third_party/tcplp/bsdtcp/tcp_timer.c - third_party/openthread - Git at Google

 /*-
  * Copyright (c) 1982, 1986, 1993
  *	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_timer.h	8.1 (Berkeley) 6/10/93
  * $FreeBSD$
  */

 #include <errno.h>
 #include <stdio.h>

 #include "../tcplp.h"
 #include "../lib/lbuf.h"
 #include "tcp_fsm.h"
 #include "tcp_timer.h"
 #include "tcp_var.h"

 #include "tcp_const.h"

 /*
  * samkumar: These options only matter if we do blackhole detection, which we
  * are not doing in TCPlp.
  */
 #if 0
 int V_tcp_pmtud_blackhole_detect = 0;
 int V_tcp_pmtud_blackhole_failed = 0;
 int V_tcp_pmtud_blackhole_activated = 0;
 int V_tcp_pmtud_blackhole_activated_min_mss = 0;
 #endif

 /*
  * TCP timer processing.
  */

 /*
  * samkumar: I changed these functions to accept "struct tcpcb* tp" their
  * argument instead of "void *xtp". This is possible since we're no longer
  * relying on FreeBSD's callout subsystem in TCPlp. I also changed them to
  * return 1 if the connection is dropped, or 0 otherwise.
  */

 int
 tcp_timer_delack(struct tcpcb* tp)
 {
 	/* samkumar: I added this, to replace the code I removed below. */
 	KASSERT(tpistimeractive(tp, TT_DELACK), ("Delack timer running, but unmarked"));
 	tpcleartimeractive(tp, TT_DELACK);

 	/*
 	 * samkumar: There used to be code here to properly handle the callout,
 	 * including edge cases (return early if the callout was reset after this
 	 * function was scheduled for execution, deactivate the callout, return
 	 * early if the INP_DROPPED flag is set on the inpcb, and assert that the
 	 * tp->t_timers state is correct).
 	 *
 	 * I also removed stats collection, locking, and vnet, throughout the code.
 	 */
 	tp->t_flags |= TF_ACKNOW;
 	(void) tcp_output(tp);
 	return 0;
 }

 int
 tcp_timer_keep(struct tcpcb* tp)
 {
 	uint32_t ticks = tcplp_sys_get_ticks();
 	struct tcptemp t_template;

 	/* samkumar: I added this, to replace the code I removed below. */
 	KASSERT(tpistimeractive(tp, TT_KEEP), ("Keep timer running, but unmarked"));
 	tpcleartimeractive(tp, TT_KEEP);

 	/*
 	 * samkumar: There used to be code here to properly handle the callout,
 	 * including edge cases (return early if the callout was reset after this
 	 * function was scheduled for execution, deactivate the callout, return
 	 * early if the INP_DROPPED flag is set on the inpcb, and assert that the
 	 * tp->t_timers state is correct).
 	 *
 	 * I also removed stats collection, locking, and vnet, throughout the code.
 	 * I commented out checks on socket options (since we don't support those).
 	 *
 	 * I also allocate t_template on the stack instead of allocating it
 	 * dynamically, on the heap.
 	 */

 	/*
 	 * Keep-alive timer went off; send something
 	 * or drop connection if idle for too long.
 	 */
 	if (tp->t_state < TCPS_ESTABLISHED)
 		goto dropit;
 	if ((always_keepalive/* || inp->inp_socket->so_options & SO_KEEPALIVE*/) &&
 	    tp->t_state <= TCPS_CLOSING) {
 		if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
 			goto dropit;
 		/*
 		 * Send a packet designed to force a response
 		 * if the peer is up and reachable:
 		 * either an ACK if the connection is still alive,
 		 * or an RST if the peer has closed the connection
 		 * due to timeout or reboot.
 		 * Using sequence number tp->snd_una-1
 		 * causes the transmitted zero-length segment
 		 * to lie outside the receive window;
 		 * by the protocol spec, this requires the
 		 * correspondent TCP to respond.
 		 */
 		tcpip_maketemplate(tp, &t_template);
 		/*
 		 * samkumar: I removed checks to make sure t_template was successfully
 		 * allocated and then free it as appropriate. This is not necessary
 		 * because I rewrote this part of the code to allocate t_template on
 		 * the stack.
 		 */
 		tcp_respond(tp, tp->instance, (struct ip6_hdr*) t_template.tt_ipgen,
 			    &t_template.tt_t,
 			    tp->rcv_nxt, tp->snd_una - 1, 0);
 		/*
 		 * samkumar: I replaced a call to callout_reset with the following
 		 * code, which resets the timer the TCPlp way.
 		 */
 		tpmarktimeractive(tp, TT_KEEP);
 		tcplp_sys_set_timer(tp, TT_KEEP, TP_KEEPINTVL(tp));
 	} else {
 		/*
 		 * samkumar: I replaced a call to callout_reset with the following
 		 * code, which resets the timer the TCPlp way.
 		 */
 		tpmarktimeractive(tp, TT_KEEP);
 		tcplp_sys_set_timer(tp, TT_KEEP, TP_KEEPIDLE(tp));
 	}

