bridge: Allow max MTU when multiple VLANs present

If the bridge is allowing multiple VLANs, some VLANs may have
different MTUs.  Instead of choosing the minimum MTU for the
bridge interface, choose the maximum MTU of the bridge members.
With this the user only needs to set a larger MTU on the member
ports that are participating in the large MTU VLANS.

Signed-off-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 4 deletions

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 9ba4ed65c52b..48dc4d2e2be3 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -424,8 +424,18 @@ int br_del_bridge(struct net *net, const char *name)
 	return ret;
 }
 
+static bool min_mtu(int a, int b)
+{
+	return a < b ? 1 : 0;
+}
+
+static bool max_mtu(int a, int b)
+{
+	return a > b ? 1 : 0;
+}
+
 /* MTU of the bridge pseudo-device: ETH_DATA_LEN or the minimum of the ports */
-int br_min_mtu(const struct net_bridge *br)
+static int __br_mtu(const struct net_bridge *br, bool (compare_fn)(int, int))
 {
 	const struct net_bridge_port *p;
 	int mtu = 0;
@@ -436,13 +446,21 @@ int br_min_mtu(const struct net_bridge *br)
 		mtu = ETH_DATA_LEN;
 	else {
 		list_for_each_entry(p, &br->port_list, list) {
-			if (!mtu  || p->dev->mtu < mtu)
+			if (!mtu || compare_fn(p->dev->mtu, mtu))
 				mtu = p->dev->mtu;
 		}
 	}
 	return mtu;
 }
 
+int br_mtu(const struct net_bridge *br)
+{
+	if (br->vlan_enabled)
+		return __br_mtu(br, max_mtu);
+	else
+		return __br_mtu(br, min_mtu);
+}
+
 static void br_set_gso_limits(struct net_bridge *br)
 {
 	unsigned int gso_max_size = GSO_MAX_SIZE;
@@ -594,7 +612,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	if (changed_addr)
 		call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
 
-	dev_set_mtu(br->dev, br_min_mtu(br));
+	dev_set_mtu(br->dev, br_mtu(br));
 	br_set_gso_limits(br);
 
 	kobject_uevent(&p->kobj, KOBJ_ADD);
@@ -641,7 +659,7 @@ int br_del_if(struct net_bridge *br, struct net_device *dev)
 	 */
 	del_nbp(p);
 
-	dev_set_mtu(br->dev, br_min_mtu(br));
+	dev_set_mtu(br->dev, br_mtu(br));
 	br_set_gso_limits(br);
 
 	spin_lock_bh(&br->lock);