batman-adv: consider network coding overhead when calculating required mtu

The module prints a warning when the MTU on the hard interface is too
small to transfer payload traffic without fragmentation. The required
MTU is calculated based on the encapsulation header size. If network
coding is compild into the module its header size is taken into
account as well.

Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 004017c..d564af2 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -269,9 +269,10 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)
 	const struct batadv_priv *bat_priv = netdev_priv(soft_iface);
 	const struct batadv_hard_iface *hard_iface;
 	/* allow big frames if all devices are capable to do so
-	 * (have MTU > 1500 + BAT_HEADER_LEN)
+	 * (have MTU > 1500 + batadv_max_header_len())
 	 */
 	int min_mtu = ETH_DATA_LEN;
+	int max_header_len = batadv_max_header_len();
 
 	if (atomic_read(&bat_priv->fragmentation))
 		goto out;
@@ -285,8 +286,7 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)
 		if (hard_iface->soft_iface != soft_iface)
 			continue;
 
-		min_mtu = min_t(int,
-				hard_iface->net_dev->mtu - BATADV_HEADER_LEN,
+		min_mtu = min_t(int, hard_iface->net_dev->mtu - max_header_len,
 				min_mtu);
 	}
 	rcu_read_unlock();
@@ -380,6 +380,7 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
 	struct batadv_priv *bat_priv;
 	struct net_device *soft_iface, *master;
 	__be16 ethertype = htons(ETH_P_BATMAN);
+	int max_header_len = batadv_max_header_len();
 	int ret;
 
 	if (hard_iface->if_status != BATADV_IF_NOT_IN_USE)
@@ -448,18 +449,18 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
 		    hard_iface->net_dev->name);
 
 	if (atomic_read(&bat_priv->fragmentation) &&
-	    hard_iface->net_dev->mtu < ETH_DATA_LEN + BATADV_HEADER_LEN)
+	    hard_iface->net_dev->mtu < ETH_DATA_LEN + max_header_len)
 		batadv_info(hard_iface->soft_iface,
-			    "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to %zi would solve the problem.\n",
+			    "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to %i would solve the problem.\n",
 			    hard_iface->net_dev->name, hard_iface->net_dev->mtu,
-			    ETH_DATA_LEN + BATADV_HEADER_LEN);
+			    ETH_DATA_LEN + max_header_len);
 
 	if (!atomic_read(&bat_priv->fragmentation) &&
-	    hard_iface->net_dev->mtu < ETH_DATA_LEN + BATADV_HEADER_LEN)
+	    hard_iface->net_dev->mtu < ETH_DATA_LEN + max_header_len)
 		batadv_info(hard_iface->soft_iface,
-			    "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. If you experience problems getting traffic through try increasing the MTU to %zi.\n",
+			    "The MTU of interface %s is too small (%i) to handle the transport of batman-adv packets. If you experience problems getting traffic through try increasing the MTU to %i.\n",
 			    hard_iface->net_dev->name, hard_iface->net_dev->mtu,
-			    ETH_DATA_LEN + BATADV_HEADER_LEN);
+			    ETH_DATA_LEN + max_header_len);
 
 	if (batadv_hardif_is_iface_up(hard_iface))
 		batadv_hardif_activate_interface(hard_iface);