 	/*
 	 * samkumar: There used to be some code here and below the "dropit" label
 	 * that handled debug tracing/probes, vnet, and locking. I removed that
 	 * code.
 	 */
 	return 0;

 dropit:
 	tp = tcp_drop(tp, ETIMEDOUT);
 	(void) tp; /* samkumar: prevent a compiler warning */
 	return 1;
 }

 int
 tcp_timer_persist(struct tcpcb* tp)
 {
 	uint32_t ticks = tcplp_sys_get_ticks();
 	int dropped = 0;

 	/* samkumar: I added this, to replace the code I removed below. */
 	KASSERT(tpistimeractive(tp, TT_PERSIST), ("Persist timer running, but unmarked"));
 	tpcleartimeractive(tp, TT_PERSIST); // mark that this timer is no longer active

 	/*
 	 * samkumar: There used to be code here to properly handle the callout,
 	 * including edge cases (return early if the callout was reset after this
 	 * function was scheduled for execution, deactivate the callout, return
 	 * early if the INP_DROPPED flag is set on the inpcb, and assert that the
 	 * tp->t_timers state is correct).
 	 *
 	 * I also removed stats collection, locking, and vnet, throughout the code.
 	 * I commented out checks on socket options (since we don't support those).
 	 */

 	/*
 	 * Persistance timer into zero window.
 	 * Force a byte to be output, if possible.
 	 */
 	/*

 	 * Hack: if the peer is dead/unreachable, we do not
 	 * time out if the window is closed.  After a full
 	 * backoff, drop the connection if the idle time
 	 * (no responses to probes) reaches the maximum
 	 * backoff that we would use if retransmitting.
 	 */

 	if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 	    (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 	     ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 		tp = tcp_drop(tp, ETIMEDOUT);
 		dropped = 1;
 		goto out;
 	}

 	/*
 	 * If the user has closed the socket then drop a persisting
 	 * connection after a much reduced timeout.
 	 */
 	if (tp->t_state > TCPS_CLOSE_WAIT &&
 	    (ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
 		tp = tcp_drop(tp, ETIMEDOUT);
 		dropped = 1;
 		goto out;
 	}

 	tcp_setpersist(tp);
 	tp->t_flags |= TF_FORCEDATA;
 	tcplp_sys_log("Persist output: %zu bytes in sendbuf", lbuf_used_space(&tp->sendbuf));
 	(void) tcp_output(tp);
 	tp->t_flags &= ~TF_FORCEDATA;

 out:
 	/*
 	 * samkumar: There used to be some code here that handled debug
 	 * tracing/probes, vnet, and locking. I removed that code.
 	 */
 	(void) tp; /* samkumar: prevent a compiler warning */
 	return dropped;
 }

 int
 tcp_timer_2msl(struct tcpcb* tp)
 {
 	uint32_t ticks = tcplp_sys_get_ticks();
 	int dropped = 0;

 	/* samkumar: I added this, to replace the code I removed below. */
 	KASSERT(tpistimeractive(tp, TT_2MSL), ("2MSL timer running, but unmarked"));
 	tpcleartimeractive(tp, TT_2MSL);

 	/*
 	 * samkumar: There used to be code here to properly handle the callout,
 	 * including edge cases (return early if the callout was reset after this
 	 * function was scheduled for execution, deactivate the callout, return
 	 * early if the INP_DROPPED flag is set on the inpcb, and assert that the
 	 * tp->t_timers state is correct).
 	 *
 	 * I also removed stats collection, locking, and vnet, throughout the code.
 	 */

 	/*
 	 * 2 MSL timeout in shutdown went off.  If we're closed but
 	 * still waiting for peer to close and connection has been idle
 	 * too long delete connection control block.  Otherwise, check
 	 * again in a bit.
 	 *
 	 * If in TIME_WAIT state just ignore as this timeout is handled in
 	 * tcp_tw_2msl_scan().
 	 *
 	 * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 	 * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 	 * Ignore fact that there were recent incoming segments.
 	 */

