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Based on kernel version 3.9. Page generated on 2013-05-02 23:13 EST.
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
- [ s390 ]
- 00-INDEX
- 3270.ChangeLog
- 3270.txt
- cds.txt
- CommonIO
- config3270.sh
- DASD
- Debugging390.txt
- driver-model.txt
- kvm.txt
- monreader.txt
- s390dbf.txt
- zfcpdump.txt
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