/* Copyright (C) 2011-2013 B.A.T.M.A.N. contributors:

   *
   * Antonio Quartulli
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of version 2 of the GNU General Public
   * License as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but
   * WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
   * 02110-1301, USA
   */
  
  #include <linux/if_ether.h>
  #include <linux/if_arp.h>

  #include <linux/if_vlan.h>

  #include <net/arp.h>

  
  #include "main.h"

  #include "hash.h"

  #include "distributed-arp-table.h"
  #include "hard-interface.h"
  #include "originator.h"
  #include "send.h"
  #include "types.h"

  #include "translation-table.h"

  static void batadv_dat_purge(struct work_struct *work);
  
  /**
   * batadv_dat_start_timer - initialise the DAT periodic worker
   * @bat_priv: the bat priv with all the soft interface information
   */
  static void batadv_dat_start_timer(struct batadv_priv *bat_priv)
  {
  	INIT_DELAYED_WORK(&bat_priv->dat.work, batadv_dat_purge);
  	queue_delayed_work(batadv_event_workqueue, &bat_priv->dat.work,
  			   msecs_to_jiffies(10000));
  }
  
  /**

   * batadv_dat_entry_free_ref - decrement the dat_entry refcounter and possibly

   * free it

   * @dat_entry: the entry to free

   */
  static void batadv_dat_entry_free_ref(struct batadv_dat_entry *dat_entry)
  {
  	if (atomic_dec_and_test(&dat_entry->refcount))
  		kfree_rcu(dat_entry, rcu);
  }
  
  /**

   * batadv_dat_to_purge - check whether a dat_entry has to be purged or not

   * @dat_entry: the entry to check
   *

   * Returns true if the entry has to be purged now, false otherwise.

   */
  static bool batadv_dat_to_purge(struct batadv_dat_entry *dat_entry)
  {
  	return batadv_has_timed_out(dat_entry->last_update,
  				    BATADV_DAT_ENTRY_TIMEOUT);
  }
  
  /**
   * __batadv_dat_purge - delete entries from the DAT local storage
   * @bat_priv: the bat priv with all the soft interface information
   * @to_purge: function in charge to decide whether an entry has to be purged or
   *	      not. This function takes the dat_entry as argument and has to
   *	      returns a boolean value: true is the entry has to be deleted,
   *	      false otherwise
   *

   * Loops over each entry in the DAT local storage and deletes it if and only if
   * the to_purge function passed as argument returns true.

   */
  static void __batadv_dat_purge(struct batadv_priv *bat_priv,
  			       bool (*to_purge)(struct batadv_dat_entry *))
  {
  	spinlock_t *list_lock; /* protects write access to the hash lists */
  	struct batadv_dat_entry *dat_entry;

  	struct hlist_node *node_tmp;

  	struct hlist_head *head;
  	uint32_t i;
  
  	if (!bat_priv->dat.hash)
  		return;
  
  	for (i = 0; i < bat_priv->dat.hash->size; i++) {
  		head = &bat_priv->dat.hash->table[i];
  		list_lock = &bat_priv->dat.hash->list_locks[i];
  
  		spin_lock_bh(list_lock);

  		hlist_for_each_entry_safe(dat_entry, node_tmp, head,

  					  hash_entry) {

  			/* if a helper function has been passed as parameter,

  			 * ask it if the entry has to be purged or not
  			 */
  			if (to_purge && !to_purge(dat_entry))
  				continue;

  			hlist_del_rcu(&dat_entry->hash_entry);

  			batadv_dat_entry_free_ref(dat_entry);
  		}
  		spin_unlock_bh(list_lock);
  	}
  }
  
  /**
   * batadv_dat_purge - periodic task that deletes old entries from the local DAT
   * hash table
   * @work: kernel work struct
   */
  static void batadv_dat_purge(struct work_struct *work)
  {
  	struct delayed_work *delayed_work;
  	struct batadv_priv_dat *priv_dat;
  	struct batadv_priv *bat_priv;
  
  	delayed_work = container_of(work, struct delayed_work, work);
  	priv_dat = container_of(delayed_work, struct batadv_priv_dat, work);
  	bat_priv = container_of(priv_dat, struct batadv_priv, dat);
  
  	__batadv_dat_purge(bat_priv, batadv_dat_to_purge);
  	batadv_dat_start_timer(bat_priv);
  }
  
  /**
   * batadv_compare_dat - comparing function used in the local DAT hash table
   * @node: node in the local table
   * @data2: second object to compare the node to
   *

   * Returns 1 if the two entries are the same, 0 otherwise.

   */
  static int batadv_compare_dat(const struct hlist_node *node, const void *data2)
  {
  	const void *data1 = container_of(node, struct batadv_dat_entry,
  					 hash_entry);
  
  	return (memcmp(data1, data2, sizeof(__be32)) == 0 ? 1 : 0);
  }

  /**

   * batadv_arp_hw_src - extract the hw_src field from an ARP packet
   * @skb: ARP packet
   * @hdr_size: size of the possible header before the ARP packet
   *

   * Returns the value of the hw_src field in the ARP packet.

