tcp_output.c 75.6 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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static inline int tcp_urg_mode(const struct tcp_sock *tp)
{
	return tp->snd_una != tp->snd_up;
}

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

struct tcp_out_options {
	u8 options;		/* bit field of OPTION_* */
	u8 ws;			/* window scale, 0 to disable */
	u8 num_sack_blocks;	/* number of SACK blocks to include */
	u16 mss;		/* 0 to disable */
	__u32 tsval, tsecr;	/* need to include OPTION_TS */
};

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/* Beware: Something in the Internet is very sensitive to the ordering of
 * TCP options, we learned this through the hard way, so be careful here.
 * Luckily we can at least blame others for their non-compliance but from
 * inter-operatibility perspective it seems that we're somewhat stuck with
 * the ordering which we have been using if we want to keep working with
 * those broken things (not that it currently hurts anybody as there isn't
 * particular reason why the ordering would need to be changed).
 *
 * At least SACK_PERM as the first option is known to lead to a disaster
 * (but it may well be that other scenarios fail similarly).
 */
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static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
			      const struct tcp_out_options *opts,
			      __u8 **md5_hash) {
	if (unlikely(OPTION_MD5 & opts->options)) {
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		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_NOP << 16) |
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			       (TCPOPT_MD5SIG << 8) |
			       TCPOLEN_MD5SIG);
		*md5_hash = (__u8 *)ptr;
		ptr += 4;
	} else {
		*md5_hash = NULL;
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	}
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	if (unlikely(opts->mss)) {
		*ptr++ = htonl((TCPOPT_MSS << 24) |
			       (TCPOLEN_MSS << 16) |
			       opts->mss);
	}

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

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

	if (unlikely(opts->ws)) {
		*ptr++ = htonl((TCPOPT_NOP << 24) |
			       (TCPOPT_WINDOW << 16) |
			       (TCPOLEN_WINDOW << 8) |
			       opts->ws);
	}

	if (unlikely(opts->num_sack_blocks)) {
		struct tcp_sack_block *sp = tp->rx_opt.dsack ?
			tp->duplicate_sack : tp->selective_acks;
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		int this_sack;

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

static unsigned tcp_syn_options(struct sock *sk, struct sk_buff *skb,
				struct tcp_out_options *opts,
				struct tcp_md5sig_key **md5) {
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned size = 0;

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#ifdef CONFIG_TCP_MD5SIG
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	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (*md5) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
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	}
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#else
	*md5 = NULL;
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#endif
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	/* We always get an MSS option.  The option bytes which will be seen in
	 * normal data packets should timestamps be used, must be in the MSS
	 * advertised.  But we subtract them from tp->mss_cache so that
	 * calculations in tcp_sendmsg are simpler etc.  So account for this
	 * fact here if necessary.  If we don't do this correctly, as a
	 * receiver we won't recognize data packets as being full sized when we
	 * should, and thus we won't abide by the delayed ACK rules correctly.
	 * SACKs don't matter, we never delay an ACK when we have any of those
	 * going out.  */
	opts->mss = tcp_advertise_mss(sk);
	size += TCPOLEN_MSS_ALIGNED;

	if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
		opts->options |= OPTION_TS;
		opts->tsval = TCP_SKB_CB(skb)->when;
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}
	if (likely(sysctl_tcp_window_scaling)) {
		opts->ws = tp->rx_opt.rcv_wscale;
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		if(likely(opts->ws))
			size += TCPOLEN_WSCALE_ALIGNED;
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	}
	if (likely(sysctl_tcp_sack)) {
		opts->options |= OPTION_SACK_ADVERTISE;
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		if (unlikely(!(OPTION_TS & opts->options)))
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			size += TCPOLEN_SACKPERM_ALIGNED;
	}

	return size;
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}

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static unsigned tcp_synack_options(struct sock *sk,
				   struct request_sock *req,
				   unsigned mss, struct sk_buff *skb,
				   struct tcp_out_options *opts,
				   struct tcp_md5sig_key **md5) {
	unsigned size = 0;
	struct inet_request_sock *ireq = inet_rsk(req);
	char doing_ts;

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#ifdef CONFIG_TCP_MD5SIG
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	*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
	if (*md5) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
513
	}
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#else
	*md5 = NULL;
516
#endif
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	/* we can't fit any SACK blocks in a packet with MD5 + TS
	   options. There was discussion about disabling SACK rather than TS in
	   order to fit in better with old, buggy kernels, but that was deemed
	   to be unnecessary. */
	doing_ts = ireq->tstamp_ok && !(*md5 && ireq->sack_ok);

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

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

	return size;
}

static unsigned tcp_established_options(struct sock *sk, struct sk_buff *skb,
					struct tcp_out_options *opts,
					struct tcp_md5sig_key **md5) {
	struct tcp_skb_cb *tcb = skb ? TCP_SKB_CB(skb) : NULL;
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned size = 0;

#ifdef CONFIG_TCP_MD5SIG
	*md5 = tp->af_specific->md5_lookup(sk, sk);
	if (unlikely(*md5)) {
		opts->options |= OPTION_MD5;
		size += TCPOLEN_MD5SIG_ALIGNED;
	}
#else
	*md5 = NULL;
#endif

	if (likely(tp->rx_opt.tstamp_ok)) {
		opts->options |= OPTION_TS;
		opts->tsval = tcb ? tcb->when : 0;
		opts->tsecr = tp->rx_opt.ts_recent;
		size += TCPOLEN_TSTAMP_ALIGNED;
	}

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

	return size;
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}
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/* This routine actually transmits TCP packets queued in by
 * tcp_do_sendmsg().  This is used by both the initial
 * transmission and possible later retransmissions.
 * All SKB's seen here are completely headerless.  It is our
 * job to build the TCP header, and pass the packet down to
 * IP so it can do the same plus pass the packet off to the
 * device.
 *
 * We are working here with either a clone of the original
 * SKB, or a fresh unique copy made by the retransmit engine.
 */
595 596
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
			    gfp_t gfp_mask)
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{
598 599 600 601
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct inet_sock *inet;
	struct tcp_sock *tp;
	struct tcp_skb_cb *tcb;
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Adam Langley 已提交
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	struct tcp_out_options opts;
	unsigned tcp_options_size, tcp_header_size;
604 605
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
606 607 608 609 610 611 612 613
	struct tcphdr *th;
	int err;

