text: /*
   * 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.
   *
   *		Implementation of the Transmission Control Protocol(TCP).
   *
   * Authors:	Ross Biro
   *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
   *		Mark Evans, <evansmp@uhura.aston.ac.uk>
   *		Corey Minyard <wf-rch!minyard@relay.EU.net>
   *		Florian La Roche, <flla@stud.uni-sb.de>
   *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
   *		Linus Torvalds, <torvalds@cs.helsinki.fi>
   *		Alan Cox, <gw4pts@gw4pts.ampr.org>
   *		Matthew Dillon, <dillon@apollo.west.oic.com>
   *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
   *		Jorge Cwik, <jorge@laser.satlink.net>
   */
  
  #include <linux/module.h>
  #include <linux/gfp.h>
  #include <net/tcp.h>
  
  int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  int sysctl_tcp_orphan_retries __read_mostly;
  int sysctl_tcp_thin_linear_timeouts __read_mostly;
  
  static void tcp_write_err(struct sock *sk)
  {
  	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  	sk->sk_error_report(sk);
  
  	tcp_done(sk);
  	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  }
  
  /* Do not allow orphaned sockets to eat all our resources.
   * This is direct violation of TCP specs, but it is required
   * to prevent DoS attacks. It is called when a retransmission timeout
   * or zero probe timeout occurs on orphaned socket.
   *
   * Criteria is still not confirmed experimentally and may change.
   * We kill the socket, if:
   * 1. If number of orphaned sockets exceeds an administratively configured
   *    limit.
   * 2. If we have strong memory pressure.
   */
  static int tcp_out_of_resources(struct sock *sk, int do_reset)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	int shift = 0;
  
  	/* If peer does not open window for long time, or did not transmit
  	 * anything for long time, penalize it. */
  	if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  		shift++;
  
  	/* If some dubious ICMP arrived, penalize even more. */
  	if (sk->sk_err_soft)
  		shift++;
  
  	if (tcp_check_oom(sk, shift)) {
  		/* Catch exceptional cases, when connection requires reset.
  		 *      1. Last segment was sent recently. */
  		if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  		    /*  2. Window is closed. */
  		    (!tp->snd_wnd && !tp->packets_out))
  			do_reset = 1;
  		if (do_reset)
  			tcp_send_active_reset(sk, GFP_ATOMIC);
  		tcp_done(sk);
  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  		return 1;
  	}
  	return 0;
  }
  
  /* Calculate maximal number or retries on an orphaned socket. */
  static int tcp_orphan_retries(struct sock *sk, int alive)
  {
  	int retries = sysctl_tcp_orphan_retries; /* May be zero. */
  
  	/* We know from an ICMP that something is wrong. */
  	if (sk->sk_err_soft && !alive)
  		retries = 0;
  
  	/* However, if socket sent something recently, select some safe
  	 * number of retries. 8 corresponds to >100 seconds with minimal
  	 * RTO of 200msec. */
  	if (retries == 0 && alive)
  		retries = 8;
  	return retries;
  }
  
  static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
  {
  	/* Black hole detection */
  	if (sysctl_tcp_mtu_probing) {
  		if (!icsk->icsk_mtup.enabled) {
  			icsk->icsk_mtup.enabled = 1;
  			tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
  		} else {
  			struct tcp_sock *tp = tcp_sk(sk);
  			int mss;
  
  			mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
  			mss = min(sysctl_tcp_base_mss, mss);
  			mss = max(mss, 68 - tp->tcp_header_len);
  			icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
  			tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
  		}
  	}
  }
  
  /* This function calculates a "timeout" which is equivalent to the timeout of a
   * TCP connection after "boundary" unsuccessful, exponentially backed-off
   * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
   * syn_set flag is set.
   */
  static bool retransmits_timed_out(struct sock *sk,
  				  unsigned int boundary,
  				  unsigned int timeout,
  				  bool syn_set)
  {
  	unsigned int linear_backoff_thresh, start_ts;
  	unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
  
  	if (!inet_csk(sk)->icsk_retransmits)
  		return false;
  
  	if (unlikely(!tcp_sk(sk)->retrans_stamp))
  		start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
  	else
  		start_ts = tcp_sk(sk)->retrans_stamp;
  
  	if (likely(timeout == 0)) {
  		linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
  
  		if (boundary <= linear_backoff_thresh)
  			timeout = ((2 << boundary) - 1) * rto_base;
  		else
  			timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
  				(boundary - linear_backoff_thresh) * TCP_RTO_MAX;
  	}
  	return (tcp_time_stamp - start_ts) >= timeout;
  }
  
