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linux/net/ipv4/tcp_input.c

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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).
*
* Version: $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
*
* Authors: Ross Biro
* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
* Mark Evans, <evansmp@uhura.aston.ac.uk>
* Corey Minyard <wf-rch!minyard@relay.EU.net>
* Florian La Roche, <flla@stud.uni-sb.de>
* Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
* Linus Torvalds, <torvalds@cs.helsinki.fi>
* Alan Cox, <gw4pts@gw4pts.ampr.org>
* Matthew Dillon, <dillon@apollo.west.oic.com>
* Arnt Gulbrandsen, <agulbra@nvg.unit.no>
* Jorge Cwik, <jorge@laser.satlink.net>
*/
/*
* Changes:
* Pedro Roque : Fast Retransmit/Recovery.
* Two receive queues.
* Retransmit queue handled by TCP.
* Better retransmit timer handling.
* New congestion avoidance.
* Header prediction.
* Variable renaming.
*
* Eric : Fast Retransmit.
* Randy Scott : MSS option defines.
* Eric Schenk : Fixes to slow start algorithm.
* Eric Schenk : Yet another double ACK bug.
* Eric Schenk : Delayed ACK bug fixes.
* Eric Schenk : Floyd style fast retrans war avoidance.
* David S. Miller : Don't allow zero congestion window.
* Eric Schenk : Fix retransmitter so that it sends
* next packet on ack of previous packet.
* Andi Kleen : Moved open_request checking here
* and process RSTs for open_requests.
* Andi Kleen : Better prune_queue, and other fixes.
* Andrey Savochkin: Fix RTT measurements in the presence of
* timestamps.
* Andrey Savochkin: Check sequence numbers correctly when
* removing SACKs due to in sequence incoming
* data segments.
* Andi Kleen: Make sure we never ack data there is not
* enough room for. Also make this condition
* a fatal error if it might still happen.
* Andi Kleen: Add tcp_measure_rcv_mss to make
* connections with MSS<min(MTU,ann. MSS)
* work without delayed acks.
* Andi Kleen: Process packets with PSH set in the
* fast path.
* J Hadi Salim: ECN support
* Andrei Gurtov,
* Pasi Sarolahti,
* Panu Kuhlberg: Experimental audit of TCP (re)transmission
* engine. Lots of bugs are found.
* Pasi Sarolahti: F-RTO for dealing with spurious RTOs
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <net/tcp.h>
#include <net/inet_common.h>
#include <linux/ipsec.h>
#include <asm/unaligned.h>
#include <net/netdma.h>
int sysctl_tcp_timestamps __read_mostly = 1;
int sysctl_tcp_window_scaling __read_mostly = 1;
int sysctl_tcp_sack __read_mostly = 1;
int sysctl_tcp_fack __read_mostly = 1;
int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
int sysctl_tcp_ecn __read_mostly;
int sysctl_tcp_dsack __read_mostly = 1;
int sysctl_tcp_app_win __read_mostly = 31;
int sysctl_tcp_adv_win_scale __read_mostly = 2;
int sysctl_tcp_stdurg __read_mostly;
int sysctl_tcp_rfc1337 __read_mostly;
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
int sysctl_tcp_frto __read_mostly;
int sysctl_tcp_nometrics_save __read_mostly;
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
int sysctl_tcp_abc __read_mostly;
#define FLAG_DATA 0x01 /* Incoming frame contained data. */
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
#define FLAG_DATA_SACKED 0x20 /* New SACK. */
#define FLAG_ECE 0x40 /* ECE in this ACK */
#define FLAG_DATA_LOST 0x80 /* SACK detected data lossage. */
#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE)
#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
#define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
#define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
#define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
/* Adapt the MSS value used to make delayed ack decision to the
* real world.
*/
static void tcp_measure_rcv_mss(struct sock *sk,
const struct sk_buff *skb)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const unsigned int lss = icsk->icsk_ack.last_seg_size;
unsigned int len;
icsk->icsk_ack.last_seg_size = 0;
/* skb->len may jitter because of SACKs, even if peer
* sends good full-sized frames.
*/
len = skb_shinfo(skb)->gso_size ?: skb->len;
if (len >= icsk->icsk_ack.rcv_mss) {
icsk->icsk_ack.rcv_mss = len;
} else {
/* Otherwise, we make more careful check taking into account,
* that SACKs block is variable.
*
* "len" is invariant segment length, including TCP header.
*/
len += skb->data - skb->h.raw;
if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
/* If PSH is not set, packet should be
* full sized, provided peer TCP is not badly broken.
* This observation (if it is correct 8)) allows
* to handle super-low mtu links fairly.
*/
(len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
!(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
/* Subtract also invariant (if peer is RFC compliant),
* tcp header plus fixed timestamp option length.
* Resulting "len" is MSS free of SACK jitter.
*/
len -= tcp_sk(sk)->tcp_header_len;
icsk->icsk_ack.last_seg_size = len;
if (len == lss) {
icsk->icsk_ack.rcv_mss = len;
return;
}
}
if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
}
}
static void tcp_incr_quickack(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
if (quickacks==0)
quickacks=2;
if (quickacks > icsk->icsk_ack.quick)
icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
}
void tcp_enter_quickack_mode(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_incr_quickack(sk);
icsk->icsk_ack.pingpong = 0;
icsk->icsk_ack.ato = TCP_ATO_MIN;
}
/* Send ACKs quickly, if "quick" count is not exhausted
* and the session is not interactive.
*/
static inline int tcp_in_quickack_mode(const struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
}
/* Buffer size and advertised window tuning.
*
* 1. Tuning sk->sk_sndbuf, when connection enters established state.
*/
static void tcp_fixup_sndbuf(struct sock *sk)
{
int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
sizeof(struct sk_buff);
if (sk->sk_sndbuf < 3 * sndmem)
sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
}
/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
*
* All tcp_full_space() is split to two parts: "network" buffer, allocated
* forward and advertised in receiver window (tp->rcv_wnd) and
* "application buffer", required to isolate scheduling/application
* latencies from network.
* window_clamp is maximal advertised window. It can be less than
* tcp_full_space(), in this case tcp_full_space() - window_clamp
* is reserved for "application" buffer. The less window_clamp is
* the smoother our behaviour from viewpoint of network, but the lower
* throughput and the higher sensitivity of the connection to losses. 8)
*
* rcv_ssthresh is more strict window_clamp used at "slow start"
* phase to predict further behaviour of this connection.
* It is used for two goals:
* - to enforce header prediction at sender, even when application
* requires some significant "application buffer". It is check #1.
* - to prevent pruning of receive queue because of misprediction
* of receiver window. Check #2.
*
* The scheme does not work when sender sends good segments opening
* window and then starts to feed us spaghetti. But it should work
* in common situations. Otherwise, we have to rely on queue collapsing.
*/
/* Slow part of check#2. */
static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
const struct sk_buff *skb)
{
/* Optimize this! */
int truesize = tcp_win_from_space(skb->truesize)/2;
int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
while (tp->rcv_ssthresh <= window) {
if (truesize <= skb->len)
return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
truesize >>= 1;
window >>= 1;
}
return 0;
}
static void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
struct sk_buff *skb)
{
/* Check #1 */
if (tp->rcv_ssthresh < tp->window_clamp &&
(int)tp->rcv_ssthresh < tcp_space(sk) &&
!tcp_memory_pressure) {
int incr;
/* Check #2. Increase window, if skb with such overhead
* will fit to rcvbuf in future.
*/
if (tcp_win_from_space(skb->truesize) <= skb->len)
incr = 2*tp->advmss;
else
incr = __tcp_grow_window(sk, tp, skb);
if (incr) {
tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
inet_csk(sk)->icsk_ack.quick |= 1;
}
}
}
/* 3. Tuning rcvbuf, when connection enters established state. */
static void tcp_fixup_rcvbuf(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
/* Try to select rcvbuf so that 4 mss-sized segments
* will fit to window and corresponding skbs will fit to our rcvbuf.
* (was 3; 4 is minimum to allow fast retransmit to work.)
*/
while (tcp_win_from_space(rcvmem) < tp->advmss)
rcvmem += 128;
if (sk->sk_rcvbuf < 4 * rcvmem)
sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
}
/* 4. Try to fixup all. It is made immediately after connection enters
* established state.
*/
static void tcp_init_buffer_space(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int maxwin;
if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
tcp_fixup_rcvbuf(sk);
if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
tcp_fixup_sndbuf(sk);
tp->rcvq_space.space = tp->rcv_wnd;
maxwin = tcp_full_space(sk);
if (tp->window_clamp >= maxwin) {
tp->window_clamp = maxwin;
if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
tp->window_clamp = max(maxwin -
(maxwin >> sysctl_tcp_app_win),
4 * tp->advmss);
}
/* Force reservation of one segment. */
if (sysctl_tcp_app_win &&
tp->window_clamp > 2 * tp->advmss &&
tp->window_clamp + tp->advmss > maxwin)
tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
tp->snd_cwnd_stamp = tcp_time_stamp;
}
/* 5. Recalculate window clamp after socket hit its memory bounds. */
static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
{
struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_ack.quick = 0;
if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
!tcp_memory_pressure &&
atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
sysctl_tcp_rmem[2]);
}
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
}
/* Initialize RCV_MSS value.
* RCV_MSS is an our guess about MSS used by the peer.
* We haven't any direct information about the MSS.
* It's better to underestimate the RCV_MSS rather than overestimate.
* Overestimations make us ACKing less frequently than needed.
* Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
*/
void tcp_initialize_rcv_mss(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
hint = min(hint, tp->rcv_wnd/2);
hint = min(hint, TCP_MIN_RCVMSS);
hint = max(hint, TCP_MIN_MSS);
inet_csk(sk)->icsk_ack.rcv_mss = hint;
}
/* Receiver "autotuning" code.
*
* The algorithm for RTT estimation w/o timestamps is based on
* Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
* <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
*
* More detail on this code can be found at
* <http://www.psc.edu/~jheffner/senior_thesis.ps>,
* though this reference is out of date. A new paper
* is pending.
*/
static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
{
u32 new_sample = tp->rcv_rtt_est.rtt;
long m = sample;
if (m == 0)
m = 1;
if (new_sample != 0) {
/* If we sample in larger samples in the non-timestamp
* case, we could grossly overestimate the RTT especially
* with chatty applications or bulk transfer apps which
* are stalled on filesystem I/O.
*
* Also, since we are only going for a minimum in the
* non-timestamp case, we do not smooth things out
* else with timestamps disabled convergence takes too
* long.
*/
if (!win_dep) {
m -= (new_sample >> 3);
new_sample += m;
} else if (m < new_sample)
new_sample = m << 3;
} else {
/* No previous measure. */
new_sample = m << 3;
}
if (tp->rcv_rtt_est.rtt != new_sample)
tp->rcv_rtt_est.rtt = new_sample;
}
static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
{
if (tp->rcv_rtt_est.time == 0)
goto new_measure;
if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
return;
tcp_rcv_rtt_update(tp,
jiffies - tp->rcv_rtt_est.time,
1);
new_measure:
tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
tp->rcv_rtt_est.time = tcp_time_stamp;
}
static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->rx_opt.rcv_tsecr &&
(TCP_SKB_CB(skb)->end_seq -
TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
}
/*
* This function should be called every time data is copied to user space.
* It calculates the appropriate TCP receive buffer space.
*/
void tcp_rcv_space_adjust(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int time;
int space;
if (tp->rcvq_space.time == 0)
goto new_measure;
time = tcp_time_stamp - tp->rcvq_space.time;
if (time < (tp->rcv_rtt_est.rtt >> 3) ||
tp->rcv_rtt_est.rtt == 0)
return;
space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
space = max(tp->rcvq_space.space, space);
if (tp->rcvq_space.space != space) {
int rcvmem;
tp->rcvq_space.space = space;
if (sysctl_tcp_moderate_rcvbuf &&
!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
int new_clamp = space;
/* Receive space grows, normalize in order to
* take into account packet headers and sk_buff
* structure overhead.
*/
space /= tp->advmss;
if (!space)
space = 1;
rcvmem = (tp->advmss + MAX_TCP_HEADER +
16 + sizeof(struct sk_buff));
while (tcp_win_from_space(rcvmem) < tp->advmss)
rcvmem += 128;
space *= rcvmem;
space = min(space, sysctl_tcp_rmem[2]);
if (space > sk->sk_rcvbuf) {
sk->sk_rcvbuf = space;
/* Make the window clamp follow along. */
tp->window_clamp = new_clamp;
}
}
}
new_measure:
tp->rcvq_space.seq = tp->copied_seq;
tp->rcvq_space.time = tcp_time_stamp;
}
/* There is something which you must keep in mind when you analyze the
* behavior of the tp->ato delayed ack timeout interval. When a
* connection starts up, we want to ack as quickly as possible. The
* problem is that "good" TCP's do slow start at the beginning of data
* transmission. The means that until we send the first few ACK's the
* sender will sit on his end and only queue most of his data, because
* he can only send snd_cwnd unacked packets at any given time. For
* each ACK we send, he increments snd_cwnd and transmits more of his
* queue. -DaveM
*/
static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
{
struct inet_connection_sock *icsk = inet_csk(sk);
u32 now;
inet_csk_schedule_ack(sk);
tcp_measure_rcv_mss(sk, skb);
tcp_rcv_rtt_measure(tp);
now = tcp_time_stamp;
if (!icsk->icsk_ack.ato) {
/* The _first_ data packet received, initialize
* delayed ACK engine.
*/
tcp_incr_quickack(sk);
icsk->icsk_ack.ato = TCP_ATO_MIN;
} else {
int m = now - icsk->icsk_ack.lrcvtime;
if (m <= TCP_ATO_MIN/2) {
/* The fastest case is the first. */
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
} else if (m < icsk->icsk_ack.ato) {
icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
if (icsk->icsk_ack.ato > icsk->icsk_rto)
icsk->icsk_ack.ato = icsk->icsk_rto;
} else if (m > icsk->icsk_rto) {
/* Too long gap. Apparently sender failed to
* restart window, so that we send ACKs quickly.
*/
tcp_incr_quickack(sk);
sk_stream_mem_reclaim(sk);
}
}
icsk->icsk_ack.lrcvtime = now;
TCP_ECN_check_ce(tp, skb);
if (skb->len >= 128)
tcp_grow_window(sk, tp, skb);
}
/* Called to compute a smoothed rtt estimate. The data fed to this
* routine either comes from timestamps, or from segments that were
* known _not_ to have been retransmitted [see Karn/Partridge
* Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
* piece by Van Jacobson.
* NOTE: the next three routines used to be one big routine.
* To save cycles in the RFC 1323 implementation it was better to break
* it up into three procedures. -- erics
*/
static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
{
struct tcp_sock *tp = tcp_sk(sk);
long m = mrtt; /* RTT */
/* The following amusing code comes from Jacobson's
* article in SIGCOMM '88. Note that rtt and mdev
* are scaled versions of rtt and mean deviation.
