/*
   * INET		An implementation of the TCP/IP protocol suite for the LINUX
   *		operating system.  INET is implemented using the  BSD Socket
   *		interface as the means of communication with the user level.
   *
   *		Generic TIME_WAIT sockets functions
   *
   *		From code orinally in TCP
   */

  #include <linux/kernel.h>

  #include <linux/kmemcheck.h>

  #include <linux/slab.h>

  #include <linux/module.h>

  #include <net/inet_hashtables.h>
  #include <net/inet_timewait_sock.h>

  #include <net/ip.h>

  /**
   *	inet_twsk_unhash - unhash a timewait socket from established hash
   *	@tw: timewait socket
   *
   *	unhash a timewait socket from established hash, if hashed.
   *	ehash lock must be held by caller.
   *	Returns 1 if caller should call inet_twsk_put() after lock release.

   */
  int inet_twsk_unhash(struct inet_timewait_sock *tw)
  {
  	if (hlist_nulls_unhashed(&tw->tw_node))
  		return 0;
  
  	hlist_nulls_del_rcu(&tw->tw_node);
  	sk_nulls_node_init(&tw->tw_node);

  	/*
  	 * We cannot call inet_twsk_put() ourself under lock,
  	 * caller must call it for us.
  	 */

  	return 1;
  }

  /**
   *	inet_twsk_bind_unhash - unhash a timewait socket from bind hash
   *	@tw: timewait socket
   *	@hashinfo: hashinfo pointer
   *
   *	unhash a timewait socket from bind hash, if hashed.
   *	bind hash lock must be held by caller.
   *	Returns 1 if caller should call inet_twsk_put() after lock release.

   */
  int inet_twsk_bind_unhash(struct inet_timewait_sock *tw,
  			  struct inet_hashinfo *hashinfo)
  {
  	struct inet_bind_bucket *tb = tw->tw_tb;
  
  	if (!tb)
  		return 0;
  
  	__hlist_del(&tw->tw_bind_node);
  	tw->tw_tb = NULL;
  	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);

  	/*
  	 * We cannot call inet_twsk_put() ourself under lock,
  	 * caller must call it for us.
  	 */

  	return 1;
  }

  /* Must be called with locally disabled BHs. */

  static void __inet_twsk_kill(struct inet_timewait_sock *tw,
  			     struct inet_hashinfo *hashinfo)

  {
  	struct inet_bind_hashbucket *bhead;

  	int refcnt;

  	/* Unlink from established hashes. */

  	spinlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);

  	spin_lock(lock);

  	refcnt = inet_twsk_unhash(tw);

  	spin_unlock(lock);

  
  	/* Disassociate with bind bucket. */

  	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), tw->tw_num,
  			hashinfo->bhash_size)];

  	spin_lock(&bhead->lock);

  	refcnt += inet_twsk_bind_unhash(tw, hashinfo);

  	spin_unlock(&bhead->lock);

  #ifdef SOCK_REFCNT_DEBUG
  	if (atomic_read(&tw->tw_refcnt) != 1) {
  		printk(KERN_DEBUG "%s timewait_sock %p refcnt=%d
  ",
  		       tw->tw_prot->name, tw, atomic_read(&tw->tw_refcnt));
  	}
  #endif

  	while (refcnt) {
  		inet_twsk_put(tw);
  		refcnt--;
  	}

  }

  static noinline void inet_twsk_free(struct inet_timewait_sock *tw)

  {

  	struct module *owner = tw->tw_prot->owner;
  	twsk_destructor((struct sock *)tw);

  #ifdef SOCK_REFCNT_DEBUG

  	pr_debug("%s timewait_sock %p released
  ", tw->tw_prot->name, tw);

  #endif

  	release_net(twsk_net(tw));
  	kmem_cache_free(tw->tw_prot->twsk_prot->twsk_slab, tw);
  	module_put(owner);
  }
  
  void inet_twsk_put(struct inet_timewait_sock *tw)
  {
  	if (atomic_dec_and_test(&tw->tw_refcnt))
  		inet_twsk_free(tw);

  }
  EXPORT_SYMBOL_GPL(inet_twsk_put);

  /*
   * Enter the time wait state. This is called with locally disabled BH.
   * Essentially we whip up a timewait bucket, copy the relevant info into it
   * from the SK, and mess with hash chains and list linkage.
   */
  void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
  			   struct inet_hashinfo *hashinfo)
  {
  	const struct inet_sock *inet = inet_sk(sk);

  	const struct inet_connection_sock *icsk = inet_csk(sk);

  	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);

  	spinlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);

  	struct inet_bind_hashbucket *bhead;
  	/* Step 1: Put TW into bind hash. Original socket stays there too.
  	   Note, that any socket with inet->num != 0 MUST be bound in
  	   binding cache, even if it is closed.
  	 */

  	bhead = &hashinfo->bhash[inet_bhashfn(twsk_net(tw), inet->inet_num,

  			hashinfo->bhash_size)];

  	spin_lock(&bhead->lock);

  	tw->tw_tb = icsk->icsk_bind_hash;

  	WARN_ON(!icsk->icsk_bind_hash);

  	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
  	spin_unlock(&bhead->lock);

  	spin_lock(lock);

  	/*
  	 * Step 2: Hash TW into TIMEWAIT chain.
  	 * Should be done before removing sk from established chain
  	 * because readers are lockless and search established first.
  	 */

  	inet_twsk_add_node_rcu(tw, &ehead->twchain);
  
  	/* Step 3: Remove SK from established hash. */
  	if (__sk_nulls_del_node_init_rcu(sk))
  		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

  	/*
  	 * Notes :

  	 * - We initially set tw_refcnt to 0 in inet_twsk_alloc()

  	 * - We add one reference for the bhash link
  	 * - We add one reference for the ehash link
  	 * - We want this refcnt update done before allowing other
  	 *   threads to find this tw in ehash chain.
  	 */
  	atomic_add(1 + 1 + 1, &tw->tw_refcnt);

  	spin_unlock(lock);

  }

  EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);

  struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk, const int state)
  {

  	struct inet_timewait_sock *tw =
  		kmem_cache_alloc(sk->sk_prot_creator->twsk_prot->twsk_slab,

  				 GFP_ATOMIC);

  	if (tw != NULL) {
  		const struct inet_sock *inet = inet_sk(sk);

  		kmemcheck_annotate_bitfield(tw, flags);

  		/* Give us an identity. */

  		tw->tw_daddr	    = inet->inet_daddr;
  		tw->tw_rcv_saddr    = inet->inet_rcv_saddr;

  		tw->tw_bound_dev_if = sk->sk_bound_dev_if;

  		tw->tw_tos	    = inet->tos;

  		tw->tw_num	    = inet->inet_num;

  		tw->tw_state	    = TCP_TIME_WAIT;
  		tw->tw_substate	    = state;

  		tw->tw_sport	    = inet->inet_sport;
  		tw->tw_dport	    = inet->inet_dport;

  		tw->tw_family	    = sk->sk_family;
  		tw->tw_reuse	    = sk->sk_reuse;

  		tw->tw_hash	    = sk->sk_hash;

  		tw->tw_ipv6only	    = 0;

  		tw->tw_transparent  = inet->transparent;

  		tw->tw_prot	    = sk->sk_prot_creator;

  		twsk_net_set(tw, hold_net(sock_net(sk)));

  		/*
  		 * Because we use RCU lookups, we should not set tw_refcnt
  		 * to a non null value before everything is setup for this
  		 * timewait socket.
  		 */
  		atomic_set(&tw->tw_refcnt, 0);

  		inet_twsk_dead_node_init(tw);

  		__module_get(tw->tw_prot->owner);

  	}
  
  	return tw;
  }

  EXPORT_SYMBOL_GPL(inet_twsk_alloc);
  
  /* Returns non-zero if quota exceeded.  */
  static int inet_twdr_do_twkill_work(struct inet_timewait_death_row *twdr,
  				    const int slot)
  {
  	struct inet_timewait_sock *tw;
  	struct hlist_node *node;
  	unsigned int killed;
  	int ret;
  
  	/* NOTE: compare this to previous version where lock
  	 * was released after detaching chain. It was racy,
  	 * because tw buckets are scheduled in not serialized context
  	 * in 2.3 (with netfilter), and with softnet it is common, because
  	 * soft irqs are not sequenced.
  	 */
  	killed = 0;
  	ret = 0;
  rescan:
  	inet_twsk_for_each_inmate(tw, node, &twdr->cells[slot]) {
  		__inet_twsk_del_dead_node(tw);
  		spin_unlock(&twdr->death_lock);
  		__inet_twsk_kill(tw, twdr->hashinfo);

  #ifdef CONFIG_NET_NS
  		NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITED);
  #endif

  		inet_twsk_put(tw);
  		killed++;
  		spin_lock(&twdr->death_lock);
  		if (killed > INET_TWDR_TWKILL_QUOTA) {
  			ret = 1;
  			break;
  		}
  
  		/* While we dropped twdr->death_lock, another cpu may have
  		 * killed off the next TW bucket in the list, therefore
  		 * do a fresh re-read of the hlist head node with the
  		 * lock reacquired.  We still use the hlist traversal
  		 * macro in order to get the prefetches.
  		 */
  		goto rescan;
  	}
  
  	twdr->tw_count -= killed;

  #ifndef CONFIG_NET_NS
  	NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITED, killed);
  #endif

  	return ret;
  }
  
  void inet_twdr_hangman(unsigned long data)
  {
  	struct inet_timewait_death_row *twdr;
  	int unsigned need_timer;
  
  	twdr = (struct inet_timewait_death_row *)data;
  	spin_lock(&twdr->death_lock);
  
  	if (twdr->tw_count == 0)
  		goto out;
  
  	need_timer = 0;
  	if (inet_twdr_do_twkill_work(twdr, twdr->slot)) {
  		twdr->thread_slots |= (1 << twdr->slot);

  		schedule_work(&twdr->twkill_work);
  		need_timer = 1;
  	} else {
  		/* We purged the entire slot, anything left?  */
  		if (twdr->tw_count)
  			need_timer = 1;

  		twdr->slot = ((twdr->slot + 1) & (INET_TWDR_TWKILL_SLOTS - 1));

  	}

  	if (need_timer)
  		mod_timer(&twdr->tw_timer, jiffies + twdr->period);
  out:
  	spin_unlock(&twdr->death_lock);
  }

  EXPORT_SYMBOL_GPL(inet_twdr_hangman);

  void inet_twdr_twkill_work(struct work_struct *work)

  {

  	struct inet_timewait_death_row *twdr =
  		container_of(work, struct inet_timewait_death_row, twkill_work);

  	int i;

  	BUILD_BUG_ON((INET_TWDR_TWKILL_SLOTS - 1) >
  			(sizeof(twdr->thread_slots) * 8));

  
  	while (twdr->thread_slots) {
  		spin_lock_bh(&twdr->death_lock);
  		for (i = 0; i < INET_TWDR_TWKILL_SLOTS; i++) {
  			if (!(twdr->thread_slots & (1 << i)))
  				continue;
  
  			while (inet_twdr_do_twkill_work(twdr, i) != 0) {
  				if (need_resched()) {
  					spin_unlock_bh(&twdr->death_lock);
  					schedule();
  					spin_lock_bh(&twdr->death_lock);
  				}
  			}
  
  			twdr->thread_slots &= ~(1 << i);
  		}
  		spin_unlock_bh(&twdr->death_lock);
  	}
  }

  EXPORT_SYMBOL_GPL(inet_twdr_twkill_work);
  
  /* These are always called from BH context.  See callers in
   * tcp_input.c to verify this.
   */
  
  /* This is for handling early-kills of TIME_WAIT sockets. */
  void inet_twsk_deschedule(struct inet_timewait_sock *tw,
  			  struct inet_timewait_death_row *twdr)
  {
  	spin_lock(&twdr->death_lock);
  	if (inet_twsk_del_dead_node(tw)) {
  		inet_twsk_put(tw);
  		if (--twdr->tw_count == 0)
  			del_timer(&twdr->tw_timer);
  	}
  	spin_unlock(&twdr->death_lock);
  	__inet_twsk_kill(tw, twdr->hashinfo);
  }

  EXPORT_SYMBOL(inet_twsk_deschedule);
  
  void inet_twsk_schedule(struct inet_timewait_sock *tw,
  		       struct inet_timewait_death_row *twdr,
  		       const int timeo, const int timewait_len)
  {
  	struct hlist_head *list;
  	int slot;
  
  	/* timeout := RTO * 3.5
  	 *
  	 * 3.5 = 1+2+0.5 to wait for two retransmits.
  	 *
  	 * RATIONALE: if FIN arrived and we entered TIME-WAIT state,
  	 * our ACK acking that FIN can be lost. If N subsequent retransmitted
  	 * FINs (or previous seqments) are lost (probability of such event
  	 * is p^(N+1), where p is probability to lose single packet and
  	 * time to detect the loss is about RTO*(2^N - 1) with exponential
  	 * backoff). Normal timewait length is calculated so, that we
  	 * waited at least for one retransmitted FIN (maximal RTO is 120sec).
  	 * [ BTW Linux. following BSD, violates this requirement waiting
  	 *   only for 60sec, we should wait at least for 240 secs.
  	 *   Well, 240 consumes too much of resources 8)
  	 * ]
  	 * This interval is not reduced to catch old duplicate and
  	 * responces to our wandering segments living for two MSLs.
  	 * However, if we use PAWS to detect
  	 * old duplicates, we can reduce the interval to bounds required
  	 * by RTO, rather than MSL. So, if peer understands PAWS, we
  	 * kill tw bucket after 3.5*RTO (it is important that this number
  	 * is greater than TS tick!) and detect old duplicates with help
  	 * of PAWS.
  	 */
  	slot = (timeo + (1 << INET_TWDR_RECYCLE_TICK) - 1) >> INET_TWDR_RECYCLE_TICK;
  
  	spin_lock(&twdr->death_lock);
  
  	/* Unlink it, if it was scheduled */
  	if (inet_twsk_del_dead_node(tw))
  		twdr->tw_count--;
  	else
  		atomic_inc(&tw->tw_refcnt);
  
  	if (slot >= INET_TWDR_RECYCLE_SLOTS) {
  		/* Schedule to slow timer */
  		if (timeo >= timewait_len) {
  			slot = INET_TWDR_TWKILL_SLOTS - 1;
  		} else {

  			slot = DIV_ROUND_UP(timeo, twdr->period);

  			if (slot >= INET_TWDR_TWKILL_SLOTS)
  				slot = INET_TWDR_TWKILL_SLOTS - 1;
  		}
  		tw->tw_ttd = jiffies + timeo;
  		slot = (twdr->slot + slot) & (INET_TWDR_TWKILL_SLOTS - 1);
  		list = &twdr->cells[slot];
  	} else {
  		tw->tw_ttd = jiffies + (slot << INET_TWDR_RECYCLE_TICK);
  
  		if (twdr->twcal_hand < 0) {
  			twdr->twcal_hand = 0;
  			twdr->twcal_jiffie = jiffies;
  			twdr->twcal_timer.expires = twdr->twcal_jiffie +
  					      (slot << INET_TWDR_RECYCLE_TICK);
  			add_timer(&twdr->twcal_timer);
  		} else {
  			if (time_after(twdr->twcal_timer.expires,
  				       jiffies + (slot << INET_TWDR_RECYCLE_TICK)))
  				mod_timer(&twdr->twcal_timer,
  					  jiffies + (slot << INET_TWDR_RECYCLE_TICK));
  			slot = (twdr->twcal_hand + slot) & (INET_TWDR_RECYCLE_SLOTS - 1);
  		}
  		list = &twdr->twcal_row[slot];
  	}
  
  	hlist_add_head(&tw->tw_death_node, list);
  
  	if (twdr->tw_count++ == 0)
  		mod_timer(&twdr->tw_timer, jiffies + twdr->period);
  	spin_unlock(&twdr->death_lock);
  }

  EXPORT_SYMBOL_GPL(inet_twsk_schedule);
  
  void inet_twdr_twcal_tick(unsigned long data)
  {
  	struct inet_timewait_death_row *twdr;
  	int n, slot;
  	unsigned long j;
  	unsigned long now = jiffies;
  	int killed = 0;
  	int adv = 0;
  
  	twdr = (struct inet_timewait_death_row *)data;
  
  	spin_lock(&twdr->death_lock);
  	if (twdr->twcal_hand < 0)
  		goto out;
  
  	slot = twdr->twcal_hand;
  	j = twdr->twcal_jiffie;
  
  	for (n = 0; n < INET_TWDR_RECYCLE_SLOTS; n++) {
  		if (time_before_eq(j, now)) {
  			struct hlist_node *node, *safe;
  			struct inet_timewait_sock *tw;
  
  			inet_twsk_for_each_inmate_safe(tw, node, safe,
  						       &twdr->twcal_row[slot]) {
  				__inet_twsk_del_dead_node(tw);
  				__inet_twsk_kill(tw, twdr->hashinfo);

  #ifdef CONFIG_NET_NS
  				NET_INC_STATS_BH(twsk_net(tw), LINUX_MIB_TIMEWAITKILLED);
  #endif

  				inet_twsk_put(tw);
  				killed++;
  			}
  		} else {
  			if (!adv) {
  				adv = 1;
  				twdr->twcal_jiffie = j;
  				twdr->twcal_hand = slot;
  			}
  
  			if (!hlist_empty(&twdr->twcal_row[slot])) {
  				mod_timer(&twdr->twcal_timer, j);
  				goto out;
  			}
  		}
  		j += 1 << INET_TWDR_RECYCLE_TICK;
  		slot = (slot + 1) & (INET_TWDR_RECYCLE_SLOTS - 1);
  	}
  	twdr->twcal_hand = -1;
  
  out:
  	if ((twdr->tw_count -= killed) == 0)
  		del_timer(&twdr->tw_timer);

  #ifndef CONFIG_NET_NS
  	NET_ADD_STATS_BH(&init_net, LINUX_MIB_TIMEWAITKILLED, killed);
  #endif

  	spin_unlock(&twdr->death_lock);
  }

  EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);

  void inet_twsk_purge(struct inet_hashinfo *hashinfo,

  		     struct inet_timewait_death_row *twdr, int family)
  {
  	struct inet_timewait_sock *tw;
  	struct sock *sk;

  	struct hlist_nulls_node *node;

  	unsigned int slot;

  	for (slot = 0; slot <= hashinfo->ehash_mask; slot++) {
  		struct inet_ehash_bucket *head = &hashinfo->ehash[slot];
  restart_rcu:
  		rcu_read_lock();

  restart:

  		sk_nulls_for_each_rcu(sk, node, &head->twchain) {

  			tw = inet_twsk(sk);

  			if ((tw->tw_family != family) ||
  				atomic_read(&twsk_net(tw)->count))

  				continue;

  			if (unlikely(!atomic_inc_not_zero(&tw->tw_refcnt)))
  				continue;

  			if (unlikely((tw->tw_family != family) ||
  				     atomic_read(&twsk_net(tw)->count))) {

  				inet_twsk_put(tw);
  				goto restart;
  			}
  
  			rcu_read_unlock();

  			local_bh_disable();

  			inet_twsk_deschedule(tw, twdr);

  			local_bh_enable();

  			inet_twsk_put(tw);

  			goto restart_rcu;

  		}

  		/* If the nulls value we got at the end of this lookup is
  		 * not the expected one, we must restart lookup.
  		 * We probably met an item that was moved to another chain.
  		 */
  		if (get_nulls_value(node) != slot)
  			goto restart;
  		rcu_read_unlock();

  	}

  }
  EXPORT_SYMBOL_GPL(inet_twsk_purge);