driver core: basic infrastructure for per-module dynamic debug messages

Base infrastructure to enable per-module debug messages.

I've introduced CONFIG_DYNAMIC_PRINTK_DEBUG, which when enabled centralizes
control of debugging statements on a per-module basis in one /proc file,
currently, <debugfs>/dynamic_printk/modules. When, CONFIG_DYNAMIC_PRINTK_DEBUG,
is not set, debugging statements can still be enabled as before, often by
defining 'DEBUG' for the proper compilation unit. Thus, this patch set has no
affect when CONFIG_DYNAMIC_PRINTK_DEBUG is not set.

The infrastructure currently ties into all pr_debug() and dev_dbg() calls. That
is, if CONFIG_DYNAMIC_PRINTK_DEBUG is set, all pr_debug() and dev_dbg() calls
can be dynamically enabled/disabled on a per-module basis.

Future plans include extending this functionality to subsystems, that define 
their own debug levels and flags.

Usage:

Dynamic debugging is controlled by the debugfs file, 
<debugfs>/dynamic_printk/modules. This file contains a list of the modules that
can be enabled. The format of the file is as follows:

	<module_name> <enabled=0/1>
		.
		.
		.

	<module_name> : Name of the module in which the debug call resides
	<enabled=0/1> : whether the messages are enabled or not

For example:

	snd_hda_intel enabled=0
	fixup enabled=1
	driver enabled=0

Enable a module:

	$echo "set enabled=1 <module_name>" > dynamic_printk/modules

Disable a module:

	$echo "set enabled=0 <module_name>" > dynamic_printk/modules

Enable all modules:

	$echo "set enabled=1 all" > dynamic_printk/modules

Disable all modules:

	$echo "set enabled=0 all" > dynamic_printk/modules

Finally, passing "dynamic_printk" at the command line enables
debugging for all modules. This mode can be turned off via the above
disable command.

[gkh: minor cleanups and tweaks to make the build work quietly]

Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/kernel-parameters.txt

@@ -1713,6 +1713,11 @@ and is between 256 and 4096 characters. It is defined in the file
 			autoconfiguration.
 			Ranges are in pairs (memory base and size).
 
+	dynamic_printk
+			Enables pr_debug()/dev_dbg() calls if
+			CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled. These can also
+			be switched on/off via <debugfs>/dynamic_printk/modules
+
 	print-fatal-signals=
 			[KNL] debug: print fatal signals
 			print-fatal-signals=1: print segfault info to

include/asm-generic/vmlinux.lds.h

@@ -268,7 +268,15 @@
 	CPU_DISCARD(init.data)						\
 	CPU_DISCARD(init.rodata)					\
 	MEM_DISCARD(init.data)						\
-	MEM_DISCARD(init.rodata)
+	MEM_DISCARD(init.rodata)					\
+	/* implement dynamic printk debug */				\
+	VMLINUX_SYMBOL(__start___verbose_strings) = .;                  \
+	*(__verbose_strings)                                            \
+	VMLINUX_SYMBOL(__stop___verbose_strings) = .;                   \
+	. = ALIGN(8);							\
+	VMLINUX_SYMBOL(__start___verbose) = .;                          \
+	*(__verbose)                                                    \
+	VMLINUX_SYMBOL(__stop___verbose) = .;
 
 #define INIT_TEXT							\
 	*(.init.text)							\

include/linux/device.h

@@ -550,7 +550,11 @@ extern const char *dev_driver_string(const struct device *dev);
 #define dev_info(dev, format, arg...)		\
 	dev_printk(KERN_INFO , dev , format , ## arg)
 
-#ifdef DEBUG
+#if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
+#define dev_dbg(dev, format, ...) do { \
+	dynamic_dev_dbg(dev, format, ##__VA_ARGS__); \
+	} while (0)
+#elif defined(DEBUG)
 #define dev_dbg(dev, format, arg...)		\
 	dev_printk(KERN_DEBUG , dev , format , ## arg)
 #else

