When tunneling IP traffic with GRE this patch makes it possible to 
export the ToS/DiffServ information to the outer IP header.
This is particularly useful in a scenario with ESP/AH where the inner IP 
header is encrypted but the packet priority/DiffServ information
should still be respected by the transporting routers (for example in an 
MPLS backbone network).

The feature is disabled by default and can be enabled on a per-interface 
basis (/proc/sys/net/ipv4/conf/ethX/gre_copy_tos).

Also does this bring Linux back in the game, as JunOS/IOS provide this 
for quite some time:
http://www.cisco.com/en/US/docs/ios/11_3/feature/guide/greqos.html
http://www.juniper.net/techpubs/software/junos/junos94/swconfig-services/configuring-a-gre-tunnel-to-copy-tos-bits-to-the-outer-ip-header.html 


Signed-off-by: Andreas Jaggi <redacted>

diff -urN vanilla-linux-2.6.29.4/include/linux/sysctl.h 
gre-copy-tos/include/linux/sysctl.h

--- vanilla-linux-2.6.29.4/include/linux/sysctl.h    2009-05-19 

01:52:34.000000000 +0200

+++ gre-copy-tos/include/linux/sysctl.h    2009-06-29 14:23:07.000000000 
+0200

@@ -490,6 +490,7 @@
    NET_IPV4_CONF_ARP_IGNORE=19,
    NET_IPV4_CONF_PROMOTE_SECONDARIES=20,
    NET_IPV4_CONF_ARP_ACCEPT=21,
+    NET_IPV4_CONF_GRE_COPY_TOS=22,