doc/rbd/rbd-exclusive-locks: mention incompatibility with advisory locks

This is due to both using the same name for the lock at the RADOS level
("rbd_lock").

Signed-off-by: Ilya Dryomov <[email protected]>

Author: idryomov

doc/rbd/rbd-exclusive-locks.rst

@@ -60,6 +60,10 @@ Exclusive locking is mostly transparent to the user:
    exclusive lock. This is exposed by the ``--exclusive`` option for ``rbd
    device map`` command.
 
+.. note::
+   The ``exclusive-lock`` feature is incompatible with RBD advisory locks
+   (the ``rbd lock add`` and ``rbd lock rm`` commands).
+
 
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