Re: [PATCH 3/4] Build grub.xen.

[Colin Watson <cjwatson@ubuntu.com>]

On Thu, Dec 12, 2013 at 03:37:41PM +0000, Colin Watson wrote:
> +if [ -z "$grub_xen_guest" ]; then
> +	# This is the copy of grub.xen installed in the dom0's filesystem.
> +	# Look for a copy in the domU's filesystem and chainload that.  This
> +	# allows us to guarantee that GRUB will be in sync with the
> +	# configuration file in the domU.  The file locations here must not
> +	# have any configure-generated substitutions applied, as the intent
> +	# is that a single grub.xen should be able to cope with a variety of
> +	# domU systems.
> +	if search --set=root --file /boot/grub/grub.xen; then
> +		linux /boot/grub/grub.xen grub_xen_guest=1
> +		boot
[...]

I talked about this with Ian Jackson in the pub last night.  We came to
the same conclusion more or less at the same time, that this is in fact
a new boot protocol; since it essentially just expects a bzImage here,
there's nothing to stop somebody for example putting a bare kernel
there.  We'd like people to be able to set up PV-GRUB2 in their dom0s
even for domUs that aren't new enough to have PV-GRUB2 inside them.
Furthermore we'd like to be able to arrange that PV-GRUB (Legacy) and
PyGRUB can at least in principle use the same boot protocol; in the case
of PV-GRUB that would presumably involve a stub menu.lst, but it
shouldn't take much more than that.  As such the file name in the domU's
filesystem shouldn't be GRUB-specific, although per Vladimir it'd be
good for it to be distinct for each architecture.

I'll put this patch series on hold for the time being (with the possible
exception of "search --exclude", which I think has been uncontroversial
so far and could perhaps be merged as a generally-useful gadget?) and
write this up as a proper protocol document for inclusion in xen.git.
Ian said he'd like to get this into Xen 4.4's documentation.  No changes
to Xen code are required as far as I know.

-- 
Colin Watson                                       [cjwatson@ubuntu.com]