Re: [dpdk-dev] [PATCH v2 3/4] net/mlx: version rdma-core glue libraries

[Marcelo Ricardo Leitner <mleitner@redhat.com>]

On Mon, Feb 05, 2018 at 03:16:21PM +0100, Thomas Monjalon wrote:
> 05/02/2018 14:44, Adrien Mazarguil:
> > On Mon, Feb 05, 2018 at 10:58:06AM -0200, Marcelo Ricardo Leitner wrote:
> > > On Mon, Feb 05, 2018 at 12:24:23PM +0000, Van Haaren, Harry wrote:
> > > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Marcelo Ricardo Leitner
> > > > > Sent: Monday, February 5, 2018 12:14 PM
> > > > > To: Adrien Mazarguil <adrien.mazarguil@6wind.com>
> > > > > Cc: Thomas Monjalon <thomas@monjalon.net>; dev@dpdk.org; Shahaf Shuler
> > > > > <shahafs@mellanox.com>; Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
> > > > > Subject: Re: [dpdk-dev] [PATCH v2 3/4] net/mlx: version rdma-core glue
> > > > > libraries
> > > > > 
> > > > > On Mon, Feb 05, 2018 at 12:24:02PM +0100, Adrien Mazarguil wrote:
> > > > > > On Sun, Feb 04, 2018 at 03:29:38PM +0100, Thomas Monjalon wrote:
> > > > > > > 02/02/2018 17:46, Adrien Mazarguil:
> > > > > > > > --- a/drivers/net/mlx4/Makefile
> > > > > > > > +++ b/drivers/net/mlx4/Makefile
> > > > > > > > @@ -33,7 +33,9 @@ include $(RTE_SDK)/mk/rte.vars.mk
> > > > > > > >
> > > > > > > >  # Library name.
> > > > > > > >  LIB = librte_pmd_mlx4.a
> > > > > > > > -LIB_GLUE = librte_pmd_mlx4_glue.so
> > > > > > > > +LIB_GLUE = $(LIB_GLUE_BASE).$(LIB_GLUE_VERSION)
> > > > > > > > +LIB_GLUE_BASE = librte_pmd_mlx4_glue.so
> > > > > > > > +LIB_GLUE_VERSION = 18.02.1
> > > > > > >
> > > > > > > You should use the version number of the release, i.e. 18.02.0
> > > > > > > Ideally, you should retrieve it from rte_version.h.
> > > > > >
> > > > > > Keep in mind this only needs to be updated when the glue API gets
> > > > > modified,
> > > > > > and this "18.02.1" string may remain unmodified for subsequent DPDK
> > > > > > releases, probably as long as the PMD doesn't use any new rdma-core calls.
> > > > > >
> > > > > > We've already backported this patch to 17.02 and 17.11, both requiring
> > > > > > different sets of Verbs calls and thus a different version, hence the
> > > > > added
> > > > > > "18.02" as a starting point. The last digit may have to be modified
> > > > > possibly
> > > > > > several times between official DPDK releases while work is being done on
> > > > > the
> > > > > > PMD (i.e. per commit).
> > > > > >
> > > > > > In short it's not meant to follow DPDK's public versioning scheme. If you
> > > > > > really think it should, doing so will make things more complex in the
> > > > > > Makefile, which will have to parse rte_version.h. What's your opinion?
> > > > > 
> > > > > What about appending date +%s output to it? It would be stricter and
> > > > > automated.
> > > > 
> > > > Adding current timestamp or date into a build breaks reproducibility of builds, so is
> > > > generally not recommended.
> > > 
> > > Then the sha1sum of mlx4_glue.h.
> > > With this the size check I mentioned on the other patch would become
> > > redundant and unnecessary.
> > 
> > Using a strong hash algorithm to version a library/symbol, while possible,
> > seems a bit overkill and results in ugliness:
> > 
> >  librte_pmd_mlx4.so.c4ca4eaf2fe975ead83453458f4f56db49e724f3

Ugh yes, but it wouldn't need to be that visible. A pointer on
mlx*_glue and a define on PMD would be enough already. As in, an
extended check to the versioning.

> > 
> > Using a weak one like CRC32 for a shorter name poses a risk of
> > collision. Moreover the next time someone decides to update all version
> > notices or modify a comment will impact that hash. We'd need to isolate the
> > symbol definition itself, ignore parameter names in function prototypes and
> > only then we may get a somewhat meaningful hash describing a given ABI.

That's what I meant with stricter. Yes it would catch such
situations, but you tell me on how much we want to protect/restrict
here.  Do you see a reason for building only the dpdk/pmd side and not
the glue library at a time?

> > 
> > Given the added complexity, is there really a problem with simple version
> > numbers we increment every time something gets modified? (Note this is
> > already how our .map files work, they're not generated automatically)
> 
> Our map files show the major version where a symbol was introduced.
> It is simple because no symbol can be introduced in a minor version.
> 
> > How about keeping things as is?

I don't really see the need of unique filenames. The next patch is
already leveraging RTE_EAL_PMD_PATH, which if versioned should be
enough for this, no?

> 
> You are using 18.02.1 while it is introduced in 18.02.0.
> If you don't want to correlate the .so version number with DPDK version
> number, maybe that 1, 2, 3 would be a simpler choice (less confusing).

+1

  Marcelo