Documentation/s390/s390dbf.txt

   1 S390 Debug Feature
   2 ==================
   3
   4 files: arch/s390/kernel/debug.c
   5        arch/s390/include/asm/debug.h
   6
   7 Description:
   8 ------------
   9 The goal of this feature is to provide a kernel debug logging API
  10 where log records can be stored efficiently in memory, where each component
  11 (e.g. device drivers) can have one separate debug log.
  12 One purpose of this is to inspect the debug logs after a production system crash
  13 in order to analyze the reason for the crash.
  14 If the system still runs but only a subcomponent which uses dbf fails,
  15 it is possible to look at the debug logs on a live system via the Linux
  16 debugfs filesystem.
  17 The debug feature may also very useful for kernel and driver development.
  18
  19 Design:
  20 -------
  21 Kernel components (e.g. device drivers) can register themselves at the debug
  22 feature with the function call debug_register(). This function initializes a
  23 debug log for the caller. For each debug log exists a number of debug areas
  24 where exactly one is active at one time.  Each debug area consists of contiguous
  25 pages in memory. In the debug areas there are stored debug entries (log records)
  26 which are written by event- and exception-calls.
  27
  28 An event-call writes the specified debug entry to the active debug
  29 area and updates the log pointer for the active area. If the end
  30 of the active debug area is reached, a wrap around is done (ring buffer)
  31 and the next debug entry will be written at the beginning of the active
  32 debug area.
  33
  34 An exception-call writes the specified debug entry to the log and
  35 switches to the next debug area. This is done in order to be sure
  36 that the records which describe the origin of the exception are not
  37 overwritten when a wrap around for the current area occurs.
  38
  39 The debug areas themselves are also ordered in form of a ring buffer.
  40 When an exception is thrown in the last debug area, the following debug
  41 entries are then written again in the very first area.
  42
  43 There are three versions for the event- and exception-calls: One for
  44 logging raw data, one for text and one for numbers.
  45
  46 Each debug entry contains the following data:
  47
  48 - Timestamp
  49 - Cpu-Number of calling task
  50 - Level of debug entry (0...6)
  51 - Return Address to caller
  52 - Flag, if entry is an exception or not
  53
  54 The debug logs can be inspected in a live system through entries in
  55 the debugfs-filesystem. Under the toplevel directory "s390dbf" there is
  56 a directory for each registered component, which is named like the
  57 corresponding component. The debugfs normally should be mounted to
  58 /sys/kernel/debug therefore the debug feature can be accessed under
  59 /sys/kernel/debug/s390dbf.
  60
  61 The content of the directories are files which represent different views
  62 to the debug log. Each component can decide which views should be
  63 used through registering them with the function debug_register_view().
  64 Predefined views for hex/ascii, sprintf and raw binary data are provided.
  65 It is also possible to define other views. The content of
  66 a view can be inspected simply by reading the corresponding debugfs file.
  67
  68 All debug logs have an actual debug level (range from 0 to 6).
  69 The default level is 3. Event and Exception functions have a 'level'
  70 parameter. Only debug entries with a level that is lower or equal
  71 than the actual level are written to the log. This means, when
  72 writing events, high priority log entries should have a low level
  73 value whereas low priority entries should have a high one.
  74 The actual debug level can be changed with the help of the debugfs-filesystem
  75 through writing a number string "x" to the 'level' debugfs file which is
  76 provided for every debug log. Debugging can be switched off completely
  77 by using "-" on the 'level' debugfs file.
  78
  79 Example:
  80
  81 > echo "-" > /sys/kernel/debug/s390dbf/dasd/level
  82
  83 It is also possible to deactivate the debug feature globally for every
  84 debug log. You can change the behavior using  2 sysctl parameters in
  85 /proc/sys/s390dbf:
  86 There are currently 2 possible triggers, which stop the debug feature
  87 globally. The first possibility is to use the "debug_active" sysctl. If
  88 set to 1 the debug feature is running. If "debug_active" is set to 0 the
  89 debug feature is turned off.
