Re: [Qemu-devel] [PULL for-2.9 4/7] cirrus: add option to disable blitter

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > +    DEFINE_PROP_BOOL("blitter", struct PCICirrusVGAState,
> 
> > +                     cirrus_vga.enable_blitter, true),
> 
> 
> The default is 'ENABLE'?

Yes.

>  I think there should be 'false'.

Just flipping it to false isn't an option.  At minimum we would have to
keep it enabled by default for older machine types, for backward
compatibility with older qemu versions.

Beside that I don't want rush it.   When flipping the default I'd do it
early in the 2.10 development cycle, so we have a few months to the next
release to see what the fallout is and decide which default we want.

But I think the most sensible approach would be to have upper management
layer handle this.  We have libosinfo, which records capabilities of
guests, and we could add a field there telling whenever the guest os in
question uses the blitter (and therefore breaks when we turn it off) or
whenever it is safe to turn it off.

cheers,
  Gerd