blob: 61ee04366b751120149b5eef49b31131132f7028 [file] [log] [blame]
/*
* 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).
*
* 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 : Retransmit queue handled by TCP.
* : Fragmentation on mtu decrease
* : Segment collapse on retransmit
* : AF independence
*
* Linus Torvalds : send_delayed_ack
* David S. Miller : Charge memory using the right skb
* during syn/ack processing.
* David S. Miller : Output engine completely rewritten.
* Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
* Cacophonix Gaul : draft-minshall-nagle-01
* J Hadi Salim : ECN support
*
*/
#define pr_fmt(fmt) "TCP: " fmt
#include <net/tcp.h>
#include <linux/compiler.h>
#include <linux/gfp.h>
#include <linux/module.h>
/* People can turn this off for buggy TCP's found in printers etc. */
int sysctl_tcp_retrans_collapse __read_mostly = 1;
/* People can turn this on to work with those rare, broken TCPs that
* interpret the window field as a signed quantity.
*/
int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
/* Default TSQ limit of two TSO segments */
int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
/* This limits the percentage of the congestion window which we
* will allow a single TSO frame to consume. Building TSO frames
* which are too large can cause TCP streams to be bursty.
*/
int sysctl_tcp_tso_win_divisor __read_mostly = 3;
int sysctl_tcp_mtu_probing __read_mostly = 0;
int sysctl_tcp_base_mss __read_mostly = TCP_BASE_MSS;
/* By default, RFC2861 behavior. */
int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
int push_one, gfp_t gfp);
/* Account for new data that has been sent to the network. */
static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
unsigned int prior_packets = tp->packets_out;
tcp_advance_send_head(sk, skb);
tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
tp->packets_out += tcp_skb_pcount(skb);
if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
tcp_rearm_rto(sk);
}
NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
tcp_skb_pcount(skb));
}
/* SND.NXT, if window was not shrunk.
* If window has been shrunk, what should we make? It is not clear at all.
* Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
* Anything in between SND.UNA...SND.UNA+SND.WND also can be already
* invalid. OK, let's make this for now:
*/
static inline __u32 tcp_acceptable_seq(const struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
if (!before(tcp_wnd_end(tp), tp->snd_nxt))
return tp->snd_nxt;
else
return tcp_wnd_end(tp);
}
/* Calculate mss to advertise in SYN segment.
* RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
*
* 1. It is independent of path mtu.
* 2. Ideally, it is maximal possible segment size i.e. 65535-40.
* 3. For IPv4 it is reasonable to calculate it from maximal MTU of
* attached devices, because some buggy hosts are confused by
* large MSS.
* 4. We do not make 3, we advertise MSS, calculated from first
* hop device mtu, but allow to raise it to ip_rt_min_advmss.
* This may be overridden via information stored in routing table.
* 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
* probably even Jumbo".
*/
static __u16 tcp_advertise_mss(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
const struct dst_entry *dst = __sk_dst_get(sk);
int mss = tp->advmss;
if (dst) {
unsigned int metric = dst_metric_advmss(dst);
if (metric < mss) {
mss = metric;
tp->advmss = mss;
}
}
return (__u16)mss;
}
/* RFC2861. Reset CWND after idle period longer RTO to "restart window".
* This is the first part of cwnd validation mechanism. */
static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
{
struct tcp_sock *tp = tcp_sk(sk);
s32 delta = tcp_time_stamp - tp->lsndtime;
u32 restart_cwnd = tcp_init_cwnd(tp, dst);
u32 cwnd = tp->snd_cwnd;
tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
tp->snd_ssthresh = tcp_current_ssthresh(sk);
restart_cwnd = min(restart_cwnd, cwnd);
while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
cwnd >>= 1;
tp->snd_cwnd = max(cwnd, restart_cwnd);
tp->snd_cwnd_stamp = tcp_time_stamp;
tp->snd_cwnd_used = 0;
}
/* Congestion state accounting after a packet has been sent. */
static void tcp_event_data_sent(struct tcp_sock *tp,
struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const u32 now = tcp_time_stamp;
const struct dst_entry *dst = __sk_dst_get(sk);
if (sysctl_tcp_slow_start_after_idle &&
(!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
tcp_cwnd_restart(sk, __sk_dst_get(sk));
tp->lsndtime = now;
/* If it is a reply for ato after last received
* packet, enter pingpong mode.
*/
if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato &&
(!dst || !dst_metric(dst, RTAX_QUICKACK)))
icsk->icsk_ack.pingpong = 1;
}
/* Account for an ACK we sent. */
static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
{
tcp_dec_quickack_mode(sk, pkts);
inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
}
u32 tcp_default_init_rwnd(u32 mss)
{
/* Initial receive window should be twice of TCP_INIT_CWND to
* enable proper sending of new unsent data during fast recovery
* (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
* limit when mss is larger than 1460.
*/
u32 init_rwnd = sysctl_tcp_default_init_rwnd;
if (mss > 1460)
init_rwnd = max((1460 * init_rwnd) / mss, 2U);
return init_rwnd;
}
/* Determine a window scaling and initial window to offer.
* Based on the assumption that the given amount of space
* will be offered. Store the results in the tp structure.
* NOTE: for smooth operation initial space offering should
* be a multiple of mss if possible. We assume here that mss >= 1.
* This MUST be enforced by all callers.
*/
void tcp_select_initial_window(int __space, __u32 mss,
__u32 *rcv_wnd, __u32 *window_clamp,
int wscale_ok, __u8 *rcv_wscale,
__u32 init_rcv_wnd)
{
unsigned int space = (__space < 0 ? 0 : __space);
/* If no clamp set the clamp to the max possible scaled window */
if (*window_clamp == 0)
(*window_clamp) = (65535 << 14);
space = min(*window_clamp, space);
/* Quantize space offering to a multiple of mss if possible. */
if (space > mss)
space = (space / mss) * mss;
/* NOTE: offering an initial window larger than 32767
* will break some buggy TCP stacks. If the admin tells us
* it is likely we could be speaking with such a buggy stack
* we will truncate our initial window offering to 32K-1
* unless the remote has sent us a window scaling option,
* which we interpret as a sign the remote TCP is not
* misinterpreting the window field as a signed quantity.
*/
if (sysctl_tcp_workaround_signed_windows)
(*rcv_wnd) = min(space, MAX_TCP_WINDOW);
else
(*rcv_wnd) = space;
(*rcv_wscale) = 0;
if (wscale_ok) {
/* Set window scaling on max possible window
* See RFC1323 for an explanation of the limit to 14
*/
space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
space = min_t(u32, space, *window_clamp);
while (space > 65535 && (*rcv_wscale) < 14) {
space >>= 1;
(*rcv_wscale)++;
}
}
if (mss > (1 << *rcv_wscale)) {
if (!init_rcv_wnd) /* Use default unless specified otherwise */
init_rcv_wnd = tcp_default_init_rwnd(mss);
*rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
}
/* Set the clamp no higher than max representable value */
(*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
}
EXPORT_SYMBOL(tcp_select_initial_window);
/* Chose a new window to advertise, update state in tcp_sock for the
* socket, and return result with RFC1323 scaling applied. The return
* value can be stuffed directly into th->window for an outgoing
* frame.
*/
static u16 tcp_select_window(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
u32 old_win = tp->rcv_wnd;
u32 cur_win = tcp_receive_window(tp);
u32 new_win = __tcp_select_window(sk);
/* Never shrink the offered window */
if (new_win < cur_win) {
/* Danger Will Robinson!
* Don't update rcv_wup/rcv_wnd here or else
* we will not be able to advertise a zero
* window in time. --DaveM
*
* Relax Will Robinson.
*/
if (new_win == 0)
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPWANTZEROWINDOWADV);
new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
}
tp->rcv_wnd = new_win;
tp->rcv_wup = tp->rcv_nxt;
/* Make sure we do not exceed the maximum possible
* scaled window.
*/
if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
new_win = min(new_win, MAX_TCP_WINDOW);
else
new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
/* RFC1323 scaling applied */
new_win >>= tp->rx_opt.rcv_wscale;
/* If we advertise zero window, disable fast path. */
if (new_win == 0) {
tp->pred_flags = 0;
if (old_win)
NET_INC_STATS(sock_net(sk),
LINUX_MIB_TCPTOZEROWINDOWADV);
} else if (old_win == 0) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
}
return new_win;
}
/* Packet ECN state for a SYN-ACK */
static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
if (!(tp->ecn_flags & TCP_ECN_OK))
TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
else if (tcp_ca_needs_ecn(sk))
INET_ECN_xmit(sk);
}
/* Packet ECN state for a SYN. */
static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->ecn_flags = 0;
if (sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
tcp_ca_needs_ecn(sk)) {
TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
tp->ecn_flags = TCP_ECN_OK;
if (tcp_ca_needs_ecn(sk))
INET_ECN_xmit(sk);
}
}
static void
tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
struct sock *sk)
{
if (inet_rsk(req)->ecn_ok) {
th->ece = 1;
if (tcp_ca_needs_ecn(sk))
INET_ECN_xmit(sk);
}
}
/* Set up ECN state for a packet on a ESTABLISHED socket that is about to
* be sent.