* This is designed to be as fast as possible
* m stands for "measurement".
*
* On a 1990 paper the rto value is changed to:
* RTO = rtt + 4 * mdev
*
* Funny. This algorithm seems to be very broken.
* These formulae increase RTO, when it should be decreased, increase
* too slowly, when it should be increased quickly, decrease too quickly
* etc. I guess in BSD RTO takes ONE value, so that it is absolutely
* does not matter how to _calculate_ it. Seems, it was trap
* that VJ failed to avoid. 8)
*/
if(m == 0)
m = 1;
if (tp->srtt != 0) {
m -= (tp->srtt >> 3); /* m is now error in rtt est */
tp->srtt += m; /* rtt = 7/8 rtt + 1/8 new */
if (m < 0) {
m = -m; /* m is now abs(error) */
m -= (tp->mdev >> 2); /* similar update on mdev */
/* This is similar to one of Eifel findings.
* Eifel blocks mdev updates when rtt decreases.
* This solution is a bit different: we use finer gain
* for mdev in this case (alpha*beta).
* Like Eifel it also prevents growth of rto,
* but also it limits too fast rto decreases,
* happening in pure Eifel.
*/
if (m > 0)
m >>= 3;
} else {
m -= (tp->mdev >> 2); /* similar update on mdev */
}
tp->mdev += m; /* mdev = 3/4 mdev + 1/4 new */
if (tp->mdev > tp->mdev_max) {
tp->mdev_max = tp->mdev;
if (tp->mdev_max > tp->rttvar)
tp->rttvar = tp->mdev_max;
}
if (after(tp->snd_una, tp->rtt_seq)) {
if (tp->mdev_max < tp->rttvar)
tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
tp->rtt_seq = tp->snd_nxt;
tp->mdev_max = TCP_RTO_MIN;
}
} else {
/* no previous measure. */
tp->srtt = m<<3; /* take the measured time to be rtt */
tp->mdev = m<<1; /* make sure rto = 3*rtt */
tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
tp->rtt_seq = tp->snd_nxt;
}
}
/* Calculate rto without backoff. This is the second half of Van Jacobson's
* routine referred to above.
*/
static inline void tcp_set_rto(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Old crap is replaced with new one. 8)
*
* More seriously:
* 1. If rtt variance happened to be less 50msec, it is hallucination.
* It cannot be less due to utterly erratic ACK generation made
* at least by solaris and freebsd. "Erratic ACKs" has _nothing_
* to do with delayed acks, because at cwnd>2 true delack timeout
* is invisible. Actually, Linux-2.4 also generates erratic
* ACKs in some circumstances.
*/
inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
/* 2. Fixups made earlier cannot be right.
* If we do not estimate RTO correctly without them,
* all the algo is pure shit and should be replaced
* with correct one. It is exactly, which we pretend to do.
*/
}
/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
* guarantees that rto is higher.
*/
static inline void tcp_bound_rto(struct sock *sk)
{
if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
}
/* Save metrics learned by this TCP session.
This function is called only, when TCP finishes successfully
i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
*/
void tcp_update_metrics(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct dst_entry *dst = __sk_dst_get(sk);
if (sysctl_tcp_nometrics_save)
return;
dst_confirm(dst);
if (dst && (dst->flags&DST_HOST)) {
const struct inet_connection_sock *icsk = inet_csk(sk);
int m;
if (icsk->icsk_backoff || !tp->srtt) {
/* This session failed to estimate rtt. Why?
* Probably, no packets returned in time.
* Reset our results.
*/
if (!(dst_metric_locked(dst, RTAX_RTT)))
dst->metrics[RTAX_RTT-1] = 0;
return;
}
m = dst_metric(dst, RTAX_RTT) - tp->srtt;
/* If newly calculated rtt larger than stored one,
* store new one. Otherwise, use EWMA. Remember,
* rtt overestimation is always better than underestimation.
*/
if (!(dst_metric_locked(dst, RTAX_RTT))) {
if (m <= 0)
dst->metrics[RTAX_RTT-1] = tp->srtt;
else
dst->metrics[RTAX_RTT-1] -= (m>>3);
}
if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
if (m < 0)
m = -m;
/* Scale deviation to rttvar fixed point */
m >>= 1;
if (m < tp->mdev)
m = tp->mdev;
if (m >= dst_metric(dst, RTAX_RTTVAR))
dst->metrics[RTAX_RTTVAR-1] = m;
else
dst->metrics[RTAX_RTTVAR-1] -=
(dst->metrics[RTAX_RTTVAR-1] - m)>>2;
}
if (tp->snd_ssthresh >= 0xFFFF) {
/* Slow start still did not finish. */
if (dst_metric(dst, RTAX_SSTHRESH) &&
!dst_metric_locked(dst, RTAX_SSTHRESH) &&
(tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
if (!dst_metric_locked(dst, RTAX_CWND) &&
tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
} else if (tp->snd_cwnd > tp->snd_ssthresh &&
icsk->icsk_ca_state == TCP_CA_Open) {
/* Cong. avoidance phase, cwnd is reliable. */
if (!dst_metric_locked(dst, RTAX_SSTHRESH))
dst->metrics[RTAX_SSTHRESH-1] =
max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
if (!dst_metric_locked(dst, RTAX_CWND))
dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
} else {
/* Else slow start did not finish, cwnd is non-sense,
ssthresh may be also invalid.
*/
if (!dst_metric_locked(dst, RTAX_CWND))
dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
if (dst->metrics[RTAX_SSTHRESH-1] &&
!dst_metric_locked(dst, RTAX_SSTHRESH) &&
tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
}
if (!dst_metric_locked(dst, RTAX_REORDERING)) {
if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
tp->reordering != sysctl_tcp_reordering)
dst->metrics[RTAX_REORDERING-1] = tp->reordering;
}
}
}
/* Numbers are taken from RFC2414. */
__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
{
__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
if (!cwnd) {
if (tp->mss_cache > 1460)
cwnd = 2;
else
cwnd = (tp->mss_cache > 1095) ? 3 : 4;
}
return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
}
/* Set slow start threshold and cwnd not falling to slow start */
void tcp_enter_cwr(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->prior_ssthresh = 0;
tp->bytes_acked = 0;
if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
tp->undo_marker = 0;
tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
tp->snd_cwnd = min(tp->snd_cwnd,
tcp_packets_in_flight(tp) + 1U);
tp->snd_cwnd_cnt = 0;
tp->high_seq = tp->snd_nxt;
tp->snd_cwnd_stamp = tcp_time_stamp;
TCP_ECN_queue_cwr(tp);
tcp_set_ca_state(sk, TCP_CA_CWR);
}
}
/* Initialize metrics on socket. */
static void tcp_init_metrics(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct dst_entry *dst = __sk_dst_get(sk);
if (dst == NULL)
goto reset;
dst_confirm(dst);
if (dst_metric_locked(dst, RTAX_CWND))
tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
if (dst_metric(dst, RTAX_SSTHRESH)) {
tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
tp->snd_ssthresh = tp->snd_cwnd_clamp;
}
if (dst_metric(dst, RTAX_REORDERING) &&
tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
tp->rx_opt.sack_ok &= ~2;
tp->reordering = dst_metric(dst, RTAX_REORDERING);
}
if (dst_metric(dst, RTAX_RTT) == 0)
goto reset;
if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
goto reset;
/* Initial rtt is determined from SYN,SYN-ACK.
* The segment is small and rtt may appear much
* less than real one. Use per-dst memory
* to make it more realistic.
*
* A bit of theory. RTT is time passed after "normal" sized packet
* is sent until it is ACKed. In normal circumstances sending small
* packets force peer to delay ACKs and calculation is correct too.
* The algorithm is adaptive and, provided we follow specs, it
* NEVER underestimate RTT. BUT! If peer tries to make some clever
* tricks sort of "quick acks" for time long enough to decrease RTT
* to low value, and then abruptly stops to do it and starts to delay
* ACKs, wait for troubles.
*/
if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
tp->srtt = dst_metric(dst, RTAX_RTT);
tp->rtt_seq = tp->snd_nxt;
}
if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
tp->mdev = dst_metric(dst, RTAX_RTTVAR);
tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
}
tcp_set_rto(sk);
tcp_bound_rto(sk);
if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
goto reset;
tp->snd_cwnd = tcp_init_cwnd(tp, dst);
tp->snd_cwnd_stamp = tcp_time_stamp;
return;
reset:
/* Play conservative. If timestamps are not
* supported, TCP will fail to recalculate correct
* rtt, if initial rto is too small. FORGET ALL AND RESET!
*/
if (!tp->rx_opt.saw_tstamp && tp->srtt) {
tp->srtt = 0;
tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
}
}
static void tcp_update_reordering(struct sock *sk, const int metric,
const int ts)
{
struct tcp_sock *tp = tcp_sk(sk);
if (metric > tp->reordering) {
tp->reordering = min(TCP_MAX_REORDERING, metric);
/* This exciting event is worth to be remembered. 8) */
if (ts)
NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
else if (IsReno(tp))
NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
else if (IsFack(tp))
NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
else
NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
#if FASTRETRANS_DEBUG > 1
printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
tp->reordering,
tp->fackets_out,
tp->sacked_out,
tp->undo_marker ? tp->undo_retrans : 0);
#endif
/* Disable FACK yet. */
tp->rx_opt.sack_ok &= ~2;
}
}
/* This procedure tags the retransmission queue when SACKs arrive.
*
* We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
* Packets in queue with these bits set are counted in variables
* sacked_out, retrans_out and lost_out, correspondingly.
*
* Valid combinations are:
* Tag InFlight Description
* 0 1 - orig segment is in flight.
* S 0 - nothing flies, orig reached receiver.
* L 0 - nothing flies, orig lost by net.
* R 2 - both orig and retransmit are in flight.
* L|R 1 - orig is lost, retransmit is in flight.
* S|R 1 - orig reached receiver, retrans is still in flight.
* (L|S|R is logically valid, it could occur when L|R is sacked,
* but it is equivalent to plain S and code short-curcuits it to S.
* L|S is logically invalid, it would mean -1 packet in flight 8))
*
* These 6 states form finite state machine, controlled by the following events:
* 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
* 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
* 3. Loss detection event of one of three flavors:
* A. Scoreboard estimator decided the packet is lost.
* A'. Reno "three dupacks" marks head of queue lost.
* A''. Its FACK modfication, head until snd.fack is lost.
* B. SACK arrives sacking data transmitted after never retransmitted
* hole was sent out.
* C. SACK arrives sacking SND.NXT at the moment, when the
* segment was retransmitted.
* 4. D-SACK added new rule: D-SACK changes any tag to S.
*
* It is pleasant to note, that state diagram turns out to be commutative,
* so that we are allowed not to be bothered by order of our actions,
* when multiple events arrive simultaneously. (see the function below).
*
* Reordering detection.
* --------------------
* Reordering metric is maximal distance, which a packet can be displaced
* in packet stream. With SACKs we can estimate it:
*
* 1. SACK fills old hole and the corresponding segment was not
* ever retransmitted -> reordering. Alas, we cannot use it
* when segment was retransmitted.
* 2. The last flaw is solved with D-SACK. D-SACK arrives
* for retransmitted and already SACKed segment -> reordering..
* Both of these heuristics are not used in Loss state, when we cannot
* account for retransmits accurately.
*/
static int
tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
struct tcp_sack_block_wire *sp = (struct tcp_sack_block_wire *)(ptr+2);
int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
int reord = tp->packets_out;
int prior_fackets;
u32 lost_retrans = 0;
int flag = 0;
int dup_sack = 0;
int i;
if (!tp->sacked_out)
tp->fackets_out = 0;
prior_fackets = tp->fackets_out;
/* SACK fastpath:
* if the only SACK change is the increase of the end_seq of
* the first block then only apply that SACK block
* and use retrans queue hinting otherwise slowpath */
flag = 1;
for (i = 0; i< num_sacks; i++) {
__u32 start_seq = ntohl(sp[i].start_seq);
__u32 end_seq = ntohl(sp[i].end_seq);
if (i == 0){
if (tp->recv_sack_cache[i].start_seq != start_seq)
flag = 0;
} else {
if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
(tp->recv_sack_cache[i].end_seq != end_seq))
flag = 0;
}
tp->recv_sack_cache[i].start_seq = start_seq;
tp->recv_sack_cache[i].end_seq = end_seq;
/* Check for D-SACK. */
if (i == 0) {
u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;
if (before(start_seq, ack)) {
dup_sack = 1;
tp->rx_opt.sack_ok |= 4;
NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
} else if (num_sacks > 1 &&
!after(end_seq, ntohl(sp[1].end_seq)) &&
!before(start_seq, ntohl(sp[1].start_seq))) {
dup_sack = 1;
tp->rx_opt.sack_ok |= 4;
NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
}
/* D-SACK for already forgotten data...
* Do dumb counting. */
if (dup_sack &&
!after(end_seq, prior_snd_una) &&
after(end_seq, tp->undo_marker))
tp->undo_retrans--;
/* Eliminate too old ACKs, but take into
* account more or less fresh ones, they can
* contain valid SACK info.
*/
if (before(ack, prior_snd_una - tp->max_window))
return 0;
}
}
if (flag)
num_sacks = 1;
else {
int j;
tp->fastpath_skb_hint = NULL;
/* order SACK blocks to allow in order walk of the retrans queue */
for (i = num_sacks-1; i > 0; i--) {
for (j = 0; j < i; j++){
if (after(ntohl(sp[j].start_seq),
ntohl(sp[j+1].start_seq))){
sp[j].start_seq = htonl(tp->recv_sack_cache[j+1].start_seq);
sp[j].end_seq = htonl(tp->recv_sack_cache[j+1].end_seq);
sp[j+1].start_seq = htonl(tp->recv_sack_cache[j].start_seq);
sp[j+1].end_seq = htonl(tp->recv_sack_cache[j].end_seq);
}
}
}
}
/* clear flag as used for different purpose in following code */
flag = 0;
for (i=0; i<num_sacks; i++, sp++) {
struct sk_buff *skb;
__u32 start_seq = ntohl(sp->start_seq);
__u32 end_seq = ntohl(sp->end_seq);
int fack_count;
/* Use SACK fastpath hint if valid */
if (tp->fastpath_skb_hint) {
skb = tp->fastpath_skb_hint;
fack_count = tp->fastpath_cnt_hint;
} else {
skb = sk->sk_write_queue.next;
fack_count = 0;
}
/* Event "B" in the comment above. */
if (after(end_seq, tp->high_seq))
flag |= FLAG_DATA_LOST;
sk_stream_for_retrans_queue_from(skb, sk) {
int in_sack, pcount;
u8 sacked;
tp->fastpath_skb_hint = skb;
tp->fastpath_cnt_hint = fack_count;
/* The retransmission queue is always in order, so
* we can short-circuit the walk early.
