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bf65c846 MCC |
1 | .. SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | ==================== | |
4 | The SCSI Tape Driver | |
5 | ==================== | |
6 | ||
1da177e4 | 7 | This file contains brief information about the SCSI tape driver. |
be2a608b | 8 | The driver is currently maintained by Kai Mäkisara (email |
1da177e4 LT |
9 | Kai.Makisara@kolumbus.fi) |
10 | ||
8038e645 | 11 | Last modified: Tue Feb 9 21:54:16 2016 by kai.makisara |
1da177e4 LT |
12 | |
13 | ||
bf65c846 MCC |
14 | Basics |
15 | ====== | |
1da177e4 LT |
16 | |
17 | The driver is generic, i.e., it does not contain any code tailored | |
18 | to any specific tape drive. The tape parameters can be specified with | |
19 | one of the following three methods: | |
20 | ||
21 | 1. Each user can specify the tape parameters he/she wants to use | |
22 | directly with ioctls. This is administratively a very simple and | |
23 | flexible method and applicable to single-user workstations. However, | |
24 | in a multiuser environment the next user finds the tape parameters in | |
25 | state the previous user left them. | |
26 | ||
27 | 2. The system manager (root) can define default values for some tape | |
28 | parameters, like block size and density using the MTSETDRVBUFFER ioctl. | |
29 | These parameters can be programmed to come into effect either when a | |
30 | new tape is loaded into the drive or if writing begins at the | |
31 | beginning of the tape. The second method is applicable if the tape | |
32 | drive performs auto-detection of the tape format well (like some | |
33 | QIC-drives). The result is that any tape can be read, writing can be | |
34 | continued using existing format, and the default format is used if | |
35 | the tape is rewritten from the beginning (or a new tape is written | |
36 | for the first time). The first method is applicable if the drive | |
37 | does not perform auto-detection well enough and there is a single | |
38 | "sensible" mode for the device. An example is a DAT drive that is | |
39 | used only in variable block mode (I don't know if this is sensible | |
40 | or not :-). | |
41 | ||
42 | The user can override the parameters defined by the system | |
43 | manager. The changes persist until the defaults again come into | |
44 | effect. | |
45 | ||
46 | 3. By default, up to four modes can be defined and selected using the minor | |
47 | number (bits 5 and 6). The number of modes can be changed by changing | |
48 | ST_NBR_MODE_BITS in st.h. Mode 0 corresponds to the defaults discussed | |
49 | above. Additional modes are dormant until they are defined by the | |
50 | system manager (root). When specification of a new mode is started, | |
51 | the configuration of mode 0 is used to provide a starting point for | |
52 | definition of the new mode. | |
53 | ||
54 | Using the modes allows the system manager to give the users choices | |
55 | over some of the buffering parameters not directly accessible to the | |
56 | users (buffered and asynchronous writes). The modes also allow choices | |
57 | between formats in multi-tape operations (the explicitly overridden | |
58 | parameters are reset when a new tape is loaded). | |
59 | ||
60 | If more than one mode is used, all modes should contain definitions | |
61 | for the same set of parameters. | |
62 | ||
63 | Many Unices contain internal tables that associate different modes to | |
64 | supported devices. The Linux SCSI tape driver does not contain such | |
65 | tables (and will not do that in future). Instead of that, a utility | |
66 | program can be made that fetches the inquiry data sent by the device, | |
67 | scans its database, and sets up the modes using the ioctls. Another | |
68 | alternative is to make a small script that uses mt to set the defaults | |
69 | tailored to the system. | |
70 | ||
71 | The driver supports fixed and variable block size (within buffer | |
72 | limits). Both the auto-rewind (minor equals device number) and | |
73 | non-rewind devices (minor is 128 + device number) are implemented. | |
74 | ||
75 | In variable block mode, the byte count in write() determines the size | |
76 | of the physical block on tape. When reading, the drive reads the next | |
77 | tape block and returns to the user the data if the read() byte count | |
78 | is at least the block size. Otherwise, error ENOMEM is returned. | |
79 | ||
80 | In fixed block mode, the data transfer between the drive and the | |
81 | driver is in multiples of the block size. The write() byte count must | |
