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Date: Mon, 13 Jul 2015 14:27:26 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/5] virtio-blk: disable scsi passthrough
 for 1.0 device
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To: Jason Wang <jasowang@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org

On Mon, Jul 13, 2015 at 05:00:51PM +0800, Jason Wang wrote:
> 
> 
> 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 <stefanha@redhat.com>
> >> Cc: Kevin Wolf <kwolf@redhat.com>
> >> Cc: qemu-block@nongnu.org
> >> Signed-off-by: Jason Wang <jasowang@redhat.com>
> > Interesting, I noticed we have a field scsi - see
> > 	commit 1ba1f2e319afdcb485963cd3f426fdffd1b725f2
> > 	Author: Paolo Bonzini <pbonzini@redhat.com>
> > 	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.

Right. Auto would then mean "!modern".

> > 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;
>     }
> 
> >
> >> ---
> >>  hw/block/virtio-blk.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> >> index 6aefda4..f30ad25 100644
> >> --- a/hw/block/virtio-blk.c
> >> +++ b/hw/block/virtio-blk.c
> >> @@ -730,7 +730,8 @@ static uint64_t virtio_blk_get_features(VirtIODevice *vdev, uint64_t features)
> >>      virtio_add_feature(&features, VIRTIO_BLK_F_GEOMETRY);
> >>      virtio_add_feature(&features, VIRTIO_BLK_F_TOPOLOGY);
> >>      virtio_add_feature(&features, VIRTIO_BLK_F_BLK_SIZE);
> >> -    virtio_add_feature(&features, VIRTIO_BLK_F_SCSI);
> >> +    if (!__virtio_has_feature(features, VIRTIO_F_VERSION_1))
> >> +        virtio_add_feature(&features, VIRTIO_BLK_F_SCSI);
> >>  
> >>      if (s->conf.config_wce) {
> >>          virtio_add_feature(&features, VIRTIO_BLK_F_CONFIG_WCE);
> >> -- 
> >> 2.1.4