On Mon, Feb 07, 2011 at 01:33:57PM -0600, Anthony Liguori wrote: > On 02/07/2011 10:07 AM, Michael S. Tsirkin wrote: > >New thread stated intentionally, the original patch is Message-ID: > ><349e93a4cfc6e1effc1b681cae53f805fdb9624e.1296713825.git.amit.s...@redhat.com> > > > >On Thu, Feb 03, 2011 at 11:47:08AM +0530, Amit Shah wrote: > >>Add a compat property for older machine types. When this is used (via > >>-M pc-0.13, for example), the new flow control mechanisms will not be > >>used. This is done to keep migration from a machine started with older > >>type on a pc-0.14+ qemu to an older machine working. > >> > >>The property is named 'flow_control' and defaults to on. > >> > >>Reported-by: Alex Williamson<alex.william...@redhat.com> > >>Signed-off-by: Amit Shah<amit.s...@redhat.com> > >So, I think there are two things that need to be agreed on: > > > >- Can we commit to support migration from new qemu version to an old one? > > We haven't in the past but downstreams do want this, > > so it makes sense to have the infrastructure upstream. > > Only within a stable release series and only when it's possible > without sacrificing integrity. I know some downstreams disagree > with this but I don't think this is a business we want to get into. > > Regards, > > Anthony Liguori > >- The infrastructure/command line option for such support. > > We have the -M flags to describe the machine that > > we are running, but that abstracts away guest-visible machine, > > which the migration format is not. > > Also, same qemu could migrate to any older version. > > So I think we would have to add a flag (call it -V for now) > > to savevm/migrate commands to specify the format to be used. > > Naturally some machines would be incompatible with > > specific -V values, that's nothing new. > > > >Pls comment.
OK, assuming we want this, let's talk about implementation. I think that spreading custom flags all over the code like this patch does would be pretty bad. What I'd like to see is a way to - map stable versions (e.g. machine type if we are going to tie to that) to savevm format using some kind of table - for save callbacks to be able to figure out what version to use -- MST
