Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16

[James Bottomley <jbottomley@parallels.com>]

On Wed, 2014-07-09 at 19:52 +0000, KY Srinivasan wrote:
> 
> > -----Original Message-----
> > From: Christoph Hellwig [mailto:hch@infradead.org]
> > Sent: Wednesday, July 9, 2014 1:43 AM
> > To: KY Srinivasan
> > Cc: linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
> > ohering@suse.com; jbottomley@parallels.com; jasowang@redhat.com;
> > apw@canonical.com; linux-scsi@vger.kernel.org; stable@vger.kernel.org
> > Subject: Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16
> > 
> > On Tue, Jul 08, 2014 at 05:46:48PM -0700, K. Y. Srinivasan wrote:
> > > Host does not handle WRITE_SAME_16; filter this command out. This
> > > patch is required to handle large devices (greater than 2 TB disks).
> > 
> > Storvsc already sets the no_write_same flag, where is the command coming
> > from?
> 
> In spite of this flag,  I see WRITE_SAME_16 being issued when I format a device bigger than 2 TB;
> I tried both xfs and ext4. Windows hosts currently do not handle unsupported commands correctly -
> The information returned is not sufficient to effect recovery in the Linux guest. While this may be addressed in
> future hosts, this patch fixes the problem.

What Christoph means is that this looks like a bug somewhere in SCSI
itself.  That means we need to find it and kill it, not add workarounds
to every driver that sets no_write_same ...

James