backing_file_user_path(): constify struct path *

Callers never use the resulting pointer to modify the struct path it
points to (nor should they).

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/file_table.c

@@ -54,7 +54,7 @@ struct backing_file {
 
 #define backing_file(f) container_of(f, struct backing_file, file)
 
-struct path *backing_file_user_path(const struct file *f)
+const struct path *backing_file_user_path(const struct file *f)
 {
 	return &backing_file(f)->user_path;
 }

include/linux/fs.h

@@ -2879,7 +2879,7 @@ struct file *dentry_open_nonotify(const struct path *path, int flags,
 				  const struct cred *cred);
 struct file *dentry_create(const struct path *path, int flags, umode_t mode,
 			   const struct cred *cred);
-struct path *backing_file_user_path(const struct file *f);
+const struct path *backing_file_user_path(const struct file *f);
 
 /*
  * When mmapping a file on a stackable filesystem (e.g., overlayfs), the file