[libvirt] [Spice-devel] [PATCH v4] qemu: Use heads parameter for QXL driver

Frediano Ziglio fziglio at redhat.com
Tue Jul 21 12:41:33 UTC 2015

> On Tue, Jul 21, 2015 at 09:36:55AM +0200, Christophe Fergeau wrote:
> >On Mon, Jul 20, 2015 at 11:25:52AM +0200, Martin Kletzander wrote:
> >> I spend all morning fixing this to be installed properly in the
> >> system.  Anyway, I finally managed to make this work and found out the
> >> guest I used for it is not ready to have multiple monitors.  Anyway,
> >> looking at everything else this definitely works, so ACK, I'll push it
> >> in a while.
> >
> >I'm still a bit worried that all existing guests will have heads='1' in
> >their XML as libvirt is adding that by default, but I don't really see a
> >way around it :-/ We should make sure libvirt stops adding it from now
> >on though ;)
> >
> Well, how would you then limit the outputs to 1?  Having said that, I
> have no idea why we started adding heads="1" automatically and playing
> with different changes, we have another bug in the parsing/formatting
> code.  You'll also won't be able to migrate from older libvirt with
> heads='1' to newer ones.  I haven't realized that.  I'm thinking about
> reverting the change in libvirt or even using heads > 1.  Although
> that won't migrate either.  So the only other thing that we can do is
> to introduce new parameter, like maxHeads.  The sound you just heard
> is me slapping my face because again there will multiple parameters
> meaning similar things...

heads specify the number of heads the emulated virtual card has. I think the problem was specify the number for QXL which never honored this setting.
I don't think you can't migrate, just after migration the machine won't allow more than 1 head.
Unfortunately the XML file does not have any field to specify the libvirt version was meant for. It would be useful to add so if you see the version it means that heads==1 means 1 if not it means is not defined.
I'm against a new parameter which specify the same meaning of another parameter. I would instead something like validHeads or headsSet with a false as default.

> >Christophe


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