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Re: [libvirt] How to avoid failure of migration/restoring/starting if cdrom is ejected inside guest?

On Tue, Aug 09, 2011 at 09:58:10AM +0800, Osier Yang wrote:
> 于 2011年08月09日 01:53, Eric Blake 写道:
> >On 08/08/2011 09:22 AM, Dave Allan wrote:
> >>>If the medium is ejected inside guest, and the source of the medium
> >>>is removed or renamed. libvirt will still tries to do cgroup setting
> >>>before starting the guest on dest side, that's the real problem. As
> >>>one will think it's reasonable to remove the source if it's
> >>>ejected. And we can't prevent one remove the source during the
> >>>migration (supposing the removing is before libvirt tries to do
> >>>cgroup setting on dest host.)
> >>
> >>Agreed, but that's a problem that I don't think we can solve except by
> >>documenting the behavior.  The libvirt documentation has always
> >>clearly stated that the storage configuration must be the same on the
> >>src and dst hosts.  We are discussing altering that constraint here in
> >>the case of medium that has been ejected, but I think we can be clear
> >>that the constraint is not being removed and that a guest's storage
> >>configuration must not be changed while a migration is in progress.
> >
> >I thought the qemu folks were working on a series of patches to
> >make cd tray state part of the migration information.  That is, if
> >you start a migration, then a guest ejects the cd, then the
> >destination will correctly see the ejected cd, even though the
> >destination was started with the tray closed.  That is, libvirt
> >should not have to poll on cd tray state in order to correctly
> >migrate, but should be able to poll on cd tray state in order to
> >report tray state to the curious user.
> >
> Agree. I don't known they are working out such patches yet. Only known they
> are trying to work out some event for the tray state.

Markus has submitted patches to qemu to migrate the tray state.  See,


so, assuming that work is accepted, eject post-migration-start will
not be a problem.

> >The migration aspect of cd tray state generally has to be solved
> >by qemu - there's nothing libvirt can do if the guest changes cd
> >tray state after migration has started but before it has
> >completed, unless libvirt can poll the source after it has paused
> >but before the destination has been unpaused and issue appropriate
> >monitor commands on the destination to resync state; but that
> >should only be necessary if qemu doesn't migrate cd tray state in
> >the first place, and requires that qemu support tray state monitor
> >commands for libvirt to use.
> >
> As far as I known, qemu still can only report the medium is ejected or
> inserted soon via "info block", and without minitor commands to change
> the tray state, or I missed something?
> Osier

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