Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set

[Paolo Bonzini]

On 22/07/2015 12:19, Michael S. Tsirkin wrote:
> > > SCSI passthrough was no longer supported in virtio 1.0, so this patch
> > > fail the get_features() when both 1.0 and scsi is set. And also only
> > > advertise VIRTIO_BLK_F_SCSI for legacy virtio-blk device.
> > 
> > Why is SCSI passthrough support not available in virtio 1.0 ? This
> > will cause a regression for any users of that as & when QEMU changes
> > to use virtio 1.0 by default. Can we not fix this regression instead.
>
> If we wanted to, we might be able to fix this but not for 2.4: we'd have
> to extend the spec and guest drivers, in some way TBD.
> 
> Paolo would be best placed to answer whether this feature is desirable
> in the future, I think the argument made when the spec was written was that
> the feature is not widely used, and virtio scsi is available as
> a replacement for people who need it.

No, the feature is not desirable in the future. There is no reason
really not to use virtio-scsi passthrough instead, since virtio-scsi has
been out for about 3 years now and is stable.

In addition, the implementation would either not be compatible with
virtio 0.9, or would be different from everything else in the spec
because it requires a particular framing for the buffers.

Paolo