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freebsd-dev/sys/netinet/tcp_output.c
Bjoern A. Zeeb 413deb1262 Padding after EOL option must be zeros according to RFC793 but 
the NOPs used are 0x01.
While we could simply pad with EOLs (which are 0x00), rather use an
explicit 0x00 constant there to not confuse poeple with 'EOL padding'.
Put in a comment saying just that.

Problem discussed on:	src-committers with andre, silby, dwhite as
			follow up to the rev. 1.161 commit of tcp_var.h.
MFC after:		11 days
2008-03-09 13:26:50 +00:00

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/*-
* 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.
* 4. 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_mac.h"
#include "opt_tcpdebug.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/domain.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mbuf.h>
#include <sys/mutex.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <net/route.h>
#include <netinet/in.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_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif
#ifdef IPSEC
#include <netipsec/ipsec.h>
#endif /*IPSEC*/
#include <machine/in_cksum.h>
#include <security/mac/mac_framework.h>
#ifdef notyet
extern struct mbuf *m_copypack();
#endif
int path_mtu_discovery = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
&path_mtu_discovery, 1, "Enable Path MTU Discovery");
int ss_fltsz = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
&ss_fltsz, 1, "Slow start flight size");
int ss_fltsz_local = 4;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
&ss_fltsz_local, 1, "Slow start flight size for local networks");
int tcp_do_newreno = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW,
&tcp_do_newreno, 0, "Enable NewReno Algorithms");
int tcp_do_tso = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
&tcp_do_tso, 0, "Enable TCP Segmentation Offload");
int tcp_do_autosndbuf = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
&tcp_do_autosndbuf, 0, "Enable automatic send buffer sizing");
int tcp_autosndbuf_inc = 8*1024;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
&tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer");
int tcp_autosndbuf_max = 256*1024;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
&tcp_autosndbuf_max, 0, "Max size of automatic send buffer");
/*
* Tcp output routine: figure out what should be sent and send it.
*/
int
tcp_output(struct tcpcb *tp)
{
struct socket *so = tp->t_inpcb->inp_socket;
long len, recwin, sendwin;
int off, flags, error;
struct mbuf *m;
struct ip *ip = NULL;
struct ipovly *ipov = NULL;
struct tcphdr *th;
u_char opt[TCP_MAXOLEN];
unsigned ipoptlen, optlen, hdrlen;
#ifdef IPSEC
unsigned ipsec_optlen = 0;
#endif
int idle, sendalot;
int sack_rxmit, sack_bytes_rxmt;
struct sackhole *p;
int tso = 0;
struct tcpopt to;
#if 0
int maxburst = TCP_MAXBURST;
#endif
#ifdef INET6
struct ip6_hdr *ip6 = NULL;
int isipv6;
isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
#endif
INP_LOCK_ASSERT(tp->t_inpcb);
/*
* 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) {
/*
* We have been idle for "a while" and no acks are
* expected to clock out any data we send --
* slow start to get ack "clock" running again.
*
* Set the slow-start flight size depending on whether
* this is a local network or not.
*/
int ss = ss_fltsz;
#ifdef INET6
if (isipv6) {
if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
ss = ss_fltsz_local;
} else
#endif /* INET6 */
if (in_localaddr(tp->t_inpcb->inp_faddr))
ss = ss_fltsz_local;
tp->snd_cwnd = tp->t_maxseg * ss;
}
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;
off = tp->snd_nxt - tp->snd_una;
sendwin = min(tp->snd_wnd, tp->snd_cwnd);
sendwin = min(sendwin, tp->snd_bwnd);
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) &&
(p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
long cwin;
cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
if (cwin < 0)
cwin = 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 = ((long)ulmin(cwin,
tp->snd_recover - p->rxmit));
} else
len = ((long)ulmin(cwin, p->end - p->rxmit));
off = p->rxmit - tp->snd_una;
KASSERT(off >= 0,("%s: sack block to the left of una : %d",
__func__, off));
if (len > 0) {
sack_rxmit = 1;
sendalot = 1;
tcpstat.tcps_sack_rexmits++;
tcpstat.tcps_sack_rexmit_bytes +=
min(len, tp->t_maxseg);
}
}
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 < so->so_snd.sb_cc)
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 = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
else {
long cwin;
/*
* We are inside of a SACK recovery episode and are
* sending new data, having retransmitted all the
* data possible in the scoreboard.
*/
len = ((long)ulmin(so->so_snd.sb_cc, 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 -
(tp->snd_nxt - tp->sack_newdata) -
sack_bytes_rxmt;
if (cwin < 0)
cwin = 0;
len = lmin(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;
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;
}
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.