include/linux/dynamic_printk.h

@@ -0,0 +1,93 @@
+#ifndef _DYNAMIC_PRINTK_H
+#define _DYNAMIC_PRINTK_H
+
+#define DYNAMIC_DEBUG_HASH_BITS 6
+#define DEBUG_HASH_TABLE_SIZE (1 << DYNAMIC_DEBUG_HASH_BITS)
+
+#define TYPE_BOOLEAN 1
+
+#define DYNAMIC_ENABLED_ALL 0
+#define DYNAMIC_ENABLED_NONE 1
+#define DYNAMIC_ENABLED_SOME 2
+
+extern int dynamic_enabled;
+
+/* dynamic_printk_enabled, and dynamic_printk_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.
+ */
+extern long long dynamic_printk_enabled;
+extern long long dynamic_printk_enabled2;
+
+struct mod_debug {
+	char *modname;
+	char *logical_modname;
+	char *flag_names;
+	int type;
+	int hash;
+	int hash2;
+} __attribute__((aligned(8)));
+
+int register_dynamic_debug_module(char *mod_name, int type, char *share_name,
+					char *flags, int hash, int hash2);
+
+#if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
+extern int unregister_dynamic_debug_module(char *mod_name);
+extern int __dynamic_dbg_enabled_helper(char *modname, int type,
+					int value, int hash);
+
+#define __dynamic_dbg_enabled(module, type, value, level, hash)  ({	     \
+	int __ret = 0;							     \
+	if (unlikely((dynamic_printk_enabled & (1LL << DEBUG_HASH)) &&	     \
+			(dynamic_printk_enabled2 & (1LL << DEBUG_HASH2))))   \
+			__ret = __dynamic_dbg_enabled_helper(module, type,   \
+								value, hash);\
+	__ret; })
+
+#define dynamic_pr_debug(fmt, ...) do {					    \
+	static char mod_name[]						    \
+	__attribute__((section("__verbose_strings")))			    \
+	 = KBUILD_MODNAME;						    \
+	static struct mod_debug descriptor				    \
+	__used								    \
+	__attribute__((section("__verbose"), aligned(8))) =		    \
+	{ mod_name, mod_name, NULL, TYPE_BOOLEAN, DEBUG_HASH, DEBUG_HASH2 };\
+	if (__dynamic_dbg_enabled(KBUILD_MODNAME, TYPE_BOOLEAN,		    \
+						0, 0, DEBUG_HASH))	    \
+		printk(KERN_DEBUG KBUILD_MODNAME ":" fmt,		    \
+				##__VA_ARGS__);				    \
+	} while (0)
+
+#define dynamic_dev_dbg(dev, format, ...) do {				    \
+	static char mod_name[]						    \
+	__attribute__((section("__verbose_strings")))			    \
+	 = KBUILD_MODNAME;						    \
+	static struct mod_debug descriptor				    \
+	__used								    \
+	__attribute__((section("__verbose"), aligned(8))) =		    \
+	{ mod_name, mod_name, NULL, TYPE_BOOLEAN, DEBUG_HASH, DEBUG_HASH2 };\
+	if (__dynamic_dbg_enabled(KBUILD_MODNAME, TYPE_BOOLEAN,		    \
+						0, 0, DEBUG_HASH))	    \
+			dev_printk(KERN_DEBUG, dev,			    \
+					KBUILD_MODNAME ": " format,	    \
+					##__VA_ARGS__);			    \
+	} while (0)
+
+#else
+
+static inline int unregister_dynamic_debug_module(const char *mod_name)
+{
+	return 0;
+}
+static inline int __dynamic_dbg_enabled_helper(char *modname, int type,
+						int value, int hash)
+{
+	return 0;
+}
+
+#define __dynamic_dbg_enabled(module, type, value, level, hash)  ({ 0; })
+#define dynamic_pr_debug(fmt, ...)  do { } while (0)
+#define dynamic_dev_dbg(dev, format, ...)  do { } while (0)
+#endif
+
+#endif

include/linux/kernel.h

@@ -16,6 +16,7 @@
 #include <linux/log2.h>
 #include <linux/typecheck.h>
 #include <linux/ratelimit.h>
+#include <linux/dynamic_printk.h>
 #include <asm/byteorder.h>
 #include <asm/bug.h>
 
@@ -303,8 +304,12 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
 #define pr_info(fmt, arg...) \
 	printk(KERN_INFO fmt, ##arg)
 
