
>> -        rte_acl_create
>> -        rte_acl_find_existing;
>> -        rte_acl_free;
>> -        rte_acl_ipv4vlan_add_rules;
>> -        rte_acl_ipv4vlan_build;
>> -        rte_acl_list_dump;
>> -        rte_acl_reset;
>> -        rte_acl_reset_rules;
>> -        rte_acl_set_ctx_classify;
>> -
>> -        local: *;
>> - };
>> -
>> -Then any uses of BIND_DEFAULT_SYMBOL that pointed to the old node should be
>> -updated to point to the new version node in any header files for all affected
>> -symbols.
>> -
>> -.. code-block:: c
>> -
>> - -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
>> - +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
>> -
>> -Lastly, any VERSION_SYMBOL macros that point to the old version node should be
>> -removed, taking care to keep, where need old code in place to support newer
>> -versions of the symbol.
>> -
>> -
>> -Running the ABI Validator
>> --------------------------
>> -
>> -The ``devtools`` directory in the DPDK source tree contains a utility program,
>> -``validate-abi.sh``, for validating the DPDK ABI based on the Linux `ABI
>> -Compliance Checker
>> -<http://ispras.linuxbase.org/index.php/ABI_compliance_checker>`_.
>> -
>> -This has a dependency on the ``abi-compliance-checker`` and ``and abi-dumper``
>> -utilities which can be installed via a package manager. For example::
>> -
>> -   sudo yum install abi-compliance-checker
>> -   sudo yum install abi-dumper
>> -
>> -The syntax of the ``validate-abi.sh`` utility is::
>> -
>> -   ./devtools/validate-abi.sh <REV1> <REV2>
>> -
>> -Where ``REV1`` and ``REV2`` are valid gitrevisions(7)
>> -https://www.kernel.org/pub/software/scm/git/docs/gitrevisions.html
>> -on the local repo.
>> -
>> -For example::
>> -
>> -   # Check between the previous and latest commit:
>> -   ./devtools/validate-abi.sh HEAD~1 HEAD
>> -
>> -   # Check on a specific compilation target:
>> -   ./devtools/validate-abi.sh -t x86_64-native-linux-gcc HEAD~1 HEAD
>> -
>> -   # Check between two tags:
>> -   ./devtools/validate-abi.sh v2.0.0 v2.1.0
>> -
>> -   # Check between git master and local topic-branch "vhost-hacking":
>> -   ./devtools/validate-abi.sh master vhost-hacking
>> -
>> -After the validation script completes (it can take a while since it need to
>> -compile both tags) it will create compatibility reports in the
>> -``./abi-check/compat_report`` directory. Listed incompatibilities can be found
>> -as follows::
>> -
>> -  grep -lr Incompatible abi-check/compat_reports/

[dpdk-dev] [PATCH v4 2/4] doc: changes to abi policy introducing major abi versions

[Ray Kinsella]

This policy change introduces major ABI versions, these are
declared every year, typically aligned with the LTS release
and are supported by subsequent releases in the following year.
This change is intended to improve ABI stabilty for those projects
consuming DPDK.

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
---
 doc/guides/contributing/abi_policy.rst | 307 ++++++++++++++++++++++++---------
 doc/guides/contributing/stable.rst     |  12 +-
 2 files changed, 227 insertions(+), 92 deletions(-)

diff --git a/doc/guides/contributing/abi_policy.rst b/doc/guides/contributing/abi_policy.rst
index 55bacb4..7446ec3 100644
--- a/doc/guides/contributing/abi_policy.rst
+++ b/doc/guides/contributing/abi_policy.rst
@@ -1,33 +1,46 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
-    Copyright 2018 The DPDK contributors
+    Copyright 2019 The DPDK contributors
 
-.. abi_api_policy:
+.. _abi_policy:
 
-DPDK ABI/API policy
-===================
+ABI Policy
+==========
 
 Description
 -----------
 
-This document details some methods for handling ABI management in the DPDK.
+This document details the management policy that ensures the long-term stability
+of the DPDK ABI and API.
 
