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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off
	(O_DIRECT)
Date: Wed, 21 May 2008 01:54:52 +0100
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Cc: Blue Swirl <blauwirbel@gmail.com>, Laurent Vivier <Laurent.Vivier@bull.net>, Kevin Wolf <kwolf@suse.de>

> > Seems like the easiest solution would be to have qcow always align its
> > writes. We don't do on the fly compression, so it should be fairly easy
> > to make this happen with minimal overhead.
>
> I did the patch you describe and post it to the mailing list on Tue, 22
> Jan 2008 11:17:09 +0100, it was called
> "[PATCH] snapshot=on and cache=off compatibility"
> but was never commented.

That patch that patch messes with O_DIRECT on an open file descriptor, which 
was generally agreed to be a bad idea.

Paul