zfs_btree_destroy_nodes
while ((rv = zfs_btree_destroy_nodes(bt, &idx)) != NULL)
while ((rv = zfs_btree_destroy_nodes(&bt, &idx)) != NULL)
while ((rs = zfs_btree_destroy_nodes(&rt->rt_root, &cookie)) !=
void *zfs_btree_destroy_nodes(zfs_btree_t *, zfs_btree_index_t **);