*/
static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
int tcp_header_len)
{
struct tcp_sock *tp = tcp_sk(sk);
if (tp->ecn_flags & TCP_ECN_OK) {
/* Not-retransmitted data segment: set ECT and inject CWR. */
if (skb->len != tcp_header_len &&
!before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
INET_ECN_xmit(sk);
if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
tcp_hdr(skb)->cwr = 1;
skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
}
} else if (!tcp_ca_needs_ecn(sk)) {
/* ACK or retransmitted segment: clear ECT|CE */
INET_ECN_dontxmit(sk);
}
if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
tcp_hdr(skb)->ece = 1;
}
}
/* Constructs common control bits of non-data skb. If SYN/FIN is present,
* auto increment end seqno.
*/
static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
{
struct skb_shared_info *shinfo = skb_shinfo(skb);
skb->ip_summed = CHECKSUM_PARTIAL;
skb->csum = 0;
TCP_SKB_CB(skb)->tcp_flags = flags;
TCP_SKB_CB(skb)->sacked = 0;
tcp_skb_pcount_set(skb, 1);
shinfo->gso_size = 0;
shinfo->gso_type = 0;
TCP_SKB_CB(skb)->seq = seq;
if (flags & (TCPHDR_SYN | TCPHDR_FIN))
seq++;
TCP_SKB_CB(skb)->end_seq = seq;
}
static inline bool tcp_urg_mode(const struct tcp_sock *tp)
{
return tp->snd_una != tp->snd_up;
}
#define OPTION_SACK_ADVERTISE (1 << 0)
#define OPTION_TS (1 << 1)
#define OPTION_MD5 (1 << 2)
#define OPTION_WSCALE (1 << 3)
#define OPTION_FAST_OPEN_COOKIE (1 << 8)
struct tcp_out_options {
u16 options; /* bit field of OPTION_* */
u16 mss; /* 0 to disable */
u8 ws; /* window scale, 0 to disable */
u8 num_sack_blocks; /* number of SACK blocks to include */
u8 hash_size; /* bytes in hash_location */
__u8 *hash_location; /* temporary pointer, overloaded */
__u32 tsval, tsecr; /* need to include OPTION_TS */
struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
};
/* Write previously computed TCP options to the packet.
*
* Beware: Something in the Internet is very sensitive to the ordering of
* TCP options, we learned this through the hard way, so be careful here.
* Luckily we can at least blame others for their non-compliance but from
* inter-operability perspective it seems that we're somewhat stuck with
* the ordering which we have been using if we want to keep working with
* those broken things (not that it currently hurts anybody as there isn't
* particular reason why the ordering would need to be changed).
*
* At least SACK_PERM as the first option is known to lead to a disaster
* (but it may well be that other scenarios fail similarly).
*/
static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
struct tcp_out_options *opts)
{
u16 options = opts->options; /* mungable copy */
if (unlikely(OPTION_MD5 & options)) {
*ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
(TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
/* overload cookie hash location */
opts->hash_location = (__u8 *)ptr;
ptr += 4;
}
if (unlikely(opts->mss)) {
*ptr++ = htonl((TCPOPT_MSS << 24) |
(TCPOLEN_MSS << 16) |
opts->mss);
}
if (likely(OPTION_TS & options)) {
if (unlikely(OPTION_SACK_ADVERTISE & options)) {
*ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
(TCPOLEN_SACK_PERM << 16) |
(TCPOPT_TIMESTAMP << 8) |
TCPOLEN_TIMESTAMP);
options &= ~OPTION_SACK_ADVERTISE;
} else {
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_NOP << 16) |
(TCPOPT_TIMESTAMP << 8) |
TCPOLEN_TIMESTAMP);
}
*ptr++ = htonl(opts->tsval);
*ptr++ = htonl(opts->tsecr);
}
if (unlikely(OPTION_SACK_ADVERTISE & options)) {
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_NOP << 16) |
(TCPOPT_SACK_PERM << 8) |
TCPOLEN_SACK_PERM);
}
if (unlikely(OPTION_WSCALE & options)) {
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_WINDOW << 16) |
(TCPOLEN_WINDOW << 8) |
opts->ws);
}
if (unlikely(opts->num_sack_blocks)) {
struct tcp_sack_block *sp = tp->rx_opt.dsack ?
tp->duplicate_sack : tp->selective_acks;
int this_sack;
*ptr++ = htonl((TCPOPT_NOP << 24) |
(TCPOPT_NOP << 16) |
(TCPOPT_SACK << 8) |
(TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
TCPOLEN_SACK_PERBLOCK)));
for (this_sack = 0; this_sack < opts->num_sack_blocks;
++this_sack) {
*ptr++ = htonl(sp[this_sack].start_seq);
*ptr++ = htonl(sp[this_sack].end_seq);
}
tp->rx_opt.dsack = 0;
}
if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
*ptr++ = htonl((TCPOPT_EXP << 24) |
((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
TCPOPT_FASTOPEN_MAGIC);
memcpy(ptr, foc->val, foc->len);
if ((foc->len & 3) == 2) {
u8 *align = ((u8 *)ptr) + foc->len;
align[0] = align[1] = TCPOPT_NOP;
}
ptr += (foc->len + 3) >> 2;
}
}
/* Compute TCP options for SYN packets. This is not the final
* network wire format yet.
*/
static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
struct tcp_out_options *opts,
struct tcp_md5sig_key **md5)
{
struct tcp_sock *tp = tcp_sk(sk);
unsigned int remaining = MAX_TCP_OPTION_SPACE;
struct tcp_fastopen_request *fastopen = tp->fastopen_req;
#ifdef CONFIG_TCP_MD5SIG
*md5 = tp->af_specific->md5_lookup(sk, sk);
if (*md5) {
opts->options |= OPTION_MD5;
remaining -= TCPOLEN_MD5SIG_ALIGNED;
}
#else
*md5 = NULL;
#endif
/* We always get an MSS option. The option bytes which will be seen in
* normal data packets should timestamps be used, must be in the MSS
* advertised. But we subtract them from tp->mss_cache so that
* calculations in tcp_sendmsg are simpler etc. So account for this
* fact here if necessary. If we don't do this correctly, as a
* receiver we won't recognize data packets as being full sized when we
* should, and thus we won't abide by the delayed ACK rules correctly.
* SACKs don't matter, we never delay an ACK when we have any of those
* going out. */
opts->mss = tcp_advertise_mss(sk);
remaining -= TCPOLEN_MSS_ALIGNED;
if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
opts->options |= OPTION_TS;
opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
opts->tsecr = tp->rx_opt.ts_recent;
remaining -= TCPOLEN_TSTAMP_ALIGNED;
}
if (likely(sysctl_tcp_window_scaling)) {
opts->ws = tp->rx_opt.rcv_wscale;
opts->options |= OPTION_WSCALE;
remaining -= TCPOLEN_WSCALE_ALIGNED;
}
if (likely(sysctl_tcp_sack)) {
opts->options |= OPTION_SACK_ADVERTISE;
if (unlikely(!(OPTION_TS & opts->options)))
remaining -= TCPOLEN_SACKPERM_ALIGNED;
}
if (fastopen && fastopen->cookie.len >= 0) {
u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
need = (need + 3) & ~3U; /* Align to 32 bits */
if (remaining >= need) {
opts->options |= OPTION_FAST_OPEN_COOKIE;
opts->fastopen_cookie = &fastopen->cookie;
remaining -= need;
tp->syn_fastopen = 1;
}
}
return MAX_TCP_OPTION_SPACE - remaining;
}
/* Set up TCP options for SYN-ACKs. */
static unsigned int tcp_synack_options(struct sock *sk,
struct request_sock *req,
unsigned int mss, struct sk_buff *skb,
struct tcp_out_options *opts,
struct tcp_md5sig_key **md5,
struct tcp_fastopen_cookie *foc)
{
struct inet_request_sock *ireq = inet_rsk(req);
unsigned int remaining = MAX_TCP_OPTION_SPACE;
#ifdef CONFIG_TCP_MD5SIG
*md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
if (*md5) {
opts->options |= OPTION_MD5;
remaining -= TCPOLEN_MD5SIG_ALIGNED;
/* We can't fit any SACK blocks in a packet with MD5 + TS
* options. There was discussion about disabling SACK
* rather than TS in order to fit in better with old,
* buggy kernels, but that was deemed to be unnecessary.
