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1.1 root 1: .\" Copyright (c) 1986 The Regents of the University of California.
2: .\" All rights reserved.
3: .\"
4: .\" Redistribution and use in source and binary forms are permitted provided
5: .\" that: (1) source distributions retain this entire copyright notice and
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14: .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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18: .\" @(#)mtio.4 6.3 (Berkeley) 6/23/90
19: .\"
20: .TH MT 4 "June 23, 1990"
21: .UC 7
22: .SH NAME
23: mt \- UNIX magtape interface
24: .SH DESCRIPTION
25: The files
26: .I "cy0s, ..., cy15s"
27: refer to the UNIX magtape drives,
28: which may be on the VERSABUS using the CIPHER tapemaster formatter
29: .IR cy (4),
30: The following description applies to any of the transport/controller pairs.
31: The files
32: .I "cy0s, ..., cy15s"
33: are read/written in 25ips,
34: The density (1600 bpi or 3200 bpi) is selected by a switch on the drive.
35: The files
36: .I "cy0s, ..., cy7s"
37: are rewound when closed.
38: The non-rewinding files are named
39: .I ncy[0-7]
40: respectively.
41: .PP
42: For compatibility, the
43: .I [n]cy*s
44: files are linked to appropriate
45: .I [n]mt*
46: files.
47: .PP
48: When a file open for writing is closed, two file-marks are written.
49: If the tape is not to be rewound
50: it is positioned with the head between the two
51: file-marks.
52: .PP
53: A standard tape consists of a
54: series of 1024 byte records terminated by two
55: file-marks.
56: To the extent possible, the system makes
57: it possible, if inefficient, to treat
58: the tape like any other file.
59: Seeks have their usual meaning and it is possible
60: to read or write a byte at a time.
61: .PP
62: The
63: .I mt
64: files discussed above are useful
65: when it is desired to access the tape in a way
66: compatible with ordinary files.
67: When foreign tapes are to be dealt with, and especially
68: when long records are to be read or written, the
69: `raw' interface is appropriate.
70: Writing in very small units is inadvisable,
71: however, because it tends to create monstrous record
72: gaps. The associated files are named
73: .I "rcy0s, ..., rcy15s,"
74: but the same minor-device considerations as for the regular files still apply,
75: as well as the appropriate
76: .I r[n]mt*
77: links.
78: .PP
79: A number of other ioctl operations are available
80: on raw magnetic tape.
81: The following definitions are from <sys/mtio.h>:
82: .PP
83: .nf
84: /*
85: * Structures and definitions for mag tape io control commands
86: */
87:
88: /* mag tape io control commands */
89: #define MTIOCTOP (('m'<<8)|1) /* do a mag tape op */
90: #define MTIOCGET (('m'<<8)|2) /* get mag tape status */
91:
92: /* structure for MTIOCTOP - mag tape op command */
93: struct mtop {
94: short mt_op; /* operations defined below */
95: daddr_t mt_count; /* how many of them */
96: };
97:
98: /* operations */
99: #define MTWEOF 0 /* write an end-of-file record */
100: #define MTFSF 1 /* forward space file */
101: #define MTBSF 2 /* backward space file */
102: #define MTFSR 3 /* forward space record */
103: #define MTBSR 4 /* backward space record */
104: #define MTREW 5 /* rewind */
105: #define MTOFFL 6 /* rewind and put the drive offline */
106: #define MTNOP 7 /* no operation, sets status only */
107:
108: /* structure for MTIOCGET - mag tape get status command */
109:
110: struct mtget {
111: short mt_type; /* type of magtape device */
112: /* the following two registers are grossly device dependent */
113: short mt_dsreg; /* ``drive status'' register */
114: short mt_erreg; /* ``error'' register */
115: /* end device-dependent registers */
116: short mt_resid; /* residual count */
117: /* the following two are not yet implemented */
118: daddr_t mt_fileno; /* file number of current position */
119: daddr_t mt_blkno; /* block number of current position */
120: /* end not yet implemented */
121: };
122:
123: /*
124: * Constants for mt_type byte
125: */
126: #define MT_ISTS 01
127: #define MT_ISHT 02
128: #define MT_ISTM 03
129: .fi
130: .ft R
131: .PP
132: Each
133: .I read
134: or
135: .I write
136: call reads or writes the next record on the tape.
137: In the write case the record has the same length as the
138: buffer given.
139: During a read, the record size is passed
140: back as the number of bytes read, provided it is no greater
141: than the buffer size;
142: if the record is long, an error is indicated.
143: In raw tape I/O seeks are ignored.
144: A zero byte count is returned when a tape mark is read,
145: but another read will fetch the first record of the
146: new tape file.
147: .SH FILES
148: /dev/mt?,
149: /dev/rmt?
150: .SH "SEE ALSO"
151: mt(1), tar(1), cy(4)
152: .SH BUGS
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