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 <[e-mail]>
Signed-off-by: Marek Lindner <[e-mail]>
Signed-off-by: Antonio Quartulli <[e-mail]>

Documentation/ABI/testing/sysfs-class-net-mesh

···
                 Defines the penalty which will be applied to an
                 originator message's tq-field on every hop.
 
+What:           /sys/class/net/<mesh_iface>/mesh/network_coding
+Date:           Nov 2012
+Contact:        Martin Hundeboll <[e-mail]>
+Description:
+                Controls whether Network Coding (using some magic
+                to send fewer wifi packets but still the same
+                content) is enabled or not.
+
 What:           /sys/class/net/<mesh_iface>/mesh/orig_interval
 Date:           May 2010
 Contact:        Marek Lindner <[e-mail]>

net/batman-adv/Kconfig

···
 	  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

net/batman-adv/Makefile

···
 batman-adv-y += hash.o
 batman-adv-y += icmp_socket.o
 batman-adv-y += main.o
+batman-adv-$(CONFIG_BATMAN_ADV_NC) += network-coding.o
 batman-adv-y += originator.o
 batman-adv-y += ring_buffer.o
 batman-adv-y += routing.o

net/batman-adv/main.c

···
 #include "vis.h"
 #include "hash.h"
 #include "bat_algo.h"
+#include "network-coding.h"
 
 
 /* List manipulations on hardif_list have to be rtnl_lock()'ed,
···
 	if (ret < 0)
 		goto err;
 
+	ret = batadv_nc_init(bat_priv);
+	if (ret < 0)
+		goto err;
+
 	atomic_set(&bat_priv->gw.reselect, 0);
 	atomic_set(&bat_priv->mesh_state, BATADV_MESH_ACTIVE);
 
···
 
 	batadv_gw_node_purge(bat_priv);
 	batadv_originator_free(bat_priv);
+	batadv_nc_free(bat_priv);
 
 	batadv_tt_free(bat_priv);
 

net/batman-adv/main.h

···
  * @BATADV_DBG_TT: translation table messages
  * @BATADV_DBG_BLA: bridge loop avoidance messages
  * @BATADV_DBG_DAT: ARP snooping and DAT related messages
+ * @BATADV_DBG_NC: network coding related messages
  * @BATADV_DBG_ALL: the union of all the above log levels
  */
 enum batadv_dbg_level {
···
 	BATADV_DBG_TT	  = BIT(2),
 	BATADV_DBG_BLA    = BIT(3),
 	BATADV_DBG_DAT    = BIT(4),
-	BATADV_DBG_ALL    = 31,
+	BATADV_DBG_NC	  = BIT(5),
+	BATADV_DBG_ALL    = 63,
 };
 
 #ifdef CONFIG_BATMAN_ADV_DEBUG

net/batman-adv/network-coding.c

···
+/* Copyright (C) 2012-2013 B.A.T.M.A.N. contributors:
+ *
+ * Martin Hundebøll, Jeppe Ledet-Pedersen
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA
+ */
+
+#include "main.h"
+#include "network-coding.h"
+
+static void batadv_nc_worker(struct work_struct *work);
+
+/**
+ * batadv_nc_start_timer - initialise the nc periodic worker
+ * @bat_priv: the bat priv with all the soft interface information
+ */
+static void batadv_nc_start_timer(struct batadv_priv *bat_priv)
+{
+	queue_delayed_work(batadv_event_workqueue, &bat_priv->nc.work,
+			   msecs_to_jiffies(10));
+}
+
+/**
+ * batadv_nc_init - initialise coding hash table and start house keeping
+ * @bat_priv: the bat priv with all the soft interface information
+ */
+int batadv_nc_init(struct batadv_priv *bat_priv)
+{
+	INIT_DELAYED_WORK(&bat_priv->nc.work, batadv_nc_worker);
+	batadv_nc_start_timer(bat_priv);
+
+	return 0;
+}
+
+/**
+ * batadv_nc_init_bat_priv - initialise the nc specific bat_priv variables
+ * @bat_priv: the bat priv with all the soft interface information
+ */
+void batadv_nc_init_bat_priv(struct batadv_priv *bat_priv)
+{
+	atomic_set(&bat_priv->network_coding, 1);
+}
+
+/**
+ * batadv_nc_worker - periodic task for house keeping related to network coding
+ * @work: kernel work struct
+ */
+static void batadv_nc_worker(struct work_struct *work)
+{
+	struct delayed_work *delayed_work;
+	struct batadv_priv_nc *priv_nc;
+	struct batadv_priv *bat_priv;
+
+	delayed_work = container_of(work, struct delayed_work, work);
+	priv_nc = container_of(delayed_work, struct batadv_priv_nc, work);
+	bat_priv = container_of(priv_nc, struct batadv_priv, nc);
+
+	/* Schedule a new check */
+	batadv_nc_start_timer(bat_priv);
+}
+
+/**
+ * batadv_nc_free - clean up network coding memory
+ * @bat_priv: the bat priv with all the soft interface information
+ */
+void batadv_nc_free(struct batadv_priv *bat_priv)
+{
+	cancel_delayed_work_sync(&bat_priv->nc.work);
+}

