Extending nftables user-space utility for custom filters

[Juergen Brendel <juergen@brendel.com>]

Hello!

I'm still very new to nftables, so hopefully my question isn't too
silly.

>From what I understand so far, one of the neat features of nftables is
that a small VM in the kernel interprets the byte code, which was sent
down to it by the nftables user-space utility.

So it seems to me that if I would like to add some fancy, specialized
type of packet filtering/processing then all I would have to do is to
extend the nftables user-space utility to create new byte code: No
updated kernel or kernel modules required.

Is my understanding correct? And if so, I have these questions:

     1. Have the features and capabilities of the in-kernel VM been
        documented somewhere? So that I know what is even possible for
        the kernel code?
     2. Is there any documentation (a howto or getting-started guide),
        which explains how to extend the user-space utility so that it
        understands new commands and can construct new byte code?

Thank you very much!

Juergen