*/
if (!before(TCP_SKB_CB(skb)->seq, end_seq))
break;
in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
!before(end_seq, TCP_SKB_CB(skb)->end_seq);
pcount = tcp_skb_pcount(skb);
if (pcount > 1 && !in_sack &&
after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
unsigned int pkt_len;
in_sack = !after(start_seq,
TCP_SKB_CB(skb)->seq);
if (!in_sack)
pkt_len = (start_seq -
TCP_SKB_CB(skb)->seq);
else
pkt_len = (end_seq -
TCP_SKB_CB(skb)->seq);
if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size))
break;
pcount = tcp_skb_pcount(skb);
}
fack_count += pcount;
sacked = TCP_SKB_CB(skb)->sacked;
/* Account D-SACK for retransmitted packet. */
if ((dup_sack && in_sack) &&
(sacked & TCPCB_RETRANS) &&
after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
tp->undo_retrans--;
/* The frame is ACKed. */
if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
if (sacked&TCPCB_RETRANS) {
if ((dup_sack && in_sack) &&
(sacked&TCPCB_SACKED_ACKED))
reord = min(fack_count, reord);
} else {
/* If it was in a hole, we detected reordering. */
if (fack_count < prior_fackets &&
!(sacked&TCPCB_SACKED_ACKED))
reord = min(fack_count, reord);
}
/* Nothing to do; acked frame is about to be dropped. */
continue;
}
if ((sacked&TCPCB_SACKED_RETRANS) &&
after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
(!lost_retrans || after(end_seq, lost_retrans)))
lost_retrans = end_seq;
if (!in_sack)
continue;
if (!(sacked&TCPCB_SACKED_ACKED)) {
if (sacked & TCPCB_SACKED_RETRANS) {
/* If the segment is not tagged as lost,
* we do not clear RETRANS, believing
* that retransmission is still in flight.
*/
if (sacked & TCPCB_LOST) {
TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
tp->lost_out -= tcp_skb_pcount(skb);
tp->retrans_out -= tcp_skb_pcount(skb);
/* clear lost hint */
tp->retransmit_skb_hint = NULL;
}
} else {
/* New sack for not retransmitted frame,
* which was in hole. It is reordering.
*/
if (!(sacked & TCPCB_RETRANS) &&
fack_count < prior_fackets)
reord = min(fack_count, reord);
if (sacked & TCPCB_LOST) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
tp->lost_out -= tcp_skb_pcount(skb);
/* clear lost hint */
tp->retransmit_skb_hint = NULL;
}
}
TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
flag |= FLAG_DATA_SACKED;
tp->sacked_out += tcp_skb_pcount(skb);
if (fack_count > tp->fackets_out)
tp->fackets_out = fack_count;
} else {
if (dup_sack && (sacked&TCPCB_RETRANS))
reord = min(fack_count, reord);
}
/* D-SACK. We can detect redundant retransmission
* in S|R and plain R frames and clear it.
* undo_retrans is decreased above, L|R frames
* are accounted above as well.
*/
if (dup_sack &&
(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= tcp_skb_pcount(skb);
tp->retransmit_skb_hint = NULL;
}
}
}
/* Check for lost retransmit. This superb idea is
* borrowed from "ratehalving". Event "C".
* Later note: FACK people cheated me again 8),
* we have to account for reordering! Ugly,
* but should help.
*/
if (lost_retrans && icsk->icsk_ca_state == TCP_CA_Recovery) {
struct sk_buff *skb;
sk_stream_for_retrans_queue(skb, sk) {
if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
break;
if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
continue;
if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
(IsFack(tp) ||
!before(lost_retrans,
TCP_SKB_CB(skb)->ack_seq + tp->reordering *
tp->mss_cache))) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= tcp_skb_pcount(skb);
/* clear lost hint */
tp->retransmit_skb_hint = NULL;
if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tp->lost_out += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
flag |= FLAG_DATA_SACKED;
NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
}
}
}
}
tp->left_out = tp->sacked_out + tp->lost_out;
if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss)
tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
#if FASTRETRANS_DEBUG > 0
BUG_TRAP((int)tp->sacked_out >= 0);
BUG_TRAP((int)tp->lost_out >= 0);
BUG_TRAP((int)tp->retrans_out >= 0);
BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
#endif
return flag;
}
/* RTO occurred, but do not yet enter loss state. Instead, transmit two new
* segments to see from the next ACKs whether any data was really missing.
* If the RTO was spurious, new ACKs should arrive.
*/
void tcp_enter_frto(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
tp->frto_counter = 1;
if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
tp->snd_una == tp->high_seq ||
(icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tcp_ca_event(sk, CA_EVENT_FRTO);
}
/* Have to clear retransmission markers here to keep the bookkeeping
* in shape, even though we are not yet in Loss state.
* If something was really lost, it is eventually caught up
* in tcp_enter_frto_loss.
*/
tp->retrans_out = 0;
tp->undo_marker = tp->snd_una;
tp->undo_retrans = 0;
sk_stream_for_retrans_queue(skb, sk) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
}
tcp_sync_left_out(tp);
tcp_set_ca_state(sk, TCP_CA_Open);
tp->frto_highmark = tp->snd_nxt;
}
/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
* which indicates that we should follow the traditional RTO recovery,
* i.e. mark everything lost and do go-back-N retransmission.
*/
static void tcp_enter_frto_loss(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int cnt = 0;
tp->sacked_out = 0;
tp->lost_out = 0;
tp->fackets_out = 0;
sk_stream_for_retrans_queue(skb, sk) {
cnt += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
/* Do not mark those segments lost that were
* forward transmitted after RTO
*/
if (!after(TCP_SKB_CB(skb)->end_seq,
tp->frto_highmark)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
}
} else {
tp->sacked_out += tcp_skb_pcount(skb);
tp->fackets_out = cnt;
}
}
tcp_sync_left_out(tp);
tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_time_stamp;
tp->undo_marker = 0;
tp->frto_counter = 0;
tp->reordering = min_t(unsigned int, tp->reordering,
sysctl_tcp_reordering);
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->frto_highmark;
TCP_ECN_queue_cwr(tp);
clear_all_retrans_hints(tp);
}
void tcp_clear_retrans(struct tcp_sock *tp)
{
tp->left_out = 0;
tp->retrans_out = 0;
tp->fackets_out = 0;
tp->sacked_out = 0;
tp->lost_out = 0;
tp->undo_marker = 0;
tp->undo_retrans = 0;
}
/* Enter Loss state. If "how" is not zero, forget all SACK information
* and reset tags completely, otherwise preserve SACKs. If receiver
* dropped its ofo queue, we will know this due to reneging detection.
*/
void tcp_enter_loss(struct sock *sk, int how)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int cnt = 0;
/* Reduce ssthresh if it has not yet been made inside this window. */
if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
(icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tcp_ca_event(sk, CA_EVENT_LOSS);
}
tp->snd_cwnd = 1;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_time_stamp;
tp->bytes_acked = 0;
tcp_clear_retrans(tp);
/* Push undo marker, if it was plain RTO and nothing
* was retransmitted. */
if (!how)
tp->undo_marker = tp->snd_una;
sk_stream_for_retrans_queue(skb, sk) {
cnt += tcp_skb_pcount(skb);
if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
tp->undo_marker = 0;
TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
} else {
tp->sacked_out += tcp_skb_pcount(skb);
tp->fackets_out = cnt;
}
}
tcp_sync_left_out(tp);
tp->reordering = min_t(unsigned int, tp->reordering,
sysctl_tcp_reordering);
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->snd_nxt;
TCP_ECN_queue_cwr(tp);
clear_all_retrans_hints(tp);
}
static int tcp_check_sack_reneging(struct sock *sk)
{
struct sk_buff *skb;
/* If ACK arrived pointing to a remembered SACK,
* it means that our remembered SACKs do not reflect
* real state of receiver i.e.
* receiver _host_ is heavily congested (or buggy).
* Do processing similar to RTO timeout.
*/
if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
struct inet_connection_sock *icsk = inet_csk(sk);
NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
tcp_enter_loss(sk, 1);
icsk->icsk_retransmits++;
tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
icsk->icsk_rto, TCP_RTO_MAX);
return 1;
}
return 0;
}
static inline int tcp_fackets_out(struct tcp_sock *tp)
{
return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
}
static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
{
return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
}
static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
{
return tp->packets_out &&
tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
}
/* Linux NewReno/SACK/FACK/ECN state machine.
* --------------------------------------
*
* "Open" Normal state, no dubious events, fast path.
* "Disorder" In all the respects it is "Open",
* but requires a bit more attention. It is entered when
* we see some SACKs or dupacks. It is split of "Open"
* mainly to move some processing from fast path to slow one.
* "CWR" CWND was reduced due to some Congestion Notification event.
* It can be ECN, ICMP source quench, local device congestion.
* "Recovery" CWND was reduced, we are fast-retransmitting.
* "Loss" CWND was reduced due to RTO timeout or SACK reneging.
*
* tcp_fastretrans_alert() is entered:
* - each incoming ACK, if state is not "Open"
* - when arrived ACK is unusual, namely:
* * SACK
* * Duplicate ACK.
* * ECN ECE.
*
* Counting packets in flight is pretty simple.
*
* in_flight = packets_out - left_out + retrans_out
*
* packets_out is SND.NXT-SND.UNA counted in packets.
*
* retrans_out is number of retransmitted segments.
*
* left_out is number of segments left network, but not ACKed yet.
*
* left_out = sacked_out + lost_out
*
* sacked_out: Packets, which arrived to receiver out of order
* and hence not ACKed. With SACKs this number is simply
* amount of SACKed data. Even without SACKs
* it is easy to give pretty reliable estimate of this number,
* counting duplicate ACKs.
*
* lost_out: Packets lost by network. TCP has no explicit
* "loss notification" feedback from network (for now).
* It means that this number can be only _guessed_.
* Actually, it is the heuristics to predict lossage that
* distinguishes different algorithms.
*
* F.e. after RTO, when all the queue is considered as lost,
* lost_out = packets_out and in_flight = retrans_out.
*
* Essentially, we have now two algorithms counting
* lost packets.
*
* FACK: It is the simplest heuristics. As soon as we decided
* that something is lost, we decide that _all_ not SACKed
* packets until the most forward SACK are lost. I.e.
* lost_out = fackets_out - sacked_out and left_out = fackets_out.
* It is absolutely correct estimate, if network does not reorder
* packets. And it loses any connection to reality when reordering
* takes place. We use FACK by default until reordering
* is suspected on the path to this destination.
*
* NewReno: when Recovery is entered, we assume that one segment
* is lost (classic Reno). While we are in Recovery and
* a partial ACK arrives, we assume that one more packet
* is lost (NewReno). This heuristics are the same in NewReno
* and SACK.
*
* Imagine, that's all! Forget about all this shamanism about CWND inflation
* deflation etc. CWND is real congestion window, never inflated, changes
* only according to classic VJ rules.
*
* Really tricky (and requiring careful tuning) part of algorithm
* is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
* The first determines the moment _when_ we should reduce CWND and,
* hence, slow down forward transmission. In fact, it determines the moment
* when we decide that hole is caused by loss, rather than by a reorder.
*
* tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
* holes, caused by lost packets.
*
* And the most logically complicated part of algorithm is undo
* heuristics. We detect false retransmits due to both too early
* fast retransmit (reordering) and underestimated RTO, analyzing
* timestamps and D-SACKs. When we detect that some segments were
* retransmitted by mistake and CWND reduction was wrong, we undo
* window reduction and abort recovery phase. This logic is hidden
* inside several functions named tcp_try_undo_<something>.
*/
/* This function decides, when we should leave Disordered state
* and enter Recovery phase, reducing congestion window.
*
* Main question: may we further continue forward transmission
* with the same cwnd?
*/
static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
{
__u32 packets_out;
/* Trick#1: The loss is proven. */
if (tp->lost_out)
return 1;
/* Not-A-Trick#2 : Classic rule... */
if (tcp_fackets_out(tp) > tp->reordering)
return 1;
/* Trick#3 : when we use RFC2988 timer restart, fast
* retransmit can be triggered by timeout of queue head.
*/
if (tcp_head_timedout(sk, tp))
return 1;
/* Trick#4: It is still not OK... But will it be useful to delay
* recovery more?
*/
packets_out = tp->packets_out;
if (packets_out <= tp->reordering &&
tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
!tcp_may_send_now(sk, tp)) {
/* We have nothing to send. This connection is limited
* either by receiver window or by application.
*/
return 1;
}
return 0;
}
/* If we receive more dupacks than we expected counting segments
* in assumption of absent reordering, interpret this as reordering.
* The only another reason could be bug in receiver TCP.
*/
static void tcp_check_reno_reordering(struct sock *sk, const int addend)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 holes;
holes = max(tp->lost_out, 1U);
holes = min(holes, tp->packets_out);
if ((tp->sacked_out + holes) > tp->packets_out) {
tp->sacked_out = tp->packets_out - holes;
tcp_update_reordering(sk, tp->packets_out + addend, 0);
}
}
/* Emulate SACKs for SACKless connection: account for a new dupack. */
static void tcp_add_reno_sack(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->sacked_out++;
tcp_check_reno_reordering(sk, 0);
tcp_sync_left_out(tp);
}
/* Account for ACK, ACKing some data in Reno Recovery phase. */
static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
{
if (acked > 0) {
/* One ACK acked hole. The rest eat duplicate ACKs. */
if (acked-1 >= tp->sacked_out)
tp->sacked_out = 0;
else
tp->sacked_out -= acked-1;
}
tcp_check_reno_reordering(sk, acked);
tcp_sync_left_out(tp);
}
static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
{
tp->sacked_out = 0;
tp->left_out = tp->lost_out;
}
/* Mark head of queue up as lost. */
static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
int packets, u32 high_seq)
{
struct sk_buff *skb;
int cnt;
BUG_TRAP(packets <= tp->packets_out);
if (tp->lost_skb_hint) {
skb = tp->lost_skb_hint;
cnt = tp->lost_cnt_hint;
} else {
skb = sk->sk_write_queue.next;
cnt = 0;
}
sk_stream_for_retrans_queue_from(skb, sk) {
/* TODO: do this better */
/* this is not the most efficient way to do this... */
tp->lost_skb_hint = skb;
tp->lost_cnt_hint = cnt;
cnt += tcp_skb_pcount(skb);
if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
break;
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
/* clear xmit_retransmit_queue hints
* if this is beyond hint */
if(tp->retransmit_skb_hint != NULL &&
before(TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) {
tp->retransmit_skb_hint = NULL;
}
}
}
tcp_sync_left_out(tp);
}
/* Account newly detected lost packet(s) */
static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
{
if (IsFack(tp)) {
int lost = tp->fackets_out - tp->reordering;
if (lost <= 0)
lost = 1;
tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
} else {
tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
}
/* New heuristics: it is possible only after we switched
* to restart timer each time when something is ACKed.
