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Documentation / s390 / s390dbf.txt

Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 EST.

1	S390 Debug Feature
2	==================
3	
4	files: arch/s390/kernel/debug.c
5	       include/asm-s390/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	void debug_unregister (debug_info_t * id);
120	
121	Parameter:     id:   handle for debug log  
122	
123	Return Value:  none 
124	
125	Description:   frees memory for a debug log     
126	               Must not be called within an interrupt handler 
127	
128	---------------------------------------------------------------------------
129	void debug_set_level (debug_info_t * id, int new_level);
130	
131	Parameter:     id:        handle for debug log  
132	               new_level: new debug level 
133	
134	Return Value:  none 
135	
136	Description:   Sets new actual debug level if new_level is valid. 
137	
138	---------------------------------------------------------------------------
139	void debug_stop_all(void);
140	
141	Parameter:     none
142	
143	Return Value:  none
144	
145	Description:   stops the debug feature if stopping is allowed. Currently
146	               used in case of a kernel oops.
147	
148	---------------------------------------------------------------------------
149	debug_entry_t* debug_event (debug_info_t* id, int level, void* data, 
150	                            int length);
151	
152	Parameter:     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	
157	Return Value:  Address of written debug entry 
158	
159	Description:   writes debug entry to active debug area (if level <= actual 
160	               debug level)    
161	
162	---------------------------------------------------------------------------
163	debug_entry_t* debug_int_event (debug_info_t * id, int level, 
164	                                unsigned int data);
165	debug_entry_t* debug_long_event(debug_info_t * id, int level,
166	                                unsigned long data);
167	
168	Parameter:     id:     handle for debug log  
169	               level:  debug level           
170	               data:   integer value for debug entry           
171	
172	Return Value:  Address of written debug entry 
173	
174	Description:   writes debug entry to active debug area (if level <= actual 
175	               debug level)    
176	
177	---------------------------------------------------------------------------
178	debug_entry_t* debug_text_event (debug_info_t * id, int level, 
179	                                 const char* data);
180	
181	Parameter:     id:     handle for debug log  
182	               level:  debug level           
183	               data:   string for debug entry  
184	
185	Return Value:  Address of written debug entry 
186	
187	Description:   writes debug entry in ascii format to active debug area 
188	               (if level <= actual debug level)     
189	
190	---------------------------------------------------------------------------
191	debug_entry_t* debug_sprintf_event (debug_info_t * id, int level, 
192	                                    char* string,...);
193	
194	Parameter:     id:    handle for debug log 
195	               level: debug level
196	               string: format string for debug entry 
197	               ...: varargs used as in sprintf()
198	
199	Return Value:  Address of written debug entry
200	
201	Description:   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	
207	debug_entry_t* debug_exception (debug_info_t* id, int level, void* data, 
208	                                int length);
209	
210	Parameter:     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	
215	Return Value:  Address of written debug entry 
216	
217	Description:   writes debug entry to active debug area (if level <= actual 
218	               debug level) and switches to next debug area  
219	
220	---------------------------------------------------------------------------
221	debug_entry_t* debug_int_exception (debug_info_t * id, int level, 
222	                                    unsigned int data);
223	debug_entry_t* debug_long_exception(debug_info_t * id, int level,
224	                                    unsigned long data);
225	
226	Parameter:     id:     handle for debug log  
227	               level:  debug level           
228	               data:   integer value for debug entry           
229	
230	Return Value:  Address of written debug entry 
231	
232	Description:   writes debug entry to active debug area (if level <= actual 
233	               debug level) and switches to next debug area  
234	
235	---------------------------------------------------------------------------
236	debug_entry_t* debug_text_exception (debug_info_t * id, int level, 
237	                                     const char* data);
238	
239	Parameter:     id:     handle for debug log  
240	               level:  debug level           
241	               data:   string for debug entry  
242	