 General Guidelines
 ------------------
 
-#. Whenever possible, ABI should be preserved
-#. ABI/API may be changed with a deprecation process
-#. The modification of symbols can generally be managed with versioning
-#. Libraries or APIs marked in ``experimental`` state may change without constraint
-#. New APIs will be marked as ``experimental`` for at least one release to allow
-   any issues found by users of the new API to be fixed quickly
-#. The addition of symbols is generally not problematic
-#. The removal of symbols generally is an ABI break and requires bumping of the
-   LIBABIVER macro
-#. Updates to the minimum hardware requirements, which drop support for hardware which
-   was previously supported, should be treated as an ABI change.
-
-What is an ABI
-~~~~~~~~~~~~~~
+#. Major ABI versions are declared every **year** and are then supported for one
+   year, typically aligned with the :ref:`LTS release <stable_lts_releases>`.
+#. The ABI version is managed at a project level in DPDK, with the ABI version
+   reflected in all :ref:`library's soname <what_is_soname>`.
+#. The ABI should be preserved and not changed lightly. ABI changes must follow
+   the outlined :ref:`deprecation process <abi_changes>`.
+#. The addition of symbols is generally not problematic. The modification of
+   symbols is managed with :ref:`ABI Versioning <abi_versioning>`.
+#. The removal of symbols is considered an :ref:`ABI breakage <abi_breakages>`,
+   once approved these will form part of the next ABI version.
+#. Libraries or APIs marked as :ref:`Experimental <experimental_apis>` are not
+   considered part of an ABI version and may change without constraint.
+#. Updates to the :ref:`minimum hardware requirements <hw_rqmts>`, which drop
+   support for hardware which was previously supported, should be treated as an
+   ABI change.
+
+.. note::
+
+   In 2019, the DPDK community stated it's intention to move to ABI stable
+   releases, over a number of release cycles. Beginning with maintaining ABI
+   stability through one year of DPDK releases starting from DPDK 19.11. This
+   policy will be reviewed in 2020, with intention of lengthening the stability
+   period.
+
+What is an ABI?
+~~~~~~~~~~~~~~~
 
 An ABI (Application Binary Interface) is the set of runtime interfaces exposed
 by a library. It is similar to an API (Application Programming Interface) but
@@ -39,30 +52,66 @@ Therefore, in the case of dynamic linking, it is critical that an ABI is
 preserved, or (when modified), done in such a way that the application is unable
 to behave improperly or in an unexpected fashion.
 
+What is an ABI version?
+~~~~~~~~~~~~~~~~~~~~~~~
 
-ABI/API Deprecation
--------------------
+An ABI version is an instance of a library's ABI at a specific release. Certain
+releases are considered by the community to be milestone releases, the yearly
+LTS for example. Supporting those milestone release's ABI for some number of
+subsequent releases is desirable to facilitate application upgrade. Those ABI
+version's aligned with milestones release are therefore called 'ABI major
+versions' and are supported for some number of releases.
+
+More details on major ABI version can be found in the :ref:`ABI versioning
+<major_abi_versions>` guide.
 
 The DPDK ABI policy
-~~~~~~~~~~~~~~~~~~~
+-------------------
+
+A major ABI version is declared every year, aligned with that year's LTS
+release, e.g. v19.11. This ABI version is then supported for one year by all
+subsequent releases within that time period, until the next LTS release, e.g.
+v20.11.
+
+At the declaration of a major ABI version, major version numbers encoded in
+libraries soname's are bumped to indicate the new version, with the minor
+version reset to ``0``. An example would be ``librte_eal.so.20.3`` would become
+``librte_eal.so.21.0``.
+
+The ABI may then change multiple times, without warning, between the last major
+ABI version increment and the HEAD label of the git tree, with the condition
+that ABI compatibility with the major ABI version is preserved and therefore
+soname's do not change.
+
+Minor versions are incremented to indicate the release of a new ABI compatible
+DPDK release, typically the DPDK quarterly releases. An example of this, might
+be that ``librte_eal.so.20.1`` would indicate the first ABI compatible DPDK
+release, following the declaration of the new major ABI version ``20``.
 
-ABI versions are set at the time of major release labeling, and the ABI may
-change multiple times, without warning, between the last release label and the
-HEAD label of the git tree.
+ABI versions, are supported by each release until such time as the next major
+ABI version is declared. At that time, the deprecation of the previous major ABI
+version will be noted in the Release Notes with guidance on individual symbol
+depreciation and upgrade notes provided.
 
-ABI versions, once released, are available until such time as their
-deprecation has been noted in the Release Notes for at least one major release
-cycle. For example consider the case where the ABI for DPDK 2.0 has been
-shipped and then a decision is made to modify it during the development of
-DPDK 2.1. The decision will be recorded in the Release Notes for the DPDK 2.1
-release and the modification will be made available in the DPDK 2.2 release.
+.. _abi_changes:
 
-ABI versions may be deprecated in whole or in part as needed by a given
-update.
+ABI Changes
+~~~~~~~~~~~
 
-Some ABI changes may be too significant to reasonably maintain multiple
-versions. In those cases ABI's may be updated without backward compatibility
-being provided. The requirements for doing so are:
+The ABI may still change after the declaration of a major ABI version, that is
+new APIs may be still added or existing APIs may be modified.
+
+.. Warning::
+
+   Note that, this policy details the method by which the ABI may be changed,
+   with due regard to preserving compatibility and observing depreciation
+   notices. This process however should not be undertaken lightly, as a general
+   rule ABI stability is extremely important for downstream consumers of DPDK.
+   The ABI should only be changed for significant reasons, such as performance
+   enhancements. ABI breakages due to changes such as reorganizing public
+   structure fields for aesthetic or readability purposes should be avoided.
+
+The requirements for changing the ABI are:
 
 #. At least 3 acknowledgments of the need to do so must be made on the
    dpdk.org mailing list.
@@ -71,34 +120,119 @@ being provided. The requirements for doing so are:
      no maintainer is available for the component, the tree/sub-tree maintainer
      for that component must acknowledge the ABI change instead.
 
