locks: provide a file lease method enabling cluster-coherent leases

[deliverable/linux.git] / fs / locks.c

diff --git a/fs/locks.c b/fs/locks.c
index a65d85c1fdc26be98030644346d2a566d2cb2ec8..94f5d8065e3a2d26d98b24944ae4fcf867c90eda 100644 (file)
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1429,7 +1429,24 @@ out:
  *     @lease: file_lock to use
  *
  *     Call this to establish a lease on the file.
- *     The fl_lmops fl_break function is required by break_lease
+ *     The (*lease)->fl_lmops->fl_break operation must be set; if not,
+ *     break_lease will oops!
+ *
+ *     This will call the filesystem's setlease file method, if
+ *     defined.  Note that there is no getlease method; instead, the
+ *     filesystem setlease method should call back to setlease() to
+ *     add a lease to the inode's lease list, where fcntl_getlease() can
+ *     find it.  Since fcntl_getlease() only reports whether the current
+ *     task holds a lease, a cluster filesystem need only do this for
+ *     leases held by processes on this node.
+ *
+ *     There is also no break_lease method; filesystems that
+ *     handle their own leases shoud break leases themselves from the
+ *     filesystem's open, create, and (on truncate) setattr methods.
+ *
+ *     Warning: the only current setlease methods exist only to disable
+ *     leases in certain cases.  More vfs changes may be required to
+ *     allow a full filesystem lease implementation.
  */
 
 int vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
@@ -1437,7 +1454,10 @@ int vfs_setlease(struct file *filp, long arg, struct file_lock **lease)
        int error;
 
        lock_kernel();
-       error = setlease(filp, arg, lease);
+       if (filp->f_op && filp->f_op->setlease)
+               error = filp->f_op->setlease(filp, arg, lease);
+       else
+               error = setlease(filp, arg, lease);
        unlock_kernel();
 
        return error;