On Tue, Nov 24, 2009 at 03:21:34PM +0100, Juan Quintela wrote: > "Michael S. Tsirkin" <m...@redhat.com> 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<dl...@redhat.com> 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