82 | be a multiple of the block size. This is not required when reading but | |
83 | may be advisable for portability. | |
84 | ||
85 | Support is provided for changing the tape partition and partitioning | |
86 | of the tape with one or two partitions. By default support for | |
87 | partitioned tape is disabled for each driver and it can be enabled | |
88 | with the ioctl MTSETDRVBUFFER. | |
89 | ||
90 | By default the driver writes one filemark when the device is closed after | |
91 | writing and the last operation has been a write. Two filemarks can be | |
92 | optionally written. In both cases end of data is signified by | |
93 | returning zero bytes for two consecutive reads. | |
94 | ||
3e51d3c9 KM |
95 | Writing filemarks without the immediate bit set in the SCSI command block acts |
96 | as a synchronization point, i.e., all remaining data form the drive buffers is | |
97 | written to tape before the command returns. This makes sure that write errors | |
98 | are caught at that point, but this takes time. In some applications, several | |
99 | consecutive files must be written fast. The MTWEOFI operation can be used to | |
100 | write the filemarks without flushing the drive buffer. Writing filemark at | |
101 | close() is always flushing the drive buffers. However, if the previous | |
102 | operation is MTWEOFI, close() does not write a filemark. This can be used if | |
103 | the program wants to close/open the tape device between files and wants to | |
104 | skip waiting. | |
105 | ||
1da177e4 LT |
106 | If rewind, offline, bsf, or seek is done and previous tape operation was |
107 | write, a filemark is written before moving tape. | |
108 | ||
109 | The compile options are defined in the file linux/drivers/scsi/st_options.h. | |
110 | ||
111 | 4. If the open option O_NONBLOCK is used, open succeeds even if the | |
112 | drive is not ready. If O_NONBLOCK is not used, the driver waits for | |
113 | the drive to become ready. If this does not happen in ST_BLOCK_SECONDS | |
114 | seconds, open fails with the errno value EIO. With O_NONBLOCK the | |
115 | device can be opened for writing even if there is a write protected | |
116 | tape in the drive (commands trying to write something return error if | |
117 | attempted). | |
118 | ||
119 | ||
bf65c846 MCC |
120 | Minor Numbers |
121 | ============= | |
1da177e4 | 122 | |
6ed33a4a JM |
123 | The tape driver currently supports up to 2^17 drives if 4 modes for |
124 | each drive are used. | |
1da177e4 | 125 | |
bf65c846 MCC |
126 | The minor numbers consist of the following bit fields:: |
127 | ||
128 | dev_upper non-rew mode dev-lower | |
129 | 20 - 8 7 6 5 4 0 | |
1da177e4 | 130 | |
1da177e4 LT |
131 | The non-rewind bit is always bit 7 (the uppermost bit in the lowermost |
132 | byte). The bits defining the mode are below the non-rewind bit. The | |
133 | remaining bits define the tape device number. This numbering is | |
134 | backward compatible with the numbering used when the minor number was | |
135 | only 8 bits wide. | |
136 | ||
137 | ||
bf65c846 MCC |
138 | Sysfs Support |
139 | ============= | |
1da177e4 LT |
140 | |
141 | The driver creates the directory /sys/class/scsi_tape and populates it with | |
142 | directories corresponding to the existing tape devices. There are autorewind | |
143 | and non-rewind entries for each mode. The names are stxy and nstxy, where x | |
144 | is the tape number and y a character corresponding to the mode (none, l, m, | |
145 | a). For example, the directories for the first tape device are (assuming four | |
146 | modes): st0 nst0 st0l nst0l st0m nst0m st0a nst0a. | |
147 | ||
148 | Each directory contains the entries: default_blksize default_compression | |
149 | default_density defined dev device driver. The file 'defined' contains 1 | |
150 | if the mode is defined and zero if not defined. The files 'default_*' contain | |
151 | the defaults set by the user. The value -1 means the default is not set. The | |
152 | file 'dev' contains the device numbers corresponding to this device. The links | |
153 | 'device' and 'driver' point to the SCSI device and driver entries. | |
154 | ||
b174be02 KM |
155 | Each directory also contains the entry 'options' which shows the currently |
156 | enabled driver and mode options. The value in the file is a bit mask where the | |
157 | bit definitions are the same as those used with MTSETDRVBUFFER in setting the | |
158 | options. | |
159 | ||
1da177e4 | 160 | A link named 'tape' is made from the SCSI device directory to the class |
bf65c846 | 161 | directory corresponding to the mode 0 auto-rewind device (e.g., st0). |
