tcp_output.c 73.8 KB
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/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Implementation of the Transmission Control Protocol(TCP).
 *
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 * Authors:	Ross Biro
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 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
 *		Florian La Roche, <flla@stud.uni-sb.de>
 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
 *		Matthew Dillon, <dillon@apollo.west.oic.com>
 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *		Jorge Cwik, <jorge@laser.satlink.net>
 */

/*
 * Changes:	Pedro Roque	:	Retransmit queue handled by TCP.
 *				:	Fragmentation on mtu decrease
 *				:	Segment collapse on retransmit
 *				:	AF independence
 *
 *		Linus Torvalds	:	send_delayed_ack
 *		David S. Miller	:	Charge memory using the right skb
 *					during syn/ack processing.
 *		David S. Miller :	Output engine completely rewritten.
 *		Andrea Arcangeli:	SYNACK carry ts_recent in tsecr.
 *		Cacophonix Gaul :	draft-minshall-nagle-01
 *		J Hadi Salim	:	ECN support
 *
 */

#include <net/tcp.h>

#include <linux/compiler.h>
#include <linux/module.h>

/* People can turn this off for buggy TCP's found in printers etc. */
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int sysctl_tcp_retrans_collapse __read_mostly = 1;
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/* People can turn this on to work with those rare, broken TCPs that
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 * interpret the window field as a signed quantity.
 */
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int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
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/* This limits the percentage of the congestion window which we
 * will allow a single TSO frame to consume.  Building TSO frames
 * which are too large can cause TCP streams to be bursty.
 */
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int sysctl_tcp_tso_win_divisor __read_mostly = 3;
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int sysctl_tcp_mtu_probing __read_mostly = 0;
int sysctl_tcp_base_mss __read_mostly = 512;
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/* By default, RFC2861 behavior.  */
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int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
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static void tcp_event_new_data_sent(struct sock *sk, struct sk_buff *skb)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	unsigned int prior_packets = tp->packets_out;
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	tcp_advance_send_head(sk, skb);
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	tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
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	/* Don't override Nagle indefinately with F-RTO */
	if (tp->frto_counter == 2)
		tp->frto_counter = 3;
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	tp->packets_out += tcp_skb_pcount(skb);
	if (!prior_packets)
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
					  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
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}

/* SND.NXT, if window was not shrunk.
 * If window has been shrunk, what should we make? It is not clear at all.
 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
 * invalid. OK, let's make this for now:
 */
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static inline __u32 tcp_acceptable_seq(struct sock *sk)
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{
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	struct tcp_sock *tp = tcp_sk(sk);

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

/* Calculate mss to advertise in SYN segment.
 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
 *
 * 1. It is independent of path mtu.
 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
 *    attached devices, because some buggy hosts are confused by
 *    large MSS.
 * 4. We do not make 3, we advertise MSS, calculated from first
 *    hop device mtu, but allow to raise it to ip_rt_min_advmss.
 *    This may be overridden via information stored in routing table.
 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
 *    probably even Jumbo".
 */
static __u16 tcp_advertise_mss(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
	int mss = tp->advmss;

	if (dst && dst_metric(dst, RTAX_ADVMSS) < mss) {
		mss = dst_metric(dst, RTAX_ADVMSS);
		tp->advmss = mss;
	}

	return (__u16)mss;
}

/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
 * This is the first part of cwnd validation mechanism. */
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static void tcp_cwnd_restart(struct sock *sk, struct dst_entry *dst)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	s32 delta = tcp_time_stamp - tp->lsndtime;
	u32 restart_cwnd = tcp_init_cwnd(tp, dst);
	u32 cwnd = tp->snd_cwnd;

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

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

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

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

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

/* Determine a window scaling and initial window to offer.
 * Based on the assumption that the given amount of space
 * will be offered. Store the results in the tp structure.
 * NOTE: for smooth operation initial space offering should
 * be a multiple of mss if possible. We assume here that mss >= 1.
 * This MUST be enforced by all callers.
 */
void tcp_select_initial_window(int __space, __u32 mss,
			       __u32 *rcv_wnd, __u32 *window_clamp,
			       int wscale_ok, __u8 *rcv_wscale)
{
	unsigned int space = (__space < 0 ? 0 : __space);

	/* If no clamp set the clamp to the max possible scaled window */
	if (*window_clamp == 0)
		(*window_clamp) = (65535 << 14);
	space = min(*window_clamp, space);

	/* Quantize space offering to a multiple of mss if possible. */
	if (space > mss)
		space = (space / mss) * mss;

	/* NOTE: offering an initial window larger than 32767
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	 * will break some buggy TCP stacks. If the admin tells us
	 * it is likely we could be speaking with such a buggy stack
	 * we will truncate our initial window offering to 32K-1
	 * unless the remote has sent us a window scaling option,
	 * which we interpret as a sign the remote TCP is not
	 * misinterpreting the window field as a signed quantity.
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	 */
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	if (sysctl_tcp_workaround_signed_windows)
		(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
	else
		(*rcv_wnd) = space;

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

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

	/* Set the clamp no higher than max representable value */
	(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
}

/* Chose a new window to advertise, update state in tcp_sock for the
 * socket, and return result with RFC1323 scaling applied.  The return
 * value can be stuffed directly into th->window for an outgoing
 * frame.
 */
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static u16 tcp_select_window(struct sock *sk)
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{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 cur_win = tcp_receive_window(tp);
	u32 new_win = __tcp_select_window(sk);

	/* Never shrink the offered window */
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	if (new_win < cur_win) {
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		/* Danger Will Robinson!
		 * Don't update rcv_wup/rcv_wnd here or else
		 * we will not be able to advertise a zero
		 * window in time.  --DaveM
		 *
		 * Relax Will Robinson.
		 */
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		new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
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	}
	tp->rcv_wnd = new_win;
	tp->rcv_wup = tp->rcv_nxt;

	/* Make sure we do not exceed the maximum possible
	 * scaled window.
	 */
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	if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
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		new_win = min(new_win, MAX_TCP_WINDOW);
	else
		new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));

	/* RFC1323 scaling applied */
	new_win >>= tp->rx_opt.rcv_wscale;

	/* If we advertise zero window, disable fast path. */
	if (new_win == 0)
		tp->pred_flags = 0;

	return new_win;
}

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

static inline void TCP_ECN_send_syn(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	tp->ecn_flags = 0;
	if (sysctl_tcp_ecn) {
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		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_ECE | TCPCB_FLAG_CWR;
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		tp->ecn_flags = TCP_ECN_OK;
	}
}

static __inline__ void
TCP_ECN_make_synack(struct request_sock *req, struct tcphdr *th)
{
	if (inet_rsk(req)->ecn_ok)
		th->ece = 1;
}

static inline void TCP_ECN_send(struct sock *sk, struct sk_buff *skb,
				int tcp_header_len)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->ecn_flags & TCP_ECN_OK) {
		/* Not-retransmitted data segment: set ECT and inject CWR. */
		if (skb->len != tcp_header_len &&
		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
			INET_ECN_xmit(sk);
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			if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
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				tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
				tcp_hdr(skb)->cwr = 1;
				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
			}
		} else {
			/* ACK or retransmitted segment: clear ECT|CE */
			INET_ECN_dontxmit(sk);
		}
		if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
			tcp_hdr(skb)->ece = 1;
	}
}