-#ifdef DEBUG
 /* If you are writing a driver, please use dev_dbg instead */
+#if defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
+#define pr_debug(fmt, ...) do { \
+	dynamic_pr_debug(fmt, ##__VA_ARGS__); \
+	} while (0)
+#elif defined(DEBUG)
 #define pr_debug(fmt, arg...) \
 	printk(KERN_DEBUG fmt, ##arg)
 #else

include/linux/module.h

@@ -345,7 +345,6 @@ struct module
 	/* Reference counts */
 	struct module_ref ref[NR_CPUS];
 #endif
-
 };
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}

kernel/module.c

@@ -784,6 +784,7 @@ sys_delete_module(const char __user *name_user, unsigned int flags)
 	mutex_lock(&module_mutex);
 	/* Store the name of the last unloaded module for diagnostic purposes */
 	strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
+	unregister_dynamic_debug_module(mod->name);
 	free_module(mod);
 
  out:
@@ -1783,6 +1784,33 @@ static inline void add_kallsyms(struct module *mod,
 }
 #endif /* CONFIG_KALLSYMS */
 
+#ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
+static void dynamic_printk_setup(Elf_Shdr *sechdrs, unsigned int verboseindex)
+{
+	struct mod_debug *debug_info;
+	unsigned long pos, end;
+	unsigned int num_verbose;
+
+	pos = sechdrs[verboseindex].sh_addr;
+	num_verbose = sechdrs[verboseindex].sh_size /
+				sizeof(struct mod_debug);
+	end = pos + (num_verbose * sizeof(struct mod_debug));
+
+	for (; pos < end; pos += sizeof(struct mod_debug)) {
+		debug_info = (struct mod_debug *)pos;
+		register_dynamic_debug_module(debug_info->modname,
+			debug_info->type, debug_info->logical_modname,
+			debug_info->flag_names, debug_info->hash,
+			debug_info->hash2);
+	}
+}
+#else
+static inline void dynamic_printk_setup(Elf_Shdr *sechdrs,
+					unsigned int verboseindex)
+{
+}
+#endif /* CONFIG_DYNAMIC_PRINTK_DEBUG */
+
 static void *module_alloc_update_bounds(unsigned long size)
 {
 	void *ret = module_alloc(size);
@@ -1831,6 +1859,7 @@ static noinline struct module *load_module(void __user *umod,
 #endif
 	unsigned int markersindex;
 	unsigned int markersstringsindex;
+	unsigned int verboseindex;
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
@@ -2117,6 +2146,7 @@ static noinline struct module *load_module(void __user *umod,
 	markersindex = find_sec(hdr, sechdrs, secstrings, "__markers");
  	markersstringsindex = find_sec(hdr, sechdrs, secstrings,
 					"__markers_strings");
+	verboseindex = find_sec(hdr, sechdrs, secstrings, "__verbose");
 
 	/* Now do relocations. */
 	for (i = 1; i < hdr->e_shnum; i++) {
@@ -2167,6 +2197,7 @@ static noinline struct module *load_module(void __user *umod,
 		marker_update_probe_range(mod->markers,
 			mod->markers + mod->num_markers);
 #endif
+	dynamic_printk_setup(sechdrs, verboseindex);
 	err = module_finalize(hdr, sechdrs, mod);
 	if (err < 0)
 		goto cleanup;

lib/Kconfig.debug

@@ -807,6 +807,61 @@ menuconfig BUILD_DOCSRC
 
 	  Say N if you are unsure.
 
+config DYNAMIC_PRINTK_DEBUG
+	bool "Enable dynamic printk() call support"
+	default n
+	depends on PRINTK
+	select PRINTK_DEBUG
+	help
+
+	  Compiles debug level messages into the kernel, which would not
+	  otherwise be available at runtime. These messages can then be
+	  enabled/disabled on a per module basis. This mechanism implicitly
+	  enables all pr_debug() and dev_dbg() calls. The impact of this
+	  compile option is a larger kernel text size of about 2%.
+
+	  Usage:
+
+	  Dynamic debugging is controlled by the debugfs file,
+	  dynamic_printk/modules. This file contains a list of the modules that
+	  can be enabled. The format of the file is the module name, followed
+	  by a set of flags that can be enabled. The first flag is always the
+	  'enabled' flag. For example:
+
+		<module_name> <enabled=0/1>
+				.
+				.
+				.
+
+	  <module_name> : Name of the module in which the debug call resides
+	  <enabled=0/1> : whether the messages are enabled or not
+
+	  From a live system:
+
+		snd_hda_intel enabled=0
+		fixup enabled=0
+		driver enabled=0
+
+	  Enable a module:
+
+	  	$echo "set enabled=1 <module_name>" > dynamic_printk/modules
+
+	  Disable a module:
+
+	  	$echo "set enabled=0 <module_name>" > dynamic_printk/modules
+
+	  Enable all modules:
+
+		$echo "set enabled=1 all" > dynamic_printk/modules
+
+	  Disable all modules:
+
+		$echo "set enabled=0 all" > dynamic_printk/modules
+
+	  Finally, passing "dynamic_printk" at the command line enables
+	  debugging for all modules. This mode can be turned off via the above
+	  disable command.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"