* Hence, we can detect timed out packets during fast
* retransmit without falling to slow start.
*/
if (!IsReno(tp) && tcp_head_timedout(sk, tp)) {
struct sk_buff *skb;
skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
: sk->sk_write_queue.next;
sk_stream_for_retrans_queue_from(skb, sk) {
if (!tcp_skb_timedout(sk, skb))
break;
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
/* clear xmit_retrans hint */
if (tp->retransmit_skb_hint &&
before(TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
tp->retransmit_skb_hint = NULL;
}
}
tp->scoreboard_skb_hint = skb;
tcp_sync_left_out(tp);
}
}
/* CWND moderation, preventing bursts due to too big ACKs
* in dubious situations.
*/
static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
{
tp->snd_cwnd = min(tp->snd_cwnd,
tcp_packets_in_flight(tp)+tcp_max_burst(tp));
tp->snd_cwnd_stamp = tcp_time_stamp;
}
/* Lower bound on congestion window is slow start threshold
* unless congestion avoidance choice decides to overide it.
*/
static inline u32 tcp_cwnd_min(const struct sock *sk)
{
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
}
/* Decrease cwnd each second ack. */
static void tcp_cwnd_down(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
int decr = tp->snd_cwnd_cnt + 1;
tp->snd_cwnd_cnt = decr&1;
decr >>= 1;
if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
tp->snd_cwnd -= decr;
tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
tp->snd_cwnd_stamp = tcp_time_stamp;
}
/* Nothing was retransmitted or returned timestamp is less
* than timestamp of the first retransmission.
*/
static inline int tcp_packet_delayed(struct tcp_sock *tp)
{
return !tp->retrans_stamp ||
(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
(__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
}
/* Undo procedures. */
#if FASTRETRANS_DEBUG > 1
static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
{
struct inet_sock *inet = inet_sk(sk);
printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
msg,
NIPQUAD(inet->daddr), ntohs(inet->dport),
tp->snd_cwnd, tp->left_out,
tp->snd_ssthresh, tp->prior_ssthresh,
tp->packets_out);
}
#else
#define DBGUNDO(x...) do { } while (0)
#endif
static void tcp_undo_cwr(struct sock *sk, const int undo)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->prior_ssthresh) {
const struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->undo_cwnd)
tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
else
tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
tp->snd_ssthresh = tp->prior_ssthresh;
TCP_ECN_withdraw_cwr(tp);
}
} else {
tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
}
tcp_moderate_cwnd(tp);
tp->snd_cwnd_stamp = tcp_time_stamp;
/* There is something screwy going on with the retrans hints after
an undo */
clear_all_retrans_hints(tp);
}
static inline int tcp_may_undo(struct tcp_sock *tp)
{
return tp->undo_marker &&
(!tp->undo_retrans || tcp_packet_delayed(tp));
}
/* People celebrate: "We love our President!" */
static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
{
if (tcp_may_undo(tp)) {
/* Happy end! We did not retransmit anything
* or our original transmission succeeded.
*/
DBGUNDO(sk, tp, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
tcp_undo_cwr(sk, 1);
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
else
NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
tp->undo_marker = 0;
}
if (tp->snd_una == tp->high_seq && IsReno(tp)) {
/* Hold old state until something *above* high_seq
* is ACKed. For Reno it is MUST to prevent false
* fast retransmits (RFC2582). SACK TCP is safe. */
tcp_moderate_cwnd(tp);
return 1;
}
tcp_set_ca_state(sk, TCP_CA_Open);
return 0;
}
/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
{
if (tp->undo_marker && !tp->undo_retrans) {
DBGUNDO(sk, tp, "D-SACK");
tcp_undo_cwr(sk, 1);
tp->undo_marker = 0;
NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
}
}
/* Undo during fast recovery after partial ACK. */
static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
int acked)
{
/* Partial ACK arrived. Force Hoe's retransmit. */
int failed = IsReno(tp) || tp->fackets_out>tp->reordering;
if (tcp_may_undo(tp)) {
/* Plain luck! Hole if filled with delayed
* packet, rather than with a retransmit.
*/
if (tp->retrans_out == 0)
tp->retrans_stamp = 0;
tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
DBGUNDO(sk, tp, "Hoe");
tcp_undo_cwr(sk, 0);
NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
/* So... Do not make Hoe's retransmit yet.
* If the first packet was delayed, the rest
* ones are most probably delayed as well.
*/
failed = 0;
}
return failed;
}
/* Undo during loss recovery after partial ACK. */
static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
{
if (tcp_may_undo(tp)) {
struct sk_buff *skb;
sk_stream_for_retrans_queue(skb, sk) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
}
clear_all_retrans_hints(tp);
DBGUNDO(sk, tp, "partial loss");
tp->lost_out = 0;
tp->left_out = tp->sacked_out;
tcp_undo_cwr(sk, 1);
NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
inet_csk(sk)->icsk_retransmits = 0;
tp->undo_marker = 0;
if (!IsReno(tp))
tcp_set_ca_state(sk, TCP_CA_Open);
return 1;
}
return 0;
}
static inline void tcp_complete_cwr(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
tp->snd_cwnd_stamp = tcp_time_stamp;
tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
}
static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
{
tp->left_out = tp->sacked_out;
if (tp->retrans_out == 0)
tp->retrans_stamp = 0;
if (flag&FLAG_ECE)
tcp_enter_cwr(sk);
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
int state = TCP_CA_Open;
if (tp->left_out || tp->retrans_out || tp->undo_marker)
state = TCP_CA_Disorder;
if (inet_csk(sk)->icsk_ca_state != state) {
tcp_set_ca_state(sk, state);
tp->high_seq = tp->snd_nxt;
}
tcp_moderate_cwnd(tp);
} else {
tcp_cwnd_down(sk);
}
}
static void tcp_mtup_probe_failed(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
icsk->icsk_mtup.probe_size = 0;
}
static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
/* FIXME: breaks with very large cwnd */
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_cwnd = tp->snd_cwnd *
tcp_mss_to_mtu(sk, tp->mss_cache) /
icsk->icsk_mtup.probe_size;
tp->snd_cwnd_cnt = 0;
tp->snd_cwnd_stamp = tcp_time_stamp;
tp->rcv_ssthresh = tcp_current_ssthresh(sk);
icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
icsk->icsk_mtup.probe_size = 0;
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
}
/* Process an event, which can update packets-in-flight not trivially.
* Main goal of this function is to calculate new estimate for left_out,
* taking into account both packets sitting in receiver's buffer and
* packets lost by network.
*
* Besides that it does CWND reduction, when packet loss is detected
* and changes state of machine.
*
* It does _not_ decide what to send, it is made in function
* tcp_xmit_retransmit_queue().
*/
static void
tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
int prior_packets, int flag)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));
/* Some technical things:
* 1. Reno does not count dupacks (sacked_out) automatically. */
if (!tp->packets_out)
tp->sacked_out = 0;
/* 2. SACK counts snd_fack in packets inaccurately. */
if (tp->sacked_out == 0)
tp->fackets_out = 0;
/* Now state machine starts.
* A. ECE, hence prohibit cwnd undoing, the reduction is required. */
if (flag&FLAG_ECE)
tp->prior_ssthresh = 0;
/* B. In all the states check for reneging SACKs. */
if (tp->sacked_out && tcp_check_sack_reneging(sk))
return;
/* C. Process data loss notification, provided it is valid. */
if ((flag&FLAG_DATA_LOST) &&
before(tp->snd_una, tp->high_seq) &&
icsk->icsk_ca_state != TCP_CA_Open &&
tp->fackets_out > tp->reordering) {
tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
}
/* D. Synchronize left_out to current state. */
tcp_sync_left_out(tp);
/* E. Check state exit conditions. State can be terminated
* when high_seq is ACKed. */
if (icsk->icsk_ca_state == TCP_CA_Open) {
if (!sysctl_tcp_frto)
BUG_TRAP(tp->retrans_out == 0);
tp->retrans_stamp = 0;
} else if (!before(tp->snd_una, tp->high_seq)) {
switch (icsk->icsk_ca_state) {
case TCP_CA_Loss:
icsk->icsk_retransmits = 0;
if (tcp_try_undo_recovery(sk, tp))
return;
break;
case TCP_CA_CWR:
/* CWR is to be held something *above* high_seq
* is ACKed for CWR bit to reach receiver. */
if (tp->snd_una != tp->high_seq) {
tcp_complete_cwr(sk);
tcp_set_ca_state(sk, TCP_CA_Open);
}
break;
case TCP_CA_Disorder:
tcp_try_undo_dsack(sk, tp);
if (!tp->undo_marker ||
/* For SACK case do not Open to allow to undo
* catching for all duplicate ACKs. */
IsReno(tp) || tp->snd_una != tp->high_seq) {
tp->undo_marker = 0;
tcp_set_ca_state(sk, TCP_CA_Open);
}
break;
case TCP_CA_Recovery:
if (IsReno(tp))
tcp_reset_reno_sack(tp);
if (tcp_try_undo_recovery(sk, tp))
return;
tcp_complete_cwr(sk);
break;
}
}
/* F. Process state. */
switch (icsk->icsk_ca_state) {
case TCP_CA_Recovery:
if (prior_snd_una == tp->snd_una) {
if (IsReno(tp) && is_dupack)
tcp_add_reno_sack(sk);
} else {
int acked = prior_packets - tp->packets_out;
if (IsReno(tp))
tcp_remove_reno_sacks(sk, tp, acked);
is_dupack = tcp_try_undo_partial(sk, tp, acked);
}
break;
case TCP_CA_Loss:
if (flag&FLAG_DATA_ACKED)
icsk->icsk_retransmits = 0;
if (!tcp_try_undo_loss(sk, tp)) {
tcp_moderate_cwnd(tp);
tcp_xmit_retransmit_queue(sk);
return;
}
if (icsk->icsk_ca_state != TCP_CA_Open)
return;
/* Loss is undone; fall through to processing in Open state. */
default:
if (IsReno(tp)) {
if (tp->snd_una != prior_snd_una)
tcp_reset_reno_sack(tp);
if (is_dupack)
tcp_add_reno_sack(sk);
}
if (icsk->icsk_ca_state == TCP_CA_Disorder)
tcp_try_undo_dsack(sk, tp);
if (!tcp_time_to_recover(sk, tp)) {
tcp_try_to_open(sk, tp, flag);
return;
}
/* MTU probe failure: don't reduce cwnd */
if (icsk->icsk_ca_state < TCP_CA_CWR &&
icsk->icsk_mtup.probe_size &&
tp->snd_una == tp->mtu_probe.probe_seq_start) {
tcp_mtup_probe_failed(sk);
/* Restores the reduction we did in tcp_mtup_probe() */
tp->snd_cwnd++;
tcp_simple_retransmit(sk);
return;
}
/* Otherwise enter Recovery state */
if (IsReno(tp))
NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
else
NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
tp->high_seq = tp->snd_nxt;
tp->prior_ssthresh = 0;
tp->undo_marker = tp->snd_una;
tp->undo_retrans = tp->retrans_out;
if (icsk->icsk_ca_state < TCP_CA_CWR) {
if (!(flag&FLAG_ECE))
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
TCP_ECN_queue_cwr(tp);
}
tp->bytes_acked = 0;
tp->snd_cwnd_cnt = 0;
tcp_set_ca_state(sk, TCP_CA_Recovery);
}
if (is_dupack || tcp_head_timedout(sk, tp))
tcp_update_scoreboard(sk, tp);
tcp_cwnd_down(sk);
tcp_xmit_retransmit_queue(sk);
}
/* Read draft-ietf-tcplw-high-performance before mucking
* with this code. (Supersedes RFC1323)
*/
static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
{
/* RTTM Rule: A TSecr value received in a segment is used to
* update the averaged RTT measurement only if the segment
* acknowledges some new data, i.e., only if it advances the
* left edge of the send window.
*
* See draft-ietf-tcplw-high-performance-00, section 3.3.
* 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
*
* Changed: reset backoff as soon as we see the first valid sample.
* If we do not, we get strongly overestimated rto. With timestamps
* samples are accepted even from very old segments: f.e., when rtt=1
* increases to 8, we retransmit 5 times and after 8 seconds delayed
* answer arrives rto becomes 120 seconds! If at least one of segments
* in window is lost... Voila. --ANK (010210)
*/
struct tcp_sock *tp = tcp_sk(sk);
const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
tcp_rtt_estimator(sk, seq_rtt);
tcp_set_rto(sk);
inet_csk(sk)->icsk_backoff = 0;
tcp_bound_rto(sk);
}
static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
{
/* We don't have a timestamp. Can only use
* packets that are not retransmitted to determine
* rtt estimates. Also, we must not reset the
* backoff for rto until we get a non-retransmitted
* packet. This allows us to deal with a situation
* where the network delay has increased suddenly.
* I.e. Karn's algorithm. (SIGCOMM '87, p5.)
*/
if (flag & FLAG_RETRANS_DATA_ACKED)
return;
tcp_rtt_estimator(sk, seq_rtt);
tcp_set_rto(sk);
inet_csk(sk)->icsk_backoff = 0;
tcp_bound_rto(sk);
}
static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
const s32 seq_rtt)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
tcp_ack_saw_tstamp(sk, flag);
else if (seq_rtt >= 0)
tcp_ack_no_tstamp(sk, seq_rtt, flag);
}
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
u32 in_flight, int good)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
}
/* Restart timer after forward progress on connection.
* RFC2988 recommends to restart timer to now+rto.
*/
static void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
{
if (!tp->packets_out) {
inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
} else {
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
}
}
static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
__u32 now, __s32 *seq_rtt)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
__u32 seq = tp->snd_una;
__u32 packets_acked;
int acked = 0;
/* If we get here, the whole TSO packet has not been
* acked.