 	/*
 	 * samkumar: The above comment about ignoring this timeout if we're in the
 	 * TIME_WAIT state no longer is true, since in TCPlp we changed how
 	 * TIME_WAIT is handled. In FreeBSD, this timer isn't used for sockets in
 	 * the TIME_WAIT state; instead the tcp_tw_2msl_scan method is called
 	 * periodically on the slow timer, and expired tcptw structs are closed and
 	 * freed. I changed it so that TIME-WAIT connections are still represented
 	 * as tcpcb's, not tcptw's, and to rely on this timer to close the
 	 * connection.
 	 *
 	 * Below, there used to be an if statement that checks the inpcb to tell
 	 * if we're in TIME-WAIT state, and return early if so. I've replaced this
 	 * with an if statement that checks the tcpcb if we're in the TIME-WAIT
 	 * state, and acts appropriately if so.
 	 */
 	if (tp->t_state == TCP6S_TIME_WAIT) {
 		tp = tcp_close(tp);
 		tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
 		dropped = 1;
 		return dropped;
 	}
 	/*
 	 * samkumar: This if statement also used to check that an inpcb is still
 	 * attached and also
 	 * (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE).
 	 * We replaced the check on that flag with a call to tpiscantrcv. We
 	 * haven't received a FIN, since we're in FIN-WAIT-2, so the only way it
 	 * would pass the check is if the user called shutdown(SHUT_RD)
 	 * or shutdown(SHUT_RDWR), which is impossible unless the host system
 	 * provides an API for that.
 	 */
 	if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 	    tpiscantrcv(tp)) {
 		tp = tcp_close(tp);
 		tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
 		dropped = 1;
 	} else {
 		if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp)) {
 			/*
 			 * samkumar: I replaced a call to callout_reset with the following
 			 * code, which resets the timer the TCPlp way.
 			 */
 			tpmarktimeractive(tp, TT_2MSL);
 			tcplp_sys_set_timer(tp, TT_2MSL, TP_KEEPINTVL(tp));
 		} else {
 			tp = tcp_close(tp);
 			tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
 			dropped = 1;
 		}
 	}
 	/*
 	 * samkumar: There used to be some code here that handled debug
 	 * tracing/probes, vnet, and locking. I removed that code.
 	 */
 	return dropped;
 }

 int
 tcp_timer_rexmt(struct tcpcb *tp)
 {
 	int rexmt;
 	uint32_t ticks = tcplp_sys_get_ticks();
 	int dropped = 0;

 	/* samkumar: I added this, to replace the code I removed below. */
 	KASSERT(tpistimeractive(tp, TT_REXMT), ("Rexmt timer running, but unmarked"));
 	tpcleartimeractive(tp, TT_REXMT);

 	/*
 	 * samkumar: There used to be code here to properly handle the callout,
 	 * including edge cases (return early if the callout was reset after this
 	 * function was scheduled for execution, deactivate the callout, return
 	 * early if the INP_DROPPED flag is set on the inpcb, and assert that the
 	 * tp->t_timers state is correct).
 	 *
 	 * I also removed stats collection, locking, and vnet, throughout the code.
 	 */

 	tcp_free_sackholes(tp);
 	/*
 	 * Retransmission timer went off.  Message has not
 	 * been acked within retransmit interval.  Back off
 	 * to a longer retransmit interval and retransmit one segment.
 	 */
 	tcplp_sys_log("rxtshift is %d", (int) tp->t_rxtshift);
 	if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 		tp->t_rxtshift = TCP_MAXRXTSHIFT;

