mtcmd
mtcmd(mt, MTWEOF, 0, 0);
mtcmd(mt, MTWEOF, 0, 0);
mtcmd(mt, MTBSR, 1, 0);
mtcmd(mt, MTREW, 0, 1);
mtcmd(mt, -1, 0, 0);
if ((error = mtcmd(mt, mtop->mt_op, 0, 0)))
error = mtcmd(mt, mtop->mt_op, mtop->mt_count, 0);
int mtcmd(struct mt_softc *, int, int, int);