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| -rw-r--r-- | Documentation/s390/s390dbf.rst | 122 |
1 files changed, 68 insertions, 54 deletions
diff --git a/Documentation/s390/s390dbf.rst b/Documentation/s390/s390dbf.rst index be42892b159e..cdb36842b898 100644 --- a/Documentation/s390/s390dbf.rst +++ b/Documentation/s390/s390dbf.rst @@ -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) @@ -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: @@ -56,29 +58,29 @@ 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:: @@ -86,21 +88,21 @@ Example:: 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. @@ -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 @@ -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); @@ -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 @@ -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); @@ -183,7 +187,7 @@ Examples static void cleanup(void) { - debug_unregister (debug_info); + debug_unregister(debug_info); } module_init(init); @@ -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: @@ -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. @@ -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 @@ -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. @@ -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 @@ -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]; @@ -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, @@ -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:: @@ -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> @@ -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 = { @@ -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........... |