From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NCxvb-00058H-LN for qemu-devel@nongnu.org; Tue, 24 Nov 2009 11:07:43 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NCxvX-00055N-2G for qemu-devel@nongnu.org; Tue, 24 Nov 2009 11:07:43 -0500 Received: from [199.232.76.173] (port=42994 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NCxvW-00055A-Tx for qemu-devel@nongnu.org; Tue, 24 Nov 2009 11:07:38 -0500 Received: from mx1.redhat.com ([209.132.183.28]:26023) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NCxvW-0000Rc-JI for qemu-devel@nongnu.org; Tue, 24 Nov 2009 11:07:38 -0500 Received: from int-mx08.intmail.prod.int.phx2.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nAOG7bc8020067 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 24 Nov 2009 11:07:37 -0500 Date: Tue, 24 Nov 2009 18:05:00 +0200 From: "Michael S. Tsirkin" Message-ID: <20091124160500.GD6737@redhat.com> References: <4B0952C9.9010803@redhat.com> <4B0BB7F6.5090103@redhat.com> <20091124140144.GK2405@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: Dor Laor , qemu-devel On Tue, Nov 24, 2009 at 03:21:34PM +0100, Juan Quintela wrote: > "Michael S. Tsirkin" wrote: > > On Tue, Nov 24, 2009 at 12:39:50PM +0200, Dor Laor wrote: > >> On 11/23/2009 02:15 PM, Juan Quintela wrote: > >>> Dor Laor wrote: > >>>> > In the last couple of days we discovered some issues regarding stable > >>>> > ABI and the robustness of the live migration protocol. Let's just jump > >>>> > right into it, ordered by complexity: > >>>> > > >>>> > 1. Control*every* feature exposed to the guest by qemu cmdline: > >>>> > > >>>> > While thinking on cross version migration, and reviewing some > >>>> > patches, I noticed that there are many times that we use feature bits > >>>> > in order to expose functionality for the guest driver - example: > >>>> > VIRTIO_BLK_F_BARRIER, but we do not control it from qemu cmdline. > >>> In my opinion this is madness, qemu command line is already too > >>> complicated. I agree with anthony to put it in the command line. > >> > >> Qemu's cmdline is currently our config file.. Actually there is nothing > >> wrong with it. Human users shouldn't be interested with these changes > >> and management software should not have problem manipulating it. > >> We do need flexibility of controlling our features like any other > >> software component. > >> > >>> I will go further, and think that this kind of issues should be put into > >>> the machine type. > >>> > >>> If you start qemu with -M pc-0.10, it should save the state in a 0.10 > >>> compatible way (that don't happens at the moment, but it should work > >>> that way). > >> > >> That's the idea - to keep it part of qdev and by default use it with -M. > > > > I think we want to keep these things separate: > > machine description should be for things that > > are both guest visible and not changeable by guest, > > so it absolutely must stay constant as long as guest > > it alive. > > That is exactly what we need here, that version of the savevm protocol > for each device is the same. > > Later, Juan. A device already supports load for a range of versions between X and Y. We want to support saving to a range of versions. Which versions to use is a separate decision which should be taken on run time, not at startup time. -- MST