Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set

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

On Wed, Jul 22, 2015 at 01:53:14PM +0200, Paolo Bonzini wrote:
> 
> 
> On 22/07/2015 13:46, Daniel P. Berrange wrote:
> > IIUC, the SCSI passthrough feature for virtio-blk is enabled by
> > setting the 'scsi=on' property on the virtio-blk device, which is
> > exposed by libvirt with XML:
> > 
> >     <disk type='block' device='lun'>
> >       <driver name='qemu' type='raw'/>
> >       <source dev='/dev/sda'/>
> >       <target dev='vda' bus='virtio'/>
> >     </disk>
> > 
> > (For use with virtio-scsi you'd just change the <target> element)
> > 
> > So if the guest is using virtio-1.0, then this will now fail to boot, or
> > cause an error from monitor hotplug. This is not too bad, but I'm just
> > wondering if there's anything else we ought to think about doing in libvirt
> > in this situation. Normally we'd try to detect unsupported things upfront
> > so we can report VIR_ERR_CONFIG_UNSUPPORTED, instead of the generic error
> > code VIR_ERR_INTERNAL_ERROR, but perhaps this is sufficiently niche to
> > not worry about it and its fine to just delegate error reporting to QEMU ?
> 
> Probably.  Note that it will be a long time before the default is
> changed to 1.0 (if it ever will).

I fully expect we'll enable modern by default in 2.5.  We'll also
disable legacy if the bus used is pcie.  We can disable modern if bus is
pci and scsi passthrough was requested.

>  Perhaps you can start warning now
> about <disk type='block' device='lun'>, and suggest using virtio-scsi
> instead?
> 
> Paolo