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17 .Dd February 17, 2020
18 .Dt MTIO 7I
19 .Os
20 .Sh NAME
21 .Nm mtio
22 .Nd general magnetic tape interface
23 .Sh SYNOPSIS
24 .In sys/types.h
25 .In sys/ioctl.h
26 .In sys/mtio.h
27 .Sh DESCRIPTION
28 1/2", 1/4", 4mm, and 8mm magnetic tape drives all share the same general
29 character device interface.
30 .Pp
31 There are two types of tape records: data records and end-of-file (EOF)
32 records.
33 .Sy EOF
34 records are also known as tape marks and file marks.
35 A record is separated by interrecord (or tape) gaps on a tape.
36 .Pp
37 End-of-recorded-media (EOM) is indicated by two
38 .Sy EOF
39 marks on 1/2\(dq tape; by one
40 .Sy EOF
41 mark on 1/4\(dq, 4mm, and 8mm cartridge tapes.
42 .Ss "1/2\(dq Reel Tape"
43 Data bytes are recorded in parallel onto the 9-track tape.
44 Since it is a
45 variable-length tape device, the number of bytes in a physical record may vary.
46 .Pp
47 The recording formats available (check specific tape drive) are 800
48 .Sy BPI ,
49 1600
50 .Sy BPI ,
51 6250
52 .Sy BPI ,
53 and data compression.
54 Actual storage capacity is a function of the recording format and the length of the tape reel.
55 For example, using a 2400 foot tape, 20 Mbyte can be stored using 800
56 .Sy BPI ,
57 40 Mbyte using 1600
58 .Sy BPI ,
59 140 Mbyte using 6250
60 .Sy BPI ,
61 or up to 700 Mbyte using data compression.
62 .Ss "1/4\(dq Cartridge Tape"
63 Data is recorded serially onto 1/4\(dq cartridge tape.
64 The number of bytes per
65 record is determined by the physical record size of the device.
66 The I/O request
67 size must be a multiple of the physical record size of the device.
68 For
69 .Sy QIC-11 ,
70 .Sy QIC-24 ,
71 and
72 .Sy QIC-150
73 tape drives, the block size is 512 bytes.
74 .Pp
75 The records are recorded on tracks in a serpentine motion.
76 As one track is
77 completed, the drive switches to the next and begins writing in the opposite
78 direction, eliminating the wasted motion of rewinding.
79 Each file, including the last, ends with one file mark.
80 .Pp
81 Storage capacity is based on the number of tracks the drive is capable of
82 recording.
83 For example, 4-track drives can only record 20 Mbyte of data on a
84 450 foot tape; 9-track drives can record up to 45 Mbyte of data on a tape of
85 the same length.
86 .Sy QIC-11
87 is the only tape format available for 4-track
88 tape drives.
89 In contrast, 9-track tape drives can use either
90 .Sy QIC-24
91 or
92 .Sy QIC-11 .
93 Storage capacity is not appreciably affected by using either format.
94 .Sy QIC-24
95 is preferable to
96 .Sy QIC-11
97 because it records a
98 reference signal to mark the position of the first track on the tape, and each
99 block has a unique block number.
100 .Pp
101 The
102 .Sy QIC-150
103 tape drives require
104 .Sy DC-6150
105 (or equivalent) tape cartridges for writing.
106 However, they can read other tape cartridges in
107 .Sy QIC-11 ,
108 .Sy QIC-24 ,
109 or
110 .Sy QIC-120
111 tape formats.
112 .Ss "8mm Cartridge Tape"
113 Data is recorded serially onto 8mm helical scan cartridge tape.
114 Since it is a
115 variable-length tape device, the number of bytes in a physical record may
116 vary.
117 The recording formats available (check specific tape drive) are standard
118 2Gbyte, 5Gbyte, and compressed format.
119 .Ss "4mm DAT Tape"
120 Data is recorded either in Digital Data Storage (DDS) tape format or in Digital
121 Data Storage, Data Compressed (DDS-DC) tape format.
122 Since it is a
123 variable-length tape device, the number of bytes in a physical record may vary.
124 The recording formats available are standard 2Gbyte and compressed format.
125 .Ss "Persistent Error Handling"
126 Persistent error handling is a modification of the current error handling
127 behaviors, BSD and SVR4.
128 With persistent error handling enabled, all tape
129 operations after an error or exception will return immediately with an error.
130 Persistent error handling can be most useful with asynchronous tape operations
131 that use the
132 .Xr aioread 3C
133 and
134 .Xr aiowrite 3C
135 functions.
136 .Pp
137 To enable persistent error handling, the ioctl
138 .Dv MTIOCPERSISTENT
139 must be issued.
140 If this ioctl succeeds, then persistent error handling is enabled and
141 changes the current error behavior.
142 This ioctl will fail if the device driver
143 does not support persistent error handling.
144 .Pp
145 With persistent error handling enabled, all tape operations after an exception
146 or error will return with the same error as the first command that failed; the
147 operations will not be executed.
148 An exception is some event that might stop
149 normal tape operations, such as an End Of File (EOF) mark or an End Of Tape
150 (EOT) mark.
151 An example of an error is a media error.
152 The
153 .Dv MTIOCLRERR
154 ioctl must be issued to allow normal tape operations to continue and to clear
155 the error.
156 .Pp
157 Disabling persistent error handling returns the error behavior to normal SVR4
158 error handling, and will not occur until all outstanding operations are
159 completed.
