On Mon, Apr 20, 2015 at 02:14:30PM +0200, Cornelia Huck wrote: > On Mon, 20 Apr 2015 11:12:37 +0200 > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > On Mon, Apr 20, 2015 at 10:54:11AM +0200, Cornelia Huck wrote: > > > On Fri, 17 Apr 2015 15:00:45 +0100 > > > Peter Maydell <peter.mayd...@linaro.org> wrote: > > > > > > > On 17 April 2015 at 14:43, Cornelia Huck <cornelia.h...@de.ibm.com> > > > > wrote: > > > > > On Fri, 17 Apr 2015 20:13:42 +0800 > > > > > Shannon Zhao <shannon.z...@linaro.org> wrote: > > > > > > > > > > [Some questions may be silly, but I'm not familiar with the > > > > > virtio-mmio > > > > > code] > > > > > > > > > >> The reason to do this is that the virtio-net-device can't expose host > > > > >> features to guest while using virtio-mmio. So the performance is low. > > > > > > > > > > So how does virtio-mmio expose any host features? > > > > > > > > The features are properties of the backend, not the transport. > > > > So for devices where we didn't set these up as "properties > > > > exist on the backend and the compatibility transport+backend > > > > wrapper devices just forward those properties to the backend", > > > > you can't set the properties. We got this right for some of > > > > the backends (eg blk) but not all of them, I think. > > > > > > The reason why blk is ok is that it adds the feature bits in its > > > ->get_features() callback. net expects the feature bits already present > > > and removes not supported ones and therefore requires > > > statically-defined bits somewhere. > > > > > > If we move the feature bits to virtio-net and virtio-scsi, it should > > > work for virtio-mmio - but the feature bit propagation from the device > > > into the transport becomes a bit useless. > > > > > > Could net and scsi add the feature bits dynamically in their > > > ->get_features() callback instead? This should work for virtio-mmio as > > > well afaics. > > > > > > In the end, we should probably end up with the same mechanism for all > > > device types. > > > > I think I would also prefer that the host features live in the > > generic virtio device structure. > > You mean in the virtio device instead of the proxy device?
Yes. > I think that > makes sense conceptually, provided we get the realize/plug sequence > correct. > > > This would make it possible > > e.g. to validate guest features on vm load in generic code. > > > > Doesn't virtio_load() already do some validation? You are right here. -- MST
