summaryrefslogtreecommitdiffstats
path: root/Documentation/s390/s390dbf.txt
blob: 2095a2704b8fcd7d0c0a233430b854e6e976ecf8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
S390 Debug Feature
==================

files: arch/s390/kernel/debug.c
       include/asm-s390/debug.h

Description:
------------
The goal of this feature is to provide a kernel debug logging API 
where log records can be stored efficiently in memory, where each component 
(e.g. device drivers) can have one separate debug log.
One purpose of this is to inspect the debug logs after a production system crash
in order to analyze the reason for the crash.
If the system still runs but only a subcomponent which uses dbf fails,
it is possible to look at the debug logs on a live system via the Linux
debugfs filesystem.
The debug feature may also very useful for kernel and driver development.

Design:
-------
Kernel components (e.g. device drivers) can register themselves at the debug 
feature with the function call debug_register(). This function initializes a 
debug log for the caller. For each debug log exists a number of debug areas 
where exactly one is active at one time.  Each debug area consists of contiguous
pages in memory. In the debug areas there are stored debug entries (log records)
which are written by event- and exception-calls. 

An event-call writes the specified debug entry to the active debug
area and updates the log pointer for the active area. If the end 
of the active debug area is reached, a wrap around is done (ring buffer) 
and the next debug entry will be written at the beginning of the active 
debug area.

An exception-call writes the specified debug entry to the log and
switches to the next debug area. This is done in order to be sure
that the records which describe the origin of the exception are not
overwritten when a wrap around for the current area occurs.

The debug areas itselve are also ordered in form of a ring buffer. 
When an exception is thrown in the last debug area, the following debug 
entries are then written again in the very first area.

There are three versions for the event- and exception-calls: One for
logging raw data, one for text and one for numbers.

Each debug entry contains the following data:

- Timestamp
- Cpu-Number of calling task
- Level of debug entry (0...6)
- Return Address to caller
- Flag, if entry is an exception or not

The debug logs can be inspected in a live system through entries in
the debugfs-filesystem. Under the toplevel directory "s390dbf" there is
a directory for each registered component, which is named like the
corresponding component. The debugfs normally should be mounted to
/sys/kernel/debug therefore the debug feature can be accessed unter
/sys/kernel/debug/s390dbf.

The content of the directories are files which represent different views
to the debug log. Each component can decide which views should be
used through registering them with the function debug_register_view().
Predefined views for hex/ascii, sprintf and raw binary data are provided.
It is also possible to define other views. The content of
a view can be inspected simply by reading the corresponding debugfs file.

All debug logs have an an actual debug level (range from 0 to 6).
The default level is 3. Event and Exception functions have a 'level'
parameter. Only debug entries with a level that is lower or equal
than the actual level are written to the log. This means, when
writing events, high priority log entries should have a low level
value whereas low priority entries should have a high one.
The actual debug level can be changed with the help of the debugfs-filesystem
through writing a number string "x" to the 'level' debugfs file which is
provided for every debug log. Debugging can be switched off completely
by using "-" on the 'level' debugfs file.

Example:

> echo "-" > /sys/kernel/debug/s390dbf/dasd/level

It is also possible to deactivate the debug feature globally for every
debug log. You can change the behavior using  2 sysctl parameters in
/proc/sys/s390dbf:
There are currently 2 possible triggers, which stop the  debug feature
globally. The first possbility is to use the "debug_active" sysctl. If
set to 1 the debug feature is running. If "debug_active" is set to 0 the
debug feature is turned off.
The second trigger which stops the debug feature is an kernel oops.
That prevents the debug feature from overwriting debug information that
happened before the oops. After an oops you can reactivate the debug feature
by piping 1 to /proc/sys/s390dbf/debug_active. Nevertheless, its not
suggested to use an oopsed kernel in an production environment.
If you want to disallow the deactivation of the debug feature, you can use
the "debug_stoppable" sysctl. If you set "debug_stoppable" to 0 the debug
feature cannot be stopped. If the debug feature is already stopped, it
will stay deactivated.

