[PATCH 5/5] batman-adv: Limit aggregation size to outgoing MTU

[Sven Eckelmann <sven@narfation.org>]

If a B.A.T.M.A.N. IV aggregated OGM was prepared, it was always assumed
that 512 bytes (BATADV_MAX_AGGREGATION_BYTES) can be transmitted. But the
outgoing MTU might be too small for these 512 bytes and the aggregation
size must be adjusted in this case. Otherwise, the aggregates will cause
unnecessary packet loss.

For now, the non-aggregated packet length is not touched.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/bat_iv_ogm.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 769d5ff779eb88de8b9d889bb3e4a3304875ea32..dbad6007871a97ee01f7295c005ab3deeff86efd 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -443,22 +443,26 @@ batadv_iv_ogm_can_aggregate(const struct batadv_ogm_packet *new_bat_ogm_packet,
 			    const struct batadv_forw_packet *forw_packet)
 {
 	struct batadv_ogm_packet *batadv_ogm_packet;
-	int aggregated_bytes = forw_packet->packet_len + packet_len;
+	unsigned int aggregated_bytes = forw_packet->packet_len + packet_len;
 	struct batadv_hard_iface *primary_if = NULL;
 	u8 packet_num = forw_packet->num_packets;
 	bool res = false;
 	unsigned long aggregation_end_time;
+	unsigned int max_bytes;
 
 	batadv_ogm_packet = (struct batadv_ogm_packet *)forw_packet->skb->data;
 	aggregation_end_time = send_time;
 	aggregation_end_time += msecs_to_jiffies(BATADV_MAX_AGGREGATION_MS);
 
+	max_bytes = min_t(unsigned int, if_outgoing->net_dev->mtu,
+			  BATADV_MAX_AGGREGATION_BYTES);
+
 	/* we can aggregate the current packet to this aggregated packet
 	 * if:
 	 *
 	 * - the send time is within our MAX_AGGREGATION_MS time
 	 * - the resulting packet won't be bigger than
-	 *   MAX_AGGREGATION_BYTES
+	 *   MAX_AGGREGATION_BYTES and MTU of the outgoing interface
 	 * - the number of packets is lower than MAX_AGGREGATION_PACKETS
 	 * otherwise aggregation is not possible
 	 */
@@ -466,7 +470,7 @@ batadv_iv_ogm_can_aggregate(const struct batadv_ogm_packet *new_bat_ogm_packet,
 	    !time_after_eq(aggregation_end_time, forw_packet->send_time))
 		return false;
 
-	if (aggregated_bytes > BATADV_MAX_AGGREGATION_BYTES)
+	if (aggregated_bytes > max_bytes)
 		return false;
 
 	if (packet_num >= BATADV_MAX_AGGREGATION_PACKETS)
@@ -551,9 +555,9 @@ static void batadv_iv_ogm_aggregate_new(const unsigned char *packet_buff,
 	unsigned int skb_size;
 	atomic_t *queue_left = own_packet ? NULL : &bat_priv->batman_queue_left;
 
-	if (atomic_read(&bat_priv->aggregated_ogms) &&
-	    packet_len < BATADV_MAX_AGGREGATION_BYTES)
-		skb_size = BATADV_MAX_AGGREGATION_BYTES;
+	if (atomic_read(&bat_priv->aggregated_ogms))
+		skb_size = max_t(unsigned int, BATADV_MAX_AGGREGATION_BYTES,
+				 packet_len);
 	else
 		skb_size = packet_len;
 

-- 
2.47.2