/* * INET An implementation of the TCP/IP protocol suite for the LINUX * operating system. INET is implemented using the BSD Socket * interface as the means of communication with the user level. * * Implementation of the Transmission Control Protocol(TCP). * * Authors: Ross Biro * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> * Mark Evans, <evansmp@uhura.aston.ac.uk> * Corey Minyard <wf-rch!minyard@relay.EU.net> * Florian La Roche, <flla@stud.uni-sb.de> * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> * Linus Torvalds, <torvalds@cs.helsinki.fi> * Alan Cox, <gw4pts@gw4pts.ampr.org> * Matthew Dillon, <dillon@apollo.west.oic.com> * Arnt Gulbrandsen, <agulbra@nvg.unit.no> * Jorge Cwik, <jorge@laser.satlink.net> */ /* * Changes: Pedro Roque : Retransmit queue handled by TCP. * : Fragmentation on mtu decrease * : Segment collapse on retransmit * : AF independence * * Linus Torvalds : send_delayed_ack * David S. Miller : Charge memory using the right skb * during syn/ack processing. * David S. Miller : Output engine completely rewritten. * Andrea Arcangeli: SYNACK carry ts_recent in tsecr. * Cacophonix Gaul : draft-minshall-nagle-01 * J Hadi Salim : ECN support * */ #include <net/tcp.h> #include <linux/compiler.h> #include <linux/gfp.h> #include <linux/module.h> /* People can turn this off for buggy TCP's found in printers etc. */ int sysctl_tcp_retrans_collapse __read_mostly = 1; /* People can turn this on to work with those rare, broken TCPs that * interpret the window field as a signed quantity. */ int sysctl_tcp_workaround_signed_windows __read_mostly = 0; /* This limits the percentage of the congestion window which we * will allow a single TSO frame to consume. Building TSO frames * which are too large can cause TCP streams to be bursty. */ int sysctl_tcp_tso_win_divisor __read_mostly = 3; int sysctl_tcp_mtu_probing __read_mostly = 0; int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS; /* By default, RFC2861 behavior. */ int sysctl_tcp_slow_start_after_idle __read_mostly = 1; int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */ EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size); /* Account for new data that has been sent to the network. */ static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); unsigned int prior_packets = tp->packets_out; tcp_advance_send_head(sk, skb); tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; /* Don't override Nagle indefinately with F-RTO */ if (tp->frto_counter == 2) tp->frto_counter = 3; tp->packets_out += tcp_skb_pcount(skb); if (!prior_packets) inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); } /* SND.NXT, if window was not shrunk. * If window has been shrunk, what should we make? It is not clear at all. * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( * Anything in between SND.UNA...SND.UNA+SND.WND also can be already * invalid. OK, let's make this for now: */ static inline __u32 tcp_acceptable_seq(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); if (!before(tcp_wnd_end(tp), tp->snd_nxt)) return tp->snd_nxt; else return tcp_wnd_end(tp); } /* Calculate mss to advertise in SYN segment. * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that: * * 1. It is independent of path mtu. * 2. Ideally, it is maximal possible segment size i.e. 65535-40. * 3. For IPv4 it is reasonable to calculate it from maximal MTU of * attached devices, because some buggy hosts are confused by * large MSS. * 4. We do not make 3, we advertise MSS, calculated from first * hop device mtu, but allow to raise it to ip_rt_min_advmss. * This may be overridden via information stored in routing table. * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, * probably even Jumbo". */ static __u16 tcp_advertise_mss(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); int mss = tp->advmss; if (dst) { unsigned int metric = dst_metric_advmss(dst); if (metric < mss) { mss = metric; tp->advmss = mss; } } return (__u16)mss; } /* RFC2861. Reset CWND after idle period longer RTO to "restart window". * This is the first part of cwnd validation mechanism. */ static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst) { struct tcp_sock *tp = tcp_sk(sk); s32 delta = tcp_time_stamp - tp->lsndtime; u32 restart_cwnd = tcp_init_cwnd(tp, dst); u32 cwnd = tp->snd_cwnd; tcp_ca_event(sk, CA_EVENT_CWND_RESTART); tp->snd_ssthresh = tcp_current_ssthresh(sk); restart_cwnd = min(restart_cwnd, cwnd); while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) cwnd >>= 1; tp->snd_cwnd = max(cwnd, restart_cwnd); tp->snd_cwnd_stamp = tcp_time_stamp; tp->snd_cwnd_used = 0; } /* Congestion state accounting after a packet has been sent. */ static void tcp_event_data_sent(struct tcp_sock *tp, struct sk_buff *skb, struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); const u32 now = tcp_time_stamp; if (sysctl_tcp_slow_start_after_idle && (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto)) tcp_cwnd_restart(sk, __sk_dst_get(sk)); tp->lsndtime = now; /* If it is a reply for ato after last received * packet, enter pingpong mode. */ if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) icsk->icsk_ack.pingpong = 1; } /* Account for an ACK we sent. */ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts) { tcp_dec_quickack_mode(sk, pkts); inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); } /* Determine a window scaling and initial window to offer. * Based on the assumption that the given amount of space * will be offered. Store the results in the tp structure. * NOTE: for smooth operation initial space offering should * be a multiple of mss if possible. We assume here that mss >= 1. * This MUST be enforced by all callers. */ void tcp_select_initial_window(int __space, __u32 mss, __u32 *rcv_wnd, __u32 *window_clamp, int wscale_ok, __u8 *rcv_wscale, __u32 init_rcv_wnd) { unsigned int space = (__space < 0 ? 0 : __space); /* If no clamp set the clamp to the max possible scaled window */ if (*window_clamp == 0) (*window_clamp) = (65535 << 14); space = min(*window_clamp, space); /* Quantize space offering to a multiple of mss if possible. */ if (space > mss) space = (space / mss) * mss; /* NOTE: offering an initial window larger than 32767 * will break some buggy TCP stacks. If the admin tells us * it is likely we could be speaking with such a buggy stack * we will truncate our initial window offering to 32K-1 * unless the remote has sent us a window scaling option, * which we interpret as a sign the remote TCP is not * misinterpreting the window field as a signed quantity. */ if (sysctl_tcp_workaround_signed_windows) (*rcv_wnd) = min(space, MAX_TCP_WINDOW); else (*rcv_wnd) = space; (*rcv_wscale) = 0; if (wscale_ok) { /* Set window scaling on max possible window * See RFC1323 for an explanation of the limit to 14 */ space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max); space = min_t(u32, space, *window_clamp); while (space > 65535 && (*rcv_wscale) < 14) { space >>= 1; (*rcv_wscale)++; } } /* Set initial window to value enough for senders, following RFC5681. */ if (mss > (1 << *rcv_wscale)) { int init_cwnd = rfc3390_bytes_to_packets(mss); /* when initializing use the value from init_rcv_wnd * rather than the default from above */ if (init_rcv_wnd) *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss); else *rcv_wnd = min(*rcv_wnd, init_cwnd * mss); } /* Set the clamp no higher than max representable value */ (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp); } EXPORT_SYMBOL(tcp_select_initial_window); /* Chose a new window to advertise, update state in tcp_sock for the * socket, and return result with RFC1323 scaling applied. The return * value can be stuffed directly into th->window for an outgoing * frame. */ static u16 tcp_select_window(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); u32 cur_win = tcp_receive_window(tp); u32 new_win = __tcp_select_window(sk); /* Never shrink the offered window */ if (new_win < cur_win) { /* Danger Will Robinson! * Don't update rcv_wup/rcv_wnd here or else * we will not be able to advertise a zero * window in time. --DaveM * * Relax Will Robinson. */ new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); } tp->rcv_wnd = new_win; tp->rcv_wup = tp->rcv_nxt; /* Make sure we do not exceed the maximum possible * scaled window. */ if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows) new_win = min(new_win, MAX_TCP_WINDOW); else new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); /* RFC1323 scaling applied */ new_win >>= tp->rx_opt.rcv_wscale; /* If we advertise zero window, disable fast path. */ if (new_win == 0) tp->pred_flags = 0; return new_win; } /* Packet ECN state for a SYN-ACK */ static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb) { TCP_SKB_CB(skb)->flags &= ~TCPHDR_CWR; if (!(tp->ecn_flags & TCP_ECN_OK)) TCP_SKB_CB(skb)->flags &= ~TCPHDR_ECE; } /* Packet ECN state for a SYN. */ static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); tp->ecn_flags = 0; if (sysctl_tcp_ecn == 1) { TCP_SKB_CB(skb)->flags |= TCPHDR_ECE | TCPHDR_CWR; tp->ecn_flags = TCP_ECN_OK; } } static __inline__ void TCP_ECN_make_synack(struct request_sock *req, struct tcphdr *th) { if (inet_rsk(req)->ecn_ok) th->ece = 1; } /* Set up ECN state for a packet on a ESTABLISHED socket that is about to * be sent. */ static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb, int tcp_header_len) { struct tcp_sock *tp = tcp_sk(sk); if (tp->ecn_flags & TCP_ECN_OK) { /* Not-retransmitted data segment: set ECT and inject CWR. */ if (skb->len != tcp_header_len && !