Date:	Fri, 17 Sep 2010 15:54:57 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Thomas Renninger <trenn@...e.de>
Cc:	bjorn.helgaas@...com, gregkh@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] Dynamic Debug: Introduce global fake module param
	module.ddebug - V3

On Thu, Sep 16, 2010 at 12:11:45AM +0200, Thomas Renninger wrote:
> 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@...e.de>
> CC: Bjorn Helgaas <bjorn.helgaas@...com>
> CC: Jason Baron <jbaron@...hat.com>
> CC: Greg KH <gregkh@...e.de>
> CC: lkml <linux-kernel@...r.kernel.org>
> ---
>  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
> 

Hi,

So i'm wondering if need to support the module.ddebug on the command
line? The ddebug_query="module foo +p" format that you introduced does
the same thing. 

Also, we can't put those large char[] arrays on the kernel stack. They
probably should be global.

thanks,

-Jason
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