*/
len = 0;
if (sendwin == 0) {
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: len < 0", __func__));
/*
* 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*bandwith product. However testing has shown this not
* to be much of an problem. At worst we are trading wasting
* of available bandwith (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.
*/
if (tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
so->so_snd.sb_cc < tcp_autosndbuf_max &&
sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
if (!sbreserve_locked(&so->so_snd,
min(so->so_snd.sb_hiwat + tcp_autosndbuf_inc,
tcp_autosndbuf_max), so, curthread))
so->so_snd.sb_flags &= ~SB_AUTOSIZE;
}
}
/*
* Truncate to the maximum segment length or enable TCP Segmentation
* Offloading (if supported by hardware) and ensure that FIN is removed
* if the length no longer contains the last data byte.
*
* 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.
*
* The length of TSO bursts is limited to TCP_MAXWIN. That limit and
* removal of FIN (if not already catched here) are handled later after
* the exact length of the TCP options are known.
*/
#ifdef IPSEC
/*
* Pre-calculate here as we save another lookup into the darknesses
* of IPsec that way and can actually decide if TSO is ok.
*/
ipsec_optlen = ipsec_hdrsiz_tcp(tp);
#endif
if (len > tp->t_maxseg) {
if ((tp->t_flags & TF_TSO) && tcp_do_tso &&
((tp->t_flags & TF_SIGNATURE) == 0) &&
tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
tp->t_inpcb->inp_options == NULL &&
tp->t_inpcb->in6p_options == NULL
#ifdef IPSEC
&& ipsec_optlen == 0
#endif
) {
tso = 1;
} else {
len = tp->t_maxseg;
sendalot = 1;
tso = 0;
}
}
if (sack_rxmit) {
if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
flags &= ~TH_FIN;
} else {
if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
flags &= ~TH_FIN;
}
recwin = sbspace(&so->so_rcv);
/*
* 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;
/*
* 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)) &&
len + off >= so->so_snd.sb_cc &&
(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;
}
/*
* Compare available window to amount of window
* known to peer (as advertised window less
* next expected input). If the difference is at least two
* max size segments, or at least 50% of the maximum possible
* window, then want to send a window update to peer.
* Skip this if the connection is in T/TCP half-open state.
* Don't send pure window updates when the peer has closed
* the connection and won't ever send more data.
*/
if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
!TCPS_HAVERCVDFIN(tp->t_state)) {
/*
* "adv" is the amount we can increase the window,
* taking into account that we are limited by
* TCP_MAXWIN << tp->rcv_scale.
*/
long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
(tp->rcv_adv - tp->rcv_nxt);
if (adv >= (long) (2 * tp->t_maxseg))
goto send;
if (2 * adv >= (long) so->so_rcv.sb_hiwat)
goto send;
}
/*
* 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->t_rxtcur);
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 (so->so_snd.sb_cc && !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);
/*
* 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);
/*
* 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.
*/
if ((tp->t_flags & TF_NOOPT) == 0) {
to.to_flags = 0;
/* Maximum segment size. */
if (flags & TH_SYN) {
tp->snd_nxt = tp->iss;
to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
to.to_flags |= TOF_MSS;
}
/* 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))) {
to.to_tsval = ticks + tp->ts_offset;
to.to_tsecr = tp->ts_recent;
to.to_flags |= TOF_TS;
/* Set receive buffer autosizing timestamp. */
if (tp->rfbuf_ts == 0 &&
(so->so_rcv.sb_flags & SB_AUTOSIZE))
tp->rfbuf_ts = ticks;
}
/* 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->t_flags & TF_SACK_PERMIT) &&
tp->rcv_numsacks > 0) {
to.to_flags |= TOF_SACK;
to.to_nsacks = tp->rcv_numsacks;
to.to_sacks = (u_char *)tp->sackblks;
}
}
#ifdef TCP_SIGNATURE
/* TCP-MD5 (RFC2385). */
#ifdef INET6
if (!isipv6 && (tp->t_flags & TF_SIGNATURE))
#else
if (tp->t_flags & TF_SIGNATURE)
#endif /* INET6 */
to.to_flags |= TOF_SIGNATURE;
#endif /* TCP_SIGNATURE */
/* Processing the options. */
hdrlen += optlen = tcp_addoptions(&to, opt);
}
#ifdef INET6
if (isipv6)
ipoptlen = ip6_optlen(tp->t_inpcb);
else
#endif
if (tp->t_inpcb->inp_options)
ipoptlen = tp->t_inpcb->inp_options->m_len -
offsetof(struct ipoption, ipopt_list);
else
ipoptlen = 0;
#ifdef IPSEC
ipoptlen += ipsec_optlen;
#endif
/*
* Adjust data length if insertion of options will
* bump the packet length beyond the t_maxopd length.