*/
ireq->tstamp_ok &= !ireq->sack_ok;
}
#else
*md5 = NULL;
#endif
/* We always send an MSS option. */
opts->mss = mss;
remaining -= TCPOLEN_MSS_ALIGNED;
if (likely(ireq->wscale_ok)) {
opts->ws = ireq->rcv_wscale;
opts->options |= OPTION_WSCALE;
remaining -= TCPOLEN_WSCALE_ALIGNED;
}
if (likely(ireq->tstamp_ok)) {
opts->options |= OPTION_TS;
opts->tsval = tcp_skb_timestamp(skb);
opts->tsecr = req->ts_recent;
remaining -= TCPOLEN_TSTAMP_ALIGNED;
}
if (likely(ireq->sack_ok)) {
opts->options |= OPTION_SACK_ADVERTISE;
if (unlikely(!ireq->tstamp_ok))
remaining -= TCPOLEN_SACKPERM_ALIGNED;
}
if (foc != NULL && foc->len >= 0) {
u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
need = (need + 3) & ~3U; /* Align to 32 bits */
if (remaining >= need) {
opts->options |= OPTION_FAST_OPEN_COOKIE;
opts->fastopen_cookie = foc;
remaining -= need;
}
}
return MAX_TCP_OPTION_SPACE - remaining;
}
/* Compute TCP options for ESTABLISHED sockets. This is not the
* final wire format yet.
*/
static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
struct tcp_out_options *opts,
struct tcp_md5sig_key **md5)
{
struct tcp_sock *tp = tcp_sk(sk);
unsigned int size = 0;
unsigned int eff_sacks;
opts->options = 0;
#ifdef CONFIG_TCP_MD5SIG
*md5 = tp->af_specific->md5_lookup(sk, sk);
if (unlikely(*md5)) {
opts->options |= OPTION_MD5;
size += TCPOLEN_MD5SIG_ALIGNED;
}
#else
*md5 = NULL;
#endif
if (likely(tp->rx_opt.tstamp_ok)) {
opts->options |= OPTION_TS;
opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
opts->tsecr = tp->rx_opt.ts_recent;
size += TCPOLEN_TSTAMP_ALIGNED;
}
eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
if (unlikely(eff_sacks)) {
const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
opts->num_sack_blocks =
min_t(unsigned int, eff_sacks,
(remaining - TCPOLEN_SACK_BASE_ALIGNED) /
TCPOLEN_SACK_PERBLOCK);
size += TCPOLEN_SACK_BASE_ALIGNED +
opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
}
return size;
}
/* TCP SMALL QUEUES (TSQ)
*
* TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
* to reduce RTT and bufferbloat.
* We do this using a special skb destructor (tcp_wfree).
*
* Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
* needs to be reallocated in a driver.
* The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
*
* Since transmit from skb destructor is forbidden, we use a tasklet
* to process all sockets that eventually need to send more skbs.
* We use one tasklet per cpu, with its own queue of sockets.
*/
struct tsq_tasklet {
struct tasklet_struct tasklet;
struct list_head head; /* queue of tcp sockets */
};
static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
static void tcp_tsq_handler(struct sock *sk)
{
if ((1 << sk->sk_state) &
(TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
0, GFP_ATOMIC);
}
/*
* One tasklet per cpu tries to send more skbs.
* We run in tasklet context but need to disable irqs when
* transferring tsq->head because tcp_wfree() might
* interrupt us (non NAPI drivers)
*/
static void tcp_tasklet_func(unsigned long data)
{
struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
LIST_HEAD(list);
unsigned long flags;
struct list_head *q, *n;
struct tcp_sock *tp;
struct sock *sk;
local_irq_save(flags);
list_splice_init(&tsq->head, &list);
local_irq_restore(flags);
list_for_each_safe(q, n, &list) {
tp = list_entry(q, struct tcp_sock, tsq_node);
list_del(&tp->tsq_node);
sk = (struct sock *)tp;
bh_lock_sock(sk);
if (!sock_owned_by_user(sk)) {
tcp_tsq_handler(sk);
} else {
/* defer the work to tcp_release_cb() */
set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
}
bh_unlock_sock(sk);
clear_bit(TSQ_QUEUED, &tp->tsq_flags);
sk_free(sk);
}
}
#define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
(1UL << TCP_WRITE_TIMER_DEFERRED) | \
(1UL << TCP_DELACK_TIMER_DEFERRED) | \
(1UL << TCP_MTU_REDUCED_DEFERRED))
/**
* tcp_release_cb - tcp release_sock() callback
* @sk: socket
*
* called from release_sock() to perform protocol dependent
* actions before socket release.
*/
void tcp_release_cb(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
unsigned long flags, nflags;
/* perform an atomic operation only if at least one flag is set */
do {
flags = tp->tsq_flags;
if (!(flags & TCP_DEFERRED_ALL))
return;
nflags = flags & ~TCP_DEFERRED_ALL;
} while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
if (flags & (1UL << TCP_TSQ_DEFERRED))
tcp_tsq_handler(sk);
/* Here begins the tricky part :
* We are called from release_sock() with :
* 1) BH disabled
* 2) sk_lock.slock spinlock held
* 3) socket owned by us (sk->sk_lock.owned == 1)
*
* But following code is meant to be called from BH handlers,
* so we should keep BH disabled, but early release socket ownership
*/
sock_release_ownership(sk);
if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
tcp_write_timer_handler(sk);
__sock_put(sk);
}
if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
tcp_delack_timer_handler(sk);
__sock_put(sk);
}
if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
__sock_put(sk);
}
}
EXPORT_SYMBOL(tcp_release_cb);
void __init tcp_tasklet_init(void)
{
int i;
for_each_possible_cpu(i) {
struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
INIT_LIST_HEAD(&tsq->head);
tasklet_init(&tsq->tasklet,
tcp_tasklet_func,
(unsigned long)tsq);
}
}
/*
* Write buffer destructor automatically called from kfree_skb.
* We can't xmit new skbs from this context, as we might already
* hold qdisc lock.
*/
void tcp_wfree(struct sk_buff *skb)
{
struct sock *sk = skb->sk;
struct tcp_sock *tp = tcp_sk(sk);
int wmem;
/* Keep one reference on sk_wmem_alloc.
* Will be released by sk_free() from here or tcp_tasklet_func()
*/
wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
/* If this softirq is serviced by ksoftirqd, we are likely under stress.
* Wait until our queues (qdisc + devices) are drained.
* This gives :
* - less callbacks to tcp_write_xmit(), reducing stress (batches)
* - chance for incoming ACK (processed by another cpu maybe)
* to migrate this flow (skb->ooo_okay will be eventually set)
*/
if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
goto out;
if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
!test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
unsigned long flags;
struct tsq_tasklet *tsq;
/* queue this socket to tasklet queue */
local_irq_save(flags);
tsq = this_cpu_ptr(&tsq_tasklet);
list_add(&tp->tsq_node, &tsq->head);
tasklet_schedule(&tsq->tasklet);
local_irq_restore(flags);
return;
}
out:
sk_free(sk);
}
/* This routine actually transmits TCP packets queued in by
* tcp_do_sendmsg(). This is used by both the initial
* transmission and possible later retransmissions.
* All SKB's seen here are completely headerless. It is our
* job to build the TCP header, and pass the packet down to
* IP so it can do the same plus pass the packet off to the
* device.
*
* We are working here with either a clone of the original
* SKB, or a fresh unique copy made by the retransmit engine.
*/
static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
gfp_t gfp_mask)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct inet_sock *inet;
struct tcp_sock *tp;
struct tcp_skb_cb *tcb;
struct tcp_out_options opts;
unsigned int tcp_options_size, tcp_header_size;
struct tcp_md5sig_key *md5;
struct tcphdr *th;
int err;
BUG_ON(!skb || !tcp_skb_pcount(skb));
if (clone_it) {
skb_mstamp_get(&skb->skb_mstamp);
if (unlikely(skb_cloned(skb)))
skb = pskb_copy(skb, gfp_mask);
else
skb = skb_clone(skb, gfp_mask);
if (unlikely(!skb))
return -ENOBUFS;
}
inet = inet_sk(sk);
tp = tcp_sk(sk);
tcb = TCP_SKB_CB(skb);
memset(&opts, 0, sizeof(opts));
if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
else
tcp_options_size = tcp_established_options(sk, skb, &opts,
&md5);
tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
if (tcp_packets_in_flight(tp) == 0)
tcp_ca_event(sk, CA_EVENT_TX_START);
/* if no packet is in qdisc/device queue, then allow XPS to select
* another queue. We can be called from tcp_tsq_handler()
* which holds one reference to sk_wmem_alloc.
*
* TODO: Ideally, in-flight pure ACK packets should not matter here.
* One way to get this would be to set skb->truesize = 2 on them.
*/
skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
skb_push(skb, tcp_header_size);
skb_reset_transport_header(skb);
skb_orphan(skb);
skb->sk = sk;
skb->destructor = tcp_wfree;
skb_set_hash_from_sk(skb, sk);
atomic_add(skb->truesize, &sk->sk_wmem_alloc);
/* Build TCP header and checksum it. */
th = tcp_hdr(skb);
th->source = inet->inet_sport;
th->dest = inet->inet_dport;
th->seq = htonl(tcb->seq);
th->ack_seq = htonl(tp->rcv_nxt);
*(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
tcb->tcp_flags);
if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
/* RFC1323: The window in SYN & SYN/ACK segments
* is never scaled.
