batman-adv: Use common Jenkins Hash implementation

[cascardo/linux.git] / net / batman-adv / network-coding.c

/* Copyright (C) 2012-2015 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, see <http://www.gnu.org/licenses/>.
 */

#include <linux/debugfs.h>

#include "main.h"
#include "hash.h"
#include "network-coding.h"
#include "send.h"
#include "originator.h"
#include "hard-interface.h"
#include "routing.h"

static struct lock_class_key batadv_nc_coding_hash_lock_class_key;
static struct lock_class_key batadv_nc_decoding_hash_lock_class_key;

static void batadv_nc_worker(struct work_struct *work);
static int batadv_nc_recv_coded_packet(struct sk_buff *skb,
                                       struct batadv_hard_iface *recv_if);

/**
 * batadv_nc_init - one-time initialization for network coding
 */
int __init batadv_nc_init(void)
{
        int ret;

        /* Register our packet type */
        ret = batadv_recv_handler_register(BATADV_CODED,
                                           batadv_nc_recv_coded_packet);

        return ret;
}

/**
 * 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_tvlv_container_update - update the network coding tvlv container
 *  after network coding setting change
 * @bat_priv: the bat priv with all the soft interface information
 */
static void batadv_nc_tvlv_container_update(struct batadv_priv *bat_priv)
{
        char nc_mode;

        nc_mode = atomic_read(&bat_priv->network_coding);

        switch (nc_mode) {
        case 0:
                batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_NC, 1);
                break;
        case 1:
                batadv_tvlv_container_register(bat_priv, BATADV_TVLV_NC, 1,
                                               NULL, 0);
                break;
        }
}

/**
 * batadv_nc_status_update - update the network coding tvlv container after
 *  network coding setting change
 * @net_dev: the soft interface net device
 */
void batadv_nc_status_update(struct net_device *net_dev)
{
        struct batadv_priv *bat_priv = netdev_priv(net_dev);

        batadv_nc_tvlv_container_update(bat_priv);
}

/**
 * batadv_nc_tvlv_ogm_handler_v1 - process incoming nc tvlv container
 * @bat_priv: the bat priv with all the soft interface information
 * @orig: the orig_node of the ogm
 * @flags: flags indicating the tvlv state (see batadv_tvlv_handler_flags)
 * @tvlv_value: tvlv buffer containing the gateway data
 * @tvlv_value_len: tvlv buffer length
 */
static void batadv_nc_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
                                          struct batadv_orig_node *orig,
                                          uint8_t flags,
                                          void *tvlv_value,
                                          uint16_t tvlv_value_len)
{
        if (flags & BATADV_TVLV_HANDLER_OGM_CIFNOTFND)
                orig->capabilities &= ~BATADV_ORIG_CAPA_HAS_NC;
        else
                orig->capabilities |= BATADV_ORIG_CAPA_HAS_NC;
}

/**
 * batadv_nc_mesh_init - initialise coding hash table and start house keeping
 * @bat_priv: the bat priv with all the soft interface information
 */
int batadv_nc_mesh_init(struct batadv_priv *bat_priv)
{
        bat_priv->nc.timestamp_fwd_flush = jiffies;
        bat_priv->nc.timestamp_sniffed_purge = jiffies;

        if (bat_priv->nc.coding_hash || bat_priv->nc.decoding_hash)
                return 0;

        bat_priv->nc.coding_hash = batadv_hash_new(128);
        if (!bat_priv->nc.coding_hash)
                goto err;

        batadv_hash_set_lock_class(bat_priv->nc.coding_hash,
                                   &batadv_nc_coding_hash_lock_class_key);

        bat_priv->nc.decoding_hash = batadv_hash_new(128);
        if (!bat_priv->nc.decoding_hash)
                goto err;

        batadv_hash_set_lock_class(bat_priv->nc.decoding_hash,
                                   &batadv_nc_decoding_hash_lock_class_key);

        INIT_DELAYED_WORK(&bat_priv->nc.work, batadv_nc_worker);
        batadv_nc_start_timer(bat_priv);

        batadv_tvlv_handler_register(bat_priv, batadv_nc_tvlv_ogm_handler_v1,
                                     NULL, BATADV_TVLV_NC, 1,
                                     BATADV_TVLV_HANDLER_OGM_CIFNOTFND);
        batadv_nc_tvlv_container_update(bat_priv);
        return 0;

err:
        return -ENOMEM;
}

/**
 * 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, 0);
        bat_priv->nc.min_tq = 200;
        bat_priv->nc.max_fwd_delay = 10;
        bat_priv->nc.max_buffer_time = 200;
}

/**
 * batadv_nc_init_orig - initialise the nc fields of an orig_node
 * @orig_node: the orig_node which is going to be initialised
 */
void batadv_nc_init_orig(struct batadv_orig_node *orig_node)
{
        INIT_LIST_HEAD(&orig_node->in_coding_list);
        INIT_LIST_HEAD(&orig_node->out_coding_list);
        spin_lock_init(&orig_node->in_coding_list_lock);
        spin_lock_init(&orig_node->out_coding_list_lock);
}

/**
 * batadv_nc_node_free_rcu - rcu callback to free an nc node and remove
 *  its refcount on the orig_node
 * @rcu: rcu pointer of the nc node
 */
static void batadv_nc_node_free_rcu(struct rcu_head *rcu)
{
        struct batadv_nc_node *nc_node;

        nc_node = container_of(rcu, struct batadv_nc_node, rcu);
        batadv_orig_node_free_ref(nc_node->orig_node);
        kfree(nc_node);
}

/**
 * batadv_nc_node_free_ref - decrements the nc node refcounter and possibly
 * frees it
 * @nc_node: the nc node to free
 */
static void batadv_nc_node_free_ref(struct batadv_nc_node *nc_node)
{
        if (atomic_dec_and_test(&nc_node->refcount))
                call_rcu(&nc_node->rcu, batadv_nc_node_free_rcu);
}

/**
 * batadv_nc_path_free_ref - decrements the nc path refcounter and possibly
 * frees it
 * @nc_path: the nc node to free
 */
static void batadv_nc_path_free_ref(struct batadv_nc_path *nc_path)
{
        if (atomic_dec_and_test(&nc_path->refcount))
                kfree_rcu(nc_path, rcu);
}

/**
 * batadv_nc_packet_free - frees nc packet
 * @nc_packet: the nc packet to free
 */
static void batadv_nc_packet_free(struct batadv_nc_packet *nc_packet)
{
        if (nc_packet->skb)
                kfree_skb(nc_packet->skb);

        batadv_nc_path_free_ref(nc_packet->nc_path);
        kfree(nc_packet);
}

/**
 * batadv_nc_to_purge_nc_node - checks whether an nc node has to be purged
 * @bat_priv: the bat priv with all the soft interface information
 * @nc_node: the nc node to check
 *
 * Returns true if the entry has to be purged now, false otherwise
 */
static bool batadv_nc_to_purge_nc_node(struct batadv_priv *bat_priv,
                                       struct batadv_nc_node *nc_node)
{
        if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
                return true;

        return batadv_has_timed_out(nc_node->last_seen, BATADV_NC_NODE_TIMEOUT);
}

/**
 * batadv_nc_to_purge_nc_path_coding - checks whether an nc path has timed out
 * @bat_priv: the bat priv with all the soft interface information
 * @nc_path: the nc path to check
 *
 * Returns true if the entry has to be purged now, false otherwise
 */
static bool batadv_nc_to_purge_nc_path_coding(struct batadv_priv *bat_priv,
                                              struct batadv_nc_path *nc_path)
{
        if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
                return true;

        /* purge the path when no packets has been added for 10 times the
         * max_fwd_delay time
         */
        return batadv_has_timed_out(nc_path->last_valid,
                                    bat_priv->nc.max_fwd_delay * 10);
}

/**
 * batadv_nc_to_purge_nc_path_decoding - checks whether an nc path has timed out
 * @bat_priv: the bat priv with all the soft interface information
 * @nc_path: the nc path to check
 *
 * Returns true if the entry has to be purged now, false otherwise
 */
static bool batadv_nc_to_purge_nc_path_decoding(struct batadv_priv *bat_priv,
                                                struct batadv_nc_path *nc_path)
{
        if (atomic_read(&bat_priv->mesh_state) != BATADV_MESH_ACTIVE)
                return true;

        /* purge the path when no packets has been added for 10 times the
         * max_buffer time
         */
        return batadv_has_timed_out(nc_path->last_valid,
                                    bat_priv->nc.max_buffer_time * 10);
}

