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freebsd-dev/sys/netinet/tcp_output.c
Richard Scheffenegger 2169f71277 tcp: use IPV6_FLOWLABEL_LEN 
Avoid magic numbers when handling the IPv6 flow ID for
DSCP and ECN fields and use the named variable instead.

Reviewed By:		tuexen, #transport
Sponsored by:		NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D39503
2023-04-11 18:53:51 +02:00

2177 lines
62 KiB
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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_kern_tls.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/arb.h>
#include <sys/domain.h>
#ifdef TCP_HHOOK
#include <sys/hhook.h>
#endif
#include <sys/kernel.h>
#ifdef KERN_TLS
#include <sys/ktls.h>
#endif
#include <sys/lock.h>
#include <sys/mbuf.h>
#include <sys/mutex.h>
#include <sys/protosw.h>
#include <sys/qmath.h>
#include <sys/sdt.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/stats.h>
#include <net/if.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/vnet.h>
#include <netinet/in.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_options.h>
#ifdef INET6
#include <netinet6/in6_pcb.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#endif
#include <netinet/tcp.h>
#define TCPOUTFLAGS
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_syncache.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcpip.h>
#include <netinet/cc/cc.h>
#include <netinet/tcp_fastopen.h>
#ifdef TCPPCAP
#include <netinet/tcp_pcap.h>
#endif
#ifdef TCP_OFFLOAD
#include <netinet/tcp_offload.h>
#endif
#include <netinet/tcp_ecn.h>
#include <netipsec/ipsec_support.h>
#include <netinet/udp.h>
#include <netinet/udp_var.h>
#include <machine/in_cksum.h>
#include <security/mac/mac_framework.h>
VNET_DEFINE(int, path_mtu_discovery) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(path_mtu_discovery), 1,
"Enable Path MTU Discovery");
VNET_DEFINE(int, tcp_do_tso) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_tso), 0,
"Enable TCP Segmentation Offload");
VNET_DEFINE(int, tcp_sendspace) = 1024*32;
#define V_tcp_sendspace VNET(tcp_sendspace)
SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_autosndbuf), 0,
"Enable automatic send buffer sizing");
VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_autosndbuf_inc), 0,
"Incrementor step size of automatic send buffer");
VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_autosndbuf_max), 0,
"Max size of automatic send buffer");
VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
#define V_tcp_sendbuf_auto_lowat VNET(tcp_sendbuf_auto_lowat)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_sendbuf_auto_lowat), 0,
"Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
/*
* Make sure that either retransmit or persist timer is set for SYN, FIN and
* non-ACK.
*/
#define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
tcp_timer_active((tp), TT_REXMT) || \
tcp_timer_active((tp), TT_PERSIST), \
("neither rexmt nor persist timer is set"))
#ifdef TCP_HHOOK
/*
* Wrapper for the TCP established output helper hook.
*/
void
hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
struct tcpopt *to, uint32_t len, int tso)
{
struct tcp_hhook_data hhook_data;
if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
hhook_data.tp = tp;
hhook_data.th = th;
hhook_data.to = to;
hhook_data.len = len;
hhook_data.tso = tso;
hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
&tp->t_osd);
}
}
#endif
/*
* CC wrapper hook functions
*/
void
cc_after_idle(struct tcpcb *tp)
{
INP_WLOCK_ASSERT(tptoinpcb(tp));
if (CC_ALGO(tp)->after_idle != NULL)
CC_ALGO(tp)->after_idle(&tp->t_ccv);
}
/*
* Tcp output routine: figure out what should be sent and send it.
*/
int
tcp_default_output(struct tcpcb *tp)
{
struct socket *so = tptosocket(tp);
struct inpcb *inp = tptoinpcb(tp);
int32_t len;
uint32_t recwin, sendwin;
uint16_t flags;
int off, error = 0; /* Keep compiler happy */
u_int if_hw_tsomaxsegcount = 0;
u_int if_hw_tsomaxsegsize = 0;
struct mbuf *m;
struct ip *ip = NULL;
struct tcphdr *th;
u_char opt[TCP_MAXOLEN];
unsigned ipoptlen, optlen, hdrlen, ulen;
#if defined(IPSEC) || defined(IPSEC_SUPPORT)
unsigned ipsec_optlen = 0;
#endif
int idle, sendalot, curticks;
int sack_rxmit, sack_bytes_rxmt;
struct sackhole *p;
int tso, mtu;
struct tcpopt to;
struct udphdr *udp = NULL;
struct tcp_log_buffer *lgb;
unsigned int wanted_cookie = 0;
unsigned int dont_sendalot = 0;
#if 0
int maxburst = TCP_MAXBURST;
#endif
#ifdef INET6
struct ip6_hdr *ip6 = NULL;
const bool isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif
#ifdef KERN_TLS
const bool hw_tls = tp->t_nic_ktls_xmit != 0;
#else
const bool hw_tls = false;
#endif
NET_EPOCH_ASSERT();
INP_WLOCK_ASSERT(inp);
#ifdef TCP_OFFLOAD
if (tp->t_flags & TF_TOE)
return (tcp_offload_output(tp));
#endif
/*
* For TFO connections in SYN_SENT or SYN_RECEIVED,
* only allow the initial SYN or SYN|ACK and those sent
* by the retransmit timer.
*/
if (IS_FASTOPEN(tp->t_flags) &&
((tp->t_state == TCPS_SYN_SENT) ||
(tp->t_state == TCPS_SYN_RECEIVED)) &&
SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
(tp->snd_nxt != tp->snd_una)) /* not a retransmit */
return (0);
/*
* Determine length of data that should be transmitted,
* and flags that will be used.
* If there is some data or critical controls (SYN, RST)
* to send, then transmit; otherwise, investigate further.
*/
idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
(tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
cc_after_idle(tp);
tp->t_flags &= ~TF_LASTIDLE;
if (idle) {
if (tp->t_flags & TF_MORETOCOME) {
tp->t_flags |= TF_LASTIDLE;
idle = 0;
}
}
again:
/*
* If we've recently taken a timeout, snd_max will be greater than
* snd_nxt. There may be SACK information that allows us to avoid
* resending already delivered data. Adjust snd_nxt accordingly.
*/
if ((tp->t_flags & TF_SACK_PERMIT) &&
SEQ_LT(tp->snd_nxt, tp->snd_max))
tcp_sack_adjust(tp);
sendalot = 0;
tso = 0;
mtu = 0;
off = tp->snd_nxt - tp->snd_una;
sendwin = min(tp->snd_wnd, tp->snd_cwnd);
flags = tcp_outflags[tp->t_state];
/*
* Send any SACK-generated retransmissions. If we're explicitly trying
* to send out new data (when sendalot is 1), bypass this function.
* If we retransmit in fast recovery mode, decrement snd_cwnd, since
* we're replacing a (future) new transmission with a retransmission
* now, and we previously incremented snd_cwnd in tcp_input().
*/
/*
* Still in sack recovery , reset rxmit flag to zero.
*/
sack_rxmit = 0;
sack_bytes_rxmt = 0;
len = 0;
p = NULL;
if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
(p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
uint32_t cwin;
cwin =
imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
/* Do not retransmit SACK segments beyond snd_recover */
if (SEQ_GT(p->end, tp->snd_recover)) {
/*
* (At least) part of sack hole extends beyond
* snd_recover. Check to see if we can rexmit data
* for this hole.
*/
if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
/*
* Can't rexmit any more data for this hole.
* That data will be rexmitted in the next
* sack recovery episode, when snd_recover
* moves past p->rxmit.
