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Re: [libvirt] [PATCH V6] support offline migration



在 2012-09-11二的 18:00 +0100,Daniel P. Berrange写道:
> > 
> > Good point - the new flag is necessary, and must be user-visible.  At
> > which point, do we argue that use of the MIGRATE_OFFLINE flag
> > automatically implies MIGRATE_PERSISTENT, or should it be an error
> > unless the user explicitly requests both flags?
> 
> It sort of depends what you consider the semantics of MIGRATE_OFFLINE to
> be. You can consider it to be a flag indicating that the guest must be
> in the shutoff state curently, or you can consider it to be a
> permission flag to indicate that migration is allowed if the guest
> is offline. The difference here is subtle - basically comes down
> to whether you raise an error if OFFLINE is set, and the guest is
> currently running.
> 
> In the case where you consider it a permission flag (which is what is
> currently implemented), then we must mandate use of the PERSISTENT
> flag, otherwise you get wierd semantics. eg The persistent config would
> not be copied if running, but would be copied if shutoff.
> 
> If you consider it a state flag, then I don't think it matters so much,
> though I would still prefer to see the MIGRATE_PERSISTENT flag specified
> explicitly. It would let you deal with a case where you have a shutoff
> guest, and you migrate the storage (using the appropriate flag) but do
> not migrate the config.
> 

Yes, implicit flags really lead to misunderstanding.

> Daniel

-- 
liguang    lig fnst cn fujitsu com
FNST linux kernel team



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