__bch_btree_node_write
__bch_btree_node_write(b, parent);
__bch_btree_node_write(b, NULL);
__bch_btree_node_write(b, &cl);
void __bch_btree_node_write(struct btree *b, struct closure *parent);
__bch_btree_node_write(b, NULL);
__bch_btree_node_write(b, NULL);