+   - The acknowledgment of a member of the technical board, as a delegate of the
+     `technical board <https://core.dpdk.org/techboard/>`_ acknowledging the
+     need for the ABI change, is also mandatory.
+
    - It is also recommended that acknowledgments from different "areas of
      interest" be sought for each deprecation, for example: from NIC vendors,
      CPU vendors, end-users, etc.
 
-#. The changes (including an alternative map file) can be included with
-   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option,
-   to provide more details about oncoming changes.
-   ``RTE_NEXT_ABI`` wrapper will be removed when it become the default ABI.
-   More preferred way to provide this information is sending the feature
-   as a separate patch and reference it in deprecation notice.
+#. Backward compatibility with the major ABI version must be maintained through
+   :ref:`abi_versioning`, with :ref:`forward-only <forward-only>` compatibility
+   offered for any ABI changes that are indicated to be part of the next ABI
+   version.
 
-#. A full deprecation cycle, as explained above, must be made to offer
-   downstream consumers sufficient warning of the change.
+   - In situations where backward compatibility is not possible, read the
+     section on :ref:`abi_breakages`.
 
-Note that the above process for ABI deprecation should not be undertaken
-lightly. ABI stability is extremely important for downstream consumers of the
-DPDK, especially when distributed in shared object form. Every effort should
-be made to preserve the ABI whenever possible. The ABI should only be changed
-for significant reasons, such as performance enhancements. ABI breakage due to
-changes such as reorganizing public structure fields for aesthetic or
-readability purposes should be avoided.
+   - No backward or forward compatibility is offered for API changes marked as
+     ``experimental``, as described in the section on :ref:`Experimental APIs
+     and Libraries <experimental_apis>`.
 
-.. note::
+#. If a newly proposed API functionally replaces an existing one, when the new
+   API becomes non-experimental, then the old one is marked with
+   ``__rte_deprecated``.
+
+    - The depreciated API should follow the notification process to be removed,
+      see  :ref:`deprecation_notices`.
+
+    - At the declaration of the next major ABI version, those ABI changes then
+      become a formal part of the new ABI and the requirement to preserve ABI
+      compatibility with the last major ABI version is then dropped.
+
+    - The responsibility for removing redundant ABI compatibility code rests
+      with the original contributor of the ABI changes, failing that, then with
+      the contributor's company and then finally with the maintainer.
+
+.. _forward-only:
+
+.. Note::
+
+   Note that forward-only compatibility is offered for those changes made
+   between major ABI versions. As a library's soname can only describe
+   compatibility with the last major ABI version, until the next major ABI
+   version is declared, these changes therefore cannot be resolved as a runtime
+   dependency through the soname. Therefore any application wishing to make use
+   of these ABI changes can only ensure that it's runtime dependencies are met
+   through Operating System package versioning.
+
+.. _hw_rqmts:
+
+.. Note::
 
    Updates to the minimum hardware requirements, which drop support for hardware
    which was previously supported, should be treated as an ABI change, and
-   follow the relevant deprecation policy procedures as above: 3 acks and
-   announcement at least one release in advance.
+   follow the relevant deprecation policy procedures as above: 3 acks, technical
+   board approval and announcement at least one release in advance.
+
+.. _abi_breakages:
+
+ABI Breakages
+~~~~~~~~~~~~~
+
+For those ABI changes that are too significant to reasonably maintain multiple
+symbol versions, there is an amended process. In these cases, ABIs may be
+updated without the requirement of backward compatibility being provided. These
+changes must follow the `same process :ref:`described above <abi_changes>` as non-breaking
+changes, however with the following additional requirements:
+
+#. ABI breaking changes (including an alternative map file) can be included with
+   deprecation notice, in wrapped way by the ``RTE_NEXT_ABI`` option, to provide
+   more details about oncoming changes. ``RTE_NEXT_ABI`` wrapper will be removed
+   at the declaration of the next major ABI version.
+
+#. Once approved, and after the depreciation notice has been observed these
+   changes will form part of the next declared major ABI version.
+
+Examples of ABI Changes
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The following are examples of allowable ABI changes occurring between
+declarations of major ABI versions.
+
+* DPDK 19.11 release, defines the function ``rte_foo()``, and ``rte_foo()``
+  as part of the major ABI version ``20``.
+
+* DPDK 20.02 release defines a new function ``rte_foo(uint8_t bar)``, and
+  this is not a problem as long as the symbol ``rte_foo@DPDK20`` is
+  preserved through :ref:`abi_versioning`.
+
+  - The new function may be marked with the ``__rte_experimental`` tag for a
+    number of releases, as described in the section :ref:`experimental_apis`.
+
+  - Once ``rte_foo(uint8_t bar)`` becomes non-experimental ``rte_foo()`` is then
+    declared as ``__rte_depreciated``, with an associated deprecation notice
+    provided.
+
+* DPDK 19.11 is not re-released to include ``rte_foo(uint8_t bar)``, the new
+  version of ``rte_foo`` only exists from DPDK 20.02 onwards as described in the
+  :ref:`note on forward-only compatibility<forward-only>`.
+
+* DPDK 20.02 release defines the experimental function ``__rte_experimental
+  rte_baz()``. This function may or may not exist in the DPDK 20.05 release.
+
+* An application ``dPacket`` wishes to use ``rte_foo(uint8_t bar)``, before the
+  declaration of the DPDK ``21`` major API version. The application can only
+  ensure it's runtime dependencies are met by specifying ``DPDK (>= 20.2)`` as
+  an explicit package dependency, as the soname only may only indicate the
+  supported major ABI version.
+
+* At the release of DPDK 20.11, the function ``rte_foo(uint8_t bar)`` becomes
+  formally part of then new major ABI version DPDK 21.0 and ``rte_foo()`` may be
+  removed.
+
+.. _deprecation_notices:
 