   */
  static uint8_t *batadv_arp_hw_src(struct sk_buff *skb, int hdr_size)
  {
  	uint8_t *addr;
  
  	addr = (uint8_t *)(skb->data + hdr_size);
  	addr += ETH_HLEN + sizeof(struct arphdr);
  
  	return addr;
  }
  
  /**
   * batadv_arp_ip_src - extract the ip_src field from an ARP packet
   * @skb: ARP packet
   * @hdr_size: size of the possible header before the ARP packet
   *

   * Returns the value of the ip_src field in the ARP packet.

   */
  static __be32 batadv_arp_ip_src(struct sk_buff *skb, int hdr_size)
  {
  	return *(__be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN);
  }
  
  /**
   * batadv_arp_hw_dst - extract the hw_dst field from an ARP packet
   * @skb: ARP packet
   * @hdr_size: size of the possible header before the ARP packet
   *

   * Returns the value of the hw_dst field in the ARP packet.

   */
  static uint8_t *batadv_arp_hw_dst(struct sk_buff *skb, int hdr_size)
  {
  	return batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN + 4;
  }
  
  /**
   * batadv_arp_ip_dst - extract the ip_dst field from an ARP packet
   * @skb: ARP packet
   * @hdr_size: size of the possible header before the ARP packet
   *

   * Returns the value of the ip_dst field in the ARP packet.

   */
  static __be32 batadv_arp_ip_dst(struct sk_buff *skb, int hdr_size)
  {
  	return *(__be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN * 2 + 4);
  }
  
  /**

   * batadv_hash_dat - compute the hash value for an IP address
   * @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_hash_dat(const void *data, uint32_t size)
  {

  	uint32_t hash = 0;

  	const struct batadv_dat_entry *dat = data;

  	hash = batadv_hash_bytes(hash, &dat->ip, sizeof(dat->ip));
  	hash = batadv_hash_bytes(hash, &dat->vid, sizeof(dat->vid));

  
  	hash += (hash << 3);
  	hash ^= (hash >> 11);
  	hash += (hash << 15);
  
  	return hash % size;
  }
  
  /**

   * batadv_dat_entry_hash_find - look for a given dat_entry in the local hash

   * table
   * @bat_priv: the bat priv with all the soft interface information
   * @ip: search key

   * @vid: VLAN identifier

   *

   * Returns the dat_entry if found, NULL otherwise.

   */
  static struct batadv_dat_entry *

  batadv_dat_entry_hash_find(struct batadv_priv *bat_priv, __be32 ip,
  			   unsigned short vid)

  {
  	struct hlist_head *head;

  	struct batadv_dat_entry to_find, *dat_entry, *dat_entry_tmp = NULL;

  	struct batadv_hashtable *hash = bat_priv->dat.hash;
  	uint32_t index;
  
  	if (!hash)
  		return NULL;

  	to_find.ip = ip;
  	to_find.vid = vid;
  
  	index = batadv_hash_dat(&to_find, hash->size);

  	head = &hash->table[index];
  
  	rcu_read_lock();

  	hlist_for_each_entry_rcu(dat_entry, head, hash_entry) {

  		if (dat_entry->ip != ip)
  			continue;
  
  		if (!atomic_inc_not_zero(&dat_entry->refcount))
  			continue;
  
  		dat_entry_tmp = dat_entry;
  		break;
  	}
  	rcu_read_unlock();
  
  	return dat_entry_tmp;
  }
  
  /**
   * batadv_dat_entry_add - add a new dat entry or update it if already exists
   * @bat_priv: the bat priv with all the soft interface information
   * @ip: ipv4 to add/edit
   * @mac_addr: mac address to assign to the given ipv4

   * @vid: VLAN identifier

   */
  static void batadv_dat_entry_add(struct batadv_priv *bat_priv, __be32 ip,

  				 uint8_t *mac_addr, unsigned short vid)

  {
  	struct batadv_dat_entry *dat_entry;
  	int hash_added;

  	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip, vid);

  	/* if this entry is already known, just update it */
  	if (dat_entry) {
  		if (!batadv_compare_eth(dat_entry->mac_addr, mac_addr))
  			memcpy(dat_entry->mac_addr, mac_addr, ETH_ALEN);
  		dat_entry->last_update = jiffies;
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,

  			   "Entry updated: %pI4 %pM (vid: %d)
  ",
  			   &dat_entry->ip, dat_entry->mac_addr,
  			   BATADV_PRINT_VID(vid));

  		goto out;
  	}
  
  	dat_entry = kmalloc(sizeof(*dat_entry), GFP_ATOMIC);
  	if (!dat_entry)
  		goto out;
  
  	dat_entry->ip = ip;

  	dat_entry->vid = vid;

  	memcpy(dat_entry->mac_addr, mac_addr, ETH_ALEN);
  	dat_entry->last_update = jiffies;
  	atomic_set(&dat_entry->refcount, 2);
  
  	hash_added = batadv_hash_add(bat_priv->dat.hash, batadv_compare_dat,

  				     batadv_hash_dat, dat_entry,

  				     &dat_entry->hash_entry);
  
  	if (unlikely(hash_added != 0)) {
  		/* remove the reference for the hash */
  		batadv_dat_entry_free_ref(dat_entry);
  		goto out;
  	}

  	batadv_dbg(BATADV_DBG_DAT, bat_priv, "New entry added: %pI4 %pM (vid: %d)
  ",
  		   &dat_entry->ip, dat_entry->mac_addr, BATADV_PRINT_VID(vid));