/**
 * batadv_nc_purge_orig_nc_nodes - go through list of nc nodes and purge stale
 *  entries
 * @bat_priv: the bat priv with all the soft interface information
 * @list: list of nc nodes
 * @lock: nc node list lock
 * @to_purge: function in charge to decide whether an entry has to be purged or
 *            not. This function takes the nc node as argument and has to return
 *            a boolean value: true if the entry has to be deleted, false
 *            otherwise
 */
static void
batadv_nc_purge_orig_nc_nodes(struct batadv_priv *bat_priv,
                              struct list_head *list,
                              spinlock_t *lock,
                              bool (*to_purge)(struct batadv_priv *,
                                               struct batadv_nc_node *))
{
        struct batadv_nc_node *nc_node, *nc_node_tmp;

        /* For each nc_node in list */
        spin_lock_bh(lock);
        list_for_each_entry_safe(nc_node, nc_node_tmp, list, list) {
                /* if an helper function has been passed as parameter,
                 * ask it if the entry has to be purged or not
                 */
                if (to_purge && !to_purge(bat_priv, nc_node))
                        continue;

                batadv_dbg(BATADV_DBG_NC, bat_priv,
                           "Removing nc_node %pM -> %pM\n",
                           nc_node->addr, nc_node->orig_node->orig);
                list_del_rcu(&nc_node->list);
                batadv_nc_node_free_ref(nc_node);
        }
        spin_unlock_bh(lock);
}

/**
 * batadv_nc_purge_orig - purges all nc node data attached of the given
 *  originator
 * @bat_priv: the bat priv with all the soft interface information
 * @orig_node: orig_node with the nc node entries to be purged
 * @to_purge: function in charge to decide whether an entry has to be purged or
 *            not. This function takes the nc node as argument and has to return
 *            a boolean value: true is the entry has to be deleted, false
 *            otherwise
 */
void batadv_nc_purge_orig(struct batadv_priv *bat_priv,
                          struct batadv_orig_node *orig_node,
                          bool (*to_purge)(struct batadv_priv *,
                                           struct batadv_nc_node *))
{
        /* Check ingoing nc_node's of this orig_node */
        batadv_nc_purge_orig_nc_nodes(bat_priv, &orig_node->in_coding_list,
                                      &orig_node->in_coding_list_lock,
                                      to_purge);

        /* Check outgoing nc_node's of this orig_node */
        batadv_nc_purge_orig_nc_nodes(bat_priv, &orig_node->out_coding_list,
                                      &orig_node->out_coding_list_lock,
                                      to_purge);
}

/**
 * batadv_nc_purge_orig_hash - traverse entire originator hash to check if they
 *  have timed out nc nodes
 * @bat_priv: the bat priv with all the soft interface information
 */
static void batadv_nc_purge_orig_hash(struct batadv_priv *bat_priv)
{
        struct batadv_hashtable *hash = bat_priv->orig_hash;
        struct hlist_head *head;
        struct batadv_orig_node *orig_node;
        uint32_t i;

        if (!hash)
                return;

        /* For each orig_node */
        for (i = 0; i < hash->size; i++) {
                head = &hash->table[i];

                rcu_read_lock();
                hlist_for_each_entry_rcu(orig_node, head, hash_entry)
                        batadv_nc_purge_orig(bat_priv, orig_node,
                                             batadv_nc_to_purge_nc_node);
                rcu_read_unlock();
        }
}

/**
 * batadv_nc_purge_paths - traverse all nc paths part of the hash and remove
 *  unused ones
 * @bat_priv: the bat priv with all the soft interface information
 * @hash: hash table containing the nc paths to check
 * @to_purge: function in charge to decide whether an entry has to be purged or
 *            not. This function takes the nc node as argument and has to return
 *            a boolean value: true is the entry has to be deleted, false
 *            otherwise
 */
static void batadv_nc_purge_paths(struct batadv_priv *bat_priv,
                                  struct batadv_hashtable *hash,
                                  bool (*to_purge)(struct batadv_priv *,
                                                   struct batadv_nc_path *))
{
        struct hlist_head *head;
        struct hlist_node *node_tmp;
        struct batadv_nc_path *nc_path;
        spinlock_t *lock; /* Protects lists in hash */
        uint32_t i;

        for (i = 0; i < hash->size; i++) {
                head = &hash->table[i];
                lock = &hash->list_locks[i];

                /* For each nc_path in this bin */
                spin_lock_bh(lock);
                hlist_for_each_entry_safe(nc_path, node_tmp, head, hash_entry) {
                        /* if an helper function has been passed as parameter,
                         * ask it if the entry has to be purged or not
                         */
                        if (to_purge && !to_purge(bat_priv, nc_path))
                                continue;

                        /* purging an non-empty nc_path should never happen, but
                         * is observed under high CPU load. Delay the purging
                         * until next iteration to allow the packet_list to be
                         * emptied first.
                         */
                        if (!unlikely(list_empty(&nc_path->packet_list))) {
                                net_ratelimited_function(printk,
                                                         KERN_WARNING
                                                         "Skipping free of non-empty nc_path (%pM -> %pM)!\n",
                                                         nc_path->prev_hop,
                                                         nc_path->next_hop);
                                continue;
                        }

                        /* nc_path is unused, so remove it */
                        batadv_dbg(BATADV_DBG_NC, bat_priv,
                                   "Remove nc_path %pM -> %pM\n",
                                   nc_path->prev_hop, nc_path->next_hop);
                        hlist_del_rcu(&nc_path->hash_entry);
                        batadv_nc_path_free_ref(nc_path);
                }
                spin_unlock_bh(lock);
        }
}

/**
 * batadv_nc_hash_key_gen - computes the nc_path hash key
 * @key: buffer to hold the final hash key
 * @src: source ethernet mac address going into the hash key
 * @dst: destination ethernet mac address going into the hash key
 */
static void batadv_nc_hash_key_gen(struct batadv_nc_path *key, const char *src,
                                   const char *dst)
{
        memcpy(key->prev_hop, src, sizeof(key->prev_hop));
        memcpy(key->next_hop, dst, sizeof(key->next_hop));
}

/**
 * batadv_nc_hash_choose - compute the hash value for an nc path
 * @data: data to hash
 * @size: size of the hash table
 *
 * Returns the selected index in the hash table for the given data.
 */
static uint32_t batadv_nc_hash_choose(const void *data, uint32_t size)
{
        const struct batadv_nc_path *nc_path = data;
        uint32_t hash = 0;

        hash = jhash(&nc_path->prev_hop, sizeof(nc_path->prev_hop), hash);
        hash = jhash(&nc_path->next_hop, sizeof(nc_path->next_hop), hash);

        return hash % size;
}

/**
 * batadv_nc_hash_compare - comparing function used in the network coding hash
 *  tables
 * @node: node in the local table
 * @data2: second object to compare the node to
 *
 * Returns 1 if the two entry are the same, 0 otherwise
 */
static int batadv_nc_hash_compare(const struct hlist_node *node,
                                  const void *data2)
{
        const struct batadv_nc_path *nc_path1, *nc_path2;

        nc_path1 = container_of(node, struct batadv_nc_path, hash_entry);
        nc_path2 = data2;

        /* Return 1 if the two keys are identical */
        if (memcmp(nc_path1->prev_hop, nc_path2->prev_hop,
                   sizeof(nc_path1->prev_hop)) != 0)
                return 0;

        if (memcmp(nc_path1->next_hop, nc_path2->next_hop,
                   sizeof(nc_path1->next_hop)) != 0)
                return 0;

        return 1;
}

/**
 * batadv_nc_hash_find - search for an existing nc path and return it
 * @hash: hash table containing the nc path
 * @data: search key
 *
 * Returns the nc_path if found, NULL otherwise.
 */
static struct batadv_nc_path *
batadv_nc_hash_find(struct batadv_hashtable *hash,
                    void *data)
{
        struct hlist_head *head;
        struct batadv_nc_path *nc_path, *nc_path_tmp = NULL;
        int index;

        if (!hash)
                return NULL;

        index = batadv_nc_hash_choose(data, hash->size);
        head = &hash->table[index];

        rcu_read_lock();
        hlist_for_each_entry_rcu(nc_path, head, hash_entry) {
                if (!batadv_nc_hash_compare(&nc_path->hash_entry, data))
                        continue;

                if (!atomic_inc_not_zero(&nc_path->refcount))
                        continue;

                nc_path_tmp = nc_path;
                break;
        }
        rcu_read_unlock();

        return nc_path_tmp;
}

/**
 * batadv_nc_send_packet - send non-coded packet and free nc_packet struct
 * @nc_packet: the nc packet to send
 */
static void batadv_nc_send_packet(struct batadv_nc_packet *nc_packet)
{
        batadv_send_skb_packet(nc_packet->skb,
                               nc_packet->neigh_node->if_incoming,
                               nc_packet->nc_path->next_hop);
        nc_packet->skb = NULL;
        batadv_nc_packet_free(nc_packet);
}

