Re: [libvirt] [PATCHv4 12/18] blockjob: implement block copy for qemu

On 04/13/2012 08:46 AM, Jiri Denemark wrote: > I guess I wasn't paying enough attention somewhere but why do we forbid block > copy for persistent domains? I understand why we want to forbid certain > operations when block copy is active but I don't see a reason for penalizing > persistent domains. It was in patch 8/18 where I added the restrictions, and hopefully documented in that commit message why limiting things to transient is a good first step: 1. the first client of live migration is oVirt, which uses transient domains 2. qemu does not (yet) provide a way to resume a mirror when restarting a domain, so anything that would require restoring a domain from saved state is broken: incoming migration, virsh restore, and virsh start after a managed save. But users would be upset if they saved a domain, only to find out that they cannot then restore it, so I squelched things one step earlier in the process, by preventing any save of a domain so that we never have a broken save image in the first place. My worry now comes from the fact that managedsave is on the list of forbidden operations. If a domain is transient, managedsave is already forbidden (it is assumed that you either don't care about the domain if the host dies, or that you are running a higher-level app like oVirt that knows how to rebuild the guest on a different host). But if a guest is persistent, and you use the libvirt-guests init script, then