MTIO(4)

NAME
mtio - magnetic tape commands

SYNOPSIS
#include <sys/types.h>
#include <sys/mtio.h>
#include <sys/ioctl.h>

DESCRIPTION
The magnetic tape devices described in sd(4) may be sent commands or queried for their status using the following ioctl calls:

    ioctl(fd, MTIOCTOP, &struct mtop)
    ioctl(fd, MTIOCGET, &struct mtget)

The struct mtop, struct mtget and associated definitions are defined in <sys/mtio.h> as follows:

/* Tape operations: ioctl(fd, MTIOCTOP, &struct mtop) */
struct mtop {
	short	mt_op;	/* Operation (MTWEOF, etc.) */
	int	mt_count;	/* Repeat count. */
};
#define MTWEOF	0	/* Write End-Of-File Marker */
#define MTFSF	1	/* Forward Space File mark */
#define MTBSF	2	/* Backward Space File mark */
#define MTFSR	3	/* Forward Space Record */
#define MTBSR	4	/* Backward Space Record */
#define MTREW	5	/* Rewind tape */
#define MTOFFL	6	/* Rewind and take Offline */
#define MTNOP	7	/* No-Operation, set status only */
#define MTRETEN	8	/* Retension (completely wind and rewind) */
#define MTERASE	9	/* Erase the tape and rewind */
#define MTEOM	10	/* Position at End-Of-Media */
#define MTMODE	11	/* Select tape density */
#define MTBLKZ	12	/* Select tape block size */
/* Tape status: ioctl(fd, MTIOCGET, &struct mtget) */
struct mtget {
	short	mt_type;	/* Type of tape device. */
	/* Device dependent "registers". */
	short	mt_dsreg;	/* Drive status register. */
	short	mt_erreg;	/* Error register. */
	/* Misc info. */
	off_t	mt_resid;	/* Residual count. */
	off_t	mt_fileno;	/* Current File Number. */
	off_t	mt_blkno;	/* Current Block Number within file. */
	off_t	mt_blksize;	/* Current block size. */
};

See mt(1) for a detailed description on what each operation does. The mt_type field is always zero, there is no use for it yet. Mt_dsreg is 0 (OK), 1 (Error), or 2 (EOF encountered.) Mt_erreg holds the SCSI sense key of the last operation. Mt_blksize is the current tape block size in bytes, zero if the block size is variable.

Note that one can issue these commands on a file descriptor that is in use to read or write data, something that mt can't do. So you can add eof markers in the middle of an output stream, or get the status of a device before a rewind-on-close tape rewinds.

The driver will automatically add an end of file marker to a tape that is written to if you execute a space command. If you write eof markers yourself then the driver will not add one extra on close.

SEE ALSO
mt(1), sd(4).

AUTHOR
Kees J. Bot (kjb@cs.vu.nl)