.\" Copyright (c) 1986 Regents of the University of California.
.\" All rights reserved. The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\" @(#)mtio.4 6.1 (Berkeley) 11/24/86
.TH MT 4 "November 24, 1986"
mt \- UNIX magtape interface
refer to the UNIX magtape drives,
which may be on the VERSABUS using the CIPHER tapemaster formatter
The following description applies to any of the transport/controller pairs.
are read/written in 25ips,
The density (1600 bpi or 3200 bpi) is selected by a switch on the drive.
The non-rewinding files are named
files are linked to appropriate
When a file open for writing is closed, two file-marks are written.
If the tape is not to be rewound
it is positioned with the head between the two
A standard tape consists of a
series of 1024 byte records terminated by two
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.
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.
Writing in very small units is inadvisable,
however, because it tends to create monstrous record
gaps. The associated files are named
but the same minor-device considerations as for the regular files still apply,
as well as the appropriate
A number of other ioctl operations are available
The following definitions are from <sys/mtio.h>:
* 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 */
short mt_op; /* operations defined below */
daddr_t mt_count; /* how many of them */
#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 */
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
call reads or writes the next record on the tape.
In the write case the record has the same length as the
During a read, the record size is passed
back as the number of bytes read, provided it is no greater
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
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