tcp_output.c 74.1 KB
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/*
 * 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).
 *
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 * Authors:	Ross Biro
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 *		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/module.h>

/* People can turn this off for buggy TCP's found in printers etc. */
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int sysctl_tcp_retrans_collapse __read_mostly = 1;
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/* People can turn this on to work with those rare, broken TCPs that
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 * interpret the window field as a signed quantity.
 */
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int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
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/* 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.
 */
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int sysctl_tcp_tso_win_divisor __read_mostly = 3;
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int sysctl_tcp_mtu_probing __read_mostly = 0;
int sysctl_tcp_base_mss __read_mostly = 512;
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/* By default, RFC2861 behavior.  */
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int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
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static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	unsigned int prior_packets = tp->packets_out;
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	tcp_advance_send_head(sk, skb);
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	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
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	/* Don't override Nagle indefinately with F-RTO */
	if (tp->frto_counter == 2)
		tp->frto_counter = 3;
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	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);
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}

/* 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:
 */
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static inline __u32 tcp_acceptable_seq(struct sock *sk)
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{
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	struct tcp_sock *tp = tcp_sk(sk);

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	if (!before(tcp_wnd_end(tp), tp->snd_nxt))
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		return tp->snd_nxt;
	else
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		return tcp_wnd_end(tp);
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}

/* 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. */
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static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	s32 delta = tcp_time_stamp - tp->lsndtime;
	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
	u32 cwnd = tp->snd_cwnd;

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

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	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
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		cwnd >>= 1;
	tp->snd_cwnd = max(cwnd, restart_cwnd);
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->snd_cwnd_used = 0;
}

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static void tcp_event_data_sent(struct tcp_sock *tp,
				struct sk_buff *skb, struct sock *sk)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
	const u32 now = tcp_time_stamp;
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	if (sysctl_tcp_slow_start_after_idle &&
	    (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
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		tcp_cwnd_restart(sk, __sk_dst_get(sk));
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	tp->lsndtime = now;

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

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static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
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{
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	tcp_dec_quickack_mode(sk, pkts);
	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
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}

/* 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
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	 * 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.
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	 */
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	if (sysctl_tcp_workaround_signed_windows)
		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
	else
		(*rcv_wnd) = space;

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	(*rcv_wscale) = 0;
	if (wscale_ok) {
		/* Set window scaling on max possible window
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		 * See RFC1323 for an explanation of the limit to 14
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		 */
		space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
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		space = min_t(u32, space, *window_clamp);
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		while (space > 65535 && (*rcv_wscale) < 14) {
			space >>= 1;
			(*rcv_wscale)++;
		}
	}

	/* Set initial window to value enough for senders,
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	 * following RFC2414. Senders, not following this RFC,
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	 * will be satisfied with 2.
	 */
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	if (mss > (1 << *rcv_wscale)) {
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		int init_cwnd = 4;
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		if (mss > 1460 * 3)
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			init_cwnd = 2;
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		else if (mss > 1460)
			init_cwnd = 3;
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		if (*rcv_wnd > init_cwnd * mss)
			*rcv_wnd = init_cwnd * mss;
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	}

	/* 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.
 */
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static u16 tcp_select_window(struct sock *sk)
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{
	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 */
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	if (new_win < cur_win) {
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		/* 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.
		 */
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		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
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	}
	tp->rcv_wnd = new_win;
	tp->rcv_wup = tp->rcv_nxt;

	/* Make sure we do not exceed the maximum possible
	 * scaled window.
	 */
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	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
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		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;
}

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static inline void TCP_ECN_send_synack(struct tcp_sock *tp, struct sk_buff *skb)
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{
	TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_CWR;
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	if (!(tp->ecn_flags & TCP_ECN_OK))
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		TCP_SKB_CB(skb)->flags &= ~TCPCB_FLAG_ECE;
}

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) {
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		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ECE | TCPCB_FLAG_CWR;
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		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;
}

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);
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			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
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				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;
	}
}

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/* 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->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 & (TCPCB_FLAG_SYN | TCPCB_FLAG_FIN))
		seq++;
	TCP_SKB_CB(skb)->end_seq = seq;
}

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static inline int tcp_urg_mode(const struct tcp_sock *tp)
{
	return tp->snd_una != tp->snd_up;
}

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#define OPTION_SACK_ADVERTISE	(1 << 0)
#define OPTION_TS		(1 << 1)
#define OPTION_MD5		(1 << 2)

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 */
	u16 mss;		/* 0 to disable */
	__u32 tsval, tsecr;	/* need to include OPTION_TS */
};

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/* 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).
 */
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static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
			      const struct tcp_out_options *opts,
			      __u8 **md5_hash) {
	if (unlikely(OPTION_MD5 & opts->options)) {
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		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_NOP << 16) |
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			       (TCPOPT_MD5SIG << 8) |
			       TCPOLEN_MD5SIG);
		*md5_hash = (__u8 *)ptr;
		ptr += 4;
	} else {
		*md5_hash = NULL;
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	}
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	if (unlikely(opts->mss)) {
		*ptr++ = htonl((TCPOPT_MSS << 24) |
			       (TCPOLEN_MSS << 16) |
			       opts->mss);
	}

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	if (likely(OPTION_TS & opts->options)) {
		if (unlikely(OPTION_SACK_ADVERTISE & opts->options)) {
			*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
				       (TCPOLEN_SACK_PERM << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
		} else {
			*ptr++ = htonl((TCPOPT_NOP << 24) |
				       (TCPOPT_NOP << 16) |
				       (TCPOPT_TIMESTAMP << 8) |
				       TCPOLEN_TIMESTAMP);
		}
		*ptr++ = htonl(opts->tsval);
		*ptr++ = htonl(opts->tsecr);
	}

	if (unlikely(OPTION_SACK_ADVERTISE & opts->options &&
		     !(OPTION_TS & opts->options))) {
		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_NOP << 16) |
			       (TCPOPT_SACK_PERM << 8) |
			       TCPOLEN_SACK_PERM);
	}

	if (unlikely(opts->ws)) {
		*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;
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		int this_sack;

