fyi - end of a very long thread, but I thought that dm had this fixed...
ric
-------- Original Message --------
Subject: MD/DM and barriers (was Re: [patch] ext2/3: document
conditions when reliable operation is possible)
Date: Thu, 27 Aug 2009 12:54:05 -0400
From: Jeff Garzik <jeff@xxxxxxxxxx>
To: Ric Wheeler <rwheeler@xxxxxxxxxx>
CC: Theodore Tso <tytso@xxxxxxx>, Rob Landley <rob@xxxxxxxxxxx>, Pavel
Machek <pavel@xxxxxx>, Florian Weimer <fweimer@xxxxxx>, Goswin von
Brederlow <goswin-v-b@xxxxxx>, kernel list
<linux-kernel@xxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxx>,
mtk.manpages@xxxxxxxxx, rdunlap@xxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx,
linux-ext4@xxxxxxxxxxxxxxx, corbet@xxxxxxx
On 08/27/2009 09:10 AM, Ric Wheeler wrote:
One thing that does need fixing for some MD configurations is to stress
again that we need to make sure that barrier operations are properly
supported or users will need to disable the write cache on devices with
volatile write caches.
Agreed; chime in on Christoph's linux-vfs thread if people have input.
I quickly glanced at MD and DM. Currently, upstream, we see a lot of
if (unlikely(bio_barrier(bio))) {
bio_endio(bio, -EOPNOTSUPP);
return 0;
}
in DM and MD make_request functions.
Only md/raid1 supports barriers at present, it seems. None of the other
MD drivers support barriers.
DM has some barrier code... but the above code was pasted from DM's
make_request function, so I am guessing that DM's barrier stuff is
incomplete and disabled at present.
I've been mentioning this issue for years... glad some people finally
noticed :)
Jeff
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