Re: [dpdk-dev] [PATCH v8 2/4] doc: changes to abi policy introducing major abi versions

[Thomas Monjalon <thomas@monjalon.net>]

Hi,
Please find the techboard comments below.

06/11/2019 10:22, Ray Kinsella:
> On 06/11/2019 09:06, Thomas Monjalon wrote:
> > 06/11/2019 09:49, Ray Kinsella:
> >> On 06/11/2019 00:11, Thomas Monjalon wrote:
> >>> 05/11/2019 16:24, Ray Kinsella:
> >>>> +#. Major ABI versions are declared every **year** and are then supported for one
> >>>> +   year, typically aligned with the :ref:`LTS release <stable_lts_releases>`.
> >>>
> >>> As discussed earlier, a major ABI version can be declared less often
> >>> than one year in the future.
> >>> An ABI is supported more than one year, because of the LTS branches.
> >>> That's why I propose to replace with this sentence:
> >>> "
> >>> Major ABI versions are declared regularly and are then supported for
> >>> at least one year, typically aligned with the :ref:`LTS release <stable_lts_releases>`.
> >>> "
> >>
> >> So look, this one was a decision of the technical board.
> > 
> > The techboard didn't decide to change the ABI every year.
> > We decided to review the duration after the first year, with a plan to extend.
> > 
> >> My position is still what was agreed was, "declared every year, and supported for one year".
> >> I like it, it's crystal clear what is the policy, until we change the policy.
> > 
> > I think it gives a wrong message.
> > 
> >> That said, I can make the change no problem, but I need some others to chime in to ok it. 
> >> Perhaps at the head of the Techboard today?
> > 
> > Yes I add it to the techboard meeting.

The techboard propose other rewords:
"supported" may be replaced with "compatibility is enforced"
"every year" may be replaced with "no more frequently than every year"
"declared" may be replaced with "could be declared"

I think you got the idea. Please adjust wording to something more accurate.

###

> >>>> +A major ABI version is declared every year, aligned with that year's LTS
> >>>> +release, e.g. v19.11. This ABI version is then supported for one year by all
> >>>> +subsequent releases within that time period, until the next LTS release, e.g.
> >>>> +v20.11.
> >>>
> >>> Let's reword like this:
> >>> "
> >>> A new major ABI version can be declared when a new LTS branch is started,

It has been suggested to replace "can" with "may".

> >>> e.g. ABI 19 for DPDK 19.11.0.
> >>> This major ABI version is then supported until the next one,
> >>> e.g. ABI 20 for DPDK 20.11.0.
> >>> All ABI changes must be detailed in the release notes.
> >>> "

My reword is wrong because ABI versions should be 20 and 21 respectively.

> >> This is more ambiguous, although what I said above stands.
> > 
> > What you said is wrong because of 2 reasons:
> > - it is not always one year for an major ABI
> 
> Well that is a point of disagreement.

The techboard agreed to remove "every year".
> 
> > - it is always longer because of LTS branch
> 
> Well I was pretty careful to qualify the ABI policy applies to releases over the year.
> To distinguish it from LTS branch. 

As above, we may replace "ABI is supported" with
"ABI compatibility is enforced".

> >> If there is general agreement with changing this part of the policy, I am ok to make 
> >> the change.
> > 
> > Yes let's review with the techboard.

Please try to reflect techboard comments while keeping something understandable :)

###

> >>>> +   ABI breakages due to changes such as reorganizing public
> >>>> +   structure fields for aesthetic or readability purposes should be avoided.
> >>>
> >>> Why it should be avoided?
> >>> If the ABI is broken anyway, I don't see any reason to not break it more.
> >>
> >> This is text from the original ABI Policy - I think the general sentiment still stands.
> >> Just because you have an ABI Breakage window doesn't mean you should feel free to break
> >> the ABI. The 3 ACKs required from Technical Board member to change the ABI, are another
> >> reflection of this. 
> >>
> >> As a general rule.
> >> Unnecessary changes should still be avoided, to reduce ABI churn between ABI versions.
> > 
> > I agree we must avoid unnecessary API changes because it requires apps to adapt.
> > But if the change is only ABI, and we are in an ABI-change window,
> > I don't see any issue

The techboard agrees that the ABI changes are unlimited but API changes must be avoided.
It is suggested to replace "ABI" with "API". I think this reword is better:
"
API changes such as reorganizing public structure fields
for aesthetic or readability purposes should be avoided.
"

###

> >>>> +Libraries marked as ``experimental`` are entirely not considered part of an ABI
> >>>> +version, and may change without warning at any time. Experimental libraries
> >>>> +always have a major version of ``0`` to indicate they exist outside of
> >>>> +ABI Versioning, with the minor version incremented with each ABI change
> >>>> +to library.
> >>>
> >>> It means not all libraries will have the same ABI version.
> >>> It is contrary of "ABI version is managed at a project level",
> >>> and I don't see a real benefit of a different version number.
> >>
> >> There is a benefit, major version 0 is a very clear indication that 
> >> the library exists outside of ABI management. 
> >> A library isn't in the ABI, until it is in the ABI - an then it gets
> >> added to the major version number. 
> >>
> >>> Anyway, some experimental functions can live inside a library
> >>> with a stable ABI version number
> >>
> >> True, but if an entire library is experimental - let's be crystal 
> >> clear about that. 
> > 
> > I would like to see what others think.

The techboard decided to keep this policy: .0 for pure experimental libs.