MTIO(4)

NAME
mtio - FreeBSD magtape interface

DESCRIPTION
The special files named /dev/[nr]st* refer to SCSI tape drives, which may be attached to the system. /dev/[nr]st*.ctl are control devices that can be used to issue ioctls to the SCSI tape driver to set parameters that are required to last beyond the unmounting of a tape.

The rewind devices automatically rewind when the last requested read, write or seek has finished, or the end of the tape has been reached. The letter ‘n’ is usually prepended to the name of the no-rewind devices.

Tapes can be written with either fixed length records or variable length records. See st(4) for more information. Two end-of-file markers mark the end of a tape, and one end-of-file marker marks the end of a tape file. If the tape is not to be rewound it is positioned with the head in between the two tape marks, where the next write will over write the second end-of-file marker.

All of the magtape devices may be manipulated with the mt(1) command.

A number of ioctl(2) operations are available on raw magnetic tape. The following definitions are from <sys/mtio.h>:

    /*
     * Structures and definitions for mag tape io control commands
     */
    /* structure for MTIOCTOP - mag tape op command */
    struct mtop {
    	short	mt_op;		/* operations defined below */
    	daddr_t	mt_count;	/* how many of them */
    };
    /* operations */
    #define MTWEOF		0	/* write an end-of-file record */
    #define MTFSF		1	/* forward space file */
    #define MTBSF		2	/* backward space file */
    #define MTFSR		3	/* forward space record */
    #define MTBSR		4	/* backward space record */
    #define MTREW		5	/* rewind */
    #define MTOFFL		6	/* rewind and put the drive offline */
    #define MTNOP		7	/* no operation, sets status only */
    #define MTCACHE		8	/* enable controller cache */
    #define MTNOCACHE	9	/* disable controller cache */
    #if defined(__FreeBSD__)
    /* Set block size for device. If device is a variable size dev		*/
    /* a non zero parameter will change the device to a fixed block size	*/
    /* device with block size set to that of the parameter passed in.	*/
    /* Resetting the block size to 0 will restore the device to a variable	*/
    /* block size device. */
    #define MTSETBSIZ	10
    /* Set density values for device. They are defined in the SCSI II spec	*/
    /* and range from 0 to 0x17. Sets the value for the opened mode only	*/
    #define MTSETDNSTY	11
    #define MTERASE		12	/* erase to EOM */
    #define MTEOD		13	/* Space to EOM */
    #define MTCOMP		14	/* select compression mode 0=off, 1=def */
    #define MTRETENS	15	/* re-tension tape */
    #endif
    /* structure for MTIOCGET - mag tape get status command */
    struct mtget {
    	short	mt_type;	/* type of magtape device */
    /* the following two registers are grossly device dependent */
    	short	mt_dsreg;	/* ``drive status'' register */
    	short	mt_erreg;	/* ``error'' register */
    /* end device-dependent registers */
    	short	mt_resid;	/* residual count */
    #if defined (__FreeBSD__)
    	daddr_t mt_blksiz;	/* presently operating blocksize */
    	daddr_t mt_density;	/* presently operating density */
    	daddr_t mt_comp;	/* presently operating compression */
    	daddr_t mt_blksiz0;	/* blocksize for mode 0 */
    	daddr_t mt_blksiz1;	/* blocksize for mode 1 */
    	daddr_t mt_blksiz2;	/* blocksize for mode 2 */
    	daddr_t mt_blksiz3;	/* blocksize for mode 3 */
    	daddr_t mt_density0;	/* density for mode 0 */
    	daddr_t mt_density1;	/* density for mode 1 */
    	daddr_t mt_density2;	/* density for mode 2 */
    	daddr_t mt_density3;	/* density for mode 3 */
    /* the following are not yet implemented */
    	u_char	mt_comp0;	/* compression type for mode 0 */
    	u_char	mt_comp1;	/* compression type for mode 1 */
    	u_char	mt_comp2;	/* compression type for mode 2 */
    	u_char	mt_comp3;	/* compression type for mode 3 */
    #endif
    	daddr_t	mt_fileno;	/* file number of current position */
    	daddr_t	mt_blkno;	/* block number of current position */
    /* end not yet implemented */
    };
    /*
     * Constants for mt_type byte.  These are the same
     * for controllers compatible with the types listed.
     */
    #define	MT_ISTS		0x01		/* TS-11 */
    #define	MT_ISHT		0x02		/* TM03 Massbus: TE16, TU45, TU77 */
    #define	MT_ISTM		0x03		/* TM11/TE10 Unibus */
    #define	MT_ISMT		0x04		/* TM78/TU78 Massbus */
    #define	MT_ISUT		0x05		/* SI TU-45 emulation on Unibus */
    #define	MT_ISCPC	0x06		/* SUN */
    #define	MT_ISAR		0x07		/* SUN */
    #define	MT_ISTMSCP	0x08		/* DEC TMSCP protocol (TU81, TK50) */
    #define MT_ISCY		0x09		/* CCI Cipher */
    #define MT_ISCT		0x0a		/* HP 1/4 tape */
    #define MT_ISFHP	0x0b		/* HP 7980 1/2 tape */
    #define MT_ISEXABYTE	0x0c		/* Exabyte */
    #define MT_ISEXA8200	0x0c		/* Exabyte EXB-8200 */
    #define MT_ISEXA8500	0x0d		/* Exabyte EXB-8500 */
    #define MT_ISVIPER1	0x0e		/* Archive Viper-150 */
    #define MT_ISPYTHON	0x0f		/* Archive Python (DAT) */
    #define MT_ISHPDAT	0x10		/* HP 35450A DAT drive */
    #define MT_ISMFOUR	0x11		/* M4 Data 1/2 9track drive */
    #define MT_ISTK50	0x12		/* DEC SCSI TK50 */
    #define MT_ISMT02	0x13		/* Emulex MT02 SCSI tape controller */
    /* mag tape io control commands */
    #define	MTIOCTOP	_IOW('m', 1, struct mtop)	/* do a mag tape op */
    #define	MTIOCGET	_IOR('m', 2, struct mtget)	/* get tape status */
    #define MTIOCIEOT	_IO('m', 3)			/* ignore EOT error */
    #define MTIOCEEOT	_IO('m', 4)			/* enable EOT error */
    #ifndef KERNEL
    #define	DEFTAPE	"/dev/nrst0"
    #endif
    #ifdef	KERNEL
    /*
     * minor device number
     */
    #define	T_UNIT		003		/* unit selection */
    #define	T_NOREWIND	004		/* no rewind on close */
    #define	T_DENSEL	030		/* density select */
    #define	T_800BPI	000		/* select  800 bpi */
    #define	T_1600BPI	010		/* select 1600 bpi */
    #define	T_6250BPI	020		/* select 6250 bpi */
    #define	T_BADBPI	030		/* undefined selection */
    #endif
    #endif /* _SYS_MTIO_H_ */

FILES
/dev/[nr]st*

SEE ALSO
mt(1), tar(1), st(4)

HISTORY
The mtio manual appeared in 4.2BSD. An i386 version first appeared in FreeBSD 2.2.

BUGS
The status should be returned in a device independent format.

The special file naming should be redone in a more consistent and understandable manner.