[dpdk-dev] [PATCH v5 4/4] docs: Add ABI documentation

[O'driscoll, Tim]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Neil Horman
> Sent: Tuesday, January 20, 2015 2:24 PM
> To: Iremonger, Bernard
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v5 4/4] docs: Add ABI documentation
> 
> On Tue, Jan 20, 2015 at 01:37:35PM +0000, Iremonger, Bernard wrote:
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas
> Monjalon
> > > Sent: Tuesday, January 20, 2015 7:15 AM
> > > To: Neil Horman
> > > Cc: dev at dpdk.org
> > > Subject: Re: [dpdk-dev] [PATCH v5 4/4] docs: Add ABI documentation
> > >
> > > Thank you Neil for writing this document.
> > > This is a really important change in DPDK.
> > > It would be very good to have comments or acknowledgement from
> several developpers. This policy
> > > would be enforced by having several Acked-by lines.
> > >
> > >
> > > 2015-01-16 10:33, Neil Horman:
> > > > Adding a document describing rudimentary ABI policy and adding notice
> > > > space for any deprecation announcements
> > > >
> > > > Signed-off-by: Neil Horman <nhorman at tuxdriver.com>
> > > > CC: Thomas Monjalon <thomas.monjalon at 6wind.com>
> > > > CC: "Richardson, Bruce" <bruce.richardson at intel.com>
> > > >
> > > > ---
> > > > Change notes:
> > > >
> > > > v5) Updated documentation to add notes from Thomas M.
> > > > ---
> > > >  doc/abi.txt | 36 ++++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 36 insertions(+)
> > > >  create mode 100644 doc/abi.txt
> > > >
> > > > diff --git a/doc/abi.txt b/doc/abi.txt new file mode 100644 index
> > > > 0000000..14be464
> > > > --- /dev/null
> > > > +++ b/doc/abi.txt
> > > > @@ -0,0 +1,36 @@
> > > > +ABI policy:
> > > > +	ABI versions are set at the time of major release labeling, and ABI
> > > > +may change multiple times between the last labeling and the HEAD
> > > > +label of the git tree without warning
> > > > +
> > > > +	ABI versions, once released are available until such time as their
> > > > +deprecation has been noted here for at least one major release cycle,
> > > > +after it has been tagged.  E.g. the ABI for DPDK 1.8 is shipped, and
> > > > +then the decision to remove it is made during the development of
> DPDK
> > > > +1.9.  The decision will be recorded here, shipped with the DPDK 1.9
> > > > +release, and actually removed when DPDK
> > > > +1.10 ships.
> > > > +
> > > > +	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 of.  In those events ABI's may be updated without
> > > > +backward compatibility provided.  The requirements for doing so are:
> > > > +	1) At least 3 acknoweldgements of the need on the dpdk.org
> > > > +	2) A full deprecation cycle must be made to offer downstream
> > > > +consumers sufficient warning of the change.  E.g. if dpdk 2.0 is
> > > > +under development when the change is proposed, a deprecation
> notice
> > > > +must be added to this file, and released with dpdk 2.0.  Then the
> change may be incorporated for
> > > dpdk 2.1
> > > > +	3) The LIBABIVER variable in the makefilei(s) where the ABI changes
> > > > +are incorporated must be incremented in parallel with the ABI changes
> > > > +themselves
> > > > +
> > > > +	Note that the above process for ABI deprecation should not be
> > > > +undertaken lightly.  ABI stability is extreemely important for
> > > > +downstream consumers of the DPDK, especially when distributed in
> > > > +shared object form.  Every effort should be made to preserve ABI
> > > > +whenever possible.  For instance, reorganizing public structure field
> > > > +for astetic or readability purposes should be avoided as it will
> > > > +cause ABI breakage.  Only significant (e.g. performance) reasons
> should be seen as cause to alter
> > > ABI.
> >
> > Hi Thomas,
> >
> > Should there be a reference to this document in the programmers guide?
> >
> Thats a good question. I think, as Thomas notes, it probably should be
> referenced in some way.  The programmers guide might be good.  What
> might be
> better would be checking the deprecation notices and adding them to the
> release
> notes for any given release.
> 
> Thoughts?

I'd suggest that the policy itself should go in, or at least be referenced from, the programmer's guide. I agree that the deprecation notices themselves should go in the release notes.

> Neil
> 
> > Regards,
> >
> > Bernard.
> >
> >