*/
BUG_ON(!after(scb->end_seq, seq));
packets_acked = tcp_skb_pcount(skb);
if (tcp_trim_head(sk, skb, seq - scb->seq))
return 0;
packets_acked -= tcp_skb_pcount(skb);
if (packets_acked) {
__u8 sacked = scb->sacked;
acked |= FLAG_DATA_ACKED;
if (sacked) {
if (sacked & TCPCB_RETRANS) {
if (sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= packets_acked;
acked |= FLAG_RETRANS_DATA_ACKED;
*seq_rtt = -1;
} else if (*seq_rtt < 0)
*seq_rtt = now - scb->when;
if (sacked & TCPCB_SACKED_ACKED)
tp->sacked_out -= packets_acked;
if (sacked & TCPCB_LOST)
tp->lost_out -= packets_acked;
if (sacked & TCPCB_URG) {
if (tp->urg_mode &&
!before(seq, tp->snd_up))
tp->urg_mode = 0;
}
} else if (*seq_rtt < 0)
*seq_rtt = now - scb->when;
if (tp->fackets_out) {
__u32 dval = min(tp->fackets_out, packets_acked);
tp->fackets_out -= dval;
}
tp->packets_out -= packets_acked;
BUG_ON(tcp_skb_pcount(skb) == 0);
BUG_ON(!before(scb->seq, scb->end_seq));
}
return acked;
}
static u32 tcp_usrtt(struct timeval *tv)
{
struct timeval now;
do_gettimeofday(&now);
return (now.tv_sec - tv->tv_sec) * 1000000 + (now.tv_usec - tv->tv_usec);
}
/* Remove acknowledged frames from the retransmission queue. */
static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
{
struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
struct sk_buff *skb;
__u32 now = tcp_time_stamp;
int acked = 0;
__s32 seq_rtt = -1;
u32 pkts_acked = 0;
void (*rtt_sample)(struct sock *sk, u32 usrtt)
= icsk->icsk_ca_ops->rtt_sample;
struct timeval tv = { .tv_sec = 0, .tv_usec = 0 };
while ((skb = skb_peek(&sk->sk_write_queue)) &&
skb != sk->sk_send_head) {
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
__u8 sacked = scb->sacked;
/* If our packet is before the ack sequence we can
* discard it as it's confirmed to have arrived at
* the other end.
*/
if (after(scb->end_seq, tp->snd_una)) {
if (tcp_skb_pcount(skb) > 1 &&
after(tp->snd_una, scb->seq))
acked |= tcp_tso_acked(sk, skb,
now, &seq_rtt);
break;
}
/* Initial outgoing SYN's get put onto the write_queue
* just like anything else we transmit. It is not
* true data, and if we misinform our callers that
* this ACK acks real data, we will erroneously exit
* connection startup slow start one packet too
* quickly. This is severely frowned upon behavior.
*/
if (!(scb->flags & TCPCB_FLAG_SYN)) {
acked |= FLAG_DATA_ACKED;
++pkts_acked;
} else {
acked |= FLAG_SYN_ACKED;
tp->retrans_stamp = 0;
}
/* MTU probing checks */
if (icsk->icsk_mtup.probe_size) {
if (!after(tp->mtu_probe.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
tcp_mtup_probe_success(sk, skb);
}
}
if (sacked) {
if (sacked & TCPCB_RETRANS) {
if(sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= tcp_skb_pcount(skb);
acked |= FLAG_RETRANS_DATA_ACKED;
seq_rtt = -1;
} else if (seq_rtt < 0) {
seq_rtt = now - scb->when;
skb_get_timestamp(skb, &tv);
}
if (sacked & TCPCB_SACKED_ACKED)
tp->sacked_out -= tcp_skb_pcount(skb);
if (sacked & TCPCB_LOST)
tp->lost_out -= tcp_skb_pcount(skb);
if (sacked & TCPCB_URG) {
if (tp->urg_mode &&
!before(scb->end_seq, tp->snd_up))
tp->urg_mode = 0;
}
} else if (seq_rtt < 0) {
seq_rtt = now - scb->when;
skb_get_timestamp(skb, &tv);
}
tcp_dec_pcount_approx(&tp->fackets_out, skb);
tcp_packets_out_dec(tp, skb);
__skb_unlink(skb, &sk->sk_write_queue);
sk_stream_free_skb(sk, skb);
clear_all_retrans_hints(tp);
}
if (acked&FLAG_ACKED) {
tcp_ack_update_rtt(sk, acked, seq_rtt);
tcp_ack_packets_out(sk, tp);
if (rtt_sample && !(acked & FLAG_RETRANS_DATA_ACKED))
(*rtt_sample)(sk, tcp_usrtt(&tv));
if (icsk->icsk_ca_ops->pkts_acked)
icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
}
#if FASTRETRANS_DEBUG > 0
BUG_TRAP((int)tp->sacked_out >= 0);
BUG_TRAP((int)tp->lost_out >= 0);
BUG_TRAP((int)tp->retrans_out >= 0);
if (!tp->packets_out && tp->rx_opt.sack_ok) {
const struct inet_connection_sock *icsk = inet_csk(sk);
if (tp->lost_out) {
printk(KERN_DEBUG "Leak l=%u %d\n",
tp->lost_out, icsk->icsk_ca_state);
tp->lost_out = 0;
}
if (tp->sacked_out) {
printk(KERN_DEBUG "Leak s=%u %d\n",
tp->sacked_out, icsk->icsk_ca_state);
tp->sacked_out = 0;
}
if (tp->retrans_out) {
printk(KERN_DEBUG "Leak r=%u %d\n",
tp->retrans_out, icsk->icsk_ca_state);
tp->retrans_out = 0;
}
}
#endif
*seq_rtt_p = seq_rtt;
return acked;
}
static void tcp_ack_probe(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
/* Was it a usable window open? */
if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
tp->snd_una + tp->snd_wnd)) {
icsk->icsk_backoff = 0;
inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
/* Socket must be waked up by subsequent tcp_data_snd_check().
* This function is not for random using!
*/
} else {
inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
TCP_RTO_MAX);
}
}
static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
{
return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
}
static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
{
const struct tcp_sock *tp = tcp_sk(sk);
return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
!((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
}
/* Check that window update is acceptable.
* The function assumes that snd_una<=ack<=snd_next.
*/
static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
const u32 ack_seq, const u32 nwin)
{
return (after(ack, tp->snd_una) ||
after(ack_seq, tp->snd_wl1) ||
(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
}
/* Update our send window.
*
* Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
* and in FreeBSD. NetBSD's one is even worse.) is wrong.
*/
static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
struct sk_buff *skb, u32 ack, u32 ack_seq)
{
int flag = 0;
u32 nwin = ntohs(skb->h.th->window);
if (likely(!skb->h.th->syn))
nwin <<= tp->rx_opt.snd_wscale;
if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
flag |= FLAG_WIN_UPDATE;
tcp_update_wl(tp, ack, ack_seq);
if (tp->snd_wnd != nwin) {
tp->snd_wnd = nwin;
/* Note, it is the only place, where
* fast path is recovered for sending TCP.
*/
tp->pred_flags = 0;
tcp_fast_path_check(sk, tp);
if (nwin > tp->max_window) {
tp->max_window = nwin;
tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
}
}
}
tp->snd_una = ack;
return flag;
}
static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
{
struct tcp_sock *tp = tcp_sk(sk);
tcp_sync_left_out(tp);
if (tp->snd_una == prior_snd_una ||
!before(tp->snd_una, tp->frto_highmark)) {
/* RTO was caused by loss, start retransmitting in
* go-back-N slow start
*/
tcp_enter_frto_loss(sk);
return;
}
if (tp->frto_counter == 1) {
/* First ACK after RTO advances the window: allow two new
* segments out.
*/
tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
} else {
/* Also the second ACK after RTO advances the window.
* The RTO was likely spurious. Reduce cwnd and continue
* in congestion avoidance
*/
tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
tcp_moderate_cwnd(tp);
}
/* F-RTO affects on two new ACKs following RTO.
* At latest on third ACK the TCP behavior is back to normal.
*/
tp->frto_counter = (tp->frto_counter + 1) % 3;
}
/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_snd_una = tp->snd_una;
u32 ack_seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
u32 prior_in_flight;
s32 seq_rtt;
int prior_packets;
/* If the ack is newer than sent or older than previous acks
* then we can probably ignore it.
*/
if (after(ack, tp->snd_nxt))
goto uninteresting_ack;
if (before(ack, prior_snd_una))
goto old_ack;
if (sysctl_tcp_abc) {
if (icsk->icsk_ca_state < TCP_CA_CWR)
tp->bytes_acked += ack - prior_snd_una;
else if (icsk->icsk_ca_state == TCP_CA_Loss)
/* we assume just one segment left network */
tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
}
if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
/* Window is constant, pure forward advance.
* No more checks are required.
* Note, we use the fact that SND.UNA>=SND.WL2.
*/
tcp_update_wl(tp, ack, ack_seq);
tp->snd_una = ack;
flag |= FLAG_WIN_UPDATE;
tcp_ca_event(sk, CA_EVENT_FAST_ACK);
NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
} else {
if (ack_seq != TCP_SKB_CB(skb)->end_seq)
flag |= FLAG_DATA;
else
NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);
if (TCP_SKB_CB(skb)->sacked)
flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
flag |= FLAG_ECE;
tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
}
/* We passed data and got it acked, remove any soft error
* log. Something worked...
*/
sk->sk_err_soft = 0;
tp->rcv_tstamp = tcp_time_stamp;
prior_packets = tp->packets_out;
if (!prior_packets)
goto no_queue;
prior_in_flight = tcp_packets_in_flight(tp);
/* See if we can take anything off of the retransmit queue. */
flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
if (tp->frto_counter)
tcp_process_frto(sk, prior_snd_una);
if (tcp_ack_is_dubious(sk, flag)) {
/* Advance CWND, if state allows this. */
if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 0);
tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
} else {
if ((flag & FLAG_DATA_ACKED))
tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
}
if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
dst_confirm(sk->sk_dst_cache);
return 1;
no_queue:
icsk->icsk_probes_out = 0;
/* If this ack opens up a zero window, clear backoff. It was
* being used to time the probes, and is probably far higher than
* it needs to be for normal retransmission.
*/
if (sk->sk_send_head)
tcp_ack_probe(sk);
return 1;
old_ack:
if (TCP_SKB_CB(skb)->sacked)
tcp_sacktag_write_queue(sk, skb, prior_snd_una);
uninteresting_ack:
SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
return 0;
}
/* Look for tcp options. Normally only called on SYN and SYNACK packets.
* But, this can also be called on packets in the established flow when
* the fast version below fails.
*/
void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
{
unsigned char *ptr;
struct tcphdr *th = skb->h.th;
int length=(th->doff*4)-sizeof(struct tcphdr);
ptr = (unsigned char *)(th + 1);
opt_rx->saw_tstamp = 0;
while(length>0) {
int opcode=*ptr++;
int opsize;
switch (opcode) {
case TCPOPT_EOL:
return;
case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
length--;
continue;
default:
opsize=*ptr++;
if (opsize < 2) /* "silly options" */
return;
if (opsize > length)
return; /* don't parse partial options */
switch(opcode) {
case TCPOPT_MSS:
if(opsize==TCPOLEN_MSS && th->syn && !estab) {
u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
if (in_mss) {
if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
in_mss = opt_rx->user_mss;
opt_rx->mss_clamp = in_mss;
}
}
break;
case TCPOPT_WINDOW:
if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
if (sysctl_tcp_window_scaling) {
__u8 snd_wscale = *(__u8 *) ptr;
opt_rx->wscale_ok = 1;
if (snd_wscale > 14) {
if(net_ratelimit())
printk(KERN_INFO "tcp_parse_options: Illegal window "
"scaling value %d >14 received.\n",
snd_wscale);
snd_wscale = 14;
}
opt_rx->snd_wscale = snd_wscale;
}
break;
case TCPOPT_TIMESTAMP:
if(opsize==TCPOLEN_TIMESTAMP) {
if ((estab && opt_rx->tstamp_ok) ||
(!estab && sysctl_tcp_timestamps)) {
opt_rx->saw_tstamp = 1;
opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
}
}
break;
case TCPOPT_SACK_PERM:
if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
if (sysctl_tcp_sack) {
opt_rx->sack_ok = 1;
tcp_sack_reset(opt_rx);
}
}
break;
case TCPOPT_SACK:
if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
!((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
opt_rx->sack_ok) {
TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
}
#ifdef CONFIG_TCP_MD5SIG
case TCPOPT_MD5SIG:
/*
* The MD5 Hash has already been
* checked (see tcp_v{4,6}_do_rcv()).
*/
break;
#endif
};
ptr+=opsize-2;
length-=opsize;
};
}
}
/* Fast parse options. This hopes to only see timestamps.
* If it is wrong it falls back on tcp_parse_options().
*/
static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
struct tcp_sock *tp)
{
if (th->doff == sizeof(struct tcphdr)>>2) {
tp->rx_opt.saw_tstamp = 0;
return 0;
} else if (tp->rx_opt.tstamp_ok &&
th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
__be32 *ptr = (__be32 *)(th + 1);
if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
| (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
tp->rx_opt.saw_tstamp = 1;
++ptr;
tp->rx_opt.rcv_tsval = ntohl(*ptr);
++ptr;
tp->rx_opt.rcv_tsecr = ntohl(*ptr);
return 1;
}
}
tcp_parse_options(skb, &tp->rx_opt, 1);
return 1;
}
static inline void tcp_store_ts_recent(struct tcp_sock *tp)
{
tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
}
static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
{
if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
/* PAWS bug workaround wrt. ACK frames, the PAWS discard
* extra check below makes sure this can only happen
* for pure ACK frames. -DaveM
*
* Not only, also it occurs for expired timestamps.
*/
if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
tcp_store_ts_recent(tp);
}
}
/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
*
* It is not fatal. If this ACK does _not_ change critical state (seqs, window)
* it can pass through stack. So, the following predicate verifies that
* this segment is not used for anything but congestion avoidance or
* fast retransmit. Moreover, we even are able to eliminate most of such
* second order effects, if we apply some small "replay" window (~RTO)
* to timestamp space.
*
* All these measures still do not guarantee that we reject wrapped ACKs
* on networks with high bandwidth, when sequence space is recycled fastly,
* but it guarantees that such events will be very rare and do not affect
* connection seriously. This doesn't look nice, but alas, PAWS is really
* buggy extension.
*
* [ Later note. Even worse! It is buggy for segments _with_ data. RFC
* states that events when retransmit arrives after original data are rare.
* It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
* the biggest problem on large power networks even with minor reordering.
* OK, let's give it small replay window. If peer clock is even 1hz, it is safe
* up to bandwidth of 18Gigabit/sec. 8) ]
*/
static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcphdr *th = skb->h.th;
u32 seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
return (/* 1. Pure ACK with correct sequence number. */
(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
/* 2. ... and duplicate ACK. */
ack == tp->snd_una &&
/* 3. ... and does not update window. */
!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
/* 4. ... and sits in replay window. */
(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
}
static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
!tcp_disordered_ack(sk, skb));
}
/* Check segment sequence number for validity.
*
* Segment controls are considered valid, if the segment
* fits to the window after truncation to the window. Acceptability
* of data (and SYN, FIN, of course) is checked separately.
* See tcp_data_queue(), for example.