	BUG_ON(!skb || !tcp_skb_pcount(skb));

	/* If congestion control is doing timestamping, we must
	 * take such a timestamp before we potentially clone/copy.
	 */
614
	if (icsk->icsk_ca_ops->flags & TCP_CONG_RTT_STAMP)
615 616 617 618 619 620 621 622 623 624
		__net_timestamp(skb);

	if (likely(clone_it)) {
		if (unlikely(skb_cloned(skb)))
			skb = pskb_copy(skb, gfp_mask);
		else
			skb = skb_clone(skb, gfp_mask);
		if (unlikely(!skb))
			return -ENOBUFS;
	}
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Linus Torvalds 已提交
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626 627 628
	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
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Adam Langley 已提交
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	memset(&opts, 0, sizeof(opts));
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Linus Torvalds 已提交
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	if (unlikely(tcb->flags & TCPCB_FLAG_SYN))
		tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
	else
		tcp_options_size = tcp_established_options(sk, skb, &opts,
							   &md5);
	tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
637

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

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

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

	if (unlikely(tcb->flags & TCPCB_FLAG_SYN)) {
		/* RFC1323: The window in SYN & SYN/ACK segments
		 * is never scaled.
		 */
658
		th->window	= htons(min(tp->rcv_wnd, 65535U));
659 660 661 662 663
	} else {
		th->window	= htons(tcp_select_window(sk));
	}
	th->check		= 0;
	th->urg_ptr		= 0;
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Linus Torvalds 已提交
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Ilpo Järvinen 已提交
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	/* The urg_mode check is necessary during a below snd_una win probe */
	if (unlikely(tcp_urg_mode(tp) &&
667 668
		     between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF))) {
		th->urg_ptr		= htons(tp->snd_up - tcb->seq);
669 670
		th->urg			= 1;
	}
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Linus Torvalds 已提交
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Adam Langley 已提交
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	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
	if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
674
		TCP_ECN_send(sk, skb, tcp_header_size);
L
Linus Torvalds 已提交
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676 677 678
#ifdef CONFIG_TCP_MD5SIG
	/* Calculate the MD5 hash, as we have all we need now */
	if (md5) {
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Adam Langley 已提交
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		sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
680
		tp->af_specific->calc_md5_hash(md5_hash_location,
681
					       md5, sk, NULL, skb);
682 683 684
	}
#endif

685
	icsk->icsk_af_ops->send_check(sk, skb->len, skb);
L
Linus Torvalds 已提交
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687 688
	if (likely(tcb->flags & TCPCB_FLAG_ACK))
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
689

690 691
	if (skb->len != tcp_header_size)
		tcp_event_data_sent(tp, skb, sk);
L
Linus Torvalds 已提交
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693
	if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
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Pavel Emelyanov 已提交
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		TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
L
Linus Torvalds 已提交
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696
	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
697
	if (likely(err <= 0))
698 699
		return err;

700
	tcp_enter_cwr(sk, 1);
701

702
	return net_xmit_eval(err);
L
Linus Torvalds 已提交
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}

705
/* This routine just queue's the buffer
L
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 *
 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 * otherwise socket can stall.
 */
static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Advance write_seq and place onto the write_queue. */
	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
	skb_header_release(skb);
717
	tcp_add_write_queue_tail(sk, skb);
718 719
	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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}

722 723
static void tcp_set_skb_tso_segs(struct sock *sk, struct sk_buff *skb,
				 unsigned int mss_now)
724
{
725
	if (skb->len <= mss_now || !sk_can_gso(sk)) {
726 727 728
		/* Avoid the costly divide in the normal
		 * non-TSO case.
		 */
729 730 731
		skb_shinfo(skb)->gso_segs = 1;
		skb_shinfo(skb)->gso_size = 0;
		skb_shinfo(skb)->gso_type = 0;
732
	} 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);
734
		skb_shinfo(skb)->gso_size = mss_now;
735
		skb_shinfo(skb)->gso_type = sk->sk_gso_type;
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Linus Torvalds 已提交
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	}
}

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/* When a modification to fackets out becomes necessary, we need to check
740
 * skb is counted to fackets_out or not.
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 */
742
static void tcp_adjust_fackets_out(struct sock *sk, struct sk_buff *skb,
I
Ilpo Järvinen 已提交
743 744
				   int decr)
{
745 746
	struct tcp_sock *tp = tcp_sk(sk);

747
	if (!tp->sacked_out || tcp_is_reno(tp))
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Ilpo Järvinen 已提交
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		return;

750
	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
756
 * packet to the list.  This won't be called frequently, I hope.
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Linus Torvalds 已提交
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 * Remember, these are still headerless SKBs at this point.
 */
759 760
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;
764
	int nsize, old_factor;
765
	int nlen;
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Linus Torvalds 已提交
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	u16 flags;

768
	BUG_ON(len > skb->len);
769

770
	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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785 786
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
787 788 789
	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;
798
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
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	TCP_SKB_CB(buff)->flags = flags;
800
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
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801

802
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
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		/* Copy and checksum data tail into the new buffer. */
804 805
		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 {
812
		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;
822
	buff->tstamp = skb->tstamp;
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Linus Torvalds 已提交
823

824 825
	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.  */
827 828
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
L
Linus Torvalds 已提交
829

830 831 832
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
833
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
834 835
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
836

837
		tp->packets_out -= diff;
838 839 840 841 842 843

		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;

844
		if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
845
			tp->lost_out -= diff;
846

