[PATCH v3 0/4] Unload linux/kernel.h

[PATCH v3 0/4] Unload linux/kernel.h

[Yury Norov (NVIDIA)]

kernel.h hosts declarations that can be placed better.

No major changes since v2. For testing details, see v2.

v1: https://lore.kernel.org/all/20251129195304.204082-1-yury.norov@gmail.com/
v2: https://lore.kernel.org/all/20251203162329.280182-1-yury.norov@gmail.com/
v3:
 - rename linux/tracing.h to linux/trace_printk.h (Steven);
 - cleanup headers better (Andy);

Yury Norov (NVIDIA) (4):
  kernel.h: drop STACK_MAGIC macro
  moduleparam: include required headers explicitly
  kernel.h: move VERIFY_OCTAL_PERMISSIONS() to sysfs.h
  tracing: move tracing declarations from kernel.h to a dedicated header

 Documentation/filesystems/sysfs.rst           |   2 +-
 .../drm/i915/gt/selftest_ring_submission.c    |   1 +
 drivers/gpu/drm/i915/i915_selftest.h          |   2 +
 include/linux/kernel.h                        | 210 +-----------------
 include/linux/moduleparam.h                   |   7 +-
 include/linux/sysfs.h                         |  13 ++
 include/linux/trace_printk.h                  | 205 +++++++++++++++++
 7 files changed, 229 insertions(+), 211 deletions(-)
 create mode 100644 include/linux/trace_printk.h

-- 
2.43.0

[PATCH v3 1/4] kernel.h: drop STACK_MAGIC macro

[Yury Norov (NVIDIA)]

The macro was introduced in 1994, v1.0.4, for stacks protection. Since
that, people found better ways to protect stacks, and now the macro is
only used by i915 selftests. Move it to a local header and drop from
the kernel.h.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
 drivers/gpu/drm/i915/gt/selftest_ring_submission.c | 1 +
 drivers/gpu/drm/i915/i915_selftest.h               | 2 ++
 include/linux/kernel.h                             | 2 --
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_ring_submission.c b/drivers/gpu/drm/i915/gt/selftest_ring_submission.c
index 87ceb0f374b6..600333ae6c8c 100644
--- a/drivers/gpu/drm/i915/gt/selftest_ring_submission.c
+++ b/drivers/gpu/drm/i915/gt/selftest_ring_submission.c
@@ -3,6 +3,7 @@
  * Copyright © 2020 Intel Corporation
  */
 
+#include "i915_selftest.h"
 #include "intel_engine_pm.h"
 #include "selftests/igt_flush_test.h"
 
diff --git a/drivers/gpu/drm/i915/i915_selftest.h b/drivers/gpu/drm/i915/i915_selftest.h
index bdf3e22c0a34..72922028f4ba 100644
--- a/drivers/gpu/drm/i915/i915_selftest.h
+++ b/drivers/gpu/drm/i915/i915_selftest.h
@@ -26,6 +26,8 @@
 
 #include <linux/types.h>
 
+#define STACK_MAGIC	0xdeadbeef
+
 struct pci_dev;
 struct drm_i915_private;
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5b46924fdff5..61d63c57bc2d 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -40,8 +40,6 @@
 
 #include <uapi/linux/kernel.h>
 
-#define STACK_MAGIC	0xdeadbeef
-
 struct completion;
 struct user;
 
-- 
2.43.0

Re: [PATCH v3 1/4] kernel.h: drop STACK_MAGIC macro

[Andi Shyti]

Hi Yuri,

On Fri, Dec 05, 2025 at 12:52:32PM -0500, Yury Norov (NVIDIA) wrote:
> The macro was introduced in 1994, v1.0.4, for stacks protection. Since
> that, people found better ways to protect stacks, and now the macro is
> only used by i915 selftests. Move it to a local header and drop from
> the kernel.h.
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Acked-by: Randy Dunlap <rdunlap@infradead.org>
> Acked-by: Jani Nikula <jani.nikula@intel.com>
> Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>

Thanks,
Andi

[PATCH v3 2/4] moduleparam: include required headers explicitly

[Yury Norov (NVIDIA)]

The following patch drops moduleparam.h dependency on kernel.h. In
preparation to it, list all the required headers explicitly.

