Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts

[Gerd Hoffmann]

On 11/24/09 15:05, Michael S. Tsirkin wrote:
> On Mon, Nov 23, 2009 at 03:13:59PM +0100, Juan Quintela wrote:
> > > But this would only kick in when using pc-0.11 or something, right?
> >
> > Yeap.
> >
> > At this point, pc-0.10 is just:
> >
> > static QEMUMachine pc_machine_v0_10 = {
> >      .name = "pc-0.10",
> >      .desc = "Standard PC, qemu 0.10",
> >      .init = pc_init_pci,
> >      .max_cpus = 255,
> >      .compat_props = (CompatProperty[]) {
> >          {
> >              .driver   = "virtio-blk-pci",
> >              .property = "class",
> >              .value    = stringify(PCI_CLASS_STORAGE_OTHER),
> >          },{
> >              .driver   = "virtio-console-pci",
> >              .property = "class",
> >              .value    = stringify(PCI_CLASS_DISPLAY_OTHER),
> >          },{
> >              .driver   = "virtio-net-pci",
> >              .property = "vectors",
> >              .value    = stringify(0),
> >          },{
> >              .driver   = "virtio-blk-pci",
> >              .property = "vectors",
> >              .value    = stringify(0),
> >          },
> >          { /* end of list */ }
> >      },
> >
> > But to really make it work, we need to take a list of each savevm format
> > change and put it here.  Notice that several changes are needed:
> > - savevm infrastructure save functions don't know about version id
> > - devices don't know to "behave" as other version
> > - other things that I have probably missed
> >
> > Later, Juan.
>
> Why do you think this the right place for it, I wonder?
> This describes the machine, it does not seem to have
> anything to do with how we migrate it.

Well.  It turns off MSI for virtio-net-pci when you start it with -M 
pc-0.10.  Which makes virtio-net-pci savevm sections compatible with the 
qemu 0.10 ...

We could add a DeviceState->savevm field and make that available as 
property for devices which need to support multiple versions.  Then you 
we can use the compat properties to switch back to the older format with 
-M pc-0.10.

cheers,
  Gerd