docs: s390: restore important non-kdoc parts of s390dbf.rst
Complements previous ("s390: include/asm/debug.h add kerneldoc markups")
which seemed to have dropped important non-kdoc parts such as
user space interface (level, size, flush)
as well as views and caution regarding strings in the sprintf view.
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <1562149189-1417-2-git-send-email-maier@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Steffen Maier
Vasily Gorbik
parent
555827c28a
commit
f11977be1a
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@ -112,6 +112,345 @@ Kernel Interfaces:
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Predefined views:
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-----------------
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extern struct debug_view debug_hex_ascii_view;
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extern struct debug_view debug_raw_view;
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extern struct debug_view debug_sprintf_view;
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Examples
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--------
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::
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/*
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* hex_ascii- + raw-view Example
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*/
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#include <linux/init.h>
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#include <asm/debug.h>
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static debug_info_t* debug_info;
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static int init(void)
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{
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/* register 4 debug areas with one page each and 4 byte data field */
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debug_info = debug_register ("test", 1, 4, 4 );
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debug_register_view(debug_info,&debug_hex_ascii_view);
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debug_register_view(debug_info,&debug_raw_view);
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debug_text_event(debug_info, 4 , "one ");
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debug_int_exception(debug_info, 4, 4711);
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debug_event(debug_info, 3, &debug_info, 4);
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return 0;
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}
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static void cleanup(void)
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{
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debug_unregister (debug_info);
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}
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module_init(init);
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module_exit(cleanup);
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::
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/*
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* sprintf-view Example
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*/
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#include <linux/init.h>
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#include <asm/debug.h>
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static debug_info_t* debug_info;
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static int init(void)
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{
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/* register 4 debug areas with one page each and data field for */
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/* format string pointer + 2 varargs (= 3 * sizeof(long)) */
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debug_info = debug_register ("test", 1, 4, sizeof(long) * 3);
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debug_register_view(debug_info,&debug_sprintf_view);
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debug_sprintf_event(debug_info, 2 , "first event in %s:%i\n",__FILE__,__LINE__);
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debug_sprintf_exception(debug_info, 1, "pointer to debug info: %p\n",&debug_info);
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return 0;
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}
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static void cleanup(void)
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{
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debug_unregister (debug_info);
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}
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module_init(init);
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module_exit(cleanup);
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Debugfs Interface
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-----------------
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Views to the debug logs can be investigated through reading the corresponding
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debugfs-files:
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Example::
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> ls /sys/kernel/debug/s390dbf/dasd
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flush hex_ascii level pages raw
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> cat /sys/kernel/debug/s390dbf/dasd/hex_ascii | sort -k2,2 -s
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00 00974733272:680099 2 - 02 0006ad7e 07 ea 4a 90 | ....
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00 00974733272:682210 2 - 02 0006ade6 46 52 45 45 | FREE
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00 00974733272:682213 2 - 02 0006adf6 07 ea 4a 90 | ....
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00 00974733272:682281 1 * 02 0006ab08 41 4c 4c 43 | EXCP
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01 00974733272:682284 2 - 02 0006ab16 45 43 4b 44 | ECKD
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01 00974733272:682287 2 - 02 0006ab28 00 00 00 04 | ....
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01 00974733272:682289 2 - 02 0006ab3e 00 00 00 20 | ...
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01 00974733272:682297 2 - 02 0006ad7e 07 ea 4a 90 | ....
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01 00974733272:684384 2 - 00 0006ade6 46 52 45 45 | FREE
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01 00974733272:684388 2 - 00 0006adf6 07 ea 4a 90 | ....
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See section about predefined views for explanation of the above output!
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Changing the debug level
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------------------------
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Example::
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> cat /sys/kernel/debug/s390dbf/dasd/level
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3
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> echo "5" > /sys/kernel/debug/s390dbf/dasd/level
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> cat /sys/kernel/debug/s390dbf/dasd/level
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5
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Flushing debug areas
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--------------------
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Debug areas can be flushed with piping the number of the desired
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area (0...n) to the debugfs file "flush". When using "-" all debug areas
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are flushed.
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Examples:
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1. Flush debug area 0::
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> echo "0" > /sys/kernel/debug/s390dbf/dasd/flush
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2. Flush all debug areas::
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> echo "-" > /sys/kernel/debug/s390dbf/dasd/flush
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Changing the size of debug areas
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------------------------------------
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It is possible the change the size of debug areas through piping
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the number of pages to the debugfs file "pages". The resize request will
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also flush the debug areas.
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Example:
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Define 4 pages for the debug areas of debug feature "dasd"::
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> echo "4" > /sys/kernel/debug/s390dbf/dasd/pages
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Stooping the debug feature
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--------------------------
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Example:
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1. Check if stopping is allowed::
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> cat /proc/sys/s390dbf/debug_stoppable
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2. Stop debug feature::
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> echo 0 > /proc/sys/s390dbf/debug_active
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lcrash Interface
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----------------
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It is planned that the dump analysis tool lcrash gets an additional command
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's390dbf' to display all the debug logs. With this tool it will be possible
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to investigate the debug logs on a live system and with a memory dump after
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a system crash.
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Investigating raw memory
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------------------------
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One last possibility to investigate the debug logs at a live
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system and after a system crash is to look at the raw memory
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under VM or at the Service Element.
