1S390 Debug Feature 2================== 3 4files: arch/s390/kernel/debug.c 5 arch/s390/include/asm/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---------------------------------------------------------------------------- 119debug_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 123Parameter: 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 133Return Value: Handle for generated debug area 134 NULL if register failed 135 136Description: Allocates memory for a debug log 137 Must not be called within an interrupt handler 138 139--------------------------------------------------------------------------- 140void debug_unregister (debug_info_t * id); 141 142Parameter: id: handle for debug log 143 144Return Value: none 145 146Description: frees memory for a debug log and removes all registered debug 147 views. 148 Must not be called within an interrupt handler 149 150--------------------------------------------------------------------------- 151void debug_set_level (debug_info_t * id, int new_level); 152 153Parameter: id: handle for debug log 154 new_level: new debug level 155 156Return Value: none 157 158Description: Sets new actual debug level if new_level is valid. 159 160--------------------------------------------------------------------------- 161void debug_stop_all(void); 162 163Parameter: none 164 165Return Value: none 166 167Description: stops the debug feature if stopping is allowed. Currently 168 used in case of a kernel oops. 169 170--------------------------------------------------------------------------- 171debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 172 int length); 173 174Parameter: id: handle for debug log 175 level: debug level 176 data: pointer to data for debug entry 177 length: length of data in bytes 178 179Return Value: Address of written debug entry 180 181Description: writes debug entry to active debug area (if level <= actual 182 debug level) 183 184--------------------------------------------------------------------------- 185debug_entry_t* debug_int_event (debug_info_t * id, int level, 186 unsigned int data); 187debug_entry_t* debug_long_event(debug_info_t * id, int level, 188 unsigned long data); 189 190Parameter: id: handle for debug log 191 level: debug level 192 data: integer value for debug entry 193 194Return Value: Address of written debug entry 195 196Description: writes debug entry to active debug area (if level <= actual 197 debug level) 198 199--------------------------------------------------------------------------- 200debug_entry_t* debug_text_event (debug_info_t * id, int level, 201 const char* data); 202 203Parameter: id: handle for debug log 204 level: debug level 205 data: string for debug entry 206 207Return Value: Address of written debug entry 208 209Description: writes debug entry in ascii format to active debug area 210 (if level <= actual debug level) 211 212--------------------------------------------------------------------------- 213debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 214 char* string,...); 215 216Parameter: id: handle for debug log 217 level: debug level 218 string: format string for debug entry 219 ...: varargs used as in sprintf() 220 221Return Value: Address of written debug entry 222 223Description: writes debug entry with format string and varargs (longs) to 224 active debug area (if level $<=$ actual debug level). 225 floats and long long datatypes cannot be used as varargs. 226 227--------------------------------------------------------------------------- 228 229debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 230 int length); 231 232Parameter: id: handle for debug log 233 level: debug level 234 data: pointer to data for debug entry 235 length: length of data in bytes 236 237Return Value: Address of written debug entry 238 239Description: writes debug entry to active debug area (if level <= actual 240 debug level) and switches to next debug area 241 242--------------------------------------------------------------------------- 243debug_entry_t* debug_int_exception (debug_info_t * id, int level, 244 unsigned int data); 245debug_entry_t* debug_long_exception(debug_info_t * id, int level, 246 unsigned long data); 247 248Parameter: id: handle for debug log 249 level: debug level 250 data: integer value for debug entry 251 252Return Value: Address of written debug entry 253 254Description: writes debug