tcp_output.c 74.6 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
 * 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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#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 */
};

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 (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(opts->mss)) {
		*ptr++ = htonl((TCPOPT_MSS << 24) |
			       (TCPOLEN_MSS << 16) |
			       opts->mss);
	}

	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;
			tp->rx_opt.eff_sacks--;
		}
	}
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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;
		size += TCPOLEN_WSCALE_ALIGNED;
	}
	if (likely(sysctl_tcp_sack)) {
		opts->options |= OPTION_SACK_ADVERTISE;
		if (unlikely(!OPTION_TS & opts->options))
			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;
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	}
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#else
	*md5 = NULL;
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#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;
		size += TCPOLEN_WSCALE_ALIGNED;
	}
	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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/* 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.
 */
577 578
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
			    gfp_t gfp_mask)
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{
580 581 582 583
	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;
586 587
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
588 589 590 591 592 593 594 595
	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.
	 */
596
	if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
597 598 599 600 601 602 603 604 605 606
		__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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608 609 610
	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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	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);
619

620 621 622
	if (tcp_packets_in_flight(tp) == 0)
		tcp_ca_event(sk, CA_EVENT_TX_START);

623 624
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
625
	skb_set_owner_w(skb, sk);
626 627

	/* Build TCP header and checksum it. */
628
	th = tcp_hdr(skb);
629 630 631 632
	th->source		= inet->sport;
	th->dest		= inet->dport;
	th->seq			= htonl(tcb->seq);
	th->ack_seq		= htonl(tp->rcv_nxt);
633
	*(((__be16 *)th) + 6)	= htons(((tcp_header_size >> 2) << 12) |
634 635 636 637 638 639
					tcb->flags);

	if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
640
		th->window	= htons(min(tp->rcv_wnd, 65535U));
641 642 643 644 645
	} 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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647
	if (unlikely(tp->urg_mode &&
648 649
		     between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF))) {
		th->urg_ptr		= htons(tp->snd_up - tcb->seq);
650 651
		th->urg			= 1;
	}
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	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
	if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
655
		TCP_ECN_send(sk, skb, tcp_header_size);
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657 658 659
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
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		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
661
		tp->af_specific->calc_md5_hash(md5_hash_location,
662
					       md5, sk, NULL, skb);
663 664 665
	}
#endif

666
	icsk->icsk_af_ops->send_check(sk, skb->len, skb);
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668 669
	if (likely(tcb->flags & TCPCB_FLAG_ACK))
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
670

671 672
	if (skb->len != tcp_header_size)
		tcp_event_data_sent(tp, skb, sk);
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674
	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
676

677
	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
678
	if (likely(err <= 0))
679 680
		return err;

681
	tcp_enter_cwr(sk, 1);
682

683
	return net_xmit_eval(err);
L
Linus Torvalds 已提交
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}

686
/* This routine just queue's the buffer
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687 688 689 690 691 692 693 694 695 696 697
 *
 * 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);
698
	tcp_add_write_queue_tail(sk, skb);
699 700
	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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}

703 704
static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,
				 unsigned int mss_now)
705
{
706
	if (skb->len <= mss_now || !sk_can_gso(sk)) {
707 708 709
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
710 711 712
		skb_shinfo(skb)->gso_segs = 1;
		skb_shinfo(skb)->gso_size = 0;
		skb_shinfo(skb)->gso_type = 0;
713
	} 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);
715
		skb_shinfo(skb)->gso_size = mss_now;
716
		skb_shinfo(skb)->gso_type = sk->sk_gso_type;
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	}
}

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/* When a modification to fackets out becomes necessary, we need to check
721
 * skb is counted to fackets_out or not.
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 */
723
static void tcp_adjust_fackets_out(struct sock *sk, struct sk_buff *skb,
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				   int decr)
{
726 727
	struct tcp_sock *tp = tcp_sk(sk);

728
	if (!tp->sacked_out || tcp_is_reno(tp))
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		return;

731
	if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
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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
737
 * packet to the list.  This won't be called frequently, I hope.
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 * Remember, these are still headerless SKBs at this point.
 */
740 741
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;
745
	int nsize, old_factor;
746
	int nlen;
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	u16 flags;

749
	BUG_ON(len > skb->len);
750

751
	tcp_clear_retrans_hints_partial(tp);
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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. */
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Herbert Xu 已提交
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766 767
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
768 769 770
	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;
779
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
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	TCP_SKB_CB(buff)->flags = flags;
781
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
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782

783
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
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		/* Copy and checksum data tail into the new buffer. */
785 786
		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 {
793
		skb->ip_summed = CHECKSUM_PARTIAL;
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		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;
803
	buff->tstamp = skb->tstamp;
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Linus Torvalds 已提交
804

805 806
	old_factor = tcp_skb_pcount(skb);

L
Linus Torvalds 已提交
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	/* Fix up tso_factor for both original and new SKB.  */
808 809
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
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Linus Torvalds 已提交
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811 812 813
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
814
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
815 816
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
817

818
		tp->packets_out -= diff;
819 820 821 822 823 824

		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;

825
		if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
826
			tp->lost_out -= diff;
827

I
Ilpo Järvinen 已提交
828 829 830 831
		/* 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);
832
		}
833
		tcp_adjust_fackets_out(sk, skb, diff);
L
Linus Torvalds 已提交
834 835 836
	}