  90 The second trigger which stops the debug feature is a kernel oops.
  91 That prevents the debug feature from overwriting debug information that
  92 happened before the oops. After an oops you can reactivate the debug feature
  93 by piping 1 to /proc/sys/s390dbf/debug_active. Nevertheless, its not
  94 suggested to use an oopsed kernel in a production environment.
  95 If you want to disallow the deactivation of the debug feature, you can use
  96 the "debug_stoppable" sysctl. If you set "debug_stoppable" to 0 the debug
  97 feature cannot be stopped. If the debug feature is already stopped, it
  98 will stay deactivated.
  99
 100 Kernel Interfaces:
 101 ------------------
 102
 103 ----------------------------------------------------------------------------
 104 debug_info_t *debug_register(char *name, int pages, int nr_areas,
 105                              int buf_size);
 106
 107 Parameter:    name:        Name of debug log (e.g. used for debugfs entry)
 108               pages:       number of pages, which will be allocated per area
 109               nr_areas:    number of debug areas
 110               buf_size:    size of data area in each debug entry
 111
 112 Return Value: Handle for generated debug area
 113               NULL if register failed
 114
 115 Description:  Allocates memory for a debug log
 116               Must not be called within an interrupt handler
 117
 118 ----------------------------------------------------------------------------
 119 debug_info_t *debug_register_mode(char *name, int pages, int nr_areas,
 120                                   int buf_size, mode_t mode, uid_t uid,
 121                                   gid_t gid);
 122
 123 Parameter:    name:        Name of debug log (e.g. used for debugfs entry)
 124               pages:       Number of pages, which will be allocated per area
 125               nr_areas:    Number of debug areas
 126               buf_size:    Size of data area in each debug entry
 127               mode:        File mode for debugfs files. E.g. S_IRWXUGO
 128               uid:         User ID for debugfs files. Currently only 0 is
 129                            supported.
 130               gid:         Group ID for debugfs files. Currently only 0 is
 131                            supported.
 132
 133 Return Value: Handle for generated debug area
 134               NULL if register failed
 135
 136 Description:  Allocates memory for a debug log
 137               Must not be called within an interrupt handler
 138
 139 ---------------------------------------------------------------------------
 140 void debug_unregister (debug_info_t * id);
 141
 142 Parameter:     id:   handle for debug log
 143
 144 Return Value:  none
 145
 146 Description:   frees memory for a debug log and removes all registered debug
 147                views.
 148                Must not be called within an interrupt handler
 149
 150 ---------------------------------------------------------------------------
 151 void debug_set_level (debug_info_t * id, int new_level);
 152
 153 Parameter:     id:        handle for debug log
 154                new_level: new debug level
 155
 156 Return Value:  none
 157
 158 Description:   Sets new actual debug level if new_level is valid.
 159
 160 ---------------------------------------------------------------------------
 161 void debug_stop_all(void);
 162
 163 Parameter:     none
 164
 165 Return Value:  none
 166
 167 Description:   stops the debug feature if stopping is allowed. Currently
 168                used in case of a kernel oops.
