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>
   */
  
  /*
   * Changes:	Pedro Roque	:	Retransmit queue handled by TCP.
   *				:	Fragmentation on mtu decrease
   *				:	Segment collapse on retransmit
   *				:	AF independence
   *
   *		Linus Torvalds	:	send_delayed_ack
   *		David S. Miller	:	Charge memory using the right skb
   *					during syn/ack processing.
   *		David S. Miller :	Output engine completely rewritten.
   *		Andrea Arcangeli:	SYNACK carry ts_recent in tsecr.
   *		Cacophonix Gaul :	draft-minshall-nagle-01
   *		J Hadi Salim	:	ECN support
   *
   */
  
  #include <net/tcp.h>
  
  #include <linux/compiler.h>
  #include <linux/module.h>
  
  /* People can turn this off for buggy TCP's found in printers etc. */
  int sysctl_tcp_retrans_collapse __read_mostly = 1;
  
  /* People can turn this on to work with those rare, broken TCPs that
   * interpret the window field as a signed quantity.
   */
  int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
  
  /* This limits the percentage of the congestion window which we
   * will allow a single TSO frame to consume.  Building TSO frames
   * which are too large can cause TCP streams to be bursty.
   */
  int sysctl_tcp_tso_win_divisor __read_mostly = 3;
  
  int sysctl_tcp_mtu_probing __read_mostly = 0;
  int sysctl_tcp_base_mss __read_mostly = 512;
  
  /* By default, RFC2861 behavior.  */
  int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
  
  /* Account for new data that has been sent to the network. */
  static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	unsigned int prior_packets = tp->packets_out;
  
  	tcp_advance_send_head(sk, skb);
  	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
  
  	/* Don't override Nagle indefinately with F-RTO */
  	if (tp->frto_counter == 2)
  		tp->frto_counter = 3;
  
  	tp->packets_out += tcp_skb_pcount(skb);
  	if (!prior_packets)
  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  					  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
  }
  
  /* SND.NXT, if window was not shrunk.
   * If window has been shrunk, what should we make? It is not clear at all.
   * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
   * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
   * invalid. OK, let's make this for now:
   */
  static inline __u32 tcp_acceptable_seq(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (!before(tcp_wnd_end(tp), tp->snd_nxt))
  		return tp->snd_nxt;
  	else
  		return tcp_wnd_end(tp);
  }
  
  /* Calculate mss to advertise in SYN segment.
   * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
   *
   * 1. It is independent of path mtu.
   * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
   * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
   *    attached devices, because some buggy hosts are confused by
   *    large MSS.
   * 4. We do not make 3, we advertise MSS, calculated from first
   *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
   *    This may be overridden via information stored in routing table.
   * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
   *    probably even Jumbo".
   */
  static __u16 tcp_advertise_mss(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct dst_entry *dst = __sk_dst_get(sk);
  	int mss = tp->advmss;
  
  	if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) {
  		mss = dst_metric(dst, RTAX_ADVMSS);
  		tp->advmss = mss;
  	}
  
  	return (__u16)mss;
  }
  
  /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
   * This is the first part of cwnd validation mechanism. */
  static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	s32 delta = tcp_time_stamp - tp->lsndtime;
  	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
  	u32 cwnd = tp->snd_cwnd;
  
  	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
  
  	tp->snd_ssthresh = tcp_current_ssthresh(sk);
  	restart_cwnd = min(restart_cwnd, cwnd);
  
  	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
  		cwnd >>= 1;
  	tp->snd_cwnd = max(cwnd, restart_cwnd);
  	tp->snd_cwnd_stamp = tcp_time_stamp;
  	tp->snd_cwnd_used = 0;
  }
  
  /* Congestion state accounting after a packet has been sent. */
  static void tcp_event_data_sent(struct tcp_sock *tp,
  				struct sk_buff *skb, struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	const u32 now = tcp_time_stamp;
  
  	if (sysctl_tcp_slow_start_after_idle &&
  	    (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
  		tcp_cwnd_restart(sk, __sk_dst_get(sk));
  
  	tp->lsndtime = now;
  
  	/* If it is a reply for ato after last received
  	 * packet, enter pingpong mode.
  	 */
  	if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
  		icsk->icsk_ack.pingpong = 1;
  }
  
  /* Account for an ACK we sent. */
  static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
  {
  	tcp_dec_quickack_mode(sk, pkts);
  	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
  }
  
  /* Determine a window scaling and initial window to offer.
   * Based on the assumption that the given amount of space
   * will be offered. Store the results in the tp structure.
   * NOTE: for smooth operation initial space offering should
   * be a multiple of mss if possible. We assume here that mss >= 1.
   * This MUST be enforced by all callers.
   */
  void tcp_select_initial_window(int __space, __u32 mss,
  			       __u32 *rcv_wnd, __u32 *window_clamp,
  			       int wscale_ok, __u8 *rcv_wscale)
  {
  	unsigned int space = (__space < 0 ? 0 : __space);
  
  	/* If no clamp set the clamp to the max possible scaled window */
  	if (*window_clamp == 0)
  		(*window_clamp) = (65535 << 14);
  	space = min(*window_clamp, space);
  
  	/* Quantize space offering to a multiple of mss if possible. */
  	if (space > mss)
  		space = (space / mss) * mss;
  
  	/* NOTE: offering an initial window larger than 32767
  	 * will break some buggy TCP stacks. If the admin tells us
  	 * it is likely we could be speaking with such a buggy stack
  	 * we will truncate our initial window offering to 32K-1
  	 * unless the remote has sent us a window scaling option,
  	 * which we interpret as a sign the remote TCP is not
  	 * misinterpreting the window field as a signed quantity.
  	 */
  	if (sysctl_tcp_workaround_signed_windows)
  		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
  	else
  		(*rcv_wnd) = space;
  
  	(*rcv_wscale) = 0;
  	if (wscale_ok) {
  		/* Set window scaling on max possible window
  		 * See RFC1323 for an explanation of the limit to 14
  		 */
  		space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
  		space = min_t(u32, space, *window_clamp);
  		while (space > 65535 && (*rcv_wscale) < 14) {
  			space >>= 1;
  			(*rcv_wscale)++;
  		}
  	}
  
  	/* Set initial window to value enough for senders,
  	 * following RFC2414. Senders, not following this RFC,
  	 * will be satisfied with 2.
  	 */
  	if (mss > (1 << *rcv_wscale)) {
  		int init_cwnd = 4;
  		if (mss > 1460 * 3)
  			init_cwnd = 2;
  		else if (mss > 1460)
  			init_cwnd = 3;
  		if (*rcv_wnd > init_cwnd * mss)
  			*rcv_wnd = init_cwnd * mss;
  	}
  
  	/* Set the clamp no higher than max representable value */
  	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
  }
  
  /* Chose a new window to advertise, update state in tcp_sock for the
   * socket, and return result with RFC1323 scaling applied.  The return
   * value can be stuffed directly into th->window for an outgoing
   * frame.
   */
  static u16 tcp_select_window(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	u32 cur_win = tcp_receive_window(tp);
  	u32 new_win = __tcp_select_window(sk);
  
  	/* Never shrink the offered window */
  	if (new_win < cur_win) {
  		/* Danger Will Robinson!
  		 * Don't update rcv_wup/rcv_wnd here or else
  		 * we will not be able to advertise a zero
  		 * window in time.  --DaveM
  		 *
  		 * Relax Will Robinson.
  		 */
  		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
  	}
  	tp->rcv_wnd = new_win;
  	tp->rcv_wup = tp->rcv_nxt;
  
  	/* Make sure we do not exceed the maximum possible
  	 * scaled window.
  	 */
  	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
  		new_win = min(new_win, MAX_TCP_WINDOW);
  	else
  		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
  
  	/* RFC1323 scaling applied */
  	new_win >>= tp->rx_opt.rcv_wscale;
  
  	/* If we advertise zero window, disable fast path. */
  	if (new_win == 0)
  		tp->pred_flags = 0;
  
  	return new_win;
  }
  
  /* Packet ECN state for a SYN-ACK */
  static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb)
  {
  	TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_CWR;
  	if (!(tp->ecn_flags & TCP_ECN_OK))
  		TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_ECE;
  }
  
  /* Packet ECN state for a SYN.  */
  static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	tp->ecn_flags = 0;
  	if (sysctl_tcp_ecn == 1) {
  		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ECE | TCPCB_FLAG_CWR;
  		tp->ecn_flags = TCP_ECN_OK;
  	}
  }
  
  static __inline__ void
  TCP_ECN_make_synack(struct request_sock *req, struct tcphdr *th)
  {
  	if (inet_rsk(req)->ecn_ok)
  		th->ece = 1;
  }
  
  /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
   * be sent.
   */
  static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
  				int tcp_header_len)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (tp->ecn_flags & TCP_ECN_OK) {
  		/* Not-retransmitted data segment: set ECT and inject CWR. */
  		if (skb->len != tcp_header_len &&
  		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
  			INET_ECN_xmit(sk);
  			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
  				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
  				tcp_hdr(skb)->cwr = 1;
  				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
  			}
  		} else {
  			/* ACK or retransmitted segment: clear ECT|CE */
  			INET_ECN_dontxmit(sk);
  		}
  		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
  			tcp_hdr(skb)->ece = 1;
  	}
  }
  
  /* Constructs common control bits of non-data skb. If SYN/FIN is present,
   * auto increment end seqno.
   */
  static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
  {
  	skb->csum = 0;
  
  	TCP_SKB_CB(skb)->flags = flags;
  	TCP_SKB_CB(skb)->sacked = 0;
  
  	skb_shinfo(skb)->gso_segs = 1;
  	skb_shinfo(skb)->gso_size = 0;
  	skb_shinfo(skb)->gso_type = 0;
  
  	TCP_SKB_CB(skb)->seq = seq;
  	if (flags & (TCPCB_FLAG_SYN | TCPCB_FLAG_FIN))
  		seq++;
  	TCP_SKB_CB(skb)->end_seq = seq;
  }
  
  static inline int tcp_urg_mode(const struct tcp_sock *tp)
  {
  	return tp->snd_una != tp->snd_up;
  }
  