entry to active debug area (if level <= actual 255 debug level) and switches to next debug area 256 257--------------------------------------------------------------------------- 258debug_entry_t* debug_text_exception (debug_info_t * id, int level, 259 const char* data); 260 261Parameter: id: handle for debug log 262 level: debug level 263 data: string for debug entry 264 265Return Value: Address of written debug entry 266 267Description: writes debug entry in ascii format to active debug area 268 (if level <= actual debug level) and switches to next debug 269 area 270 271--------------------------------------------------------------------------- 272debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level, 273 char* string,...); 274 275Parameter: id: handle for debug log 276 level: debug level 277 string: format string for debug entry 278 ...: varargs used as in sprintf() 279 280Return Value: Address of written debug entry 281 282Description: writes debug entry with format string and varargs (longs) to 283 active debug area (if level $<=$ actual debug level) and 284 switches to next debug area. 285 floats and long long datatypes cannot be used as varargs. 286 287--------------------------------------------------------------------------- 288 289int debug_register_view (debug_info_t * id, struct debug_view *view); 290 291Parameter: id: handle for debug log 292 view: pointer to debug view struct 293 294Return Value: 0 : ok 295 < 0: Error 296 297Description: registers new debug view and creates debugfs dir entry 298 299--------------------------------------------------------------------------- 300int debug_unregister_view (debug_info_t * id, struct debug_view *view); 301 302Parameter: id: handle for debug log 303 view: pointer to debug view struct 304 305Return Value: 0 : ok 306 < 0: Error 307 308Description: unregisters debug view and removes debugfs dir entry 309 310 311 312Predefined views: 313----------------- 314 315extern struct debug_view debug_hex_ascii_view; 316extern struct debug_view debug_raw_view; 317extern struct debug_view debug_sprintf_view; 318 319Examples 320-------- 321 322/* 323 * hex_ascii- + raw-view Example 324 */ 325 326#include <linux/init.h> 327#include <asm/debug.h> 328 329static debug_info_t* debug_info; 330 331static int init(void) 332{ 333 /* register 4 debug areas with one page each and 4 byte data field */ 334 335 debug_info = debug_register ("test", 1, 4, 4 ); 336 debug_register_view(debug_info,&debug_hex_ascii_view); 337 debug_register_view(debug_info,&debug_raw_view); 338 339 debug_text_event(debug_info, 4 , "one "); 340 debug_int_exception(debug_info, 4, 4711); 341 debug_event(debug_info, 3, &debug_info, 4); 342 343 return 0; 344} 345 346static void cleanup(void) 347{ 348 debug_unregister (debug_info); 349} 350 351module_init(init); 352module_exit(cleanup); 353 354--------------------------------------------------------------------------- 355 356/* 357 * sprintf-view Example 358 */ 359 360#include <linux/init.h> 361#include <asm/debug.h> 362 363static debug_info_t* debug_info; 364 365static int init(void) 366{ 367 /* register 4 debug areas with one page each and data field for */ 368 /* format string pointer + 2 varargs (= 3 * sizeof(long)) */ 369 370 debug_info = debug_register ("test", 1, 4, sizeof(long) * 3); 371 debug_register_view(debug_info,&debug_sprintf_view); 372 373 debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__); 374 debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info); 375 376 return 0; 377} 378 379static void cleanup(void) 380{ 381 debug_unregister (debug_info); 382} 383 384module_init(init); 385module_exit(cleanup); 386 387 388 389Debugfs Interface 390---------------- 391Views to the debug logs can be investigated through reading the corresponding 392debugfs-files: 393 394Example: 395 396> ls /sys/kernel/debug/s390dbf/dasd 397flush hex_ascii level pages raw 398> cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1 39900 00974733272:680099 2 - 02 0006ad7e 07 ea 4a 90 | .... 40000 00974733272:682210 2 - 02 0006ade6 46 52 45 45 | FREE 40100 00974733272:682213 2 - 02 0006adf6 07 ea 4a 90 | .... 40200 00974733272:682281 1 * 02 0006ab08 41 4c 4c 43 | EXCP 40301 00974733272:682284 2 - 02 0006ab16 45 43 4b 44 | ECKD 40401 00974733272:682287 2 - 02 0006ab28 00 00 00 04 | .... 40501 00974733272:682289 2 - 02 0006ab3e 00 00 00 20 | ... 