[Qemu-devel] Re: [SeaBIOS] [PATCH 0/8] option rom loading overhaul.

[Anthony Liguori]

Gerd Hoffmann wrote:
> On 12/18/09 15:35, Anthony Liguori wrote:
>
> > I know this series carries a good bit of risk but I'd like to bring it
> > in 0.12.0. Because this has a guest visible change to the PCI devices,
> > we cannot carry it in stable-0.12 post release and I think the
> > functionality it brings it's very important.
>
> The guest visible change automatically raises the question:
> Do we need to do something for -M pc-0.11?  Like loading the pci roms 
> via fw_cfg too so the guest doesn't see the new pci rom bar?

Yes, we do.  We can fix that problem as a stable-0.12 update though.   
Right now, migration with pc-0.11 is broken in other areas too.

> Oh, and while thinking about compatibility issues:  What about 
> migration?  I think we have to save rom_offset in case $pcidevice has 
> a rom bar, otherwise your roms are gone after migration.  Which you 
> wouldn't notice until reboot though.

It's really unclear to me the best way to handle live migration.  The 
rom_offset is not enough because unfortunately it's not stable after 
invocations of qemu.  I think we're going to have to actually save the 
some contents with the PCIDevices.

For 0.13, we need to change the way that we migrate memory to fix this 
problem properly.

> Is 0.11 -> 0.12 migration supposed to work?  That could become quite 
> nasty too.  But maybe that is impossible anyway due to the switch to 
> seabios?

In theory, it should work.  SeaBIOS should not be a guest visible change 
because the guest should not depend on what BIOS we're using.  While 
it's probably debatable about whether that's true, what's really 
important is whether it's actually functional.  IOW, can we migrate, 
reboot Windows, and not have Windows freak out about the underlying 
machine changing.

If we can make the migration work, I suspect it won't be until 0.12.3 or 
0.12.4.

Regards,

Anthony Liguori