[PATCH] Dynamic Debug: Introduce global fake module param module.ddebug

From: Thomas Renninger
Date: Mon Jul 26 2010 - 08:12:45 EST

This patch is based on 2.6.35-rc5 + this patchset I posted recently:
[patch 0/3] Dynamic Debug providing early boot debug messages via boot parameter

It would be great to see these getting merged into 2.6.36...




Dynamic Debug: Introduce global fake module param module.ddebug

Dynamic Debug allows enabling of pr_debug or KERN_DEBUG messages at runtime.
This is controlled via /sys/kernel/debug/dynamic_debug/control.
One major drawback is that the whole initialization of a module cannot be
tracked, because ddebug is only aware of debug strings of loaded modules.
But this is the most interesting part...

This patch introduces a fake module parameter module.ddebug(not shown in
/sys/module/*/parameters, thus it does not use any resources/memory).

If a module gets ddebug passed as a module parameter (e.g. via module.ddebug
kernel boot param or via "modprobe module ddebug"), all debug strings of this
module get activated by issuing "module module_name +p" internally
(not via sysfs) when the module gets loaded.

Possible enhancements for the future if ddebug might get extended with
further flags:
Then module.ddebug="p" would be the same as module.ddebug, but if there
is a "x" ddebug flag added, one could pass:
which would result in such a dynamic debug query:
module module_name +xp

One not handled side-effect of this patch:
Modules must not use "ddebug" module parameter or it will get ignored.
I tried to find a compile time check, but I could not see how that
is possible. Possibly a run-time check or at least documentation (where?)
should get added, that "ddebug" must not get used as a module parameter.

Tested with:
options hp-wmi ddebug
in modprobe.conf.local
-> works and pr_debug messages issued at module initialization time show
up. Also "p" flag gets set for the whole hp-wmi module debug strings:
grep hp-wmi /sys/../dynamic_debug/control

Signed-off-by: Thomas Renninger <trenn@xxxxxxx>

include/linux/dynamic_debug.h | 5 +++++
kernel/params.c | 9 ++++++++-
lib/dynamic_debug.c | 2 +-
3 files changed, 14 insertions(+), 2 deletions(-)

Index: linux-platform_drivers/kernel/params.c
--- linux-platform_drivers.orig/kernel/params.c
+++ linux-platform_drivers/kernel/params.c
@@ -24,6 +24,7 @@
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/ctype.h>
+#include <linux/dynamic_debug.h>

#if 0
#define DEBUGP printk
@@ -132,7 +133,7 @@ int parse_args(const char *name,
unsigned num,
int (*unknown)(char *param, char *val))
- char *param, *val;
+ char *param, *val, ddebug[1024];

DEBUGP("Parsing ARGS: %s\n", args);

@@ -144,6 +145,12 @@ int parse_args(const char *name,
int irq_was_disabled;

args = next_arg(args, &param, &val);
+ if (parameq(param, "ddebug")) {
+ sprintf(ddebug, "module %s +p", name);
+ ddebug_exec_query(ddebug);
+ continue;
+ }
irq_was_disabled = irqs_disabled();
ret = parse_one(param, val, params, num, unknown);
if (irq_was_disabled && !irqs_disabled()) {
Index: linux-platform_drivers/include/linux/dynamic_debug.h
--- linux-platform_drivers.orig/include/linux/dynamic_debug.h
+++ linux-platform_drivers/include/linux/dynamic_debug.h
@@ -41,6 +41,7 @@ int ddebug_add_module(struct _ddebug *ta

extern int ddebug_remove_module(const char *mod_name);
+extern int ddebug_exec_query(char *query_string);

#define __dynamic_dbg_enabled(dd) ({ \
int __ret = 0; \
@@ -77,6 +78,10 @@ static inline int ddebug_remove_module(c
return 0;
+static inline int ddebug_exec_query(char *query_string)
+ return 0;

#define dynamic_pr_debug(fmt, ...) \
do { if (0) printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); } while (0)
Index: linux-platform_drivers/lib/dynamic_debug.c
--- linux-platform_drivers.orig/lib/dynamic_debug.c
+++ linux-platform_drivers/lib/dynamic_debug.c
@@ -429,7 +429,7 @@ static int ddebug_parse_flags(const char
return 0;

-static int ddebug_exec_query(char *query_string)
+int ddebug_exec_query(char *query_string)
unsigned int flags = 0, mask = 0;
struct ddebug_query query;
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