40601 00974733272:682297 2 - 02 0006ad7e 07 ea 4a 90 | .... 40701 00974733272:684384 2 - 00 0006ade6 46 52 45 45 | FREE 40801 00974733272:684388 2 - 00 0006adf6 07 ea 4a 90 | .... 409 410See section about predefined views for explanation of the above output! 411 412Changing the debug level 413------------------------ 414 415Example: 416 417 418> cat /sys/kernel/debug/s390dbf/dasd/level 4193 420> echo "5" > /sys/kernel/debug/s390dbf/dasd/level 421> cat /sys/kernel/debug/s390dbf/dasd/level 4225 423 424Flushing debug areas 425-------------------- 426Debug areas can be flushed with piping the number of the desired 427area (0...n) to the debugfs file "flush". When using "-" all debug areas 428are flushed. 429 430Examples: 431 4321. Flush debug area 0: 433> echo "0" > /sys/kernel/debug/s390dbf/dasd/flush 434 4352. Flush all debug areas: 436> echo "-" > /sys/kernel/debug/s390dbf/dasd/flush 437 438Changing the size of debug areas 439------------------------------------ 440It is possible the change the size of debug areas through piping 441the number of pages to the debugfs file "pages". The resize request will 442also flush the debug areas. 443 444Example: 445 446Define 4 pages for the debug areas of debug feature "dasd": 447> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages 448 449Stooping the debug feature 450-------------------------- 451Example: 452 4531. Check if stopping is allowed 454> cat /proc/sys/s390dbf/debug_stoppable 4552. Stop debug feature 456> echo 0 > /proc/sys/s390dbf/debug_active 457 458lcrash Interface 459---------------- 460It is planned that the dump analysis tool lcrash gets an additional command 461's390dbf' to display all the debug logs. With this tool it will be possible 462to investigate the debug logs on a live system and with a memory dump after 463a system crash. 464 465Investigating raw memory 466------------------------ 467One last possibility to investigate the debug logs at a live 468system and after a system crash is to look at the raw memory 469under VM or at the Service Element. 470It is possible to find the anker of the debug-logs through 471the 'debug_area_first' symbol in the System map. Then one has 472to follow the correct pointers of the data-structures defined 473in debug.h and find the debug-areas in memory. 474Normally modules which use the debug feature will also have 475a global variable with the pointer to the debug-logs. Following 476this pointer it will also be possible to find the debug logs in 477memory. 478 479For this method it is recommended to use '16 * x + 4' byte (x = 0..n) 480for the length of the data field in debug_register() in 481order to see the debug entries well formatted. 482 483 484Predefined Views 485---------------- 486 487There are three predefined views: hex_ascii, raw and sprintf. 488The hex_ascii view shows the data field in hex and ascii representation 489(e.g. '45 43 4b 44 | ECKD'). 490The raw view returns a bytestream as the debug areas are stored in memory. 491 492The sprintf view formats the debug entries in the same way as the sprintf 493function would do. The sprintf event/exception functions write to the 494debug entry a pointer to the format string (size = sizeof(long)) 495and for each vararg a long value. So e.g. for a debug entry with a format 496string plus two varargs one would need to allocate a (3 * sizeof(long)) 497byte data area in the debug_register() function. 498 499IMPORTANT: Using "%s" in sprintf event functions is dangerous. You can only 500use "%s" in the sprintf event functions, if the memory for the passed string is 501available as long as the debug feature exists. The reason behind this is that 502due to performance considerations only a pointer to the string is stored in 503the debug feature. If you log a string that is freed afterwards, you will get 504an OOPS when inspecting the debug feature, because then the debug feature will 505access the already freed memory. 506 507NOTE: If using the sprintf view do NOT use other event/exception functions 508than the sprintf-event and -exception functions. 