Pretty sure that one's for userspace programming. In which case, I'd recommend The Linux Programming Interface instead, which is written by the same person who

Pretty sure that one's for userspace programming. In which case, I'd recommend The Linux Programming Interface instead, which is written by the same person who maintains the Linux man-pages. There isn't much of a central source on kernel hacking that isn't outdated by now, though some reasonably good books on device drivers are still out there and relevant. Beyond that, reading the kernel's Documentation directory, LWN articles and the recent "Linux Insides" series being posted here is your best bet, along with stalking the LKML, of course.