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
 147                Must not be called within an interrupt handler
 148
 149 ---------------------------------------------------------------------------
 150 void debug_set_level (debug_info_t * id, int new_level);
 151
 152 Parameter:     id:        handle for debug log
 153                new_level: new debug level
 154
 155 Return Value:  none
 156
 157 Description:   Sets new actual debug level if new_level is valid.
 158
 159 ---------------------------------------------------------------------------
 160 void debug_stop_all(void);
 161
 162 Parameter:     none
 163
 164 Return Value:  none
 165
 166 Description:   stops the debug feature if stopping is allowed. Currently
 167                used in case of a kernel oops.
 168
 169 ---------------------------------------------------------------------------
 170 debug_entry_t* debug_event (debug_info_t* id, int level, void* data,
 171                             int length);
 172
 173 Parameter:     id:     handle for debug log
 174                level:  debug level
 175                data:   pointer to data for debug entry
 176                length: length of data in bytes
 177
 178 Return Value:  Address of written debug entry
 179
 180 Description:   writes debug entry to active debug area (if level <= actual
 181                debug level)
 182
 183 ---------------------------------------------------------------------------
 184 debug_entry_t* debug_int_event (debug_info_t * id, int level,
 185                                 unsigned int data);
 186 debug_entry_t* debug_long_event(debug_info_t * id, int level,
 187                                 unsigned long data);
 188
 189 Parameter:     id:     handle for debug log
 190                level:  debug level
 191                data:   integer value for debug entry
 192
 193 Return Value:  Address of written debug entry
 194
 195 Description:   writes debug entry to active debug area (if level <= actual
 196                debug level)
 197
 198 ---------------------------------------------------------------------------
 199 debug_entry_t* debug_text_event (debug_info_t * id, int level,
 200                                  const char* data);
 201
 202 Parameter:     id:     handle for debug log
 203                level:  debug level
 204                data:   string for debug entry
 205
 206 Return Value:  Address of written debug entry
 207
 208 Description:   writes debug entry in ascii format to active debug area
 209                (if level <= actual debug level)
 210
 211 ---------------------------------------------------------------------------
 212 debug_entry_t* debug_sprintf_event (debug_info_t * id, int level,
 213                                     char* string,...);
 214
 215 Parameter:     id:    handle for debug log
 216                level: debug level
 217                string: format string for debug entry
 218                ...: varargs used as in sprintf()
 219
 220 Return Value:  Address of written debug entry
 221
 222 Description:   writes debug entry with format string and varargs (longs) to
 223                active debug area (if level $<=$ actual debug level).
 224                floats and long long datatypes cannot be used as varargs.
 225
 226 ---------------------------------------------------------------------------
 227
 228 debug_entry_t* debug_exception (debug_info_t* id, int level, void* data,
 229                                 int length);
 230
 231 Parameter:     id:     handle for debug log
 232                level:  debug level
 233                data:   pointer to data for debug entry
 234                length: length of data in bytes
 235
 236 Return Value:  Address of written debug entry
 237
 238 Description:   writes debug entry to active debug area (if level <= actual
 239                debug level) and switches to next debug area
 240
 241 ---------------------------------------------------------------------------
 242 debug_entry_t* debug_int_exception (debug_info_t * id, int level,
 243                                     unsigned int data);
 244 debug_entry_t* debug_long_exception(debug_info_t * id, int level,
 245                                     unsigned long data);
 246
 247 Parameter:     id:     handle for debug log
 248                level:  debug level
 249                data:   integer value for debug entry
 250
 251 Return Value:  Address of written debug entry
 252
 253 Description:   writes debug entry to active debug area (if level <= actual
 254                debug level) and switches to next debug area
 255
 256 ---------------------------------------------------------------------------
 257 debug_entry_t* debug_text_exception (debug_info_t * id, int level,
 258                                      const char* data);
 259
 260 Parameter:     id:     handle for debug log
 261                level:  debug level
 262                data:   string for debug entry
 263
 264 Return Value:  Address of written debug entry
 265
 266 Description:   writes debug entry in ascii format to active debug area
 267                (if level <= actual debug level) and switches to next debug
 268                area
 269
 270 ---------------------------------------------------------------------------
 271 debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
 272                                         char* string,...);
 273
 274 Parameter:     id:    handle for debug log
 275                level: debug level
 276                string: format string for debug entry
 277                ...: varargs used as in sprintf()
 278
 279 Return Value:  Address of written debug entry
 280
 281 Description:   writes debug entry with format string and varargs (longs) to
 282                active debug area (if level $<=$ actual debug level) and
 283                switches to next debug area.
