netdev - Re: [PATCH] Implement IP_UNICAST

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Date:	Fri, 27 Jan 2012 08:30:30 -0700
From:	"Erich E. Hoover" <ehoover@...es.edu>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	Linux Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] Implement IP_UNICAST_IF socket option.

On Fri, Jan 27, 2012 at 2:01 AM, Hagen Paul Pfeifer <hagen@...u.net> wrote:
> On Thu, 26 Jan 2012 16:57:48 -0700, "Erich E. Hoover" wrote:
>> The IP_UNICAST_IF feature is needed by the Wine project.  This patch
>> implements the feature by setting the outgoing interface in the same
>> fashion as that of IP_PKTINFO.
>
> Why duplicate functionality - rewrite your application and use IP_PKTINFO
> or bind() your socket. This patch duplicate already existing functionality
> (and bloat inet_sock unnecessarily).

The IP_UNICAST_IF feature works on broadcast packets, so bind() won't
do the trick.  Also, native Windows applications have the ability to
use both IP_PKTINFO and IP_UNICAST_IF on the same socket, so using
IP_PKTINFO to implement IP_UNICAST_IF might break some applications.
Even so, I did attempt to do this and Alexandre was unsatisfied with
the approach since it required a significant amount of extra code and
the extra communication between the "server" and "user" components of
Wine significantly slowed down socket performance.  Alexendre
indicated that I need to get this functionality added to the kernel to
implement the feature properly, so here I am.

I'm hoping that I can also use this feature, combined with Linux
Socket Filtering, to allow Windows applications to use bind() and have
the socket still work with broadcast packets.  IP_UNICAST_IF is a
relatively new feature, older Windows applications used bind() instead
(Windows bind() still captures broadcast packets).  I've been working
on different ways to get Wine to handle this capability for a long
time and I'd really like to be able to finally check this bug off of
my list.

Anyway, thank you for taking the time to look at my patch.  I really
appreciate and I hope that I've satisfactorily answered your question.

Erich Hoover
ehoover@...es.edu
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