Documentation/s390/s390dbf.txt

   1 S390 Debug Feature
   2 ==================
   3
   4 files: arch/s390/kernel/debug.c
   5        include/asm-s390/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 itselve 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 unter
  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 an 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 an 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 void debug_unregister (debug_info_t * id);
 120
 121 Parameter:     id:   handle for debug log
 122
 123 Return Value:  none
 124
 125 Description:   frees memory for a debug log
 126                Must not be called within an interrupt handler
 127
 128 ---------------------------------------------------------------------------
 129 void debug_set_level (debug_info_t * id, int new_level);
 130
 131 Parameter:     id:        handle for debug log
 132                new_level: new debug level
 133
 134 Return Value:  none
 135
 136 Description:   Sets new actual debug level if new_level is valid.
 137
 138 ---------------------------------------------------------------------------
 139 void debug_stop_all(void);
 140
 141 Parameter:     none
 142
 143 Return Value:  none
 144
 145 Description:   stops the debug feature if stopping is allowed. Currently
 146                used in case of a kernel oops.
 147
 148 ---------------------------------------------------------------------------
 149 debug_entry_t* debug_event (debug_info_t* id, int level, void* data,
 150                             int length);
 151
 152 Parameter:     id:     handle for debug log
 153                level:  debug level
 154                data:   pointer to data for debug entry
 155                length: length of data in bytes
 156
 157 Return Value:  Address of written debug entry
 158
 159 Description:   writes debug entry to active debug area (if level <= actual
 160                debug level)
 161
 162 ---------------------------------------------------------------------------
 163 debug_entry_t* debug_int_event (debug_info_t * id, int level,
 164                                 unsigned int data);
 165 debug_entry_t* debug_long_event(debug_info_t * id, int level,
 166                                 unsigned long data);
 167
 168 Parameter:     id:     handle for debug log
 169                level:  debug level
 170                data:   integer value for debug entry
 171
 172 Return Value:  Address of written debug entry
 173
 174 Description:   writes debug entry to active debug area (if level <= actual
 175                debug level)
 176
 177 ---------------------------------------------------------------------------
 178 debug_entry_t* debug_text_event (debug_info_t * id, int level,
 179                                  const char* data);
 180
 181 Parameter:     id:     handle for debug log
 182                level:  debug level
 183                data:   string for debug entry
 184
 185 Return Value:  Address of written debug entry
 186
 187 Description:   writes debug entry in ascii format to active debug area
 188                (if level <= actual debug level)
 189
 190 ---------------------------------------------------------------------------
 191 debug_entry_t* debug_sprintf_event (debug_info_t * id, int level,
 192                                     char* string,...);
 193
 194 Parameter:     id:    handle for debug log
 195                level: debug level
 196                string: format string for debug entry
 197                ...: varargs used as in sprintf()
 198
 199 Return Value:  Address of written debug entry
 200
 201 Description:   writes debug entry with format string and varargs (longs) to
 202                active debug area (if level $<=$ actual debug level).
 203                floats and long long datatypes cannot be used as varargs.
 204
 205 ---------------------------------------------------------------------------
 206
 207 debug_entry_t* debug_exception (debug_info_t* id, int level, void* data,
 208                                 int length);
 209
 210 Parameter:     id:     handle for debug log
 211                level:  debug level
 212                data:   pointer to data for debug entry
 213                length: length of data in bytes
 214
 215 Return Value:  Address of written debug entry
 216
 217 Description:   writes debug entry to active debug area (if level <= actual
 218                debug level) and switches to next debug area
 219
 220 ---------------------------------------------------------------------------
 221 debug_entry_t* debug_int_exception (debug_info_t * id, int level,
 222                                     unsigned int data);
 223 debug_entry_t* debug_long_exception(debug_info_t * id, int level,
 224                                     unsigned long data);
 225
 226 Parameter:     id:     handle for debug log
 227                level:  debug level
 228                data:   integer value for debug entry
 229
 230 Return Value:  Address of written debug entry
 231
 232 Description:   writes debug entry to active debug area (if level <= actual
 233                debug level) and switches to next debug area
 234
 235 ---------------------------------------------------------------------------
 236 debug_entry_t* debug_text_exception (debug_info_t * id, int level,
 237                                      const char* data);
 238
 239 Parameter:     id:     handle for debug log
 240                level:  debug level
 241                data:   string for debug entry
 242
 243 Return Value:  Address of written debug entry
 244
 245 Description:   writes debug entry in ascii format to active debug area
 246                (if level <= actual debug level) and switches to next debug
 247                area
 248
 249 ---------------------------------------------------------------------------
 250 debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
 251                                         char* string,...);
 252
 253 Parameter:     id:    handle for debug log
 254                level: debug level
 255                string: format string for debug entry
 256                ...: varargs used as in sprintf()
 257
 258 Return Value:  Address of written debug entry
 259
 260 Description:   writes debug entry with format string and varargs (longs) to
 261                active debug area (if level $<=$ actual debug level) and
 262                switches to next debug area.