*
* Also, controls (RST is main one) are accepted using RCV.WUP instead
* of RCV.NXT. Peer still did not advance his SND.UNA when we
* delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
* (borrowed from freebsd)
*/
static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
return !before(end_seq, tp->rcv_wup) &&
!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
}
/* When we get a reset we do this. */
static void tcp_reset(struct sock *sk)
{
/* We want the right error as BSD sees it (and indeed as we do). */
switch (sk->sk_state) {
case TCP_SYN_SENT:
sk->sk_err = ECONNREFUSED;
break;
case TCP_CLOSE_WAIT:
sk->sk_err = EPIPE;
break;
case TCP_CLOSE:
return;
default:
sk->sk_err = ECONNRESET;
}
if (!sock_flag(sk, SOCK_DEAD))
sk->sk_error_report(sk);
tcp_done(sk);
}
/*
* Process the FIN bit. This now behaves as it is supposed to work
* and the FIN takes effect when it is validly part of sequence
* space. Not before when we get holes.
*
* If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
* (and thence onto LAST-ACK and finally, CLOSE, we never enter
* TIME-WAIT)
*
* If we are in FINWAIT-1, a received FIN indicates simultaneous
* close and we go into CLOSING (and later onto TIME-WAIT)
*
* If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
*/
static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
{
struct tcp_sock *tp = tcp_sk(sk);
inet_csk_schedule_ack(sk);
sk->sk_shutdown |= RCV_SHUTDOWN;
sock_set_flag(sk, SOCK_DONE);
switch (sk->sk_state) {
case TCP_SYN_RECV:
case TCP_ESTABLISHED:
/* Move to CLOSE_WAIT */
tcp_set_state(sk, TCP_CLOSE_WAIT);
inet_csk(sk)->icsk_ack.pingpong = 1;
break;
case TCP_CLOSE_WAIT:
case TCP_CLOSING:
/* Received a retransmission of the FIN, do
* nothing.
*/
break;
case TCP_LAST_ACK:
/* RFC793: Remain in the LAST-ACK state. */
break;
case TCP_FIN_WAIT1:
/* This case occurs when a simultaneous close
* happens, we must ack the received FIN and
* enter the CLOSING state.
*/
tcp_send_ack(sk);
tcp_set_state(sk, TCP_CLOSING);
break;
case TCP_FIN_WAIT2:
/* Received a FIN -- send ACK and enter TIME_WAIT. */
tcp_send_ack(sk);
tcp_time_wait(sk, TCP_TIME_WAIT, 0);
break;
default:
/* Only TCP_LISTEN and TCP_CLOSE are left, in these
* cases we should never reach this piece of code.
*/
printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
__FUNCTION__, sk->sk_state);
break;
};
/* It _is_ possible, that we have something out-of-order _after_ FIN.
* Probably, we should reset in this case. For now drop them.
*/
__skb_queue_purge(&tp->out_of_order_queue);
if (tp->rx_opt.sack_ok)
tcp_sack_reset(&tp->rx_opt);
sk_stream_mem_reclaim(sk);
if (!sock_flag(sk, SOCK_DEAD)) {
sk->sk_state_change(sk);
/* Do not send POLL_HUP for half duplex close. */
if (sk->sk_shutdown == SHUTDOWN_MASK ||
sk->sk_state == TCP_CLOSE)
sk_wake_async(sk, 1, POLL_HUP);
else
sk_wake_async(sk, 1, POLL_IN);
}
}
static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
{
if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
if (before(seq, sp->start_seq))
sp->start_seq = seq;
if (after(end_seq, sp->end_seq))
sp->end_seq = end_seq;
return 1;
}
return 0;
}
static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
if (before(seq, tp->rcv_nxt))
NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
else
NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
tp->rx_opt.dsack = 1;
tp->duplicate_sack[0].start_seq = seq;
tp->duplicate_sack[0].end_seq = end_seq;
tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
}
}
static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
if (!tp->rx_opt.dsack)
tcp_dsack_set(tp, seq, end_seq);
else
tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
}
static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
tcp_enter_quickack_mode(sk);
if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
u32 end_seq = TCP_SKB_CB(skb)->end_seq;
if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
end_seq = tp->rcv_nxt;
tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
}
}
tcp_send_ack(sk);
}
/* These routines update the SACK block as out-of-order packets arrive or
* in-order packets close up the sequence space.
*/
static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
{
int this_sack;
struct tcp_sack_block *sp = &tp->selective_acks[0];
struct tcp_sack_block *swalk = sp+1;
/* See if the recent change to the first SACK eats into
* or hits the sequence space of other SACK blocks, if so coalesce.
*/
for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
int i;
/* Zap SWALK, by moving every further SACK up by one slot.
* Decrease num_sacks.
*/
tp->rx_opt.num_sacks--;
tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
sp[i] = sp[i+1];
continue;
}
this_sack++, swalk++;
}
}
static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
{
__u32 tmp;
tmp = sack1->start_seq;
sack1->start_seq = sack2->start_seq;
sack2->start_seq = tmp;
tmp = sack1->end_seq;
sack1->end_seq = sack2->end_seq;
sack2->end_seq = tmp;
}
static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_sack_block *sp = &tp->selective_acks[0];
int cur_sacks = tp->rx_opt.num_sacks;
int this_sack;
if (!cur_sacks)
goto new_sack;
for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
if (tcp_sack_extend(sp, seq, end_seq)) {
/* Rotate this_sack to the first one. */
for (; this_sack>0; this_sack--, sp--)
tcp_sack_swap(sp, sp-1);
if (cur_sacks > 1)
tcp_sack_maybe_coalesce(tp);
return;
}
}
/* Could not find an adjacent existing SACK, build a new one,
* put it at the front, and shift everyone else down. We
* always know there is at least one SACK present already here.
*
* If the sack array is full, forget about the last one.
*/
if (this_sack >= 4) {
this_sack--;
tp->rx_opt.num_sacks--;
sp--;
}
for(; this_sack > 0; this_sack--, sp--)
*sp = *(sp-1);
new_sack:
/* Build the new head SACK, and we're done. */
sp->start_seq = seq;
sp->end_seq = end_seq;
tp->rx_opt.num_sacks++;
tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
}
/* RCV.NXT advances, some SACKs should be eaten. */
static void tcp_sack_remove(struct tcp_sock *tp)
{
struct tcp_sack_block *sp = &tp->selective_acks[0];
int num_sacks = tp->rx_opt.num_sacks;
int this_sack;
/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
if (skb_queue_empty(&tp->out_of_order_queue)) {
tp->rx_opt.num_sacks = 0;
tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
return;
}
for(this_sack = 0; this_sack < num_sacks; ) {
/* Check if the start of the sack is covered by RCV.NXT. */
if (!before(tp->rcv_nxt, sp->start_seq)) {
int i;
/* RCV.NXT must cover all the block! */
BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
/* Zap this SACK, by moving forward any other SACKS. */
for (i=this_sack+1; i < num_sacks; i++)
tp->selective_acks[i-1] = tp->selective_acks[i];
num_sacks--;
continue;
}
this_sack++;
sp++;
}
if (num_sacks != tp->rx_opt.num_sacks) {
tp->rx_opt.num_sacks = num_sacks;
tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
}
}
/* This one checks to see if we can put data from the
* out_of_order queue into the receive_queue.
*/
static void tcp_ofo_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
__u32 dsack_high = tp->rcv_nxt;
struct sk_buff *skb;
while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
break;
if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
__u32 dsack = dsack_high;
if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
dsack_high = TCP_SKB_CB(skb)->end_seq;
tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
}
if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
SOCK_DEBUG(sk, "ofo packet was already received \n");
__skb_unlink(skb, &tp->out_of_order_queue);
__kfree_skb(skb);
continue;
}
SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(skb)->end_seq);
__skb_unlink(skb, &tp->out_of_order_queue);
__skb_queue_tail(&sk->sk_receive_queue, skb);
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
if(skb->h.th->fin)
tcp_fin(skb, sk, skb->h.th);
}
}
static int tcp_prune_queue(struct sock *sk);
static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
{
struct tcphdr *th = skb->h.th;
struct tcp_sock *tp = tcp_sk(sk);
int eaten = -1;
if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
goto drop;
__skb_pull(skb, th->doff*4);
TCP_ECN_accept_cwr(tp, skb);
if (tp->rx_opt.dsack) {
tp->rx_opt.dsack = 0;
tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
4 - tp->rx_opt.tstamp_ok);
}
/* Queue data for delivery to the user.
* Packets in sequence go to the receive queue.
* Out of sequence packets to the out_of_order_queue.
*/
if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
if (tcp_receive_window(tp) == 0)
goto out_of_window;
/* Ok. In sequence. In window. */
if (tp->ucopy.task == current &&
tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
sock_owned_by_user(sk) && !tp->urg_data) {
int chunk = min_t(unsigned int, skb->len,
tp->ucopy.len);
__set_current_state(TASK_RUNNING);
local_bh_enable();
if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
tp->ucopy.len -= chunk;
tp->copied_seq += chunk;
eaten = (chunk == skb->len && !th->fin);
tcp_rcv_space_adjust(sk);
}
local_bh_disable();
}
if (eaten <= 0) {
queue_and_out:
if (eaten < 0 &&
(atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
!sk_stream_rmem_schedule(sk, skb))) {
if (tcp_prune_queue(sk) < 0 ||
!sk_stream_rmem_schedule(sk, skb))
goto drop;
}
sk_stream_set_owner_r(skb, sk);
__skb_queue_tail(&sk->sk_receive_queue, skb);
}
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
if(skb->len)
tcp_event_data_recv(sk, tp, skb);
if(th->fin)
tcp_fin(skb, sk, th);
if (!skb_queue_empty(&tp->out_of_order_queue)) {
tcp_ofo_queue(sk);
/* RFC2581. 4.2. SHOULD send immediate ACK, when
* gap in queue is filled.
*/
if (skb_queue_empty(&tp->out_of_order_queue))
inet_csk(sk)->icsk_ack.pingpong = 0;
}
if (tp->rx_opt.num_sacks)
tcp_sack_remove(tp);
tcp_fast_path_check(sk, tp);
if (eaten > 0)
__kfree_skb(skb);
else if (!sock_flag(sk, SOCK_DEAD))
sk->sk_data_ready(sk, 0);
return;
}
if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
/* A retransmit, 2nd most common case. Force an immediate ack. */
NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
out_of_window:
tcp_enter_quickack_mode(sk);
inet_csk_schedule_ack(sk);
drop:
__kfree_skb(skb);
return;
}
/* Out of window. F.e. zero window probe. */
if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
goto out_of_window;
tcp_enter_quickack_mode(sk);
if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
/* Partial packet, seq < rcv_next < end_seq */
SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
TCP_SKB_CB(skb)->end_seq);
tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
/* If window is closed, drop tail of packet. But after
* remembering D-SACK for its head made in previous line.
*/
if (!tcp_receive_window(tp))
goto out_of_window;
goto queue_and_out;
}
TCP_ECN_check_ce(tp, skb);
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
!sk_stream_rmem_schedule(sk, skb)) {
if (tcp_prune_queue(sk) < 0 ||
!sk_stream_rmem_schedule(sk, skb))
goto drop;
}
/* Disable header prediction. */
tp->pred_flags = 0;
inet_csk_schedule_ack(sk);
SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
sk_stream_set_owner_r(skb, sk);
if (!skb_peek(&tp->out_of_order_queue)) {
/* Initial out of order segment, build 1 SACK. */
if (tp->rx_opt.sack_ok) {
tp->rx_opt.num_sacks = 1;
tp->rx_opt.dsack = 0;
tp->rx_opt.eff_sacks = 1;
tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
tp->selective_acks[0].end_seq =
TCP_SKB_CB(skb)->end_seq;
}
__skb_queue_head(&tp->out_of_order_queue,skb);
} else {
struct sk_buff *skb1 = tp->out_of_order_queue.prev;
u32 seq = TCP_SKB_CB(skb)->seq;
u32 end_seq = TCP_SKB_CB(skb)->end_seq;
if (seq == TCP_SKB_CB(skb1)->end_seq) {
__skb_append(skb1, skb, &tp->out_of_order_queue);
if (!tp->rx_opt.num_sacks ||
tp->selective_acks[0].end_seq != seq)
goto add_sack;
/* Common case: data arrive in order after hole. */
tp->selective_acks[0].end_seq = end_seq;
return;
}
/* Find place to insert this segment. */
do {
if (!after(TCP_SKB_CB(skb1)->seq, seq))
break;
} while ((skb1 = skb1->prev) !=
(struct sk_buff*)&tp->out_of_order_queue);
/* Do skb overlap to previous one? */
if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
before(seq, TCP_SKB_CB(skb1)->end_seq)) {
if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
/* All the bits are present. Drop. */
__kfree_skb(skb);
tcp_dsack_set(tp, seq, end_seq);
goto add_sack;
}
if (after(seq, TCP_SKB_CB(skb1)->seq)) {
/* Partial overlap. */
tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
} else {
skb1 = skb1->prev;
}
}
__skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
/* And clean segments covered by new one as whole. */
while ((skb1 = skb->next) !=
(struct sk_buff*)&tp->out_of_order_queue &&
after(end_seq, TCP_SKB_CB(skb1)->seq)) {
if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
break;
}
__skb_unlink(skb1, &tp->out_of_order_queue);
tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
__kfree_skb(skb1);
}
add_sack:
if (tp->rx_opt.sack_ok)
tcp_sack_new_ofo_skb(sk, seq, end_seq);
}
}
/* Collapse contiguous sequence of skbs head..tail with
* sequence numbers start..end.
* Segments with FIN/SYN are not collapsed (only because this
* simplifies code)
*/
static void
tcp_collapse(struct sock *sk, struct sk_buff_head *list,
struct sk_buff *head, struct sk_buff *tail,
u32 start, u32 end)
{
struct sk_buff *skb;
/* First, check that queue is collapsible and find
* the point where collapsing can be useful. */
for (skb = head; skb != tail; ) {
/* No new bits? It is possible on ofo queue. */
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
struct sk_buff *next = skb->next;
__skb_unlink(skb, list);
__kfree_skb(skb);
NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
skb = next;
continue;
}
/* The first skb to collapse is:
* - not SYN/FIN and
* - bloated or contains data before "start" or
* overlaps to the next one.