/**
 * batadv_nc_sniffed_purge - Checks timestamp of given sniffed nc_packet.
 * @bat_priv: the bat priv with all the soft interface information
 * @nc_path: the nc path the packet belongs to
 * @nc_packet: the nc packet to be checked
 *
 * Checks whether the given sniffed (overheard) nc_packet has hit its buffering
 * timeout. If so, the packet is no longer kept and the entry deleted from the
 * queue. Has to be called with the appropriate locks.
 *
 * Returns false as soon as the entry in the fifo queue has not been timed out
 * yet and true otherwise.
 */
static bool batadv_nc_sniffed_purge(struct batadv_priv *bat_priv,
                                    struct batadv_nc_path *nc_path,
                                    struct batadv_nc_packet *nc_packet)
{
        unsigned long timeout = bat_priv->nc.max_buffer_time;
        bool res = false;

        /* Packets are added to tail, so the remaining packets did not time
         * out and we can stop processing the current queue
         */
        if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_ACTIVE &&
            !batadv_has_timed_out(nc_packet->timestamp, timeout))
                goto out;

        /* purge nc packet */
        list_del(&nc_packet->list);
        batadv_nc_packet_free(nc_packet);

        res = true;

out:
        return res;
}

/**
 * batadv_nc_fwd_flush - Checks the timestamp of the given nc packet.
 * @bat_priv: the bat priv with all the soft interface information
 * @nc_path: the nc path the packet belongs to
 * @nc_packet: the nc packet to be checked
 *
 * Checks whether the given nc packet has hit its forward timeout. If so, the
 * packet is no longer delayed, immediately sent and the entry deleted from the
 * queue. Has to be called with the appropriate locks.
 *
 * Returns false as soon as the entry in the fifo queue has not been timed out
 * yet and true otherwise.
 */
static bool batadv_nc_fwd_flush(struct batadv_priv *bat_priv,
                                struct batadv_nc_path *nc_path,
                                struct batadv_nc_packet *nc_packet)
{
        unsigned long timeout = bat_priv->nc.max_fwd_delay;

        /* Packets are added to tail, so the remaining packets did not time
         * out and we can stop processing the current queue
         */
        if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_ACTIVE &&
            !batadv_has_timed_out(nc_packet->timestamp, timeout))
                return false;

        /* Send packet */
        batadv_inc_counter(bat_priv, BATADV_CNT_FORWARD);
        batadv_add_counter(bat_priv, BATADV_CNT_FORWARD_BYTES,
                           nc_packet->skb->len + ETH_HLEN);
        list_del(&nc_packet->list);
        batadv_nc_send_packet(nc_packet);

        return true;
}

/**
 * batadv_nc_process_nc_paths - traverse given nc packet pool and free timed out
 *  nc packets
 * @bat_priv: the bat priv with all the soft interface information
 * @hash: to be processed hash table
 * @process_fn: Function called to process given nc packet. Should return true
 *              to encourage this function to proceed with the next packet.
 *              Otherwise the rest of the current queue is skipped.
 */
static void
batadv_nc_process_nc_paths(struct batadv_priv *bat_priv,
                           struct batadv_hashtable *hash,
                           bool (*process_fn)(struct batadv_priv *,
                                              struct batadv_nc_path *,
                                              struct batadv_nc_packet *))
{
        struct hlist_head *head;
        struct batadv_nc_packet *nc_packet, *nc_packet_tmp;
        struct batadv_nc_path *nc_path;
        bool ret;
        int i;

        if (!hash)
                return;

        /* Loop hash table bins */
        for (i = 0; i < hash->size; i++) {
                head = &hash->table[i];

                /* Loop coding paths */
                rcu_read_lock();
                hlist_for_each_entry_rcu(nc_path, head, hash_entry) {
                        /* Loop packets */
                        spin_lock_bh(&nc_path->packet_list_lock);
                        list_for_each_entry_safe(nc_packet, nc_packet_tmp,
                                                 &nc_path->packet_list, list) {
                                ret = process_fn(bat_priv, nc_path, nc_packet);
                                if (!ret)
                                        break;
                        }
                        spin_unlock_bh(&nc_path->packet_list_lock);
                }
                rcu_read_unlock();
        }
}

/**
 * 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;
        unsigned long timeout;

        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);

        batadv_nc_purge_orig_hash(bat_priv);
        batadv_nc_purge_paths(bat_priv, bat_priv->nc.coding_hash,
                              batadv_nc_to_purge_nc_path_coding);
        batadv_nc_purge_paths(bat_priv, bat_priv->nc.decoding_hash,
                              batadv_nc_to_purge_nc_path_decoding);

        timeout = bat_priv->nc.max_fwd_delay;

        if (batadv_has_timed_out(bat_priv->nc.timestamp_fwd_flush, timeout)) {
                batadv_nc_process_nc_paths(bat_priv, bat_priv->nc.coding_hash,
                                           batadv_nc_fwd_flush);
                bat_priv->nc.timestamp_fwd_flush = jiffies;
        }

        if (batadv_has_timed_out(bat_priv->nc.timestamp_sniffed_purge,
                                 bat_priv->nc.max_buffer_time)) {
                batadv_nc_process_nc_paths(bat_priv, bat_priv->nc.decoding_hash,
                                           batadv_nc_sniffed_purge);
                bat_priv->nc.timestamp_sniffed_purge = jiffies;
        }

        /* Schedule a new check */
        batadv_nc_start_timer(bat_priv);
}

/**
 * batadv_can_nc_with_orig - checks whether the given orig node is suitable for
 *  coding or not
 * @bat_priv: the bat priv with all the soft interface information
 * @orig_node: neighboring orig node which may be used as nc candidate
 * @ogm_packet: incoming ogm packet also used for the checks
 *
 * Returns true if:
 *  1) The OGM must have the most recent sequence number.
 *  2) The TTL must be decremented by one and only one.
 *  3) The OGM must be received from the first hop from orig_node.
 *  4) The TQ value of the OGM must be above bat_priv->nc.min_tq.
 */
static bool batadv_can_nc_with_orig(struct batadv_priv *bat_priv,
                                    struct batadv_orig_node *orig_node,
                                    struct batadv_ogm_packet *ogm_packet)
{
        struct batadv_orig_ifinfo *orig_ifinfo;
        uint32_t last_real_seqno;
        uint8_t last_ttl;

        orig_ifinfo = batadv_orig_ifinfo_get(orig_node, BATADV_IF_DEFAULT);
        if (!orig_ifinfo)
                return false;

        last_ttl = orig_ifinfo->last_ttl;
        last_real_seqno = orig_ifinfo->last_real_seqno;
        batadv_orig_ifinfo_free_ref(orig_ifinfo);

        if (last_real_seqno != ntohl(ogm_packet->seqno))
                return false;
        if (last_ttl != ogm_packet->ttl + 1)
                return false;
        if (!batadv_compare_eth(ogm_packet->orig, ogm_packet->prev_sender))
                return false;
        if (ogm_packet->tq < bat_priv->nc.min_tq)
                return false;

        return true;
}

/**
 * batadv_nc_find_nc_node - search for an existing nc node and return it
 * @orig_node: orig node originating the ogm packet
 * @orig_neigh_node: neighboring orig node from which we received the ogm packet
 *  (can be equal to orig_node)
 * @in_coding: traverse incoming or outgoing network coding list
 *
 * Returns the nc_node if found, NULL otherwise.
 */
static struct batadv_nc_node
*batadv_nc_find_nc_node(struct batadv_orig_node *orig_node,
                        struct batadv_orig_node *orig_neigh_node,
                        bool in_coding)
{
        struct batadv_nc_node *nc_node, *nc_node_out = NULL;
        struct list_head *list;

        if (in_coding)
                list = &orig_neigh_node->in_coding_list;
        else
                list = &orig_neigh_node->out_coding_list;

        /* Traverse list of nc_nodes to orig_node */
        rcu_read_lock();
        list_for_each_entry_rcu(nc_node, list, list) {
                if (!batadv_compare_eth(nc_node->addr, orig_node->orig))
                        continue;

                if (!atomic_inc_not_zero(&nc_node->refcount))
                        continue;