		*ptr++ = htonl((TCPOPT_NOP  << 24) |
			       (TCPOPT_NOP  << 16) |
			       (TCPOPT_SACK <<  8) |
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			       (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
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						     TCPOLEN_SACK_PERBLOCK)));
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		for (this_sack = 0; this_sack < opts->num_sack_blocks;
		     ++this_sack) {
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			*ptr++ = htonl(sp[this_sack].start_seq);
			*ptr++ = htonl(sp[this_sack].end_seq);
		}
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		if (tp->rx_opt.dsack) {
			tp->rx_opt.dsack = 0;
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			tp->rx_opt.eff_sacks = tp->rx_opt.num_sacks;
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		}
	}
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}

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);
	unsigned size = 0;

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#ifdef CONFIG_TCP_MD5SIG
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	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
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	}
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#else
	*md5 = NULL;
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#endif
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	/* 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);
	size += 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;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}
	if (likely(sysctl_tcp_window_scaling)) {
		opts->ws = tp->rx_opt.rcv_wscale;
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		if (likely(opts->ws))
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			size += TCPOLEN_WSCALE_ALIGNED;
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	}
	if (likely(sysctl_tcp_sack)) {
		opts->options |= OPTION_SACK_ADVERTISE;
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		if (unlikely(!(OPTION_TS & opts->options)))
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			size += TCPOLEN_SACKPERM_ALIGNED;
	}

	return size;
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}

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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) {
	unsigned size = 0;
	struct inet_request_sock *ireq = inet_rsk(req);
	char doing_ts;

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#ifdef CONFIG_TCP_MD5SIG
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	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
	if (*md5) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
513
	}
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#else
	*md5 = NULL;
516
#endif
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	/* 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. */
	doing_ts = ireq->tstamp_ok && !(*md5 && ireq->sack_ok);

	opts->mss = mss;
	size += TCPOLEN_MSS_ALIGNED;

	if (likely(ireq->wscale_ok)) {
		opts->ws = ireq->rcv_wscale;
529
		if (likely(opts->ws))
530
			size += TCPOLEN_WSCALE_ALIGNED;
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	}
	if (likely(doing_ts)) {
		opts->options |= OPTION_TS;
		opts->tsval = TCP_SKB_CB(skb)->when;
		opts->tsecr = req->ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}
	if (likely(ireq->sack_ok)) {
		opts->options |= OPTION_SACK_ADVERTISE;
		if (unlikely(!doing_ts))
			size += TCPOLEN_SACKPERM_ALIGNED;
	}

	return size;
}

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;

#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;
	}

	if (unlikely(tp->rx_opt.eff_sacks)) {
		const unsigned remaining = MAX_TCP_OPTION_SPACE - size;
		opts->num_sack_blocks =
			min_t(unsigned, tp->rx_opt.eff_sacks,
			      (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
			      TCPOLEN_SACK_PERBLOCK);
		size += TCPOLEN_SACK_BASE_ALIGNED +
			opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
	}

	return size;
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Stephen Hemminger 已提交
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}
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Linus Torvalds 已提交
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/* 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.
 */
595 596
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
			    gfp_t gfp_mask)
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{
598 599 600 601
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct inet_sock *inet;
	struct tcp_sock *tp;
	struct tcp_skb_cb *tcb;
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Adam Langley 已提交
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	struct tcp_out_options opts;
	unsigned tcp_options_size, tcp_header_size;
604 605
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
606 607 608 609 610 611 612 613
	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.
	 */
614
	if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
615 616 617 618 619 620 621 622 623 624
		__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;
	}
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Linus Torvalds 已提交
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626 627 628
	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
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	memset(&opts, 0, sizeof(opts));
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Linus Torvalds 已提交
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	if (unlikely(tcb->flags & TCPCB_FLAG_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);
637

638 639 640
	if (tcp_packets_in_flight(tp) == 0)
		tcp_ca_event(sk, CA_EVENT_TX_START);

641 642
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
643
	skb_set_owner_w(skb, sk);
644 645

	/* Build TCP header and checksum it. */
646
	th = tcp_hdr(skb);
647 648 649 650
	th->source		= inet->sport;
	th->dest		= inet->dport;
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
651
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
652 653 654 655 656 657
					tcb->flags);

	if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
658
		th->window	= htons(min(tp->rcv_wnd, 65535U));
659 660 661 662 663
	} else {
		th->window	= htons(tcp_select_window(sk));
	}
	th->check		= 0;
	th->urg_ptr		= 0;
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Linus Torvalds 已提交
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Ilpo Järvinen 已提交
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	/* The urg_mode check is necessary during a below snd_una win probe */
666 667 668 669 670 671 672 673
	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 = 0xFFFF;
			th->urg = 1;
		}
674
	}
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Linus Torvalds 已提交
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Adam Langley 已提交
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	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
	if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
678
		TCP_ECN_send(sk, skb, tcp_header_size);
L
Linus Torvalds 已提交
679

680 681 682
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
A
Adam Langley 已提交
683
		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
684
		tp->af_specific->calc_md5_hash(md5_hash_location,
685
					       md5, sk, NULL, skb);
686 687 688
	}
#endif

689
	icsk->icsk_af_ops->send_check(sk, skb->len, skb);
L
Linus Torvalds 已提交
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691 692
	if (likely(tcb->flags & TCPCB_FLAG_ACK))
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
693

694 695
	if (skb->len != tcp_header_size)
		tcp_event_data_sent(tp, skb, sk);
L
Linus Torvalds 已提交
696

697
	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
P
Pavel Emelyanov 已提交
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		TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
L
Linus Torvalds 已提交
699

700
	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
701
	if (likely(err <= 0))
702 703
		return err;

704
	tcp_enter_cwr(sk, 1);
705

706
	return net_xmit_eval(err);
L
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}

709
/* This routine just queue's the buffer
L
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 *
 * 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);
721
	tcp_add_write_queue_tail(sk, skb);
722 723
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
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Linus Torvalds 已提交
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}

