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Diffstat (limited to 'Documentation/s390/s390dbf.txt')
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diff --git a/Documentation/s390/s390dbf.txt b/Documentation/s390/s390dbf.txt new file mode 100644 index 0000000..2d1cd93 --- /dev/null +++ b/Documentation/s390/s390dbf.txt @@ -0,0 +1,615 @@ +S390 Debug Feature +================== + +files: arch/s390/kernel/debug.c + include/asm-s390/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 failes, +it is possible to look at the debug logs on a live system via the Linux proc +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 itselve 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 proc-filesystem. Under the path /proc/s390dbf there is +a directory for each registered component, which is named like the +corresponding component. + +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 proc file. + +All debug logs have an 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 proc-filesystem +through writing a number string "x" to the 'level' proc file which is +provided for every debug log. Debugging can be switched off completely +by using "-" on the 'level' proc file. + +Example: + +> echo "-" > /proc/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 possbility 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 an 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 an 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_index, int nr_areas, + int buf_size); + +Parameter: name: Name of debug log (e.g. used for proc entry) + pages_index: 2^pages_index pages 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 + +--------------------------------------------------------------------------- +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 proc 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 proc 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", 0, 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", 0, 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); + + + +ProcFS Interface +---------------- +Views to the debug logs can be investigated through reading the corresponding +proc-files: + +Example: + +> ls /proc/s390dbf/dasd +flush hex_ascii level raw +> cat /proc/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 /proc/s390dbf/dasd/level +3 +> echo "5" > /proc/s390dbf/dasd/level +> cat /proc/s390dbf/dasd/level +5 + +Flushing debug areas +-------------------- +Debug areas can be flushed with piping the number of the desired +area (0...n) to the proc file "flush". When using "-" all debug areas +are flushed. + +Examples: + +1. Flush debug area 0: +> echo "0" > /proc/s390dbf/dasd/flush + +2. Flush all debug areas: +> echo "-" > /proc/s390dbf/dasd/flush + +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/expection fuctions 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. + + +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 proc 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 debug-proc 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 proc fs, 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" > /proc/s390dbf/dasd/level). + +For header_proc there can be used the default function +debug_dflt_header_fn() which is defined in 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 /proc/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 |