Suggested-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
 include/linux/moduleparam.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 6907aedc4f74..ca7c8107c7c8 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -2,9 +2,14 @@
 #ifndef _LINUX_MODULE_PARAMS_H
 #define _LINUX_MODULE_PARAMS_H
 /* (C) Copyright 2001, 2002 Rusty Russell IBM Corporation */
+
+#include <linux/array_size.h>
+#include <linux/build_bug.h>
+#include <linux/compiler.h>
 #include <linux/init.h>
 #include <linux/stringify.h>
 #include <linux/kernel.h>
+#include <linux/types.h>
 
 /*
  * The maximum module name length, including the NUL byte.
-- 
2.43.0

[PATCH v3 3/4] kernel.h: move VERIFY_OCTAL_PERMISSIONS() to sysfs.h

[Yury Norov (NVIDIA)]

The macro is related to sysfs, but is defined in kernel.h. Move it to
the proper header, and unload the generic kernel.h.

Now that the macro is removed from kernel.h, linux/moduleparam.h is
decoupled, and kernel.h inclusion can be removed.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
 Documentation/filesystems/sysfs.rst |  2 +-
 include/linux/kernel.h              | 12 ------------
 include/linux/moduleparam.h         |  2 +-
 include/linux/sysfs.h               | 13 +++++++++++++
 4 files changed, 15 insertions(+), 14 deletions(-)

diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst
index 2703c04af7d0..ffcef4d6bc8d 100644
--- a/Documentation/filesystems/sysfs.rst
+++ b/Documentation/filesystems/sysfs.rst
@@ -120,7 +120,7 @@ is equivalent to doing::
 	    .store = store_foo,
     };
 
-Note as stated in include/linux/kernel.h "OTHER_WRITABLE?  Generally
+Note as stated in include/linux/sysfs.h "OTHER_WRITABLE?  Generally
 considered a bad idea." so trying to set a sysfs file writable for
 everyone will fail reverting to RO mode for "Others".
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 61d63c57bc2d..5b879bfea948 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -389,16 +389,4 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 # define REBUILD_DUE_TO_DYNAMIC_FTRACE
 #endif
 
-/* Permissions on a sysfs file: you didn't miss the 0 prefix did you? */
-#define VERIFY_OCTAL_PERMISSIONS(perms)						\
-	(BUILD_BUG_ON_ZERO((perms) < 0) +					\
-	 BUILD_BUG_ON_ZERO((perms) > 0777) +					\
-	 /* USER_READABLE >= GROUP_READABLE >= OTHER_READABLE */		\
-	 BUILD_BUG_ON_ZERO((((perms) >> 6) & 4) < (((perms) >> 3) & 4)) +	\
-	 BUILD_BUG_ON_ZERO((((perms) >> 3) & 4) < ((perms) & 4)) +		\
-	 /* USER_WRITABLE >= GROUP_WRITABLE */					\
-	 BUILD_BUG_ON_ZERO((((perms) >> 6) & 2) < (((perms) >> 3) & 2)) +	\
-	 /* OTHER_WRITABLE?  Generally considered a bad idea. */		\
-	 BUILD_BUG_ON_ZERO((perms) & 2) +					\
-	 (perms))
 #endif
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index ca7c8107c7c8..dd2d990b2611 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -8,7 +8,7 @@
 #include <linux/compiler.h>
 #include <linux/init.h>
 #include <linux/stringify.h>
-#include <linux/kernel.h>
+#include <linux/sysfs.h>
 #include <linux/types.h>
 
 /*
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 9a25a2911652..15ee3ef33991 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -798,4 +798,17 @@ static inline void sysfs_put(struct kernfs_node *kn)
 	kernfs_put(kn);
 }
 
+/* Permissions on a sysfs file: you didn't miss the 0 prefix did you? */
+#define VERIFY_OCTAL_PERMISSIONS(perms)						\
+	(BUILD_BUG_ON_ZERO((perms) < 0) +					\
+	 BUILD_BUG_ON_ZERO((perms) > 0777) +					\
+	 /* USER_READABLE >= GROUP_READABLE >= OTHER_READABLE */		\
+	 BUILD_BUG_ON_ZERO((((perms) >> 6) & 4) < (((perms) >> 3) & 4)) +	\
+	 BUILD_BUG_ON_ZERO((((perms) >> 3) & 4) < ((perms) & 4)) +		\
+	 /* USER_WRITABLE >= GROUP_WRITABLE */					\
+	 BUILD_BUG_ON_ZERO((((perms) >> 6) & 2) < (((perms) >> 3) & 2)) +	\
+	 /* OTHER_WRITABLE?  Generally considered a bad idea. */		\
+	 BUILD_BUG_ON_ZERO((perms) & 2) +					\
+	 (perms))
+
 #endif /* _SYSFS_H_ */
-- 
2.43.0

[PATCH v3 4/4] tracing: move tracing declarations from kernel.h to a dedicated header

[Yury Norov (NVIDIA)]

Tracing is a half of the kernel.h in terms of LOCs, although it's
a self-consistent part. It is intended for quick debugging purposes
and isn't used by the normal tracing utilities.

