debugfs: improve DEFINE_DEBUGFS_ATTRIBUTE for !CONFIG_DEBUG_FS

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>

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 4d3f0d1aec73b856552f5d5e30b706ef5d2e04ec..1b413a9aab81c6b1d8070aa734af967952050fb6 100644 (file)
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -62,6 +62,21 @@ static inline const struct file_operations *debugfs_real_fops(struct file *filp)
        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 *file, char __user *buf,
 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_finish(int srcu_idx)
        __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)