From: Jamie Lokier <jamie@shareable.org>
To: qemu-devel@nongnu.org
Cc: Laurent Vivier <Laurent.Vivier@bull.net>
Subject: Re: [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT)
Date: Wed, 30 Apr 2008 01:02:19 +0100 [thread overview]
Message-ID: <20080430000217.GB25408@shareable.org> (raw)
In-Reply-To: <48173591.9010609@suse.de>
Kevin Wolf wrote:
> Disabling O_DIRECT for a single aio request is impossible (after all,
> aio is asynchronous), and disabling it for at least one aio request is
> going to be ugly.
You could try opening two fds to the same file/blockdev, one with
O_DIRECT set. Then you can disable O_DIRECT as you like per aio
request, by choosing the fd.
I'm not sure if that works, though. On some OSes, if a file has any
non-O_DIRECT open descriptor, all I/O is buffered ignoring the
O_DIRECT flag. If both are allowed simultaneously, I'm not sure what
happens with cache-coherency between direct I/Os and buffered I/Os.
-- Jamie
prev parent reply other threads:[~2008-04-30 0:02 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-17 13:31 [Qemu-devel] [PATCH] Align file accesses with cache=off (O_DIRECT) Kevin Wolf
2008-04-28 15:34 ` Kevin Wolf
2008-04-29 9:01 ` Laurent Vivier
2008-04-29 14:49 ` Kevin Wolf
2008-04-29 15:48 ` Laurent Vivier
2008-04-29 16:21 ` Kevin Wolf
2008-04-29 16:48 ` Laurent Vivier
2008-04-30 9:21 ` Kevin Wolf
2008-04-30 9:59 ` Laurent Vivier
2008-04-30 12:08 ` Kevin Wolf
2008-04-30 14:30 ` Blue Swirl
2008-04-30 21:05 ` Kevin Wolf
2008-05-01 14:35 ` Blue Swirl
2008-05-01 17:55 ` Kevin Wolf
2008-05-06 8:44 ` Kevin Wolf
2008-05-06 9:02 ` Laurent Vivier
2008-05-06 16:42 ` Blue Swirl
2008-05-06 16:56 ` Kevin Wolf
2008-05-06 17:23 ` Blue Swirl
2008-04-30 0:05 ` Jamie Lokier
2008-04-30 0:02 ` Jamie Lokier [this message]
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