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>

Documentation/networking/batman-adv.txt

@@ -67,10 +67,11 @@ To deactivate an interface you have  to  write  "none"  into  its
 All  mesh  wide  settings  can be found in batman's own interface
 folder:
 
-#  ls  /sys/class/net/bat0/mesh/
-# aggregated_ogms   fragmentation gw_sel_class   vis_mode
-# ap_isolation      gw_bandwidth  hop_penalty
-# bonding           gw_mode       orig_interval
+# ls /sys/class/net/bat0/mesh/
+# aggregated_ogms        fragmentation          hop_penalty
+# ap_isolation           gw_bandwidth           log_level
+# bonding                gw_mode                orig_interval
+# bridge_loop_avoidance  gw_sel_class           vis_mode
 
 
 There is a special folder for debugging information:
@@ -202,12 +203,13 @@ abled  during run time. Following log_levels are defined:
 1 - Enable messages related to routing / flooding / broadcasting
 2 - Enable messages related to route added / changed / deleted
 4 - Enable messages related to translation table operations
-7 - Enable all messages
+8 - Enable messages related to bridge loop avoidance
+15 - enable all messages
 
 The debug output can be changed at runtime  using  the  file
 /sys/class/net/bat0/mesh/log_level. e.g.
 
-# echo 2 > /sys/class/net/bat0/mesh/log_level
+# echo 6 > /sys/class/net/bat0/mesh/log_level
 
 will enable debug messages for when routes change.
 

net/batman-adv/Kconfig

@@ -4,7 +4,7 @@
 
 config BATMAN_ADV
 	tristate "B.A.T.M.A.N. Advanced Meshing Protocol"
-	depends on NET
+	depends on NET && INET
 	select CRC16
         default n
 	help

net/batman-adv/Makefile

@@ -23,6 +23,7 @@ batman-adv-y += bat_debugfs.o
 batman-adv-y += bat_iv_ogm.o
 batman-adv-y += bat_sysfs.o
 batman-adv-y += bitarray.o
+batman-adv-y += bridge_loop_avoidance.o
 batman-adv-y += gateway_client.o
 batman-adv-y += gateway_common.o
 batman-adv-y += hard-interface.o

net/batman-adv/bat_sysfs.c

@@ -398,7 +398,7 @@ BAT_ATTR_UINT(gw_sel_class, S_IRUGO | S_IWUSR, 1, TQ_MAX_VALUE,
 static BAT_ATTR(gw_bandwidth, S_IRUGO | S_IWUSR, show_gw_bwidth,
 		store_gw_bwidth);
 #ifdef CONFIG_BATMAN_ADV_DEBUG
-BAT_ATTR_UINT(log_level, S_IRUGO | S_IWUSR, 0, 7, NULL);
+BAT_ATTR_UINT(log_level, S_IRUGO | S_IWUSR, 0, 15, NULL);
 #endif
 
 static struct bat_attribute *mesh_attrs[] = {