[PATCH] enable ethtool for xen loopback interface (network in dom0)

[PATCH] enable ethtool for xen loopback interface (network in dom0)

[Jan Niehusmann]

Hi,

this patch allows disabling the tx checksums on the xen loopback
interface, which is used for the virtual interfaces of dom0 instead 
of netfront/netback.

I need to issue ethtool -K eth0 tx off to work around a bad checksum
problem, which has been reported for domUs a few months ago. I'm
bridging dom0's eth0 to a domU where I do NAT to a different virtual
interface. Without this change, I get lots of packets with bad
checksums.

Jan

Signed-off-by: Jan Niehusmann <jan@gondor.com>

--- linux-2.6.12/drivers/xen/netback/loopback.c.orig	2006-01-14 12:46:42.000000000 +0100
+++ linux-2.6.12/drivers/xen/netback/loopback.c	2006-01-14 11:59:49.000000000 +0100
@@ -27,6 +27,7 @@
 #include <linux/inetdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/skbuff.h>
+#include <linux/ethtool.h>
 #include <net/dst.h>
 
 static int nloopbacks = 8;
@@ -122,6 +123,12 @@
 	/*dev->mtu             = 16*1024;*/
 }
 
+static struct ethtool_ops network_ethtool_ops =
+{
+	.get_tx_csum = ethtool_op_get_tx_csum,
+	.set_tx_csum = ethtool_op_set_tx_csum,
+};
+
 static int __init make_loopback(int i)
 {
 	struct net_device *dev1, *dev2;
@@ -141,6 +148,8 @@
 	dev1->features |= NETIF_F_NO_CSUM;
 	dev2->features |= NETIF_F_IP_CSUM;
 
+	SET_ETHTOOL_OPS(dev2, &network_ethtool_ops);
+
 	/*
 	 * Initialise a dummy MAC address for the 'dummy backend' interface. We
 	 * choose the numerically largest non-broadcast address to prevent the

Re: [PATCH] enable ethtool for xen loopback interface(network in dom0)

[Greg Brackley]

----- Original Message ----- 
From: "Jan Niehusmann" <jan@gondor.com>
> this patch allows disabling the tx checksums on the xen loopback
> interface, which is used for the virtual interfaces of dom0 instead
> of netfront/netback.

Great patch thanks. I finally got around to upgrading a box to Xen 3.0 
testing (changeset 8269:a91e4dcf629d), applied the patch and it works a 
dream.  I can now bridge the xen0 domain onto a VLAN interface with a 
pro/1000 MT server NIC (82546EB).

I am using Fedora Core 4 (which doesn't appear to support -K ethtool options 
in the initscripts), and have added a /sbin/ifup-local script [1] to the 
system. This in conjunction with adding 'ETHTOOL_KOPTS="tx off"' [2] to my 
interface configuration works well (Note: I use the standard initscripts to 
bring up the networking, and not 'network-bridge').

I'm concerned that there may be some performance hit with software 
checksumming, but I'm happy with working rather than faster. Getting jumbo 
frame support in the domU's would be probably be a better performance boost.

Greg :-)

--
[1] /sbin/ifup-local
#!/bin/sh

cd /etc/sysconfig/network-scripts
. network-functions

[ -f ../network ] && . ../network

CONFIG="ifcfg-${1}"
source_config

if [ -n "$ETHTOOL_KOPTS" ] ; then
        REALDEVICE=${DEVICE%%:*}
        /sbin/ethtool -K ${REALDEVICE} $ETHTOOL_KOPTS
fi


[2]  /etc/sysconfig/network-scripts/ifcfg-veth0
DEVICE=veth0
TYPE=Ethernet
ONBOOT=yes
IPADDR=192.168.133.1
NETMASK=255.255.255.0
MACADDR=00:aa:00:00:85:01
NOZEROCONF=yes
GATEWAY=192.168.133.254
ARP=yes
ETHTOOL_KOPTS="tx off"