ovl: copy up inode flags

On inode creation copy certain inode flags from the underlying real inode
to the overlay inode.

This is in preparation for moving overlay functionality out of the VFS.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/overlayfs.h

@@ -350,6 +350,13 @@ static inline void ovl_copyattr(struct inode *from, struct inode *to)
 	to->i_ctime = from->i_ctime;
 }
 
+static inline void ovl_copyflags(struct inode *from, struct inode *to)
+{
+	unsigned int mask = S_SYNC | S_IMMUTABLE | S_APPEND | S_NOATIME;
+
+	inode_set_flags(to, from->i_flags & mask, mask);
+}
+
 /* dir.c */
 extern const struct inode_operations ovl_dir_inode_operations;
 int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,

fs/overlayfs/util.c

@@ -310,6 +310,7 @@ void ovl_inode_init(struct inode *inode, struct dentry *upperdentry,
 		OVL_I(inode)->lower = igrab(d_inode(lowerdentry));
 
 	ovl_copyattr(realinode, inode);
+	ovl_copyflags(realinode, inode);
 	if (!inode->i_ino)
 		inode->i_ino = realinode->i_ino;
 }