driver core: basic infrastructure for per-module dynamic debug messages

Base infrastructure to enable per-module debug messages.

I've introduced CONFIG_DYNAMIC_PRINTK_DEBUG, which when enabled centralizes
control of debugging statements on a per-module basis in one /proc file,
currently, <debugfs>/dynamic_printk/modules. When, CONFIG_DYNAMIC_PRINTK_DEBUG,
is not set, debugging statements can still be enabled as before, often by
defining 'DEBUG' for the proper compilation unit. Thus, this patch set has no
affect when CONFIG_DYNAMIC_PRINTK_DEBUG is not set.

The infrastructure currently ties into all pr_debug() and dev_dbg() calls. That
is, if CONFIG_DYNAMIC_PRINTK_DEBUG is set, all pr_debug() and dev_dbg() calls
can be dynamically enabled/disabled on a per-module basis.

Future plans include extending this functionality to subsystems, that define 
their own debug levels and flags.

Usage:

Dynamic debugging is controlled by the debugfs file, 
<debugfs>/dynamic_printk/modules. This file contains a list of the modules that
can be enabled. The format of the file is as follows:

	<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

For example:

	snd_hda_intel enabled=0
	fixup enabled=1
	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.

[gkh: minor cleanups and tweaks to make the build work quietly]

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 55 insertions, 0 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index aa81d2848448..31d784dd80d0 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -807,6 +807,61 @@ menuconfig BUILD_DOCSRC
 
           Say N if you are unsure.
 
+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.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"