/* * 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 1.146 2002/02/01 22:01:04 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 #include /* People can turn this off for buggy TCP's found in printers etc. */ int sysctl_tcp_retrans_collapse = 1; /* People can turn this on to work with those rare, broken TCPs that * interpret the window field as a signed quantity. */ int sysctl_tcp_workaround_signed_windows = 0; /* This limits the percentage of the congestion window which we * will allow a single TSO frame to consume. Building TSO frames * which are too large can cause TCP streams to be bursty. */ int sysctl_tcp_tso_win_divisor = 3; int sysctl_tcp_mtu_probing = 0; int sysctl_tcp_base_mss = 512; static void update_send_head(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb) { sk->sk_send_head = skb->next; if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue) sk->sk_send_head = NULL; tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; tcp_packets_out_inc(sk, tp, skb); } /* SND.NXT, if window was not shrunk. * If window has been shrunk, what should we make? It is not clear at all. * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( * Anything in between SND.UNA...SND.UNA+SND.WND also can be already * invalid. OK, let's make this for now: */ static inline __u32 tcp_acceptable_seq(struct sock *sk, struct tcp_sock *tp) { 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 overridden via information stored in routing table. * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, * probably even Jumbo". */ static __u16 tcp_advertise_mss(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); int mss = tp->advmss; if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) { mss = dst_metric(dst, RTAX_ADVMSS); tp->advmss = mss; } return (__u16)mss; } /* RFC2861. Reset CWND after idle period longer RTO to "restart window". * This is the first part of cwnd validation mechanism. */ static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst) { struct tcp_sock *tp = tcp_sk(sk); s32 delta = tcp_time_stamp - tp->lsndtime; u32 restart_cwnd = tcp_init_cwnd(tp, dst); u32 cwnd = tp->snd_cwnd; tcp_ca_event(sk, CA_EVENT_CWND_RESTART); tp->snd_ssthresh = tcp_current_ssthresh(sk); restart_cwnd = min(restart_cwnd, cwnd); while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) cwnd >>= 1; tp->snd_cwnd = max(cwnd, restart_cwnd); tp->snd_cwnd_stamp = tcp_time_stamp; tp->snd_cwnd_used = 0; } static void tcp_event_data_sent(struct tcp_sock *tp, struct sk_buff *skb, struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); const u32 now = tcp_time_stamp; if (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto) tcp_cwnd_restart(sk, __sk_dst_get(sk)); tp->lsndtime = now; /* If it is a reply for ato after last received * packet, enter pingpong mode. */ if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) icsk->icsk_ack.pingpong = 1; } static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts) { tcp_dec_quickack_mode(sk, pkts); inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); } /* Determine a window scaling and initial window to offer. * Based on the assumption that the given amount of space * will be offered. Store the results in the tp structure. * NOTE: for smooth operation initial space offering should * be a multiple of mss if possible. We assume here that mss >= 1. * This MUST be enforced by all callers. */ void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd, __u32 *window_clamp, int wscale_ok, __u8 *rcv_wscale) { unsigned int space = (__space < 0 ? 0 : __space); /* If no clamp set the clamp to the max possible scaled window */ if (*window_clamp == 0) (*window_clamp) = (65535 << 14); space = min(*window_clamp, space); /* Quantize space offering to a multiple of mss if possible. */ if (space > mss) space = (space / mss) * mss; /* NOTE: offering an initial window larger than 32767 * will break some buggy TCP stacks. If the admin tells us * it is likely we could be speaking with such a buggy stack * we will truncate our initial window offering to 32K-1 * unless the remote has sent us a window scaling option, * which we interpret as a sign the remote TCP is not * misinterpreting the window field as a signed quantity. */ if (sysctl_tcp_workaround_signed_windows) (*rcv_wnd) = min(space, MAX_TCP_WINDOW); else (*rcv_wnd) = space; (*rcv_wscale) = 0; if (wscale_ok) { /* Set window scaling on max possible window * See RFC1323 for an explanation of the limit to 14 */ space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max); while (space > 65535 && (*rcv_wscale) < 14) { space >>= 1; (*rcv_wscale)++; } } /* Set initial window to value enough for senders, * following RFC2414. Senders, not following this RFC, * will be satisfied with 2. */ if (mss > (1<<*rcv_wscale)) { int init_cwnd = 4; if (mss > 1460*3) init_cwnd = 2; else if (mss > 1460) init_cwnd = 3; if (*rcv_wnd > init_cwnd*mss) *rcv_wnd = init_cwnd*mss; } /* Set the clamp no higher than max representable value */ (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp); } /* Chose a new window to advertise, update state in tcp_sock for the * socket, and return result with RFC1323 scaling applied. The return * value can be stuffed directly into th->window for an outgoing * frame. */ static u16 tcp_select_window(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); u32 cur_win = tcp_receive_window(tp); u32 new_win = __tcp_select_window(sk); /* Never shrink the offered window */ if(new_win < cur_win) { /* Danger Will Robinson! * Don't update rcv_wup/rcv_wnd here or else * we will not be able to advertise a zero * window in time. --DaveM * * Relax Will Robinson. */ new_win = cur_win; } tp->rcv_wnd = new_win; tp->rcv_wup = tp->rcv_nxt; /* Make sure we do not exceed the maximum possible * scaled window. */ if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows) new_win = min(new_win, MAX_TCP_WINDOW); else new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); /* RFC1323 scaling applied */ new_win >>= tp->rx_opt.rcv_wscale; /* If we advertise zero window, disable fast path. */ if (new_win == 0) tp->pred_flags = 0; return new_win; } static void tcp_build_and_update_options(__u32 *ptr, struct tcp_sock *tp, __u32 tstamp) { if (tp->rx_opt.tstamp_ok) { *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); *ptr++ = htonl(tstamp); *ptr++ = htonl(tp->rx_opt.ts_recent); } if (tp->rx_opt.eff_sacks) { struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack : tp->selective_acks; int this_sack; *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_SACK << 8) | (TCPOLEN_SACK_BASE + (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK))); for(this_sack = 0; this_sack < tp->rx_opt.eff_sacks; this_sack++) { *ptr++ = htonl(sp[this_sack].start_seq); *ptr++ = htonl(sp[this_sack].end_seq); } if (tp->rx_opt.dsack) { tp->rx_opt.dsack = 0; tp->rx_opt.eff_sacks--; } } } /* Construct a tcp options header for a SYN or SYN_ACK packet. * If this is every changed make sure to change the definition of * MAX_SYN_SIZE to match the new maximum number of options that you * can generate. */ static void tcp_syn_build_options(__u32 *ptr, int mss, int ts, int sack, int offer_wscale, int wscale, __u32 tstamp, __u32 ts_recent) { /* We always get an MSS option. * The option bytes which will be seen in normal data * packets should timestamps be used, must be in the MSS * advertised. But we subtract them from tp->mss_cache so * that calculations in tcp_sendmsg are simpler etc. * So account for this fact here if necessary. If we * don't do this correctly, as a receiver we won't * recognize data packets as being full sized when we * should, and thus we won't abide by the delayed ACK * rules correctly. * SACKs don't matter, we never delay an ACK when we * have any of those going out. */ *ptr++ = htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | mss); if (ts) { if(sack) *ptr++ = __constant_htonl((TCPOPT_SACK_PERM << 24) | (TCPOLEN_SACK_PERM << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); else *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); *ptr++ = htonl(tstamp); /* TSVAL */ *ptr++ = htonl(ts_recent); /* TSECR */ } else if(sack) *ptr++ = __constant_htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_SACK_PERM << 8) | TCPOLEN_SACK_PERM); if (offer_wscale) *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_WINDOW << 16) | (TCPOLEN_WINDOW << 8) | (wscale)); } /* This routine actually transmits TCP packets queued in by * tcp_do_sendmsg(). This is used by both the initial * transmission and possible later retransmissions. * All SKB's seen here are completely headerless. It is our * job to build the TCP header, and pass the packet down to * IP so it can do the same plus pass the packet off to the * device. * * We are working here with either a clone of the original * SKB, or a fresh unique copy made by the retransmit engine. */ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, gfp_t gfp_mask) { const struct inet_connection_sock *icsk = inet_csk(sk); struct inet_sock *inet; struct tcp_sock *tp; struct tcp_skb_cb *tcb; int tcp_header_size; struct tcphdr *th; int sysctl_flags; int err; BUG_ON(!skb || !tcp_skb_pcount(skb)); /* If congestion control is doing timestamping, we must * take such a timestamp before we potentially clone/copy. */ if (icsk->icsk_ca_ops->rtt_sample) __net_timestamp(skb); if (likely(clone_it)) { if (unlikely(skb_cloned(skb))) skb = pskb_copy(skb, gfp_mask); else skb = skb_clone(skb, gfp_mask); if (unlikely(!skb)) return -ENOBUFS; } inet = inet_sk(sk); tp = tcp_sk(sk); tcb = TCP_SKB_CB(skb); tcp_header_size = tp->tcp_header_len; #define SYSCTL_FLAG_TSTAMPS 0x1 #define SYSCTL_FLAG_WSCALE 0x2 #define SYSCTL_FLAG_SACK 0x4 sysctl_flags = 0; if (unlikely(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 (unlikely(tp->rx_opt.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->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK)); } if (tcp_packets_in_flight(tp) == 0) tcp_ca_event(sk, CA_EVENT_TX_START); 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 = inet->sport; th->dest = inet->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 (unlikely(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 (unlikely(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 (unlikely(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->rx_opt.rcv_wscale, tcb->when, tp->rx_opt.ts_recent); } else { tcp_build_and_update_options((__u32 *)(th + 1), tp, tcb->when); TCP_ECN_send(sk, tp, skb, tcp_header_size); } icsk->icsk_af_ops->send_check(sk, skb->len, skb); if (likely(tcb->flags & TCPCB_FLAG_ACK)) tcp_event_ack_sent(sk, tcp_skb_pcount(skb)); if (skb->len != tcp_header_size) tcp_event_data_sent(tp, skb, sk); TCP_INC_STATS(TCP_MIB_OUTSEGS); err = icsk->icsk_af_ops->queue_xmit(skb, 0); if (likely(err <= 0)) return err; tcp_enter_cwr(sk); /* 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; #undef SYSCTL_FLAG_TSTAMPS #undef SYSCTL_FLAG_WSCALE #undef SYSCTL_FLAG_SACK } /* This routine just queue's the buffer * * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, * otherwise socket can stall. */ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); /* Advance write_seq and place onto the write_queue. */ tp->write_seq = TCP_SKB_CB(skb)->end_seq; skb_header_release(skb); __skb_queue_tail(&sk->sk_write_queue, skb); sk_charge_skb(sk, skb); /* Queue it, remembering where we must start sending. */ if (sk->sk_send_head == NULL) sk->sk_send_head = skb; } static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) { if (skb->len <= mss_now || !(sk->sk_route_caps & NETIF_F_TSO)) { /* Avoid the costly divide in the normal * non-TSO case. */ skb_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 0; } else { unsigned int factor; factor = skb->len + (mss_now - 1); factor /= mss_now; skb_shinfo(skb)->tso_segs = factor; skb_shinfo(skb)->tso_size = mss_now; } } /* Function to create two new TCP segments. Shrinks the given segment * to the specified size and appends a new segment with the rest of the * packet to the list. This won't be called frequently, I hope. * Remember, these are still headerless SKBs at this point. */ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss_now) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *buff; int nsize, old_factor; int nlen; u16 flags; BUG_ON(len > skb->len); clear_all_retrans_hints(tp); nsize = skb_headlen(skb) - len; if (nsize < 0) nsize = 0; 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 = sk_stream_alloc_skb(sk, nsize, GFP_ATOMIC); if (buff == NULL) return -ENOMEM; /* We'll just try again later. */ sk_charge_skb(sk, buff); nlen = skb->len - len - nsize; buff->truesize += nlen; skb->truesize -= nlen; /* Correct the sequence numbers. */ TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; /* PSH and FIN should only be set in the second packet. */ flags = TCP_SKB_CB(skb)->flags; TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH); TCP_SKB_CB(buff)->flags = flags; TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; 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; buff->tstamp = skb->tstamp; old_factor = tcp_skb_pcount(skb); /* Fix up tso_factor for both original and new SKB. */ tcp_set_skb_tso_segs(sk, skb, mss_now); tcp_set_skb_tso_segs(sk, buff, mss_now); /* If this packet has been sent out already, we must * adjust the various packet counters. */ if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { int diff = old_factor - tcp_skb_pcount(skb) - tcp_skb_pcount(buff); tp->packets_out -= diff; if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) tp->sacked_out -= diff; if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) tp->retrans_out -= diff; if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) { tp->lost_out -= diff; tp->left_out -= diff; } if (diff > 0) { /* Adjust Reno SACK estimate. */ if (!tp->rx_opt.sack_ok) { tp->sacked_out -= diff; if ((int)tp->sacked_out < 0) tp->sacked_out = 0; tcp_sync_left_out(tp); } tp->fackets_out -= diff; if ((int)tp->fackets_out < 0) tp->fackets_out = 0; } } /* Link BUFF into the send queue. */ skb_header_release(buff); __skb_append(skb, buff, &sk->sk_write_queue); return 0; } /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c * eventually). The difference is that pulled data not copied, but * immediately discarded. */ static void __pskb_trim_head(struct sk_buff *skb, int len) { int i, k, eat; eat = len; k = 0; for (i=0; inr_frags; i++) { if (skb_shinfo(skb)->frags[i].size <= eat) { put_page(skb_shinfo(skb)->frags[i].page); eat -= skb_shinfo(skb)->frags[i].size; } else { skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i]; if (eat) { skb_shinfo(skb)->frags[k].page_offset += eat; skb_shinfo(skb)->frags[k].size -= eat; eat = 0; } k++; } } skb_shinfo(skb)->nr_frags = k; skb->tail = skb->data; skb->data_len -= len; skb->len = skb->data_len; } int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) { if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) return -ENOMEM; /* If len == headlen, we avoid __skb_pull to preserve alignment. */ if (unlikely(len < skb_headlen(skb))) __skb_pull(skb, len); else __pskb_trim_head(skb, len - skb_headlen(skb)); TCP_SKB_CB(skb)->seq += len; skb->ip_summed = CHECKSUM_HW; skb->truesize -= len; sk->sk_wmem_queued -= len; sk->sk_forward_alloc += len; sock_set_flag(sk, SOCK_QUEUE_SHRUNK); /* Any change of skb->len requires recalculation of tso * factor and mss. */ if (tcp_skb_pcount(skb) > 1) tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1)); return 0; } /* Not accounting for SACKs here. */ int tcp_mtu_to_mss(struct sock *sk, int pmtu) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mss_now; /* Calculate base mss without TCP options: It is MMS_S - sizeof(tcphdr) of rfc1122 */ mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr); /* Clamp it (mss_clamp does not include tcp options) */ if (mss_now > tp->rx_opt.mss_clamp) mss_now = tp->rx_opt.mss_clamp; /* Now subtract optional transport overhead */ mss_now -= icsk->icsk_ext_hdr_len; /* Then reserve room for full set of TCP options and 8 bytes of data */ if (mss_now < 48) mss_now = 48; /* Now subtract TCP options size, not including SACKs */ mss_now -= tp->tcp_header_len - sizeof(struct tcphdr); return mss_now; } /* Inverse of above */ int tcp_mss_to_mtu(struct sock *sk, int mss) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mtu; mtu = mss + tp->tcp_header_len + icsk->icsk_ext_hdr_len + icsk->icsk_af_ops->net_header_len; return mtu; } void tcp_mtup_init(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1; icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) + icsk->icsk_af_ops->net_header_len; icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss); icsk->icsk_mtup.probe_size = 0; } /* This function synchronize snd mss to current pmtu/exthdr set. tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts for TCP options, but includes only bare TCP header. tp->rx_opt.mss_clamp is mss negotiated at connection setup. It is minimum of user_mss and mss received with SYN. It also does not include TCP options. inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. tp->mss_cache is current effective sending mss, including all tcp options except for SACKs. It is evaluated, taking into account current pmtu, but never exceeds tp->rx_opt.mss_clamp. NOTE1. rfc1122 clearly states that advertised MSS DOES NOT include either tcp or ip options. NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache are READ ONLY outside this function. --ANK (980731) */ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mss_now; if (icsk->icsk_mtup.search_high > pmtu) icsk->icsk_mtup.search_high = pmtu; mss_now = tcp_mtu_to_mss(sk, pmtu); /* 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 */ icsk->icsk_pmtu_cookie = pmtu; if (icsk->icsk_mtup.enabled) mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)); tp->mss_cache = mss_now; return mss_now; } /* Compute the current effective MSS, taking SACKs and IP options, * and even PMTU discovery events into account. * * LARGESEND note: !urg_mode is overkill, only frames up to snd_up * cannot be large. However, taking into account rare use of URG, this * is not a big flaw. */ unsigned int tcp_current_mss(struct sock *sk, int large_allowed) { struct tcp_sock *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); u32 mss_now; u16 xmit_size_goal; int doing_tso = 0; mss_now = tp->mss_cache; if (large_allowed && (sk->sk_route_caps & NETIF_F_TSO) && !tp->urg_mode) doing_tso = 1; if (dst) { u32 mtu = dst_mtu(dst); if (mtu != inet_csk(sk)->icsk_pmtu_cookie) mss_now = tcp_sync_mss(sk, mtu); } if (tp->rx_opt.eff_sacks) mss_now -= (TCPOLEN_SACK_BASE_ALIGNED + (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK)); xmit_size_goal = mss_now; if (doing_tso) { xmit_size_goal = (65535 - inet_csk(sk)->icsk_af_ops->net_header_len - inet_csk(sk)->icsk_ext_hdr_len - tp->tcp_header_len); if (tp->max_window && (xmit_size_goal > (tp->max_window >> 1))) xmit_size_goal = max((tp->max_window >> 1), 68U - tp->tcp_header_len); xmit_size_goal -= (xmit_size_goal % mss_now); } tp->xmit_size_goal = xmit_size_goal; return mss_now; } /* Congestion window validation. (RFC2861) */ static void tcp_cwnd_validate(struct sock *sk, struct tcp_sock *tp) { __u32 packets_out = tp->packets_out; if (packets_out >= tp->snd_cwnd) { /* Network is feed fully. */ tp->snd_cwnd_used = 0; tp->snd_cwnd_stamp = tcp_time_stamp; } else { /* Network starves. */ if (tp->packets_out > tp->snd_cwnd_used) tp->snd_cwnd_used = tp->packets_out; if ((s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto) tcp_cwnd_application_limited(sk); } } static unsigned int tcp_window_allows(struct tcp_sock *tp, struct sk_buff *skb, unsigned int mss_now, unsigned int cwnd) { u32 window, cwnd_len; window = (tp->snd_una + tp->snd_wnd - TCP_SKB_CB(skb)->seq); cwnd_len = mss_now * cwnd; return min(window, cwnd_len); } /* Can at least one segment of SKB be sent right now, according to the * congestion window rules? If so, return how many segments are allowed. */ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *skb) { u32 