Early Lock Cancellation
^^^^^^^^^^^^^^^^^^^^^^^
[[early-lock-cancellation]]

In some circumstances (see <<mds-reint-setattr-rpc>>) a client holding
a lock "knows" that the operation it is initiating will necessitate
canceling a lock that it holds. In such a circumstance the lock is
said to be "in conflict" with the operation. For example, a side
effect of the GNU 'fileutils' is that it always issues a 'stat' prior
to other update operations, so when issuing an update to a resource
attribute on the MDT a) the client will already have a read lock on
the resource, and b) the MDT will then need a lock on that same
resource in order to perform the update. Rather than waiting for an
additional round of RPCs to carry out the lock cancellation (on the
client) the RPC requesting the update can include a cancellation of
the lock as part of its request. This proactive lock cancellation is
called "early lock cancellation" or sometimes ELC.