From: Ed Cashin <ecashin@coraid.com>
Date: Wed, 9 Sep 2009 14:00:51 -0400
To: alan@lxorguk.ukuu.org.uk, ecashin@coraid.com, jens.axboe@oracle.com,
       akpm@linux-foundation.org, apw@canonical.com, bonbons@linux-vserver.org,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] aoe: end barrier bios with EOPNOTSUPP
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In-Reply-To: <20090909180804.3e62331a@lxorguk.ukuu.org.uk>
References: <200909021955.n82JtkrI032267@imap1.linux-foundation.org>
	<20090903063539.GH12579@kernel.dk>
	<2339aa04a4e8fb440a52624273728352@coraid.com>
	<20090904183525.GB18599@kernel.dk>
	<f48e25c99e41e375f2ddd85989cd39e1@coraid.com>
	<20090905051735.GH18599@kernel.dk>
	<366469f19c41e0150028b886f6859019@coraid.com>
	<20090908193540.GB18599@kernel.dk>
	<60772f633c524ba873f569966fccd6ce@coraid.com>
	<20090909180804.3e62331a@lxorguk.ukuu.org.uk>
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On Wed Sep  9 13:06:42 EDT 2009, alan@lxorguk.ukuu.org.uk wrote:
> > The bio in question is a barrier.  Jens Axboe suggested that such bios
> > need to be recognized and ended with -EOPNOTSUPP by any driver that
> > provides its own ->make_request_fn handler and does not handle
> > barriers.
> > 
> > In testing the changes below eliminate the BUG.
> 
> Presumably AoE should actually issue an ATA cache flush for this case ?

Yes.  The aoe driver juggles a set of in-process I/O operations that
have been sent to the AoE target but have not yet received responses.

To implement the barrier, it would stop generating new AoE write
commands, wait for AoE write responses for all the outstanding write
commands, issue the ATA cache flush command, wait for the response to
the flush, and then resume normal activity.

-- 
  Ed
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