Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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 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 bool debug_level_enabled (debug_info_t * id, int level); 162 163 Parameter: id: handle for debug log 164 level: debug level 165 166 Return Value: True if level is less or equal to the current debug level. 167 168 Description: Returns true if debug events for the specified level would be 169 logged. Otherwise returns false. 170 --------------------------------------------------------------------------- 171 void debug_stop_all(void); 172 173 Parameter: none 174 175 Return Value: none 176 177 Description: stops the debug feature if stopping is allowed. Currently 178 used in case of a kernel oops. 179 180 --------------------------------------------------------------------------- 181 debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 182 int length); 183 184 Parameter: id: handle for debug log 185 level: debug level 186 data: pointer to data for debug entry 187 length: length of data in bytes 188 189 Return Value: Address of written debug entry 190 191 Description: writes debug entry to active debug area (if level <= actual 192 debug level) 193 194 --------------------------------------------------------------------------- 195 debug_entry_t* debug_int_event (debug_info_t * id, int level, 196 unsigned int data); 197 debug_entry_t* debug_long_event(debug_info_t * id, int level, 198 unsigned long data); 199 200 Parameter: id: handle for debug log 201 level: debug level 202 data: integer value for debug entry 203 204 Return Value: Address of written debug entry 205 206 Description: writes debug entry to active debug area (if level <= actual 207 debug level) 208 209 --------------------------------------------------------------------------- 210 debug_entry_t* debug_text_event (debug_info_t * id, int level, 211 const char* data); 212 213 Parameter: id: handle for debug log 214 level: debug level 215 data: string for debug entry 216 217 Return Value: Address of written debug entry 218 219 Description: writes debug entry in ascii format to active debug area 220 (if level <= actual debug level) 221 222 --------------------------------------------------------------------------- 223 debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 224 char* string,...); 225 226 Parameter: id: handle for debug log 227 level: debug level 228 string: format string for debug entry 229 ...: varargs used as in sprintf() 230 231 Return Value: Address of written debug entry 232 233 Description: writes debug entry with format string and varargs (longs) to 234 active debug area (if level $<=$ actual debug level). 235 floats and long long datatypes cannot be used as varargs. 236 237 --------------------------------------------------------------------------- 238 239 debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 240 int length); 241 242 Parameter: id: handle for debug log 243 level: debug level 244 data: pointer to data for debug entry 245 length: length of data in bytes 246 247 Return Value: Address of written debug entry 248 249 Description: writes debug entry to active debug area (if level <= actual 250 debug level) and switches to next debug area 251 252 --------------------------------------------------------------------------- 253 debug_entry_t* debug_int_exception (debug_info_t * id, int level, 254 unsigned int data); 255 debug_entry_t* debug_long_exception(debug_info_t * id, int level, 256 unsigned long data); 257 258 Parameter: id: handle for debug log 259 level: debug level 260 data: integer value for debug entry 261 262 Return Value: Address of written debug entry 263 264 Description: writes debug entry to active debug area (if level <= actual 265 debug level) and switches to next debug area 266 267 --------------------------------------------------------------------------- 268 debug_entry_t* debug_text_exception (debug_info_t * id, int level, 269 const char* data); 270 271 Parameter: id: handle for debug log 272 level: debug level 273 data: string for debug entry 274 275 Return Value: Address of written debug entry 276 277 Description: writes debug entry in ascii format to active debug area 278 (if level <= actual