linux-kernel - Re: dm-crypt: never use write same (was Re: [v3.7 Regression] [SCSI] sd: Implement support for WRITE SAME)

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Message-ID: <20150713180155.GD30898@redhat.com>
Date:	Mon, 13 Jul 2015 14:01:55 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Milan Broz <mbroz@...hat.com>
Cc:	Joseph Salisbury <joseph.salisbury@...onical.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-kernel@...r.kernel.org, JBottomley@...allels.com,
	Kernel Team <kernel-team@...ts.ubuntu.com>, jgarzik@...hat.com
Subject: Re: dm-crypt: never use write same (was Re: [v3.7 Regression] [SCSI]
 sd: Implement support for WRITE SAME)

On Mon, Jul 13 2015 at  1:01pm -0400,
Milan Broz <mbroz@...hat.com> wrote:

> (sorry, resending again, not sure if it was sent correctly)
> 
> On 07/13/2015 06:33 PM, Joseph Salisbury wrote:
> > Hi Milan,
> > 
> > The Ubuntu kernel has been carrying this patch since the discussion[0]
> > we were having about the bug.  I don't see that patch was ever included
> > in mainline.  Do you happen to know if this patch is still needed or was
> > the bug we were seeing fixed in some other way?
> 
> I think it was superseded by later Mike's approach to reverse the logic
> - disable write same for all targets and require to explicitly allow it.
> 
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/md/dm-table.c?id=c1a94672a830e01d58c7c7e8de530c3f136d6ff2
> (+later patches)
> 
> So I think we do no need this patch upstream anymore.
> 
> Mike, am I right here?

Yeah, a DM target needs to opt-in by setting ti->num_write_same_bios
(only linear, stripe and mpath do at this time).
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