*/
th->window = htons(min(tp->rcv_wnd, 65535U));
} else {
th->window = htons(tcp_select_window(sk));
}
th->check = 0;
th->urg_ptr = 0;
/* The urg_mode check is necessary during a below snd_una win probe */
if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
if (before(tp->snd_up, tcb->seq + 0x10000)) {
th->urg_ptr = htons(tp->snd_up - tcb->seq);
th->urg = 1;
} else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
th->urg_ptr = htons(0xFFFF);
th->urg = 1;
}
}
tcp_options_write((__be32 *)(th + 1), tp, &opts);
if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
tcp_ecn_send(sk, skb, tcp_header_size);
#ifdef CONFIG_TCP_MD5SIG
/* Calculate the MD5 hash, as we have all we need now */
if (md5) {
sk_nocaps_add(sk, NETIF_F_GSO_MASK);
tp->af_specific->calc_md5_hash(opts.hash_location,
md5, sk, NULL, skb);
}
#endif
icsk->icsk_af_ops->send_check(sk, skb);
if (likely(tcb->tcp_flags & TCPHDR_ACK))
tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
if (skb->len != tcp_header_size)
tcp_event_data_sent(tp, sk);
if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
tcp_skb_pcount(skb));
/* OK, its time to fill skb_shinfo(skb)->gso_segs */
skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
/* Our usage of tstamp should remain private */
skb->tstamp.tv64 = 0;
/* Cleanup our debris for IP stacks */
memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
sizeof(struct inet6_skb_parm)));
err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
if (likely(err <= 0))
return err;
tcp_enter_cwr(sk);
return net_xmit_eval(err);
}
/* This routine just queues the buffer for sending.
*
* NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
* otherwise socket can stall.
*/
static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Advance write_seq and place onto the write_queue. */
tp->write_seq = TCP_SKB_CB(skb)->end_seq;
__skb_header_release(skb);
tcp_add_write_queue_tail(sk, skb);
sk->sk_wmem_queued += skb->truesize;
sk_mem_charge(sk, skb->truesize);
}
/* Initialize TSO segments for a packet. */
static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
unsigned int mss_now)
{
struct skb_shared_info *shinfo = skb_shinfo(skb);
/* Make sure we own this skb before messing gso_size/gso_segs */
WARN_ON_ONCE(skb_cloned(skb));
if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
/* Avoid the costly divide in the normal
* non-TSO case.
*/
tcp_skb_pcount_set(skb, 1);
shinfo->gso_size = 0;
shinfo->gso_type = 0;
} else {
tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
shinfo->gso_size = mss_now;
shinfo->gso_type = sk->sk_gso_type;
}
}
/* When a modification to fackets out becomes necessary, we need to check
* skb is counted to fackets_out or not.
*/
static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
int decr)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tp->sacked_out || tcp_is_reno(tp))
return;
if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
tp->fackets_out -= decr;
}
/* Pcount in the middle of the write queue got changed, we need to do various
* tweaks to fix counters
*/
static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
{
struct tcp_sock *tp = tcp_sk(sk);
tp->packets_out -= decr;
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
tp->sacked_out -= decr;
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= decr;
if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
tp->lost_out -= decr;
/* Reno case is special. Sigh... */
if (tcp_is_reno(tp) && decr > 0)
tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
tcp_adjust_fackets_out(sk, skb, decr);
if (tp->lost_skb_hint &&
before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
(tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
tp->lost_cnt_hint -= decr;
tcp_verify_left_out(tp);
}
static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
{
struct skb_shared_info *shinfo = skb_shinfo(skb);
if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
!before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
shinfo->tx_flags &= ~tsflags;
shinfo2->tx_flags |= tsflags;
swap(shinfo->tskey, shinfo2->tskey);
}
}
/* Function to create two new TCP segments. Shrinks the given segment
* to the specified size and appends a new segment with the rest of the
* packet to the list. This won't be called frequently, I hope.
* Remember, these are still headerless SKBs at this point.
*/
int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
unsigned int mss_now, gfp_t gfp)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *buff;
int nsize, old_factor;
int nlen;
u8 flags;
if (WARN_ON(len > skb->len))
return -EINVAL;
nsize = skb_headlen(skb) - len;
if (nsize < 0)
nsize = 0;
if (skb_unclone(skb, gfp))
return -ENOMEM;
/* Get a new skb... force flag on. */
buff = sk_stream_alloc_skb(sk, nsize, gfp);
if (buff == NULL)
return -ENOMEM; /* We'll just try again later. */
sk->sk_wmem_queued += buff->truesize;
sk_mem_charge(sk, buff->truesize);
nlen = skb->len - len - nsize;
buff->truesize += nlen;
skb->truesize -= nlen;
/* Correct the sequence numbers. */
TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
/* PSH and FIN should only be set in the second packet. */
flags = TCP_SKB_CB(skb)->tcp_flags;
TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
TCP_SKB_CB(buff)->tcp_flags = flags;
TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
/* Copy and checksum data tail into the new buffer. */
buff->csum = csum_partial_copy_nocheck(skb->data + len,
skb_put(buff, nsize),
nsize, 0);
skb_trim(skb, len);
skb->csum = csum_block_sub(skb->csum, buff->csum, len);
} else {
skb->ip_summed = CHECKSUM_PARTIAL;
skb_split(skb, buff, len);
}
buff->ip_summed = skb->ip_summed;
buff->tstamp = skb->tstamp;
tcp_fragment_tstamp(skb, buff);
old_factor = tcp_skb_pcount(skb);
/* Fix up tso_factor for both original and new SKB. */
tcp_set_skb_tso_segs(sk, skb, mss_now);
tcp_set_skb_tso_segs(sk, buff, mss_now);
/* If this packet has been sent out already, we must
* adjust the various packet counters.
*/
if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
int diff = old_factor - tcp_skb_pcount(skb) -
tcp_skb_pcount(buff);
if (diff)
tcp_adjust_pcount(sk, skb, diff);
}
/* Link BUFF into the send queue. */
__skb_header_release(buff);
tcp_insert_write_queue_after(skb, buff, sk);
return 0;
}
/* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
* eventually). The difference is that pulled data not copied, but
* immediately discarded.
*/
static void __pskb_trim_head(struct sk_buff *skb, int len)
{
struct skb_shared_info *shinfo;
int i, k, eat;
eat = min_t(int, len, skb_headlen(skb));
if (eat) {
__skb_pull(skb, eat);
len -= eat;
if (!len)
return;
}
eat = len;
k = 0;
shinfo = skb_shinfo(skb);
for (i = 0; i < shinfo->nr_frags; i++) {
int size = skb_frag_size(&shinfo->frags[i]);
if (size <= eat) {
skb_frag_unref(skb, i);
eat -= size;
} else {
shinfo->frags[k] = shinfo->frags[i];
if (eat) {
shinfo->frags[k].page_offset += eat;
skb_frag_size_sub(&shinfo->frags[k], eat);
eat = 0;
}
k++;
}
}
shinfo->nr_frags = k;
skb_reset_tail_pointer(skb);
skb->data_len -= len;
skb->len = skb->data_len;
}
/* Remove acked data from a packet in the transmit queue. */
int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
{
if (skb_unclone(skb, GFP_ATOMIC))
return -ENOMEM;
__pskb_trim_head(skb, len);
TCP_SKB_CB(skb)->seq += len;
skb->ip_summed = CHECKSUM_PARTIAL;
skb->truesize -= len;
sk->sk_wmem_queued -= len;
sk_mem_uncharge(sk, len);
sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
/* Any change of skb->len requires recalculation of tso factor. */
if (tcp_skb_pcount(skb) > 1)
tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
return 0;
}
/* Calculate MSS not accounting any TCP options. */
static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
int mss_now;
/* Calculate base mss without TCP options:
It is MMS_S - sizeof(tcphdr) of rfc1122
*/
mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
if (icsk->icsk_af_ops->net_frag_header_len) {
const struct dst_entry *dst = __sk_dst_get(sk);
if (dst && dst_allfrag(dst))
mss_now -= icsk->icsk_af_ops->net_frag_header_len;
}
/* Clamp it (mss_clamp does not include tcp options) */
if (mss_now > tp->rx_opt.mss_clamp)
mss_now = tp->rx_opt.mss_clamp;
/* Now subtract optional transport overhead */
mss_now -= icsk->icsk_ext_hdr_len;
/* Then reserve room for full set of TCP options and 8 bytes of data */
if (mss_now < 48)
mss_now = 48;
return mss_now;
}
/* Calculate MSS. Not accounting for SACKs here. */
int tcp_mtu_to_mss(struct sock *sk, int pmtu)
{
/* Subtract TCP options size, not including SACKs */
return __tcp_mtu_to_mss(sk, pmtu) -
(tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
}
/* Inverse of above */
int tcp_mss_to_mtu(struct sock *sk, int mss)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
int mtu;
mtu = mss +
tp->tcp_header_len +
icsk->icsk_ext_hdr_len +
icsk->icsk_af_ops->net_header_len;
/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
if (icsk->icsk_af_ops->net_frag_header_len) {
const struct dst_entry *dst = __sk_dst_get(sk);
if (dst && dst_allfrag(dst))
mtu += icsk->icsk_af_ops->net_frag_header_len;
}
return mtu;
}
/* MTU probing init per socket */
void tcp_mtup_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
icsk->icsk_af_ops->net_header_len;
icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
icsk->icsk_mtup.probe_size = 0;
}
EXPORT_SYMBOL(tcp_mtup_init);
/* This function synchronize snd mss to current pmtu/exthdr set.
tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
for TCP options, but includes only bare TCP header.
tp->rx_opt.mss_clamp is mss negotiated at connection setup.
