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Dynamic Debug: Introduce ddebug_query= boot parameter 

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
applied.


Signed-off-by: Thomas Renninger <trenn@suse.de>
Acked-by: jbaron@redhat.com
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Thomas Renninger 2010-08-06 16:11:02 +02:00 committed by Greg Kroah-Hartman
parent fd89cfb871
commit a648ec05bb
3 changed files with 52 additions and 2 deletions
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22
Documentation/dynamic-debug-howto.txt
View File

@ -24,7 +24,7 @@ Dynamic debug has even more useful features:
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 flags specification.
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:
ddebug_query="QUERY"
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.
Examples
========

7
Documentation/kernel-parameters.txt
View File

@ -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.
@ -570,6 +571,10 @@ and is between 256 and 4096 characters. It is defined in the file
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).
debug_locks_verbose=

25
lib/dynamic_debug.c
View File

@ -450,6 +450,19 @@ static int ddebug_exec_query(char *query_string)
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(void)
}
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);
}
out_free:
if (ret) {
ddebug_remove_all_tables();