Kernel Interfaces:
------------------

----------------------------------------------------------------------------
debug_info_t *debug_register(char *name, int pages, int nr_areas,
                             int buf_size);

Parameter:    name:        Name of debug log (e.g. used for debugfs entry)
              pages:       number of pages, which will be allocated per area
              nr_areas:    number of debug areas
              buf_size:    size of data area in each debug entry

Return Value: Handle for generated debug area   
              NULL if register failed 

Description:  Allocates memory for a debug log     
              Must not be called within an interrupt handler 

---------------------------------------------------------------------------
void debug_unregister (debug_info_t * id);

Parameter:     id:   handle for debug log  

Return Value:  none 

Description:   frees memory for a debug log     
               Must not be called within an interrupt handler 

---------------------------------------------------------------------------
void debug_set_level (debug_info_t * id, int new_level);

Parameter:     id:        handle for debug log  
               new_level: new debug level 

Return Value:  none 

Description:   Sets new actual debug level if new_level is valid. 

---------------------------------------------------------------------------
void debug_stop_all(void);

Parameter:     none

Return Value:  none

Description:   stops the debug feature if stopping is allowed. Currently
               used in case of a kernel oops.

---------------------------------------------------------------------------
debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 
                            int length);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   pointer to data for debug entry  
               length: length of data in bytes       

Return Value:  Address of written debug entry 

Description:   writes debug entry to active debug area (if level <= actual 
               debug level)    

---------------------------------------------------------------------------
debug_entry_t* debug_int_event (debug_info_t * id, int level, 
                                unsigned int data);
debug_entry_t* debug_long_event(debug_info_t * id, int level,
                                unsigned long data);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   integer value for debug entry           

Return Value:  Address of written debug entry 

Description:   writes debug entry to active debug area (if level <= actual 
               debug level)    

---------------------------------------------------------------------------
debug_entry_t* debug_text_event (debug_info_t * id, int level, 
                                 const char* data);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   string for debug entry  

Return Value:  Address of written debug entry 

Description:   writes debug entry in ascii format to active debug area 
               (if level <= actual debug level)     

---------------------------------------------------------------------------
debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 
                                    char* string,...);

Parameter:     id:    handle for debug log 
               level: debug level
               string: format string for debug entry 
               ...: varargs used as in sprintf()

Return Value:  Address of written debug entry

Description:   writes debug entry with format string and varargs (longs) to 
               active debug area (if level $<=$ actual debug level). 
               floats and long long datatypes cannot be used as varargs.

---------------------------------------------------------------------------

debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 
                                int length);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   pointer to data for debug entry  
               length: length of data in bytes       

Return Value:  Address of written debug entry 

Description:   writes debug entry to active debug area (if level <= actual 
               debug level) and switches to next debug area  

---------------------------------------------------------------------------
debug_entry_t* debug_int_exception (debug_info_t * id, int level, 
                                    unsigned int data);
debug_entry_t* debug_long_exception(debug_info_t * id, int level,
                                    unsigned long data);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   integer value for debug entry           

Return Value:  Address of written debug entry 

Description:   writes debug entry to active debug area (if level <= actual 
               debug level) and switches to next debug area  

---------------------------------------------------------------------------
debug_entry_t* debug_text_exception (debug_info_t * id, int level, 
                                     const char* data);

Parameter:     id:     handle for debug log  
               level:  debug level           
               data:   string for debug entry  

Return Value:  Address of written debug entry 

Description:   writes debug entry in ascii format to active debug area 
               (if level <= actual debug level) and switches to next debug 
               area  

---------------------------------------------------------------------------
debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
                                        char* string,...);

Parameter:     id:    handle for debug log  
               level: debug level  
               string: format string for debug entry  
               ...: varargs used as in sprintf()

Return Value:  Address of written debug entry 

Description:   writes debug entry with format string and varargs (longs) to 
               active debug area (if level $<=$ actual debug level) and
               switches to next debug area. 
               floats and long long datatypes cannot be used as varargs.

---------------------------------------------------------------------------

int debug_register_view (debug_info_t * id, struct debug_view *view);

Parameter:     id:    handle for debug log  
               view:  pointer to debug view struct 

Return Value:  0  : ok 
               < 0: Error 

Description:   registers new debug view and creates debugfs dir entry

---------------------------------------------------------------------------
int debug_unregister_view (debug_info_t * id, struct debug_view *view); 

Parameter:     id:    handle for debug log  
               view:  pointer to debug view struct 

Return Value:  0  : ok 
               < 0: Error 

Description:   unregisters debug view and removes debugfs dir entry



Predefined views:
-----------------

extern struct debug_view debug_hex_ascii_view;
extern struct debug_view debug_raw_view;
extern struct debug_view debug_sprintf_view;

