[PATCH 1/4] Dynamic Debug: Introduce global fake module param module.ddebug - V3

From: Thomas Renninger
Date: Wed Sep 15 2010 - 18:11:59 EST

Dynamic Debug allows enabling of pr_debug and dev_dbg 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 passes ddebug 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:
module.ddebug=flags
Then module.ddebug="p" would be the same as module.ddebug, but if there
is a "x" ddebug flag added, one could pass:
module.ddebug="xp"
which would result in such a dynamic debug query:
module module_name +xp

Modules must not use "ddebug" as module parameter or it will get ignored.
If it's tried, a warning will show up at module load time that it will get
ignored (only works for not built-in modules).

Tested with (additional added pr_debug messages):
options hp-wmi ddebug
in modprobe.conf
-> works and pr_debug messages issued at module initialization time show
up. Also "p" flag gets set for the whole hp-wmi module:
grep hp-wmi /sys/../dynamic_debug/control
also tested with compiled-in modules, e.g. pnp.ddebug and an additional
patch later in the patch series which instruments pnp code to work with ddebug.

Signed-off-by: Thomas Renninger <trenn@xxxxxxx>
CC: Bjorn Helgaas <bjorn.helgaas@xxxxxx>
CC: Jason Baron <jbaron@xxxxxxxxxx>
CC: Greg KH <gregkh@xxxxxxx>
CC: lkml <linux-kernel@xxxxxxxxxxxxxxx>
---
Documentation/dynamic-debug-howto.txt | 28 ++++++++++-
include/linux/dynamic_debug.h | 15 ++++++
include/linux/moduleparam.h | 3 +
kernel/module.c | 1 +
kernel/params.c | 13 +++++-
lib/dynamic_debug.c | 86 +++++++++++++++++++++++++++++++-
6 files changed, 141 insertions(+), 5 deletions(-)

diff --git a/Documentation/dynamic-debug-howto.txt b/Documentation/dynamic-debug-howto.txt
index 58ea64a..ebbbbdd 100644
--- a/Documentation/dynamic-debug-howto.txt
+++ b/Documentation/dynamic-debug-howto.txt
@@ -213,7 +213,7 @@ 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
+Debug Messages during Boot Process
==================================

To be able to activate debug messages during the boot process,
@@ -232,6 +232,32 @@ PCI (or other devices) initialization also is a hot candidate for using
this boot parameter for debugging purposes.


+Debug Messages at Module Initialization Time
+============================================
+
+Enabling debug messages inside a module is only possible if the module itself
+is loaded already. If you unload a module, the dynamic debug flags associated
+to its debug messages are lost.
+Therefore, enabling debug messages that get processed at module initialization
+time through the <debugfs>/dynamic_debug/control interface is not possible.
+Instead, a "ddebug" module paramter can be passed:
+
+ - via kernel boot parameter:
+ module.ddebug
+
+ - as an ordinary module parameter via modprobe
+ modprobe module ddebug
+
+ - or the parameter can be used permanently via modprobe.conf(.local)
+ options module ddebug
+
+The ddebug option is not implemented as an ordinary module parameter and thus
+will not show up in /sys/module/module_name/parameters/ddebug
+The settings can get reverted through the sysfs interface again when the
+module got loaded as soon as debug messages are not needed anymore:
+echo "module module_name -p" > <debugfs>/dynamic_debug/control
+as described in the "Command Language Reference" chapter above.
+
Examples
========

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 52c0da4..56c0c3a 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -39,8 +39,13 @@ struct _ddebug {
int ddebug_add_module(struct _ddebug *tab, unsigned int n,
const char *modname);

+struct kernel_param;
+
#if defined(CONFIG_DYNAMIC_DEBUG)
extern int ddebug_remove_module(const char *mod_name);
+extern int ddebug_exec_query(char *query_string);
+extern void ddebug_module_parse_args(const char *name, char* args,
+ struct kernel_param *params, unsigned num);