726 727
static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,
				 unsigned int mss_now)
728
{
729
	if (skb->len <= mss_now || !sk_can_gso(sk)) {
730 731 732
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
733 734 735
		skb_shinfo(skb)->gso_segs = 1;
		skb_shinfo(skb)->gso_size = 0;
		skb_shinfo(skb)->gso_type = 0;
736
	} else {
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Ilpo Järvinen 已提交
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		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss_now);
738
		skb_shinfo(skb)->gso_size = mss_now;
739
		skb_shinfo(skb)->gso_type = sk->sk_gso_type;
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Linus Torvalds 已提交
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	}
}

I
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/* When a modification to fackets out becomes necessary, we need to check
744
 * skb is counted to fackets_out or not.
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 */
746
static void tcp_adjust_fackets_out(struct sock *sk, struct sk_buff *skb,
I
Ilpo Järvinen 已提交
747 748
				   int decr)
{
749 750
	struct tcp_sock *tp = tcp_sk(sk);

751
	if (!tp->sacked_out || tcp_is_reno(tp))
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Ilpo Järvinen 已提交
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		return;

754
	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
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Ilpo Järvinen 已提交
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		tp->fackets_out -= decr;
}

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/* 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
760
 * packet to the list.  This won't be called frequently, I hope.
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Linus Torvalds 已提交
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 * Remember, these are still headerless SKBs at this point.
 */
763 764
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
		 unsigned int mss_now)
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Linus Torvalds 已提交
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{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
768
	int nsize, old_factor;
769
	int nlen;
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	u16 flags;

772
	BUG_ON(len > skb->len);
773

L
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	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. */
H
Herbert Xu 已提交
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788 789
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
790 791 792
	nlen = skb->len - len - nsize;
	buff->truesize += nlen;
	skb->truesize -= nlen;
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	/* 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;
801
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
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Linus Torvalds 已提交
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	TCP_SKB_CB(buff)->flags = flags;
803
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
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Linus Torvalds 已提交
804

805
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
806
		/* Copy and checksum data tail into the new buffer. */
807 808
		buff->csum = csum_partial_copy_nocheck(skb->data + len,
						       skb_put(buff, nsize),
L
Linus Torvalds 已提交
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						       nsize, 0);

		skb_trim(skb, len);

		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
	} else {
815
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
816 817 818 819 820 821 822 823 824
		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;
825
	buff->tstamp = skb->tstamp;
L
Linus Torvalds 已提交
826

827 828
	old_factor = tcp_skb_pcount(skb);

L
Linus Torvalds 已提交
829
	/* Fix up tso_factor for both original and new SKB.  */
830 831
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
L
Linus Torvalds 已提交
832

833 834 835
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
836
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
837 838
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
839

840
		tp->packets_out -= diff;
841 842 843 844 845 846

		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;

847
		if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
848
			tp->lost_out -= diff;
849

I
Ilpo Järvinen 已提交
850 851 852 853
		/* Adjust Reno SACK estimate. */
		if (tcp_is_reno(tp) && diff > 0) {
			tcp_dec_pcount_approx_int(&tp->sacked_out, diff);
			tcp_verify_left_out(tp);
854
		}
855
		tcp_adjust_fackets_out(sk, skb, diff);
856 857 858 859 860 861

		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))
			tp->lost_cnt_hint -= diff;
L
Linus Torvalds 已提交
862 863 864
	}

	/* Link BUFF into the send queue. */
865
	skb_header_release(buff);
866
	tcp_insert_write_queue_after(skb, buff, sk);
L
Linus Torvalds 已提交
867 868 869 870 871 872 873 874

	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.
 */
875
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
876 877 878 879 880
{
	int i, k, eat;

	eat = len;
	k = 0;
881
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
L
Linus Torvalds 已提交
882 883 884 885 886 887 888 889 890 891 892 893 894 895 896
		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;

897
	skb_reset_tail_pointer(skb);
L
Linus Torvalds 已提交
898 899 900 901 902 903
	skb->data_len -= len;
	skb->len = skb->data_len;
}

int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
904
	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
L
Linus Torvalds 已提交
905 906
		return -ENOMEM;

907 908
	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
	if (unlikely(len < skb_headlen(skb)))
L
Linus Torvalds 已提交
909
		__skb_pull(skb, len);
910 911
	else
		__pskb_trim_head(skb, len - skb_headlen(skb));
L
Linus Torvalds 已提交
912 913

	TCP_SKB_CB(skb)->seq += len;
914
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
915 916 917

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
918
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
919 920 921 922 923 924
	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)
925
		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
L
Linus Torvalds 已提交
926 927 928 929

	return 0;
}

J
John Heffner 已提交
930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980
/* 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) +
981
			       icsk->icsk_af_ops->net_header_len;
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John Heffner 已提交
982 983 984 985
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
	icsk->icsk_mtup.probe_size = 0;
}

986 987 988 989 990 991 992 993 994
/* Bound MSS / TSO packet size with the half of the window */
static int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
{
	if (tp->max_window && pktsize > (tp->max_window >> 1))
		return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
	else
		return pktsize;
}

L
Linus Torvalds 已提交
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/* 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.
S
Stephen Hemminger 已提交
1001
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
1002 1003
   It also does not include TCP options.

1004
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
1005 1006 1007 1008 1009 1010 1011 1012 1013

   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.

