1S390 Debug Feature 2================== 3 4files: arch/s390/kernel/debug.c 5 include/asm-s390/debug.h 6 7Description: 8------------ 9The goal of this feature is to provide a kernel debug logging API 10where log records can be stored efficiently in memory, where each component 11(e.g. device drivers) can have one separate debug log. 12One purpose of this is to inspect the debug logs after a production system crash 13in order to analyze the reason for the crash. 14If the system still runs but only a subcomponent which uses dbf fails, 15it is possible to look at the debug logs on a live system via the Linux 16debugfs filesystem. 17The debug feature may also very useful for kernel and driver development. 18 19Design: 20------- 21Kernel components (e.g. device drivers) can register themselves at the debug 22feature with the function call debug_register(). This function initializes a 23debug log for the caller. For each debug log exists a number of debug areas 24where exactly one is active at one time. Each debug area consists of contiguous 25pages in memory. In the debug areas there are stored debug entries (log records) 26which are written by event- and exception-calls. 27 28An event-call writes the specified debug entry to the active debug 29area and updates the log pointer for the active area. If the end 30of the active debug area is reached, a wrap around is done (ring buffer) 31and the next debug entry will be written at the beginning of the active 32debug area. 33 34An exception-call writes the specified debug entry to the log and 35switches to the next debug area. This is done in order to be sure 36that the records which describe the origin of the exception are not 37overwritten when a wrap around for the current area occurs. 38 39The debug areas themselves are also ordered in form of a ring buffer. 40When an exception is thrown in the last debug area, the following debug 41entries are then written again in the very first area. 42 43There are three versions for the event- and exception-calls: One for 44logging raw data, one for text and one for numbers. 45 46Each 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 54The debug logs can be inspected in a live system through entries in 55the debugfs-filesystem. Under the toplevel directory "s390dbf" there is 56a directory for each registered component, which is named like the 57corresponding 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 61The content of the directories are files which represent different views 62to the debug log. Each component can decide which views should be 63used through registering them with the function debug_register_view(). 64Predefined views for hex/ascii, sprintf and raw binary data are provided. 65It is also possible to define other views. The content of 66a view can be inspected simply by reading the corresponding debugfs file. 67 68All debug logs have an actual debug level (range from 0 to 6). 69The default level is 3. Event and Exception functions have a 'level' 70parameter. Only debug entries with a level that is lower or equal 71than the actual level are written to the log. This means, when 72writing events, high priority log entries should have a low level 73value whereas low priority entries should have a high one. 74The actual debug level can be changed with the help of the debugfs-filesystem 75through writing a number string "x" to the 'level' debugfs file which is 76provided for every debug log. Debugging can be switched off completely 77by using "-" on the 'level' debugfs file. 78 79Example: 80 81> echo "-" > /sys/kernel/debug/s390dbf/dasd/level 82 83It is also possible to deactivate the debug feature globally for every 84debug log. You can change the behavior using 2 sysctl parameters in 85/proc/sys/s390dbf: 86There are currently 2 possible triggers, which stop the debug feature 87globally. The first possibility is to use the "debug_active" sysctl. If 88set to 1 the debug feature is running. If "debug_active" is set to 0 the 89debug feature is turned off. 90The second trigger which stops the debug feature is a kernel oops. 91That prevents the debug feature from overwriting debug information that 92happened before the oops. After an oops you can reactivate the debug feature 93by piping 1 to /proc/sys/s390dbf/debug_active. Nevertheless, its not 94suggested to use an oopsed kernel in a production environment. 95If you want to disallow the deactivation of the debug feature, you can use 96the "debug_stoppable" sysctl. If you set "debug_stoppable" to 0 the debug 97feature cannot be stopped. If the debug feature is already stopped, it 98will stay deactivated. 