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

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

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

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.

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)

How about keeping things as is?

-- 
Adrien Mazarguil
6WIND