ovl: index all non-dir on copy up for NFS export

With the NFS export feature enabled, all non-dir are indexed on copy up.
The copy up origin inode of an indexed non-dir can be used as a unique
identifier of the overlay object.

The full index is also used for consistency verfication, like detecting
multiple non-hardlink uppers with the same 'origin' on lookup.

Directory index on copy up will be implemented by following patch.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/util.c

@@ -473,6 +473,10 @@ bool ovl_need_index(struct dentry *dentry)
 	if (!lower || !ovl_indexdir(dentry->d_sb))
 		return false;
 
+	/* Index all files for NFS export and consistency verification */
+	if (!d_is_dir(lower) && ovl_index_all(dentry->d_sb))
+		return true;
+
 	/* Index only lower hardlinks on copy up */
 	if (!d_is_dir(lower) && d_inode(lower)->i_nlink > 1)
 		return true;