1ST(4)                      Linux Programmer's Manual                     ST(4)
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NAME

6       st - SCSI tape device
7

SYNOPSIS

9       #include <sys/mtio.h>
10
11       int ioctl(int fd, int request [, (void *)arg3]);
12       int ioctl(int fd, MTIOCTOP, (struct mtop *)mt_cmd);
13       int ioctl(int fd, MTIOCGET, (struct mtget *)mt_status);
14       int ioctl(int fd, MTIOCPOS, (struct mtpos *)mt_pos);
15

DESCRIPTION

17       The st driver provides the interface to a variety of SCSI tape devices.
18       Currently, the driver takes control of all  detected  devices  of  type
19       “sequential-access”.  The st driver uses major device number 9.
20
21       Each  device  uses eight minor device numbers.  The lowermost five bits
22       in the minor numbers are assigned sequentially in the order  of  detec‐
23       tion.   In  the 2.6 kernel, the bits above the eight lowermost bits are
24       concatenated to the five lowermost bits to form the tape  number.   The
25       minor numbers can be grouped into two sets of four numbers: the princi‐
26       pal (auto-rewind) minor device numbers, n, and the  “no-rewind”  device
27       numbers,  (n  + 128).  Devices opened using the principal device number
28       will be sent a REWIND command when they are closed.  Devices opened us‐
29       ing  the “no-rewind” device number will not.  (Note that using an auto-
30       rewind device for positioning the tape with, for instance, mt does  not
31       lead  to  the  desired result: the tape is rewound after the mt command
32       and the next command starts from the beginning of the tape).
33
34       Within each group, four minor numbers are available to  define  devices
35       with different characteristics (block size, compression, density, etc.)
36       When the system starts up, only the first  device  is  available.   The
37       other  three are activated when the default characteristics are defined
38       (see below).  (By changing compile-time constants, it  is  possible  to
39       change  the  balance  between the maximum number of tape drives and the
40       number of minor numbers for each drive.  The default allocation  allows
41       control  of 32 tape drives.  For instance, it is possible to control up
42       to 64 tape drives with two minor numbers for different options.)
43
44       Devices are typically created by:
45
46           mknod -m 666 /dev/st0 c 9 0
47           mknod -m 666 /dev/st0l c 9 32
48           mknod -m 666 /dev/st0m c 9 64
49           mknod -m 666 /dev/st0a c 9 96
50           mknod -m 666 /dev/nst0 c 9 128
51           mknod -m 666 /dev/nst0l c 9 160
52           mknod -m 666 /dev/nst0m c 9 192
53           mknod -m 666 /dev/nst0a c 9 224
54
55       There is no corresponding block device.
56
57       The driver uses an internal buffer that has to be large enough to  hold
58       at  least one tape block.  In kernels before 2.1.121, the buffer is al‐
59       located as one contiguous block.  This limits the  block  size  to  the
60       largest  contiguous  block  of memory the kernel allocator can provide.
61       The limit is currently 128 kB for 32-bit architectures and  256 kB  for
62       64-bit architectures.  In newer kernels the driver allocates the buffer
63       in several parts if necessary.  By default, the maximum number of parts
64       is  16.   This means that the maximum block size is very large (2 MB if
65       allocation of 16 blocks of 128 kB succeeds).
66
67       The driver's internal buffer size is determined by a compile-time  con‐
68       stant  which  can be overridden with a kernel startup option.  In addi‐
69       tion to this, the driver tries to allocate a larger temporary buffer at
70       run  time if necessary.  However, run-time allocation of large contigu‐
71       ous blocks of memory may fail and it is advisable not to rely too  much
72       on  dynamic buffer allocation with kernels older than 2.1.121 (this ap‐
73       plies also to demand-loading the driver with kerneld or kmod).
74
75       The driver does not specifically support any tape drive brand or model.
76       After  system start-up the tape device options are defined by the drive
77       firmware.  For example, if the drive firmware selects fixed-block mode,
78       the tape device uses fixed-block mode.  The options can be changed with
79       explicit ioctl(2) calls and remain in effect when the device is  closed
80       and reopened.  Setting the options affects both the auto-rewind and the
81       nonrewind device.
82
83       Different options can be specified for the different devices within the
84       subgroup  of  four.  The options take effect when the device is opened.
85       For example, the system administrator can define one device that writes
86       in  fixed-block mode with a certain block size, and one which writes in
87       variable-block mode (if the drive supports both modes).
88
89       The driver supports tape partitions if they are supported by the drive.
90       (Note that the tape partitions have nothing to do with disk partitions.
91       A partitioned tape can be seen as  several  logical  tapes  within  one