*/
p = NULL;
goto after_sack_rexmit;
} else {
/* Can rexmit part of the current hole */
len = ((int32_t)ulmin(cwin,
SEQ_SUB(tp->snd_recover, p->rxmit)));
}
} else {
len = ((int32_t)ulmin(cwin,
SEQ_SUB(p->end, p->rxmit)));
}
if (len > 0) {
off = SEQ_SUB(p->rxmit, tp->snd_una);
KASSERT(off >= 0,("%s: sack block to the left of una : %d",
__func__, off));
sack_rxmit = 1;
sendalot = 1;
TCPSTAT_INC(tcps_sack_rexmits);
TCPSTAT_ADD(tcps_sack_rexmit_bytes,
min(len, tcp_maxseg(tp)));
}
}
after_sack_rexmit:
/*
* Get standard flags, and add SYN or FIN if requested by 'hidden'
* state flags.
*/
if (tp->t_flags & TF_NEEDFIN)
flags |= TH_FIN;
if (tp->t_flags & TF_NEEDSYN)
flags |= TH_SYN;
SOCKBUF_LOCK(&so->so_snd);
/*
* If in persist timeout with window of 0, send 1 byte.
* Otherwise, if window is small but nonzero
* and timer expired, we will send what we can
* and go to transmit state.
*/
if (tp->t_flags & TF_FORCEDATA) {
if (sendwin == 0) {
/*
* If we still have some data to send, then
* clear the FIN bit. Usually this would
* happen below when it realizes that we
* aren't sending all the data. However,
* if we have exactly 1 byte of unsent data,
* then it won't clear the FIN bit below,
* and if we are in persist state, we wind
* up sending the packet without recording
* that we sent the FIN bit.
*
* We can't just blindly clear the FIN bit,
* because if we don't have any more data
* to send then the probe will be the FIN
* itself.
*/
if (off < sbused(&so->so_snd))
flags &= ~TH_FIN;
sendwin = 1;
} else {
tcp_timer_activate(tp, TT_PERSIST, 0);
tp->t_rxtshift = 0;
}
}
/*
* If snd_nxt == snd_max and we have transmitted a FIN, the
* offset will be > 0 even if so_snd.sb_cc is 0, resulting in
* a negative length. This can also occur when TCP opens up
* its congestion window while receiving additional duplicate
* acks after fast-retransmit because TCP will reset snd_nxt
* to snd_max after the fast-retransmit.
*
* In the normal retransmit-FIN-only case, however, snd_nxt will
* be set to snd_una, the offset will be 0, and the length may
* wind up 0.
*
* If sack_rxmit is true we are retransmitting from the scoreboard
* in which case len is already set.
*/
if (sack_rxmit == 0) {
if (sack_bytes_rxmt == 0)
len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
off);
else {
int32_t cwin;
/*
* We are inside of a SACK recovery episode and are
* sending new data, having retransmitted all the
* data possible in the scoreboard.
*/
len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
off);
/*
* Don't remove this (len > 0) check !
* We explicitly check for len > 0 here (although it
* isn't really necessary), to work around a gcc
* optimization issue - to force gcc to compute
* len above. Without this check, the computation
* of len is bungled by the optimizer.
*/
if (len > 0) {
cwin = tp->snd_cwnd - imax(0, (int32_t)
(tp->snd_nxt - tp->snd_recover)) -
sack_bytes_rxmt;
if (cwin < 0)
cwin = 0;
len = imin(len, cwin);
}
}
}
/*
* Lop off SYN bit if it has already been sent. However, if this
* is SYN-SENT state and if segment contains data and if we don't
* know that foreign host supports TAO, suppress sending segment.
*/
if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
if (tp->t_state != TCPS_SYN_RECEIVED)
flags &= ~TH_SYN;
/*
* When sending additional segments following a TFO SYN|ACK,
* do not include the SYN bit.
*/
if (IS_FASTOPEN(tp->t_flags) &&
(tp->t_state == TCPS_SYN_RECEIVED))
flags &= ~TH_SYN;
off--, len++;
}
/*
* Be careful not to send data and/or FIN on SYN segments.
* This measure is needed to prevent interoperability problems
* with not fully conformant TCP implementations.
*/
if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
len = 0;
flags &= ~TH_FIN;
}
/*
* On TFO sockets, ensure no data is sent in the following cases:
*
* - When retransmitting SYN|ACK on a passively-created socket
*
* - When retransmitting SYN on an actively created socket
*
* - When sending a zero-length cookie (cookie request) on an
* actively created socket
*
* - When the socket is in the CLOSED state (RST is being sent)
*/
if (IS_FASTOPEN(tp->t_flags) &&
(((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
((tp->t_state == TCPS_SYN_SENT) &&
(tp->t_tfo_client_cookie_len == 0)) ||
(flags & TH_RST)))
len = 0;
if (len <= 0) {
/*
* If FIN has been sent but not acked,
* but we haven't been called to retransmit,
* len will be < 0. Otherwise, window shrank
* after we sent into it. If window shrank to 0,
* cancel pending retransmit, pull snd_nxt back
* to (closed) window, and set the persist timer
* if it isn't already going. If the window didn't
* close completely, just wait for an ACK.
*
* We also do a general check here to ensure that
* we will set the persist timer when we have data
* to send, but a 0-byte window. This makes sure
* the persist timer is set even if the packet
* hits one of the "goto send" lines below.
*/
len = 0;
if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
(off < (int) sbavail(&so->so_snd)) &&
!tcp_timer_active(tp, TT_PERSIST)) {
tcp_timer_activate(tp, TT_REXMT, 0);
tp->t_rxtshift = 0;
tp->snd_nxt = tp->snd_una;
if (!tcp_timer_active(tp, TT_PERSIST))
tcp_setpersist(tp);
}
}
/* len will be >= 0 after this point. */
KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
tcp_sndbuf_autoscale(tp, so, sendwin);
/*
* Decide if we can use TCP Segmentation Offloading (if supported by
* hardware).
*
* TSO may only be used if we are in a pure bulk sending state. The
* presence of TCP-MD5, SACK retransmits, SACK advertizements and
* IP options prevent using TSO. With TSO the TCP header is the same
* (except for the sequence number) for all generated packets. This
* makes it impossible to transmit any options which vary per generated
* segment or packet.
*
* IPv4 handling has a clear separation of ip options and ip header
* flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
* the right thing below to provide length of just ip options and thus
* checking for ipoptlen is enough to decide if ip options are present.
*/
#if defined(IPSEC) || defined(IPSEC_SUPPORT)
/*
* Pre-calculate here as we save another lookup into the darknesses
* of IPsec that way and can actually decide if TSO is ok.
