bcache_btree
ret = bcache_btree(check_recurse, p, b, op);
ret = bcache_btree(check_recurse, p, c->root, &op);
ret = bcache_btree(map_nodes_recurse, k, b,
: bcache_btree(map_keys_recurse, k,
ret = bcache_btree(map_keys_recurse,