Anthony Liguori<address@hidden> writes:
On 07/06/2011 11:04 AM, Gerd Hoffmann wrote:
Hi folks,
We'll need to figure a sane way to handle migration to older versions
with new sections, i.e. devices which used to not save state before do now.
We already have one case in tree: usb. qemu 0.14 saves state for usb-hid
devices and the usb-hub, whereas qemu 0.13 and older don't. You can't
migrate a vm with a usb-tablet from 0.14 to 0.13 because of that even if
you use -M pc-0.13.
Because if you did migrate, you would actively break the guest during
migration. So why is this a problem?
This comes up a lot. We shouldn't enable migration if we know the
guest is going to break during migration. That's a feature, not a
bug.
Not so fast :)
I agree that throwing away unrecognized migration data is unsafe, and
should not be done. Now let me present my little problem.
I'm working on making migration preserve "tray status": open/closed,
locked/unlocked.
For ide-cd, I can stick a subsection "ide_drive/tray_state" into section
"ide_drive". Needed only if the tray is open or locked. This gives
users a chance to migrate to older versions, and is perfectly safe.
scsi-cd doesn't have a section, yet. What now?