*/
#ifdef INET6
if (isipv6 && IPSEC_ENABLED(ipv6))
ipsec_optlen = IPSEC_HDRSIZE(ipv6, inp);
#ifdef INET
else
#endif
#endif /* INET6 */
#ifdef INET
if (IPSEC_ENABLED(ipv4))
ipsec_optlen = IPSEC_HDRSIZE(ipv4, inp);
#endif /* INET */
#endif /* IPSEC */
#ifdef INET6
if (isipv6)
ipoptlen = ip6_optlen(inp);
else
#endif
if (inp->inp_options)
ipoptlen = inp->inp_options->m_len -
offsetof(struct ipoption, ipopt_list);
else
ipoptlen = 0;
#if defined(IPSEC) || defined(IPSEC_SUPPORT)
ipoptlen += ipsec_optlen;
#endif
if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
(tp->t_port == 0) &&
((tp->t_flags & TF_SIGNATURE) == 0) &&
tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
ipoptlen == 0 && !(flags & TH_SYN))
tso = 1;
if (sack_rxmit) {
if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
flags &= ~TH_FIN;
} else {
if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
sbused(&so->so_snd)))
flags &= ~TH_FIN;
}
recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
(long)TCP_MAXWIN << tp->rcv_scale);
/*
* Sender silly window avoidance. We transmit under the following
* conditions when len is non-zero:
*
* - We have a full segment (or more with TSO)
* - This is the last buffer in a write()/send() and we are
* either idle or running NODELAY
* - we've timed out (e.g. persist timer)
* - we have more then 1/2 the maximum send window's worth of
* data (receiver may be limited the window size)
* - we need to retransmit
*/
if (len) {
if (len >= tp->t_maxseg)
goto send;
/*
* As the TCP header options are now
* considered when setting up the initial
* window, we would not send the last segment
* if we skip considering the option length here.
* Note: this may not work when tcp headers change
* very dynamically in the future.
*/
if ((((tp->t_flags & TF_SIGNATURE) ?
PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
((tp->t_flags & TF_RCVD_TSTMP) ?
PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
len) >= tp->t_maxseg)
goto send;
/*
* NOTE! on localhost connections an 'ack' from the remote
* end may occur synchronously with the output and cause
* us to flush a buffer queued with moretocome. XXX
*
* note: the len + off check is almost certainly unnecessary.
*/
if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
(idle || (tp->t_flags & TF_NODELAY)) &&
(uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
(tp->t_flags & TF_NOPUSH) == 0) {
goto send;
}
if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
goto send;
if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
goto send;
if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
goto send;
if (sack_rxmit)
goto send;
}
/*
* Sending of standalone window updates.
*
* Window updates are important when we close our window due to a
* full socket buffer and are opening it again after the application
* reads data from it. Once the window has opened again and the
* remote end starts to send again the ACK clock takes over and
* provides the most current window information.
*
* We must avoid the silly window syndrome whereas every read
* from the receive buffer, no matter how small, causes a window
* update to be sent. We also should avoid sending a flurry of
* window updates when the socket buffer had queued a lot of data
* and the application is doing small reads.
*
* Prevent a flurry of pointless window updates by only sending
* an update when we can increase the advertized window by more
* than 1/4th of the socket buffer capacity. When the buffer is
* getting full or is very small be more aggressive and send an
* update whenever we can increase by two mss sized segments.
* In all other situations the ACK's to new incoming data will
* carry further window increases.
*
* Don't send an independent window update if a delayed
* ACK is pending (it will get piggy-backed on it) or the
* remote side already has done a half-close and won't send
* more data. Skip this if the connection is in T/TCP
* half-open state.
*/
if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
!(tp->t_flags & TF_DELACK) &&
!TCPS_HAVERCVDFIN(tp->t_state)) {
/*
* "adv" is the amount we could increase the window,
* taking into account that we are limited by
* TCP_MAXWIN << tp->rcv_scale.
*/
int32_t adv;
int oldwin;
adv = recwin;
if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
oldwin = (tp->rcv_adv - tp->rcv_nxt);
if (adv > oldwin)
adv -= oldwin;
else
adv = 0;
} else
oldwin = 0;
/*
* If the new window size ends up being the same as or less
* than the old size when it is scaled, then don't force
* a window update.
*/
if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
goto dontupdate;
if (adv >= (int32_t)(2 * tp->t_maxseg) &&
(adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
recwin <= (so->so_rcv.sb_hiwat / 8) ||
so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
adv >= TCP_MAXWIN << tp->rcv_scale))
goto send;
if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
goto send;
}
dontupdate:
/*
* Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
* is also a catch-all for the retransmit timer timeout case.
*/
if (tp->t_flags & TF_ACKNOW)
goto send;
if ((flags & TH_RST) ||
((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
goto send;
if (SEQ_GT(tp->snd_up, tp->snd_una))
goto send;
/*
* If our state indicates that FIN should be sent
* and we have not yet done so, then we need to send.
*/
if (flags & TH_FIN &&
((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
goto send;
/*
* In SACK, it is possible for tcp_output to fail to send a segment
* after the retransmission timer has been turned off. Make sure
* that the retransmission timer is set.
*/
if ((tp->t_flags & TF_SACK_PERMIT) &&
SEQ_GT(tp->snd_max, tp->snd_una) &&
!tcp_timer_active(tp, TT_REXMT) &&
!tcp_timer_active(tp, TT_PERSIST)) {
tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
goto just_return;
}
/*
* TCP window updates are not reliable, rather a polling protocol
* using ``persist'' packets is used to insure receipt of window
* updates. The three ``states'' for the output side are:
* idle not doing retransmits or persists
* persisting to move a small or zero window
* (re)transmitting and thereby not persisting
*
* tcp_timer_active(tp, TT_PERSIST)
* is true when we are in persist state.
* (tp->t_flags & TF_FORCEDATA)
* is set when we are called to send a persist packet.
* tcp_timer_active(tp, TT_REXMT)
* is set when we are retransmitting
* The output side is idle when both timers are zero.
*
* If send window is too small, there is data to transmit, and no
* retransmit or persist is pending, then go to persist state.
* If nothing happens soon, send when timer expires:
* if window is nonzero, transmit what we can,
* otherwise force out a byte.
*/
if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
!tcp_timer_active(tp, TT_PERSIST)) {
tp->t_rxtshift = 0;
tcp_setpersist(tp);
}
/*
* No reason to send a segment, just return.
*/
just_return:
SOCKBUF_UNLOCK(&so->so_snd);
return (0);
send:
SOCKBUF_LOCK_ASSERT(&so->so_snd);
if (len > 0) {
if (len >= tp->t_maxseg)
tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
else
tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
}
/*
* Before ESTABLISHED, force sending of initial options
* unless TCP set not to do any options.
* NOTE: we assume that the IP/TCP header plus TCP options
* always fit in a single mbuf, leaving room for a maximum
* link header, i.e.
* max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
*/
optlen = 0;
#ifdef INET6
if (isipv6)
hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
else
#endif
hdrlen = sizeof (struct tcpiphdr);
if (flags & TH_SYN) {
tp->snd_nxt = tp->iss;
}
/*
* Compute options for segment.
* We only have to care about SYN and established connection
* segments. Options for SYN-ACK segments are handled in TCP
* syncache.
*/
to.to_flags = 0;
if ((tp->t_flags & TF_NOOPT) == 0) {
/* Maximum segment size. */
if (flags & TH_SYN) {
to.to_mss = tcp_mssopt(&inp->inp_inc);
if (tp->t_port)
to.to_mss -= V_tcp_udp_tunneling_overhead;
to.to_flags |= TOF_MSS;
/*
* On SYN or SYN|ACK transmits on TFO connections,
* only include the TFO option if it is not a
* retransmit, as the presence of the TFO option may
* have caused the original SYN or SYN|ACK to have
* been dropped by a middlebox.
*/
if (IS_FASTOPEN(tp->t_flags) &&
(tp->t_rxtshift == 0)) {
if (tp->t_state == TCPS_SYN_RECEIVED) {
to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
to.to_tfo_cookie =
(u_int8_t *)&tp->t_tfo_cookie.server;
to.to_flags |= TOF_FASTOPEN;
wanted_cookie = 1;
} else if (tp->t_state == TCPS_SYN_SENT) {
to.to_tfo_len =
tp->t_tfo_client_cookie_len;
to.to_tfo_cookie =
tp->t_tfo_cookie.client;
to.to_flags |= TOF_FASTOPEN;
wanted_cookie = 1;
/*
* If we wind up having more data to
* send with the SYN than can fit in
* one segment, don't send any more
* until the SYN|ACK comes back from
* the other end.