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It is possible to find the anker of the debug-logs through
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the 'debug_area_first' symbol in the System map. Then one has
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to follow the correct pointers of the data-structures defined
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in debug.h and find the debug-areas in memory.
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Normally modules which use the debug feature will also have
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a global variable with the pointer to the debug-logs. Following
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this pointer it will also be possible to find the debug logs in
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memory.
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For this method it is recommended to use '16 * x + 4' byte (x = 0..n)
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for the length of the data field in debug_register() in
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order to see the debug entries well formatted.
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Predefined Views
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----------------
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There are three predefined views: hex_ascii, raw and sprintf.
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The hex_ascii view shows the data field in hex and ascii representation
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(e.g. '45 43 4b 44 | ECKD').
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The raw view returns a bytestream as the debug areas are stored in memory.
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The sprintf view formats the debug entries in the same way as the sprintf
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function would do. The sprintf event/exception functions write to the
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debug entry a pointer to the format string (size = sizeof(long))
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and for each vararg a long value. So e.g. for a debug entry with a format
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string plus two varargs one would need to allocate a (3 * sizeof(long))
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byte data area in the debug_register() function.
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IMPORTANT:
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Using "%s" in sprintf event functions is dangerous. You can only
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use "%s" in the sprintf event functions, if the memory for the passed string
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is available as long as the debug feature exists. The reason behind this is
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that due to performance considerations only a pointer to the string is stored
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in the debug feature. If you log a string that is freed afterwards, you will
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get an OOPS when inspecting the debug feature, because then the debug feature
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will access the already freed memory.
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NOTE:
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If using the sprintf view do NOT use other event/exception functions
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than the sprintf-event and -exception functions.
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The format of the hex_ascii and sprintf view is as follows:
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- Number of area
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- Timestamp (formatted as seconds and microseconds since 00:00:00 Coordinated
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Universal Time (UTC), January 1, 1970)
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- level of debug entry
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- Exception flag (* = Exception)
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- Cpu-Number of calling task
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- Return Address to caller
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- data field
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The format of the raw view is:
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- Header as described in debug.h
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- datafield
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A typical line of the hex_ascii view will look like the following (first line
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is only for explanation and will not be displayed when 'cating' the view):
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area time level exception cpu caller data (hex + ascii)
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--------------------------------------------------------------------------
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00 00964419409:440690 1 - 00 88023fe
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Defining views
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--------------
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Views are specified with the 'debug_view' structure. There are defined
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callback functions which are used for reading and writing the debugfs files::
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struct debug_view {
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char name[DEBUG_MAX_PROCF_LEN];
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debug_prolog_proc_t* prolog_proc;
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debug_header_proc_t* header_proc;
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debug_format_proc_t* format_proc;
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debug_input_proc_t* input_proc;
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void* private_data;
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};
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where::
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typedef int (debug_header_proc_t) (debug_info_t* id,
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struct debug_view* view,
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int area,
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debug_entry_t* entry,
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char* out_buf);
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typedef int (debug_format_proc_t) (debug_info_t* id,
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struct debug_view* view, char* out_buf,
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const char* in_buf);
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typedef int (debug_prolog_proc_t) (debug_info_t* id,
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struct debug_view* view,
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char* out_buf);
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typedef int (debug_input_proc_t) (debug_info_t* id,
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struct debug_view* view,
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struct file* file, const char* user_buf,
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size_t in_buf_size, loff_t* offset);
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The "private_data" member can be used as pointer to view specific data.
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It is not used by the debug feature itself.
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The output when reading a debugfs file is structured like this::
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"prolog_proc output"
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"header_proc output 1" "format_proc output 1"
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"header_proc output 2" "format_proc output 2"
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"header_proc output 3" "format_proc output 3"
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...
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When a view is read from the debugfs, the Debug Feature calls the
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'prolog_proc' once for writing the prolog.
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Then 'header_proc' and 'format_proc' are called for each
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existing debug entry.
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The input_proc can be used to implement functionality when it is written to
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the view (e.g. like with 'echo "0" > /sys/kernel/debug/s390dbf/dasd/level).
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For header_proc there can be used the default function
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debug_dflt_header_fn() which is defined in debug.h.
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and which produces the same header output as the predefined views.
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E.g::
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00 00964419409:440761 2 - 00 88023ec
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In order to see how to use the callback functions check the implementation
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of the default views!
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Example::
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#include <asm/debug.h>
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#define UNKNOWNSTR "data: %08x"
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const char* messages[] =
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{"This error...........\n",
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"That error...........\n",
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"Problem..............\n",
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"Something went wrong.\n",
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"Everything ok........\n",
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NULL
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};
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static int debug_test_format_fn(
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debug_info_t * id, struct debug_view *view,
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char *out_buf, const char *in_buf
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)
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{
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int i, rc = 0;
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if(id->buf_size >= 4) {
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int msg_nr = *((int*)in_buf);
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if(msg_nr < sizeof(messages)/sizeof(char*) - 1)
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rc += sprintf(out_buf, "%s", messages[msg_nr]);
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else
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rc += sprintf(out_buf, UNKNOWNSTR, msg_nr);
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}
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out:
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return rc;
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}
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struct debug_view debug_test_view = {
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"myview", /* name of view */
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NULL, /* no prolog */
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&debug_dflt_header_fn, /* default header for each entry */
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&debug_test_format_fn, /* our own format function */
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NULL, /* no input function */
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NULL /* no private data */
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};
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test:
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=====
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::
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debug_info_t *debug_info;
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