Examples of kfilter_register(9)?

[Marc Tooley <netbsdMLpostNO%spam.quake.ca@localhost>]

I realise the best documentation of a function is the source of the 
function itself, but there's scant even of that inside 
sys/kern/kern_event.c for me to pore over.

I am interested in learning more of this: is there an example somewhere 
of its use? A straight grep and a google search for this function turns 
up literally nothing.. anywhere, even in -current src.

I realise also that this function is designed for kernel modules, kernel 
sub-systems, and drivers, so I know I'm not going to be able to just 
monkey around with it in userspace, but I'm still interested in seeing 
an example, or hearing a description of what it was designed to do and 
what purpose it was designed to serve.

Thanks in advance!

-Marc Tooley