For my day job, I recently added a feature to our NetBSD-based IP stack
which might be of interest to others.  It allows unconnected datagram
sockets (currently implemented only for UDP but there's no reason why it
couldn't be extended for raw IP sockets as well) to receive the ICMP error
notifications via OOB data.

After being enabled via a IP_ERROOB setsockopt, when a ICMP error is
received and communicated to UDP via its pr_ctlinput entry point the
original destination address is extracted and a OOB (MT_OOBDATA) message is
added to the receive socket buffer with the address being the extracted
destination and the data being an integer containing the error (which would
normally be placed in so_error of the socket structure).

This requires you to use recvmsg(2) and check the msg_flags on each packet
to see if you received as an error notification as OOB data, but is fairly
painless and useful.  It also means that traceroute could be done completely
without any needs for privileges.

Is there any interest in me getting this feature contributed back to NetBSD?
-- 
Matt Thomas                     email: matt@3am-software.com
3am Software Foundry              www: http://3am-software.com/bio/matt/
Cupertino, CA              disclaimer: I avow all knowledge of this message.