	/* Link BUFF into the send queue. */
837
	skb_header_release(buff);
838
	tcp_insert_write_queue_after(skb, buff, sk);
L
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839 840 841 842 843 844 845 846

	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.
 */
847
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
848 849 850 851 852
{
	int i, k, eat;

	eat = len;
	k = 0;
853
	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
L
Linus Torvalds 已提交
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		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;

869
	skb_reset_tail_pointer(skb);
L
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870 871 872 873 874 875
	skb->data_len -= len;
	skb->len = skb->data_len;
}

int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
876
	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
L
Linus Torvalds 已提交
877 878
		return -ENOMEM;

879 880
	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
	if (unlikely(len < skb_headlen(skb)))
L
Linus Torvalds 已提交
881
		__skb_pull(skb, len);
882 883
	else
		__pskb_trim_head(skb, len - skb_headlen(skb));
L
Linus Torvalds 已提交
884 885

	TCP_SKB_CB(skb)->seq += len;
886
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
887 888 889

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
890
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
891 892 893 894 895 896
	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)
897
		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
L
Linus Torvalds 已提交
898 899 900 901

	return 0;
}

J
John Heffner 已提交
902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952
/* 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) +
953
			       icsk->icsk_af_ops->net_header_len;
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	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
	icsk->icsk_mtup.probe_size = 0;
}

958 959 960 961 962 963 964 965 966
/* 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
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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
973
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
974 975
   It also does not include TCP options.

976
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
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977 978 979 980 981 982 983 984 985

   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.

986 987
   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
   are READ ONLY outside this function.		--ANK (980731)
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 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
992
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
993
	int mss_now;
L
Linus Torvalds 已提交
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J
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995 996
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
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J
John Heffner 已提交
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	mss_now = tcp_mtu_to_mss(sk, pmtu);
999
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1000 1001

	/* And store cached results */
1002
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1003 1004
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1005
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016

	return mss_now;
}

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 *
 * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
 * cannot be large. However, taking into account rare use of URG, this
 * is not a big flaw.
 */
1017
unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
L
Linus Torvalds 已提交
1018 1019 1020
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
1021 1022 1023
	u32 mss_now;
	u16 xmit_size_goal;
	int doing_tso = 0;
A
Adam Langley 已提交
1024 1025 1026
	unsigned header_len;
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1027 1028 1029

	mss_now = tp->mss_cache;

1030
	if (large_allowed && sk_can_gso(sk) && !tp->urg_mode)
1031
		doing_tso = 1;
L
Linus Torvalds 已提交
1032 1033 1034

	if (dst) {
		u32 mtu = dst_mtu(dst);
1035
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1036 1037 1038
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1039 1040 1041 1042 1043 1044 1045 1046 1047 1048
	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;
	}
1049

1050
	xmit_size_goal = mss_now;
L
Linus Torvalds 已提交
1051

1052
	if (doing_tso) {
1053
		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
1054
				  inet_csk(sk)->icsk_af_ops->net_header_len -
1055 1056
				  inet_csk(sk)->icsk_ext_hdr_len -
				  tp->tcp_header_len);
L
Linus Torvalds 已提交
1057

1058
		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
1059
		xmit_size_goal -= (xmit_size_goal % mss_now);
L
Linus Torvalds 已提交
1060
	}
1061
	tp->xmit_size_goal = xmit_size_goal;
L
Linus Torvalds 已提交
1062 1063 1064 1065

	return mss_now;
}

1066
/* Congestion window validation. (RFC2861) */
1067
static void tcp_cwnd_validate(struct sock *sk)
1068
{
1069
	struct tcp_sock *tp = tcp_sk(sk);
1070

1071
	if (tp->packets_out >= tp->snd_cwnd) {
1072 1073 1074 1075 1076 1077 1078 1079
		/* 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;

1080 1081
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1082 1083 1084 1085
			tcp_cwnd_application_limited(sk);
	}
}

1086 1087 1088 1089
/* 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).
1090 1091 1092 1093 1094 1095 1096
 *
 * 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.
1097 1098
 */
static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb,
1099
					unsigned int mss_now, unsigned int cwnd)
1100
{
1101 1102
	struct tcp_sock *tp = tcp_sk(sk);
	u32 needed, window, cwnd_len;
1103

1104
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1105
	cwnd_len = mss_now * cwnd;
1106 1107 1108 1109

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

1110 1111
	needed = min(skb->len, window);

1112
	if (cwnd_len <= needed)
1113 1114 1115
		return cwnd_len;

	return needed - needed % mss_now;
1116 1117 1118 1119 1120
}

/* 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.
 */
1121 1122
static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
					 struct sk_buff *skb)
1123 1124 1125 1126
{
	u32 in_flight, cwnd;

	/* Don't be strict about the congestion window for the final FIN.  */
1127 1128
	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141
		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.
 */
1142 1143
static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
			     unsigned int mss_now)
1144 1145 1146
{
	int tso_segs = tcp_skb_pcount(skb);

1147
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1148
		tcp_set_skb_tso_segs(sk, skb, mss_now);
1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}

static inline int tcp_minshall_check(const struct tcp_sock *tp)
{
	return after(tp->snd_sml,tp->snd_una) &&
		!after(tp->snd_sml, tp->snd_nxt);
}

