From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=52268 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OOvRL-0007e8-K3 for qemu-devel@nongnu.org; Wed, 16 Jun 2010 12:26:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OOvR5-0003tQ-M9 for qemu-devel@nongnu.org; Wed, 16 Jun 2010 12:25:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57895) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OOvR5-0003tE-FC for qemu-devel@nongnu.org; Wed, 16 Jun 2010 12:25:55 -0400 Date: Wed, 16 Jun 2010 17:25:44 +0100 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] Re: [CFR 6/10] cont command Message-ID: <20100616162544.GS13996@redhat.com> References: <1276619430-15871-1-git-send-email-aliguori@us.ibm.com> <1276619430-15871-7-git-send-email-aliguori@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: Markus Armbruster , Anthony Liguori , qemu-devel@nongnu.org, Stefan Hajnoczi , Luiz Capitulino On Wed, Jun 16, 2010 at 03:11:24PM +0200, Juan Quintela wrote: > Anthony Liguori wrote: > > cont > > ---- > > > > Resume emulation. > > > > Arguments: None. > > > > Example: > > > > -> { "execute": "cont" } > > <- { "return": {} } > > 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. > - 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 -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|