  
  out:
  	if (dat_entry)
  		batadv_dat_entry_free_ref(dat_entry);
  }

  #ifdef CONFIG_BATMAN_ADV_DEBUG
  
  /**
   * batadv_dbg_arp - print a debug message containing all the ARP packet details
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: ARP packet
   * @type: ARP type
   * @hdr_size: size of the possible header before the ARP packet
   * @msg: message to print together with the debugging information
   */
  static void batadv_dbg_arp(struct batadv_priv *bat_priv, struct sk_buff *skb,
  			   uint16_t type, int hdr_size, char *msg)
  {
  	struct batadv_unicast_4addr_packet *unicast_4addr_packet;
  	struct batadv_bcast_packet *bcast_pkt;
  	uint8_t *orig_addr;
  	__be32 ip_src, ip_dst;
  
  	if (msg)
  		batadv_dbg(BATADV_DBG_DAT, bat_priv, "%s
  ", msg);
  
  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);
  	batadv_dbg(BATADV_DBG_DAT, bat_priv,
  		   "ARP MSG = [src: %pM-%pI4 dst: %pM-%pI4]
  ",
  		   batadv_arp_hw_src(skb, hdr_size), &ip_src,
  		   batadv_arp_hw_dst(skb, hdr_size), &ip_dst);
  
  	if (hdr_size == 0)
  		return;

  	unicast_4addr_packet = (struct batadv_unicast_4addr_packet *)skb->data;
  
  	switch (unicast_4addr_packet->u.header.packet_type) {
  	case BATADV_UNICAST:
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "* encapsulated within a UNICAST packet
  ");
  		break;
  	case BATADV_UNICAST_4ADDR:
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "* encapsulated within a UNICAST_4ADDR packet (src: %pM)
  ",
  			   unicast_4addr_packet->src);
  		switch (unicast_4addr_packet->subtype) {
  		case BATADV_P_DAT_DHT_PUT:
  			batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DAT_DHT_PUT
  ");
  			break;
  		case BATADV_P_DAT_DHT_GET:
  			batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DAT_DHT_GET
  ");
  			break;
  		case BATADV_P_DAT_CACHE_REPLY:
  			batadv_dbg(BATADV_DBG_DAT, bat_priv,
  				   "* type: DAT_CACHE_REPLY
  ");
  			break;
  		case BATADV_P_DATA:
  			batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: DATA
  ");
  			break;
  		default:
  			batadv_dbg(BATADV_DBG_DAT, bat_priv, "* type: Unknown (%u)!
  ",
  				   unicast_4addr_packet->u.header.packet_type);
  		}
  		break;
  	case BATADV_BCAST:
  		bcast_pkt = (struct batadv_bcast_packet *)unicast_4addr_packet;
  		orig_addr = bcast_pkt->orig;
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "* encapsulated within a BCAST packet (src: %pM)
  ",
  			   orig_addr);
  		break;
  	default:
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "* encapsulated within an unknown packet type (0x%x)
  ",
  			   unicast_4addr_packet->u.header.packet_type);
  	}
  }
  
  #else
  
  static void batadv_dbg_arp(struct batadv_priv *bat_priv, struct sk_buff *skb,
  			   uint16_t type, int hdr_size, char *msg)
  {
  }
  
  #endif /* CONFIG_BATMAN_ADV_DEBUG */

  /**

   * batadv_is_orig_node_eligible - check whether a node can be a DHT candidate
   * @res: the array with the already selected candidates
   * @select: number of already selected candidates
   * @tmp_max: address of the currently evaluated node
   * @max: current round max address
   * @last_max: address of the last selected candidate
   * @candidate: orig_node under evaluation
   * @max_orig_node: last selected candidate
   *

   * Returns true if the node has been elected as next candidate or false
   * otherwise.

   */
  static bool batadv_is_orig_node_eligible(struct batadv_dat_candidate *res,
  					 int select, batadv_dat_addr_t tmp_max,
  					 batadv_dat_addr_t max,
  					 batadv_dat_addr_t last_max,
  					 struct batadv_orig_node *candidate,
  					 struct batadv_orig_node *max_orig_node)
  {
  	bool ret = false;
  	int j;

  	/* check if orig node candidate is running DAT */
  	if (!(candidate->capabilities & BATADV_ORIG_CAPA_HAS_DAT))
  		goto out;

  	/* Check if this node has already been selected... */
  	for (j = 0; j < select; j++)
  		if (res[j].orig_node == candidate)
  			break;
  	/* ..and possibly skip it */
  	if (j < select)
  		goto out;
  	/* sanity check: has it already been selected? This should not happen */
  	if (tmp_max > last_max)
  		goto out;
  	/* check if during this iteration an originator with a closer dht
  	 * address has already been found
  	 */
  	if (tmp_max < max)
  		goto out;
  	/* this is an hash collision with the temporary selected node. Choose
  	 * the one with the lowest address
  	 */

  	if ((tmp_max == max) && max_orig_node &&

  	    (batadv_compare_eth(candidate->orig, max_orig_node->orig) > 0))
  		goto out;
  
  	ret = true;
  out:
  	return ret;
  }
  
  /**
   * batadv_choose_next_candidate - select the next DHT candidate
   * @bat_priv: the bat priv with all the soft interface information
   * @cands: candidates array
   * @select: number of candidates already present in the array
   * @ip_key: key to look up in the DHT
   * @last_max: pointer where the address of the selected candidate will be saved
   */
  static void batadv_choose_next_candidate(struct batadv_priv *bat_priv,
  					 struct batadv_dat_candidate *cands,
  					 int select, batadv_dat_addr_t ip_key,
  					 batadv_dat_addr_t *last_max)
  {
  	batadv_dat_addr_t max = 0, tmp_max = 0;
  	struct batadv_orig_node *orig_node, *max_orig_node = NULL;
  	struct batadv_hashtable *hash = bat_priv->orig_hash;

  	struct hlist_head *head;
  	int i;
  
