Re: [Xen-devel] [RFC PATCH] xen-block: introduces extra request to pass-through SCSI commands

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> Sent: 02 March 2016 17:23
> To: Ian Jackson
> Cc: Bob Liu; Juergen Gross; xen-devel@xxxxxxxxxxxxx; jbeulich@xxxxxxxx;
> Roger Pau Monne; Paul Durrant
> Subject: Re: [RFC PATCH] xen-block: introduces extra request to pass-
> through SCSI commands
> 
> On Wed, Mar 02, 2016 at 02:44:12PM +0000, Ian Jackson wrote:
> > Bob Liu writes ("Re: [RFC PATCH] xen-block: introduces extra request to
> pass-through SCSI commands"):
> > > On 03/02/2016 07:40 PM, Ian Jackson wrote:
> > > > I can't see how that could cause anything but pain.  In many cases
> > > > "the underlying SCSI storage target" wouldn't be well defined.  Even
> > > > if it was, these side channel SCSI commands are likely to Go Wrong in
> > > > exciting ways.
> > > >
> > > > What SCSI commands do you want to send ?
> > >
> > > * INQUIRY
> >
> > ... but why ?
> 
> Need to expose VPD information to the guest for application usage.
> 
> >
> > > * PERSISTENT RESERVE IN
> > > * PERSISTENT RESERVE OUT
> > >
> > > This is for Failover Clusters in Windows, not sure whether more
> > > commands are required.  I didn't get a required scsi commands list
> > > in the failover document.
> >
> > So you want to be able to reserve the volume against concurrent
> > access ?  If you're using LVM, such a reservation should apply to the
> > LVM LV, not to the underlying physical storage device, clearly.  So I
> > think LIO [1] + PVSCSI might be what you want.
> >
> 
> Except it would mean writting a new Windows PV driver and replacing the
> existing block one.

Actually, that's quite desirable. The existing driver is actually a SCSI HBA 
driver (because that's all you can write is you use thr Windows STORPORT 
wrapper... which you need to if you want to pass WHQL) so making it use a PV 
scsi protocol would probably make it smaller since all the scsi <-> blkif 
translation code could be ripped out and all the stuff to synthesize INQUIRY 
responses based on vbd data in xenstore could go away too.

  Paul

> 
> 
> > Ian.
> >
> > [1] http://linux-iscsi.org/wiki/LIO

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