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/* Constructs common control bits of non-data skb. If SYN/FIN is present,
 * auto increment end seqno.
 */
static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
{
	skb->csum = 0;

	TCP_SKB_CB(skb)->flags = flags;
	TCP_SKB_CB(skb)->sacked = 0;

	skb_shinfo(skb)->gso_segs = 1;
	skb_shinfo(skb)->gso_size = 0;
	skb_shinfo(skb)->gso_type = 0;

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

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

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

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

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

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

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

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

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

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

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

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

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

	return size;
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}

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

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

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

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

	return size;
}

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

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

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

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

	return size;
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Stephen Hemminger 已提交
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}
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/* 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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	struct tcp_out_options opts;
	unsigned tcp_options_size, tcp_header_size;
604 605
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
606 607 608 609 610 611 612 613
	struct tcphdr *th;
	int err;

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

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

	if (likely(clone_it)) {
		if (unlikely(skb_cloned(skb)))
			skb = pskb_copy(skb, gfp_mask);
		else
			skb = skb_clone(skb, gfp_mask);
		if (unlikely(!skb))
			return -ENOBUFS;
	}
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Linus Torvalds 已提交
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626 627 628
	inet = inet_sk(sk);
	tp = tcp_sk(sk);
	tcb = TCP_SKB_CB(skb);
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	memset(&opts, 0, sizeof(opts));
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	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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Ilpo Järvinen 已提交
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	/* The urg_mode check is necessary during a below snd_una win probe */
666 667 668 669 670 671 672 673
	if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
		if (before(tp->snd_up, tcb->seq + 0x10000)) {
			th->urg_ptr = htons(tp->snd_up - tcb->seq);
			th->urg = 1;
		} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
			th->urg_ptr = 0xFFFF;
			th->urg = 1;
		}
674
	}
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Linus Torvalds 已提交
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	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
	if (likely((tcb->flags & TCPCB_FLAG_SYN) == 0))
678
		TCP_ECN_send(sk, skb, tcp_header_size);
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Linus Torvalds 已提交
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680 681 682
#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;
684
		tp->af_specific->calc_md5_hash(md5_hash_location,
685
					       md5, sk, NULL, skb);
686 687 688
	}
#endif

689
	icsk->icsk_af_ops->send_check(sk, skb->len, skb);
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Linus Torvalds 已提交
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691 692
	if (likely(tcb->flags & TCPCB_FLAG_ACK))
		tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
L
Linus Torvalds 已提交
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694 695
	if (skb->len != tcp_header_size)
		tcp_event_data_sent(tp, skb, sk);
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697
	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);
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Linus Torvalds 已提交
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700
	err = icsk->icsk_af_ops->queue_xmit(skb, 0);
701
	if (likely(err <= 0))
702 703
		return err;

704
	tcp_enter_cwr(sk, 1);
705

706
	return net_xmit_eval(err);
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}

709
/* This routine just queue's the buffer
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 *
 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
 * otherwise socket can stall.
 */
static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Advance write_seq and place onto the write_queue. */
	tp->write_seq = TCP_SKB_CB(skb)->end_seq;
	skb_header_release(skb);
721
	tcp_add_write_queue_tail(sk, skb);
722 723
	sk->sk_wmem_queued += skb->truesize;
	sk_mem_charge(sk, skb->truesize);
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Linus Torvalds 已提交
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}

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

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

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

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

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/* Function to create two new TCP segments.  Shrinks the given segment
 * to the specified size and appends a new segment with the rest of the
760
 * packet to the list.  This won't be called frequently, I hope.
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Linus Torvalds 已提交
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 * Remember, these are still headerless SKBs at this point.
 */
763 764
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
		 unsigned int mss_now)
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Linus Torvalds 已提交
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{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;
768
	int nsize, old_factor;
769
	int nlen;
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	u16 flags;

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

774
	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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789 790
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
791 792 793
	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;
802
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
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	TCP_SKB_CB(buff)->flags = flags;
804
	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
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806
	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
L
Linus Torvalds 已提交
807
		/* Copy and checksum data tail into the new buffer. */
808 809
		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 {
816
		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;
826
	buff->tstamp = skb->tstamp;
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Linus Torvalds 已提交
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828 829
	old_factor = tcp_skb_pcount(skb);

L
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	/* Fix up tso_factor for both original and new SKB.  */
831 832
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
L
Linus Torvalds 已提交
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834 835 836
	/* If this packet has been sent out already, we must
	 * adjust the various packet counters.
	 */
837
	if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
838 839
		int diff = old_factor - tcp_skb_pcount(skb) -
			tcp_skb_pcount(buff);
L
Linus Torvalds 已提交
840

841
		tp->packets_out -= diff;
842 843 844 845 846 847

		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;

848
		if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
849
			tp->lost_out -= diff;
850

I
Ilpo Järvinen 已提交
851 852 853 854
		/* 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);
855
		}
856
		tcp_adjust_fackets_out(sk, skb, diff);
L
Linus Torvalds 已提交
857 858 859
	}

	/* Link BUFF into the send queue. */
860
	skb_header_release(buff);
861
	tcp_insert_write_queue_after(skb, buff, sk);
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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.
 */
870
static void __pskb_trim_head(struct sk_buff *skb, int len)
L
Linus Torvalds 已提交
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{
	int i, k, eat;

	eat = len;
	k = 0;
876
	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;

892
	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)
{
899
	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
L
Linus Torvalds 已提交
900 901
		return -ENOMEM;

902 903
	/* If len == headlen, we avoid __skb_pull to preserve alignment. */
	if (unlikely(len < skb_headlen(skb)))
L
Linus Torvalds 已提交
904
		__skb_pull(skb, len);
905 906
	else
		__pskb_trim_head(skb, len - skb_headlen(skb));
L
Linus Torvalds 已提交
907 908

	TCP_SKB_CB(skb)->seq += len;
909
	skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
910 911 912

	skb->truesize	     -= len;
	sk->sk_wmem_queued   -= len;
913
	sk_mem_uncharge(sk, len);
L
Linus Torvalds 已提交
914 915 916 917 918 919
	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)
920
		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk, 1));
L
Linus Torvalds 已提交
921 922 923 924

	return 0;
}

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

981 982 983 984 985 986 987 988 989
/* Bound MSS / TSO packet size with the half of the window */
static int tcp_bound_to_half_wnd(struct tcp_sock *tp, int pktsize)
{
	if (tp->max_window && pktsize > (tp->max_window >> 1))
		return max(tp->max_window >> 1, 68U - tp->tcp_header_len);
	else
		return pktsize;
}

L
Linus Torvalds 已提交
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/* This function synchronize snd mss to current pmtu/exthdr set.

   tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
   for TCP options, but includes only bare TCP header.

   tp->rx_opt.mss_clamp is mss negotiated at connection setup.
S
Stephen Hemminger 已提交
996
   It is minimum of user_mss and mss received with SYN.
L
Linus Torvalds 已提交
997 998
   It also does not include TCP options.