 		tp = tcp_drop(tp, tp->t_softerror ?
 			      tp->t_softerror : ETIMEDOUT);
 		dropped = 1;
 		goto out;
 	}
 	if (tp->t_state == TCPS_SYN_SENT) {
 		/*
 		 * If the SYN was retransmitted, indicate CWND to be
 		 * limited to 1 segment in cc_conn_init().
 		 */
 		tp->snd_cwnd = 1;
 	} else if (tp->t_rxtshift == 1) {
 		/*
 		 * first retransmit; record ssthresh and cwnd so they can
 		 * be recovered if this turns out to be a "bad" retransmit.
 		 * A retransmit is considered "bad" if an ACK for this
 		 * segment is received within RTT/2 interval; the assumption
 		 * here is that the ACK was already in flight.  See
 		 * "On Estimating End-to-End Network Path Properties" by
 		 * Allman and Paxson for more details.
 		 */
 		tp->snd_cwnd_prev = tp->snd_cwnd;
 		tp->snd_ssthresh_prev = tp->snd_ssthresh;
 		tp->snd_recover_prev = tp->snd_recover;
 		if (IN_FASTRECOVERY(tp->t_flags))
 			tp->t_flags |= TF_WASFRECOVERY;
 		else
 			tp->t_flags &= ~TF_WASFRECOVERY;
 		if (IN_CONGRECOVERY(tp->t_flags))
 			tp->t_flags |= TF_WASCRECOVERY;
 		else
 			tp->t_flags &= ~TF_WASCRECOVERY;
 		tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 		tp->t_flags |= TF_PREVVALID;
 	} else
 		tp->t_flags &= ~TF_PREVVALID;
 	if (tp->t_state == TCPS_SYN_SENT)
 		rexmt = TCPTV_RTOBASE * tcp_syn_backoff[tp->t_rxtshift];
 	else
 		rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 	TCPT_RANGESET(tp->t_rxtcur, rexmt,
 		      tp->t_rttmin, TCPTV_REXMTMAX);

 	/*
 	 * samkumar: There used to be more than 100 lines of code here, which
 	 * implemented a feature called blackhole detection. The idea here is that
 	 * some routers may silently discard packets whose MTU is too large,
 	 * instead of fragmenting the packet or sending an ICMP packet to give
 	 * feedback to the host. Blackhole detection decreases the MTU in response
 	 * to packet loss in case the packets are being dropped by such a router.
 	 *
 	 * In TCPlp, we do not do blackhole detection because we use a small MTU
 	 * (hundreds of bytes) that is unlikely to be too large for intermediate
 	 * routers in the Internet. The edge low-power wireless network is
 	 * assumed to be engineered to handle 6LoWPAN correctly.
 	 */

 	/*
 	 * Disable RFC1323 and SACK if we haven't got any response to
 	 * our third SYN to work-around some broken terminal servers
 	 * (most of which have hopefully been retired) that have bad VJ
 	 * header compression code which trashes TCP segments containing
 	 * unknown-to-them TCP options.
 	 */
 	if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
 	    (tp->t_rxtshift == 3))
 		tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_SACK_PERMIT);
 	/*
 	 * If we backed off this far, our srtt estimate is probably bogus.
 	 * Clobber it so we'll take the next rtt measurement as our srtt;
 	 * move the current srtt into rttvar to keep the current
 	 * retransmit times until then.
 	 */
 	if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 		/*
 		 * samkumar: Here, there used to be a call to "in6_losing", used to
 		 * inform the lower layers about bad connectivity so it can search for
 		 * different routes. The call was wrapped in a check on the inpcb's
 		 * flags to check for IPv6 (which isn't relevant to us, since TCPlp
 		 * assumes IPv6).
 		 */
 		tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 		tp->t_srtt = 0;
 	}
 	tp->snd_nxt = tp->snd_una;
 	tp->snd_recover = tp->snd_max;
 	/*
 	 * Force a segment to be sent.
 	 */
 	tp->t_flags |= TF_ACKNOW;
 	/*
 	 * If timing a segment in this window, stop the timer.
 	 */
 	tp->t_rtttime = 0;

 	cc_cong_signal(tp, NULL, CC_RTO);

 	(void) tcp_output(tp);

 out:
 	/*
 	 * samkumar: There used to be some code here that handled debug
 	 * tracing/probes, vnet, and locking. I removed that code.
 	 */
 	(void) tp; /* samkumar: Prevent a compiler warning */
 	return dropped;
 }

 int
 tcp_timer_active(struct tcpcb *tp, uint32_t timer_type)
 {
 	return tpistimeractive(tp, timer_type);
 }

 void
 tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, uint32_t delta) {
 	if (delta) {
 		tpmarktimeractive(tp, timer_type);
 		if (tpistimeractive(tp, TT_REXMT) && tpistimeractive(tp, TT_PERSIST)) {
 			tcplp_sys_panic("TCP CRITICAL FAILURE: Retransmit and Persist timers are simultaneously running!");
 		}
 		tcplp_sys_set_timer(tp, timer_type, (uint32_t) delta);
 	} else {
 		tpcleartimeractive(tp, timer_type);
 		tcplp_sys_stop_timer(tp, timer_type);
 	}
 }

