traverse_visitbp
err = traverse_visitbp(td, dnp, &cbp[i], &czb);
err = traverse_visitbp(td, dnp, &dnp->dn_blkptr[j], &czb);
err = traverse_visitbp(td, dnp, DN_SPILL_BLKPTR(dnp), &czb);
(void) traverse_visitbp(&td, NULL, td.td_rootbp, &czb);
err = traverse_visitbp(&td, NULL, rootbp, &czb);