160 Applications should wait for all outstanding operations to complete
161 before disabling persistent error handling.
162 Closing the device will also
163 disable persistent error handling and clear any errors or exceptions.
164 .Pp
165 The
166 .Sx Read Operation
167 and
168 .Sx Write Operation
169 subsections contain more pertinent information regarding persistent error handling.
170 .Ss "Read Operation"
171 The
172 .Xr read 2
173 function reads the next record on the tape.
174 The record size is passed back as the number of bytes read, provided it is not
175 greater than the number requested.
176 When a tape mark or end of data is read, a zero byte count is
177 returned; all successive reads after the zero read will return an error and
178 .Va errno
179 will be set to
180 .Er EIO .
181 To move to the next file, an
182 .Dv MTFSF
183 ioctl can be issued before or after the read causing the error.
184 This error
185 handling behavior is different from the older
186 .Sy BSD
187 behavior, where another read will fetch the first record of the next tape file.
188 If the
189 .Sy BSD
190 behavior is required, device names containing the letter
191 .Ql b
192 (for
193 .Sy BSD
194 behavior) in the final component should be used.
195 If persistent error handling
196 was enabled with either the BSD or SVR4 tape device behavior, all operations
197 after this read error will return
198 .Er EIO
199 errors until the
200 .Dv MTIOCLRERR
201 ioctl is issued.
202 An
203 .Dv MTFSF
204 ioctl can then be issued.
205 .Pp
206 Two successful successive reads that both return zero byte counts indicate
207 .Sy EOM
208 on the tape.
209 No further reading should be performed past the
210 .Sy EOM .
211 .Pp
212 Fixed-length I/O tape devices require the number of bytes read to be a multiple
213 of the physical record size.
214 For example, 1/4\(dq cartridge tape devices only read
215 multiples of 512 bytes.
216 If the blocking factor is greater than 64,512 bytes
217 (minphys limit), fixed-length I/O tape devices read multiple records.
218 .Pp
219 Most tape devices which support variable-length I/O operations may read a range
220 of 1 to 65,535 bytes.
221 If the record size exceeds 65,535 bytes, the driver reads
222 multiple records to satisfy the request.
223 These multiple records are limited to
224 65,534 bytes.
225 Newer variable-length tape drivers may relax the above limitation
226 and allow applications to read record sizes larger than 65,534.
227 Refer to the
228 specific tape driver man page for details.
229 .Pp
230 Reading past logical
231 .Sy EOT
232 is transparent to the user.
233 A read operation
234 should never hit physical EOT.
235 .Pp
236 Read requests that are lesser than a physical tape record are not allowed.
237 Appropriate error is returned.
238 .Ss "Write Operation"
239 The
240 .Xr write 2
241 function writes the next record on the tape.
242 The record has
243 the same length as the given buffer.
244 .Pp
245 Writing is allowed on 1/4" tape at either the beginning of tape or after the
246 last written file on the tape.
247 With the Exabyte 8200, data may be appended only
248 at the beginning of tape, before a filemark, or after the last written file on
249 the tape.
250 .Pp
251 Writing is not so restricted on 1/2\(dq, 4mm, and the other 8mm cartridge tape
252 drives.
253 Care should be used when appending files onto 1/2\(dq reel tape devices,
254 since an extra file mark is appended after the last file to mark the
255 .Sy EOM .
256 This extra file mark must be overwritten to prevent the creation of a null file.
257 To facilitate write append operations, a space to the
258 .Sy EOM
259 ioctl is provided.
260 Care should be taken when overwriting records; the erase head is just
261 forward of the write head and any following records will also be erased.
262 .Pp
263 Fixed-length I/O tape devices require the number of bytes written to be a
264 multiple of the physical record size.
265 For example, 1/4\(dq cartridge tape devices
266 only write multiples of 512 bytes.
267 .Pp
268 Fixed-length I/O tape devices write multiple records if the blocking factor is
269 greater than 64,512 bytes (minphys limit).
270 These multiple writes are limited to
271 64,512 bytes.
272 For example, if a write request is issued for 65,536 bytes using
273 a 1/4\(dq cartridge tape, two writes are issued; the first for 64,512 bytes and
274 the second for 1024 bytes.
275 .Pp
276 Most tape devices which support variable-length I/O operations may write a
277 range of 1 to 65,535 bytes.
278 If the record size exceeds 65,535 bytes, the driver
279 writes multiple records to satisfy the request.
280 These multiple records are
281 limited to 65,534 bytes.
282 As an example, if a write request for 65,540 bytes is
283 issued, two records are written; one for 65,534 bytes followed by another
284 record for 6 bytes.
285 Newer variable-length tape drivers may relax the above
286 limitation and allow applications to write record sizes larger than 65,534.
287 effer to the specific tape driver man page for details.
288 .Pp
289 When logical
290 .Sy EOT
291 is encountered during a write, that write operation
292 completes and the number of bytes successfully transferred is returned (note
293 that a 'short write' may have occurred and not all the requested bytes would
294 have been transferred.
295 The actual amount of data written will depend on the
296 type of device being used).
297 The next write will return a zero byte count.
298 A third write will successfully transfer some bytes (as indicated by the
299 returned byte count, which again could be a short write); the fourth will
300 transfer zero bytes, and so on, until the physical
301 .Sy EOT
302 is reached and all writes will
303 fail with
304 .Er EIO .
