extern config_t *new_config(void) __attribute__ ((__malloc__));
extern void free_config(config_t *);
extern void config_add(avl_tree_t *, config_t *);
-extern config_t *lookup_config(avl_tree_t *, char *);
-extern config_t *lookup_config_next(avl_tree_t *, const config_t *);
+extern config_t *lookup_config(const avl_tree_t *, char *);
+extern config_t *lookup_config_next(const avl_tree_t *, const config_t *);
extern bool get_config_bool(const config_t *, bool *);
extern bool get_config_int(const config_t *, int *);
extern bool get_config_string(const config_t *, char **);