From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1M1Rhl-00020Q-5D for qemu-devel@nongnu.org; Tue, 05 May 2009 16:57:33 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1M1Rhg-0001ts-Is for qemu-devel@nongnu.org; Tue, 05 May 2009 16:57:32 -0400 Received: from [199.232.76.173] (port=35044 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1M1Rhg-0001to-Ey for qemu-devel@nongnu.org; Tue, 05 May 2009 16:57:28 -0400 Received: from verein.lst.de ([213.95.11.210]:38872) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_3DES_EDE_CBC_SHA1:24) (Exim 4.60) (envelope-from ) id 1M1Rhf-0007Mn-J9 for qemu-devel@nongnu.org; Tue, 05 May 2009 16:57:28 -0400 Date: Tue, 5 May 2009 22:57:16 +0200 From: Christoph Hellwig Subject: Re: [Qemu-devel] barriers: block layer preparations Message-ID: <20090505205716.GA24320@lst.de> References: <20090505120804.GA30651@lst.de> <20090505120817.GA30721@lst.de> <4A00446B.7070404@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A00446B.7070404@redhat.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Christoph Hellwig , qemu-devel@nongnu.org On Tue, May 05, 2009 at 04:51:39PM +0300, Avi Kivity wrote: > >+ qcow_aio_write_cb, acb, 2); > > > > 2? Typo. > An alternative approach is to add a new op, bdrv_aio_barrier(), > submitted immediately after the write. It's probably more complicated > overall. Yeah, it sounds more complicated to implement to me. > A barrier for read can be meaningful if the guest wishes to read a > known-to-be-stable write. I don't think any guest can make use of this > though. I don't know of any storage standard having anything like this or any OS taking advantage of it. I'd be happy to review anything like that, though.