Function zfs_btree_first

freebsd/contrib/openzfs/module/zfs/btree.c:1071–1079

* Return the first element in the tree, and put its location in where if * non-null. */

 * non-null.
 */
void *
zfs_btree_first(zfs_btree_t *tree, zfs_btree_index_t *where)
{
	if (tree->bt_height == -1) {
		ASSERT0(tree->bt_num_elems);
		return (NULL);
	}
	return (zfs_btree_first_helper(tree->bt_root, where));
}

/*
 * Find the last element in the subtree rooted at hdr, return its value and