[libvirt] [RFC] Adding a "none" model for video cards

[Eric Blake]

On 07/30/2014 03:51 AM, Jean-Baptiste Rouault wrote:
> Hi,
> 
> I'm trying to run vexpress-a9 virtual machines (armv7l architecture) using 
> libvirt.
> 
> The vexpress-a9 doesn't support vga cards, but libvirt adds a video "cirrus" 
> video card when there is a "graphics" element in the domain xml. This prevents 
> the domain from booting.
> 
> At the moment, the only workaround I found is to add the following to my xml 
> file :
> <qemu:commandline>
>   <qemu:arg value='-vga'/>
>   <qemu:arg value='none'/>
> </qemu:commandline>
> 
> What do you think about adding a "none" model type for video cards ? I know it 
> is a bit strange to declare a video card in order to have none...
> I don't know the QEMU driver well, but maybe this could be handled by the 
> driver ? i.e. "no VGA card when the machine is vexpress-a9".

Not the first time we've had to do that (for example, we support 'none'
for the memballoon device, as well as for a <seclabel> tag when there is
no labeling to be done), all to maintain back-compat where the defaults
auto-populate devices.  So your idea sounds reasonable on that front.

However, I also wonder if this is a case where our code for post-parse
touchups could be made smarter to not provide a cirrus default on
architectures that don't support it, so that you would get the correct
behavior without having to use an explicit none.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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