 284                floats and long long datatypes cannot be used as varargs.
 285
 286 ---------------------------------------------------------------------------
 287
 288 int debug_register_view (debug_info_t * id, struct debug_view *view);
 289
 290 Parameter:     id:    handle for debug log
 291                view:  pointer to debug view struct
 292
 293 Return Value:  0  : ok
 294                < 0: Error
 295
 296 Description:   registers new debug view and creates debugfs dir entry
 297
 298 ---------------------------------------------------------------------------
 299 int debug_unregister_view (debug_info_t * id, struct debug_view *view);
 300
 301 Parameter:     id:    handle for debug log
 302                view:  pointer to debug view struct
 303
 304 Return Value:  0  : ok
 305                < 0: Error
 306
 307 Description:   unregisters debug view and removes debugfs dir entry
 308
 309
 310
 311 Predefined views:
 312 -----------------
 313
 314 extern struct debug_view debug_hex_ascii_view;
 315 extern struct debug_view debug_raw_view;
 316 extern struct debug_view debug_sprintf_view;
 317
 318 Examples
 319 --------
 320
 321 /*
 322  * hex_ascii- + raw-view Example
 323  */
 324
 325 #include <linux/init.h>
 326 #include <asm/debug.h>
 327
 328 static debug_info_t* debug_info;
 329
 330 static int init(void)
 331 {
 332     /* register 4 debug areas with one page each and 4 byte data field */
 333
 334     debug_info = debug_register ("test", 1, 4, 4 );
 335     debug_register_view(debug_info,&debug_hex_ascii_view);
 336     debug_register_view(debug_info,&debug_raw_view);
 337
 338     debug_text_event(debug_info, 4 , "one ");
 339     debug_int_exception(debug_info, 4, 4711);
 340     debug_event(debug_info, 3, &debug_info, 4);
 341
 342     return 0;
 343 }
 344
 345 static void cleanup(void)
 346 {
 347     debug_unregister (debug_info);
 348 }
 349
 350 module_init(init);
 351 module_exit(cleanup);
 352
 353 ---------------------------------------------------------------------------
 354
 355 /*
 356  * sprintf-view Example
 357  */
 358
 359 #include <linux/init.h>
 360 #include <asm/debug.h>
 361
 362 static debug_info_t* debug_info;
 363
 364 static int init(void)
 365 {
 366     /* register 4 debug areas with one page each and data field for */
 367     /* format string pointer + 2 varargs (= 3 * sizeof(long))       */
 368
 369     debug_info = debug_register ("test", 1, 4, sizeof(long) * 3);
 370     debug_register_view(debug_info,&debug_sprintf_view);
 371
 372     debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
 373     debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);
 374
 375     return 0;
 376 }
 377
 378 static void cleanup(void)
 379 {
 380     debug_unregister (debug_info);
 381 }
 382
 383 module_init(init);
 384 module_exit(cleanup);
 385
 386
 387
 388 Debugfs Interface
 389 ----------------
 390 Views to the debug logs can be investigated through reading the corresponding
 391 debugfs-files:
 392
 393 Example:
 394
 395 > ls /sys/kernel/debug/s390dbf/dasd
 396 flush  hex_ascii  level pages raw
 397 > cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1
 398 00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
 399 00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
 400 00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
 401 00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP
 402 01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
 403 01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
 404 01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ...
 405 01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
 406 01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
 407 01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....
 408
 409 See section about predefined views for explanation of the above output!
 410
 411 Changing the debug level
 412 ------------------------
 413
 414 Example:
 415
 416
 417 > cat /sys/kernel/debug/s390dbf/dasd/level
 418 3
 419 > echo "5" > /sys/kernel/debug/s390dbf/dasd/level
 420 > cat /sys/kernel/debug/s390dbf/dasd/level
 421 5
 422
 423 Flushing debug areas
 424 --------------------
 425 Debug areas can be flushed with piping the number of the desired
 426 area (0...n) to the debugfs file "flush". When using "-" all debug areas
 427 are flushed.