lib/Makefile

@@ -81,6 +81,8 @@ obj-$(CONFIG_HAVE_LMB) += lmb.o
 
 obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
 
+obj-$(CONFIG_DYNAMIC_PRINTK_DEBUG) += dynamic_printk.o
+
 hostprogs-y	:= gen_crc32table
 clean-files	:= crc32table.h
 

lib/dynamic_printk.c

@@ -0,0 +1,418 @@
+/*
+ * lib/dynamic_printk.c
+ *
+ * make pr_debug()/dev_dbg() calls runtime configurable based upon their
+ * their source module.
+ *
+ * Copyright (C) 2008 Red Hat, Inc., Jason Baron <jbaron@redhat.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/seq_file.h>
+#include <linux/debugfs.h>
+#include <linux/fs.h>
+
+extern struct mod_debug __start___verbose[];
+extern struct mod_debug __stop___verbose[];
+
+struct debug_name {
+	struct hlist_node hlist;
+	struct hlist_node hlist2;
+	int hash1;
+	int hash2;
+	char *name;
+	int enable;
+	int type;
+};
+
+static int nr_entries;
+static int num_enabled;
+int dynamic_enabled = DYNAMIC_ENABLED_NONE;
+static struct hlist_head module_table[DEBUG_HASH_TABLE_SIZE] =
+	{ [0 ... DEBUG_HASH_TABLE_SIZE-1] = HLIST_HEAD_INIT };
+static struct hlist_head module_table2[DEBUG_HASH_TABLE_SIZE] =
+	{ [0 ... DEBUG_HASH_TABLE_SIZE-1] = HLIST_HEAD_INIT };
+static DECLARE_MUTEX(debug_list_mutex);
+
+/* dynamic_printk_enabled, and dynamic_printk_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.
+ */
+long long dynamic_printk_enabled;
+EXPORT_SYMBOL_GPL(dynamic_printk_enabled);
+long long dynamic_printk_enabled2;
+EXPORT_SYMBOL_GPL(dynamic_printk_enabled2);
+
+/* returns the debug module pointer. */
+static struct debug_name *find_debug_module(char *module_name)
+{
+	int i;
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct debug_name *element;
+
+	element = NULL;
+	for (i = 0; i < DEBUG_HASH_TABLE_SIZE; i++) {
+		head = &module_table[i];
+		hlist_for_each_entry_rcu(element, node, head, hlist)
+			if (!strcmp(element->name, module_name))
+				return element;
+	}
+	return NULL;
+}
+
+/* returns the debug module pointer. */
+static struct debug_name *find_debug_module_hash(char *module_name, int hash)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct debug_name *element;
+
+	element = NULL;
+	head = &module_table[hash];
+	hlist_for_each_entry_rcu(element, node, head, hlist)
+		if (!strcmp(element->name, module_name))
+			return element;
+	return NULL;
+}
+
+/* caller must hold mutex*/
+static int __add_debug_module(char *mod_name, int hash, int hash2)
+{
+	struct debug_name *new;
+	char *module_name;
+	int ret = 0;
+
+	if (find_debug_module(mod_name)) {
+		ret = -EINVAL;
+		goto out;
+	}
+	module_name = kmalloc(strlen(mod_name) + 1, GFP_KERNEL);
+	if (!module_name) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	module_name = strcpy(module_name, mod_name);
+	module_name[strlen(mod_name)] = '\0';
+	new = kzalloc(sizeof(struct debug_name), GFP_KERNEL);
+	if (!new) {
+		kfree(module_name);
+		ret = -ENOMEM;
+		goto out;
+	}
+	INIT_HLIST_NODE(&new->hlist);
+	INIT_HLIST_NODE(&new->hlist2);
+	new->name = module_name;
+	new->hash1 = hash;
+	new->hash2 = hash2;
+	hlist_add_head_rcu(&new->hlist, &module_table[hash]);
+	hlist_add_head_rcu(&new->hlist2, &module_table2[hash2]);
+	nr_entries++;
+out:
+	return ret;
+}
+
+int unregister_dynamic_debug_module(char *mod_name)
+{
+	struct debug_name *element;
+	int ret = 0;
+
+	down(&debug_list_mutex);
+	element = find_debug_module(mod_name);
+	if (!element) {
+		ret = -EINVAL;
+		goto out;
+	}