999
   inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
L
Linus Torvalds 已提交
1000 1001 1002 1003 1004 1005 1006 1007 1008

   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.

1009 1010
   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
1011 1012 1013 1014
 */
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
	struct tcp_sock *tp = tcp_sk(sk);
1015
	struct inet_connection_sock *icsk = inet_csk(sk);
J
John Heffner 已提交
1016
	int mss_now;
L
Linus Torvalds 已提交
1017

J
John Heffner 已提交
1018 1019
	if (icsk->icsk_mtup.search_high > pmtu)
		icsk->icsk_mtup.search_high = pmtu;
L
Linus Torvalds 已提交
1020

J
John Heffner 已提交
1021
	mss_now = tcp_mtu_to_mss(sk, pmtu);
1022
	mss_now = tcp_bound_to_half_wnd(tp, mss_now);
L
Linus Torvalds 已提交
1023 1024

	/* And store cached results */
1025
	icsk->icsk_pmtu_cookie = pmtu;
J
John Heffner 已提交
1026 1027
	if (icsk->icsk_mtup.enabled)
		mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1028
	tp->mss_cache = mss_now;
L
Linus Torvalds 已提交
1029 1030 1031 1032 1033 1034 1035

	return mss_now;
}

/* Compute the current effective MSS, taking SACKs and IP options,
 * and even PMTU discovery events into account.
 */
1036
unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
L
Linus Torvalds 已提交
1037 1038 1039
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);
1040 1041 1042
	u32 mss_now;
	u16 xmit_size_goal;
	int doing_tso = 0;
A
Adam Langley 已提交
1043 1044 1045
	unsigned header_len;
	struct tcp_out_options opts;
	struct tcp_md5sig_key *md5;
1046 1047 1048

	mss_now = tp->mss_cache;

1049
	if (large_allowed && sk_can_gso(sk))
1050
		doing_tso = 1;
L
Linus Torvalds 已提交
1051 1052 1053

	if (dst) {
		u32 mtu = dst_mtu(dst);
1054
		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
L
Linus Torvalds 已提交
1055 1056 1057
			mss_now = tcp_sync_mss(sk, mtu);
	}

A
Adam Langley 已提交
1058 1059 1060 1061 1062 1063 1064 1065 1066 1067
	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;
	}
1068

1069
	xmit_size_goal = mss_now;
L
Linus Torvalds 已提交
1070

1071
	if (doing_tso) {
1072
		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
1073
				  inet_csk(sk)->icsk_af_ops->net_header_len -
1074 1075
				  inet_csk(sk)->icsk_ext_hdr_len -
				  tp->tcp_header_len);
L
Linus Torvalds 已提交
1076

1077
		xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
1078
		xmit_size_goal -= (xmit_size_goal % mss_now);
L
Linus Torvalds 已提交
1079
	}
1080
	tp->xmit_size_goal = xmit_size_goal;
L
Linus Torvalds 已提交
1081 1082 1083 1084

	return mss_now;
}

1085
/* Congestion window validation. (RFC2861) */
1086
static void tcp_cwnd_validate(struct sock *sk)
1087
{
1088
	struct tcp_sock *tp = tcp_sk(sk);
1089

1090
	if (tp->packets_out >= tp->snd_cwnd) {
1091 1092 1093 1094 1095 1096 1097 1098
		/* 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;

1099 1100
		if (sysctl_tcp_slow_start_after_idle &&
		    (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1101 1102 1103 1104
			tcp_cwnd_application_limited(sk);
	}
}

1105 1106 1107 1108
/* 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).
1109 1110 1111 1112 1113 1114 1115
 *
 * 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.
1116 1117
 */
static unsigned int tcp_mss_split_point(struct sock *sk, struct sk_buff *skb,
1118
					unsigned int mss_now, unsigned int cwnd)
1119
{
1120 1121
	struct tcp_sock *tp = tcp_sk(sk);
	u32 needed, window, cwnd_len;
1122

1123
	window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1124
	cwnd_len = mss_now * cwnd;
1125 1126 1127 1128

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

1129 1130
	needed = min(skb->len, window);

1131
	if (cwnd_len <= needed)
1132 1133 1134
		return cwnd_len;

	return needed - needed % mss_now;
1135 1136 1137 1138 1139
}

/* 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.
 */
1140 1141
static inline unsigned int tcp_cwnd_test(struct tcp_sock *tp,
					 struct sk_buff *skb)
1142 1143 1144 1145
{
	u32 in_flight, cwnd;

	/* Don't be strict about the congestion window for the final FIN.  */
1146 1147
	if ((TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN) &&
	    tcp_skb_pcount(skb) == 1)
1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160
		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.
 */
1161 1162
static int tcp_init_tso_segs(struct sock *sk, struct sk_buff *skb,
			     unsigned int mss_now)
1163 1164 1165
{
	int tso_segs = tcp_skb_pcount(skb);

1166
	if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1167
		tcp_set_skb_tso_segs(sk, skb, mss_now);
1168 1169 1170 1171 1172 1173 1174
		tso_segs = tcp_skb_pcount(skb);
	}
	return tso_segs;
}

static inline int tcp_minshall_check(const struct tcp_sock *tp)
{
1175
	return after(tp->snd_sml, tp->snd_una) &&
1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186
		!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,
1187
				  const struct sk_buff *skb,
1188 1189 1190
				  unsigned mss_now, int nonagle)
{
	return (skb->len < mss_now &&
1191 1192
		((nonagle & TCP_NAGLE_CORK) ||
		 (!nonagle && tp->packets_out && tcp_minshall_check(tp))));
1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209
}

/* 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;

1210 1211 1212
	/* 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
1213
	if (tcp_urg_mode(tp) || (tp->frto_counter == 2) ||
1214 1215 1216 1217 1218 1219 1220 1221 1222 1223
	    (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? */
1224 1225
static inline int tcp_snd_wnd_test(struct tcp_sock *tp, struct sk_buff *skb,
				   unsigned int cur_mss)
1226 1227 1228 1229 1230 1231
{
	u32 end_seq = TCP_SKB_CB(skb)->end_seq;

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

1232
	return !after(end_seq, tcp_wnd_end(tp));
1233 1234
}

1235
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1236 1237 1238 1239 1240 1241 1242 1243 1244
 * 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;