/* Return 0, if packet can be sent now without violation Nagle's rules:
 * 1. It is full sized.
 * 2. Or it contains FIN. (already checked by caller)
 * 3. Or TCP_NODELAY was set.
 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
 *    With Minshall's modification: all sent small packets are ACKed.
 */
static inline int tcp_nagle_check(const struct tcp_sock *tp,
1168
				  const struct sk_buff *skb,
1169 1170 1171
				  unsigned mss_now, int nonagle)
{
	return (skb->len < mss_now &&
1172 1173
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp))));
1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190
}

/* 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;

1191 1192 1193 1194
	/* Don't use the nagle rule for urgent data (or for the final FIN).
	 * Nagle can be ignored during F-RTO too (see RFC4138).
	 */
	if (tp->urg_mode || (tp->frto_counter == 2) ||
1195 1196 1197 1198 1199 1200 1201 1202 1203 1204
	    (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? */
1205 1206
static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb,
				   unsigned int cur_mss)
1207 1208 1209 1210 1211 1212
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

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

1213
	return !after(end_seq, tcp_wnd_end(tp));
1214 1215
}

1216
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1217 1218 1219 1220 1221 1222 1223 1224 1225
 * 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;

1226
	tcp_init_tso_segs(sk, skb, cur_mss);
1227 1228 1229 1230 1231

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

	cwnd_quota = tcp_cwnd_test(tp, skb);
1232
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1233 1234 1235 1236 1237
		cwnd_quota = 0;

	return cwnd_quota;
}

1238
int tcp_may_send_now(struct sock *sk)
1239
{
1240
	struct tcp_sock *tp = tcp_sk(sk);
1241
	struct sk_buff *skb = tcp_send_head(sk);
1242 1243 1244 1245

	return (skb &&
		tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
			     (tcp_skb_is_last(sk, skb) ?
1246
			      tp->nonagle : TCP_NAGLE_PUSH)));
1247 1248 1249 1250 1251 1252 1253 1254 1255
}

/* 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).
 */
1256 1257
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
			unsigned int mss_now)
1258 1259 1260 1261 1262 1263
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
	u16 flags;

	/* All of a TSO frame must be composed of paged data.  */
1264 1265
	if (skb->len != skb->data_len)
		return tcp_fragment(sk, skb, len, mss_now);
1266

1267
	buff = sk_stream_alloc_skb(sk, 0, GFP_ATOMIC);
1268 1269 1270
	if (unlikely(buff == NULL))
		return -ENOMEM;

1271 1272
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1273
	buff->truesize += nlen;
1274 1275 1276 1277 1278 1279 1280 1281 1282
	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;
1283
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
1284 1285 1286 1287 1288
	TCP_SKB_CB(buff)->flags = flags;

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

1289
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1290 1291 1292
	skb_split(skb, buff, len);

	/* Fix up tso_factor for both original and new SKB.  */
1293 1294
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
1295 1296 1297

	/* Link BUFF into the send queue. */
	skb_header_release(buff);
1298
	tcp_insert_write_queue_after(skb, buff, sk);
1299 1300 1301 1302 1303 1304 1305 1306 1307

	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.
 */
1308
static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1309
{
1310
	struct tcp_sock *tp = tcp_sk(sk);
1311
	const struct inet_connection_sock *icsk = inet_csk(sk);
1312 1313 1314
	u32 send_win, cong_win, limit, in_flight;

	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
J
John Heffner 已提交
1315
		goto send_now;
1316

1317
	if (icsk->icsk_ca_state != TCP_CA_Open)
J
John Heffner 已提交
1318 1319 1320
		goto send_now;

	/* Defer for less than two clock ticks. */
I
Ilpo Järvinen 已提交
1321 1322
	if (tp->tso_deferred &&
	    ((jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
J
John Heffner 已提交
1323
		goto send_now;
1324

1325 1326
	in_flight = tcp_packets_in_flight(tp);

1327
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1328

1329
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1330 1331 1332 1333 1334 1335

	/* 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);

1336
	/* If a full-sized TSO skb can be sent, do it. */
1337
	if (limit >= sk->sk_gso_max_size)
J
John Heffner 已提交
1338
		goto send_now;
1339

1340 1341 1342 1343 1344 1345 1346 1347
	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
1348
			goto send_now;
1349 1350 1351 1352 1353 1354 1355
	} 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
1356
			goto send_now;
1357 1358 1359
	}

	/* Ok, it looks like it is advisable to defer.  */
1360
	tp->tso_deferred = 1 | (jiffies << 1);
J
John Heffner 已提交
1361

1362
	return 1;
J
John Heffner 已提交
1363 1364 1365 1366

send_now:
	tp->tso_deferred = 0;
	return 0;
1367 1368
}

J
John Heffner 已提交
1369 1370 1371
/* 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,
1372 1373
 *         -1 otherwise
 */
J
John Heffner 已提交
1374 1375 1376 1377 1378 1379 1380
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;
1381
	int size_needed;
J
John Heffner 已提交
1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397
	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);
1398
	probe_size = 2 * tp->mss_cache;
1399
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
J
John Heffner 已提交
1400 1401 1402 1403 1404 1405
	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? */
1406
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1407 1408
		return -1;

1409 1410
	if (tp->snd_wnd < size_needed)
		return -1;
1411
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1412
		return 0;
J
John Heffner 已提交
1413

1414 1415 1416
	/* 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
1417 1418 1419 1420 1421 1422 1423 1424
			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;
1425 1426
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1427

1428
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1429 1430 1431 1432 1433 1434

