linux-kernel - RE: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME

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Date:	Wed, 9 Jul 2014 21:14:00 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	James Bottomley <jbottomley@...allels.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"ohering@...e.com" <ohering@...e.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>
Subject: RE: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16



> -----Original Message-----
> From: James Bottomley [mailto:jbottomley@...allels.com]
> Sent: Wednesday, July 9, 2014 12:57 PM
> To: KY Srinivasan
> Cc: linux-kernel@...r.kernel.org; hch@...radead.org;
> devel@...uxdriverproject.org; apw@...onical.com; stable@...r.kernel.org;
> linux-scsi@...r.kernel.org; ohering@...e.com; jasowang@...hat.com
> Subject: Re: [PATCH 4/8] Drivers: scsi: storvsc: Filter WRITE_SAME_16
> 
> On Wed, 2014-07-09 at 19:52 +0000, KY Srinivasan wrote:
> >
> > > -----Original Message-----
> > > From: Christoph Hellwig [mailto:hch@...radead.org]
> > > Sent: Wednesday, July 9, 2014 1:43 AM
> > > To: KY Srinivasan
> > > Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
> > > ohering@...e.com; jbottomley@...allels.com; jasowang@...hat.com;
> > > apw@...onical.com; linux-scsi@...r.kernel.org;
> > > stable@...r.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,

I will try to isolate this issue in the SCSI stack. If it is ok with you guys, I would still want to filter WRITE_SAME_16
(as we currently do WRITE_SAME) in our driver since this would address the problem for a large number of
customers on our platform.

Regards,

K. Y

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