1014 1015
   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
   are READ ONLY outside this function.		--ANK (980731)
L
Linus Torvalds 已提交
1016 1017 1018 1019
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1020
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1021
	int mss_now;
L
Linus Torvalds 已提交
1022

J
John Heffner 已提交
1023 1024
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1025

J
John Heffner 已提交
1026
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1027
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1028 1029

	/* And store cached results */
1030
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1031 1032
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1033
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1034 1035 1036 1037 1038 1039 1040

	return mss_now;
}

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
1041
unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
L
Linus Torvalds 已提交
1042 1043 1044
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
1045 1046 1047
	u32 mss_now;
	u16 xmit_size_goal;
	int doing_tso = 0;
A
Adam Langley 已提交
1048 1049 1050
	unsigned header_len;
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1051 1052 1053

	mss_now = tp->mss_cache;

1054
	if (large_allowed && sk_can_gso(sk))
1055
		doing_tso = 1;
L
Linus Torvalds 已提交
1056 1057 1058

	if (dst) {
		u32 mtu = dst_mtu(dst);
1059
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1060 1061 1062
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1063 1064 1065 1066 1067 1068 1069 1070 1071 1072
	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;
	}
1073

1074
	xmit_size_goal = mss_now;
L
Linus Torvalds 已提交
1075

1076
	if (doing_tso) {
1077
		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
1078
				  inet_csk(sk)->icsk_af_ops->net_header_len -
1079 1080
				  inet_csk(sk)->icsk_ext_hdr_len -
				  tp->tcp_header_len);
L
Linus Torvalds 已提交
1081

1082
		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
1083
		xmit_size_goal -= (xmit_size_goal % mss_now);
L
Linus Torvalds 已提交
1084
	}
1085
	tp->xmit_size_goal = xmit_size_goal;
L
Linus Torvalds 已提交
1086 1087 1088 1089

	return mss_now;
}

1090
/* Congestion window validation. (RFC2861) */
1091
static void tcp_cwnd_validate(struct sock *sk)
1092
{
1093
	struct tcp_sock *tp = tcp_sk(sk);
1094

1095
	if (tp->packets_out >= tp->snd_cwnd) {
1096 1097 1098 1099 1100 1101 1102 1103
		/* 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;

1104 1105
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1106 1107 1108 1109
			tcp_cwnd_application_limited(sk);
	}
}

1110 1111 1112 1113
/* 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).
1114 1115 1116 1117 1118 1119 1120
 *
 * 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.
1121 1122
 */
static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb,
1123
					unsigned int mss_now, unsigned int cwnd)
1124
{
1125 1126
	struct tcp_sock *tp = tcp_sk(sk);
	u32 needed, window, cwnd_len;
1127

1128
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1129
	cwnd_len = mss_now * cwnd;
1130 1131 1132 1133

	if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
		return cwnd_len;

1134 1135
	needed = min(skb->len, window);

1136
	if (cwnd_len <= needed)
1137 1138 1139
		return cwnd_len;

	return needed - needed % mss_now;
1140 1141 1142 1143 1144
}

/* 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.
 */
1145 1146
static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
					 struct sk_buff *skb)
1147 1148 1149 1150
{
	u32 in_flight, cwnd;

	/* Don't be strict about the congestion window for the final FIN.  */
1151 1152
	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165
		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.
 */
1166 1167
static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
			     unsigned int mss_now)
1168 1169 1170
{
	int tso_segs = tcp_skb_pcount(skb);

1171
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1172
		tcp_set_skb_tso_segs(sk, skb, mss_now);
1173 1174 1175 1176 1177 1178 1179
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}

static inline int tcp_minshall_check(const struct tcp_sock *tp)
{
1180
	return after(tp->snd_sml, tp->snd_una) &&
1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191
		!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,
1192
				  const struct sk_buff *skb,
1193 1194 1195
				  unsigned mss_now, int nonagle)
{
	return (skb->len < mss_now &&
1196 1197
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp))));
1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214
}

/* 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;

1215 1216 1217
	/* Don't use the nagle rule for urgent data (or for the final FIN).
	 * Nagle can be ignored during F-RTO too (see RFC4138).
	 */
I
Ilpo Järvinen 已提交
1218
	if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1219 1220 1221 1222 1223 1224 1225 1226 1227 1228
	    (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? */
1229 1230
static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb,
				   unsigned int cur_mss)
1231 1232 1233 1234 1235 1236
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

	if (skb->len > cur_mss)
		end_seq = TCP_SKB_CB(skb)->seq + cur_mss;

1237
	return !after(end_seq, tcp_wnd_end(tp));
1238 1239
}

1240
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1241 1242 1243 1244 1245 1246 1247 1248 1249
 * 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;

1250
	tcp_init_tso_segs(sk, skb, cur_mss);
1251 1252 1253 1254 1255

	if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
		return 0;

	cwnd_quota = tcp_cwnd_test(tp, skb);
1256
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1257 1258 1259 1260 1261
		cwnd_quota = 0;

	return cwnd_quota;
}

1262
int tcp_may_send_now(struct sock *sk)
1263
{
1264
	struct tcp_sock *tp = tcp_sk(sk);
1265
	struct sk_buff *skb = tcp_send_head(sk);
1266 1267 1268 1269

	return (skb &&
		tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
			     (tcp_skb_is_last(sk, skb) ?
1270
			      tp->nonagle : TCP_NAGLE_PUSH)));
1271 1272 1273 1274 1275 1276 1277 1278 1279
}

/* 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).
 */
1280 1281
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
			unsigned int mss_now)
1282 1283 1284 1285 1286 1287
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
	u16 flags;

	/* All of a TSO frame must be composed of paged data.  */
1288 1289
	if (skb->len != skb->data_len)
		return tcp_fragment(sk, skb, len, mss_now);
1290

1291
	buff = sk_stream_alloc_skb(sk, 0, GFP_ATOMIC);
1292 1293 1294
	if (unlikely(buff == NULL))
		return -ENOMEM;

1295 1296
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1297
	buff->truesize += nlen;
1298 1299 1300 1301 1302 1303 1304 1305 1306
	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;
1307
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
1308 1309 1310 1311 1312
	TCP_SKB_CB(buff)->flags = flags;

	/* This packet was never sent out yet, so no SACK bits. */
	TCP_SKB_CB(buff)->sacked = 0;

1313
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1314 1315 1316
	skb_split(skb, buff, len);

	/* Fix up tso_factor for both original and new SKB.  */
1317 1318
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
1319 1320 1321

	/* Link BUFF into the send queue. */
	skb_header_release(buff);
1322
	tcp_insert_write_queue_after(skb, buff, sk);
1323 1324 1325 1326 1327 1328 1329 1330 1331