*/
dont_sendalot = 1;
}
}
}
/* Window scaling. */
if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
to.to_wscale = tp->request_r_scale;
to.to_flags |= TOF_SCALE;
}
/* Timestamps. */
if ((tp->t_flags & TF_RCVD_TSTMP) ||
((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
curticks = tcp_ts_getticks();
to.to_tsval = curticks + tp->ts_offset;
to.to_tsecr = tp->ts_recent;
to.to_flags |= TOF_TS;
if (tp->t_rxtshift == 1)
tp->t_badrxtwin = curticks;
}
/* Set receive buffer autosizing timestamp. */
if (tp->rfbuf_ts == 0 &&
(so->so_rcv.sb_flags & SB_AUTOSIZE))
tp->rfbuf_ts = tcp_ts_getticks();
/* Selective ACK's. */
if (tp->t_flags & TF_SACK_PERMIT) {
if (flags & TH_SYN)
to.to_flags |= TOF_SACKPERM;
else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
tp->rcv_numsacks > 0) {
to.to_flags |= TOF_SACK;
to.to_nsacks = tp->rcv_numsacks;
to.to_sacks = (u_char *)tp->sackblks;
}
}
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
/* TCP-MD5 (RFC2385). */
/*
* Check that TCP_MD5SIG is enabled in tcpcb to
* account the size needed to set this TCP option.
*/
if (tp->t_flags & TF_SIGNATURE)
to.to_flags |= TOF_SIGNATURE;
#endif /* TCP_SIGNATURE */
/* Processing the options. */
hdrlen += optlen = tcp_addoptions(&to, opt);
/*
* If we wanted a TFO option to be added, but it was unable
* to fit, ensure no data is sent.
*/
if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
!(to.to_flags & TOF_FASTOPEN))
len = 0;
}
if (tp->t_port) {
if (V_tcp_udp_tunneling_port == 0) {
/* The port was removed?? */
SOCKBUF_UNLOCK(&so->so_snd);
return (EHOSTUNREACH);
}
hdrlen += sizeof(struct udphdr);
}
/*
* Adjust data length if insertion of options will
* bump the packet length beyond the t_maxseg length.
* Clear the FIN bit because we cut off the tail of
* the segment.
*/
if (len + optlen + ipoptlen > tp->t_maxseg) {
flags &= ~TH_FIN;
if (tso) {
u_int if_hw_tsomax;
u_int moff;
int max_len;
/* extract TSO information */
if_hw_tsomax = tp->t_tsomax;
if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
/*
* Limit a TSO burst to prevent it from
* overflowing or exceeding the maximum length
* allowed by the network interface:
*/
KASSERT(ipoptlen == 0,
("%s: TSO can't do IP options", __func__));
/*
* Check if we should limit by maximum payload
* length:
*/
if (if_hw_tsomax != 0) {
/* compute maximum TSO length */
max_len = (if_hw_tsomax - hdrlen -
max_linkhdr);
if (max_len <= 0) {
len = 0;
} else if (len > max_len) {
sendalot = 1;
len = max_len;
}
}
/*
* Prevent the last segment from being
* fractional unless the send sockbuf can be
* emptied:
*/
max_len = (tp->t_maxseg - optlen);
if (((uint32_t)off + (uint32_t)len) <
sbavail(&so->so_snd)) {
moff = len % max_len;
if (moff != 0) {
len -= moff;
sendalot = 1;
}
}
/*
* In case there are too many small fragments
* don't use TSO:
*/
if (len <= max_len) {
len = max_len;
sendalot = 1;
tso = 0;
}
/*
* Send the FIN in a separate segment
* after the bulk sending is done.
* We don't trust the TSO implementations
* to clear the FIN flag on all but the
* last segment.
*/
if (tp->t_flags & TF_NEEDFIN)
sendalot = 1;
} else {
if (optlen + ipoptlen >= tp->t_maxseg) {
/*
* Since we don't have enough space to put
* the IP header chain and the TCP header in
* one packet as required by RFC 7112, don't
* send it. Also ensure that at least one
* byte of the payload can be put into the
* TCP segment.
*/
SOCKBUF_UNLOCK(&so->so_snd);
error = EMSGSIZE;
sack_rxmit = 0;
goto out;
}
len = tp->t_maxseg - optlen - ipoptlen;
sendalot = 1;
if (dont_sendalot)
sendalot = 0;
}
} else
tso = 0;
KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
("%s: len > IP_MAXPACKET", __func__));
/*#ifdef DIAGNOSTIC*/
#ifdef INET6
if (max_linkhdr + hdrlen > MCLBYTES)
#else
if (max_linkhdr + hdrlen > MHLEN)
#endif
panic("tcphdr too big");
/*#endif*/
/*
* This KASSERT is here to catch edge cases at a well defined place.
* Before, those had triggered (random) panic conditions further down.
*/
KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
/*
* Grab a header mbuf, attaching a copy of data to
* be transmitted, and initialize the header from
* the template for sends on this connection.
*/
if (len) {
struct mbuf *mb;
struct sockbuf *msb;
u_int moff;
if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
TCPSTAT_INC(tcps_sndprobe);
#ifdef STATS
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
stats_voi_update_abs_u32(tp->t_stats,
VOI_TCP_RETXPB, len);
else
stats_voi_update_abs_u64(tp->t_stats,
VOI_TCP_TXPB, len);
#endif /* STATS */
} else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
tp->t_sndrexmitpack++;
TCPSTAT_INC(tcps_sndrexmitpack);
TCPSTAT_ADD(tcps_sndrexmitbyte, len);
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
len);
#endif /* STATS */
} else {
TCPSTAT_INC(tcps_sndpack);
TCPSTAT_ADD(tcps_sndbyte, len);
#ifdef STATS
stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
len);
#endif /* STATS */
}
#ifdef INET6
if (MHLEN < hdrlen + max_linkhdr)
m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
else
#endif
m = m_gethdr(M_NOWAIT, MT_DATA);
if (m == NULL) {
SOCKBUF_UNLOCK(&so->so_snd);
error = ENOBUFS;
sack_rxmit = 0;
goto out;
}
m->m_data += max_linkhdr;
m->m_len = hdrlen;
/*
* Start the m_copy functions from the closest mbuf
* to the offset in the socket buffer chain.
*/
mb = sbsndptr_noadv(&so->so_snd, off, &moff);
if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
m_copydata(mb, moff, len,
mtod(m, caddr_t) + hdrlen);
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
sbsndptr_adv(&so->so_snd, mb, len);
m->m_len += len;
} else {
if (SEQ_LT(tp->snd_nxt, tp->snd_max))
msb = NULL;
else
msb = &so->so_snd;
m->m_next = tcp_m_copym(mb, moff,
&len, if_hw_tsomaxsegcount,
if_hw_tsomaxsegsize, msb, hw_tls);
if (len <= (tp->t_maxseg - optlen)) {
/*
* Must have ran out of mbufs for the copy
* shorten it to no longer need tso. Lets
* not put on sendalot since we are low on
* mbufs.
*/
tso = 0;
}
if (m->m_next == NULL) {
SOCKBUF_UNLOCK(&so->so_snd);
(void) m_free(m);
error = ENOBUFS;
sack_rxmit = 0;
goto out;
}
}
/*
* If we're sending everything we've got, set PUSH.
