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-S390 Debug Feature
-==================
-
-files: arch/s390/kernel/debug.c
- arch/s390/include/asm/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 fails,
-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 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.
-
-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 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().
-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'
-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 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
-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
-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
-
-----------------------------------------------------------------------------
-debug_info_t *debug_register_mode(char *name, int pages, int nr_areas,
- int buf_size, mode_t mode, uid_t uid,
- gid_t gid);
-
-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
- mode: File mode for debugfs files. E.g. S_IRWXUGO
- uid: User ID for debugfs files. Currently only 0 is
- supported.
- gid: Group ID for debugfs files. Currently only 0 is
- supported.
-
-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.
-
-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;
-...
-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