netgraph and kqueue together - socket problems

[Jonas Bulow]

Hi,

I'm trying to use netgraph and kqueue together and ran into some 
problems. I hope someone can enligthen me what I'm missing.

I register EVFILT_READ and EVFILT_WRITE on a netgraph-socket connected 
to a netgraph echo-node. The EVFILT_WRITE-filter returns immediately 
from the kevent call saying there is 20480 bytes remaining in the write 
buffer (in the event data field). Then I write 20480 using NgSendData. 
NgSendData encounters an error: "No buffer space available".

When I write fewer but smaller chunks of data, say ~3000 bytes, the next 
call to kevent returns the same amount of remaining space in the write 
buffer. The kqueue event data field never change from 20480 for the 
EVFILT_WRITE-filter.

Now I understand that there are some overhead in the NgSendData. It's 
not just my data that are written through the socket. The addressing 
data adds some data when NgSendData calls sendto. Right?

But, how do I calculate the true amount of remaining buffer space 
available for me when I call NgSendData?

And, why does kevent EVFILT_WRITE always say 20480 on repeated calls to 
kevent on a netgraph-socket, even if I have successfully written some 
data between the calls to kevent?

The netgraph-node the programming is talking to is a echo-node set up with:

#ngctl mkpeer echo dummy foo

Regards,
	Jonas