  	/* if no node is eligible as candidate, leave the candidate type as
  	 * NOT_FOUND
  	 */
  	cands[select].type = BATADV_DAT_CANDIDATE_NOT_FOUND;

  	/* iterate over the originator list and find the node with the closest

  	 * dat_address which has not been selected yet
  	 */
  	for (i = 0; i < hash->size; i++) {
  		head = &hash->table[i];
  
  		rcu_read_lock();

  		hlist_for_each_entry_rcu(orig_node, head, hash_entry) {

  			/* the dht space is a ring using unsigned addresses */

  			tmp_max = BATADV_DAT_ADDR_MAX - orig_node->dat_addr +
  				  ip_key;
  
  			if (!batadv_is_orig_node_eligible(cands, select,
  							  tmp_max, max,
  							  *last_max, orig_node,
  							  max_orig_node))
  				continue;
  
  			if (!atomic_inc_not_zero(&orig_node->refcount))
  				continue;
  
  			max = tmp_max;
  			if (max_orig_node)
  				batadv_orig_node_free_ref(max_orig_node);
  			max_orig_node = orig_node;
  		}
  		rcu_read_unlock();
  	}
  	if (max_orig_node) {
  		cands[select].type = BATADV_DAT_CANDIDATE_ORIG;
  		cands[select].orig_node = max_orig_node;
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "dat_select_candidates() %d: selected %pM addr=%u dist=%u
  ",
  			   select, max_orig_node->orig, max_orig_node->dat_addr,
  			   max);
  	}
  	*last_max = max;
  }
  
  /**

   * batadv_dat_select_candidates - select the nodes which the DHT message has to

   * be sent to
   * @bat_priv: the bat priv with all the soft interface information
   * @ip_dst: ipv4 to look up in the DHT
   *
   * An originator O is selected if and only if its DHT_ID value is one of three
   * closest values (from the LEFT, with wrap around if needed) then the hash
   * value of the key. ip_dst is the key.
   *

   * Returns the candidate array of size BATADV_DAT_CANDIDATE_NUM.

   */
  static struct batadv_dat_candidate *
  batadv_dat_select_candidates(struct batadv_priv *bat_priv, __be32 ip_dst)
  {
  	int select;
  	batadv_dat_addr_t last_max = BATADV_DAT_ADDR_MAX, ip_key;
  	struct batadv_dat_candidate *res;
  
  	if (!bat_priv->orig_hash)
  		return NULL;
  
  	res = kmalloc(BATADV_DAT_CANDIDATES_NUM * sizeof(*res), GFP_ATOMIC);
  	if (!res)
  		return NULL;
  
  	ip_key = (batadv_dat_addr_t)batadv_hash_dat(&ip_dst,
  						    BATADV_DAT_ADDR_MAX);
  
  	batadv_dbg(BATADV_DBG_DAT, bat_priv,
  		   "dat_select_candidates(): IP=%pI4 hash(IP)=%u
  ", &ip_dst,
  		   ip_key);
  
  	for (select = 0; select < BATADV_DAT_CANDIDATES_NUM; select++)
  		batadv_choose_next_candidate(bat_priv, res, select, ip_key,
  					     &last_max);
  
  	return res;
  }
  
  /**
   * batadv_dat_send_data - send a payload to the selected candidates
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: payload to send
   * @ip: the DHT key
   * @packet_subtype: unicast4addr packet subtype to use
   *

   * This function copies the skb with pskb_copy() and is sent as unicast packet
   * to each of the selected candidates.

   *

   * Returns true if the packet is sent to at least one candidate, false
   * otherwise.

   */
  static bool batadv_dat_send_data(struct batadv_priv *bat_priv,
  				 struct sk_buff *skb, __be32 ip,
  				 int packet_subtype)
  {
  	int i;
  	bool ret = false;
  	int send_status;
  	struct batadv_neigh_node *neigh_node = NULL;
  	struct sk_buff *tmp_skb;
  	struct batadv_dat_candidate *cand;
  
  	cand = batadv_dat_select_candidates(bat_priv, ip);
  	if (!cand)
  		goto out;
  
  	batadv_dbg(BATADV_DBG_DAT, bat_priv, "DHT_SEND for %pI4
  ", &ip);
  
  	for (i = 0; i < BATADV_DAT_CANDIDATES_NUM; i++) {
  		if (cand[i].type == BATADV_DAT_CANDIDATE_NOT_FOUND)
  			continue;
  