Examples
--------

/*
 * hex_ascii- + raw-view Example
 */

#include <linux/init.h>
#include <asm/debug.h>

static debug_info_t* debug_info;

static int init(void)
{
    /* register 4 debug areas with one page each and 4 byte data field */

    debug_info = debug_register ("test", 1, 4, 4 );
    debug_register_view(debug_info,&debug_hex_ascii_view);
    debug_register_view(debug_info,&debug_raw_view);

    debug_text_event(debug_info, 4 , "one ");
    debug_int_exception(debug_info, 4, 4711);
    debug_event(debug_info, 3, &debug_info, 4);

    return 0;
}

static void cleanup(void)
{
    debug_unregister (debug_info);
}

module_init(init);
module_exit(cleanup);

---------------------------------------------------------------------------

/*
 * sprintf-view Example
 */

#include <linux/init.h>
#include <asm/debug.h>

static debug_info_t* debug_info;

static int init(void)
{
    /* register 4 debug areas with one page each and data field for */
    /* format string pointer + 2 varargs (= 3 * sizeof(long))       */

    debug_info = debug_register ("test", 1, 4, sizeof(long) * 3);
    debug_register_view(debug_info,&debug_sprintf_view);

    debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
    debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);

    return 0;
}

static void cleanup(void)
{
    debug_unregister (debug_info);
}

module_init(init);
module_exit(cleanup);



Debugfs Interface
----------------
Views to the debug logs can be investigated through reading the corresponding 
debugfs-files:

Example:

> ls /sys/kernel/debug/s390dbf/dasd
flush  hex_ascii  level pages raw
> cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1
00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP 
01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ... 
01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....

See section about predefined views for explanation of the above output!

Changing the debug level
------------------------

Example:


> cat /sys/kernel/debug/s390dbf/dasd/level
3
> echo "5" > /sys/kernel/debug/s390dbf/dasd/level
> cat /sys/kernel/debug/s390dbf/dasd/level
5

Flushing debug areas
--------------------
Debug areas can be flushed with piping the number of the desired
area (0...n) to the debugfs file "flush". When using "-" all debug areas
are flushed.

Examples:

1. Flush debug area 0:
> echo "0" > /sys/kernel/debug/s390dbf/dasd/flush

2. Flush all debug areas:
> echo "-" > /sys/kernel/debug/s390dbf/dasd/flush

Changing the size of debug areas
------------------------------------
It is possible the change the size of debug areas through piping
the number of pages to the debugfs file "pages". The resize request will
also flush the debug areas.

Example:

Define 4 pages for the debug areas of debug feature "dasd":
> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages

Stooping the debug feature
--------------------------
Example:

1. Check if stopping is allowed
> cat /proc/sys/s390dbf/debug_stoppable
2. Stop debug feature
> echo 0 > /proc/sys/s390dbf/debug_active

lcrash Interface
----------------
It is planned that the dump analysis tool lcrash gets an additional command
's390dbf' to display all the debug logs. With this tool it will be possible 
to investigate the debug logs on a live system and with a memory dump after 
a system crash.

Investigating raw memory
------------------------
One last possibility to investigate the debug logs at a live
system and after a system crash is to look at the raw memory
under VM or at the Service Element.
It is possible to find the anker of the debug-logs through
the 'debug_area_first' symbol in the System map. Then one has
to follow the correct pointers of the data-structures defined
in debug.h and find the debug-areas in memory.
Normally modules which use the debug feature will also have
a global variable with the pointer to the debug-logs. Following
this pointer it will also be possible to find the debug logs in
memory.

For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
for the length of the data field in debug_register() in
order to see the debug entries well formatted.


Predefined Views
----------------

There are three predefined views: hex_ascii, raw and sprintf. 
The hex_ascii view shows the data field in hex and ascii representation 
(e.g. '45 43 4b 44 | ECKD'). 
The raw view returns a bytestream as the debug areas are stored in memory.

The sprintf view formats the debug entries in the same way as the sprintf
function would do. The sprintf event/exception functions write to the
debug entry a pointer to the format string (size = sizeof(long)) 
and for each vararg a long value. So e.g. for a debug entry with a format 
string plus two varargs one would need to allocate a (3 * sizeof(long)) 
byte data area in the debug_register() function.


NOTE: If using the sprintf view do NOT use other event/exception functions
than the sprintf-event and -exception functions.