in_flight, cwnd; /* Don't be strict about the congestion window for the final FIN. */ if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) return 1; in_flight = tcp_packets_in_flight(tp); cwnd = tp->snd_cwnd; if (in_flight < cwnd) return (cwnd - in_flight); return 0; } /* This must be invoked the first time we consider transmitting * SKB onto the wire. */ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) { int tso_segs = tcp_skb_pcount(skb); if (!tso_segs || (tso_segs > 1 && skb_shinfo(skb)->tso_size != mss_now)) { tcp_set_skb_tso_segs(sk, skb, mss_now); tso_segs = tcp_skb_pcount(skb); } return tso_segs; } static inline int tcp_minshall_check(const struct tcp_sock *tp) { return after(tp->snd_sml,tp->snd_una) && !after(tp->snd_sml, tp->snd_nxt); } /* Return 0, if packet can be sent now without violation Nagle's rules: * 1. It is full sized. * 2. Or it contains FIN. (already checked by caller) * 3. Or TCP_NODELAY was set. * 4. Or TCP_CORK is not set, and all sent packets are ACKed. * With Minshall's modification: all sent small packets are ACKed. */ static inline int tcp_nagle_check(const struct tcp_sock *tp, const struct sk_buff *skb, unsigned mss_now, int nonagle) { return (skb->len < mss_now && ((nonagle&TCP_NAGLE_CORK) || (!nonagle && tp->packets_out && tcp_minshall_check(tp)))); } /* Return non-zero if the Nagle test allows this packet to be * sent now. */ static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss, int nonagle) { /* Nagle rule does not apply to frames, which sit in the middle of the * write_queue (they have no chances to get new data). * * This is implemented in the callers, where they modify the 'nonagle' * argument based upon the location of SKB in the send queue. */ if (nonagle & TCP_NAGLE_PUSH) return 1; /* Don't use the nagle rule for urgent data (or for the final FIN). */ if (tp->urg_mode || (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)) return 1; if (!tcp_nagle_check(tp, skb, cur_mss, nonagle)) return 1; return 0; } /* Does at least the first segment of SKB fit into the send window? */ static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss) { u32 end_seq = TCP_SKB_CB(skb)->end_seq; if (skb->len > cur_mss) end_seq = TCP_SKB_CB(skb)->seq + cur_mss; return !after(end_seq, tp->snd_una + tp->snd_wnd); } /* This checks if the data bearing packet SKB (usually sk->sk_send_head) * should be put on the wire right now. If so, it returns the number of * packets allowed by the congestion window. */ static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb, unsigned int cur_mss, int nonagle) { struct tcp_sock *tp = tcp_sk(sk); unsigned int cwnd_quota; tcp_init_tso_segs(sk, skb, cur_mss); if (!tcp_nagle_test(tp, skb, cur_mss, nonagle)) return 0; cwnd_quota = tcp_cwnd_test(tp, skb); if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss)) cwnd_quota = 0; return cwnd_quota; } static inline int tcp_skb_is_last(const struct sock *sk, const struct sk_buff *skb) { return skb->next == (struct sk_buff *)&sk->sk_write_queue; } int tcp_may_send_now(struct sock *sk, struct tcp_sock *tp) { struct sk_buff *skb = sk->sk_send_head; return (skb && tcp_snd_test(sk, skb, tcp_current_mss(sk, 1), (tcp_skb_is_last(sk, skb) ? TCP_NAGLE_PUSH : tp->nonagle))); } /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet * which is put after SKB on the list. It is very much like * tcp_fragment() except that it may make several kinds of assumptions * in order to speed up the splitting operation. In particular, we * know that all the data is in scatter-gather pages, and that the * packet has never been sent out before (and thus is not cloned). */ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, unsigned int mss_now) { struct sk_buff *buff; int nlen = skb->len - len; u16 flags; /* All of a TSO frame must be composed of paged data. */ if (skb->len != skb->data_len) return tcp_fragment(sk, skb, len, mss_now); buff = sk_stream_alloc_pskb(sk, 0, 0, GFP_ATOMIC); if (unlikely(buff == NULL)) return -ENOMEM; sk_charge_skb(sk, buff); buff->truesize += nlen; skb->truesize -= nlen; /* Correct the sequence numbers. */ TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; /* PSH and FIN should only be set in the second packet. */ flags = TCP_SKB_CB(skb)->flags; TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH); TCP_SKB_CB(buff)->flags = flags; /* This packet was never sent out yet, so no SACK bits. */ TCP_SKB_CB(buff)->sacked = 0; buff->ip_summed = skb->ip_summed = CHECKSUM_HW; skb_split(skb, buff, len); /* Fix up tso_factor for both original and new SKB. */ tcp_set_skb_tso_segs(sk, skb, mss_now); tcp_set_skb_tso_segs(sk, buff, mss_now); /* Link BUFF into the send queue. */ skb_header_release(buff); __skb_append(skb, buff, &sk->sk_write_queue); return 0; } /* Try to defer sending, if possible, in order to minimize the amount * of TSO splitting we do. View it as a kind of TSO Nagle test. * * This algorithm is from John Heffner. */ static int tcp_tso_should_defer(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb) { const struct inet_connection_sock *icsk = inet_csk(sk); u32 send_win, cong_win, limit, in_flight; if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) return 0; if (icsk->icsk_ca_state != TCP_CA_Open) return 0; in_flight = tcp_packets_in_flight(tp); BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight)); send_win = (tp->snd_una + tp->snd_wnd) - TCP_SKB_CB(skb)->seq; /* From in_flight test above, we know that cwnd > in_flight. */ cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache; limit = min(send_win, cong_win); /* If a full-sized TSO skb can be sent, do it. */ if (limit >= 65536) return 0; if (sysctl_tcp_tso_win_divisor) { u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache); /* If at least some fraction of a window is available, * just use it. */ chunk /= sysctl_tcp_tso_win_divisor; if (limit >= chunk) return 0; } else { /* Different approach, try not to defer past a single * ACK. Receiver should ACK every other full sized * frame, so if we have space for more than 3 frames * then send now. */ if (limit > tcp_max_burst(tp) * tp->mss_cache) return 0; } /* Ok, it looks like it is advisable to defer. */ return 1; } /* Create a new MTU probe if we are ready. * Returns 0 if we should wait to probe (no cwnd available), * 1 if a probe was sent, * -1 otherwise */ static int tcp_mtu_probe(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); struct sk_buff *skb, *nskb, *next; int len; int probe_size; unsigned int pif; int copy; int mss_now; /* Not currently probing/verifying, * not in recovery, * have enough cwnd, and * not SACKing (the variable headers throw things