  		neigh_node = batadv_orig_node_get_router(cand[i].orig_node);
  		if (!neigh_node)
  			goto free_orig;
  
  		tmp_skb = pskb_copy(skb, GFP_ATOMIC);

  		if (!batadv_send_skb_prepare_unicast_4addr(bat_priv, tmp_skb,
  							   cand[i].orig_node,
  							   packet_subtype)) {

  			kfree_skb(tmp_skb);
  			goto free_neigh;
  		}
  
  		send_status = batadv_send_skb_packet(tmp_skb,
  						     neigh_node->if_incoming,
  						     neigh_node->addr);

  		if (send_status == NET_XMIT_SUCCESS) {
  			/* count the sent packet */
  			switch (packet_subtype) {
  			case BATADV_P_DAT_DHT_GET:
  				batadv_inc_counter(bat_priv,
  						   BATADV_CNT_DAT_GET_TX);
  				break;
  			case BATADV_P_DAT_DHT_PUT:
  				batadv_inc_counter(bat_priv,
  						   BATADV_CNT_DAT_PUT_TX);
  				break;
  			}

  			/* packet sent to a candidate: return true */
  			ret = true;

  		}

  free_neigh:
  		batadv_neigh_node_free_ref(neigh_node);
  free_orig:
  		batadv_orig_node_free_ref(cand[i].orig_node);
  	}
  
  out:
  	kfree(cand);
  	return ret;
  }

  
  /**

   * batadv_dat_tvlv_container_update - update the dat tvlv container after dat
   *  setting change
   * @bat_priv: the bat priv with all the soft interface information
   */
  static void batadv_dat_tvlv_container_update(struct batadv_priv *bat_priv)
  {
  	char dat_mode;
  
  	dat_mode = atomic_read(&bat_priv->distributed_arp_table);
  
  	switch (dat_mode) {
  	case 0:
  		batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_DAT, 1);
  		break;
  	case 1:
  		batadv_tvlv_container_register(bat_priv, BATADV_TVLV_DAT, 1,
  					       NULL, 0);
  		break;
  	}
  }
  
  /**
   * batadv_dat_status_update - update the dat tvlv container after dat
   *  setting change
   * @net_dev: the soft interface net device
   */
  void batadv_dat_status_update(struct net_device *net_dev)
  {
  	struct batadv_priv *bat_priv = netdev_priv(net_dev);
  	batadv_dat_tvlv_container_update(bat_priv);
  }
  
  /**
   * batadv_gw_tvlv_ogm_handler_v1 - process incoming dat 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_dat_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_DAT;
  	else
  		orig->capabilities |= BATADV_ORIG_CAPA_HAS_DAT;
  }
  
  /**

   * batadv_dat_hash_free - free the local DAT hash table
   * @bat_priv: the bat priv with all the soft interface information
   */
  static void batadv_dat_hash_free(struct batadv_priv *bat_priv)
  {

  	if (!bat_priv->dat.hash)
  		return;

  	__batadv_dat_purge(bat_priv, NULL);
  
  	batadv_hash_destroy(bat_priv->dat.hash);
  
  	bat_priv->dat.hash = NULL;
  }
  
  /**
   * batadv_dat_init - initialise the DAT internals
   * @bat_priv: the bat priv with all the soft interface information
   */
  int batadv_dat_init(struct batadv_priv *bat_priv)
  {
  	if (bat_priv->dat.hash)
  		return 0;
  
  	bat_priv->dat.hash = batadv_hash_new(1024);
  
  	if (!bat_priv->dat.hash)
  		return -ENOMEM;
  
  	batadv_dat_start_timer(bat_priv);

  	batadv_tvlv_handler_register(bat_priv, batadv_dat_tvlv_ogm_handler_v1,
  				     NULL, BATADV_TVLV_DAT, 1,
  				     BATADV_TVLV_HANDLER_OGM_CIFNOTFND);
  	batadv_dat_tvlv_container_update(bat_priv);

  	return 0;
  }
  
  /**
   * batadv_dat_free - free the DAT internals
   * @bat_priv: the bat priv with all the soft interface information
   */
  void batadv_dat_free(struct batadv_priv *bat_priv)
  {

  	batadv_tvlv_container_unregister(bat_priv, BATADV_TVLV_DAT, 1);
  	batadv_tvlv_handler_unregister(bat_priv, BATADV_TVLV_DAT, 1);

  	cancel_delayed_work_sync(&bat_priv->dat.work);
  
  	batadv_dat_hash_free(bat_priv);
  }
  
  /**
   * batadv_dat_cache_seq_print_text - print the local DAT hash table
   * @seq: seq file to print on
   * @offset: not used
   */
  int batadv_dat_cache_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->dat.hash;
  	struct batadv_dat_entry *dat_entry;
  	struct batadv_hard_iface *primary_if;

  	struct hlist_head *head;
  	unsigned long last_seen_jiffies;
  	int last_seen_msecs, last_seen_secs, last_seen_mins;
  	uint32_t i;
  
  	primary_if = batadv_seq_print_text_primary_if_get(seq);
  	if (!primary_if)
  		goto out;
  
  	seq_printf(seq, "Distributed ARP Table (%s):
  ", net_dev->name);

  	seq_printf(seq, "          %-7s          %-9s %4s %11s
  ", "IPv4",
  		   "MAC", "VID", "last-seen");