 169
 170 ---------------------------------------------------------------------------
 171 debug_entry_t* debug_event (debug_info_t* id, int level, void* data,
 172                             int length);
 173
 174 Parameter:     id:     handle for debug log
 175                level:  debug level
 176                data:   pointer to data for debug entry
 177                length: length of data in bytes
 178
 179 Return Value:  Address of written debug entry
 180
 181 Description:   writes debug entry to active debug area (if level <= actual
 182                debug level)
 183
 184 ---------------------------------------------------------------------------
 185 debug_entry_t* debug_int_event (debug_info_t * id, int level,
 186                                 unsigned int data);
 187 debug_entry_t* debug_long_event(debug_info_t * id, int level,
 188                                 unsigned long data);
 189
 190 Parameter:     id:     handle for debug log
 191                level:  debug level
 192                data:   integer value for debug entry
 193
 194 Return Value:  Address of written debug entry
 195
 196 Description:   writes debug entry to active debug area (if level <= actual
 197                debug level)
 198
 199 ---------------------------------------------------------------------------
 200 debug_entry_t* debug_text_event (debug_info_t * id, int level,
 201                                  const char* data);
 202
 203 Parameter:     id:     handle for debug log
 204                level:  debug level
 205                data:   string for debug entry
 206
 207 Return Value:  Address of written debug entry
 208
 209 Description:   writes debug entry in ascii format to active debug area
 210                (if level <= actual debug level)
 211
 212 ---------------------------------------------------------------------------
 213 debug_entry_t* debug_sprintf_event (debug_info_t * id, int level,
 214                                     char* string,...);
 215
 216 Parameter:     id:    handle for debug log
 217                level: debug level
 218                string: format string for debug entry
 219                ...: varargs used as in sprintf()
 220
 221 Return Value:  Address of written debug entry
 222
 223 Description:   writes debug entry with format string and varargs (longs) to
 224                active debug area (if level $<=$ actual debug level).
 225                floats and long long datatypes cannot be used as varargs.
 226
 227 ---------------------------------------------------------------------------
 228
 229 debug_entry_t* debug_exception (debug_info_t* id, int level, void* data,
 230                                 int length);
 231
 232 Parameter:     id:     handle for debug log
 233                level:  debug level
 234                data:   pointer to data for debug entry
 235                length: length of data in bytes
 236
 237 Return Value:  Address of written debug entry
 238
 239 Description:   writes debug entry to active debug area (if level <= actual
 240                debug level) and switches to next debug area
 241
 242 ---------------------------------------------------------------------------
 243 debug_entry_t* debug_int_exception (debug_info_t * id, int level,
 244                                     unsigned int data);
 245 debug_entry_t* debug_long_exception(debug_info_t * id, int level,
 246                                     unsigned long data);
 247
 248 Parameter:     id:     handle for debug log
 249                level:  debug level
 250                data:   integer value for debug entry
 251
 252 Return Value:  Address of written debug entry
 253
 254 Description:   writes debug entry to active debug area (if level <= actual
 255                debug level) and switches to next debug area
 256
 257 ---------------------------------------------------------------------------
 258 debug_entry_t* debug_text_exception (debug_info_t * id, int level,
 259                                      const char* data);
 260
 261 Parameter:     id:     handle for debug log
 262                level:  debug level
 263                data:   string for debug entry
 264
 265 Return Value:  Address of written debug entry
 266
 267 Description:   writes debug entry in ascii format to active debug area
 268                (if level <= actual debug level) and switches to next debug
 269                area
 270
 271 ---------------------------------------------------------------------------
 272 debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
 273                                         char* string,...);
 274
 275 Parameter:     id:    handle for debug log
 276                level: debug level
 277                string: format string for debug entry
 278                ...: varargs used as in sprintf()
 279
 280 Return Value:  Address of written debug entry
 281
 282 Description:   writes debug entry with format string and varargs (longs) to
 283                active debug area (if level $<=$ actual debug level) and
 284                switches to next debug area.
 285                floats and long long datatypes cannot be used as varargs.
