linux-kernel - Re: dynamic_printk documentation

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Message-ID: <20081223162229.GB4126@redhat.com>
Date:	Tue, 23 Dec 2008 11:22:29 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Tilman Schmidt <t.schmidt@...enixsoftware.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: dynamic_printk documentation

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.

thanks,

-Jason


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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