debug level) and switches to next debug 279 area 280 281 --------------------------------------------------------------------------- 282 debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level, 283 char* string,...); 284 285 Parameter: id: handle for debug log 286 level: debug level 287 string: format string for debug entry 288 ...: varargs used as in sprintf() 289 290 Return Value: Address of written debug entry 291 292 Description: writes debug entry with format string and varargs (longs) to 293 active debug area (if level $<=$ actual debug level) and 294 switches to next debug area. 295 floats and long long datatypes cannot be used as varargs. 296 297 --------------------------------------------------------------------------- 298 299 int debug_register_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: registers new debug view and creates debugfs dir entry 308 309 --------------------------------------------------------------------------- 310 int debug_unregister_view (debug_info_t * id, struct debug_view *view); 311 312 Parameter: id: handle for debug log 313 view: pointer to debug view struct 314 315 Return Value: 0 : ok 316 < 0: Error 317 318 Description: unregisters debug view and removes debugfs dir entry 319 320 321 322 Predefined views: 323 ----------------- 324 325 extern struct debug_view debug_hex_ascii_view; 326 extern struct debug_view debug_raw_view; 327 extern struct debug_view debug_sprintf_view; 328 329 Examples 330 -------- 331 332 /* 333 * hex_ascii- + raw-view Example 334 */ 335 336 #include <linux/init.h> 337 #include <asm/debug.h> 338 339 static debug_info_t* debug_info; 340 341 static int init(void) 342 { 343 /* register 4 debug areas with one page each and 4 byte data field */ 344 345 debug_info = debug_register ("test", 1, 4, 4 ); 346 debug_register_view(debug_info,&debug_hex_ascii_view); 347 debug_register_view(debug_info,&debug_raw_view); 348 349 debug_text_event(debug_info, 4 , "one "); 350 debug_int_exception(debug_info, 4, 4711); 351 debug_event(debug_info, 3, &debug_info, 4); 352 353 return 0; 354 } 355 356 static void cleanup(void) 357 { 358 debug_unregister (debug_info); 359 } 360 361 module_init(init); 362 module_exit(cleanup); 363 364 --------------------------------------------------------------------------- 365 366 /* 367 * sprintf-view Example 368 */ 369 370 #include <linux/init.h> 371 #include <asm/debug.h> 372 373 static debug_info_t* debug_info; 374 375 static int init(void) 376 { 377 /* register 4 debug areas with one page each and data field for */ 378 /* format string pointer + 2 varargs (= 3 * sizeof(long)) */ 379 380 debug_info = debug_register ("test", 1, 4, sizeof(long) * 3); 381 debug_register_view(debug_info,&debug_sprintf_view); 382 383 debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__); 384 debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info); 385 386 return 0; 387 } 388 389 static void cleanup(void) 390 { 391 debug_unregister (debug_info); 392 } 393 394 module_init(init); 395 module_exit(cleanup); 396 397 398 399 Debugfs Interface 400 ---------------- 401 Views to the debug logs can be investigated through reading the corresponding 402 debugfs-files: 403 404 Example: 405 406 > ls /sys/kernel/debug/s390dbf/dasd 407 flush hex_ascii level pages raw 408 > cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort -k2,2 -s 409 00 00974733272:680099 2 - 02 0006ad7e 07 ea 4a 90 | .... 410 00 00974733272:682210 2 - 02 0006ade6 46 52 45 45 | FREE 411 00 00974733272:682213 2 - 02 0006adf6 07 ea 4a 90 | .... 412 00 00974733272:682281 1 * 02 0006ab08 41 4c 4c 43 | EXCP 413 01 00974733272:682284 2 - 02 0006ab16 45 43 4b 44 | ECKD 414 01 00974733272:682287 2 - 02 0006ab28 00 00 00 04 | .... 415 01 00974733272:682289 2 - 02 0006ab3e 00 00 00 20 | ... 416 01 00974733272:682297 2 - 02 0006ad7e 07 ea 4a 90 | .... 417 01 00974733272:684384 2 - 00 0006ade6 46 52 45 45 | FREE 418 01 00974733272:684388 2 - 00 0006adf6 07 ea 4a 90 | .... 419 420 See section about predefined views for explanation of the above output! 