 263                floats and long long datatypes cannot be used as varargs.
 264
 265 ---------------------------------------------------------------------------
 266
 267 int debug_register_view (debug_info_t * id, struct debug_view *view);
 268
 269 Parameter:     id:    handle for debug log
 270                view:  pointer to debug view struct
 271
 272 Return Value:  0  : ok
 273                < 0: Error
 274
 275 Description:   registers new debug view and creates debugfs dir entry
 276
 277 ---------------------------------------------------------------------------
 278 int debug_unregister_view (debug_info_t * id, struct debug_view *view);
 279
 280 Parameter:     id:    handle for debug log
 281                view:  pointer to debug view struct
 282
 283 Return Value:  0  : ok
 284                < 0: Error
 285
 286 Description:   unregisters debug view and removes debugfs dir entry
 287
 288
 289
 290 Predefined views:
 291 -----------------
 292
 293 extern struct debug_view debug_hex_ascii_view;
 294 extern struct debug_view debug_raw_view;
 295 extern struct debug_view debug_sprintf_view;
 296
 297 Examples
 298 --------
 299
 300 /*
 301  * hex_ascii- + raw-view Example
 302  */
 303
 304 #include <linux/init.h>
 305 #include <asm/debug.h>
 306
 307 static debug_info_t* debug_info;
 308
 309 static int init(void)
 310 {
 311     /* register 4 debug areas with one page each and 4 byte data field */
 312
 313     debug_info = debug_register ("test", 1, 4, 4 );
 314     debug_register_view(debug_info,&debug_hex_ascii_view);
 315     debug_register_view(debug_info,&debug_raw_view);
 316
 317     debug_text_event(debug_info, 4 , "one ");
 318     debug_int_exception(debug_info, 4, 4711);
 319     debug_event(debug_info, 3, &debug_info, 4);
 320
 321     return 0;
 322 }
 323
 324 static void cleanup(void)
 325 {
 326     debug_unregister (debug_info);
 327 }
 328
 329 module_init(init);
 330 module_exit(cleanup);
 331
 332 ---------------------------------------------------------------------------
 333
 334 /*
 335  * sprintf-view Example
 336  */
 337
 338 #include <linux/init.h>
 339 #include <asm/debug.h>
 340
 341 static debug_info_t* debug_info;
 342
 343 static int init(void)
 344 {
 345     /* register 4 debug areas with one page each and data field for */
 346     /* format string pointer + 2 varargs (= 3 * sizeof(long))       */
 347
 348     debug_info = debug_register ("test", 1, 4, sizeof(long) * 3);
 349     debug_register_view(debug_info,&debug_sprintf_view);
 350
 351     debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
 352     debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);
 353
 354     return 0;
 355 }
 356
 357 static void cleanup(void)
 358 {
 359     debug_unregister (debug_info);
 360 }
 361
 362 module_init(init);
 363 module_exit(cleanup);
 364
 365
 366
 367 Debugfs Interface
 368 ----------------
 369 Views to the debug logs can be investigated through reading the corresponding
 370 debugfs-files:
 371
 372 Example:
 373
 374 > ls /sys/kernel/debug/s390dbf/dasd
 375 flush  hex_ascii  level pages raw
 376 > cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1
 377 00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
 378 00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
 379 00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
 380 00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP
 381 01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
 382 01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
 383 01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ...
 384 01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
 385 01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
 386 01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....
