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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Wed, 15 Jul 2015 09:57:21 +0200
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Subject: Re: [Qemu-devel] [PATCH V2 2/5] virtio-blk: advertise scsi only
	when scsi is set
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To: Jason Wang <jasowang@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, cornelia.huck@de.ibm.com, qemu-block@nongnu.org, stefanha@redhat.com, mst@redhat.com



On 15/07/2015 07:29, Jason Wang wrote:
> 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>
> ---
>  hw/block/virtio-blk.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 4c27974..761d763 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -731,7 +731,9 @@ 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 (s->conf.scsi) {
> +        virtio_add_feature(&features, VIRTIO_BLK_F_SCSI);
> +    }

This must only be done for newer machine types only, or you change guest
ABI for scsi=off.  Effectively you have to split it in two properties,
"scsi" and "always_set_f_scsi".

Paolo