btree_walk_data_t
btree_walk_data_t *bwd = wsp->walk_data;
btree_walk_data_t *bwd;
bwd = mdb_zalloc(sizeof (btree_walk_data_t), UM_SLEEP);
btree_walk_data_t *bwd = (btree_walk_data_t *)wsp->walk_data;