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>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index 1438e2322d5c..4d3f0d1aec73 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -45,6 +45,23 @@ extern struct dentry *arch_debugfs_dir;
 
 extern struct srcu_struct debugfs_srcu;
 
+/**
+ * debugfs_real_fops - getter for the real file operation
+ * @filp: a pointer to a struct file
+ *
+ * Must only be called under the protection established by
+ * debugfs_use_file_start().
+ */
+static inline const struct file_operations *debugfs_real_fops(struct file *filp)
+	__must_hold(&debugfs_srcu)
+{
+	/*
+	 * Neither the pointer to the struct file_operations, nor its
+	 * contents ever change -- srcu_dereference() is not needed here.
+	 */
+	return filp->f_path.dentry->d_fsdata;
+}
+
 #if defined(CONFIG_DEBUG_FS)
 
 struct dentry *debugfs_create_file(const char *name, umode_t mode,