                /* Found a match */
                nc_node_out = nc_node;
                break;
        }
        rcu_read_unlock();

        return nc_node_out;
}

/**
 * batadv_nc_get_nc_node - retrieves an nc node or creates the entry if it was
 *  not found
 * @bat_priv: the bat priv with all the soft interface information
 * @orig_node: orig node originating the ogm packet
 * @orig_neigh_node: neighboring orig node from which we received the ogm packet
 *  (can be equal to orig_node)
 * @in_coding: traverse incoming or outgoing network coding list
 *
 * Returns the nc_node if found or created, NULL in case of an error.
 */
static struct batadv_nc_node
*batadv_nc_get_nc_node(struct batadv_priv *bat_priv,
                       struct batadv_orig_node *orig_node,
                       struct batadv_orig_node *orig_neigh_node,
                       bool in_coding)
{
        struct batadv_nc_node *nc_node;
        spinlock_t *lock; /* Used to lock list selected by "int in_coding" */
        struct list_head *list;

        /* Check if nc_node is already added */
        nc_node = batadv_nc_find_nc_node(orig_node, orig_neigh_node, in_coding);

        /* Node found */
        if (nc_node)
                return nc_node;

        nc_node = kzalloc(sizeof(*nc_node), GFP_ATOMIC);
        if (!nc_node)
                return NULL;

        if (!atomic_inc_not_zero(&orig_neigh_node->refcount))
                goto free;

        /* Initialize nc_node */
        INIT_LIST_HEAD(&nc_node->list);
        ether_addr_copy(nc_node->addr, orig_node->orig);
        nc_node->orig_node = orig_neigh_node;
        atomic_set(&nc_node->refcount, 2);

        /* Select ingoing or outgoing coding node */
        if (in_coding) {
                lock = &orig_neigh_node->in_coding_list_lock;
                list = &orig_neigh_node->in_coding_list;
        } else {
                lock = &orig_neigh_node->out_coding_list_lock;
                list = &orig_neigh_node->out_coding_list;
        }

        batadv_dbg(BATADV_DBG_NC, bat_priv, "Adding nc_node %pM -> %pM\n",
                   nc_node->addr, nc_node->orig_node->orig);

        /* Add nc_node to orig_node */
        spin_lock_bh(lock);
        list_add_tail_rcu(&nc_node->list, list);
        spin_unlock_bh(lock);

        return nc_node;

free:
        kfree(nc_node);
        return NULL;
}

/**
 * batadv_nc_update_nc_node - updates stored incoming and outgoing nc node structs
 *  (best called on incoming OGMs)
 * @bat_priv: the bat priv with all the soft interface information
 * @orig_node: orig node originating the ogm packet
 * @orig_neigh_node: neighboring orig node from which we received the ogm packet
 *  (can be equal to orig_node)
 * @ogm_packet: incoming ogm packet
 * @is_single_hop_neigh: orig_node is a single hop neighbor
 */
void batadv_nc_update_nc_node(struct batadv_priv *bat_priv,
                              struct batadv_orig_node *orig_node,
                              struct batadv_orig_node *orig_neigh_node,
                              struct batadv_ogm_packet *ogm_packet,
                              int is_single_hop_neigh)
{
        struct batadv_nc_node *in_nc_node = NULL, *out_nc_node = NULL;

        /* Check if network coding is enabled */
        if (!atomic_read(&bat_priv->network_coding))
                goto out;

        /* check if orig node is network coding enabled */
        if (!(orig_node->capabilities & BATADV_ORIG_CAPA_HAS_NC))
                goto out;

        /* accept ogms from 'good' neighbors and single hop neighbors */
        if (!batadv_can_nc_with_orig(bat_priv, orig_node, ogm_packet) &&
            !is_single_hop_neigh)
                goto out;

        /* Add orig_node as in_nc_node on hop */
        in_nc_node = batadv_nc_get_nc_node(bat_priv, orig_node,
                                           orig_neigh_node, true);
        if (!in_nc_node)
                goto out;

        in_nc_node->last_seen = jiffies;

        /* Add hop as out_nc_node on orig_node */
        out_nc_node = batadv_nc_get_nc_node(bat_priv, orig_neigh_node,
                                            orig_node, false);
        if (!out_nc_node)
                goto out;

        out_nc_node->last_seen = jiffies;

out:
        if (in_nc_node)
                batadv_nc_node_free_ref(in_nc_node);
        if (out_nc_node)
                batadv_nc_node_free_ref(out_nc_node);
}

/**
 * batadv_nc_get_path - get existing nc_path or allocate a new one
 * @bat_priv: the bat priv with all the soft interface information
 * @hash: hash table containing the nc path
 * @src: ethernet source address - first half of the nc path search key
 * @dst: ethernet destination address - second half of the nc path search key
 *
 * Returns pointer to nc_path if the path was found or created, returns NULL
 * on error.
 */
static struct batadv_nc_path *batadv_nc_get_path(struct batadv_priv *bat_priv,
                                                 struct batadv_hashtable *hash,
                                                 uint8_t *src,
                                                 uint8_t *dst)
{
        int hash_added;
        struct batadv_nc_path *nc_path, nc_path_key;

        batadv_nc_hash_key_gen(&nc_path_key, src, dst);

        /* Search for existing nc_path */
        nc_path = batadv_nc_hash_find(hash, (void *)&nc_path_key);

        if (nc_path) {
                /* Set timestamp to delay removal of nc_path */
                nc_path->last_valid = jiffies;
                return nc_path;
        }

        /* No existing nc_path was found; create a new */
        nc_path = kzalloc(sizeof(*nc_path), GFP_ATOMIC);

        if (!nc_path)
                return NULL;

        /* Initialize nc_path */
        INIT_LIST_HEAD(&nc_path->packet_list);
        spin_lock_init(&nc_path->packet_list_lock);
        atomic_set(&nc_path->refcount, 2);
        nc_path->last_valid = jiffies;
        ether_addr_copy(nc_path->next_hop, dst);
        ether_addr_copy(nc_path->prev_hop, src);

        batadv_dbg(BATADV_DBG_NC, bat_priv, "Adding nc_path %pM -> %pM\n",
                   nc_path->prev_hop,
                   nc_path->next_hop);

        /* Add nc_path to hash table */
        hash_added = batadv_hash_add(hash, batadv_nc_hash_compare,
                                     batadv_nc_hash_choose, &nc_path_key,
                                     &nc_path->hash_entry);

        if (hash_added < 0) {
                kfree(nc_path);
                return NULL;
        }

        return nc_path;
}

/**
 * batadv_nc_random_weight_tq - scale the receivers TQ-value to avoid unfair
 *  selection of a receiver with slightly lower TQ than the other
 * @tq: to be weighted tq value
 */
static uint8_t batadv_nc_random_weight_tq(uint8_t tq)
{
        uint8_t rand_val, rand_tq;

        get_random_bytes(&rand_val, sizeof(rand_val));

        /* randomize the estimated packet loss (max TQ - estimated TQ) */
        rand_tq = rand_val * (BATADV_TQ_MAX_VALUE - tq);

        /* normalize the randomized packet loss */
        rand_tq /= BATADV_TQ_MAX_VALUE;

        /* convert to (randomized) estimated tq again */
        return BATADV_TQ_MAX_VALUE - rand_tq;
}

/**
 * batadv_nc_memxor - XOR destination with source
 * @dst: byte array to XOR into
 * @src: byte array to XOR from
 * @len: length of destination array
 */
static void batadv_nc_memxor(char *dst, const char *src, unsigned int len)
{
        unsigned int i;

        for (i = 0; i < len; ++i)
                dst[i] ^= src[i];
}

/**
 * batadv_nc_code_packets - code a received unicast_packet with an nc packet
 *  into a coded_packet and send it
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: data skb to forward
 * @ethhdr: pointer to the ethernet header inside the skb
 * @nc_packet: structure containing the packet to the skb can be coded with
 * @neigh_node: next hop to forward packet to
 *
 * Returns true if both packets are consumed, false otherwise.
 */
static bool batadv_nc_code_packets(struct batadv_priv *bat_priv,
                                   struct sk_buff *skb,
                                   struct ethhdr *ethhdr,
                                   struct batadv_nc_packet *nc_packet,
                                   struct batadv_neigh_node *neigh_node)
{
        uint8_t tq_weighted_neigh, tq_weighted_coding, tq_tmp;
        struct sk_buff *skb_dest, *skb_src;
        struct batadv_unicast_packet *packet1;
        struct batadv_unicast_packet *packet2;
        struct batadv_coded_packet *coded_packet;
        struct batadv_neigh_node *neigh_tmp, *router_neigh;
        struct batadv_neigh_node *router_coding = NULL;
        struct batadv_neigh_ifinfo *router_neigh_ifinfo = NULL;
        struct batadv_neigh_ifinfo *router_coding_ifinfo = NULL;
        uint8_t *first_source, *first_dest, *second_source, *second_dest;
        __be32 packet_id1, packet_id2;
        size_t count;
        bool res = false;
        int coding_len;
        int unicast_size = sizeof(*packet1);
        int coded_size = sizeof(*coded_packet);
        int header_add = coded_size - unicast_size;

