On Sun, 2012-10-07 at 10:51 -0400, Christoph Hellwig wrote: 
> On Sat, Oct 06, 2012 at 11:11:50PM -0700, Nicholas A. Bellinger wrote:
> > On Sat, 2012-10-06 at 21:49 -0400, Christoph Hellwig wrote:
> > > Currenly all non-pscsi bakcneds report their standards version as
> > > SPC 2 via ->get_device_rev.
> > 
> > No, the proper on-the-wire bits to signal SPC-3 compliance are already
> > being returned by virtual backend drivers within standard INQUIRY
> > payload data.  
> 
> I missed that, but it doesn't matter for the point I was making, which
> is the code to special case the SCSI_2 case, which can't happen for
> any virtual backend.

Regardless of if an virtual backend reports a SPC-3 version (0x05) in
INQUIRY response, an initiator is still allowed to fall back to using
legacy SCSI-2 reservations instead of SPC-3 persistent reservations.  I
can think of at least one mainstream SCSI initiator that does this.

Also, I think your mistaken about ALUA and SCSI-2 compatibility.  ALUA
is an SPC-3 and above specific feature.

> In addition it also can't happen for pscsi as
> we don't wire up any command emulation but REPORT LUNS for it any more,
> effectively making it dead code.
> 

pSCSI has always NOP'ed the reservation + ALUA function pointers within
core_setup_reservations() and core_setup_alua().

--nab

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