+	hlist_del_rcu(&element->hlist);
+	hlist_del_rcu(&element->hlist2);
+	synchronize_rcu();
+	kfree(element->name);
+	if (element->enable)
+		num_enabled--;
+	kfree(element);
+	nr_entries--;
+out:
+	up(&debug_list_mutex);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(unregister_dynamic_debug_module);
+
+int register_dynamic_debug_module(char *mod_name, int type, char *share_name,
+					char *flags, int hash, int hash2)
+{
+	struct debug_name *elem;
+	int ret = 0;
+
+	down(&debug_list_mutex);
+	elem = find_debug_module(mod_name);
+	if (!elem) {
+		if (__add_debug_module(mod_name, hash, hash2))
+			goto out;
+		elem = find_debug_module(mod_name);
+		if (dynamic_enabled == DYNAMIC_ENABLED_ALL &&
+				!strcmp(mod_name, share_name)) {
+			elem->enable = true;
+			num_enabled++;
+		}
+	}
+	elem->type |= type;
+out:
+	up(&debug_list_mutex);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(register_dynamic_debug_module);
+
+int __dynamic_dbg_enabled_helper(char *mod_name, int type, int value, int hash)
+{
+	struct debug_name *elem;
+	int ret = 0;
+
+	if (dynamic_enabled == DYNAMIC_ENABLED_ALL)
+		return 1;
+	rcu_read_lock();
+	elem = find_debug_module_hash(mod_name, hash);
+	if (elem && elem->enable)
+		ret = 1;
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__dynamic_dbg_enabled_helper);
+
+static void set_all(bool enable)
+{
+	struct debug_name *e;
+	struct hlist_node *node;
+	int i;
+	long long enable_mask;
+
+	for (i = 0; i < DEBUG_HASH_TABLE_SIZE; i++) {
+		if (module_table[i].first != NULL) {
+			hlist_for_each_entry(e, node, &module_table[i], hlist) {
+				e->enable = enable;
+			}
+		}
+	}
+	if (enable)
+		enable_mask = ULLONG_MAX;
+	else
+		enable_mask = 0;
+	dynamic_printk_enabled = enable_mask;
+	dynamic_printk_enabled2 = enable_mask;
+}
+
+static int disabled_hash(int i, bool first_table)
+{
+	struct debug_name *e;
+	struct hlist_node *node;
+
+	if (first_table) {
+		hlist_for_each_entry(e, node, &module_table[i], hlist) {
+			if (e->enable)
+				return 0;
+		}
+	} else {
+		hlist_for_each_entry(e, node, &module_table2[i], hlist2) {
+			if (e->enable)
+				return 0;
+		}
+	}
+	return 1;
+}
+
+static ssize_t pr_debug_write(struct file *file, const char __user *buf,
+				size_t length, loff_t *ppos)
+{
+	char *buffer, *s, *value_str, *setting_str;
+	int err, value;
+	struct debug_name *elem = NULL;
+	int all = 0;
+
+	if (length > PAGE_SIZE || length < 0)
+		return -EINVAL;
+
+	buffer = (char *)__get_free_page(GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	err = -EFAULT;
+	if (copy_from_user(buffer, buf, length))
+		goto out;
+
+	err = -EINVAL;
+	if (length < PAGE_SIZE)
+		buffer[length] = '\0';
+	else if (buffer[PAGE_SIZE-1])
+		goto out;
+
+	err = -EINVAL;
+	down(&debug_list_mutex);
+
+	if (strncmp("set", buffer, 3))
+		goto out_up;
+	s = buffer + 3;
+	setting_str = strsep(&s, "=");
+	if (s == NULL)
+		goto out_up;
+	setting_str = strstrip(setting_str);
+	value_str = strsep(&s, " ");
+	if (s == NULL)
+		goto out_up;
+	s = strstrip(s);
+	if (!strncmp(s, "all", 3))
+		all = 1;
+	else
+		elem = find_debug_module(s);
+	if (!strncmp(setting_str, "enable", 6)) {
+		value = !!simple_strtol(value_str, NULL, 10);
+		if (all) {
+			if (value) {
+				set_all(true);
+				num_enabled = nr_entries;
+				dynamic_enabled = DYNAMIC_ENABLED_ALL;
+			} else {
+				set_all(false);
+				num_enabled = 0;
+				dynamic_enabled = DYNAMIC_ENABLED_NONE;
+			}
+			err = 0;
