linux-kernel - Should a block device enforce block atomicity?

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Message-ID: <ce513bcc0806292351t7f4ad933l920112381f4ebb4@mail.gmail.com>
Date:	Mon, 30 Jun 2008 09:51:16 +0300
From:	"Erez Zilber" <erezzi.list@...il.com>
To:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Should a block device enforce block atomicity?

Hi,

I have a question about block devices and whether they are required to
enforce block atomicity:

I read the code of drivers/block/brd.c, and I didn't see any locking
when blocks are read/written. I also looked at the block layer code
that calls brd and didn't find any locking there. Does it mean that
there's no block atomicity (i.e. multiple threads can write a single
block at the same time)? Is there any hidden assumption here? Is this
the responsibility of the application to do that (e.g. not start a
WRITE request before other READ/WRITE requests to the same block were
completed)?

Thanks,
Erez
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