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

  		hlist_for_each_entry_rcu(dat_entry, head, hash_entry) {

  			last_seen_jiffies = jiffies - dat_entry->last_update;
  			last_seen_msecs = jiffies_to_msecs(last_seen_jiffies);
  			last_seen_mins = last_seen_msecs / 60000;
  			last_seen_msecs = last_seen_msecs % 60000;
  			last_seen_secs = last_seen_msecs / 1000;

  			seq_printf(seq, " * %15pI4 %14pM %4i %6i:%02i
  ",

  				   &dat_entry->ip, dat_entry->mac_addr,

  				   BATADV_PRINT_VID(dat_entry->vid),

  				   last_seen_mins, last_seen_secs);
  		}
  		rcu_read_unlock();
  	}
  
  out:
  	if (primary_if)
  		batadv_hardif_free_ref(primary_if);
  	return 0;
  }

  
  /**
   * batadv_arp_get_type - parse an ARP packet and gets the type
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: packet to analyse
   * @hdr_size: size of the possible header before the ARP packet in the skb
   *

   * Returns the ARP type if the skb contains a valid ARP packet, 0 otherwise.

   */
  static uint16_t batadv_arp_get_type(struct batadv_priv *bat_priv,
  				    struct sk_buff *skb, int hdr_size)
  {
  	struct arphdr *arphdr;
  	struct ethhdr *ethhdr;
  	__be32 ip_src, ip_dst;

  	uint8_t *hw_src, *hw_dst;

  	uint16_t type = 0;
  
  	/* pull the ethernet header */
  	if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN)))
  		goto out;
  
  	ethhdr = (struct ethhdr *)(skb->data + hdr_size);
  
  	if (ethhdr->h_proto != htons(ETH_P_ARP))
  		goto out;
  
  	/* pull the ARP payload */
  	if (unlikely(!pskb_may_pull(skb, hdr_size + ETH_HLEN +
  				    arp_hdr_len(skb->dev))))
  		goto out;
  
  	arphdr = (struct arphdr *)(skb->data + hdr_size + ETH_HLEN);

  	/* check whether the ARP packet carries a valid IP information */

  	if (arphdr->ar_hrd != htons(ARPHRD_ETHER))
  		goto out;
  
  	if (arphdr->ar_pro != htons(ETH_P_IP))
  		goto out;
  
  	if (arphdr->ar_hln != ETH_ALEN)
  		goto out;
  
  	if (arphdr->ar_pln != 4)
  		goto out;
  
  	/* Check for bad reply/request. If the ARP message is not sane, DAT
  	 * will simply ignore it
  	 */
  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);
  	if (ipv4_is_loopback(ip_src) || ipv4_is_multicast(ip_src) ||

  	    ipv4_is_loopback(ip_dst) || ipv4_is_multicast(ip_dst) ||
  	    ipv4_is_zeronet(ip_src) || ipv4_is_lbcast(ip_src) ||
  	    ipv4_is_zeronet(ip_dst) || ipv4_is_lbcast(ip_dst))

  		goto out;

  	hw_src = batadv_arp_hw_src(skb, hdr_size);
  	if (is_zero_ether_addr(hw_src) || is_multicast_ether_addr(hw_src))
  		goto out;

  	/* don't care about the destination MAC address in ARP requests */

  	if (arphdr->ar_op != htons(ARPOP_REQUEST)) {
  		hw_dst = batadv_arp_hw_dst(skb, hdr_size);
  		if (is_zero_ether_addr(hw_dst) ||
  		    is_multicast_ether_addr(hw_dst))
  			goto out;
  	}

  	type = ntohs(arphdr->ar_op);
  out:
  	return type;
  }

  
  /**

   * batadv_dat_get_vid - extract the VLAN identifier from skb if any
   * @skb: the buffer containing the packet to extract the VID from
   * @hdr_size: the size of the batman-adv header encapsulating the packet
   *
   * If the packet embedded in the skb is vlan tagged this function returns the
   * VID with the BATADV_VLAN_HAS_TAG flag. Otherwise BATADV_NO_FLAGS is returned.
   */
  static unsigned short batadv_dat_get_vid(struct sk_buff *skb, int *hdr_size)
  {
  	unsigned short vid;
  
  	vid = batadv_get_vid(skb, *hdr_size);
  
  	/* ARP parsing functions jump forward of hdr_size + ETH_HLEN.
  	 * If the header contained in the packet is a VLAN one (which is longer)
  	 * hdr_size is updated so that the functions will still skip the
  	 * correct amount of bytes.
  	 */
  	if (vid & BATADV_VLAN_HAS_TAG)
  		*hdr_size += VLAN_HLEN;
  
  	return vid;
  }
  
  /**

   * batadv_dat_snoop_outgoing_arp_request - snoop the ARP request and try to
   * answer using DAT
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: packet to check
   *
   * Returns true if the message has been sent to the dht candidates, false

   * otherwise. In case of a positive return value the message has to be enqueued
   * to permit the fallback.

