Good kernel developers book/manual available?

[Garrett Cooper]

Hello,
    I was wondering if there was any particular technical book or manual 
available that anyone would suggest for describing the FreeBSD kernel, 
as I have recently picked up a Linux 2.6 kernel book and I want to 
obtain a more holistic scope of the proper way to code an operating 
system kernel as well as code for a system kernel, as opposed to just 
one set of dogmatic approaches for doing it from Linus/the authors.
    I prefer printed media compared to online media, but either-or would 
be extremely helpful.
    Thank you for your help,
-Garrett