magtape

[utzoo!duke!decvax!ucbvax!CSVAX.wnj at Berkeley]

here is the man page for the mag tape ioctls which are in 4.1bsd, the latest
vax release from berkeley.  tom ferrin at ucsf has also moved these
to pdp-11.  these exist in tape drivers for te16/tu45/tu77, unibus ts-11
and unibus tm emulation (e.g. emulex tc-11 with kennedy tape drives).
       	bill joy
---
	.TH MT 4 4/1/81
	.SH NAME
	mt \- UNIX magtape interface
	.SH DESCRIPTION
	The files
	.I "mt0, ..., mt15"
	refer to the UNIX magtape drives,
	which may be on the MASSBUS using the TM03 formatter
	.IR ht (4),
	or on the UNIBUS using either the TM11 or TS11 formatters
	.IR tm (4)
	or
	.IR ts (4).
	The following description applies to any of the transport/controller pairs.
	The files
	.I "mt0, ..., mt7"
	are 800bpi, and
	.I "mt8, ..., mt15"
	are 1600bpi.
	(But note that only 1600 bpi is available with the TS11.)
	The files
	.I "mt0, ..., mt3"
	and
	.I "mt8, ..., mt11"
	are rewound when closed; the others are not.
	When a file open for writing is closed, two end-of-files are written.
	If the tape is not to be rewound
	it is positioned with the head between the two
	tapemarks.
	.PP
	A standard tape consists of a
	series of 1024 byte records terminated by an
	end-of-file.
	To the extent possible, the system makes
	it possible, if inefficient, to treat
	the tape like any other file.
	Seeks have their usual meaning and it is possible
	to read or write a byte at a time.
	Writing in very small units is inadvisable,
	however, because it tends to create monstrous record
	gaps.
	.PP
	The
	.I mt
	files discussed above are useful
	when it is desired to access the tape in a way
	compatible with ordinary files.
	When foreign tapes are to be dealt with, and especially
	when long records are to be read or written, the
	`raw' interface is appropriate.
	The associated files are named
	.I "rmt0, ..., rmt15,"
	but the same minor-device considerations as for the regular files still apply.
	A number of other ioctl operations are available
	on raw magnetic tape.
	The following definitions are from <sys/mtio.h>:
	.PP
	.nf
	/*
	 * Structures and definitions for mag tape io control commands
	 */

	/* mag tape io control commands */
	#define MTIOCTOP	(('m'<<8)|1)	/* do a mag tape op */
	#define MTIOCGET	(('m'<<8)|2)	/* get mag tape status */

	/* 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 */

	/* 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 */
	/* the following two are not yet implemented */
		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
	 */
	#define MT_ISTS		01
	#define MT_ISHT		02
	#define MT_ISTM		03
	.fi
	.ft R
	.PP
	Each
	.I read
	or
	.I write
	call reads or writes the next record on the tape.
	In the write case the record has the same length as the
	buffer given.
	During a read, the record size is passed
	back as the number of bytes read, provided it is no greater
	than the buffer size;
	if the record is long, an error is indicated.
	In raw tape I/O seeks are ignored.
	A zero byte count is returned when a tape mark is read,
	but another read will fetch the first record of the
	new tape file.
	.SH FILES
	/dev/mt?,
	/dev/rmt?
	.SH "SEE ALSO"
	mt(1), tar(1), tp(1), ht(4), tm(4), ts(4)
	.SH BUGS