debugfs: introduce a public file_operations accessor

This patch introduces an accessor which can be used
by the users of debugfs (drivers, fs, ...) to get the
original file_operations struct. It also removes the
REAL_FOPS_DEREF macro in file.c and converts the code
to use the public version.

Previously, REAL_FOPS_DEREF was only available within
the file.c of debugfs. But having a public getter
available for debugfs users is important as some
drivers (carl9170 and b43) use the pointer of the
original file_operations in conjunction with container_of()
within their debugfs implementations.

Reviewed-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Cc: stable <stable@vger.kernel.org> # 4.7+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 592059f..309f4e9 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -97,9 +97,6 @@
 
 #define F_DENTRY(filp) ((filp)->f_path.dentry)
 
-#define REAL_FOPS_DEREF(dentry)					\
-	((const struct file_operations *)(dentry)->d_fsdata)
-
 static int open_proxy_open(struct inode *inode, struct file *filp)
 {
 	const struct dentry *dentry = F_DENTRY(filp);
@@ -112,7 +109,7 @@
 		goto out;
 	}
 
-	real_fops = REAL_FOPS_DEREF(dentry);
+	real_fops = debugfs_real_fops(filp);
 	real_fops = fops_get(real_fops);
 	if (!real_fops) {
 		/* Huh? Module did not clean up after itself at exit? */
@@ -143,7 +140,7 @@
 {									\
 	const struct dentry *dentry = F_DENTRY(filp);			\
 	const struct file_operations *real_fops =			\
-		REAL_FOPS_DEREF(dentry);				\
+		debugfs_real_fops(filp);				\
 	int srcu_idx;							\
 	ret_type r;							\
 									\
@@ -176,7 +173,7 @@
 				struct poll_table_struct *wait)
 {
 	const struct dentry *dentry = F_DENTRY(filp);
-	const struct file_operations *real_fops = REAL_FOPS_DEREF(dentry);
+	const struct file_operations *real_fops = debugfs_real_fops(filp);
 	int srcu_idx;
 	unsigned int r = 0;
 
@@ -193,7 +190,7 @@
 static int full_proxy_release(struct inode *inode, struct file *filp)
 {
 	const struct dentry *dentry = F_DENTRY(filp);
-	const struct file_operations *real_fops = REAL_FOPS_DEREF(dentry);
+	const struct file_operations *real_fops = debugfs_real_fops(filp);
 	const struct file_operations *proxy_fops = filp->f_op;
 	int r = 0;
 
@@ -241,7 +238,7 @@
 		goto out;
 	}
 
-	real_fops = REAL_FOPS_DEREF(dentry);
+	real_fops = debugfs_real_fops(filp);
 	real_fops = fops_get(real_fops);
 	if (!real_fops) {
 		/* Huh? Module did not cleanup after itself at exit? */