  /* A write timeout has occurred. Process the after effects. */
  static int tcp_write_timeout(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int retry_until;
  	bool do_reset, syn_set = false;
  
  	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
  		if (icsk->icsk_retransmits)
  			dst_negative_advice(sk);
  		retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
  		syn_set = true;
  	} else {
  		if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
  			/* Black hole detection */
  			tcp_mtu_probing(icsk, sk);
  
  			dst_negative_advice(sk);
  		}
  
  		retry_until = sysctl_tcp_retries2;
  		if (sock_flag(sk, SOCK_DEAD)) {
  			const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
  
  			retry_until = tcp_orphan_retries(sk, alive);
  			do_reset = alive ||
  				!retransmits_timed_out(sk, retry_until, 0, 0);
  
  			if (tcp_out_of_resources(sk, do_reset))
  				return 1;
  		}
  	}
  
  	if (retransmits_timed_out(sk, retry_until,
  				  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
  		/* Has it gone just too far? */
  		tcp_write_err(sk);
  		return 1;
  	}
  	return 0;
  }
  
  void tcp_delack_timer_handler(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	sk_mem_reclaim_partial(sk);
  
  	if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
  		goto out;
  
  	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
  		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
  		goto out;
  	}
  	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
  
  	if (!skb_queue_empty(&tp->ucopy.prequeue)) {
  		struct sk_buff *skb;
  
  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
  
  		while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
  			sk_backlog_rcv(sk, skb);
  
  		tp->ucopy.memory = 0;
  	}
  
  	if (inet_csk_ack_scheduled(sk)) {
  		if (!icsk->icsk_ack.pingpong) {
  			/* Delayed ACK missed: inflate ATO. */
  			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
  		} else {
  			/* Delayed ACK missed: leave pingpong mode and
  			 * deflate ATO.
  			 */
  			icsk->icsk_ack.pingpong = 0;
  			icsk->icsk_ack.ato      = TCP_ATO_MIN;
  		}
  		tcp_send_ack(sk);
  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
  	}
  
  out:
  	if (sk_under_memory_pressure(sk))
  		sk_mem_reclaim(sk);
  }
  
  static void tcp_delack_timer(unsigned long data)
  {
  	struct sock *sk = (struct sock *)data;
  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {
  		tcp_delack_timer_handler(sk);
  	} else {
  		inet_csk(sk)->icsk_ack.blocked = 1;
  		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
  		/* deleguate our work to tcp_release_cb() */
  		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
  			sock_hold(sk);
  	}
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  static void tcp_probe_timer(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	int max_probes;
  
  	if (tp->packets_out || !tcp_send_head(sk)) {
  		icsk->icsk_probes_out = 0;
  		return;
  	}
  
  	/* *WARNING* RFC 1122 forbids this
  	 *
  	 * It doesn't AFAIK, because we kill the retransmit timer -AK
  	 *
  	 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
  	 * this behaviour in Solaris down as a bug fix. [AC]
  	 *
  	 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
  	 * even if they advertise zero window. Hence, connection is killed only
  	 * if we received no ACKs for normal connection timeout. It is not killed
  	 * only because window stays zero for some time, window may be zero
  	 * until armageddon and even later. We are in full accordance
  	 * with RFCs, only probe timer combines both retransmission timeout
  	 * and probe timeout in one bottle.				--ANK
  	 */
  	max_probes = sysctl_tcp_retries2;
  
  	if (sock_flag(sk, SOCK_DEAD)) {
  		const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
  
  		max_probes = tcp_orphan_retries(sk, alive);
  
  		if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
  			return;
  	}
  
  	if (icsk->icsk_probes_out > max_probes) {
  		tcp_write_err(sk);
  	} else {
  		/* Only send another probe if we didn't close things up. */
  		tcp_send_probe0(sk);
  	}
  }
  