99 100Kernel Interfaces: 101------------------ 102 103---------------------------------------------------------------------------- 104debug_info_t *debug_register(char *name, int pages, int nr_areas, 105 int buf_size); 106 107Parameter: 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 112Return Value: Handle for generated debug area 113 NULL if register failed 114 115Description: Allocates memory for a debug log 116 Must not be called within an interrupt handler 117 118--------------------------------------------------------------------------- 119void debug_unregister (debug_info_t * id); 120 121Parameter: id: handle for debug log 122 123Return Value: none 124 125Description: frees memory for a debug log 126 Must not be called within an interrupt handler 127 128--------------------------------------------------------------------------- 129void debug_set_level (debug_info_t * id, int new_level); 130 131Parameter: id: handle for debug log 132 new_level: new debug level 133 134Return Value: none 135 136Description: Sets new actual debug level if new_level is valid. 137 138--------------------------------------------------------------------------- 139void debug_stop_all(void); 140 141Parameter: none 142 143Return Value: none 144 145Description: stops the debug feature if stopping is allowed. Currently 146 used in case of a kernel oops. 147 148--------------------------------------------------------------------------- 149debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 150 int length); 151 152Parameter: 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 157Return Value: Address of written debug entry 158 159Description: writes debug entry to active debug area (if level <= actual 160 debug level) 161 162--------------------------------------------------------------------------- 163debug_entry_t* debug_int_event (debug_info_t * id, int level, 164 unsigned int data); 165debug_entry_t* debug_long_event(debug_info_t * id, int level, 166 unsigned long data); 167 168Parameter: id: handle for debug log 169 level: debug level 170 data: integer value for debug entry 171 172Return Value: Address of written debug entry 173 174Description: writes debug entry to active debug area (if level <= actual 175 debug level) 176 177--------------------------------------------------------------------------- 178debug_entry_t* debug_text_event (debug_info_t * id, int level, 179 const char* data); 180 181Parameter: id: handle for debug log 182 level: debug level 183 data: string for debug entry 184 185Return Value: Address of written debug entry 186 187Description: writes debug entry in ascii format to active debug area 188 (if level <= actual debug level) 189 190--------------------------------------------------------------------------- 191debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 192 char* string,...); 193 194Parameter: id: handle for debug log 195 level: debug level 196 string: format string for debug entry 197 ...: varargs used as in sprintf() 198 199Return Value: Address of written debug entry 200 201Description: 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 207debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 208 int length); 209 210Parameter: 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 215Return Value: Address of written debug entry 216 217Description: writes debug entry to active debug area (if level <= actual 218 debug level) and switches to next debug area 219 220--------------------------------------------------------------------------- 221debug_entry_t* debug_int_exception (debug_info_t * id, int level, 222 unsigned int data); 223debug_entry_t* debug_long_exception(debug_info_t * id, int level, 224 unsigned long data); 225 226Parameter: id: handle for debug log 227 level: debug level 228 data: integer value for debug entry 229 230Return Value: Address of written debug entry 231 232Description: writes debug entry to active debug area (if level <= actual 233 debug level) and switches to next debug area 234 235--------------------------------------------------------------------------- 236debug_entry_t* debug_text_exception (debug_info_t * id, int level, 237 const char* data); 238 239Parameter: id: handle for debug log 240 level: debug level 241 data: string for debug entry 242 243Return Value: Address of written debug entry 244 245Description: 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--------------------------------------------------------------------------- 250debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level, 251 char* string,...); 252 