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Date: Mon, 13 Jul 2015 16:41:29 +0200
From: Cornelia Huck <cornelia.huck@de.ibm.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: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Mon, 13 Jul 2015 16:34:30 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> 
> 
> On 13/07/2015 15:20, Cornelia Huck wrote:
> > This would imply that any transitional device cannot offer scsi,
> > doesn't it?
> > 
> > We have two layers interacting here: virtio-blk which may or may not
> > offer scsi support, and the transport layer which may or may not offer
> > VERSION_1 support. Failing scsi commands if VERSION_1 has been
> > negotiated makes sense to me; but I don't want to disable scsi config a
> > priori because the driver might negotiate VERSION_1. This would imply
> > that virtio-blk over virtio-ccw would never offer scsi once we enable
> > virtio-1 support, and it kind of defeats the purpose of a transitional
> > device for me.
> > 
> > (The other way round - fail negotiating revison 1 if the device was
> > configured with scsi support - makes more sense to me.)
> 
> For newer machine types, it would make sense to block VIRTIO_BLK_F_SCSI
> altogether if !blk->conf.scsi.  Would that fix the problem for you too?

This is probably a sensible approach, and it can be contained in
virtio-block, no?