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dynamic debug: update docs

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updates the documentation for 'dynamic debug' feature.

Signed-off-by: Greg Banks <gnb@sgi.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jason Baron
2009-02-05 11:53:15 -05:00
committed by Greg Kroah-Hartman
parent e9d376f0fa
commit 86151fdf38
2 changed files with 273 additions and 31 deletions
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72
lib/Kconfig.debug
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@@ -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"