	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;
1435
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1436

1437 1438
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1439
	len = 0;
1440
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1441 1442 1443 1444 1445
		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,
1446 1447
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1448 1449 1450 1451 1452

		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;
1453
			tcp_unlink_write_queue(skb, sk);
1454
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1455 1456
		} else {
			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
1457
						   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
J
John Heffner 已提交
1458 1459
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1460
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1461 1462
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1463 1464 1465 1466 1467 1468 1469 1470
			} else {
				__pskb_trim_head(skb, copy);
				tcp_set_skb_tso_segs(sk, skb, mss_now);
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1471 1472 1473

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1474 1475 1476 1477 1478 1479 1480 1481
	}
	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
1482
		 * effectively two packets. */
J
John Heffner 已提交
1483
		tp->snd_cwnd--;
1484
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
1485 1486

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1487 1488
		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
1489 1490 1491 1492 1493 1494 1495

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
1496 1497 1498 1499 1500 1501 1502
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
 * Returns 1, if no segments are in flight and we have queued segments, but
 * cannot send anything now because of SWS or another problem.
 */
1503
static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
L
Linus Torvalds 已提交
1504 1505
{
	struct tcp_sock *tp = tcp_sk(sk);
1506
	struct sk_buff *skb;
1507 1508
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
1509
	int result;
L
Linus Torvalds 已提交
1510 1511 1512 1513 1514

	/* 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.
	 */
1515 1516
	if (unlikely(sk->sk_state == TCP_CLOSE))
		return 0;
L
Linus Torvalds 已提交
1517

1518
	sent_pkts = 0;
J
John Heffner 已提交
1519 1520 1521 1522 1523 1524 1525 1526

	/* Do MTU probing. */
	if ((result = tcp_mtu_probe(sk)) == 0) {
		return 0;
	} else if (result > 0) {
		sent_pkts = 1;
	}

1527
	while ((skb = tcp_send_head(sk))) {
1528 1529
		unsigned int limit;

1530
		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1531
		BUG_ON(!tso_segs);
1532

1533 1534 1535 1536 1537 1538 1539
		cwnd_quota = tcp_cwnd_test(tp, skb);
		if (!cwnd_quota)
			break;

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

1540 1541 1542 1543 1544 1545
		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 {
1546
			if (tcp_tso_should_defer(sk, skb))
1547 1548
				break;
		}
1549

1550
		limit = mss_now;
1551 1552 1553
		if (tso_segs > 1)
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
L
Linus Torvalds 已提交
1554

1555 1556 1557 1558
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			break;

1559
		TCP_SKB_CB(skb)->when = tcp_time_stamp;
1560

1561
		if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC)))
1562
			break;
L
Linus Torvalds 已提交
1563

1564 1565 1566
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
1567
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
1568

1569
		tcp_minshall_update(tp, mss_now, skb);
1570
		sent_pkts++;
1571
	}
L
Linus Torvalds 已提交
1572

1573
	if (likely(sent_pkts)) {
1574
		tcp_cwnd_validate(sk);
1575
		return 0;
L
Linus Torvalds 已提交
1576
	}
1577
	return !tp->packets_out && tcp_send_head(sk);
L
Linus Torvalds 已提交
1578 1579
}

1580 1581 1582 1583
/* 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.
 */
1584 1585
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
1586
{
1587
	struct sk_buff *skb = tcp_send_head(sk);
1588 1589

	if (skb) {
1590
		if (tcp_write_xmit(sk, cur_mss, nonagle))
1591
			tcp_check_probe_timer(sk);
1592 1593 1594
	}
}

1595 1596 1597 1598 1599
/* 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)
{
1600
	struct sk_buff *skb = tcp_send_head(sk);
1601 1602 1603 1604
	unsigned int tso_segs, cwnd_quota;

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

1605
	tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1606 1607 1608
	cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH);

	if (likely(cwnd_quota)) {
1609 1610
		unsigned int limit;

1611 1612
		BUG_ON(!tso_segs);

1613
		limit = mss_now;
1614 1615 1616
		if (tso_segs > 1)
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
1617

1618 1619 1620 1621
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			return;

1622 1623 1624
		/* Send it out now. */
		TCP_SKB_CB(skb)->when = tcp_time_stamp;

1625
		if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) {
1626
			tcp_event_new_data_sent(sk, skb);
1627
			tcp_cwnd_validate(sk);
1628 1629 1630 1631 1632
			return;
		}
	}
}

L
Linus Torvalds 已提交
1633 1634
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
1635
 *
L
Linus Torvalds 已提交
1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653
 * 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.
1654
 *
L
Linus Torvalds 已提交
1655 1656
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
1657
 *
L
Linus Torvalds 已提交
1658
 * BSD seems to make the following compromise:
1659
 *
L
Linus Torvalds 已提交
1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686
 *	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)
{
1687
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1688
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
1689
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
1690 1691 1692 1693 1694
	 * 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
	 */
1695
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
1696 1697 1698 1699 1700
	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)
1701
		mss = full_space;
L
Linus Torvalds 已提交
1702

1703
	if (free_space < (full_space >> 1)) {
1704
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
1705 1706

		if (tcp_memory_pressure)
1707 1708
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740

