zfs_btree_prev
data = zfs_btree_prev(bt, &bt_idx, &bt_idx);
ASSERT3P((rv = zfs_btree_prev(bt, &bt_idx, &bt_idx2)), !=,
VERIFY3P(zfs_btree_prev(tree, &idx, &idx), !=, NULL);
VERIFY3P(zfs_btree_prev(tree, &idx, &idx), !=, NULL);
rs_before = zfs_btree_prev(&rt->rt_root, &where, &where_before);
void *zfs_btree_prev(zfs_btree_t *, const zfs_btree_index_t *,
range_seg_t *rs = zfs_btree_prev(&segs->rt_root, &where,