Re: [dpdk-dev] How to manage new APIs added after major ABI release?

["Kinsella, Ray" <ray.kinsella@intel.com>]

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson@intel.com>
> Sent: Tuesday 10 December 2019 14:37
> To: Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: Kinsella, Ray <ray.kinsella@intel.com>; Thomas Monjalon
> <thomas@monjalon.net>; David Marchand <david.marchand@redhat.com>; Luca
> Boccassi <bluca@debian.org>; Christian Ehrhardt
> <christian.ehrhardt@canonical.com>; Timothy Redaelli
> <tredaelli@redhat.com>; Kevin Traynor <ktraynor@redhat.com>; dpdk-dev
> <dev@dpdk.org>; Laatz, Kevin <kevin.laatz@intel.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>; Neil Horman <nhorman@redhat.com>
> Subject: Re: How to manage new APIs added after major ABI release?
> 
> On Tue, Dec 10, 2019 at 12:40:53PM +0000, Ferruh Yigit wrote:
> > On 12/10/2019 12:04 PM, Bruce Richardson wrote:
> > > On Tue, Dec 10, 2019 at 11:56:28AM +0000, Ferruh Yigit wrote:
> > >> Hi,
> > >>
> > >> With new process, the major ABI releases will be compatible until
> > >> it is deprecated (until next LTS for now), like current ABI
> version
> > >> is 20 in DPDK_19.11 and DPDK versions until DPDK_20.11 will be ABI
> > >> compatible with this version.
> > >>
> > >> But if we introduce a new API after major ABI, say in 20.02
> > >> release, are we allowed to break the ABI for that API before
> DPDK_20.11?
> > >>
> > >> If we allow it break, following problem will be observed:
> > >> Assume an application using .so.20.1 library, and using the new
> API
> > >> introduced in 20.02, lets say foo(), but when application switches
> > >> to .so.20.2 (released via DPDK_20.05), application will fail
> > >> because of ABI breakage in foo().
> > >>
> > >> I think it is fair that application expects forward compatibility
> > >> in minor versions of a shared library.
> > >> Like if application linked against .so.20.2, fair to expect
> > >> .so.20.3, .so.20.4 etc will work fine. I think currently only
> .so.20.0 is fully forward compatible.
> > >>
> > >> If we all agree on this, we may need to tweak the process a
> little,
> > >> but before diving into implementation details, I would like to be
> sure we are in same page.
> > >>
> > >
> > > Well, any new API's generally come in as experimental, in which
> case
> > > changes are allowed, and breakage can be expected. If they are not
> > > experiemental, then the ABI policy applies to them in that they
> > > cannot change since they are part of the .21 ABI, even if that ABI
> > > is not fully complete yet. For any application only using stable,
> > > non-experimental functions, forward compatibility must be
> maintained IMHO.
> > >
> >
> > Talking about not experimental APIs, experimental ones free from the
> process.
> >
> > And when and API added in 20.02 (ABI_20.1) it is kind of still
> ABI_20,
> > because it should be supported for following ABI_20.x, instead of
> > calling it ABI_21, and this minor tweak (and mind shift) in .map
> files can be our solution.
> 
> Related at what to do with adding versions between major ABI versions,
> when investigating with Kevin the ABI checking we have made an
> unpleasant
> discovery:
> 
> This minor version bumping from 20.0 to 20.1 has apparently already
> broken our ABI according to libabigail.
> 
> The Gory Details [skip to the end for suggestions to fix]
> ------------------------------------------------------------
> 
> The reason for this is that the soversion encoded in each library -
> whether built with meson or make - is the full 20.0 version, not just
> the major ABI
> .20 part. Then when apps link against DPDK, they actually encode the
> 20.0.
> 
> So what this means is that currently - using a make build as an example
> here - ldd on the latest head build gives:
> 
>  LD_LIBRARY_PATH=$(pwd)/x86_64-native-linux-gcc/lib ldd x86_64-native-
> linux-gcc/app/testpmd | head
>         linux-vdso.so.1 (0x00007fff6813d000)
>         librte_pmd_bond.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pmd_bond.so.20.1 (0x00007f36d723c000)
>         librte_pmd_dpaa.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pmd_dpaa.so.20.1 (0x00007f36d7229000)
>         librte_mempool_dpaa.so.20.1 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc/lib/librte_mempool_dpaa.so.20.1 (0x00007f36d7224000)