		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)
1741
			window = (free_space / mss) * mss;
1742
		else if (mss == full_space &&
1743
			 free_space > window + (full_space >> 1))
1744
			window = free_space;
L
Linus Torvalds 已提交
1745 1746 1747 1748 1749 1750
	}

	return window;
}

/* Attempt to collapse two adjacent SKB's during retransmission. */
1751 1752
static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb,
				     int mss_now)
L
Linus Torvalds 已提交
1753 1754
{
	struct tcp_sock *tp = tcp_sk(sk);
1755
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1756 1757
	int skb_size, next_skb_size;
	u16 flags;
L
Linus Torvalds 已提交
1758 1759 1760 1761

	/* The first test we must make is that neither of these two
	 * SKB's are still referenced by someone else.
	 */
1762 1763
	if (skb_cloned(skb) || skb_cloned(next_skb))
		return;
L
Linus Torvalds 已提交
1764

1765 1766 1767
	skb_size = skb->len;
	next_skb_size = next_skb->len;
	flags = TCP_SKB_CB(skb)->flags;
L
Linus Torvalds 已提交
1768

1769 1770 1771
	/* Also punt if next skb has been SACK'd. */
	if (TCP_SKB_CB(next_skb)->sacked & TCPCB_SACKED_ACKED)
		return;
L
Linus Torvalds 已提交
1772

1773 1774 1775
	/* Next skb is out of window. */
	if (after(TCP_SKB_CB(next_skb)->end_seq, tcp_wnd_end(tp)))
		return;
L
Linus Torvalds 已提交
1776

1777 1778 1779 1780 1781 1782 1783
	/* Punt if not enough space exists in the first SKB for
	 * the data in the second, or the total combined payload
	 * would exceed the MSS.
	 */
	if ((next_skb_size > skb_tailroom(skb)) ||
	    ((skb_size + next_skb_size) > mss_now))
		return;
L
Linus Torvalds 已提交
1784

1785
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1786

1787
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
1788

1789 1790
	/* Ok.	We will be able to collapse the packet. */
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
1791

1792 1793
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
1794

1795 1796
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1797

1798 1799
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
1800

1801 1802
	/* 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
1803

1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826
	/* Merge over control information. */
	flags |= TCP_SKB_CB(next_skb)->flags; /* This moves PSH/FIN etc. over */
	TCP_SKB_CB(skb)->flags = flags;

	/* All done, get rid of second SKB and account for it so
	 * packet counting does not break.
	 */
	TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
	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 */
	tcp_clear_retrans_hints_partial(tp);

	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
1827 1828 1829
}

/* Do a simple retransmit without using the backoff mechanisms in
1830
 * tcp_timer. This is used for path mtu discovery.
L
Linus Torvalds 已提交
1831
 * The socket is already locked here.
1832
 */
L
Linus Torvalds 已提交
1833 1834
void tcp_simple_retransmit(struct sock *sk)
{
1835
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1836 1837 1838 1839 1840
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	unsigned int mss = tcp_current_mss(sk, 0);
	int lost = 0;

1841 1842 1843
	tcp_for_write_queue(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;
1844
		if (skb->len > mss &&
1845 1846
		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1847 1848 1849
				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
				tp->retrans_out -= tcp_skb_pcount(skb);
			}
1850
			if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST)) {
L
Linus Torvalds 已提交
1851 1852 1853 1854 1855 1856 1857
				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
				tp->lost_out += tcp_skb_pcount(skb);
				lost = 1;
			}
		}
	}

1858
	tcp_clear_all_retrans_hints(tp);
1859

L
Linus Torvalds 已提交
1860 1861 1862
	if (!lost)
		return;

1863 1864 1865
	if (tcp_is_reno(tp))
		tcp_limit_reno_sacked(tp);

1866
	tcp_verify_left_out(tp);
L
Linus Torvalds 已提交
1867

1868
	/* Don't muck with the congestion window here.
L
Linus Torvalds 已提交
1869 1870 1871 1872
	 * Reason is that we do not increase amount of _data_
	 * in network, but units changed and effective
	 * cwnd/ssthresh really reduced now.
	 */
1873
	if (icsk->icsk_ca_state != TCP_CA_Loss) {
L
Linus Torvalds 已提交
1874
		tp->high_seq = tp->snd_nxt;
1875
		tp->snd_ssthresh = tcp_current_ssthresh(sk);
L
Linus Torvalds 已提交
1876 1877
		tp->prior_ssthresh = 0;
		tp->undo_marker = 0;
1878
		tcp_set_ca_state(sk, TCP_CA_Loss);
L
Linus Torvalds 已提交
1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889
	}
	tcp_xmit_retransmit_queue(sk);
}

/* This retransmits one SKB.  Policy decisions and retransmit queue
 * state updates are done by the caller.  Returns non-zero if an
 * error occurred which prevented the send.
 */
int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);
J
John Heffner 已提交
1890
	struct inet_connection_sock *icsk = inet_csk(sk);
1891
	unsigned int cur_mss;
L
Linus Torvalds 已提交
1892 1893
	int err;

J
John Heffner 已提交
1894 1895 1896 1897 1898
	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

L
Linus Torvalds 已提交
1899
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
1900
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912
	 */
	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;
	}

1913 1914 1915 1916 1917
	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
1918 1919 1920 1921 1922
	/* 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.
	 */
1923
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))
L
Linus Torvalds 已提交
1924 1925 1926 1927
	    && TCP_SKB_CB(skb)->seq != tp->snd_una)
		return -EAGAIN;

	if (skb->len > cur_mss) {
1928
		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
L
Linus Torvalds 已提交
1929 1930 1931 1932
			return -ENOMEM; /* We'll try again later. */
	}

