[PATCH] Configurable tap interface MTU

["Ed Swierk" <eswierk@arastra.com>]

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This patch makes it possible to change the MTU on a tap interface.
Increasing the MTU beyond the 1500-byte default is useful for
applications that interoperate with Ethernet devices supporting jumbo
frames.

The patch caps the MTU somewhat arbitrarily at 16000 bytes. This is
slightly lower than the value used by the e1000 driver, so it seems
like a safe upper limit.

Signed-off-by: Ed Swierk <eswierk@arastra.com>

---

[-- Attachment #2: tap-change-mtu.patch --]
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Index: linux-2.6.22.6/drivers/net/tun.c
===================================================================
--- linux-2.6.22.6.orig/drivers/net/tun.c
+++ linux-2.6.22.6/drivers/net/tun.c
@@ -171,6 +171,18 @@ tun_net_mclist(struct net_device *dev)
 	}
 }
 
+#define MIN_MTU 68
+#define MAX_MTU 16000
+
+static int
+tun_net_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 struct net_device_stats *tun_net_stats(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
@@ -200,6 +212,7 @@ static void tun_net_init(struct net_devi
 		dev->set_multicast_list = tun_net_mclist;
 
 		ether_setup(dev);
+		dev->change_mtu = tun_net_change_mtu;
 
 		/* random address already created for us by tun_set_iff, use it */
 		memcpy(dev->dev_addr, tun->dev_addr, min(sizeof(tun->dev_addr), sizeof(dev->dev_addr)) );