[dpdk-dev] [PATCH v2] doc: announce API changes for Windows compatibility

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

Windows socket headers define `s_addr`, `min`, and `max` macros which
break structure definitions containing fields with one of these names.
Undefining those macros would break some consumers as well.

Example 1:

    #include <winsock2.h>
    #include <rte_ether.h>
    struct in_addr addr;
    /* addr.s_addr = 0;     ERROR: s_addr undefined by DPDK */

Example 2:

    #include <rte_ether.h>
    #include <winsock2.h>
    struct rte_ether_hdr eh;
    /* eh.s_addr.addr_bytes[0] = 0;     ERROR: `addr_s` is a macro */

It is proposed to rename the conflicting fields on DPDK side,
because Win32 API has wider use and is slower and harder to change.

New names are left unspecified, open suggestions:

* `struct rte_ether_hdr` (by Stephen Hemminger):

    * `s_addr` -> `ether_shost`
    * `d_addr` -> `ether_dhost` (for consistency)

* `struct rte_param_log2_range`, `struct rte_crypto_param_range`:

    * `min` -> `minimum`
    * `max` -> `maximum`

For `s_addr`, a workaround is possible to use it until 21.11.
For `min` and `max`, no workaround seems available. If cryptodev or
compressdev is going to be enabled on Windows before 21.11, the only
option seems to use a new name on Windows (using #ifdef).

Workaround for `s_addr` is to define `struct rte_ether_hdr`
in such a away that it can be used with or without `s_addr` macro
(as defined on Windows):

    #pragma push_macro("s_addr")
    #ifdef s_addr
    #undef s_addr
    #endif

    struct rte_ether_hdr {
        struct rte_ether_addr d_addr; /**< Destination address. */
        RTE_STD_C11
        union {
            struct rte_ether_addr s_addr; /**< Source address. */
            struct {
                struct rte_ether_addr S_un;
                /**< MUST NOT be used directly, only via s_addr */
            } S_addr;
            /**< MUST NOT be used directly, only via s_addr */
        };
        uint16_t ether_type; /**< Frame type. */
    } __rte_aligned(2);

    #pragma pop_macro("s_addr")

Signed-off-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
---
v2: * Propose to rename all problematic fields identified so far.
    * Leave future names unspecified, no need to promise now.
    * Propose better names for MAC addresses (Stephen Hemminger).

Thread about `s_addr` workaround:
https://mails.dpdk.org/archives/dev/2021-March/200700.html
Tyler Retzlaff confirmed offline that Microsoft took similar approach.

 doc/guides/rel_notes/deprecation.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/doc/guides/rel_notes/deprecation.rst b/doc/guides/rel_notes/deprecation.rst
index 64629e0641..854618f091 100644
--- a/doc/guides/rel_notes/deprecation.rst
+++ b/doc/guides/rel_notes/deprecation.rst
@@ -130,3 +130,12 @@ Deprecation Notices
 * cmdline: ``cmdline`` structure will be made opaque to hide platform-specific
   content. On Linux and FreeBSD, supported prior to DPDK 20.11,
   original structure will be kept until DPDK 21.11.
+
+* net: ``s_addr`` and ``d_addr`` fields of ``rte_ether_hdr`` structure
+  will be renamed in DPDK 20.11 to avoid conflict with Windows Sockets headers.
+
+* compressdev: ``min`` and ``max`` fields of ``rte_param_log2_range`` structure
+  will be renamed in DPDK 20.11 to avoid conflict with Windows Sockets headers.
+
+* cryptodev: ``min`` and ``max`` fields of ``rte_crypto_param_range`` structure
+  will be renamed in DPDK 20.11 to avoid conflict with Windows Sockets headers.
-- 
2.29.2