[libvirt] Exposing qemu support for SDL via capabilities

[Daniel P. Berrange]

On Fri, Jul 08, 2011 at 09:19:46AM -0500, Adam Litke wrote:
> Hi all,
> 
> In order to nicely support domains that use qemu's SDL support,
> libvirt-cim is looking for a way to confirm if the underlying qemu
> emulator can support SDL.  Libvirt already knows this information
> internally.  It seems to me that the best way to provide this
> information is by reporting it as a guest feature via the capabilities
> API call.  I was thinking the node '/capabilities/guest/features/sdl'
> could be added when qemu supports SDL.
> 
> Is this a good idea?

Yes & no. I think in general it would be desirable to expose more info
about supported features, but this is really opening a can of worms
because figuring out just what info needs exposing & in what format
is non-trivial. Even QEMU itself still can't provide this info in any
usable fashion, hence we're still parsing -help which really sucks.
Just adding an '/sdl' element seems simple but I don't think it is
a long term sustainable strategy.

If we added info about all supported features to the capabilities XML,
we will end up with an absolutely enourmous XML document that will no
longer be practically useful to administrators because it will be 99%
irrelevant info about devices hiding the 1% they really want about the
supported virt options.

So if we are to expose info about supported device model properties
then I think it would have to be in a separate API / XML schema, and
I think we want to get QEMU to provide the data in a more usable
manner than currently.

Daniel
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