Documentation/s390/s390dbf.txt - LeafOS-Devices/android_kernel_realme_mt6785 - Gitiles

 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 failes,
 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
	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 failes,
	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