* (This will keep happy those implementations which only
* give data to the user when a buffer fills or
* a PUSH comes in.)
*/
if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
!(flags & TH_SYN))
flags |= TH_PUSH;
SOCKBUF_UNLOCK(&so->so_snd);
} else {
SOCKBUF_UNLOCK(&so->so_snd);
if (tp->t_flags & TF_ACKNOW)
TCPSTAT_INC(tcps_sndacks);
else if (flags & (TH_SYN|TH_FIN|TH_RST))
TCPSTAT_INC(tcps_sndctrl);
else if (SEQ_GT(tp->snd_up, tp->snd_una))
TCPSTAT_INC(tcps_sndurg);
else
TCPSTAT_INC(tcps_sndwinup);
m = m_gethdr(M_NOWAIT, MT_DATA);
if (m == NULL) {
error = ENOBUFS;
sack_rxmit = 0;
goto out;
}
#ifdef INET6
if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
MHLEN >= hdrlen) {
M_ALIGN(m, hdrlen);
} else
#endif
m->m_data += max_linkhdr;
m->m_len = hdrlen;
}
SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
m->m_pkthdr.rcvif = (struct ifnet *)0;
#ifdef MAC
mac_inpcb_create_mbuf(inp, m);
#endif
#ifdef INET6
if (isipv6) {
ip6 = mtod(m, struct ip6_hdr *);
if (tp->t_port) {
udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
udp->uh_sport = htons(V_tcp_udp_tunneling_port);
udp->uh_dport = tp->t_port;
ulen = hdrlen + len - sizeof(struct ip6_hdr);
udp->uh_ulen = htons(ulen);
th = (struct tcphdr *)(udp + 1);
} else {
th = (struct tcphdr *)(ip6 + 1);
}
tcpip_fillheaders(inp, tp->t_port, ip6, th);
} else
#endif /* INET6 */
{
ip = mtod(m, struct ip *);
if (tp->t_port) {
udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
udp->uh_sport = htons(V_tcp_udp_tunneling_port);
udp->uh_dport = tp->t_port;
ulen = hdrlen + len - sizeof(struct ip);
udp->uh_ulen = htons(ulen);
th = (struct tcphdr *)(udp + 1);
} else
th = (struct tcphdr *)(ip + 1);
tcpip_fillheaders(inp, tp->t_port, ip, th);
}
/*
* Fill in fields, remembering maximum advertised
* window for use in delaying messages about window sizes.
* If resending a FIN, be sure not to use a new sequence number.
*/
if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
tp->snd_nxt == tp->snd_max)
tp->snd_nxt--;
/*
* If we are starting a connection, send ECN setup
* SYN packet. If we are on a retransmit, we may
* resend those bits a number of times as per
* RFC 3168.
*/
if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
flags |= tcp_ecn_output_syn_sent(tp);
}
/* Also handle parallel SYN for ECN */
if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
(tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
if ((tp->t_state == TCPS_SYN_RECEIVED) &&
(tp->t_flags2 & TF2_ECN_SND_ECE))
tp->t_flags2 &= ~TF2_ECN_SND_ECE;
#ifdef INET6
if (isipv6) {
ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << IPV6_FLOWLABEL_LEN);
ip6->ip6_flow |= htonl(ect << IPV6_FLOWLABEL_LEN);
}
else
#endif
{
ip->ip_tos &= ~IPTOS_ECN_MASK;
ip->ip_tos |= ect;
}
}
/*
* If we are doing retransmissions, then snd_nxt will
* not reflect the first unsent octet. For ACK only
* packets, we do not want the sequence number of the
* retransmitted packet, we want the sequence number
* of the next unsent octet. So, if there is no data
* (and no SYN or FIN), use snd_max instead of snd_nxt
* when filling in ti_seq. But if we are in persist
* state, snd_max might reflect one byte beyond the
* right edge of the window, so use snd_nxt in that
* case, since we know we aren't doing a retransmission.
* (retransmit and persist are mutually exclusive...)
*/
if (sack_rxmit == 0) {
if (len || (flags & (TH_SYN|TH_FIN)) ||
tcp_timer_active(tp, TT_PERSIST))
th->th_seq = htonl(tp->snd_nxt);
else
th->th_seq = htonl(tp->snd_max);
} else {
th->th_seq = htonl(p->rxmit);
p->rxmit += len;
/*
* Lost Retransmission Detection
* trigger resending of a (then
* still existing) hole, when
* fack acks recoverypoint.
*/
if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
p->rxmit = tp->snd_recover;
tp->sackhint.sack_bytes_rexmit += len;
}
if (IN_RECOVERY(tp->t_flags)) {
/*
* Account all bytes transmitted while
* IN_RECOVERY, simplifying PRR and
* Lost Retransmit Detection
*/
tp->sackhint.prr_out += len;
}
th->th_ack = htonl(tp->rcv_nxt);
if (optlen) {
bcopy(opt, th + 1, optlen);
th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
}
tcp_set_flags(th, flags);
/*
* Calculate receive window. Don't shrink window,
* but avoid silly window syndrome.
* If a RST segment is sent, advertise a window of zero.
*/
if (flags & TH_RST) {
recwin = 0;
} else {
if (recwin < (so->so_rcv.sb_hiwat / 4) &&
recwin < tp->t_maxseg)
recwin = 0;
if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
recwin < (tp->rcv_adv - tp->rcv_nxt))
recwin = (tp->rcv_adv - tp->rcv_nxt);
}
/*
* According to RFC1323 the window field in a SYN (i.e., a <SYN>
* or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
* case is handled in syncache.
*/
if (flags & TH_SYN)
th->th_win = htons((u_short)
(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
else {
/* Avoid shrinking window with window scaling. */
recwin = roundup2(recwin, 1 << tp->rcv_scale);
th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
}
/*
* Adjust the RXWIN0SENT flag - indicate that we have advertised
* a 0 window. This may cause the remote transmitter to stall. This
* flag tells soreceive() to disable delayed acknowledgements when
* draining the buffer. This can occur if the receiver is attempting
* to read more data than can be buffered prior to transmitting on
* the connection.
*/
if (th->th_win == 0) {
tp->t_sndzerowin++;
tp->t_flags |= TF_RXWIN0SENT;
} else
tp->t_flags &= ~TF_RXWIN0SENT;
if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
th->th_flags |= TH_URG;
} else
/*
* If no urgent pointer to send, then we pull
* the urgent pointer to the left edge of the send window
* so that it doesn't drift into the send window on sequence
* number wraparound.
*/
tp->snd_up = tp->snd_una; /* drag it along */
/*
* Put TCP length in extended header, and then
* checksum extended header and data.
*/
m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
if (to.to_flags & TOF_SIGNATURE) {
/*
* Calculate MD5 signature and put it into the place
* determined before.
* NOTE: since TCP options buffer doesn't point into
* mbuf's data, calculate offset and use it.
*/
if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
(u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
/*
* Do not send segment if the calculation of MD5
* digest has failed.
*/
m_freem(m);
goto out;
}
}
#endif
#ifdef INET6
if (isipv6) {
/*
* There is no need to fill in ip6_plen right now.
* It will be filled later by ip6_output.