It is minimum of user_mss and mss received with SYN.
It also does not include TCP options.
inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
tp->mss_cache is current effective sending mss, including
all tcp options except for SACKs. It is evaluated,
taking into account current pmtu, but never exceeds
tp->rx_opt.mss_clamp.
NOTE1. rfc1122 clearly states that advertised MSS
DOES NOT include either tcp or ip options.
NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
are READ ONLY outside this function. --ANK (980731)
*/
unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
int mss_now;
if (icsk->icsk_mtup.search_high > pmtu)
icsk->icsk_mtup.search_high = pmtu;
mss_now = tcp_mtu_to_mss(sk, pmtu);
mss_now = tcp_bound_to_half_wnd(tp, mss_now);
/* And store cached results */
icsk->icsk_pmtu_cookie = pmtu;
if (icsk->icsk_mtup.enabled)
mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
tp->mss_cache = mss_now;
return mss_now;
}
EXPORT_SYMBOL(tcp_sync_mss);
/* Compute the current effective MSS, taking SACKs and IP options,
* and even PMTU discovery events into account.
*/
unsigned int tcp_current_mss(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct dst_entry *dst = __sk_dst_get(sk);
u32 mss_now;
unsigned int header_len;
struct tcp_out_options opts;
struct tcp_md5sig_key *md5;
mss_now = tp->mss_cache;
if (dst) {
u32 mtu = dst_mtu(dst);
if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
mss_now = tcp_sync_mss(sk, mtu);
}
header_len = tcp_established_options(sk, NULL, &opts, &md5) +
sizeof(struct tcphdr);
/* The mss_cache is sized based on tp->tcp_header_len, which assumes
* some common options. If this is an odd packet (because we have SACK
* blocks etc) then our calculated header_len will be different, and
* we have to adjust mss_now correspondingly */
if (header_len != tp->tcp_header_len) {
int delta = (int) header_len - tp->tcp_header_len;
mss_now -= delta;
}
return mss_now;
}
/* 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.
*/
static 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 void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
{
struct tcp_sock *tp = tcp_sk(sk);
/* Track the maximum number of outstanding packets in each
* window, and remember whether we were cwnd-limited then.
*/
if (!before(tp->snd_una, tp->max_packets_seq) ||
tp->packets_out > tp->max_packets_out) {
tp->max_packets_out = tp->packets_out;
tp->max_packets_seq = tp->snd_nxt;
tp->is_cwnd_limited = is_cwnd_limited;
}
if (tcp_is_cwnd_limited(sk)) {
/* Network is feed fully. */
tp->snd_cwnd_used = 0;
tp->snd_cwnd_stamp = tcp_time_stamp;
} else {
/* Network starves. */
if (tp->packets_out > tp->snd_cwnd_used)
tp->snd_cwnd_used = tp->packets_out;
if (sysctl_tcp_slow_start_after_idle &&
(s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
tcp_cwnd_application_limited(sk);
}
}
/* Minshall's variant of the Nagle send check. */
static bool tcp_minshall_check(const struct tcp_sock *tp)
{
return after(tp->snd_sml, tp->snd_una) &&
!after(tp->snd_sml, tp->snd_nxt);
}
/* Update snd_sml if this skb is under mss
* Note that a TSO packet might end with a sub-mss segment
* The test is really :
* if ((skb->len % mss) != 0)
* tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
* But we can avoid doing the divide again given we already have
* skb_pcount = skb->len / mss_now
*/
static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
const struct sk_buff *skb)
{
if (skb->len < tcp_skb_pcount(skb) * mss_now)
tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
}
/* Return false, if packet can be sent now without violation Nagle's rules:
* 1. It is full sized. (provided by caller in %partial bool)
* 2. Or it contains FIN. (already checked by caller)
* 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
* 4. Or TCP_CORK is not set, and all sent packets are ACKed.
* With Minshall's modification: all sent small packets are ACKed.
*/
static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
int nonagle)
{
return partial &&
((nonagle & TCP_NAGLE_CORK) ||
(!nonagle && tp->packets_out && tcp_minshall_check(tp)));
}
/* Returns the portion of skb which can be sent right away */
static unsigned int tcp_mss_split_point(const struct sock *sk,
const struct sk_buff *skb,
unsigned int mss_now,
unsigned int max_segs,
int nonagle)
{
const struct tcp_sock *tp = tcp_sk(sk);
u32 partial, needed, window, max_len;
window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
max_len = mss_now * max_segs;
if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
return max_len;
needed = min(skb->len, window);
if (max_len <= needed)
return max_len;
partial = needed % mss_now;
/* If last segment is not a full MSS, check if Nagle rules allow us
* to include this last segment in this skb.
* Otherwise, we'll split the skb at last MSS boundary
*/
if (tcp_nagle_check(partial != 0, tp, nonagle))
return needed - partial;
return needed;
}
/* Can at least one segment of SKB be sent right now, according to the
* congestion window rules? If so, return how many segments are allowed.
*/
static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
const struct sk_buff *skb)
{
u32 in_flight, cwnd;
/* Don't be strict about the congestion window for the final FIN. */
if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
tcp_skb_pcount(skb) == 1)
return 1;
in_flight = tcp_packets_in_flight(tp);
cwnd = tp->snd_cwnd;
if (in_flight < cwnd)
return (cwnd - in_flight);
return 0;
}
/* Initialize TSO state of a skb.
* This must be invoked the first time we consider transmitting
* SKB onto the wire.
*/
static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
unsigned int mss_now)
{
int tso_segs = tcp_skb_pcount(skb);
if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
tcp_set_skb_tso_segs(sk, skb, mss_now);
tso_segs = tcp_skb_pcount(skb);
}
return tso_segs;
}
/* Return true if the Nagle test allows this packet to be
* sent now.
*/
static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
unsigned int cur_mss, int nonagle)
{
/* Nagle rule does not apply to frames, which sit in the middle of the
* write_queue (they have no chances to get new data).
*
* This is implemented in the callers, where they modify the 'nonagle'
* argument based upon the location of SKB in the send queue.
*/
if (nonagle & TCP_NAGLE_PUSH)
return true;
/* Don't use the nagle rule for urgent data (or for the final FIN). */
if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
return true;
if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
return true;
return false;
}
/* Does at least the first segment of SKB fit into the send window? */
static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
const struct sk_buff *skb,
unsigned int cur_mss)
{
u32 end_seq = TCP_SKB_CB(skb)->end_seq;
if (skb->len > cur_mss)
end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
return !after(end_seq, tcp_wnd_end(tp));
}
/* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
* should be put on the wire right now. If so, it returns the number of
* packets allowed by the congestion window.
*/
static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
unsigned int cur_mss, int nonagle)
{
const struct tcp_sock *tp = tcp_sk(sk);
unsigned int cwnd_quota;
tcp_init_tso_segs(sk, skb, cur_mss);
if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
return 0;
cwnd_quota = tcp_cwnd_test(tp, skb);
if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
cwnd_quota = 0;
return cwnd_quota;
}
/* Test if sending is allowed right now. */
bool tcp_may_send_now(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb = tcp_send_head(sk);
return skb &&
tcp_snd_test(sk, skb, tcp_current_mss(sk),
(tcp_skb_is_last(sk, skb) ?
tp->nonagle : TCP_NAGLE_PUSH));
}
/* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
* which is put after SKB on the list. It is very much like
* tcp_fragment() except that it may make several kinds of assumptions
* in order to speed up the splitting operation. In particular, we
* know that all the data is in scatter-gather pages, and that the
* packet has never been sent out before (and thus is not cloned).