   */
  bool batadv_dat_snoop_outgoing_arp_request(struct batadv_priv *bat_priv,
  					   struct sk_buff *skb)
  {
  	uint16_t type = 0;
  	__be32 ip_dst, ip_src;
  	uint8_t *hw_src;
  	bool ret = false;
  	struct batadv_dat_entry *dat_entry = NULL;
  	struct sk_buff *skb_new;

  	int hdr_size = 0;
  	unsigned short vid;

  	if (!atomic_read(&bat_priv->distributed_arp_table))
  		goto out;

  	vid = batadv_dat_get_vid(skb, &hdr_size);
  
  	type = batadv_arp_get_type(bat_priv, skb, hdr_size);

  	/* If the node gets an ARP_REQUEST it has to send a DHT_GET unicast
  	 * message to the selected DHT candidates
  	 */
  	if (type != ARPOP_REQUEST)
  		goto out;

  	batadv_dbg_arp(bat_priv, skb, type, hdr_size,
  		       "Parsing outgoing ARP REQUEST");

  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	hw_src = batadv_arp_hw_src(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);

  	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

  	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);

  	if (dat_entry) {

  		/* If the ARP request is destined for a local client the local
  		 * client will answer itself. DAT would only generate a
  		 * duplicate packet.
  		 *
  		 * Moreover, if the soft-interface is enslaved into a bridge, an
  		 * additional DAT answer may trigger kernel warnings about
  		 * a packet coming from the wrong port.
  		 */

  		if (batadv_is_my_client(bat_priv, dat_entry->mac_addr,
  					BATADV_NO_FLAGS)) {

  			ret = true;
  			goto out;
  		}

  		skb_new = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_src,

  				     bat_priv->soft_iface, ip_dst, hw_src,

  				     dat_entry->mac_addr, hw_src);
  		if (!skb_new)
  			goto out;

  		if (vid & BATADV_VLAN_HAS_TAG)
  			skb_new = vlan_insert_tag(skb_new, htons(ETH_P_8021Q),
  						  vid & VLAN_VID_MASK);

  		skb_reset_mac_header(skb_new);
  		skb_new->protocol = eth_type_trans(skb_new,

  						   bat_priv->soft_iface);

  		bat_priv->stats.rx_packets++;

  		bat_priv->stats.rx_bytes += skb->len + ETH_HLEN + hdr_size;

  		bat_priv->soft_iface->last_rx = jiffies;

  
  		netif_rx(skb_new);
  		batadv_dbg(BATADV_DBG_DAT, bat_priv, "ARP request replied locally
  ");
  		ret = true;
  	} else {

  		/* Send the request to the DHT */

  		ret = batadv_dat_send_data(bat_priv, skb, ip_dst,
  					   BATADV_P_DAT_DHT_GET);
  	}
  out:
  	if (dat_entry)
  		batadv_dat_entry_free_ref(dat_entry);

  	return ret;
  }
  
  /**
   * batadv_dat_snoop_incoming_arp_request - snoop the ARP request and try to
   * answer using the local DAT storage
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: packet to check
   * @hdr_size: size of the encapsulation header
   *

   * Returns true if the request has been answered, false otherwise.

   */
  bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
  					   struct sk_buff *skb, int hdr_size)
  {
  	uint16_t type;
  	__be32 ip_src, ip_dst;
  	uint8_t *hw_src;
  	struct sk_buff *skb_new;

  	struct batadv_dat_entry *dat_entry = NULL;
  	bool ret = false;

  	unsigned short vid;

  	int err;

  	if (!atomic_read(&bat_priv->distributed_arp_table))
  		goto out;

  	vid = batadv_dat_get_vid(skb, &hdr_size);

  	type = batadv_arp_get_type(bat_priv, skb, hdr_size);
  	if (type != ARPOP_REQUEST)
  		goto out;
  
  	hw_src = batadv_arp_hw_src(skb, hdr_size);
  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);
  
  	batadv_dbg_arp(bat_priv, skb, type, hdr_size,
  		       "Parsing incoming ARP REQUEST");

  	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);

  	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);

  	if (!dat_entry)
  		goto out;

  	skb_new = arp_create(ARPOP_REPLY, ETH_P_ARP, ip_src,

  			     bat_priv->soft_iface, ip_dst, hw_src,

  			     dat_entry->mac_addr, hw_src);
  
  	if (!skb_new)
  		goto out;

  	if (vid & BATADV_VLAN_HAS_TAG)
  		skb_new = vlan_insert_tag(skb_new, htons(ETH_P_8021Q),
  					  vid & VLAN_VID_MASK);

  	/* To preserve backwards compatibility, the node has choose the outgoing
  	 * format based on the incoming request packet type. The assumption is
  	 * that a node not using the 4addr packet format doesn't support it.