92       medium.)   Partition  support  has to be enabled with an ioctl(2).  The
93       tape location is  preserved  within  each  partition  across  partition
94       changes.  The partition used for subsequent tape operations is selected
95       with an ioctl(2).  The partition switch is executed together  with  the
96       next  tape  operation in order to avoid unnecessary tape movement.  The
97       maximum number of partitions on a tape is  defined  by  a  compile-time
98       constant  (originally  four).  The driver contains an ioctl(2) that can
99       format a tape with either one or two partitions.
100
101       Device /dev/tape is usually created as a hard or soft link to  the  de‐
102       fault tape device on the system.
103
104       Starting  from  kernel 2.6.2, the driver exports in the sysfs directory
105       /sys/class/scsi_tape the attached devices and some parameters  assigned
106       to the devices.
107
108   Data transfer
109       The  driver  supports  operation in both fixed-block mode and variable-
110       block mode (if supported by the drive).  In fixed-block mode the  drive
111       writes blocks of the specified size and the block size is not dependent
112       on the byte counts of the write system calls.  In  variable-block  mode
113       one tape block is written for each write call and the byte count deter‐
114       mines the size of the corresponding tape block.  Note that  the  blocks
115       on  the tape don't contain any information about the writing mode: when
116       reading, the only important thing is to use commands  that  accept  the
117       block sizes on the tape.
118
119       In  variable-block  mode the read byte count does not have to match the
120       tape block size exactly.  If the byte count is  larger  than  the  next
121       block on tape, the driver returns the data and the function returns the
122       actual block size.  If the block size is larger than the byte count, an
123       error is returned.
124
125       In  fixed-block mode the read byte counts can be arbitrary if buffering
126       is enabled, or a multiple of the tape block size if buffering  is  dis‐
127       abled.   Kernels  before 2.1.121 allow writes with arbitrary byte count
128       if buffering is enabled.  In all other  cases  (kernel  before  2.1.121
129       with buffering disabled or newer kernel) the write byte count must be a
130       multiple of the tape block size.
131
132       In the 2.6 kernel, the driver tries to use direct transfers between the
133       user  buffer and the device.  If this is not possible, the driver's in‐
134       ternal buffer is used.  The reasons for not using direct transfers  in‐
135       clude  improper  alignment of the user buffer (default is 512 bytes but
136       this can be changed by the HBA driver), one or more pages of  the  user
137       buffer not reachable by the SCSI adapter, and so on.
138
139       A  filemark is automatically written to tape if the last tape operation
140       before close was a write.
141
142       When a filemark is encountered while reading,  the  following  happens.
143       If  there  are data remaining in the buffer when the filemark is found,
144       the buffered data is returned.  The next read returns zero bytes.   The
145       following  read  returns  data from the next file.  The end of recorded
146       data is signaled by returning  zero  bytes  for  two  consecutive  read
147       calls.  The third read returns an error.
148
149   Ioctls
150       The  driver  supports three ioctl(2) requests.  Requests not recognized
151       by the st driver are passed to the SCSI driver.  The definitions  below
152       are from /usr/include/linux/mtio.h:
153
154   MTIOCTOP — perform a tape operation
155       This request takes an argument of type (struct mtop *).  Not all drives
156       support all operations.  The driver returns an EIO error if  the  drive
157       rejects an operation.
158
159           /* Structure for MTIOCTOP - mag tape op command: */
160           struct mtop {
161               short   mt_op;       /* operations defined below */
162               int     mt_count;    /* how many of them */
163           };
164
165       Magnetic tape operations for normal tape use:
166
167       MTBSF  Backward space over mt_count filemarks.
168
169       MTBSFM Backward  space over mt_count filemarks.  Reposition the tape to
170              the EOT side of the last filemark.
171
172       MTBSR  Backward space over mt_count records (tape blocks).
173
174       MTBSS  Backward space over mt_count setmarks.
175
176       MTCOMPRESSION
177              Enable compression of tape data within the drive if mt_count  is
178              nonzero  and disable compression if mt_count is zero.  This com‐
179              mand uses the MODE page 15 supported by most DATs.
180
181       MTEOM  Go to the end of the recorded media (for appending files).
182
183       MTERASE
184              Erase tape.  With 2.6 kernel, short erase (mark tape  empty)  is
185              performed if the argument is zero.  Otherwise, long erase (erase
186              all) is done.
187
188       MTFSF  Forward space over mt_count filemarks.
189
190       MTFSFM Forward space over mt_count filemarks.  Reposition the  tape  to