 387
 388 See section about predefined views for explanation of the above output!
 389
 390 Changing the debug level
 391 ------------------------
 392
 393 Example:
 394
 395
 396 > cat /sys/kernel/debug/s390dbf/dasd/level
 397 3
 398 > echo "5" > /sys/kernel/debug/s390dbf/dasd/level
 399 > cat /sys/kernel/debug/s390dbf/dasd/level
 400 5
 401
 402 Flushing debug areas
 403 --------------------
 404 Debug areas can be flushed with piping the number of the desired
 405 area (0...n) to the debugfs file "flush". When using "-" all debug areas
 406 are flushed.
 407
 408 Examples:
 409
 410 1. Flush debug area 0:
 411 > echo "0" > /sys/kernel/debug/s390dbf/dasd/flush
 412
 413 2. Flush all debug areas:
 414 > echo "-" > /sys/kernel/debug/s390dbf/dasd/flush
 415
 416 Changing the size of debug areas
 417 ------------------------------------
 418 It is possible the change the size of debug areas through piping
 419 the number of pages to the debugfs file "pages". The resize request will
 420 also flush the debug areas.
 421
 422 Example:
 423
 424 Define 4 pages for the debug areas of debug feature "dasd":
 425 > echo "4" > /sys/kernel/debug/s390dbf/dasd/pages
 426
 427 Stooping the debug feature
 428 --------------------------
 429 Example:
 430
 431 1. Check if stopping is allowed
 432 > cat /proc/sys/s390dbf/debug_stoppable
 433 2. Stop debug feature
 434 > echo 0 > /proc/sys/s390dbf/debug_active
 435
 436 lcrash Interface
 437 ----------------
 438 It is planned that the dump analysis tool lcrash gets an additional command
 439 's390dbf' to display all the debug logs. With this tool it will be possible
 440 to investigate the debug logs on a live system and with a memory dump after
 441 a system crash.
 442
 443 Investigating raw memory
 444 ------------------------
 445 One last possibility to investigate the debug logs at a live
 446 system and after a system crash is to look at the raw memory
 447 under VM or at the Service Element.
 448 It is possible to find the anker of the debug-logs through
 449 the 'debug_area_first' symbol in the System map. Then one has
 450 to follow the correct pointers of the data-structures defined
 451 in debug.h and find the debug-areas in memory.
 452 Normally modules which use the debug feature will also have
 453 a global variable with the pointer to the debug-logs. Following
 454 this pointer it will also be possible to find the debug logs in
 455 memory.
 456
 457 For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
 458 for the length of the data field in debug_register() in
 459 order to see the debug entries well formatted.
 460
 461
 462 Predefined Views
 463 ----------------
 464
 465 There are three predefined views: hex_ascii, raw and sprintf.
 466 The hex_ascii view shows the data field in hex and ascii representation
 467 (e.g. '45 43 4b 44 | ECKD').
 468 The raw view returns a bytestream as the debug areas are stored in memory.
 469
 470 The sprintf view formats the debug entries in the same way as the sprintf
 471 function would do. The sprintf event/exception functions write to the
 472 debug entry a pointer to the format string (size = sizeof(long))
 473 and for each vararg a long value. So e.g. for a debug entry with a format
 474 string plus two varargs one would need to allocate a (3 * sizeof(long))
 475 byte data area in the debug_register() function.
 476
 477
 478 NOTE: If using the sprintf view do NOT use other event/exception functions
 479 than the sprintf-event and -exception functions.
 480
 481 The format of the hex_ascii and sprintf view is as follows:
 482 - Number of area
 483 - Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated
 484   Universal Time (UTC), January 1, 1970)
 485 - level of debug entry
 486 - Exception flag (* = Exception)
 487 - Cpu-Number of calling task
 488 - Return Address to caller
 489 - data field
 490
 491 The format of the raw view is:
 492 - Header as described in debug.h
 493 - datafield
 494
 495 A typical line of the hex_ascii view will look like the following (first line
 496 is only for explanation and will not be displayed when 'cating' the view):
 497
 498 area  time           level exception cpu caller    data (hex + ascii)
 499 --------------------------------------------------------------------------
 500 00    00964419409:440690 1 -         00  88023fe
 501
 502
 503 Defining views
 504 --------------
 505
 506 Views are specified with the 'debug_view' structure. There are defined
 507 callback functions which are used for reading and writing the debugfs files:
 508
 509 struct debug_view {
 510         char name[DEBUG_MAX_PROCF_LEN];
 511         debug_prolog_proc_t* prolog_proc;
 512         debug_header_proc_t* header_proc;
 513         debug_format_proc_t* format_proc;
 514         debug_input_proc_t*  input_proc;
 515         void*                private_data;
 516 };
 517
 518 where
 519
 520 typedef int (debug_header_proc_t) (debug_info_t* id,
 521                                    struct debug_view* view,
 522                                    int area,
 523                                    debug_entry_t* entry,
 524                                    char* out_buf);
 525
 526 typedef int (debug_format_proc_t) (debug_info_t* id,
 527                                    struct debug_view* view, char* out_buf,
 528                                    const char* in_buf);
 529 typedef int (debug_prolog_proc_t) (debug_info_t* id,
 530                                    struct debug_view* view,
 531                                    char* out_buf);
 532 typedef int (debug_input_proc_t) (debug_info_t* id,
 533                                   struct debug_view* view,
 534                                   struct file* file, const char* user_buf,
 535                                   size_t in_buf_size, loff_t* offset);
