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Date: Wed, 21 May 2008 00:13:03 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off
	(O_DIRECT)
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To: Laurent Vivier <Laurent.Vivier@bull.net>
Cc: Blue Swirl <blauwirbel@gmail.com>, qemu-devel@nongnu.org, Kevin Wolf <kwolf@suse.de>

Laurent Vivier wrote:
> Sector unaligned guest offset are converted to sector aligned offset.

The guest cannot give a sector unaligned offset.  How can it?  It
specifies offset in sectors, through the IDE or SCSI interfaces.

> Sector aligned guest offset are written as is.
> 
> And as we use O_DIRECT and aligned offset and data count I think we
> increase disk integrity (regarding the case without O_DIRECT and without
> aligned access...), so we should document the case without O_DIRECT use,
> not the case with O_DIRECT use...

That's fine, for direct-mapped formats.  I'm thinking of qcow format
etc. where guest aligned writes are sometimes translated to unaligned
(is this even true?).

-- Jamie