/* Copyright (C) 2013-2016  B.A.T.M.A.N. contributors:

   *
   * Martin Hundebøll <martin@hundeboll.net>
   *
   * 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 "fragmentation.h"

  #include "main.h"
  
  #include <linux/atomic.h>
  #include <linux/byteorder/generic.h>
  #include <linux/etherdevice.h>
  #include <linux/fs.h>
  #include <linux/if_ether.h>
  #include <linux/jiffies.h>
  #include <linux/kernel.h>

  #include <linux/lockdep.h>

  #include <linux/netdevice.h>
  #include <linux/pkt_sched.h>
  #include <linux/skbuff.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/string.h>
  
  #include "hard-interface.h"

  #include "originator.h"

  #include "packet.h"

  #include "routing.h"

  #include "send.h"

  #include "soft-interface.h"

  /**
   * batadv_frag_clear_chain - delete entries in the fragment buffer chain
   * @head: head of chain with entries.
   *
   * Free fragments in the passed hlist. Should be called with appropriate lock.
   */
  static void batadv_frag_clear_chain(struct hlist_head *head)
  {
  	struct batadv_frag_list_entry *entry;
  	struct hlist_node *node;
  
  	hlist_for_each_entry_safe(entry, node, head, list) {
  		hlist_del(&entry->list);
  		kfree_skb(entry->skb);
  		kfree(entry);
  	}
  }
  
  /**
   * batadv_frag_purge_orig - free fragments associated to an orig
   * @orig_node: originator to free fragments from
   * @check_cb: optional function to tell if an entry should be purged
   */
  void batadv_frag_purge_orig(struct batadv_orig_node *orig_node,
  			    bool (*check_cb)(struct batadv_frag_table_entry *))
  {
  	struct batadv_frag_table_entry *chain;

  	u8 i;

  
  	for (i = 0; i < BATADV_FRAG_BUFFER_COUNT; i++) {
  		chain = &orig_node->fragments[i];

  		spin_lock_bh(&chain->lock);

  
  		if (!check_cb || check_cb(chain)) {

  			batadv_frag_clear_chain(&chain->head);
  			chain->size = 0;

  		}

  		spin_unlock_bh(&chain->lock);

  	}
  }
  
  /**
   * batadv_frag_size_limit - maximum possible size of packet to be fragmented
   *

   * Return: the maximum size of payload that can be fragmented.

   */
  static int batadv_frag_size_limit(void)
  {
  	int limit = BATADV_FRAG_MAX_FRAG_SIZE;
  
  	limit -= sizeof(struct batadv_frag_packet);
  	limit *= BATADV_FRAG_MAX_FRAGMENTS;
  
  	return limit;
  }
  
  /**
   * batadv_frag_init_chain - check and prepare fragment chain for new fragment
   * @chain: chain in fragments table to init
   * @seqno: sequence number of the received fragment
   *
   * Make chain ready for a fragment with sequence number "seqno". Delete existing
   * entries if they have an "old" sequence number.
   *
   * Caller must hold chain->lock.
   *

   * Return: true if chain is empty and caller can just insert the new fragment

   * without searching for the right position.
   */
  static bool batadv_frag_init_chain(struct batadv_frag_table_entry *chain,

  				   u16 seqno)

  {

  	lockdep_assert_held(&chain->lock);

  	if (chain->seqno == seqno)
  		return false;
  
  	if (!hlist_empty(&chain->head))
  		batadv_frag_clear_chain(&chain->head);
  
  	chain->size = 0;
  	chain->seqno = seqno;
  
  	return true;
  }
  
  /**
   * batadv_frag_insert_packet - insert a fragment into a fragment chain
   * @orig_node: originator that the fragment was received from
   * @skb: skb to insert
   * @chain_out: list head to attach complete chains of fragments to
   *
   * Insert a new fragment into the reverse ordered chain in the right table
   * entry. The hash table entry is cleared if "old" fragments exist in it.
   *

   * Return: true if skb is buffered, false on error. If the chain has all the

   * fragments needed to merge the packet, the chain is moved to the passed head
   * to avoid locking the chain in the table.
   */
  static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
  				      struct sk_buff *skb,
  				      struct hlist_head *chain_out)
  {
  	struct batadv_frag_table_entry *chain;
  	struct batadv_frag_list_entry *frag_entry_new = NULL, *frag_entry_curr;

  	struct batadv_frag_list_entry *frag_entry_last = NULL;

  	struct batadv_frag_packet *frag_packet;

  	u8 bucket;
  	u16 seqno, hdr_size = sizeof(struct batadv_frag_packet);

  	bool ret = false;
  
