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Re: [Qemu-devel] migration: new sections and backward compatibility.
From: |
Alexander Graf |
Subject: |
Re: [Qemu-devel] migration: new sections and backward compatibility. |
Date: |
Thu, 7 Jul 2011 01:32:45 +0200 |
On 06.07.2011, at 22:01, Anthony Liguori wrote:
> On 07/06/2011 12:28 PM, Avi Kivity wrote:
>> On 07/06/2011 07:04 PM, 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.
>>>
>>> More cases are lurking. AHCI doesn't support migration today but
>>> probably will some day. Markus mentioned that scsi-disk will face that
>>> issue too. And that list probably isn't complete.
>>>
>>> Subsections don't help here as there is no toplevel section in the
>>> first place.
>>>
>>> Ideas anyone? Maybe allow test functions like we have for subsections
>>> for toplevel sections too, so we have a way to skip the section
>>> altogether on savevm?
>>>
>>> We probably also want a way to fail the migration in case the target
>>> machine doesn't support migration for $device, especially for $device
>>> == ahci to avoid data loss. For the usb-tablet it isn't that
>>> problematic, in the best case the guest just resets the device and
>>> goes on, in the worst case the mouse is dead.
>>>
>>
>> How did AHCI get in without migration? It's relatively new, is it not?
>
> We don't have a hard policy about not merging devices that don't support
> migration.
>
> Since migration must be supported forever, I'd rather see a device get some
> solid testing before it starts doing live migration. That said, we should
> probably do this consciously by explicitly marking the device non-migrateable.
Can't we just implicitly fail migration whenever there's a device in the tree
that doesn't have VMSTATE?
Alex
Re: [Qemu-devel] migration: new sections and backward compatibility., Avi Kivity, 2011/07/06
- Re: [Qemu-devel] migration: new sections and backward compatibility., Anthony Liguori, 2011/07/06
- Re: [Qemu-devel] migration: new sections and backward compatibility.,
Alexander Graf <=
- Re: [Qemu-devel] migration: new sections and backward compatibility., Gerd Hoffmann, 2011/07/07
- Re: [Qemu-devel] migration: new sections and backward compatibility., Avi Kivity, 2011/07/07
- Re: [Qemu-devel] migration: new sections and backward compatibility., Jes Sorensen, 2011/07/08
- Re: [Qemu-devel] migration: new sections and backward compatibility., Peter Maydell, 2011/07/08
- Re: [Qemu-devel] migration: new sections and backward compatibility., Gerd Hoffmann, 2011/07/08
Re: [Qemu-devel] migration: new sections and backward compatibility., Anthony Liguori, 2011/07/07