off) */ if (!icsk->icsk_mtup.enabled || icsk->icsk_mtup.probe_size || inet_csk(sk)->icsk_ca_state != TCP_CA_Open || tp->snd_cwnd < 11 || tp->rx_opt.eff_sacks) return -1; /* Very simple search strategy: just double the MSS. */ mss_now = tcp_current_mss(sk, 0); probe_size = 2*tp->mss_cache; if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) { /* TODO: set timer for probe_converge_event */ return -1; } /* Have enough data in the send queue to probe? */ len = 0; if ((skb = sk->sk_send_head) == NULL) return -1; while ((len += skb->len) < probe_size && !tcp_skb_is_last(sk, skb)) skb = skb->next; if (len < probe_size) return -1; /* Receive window check. */ if (after(TCP_SKB_CB(skb)->seq + probe_size, tp->snd_una + tp->snd_wnd)) { if (tp->snd_wnd < probe_size) return -1; else return 0; } /* Do we need to wait to drain cwnd? */ pif = tcp_packets_in_flight(tp); if (pif + 2 > tp->snd_cwnd) { /* With no packets in flight, don't stall. */ if (pif == 0) return -1; else return 0; } /* We're allowed to probe. Build it now. */ if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL) return -1; sk_charge_skb(sk, nskb); skb = sk->sk_send_head; __skb_insert(nskb, skb->prev, skb, &sk->sk_write_queue); sk->sk_send_head = nskb; TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq; TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size; TCP_SKB_CB(nskb)->flags = TCPCB_FLAG_ACK; TCP_SKB_CB(nskb)->sacked = 0; nskb->csum = 0; if (skb->ip_summed == CHECKSUM_HW) nskb->ip_summed = CHECKSUM_HW; len = 0; while (len < probe_size) { next = skb->next; copy = min_t(int, skb->len, probe_size - len); if (nskb->ip_summed) skb_copy_bits(skb, 0, skb_put(nskb, copy), copy); else nskb->csum = skb_copy_and_csum_bits(skb, 0, skb_put(nskb, copy), copy, nskb->csum); if (skb->len <= copy) { /* We've eaten all the data from this skb. * Throw it away. */ TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags; __skb_unlink(skb, &sk->sk_write_queue); sk_stream_free_skb(sk, skb); } else { TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags & ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH); if (!skb_shinfo(skb)->nr_frags) { skb_pull(skb, copy); if (skb->ip_summed != CHECKSUM_HW) skb->csum = csum_partial(skb->data, skb->len, 0); } else { __pskb_trim_head(skb, copy); tcp_set_skb_tso_segs(sk, skb, mss_now); } TCP_SKB_CB(skb)->seq += copy; } len += copy; skb = next; } tcp_init_tso_segs(sk, nskb, nskb->len); /* We're ready to send. If this fails, the probe will * be resegmented into mss-sized pieces by tcp_write_xmit(). */ TCP_SKB_CB(nskb)->when = tcp_time_stamp; if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) { /* Decrement cwnd here because we are sending * effectively two packets. */ tp->snd_cwnd--; update_send_head(sk, tp, nskb); icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len); tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq; tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq; return 1; } return -1; } /* This routine writes packets to the network. It advances the * send_head. This happens as incoming acks open up the remote * window for us. * * Returns 1, if no segments are in flight and we have queued segments, but * cannot send anything now because of SWS or another problem. */ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; unsigned int tso_segs, sent_pkts; int cwnd_quota; int result; /* If we are closed, the bytes will have to remain here. * In time closedown will finish, we empty the write queue and all * will be happy. */ if (unlikely(sk->sk_state == TCP_CLOSE)) return 0; sent_pkts = 0; /* Do MTU probing. */ if ((result = tcp_mtu_probe(sk)) == 0) { return 0; } else if (result > 0) { sent_pkts = 1; } while ((skb = sk->sk_send_head)) { unsigned int limit; tso_segs = tcp_init_tso_segs(sk, skb, mss_now); BUG_ON(!tso_segs); cwnd_quota = tcp_cwnd_test(tp, skb); if (!cwnd_quota) break; if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) break; if (tso_segs == 1) { if (unlikely(!tcp_nagle_test(tp, skb, mss_now, (tcp_skb_is_last(sk, skb) ? nonagle : TCP_NAGLE_PUSH)))) break; } else { if (tcp_tso_should_defer(sk, tp, skb)) break; } limit = mss_now; if (tso_segs > 1) { limit = tcp_window_allows(tp, skb, mss_now, cwnd_quota); if (skb->len < limit) { unsigned int trim = skb->len % mss_now; if (trim) limit = skb->len - trim; } } if (skb->len > limit && unlikely(tso_fragment(sk, skb, limit, mss_now))) break; TCP_SKB_CB(skb)->when = tcp_time_stamp; if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC))) break; /* Advance the send_head. This one is sent out. * This call will increment packets_out. */ update_send_head(sk, tp, skb); tcp_minshall_update(tp, mss_now, skb); sent_pkts++; } if (likely(sent_pkts)) { tcp_cwnd_validate(sk, tp); return 0; } return !tp->packets_out && sk->sk_send_head; } /* Push out any pending frames which were held back due to * TCP_CORK or attempt at coalescing tiny packets. * The socket must be locked by the caller. */ void __tcp_push_pending_frames(struct sock *sk, struct tcp_sock *tp, unsigned int cur_mss, int nonagle) { struct sk_buff *skb = sk->sk_send_head; if (skb) { if (tcp_write_xmit(sk, cur_mss, nonagle)) tcp_check_probe_timer(sk, tp); } } /* Send _single_ skb sitting at the send head. This function requires * true push pending frames to setup probe timer etc. */ void tcp_push_one(struct sock *sk, unsigned int mss_now) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb = sk->sk_send_head; unsigned int tso_segs, cwnd_quota; BUG_ON(!skb || skb->len < mss_now); tso_segs = tcp_init_tso_segs(sk, skb, mss_now); cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH); if (likely(cwnd_quota)) { unsigned int limit; BUG_ON(!tso_segs); limit = mss_now; if (tso_segs > 1) { limit = tcp_window_allows(tp, skb, mss_now, cwnd_quota); if (skb->len < limit) { unsigned int trim = skb->len % mss_now; if (trim) limit = skb->len - trim; } } if (skb->len > limit && unlikely(tso_fragment(sk, skb, limit, mss_now))) return; /* Send it out now. */ TCP_SKB_CB(skb)->when = tcp_time_stamp; if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) { update_send_head(sk, tp, skb); tcp_cwnd_validate(sk, tp); return; } } } /* This function returns the amount that we can raise the * usable window based on the following constraints * * 1. The window can never be shrunk once it is offered (RFC 793) * 2. We limit memory per socket * * RFC 1122: * "the suggested [SWS] avoidance algorithm for the receiver is to keep * RECV.NEXT + RCV.WIN fixed until: * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" * * i.e. don't raise the right edge of the window until you can raise * it at least MSS bytes. * * Unfortunately, the recommended algorithm