1da177e4 LT |
162 | |
163 | ||
bf65c846 MCC |
164 | Sysfs and Statistics for Tape Devices |
165 | ===================================== | |
05545c92 SS |
166 | |
167 | The st driver maintains statistics for tape drives inside the sysfs filesystem. | |
168 | The following method can be used to locate the statistics that are | |
169 | available (assuming that sysfs is mounted at /sys): | |
170 | ||
171 | 1. Use opendir(3) on the directory /sys/class/scsi_tape | |
172 | 2. Use readdir(3) to read the directory contents | |
173 | 3. Use regcomp(3)/regexec(3) to match directory entries to the extended | |
bf65c846 | 174 | regular expression "^st[0-9]+$" |
05545c92 | 175 | 4. Access the statistics from the /sys/class/scsi_tape/<match>/stats |
bf65c846 MCC |
176 | directory (where <match> is a directory entry from /sys/class/scsi_tape |
177 | that matched the extended regular expression) | |
05545c92 SS |
178 | |
179 | The reason for using this approach is that all the character devices | |
180 | pointing to the same tape drive use the same statistics. That means | |
181 | that st0 would have the same statistics as nst0. | |
182 | ||
183 | The directory contains the following statistics files: | |
184 | ||
bf65c846 MCC |
185 | 1. in_flight |
186 | - The number of I/Os currently outstanding to this device. | |
187 | 2. io_ns | |
188 | - The amount of time spent waiting (in nanoseconds) for all I/O | |
05545c92 SS |
189 | to complete (including read and write). This includes tape movement |
190 | commands such as seeking between file or set marks and implicit tape | |
191 | movement such as when rewind on close tape devices are used. | |
bf65c846 MCC |
192 | 3. other_cnt |
193 | - The number of I/Os issued to the tape drive other than read or | |
05545c92 SS |
194 | write commands. The time taken to complete these commands uses the |
195 | following calculation io_ms-read_ms-write_ms. | |
bf65c846 MCC |
196 | 4. read_byte_cnt |
197 | - The number of bytes read from the tape drive. | |
198 | 5. read_cnt | |
199 | - The number of read requests issued to the tape drive. | |
200 | 6. read_ns | |
201 | - The amount of time (in nanoseconds) spent waiting for read | |
05545c92 | 202 | requests to complete. |
bf65c846 MCC |
203 | 7. write_byte_cnt |
204 | - The number of bytes written to the tape drive. | |
205 | 8. write_cnt | |
206 | - The number of write requests issued to the tape drive. | |
207 | 9. write_ns | |
208 | - The amount of time (in nanoseconds) spent waiting for write | |
05545c92 | 209 | requests to complete. |
bf65c846 MCC |
210 | 10. resid_cnt |
211 | - The number of times during a read or write we found | |
05545c92 SS |
212 | the residual amount to be non-zero. This should mean that a program |
213 | is issuing a read larger thean the block size on tape. For write | |
214 | not all data made it to tape. | |
215 | ||
bf65c846 MCC |
216 | .. Note:: |
217 | ||
218 | The in_flight value is incremented when an I/O starts the I/O | |
219 | itself is not added to the statistics until it completes. | |
05545c92 SS |
220 | |
221 | The total of read_cnt, write_cnt, and other_cnt may not total to the same | |
222 | value as iodone_cnt at the device level. The tape statistics only count | |
223 | I/O issued via the st module. | |
224 | ||
225 | When read the statistics may not be temporally consistent while I/O is in | |
226 | progress. The individual values are read and written to atomically however | |
227 | when reading them back via sysfs they may be in the process of being | |
228 | updated when starting an I/O or when it is completed. | |
229 | ||
230 | The value shown in in_flight is incremented before any statstics are | |
231 | updated and decremented when an I/O completes after updating statistics. | |
232 | The value of in_flight is 0 when there are no I/Os outstanding that are | |
233 | issued by the st driver. Tape statistics do not take into account any | |
234 | I/O performed via the sg device. | |
235 | ||
bf65c846 MCC |
236 | BSD and Sys V Semantics |
237 | ======================= | |
1da177e4 LT |
238 | |
239 | The user can choose between these two behaviours of the tape driver by | |
240 | defining the value of the symbol ST_SYSV. The semantics differ when a | |
241 | file being read is closed. The BSD semantics leaves the tape where it | |
242 | currently is whereas the SYS V semantics moves the tape past the next | |
243 | filemark unless the filemark has just been crossed. | |
244 | ||
245 | The default is BSD semantics. | |
246 | ||
247 | ||
bf65c846 MCC |
