/* * 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 1.122 2000/02/21 15:51:41 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 * */ #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 = &sk->tp_pinfo.af_tcp; tp->send_head = tp->send_head->next; if (tp->send_head == (struct sk_buff *) &sk->write_queue) tp->send_head = NULL; } /* 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; } static __inline__ void tcp_event_data_sent(struct tcp_opt *tp, struct sk_buff *skb) { /* If we had a reply for ato after last received * packet, enter pingpong mode. */ if ((u32)(tp->lsndtime - tp->ack.lrcvtime) < tp->ack.ato) tp->ack.pingpong = 1; tp->lsndtime = tcp_time_stamp; } static __inline__ void tcp_event_ack_sent(struct sock *sk) { struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp); tcp_dec_quickack_mode(tp); tp->ack.pending = 0; tp->ack.rcv_segs = 0; tcp_clear_xmit_timer(sk, TCP_TIME_DACK); } /* 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->sack_ok && tp->num_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->num_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(TCP_SKB_CB(skb)->seq); th->ack_seq = htonl(tp->rcv_nxt); th->doff = (tcp_header_size >> 2); th->res1 = 0; *(((__u8 *)th) + 13) = tcb->flags; th->check = 0; th->urg_ptr = ntohs(tcb->urg_ptr); if(tcb->flags & TCPCB_FLAG_SYN) { /* RFC1323: The window in SYN & SYN/ACK segments * is never scaled. */ th->window = htons(tp->rcv_wnd); 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, TCP_SKB_CB(skb)->when, tp->ts_recent); } else { th->window = htons(tcp_select_window(sk)); tcp_build_and_update_options((__u32 *)(th + 1), tp, TCP_SKB_CB(skb)->when); } tp->af_specific->send_check(sk, th, skb->len, skb); if (th->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_cong_avoid(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); if (!force_queue && tp->send_head == NULL && 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, GFP_KERNEL)) == 0) { tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; tcp_minshall_update(tp, cur_mss, skb->len); tp->packets_out++; if(!tcp_timer_is_set(sk, TCP_TIME_RETRANS)) 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 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len) { struct sk_buff *buff; int nsize = skb->len - len; u16 flags; /* Get a new skb... force flag on. */ buff = sock_wmalloc(sk, (nsize + MAX_TCP_HEADER + 15), 1, GFP_ATOMIC); if (buff == NULL) return -ENOMEM; /* We'll just try again later. */ /* 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); if(flags & TCPCB_FLAG_URG) { u16 old_urg_ptr = TCP_SKB_CB(skb)->urg_ptr; /* Urgent data is always a pain in the ass. */ if(old_urg_ptr > len) { TCP_SKB_CB(skb)->flags &= ~(TCPCB_FLAG_URG); TCP_SKB_CB(skb)->urg_ptr = 0; TCP_SKB_CB(buff)->urg_ptr = old_urg_ptr - len; } else { flags &= ~(TCPCB_FLAG_URG); } } if(!(flags & TCPCB_FLAG_URG)) TCP_SKB_CB(buff)->urg_ptr = 0; TCP_SKB_CB(buff)->flags = flags; TCP_SKB_CB(buff)->sacked = 0; /* 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 * * NOTE: several days after I added this, Dave repaired * tcp_simple_retransmit() and it should not use ->when * of never sent skbs more. I am not sure, so that * this line remains until more careful investigation. --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), 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. */ int tcp_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); /* Anything on the transmit queue that fits the window can * be added providing we are: * * a) following SWS avoidance [and Nagle algorithm] * b) not exceeding our congestion window. * c) not retransmitting [Nagle] */ while((skb = tp->send_head) && tcp_snd_test(tp, skb, mss_now, tcp_skb_is_last(sk, skb))) { 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->snd_nxt = TCP_SKB_CB(skb)->end_seq; tcp_minshall_update(tp, mss_now, skb->len); tp->packets_out++; sent_pkts = 1; } /* If we sent anything, make sure the retransmit * timer is active. */ if (sent_pkts) { if (!tcp_timer_is_set(sk, TCP_TIME_RETRANS)) tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto); 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. * 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 (free_space > ((int) tp->window_clamp)) free_space = tp->window_clamp; if (tp->window_clamp < mss) mss = tp->window_clamp; if (free_space < min((int)tp->window_clamp, tcp_full_space(sk)) / 2) { /* THIS IS _VERY_ GOOD PLACE to play window clamp. * if free_space becomes suspiciously low * verify ratio rmem_alloc/(rcv_nxt - copied_seq), * and if we predict that when free_space will be lower mss, * rmem_alloc will run out of rcvbuf*2, shrink window_clamp. * It will eliminate most of prune events! Very simple, * it is the next thing to do. --ANK * * Provided we found a way to raise it back... --ANK */ tp->ack.quick = 0; if (free_space < ((int) (mss/2))) return 0; } /* 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 void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int mss_now) { 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; /* Punt if the first SKB has URG set. */ if(flags & TCPCB_FLAG_URG) return; /* Also punt if next skb has been SACK'd. */ if(TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED) 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 */ if(flags & TCPCB_FLAG_URG) { u16 urgptr = TCP_SKB_CB(next_skb)->urg_ptr; TCP_SKB_CB(skb)->urg_ptr = urgptr + skb_size; } TCP_SKB_CB(skb)->flags = flags; /* All done, get rid of second SKB and account for it so * packet counting does not break. */ kfree_skb(next_skb); sk->tp_pinfo.af_tcp.