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>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 850b184e5b04..00840d5784fe 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1343,6 +1343,12 @@ struct batadv_priv_mcast {
 	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)
 	 */