From: Mark McLoughlin <markmc@redhat.com>
Date: Wed, 26 Nov 2008 17:40:56 +0000
Subject: [net] virtio_net: jumbo frame support
Message-id: 1227721256.24571.3.camel@blaa
O-Subject: [RHEL5.3 PATCH] virtio_net: jumbo frame support
Bugzilla: 473114
RH-Acked-by: Chris Wright <chrisw@redhat.com>
RH-Acked-by: Neil Horman <nhorman@redhat.com>
RH-Acked-by: Don Dutile <ddutile@redhat.com>
RH-Acked-by: Herbert Xu <herbert.xu@redhat.com>
RH-Acked-by: David Miller <davem@redhat.com>

https://bugzilla.redhat.com/473114

This is a trivial patch to allow users to configure virtio_net with
an MTU larger than 1500 bytes.

We don't really have a max tx frame size limit, so there should be
nothing preventing us supporting larger frames.

Patch sent upstream here:

  http://kerneltrap.org/mailarchive/linux-netdev/2008/11/26/4239974

Tested locally with no obvious problems; the performance team has
tested this too and found that using jumbo frames (9000 byte MTU) can
improve external->guest throughput by over 300%.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 8e8da1d..06763b9 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -505,6 +505,17 @@ static struct ethtool_ops virtnet_ethtool_ops = {
 	.get_tso = ethtool_op_get_tso,
 };
 
+#define MIN_MTU 68
+#define MAX_MTU 65535
+
+static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int err;
@@ -521,6 +532,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	dev->stop = virtnet_close;
 	dev->hard_start_xmit = start_xmit;
 	dev->get_stats = virtnet_get_stats;
+	dev->change_mtu = virtnet_change_mtu;
 	dev->features = NETIF_F_HIGHDMA;
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	dev->poll_controller = virtnet_netpoll;