	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.
 */
1332
static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1333
{
1334
	struct tcp_sock *tp = tcp_sk(sk);
1335
	const struct inet_connection_sock *icsk = inet_csk(sk);
1336 1337 1338
	u32 send_win, cong_win, limit, in_flight;

	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
J
John Heffner 已提交
1339
		goto send_now;
1340

1341
	if (icsk->icsk_ca_state != TCP_CA_Open)
J
John Heffner 已提交
1342 1343 1344
		goto send_now;

	/* Defer for less than two clock ticks. */
I
Ilpo Järvinen 已提交
1345
	if (tp->tso_deferred &&
1346
	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
J
John Heffner 已提交
1347
		goto send_now;
1348

1349 1350
	in_flight = tcp_packets_in_flight(tp);

1351
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1352

1353
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1354 1355 1356 1357 1358 1359

	/* 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);

1360
	/* If a full-sized TSO skb can be sent, do it. */
1361
	if (limit >= sk->sk_gso_max_size)
J
John Heffner 已提交
1362
		goto send_now;
1363

1364 1365 1366 1367
	/* 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;

1368 1369 1370 1371 1372 1373 1374 1375
	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)
J
John Heffner 已提交
1376
			goto send_now;
1377 1378 1379 1380 1381 1382 1383
	} 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)
J
John Heffner 已提交
1384
			goto send_now;
1385 1386 1387
	}

	/* Ok, it looks like it is advisable to defer.  */
1388
	tp->tso_deferred = 1 | (jiffies << 1);
J
John Heffner 已提交
1389

1390
	return 1;
J
John Heffner 已提交
1391 1392 1393 1394

send_now:
	tp->tso_deferred = 0;
	return 0;
1395 1396
}

J
John Heffner 已提交
1397 1398 1399
/* 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,
1400 1401
 *         -1 otherwise
 */
J
John Heffner 已提交
1402 1403 1404 1405 1406 1407 1408
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;
1409
	int size_needed;
J
John Heffner 已提交
1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425
	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);
1426
	probe_size = 2 * tp->mss_cache;
1427
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
J
John Heffner 已提交
1428 1429 1430 1431 1432 1433
	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? */
1434
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1435 1436
		return -1;

1437 1438
	if (tp->snd_wnd < size_needed)
		return -1;
1439
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1440
		return 0;
J
John Heffner 已提交
1441

1442 1443 1444
	/* 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))
J
John Heffner 已提交
1445 1446 1447 1448 1449 1450 1451 1452
			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;
1453 1454
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1455

1456
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1457 1458 1459 1460 1461 1462

	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;
1463
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1464

1465 1466
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1467
	len = 0;
1468
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1469 1470 1471 1472 1473
		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,
1474 1475
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1476 1477 1478 1479 1480

		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;
1481
			tcp_unlink_write_queue(skb, sk);
1482
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1483 1484
		} else {
			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
1485
						   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
J
John Heffner 已提交
1486 1487
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1488
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1489 1490
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1491 1492 1493 1494 1495 1496 1497 1498
			} else {
				__pskb_trim_head(skb, copy);
				tcp_set_skb_tso_segs(sk, skb, mss_now);
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1499 1500 1501

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1502 1503 1504 1505 1506 1507 1508 1509
	}
	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
1510
		 * effectively two packets. */
J
John Heffner 已提交
1511
		tp->snd_cwnd--;
1512
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
1513 1514

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1515 1516
		tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
		tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
J
John Heffner 已提交
1517 1518 1519 1520 1521 1522 1523

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
1524 1525 1526 1527
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
1528 1529 1530 1531
 * 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.
 *
L
Linus Torvalds 已提交
1532 1533 1534
 * Returns 1, if no segments are in flight and we have queued segments, but
 * cannot send anything now because of SWS or another problem.
 */
1535 1536
static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			  int push_one, gfp_t gfp)
L
Linus Torvalds 已提交
1537 1538
{
	struct tcp_sock *tp = tcp_sk(sk);
1539
	struct sk_buff *skb;
1540 1541
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
1542
	int result;
L
Linus Torvalds 已提交
1543

1544
	sent_pkts = 0;
J
John Heffner 已提交
1545

1546 1547 1548 1549 1550 1551 1552 1553
	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
			return 0;
		} else if (result > 0) {
			sent_pkts = 1;
		}
J
John Heffner 已提交
1554 1555
	}

1556
	while ((skb = tcp_send_head(sk))) {
1557 1558
		unsigned int limit;

1559
		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1560
		BUG_ON(!tso_segs);
1561

1562 1563 1564 1565 1566 1567 1568
		cwnd_quota = tcp_cwnd_test(tp, skb);
		if (!cwnd_quota)
			break;

		if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
			break;

1569 1570 1571 1572 1573 1574
		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 {
1575
			if (!push_one && tcp_tso_should_defer(sk, skb))
1576 1577
				break;
		}
1578

1579
		limit = mss_now;
1580
		if (tso_segs > 1 && !tcp_urg_mode(tp))
1581 1582
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
L
Linus Torvalds 已提交
1583

1584 1585 1586 1587
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			break;

1588
		TCP_SKB_CB(skb)->when = tcp_time_stamp;
1589

1590
		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
1591
			break;
L
Linus Torvalds 已提交
1592

1593 1594 1595
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
1596
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
1597

1598
		tcp_minshall_update(tp, mss_now, skb);
1599
		sent_pkts++;
1600 1601 1602

		if (push_one)
			break;
1603
	}
L
Linus Torvalds 已提交
1604

1605
	if (likely(sent_pkts)) {
1606
		tcp_cwnd_validate(sk);
1607
		return 0;
L
Linus Torvalds 已提交
1608
	}
1609
	return !tp->packets_out && tcp_send_head(sk);
L
Linus Torvalds 已提交
1610 1611
}

1612 1613 1614 1615
/* 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.
 */
1616 1617
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
1618
{
1619
	struct sk_buff *skb = tcp_send_head(sk);
1620

