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

["Michael S. Tsirkin" <mst@redhat.com>]

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?
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.

> ---
>  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