R_CANCEL
mputm(md, R_CANCEL, MOKMORE, oerrno, rid);
mputm(md, R_CANCEL, MOK, oerrno, rid);
mputm(md, R_CANCEL, MOK, MUNKNOWN, "");
if (rcv_msg(svc, R_CANCEL, &more, &status, &req_id) < 0)