From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1JyjEn-0002FB-II for qemu-devel@nongnu.org; Wed, 21 May 2008 03:59:53 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1JyjEk-0002EY-Sx for qemu-devel@nongnu.org; Wed, 21 May 2008 03:59:53 -0400 Received: from [199.232.76.173] (port=41419 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1JyjEk-0002ET-QH for qemu-devel@nongnu.org; Wed, 21 May 2008 03:59:50 -0400 Received: from mx20.gnu.org ([199.232.41.8]:19461) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1JyjEk-00037X-HP for qemu-devel@nongnu.org; Wed, 21 May 2008 03:59:50 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1JyjEj-00047H-Ay for qemu-devel@nongnu.org; Wed, 21 May 2008 03:59:49 -0400 Subject: Re: [Qemu-devel] Re: [PATCH][v2] Align file accesses with cache=off (O_DIRECT) From: Laurent Vivier In-Reply-To: <200805210154.52667.paul@codesourcery.com> References: <1211283126.4314.70.camel@frecb07144> <200805202352.17807.paul@codesourcery.com> <1211324394.4217.2.camel@frecb07144> <200805210154.52667.paul@codesourcery.com> Content-Type: text/plain; charset=utf-8 Date: Wed, 21 May 2008 09:59:42 +0200 Message-Id: <1211356782.4300.4.camel@frecb07144> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paul Brook Cc: Blue Swirl , qemu-devel@nongnu.org, Kevin Wolf Le mercredi 21 mai 2008 =C3=A0 01:54 +0100, Paul Brook a =C3=A9crit : > > > 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=3Don and cache=3Doff compatibility" > > but was never commented. >=20 > That patch that patch messes with O_DIRECT on an open file descriptor, = which=20 > was generally agreed to be a bad idea. I agree with that, it's why I sent a new patch yesterday. But look at the second part of the (first) patch that try to align qcow buffers (it was to answer to your comment). Moreover we can't align all data, so we have to make some buffer/count/offset alignment in block-raw-posix.c. I sincerely think that the patch I sent yesterday must be apply. Laurent --=20 ------------- Laurent.Vivier@bull.net --------------- "The best way to predict the future is to invent it." - Alan Kay