The format of the hex_ascii and sprintf view is as follows:
- Number of area
- Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated 
  Universal Time (UTC), January 1, 1970)
- level of debug entry
- Exception flag (* = Exception)
- Cpu-Number of calling task
- Return Address to caller
- data field

The format of the raw view is:
- Header as described in debug.h
- datafield 

A typical line of the hex_ascii view will look like the following (first line 
is only for explanation and will not be displayed when 'cating' the view):

area  time           level exception cpu caller    data (hex + ascii)
--------------------------------------------------------------------------
00    00964419409:440690 1 -         00  88023fe   


Defining views
--------------

Views are specified with the 'debug_view' structure. There are defined
callback functions which are used for reading and writing the debugfs files:

struct debug_view {
        char name[DEBUG_MAX_PROCF_LEN];  
        debug_prolog_proc_t* prolog_proc; 
        debug_header_proc_t* header_proc;
        debug_format_proc_t* format_proc;
        debug_input_proc_t*  input_proc;
	void*                private_data;
};

where

typedef int (debug_header_proc_t) (debug_info_t* id,
                                   struct debug_view* view,
                                   int area,
                                   debug_entry_t* entry,
                                   char* out_buf);

typedef int (debug_format_proc_t) (debug_info_t* id,
                                   struct debug_view* view, char* out_buf,
                                   const char* in_buf);
typedef int (debug_prolog_proc_t) (debug_info_t* id,
                                   struct debug_view* view,
                                   char* out_buf);
typedef int (debug_input_proc_t) (debug_info_t* id,
                                  struct debug_view* view,
                                  struct file* file, const char* user_buf,
                                  size_t in_buf_size, loff_t* offset);


The "private_data" member can be used as pointer to view specific data.
It is not used by the debug feature itself.

The output when reading a debugfs file is structured like this:

"prolog_proc output"

"header_proc output 1"  "format_proc output 1"
"header_proc output 2"  "format_proc output 2"
"header_proc output 3"  "format_proc output 3"
...

When a view is read from the debugfs, the Debug Feature calls the
'prolog_proc' once for writing the prolog.
Then 'header_proc' and 'format_proc' are called for each 
existing debug entry.

The input_proc can be used to implement functionality when it is written to 
the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).

For header_proc there can be used the default function
debug_dflt_header_fn() which is defined in in debug.h.
and which produces the same header output as the predefined views.
E.g:
00 00964419409:440761 2 - 00 88023ec

In order to see how to use the callback functions check the implementation
of the default views!

Example

#include <asm/debug.h>

#define UNKNOWNSTR "data: %08x"

const char* messages[] =
{"This error...........\n",
 "That error...........\n",
 "Problem..............\n",
 "Something went wrong.\n",
 "Everything ok........\n",
 NULL
};

static int debug_test_format_fn(
   debug_info_t * id, struct debug_view *view, 
   char *out_buf, const char *in_buf
)
{
  int i, rc = 0;

  if(id->buf_size >= 4) {
     int msg_nr = *((int*)in_buf);
     if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
        rc += sprintf(out_buf, "%s", messages[msg_nr]);	
     else
        rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
  }
 out:
   return rc;
}

struct debug_view debug_test_view = {
  "myview",                 /* name of view */
  NULL,                     /* no prolog */
  &debug_dflt_header_fn,    /* default header for each entry */
  &debug_test_format_fn,    /* our own format function */
  NULL,                     /* no input function */
  NULL                      /* no private data */
};

=====
test:
=====
debug_info_t *debug_info;
...
debug_info = debug_register ("test", 0, 4, 4 ));
debug_register_view(debug_info, &debug_test_view);
for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);

> cat /sys/kernel/debug/s390dbf/test/myview
00 00964419734:611402 1 - 00 88042ca   This error...........
00 00964419734:611405 1 - 00 88042ca   That error...........
00 00964419734:611408 1 - 00 88042ca   Problem..............
00 00964419734:611411 1 - 00 88042ca   Something went wrong.
00 00964419734:611414 1 - 00 88042ca   Everything ok........
00 00964419734:611417 1 - 00 88042ca   data: 00000005
00 00964419734:611419 1 - 00 88042ca   data: 00000006
00 00964419734:611422 1 - 00 88042ca   data: 00000007
00 00964419734:611425 1 - 00 88042ca   data: 00000008
00 00964419734:611428 1 - 00 88042ca   data: 00000009