Re: [Qemu-devel] [PATCH 2/5] virtio-blk: disable scsi passthrough for 1.0 device

[Cornelia Huck]

On Mon, 13 Jul 2015 11:56:51 +0200
Kevin Wolf <address@hidden> wrote:

> Am 13.07.2015 um 11:00 hat Jason Wang geschrieben:
> > 
> > 
> > On 07/13/2015 03:46 PM, Michael S. Tsirkin wrote:
> > > On Mon, Jul 13, 2015 at 01:46:48PM +0800, Jason Wang wrote:
> > >> VIRTIO_BLK_F_SCSI was no longer supported in 1.0. So disable it.
> > >>
> > >> Cc: Stefan Hajnoczi <address@hidden>
> > >> Cc: Kevin Wolf <address@hidden>
> > >> Cc: address@hidden
> > >> Signed-off-by: Jason Wang <address@hidden>
> > > Interesting, I noticed we have a field scsi - see
> > >   commit 1ba1f2e319afdcb485963cd3f426fdffd1b725f2
> > >   Author: Paolo Bonzini <address@hidden>
> > >   Date:   Fri Dec 23 15:39:03 2011 +0100
> > >
> > >       virtio-blk: refuse SG_IO requests with scsi=off
> > >
> > > but it doesn't seem to be propagated to guest features in
> > > any way.
> > >
> > > Maybe we should fix that, making that flag AutoOnOff?
> > 
> > Looks ok but auto may need some compat work since default is true.
> > 
> > > Then, if user explicitly requested scsi=on with a modern
> > > interface then we can error out cleanly.
> > >
> > > Given scsi flag is currently ignored, I think
> > > this can be a patch on top.
> > 
> > Looks like virtio_blk_handle_scsi_req() check this:
> > 
> >     if (!blk->conf.scsi) {
> >         status = VIRTIO_BLK_S_UNSUPP;
> >         goto fail;
> >     }
> 
> So we should be checking the same condition for the feature flag and
> error out in the init function if we have a VERSION_1 device and
> blk->conf.scsi is set.

Hm, I wonder how this plays with transports that want to make the
virtio-1 vs. legacy decision post-init? For virtio-ccw, I basically
only want to offer VERSION_1 if the driver negotiated revision >= 1.
I'd need to check for !scsi as well before I can add this feature bit
then? Have the init function set a blocker for VERSION_1 so that the
driver may only negotiate revision 0?