 void
 tcp_cancel_timers(struct tcpcb* tp) {
 	tpcleartimeractive(tp, TT_DELACK);
 	tcplp_sys_stop_timer(tp, TT_DELACK);
 	tpcleartimeractive(tp, TT_REXMT);
 	tcplp_sys_stop_timer(tp, TT_REXMT);
 	tpcleartimeractive(tp, TT_PERSIST);
 	tcplp_sys_stop_timer(tp, TT_PERSIST);
 	tpcleartimeractive(tp, TT_KEEP);
 	tcplp_sys_stop_timer(tp, TT_KEEP);
 	tpcleartimeractive(tp, TT_2MSL);
 	tcplp_sys_stop_timer(tp, TT_2MSL);
 }
	/*-
	* Copyright (c) 1982, 1986, 1993
	* 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_timer.h 8.1 (Berkeley) 6/10/93
	* $FreeBSD$
	*/

	#include <errno.h>
	#include <stdio.h>

	#include "../tcplp.h"
	#include "../lib/lbuf.h"
	#include "tcp_fsm.h"
	#include "tcp_timer.h"
	#include "tcp_var.h"

	#include "tcp_const.h"

	/*
	* samkumar: These options only matter if we do blackhole detection, which we
	* are not doing in TCPlp.
	*/
	#if 0
	int V_tcp_pmtud_blackhole_detect = 0;
	int V_tcp_pmtud_blackhole_failed = 0;
	int V_tcp_pmtud_blackhole_activated = 0;
	int V_tcp_pmtud_blackhole_activated_min_mss = 0;
	#endif

	/*
	* TCP timer processing.
	*/

	/*
	* samkumar: I changed these functions to accept "struct tcpcb* tp" their
	* argument instead of "void *xtp". This is possible since we're no longer
	* relying on FreeBSD's callout subsystem in TCPlp. I also changed them to
	* return 1 if the connection is dropped, or 0 otherwise.
	*/

	int
	tcp_timer_delack(struct tcpcb* tp)
	{
	/* samkumar: I added this, to replace the code I removed below. */
	KASSERT(tpistimeractive(tp, TT_DELACK), ("Delack timer running, but unmarked"));
	tpcleartimeractive(tp, TT_DELACK);

	/*
	* samkumar: There used to be code here to properly handle the callout,
	* including edge cases (return early if the callout was reset after this
	* function was scheduled for execution, deactivate the callout, return
	* early if the INP_DROPPED flag is set on the inpcb, and assert that the
	* tp->t_timers state is correct).
	*
	* I also removed stats collection, locking, and vnet, throughout the code.
	*/
	tp->t_flags \|= TF_ACKNOW;
	(void) tcp_output(tp);
	return 0;
	}

	int
	tcp_timer_keep(struct tcpcb* tp)
	{
	uint32_t ticks = tcplp_sys_get_ticks();
	struct tcptemp t_template;

	/* samkumar: I added this, to replace the code I removed below. */
	KASSERT(tpistimeractive(tp, TT_KEEP), ("Keep timer running, but unmarked"));
	tpcleartimeractive(tp, TT_KEEP);

	/*
	* samkumar: There used to be code here to properly handle the callout,
	* including edge cases (return early if the callout was reset after this
	* function was scheduled for execution, deactivate the callout, return
	* early if the INP_DROPPED flag is set on the inpcb, and assert that the
	* tp->t_timers state is correct).
	*
	* I also removed stats collection, locking, and vnet, throughout the code.
	* I commented out checks on socket options (since we don't support those).
	*
	* I also allocate t_template on the stack instead of allocating it
	* dynamically, on the heap.
	*/

	/*
	* Keep-alive timer went off; send something
	* or drop connection if idle for too long.
	*/
	if (tp->t_state < TCPS_ESTABLISHED)
	goto dropit;
	if ((always_keepalive/* \|\| inp->inp_socket->so_options & SO_KEEPALIVE*/) &&
	tp->t_state <= TCPS_CLOSING) {
	if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
	goto dropit;
	/*
	* Send a packet designed to force a response
	* if the peer is up and reachable:
	* either an ACK if the connection is still alive,
	* or an RST if the peer has closed the connection
	* due to timeout or reboot.
	* Using sequence number tp->snd_una-1
	* causes the transmitted zero-length segment
	* to lie outside the receive window;
	* by the protocol spec, this requires the
	* correspondent TCP to respond.
	*/
	tcpip_maketemplate(tp, &t_template);
	/*
	* samkumar: I removed checks to make sure t_template was successfully
	* allocated and then free it as appropriate. This is not necessary
	* because I rewrote this part of the code to allocate t_template on
	* the stack.
	*/
	tcp_respond(tp, tp->instance, (struct ip6_hdr*) t_template.tt_ipgen,
	&t_template.tt_t,
	tp->rcv_nxt, tp->snd_una - 1, 0);
	/*
	* samkumar: I replaced a call to callout_reset with the following
	* code, which resets the timer the TCPlp way.
	*/
	tpmarktimeractive(tp, TT_KEEP);
	tcplp_sys_set_timer(tp, TT_KEEP, TP_KEEPINTVL(tp));
	} else {
	/*
	* samkumar: I replaced a call to callout_reset with the following
	* code, which resets the timer the TCPlp way.
	*/
	tpmarktimeractive(tp, TT_KEEP);
	tcplp_sys_set_timer(tp, TT_KEEP, TP_KEEPIDLE(tp));
	}