191              the BOT side of the last filemark.
192
193       MTFSR  Forward space over mt_count records (tape blocks).
194
195       MTFSS  Forward space over mt_count setmarks.
196
197       MTLOAD Execute  the SCSI load command.  A special case is available for
198              some   HP   autoloaders.    If   mt_count   is   the    constant
199              MT_ST_HPLOADER_OFFSET  plus  a number, the number is sent to the
200              drive to control the autoloader.
201
202       MTLOCK Lock the tape drive door.
203
204       MTMKPART
205              Format the tape into one or two partitions.  If mt_count is pos‐
206              itive, it gives the size of partition 1 and partition 0 contains
207              the rest of the tape.  If mt_count is zero, the tape is  format‐
208              ted  into  one  partition.   From kernel version 4.6, a negative
209              mt_count specifies the size of partition 0 and the rest  of  the
210              tape  contains partition 1.  The physical ordering of partitions
211              depends on the drive.  This command is not allowed for  a  drive
212              unless  the  partition  support  is  enabled  for the drive (see
213              MT_ST_CAN_PARTITIONS below).
214
215       MTNOP  No op—flushes the driver's buffer as a side effect.   Should  be
216              used before reading status with MTIOCGET.
217
218       MTOFFL Rewind and put the drive off line.
219
220       MTRESET
221              Reset drive.
222
223       MTRETEN
224              Re-tension tape.
225
226       MTREW  Rewind.
227
228       MTSEEK Seek to the tape block number specified in mt_count.  This oper‐
229              ation requires either a SCSI-2 drive that  supports  the  LOCATE
230              command   (device-specific  address)  or  a  Tandberg-compatible
231              SCSI-1 drive (Tandberg, Archive Viper, Wangtek, ...).  The block
232              number should be one that was previously returned by MTIOCPOS if
233              device-specific addresses are used.
234
235       MTSETBLK
236              Set the drive's block length to the value specified in mt_count.
237              A  block  length  of  zero sets the drive to variable block size
238              mode.
239
240       MTSETDENSITY
241              Set the tape density to the code in mt_count.  The density codes
242              supported by a drive can be found from the drive documentation.
243
244       MTSETPART
245              The  active  partition  is switched to mt_count.  The partitions
246              are numbered from zero.  This command is not allowed for a drive
247              unless  the  partition  support  is  enabled  for the drive (see
248              MT_ST_CAN_PARTITIONS below).
249
250       MTUNLOAD
251              Execute the SCSI unload command (does not eject the tape).
252
253       MTUNLOCK
254              Unlock the tape drive door.
255
256       MTWEOF Write mt_count filemarks.
257
258       MTWSM  Write mt_count setmarks.
259
260       Magnetic tape operations for setting of device options  (by  the  supe‐
261       ruser):
262
263       MTSETDRVBUFFER
264              Set  various  drive and driver options according to bits encoded
265              in mt_count.  These consist of the drive's buffering mode, a set
266              of  Boolean driver options, the buffer write threshold, defaults
267              for the block size and density, and timeouts  (only  in  kernels
268              2.1  and later).  A single operation can affect only one item in
269              the list below (the Booleans counted as one item.)
270
271              A value having zeros in the high-order 4 bits will  be  used  to
272              set the drive's buffering mode.  The buffering modes are:
273
274                   0   The drive will not report GOOD status on write commands
275                       until the data  blocks  are  actually  written  to  the
276                       medium.
277
278                   1   The  drive  may report GOOD status on write commands as
279                       soon as all  the  data  has  been  transferred  to  the
280                       drive's internal buffer.
281
282                   2   The  drive  may report GOOD status on write commands as
283                       soon as (a) all the data has been  transferred  to  the
284                       drive's internal buffer, and (b) all buffered data from
285                       different initiators has been successfully  written  to
286                       the medium.
287
288              To  control  the  write threshold the value in mt_count must in‐
289              clude the constant MT_ST_WRITE_THRESHOLD  bitwise  ORed  with  a
290              block  count  in  the  low  28  bits.  The block count refers to
291              1024-byte blocks, not the physical block size on the tape.   The
292              threshold  cannot  exceed the driver's internal buffer size (see
293              DESCRIPTION, above).
294
295              To set and clear the Boolean options the value in mt_count  must
296              include  one of the constants MT_ST_BOOLEANS, MT_ST_SETBOOLEANS,
