On 09/06/2021 13.49, Gerd Hoffmann wrote:
On Wed, Jun 09, 2021 at 12:29:58PM +0100, Daniel P. Berrangé wrote:
On Wed, Jun 09, 2021 at 01:24:05PM +0200, Gerd Hoffmann wrote:
On Wed, Jun 09, 2021 at 12:02:40PM +0200, Thomas Huth wrote:
Libvirt's "domcapabilities" command has a way to state whether certain graphic frontends are available in QEMU or not. Originally, libvirt looked at the "--help" output of the QEMU binary to determine whether SDL was available or not (by looking for the "-sdl" parameter in the help text), but since libvirt stopped doing this analysis of the help text, the detection of SDL is currently broken, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1790902
QEMU should provide a way via the QMP interface instead. The simplest way, without introducing additional commands, is to make the DisplayType enum entries conditional, so that the enum only contains the entries if the corresponding CONFIG_xxx switches have been set.
Hmm, that'll break for the "dnf remove qemu-ui-sdl" case ...
Note tht libvirt invalidates its cache of QEMU capabilities when it sees the /usr/lib64/qemu directory timestamp change. So it ought to pick up changes caused by installing/removing QEMU modules, and apply this to future queries for domcapabilities, or when starting future QEMU guests.
That'll work fine for modules implementing qom objects / devices, because the list of available objects changes accordingly and libvirt can see that.
The #if CONFIG_SDL approach will not work because qemu will continue to report sdl as supported even when the sdl module is not installed any more.
I guess we'd need a separate QMP command to fix that, which tries to load the modules first when being called? Something similar to what is being done in qemu_display_help() ? That's certainly doable, too, just a little bit more complex... do we want that? Or is the quick-n-easy way via the schema good enough for most use cases? (I'm not that familiar with "virsh domcapabilities" ... is there any real usage for the <graphics> section or is this rather cosmetical?) Thomas PS: My CI runs with the patch just finished, and apparently I missed some #ifdefs in other parts of the code ... so I need to respin this patch anyway, no matter which direction we decide to go...