Re: [RFC QEMU PATCH] ui: Make the DisplayType enum entries conditional

["Daniel P. Berrangé" <berrange@redhat.com>]

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.

Note, however, that capabilities are preserved at the time each
the QEMU process is started.

IOW, if you boot QEMU, then remove a QEMU module, then attempt to
use a feature that implies loading of the removed QEMU module,
libvirt won't know the module has been removed for the running
QEMU.


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|