297              MT_ST_CLEARBOOLEANS,  or  MT_ST_DEFBOOLEANS  bitwise  ORed  with
298              whatever combination of the following options is desired.  Using
299              MT_ST_BOOLEANS the options can be set to the values  defined  in
300              the  corresponding bits.  With MT_ST_SETBOOLEANS the options can
301              be  selectively  set  and  with  MT_ST_DEFBOOLEANS   selectively
302              cleared.
303
304              The  default  options  for a tape device are set with MT_ST_DEF‐
305              BOOLEANS.  A nonactive tape device (e.g., device with  minor  32
306              or 160) is activated when the default options for it are defined
307              the first time.  An activated device inherits  from  the  device
308              activated at start-up the options not set explicitly.
309
310              The Boolean options are:
311
312              MT_ST_BUFFER_WRITES (Default: true)
313                     Buffer all write operations in fixed-block mode.  If this
314                     option is false and the drive uses a  fixed  block  size,
315                     then  all  write operations must be for a multiple of the
316                     block size.  This option must be set false to write reli‐
317                     able multivolume archives.
318
319              MT_ST_ASYNC_WRITES (Default: true)
320                     When this option is true, write operations return immedi‐
321                     ately without waiting for the data to be  transferred  to
322                     the drive if the data fits into the driver's buffer.  The
323                     write threshold determines how full the  buffer  must  be
324                     before  a  new  SCSI write command is issued.  Any errors
325                     reported by the drive will be held until the next  opera‐
326                     tion.   This  option  must be set false to write reliable
327                     multivolume archives.
328
329              MT_ST_READ_AHEAD (Default: true)
330                     This option causes the driver to provide  read  buffering
331                     and  read-ahead  in  fixed-block mode.  If this option is
332                     false and the drive uses a fixed  block  size,  then  all
333                     read operations must be for a multiple of the block size.
334
335              MT_ST_TWO_FM (Default: false)
336                     This  option  modifies the driver behavior when a file is
337                     closed.  The normal action is to write a single filemark.
338                     If  the  option  is true, the driver will write two file‐
339                     marks and backspace over the second one.
340
341                     Note: This option should not be set  true  for  QIC  tape
342                     drives  since  they  are  unable to overwrite a filemark.
343                     These drives detect the end of recorded data  by  testing
344                     for  blank  tape  rather  than two consecutive filemarks.
345                     Most other current drives also detect the end of recorded
346                     data  and  using  two filemarks is usually necessary only
347                     when interchanging tapes with some other systems.
348
349              MT_ST_DEBUGGING (Default: false)
350                     This option turns on various debugging messages from  the
351                     driver  (effective  only  if the driver was compiled with
352                     DEBUG defined nonzero).
353
354              MT_ST_FAST_EOM (Default: false)
355                     This option causes the MTEOM operation  to  be  sent  di‐
356                     rectly  to  the drive, potentially speeding up the opera‐
357                     tion but causing the driver to lose track of the  current
358                     file  number  normally  returned by the MTIOCGET request.
359                     If MT_ST_FAST_EOM is false, the driver will respond to an
360                     MTEOM request by forward spacing over files.
361
362              MT_ST_AUTO_LOCK (Default: false)
363                     When  this  option is true, the drive door is locked when
364                     the device file is opened and unlocked when it is closed.
365
366              MT_ST_DEF_WRITES (Default: false)
367                     The tape options (block size,  mode,  compression,  etc.)
368                     may  change  when  changing  from  one device linked to a
369                     drive to another device linked to the same drive  depend‐
370                     ing  on how the devices are defined.  This option defines
371                     when the changes are enforced by the driver  using  SCSI-
372                     commands  and when the drives auto-detection capabilities
373                     are relied upon.  If this option  is  false,  the  driver
374                     sends  the  SCSI-commands  immediately when the device is
375                     changed.  If the option is true,  the  SCSI-commands  are
376                     not  sent  until a write is requested.  In this case, the
377                     drive firmware is allowed to detect  the  tape  structure
378                     when  reading and the SCSI-commands are used only to make