  	/* Linearize packet to avoid linearizing 16 packets in a row when doing
  	 * the later merge. Non-linear merge should be added to remove this
  	 * linearization.
  	 */
  	if (skb_linearize(skb) < 0)
  		goto err;
  
  	frag_packet = (struct batadv_frag_packet *)skb->data;
  	seqno = ntohs(frag_packet->seqno);
  	bucket = seqno % BATADV_FRAG_BUFFER_COUNT;
  
  	frag_entry_new = kmalloc(sizeof(*frag_entry_new), GFP_ATOMIC);
  	if (!frag_entry_new)
  		goto err;
  
  	frag_entry_new->skb = skb;
  	frag_entry_new->no = frag_packet->no;
  
  	/* Select entry in the "chain table" and delete any prior fragments
  	 * with another sequence number. batadv_frag_init_chain() returns true,
  	 * if the list is empty at return.
  	 */
  	chain = &orig_node->fragments[bucket];
  	spin_lock_bh(&chain->lock);
  	if (batadv_frag_init_chain(chain, seqno)) {
  		hlist_add_head(&frag_entry_new->list, &chain->head);
  		chain->size = skb->len - hdr_size;
  		chain->timestamp = jiffies;

  		chain->total_size = ntohs(frag_packet->total_size);

  		ret = true;
  		goto out;
  	}
  
  	/* Find the position for the new fragment. */
  	hlist_for_each_entry(frag_entry_curr, &chain->head, list) {
  		/* Drop packet if fragment already exists. */
  		if (frag_entry_curr->no == frag_entry_new->no)
  			goto err_unlock;
  
  		/* Order fragments from highest to lowest. */
  		if (frag_entry_curr->no < frag_entry_new->no) {
  			hlist_add_before(&frag_entry_new->list,
  					 &frag_entry_curr->list);
  			chain->size += skb->len - hdr_size;
  			chain->timestamp = jiffies;
  			ret = true;
  			goto out;
  		}

  
  		/* store current entry because it could be the last in list */
  		frag_entry_last = frag_entry_curr;

  	}

  	/* Reached the end of the list, so insert after 'frag_entry_last'. */
  	if (likely(frag_entry_last)) {

  		hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);

  		chain->size += skb->len - hdr_size;
  		chain->timestamp = jiffies;
  		ret = true;
  	}
  
  out:
  	if (chain->size > batadv_frag_size_limit() ||

  	    chain->total_size != ntohs(frag_packet->total_size) ||
  	    chain->total_size > batadv_frag_size_limit()) {

  		/* Clear chain if total size of either the list or the packet

  		 * exceeds the maximum size of one merged packet. Don't allow
  		 * packets to have different total_size.

  		 */
  		batadv_frag_clear_chain(&chain->head);
  		chain->size = 0;
  	} else if (ntohs(frag_packet->total_size) == chain->size) {
  		/* All fragments received. Hand over chain to caller. */
  		hlist_move_list(&chain->head, chain_out);
  		chain->size = 0;
  	}
  
  err_unlock:
  	spin_unlock_bh(&chain->lock);
  
  err:
  	if (!ret)
  		kfree(frag_entry_new);
  
  	return ret;
  }
  
  /**
   * batadv_frag_merge_packets - merge a chain of fragments
   * @chain: head of chain with fragments

   *
   * Expand the first skb in the chain and copy the content of the remaining
   * skb's into the expanded one. After doing so, clear the chain.
   *

   * Return: the merged skb or NULL on error.

   */
  static struct sk_buff *

  batadv_frag_merge_packets(struct hlist_head *chain)

  {
  	struct batadv_frag_packet *packet;
  	struct batadv_frag_list_entry *entry;
  	struct sk_buff *skb_out = NULL;
  	int size, hdr_size = sizeof(struct batadv_frag_packet);

  	/* Remove first entry, as this is the destination for the rest of the
  	 * fragments.
  	 */
  	entry = hlist_entry(chain->first, struct batadv_frag_list_entry, list);
  	hlist_del(&entry->list);
  	skb_out = entry->skb;
  	kfree(entry);

  	packet = (struct batadv_frag_packet *)skb_out->data;
  	size = ntohs(packet->total_size);

