[Qemu-devel] Re: [PATCH 3/3] disk: don't read from disk until the guest starts

[Anthony Liguori]

On 09/13/2010 08:39 AM, Kevin Wolf wrote:
> > Yeah, one of the key design points of live migration is to minimize the
> > number of failure scenarios where you lose a VM.  If someone typed the
> > wrong command line or shared storage hasn't been mounted yet and we
> > delay failure until live migration is in the critical path, that would
> > be terribly unfortunate.
> >      
> We would catch most of them if we try to open the image when migration
> starts and immediately close it again until migration is (almost)
> completed, so that no other code can possibly use it before the source
> has really closed it.
>    

I think the only real advantage is that we fix NFS migration, right?

But if we do invalidate_cache() as you suggested with a close/open of 
the qcow2 layer, and also acquire and release a lock in the file layer 
by propagating the invalidate_cache(), that should work robustly with NFS.

I think that's a simpler change.  Do you see additional advantages to 
delaying the open?

Regards,

anthony Liguori

> Kevin
>