 428
 429 Examples:
 430
 431 1. Flush debug area 0:
 432 > echo "0" > /sys/kernel/debug/s390dbf/dasd/flush
 433
 434 2. Flush all debug areas:
 435 > echo "-" > /sys/kernel/debug/s390dbf/dasd/flush
 436
 437 Changing the size of debug areas
 438 ------------------------------------
 439 It is possible the change the size of debug areas through piping
 440 the number of pages to the debugfs file "pages". The resize request will
 441 also flush the debug areas.
 442
 443 Example:
 444
 445 Define 4 pages for the debug areas of debug feature "dasd":
 446 > echo "4" > /sys/kernel/debug/s390dbf/dasd/pages
 447
 448 Stooping the debug feature
 449 --------------------------
 450 Example:
 451
 452 1. Check if stopping is allowed
 453 > cat /proc/sys/s390dbf/debug_stoppable
 454 2. Stop debug feature
 455 > echo 0 > /proc/sys/s390dbf/debug_active
 456
 457 lcrash Interface
 458 ----------------
 459 It is planned that the dump analysis tool lcrash gets an additional command
 460 's390dbf' to display all the debug logs. With this tool it will be possible
 461 to investigate the debug logs on a live system and with a memory dump after
 462 a system crash.
 463
 464 Investigating raw memory
 465 ------------------------
 466 One last possibility to investigate the debug logs at a live
 467 system and after a system crash is to look at the raw memory
 468 under VM or at the Service Element.
 469 It is possible to find the anker of the debug-logs through
 470 the 'debug_area_first' symbol in the System map. Then one has
 471 to follow the correct pointers of the data-structures defined
 472 in debug.h and find the debug-areas in memory.
 473 Normally modules which use the debug feature will also have
 474 a global variable with the pointer to the debug-logs. Following
 475 this pointer it will also be possible to find the debug logs in
 476 memory.
 477
 478 For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
 479 for the length of the data field in debug_register() in
 480 order to see the debug entries well formatted.
 481
 482
 483 Predefined Views
 484 ----------------
 485
 486 There are three predefined views: hex_ascii, raw and sprintf.
 487 The hex_ascii view shows the data field in hex and ascii representation
 488 (e.g. '45 43 4b 44 | ECKD').
 489 The raw view returns a bytestream as the debug areas are stored in memory.
 490
 491 The sprintf view formats the debug entries in the same way as the sprintf
 492 function would do. The sprintf event/exception functions write to the
 493 debug entry a pointer to the format string (size = sizeof(long))
 494 and for each vararg a long value. So e.g. for a debug entry with a format
 495 string plus two varargs one would need to allocate a (3 * sizeof(long))
 496 byte data area in the debug_register() function.
 497
 498 IMPORTANT: Using "%s" in sprintf event functions is dangerous. You can only
 499 use "%s" in the sprintf event functions, if the memory for the passed string is
 500 available as long as the debug feature exists. The reason behind this is that
 501 due to performance considerations only a pointer to the string is stored in
 502 the debug feature. If you log a string that is freed afterwards, you will get
 503 an OOPS when inspecting the debug feature, because then the debug feature will
 504 access the already freed memory.
 505
 506 NOTE: If using the sprintf view do NOT use other event/exception functions
 507 than the sprintf-event and -exception functions.
 508
 509 The format of the hex_ascii and sprintf view is as follows:
 510 - Number of area
 511 - Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated
 512   Universal Time (UTC), January 1, 1970)
 513 - level of debug entry
 514 - Exception flag (* = Exception)
 515 - Cpu-Number of calling task
 516 - Return Address to caller
 517 - data field
 518
 519 The format of the raw view is:
 520 - Header as described in debug.h
 521 - datafield
 522
 523 A typical line of the hex_ascii view will look like the following (first line
 524 is only for explanation and will not be displayed when 'cating' the view):
 525
 526 area  time           level exception cpu caller    data (hex + ascii)
 527 --------------------------------------------------------------------------
 528 00    00964419409:440690 1 -         00  88023fe
 529
 530
 531 Defining views
 532 --------------
 533
 534 Views are specified with the 'debug_view' structure. There are defined
 535 callback functions which are used for reading and writing the debugfs files:
 536
 537 struct debug_view {
 538         char name[DEBUG_MAX_PROCF_LEN];
 539         debug_prolog_proc_t* prolog_proc;
 540         debug_header_proc_t* header_proc;
 541         debug_format_proc_t* format_proc;
 542         debug_input_proc_t*  input_proc;
 543         void*                private_data;
 544 };
 545
 546 where
 547
 548 typedef int (debug_header_proc_t) (debug_info_t* id,
 549                                    struct debug_view* view,
 550                                    int area,
 551                                    debug_entry_t* entry,
 552                                    char* out_buf);
 553
 554 typedef int (debug_format_proc_t) (debug_info_t* id,
 555                                    struct debug_view* view, char* out_buf,
 556                                    const char* in_buf);
 557 typedef int (debug_prolog_proc_t) (debug_info_t* id,
 558                                    struct debug_view* view,
 559                                    char* out_buf);
 560 typedef int (debug_input_proc_t) (debug_info_t* id,
 561                                   struct debug_view* view,
 562                                   struct file* file, const char* user_buf,
 563                                   size_t in_buf_size, loff_t* offset);
