From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NHbnK-0008LD-RS for qemu-devel@nongnu.org; Mon, 07 Dec 2009 06:30:22 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NHbnG-0008JP-Sx for qemu-devel@nongnu.org; Mon, 07 Dec 2009 06:30:22 -0500 Received: from [199.232.76.173] (port=40450 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NHbnG-0008JE-KI for qemu-devel@nongnu.org; Mon, 07 Dec 2009 06:30:18 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24132) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NHbnG-0001sT-2g for qemu-devel@nongnu.org; Mon, 07 Dec 2009 06:30:18 -0500 Date: Mon, 7 Dec 2009 11:30:14 +0000 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH] Disk image shared and exclusive locks. Message-ID: <20091207113014.GK24530@redhat.com> References: <4B1943A0.7030509@codemonkey.ws> <20091204215517.GA5938@amd.home.annexia.org> <4B198D5B.5080803@codemonkey.ws> <4B1A98D9.7010408@redhat.com> <4B1A9C9F.5040705@codemonkey.ws> <4B1A9E83.2050103@redhat.com> <4B1A9F8C.3010106@codemonkey.ws> <20091207103128.GA26970@shareable.org> <20091207104517.GJ24530@redhat.com> <20091207111953.GA29980@shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091207111953.GA29980@shareable.org> Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jamie Lokier Cc: "Richard W.M. Jones" , qemu-devel@nongnu.org, Avi Kivity On Mon, Dec 07, 2009 at 11:19:54AM +0000, Jamie Lokier wrote: > Daniel P. Berrange wrote: > > > Sometimes shared access to a raw image (partitioned or whole disk > > > filesystem) is ok, and sometimes it is not ok. Only the user knows > > > the difference, because only the user knows if the guests they are > > > running use distinct partitions in the same raw image, or cooperative > > > access to a shard image. > > > > > > But does it make sense to request a shared lock in that case? Not > > > really. If you have a group of guests correctly sharing an image, you > > > still want to prevent running the same group a second time - and a > > > shared lock wouldn't do that, because each group would be requesting > > > shared locks. > > > > > > So the distinction read/write makes more sense. Can anyone think of a > > > situation where a shared lock on an image opened for writing is useful? > > > > Isn't this what Richard has already done ? The patch implements 'shared' > > as a 'F_RDLCK' lock and 'exclusive' as 'F_WRLCK': > > No, the question is whether it makes sense to provide a 'shared' > option on the command line, or simply to always map: > > image opened read only => F_FDLCK > image opened writable => F_WRLCK > > and provide only a single command line option: 'lock'. That doesn't work in the case of setting up a clustered filesystem shared between guests. That requires that the disk be opened writable, but with a shared (F_RDLOCK) lock. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|