  /*
   *	The TCP retransmit timer.
   */
  
  void tcp_retransmit_timer(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	if (tp->early_retrans_delayed) {
  		tcp_resume_early_retransmit(sk);
  		return;
  	}
  
  	if (!tp->packets_out)
  		goto out;
  
  	WARN_ON(tcp_write_queue_empty(sk));
  
  	if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
  	    !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
  		/* Receiver dastardly shrinks window. Our retransmits
  		 * become zero probes, but we should not timeout this
  		 * connection. If the socket is an orphan, time it out,
  		 * we cannot allow such beasts to hang infinitely.
  		 */
  		struct inet_sock *inet = inet_sk(sk);
  		if (sk->sk_family == AF_INET) {
  			LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
  				       &inet->inet_daddr,
  				       ntohs(inet->inet_dport), inet->inet_num,
  				       tp->snd_una, tp->snd_nxt);
  		}
  #if IS_ENABLED(CONFIG_IPV6)
  		else if (sk->sk_family == AF_INET6) {
  			struct ipv6_pinfo *np = inet6_sk(sk);
  			LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
  				       &np->daddr,
  				       ntohs(inet->inet_dport), inet->inet_num,
  				       tp->snd_una, tp->snd_nxt);
  		}
  #endif
  		if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
  			tcp_write_err(sk);
  			goto out;
  		}
  		tcp_enter_loss(sk, 0);
  		tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
  		__sk_dst_reset(sk);
  		goto out_reset_timer;
  	}
  
  	if (tcp_write_timeout(sk))
  		goto out;
  
  	if (icsk->icsk_retransmits == 0) {
  		int mib_idx;
  
  		if (icsk->icsk_ca_state == TCP_CA_Recovery) {
  			if (tcp_is_sack(tp))
  				mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
  			else
  				mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
  		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {
  			mib_idx = LINUX_MIB_TCPLOSSFAILURES;
  		} else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
  			   tp->sacked_out) {
  			if (tcp_is_sack(tp))
  				mib_idx = LINUX_MIB_TCPSACKFAILURES;
  			else
  				mib_idx = LINUX_MIB_TCPRENOFAILURES;
  		} else {
  			mib_idx = LINUX_MIB_TCPTIMEOUTS;
  		}
  		NET_INC_STATS_BH(sock_net(sk), mib_idx);
  	}
  
  	if (tcp_use_frto(sk)) {
  		tcp_enter_frto(sk);
  	} else {
  		tcp_enter_loss(sk, 0);
  	}
  
  	if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
  		/* Retransmission failed because of local congestion,
  		 * do not backoff.
  		 */
  		if (!icsk->icsk_retransmits)
  			icsk->icsk_retransmits = 1;
  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  					  min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
  					  TCP_RTO_MAX);
  		goto out;
  	}
  
  	/* Increase the timeout each time we retransmit.  Note that
  	 * we do not increase the rtt estimate.  rto is initialized
  	 * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
  	 * that doubling rto each time is the least we can get away with.
  	 * In KA9Q, Karn uses this for the first few times, and then
  	 * goes to quadratic.  netBSD doubles, but only goes up to *64,
  	 * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
  	 * defined in the protocol as the maximum possible RTT.  I guess
  	 * we'll have to use something other than TCP to talk to the
  	 * University of Mars.
  	 *
  	 * PAWS allows us longer timeouts and large windows, so once
  	 * implemented ftp to mars will work nicely. We will have to fix
  	 * the 120 second clamps though!
  	 */
  	icsk->icsk_backoff++;
  	icsk->icsk_retransmits++;
  
  out_reset_timer:
  	/* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
  	 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
  	 * might be increased if the stream oscillates between thin and thick,
  	 * thus the old value might already be too high compared to the value
  	 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
  	 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
  	 * exponential backoff behaviour to avoid continue hammering
  	 * linear-timeout retransmissions into a black hole
  	 */
  	if (sk->sk_state == TCP_ESTABLISHED &&
  	    (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
  	    tcp_stream_is_thin(tp) &&
  	    icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
  		icsk->icsk_backoff = 0;
  		icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
  	} else {
  		/* Use normal (exponential) backoff */
  		icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
  	}
  	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
  	if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
  		__sk_dst_reset(sk);
  
