最終更新:2016-04-08 (金) 17:30:50 (2938d)  

CONFIG_DYNAMIC_DEBUG
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Enable dynamic printk() support

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  • Compiles debug level messages into the kernel, which would not
otherwise be available at runtime. These messages can then be
enabled/disabled based on various levels of scope - per source file,
function, module, format string, and line number. This mechanism
implicitly compiles in all pr_debug() and dev_dbg() calls, which
enlarges the kernel text size by about 2%.

If a source file is compiled with DEBUG flag set, any
pr_debug() calls in it are enabled by default, but can be
disabled at runtime as below.  Note that DEBUG flag is
turned on by many CONFIG_*DEBUG* options.

Usage:

Dynamic debugging is controlled via the 'dynamic_debug/control' 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/control. This
file contains a list of the debug statements that can be enabled. The
format for each line of the file is:

      filename:lineno [module]function flags format

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:

      nullarbor:~ # cat <debugfs>/dynamic_debug/control
      # 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"

Example usage:

      // enable the message at line 1603 of file svcsock.c
      nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >
                                      <debugfs>/dynamic_debug/control

      // enable all the messages in file svcsock.c
      nullarbor:~ # echo -n 'file svcsock.c +p' >
                                      <debugfs>/dynamic_debug/control

      // enable all the messages in the NFS server module
      nullarbor:~ # echo -n 'module nfsd +p' >
                                      <debugfs>/dynamic_debug/control

      // enable all 12 messages in the function svc_process()
      nullarbor:~ # echo -n 'func svc_process +p' >
                                      <debugfs>/dynamic_debug/control

      // disable all 12 messages in the function svc_process()
      nullarbor:~ # echo -n 'func svc_process -p' >
                                      <debugfs>/dynamic_debug/control

See Documentation/dynamic-debug-howto.txt for additional information.
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メモ

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対応

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debugfs

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例

  • For example, if you want to enable printing from source file 'svcsock.c', line 1603 you simply do: 
    nullarbor:~ # echo 'file svcsock.c line 1603 +p' > <debugfs>/dynamic_debug/control
    有効化/無効化の方法はいくつかあります。

例えば、

svcsock.cの全てのpr_debug()を有効化
echo -n 'file svcsock.c +p' > <debugfs>/dynamic_debug/control
svcsock.cの1603行目のpr_debug()を有効化
echo -n 'file svcsock.c line 1603 +p' > <debugfs>/dynamic_debug/control
imx.cのimx_int()内の全てのpr_debug()を有効化
echo -n 'file imx.c func imx_int +p' > /sys/kernel/debug/dynamic_debug/control
※ 無効化の際は、最後の"+p"を"-p"と指定してください
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