unlocked_ioctl explanation

I am aware that ioctl has been superseeded by unlocked_ioctl. I've been looking through patches and this seems to be BKL related. Could someone explain further the differences and reasons for the new ioctl prototype and name? I guess 'unlocked' means BKL is no longer held inside ioctl, right? What precautions should we take when using unlocked_ioctl ? Greetings, Ezequiel.