linux-kernel - Re: dynamic_printk documentation

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Date:	Sun, 4 Jan 2009 07:48:39 +1300
From:	"Michael Kerrisk" <mtk.manpages@...il.com>
To:	"Jason Baron" <jbaron@...hat.com>
Cc:	"Tilman Schmidt" <t.schmidt@...enixsoftware.de>,
	linux-kernel@...r.kernel.org,
	"Michael Kerrisk" <mtk.manpages@...il.com>
Subject: Re: dynamic_printk documentation

On Wed, Dec 24, 2008 at 5:22 AM, Jason Baron <jbaron@...hat.com> wrote:
> On Tue, Dec 23, 2008 at 01:25:25PM +0100, Tilman Schmidt wrote:
>> Where is the current debugfs interface to dynamic_printk documented?
>> From the source in lib/dynamic_printk.c I deduced that
>>
>> echo "set enable=1 <module_name>" > /sys/kernel/debug/dynamic_printk/modules
>>
>> should enable debug output for module <module_name>, and verified
>> experimentally that this does indeed work. Is that already described
>> somewhere I just overlooked? If not, I would propose creating a file
>> Documentation/dynamic_printk.txt.
>>
>> Thanks,
>> Tilman
>
> hi,
>
> Most of it is with the config parameter definition in lib/Kconfig.debug
> (copied below). I can propose copying it into Documentation/ if you think it'd
> be useful.

That would make some sense.  Kconfig isn't usually the place where
where one expects to look for usage documentation.

Cheers,

Michael

> config DYNAMIC_PRINTK_DEBUG
>        bool "Enable dynamic printk() call support"
>        default n
>        depends on PRINTK
>        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%.
>
>          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:
>
>                <module_name> <enabled=0/1>
>                                .
>                                .
>                                .
>
>          <module_name> : Name of the module in which the debug call resides
>          <enabled=0/1> : whether the messages are enabled or not
>
>          From a live system:
>
>                snd_hda_intel enabled=0
>                fixup enabled=0
>                driver enabled=0
>
>          Enable a module:
>
>                $echo "set enabled=1 <module_name>" > dynamic_printk/modules
>
>          Disable a module:
>
>                $echo "set enabled=0 <module_name>" > dynamic_printk/modules
>
>          Enable all modules:
>
>                $echo "set enabled=1 all" > dynamic_printk/modules
>
>          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.
>
> --
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-- 
Michael Kerrisk Linux man-pages maintainer;
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