From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=34698 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OOwFx-0005Sv-Ml for qemu-devel@nongnu.org; Wed, 16 Jun 2010 13:18:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OOwFw-0005YL-KA for qemu-devel@nongnu.org; Wed, 16 Jun 2010 13:18:29 -0400 Received: from mail-iw0-f173.google.com ([209.85.214.173]:58049) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OOwFw-0005Y5-Fo for qemu-devel@nongnu.org; Wed, 16 Jun 2010 13:18:28 -0400 Received: by iwn10 with SMTP id 10so6715837iwn.4 for ; Wed, 16 Jun 2010 10:18:27 -0700 (PDT) Message-ID: <4C190760.9070605@codemonkey.ws> Date: Wed, 16 Jun 2010 12:18:24 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [CFR 6/10] cont command References: <1276619430-15871-1-git-send-email-aliguori@us.ibm.com> <1276619430-15871-7-git-send-email-aliguori@us.ibm.com> <20100616162544.GS13996@redhat.com> In-Reply-To: <20100616162544.GS13996@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Anthony Liguori , Stefan Hajnoczi , Juan Quintela , Markus Armbruster , qemu-devel@nongnu.org, Luiz Capitulino On 06/16/2010 11:25 AM, Daniel P. Berrange wrote: > >> This is related to the commands, not QMP per se: >> >> Once that we are talking about "cont" command. There are two cases that >> we need to think of: >> >> - incoming migration: >> >> If you start with -incoming foo, and then run "cont" on the monitor >> without having started the migration .... corruption is ensured. >> > This is why '-incoming' command line arg should die, and be replaced > with a 'incoming' monitor command that would simply not allow 'cont' > to be run until it completed. > > For that matter, even with '-incoming' arg on command line we could > refuse to honour 'cont' until the incoming migration had been done. > If we had an incoming migration command, I think we'd have to think careful about it's semantics. Is it reasonable to allow a machine that's otherwise running to do an incoming command? Regards, Anthony Liguori >> - outgoing migration >> >> After sucessful migration, we can issue "cont" command in source, and >> having source and target running at the same time -> disk corruption >> again. >> > This doesn't have to mean corruption. eg two machines using cluster-LVM. > The target QEMU is using a writable snapshot of the volume the source > QEMU is using. So you could in fact start the source again and have two > copies of the guest running at once. At the QEMU level I don't think we > should try to force policy of this kind, since it'll prevent people > experimenting with interesting new use cases. There are also soooooooo > many other ways you can trash your data with multiple hosts. If you > want safe migration, use a management app which adds a level of policy > to protect against stupid decisions > > Daniel >