	/*
	* samkumar: There used to be some code here and below the "dropit" label
	* that handled debug tracing/probes, vnet, and locking. I removed that
	* code.
	*/
	return 0;

	dropit:
	tp = tcp_drop(tp, ETIMEDOUT);
	(void) tp; /* samkumar: prevent a compiler warning */
	return 1;
	}

	int
	tcp_timer_persist(struct tcpcb* tp)
	{
	uint32_t ticks = tcplp_sys_get_ticks();
	int dropped = 0;

	/* samkumar: I added this, to replace the code I removed below. */
	KASSERT(tpistimeractive(tp, TT_PERSIST), ("Persist timer running, but unmarked"));
	tpcleartimeractive(tp, TT_PERSIST); // mark that this timer is no longer active

	/*
	* samkumar: There used to be code here to properly handle the callout,
	* including edge cases (return early if the callout was reset after this
	* function was scheduled for execution, deactivate the callout, return
	* early if the INP_DROPPED flag is set on the inpcb, and assert that the
	* tp->t_timers state is correct).
	*
	* I also removed stats collection, locking, and vnet, throughout the code.
	* I commented out checks on socket options (since we don't support those).
	*/

	/*
	* Persistance timer into zero window.
	* Force a byte to be output, if possible.
	*/
	/*

	* Hack: if the peer is dead/unreachable, we do not
	* time out if the window is closed. After a full
	* backoff, drop the connection if the idle time
	* (no responses to probes) reaches the maximum
	* backoff that we would use if retransmitting.
	*/

	if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
	(ticks - tp->t_rcvtime >= tcp_maxpersistidle \|\|
	ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
	tp = tcp_drop(tp, ETIMEDOUT);
	dropped = 1;
	goto out;
	}

	/*
	* If the user has closed the socket then drop a persisting
	* connection after a much reduced timeout.
	*/
	if (tp->t_state > TCPS_CLOSE_WAIT &&
	(ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
	tp = tcp_drop(tp, ETIMEDOUT);
	dropped = 1;
	goto out;
	}

	tcp_setpersist(tp);
	tp->t_flags \|= TF_FORCEDATA;
	tcplp_sys_log("Persist output: %zu bytes in sendbuf", lbuf_used_space(&tp->sendbuf));
	(void) tcp_output(tp);
	tp->t_flags &= ~TF_FORCEDATA;

	out:
	/*
	* samkumar: There used to be some code here that handled debug
	* tracing/probes, vnet, and locking. I removed that code.
	*/
	(void) tp; /* samkumar: prevent a compiler warning */
	return dropped;
	}

	int
	tcp_timer_2msl(struct tcpcb* tp)
	{
	uint32_t ticks = tcplp_sys_get_ticks();
	int dropped = 0;

	/* samkumar: I added this, to replace the code I removed below. */
	KASSERT(tpistimeractive(tp, TT_2MSL), ("2MSL timer running, but unmarked"));
	tpcleartimeractive(tp, TT_2MSL);

	/*
	* samkumar: There used to be code here to properly handle the callout,
	* including edge cases (return early if the callout was reset after this
	* function was scheduled for execution, deactivate the callout, return
	* early if the INP_DROPPED flag is set on the inpcb, and assert that the
	* tp->t_timers state is correct).
	*
	* I also removed stats collection, locking, and vnet, throughout the code.
	*/

	/*
	* 2 MSL timeout in shutdown went off. If we're closed but
	* still waiting for peer to close and connection has been idle
	* too long delete connection control block. Otherwise, check
	* again in a bit.
	*
	* If in TIME_WAIT state just ignore as this timeout is handled in
	* tcp_tw_2msl_scan().
	*
	* If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
	* there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
	* Ignore fact that there were recent incoming segments.
	*/