 Examples of Deprecation Notices
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -106,46 +240,42 @@ Examples of Deprecation Notices
 The following are some examples of ABI deprecation notices which would be
 added to the Release Notes:
 
-* The Macro ``#RTE_FOO`` is deprecated and will be removed with version 2.0,
-  to be replaced with the inline function ``rte_foo()``.
+* The Macro ``#RTE_FOO`` is deprecated and will be removed with ABI version
+  21, to be replaced with the inline function ``rte_foo()``.
 
 * The function ``rte_mbuf_grok()`` has been updated to include a new parameter
-  in version 2.0. Backwards compatibility will be maintained for this function
-  until the release of version 2.1
+  in version 20.2. Backwards compatibility will be maintained for this function
+  until the release of the new DPDK major ABI version 21, in DPDK version
+  20.11.
 
-* The members of ``struct rte_foo`` have been reorganized in release 2.0 for
+* The members of ``struct rte_foo`` have been reorganized in DPDK 20.02 for
   performance reasons. Existing binary applications will have backwards
-  compatibility in release 2.0, while newly built binaries will need to
-  reference the new structure variant ``struct rte_foo2``. Compatibility will
-  be removed in release 2.2, and all applications will require updating and
+  compatibility in release 20.02, while newly built binaries will need to
+  reference the new structure variant ``struct rte_foo2``. Compatibility will be
+  removed in release 20.11, and all applications will require updating and
   rebuilding to the new structure at that time, which will be renamed to the
   original ``struct rte_foo``.
 
 * Significant ABI changes are planned for the ``librte_dostuff`` library. The
-  upcoming release 2.0 will not contain these changes, but release 2.1 will,
+  upcoming release 20.02 will not contain these changes, but release 20.11 will,
   and no backwards compatibility is planned due to the extensive nature of
-  these changes. Binaries using this library built prior to version 2.1 will
+  these changes. Binaries using this library built prior to ABI version 21 will
   require updating and recompilation.
 
-New API replacing previous one
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-If a new API proposed functionally replaces an existing one, when the new API
-becomes non-experimental then the old one is marked with ``__rte_deprecated``.
-Deprecated APIs are removed completely just after the next LTS.
-
-Reminder that old API should follow deprecation process to be removed.
+.. _experimental_apis:
 
+Experimental
+------------
 
-Experimental APIs
------------------
+APIs
+~~~~
 
-APIs marked as ``experimental`` are not considered part of the ABI and may
-change without warning at any time.  Since changes to APIs are most likely
-immediately after their introduction, as users begin to take advantage of
-those new APIs and start finding issues with them, new DPDK APIs will be
-automatically marked as ``experimental`` to allow for a period of stabilization
-before they become part of a tracked ABI.
+APIs marked as ``experimental`` are not considered part of an ABI version and
+may change without warning at any time. Since changes to APIs are most likely
+immediately after their introduction, as users begin to take advantage of those
+new APIs and start finding issues with them, new DPDK APIs will be automatically
+marked as ``experimental`` to allow for a period of stabilization before they
+become part of a tracked ABI version.
 
 Note that marking an API as experimental is a multi step process.
 To mark an API as experimental, the symbols which are desired to be exported
@@ -163,7 +293,16 @@ In addition to tagging the code with ``__rte_experimental``,
 the doxygen markup must also contain the EXPERIMENTAL string,
 and the MAINTAINERS file should note the EXPERIMENTAL libraries.
 