Move it to a separate header. If someone needs to just throw a
trace_printk() in their driver, they will not have to pull all
the heavy tracing machinery.

This is a pure move, except for removing a few 'extern's.

Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
 include/linux/kernel.h       | 196 +--------------------------------
 include/linux/trace_printk.h | 205 +++++++++++++++++++++++++++++++++++
 2 files changed, 206 insertions(+), 195 deletions(-)
 create mode 100644 include/linux/trace_printk.h

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5b879bfea948..a377335e01da 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -32,7 +32,7 @@
 #include <linux/build_bug.h>
 #include <linux/sprintf.h>
 #include <linux/static_call_types.h>
-#include <linux/instruction_pointer.h>
+#include <linux/trace_printk.h>
 #include <linux/util_macros.h>
 #include <linux/wordpart.h>
 
@@ -190,200 +190,6 @@ enum system_states {
 };
 extern enum system_states system_state;
 
-/*
- * General tracing related utility functions - trace_printk(),
- * tracing_on/tracing_off and tracing_start()/tracing_stop
- *
- * Use tracing_on/tracing_off when you want to quickly turn on or off
- * tracing. It simply enables or disables the recording of the trace events.
- * This also corresponds to the user space /sys/kernel/tracing/tracing_on
- * file, which gives a means for the kernel and userspace to interact.
- * Place a tracing_off() in the kernel where you want tracing to end.
- * From user space, examine the trace, and then echo 1 > tracing_on
- * to continue tracing.
- *
- * tracing_stop/tracing_start has slightly more overhead. It is used
- * by things like suspend to ram where disabling the recording of the
- * trace is not enough, but tracing must actually stop because things
- * like calling smp_processor_id() may crash the system.
- *
- * Most likely, you want to use tracing_on/tracing_off.
- */
-
-enum ftrace_dump_mode {
-	DUMP_NONE,
-	DUMP_ALL,
-	DUMP_ORIG,
-	DUMP_PARAM,
-};
-
-#ifdef CONFIG_TRACING
-void tracing_on(void);
-void tracing_off(void);
-int tracing_is_on(void);
-void tracing_snapshot(void);
-void tracing_snapshot_alloc(void);
-
-extern void tracing_start(void);
-extern void tracing_stop(void);
-
-static inline __printf(1, 2)
-void ____trace_printk_check_format(const char *fmt, ...)
-{
-}
-#define __trace_printk_check_format(fmt, args...)			\
-do {									\
-	if (0)								\
-		____trace_printk_check_format(fmt, ##args);		\
-} while (0)
-
-/**
- * trace_printk - printf formatting in the ftrace buffer
- * @fmt: the printf format for printing
- *
- * Note: __trace_printk is an internal function for trace_printk() and
- *       the @ip is passed in via the trace_printk() macro.
- *
- * This function allows a kernel developer to debug fast path sections
- * that printk is not appropriate for. By scattering in various
- * printk like tracing in the code, a developer can quickly see
- * where problems are occurring.
- *
- * This is intended as a debugging tool for the developer only.
- * Please refrain from leaving trace_printks scattered around in
- * your code. (Extra memory is used for special buffers that are
- * allocated when trace_printk() is used.)
- *
- * A little optimization trick is done here. If there's only one
- * argument, there's no need to scan the string for printf formats.
- * The trace_puts() will suffice. But how can we take advantage of
- * using trace_puts() when trace_printk() has only one argument?
- * By stringifying the args and checking the size we can tell
- * whether or not there are args. __stringify((__VA_ARGS__)) will
- * turn into "()\0" with a size of 3 when there are no args, anything
- * else will be bigger. All we need to do is define a string to this,
- * and then take its size and compare to 3. If it's bigger, use
- * do_trace_printk() otherwise, optimize it to trace_puts(). Then just
- * let gcc optimize the rest.
- */
-
-#define trace_printk(fmt, ...)				\
-do {							\