+		} else {
+			if (elem) {
+				if (value && (elem->enable == 0)) {
+					dynamic_printk_enabled |=
+							(1LL << elem->hash1);
+					dynamic_printk_enabled2 |=
+							(1LL << elem->hash2);
+					elem->enable = 1;
+					num_enabled++;
+					dynamic_enabled = DYNAMIC_ENABLED_SOME;
+					err = 0;
+					printk(KERN_DEBUG
+					       "debugging enabled for module %s",
+					       elem->name);
+				} else if (!value && (elem->enable == 1)) {
+					elem->enable = 0;
+					num_enabled--;
+					if (disabled_hash(elem->hash1, true))
+						dynamic_printk_enabled &=
+							~(1LL << elem->hash1);
+					if (disabled_hash(elem->hash2, false))
+						dynamic_printk_enabled2 &=
+							~(1LL << elem->hash2);
+					if (num_enabled)
+						dynamic_enabled =
+							DYNAMIC_ENABLED_SOME;
+					else
+						dynamic_enabled =
+							DYNAMIC_ENABLED_NONE;
+					err = 0;
+					printk(KERN_DEBUG
+					       "debugging disabled for module "
+					       "%s", elem->name);
+				}
+			}
+		}
+	}
+	if (!err)
+		err = length;
+out_up:
+	up(&debug_list_mutex);
+out:
+	free_page((unsigned long)buffer);
+	return err;
+}
+
+static void *pr_debug_seq_start(struct seq_file *f, loff_t *pos)
+{
+	return (*pos < DEBUG_HASH_TABLE_SIZE) ? pos : NULL;
+}
+
+static void *pr_debug_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	(*pos)++;
+	if (*pos >= DEBUG_HASH_TABLE_SIZE)
+		return NULL;
+	return pos;
+}
+
+static void pr_debug_seq_stop(struct seq_file *s, void *v)
+{
+	/* Nothing to do */
+}
+
+static int pr_debug_seq_show(struct seq_file *s, void *v)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct debug_name *elem;
+	unsigned int i = *(loff_t *) v;
+
+	rcu_read_lock();
+	head = &module_table[i];
+	hlist_for_each_entry_rcu(elem, node, head, hlist) {
+		seq_printf(s, "%s enabled=%d", elem->name, elem->enable);
+		seq_printf(s, "\n");
+	}
+	rcu_read_unlock();
+	return 0;
+}
+
+static struct seq_operations pr_debug_seq_ops = {
+	.start = pr_debug_seq_start,
+	.next  = pr_debug_seq_next,
+	.stop  = pr_debug_seq_stop,
+	.show  = pr_debug_seq_show
+};
+
+static int pr_debug_open(struct inode *inode, struct file *filp)
+{
+	return seq_open(filp, &pr_debug_seq_ops);
+}
+
+static const struct file_operations pr_debug_operations = {
+	.open		= pr_debug_open,
+	.read		= seq_read,
+	.write		= pr_debug_write,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static int __init dynamic_printk_init(void)
+{
+	struct dentry *dir, *file;
+	struct mod_debug *iter;
+	unsigned long value;
+
+	dir = debugfs_create_dir("dynamic_printk", NULL);
+	if (!dir)
+		return -ENOMEM;
+	file = debugfs_create_file("modules", 0644, dir, NULL,
+					&pr_debug_operations);
+	if (!file) {
+		debugfs_remove(dir);
+		return -ENOMEM;
+	}
+	for (value = (unsigned long)__start___verbose;
+		value < (unsigned long)__stop___verbose;
+		value += sizeof(struct mod_debug)) {
+			iter = (struct mod_debug *)value;
+			register_dynamic_debug_module(iter->modname,
+				iter->type,
+				iter->logical_modname,
+				iter->flag_names, iter->hash, iter->hash2);
+	}
+	return 0;
+}
+module_init(dynamic_printk_init);
+/* may want to move this earlier so we can get traces as early as possible */
+
+static int __init dynamic_printk_setup(char *str)
+{
+	if (str)
+		return -ENOENT;
+	set_all(true);
+	return 0;
+}
+/* Use early_param(), so we can get debug output as early as possible */
+early_param("dynamic_printk", dynamic_printk_setup);

