ipv4: Implement IP_UNICAST_IF socket option.
authorErich E. Hoover <ehoover@mines.edu>
Wed, 8 Feb 2012 09:11:07 +0000 (09:11 +0000)
committerDavid S. Miller <davem@davemloft.net>
Wed, 8 Feb 2012 20:52:45 +0000 (15:52 -0500)
commit76e21053b5bf33a07c76f99d27a74238310e3c71
tree70ac2a67be8f19da96896950447567e156975149
parent43480aecb1f538d4f6dd8b2c5d2b71fb98659072
ipv4: Implement IP_UNICAST_IF socket option.

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_MULTICAST_IF.  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.
* Like SO_BINDTODEVICE, bind() restricts both outbound and inbound
traffic.

Signed-off-by: Erich E. Hoover <ehoover@mines.edu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/linux/in.h
include/net/inet_sock.h
net/ipv4/ip_sockglue.c
net/ipv4/ping.c
net/ipv4/raw.c
net/ipv4/udp.c