breaks header prediction, * since header prediction assumes th->window stays fixed. * * Strictly speaking, keeping th->window fixed violates the receiver * side SWS prevention criteria. The problem is that under this rule * a stream of single byte packets will cause the right side of the * window to always advance by a single byte. * * Of course, if the sender implements sender side SWS prevention * then this will not be a problem. * * BSD seems to make the following compromise: * * If the free space is less than the 1/4 of the maximum * space available and the free space is less than 1/2 mss, * then set the window to 0. * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] * Otherwise, just prevent the window from shrinking * and from being larger than the largest representable value. * * This prevents incremental opening of the window in the regime * where TCP is limited by the speed of the reader side taking * data out of the TCP receive queue. It does nothing about * those cases where the window is constrained on the sender side * because the pipeline is full. * * BSD also seems to "accidentally" limit itself to windows that are a * multiple of MSS, at least until the free space gets quite small. * This would appear to be a side effect of the mbuf implementation. * Combining these two algorithms results in the observed behavior * of having a fixed window size at almost all times. * * Below we obtain similar behavior by forcing the offered window to * a multiple of the mss when it is feasible to do so. * * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. * Regular options like TIMESTAMP are taken into account. */ u32 __tcp_select_window(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); /* MSS for the peer's data. Previous versions used mss_clamp * here. I don't know if the value based on our guesses * of peer's MSS is better for the performance. It's more correct * but may be worse for the performance because of rcv_mss * fluctuations. --SAW 1998/11/1 */ int mss = icsk->icsk_ack.rcv_mss; int free_space = tcp_space(sk); int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk)); int window; if (mss > full_space) mss = full_space; if (free_space < full_space/2) { icsk->icsk_ack.quick = 0; if (tcp_memory_pressure) tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U*tp->advmss); if (free_space < mss) return 0; } if (free_space > tp->rcv_ssthresh) free_space = tp->rcv_ssthresh; /* Don't do rounding if we are using window scaling, since the * scaled window will not line up with the MSS boundary anyway. */ window = tp->rcv_wnd; if (tp->rx_opt.rcv_wscale) { window = free_space; /* Advertise enough space so that it won't get scaled away. * Import case: prevent zero window announcement if * 1< mss. */ if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window) window = (((window >> tp->rx_opt.rcv_wscale) + 1) << tp->rx_opt.rcv_wscale); } else { /* Get the largest window that is a nice multiple of mss. * Window clamp already applied above. * If our current window offering is within 1 mss of the * free space we just keep it. This prevents the divide * and multiply from happening most of the time. * We also don't do any window rounding when the free space * is too small. */ if (window <= free_space - mss || window > free_space) window = (free_space/mss)*mss; } 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_sock *tp = tcp_sk(sk); 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; BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1); /* changing transmit queue under us so clear hints */ clear_all_retrans_hints(tp); /* Ok. We will be able to collapse the packet. */ __skb_unlink(next_skb, &sk->sk_write_queue); 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 -= tcp_skb_pcount(next_skb); if (TCP_SKB_CB(next_skb)->sacked&TCPCB_LOST) { tp->lost_out -= tcp_skb_pcount(next_skb); tp->left_out -= tcp_skb_pcount(next_skb); } /* Reno case is special. Sigh... */ if (!tp->rx_opt.sack_ok && tp->sacked_out) { tcp_dec_pcount_approx(&tp->sacked_out, next_skb); tp->left_out -= tcp_skb_pcount(next_skb); } /* Not quite right: it can be > snd.fack, but * it is better to underestimate fackets. */ tcp_dec_pcount_approx(&tp->fackets_out, next_skb); tcp_packets_out_dec(tp, next_skb); sk_stream_free_skb(sk, next_skb); } } /* 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) { const struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; unsigned int mss = tcp_current_mss(sk, 0); int lost = 0; sk_stream_for_retrans_queue(skb, sk) { 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 -= tcp_skb_pcount(skb); } if (!(TCP_SKB_CB(skb)->sacked&TCPCB_LOST)) { TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; tp->lost_out += tcp_skb_pcount(skb); lost = 1; } } } clear_all_retrans_hints(tp); 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 (icsk->icsk_ca_state != TCP_CA_Loss) { tp->high_seq = tp->snd_nxt; tp->snd_ssthresh = tcp_current_ssthresh(sk); tp->prior_ssthresh = 0; tp->undo_marker = 0; tcp_set_ca_state(sk, 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_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); unsigned int cur_mss = tcp_current_mss(sk, 0); int err; /* Inconslusive MTU probe */ if (icsk->icsk_mtup.probe_size) { icsk->icsk_mtup.probe_size = 0; } /* Do not sent more than we queued. 1/4 is reserved for possible * copying overhead: fragmentation, tunneling, mangling etc. */ if (atomic_read(&sk->sk_wmem_alloc) > min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf)) return -EAGAIN; if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) BUG(); if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) return -ENOMEM; } /* If 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, cur_mss)) return -ENOMEM; /* We'll try again later. */ } /* 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 != sk->sk_send_head) && (skb->next != (struct sk_buff *)&sk->sk_write_queue) && (skb_shinfo(skb)->nr_frags == 0 && skb_shinfo(skb->next)->nr_frags == 0) && (tcp_skb_pcount(skb) == 1 && tcp_skb_pcount(skb->next) == 1) && (sysctl_tcp_retrans_collapse != 0)) tcp_retrans_try_collapse(sk, skb, cur_mss); if (inet_csk(sk)->icsk_af_ops->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_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 0; 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, 1, GFP_ATOMIC); if (err == 0) { /* Update global TCP statistics. */ TCP_INC_STATS(TCP_MIB_RETRANSSEGS); tp->total_retrans++; #if FASTRETRANS_DEBUG > 0 if (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) { if (net_ratelimit()) printk(KERN_DEBUG "retrans_out leaked.