>         librte_pmd_ixgbe.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pmd_ixgbe.so.20.1 (0x00007f36d71ba000)
>         librte_pmd_i40e.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pmd_i40e.so.20.1 (0x00007f36d7126000)
>         librte_pmd_bnxt.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pmd_bnxt.so.20.1 (0x00007f36d70e5000)
>         librte_pmd_softnic.so.20.1 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc/lib/librte_pmd_softnic.so.20.1 (0x00007f36d70b7000)
>         librte_flow_classify.so.0.201 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc/lib/librte_flow_classify.so.0.201 (0x00007f36d70b1000)
>         librte_pipeline.so.20.1 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc/lib/librte_pipeline.so.20.1 (0x00007f36d7088000) ...
> 
> Similarly ldd on a 19.11 checkout gives:
> 
> LD_LIBRARY_PATH=$(pwd)/x86_64-native-linux-gcc_v19.11/lib ldd x86_64-
> native-linux-gcc_v19.11/app/testpmd | head
>         linux-vdso.so.1 (0x00007ffc2a964000)
>         librte_pmd_bond.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pmd_bond.so.20.0 (0x00007fd4dc6b6000)
>         librte_pmd_dpaa.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pmd_dpaa.so.20.0 (0x00007fd4dc6a3000)
>         librte_mempool_dpaa.so.20.0 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc_v19.11/lib/librte_mempool_dpaa.so.20.0
> (0x00007fd4dc69e000)
>         librte_pmd_ixgbe.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pmd_ixgbe.so.20.0 (0x00007fd4dc634000)
>         librte_pmd_i40e.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pmd_i40e.so.20.0 (0x00007fd4dc5a0000)
>         librte_pmd_bnxt.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pmd_bnxt.so.20.0 (0x00007fd4dc55d000)
>         librte_pmd_softnic.so.20.0 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc_v19.11/lib/librte_pmd_softnic.so.20.0
> (0x00007fd4dc531000)
>         librte_flow_classify.so.0.200 => /home/bruce/dpdk.org/x86_64-
> native-linux-gcc_v19.11/lib/librte_flow_classify.so.0.200
> (0x00007fd4dc52b000)
>         librte_pipeline.so.20.0 => /home/bruce/dpdk.org/x86_64-native-
> linux-gcc_v19.11/lib/librte_pipeline.so.20.0 (0x00007fd4dc502000)
> 
> The final check - using the 19.11 compiled testpmd with the library
> path set to 20.02 versionned libs:
> 
> LD_LIBRARY_PATH=$(pwd)/x86_64-native-linux-gcc/lib ldd x86_64-native-
> linux-gcc_v19.11/app/testpmd | head
>         linux-vdso.so.1 (0x00007ffc711fc000)
>         librte_pmd_bond.so.20.0 => not found
>         librte_pmd_dpaa.so.20.0 => not found
>         librte_mempool_dpaa.so.20.0 => not found
>         librte_pmd_ixgbe.so.20.0 => not found
>         librte_pmd_i40e.so.20.0 => not found
>         librte_pmd_bnxt.so.20.0 => not found
>         librte_pmd_softnic.so.20.0 => not found
>         librte_flow_classify.so.0.200 => not found
>         librte_pipeline.so.20.0 => not found
> 
> Fixing This
> -----------
> 
> To fix this, we need to ensure that the SONAME remains constant across
> the releases. Therefore, I currently see two options:
> 
> 1. keep 20.0 as the version and soname across all releases in 2020,
> i.e.
>   just revert the ABIVERSION change patch. Trouble there is how to
> track
>   20.02 vs 20.05 etc. etc.
> 
> 2. remove the .0, .1 from the SONAMES stored in the libraries. This has
> the
>   advantage of keeping the existing planned schemes, but has the really
> big
>   downside of breaking ABI compatibility with anyone who has already
>   compiled with 19.11.
> 
> Personally, of the two options - unless someone can come up with a
> third option - I'd tend towards the second, fixing the builds to remove
> the .0 in the soname, and releasing that ASAP as 19.11.1 before 19.11
> gets widespread adoption. Since this ABI stability is new, teething
> problems may be expected.
> 
> Thoughts and comments?
> /Bruce
> 
> BTW: For meson, the patch for option 2 is just to remove the so_version
> variable and all references to it from lib/meson.build and
> drivers/meson.build. Haven't looked into a "make" fix yet.

From the DPDK ABI Version Document ...

A library's 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

https://doc.dpdk.org/guides/contributing/abi_versioning.html