248 | Buffering |
249 | ========= | |
1da177e4 LT |
250 | |
251 | The driver tries to do transfers directly to/from user space. If this | |
252 | is not possible, a driver buffer allocated at run-time is used. If | |
253 | direct i/o is not possible for the whole transfer, the driver buffer | |
254 | is used (i.e., bounce buffers for individual pages are not | |
255 | used). Direct i/o can be impossible because of several reasons, e.g.: | |
bf65c846 | 256 | |
1da177e4 LT |
257 | - one or more pages are at addresses not reachable by the HBA |
258 | - the number of pages in the transfer exceeds the number of | |
259 | scatter/gather segments permitted by the HBA | |
260 | - one or more pages can't be locked into memory (should not happen in | |
261 | any reasonable situation) | |
262 | ||
263 | The size of the driver buffers is always at least one tape block. In fixed | |
264 | block mode, the minimum buffer size is defined (in 1024 byte units) by | |
265 | ST_FIXED_BUFFER_BLOCKS. With small block size this allows buffering of | |
266 | several blocks and using one SCSI read or write to transfer all of the | |
267 | blocks. Buffering of data across write calls in fixed block mode is | |
268 | allowed if ST_BUFFER_WRITES is non-zero and direct i/o is not used. | |
269 | Buffer allocation uses chunks of memory having sizes 2^n * (page | |
270 | size). Because of this the actual buffer size may be larger than the | |
271 | minimum allowable buffer size. | |
272 | ||
273 | NOTE that if direct i/o is used, the small writes are not buffered. This may | |
274 | cause a surprise when moving from 2.4. There small writes (e.g., tar without | |
275 | -b option) may have had good throughput but this is not true any more with | |
276 | 2.6. Direct i/o can be turned off to solve this problem but a better solution | |
277 | is to use bigger write() byte counts (e.g., tar -b 64). | |
278 | ||
279 | Asynchronous writing. Writing the buffer contents to the tape is | |
280 | started and the write call returns immediately. The status is checked | |
281 | at the next tape operation. Asynchronous writes are not done with | |
282 | direct i/o and not in fixed block mode. | |
283 | ||
284 | Buffered writes and asynchronous writes may in some rare cases cause | |
285 | problems in multivolume operations if there is not enough space on the | |
286 | tape after the early-warning mark to flush the driver buffer. | |
287 | ||
288 | Read ahead for fixed block mode (ST_READ_AHEAD). Filling the buffer is | |
289 | attempted even if the user does not want to get all of the data at | |
290 | this read command. Should be disabled for those drives that don't like | |
291 | a filemark to truncate a read request or that don't like backspacing. | |
292 | ||
293 | Scatter/gather buffers (buffers that consist of chunks non-contiguous | |
294 | in the physical memory) are used if contiguous buffers can't be | |
295 | allocated. To support all SCSI adapters (including those not | |
296 | supporting scatter/gather), buffer allocation is using the following | |
297 | three kinds of chunks: | |
bf65c846 | 298 | |
1da177e4 | 299 | 1. The initial segment that is used for all SCSI adapters including |
bf65c846 MCC |
300 | those not supporting scatter/gather. The size of this buffer will be |
301 | (PAGE_SIZE << ST_FIRST_ORDER) bytes if the system can give a chunk of | |
302 | this size (and it is not larger than the buffer size specified by | |
303 | ST_BUFFER_BLOCKS). If this size is not available, the driver halves | |
304 | the size and tries again until the size of one page. The default | |
305 | settings in st_options.h make the driver to try to allocate all of the | |
306 | buffer as one chunk. | |
1da177e4 | 307 | 2. The scatter/gather segments to fill the specified buffer size are |
bf65c846 MCC |
308 | allocated so that as many segments as possible are used but the number |
309 | of segments does not exceed ST_FIRST_SG. | |
1da177e4 | 310 | 3. The remaining segments between ST_MAX_SG (or the module parameter |
bf65c846 MCC |
311 | max_sg_segs) and the number of segments used in phases 1 and 2 |
312 | are used to extend the buffer at run-time if this is necessary. The | |
313 | number of scatter/gather segments allowed for the SCSI adapter is not | |
314 | exceeded if it is smaller than the maximum number of scatter/gather | |
315 | segments specified. If the maximum number allowed for the SCSI adapter | |
316 | is smaller than the number of segments used in phases 1 and 2, | |
317 | extending the buffer will always fail. | |
1da177e4 LT |
318 | |
