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>

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