batman-adv: improved roaming mechanism

With the current client announcement implementation, in case of roaming,
an update is triggered on the new AP serving the client. At that point
the new information is spread around by means of the OGM broadcasting
mechanism. Until this operations is not executed, no node is able to
correctly route traffic towards the client. This obviously causes packet
drops and introduces a delay in the time needed by the client to recover
its connections.

A new packet type called ROAMING_ADVERTISEMENT is added to account this
issue.

This message is sent in case of roaming from the new AP serving the
client to the old one and will contain the client MAC address. In this
way an out-of-OGM update is immediately committed, so that the old node
can update its global translation table. Traffic reaching this node will
then be redirected to the correct destination utilising the fresher
information. Thus reducing the packet drops and the connection recovery
delay.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Sven Eckelmann <sven@narfation.org>

1 files changed, 57 insertions, 4 deletions

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 8b0f8330b06d..05d50ca3c4db 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -93,6 +93,9 @@ static void update_transtable(struct bat_priv *bat_priv,
 		spin_lock_bh(&bat_priv->tt_ghash_lock);
 		orig_node->tt_crc = tt_global_crc(bat_priv, orig_node);
 		spin_unlock_bh(&bat_priv->tt_ghash_lock);
+		/* Roaming phase is over: tables are in sync again. I can
+		 * unset the flag */
+		orig_node->tt_poss_change = false;
 	} else {
 		/* if we missed more than one change or our tables are not
 		 * in sync anymore -> request fresh tt data */
@@ -1252,6 +1255,54 @@ out:
 	return NET_RX_DROP;
 }
 
+int recv_roam_adv(struct sk_buff *skb, struct hard_iface *recv_if)
+{
+	struct bat_priv *bat_priv = netdev_priv(recv_if->soft_iface);
+	struct roam_adv_packet *roam_adv_packet;
+	struct orig_node *orig_node;
+	struct ethhdr *ethhdr;
+
+	/* drop packet if it has not necessary minimum size */
+	if (unlikely(!pskb_may_pull(skb, sizeof(struct roam_adv_packet))))
+		goto out;
+
+	ethhdr = (struct ethhdr *)skb_mac_header(skb);
+
+	/* packet with unicast indication but broadcast recipient */
+	if (is_broadcast_ether_addr(ethhdr->h_dest))
+		goto out;
+
+	/* packet with broadcast sender address */
+	if (is_broadcast_ether_addr(ethhdr->h_source))
+		goto out;
+
+	roam_adv_packet = (struct roam_adv_packet *)skb->data;
+
+	if (!is_my_mac(roam_adv_packet->dst))
+		return route_unicast_packet(skb, recv_if);
+
+	orig_node = orig_hash_find(bat_priv, roam_adv_packet->src);
+	if (!orig_node)
+		goto out;
+
+	bat_dbg(DBG_TT, bat_priv, "Received ROAMING_ADV from %pM "
+		"(client %pM)\n", roam_adv_packet->src,
+		roam_adv_packet->client);
+
+	tt_global_add(bat_priv, orig_node, roam_adv_packet->client,
+		      atomic_read(&orig_node->last_ttvn) + 1, true);
+
+	/* Roaming phase starts: I have new information but the ttvn has not
+	 * been incremented yet. This flag will make me check all the incoming
+	 * packets for the correct destination. */
+	bat_priv->tt_poss_change = true;
+
+	orig_node_free_ref(orig_node);
+out:
+	/* returning NET_RX_DROP will make the caller function kfree the skb */
+	return NET_RX_DROP;
+}
+
 /* find a suitable router for this originator, and use
  * bonding if possible. increases the found neighbors
  * refcount.*/
@@ -1445,6 +1496,7 @@ static int check_unicast_ttvn(struct bat_priv *bat_priv,
 	struct ethhdr *ethhdr;
 	struct hard_iface *primary_if;
 	struct unicast_packet *unicast_packet;
+	bool tt_poss_change;
 
 	/* I could need to modify it */
 	if (skb_cow(skb, sizeof(struct unicast_packet)) < 0)
@@ -1452,27 +1504,28 @@ static int check_unicast_ttvn(struct bat_priv *bat_priv,
 
 	unicast_packet = (struct unicast_packet *)skb->data;
 
-	if (is_my_mac(unicast_packet->dest))
+	if (is_my_mac(unicast_packet->dest)) {
+		tt_poss_change = bat_priv->tt_poss_change;
 		curr_ttvn = (uint8_t)atomic_read(&bat_priv->ttvn);
-	else {
+	} else {
 		orig_node = orig_hash_find(bat_priv, unicast_packet->dest);
 
 		if (!orig_node)
 			return 0;
 
 		curr_ttvn = (uint8_t)atomic_read(&orig_node->last_ttvn);
+		tt_poss_change = orig_node->tt_poss_change;
 		orig_node_free_ref(orig_node);
 	}
 
 	/* Check whether I have to reroute the packet */
-	if (seq_before(unicast_packet->ttvn, curr_ttvn)) {
+	if (seq_before(unicast_packet->ttvn, curr_ttvn) || tt_poss_change) {
 		/* Linearize the skb before accessing it */
 		if (skb_linearize(skb) < 0)
 			return 0;
 
 		ethhdr = (struct ethhdr *)(skb->data +
 			sizeof(struct unicast_packet));
-
 		orig_node = transtable_search(bat_priv, ethhdr->h_dest);
 
 		if (!orig_node) {