Ok. I didn't make 2.4.0 in 2000. Tough. I tried, but we had some

[davej-history.git] / net / ipv4 / tcp_output.c

/*
 * 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).
 *
 * Version: $Id: tcp_output.c,v 1.129 2000/11/28 17:04:10 davem Exp $
 *
 * Authors: Ross Biro, <bir7@leland.Stanford.Edu>
 * 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/smp_lock.h>

/* People can turn this off for buggy TCP's found in printers etc. */
int sysctl_tcp_retrans_collapse =1;

static __inline__
voidupdate_send_head(struct sock *sk,struct tcp_opt *tp,struct sk_buff *skb)
{
 tp->send_head = skb->next;
if(tp->send_head == (struct sk_buff *) &sk->write_queue)
 tp->send_head = NULL;
 tp->snd_nxt =TCP_SKB_CB(skb)->end_seq;
if(tp->packets_out++ ==0)
tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
}

/* 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_opt *tp)
{
if(!before(tp->snd_una+tp->snd_wnd, tp->snd_nxt))
return tp->snd_nxt;
else
return tp->snd_una+tp->snd_wnd;
}

/* 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 overriden 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_opt *tp = &(sk->tp_pinfo.af_tcp);
struct dst_entry *dst =__sk_dst_get(sk);
int mss = tp->advmss;

if(dst && dst->advmss < mss) {
 mss = dst->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 voidtcp_cwnd_restart(struct tcp_opt *tp)
{
 s32 delta = tcp_time_stamp - tp->lsndtime;
 u32 restart_cwnd =tcp_init_cwnd(tp);
 u32 cwnd = tp->snd_cwnd;

 tp->snd_ssthresh =tcp_current_ssthresh(tp);
 restart_cwnd =min(restart_cwnd, cwnd);

while((delta -= tp->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;
}

static __inline__ voidtcp_event_data_sent(struct tcp_opt *tp,struct sk_buff *skb)
{
 u32 now = tcp_time_stamp;

if(!tp->packets_out && (s32)(now - tp->lsndtime) > tp->rto)
tcp_cwnd_restart(tp);

 tp->lsndtime = now;

/* If it is a reply for ato after last received
 * packet, enter pingpong mode.
 */
if((u32)(now - tp->ack.lrcvtime) < tp->ack.ato)
 tp->ack.pingpong =1;
}

static __inline__ voidtcp_event_ack_sent(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);

tcp_dec_quickack_mode(tp);
tcp_clear_xmit_timer(sk, TCP_TIME_DACK);
}

/* Chose a new window to advertise, update state in tcp_opt 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 __inline__ u16 tcp_select_window(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
 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 = cur_win;
}
 tp->rcv_wnd = new_win;
 tp->rcv_wup = tp->rcv_nxt;

/* RFC1323 scaling applied */
 new_win >>= tp->rcv_wscale;

#ifdef TCP_FORMAL_WINDOW
if(new_win ==0) {
/* If we advertise zero window, disable fast path. */
 tp->pred_flags =0;
}else if(cur_win ==0&& tp->pred_flags ==0&&
skb_queue_len(&tp->out_of_order_queue) ==0&&
!tp->urg_data) {
/* If we open zero window, enable fast path.
 Without this it will be open by the first data packet,
 it is too late to merge checksumming to copy.
 */
tcp_fast_path_on(tp);
}
#endif

return new_win;
}


/* 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.
 */
inttcp_transmit_skb(struct sock *sk,struct sk_buff *skb)
{
if(skb != NULL) {
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct tcp_skb_cb *tcb =TCP_SKB_CB(skb);
int tcp_header_size = tp->tcp_header_len;
struct tcphdr *th;
int sysctl_flags;
int err;

#define SYSCTL_FLAG_TSTAMPS 0x1
#define SYSCTL_FLAG_WSCALE 0x2
#define SYSCTL_FLAG_SACK 0x4

 sysctl_flags =0;
if(tcb->flags & TCPCB_FLAG_SYN) {
 tcp_header_size =sizeof(struct tcphdr) + TCPOLEN_MSS;
if(sysctl_tcp_timestamps) {
 tcp_header_size += TCPOLEN_TSTAMP_ALIGNED;
 sysctl_flags |= SYSCTL_FLAG_TSTAMPS;
}
if(sysctl_tcp_window_scaling) {
 tcp_header_size += TCPOLEN_WSCALE_ALIGNED;
 sysctl_flags |= SYSCTL_FLAG_WSCALE;
}
if(sysctl_tcp_sack) {
 sysctl_flags |= SYSCTL_FLAG_SACK;
if(!(sysctl_flags & SYSCTL_FLAG_TSTAMPS))
 tcp_header_size += TCPOLEN_SACKPERM_ALIGNED;
}
}else if(tp->eff_sacks) {
/* A SACK is 2 pad bytes, a 2 byte header, plus
 * 2 32-bit sequence numbers for each SACK block.
 */
 tcp_header_size += (TCPOLEN_SACK_BASE_ALIGNED +
(tp->eff_sacks * TCPOLEN_SACK_PERBLOCK));
}
 th = (struct tcphdr *)skb_push(skb, tcp_header_size);
 skb->h.th = th;
skb_set_owner_w(skb, sk);

/* Build TCP header and checksum it. */
 th->source = sk->sport;
 th->dest = sk->dport;
 th->seq =htonl(tcb->seq);
 th->ack_seq =htonl(tp->rcv_nxt);
*(((__u16 *)th) +6) =htons(((tcp_header_size >>2) <<12) | tcb->flags);
if(tcb->flags & TCPCB_FLAG_SYN) {
/* RFC1323: The window in SYN & SYN/ACK segments
 * is never scaled.
 */
 th->window =htons(tp->rcv_wnd);
}else{
 th->window =htons(tcp_select_window(sk));
}
 th->check =0;
 th->urg_ptr =0;

if(tp->urg_mode &&
between(tp->snd_up, tcb->seq+1, tcb->seq+0xFFFF)) {
 th->urg_ptr =htons(tp->snd_up-tcb->seq);
 th->urg =1;
}

if(tcb->flags & TCPCB_FLAG_SYN) {
tcp_syn_build_options((__u32 *)(th +1),
tcp_advertise_mss(sk),
(sysctl_flags & SYSCTL_FLAG_TSTAMPS),
(sysctl_flags & SYSCTL_FLAG_SACK),
(sysctl_flags & SYSCTL_FLAG_WSCALE),
 tp->rcv_wscale,
 tcb->when,
 tp->ts_recent);
}else{
tcp_build_and_update_options((__u32 *)(th +1),
 tp, tcb->when);

TCP_ECN_send(sk, tp, skb, tcp_header_size);
}
 tp->af_specific->send_check(sk, th, skb->len, skb);

if(tcb->flags & TCPCB_FLAG_ACK)
tcp_event_ack_sent(sk);

if(skb->len != tcp_header_size)
tcp_event_data_sent(tp, skb);

TCP_INC_STATS(TcpOutSegs);

 err = tp->af_specific->queue_xmit(skb);
if(err <=0)
return err;

tcp_enter_cwr(tp);

/* NET_XMIT_CN is special. It does not guarantee,
 * that this packet is lost. It tells that device
 * is about to start to drop packets or already
 * drops some packets of the same priority and
 * invokes us to send less aggressively.
 */
return err == NET_XMIT_CN ?0: err;
}
return-ENOBUFS;
#undef SYSCTL_FLAG_TSTAMPS
#undef SYSCTL_FLAG_WSCALE
#undef SYSCTL_FLAG_SACK
}


/* This is the main buffer sending routine. We queue the buffer
 * and decide whether to queue or transmit now.
 *
 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 * otherwise socket can stall.
 */
voidtcp_send_skb(struct sock *sk,struct sk_buff *skb,int force_queue,unsigned cur_mss)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);

/* Advance write_seq and place onto the write_queue. */
 tp->write_seq =TCP_SKB_CB(skb)->end_seq;
__skb_queue_tail(&sk->write_queue, skb);
tcp_charge_skb(sk, skb);

if(!force_queue && tp->send_head == NULL &&tcp_snd_test(tp, skb, cur_mss, tp->nonagle)) {
/* Send it out now. */
TCP_SKB_CB(skb)->when = tcp_time_stamp;
if(tcp_transmit_skb(sk,skb_clone(skb, sk->allocation)) ==0) {
 tp->snd_nxt =TCP_SKB_CB(skb)->end_seq;
tcp_minshall_update(tp, cur_mss, skb);
if(tp->packets_out++ ==0)
tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
return;
}
}
/* Queue it, remembering where we must start sending. */
if(tp->send_head == NULL)
 tp->send_head = skb;
}

/* 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.
 */
static inttcp_fragment(struct sock *sk,struct sk_buff *skb, u32 len)
{
struct tcp_opt *tp = &sk->tp_pinfo.af_tcp;
struct sk_buff *buff;
int nsize = skb->len - len;
 u16 flags;

/* Get a new skb... force flag on. */
 buff =tcp_alloc_skb(sk, nsize + MAX_TCP_HEADER, GFP_ATOMIC);
if(buff == NULL)
return-ENOMEM;/* We'll just try again later. */
tcp_charge_skb(sk, buff);

/* Reserve space for headers. */
skb_reserve(buff, MAX_TCP_HEADER);

/* 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;

/* 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&(TCPCB_LOST|TCPCB_EVER_RETRANS|TCPCB_AT_TAIL);
if(TCP_SKB_CB(buff)->sacked&TCPCB_LOST) {
 tp->lost_out++;
 tp->left_out++;
}
TCP_SKB_CB(buff)->sacked &= ~TCPCB_AT_TAIL;

/* Copy and checksum data tail into the new buffer. */
 buff->csum =csum_partial_copy_nocheck(skb->data + len,skb_put(buff, nsize),
 nsize,0);

/* This takes care of the FIN sequence number too. */
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(buff)->seq;
skb_trim(skb, len);

/* Rechecksum original buffer. */
 skb->csum =csum_partial(skb->data, skb->len,0);

/* 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;

/* Link BUFF into the send queue. */
__skb_append(skb, buff);

return0;
}

/* This function synchronize snd mss to current pmtu/exthdr set.

 tp->user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
 for TCP options, but includes only bare TCP header.

 tp->mss_clamp is mss negotiated at connection setup.
 It is minumum of user_mss and mss received with SYN.
 It also does not include TCP options.

 tp->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->mss_clamp.

 NOTE1. rfc1122 clearly states that advertised MSS
 DOES NOT include either tcp or ip options.

 NOTE2. tp->pmtu_cookie and tp->mss_cache are READ ONLY outside
 this function. --ANK (980731)
 */

inttcp_sync_mss(struct sock *sk, u32 pmtu)
{
struct tcp_opt *tp = &sk->tp_pinfo.af_tcp;
int mss_now;

/* Calculate base mss without TCP options:
 It is MMS_S - sizeof(tcphdr) of rfc1122
 */

 mss_now = pmtu - tp->af_specific->net_header_len -sizeof(struct tcphdr);

/* Clamp it (mss_clamp does not include tcp options) */
if(mss_now > tp->mss_clamp)
 mss_now = tp->mss_clamp;

/* Now subtract optional transport overhead */
 mss_now -= tp->ext_header_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);

/* Bound mss with half of window */
if(tp->max_window && mss_now > (tp->max_window>>1))
 mss_now =max((tp->max_window>>1),68- tp->tcp_header_len);

/* And store cached results */
 tp->pmtu_cookie = pmtu;
 tp->mss_cache = mss_now;
return mss_now;
}


/* This routine writes packets to the network. It advances the
 * send_head. This happens as incoming acks open up the remote
 * window for us.
 *
 * Returns 1, if no segments are in flight and we have queued segments, but
 * cannot send anything now because of SWS or another problem.
 */
inttcp_write_xmit(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
unsigned int mss_now;

/* 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(sk->state != TCP_CLOSE) {
struct sk_buff *skb;
int sent_pkts =0;

/* Account for SACKS, we may need to fragment due to this.
 * It is just like the real MSS changing on us midstream.
 * We also handle things correctly when the user adds some
 * IP options mid-stream. Silly to do, but cover it.
 */
 mss_now =tcp_current_mss(sk);

while((skb = tp->send_head) &&
tcp_snd_test(tp, skb, mss_now,tcp_skb_is_last(sk, skb) ? tp->nonagle :1)) {
if(skb->len > mss_now) {
if(tcp_fragment(sk, skb, mss_now))
break;
}

TCP_SKB_CB(skb)->when = tcp_time_stamp;
if(tcp_transmit_skb(sk,skb_clone(skb, GFP_ATOMIC)))
break;
/* Advance the send_head. This one is sent out. */
update_send_head(sk, tp, skb);
tcp_minshall_update(tp, mss_now, skb);
 sent_pkts =1;
}

if(sent_pkts) {
tcp_cwnd_validate(sk, tp);
return0;
}

return!tp->packets_out && tp->send_head;
}
return0;
}

/* 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 tcp_opt *tp = &sk->tp_pinfo.af_tcp;
/* MSS for the peer's data. Previous verions 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
 */
unsigned int mss = tp->ack.rcv_mss;
int free_space;
 u32 window;

/* Sometimes free_space can be < 0. */
 free_space =tcp_space(sk);
if(tp->window_clamp < mss)
 mss = tp->window_clamp;

if(free_space < (int)min(tp->window_clamp,tcp_full_space(sk)) /2) {
 tp->ack.quick =0;

if(tcp_memory_pressure)
 tp->rcv_ssthresh =min(tp->rcv_ssthresh,4*tp->advmss);

if(free_space < ((int)mss))
return0;
}

if(free_space > tp->rcv_ssthresh)
 free_space = tp->rcv_ssthresh;

/* 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.
 */
 window = tp->rcv_wnd;
if((((int) window) <= (free_space - ((int) mss))) ||
(((int) window) > free_space))
 window = (((unsigned int) free_space)/mss)*mss;

return window;
}

/* Attempt to collapse two adjacent SKB's during retransmission. */
static voidtcp_retrans_try_collapse(struct sock *sk,struct sk_buff *skb,int mss_now)
{
struct tcp_opt *tp = &sk->tp_pinfo.af_tcp;
struct sk_buff *next_skb = skb->next;

/* The first test we must make is that neither of these two
 * SKB's are still referenced by someone else.
 */
if(!skb_cloned(skb) && !skb_cloned(next_skb)) {
int skb_size = skb->len, next_skb_size = next_skb->len;
 u16 flags =TCP_SKB_CB(skb)->flags;

/* Also punt if next skb has been SACK'd. */
if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
return;

/* Next skb is out of window. */
if(after(TCP_SKB_CB(next_skb)->end_seq, tp->snd_una+tp->snd_wnd))
return;

/* Punt if not enough space exists in the first SKB for
 * the data in the second, or the total combined payload
 * would exceed the MSS.
 */
if((next_skb_size >skb_tailroom(skb)) ||
((skb_size + next_skb_size) > mss_now))
return;

/* Ok. We will be able to collapse the packet. */
__skb_unlink(next_skb, next_skb->list);

if(skb->len %4) {
/* Must copy and rechecksum all data. */
memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
 skb->csum =csum_partial(skb->data, skb->len,0);
}else{
/* Optimize, actually we could also combine next_skb->csum
 * to skb->csum using a single add w/carry operation too.
 */
 skb->csum =csum_partial_copy_nocheck(next_skb->data,
skb_put(skb, next_skb_size),
 next_skb_size, skb->csum);
}

/* Update sequence range on original skb. */
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(next_skb)->end_seq;

/* Merge over control information. */
 flags |=TCP_SKB_CB(next_skb)->flags;/* This moves PSH/FIN etc. over */
TCP_SKB_CB(skb)->flags = 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|TCPCB_AT_TAIL);
if(TCP_SKB_CB(next_skb)->sacked&TCPCB_SACKED_RETRANS)
 tp->retrans_out--;
if(TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) {
 tp->lost_out--;
 tp->left_out--;
}
if(!tp->sack_ok && tp->sacked_out) {
/* Reno case is special. Sigh... */
 tp->sacked_out--;
 tp->left_out--;
}
/* Not quite right: it can be > snd.fack, but
 * it is better to underestimate fackets.
 */
if(tp->fackets_out)
 tp->fackets_out--;
tcp_free_skb(sk, next_skb);
 tp->packets_out--;
}
}

/* Do a simple retransmit without using the backoff mechanisms in
 * tcp_timer. This is used for path mtu discovery. 
 * The socket is already locked here.
 */
voidtcp_simple_retransmit(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct sk_buff *skb;
unsigned int mss =tcp_current_mss(sk);
int lost =0;

for_retrans_queue(skb, sk, tp) {
if(skb->len > mss &&
!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
if(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
 tp->retrans_out--;
}
if(!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 tp->lost_out++;
 lost =1;
}
}
}

if(!lost)
return;

 tp->left_out = tp->sacked_out + tp->lost_out;

/* Don't muck with the congestion window here.
 * Reason is that we do not increase amount of _data_
 * in network, but units changed and effective
 * cwnd/ssthresh really reduced now.
 */
if(tp->ca_state != TCP_CA_Loss) {
 tp->high_seq = tp->snd_nxt;
 tp->snd_ssthresh =tcp_current_ssthresh(tp);
 tp->prior_ssthresh =0;
 tp->undo_marker =0;
 tp->ca_state = TCP_CA_Loss;
}
tcp_xmit_retransmit_queue(sk);
}

/* 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.
 */
inttcp_retransmit_skb(struct sock *sk,struct sk_buff *skb)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
unsigned int cur_mss =tcp_current_mss(sk);
int err;

/* Do not sent more than we queued. 1/4 is reserved for possible
 * copying overhead: frgagmentation, tunneling, mangling etc.
 */
if(atomic_read(&sk->wmem_alloc) >min(sk->wmem_queued+(sk->wmem_queued>>2),sk->sndbuf))
return-EAGAIN;

if(skb->len > cur_mss) {
if(tcp_fragment(sk, skb, cur_mss))
return-ENOMEM;/* We'll try again later. */

/* New SKB created, account for it. */
 tp->packets_out++;
}

/* Collapse two adjacent packets if worthwhile and we can. */
if(!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
(skb->len < (cur_mss >>1)) &&
(skb->next != tp->send_head) &&
(skb->next != (struct sk_buff *)&sk->write_queue) &&
(sysctl_tcp_retrans_collapse !=0))
tcp_retrans_try_collapse(sk, skb, cur_mss);

if(tp->af_specific->rebuild_header(sk))
return-EHOSTUNREACH;/* Routing failure or similar. */

/* 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)) {
TCP_SKB_CB(skb)->seq =TCP_SKB_CB(skb)->end_seq -1;
skb_trim(skb,0);
 skb->csum =0;
}

/* 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_cloned(skb) ?
skb_copy(skb, GFP_ATOMIC):
skb_clone(skb, GFP_ATOMIC)));

if(err ==0) {
/* Update global TCP statistics. */
TCP_INC_STATS(TcpRetransSegs);

#if FASTRETRANS_DEBUG > 0
if(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) {
if(net_ratelimit())
printk(KERN_DEBUG "retrans_out leaked.\n");
}
#endif
TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
 tp->retrans_out++;

/* 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;
}

/* 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.
 */
voidtcp_xmit_retransmit_queue(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct sk_buff *skb;
int packet_cnt = tp->lost_out;

/* First pass: retransmit lost packets. */
if(packet_cnt) {
for_retrans_queue(skb, sk, tp) {
 __u8 sacked =TCP_SKB_CB(skb)->sacked;

if(tcp_packets_in_flight(tp) >= tp->snd_cwnd)
return;

if(sacked&TCPCB_LOST) {
if(!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
if(tcp_retransmit_skb(sk, skb))
return;
if(tp->ca_state != TCP_CA_Loss)
NET_INC_STATS_BH(TCPFastRetrans);
else
NET_INC_STATS_BH(TCPSlowStartRetrans);

if(skb ==skb_peek(&sk->write_queue))
tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
}

if(--packet_cnt <=0)
break;
}
}
}

/* OK, demanded retransmission is finished. */

/* Forward retransmissions are possible only during Recovery. */
if(tp->ca_state != TCP_CA_Recovery)
return;

/* No forward retransmissions in Reno are possible. */
if(!tp->sack_ok)
return;

/* Yeah, we have to make difficult choice between forward transmission
 * and retransmission... Both ways have their merits...
 *
 * For now we do not retrnamsit anything, while we have some new
 * segments to send.
 */

if(tcp_may_send_now(sk, tp))
return;

 packet_cnt =0;

for_retrans_queue(skb, sk, tp) {
if(++packet_cnt > tp->fackets_out)
break;

if(tcp_packets_in_flight(tp) >= tp->snd_cwnd)
break;

if(TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
continue;

/* Ok, retransmit it. */
if(tcp_retransmit_skb(sk, skb))
break;

if(skb ==skb_peek(&sk->write_queue))
tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);

NET_INC_STATS_BH(TCPForwardRetrans);
}
}


/* Send a fin. The caller locks the socket for us. This cannot be
 * allowed to fail queueing a FIN frame under any circumstances.
 */
voidtcp_send_fin(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct sk_buff *skb =skb_peek_tail(&sk->write_queue);
unsigned int mss_now;

/* Optimization, tack on the FIN if we have a queue of
 * unsent frames. But be careful about outgoing SACKS
 * and IP options.
 */
 mss_now =tcp_current_mss(sk);

/* Please, find seven differences of 2.3.33 and loook
 * what I broke here. 8) --ANK
 */

if(tp->send_head != NULL) {
/* tcp_write_xmit() takes care of the rest. */
TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN;
TCP_SKB_CB(skb)->end_seq++;
 tp->write_seq++;

/* Special case to avoid Nagle bogosity. If this
 * segment is the last segment, and it was queued
 * due to Nagle/SWS-avoidance, send it out now.
 */
if(tp->send_head == skb &&
!after(tp->write_seq, tp->snd_una + tp->snd_wnd)) {
TCP_SKB_CB(skb)->when = tcp_time_stamp;
if(!tcp_transmit_skb(sk,skb_clone(skb, GFP_KERNEL)))
update_send_head(sk, tp, skb);
else
tcp_check_probe_timer(sk, tp);
}
}else{
/* Socket is locked, keep trying until memory is available. */
for(;;) {
 skb =alloc_skb(MAX_TCP_HEADER, GFP_KERNEL);
if(skb)
break;
 current->policy |= SCHED_YIELD;
schedule();
}

/* Reserve space for headers and prepare control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
 skb->csum =0;
TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
TCP_SKB_CB(skb)->sacked =0;

/* FIN eats a sequence byte, write_seq advanced by tcp_send_skb(). */
TCP_SKB_CB(skb)->seq = tp->write_seq;
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(skb)->seq +1;
tcp_send_skb(sk, skb,0, mss_now);
__tcp_push_pending_frames(sk, tp, mss_now,1);
}
}

/* 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 draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM
 */
voidtcp_send_active_reset(struct sock *sk,int priority)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
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(TCPAbortFailed);
return;
}

/* Reserve space for headers and prepare control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
 skb->csum =0;
TCP_SKB_CB(skb)->flags = (TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
TCP_SKB_CB(skb)->sacked =0;

/* Send it off. */
TCP_SKB_CB(skb)->seq =tcp_acceptable_seq(sk, tp);
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(skb)->seq;
TCP_SKB_CB(skb)->when = tcp_time_stamp;
if(tcp_transmit_skb(sk, skb))
NET_INC_STATS(TCPAbortFailed);
}

/* 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.
 */
inttcp_send_synack(struct sock *sk)
{
struct sk_buff* skb;

 skb =skb_peek(&sk->write_queue);
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;
__skb_unlink(skb, &sk->write_queue);
__skb_queue_head(&sk->write_queue, nskb);
tcp_free_skb(sk, skb);
tcp_charge_skb(sk, nskb);
 skb = nskb;
}

TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK;
TCP_ECN_send_synack(&sk->tp_pinfo.af_tcp, skb);
}
TCP_SKB_CB(skb)->when = tcp_time_stamp;
returntcp_transmit_skb(sk,skb_clone(skb, GFP_ATOMIC));
}

/*
 * Prepare a SYN-ACK.
 */
struct sk_buff *tcp_make_synack(struct sock *sk,struct dst_entry *dst,
struct open_request *req)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct tcphdr *th;
int tcp_header_size;
struct sk_buff *skb;

 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 =dst_clone(dst);

 tcp_header_size = (sizeof(struct tcphdr) + TCPOLEN_MSS +
(req->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED :0) +
(req->wscale_ok ? TCPOLEN_WSCALE_ALIGNED :0) +
/* SACK_PERM is in the place of NOP NOP of TS */
((req->sack_ok && !req->tstamp_ok) ? TCPOLEN_SACKPERM_ALIGNED :0));
 skb->h.th = th = (struct tcphdr *)skb_push(skb, tcp_header_size);

memset(th,0,sizeof(struct tcphdr));
 th->syn =1;
 th->ack =1;
TCP_ECN_make_synack(req, th);
 th->source = sk->sport;
 th->dest = req->rmt_port;
TCP_SKB_CB(skb)->seq = req->snt_isn;
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(skb)->seq +1;
 th->seq =htonl(TCP_SKB_CB(skb)->seq);
 th->ack_seq =htonl(req->rcv_isn +1);
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->window;
/* tcp_full_space because it is guaranteed to be the first packet */
tcp_select_initial_window(tcp_full_space(sk),
 dst->advmss - (req->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED :0),
&req->rcv_wnd,
&req->window_clamp,
 req->wscale_ok,
&rcv_wscale);
 req->rcv_wscale = rcv_wscale;
}

/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
 th->window =htons(req->rcv_wnd);

TCP_SKB_CB(skb)->when = tcp_time_stamp;
tcp_syn_build_options((__u32 *)(th +1), dst->advmss, req->tstamp_ok,
 req->sack_ok, req->wscale_ok, req->rcv_wscale,
TCP_SKB_CB(skb)->when,
 req->ts_recent);

 skb->csum =0;
 th->doff = (tcp_header_size >>2);
TCP_INC_STATS(TcpOutSegs);
return skb;
}

inttcp_connect(struct sock *sk,struct sk_buff *buff)
{
struct dst_entry *dst =__sk_dst_get(sk);
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);

/* Reserve space for headers. */
skb_reserve(buff, MAX_TCP_HEADER);

/* 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);

/* If user gave his TCP_MAXSEG, record it to clamp */
if(tp->user_mss)
 tp->mss_clamp = tp->user_mss;
 tp->max_window =0;
tcp_sync_mss(sk, dst->pmtu);

if(!tp->window_clamp)
 tp->window_clamp = dst->window;
 tp->advmss = dst->advmss;
tcp_initialize_rcv_mss(sk);

tcp_select_initial_window(tcp_full_space(sk),
 tp->advmss - (tp->ts_recent_stamp ? tp->tcp_header_len -sizeof(struct tcphdr) :0),
&tp->rcv_wnd,
&tp->window_clamp,
 sysctl_tcp_window_scaling,
&tp->rcv_wscale);

 tp->rcv_ssthresh = tp->rcv_wnd;

/* Socket identity change complete, no longer
 * in TCP_CLOSE, so enter ourselves into the
 * hash tables.
 */
tcp_set_state(sk,TCP_SYN_SENT);
if(tp->af_specific->hash_connecting(sk))
goto err_out;

 sk->err =0;
 sk->done =0;
 tp->snd_wnd =0;
tcp_init_wl(tp, tp->write_seq,0);
 tp->snd_una = tp->write_seq;
 tp->snd_sml = tp->write_seq;
 tp->rcv_nxt =0;
 tp->rcv_wup =0;
 tp->copied_seq =0;

 tp->rto = TCP_TIMEOUT_INIT;
 tp->retransmits =0;
tcp_clear_retrans(tp);

TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN;
TCP_ECN_send_syn(tp, buff);
TCP_SKB_CB(buff)->sacked =0;
 buff->csum =0;
TCP_SKB_CB(buff)->seq = tp->write_seq++;
TCP_SKB_CB(buff)->end_seq = tp->write_seq;
 tp->snd_nxt = tp->write_seq;
 tp->pushed_seq = tp->write_seq;

/* Send it off. */
TCP_SKB_CB(buff)->when = tcp_time_stamp;
 tp->retrans_stamp =TCP_SKB_CB(buff)->when;
__skb_queue_tail(&sk->write_queue, buff);
tcp_charge_skb(sk, buff);
 tp->packets_out++;
tcp_transmit_skb(sk,skb_clone(buff, GFP_KERNEL));
TCP_INC_STATS(TcpActiveOpens);

/* Timer for repeating the SYN until an answer. */
tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto);
return0;

err_out:
tcp_set_state(sk,TCP_CLOSE);
kfree_skb(buff);
return-EADDRNOTAVAIL;
}

/* 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.
 */
voidtcp_send_delayed_ack(struct sock *sk)
{
struct tcp_opt *tp = &sk->tp_pinfo.af_tcp;
int ato = tp->ack.ato;
unsigned long timeout;

if(ato > TCP_DELACK_MIN) {
int max_ato = HZ/2;

if(tp->ack.pingpong || (tp->ack.pending&TCP_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 tp->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(tp->ack.pending&TCP_ACK_TIMER) {
/* If delack timer was blocked or is about to expire,
 * send ACK now.
 */
if(tp->ack.blocked ||time_before_eq(tp->ack.timeout, jiffies+(ato>>2))) {
tcp_send_ack(sk);
return;
}

if(!time_before(timeout, tp->ack.timeout))
 timeout = tp->ack.timeout;
}
 tp->ack.pending |= TCP_ACK_SCHED|TCP_ACK_TIMER;
 tp->ack.timeout = timeout;
if(!mod_timer(&tp->delack_timer, timeout))
sock_hold(sk);

#ifdef TCP_FORMAL_WINDOW
/* Explanation. Header prediction path does not handle
 * case of zero window. If we send ACK immediately, pred_flags
 * are reset when sending ACK. If rcv_nxt is advanced and
 * ack is not sent, than delayed ack is scheduled.
 * Hence, it is the best place to check for zero window.
 */
if(tp->pred_flags) {
if(tcp_receive_window(tp) ==0)
 tp->pred_flags =0;
}else{
if(skb_queue_len(&tp->out_of_order_queue) ==0&&
!tp->urg_data)
tcp_fast_path_on(tp);
}
#endif
}

/* This routine sends an ack and also updates the window. */
voidtcp_send_ack(struct sock *sk)
{
/* If we have been reset, we may not send again. */
if(sk->state != TCP_CLOSE) {
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct sk_buff *buff;

/* 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) {
tcp_schedule_ack(tp);
 tp->ack.ato = TCP_ATO_MIN;
tcp_reset_xmit_timer(sk, TCP_TIME_DACK, TCP_DELACK_MAX);
return;
}

/* Reserve space for headers and prepare control bits. */
skb_reserve(buff, MAX_TCP_HEADER);
 buff->csum =0;
TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK;
TCP_SKB_CB(buff)->sacked =0;

/* Send it off, this clears delayed acks for us. */
TCP_SKB_CB(buff)->seq =TCP_SKB_CB(buff)->end_seq =tcp_acceptable_seq(sk, tp);
TCP_SKB_CB(buff)->when = tcp_time_stamp;
tcp_transmit_skb(sk, buff);
}
}

/* 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 inttcp_xmit_probe_skb(struct sock *sk,int urgent)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
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);
 skb->csum =0;
TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK;
TCP_SKB_CB(skb)->sacked = urgent;

/* Use a previous sequence. This should cause the other
 * end to send an ack. Don't queue or clone SKB, just
 * send it.
 */
TCP_SKB_CB(skb)->seq = urgent ? tp->snd_una : tp->snd_una -1;
TCP_SKB_CB(skb)->end_seq =TCP_SKB_CB(skb)->seq;
TCP_SKB_CB(skb)->when = tcp_time_stamp;
returntcp_transmit_skb(sk, skb);
}

inttcp_write_wakeup(struct sock *sk)
{
if(sk->state != TCP_CLOSE) {
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
struct sk_buff *skb;

if((skb = tp->send_head) != NULL &&
before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) {
int err;
int mss =tcp_current_mss(sk);
int seg_size = tp->snd_una+tp->snd_wnd-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))
return-1;
}
TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
TCP_SKB_CB(skb)->when = tcp_time_stamp;
 err =tcp_transmit_skb(sk,skb_clone(skb, GFP_ATOMIC));
if(!err) {
update_send_head(sk, tp, skb);
}
return err;
}else{
if(tp->urg_mode &&
between(tp->snd_up, tp->snd_una+1, tp->snd_una+0xFFFF))
tcp_xmit_probe_skb(sk, TCPCB_URG);
returntcp_xmit_probe_skb(sk,0);
}
}
return-1;
}

/* A window probe timeout has occurred. If window is not closed send
 * a partial packet else a zero probe.
 */
voidtcp_send_probe0(struct sock *sk)
{
struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
int err;

 err =tcp_write_wakeup(sk);

if(tp->packets_out || !tp->send_head) {
/* Cancel probe timer, if it is not required. */
 tp->probes_out =0;
 tp->backoff =0;
return;
}

if(err <=0) {
 tp->backoff++;
 tp->probes_out++;
tcp_reset_xmit_timer(sk, TCP_TIME_PROBE0,
min(tp->rto << tp->backoff, TCP_RTO_MAX));
}else{
/* If packet was not sent due to local congestion,
 * do not backoff and do not remember probes_out.
 * Let local senders to fight for local resources.
 *
 * Use accumulated backoff yet.
 */
if(!tp->probes_out)
 tp->probes_out=1;
tcp_reset_xmit_timer(sk, TCP_TIME_PROBE0,
min(tp->rto << tp->backoff, TCP_RESOURCE_PROBE_INTERVAL));
}
}