509 510The format of the hex_ascii and sprintf view is as follows: 511- Number of area 512- Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated 513 Universal Time (UTC), January 1, 1970) 514- level of debug entry 515- Exception flag (* = Exception) 516- Cpu-Number of calling task 517- Return Address to caller 518- data field 519 520The format of the raw view is: 521- Header as described in debug.h 522- datafield 523 524A typical line of the hex_ascii view will look like the following (first line 525is only for explanation and will not be displayed when 'cating' the view): 526 527area time level exception cpu caller data (hex + ascii) 528-------------------------------------------------------------------------- 52900 00964419409:440690 1 - 00 88023fe 530 531 532Defining views 533-------------- 534 535Views are specified with the 'debug_view' structure. There are defined 536callback functions which are used for reading and writing the debugfs files: 537 538struct debug_view { 539 char name[DEBUG_MAX_PROCF_LEN]; 540 debug_prolog_proc_t* prolog_proc; 541 debug_header_proc_t* header_proc; 542 debug_format_proc_t* format_proc; 543 debug_input_proc_t* input_proc; 544 void* private_data; 545}; 546 547where 548 549typedef int (debug_header_proc_t) (debug_info_t* id, 550 struct debug_view* view, 551 int area, 552 debug_entry_t* entry, 553 char* out_buf); 554 555typedef int (debug_format_proc_t) (debug_info_t* id, 556 struct debug_view* view, char* out_buf, 557 const char* in_buf); 558typedef int (debug_prolog_proc_t) (debug_info_t* id, 559 struct debug_view* view, 560 char* out_buf); 561typedef int (debug_input_proc_t) (debug_info_t* id, 562 struct debug_view* view, 563 struct file* file, const char* user_buf, 564 size_t in_buf_size, loff_t* offset); 565 566 567The "private_data" member can be used as pointer to view specific data. 568It is not used by the debug feature itself. 569 570The output when reading a debugfs file is structured like this: 571 572"prolog_proc output" 573 574"header_proc output 1" "format_proc output 1" 575"header_proc output 2" "format_proc output 2" 576"header_proc output 3" "format_proc output 3" 577... 578 579When a view is read from the debugfs, the Debug Feature calls the 580'prolog_proc' once for writing the prolog. 581Then 'header_proc' and 'format_proc' are called for each 582existing debug entry. 583 584The input_proc can be used to implement functionality when it is written to 585the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level). 586 587For header_proc there can be used the default function 588debug_dflt_header_fn() which is defined in debug.h. 589and which produces the same header output as the predefined views. 590E.g: 59100 00964419409:440761 2 - 00 88023ec 592 593In order to see how to use the callback functions check the implementation 594of the default views! 595 596Example 597 598#include <asm/debug.h> 599 600#define UNKNOWNSTR "data: %08x" 601 602const char* messages[] = 603{"This error...........\n", 604 "That error...........\n", 605 "Problem..............\n", 606 "Something went wrong.\n", 607 "Everything ok........\n", 608 NULL 609}; 610 611static int debug_test_format_fn( 612 debug_info_t * id, struct debug_view *view, 613 char *out_buf, const char *in_buf 614) 615{ 616 int i, rc = 0; 617 618 if(id->buf_size >= 4) { 619 int msg_nr = *((int*)in_buf); 620 if(msg_nr < sizeof(messages)/sizeof(char*) - 1) 621 rc += sprintf(out_buf, "%s", messages[msg_nr]); 622 else 623 rc += sprintf(out_buf, UNKNOWNSTR, msg_nr); 624 } 625 out: 626 return rc; 627} 628 629struct debug_view debug_test_view = { 630 "myview", /* name of view */ 631 NULL, /* no prolog */ 632 &debug_dflt_header_fn, /* default header for each entry */ 633 &debug_test_format_fn, /* our own format function */ 634 NULL, /* no input function */ 635 NULL /* no private data */ 636}; 637 638===== 639test: 640===== 641debug_info_t *debug_info; 642... 643debug_info = debug_register ("test", 0, 4, 4 )); 644debug_register_view(debug_info, &debug_test_view); 645for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i); 646 647> cat /sys/kernel/debug/s390dbf/test/myview 64800 00964419734:611402 1 - 00 88042ca This error........... 64900 00964419734:611405 1 - 00 88042ca That error........... 65000 00964419734:611408 1 - 00 88042ca Problem.............. 65100 00964419734:611411 1 - 00 88042ca Something went wrong. 65200 00964419734:611414 1 - 00 88042ca Everything ok........ 65300 00964419734:611417 1 - 00 88042ca data: 00000005 65400 00964419734:611419 1 - 00 88042ca data: 00000006 65500 00964419734:611422 1 - 00 88042ca data: 00000007 65600 00964419734:611425 1 - 00 88042ca data: 00000008 65700 00964419734:611428 1 - 00 88042ca data: 00000009 658