1621 1622 1623 1624 1625 1626 1627 1628 1629 1630
	if (!skb)
		return;

	/* 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;

1631
	if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC))
1632
		tcp_check_probe_timer(sk);
1633 1634
}

1635 1636 1637 1638 1639
/* 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)
{
1640
	struct sk_buff *skb = tcp_send_head(sk);
1641 1642 1643

	BUG_ON(!skb || skb->len < mss_now);

1644
	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
1645 1646
}

L
Linus Torvalds 已提交
1647 1648
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
1649
 *
L
Linus Torvalds 已提交
1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667
 * 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.
1668
 *
L
Linus Torvalds 已提交
1669 1670
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
1671
 *
L
Linus Torvalds 已提交
1672
 * BSD seems to make the following compromise:
1673
 *
L
Linus Torvalds 已提交
1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700
 *	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)
{
1701
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1702
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
1703
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
1704 1705 1706 1707 1708
	 * 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
	 */
1709
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
1710 1711 1712 1713 1714
	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)
1715
		mss = full_space;
L
Linus Torvalds 已提交
1716

1717
	if (free_space < (full_space >> 1)) {
1718
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
1719 1720

		if (tcp_memory_pressure)
1721 1722
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754

		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)
1755
			window = (free_space / mss) * mss;
1756
		else if (mss == full_space &&
1757
			 free_space > window + (full_space >> 1))
1758
			window = free_space;
L
Linus Torvalds 已提交
1759 1760 1761 1762 1763
	}

	return window;
}

1764 1765
/* Collapses two adjacent SKB's during retransmission. */
static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
L
Linus Torvalds 已提交
1766 1767
{
	struct tcp_sock *tp = tcp_sk(sk);
1768
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1769
	int skb_size, next_skb_size;
L
Linus Torvalds 已提交
1770

1771 1772
	skb_size = skb->len;
	next_skb_size = next_skb->len;
L
Linus Torvalds 已提交
1773

1774
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1775

1776
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
1777

1778
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
1779

1780 1781
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
1782

1783 1784
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1785

1786 1787
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
1788

1789 1790
	/* Update sequence range on original skb. */
	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
L
Linus Torvalds 已提交
1791

1792 1793
	/* Merge over control information. This moves PSH/FIN etc. over */
	TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(next_skb)->flags;
1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810

	/* 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;
	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);
	/* Reno case is special. Sigh... */
	if (tcp_is_reno(tp) && tp->sacked_out)
		tcp_dec_pcount_approx(&tp->sacked_out, next_skb);

	tcp_adjust_fackets_out(sk, next_skb, tcp_skb_pcount(next_skb));
	tp->packets_out -= tcp_skb_pcount(next_skb);

	/* changed transmit queue under us so clear hints */
1811 1812 1813
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
1814 1815

	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
1816 1817
}

1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873
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;
}

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 & TCPCB_FLAG_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);
	}
}

L
Linus Torvalds 已提交
1874 1875 1876 1877 1878 1879 1880
/* 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);
J
John Heffner 已提交
1881
	struct inet_connection_sock *icsk = inet_csk(sk);
1882
	unsigned int cur_mss;
L
Linus Torvalds 已提交
1883 1884
	int err;

J
John Heffner 已提交
1885 1886 1887 1888 1889
	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

L
Linus Torvalds 已提交
1890
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
1891
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903
	 */
	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;
	}

1904 1905 1906 1907 1908
	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
		return -EHOSTUNREACH; /* Routing failure or similar. */

	cur_mss = tcp_current_mss(sk, 0);

L
Linus Torvalds 已提交
1909 1910 1911 1912 1913
	/* 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.
	 */
1914
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))
L
Linus Torvalds 已提交
1915 1916 1917 1918
	    && TCP_SKB_CB(skb)->seq != tp->snd_una)
		return -EAGAIN;

	if (skb->len > cur_mss) {
1919
		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
L
Linus Torvalds 已提交
1920
			return -ENOMEM; /* We'll try again later. */
1921 1922
	} else {
		tcp_init_tso_segs(sk, skb, cur_mss);
L
Linus Torvalds 已提交
1923 1924
	}

1925
	tcp_retrans_try_collapse(sk, skb, cur_mss);
L
Linus Torvalds 已提交
1926 1927 1928 1929 1930

	/* 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.
	 */
S
Stephen Hemminger 已提交
1931 1932 1933
	if (skb->len > 0 &&
	    (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
	    tp->snd_una == (TCP_SKB_CB(skb)->end_seq - 1)) {
L
Linus Torvalds 已提交
1934
		if (!pskb_trim(skb, 0)) {
1935 1936 1937
			/* 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);
L
Linus Torvalds 已提交
1938 1939 1940 1941 1942 1943 1944 1945 1946
			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;

1947
	err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
1948 1949 1950

	if (err == 0) {
		/* Update global TCP statistics. */
P
Pavel Emelyanov 已提交
1951
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
L
Linus Torvalds 已提交
1952 1953 1954 1955

		tp->total_retrans++;

#if FASTRETRANS_DEBUG > 0
1956
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1957 1958 1959 1960
			if (net_ratelimit())
				printk(KERN_DEBUG "retrans_out leaked.\n");
		}
#endif
1961 1962
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
L
Linus Torvalds 已提交
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979
		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;
}

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
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;
}

L
Linus Torvalds 已提交
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016
/* 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)
{
2017
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2018 2019
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2020
	struct sk_buff *hole = NULL;
2021
	u32 last_lost;
2022
	int mib_idx;
2023
	int fwd_rexmitting = 0;
2024

2025 2026 2027
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2028
	if (tp->retransmit_skb_hint) {
2029
		skb = tp->retransmit_skb_hint;
2030 2031 2032 2033
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2034
		skb = tcp_write_queue_head(sk);
2035 2036
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2037

2038 2039
	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;
L
Linus Torvalds 已提交
2040

2041 2042 2043
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2044 2045
		if (hole == NULL)
			tp->retransmit_skb_hint = skb;
2046 2047 2048 2049 2050 2051 2052 2053 2054 2055

