From mboxrd@z Thu Jan  1 00:00:00 1970
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: Re: SCSI's heuristics for enabling WRITE SAME still need work [was:
 dm mpath: disable WRITE SAME if it fails]
Date: Tue, 24 Sep 2013 06:25:39 -0700
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>, Mike Snitzer <snitzer@redhat.com>, dm-devel@redhat.com, linux-scsi@vger.kernel.org

On Tue, 2013-09-24 at 11:37 +0200, Paolo Bonzini wrote:
> Il 21/09/2013 00:03, Martin K. Petersen ha scritto:
> > 
> > The major headache here of course is that WRITE SAME is inherently
> > destructive. We can't just fire off one during discovery and see if it
> > works. For WRITE you can issue a command with a transfer length of 0 to
> > see if things work. But unfortunately for WRITE SAME a transfer length
> > of zero means "wipe the entire device". Yikes!
> 
> What about WRITE SAME with an out-of-range lba?  Or lba equal to the
> size of the disk and #blocks equal to zero.

That's inviting undefined behaviour in a data destructive command ...
not something we really want to do.

James