319 | ||
bf65c846 MCC |
320 | EOM Behaviour When Writing |
321 | ========================== | |
1da177e4 LT |
322 | |
323 | When the end of medium early warning is encountered, the current write | |
324 | is finished and the number of bytes is returned. The next write | |
325 | returns -1 and errno is set to ENOSPC. To enable writing a trailer, | |
326 | the next write is allowed to proceed and, if successful, the number of | |
327 | bytes is returned. After this, -1 and the number of bytes are | |
328 | alternately returned until the physical end of medium (or some other | |
329 | error) is encountered. | |
330 | ||
bf65c846 MCC |
331 | Module Parameters |
332 | ================= | |
1da177e4 LT |
333 | |
334 | The buffer size, write threshold, and the maximum number of allocated buffers | |
335 | are configurable when the driver is loaded as a module. The keywords are: | |
336 | ||
bf65c846 | 337 | ========================== =========================================== |
1da177e4 LT |
338 | buffer_kbs=xxx the buffer size for fixed block mode is set |
339 | to xxx kilobytes | |
340 | write_threshold_kbs=xxx the write threshold in kilobytes set to xxx | |
341 | max_sg_segs=xxx the maximum number of scatter/gather | |
342 | segments | |
343 | try_direct_io=x try direct transfer between user buffer and | |
344 | tape drive if this is non-zero | |
bf65c846 | 345 | ========================== =========================================== |
1da177e4 LT |
346 | |
347 | Note that if the buffer size is changed but the write threshold is not | |
348 | set, the write threshold is set to the new buffer size - 2 kB. | |
349 | ||
350 | ||
bf65c846 MCC |
351 | Boot Time Configuration |
352 | ======================= | |
1da177e4 LT |
353 | |
354 | If the driver is compiled into the kernel, the same parameters can be | |
355 | also set using, e.g., the LILO command line. The preferred syntax is | |
670e9f34 | 356 | to use the same keyword used when loading as module but prepended |
1da177e4 LT |
357 | with 'st.'. For instance, to set the maximum number of scatter/gather |
358 | segments, the parameter 'st.max_sg_segs=xx' should be used (xx is the | |
359 | number of scatter/gather segments). | |
360 | ||
361 | For compatibility, the old syntax from early 2.5 and 2.4 kernel | |
362 | versions is supported. The same keywords can be used as when loading | |
363 | the driver as module. If several parameters are set, the keyword-value | |
364 | pairs are separated with a comma (no spaces allowed). A colon can be | |
365 | used instead of the equal mark. The definition is prepended by the | |
bf65c846 | 366 | string st=. Here is an example:: |
1da177e4 | 367 | |
fa00e7e1 | 368 | st=buffer_kbs:64,write_threshold_kbs:60 |
1da177e4 | 369 | |
bf65c846 | 370 | The following syntax used by the old kernel versions is also supported:: |
1da177e4 LT |
371 | |
372 | st=aa[,bb[,dd]] | |
373 | ||
bf65c846 | 374 | where: |
1da177e4 | 375 | |
bf65c846 MCC |
376 | - aa is the buffer size for fixed block mode in 1024 byte units |
377 | - bb is the write threshold in 1024 byte units | |
378 | - dd is the maximum number of scatter/gather segments | |
1da177e4 | 379 | |
bf65c846 MCC |
380 | |
381 | IOCTLs | |
382 | ====== | |
1da177e4 LT |
383 | |
384 | The tape is positioned and the drive parameters are set with ioctls | |
385 | defined in mtio.h The tape control program 'mt' uses these ioctls. Try | |
386 | to find an mt that supports all of the Linux SCSI tape ioctls and | |
387 | opens the device for writing if the tape contents will be modified | |
388 | (look for a package mt-st* from the Linux ftp sites; the GNU mt does | |
389 | not open for writing for, e.g., erase). | |
390 | ||
391 | The supported ioctls are: | |
392 | ||
393 | The following use the structure mtop: | |
394 | ||
bf65c846 MCC |
395 | MTFSF |
396 | Space forward over count filemarks. Tape positioned after filemark. | |
397 | MTFSFM | |
398 | As above but tape positioned before filemark. | |
399 | MTBSF | |
400 | Space backward over count filemarks. Tape positioned before | |
1da177e4 | 401 | filemark. |
bf65c846 MCC |
402 | MTBSFM |
403 | As above but ape positioned after filemark. | |
404 | MTFSR | |
405 | Space forward over count records. | |
406 | MTBSR | |
407 | Space backward over count records. | |
408 | MTFSS | |
409 | Space forward over count setmarks. | |
410 | MTBSS | |
411 | Space backward over count setmarks. | |
412 | MTWEOF | |
413 | Write count filemarks. | |
414 | MTWEOFI | |
415 | Write count filemarks with immediate bit set (i.e., does not | |
