Re: [Qemu-devel] [PATCH 2/3] move vm stop/start to migrate_set_state

[Anthony Liguori]

Jamie Lokier wrote:
> Anthony Liguori wrote:
>   
> > Paolo Bonzini wrote:
> >     
> > > On 07/09/2009 03:45 PM, Anthony Liguori wrote:
> > >       
> > > > How does the disk become full during the final stage?  The guest isn't
> > > > running.
> > > >         
> > > The host disk can become full and cause a "migrate exec" to fail.  Or 
> > > for network migration migration, you could have the connection drop 
> > > exactly during the final stage.  In this case, the VM would be 
> > > unconditionally restarted.
> > >       
> > Because migration failed.  Is that not the desired behavior?  It seems 
> > like it is to me.
> >
> > If I try to do a live migration, it should either succeed and my guest 
> > experiences minimal downtime or it should fail and my guest should 
> > experience minimal downtime.
> >     
>
> What happens if the destination host sends "migration completed", and
> then the connection drops before that message is delivered reliably to
> the sending host?
>   

We don't check the return value of close so the last possible place 
failure can occur is the last write.  By definition, if the write 
failed, the migration session could not have been completed successfully.

Migration is unidirectional.  There is no "migration completed" message 
from the destination.  We're very conservative wrt restarting the source.

Regards,

Anthony Liguori