From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KLIye-0007HL-KN for qemu-devel@nongnu.org; Tue, 22 Jul 2008 10:36:32 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KLIya-0007Dr-Ud for qemu-devel@nongnu.org; Tue, 22 Jul 2008 10:36:31 -0400 Received: from [199.232.76.173] (port=55371 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KLIya-0007Dk-Kt for qemu-devel@nongnu.org; Tue, 22 Jul 2008 10:36:28 -0400 Received: from il.qumranet.com ([212.179.150.194]:38935) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KLIya-0004Bf-2v for qemu-devel@nongnu.org; Tue, 22 Jul 2008 10:36:28 -0400 Message-ID: <4885F068.2060902@qumranet.com> Date: Tue, 22 Jul 2008 17:36:24 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] qcow2 - safe on kill? safe on power fail? References: <47CF0E0C.9030807@quinthar.com> <47CF16C5.6040102@codemonkey.ws> <20080721181031.GA31773@shareable.org> <4884E6F1.5020205@codemonkey.ws> <48850A99.7070005@codemonkey.ws> <48857926.5020708@qumranet.com> <4885EA8B.5050908@codemonkey.ws> In-Reply-To: <4885EA8B.5050908@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Anthony Liguori wrote: > Avi Kivity wrote: >> Journalling is so out of fashion. It's better to sequence the >> operations so that failure results in a leak instead of corruption. > > Since the metadata is being updated synchronously, you could probably > get away with a pretty simple journal. Maybe even a single field that > contains the offset you are allocating which then gets reset once the > allocation was completed. > > Why would you want to get away with a simple journal when you can get away without one? It's a simple matter of allocating, making sure the allocation is on disk, and recording that allocation in the tables. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.