        /* TODO: do we need to consider the outgoing interface for
         * coded packets?
         */
        router_neigh = batadv_orig_router_get(neigh_node->orig_node,
                                              BATADV_IF_DEFAULT);
        if (!router_neigh)
                goto out;

        router_neigh_ifinfo = batadv_neigh_ifinfo_get(router_neigh,
                                                      BATADV_IF_DEFAULT);
        if (!router_neigh_ifinfo)
                goto out;

        neigh_tmp = nc_packet->neigh_node;
        router_coding = batadv_orig_router_get(neigh_tmp->orig_node,
                                               BATADV_IF_DEFAULT);
        if (!router_coding)
                goto out;

        router_coding_ifinfo = batadv_neigh_ifinfo_get(router_coding,
                                                       BATADV_IF_DEFAULT);
        if (!router_coding_ifinfo)
                goto out;

        tq_tmp = router_neigh_ifinfo->bat_iv.tq_avg;
        tq_weighted_neigh = batadv_nc_random_weight_tq(tq_tmp);
        tq_tmp = router_coding_ifinfo->bat_iv.tq_avg;
        tq_weighted_coding = batadv_nc_random_weight_tq(tq_tmp);

        /* Select one destination for the MAC-header dst-field based on
         * weighted TQ-values.
         */
        if (tq_weighted_neigh >= tq_weighted_coding) {
                /* Destination from nc_packet is selected for MAC-header */
                first_dest = nc_packet->nc_path->next_hop;
                first_source = nc_packet->nc_path->prev_hop;
                second_dest = neigh_node->addr;
                second_source = ethhdr->h_source;
                packet1 = (struct batadv_unicast_packet *)nc_packet->skb->data;
                packet2 = (struct batadv_unicast_packet *)skb->data;
                packet_id1 = nc_packet->packet_id;
                packet_id2 = batadv_skb_crc32(skb,
                                              skb->data + sizeof(*packet2));
        } else {
                /* Destination for skb is selected for MAC-header */
                first_dest = neigh_node->addr;
                first_source = ethhdr->h_source;
                second_dest = nc_packet->nc_path->next_hop;
                second_source = nc_packet->nc_path->prev_hop;
                packet1 = (struct batadv_unicast_packet *)skb->data;
                packet2 = (struct batadv_unicast_packet *)nc_packet->skb->data;
                packet_id1 = batadv_skb_crc32(skb,
                                              skb->data + sizeof(*packet1));
                packet_id2 = nc_packet->packet_id;
        }

        /* Instead of zero padding the smallest data buffer, we
         * code into the largest.
         */
        if (skb->len <= nc_packet->skb->len) {
                skb_dest = nc_packet->skb;
                skb_src = skb;
        } else {
                skb_dest = skb;
                skb_src = nc_packet->skb;
        }

        /* coding_len is used when decoding the packet shorter packet */
        coding_len = skb_src->len - unicast_size;

        if (skb_linearize(skb_dest) < 0 || skb_linearize(skb_src) < 0)
                goto out;

        skb_push(skb_dest, header_add);

        coded_packet = (struct batadv_coded_packet *)skb_dest->data;
        skb_reset_mac_header(skb_dest);

        coded_packet->packet_type = BATADV_CODED;
        coded_packet->version = BATADV_COMPAT_VERSION;
        coded_packet->ttl = packet1->ttl;

        /* Info about first unicast packet */
        ether_addr_copy(coded_packet->first_source, first_source);
        ether_addr_copy(coded_packet->first_orig_dest, packet1->dest);
        coded_packet->first_crc = packet_id1;
        coded_packet->first_ttvn = packet1->ttvn;

        /* Info about second unicast packet */
        ether_addr_copy(coded_packet->second_dest, second_dest);
        ether_addr_copy(coded_packet->second_source, second_source);
        ether_addr_copy(coded_packet->second_orig_dest, packet2->dest);
        coded_packet->second_crc = packet_id2;
        coded_packet->second_ttl = packet2->ttl;
        coded_packet->second_ttvn = packet2->ttvn;
        coded_packet->coded_len = htons(coding_len);

        /* This is where the magic happens: Code skb_src into skb_dest */
        batadv_nc_memxor(skb_dest->data + coded_size,
                         skb_src->data + unicast_size, coding_len);

        /* Update counters accordingly */
        if (BATADV_SKB_CB(skb_src)->decoded &&
            BATADV_SKB_CB(skb_dest)->decoded) {
                /* Both packets are recoded */
                count = skb_src->len + ETH_HLEN;
                count += skb_dest->len + ETH_HLEN;
                batadv_add_counter(bat_priv, BATADV_CNT_NC_RECODE, 2);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_RECODE_BYTES, count);
        } else if (!BATADV_SKB_CB(skb_src)->decoded &&
                   !BATADV_SKB_CB(skb_dest)->decoded) {
                /* Both packets are newly coded */
                count = skb_src->len + ETH_HLEN;
                count += skb_dest->len + ETH_HLEN;
                batadv_add_counter(bat_priv, BATADV_CNT_NC_CODE, 2);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_CODE_BYTES, count);
        } else if (BATADV_SKB_CB(skb_src)->decoded &&
                   !BATADV_SKB_CB(skb_dest)->decoded) {
                /* skb_src recoded and skb_dest is newly coded */
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_RECODE);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_RECODE_BYTES,
                                   skb_src->len + ETH_HLEN);
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_CODE);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_CODE_BYTES,
                                   skb_dest->len + ETH_HLEN);
        } else if (!BATADV_SKB_CB(skb_src)->decoded &&
                   BATADV_SKB_CB(skb_dest)->decoded) {
                /* skb_src is newly coded and skb_dest is recoded */
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_CODE);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_CODE_BYTES,
                                   skb_src->len + ETH_HLEN);
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_RECODE);
                batadv_add_counter(bat_priv, BATADV_CNT_NC_RECODE_BYTES,
                                   skb_dest->len + ETH_HLEN);
        }

        /* skb_src is now coded into skb_dest, so free it */
        kfree_skb(skb_src);

        /* avoid duplicate free of skb from nc_packet */
        nc_packet->skb = NULL;
        batadv_nc_packet_free(nc_packet);

        /* Send the coded packet and return true */
        batadv_send_skb_packet(skb_dest, neigh_node->if_incoming, first_dest);
        res = true;
out:
        if (router_neigh)
                batadv_neigh_node_free_ref(router_neigh);
        if (router_coding)
                batadv_neigh_node_free_ref(router_coding);
        if (router_neigh_ifinfo)
                batadv_neigh_ifinfo_free_ref(router_neigh_ifinfo);
        if (router_coding_ifinfo)
                batadv_neigh_ifinfo_free_ref(router_coding_ifinfo);
        return res;
}

/**
 * batadv_nc_skb_coding_possible - true if a decoded skb is available at dst.
 * @skb: data skb to forward
 * @dst: destination mac address of the other skb to code with
 * @src: source mac address of skb
 *
 * Whenever we network code a packet we have to check whether we received it in
 * a network coded form. If so, we may not be able to use it for coding because
 * some neighbors may also have received (overheard) the packet in the network
 * coded form without being able to decode it. It is hard to know which of the
 * neighboring nodes was able to decode the packet, therefore we can only
 * re-code the packet if the source of the previous encoded packet is involved.
 * Since the source encoded the packet we can be certain it has all necessary
 * decode information.
 *
 * Returns true if coding of a decoded packet is allowed.
 */
static bool batadv_nc_skb_coding_possible(struct sk_buff *skb,
                                          uint8_t *dst, uint8_t *src)
{
        if (BATADV_SKB_CB(skb)->decoded && !batadv_compare_eth(dst, src))
                return false;
        return true;
}