-	char _______STR[] = __stringify((__VA_ARGS__));	\
-	if (sizeof(_______STR) > 3)			\
-		do_trace_printk(fmt, ##__VA_ARGS__);	\
-	else						\
-		trace_puts(fmt);			\
-} while (0)
-
-#define do_trace_printk(fmt, args...)					\
-do {									\
-	static const char *trace_printk_fmt __used			\
-		__section("__trace_printk_fmt") =			\
-		__builtin_constant_p(fmt) ? fmt : NULL;			\
-									\
-	__trace_printk_check_format(fmt, ##args);			\
-									\
-	if (__builtin_constant_p(fmt))					\
-		__trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);	\
-	else								\
-		__trace_printk(_THIS_IP_, fmt, ##args);			\
-} while (0)
-
-extern __printf(2, 3)
-int __trace_bprintk(unsigned long ip, const char *fmt, ...);
-
-extern __printf(2, 3)
-int __trace_printk(unsigned long ip, const char *fmt, ...);
-
-/**
- * trace_puts - write a string into the ftrace buffer
- * @str: the string to record
- *
- * Note: __trace_bputs is an internal function for trace_puts and
- *       the @ip is passed in via the trace_puts macro.
- *
- * This is similar to trace_printk() but is made for those really fast
- * paths that a developer wants the least amount of "Heisenbug" effects,
- * where the processing of the print format is still too much.
- *
- * This function allows a kernel developer to debug fast path sections
- * that printk is not appropriate for. By scattering in various
- * printk like tracing in the code, a developer can quickly see
- * where problems are occurring.
- *
- * This is intended as a debugging tool for the developer only.
- * Please refrain from leaving trace_puts scattered around in
- * your code. (Extra memory is used for special buffers that are
- * allocated when trace_puts() is used.)
- *
- * Returns: 0 if nothing was written, positive # if string was.
- *  (1 when __trace_bputs is used, strlen(str) when __trace_puts is used)
- */
-
-#define trace_puts(str) ({						\
-	static const char *trace_printk_fmt __used			\
-		__section("__trace_printk_fmt") =			\
-		__builtin_constant_p(str) ? str : NULL;			\
-									\
-	if (__builtin_constant_p(str))					\
-		__trace_bputs(_THIS_IP_, trace_printk_fmt);		\
-	else								\
-		__trace_puts(_THIS_IP_, str, strlen(str));		\
-})
-extern int __trace_bputs(unsigned long ip, const char *str);
-extern int __trace_puts(unsigned long ip, const char *str, int size);
-
-extern void trace_dump_stack(int skip);
-
-/*
- * The double __builtin_constant_p is because gcc will give us an error
- * if we try to allocate the static variable to fmt if it is not a
- * constant. Even with the outer if statement.
- */
-#define ftrace_vprintk(fmt, vargs)					\
-do {									\
-	if (__builtin_constant_p(fmt)) {				\
-		static const char *trace_printk_fmt __used		\
-		  __section("__trace_printk_fmt") =			\
-			__builtin_constant_p(fmt) ? fmt : NULL;		\
-									\
-		__ftrace_vbprintk(_THIS_IP_, trace_printk_fmt, vargs);	\
-	} else								\
-		__ftrace_vprintk(_THIS_IP_, fmt, vargs);		\
-} while (0)
-
-extern __printf(2, 0) int
-__ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap);
-
-extern __printf(2, 0) int
-__ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);
-
-extern void ftrace_dump(enum ftrace_dump_mode oops_dump_mode);
-#else
-static inline void tracing_start(void) { }
-static inline void tracing_stop(void) { }
-static inline void trace_dump_stack(int skip) { }
-
-static inline void tracing_on(void) { }
-static inline void tracing_off(void) { }
-static inline int tracing_is_on(void) { return 0; }
-static inline void tracing_snapshot(void) { }
-static inline void tracing_snapshot_alloc(void) { }
-
-static inline __printf(1, 2)
-int trace_printk(const char *fmt, ...)
-{
-	return 0;
-}
-static __printf(1, 0) inline int
-ftrace_vprintk(const char *fmt, va_list ap)
-{
-	return 0;
-}
-static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
-#endif /* CONFIG_TRACING */
-
 /* Rebuild everything on CONFIG_DYNAMIC_FTRACE */
 #ifdef CONFIG_DYNAMIC_FTRACE