*/
if (!skb->h.th->syn && !skb->h.th->fin &&
(tcp_win_from_space(skb->truesize) > skb->len ||
before(TCP_SKB_CB(skb)->seq, start) ||
(skb->next != tail &&
TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
break;
/* Decided to skip this, advance start seq. */
start = TCP_SKB_CB(skb)->end_seq;
skb = skb->next;
}
if (skb == tail || skb->h.th->syn || skb->h.th->fin)
return;
while (before(start, end)) {
struct sk_buff *nskb;
int header = skb_headroom(skb);
int copy = SKB_MAX_ORDER(header, 0);
/* Too big header? This can happen with IPv6. */
if (copy < 0)
return;
if (end-start < copy)
copy = end-start;
nskb = alloc_skb(copy+header, GFP_ATOMIC);
if (!nskb)
return;
skb_reserve(nskb, header);
memcpy(nskb->head, skb->head, header);
nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
__skb_insert(nskb, skb->prev, skb, list);
sk_stream_set_owner_r(nskb, sk);
/* Copy data, releasing collapsed skbs. */
while (copy > 0) {
int offset = start - TCP_SKB_CB(skb)->seq;
int size = TCP_SKB_CB(skb)->end_seq - start;
BUG_ON(offset < 0);
if (size > 0) {
size = min(copy, size);
if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
BUG();
TCP_SKB_CB(nskb)->end_seq += size;
copy -= size;
start += size;
}
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
struct sk_buff *next = skb->next;
__skb_unlink(skb, list);
__kfree_skb(skb);
NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
skb = next;
if (skb == tail || skb->h.th->syn || skb->h.th->fin)
return;
}
}
}
}
/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
* and tcp_collapse() them until all the queue is collapsed.
*/
static void tcp_collapse_ofo_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
struct sk_buff *head;
u32 start, end;
if (skb == NULL)
return;
start = TCP_SKB_CB(skb)->seq;
end = TCP_SKB_CB(skb)->end_seq;
head = skb;
for (;;) {
skb = skb->next;
/* Segment is terminated when we see gap or when
* we are at the end of all the queue. */
if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
after(TCP_SKB_CB(skb)->seq, end) ||
before(TCP_SKB_CB(skb)->end_seq, start)) {
tcp_collapse(sk, &tp->out_of_order_queue,
head, skb, start, end);
head = skb;
if (skb == (struct sk_buff *)&tp->out_of_order_queue)
break;
/* Start new segment */
start = TCP_SKB_CB(skb)->seq;
end = TCP_SKB_CB(skb)->end_seq;
} else {
if (before(TCP_SKB_CB(skb)->seq, start))
start = TCP_SKB_CB(skb)->seq;
if (after(TCP_SKB_CB(skb)->end_seq, end))
end = TCP_SKB_CB(skb)->end_seq;
}
}
}
/* Reduce allocated memory if we can, trying to get
* the socket within its memory limits again.
*
* Return less than zero if we should start dropping frames
* until the socket owning process reads some of the data
* to stabilize the situation.
*/
static int tcp_prune_queue(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
tcp_clamp_window(sk, tp);
else if (tcp_memory_pressure)
tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
tcp_collapse_ofo_queue(sk);
tcp_collapse(sk, &sk->sk_receive_queue,
sk->sk_receive_queue.next,
(struct sk_buff*)&sk->sk_receive_queue,
tp->copied_seq, tp->rcv_nxt);
sk_stream_mem_reclaim(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
return 0;
/* Collapsing did not help, destructive actions follow.
* This must not ever occur. */
/* First, purge the out_of_order queue. */
if (!skb_queue_empty(&tp->out_of_order_queue)) {
NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
__skb_queue_purge(&tp->out_of_order_queue);
/* Reset SACK state. A conforming SACK implementation will
* do the same at a timeout based retransmit. When a connection
* is in a sad state like this, we care only about integrity
* of the connection not performance.
*/
if (tp->rx_opt.sack_ok)
tcp_sack_reset(&tp->rx_opt);
sk_stream_mem_reclaim(sk);
}
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
return 0;
/* If we are really being abused, tell the caller to silently
* drop receive data on the floor. It will get retransmitted
* and hopefully then we'll have sufficient space.
*/
NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
/* Massive buffer overcommit. */
tp->pred_flags = 0;
return -1;
}
/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
* As additional protections, we do not touch cwnd in retransmission phases,
* and if application hit its sndbuf limit recently.
*/
void tcp_cwnd_application_limited(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
/* Limited by application or receiver window. */
u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
u32 win_used = max(tp->snd_cwnd_used, init_win);
if (win_used < tp->snd_cwnd) {
tp->snd_ssthresh = tcp_current_ssthresh(sk);
tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
}
tp->snd_cwnd_used = 0;
}
tp->snd_cwnd_stamp = tcp_time_stamp;
}
static int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
{
/* If the user specified a specific send buffer setting, do
* not modify it.
*/
if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
return 0;
/* If we are under global TCP memory pressure, do not expand. */
if (tcp_memory_pressure)
return 0;
/* If we are under soft global TCP memory pressure, do not expand. */
if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
return 0;
/* If we filled the congestion window, do not expand. */
if (tp->packets_out >= tp->snd_cwnd)
return 0;
return 1;
}
/* When incoming ACK allowed to free some skb from write_queue,
* we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
* on the exit from tcp input handler.
*
* PROBLEM: sndbuf expansion does not work well with largesend.
*/
static void tcp_new_space(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tcp_should_expand_sndbuf(sk, tp)) {
int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
demanded = max_t(unsigned int, tp->snd_cwnd,
tp->reordering + 1);
sndmem *= 2*demanded;
if (sndmem > sk->sk_sndbuf)
sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
tp->snd_cwnd_stamp = tcp_time_stamp;
}
sk->sk_write_space(sk);
}
static void tcp_check_space(struct sock *sk)
{
if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
if (sk->sk_socket &&
test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
tcp_new_space(sk);
}
}
static inline void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
{
tcp_push_pending_frames(sk, tp);
tcp_check_space(sk);
}
/*
* Check if sending an ack is needed.
*/
static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
{
struct tcp_sock *tp = tcp_sk(sk);
/* More than one full frame received... */
if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
/* ... and right edge of window advances far enough.
* (tcp_recvmsg() will send ACK otherwise). Or...
*/
&& __tcp_select_window(sk) >= tp->rcv_wnd) ||
/* We ACK each frame or... */
tcp_in_quickack_mode(sk) ||
/* We have out of order data. */
(ofo_possible &&
skb_peek(&tp->out_of_order_queue))) {
/* Then ack it now */
tcp_send_ack(sk);
} else {
/* Else, send delayed ack. */
tcp_send_delayed_ack(sk);
}
}
static inline void tcp_ack_snd_check(struct sock *sk)
{
if (!inet_csk_ack_scheduled(sk)) {
/* We sent a data segment already. */
return;
}
__tcp_ack_snd_check(sk, 1);
}
/*
* This routine is only called when we have urgent data
* signaled. Its the 'slow' part of tcp_urg. It could be
* moved inline now as tcp_urg is only called from one
* place. We handle URGent data wrong. We have to - as
* BSD still doesn't use the correction from RFC961.
* For 1003.1g we should support a new option TCP_STDURG to permit
* either form (or just set the sysctl tcp_stdurg).
*/
static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 ptr = ntohs(th->urg_ptr);
if (ptr && !sysctl_tcp_stdurg)
ptr--;
ptr += ntohl(th->seq);
/* Ignore urgent data that we've already seen and read. */
if (after(tp->copied_seq, ptr))
return;
/* Do not replay urg ptr.
*
* NOTE: interesting situation not covered by specs.
* Misbehaving sender may send urg ptr, pointing to segment,
* which we already have in ofo queue. We are not able to fetch
* such data and will stay in TCP_URG_NOTYET until will be eaten
* by recvmsg(). Seems, we are not obliged to handle such wicked
* situations. But it is worth to think about possibility of some
* DoSes using some hypothetical application level deadlock.
*/
if (before(ptr, tp->rcv_nxt))
return;
/* Do we already have a newer (or duplicate) urgent pointer? */
if (tp->urg_data && !after(ptr, tp->urg_seq))
return;
/* Tell the world about our new urgent pointer. */
sk_send_sigurg(sk);
/* We may be adding urgent data when the last byte read was
* urgent. To do this requires some care. We cannot just ignore
* tp->copied_seq since we would read the last urgent byte again
* as data, nor can we alter copied_seq until this data arrives
* or we break the semantics of SIOCATMARK (and thus sockatmark())
*
* NOTE. Double Dutch. Rendering to plain English: author of comment
* above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
* and expect that both A and B disappear from stream. This is _wrong_.
* Though this happens in BSD with high probability, this is occasional.
* Any application relying on this is buggy. Note also, that fix "works"
* only in this artificial test. Insert some normal data between A and B and we will
* decline of BSD again. Verdict: it is better to remove to trap
* buggy users.
*/
if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
!sock_flag(sk, SOCK_URGINLINE) &&
tp->copied_seq != tp->rcv_nxt) {
struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
tp->copied_seq++;
if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
__skb_unlink(skb, &sk->sk_receive_queue);
__kfree_skb(skb);
}
}
tp->urg_data = TCP_URG_NOTYET;
tp->urg_seq = ptr;
/* Disable header prediction. */
tp->pred_flags = 0;
}
/* This is the 'fast' part of urgent handling. */
static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Check if we get a new urgent pointer - normally not. */
if (th->urg)
tcp_check_urg(sk,th);
/* Do we wait for any urgent data? - normally not... */
if (tp->urg_data == TCP_URG_NOTYET) {
u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
th->syn;
/* Is the urgent pointer pointing into this packet? */
if (ptr < skb->len) {
u8 tmp;
if (skb_copy_bits(skb, ptr, &tmp, 1))
BUG();
tp->urg_data = TCP_URG_VALID | tmp;
if (!sock_flag(sk, SOCK_DEAD))
sk->sk_data_ready(sk, 0);
}
}
}
static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
{
struct tcp_sock *tp = tcp_sk(sk);
int chunk = skb->len - hlen;
int err;
local_bh_enable();
if (skb->ip_summed==CHECKSUM_UNNECESSARY)
err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
else
err = skb_copy_and_csum_datagram_iovec(skb, hlen,
tp->ucopy.iov);
if (!err) {
tp->ucopy.len -= chunk;
tp->copied_seq += chunk;
tcp_rcv_space_adjust(sk);
}
local_bh_disable();
return err;
}
static __sum16 __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
{
__sum16 result;
if (sock_owned_by_user(sk)) {
local_bh_enable();
result = __tcp_checksum_complete(skb);
local_bh_disable();
} else {
result = __tcp_checksum_complete(skb);
}
return result;
}
static inline int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
{
return skb->ip_summed != CHECKSUM_UNNECESSARY &&
__tcp_checksum_complete_user(sk, skb);
}
#ifdef CONFIG_NET_DMA
static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, int hlen)
{
struct tcp_sock *tp = tcp_sk(sk);
int chunk = skb->len - hlen;
int dma_cookie;
int copied_early = 0;
if (tp->ucopy.wakeup)
return 0;
if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
tp->ucopy.dma_chan = get_softnet_dma();
if (tp->ucopy.dma_chan && skb->ip_summed == CHECKSUM_UNNECESSARY) {
dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
skb, hlen, tp->ucopy.iov, chunk, tp->ucopy.pinned_list);
if (dma_cookie < 0)
goto out;
tp->ucopy.dma_cookie = dma_cookie;
copied_early = 1;
tp->ucopy.len -= chunk;
tp->copied_seq += chunk;
tcp_rcv_space_adjust(sk);
if ((tp->ucopy.len == 0) ||
(tcp_flag_word(skb->h.th) & TCP_FLAG_PSH) ||
(atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
tp->ucopy.wakeup = 1;
sk->sk_data_ready(sk, 0);
}
} else if (chunk > 0) {
tp->ucopy.wakeup = 1;
sk->sk_data_ready(sk, 0);
}
out:
return copied_early;
}
#endif /* CONFIG_NET_DMA */
/*
* TCP receive function for the ESTABLISHED state.
*
* It is split into a fast path and a slow path. The fast path is
* disabled when:
* - A zero window was announced from us - zero window probing
* is only handled properly in the slow path.
* - Out of order segments arrived.
* - Urgent data is expected.
* - There is no buffer space left
* - Unexpected TCP flags/window values/header lengths are received
* (detected by checking the TCP header against pred_flags)
* - Data is sent in both directions. Fast path only supports pure senders
* or pure receivers (this means either the sequence number or the ack
* value must stay constant)
* - Unexpected TCP option.
*
* When these conditions are not satisfied it drops into a standard
* receive procedure patterned after RFC793 to handle all cases.
* The first three cases are guaranteed by proper pred_flags setting,
* the rest is checked inline. Fast processing is turned on in
* tcp_data_queue when everything is OK.
*/
int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
struct tcphdr *th, unsigned len)
{
struct tcp_sock *tp = tcp_sk(sk);
/*
* Header prediction.
* The code loosely follows the one in the famous
* "30 instruction TCP receive" Van Jacobson mail.
*
* Van's trick is to deposit buffers into socket queue
* on a device interrupt, to call tcp_recv function
* on the receive process context and checksum and copy
* the buffer to user space. smart...
*
* Our current scheme is not silly either but we take the
* extra cost of the net_bh soft interrupt processing...
* We do checksum and copy also but from device to kernel.
*/
tp->rx_opt.saw_tstamp = 0;
/* pred_flags is 0xS?10 << 16 + snd_wnd
* if header_prediction is to be made
* 'S' will always be tp->tcp_header_len >> 2
* '?' will be 0 for the fast path, otherwise pred_flags is 0 to
* turn it off (when there are holes in the receive
* space for instance)
* PSH flag is ignored.
*/
if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
int tcp_header_len = tp->tcp_header_len;
/* Timestamp header prediction: tcp_header_len
* is automatically equal to th->doff*4 due to pred_flags
* match.
*/
/* Check timestamp */
if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
__be32 *ptr = (__be32 *)(th + 1);
/* No? Slow path! */
if (*ptr != htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
| (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
goto slow_path;
tp->rx_opt.saw_tstamp = 1;
++ptr;
tp->rx_opt.rcv_tsval = ntohl(*ptr);
++ptr;
tp->rx_opt.rcv_tsecr = ntohl(*ptr);
/* If PAWS failed, check it more carefully in slow path */
if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
goto slow_path;
/* DO NOT update ts_recent here, if checksum fails
* and timestamp was corrupted part, it will result
* in a hung connection since we will drop all
* future packets due to the PAWS test.
*/
}
if (len <= tcp_header_len) {
/* Bulk data transfer: sender */
if (len == tcp_header_len) {
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
/* We know that such packets are checksummed
* on entry.