I
Ilpo Järvinen 已提交
847 848 849 850
		/* 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);
851
		}
852
		tcp_adjust_fackets_out(sk, skb, diff);
L
Linus Torvalds 已提交
853 854 855
	}

	/* Link BUFF into the send queue. */
856
	skb_header_release(buff);
857
	tcp_insert_write_queue_after(skb, buff, sk);
L
Linus Torvalds 已提交
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	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.
 */
866
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
867 868 869 870 871
{
	int i, k, eat;

	eat = len;
	k = 0;
872
	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;

888
	skb_reset_tail_pointer(skb);
L
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	skb->data_len -= len;
	skb->len = skb->data_len;
}

int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
895
	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
L
Linus Torvalds 已提交
896 897
		return -ENOMEM;

898 899
	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
	if (unlikely(len < skb_headlen(skb)))
L
Linus Torvalds 已提交
900
		__skb_pull(skb, len);
901 902
	else
		__pskb_trim_head(skb, len - skb_headlen(skb));
L
Linus Torvalds 已提交
903 904

	TCP_SKB_CB(skb)->seq += len;
905
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
906 907 908

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
909
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
910 911 912 913 914 915
	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)
916
		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
L
Linus Torvalds 已提交
917 918 919 920

	return 0;
}

J
John Heffner 已提交
921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971
/* 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) +
972
			       icsk->icsk_af_ops->net_header_len;
J
John Heffner 已提交
973 974 975 976
	icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
	icsk->icsk_mtup.probe_size = 0;
}

977 978 979 980 981 982 983 984 985
/* Bound MSS / TSO packet size with the half of the window */
static int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
{
	if (tp->max_window && pktsize > (tp->max_window >> 1))
		return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
	else
		return pktsize;
}

L
Linus Torvalds 已提交
986 987 988 989 990 991
/* 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
992
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
993 994
   It also does not include TCP options.

995
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
996 997 998 999 1000 1001 1002 1003 1004

   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.

1005 1006
   NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
   are READ ONLY outside this function.		--ANK (980731)
L
Linus Torvalds 已提交
1007 1008 1009 1010
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1011
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1012
	int mss_now;
L
Linus Torvalds 已提交
1013

J
John Heffner 已提交
1014 1015
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1016

J
John Heffner 已提交
1017
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1018
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1019 1020

	/* And store cached results */
1021
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1022 1023
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1024
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1025 1026 1027 1028 1029 1030 1031

	return mss_now;
}

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
1032
unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
L
Linus Torvalds 已提交
1033 1034 1035
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
1036 1037 1038
	u32 mss_now;
	u16 xmit_size_goal;
	int doing_tso = 0;
A
Adam Langley 已提交
1039 1040 1041
	unsigned header_len;
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1042 1043 1044

	mss_now = tp->mss_cache;

1045
	if (large_allowed && sk_can_gso(sk))
1046
		doing_tso = 1;
L
Linus Torvalds 已提交
1047 1048 1049

	if (dst) {
		u32 mtu = dst_mtu(dst);
1050
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1051 1052 1053
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1054 1055 1056 1057 1058 1059 1060 1061 1062 1063
	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;
	}
1064

1065
	xmit_size_goal = mss_now;
L
Linus Torvalds 已提交
1066

1067
	if (doing_tso) {
1068
		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
1069
				  inet_csk(sk)->icsk_af_ops->net_header_len -
1070 1071
				  inet_csk(sk)->icsk_ext_hdr_len -
				  tp->tcp_header_len);
L
Linus Torvalds 已提交
1072

1073
		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
1074
		xmit_size_goal -= (xmit_size_goal % mss_now);
L
Linus Torvalds 已提交
1075
	}
1076
	tp->xmit_size_goal = xmit_size_goal;
L
Linus Torvalds 已提交
1077 1078 1079 1080

	return mss_now;
}

1081
/* Congestion window validation. (RFC2861) */
1082
static void tcp_cwnd_validate(struct sock *sk)
1083
{
1084
	struct tcp_sock *tp = tcp_sk(sk);
1085

1086
	if (tp->packets_out >= tp->snd_cwnd) {
1087 1088 1089 1090 1091 1092 1093 1094
		/* 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;

1095 1096
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1097 1098 1099 1100
			tcp_cwnd_application_limited(sk);
	}
}

1101 1102 1103 1104
/* 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).
1105 1106 1107 1108 1109 1110 1111
 *
 * 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.
1112 1113
 */
static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb,
1114
					unsigned int mss_now, unsigned int cwnd)
1115
{
1116 1117
	struct tcp_sock *tp = tcp_sk(sk);
	u32 needed, window, cwnd_len;
1118

1119
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1120
	cwnd_len = mss_now * cwnd;
1121 1122 1123 1124

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

1125 1126
	needed = min(skb->len, window);

1127
	if (cwnd_len <= needed)
1128 1129 1130
		return cwnd_len;

	return needed - needed % mss_now;
1131 1132 1133 1134 1135
}

/* 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.
 */
1136 1137
static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
					 struct sk_buff *skb)
1138 1139 1140 1141
{
	u32 in_flight, cwnd;

	/* Don't be strict about the congestion window for the final FIN.  */
1142 1143
	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156
		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.
 */
1157 1158
static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
			     unsigned int mss_now)
1159 1160 1161
{
	int tso_segs = tcp_skb_pcount(skb);

1162
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1163
		tcp_set_skb_tso_segs(sk, skb, mss_now);
1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182
		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,
1183
				  const struct sk_buff *skb,
1184 1185 1186
				  unsigned mss_now, int nonagle)
{
	return (skb->len < mss_now &&
1187 1188
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp))));
1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205
}

/* 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;

1206 1207 1208
	/* Don't use the nagle rule for urgent data (or for the final FIN).
	 * Nagle can be ignored during F-RTO too (see RFC4138).
	 */
I
Ilpo Järvinen 已提交
1209
	if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1210 1211 1212 1213 1214 1215 1216 1217 1218 1219
	    (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? */
1220 1221
static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb,
				   unsigned int cur_mss)
1222 1223 1224 1225 1226 1227
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

