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>

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);

net/batman-adv/main.c

@@ -255,6 +255,31 @@ batadv_seq_print_text_primary_if_get(struct seq_file *seq)
 	return primary_if;
 }
 
+/**
+ * batadv_max_header_len - calculate maximum encapsulation overhead for a
+ *  payload packet
+ *
+ * Return the maximum encapsulation overhead in bytes.
+ */
+int batadv_max_header_len(void)
+{
+	int header_len = 0;
+
+	header_len = max_t(int, header_len,
+			   sizeof(struct batadv_unicast_packet));
+	header_len = max_t(int, header_len,
+			   sizeof(struct batadv_unicast_4addr_packet));
+	header_len = max_t(int, header_len,
+			   sizeof(struct batadv_bcast_packet));
+
+#ifdef CONFIG_BATMAN_ADV_NC
+	header_len = max_t(int, header_len,
+			   sizeof(struct batadv_coded_packet));
+#endif
+
+	return header_len;
+}
+
 /**
  * batadv_skb_set_priority - sets skb priority according to packet content
  * @skb: the packet to be sent

net/batman-adv/main.h

@@ -191,6 +191,7 @@ void batadv_mesh_free(struct net_device *soft_iface);
 int batadv_is_my_mac(struct batadv_priv *bat_priv, const uint8_t *addr);
 struct batadv_hard_iface *
 batadv_seq_print_text_primary_if_get(struct seq_file *seq);
+int batadv_max_header_len(void);
 void batadv_skb_set_priority(struct sk_buff *skb, int offset);
 int batadv_batman_skb_recv(struct sk_buff *skb, struct net_device *dev,
 			   struct packet_type *ptype,

net/batman-adv/soft-interface.c

@@ -626,7 +626,7 @@ static void batadv_softif_init_early(struct net_device *dev)
 	 */
 	dev->mtu = ETH_DATA_LEN;
 	/* reserve more space in the skbuff for our header */
-	dev->hard_header_len = BATADV_HEADER_LEN;
+	dev->hard_header_len = batadv_max_header_len();
 
 	/* generate random address */
 	eth_hw_addr_random(dev);

net/batman-adv/types.h

@@ -24,13 +24,6 @@
 #include "bitarray.h"
 #include <linux/kernel.h>
 
-/**
- * Maximum overhead for the encapsulation for a payload packet
- */
-#define BATADV_HEADER_LEN \
-	(ETH_HLEN + max(sizeof(struct batadv_unicast_packet), \
-			sizeof(struct batadv_bcast_packet)))
-
 #ifdef CONFIG_BATMAN_ADV_DAT
 
 /* batadv_dat_addr_t is the type used for all DHT addresses. If it is changed,