-For removing the experimental tag associated with an API, deprecation notice
-is not required. Though, an API should remain in experimental state for at least
-one release. Thereafter, normal process of posting patch for review to mailing
-list can be followed.
+For removing the experimental tag associated with an API, deprecation notice is
+not required. Though, an API should remain in experimental state for at least
+one release. Thereafter, the normal process of posting patch for review to
+mailing list can be followed.
+
+Libraries
+~~~~~~~~~
+
+Libraries marked as ``experimental`` are entirely not considered part of an ABI
+version, and may change without warning at any time. Experimental libraries
+always have a major version of ``0`` to indicate they exist outside of
+:ref:`abi_versioning` , with the minor version incremented with each ABI change
+to library.
diff --git a/doc/guides/contributing/stable.rst b/doc/guides/contributing/stable.rst
index 6a5eee9..2b563d4 100644
--- a/doc/guides/contributing/stable.rst
+++ b/doc/guides/contributing/stable.rst
@@ -1,7 +1,7 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
     Copyright 2018 The DPDK contributors
 
-.. stable_lts_releases:
+.. _stable_lts_releases:
 
 DPDK Stable Releases and Long Term Support
 ==========================================
@@ -53,6 +53,9 @@ year's November (X.11) release will be maintained as an LTS for 2 years.
 After the X.11 release, an LTS branch will be created for it at
 http://git.dpdk.org/dpdk-stable where bugfixes will be backported to.
 
+A LTS release may align with the declaration of a new major ABI version,
+please read the :ref:`abi_policy` for more information.
+
 It is anticipated that there will be at least 4 releases per year of the LTS
 or approximately 1 every 3 months. However, the cadence can be shorter or
 longer depending on the number and criticality of the backported
@@ -119,10 +122,3 @@ A Stable Release will be released by:
   list.
 
 Stable releases are available on the `dpdk.org download page <http://core.dpdk.org/download/>`_.
-
-
-ABI
----
-
-The Stable Release should not be seen as a way of breaking or circumventing
-the DPDK ABI policy.
-- 
2.7.4

[dpdk-dev] [PATCH v4 3/4] doc: updates to versioning guide for abi versions

[Ray Kinsella]

Updates to the ABI versioning guide, to account for the changes to the DPDK
ABI/API policy. Fixes for references to abi versioning and policy guides.

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
---
 doc/guides/contributing/abi_versioning.rst | 248 +++++++++++++++++++----------
 doc/guides/contributing/patches.rst        |   6 +-
 doc/guides/rel_notes/deprecation.rst       |   2 +-
 3 files changed, 172 insertions(+), 84 deletions(-)

diff --git a/doc/guides/contributing/abi_versioning.rst b/doc/guides/contributing/abi_versioning.rst
index 53e6ac0..76c63c8 100644
--- a/doc/guides/contributing/abi_versioning.rst
+++ b/doc/guides/contributing/abi_versioning.rst
@@ -1,44 +1,134 @@
 ..  SPDX-License-Identifier: BSD-3-Clause
     Copyright 2018 The DPDK contributors
 
-.. library_versioning:
+.. _abi_versioning:
 
-Library versioning
+ABI Versioning
+==============
+
+This document details the mechanics of ABI version management in DPDK.
+
+.. _what_is_soname:
+
+What is a library's soname?
+---------------------------
+
+System libraries usually adopt the familiar major and minor version naming
+convention, where major versions (e.g. ``librte_eal 20.x, 21.x``) are presumed
+to be ABI incompatible with each other and minor versions (e.g. ``librte_eal
+20.1, 20.2``) are presumed to be ABI compatible. A library's `soname
+<https://en.wikipedia.org/wiki/Soname>`_. is typically used to provide backward
+compatibility information about a given library, describing the lowest common
+denominator ABI supported by the library. The soname or logical name for the
+library, is typically comprised of the library's name and major version e.g.
+``librte_eal.so.20``.
+
+During an application's build process, a library's soname is noted as a runtime
+dependency of the application. This information is then used by the `dynamic
+linker <https://en.wikipedia.org/wiki/Dynamic_linker>`_ when resolving the
+applications dependencies at runtime, to load a library supporting the correct
+ABI version. The library loaded at runtime therefore, may be a minor revision
+supporting the same major ABI version (e.g. ``librte_eal.20.2``), as the library
+used to link the application (e.g ``librte_eal.20.0``).
+
+.. _major_abi_versions:
+
+Major ABI versions
 ------------------
 
-Downstreams might want to provide different DPDK releases at the same time to
-support multiple consumers of DPDK linked against older and newer sonames.
+An ABI version change to a given library, especially in core libraries such as
+``librte_mbuf``, may cause an implicit ripple effect on the ABI of it's
+consuming libraries, causing ABI breakages. There may however be no explicit
+reason to bump a dependent library's ABI version, as there may have been no
+obvious change to the dependent library's API, even though the library's ABI
+compatibility will have been broken.
+
+This interdependence of DPDK libraries, means that ABI versioning of libraries
+is more manageable at a project level, with all project libraries sharing a
+**single ABI version**. In addition, the need to maintain a stable ABI for some
+number of releases as described in the section :ref:`abi_policy`, means
+that ABI version increments need to carefully planned and managed at a project
+level.
+
+Major ABI versions are therefore declared typically aligned with an LTS release
+and is then supported some number of subsequent releases, shared across all
+libraries. This means that a single project level ABI version, reflected in all
+individual library's soname, library filenames and associated version maps
+persists over multiple releases.
+
+.. code-block:: none
+
+ $ head ./lib/librte_acl/rte_acl_version.map
+ DPDK_20 {
+        global:
+ ...
 
