rebased target userback repo available

Hi all,

In case anyone is interested in playing with it, I've rebased Shaohua's userspace backend patches to nab's latest for-next repo.

There's growing interest in this capability, so Shaohua I hope you don't mind me taking the initiative to move towards seeing your work merged :)

git repo at https://github.com/agrover/linux.git target_userback

Regards -- Andy