379                     sure that a tape is  written  according  to  the  correct
380                     specification.
381
382              MT_ST_CAN_BSR (Default: false)
383                     When  read-ahead  is  used,  the  tape  must sometimes be
384                     spaced backward to the correct position when  the  device
385                     is  closed  and  the  SCSI command to space backward over
386                     records is used for  this  purpose.   Some  older  drives
387                     can't  process  this command reliably and this option can
388                     be used to instruct the driver not to  use  the  command.
389                     The  end  result is that, with read-ahead and fixed-block
390                     mode, the tape may not be correctly positioned  within  a
391                     file when the device is closed.  With 2.6 kernel, the de‐
392                     fault is true for drives supporting SCSI-3.
393
394              MT_ST_NO_BLKLIMS (Default: false)
395                     Some drives don't accept the READ BLOCK LIMITS SCSI  com‐
396                     mand.   If this is used, the driver does not use the com‐
397                     mand.  The drawback is that the driver can't check before
398                     sending commands if the selected block size is acceptable
399                     to the drive.
400
401              MT_ST_CAN_PARTITIONS (Default: false)
402                     This option enables support for several partitions within
403                     a  tape.   The  option applies to all devices linked to a
404                     drive.
405
406              MT_ST_SCSI2LOGICAL (Default: false)
407                     This option instructs the driver to use the logical block
408                     addresses  defined in the SCSI-2 standard when performing
409                     the seek and tell operations (both with MTSEEK and MTIOC‐
410                     POS  commands  and when changing tape partition).  Other‐
411                     wise, the device-specific  addresses  are  used.   It  is
412                     highly advisable to set this option if the drive supports
413                     the logical addresses because they count also  filemarks.
414                     There are some drives that support only the logical block
415                     addresses.
416
417              MT_ST_SYSV (Default: false)
418                     When this option is enabled, the  tape  devices  use  the
419                     System  V  semantics.   Otherwise,  the BSD semantics are
420                     used.  The most important difference between  the  seman‐
421                     tics  is  what  happens when a device used for reading is
422                     closed: in System V semantics the tape is spaced  forward
423                     past the next filemark if this has not happened while us‐
424                     ing the device.  In BSD semantics the  tape  position  is
425                     not changed.
426
427              MT_NO_WAIT (Default: false)
428                     Enables  immediate mode (i.e., don't wait for the command
429                     to finish) for some commands (e.g., rewind).
430
431              An example:
432
433                  struct mtop mt_cmd;
434                  mt_cmd.mt_op = MTSETDRVBUFFER;
435                  mt_cmd.mt_count = MT_ST_BOOLEANS |
436                          MT_ST_BUFFER_WRITES | MT_ST_ASYNC_WRITES;
437                  ioctl(fd, MTIOCTOP, mt_cmd);
438
439              The  default  block  size  for  a  device  can   be   set   with
440              MT_ST_DEF_BLKSIZE  and  the default density code can be set with
441              MT_ST_DEFDENSITY.  The values for the parameters are or'ed  with
442              the operation code.
443
444              With kernels 2.1.x and later, the timeout values can be set with
445              the subcommand MT_ST_SET_TIMEOUT ORed with the timeout  in  sec‐
446              onds.   The  long  timeout  (used for rewinds and other commands
447              that may take a long time) can be set with  MT_ST_SET_LONG_TIME‐
448              OUT.  The kernel defaults are very long to make sure that a suc‐
449              cessful command is not timed out with  any  drive.   Because  of
450              this,  the  driver may seem stuck even if it is only waiting for
451              the timeout.  These commands can be used to set  more  practical
452              values  for  a  specific drive.  The timeouts set for one device
453              apply for all devices linked to the same drive.
454
455              Starting from kernels 2.4.19 and 2.5.43, the driver  supports  a
456              status  bit which indicates whether the drive requests cleaning.
457              The method used by the drive to return cleaning  information  is
458              set  using  the MT_ST_SEL_CLN subcommand.  If the value is zero,
459              the cleaning bit is always zero.   If  the  value  is  one,  the
460              TapeAlert  data  defined in the SCSI-3 standard is used (not yet
461              implemented).  Values 2–17 are reserved.  If  the  lowest  eight