  	/* Make room for the rest of the fragments. */

  	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {

  		kfree_skb(skb_out);
  		skb_out = NULL;
  		goto free;
  	}
  
  	/* Move the existing MAC header to just before the payload. (Override
  	 * the fragment header.)
  	 */
  	skb_pull_rcsum(skb_out, hdr_size);
  	memmove(skb_out->data - ETH_HLEN, skb_mac_header(skb_out), ETH_HLEN);
  	skb_set_mac_header(skb_out, -ETH_HLEN);
  	skb_reset_network_header(skb_out);
  	skb_reset_transport_header(skb_out);
  
  	/* Copy the payload of the each fragment into the last skb */
  	hlist_for_each_entry(entry, chain, list) {
  		size = entry->skb->len - hdr_size;
  		memcpy(skb_put(skb_out, size), entry->skb->data + hdr_size,
  		       size);
  	}
  
  free:
  	/* Locking is not needed, because 'chain' is not part of any orig. */
  	batadv_frag_clear_chain(chain);
  	return skb_out;
  }
  
  /**
   * batadv_frag_skb_buffer - buffer fragment for later merge
   * @skb: skb to buffer
   * @orig_node_src: originator that the skb is received from
   *
   * Add fragment to buffer and merge fragments if possible.
   *
   * There are three possible outcomes: 1) Packet is merged: Return true and
   * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
   * to NULL; 3) Error: Return false and leave skb as is.

   *
   * Return: true when packet is merged or buffered, false when skb is not not
   * used.

   */
  bool batadv_frag_skb_buffer(struct sk_buff **skb,
  			    struct batadv_orig_node *orig_node_src)
  {
  	struct sk_buff *skb_out = NULL;
  	struct hlist_head head = HLIST_HEAD_INIT;
  	bool ret = false;
  
  	/* Add packet to buffer and table entry if merge is possible. */
  	if (!batadv_frag_insert_packet(orig_node_src, *skb, &head))
  		goto out_err;
  
  	/* Leave if more fragments are needed to merge. */
  	if (hlist_empty(&head))
  		goto out;

  	skb_out = batadv_frag_merge_packets(&head);

  	if (!skb_out)
  		goto out_err;
  
  out:
  	*skb = skb_out;
  	ret = true;
  out_err:
  	return ret;
  }
  
  /**
   * batadv_frag_skb_fwd - forward fragments that would exceed MTU when merged
   * @skb: skb to forward
   * @recv_if: interface that the skb is received on
   * @orig_node_src: originator that the skb is received from
   *
   * Look up the next-hop of the fragments payload and check if the merged packet
   * will exceed the MTU towards the next-hop. If so, the fragment is forwarded
   * without merging it.
   *

   * Return: true if the fragment is consumed/forwarded, false otherwise.

   */
  bool batadv_frag_skb_fwd(struct sk_buff *skb,
  			 struct batadv_hard_iface *recv_if,
  			 struct batadv_orig_node *orig_node_src)
  {
  	struct batadv_priv *bat_priv = netdev_priv(recv_if->soft_iface);
  	struct batadv_orig_node *orig_node_dst = NULL;
  	struct batadv_neigh_node *neigh_node = NULL;
  	struct batadv_frag_packet *packet;

  	u16 total_size;

  	bool ret = false;
  
  	packet = (struct batadv_frag_packet *)skb->data;
  	orig_node_dst = batadv_orig_hash_find(bat_priv, packet->dest);
  	if (!orig_node_dst)
  		goto out;
  
  	neigh_node = batadv_find_router(bat_priv, orig_node_dst, recv_if);
  	if (!neigh_node)
  		goto out;
  
  	/* Forward the fragment, if the merged packet would be too big to
  	 * be assembled.
  	 */
  	total_size = ntohs(packet->total_size);
  	if (total_size > neigh_node->if_incoming->net_dev->mtu) {
  		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_FWD);
  		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_FWD_BYTES,
  				   skb->len + ETH_HLEN);

  		packet->ttl--;

  		batadv_send_unicast_skb(skb, neigh_node);

  		ret = true;
  	}
  
  out:
  	if (orig_node_dst)

  		batadv_orig_node_put(orig_node_dst);

  	if (neigh_node)

  		batadv_neigh_node_put(neigh_node);

  	return ret;
  }

  
  /**
   * batadv_frag_create - create a fragment from skb
   * @skb: skb to create fragment from
   * @frag_head: header to use in new fragment
   * @mtu: size of new fragment
   *
   * Split the passed skb into two fragments: A new one with size matching the
   * passed mtu and the old one with the rest. The new skb contains data from the
   * tail of the old skb.
   *

   * Return: the new fragment, NULL on error.