  #define OPTION_SACK_ADVERTISE	(1 << 0)
  #define OPTION_TS		(1 << 1)
  #define OPTION_MD5		(1 << 2)
  #define OPTION_WSCALE		(1 << 3)
  
  struct tcp_out_options {
  	u8 options;		/* bit field of OPTION_* */
  	u8 ws;			/* window scale, 0 to disable */
  	u8 num_sack_blocks;	/* number of SACK blocks to include */
  	u16 mss;		/* 0 to disable */
  	__u32 tsval, tsecr;	/* need to include OPTION_TS */
  };
  
  /* Write previously computed TCP options to the packet.
   *
   * Beware: Something in the Internet is very sensitive to the ordering of
   * TCP options, we learned this through the hard way, so be careful here.
   * Luckily we can at least blame others for their non-compliance but from
   * inter-operatibility perspective it seems that we're somewhat stuck with
   * the ordering which we have been using if we want to keep working with
   * those broken things (not that it currently hurts anybody as there isn't
   * particular reason why the ordering would need to be changed).
   *
   * At least SACK_PERM as the first option is known to lead to a disaster
   * (but it may well be that other scenarios fail similarly).
   */
  static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
  			      const struct tcp_out_options *opts,
  			      __u8 **md5_hash) {
  	if (unlikely(OPTION_MD5 & opts->options)) {
  		*ptr++ = htonl((TCPOPT_NOP << 24) |
  			       (TCPOPT_NOP << 16) |
  			       (TCPOPT_MD5SIG << 8) |
  			       TCPOLEN_MD5SIG);
  		*md5_hash = (__u8 *)ptr;
  		ptr += 4;
  	} else {
  		*md5_hash = NULL;
  	}
  
  	if (unlikely(opts->mss)) {
  		*ptr++ = htonl((TCPOPT_MSS << 24) |
  			       (TCPOLEN_MSS << 16) |
  			       opts->mss);
  	}
  
  	if (likely(OPTION_TS & opts->options)) {
  		if (unlikely(OPTION_SACK_ADVERTISE & opts->options)) {
  			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
  				       (TCPOLEN_SACK_PERM << 16) |
  				       (TCPOPT_TIMESTAMP << 8) |
  				       TCPOLEN_TIMESTAMP);
  		} else {
  			*ptr++ = htonl((TCPOPT_NOP << 24) |
  				       (TCPOPT_NOP << 16) |
  				       (TCPOPT_TIMESTAMP << 8) |
  				       TCPOLEN_TIMESTAMP);
  		}
  		*ptr++ = htonl(opts->tsval);
  		*ptr++ = htonl(opts->tsecr);
  	}
  
  	if (unlikely(OPTION_SACK_ADVERTISE & opts->options &&
  		     !(OPTION_TS & opts->options))) {
  		*ptr++ = htonl((TCPOPT_NOP << 24) |
  			       (TCPOPT_NOP << 16) |
  			       (TCPOPT_SACK_PERM << 8) |
  			       TCPOLEN_SACK_PERM);
  	}
  
  	if (unlikely(OPTION_WSCALE & opts->options)) {
  		*ptr++ = htonl((TCPOPT_NOP << 24) |
  			       (TCPOPT_WINDOW << 16) |
  			       (TCPOLEN_WINDOW << 8) |
  			       opts->ws);
  	}
  
  	if (unlikely(opts->num_sack_blocks)) {
  		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
  			tp->duplicate_sack : tp->selective_acks;
  		int this_sack;
  
  		*ptr++ = htonl((TCPOPT_NOP  << 24) |
  			       (TCPOPT_NOP  << 16) |
  			       (TCPOPT_SACK <<  8) |
  			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
  						     TCPOLEN_SACK_PERBLOCK)));
  
  		for (this_sack = 0; this_sack < opts->num_sack_blocks;
  		     ++this_sack) {
  			*ptr++ = htonl(sp[this_sack].start_seq);
  			*ptr++ = htonl(sp[this_sack].end_seq);
  		}
  
  		tp->rx_opt.dsack = 0;
  	}
  }
  
  /* Compute TCP options for SYN packets. This is not the final
   * network wire format yet.
   */
  static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
  				struct tcp_out_options *opts,
  				struct tcp_md5sig_key **md5) {
  	struct tcp_sock *tp = tcp_sk(sk);
  	unsigned size = 0;
  
  #ifdef CONFIG_TCP_MD5SIG
  	*md5 = tp->af_specific->md5_lookup(sk, sk);
  	if (*md5) {
  		opts->options |= OPTION_MD5;
  		size += TCPOLEN_MD5SIG_ALIGNED;
  	}
  #else
  	*md5 = NULL;
  #endif
  
  	/* We always get an MSS option.  The option bytes which will be seen in
  	 * normal data packets should timestamps be used, must be in the MSS
  	 * advertised.  But we subtract them from tp->mss_cache so that
  	 * calculations in tcp_sendmsg are simpler etc.  So account for this
  	 * fact here if necessary.  If we don't do this correctly, as a
  	 * receiver we won't recognize data packets as being full sized when we
  	 * should, and thus we won't abide by the delayed ACK rules correctly.
  	 * SACKs don't matter, we never delay an ACK when we have any of those
  	 * going out.  */
  	opts->mss = tcp_advertise_mss(sk);
  	size += TCPOLEN_MSS_ALIGNED;
  
  	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
  		opts->options |= OPTION_TS;
  		opts->tsval = TCP_SKB_CB(skb)->when;
  		opts->tsecr = tp->rx_opt.ts_recent;
  		size += TCPOLEN_TSTAMP_ALIGNED;
  	}
  	if (likely(sysctl_tcp_window_scaling)) {
  		opts->ws = tp->rx_opt.rcv_wscale;
  		opts->options |= OPTION_WSCALE;
  		size += TCPOLEN_WSCALE_ALIGNED;
  	}
  	if (likely(sysctl_tcp_sack)) {
  		opts->options |= OPTION_SACK_ADVERTISE;
  		if (unlikely(!(OPTION_TS & opts->options)))
  			size += TCPOLEN_SACKPERM_ALIGNED;
  	}
  
  	return size;
  }
  
  /* Set up TCP options for SYN-ACKs. */
  static unsigned tcp_synack_options(struct sock *sk,
  				   struct request_sock *req,
  				   unsigned mss, struct sk_buff *skb,
  				   struct tcp_out_options *opts,
  				   struct tcp_md5sig_key **md5) {
  	unsigned size = 0;
  	struct inet_request_sock *ireq = inet_rsk(req);
  	char doing_ts;
  
  #ifdef CONFIG_TCP_MD5SIG
  	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
  	if (*md5) {
  		opts->options |= OPTION_MD5;
  		size += TCPOLEN_MD5SIG_ALIGNED;
  	}
  #else
  	*md5 = NULL;
  #endif
  
  	/* we can't fit any SACK blocks in a packet with MD5 + TS
  	   options. There was discussion about disabling SACK rather than TS in
  	   order to fit in better with old, buggy kernels, but that was deemed
  	   to be unnecessary. */
  	doing_ts = ireq->tstamp_ok && !(*md5 && ireq->sack_ok);
  
  	opts->mss = mss;
  	size += TCPOLEN_MSS_ALIGNED;
  
  	if (likely(ireq->wscale_ok)) {
  		opts->ws = ireq->rcv_wscale;
  		opts->options |= OPTION_WSCALE;
  		size += TCPOLEN_WSCALE_ALIGNED;
  	}
  	if (likely(doing_ts)) {
  		opts->options |= OPTION_TS;
  		opts->tsval = TCP_SKB_CB(skb)->when;
  		opts->tsecr = req->ts_recent;
  		size += TCPOLEN_TSTAMP_ALIGNED;
  	}
  	if (likely(ireq->sack_ok)) {
  		opts->options |= OPTION_SACK_ADVERTISE;
  		if (unlikely(!doing_ts))
  			size += TCPOLEN_SACKPERM_ALIGNED;
  	}
  
  	return size;
  }
  
  /* Compute TCP options for ESTABLISHED sockets. This is not the
   * final wire format yet.
   */
  static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb,
  					struct tcp_out_options *opts,
  					struct tcp_md5sig_key **md5) {
  	struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
  	struct tcp_sock *tp = tcp_sk(sk);
  	unsigned size = 0;
  	unsigned int eff_sacks;
  
  #ifdef CONFIG_TCP_MD5SIG
  	*md5 = tp->af_specific->md5_lookup(sk, sk);
  	if (unlikely(*md5)) {
  		opts->options |= OPTION_MD5;
  		size += TCPOLEN_MD5SIG_ALIGNED;
  	}
  #else
  	*md5 = NULL;
  #endif
  
  	if (likely(tp->rx_opt.tstamp_ok)) {
  		opts->options |= OPTION_TS;
  		opts->tsval = tcb ? tcb->when : 0;
  		opts->tsecr = tp->rx_opt.ts_recent;
  		size += TCPOLEN_TSTAMP_ALIGNED;
  	}
  
  	eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
  	if (unlikely(eff_sacks)) {
  		const unsigned remaining = MAX_TCP_OPTION_SPACE - size;
  		opts->num_sack_blocks =
  			min_t(unsigned, eff_sacks,
  			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
  			      TCPOLEN_SACK_PERBLOCK);
  		size += TCPOLEN_SACK_BASE_ALIGNED +
  			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
  	}
  
  	return size;
  }
  
  /* This routine actually transmits TCP packets queued in by
   * tcp_do_sendmsg().  This is used by both the initial
   * transmission and possible later retransmissions.
   * All SKB's seen here are completely headerless.  It is our
   * job to build the TCP header, and pass the packet down to
   * IP so it can do the same plus pass the packet off to the
   * device.
   *
   * We are working here with either a clone of the original
   * SKB, or a fresh unique copy made by the retransmit engine.
   */
  static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
  			    gfp_t gfp_mask)
  {
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  	struct inet_sock *inet;
  	struct tcp_sock *tp;
  	struct tcp_skb_cb *tcb;
  	struct tcp_out_options opts;
  	unsigned tcp_options_size, tcp_header_size;
  	struct tcp_md5sig_key *md5;
  	__u8 *md5_hash_location;
  	struct tcphdr *th;
  	int err;
  
  	BUG_ON(!skb || !tcp_skb_pcount(skb));
  
  	/* If congestion control is doing timestamping, we must
  	 * take such a timestamp before we potentially clone/copy.
  	 */
  	if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
  		__net_timestamp(skb);
  
  	if (likely(clone_it)) {
  		if (unlikely(skb_cloned(skb)))
  			skb = pskb_copy(skb, gfp_mask);
  		else
  			skb = skb_clone(skb, gfp_mask);
  		if (unlikely(!skb))
  			return -ENOBUFS;
  	}
  
  	inet = inet_sk(sk);
  	tp = tcp_sk(sk);
  	tcb = TCP_SKB_CB(skb);
  	memset(&opts, 0, sizeof(opts));
  
  	if (unlikely(tcb->flags & TCPCB_FLAG_SYN))
  		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
  	else
  		tcp_options_size = tcp_established_options(sk, skb, &opts,
  							   &md5);
  	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
  
  	if (tcp_packets_in_flight(tp) == 0)
  		tcp_ca_event(sk, CA_EVENT_TX_START);
  
  	skb_push(skb, tcp_header_size);
  	skb_reset_transport_header(skb);
  	skb_set_owner_w(skb, sk);
  
  	/* Build TCP header and checksum it. */
  	th = tcp_hdr(skb);
  	th->source		= inet->sport;
  	th->dest		= inet->dport;
  	th->seq			= htonl(tcb->seq);
  	th->ack_seq		= htonl(tp->rcv_nxt);
  	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
  					tcb->flags);
  
  	if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
  		/* RFC1323: The window in SYN & SYN/ACK segments
  		 * is never scaled.
  		 */
  		th->window	= htons(min(tp->rcv_wnd, 65535U));
  	} else {
  		th->window	= htons(tcp_select_window(sk));
  	}
  	th->check		= 0;
  	th->urg_ptr		= 0;
  
  	/* The urg_mode check is necessary during a below snd_una win probe */
  	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
  		if (before(tp->snd_up, tcb->seq + 0x10000)) {
  			th->urg_ptr = htons(tp->snd_up - tcb->seq);
  			th->urg = 1;
  		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
  			th->urg_ptr = 0xFFFF;
  			th->urg = 1;
  		}
  	}
  
  	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
  	if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
  		TCP_ECN_send(sk, skb, tcp_header_size);
  
  #ifdef CONFIG_TCP_MD5SIG
  	/* Calculate the MD5 hash, as we have all we need now */
  	if (md5) {
  		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
  		tp->af_specific->calc_md5_hash(md5_hash_location,
  					       md5, sk, NULL, skb);
  	}
  #endif
  
  	icsk->icsk_af_ops->send_check(sk, skb->len, skb);
  
  	if (likely(tcb->flags & TCPCB_FLAG_ACK))
  		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
  
  	if (skb->len != tcp_header_size)
  		tcp_event_data_sent(tp, skb, sk);
  
  	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
  		TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
  
  	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
  	if (likely(err <= 0))
  		return err;
  
  	tcp_enter_cwr(sk, 1);
  
  	return net_xmit_eval(err);
  }
  
  /* This routine just queues the buffer for sending.
   *
   * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
   * otherwise socket can stall.
   */
  static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* Advance write_seq and place onto the write_queue. */
  	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
  	skb_header_release(skb);
  	tcp_add_write_queue_tail(sk, skb);
  	sk->sk_wmem_queued += skb->truesize;
  	sk_mem_charge(sk, skb->truesize);
  }
  
  /* Initialize TSO segments for a packet. */
  static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,
  				 unsigned int mss_now)
  {
  	/* Make sure we own this skb before messing gso_size/gso_segs */
  	WARN_ON_ONCE(skb_cloned(skb));
  
  	if (skb->len <= mss_now || !sk_can_gso(sk) ||
  	    skb->ip_summed == CHECKSUM_NONE) {
  		/* Avoid the costly divide in the normal
  		 * non-TSO case.
  		 */
  		skb_shinfo(skb)->gso_segs = 1;
  		skb_shinfo(skb)->gso_size = 0;
  		skb_shinfo(skb)->gso_type = 0;
  	} else {
  		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
  		skb_shinfo(skb)->gso_size = mss_now;
  		skb_shinfo(skb)->gso_type = sk->sk_gso_type;
  	}
  }
  
  /* When a modification to fackets out becomes necessary, we need to check
   * skb is counted to fackets_out or not.
   */
  static void tcp_adjust_fackets_out(struct sock *sk, struct sk_buff *skb,
  				   int decr)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (!tp->sacked_out || tcp_is_reno(tp))
  		return;
  
  	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
  		tp->fackets_out -= decr;
  }
  
  /* Pcount in the middle of the write queue got changed, we need to do various
   * tweaks to fix counters
   */
  static void tcp_adjust_pcount(struct sock *sk, struct sk_buff *skb, int decr)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	tp->packets_out -= decr;
  
  	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
  		tp->sacked_out -= decr;
  	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
  		tp->retrans_out -= decr;
  	if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
  		tp->lost_out -= decr;
  
  	/* Reno case is special. Sigh... */
  	if (tcp_is_reno(tp) && decr > 0)
  		tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
  
  	tcp_adjust_fackets_out(sk, skb, decr);
  
  	if (tp->lost_skb_hint &&
  	    before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
  	    (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
  		tp->lost_cnt_hint -= decr;
  
  	tcp_verify_left_out(tp);
  }
  
  /* Function to create two new TCP segments.  Shrinks the given segment
   * to the specified size and appends a new segment with the rest of the
   * packet to the list.  This won't be called frequently, I hope.
   * Remember, these are still headerless SKBs at this point.
   */
  int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
  		 unsigned int mss_now)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *buff;
  	int nsize, old_factor;
  	int nlen;
  	u8 flags;
  
  	BUG_ON(len > skb->len);
  
  	nsize = skb_headlen(skb) - len;
  	if (nsize < 0)
  		nsize = 0;
  
  	if (skb_unclone(skb, GFP_ATOMIC))
  		return -ENOMEM;
  
  	/* Get a new skb... force flag on. */
  	buff = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC);
  	if (buff == NULL)
  		return -ENOMEM; /* We'll just try again later. */
  
  	sk->sk_wmem_queued += buff->truesize;
  	sk_mem_charge(sk, buff->truesize);
  	nlen = skb->len - len - nsize;
  	buff->truesize += nlen;
  	skb->truesize -= nlen;
  
  	/* Correct the sequence numbers. */
  	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
  	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
  	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
  
  	/* PSH and FIN should only be set in the second packet. */
  	flags = TCP_SKB_CB(skb)->flags;
  	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
  	TCP_SKB_CB(buff)->flags = flags;
  	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
  
  	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
  		/* Copy and checksum data tail into the new buffer. */
  		buff->csum = csum_partial_copy_nocheck(skb->data + len,
  						       skb_put(buff, nsize),
  						       nsize, 0);
  
  		skb_trim(skb, len);
  
  		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
  	} else {
  		skb->ip_summed = CHECKSUM_PARTIAL;
  		skb_split(skb, buff, len);
  	}
  
  	buff->ip_summed = skb->ip_summed;
  
  	/* Looks stupid, but our code really uses when of
  	 * skbs, which it never sent before. --ANK
  	 */
  	TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
  	buff->tstamp = skb->tstamp;
  
  	old_factor = tcp_skb_pcount(skb);
  
  	/* Fix up tso_factor for both original and new SKB.  */
  	tcp_set_skb_tso_segs(sk, skb, mss_now);
  	tcp_set_skb_tso_segs(sk, buff, mss_now);
  
  	/* If this packet has been sent out already, we must
  	 * adjust the various packet counters.
  	 */
  	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
  		int diff = old_factor - tcp_skb_pcount(skb) -
  			tcp_skb_pcount(buff);
  
  		if (diff)
  			tcp_adjust_pcount(sk, skb, diff);
  	}
  
  	/* Link BUFF into the send queue. */
  	skb_header_release(buff);
  	tcp_insert_write_queue_after(skb, buff, sk);
  
  	return 0;
  }
  
  /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
   * eventually). The difference is that pulled data not copied, but
   * immediately discarded.
   */
  static void __pskb_trim_head(struct sk_buff *skb, int len)
  {
  	int i, k, eat;
  
  	eat = len;
  	k = 0;
  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  		if (skb_shinfo(skb)->frags[i].size <= eat) {
  			put_page(skb_shinfo(skb)->frags[i].page);
  			eat -= skb_shinfo(skb)->frags[i].size;
  		} else {
  			skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
  			if (eat) {
  				skb_shinfo(skb)->frags[k].page_offset += eat;
  				skb_shinfo(skb)->frags[k].size -= eat;
  				eat = 0;
  			}
  			k++;
  		}
  	}
  	skb_shinfo(skb)->nr_frags = k;
  
  	skb_reset_tail_pointer(skb);
  	skb->data_len -= len;
  	skb->len = skb->data_len;
  }
  
  /* Remove acked data from a packet in the transmit queue. */
  int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
  {
  	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
  		return -ENOMEM;
  
  	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
  	if (unlikely(len < skb_headlen(skb)))
  		__skb_pull(skb, len);
  	else
  		__pskb_trim_head(skb, len - skb_headlen(skb));
  
  	TCP_SKB_CB(skb)->seq += len;
  	skb->ip_summed = CHECKSUM_PARTIAL;
  
  	skb->truesize	     -= len;
  	sk->sk_wmem_queued   -= len;
  	sk_mem_uncharge(sk, len);
  	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
  
  	/* Any change of skb->len requires recalculation of tso factor. */
  	if (tcp_skb_pcount(skb) > 1)
  		tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
  
  	return 0;
  }
  
  /* Calculate MSS. Not accounting for SACKs here.  */
  int tcp_mtu_to_mss(struct sock *sk, int pmtu)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int mss_now;
  
  	/* Calculate base mss without TCP options:
  	   It is MMS_S - sizeof(tcphdr) of rfc1122
  	 */
  	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
  
  	/* Clamp it (mss_clamp does not include tcp options) */
  	if (mss_now > tp->rx_opt.mss_clamp)
  		mss_now = tp->rx_opt.mss_clamp;
  
  	/* Now subtract optional transport overhead */
  	mss_now -= icsk->icsk_ext_hdr_len;
  
  	/* Then reserve room for full set of TCP options and 8 bytes of data */
  	if (mss_now < 48)
  		mss_now = 48;
  
  	/* Now subtract TCP options size, not including SACKs */
  	mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
  
  	return mss_now;
  }
  
  /* Inverse of above */
  int tcp_mss_to_mtu(struct sock *sk, int mss)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int mtu;
  
  	mtu = mss +
  	      tp->tcp_header_len +
  	      icsk->icsk_ext_hdr_len +
  	      icsk->icsk_af_ops->net_header_len;
  
  	return mtu;
  }
  
  /* MTU probing init per socket */
  void tcp_mtup_init(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  
  	icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
  	icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
  			       icsk->icsk_af_ops->net_header_len;
  	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
  	icsk->icsk_mtup.probe_size = 0;
  }
  
  /* This function synchronize snd mss to current pmtu/exthdr set.
  
     tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
     for TCP options, but includes only bare TCP header.
  
     tp->rx_opt.mss_clamp is mss negotiated at connection setup.
     It is minimum of user_mss and mss received with SYN.
     It also does not include TCP options.
  
     inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
  
     tp->mss_cache is current effective sending mss, including
     all tcp options except for SACKs. It is evaluated,
     taking into account current pmtu, but never exceeds
     tp->rx_opt.mss_clamp.
  
     NOTE1. rfc1122 clearly states that advertised MSS
     DOES NOT include either tcp or ip options.
  
     NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
     are READ ONLY outside this function.		--ANK (980731)
   */
  unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int mss_now;
  
  	if (icsk->icsk_mtup.search_high > pmtu)
  		icsk->icsk_mtup.search_high = pmtu;
  
  	mss_now = tcp_mtu_to_mss(sk, pmtu);
  	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
  
  	/* And store cached results */
  	icsk->icsk_pmtu_cookie = pmtu;
  	if (icsk->icsk_mtup.enabled)
  		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
  	tp->mss_cache = mss_now;
  
  	return mss_now;
  }
  
  /* Compute the current effective MSS, taking SACKs and IP options,
   * and even PMTU discovery events into account.
   */
  unsigned int tcp_current_mss(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct dst_entry *dst = __sk_dst_get(sk);
  	u32 mss_now;
  	unsigned header_len;
  	struct tcp_out_options opts;
  	struct tcp_md5sig_key *md5;
  
  	mss_now = tp->mss_cache;
  
  	if (dst) {
  		u32 mtu = dst_mtu(dst);
  		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
  			mss_now = tcp_sync_mss(sk, mtu);
  	}
  
  	header_len = tcp_established_options(sk, NULL, &opts, &md5) +
  		     sizeof(struct tcphdr);
  	/* The mss_cache is sized based on tp->tcp_header_len, which assumes
  	 * some common options. If this is an odd packet (because we have SACK
  	 * blocks etc) then our calculated header_len will be different, and
  	 * we have to adjust mss_now correspondingly */
  	if (header_len != tp->tcp_header_len) {
  		int delta = (int) header_len - tp->tcp_header_len;
  		mss_now -= delta;
  	}
  
  	return mss_now;
  }
  
  /* Congestion window validation. (RFC2861) */
  static void tcp_cwnd_validate(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	if (tp->packets_out >= tp->snd_cwnd) {
  		/* Network is feed fully. */
  		tp->snd_cwnd_used = 0;
  		tp->snd_cwnd_stamp = tcp_time_stamp;
  	} else {
  		/* Network starves. */
  		if (tp->packets_out > tp->snd_cwnd_used)
  			tp->snd_cwnd_used = tp->packets_out;
  
  		if (sysctl_tcp_slow_start_after_idle &&
  		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
  			tcp_cwnd_application_limited(sk);
  	}
  }
  
  /* Returns the portion of skb which can be sent right away without
   * introducing MSS oddities to segment boundaries. In rare cases where
   * mss_now != mss_cache, we will request caller to create a small skb
   * per input skb which could be mostly avoided here (if desired).
   *
   * We explicitly want to create a request for splitting write queue tail
   * to a small skb for Nagle purposes while avoiding unnecessary modulos,
   * thus all the complexity (cwnd_len is always MSS multiple which we
   * return whenever allowed by the other factors). Basically we need the
   * modulo only when the receiver window alone is the limiting factor or
   * when we would be allowed to send the split-due-to-Nagle skb fully.
   */
  static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb,
  					unsigned int mss_now, unsigned int cwnd)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	u32 needed, window, cwnd_len;
  
  	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
  	cwnd_len = mss_now * cwnd;
  
  	if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
  		return cwnd_len;
  
  	needed = min(skb->len, window);
  
  	if (cwnd_len <= needed)
  		return cwnd_len;
  
  	return needed - needed % mss_now;
  }
  
  /* Can at least one segment of SKB be sent right now, according to the
   * congestion window rules?  If so, return how many segments are allowed.
   */
  static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
  					 struct sk_buff *skb)
  {
  	u32 in_flight, cwnd;
  
  	/* Don't be strict about the congestion window for the final FIN.  */
  	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
  	    tcp_skb_pcount(skb) == 1)
  		return 1;
  
  	in_flight = tcp_packets_in_flight(tp);
  	cwnd = tp->snd_cwnd;
  	if (in_flight < cwnd)
  		return (cwnd - in_flight);
  
  	return 0;
  }
  
  /* Intialize TSO state of a skb.
   * This must be invoked the first time we consider transmitting
   * SKB onto the wire.
   */
  static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
  			     unsigned int mss_now)
  {
  	int tso_segs = tcp_skb_pcount(skb);
  
  	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
  		tcp_set_skb_tso_segs(sk, skb, mss_now);
  		tso_segs = tcp_skb_pcount(skb);
  	}
  	return tso_segs;
  }
  
  /* Minshall's variant of the Nagle send check. */
  static inline int tcp_minshall_check(const struct tcp_sock *tp)
  {
  	return after(tp->snd_sml, tp->snd_una) &&
  		!after(tp->snd_sml, tp->snd_nxt);
  }
  
  /* Return 0, if packet can be sent now without violation Nagle's rules:
   * 1. It is full sized.
   * 2. Or it contains FIN. (already checked by caller)
   * 3. Or TCP_NODELAY was set.
   * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
   *    With Minshall's modification: all sent small packets are ACKed.
   */
  static inline int tcp_nagle_check(const struct tcp_sock *tp,
  				  const struct sk_buff *skb,
  				  unsigned mss_now, int nonagle)
  {
  	return (skb->len < mss_now &&
  		((nonagle & TCP_NAGLE_CORK) ||
  		 (!nonagle && tp->packets_out && tcp_minshall_check(tp))));
  }
  
  /* Return non-zero if the Nagle test allows this packet to be
   * sent now.
   */
  static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb,
  				 unsigned int cur_mss, int nonagle)
  {
  	/* Nagle rule does not apply to frames, which sit in the middle of the
  	 * write_queue (they have no chances to get new data).
  	 *
  	 * This is implemented in the callers, where they modify the 'nonagle'
  	 * argument based upon the location of SKB in the send queue.
  	 */
  	if (nonagle & TCP_NAGLE_PUSH)
  		return 1;
  
  	/* Don't use the nagle rule for urgent data (or for the final FIN).
  	 * Nagle can be ignored during F-RTO too (see RFC4138).
  	 */
  	if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
  	    (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN))
  		return 1;
  
  	if (!tcp_nagle_check(tp, skb, cur_mss, nonagle))
  		return 1;
  
  	return 0;
  }
  
  /* Does at least the first segment of SKB fit into the send window? */
  static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb,
  				   unsigned int cur_mss)
  {
  	u32 end_seq = TCP_SKB_CB(skb)->end_seq;
  
  	if (skb->len > cur_mss)
  		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
  
  	return !after(end_seq, tcp_wnd_end(tp));
  }
  
  /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
   * should be put on the wire right now.  If so, it returns the number of
   * packets allowed by the congestion window.
   */
  static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb,
  				 unsigned int cur_mss, int nonagle)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	unsigned int cwnd_quota;
  
  	tcp_init_tso_segs(sk, skb, cur_mss);
  
  	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
  		return 0;
  
  	cwnd_quota = tcp_cwnd_test(tp, skb);
  	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
  		cwnd_quota = 0;
  
  	return cwnd_quota;
  }
  
  /* Test if sending is allowed right now. */
  int tcp_may_send_now(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb = tcp_send_head(sk);
  
  	return (skb &&
  		tcp_snd_test(sk, skb, tcp_current_mss(sk),
  			     (tcp_skb_is_last(sk, skb) ?
  			      tp->nonagle : TCP_NAGLE_PUSH)));
  }
  
  /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
   * which is put after SKB on the list.  It is very much like
   * tcp_fragment() except that it may make several kinds of assumptions
   * in order to speed up the splitting operation.  In particular, we
   * know that all the data is in scatter-gather pages, and that the
   * packet has never been sent out before (and thus is not cloned).
   */
  static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
  			unsigned int mss_now)
  {
  	struct sk_buff *buff;
  	int nlen = skb->len - len;
  	u8 flags;
  
  	/* All of a TSO frame must be composed of paged data.  */
  	if (skb->len != skb->data_len)
  		return tcp_fragment(sk, skb, len, mss_now);
  
  	buff = sk_stream_alloc_skb(sk, 0, GFP_ATOMIC);
  	if (unlikely(buff == NULL))
  		return -ENOMEM;
  
  	sk->sk_wmem_queued += buff->truesize;
  	sk_mem_charge(sk, buff->truesize);
  	buff->truesize += nlen;
  	skb->truesize -= nlen;
  
  	/* Correct the sequence numbers. */
  	TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
  	TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
  	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
  
  	/* PSH and FIN should only be set in the second packet. */
  	flags = TCP_SKB_CB(skb)->flags;
  	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
  	TCP_SKB_CB(buff)->flags = flags;
  
  	/* This packet was never sent out yet, so no SACK bits. */
  	TCP_SKB_CB(buff)->sacked = 0;
  
  	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
  	skb_split(skb, buff, len);
  
  	/* Fix up tso_factor for both original and new SKB.  */
  	tcp_set_skb_tso_segs(sk, skb, mss_now);
  	tcp_set_skb_tso_segs(sk, buff, mss_now);
  
  	/* Link BUFF into the send queue. */
  	skb_header_release(buff);
  	tcp_insert_write_queue_after(skb, buff, sk);
  
  	return 0;
  }
  
  /* Try to defer sending, if possible, in order to minimize the amount
   * of TSO splitting we do.  View it as a kind of TSO Nagle test.
   *
   * This algorithm is from John Heffner.
   */
  static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  	u32 send_win, cong_win, limit, in_flight;
  
  	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
  		goto send_now;
  
  	if (icsk->icsk_ca_state != TCP_CA_Open)
  		goto send_now;
  
  	/* Defer for less than two clock ticks. */
  	if (tp->tso_deferred &&
  	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
  		goto send_now;
  
  	in_flight = tcp_packets_in_flight(tp);
  
  	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
  
  	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
  
  	/* From in_flight test above, we know that cwnd > in_flight.  */
  	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
  
  	limit = min(send_win, cong_win);
  
  	/* If a full-sized TSO skb can be sent, do it. */
  	if (limit >= sk->sk_gso_max_size)
  		goto send_now;
  
  	/* Middle in queue won't get any more data, full sendable already? */
  	if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
  		goto send_now;
  
  	if (sysctl_tcp_tso_win_divisor) {
  		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
  
  		/* If at least some fraction of a window is available,
  		 * just use it.
  		 */
  		chunk /= sysctl_tcp_tso_win_divisor;
  		if (limit >= chunk)
  			goto send_now;
  	} else {
  		/* Different approach, try not to defer past a single
  		 * ACK.  Receiver should ACK every other full sized
  		 * frame, so if we have space for more than 3 frames
  		 * then send now.
  		 */
  		if (limit > tcp_max_burst(tp) * tp->mss_cache)
  			goto send_now;
  	}
  
  	/* Ok, it looks like it is advisable to defer.
  	 * Do not rearm the timer if already set to not break TCP ACK clocking.
  	 */
  	if (!tp->tso_deferred)
  		tp->tso_deferred = 1 | (jiffies << 1);
  
  	return 1;
  
  send_now:
  	tp->tso_deferred = 0;
  	return 0;
  }
  
  /* Create a new MTU probe if we are ready.
   * MTU probe is regularly attempting to increase the path MTU by
   * deliberately sending larger packets.  This discovers routing
   * changes resulting in larger path MTUs.
   *
   * Returns 0 if we should wait to probe (no cwnd available),
   *         1 if a probe was sent,
   *         -1 otherwise
   */
  static int tcp_mtu_probe(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct sk_buff *skb, *nskb, *next;
  	int len;
  	int probe_size;
  	int size_needed;
  	int copy;
  	int mss_now;
  
  	/* Not currently probing/verifying,
  	 * not in recovery,
  	 * have enough cwnd, and
  	 * not SACKing (the variable headers throw things off) */
  	if (!icsk->icsk_mtup.enabled ||
  	    icsk->icsk_mtup.probe_size ||
  	    inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
  	    tp->snd_cwnd < 11 ||
  	    tp->rx_opt.num_sacks || tp->rx_opt.dsack)
  		return -1;
  
  	/* Very simple search strategy: just double the MSS. */
  	mss_now = tcp_current_mss(sk);
  	probe_size = 2 * tp->mss_cache;
  	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
  	if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
  		/* TODO: set timer for probe_converge_event */
  		return -1;
  	}
  
  	/* Have enough data in the send queue to probe? */
  	if (tp->write_seq - tp->snd_nxt < size_needed)
  		return -1;
  
  	if (tp->snd_wnd < size_needed)
  		return -1;
  	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
  		return 0;
  
  	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
  	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
  		if (!tcp_packets_in_flight(tp))
  			return -1;
  		else
  			return 0;
  	}
  
  	/* We're allowed to probe.  Build it now. */
  	if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
  		return -1;
  	sk->sk_wmem_queued += nskb->truesize;
  	sk_mem_charge(sk, nskb->truesize);
  
  	skb = tcp_send_head(sk);
  
  	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
  	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
  	TCP_SKB_CB(nskb)->flags = TCPCB_FLAG_ACK;
  	TCP_SKB_CB(nskb)->sacked = 0;
  	nskb->csum = 0;
  	nskb->ip_summed = skb->ip_summed;
  
  	tcp_insert_write_queue_before(nskb, skb, sk);
  
  	len = 0;
  	tcp_for_write_queue_from_safe(skb, next, sk) {
  		copy = min_t(int, skb->len, probe_size - len);
  		if (nskb->ip_summed)
  			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
  		else
  			nskb->csum = skb_copy_and_csum_bits(skb, 0,
  							    skb_put(nskb, copy),
  							    copy, nskb->csum);
  
  		if (skb->len <= copy) {
  			/* We've eaten all the data from this skb.
  			 * Throw it away. */
  			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags;
  			tcp_unlink_write_queue(skb, sk);
  			sk_wmem_free_skb(sk, skb);
  		} else {
  			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
  						   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
  			if (!skb_shinfo(skb)->nr_frags) {
  				skb_pull(skb, copy);
  				if (skb->ip_summed != CHECKSUM_PARTIAL)
  					skb->csum = csum_partial(skb->data,
  								 skb->len, 0);
  			} else {
  				__pskb_trim_head(skb, copy);
  				tcp_set_skb_tso_segs(sk, skb, mss_now);
  			}
  			TCP_SKB_CB(skb)->seq += copy;
  		}
  
  		len += copy;
  
  		if (len >= probe_size)
  			break;
  	}
  	tcp_init_tso_segs(sk, nskb, nskb->len);
  
  	/* We're ready to send.  If this fails, the probe will
  	 * be resegmented into mss-sized pieces by tcp_write_xmit(). */
  	TCP_SKB_CB(nskb)->when = tcp_time_stamp;
  	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
  		/* Decrement cwnd here because we are sending
  		 * effectively two packets. */
  		tp->snd_cwnd--;
  		tcp_event_new_data_sent(sk, nskb);
  
  		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
  		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
  		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
  
  		return 1;
  	}
  
  	return -1;
  }
  
  /* This routine writes packets to the network.  It advances the
   * send_head.  This happens as incoming acks open up the remote
   * window for us.
   *
   * LARGESEND note: !tcp_urg_mode is overkill, only frames between
   * snd_up-64k-mss .. snd_up cannot be large. However, taking into
   * account rare use of URG, this is not a big flaw.
   *
   * Returns 1, if no segments are in flight and we have queued segments, but
   * cannot send anything now because of SWS or another problem.
   */
  static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
  			  int push_one, gfp_t gfp)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb;
  	unsigned int tso_segs, sent_pkts;
  	int cwnd_quota;
  	int result;
  
  	sent_pkts = 0;
  
  	if (!push_one) {
  		/* Do MTU probing. */
  		result = tcp_mtu_probe(sk);
  		if (!result) {
  			return 0;
  		} else if (result > 0) {
  			sent_pkts = 1;
  		}
  	}
  
  	while ((skb = tcp_send_head(sk))) {
  		unsigned int limit;
  
  		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
  		BUG_ON(!tso_segs);
  
  		cwnd_quota = tcp_cwnd_test(tp, skb);
  		if (!cwnd_quota)
  			break;
  
  		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
  			break;
  
  		if (tso_segs == 1) {
  			if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
  						     (tcp_skb_is_last(sk, skb) ?
  						      nonagle : TCP_NAGLE_PUSH))))
  				break;
  		} else {
  			if (!push_one && tcp_tso_should_defer(sk, skb))
  				break;
  		}
  
  		limit = mss_now;
  		if (tso_segs > 1 && !tcp_urg_mode(tp))
  			limit = tcp_mss_split_point(sk, skb, mss_now,
  						    cwnd_quota);
  
  		if (skb->len > limit &&
  		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
  			break;
  
  		TCP_SKB_CB(skb)->when = tcp_time_stamp;
  
  		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
  			break;
  
  		/* Advance the send_head.  This one is sent out.
  		 * This call will increment packets_out.
  		 */
  		tcp_event_new_data_sent(sk, skb);
  
  		tcp_minshall_update(tp, mss_now, skb);
  		sent_pkts++;
  
  		if (push_one)
  			break;
  	}
  
  	if (likely(sent_pkts)) {
  		tcp_cwnd_validate(sk);
  		return 0;
  	}
  	return !tp->packets_out && tcp_send_head(sk);
  }
  
  /* Push out any pending frames which were held back due to
   * TCP_CORK or attempt at coalescing tiny packets.
   * The socket must be locked by the caller.
   */
  void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
  			       int nonagle)
  {
  	struct sk_buff *skb = tcp_send_head(sk);
  
  	if (!skb)
  		return;
  
  	/* If we are closed, the bytes will have to remain here.
  	 * In time closedown will finish, we empty the write queue and
  	 * all will be happy.
  	 */
  	if (unlikely(sk->sk_state == TCP_CLOSE))
  		return;
  
  	if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC))
  		tcp_check_probe_timer(sk);
  }
  
  /* Send _single_ skb sitting at the send head. This function requires
   * true push pending frames to setup probe timer etc.
   */
  void tcp_push_one(struct sock *sk, unsigned int mss_now)
  {
  	struct sk_buff *skb = tcp_send_head(sk);
  
  	BUG_ON(!skb || skb->len < mss_now);
  
  	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
  }
  
  /* This function returns the amount that we can raise the
   * usable window based on the following constraints
   *
   * 1. The window can never be shrunk once it is offered (RFC 793)
   * 2. We limit memory per socket
   *
   * RFC 1122:
   * "the suggested [SWS] avoidance algorithm for the receiver is to keep
   *  RECV.NEXT + RCV.WIN fixed until:
   *  RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
   *
   * i.e. don't raise the right edge of the window until you can raise
   * it at least MSS bytes.
   *
   * Unfortunately, the recommended algorithm breaks header prediction,
   * since header prediction assumes th->window stays fixed.
   *
   * Strictly speaking, keeping th->window fixed violates the receiver
   * side SWS prevention criteria. The problem is that under this rule
   * a stream of single byte packets will cause the right side of the
   * window to always advance by a single byte.
   *
   * Of course, if the sender implements sender side SWS prevention
   * then this will not be a problem.
   *
   * BSD seems to make the following compromise:
   *
   *	If the free space is less than the 1/4 of the maximum
   *	space available and the free space is less than 1/2 mss,
   *	then set the window to 0.
   *	[ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
   *	Otherwise, just prevent the window from shrinking
   *	and from being larger than the largest representable value.
   *
   * This prevents incremental opening of the window in the regime
   * where TCP is limited by the speed of the reader side taking
   * data out of the TCP receive queue. It does nothing about
   * those cases where the window is constrained on the sender side
   * because the pipeline is full.
   *
   * BSD also seems to "accidentally" limit itself to windows that are a
   * multiple of MSS, at least until the free space gets quite small.
   * This would appear to be a side effect of the mbuf implementation.
   * Combining these two algorithms results in the observed behavior
   * of having a fixed window size at almost all times.
   *
   * Below we obtain similar behavior by forcing the offered window to
   * a multiple of the mss when it is feasible to do so.
   *
   * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
   * Regular options like TIMESTAMP are taken into account.
   */
  u32 __tcp_select_window(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	/* MSS for the peer's data.  Previous versions used mss_clamp
  	 * here.  I don't know if the value based on our guesses
  	 * of peer's MSS is better for the performance.  It's more correct
  	 * but may be worse for the performance because of rcv_mss
  	 * fluctuations.  --SAW  1998/11/1
  	 */
  	int mss = icsk->icsk_ack.rcv_mss;
  	int free_space = tcp_space(sk);
  	int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
  	int window;
  
  	if (mss > full_space)
  		mss = full_space;
  
  	if (free_space < (full_space >> 1)) {
  		icsk->icsk_ack.quick = 0;
  
  		if (tcp_memory_pressure)
  			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
  					       4U * tp->advmss);
  
  		if (free_space < mss)
  			return 0;
  	}
  
  	if (free_space > tp->rcv_ssthresh)
  		free_space = tp->rcv_ssthresh;
  
  	/* Don't do rounding if we are using window scaling, since the
  	 * scaled window will not line up with the MSS boundary anyway.
  	 */
  	window = tp->rcv_wnd;
  	if (tp->rx_opt.rcv_wscale) {
  		window = free_space;
  
  		/* Advertise enough space so that it won't get scaled away.
  		 * Import case: prevent zero window announcement if
  		 * 1<<rcv_wscale > mss.
  		 */
  		if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
  			window = (((window >> tp->rx_opt.rcv_wscale) + 1)
  				  << tp->rx_opt.rcv_wscale);
  	} else {
  		/* Get the largest window that is a nice multiple of mss.
  		 * Window clamp already applied above.
  		 * If our current window offering is within 1 mss of the
  		 * free space we just keep it. This prevents the divide
  		 * and multiply from happening most of the time.
  		 * We also don't do any window rounding when the free space
  		 * is too small.
  		 */
  		if (window <= free_space - mss || window > free_space)
  			window = (free_space / mss) * mss;
  		else if (mss == full_space &&
  			 free_space > window + (full_space >> 1))
  			window = free_space;
  	}
  
  	return window;
  }
  
  /* Collapses two adjacent SKB's during retransmission. */
  static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
  	int skb_size, next_skb_size;
  
  	skb_size = skb->len;
  	next_skb_size = next_skb->len;
  
  	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
  
  	tcp_highest_sack_combine(sk, next_skb, skb);
  
  	tcp_unlink_write_queue(next_skb, sk);
  
  	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
  				  next_skb_size);
  
  	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
  		skb->ip_summed = CHECKSUM_PARTIAL;
  
  	if (skb->ip_summed != CHECKSUM_PARTIAL)
  		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
  
  	/* Update sequence range on original skb. */
  	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
  
  	/* Merge over control information. This moves PSH/FIN etc. over */
  	TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(next_skb)->flags;
  
  	/* All done, get rid of second SKB and account for it so
  	 * packet counting does not break.
  	 */
  	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
  
  	/* changed transmit queue under us so clear hints */
  	tcp_clear_retrans_hints_partial(tp);
  	if (next_skb == tp->retransmit_skb_hint)
  		tp->retransmit_skb_hint = skb;
  
  	tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
  
  	sk_wmem_free_skb(sk, next_skb);
  }
  
  /* Check if coalescing SKBs is legal. */
  static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
  {
  	if (tcp_skb_pcount(skb) > 1)
  		return 0;
  	/* TODO: SACK collapsing could be used to remove this condition */
  	if (skb_shinfo(skb)->nr_frags != 0)
  		return 0;
  	if (skb_cloned(skb))
  		return 0;
  	if (skb == tcp_send_head(sk))
  		return 0;
  	/* Some heurestics for collapsing over SACK'd could be invented */
  	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
  		return 0;
  
  	return 1;
  }
  
  /* Collapse packets in the retransmit queue to make to create
   * less packets on the wire. This is only done on retransmission.
   */
  static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
  				     int space)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb = to, *tmp;
  	int first = 1;
  
  	if (!sysctl_tcp_retrans_collapse)
  		return;
  	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)
  		return;
  
  	tcp_for_write_queue_from_safe(skb, tmp, sk) {
  		if (!tcp_can_collapse(sk, skb))
  			break;
  
  		space -= skb->len;
  
  		if (first) {
  			first = 0;
  			continue;
  		}
  
  		if (space < 0)
  			break;
  		/* Punt if not enough space exists in the first SKB for
  		 * the data in the second
  		 */
  		if (skb->len > skb_tailroom(to))
  			break;
  
  		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
  			break;
  
  		tcp_collapse_retrans(sk, to);
  	}
  }
  
  /* This retransmits one SKB.  Policy decisions and retransmit queue
   * state updates are done by the caller.  Returns non-zero if an
   * error occurred which prevented the send.
   */
  int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	unsigned int cur_mss;
  	int err;
  
  	/* Inconslusive MTU probe */
  	if (icsk->icsk_mtup.probe_size) {
  		icsk->icsk_mtup.probe_size = 0;
  	}
  
  	/* Do not sent more than we queued. 1/4 is reserved for possible
  	 * copying overhead: fragmentation, tunneling, mangling etc.
  	 */
  	if (atomic_read(&sk->sk_wmem_alloc) >
  	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
  		return -EAGAIN;
  
  	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
  		if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
  			BUG();
  		if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
  			return -ENOMEM;
  	}
  
  	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
  		return -EHOSTUNREACH; /* Routing failure or similar. */
  
  	cur_mss = tcp_current_mss(sk);
  
  	/* If receiver has shrunk his window, and skb is out of
  	 * new window, do not retransmit it. The exception is the
  	 * case, when window is shrunk to zero. In this case
  	 * our retransmit serves as a zero window probe.
  	 */
  	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))
  	    && TCP_SKB_CB(skb)->seq != tp->snd_una)
  		return -EAGAIN;
  
  	if (skb->len > cur_mss) {
  		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
  			return -ENOMEM; /* We'll try again later. */
  	} else {
  		int oldpcount = tcp_skb_pcount(skb);
  
  		if (unlikely(oldpcount > 1)) {
  			if (skb_unclone(skb, GFP_ATOMIC))
  				return -ENOMEM;
  			tcp_init_tso_segs(sk, skb, cur_mss);
  			tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
  		}
  	}
  
  	tcp_retrans_try_collapse(sk, skb, cur_mss);
  
  	/* Some Solaris stacks overoptimize and ignore the FIN on a
  	 * retransmit when old data is attached.  So strip it off
  	 * since it is cheap to do so and saves bytes on the network.
  	 */
  	if (skb->len > 0 &&
  	    (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
  	    tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
  		if (!pskb_trim(skb, 0)) {
  			/* Reuse, even though it does some unnecessary work */
  			tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1,
  					     TCP_SKB_CB(skb)->flags);
  			skb->ip_summed = CHECKSUM_NONE;
  		}
  	}
  
  	/* Make a copy, if the first transmission SKB clone we made
  	 * is still in somebody's hands, else make a clone.
  	 */
  	TCP_SKB_CB(skb)->when = tcp_time_stamp;
  
  	err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
  
  	if (err == 0) {
  		/* Update global TCP statistics. */
  		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
  
  		tp->total_retrans++;
  
  #if FASTRETRANS_DEBUG > 0
  		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
  			if (net_ratelimit())
  				printk(KERN_DEBUG "retrans_out leaked.\n");
  		}
  #endif
  		if (!tp->retrans_out)
  			tp->lost_retrans_low = tp->snd_nxt;
  		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
  		tp->retrans_out += tcp_skb_pcount(skb);
  
  		/* Save stamp of the first retransmit. */
  		if (!tp->retrans_stamp)
  			tp->retrans_stamp = TCP_SKB_CB(skb)->when;
  
  		tp->undo_retrans++;
  