/**
 * batadv_nc_path_search - Find the coding path matching in_nc_node and
 *  out_nc_node to retrieve a buffered packet that can be used for coding.
 * @bat_priv: the bat priv with all the soft interface information
 * @in_nc_node: pointer to skb next hop's neighbor nc node
 * @out_nc_node: pointer to skb source's neighbor nc node
 * @skb: data skb to forward
 * @eth_dst: next hop mac address of skb
 *
 * Returns true if coding of a decoded skb is allowed.
 */
static struct batadv_nc_packet *
batadv_nc_path_search(struct batadv_priv *bat_priv,
                      struct batadv_nc_node *in_nc_node,
                      struct batadv_nc_node *out_nc_node,
                      struct sk_buff *skb,
                      uint8_t *eth_dst)
{
        struct batadv_nc_path *nc_path, nc_path_key;
        struct batadv_nc_packet *nc_packet_out = NULL;
        struct batadv_nc_packet *nc_packet, *nc_packet_tmp;
        struct batadv_hashtable *hash = bat_priv->nc.coding_hash;
        int idx;

        if (!hash)
                return NULL;

        /* Create almost path key */
        batadv_nc_hash_key_gen(&nc_path_key, in_nc_node->addr,
                               out_nc_node->addr);
        idx = batadv_nc_hash_choose(&nc_path_key, hash->size);

        /* Check for coding opportunities in this nc_path */
        rcu_read_lock();
        hlist_for_each_entry_rcu(nc_path, &hash->table[idx], hash_entry) {
                if (!batadv_compare_eth(nc_path->prev_hop, in_nc_node->addr))
                        continue;

                if (!batadv_compare_eth(nc_path->next_hop, out_nc_node->addr))
                        continue;

                spin_lock_bh(&nc_path->packet_list_lock);
                if (list_empty(&nc_path->packet_list)) {
                        spin_unlock_bh(&nc_path->packet_list_lock);
                        continue;
                }

                list_for_each_entry_safe(nc_packet, nc_packet_tmp,
                                         &nc_path->packet_list, list) {
                        if (!batadv_nc_skb_coding_possible(nc_packet->skb,
                                                           eth_dst,
                                                           in_nc_node->addr))
                                continue;

                        /* Coding opportunity is found! */
                        list_del(&nc_packet->list);
                        nc_packet_out = nc_packet;
                        break;
                }

                spin_unlock_bh(&nc_path->packet_list_lock);
                break;
        }
        rcu_read_unlock();

        return nc_packet_out;
}

/**
 * batadv_nc_skb_src_search - Loops through the list of neighoring nodes of the
 *  skb's sender (may be equal to the originator).
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: data skb to forward
 * @eth_dst: next hop mac address of skb
 * @eth_src: source mac address of skb
 * @in_nc_node: pointer to skb next hop's neighbor nc node
 *
 * Returns an nc packet if a suitable coding packet was found, NULL otherwise.
 */
static struct batadv_nc_packet *
batadv_nc_skb_src_search(struct batadv_priv *bat_priv,
                         struct sk_buff *skb,
                         uint8_t *eth_dst,
                         uint8_t *eth_src,
                         struct batadv_nc_node *in_nc_node)
{
        struct batadv_orig_node *orig_node;
        struct batadv_nc_node *out_nc_node;
        struct batadv_nc_packet *nc_packet = NULL;

        orig_node = batadv_orig_hash_find(bat_priv, eth_src);
        if (!orig_node)
                return NULL;

        rcu_read_lock();
        list_for_each_entry_rcu(out_nc_node,
                                &orig_node->out_coding_list, list) {
                /* Check if the skb is decoded and if recoding is possible */
                if (!batadv_nc_skb_coding_possible(skb,
                                                   out_nc_node->addr, eth_src))
                        continue;

                /* Search for an opportunity in this nc_path */
                nc_packet = batadv_nc_path_search(bat_priv, in_nc_node,
                                                  out_nc_node, skb, eth_dst);
                if (nc_packet)
                        break;
        }
        rcu_read_unlock();

        batadv_orig_node_free_ref(orig_node);
        return nc_packet;
}

/**
 * batadv_nc_skb_store_before_coding - set the ethernet src and dst of the
 *  unicast skb before it is stored for use in later decoding
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: data skb to store
 * @eth_dst_new: new destination mac address of skb
 */
static void batadv_nc_skb_store_before_coding(struct batadv_priv *bat_priv,
                                              struct sk_buff *skb,
                                              uint8_t *eth_dst_new)
{
        struct ethhdr *ethhdr;

        /* Copy skb header to change the mac header */
        skb = pskb_copy_for_clone(skb, GFP_ATOMIC);
        if (!skb)
                return;

        /* Set the mac header as if we actually sent the packet uncoded */
        ethhdr = eth_hdr(skb);
        ether_addr_copy(ethhdr->h_source, ethhdr->h_dest);
        ether_addr_copy(ethhdr->h_dest, eth_dst_new);

        /* Set data pointer to MAC header to mimic packets from our tx path */
        skb_push(skb, ETH_HLEN);

        /* Add the packet to the decoding packet pool */
        batadv_nc_skb_store_for_decoding(bat_priv, skb);

        /* batadv_nc_skb_store_for_decoding() clones the skb, so we must free
         * our ref
         */
        kfree_skb(skb);
}

/**
 * batadv_nc_skb_dst_search - Loops through list of neighboring nodes to dst.
 * @skb: data skb to forward
 * @neigh_node: next hop to forward packet to
 * @ethhdr: pointer to the ethernet header inside the skb
 *
 * Loops through list of neighboring nodes the next hop has a good connection to
 * (receives OGMs with a sufficient quality). We need to find a neighbor of our
 * next hop that potentially sent a packet which our next hop also received
 * (overheard) and has stored for later decoding.
 *
 * Returns true if the skb was consumed (encoded packet sent) or false otherwise
 */
static bool batadv_nc_skb_dst_search(struct sk_buff *skb,
                                     struct batadv_neigh_node *neigh_node,
                                     struct ethhdr *ethhdr)
{
        struct net_device *netdev = neigh_node->if_incoming->soft_iface;
        struct batadv_priv *bat_priv = netdev_priv(netdev);
        struct batadv_orig_node *orig_node = neigh_node->orig_node;
        struct batadv_nc_node *nc_node;
        struct batadv_nc_packet *nc_packet = NULL;

        rcu_read_lock();
        list_for_each_entry_rcu(nc_node, &orig_node->in_coding_list, list) {
                /* Search for coding opportunity with this in_nc_node */
                nc_packet = batadv_nc_skb_src_search(bat_priv, skb,
                                                     neigh_node->addr,
                                                     ethhdr->h_source, nc_node);

                /* Opportunity was found, so stop searching */
                if (nc_packet)
                        break;
        }
        rcu_read_unlock();

        if (!nc_packet)
                return false;

        /* Save packets for later decoding */
        batadv_nc_skb_store_before_coding(bat_priv, skb,
                                          neigh_node->addr);
        batadv_nc_skb_store_before_coding(bat_priv, nc_packet->skb,
                                          nc_packet->neigh_node->addr);

        /* Code and send packets */
        if (batadv_nc_code_packets(bat_priv, skb, ethhdr, nc_packet,
                                   neigh_node))
                return true;

        /* out of mem ? Coding failed - we have to free the buffered packet
         * to avoid memleaks. The skb passed as argument will be dealt with
         * by the calling function.
         */
        batadv_nc_send_packet(nc_packet);
        return false;
}

/**
 * batadv_nc_skb_add_to_path - buffer skb for later encoding / decoding
 * @skb: skb to add to path
 * @nc_path: path to add skb to
 * @neigh_node: next hop to forward packet to
 * @packet_id: checksum to identify packet
 *
 * Returns true if the packet was buffered or false in case of an error.
 */
static bool batadv_nc_skb_add_to_path(struct sk_buff *skb,
                                      struct batadv_nc_path *nc_path,
                                      struct batadv_neigh_node *neigh_node,
                                      __be32 packet_id)
{
        struct batadv_nc_packet *nc_packet;

        nc_packet = kzalloc(sizeof(*nc_packet), GFP_ATOMIC);
        if (!nc_packet)
                return false;

        /* Initialize nc_packet */
        nc_packet->timestamp = jiffies;
        nc_packet->packet_id = packet_id;
        nc_packet->skb = skb;
        nc_packet->neigh_node = neigh_node;
        nc_packet->nc_path = nc_path;