*/
tcp_ack(sk, skb, 0);
__kfree_skb(skb);
tcp_data_snd_check(sk, tp);
return 0;
} else { /* Header too small */
TCP_INC_STATS_BH(TCP_MIB_INERRS);
goto discard;
}
} else {
int eaten = 0;
int copied_early = 0;
if (tp->copied_seq == tp->rcv_nxt &&
len - tcp_header_len <= tp->ucopy.len) {
#ifdef CONFIG_NET_DMA
if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
copied_early = 1;
eaten = 1;
}
#endif
if (tp->ucopy.task == current && sock_owned_by_user(sk) && !copied_early) {
__set_current_state(TASK_RUNNING);
if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
eaten = 1;
}
if (eaten) {
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) +
TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
tcp_rcv_rtt_measure_ts(sk, skb);
__skb_pull(skb, tcp_header_len);
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
}
if (copied_early)
tcp_cleanup_rbuf(sk, skb->len);
}
if (!eaten) {
if (tcp_checksum_complete_user(sk, skb))
goto csum_error;
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
*/
if (tcp_header_len ==
(sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
tp->rcv_nxt == tp->rcv_wup)
tcp_store_ts_recent(tp);
tcp_rcv_rtt_measure_ts(sk, skb);
if ((int)skb->truesize > sk->sk_forward_alloc)
goto step5;
NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
/* Bulk data transfer: receiver */
__skb_pull(skb,tcp_header_len);
__skb_queue_tail(&sk->sk_receive_queue, skb);
sk_stream_set_owner_r(skb, sk);
tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
}
tcp_event_data_recv(sk, tp, skb);
if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
/* Well, only one small jumplet in fast path... */
tcp_ack(sk, skb, FLAG_DATA);
tcp_data_snd_check(sk, tp);
if (!inet_csk_ack_scheduled(sk))
goto no_ack;
}
__tcp_ack_snd_check(sk, 0);
no_ack:
#ifdef CONFIG_NET_DMA
if (copied_early)
__skb_queue_tail(&sk->sk_async_wait_queue, skb);
else
#endif
if (eaten)
__kfree_skb(skb);
else
sk->sk_data_ready(sk, 0);
return 0;
}
}
slow_path:
if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
goto csum_error;
/*
* RFC1323: H1. Apply PAWS check first.
*/
if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
tcp_paws_discard(sk, skb)) {
if (!th->rst) {
NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
tcp_send_dupack(sk, skb);
goto discard;
}
/* Resets are accepted even if PAWS failed.
ts_recent update must be made after we are sure
that the packet is in window.
*/
}
/*
* Standard slow path.
*/
if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
/* RFC793, page 37: "In all states except SYN-SENT, all reset
* (RST) segments are validated by checking their SEQ-fields."
* And page 69: "If an incoming segment is not acceptable,
* an acknowledgment should be sent in reply (unless the RST bit
* is set, if so drop the segment and return)".
*/
if (!th->rst)
tcp_send_dupack(sk, skb);
goto discard;
}
if(th->rst) {
tcp_reset(sk);
goto discard;
}
tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
TCP_INC_STATS_BH(TCP_MIB_INERRS);
NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
tcp_reset(sk);
return 1;
}
step5:
if(th->ack)
tcp_ack(sk, skb, FLAG_SLOWPATH);
tcp_rcv_rtt_measure_ts(sk, skb);
/* Process urgent data. */
tcp_urg(sk, skb, th);
/* step 7: process the segment text */
tcp_data_queue(sk, skb);
tcp_data_snd_check(sk, tp);
tcp_ack_snd_check(sk);
return 0;
csum_error:
TCP_INC_STATS_BH(TCP_MIB_INERRS);
discard:
__kfree_skb(skb);
return 0;
}
static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
struct tcphdr *th, unsigned len)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
int saved_clamp = tp->rx_opt.mss_clamp;
tcp_parse_options(skb, &tp->rx_opt, 0);
if (th->ack) {
/* rfc793:
* "If the state is SYN-SENT then
* first check the ACK bit
* If the ACK bit is set
* If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
* a reset (unless the RST bit is set, if so drop
* the segment and return)"
*
* We do not send data with SYN, so that RFC-correct
* test reduces to:
*/
if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
goto reset_and_undo;
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
!between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
tcp_time_stamp)) {
NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
goto reset_and_undo;
}
/* Now ACK is acceptable.
*
* "If the RST bit is set
* If the ACK was acceptable then signal the user "error:
* connection reset", drop the segment, enter CLOSED state,
* delete TCB, and return."
*/
if (th->rst) {
tcp_reset(sk);
goto discard;
}
/* rfc793:
* "fifth, if neither of the SYN or RST bits is set then
* drop the segment and return."
*
* See note below!
* --ANK(990513)
*/
if (!th->syn)
goto discard_and_undo;
/* rfc793:
* "If the SYN bit is on ...
* are acceptable then ...
* (our SYN has been ACKed), change the connection
* state to ESTABLISHED..."
*/
TCP_ECN_rcv_synack(tp, th);
tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
tcp_ack(sk, skb, FLAG_SLOWPATH);
/* Ok.. it's good. Set up sequence numbers and
* move to established.
*/
tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
*/
tp->snd_wnd = ntohs(th->window);
tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
if (!tp->rx_opt.wscale_ok) {
tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
tp->window_clamp = min(tp->window_clamp, 65535U);
}
if (tp->rx_opt.saw_tstamp) {
tp->rx_opt.tstamp_ok = 1;
tp->tcp_header_len =
sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
tcp_store_ts_recent(tp);
} else {
tp->tcp_header_len = sizeof(struct tcphdr);
}
if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
tp->rx_opt.sack_ok |= 2;
tcp_mtup_init(sk);
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
tcp_initialize_rcv_mss(sk);
/* Remember, tcp_poll() does not lock socket!
* Change state from SYN-SENT only after copied_seq
* is initialized. */
tp->copied_seq = tp->rcv_nxt;
smp_mb();
tcp_set_state(sk, TCP_ESTABLISHED);
security_inet_conn_established(sk, skb);
/* Make sure socket is routed, for correct metrics. */
icsk->icsk_af_ops->rebuild_header(sk);
tcp_init_metrics(sk);
tcp_init_congestion_control(sk);
/* Prevent spurious tcp_cwnd_restart() on first data
* packet.
*/
tp->lsndtime = tcp_time_stamp;
tcp_init_buffer_space(sk);
if (sock_flag(sk, SOCK_KEEPOPEN))
inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
if (!tp->rx_opt.snd_wscale)
__tcp_fast_path_on(tp, tp->snd_wnd);
else
tp->pred_flags = 0;
if (!sock_flag(sk, SOCK_DEAD)) {
sk->sk_state_change(sk);
sk_wake_async(sk, 0, POLL_OUT);
}
if (sk->sk_write_pending ||
icsk->icsk_accept_queue.rskq_defer_accept ||
icsk->icsk_ack.pingpong) {
/* Save one ACK. Data will be ready after
* several ticks, if write_pending is set.
*
* It may be deleted, but with this feature tcpdumps
* look so _wonderfully_ clever, that I was not able
* to stand against the temptation 8) --ANK
*/
inet_csk_schedule_ack(sk);
icsk->icsk_ack.lrcvtime = tcp_time_stamp;
icsk->icsk_ack.ato = TCP_ATO_MIN;
tcp_incr_quickack(sk);
tcp_enter_quickack_mode(sk);
inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
TCP_DELACK_MAX, TCP_RTO_MAX);
discard:
__kfree_skb(skb);
return 0;
} else {
tcp_send_ack(sk);
}
return -1;
}
/* No ACK in the segment */
if (th->rst) {
/* rfc793:
* "If the RST bit is set
*
* Otherwise (no ACK) drop the segment and return."
*/
goto discard_and_undo;
}
/* PAWS check. */
if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
goto discard_and_undo;
if (th->syn) {
/* We see SYN without ACK. It is attempt of
* simultaneous connect with crossed SYNs.
* Particularly, it can be connect to self.
*/
tcp_set_state(sk, TCP_SYN_RECV);
if (tp->rx_opt.saw_tstamp) {
tp->rx_opt.tstamp_ok = 1;
tcp_store_ts_recent(tp);
tp->tcp_header_len =
sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
} else {
tp->tcp_header_len = sizeof(struct tcphdr);
}
tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
/* RFC1323: The window in SYN & SYN/ACK segments is
* never scaled.
*/
tp->snd_wnd = ntohs(th->window);
tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
tp->max_window = tp->snd_wnd;
TCP_ECN_rcv_syn(tp, th);
tcp_mtup_init(sk);
tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
tcp_initialize_rcv_mss(sk);
tcp_send_synack(sk);
#if 0
/* Note, we could accept data and URG from this segment.
* There are no obstacles to make this.
*
* However, if we ignore data in ACKless segments sometimes,
* we have no reasons to accept it sometimes.
* Also, seems the code doing it in step6 of tcp_rcv_state_process
* is not flawless. So, discard packet for sanity.
* Uncomment this return to process the data.
*/
return -1;
#else
goto discard;
#endif
}
/* "fifth, if neither of the SYN or RST bits is set then
* drop the segment and return."
*/
discard_and_undo:
tcp_clear_options(&tp->rx_opt);
tp->rx_opt.mss_clamp = saved_clamp;
goto discard;
reset_and_undo:
tcp_clear_options(&tp->rx_opt);
tp->rx_opt.mss_clamp = saved_clamp;
return 1;
}
/*
* This function implements the receiving procedure of RFC 793 for
* all states except ESTABLISHED and TIME_WAIT.
* It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
* address independent.
*/
int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
struct tcphdr *th, unsigned len)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
int queued = 0;
tp->rx_opt.saw_tstamp = 0;
switch (sk->sk_state) {
case TCP_CLOSE:
goto discard;
case TCP_LISTEN:
if(th->ack)
return 1;
if(th->rst)
goto discard;
if(th->syn) {
if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
return 1;
/* Now we have several options: In theory there is
* nothing else in the frame. KA9Q has an option to
* send data with the syn, BSD accepts data with the
* syn up to the [to be] advertised window and
* Solaris 2.1 gives you a protocol error. For now
* we just ignore it, that fits the spec precisely
* and avoids incompatibilities. It would be nice in
* future to drop through and process the data.
*
* Now that TTCP is starting to be used we ought to
* queue this data.
* But, this leaves one open to an easy denial of
* service attack, and SYN cookies can't defend
* against this problem. So, we drop the data
* in the interest of security over speed.
*/
goto discard;
}
goto discard;
case TCP_SYN_SENT:
queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
if (queued >= 0)
return queued;
/* Do step6 onward by hand. */
tcp_urg(sk, skb, th);
__kfree_skb(skb);
tcp_data_snd_check(sk, tp);
return 0;
}
if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
tcp_paws_discard(sk, skb)) {
if (!th->rst) {
NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
tcp_send_dupack(sk, skb);
goto discard;
}
/* Reset is accepted even if it did not pass PAWS. */
}
/* step 1: check sequence number */
if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
if (!th->rst)
tcp_send_dupack(sk, skb);
goto discard;
}
/* step 2: check RST bit */
if(th->rst) {
tcp_reset(sk);
goto discard;
}
tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
/* step 3: check security and precedence [ignored] */
/* step 4:
*
* Check for a SYN in window.
*/
if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
tcp_reset(sk);
return 1;
}
/* step 5: check the ACK field */
if (th->ack) {
int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
switch(sk->sk_state) {
case TCP_SYN_RECV:
if (acceptable) {
tp->copied_seq = tp->rcv_nxt;
smp_mb();
tcp_set_state(sk, TCP_ESTABLISHED);
sk->sk_state_change(sk);
/* Note, that this wakeup is only for marginal
* crossed SYN case. Passively open sockets
* are not waked up, because sk->sk_sleep ==
* NULL and sk->sk_socket == NULL.
*/
if (sk->sk_socket) {
sk_wake_async(sk,0,POLL_OUT);
}
tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
tp->snd_wnd = ntohs(th->window) <<
tp->rx_opt.snd_wscale;
tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
TCP_SKB_CB(skb)->seq);
/* tcp_ack considers this ACK as duplicate
* and does not calculate rtt.
* Fix it at least with timestamps.
*/
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
!tp->srtt)
tcp_ack_saw_tstamp(sk, 0);
if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
/* Make sure socket is routed, for
* correct metrics.
*/
icsk->icsk_af_ops->rebuild_header(sk);
tcp_init_metrics(sk);
tcp_init_congestion_control(sk);
/* Prevent spurious tcp_cwnd_restart() on
* first data packet.
*/
tp->lsndtime = tcp_time_stamp;
tcp_mtup_init(sk);
tcp_initialize_rcv_mss(sk);
tcp_init_buffer_space(sk);
tcp_fast_path_on(tp);
} else {
return 1;
}
break;
case TCP_FIN_WAIT1:
if (tp->snd_una == tp->write_seq) {
tcp_set_state(sk, TCP_FIN_WAIT2);
sk->sk_shutdown |= SEND_SHUTDOWN;
dst_confirm(sk->sk_dst_cache);
if (!sock_flag(sk, SOCK_DEAD))
/* Wake up lingering close() */
sk->sk_state_change(sk);
else {
int tmo;
if (tp->linger2 < 0 ||
(TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
tcp_done(sk);
NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
return 1;
}
tmo = tcp_fin_time(sk);
if (tmo > TCP_TIMEWAIT_LEN) {
inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
} else if (th->fin || sock_owned_by_user(sk)) {
/* Bad case. We could lose such FIN otherwise.
* It is not a big problem, but it looks confusing
* and not so rare event. We still can lose it now,
* if it spins in bh_lock_sock(), but it is really
* marginal case.
*/
inet_csk_reset_keepalive_timer(sk, tmo);
} else {
tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
goto discard;
}
}
}
break;
case TCP_CLOSING:
if (tp->snd_una == tp->write_seq) {
tcp_time_wait(sk, TCP_TIME_WAIT, 0);
goto discard;
}
break;
case TCP_LAST_ACK:
if (tp->snd_una == tp->write_seq) {
tcp_update_metrics(sk);
tcp_done(sk);
goto discard;
}
break;
}
} else
goto discard;
/* step 6: check the URG bit */
tcp_urg(sk, skb, th);
/* step 7: process the segment text */
switch (sk->sk_state) {
case TCP_CLOSE_WAIT:
case TCP_CLOSING:
case TCP_LAST_ACK:
if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
break;
case TCP_FIN_WAIT1:
case TCP_FIN_WAIT2:
/* RFC 793 says to queue data in these states,
* RFC 1122 says we MUST send a reset.
* BSD 4.4 also does reset.
*/
if (sk->sk_shutdown & RCV_SHUTDOWN) {
if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
tcp_reset(sk);
return 1;
}
}
/* Fall through */
case TCP_ESTABLISHED:
tcp_data_queue(sk, skb);
queued = 1;
break;
}
/* tcp_data could move socket to TIME-WAIT */
if (sk->sk_state != TCP_CLOSE) {
tcp_data_snd_check(sk, tp);
tcp_ack_snd_check(sk);
}
if (!queued) {
discard:
__kfree_skb(skb);
}
return 0;
}
EXPORT_SYMBOL(sysctl_tcp_ecn);
EXPORT_SYMBOL(sysctl_tcp_reordering);
EXPORT_SYMBOL(tcp_parse_options);
EXPORT_SYMBOL(tcp_rcv_established);
EXPORT_SYMBOL(tcp_rcv_state_process);
EXPORT_SYMBOL(tcp_initialize_rcv_mss);
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