  		/* snd_nxt is stored to detect loss of retransmitted segment,
  		 * see tcp_input.c tcp_sacktag_write_queue().
  		 */
  		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
  	}
  	return err;
  }
  
  /* Check if we forward retransmits are possible in the current
   * window/congestion state.
   */
  static int tcp_can_forward_retransmit(struct sock *sk)
  {
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* Forward retransmissions are possible only during Recovery. */
  	if (icsk->icsk_ca_state != TCP_CA_Recovery)
  		return 0;
  
  	/* No forward retransmissions in Reno are possible. */
  	if (tcp_is_reno(tp))
  		return 0;
  
  	/* Yeah, we have to make difficult choice between forward transmission
  	 * and retransmission... Both ways have their merits...
  	 *
  	 * For now we do not retransmit anything, while we have some new
  	 * segments to send. In the other cases, follow rule 3 for
  	 * NextSeg() specified in RFC3517.
  	 */
  
  	if (tcp_may_send_now(sk))
  		return 0;
  
  	return 1;
  }
  
  /* This gets called after a retransmit timeout, and the initially
   * retransmitted data is acknowledged.  It tries to continue
   * resending the rest of the retransmit queue, until either
   * we've sent it all or the congestion window limit is reached.
   * If doing SACK, the first ACK which comes back for a timeout
   * based retransmit packet might feed us FACK information again.
   * If so, we use it to avoid unnecessarily retransmissions.
   */
  void tcp_xmit_retransmit_queue(struct sock *sk)
  {
  	const struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb;
  	struct sk_buff *hole = NULL;
  	u32 last_lost;
  	int mib_idx;
  	int fwd_rexmitting = 0;
  
  	if (!tp->packets_out)
  		return;
  
  	if (!tp->lost_out)
  		tp->retransmit_high = tp->snd_una;
  
  	if (tp->retransmit_skb_hint) {
  		skb = tp->retransmit_skb_hint;
  		last_lost = TCP_SKB_CB(skb)->end_seq;
  		if (after(last_lost, tp->retransmit_high))
  			last_lost = tp->retransmit_high;
  	} else {
  		skb = tcp_write_queue_head(sk);
  		last_lost = tp->snd_una;
  	}
  
  	tcp_for_write_queue_from(skb, sk) {
  		__u8 sacked = TCP_SKB_CB(skb)->sacked;
  
  		if (skb == tcp_send_head(sk))
  			break;
  		/* we could do better than to assign each time */
  		if (hole == NULL)
  			tp->retransmit_skb_hint = skb;
  
  		/* Assume this retransmit will generate
  		 * only one packet for congestion window
  		 * calculation purposes.  This works because
  		 * tcp_retransmit_skb() will chop up the
  		 * packet to be MSS sized and all the
  		 * packet counting works out.
  		 */
  		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
  			return;
  
  		if (fwd_rexmitting) {
  begin_fwd:
  			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
  				break;
  			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
  
  		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
  			tp->retransmit_high = last_lost;
  			if (!tcp_can_forward_retransmit(sk))
  				break;
  			/* Backtrack if necessary to non-L'ed skb */
  			if (hole != NULL) {
  				skb = hole;
  				hole = NULL;
  			}
  			fwd_rexmitting = 1;
  			goto begin_fwd;
  
  		} else if (!(sacked & TCPCB_LOST)) {
  			if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
  				hole = skb;
  			continue;
  
  		} else {
  			last_lost = TCP_SKB_CB(skb)->end_seq;
  			if (icsk->icsk_ca_state != TCP_CA_Loss)
  				mib_idx = LINUX_MIB_TCPFASTRETRANS;
  			else
  				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
  		}
  
  		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
  			continue;
  
  		if (tcp_retransmit_skb(sk, skb))
  			return;
  		NET_INC_STATS_BH(sock_net(sk), mib_idx);
  
  		if (skb == tcp_write_queue_head(sk))
  			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  						  inet_csk(sk)->icsk_rto,
  						  TCP_RTO_MAX);
  	}
  }
  
  /* Send a FIN. The caller locks the socket for us.
   * We should try to send a FIN packet really hard, but eventually give up.
   */
  void tcp_send_fin(struct sock *sk)
  {
  	struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  
  	/* Optimization, tack on the FIN if we have one skb in write queue and
  	 * this skb was not yet sent, or we are under memory pressure.
  	 * Note: in the latter case, FIN packet will be sent after a timeout,
  	 * as TCP stack thinks it has already been transmitted.
  	 */
  	if (tskb && (tcp_send_head(sk) || tcp_memory_pressure)) {
  coalesce:
  		TCP_SKB_CB(tskb)->flags |= TCPCB_FLAG_FIN;
  		TCP_SKB_CB(tskb)->end_seq++;
  		tp->write_seq++;
  		if (!tcp_send_head(sk)) {
  			/* This means tskb was already sent.
  			 * Pretend we included the FIN on previous transmit.
  			 * We need to set tp->snd_nxt to the value it would have
  			 * if FIN had been sent. This is because retransmit path
  			 * does not change tp->snd_nxt.
  			 */
  			tp->snd_nxt++;
  			return;
  		}
  	} else {
  		skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
  		if (unlikely(!skb)) {
  			if (tskb)
  				goto coalesce;
  			return;
  		}
  
  		/* Reserve space for headers and prepare control bits. */
  		skb_reserve(skb, MAX_TCP_HEADER);
  		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
  		tcp_init_nondata_skb(skb, tp->write_seq,
  				     TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
  		tcp_queue_skb(sk, skb);
  	}
  	__tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
  }
  
  /* We get here when a process closes a file descriptor (either due to
   * an explicit close() or as a byproduct of exit()'ing) and there
   * was unread data in the receive queue.  This behavior is recommended
   * by RFC 2525, section 2.17.  -DaveM
   */
  void tcp_send_active_reset(struct sock *sk, gfp_t priority)
  {
  	struct sk_buff *skb;
  
  	/* NOTE: No TCP options attached and we never retransmit this. */
  	skb = alloc_skb(MAX_TCP_HEADER, priority);
  	if (!skb) {
  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
  		return;
  	}
  
  	/* Reserve space for headers and prepare control bits. */
  	skb_reserve(skb, MAX_TCP_HEADER);
  	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
  			     TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
  	/* Send it off. */
  	TCP_SKB_CB(skb)->when = tcp_time_stamp;
  	if (tcp_transmit_skb(sk, skb, 0, priority))
  		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
  
  	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
  }
  
  /* Send a crossed SYN-ACK during socket establishment.
   * WARNING: This routine must only be called when we have already sent
   * a SYN packet that crossed the incoming SYN that caused this routine
   * to get called. If this assumption fails then the initial rcv_wnd
   * and rcv_wscale values will not be correct.
   */
  int tcp_send_synack(struct sock *sk)
  {
  	struct sk_buff *skb;
  
  	skb = tcp_write_queue_head(sk);
  	if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)) {
  		printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
  		return -EFAULT;
  	}
  	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_ACK)) {
  		if (skb_cloned(skb)) {
  			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
  			if (nskb == NULL)
  				return -ENOMEM;
  			tcp_unlink_write_queue(skb, sk);
  			skb_header_release(nskb);
  			__tcp_add_write_queue_head(sk, nskb);
  			sk_wmem_free_skb(sk, skb);
  			sk->sk_wmem_queued += nskb->truesize;
  			sk_mem_charge(sk, nskb->truesize);
  			skb = nskb;
  		}
  
  		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
  		TCP_ECN_send_synack(tcp_sk(sk), skb);
  	}
  	TCP_SKB_CB(skb)->when = tcp_time_stamp;
  	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
  }
  
  /* Prepare a SYN-ACK. */
  struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
  				struct request_sock *req)
  {
  	struct inet_request_sock *ireq = inet_rsk(req);
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct tcphdr *th;
  	int tcp_header_size;
  	struct tcp_out_options opts;
  	struct sk_buff *skb;
  	struct tcp_md5sig_key *md5;
  	__u8 *md5_hash_location;
  	int mss;
  
  	skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC);
  	if (skb == NULL)
  		return NULL;
  
  	/* Reserve space for headers. */
  	skb_reserve(skb, MAX_TCP_HEADER);
  
  	skb_dst_set(skb, dst_clone(dst));
  
  	mss = dst_metric(dst, RTAX_ADVMSS);
  	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
  		mss = tp->rx_opt.user_mss;
  
  	if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
  		__u8 rcv_wscale;
  		/* Set this up on the first call only */
  		req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
  		/* tcp_full_space because it is guaranteed to be the first packet */
  		tcp_select_initial_window(tcp_full_space(sk),
  			mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
  			&req->rcv_wnd,
  			&req->window_clamp,
  			ireq->wscale_ok,
  			&rcv_wscale);
  		ireq->rcv_wscale = rcv_wscale;
  	}
  
  	memset(&opts, 0, sizeof(opts));
  #ifdef CONFIG_SYN_COOKIES
  	if (unlikely(req->cookie_ts))
  		TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
  	else
  #endif
  	TCP_SKB_CB(skb)->when = tcp_time_stamp;
  	tcp_header_size = tcp_synack_options(sk, req, mss,
  					     skb, &opts, &md5) +
  			  sizeof(struct tcphdr);
  
  	skb_push(skb, tcp_header_size);
  	skb_reset_transport_header(skb);
  
  	th = tcp_hdr(skb);
  	memset(th, 0, sizeof(struct tcphdr));
  	th->syn = 1;
  	th->ack = 1;
  	TCP_ECN_make_synack(req, th);
  	th->source = ireq->loc_port;
  	th->dest = ireq->rmt_port;
  	/* Setting of flags are superfluous here for callers (and ECE is
  	 * not even correctly set)
  	 */
  	tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
  			     TCPCB_FLAG_SYN | TCPCB_FLAG_ACK);
  	th->seq = htonl(TCP_SKB_CB(skb)->seq);
  	th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
  
