btree_get_prev
val = btree_get_prev(&head->h, &btree_geo128,
return btree_get_prev(&head->h, BTREE_TYPE_GEO, (unsigned long *)key);
void *val = btree_get_prev(&head->h, BTREE_TYPE_GEO, &_key);
void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
EXPORT_SYMBOL_GPL(btree_get_prev);