net/batman-adv/network-coding.h

···
+/* Copyright (C) 2012-2013 B.A.T.M.A.N. contributors:
+ *
+ * Martin Hundebøll, Jeppe Ledet-Pedersen
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA
+ */
+
+#ifndef _NET_BATMAN_ADV_NETWORK_CODING_H_
+#define _NET_BATMAN_ADV_NETWORK_CODING_H_
+
+#ifdef CONFIG_BATMAN_ADV_NC
+
+int batadv_nc_init(struct batadv_priv *bat_priv);
+void batadv_nc_free(struct batadv_priv *bat_priv);
+void batadv_nc_init_bat_priv(struct batadv_priv *bat_priv);
+
+#else /* ifdef CONFIG_BATMAN_ADV_NC */
+
+static inline int batadv_nc_init(struct batadv_priv *bat_priv)
+{
+	return 0;
+}
+
+static inline void batadv_nc_free(struct batadv_priv *bat_priv)
+{
+	return;
+}
+
+static inline void batadv_nc_init_bat_priv(struct batadv_priv *bat_priv)
+{
+	return;
+}
+
+#endif /* ifdef CONFIG_BATMAN_ADV_NC */
+
+#endif /* _NET_BATMAN_ADV_NETWORK_CODING_H_ */

net/batman-adv/soft-interface.c

···
 #include <linux/if_ether.h>
 #include "unicast.h"
 #include "bridge_loop_avoidance.h"
+#include "network-coding.h"
 
 
 static int batadv_get_settings(struct net_device *dev, struct ethtool_cmd *cmd);
···
 	ret = batadv_algo_select(bat_priv, batadv_routing_algo);
 	if (ret < 0)
 		goto unreg_soft_iface;
+
+	batadv_nc_init_bat_priv(bat_priv);
 
 	ret = batadv_sysfs_add_meshif(soft_iface);
 	if (ret < 0)

net/batman-adv/sysfs.c

···
 #ifdef CONFIG_BATMAN_ADV_DEBUG
 BATADV_ATTR_SIF_UINT(log_level, S_IRUGO | S_IWUSR, 0, BATADV_DBG_ALL, NULL);
 #endif
+#ifdef CONFIG_BATMAN_ADV_NC
+BATADV_ATTR_SIF_BOOL(network_coding, S_IRUGO | S_IWUSR, NULL);
+#endif
 
 static struct batadv_attribute *batadv_mesh_attrs[] = {
 	&batadv_attr_aggregated_ogms,
···
 	&batadv_attr_gw_bandwidth,
 #ifdef CONFIG_BATMAN_ADV_DEBUG
 	&batadv_attr_log_level,
+#endif
+#ifdef CONFIG_BATMAN_ADV_NC
+	&batadv_attr_network_coding,
 #endif
 	NULL,
 };

net/batman-adv/types.h

···
 #endif
 
 /**
+ * struct batadv_priv_nc - per mesh interface network coding private data
+ * @work: work queue callback item for cleanup
+ */
+struct batadv_priv_nc {
+	struct delayed_work work;
+};
+
+/**
  * struct batadv_priv - per mesh interface data
  * @mesh_state: current status of the mesh (inactive/active/deactivating)
  * @soft_iface: net device which holds this struct as private data
···
  * @tt: translation table data
  * @vis: vis data
  * @dat: distributed arp table data
+ * @network_coding: bool indicating whether network coding is enabled
+ * @batadv_priv_nc: network coding data
  */
 struct batadv_priv {
 	atomic_t mesh_state;
···
 #ifdef CONFIG_BATMAN_ADV_DAT
 	struct batadv_priv_dat dat;
 #endif
+#ifdef CONFIG_BATMAN_ADV_NC
+	atomic_t network_coding;
+	struct batadv_priv_nc nc;
+#endif /* CONFIG_BATMAN_ADV_NC */
 };
 
 /**