+extern void space_map_ref_create(avl_tree_t *t);
+extern void space_map_ref_destroy(avl_tree_t *t);
+extern void space_map_ref_add_seg(avl_tree_t *t,
+ uint64_t start, uint64_t end, int64_t refcnt);
+extern void space_map_ref_add_map(avl_tree_t *t,
+ space_map_t *sm, int64_t refcnt);
+extern void space_map_ref_generate_map(avl_tree_t *t,
+ space_map_t *sm, int64_t minref);
+