From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KOyPJ-0000yx-0S for qemu-devel@nongnu.org; Fri, 01 Aug 2008 13:27:13 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KOyPH-0000w6-94 for qemu-devel@nongnu.org; Fri, 01 Aug 2008 13:27:12 -0400 Received: from [199.232.76.173] (port=47830 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KOyPH-0000vx-36 for qemu-devel@nongnu.org; Fri, 01 Aug 2008 13:27:11 -0400 Received: from mail2.shareable.org ([80.68.89.115]:33112) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1KOyPG-0003y0-Vz for qemu-devel@nongnu.org; Fri, 01 Aug 2008 13:27:11 -0400 Received: from jamie by mail2.shareable.org with local (Exim 4.63) (envelope-from ) id 1KOyPF-0006l0-0E for qemu-devel@nongnu.org; Fri, 01 Aug 2008 18:27:09 +0100 Date: Fri, 1 Aug 2008 18:27:08 +0100 From: Jamie Lokier Subject: Re: [Qemu-devel] PATCH: v3 Allow control over drive file open mode Message-ID: <20080801172708.GE25063@shareable.org> References: <20080801102949.GN23993@redhat.com> <48932751.5040303@codemonkey.ws> <18579.16494.791024.25671@mariner.uk.xensource.com> <4893448C.1050508@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4893448C.1050508@codemonkey.ws> 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: > Down the road, you do a savevm. savevm has to create a checkpoint in > all disk images. The checkpoint will be empty in boo.img but it still > needs to create one. An alternative scenario would be a read-only root fs: > > qemu-system-x86_64 -drive file=rootfs.img,read-only=on > > Where you wanted to be able to do a savevm. I agree this could be useful (despite my wariness of snapshots :) In which case, it would be all-the-more useful if it worked correctly when multiple QEMU instances are using the image file. "Down the road" - you might not know in advance that you're wishing to save a snapshot, and by then you might have other running QEMU instances using that image which you don't want to kill, and of course if you can't snapshot one, you can't snapshot any of them to shut them down temporarily. It should be enough to take an advisory lock during the savevm writes, shouldn't it? -- Jamie