305 .Pp
306 When logical
307 .Sy EOT
308 is encountered with persistent error handling enabled,
309 the current write may complete or be a short write.
310 The next write will return a zero byte count.
311 At this point an application should act appropriately for
312 end of tape cleanup or issue yet another write, which will return the error
313 .Er ENOSPC .
314 After clearing the exception with
315 .Dv MTIOCLRERR ,
316 the next write will succeed (possibly short), followed by another zero byte
317 write count, and then another
318 .Er ENOSPC
319 error.
320 .Pp
321 Allowing writes after
322 .Sy EOT
323 has been encountered enables the flushing of buffers.
324 However, it is strongly recommended to terminate the writing and close
325 the file as soon as possible.
326 .Pp
327 Seeks are ignored in tape I/O.
328 .Ss "Close Operation"
329 Magnetic tapes are rewound when closed, except when the "no-rewind" devices
330 have been specified.
331 The names of no-rewind device files use the letter
332 .Ql n
333 as the end of the final component.
334 The no-rewind version of
335 .Pa /dev/rmt/0l
336 is
337 .Pa /dev/rmt/0ln .
338 In case of error for a no-rewind device, the next open rewinds the device.
339 .Pp
340 If the driver was opened for reading and a no-rewind device has been specified,
341 the close advances the tape past the next filemark (unless the current file
342 position is at
343 .Sy EOM ) ,
344 leaving the tape correctly positioned to read the first record of the next file.
345 However, if the tape is at the first record of a
346 file it doesn't advance again to the first record of the next file.
347 These semantics are different from the older
348 .Sy BSD
349 behavior.
350 If
351 .Sy BSD
352 behavior is required where no implicit space operation is executed on close,
353 the non-rewind device name containing the letter
354 .Ql b
355 (for
356 .Sy BSD
357 behavior) in the final component should be specified.
358 .Pp
359 If data was written, a file mark is automatically written by the driver upon
360 close.
361 If the rewinding device was specified, the tape will be rewound after
362 the file mark is written.
363 If the user wrote a file mark prior to closing, then
364 no file mark is written upon close.
365 If a file positioning ioctl, like rewind,
366 is issued after writing, a file mark is written before repositioning the tape.
367 .Pp
368 All buffers are flushed on closing a tape device.
369 Hence, it is strongly recommended that the application wait for all buffers to
370 be flushed before closing the device.
371 This can be done by writing a filemark via
372 .Dv MTWEOF ,
373 even with a zero count.
374 .Pp
375 Note that for 1/2\(dq reel tape devices, two file marks are written to mark the
376 .Sy EOM
377 before rewinding or performing a file positioning ioctl.
378 If the user
379 wrote a file mark before closing a 1/2\(dq reel tape device, the driver will
380 always write a file mark before closing to insure that the end of recorded
381 media is marked properly.
382 If the non-rewinding device was specified, two file
383 marks are written and the tape is left positioned between the two so that the
384 second one is overwritten on a subsequent
385 .Xr open 2
386 and
387 .Xr write 2 .
388 .Pp
389 If no data was written and the driver was opened for
390 .Sy WRITE-ONLY
391 access, one or two file marks are written, thus creating a null file.
392 .Pp
393 After closing the device, persistent error handling will be disabled and any
394 error or exception will be cleared.
395 .Sh IOCTLS
396 Not all devices support all
397 .Sy ioctls .
398 The driver returns an
399 .Er ENOTTY
400 error on unsupported ioctls.
401 .Pp
402 The following structure definitions for magnetic tape
403 .Xr ioctl 2
404 commands are from
405 .In sys/mtio.h .
406 .Pp
407 The minor device byte structure is:
408 .Bd -literal
409 15 7 6 5 4 3 2 1 0
410 ________________________________________________________________________
411 Unit # BSD Reserved Density Density No rewind Unit #
412 Bits 7-15 behavior Select Select on Close Bits 0-1
413 .Ed
414 .Bd -literal
415 /*
416 * Layout of minor device byte:
417 */
418 #define MTUNIT(dev) (((minor(dev) & 0xff80) >> 5) + (minor(dev) & 0x3))
419 #define MT_NOREWIND (1 <<2)
420 #define MT_DENSITY_MASK (3 <<3)
421 #define MT_DENSITY1 (0 <<3) /* Lowest density/format */
422 #define MT_DENSITY2 (1 <<3)
423 #define MT_DENSITY3 (2 <<3)
424 #define MT_DENSITY4 (3 <<3) /* Highest density/format */
425 #define MTMINOR(unit) (((unit & 0x7fc) << 5) + (unit & 0x3))
426 #define MT_BSD (1 <<6) /* BSD behavior on close */
427
428 /* Structure for MTIOCTOP - magnetic tape operation command */
429
430 struct mtop {
431 short mt_op; /* operation */
432 daddr_t mt_count; /* number of operations */
433 };