	/* Collapse two adjacent packets if worthwhile and we can. */
S
Stephen Hemminger 已提交
1933 1934 1935 1936
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
	    (skb->len < (cur_mss >> 1)) &&
	    (tcp_write_queue_next(sk, skb) != tcp_send_head(sk)) &&
	    (!tcp_skb_is_last(sk, skb)) &&
1937 1938 1939 1940
	    (skb_shinfo(skb)->nr_frags == 0 &&
	     skb_shinfo(tcp_write_queue_next(sk, skb))->nr_frags == 0) &&
	    (tcp_skb_pcount(skb) == 1 &&
	     tcp_skb_pcount(tcp_write_queue_next(sk, skb)) == 1) &&
S
Stephen Hemminger 已提交
1941
	    (sysctl_tcp_retrans_collapse != 0))
L
Linus Torvalds 已提交
1942 1943 1944 1945 1946 1947
		tcp_retrans_try_collapse(sk, skb, cur_mss);

	/* Some Solaris stacks overoptimize and ignore the FIN on a
	 * retransmit when old data is attached.  So strip it off
	 * since it is cheap to do so and saves bytes on the network.
	 */
S
Stephen Hemminger 已提交
1948 1949 1950
	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
1951
		if (!pskb_trim(skb, 0)) {
1952 1953 1954
			/* 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
1955 1956 1957 1958 1959 1960 1961 1962 1963
			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;

1964
	err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
1965 1966 1967

	if (err == 0) {
		/* Update global TCP statistics. */
P
Pavel Emelyanov 已提交
1968
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
L
Linus Torvalds 已提交
1969 1970 1971 1972

		tp->total_retrans++;

#if FASTRETRANS_DEBUG > 0
1973
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1974 1975 1976 1977
			if (net_ratelimit())
				printk(KERN_DEBUG "retrans_out leaked.\n");
		}
#endif
1978 1979
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
L
Linus Torvalds 已提交
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
		TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
		tp->retrans_out += tcp_skb_pcount(skb);

		/* Save stamp of the first retransmit. */
		if (!tp->retrans_stamp)
			tp->retrans_stamp = TCP_SKB_CB(skb)->when;

		tp->undo_retrans++;

		/* snd_nxt is stored to detect loss of retransmitted segment,
		 * see tcp_input.c tcp_sacktag_write_queue().
		 */
		TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
	}
	return err;
}

/* This gets called after a retransmit timeout, and the initially
 * retransmitted data is acknowledged.  It tries to continue
 * resending the rest of the retransmit queue, until either
 * we've sent it all or the congestion window limit is reached.
 * If doing SACK, the first ACK which comes back for a timeout
 * based retransmit packet might feed us FACK information again.
 * If so, we use it to avoid unnecessarily retransmissions.
 */
void tcp_xmit_retransmit_queue(struct sock *sk)
{
2007
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2008 2009
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2010 2011 2012 2013 2014
	int packet_cnt;

	if (tp->retransmit_skb_hint) {
		skb = tp->retransmit_skb_hint;
		packet_cnt = tp->retransmit_cnt_hint;
2015
	} else {
2016
		skb = tcp_write_queue_head(sk);
2017 2018
		packet_cnt = 0;
	}
L
Linus Torvalds 已提交
2019 2020

	/* First pass: retransmit lost packets. */
2021
	if (tp->lost_out) {
2022
		tcp_for_write_queue_from(skb, sk) {
L
Linus Torvalds 已提交
2023 2024
			__u8 sacked = TCP_SKB_CB(skb)->sacked;

2025 2026
			if (skb == tcp_send_head(sk))
				break;
2027 2028 2029 2030
			/* we could do better than to assign each time */
			tp->retransmit_skb_hint = skb;
			tp->retransmit_cnt_hint = packet_cnt;

L
Linus Torvalds 已提交
2031 2032 2033 2034 2035 2036 2037 2038 2039 2040
			/* 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;

2041
			if (sacked & TCPCB_LOST) {
2042
				if (!(sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
2043 2044
					int mib_idx;

2045 2046
					if (tcp_retransmit_skb(sk, skb)) {
						tp->retransmit_skb_hint = NULL;
L
Linus Torvalds 已提交
2047
						return;
2048
					}
2049
					if (icsk->icsk_ca_state != TCP_CA_Loss)
2050
						mib_idx = LINUX_MIB_TCPFASTRETRANS;
L
Linus Torvalds 已提交
2051
					else
2052
						mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2053
					NET_INC_STATS_BH(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2054

2055
					if (skb == tcp_write_queue_head(sk))
2056
						inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2057 2058
									  inet_csk(sk)->icsk_rto,
									  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2059 2060
				}

2061 2062
				packet_cnt += tcp_skb_pcount(skb);
				if (packet_cnt >= tp->lost_out)
L
Linus Torvalds 已提交
2063 2064 2065 2066 2067 2068 2069 2070
					break;
			}
		}
	}

	/* OK, demanded retransmission is finished. */

	/* Forward retransmissions are possible only during Recovery. */
2071
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
L
Linus Torvalds 已提交
2072 2073 2074
		return;

	/* No forward retransmissions in Reno are possible. */
2075
	if (tcp_is_reno(tp))
L
Linus Torvalds 已提交
2076 2077 2078 2079 2080 2081
		return;

