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1.1 root 1: .TH MT 4
2: .CT 2 comm_mach
3: .SH NAME
4: mt \- magtape interface
5: .SH SYNOPSIS
6: .B #include <sys/types.h>
7: .br
8: .B #include <sys/mtio.h>
9: .SH DESCRIPTION
10: The
11: .I rmt
12: files refer to magnetic tape drives.
13: Filenames beginning with
14: .L rmt
15: are rewound when closed;
16: those beginning with
17: .L nrmt
18: are not.
19: When a file open for writing is closed, two file marks are written.
20: If the tape is not to be rewound,
21: it is positioned with the head between the two
22: file marks.
23: .PP
24: Conventionally
25: .B rmt0
26: is 800,
27: .B rmt1
28: is 1600,
29: and
30: .B rmt2
31: is 6250 bpi.
32: .PP
33: Each
34: .IR read (2)
35: or
36: .IR write
37: call reads or writes the next record on the tape.
38: .I Read
39: returns at most a single record;
40: the return value is the record size.
41: If the next record is larger than the read buffer,
42: an error is returned.
43: A file mark causes
44: .I read
45: to return 0;
46: the next
47: .I read
48: will return the next record.
49: Seeks are ignored.
50: .PP
51: An
52: .IR ioctl (2)
53: call performs special operations:
54: .TF MTIOCEEOT
55: .TP
56: .B MTIOCTOP
57: perform a suboperation encoded as below in the
58: .B mt_op
59: field of a structure whose address is passed
60: as the third argument of
61: .I ioctl.
62: .IP
63: .EX
64: .ta \w'struct 'u +\w'daddr_t 'u +\w'mt_count; 'u
65: struct mtop {
66: short mt_op; /* operation */
67: daddr_t mt_count; /* repeat count */
68: };
69: .EE
70: .PD0
71: .RS
72: .TF MTOFFL
73: .TP
74: .B MTWEOF
75: write an end-of-file record
76: .TP
77: .B MTFSF
78: forward space file
79: .TP
80: .B MTBSF
81: backward space file
82: .TP
83: .B MTFSR
84: forward space record
85: .TP
86: .B MTBSR
87: backward space record
88: .TP
89: .B MTREW
90: rewind
91: .TP
92: .B MTOFFL
93: rewind and put the drive offline
94: .RE
95: .PD
96: .PP
97: The files described above provide a `raw' interface.
98: There is also a `block' interface which attempts to treat the tape
99: like an ordinary file as much as possible.
100: Block tapes are accessed through files with names beginning with
101: .L mt
102: or
103: .LR nmt .
104: Such a tape contains a single file,
105: consisting of a series of 1024-byte records
106: followed by a file mark.
107: Seeks have their usual meaning,
108: and it is possible to read and write a byte at a time,
109: though writing in very small units may create enormous record gaps.
110: The file always ends at the most recently written byte.
111: .PP
112: Conventions for minor device numbers
113: vary among different hardware drivers:
114: .IP ""
115: For the TU78,
116: the drive unit number
117: is encoded in the two low-order bits.
118: Adding 4 prevents the tape from rewinding at close time.
119: Adding 8 selects 6250 bpi for writing;
120: the default is 1600.
121: The tape drive senses density automatically when reading.
122: .IP
123: The TE16 is like the TU78,
124: except that the default density is 800 bpi,
125: and adding 8 to the device number selects 1600.
126: .IP
127: For TMSCP tape drives such as the TU81 and the TK50,
128: the unit number is encoded in the three low-order bits.
129: Adding 128 prevents the tape from rewinding on close.
130: Density is selected by octal bits 070;
131: the eight possible values represent
132: eight different device-dependent tape formats.
133: For 9-track tape drives,
134: add 0 for 800 bpi,
135: 8 for 1600,
136: 16 for 6250.
137: For TK50 cartridge drives,
138: add 24 (old-style block format).
139: For TK70 drives,
140: add 8.
141: The tape drives sense density automatically on reading,
142: but if a drive
143: doesn't support a particular density,
144: the hardware may complain when the device is opened.
145: .SH FILES
146: .F /dev/mt?
147: .br
148: .F /dev/rmt?
149: .br
150: .F /dev/nmt?
151: .br
152: .F /dev/nrmt?
153: .SH "SEE ALSO"
154: .IR tape (1)
155: .SH BUGS
156: If any non-data error is encountered,
157: the tape drivers generally refuse to do anything
158: more until closed.
159: .br
160: The naming convention behaves poorly with multiple tape drives.
161: .br
162: Block tape has probably outlived its usefulness.
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