   */
  static struct sk_buff *batadv_frag_create(struct sk_buff *skb,
  					  struct batadv_frag_packet *frag_head,
  					  unsigned int mtu)
  {
  	struct sk_buff *skb_fragment;
  	unsigned header_size = sizeof(*frag_head);
  	unsigned fragment_size = mtu - header_size;
  
  	skb_fragment = netdev_alloc_skb(NULL, mtu + ETH_HLEN);
  	if (!skb_fragment)
  		goto err;
  
  	skb->priority = TC_PRIO_CONTROL;
  
  	/* Eat the last mtu-bytes of the skb */
  	skb_reserve(skb_fragment, header_size + ETH_HLEN);
  	skb_split(skb, skb_fragment, skb->len - fragment_size);
  
  	/* Add the header */
  	skb_push(skb_fragment, header_size);
  	memcpy(skb_fragment->data, frag_head, header_size);
  
  err:
  	return skb_fragment;
  }
  
  /**
   * batadv_frag_send_packet - create up to 16 fragments from the passed skb
   * @skb: skb to create fragments from
   * @orig_node: final destination of the created fragments
   * @neigh_node: next-hop of the created fragments
   *

   * Return: true on success, false otherwise.

   */
  bool batadv_frag_send_packet(struct sk_buff *skb,
  			     struct batadv_orig_node *orig_node,
  			     struct batadv_neigh_node *neigh_node)
  {
  	struct batadv_priv *bat_priv;

  	struct batadv_hard_iface *primary_if = NULL;

  	struct batadv_frag_packet frag_header;
  	struct sk_buff *skb_fragment;
  	unsigned mtu = neigh_node->if_incoming->net_dev->mtu;
  	unsigned header_size = sizeof(frag_header);
  	unsigned max_fragment_size, max_packet_size;

  	bool ret = false;

  
  	/* To avoid merge and refragmentation at next-hops we never send
  	 * fragments larger than BATADV_FRAG_MAX_FRAG_SIZE
  	 */
  	mtu = min_t(unsigned, mtu, BATADV_FRAG_MAX_FRAG_SIZE);

  	max_fragment_size = mtu - header_size;

  	max_packet_size = max_fragment_size * BATADV_FRAG_MAX_FRAGMENTS;
  
  	/* Don't even try to fragment, if we need more than 16 fragments */
  	if (skb->len > max_packet_size)
  		goto out_err;
  
  	bat_priv = orig_node->bat_priv;
  	primary_if = batadv_primary_if_get_selected(bat_priv);
  	if (!primary_if)
  		goto out_err;
  
  	/* Create one header to be copied to all fragments */

  	frag_header.packet_type = BATADV_UNICAST_FRAG;
  	frag_header.version = BATADV_COMPAT_VERSION;
  	frag_header.ttl = BATADV_TTL;

  	frag_header.seqno = htons(atomic_inc_return(&bat_priv->frag_seqno));
  	frag_header.reserved = 0;
  	frag_header.no = 0;
  	frag_header.total_size = htons(skb->len);

  	ether_addr_copy(frag_header.orig, primary_if->net_dev->dev_addr);
  	ether_addr_copy(frag_header.dest, orig_node->orig);

  
  	/* Eat and send fragments from the tail of skb */
  	while (skb->len > max_fragment_size) {
  		skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
  		if (!skb_fragment)
  			goto out_err;
  
  		batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
  		batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
  				   skb_fragment->len + ETH_HLEN);

  		batadv_send_unicast_skb(skb_fragment, neigh_node);

  		frag_header.no++;
  
  		/* The initial check in this function should cover this case */
  		if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1)
  			goto out_err;
  	}
  
  	/* Make room for the fragment header. */
  	if (batadv_skb_head_push(skb, header_size) < 0 ||
  	    pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0)
  		goto out_err;
  
  	memcpy(skb->data, &frag_header, header_size);
  
  	/* Send the last fragment */
  	batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_TX);
  	batadv_add_counter(bat_priv, BATADV_CNT_FRAG_TX_BYTES,
  			   skb->len + ETH_HLEN);

  	batadv_send_unicast_skb(skb, neigh_node);

  	ret = true;

  out_err:

  	if (primary_if)

  		batadv_hardif_put(primary_if);

  
  	return ret;

  }