 536
 537
 538 The "private_data" member can be used as pointer to view specific data.
 539 It is not used by the debug feature itself.
 540
 541 The output when reading a debugfs file is structured like this:
 542
 543 "prolog_proc output"
 544
 545 "header_proc output 1"  "format_proc output 1"
 546 "header_proc output 2"  "format_proc output 2"
 547 "header_proc output 3"  "format_proc output 3"
 548 ...
 549
 550 When a view is read from the debugfs, the Debug Feature calls the
 551 'prolog_proc' once for writing the prolog.
 552 Then 'header_proc' and 'format_proc' are called for each
 553 existing debug entry.
 554
 555 The input_proc can be used to implement functionality when it is written to
 556 the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).
 557
 558 For header_proc there can be used the default function
 559 debug_dflt_header_fn() which is defined in debug.h.
 560 and which produces the same header output as the predefined views.
 561 E.g:
 562 00 00964419409:440761 2 - 00 88023ec
 563
 564 In order to see how to use the callback functions check the implementation
 565 of the default views!
 566
 567 Example
 568
 569 #include <asm/debug.h>
 570
 571 #define UNKNOWNSTR "data: %08x"
 572
 573 const char* messages[] =
 574 {"This error...........\n",
 575  "That error...........\n",
 576  "Problem..............\n",
 577  "Something went wrong.\n",
 578  "Everything ok........\n",
 579  NULL
 580 };
 581
 582 static int debug_test_format_fn(
 583    debug_info_t * id, struct debug_view *view,
 584    char *out_buf, const char *in_buf
 585 )
 586 {
 587   int i, rc = 0;
 588
 589   if(id->buf_size >= 4) {
 590      int msg_nr = *((int*)in_buf);
 591      if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
 592         rc += sprintf(out_buf, "%s", messages[msg_nr]);
 593      else
 594         rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
 595   }
 596  out:
 597    return rc;
 598 }
 599
 600 struct debug_view debug_test_view = {
 601   "myview",                 /* name of view */
 602   NULL,                     /* no prolog */
 603   &debug_dflt_header_fn,    /* default header for each entry */
 604   &debug_test_format_fn,    /* our own format function */
 605   NULL,                     /* no input function */
 606   NULL                      /* no private data */
 607 };
 608
 609 =====
 610 test:
 611 =====
 612 debug_info_t *debug_info;
 613 ...
 614 debug_info = debug_register ("test", 0, 4, 4 ));
 615 debug_register_view(debug_info, &debug_test_view);
 616 for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);
 617
 618 > cat /sys/kernel/debug/s390dbf/test/myview
 619 00 00964419734:611402 1 - 00 88042ca   This error...........
 620 00 00964419734:611405 1 - 00 88042ca   That error...........
 621 00 00964419734:611408 1 - 00 88042ca   Problem..............
 622 00 00964419734:611411 1 - 00 88042ca   Something went wrong.
 623 00 00964419734:611414 1 - 00 88042ca   Everything ok........
 624 00 00964419734:611417 1 - 00 88042ca   data: 00000005
 625 00 00964419734:611419 1 - 00 88042ca   data: 00000006
 626 00 00964419734:611422 1 - 00 88042ca   data: 00000007
 627 00 00964419734:611425 1 - 00 88042ca   data: 00000008
 628 00 00964419734:611428 1 - 00 88042ca   data: 00000009