Linux Ethernet Bridging - Apr 2007 - [Bridge] [PATCH 2.6] bridge -- support different MTU sizes

On Thu, 8 Jul 2004 10:41:43 -0700
Stephen Hemminger <shemminger@osdl.org> wrote:
> This patch adds support for different size MTU's to bridging.
> It is useful for bridging Ethernet's with jumbo frames, etc.
> 
> The mtu of the bridge pseudo-device is maintained as the minimum
> of all the underlying ports.  And when forwarding a frame through
> the bridge, it will drop the frame if the outgoing port's MTU
> is less than the frame size (as per 802 standard).
Looks fine, applied.

This patch adds support for different size MTU's to bridging.
It is useful for bridging Ethernet's with jumbo frames, etc.

The mtu of the bridge pseudo-device is maintained as the minimum
of all the underlying ports.  And when forwarding a frame through
the bridge, it will drop the frame if the outgoing port's MTU
is less than the frame size (as per 802 standard).

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>


diff -Nru a/net/bridge/br_device.c b/net/bridge/br_device.c
--- a/net/bridge/br_device.c	2004-06-30 11:48:01 -07:00
+++ b/net/bridge/br_device.c	2004-06-30 11:48:01 -07:00
@@ -89,6 +89,15 @@
 	return 0;
 }
 
+static int br_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if ((new_mtu < 68) || new_mtu > br_min_mtu(dev->priv))
+		return -EINVAL;
+
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static int br_dev_accept_fastpath(struct net_device *dev, struct dst_entry
*dst)
 {
 	return -1;
@@ -105,6 +114,7 @@
 	dev->hard_start_xmit = br_dev_xmit;
 	dev->open = br_dev_open;
 	dev->set_multicast_list = br_dev_set_multicast_list;
+	dev->change_mtu = br_change_mtu;
 	dev->destructor = free_netdev;
 	SET_MODULE_OWNER(dev);
 	dev->stop = br_dev_stop;
diff -Nru a/net/bridge/br_forward.c b/net/bridge/br_forward.c
--- a/net/bridge/br_forward.c	2004-06-30 11:48:01 -07:00
+++ b/net/bridge/br_forward.c	2004-06-30 11:48:01 -07:00
@@ -22,7 +22,8 @@
 static inline int should_deliver(const struct net_bridge_port *p, 
 				 const struct sk_buff *skb)
 {
-	if (skb->dev == p->dev ||
+	if (skb->dev == p->dev ||
+	    skb->len > p->dev->mtu ||
 	    p->state != BR_STATE_FORWARDING)
 		return 0;
 
diff -Nru a/net/bridge/br_if.c b/net/bridge/br_if.c
--- a/net/bridge/br_if.c	2004-06-30 11:48:01 -07:00
+++ b/net/bridge/br_if.c	2004-06-30 11:48:01 -07:00
@@ -295,6 +295,24 @@
 	return ret;
 }
 
+int br_min_mtu(const struct net_bridge *br)
+{
+	const struct net_bridge_port *p;
+	int mtu = 0;
+
+	ASSERT_RTNL();
+
+	if (list_empty(&br->port_list))
+		mtu = 1500;
+	else {
+		list_for_each_entry(p, &br->port_list, list) {
+			if (!mtu  || p->dev->mtu < mtu)
+				mtu = p->dev->mtu;
+		}
+	}
+	return mtu;
+}
+
 /* called with RTNL */
 int br_add_if(struct net_bridge *br, struct net_device *dev)
 {
@@ -328,6 +346,8 @@
 		if ((br->dev->flags & IFF_UP) && (dev->flags &
IFF_UP))
 			br_stp_enable_port(p);
 		spin_unlock_bh(&br->lock);
+
+		br->dev->mtu = br_min_mtu(br);
 	}
 
 	return err;
diff -Nru a/net/bridge/br_notify.c b/net/bridge/br_notify.c
--- a/net/bridge/br_notify.c	2004-06-30 11:48:01 -07:00
+++ b/net/bridge/br_notify.c	2004-06-30 11:48:01 -07:00
@@ -47,6 +47,10 @@
 		spin_unlock_bh(&br->lock);
 		break;
 
+	case NETDEV_CHANGEMTU:
+		br->dev->mtu = br_min_mtu(br);
+		break;
+
 	case NETDEV_DOWN:
 		if (br->dev->flags & IFF_UP) {
 			spin_lock_bh(&br->lock);
diff -Nru a/net/bridge/br_private.h b/net/bridge/br_private.h
--- a/net/bridge/br_private.h	2004-06-30 11:48:01 -07:00
+++ b/net/bridge/br_private.h	2004-06-30 11:48:01 -07:00
@@ -168,6 +168,7 @@
 	      struct net_device *dev);
 extern int br_del_if(struct net_bridge *br,
 	      struct net_device *dev);
+extern int br_min_mtu(const struct net_bridge *br);
 
 /* br_input.c */
 extern int br_handle_frame_finish(struct sk_buff *skb);