bibliography to understand dfly kernel better ?

Hi all,

I was pondering reading a book to understand DragonFlyBSD kernel better.
I know there is no such specialised item, but might "Design and 
implementation  of the BSD system" help ? And which one to pick up, 
between the 4.4 classical or the newer FreeBSD one ? (which covers 5.x, 
so I guess it's not too relevant, but since it is fresher, maybe...)

Anyway. I've studied the Tanenbaum already, and am trying to get a 
better focus.

Thanks for your suggestions,

gregg
++