net/netfilter/nf_conntrack_pptp.c

@@ -65,7 +65,7 @@ void
 			     struct nf_conntrack_expect *exp) __read_mostly;
 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
 
-#ifdef DEBUG
+#if defined(DEBUG) || defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
 /* PptpControlMessageType names */
 const char *const pptp_msg_name[] = {
 	"UNKNOWN_MESSAGE",

scripts/Makefile.lib

@@ -96,6 +96,14 @@ basename_flags = -D"KBUILD_BASENAME=KBUILD_STR($(call name-fix,$(basetarget)))"
 modname_flags  = $(if $(filter 1,$(words $(modname))),\
                  -D"KBUILD_MODNAME=KBUILD_STR($(call name-fix,$(modname)))")
 
+#hash values
+ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
+debug_flags = -D"DEBUG_HASH=$(shell ./scripts/basic/hash djb2 $(@D)$(modname))"\
+              -D"DEBUG_HASH2=$(shell ./scripts/basic/hash r5 $(@D)$(modname))"
+else
+debug_flags =
+endif
+
 orig_c_flags   = $(KBUILD_CFLAGS) $(ccflags-y) $(CFLAGS_$(basetarget).o)
 _c_flags       = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(orig_c_flags))
 _a_flags       = $(KBUILD_AFLAGS) $(asflags-y) $(AFLAGS_$(basetarget).o)
@@ -121,7 +129,8 @@ endif
 
 c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 		 $(__c_flags) $(modkern_cflags) \
-		 -D"KBUILD_STR(s)=\#s" $(basename_flags) $(modname_flags)
+		 -D"KBUILD_STR(s)=\#s" $(basename_flags) $(modname_flags) \
+		  $(debug_flags)
 
 a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 		 $(__a_flags) $(modkern_aflags)

scripts/basic/Makefile

@@ -9,7 +9,7 @@
 # fixdep: 	 Used to generate dependency information during build process
 # docproc:	 Used in Documentation/DocBook
 
-hostprogs-y	:= fixdep docproc
+hostprogs-y	:= fixdep docproc hash
 always		:= $(hostprogs-y)
 
 # fixdep is needed to compile other host programs

scripts/basic/hash.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2008 Red Hat, Inc., Jason Baron <jbaron@redhat.com>
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define DYNAMIC_DEBUG_HASH_BITS 6
+
+static const char *program;
+
+static void usage(void)
+{
+	printf("Usage: %s <djb2|r5> <modname>\n", program);
+	exit(1);
+}
+
+/* djb2 hashing algorithm by Dan Bernstein. From:
+ * http://www.cse.yorku.ca/~oz/hash.html
+ */
+
+unsigned int djb2_hash(char *str)
+{
+	unsigned long hash = 5381;
+	int c;
+
+	c = *str;
+	while (c) {
+		hash = ((hash << 5) + hash) + c;
+		c = *++str;
+	}
+	return (unsigned int)(hash & ((1 << DYNAMIC_DEBUG_HASH_BITS) - 1));
+}
+
+unsigned int r5_hash(char *str)
+{
+	unsigned long hash = 0;
+	int c;
+
+	c = *str;
+	while (c) {
+		hash = (hash + (c << 4) + (c >> 4)) * 11;
+		c = *++str;
+	}
+	return (unsigned int)(hash & ((1 << DYNAMIC_DEBUG_HASH_BITS) - 1));
+}
+
+int main(int argc, char *argv[])
+{
+	program = argv[0];
+
+	if (argc != 3)
+		usage();
+	if (!strcmp(argv[1], "djb2"))
+		printf("%d\n", djb2_hash(argv[2]));
+	else if (!strcmp(argv[1], "r5"))
+		printf("%d\n", r5_hash(argv[2]));
+	else
+		usage();
+	exit(0);
+}
+