-Also due to the interdependencies that DPDK libraries can have applications
-might end up with an executable space in which multiple versions of a library
-are mapped by ld.so.
+ $ head ./lib/librte_eal/rte_eal_version.map
+ DPDK_20 {
+        global:
+ ...
 
-Think of LibA that got an ABI bump and LibB that did not get an ABI bump but is
-depending on LibA.
+When an ABI change is made between major ABI versions to a given library, a new
+section is added to that library's version map describing the impending new ABI
+version, as described in the section :ref:`example_abi_macro_usage`. The
+library's soname and filename however do not change, e.g. ``libacl.so.20``, as
+ABI compatibility with the last major ABI version continues to be preserved for
+that library.
 
-.. note::
+.. code-block:: none
 
-    Application
-    \-> LibA.old
-    \-> LibB.new -> LibA.new
+ $ head ./lib/librte_acl/rte_acl_version.map
+ DPDK_20 {
+        global:
+ ...
 
-That is a conflict which can be avoided by setting ``CONFIG_RTE_MAJOR_ABI``.
-If set, the value of ``CONFIG_RTE_MAJOR_ABI`` overwrites all - otherwise per
-library - versions defined in the libraries ``LIBABIVER``.
-An example might be ``CONFIG_RTE_MAJOR_ABI=16.11`` which will make all libraries
-``librte<?>.so.16.11`` instead of ``librte<?>.so.<LIBABIVER>``.
+ DPDK_21 {
+        global:
+
+ } DPDK_20;
+ ...
 
+ $ head ./lib/librte_eal/rte_eal_version.map
+ DPDK_20 {
+        global:
+ ...
+
+However when a new ABI version is declared, for example DPDK ``21``, old
+depreciated functions may be safely removed at this point and the entire old
+major ABI version removed, see the section :ref:`deprecating_entire_abi` on
+how this may be done.
+
+.. code-block:: none
+
+ $ head ./lib/librte_acl/rte_acl_version.map
+ DPDK_21 {
+        global:
+ ...
+
+ $ head ./lib/librte_eal/rte_eal_version.map
+ DPDK_21 {
+        global:
+ ...
+
+At the same time, the major ABI version is changed atomically across all
+libraries by incrementing the major version in individual library's soname, e.g.
+``libacl.so.21``. This is done by bumping the LIBABIVER number in the libraries
+Makefile to indicate to dynamic linking applications that this is a later, and
+possibly incompatible library version:
+
+.. code-block:: c
+
+   -LIBABIVER := 20
+   +LIBABIVER := 21
 
-ABI versioning
---------------
 
 Versioning Macros
-~~~~~~~~~~~~~~~~~
+-----------------
 
 When a symbol is exported from a library to provide an API, it also provides a
 calling convention (ABI) that is embodied in its name, return type and
 arguments. Occasionally that function may need to change to accommodate new
-functionality or behavior. When that occurs, it is desirable to allow for
+functionality or behavior. When that occurs, it is may be required to allow for
 backward compatibility for a time with older binaries that are dynamically
 linked to the DPDK.
 
@@ -61,8 +151,10 @@ The macros exported are:
   fully qualified function ``p``, so that if a symbol becomes versioned, it
   can still be mapped back to the public symbol name.
 
+.. _example_abi_macro_usage:
+
 Examples of ABI Macro use
-^^^^^^^^^^^^^^^^^^^^^^^^^
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Updating a public API
 _____________________
@@ -106,16 +198,16 @@ maintain previous ABI versions that are accessible only to previously compiled
 binaries
 
 The addition of a parameter to the function is ABI breaking as the function is
-public, and existing application may use it in its current form.  However, the
+public, and existing application may use it in its current form. However, the
 compatibility macros in DPDK allow a developer to use symbol versioning so that
 multiple functions can be mapped to the same public symbol based on when an
-application was linked to it.  To see how this is done, we start with the
-requisite libraries version map file.  Initially the version map file for the
-acl library looks like this
+application was linked to it. To see how this is done, we start with the
+requisite libraries version map file. Initially the version map file for the acl
+library looks like this
 
 .. code-block:: none
 
-   DPDK_2.0 {
+   DPDK_20 {
         global:
 
         rte_acl_add_rules;
@@ -141,7 +233,7 @@ This file needs to be modified as follows
 
 .. code-block:: none
 
-   DPDK_2.0 {
+   DPDK_20 {
         global:
 
         rte_acl_add_rules;
@@ -163,16 +255,16 @@ This file needs to be modified as follows
         local: *;
    };
 