  	 */
  	if (hdr_size == sizeof(struct batadv_unicast_4addr_packet))

  		err = batadv_send_skb_via_tt_4addr(bat_priv, skb_new,
  						   BATADV_P_DAT_CACHE_REPLY,
  						   vid);

  	else

  		err = batadv_send_skb_via_tt(bat_priv, skb_new, vid);

  	if (err != NET_XMIT_DROP) {

  		batadv_inc_counter(bat_priv, BATADV_CNT_DAT_CACHED_REPLY_TX);

  		ret = true;

  	}

  out:
  	if (dat_entry)
  		batadv_dat_entry_free_ref(dat_entry);

  	if (ret)
  		kfree_skb(skb);
  	return ret;
  }
  
  /**
   * batadv_dat_snoop_outgoing_arp_reply - snoop the ARP reply and fill the DHT
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: packet to check
   */
  void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
  					 struct sk_buff *skb)
  {
  	uint16_t type;
  	__be32 ip_src, ip_dst;
  	uint8_t *hw_src, *hw_dst;

  	int hdr_size = 0;
  	unsigned short vid;

  	if (!atomic_read(&bat_priv->distributed_arp_table))
  		return;

  	vid = batadv_dat_get_vid(skb, &hdr_size);
  
  	type = batadv_arp_get_type(bat_priv, skb, hdr_size);

  	if (type != ARPOP_REPLY)
  		return;

  	batadv_dbg_arp(bat_priv, skb, type, hdr_size,
  		       "Parsing outgoing ARP REPLY");

  	hw_src = batadv_arp_hw_src(skb, hdr_size);
  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	hw_dst = batadv_arp_hw_dst(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);

  	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
  	batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

  
  	/* Send the ARP reply to the candidates for both the IP addresses that

  	 * the node obtained from the ARP reply

  	 */
  	batadv_dat_send_data(bat_priv, skb, ip_src, BATADV_P_DAT_DHT_PUT);
  	batadv_dat_send_data(bat_priv, skb, ip_dst, BATADV_P_DAT_DHT_PUT);
  }
  /**
   * batadv_dat_snoop_incoming_arp_reply - snoop the ARP reply and fill the local
   * DAT storage only
   * @bat_priv: the bat priv with all the soft interface information
   * @skb: packet to check

   * @hdr_size: size of the encapsulation header

   */
  bool batadv_dat_snoop_incoming_arp_reply(struct batadv_priv *bat_priv,
  					 struct sk_buff *skb, int hdr_size)
  {
  	uint16_t type;
  	__be32 ip_src, ip_dst;
  	uint8_t *hw_src, *hw_dst;
  	bool ret = false;

  	unsigned short vid;

  	if (!atomic_read(&bat_priv->distributed_arp_table))
  		goto out;

  	vid = batadv_dat_get_vid(skb, &hdr_size);

  	type = batadv_arp_get_type(bat_priv, skb, hdr_size);
  	if (type != ARPOP_REPLY)
  		goto out;
  
  	batadv_dbg_arp(bat_priv, skb, type, hdr_size,
  		       "Parsing incoming ARP REPLY");
  
  	hw_src = batadv_arp_hw_src(skb, hdr_size);
  	ip_src = batadv_arp_ip_src(skb, hdr_size);
  	hw_dst = batadv_arp_hw_dst(skb, hdr_size);
  	ip_dst = batadv_arp_ip_dst(skb, hdr_size);
  
  	/* Update our internal cache with both the IP addresses the node got
  	 * within the ARP reply
  	 */

  	batadv_dat_entry_add(bat_priv, ip_src, hw_src, vid);
  	batadv_dat_entry_add(bat_priv, ip_dst, hw_dst, vid);

  
  	/* if this REPLY is directed to a client of mine, let's deliver the
  	 * packet to the interface
  	 */

  	ret = !batadv_is_my_client(bat_priv, hw_dst, vid);

  out:

  	if (ret)
  		kfree_skb(skb);

  	/* if ret == false -> packet has to be delivered to the interface */
  	return ret;
  }
  
  /**
   * batadv_dat_drop_broadcast_packet - check if an ARP request has to be dropped

   * (because the node has already obtained the reply via DAT) or not

   * @bat_priv: the bat priv with all the soft interface information
   * @forw_packet: the broadcast packet
   *

   * Returns true if the node can drop the packet, false otherwise.

   */
  bool batadv_dat_drop_broadcast_packet(struct batadv_priv *bat_priv,
  				      struct batadv_forw_packet *forw_packet)
  {
  	uint16_t type;
  	__be32 ip_dst;
  	struct batadv_dat_entry *dat_entry = NULL;
  	bool ret = false;

  	int hdr_size = sizeof(struct batadv_bcast_packet);
  	unsigned short vid;

  	if (!atomic_read(&bat_priv->distributed_arp_table))
  		goto out;

  	/* If this packet is an ARP_REQUEST and the node already has the
  	 * information that it is going to ask, then the packet can be dropped
  	 */
  	if (forw_packet->num_packets)
  		goto out;

  	vid = batadv_dat_get_vid(forw_packet->skb, &hdr_size);
  
  	type = batadv_arp_get_type(bat_priv, forw_packet->skb, hdr_size);

  	if (type != ARPOP_REQUEST)
  		goto out;

  	ip_dst = batadv_arp_ip_dst(forw_packet->skb, hdr_size);
  	dat_entry = batadv_dat_entry_hash_find(bat_priv, ip_dst, vid);

  	/* check if the node already got this entry */
  	if (!dat_entry) {
  		batadv_dbg(BATADV_DBG_DAT, bat_priv,
  			   "ARP Request for %pI4: fallback
  ", &ip_dst);
  		goto out;
  	}
  
  	batadv_dbg(BATADV_DBG_DAT, bat_priv,
  		   "ARP Request for %pI4: fallback prevented
  ", &ip_dst);
  	ret = true;
  
  out:
  	if (dat_entry)
  		batadv_dat_entry_free_ref(dat_entry);
  	return ret;
  }