	/* Yeah, we have to make difficult choice between forward transmission
	 * and retransmission... Both ways have their merits...
	 *
	 * For now we do not retransmit anything, while we have some new
2082 2083
	 * segments to send. In the other cases, follow rule 3 for
	 * NextSeg() specified in RFC3517.
L
Linus Torvalds 已提交
2084 2085
	 */

2086
	if (tcp_may_send_now(sk))
L
Linus Torvalds 已提交
2087 2088
		return;

2089 2090 2091 2092 2093
	/* If nothing is SACKed, highest_sack in the loop won't be valid */
	if (!tp->sacked_out)
		return;

	if (tp->forward_skb_hint)
2094
		skb = tp->forward_skb_hint;
2095
	else
2096
		skb = tcp_write_queue_head(sk);
2097

2098 2099 2100
	tcp_for_write_queue_from(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;
2101
		tp->forward_skb_hint = skb;
L
Linus Torvalds 已提交
2102

2103
		if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
L
Linus Torvalds 已提交
2104 2105 2106 2107 2108 2109 2110 2111 2112
			break;

		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
			break;

		if (TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS)
			continue;

		/* Ok, retransmit it. */
2113 2114
		if (tcp_retransmit_skb(sk, skb)) {
			tp->forward_skb_hint = NULL;
L
Linus Torvalds 已提交
2115
			break;
2116
		}
L
Linus Torvalds 已提交
2117

2118
		if (skb == tcp_write_queue_head(sk))
2119 2120 2121
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2122

2123
		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFORWARDRETRANS);
L
Linus Torvalds 已提交
2124 2125 2126 2127 2128 2129 2130 2131
	}
}

/* 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)
{
2132
	struct tcp_sock *tp = tcp_sk(sk);
2133
	struct sk_buff *skb = tcp_write_queue_tail(sk);
L
Linus Torvalds 已提交
2134
	int mss_now;
2135

L
Linus Torvalds 已提交
2136 2137 2138 2139 2140 2141
	/* 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);

2142
	if (tcp_send_head(sk) != NULL) {
L
Linus Torvalds 已提交
2143 2144 2145 2146 2147 2148
		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 (;;) {
2149
			skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
L
Linus Torvalds 已提交
2150 2151 2152 2153 2154 2155 2156 2157
			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(). */
2158 2159
		tcp_init_nondata_skb(skb, tp->write_seq,
				     TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
L
Linus Torvalds 已提交
2160 2161
		tcp_queue_skb(sk, skb);
	}
2162
	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2163 2164 2165 2166 2167
}

/* 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
2168
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2169
 */
A
Al Viro 已提交
2170
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2171 2172 2173 2174 2175 2176
{
	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
2177
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2178 2179 2180 2181 2182
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2183 2184
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
			     TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
L
Linus Torvalds 已提交
2185 2186
	/* Send it off. */
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2187
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2188
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2189

P
Pavel Emelyanov 已提交
2190
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2191 2192 2193 2194 2195 2196 2197 2198 2199
}

/* 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)
{
2200
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2201

2202
	skb = tcp_write_queue_head(sk);
2203
	if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)) {
L
Linus Torvalds 已提交
2204 2205 2206
		printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
		return -EFAULT;
	}
2207
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_ACK)) {
L
Linus Torvalds 已提交
2208 2209 2210 2211
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
			if (nskb == NULL)
				return -ENOMEM;
2212
			tcp_unlink_write_queue(skb, sk);
L
Linus Torvalds 已提交
2213
			skb_header_release(nskb);
2214
			__tcp_add_write_queue_head(sk, nskb);
2215 2216 2217
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2218 2219 2220 2221 2222 2223 2224
			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;
2225
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2226 2227 2228 2229 2230
}

/*
 * Prepare a SYN-ACK.
 */
2231 2232
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
				struct request_sock *req)
L
Linus Torvalds 已提交
2233
{
2234
	struct inet_request_sock *ireq = inet_rsk(req);
L
Linus Torvalds 已提交
2235 2236 2237
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	int tcp_header_size;
A
Adam Langley 已提交
2238
	struct tcp_out_options opts;
L
Linus Torvalds 已提交
2239
	struct sk_buff *skb;
2240 2241
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
L
Linus Torvalds 已提交
2242 2243 2244 2245 2246 2247 2248 2249 2250 2251

	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);

A
Adam Langley 已提交
2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271
	if (req->rcv_wnd == 0) { /* ignored for retransmitted syns */
		__u8 rcv_wscale;
		/* Set this up on the first call only */
		req->window_clamp = tp->window_clamp ? : dst_metric(dst, RTAX_WINDOW);
		/* tcp_full_space because it is guaranteed to be the first packet */
		tcp_select_initial_window(tcp_full_space(sk),
			dst_metric(dst, RTAX_ADVMSS) - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
			&req->rcv_wnd,
			&req->window_clamp,
			ireq->wscale_ok,
			&rcv_wscale);
		ireq->rcv_wscale = rcv_wscale;
	}

	memset(&opts, 0, sizeof(opts));
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
	tcp_header_size = tcp_synack_options(sk, req,
					     dst_metric(dst, RTAX_ADVMSS),
					     skb, &opts, &md5) +
			  sizeof(struct tcphdr);
2272