        /* Add coding packet to list */
        spin_lock_bh(&nc_path->packet_list_lock);
        list_add_tail(&nc_packet->list, &nc_path->packet_list);
        spin_unlock_bh(&nc_path->packet_list_lock);

        return true;
}

/**
 * batadv_nc_skb_forward - try to code a packet or add it to the coding packet
 *  buffer
 * @skb: data skb to forward
 * @neigh_node: next hop to forward packet to
 *
 * Returns true if the skb was consumed (encoded packet sent) or false otherwise
 */
bool batadv_nc_skb_forward(struct sk_buff *skb,
                           struct batadv_neigh_node *neigh_node)
{
        const struct net_device *netdev = neigh_node->if_incoming->soft_iface;
        struct batadv_priv *bat_priv = netdev_priv(netdev);
        struct batadv_unicast_packet *packet;
        struct batadv_nc_path *nc_path;
        struct ethhdr *ethhdr = eth_hdr(skb);
        __be32 packet_id;
        u8 *payload;

        /* Check if network coding is enabled */
        if (!atomic_read(&bat_priv->network_coding))
                goto out;

        /* We only handle unicast packets */
        payload = skb_network_header(skb);
        packet = (struct batadv_unicast_packet *)payload;
        if (packet->packet_type != BATADV_UNICAST)
                goto out;

        /* Try to find a coding opportunity and send the skb if one is found */
        if (batadv_nc_skb_dst_search(skb, neigh_node, ethhdr))
                return true;

        /* Find or create a nc_path for this src-dst pair */
        nc_path = batadv_nc_get_path(bat_priv,
                                     bat_priv->nc.coding_hash,
                                     ethhdr->h_source,
                                     neigh_node->addr);

        if (!nc_path)
                goto out;

        /* Add skb to nc_path */
        packet_id = batadv_skb_crc32(skb, payload + sizeof(*packet));
        if (!batadv_nc_skb_add_to_path(skb, nc_path, neigh_node, packet_id))
                goto free_nc_path;

        /* Packet is consumed */
        return true;

free_nc_path:
        batadv_nc_path_free_ref(nc_path);
out:
        /* Packet is not consumed */
        return false;
}

/**
 * batadv_nc_skb_store_for_decoding - save a clone of the skb which can be used
 *  when decoding coded packets
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: data skb to store
 */
void batadv_nc_skb_store_for_decoding(struct batadv_priv *bat_priv,
                                      struct sk_buff *skb)
{
        struct batadv_unicast_packet *packet;
        struct batadv_nc_path *nc_path;
        struct ethhdr *ethhdr = eth_hdr(skb);
        __be32 packet_id;
        u8 *payload;

        /* Check if network coding is enabled */
        if (!atomic_read(&bat_priv->network_coding))
                goto out;

        /* Check for supported packet type */
        payload = skb_network_header(skb);
        packet = (struct batadv_unicast_packet *)payload;
        if (packet->packet_type != BATADV_UNICAST)
                goto out;

        /* Find existing nc_path or create a new */
        nc_path = batadv_nc_get_path(bat_priv,
                                     bat_priv->nc.decoding_hash,
                                     ethhdr->h_source,
                                     ethhdr->h_dest);

        if (!nc_path)
                goto out;

        /* Clone skb and adjust skb->data to point at batman header */
        skb = skb_clone(skb, GFP_ATOMIC);
        if (unlikely(!skb))
                goto free_nc_path;

        if (unlikely(!pskb_may_pull(skb, ETH_HLEN)))
                goto free_skb;

        if (unlikely(!skb_pull_rcsum(skb, ETH_HLEN)))
                goto free_skb;

        /* Add skb to nc_path */
        packet_id = batadv_skb_crc32(skb, payload + sizeof(*packet));
        if (!batadv_nc_skb_add_to_path(skb, nc_path, NULL, packet_id))
                goto free_skb;

        batadv_inc_counter(bat_priv, BATADV_CNT_NC_BUFFER);
        return;

free_skb:
        kfree_skb(skb);
free_nc_path:
        batadv_nc_path_free_ref(nc_path);
out:
        return;
}

/**
 * batadv_nc_skb_store_sniffed_unicast - check if a received unicast packet
 *  should be saved in the decoding buffer and, if so, store it there
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: unicast skb to store
 */
void batadv_nc_skb_store_sniffed_unicast(struct batadv_priv *bat_priv,
                                         struct sk_buff *skb)
{
        struct ethhdr *ethhdr = eth_hdr(skb);

        if (batadv_is_my_mac(bat_priv, ethhdr->h_dest))
                return;

        /* Set data pointer to MAC header to mimic packets from our tx path */
        skb_push(skb, ETH_HLEN);

        batadv_nc_skb_store_for_decoding(bat_priv, skb);
}

/**
 * batadv_nc_skb_decode_packet - decode given skb using the decode data stored
 *  in nc_packet
 * @bat_priv: the bat priv with all the soft interface information
 * @skb: unicast skb to decode
 * @nc_packet: decode data needed to decode the skb
 *
 * Returns pointer to decoded unicast packet if the packet was decoded or NULL
 * in case of an error.
 */
static struct batadv_unicast_packet *
batadv_nc_skb_decode_packet(struct batadv_priv *bat_priv, struct sk_buff *skb,
                            struct batadv_nc_packet *nc_packet)
{
        const int h_size = sizeof(struct batadv_unicast_packet);
        const int h_diff = sizeof(struct batadv_coded_packet) - h_size;
        struct batadv_unicast_packet *unicast_packet;
        struct batadv_coded_packet coded_packet_tmp;
        struct ethhdr *ethhdr, ethhdr_tmp;
        uint8_t *orig_dest, ttl, ttvn;
        unsigned int coding_len;
        int err;

        /* Save headers temporarily */
        memcpy(&coded_packet_tmp, skb->data, sizeof(coded_packet_tmp));
        memcpy(&ethhdr_tmp, skb_mac_header(skb), sizeof(ethhdr_tmp));

        if (skb_cow(skb, 0) < 0)
                return NULL;

        if (unlikely(!skb_pull_rcsum(skb, h_diff)))
                return NULL;

        /* Data points to batman header, so set mac header 14 bytes before
         * and network to data
         */
        skb_set_mac_header(skb, -ETH_HLEN);
        skb_reset_network_header(skb);

        /* Reconstruct original mac header */
        ethhdr = eth_hdr(skb);
        *ethhdr = ethhdr_tmp;

        /* Select the correct unicast header information based on the location
         * of our mac address in the coded_packet header
         */
        if (batadv_is_my_mac(bat_priv, coded_packet_tmp.second_dest)) {
                /* If we are the second destination the packet was overheard,
                 * so the Ethernet address must be copied to h_dest and
                 * pkt_type changed from PACKET_OTHERHOST to PACKET_HOST
                 */
                ether_addr_copy(ethhdr->h_dest, coded_packet_tmp.second_dest);
                skb->pkt_type = PACKET_HOST;

                orig_dest = coded_packet_tmp.second_orig_dest;
                ttl = coded_packet_tmp.second_ttl;
                ttvn = coded_packet_tmp.second_ttvn;
        } else {
                orig_dest = coded_packet_tmp.first_orig_dest;
                ttl = coded_packet_tmp.ttl;
                ttvn = coded_packet_tmp.first_ttvn;
        }

        coding_len = ntohs(coded_packet_tmp.coded_len);

        if (coding_len > skb->len)
                return NULL;

        /* Here the magic is reversed:
         *   extract the missing packet from the received coded packet
         */
        batadv_nc_memxor(skb->data + h_size,
                         nc_packet->skb->data + h_size,
                         coding_len);

        /* Resize decoded skb if decoded with larger packet */
        if (nc_packet->skb->len > coding_len + h_size) {
                err = pskb_trim_rcsum(skb, coding_len + h_size);
                if (err)
                        return NULL;
        }

