[PATCH 1/3] docs: s390: restore important non-kdoc parts of s390dbf.rst

Steffen Maier
2019-07-03T10:20:24Z

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>
---
Documentation/s390/s390dbf.rst | 339 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 339 insertions(+)

diff --git a/Documentation/s390/s390dbf.rst b/Documentation/s390/s390dbf.rst
index d2595b548879..01d66251643d 100644
--- a/Documentation/s390/s390dbf.rst
+++ b/Documentation/s390/s390dbf.rst
@@ -112,6 +112,345 @@ Kernel Interfaces:
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;
--
1.8.3.1