434
435 /* Structure for MTIOCLTOP - magnetic tape operation command */
436 Works exactly like MTIOCTOP except passes 64 bit mt_count values.
437 struct mtlop {
438 short mt_op;
439 short pad[3];
440 int64_t mt_count;
441 };
442 .Ed
443 .Pp
444 The following operations of
445 .Dv MTIOCTOP
446 and
447 .Dv MTIOCLTOP
448 ioctls are supported:
449 .Pp
450 .Bl -tag -width MTIOCGETERROR -compact -offset 2n
451 .It Dv MTWEOF
452 Write an end-of-file record
453 .It Dv MTFSF
454 Forward space over file mark
455 .It Dv MTBSF
456 Backward space over file mark (1/2", 8mm only)
457 .It Dv MTFSR
458 Forward space to inter-record gap
459 .It Dv MTBSR
460 Backward space to inter-record gap
461 .It Dv MTREW
462 Rewind
463 .It Dv MTOFFL
464 Rewind and take the drive off-line
465 .It Dv MTNOP
466 No operation, sets status only
467 .It Dv MTRETEN
468 Retension the tape (cartridge tape only)
469 .It Dv MTERASE
470 Erase the entire tape and rewind
471 .It Dv MTEOM
472 Position to EOM
473 .It Dv MTNBSF
474 Backward space file to beginning of file
475 .It Dv MTSRSZ
476 Set record size
477 .It Dv MTGRSZ
478 Get record size
479 .It Dv MTTELL
480 Get current position
481 .It Dv MTSEEK
482 Go to requested position
483 .It Dv MTFSSF
484 Forward to requested number of sequential file marks
485 .It Dv MTBSSF
486 Backward to requested number of sequential file marks
487 .It Dv MTLOCK
488 Prevent media removal
489 .It Dv MTUNLOCK
490 Allow media removal
491 .It Dv MTLOAD
492 Load the next tape cartridge into the tape drive
493 .It Dv MTIOCGETERROR
494 Retrieve error records from the st driver
495 .El
496 .Bd -literal -offset 2n
497 /* structure for MTIOCGET - magnetic tape get status command */
498
499 struct mtget {
500 short mt_type; /* type of magtape device */
501
502 /* the following two registers are device dependent */
503 short mt_dsreg; /* "drive status" register */
504 short mt_erreg; /* "error" register */
505
506 /* optional error info. */
507 daddr_t mt_resid; /* residual count */
508 daddr_t mt_fileno; /* file number of current position */
509 daddr_t mt_blkno; /* block number of current position */
510 ushort_t mt_flags;
511 short mt_bf; /* optimum blocking factor */
512 };
513
514 /* structure for MTIOCGETDRIVETYPE - get tape config data command */
515 struct mtdrivetype_request {
516 int size;
517 struct mtdrivetype *mtdtp;
518 };
519 struct mtdrivetype {
520 char name[64]; /* Name, for debug */
521 char vid[25]; /* Vendor id and product id */
522 char type; /* Drive type for driver */
523 int bsize; /* Block size */
524 int options; /* Drive options */
525 int max_rretries; /* Max read retries */
526 int max_wretries; /* Max write retries */
527 uchar_t densities[MT_NDENSITIES]; /* density codes,low->hi */
528 uchar_t default_density; /* Default density chosen */
529 uchar_t speeds[MT_NSPEEDS]; /* speed codes, low->hi */
530 ushort_t non_motion_timeout; /* Seconds for non-motion */
531 ushort_t io_timeout; /* Seconds for data to from tape */
532 ushort_t rewind_timeout; /* Seconds to rewind */
533 ushort_t space_timeout; /* Seconds to space anywhere */
534 ushort_t load_timeout; /* Seconds to load tape and ready */
535 ushort_t unload_timeout; /* Seconds to unload */
536 ushort_t erase_timeout; /* Seconds to do long erase */
537 };
538 .Ed
539 .Bd -literal -offset 2n
540 /* structure for MTIOCGETPOS and MTIOCRESTPOS - get/set tape position */
541 /*
542 * eof/eot/eom codes.
543 */
544 typedef enum {
545 ST_NO_EOF,
546 ST_EOF_PENDING, /* filemrk pending */
547 ST_EOF, /* at filemark */
548 ST_EOT_PENDING, /* logical eot pend. */
549 ST_EOT, /* at logical eot */
550 ST_EOM, /* at physical eot */
551 ST_WRITE_AFTER_EOM /* flag allowing writes after EOM */
552 } pstatus;
553
554 typedef enum { invalid, legacy, logical } posmode;
555
556 typedef struct tapepos {
557 uint64_t lgclblkno; /* Blks from start of partition */
558 int32_t fileno; /* Num. of current file */
559 int32_t blkno; /* Blk number in current file */
560 int32_t partition; /* Current partition */
561 pstatus eof; /* eof states */
562 posmode pmode; /* which pos. data is valid */
563 char pad[4];
564 } tapepos_t;
565 .Ed
566 .Pp
567 .Bd -ragged -compact
568 If the
569 .Fa pmode
570 is legacy,
571 .Fa fileno
572 and
573 .Fa blkno
574 fields are valid.
575 .Pp
576 If the
577 .Fa pmode
578 is logical,
579 .Fa lgclblkno
580 field is valid.
581 .Ed
582 .Pp
583 The
584 .Dv MTWEOF
585 ioctl is used for writing file marks to tape.
586 Not only does
587 this signify the end of a file, but also usually has the side effect of
588 flushing all buffers in the tape drive to the tape medium.
589 A zero count
590 .Dv MTWEOF
591 will just flush all the buffers and will not write any file marks.
592 Because a successful completion of this tape operation will guarantee that all
593 tape data has been written to the tape medium, it is recommended that this tape
594 operation be issued before closing a tape device.
595 .Pp
596 When spacing forward over a record (either data or
597 .Sy EOF ) ,
598 the tape head is
599 positioned in the tape gap between the record just skipped and the next record.
