From: trenn on
Dynamic debug lacks the ability to enable debug messages at boot time.
One could patch initramfs or service startup scripts to write to
/sys/../dynamic_debug/control, but this sucks.

This patch makes it possible to pass a query in the same format one can
write to /sys/../dynamic_debug/control via boot param.
When dynamic debug gets initialized, this query will automatically be

Signed-off-by: Thomas Renninger <trenn(a)>
CC: jbaron(a)
CC: linux-kernel(a)
CC: yehuda(a)

Documentation/dynamic-debug-howto.txt | 22 +++++++++++++++++++++-
Documentation/kernel-parameters.txt | 7 ++++++-
lib/dynamic_debug.c | 25 +++++++++++++++++++++++++
3 files changed, 52 insertions(+), 2 deletions(-)

Index: linux-2.6.34-master/lib/dynamic_debug.c
--- linux-2.6.34-master.orig/lib/dynamic_debug.c
+++ linux-2.6.34-master/lib/dynamic_debug.c
@@ -450,6 +450,19 @@ static int ddebug_exec_query(char *query
return 0;

+static __initdata char ddebug_setup_string[1024];
+static __init int ddebug_setup_query(char *str)
+ if (strlen(str) >= 1024) {
+ pr_warning("ddebug boot param string too large\n");
+ return 0;
+ }
+ strcpy(ddebug_setup_string, str);
+ return 1;
+__setup("ddebug_query=", ddebug_setup_query);
* File_ops->write method for <debugfs>/dynamic_debug/conrol. Gathers the
* command text from userspace, parses and executes it.
@@ -769,6 +782,18 @@ static int __init dynamic_debug_init(voi
ret = ddebug_add_module(iter_start, n, modname);
+ /* ddebug_query boot param got passed -> set it up */
+ if (ddebug_setup_string[0] != '\0') {
+ ret = ddebug_exec_query(ddebug_setup_string);
+ if (ret)
+ pr_warning("Invalid ddebug boot param %s",
+ ddebug_setup_string);
+ else
+ pr_info("ddebug initialized with string %s",
+ ddebug_setup_string);
+ }
if (ret) {
Index: linux-2.6.34-master/Documentation/dynamic-debug-howto.txt
--- linux-2.6.34-master.orig/Documentation/dynamic-debug-howto.txt
+++ linux-2.6.34-master/Documentation/dynamic-debug-howto.txt
@@ -24,7 +24,7 @@ Dynamic debug has even more useful featu
read to display the complete list of known debug statements, to help guide you

Controlling dynamic debug Behaviour

The behaviour of pr_debug()/dev_debug()s are controlled via writing to a
control file in the 'debugfs' filesystem. Thus, you must first mount the debugfs
@@ -212,6 +212,26 @@ Note the regexp ^[-+=][scp]+$ matches a
Note also that there is no convenient syntax to remove all
the flags at once, you need to use "-psc".

+Debug messages during boot process
+To be able to activate debug messages during the boot process,
+even before userspace and debugfs exists, use the boot parameter:
+QUERY follows the syntax described above, but must not exceed 1023
+characters. The enablement of debug messages is done as an arch_initcall.
+Thus you can enable debug messages in all code processed after this
+arch_initcall via this boot parameter.
+On an x86 system for example ACPI enablement is a subsys_initcall and
+ddebug_query="file ec.c +p"
+will show early Embedded Controller transactions during ACPI setup if
+your machine (typically a laptop) has an Embedded Controller.
+PCI (or other devices) initialization also is a hot candidate for using
+this boot parameter for debugging purposes.

Index: linux-2.6.34-master/Documentation/kernel-parameters.txt
--- linux-2.6.34-master.orig/Documentation/kernel-parameters.txt
+++ linux-2.6.34-master/Documentation/kernel-parameters.txt
@@ -43,10 +43,11 @@ parameter is applicable:
AVR32 AVR32 architecture is enabled.
AX25 Appropriate AX.25 support is enabled.
BLACKFIN Blackfin architecture is enabled.
- DRM Direct Rendering Management support is enabled.
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
EIDE EIDE/ATAPI support is enabled.
+ DRM Direct Rendering Management support is enabled.
+ DYNAMIC_DEBUG Build in debug messages and enable them at runtime
FB The frame buffer device is enabled.
GCOV GCOV profiling is enabled.
HW Appropriate hardware is enabled.
@@ -601,6 +602,10 @@ and is between 256 and 4096 characters.
Format: <port#>,<type>
See also Documentation/input/joystick-parport.txt

+ ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
+ time. See Documentation/dynamic-debug-howto.txt for
+ details.
debug [KNL] Enable kernel debugging (events log level).


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