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) { INET_ECN_xmit(sk); if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) { tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; tcp_hdr(skb)->cwr = 1; skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN; } } else { /* ACK or retransmitted segment: clear ECT|CE */ INET_ECN_dontxmit(sk); } if (tp->ecn_flags & TCP_ECN_DEMAND_CWR) tcp_hdr(skb)->ece = 1; } } /* Constructs common control bits of non-data skb. If SYN/FIN is present, * auto increment end seqno. */ static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags) { skb->ip_summed = CHECKSUM_PARTIAL; skb->csum = 0; TCP_SKB_CB(skb)->flags = flags; TCP_SKB_CB(skb)->sacked = 0; skb_shinfo(skb)->gso_segs = 1; skb_shinfo(skb)->gso_size = 0; skb_shinfo(skb)->gso_type = 0; TCP_SKB_CB(skb)->seq = seq; if (flags & (TCPHDR_SYN | TCPHDR_FIN)) seq++; TCP_SKB_CB(skb)->end_seq = seq; } static inline int tcp_urg_mode(const struct tcp_sock *tp) { return tp->snd_una != tp->snd_up; } #define OPTION_SACK_ADVERTISE (1 << 0) #define OPTION_TS (1 << 1) #define OPTION_MD5 (1 << 2) #define OPTION_WSCALE (1 << 3) #define OPTION_COOKIE_EXTENSION (1 << 4) struct tcp_out_options { u8 options; /* bit field of OPTION_* */ u8 ws; /* window scale, 0 to disable */ u8 num_sack_blocks; /* number of SACK blocks to include */ u8 hash_size; /* bytes in hash_location */ u16 mss; /* 0 to disable */ __u32 tsval, tsecr; /* need to include OPTION_TS */ __u8 *hash_location; /* temporary pointer, overloaded */ }; /* The sysctl int routines are generic, so check consistency here. */ static u8 tcp_cookie_size_check(u8 desired) { int cookie_size; if (desired > 0) /* previously specified */ return desired; cookie_size = ACCESS_ONCE(sysctl_tcp_cookie_size); if (cookie_size <= 0) /* no default specified */ return 0; if (cookie_size <= TCP_COOKIE_MIN) /* value too small, specify minimum */ return TCP_COOKIE_MIN; if (cookie_size >= TCP_COOKIE_MAX) /* value too large, specify maximum */ return TCP_COOKIE_MAX; if (cookie_size & 1) /* 8-bit multiple, illegal, fix it */ cookie_size++; return (u8)cookie_size; } /* Write previously computed TCP options to the packet. * * Beware: Something in the Internet is very sensitive to the ordering of * TCP options, we learned this through the hard way, so be careful here. * Luckily we can at least blame others for their non-compliance but from * inter-operatibility perspective it seems that we're somewhat stuck with * the ordering which we have been using if we want to keep working with * those broken things (not that it currently hurts anybody as there isn't * particular reason why the ordering would need to be changed). * * At least SACK_PERM as the first option is known to lead to a disaster * (but it may well be that other scenarios fail similarly). */ static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp, struct tcp_out_options *opts) { u8 options = opts->options; /* mungable copy */ /* Having both authentication and cookies for security is redundant, * and there's certainly not enough room. Instead, the cookie-less * extension variant is proposed. * * Consider the pessimal case with authentication. The options * could look like: * COOKIE|MD5(20) + MSS(4) + SACK|TS(12) + WSCALE(4) == 40 */ if (unlikely(OPTION_MD5 & options)) { if (unlikely(OPTION_COOKIE_EXTENSION & options)) { *ptr++ = htonl((TCPOPT_COOKIE << 24) | (TCPOLEN_COOKIE_BASE << 16) | (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG); } else { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG); } options &= ~OPTION_COOKIE_EXTENSION; /* overload cookie hash location */ opts->hash_location = (__u8 *)ptr; ptr += 4; } if (unlikely(opts->mss)) { *ptr++ = htonl((TCPOPT_MSS << 24) | (TCPOLEN_MSS << 16) | opts->mss); } if (likely(OPTION_TS & options)) { if (unlikely(OPTION_SACK_ADVERTISE & options)) { *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | (TCPOLEN_SACK_PERM << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); options &= ~OPTION_SACK_ADVERTISE; } else { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP); } *ptr++ = htonl(opts->tsval); *ptr++ = htonl(opts->tsecr); } /* Specification requires after timestamp, so do it now. * * Consider the pessimal case without authentication. The options * could look like: * MSS(4) + SACK|TS(12) + COOKIE(20) + WSCALE(4) == 40 */ if (unlikely(OPTION_COOKIE_EXTENSION & options)) { __u8 *cookie_copy = opts->hash_location; u8 cookie_size = opts->hash_size; /* 8-bit multiple handled in tcp_cookie_size_check() above, * and elsewhere. */ if (0x2 & cookie_size) { __u8 *p = (__u8 *)ptr; /* 16-bit multiple */ *p++ = TCPOPT_COOKIE; *p++ = TCPOLEN_COOKIE_BASE + cookie_size; *p++ = *cookie_copy++; *p++ = *cookie_copy++; ptr++; cookie_size -= 2; } else { /* 32-bit multiple */ *ptr++ = htonl(((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_COOKIE << 8) | TCPOLEN_COOKIE_BASE) + cookie_size); } if (cookie_size > 0) { memcpy(ptr, cookie_copy, cookie_size); ptr += (cookie_size / 4); } } if (unlikely(OPTION_SACK_ADVERTISE & options)) { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_SACK_PERM << 8) | TCPOLEN_SACK_PERM); } if (unlikely(OPTION_WSCALE & options)) { *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_WINDOW << 16) | (TCPOLEN_WINDOW << 8) | opts->ws); } if (unlikely(opts->num_sack_blocks)) { struct tcp_sack_block *sp = tp->rx_opt.dsack ? tp->duplicate_sack : tp->selective_acks; int this_sack; *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | (TCPOPT_SACK << 8) | (TCPOLEN_SACK_BASE + (opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK))); for (this_sack = 0; this_sack < opts->num_sack_blocks; ++this_sack) { *ptr++ = htonl(sp[this_sack].start_seq); *ptr++ = htonl(sp[this_sack].end_seq); } tp->rx_opt.dsack = 0; } } /* Compute TCP options for SYN packets. This is not the final * network wire format yet. */ static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb, struct tcp_out_options *opts, struct tcp_md5sig_key **md5) { struct tcp_sock *tp = tcp_sk(sk); struct tcp_cookie_values *cvp = tp->cookie_values; unsigned remaining = MAX_TCP_OPTION_SPACE; u8 cookie_size = (!tp->rx_opt.cookie_out_never && cvp != NULL) ? tcp_cookie_size_check(cvp->cookie_desired) : 0; #ifdef CONFIG_TCP_MD5SIG *md5 = tp->af_specific->md5_lookup(sk, sk); if (*md5) { opts->options |= OPTION_MD5; remaining -= TCPOLEN_MD5SIG_ALIGNED; } #else *md5 = NULL; #endif /* We always get an MSS option. The option bytes which will be seen in * normal data packets should timestamps be used, must be in the MSS * advertised. But we subtract them from tp->mss_cache so that * calculations in tcp_sendmsg are simpler etc. So account for this * fact here if necessary. If we don't do this correctly, as a * receiver we won't recognize data packets as being full sized when we * should, and thus we won't abide by the delayed ACK rules correctly. * SACKs don't matter, we never delay an ACK when we have any of those * going out. */ opts->mss = tcp_advertise_mss(sk); remaining -= TCPOLEN_MSS_ALIGNED; if (likely(sysctl_tcp_timestamps && *md5 == NULL)) { opts->options |= OPTION_TS; opts->tsval = TCP_SKB_CB(skb)->when; opts->tsecr = tp->rx_opt.ts_recent; remaining -= TCPOLEN_TSTAMP_ALIGNED; } if (likely(sysctl_tcp_window_scaling)) { opts->ws = tp->rx_opt.rcv_wscale; opts->options |= OPTION_WSCALE; remaining -= TCPOLEN_WSCALE_ALIGNED; } if (likely(sysctl_tcp_sack)) { opts->options |= OPTION_SACK_ADVERTISE; if (unlikely(!(OPTION_TS & opts->options))) remaining -= TCPOLEN_SACKPERM_ALIGNED; } /* Note that timestamps are required by the specification. * * Odd numbers of bytes are prohibited by the specification, ensuring * that the cookie is 16-bit aligned, and the resulting cookie pair is * 32-bit aligned. */ if (*md5 == NULL && (OPTION_TS & opts->options) && cookie_size > 0) { int need = TCPOLEN_COOKIE_BASE + cookie_size; if (0x2 & need) { /* 32-bit multiple */ need += 2; /* NOPs */ if (need > remaining) { /* try shrinking cookie to fit */ cookie_size -= 2; need -= 4; } } while (need > remaining && TCP_COOKIE_MIN <= cookie_size) { cookie_size -= 4; need -= 4; } if (TCP_COOKIE_MIN <= cookie_size) { opts->options |= OPTION_COOKIE_EXTENSION; opts->hash_location = (__u8 *)&cvp->cookie_pair[0]; opts->hash_size = cookie_size; /* Remember for future incarnations. */ cvp->cookie_desired = cookie_size; if (cvp->cookie_desired != cvp->cookie_pair_size) { /* Currently use random bytes as a nonce, * assuming these are completely unpredictable * by hostile users of the same system. */ get_random_bytes(&cvp->cookie_pair[0], cookie_size); cvp->cookie_pair_size = cookie_size; } remaining -= need; } } return MAX_TCP_OPTION_SPACE - remaining; } /* Set up TCP options for SYN-ACKs. */ static unsigned tcp_synack_options(struct sock *sk, struct request_sock *req, unsigned mss, struct sk_buff *skb, struct tcp_out_options *opts, struct tcp_md5sig_key **md5, struct tcp_extend_values *xvp) { struct inet_request_sock *ireq = inet_rsk(req); unsigned remaining = MAX_TCP_OPTION_SPACE; u8 cookie_plus = (xvp != NULL && !xvp->cookie_out_never) ? xvp->cookie_plus : 0; #ifdef CONFIG_TCP_MD5SIG *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req); if (*md5) { opts->options |= OPTION_MD5; remaining -= TCPOLEN_MD5SIG_ALIGNED; /* We can't fit any SACK blocks in a packet