 # define REBUILD_DUE_TO_DYNAMIC_FTRACE
diff --git a/include/linux/trace_printk.h b/include/linux/trace_printk.h
new file mode 100644
index 000000000000..5c9785c49c8e
--- /dev/null
+++ b/include/linux/trace_printk.h
@@ -0,0 +1,205 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_TRACE_PRINTK_H
+#define _LINUX_TRACE_PRINTK_H
+
+#include <linux/compiler_attributes.h>
+#include <linux/instruction_pointer.h>
+#include <linux/stddef.h>
+#include <linux/stringify.h>
+#include <linux/string.h>
+
+/*
+ * General tracing related utility functions - trace_printk(),
+ * tracing_on/tracing_off and tracing_start()/tracing_stop
+ *
+ * Use tracing_on/tracing_off when you want to quickly turn on or off
+ * tracing. It simply enables or disables the recording of the trace events.
+ * This also corresponds to the user space /sys/kernel/tracing/tracing_on
+ * file, which gives a means for the kernel and userspace to interact.
+ * Place a tracing_off() in the kernel where you want tracing to end.
+ * From user space, examine the trace, and then echo 1 > tracing_on
+ * to continue tracing.
+ *
+ * tracing_stop/tracing_start has slightly more overhead. It is used
+ * by things like suspend to ram where disabling the recording of the
+ * trace is not enough, but tracing must actually stop because things
+ * like calling smp_processor_id() may crash the system.
+ *
+ * Most likely, you want to use tracing_on/tracing_off.
+ */
+
+enum ftrace_dump_mode {
+	DUMP_NONE,
+	DUMP_ALL,
+	DUMP_ORIG,
+	DUMP_PARAM,
+};
+
+#ifdef CONFIG_TRACING
+void tracing_on(void);
+void tracing_off(void);
+int tracing_is_on(void);
+void tracing_snapshot(void);
+void tracing_snapshot_alloc(void);
+
+void tracing_start(void);
+void tracing_stop(void);
+
+static inline __printf(1, 2)
+void ____trace_printk_check_format(const char *fmt, ...)
+{
+}
+#define __trace_printk_check_format(fmt, args...)			\
+do {									\
+	if (0)								\
+		____trace_printk_check_format(fmt, ##args);		\
+} while (0)
+
+/**
+ * trace_printk - printf formatting in the ftrace buffer
+ * @fmt: the printf format for printing
+ *
+ * Note: __trace_printk is an internal function for trace_printk() and
+ *       the @ip is passed in via the trace_printk() macro.
+ *
+ * This function allows a kernel developer to debug fast path sections
+ * that printk is not appropriate for. By scattering in various
+ * printk like tracing in the code, a developer can quickly see
+ * where problems are occurring.
+ *
+ * This is intended as a debugging tool for the developer only.
+ * Please refrain from leaving trace_printks scattered around in
+ * your code. (Extra memory is used for special buffers that are
+ * allocated when trace_printk() is used.)
+ *
+ * A little optimization trick is done here. If there's only one
+ * argument, there's no need to scan the string for printf formats.
+ * The trace_puts() will suffice. But how can we take advantage of
+ * using trace_puts() when trace_printk() has only one argument?
+ * By stringifying the args and checking the size we can tell
+ * whether or not there are args. __stringify((__VA_ARGS__)) will
+ * turn into "()\0" with a size of 3 when there are no args, anything
+ * else will be bigger. All we need to do is define a string to this,
+ * and then take its size and compare to 3. If it's bigger, use
+ * do_trace_printk() otherwise, optimize it to trace_puts(). Then just
+ * let gcc optimize the rest.
+ */
+
+#define trace_printk(fmt, ...)				\
+do {							\
+	char _______STR[] = __stringify((__VA_ARGS__));	\
+	if (sizeof(_______STR) > 3)			\
+		do_trace_printk(fmt, ##__VA_ARGS__);	\
+	else						\
+		trace_puts(fmt);			\
+} while (0)
+
+#define do_trace_printk(fmt, args...)					\
+do {									\
+	static const char *trace_printk_fmt __used			\
+		__section("__trace_printk_fmt") =			\
+		__builtin_constant_p(fmt) ? fmt : NULL;			\
+									\
+	__trace_printk_check_format(fmt, ##args);			\
+									\
+	if (__builtin_constant_p(fmt))					\
