nfsd: change heuristic for selecting the client_tracking_ops

First, try to use the new usermodehelper upcall. It should succeed or
fail quickly, so there's little cost to doing so.

If it fails, and the legacy tracking dir exists, use that. If it
doesn't exist then fall back to using nfsdcld.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4recover.c

@@ -1064,17 +1064,35 @@ nfsd4_client_tracking_init(struct net *net)
 	int status;
 	struct path path;
 
-	if (!client_tracking_ops) {
-		client_tracking_ops = &nfsd4_cld_tracking_ops;
-		status = kern_path(nfs4_recoverydir(), LOOKUP_FOLLOW, &path);
-		if (!status) {
-			if (S_ISDIR(path.dentry->d_inode->i_mode))
-				client_tracking_ops =
-						&nfsd4_legacy_tracking_ops;
-			path_put(&path);
-		}
+	/* just run the init if it the method is already decided */
+	if (client_tracking_ops)
+		goto do_init;
+
+	/*
+	 * First, try a UMH upcall. It should succeed or fail quickly, so
+	 * there's little harm in trying that first.
+	 */
+	client_tracking_ops = &nfsd4_umh_tracking_ops;
+	status = client_tracking_ops->init(net);
+	if (!status)
+		return status;
+
+	/*
+	 * See if the recoverydir exists and is a directory. If it is,
+	 * then use the legacy ops.
+	 */
+	client_tracking_ops = &nfsd4_legacy_tracking_ops;
+	status = kern_path(nfs4_recoverydir(), LOOKUP_FOLLOW, &path);
+	if (!status) {
+		status = S_ISDIR(path.dentry->d_inode->i_mode);
+		path_put(&path);
+		if (status)
+			goto do_init;
 	}
 
+	/* Finally, try to use nfsdcld */
+	client_tracking_ops = &nfsd4_cld_tracking_ops;
+do_init:
 	status = client_tracking_ops->init(net);
 	if (status) {
 		printk(KERN_WARNING "NFSD: Unable to initialize client "