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

1228
	return !after(end_seq, tcp_wnd_end(tp));
1229 1230
}

1231
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1232 1233 1234 1235 1236 1237 1238 1239 1240
 * 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;

1241
	tcp_init_tso_segs(sk, skb, cur_mss);
1242 1243 1244 1245 1246

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

	cwnd_quota = tcp_cwnd_test(tp, skb);
1247
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1248 1249 1250 1251 1252
		cwnd_quota = 0;

	return cwnd_quota;
}

1253
int tcp_may_send_now(struct sock *sk)
1254
{
1255
	struct tcp_sock *tp = tcp_sk(sk);
1256
	struct sk_buff *skb = tcp_send_head(sk);
1257 1258 1259 1260

	return (skb &&
		tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
			     (tcp_skb_is_last(sk, skb) ?
1261
			      tp->nonagle : TCP_NAGLE_PUSH)));
1262 1263 1264 1265 1266 1267 1268 1269 1270
}

/* 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).
 */
1271 1272
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
			unsigned int mss_now)
1273 1274 1275 1276 1277 1278
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
	u16 flags;

	/* All of a TSO frame must be composed of paged data.  */
1279 1280
	if (skb->len != skb->data_len)
		return tcp_fragment(sk, skb, len, mss_now);
1281

1282
	buff = sk_stream_alloc_skb(sk, 0, GFP_ATOMIC);
1283 1284 1285
	if (unlikely(buff == NULL))
		return -ENOMEM;

1286 1287
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1288
	buff->truesize += nlen;
1289 1290 1291 1292 1293 1294 1295 1296 1297
	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;
1298
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
1299 1300 1301 1302 1303
	TCP_SKB_CB(buff)->flags = flags;

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

1304
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1305 1306 1307
	skb_split(skb, buff, len);

	/* Fix up tso_factor for both original and new SKB.  */
1308 1309
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
1310 1311 1312

	/* Link BUFF into the send queue. */
	skb_header_release(buff);
1313
	tcp_insert_write_queue_after(skb, buff, sk);
1314 1315 1316 1317 1318 1319 1320 1321 1322

	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.
 */
1323
static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1324
{
1325
	struct tcp_sock *tp = tcp_sk(sk);
1326
	const struct inet_connection_sock *icsk = inet_csk(sk);
1327 1328 1329
	u32 send_win, cong_win, limit, in_flight;

	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
J
John Heffner 已提交
1330
		goto send_now;
1331

1332
	if (icsk->icsk_ca_state != TCP_CA_Open)
J
John Heffner 已提交
1333 1334 1335
		goto send_now;

	/* Defer for less than two clock ticks. */
I
Ilpo Järvinen 已提交
1336 1337
	if (tp->tso_deferred &&
	    ((jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
J
John Heffner 已提交
1338
		goto send_now;
1339

1340 1341
	in_flight = tcp_packets_in_flight(tp);

1342
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1343

1344
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1345 1346 1347 1348 1349 1350

	/* 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);

1351
	/* If a full-sized TSO skb can be sent, do it. */
1352
	if (limit >= sk->sk_gso_max_size)
J
John Heffner 已提交
1353
		goto send_now;
1354

1355 1356 1357 1358 1359 1360 1361 1362
	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
1363
			goto send_now;
1364 1365 1366 1367 1368 1369 1370
	} 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
1371
			goto send_now;
1372 1373 1374
	}

	/* Ok, it looks like it is advisable to defer.  */
1375
	tp->tso_deferred = 1 | (jiffies << 1);
J
John Heffner 已提交
1376

1377
	return 1;
J
John Heffner 已提交
1378 1379 1380 1381

send_now:
	tp->tso_deferred = 0;
	return 0;
1382 1383
}

J
John Heffner 已提交
1384 1385 1386
/* 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,
1387 1388
 *         -1 otherwise
 */
J
John Heffner 已提交
1389 1390 1391 1392 1393 1394 1395
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;
1396
	int size_needed;
J
John Heffner 已提交
1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412
	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);
1413
	probe_size = 2 * tp->mss_cache;
1414
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
J
John Heffner 已提交
1415 1416 1417 1418 1419 1420
	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? */
1421
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1422 1423
		return -1;

1424 1425
	if (tp->snd_wnd < size_needed)
		return -1;
1426
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1427
		return 0;
J
John Heffner 已提交
1428

1429 1430 1431
	/* 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
1432 1433 1434 1435 1436 1437 1438 1439
			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;
1440 1441
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1442

1443
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1444 1445 1446 1447 1448 1449

	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;
1450
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1451

1452 1453
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1454
	len = 0;
1455
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1456 1457 1458 1459 1460
		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,
1461 1462
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1463 1464 1465 1466 1467

		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;
1468
			tcp_unlink_write_queue(skb, sk);
1469
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1470 1471
		} else {
			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
1472
						   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
J
John Heffner 已提交
1473 1474
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1475
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1476 1477
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1478 1479 1480 1481 1482 1483 1484 1485
			} else {
				__pskb_trim_head(skb, copy);
				tcp_set_skb_tso_segs(sk, skb, mss_now);
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1486 1487 1488

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1489 1490 1491 1492 1493 1494 1495 1496
	}
	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
1497
		 * effectively two packets. */
J
John Heffner 已提交
1498
		tp->snd_cwnd--;
1499
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
1500 1501

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1502 1503
		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
1504 1505 1506 1507 1508 1509 1510

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
1511 1512 1513 1514
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
1515 1516 1517 1518
 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
 * account rare use of URG, this is not a big flaw.
 *
L
Linus Torvalds 已提交
1519 1520 1521
 * Returns 1, if no segments are in flight and we have queued segments, but
 * cannot send anything now because of SWS or another problem.
 */
1522
static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
L
Linus Torvalds 已提交
1523 1524
{
	struct tcp_sock *tp = tcp_sk(sk);
1525
	struct sk_buff *skb;
1526 1527
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
1528
	int result;
L
Linus Torvalds 已提交
1529 1530 1531 1532 1533

