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Re: [Xen-devel] libxl stable API (Re: 4.2 TODO update)

On Wed, 2012-03-14 at 11:16 +0000, Ian Jackson wrote:
> Ian Campbell writes ("[Xen-devel] libxl stable API (Re:  4.2 TODO update)"):
> > Lastly we also to decide what we want to do about ABI (as opposed to
> > API) compatibility. Obviously if we change the ABI then we should change
> > the SONAME, but is this something we want to commit to avoiding? i.e.
> > should it be possible to build a downstream against libxl.so.2.0 (the
> > current libxl soname) from 4.2 and expect that dropping in libxl.so.2.0
> > >from 4.3 will Just Work against the new hypervisor interfaces? Or do we
> > expect that 4.3 will provide libxl.so.2.1 and that the same downstream
> > source can be built twice? (e.g. with the correct one selected via some
> > plugin mechanism). Obviously avoiding ABI changes is a lot harder and
> > I'm not sure if that is something we are able to commit to at this stage
> > (and I'm not sure how good we would be at it even if we did try and make
> > that commitment).
> I agree with most of what you say.

Thanks. I shall add "agree & document compatibility guarantees +
associated technical measures" to the TODO list.

> I don't think we can commit to not making ABI changes.  It is thus an
> unfortunate fact that the whole stack, from libxl caller on down to
> the hypervisor, will have to change together when the version of Xen
> is updated.

Right. We can strive to make this a straight rebuild with no source
changes (somewhat akin to a binNMU in Debian-speak).

> > >               * Safe fork vs. fd handling hooks. This is an API
> > >                 addition, so maybe not required fro stable API, bit need
> > >                 to have for 4.2? (Ian J, patches posted)
> I think this is important to have.  It will imply changes to quite a
> few ordinary api functions.

Thanks, I will update the commentary accordingly in the next iteration.


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