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[dm-devel] Re: Barriers still not passing on simple dm devices...

From: Bodo Eggert <7eggert gmx de>
To: Eric Sandeen <sandeen redhat com>, device-mapper development <dm-devel redhat com>, Linux Kernel Mailing List <linux-kernel vger kernel org>, Jens Axboe <jens axboe oracle com>, Andi Kleen <andi firstfloor org>, " \"MASON"@redhat.com, CHRISTOPHER <CHRIS MASON oracle com>
Cc:
Subject: [dm-devel] Re: Barriers still not passing on simple dm devices...
Date: Mon, 23 Mar 2009 22:52:31 +0100

Eric Sandeen <sandeen redhat com> wrote:

> I've noticed that on 2.6.29-rcX, with Andi's patch
> (ab4c1424882be9cd70b89abf2b484add355712fa, dm: support barriers on
> simple devices) barriers are still getting rejected on these simple devices.

> So what's the right way around this?  What should dm (or md for that
> matter) advertise on their queues about ordered-ness?  Should there be
> some sort of "QUEUE_ORDERED_PASSTHROUGH" or something to say "this level
> doesn't care, ask the next level" or somesuch?  Or should it inherit the
> flag from the next level down?  Ideas?

IMO each block device SHOULD provide barriers - either native or emulated,
and each meta device MUST provide emulated barriers if it provides dynamic
device binding and barriers.

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