Patch "debugfs: improve DEFINE_DEBUGFS_ATTRIBUTE for !CONFIG_DEBUG_FS" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    debugfs: improve DEFINE_DEBUGFS_ATTRIBUTE for !CONFIG_DEBUG_FS

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     debugfs-improve-define_debugfs_attribute-for-config_debug_fs.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 7f847dd31736f1284538e54f46cf10e63929eb7f Mon Sep 17 00:00:00 2001
From: Arnd Bergmann <arnd@arndb.de>
Date: Thu, 20 Oct 2016 22:07:53 +0200
Subject: debugfs: improve DEFINE_DEBUGFS_ATTRIBUTE for !CONFIG_DEBUG_FS
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Arnd Bergmann <arnd@arndb.de>

commit 7f847dd31736f1284538e54f46cf10e63929eb7f upstream.

The slp_s0_residency_usec debugfs file currently uses
DEFINE_DEBUGFS_ATTRIBUTE(), but that macro cannot really be used to
define files outside of the debugfs code, as it has no reference to
the get/set functions if CONFIG_DEBUG_FS is not defined:

drivers/platform/x86/intel_pmc_core.c:80:12: error: ‘pmc_core_dev_state_get’ defined but not used [-Werror=unused-function]

This fixes the macro to always contain the reference, and instead rely
on the stubbed-out debugfs_create_file to not actually refer to
its arguments so the compiler can still drop the reference.
This works because the attribute definition is always 'static',
and the dead-code removal silently drops all static symbols
that are not used.

Fixes: c64688081490 ("debugfs: add support for self-protecting attribute file fops")
Fixes: df2294fb6428 ("intel_pmc_core: Convert to DEFINE_DEBUGFS_ATTRIBUTE")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[nicstange@gmail.com: Add dummy implementations of debugfs_attr_read() and
  debugfs_attr_write() in order to protect against possibly broken dead
  code elimination and to improve readability.
  Correct CONFIG_DEBUGFS_FS -> CONFIG_DEBUG_FS typo in changelog.]
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/linux/debugfs.h |   44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -62,6 +62,21 @@ static inline const struct file_operatio
 	return filp->f_path.dentry->d_fsdata;
 }
 
+#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
+static int __fops ## _open(struct inode *inode, struct file *file)	\
+{									\
+	__simple_attr_check_format(__fmt, 0ull);			\
+	return simple_attr_open(inode, file, __get, __set, __fmt);	\
+}									\
+static const struct file_operations __fops = {				\
+	.owner	 = THIS_MODULE,						\
+	.open	 = __fops ## _open,					\
+	.release = simple_attr_release,					\
+	.read	 = debugfs_attr_read,					\
+	.write	 = debugfs_attr_write,					\
+	.llseek  = generic_file_llseek,					\
+}
+
 #if defined(CONFIG_DEBUG_FS)
 
 struct dentry *debugfs_create_file(const char *name, umode_t mode,
@@ -99,21 +114,6 @@ ssize_t debugfs_attr_read(struct file *f
 ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
 			size_t len, loff_t *ppos);
 
-#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
-static int __fops ## _open(struct inode *inode, struct file *file)	\
-{									\
-	__simple_attr_check_format(__fmt, 0ull);			\
-	return simple_attr_open(inode, file, __get, __set, __fmt);	\
-}									\
-static const struct file_operations __fops = {				\
-	.owner	 = THIS_MODULE,					\
-	.open	 = __fops ## _open,					\
-	.release = simple_attr_release,				\
-	.read	 = debugfs_attr_read,					\
-	.write	 = debugfs_attr_write,					\
-	.llseek  = generic_file_llseek,				\
-}
-
 struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
                 struct dentry *new_dir, const char *new_name);
 
@@ -233,8 +233,18 @@ static inline void debugfs_use_file_fini
 	__releases(&debugfs_srcu)
 { }
 
-#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)	\
-	static const struct file_operations __fops = { 0 }
+static inline ssize_t debugfs_attr_read(struct file *file, char __user *buf,
+					size_t len, loff_t *ppos)
+{
+	return -ENODEV;
+}
+
+static inline ssize_t debugfs_attr_write(struct file *file,
+					const char __user *buf,
+					size_t len, loff_t *ppos)
+{
+	return -ENODEV;
+}
 
 static inline struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
                 struct dentry *new_dir, char *new_name)


Patches currently in stable-queue which might be from arnd@arndb.de are

queue-4.9/debugfs-improve-define_debugfs_attribute-for-config_debug_fs.patch