with MD5 + TS * options. There was discussion about disabling SACK * rather than TS in order to fit in better with old, * buggy kernels, but that was deemed to be unnecessary. */ ireq->tstamp_ok &= !ireq->sack_ok; } #else *md5 = NULL; #endif /* We always send an MSS option. */ opts->mss = mss; remaining -= TCPOLEN_MSS_ALIGNED; if (likely(ireq->wscale_ok)) { opts->ws = ireq->rcv_wscale; opts->options |= OPTION_WSCALE; remaining -= TCPOLEN_WSCALE_ALIGNED; } if (likely(ireq->tstamp_ok)) { opts->options |= OPTION_TS; opts->tsval = TCP_SKB_CB(skb)->when; opts->tsecr = req->ts_recent; remaining -= TCPOLEN_TSTAMP_ALIGNED; } if (likely(ireq->sack_ok)) { opts->options |= OPTION_SACK_ADVERTISE; if (unlikely(!ireq->tstamp_ok)) remaining -= TCPOLEN_SACKPERM_ALIGNED; } /* Similar rationale to tcp_syn_options() applies here, too. * If the <SYN> options fit, the same options should fit now! */ if (*md5 == NULL && ireq->tstamp_ok && cookie_plus > TCPOLEN_COOKIE_BASE) { int need = cookie_plus; /* has TCPOLEN_COOKIE_BASE */ if (0x2 & need) { /* 32-bit multiple */ need += 2; /* NOPs */ } if (need <= remaining) { opts->options |= OPTION_COOKIE_EXTENSION; opts->hash_size = cookie_plus - TCPOLEN_COOKIE_BASE; remaining -= need; } else { /* There's no error return, so flag it. */ xvp->cookie_out_never = 1; /* true */ opts->hash_size = 0; } } return MAX_TCP_OPTION_SPACE - remaining; } /* Compute TCP options for ESTABLISHED sockets. This is not the * final wire format yet. */ static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb, struct tcp_out_options *opts, struct tcp_md5sig_key **md5) { struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL; struct tcp_sock *tp = tcp_sk(sk); unsigned size = 0; unsigned int eff_sacks; #ifdef CONFIG_TCP_MD5SIG *md5 = tp->af_specific->md5_lookup(sk, sk); if (unlikely(*md5)) { opts->options |= OPTION_MD5; size += TCPOLEN_MD5SIG_ALIGNED; } #else *md5 = NULL; #endif if (likely(tp->rx_opt.tstamp_ok)) { opts->options |= OPTION_TS; opts->tsval = tcb ? tcb->when : 0; opts->tsecr = tp->rx_opt.ts_recent; size += TCPOLEN_TSTAMP_ALIGNED; } eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack; if (unlikely(eff_sacks)) { const unsigned remaining = MAX_TCP_OPTION_SPACE - size; opts->num_sack_blocks = min_t(unsigned, eff_sacks, (remaining - TCPOLEN_SACK_BASE_ALIGNED) / TCPOLEN_SACK_PERBLOCK); size += TCPOLEN_SACK_BASE_ALIGNED + opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK; } return size; } /* This routine actually transmits TCP packets queued in by * tcp_do_sendmsg(). This is used by both the initial * transmission and possible later retransmissions. * All SKB's seen here are completely headerless. It is our * job to build the TCP header, and pass the packet down to * IP so it can do the same plus pass the packet off to the * device. * * We are working here with either a clone of the original * SKB, or a fresh unique copy made by the retransmit engine. */ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, gfp_t gfp_mask) { const struct inet_connection_sock *icsk = inet_csk(sk); struct inet_sock *inet; struct tcp_sock *tp; struct tcp_skb_cb *tcb; struct tcp_out_options opts; unsigned tcp_options_size, tcp_header_size; struct tcp_md5sig_key *md5; struct tcphdr *th; int err; BUG_ON(!skb || !tcp_skb_pcount(skb)); /* If congestion control is doing timestamping, we must * take such a timestamp before we potentially clone/copy. */ if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP) __net_timestamp(skb); if (likely(clone_it)) { if (unlikely(skb_cloned(skb))) skb = pskb_copy(skb, gfp_mask); else skb = skb_clone(skb, gfp_mask); if (unlikely(!skb)) return -ENOBUFS; } inet = inet_sk(sk); tp = tcp_sk(sk); tcb = TCP_SKB_CB(skb); memset(&opts, 0, sizeof(opts)); if (unlikely(tcb->flags & TCPHDR_SYN)) tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5); else tcp_options_size = tcp_established_options(sk, skb, &opts, &md5); tcp_header_size = tcp_options_size + sizeof(struct tcphdr); if (tcp_packets_in_flight(tp) == 0) { tcp_ca_event(sk, CA_EVENT_TX_START); skb->ooo_okay = 1; } else skb->ooo_okay = 0; skb_push(skb, tcp_header_size); skb_reset_transport_header(skb); skb_set_owner_w(skb, sk); /* Build TCP header and checksum it. */ th = tcp_hdr(skb); th->source = inet->inet_sport; th->dest = inet->inet_dport; th->seq = htonl(tcb->seq); th->ack_seq = htonl(tp->rcv_nxt); *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | tcb->flags); if (unlikely(tcb->flags & TCPHDR_SYN)) { /* RFC1323: The window in SYN & SYN/ACK segments * is never scaled. */ th->window = htons(min(tp->rcv_wnd, 65535U)); } else { th->window = htons(tcp_select_window(sk)); } th->check = 0; th->urg_ptr = 0; /* The urg_mode check is necessary during a below snd_una win probe */ if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) { if (before(tp->snd_up, tcb->seq + 0x10000)) { th->urg_ptr = htons(tp->snd_up - tcb->seq); th->urg = 1; } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { th->urg_ptr = htons(0xFFFF); th->urg = 1; } } tcp_options_write((__be32 *)(th + 1), tp, &opts); if (likely((tcb->flags & TCPHDR_SYN) == 0)) TCP_ECN_send(sk, skb, tcp_header_size); #ifdef CONFIG_TCP_MD5SIG /* Calculate the MD5 hash, as we have all we need now */ if (md5) { sk_nocaps_add(sk, NETIF_F_GSO_MASK); tp->af_specific->calc_md5_hash(opts.hash_location, md5, sk, NULL, skb); } #endif icsk->icsk_af_ops->send_check(sk, skb); if (likely(tcb->flags & TCPHDR_ACK)) tcp_event_ack_sent(sk, tcp_skb_pcount(skb)); if (skb->len != tcp_header_size) tcp_event_data_sent(tp, skb, sk); if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq) TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb)); err = icsk->icsk_af_ops->queue_xmit(skb); if (likely(err <= 0)) return err; tcp_enter_cwr(sk, 1); return net_xmit_eval(err); } /* This routine just queues the buffer for sending. * * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, * otherwise socket can stall. */ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); /* Advance write_seq and place onto the write_queue. */ tp->write_seq = TCP_SKB_CB(skb)->end_seq; skb_header_release(skb); tcp_add_write_queue_tail(sk, skb); sk->sk_wmem_queued += skb->truesize; sk_mem_charge(sk, skb->truesize); } /* Initialize TSO segments for a packet. */ static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) { if (skb->len <= mss_now || !sk_can_gso(sk) || skb->ip_summed == CHECKSUM_NONE) { /* Avoid the costly divide in the normal * non-TSO case. */ skb_shinfo(skb)->gso_segs = 1; skb_shinfo(skb)->gso_size = 0; skb_shinfo(skb)->gso_type = 0; } else { skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now); skb_shinfo(skb)->gso_size = mss_now; skb_shinfo(skb)->gso_type = sk->sk_gso_type; } } /* When a modification to fackets out becomes necessary, we need to check * skb is counted to fackets_out or not. */ static void tcp_adjust_fackets_out(struct sock *sk, struct sk_buff *skb, int decr) { struct tcp_sock *tp = tcp_sk(sk); if (!tp->sacked_out || tcp_is_reno(tp)) return; if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq)) tp->fackets_out -= decr; } /* Pcount in the middle of the write queue got changed, we need to do various * tweaks to fix counters */ static void tcp_adjust_pcount(struct sock *sk, struct sk_buff *skb, int decr) { struct tcp_sock *tp = tcp_sk(sk); tp->packets_out -= decr; if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) tp->sacked_out -= decr; if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) tp->retrans_out -= decr; if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) tp->lost_out -= decr; /* Reno case is special. Sigh... */ if (tcp_is_reno(tp) && decr > 0) tp->sacked_out -= min_t(u32, tp->sacked_out, decr); tcp_adjust_fackets_out(sk, skb, decr); if (tp->lost_skb_hint && before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) && (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))) tp->lost_cnt_hint -= decr; tcp_verify_left_out(tp); } /* Function to create two new TCP segments. Shrinks the given segment * to the specified size and appends a new segment with the rest of the * packet to the list. This won't be called frequently, I hope. * Remember, these are still headerless SKBs at this point. */ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss_now) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *buff; int nsize, old_factor; int nlen; u8 flags; BUG_ON(len > skb->len); nsize = skb_headlen(skb) - len; if (nsize < 0) nsize = 0; if (skb_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->sk_wmem_queued += buff->truesize; sk_mem_charge(sk, buff->truesize); nlen = skb->len - len - nsize; buff->truesize += nlen; skb->truesize -= nlen; /* Correct the sequence numbers. */ TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; /* PSH and FIN should only be set in the second packet. */ flags = TCP_SKB_CB(skb)->flags; TCP_SKB_CB(skb)->flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); TCP_SKB_CB(buff)->flags = flags; TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) { /* Copy and checksum data tail into the new buffer. */ buff->csum = csum_partial_copy_nocheck(skb->data + len, skb_put(buff, nsize), nsize, 0); skb_trim(skb, len); skb->csum = csum_block_sub(skb->csum, buff->csum, len); } else { skb->ip_summed = CHECKSUM_PARTIAL; skb_split(skb, buff, len); } buff->ip_summed = skb->ip_summed; /* Looks stupid, but our code really uses when of * skbs, which it never sent before. --ANK */ TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when; buff->tstamp = skb->tstamp; old_factor = tcp_skb_pcount(skb); /* Fix up tso_factor for both original and new SKB. */ tcp_set_skb_tso_segs(sk, skb, mss_now); tcp_set_skb_tso_segs(sk, buff, mss_now); /* If this packet has been sent out already, we must * adjust the various packet counters. */ if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { int diff = old_factor - tcp_skb_pcount(skb) - tcp_skb_pcount(buff); if (diff) tcp_adjust_pcount(sk, skb, diff); } /* Link BUFF into the send queue. */ skb_header_release(buff); tcp_insert_write_queue_after(skb, buff, sk); return 0; } /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c * eventually). The difference is that pulled data not copied, but * immediately discarded. */ static void __pskb_trim_head(struct sk_buff *skb, int len) { int i, k, eat; eat = len; k = 0; for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) { if (skb_shinfo(skb)->frags[i].size <= eat) { put_page(skb_shinfo(skb)->frags[i].page); eat -= skb_shinfo(skb)->frags[i].size; } else { skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i]; if (eat) { skb_shinfo(skb)->frags[k].page_offset += eat; skb_shinfo(skb)->frags[k].size -= eat; eat = 0; } k++; } } skb_shinfo(skb)->nr_frags = k; skb_reset_tail_pointer(skb); skb->data_len -= len; skb->len = skb->data_len; } /* Remove acked data from a packet in the transmit queue. */ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) { if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC)) return -ENOMEM; /* If len == headlen, we avoid __skb_pull to preserve alignment. */ if (unlikely(len < skb_headlen(skb))) __skb_pull(skb, len); else __pskb_trim_head(skb, len - skb_headlen(skb)); TCP_SKB_CB(skb)->seq += len; skb->ip_summed = CHECKSUM_PARTIAL; skb->truesize -= len; sk->sk_wmem_queued -= len; sk_mem_uncharge(sk, len); sock_set_flag(sk, SOCK_QUEUE_SHRUNK); /* Any change of skb->len requires recalculation of tso * factor and mss. */ if (tcp_skb_pcount(skb) > 1) tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk)); return 0; } /* Calculate MSS. Not accounting for SACKs here. */ int tcp_mtu_to_mss(struct sock *sk, int pmtu) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mss_now; /* Calculate base mss without TCP options: It is MMS_S - sizeof(tcphdr) of rfc1122 */ mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr); /* Clamp it (mss_clamp does not include tcp options) */ if (mss_now > tp->rx_opt.mss_clamp) mss_now = tp->rx_opt.mss_clamp; /* Now subtract optional transport overhead */ mss_now -= icsk->icsk_ext_hdr_len; /* Then reserve room for full set of TCP options and 8 bytes of data */ if (mss_now < 48) mss_now = 48; /* Now subtract TCP options size, not including SACKs */ mss_now -= tp->tcp_header_len - sizeof(struct tcphdr); return mss_now; } /* Inverse of above */ int tcp_mss_to_mtu(struct sock *sk, int mss) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mtu; mtu = mss + tp->tcp_header_len + icsk->icsk_ext_hdr_len + icsk->icsk_af_ops->net_header_len; return mtu; } /* MTU probing init per socket */ void tcp_mtup_init(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1; icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) + icsk->icsk_af_ops->net_header_len; icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss); icsk->icsk_mtup.probe_size = 0; } EXPORT_SYMBOL(tcp_mtup_init); /* This function synchronize snd mss to current pmtu/exthdr set. tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts for TCP options, but includes only bare TCP header. tp->rx_opt.mss_clamp is mss negotiated at connection setup. It is minimum of user_mss and mss received with SYN. It also does not include TCP options. inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. tp->mss_cache is current effective sending mss, including all tcp options except for SACKs. It is evaluated, taking into account current pmtu, but never exceeds tp->rx_opt.mss_clamp. NOTE1. rfc1122 clearly states that advertised MSS DOES NOT include either tcp or ip options. NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache are READ ONLY outside this function. --ANK (980731) */ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); int mss_now; if (icsk->icsk_mtup.search_high > pmtu) icsk->icsk_mtup.search_high = pmtu; mss_now = tcp_mtu_to_mss(sk, pmtu); mss_now = tcp_bound_to_half_wnd(tp, mss_now); /* And store cached results */ icsk->icsk_pmtu_cookie = pmtu; if (icsk->icsk_mtup.enabled) mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)); tp->mss_cache = mss_now; return mss_now; } EXPORT_SYMBOL(tcp_sync_mss); /* Compute the current effective MSS, taking SACKs and IP options, * and even PMTU discovery events into account. */ unsigned int tcp_current_mss(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct dst_entry *dst = __sk_dst_get(sk); u32 mss_now; unsigned header_len; struct tcp_out_options opts; struct tcp_md5sig_key *md5; mss_now = tp->mss_cache; if (dst) { u32 mtu = dst_mtu(dst); if (mtu != inet_csk(sk)->icsk_pmtu_cookie) mss_now = tcp_sync_mss(sk, mtu); } header_len = tcp_established_options(sk, NULL, &opts, &md5) + sizeof(struct tcphdr); /* The mss_cache is sized based on tp->tcp_header_len, which assumes * some common options. If this is an odd packet (because we have SACK * blocks etc) then our calculated header_len will be different, and * we have to adjust mss_now correspondingly */ if (header_len != tp->tcp_header_len) { int delta = (int) header_len - tp->tcp_header_len; mss_now -= delta; } return mss_now; } /* Congestion window validation. (RFC2861) */ static void tcp_cwnd_validate(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); if (tp->packets_out >= tp->snd_cwnd) { /* Network is feed fully. */ tp->snd_cwnd_used = 0; tp->snd_cwnd_stamp = tcp_time_stamp; } else { /* Network starves. */ if (tp->packets_out > tp->snd_cwnd_used) tp->snd_cwnd_used = tp->packets_out; if (sysctl_tcp_slow_start_after_idle && (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto) tcp_cwnd_application_limited(sk); } } /* Returns the portion of skb which can be sent right away without * introducing MSS oddities to segment boundaries. In rare cases where * mss_now != mss_cache, we will request caller to create a small skb * per input skb which could be mostly avoided here (if desired). * * We explicitly want to create a request for splitting write queue tail * to a small skb for Nagle purposes while avoiding unnecessary modulos, * thus all the complexity (cwnd_len is always MSS multiple which we * return whenever allowed by the other factors). Basically we need the * modulo only when the receiver window alone is the limiting factor or * when we would be allowed to send the split-due-to-Nagle skb fully. */ static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb, unsigned int mss_now, unsigned int cwnd) { struct tcp_sock *tp = tcp_sk(sk); u32 needed, window, cwnd_len; window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; cwnd_len = mss_now * cwnd; if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk))) return cwnd_len; needed = min(skb->len, window); if (cwnd_len <= needed) return cwnd_len; return needed - needed % mss_now; } /* Can at least one segment of SKB be sent right now, according to the * congestion window rules? If so, return how many segments are allowed. */ static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp, struct sk_buff *skb) { u32 in_flight, cwnd; /* Don't be strict about the congestion window for the final FIN. */ if ((TCP_SKB_CB(skb)->flags & TCPHDR_FIN) && tcp_skb_pcount(skb) == 1) return 1; in_flight = tcp_packets_in_flight(tp); cwnd = tp->snd_cwnd; if (in_flight < cwnd) return (cwnd - in_flight); return 0; } /* Intialize TSO state of a skb. * This must be invoked the first time we consider transmitting * SKB onto the wire. */ static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb, unsigned int mss_now) { int tso_segs = tcp_skb_pcount(skb); if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) { tcp_set_skb_tso_segs(sk, skb, mss_now); tso_segs = tcp_skb_pcount(skb); } return tso_segs; } /* Minshall's variant of the Nagle send check. */ static inline int tcp_minshall_check(const struct tcp_sock *tp) { return after(tp->snd_sml, tp->snd_una) && !after(tp->snd_sml, tp->snd_nxt); } /* Return 0, if packet can be sent now without violation Nagle's rules: * 1. It is full sized. * 2. Or it contains FIN. (already checked by caller) * 3. Or TCP_NODELAY was set. * 4. Or TCP_CORK is not set, and all sent packets are ACKed. * With Minshall's modification: all sent small packets are ACKed. */ static inline int tcp_nagle_check(const struct tcp_sock *tp, const struct sk_buff *skb, unsigned mss_now, int nonagle) { return skb->len < mss_now && ((nonagle & TCP_NAGLE_CORK) || (!nonagle && tp->packets_out && tcp_minshall_check(tp))); } /* Return non-zero if the Nagle test allows this packet to be * sent now. */ static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss, int nonagle) { /* Nagle rule does not apply to frames, which sit in the middle of the * write_queue (they have no chances to get new data). * * This is implemented in the callers, where they modify the 'nonagle' * argument based upon the location of SKB in the send queue. */ if (nonagle & TCP_NAGLE_PUSH) return 1; /* Don't use the nagle rule for urgent data (or for the final FIN). * Nagle can be ignored during F-RTO too (see RFC4138). */ if (tcp_urg_mode(tp) || (tp->frto_counter == 2) || (TCP_SKB_CB(skb)->flags & TCPHDR_FIN)) return 1; if (!tcp_nagle_check(tp, skb, cur_mss, nonagle)) return 1; return 0; } /* Does at least the first segment of SKB fit into the send window? */ static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb, unsigned int cur_mss) { u32 end_seq = TCP_SKB_CB(skb)->end_seq; if (skb->len > cur_mss) end_seq = TCP_SKB_CB(skb)->seq + cur_mss; return !after(end_seq, tcp_wnd_end(tp)); } /* This checks if the data bearing packet SKB (usually tcp_send_head(sk)) * should be put on the wire right now. If so, it returns the number of * packets allowed by the congestion window. */ static unsigned int tcp_snd_test(struct sock *sk, struct sk_buff *skb, unsigned int cur_mss, int nonagle) { struct tcp_sock *tp = tcp_sk(sk); unsigned int cwnd_quota; tcp_init_tso_segs(sk, skb, cur_mss); if (!tcp_nagle_test(tp, skb, cur_mss, nonagle)) return 0; cwnd_quota = tcp_cwnd_test(tp, skb); if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss)) cwnd_quota = 0; return cwnd_quota; } /* Test if sending is allowed right now. */ int tcp_may_send_now(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb = tcp_send_head(sk); return skb && tcp_snd_test(sk, skb, tcp_current_mss(sk), (tcp_skb_is_last(sk, skb) ? tp->nonagle : TCP_NAGLE_PUSH)); } /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet * which is put after SKB on the list. It is very much like * tcp_fragment() except that it may make several kinds of assumptions * in order to speed up the splitting operation. In particular, we * know that all the data is in scatter-gather pages, and that the * packet has never been sent out before (and thus is not cloned). */ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, unsigned int mss_now, gfp_t gfp) { struct sk_buff *buff; int nlen = skb->len - len; u8 flags; /* All of a TSO frame must be composed of paged data. */ if (skb->len != skb->data_len) return tcp_fragment(sk, skb, len, mss_now); buff = sk_stream_alloc_skb(sk, 0, gfp); if (unlikely(buff == NULL)) return -ENOMEM; sk->sk_wmem_queued += buff->truesize; sk_mem_charge(sk, buff->truesize); buff->truesize += nlen; skb->truesize -= nlen; /* Correct the sequence numbers. */ TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; /* PSH and FIN should only be set in the second packet. */ flags = TCP_SKB_CB(skb)->flags; TCP_SKB_CB(skb)->flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); TCP_SKB_CB(buff)->flags = flags; /* This packet was never sent out yet, so no SACK bits. */ TCP_SKB_CB(buff)->sacked = 0; buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL; skb_split(skb, buff, len); /* Fix up tso_factor for both original and new SKB. */ tcp_set_skb_tso_segs(sk, skb, mss_now); tcp_set_skb_tso_segs(sk, buff, mss_now); /* Link BUFF into the send queue. */ skb_header_release(buff); tcp_insert_write_queue_after(skb, buff, sk); return 0; } /* Try to defer sending, if possible, in order to minimize the amount * of TSO splitting we do. View it as a kind of TSO Nagle test. * * This algorithm is from John Heffner. */ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); const struct inet_connection_sock *icsk = inet_csk(sk); u32 send_win, cong_win, limit, in_flight; int win_divisor; if (TCP_SKB_CB(skb)->flags & TCPHDR_FIN) goto send_now; if (icsk->icsk_ca_state != TCP_CA_Open) goto send_now; /* Defer for less than two clock ticks. */ if (tp->tso_deferred && (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1) goto send_now; in_flight = tcp_packets_in_flight(tp); BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight)); send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; /* From in_flight test above, we know that cwnd > in_flight. */ cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache; limit = min(send_win, cong_win); /* If a full-sized TSO skb can be sent, do it. */ if (limit >= sk->sk_gso_max_size) goto send_now; /* Middle in queue won't get any more data, full sendable already? */ if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len)) goto send_now; win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor); if (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 /= win_divisor; if (limit >= chunk) goto send_now; } else { /* Different approach, try not to defer past a single * ACK. Receiver should ACK every other full sized * frame, so if we have space for more than 3 frames * then send now. */ if (limit > tcp_max_burst(tp) * tp->mss_cache) goto send_now; } /* Ok, it looks like it is advisable to defer. */ tp->tso_deferred = 1 | (jiffies << 1); return 1; send_now: tp->tso_deferred = 0; return 0; } /* Create a new MTU probe if we are ready. * MTU probe is regularly attempting to increase the path MTU by * deliberately sending larger packets. This discovers routing * changes resulting in larger path MTUs. * * Returns 0 if we should wait to probe (no cwnd available), * 1 if a probe was sent, * -1 otherwise */ static int tcp_mtu_probe(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); struct sk_buff *skb, *nskb, *next; int len; int probe_size; int size_needed; int copy; int mss_now; /* Not currently probing/verifying, * not in recovery, * have enough cwnd, and * not SACKing (the variable headers throw things off) */ if (!icsk->icsk_mtup.enabled || icsk->icsk_mtup.probe_size || inet_csk(sk)->icsk_ca_state != TCP_CA_Open || tp->snd_cwnd < 11 || tp->rx_opt.num_sacks || tp->rx_opt.dsack) return -1; /* Very simple search strategy: just double the MSS. */ mss_now = tcp_current_mss(sk); probe_size = 2 * tp->mss_cache; size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) { /* TODO: set timer for probe_converge_event */ return -1; } /* Have enough data in the send queue to probe? */ if (tp->write_seq - tp->snd_nxt < size_needed) return -1; if (tp->snd_wnd < size_needed) return -1; if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp))) return 0; /* Do we need to wait to drain cwnd? With none in flight, don't stall */ if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) { if (!tcp_packets_in_flight(tp)) return -1; else return 0; } /* We're allowed to probe. Build it now. */ if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL) return -1; sk->sk_wmem_queued += nskb->truesize; sk_mem_charge(sk, nskb->truesize); skb = tcp_send_head(sk); TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq; TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size; TCP_SKB_CB(nskb)->flags = TCPHDR_ACK; TCP_SKB_CB(nskb)->sacked = 0; nskb->csum = 0; nskb->ip_summed = skb->ip_summed; tcp_insert_write_queue_before(nskb, skb, sk); len = 0; tcp_for_write_queue_from_safe(skb, next, sk) { copy = min_t(int, skb->len, probe_size - len); if (nskb->ip_summed) skb_copy_bits(skb, 0, skb_put(nskb, copy), copy); else nskb->csum = skb_copy_and_csum_bits(skb, 0, skb_put(nskb, copy), copy, nskb->csum); if (skb->len <= copy) { /* We've eaten all the data from this skb. * Throw it away. */ TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags; tcp_unlink_write_queue(skb, sk); sk_wmem_free_skb(sk, skb); } else { TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags & ~(TCPHDR_FIN|TCPHDR_PSH); if (!skb_shinfo(skb)->nr_frags) { skb_pull(skb, copy); if (skb->ip_summed != CHECKSUM_PARTIAL) skb->csum = csum_partial(skb->data, skb->len, 0); } else { __pskb_trim_head(skb, copy); tcp_set_skb_tso_segs(sk, skb, mss_now); } TCP_SKB_CB(skb)->seq += copy; } len += copy; if (len >= probe_size) break; } tcp_init_tso_segs(sk, nskb, nskb->len); /* We're ready to send. If this fails, the probe will * be resegmented into mss-sized pieces by tcp_write_xmit(). */ TCP_SKB_CB(nskb)->when = tcp_time_stamp; if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) { /* Decrement cwnd here because we are sending * effectively two packets. */ tp->snd_cwnd--; tcp_event_new_data_sent(sk, nskb); icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len); tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq; tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq; return 1; } return -1; } /* This routine writes packets to the network. It advances the * send_head. This happens as incoming acks open up the remote * window for us. * * LARGESEND note: !tcp_urg_mode is overkill, only frames between * snd_up-64k-mss .. snd_up cannot be large. However, taking into * account rare use of URG, this is not a big flaw. * * Returns 1, if no segments are in flight and we have queued segments, but * cannot send anything now because of SWS or another problem. */ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, int push_one, gfp_t gfp) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; unsigned int tso_segs, sent_pkts; int cwnd_quota; int result; sent_pkts = 0; if (!push_one) { /* Do MTU probing. */ result = tcp_mtu_probe(sk); if (!result) { return 0; } else if (result > 0) { sent_pkts = 1; } } while ((skb = tcp_send_head(sk))) { unsigned int limit; tso_segs = tcp_init_tso_segs(sk, skb, mss_now); BUG_ON(!tso_segs); cwnd_quota = tcp_cwnd_test(tp, skb); if (!cwnd_quota) break; if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) break; if (tso_segs == 1) { if (unlikely(!tcp_nagle_test(tp, skb, mss_now, (tcp_skb_is_last(sk, skb) ? nonagle : TCP_NAGLE_PUSH)))) break; } else { if (!push_one && tcp_tso_should_defer(sk, skb)) break; } limit = mss_now; if (tso_segs > 1 && !tcp_urg_mode(tp)) limit = tcp_mss_split_point(sk, skb, mss_now, cwnd_quota); if (skb->len > limit && unlikely(tso_fragment(sk, skb, limit, mss_now, gfp))) break; TCP_SKB_CB(skb)->when = tcp_time_stamp; if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp))) break; /* Advance the send_head. This one is sent out. * This call will increment packets_out. */ tcp_event_new_data_sent(sk, skb); tcp_minshall_update(tp, mss_now, skb); sent_pkts++; if (push_one) break; } if (likely(sent_pkts)) { tcp_cwnd_validate(sk); return 0; } return !tp->packets_out && tcp_send_head(sk); } /* Push out any pending frames which were held back due to * TCP_CORK or attempt at coalescing tiny packets. * The socket must be locked by the caller. */ void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, int nonagle) { /* If we are closed, the bytes will have to remain here. * In time closedown will finish, we empty the write queue and * all will be happy. */ if (unlikely(sk->sk_state == TCP_CLOSE)) return; if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC)) tcp_check_probe_timer(sk); } /* Send _single_ skb sitting at the send head. This function requires * true push pending frames to setup probe timer etc. */ void tcp_push_one(struct sock *sk, unsigned int mss_now) { struct sk_buff *skb = tcp_send_head(sk); BUG_ON(!skb || skb->len < mss_now); tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation); } /* This function returns the amount that we can raise the * usable window based on the following constraints * * 1. The window can never be shrunk once it is offered (RFC 793) * 2. We limit memory per socket * * RFC 1122: * "the suggested [SWS] avoidance algorithm for the receiver is to keep * RECV.NEXT + RCV.WIN fixed until: * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" * * i.e. don't raise the right edge of the window until you can raise * it at least MSS bytes. * * Unfortunately, the recommended algorithm breaks header prediction, * since header prediction assumes th->window stays fixed. * * Strictly speaking, keeping th->window fixed violates the receiver * side SWS prevention criteria. The problem is that under this rule * a stream of single byte packets will cause the right side of the * window to always advance by a single byte. * * Of course, if the sender implements sender side SWS prevention * then this will not be a problem. * * BSD seems to make the following compromise: * * If the free space is less than the 1/4 of the maximum * space available and the free space is less than 1/2 mss, * then set the window to 0. * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] * Otherwise, just prevent the window from shrinking * and from being larger than the largest representable value. * * This prevents incremental opening of the window in the regime * where TCP is limited by the speed of the reader side taking * data out of the TCP receive queue. It does nothing about * those cases where the window is constrained on the sender side * because the pipeline is full. * * BSD also seems to "accidentally" limit itself to windows that are a * multiple of MSS, at least until the free space gets quite small. * This would appear to be a side effect of the mbuf implementation. * Combining these two algorithms results in the observed behavior * of having a fixed window size at almost all times. * * Below we obtain similar behavior by forcing the offered window to * a multiple of the mss when it is feasible to do so. * * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. * Regular options like TIMESTAMP are taken into account. */ u32 __tcp_select_window(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); /* MSS for the peer's data. Previous versions used mss_clamp * here. I don't know if the value based on our guesses * of peer's MSS is better for the performance. It's more correct * but may be worse for the performance because of rcv_mss * fluctuations. --SAW 1998/11/1 */ int mss = icsk->icsk_ack.rcv_mss; int free_space = tcp_space(sk); int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk)); int window; if (mss > full_space) mss = full_space; if (free_space < (full_space >> 1)) { icsk->icsk_ack.quick = 0; if (tcp_memory_pressure) tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); if (free_space < mss) return 0; } if (free_space > tp->rcv_ssthresh) free_space = tp->rcv_ssthresh; /* Don't do rounding if we are using window scaling, since the * scaled window will not line up with the MSS boundary anyway. */ window = tp->rcv_wnd; if (tp->rx_opt.rcv_wscale) { window = free_space; /* Advertise enough space so that it won't get scaled away. * Import case: prevent zero window announcement if * 1<<rcv_wscale > mss. */ if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window) window = (((window >> tp->rx_opt.rcv_wscale) + 1) << tp->rx_opt.rcv_wscale); } else { /* Get the largest window that is a nice multiple of mss. * Window clamp already applied above. * If our current window offering is within 1 mss of the * free space we just keep it. This prevents the divide * and multiply from happening most of the time. * We also don't do any window rounding when the free space * is too small. */ if (window <= free_space - mss || window > free_space) window = (free_space / mss) * mss; else if (mss == full_space && free_space > window + (full_space >> 1)) window = free_space; } return window; } /* Collapses two adjacent SKB's during retransmission. */ static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *next_skb = tcp_write_queue_next(sk, skb); int skb_size, next_skb_size; skb_size = skb->len; next_skb_size = next_skb->len; BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1); tcp_highest_sack_combine(sk, next_skb, skb); tcp_unlink_write_queue(next_skb, sk); skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size), next_skb_size); if (next_skb->ip_summed == CHECKSUM_PARTIAL) skb->ip_summed = CHECKSUM_PARTIAL; if (skb->ip_summed != CHECKSUM_PARTIAL) skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size); /* Update sequence range on original skb. */ TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq; /* Merge over control information. This moves PSH/FIN etc. over */ TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(next_skb)->flags; /* All done, get rid of second SKB and account for it so * packet counting does not break. */ TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS; /* changed transmit queue under us so clear hints */ tcp_clear_retrans_hints_partial(tp); if (next_skb == tp->retransmit_skb_hint) tp->retransmit_skb_hint = skb; tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb)); sk_wmem_free_skb(sk, next_skb); } /* Check if coalescing SKBs is legal. */ static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb) { if (tcp_skb_pcount(skb) > 1) return 0; /* TODO: SACK collapsing could be used to remove this condition */ if (skb_shinfo(skb)->nr_frags != 0) return 0; if (skb_cloned(skb)) return 0; if (skb == tcp_send_head(sk)) return 0; /* Some heurestics for collapsing over SACK'd could be invented */ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) return 0; return 1; } /* Collapse packets in the retransmit queue to make to create * less packets on the wire. This is only done on retransmission. */ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, int space) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb = to, *tmp; int first = 1; if (!sysctl_tcp_retrans_collapse) return; if (TCP_SKB_CB(skb)->flags & TCPHDR_SYN) return; tcp_for_write_queue_from_safe(skb, tmp, sk) { if (!tcp_can_collapse(sk, skb)) break; space -= skb->len; if (first) { first = 0; continue; } if (space < 0) break; /* Punt if not enough space exists in the first SKB for * the data in the second */ if (skb->len > skb_tailroom(to)) break; if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp))) break; tcp_collapse_retrans(sk, to); } } /* This retransmits one SKB. Policy decisions and retransmit queue * state updates are done by the caller. Returns non-zero if an * error occurred which prevented the send. */ int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); unsigned int cur_mss; int err; /* Inconslusive MTU probe */ if (icsk->icsk_mtup.probe_size) { icsk->icsk_mtup.probe_size = 0; } /* Do not sent more than we queued. 1/4 is reserved for possible * copying overhead: fragmentation, tunneling, mangling etc. */ if (atomic_read(&sk->sk_wmem_alloc) > min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf)) return -EAGAIN; if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) BUG(); if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) return -ENOMEM; } if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) return -EHOSTUNREACH; /* Routing failure or similar. */ cur_mss = tcp_current_mss(sk); /* If receiver has shrunk his window, and skb is out of * new window, do not retransmit it. The exception is the * case, when window is shrunk to zero. In this case * our retransmit serves as a zero window probe. */ if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) && TCP_SKB_CB(skb)->seq != tp->snd_una) return -EAGAIN; if (skb->len > cur_mss) { if (tcp_fragment(sk, skb, cur_mss, cur_mss)) return -ENOMEM; /* We'll try again later. */ } else { int oldpcount = tcp_skb_pcount(skb); if (unlikely(oldpcount > 1)) { tcp_init_tso_segs(sk, skb, cur_mss); tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb)); } } tcp_retrans_try_collapse(sk, skb, cur_mss); /* Some Solaris stacks overoptimize and ignore the FIN on a * retransmit when old data is attached. So strip it off * since it is cheap to do so and saves bytes on the network. */ if (skb->len > 0 && (TCP_SKB_CB(skb)->flags & TCPHDR_FIN) && tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) { if (!pskb_trim(skb, 0)) { /* Reuse, even though it does some unnecessary work */ tcp_init_nondata_skb(skb, TCP_SKB_CB(skb)->end_seq - 1, TCP_SKB_CB(skb)->flags); skb->ip_summed = CHECKSUM_NONE; } } /* Make a copy, if the first transmission SKB clone we made * is still in somebody's hands, else make a clone. */ TCP_SKB_CB(skb)->when = tcp_time_stamp; err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); if (err == 0) { /* Update global TCP statistics. */ TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS); tp->total_retrans++; #if FASTRETRANS_DEBUG > 0 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { if (net_ratelimit()) printk(KERN_DEBUG "retrans_out leaked.