batman-adv: Modified forwarding behaviour for multicast packets

With this patch a multicast packet is not always simply flooded anymore,
the behaviour for the following cases is changed to reduce
unnecessary overhead:

If all nodes within the horizon of a certain node have signalized
multicast listener announcement capability then an IPv6 multicast packet
with a destination of IPv6 link-local scope (excluding ff02::1) coming
from the upstream of this node...

* ...is dropped if there is no according multicast listener in the
  translation table,
* ...is forwarded via unicast if there is a single node with interested
  multicast listeners
* ...and otherwise still gets flooded.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

Documentation/ABI/testing/sysfs-class-net-mesh

@@ -76,6 +76,15 @@ Description:
 		is used to classify clients as "isolated" by the
 		Extended Isolation feature.
 
+What:           /sys/class/net/<mesh_iface>/mesh/multicast_mode
+Date:           Feb 2014
+Contact:        Linus Lüssing <linus.luessing@web.de>
+Description:
+                Indicates whether multicast optimizations are enabled
+                or disabled. If set to zero then all nodes in the
+                mesh are going to use classic flooding for any
+                multicast packet with no optimizations.
+
 What:           /sys/class/net/<mesh_iface>/mesh/network_coding
 Date:           Nov 2012
 Contact:        Martin Hundeboll <martin@hundeboll.net>

net/batman-adv/multicast.c

@@ -20,6 +20,7 @@
 #include "originator.h"
 #include "hard-interface.h"
 #include "translation-table.h"
+#include "multicast.h"
 
 /**
  * batadv_mcast_mla_softif_get - get softif multicast listeners
@@ -246,6 +247,131 @@ void batadv_mcast_mla_update(struct batadv_priv *bat_priv)
 	batadv_mcast_mla_list_free(&mcast_list);
 }
 
+/**
+ * batadv_mcast_forw_mode_check_ipv6 - check for optimized forwarding potential
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the IPv6 packet to check
+ *
+ * Checks whether the given IPv6 packet has the potential to be forwarded with a
+ * mode more optimal than classic flooding.
+ *
+ * If so then returns 0. Otherwise -EINVAL is returned or -ENOMEM if we are out
+ * of memory.
+ */
+static int batadv_mcast_forw_mode_check_ipv6(struct batadv_priv *bat_priv,
+					     struct sk_buff *skb)
+{
+	struct ipv6hdr *ip6hdr;
+
+	/* We might fail due to out-of-memory -> drop it */
+	if (!pskb_may_pull(skb, sizeof(struct ethhdr) + sizeof(*ip6hdr)))
+		return -ENOMEM;
+
+	ip6hdr = ipv6_hdr(skb);
+
+	/* TODO: Implement Multicast Router Discovery (RFC4286),
+	 * then allow scope > link local, too
+	 */
+	if (IPV6_ADDR_MC_SCOPE(&ip6hdr->daddr) != IPV6_ADDR_SCOPE_LINKLOCAL)
+		return -EINVAL;
+
+	/* link-local-all-nodes multicast listeners behind a bridge are
+	 * not snoopable (see RFC4541, section 3, paragraph 3)
+	 */
+	if (ipv6_addr_is_ll_all_nodes(&ip6hdr->daddr))
+		return -EINVAL;
+
+	return 0;
+}
+
+/**
+ * batadv_mcast_forw_mode_check - check for optimized forwarding potential
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the multicast frame to check
+ *
+ * Checks whether the given multicast ethernet frame has the potential to be
+ * forwarded with a mode more optimal than classic flooding.
+ *
+ * If so then returns 0. Otherwise -EINVAL is returned or -ENOMEM if we are out
+ * of memory.
+ */
+static int batadv_mcast_forw_mode_check(struct batadv_priv *bat_priv,
+					struct sk_buff *skb)
+{
+	struct ethhdr *ethhdr = eth_hdr(skb);
+
+	if (!atomic_read(&bat_priv->multicast_mode))
+		return -EINVAL;
+
+	if (atomic_read(&bat_priv->mcast.num_disabled))
+		return -EINVAL;
+
+	switch (ntohs(ethhdr->h_proto)) {
+	case ETH_P_IPV6:
+		return batadv_mcast_forw_mode_check_ipv6(bat_priv, skb);
+	default:
+		return -EINVAL;
+	}
+}
+
+/**
+ * batadv_mcast_forw_tt_node_get - get a multicast tt node
+ * @bat_priv: the bat priv with all the soft interface information
+ * @ethhdr: the ether header containing the multicast destination
+ *
+ * Returns an orig_node matching the multicast address provided by ethhdr
+ * via a translation table lookup. This increases the returned nodes refcount.
+ */
+static struct batadv_orig_node *
+batadv_mcast_forw_tt_node_get(struct batadv_priv *bat_priv,
+			      struct ethhdr *ethhdr)
+{
+	return batadv_transtable_search(bat_priv, ethhdr->h_source,
+					ethhdr->h_dest, BATADV_NO_FLAGS);
+}
+
+/**
+ * batadv_mcast_forw_mode - check on how to forward a multicast packet
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: The multicast packet to check
+ * @orig: an originator to be set to forward the skb to
+ *
+ * Returns the forwarding mode as enum batadv_forw_mode and in case of
+ * BATADV_FORW_SINGLE set the orig to the single originator the skb
+ * should be forwarded to.
+ */
+enum batadv_forw_mode
+batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
+		       struct batadv_orig_node **orig)
+{
+	struct ethhdr *ethhdr;
+	int ret, tt_count;
+
+	ret = batadv_mcast_forw_mode_check(bat_priv, skb);
+	if (ret == -ENOMEM)
+		return BATADV_FORW_NONE;
+	else if (ret < 0)
+		return BATADV_FORW_ALL;
+
+	ethhdr = eth_hdr(skb);
+
+	tt_count = batadv_tt_global_hash_count(bat_priv, ethhdr->h_dest,
+					       BATADV_NO_FLAGS);
+
+	switch (tt_count) {
+	case 1:
+		*orig = batadv_mcast_forw_tt_node_get(bat_priv, ethhdr);
+		if (*orig)
+			return BATADV_FORW_SINGLE;
+
+		/* fall through */
+	case 0:
+		return BATADV_FORW_NONE;
+	default:
+		return BATADV_FORW_ALL;
+	}
+}
+
 /**
  * batadv_mcast_tvlv_ogm_handler_v1 - process incoming multicast tvlv container
  * @bat_priv: the bat priv with all the soft interface information

