dynamic debug: combine dprintk and dynamic printk

This patch combines Greg Bank's dprintk() work with the existing dynamic
printk patchset, we are now calling it 'dynamic debug'.

The new feature of this patchset is a richer /debugfs control file interface,
(an example output from my system is at the bottom), which allows fined grained
control over the the debug output. The output can be controlled by function,
file, module, format string, and line number.

for example, enabled all debug messages in module 'nf_conntrack':

echo -n 'module nf_conntrack +p' > /mnt/debugfs/dynamic_debug/control

to disable them:

echo -n 'module nf_conntrack -p' > /mnt/debugfs/dynamic_debug/control

A further explanation can be found in the documentation patch.

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

Documentation/kernel-parameters.txt

@@ -1816,11 +1816,6 @@ 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

@@ -80,6 +80,11 @@
 	VMLINUX_SYMBOL(__start___tracepoints) = .;			\
 	*(__tracepoints)						\
 	VMLINUX_SYMBOL(__stop___tracepoints) = .;			\
+	/* implement dynamic printk debug */				\
+	. = ALIGN(8);							\
+	VMLINUX_SYMBOL(__start___verbose) = .;                          \
+	*(__verbose)                                                    \
+	VMLINUX_SYMBOL(__stop___verbose) = .;				\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()
 
@@ -309,15 +314,7 @@
 	CPU_DISCARD(init.data)						\
 	CPU_DISCARD(init.rodata)					\
 	MEM_DISCARD(init.data)						\
-	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) = .;
+	MEM_DISCARD(init.rodata)
 
 #define INIT_TEXT							\
 	*(.init.text)							\

include/linux/device.h

@@ -582,7 +582,7 @@ extern const char *dev_driver_string(const struct device *dev);
 #if defined(DEBUG)
 #define dev_dbg(dev, format, arg...)		\
 	dev_printk(KERN_DEBUG , dev , format , ## arg)
-#elif defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
+#elif defined(CONFIG_DYNAMIC_DEBUG)
 #define dev_dbg(dev, format, ...) do { \
 	dynamic_dev_dbg(dev, format, ##__VA_ARGS__); \
 	} while (0)

include/linux/dynamic_debug.h

@@ -0,0 +1,88 @@
+#ifndef _DYNAMIC_DEBUG_H
+#define _DYNAMIC_DEBUG_H
+
+/* 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_debug_enabled;
+extern long long dynamic_debug_enabled2;
+
+/*
+ * An instance of this structure is created in a special
+ * ELF section at every dynamic debug callsite.  At runtime,
+ * the special section is treated as an array of these.
+ */
+struct _ddebug {
+	/*
+	 * These fields are used to drive the user interface
+	 * for selecting and displaying debug callsites.
+	 */
+	const char *modname;
+	const char *function;
+	const char *filename;
+	const char *format;
+	char primary_hash;
+	char secondary_hash;
+	unsigned int lineno:24;
+	/*
+ 	 * The flags field controls the behaviour at the callsite.
+ 	 * The bits here are changed dynamically when the user
+ 	 * writes commands to <debugfs>/dynamic_debug/ddebug
+	 */
+#define _DPRINTK_FLAGS_PRINT   (1<<0)  /* printk() a message using the format */
+#define _DPRINTK_FLAGS_DEFAULT 0
+	unsigned int flags:8;
+} __attribute__((aligned(8)));
+
+
+int ddebug_add_module(struct _ddebug *tab, unsigned int n,
+				const char *modname);
+
+#if defined(CONFIG_DYNAMIC_DEBUG)
+extern int ddebug_remove_module(char *mod_name);
+
+#define __dynamic_dbg_enabled(dd)  ({	     \
+	int __ret = 0;							     \
+	if (unlikely((dynamic_debug_enabled & (1LL << DEBUG_HASH)) &&	     \
+			(dynamic_debug_enabled2 & (1LL << DEBUG_HASH2))))   \
+				if (unlikely(dd.flags))			     \
+					__ret = 1;			     \
+	__ret; })
+
+#define dynamic_pr_debug(fmt, ...) do {					\
+	static struct _ddebug descriptor				\
+	__used								\
+	__attribute__((section("__verbose"), aligned(8))) =		\
+	{ KBUILD_MODNAME, __func__, __FILE__, fmt, DEBUG_HASH,	\
+		DEBUG_HASH2, __LINE__, _DPRINTK_FLAGS_DEFAULT };	\
+	if (__dynamic_dbg_enabled(descriptor))				\
+		printk(KERN_DEBUG KBUILD_MODNAME ":" fmt,		\
+				##__VA_ARGS__);				\
+	} while (0)
+
+
+#define dynamic_dev_dbg(dev, fmt, ...) do {				\
+	static struct _ddebug descriptor				\
+	__used								\
+	__attribute__((section("__verbose"), aligned(8))) =		\
+	{ KBUILD_MODNAME, __func__, __FILE__, fmt, DEBUG_HASH,	\
+		DEBUG_HASH2, __LINE__, _DPRINTK_FLAGS_DEFAULT };	\
+	if (__dynamic_dbg_enabled(descriptor))				\
+			dev_printk(KERN_DEBUG, dev,			\
+					KBUILD_MODNAME ": " fmt,	\
+					##__VA_ARGS__);			\
+	} while (0)
+
+#else
+
+static inline int ddebug_remove_module(char *mod)
+{
+	return 0;
+}
+
+#define dynamic_pr_debug(fmt, ...)  do { } while (0)
+#define dynamic_dev_dbg(dev, format, ...)  do { } while (0)
+#endif
+
+#endif

