Re: [Qemu-devel] [PATCH 16/46] Add migration-capability boolean for postcopy-ram.

[Paolo Bonzini]

Il 07/07/2014 22:23, Dr. David Alan Gilbert ha scritto:
> I think what I need to do for that is:
>    1) As for precopy add the option not to start the destination CPU on entry 
> to postcopy;
>       I think that's OK, because we can carry on in postcopy mode even if the 
> destination
>       CPU isn't running, we just won't generate page requests.
>
> Admittedly I don't quite understand how (1) is supposed to interact with device
> state.

This is just passing "-S" on the destination side.  Device state is 
treated the same as without "-S" and can still generate page requests. 
The only difference is whether you have a vm_start() or not.

I think it should be possible to restart the VM on the source side after 
postcopy migration, as long as migration has failed or has been 
canceled.  Whether that makes sense or causes dire disk corruption 
depends on the particular scenario, but then the same holds for precopy 
and we don't try at all to prevent "cont" at the end of migration.  It 
makes it much easier for libvirt to restart the source if it cannot 
continue on the destination.

Paolo