*/
static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
unsigned int mss_now, gfp_t gfp)
{
struct sk_buff *buff;
int nlen = skb->len - len;
u8 flags;
/* All of a TSO frame must be composed of paged data. */
if (skb->len != skb->data_len)
return tcp_fragment(sk, skb, len, mss_now, gfp);
buff = sk_stream_alloc_skb(sk, 0, gfp);
if (unlikely(buff == NULL))
return -ENOMEM;
sk->sk_wmem_queued += buff->truesize;
sk_mem_charge(sk, buff->truesize);
buff->truesize += nlen;
skb->truesize -= nlen;
/* Correct the sequence numbers. */
TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
/* PSH and FIN should only be set in the second packet. */
flags = TCP_SKB_CB(skb)->tcp_flags;
TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
TCP_SKB_CB(buff)->tcp_flags = flags;
/* This packet was never sent out yet, so no SACK bits. */
TCP_SKB_CB(buff)->sacked = 0;
buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
skb_split(skb, buff, len);
tcp_fragment_tstamp(skb, buff);
/* Fix up tso_factor for both original and new SKB. */
tcp_set_skb_tso_segs(sk, skb, mss_now);
tcp_set_skb_tso_segs(sk, buff, mss_now);
/* Link BUFF into the send queue. */
__skb_header_release(buff);
tcp_insert_write_queue_after(skb, buff, sk);
return 0;
}
/* Try to defer sending, if possible, in order to minimize the amount
* of TSO splitting we do. View it as a kind of TSO Nagle test.
*
* This algorithm is from John Heffner.
*/
static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
bool *is_cwnd_limited)
{
struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
u32 send_win, cong_win, limit, in_flight;
int win_divisor;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
goto send_now;
if (icsk->icsk_ca_state != TCP_CA_Open)
goto send_now;
/* Defer for less than two clock ticks. */
if (tp->tso_deferred &&
(((u32)jiffies << 1) >> 1) - (tp->tso_deferred >> 1) > 1)
goto send_now;
in_flight = tcp_packets_in_flight(tp);
BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
/* From in_flight test above, we know that cwnd > in_flight. */
cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
limit = min(send_win, cong_win);
/* If a full-sized TSO skb can be sent, do it. */
if (limit >= min_t(unsigned int, sk->sk_gso_max_size,
tp->xmit_size_goal_segs * tp->mss_cache))
goto send_now;
/* Middle in queue won't get any more data, full sendable already? */
if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
goto send_now;
win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
if (win_divisor) {
u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
/* If at least some fraction of a window is available,
* just use it.
*/
chunk /= win_divisor;
if (limit >= chunk)
goto send_now;
} else {
/* Different approach, try not to defer past a single
* ACK. Receiver should ACK every other full sized
* frame, so if we have space for more than 3 frames
* then send now.
*/
if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
goto send_now;
}
/* Ok, it looks like it is advisable to defer.
* Do not rearm the timer if already set to not break TCP ACK clocking.
*/
if (!tp->tso_deferred)
tp->tso_deferred = 1 | (jiffies << 1);
if (cong_win < send_win && cong_win < skb->len)
*is_cwnd_limited = true;
return true;
send_now:
tp->tso_deferred = 0;
return false;
}
/* Create a new MTU probe if we are ready.
* MTU probe is regularly attempting to increase the path MTU by
* deliberately sending larger packets. This discovers routing
* changes resulting in larger path MTUs.
*
* Returns 0 if we should wait to probe (no cwnd available),
* 1 if a probe was sent,
* -1 otherwise
*/
static int tcp_mtu_probe(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
struct sk_buff *skb, *nskb, *next;
int len;
int probe_size;
int size_needed;
int copy;
int mss_now;
/* Not currently probing/verifying,
* not in recovery,
* have enough cwnd, and
* not SACKing (the variable headers throw things off) */
if (!icsk->icsk_mtup.enabled ||
icsk->icsk_mtup.probe_size ||
inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
tp->snd_cwnd < 11 ||
tp->rx_opt.num_sacks || tp->rx_opt.dsack)
return -1;
/* Very simple search strategy: just double the MSS. */
mss_now = tcp_current_mss(sk);
probe_size = 2 * tp->mss_cache;
size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
/* TODO: set timer for probe_converge_event */
return -1;
}
/* Have enough data in the send queue to probe? */
if (tp->write_seq - tp->snd_nxt < size_needed)
return -1;
if (tp->snd_wnd < size_needed)
return -1;
if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
return 0;
/* Do we need to wait to drain cwnd? With none in flight, don't stall */
if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
if (!tcp_packets_in_flight(tp))
return -1;
else
return 0;
}
/* We're allowed to probe. Build it now. */
if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
return -1;
sk->sk_wmem_queued += nskb->truesize;
sk_mem_charge(sk, nskb->truesize);
skb = tcp_send_head(sk);
TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
TCP_SKB_CB(nskb)->sacked = 0;
nskb->csum = 0;
nskb->ip_summed = skb->ip_summed;
tcp_insert_write_queue_before(nskb, skb, sk);
len = 0;
tcp_for_write_queue_from_safe(skb, next, sk) {
copy = min_t(int, skb->len, probe_size - len);
if (nskb->ip_summed)
skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
else
nskb->csum = skb_copy_and_csum_bits(skb, 0,
skb_put(nskb, copy),
copy, nskb->csum);
if (skb->len <= copy) {
/* We've eaten all the data from this skb.
* Throw it away. */
TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
tcp_unlink_write_queue(skb, sk);
sk_wmem_free_skb(sk, skb);
} else {
TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
~(TCPHDR_FIN|TCPHDR_PSH);
if (!skb_shinfo(skb)->nr_frags) {
skb_pull(skb, copy);
if (skb->ip_summed != CHECKSUM_PARTIAL)
skb->csum = csum_partial(skb->data,
skb->len, 0);
} else {
__pskb_trim_head(skb, copy);
tcp_set_skb_tso_segs(sk, skb, mss_now);
}
TCP_SKB_CB(skb)->seq += copy;
}
len += copy;
if (len >= probe_size)
break;
}
tcp_init_tso_segs(sk, nskb, nskb->len);
/* We're ready to send. If this fails, the probe will
* be resegmented into mss-sized pieces by tcp_write_xmit().
*/
if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
/* Decrement cwnd here because we are sending
* effectively two packets. */
tp->snd_cwnd--;
tcp_event_new_data_sent(sk, nskb);
icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
return 1;
}
return -1;
}
/* This routine writes packets to the network. It advances the
* send_head. This happens as incoming acks open up the remote
* window for us.
*
* LARGESEND note: !tcp_urg_mode is overkill, only frames between
* snd_up-64k-mss .. snd_up cannot be large. However, taking into
* account rare use of URG, this is not a big flaw.
*
* Send at most one packet when push_one > 0. Temporarily ignore
* cwnd limit to force at most one packet out when push_one == 2.
* Returns true, if no segments are in flight and we have queued segments,
* but cannot send anything now because of SWS or another problem.
*/
static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
int push_one, gfp_t gfp)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
unsigned int tso_segs, sent_pkts;
int cwnd_quota;
int result;
bool is_cwnd_limited = false;
sent_pkts = 0;
if (!push_one) {
/* Do MTU probing. */
result = tcp_mtu_probe(sk);
if (!result) {
return false;
} else if (result > 0) {
sent_pkts = 1;
}
}
while ((skb = tcp_send_head(sk))) {
unsigned int limit;
tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
BUG_ON(!tso_segs);
if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
/* "skb_mstamp" is used as a start point for the retransmit timer */
skb_mstamp_get(&skb->skb_mstamp);
goto repair; /* Skip network transmission */
}
cwnd_quota = tcp_cwnd_test(tp, skb);
if (!cwnd_quota) {
is_cwnd_limited = true;
if (push_one == 2)
/* Force out a loss probe pkt. */
cwnd_quota = 1;
else
break;
}
if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
break;
if (tso_segs == 1) {
if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
(tcp_skb_is_last(sk, skb) ?
nonagle : TCP_NAGLE_PUSH))))
break;
} else {
if (!push_one &&
tcp_tso_should_defer(sk, skb, &is_cwnd_limited))
break;
}
/* TCP Small Queues :
* Control number of packets in qdisc/devices to two packets / or ~1 ms.
* This allows for :
* - better RTT estimation and ACK scheduling
* - faster recovery
* - high rates
* Alas, some drivers / subsystems require a fair amount
* of queued bytes to ensure line rate.
* One example is wifi aggregation (802.11 AMPDU)
*/
limit = max_t(unsigned int, sysctl_tcp_limit_output_bytes,
sk->sk_pacing_rate >> 10);
if (atomic_read(&sk->sk_wmem_alloc) > limit) {
set_bit(TSQ_THROTTLED, &tp->tsq_flags);
/* It is possible TX completion already happened
* before we set TSQ_THROTTLED, so we must
* test again the condition.
*/
smp_mb__after_atomic();
if (atomic_read(&sk->sk_wmem_alloc) > limit)
break;
}
limit = mss_now;
if (tso_segs > 1 && !tcp_urg_mode(tp))
limit = tcp_mss_split_point(sk, skb, mss_now,
min_t(unsigned int,
cwnd_quota,
sk->sk_gso_max_segs),
nonagle);
if (skb->len > limit &&
unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
break;
if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
break;
repair:
/* Advance the send_head. This one is sent out.
* This call will increment packets_out.
