net/batman-adv/fragmentation.c - kernel/msm-4.9 - Gitiles

 /* Copyright (C) 2013-2014 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 "main.h"
 #include "fragmentation.h"
 #include "send.h"
 #include "originator.h"
 #include "routing.h"
 #include "hard-interface.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;
 	uint8_t i;

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

 		if (!check_cb || check_cb(chain)) {
 			batadv_frag_clear_chain(&orig_node->fragments[i].head);
 			orig_node->fragments[i].size = 0;
 		}

 		spin_unlock_bh(&orig_node->fragments[i].lock);
 	}
 }

 /**
  * batadv_frag_size_limit - maximum possible size of packet to be fragmented
  *
  * Returns 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.
  *
  * Returns 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,
 				   uint16_t seqno)
 {
 	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.
  *
  * Returns 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;
 	uint8_t bucket;
 	uint16_t 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;
 		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() ||
 	    ntohs(frag_packet->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.
 		 */
 		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
  * @skb: packet with total size of skb after merging
  *
  * 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.
  *
  * Returns the merged skb or NULL on error.
  */
 static struct sk_buff *
 batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
 {
 	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);

 	/* Make sure incoming skb has non-bogus data. */
 	packet = (struct batadv_frag_packet *)skb->data;
 	size = ntohs(packet->total_size);
 	if (size > batadv_frag_size_limit())
 		goto free;

 	/* 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);

 	/* 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.
  */
 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, *skb);
 	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.
  *
  * Returns 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;
 	uint16_t 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_skb_packet(skb, neigh_node->if_incoming,
 				       neigh_node->addr);
 		ret = true;
 	}

 out:
 	if (orig_node_dst)
 		batadv_orig_node_free_ref(orig_node_dst);
 	if (neigh_node)
 		batadv_neigh_node_free_ref(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.
  *
  * Returns 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
  *
  * Returns 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_skb_packet(skb_fragment, neigh_node->if_incoming,
 				       neigh_node->addr);
 		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_skb_packet(skb, neigh_node->if_incoming, neigh_node->addr);

 	ret = true;

 out_err:
 	if (primary_if)
 		batadv_hardif_free_ref(primary_if);

 	return ret;
 }
	/* Copyright (C) 2013-2014 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 "main.h"
	#include "fragmentation.h"
	#include "send.h"
	#include "originator.h"
	#include "routing.h"
	#include "hard-interface.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;
	uint8_t i;

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

	if (!check_cb \|\| check_cb(chain)) {
	batadv_frag_clear_chain(&orig_node->fragments[i].head);
	orig_node->fragments[i].size = 0;
	}

	spin_unlock_bh(&orig_node->fragments[i].lock);
	}
	}

	/**
	* batadv_frag_size_limit - maximum possible size of packet to be fragmented
	*
	* Returns 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.
	*
	* Returns 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,
	uint16_t seqno)
	{
	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.
	*
	* Returns 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;
	uint8_t bucket;
	uint16_t 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;
	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() \|\|
	ntohs(frag_packet->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.
	*/
	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
	* @skb: packet with total size of skb after merging
	*
	* 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.
	*
	* Returns the merged skb or NULL on error.
	*/
	static struct sk_buff *
	batadv_frag_merge_packets(struct hlist_head chain, struct sk_buff skb)
	{
	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);

	/* Make sure incoming skb has non-bogus data. */
	packet = (struct batadv_frag_packet *)skb->data;
	size = ntohs(packet->total_size);
	if (size > batadv_frag_size_limit())
	goto free;

	/* 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);

	/* 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.
	*/
	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, *skb);
	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.
	*
	* Returns 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;
	uint16_t 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_skb_packet(skb, neigh_node->if_incoming,
	neigh_node->addr);
	ret = true;
	}

	out:
	if (orig_node_dst)
	batadv_orig_node_free_ref(orig_node_dst);
	if (neigh_node)
	batadv_neigh_node_free_ref(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.
	*
	* Returns 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
	*
	* Returns 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_skb_packet(skb_fragment, neigh_node->if_incoming,
	neigh_node->addr);
	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_skb_packet(skb, neigh_node->if_incoming, neigh_node->addr);

	ret = true;

	out_err:
	if (primary_if)
	batadv_hardif_free_ref(primary_if);

	return ret;
	}