 286
 287 ---------------------------------------------------------------------------
 288
 289 int debug_register_view (debug_info_t * id, struct debug_view *view);
 290
 291 Parameter:     id:    handle for debug log
 292                view:  pointer to debug view struct
 293
 294 Return Value:  0  : ok
 295                < 0: Error
 296
 297 Description:   registers new debug view and creates debugfs dir entry
 298
 299 ---------------------------------------------------------------------------
 300 int debug_unregister_view (debug_info_t * id, struct debug_view *view);
 301
 302 Parameter:     id:    handle for debug log
 303                view:  pointer to debug view struct
 304
 305 Return Value:  0  : ok
 306                < 0: Error
 307
 308 Description:   unregisters debug view and removes debugfs dir entry
 309
 310
 311
 312 Predefined views:
 313 -----------------
 314
 315 extern struct debug_view debug_hex_ascii_view;
 316 extern struct debug_view debug_raw_view;
 317 extern struct debug_view debug_sprintf_view;
 318
 319 Examples
 320 --------
 321
 322 /*
 323  * hex_ascii- + raw-view Example
 324  */
 325
 326 #include <linux/init.h>
 327 #include <asm/debug.h>
 328
 329 static debug_info_t* debug_info;
 330
 331 static int init(void)
 332 {
 333     /* register 4 debug areas with one page each and 4 byte data field */
 334
 335     debug_info = debug_register ("test", 1, 4, 4 );
 336     debug_register_view(debug_info,&debug_hex_ascii_view);
 337     debug_register_view(debug_info,&debug_raw_view);
 338
 339     debug_text_event(debug_info, 4 , "one ");
 340     debug_int_exception(debug_info, 4, 4711);
 341     debug_event(debug_info, 3, &debug_info, 4);
 342
 343     return 0;
 344 }
 345
 346 static void cleanup(void)
 347 {
 348     debug_unregister (debug_info);
 349 }
 350
 351 module_init(init);
 352 module_exit(cleanup);
 353
 354 ---------------------------------------------------------------------------
 355
 356 /*
 357  * sprintf-view Example
 358  */
 359
 360 #include <linux/init.h>
 361 #include <asm/debug.h>
 362
 363 static debug_info_t* debug_info;
 364
 365 static int init(void)
 366 {
 367     /* register 4 debug areas with one page each and data field for */
 368     /* format string pointer + 2 varargs (= 3 * sizeof(long))       */
 369
 370     debug_info = debug_register ("test", 1, 4, sizeof(long) * 3);
 371     debug_register_view(debug_info,&debug_sprintf_view);
 372
 373     debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
 374     debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);
 375
 376     return 0;
 377 }
 378
 379 static void cleanup(void)
 380 {
 381     debug_unregister (debug_info);
 382 }
 383
 384 module_init(init);
 385 module_exit(cleanup);
 386
 387
 388
 389 Debugfs Interface
 390 ----------------
 391 Views to the debug logs can be investigated through reading the corresponding
 392 debugfs-files:
 393
 394 Example:
 395
 396 > ls /sys/kernel/debug/s390dbf/dasd
 397 flush  hex_ascii  level pages raw
 398 > cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1
 399 00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
 400 00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
 401 00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
 402 00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP
 403 01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
 404 01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
 405 01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ...
 406 01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
 407 01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
 408 01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....
 409
 410 See section about predefined views for explanation of the above output!
 411
 412 Changing the debug level
 413 ------------------------
 414
 415 Example:
 416
 417
 418 > cat /sys/kernel/debug/s390dbf/dasd/level
 419 3
 420 > echo "5" > /sys/kernel/debug/s390dbf/dasd/level
 421 > cat /sys/kernel/debug/s390dbf/dasd/level
 422 5
 423
 424 Flushing debug areas
 425 --------------------
 426 Debug areas can be flushed with piping the number of the desired
 427 area (0...n) to the debugfs file "flush". When using "-" all debug areas
 428 are flushed.
 429
 430 Examples:
 431
 432 1. Flush debug area 0:
 433 > echo "0" > /sys/kernel/debug/s390dbf/dasd/flush
 434
 435 2. Flush all debug areas:
 436 > echo "-" > /sys/kernel/debug/s390dbf/dasd/flush
 437
 438 Changing the size of debug areas
 439 ------------------------------------
 440 It is possible the change the size of debug areas through piping
 441 the number of pages to the debugfs file "pages". The resize request will
 442 also flush the debug areas.
