4 files changed, 557 insertions, 7 deletions
diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c
index ff4985d84726..2c38c540c6db 100644
--- a/net/batman-adv/network-coding.c
+++ b/net/batman-adv/network-coding.c
@@ -20,10 +20,14 @@
 #include <linux/debugfs.h>
 #include "main.h"
+#include "hash.h"
 #include "network-coding.h"
+#include "send.h"
 #include "originator.h"
 #include "hard-interface.h"
+static struct lock_class_key batadv_nc_coding_hash_lock_class_key;
 static void batadv_nc_worker(struct work_struct *work);
 /**
@@ -42,10 +46,25 @@ static void batadv_nc_start_timer(struct batadv_priv *bat_priv)
 */
 int batadv_nc_init(struct batadv_priv *bat_priv)
 {
+        bat_priv->nc.timestamp_fwd_flush = jiffies;
+        if (bat_priv->nc.coding_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);
        INIT_DELAYED_WORK(&bat_priv->nc.work, batadv_nc_worker);
        batadv_nc_start_timer(bat_priv);
        return 0;
+err:
+        return -ENOMEM;
 }
 /**
@@ -56,6 +75,7 @@ void batadv_nc_init_bat_priv(struct batadv_priv *bat_priv)
 {
        atomic_set(&bat_priv->network_coding, 1);
        bat_priv->nc.min_tq = 200;
+        bat_priv->nc.max_fwd_delay = 10;
 }
 /**
@@ -96,6 +116,30 @@ static void batadv_nc_node_free_ref(struct batadv_nc_node *nc_node)
 }
 /**
+ * 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
@@ -112,6 +156,26 @@ static bool batadv_nc_to_purge_nc_node(struct batadv_priv *bat_priv,
 }
 /**
+ * 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_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
@@ -203,6 +267,262 @@ static void batadv_nc_purge_orig_hash(struct batadv_priv *bat_priv)
 }
 /**
+ * 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 = batadv_hash_bytes(hash, &nc_path->prev_hop,
+                                 sizeof(nc_path->prev_hop));
+        hash = batadv_hash_bytes(hash, &nc_path->next_hop,
+                                 sizeof(nc_path->next_hop));
+        hash += (hash << 3);
+        hash ^= (hash >> 11);
+        hash += (hash << 15);
+        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_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
 */
@@ -211,12 +531,23 @@ 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);
+        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;
+        }
        /* Schedule a new check */
        batadv_nc_start_timer(bat_priv);
@@ -407,12 +738,163 @@ out:
 }
 /**
+ * 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;
+        memcpy(nc_path->next_hop, dst, ETH_ALEN);
+        memcpy(nc_path->prev_hop, src, ETH_ALEN);
+        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_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
+ * @ethhdr: pointer to the ethernet header inside the skb
+ *
+ * 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,
+                           struct ethhdr *ethhdr)
+{
+        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;
+        __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->header.packet_type != BATADV_UNICAST)
+                goto out;
+        /* 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_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);
+        batadv_nc_purge_paths(bat_priv, bat_priv->nc.coding_hash, NULL);
+        batadv_hash_destroy(bat_priv->nc.coding_hash);
 }
 /**
@@ -488,6 +970,11 @@ int batadv_nc_init_debugfs(struct batadv_priv *bat_priv)
        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;
        return 0;
 out:
diff --git a/net/batman-adv/network-coding.h b/net/batman-adv/network-coding.h
index 4c56cd98d9de..c32602a3939a 100644
--- a/net/batman-adv/network-coding.h
+++ b/net/batman-adv/network-coding.h
@@ -35,6 +35,9 @@ void batadv_nc_purge_orig(struct batadv_priv *bat_priv,
                                           struct batadv_nc_node *));
 void batadv_nc_init_bat_priv(struct batadv_priv *bat_priv);
 void batadv_nc_init_orig(struct batadv_orig_node *orig_node);
+bool batadv_nc_skb_forward(struct sk_buff *skb,
+                           struct batadv_neigh_node *neigh_node,
+                           struct ethhdr *ethhdr);
 int batadv_nc_nodes_seq_print_text(struct seq_file *seq, void *offset);
 int batadv_nc_init_debugfs(struct batadv_priv *bat_priv);
@@ -79,6 +82,13 @@ static inline void batadv_nc_init_orig(struct batadv_orig_node *orig_node)
        return;
 }
+static inline bool batadv_nc_skb_forward(struct sk_buff *skb,