1245
	tcp_init_tso_segs(sk, skb, cur_mss);
1246 1247 1248 1249 1250

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

	cwnd_quota = tcp_cwnd_test(tp, skb);
1251
	if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1252 1253 1254 1255 1256
		cwnd_quota = 0;

	return cwnd_quota;
}

1257
int tcp_may_send_now(struct sock *sk)
1258
{
1259
	struct tcp_sock *tp = tcp_sk(sk);
1260
	struct sk_buff *skb = tcp_send_head(sk);
1261 1262 1263 1264

	return (skb &&
		tcp_snd_test(sk, skb, tcp_current_mss(sk, 1),
			     (tcp_skb_is_last(sk, skb) ?
1265
			      tp->nonagle : TCP_NAGLE_PUSH)));
1266 1267 1268 1269 1270 1271 1272 1273 1274
}

/* 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).
 */
1275 1276
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
			unsigned int mss_now)
1277 1278 1279 1280 1281 1282
{
	struct sk_buff *buff;
	int nlen = skb->len - len;
	u16 flags;

	/* All of a TSO frame must be composed of paged data.  */
1283 1284
	if (skb->len != skb->data_len)
		return tcp_fragment(sk, skb, len, mss_now);
1285

1286
	buff = sk_stream_alloc_skb(sk, 0, GFP_ATOMIC);
1287 1288 1289
	if (unlikely(buff == NULL))
		return -ENOMEM;

1290 1291
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
1292
	buff->truesize += nlen;
1293 1294 1295 1296 1297 1298 1299 1300 1301
	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;
1302
	TCP_SKB_CB(skb)->flags = flags & ~(TCPCB_FLAG_FIN | TCPCB_FLAG_PSH);
1303 1304 1305 1306 1307
	TCP_SKB_CB(buff)->flags = flags;

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

1308
	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1309 1310 1311
	skb_split(skb, buff, len);

	/* Fix up tso_factor for both original and new SKB.  */
1312 1313
	tcp_set_skb_tso_segs(sk, skb, mss_now);
	tcp_set_skb_tso_segs(sk, buff, mss_now);
1314 1315 1316

	/* Link BUFF into the send queue. */
	skb_header_release(buff);
1317
	tcp_insert_write_queue_after(skb, buff, sk);
1318 1319 1320 1321 1322 1323 1324 1325 1326

	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.
 */
1327
static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
1328
{
1329
	struct tcp_sock *tp = tcp_sk(sk);
1330
	const struct inet_connection_sock *icsk = inet_csk(sk);
1331 1332 1333
	u32 send_win, cong_win, limit, in_flight;

	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN)
J
John Heffner 已提交
1334
		goto send_now;
1335

1336
	if (icsk->icsk_ca_state != TCP_CA_Open)
J
John Heffner 已提交
1337 1338 1339
		goto send_now;

	/* Defer for less than two clock ticks. */
I
Ilpo Järvinen 已提交
1340
	if (tp->tso_deferred &&
1341
	    (((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
J
John Heffner 已提交
1342
		goto send_now;
1343

1344 1345
	in_flight = tcp_packets_in_flight(tp);

1346
	BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1347

1348
	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1349 1350 1351 1352 1353 1354

	/* 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);

1355
	/* If a full-sized TSO skb can be sent, do it. */
1356
	if (limit >= sk->sk_gso_max_size)
J
John Heffner 已提交
1357
		goto send_now;
1358

1359 1360 1361 1362 1363 1364 1365 1366
	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
1367
			goto send_now;
1368 1369 1370 1371 1372 1373 1374
	} 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
1375
			goto send_now;
1376 1377 1378
	}

	/* Ok, it looks like it is advisable to defer.  */
1379
	tp->tso_deferred = 1 | (jiffies << 1);
J
John Heffner 已提交
1380

1381
	return 1;
J
John Heffner 已提交
1382 1383 1384 1385

send_now:
	tp->tso_deferred = 0;
	return 0;
1386 1387
}

J
John Heffner 已提交
1388 1389 1390
/* 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,
1391 1392
 *         -1 otherwise
 */
J
John Heffner 已提交
1393 1394 1395 1396 1397 1398 1399
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;
1400
	int size_needed;
J
John Heffner 已提交
1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416
	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);
1417
	probe_size = 2 * tp->mss_cache;
1418
	size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
J
John Heffner 已提交
1419 1420 1421 1422 1423 1424
	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? */
1425
	if (tp->write_seq - tp->snd_nxt < size_needed)
J
John Heffner 已提交
1426 1427
		return -1;

1428 1429
	if (tp->snd_wnd < size_needed)
		return -1;
1430
	if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1431
		return 0;
J
John Heffner 已提交
1432

1433 1434 1435
	/* 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
1436 1437 1438 1439 1440 1441 1442 1443
			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;
1444 1445
	sk->sk_wmem_queued += nskb->truesize;
	sk_mem_charge(sk, nskb->truesize);
J
John Heffner 已提交
1446

1447
	skb = tcp_send_head(sk);
J
John Heffner 已提交
1448 1449 1450 1451 1452 1453

	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;
1454
	nskb->ip_summed = skb->ip_summed;
J
John Heffner 已提交
1455

1456 1457
	tcp_insert_write_queue_before(nskb, skb, sk);

J
John Heffner 已提交
1458
	len = 0;
1459
	tcp_for_write_queue_from_safe(skb, next, sk) {
J
John Heffner 已提交
1460 1461 1462 1463 1464
		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,
1465 1466
							    skb_put(nskb, copy),
							    copy, nskb->csum);
J
John Heffner 已提交
1467 1468 1469 1470 1471

		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;
1472
			tcp_unlink_write_queue(skb, sk);
1473
			sk_wmem_free_skb(sk, skb);
J
John Heffner 已提交
1474 1475
		} else {
			TCP_SKB_CB(nskb)->flags |= TCP_SKB_CB(skb)->flags &
1476
						   ~(TCPCB_FLAG_FIN|TCPCB_FLAG_PSH);
J
John Heffner 已提交
1477 1478
			if (!skb_shinfo(skb)->nr_frags) {
				skb_pull(skb, copy);
1479
				if (skb->ip_summed != CHECKSUM_PARTIAL)
1480 1481
					skb->csum = csum_partial(skb->data,
								 skb->len, 0);
J
John Heffner 已提交
1482 1483 1484 1485 1486 1487 1488 1489
			} else {
				__pskb_trim_head(skb, copy);
				tcp_set_skb_tso_segs(sk, skb, mss_now);
			}
			TCP_SKB_CB(skb)->seq += copy;
		}

		len += copy;
1490 1491 1492

		if (len >= probe_size)
			break;
J
John Heffner 已提交
1493 1494 1495 1496 1497 1498 1499 1500
	}
	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
1501
		 * effectively two packets. */
J
John Heffner 已提交
1502
		tp->snd_cwnd--;
1503
		tcp_event_new_data_sent(sk, nskb);
J
John Heffner 已提交
1504 1505