	/* 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.
	 */
1534 1535
	if (unlikely(sk->sk_state == TCP_CLOSE))
		return 0;
L
Linus Torvalds 已提交
1536

1537
	sent_pkts = 0;
J
John Heffner 已提交
1538 1539 1540 1541 1542 1543 1544 1545

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

1546
	while ((skb = tcp_send_head(sk))) {
1547 1548
		unsigned int limit;

1549
		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1550
		BUG_ON(!tso_segs);
1551

1552 1553 1554 1555 1556 1557 1558
		cwnd_quota = tcp_cwnd_test(tp, skb);
		if (!cwnd_quota)
			break;

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

1559 1560 1561 1562 1563 1564
		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 {
1565
			if (tcp_tso_should_defer(sk, skb))
1566 1567
				break;
		}
1568

1569
		limit = mss_now;
1570
		if (tso_segs > 1 && !tcp_urg_mode(tp))
1571 1572
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
L
Linus Torvalds 已提交
1573

1574 1575 1576 1577
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			break;

1578
		TCP_SKB_CB(skb)->when = tcp_time_stamp;
1579

1580
		if (unlikely(tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC)))
1581
			break;
L
Linus Torvalds 已提交
1582

1583 1584 1585
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
1586
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
1587

1588
		tcp_minshall_update(tp, mss_now, skb);
1589
		sent_pkts++;
1590
	}
L
Linus Torvalds 已提交
1591

1592
	if (likely(sent_pkts)) {
1593
		tcp_cwnd_validate(sk);
1594
		return 0;
L
Linus Torvalds 已提交
1595
	}
1596
	return !tp->packets_out && tcp_send_head(sk);
L
Linus Torvalds 已提交
1597 1598
}

1599 1600 1601 1602
/* 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.
 */
1603 1604
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
1605
{
1606
	struct sk_buff *skb = tcp_send_head(sk);
1607 1608

	if (skb) {
1609
		if (tcp_write_xmit(sk, cur_mss, nonagle))
1610
			tcp_check_probe_timer(sk);
1611 1612 1613
	}
}

1614 1615 1616 1617 1618
/* 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)
{
1619
	struct tcp_sock *tp = tcp_sk(sk);
1620
	struct sk_buff *skb = tcp_send_head(sk);
1621 1622 1623 1624
	unsigned int tso_segs, cwnd_quota;

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

1625
	tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1626 1627 1628
	cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH);

	if (likely(cwnd_quota)) {
1629 1630
		unsigned int limit;

1631 1632
		BUG_ON(!tso_segs);

1633
		limit = mss_now;
1634
		if (tso_segs > 1 && !tcp_urg_mode(tp))
1635 1636
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
1637

1638 1639 1640 1641
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			return;

1642 1643 1644
		/* Send it out now. */
		TCP_SKB_CB(skb)->when = tcp_time_stamp;

1645
		if (likely(!tcp_transmit_skb(sk, skb, 1, sk->sk_allocation))) {
1646
			tcp_event_new_data_sent(sk, skb);
1647
			tcp_cwnd_validate(sk);
1648 1649 1650 1651 1652
			return;
		}
	}
}

L
Linus Torvalds 已提交
1653 1654
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
1655
 *
L
Linus Torvalds 已提交
1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673
 * 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.
1674
 *
L
Linus Torvalds 已提交
1675 1676
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
1677
 *
L
Linus Torvalds 已提交
1678
 * BSD seems to make the following compromise:
1679
 *
L
Linus Torvalds 已提交
1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706
 *	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)
{
1707
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1708
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
1709
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
1710 1711 1712 1713 1714
	 * 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
	 */
1715
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
1716 1717 1718 1719 1720
	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)
1721
		mss = full_space;
L
Linus Torvalds 已提交
1722

1723
	if (free_space < (full_space >> 1)) {
1724
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
1725 1726

		if (tcp_memory_pressure)
1727 1728
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760

		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)
1761
			window = (free_space / mss) * mss;
1762
		else if (mss == full_space &&
1763
			 free_space > window + (full_space >> 1))
1764
			window = free_space;
L
Linus Torvalds 已提交
1765 1766 1767 1768 1769 1770
	}

	return window;
}

/* Attempt to collapse two adjacent SKB's during retransmission. */
1771 1772
static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb,
				     int mss_now)
L
Linus Torvalds 已提交
1773 1774
{
	struct tcp_sock *tp = tcp_sk(sk);
1775
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1776 1777
	int skb_size, next_skb_size;
	u16 flags;
L
Linus Torvalds 已提交
1778 1779 1780 1781

	/* The first test we must make is that neither of these two
	 * SKB's are still referenced by someone else.
	 */
1782 1783
	if (skb_cloned(skb) || skb_cloned(next_skb))
		return;
L
Linus Torvalds 已提交
1784

1785 1786 1787
	skb_size = skb->len;
	next_skb_size = next_skb->len;
	flags = TCP_SKB_CB(skb)->flags;
L
Linus Torvalds 已提交
1788

1789 1790 1791
	/* 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
1792

1793 1794 1795
	/* 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
1796

1797 1798 1799 1800 1801 1802 1803
	/* 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
1804

1805
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1806

1807
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
1808

1809 1810
	/* Ok.	We will be able to collapse the packet. */
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
1811

1812 1813
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
1814

1815 1816
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1817

1818 1819
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
1820

1821 1822
	/* 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
1823

1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843
	/* 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 */
1844 1845 1846
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
1847 1848

	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
1849 1850 1851
}

/* Do a simple retransmit without using the backoff mechanisms in
1852
 * tcp_timer. This is used for path mtu discovery.
L
Linus Torvalds 已提交
1853
 * The socket is already locked here.
1854
 */
L
Linus Torvalds 已提交
1855 1856
void tcp_simple_retransmit(struct sock *sk)
{
1857
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1858 1859 1860
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	unsigned int mss = tcp_current_mss(sk, 0);
1861
	u32 prior_lost = tp->lost_out;
L
Linus Torvalds 已提交
1862