 443
 444 Example:
 445
 446 Define 4 pages for the debug areas of debug feature "dasd":
 447 > echo "4" > /sys/kernel/debug/s390dbf/dasd/pages
 448
 449 Stooping the debug feature
 450 --------------------------
 451 Example:
 452
 453 1. Check if stopping is allowed
 454 > cat /proc/sys/s390dbf/debug_stoppable
 455 2. Stop debug feature
 456 > echo 0 > /proc/sys/s390dbf/debug_active
 457
 458 lcrash Interface
 459 ----------------
 460 It is planned that the dump analysis tool lcrash gets an additional command
 461 's390dbf' to display all the debug logs. With this tool it will be possible
 462 to investigate the debug logs on a live system and with a memory dump after
 463 a system crash.
 464
 465 Investigating raw memory
 466 ------------------------
 467 One last possibility to investigate the debug logs at a live
 468 system and after a system crash is to look at the raw memory
 469 under VM or at the Service Element.
 470 It is possible to find the anker of the debug-logs through
 471 the 'debug_area_first' symbol in the System map. Then one has
 472 to follow the correct pointers of the data-structures defined
 473 in debug.h and find the debug-areas in memory.
 474 Normally modules which use the debug feature will also have
 475 a global variable with the pointer to the debug-logs. Following
 476 this pointer it will also be possible to find the debug logs in
 477 memory.
 478
 479 For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
 480 for the length of the data field in debug_register() in
 481 order to see the debug entries well formatted.
 482
 483
 484 Predefined Views
 485 ----------------
 486
 487 There are three predefined views: hex_ascii, raw and sprintf.
 488 The hex_ascii view shows the data field in hex and ascii representation
 489 (e.g. '45 43 4b 44 | ECKD').
 490 The raw view returns a bytestream as the debug areas are stored in memory.
 491
 492 The sprintf view formats the debug entries in the same way as the sprintf
 493 function would do. The sprintf event/exception functions write to the
 494 debug entry a pointer to the format string (size = sizeof(long))
 495 and for each vararg a long value. So e.g. for a debug entry with a format
 496 string plus two varargs one would need to allocate a (3 * sizeof(long))
 497 byte data area in the debug_register() function.
 498
 499 IMPORTANT: Using "%s" in sprintf event functions is dangerous. You can only
 500 use "%s" in the sprintf event functions, if the memory for the passed string is
 501 available as long as the debug feature exists. The reason behind this is that
 502 due to performance considerations only a pointer to the string is stored in
 503 the debug feature. If you log a string that is freed afterwards, you will get
 504 an OOPS when inspecting the debug feature, because then the debug feature will
 505 access the already freed memory.
 506
 507 NOTE: If using the sprintf view do NOT use other event/exception functions
 508 than the sprintf-event and -exception functions.
 509
 510 The format of the hex_ascii and sprintf view is as follows:
 511 - Number of area
 512 - Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated
 513   Universal Time (UTC), January 1, 1970)
 514 - level of debug entry
 515 - Exception flag (* = Exception)
 516 - Cpu-Number of calling task
 517 - Return Address to caller
 518 - data field
 519
 520 The format of the raw view is:
 521 - Header as described in debug.h
 522 - datafield
 523
 524 A typical line of the hex_ascii view will look like the following (first line
 525 is only for explanation and will not be displayed when 'cating' the view):
 526
 527 area  time           level exception cpu caller    data (hex + ascii)
 528 --------------------------------------------------------------------------
 529 00    00964419409:440690 1 -         00  88023fe
 530
 531
 532 Defining views
 533 --------------
 534
 535 Views are specified with the 'debug_view' structure. There are defined
 536 callback functions which are used for reading and writing the debugfs files:
 537
 538 struct debug_view {
 539         char name[DEBUG_MAX_PROCF_LEN];
 540         debug_prolog_proc_t* prolog_proc;
 541         debug_header_proc_t* header_proc;
 542         debug_format_proc_t* format_proc;
 543         debug_input_proc_t*  input_proc;
 544         void*                private_data;
 545 };
 546
 547 where
 548
 549 typedef int (debug_header_proc_t) (debug_info_t* id,
 550                                    struct debug_view* view,
 551                                    int area,
 552                                    debug_entry_t* entry,
 553                                    char* out_buf);
 554
 555 typedef int (debug_format_proc_t) (debug_info_t* id,
 556                                    struct debug_view* view, char* out_buf,
 557                                    const char* in_buf);
 558 typedef int (debug_prolog_proc_t) (debug_info_t* id,
 559                                    struct debug_view* view,
 560                                    char* out_buf);
 561 typedef int (debug_input_proc_t) (debug_info_t* id,
 562                                   struct debug_view* view,
 563                                   struct file* file, const char* user_buf,
 564                                   size_t in_buf_size, loff_t* offset);