462              bits are >= 18, bits from the extended sense data are used.  The
463              bits 9–16 specify a mask to select the bits to look at  and  the
464              bits 17–23 specify the bit pattern to look for.  If the bit pat‐
465              tern is zero, one or more  bits  under  the  mask  indicate  the
466              cleaning  request.   If the pattern is nonzero, the pattern must
467              match the masked sense data byte.
468
469   MTIOCGET — get status
470       This request takes an argument of type (struct mtget *).
471
472           /* structure for MTIOCGET - mag tape get status command */
473           struct mtget {
474               long     mt_type;
475               long     mt_resid;
476               /* the following registers are device dependent */
477               long     mt_dsreg;
478               long     mt_gstat;
479               long     mt_erreg;
480               /* The next two fields are not always used */
481               daddr_t  mt_fileno;
482               daddr_t  mt_blkno;
483           };
484
485       mt_type
486              The header file defines many values for mt_type, but the current
487              driver reports only the generic types MT_ISSCSI1 (Generic SCSI-1
488              tape) and MT_ISSCSI2 (Generic SCSI-2 tape).
489
490       mt_resid
491              contains the current tape partition number.
492
493       mt_dsreg
494              reports the drive's current settings for block size (in the  low
495              24 bits) and density (in the high 8 bits).  These fields are de‐
496              fined  by  MT_ST_BLKSIZE_SHIFT,  MT_ST_BLKSIZE_MASK,  MT_ST_DEN‐
497              SITY_SHIFT, and MT_ST_DENSITY_MASK.
498
499       mt_gstat
500              reports  generic  (device  independent) status information.  The
501              header file defines macros for testing these status bits:
502
503              GMT_EOF(x): The tape is positioned just after a filemark (always
504                  false after an MTSEEK operation).
505
506              GMT_BOT(x): The tape is positioned at the beginning of the first
507                  file (always false after an MTSEEK operation).
508
509              GMT_EOT(x): A tape operation has reached  the  physical  End  Of
510                  Tape.
511
512              GMT_SM(x): The tape is currently positioned at a setmark (always
513                  false after an MTSEEK operation).
514
515              GMT_EOD(x): The tape is positioned at the end of recorded data.
516
517              GMT_WR_PROT(x): The drive is write-protected.  For  some  drives
518                  this  can  also mean that the drive does not support writing
519                  on the current medium type.
520
521              GMT_ONLINE(x): The last open(2) found the drive with a  tape  in
522                  place and ready for operation.
523
524              GMT_D_6250(x),  GMT_D_1600(x), GMT_D_800(x): This “generic” sta‐
525                  tus information reports  the  current  density  setting  for
526                  9-track ½" tape drives only.
527
528              GMT_DR_OPEN(x): The drive does not have a tape in place.
529
530              GMT_IM_REP_EN(x):  Immediate  report  mode.   This bit is set if
531                  there are no guarantees that the data  has  been  physically
532                  written  to the tape when the write call returns.  It is set
533                  zero only when the driver does not buffer data and the drive
534                  is set not to buffer data.
535
536              GMT_CLN(x):  The  drive  has requested cleaning.  Implemented in
537                  kernels since 2.4.19 and 2.5.43.
538
539       mt_erreg
540              The only field defined in mt_erreg is the recovered error  count
541              in  the  low  16  bits  (as  defined  by MT_ST_SOFTERR_SHIFT and
542              MT_ST_SOFTERR_MASK).  Due to inconsistencies in the  way  drives
543              report  recovered  errors,  this  count  is often not maintained
544              (most drives do not by default report soft errors but  this  can
545              be changed with a SCSI MODE SELECT command).
546
547       mt_fileno
548              reports the current file number (zero-based).  This value is set
549              to -1 when the file number is unknown (e.g., after MTBSS or  MT‐
550              SEEK).
551
552       mt_blkno
553              reports  the  block number (zero-based) within the current file.
554              This value is set to -1 when the block number is unknown  (e.g.,
555              after MTBSF, MTBSS, or MTSEEK).
556
557   MTIOCPOS — get tape position
558       This request takes an argument of type (struct mtpos *) and reports the
559       drive's notion of the current tape block number, which is not the  same
560       as  mt_blkno  returned  by MTIOCGET.  This drive must be a SCSI-2 drive
561       that supports the READ POSITION command (device-specific address) or  a
562       Tandberg-compatible SCSI-1 drive (Tandberg, Archive Viper, Wangtek, ...
563       ).
564
565           /* structure for MTIOCPOS - mag tape get position command */
566           struct mtpos {
567               long mt_blkno;    /* current block number */
568           };
569