		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1506 1507
		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
1508 1509 1510 1511 1512 1513 1514

		return 1;
	}

	return -1;
}

L
Linus Torvalds 已提交
1515 1516 1517 1518
/* This routine writes packets to the network.  It advances the
 * send_head.  This happens as incoming acks open up the remote
 * window for us.
 *
1519 1520 1521 1522
 * 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
1523 1524 1525
 * Returns 1, if no segments are in flight and we have queued segments, but
 * cannot send anything now because of SWS or another problem.
 */
1526 1527
static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
			  int push_one, gfp_t gfp)
L
Linus Torvalds 已提交
1528 1529
{
	struct tcp_sock *tp = tcp_sk(sk);
1530
	struct sk_buff *skb;
1531 1532
	unsigned int tso_segs, sent_pkts;
	int cwnd_quota;
J
John Heffner 已提交
1533
	int result;
L
Linus Torvalds 已提交
1534

1535
	sent_pkts = 0;
J
John Heffner 已提交
1536

1537 1538 1539 1540 1541 1542 1543 1544
	if (!push_one) {
		/* Do MTU probing. */
		result = tcp_mtu_probe(sk);
		if (!result) {
			return 0;
		} else if (result > 0) {
			sent_pkts = 1;
		}
J
John Heffner 已提交
1545 1546
	}

1547
	while ((skb = tcp_send_head(sk))) {
1548 1549
		unsigned int limit;

1550
		tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
1551
		BUG_ON(!tso_segs);
1552

1553 1554 1555 1556 1557 1558 1559
		cwnd_quota = tcp_cwnd_test(tp, skb);
		if (!cwnd_quota)
			break;

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

1560 1561 1562 1563 1564 1565
		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 {
1566
			if (!push_one && tcp_tso_should_defer(sk, skb))
1567 1568
				break;
		}
1569

1570
		limit = mss_now;
1571
		if (tso_segs > 1 && !tcp_urg_mode(tp))
1572 1573
			limit = tcp_mss_split_point(sk, skb, mss_now,
						    cwnd_quota);
L
Linus Torvalds 已提交
1574

1575 1576 1577 1578
		if (skb->len > limit &&
		    unlikely(tso_fragment(sk, skb, limit, mss_now)))
			break;

1579
		TCP_SKB_CB(skb)->when = tcp_time_stamp;
1580

1581
		if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
1582
			break;
L
Linus Torvalds 已提交
1583

1584 1585 1586
		/* Advance the send_head.  This one is sent out.
		 * This call will increment packets_out.
		 */
1587
		tcp_event_new_data_sent(sk, skb);
L
Linus Torvalds 已提交
1588

1589
		tcp_minshall_update(tp, mss_now, skb);
1590
		sent_pkts++;
1591 1592 1593

		if (push_one)
			break;
1594
	}
L
Linus Torvalds 已提交
1595

1596
	if (likely(sent_pkts)) {
1597
		tcp_cwnd_validate(sk);
1598
		return 0;
L
Linus Torvalds 已提交
1599
	}
1600
	return !tp->packets_out && tcp_send_head(sk);
L
Linus Torvalds 已提交
1601 1602
}

1603 1604 1605 1606
/* 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.
 */
1607 1608
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
			       int nonagle)
1609
{
1610
	struct sk_buff *skb = tcp_send_head(sk);
1611

1612 1613 1614 1615 1616 1617 1618 1619 1620 1621
	if (!skb)
		return;

	/* If we are closed, the bytes will have to remain here.
	 * In time closedown will finish, we empty the write queue and
	 * all will be happy.
	 */
	if (unlikely(sk->sk_state == TCP_CLOSE))
		return;

1622
	if (tcp_write_xmit(sk, cur_mss, nonagle, 0, GFP_ATOMIC))
1623
		tcp_check_probe_timer(sk);
1624 1625
}

1626 1627 1628 1629 1630
/* 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)
{
1631
	struct sk_buff *skb = tcp_send_head(sk);
1632 1633 1634

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

1635
	tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
1636 1637
}

L
Linus Torvalds 已提交
1638 1639
/* This function returns the amount that we can raise the
 * usable window based on the following constraints
1640
 *
L
Linus Torvalds 已提交
1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658
 * 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.
1659
 *
L
Linus Torvalds 已提交
1660 1661
 * Of course, if the sender implements sender side SWS prevention
 * then this will not be a problem.
1662
 *
L
Linus Torvalds 已提交
1663
 * BSD seems to make the following compromise:
1664
 *
L
Linus Torvalds 已提交
1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691
 *	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)
{
1692
	struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
1693
	struct tcp_sock *tp = tcp_sk(sk);
S
Stephen Hemminger 已提交
1694
	/* MSS for the peer's data.  Previous versions used mss_clamp
L
Linus Torvalds 已提交
1695 1696 1697 1698 1699
	 * 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
	 */
1700
	int mss = icsk->icsk_ack.rcv_mss;
L
Linus Torvalds 已提交
1701 1702 1703 1704 1705
	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)
1706
		mss = full_space;
L
Linus Torvalds 已提交
1707

1708
	if (free_space < (full_space >> 1)) {
1709
		icsk->icsk_ack.quick = 0;
L
Linus Torvalds 已提交
1710 1711

		if (tcp_memory_pressure)
1712 1713
			tp->rcv_ssthresh = min(tp->rcv_ssthresh,
					       4U * tp->advmss);
L
Linus Torvalds 已提交
1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745

		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)
1746
			window = (free_space / mss) * mss;
1747
		else if (mss == full_space &&
1748
			 free_space > window + (full_space >> 1))
1749
			window = free_space;
L
Linus Torvalds 已提交
1750 1751 1752 1753 1754
	}

	return window;
}

1755 1756
/* Collapses two adjacent SKB's during retransmission. */
static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
L
Linus Torvalds 已提交
1757 1758
{
	struct tcp_sock *tp = tcp_sk(sk);
1759
	struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
1760 1761
	int skb_size, next_skb_size;
	u16 flags;
L
Linus Torvalds 已提交
1762

1763 1764 1765
	skb_size = skb->len;
	next_skb_size = next_skb->len;
	flags = TCP_SKB_CB(skb)->flags;
L
Linus Torvalds 已提交
1766

1767
	BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
1768

1769
	tcp_highest_sack_combine(sk, next_skb, skb);
L
Linus Torvalds 已提交
1770

1771
	tcp_unlink_write_queue(next_skb, sk);
L
Linus Torvalds 已提交
1772

1773 1774
	skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
				  next_skb_size);
L
Linus Torvalds 已提交
1775

1776 1777
	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
		skb->ip_summed = CHECKSUM_PARTIAL;
L
Linus Torvalds 已提交
1778

1779 1780
	if (skb->ip_summed != CHECKSUM_PARTIAL)
		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
L
Linus Torvalds 已提交
1781

