s390dbf.txt

《嵌入式系统设计与实例开发实验教材二源码》Linux内核移植与编译实验

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 seperate 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 usefull 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 that 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

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. 
---------------------------------------------------------------------------
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/module.h>
#include <asm/debug.h>

static debug_info_t* debug_info;

int init_module(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 ");