		/* 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;
L
Linus Torvalds 已提交
2056

2057 2058 2059 2060 2061
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2062

2063
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2064
			tp->retransmit_high = last_lost;
2065 2066 2067 2068 2069 2070 2071 2072 2073
			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;
L
Linus Torvalds 已提交
2074

2075
		} else if (!(sacked & TCPCB_LOST)) {
2076
			if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2077 2078
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2079

2080
		} else {
2081
			last_lost = TCP_SKB_CB(skb)->end_seq;
2082 2083 2084 2085 2086
			if (icsk->icsk_ca_state != TCP_CA_Loss)
				mib_idx = LINUX_MIB_TCPFASTRETRANS;
			else
				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
		}
L
Linus Torvalds 已提交
2087

2088
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2089 2090
			continue;

2091
		if (tcp_retransmit_skb(sk, skb))
2092 2093
			return;
		NET_INC_STATS_BH(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2094

2095
		if (skb == tcp_write_queue_head(sk))
2096 2097 2098
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2099 2100 2101 2102 2103 2104 2105 2106
	}
}

/* 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)
{
2107
	struct tcp_sock *tp = tcp_sk(sk);
2108
	struct sk_buff *skb = tcp_write_queue_tail(sk);
L
Linus Torvalds 已提交
2109
	int mss_now;
2110

L
Linus Torvalds 已提交
2111 2112 2113 2114 2115 2116
	/* 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);

2117
	if (tcp_send_head(sk) != NULL) {
L
Linus Torvalds 已提交
2118 2119 2120 2121 2122 2123
		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 (;;) {
2124
			skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
L
Linus Torvalds 已提交
2125 2126 2127 2128 2129 2130 2131 2132
			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(). */
2133 2134
		tcp_init_nondata_skb(skb, tp->write_seq,
				     TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
L
Linus Torvalds 已提交
2135 2136
		tcp_queue_skb(sk, skb);
	}
2137
	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2138 2139 2140 2141 2142
}

/* 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
2143
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2144
 */
A
Al Viro 已提交
2145
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2146 2147 2148 2149 2150 2151
{
	struct sk_buff *skb;

	/* NOTE: No TCP options attached and we never retransmit this. */
	skb = alloc_skb(MAX_TCP_HEADER, priority);
	if (!skb) {
P
Pavel Emelyanov 已提交
2152
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2153 2154 2155 2156 2157
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2158 2159
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
			     TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
L
Linus Torvalds 已提交
2160 2161
	/* Send it off. */
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2162
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2163
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2164

P
Pavel Emelyanov 已提交
2165
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2166 2167 2168 2169 2170 2171 2172 2173 2174
}

/* 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)
{
2175
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2176

2177
	skb = tcp_write_queue_head(sk);
2178
	if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)) {
L
Linus Torvalds 已提交
2179 2180 2181
		printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
		return -EFAULT;
	}
2182
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_ACK)) {
L
Linus Torvalds 已提交
2183 2184 2185 2186
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
			if (nskb == NULL)
				return -ENOMEM;
2187
			tcp_unlink_write_queue(skb, sk);
L
Linus Torvalds 已提交
2188
			skb_header_release(nskb);
2189
			__tcp_add_write_queue_head(sk, nskb);
2190 2191 2192
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2193 2194 2195 2196 2197 2198 2199
			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;
2200
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2201 2202 2203 2204 2205
}

/*
 * Prepare a SYN-ACK.
 */
2206 2207
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
				struct request_sock *req)
L
Linus Torvalds 已提交
2208
{
2209
	struct inet_request_sock *ireq = inet_rsk(req);
L
Linus Torvalds 已提交
2210 2211 2212
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	int tcp_header_size;
A
Adam Langley 已提交
2213
	struct tcp_out_options opts;
L
Linus Torvalds 已提交
2214
	struct sk_buff *skb;
2215 2216
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
2217
	int mss;
L
Linus Torvalds 已提交
2218 2219 2220 2221 2222 2223 2224 2225 2226 2227

	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);

2228 2229 2230 2231
	mss = dst_metric(dst, RTAX_ADVMSS);
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
		mss = tp->rx_opt.user_mss;

A
Adam Langley 已提交
2232 2233 2234 2235 2236 2237
	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),
2238
			mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
A
Adam Langley 已提交
2239 2240 2241 2242 2243 2244 2245 2246
			&req->rcv_wnd,
			&req->window_clamp,
			ireq->wscale_ok,
			&rcv_wscale);
		ireq->rcv_wscale = rcv_wscale;
	}

	memset(&opts, 0, sizeof(opts));
2247 2248 2249 2250 2251
#ifdef CONFIG_SYN_COOKIES
	if (unlikely(req->cookie_ts))
		TCP_SKB_CB(skb)->when = cookie_init_timestamp(req);
	else
#endif
A
Adam Langley 已提交
2252
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2253
	tcp_header_size = tcp_synack_options(sk, req, mss,
A
Adam Langley 已提交
2254 2255
					     skb, &opts, &md5) +
			  sizeof(struct tcphdr);
2256

2257 2258
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
2259

2260
	th = tcp_hdr(skb);
L
Linus Torvalds 已提交
2261 2262 2263 2264
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
	TCP_ECN_make_synack(req, th);
2265
	th->source = ireq->loc_port;
2266
	th->dest = ireq->rmt_port;
2267 2268 2269 2270 2271
	/* 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,
			     TCPCB_FLAG_SYN | TCPCB_FLAG_ACK);
L
Linus Torvalds 已提交
2272
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2273
	th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
L
Linus Torvalds 已提交
2274 2275

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2276
	th->window = htons(min(req->rcv_wnd, 65535U));
A
Adam Langley 已提交
2277
	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
L
Linus Torvalds 已提交
2278
	th->doff = (tcp_header_size >> 2);
P
Pavel Emelyanov 已提交
2279
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
2280 2281 2282 2283 2284