* Clear the FIN bit because we cut off the tail of
* the segment.
*
* When doing TSO limit a burst to TCP_MAXWIN minus the
* IP, TCP and Options length to keep ip->ip_len from
* overflowing. Prevent the last segment from being
* fractional thus making them all equal sized and set
* the flag to continue sending. TSO is disabled when
* IP options or IPSEC are present.
*/
if (len + optlen + ipoptlen > tp->t_maxopd) {
flags &= ~TH_FIN;
if (tso) {
if (len > TCP_MAXWIN - hdrlen - optlen) {
len = TCP_MAXWIN - hdrlen - optlen;
len = len - (len % (tp->t_maxopd - optlen));
sendalot = 1;
} else if (tp->t_flags & TF_NEEDFIN)
sendalot = 1;
} else {
len = tp->t_maxopd - optlen - ipoptlen;
sendalot = 1;
}
}
/*#ifdef DIAGNOSTIC*/
#ifdef INET6
if (max_linkhdr + hdrlen > MCLBYTES)
#else
if (max_linkhdr + hdrlen > MHLEN)
#endif
panic("tcphdr too big");
/*#endif*/
/*
* 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;
u_int moff;
if ((tp->t_flags & TF_FORCEDATA) && len == 1)
tcpstat.tcps_sndprobe++;
else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
tcpstat.tcps_sndrexmitpack++;
tcpstat.tcps_sndrexmitbyte += len;
} else {
tcpstat.tcps_sndpack++;
tcpstat.tcps_sndbyte += len;
}
#ifdef notyet
if ((m = m_copypack(so->so_snd.sb_mb, off,
(int)len, max_linkhdr + hdrlen)) == 0) {
SOCKBUF_UNLOCK(&so->so_snd);
error = ENOBUFS;
goto out;
}
/*
* m_copypack left space for our hdr; use it.
*/
m->m_len += hdrlen;
m->m_data -= hdrlen;
#else
MGETHDR(m, M_DONTWAIT, MT_DATA);
if (m == NULL) {
SOCKBUF_UNLOCK(&so->so_snd);
error = ENOBUFS;
goto out;
}
#ifdef INET6
if (MHLEN < hdrlen + max_linkhdr) {
MCLGET(m, M_DONTWAIT);
if ((m->m_flags & M_EXT) == 0) {
SOCKBUF_UNLOCK(&so->so_snd);
m_freem(m);
error = ENOBUFS;
goto out;
}
}
#endif
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(&so->so_snd, off, len, &moff);
if (len <= MHLEN - hdrlen - max_linkhdr) {
m_copydata(mb, moff, (int)len,
mtod(m, caddr_t) + hdrlen);
m->m_len += len;
} else {
m->m_next = m_copy(mb, moff, (int)len);
if (m->m_next == NULL) {
SOCKBUF_UNLOCK(&so->so_snd);
(void) m_free(m);
error = ENOBUFS;
goto out;
}
}
#endif
/*
* 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 (off + len == so->so_snd.sb_cc)
flags |= TH_PUSH;
SOCKBUF_UNLOCK(&so->so_snd);
} else {
SOCKBUF_UNLOCK(&so->so_snd);
if (tp->t_flags & TF_ACKNOW)
tcpstat.tcps_sndacks++;
else if (flags & (TH_SYN|TH_FIN|TH_RST))
tcpstat.tcps_sndctrl++;
else if (SEQ_GT(tp->snd_up, tp->snd_una))
tcpstat.tcps_sndurg++;
else
tcpstat.tcps_sndwinup++;
MGETHDR(m, M_DONTWAIT, MT_DATA);
if (m == NULL) {
error = ENOBUFS;
goto out;
}
#ifdef INET6
if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
MHLEN >= hdrlen) {
MH_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(tp->t_inpcb, m);
#endif
#ifdef INET6
if (isipv6) {
ip6 = mtod(m, struct ip6_hdr *);
th = (struct tcphdr *)(ip6 + 1);
tcpip_fillheaders(tp->t_inpcb, ip6, th);
} else
#endif /* INET6 */
{
ip = mtod(m, struct ip *);
ipov = (struct ipovly *)ip;
th = (struct tcphdr *)(ip + 1);
tcpip_fillheaders(tp->t_inpcb, 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 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;
tp->sackhint.sack_bytes_rexmit += len;
}
th->th_ack = htonl(tp->rcv_nxt);
if (optlen) {
bcopy(opt, th + 1, optlen);
th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
}
th->th_flags = flags;
/*
* Calculate receive window. Don't shrink window,
* but avoid silly window syndrome.