421 422 Changing the debug level 423 ------------------------ 424 425 Example: 426 427 428 > cat /sys/kernel/debug/s390dbf/dasd/level 429 3 430 > echo "5" > /sys/kernel/debug/s390dbf/dasd/level 431 > cat /sys/kernel/debug/s390dbf/dasd/level 432 5 433 434 Flushing debug areas 435 -------------------- 436 Debug areas can be flushed with piping the number of the desired 437 area (0...n) to the debugfs file "flush". When using "-" all debug areas 438 are flushed. 439 440 Examples: 441 442 1. Flush debug area 0: 443 > echo "0" > /sys/kernel/debug/s390dbf/dasd/flush 444 445 2. Flush all debug areas: 446 > echo "-" > /sys/kernel/debug/s390dbf/dasd/flush 447 448 Changing the size of debug areas 449 ------------------------------------ 450 It is possible the change the size of debug areas through piping 451 the number of pages to the debugfs file "pages". The resize request will 452 also flush the debug areas. 453 454 Example: 455 456 Define 4 pages for the debug areas of debug feature "dasd": 457 > echo "4" > /sys/kernel/debug/s390dbf/dasd/pages 458 459 Stooping the debug feature 460 -------------------------- 461 Example: 462 463 1. Check if stopping is allowed 464 > cat /proc/sys/s390dbf/debug_stoppable 465 2. Stop debug feature 466 > echo 0 > /proc/sys/s390dbf/debug_active 467 468 lcrash Interface 469 ---------------- 470 It is planned that the dump analysis tool lcrash gets an additional command 471 's390dbf' to display all the debug logs. With this tool it will be possible 472 to investigate the debug logs on a live system and with a memory dump after 473 a system crash. 474 475 Investigating raw memory 476 ------------------------ 477 One last possibility to investigate the debug logs at a live 478 system and after a system crash is to look at the raw memory 479 under VM or at the Service Element. 480 It is possible to find the anker of the debug-logs through 481 the 'debug_area_first' symbol in the System map. Then one has 482 to follow the correct pointers of the data-structures defined 483 in debug.h and find the debug-areas in memory. 484 Normally modules which use the debug feature will also have 485 a global variable with the pointer to the debug-logs. Following 486 this pointer it will also be possible to find the debug logs in 487 memory. 488 489 For this method it is recommended to use '16 * x + 4' byte (x = 0..n) 490 for the length of the data field in debug_register() in 491 order to see the debug entries well formatted. 492 493 494 Predefined Views 495 ---------------- 496 497 There are three predefined views: hex_ascii, raw and sprintf. 498 The hex_ascii view shows the data field in hex and ascii representation 499 (e.g. '45 43 4b 44 | ECKD'). 500 The raw view returns a bytestream as the debug areas are stored in memory. 501 502 The sprintf view formats the debug entries in the same way as the sprintf 503 function would do. The sprintf event/exception functions write to the 504 debug entry a pointer to the format string (size = sizeof(long)) 505 and for each vararg a long value. So e.g. for a debug entry with a format 506 string plus two varargs one would need to allocate a (3 * sizeof(long)) 507 byte data area in the debug_register() function. 508 509 IMPORTANT: Using "%s" in sprintf event functions is dangerous. You can only 510 use "%s" in the sprintf event functions, if the memory for the passed string is 511 available as long as the debug feature exists. The reason behind this is that 512 due to performance considerations only a pointer to the string is stored in 513 the debug feature. If you log a string that is freed afterwards, you will get 514 an OOPS when inspecting the debug feature, because then the debug feature will 515 access the already freed memory. 516 517 NOTE: If using the sprintf view do NOT use other event/exception functions 518 than the sprintf-event and -exception functions. 