        /* Create decoded unicast packet */
        unicast_packet = (struct batadv_unicast_packet *)skb->data;
        unicast_packet->packet_type = BATADV_UNICAST;
        unicast_packet->version = BATADV_COMPAT_VERSION;
        unicast_packet->ttl = ttl;
        ether_addr_copy(unicast_packet->dest, orig_dest);
        unicast_packet->ttvn = ttvn;

        batadv_nc_packet_free(nc_packet);
        return unicast_packet;
}

/**
 * batadv_nc_find_decoding_packet - search through buffered decoding data to
 *  find the data needed to decode the coded packet
 * @bat_priv: the bat priv with all the soft interface information
 * @ethhdr: pointer to the ethernet header inside the coded packet
 * @coded: coded packet we try to find decode data for
 *
 * Returns pointer to nc packet if the needed data was found or NULL otherwise.
 */
static struct batadv_nc_packet *
batadv_nc_find_decoding_packet(struct batadv_priv *bat_priv,
                               struct ethhdr *ethhdr,
                               struct batadv_coded_packet *coded)
{
        struct batadv_hashtable *hash = bat_priv->nc.decoding_hash;
        struct batadv_nc_packet *tmp_nc_packet, *nc_packet = NULL;
        struct batadv_nc_path *nc_path, nc_path_key;
        uint8_t *dest, *source;
        __be32 packet_id;
        int index;

        if (!hash)
                return NULL;

        /* Select the correct packet id based on the location of our mac-addr */
        dest = ethhdr->h_source;
        if (!batadv_is_my_mac(bat_priv, coded->second_dest)) {
                source = coded->second_source;
                packet_id = coded->second_crc;
        } else {
                source = coded->first_source;
                packet_id = coded->first_crc;
        }

        batadv_nc_hash_key_gen(&nc_path_key, source, dest);
        index = batadv_nc_hash_choose(&nc_path_key, hash->size);

        /* Search for matching coding path */
        rcu_read_lock();
        hlist_for_each_entry_rcu(nc_path, &hash->table[index], hash_entry) {
                /* Find matching nc_packet */
                spin_lock_bh(&nc_path->packet_list_lock);
                list_for_each_entry(tmp_nc_packet,
                                    &nc_path->packet_list, list) {
                        if (packet_id == tmp_nc_packet->packet_id) {
                                list_del(&tmp_nc_packet->list);

                                nc_packet = tmp_nc_packet;
                                break;
                        }
                }
                spin_unlock_bh(&nc_path->packet_list_lock);

                if (nc_packet)
                        break;
        }
        rcu_read_unlock();

        if (!nc_packet)
                batadv_dbg(BATADV_DBG_NC, bat_priv,
                           "No decoding packet found for %u\n", packet_id);

        return nc_packet;
}

/**
 * batadv_nc_recv_coded_packet - try to decode coded packet and enqueue the
 *  resulting unicast packet
 * @skb: incoming coded packet
 * @recv_if: pointer to interface this packet was received on
 */
static int batadv_nc_recv_coded_packet(struct sk_buff *skb,
                                       struct batadv_hard_iface *recv_if)
{
        struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
        struct batadv_unicast_packet *unicast_packet;
        struct batadv_coded_packet *coded_packet;
        struct batadv_nc_packet *nc_packet;
        struct ethhdr *ethhdr;
        int hdr_size = sizeof(*coded_packet);

        /* Check if network coding is enabled */
        if (!atomic_read(&bat_priv->network_coding))
                return NET_RX_DROP;

        /* Make sure we can access (and remove) header */
        if (unlikely(!pskb_may_pull(skb, hdr_size)))
                return NET_RX_DROP;

        coded_packet = (struct batadv_coded_packet *)skb->data;
        ethhdr = eth_hdr(skb);

        /* Verify frame is destined for us */
        if (!batadv_is_my_mac(bat_priv, ethhdr->h_dest) &&
            !batadv_is_my_mac(bat_priv, coded_packet->second_dest))
                return NET_RX_DROP;

        /* Update stat counter */
        if (batadv_is_my_mac(bat_priv, coded_packet->second_dest))
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_SNIFFED);

        nc_packet = batadv_nc_find_decoding_packet(bat_priv, ethhdr,
                                                   coded_packet);
        if (!nc_packet) {
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_DECODE_FAILED);
                return NET_RX_DROP;
        }

        /* Make skb's linear, because decoding accesses the entire buffer */
        if (skb_linearize(skb) < 0)
                goto free_nc_packet;

        if (skb_linearize(nc_packet->skb) < 0)
                goto free_nc_packet;

        /* Decode the packet */
        unicast_packet = batadv_nc_skb_decode_packet(bat_priv, skb, nc_packet);
        if (!unicast_packet) {
                batadv_inc_counter(bat_priv, BATADV_CNT_NC_DECODE_FAILED);
                goto free_nc_packet;
        }

        /* Mark packet as decoded to do correct recoding when forwarding */
        BATADV_SKB_CB(skb)->decoded = true;
        batadv_inc_counter(bat_priv, BATADV_CNT_NC_DECODE);
        batadv_add_counter(bat_priv, BATADV_CNT_NC_DECODE_BYTES,
                           skb->len + ETH_HLEN);
        return batadv_recv_unicast_packet(skb, recv_if);

free_nc_packet:
        batadv_nc_packet_free(nc_packet);
        return NET_RX_DROP;
}

/**
 * batadv_nc_mesh_free - clean up network coding memory
 * @bat_priv: the bat priv with all the soft interface information
 */
void batadv_nc_mesh_free(struct batadv_priv *bat_priv)
{
        batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_NC, 1);
        batadv_tvlv_handler_unregister(bat_priv, BATADV_TVLV_NC, 1);
        cancel_delayed_work_sync(&bat_priv->nc.work);

        batadv_nc_purge_paths(bat_priv, bat_priv->nc.coding_hash, NULL);
        batadv_hash_destroy(bat_priv->nc.coding_hash);
        batadv_nc_purge_paths(bat_priv, bat_priv->nc.decoding_hash, NULL);
        batadv_hash_destroy(bat_priv->nc.decoding_hash);
}

/**
 * batadv_nc_nodes_seq_print_text - print the nc node information
 * @seq: seq file to print on
 * @offset: not used
 */
int batadv_nc_nodes_seq_print_text(struct seq_file *seq, void *offset)
{
        struct net_device *net_dev = (struct net_device *)seq->private;
        struct batadv_priv *bat_priv = netdev_priv(net_dev);
        struct batadv_hashtable *hash = bat_priv->orig_hash;
        struct batadv_hard_iface *primary_if;
        struct hlist_head *head;
        struct batadv_orig_node *orig_node;
        struct batadv_nc_node *nc_node;
        int i;

        primary_if = batadv_seq_print_text_primary_if_get(seq);
        if (!primary_if)
                goto out;

        /* Traverse list of originators */
        for (i = 0; i < hash->size; i++) {
                head = &hash->table[i];

                /* For each orig_node in this bin */
                rcu_read_lock();
                hlist_for_each_entry_rcu(orig_node, head, hash_entry) {
                        /* no need to print the orig node if it does not have
                         * network coding neighbors
                         */
                        if (list_empty(&orig_node->in_coding_list) &&
                            list_empty(&orig_node->out_coding_list))
                                continue;

                        seq_printf(seq, "Node:      %pM\n", orig_node->orig);

                        seq_puts(seq, " Ingoing:  ");
                        /* For each in_nc_node to this orig_node */
                        list_for_each_entry_rcu(nc_node,
                                                &orig_node->in_coding_list,
                                                list)
                                seq_printf(seq, "%pM ",
                                           nc_node->addr);
                        seq_puts(seq, "\n");

                        seq_puts(seq, " Outgoing: ");
                        /* For out_nc_node to this orig_node */
                        list_for_each_entry_rcu(nc_node,
                                                &orig_node->out_coding_list,
                                                list)
                                seq_printf(seq, "%pM ",
                                           nc_node->addr);
                        seq_puts(seq, "\n\n");
                }
                rcu_read_unlock();
        }

out:
        if (primary_if)
                batadv_hardif_free_ref(primary_if);
        return 0;
}

/**
 * batadv_nc_init_debugfs - create nc folder and related files in debugfs
 * @bat_priv: the bat priv with all the soft interface information
 */
int batadv_nc_init_debugfs(struct batadv_priv *bat_priv)
{
        struct dentry *nc_dir, *file;

        nc_dir = debugfs_create_dir("nc", bat_priv->debug_dir);
        if (!nc_dir)
                goto out;

        file = debugfs_create_u8("min_tq", S_IRUGO | S_IWUSR, nc_dir,
                                 &bat_priv->nc.min_tq);
        if (!file)
                goto out;

        file = debugfs_create_u32("max_fwd_delay", S_IRUGO | S_IWUSR, nc_dir,
                                  &bat_priv->nc.max_fwd_delay);
        if (!file)
                goto out;

        file = debugfs_create_u32("max_buffer_time", S_IRUGO | S_IWUSR, nc_dir,
                                  &bat_priv->nc.max_buffer_time);
        if (!file)
                goto out;

        return 0;

out:
        return -ENOMEM;
}