batman-adv: add basic bridge loop avoidance code

This second version of the bridge loop avoidance for batman-adv
avoids loops between the mesh and a backbone (usually a LAN).

By connecting multiple batman-adv mesh nodes to the same ethernet
segment a loop can be created when the soft-interface is bridged
into that ethernet segment. A simple visualization of the loop
involving the most common case - a LAN as ethernet segment:

node1  <-- LAN  -->  node2
  |                   |
wifi   <-- mesh -->  wifi

Packets from the LAN (e.g. ARP broadcasts) will circle forever from
node1 or node2 over the mesh back into the LAN.

With this patch, batman recognizes backbone gateways, nodes which are
part of the mesh and backbone/LAN at the same time. Each backbone
gateway "claims" clients from within the mesh to handle them
exclusively. By restricting that only responsible backbone gateways
may handle their claimed clients traffic, loops are effectively
avoided.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/batman-adv/packet.h b/net/batman-adv/packet.h
index 45e75ed6637d..59800e82371a 100644
--- a/net/batman-adv/packet.h
+++ b/net/batman-adv/packet.h
@@ -90,6 +90,23 @@ enum tt_client_flags {
         TT_CLIENT_PENDING = 1 << 10
 };
 
+/* claim frame types for the bridge loop avoidance */
+enum bla_claimframe {
+        CLAIM_TYPE_ADD          = 0x00,
+        CLAIM_TYPE_DEL          = 0x01,
+        CLAIM_TYPE_ANNOUNCE     = 0x02,
+        CLAIM_TYPE_REQUEST      = 0x03
+};
+
+/* the destination hardware field in the ARP frame is used to
+ * transport the claim type and the group id
+ */
+struct bla_claim_dst {
+        uint8_t magic[3];       /* FF:43:05 */
+        uint8_t type;           /* bla_claimframe */
+        uint16_t group;         /* group id */
+} __packed;
+
 struct batman_header {
         uint8_t  packet_type;
         uint8_t  version;  /* batman version field */