bpf and BIOCSFEEDBACK

[Mark Davies <mark%ecs.vuw.ac.nz@localhost>]

I'm trying to get the dynamips emulator working - specifically the pcap 
based nio_gen_eth that allows the emulated network to interact with real 
networks -- does this by using pcap to inject and read packets from the 
host machine's ethernet interface.  This works fine when talking to other 
machines on the physical network but fails to communicate with the host 
machine itself.

FreeBSD fixed this problem (in patches in the dynamips port) by setting 
BIOCSFEEDBACK on the bpf device but if I try that on NetBSD it doesn't seem 
to make a difference.  From sprinkling a few printf's in bpf.c I can see 
that if_input is being called but I can't tell what happens after that.

Suggestions on why this isn't working or how to track it down much 
appreciated.

[I've mostly been testing this on a 5.1_RC1 system - having backported the 
feedback support from current to it,
http://mail-index.netbsd.org/source-changes/2010/03/13/msg007757.html, but 
i did try a current monolithic kernel at one point to confirm that it 
wasn't an issue with the backport and had the same behaviour]

cheers
mark