600 When spacing forward over file marks (EOF records), the tape head is positioned
601 in the tape gap between the next
602 .Sy EOF
603 record and the record that follows it.
604 .Pp
605 When spacing backward over a record (either data or
606 .Sy EOF ) ,
607 the tape head is positioned in the tape gap immediately preceding the tape
608 record where the tape head is currently positioned.
609 When spacing backward over file marks (EOF records), the tape head is
610 positioned in the tape gap preceding the
611 .Sy EOF .
612 Thus the next read would fetch the
613 .Sy EOF .
614 .Pp
615 Record skipping does not go past a file mark; file skipping does not go past
616 the
617 .Sy EOM .
618 After an
619 .Dv MTFSR
620 <huge number> command, the driver leaves
621 the tape logically positioned
622 .Em before
623 the
624 .Sy EOF .
625 A related feature is that
626 .Sy EOF Ns s
627 remain pending until the tape is closed.
628 For example, a program
629 which first reads all the records of a file up to and including the \fBEOF\fR
630 and then performs an
631 .Dv MTFSF
632 command will leave the tape positioned just
633 after that same
634 .Sy EOF ,
635 rather than skipping the next file.
636 .Pp
637 The
638 .Dv MTNBSF
639 and
640 .Dv MTFSF
641 operations are inverses.
642 Thus, an
643 .Dq Dv MTFSF \(mi1
644 is equivalent to an
645 .Dq Dv MTNBSF 1 .
646 An
647 .Dq Dv MTNBSF 0
648 is the same as
649 .Dq Dv MTFSF 0 ;
650 both position the tape device at the beginning of the current file.
651 .Pp
652 .Dv MTBSF
653 moves the tape backwards by file marks.
654 The tape position will end
655 on the beginning of the tape side of the desired file mark.
656 An
657 .Dq Dv MTBSF 0
658 will position the tape at the end of the current file, before the filemark.
659 .Pp
660 .Dv MTBSR
661 and
662 .Dv MTFSR
663 operations perform much like space file operations,
664 except that they move by records instead of files.
665 Variable-length I/O devices
666 (1/2\(dq reel, for example) space actual records; fixed-length I/O devices space
667 physical records (blocks).
668 1/4\(dq cartridge tape, for example, spaces 512 byte
669 physical records.
670 The status ioctl residual count contains the number of files
671 or records not skipped.
672 .Pp
673 .Dv MTFSSF
674 and
675 .Dv MTBSSF
676 space forward or backward, respectively, to the next
677 occurrence of the requested number of file marks, one following another.
678 If there are more sequential file marks on tape than were requested, it spaces
679 over the requested number and positions after the requested file mark.
680 Note that not all drives support this command and if a request is sent to a
681 drive that does not,
682 .Er ENOTTY
683 is returned.
684 .Pp
685 .Dv MTOFFL
686 rewinds and, if appropriate, takes the device off-line by unloading the tape.
687 It is recommended that the device be closed after offlining
688 and then re-opened after a tape has been inserted to facilitate portability to
689 other platforms and other operating systems.
690 Attempting to re-open the device
691 with no tape will result in an error unless the
692 .Dv O_NDELAY
693 flag is used.
694 .Po
695 See
696 .Xr open 2 .
697 .Pc
698 .Pp
699 The
700 .Dv MTRETEN
701 retension ioctl applies only to 1/4\(dq cartridge tape devices.
702 It is used to restore tape tension, improving the tape's soft error rate after
703 extensive start-stop operations or long-term storage.
704 .Pp
705 .Dv MTERASE
706 rewinds the tape, erases it completely, and returns to the
707 beginning of tape.
708 Erasing may take a long time depending on the device and/or
709 tapes.
710 For time details, refer to the drive specific manual.
711 .Pp
712 .Dv MTEOM
713 positions the tape at a location just after the last file written
714 on the tape.
715 For 1/4\(dq cartridge and 8mm tape, this is after the last file mark
716 on the tape.
717 For 1/2\(dq reel tape, this is just after the first file mark but
718 before the second (and last) file mark on the tape.
719 Additional files can then
720 be appended onto the tape from that point.
721 .Pp
722 Note the difference between
723 .Dv MTBSF
724 (backspace over file mark) and
725 .Dv MTNBSF
726 (backspace file to beginning of file).
727 The former moves the tape
728 backward until it crosses an
729 .Sy EOF
730 mark, leaving the tape positioned
731 .Em before
732 the file mark.
733 The latter leaves the tape positioned
734 .Em after
735 the file mark.
736 Hence,
737 .Dq Dv MTNBSF n
738 is equivalent to
739 .Dq Dv MTBSF (n+1)
740 followed by
741 .Dq Dv MTFSF 1 .
742 The 1/4\(dq cartridge tape devices do not support
743 .Dv MTBSF .
744 .Pp
745 .Dv MTSRSZ
746 and
747 .Dv MTGRSZ
748 are used to set and get fixed record lengths.
749 The
750 .Dv MTSRSZ
751 ioctl allows variable length and fixed length tape drives that
752 support multiple record sizes to set the record length.
753 The
754 .Fa mt_count
755 field of the
756 .Vt mtop
757 struct is used to pass the record size to/from the
758 .Xr st 7D
759 driver.
760 A value of
761 .Ql 0
762 indicates variable record size.
763 The
764 .Dv MTSRSZ
765 ioctl makes a variable-length tape device behave like a
766 fixed-length tape device.
767 Refer to the specific tape driver man page for
768 details.
