[PATCH] Allow cluster-wide flock

Below is a patch that lets a cluster filesystem (such as GFS) implement
flock across the cluster.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/locks.c

@@ -1317,6 +1317,33 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 	return error;
 }
 
+/**
+ * flock_lock_file_wait - Apply a FLOCK-style lock to a file
+ * @filp: The file to apply the lock to
+ * @fl: The lock to be applied
+ *
+ * Add a FLOCK style lock to a file.
+ */
+int flock_lock_file_wait(struct file *filp, struct file_lock *fl)
+{
+	int error;
+	might_sleep();
+	for (;;) {
+		error = flock_lock_file(filp, fl);
+		if ((error != -EAGAIN) || !(fl->fl_flags & FL_SLEEP))
+			break;
+		error = wait_event_interruptible(fl->fl_wait, !fl->fl_next);
+		if (!error)
+			continue;
+
+		locks_delete_block(fl);
+		break;
+	}
+	return error;
+}
+
+EXPORT_SYMBOL(flock_lock_file_wait);
+
 /**
  *	sys_flock: - flock() system call.
  *	@fd: the file descriptor to lock.
@@ -1365,17 +1392,12 @@ asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
 	if (error)
 		goto out_free;
 
-	for (;;) {
-		error = flock_lock_file(filp, lock);
-		if ((error != -EAGAIN) || !can_sleep)
-			break;
-		error = wait_event_interruptible(lock->fl_wait, !lock->fl_next);
-		if (!error)
-			continue;
-
-		locks_delete_block(lock);
-		break;
-	}
+	if (filp->f_op && filp->f_op->flock)
+		error = filp->f_op->flock(filp,
+					  (can_sleep) ? F_SETLKW : F_SETLK,
+					  lock);
+	else
+		error = flock_lock_file_wait(filp, lock);
 
  out_free:
 	if (list_empty(&lock->fl_link)) {
@@ -1732,6 +1754,12 @@ void locks_remove_flock(struct file *filp)
 	if (!inode->i_flock)
 		return;
 
+	if (filp->f_op && filp->f_op->flock) {
+		struct file_lock fl = { .fl_flags = FL_FLOCK,
+					.fl_type = F_UNLCK };
+		filp->f_op->flock(filp, F_SETLKW, &fl);
+	}
+
 	lock_kernel();
 	before = &inode->i_flock;
 

include/linux/fs.h

@@ -695,6 +695,7 @@ extern int posix_lock_file_wait(struct file *, struct file_lock *);
 extern void posix_block_lock(struct file_lock *, struct file_lock *);
 extern void posix_unblock_lock(struct file *, struct file_lock *);
 extern int posix_locks_deadlock(struct file_lock *, struct file_lock *);
+extern int flock_lock_file_wait(struct file *filp, struct file_lock *fl);
 extern int __break_lease(struct inode *inode, unsigned int flags);
 extern void lease_get_mtime(struct inode *, struct timespec *time);
 extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
@@ -912,6 +913,7 @@ struct file_operations {
 	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 	int (*check_flags)(int);
 	int (*dir_notify)(struct file *filp, unsigned long arg);
+	int (*flock) (struct file *, int, struct file_lock *);
 };
 
 struct inode_operations {