#define __dynamic_dbg_enabled(dd) ({ \
int __ret = 0; \
@@ -77,6 +82,16 @@ static inline int ddebug_remove_module(const char *mod)
{
return 0;
}
+static inline int ddebug_exec_query(char *query_string)
+{
+ return 0;
+}
+static incline void ddebug_module_parse_args(const char *name, char* args,
+ struct kernel_param *params,
+ unsigned num)
+{
+ return 0;
+}

#define dynamic_pr_debug(fmt, ...) \
do { if (0) printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__); } while (0)
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 82a9124..ab0c88c 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -251,4 +251,7 @@ static inline void module_param_sysfs_remove(struct module *mod)
{ }
#endif

+/* For being able to parse parameters the same way params.c does */
+extern char *next_arg(char *args, char **param, char **val);
+
#endif /* _LINUX_MODULE_PARAMS_H */
diff --git a/kernel/module.c b/kernel/module.c
index d0b5f8d..3912e12 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2628,6 +2628,7 @@ static struct module *load_module(void __user *umod,
list_add_rcu(&mod->list, &modules);
mutex_unlock(&module_mutex);

+ ddebug_module_parse_args(mod->name, mod->args, mod->kp, mod->num_kp);
/* Module is ready to execute: parsing args may do that. */
err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp, NULL);
if (err < 0)
diff --git a/kernel/params.c b/kernel/params.c
index 0b30ecd..df06dc0 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -54,6 +54,7 @@ static int parse_one(char *param,
int (*handle_unknown)(char *param, char *val))
{
unsigned int i;
+ char *tmp;

/* Find parameter */
for (i = 0; i < num_params; i++) {
@@ -64,6 +65,16 @@ static int parse_one(char *param,
}
}

+ /*
+ * Ignore ddebug module params and module.ddebug boot params:
+ * Documentation/dynamic-debug-howto.txt
+ */
+ tmp = strstr(param, ".ddebug");
+ if (parameq(param, "ddebug") || (tmp && strlen(tmp) == 7)) {
+ DEBUGP("Ignoring ddebug parameter %s\n", param);
+ return 0;
+ }
+
if (handle_unknown) {
DEBUGP("Unknown argument: calling %p\n", handle_unknown);
return handle_unknown(param, val);
@@ -75,7 +86,7 @@ static int parse_one(char *param,

/* You can use " around spaces, but can't escape ". */
/* Hyphens and underscores equivalent in parameter names. */
-static char *next_arg(char *args, char **param, char **val)
+char *next_arg(char *args, char **param, char **val)
{
unsigned int i, equals = 0;
int in_quote = 0, quoted = 0;
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index a687d90..826ea2e 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -10,6 +10,7 @@
*/

#include <linux/kernel.h>
+#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kallsyms.h>
@@ -27,9 +28,13 @@
#include <linux/debugfs.h>
#include <linux/slab.h>

+#include <asm/setup.h>
+
extern struct _ddebug __start___verbose[];
extern struct _ddebug __stop___verbose[];

+#define DDEBUG_STRING_SIZE 1024
+
/* dynamic_debug_enabled, and dynamic_debug_enabled2 are bitmasks in which
* bit n is set to 1 if any modname hashes into the bucket n, 0 otherwise. They
* use independent hash functions, to reduce the chance of false positives.
@@ -429,7 +434,7 @@ static int ddebug_parse_flags(const char *str, unsigned int *flagsp,
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;
@@ -437,6 +442,9 @@ static int ddebug_exec_query(char *query_string)
int nwords;
char *words[MAXWORDS];

+ if (verbose)
+ printk(KERN_INFO "%s: got query: %s\n", __func__, query_string);
+
nwords = ddebug_tokenize(query_string, words, MAXWORDS);
if (nwords <= 0)
return -EINVAL;
@@ -450,10 +458,10 @@ static int ddebug_exec_query(char *query_string)
return 0;
}

