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

[Colin Watson]

On Fri, Nov 04, 2016 at 12:25:39AM +0000, Ian Jackson wrote:
> 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.

[Technically you CCed grub at p.d.o rather than grub2 at p.d.o, but no matter.
CC corrected.]

> 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.

This is correct.

> I doubt it statically links against
> libxen* libraries, but I don't think I can entirely rule it out.

Indeed, it doesn't.  All the Xen interaction is in freestanding boot
code that has no legitimate reason to link against the userspace
libraries.

> 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.)

It appears that upstream took a copy a little while back (upstream
commit e07badcc31babb24ace4f96444bc484502427d3a), but I didn't notice
this when preparing packages of 2.02~beta3.  I'll test whether the
package still builds correctly without libxen-dev and if so I'll upload
without that build-dependency.

In any case, I don't think grub2 needs to be rebuilt for this
transition.

Thanks,

-- 
Colin Watson                                       [cjwatson at debian.org]