MTBSR
(void) rmtioctl(MTBSR, 1);
static struct mtop bsr = { MTBSR, 1 };
{ "bsr", MTBSR, O_RDONLY, 1 },
ctlcmd = MTBSR;
session->ns_tape.td_fd, MTBSR, 1);
tapeop.mt_op = MTBSR;
mtcmd.mt_op = MTBSR;
case MTBSR:
case MTBSR: