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

  #include <net/ip.h>

  
  /* 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;
  	struct inet_bind_bucket *tb;
  	/* Unlink from established hashes. */

  	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, tw->tw_hash);

  
  	write_lock(&ehead->lock);
  	if (hlist_unhashed(&tw->tw_node)) {
  		write_unlock(&ehead->lock);
  		return;
  	}
  	__hlist_del(&tw->tw_node);
  	sk_node_init(&tw->tw_node);
  	write_unlock(&ehead->lock);
  
  	/* Disassociate with bind bucket. */
  	bhead = &hashinfo->bhash[inet_bhashfn(tw->tw_num, hashinfo->bhash_size)];
  	spin_lock(&bhead->lock);
  	tb = tw->tw_tb;
  	__hlist_del(&tw->tw_bind_node);
  	tw->tw_tb = NULL;
  	inet_bind_bucket_destroy(hashinfo->bind_bucket_cachep, tb);
  	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
  	inet_twsk_put(tw);
  }
  
  /*
   * 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);

  	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(inet->num, hashinfo->bhash_size)];
  	spin_lock(&bhead->lock);

  	tw->tw_tb = icsk->icsk_bind_hash;
  	BUG_TRAP(icsk->icsk_bind_hash);

  	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
  	spin_unlock(&bhead->lock);
  
  	write_lock(&ehead->lock);
  
  	/* Step 2: Remove SK from established hash. */
  	if (__sk_del_node_init(sk))
  		sock_prot_dec_use(sk->sk_prot);

  	/* Step 3: Hash TW into TIMEWAIT chain. */
  	inet_twsk_add_node(tw, &ehead->twchain);

  	atomic_inc(&tw->tw_refcnt);
  
  	write_unlock(&ehead->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);
  
  		/* Give us an identity. */
  		tw->tw_daddr	    = inet->daddr;
  		tw->tw_rcv_saddr    = inet->rcv_saddr;
  		tw->tw_bound_dev_if = sk->sk_bound_dev_if;
  		tw->tw_num	    = inet->num;
  		tw->tw_state	    = TCP_TIME_WAIT;
  		tw->tw_substate	    = state;
  		tw->tw_sport	    = inet->sport;
  		tw->tw_dport	    = 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_prot	    = sk->sk_prot_creator;
  		atomic_set(&tw->tw_refcnt, 1);
  		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);
  		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;
  	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITED, killed);
  
  	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);
  
  extern void twkill_slots_invalid(void);

  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;
  
  	if ((INET_TWDR_TWKILL_SLOTS - 1) > (sizeof(twdr->thread_slots) * 8))
  		twkill_slots_invalid();
  
  	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 = (timeo + twdr->period - 1) / 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);
  				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);
  	NET_ADD_STATS_BH(LINUX_MIB_TIMEWAITKILLED, killed);
  	spin_unlock(&twdr->death_lock);
  }
  
  EXPORT_SYMBOL_GPL(inet_twdr_twcal_tick);