243	Return Value:  Address of written debug entry 
244	
245	Description:   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	---------------------------------------------------------------------------
250	debug_entry_t* debug_sprintf_exception (debug_info_t * id, int level,
251	                                        char* string,...);
252	
253	Parameter:     id:    handle for debug log  
254	               level: debug level  
255	               string: format string for debug entry  
256	               ...: varargs used as in sprintf()
257	
258	Return Value:  Address of written debug entry 
259	
260	Description:   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	
267	int debug_register_view (debug_info_t * id, struct debug_view *view);
268	
269	Parameter:     id:    handle for debug log  
270	               view:  pointer to debug view struct 
271	
272	Return Value:  0  : ok 
273	               < 0: Error 
274	
275	Description:   registers new debug view and creates debugfs dir entry
276	
277	---------------------------------------------------------------------------
278	int debug_unregister_view (debug_info_t * id, struct debug_view *view); 
279	
280	Parameter:     id:    handle for debug log  
281	               view:  pointer to debug view struct 
282	
283	Return Value:  0  : ok 
284	               < 0: Error 
285	
286	Description:   unregisters debug view and removes debugfs dir entry
287	
288	
289	
290	Predefined views:
291	-----------------
292	
293	extern struct debug_view debug_hex_ascii_view;
294	extern struct debug_view debug_raw_view;
295	extern struct debug_view debug_sprintf_view;
296	
297	Examples
298	--------
299	
300	/*
301	 * hex_ascii- + raw-view Example
302	 */
303	
304	#include <linux/init.h>
305	#include <asm/debug.h>
306	
307	static debug_info_t* debug_info;
308	
309	static 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	
324	static void cleanup(void)
325	{
326	    debug_unregister (debug_info);
327	}
328	
329	module_init(init);
330	module_exit(cleanup);
331	
332	---------------------------------------------------------------------------
333	
334	/*
335	 * sprintf-view Example
336	 */
337	
338	#include <linux/init.h>
339	#include <asm/debug.h>
340	
341	static debug_info_t* debug_info;
342	
343	static 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	
357	static void cleanup(void)
358	{
359	    debug_unregister (debug_info);
360	}
361	
362	module_init(init);
363	module_exit(cleanup);
364	
365	
366	
367	Debugfs Interface
368	----------------
369	Views to the debug logs can be investigated through reading the corresponding 
370	debugfs-files:
371	
372	Example:
373	
374	> ls /sys/kernel/debug/s390dbf/dasd
375	flush  hex_ascii  level pages raw
376	> cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort +1
377	00 00974733272:680099 2 - 02 0006ad7e  07 ea 4a 90 | ....
378	00 00974733272:682210 2 - 02 0006ade6  46 52 45 45 | FREE
379	00 00974733272:682213 2 - 02 0006adf6  07 ea 4a 90 | ....
380	00 00974733272:682281 1 * 02 0006ab08  41 4c 4c 43 | EXCP 
381	01 00974733272:682284 2 - 02 0006ab16  45 43 4b 44 | ECKD
382	01 00974733272:682287 2 - 02 0006ab28  00 00 00 04 | ....
383	01 00974733272:682289 2 - 02 0006ab3e  00 00 00 20 | ... 
384	01 00974733272:682297 2 - 02 0006ad7e  07 ea 4a 90 | ....
385	01 00974733272:684384 2 - 00 0006ade6  46 52 45 45 | FREE
386	01 00974733272:684388 2 - 00 0006adf6  07 ea 4a 90 | ....
387	
388	See section about predefined views for explanation of the above output!
389	
390	Changing the debug level
391	------------------------
392	
393	Example:
394	
395	
396	> cat /sys/kernel/debug/s390dbf/dasd/level
397	3
398	> echo "5" > /sys/kernel/debug/s390dbf/dasd/level
399	> cat /sys/kernel/debug/s390dbf/dasd/level
400	5
401	
402	Flushing debug areas
403	--------------------
404	Debug areas can be flushed with piping the number of the desired
405	area (0...n) to the debugfs file "flush". When using "-" all debug areas
406	are flushed.
407	
408	Examples:
409	
410	1. Flush debug area 0:
411	> echo "0" > /sys/kernel/debug/s390dbf/dasd/flush
412	
413	2. Flush all debug areas:
414	> echo "-" > /sys/kernel/debug/s390dbf/dasd/flush
415	
416	Changing the size of debug areas
417	------------------------------------
418	It is possible the change the size of debug areas through piping
419	the number of pages to the debugfs file "pages". The resize request will
420	also flush the debug areas.
421	
422	Example:
423	
424	Define 4 pages for the debug areas of debug feature "dasd":
425	> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages
426	
427	Stooping the debug feature
428	--------------------------
429	Example:
430	
431	1. Check if stopping is allowed
432	> cat /proc/sys/s390dbf/debug_stoppable
433	2. Stop debug feature
434	> echo 0 > /proc/sys/s390dbf/debug_active
435	
436	lcrash Interface
437	----------------
438	It 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 
440	to investigate the debug logs on a live system and with a memory dump after 
441	a system crash.
