[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] migration: new sections and backward compatibility.
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] migration: new sections and backward compatibility. |
Date: |
Thu, 07 Jul 2011 11:23:31 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) |
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?
Re: [Qemu-devel] migration: new sections and backward compatibility., Avi Kivity, 2011/07/06