1863 1864 1865
	tcp_for_write_queue(skb, sk) {
		if (skb == tcp_send_head(sk))
			break;
1866
		if (skb->len > mss &&
1867 1868
		    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1869 1870 1871
				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
				tp->retrans_out -= tcp_skb_pcount(skb);
			}
1872
			tcp_skb_mark_lost_uncond_verify(tp, skb);
L
Linus Torvalds 已提交
1873 1874 1875
		}
	}

1876
	tcp_clear_retrans_hints_partial(tp);
1877

1878
	if (prior_lost == tp->lost_out)
L
Linus Torvalds 已提交
1879 1880
		return;

1881 1882 1883
	if (tcp_is_reno(tp))
		tcp_limit_reno_sacked(tp);

1884
	tcp_verify_left_out(tp);
L
Linus Torvalds 已提交
1885

1886
	/* Don't muck with the congestion window here.
L
Linus Torvalds 已提交
1887 1888 1889 1890
	 * Reason is that we do not increase amount of _data_
	 * in network, but units changed and effective
	 * cwnd/ssthresh really reduced now.
	 */
1891
	if (icsk->icsk_ca_state != TCP_CA_Loss) {
L
Linus Torvalds 已提交
1892
		tp->high_seq = tp->snd_nxt;
1893
		tp->snd_ssthresh = tcp_current_ssthresh(sk);
L
Linus Torvalds 已提交
1894 1895
		tp->prior_ssthresh = 0;
		tp->undo_marker = 0;
1896
		tcp_set_ca_state(sk, TCP_CA_Loss);
L
Linus Torvalds 已提交
1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907
	}
	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
1908
	struct inet_connection_sock *icsk = inet_csk(sk);
1909
	unsigned int cur_mss;
L
Linus Torvalds 已提交
1910 1911
	int err;

J
John Heffner 已提交
1912 1913 1914 1915 1916
	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

L
Linus Torvalds 已提交
1917
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
1918
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930
	 */
	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;
	}

1931 1932 1933 1934 1935
	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
1936 1937 1938 1939 1940
	/* 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.
	 */
1941
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))
L
Linus Torvalds 已提交
1942 1943 1944 1945
	    && TCP_SKB_CB(skb)->seq != tp->snd_una)
		return -EAGAIN;

	if (skb->len > cur_mss) {
1946
		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
L
Linus Torvalds 已提交
1947 1948 1949 1950
			return -ENOMEM; /* We'll try again later. */
	}

	/* Collapse two adjacent packets if worthwhile and we can. */
S
Stephen Hemminger 已提交
1951 1952 1953
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN) &&
	    (skb->len < (cur_mss >> 1)) &&
	    (!tcp_skb_is_last(sk, skb)) &&
1954
	    (tcp_write_queue_next(sk, skb) != tcp_send_head(sk)) &&
1955 1956 1957 1958
	    (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
1959
	    (sysctl_tcp_retrans_collapse != 0))
L
Linus Torvalds 已提交
1960 1961 1962 1963 1964 1965
		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
1966 1967 1968
	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
1969
		if (!pskb_trim(skb, 0)) {
1970 1971 1972
			/* 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
1973 1974 1975 1976 1977 1978 1979 1980 1981
			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;

1982
	err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
1983 1984 1985

	if (err == 0) {
		/* Update global TCP statistics. */
P
Pavel Emelyanov 已提交
1986
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
L
Linus Torvalds 已提交
1987 1988 1989 1990

		tp->total_retrans++;

#if FASTRETRANS_DEBUG > 0
1991
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1992 1993 1994 1995
			if (net_ratelimit())
				printk(KERN_DEBUG "retrans_out leaked.\n");
		}
#endif
1996 1997
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
L
Linus Torvalds 已提交
1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
		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;
}

2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041
static int tcp_can_forward_retransmit(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_sock *tp = tcp_sk(sk);

	/* Forward retransmissions are possible only during Recovery. */
	if (icsk->icsk_ca_state != TCP_CA_Recovery)
		return 0;

	/* No forward retransmissions in Reno are possible. */
	if (tcp_is_reno(tp))
		return 0;

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

	if (tcp_may_send_now(sk))
		return 0;

	return 1;
}

L
Linus Torvalds 已提交
2042 2043 2044 2045 2046 2047 2048 2049 2050 2051
/* 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)
{
2052
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2053 2054
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2055
	struct sk_buff *hole = NULL;
2056
	u32 last_lost;
2057
	int mib_idx;
2058
	int fwd_rexmitting = 0;
2059

2060 2061 2062
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2063
	if (tp->retransmit_skb_hint) {
2064
		skb = tp->retransmit_skb_hint;
2065 2066 2067 2068
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2069
		skb = tcp_write_queue_head(sk);
2070 2071
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2072 2073

	/* First pass: retransmit lost packets. */
2074 2075
	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;
L
Linus Torvalds 已提交
2076

2077 2078 2079
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2080 2081
		if (hole == NULL)
			tp->retransmit_skb_hint = skb;
2082 2083 2084 2085 2086 2087 2088 2089 2090 2091

		/* Assume this retransmit will generate
		 * only one packet for congestion window
		 * calculation purposes.  This works because
		 * tcp_retransmit_skb() will chop up the
		 * packet to be MSS sized and all the
		 * packet counting works out.
		 */
		if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
			return;
L
Linus Torvalds 已提交
2092

2093 2094 2095 2096 2097
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2098

2099
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2100
			tp->retransmit_high = last_lost;
2101 2102 2103 2104 2105 2106 2107 2108 2109
			if (!tcp_can_forward_retransmit(sk))
				break;
			/* Backtrack if necessary to non-L'ed skb */
			if (hole != NULL) {
				skb = hole;
				hole = NULL;
			}
			fwd_rexmitting = 1;
			goto begin_fwd;
L
Linus Torvalds 已提交
2110