3e51d3c9 | 416 | wait until data is on tape) |
bf65c846 MCC |
417 | MTWSM |
418 | Write count setmarks. | |
419 | MTREW | |
420 | Rewind tape. | |
421 | MTOFFL | |
422 | Set device off line (often rewind plus eject). | |
423 | MTNOP | |
424 | Do nothing except flush the buffers. | |
425 | MTRETEN | |
426 | Re-tension tape. | |
427 | MTEOM | |
428 | Space to end of recorded data. | |
429 | MTERASE | |
430 | Erase tape. If the argument is zero, the short erase command | |
1da177e4 LT |
431 | is used. The long erase command is used with all other values |
432 | of the argument. | |
bf65c846 MCC |
433 | MTSEEK |
434 | Seek to tape block count. Uses Tandberg-compatible seek (QFA) | |
1da177e4 LT |
435 | for SCSI-1 drives and SCSI-2 seek for SCSI-2 drives. The file and |
436 | block numbers in the status are not valid after a seek. | |
bf65c846 MCC |
437 | MTSETBLK |
438 | Set the drive block size. Setting to zero sets the drive into | |
1da177e4 | 439 | variable block mode (if applicable). |
bf65c846 MCC |
440 | MTSETDENSITY |
441 | Sets the drive density code to arg. See drive | |
1da177e4 | 442 | documentation for available codes. |
bf65c846 MCC |
443 | MTLOCK and MTUNLOCK |
444 | Explicitly lock/unlock the tape drive door. | |
445 | MTLOAD and MTUNLOAD | |
446 | Explicitly load and unload the tape. If the | |
1da177e4 LT |
447 | command argument x is between MT_ST_HPLOADER_OFFSET + 1 and |
448 | MT_ST_HPLOADER_OFFSET + 6, the number x is used sent to the | |
449 | drive with the command and it selects the tape slot to use of | |
450 | HP C1553A changer. | |
bf65c846 MCC |
451 | MTCOMPRESSION |
452 | Sets compressing or uncompressing drive mode using the | |
1da177e4 LT |
453 | SCSI mode page 15. Note that some drives other methods for |
454 | control of compression. Some drives (like the Exabytes) use | |
455 | density codes for compression control. Some drives use another | |
456 | mode page but this page has not been implemented in the | |
457 | driver. Some drives without compression capability will accept | |
458 | any compression mode without error. | |
bf65c846 MCC |
459 | MTSETPART |
460 | Moves the tape to the partition given by the argument at the | |
1da177e4 LT |
461 | next tape operation. The block at which the tape is positioned |
462 | is the block where the tape was previously positioned in the | |
463 | new active partition unless the next tape operation is | |
464 | MTSEEK. In this case the tape is moved directly to the block | |
465 | specified by MTSEEK. MTSETPART is inactive unless | |
466 | MT_ST_CAN_PARTITIONS set. | |
bf65c846 MCC |
467 | MTMKPART |
468 | Formats the tape with one partition (argument zero) or two | |
8038e645 KM |
469 | partitions (argument non-zero). If the argument is positive, |
470 | it specifies the size of partition 1 in megabytes. For DDS | |
471 | drives and several early drives this is the physically first | |
472 | partition of the tape. If the argument is negative, its absolute | |
473 | value specifies the size of partition 0 in megabytes. This is | |
474 | the physically first partition of many later drives, like the | |
475 | LTO drives from LTO-5 upwards. The drive has to support partitions | |
476 | with size specified by the initiator. Inactive unless | |
477 | MT_ST_CAN_PARTITIONS set. | |
1da177e4 LT |
478 | MTSETDRVBUFFER |
479 | Is used for several purposes. The command is obtained from count | |
480 | with mask MT_SET_OPTIONS, the low order bits are used as argument. | |
481 | This command is only allowed for the superuser (root). The | |
482 | subcommands are: | |
bf65c846 MCC |
483 | |
484 | * 0 | |
1da177e4 LT |
485 | The drive buffer option is set to the argument. Zero means |
486 | no buffering. | |
bf65c846 | 487 | * MT_ST_BOOLEANS |
1da177e4 LT |
488 | Sets the buffering options. The bits are the new states |
489 | (enabled/disabled) the following options (in the | |
490 | parenthesis is specified whether the option is global or | |
491 | can be specified differently for each mode): | |
bf65c846 MCC |
492 | |
493 | MT_ST_BUFFER_WRITES | |
494 | write buffering (mode) | |
495 | MT_ST_ASYNC_WRITES | |
496 | asynchronous writes (mode) | |
497 | MT_ST_READ_AHEAD | |
498 | read ahead (mode) | |
499 | MT_ST_TWO_FM | |
500 | writing of two filemarks (global) | |
501 | MT_ST_FAST_EOM | |
502 | using the SCSI spacing to EOD (global) | |
503 | MT_ST_AUTO_LOCK | |
504 | automatic locking of the drive door (global) | |
505 | MT_ST_DEF_WRITES | |
506 | the defaults are meant only for writes (mode) | |
507 | MT_ST_CAN_BSR | |
508 | backspacing over more than one records can | |
