Update knl code to linux-3.12

I've read your article at http://monoist.atmarkit.co.jp/mn/kw/file_sys.html.
I tried to build your tarfs on Ubuntu 12.04 but build was failed with kernel changes.

So I tried to upgrade your tarfs and then I can read files in tarfs on Ubuntu and linux-3.12 kernel.
Please check this patches.