linux-kernel - Re: [dm-devel] [PATCH] block: silently error unsupported empty barriers too

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Message-ID: <Pine.LNX.4.64.0908062148060.8764@hs20-bc2-1.build.redhat.com>
Date:	Thu, 6 Aug 2009 21:50:49 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Alasdair G Kergon <agk@...hat.com>
cc:	Mark McLoughlin <markmc@...hat.com>,
	device-mapper development <dm-devel@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [dm-devel] [PATCH] block: silently error unsupported empty
 barriers too

On Thu, 6 Aug 2009, Alasdair G Kergon wrote:

> On Thu, Aug 06, 2009 at 12:14:17PM +0100, Mark McLoughlin wrote:
> > We should error all barriers, even empty barriers, on devices like
> > virtio_blk which don't support them.
>  
> Have you considered whether or not virtio_blk actually needs to
> support empty barriers?
> 
> Alasdair

This is only for request-based drivers, where it is the responsibility of 
blk-core to translate barriers. I think the empty barrier request anyway 
in blk_do_ordered, but with an error message. So the patch changes it to 
discard it early and queitly. It seems ok.

Mikulas
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