442	
443	Investigating raw memory
444	------------------------
445	One last possibility to investigate the debug logs at a live
446	system and after a system crash is to look at the raw memory
447	under VM or at the Service Element.
448	It is possible to find the anker of the debug-logs through
449	the 'debug_area_first' symbol in the System map. Then one has
450	to follow the correct pointers of the data-structures defined
451	in debug.h and find the debug-areas in memory.
452	Normally modules which use the debug feature will also have
453	a global variable with the pointer to the debug-logs. Following
454	this pointer it will also be possible to find the debug logs in
455	memory.
456	
457	For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
458	for the length of the data field in debug_register() in
459	order to see the debug entries well formatted.
460	
461	
462	Predefined Views
463	----------------
464	
465	There are three predefined views: hex_ascii, raw and sprintf. 
466	The hex_ascii view shows the data field in hex and ascii representation 
467	(e.g. '45 43 4b 44 | ECKD'). 
468	The raw view returns a bytestream as the debug areas are stored in memory.
469	
470	The sprintf view formats the debug entries in the same way as the sprintf
471	function would do. The sprintf event/exception functions write to the
472	debug entry a pointer to the format string (size = sizeof(long)) 
473	and for each vararg a long value. So e.g. for a debug entry with a format 
474	string plus two varargs one would need to allocate a (3 * sizeof(long)) 
475	byte data area in the debug_register() function.
476	
477	
478	NOTE: If using the sprintf view do NOT use other event/exception functions
479	than the sprintf-event and -exception functions.
480	
481	The 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	
491	The format of the raw view is:
492	- Header as described in debug.h
493	- datafield 
494	
495	A typical line of the hex_ascii view will look like the following (first line 
496	is only for explanation and will not be displayed when 'cating' the view):
497	
498	area  time           level exception cpu caller    data (hex + ascii)
499	--------------------------------------------------------------------------
500	00    00964419409:440690 1 -         00  88023fe   
501	
502	
503	Defining views
504	--------------
505	
506	Views are specified with the 'debug_view' structure. There are defined
507	callback functions which are used for reading and writing the debugfs files:
508	
509	struct 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	
518	where
519	
520	typedef 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	
526	typedef int (debug_format_proc_t) (debug_info_t* id,
527	                                   struct debug_view* view, char* out_buf,
528	                                   const char* in_buf);
529	typedef int (debug_prolog_proc_t) (debug_info_t* id,
530	                                   struct debug_view* view,
531	                                   char* out_buf);
532	typedef 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	
538	The "private_data" member can be used as pointer to view specific data.
539	It is not used by the debug feature itself.
540	
541	The 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	
550	When a view is read from the debugfs, the Debug Feature calls the
551	'prolog_proc' once for writing the prolog.
552	Then 'header_proc' and 'format_proc' are called for each 
553	existing debug entry.
554	
555	The input_proc can be used to implement functionality when it is written to 
556	the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).
557	
558	For header_proc there can be used the default function
559	debug_dflt_header_fn() which is defined in debug.h.
560	and which produces the same header output as the predefined views.
561	E.g:
562	00 00964419409:440761 2 - 00 88023ec
563	
564	In order to see how to use the callback functions check the implementation
565	of the default views!
566	
567	Example
568	
569	#include <asm/debug.h>
570	
571	#define UNKNOWNSTR "data: %08x"
572	
573	const 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	
582	static 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	
600	struct 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	=====
610	test:
611	=====
612	debug_info_t *debug_info;
613	...
614	debug_info = debug_register ("test", 0, 4, 4 ));
615	debug_register_view(debug_info, &debug_test_view);
616	for(i = 0; i < 10; i ++) debug_int_event(debug_info, 1, i);
617	
618	> cat /sys/kernel/debug/s390dbf/test/myview
619	00 00964419734:611402 1 - 00 88042ca   This error...........
620	00 00964419734:611405 1 - 00 88042ca   That error...........
621	00 00964419734:611408 1 - 00 88042ca   Problem..............
622	00 00964419734:611411 1 - 00 88042ca   Something went wrong.
623	00 00964419734:611414 1 - 00 88042ca   Everything ok........
624	00 00964419734:611417 1 - 00 88042ca   data: 00000005
625	00 00964419734:611419 1 - 00 88042ca   data: 00000006
626	00 00964419734:611422 1 - 00 88042ca   data: 00000007
627	00 00964419734:611425 1 - 00 88042ca   data: 00000008
628	00 00964419734:611428 1 - 00 88042ca   data: 00000009
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