769 .Pp
770 .Dv MTLOAD
771 loads the next tape cartridge into the tape drive.
772 This is generally only used with stacker and tower type tape drives which handle
773 multiple tapes per tape drive.
774 A tape device without a tape inserted can be
775 opened with the
776 .Dv O_NDELAY
777 flag, in order to execute this operation.
778 .Pp
779 .Dv MTIOCGETERROR
780 allows user-level applications to retrieve error records
781 from the
782 .Xr st 7D
783 driver.
784 An error record consists of the SCSI command cdb
785 which causes the error and a
786 .Xr scsi_arq_status 9S
787 structure if available.
788 The user-level application is responsible for allocating and releasing the
789 memory for
790 .Fa mtee_cdb_buf
791 and
792 .Fa scsi_arq_status of each
793 .Vt mterror_entry .
794 Before issuing the ioctl, the
795 .Fa mtee_arq_status_len
796 value should be at least equal to
797 .Ql sizeof (struct scsi_arq_status) .
798 If more sense data than the size of
799 .Xr scsi_arq_status 9S
800 is desired, the
801 .Fa mtee_arq_status_len
802 may be larger than
803 .Ql sizeof (struct scsi_arq_status)
804 by the amount of additional extended sense data desired.
805 The
806 .Fa es_add_len
807 field of
808 .Xr scsi_extended_sense 9S
809 can be used to determine the amount of valid sense data returned by the device.
810 .Pp
811 The
812 .Dv MTIOCGET
813 get status
814 .Xr ioctl 2
815 call returns the drive ID
816 .Pq Fa mt_type ,
817 sense key error
818 .Pq Fa mt_erreg ,
819 file number
820 .Pq Fa mt_fileno ,
821 optimum blocking factor
822 .Pq Fa mt_bf
823 and record number
824 .Pq Fa mt_blkno
825 of the last error.
826 The residual count
827 .Pq Fa mt_resid
828 is set to the number of bytes not transferred or files/records not spaced.
829 The flags word
830 .Pq Fa mt_flags
831 contains information indicating if the device is SCSI, if the device is a reel
832 device and whether the device supports absolute file positioning.
833 The
834 .Fa mt_flags
835 also indicates if the device is requesting cleaning media be used, whether the
836 device is capable of reporting the requirement of cleaning media and if the
837 currently loaded media is WORM (Write Once Read Many) media.
838 .Pp
839 Note \(em When tape alert cleaning is managed by the st driver, the tape
840 target driver may continue to return a
841 .Dq drive needs cleaning
842 status unless an
843 .Dv MTIOCGE
844 .Xr ioct 2
845 call is made while the cleaning media is in the drive.
846 .Pp
847 The
848 .Dv MTIOCGETDRIVETYPE
849 get drivetype ioctl call returns the name of the
850 tape drive as defined in
851 .Pa st.conf
852 .Pq Fa name ,
853 Vendor
854 .Sy ID
855 and model
856 .Pq Fa product ,
857 .Sy ID
858 .Pq Fa vid ,
859 type of tape device
860 .Pq Fa type ,
861 block size
862 .Pq Fa size ,
863 drive options
864 .Pq Fa options ,
865 maximum read retry count
866 .Pq Fa max_rretries ,
867 maximum write retry count
868 .Pq Fa max_wretries ,
869 densities supported by the drive
870 .Pq Fa densities ,
871 and default density of the tape drive
872 .Pq Fa default_density .
873 .Pp
874 The
875 .Dv MTIOCGETPOS
876 ioctl returns the current tape position of the drive.
877 It is returned in struct tapepos as defined in
878 .Pa /usr/include/sys/scsi/targets/stdef.h .
879 .Pp
880 The
881 .Dv MTIOCRESTPOS
882 ioctl restores a saved position from the
883 .Dv MTIOCGETPOS .
884 .Ss "Persistent Error Handling IOCTLs and Asynchronous Tape Operations"
885 .Bl -tag -width MTIOCPERSISTENTSTATUS -compact
886 .It Dv MTIOCPERSISTENT
887 enables/disables persistent error handling
888 .It Dv MTIOCPERSISTENTSTATUS
889 queries for persistent error handling
890 .It Dv MTIOCLRERR
891 clears persistent error handling
892 .It Dv MTIOCGUARANTEEDORDER
893 checks whether driver guarantees order of I/O's
894 .El
895 .Pp
896 The
897 .Dv MTIOCPERSISTENT
898 ioctl enables or disables persistent error handling.
899 It takes as an argument a pointer to an integer that turns it either on or off.
900 If the ioctl succeeds, the desired operation was successful.
901 It will wait for
902 all outstanding I/O's to complete before changing the persistent error handling
903 status.
904 For example,
905 .Bd -literal -offset 2n
906 int on = 1;
907 ioctl(fd, MTIOCPERSISTENT, &on);
908 int off = 0;
909 ioctl(fd, MTIOCPERSISTENT, &off);
910 .Ed
911 .Pp
912 The
913 .Dv MTIOCPERSISTENTSTATUS
914 ioctl enables or disables persistent error
915 handling.
916 It takes as an argument a pointer to an integer inserted by the
917 driver.
918 The integer can be either 1 if persistent error handling is
919 .Sq on ,
920 or 0 if persistent error handling is
921 .Sq off .