*/
tcp_event_new_data_sent(sk, skb);
tcp_minshall_update(tp, mss_now, skb);
sent_pkts += tcp_skb_pcount(skb);
if (push_one)
break;
}
if (likely(sent_pkts)) {
if (tcp_in_cwnd_reduction(sk))
tp->prr_out += sent_pkts;
/* Send one loss probe per tail loss episode. */
if (push_one != 2)
tcp_schedule_loss_probe(sk);
tcp_cwnd_validate(sk, is_cwnd_limited);
return false;
}
return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
}
bool tcp_schedule_loss_probe(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
u32 timeout, tlp_time_stamp, rto_time_stamp;
u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
return false;
/* No consecutive loss probes. */
if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
tcp_rearm_rto(sk);
return false;
}
/* Don't do any loss probe on a Fast Open connection before 3WHS
* finishes.
*/
if (sk->sk_state == TCP_SYN_RECV)
return false;
/* TLP is only scheduled when next timer event is RTO. */
if (icsk->icsk_pending != ICSK_TIME_RETRANS)
return false;
/* Schedule a loss probe in 2*RTT for SACK capable connections
* in Open state, that are either limited by cwnd or application.
*/
if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
!tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
return false;
if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
tcp_send_head(sk))
return false;
/* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
* for delayed ack when there's one outstanding packet.
*/
timeout = rtt << 1;
if (tp->packets_out == 1)
timeout = max_t(u32, timeout,
(rtt + (rtt >> 1) + TCP_DELACK_MAX));
timeout = max_t(u32, timeout, msecs_to_jiffies(10));
/* If RTO is shorter, just schedule TLP in its place. */
tlp_time_stamp = tcp_time_stamp + timeout;
rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
s32 delta = rto_time_stamp - tcp_time_stamp;
if (delta > 0)
timeout = delta;
}
inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
TCP_RTO_MAX);
return true;
}
/* Thanks to skb fast clones, we can detect if a prior transmit of
* a packet is still in a qdisc or driver queue.
* In this case, there is very little point doing a retransmit !
* Note: This is called from BH context only.
*/
static bool skb_still_in_host_queue(const struct sock *sk,
const struct sk_buff *skb)
{
if (unlikely(skb_fclone_busy(sk, skb))) {
NET_INC_STATS_BH(sock_net(sk),
LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
return true;
}
return false;
}
/* When probe timeout (PTO) fires, send a new segment if one exists, else
* retransmit the last segment.
*/
void tcp_send_loss_probe(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
int pcount;
int mss = tcp_current_mss(sk);
int err = -1;
if (tcp_send_head(sk) != NULL) {
err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
goto rearm_timer;
}
/* At most one outstanding TLP retransmission. */
if (tp->tlp_high_seq)
goto rearm_timer;
/* Retransmit last segment. */
skb = tcp_write_queue_tail(sk);
if (WARN_ON(!skb))
goto rearm_timer;
if (skb_still_in_host_queue(sk, skb))
goto rearm_timer;
pcount = tcp_skb_pcount(skb);
if (WARN_ON(!pcount))
goto rearm_timer;
if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
GFP_ATOMIC)))
goto rearm_timer;
skb = tcp_write_queue_tail(sk);
}
if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
goto rearm_timer;
err = __tcp_retransmit_skb(sk, skb);
/* Record snd_nxt for loss detection. */
if (likely(!err))
tp->tlp_high_seq = tp->snd_nxt;
rearm_timer:
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
inet_csk(sk)->icsk_rto,
TCP_RTO_MAX);
if (likely(!err))
NET_INC_STATS_BH(sock_net(sk),
LINUX_MIB_TCPLOSSPROBES);
}
/* Push out any pending frames which were held back due to
* TCP_CORK or attempt at coalescing tiny packets.
* The socket must be locked by the caller.
*/
void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
int nonagle)
{
/* If we are closed, the bytes will have to remain here.
* In time closedown will finish, we empty the write queue and
* all will be happy.
*/
if (unlikely(sk->sk_state == TCP_CLOSE))
return;
if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
sk_gfp_atomic(sk, GFP_ATOMIC)))
tcp_check_probe_timer(sk);
}
/* Send _single_ skb sitting at the send head. This function requires
* true push pending frames to setup probe timer etc.
*/
void tcp_push_one(struct sock *sk, unsigned int mss_now)
{
struct sk_buff *skb = tcp_send_head(sk);
BUG_ON(!skb || skb->len < mss_now);
tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
}
/* This function returns the amount that we can raise the
* usable window based on the following constraints
*
* 1. The window can never be shrunk once it is offered (RFC 793)
* 2. We limit memory per socket
*
* RFC 1122:
* "the suggested [SWS] avoidance algorithm for the receiver is to keep
* RECV.NEXT + RCV.WIN fixed until:
* RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
*
* i.e. don't raise the right edge of the window until you can raise
* it at least MSS bytes.
*
* Unfortunately, the recommended algorithm breaks header prediction,
* since header prediction assumes th->window stays fixed.
*
* Strictly speaking, keeping th->window fixed violates the receiver
* side SWS prevention criteria. The problem is that under this rule
* a stream of single byte packets will cause the right side of the
* window to always advance by a single byte.
*
* Of course, if the sender implements sender side SWS prevention
* then this will not be a problem.
*
* BSD seems to make the following compromise:
*
* If the free space is less than the 1/4 of the maximum
* space available and the free space is less than 1/2 mss,
* then set the window to 0.
* [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
* Otherwise, just prevent the window from shrinking
* and from being larger than the largest representable value.
*
* This prevents incremental opening of the window in the regime
* where TCP is limited by the speed of the reader side taking
* data out of the TCP receive queue. It does nothing about
* those cases where the window is constrained on the sender side
* because the pipeline is full.
*
* BSD also seems to "accidentally" limit itself to windows that are a
* multiple of MSS, at least until the free space gets quite small.
* This would appear to be a side effect of the mbuf implementation.
* Combining these two algorithms results in the observed behavior
* of having a fixed window size at almost all times.
*
* Below we obtain similar behavior by forcing the offered window to
* a multiple of the mss when it is feasible to do so.
*
* Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
* Regular options like TIMESTAMP are taken into account.
*/
u32 __tcp_select_window(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
/* MSS for the peer's data. Previous versions used mss_clamp
* here. I don't know if the value based on our guesses
* of peer's MSS is better for the performance. It's more correct
* but may be worse for the performance because of rcv_mss
* fluctuations. --SAW 1998/11/1
*/
int mss = icsk->icsk_ack.rcv_mss;
int free_space = tcp_space(sk);
int allowed_space = tcp_full_space(sk);
int full_space = min_t(int, tp->window_clamp, allowed_space);
int window;
if (mss > full_space)
mss = full_space;
if (free_space < (full_space >> 1)) {
icsk->icsk_ack.quick = 0;
if (sk_under_memory_pressure(sk))
tp->rcv_ssthresh = min(tp->rcv_ssthresh,
4U * tp->advmss);
/* free_space might become our new window, make sure we don't
* increase it due to wscale.
*/
free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
/* if free space is less than mss estimate, or is below 1/16th
* of the maximum allowed, try to move to zero-window, else
* tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
* new incoming data is dropped due to memory limits.
* With large window, mss test triggers way too late in order
* to announce zero window in time before rmem limit kicks in.
*/
if (free_space < (allowed_space >> 4) || free_space < mss)
return 0;
}
if (free_space > tp->rcv_ssthresh)
free_space = tp->rcv_ssthresh;
/* Don't do rounding if we are using window scaling, since the
* scaled window will not line up with the MSS boundary anyway.
*/
window = tp->rcv_wnd;
if (tp->rx_opt.rcv_wscale) {
window = free_space;
/* Advertise enough space so that it won't get scaled away.
* Import case: prevent zero window announcement if
* 1<<rcv_wscale > mss.
*/
if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
window = (((window >> tp->rx_opt.rcv_wscale) + 1)
<< tp->rx_opt.rcv_wscale);
} else {
/* Get the largest window that is a nice multiple of mss.
* Window clamp already applied above.
* If our current window offering is within 1 mss of the
* free space we just keep it. This prevents the divide
* and multiply from happening most of the time.
* We also don't do any window rounding when the free space
* is too small.
*/
if (window <= free_space - mss || window > free_space)
window = (free_space / mss) * mss;
else if (mss == full_space &&
free_space > window + (full_space >> 1))
window = free_space;
}
return window;
}
/* Collapses two adjacent SKB's during retransmission. */
static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
int skb_size, next_skb_size;
skb_size = skb->len;
next_skb_size = next_skb->len;
BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
tcp_highest_sack_combine(sk, next_skb, skb);
tcp_unlink_write_queue(next_skb, sk);
skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
next_skb_size);
if (next_skb->ip_summed == CHECKSUM_PARTIAL)
skb->ip_summed = CHECKSUM_PARTIAL;
if (skb->ip_summed != CHECKSUM_PARTIAL)
skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
/* Update sequence range on original skb. */
TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
/* Merge over control information. This moves PSH/FIN etc. over */
TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
/* All done, get rid of second SKB and account for it so
* packet counting does not break.