*/
if (tp->t_port) {
m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
th->th_sum = htons(0);
UDPSTAT_INC(udps_opackets);
} else {
m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
th->th_sum = in6_cksum_pseudo(ip6,
sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
0);
}
}
#endif
#if defined(INET6) && defined(INET)
else
#endif
#ifdef INET
{
if (tp->t_port) {
m->m_pkthdr.csum_flags = CSUM_UDP;
m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
th->th_sum = htons(0);
UDPSTAT_INC(udps_opackets);
} else {
m->m_pkthdr.csum_flags = CSUM_TCP;
m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
th->th_sum = in_pseudo(ip->ip_src.s_addr,
ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
IPPROTO_TCP + len + optlen));
}
/* IP version must be set here for ipv4/ipv6 checking later */
KASSERT(ip->ip_v == IPVERSION,
("%s: IP version incorrect: %d", __func__, ip->ip_v));
}
#endif
/*
* Enable TSO and specify the size of the segments.
* The TCP pseudo header checksum is always provided.
*/
if (tso) {
KASSERT(len > tp->t_maxseg - optlen,
("%s: len <= tso_segsz", __func__));
m->m_pkthdr.csum_flags |= CSUM_TSO;
m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
}
KASSERT(len + hdrlen == m_length(m, NULL),
("%s: mbuf chain shorter than expected: %d + %u != %u",
__func__, len, hdrlen, m_length(m, NULL)));
#ifdef TCP_HHOOK
/* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
hhook_run_tcp_est_out(tp, th, &to, len, tso);
#endif
TCP_PROBE3(debug__output, tp, th, m);
/* We're getting ready to send; log now. */
/* XXXMT: We are not honoring verbose logging. */
if (tcp_bblogging_on(tp))
lgb = tcp_log_event(tp, th, &so->so_rcv, &so->so_snd,
TCP_LOG_OUT, ERRNO_UNK, len, NULL, false, NULL, NULL, 0,
NULL);
else
lgb = NULL;
/*
* Fill in IP length and desired time to live and
* send to IP level. There should be a better way
* to handle ttl and tos; we could keep them in
* the template, but need a way to checksum without them.
*/
/*
* m->m_pkthdr.len should have been set before checksum calculation,
* because in6_cksum() need it.
*/
#ifdef INET6
if (isipv6) {
/*
* we separately set hoplimit for every segment, since the
* user might want to change the value via setsockopt.
* Also, desired default hop limit might be changed via
* Neighbor Discovery.
*/
ip6->ip6_hlim = in6_selecthlim(inp, NULL);
/*
* Set the packet size here for the benefit of DTrace probes.
* ip6_output() will set it properly; it's supposed to include
* the option header lengths as well.
*/
ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
tp->t_flags2 |= TF2_PLPMTU_PMTUD;
else
tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
if (tp->t_state == TCPS_SYN_SENT)
TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
TCP_PROBE5(send, NULL, tp, ip6, tp, th);
#ifdef TCPPCAP
/* Save packet, if requested. */
tcp_pcap_add(th, m, &(tp->t_outpkts));
#endif
/* TODO: IPv6 IP6TOS_ECT bit on */
error = ip6_output(m, inp->in6p_outputopts, &inp->inp_route6,
((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
NULL, NULL, inp);
if (error == EMSGSIZE && inp->inp_route6.ro_nh != NULL)
mtu = inp->inp_route6.ro_nh->nh_mtu;
}
#endif /* INET6 */
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
ip->ip_len = htons(m->m_pkthdr.len);
#ifdef INET6
if (inp->inp_vflag & INP_IPV6PROTO)
ip->ip_ttl = in6_selecthlim(inp, NULL);
#endif /* INET6 */
/*
* If we do path MTU discovery, then we set DF on every packet.
* This might not be the best thing to do according to RFC3390
* Section 2. However the tcp hostcache migitates the problem
* so it affects only the first tcp connection with a host.
*
* NB: Don't set DF on small MTU/MSS to have a safe fallback.
*/
if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
tp->t_flags2 |= TF2_PLPMTU_PMTUD;
if (tp->t_port == 0 || len < V_tcp_minmss) {
ip->ip_off |= htons(IP_DF);
}
} else {
tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
}
if (tp->t_state == TCPS_SYN_SENT)
TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
TCP_PROBE5(send, NULL, tp, ip, tp, th);
#ifdef TCPPCAP
/* Save packet, if requested. */
tcp_pcap_add(th, m, &(tp->t_outpkts));
#endif
error = ip_output(m, inp->inp_options, &inp->inp_route,
((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, inp);
if (error == EMSGSIZE && inp->inp_route.ro_nh != NULL)
mtu = inp->inp_route.ro_nh->nh_mtu;
}
#endif /* INET */
if (lgb != NULL) {
lgb->tlb_errno = error;
lgb = NULL;
}
out:
if (error == 0)
tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
/*
* In transmit state, time the transmission and arrange for
* the retransmit. In persist state, just set snd_max.
*/
if ((tp->t_flags & TF_FORCEDATA) == 0 ||
!tcp_timer_active(tp, TT_PERSIST)) {
tcp_seq startseq = tp->snd_nxt;
/*
* Advance snd_nxt over sequence space of this segment.
*/
if (flags & (TH_SYN|TH_FIN)) {
if (flags & TH_SYN)
tp->snd_nxt++;
if (flags & TH_FIN) {
tp->snd_nxt++;
tp->t_flags |= TF_SENTFIN;
}
}
if (sack_rxmit)
goto timer;
tp->snd_nxt += len;
if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
/*
* Update "made progress" indication if we just
* added new data to an empty socket buffer.
*/
if (tp->snd_una == tp->snd_max)
tp->t_acktime = ticks;
tp->snd_max = tp->snd_nxt;
/*
* Time this transmission if not a retransmission and
* not currently timing anything.
*/
tp->t_sndtime = ticks;
if (tp->t_rtttime == 0) {
tp->t_rtttime = ticks;
tp->t_rtseq = startseq;
TCPSTAT_INC(tcps_segstimed);
}
#ifdef STATS
if (!(tp->t_flags & TF_GPUTINPROG) && len) {
tp->t_flags |= TF_GPUTINPROG;
tp->gput_seq = startseq;
tp->gput_ack = startseq +
ulmin(sbavail(&so->so_snd) - off, sendwin);
tp->gput_ts = tcp_ts_getticks();
}
#endif /* STATS */
}
/*
* Set retransmit timer if not currently set,
* and not doing a pure ack or a keep-alive probe.
* Initial value for retransmit timer is smoothed
* round-trip time + 2 * round-trip time variance.
* Initialize shift counter which is used for backoff
* of retransmit time.
*/
timer:
if (!tcp_timer_active(tp, TT_REXMT) &&
((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
(tp->snd_nxt != tp->snd_una))) {
if (tcp_timer_active(tp, TT_PERSIST)) {
tcp_timer_activate(tp, TT_PERSIST, 0);
tp->t_rxtshift = 0;
}
tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
} else if (len == 0 && sbavail(&so->so_snd) &&
!tcp_timer_active(tp, TT_REXMT) &&
!tcp_timer_active(tp, TT_PERSIST)) {
/*
* Avoid a situation where we do not set persist timer
* after a zero window condition. For example:
* 1) A -> B: packet with enough data to fill the window
* 2) B -> A: ACK for #1 + new data (0 window
* advertisement)
* 3) A -> B: ACK for #2, 0 len packet
*
* In this case, A will not activate the persist timer,
* because it chose to send a packet. Unless tcp_output
* is called for some other reason (delayed ack timer,
* another input packet from B, socket syscall), A will
* not send zero window probes.
*
* So, if you send a 0-length packet, but there is data
* in the socket buffer, and neither the rexmt or
* persist timer is already set, then activate the
* persist timer.
