dynamic_debug: add an option to enable dynamic debug for modules only

Instead of enabling dynamic debug globally with CONFIG_DYNAMIC_DEBUG,
CONFIG_DYNAMIC_DEBUG_CORE will only enable core function of dynamic
debug.  With the DYNAMIC_DEBUG_MODULE defined for any modules, dynamic
debug will be tied to them.

This is useful for people who only want to enable dynamic debug for
kernel modules without worrying about kernel image size and memory
consumption is increasing too much.

[orson.zhai@unisoc.com: v2]
  Link: http://lkml.kernel.org/r/1587408228-10861-1-git-send-email-orson.unisoc@gmail.comSigned-off-by: Orson Zhai <orson.zhai@unisoc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: http://lkml.kernel.org/r/1586521984-5890-1-git-send-email-orson.unisoc@gmail.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/admin-guide/dynamic-debug-howto.rst

@@ -13,6 +13,11 @@ kernel code to obtain additional kernel information.  Currently, if
 ``print_hex_dump_debug()``/``print_hex_dump_bytes()`` calls can be dynamically
 enabled per-callsite.
 
+If you do not want to enable dynamic debug globally (i.e. in some embedded
+system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic
+debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any
+modules which you'd like to dynamically debug later.
+
 If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is just
 shortcut for ``print_hex_dump(KERN_DEBUG)``.
 

include/linux/dev_printk.h

@@ -109,7 +109,8 @@ void _dev_info(const struct device *dev, const char *fmt, ...)
 #define dev_info(dev, fmt, ...)						\
 	_dev_info(dev, dev_fmt(fmt), ##__VA_ARGS__)
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define dev_dbg(dev, fmt, ...)						\
 	dynamic_dev_dbg(dev, dev_fmt(fmt), ##__VA_ARGS__)
 #elif defined(DEBUG)
@@ -181,7 +182,8 @@ do {									\
 	dev_level_ratelimited(dev_notice, dev, fmt, ##__VA_ARGS__)
 #define dev_info_ratelimited(dev, fmt, ...)				\
 	dev_level_ratelimited(dev_info, dev, fmt, ##__VA_ARGS__)
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 /* descriptor check is first to prevent flooding with "callbacks suppressed" */
 #define dev_dbg_ratelimited(dev, fmt, ...)				\
 do {									\

include/linux/dynamic_debug.h

@@ -48,7 +48,7 @@ struct _ddebug {
 
 
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG_CORE)
 int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 				const char *modname);
 extern int ddebug_remove_module(const char *mod_name);

include/linux/net.h

@@ -264,7 +264,8 @@ do {								\
 	net_ratelimited_function(pr_warn, fmt, ##__VA_ARGS__)
 #define net_info_ratelimited(fmt, ...)				\
 	net_ratelimited_function(pr_info, fmt, ##__VA_ARGS__)
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define net_dbg_ratelimited(fmt, ...)					\
 do {									\
 	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);			\

include/linux/netdevice.h

@@ -4942,7 +4942,8 @@ do {								\
 #define MODULE_ALIAS_NETDEV(device) \
 	MODULE_ALIAS("netdev-" device)
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define netdev_dbg(__dev, format, args...)			\
 do {								\
 	dynamic_netdev_dbg(__dev, format, ##args);		\
@@ -5012,7 +5013,8 @@ do {								\
 #define netif_info(priv, type, dev, fmt, args...)		\
 	netif_level(info, priv, type, dev, fmt, ##args)
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define netif_dbg(priv, type, netdev, format, args...)		\
 do {								\
 	if (netif_msg_##type(priv))				\

include/linux/printk.h

@@ -399,7 +399,8 @@ extern int kptr_restrict;
 
 
 /* If you are writing a driver, please use dev_dbg instead */
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #include <linux/dynamic_debug.h>
 
 /**
@@ -535,7 +536,8 @@ extern int kptr_restrict;
 #endif
 
 /* If you are writing a driver, please use dev_dbg instead */
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 /* descriptor check is first to prevent flooding with "callbacks suppressed" */
 #define pr_debug_ratelimited(fmt, ...)					\
 do {									\
@@ -582,7 +584,8 @@ static inline void print_hex_dump_bytes(const char *prefix_str, int prefix_type,
 
 #endif
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define print_hex_dump_debug(prefix_str, prefix_type, rowsize,	\
 			     groupsize, buf, len, ascii)	\
 	dynamic_hex_dump(prefix_str, prefix_type, rowsize,	\

include/rdma/ib_verbs.h

@@ -100,7 +100,8 @@ void ibdev_notice(const struct ib_device *ibdev, const char *format, ...);
 __printf(2, 3) __cold
 void ibdev_info(const struct ib_device *ibdev, const char *format, ...);
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 #define ibdev_dbg(__dev, format, args...)                       \
 	dynamic_ibdev_dbg(__dev, format, ##args)
 #else
@@ -133,7 +134,8 @@ do {                                                                    \
 #define ibdev_info_ratelimited(ibdev, fmt, ...) \
 	ibdev_level_ratelimited(ibdev_info, ibdev, fmt, ##__VA_ARGS__)
 
-#if defined(CONFIG_DYNAMIC_DEBUG)
+#if defined(CONFIG_DYNAMIC_DEBUG) || \
+	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
 /* descriptor check is first to prevent flooding with "callbacks suppressed" */
 #define ibdev_dbg_ratelimited(ibdev, fmt, ...)                          \
 do {                                                                    \

lib/Kconfig.debug

@@ -99,6 +99,7 @@ config DYNAMIC_DEBUG
 	default n
 	depends on PRINTK
 	depends on (DEBUG_FS || PROC_FS)
+	select DYNAMIC_DEBUG_CORE
 	help
 
 	  Compiles debug level messages into the kernel, which would not
@@ -165,6 +166,17 @@ config DYNAMIC_DEBUG
 	  See Documentation/admin-guide/dynamic-debug-howto.rst for additional
 	  information.
 
+config DYNAMIC_DEBUG_CORE
+	bool "Enable core function of dynamic debug support"
+	depends on PRINTK
+	depends on (DEBUG_FS || PROC_FS)
+	help
+	  Enable core functional support of dynamic debug. It is useful
+	  when you want to tie dynamic debug to your kernel modules with
+	  DYNAMIC_DEBUG_MODULE defined for each of them, especially for
+	  the case of embedded system where the kernel image size is
+	  sensitive for people.
+
 config SYMBOLIC_ERRNAME
 	bool "Support symbolic error names in printf"
 	default y if PRINTK

lib/Makefile

@@ -190,7 +190,7 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o
 
 obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
 
-obj-$(CONFIG_DYNAMIC_DEBUG) += dynamic_debug.o
+obj-$(CONFIG_DYNAMIC_DEBUG_CORE) += dynamic_debug.o
 obj-$(CONFIG_SYMBOLIC_ERRNAME) += errname.o
 
 obj-$(CONFIG_NLATTR) += nlattr.o

lib/dynamic_debug.c

@@ -1032,9 +1032,14 @@ static int __init dynamic_debug_init(void)
 	int verbose_bytes = 0;
 
 	if (&__start___verbose == &__stop___verbose) {
+		if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
 			pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
 			return 1;
 		}
+		pr_info("Ignore empty _ddebug table in a CONFIG_DYNAMIC_DEBUG_CORE build\n");
+		ddebug_init_success = 1;
+		return 0;
+	}
 	iter = __start___verbose;
 	modname = iter->modname;
 	iter_start = iter;