+                                         struct batadv_neigh_node *neigh_node,
+                                         struct ethhdr *ethhdr)
+{
+        return false;
+}
 static inline int batadv_nc_nodes_seq_print_text(struct seq_file *seq,
                                                 void *offset)
 {
diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 322c97ac10c7..44fda7c6171e 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -29,6 +29,7 @@
 #include "unicast.h"
 #include "bridge_loop_avoidance.h"
 #include "distributed-arp-table.h"
+#include "network-coding.h"
 static int batadv_route_unicast_packet(struct sk_buff *skb,
                                       struct batadv_hard_iface *recv_if);
@@ -860,14 +861,17 @@ static int batadv_route_unicast_packet(struct sk_buff *skb,
        /* decrement ttl */
        unicast_packet->header.ttl--;
-        /* Update stats counter */
+        /* network code packet if possible */
-        batadv_inc_counter(bat_priv, BATADV_CNT_FORWARD);
+        if (batadv_nc_skb_forward(skb, neigh_node, ethhdr)) {
-        batadv_add_counter(bat_priv, BATADV_CNT_FORWARD_BYTES,
-                           skb->len + ETH_HLEN);
-        /* route it */
-        if (batadv_send_skb_to_orig(skb, orig_node, recv_if))
                ret = NET_RX_SUCCESS;
+        } else if (batadv_send_skb_to_orig(skb, orig_node, recv_if)) {
+                ret = NET_RX_SUCCESS;
+                /* Update stats counter */
+                batadv_inc_counter(bat_priv, BATADV_CNT_FORWARD);
+                batadv_add_counter(bat_priv, BATADV_CNT_FORWARD_BYTES,
+                                   skb->len + ETH_HLEN);
+        }
 out:
        if (neigh_node)
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 1544ab40bedd..43caf7f493c1 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -442,11 +442,19 @@ struct batadv_priv_dat {
 * @work: work queue callback item for cleanup
 * @debug_dir: dentry for nc subdir in batman-adv directory in debugfs
 * @min_tq: only consider neighbors for encoding if neigh_tq > min_tq
+ * @max_fwd_delay: maximum packet forward delay to allow coding of packets
+ * @timestamp_fwd_flush: timestamp of last forward packet queue flush
+ * @coding_hash: Hash table used to buffer skbs while waiting for another
+ *  incoming skb to code it with. Skbs are added to the buffer just before being
+ *  forwarded in routing.c
 */
 struct batadv_priv_nc {
        struct delayed_work work;
        struct dentry *debug_dir;
        u8 min_tq;
+        u32 max_fwd_delay;
+        unsigned long timestamp_fwd_flush;
+        struct batadv_hashtable *coding_hash;
 };
 /**
@@ -748,6 +756,47 @@ struct batadv_nc_node {
 };
 /**
+ * struct batadv_nc_path - network coding path
+ * @hash_entry: next and prev pointer for the list handling
+ * @rcu: struct used for freeing in an RCU-safe manner
+ * @refcount: number of contexts the object is used by
+ * @packet_list: list of buffered packets for this path
+ * @packet_list_lock: access lock for packet list
+ * @next_hop: next hop (destination) of path
+ * @prev_hop: previous hop (source) of path
+ * @last_valid: timestamp for last validation of path
+ */
+struct batadv_nc_path {
+        struct hlist_node hash_entry;
+        struct rcu_head rcu;
+        atomic_t refcount;
+        struct list_head packet_list;
+        spinlock_t packet_list_lock; /* Protects packet_list */
+        uint8_t next_hop[ETH_ALEN];
+        uint8_t prev_hop[ETH_ALEN];
+        unsigned long last_valid;
+};
+/**
+ * struct batadv_nc_packet - network coding packet used when coding and
+ *  decoding packets
+ * @list: next and prev pointer for the list handling
+ * @packet_id: crc32 checksum of skb data
+ * @timestamp: field containing the info when the packet was added to path
+ * @neigh_node: pointer to original next hop neighbor of skb
+ * @skb: skb which can be encoded or used for decoding
+ * @nc_path: pointer to path this nc packet is attached to
+ */
+struct batadv_nc_packet {
+        struct list_head list;
+        __be32 packet_id;
+        unsigned long timestamp;
+        struct batadv_neigh_node *neigh_node;
+        struct sk_buff *skb;
+        struct batadv_nc_path *nc_path;
+};
+/**
 * struct batadv_forw_packet - structure for bcast packets to be sent/forwarded
 * @list: list node for batadv_socket_client::queue_list
 * @send_time: execution time for delayed_work (packet sending)