[linux-lvm] [PATCH 01/10] lvchange: Allow cluster lock conversion

[David Teigland]

On Tue, Mar 19, 2013 at 01:32:41PM +0000, Vladislav Bogdanov wrote:
> Allow clvm locks to be converted shared <-> exclusive with corosync/dlm.
> 
> Without this it is impossible to alow both
> * VM migration (shared lock is required)
> * host-side snapshots of VM disks (exlusive lock is required)
> 
> Locks are only converted if --force parameter passed to lvchange.
> 
> Internally LKF_CONVERT flag is passed to dlm, so that is a real lock
> conversion.
> 
> Also deny release of an exclusive lock on a remote note without --force
> flag to lvchange -an.

I'm trying to figure out why the code doesn't already use CONVERT when
possible; I would have expected it to.  (It has to be combined with
NOQUEUE to avoid deadlocks.)  What happens now without this force/CONVERT
patch? a new lock created/requested?