#ifdef CONFIG_TCP_MD5SIG
	/* Okay, we have all we need - do the md5 hash if needed */
	if (md5) {
		tp->af_specific->calc_md5_hash(md5_hash_location,
2285
					       md5, NULL, req, skb);
2286 2287 2288
	}
#endif

L
Linus Torvalds 已提交
2289 2290 2291
	return skb;
}

2292
/*
L
Linus Torvalds 已提交
2293
 * Do all connect socket setups that can be done AF independent.
2294
 */
S
Stephen Hemminger 已提交
2295
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306
{
	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);

2307 2308 2309 2310 2311
#ifdef CONFIG_TCP_MD5SIG
	if (tp->af_specific->md5_lookup(sk, sk) != NULL)
		tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
#endif

L
Linus Torvalds 已提交
2312 2313 2314 2315
	/* 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;
J
John Heffner 已提交
2316
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
2317 2318 2319 2320 2321
	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);
2322 2323 2324
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
		tp->advmss = tp->rx_opt.user_mss;

L
Linus Torvalds 已提交
2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342
	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;
I
Ilpo Järvinen 已提交
2343
	tp->snd_up = tp->write_seq;
L
Linus Torvalds 已提交
2344 2345 2346 2347
	tp->rcv_nxt = 0;
	tp->rcv_wup = 0;
	tp->copied_seq = 0;

2348 2349
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
2350 2351 2352 2353 2354
	tcp_clear_retrans(tp);
}

/*
 * Build a SYN and send it off.
2355
 */
L
Linus Torvalds 已提交
2356 2357 2358 2359 2360 2361 2362
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;

	tcp_connect_init(sk);

2363
	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
L
Linus Torvalds 已提交
2364 2365 2366 2367 2368 2369
	if (unlikely(buff == NULL))
		return -ENOBUFS;

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

2370
	tp->snd_nxt = tp->write_seq;
2371 2372
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
	TCP_ECN_send_syn(sk, buff);
L
Linus Torvalds 已提交
2373 2374 2375 2376 2377

	/* Send it off. */
	TCP_SKB_CB(buff)->when = tcp_time_stamp;
	tp->retrans_stamp = TCP_SKB_CB(buff)->when;
	skb_header_release(buff);
2378
	__tcp_add_write_queue_tail(sk, buff);
2379 2380
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
L
Linus Torvalds 已提交
2381
	tp->packets_out += tcp_skb_pcount(buff);
2382
	tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
2383 2384 2385 2386 2387 2388

	/* 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;
P
Pavel Emelyanov 已提交
2389
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
2390 2391

	/* Timer for repeating the SYN until an answer. */
2392 2393
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
2394 2395 2396 2397 2398 2399 2400 2401 2402
	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)
{
2403 2404
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
2405 2406 2407
	unsigned long timeout;

	if (ato > TCP_DELACK_MIN) {
2408
		const struct tcp_sock *tp = tcp_sk(sk);
2409
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
2410

2411 2412
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
2413 2414 2415 2416 2417
			max_ato = TCP_DELACK_MAX;

		/* Slow path, intersegment interval is "high". */

		/* If some rtt estimate is known, use it to bound delayed ack.
2418
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
2419 2420 2421
		 * directly.
		 */
		if (tp->srtt) {
2422
			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
L
Linus Torvalds 已提交
2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434

			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. */
2435
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
2436 2437 2438
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
2439 2440
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
2441 2442 2443 2444
			tcp_send_ack(sk);
			return;
		}

2445 2446
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
2447
	}
2448 2449 2450
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
L
Linus Torvalds 已提交
2451 2452 2453 2454 2455
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
2456
	struct sk_buff *buff;
L
Linus Torvalds 已提交
2457

2458 2459 2460
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
L
Linus Torvalds 已提交
2461

2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472
	/* 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;
L
Linus Torvalds 已提交
2473
	}
2474 2475 2476

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
2477
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);
2478 2479 2480 2481

	/* 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);
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}

/* 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);
2502
	if (skb == NULL)
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		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.
	 */
2511
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
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	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2513
	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
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}

int tcp_write_wakeup(struct sock *sk)
{
2518 2519
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
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2521 2522 2523 2524 2525 2526 2527 2528 2529 2530 2531 2532 2533 2534 2535 2536 2537 2538 2539
	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, 0);
		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);
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			TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2541 2542 2543 2544 2545 2546 2547 2548 2549 2550 2551 2552
			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)
			tcp_event_new_data_sent(sk, skb);
		return err;
	} else {
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Ilpo Järvinen 已提交
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		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
2554 2555
			tcp_xmit_probe_skb(sk, 1);
		return tcp_xmit_probe_skb(sk, 0);
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	}
}

/* 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)
{
2564
	struct inet_connection_sock *icsk = inet_csk(sk);
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	struct tcp_sock *tp = tcp_sk(sk);
	int err;

	err = tcp_write_wakeup(sk);

2570
	if (tp->packets_out || !tcp_send_head(sk)) {
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		/* Cancel probe timer, if it is not required. */
2572
		icsk->icsk_probes_out = 0;
2573
		icsk->icsk_backoff = 0;
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		return;
	}

	if (err <= 0) {
2578 2579
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
2580
		icsk->icsk_probes_out++;
2581
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2582 2583
					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
					  TCP_RTO_MAX);
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	} else {
		/* If packet was not sent due to local congestion,
2586
		 * do not backoff and do not remember icsk_probes_out.
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		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
2591 2592
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
2593
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2594
					  min(icsk->icsk_rto << icsk->icsk_backoff,
2595 2596
					      TCP_RESOURCE_PROBE_INTERVAL),
					  TCP_RTO_MAX);
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	}
}

2600
EXPORT_SYMBOL(tcp_select_initial_window);
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EXPORT_SYMBOL(tcp_connect);
EXPORT_SYMBOL(tcp_make_synack);
EXPORT_SYMBOL(tcp_simple_retransmit);
EXPORT_SYMBOL(tcp_sync_mss);
J
John Heffner 已提交
2605
EXPORT_SYMBOL(tcp_mtup_init);