\n"); } #endif if (!tp->retrans_out) tp->lost_retrans_low = tp->snd_nxt; TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; tp->retrans_out += tcp_skb_pcount(skb); /* Save stamp of the first retransmit. */ if (!tp->retrans_stamp) tp->retrans_stamp = TCP_SKB_CB(skb)->when; tp->undo_retrans++; /* snd_nxt is stored to detect loss of retransmitted segment, * see tcp_input.c tcp_sacktag_write_queue(). */ TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt; } return err; } /* Check if we forward retransmits are possible in the current * window/congestion state. */ static int tcp_can_forward_retransmit(struct sock *sk) { const struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); /* Forward retransmissions are possible only during Recovery. */ if (icsk->icsk_ca_state != TCP_CA_Recovery) return 0; /* No forward retransmissions in Reno are possible. */ if (tcp_is_reno(tp)) return 0; /* Yeah, we have to make difficult choice between forward transmission * and retransmission... Both ways have their merits... * * For now we do not retransmit anything, while we have some new * segments to send. In the other cases, follow rule 3 for * NextSeg() specified in RFC3517. */ if (tcp_may_send_now(sk)) return 0; return 1; } /* This gets called after a retransmit timeout, and the initially * retransmitted data is acknowledged. It tries to continue * resending the rest of the retransmit queue, until either * we've sent it all or the congestion window limit is reached. * If doing SACK, the first ACK which comes back for a timeout * based retransmit packet might feed us FACK information again. * If so, we use it to avoid unnecessarily retransmissions. */ void tcp_xmit_retransmit_queue(struct sock *sk) { const struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; struct sk_buff *hole = NULL; u32 last_lost; int mib_idx; int fwd_rexmitting = 0; if (!tp->packets_out) return; if (!tp->lost_out) tp->retransmit_high = tp->snd_una; if (tp->retransmit_skb_hint) { skb = tp->retransmit_skb_hint; last_lost = TCP_SKB_CB(skb)->end_seq; if (after(last_lost, tp->retransmit_high)) last_lost = tp->retransmit_high; } else { skb = tcp_write_queue_head(sk); last_lost = tp->snd_una; } tcp_for_write_queue_from(skb, sk) { __u8 sacked = TCP_SKB_CB(skb)->sacked; if (skb == tcp_send_head(sk)) break; /* we could do better than to assign each time */ if (hole == NULL) tp->retransmit_skb_hint = skb; /* Assume this retransmit will generate * only one packet for congestion window * calculation purposes. This works because * tcp_retransmit_skb() will chop up the * packet to be MSS sized and all the * packet counting works out. */ if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) return; if (fwd_rexmitting) { begin_fwd: if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp))) break; mib_idx = LINUX_MIB_TCPFORWARDRETRANS; } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) { tp->retransmit_high = last_lost; if (!tcp_can_forward_retransmit(sk)) break; /* Backtrack if necessary to non-L'ed skb */ if (hole != NULL) { skb = hole; hole = NULL; } fwd_rexmitting = 1; goto begin_fwd; } else if (!(sacked & TCPCB_LOST)) { if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED))) hole = skb; continue; } else { last_lost = TCP_SKB_CB(skb)->end_seq; if (icsk->icsk_ca_state != TCP_CA_Loss) mib_idx = LINUX_MIB_TCPFASTRETRANS; else mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS; } if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS)) continue; if (tcp_retransmit_skb(sk, skb)) return; NET_INC_STATS_BH(sock_net(sk), mib_idx); if (skb == tcp_write_queue_head(sk)) inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); } } /* Send a fin. The caller locks the socket for us. 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 = tcp_write_queue_tail(sk); int mss_now; /* Optimization, tack on the FIN if we have a queue of * unsent frames. But be careful about outgoing SACKS * and IP options. */ mss_now = tcp_current_mss(sk); if (tcp_send_head(sk) != NULL) { TCP_SKB_CB(skb)->flags |= TCPHDR_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, sk->sk_allocation); if (skb) break; yield(); } /* Reserve space for headers and prepare control bits. */ skb_reserve(skb, MAX_TCP_HEADER); /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ tcp_init_nondata_skb(skb, tp->write_seq, TCPHDR_ACK | TCPHDR_FIN); tcp_queue_skb(sk, skb); } __tcp_push_pending_frames(sk, 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 RFC 2525, section 2.17. -DaveM */ void tcp_send_active_reset(struct sock *sk, gfp_t priority) { struct sk_buff *skb; /* NOTE: No TCP options attached and we never retransmit this. */ skb = alloc_skb(MAX_TCP_HEADER, priority); if (!skb) { NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); return; } /* Reserve space for headers and prepare control bits. */ skb_reserve(skb, MAX_TCP_HEADER); tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk), TCPHDR_ACK | TCPHDR_RST); /* Send it off. */ TCP_SKB_CB(skb)->when = tcp_time_stamp; if (tcp_transmit_skb(sk, skb, 0, priority)) NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); } /* Send a crossed SYN-ACK during socket establishment. * WARNING: This routine must only be called when we have already sent * a SYN packet that crossed the incoming SYN that caused this routine * to get called. If this assumption fails then the initial rcv_wnd * and rcv_wscale values will not be correct. */ int tcp_send_synack(struct sock *sk) { struct sk_buff *skb; skb = tcp_write_queue_head(sk); if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPHDR_SYN)) { printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n"); return -EFAULT; } if (!(TCP_SKB_CB(skb)->flags & TCPHDR_ACK)) { if (skb_cloned(skb)) { struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC); if (nskb == NULL) return -ENOMEM; tcp_unlink_write_queue(skb, sk); skb_header_release(nskb); __tcp_add_write_queue_head(sk, nskb); sk_wmem_free_skb(sk, skb); sk->sk_wmem_queued += nskb->truesize; sk_mem_charge(sk, nskb->truesize); skb = nskb; } TCP_SKB_CB(skb)->flags |= TCPHDR_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 request_values *rvp) { struct tcp_out_options opts; struct tcp_extend_values *xvp = tcp_xv(rvp); struct inet_request_sock *ireq = inet_rsk(req); struct tcp_sock *tp = tcp_sk(sk); const struct tcp_cookie_values *cvp = tp->cookie_values; struct tcphdr *th; struct sk_buff *skb; struct tcp_md5sig_key *md5; int tcp_header_size; int mss; int s_data_desired = 0; if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired) s_data_desired = cvp->s_data_desired; skb = sock_wmalloc(sk, MAX_TCP_HEADER + 15 + s_data_desired, 1, GFP_ATOMIC); if (skb == NULL) return NULL; /* Reserve space for headers. */ skb_reserve(skb, MAX_TCP_HEADER); skb_dst_set(skb, dst_clone(dst)); mss = dst_metric_advmss(dst); if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss) mss = tp->rx_opt.user_mss; if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */ __u8 rcv_wscale; /* Set this up on the first call only */ req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW); /* limit the window selection if the user enforce a smaller rx buffer */ if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && (req->window_clamp > tcp_full_space(sk) || req->window_clamp == 0)) req->window_clamp = tcp_full_space(sk); /* tcp_full_space because it is guaranteed to be the first packet */ tcp_select_initial_window(tcp_full_space(sk), mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), &req->rcv_wnd, &req->window_clamp, ireq->wscale_ok, &rcv_wscale, dst_metric(dst, RTAX_INITRWND)); ireq->rcv_wscale = rcv_wscale; } memset(&opts, 0, sizeof(opts)); #ifdef CONFIG_SYN_COOKIES if (unlikely(req->cookie_ts)) TCP_SKB_CB(skb)->when = cookie_init_timestamp(req); else #endif TCP_SKB_CB(skb)->when = tcp_time_stamp; tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, &md5, xvp) + sizeof(*th); skb_push(skb, tcp_header_size); skb_reset_transport_header(skb); th = tcp_hdr(skb); memset(th, 0, sizeof(struct tcphdr)); th->syn = 1; th->ack = 1; TCP_ECN_make_synack(req, th); th->source = ireq->loc_port; th->dest = ireq->rmt_port; /* Setting of flags are superfluous here for callers (and ECE is * not even correctly set) */ tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn, TCPHDR_SYN | TCPHDR_ACK); if (OPTION_COOKIE_EXTENSION & opts.options) { if (s_data_desired) { u8 *buf = skb_put(skb, s_data_desired); /* copy data directly from the listening socket. */ memcpy(buf, cvp->s_data_payload, s_data_desired); TCP_SKB_CB(skb)->end_seq += s_data_desired; } if (opts.hash_size > 0) { __u32 workspace[SHA_WORKSPACE_WORDS]; u32 *mess = &xvp->cookie_bakery[COOKIE_DIGEST_WORDS]; u32 *tail = &mess[COOKIE_MESSAGE_WORDS-1]; /* Secret recipe depends on the Timestamp, (future) * Sequence and Acknowledgment Numbers, Initiator * Cookie, and others handled by IP variant caller. */ *tail-- ^= opts.tsval; *tail-- ^= tcp_rsk(req)->rcv_isn + 1; *tail-- ^= TCP_SKB_CB(skb)->seq + 1; /* recommended */ *tail-- ^= (((__force u32)th->dest << 16) | (__force u32)th->source); *tail-- ^= (u32)(unsigned long)cvp; /* per sockopt */ sha_transform((__u32 *)&xvp->cookie_bakery[0], (char *)mess, &workspace[0]); opts.hash_location = (__u8 *)&xvp->cookie_bakery[0]; } } th->seq = htonl(TCP_SKB_CB(skb)->seq); th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1); /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */ th->window = htons(min(req->rcv_wnd, 65535U)); tcp_options_write((__be32 *)(th + 1), tp, &opts); th->doff = (tcp_header_size >> 2); TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, tcp_skb_pcount(skb)); #ifdef CONFIG_TCP_MD5SIG /* Okay, we have all we need - do the md5 hash if needed */ if (md5) { tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location, md5, NULL, req, skb); } #endif return skb; } EXPORT_SYMBOL(tcp_make_synack); /* Do all connect socket setups that can be done AF independent. */ static void tcp_connect_init(struct sock *sk) { struct dst_entry *dst = __sk_dst_get(sk); struct tcp_sock *tp = tcp_sk(sk); __u8 rcv_wscale; /* We'll fix this up when we get a response from the other end. * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. */ tp->tcp_header_len = sizeof(struct tcphdr) + (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0); #ifdef CONFIG_TCP_MD5SIG if (tp->af_specific->md5_lookup(sk, sk) != NULL) tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; #endif /* If user gave his TCP_MAXSEG, record it to clamp */ if (tp->rx_opt.user_mss) tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; tp->max_window = 0; tcp_mtup_init(sk); tcp_sync_mss(sk, dst_mtu(dst)); if (!tp->window_clamp) tp->window_clamp = dst_metric(dst, RTAX_WINDOW); tp->advmss = dst_metric_advmss(dst); if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss) tp->advmss = tp->rx_opt.user_mss; tcp_initialize_rcv_mss(sk); /* limit the window selection if the user enforce a smaller rx buffer */ if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0)) tp->window_clamp = tcp_full_space(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, dst_metric(dst, RTAX_INITRWND)); tp->rx_opt.rcv_wscale = rcv_wscale; tp->rcv_ssthresh = tp->rcv_wnd; sk->sk_err = 0; sock_reset_flag(sk, SOCK_DONE); tp->snd_wnd = 0; tcp_init_wl(tp, 0); tp->snd_una = tp->write_seq; tp->snd_sml = tp->write_seq; tp->snd_up = tp->write_seq; tp->rcv_nxt = 0; tp->rcv_wup = 0; tp->copied_seq = 0; inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; inet_csk(sk)->icsk_retransmits = 0; tcp_clear_retrans(tp); } /* Build a SYN and send it off. */ int tcp_connect(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *buff; int err; 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); tp->snd_nxt = tp->write_seq; tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN); TCP_ECN_send_syn(sk, buff); /* Send it off. */ TCP_SKB_CB(buff)->when = tcp_time_stamp; tp->retrans_stamp = TCP_SKB_CB(buff)->when; skb_header_release(buff); __tcp_add_write_queue_tail(sk, buff); sk->sk_wmem_queued += buff->truesize; sk_mem_charge(sk, buff->truesize); tp->packets_out += tcp_skb_pcount(buff); err = tcp_transmit_skb(sk, buff, 1, sk->sk_allocation); if (err == -ECONNREFUSED) return err; /* We change tp->snd_nxt after the tcp_transmit_skb() call * in order to make this packet get counted in tcpOutSegs. */ tp->snd_nxt = tp->write_seq; tp->pushed_seq = tp->write_seq; TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS); /* Timer for repeating the SYN until an answer. */ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX); return 0; } EXPORT_SYMBOL(tcp_connect); /* Send out a delayed ack, the caller does the policy checking * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() * for details. */ void tcp_send_delayed_ack(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); int ato = icsk->icsk_ack.ato; unsigned long timeout; if (ato > TCP_DELACK_MIN) { const struct tcp_sock *tp = tcp_sk(sk); int max_ato = HZ / 2; if (icsk->icsk_ack.pingpong || (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) max_ato = TCP_DELACK_MAX; /* Slow path, intersegment interval is "high". */ /* If some rtt estimate is known, use it to bound delayed ack. * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements * directly. */ if (tp->srtt) { int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN); if (rtt < max_ato) max_ato = rtt; } ato = min(ato, max_ato); } /* Stay within the limit we were given */ timeout = jiffies + ato; /* Use new timeout only if there wasn't a older one earlier. */ if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { /* If delack timer was blocked or is about to expire, * send ACK now. */ if (icsk->icsk_ack.blocked || time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { tcp_send_ack(sk); return; } if (!time_before(timeout, icsk->icsk_ack.timeout)) timeout = icsk->icsk_ack.timeout; } icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; icsk->icsk_ack.timeout = timeout; sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); } /* This routine sends an ack and also updates the window. */ void tcp_send_ack(struct sock *sk) { struct sk_buff *buff; /* If we have been reset, we may not send again. */ if (sk->sk_state == TCP_CLOSE) return; /* We are not putting this on the write queue, so * tcp_transmit_skb() will set the ownership to this * sock. */ buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); if (buff == NULL) { inet_csk_schedule_ack(sk); inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN; inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, TCP_DELACK_MAX, TCP_RTO_MAX); return; } /* Reserve space for headers and prepare control bits. */ skb_reserve(buff, MAX_TCP_HEADER); tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK); /* Send it off, this clears delayed acks for us. */ TCP_SKB_CB(buff)->when = tcp_time_stamp; tcp_transmit_skb(sk, buff, 0, GFP_ATOMIC); } /* This routine sends a packet with an out of date sequence * number. It assumes the other end will try to ack it. * * Question: what should we make while urgent mode? * 4.4BSD forces sending single byte of data. We cannot send * out of window data, because we have SND.NXT==SND.MAX... * * Current solution: to send TWO zero-length segments in urgent mode: * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is * out-of-date with SND.UNA-1 to probe window. */ static int tcp_xmit_probe_skb(struct sock *sk, int urgent) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; /* We don't queue it, tcp_transmit_skb() sets ownership. */ skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); if (skb == NULL) return -1; /* Reserve space for headers and set control bits. */ skb_reserve(skb, MAX_TCP_HEADER); /* Use a previous sequence. This should cause the other * end to send an ack. Don't queue or clone SKB, just * send it. */ tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK); TCP_SKB_CB(skb)->when = tcp_time_stamp; return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC); } /* Initiate keepalive or window probe from timer. */ int tcp_write_wakeup(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; if (sk->sk_state == TCP_CLOSE) return -1; if ((skb = tcp_send_head(sk)) != NULL && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) { int err; unsigned int mss = tcp_current_mss(sk); unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq)) tp->pushed_seq = TCP_SKB_CB(skb)->end_seq; /* We are probing the opening of a window * but the window size is != 0 * must have been a result SWS avoidance ( sender ) */ if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq || skb->len > mss) { seg_size = min(seg_size, mss); TCP_SKB_CB(skb)->flags |= TCPHDR_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 |= TCPHDR_PSH; TCP_SKB_CB(skb)->when = tcp_time_stamp; err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); if (!err) tcp_event_new_data_sent(sk, skb); return err; } else { if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF)) tcp_xmit_probe_skb(sk, 1); return tcp_xmit_probe_skb(sk, 0); } } /* A window probe timeout has occurred. If window is not closed send * a partial packet else a zero probe. */ void tcp_send_probe0(struct sock *sk) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); int err; err = tcp_write_wakeup(sk); if (tp->packets_out || !tcp_send_head(sk)) { /* Cancel probe timer, if it is not required. */ icsk->icsk_probes_out = 0; icsk->icsk_backoff = 0; return; } if (err <= 0) { if (icsk->icsk_backoff < sysctl_tcp_retries2) icsk->icsk_backoff++; icsk->icsk_probes_out++; inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX), TCP_RTO_MAX); } else { /* If packet was not sent due to local congestion, * do not backoff and do not remember icsk_probes_out. * Let local senders to fight for local resources. * * Use accumulated backoff yet. */ if (!icsk->icsk_probes_out) icsk->icsk_probes_out = 1; inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RESOURCE_PROBE_INTERVAL), TCP_RTO_MAX); } }