253Parameter: id: handle for debug log 254 level: debug level 255 string: format string for debug entry 256 ...: varargs used as in sprintf() 257 258Return Value: Address of written debug entry 259 260Description: 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 267int debug_register_view (debug_info_t * id, struct debug_view *view); 268 269Parameter: id: handle for debug log 270 view: pointer to debug view struct 271 272Return Value: 0 : ok 273 < 0: Error 274 275Description: registers new debug view and creates debugfs dir entry 276 277--------------------------------------------------------------------------- 278int debug_unregister_view (debug_info_t * id, struct debug_view *view); 279 280Parameter: id: handle for debug log 281 view: pointer to debug view struct 282 283Return Value: 0 : ok 284 < 0: Error 285 286Description: unregisters debug view and removes debugfs dir entry 287 288 289 290Predefined views: 291----------------- 292 293extern struct debug_view debug_hex_ascii_view; 294extern struct debug_view debug_raw_view; 295extern struct debug_view debug_sprintf_view; 296 297Examples 298-------- 299 300/* 301 * hex_ascii- + raw-view Example 302 */ 303 304#include <linux/init.h> 305#include <asm/debug.h> 306 307static debug_info_t* debug_info; 308 309static 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 324static void cleanup(void) 325{ 326 debug_unregister (debug_info); 327} 328 329module_init(init); 330module_exit(cleanup); 331 332--------------------------------------------------------------------------- 333 334/* 335 * sprintf-view Example 336 */ 337 338#include <linux/init.h> 339#include <asm/debug.h> 340 341static debug_info_t* debug_info; 342 343static 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 357static void cleanup(void) 358{ 359 debug_unregister (debug_info); 360} 361 362module_init(init); 363module_exit(cleanup); 364 365 366 367Debugfs Interface 368---------------- 369Views to the debug logs can be investigated through reading the corresponding 370debugfs-files: 371 372Example: 373 374> ls /sys/kernel/debug/s390dbf/dasd 375flush hex_ascii level pages raw 376> cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1 37700 00974733272:680099 2 - 02 0006ad7e 07 ea 4a 90 | .... 37800 00974733272:682210 2 - 02 0006ade6 46 52 45 45 | FREE 37900 00974733272:682213 2 - 02 0006adf6 07 ea 4a 90 | .... 38000 00974733272:682281 1 * 02 0006ab08 41 4c 4c 43 | EXCP 38101 00974733272:682284 2 - 02 0006ab16 45 43 4b 44 | ECKD 38201 00974733272:682287 2 - 02 0006ab28 00 00 00 04 | .... 38301 00974733272:682289 2 - 02 0006ab3e 00 00 00 20 | ... 38401 00974733272:682297 2 - 02 0006ad7e 07 ea 4a 90 | .... 38501 00974733272:684384 2 - 00 0006ade6 46 52 45 45 | FREE 38601 00974733272:684388 2 - 00 0006adf6 07 ea 4a 90 | .... 387 388See section about predefined views for explanation of the above output! 389 390Changing the debug level 391------------------------ 392 393Example: 394 395 396> cat /sys/kernel/debug/s390dbf/dasd/level 3973 398> echo "5" > /sys/kernel/debug/s390dbf/dasd/level 399> cat /sys/kernel/debug/s390dbf/dasd/level 4005 401 402Flushing debug areas 403-------------------- 404Debug areas can be flushed with piping the number of the desired 405area (0...n) to the debugfs file "flush". When using "-" all debug areas 406are flushed. 407 408Examples: 409 4101. Flush debug area 0: 411> echo "0" > /sys/kernel/debug/s390dbf/dasd/flush 412 4132. Flush all debug areas: 414> echo "-" > /sys/kernel/debug/s390dbf/dasd/flush 415 416Changing the size of debug areas 417------------------------------------ 418It is possible the change the size of debug areas through piping 419the number of pages to the debugfs file "pages". The resize request will 420also flush the debug areas. 421 422Example: 423 424Define 4 pages for the debug areas of debug feature "dasd": 425> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages 426 427Stooping the debug feature 428-------------------------- 429Example: 430 4311. Check if stopping is allowed 432> cat /proc/sys/s390dbf/debug_stoppable 4332. Stop debug feature 434> echo 0 > /proc/sys/s390dbf/debug_active 435 436lcrash Interface 437---------------- 438It 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 440to investigate the debug logs on a live system and with a memory dump after 441a system crash. 442 443Investigating raw memory 444------------------------ 445One last possibility to investigate the debug logs at a live 446system and after a system crash is to look at the raw memory 447under VM or at the Service Element. 