Path Lookup
~~~~~~~~~~~
[[path-lookup]]

When an operation is to be performed on a file or directory (the
"target"), say a 'stat' command, the target is specified with a path.
The Lustre client host maintains a cache of information about
directories and files. The first time a target is visited the cache
must be loaded with that information. To get the information the
client requests a 'concurrent read: LOOKUP IBITS' lock on each path
element from the root (of the Lustre file system) up to the target.
The type of the lock requested for the target will depend on the
operation being performed. The client does not need to send a new lock
request for a path element if it is currently holding a compatible
lock in its cache.

Each lock request is accompanied by an "intent" that characterizes
the intended operation for which the lock is being acquired. For path
elements before the target the intent is a 'lookup' and for the target
the intent corresponds to an operation on the target. For example, in
a 'stat' command the lock's intent for the target will be a getattr.