batman-adv: mcast: implement multicast packet generation

Implement the preparation of a batman-adv multicast packet and use this
under certain conditions.

For one thing this implements the capability to push a complete
batman-adv multicast packet header, including a tracker TVLV with all
originator destinations that have signaled interest in it, onto a given
ethernet frame with an IP multicast packet inside.

For another checks are implemented to determine if encapsulating a
multicast packet in this new batman-adv multicast packet type and using
it is feasible. Those checks are:

1) Have all nodes signaled that they are capable of handling the new
   batman-adv multicast packet type?
2) Do all active hard interfaces of all nodes, including us, have an MTU
   of at least 1280 bytes?
3) Does a complete multicast packet header with all its destination
   addresses fit onto the given multicast packet / ethernet frame and
   does not exceed 1280 bytes?

If all checks passed then the new batman-adv multicast packet type will
be used for transmission and distribution. Otherwise we fall back to one or
more batman-adv unicast packet transmissions, if possible. Or if not
possible we will fall back to classic flooding through a batman-adv
broadcast packet.
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/multicast.c

@@ -1169,17 +1169,62 @@ static int batadv_mcast_forw_rtr_count(struct batadv_priv *bat_priv,
 	}
 }
 
+/**
+ * batadv_mcast_forw_mode_by_count() - get forwarding mode by count
+ * @bat_priv: the bat priv with all the soft interface information
+ * @skb: the multicast packet to check
+ * @vid: the vlan identifier
+ * @is_routable: stores whether the destination is routable
+ * @count: the number of originators the multicast packet need to be sent to
+ *
+ * For a multicast packet with multiple destination originators, checks which
+ * mode to use. For BATADV_FORW_MCAST it also encapsulates the packet with a
+ * complete batman-adv multicast header.
+ *
+ * Return:
+ *	BATADV_FORW_MCAST: If all nodes have multicast packet routing
+ *	capabilities and an MTU >= 1280 on all hard interfaces (including us)
+ *	and the encapsulated multicast packet with all destination addresses
+ *	would still fit into an 1280 bytes batman-adv multicast packet
+ *	(excluding the outer ethernet frame) and we could successfully push
+ *	the full batman-adv multicast packet header.
+ *	BATADV_FORW_UCASTS: If the packet cannot be sent in a batman-adv
+ *	multicast packet and the amount of batman-adv unicast packets needed
+ *	is smaller or equal to the configured multicast fanout.
+ *	BATADV_FORW_BCAST: Otherwise.
+ */
+static enum batadv_forw_mode
+batadv_mcast_forw_mode_by_count(struct batadv_priv *bat_priv,
+				struct sk_buff *skb, unsigned short vid,
+				int is_routable, int count)
+{
+	unsigned int mcast_hdrlen = batadv_mcast_forw_packet_hdrlen(count);
+	u8 own_tvlv_flags = bat_priv->mcast.mla_flags.tvlv_flags;
+
+	if (!atomic_read(&bat_priv->mcast.num_no_mc_ptype_capa) &&
+	    own_tvlv_flags & BATADV_MCAST_HAVE_MC_PTYPE_CAPA &&
+	    skb->len + mcast_hdrlen <= IPV6_MIN_MTU &&
+	    batadv_mcast_forw_push(bat_priv, skb, vid, is_routable, count))
+		return BATADV_FORW_MCAST;
+
+	if (count <= atomic_read(&bat_priv->multicast_fanout))
+		return BATADV_FORW_UCASTS;
+
+	return BATADV_FORW_BCAST;
+}
+
 /**
  * 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
+ * @vid: the vlan identifier
  * @is_routable: stores whether the destination is routable
  *
  * Return: The forwarding mode as enum batadv_forw_mode.
  */
 enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       int *is_routable)
+		       unsigned short vid, int *is_routable)
 {
 	int ret, tt_count, ip_count, unsnoop_count, total_count;
 	bool is_unsnoopable = false;
@@ -1209,10 +1254,8 @@ batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
 	else if (unsnoop_count)
 		return BATADV_FORW_BCAST;
 