*/
if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
recwin < (long)tp->t_maxseg)
recwin = 0;
if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
recwin = (long)TCP_MAXWIN << tp->rcv_scale;
/*
* 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
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 then can be buffered prior to transmitting on
* the connection.
*/
if (recwin == 0)
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 */
#ifdef TCP_SIGNATURE
#ifdef INET6
if (!isipv6)
#endif
if (tp->t_flags & TF_SIGNATURE) {
int sigoff = to.to_signature - opt;
tcp_signature_compute(m, sizeof(struct ip), len, optlen,
(u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
}
#endif
/*
* Put TCP length in extended header, and then
* checksum extended header and data.
*/
m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
#ifdef INET6
if (isipv6)
/*
* ip6_plen is not need to be filled now, and will be filled
* in ip6_output.
*/
th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
sizeof(struct tcphdr) + optlen + len);
else
#endif /* INET6 */
{
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));
}
/*
* Enable TSO and specify the size of the segments.
* The TCP pseudo header checksum is always provided.
* XXX: Fixme: This is currently not the case for IPv6.
*/
if (tso) {
m->m_pkthdr.csum_flags = CSUM_TSO;
m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
}
/*
* 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)) {
tp->snd_max = tp->snd_nxt;
/*
* Time this transmission if not a retransmission and
* not currently timing anything.
*/
if (tp->t_rtttime == 0) {
tp->t_rtttime = ticks;
tp->t_rtseq = startseq;
tcpstat.tcps_segstimed++;
}
}
/*
* 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->t_rxtcur);
}
} 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 + len;
}
#ifdef TCPDEBUG
/*
* Trace.
*/
if (so->so_options & SO_DEBUG) {
u_short save = 0;
#ifdef INET6
if (!isipv6)
#endif
{
save = ipov->ih_len;
ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
}
tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
#ifdef INET6
if (!isipv6)
#endif
ipov->ih_len = save;
}
#endif
/*
* 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 cksum calcuration,
* 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(tp->t_inpcb, NULL);
/* TODO: IPv6 IP6TOS_ECT bit on */
error = ip6_output(m,
tp->t_inpcb->in6p_outputopts, NULL,
((so->so_options & SO_DONTROUTE) ?
IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb);
} else
#endif /* INET6 */
{
ip->ip_len = m->m_pkthdr.len;
#ifdef INET6
if (INP_CHECK_SOCKAF(so, AF_INET6))
ip->ip_ttl = in6_selecthlim(tp->t_inpcb, 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.
*/
if (path_mtu_discovery)
ip->ip_off |= IP_DF;
error = ip_output(m, tp->t_inpcb->inp_options, NULL,
((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
tp->t_inpcb);
}
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"));
} else
tp->snd_nxt -= len;
}
out:
SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
switch (error) {
case EPERM:
tp->t_softerror = error;
return (error);
case ENOBUFS:
if (!tcp_timer_active(tp, TT_REXMT) &&
!tcp_timer_active(tp, TT_PERSIST))
tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
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.
*
* tcp_mtudisc() will find out the new MTU and as
* its last action, initiate retransmission, so it
* is important to not do so here.
*
* If TSO was active we either got an interface
* without TSO capabilits or TSO was turned off.
* Disable it for this connection as too and
* immediatly retry with MSS sized segments generated
* by this function.
*/
if (tso)
tp->t_flags &= ~TF_TSO;
tcp_mtudisc(tp->t_inpcb, 0);
return (0);
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.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 (recwin > 0 && 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 && (!tcp_do_newreno || --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;
if (tcp_timer_active(tp, TT_REXMT))
panic("tcp_setpersist: retransmit pending");
/*
* Start/restart persistance timer.
*/
TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
TCPTV_PERSMIN, TCPTV_PERSMAX);
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_int mask, optlen = 0;
for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
if ((to->to_flags & mask) != mask)
continue;
switch (to->to_flags & mask) {
case TOF_MSS:
while (optlen % 4) {
optlen += TCPOLEN_NOP;
*optp++ = TCPOPT_NOP;
}
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;
}
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;
}
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;
}
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)
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 < 2 + 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.tcps_sack_send_blocks++;
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 EOLs are zeros use an explicit 0x00 here to not confuse
* people with padding of EOLs.
*/
while (optlen % 4) {
optlen += 1;
*optp++ = 0x00;
}
KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
return (optlen);
}
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