 565
 566
 567 The "private_data" member can be used as pointer to view specific data.
 568 It is not used by the debug feature itself.
 569
 570 The output when reading a debugfs file is structured like this:
 571
 572 "prolog_proc output"
 573
 574 "header_proc output 1"  "format_proc output 1"
 575 "header_proc output 2"  "format_proc output 2"
 576 "header_proc output 3"  "format_proc output 3"
 577 ...
 578
 579 When a view is read from the debugfs, the Debug Feature calls the
 580 'prolog_proc' once for writing the prolog.
 581 Then 'header_proc' and 'format_proc' are called for each
 582 existing debug entry.
 583
 584 The input_proc can be used to implement functionality when it is written to
 585 the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).
 586
 587 For header_proc there can be used the default function
 588 debug_dflt_header_fn() which is defined in debug.h.
 589 and which produces the same header output as the predefined views.
 590 E.g:
 591 00 00964419409:440761 2 - 00 88023ec
 592
 593 In order to see how to use the callback functions check the implementation
 594 of the default views!
 595
 596 Example
 597
 598 #include <asm/debug.h>
 599
 600 #define UNKNOWNSTR "data: %08x"
 601
 602 const char* messages[] =
 603 {"This error...........\n",
 604  "That error...........\n",
 605  "Problem..............\n",
 606  "Something went wrong.\n",
 607  "Everything ok........\n",
 608  NULL
 609 };
 610
 611 static int debug_test_format_fn(
 612    debug_info_t * id, struct debug_view *view,
 613    char *out_buf, const char *in_buf
 614 )
 615 {
 616   int i, rc = 0;
 617
 618   if(id->buf_size >= 4) {
 619      int msg_nr = *((int*)in_buf);
 620      if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
 621         rc += sprintf(out_buf, "%s", messages[msg_nr]);
 622      else
 623         rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
 624   }
 625  out:
 626    return rc;
 627 }
 628
 629 struct debug_view debug_test_view = {
 630   "myview",                 /* name of view */
 631   NULL,                     /* no prolog */
 632   &debug_dflt_header_fn,    /* default header for each entry */
 633   &debug_test_format_fn,    /* our own format function */
 634   NULL,                     /* no input function */
 635   NULL                      /* no private data */
 636 };
 637
 638 =====
 639 test:
 640 =====
 641 debug_info_t *debug_info;
 642 ...
 643 debug_info = debug_register ("test", 0, 4, 4 ));
 644 debug_register_view(debug_info, &debug_test_view);
 645 for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);
 646
 647 > cat /sys/kernel/debug/s390dbf/test/myview
 648 00 00964419734:611402 1 - 00 88042ca   This error...........
 649 00 00964419734:611405 1 - 00 88042ca   That error...........
 650 00 00964419734:611408 1 - 00 88042ca   Problem..............
 651 00 00964419734:611411 1 - 00 88042ca   Something went wrong.
 652 00 00964419734:611414 1 - 00 88042ca   Everything ok........
 653 00 00964419734:611417 1 - 00 88042ca   data: 00000005
 654 00 00964419734:611419 1 - 00 88042ca   data: 00000006
 655 00 00964419734:611422 1 - 00 88042ca   data: 00000007
 656 00 00964419734:611425 1 - 00 88042ca   data: 00000008
 657 00 00964419734:611428 1 - 00 88042ca   data: 00000009