include/linux/kernel.h

@@ -16,7 +16,7 @@
 #include <linux/log2.h>
 #include <linux/typecheck.h>
 #include <linux/ratelimit.h>
-#include <linux/dynamic_printk.h>
+#include <linux/dynamic_debug.h>
 #include <asm/byteorder.h>
 #include <asm/bug.h>
 
@@ -358,7 +358,7 @@ static inline char *pack_hex_byte(char *buf, u8 byte)
 #if defined(DEBUG)
 #define pr_debug(fmt, ...) \
 	printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
-#elif defined(CONFIG_DYNAMIC_PRINTK_DEBUG)
+#elif defined(CONFIG_DYNAMIC_DEBUG)
 #define pr_debug(fmt, ...) do { \
 	dynamic_pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
 	} while (0)

kernel/module.c

@@ -822,7 +822,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 	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);
+	ddebug_remove_module(mod->name);
 	free_module(mod);
 
  out:
@@ -1827,19 +1827,13 @@ static inline void add_kallsyms(struct module *mod,
 }
 #endif /* CONFIG_KALLSYMS */
 
-static void dynamic_printk_setup(struct mod_debug *debug, unsigned int num)
+static void dynamic_debug_setup(struct _ddebug *debug, unsigned int num)
 {
-#ifdef CONFIG_DYNAMIC_PRINTK_DEBUG
-	unsigned int i;
-
-	for (i = 0; i < num; i++) {
-		register_dynamic_debug_module(debug[i].modname,
-					      debug[i].type,
-					      debug[i].logical_modname,
-					      debug[i].flag_names,
-					      debug[i].hash, debug[i].hash2);
-	}
-#endif /* CONFIG_DYNAMIC_PRINTK_DEBUG */
+#ifdef CONFIG_DYNAMIC_DEBUG
+	if (ddebug_add_module(debug, num, debug->modname))
+		printk(KERN_ERR "dynamic debug error adding module: %s\n",
+					debug->modname);
+#endif
 }
 
 static void *module_alloc_update_bounds(unsigned long size)
@@ -2213,12 +2207,13 @@ static noinline struct module *load_module(void __user *umod,
 	add_kallsyms(mod, sechdrs, symindex, strindex, secstrings);
 
 	if (!mod->taints) {
-		struct mod_debug *debug;
+		struct _ddebug *debug;
 		unsigned int num_debug;
 
 		debug = section_objs(hdr, sechdrs, secstrings, "__verbose",
 				     sizeof(*debug), &num_debug);
-		dynamic_printk_setup(debug, num_debug);
+		if (debug)
+			dynamic_debug_setup(debug, num_debug);
 	}
 
 	/* sechdrs[0].sh_size is always zero */

lib/Kconfig.debug

@@ -847,7 +847,7 @@ config BUILD_DOCSRC
 
 	  Say N if you are unsure.
 
-config DYNAMIC_PRINTK_DEBUG
+config DYNAMIC_DEBUG
 	bool "Enable dynamic printk() call support"
 	default n
 	depends on PRINTK

lib/Makefile

@@ -82,7 +82,7 @@ obj-$(CONFIG_HAVE_LMB) += lmb.o
 
 obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
 
-obj-$(CONFIG_DYNAMIC_PRINTK_DEBUG) += dynamic_printk.o
+obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
 
 hostprogs-y	:= gen_crc32table
 clean-files	:= crc32table.h