922 It will not wait for outstanding I/O's.
923 For example,
924 .Bd -literal -offset 2n
925 int query;
926 ioctl(fd, MTIOCPERSISTENTSTATUS, &query);
927 .Ed
928 .Pp
929 The
930 .Dv MTIOCLRERR
931 ioctl clears persistent error handling and allows tape
932 operations to continual normally.
933 This ioctl requires no argument and will
934 always succeed, even if persistent error handling has not been enabled.
935 It will wait for any outstanding I/O's before it clears the error.
936 .Pp
937 The
938 .Dv MTIOCGUARANTEEDORDER
939 ioctl is used to determine whether the driver
940 guarantees the order of I/O's.
941 It takes no argument.
942 If the ioctl succeeds, the driver will support guaranteed order.
943 If the driver does not support guaranteed order, then it should not be used
944 for asynchronous I/O with
945 .Xr libaio 3lib .
946 It will wait for any outstanding I/O's before it returns.
947 For example,
948 .Bd -literal -offset 2n
949 ioctl(fd, MTIOCGUARANTEEDORDER)
950 .Ed
951 .Pp
952 See the
953 .Sx Persistent Error Handling
954 subsection above for more information on persistent error handling.
955 .Ss "Asynchronous and State Change IOCTLS"
956 .Bl -tag -width 1n
957 .It Dv MTIOCSTATE
958 This ioctl blocks until the state of the drive, inserted or ejected, is
959 changed.
960 The argument is a pointer to a
961 .Vt enum mtio_state ,
962 whose possible enumerations are listed below.
963 The initial value should be either the last reported state of the drive, or
964 .Dv MTIO_NONE .
965 Upon return, the
966 enum pointed to by the argument is updated with the current state of the drive.
967 .Bd -literal -offset 2n
968 enum mtio_state {
969 MTIO_NONE /* Return tape's current state */
970 MTIO_EJECTED /* Tape state is "ejected" */
971 MTIO_INSERTED /* Tape state is "inserted" */
972 };
973 .Ed
974 .El
975 .Pp
976 When using asynchronous operations, most ioctls will wait for all outstanding
977 commands to complete before they are executed.
978 .Ss "IOCTLS for Multi-initiator Configurations"
979 .Bl -tag -width MTIOCFORCERESERVE -compact
980 .It Dv MTIOCRESERVE
981 reserve the tape drive
982 .It Dv MTIOCRELEASE
983 revert back to the default behavior of reserve on open/release on close
984 .It Dv MTIOCFORCERESERVE
985 reserve the tape unit by breaking reservation held by another host
986 .El
987 .Pp
988 The
989 .Dv MTIOCRESERVE
990 ioctl reserves the tape drive such that it does not
991 release the tape drive at close.
992 This changes the default behavior of releasing the device upon close.
993 Reserving the tape drive that is already reserved has no effect.
994 For example,
995 .Bd -literal -offset 2n
996 ioctl(fd, MTIOCRESERVE);
997 .Ed
998 .Pp
999 The
1000 .Dv MTIOCRELEASE
1001 ioctl reverts back to the default behavior of reserve on
1002 open/release on close operation, and a release will occur during the next
1003 close.
1004 Releasing the tape drive that is already released has no effect.
1005 For example,
1006 .Bd -literal -offset 2n
1007 ioctl(fd, MTIOCRELEASE);
1008 .Ed
1009 .Pp
1010 The
1011 .Dv MTIOCFORCERESERVE
1012 ioctl breaks a reservation held by another host, interrupting any I/O in
1013 progress by that other host, and then reserves the tape unit.
1014 This ioctl can be executed only with super-user privileges.
1015 It is recommended to open the tape device in
1016 .Dv O_NDELAY
1017 mode when this ioctl needs to be executed, otherwise the open will fail if
1018 another host indeed has it reserved.
1019 For example,
1020 .Bd -literal -offset 2n
1021 ioctl(fd, MTIOCFORCERESERVE);
1022 .Ed
1023 .Ss "IOCTLS for Handling Tape Configuration Options"
1024 .Bl -tag -width MTIOCREADIGNOREEOFS
1025 .It Dv MTIOCSHORTFMK
1026 enables/disables support for writing short filemarks.
1027 This is specific to Exabyte drives.
1028 .It Dv MTIOCREADIGNOREILI
1029 enables/disables suppress incorrect length indicator (SILI) support during reads
1030 .It Dv MTIOCREADIGNOREEOFS
1031 enables/disables support for reading past two EOF marks which otherwise indicate
1032 End-Of-recording-Media (EOM) in the case of 1/2\(dq reel tape drives
1033 .El
1034 .Pp
1035 The
1036 .Dv MTIOCSHORTFMK
1037 ioctl enables or disables support for short filemarks.
1038 This ioctl is only applicable to Exabyte drives which support short filemarks.
1039 As an argument, it takes a pointer to an integer.
1040 If 0 (zero) is the specified integer, then long filemarks will be written.
1041 If 1 is the specified integer, then short filemarks will be written.
1042 The specified tape behavior will be in effect until the device is closed.
1043 .Pp
1044 For example:
1045 .Bd -literal -offset 2n
1046 int on = 1;
1047 int off = 0;
1048 /* enable short filemarks */
1049 ioctl(fd, MTIOSHORTFMK, &on);
1050 /* disable short filemarks */
1051 ioctl(fd, MTIOCSHORTFMK, &off);
1052 .Ed
1053 .Pp
1054 Tape drives which do not support short filemarks will return an
1055 .Va errno
1056 of
1057 .Er ENOTTY .