-	if (total_count <= atomic_read(&bat_priv->multicast_fanout))
-		return BATADV_FORW_UCASTS;
-
-	return BATADV_FORW_BCAST;
+	return batadv_mcast_forw_mode_by_count(bat_priv, skb, vid, *is_routable,
+					       total_count);
 }
 
 /**
@@ -1772,6 +1815,31 @@ static void batadv_mcast_want_rtr6_update(struct batadv_priv *bat_priv,
 	}
 }
 
+/**
+ * batadv_mcast_have_mc_ptype_update() - update multicast packet type counter
+ * @bat_priv: the bat priv with all the soft interface information
+ * @orig: the orig_node which multicast state might have changed of
+ * @mcast_flags: flags indicating the new multicast state
+ *
+ * If the BATADV_MCAST_HAVE_MC_PTYPE_CAPA flag of this originator, orig, has
+ * toggled then this method updates the counter accordingly.
+ */
+static void batadv_mcast_have_mc_ptype_update(struct batadv_priv *bat_priv,
+					      struct batadv_orig_node *orig,
+					      u8 mcast_flags)
+{
+	lockdep_assert_held(&orig->mcast_handler_lock);
+
+	/* switched from flag set to unset */
+	if (!(mcast_flags & BATADV_MCAST_HAVE_MC_PTYPE_CAPA) &&
+	    orig->mcast_flags & BATADV_MCAST_HAVE_MC_PTYPE_CAPA)
+		atomic_inc(&bat_priv->mcast.num_no_mc_ptype_capa);
+	/* switched from flag unset to set */
+	else if (mcast_flags & BATADV_MCAST_HAVE_MC_PTYPE_CAPA &&
+		 !(orig->mcast_flags & BATADV_MCAST_HAVE_MC_PTYPE_CAPA))
+		atomic_dec(&bat_priv->mcast.num_no_mc_ptype_capa);
+}
+
 /**
  * batadv_mcast_tvlv_flags_get() - get multicast flags from an OGM TVLV
  * @enabled: whether the originator has multicast TVLV support enabled
@@ -1840,6 +1908,7 @@ static void batadv_mcast_tvlv_ogm_handler(struct batadv_priv *bat_priv,
 	batadv_mcast_want_ipv6_update(bat_priv, orig, mcast_flags);
 	batadv_mcast_want_rtr4_update(bat_priv, orig, mcast_flags);
 	batadv_mcast_want_rtr6_update(bat_priv, orig, mcast_flags);
+	batadv_mcast_have_mc_ptype_update(bat_priv, orig, mcast_flags);
 
 	orig->mcast_flags = mcast_flags;
 	spin_unlock_bh(&orig->mcast_handler_lock);

net/batman-adv/multicast.h

@@ -11,6 +11,7 @@
 
 #include <linux/netlink.h>
 #include <linux/skbuff.h>
+#include <linux/types.h>
 
 /**
  * enum batadv_forw_mode - the way a packet should be forwarded as
@@ -28,6 +29,12 @@ enum batadv_forw_mode {
 	 */
 	BATADV_FORW_UCASTS,
 
+	/**
+	 * @BATADV_FORW_MCAST: forward the packet to some nodes via a
+	 *  batman-adv multicast packet
+	 */
+	BATADV_FORW_MCAST,
+
 	/** @BATADV_FORW_NONE: don't forward, drop it */
 	BATADV_FORW_NONE,
 };
@@ -36,7 +43,7 @@ enum batadv_forw_mode {
 
 enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       int *is_routable);
+		       unsigned short vid, int *is_routable);
 
 int batadv_mcast_forw_send(struct batadv_priv *bat_priv, struct sk_buff *skb,
 			   unsigned short vid, int is_routable);
@@ -57,11 +64,18 @@ void batadv_mcast_purge_orig(struct batadv_orig_node *orig_node);
 int batadv_mcast_forw_tracker_tvlv_handler(struct batadv_priv *bat_priv,
 					   struct sk_buff *skb);
 