1da177e4 | 509 | be used for repositioning the tape (global) |
bf65c846 MCC |
510 | MT_ST_NO_BLKLIMS |
511 | the driver does not ask the block limits | |
1da177e4 LT |
512 | from the drive (block size can be changed only to |
513 | variable) (global) | |
bf65c846 MCC |
514 | MT_ST_CAN_PARTITIONS |
515 | enables support for partitioned | |
1da177e4 | 516 | tapes (global) |
bf65c846 MCC |
517 | MT_ST_SCSI2LOGICAL |
518 | the logical block number is used in | |
1da177e4 LT |
519 | the MTSEEK and MTIOCPOS for SCSI-2 drives instead of |
520 | the device dependent address. It is recommended to set | |
521 | this flag unless there are tapes using the device | |
522 | dependent (from the old times) (global) | |
bf65c846 MCC |
523 | MT_ST_SYSV |
524 | sets the SYSV semantics (mode) | |
525 | MT_ST_NOWAIT | |
526 | enables immediate mode (i.e., don't wait for | |
1da177e4 | 527 | the command to finish) for some commands (e.g., rewind) |
bf65c846 MCC |
528 | MT_ST_NOWAIT_EOF |
529 | enables immediate filemark mode (i.e. when | |
c743e44f LD |
530 | writing a filemark, don't wait for it to complete). Please |
531 | see the BASICS note about MTWEOFI with respect to the | |
532 | possible dangers of writing immediate filemarks. | |
bf65c846 MCC |
533 | MT_ST_SILI |
534 | enables setting the SILI bit in SCSI commands when | |
40f6b36c KM |
535 | reading in variable block mode to enhance performance when |
536 | reading blocks shorter than the byte count; set this only | |
537 | if you are sure that the drive supports SILI and the HBA | |
538 | correctly returns transfer residuals | |
bf65c846 MCC |
539 | MT_ST_DEBUGGING |
540 | debugging (global; debugging must be | |
1da177e4 | 541 | compiled into the driver) |
bf65c846 MCC |
542 | |
543 | * MT_ST_SETBOOLEANS, MT_ST_CLEARBOOLEANS | |
1da177e4 | 544 | Sets or clears the option bits. |
bf65c846 | 545 | * MT_ST_WRITE_THRESHOLD |
1da177e4 LT |
546 | Sets the write threshold for this device to kilobytes |
547 | specified by the lowest bits. | |
bf65c846 | 548 | * MT_ST_DEF_BLKSIZE |
1da177e4 LT |
549 | Defines the default block size set automatically. Value |
550 | 0xffffff means that the default is not used any more. | |
bf65c846 | 551 | * MT_ST_DEF_DENSITY, MT_ST_DEF_DRVBUFFER |
1da177e4 LT |
552 | Used to set or clear the density (8 bits), and drive buffer |
553 | state (3 bits). If the value is MT_ST_CLEAR_DEFAULT | |
554 | (0xfffff) the default will not be used any more. Otherwise | |
555 | the lowermost bits of the value contain the new value of | |
556 | the parameter. | |
bf65c846 | 557 | * MT_ST_DEF_COMPRESSION |
1da177e4 LT |
558 | The compression default will not be used if the value of |
559 | the lowermost byte is 0xff. Otherwise the lowermost bit | |
560 | contains the new default. If the bits 8-15 are set to a | |
561 | non-zero number, and this number is not 0xff, the number is | |
562 | used as the compression algorithm. The value | |
563 | MT_ST_CLEAR_DEFAULT can be used to clear the compression | |
564 | default. | |
bf65c846 | 565 | * MT_ST_SET_TIMEOUT |
1da177e4 LT |
566 | Set the normal timeout in seconds for this device. The |
567 | default is 900 seconds (15 minutes). The timeout should be | |
568 | long enough for the retries done by the device while | |
569 | reading/writing. | |
bf65c846 | 570 | * MT_ST_SET_LONG_TIMEOUT |
1da177e4 LT |
571 | Set the long timeout that is used for operations that are |
572 | known to take a long time. The default is 14000 seconds | |
573 | (3.9 hours). For erase this value is further multiplied by | |
574 | eight. | |
bf65c846 | 575 | * MT_ST_SET_CLN |
1da177e4 LT |
576 | Set the cleaning request interpretation parameters using |
577 | the lowest 24 bits of the argument. The driver can set the | |
578 | generic status bit GMT_CLN if a cleaning request bit pattern | |
579 | is found from the extended sense data. Many drives set one or | |
580 | more bits in the extended sense data when the drive needs | |
581 | cleaning. The bits are device-dependent. The driver is | |
582 | given the number of the sense data byte (the lowest eight | |
583 | bits of the argument; must be >= 18 (values 1 - 17 | |
bf65c846 | 584 | reserved) and <= the maximum requested sense data sixe), |
1da177e4 LT |
585 | a mask to select the relevant bits (the bits 9-16), and the |
586 | bit pattern (bits 17-23). If the bit pattern is zero, one | |
587 | or more bits under the mask indicate cleaning request. If | |
588 | the pattern is non-zero, the pattern must match the masked | |
589 | sense data byte. | |
590 | ||
