No display in Xen PV guests: "This VM has no graphic display device."

[Dario Faggioli]

Hello everyone,

We've found an issue that manifests in Xen PV guests. We have
encountered it when testing our (SUSE and openSUSE) packaged version of
9.1.x, but I've been able to reproduce it even using the upstream
master branch.

QEMU 8.2.8 works fine, so something happened during 9.0 or 9.1
development (and not backported to stable).

Basically, it's enough to try to create a Xen PV guest with virt-
manager and the only output of the virt-manager window will be "This VM
has no graphic display device" (while, e.g., `xl console <domid>` works
fine).

There is some additional info in this bug, but not all of that makes
sense (we were in a hurry for a fix, and this is not my area :-/):

https://bugzilla.suse.com/show_bug.cgi?id=1232712

However, what I eventually figured out though (through a couple of
bisections), is that if I revert _both_:

- 6ece1df966 hw/xen: Register framebuffer backend via xen_backend_init()
- e99441a379 ui/curses: Do not use console_select().

Things work again.

As I said, this is not my field, so there's not much more that I can
say for now. Nevertheless, I'm happy to try to help as much as I can
(e.g., testing theories, trying patches, etc)... So let me know what I
can do. :-)

Regards,
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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