Bug#842919: transition: xen (vs. grub2)

[Ian Jackson]

Hi, grub2 maintainers.  I'm CCing you into this conversation in the
hope you can help explain the semantics of the grub2 package's
build-dependency on libxen-dev.

I will quote the whole transition mail:

Emilio Pozuelo Monfort writes ("Re: Bug#842919: transition: xen"):
> On 02/11/16 11:47, Ian Jackson wrote:
> > Package: release.debian.org
> > Severity: normal
> > User: release.debian.org at packages.debian.org
> > Usertags: transition
> > 
> > Hi.  This is the update from Xen 4.6 to Xen 4.8, as previously
> > discussed.  (Currently, Xen 4.8.0 RC3.  I expect the Xen 4.8.0 release
> > to be out by the time Debian freezes.)
> > 
> > libxen-* contains libraries needed for management tools.   The
> > corresponding xen-utils-* packages are intended to be coinstallable,
> > so perhaps a "smooth" transition may still be possible ?  (Contrary to
> > what the autogenerated transition tracker thinks.)
> > 
> > All that is needed from the build-rdeps is a rebuild.  That is, of:
> >   libvirt qemu xenwatch python-pyxenstore collectd grub2
> > 
> > I have checked that they all build against the new libxen{-4.8,-dev},
> > at least on amd64.  I don't anticipate trouble on other architectures.
> 
> The ben tracker only lists qemu and libvirt as rdeps of the binaries
> that are removed in the new version. Why do the other packages need
> a rebuild? Do any of them statically link libxen or something?

(Emilio will see that I discussed other the packages in another mail.
Also, I am somewhat full of wine right now, so my answers may be
wrong.  It seemed better to reply sooner.  My work hat can produce
more sober replues tomorrow.  Regarding grub2:)

I don't know why grub2 Build-Depends libxen-dev.  None of the binaries
in my test-rebuild end up Depending on libxen-4.8.

Perhaps the B-D is just because it needs a copy of the Xen public
headers for the hypervisor API.  I doubt it statically links against
libxen* libraries, but I don't think I can entirely rule it out.
There is a binary grub-xen-bin which is probably relevant.

grub-xen-bin contains grub compiled for the Xen PV environment: that
is, to run directly under Xen as part of a guest startup.  It will
need header files describing the Xen public ABI.  These are the "Xen
public headers", and because of Xen's ABI compatibility guarantees the
normal upstream recommendation is to actually copy those into the
trees of projects which are building binaries to run on Xen.  (So for
example Linux has its own - modified - copies.)

If this is the only reason why grub2 Build-Depends libxen-dev then
there is no need to rebuild grub2.

It seems unlikely to me that grub2 could somehow statically link
actual libxen-dev library code (and statically embed it into a grub
binary), but perhaps I'm just not being imaginative enough.

And I guess it is possible that grub2 has some other function which
somehow embeds pieces from libxen-dev.

I hope the grub2 maintainers will be able to shed some light.

Thanks,
Ian.

-- 
Ian Jackson <ijackson at chiark.greenend.org.uk>   These opinions are my own.

If I emailed you from an address @fyvzl.net or @evade.org.uk, that is
a private address which bypasses my fierce spamfilter.
.