What were you trying to do that didn't work?

In the context of PR-based recovery in lvmlockd, there is a rare case in which the lvmlockd PR key may contain the incorrect host generation number.

1. In lockstart, lvmlockd reads the sanlock generation from the local host's host_id lease on disk, before calling add_lockspace. That generation is returned to the vgchange lockstart command as prev_generation.

2. In lockstart, lvmlockd then calls sanlock_add_lockspace which increments the local generation number on disk, so lockstart results in the host running with prev_generation+1.

3. vgchange lockstart ensures that the registered PR key for the host (when using a host_id+gen key) includes the generation prev_generation+1, so it matches the currently running generation.

On rare occasions, in sanlock_add_lockspace (step 2) the new generation number can be the previous ondisk generation +2, rather than the usual +1. 

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