Wildcard-socket simplification hits a wall

Kurt Roeckx kurt at roeckx.be
Sat Apr 1 09:33:04 UTC 2017

On Fri, Mar 31, 2017 at 07:30:05PM -0400, Eric S. Raymond wrote:
> Kurt Roeckx <kurt at roeckx.be>:
> > > One might expect this to be available via a CMSG lookup into recmvsg's
> > > per-package auxiliary headers, analogously to the way we now get the
> > > packet-arrival timestamp (see ntpd/ntp_packetstamp.c).  It's the only
> > > place for the information to be that has the right locality.
> > 
> > Have you look to things like IP_PKTINFO?
> Nope.  Thanks to the @!%^#~! crappy documentation, I didn't know that was an
> identifier of interest until you pointed it out. Neither the CMSG(3) or ip(7)
> manual pages hint that it exists.  Because heaven forfend that they should
> either list CMSG capabilities or point unambiguously at someplace that
> does, that would be too fscking much like being *helpful*.
> *grumble*
> Now that I've looked at it, it halfway solves the problem in a rather
> frustrating way...maybe.  Or maybe not at all.  Yeah, it means you can
> back out an "interface index" which designates a physical interface, or its
> local address. But then you have the problem of intepreting that index or
> address.

I was under the impression that you can also use that index when
sending something.


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