/* * 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 1.144 2001/11/06 22:21:08 davem Exp $ * * Authors: Ross Biro, * Fred N. van Kempen, * Mark Evans, * Corey Minyard * Florian La Roche, * Charles Hedrick, * Linus Torvalds, * Alan Cox, * Matthew Dillon, * Arnt Gulbrandsen, * Jorge Cwik, */ /* * 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 #include #include /* People can turn this off for buggy TCP's found in printers etc. */ int sysctl_tcp_retrans_collapse = 1; static __inline__ void update_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 void tcp_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; if (tcp_is_vegas(tp)) tcp_vegas_enable(tp); 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__ void tcp_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__ void tcp_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); } /* from 2.6's ALIGN, used in tcp_select_window() */ #define ALIGN_WIN(x,a) __ALIGN_MASK(x,(typeof(x))(a)-1) #define __ALIGN_MASK(x,mask) (((x)+(mask))&~(mask)) /* 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 = ALIGN_WIN(cur_win, 1 << tp->rcv_wscale); } tp->rcv_wnd = new_win; tp->rcv_wup = tp->rcv_nxt; /* RFC1323 scaling applied */ new_win >>= tp->rcv_wscale; /* If we advertise zero window, disable fast path. */ if (new_win == 0) tp->pred_flags = 0; 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. */ int tcp_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)); } /* * If the connection is idle and we are restarting, * then we don't want to do any Vegas calculations * until we get fresh RTT samples. So when we * restart, we reset our Vegas state to a clean * slate. After we get acks for this flight of * packets, _then_ we can make Vegas calculations * again. */ if (tcp_is_vegas(tp) && tcp_packets_in_flight(tp) == 0) tcp_vegas_enable(tp); 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, 0); 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. */ void tcp_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; } /* 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 cur_mss) { struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp); struct sk_buff *skb = tp->send_head; if (tcp_snd_test(tp, skb, cur_mss, 1)) { /* Send it out now. */ TCP_SKB_CB(skb)->when = tcp_time_stamp; if (tcp_transmit_skb(sk, skb_clone(skb, sk->allocation)) == 0) { 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); return; } } } /* Split fragmented skb to two parts at length len. */ static void skb_split(struct sk_buff *skb, struct sk_buff *skb1, u32 len) { int i; int pos = skb->len - skb->data_len; if (len < pos) { /* Split line is inside header. */ memcpy(skb_put(skb1, pos-len), skb->data + len, pos-len); /* And move data appendix as is. */ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) skb_shinfo(skb1)->frags[i] = skb_shinfo(skb)->frags[i]; skb_shinfo(skb1)->nr_frags = skb_shinfo(skb)->nr_frags; skb_shinfo(skb)->nr_frags = 0; skb1->data_len = skb->data_len; skb1->len += skb1->data_len; skb->data_len = 0; skb->len = len; skb->tail = skb->data+len; } else { int k = 0; int nfrags = skb_shinfo(skb)->nr_frags; /* Second chunk has no header, nothing to copy. */ skb_shinfo(skb)->nr_frags = 0; skb1->len = skb1->data_len = skb->len - len; skb->len = len; skb->data_len = len - pos; for (i=0; ifrags[i].size; if (pos + size > len) { skb_shinfo(skb1)->frags[k] = skb_shinfo(skb)->frags[i]; if (pos < len) { /* Split frag. * We have to variants in this case: * 1. Move all the frag to the second * part, if it is possible. F.e. * this approach is mandatory for TUX, * where splitting is expensive. * 2. Split is accurately. We make this. */ get_page(skb_shinfo(skb)->frags[i].page); skb_shinfo(skb1)->frags[0].page_offset += (len-pos); skb_shinfo(skb1)->frags[0].size -= (len-pos); skb_shinfo(skb)->frags[i].size = len-pos; skb_shinfo(skb)->nr_frags++; } k++; } else { skb_shinfo(skb)->nr_frags++; } pos += size; } skb_shinfo(skb1)->nr_frags = k; } } /* 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 int tcp_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; if (skb_cloned(skb) && skb_is_nonlinear(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) return -ENOMEM; /* Get a new skb... force flag on. */ buff = tcp_alloc_skb(sk, nsize, GFP_ATOMIC); if (buff == NULL) return -ENOMEM; /* We'll just try again later. */ tcp_charge_skb(sk, buff); /* 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&(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(skb)->sacked &= ~TCPCB_AT_TAIL; if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_HW) { /* 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_HW; 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; /* Link BUFF into the send queue. */ __skb_append(skb, buff); return 0; } /* 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) */ int tcp_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), 68U - 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. */ int tcp_write_xmit(struct sock *sk, int nonagle) { 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) ? 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); return 0; } return !tp->packets_out && tp->send_head; } return 0; } /* 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 */ int mss = tp->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/2) { tp->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; /* 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 (window <= free_space - mss || window > free_space) window = (free_space/mss)*mss; else if (mss == full_space && free_space > window + full_space/2) window = free_space; return window; } /* Attempt to collapse two adjacent SKB's during retransmission. */ static void tcp_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); memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size); if (next_skb->ip_summed == CHECKSUM_HW) skb->ip_summed = CHECKSUM_HW; if (skb->ip_summed != CHECKSUM_HW) 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. */ 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--; } /* Reno case is special. Sigh... */ if (!tp->sack_ok && tp->sacked_out) { 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. */ void tcp_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; tcp_sync_left_out(tp); /* 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; tcp_set_ca_state(tp, 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. */ int tcp_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 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, tp->snd_una+tp->snd_wnd) && TCP_SKB_CB(skb)->seq != tp->snd_una) 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) && (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) && (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)) { if (!pskb_trim(skb, 0)) { TCP_SKB_CB(skb)->seq = TCP_SKB_CB(skb)->end_seq - 1; skb->ip_summed = CHECKSUM_NONE; 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) ? pskb_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. */ void tcp_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. */ void tcp_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); if(tp->send_head != NULL) { TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_FIN; TCP_SKB_CB(skb)->end_seq++; tp->write_seq++; } else { /* Socket is locked, keep trying until memory is available. */ for (;;) { skb = alloc_skb(MAX_TCP_HEADER, GFP_KERNEL); if (skb) break; yield(); } /* 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, 1, 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 */ void tcp_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. */ int tcp_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; return tcp_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; } /* * Do all connect socket setups that can be done AF independent. */ static inline void tcp_connect_init(struct sock *sk) { struct dst_entry *dst = __sk_dst_get(sk); struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp); /* 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_ca_init(tp); 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; 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); } /* * Build a SYN and send it off. */ int tcp_connect(struct sock *sk) { struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp); struct sk_buff *buff; tcp_connect_init(sk); buff = alloc_skb(MAX_TCP_HEADER + 15, sk->allocation); if (unlikely(buff == NULL)) return -ENOBUFS; /* Reserve space for headers. */ skb_reserve(buff, MAX_TCP_HEADER); 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; tcp_ca_init(tp); /* 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); 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 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); } /* This routine sends an ack and also updates the window. */ void tcp_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 int tcp_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; return tcp_transmit_skb(sk, skb); } int tcp_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); return tcp_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. */ void tcp_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) { if (tp->backoff < sysctl_tcp_retries2) 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)); } }