bpf writes on tun device

[Bruce M Simpson]

On Tue, Jun 07, 2005 at 10:19:29PM +1200, Matthew Luckie wrote:
> Please review.

This is good and useful work. It looks like something which has been in
need of cleanup for a while.

Unfortunately my current situation re resources (time and infrastructure)
means that whilst I can review and commit code it's difficult for me to test
it (unless it's userland) hopefully this will improve in the next week or two.

I'd be wary of changing the definition of DLT_NULL however -- it literally
means 'there's nothing here apart from raw data', and changing this notion
would mean that we have to change it everywhere, including bpf clients,
because the change being proposed would make DLT_NULL mean 'there's a 32-bit
integer in front of everything else which is raw data', which is something
else.

I'd suggest a name like DLT_PSEUDO might be better -- it may be helpful to
get review for the change from the NetBSD and OpenBSD guys too, as well as
the tcpdump.org guys.

Looking at style, it might be better if the driver(s) were changed to
explicitly use a 32-bit wide int type such as u_int32_t for the address
family header field in their bpfattach() calls. ICHDRLEN is odd man out,
but it is #define'd to be the same thing; I would update it there also.

A white space pass should probably also be done last thing to be sure.
I have no idea about ng_sppp.c I'm afraid.

It helps my dayjob because we're currently looking at what it would take to
integrate a code drop of the IS-IS routing protocol by one of our students --
unfortunately to remain backwards compatible with existing IS-IS deployments
out there, we need to be able to speak link layer IS-IS as well as IPv4
encapsulated IS-IS.

Of course to do this, we need bpf write support for the appropriate link
layers. The more link layers we have support for bpf writes, particularly
across the software loopback and tunnel type links, the better it is for
testing and integration, as well as running IS-IS directly over a VPN
on FreeBSD.

Thanks,
BMS