net/batman-adv/multicast.h

@@ -18,10 +18,28 @@
 #ifndef _NET_BATMAN_ADV_MULTICAST_H_
 #define _NET_BATMAN_ADV_MULTICAST_H_
 
+/**
+ * batadv_forw_mode - the way a packet should be forwarded as
+ * @BATADV_FORW_ALL: forward the packet to all nodes (currently via classic
+ *  flooding)
+ * @BATADV_FORW_SINGLE: forward the packet to a single node (currently via the
+ *  BATMAN unicast routing protocol)
+ * @BATADV_FORW_NONE: don't forward, drop it
+ */
+enum batadv_forw_mode {
+	BATADV_FORW_ALL,
+	BATADV_FORW_SINGLE,
+	BATADV_FORW_NONE,
+};
+
 #ifdef CONFIG_BATMAN_ADV_MCAST
 
 void batadv_mcast_mla_update(struct batadv_priv *bat_priv);
 
+enum batadv_forw_mode
+batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
+		       struct batadv_orig_node **mcast_single_orig);
+
 void batadv_mcast_init(struct batadv_priv *bat_priv);
 
 void batadv_mcast_free(struct batadv_priv *bat_priv);
@@ -35,6 +53,13 @@ static inline void batadv_mcast_mla_update(struct batadv_priv *bat_priv)
 	return;
 }
 
+static inline enum batadv_forw_mode
+batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
+		       struct batadv_orig_node **mcast_single_orig)
+{
+	return BATADV_FORW_ALL;
+}
+
 static inline int batadv_mcast_init(struct batadv_priv *bat_priv)
 {
 	return 0;

net/batman-adv/send.c

@@ -248,11 +248,11 @@ bool batadv_send_skb_prepare_unicast_4addr(struct batadv_priv *bat_priv,
  *
  * Returns NET_XMIT_DROP in case of error or NET_XMIT_SUCCESS otherwise.
  */
-static int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
-				   struct sk_buff *skb, int packet_type,
-				   int packet_subtype,
-				   struct batadv_orig_node *orig_node,
-				   unsigned short vid)
+int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
+			    struct sk_buff *skb, int packet_type,
+			    int packet_subtype,
+			    struct batadv_orig_node *orig_node,
+			    unsigned short vid)
 {
 	struct ethhdr *ethhdr;
 	struct batadv_unicast_packet *unicast_packet;