-   DPDK_2.1 {
+   DPDK_21 {
         global:
         rte_acl_create;
 
-   } DPDK_2.0;
+   } DPDK_20;
 
 The addition of the new block tells the linker that a new version node is
-available (DPDK_2.1), which contains the symbol rte_acl_create, and inherits the
-symbols from the DPDK_2.0 node.  This list is directly translated into a list of
-exported symbols when DPDK is compiled as a shared library
+available (DPDK_21), which contains the symbol rte_acl_create, and inherits
+the symbols from the DPDK_20 node. This list is directly translated into a
+list of exported symbols when DPDK is compiled as a shared library
 
 Next, we need to specify in the code which function map to the rte_acl_create
 symbol at which versions.  First, at the site of the initial symbol definition,
@@ -191,22 +283,22 @@ with the public symbol name
 
 Note that the base name of the symbol was kept intact, as this is conducive to
 the macros used for versioning symbols.  That is our next step, mapping this new
-symbol name to the initial symbol name at version node 2.0.  Immediately after
+symbol name to the initial symbol name at version node 20.  Immediately after
 the function, we add this line of code
 
 .. code-block:: c
 
-   VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+   VERSION_SYMBOL(rte_acl_create, _v20, 20);
 
 Remembering to also add the rte_compat.h header to the requisite c file where
-these changes are being made.  The above macro instructs the linker to create a
-new symbol ``rte_acl_create@DPDK_2.0``, which matches the symbol created in older
-builds, but now points to the above newly named function.  We have now mapped
-the original rte_acl_create symbol to the original function (but with a new
-name)
+these changes are being made. The above macro instructs the linker to create a
+new symbol ``rte_acl_create@DPDK_20``, which matches the symbol created in
+older builds, but now points to the above newly named function. We have now
+mapped the original rte_acl_create symbol to the original function (but with a
+new name)
 
-Next, we need to create the 2.1 version of the symbol.  We create a new function
-name, with a different suffix, and  implement it appropriately
+Next, we need to create the 21 version of the symbol. We create a new function
+name, with a different suffix, and implement it appropriately
 
 .. code-block:: c
 
@@ -220,12 +312,12 @@ name, with a different suffix, and  implement it appropriately
         return ctx;
    }
 
-This code serves as our new API call.  Its the same as our old call, but adds
-the new parameter in place.  Next we need to map this function to the symbol
-``rte_acl_create@DPDK_2.1``.  To do this, we modify the public prototype of the call
-in the header file, adding the macro there to inform all including applications,
-that on re-link, the default rte_acl_create symbol should point to this
-function.  Note that we could do this by simply naming the function above
+This code serves as our new API call. Its the same as our old call, but adds the
+new parameter in place. Next we need to map this function to the symbol
+``rte_acl_create@DPDK_21``. To do this, we modify the public prototype of the
+call in the header file, adding the macro there to inform all including
+applications, that on re-link, the default rte_acl_create symbol should point to
+this function. Note that we could do this by simply naming the function above
 rte_acl_create, and the linker would chose the most recent version tag to apply
 in the version script, but we can also do this in the header file
 
@@ -233,11 +325,11 @@ in the version script, but we can also do this in the header file
 
    struct rte_acl_ctx *
    -rte_acl_create(const struct rte_acl_param *param);
-   +rte_acl_create(const struct rte_acl_param *param, int debug);
-   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+   +rte_acl_create_v21(const struct rte_acl_param *param, int debug);
+   +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 21);
 
 The BIND_DEFAULT_SYMBOL macro explicitly tells applications that include this
-header, to link to the rte_acl_create_v21 function and apply the DPDK_2.1
+header, to link to the rte_acl_create_v21 function and apply the DPDK_21
 version node to it.  This method is more explicit and flexible than just
 re-implementing the exact symbol name, and allows for other features (such as
 linking to the old symbol version by default, when the new ABI is to be opt-in
@@ -257,6 +349,7 @@ assumption is that the most recent version of the symbol is the one you want to
 map.  So, back in the C file where, immediately after ``rte_acl_create_v21`` is
 defined, we add this
 
+
 .. code-block:: c
 
    struct rte_acl_ctx *
@@ -270,21 +363,22 @@ That tells the compiler that, when building a static library, any calls to the
 symbol ``rte_acl_create`` should be linked to ``rte_acl_create_v21``
 
 That's it, on the next shared library rebuild, there will be two versions of
-rte_acl_create, an old DPDK_2.0 version, used by previously built applications,
-and a new DPDK_2.1 version, used by future built applications.
+rte_acl_create, an old DPDK_20 version, used by previously built applications,
+and a new DPDK_21 version, used by future built applications.
 
