docs: s390: restore important non-kdoc parts of s390dbf.rst

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 -k2,2 -s

  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.

IMPORTANT:

  Using "%s" in sprintf event functions is dangerous. You can only

  use "%s" in the sprintf event functions, if the memory for the passed string

  is available as long as the debug feature exists. The reason behind this is

  that due to performance considerations only a pointer to the string is stored

  in  the debug feature. If you log a string that is freed afterwards, you will

  get an OOPS when inspecting the debug feature, because then the debug feature

  will access the already freed memory.

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 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;