[dpdk-dev] [PATCH 0/4] Add DSO symbol versioning to support backwards compatibility

[Neil Horman]

On Fri, Sep 26, 2014 at 03:02:55PM -0700, Stephen Hemminger wrote:
> On Fri, 26 Sep 2014 10:45:49 -0400
> Neil Horman <nhorman at tuxdriver.com> wrote:
> 
> > On Fri, Sep 26, 2014 at 12:41:33PM +0200, Thomas Monjalon wrote:
> > > Hi Neil,
> > > 
> > > 2014-09-24 14:19, Neil Horman:
> > > > Ping Thomas. I know you're busy, but I would like this to not fall off anyones
> > > > radar.  You alluded to concerns regarding what, for lack of a better term,
> > > > ABI/API lockin.  I had asked you to enuumerate/elaborate on specifics, but never
> > > > heard back.  Are there further specifics you wish to discuss, or are you
> > > > satisfied with the above answers?
> > > 
> > > Sorry for not being very reactive on this thread.
> > > All this discussion is very interesting but it's really not the proper
> > > time to apply it. As you said, it requires an extra effort. I'm not saying
> > > it will never be integrated. I'm just saying that we cannot change
> > > everything at the same time.
> > > 
> > > Let me sum up the situation. This community project has been very active
> > > for few months now. First, we learnt how to make some releases together
> > > and we are improving the process to be able to deliver a new major release
> > > every 4 months while having some good quality process.
> > > But these releases are still not complete because documentation is not
> > > integrated yet. Then developers should have a role in documentation updates.
> > > We also need to integrate and learn how to use more tools to be more
> > > efficient and improve quality.
> > > 
> > > So the question is "when should we care about API compatibility"?
> > > And the answer is: ASAP, but not now. I feel next year is a better target.
> > > Because the most important priority is to move together at a pace which
> > > allow most of us to stay in the race.
> > > 
> > 
> > 
> > I'm sorry Thomas, I don't accept this.  I asked you for details as to your
> > concerns regarding this patch series, and you've provided more vague comments.
> > I need details to address
> > 
> > You say it requires extra effort, you're right it does.  Any feature that you
> > integreate requires some additional effort.  How is this patch any different
> > from adding the acl library or any other new API?  Everything requires
> > maintenence, thats how software works.  What specfically about this patch series
> > makes the effort insurmountable to you?
> > 
> > You say you're improving your process.  Great, this patch aids in that process
> > by ensuring backwards compatibility for a period of time.  Given that the API
> > and ABI can still evolve within this framework, as I've described, how is this
> > patch series not a significant step forward toward your goal of quality process.
> > 
> > You say documentation isn't integrated.  So, what does getting documentation
> > integrated have to do with this patch set, or any other?  I don't see you
> > holding any other patches based on documentation.  Again, nothing in this series
> > prevents evolution of the API or ABI.  If you're hope is to wait until
> > everything is perfect, then apply some control to the public facing API, and get
> > it all documented, none of thosse things will ever happen, I promise you.
> > 
> > You say you also need to learn to use more tools to be more efficient and
> > improve quality.  Great!  Thats exactly what this is. If we mandate even a short
> > term commitment to ABI stability (1 single relese worth of time), we will
> > quickly identify what API's change quickly and where we need to be cautious with
> > our API design.  If you just assume that developers will get better of their own
> > volition, it will never happen.
> > 
> > You say this should go in next year, but not now.  When exactly?  What event do
> > you forsee occuring in the next 12-18 months that will change everything such
> > that we can start supporing an ABI for more than just a few weeks at the head of
> > the tree?  
> > 
> > To this end, I just did a quick search through the git history for dpdk to look
> > at the histories of all the header files that are exposed via the makefile
> > SYMLINK command (given that that provides a list of header files that
> > applications can include, and embodies all the function symbols and data types
> > applications have access to.
> > 
> > There are 179 total commits in that list
> > Of those, a bit of spot checking suggests that about 10-15% of them actually
> > change ABI, and many of those came from Bruce's rework of the mbuf structure.
> > That about 17-20 instances over the last 2 years where an ABI update would have
> > been needed.  That seems pretty reasonable to me.  Where exactly is your concern
> > here?
> > 
> > Neil
> 
> Isn't ABI stablity a distro responsibility not a project responsibility?
> I have lots more API/ABI changes, just been too busy trying to release a real
> product using DPDK to upstream all the changes.
> 
No.  How well would glibc or any major library work without ABI stability?
Its definately a distros responsibility to not break ABI with backports from
upstream within a major release, but its upstreams responsibility to maintain
ABI for some period of time to prevent immediate distro breakage with an update.
Often libraries provide this by simply taking lots of care in their ABI
design, but if ABI flexibility is a need, providing some level of backwards
compatibility must fall on the upstream project.
Neil

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