591 | (The cleaning bit is set if the additional sense code and | |
592 | qualifier 00h 17h are seen regardless of the setting of | |
593 | MT_ST_SET_CLN.) | |
594 | ||
595 | The following ioctl uses the structure mtpos: | |
bf65c846 MCC |
596 | |
597 | MTIOCPOS | |
598 | Reads the current position from the drive. Uses | |
1da177e4 LT |
599 | Tandberg-compatible QFA for SCSI-1 drives and the SCSI-2 |
600 | command for the SCSI-2 drives. | |
601 | ||
602 | The following ioctl uses the structure mtget to return the status: | |
bf65c846 MCC |
603 | |
604 | MTIOCGET | |
605 | Returns some status information. | |
1da177e4 LT |
606 | The file number and block number within file are returned. The |
607 | block is -1 when it can't be determined (e.g., after MTBSF). | |
608 | The drive type is either MTISSCSI1 or MTISSCSI2. | |
609 | The number of recovered errors since the previous status call | |
610 | is stored in the lower word of the field mt_erreg. | |
611 | The current block size and the density code are stored in the field | |
612 | mt_dsreg (shifts for the subfields are MT_ST_BLKSIZE_SHIFT and | |
613 | MT_ST_DENSITY_SHIFT). | |
614 | The GMT_xxx status bits reflect the drive status. GMT_DR_OPEN | |
615 | is set if there is no tape in the drive. GMT_EOD means either | |
616 | end of recorded data or end of tape. GMT_EOT means end of tape. | |
617 | ||
618 | ||
bf65c846 MCC |
619 | Miscellaneous Compile Options |
620 | ============================= | |
1da177e4 LT |
621 | |
622 | The recovered write errors are considered fatal if ST_RECOVERED_WRITE_FATAL | |
623 | is defined. | |
624 | ||
625 | The maximum number of tape devices is determined by the define | |
626 | ST_MAX_TAPES. If more tapes are detected at driver initialization, the | |
627 | maximum is adjusted accordingly. | |
628 | ||
629 | Immediate return from tape positioning SCSI commands can be enabled by | |
630 | defining ST_NOWAIT. If this is defined, the user should take care that | |
631 | the next tape operation is not started before the previous one has | |
632 | finished. The drives and SCSI adapters should handle this condition | |
633 | gracefully, but some drive/adapter combinations are known to hang the | |
634 | SCSI bus in this case. | |
635 | ||
636 | The MTEOM command is by default implemented as spacing over 32767 | |
637 | filemarks. With this method the file number in the status is | |
638 | correct. The user can request using direct spacing to EOD by setting | |
639 | ST_FAST_EOM 1 (or using the MT_ST_OPTIONS ioctl). In this case the file | |
640 | number will be invalid. | |
641 | ||
642 | When using read ahead or buffered writes the position within the file | |
643 | may not be correct after the file is closed (correct position may | |
644 | require backspacing over more than one record). The correct position | |
645 | within file can be obtained if ST_IN_FILE_POS is defined at compile | |
646 | time or the MT_ST_CAN_BSR bit is set for the drive with an ioctl. | |
647 | (The driver always backs over a filemark crossed by read ahead if the | |
648 | user does not request data that far.) | |
649 | ||
650 | ||
bf65c846 MCC |
651 | Debugging Hints |
652 | =============== | |
1da177e4 | 653 | |
2bec708a LO |
654 | Debugging code is now compiled in by default but debugging is turned off |
655 | with the kernel module parameter debug_flag defaulting to 0. Debugging | |
656 | can still be switched on and off with an ioctl. To enable debug at | |
657 | module load time add debug_flag=1 to the module load options, the | |
d9b43a10 SS |
658 | debugging output is not voluminous. Debugging can also be enabled |
659 | and disabled by writing a '0' (disable) or '1' (enable) to the sysfs | |
660 | file /sys/bus/scsi/drivers/st/debug_flag. | |
1da177e4 LT |
661 | |
662 | If the tape seems to hang, I would be very interested to hear where | |
663 | the driver is waiting. With the command 'ps -l' you can see the state | |
664 | of the process using the tape. If the state is D, the process is | |
665 | waiting for something. The field WCHAN tells where the driver is | |
666 | waiting. If you have the current System.map in the correct place (in | |
667 | /boot for the procps I use) or have updated /etc/psdatabase (for kmem | |
668 | ps), ps writes the function name in the WCHAN field. If not, you have | |
669 | to look up the function from System.map. | |
670 | ||
671 | Note also that the timeouts are very long compared to most other | |
672 | drivers. This means that the Linux driver may appear hung although the | |
673 | real reason is that the tape firmware has got confused. |