	/*
	* samkumar: The above comment about ignoring this timeout if we're in the
	* TIME_WAIT state no longer is true, since in TCPlp we changed how
	* TIME_WAIT is handled. In FreeBSD, this timer isn't used for sockets in
	* the TIME_WAIT state; instead the tcp_tw_2msl_scan method is called
	* periodically on the slow timer, and expired tcptw structs are closed and
	* freed. I changed it so that TIME-WAIT connections are still represented
	* as tcpcb's, not tcptw's, and to rely on this timer to close the
	* connection.
	*
	* Below, there used to be an if statement that checks the inpcb to tell
	* if we're in TIME-WAIT state, and return early if so. I've replaced this
	* with an if statement that checks the tcpcb if we're in the TIME-WAIT
	* state, and acts appropriately if so.
	*/
	if (tp->t_state == TCP6S_TIME_WAIT) {
	tp = tcp_close(tp);
	tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
	dropped = 1;
	return dropped;
	}
	/*
	* samkumar: This if statement also used to check that an inpcb is still
	* attached and also
	* (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE).
	* We replaced the check on that flag with a call to tpiscantrcv. We
	* haven't received a FIN, since we're in FIN-WAIT-2, so the only way it
	* would pass the check is if the user called shutdown(SHUT_RD)
	* or shutdown(SHUT_RDWR), which is impossible unless the host system
	* provides an API for that.
	*/
	if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
	tpiscantrcv(tp)) {
	tp = tcp_close(tp);
	tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
	dropped = 1;
	} else {
	if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp)) {
	/*
	* samkumar: I replaced a call to callout_reset with the following
	* code, which resets the timer the TCPlp way.
	*/
	tpmarktimeractive(tp, TT_2MSL);
	tcplp_sys_set_timer(tp, TT_2MSL, TP_KEEPINTVL(tp));
	} else {
	tp = tcp_close(tp);
	tcplp_sys_connection_lost(tp, CONN_LOST_NORMAL);
	dropped = 1;
	}
	}
	/*
	* samkumar: There used to be some code here that handled debug
	* tracing/probes, vnet, and locking. I removed that code.
	*/
	return dropped;
	}

	int
	tcp_timer_rexmt(struct tcpcb *tp)
	{
	int rexmt;
	uint32_t ticks = tcplp_sys_get_ticks();
	int dropped = 0;

	/* samkumar: I added this, to replace the code I removed below. */
	KASSERT(tpistimeractive(tp, TT_REXMT), ("Rexmt timer running, but unmarked"));
	tpcleartimeractive(tp, TT_REXMT);

	/*
	* samkumar: There used to be code here to properly handle the callout,
	* including edge cases (return early if the callout was reset after this
	* function was scheduled for execution, deactivate the callout, return
	* early if the INP_DROPPED flag is set on the inpcb, and assert that the
	* tp->t_timers state is correct).
	*
	* I also removed stats collection, locking, and vnet, throughout the code.
	*/

	tcp_free_sackholes(tp);
	/*
	* Retransmission timer went off. Message has not
	* been acked within retransmit interval. Back off
	* to a longer retransmit interval and retransmit one segment.
	*/
	tcplp_sys_log("rxtshift is %d", (int) tp->t_rxtshift);
	if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
	tp->t_rxtshift = TCP_MAXRXTSHIFT;

	tp = tcp_drop(tp, tp->t_softerror ?
	tp->t_softerror : ETIMEDOUT);
	dropped = 1;
	goto out;
	}
	if (tp->t_state == TCPS_SYN_SENT) {
	/*
	* If the SYN was retransmitted, indicate CWND to be
	* limited to 1 segment in cc_conn_init().
	*/
	tp->snd_cwnd = 1;
	} else if (tp->t_rxtshift == 1) {
	/*
	* first retransmit; record ssthresh and cwnd so they can
	* be recovered if this turns out to be a "bad" retransmit.
	* A retransmit is considered "bad" if an ACK for this
	* segment is received within RTT/2 interval; the assumption
	* here is that the ACK was already in flight. See
	* "On Estimating End-to-End Network Path Properties" by
	* Allman and Paxson for more details.
	*/
	tp->snd_cwnd_prev = tp->snd_cwnd;
	tp->snd_ssthresh_prev = tp->snd_ssthresh;
	tp->snd_recover_prev = tp->snd_recover;
	if (IN_FASTRECOVERY(tp->t_flags))
	tp->t_flags \|= TF_WASFRECOVERY;
	else
	tp->t_flags &= ~TF_WASFRECOVERY;
	if (IN_CONGRECOVERY(tp->t_flags))
	tp->t_flags \|= TF_WASCRECOVERY;
	else
	tp->t_flags &= ~TF_WASCRECOVERY;
	tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
	tp->t_flags \|= TF_PREVVALID;
	} else
	tp->t_flags &= ~TF_PREVVALID;
	if (tp->t_state == TCPS_SYN_SENT)
	rexmt = TCPTV_RTOBASE * tcp_syn_backoff[tp->t_rxtshift];
	else
	rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
	TCPT_RANGESET(tp->t_rxtcur, rexmt,
	tp->t_rttmin, TCPTV_REXMTMAX);