*/
tp->t_rxtshift = 0;
tcp_setpersist(tp);
}
} else {
/*
* Persist case, update snd_max but since we are in
* persist mode (no window) we do not update snd_nxt.
*/
int xlen = len;
if (flags & TH_SYN)
++xlen;
if (flags & TH_FIN) {
++xlen;
tp->t_flags |= TF_SENTFIN;
}
if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
tp->snd_max = tp->snd_nxt + xlen;
}
if ((error == 0) &&
(TCPS_HAVEESTABLISHED(tp->t_state) &&
(tp->t_flags & TF_SACK_PERMIT) &&
tp->rcv_numsacks > 0)) {
/* Clean up any DSACK's sent */
tcp_clean_dsack_blocks(tp);
}
if (error) {
/*
* We know that the packet was lost, so back out the
* sequence number advance, if any.
*
* If the error is EPERM the packet got blocked by the
* local firewall. Normally we should terminate the
* connection but the blocking may have been spurious
* due to a firewall reconfiguration cycle. So we treat
* it like a packet loss and let the retransmit timer and
* timeouts do their work over time.
* XXX: It is a POLA question whether calling tcp_drop right
* away would be the really correct behavior instead.
*/
if (((tp->t_flags & TF_FORCEDATA) == 0 ||
!tcp_timer_active(tp, TT_PERSIST)) &&
((flags & TH_SYN) == 0) &&
(error != EPERM)) {
if (sack_rxmit) {
p->rxmit -= len;
tp->sackhint.sack_bytes_rexmit -= len;
KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
("sackhint bytes rtx >= 0"));
KASSERT((flags & TH_FIN) == 0,
("error while FIN with SACK rxmit"));
} else {
tp->snd_nxt -= len;
if (flags & TH_FIN)
tp->snd_nxt--;
}
}
SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
switch (error) {
case EACCES:
case EPERM:
tp->t_softerror = error;
return (error);
case ENOBUFS:
TCP_XMIT_TIMER_ASSERT(tp, len, flags);
tp->snd_cwnd = tp->t_maxseg;
return (0);
case EMSGSIZE:
/*
* For some reason the interface we used initially
* to send segments changed to another or lowered
* its MTU.
* If TSO was active we either got an interface
* without TSO capabilits or TSO was turned off.
* If we obtained mtu from ip_output() then update
* it and try again.
*/
if (tso)
tp->t_flags &= ~TF_TSO;
if (mtu != 0) {
tcp_mss_update(tp, -1, mtu, NULL, NULL);
goto again;
}
return (error);
case EHOSTDOWN:
case EHOSTUNREACH:
case ENETDOWN:
case ENETUNREACH:
if (TCPS_HAVERCVDSYN(tp->t_state)) {
tp->t_softerror = error;
return (0);
}
/* FALLTHROUGH */
default:
return (error);
}
}
TCPSTAT_INC(tcps_sndtotal);
/*
* Data sent (as far as we can tell).
* If this advertises a larger window than any other segment,
* then remember the size of the advertised window.
* Any pending ACK has now been sent.
*/
if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
tp->rcv_adv = tp->rcv_nxt + recwin;
tp->last_ack_sent = tp->rcv_nxt;
tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
if (tcp_timer_active(tp, TT_DELACK))
tcp_timer_activate(tp, TT_DELACK, 0);
#if 0
/*
* This completely breaks TCP if newreno is turned on. What happens
* is that if delayed-acks are turned on on the receiver, this code
* on the transmitter effectively destroys the TCP window, forcing
* it to four packets (1.5Kx4 = 6K window).
*/
if (sendalot && --maxburst)
goto again;
#endif
if (sendalot)
goto again;
return (0);
}
void
tcp_setpersist(struct tcpcb *tp)
{
int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
int tt;
int maxunacktime;
tp->t_flags &= ~TF_PREVVALID;
if (tcp_timer_active(tp, TT_REXMT))
panic("tcp_setpersist: retransmit pending");
/*
* If the state is already closed, don't bother.
*/
if (tp->t_state == TCPS_CLOSED)
return;
/*
* Start/restart persistence timer.
*/
TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
tcp_persmin, tcp_persmax);
if (TP_MAXUNACKTIME(tp) && tp->t_acktime) {
maxunacktime = tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks;
if (maxunacktime < 1)
maxunacktime = 1;
if (maxunacktime < tt)
tt = maxunacktime;
}
tcp_timer_activate(tp, TT_PERSIST, tt);
if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
tp->t_rxtshift++;
}
/*
* Insert TCP options according to the supplied parameters to the place
* optp in a consistent way. Can handle unaligned destinations.
*
* The order of the option processing is crucial for optimal packing and
* alignment for the scarce option space.
*
* The optimal order for a SYN/SYN-ACK segment is:
* MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
* Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
*
* The SACK options should be last. SACK blocks consume 8*n+2 bytes.
* So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
* At minimum we need 10 bytes (to generate 1 SACK block). If both
* TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
* we only have 10 bytes for SACK options (40 - (12 + 18)).
*/
int
tcp_addoptions(struct tcpopt *to, u_char *optp)
{
u_int32_t mask, optlen = 0;
for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
if ((to->to_flags & mask) != mask)
continue;
if (optlen == TCP_MAXOLEN)
break;
switch (to->to_flags & mask) {
case TOF_MSS:
while (optlen % 4) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
continue;
optlen += TCPOLEN_MAXSEG;
*optp++ = TCPOPT_MAXSEG;
*optp++ = TCPOLEN_MAXSEG;
to->to_mss = htons(to->to_mss);
bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
optp += sizeof(to->to_mss);
break;
case TOF_SCALE:
while (!optlen || optlen % 2 != 1) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
continue;
optlen += TCPOLEN_WINDOW;
*optp++ = TCPOPT_WINDOW;
*optp++ = TCPOLEN_WINDOW;
*optp++ = to->to_wscale;
break;
case TOF_SACKPERM:
while (optlen % 2) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
continue;
optlen += TCPOLEN_SACK_PERMITTED;
*optp++ = TCPOPT_SACK_PERMITTED;
*optp++ = TCPOLEN_SACK_PERMITTED;
break;
case TOF_TS:
while (!optlen || optlen % 4 != 2) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
continue;
optlen += TCPOLEN_TIMESTAMP;
*optp++ = TCPOPT_TIMESTAMP;
*optp++ = TCPOLEN_TIMESTAMP;
to->to_tsval = htonl(to->to_tsval);
to->to_tsecr = htonl(to->to_tsecr);
bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
optp += sizeof(to->to_tsval);
bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
optp += sizeof(to->to_tsecr);
break;
case TOF_SIGNATURE:
{
int siglen = TCPOLEN_SIGNATURE - 2;
while (!optlen || optlen % 4 != 2) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
to->to_flags &= ~TOF_SIGNATURE;
continue;
}
optlen += TCPOLEN_SIGNATURE;
*optp++ = TCPOPT_SIGNATURE;
*optp++ = TCPOLEN_SIGNATURE;
to->to_signature = optp;
while (siglen--)
*optp++ = 0;
break;
}
case TOF_SACK:
{
int sackblks = 0;
struct sackblk *sack = (struct sackblk *)to->to_sacks;
tcp_seq sack_seq;
while (!optlen || optlen % 4 != 2) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
continue;
optlen += TCPOLEN_SACKHDR;
*optp++ = TCPOPT_SACK;
sackblks = min(to->to_nsacks,
(TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
*optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
while (sackblks--) {
sack_seq = htonl(sack->start);
bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
optp += sizeof(sack_seq);
sack_seq = htonl(sack->end);
bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
optp += sizeof(sack_seq);
optlen += TCPOLEN_SACK;
sack++;
}
TCPSTAT_INC(tcps_sack_send_blocks);
break;
}
case TOF_FASTOPEN:
{
int total_len;
/* XXX is there any point to aligning this option? */
total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
if (TCP_MAXOLEN - optlen < total_len) {
to->to_flags &= ~TOF_FASTOPEN;
continue;
}
*optp++ = TCPOPT_FAST_OPEN;
*optp++ = total_len;
if (to->to_tfo_len > 0) {
bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
optp += to->to_tfo_len;
}
optlen += total_len;
break;
}
default:
panic("%s: unknown TCP option type", __func__);
break;
}
}
/* Terminate and pad TCP options to a 4 byte boundary. */
if (optlen % 4) {
optlen += TCPOLEN_EOL;
*optp++ = TCPOPT_EOL;
}
/*
* According to RFC 793 (STD0007):
* "The content of the header beyond the End-of-Option option
* must be header padding (i.e., zero)."