+		__trace_bprintk(_THIS_IP_, trace_printk_fmt, ##args);	\
+	else								\
+		__trace_printk(_THIS_IP_, fmt, ##args);			\
+} while (0)
+
+__printf(2, 3)
+int __trace_bprintk(unsigned long ip, const char *fmt, ...);
+
+__printf(2, 3)
+int __trace_printk(unsigned long ip, const char *fmt, ...);
+
+/**
+ * trace_puts - write a string into the ftrace buffer
+ * @str: the string to record
+ *
+ * Note: __trace_bputs is an internal function for trace_puts and
+ *       the @ip is passed in via the trace_puts macro.
+ *
+ * This is similar to trace_printk() but is made for those really fast
+ * paths that a developer wants the least amount of "Heisenbug" effects,
+ * where the processing of the print format is still too much.
+ *
+ * This function allows a kernel developer to debug fast path sections
+ * that printk is not appropriate for. By scattering in various
+ * printk like tracing in the code, a developer can quickly see
+ * where problems are occurring.
+ *
+ * This is intended as a debugging tool for the developer only.
+ * Please refrain from leaving trace_puts scattered around in
+ * your code. (Extra memory is used for special buffers that are
+ * allocated when trace_puts() is used.)
+ *
+ * Returns: 0 if nothing was written, positive # if string was.
+ *  (1 when __trace_bputs is used, strlen(str) when __trace_puts is used)
+ */
+
+#define trace_puts(str) ({						\
+	static const char *trace_printk_fmt __used			\
+		__section("__trace_printk_fmt") =			\
+		__builtin_constant_p(str) ? str : NULL;			\
+									\
+	if (__builtin_constant_p(str))					\
+		__trace_bputs(_THIS_IP_, trace_printk_fmt);		\
+	else								\
+		__trace_puts(_THIS_IP_, str, strlen(str));		\
+})
+int __trace_bputs(unsigned long ip, const char *str);
+int __trace_puts(unsigned long ip, const char *str, int size);
+
+void trace_dump_stack(int skip);
+
+/*
+ * The double __builtin_constant_p is because gcc will give us an error
+ * if we try to allocate the static variable to fmt if it is not a
+ * constant. Even with the outer if statement.
+ */
+#define ftrace_vprintk(fmt, vargs)					\
+do {									\
+	if (__builtin_constant_p(fmt)) {				\
+		static const char *trace_printk_fmt __used		\
+		  __section("__trace_printk_fmt") =			\
+			__builtin_constant_p(fmt) ? fmt : NULL;		\
+									\
+		__ftrace_vbprintk(_THIS_IP_, trace_printk_fmt, vargs);	\
+	} else								\
+		__ftrace_vprintk(_THIS_IP_, fmt, vargs);		\
+} while (0)
+
+__printf(2, 0) int
+__ftrace_vbprintk(unsigned long ip, const char *fmt, va_list ap);
+
+__printf(2, 0) int
+__ftrace_vprintk(unsigned long ip, const char *fmt, va_list ap);
+
+void ftrace_dump(enum ftrace_dump_mode oops_dump_mode);
+#else
+static inline void tracing_start(void) { }
+static inline void tracing_stop(void) { }
+static inline void trace_dump_stack(int skip) { }
+
+static inline void tracing_on(void) { }
+static inline void tracing_off(void) { }
+static inline int tracing_is_on(void) { return 0; }
+static inline void tracing_snapshot(void) { }
+static inline void tracing_snapshot_alloc(void) { }
+
+static inline __printf(1, 2)
+int trace_printk(const char *fmt, ...)
+{
+	return 0;
+}
+static __printf(1, 0) inline int
+ftrace_vprintk(const char *fmt, va_list ap)
+{
+	return 0;
+}
+static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
+#endif /* CONFIG_TRACING */
+
+#endif
-- 
2.43.0

Re: [PATCH v3 4/4] tracing: move tracing declarations from kernel.h to a dedicated header

[Andy Shevchenko]

On Fri, Dec 05, 2025 at 12:52:35PM -0500, Yury Norov (NVIDIA) wrote:
> Tracing is a half of the kernel.h in terms of LOCs, although it's
> a self-consistent part. It is intended for quick debugging purposes
> and isn't used by the normal tracing utilities.
> 
> Move it to a separate header. If someone needs to just throw a
> trace_printk() in their driver, they will not have to pull all
> the heavy tracing machinery.
> 
> This is a pure move, except for removing a few 'extern's.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko