Design
From NFSv4
We don't have much by way of design documentation yet--at this point, if you really need to understand how something works, you'll need to read the code.
The relevant bits of kernel code are mostly in:
There are some rough notes which aren't about NFSv4 specifically, but may help in understanding some of the relevant kernel code.
There are pages about ACLs and about server IPv6 support.
Also, we have a rough overview of the features currently supported by mainline kernels:
Some notes on server exports.
