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docs: s390: s390dbf: typos and formatting, update crash command
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Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <1562149189-1417-4-git-send-email-maier@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
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steffen-maier authored and Vasily Gorbik committed Jul 5, 2019
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Showing 1 changed file with 68 additions and 54 deletions.
122 changes: 68 additions & 54 deletions Documentation/s390/s390dbf.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,8 @@ 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
feature with the function call :c:func:`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)
Expand All @@ -44,8 +45,9 @@ The debug areas themselves 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.
There are four versions for the event- and exception-calls: One for
logging raw data, one for text, one for numbers (unsigned int and long),
and one for sprintf-like formatted strings.

Each debug entry contains the following data:

Expand All @@ -56,51 +58,51 @@ Each debug entry contains the following data:
- 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
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 under
/sys/kernel/debug/s390dbf.
``/sys/kernel/debug`` therefore the debug feature can be accessed under
``/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().
used through registering them with the function :c:func:`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 actual debug level (range from 0 to 6).
The default level is 3. Event and Exception functions have a 'level'
The default level is 3. Event and Exception functions have a :c:data:`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
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.
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:
``/proc/sys/s390dbf``:

There are currently 2 possible triggers, which stop the debug feature
globally. The first possibility is to use the "debug_active" sysctl. If
set to 1 the debug feature is running. If "debug_active" is set to 0 the
globally. The first possibility 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 a 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
by piping 1 to ``/proc/sys/s390dbf/debug_active``. Nevertheless, it's not
suggested to use an oopsed kernel in a 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
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.

Expand All @@ -113,16 +115,18 @@ Kernel Interfaces:
Predefined views:
-----------------

extern struct debug_view debug_hex_ascii_view;
.. code-block:: c
extern struct debug_view debug_raw_view;
extern struct debug_view debug_hex_ascii_view;
extern struct debug_view debug_sprintf_view;
extern struct debug_view debug_raw_view;
extern struct debug_view debug_sprintf_view;
Examples
--------

::
.. code-block:: c
/*
* hex_ascii- + raw-view Example
Expand All @@ -131,15 +135,15 @@ Examples
#include <linux/init.h>
#include <asm/debug.h>
static debug_info_t* debug_info;
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_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);
Expand All @@ -150,13 +154,13 @@ Examples
static void cleanup(void)
{
debug_unregister (debug_info);
debug_unregister(debug_info);
}
module_init(init);
module_exit(cleanup);
::
.. code-block:: c
/*
* sprintf-view Example
Expand All @@ -165,15 +169,15 @@ Examples
#include <linux/init.h>
#include <asm/debug.h>
static debug_info_t* debug_info;
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_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);
Expand All @@ -183,7 +187,7 @@ Examples
static void cleanup(void)
{
debug_unregister (debug_info);
debug_unregister(debug_info);
}
module_init(init);
Expand Down Expand Up @@ -252,7 +256,7 @@ Define 4 pages for the debug areas of debug feature "dasd"::

> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages

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

Expand All @@ -264,10 +268,11 @@ Example:

> echo 0 > /proc/sys/s390dbf/debug_active

lcrash Interface
crash 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
The ``crash`` tool since v5.1.0 has a built-in command
``s390dbf`` to display all the debug logs or export them to the file system.
With this tool it is possible
to investigate the debug logs on a live system and with a memory dump after
a system crash.

Expand All @@ -276,8 +281,8 @@ 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
It is possible to find the anchor 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
Expand All @@ -286,7 +291,7 @@ 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
for the length of the data field in :c:func:`debug_register()` in
order to see the debug entries well formatted.


Expand All @@ -295,7 +300,7 @@ 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').
(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
Expand Down Expand Up @@ -335,18 +340,20 @@ The format of the raw view is:
- 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):
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
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::
callback functions which are used for reading and writing the debugfs files:

.. code-block:: c
struct debug_view {
char name[DEBUG_MAX_PROCF_LEN];
Expand All @@ -357,7 +364,9 @@ callback functions which are used for reading and writing the debugfs files::
void* private_data;
};
where::
where:

.. code-block:: c
typedef int (debug_header_proc_t) (debug_info_t* id,
struct debug_view* view,
Expand Down Expand Up @@ -395,10 +404,10 @@ 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).
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.
:c:func:`debug_dflt_header_fn()` which is defined in debug.h.
and which produces the same header output as the predefined views.
E.g::

Expand All @@ -407,7 +416,9 @@ E.g::
In order to see how to use the callback functions check the implementation
of the default views!

Example::
Example:

.. code-block:: c
#include <asm/debug.h>
Expand All @@ -423,21 +434,20 @@ Example::
};
static int debug_test_format_fn(
debug_info_t * id, struct debug_view *view,
debug_info_t *id, struct debug_view *view,
char *out_buf, const char *in_buf
)
{
int i, rc = 0;
if(id->buf_size >= 4) {
if (id->buf_size >= 4) {
int msg_nr = *((int*)in_buf);
if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
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;
return rc;
}
struct debug_view debug_test_view = {
Expand All @@ -452,13 +462,17 @@ Example::
test:
=====

::
.. code-block:: c
debug_info_t *debug_info;
int i;
...
debug_info = debug_register ("test", 0, 4, 4 ));
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);
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...........
Expand Down

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