On Thu, 27 Nov 2014 17:42:11 +0200 "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > On Thu, Nov 27, 2014 at 04:31:39PM +0100, Cornelia Huck wrote: > > On Thu, 27 Nov 2014 17:24:22 +0200 > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > > > On Thu, Nov 27, 2014 at 04:16:33PM +0100, Cornelia Huck wrote: > > > > Yet another version of the virtio-1 support patches. > > > > > > > > This one has seen some (very) light testing with the virtio-1 guest > > > > support patches currently on vhost-next. > > > > > > > > Changes from v3: > > > > > > > > - Add support for FEATURES_OK. We refuse to set features after the > > > > driver has set this in the status field, and we allow to fail > > > > setting the status if the features are inconsistent. > > > > - Add missing virtio-1 changes for virtio-net (header size and mac). > > > > - Dropped setting the VERSION_1 bit for virtio-blk: There's still > > > > some stuff missing. > > > > > > > > For virtio-blk, we need to validate the feature bits if version 1 is > > > > negotiated: some legacy features are not allowed in that case. I'm not > > > > quite sure how to handle this, though. We could use the new > > > > validate_features callback to verify that the driver negotiated a > > > > sensible feature set, but that would require us to offer a superset > > > > of legacy and version 1 bits, which feels wrong. Any ideas? > > > > > > No, that's violating the spec. > > > I think the simplest way is to have separate features and > > > legacy_features fields. Present the correct one depending on which > > > revision was negotiated. > > > > But revisions are a virtio-ccw only thing - what can other transports > > do here? > > Other transports have different ways to deal with this. > For example virtio pci exposes a legacy header and > a modern header. Legacy header will expose old features, > modern one - new features. > > mmio simply does not support transitional devices. > So qemu user will have to specify virtio 1.0 or 0.9 for mmio. > > Other transports are out of virtio 1.0 spec so > they just use legacy features. > > > The basic problem is that we decide via a feature bit that > > needs to be negotiated which feature bits we want to present. > > Consider wce as one example. This is not needed for modern guests, so > we can just mask it from modern feature mask. Consider virtio blk scsi > commands as another example. this feature is not supported in virtio > 1.0, so we must mask it from modern feature mask. > > Seems the same handling works in all cases? This was just what I was talking about... > > > > pci and > > mmio don't have a way to know whether the driver wants to use 1.0 or > > legacy prior to feature negotiation, do they? > > pci does. mmio doesn't but it does not want to support transitional > devices. > So we should have a per-device callback into the transport layer, say check_legacy()? For ccw, this would check for the negotiated revision; for mmio, it could check a device property configured with the device; and for pci, whatever the mechanism is there :) A transport not implementing this callback is simply considered legacy-only. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