 564
 565
 566 The "private_data" member can be used as pointer to view specific data.
 567 It is not used by the debug feature itself.
 568
 569 The output when reading a debugfs file is structured like this:
 570
 571 "prolog_proc output"
 572
 573 "header_proc output 1"  "format_proc output 1"
 574 "header_proc output 2"  "format_proc output 2"
 575 "header_proc output 3"  "format_proc output 3"
 576 ...
 577
 578 When a view is read from the debugfs, the Debug Feature calls the
 579 'prolog_proc' once for writing the prolog.
 580 Then 'header_proc' and 'format_proc' are called for each
 581 existing debug entry.
 582
 583 The input_proc can be used to implement functionality when it is written to
 584 the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).
 585
 586 For header_proc there can be used the default function
 587 debug_dflt_header_fn() which is defined in debug.h.
 588 and which produces the same header output as the predefined views.
 589 E.g:
 590 00 00964419409:440761 2 - 00 88023ec
 591
 592 In order to see how to use the callback functions check the implementation
 593 of the default views!
 594
 595 Example
 596
 597 #include <asm/debug.h>
 598
 599 #define UNKNOWNSTR "data: %08x"
 600
 601 const char* messages[] =
 602 {"This error...........\n",
 603  "That error...........\n",
 604  "Problem..............\n",
 605  "Something went wrong.\n",
 606  "Everything ok........\n",
 607  NULL
 608 };
 609
 610 static int debug_test_format_fn(
 611    debug_info_t * id, struct debug_view *view,
 612    char *out_buf, const char *in_buf
 613 )
 614 {
 615   int i, rc = 0;
 616
 617   if(id->buf_size >= 4) {
 618      int msg_nr = *((int*)in_buf);
 619      if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
 620         rc += sprintf(out_buf, "%s", messages[msg_nr]);
 621      else
 622         rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
 623   }
 624  out:
 625    return rc;
 626 }
 627
 628 struct debug_view debug_test_view = {
 629   "myview",                 /* name of view */
 630   NULL,                     /* no prolog */
 631   &debug_dflt_header_fn,    /* default header for each entry */
 632   &debug_test_format_fn,    /* our own format function */
 633   NULL,                     /* no input function */
 634   NULL                      /* no private data */
 635 };
 636
 637 =====
 638 test:
 639 =====
 640 debug_info_t *debug_info;
 641 ...
 642 debug_info = debug_register ("test", 0, 4, 4 ));
 643 debug_register_view(debug_info, &debug_test_view);
 644 for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);
 645
 646 > cat /sys/kernel/debug/s390dbf/test/myview
 647 00 00964419734:611402 1 - 00 88042ca   This error...........
 648 00 00964419734:611405 1 - 00 88042ca   That error...........
 649 00 00964419734:611408 1 - 00 88042ca   Problem..............
 650 00 00964419734:611411 1 - 00 88042ca   Something went wrong.
 651 00 00964419734:611414 1 - 00 88042ca   Everything ok........
 652 00 00964419734:611417 1 - 00 88042ca   data: 00000005
 653 00 00964419734:611419 1 - 00 88042ca   data: 00000006
 654 00 00964419734:611422 1 - 00 88042ca   data: 00000007
 655 00 00964419734:611425 1 - 00 88042ca   data: 00000008
 656 00 00964419734:611428 1 - 00 88042ca   data: 00000009