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

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.