[RBTREE]: Add rb_last()

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@redhat.com>

include/linux/rbtree.h

@@ -123,6 +123,7 @@ extern void rb_erase(struct rb_node *, struct rb_root *);
 extern struct rb_node *rb_next(struct rb_node *);
 extern struct rb_node *rb_prev(struct rb_node *);
 extern struct rb_node *rb_first(struct rb_root *);
+extern struct rb_node *rb_last(struct rb_root *);
 
 /* Fast replacement of a single node without remove/rebalance/add/rebalance */
 extern void rb_replace_node(struct rb_node *victim, struct rb_node *new, 

lib/rbtree.c

@@ -312,6 +312,19 @@ struct rb_node *rb_first(struct rb_root *root)
 }
 EXPORT_SYMBOL(rb_first);
 
+struct rb_node *rb_last(struct rb_root *root)
+{
+	struct rb_node	*n;
+
+	n = root->rb_node;
+	if (!n)
+		return NULL;
+	while (n->rb_right)
+		n = n->rb_right;
+	return n;
+}
+EXPORT_SYMBOL(rb_last);
+
 struct rb_node *rb_next(struct rb_node *node)
 {
 	/* If we have a right-hand child, go down and then left as far