From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54165 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PsJ7y-0002Ev-Fk for qemu-devel@nongnu.org; Wed, 23 Feb 2011 13:07:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PsJ7w-0007hL-T8 for qemu-devel@nongnu.org; Wed, 23 Feb 2011 13:07:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39261) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PsJ7w-0007gj-Gk for qemu-devel@nongnu.org; Wed, 23 Feb 2011 13:07:52 -0500 Date: Wed, 23 Feb 2011 14:49:18 -0300 From: Marcelo Tosatti Subject: Re: [Qemu-devel] Re: [patch 2/3] Add support for live block copy Message-ID: <20110223174917.GA4630@amt.cnet> References: <20110222170004.808373778@redhat.com> <20110222170115.710717278@redhat.com> <4D642181.4080509@codemonkey.ws> <20110222210735.GA9372@amt.cnet> <4D64266A.3060106@codemonkey.ws> <20110222230935.GA11082@amt.cnet> <4D644343.4050800@codemonkey.ws> <4D65051A.6070707@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4D65051A.6070707@redhat.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Jes.Sorensen@redhat.com, qemu-devel@nongnu.org On Wed, Feb 23, 2011 at 03:01:14PM +0200, Avi Kivity wrote: > On 02/23/2011 01:14 AM, Anthony Liguori wrote: > > > >-drive already ties into the qemuopts infrastructure and we have > >readconfig and writeconfig. I don't think we're missing any major > >pieces to do this in a more proper fashion. > > The problem with qemu config files is that it splits the > authoritative source of where images are stored into two. Is it in > the management tool's database or is it in qemu's config file? > > For the problem at hand, one solution is to make qemu stop after the > copy, and then management can issue an additional command to > rearrange the disk and resume the guest. A drawback here is that if > management dies, the guest is stopped until it restarts. We also > make management latency guest visible, even if it doesn't die at an > inconvenient place. > > An alternative approach is to have the copy be performed by a new > layered block format driver: > > - create a new image, type = live-copy, containing three pieces of > information > - source image > - destination image > - copy state (initially nothing is copied) > - tell qemu switch to the new image > - qemu starts copying, updates copy state as needed > - copy finishes, event is emitted; reads and writes still serviced > - management receives event, switches qemu to destination image > - management removes live-copy image > > If management dies while this is happening, it can simply query the > state of the copy. > Similarly, if qemu dies, the copy state is persistent (could be 0/1 or > real range of blocks). You don't know if a given block is uptodate or not without the dirty bitmap. So unless you also keep track of dirty log somehow, this is meaningless. So a commit file as proposed indicates copy state (in 0/1 fashion). The difference in your proposal is that such information is stored inside a special purpose image format?