	/*
	* samkumar: There used to be more than 100 lines of code here, which
	* implemented a feature called blackhole detection. The idea here is that
	* some routers may silently discard packets whose MTU is too large,
	* instead of fragmenting the packet or sending an ICMP packet to give
	* feedback to the host. Blackhole detection decreases the MTU in response
	* to packet loss in case the packets are being dropped by such a router.
	*
	* In TCPlp, we do not do blackhole detection because we use a small MTU
	* (hundreds of bytes) that is unlikely to be too large for intermediate
	* routers in the Internet. The edge low-power wireless network is
	* assumed to be engineered to handle 6LoWPAN correctly.
	*/

	/*
	* Disable RFC1323 and SACK if we haven't got any response to
	* our third SYN to work-around some broken terminal servers
	* (most of which have hopefully been retired) that have bad VJ
	* header compression code which trashes TCP segments containing
	* unknown-to-them TCP options.
	*/
	if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
	(tp->t_rxtshift == 3))
	tp->t_flags &= ~(TF_REQ_SCALE\|TF_REQ_TSTMP\|TF_SACK_PERMIT);
	/*
	* If we backed off this far, our srtt estimate is probably bogus.
	* Clobber it so we'll take the next rtt measurement as our srtt;
	* move the current srtt into rttvar to keep the current
	* retransmit times until then.
	*/
	if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
	/*
	* samkumar: Here, there used to be a call to "in6_losing", used to
	* inform the lower layers about bad connectivity so it can search for
	* different routes. The call was wrapped in a check on the inpcb's
	* flags to check for IPv6 (which isn't relevant to us, since TCPlp
	* assumes IPv6).
	*/
	tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
	tp->t_srtt = 0;
	}
	tp->snd_nxt = tp->snd_una;
	tp->snd_recover = tp->snd_max;
	/*
	* Force a segment to be sent.
	*/
	tp->t_flags \|= TF_ACKNOW;
	/*
	* If timing a segment in this window, stop the timer.
	*/
	tp->t_rtttime = 0;

	cc_cong_signal(tp, NULL, CC_RTO);

	(void) tcp_output(tp);

	out:
	/*
	* samkumar: There used to be some code here that handled debug
	* tracing/probes, vnet, and locking. I removed that code.
	*/
	(void) tp; /* samkumar: Prevent a compiler warning */
	return dropped;
	}

	int
	tcp_timer_active(struct tcpcb *tp, uint32_t timer_type)
	{
	return tpistimeractive(tp, timer_type);
	}

	void
	tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, uint32_t delta) {
	if (delta) {
	tpmarktimeractive(tp, timer_type);
	if (tpistimeractive(tp, TT_REXMT) && tpistimeractive(tp, TT_PERSIST)) {
	tcplp_sys_panic("TCP CRITICAL FAILURE: Retransmit and Persist timers are simultaneously running!");
	}
	tcplp_sys_set_timer(tp, timer_type, (uint32_t) delta);
	} else {
	tpcleartimeractive(tp, timer_type);
	tcplp_sys_stop_timer(tp, timer_type);
	}
	}

	void
	tcp_cancel_timers(struct tcpcb* tp) {
	tpcleartimeractive(tp, TT_DELACK);
	tcplp_sys_stop_timer(tp, TT_DELACK);
	tpcleartimeractive(tp, TT_REXMT);
	tcplp_sys_stop_timer(tp, TT_REXMT);
	tpcleartimeractive(tp, TT_PERSIST);
	tcplp_sys_stop_timer(tp, TT_PERSIST);
	tpcleartimeractive(tp, TT_KEEP);
	tcplp_sys_stop_timer(tp, TT_KEEP);
	tpcleartimeractive(tp, TT_2MSL);
	tcplp_sys_stop_timer(tp, TT_2MSL);
	}