2273 2274
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
2275

2276
	th = tcp_hdr(skb);
L
Linus Torvalds 已提交
2277 2278 2279 2280 2281
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
	TCP_ECN_make_synack(req, th);
	th->source = inet_sk(sk)->sport;
2282
	th->dest = ireq->rmt_port;
2283 2284 2285 2286 2287
	/* 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
2288
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2289
	th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
L
Linus Torvalds 已提交
2290 2291

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2292
	th->window = htons(min(req->rcv_wnd, 65535U));
2293 2294 2295 2296 2297
#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
2298
	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
L
Linus Torvalds 已提交
2299
	th->doff = (tcp_header_size >> 2);
P
Pavel Emelyanov 已提交
2300
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
2301 2302 2303 2304 2305

#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,
2306
					       md5, NULL, req, skb);
2307 2308 2309
	}
#endif

L
Linus Torvalds 已提交
2310 2311 2312
	return skb;
}

2313
/*
L
Linus Torvalds 已提交
2314
 * Do all connect socket setups that can be done AF independent.
2315
 */
S
Stephen Hemminger 已提交
2316
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327
{
	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);

2328 2329 2330 2331 2332
#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
2333 2334 2335 2336
	/* 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
2337
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364
	tcp_sync_mss(sk, dst_mtu(dst));

	if (!tp->window_clamp)
		tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
	tp->advmss = dst_metric(dst, RTAX_ADVMSS);
	tcp_initialize_rcv_mss(sk);

	tcp_select_initial_window(tcp_full_space(sk),
				  tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
				  &tp->rcv_wnd,
				  &tp->window_clamp,
				  sysctl_tcp_window_scaling,
				  &rcv_wscale);

	tp->rx_opt.rcv_wscale = rcv_wscale;
	tp->rcv_ssthresh = tp->rcv_wnd;

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);
	tp->snd_wnd = 0;
	tcp_init_wl(tp, tp->write_seq, 0);
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
	tp->rcv_nxt = 0;
	tp->rcv_wup = 0;
	tp->copied_seq = 0;

2365 2366
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
2367 2368 2369 2370 2371
	tcp_clear_retrans(tp);
}

/*
 * Build a SYN and send it off.
2372
 */
L
Linus Torvalds 已提交
2373 2374 2375 2376 2377 2378 2379
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;

	tcp_connect_init(sk);

2380
	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
L
Linus Torvalds 已提交
2381 2382 2383 2384 2385 2386
	if (unlikely(buff == NULL))
		return -ENOBUFS;

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

2387
	tp->snd_nxt = tp->write_seq;
2388 2389
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
	TCP_ECN_send_syn(sk, buff);
L
Linus Torvalds 已提交
2390 2391 2392 2393 2394

	/* Send it off. */
	TCP_SKB_CB(buff)->when = tcp_time_stamp;
	tp->retrans_stamp = TCP_SKB_CB(buff)->when;
	skb_header_release(buff);
2395
	__tcp_add_write_queue_tail(sk, buff);
2396 2397
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
L
Linus Torvalds 已提交
2398
	tp->packets_out += tcp_skb_pcount(buff);
2399
	tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
2400 2401 2402 2403 2404 2405

	/* 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
2406
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
2407 2408

	/* Timer for repeating the SYN until an answer. */
2409 2410
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
2411 2412 2413 2414 2415 2416 2417 2418 2419
	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)
{
2420 2421
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
2422 2423 2424
	unsigned long timeout;

	if (ato > TCP_DELACK_MIN) {
2425
		const struct tcp_sock *tp = tcp_sk(sk);
2426
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
2427

2428 2429
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
2430 2431 2432 2433 2434
			max_ato = TCP_DELACK_MAX;

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

		/* If some rtt estimate is known, use it to bound delayed ack.
2435
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
2436 2437 2438
		 * directly.
		 */
		if (tp->srtt) {
2439
			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
L
Linus Torvalds 已提交
2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451

			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. */
2452
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
2453 2454 2455
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
2456 2457
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
2458 2459 2460 2461
			tcp_send_ack(sk);
			return;
		}

2462 2463
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
2464
	}
2465 2466 2467
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
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}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
2473
	struct sk_buff *buff;
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2475 2476 2477
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
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	/* 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;
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	}
2491 2492 2493

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
2494
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);
2495 2496 2497 2498

	/* 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);
2519
	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.
	 */
2528
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
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	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2530
	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
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}

int tcp_write_wakeup(struct sock *sk)
{
2535 2536
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
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	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;
2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573
			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 {
		if (tp->urg_mode &&
		    between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
			tcp_xmit_probe_skb(sk, 1);
		return tcp_xmit_probe_skb(sk, 0);
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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)
{
2582
	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);

2588
	if (tp->packets_out || !tcp_send_head(sk)) {
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		/* Cancel probe timer, if it is not required. */
2590
		icsk->icsk_probes_out = 0;
2591
		icsk->icsk_backoff = 0;
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		return;
	}

	if (err <= 0) {
2596 2597
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
2598
		icsk->icsk_probes_out++;
2599
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2600 2601
					  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,
2604
		 * 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.
		 */
2609 2610
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
2611
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2612
					  min(icsk->icsk_rto << icsk->icsk_backoff,
2613 2614
					      TCP_RESOURCE_PROBE_INTERVAL),
					  TCP_RTO_MAX);
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	}
}

2618
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);
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John Heffner 已提交
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EXPORT_SYMBOL(tcp_mtup_init);