Re: [Qemu-devel] migration: new sections and backward compatibility.

[Gerd Hoffmann]

  Hi,

> 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?

Experimental patch for usb attached (actually two, the first is pure 
code motion though so the second with the actual changes becomes more 
readable).

That makes migration support switchable using a property, so we can use 
compatibility properties to disable sending the section to an older version.

That requires usb-hid.c call vmstate_register manually.  Not that nice.
We could move the needed() callback from VMStateSubsection to 
VMStateDescription, so it is possible to send complete sections 
conditionally.

Comments?

cheers,
  Gerd

0001-move-code.patch
Description: Text document

0002-usb-hid-make-migration-support-conditional.patch
Description: Text document