dynamic debug: update docs

[linux-2.6-omap-h63xx.git] / lib / Kconfig.debug

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0dd1c04c7323bfaec53ee371a6b6469f40a5f157..8fee0a13ac589a9484b89472274e1d77c44f5f0b 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -848,59 +848,69 @@ config BUILD_DOCSRC
          Say N if you are unsure.
 
 config DYNAMIC_DEBUG
-       bool "Enable dynamic printk() call support"
+       bool "Enable dynamic printk() support"
        default n
        depends on PRINTK
+       depends on DEBUG_FS
        select PRINTK_DEBUG
        help
 
          Compiles debug level messages into the kernel, which would not
          otherwise be available at runtime. These messages can then be
-         enabled/disabled on a per module basis. This mechanism implicitly
-         enables all pr_debug() and dev_dbg() calls. The impact of this
-         compile option is a larger kernel text size of about 2%.
+         enabled/disabled based on various levels of scope - per source file,
+         function, module, format string, and line number. This mechanism
+         implicitly enables all pr_debug() and dev_dbg() calls. The impact of
+         this compile option is a larger kernel text size of about 2%.
 
          Usage:
 
-         Dynamic debugging is controlled by the debugfs file,
-         dynamic_printk/modules. This file contains a list of the modules that
-         can be enabled. The format of the file is the module name, followed
-         by a set of flags that can be enabled. The first flag is always the
-         'enabled' flag. For example:
+         Dynamic debugging is controlled via the 'dynamic_debug/ddebug' file,
+         which is contained in the 'debugfs' filesystem. Thus, the debugfs
+         filesystem must first be mounted before making use of this feature.
+         We refer the control file as: <debugfs>/dynamic_debug/ddebug. This
+         file contains a list of the debug statements that can be enabled. The
+         format for each line of the file is:
 
-               <module_name> <enabled=0/1>
-                               .
-                               .
-                               .
+               filename:lineno [module]function flags format
 
-         <module_name> : Name of the module in which the debug call resides
-         <enabled=0/1> : whether the messages are enabled or not
+         filename : source file of the debug statement
+         lineno : line number of the debug statement
+         module : module that contains the debug statement
+         function : function that contains the debug statement
+          flags : 'p' means the line is turned 'on' for printing
+          format : the format used for the debug statement
 
          From a live system:
 
-               snd_hda_intel enabled=0
-               fixup enabled=0
-               driver enabled=0
+               nullarbor:~ # cat <debugfs>/dynamic_debug/ddebug
+               # filename:lineno [module]function flags format
+               fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012"
+               fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012"
+               fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012"
 
-         Enable a module:
+         Example usage:
 
-               $echo "set enabled=1 <module_name>" > dynamic_printk/modules
+               // enable the message at line 1603 of file svcsock.c
+               nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
+                                               <debugfs>/dynamic_debug/ddebug
 
-         Disable a module:
+               // enable all the messages in file svcsock.c
+               nullarbor:~ # echo -n 'file svcsock.c +p' >
+                                               <debugfs>/dynamic_debug/ddebug
 
-               $echo "set enabled=0 <module_name>" > dynamic_printk/modules
+               // enable all the messages in the NFS server module
+               nullarbor:~ # echo -n 'module nfsd +p' >
+                                               <debugfs>/dynamic_debug/ddebug
 
-         Enable all modules:
+               // enable all 12 messages in the function svc_process()
+               nullarbor:~ # echo -n 'func svc_process +p' >
+                                               <debugfs>/dynamic_debug/ddebug
 
-               $echo "set enabled=1 all" > dynamic_printk/modules
+               // disable all 12 messages in the function svc_process()
+               nullarbor:~ # echo -n 'func svc_process -p' >
+                                               <debugfs>/dynamic_debug/ddebug
 
-         Disable all modules:
-
-               $echo "set enabled=0 all" > dynamic_printk/modules
-
-         Finally, passing "dynamic_printk" at the command line enables
-         debugging for all modules. This mode can be turned off via the above
-         disable command.
+         See Documentation/dynamic-debug-howto.txt for additional information.
 
 source "samples/Kconfig"