519 520 The format of the hex_ascii and sprintf view is as follows: 521 - Number of area 522 - Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated 523 Universal Time (UTC), January 1, 1970) 524 - level of debug entry 525 - Exception flag (* = Exception) 526 - Cpu-Number of calling task 527 - Return Address to caller 528 - data field 529 530 The format of the raw view is: 531 - Header as described in debug.h 532 - datafield 533 534 A typical line of the hex_ascii view will look like the following (first line 535 is only for explanation and will not be displayed when 'cating' the view): 536 537 area time level exception cpu caller data (hex + ascii) 538 -------------------------------------------------------------------------- 539 00 00964419409:440690 1 - 00 88023fe 540 541 542 Defining views 543 -------------- 544 545 Views are specified with the 'debug_view' structure. There are defined 546 callback functions which are used for reading and writing the debugfs files: 547 548 struct debug_view { 549 char name[DEBUG_MAX_PROCF_LEN]; 550 debug_prolog_proc_t* prolog_proc; 551 debug_header_proc_t* header_proc; 552 debug_format_proc_t* format_proc; 553 debug_input_proc_t* input_proc; 554 void* private_data; 555 }; 556 557 where 558 559 typedef int (debug_header_proc_t) (debug_info_t* id, 560 struct debug_view* view, 561 int area, 562 debug_entry_t* entry, 563 char* out_buf); 564 565 typedef int (debug_format_proc_t) (debug_info_t* id, 566 struct debug_view* view, char* out_buf, 567 const char* in_buf); 568 typedef int (debug_prolog_proc_t) (debug_info_t* id, 569 struct debug_view* view, 570 char* out_buf); 571 typedef int (debug_input_proc_t) (debug_info_t* id, 572 struct debug_view* view, 573 struct file* file, const char* user_buf, 574 size_t in_buf_size, loff_t* offset); 575 576 577 The "private_data" member can be used as pointer to view specific data. 578 It is not used by the debug feature itself. 579 580 The output when reading a debugfs file is structured like this: 581 582 "prolog_proc output" 583 584 "header_proc output 1" "format_proc output 1" 585 "header_proc output 2" "format_proc output 2" 586 "header_proc output 3" "format_proc output 3" 587 ... 588 589 When a view is read from the debugfs, the Debug Feature calls the 590 'prolog_proc' once for writing the prolog. 591 Then 'header_proc' and 'format_proc' are called for each 592 existing debug entry. 593 594 The input_proc can be used to implement functionality when it is written to 595 the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level). 596 597 For header_proc there can be used the default function 598 debug_dflt_header_fn() which is defined in debug.h. 599 and which produces the same header output as the predefined views. 600 E.g: 601 00 00964419409:440761 2 - 00 88023ec 602 603 In order to see how to use the callback functions check the implementation 604 of the default views! 605 606 Example 607 608 #include <asm/debug.h> 609 610 #define UNKNOWNSTR "data: %08x" 611 612 const char* messages[] = 613 {"This error...........\n", 614 "That error...........\n", 615 "Problem..............\n", 616 "Something went wrong.\n", 617 "Everything ok........\n", 618 NULL 619 }; 620 621 static int debug_test_format_fn( 622 debug_info_t * id, struct debug_view *view, 623 char *out_buf, const char *in_buf 624 ) 625 { 626 int i, rc = 0; 627 628 if(id->buf_size >= 4) { 629 int msg_nr = *((int*)in_buf); 630 if(msg_nr < sizeof(messages)/sizeof(char*) - 1) 631 rc += sprintf(out_buf, "%s", messages[msg_nr]); 632 else 633 rc += sprintf(out_buf, UNKNOWNSTR, msg_nr); 634 } 635 out: 636 return rc; 637 } 638 639 struct debug_view debug_test_view = { 640 "myview", /* name of view */ 641 NULL, /* no prolog */ 642 &debug_dflt_header_fn, /* default header for each entry */ 643 &debug_test_format_fn, /* our own format function */ 644 NULL, /* no input function */ 645 NULL /* no private data */ 646 }; 647 648 ===== 649 test: 650 ===== 651 debug_info_t *debug_info; 652 ... 653 debug_info = debug_register ("test", 0, 4, 4 )); 654 debug_register_view(debug_info, &debug_test_view); 655 for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i); 656 657 > cat /sys/kernel/debug/s390dbf/test/myview 658 00 00964419734:611402 1 - 00 88042ca This error........... 659 00 00964419734:611405 1 - 00 88042ca That error........... 660 00 00964419734:611408 1 - 00 88042ca Problem.............. 661 00 00964419734:611411 1 - 00 88042ca Something went wrong. 662 00 00964419734:611414 1 - 00 88042ca Everything ok........ 663 00 00964419734:611417 1 - 00 88042ca data: 00000005 664 00 00964419734:611419 1 - 00 88042ca data: 00000006 665 00 00964419734:611422 1 - 00 88042ca data: 00000007 666 00 00964419734:611425 1 - 00 88042ca data: 00000008 667 00 00964419734:611428 1 - 00 88042ca data: 00000009