-static __initdata char ddebug_setup_string[1024];
+static __initdata char ddebug_setup_string[DDEBUG_STRING_SIZE];
static __init int ddebug_setup_query(char *str)
{
- if (strlen(str) >= 1024) {
+ if (strlen(str) >= DDEBUG_STRING_SIZE) {
pr_warning("ddebug boot param string too large\n");
return 0;
}
@@ -704,6 +712,76 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
}
EXPORT_SYMBOL_GPL(ddebug_add_module);

+/* We search for *ddebug* module params */
+void ddebug_module_parse_args(const char *name, char* args,
+ struct kernel_param *params, unsigned num)
+{
+ char ddebug[DDEBUG_STRING_SIZE], *param, *val, *args_it, *arg_dup_ptr;
+ int i;
+
+ /*
+ * We must not modify the passed args string and need to store the
+ * kstrdup pointer to be able to free memory later, TBD: find a way
+ * to do this nicer
+ */
+ arg_dup_ptr = args_it = kstrdup(args, GFP_KERNEL);
+
+ if (verbose)
+ printk(KERN_INFO "%s: Parsing ARGS: -%s- of %s\n",
+ __func__, args_it, name);
+
+ for (i = 0; i < num; i++) {
+ if (!strcmp("ddebug", params[i].name))
+ pr_warning("Module %s uses reserved keyword "
+ "*ddebug* as parameter\n", name);
+ }
+
+ /* Chew leading spaces */
+ args_it = skip_spaces(args_it);
+
+ while (*args_it) {
+ args_it = next_arg(args_it, &param, &val);
+ if (verbose)
+ printk(KERN_INFO "%s: Param: %s, val: %s\n",
+ __func__, param, val);
+ if (!strcmp(param, "ddebug")) {
+ pr_info("Enabling debugging for module %s\n", name);
+ snprintf(ddebug, DDEBUG_STRING_SIZE, "module %s +p",
+ name);
+ ddebug_exec_query(ddebug);
+ }
+ }
+ kfree(arg_dup_ptr);
+ if (verbose)
+ printk(KERN_INFO "%s: Finished %s parsing\n", __func__, name);
+}
+/* We search for module.ddebug kernel boot params */
+static void ddebug_boot_parse_args(void)
+{
+ char tmp_cmd_arr[COMMAND_LINE_SIZE], *tmp_cmd_ptr, *param, *val, *tmp;
+ char module[MODULE_NAME_LEN], ddebug[DDEBUG_STRING_SIZE];
+
+ /* next_arg touches the passed buffer and chops each argument */
+ strlcpy(tmp_cmd_arr, saved_command_line, COMMAND_LINE_SIZE);
+ /* Chew leading spaces */
+ tmp_cmd_ptr = skip_spaces(tmp_cmd_arr);
+
+ while (*tmp_cmd_ptr) {
+ tmp_cmd_ptr = next_arg(tmp_cmd_ptr, &param, &val);
+ if (verbose)
+ printk(KERN_INFO "%s: Param: %s, val: %s\n",
+ __func__, param, val);
+ tmp = strstr(param, ".ddebug");
+ if (tmp && strlen(tmp) == 7) {
+ strlcpy(module, param, tmp - param + 1);
+ pr_info("Enabling debugging for module %s\n", module);
+ snprintf(ddebug, DDEBUG_STRING_SIZE, "module %s +p",
+ module);
+ ddebug_exec_query(ddebug);
+ }
+ }
+}
+
static void ddebug_table_free(struct ddebug_table *dt)
{
list_del_init(&dt->link);
@@ -805,6 +883,8 @@ static int __init dynamic_debug_init(void)
ddebug_setup_string);
}

+ ddebug_boot_parse_args();
+
out_free:
if (ret)
ddebug_remove_all_tables();
--
1.6.0.2

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