[B.A.T.M.A.N.] [PATCH 01/10] batman-adv: fix soft-interface MTU computation

Antonio Quartulli
2014-02-17T20:48:40Z

The current MTU computation always returns a value
smaller than 1500bytes even if the real interfaces
have an MTU large enough to compensate the batman-adv
overhead.

Fix the computation by properly returning the highest
admitted value.

Introduced by a19d3d85e1b854e4a483a55d740a42458085560d
("batman-adv: limit local translation table max size")

Reported-by: Russell Senior <russell@personaltelco.net>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
---
net/batman-adv/hard-interface.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 3d417d3..b851cc5 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -241,7 +241,7 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)
{
struct batadv_priv *bat_priv = netdev_priv(soft_iface);
const struct batadv_hard_iface *hard_iface;
- int min_mtu = ETH_DATA_LEN;
+ int min_mtu = INT_MAX;

rcu_read_lock();
list_for_each_entry_rcu(hard_iface, &batadv_hardif_list, list) {
@@ -256,8 +256,6 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)
}
rcu_read_unlock();

- atomic_set(&bat_priv->packet_size_max, min_mtu);
-
if (atomic_read(&bat_priv->fragmentation) == 0)
goto out;

@@ -268,13 +266,21 @@ int batadv_hardif_min_mtu(struct net_device *soft_iface)
min_mtu = min_t(int, min_mtu, BATADV_FRAG_MAX_FRAG_SIZE);
min_mtu -= sizeof(struct batadv_frag_packet);
min_mtu *= BATADV_FRAG_MAX_FRAGMENTS;
- atomic_set(&bat_priv->packet_size_max, min_mtu);
-
- /* with fragmentation enabled we can fragment external packets easily */
- min_mtu = min_t(int, min_mtu, ETH_DATA_LEN);

out:
- return min_mtu - batadv_max_header_len();
+ /* report to the other components the maximum amount of bytes that
+ * batman-adv can send over the wire (without considering the payload
+ * overhead). For example, this value is used by TT to compute the
+ * maximum local table table size
+ */
+ atomic_set(&bat_priv->packet_size_max, min_mtu);
+
+ /* the real soft-interface MTU is computed by removing the payload
+ * overhead from the maximum amount of bytes that was just computed.
+ *
+ * However batman-adv does not support MTUs bigger than ETH_DATA_LEN
+ */
+ return min_t(int, min_mtu - batadv_max_header_len(), ETH_DATA_LEN);
}

/* adjusts the MTU if a new interface with a smaller MTU appeared. */
--
1.8.5.3