1782 1783
	/* 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
1784

1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804
	/* 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 */
1805 1806 1807
	tcp_clear_retrans_hints_partial(tp);
	if (next_skb == tp->retransmit_skb_hint)
		tp->retransmit_skb_hint = skb;
1808 1809

	sk_wmem_free_skb(sk, next_skb);
L
Linus Torvalds 已提交
1810 1811
}

1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867
static int tcp_can_collapse(struct sock *sk, struct sk_buff *skb)
{
	if (tcp_skb_pcount(skb) > 1)
		return 0;
	/* TODO: SACK collapsing could be used to remove this condition */
	if (skb_shinfo(skb)->nr_frags != 0)
		return 0;
	if (skb_cloned(skb))
		return 0;
	if (skb == tcp_send_head(sk))
		return 0;
	/* Some heurestics for collapsing over SACK'd could be invented */
	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
		return 0;

	return 1;
}

static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
				     int space)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = to, *tmp;
	int first = 1;

	if (!sysctl_tcp_retrans_collapse)
		return;
	if (TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)
		return;

	tcp_for_write_queue_from_safe(skb, tmp, sk) {
		if (!tcp_can_collapse(sk, skb))
			break;

		space -= skb->len;

		if (first) {
			first = 0;
			continue;
		}

		if (space < 0)
			break;
		/* Punt if not enough space exists in the first SKB for
		 * the data in the second
		 */
		if (skb->len > skb_tailroom(to))
			break;

		if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
			break;

		tcp_collapse_retrans(sk, to);
	}
}

L
Linus Torvalds 已提交
1868 1869 1870 1871 1872 1873 1874
/* 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
1875
	struct inet_connection_sock *icsk = inet_csk(sk);
1876
	unsigned int cur_mss;
L
Linus Torvalds 已提交
1877 1878
	int err;

J
John Heffner 已提交
1879 1880 1881 1882 1883
	/* Inconslusive MTU probe */
	if (icsk->icsk_mtup.probe_size) {
		icsk->icsk_mtup.probe_size = 0;
	}

L
Linus Torvalds 已提交
1884
	/* Do not sent more than we queued. 1/4 is reserved for possible
S
Stephen Hemminger 已提交
1885
	 * copying overhead: fragmentation, tunneling, mangling etc.
L
Linus Torvalds 已提交
1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897
	 */
	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;
	}

1898 1899 1900 1901 1902
	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
1903 1904 1905 1906 1907
	/* 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.
	 */
1908
	if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))
L
Linus Torvalds 已提交
1909 1910 1911 1912
	    && TCP_SKB_CB(skb)->seq != tp->snd_una)
		return -EAGAIN;

	if (skb->len > cur_mss) {
1913
		if (tcp_fragment(sk, skb, cur_mss, cur_mss))
L
Linus Torvalds 已提交
1914 1915 1916
			return -ENOMEM; /* We'll try again later. */
	}

1917
	tcp_retrans_try_collapse(sk, skb, cur_mss);
L
Linus Torvalds 已提交
1918 1919 1920 1921 1922

	/* 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
1923 1924 1925
	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
1926
		if (!pskb_trim(skb, 0)) {
1927 1928 1929
			/* 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
1930 1931 1932 1933 1934 1935 1936 1937 1938
			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;

1939
	err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
1940 1941 1942

	if (err == 0) {
		/* Update global TCP statistics. */
P
Pavel Emelyanov 已提交
1943
		TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
L
Linus Torvalds 已提交
1944 1945 1946 1947

		tp->total_retrans++;

#if FASTRETRANS_DEBUG > 0
1948
		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
L
Linus Torvalds 已提交
1949 1950 1951 1952
			if (net_ratelimit())
				printk(KERN_DEBUG "retrans_out leaked.\n");
		}
#endif
1953 1954
		if (!tp->retrans_out)
			tp->lost_retrans_low = tp->snd_nxt;
L
Linus Torvalds 已提交
1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971
		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;
}

1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
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
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008
/* 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)
{
2009
	const struct inet_connection_sock *icsk = inet_csk(sk);
L
Linus Torvalds 已提交
2010 2011
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
2012
	struct sk_buff *hole = NULL;
2013
	u32 last_lost;
2014
	int mib_idx;
2015
	int fwd_rexmitting = 0;
2016

2017 2018 2019
	if (!tp->lost_out)
		tp->retransmit_high = tp->snd_una;

2020
	if (tp->retransmit_skb_hint) {
2021
		skb = tp->retransmit_skb_hint;
2022 2023 2024 2025
		last_lost = TCP_SKB_CB(skb)->end_seq;
		if (after(last_lost, tp->retransmit_high))
			last_lost = tp->retransmit_high;
	} else {
2026
		skb = tcp_write_queue_head(sk);
2027 2028
		last_lost = tp->snd_una;
	}
L
Linus Torvalds 已提交
2029

2030 2031
	tcp_for_write_queue_from(skb, sk) {
		__u8 sacked = TCP_SKB_CB(skb)->sacked;
L
Linus Torvalds 已提交
2032

2033 2034 2035
		if (skb == tcp_send_head(sk))
			break;
		/* we could do better than to assign each time */
2036 2037
		if (hole == NULL)
			tp->retransmit_skb_hint = skb;
2038 2039 2040 2041 2042 2043 2044 2045 2046 2047

		/* 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
2048

2049 2050 2051 2052 2053
		if (fwd_rexmitting) {
begin_fwd:
			if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
				break;
			mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2054

2055
		} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2056
			tp->retransmit_high = last_lost;
2057 2058 2059 2060 2061 2062 2063 2064 2065
			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
2066

2067 2068 2069 2070
		} else if (!(sacked & TCPCB_LOST)) {
			if (hole == NULL && !(sacked & TCPCB_SACKED_RETRANS))
				hole = skb;
			continue;
L
Linus Torvalds 已提交
2071

2072
		} else {
2073
			last_lost = TCP_SKB_CB(skb)->end_seq;
2074 2075 2076 2077 2078
			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
2079

2080
		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
L
Linus Torvalds 已提交
2081 2082
			continue;

2083
		if (tcp_retransmit_skb(sk, skb))
2084 2085
			return;
		NET_INC_STATS_BH(sock_net(sk), mib_idx);
L
Linus Torvalds 已提交
2086

2087
		if (skb == tcp_write_queue_head(sk))
2088 2089 2090
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
						  inet_csk(sk)->icsk_rto,
						  TCP_RTO_MAX);
L
Linus Torvalds 已提交
2091 2092 2093 2094 2095 2096 2097 2098
	}
}

/* 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)
{
2099
	struct tcp_sock *tp = tcp_sk(sk);
2100
	struct sk_buff *skb = tcp_write_queue_tail(sk);
L
Linus Torvalds 已提交
2101
	int mss_now;
2102

L
Linus Torvalds 已提交
2103 2104 2105 2106 2107 2108
	/* 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);