RETURN VALUE

571       EACCES An attempt was made to write or erase  a  write-protected  tape.
572              (This error is not detected during open(2).)
573
574       EBUSY  The  device  is already in use or the driver was unable to allo‐
575              cate a buffer.
576
577       EFAULT The command parameters point to  memory  not  belonging  to  the
578              calling process.
579
580       EINVAL An  ioctl(2)  had an invalid argument, or a requested block size
581              was invalid.
582
583       EIO    The requested operation could not be completed.
584
585       ENOMEM The byte count in read(2) is  smaller  than  the  next  physical
586              block  on  the  tape.   (Before 2.2.18 and 2.4.0 the extra bytes
587              have been silently ignored.)
588
589       ENOSPC A write operation  could  not  be  completed  because  the  tape
590              reached end-of-medium.
591
592       ENOSYS Unknown ioctl(2).
593
594       ENXIO  During opening, the tape device does not exist.
595
596       EOVERFLOW
597              An  attempt  was  made  to read or write a variable-length block
598              that is larger than the driver's internal buffer.
599
600       EROFS  Open is attempted with O_WRONLY or O_RDWR when the tape  in  the
601              drive is write-protected.
602

FILES

604       /dev/st*
605              the auto-rewind SCSI tape devices
606
607       /dev/nst*
608              the nonrewind SCSI tape devices
609

NOTES

611       1.  When exchanging data between systems, both systems have to agree on
612           the physical tape block size.  The  parameters  of  a  drive  after
613           startup  are  often  not  the  ones most operating systems use with
614           these devices.  Most systems use drives in variable-block  mode  if
615           the  drive supports that mode.  This applies to most modern drives,
616           including DATs, 8mm helical scan drives, DLTs, etc.  It may be  ad‐
617           visable  to  use  these drives in variable-block mode also in Linux
618           (i.e., use MTSETBLK or MTSETDEFBLK at system  startup  to  set  the
619           mode),  at  least  when exchanging data with a foreign system.  The
620           drawback of this is that a fairly large tape block size has  to  be
621           used to get acceptable data transfer rates on the SCSI bus.
622
623       2.  Many programs (e.g., tar(1)) allow the user to specify the blocking
624           factor on the command line.  Note that this determines the physical
625           block size on tape only in variable-block mode.
626
627       3.  In  order  to  use SCSI tape drives, the basic SCSI driver, a SCSI-
628           adapter driver and the SCSI tape driver must be  either  configured
629           into  the  kernel or loaded as modules.  If the SCSI-tape driver is
630           not present, the drive is recognized but the tape support described
631           in this page is not available.
632
633       4.  The  driver  writes  error  messages to the console/log.  The SENSE
634           codes written into some messages are  automatically  translated  to
635           text if verbose SCSI messages are enabled in kernel configuration.
636
637       5.  The  driver's  internal  buffering allows good throughput in fixed-
638           block mode also with small read(2) and write(2) byte counts.   With
639           direct transfers this is not possible and may cause a surprise when
640           moving to the 2.6 kernel.  The solution is to tell the software  to
641           use  larger  transfers (often telling it to use larger blocks).  If
642           this is not possible, direct transfers can be disabled.
643

SEE ALSO

645       mt(1)
646
647       The file drivers/scsi/README.st or Documentation/scsi/st.txt (kernel >=
648       2.6)  in the Linux kernel source tree contains the most recent informa‐
649       tion about the driver and its configuration possibilities
650

COLOPHON

652       This page is part of release 5.10 of the Linux  man-pages  project.   A
653       description  of  the project, information about reporting bugs, and the
654       latest    version    of    this    page,    can     be     found     at
655       https://www.kernel.org/doc/man-pages/.
656
657
658
659Linux                             2020-04-11                             ST(4)
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