libfs: add simple_open()

debugfs and a few other drivers use an open-coded version of
simple_open() to pass a pointer from the file to the read/write file
ops.  Add support for this simple case to libfs so that we can remove
the many duplicate copies of this simple function.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/libfs.c

diff --git a/fs/libfs.c b/fs/libfs.c
index 4a0d1f0..358094f 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -264,6 +264,13 @@
 	return ERR_PTR(-ENOMEM);
 }
 
+int simple_open(struct inode *inode, struct file *file)
+{
+	if (inode->i_private)
+		file->private_data = inode->i_private;
+	return 0;
+}
+
 int simple_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
 {
 	struct inode *inode = old_dentry->d_inode;
@@ -984,6 +991,7 @@
 EXPORT_SYMBOL(simple_empty);
 EXPORT_SYMBOL(simple_fill_super);
 EXPORT_SYMBOL(simple_getattr);
+EXPORT_SYMBOL(simple_open);
 EXPORT_SYMBOL(simple_link);
 EXPORT_SYMBOL(simple_lookup);
 EXPORT_SYMBOL(simple_pin_fs);