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, *old_next_skb; unsigned int mss = tcp_current_mss(sk); /* Don't muck with the congestion window here. */ tp->dup_acks = 0; tp->high_seq = tp->snd_nxt; tp->retrans_head = NULL; /* Input control flow will see that this was retransmitted * and not use it for RTT calculation in the absence of * the timestamp option. */ for (old_next_skb = skb = skb_peek(&sk->write_queue); ((skb != tp->send_head) && (skb != (struct sk_buff *)&sk->write_queue)); skb = skb->next) { int resend_skb = 0; /* Our goal is to push out the packets which we * sent already, but are being chopped up now to * account for the PMTU information we have. * * As we resend the queue, packets are fragmented * into two pieces, and when we try to send the * second piece it may be collapsed together with * a subsequent packet, and so on. -DaveM */ if (old_next_skb != skb || skb->len > mss) resend_skb = 1; old_next_skb = skb->next; if (resend_skb != 0) { if (tcp_retransmit_skb(sk, skb)) break; } } } static __inline__ void update_retrans_head(struct sock *sk) { struct tcp_opt *tp = &sk->tp_pinfo.af_tcp; tp->retrans_head = tp->retrans_head->next; if((tp->retrans_head == tp->send_head) || (tp->retrans_head == (struct sk_buff *) &sk->write_queue)) { tp->retrans_head = NULL; tp->rexmt_done = 1; } } /* 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); #ifdef TCP_DEBUG /* It was possible this summer, that retransmit timer * raced with its deletion and hit socket with packets_out==0. * I fixed it, but preserved the check in the place, * where the fault occured. --ANK */ if (skb == NULL) { printk("tcp_retransmit_skb: bug, skb==NULL, caller=%p\n", NET_CALLER(sk)); return -EFAULT; } #endif 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; } /* Ok, we're gonna send it out, update state. */ TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_RETRANS; tp->retrans_out++; /* 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; if(skb_cloned(skb)) skb = skb_copy(skb, GFP_ATOMIC); else skb = skb_clone(skb, GFP_ATOMIC); /* Update global TCP statistics and return success. */ TCP_INC_STATS(TcpRetransSegs); return tcp_transmit_skb(sk, skb); } /* 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; if (tp->retrans_head == NULL && tp->rexmt_done == 0) tp->retrans_head = skb_peek(&sk->write_queue); if (tp->retrans_head == tp->send_head) tp->retrans_head = NULL; /* Each time, advance the retrans_head if we got * a packet out or we skipped one because it was * SACK'd. -DaveM */ while ((skb = tp->retrans_head) != NULL) { /* If it has been ack'd by a SACK block, we don't * retransmit it. */ if(!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) { /* Send it out, punt if error occurred. */ if(tcp_retransmit_skb(sk, skb)) break; update_retrans_head(sk); /* Stop retransmitting if we've hit the congestion * window limit. */ if (tp->retrans_out >= tp->snd_cwnd) break; } else { update_retrans_head(sk); } } } /* Using FACK information, retransmit all missing frames at the receiver * up to the forward most SACK'd packet (tp->fackets_out) if the packet * has not been retransmitted already. */ void tcp_fack_retransmit(struct sock *sk) { struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp); struct sk_buff *skb = skb_peek(&sk->write_queue); int packet_cnt = 0; while((skb != NULL) && (skb != tp->send_head) && (skb != (struct sk_buff *)&sk->write_queue)) { __u8 sacked = TCP_SKB_CB(skb)->sacked; if(sacked & (TCPCB_SACKED_ACKED | TCPCB_SACKED_RETRANS)) goto next_packet; /* Ok, retransmit it. */ if(tcp_retransmit_skb(sk, skb)) break; if(tcp_packets_in_flight(tp) >= tp->snd_cwnd) break; next_packet: packet_cnt++; if(packet_cnt >= tp->fackets_out) break; skb = skb->next; } } /* 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); /* 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. * * Hmm... actually it overrides also congestion * avoidance (OK for FIN) and retransmit phase * (not OK? Added.). */ if(tp->send_head == skb && !after(tp->write_seq, tp->snd_una + tp->snd_wnd) && !tp->retransmits) { TCP_SKB_CB(skb)->when = tcp_time_stamp; if (!tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC))) { update_send_head(sk); tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; tp->packets_out++; if(!tcp_timer_is_set(sk, TCP_TIME_RETRANS)) tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto); } else tcp_check_probe_timer(sk, tp); } } else { /* Socket is locked, keep trying until memory is available. */ for (;;) { skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, 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; TCP_SKB_CB(skb)->urg_ptr = 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); } } /* 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 + 15, priority); if (!skb) 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; TCP_SKB_CB(skb)->urg_ptr = 0; /* Send it off. */ TCP_SKB_CB(skb)->seq = tp->snd_nxt; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq; TCP_SKB_CB(skb)->when = tcp_time_stamp; tcp_transmit_skb(sk, skb); } /* 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 tcp_opt* tp = &(sk->tp_pinfo.af_tcp); struct sk_buff* skb; skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15, 1, GFP_ATOMIC); if (skb == NULL) return -ENOMEM; /* 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_SYN); TCP_SKB_CB(skb)->sacked = 0; TCP_SKB_CB(skb)->urg_ptr = 0; /* SYN eats a sequence byte. */ TCP_SKB_CB(skb)->seq = tp->snd_una; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1; __skb_queue_tail(&sk->write_queue, skb); TCP_SKB_CB(skb)->when = tcp_time_stamp; tp->packets_out++; 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; 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 ? : skb->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; } int tcp_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); tcp_initialize_rcv_mss(sk); if (!tp->window_clamp) tp->window_clamp = dst->window; tp->advmss = dst->advmss; tcp_select_initial_window(tcp_full_space(sk), tp->advmss - (tp->tcp_header_len - sizeof(struct tcphdr)), &tp->rcv_wnd, &tp->window_clamp, sysctl_tcp_window_scaling, &tp->rcv_wscale); /* 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; tp->snd_wl1 = 0; tp->snd_wl2 = tp->write_seq; 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; tcp_init_xmit_timers(sk); tp->retransmits = 0; tp->fackets_out = 0; tp->retrans_out = 0; TCP_SKB_CB(buff)->flags = TCPCB_FLAG_SYN; TCP_SKB_CB(buff)->sacked = 0; TCP_SKB_CB(buff)->urg_ptr = 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; /* Send it off. */ TCP_SKB_CB(buff)->when = tcp_time_stamp; tp->syn_stamp = TCP_SKB_CB(buff)->when; __skb_queue_tail(&sk->write_queue, 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; 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. */ void tcp_send_delayed_ack(struct sock *sk) { struct tcp_opt *tp = &sk->tp_pinfo.af_tcp; unsigned long timeout; /* Stay within the limit we were given */ timeout = jiffies + tp->ack.ato; /* Use new timeout only if there wasn't a older one earlier. */ spin_lock_bh(&sk->timer_lock); if (!tp->delack_timer.prev || !del_timer(&tp->delack_timer)) { sock_hold(sk); tp->delack_timer.expires = timeout; } else { /* If delack timer was blocked or is about to expire, * send ACK now. */ if (tp->ack.blocked || time_before_eq(tp->delack_timer.expires, jiffies+(tp->ack.ato>>2))) { spin_unlock_bh(&sk->timer_lock); tcp_send_ack(sk); __sock_put(sk); return; } if (time_before(timeout, tp->delack_timer.expires)) tp->delack_timer.expires = timeout; } add_timer(&tp->delack_timer); spin_unlock_bh(&sk->timer_lock); #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. */ 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 + 15, GFP_ATOMIC); if (buff == NULL) { tp->ack.pending = 1; tp->ack.ato = TCP_ATO_MAX; 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; TCP_SKB_CB(buff)->urg_ptr = 0; /* Send it off, this clears delayed acks for us. */ TCP_SKB_CB(buff)->seq = TCP_SKB_CB(buff)->end_seq = tp->snd_nxt; 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. */ 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; /* Now this function is never called, while * we have something not ACKed in queue. */ BUG_TRAP(tp->snd_una == tp->snd_nxt); if (tp->snd_wnd > (tp->snd_nxt-tp->snd_una) && ((skb = tp->send_head) != NULL)) { int err; unsigned long win_size; /* We are probing the opening of a window * but the window size is != 0 * must have been a result SWS avoidance ( sender ) */ win_size = tp->snd_wnd - (tp->snd_nxt - tp->snd_una); if (win_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq) { if (tcp_fragment(sk, skb, win_size)) return -1; } 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->snd_nxt = TCP_SKB_CB(skb)->end_seq; tp->packets_out++; if (!tcp_timer_is_set(sk, TCP_TIME_RETRANS)) tcp_reset_xmit_timer(sk, TCP_TIME_RETRANS, tp->rto); } return err; } else { /* We don't queue it, tcp_transmit_skb() sets ownership. */ skb = alloc_skb(MAX_TCP_HEADER + 15, 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 = 0; TCP_SKB_CB(skb)->urg_ptr = 0; /* Use a previous sequence. This should cause the other * end to send an ack. Don't queue or clone SKB, just * send it. * * RED-PEN: logically it should be snd_una-1. * snd_nxt-1 will not be acked. snd_una==snd_nxt * in this place however. Right? */ TCP_SKB_CB(skb)->seq = 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); } } 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) { 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)); } }