 
 Deprecating part of a public API
 ________________________________
 
-Lets assume that you've done the above update, and after a few releases have
-passed you decide you would like to retire the old version of the function.
-After having gone through the ABI deprecation announcement process, removal is
-easy.  Start by removing the symbol from the requisite version map file:
+Lets assume that you've done the above update, and in preparation for the next
+major ABI version you decide you would like to retire the old version of the
+function. After having gone through the ABI deprecation announcement process,
+removal is easy. Start by removing the symbol from the requisite version map
+file:
 
 .. code-block:: none
 
-   DPDK_2.0 {
+   DPDK_20 {
         global:
 
         rte_acl_add_rules;
@@ -306,48 +400,42 @@ easy.  Start by removing the symbol from the requisite version map file:
         local: *;
    };
 
-   DPDK_2.1 {
+   DPDK_21 {
         global:
         rte_acl_create;
-   } DPDK_2.0;
+   } DPDK_20;
 
 
 Next remove the corresponding versioned export.
 
 .. code-block:: c
 
- -VERSION_SYMBOL(rte_acl_create, _v20, 2.0);
+ -VERSION_SYMBOL(rte_acl_create, _v20, 20);
 
 
 Note that the internal function definition could also be removed, but its used
-in our example by the newer version _v21, so we leave it in place.  This is a
-coding style choice.
-
-Lastly, we need to bump the LIBABIVER number for this library in the Makefile to
-indicate to applications doing dynamic linking that this is a later, and
-possibly incompatible library version:
-
-.. code-block:: c
+in our example by the newer version v21, so we leave it in place and declare it
+as static. This is a coding style choice.
 
-   -LIBABIVER := 1
-   +LIBABIVER := 2
+.. _deprecating_entire_abi:
 
 Deprecating an entire ABI version
 _________________________________
 
-While removing a symbol from and ABI may be useful, it is often more practical
-to remove an entire version node at once.  If a version node completely
-specifies an API, then removing part of it, typically makes it incomplete.  In
-those cases it is better to remove the entire node
+While removing a symbol from an ABI may be useful, it is more practical to
+remove an entire version node at once, as is typically done at the declaration
+of a major ABI version. If a version node completely specifies an API, then
+removing part of it, typically makes it incomplete. In those cases it is better
+to remove the entire node.
 
 To do this, start by modifying the version map file, such that all symbols from
-the node to be removed are merged into the next node in the map
+the node to be removed are merged into the next node in the map.
 
 In the case of our map above, it would transform to look as follows
 
 .. code-block:: none
 
-   DPDK_2.1 {
+   DPDK_21 {
         global:
 
         rte_acl_add_rules;
@@ -375,8 +463,8 @@ symbols.
 
 .. code-block:: c
 
- -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 2.0);
- +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 2.1);
+ -BIND_DEFAULT_SYMBOL(rte_acl_create, _v20, 20);
+ +BIND_DEFAULT_SYMBOL(rte_acl_create, _v21, 21);
 
 Lastly, any VERSION_SYMBOL macros that point to the old version node should be
 removed, taking care to keep, where need old code in place to support newer
diff --git a/doc/guides/contributing/patches.rst b/doc/guides/contributing/patches.rst
index 9e1013b..d63c9f5 100644
--- a/doc/guides/contributing/patches.rst
+++ b/doc/guides/contributing/patches.rst
@@ -156,9 +156,9 @@ Make your planned changes in the cloned ``dpdk`` repo. Here are some guidelines
 
   * For other PMDs and more info, refer to the ``MAINTAINERS`` file.
 
-* New external functions should be added to the local ``version.map`` file.
-  See the :doc:`Guidelines for ABI policy and versioning </contributing/versioning>`.
-  New external functions should also be added in alphabetical order.
+* New external functions should be added to the local ``version.map`` file. See
+  the :ref:`ABI policy <abi_policy>` and :ref:`ABI versioning <abi_versioning>`
+  guides. New external functions should also be added in alphabetical order.
 
 * Important changes will require an addition to the release notes in ``doc/guides/rel_notes/``.
   See the :ref:`Release Notes section of the Documentation Guidelines <doc_guidelines>` for details.
diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 0ee8533..2e163a5 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -4,7 +4,7 @@
 ABI and API Deprecation
 =======================
 
-See the :doc:`guidelines document for details of the ABI policy </contributing/versioning>`.
+See the :ref:`guidelines document for details of the ABI policy <abi_policy>`.
 API and ABI deprecation notices are to be posted here.
 
 
-- 
2.7.4

[dpdk-dev] [PATCH v4 4/4] doc: add maintainer for abi policy

[Ray Kinsella]

Add an entry to the maintainer file for the abi policy.

Signed-off-by: Ray Kinsella <mdr@ashroe.eu>
---
 MAINTAINERS | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index b3d9aad..d231f03 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -80,6 +80,10 @@ M: Marko Kovacevic <marko.kovacevic@intel.com>
 F: README
 F: doc/
 
+ABI Policy
+M: Ray Kinsella <mdr@ashroe.eu>
+F: doc/guides/contributing/abi_*.rst
+
 Developers and Maintainers Tools
 M: Thomas Monjalon <thomas@monjalon.net>
 F: MAINTAINERS
-- 
2.7.4