2111 2112 2113 2114
		} else if (!(sacked & TCPCB_LOST)) {
			if (hole == NULL && !(sacked & TCPCB_SACKED_RETRANS))
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2115

2116
		} else {
2117
			last_lost = TCP_SKB_CB(skb)->end_seq;
2118 2119 2120 2121 2122
			if (icsk->icsk_ca_state != TCP_CA_Loss)
				mib_idx = LINUX_MIB_TCPFASTRETRANS;
			else
				mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
		}
L
Linus Torvalds 已提交
2123

2124
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2125 2126
			continue;

2127
		if (tcp_retransmit_skb(sk, skb))
2128 2129
			return;
		NET_INC_STATS_BH(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2130

2131
		if (skb == tcp_write_queue_head(sk))
2132 2133 2134
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2135 2136 2137 2138 2139 2140 2141 2142
	}
}

/* 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)
{
2143
	struct tcp_sock *tp = tcp_sk(sk);
2144
	struct sk_buff *skb = tcp_write_queue_tail(sk);
L
Linus Torvalds 已提交
2145
	int mss_now;
2146

L
Linus Torvalds 已提交
2147 2148 2149 2150 2151 2152
	/* 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);

2153
	if (tcp_send_head(sk) != NULL) {
L
Linus Torvalds 已提交
2154 2155 2156 2157 2158 2159
		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 (;;) {
2160
			skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
L
Linus Torvalds 已提交
2161 2162 2163 2164 2165 2166 2167 2168
			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(). */
2169 2170
		tcp_init_nondata_skb(skb, tp->write_seq,
				     TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
L
Linus Torvalds 已提交
2171 2172
		tcp_queue_skb(sk, skb);
	}
2173
	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2174 2175 2176 2177 2178
}

/* 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
2179
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2180
 */
A
Al Viro 已提交
2181
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2182 2183 2184 2185 2186 2187
{
	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
2188
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2189 2190 2191 2192 2193
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2194 2195
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
			     TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
L
Linus Torvalds 已提交
2196 2197
	/* Send it off. */
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2198
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2199
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2200

P
Pavel Emelyanov 已提交
2201
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2202 2203 2204 2205 2206 2207 2208 2209 2210
}

/* 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)
{
2211
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2212

2213
	skb = tcp_write_queue_head(sk);
2214
	if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)) {
L
Linus Torvalds 已提交
2215 2216 2217
		printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
		return -EFAULT;
	}
2218
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_ACK)) {
L
Linus Torvalds 已提交
2219 2220 2221 2222
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
			if (nskb == NULL)
				return -ENOMEM;
2223
			tcp_unlink_write_queue(skb, sk);
L
Linus Torvalds 已提交
2224
			skb_header_release(nskb);
2225
			__tcp_add_write_queue_head(sk, nskb);
2226 2227 2228
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2229 2230 2231 2232 2233 2234 2235
			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;
2236
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2237 2238 2239 2240 2241
}

/*
 * Prepare a SYN-ACK.
 */
2242 2243
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
				struct request_sock *req)
L
Linus Torvalds 已提交
2244
{
2245
	struct inet_request_sock *ireq = inet_rsk(req);
L
Linus Torvalds 已提交
2246 2247 2248
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	int tcp_header_size;
A
Adam Langley 已提交
2249
	struct tcp_out_options opts;
L
Linus Torvalds 已提交
2250
	struct sk_buff *skb;
2251 2252
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
2253
	int mss;
L
Linus Torvalds 已提交
2254 2255 2256 2257 2258 2259 2260 2261 2262 2263

	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);

2264 2265 2266 2267
	mss = dst_metric(dst, RTAX_ADVMSS);
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
		mss = tp->rx_opt.user_mss;

A
Adam Langley 已提交
2268 2269 2270 2271 2272 2273
	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),
2274
			mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
A
Adam Langley 已提交
2275 2276 2277 2278 2279 2280 2281 2282
			&req->rcv_wnd,
			&req->window_clamp,
			ireq->wscale_ok,
			&rcv_wscale);
		ireq->rcv_wscale = rcv_wscale;
	}

	memset(&opts, 0, sizeof(opts));
2283 2284 2285 2286 2287
#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
2288
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2289
	tcp_header_size = tcp_synack_options(sk, req, mss,
A
Adam Langley 已提交
2290 2291
					     skb, &opts, &md5) +
			  sizeof(struct tcphdr);
2292

2293 2294
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
2295

2296
	th = tcp_hdr(skb);
L
Linus Torvalds 已提交
2297 2298 2299 2300
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
	TCP_ECN_make_synack(req, th);
2301
	th->source = ireq->loc_port;
2302
	th->dest = ireq->rmt_port;
2303 2304 2305 2306 2307
	/* 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
2308
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2309
	th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
L
Linus Torvalds 已提交
2310 2311

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2312
	th->window = htons(min(req->rcv_wnd, 65535U));
A
Adam Langley 已提交
2313
	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
L
Linus Torvalds 已提交
2314
	th->doff = (tcp_header_size >> 2);
P
Pavel Emelyanov 已提交
2315
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
2316 2317 2318 2319 2320

#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,
2321
					       md5, NULL, req, skb);
2322 2323 2324
	}
#endif

L
Linus Torvalds 已提交
2325 2326 2327
	return skb;
}

2328
/*
L
Linus Torvalds 已提交
2329
 * Do all connect socket setups that can be done AF independent.
2330
 */
S
Stephen Hemminger 已提交
2331
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342
{
	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);

2343 2344 2345 2346 2347
#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
2348 2349 2350 2351
	/* 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
2352
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
2353 2354 2355 2356 2357
	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);
2358 2359 2360
	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
		tp->advmss = tp->rx_opt.user_mss;

L
Linus Torvalds 已提交
2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378
	tcp_initialize_rcv_mss(sk);