2109
	if (tcp_send_head(sk) != NULL) {
L
Linus Torvalds 已提交
2110 2111 2112 2113 2114 2115
		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 (;;) {
2116
			skb = alloc_skb_fclone(MAX_TCP_HEADER, GFP_KERNEL);
L
Linus Torvalds 已提交
2117 2118 2119 2120 2121 2122 2123 2124
			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(). */
2125 2126
		tcp_init_nondata_skb(skb, tp->write_seq,
				     TCPCB_FLAG_ACK | TCPCB_FLAG_FIN);
L
Linus Torvalds 已提交
2127 2128
		tcp_queue_skb(sk, skb);
	}
2129
	__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
L
Linus Torvalds 已提交
2130 2131 2132 2133 2134
}

/* 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
2135
 * by RFC 2525, section 2.17.  -DaveM
L
Linus Torvalds 已提交
2136
 */
A
Al Viro 已提交
2137
void tcp_send_active_reset(struct sock *sk, gfp_t priority)
L
Linus Torvalds 已提交
2138 2139 2140 2141 2142 2143
{
	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
2144
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
L
Linus Torvalds 已提交
2145 2146 2147 2148 2149
		return;
	}

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
2150 2151
	tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
			     TCPCB_FLAG_ACK | TCPCB_FLAG_RST);
L
Linus Torvalds 已提交
2152 2153
	/* Send it off. */
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2154
	if (tcp_transmit_skb(sk, skb, 0, priority))
P
Pavel Emelyanov 已提交
2155
		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2156

P
Pavel Emelyanov 已提交
2157
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
L
Linus Torvalds 已提交
2158 2159 2160 2161 2162 2163 2164 2165 2166
}

/* 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)
{
2167
	struct sk_buff *skb;
L
Linus Torvalds 已提交
2168

2169
	skb = tcp_write_queue_head(sk);
2170
	if (skb == NULL || !(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_SYN)) {
L
Linus Torvalds 已提交
2171 2172 2173
		printk(KERN_DEBUG "tcp_send_synack: wrong queue state\n");
		return -EFAULT;
	}
2174
	if (!(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_ACK)) {
L
Linus Torvalds 已提交
2175 2176 2177 2178
		if (skb_cloned(skb)) {
			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
			if (nskb == NULL)
				return -ENOMEM;
2179
			tcp_unlink_write_queue(skb, sk);
L
Linus Torvalds 已提交
2180
			skb_header_release(nskb);
2181
			__tcp_add_write_queue_head(sk, nskb);
2182 2183 2184
			sk_wmem_free_skb(sk, skb);
			sk->sk_wmem_queued += nskb->truesize;
			sk_mem_charge(sk, nskb->truesize);
L
Linus Torvalds 已提交
2185 2186 2187 2188 2189 2190 2191
			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;
2192
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
L
Linus Torvalds 已提交
2193 2194 2195 2196 2197
}

/*
 * Prepare a SYN-ACK.
 */
2198 2199
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
				struct request_sock *req)
L
Linus Torvalds 已提交
2200
{
2201
	struct inet_request_sock *ireq = inet_rsk(req);
L
Linus Torvalds 已提交
2202 2203 2204
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcphdr *th;
	int tcp_header_size;
A
Adam Langley 已提交
2205
	struct tcp_out_options opts;
L
Linus Torvalds 已提交
2206
	struct sk_buff *skb;
2207 2208
	struct tcp_md5sig_key *md5;
	__u8 *md5_hash_location;
2209
	int mss;
L
Linus Torvalds 已提交
2210 2211 2212 2213 2214 2215 2216 2217 2218 2219

	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);

2220 2221 2222 2223
	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
2224 2225 2226 2227 2228 2229
	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),
2230
			mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0),
A
Adam Langley 已提交
2231 2232 2233 2234 2235 2236 2237 2238
			&req->rcv_wnd,
			&req->window_clamp,
			ireq->wscale_ok,
			&rcv_wscale);
		ireq->rcv_wscale = rcv_wscale;
	}

	memset(&opts, 0, sizeof(opts));
2239 2240 2241 2242 2243
#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
2244
	TCP_SKB_CB(skb)->when = tcp_time_stamp;
2245
	tcp_header_size = tcp_synack_options(sk, req, mss,
A
Adam Langley 已提交
2246 2247
					     skb, &opts, &md5) +
			  sizeof(struct tcphdr);
2248

2249 2250
	skb_push(skb, tcp_header_size);
	skb_reset_transport_header(skb);
L
Linus Torvalds 已提交
2251

2252
	th = tcp_hdr(skb);
L
Linus Torvalds 已提交
2253 2254 2255 2256
	memset(th, 0, sizeof(struct tcphdr));
	th->syn = 1;
	th->ack = 1;
	TCP_ECN_make_synack(req, th);
2257
	th->source = ireq->loc_port;
2258
	th->dest = ireq->rmt_port;
2259 2260 2261 2262 2263
	/* 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
2264
	th->seq = htonl(TCP_SKB_CB(skb)->seq);
2265
	th->ack_seq = htonl(tcp_rsk(req)->rcv_isn + 1);
L
Linus Torvalds 已提交
2266 2267

	/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2268
	th->window = htons(min(req->rcv_wnd, 65535U));
A
Adam Langley 已提交
2269
	tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);
L
Linus Torvalds 已提交
2270
	th->doff = (tcp_header_size >> 2);
P
Pavel Emelyanov 已提交
2271
	TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS);
2272 2273 2274 2275 2276

#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,
2277
					       md5, NULL, req, skb);
2278 2279 2280
	}
#endif

L
Linus Torvalds 已提交
2281 2282 2283
	return skb;
}

2284
/*
L
Linus Torvalds 已提交
2285
 * Do all connect socket setups that can be done AF independent.
2286
 */
S
Stephen Hemminger 已提交
2287
static void tcp_connect_init(struct sock *sk)
L
Linus Torvalds 已提交
2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298
{
	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);

2299 2300 2301 2302 2303
#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
2304 2305 2306 2307
	/* 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
2308
	tcp_mtup_init(sk);
L
Linus Torvalds 已提交
2309 2310 2311 2312 2313
	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);
2314 2315 2316
	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
2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334
	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
2335
	tp->snd_up = tp->write_seq;
L
Linus Torvalds 已提交
2336 2337 2338 2339
	tp->rcv_nxt = 0;
	tp->rcv_wup = 0;
	tp->copied_seq = 0;

2340 2341
	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
	inet_csk(sk)->icsk_retransmits = 0;
L
Linus Torvalds 已提交
2342 2343 2344 2345 2346
	tcp_clear_retrans(tp);
}

/*
 * Build a SYN and send it off.
2347
 */
L
Linus Torvalds 已提交
2348 2349 2350 2351 2352 2353 2354
int tcp_connect(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *buff;

	tcp_connect_init(sk);

2355
	buff = alloc_skb_fclone(MAX_TCP_HEADER + 15, sk->sk_allocation);
L
Linus Torvalds 已提交
2356 2357 2358 2359 2360 2361
	if (unlikely(buff == NULL))
		return -ENOBUFS;

