I've been mulling over the previous advice I got and reading over the
networking code, and I hope I have some more intelligent questions
now. It seems I really have two somewhat independent issues to
resolve with respect to IP-over-IB address resolution:
- IPoIB adds a second InfiniBand-specific path record lookup after
the normal ARP/ND lookup. I think I have a handle on how this can
be added to net/ipv4/arp.c.
- For InfiniBand, the layer 2 header is built and parsed by the
hardware without a chance for software to see it. In fact, once we
have completed the 2 stage resolution as described above, the
network driver has to pass this path information to the IB hardware
and get an "address handle" back, which it uses to actually send
packets. It seems the existing hard_header, hard_header_cache and
header_cache_update are not really applicable.
My ideal solution would be some way for the driver have the packets
passed to its hard_start_xmit method with the address handle in the
skb->cb field (or another field if it's acceptable/desirable to add
a field for this to struct sk_buff -- I notice a number of
#ifdef'ed fields in there already, but I'm not sure if that type of
thing is just old cruft or still OK).
Also it would be nice is that address handle could be taken
directly from the struct neighbor -- after all, we should be able
to get it without requiring the driver to do any lookup from HW
address to address handle.
Finally, address handles need to be freed eventually, and I
don't see a way for a driver to find out when an ARP entry is being
destroyed. Am I missing something, or is this something else I'll
need to add? What would be an acceptable way to add this to the
I'd really appreciate another dose of cluestick...