-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 *);
-extern struct rb_node *rb_nth(struct rb_node *node, unsigned n);
-extern int rb_rank(struct rb_node *node, unsigned *rank);
+extern struct rb_node *rb_next(const struct rb_node *);
+extern struct rb_node *rb_prev(const struct rb_node *);
+extern struct rb_node *rb_first(const struct rb_root *);
+extern struct rb_node *rb_last(const struct rb_root *);
+
+extern struct rb_node *rb_nth(const struct rb_node *node, unsigned n);
+extern int rb_rank(const struct rb_node *node, unsigned *rank);