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Date:	Thu, 10 Jul 2014 22:12:46 +0000
From:	James Bottomley <jbottomley@...allels.com>
To:	"kys@...rosoft.com" <kys@...rosoft.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mkp@....net" <mkp@....net>,
	"apw@...onical.com" <apw@...onical.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"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

On Thu, 2014-07-10 at 21:02 +0000, KY Srinivasan wrote:
> 
> > -----Original Message-----
> > From: James Bottomley [mailto:jbottomley@...allels.com]
> > Sent: Wednesday, July 9, 2014 3:27 PM
> > To: KY Srinivasan
> > Cc: linux-kernel@...r.kernel.org; mkp@....net; 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 21:14 +0000, KY Srinivasan wrote:
> > >
> > > > -----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.
> > 
> > If we fix it at source, why would there be any need to filter?  That's the
> > reason the no_write_same flag was introduced.  If we can find and fix the
> > bug, it can go back into the stable trees as a bug fix, hence nothing should
> > ever emit write_same(10 or 16) and additional driver code is redundant (and
> > counter productive, since if this ever breaks again you're our best canary).
> > 
> > This looks like it might be the problem but Martin should confirm (I think the
> > problem comes to us from the RC16 code which unconditionally sets WS16).
> > 
> > James
> 
> James,
> 
> This patch works for me; are you planning on committing this patch.

OK, if we go with this we can add your tested by.

It's not going in until Martin takes a look because there may be a
better way of doing this.

James

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