  out:;
  }
  
  void tcp_write_timer_handler(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int event;
  
  	if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
  		goto out;
  
  	if (time_after(icsk->icsk_timeout, jiffies)) {
  		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
  		goto out;
  	}
  
  	event = icsk->icsk_pending;
  	icsk->icsk_pending = 0;
  
  	switch (event) {
  	case ICSK_TIME_RETRANS:
  		tcp_retransmit_timer(sk);
  		break;
  	case ICSK_TIME_PROBE0:
  		tcp_probe_timer(sk);
  		break;
  	}
  
  out:
  	sk_mem_reclaim(sk);
  }
  
  static void tcp_write_timer(unsigned long data)
  {
  	struct sock *sk = (struct sock *)data;
  
  	bh_lock_sock(sk);
  	if (!sock_owned_by_user(sk)) {
  		tcp_write_timer_handler(sk);
  	} else {
  		/* deleguate our work to tcp_release_cb() */
  		if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
  			sock_hold(sk);
  	}
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  /*
   *	Timer for listening sockets
   */
  
  static void tcp_synack_timer(struct sock *sk)
  {
  	inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
  				   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
  }
  
  void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
  {
  	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
  }
  EXPORT_SYMBOL(tcp_syn_ack_timeout);
  
  void tcp_set_keepalive(struct sock *sk, int val)
  {
  	if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
  		return;
  
  	if (val && !sock_flag(sk, SOCK_KEEPOPEN))
  		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
  	else if (!val)
  		inet_csk_delete_keepalive_timer(sk);
  }
  
  
  static void tcp_keepalive_timer (unsigned long data)
  {
  	struct sock *sk = (struct sock *) data;
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	u32 elapsed;
  
  	/* Only process if socket is not in use. */
  	bh_lock_sock(sk);
  	if (sock_owned_by_user(sk)) {
  		/* Try again later. */
  		inet_csk_reset_keepalive_timer (sk, HZ/20);
  		goto out;
  	}
  
  	if (sk->sk_state == TCP_LISTEN) {
  		tcp_synack_timer(sk);
  		goto out;
  	}
  
  	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
  		if (tp->linger2 >= 0) {
  			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
  
  			if (tmo > 0) {
  				tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
  				goto out;
  			}
  		}
  		tcp_send_active_reset(sk, GFP_ATOMIC);
  		goto death;
  	}
  
  	if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
  		goto out;
  
  	elapsed = keepalive_time_when(tp);
  
  	/* It is alive without keepalive 8) */
  	if (tp->packets_out || tcp_send_head(sk))
  		goto resched;
  
  	elapsed = keepalive_time_elapsed(tp);
  
  	if (elapsed >= keepalive_time_when(tp)) {
  		/* If the TCP_USER_TIMEOUT option is enabled, use that
  		 * to determine when to timeout instead.
  		 */
  		if ((icsk->icsk_user_timeout != 0 &&
  		    elapsed >= icsk->icsk_user_timeout &&
  		    icsk->icsk_probes_out > 0) ||
  		    (icsk->icsk_user_timeout == 0 &&
  		    icsk->icsk_probes_out >= keepalive_probes(tp))) {
  			tcp_send_active_reset(sk, GFP_ATOMIC);
  			tcp_write_err(sk);
  			goto out;
  		}
  		if (tcp_write_wakeup(sk) <= 0) {
  			icsk->icsk_probes_out++;
  			elapsed = keepalive_intvl_when(tp);
  		} else {
  			/* If keepalive was lost due to local congestion,
  			 * try harder.
  			 */
  			elapsed = TCP_RESOURCE_PROBE_INTERVAL;
  		}
  	} else {
  		/* It is tp->rcv_tstamp + keepalive_time_when(tp) */
  		elapsed = keepalive_time_when(tp) - elapsed;
  	}
  
  	sk_mem_reclaim(sk);
  
  resched:
  	inet_csk_reset_keepalive_timer (sk, elapsed);
  	goto out;
  
  death:
  	tcp_done(sk);
  
  out:
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  void tcp_init_xmit_timers(struct sock *sk)
  {
  	inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  				  &tcp_keepalive_timer);
  }
  EXPORT_SYMBOL(tcp_init_xmit_timers);
  