448It is possible to find the anker of the debug-logs through 449the 'debug_area_first' symbol in the System map. Then one has 450to follow the correct pointers of the data-structures defined 451in debug.h and find the debug-areas in memory. 452Normally modules which use the debug feature will also have 453a global variable with the pointer to the debug-logs. Following 454this pointer it will also be possible to find the debug logs in 455memory. 456 457For this method it is recommended to use '16 * x + 4' byte (x = 0..n) 458for the length of the data field in debug_register() in 459order to see the debug entries well formatted. 460 461 462Predefined Views 463---------------- 464 465There are three predefined views: hex_ascii, raw and sprintf. 466The hex_ascii view shows the data field in hex and ascii representation 467(e.g. '45 43 4b 44 | ECKD'). 468The raw view returns a bytestream as the debug areas are stored in memory. 469 470The sprintf view formats the debug entries in the same way as the sprintf 471function would do. The sprintf event/exception functions write to the 472debug entry a pointer to the format string (size = sizeof(long)) 473and for each vararg a long value. So e.g. for a debug entry with a format 474string plus two varargs one would need to allocate a (3 * sizeof(long)) 475byte data area in the debug_register() function. 476 477 478NOTE: If using the sprintf view do NOT use other event/exception functions 479than the sprintf-event and -exception functions. 480 481The 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 491The format of the raw view is: 492- Header as described in debug.h 493- datafield 494 495A typical line of the hex_ascii view will look like the following (first line 496is only for explanation and will not be displayed when 'cating' the view): 497 498area time level exception cpu caller data (hex + ascii) 499-------------------------------------------------------------------------- 50000 00964419409:440690 1 - 00 88023fe 501 502 503Defining views 504-------------- 505 506Views are specified with the 'debug_view' structure. There are defined 507callback functions which are used for reading and writing the debugfs files: 508 509struct 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 518where 519 520typedef 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 526typedef int (debug_format_proc_t) (debug_info_t* id, 527 struct debug_view* view, char* out_buf, 528 const char* in_buf); 529typedef int (debug_prolog_proc_t) (debug_info_t* id, 530 struct debug_view* view, 531 char* out_buf); 532typedef 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 538The "private_data" member can be used as pointer to view specific data. 539It is not used by the debug feature itself. 540 541The 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 550When a view is read from the debugfs, the Debug Feature calls the 551'prolog_proc' once for writing the prolog. 552Then 'header_proc' and 'format_proc' are called for each 553existing debug entry. 554 555The input_proc can be used to implement functionality when it is written to 556the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level). 557 558For header_proc there can be used the default function 559debug_dflt_header_fn() which is defined in debug.h. 560and which produces the same header output as the predefined views. 561E.g: 56200 00964419409:440761 2 - 00 88023ec 563 564In order to see how to use the callback functions check the implementation 565of the default views! 566 567Example 568 569#include <asm/debug.h> 570 571#define UNKNOWNSTR "data: %08x" 572 573const 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 582static 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 600struct 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===== 610test: 611===== 612debug_info_t *debug_info; 613... 614debug_info = debug_register ("test", 0, 4, 4 )); 615debug_register_view(debug_info, &debug_test_view); 616for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i); 617 618> cat /sys/kernel/debug/s390dbf/test/myview 61900 00964419734:611402 1 - 00 88042ca This error........... 62000 00964419734:611405 1 - 00 88042ca That error........... 62100 00964419734:611408 1 - 00 88042ca Problem.............. 62200 00964419734:611411 1 - 00 88042ca Something went wrong. 62300 00964419734:611414 1 - 00 88042ca Everything ok........ 62400 00964419734:611417 1 - 00 88042ca data: 00000005 62500 00964419734:611419 1 - 00 88042ca data: 00000006 62600 00964419734:611422 1 - 00 88042ca data: 00000007 62700 00964419734:611425 1 - 00 88042ca data: 00000008 62800 00964419734:611428 1 - 00 88042ca data: 00000009 629