net/batman-adv/send.h

@@ -36,6 +36,11 @@ bool batadv_send_skb_prepare_unicast_4addr(struct batadv_priv *bat_priv,
 					   struct sk_buff *skb,
 					   struct batadv_orig_node *orig_node,
 					   int packet_subtype);
+int batadv_send_skb_unicast(struct batadv_priv *bat_priv,
+			    struct sk_buff *skb, int packet_type,
+			    int packet_subtype,
+			    struct batadv_orig_node *orig_node,
+			    unsigned short vid);
 int batadv_send_skb_via_tt_generic(struct batadv_priv *bat_priv,
 				   struct sk_buff *skb, int packet_type,
 				   int packet_subtype, uint8_t *dst_hint,

net/batman-adv/soft-interface.c

@@ -32,6 +32,7 @@
 #include <linux/ethtool.h>
 #include <linux/etherdevice.h>
 #include <linux/if_vlan.h>
+#include "multicast.h"
 #include "bridge_loop_avoidance.h"
 #include "network-coding.h"
 
@@ -170,6 +171,8 @@ static int batadv_interface_tx(struct sk_buff *skb,
 	unsigned short vid;
 	uint32_t seqno;
 	int gw_mode;
+	enum batadv_forw_mode forw_mode;
+	struct batadv_orig_node *mcast_single_orig = NULL;
 
 	if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
 		goto dropped;
@@ -247,9 +250,19 @@ static int batadv_interface_tx(struct sk_buff *skb,
 			 * directed to a DHCP server
 			 */
 			goto dropped;
-	}
 
 send:
+		if (do_bcast && !is_broadcast_ether_addr(ethhdr->h_dest)) {
+			forw_mode = batadv_mcast_forw_mode(bat_priv, skb,
+							   &mcast_single_orig);
+			if (forw_mode == BATADV_FORW_NONE)
+				goto dropped;
+
+			if (forw_mode == BATADV_FORW_SINGLE)
+				do_bcast = false;
+		}
+	}
+
 	batadv_skb_set_priority(skb, 0);
 
 	/* ethernet packet should be broadcasted */
@@ -301,6 +314,10 @@ static int batadv_interface_tx(struct sk_buff *skb,
 			if (ret)
 				goto dropped;
 			ret = batadv_send_skb_via_gw(bat_priv, skb, vid);
+		} else if (mcast_single_orig) {
+			ret = batadv_send_skb_unicast(bat_priv, skb,
+						      BATADV_UNICAST, 0,
+						      mcast_single_orig, vid);
 		} else {
 			if (batadv_dat_snoop_outgoing_arp_request(bat_priv,
 								  skb))
@@ -691,6 +708,7 @@ static int batadv_softif_init_late(struct net_device *dev)
 #endif
 #ifdef CONFIG_BATMAN_ADV_MCAST
 	bat_priv->mcast.flags = BATADV_NO_FLAGS;
+	atomic_set(&bat_priv->multicast_mode, 1);
 	atomic_set(&bat_priv->mcast.num_disabled, 0);
 #endif
 	atomic_set(&bat_priv->gw_mode, BATADV_GW_MODE_OFF);

net/batman-adv/sysfs.c

@@ -539,6 +539,9 @@ BATADV_ATTR_SIF_UINT(gw_sel_class, S_IRUGO | S_IWUSR, 1, BATADV_TQ_MAX_VALUE,
 		     batadv_post_gw_reselect);
 static BATADV_ATTR(gw_bandwidth, S_IRUGO | S_IWUSR, batadv_show_gw_bwidth,
 		   batadv_store_gw_bwidth);
+#ifdef CONFIG_BATMAN_ADV_MCAST
+BATADV_ATTR_SIF_BOOL(multicast_mode, S_IRUGO | S_IWUSR, NULL);
+#endif
 #ifdef CONFIG_BATMAN_ADV_DEBUG
 BATADV_ATTR_SIF_UINT(log_level, S_IRUGO | S_IWUSR, 0, BATADV_DBG_ALL, NULL);
 #endif
@@ -557,6 +560,9 @@ static struct batadv_attribute *batadv_mesh_attrs[] = {
 #endif
 #ifdef CONFIG_BATMAN_ADV_DAT
 	&batadv_attr_distributed_arp_table,
+#endif
+#ifdef CONFIG_BATMAN_ADV_MCAST
+	&batadv_attr_multicast_mode,
 #endif
 	&batadv_attr_fragmentation,
 	&batadv_attr_routing_algo,