locks: factor out generic/filesystem switch from test_lock

Factor out the code that switches between generic and filesystem-specific lock
methods; eventually we want to call this from lock managers (lockd and nfsd)
too; currently they only call the generic methods.

This patch does that for test_lock.

Note that this hasn't been necessary until recently, because the few
filesystems that define ->lock() (nfs, cifs...) aren't exportable via NFS.
However GFS (and, in the future, other cluster filesystems) need to implement
their own locking to get cluster-coherent locking, and also want to be able to
export locking to NFS (lockd and NFSv4).

So we accomplish this by factoring out code such as this and exporting it for
the use of lockd and nfsd.

Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>

fs/locks.c

@@ -1611,6 +1611,24 @@ asmlinkage long sys_flock(unsigned int fd, unsigned int cmd)
 	return error;
 }
 
+/**
+ * vfs_test_lock - test file byte range lock
+ * @filp: The file to test lock for
+ * @fl: The lock to test
+ * @conf: Place to return a copy of the conflicting lock, if found
+ *
+ * Returns -ERRNO on failure.  Indicates presence of conflicting lock by
+ * setting conf->fl_type to something other than F_UNLCK.
+ */
+int vfs_test_lock(struct file *filp, struct file_lock *fl)
+{
+	if (filp->f_op && filp->f_op->lock)
+		return filp->f_op->lock(filp, F_GETLK, fl);
+	posix_test_lock(filp, fl);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(vfs_test_lock);
+
 static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
 {
 	flock->l_pid = fl->fl_pid;
@@ -1663,12 +1681,9 @@ int fcntl_getlk(struct file *filp, struct flock __user *l)
 	if (error)
 		goto out;
 
-	if (filp->f_op && filp->f_op->lock) {
-		error = filp->f_op->lock(filp, F_GETLK, &file_lock);
-		if (error < 0)
-			goto out;
-	} else
-		posix_test_lock(filp, &file_lock);
+	error = vfs_test_lock(filp, &file_lock);
+	if (error)
+		goto out;
 
 	flock.l_type = file_lock.fl_type;
 	if (file_lock.fl_type != F_UNLCK) {
@@ -1797,13 +1812,10 @@ int fcntl_getlk64(struct file *filp, struct flock64 __user *l)
 	if (error)
 		goto out;
 
-	if (filp->f_op && filp->f_op->lock) {
-		error = filp->f_op->lock(filp, F_GETLK, &file_lock);
-		if (error < 0)
-			goto out;
-	} else
-		posix_test_lock(filp, &file_lock);
-
+	error = vfs_test_lock(filp, &file_lock);
+	if (error)
+		goto out;
+
 	flock.l_type = file_lock.fl_type;
 	if (file_lock.fl_type != F_UNLCK)
 		posix_lock_to_flock64(&flock, &file_lock);

include/linux/fs.h

@@ -856,6 +856,7 @@ extern int posix_lock_file_conf(struct file *, struct file_lock *, struct file_l
 extern int posix_lock_file(struct file *, struct file_lock *);
 extern int posix_lock_file_wait(struct file *, struct file_lock *);
 extern int posix_unblock_lock(struct file *, struct file_lock *);
+extern int vfs_test_lock(struct file *, 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);