Bug#776450: Xen PVH support for grub-xen in Buster

[Hans van Kranenburg]

On 1/5/19 10:51 PM, Hans van Kranenburg wrote:
> [...]
> 
> I'll try to see if I can get things working when creating a grub image
> using the grub-xen-host_grub.cfg like we have already, and then put
> module stuff and a grub.cfg on the domU filesystem.

Hm, so I have a PV (or PVH) domU in a test environment here, and I tried
to use it in the Debian way of booting it.

If I install grub-xen-bin inside the domU then I get some stuff, but not
update-grub. When I just also install grub2 it drags in more stuff, and
then I end up with update-grub and a /boot/grub/grub.cfg file as result.

If I install grub-xen-host in the dom0 and use kernel =
"/usr/lib/grub-xen/grub-x86_64-xen.bin" in the guest config, then I get
a nice ascii art blue grub menu on the serial console when starting the
domU with xen create -c.

So, that's good, that's the already working PV scenario.

Now I want to have the same for PVH.

The config file I'm using is (debian.cfg):

---- >8 ----
if search -s -f /boot/grub/grub.cfg ; then
	echo "Reading (${root})/boot/grub/grub.cfg"
	configfile /boot/grub/grub.cfg
fi

if search -s -f /grub/grub.cfg ; then
	echo "Reading (${root})/grub/grub.cfg"
	configfile /grub/grub.cfg
fi
---- >8 ----

Now I do (with my custom compile blah as shown before):

-$ ./grub-mkstandalone --grub-mkimage=./grub-mkimage -o
out/grub-i386-xen_pvh-debian -O i386-xen_pvh -d grub-core/
boot/grub/grub.cfg=debian.cfg

-$ scp out/grub-i386-xen_pvh-debian root at dom0:

In the guest config file on the dom0, I've set:

---- >8 ----
kernel = "/root/grub-i386-xen_pvh-debian"
type = "pvh"
---- >8 ----

I just copied *.mod that I got from my grub build (with the make blah
shown before) into /usr/lib/grub/i386-xen_pvh of the domU, and that's
probably a very naive thing to do, since I mostly don't know what I'm
doing at this point. I especially have no idea how the booting grub
image from the dom0 would know to do anything with a file from
/usr/lib/grub/<whatever> inside the domU filesystem, but apparently the
current PV things do that.

When trying to start that, I get:

Reading (memdisk)/boot/grub/grub.cfg

and then it exits back to the dom0 prompt and the domU is gone.

This is where my been-there-done-that ends. It still feels like it's
very close, but I have no clue.

Hopefully this will ring some bells. :)

If needed, we can ask some help from the author of the xen_pvh grub
patchset.

Thanks,
Hans