[libvirt] [RFC] default video device type

[Martin Kletzander]

On Mon, Oct 07, 2019 at 02:56:11PM +0200, Pavel Mores wrote:
>
>Hi,
>
>I'm looking into fixing
>
>https://bugzilla.redhat.com/show_bug.cgi?id=1668141
>
>(as a short summary, if a graphics device is added to XML that has no video
>device, libvirt automatically adds a video device which is always of type
>'cirrus' - even if the underlying qemu doesn't support cirrus).
>
>I'm able to affect the behaviour in question by using qemu capabilities in
>qemuDomainDeviceVideoDefPostParse(), see proof-of-concept change in [1].  I
>have a couple of questions though:
>
>1) is this a proper place and approach to fix the bug?

I don't think so because the guest ABI could change.  Imagine there is an
application that just starts a simple VM (with graphics with no model) and out
of nowhere (after a long time) they upgrade libvirt and qemu and the VM will
look differently.

>2) what would be the full specification of expected behaviour?  The bug report
>   only states that the video type shouldn't be cirrus but doesn't say what it
>   should be. [2] gives some information about the order of preference of video
>   device types but I was wondering if there are any opinions about this on this
>   list?
>

Reading the BZ it looks to me like virt-manager should allow choosing cirrus and
the different default could be chosen in virt-manager.  The BZ is not well
described, to be honest.

Martin
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