batman-adv: network coding - add the initial infrastructure code

Network coding exploits the 802.11 shared medium to allow multiple
packets to be sent in a single transmission. In brief, a relay can XOR
two packets, and send the coded packet to two destinations. The
receivers can decode one of the original packets by XOR'ing the coded
packet with the other original packet. This will lead to increased
throughput in topologies where two packets cross one relay.

In a simple topology with three nodes, it takes four transmissions
without network coding to get one packet from Node A to Node B and one
from Node B to Node A:

 1.  Node A  ---- p1 --->  Node R                Node B
 2.  Node A                Node R  <--- p2 ----  Node B
 3.  Node A  <--- p2 ----  Node R                Node B
 4.  Node A                Node R  ---- p1 --->  Node B

With network coding, the relay only needs one transmission, which saves
us one slot of valuable airtime:

 1.  Node A  ---- p1 --->  Node R                Node B
 2.  Node A                Node R  <--- p2 ----  Node B
 3.  Node A  <- p1 x p2 -  Node R  - p1 x p2 ->  Node B

The same principle holds for a topology including five nodes. Here the
packets from Node A and Node B are overheard by Node C and Node D,
respectively. This allows Node R to send a network coded packet to save
one transmission:

   Node A                  Node B

    |     \              /    |
    |      p1          p2     |
    |       \          /      |
    p1       > Node R <       p2
    |                         |
    |         /      \        |
    |    p1 x p2    p1 x p2   |
    v       /          \      v
           /            \
   Node C <              > Node D

More information is available on the open-mesh.org wiki[1].

This patch adds the initial code to support network coding in
batman-adv. It sets up a worker thread to do house keeping and adds a
sysfs file to enable/disable network coding. The feature is disabled by
default, as it requires a wifi-driver with working promiscuous mode, and
also because it adds a small delay at each hop.

[1] http://www.open-mesh.org/projects/batman-adv/wiki/Catwoman

Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/net/batman-adv/Kconfig b/net/batman-adv/Kconfig
index 8d8afb134b3a..fa780b76630e 100644
--- a/net/batman-adv/Kconfig
+++ b/net/batman-adv/Kconfig
@@ -36,6 +36,20 @@ config BATMAN_ADV_DAT
           mesh networks. If you think that your network does not need
           this option you can safely remove it and save some space.
 
+config BATMAN_ADV_NC
+        bool "Network Coding"
+        depends on BATMAN_ADV
+        default n
+        help
+          This option enables network coding, a mechanism that aims to
+          increase the overall network throughput by fusing multiple
+          packets in one transmission.
+          Note that interfaces controlled by batman-adv must be manually
+          configured to have promiscuous mode enabled in order to make
+          network coding work.
+          If you think that your network does not need this feature you
+          can safely disable it and save some space.
+
 config BATMAN_ADV_DEBUG
         bool "B.A.T.M.A.N. debugging"
         depends on BATMAN_ADV