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

2362
	tp->snd_nxt = tp->write_seq;
2363 2364
	tcp_init_nondata_skb(buff, tp->write_seq++, TCPCB_FLAG_SYN);
	TCP_ECN_send_syn(sk, buff);
L
Linus Torvalds 已提交
2365 2366 2367 2368 2369

	/* Send it off. */
	TCP_SKB_CB(buff)->when = tcp_time_stamp;
	tp->retrans_stamp = TCP_SKB_CB(buff)->when;
	skb_header_release(buff);
2370
	__tcp_add_write_queue_tail(sk, buff);
2371 2372
	sk->sk_wmem_queued += buff->truesize;
	sk_mem_charge(sk, buff->truesize);
L
Linus Torvalds 已提交
2373
	tp->packets_out += tcp_skb_pcount(buff);
2374
	tcp_transmit_skb(sk, buff, 1, GFP_KERNEL);
2375 2376 2377 2378 2379 2380

	/* 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
2381
	TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
L
Linus Torvalds 已提交
2382 2383

	/* Timer for repeating the SYN until an answer. */
2384 2385
	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
				  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
L
Linus Torvalds 已提交
2386 2387 2388 2389 2390 2391 2392 2393 2394
	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)
{
2395 2396
	struct inet_connection_sock *icsk = inet_csk(sk);
	int ato = icsk->icsk_ack.ato;
L
Linus Torvalds 已提交
2397 2398 2399
	unsigned long timeout;

	if (ato > TCP_DELACK_MIN) {
2400
		const struct tcp_sock *tp = tcp_sk(sk);
2401
		int max_ato = HZ / 2;
L
Linus Torvalds 已提交
2402

2403 2404
		if (icsk->icsk_ack.pingpong ||
		    (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
L
Linus Torvalds 已提交
2405 2406 2407 2408 2409
			max_ato = TCP_DELACK_MAX;

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

		/* If some rtt estimate is known, use it to bound delayed ack.
2410
		 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
L
Linus Torvalds 已提交
2411 2412 2413
		 * directly.
		 */
		if (tp->srtt) {
2414
			int rtt = max(tp->srtt >> 3, TCP_DELACK_MIN);
L
Linus Torvalds 已提交
2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426

			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. */
2427
	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
L
Linus Torvalds 已提交
2428 2429 2430
		/* If delack timer was blocked or is about to expire,
		 * send ACK now.
		 */
2431 2432
		if (icsk->icsk_ack.blocked ||
		    time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
L
Linus Torvalds 已提交
2433 2434 2435 2436
			tcp_send_ack(sk);
			return;
		}

2437 2438
		if (!time_before(timeout, icsk->icsk_ack.timeout))
			timeout = icsk->icsk_ack.timeout;
L
Linus Torvalds 已提交
2439
	}
2440 2441 2442
	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
	icsk->icsk_ack.timeout = timeout;
	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
L
Linus Torvalds 已提交
2443 2444 2445 2446 2447
}

/* This routine sends an ack and also updates the window. */
void tcp_send_ack(struct sock *sk)
{
2448
	struct sk_buff *buff;
L
Linus Torvalds 已提交
2449

2450 2451 2452
	/* If we have been reset, we may not send again. */
	if (sk->sk_state == TCP_CLOSE)
		return;
L
Linus Torvalds 已提交
2453

2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464
	/* 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
2465
	}
2466 2467 2468

	/* Reserve space for headers and prepare control bits. */
	skb_reserve(buff, MAX_TCP_HEADER);
2469
	tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPCB_FLAG_ACK);
2470 2471 2472 2473

	/* 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);
L
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);
2494
	if (skb == NULL)
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		return -1;

	/* Reserve space for headers and set control bits. */
	skb_reserve(skb, MAX_TCP_HEADER);
	/* Use a previous sequence.  This should cause the other
	 * end to send an ack.  Don't queue or clone SKB, just
	 * send it.
	 */
2503
	tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPCB_FLAG_ACK);
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	TCP_SKB_CB(skb)->when = tcp_time_stamp;
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	return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
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}

int tcp_write_wakeup(struct sock *sk)
{
2510 2511
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
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	if (sk->sk_state == TCP_CLOSE)
		return -1;

	if ((skb = tcp_send_head(sk)) != NULL &&
	    before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
		int err;
		unsigned int mss = tcp_current_mss(sk, 0);
		unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;

		if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
			tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;

		/* We are probing the opening of a window
		 * but the window size is != 0
		 * must have been a result SWS avoidance ( sender )
		 */
		if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
		    skb->len > mss) {
			seg_size = min(seg_size, mss);
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			TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
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			if (tcp_fragment(sk, skb, seg_size, mss))
				return -1;
		} else if (!tcp_skb_pcount(skb))
			tcp_set_skb_tso_segs(sk, skb, mss);

		TCP_SKB_CB(skb)->flags |= TCPCB_FLAG_PSH;
		TCP_SKB_CB(skb)->when = tcp_time_stamp;
		err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
		if (!err)
			tcp_event_new_data_sent(sk, skb);
		return err;
	} else {
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Ilpo Järvinen 已提交
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		if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
2546 2547
			tcp_xmit_probe_skb(sk, 1);
		return tcp_xmit_probe_skb(sk, 0);
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	}
}

/* A window probe timeout has occurred.  If window is not closed send
 * a partial packet else a zero probe.
 */
void tcp_send_probe0(struct sock *sk)
{
2556
	struct inet_connection_sock *icsk = inet_csk(sk);
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	struct tcp_sock *tp = tcp_sk(sk);
	int err;

	err = tcp_write_wakeup(sk);

2562
	if (tp->packets_out || !tcp_send_head(sk)) {
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		/* Cancel probe timer, if it is not required. */
2564
		icsk->icsk_probes_out = 0;
2565
		icsk->icsk_backoff = 0;
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		return;
	}

	if (err <= 0) {
2570 2571
		if (icsk->icsk_backoff < sysctl_tcp_retries2)
			icsk->icsk_backoff++;
2572
		icsk->icsk_probes_out++;
2573
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2574 2575
					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
					  TCP_RTO_MAX);
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	} else {
		/* If packet was not sent due to local congestion,
2578
		 * do not backoff and do not remember icsk_probes_out.
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		 * Let local senders to fight for local resources.
		 *
		 * Use accumulated backoff yet.
		 */
2583 2584
		if (!icsk->icsk_probes_out)
			icsk->icsk_probes_out = 1;
2585
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2586
					  min(icsk->icsk_rto << icsk->icsk_backoff,
2587 2588
					      TCP_RESOURCE_PROBE_INTERVAL),
					  TCP_RTO_MAX);
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	}
}

2592
EXPORT_SYMBOL(tcp_select_initial_window);
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EXPORT_SYMBOL(tcp_connect);
EXPORT_SYMBOL(tcp_make_synack);
EXPORT_SYMBOL(tcp_simple_retransmit);
EXPORT_SYMBOL(tcp_sync_mss);
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John Heffner 已提交
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EXPORT_SYMBOL(tcp_mtup_init);