[libvirt] [Qemu-devel] clean/simple Q35 support in libvirt+QEMU for guest OSes that don't support virtio-1.0

[Andrea Bolognani]

On Fri, 2018-08-17 at 11:43 +0100, Daniel P. Berrangé wrote:
> On Fri, Aug 17, 2018 at 12:35:11PM +0200, Andrea Bolognani wrote:
> > If we decide we want to explicitly spell out the options instead
> > of relying on QEMU changing behavior based on the slot type, which
> > is probably a good idea anyway, I think we should have
> > 
> >   virtio-0.9 => disable-legacy=no,disable-modern=no
> >   virtio-1.0 => disable-legacy=yes,disable-modern=no
> > 
> > There's basically no reason to have a device legacy-only rather
> > than transitional, and spelling out both options instead of only
> > one of them just seems more robust.
> 
> From a testing POV it is desirable to be able to have legacy-only.
> There is also possibility that guest OS impl 1.0 in a buggy manner,
> so forcing legacy only is desirable.
> 
> The existing device still already provides a transitional option
> on i440fx, and on Q35 if you do explicit placement in a PCI slot.
> So I don't think there's a good reason to have a second transitional
> device type, especially if we're naming it virtio-0.9, it is rather
> misleading if it would be in fact able to run virtio-1.0 mode.

Sounds reasonable.

-- 
Andrea Bolognani / Red Hat / Virtualization