1058 .Pp
1059 The
1060 .Dv MTIOCREADIGNOREILI
1061 ioctl enables or disables the suppress incorrect
1062 length indicator (SILI) support during reads.
1063 As an argument, it takes a pointer to an integer.
1064 If 0 (zero) is the specified integer, SILI will not be
1065 used during reads and incorrect length indicator will not be suppressed.
1066 If 1 is the specified integer, SILI will be used during reads and incorrect
1067 length indicator will be suppressed.
1068 The specified tape behavior will be in effect until the device is closed.
1069 .Pp
1070 For example:
1071 .Bd -literal -offset 2n
1072 int on = 1;
1073 int off = 0;
1074 ioctl(fd, MTIOREADIGNOREILI, &on);
1075 ioctl(fd, MTIOREADIGNOREILI, &off);
1076 .Ed
1077 .Pp
1078 The
1079 .Dv MTIOCREADIGNOREEOFS
1080 ioctl enables or disables support for reading
1081 past double EOF marks which otherwise indicate End-Of-recorded-media (EOM) in
1082 the case of 1/2\(dq reel tape drives.
1083 As an argument, it takes a pointer to an integer.
1084 If 0 (zero) is the specified integer, then double EOF marks indicate
1085 End-Of-recorded-media (EOD).
1086 If 1 is the specified integer, the double EOF marks no longer indicate EOM,
1087 thus allowing applications to read past two EOF marks.
1088 In this case it is the responsibility of the application to detect
1089 end-of-recorded-media (EOM).
1090 The specified tape behavior will be in effect until the device is closed.
1091 .Pp
1092 For example:
1093 .Bd -literal -offset 2n
1094 int on = 1;
1095 int off = 0;
1096 ioctl(fd, MTIOREADIGNOREEOFS, &on);
1097 ioctl(fd, MTIOREADIGNOREEOFS, &off);
1098 .Ed
1099 .Pp
1100 Tape drives other than 1/2\(dq reel tapes will return an
1101 .Va errno
1102 of
1103 .Er ENOTTY .
1104 .Sh FILES
1105 .Pa /dev/rmt/ Ns Ao unit number Ac \
1106 Ns Ao density Ac \
1107 Ns Bo Ao BSD behavior Ac Bc \
1108 Ns Bo Ao no rewind Ac Bc
1109 .Pp
1110 Where
1111 .Aq density
1112 can be
1113 .Ql l ,
1114 .Ql m ,
1115 .Ql h ,
1116 .Ql u/c
1117 (low, medium, high, ultra/compressed, respectively), the
1118 .Aq BSD behavior
1119 option is
1120 .Ql b , and the
1121 .Aq no rewind
1122 option is
1123 .Ql n .
1124 .Pp
1125 For example,
1126 .Pa /dev/rmt/0hbn
1127 specifies unit 0, high density,
1128 .Sy BSD
1129 behavior and no rewind.
1130 .Sh EXAMPLES
1131 .Bl -inset
1132 .It Sy Example 1
1133 Tape Positioning and Tape Drives
1134 .Pp
1135 Suppose you have written three files to the non-rewinding 1/2\(dq tape device,
1136 .Pa /dev/rmt/0ln ,
1137 and that you want to go back and
1138 .Xr dd 1M
1139 the second file off the tape.
1140 The commands to do this are:
1141 .Bd -literal -offset 2n
1142 mt -F /dev/rmt/0lbn bsf 3
1143 mt -F /dev/rmt/0lbn fsf 1
1144 dd if=/dev/rmt/0ln
1145 .Ed
1146 .Pp
1147 To accomplish the same tape positioning in a C program, followed by a get
1148 status ioctl:
1149 .Bd -literal -offset 2n
1150 struct mtop mt_command;
1151 struct mtget mt_status;
1152 mt_command.mt_op = MTBSF;
1153 mt_command.mt_count = 3;
1154 ioctl(fd, MTIOCTOP, &mt_command);
1155 mt_command.mt_op = MTFSF;
1156 mt_command.mt_count = 1;
1157 ioctl(fd, MTIOCTOP, &mt_command);
1158 ioctl(fd, MTIOCGET, (char *)&mt_status);
1159 .Ed
1160 .Pp
1161 or
1162 .Bd -literal -offset 2n
1163 mt_command.mt_op = MTNBSF;
1164 mt_command.mt_count = 2;
1165 ioctl(fd, MTIOCTOP, &mt_command);
1166 ioctl(fd, MTIOCGET, (char *)&mt_status);
1167 .Ed
1168 .Pp
1169 To get information about the tape drive:
1170 .Bd -literal -offset 2n
1171 struct mtdrivetype mtdt;
1172 struct mtdrivetype_request mtreq;
1173 mtreq.size = sizeof(struct mtdrivetype);
1174 mtreq.mtdtp = &mtdt;
1175 ioctl(fd, MTIOCGETDRIVETYPE, &mtreq);
1176 .Ed
1177 .El
1178 .Sh SEE ALSO
1179 .Xr mt 1 ,
1180 .Xr tar 1 ,
1181 .Xr dd 1M ,
1182 .Xr open 2 ,
1183 .Xr read 2 ,
1184 .Xr write 2 ,
1185 .Xr aioread 3C ,
1186 .Xr aiowrite 3C ,
1187 .Xr ar.h 3HEAD ,
1188 .Xr st 7D
1189 .Pp
1190 .%T 1/4 Inch Tape Drive Tutorial