+unsigned int batadv_mcast_forw_packet_hdrlen(unsigned int num_dests);
+
+bool batadv_mcast_forw_push(struct batadv_priv *bat_priv, struct sk_buff *skb,
+			    unsigned short vid, int is_routable, int count);
+
+int batadv_mcast_forw_mcsend(struct batadv_priv *bat_priv, struct sk_buff *skb);
+
 #else
 
 static inline enum batadv_forw_mode
 batadv_mcast_forw_mode(struct batadv_priv *bat_priv, struct sk_buff *skb,
-		       int *is_routable)
+		       unsigned short vid, int *is_routable)
 {
 	return BATADV_FORW_BCAST;
 }
@@ -99,6 +113,13 @@ static inline void batadv_mcast_purge_orig(struct batadv_orig_node *orig_node)
 {
 }
 
+static inline int batadv_mcast_forw_mcsend(struct batadv_priv *bat_priv,
+					   struct sk_buff *skb)
+{
+	kfree_skb(skb);
+	return NET_XMIT_DROP;
+}
+
 #endif /* CONFIG_BATMAN_ADV_MCAST */
 
 #endif /* _NET_BATMAN_ADV_MULTICAST_H_ */

net/batman-adv/soft-interface.c

@@ -301,12 +301,13 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 
 send:
 		if (do_bcast && !is_broadcast_ether_addr(ethhdr->h_dest)) {
-			forw_mode = batadv_mcast_forw_mode(bat_priv, skb,
+			forw_mode = batadv_mcast_forw_mode(bat_priv, skb, vid,
 							   &mcast_is_routable);
 			switch (forw_mode) {
 			case BATADV_FORW_BCAST:
 				break;
 			case BATADV_FORW_UCASTS:
+			case BATADV_FORW_MCAST:
 				do_bcast = false;
 				break;
 			case BATADV_FORW_NONE:
@@ -365,6 +366,8 @@ static netdev_tx_t batadv_interface_tx(struct sk_buff *skb,
 		} else if (forw_mode == BATADV_FORW_UCASTS) {
 			ret = batadv_mcast_forw_send(bat_priv, skb, vid,
 						     mcast_is_routable);
+		} else if (forw_mode == BATADV_FORW_MCAST) {
+			ret = batadv_mcast_forw_mcsend(bat_priv, skb);
 		} else {
 			if (batadv_dat_snoop_outgoing_arp_request(bat_priv,
 								  skb))
@@ -762,6 +765,7 @@ static int batadv_softif_init_late(struct net_device *dev)
 	atomic_set(&bat_priv->mcast.num_want_all_unsnoopables, 0);
 	atomic_set(&bat_priv->mcast.num_want_all_ipv4, 0);
 	atomic_set(&bat_priv->mcast.num_want_all_ipv6, 0);
+	atomic_set(&bat_priv->mcast.num_no_mc_ptype_capa, 0);
 #endif
 	atomic_set(&bat_priv->gw.mode, BATADV_GW_MODE_OFF);
 	atomic_set(&bat_priv->gw.bandwidth_down, 100);

net/batman-adv/types.h

@@ -1342,6 +1342,12 @@ struct batadv_priv_mcast {
 	/** @num_want_all_rtr6: counter for items in want_all_rtr6_list */
 	atomic_t num_want_all_rtr6;
 
+	/**
+	 * @num_no_mc_ptype_capa: counter for number of nodes without the
+	 *  BATADV_MCAST_HAVE_MC_PTYPE_CAPA flag
+	 */
+	atomic_t num_no_mc_ptype_capa;
+
 	/**
 	 * @want_lists_lock: lock for protecting modifications to mcasts
 	 *  want_all_{unsnoopables,ipv4,ipv6}_list (traversals are rcu-locked)