*/
TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
/* changed transmit queue under us so clear hints */
tcp_clear_retrans_hints_partial(tp);
if (next_skb == tp->retransmit_skb_hint)
tp->retransmit_skb_hint = skb;
tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
sk_wmem_free_skb(sk, next_skb);
}
/* Check if coalescing SKBs is legal. */
static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
{
if (tcp_skb_pcount(skb) > 1)
return false;
/* TODO: SACK collapsing could be used to remove this condition */
if (skb_shinfo(skb)->nr_frags != 0)
return false;
if (skb_cloned(skb))
return false;
if (skb == tcp_send_head(sk))
return false;
/* Some heurestics for collapsing over SACK'd could be invented */
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
return false;
return true;
}
/* Collapse packets in the retransmit queue to make to create
* less packets on the wire. This is only done on retransmission.
*/
static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
int space)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb = to, *tmp;
bool first = true;
if (!sysctl_tcp_retrans_collapse)
return;
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
return;
tcp_for_write_queue_from_safe(skb, tmp, sk) {
if (!tcp_can_collapse(sk, skb))
break;
space -= skb->len;
if (first) {
first = false;
continue;
}
if (space < 0)
break;
/* Punt if not enough space exists in the first SKB for
* the data in the second
*/
if (skb->len > skb_availroom(to))
break;
if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
break;
tcp_collapse_retrans(sk, to);
}
}
/* This retransmits one SKB. Policy decisions and retransmit queue
* state updates are done by the caller. Returns non-zero if an
* error occurred which prevented the send.
*/
int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
unsigned int cur_mss;
int err;
/* Inconslusive MTU probe */
if (icsk->icsk_mtup.probe_size) {
icsk->icsk_mtup.probe_size = 0;
}
/* Do not sent more than we queued. 1/4 is reserved for possible
* copying overhead: fragmentation, tunneling, mangling etc.
*/
if (atomic_read(&sk->sk_wmem_alloc) >
min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
return -EAGAIN;
if (skb_still_in_host_queue(sk, skb))
return -EBUSY;
if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
BUG();
if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
return -ENOMEM;
}
if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
return -EHOSTUNREACH; /* Routing failure or similar. */
cur_mss = tcp_current_mss(sk);
/* If receiver has shrunk his window, and skb is out of
* new window, do not retransmit it. The exception is the
* case, when window is shrunk to zero. In this case
* our retransmit serves as a zero window probe.
*/
if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
TCP_SKB_CB(skb)->seq != tp->snd_una)
return -EAGAIN;
if (skb->len > cur_mss) {
if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
return -ENOMEM; /* We'll try again later. */
} else {
int oldpcount = tcp_skb_pcount(skb);
if (unlikely(oldpcount > 1)) {
if (skb_unclone(skb, GFP_ATOMIC))
return -ENOMEM;
tcp_init_tso_segs(sk, skb, cur_mss);
tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
}
}
tcp_retrans_try_collapse(sk, skb, cur_mss);
/* Make a copy, if the first transmission SKB clone we made
* is still in somebody's hands, else make a clone.
*/
/* make sure skb->data is aligned on arches that require it
* and check if ack-trimming & collapsing extended the headroom
* beyond what csum_start can cover.
*/
if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
skb_headroom(skb) >= 0xFFFF)) {
struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
GFP_ATOMIC);
err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
-ENOBUFS;
} else {
err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
}
if (likely(!err)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
/* Update global TCP statistics. */
TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
tp->total_retrans++;
}
return err;
}
int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
int err = __tcp_retransmit_skb(sk, skb);
if (err == 0) {
#if FASTRETRANS_DEBUG > 0
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
net_dbg_ratelimited("retrans_out leaked\n");
}
#endif
if (!tp->retrans_out)
tp->lost_retrans_low = tp->snd_nxt;
TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
tp->retrans_out += tcp_skb_pcount(skb);
/* Save stamp of the first retransmit. */
if (!tp->retrans_stamp)
tp->retrans_stamp = tcp_skb_timestamp(skb);
/* snd_nxt is stored to detect loss of retransmitted segment,
* see tcp_input.c tcp_sacktag_write_queue().
*/
TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
} else if (err != -EBUSY) {
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
}
if (tp->undo_retrans < 0)
tp->undo_retrans = 0;
tp->undo_retrans += tcp_skb_pcount(skb);
return err;
}
/* Check if we forward retransmits are possible in the current
* window/congestion state.
*/
static bool tcp_can_forward_retransmit(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_sock *tp = tcp_sk(sk);
/* Forward retransmissions are possible only during Recovery. */
if (icsk->icsk_ca_state != TCP_CA_Recovery)
return false;
/* No forward retransmissions in Reno are possible. */
if (tcp_is_reno(tp))
return false;
/* Yeah, we have to make difficult choice between forward transmission
* and retransmission... Both ways have their merits...
*
* For now we do not retransmit anything, while we have some new
* segments to send. In the other cases, follow rule 3 for
* NextSeg() specified in RFC3517.
*/
if (tcp_may_send_now(sk))
return false;
return true;
}
/* This gets called after a retransmit timeout, and the initially
* retransmitted data is acknowledged. It tries to continue
* resending the rest of the retransmit queue, until either
* we've sent it all or the congestion window limit is reached.
* If doing SACK, the first ACK which comes back for a timeout
* based retransmit packet might feed us FACK information again.
* If so, we use it to avoid unnecessarily retransmissions.
*/
void tcp_xmit_retransmit_queue(struct sock *sk)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
struct sk_buff *hole = NULL;
u32 last_lost;
int mib_idx;
int fwd_rexmitting = 0;
if (!tp->packets_out)
return;
if (!tp->lost_out)
tp->retransmit_high = tp->snd_una;
if (tp->retransmit_skb_hint) {
skb = tp->retransmit_skb_hint;
last_lost = TCP_SKB_CB(skb)->end_seq;
if (after(last_lost, tp->retransmit_high))
last_lost = tp->retransmit_high;
} else {
skb = tcp_write_queue_head(sk);
last_lost = tp->snd_una;
}
tcp_for_write_queue_from(skb, sk) {
__u8 sacked = TCP_SKB_CB(skb)->sacked;
if (skb == tcp_send_head(sk))
break;
/* we could do better than to assign each time */
if (hole == NULL)
tp->retransmit_skb_hint = skb;
/* Assume this retransmit will generate
* only one packet for congestion window
* calculation purposes. This works because
* tcp_retransmit_skb() will chop up the
* packet to be MSS sized and all the
* packet counting works out.
*/
if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
return;
if (fwd_rexmitting) {
begin_fwd:
if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
break;
mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
} else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
tp->retransmit_high = last_lost;
if (!tcp_can_forward_retransmit(sk))
break;
/* Backtrack if necessary to non-L'ed skb */
if (hole != NULL) {
skb = hole;
hole = NULL;
}
fwd_rexmitting = 1;
goto begin_fwd;
} else if (!(sacked & TCPCB_LOST)) {
if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
hole = skb;
continue;
} else {
last_lost = TCP_SKB_CB(skb)->end_seq;
if (icsk->icsk_ca_state != TCP_CA_Loss)
mib_idx = LINUX_MIB_TCPFASTRETRANS;
else
mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
}
if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
continue;
if (tcp_retransmit_skb(sk, skb))
return;
NET_INC_STATS_BH(sock_net(sk), mib_idx);
if (tcp_in_cwnd_reduction(sk))
tp->prr_out += tcp_skb_pcount(skb);
if (skb == tcp_write_queue_head(sk))
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
inet_csk(sk)->icsk_rto,
TCP_RTO_MAX);
}
}
/* Send a fin. The caller locks the socket for us. This cannot be
* allowed to fail queueing a FIN frame under any circumstances.
*/
void tcp_send_fin(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb = tcp_write_queue_tail(sk);
int mss_now;
/* Optimization, tack on the FIN if we have a queue of
* unsent frames. But be careful about outgoing SACKS
* and IP options.
*/
mss_now = tcp_current_mss(sk);
if (tcp_send_head(sk) != NULL) {
TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
TCP_SKB_CB(skb)->end_seq++;
tp->write_seq++;
} else {
/* Socket is locked, keep trying until memory is available. */
for (;;) {
skb = alloc_skb_fclone(MAX_TCP_HEADER,
sk->sk_allocation);
if (skb)
break;
yield();
}
/* Reserve space for headers and prepare control bits. */
skb_reserve(skb, MAX_TCP_HEADER);
/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
tcp_init_nondata_skb(skb, tp->write_seq,
TCPHDR_ACK | TCPHDR_FIN);
tcp_queue_skb(sk, skb);
}
__tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
}
/* We get here when a process closes a file descriptor (either due to
* an explicit close() or as a byproduct of exit()'ing) and there