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

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

	sk->sk_err = 0;
	sock_reset_flag(sk, SOCK_DONE);
	tp->snd_wnd = 0;
	tcp_init_wl(tp, tp->write_seq, 0);
	tp->snd_una = tp->write_seq;
	tp->snd_sml = tp->write_seq;
I
Ilpo Järvinen 已提交
2379
	tp->snd_up = tp->write_seq;
L
Linus Torvalds 已提交
2380 2381 2382 2383
	tp->rcv_nxt = 0;
	tp->rcv_wup = 0;
	tp->copied_seq = 0;

2384 2385
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
2386 2387 2388 2389 2390
	tcp_clear_retrans(tp);
}

/*
 * Build a SYN and send it off.
2391
 */
L
Linus Torvalds 已提交
2392 2393 2394 2395 2396 2397 2398
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;

	tcp_connect_init(sk);

2399
	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
L
Linus Torvalds 已提交
2400 2401 2402 2403 2404 2405
	if (unlikely(buff == NULL))
		return -ENOBUFS;

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

2406
	tp->snd_nxt = tp->write_seq;
2407 2408
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
	TCP_ECN_send_syn(sk, buff);
L
Linus Torvalds 已提交
2409 2410 2411 2412 2413

	/* Send it off. */
	TCP_SKB_CB(buff)->when = tcp_time_stamp;
	tp->retrans_stamp = TCP_SKB_CB(buff)->when;
	skb_header_release(buff);
2414
	__tcp_add_write_queue_tail(sk, buff);
2415 2416
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
L
Linus Torvalds 已提交
2417
	tp->packets_out += tcp_skb_pcount(buff);
2418
	tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
2419 2420 2421 2422 2423 2424

	/* 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
2425
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
2426 2427

	/* Timer for repeating the SYN until an answer. */
2428 2429
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
2430 2431 2432 2433 2434 2435 2436 2437 2438
	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)
{
2439 2440
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
2441 2442 2443
	unsigned long timeout;

	if (ato > TCP_DELACK_MIN) {
2444
		const struct tcp_sock *tp = tcp_sk(sk);
2445
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
2446

2447 2448
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
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Linus Torvalds 已提交
2449 2450 2451 2452 2453
			max_ato = TCP_DELACK_MAX;

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

		/* If some rtt estimate is known, use it to bound delayed ack.
2454
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
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		 * directly.
		 */
		if (tp->srtt) {
2458
			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
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Linus Torvalds 已提交
2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470

			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. */
2471
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
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		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
2475 2476
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
2477 2478 2479 2480
			tcp_send_ack(sk);
			return;
		}

2481 2482
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
2483
	}
2484 2485 2486
	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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Linus Torvalds 已提交
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}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
2492
	struct sk_buff *buff;
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Linus Torvalds 已提交
2493

2494 2495 2496
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
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Linus Torvalds 已提交
2497

2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508
	/* We are not putting this on the write queue, so
	 * tcp_transmit_skb() will set the ownership to this
	 * sock.
	 */
	buff = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
	if (buff == NULL) {
		inet_csk_schedule_ack(sk);
		inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
					  TCP_DELACK_MAX, TCP_RTO_MAX);
		return;
L
Linus Torvalds 已提交
2509
	}
2510 2511 2512

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
2513
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);
2514 2515 2516 2517

	/* 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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Linus Torvalds 已提交
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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);
2538
	if (skb == NULL)
L
Linus Torvalds 已提交
2539 2540 2541 2542 2543 2544 2545 2546
		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.
	 */
2547
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
L
Linus Torvalds 已提交
2548
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2549
	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
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Linus Torvalds 已提交
2550 2551 2552 2553
}

int tcp_write_wakeup(struct sock *sk)
{
2554 2555
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2556

2557 2558 2559 2560 2561 2562 2563 2564 2565 2566 2567 2568 2569 2570 2571 2572 2573 2574 2575
	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);
L
Linus Torvalds 已提交
2576
			TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
2577 2578 2579 2580 2581 2582 2583 2584 2585 2586 2587 2588
			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 {
I
Ilpo Järvinen 已提交
2589
		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
2590 2591
			tcp_xmit_probe_skb(sk, 1);
		return tcp_xmit_probe_skb(sk, 0);
L
Linus Torvalds 已提交
2592 2593 2594 2595 2596 2597 2598 2599
	}
}

/* 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)
{
2600
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2601 2602 2603 2604 2605
	struct tcp_sock *tp = tcp_sk(sk);
	int err;

	err = tcp_write_wakeup(sk);

2606
	if (tp->packets_out || !tcp_send_head(sk)) {
L
Linus Torvalds 已提交
2607
		/* Cancel probe timer, if it is not required. */
2608
		icsk->icsk_probes_out = 0;
2609
		icsk->icsk_backoff = 0;
L
Linus Torvalds 已提交
2610 2611 2612 2613
		return;
	}

	if (err <= 0) {
2614 2615
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
2616
		icsk->icsk_probes_out++;
2617
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2618 2619
					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
					  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2620 2621
	} else {
		/* If packet was not sent due to local congestion,
2622
		 * do not backoff and do not remember icsk_probes_out.
L
Linus Torvalds 已提交
2623 2624 2625 2626
		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
2627 2628
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
2629
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2630
					  min(icsk->icsk_rto << icsk->icsk_backoff,
2631 2632
					      TCP_RESOURCE_PROBE_INTERVAL),
					  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2633 2634 2635
	}
}

2636
EXPORT_SYMBOL(tcp_select_initial_window);
L
Linus Torvalds 已提交
2637 2638 2639 2640
EXPORT_SYMBOL(tcp_connect);
EXPORT_SYMBOL(tcp_make_synack);
EXPORT_SYMBOL(tcp_simple_retransmit);
EXPORT_SYMBOL(tcp_sync_mss);
J
John Heffner 已提交
2641
EXPORT_SYMBOL(tcp_mtup_init);