\n"); } #endif TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; tp->retrans_out += tcp_skb_pcount(skb); /* Save stamp of the first retransmit. */ if (!tp->retrans_stamp) tp->retrans_stamp = TCP_SKB_CB(skb)->when; tp->undo_retrans++; /* snd_nxt is stored to detect loss of retransmitted segment, * see tcp_input.c tcp_sacktag_write_queue(). */ TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt; } return err; } /* This gets called after a retransmit timeout, and the initially * retransmitted data is acknowledged. It tries to continue * resending the rest of the retransmit queue, until either * we've sent it all or the congestion window limit is reached. * If doing SACK, the first ACK which comes back for a timeout * based retransmit packet might feed us FACK information again. * If so, we use it to avoid unnecessarily retransmissions. */ void tcp_xmit_retransmit_queue(struct sock *sk) { const struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; int packet_cnt; if (tp->retransmit_skb_hint) { skb = tp->retransmit_skb_hint; packet_cnt = tp->retransmit_cnt_hint; }else{ skb = sk->sk_write_queue.next; packet_cnt = 0; } /* First pass: retransmit lost packets. */ if (tp->lost_out) { sk_stream_for_retrans_queue_from(skb, sk) { __u8 sacked = TCP_SKB_CB(skb)->sacked; /* we could do better than to assign each time */ tp->retransmit_skb_hint = skb; tp->retransmit_cnt_hint = packet_cnt; /* Assume this retransmit will generate * only one packet for congestion window * calculation purposes. This works because * tcp_retransmit_skb() will chop up the * packet to be MSS sized and all the * packet counting works out. */ if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) return; if (sacked & TCPCB_LOST) { if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) { if (tcp_retransmit_skb(sk, skb)) { tp->retransmit_skb_hint = NULL; return; } if (icsk->icsk_ca_state != TCP_CA_Loss) NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS); else NET_INC_STATS_BH(LINUX_MIB_TCPSLOWSTARTRETRANS); if (skb == skb_peek(&sk->sk_write_queue)) inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); } packet_cnt += tcp_skb_pcount(skb); if (packet_cnt >= tp->lost_out) break; } } } /* OK, demanded retransmission is finished. */ /* Forward retransmissions are possible only during Recovery. */ if (icsk->icsk_ca_state != TCP_CA_Recovery) return; /* No forward retransmissions in Reno are possible. */ if (!tp->rx_opt.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 retransmit anything, while we have some new * segments to send. */ if (tcp_may_send_now(sk, tp)) return; if (tp->forward_skb_hint) { skb = tp->forward_skb_hint; packet_cnt = tp->forward_cnt_hint; } else{ skb = sk->sk_write_queue.next; packet_cnt = 0; } sk_stream_for_retrans_queue_from(skb, sk) { tp->forward_cnt_hint = packet_cnt; tp->forward_skb_hint = skb; /* Similar to the retransmit loop above we * can pretend that the retransmitted SKB * we send out here will be composed of one * real MSS sized packet because tcp_retransmit_skb() * will fragment it if necessary. */ 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)) { tp->forward_skb_hint = NULL; break; } if (skb == skb_peek(&sk->sk_write_queue)) inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); NET_INC_STATS_BH(LINUX_MIB_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_sock *tp = tcp_sk(sk); struct sk_buff *skb = skb_peek_tail(&sk->sk_write_queue); 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, 1); if (sk->sk_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_fclone(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; skb_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 0; /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ TCP_SKB_CB(skb)->seq = tp->write_seq; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1; tcp_queue_skb(sk, skb); } __tcp_push_pending_frames(sk, tp, mss_now, TCP_NAGLE_OFF); } /* We get here when a process closes a file descriptor (either due to * an explicit close() or as a byproduct of exit()'ing) and there * was unread data in the receive queue. This behavior is recommended * by draft-ietf-tcpimpl-prob-03.txt section 3.10. -DaveM */ void tcp_send_active_reset(struct sock *sk, gfp_t priority) { struct tcp_sock *tp = tcp_sk(sk); 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(LINUX_MIB_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; skb_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 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, 0, priority)) NET_INC_STATS(LINUX_MIB_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->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->sk_write_queue); skb_header_release(nskb); __skb_queue_head(&sk->sk_write_queue, nskb); sk_stream_free_skb(sk, skb); sk_charge_skb(sk, nskb); skb = nskb; } TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ACK; TCP_ECN_send_synack(tcp_sk(sk), skb); } TCP_SKB_CB(skb)->when = tcp_time_stamp; return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); } /* * Prepare a SYN-ACK. */ struct sk_buff * tcp_make_synack(struct sock *sk, struct dst_entry *dst, struct request_sock *req) { struct inet_request_sock *ireq = inet_rsk(req); struct tcp_sock *tp = tcp_sk(sk); struct tcphdr *th; int tcp_header_size; struct 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 + (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0) + (ireq->wscale_ok ? TCPOLEN_WSCALE_ALIGNED : 0) + /* SACK_PERM is in the place of NOP NOP of TS */ ((ireq->sack_ok && !ireq->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; if (dst->dev->features&NETIF_F_TSO) ireq->ecn_ok = 0; TCP_ECN_make_synack(req, th); th->source = inet_sk(sk)->sport; th->dest = ireq->rmt_port; TCP_SKB_CB(skb)->seq = tcp_rsk(req)->snt_isn; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + 1; TCP_SKB_CB(skb)->sacked = 0; skb_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 0; th->seq = htonl(TCP_SKB_CB(skb)->seq); th->ack_seq = htonl(tcp_rsk(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_metric(dst, RTAX_WINDOW); /* tcp_full_space because it is guaranteed to be the first packet */ tcp_select_initial_window(tcp_full_space(sk), dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), &req->rcv_wnd, &req->window_clamp, ireq->wscale_ok, &rcv_wscale); ireq->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_metric(dst, RTAX_ADVMSS), ireq->tstamp_ok, ireq->sack_ok, ireq->wscale_ok, ireq->rcv_wscale, TCP_SKB_CB(skb)->when, req->ts_recent); skb->csum = 0; th->doff = (tcp_header_size >> 2); TCP_INC_STATS(TCP_MIB_OUTSEGS); return skb; } /* * Do all connect socket setups that can be done AF independent. */ static void tcp_connect_init(struct sock *sk) { struct dst_entry *dst = __sk_dst_get(sk); struct tcp_sock *tp = tcp_sk(sk); __u8 rcv_wscale; /* We'll fix this up when we get a response from the other end. * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. */ tp->tcp_header_len = sizeof(struct tcphdr) + (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0); /* If user gave his TCP_MAXSEG, record it to clamp */ if (tp->rx_opt.user_mss) tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; tp->max_window = 0; tcp_mtup_init(sk); tcp_sync_mss(sk, dst_mtu(dst)); if (!tp->window_clamp) tp->window_clamp = dst_metric(dst, RTAX_WINDOW); tp->advmss = dst_metric(dst, RTAX_ADVMSS); tcp_initialize_rcv_mss(sk); tcp_select_initial_window(tcp_full_space(sk), tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0), &tp->rcv_wnd, &tp->window_clamp, sysctl_tcp_window_scaling, &rcv_wscale); tp->rx_opt.rcv_wscale = rcv_wscale; tp->rcv_ssthresh = tp->rcv_wnd; sk->sk_err = 0; sock_reset_flag(sk, SOCK_DONE); tp->snd_wnd = 0; tcp_init_wl(tp, 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; inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; inet_csk(sk)->icsk_retransmits = 0; tcp_clear_retrans(tp); } /* * Build a SYN and send it off. */ int tcp_connect(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *buff; tcp_connect_init(sk); buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->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(sk, tp, buff); TCP_SKB_CB(buff)->sacked = 0; skb_shinfo(buff)->tso_segs = 1; skb_shinfo(buff)->tso_size = 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_header_release(buff); __skb_queue_tail(&sk->sk_write_queue, buff); sk_charge_skb(sk, buff); tp->packets_out += tcp_skb_pcount(buff); tcp_transmit_skb(sk, buff, 1, GFP_KERNEL); TCP_INC_STATS(TCP_MIB_ACTIVEOPENS); /* Timer for repeating the SYN until an answer. */ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); return 0; } /* Send out a delayed ack, the caller does the policy checking * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() * for details. */ void tcp_send_delayed_ack(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); int ato = icsk->icsk_ack.ato; unsigned long timeout; if (ato > TCP_DELACK_MIN) { const struct tcp_sock *tp = tcp_sk(sk); int max_ato = HZ/2; if (icsk->icsk_ack.pingpong || (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) max_ato = TCP_DELACK_MAX; /* Slow path, intersegment interval is "high". */ /* If some rtt estimate is known, use it to bound delayed ack. * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements * directly. */ if (tp->srtt) { int rtt = max(tp->srtt>>3, TCP_DELACK_MIN); if (rtt < max_ato) max_ato = rtt; } ato = min(ato, max_ato); } /* Stay within the limit we were given */ timeout = jiffies + ato; /* Use new timeout only if there wasn't a older one earlier. */ if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { /* If delack timer was blocked or is about to expire, * send ACK now. */ if (icsk->icsk_ack.blocked || time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { tcp_send_ack(sk); return; } if (!time_before(timeout, icsk->icsk_ack.timeout)) timeout = icsk->icsk_ack.timeout; } icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; icsk->icsk_ack.timeout = timeout; sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); } /* This routine sends an ack and also updates the window. */ void tcp_send_ack(struct sock *sk) { /* If we have been reset, we may not send again. */ if (sk->sk_state != TCP_CLOSE) { struct tcp_sock *tp = tcp_sk(sk); 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) { inet_csk_schedule_ack(sk); inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN; inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, TCP_DELACK_MAX, TCP_RTO_MAX); return; } /* Reserve space for headers and prepare control bits. */ skb_reserve(buff, MAX_TCP_HEADER); buff->csum = 0; TCP_SKB_CB(buff)->flags = TCPCB_FLAG_ACK; TCP_SKB_CB(buff)->sacked = 0; skb_shinfo(buff)->tso_segs = 1; skb_shinfo(buff)->tso_size = 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, 0, GFP_ATOMIC); } } /* This routine sends a packet with an out of date sequence * number. It assumes the other end will try to ack it. * * Question: what should we make while urgent mode? * 4.4BSD forces sending single byte of data. We cannot send * out of window data, because we have SND.NXT==SND.MAX... * * Current solution: to send TWO zero-length segments in urgent mode: * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is * out-of-date with SND.UNA-1 to probe window. */ static int tcp_xmit_probe_skb(struct sock *sk, int urgent) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; /* We don't queue it, tcp_transmit_skb() sets ownership. */ skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); if (skb == NULL) return -1; /* Reserve space for headers and set control bits. */ skb_reserve(skb, MAX_TCP_HEADER); skb->csum = 0; TCP_SKB_CB(skb)->flags = TCPCB_FLAG_ACK; TCP_SKB_CB(skb)->sacked = urgent; skb_shinfo(skb)->tso_segs = 1; skb_shinfo(skb)->tso_size = 0; /* 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, 0, GFP_ATOMIC); } int tcp_write_wakeup(struct sock *sk) { if (sk->sk_state != TCP_CLOSE) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; if ((skb = sk->sk_send_head) != NULL && before(TCP_SKB_CB(skb)->seq, tp->snd_una+tp->snd_wnd)) { int err; unsigned int mss = tcp_current_mss(sk, 0); unsigned 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, mss)) return -1; } else if (!tcp_skb_pcount(skb)) tcp_set_skb_tso_segs(sk, skb, mss); TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH; TCP_SKB_CB(skb)->when = tcp_time_stamp; err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); if (!err) { 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 inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); int err; err = tcp_write_wakeup(sk); if (tp->packets_out || !sk->sk_send_head) { /* Cancel probe timer, if it is not required. */ icsk->icsk_probes_out = 0; icsk->icsk_backoff = 0; return; } if (err <= 0) { if (icsk->icsk_backoff < sysctl_tcp_retries2) icsk->icsk_backoff++; icsk->icsk_probes_out++; inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), TCP_RTO_MAX); } else { /* If packet was not sent due to local congestion, * do not backoff and do not remember icsk_probes_out. * Let local senders to fight for local resources. * * Use accumulated backoff yet. */ if (!icsk->icsk_probes_out) icsk->icsk_probes_out = 1; inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RESOURCE_PROBE_INTERVAL), TCP_RTO_MAX); } } EXPORT_SYMBOL(tcp_connect); EXPORT_SYMBOL(tcp_make_synack); EXPORT_SYMBOL(tcp_simple_retransmit); EXPORT_SYMBOL(tcp_sync_mss); EXPORT_SYMBOL(sysctl_tcp_tso_win_divisor); EXPORT_SYMBOL(tcp_mtup_init);