ypfilter
static void ypfilter(DBM *fdb, datum *inkey, datum *outkey, datum *val,
ypfilter(fdb, NULL,
ypfilter(fdb, &req.keydat,
ypfilter(fdb, (datum *) NULL, &resp.keydat, &resp.valdat,
ypfilter(fdb, &resp.keydat, &resp.keydat, &resp.valdat,