netdev - Re: [PATCH v2] Implement IP_UNICAST

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Date:	Thu, 2 Feb 2012 18:38:40 -0700
From:	"Erich E. Hoover" <ehoover@...es.edu>
To:	Xiaochun Lu <xiaoclu@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Netdev <netdev@...r.kernel.org>,
	"shawn.lu" <shawn.lu@...cssion.com>
Subject: Re: [PATCH v2] Implement IP_UNICAST_IF socket option.

On Thu, Feb 2, 2012 at 6:19 PM, Xiaochun Lu <xiaoclu@...il.com> wrote:
> Hi, Erich E. Hoover:
>
> Can you give more detail on why we need invent another binding to
> device option in your patch log?  Why SO_BINDTODEVICE or IP_PKTINFO
> can't server your need?

Sure, how about adding something like the following?:
---
The IP_UNICAST_IF feature is needed by the Wine project.  This patch
implements the feature by setting the outgoing interface in a similar
fashion to that of IP_PKTINFO.  A separate option is needed to handle
this feature since the existing options do not provide all of the
characteristics required by IP_UNICAST_IF, a summary is provided
below.

SO_BINDTODEVICE:
* SO_BINDTODEVICE requires administrative privileges, IP_UNICAST_IF
does not.  From reading some old mailing list articles my
understanding is that SO_BINDTODEVICE requires administrative
privileges because it can override the administrator's routing
settings.
* The SO_BINDTODEVICE option restricts both outbound and inbound
traffic, IP_UNICAST_IF only impacts outbound traffic.

IP_PKTINFO:
* Since IP_PKTINFO and IP_UNICAST_IF are independent options,
implementing IP_UNICAST_IF with IP_PKTINFO will likely break some
applications.
* Implementing IP_UNICAST_IF on top of IP_PKTINFO significantly
complicates the Wine codebase and reduces the socket performance
(doing this requires a lot of extra communication between the "server"
and "user" layers).

bind():
* bind() does not work on broadcast packets, IP_UNICAST_IF is
specifically intended to work with broadcast packets.
---

Erich Hoover
ehoover@...es.edu
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