* and later: "The padding is composed of zeros."
*/
while (optlen % 4) {
optlen += TCPOLEN_PAD;
*optp++ = TCPOPT_PAD;
}
KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
return (optlen);
}
/*
* This is a copy of m_copym(), taking the TSO segment size/limit
* constraints into account, and advancing the sndptr as it goes.
*/
struct mbuf *
tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
{
#ifdef KERN_TLS
struct ktls_session *tls, *ntls;
struct mbuf *start __diagused;
#endif
struct mbuf *n, **np;
struct mbuf *top;
int32_t off = off0;
int32_t len = *plen;
int32_t fragsize;
int32_t len_cp = 0;
int32_t *pkthdrlen;
uint32_t mlen, frags;
bool copyhdr;
KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
if (off == 0 && m->m_flags & M_PKTHDR)
copyhdr = true;
else
copyhdr = false;
while (off > 0) {
KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
if (off < m->m_len)
break;
off -= m->m_len;
if ((sb) && (m == sb->sb_sndptr)) {
sb->sb_sndptroff += m->m_len;
sb->sb_sndptr = m->m_next;
}
m = m->m_next;
}
np = &top;
top = NULL;
pkthdrlen = NULL;
#ifdef KERN_TLS
if (hw_tls && (m->m_flags & M_EXTPG))
tls = m->m_epg_tls;
else
tls = NULL;
start = m;
#endif
while (len > 0) {
if (m == NULL) {
KASSERT(len == M_COPYALL,
("tcp_m_copym, length > size of mbuf chain"));
*plen = len_cp;
if (pkthdrlen != NULL)
*pkthdrlen = len_cp;
break;
}
#ifdef KERN_TLS
if (hw_tls) {
if (m->m_flags & M_EXTPG)
ntls = m->m_epg_tls;
else
ntls = NULL;
/*
* Avoid mixing TLS records with handshake
* data or TLS records from different
* sessions.
*/
if (tls != ntls) {
MPASS(m != start);
*plen = len_cp;
if (pkthdrlen != NULL)
*pkthdrlen = len_cp;
break;
}
}
#endif
mlen = min(len, m->m_len - off);
if (seglimit) {
/*
* For M_EXTPG mbufs, add 3 segments
* + 1 in case we are crossing page boundaries
* + 2 in case the TLS hdr/trailer are used
* It is cheaper to just add the segments
* than it is to take the cache miss to look
* at the mbuf ext_pgs state in detail.
*/
if (m->m_flags & M_EXTPG) {
fragsize = min(segsize, PAGE_SIZE);
frags = 3;
} else {
fragsize = segsize;
frags = 0;
}
/* Break if we really can't fit anymore. */
if ((frags + 1) >= seglimit) {
*plen = len_cp;
if (pkthdrlen != NULL)
*pkthdrlen = len_cp;
break;
}
/*
* Reduce size if you can't copy the whole
* mbuf. If we can't copy the whole mbuf, also
* adjust len so the loop will end after this
* mbuf.
*/
if ((frags + howmany(mlen, fragsize)) >= seglimit) {
mlen = (seglimit - frags - 1) * fragsize;
len = mlen;
*plen = len_cp + len;
if (pkthdrlen != NULL)
*pkthdrlen = *plen;
}
frags += howmany(mlen, fragsize);
if (frags == 0)
frags++;
seglimit -= frags;
KASSERT(seglimit > 0,
("%s: seglimit went too low", __func__));
}
if (copyhdr)
n = m_gethdr(M_NOWAIT, m->m_type);
else
n = m_get(M_NOWAIT, m->m_type);
*np = n;
if (n == NULL)
goto nospace;
if (copyhdr) {
if (!m_dup_pkthdr(n, m, M_NOWAIT))
goto nospace;
if (len == M_COPYALL)
n->m_pkthdr.len -= off0;
else
n->m_pkthdr.len = len;
pkthdrlen = &n->m_pkthdr.len;
copyhdr = false;
}
n->m_len = mlen;
len_cp += n->m_len;
if (m->m_flags & (M_EXT|M_EXTPG)) {
n->m_data = m->m_data + off;
mb_dupcl(n, m);
} else
bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
(u_int)n->m_len);
if (sb && (sb->sb_sndptr == m) &&
((n->m_len + off) >= m->m_len) && m->m_next) {
sb->sb_sndptroff += m->m_len;
sb->sb_sndptr = m->m_next;
}
off = 0;
if (len != M_COPYALL) {
len -= n->m_len;
}
m = m->m_next;
np = &n->m_next;
}
return (top);
nospace:
m_freem(top);
return (NULL);
}
void
tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
{
/*
* Automatic sizing of send socket buffer. Often the send buffer
* size is not optimally adjusted to the actual network conditions
* at hand (delay bandwidth product). Setting the buffer size too
* small limits throughput on links with high bandwidth and high
* delay (eg. trans-continental/oceanic links). Setting the
* buffer size too big consumes too much real kernel memory,
* especially with many connections on busy servers.
*
* The criteria to step up the send buffer one notch are:
* 1. receive window of remote host is larger than send buffer
* (with a fudge factor of 5/4th);
* 2. send buffer is filled to 7/8th with data (so we actually
* have data to make use of it);
* 3. send buffer fill has not hit maximal automatic size;
* 4. our send window (slow start and cogestion controlled) is
* larger than sent but unacknowledged data in send buffer.
*
* The remote host receive window scaling factor may limit the
* growing of the send buffer before it reaches its allowed
* maximum.
*
* It scales directly with slow start or congestion window
* and does at most one step per received ACK. This fast
* scaling has the drawback of growing the send buffer beyond
* what is strictly necessary to make full use of a given
* delay*bandwidth product. However testing has shown this not
* to be much of an problem. At worst we are trading wasting
* of available bandwidth (the non-use of it) for wasting some
* socket buffer memory.
*
* TODO: Shrink send buffer during idle periods together
* with congestion window. Requires another timer. Has to
* wait for upcoming tcp timer rewrite.
*
* XXXGL: should there be used sbused() or sbavail()?
*/
if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
int lowat;
lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
sbused(&so->so_snd) >=
(so->so_snd.sb_hiwat / 8 * 7) - lowat &&
sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
sendwin >= (sbused(&so->so_snd) -
(tp->snd_nxt - tp->snd_una))) {
if (!sbreserve_locked(so, SO_SND,
min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
V_tcp_autosndbuf_max), curthread))
so->so_snd.sb_flags &= ~SB_AUTOSIZE;
}
}
}
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