  	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
  	th->window = htons(min(req->rcv_wnd, 65535U));
  	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
  	th->doff = (tcp_header_size >> 2);
  	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
  
  #ifdef CONFIG_TCP_MD5SIG
  	/* Okay, we have all we need - do the md5 hash if needed */
  	if (md5) {
  		tcp_rsk(req)->af_specific->calc_md5_hash(md5_hash_location,
  					       md5, NULL, req, skb);
  	}
  #endif
  
  	return skb;
  }
  
  /* Do all connect socket setups that can be done AF independent. */
  static void tcp_connect_init(struct sock *sk)
  {
  	struct dst_entry *dst = __sk_dst_get(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	__u8 rcv_wscale;
  
  	/* We'll fix this up when we get a response from the other end.
  	 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
  	 */
  	tp->tcp_header_len = sizeof(struct tcphdr) +
  		(sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
  
  #ifdef CONFIG_TCP_MD5SIG
  	if (tp->af_specific->md5_lookup(sk, sk) != NULL)
  		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
  #endif
  
  	/* If user gave his TCP_MAXSEG, record it to clamp */
  	if (tp->rx_opt.user_mss)
  		tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
  	tp->max_window = 0;
  	tcp_mtup_init(sk);
  	tcp_sync_mss(sk, dst_mtu(dst));
  
  	if (!tp->window_clamp)
  		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
  	tp->advmss = dst_metric(dst, RTAX_ADVMSS);
  	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
  		tp->advmss = tp->rx_opt.user_mss;
  
  	tcp_initialize_rcv_mss(sk);
  
  	tcp_select_initial_window(tcp_full_space(sk),
  				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
  				  &tp->rcv_wnd,
  				  &tp->window_clamp,
  				  sysctl_tcp_window_scaling,
  				  &rcv_wscale);
  
  	tp->rx_opt.rcv_wscale = rcv_wscale;
  	tp->rcv_ssthresh = tp->rcv_wnd;
  
  	sk->sk_err = 0;
  	sock_reset_flag(sk, SOCK_DONE);
  	tp->snd_wnd = 0;
  	tcp_init_wl(tp, 0);
  	tp->snd_una = tp->write_seq;
  	tp->snd_sml = tp->write_seq;
  	tp->snd_up = tp->write_seq;
  	tp->rcv_nxt = 0;
  	tp->rcv_wup = 0;
  	tp->copied_seq = 0;
  
  	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
  	inet_csk(sk)->icsk_retransmits = 0;
  	tcp_clear_retrans(tp);
  }
  
  /* Build a SYN and send it off. */
  int tcp_connect(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *buff;
  
  	tcp_connect_init(sk);
  
  	buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
  	if (unlikely(!buff))
  		return -ENOBUFS;
  
  	tp->snd_nxt = tp->write_seq;
  	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
  	TCP_ECN_send_syn(sk, buff);
  
  	/* Send it off. */
  	TCP_SKB_CB(buff)->when = tcp_time_stamp;
  	tp->retrans_stamp = TCP_SKB_CB(buff)->when;
  	skb_header_release(buff);
  	__tcp_add_write_queue_tail(sk, buff);
  	sk->sk_wmem_queued += buff->truesize;
  	sk_mem_charge(sk, buff->truesize);
  	tp->packets_out += tcp_skb_pcount(buff);
  	tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
  
  	/* We change tp->snd_nxt after the tcp_transmit_skb() call
  	 * in order to make this packet get counted in tcpOutSegs.
  	 */
  	tp->snd_nxt = tp->write_seq;
  	tp->pushed_seq = tp->write_seq;
  	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
  
  	/* Timer for repeating the SYN until an answer. */
  	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
  				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
  	return 0;
  }
  
  /* Send out a delayed ack, the caller does the policy checking
   * to see if we should even be here.  See tcp_input.c:tcp_ack_snd_check()
   * for details.
   */
  void tcp_send_delayed_ack(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	int ato = icsk->icsk_ack.ato;
  	unsigned long timeout;
  
  	if (ato > TCP_DELACK_MIN) {
  		const struct tcp_sock *tp = tcp_sk(sk);
  		int max_ato = HZ / 2;
  
  		if (icsk->icsk_ack.pingpong ||
  		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
  			max_ato = TCP_DELACK_MAX;
  
  		/* Slow path, intersegment interval is "high". */
  
  		/* If some rtt estimate is known, use it to bound delayed ack.
  		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
  		 * directly.
  		 */
  		if (tp->srtt) {
  			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
  
  			if (rtt < max_ato)
  				max_ato = rtt;
  		}
  
  		ato = min(ato, max_ato);
  	}
  
  	/* Stay within the limit we were given */
  	timeout = jiffies + ato;
  
  	/* Use new timeout only if there wasn't a older one earlier. */
  	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
  		/* If delack timer was blocked or is about to expire,
  		 * send ACK now.
  		 */
  		if (icsk->icsk_ack.blocked ||
  		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
  			tcp_send_ack(sk);
  			return;
  		}
  
  		if (!time_before(timeout, icsk->icsk_ack.timeout))
  			timeout = icsk->icsk_ack.timeout;
  	}
  	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
  	icsk->icsk_ack.timeout = timeout;
  	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
  }
  
  /* This routine sends an ack and also updates the window. */
  void tcp_send_ack(struct sock *sk)
  {
  	struct sk_buff *buff;
  
  	/* If we have been reset, we may not send again. */
  	if (sk->sk_state == TCP_CLOSE)
  		return;
  
  	/* We are not putting this on the write queue, so
  	 * tcp_transmit_skb() will set the ownership to this
  	 * sock.
  	 */
  	buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
  	if (buff == NULL) {
  		inet_csk_schedule_ack(sk);
  		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
  					  TCP_DELACK_MAX, TCP_RTO_MAX);
  		return;
  	}
  
  	/* Reserve space for headers and prepare control bits. */
  	skb_reserve(buff, MAX_TCP_HEADER);
  	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);
  
  	/* Send it off, this clears delayed acks for us. */
  	TCP_SKB_CB(buff)->when = tcp_time_stamp;
  	tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC);
  }
  
  /* This routine sends a packet with an out of date sequence
   * number. It assumes the other end will try to ack it.
   *
   * Question: what should we make while urgent mode?
   * 4.4BSD forces sending single byte of data. We cannot send
   * out of window data, because we have SND.NXT==SND.MAX...
   *
   * Current solution: to send TWO zero-length segments in urgent mode:
   * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
   * out-of-date with SND.UNA-1 to probe window.
   */
  static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb;
  
  	/* We don't queue it, tcp_transmit_skb() sets ownership. */
  	skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
  	if (skb == NULL)
  		return -1;
  
  	/* Reserve space for headers and set control bits. */
  	skb_reserve(skb, MAX_TCP_HEADER);
  	/* Use a previous sequence.  This should cause the other
  	 * end to send an ack.  Don't queue or clone SKB, just
  	 * send it.
  	 */
  	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
  	TCP_SKB_CB(skb)->when = tcp_time_stamp;
  	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
  }
  
  /* Initiate keepalive or window probe from timer. */
  int tcp_write_wakeup(struct sock *sk)
  {
  	struct tcp_sock *tp = tcp_sk(sk);
  	struct sk_buff *skb;
  
  	if (sk->sk_state == TCP_CLOSE)
  		return -1;
  
  	if ((skb = tcp_send_head(sk)) != NULL &&
  	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
  		int err;
  		unsigned int mss = tcp_current_mss(sk);
  		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
  
  		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
  			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
  
  		/* We are probing the opening of a window
  		 * but the window size is != 0
  		 * must have been a result SWS avoidance ( sender )
  		 */
  		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
  		    skb->len > mss) {
  			seg_size = min(seg_size, mss);
  			TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
  			if (tcp_fragment(sk, skb, seg_size, mss))
  				return -1;
  		} else if (!tcp_skb_pcount(skb))
  			tcp_set_skb_tso_segs(sk, skb, mss);
  
  		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
  		TCP_SKB_CB(skb)->when = tcp_time_stamp;
  		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
  		if (!err)
  			tcp_event_new_data_sent(sk, skb);
  		return err;
  	} else {
  		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
  			tcp_xmit_probe_skb(sk, 1);
  		return tcp_xmit_probe_skb(sk, 0);
  	}
  }
  
  /* A window probe timeout has occurred.  If window is not closed send
   * a partial packet else a zero probe.
   */
  void tcp_send_probe0(struct sock *sk)
  {
  	struct inet_connection_sock *icsk = inet_csk(sk);
  	struct tcp_sock *tp = tcp_sk(sk);
  	int err;
  
  	err = tcp_write_wakeup(sk);
  
  	if (tp->packets_out || !tcp_send_head(sk)) {
  		/* Cancel probe timer, if it is not required. */
  		icsk->icsk_probes_out = 0;
  		icsk->icsk_backoff = 0;
  		return;
  	}
  
  	if (err <= 0) {
  		if (icsk->icsk_backoff < sysctl_tcp_retries2)
  			icsk->icsk_backoff++;
  		icsk->icsk_probes_out++;
  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
  					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
  					  TCP_RTO_MAX);
  	} else {
  		/* If packet was not sent due to local congestion,
  		 * do not backoff and do not remember icsk_probes_out.
  		 * Let local senders to fight for local resources.
  		 *
  		 * Use accumulated backoff yet.
  		 */
  		if (!icsk->icsk_probes_out)
  			icsk->icsk_probes_out = 1;
  		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
  					  min(icsk->icsk_rto << icsk->icsk_backoff,
  					      TCP_RESOURCE_PROBE_INTERVAL),
  					  TCP_RTO_MAX);
  	}
  }
  
  EXPORT_SYMBOL(tcp_select_initial_window);
  EXPORT_SYMBOL(tcp_connect);
  EXPORT_SYMBOL(tcp_make_synack);
  EXPORT_SYMBOL(tcp_simple_retransmit);
  EXPORT_SYMBOL(tcp_sync_mss);
  EXPORT_SYMBOL(tcp_mtup_init);
  