/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2009-2010
 * 	Swinburne University of Technology, Melbourne, Australia
 * Copyright (c) 2010 Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2010-2011 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed at the Centre for Advanced Internet
 * Architectures, Swinburne University of Technology, by David Hayes, made
 * possible in part by a grant from the Cisco University Research Program Fund
 * at Community Foundation Silicon Valley.
 *
 * Portions of this software were developed at the Centre for Advanced
 * Internet Architectures, Swinburne University of Technology, Melbourne,
 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: releng/12.0/sys/netinet/khelp/h_ertt.c 326272 2017-11-27 15:23:17Z pfg $");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/mbuf.h>
#include <sys/module.h>
#include <sys/hhook.h>
#include <sys/khelp.h>
#include <sys/module_khelp.h>
#include <sys/socket.h>
#include <sys/sockopt.h>

#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_var.h>

#include <netinet/khelp/h_ertt.h>

#include <vm/uma.h>

uma_zone_t txseginfo_zone;

/* Smoothing factor for delayed ack guess. */
#define	DLYACK_SMOOTH	5

/* Max number of time stamp errors allowed in a session. */
#define	MAX_TS_ERR	10

static int ertt_packet_measurement_hook(int hhook_type, int hhook_id,
    void *udata, void *ctx_data, void *hdata, struct osd *hosd);
static int ertt_add_tx_segment_info_hook(int hhook_type, int hhook_id,
    void *udata, void *ctx_data, void *hdata, struct osd *hosd);
static int ertt_mod_init(void);
static int ertt_mod_destroy(void);
static int ertt_uma_ctor(void *mem, int size, void *arg, int flags);
static void ertt_uma_dtor(void *mem, int size, void *arg);

/*
 * Contains information about the sent segment for comparison with the
 * corresponding ack.
 */
struct txseginfo {
	/* Segment length. */
	uint32_t	len;
	/* Segment sequence number. */
	tcp_seq		seq;
	/* Time stamp indicating when the packet was sent. */
	uint32_t	tx_ts;
	/* Last received receiver ts (if the TCP option is used). */
	uint32_t	rx_ts;
	uint32_t	flags;
	TAILQ_ENTRY (txseginfo) txsegi_lnk;
};

/* Flags for struct txseginfo. */
#define	TXSI_TSO		0x01 /* TSO was used for this entry. */
#define	TXSI_RTT_MEASURE_START	0x02 /* Start a per RTT measurement. */
#define	TXSI_RX_MEASURE_END	0x04 /* Measure the rx rate until this txsi. */

struct helper ertt_helper = {
	.mod_init = ertt_mod_init,
	.mod_destroy = ertt_mod_destroy,
	.h_flags = HELPER_NEEDS_OSD,
	.h_classes = HELPER_CLASS_TCP
};

/* Define the helper hook info required by ERTT. */
struct hookinfo ertt_hooks[] = {
	{
		.hook_type = HHOOK_TYPE_TCP,
		.hook_id = HHOOK_TCP_EST_IN,
		.hook_udata = NULL,
		.hook_func = &ertt_packet_measurement_hook
	},
	{
		.hook_type = HHOOK_TYPE_TCP,
		.hook_id = HHOOK_TCP_EST_OUT,
		.hook_udata = NULL,
		.hook_func = &ertt_add_tx_segment_info_hook
	}
};

/* Flags to indicate how marked_packet_rtt should handle this txsi. */
#define	MULTI_ACK		0x01 /* More than this txsi is acked. */
#define	OLD_TXSI		0x02 /* TXSI is old according to timestamps. */
#define	CORRECT_ACK		0X04 /* Acks this TXSI. */
#define	FORCED_MEASUREMENT	0X08 /* Force an RTT measurement. */

/*
 * This fuction measures the RTT of a particular segment/ack pair, or the next
 * closest if this will yield an inaccurate result due to delayed acking or
 * other issues.
 */
static void inline
marked_packet_rtt(struct txseginfo *txsi, struct ertt *e_t, struct tcpcb *tp,
    uint32_t *pmeasurenext, int *pmeasurenext_len, int *prtt_bytes_adjust,
    int mflag)
{

	/*
	 * If we can't measure this one properly due to delayed acking adjust
	 * byte counters and flag to measure next txsi. Note that since the
	 * marked packet's transmitted bytes are measured we need to subtract the
	 * transmitted bytes. Then pretend the next txsi was marked.
	 */
	if (mflag & (MULTI_ACK|OLD_TXSI)) {
		*pmeasurenext = txsi->tx_ts;
		*pmeasurenext_len = txsi->len;
		*prtt_bytes_adjust += *pmeasurenext_len;
	} else {
		if (mflag & FORCED_MEASUREMENT) {
			e_t->markedpkt_rtt = tcp_ts_getticks() -
			    *pmeasurenext + 1;
			e_t->bytes_tx_in_marked_rtt = e_t->bytes_tx_in_rtt +
			    *pmeasurenext_len - *prtt_bytes_adjust;
		} else {
			e_t->markedpkt_rtt = tcp_ts_getticks() -
			    txsi->tx_ts + 1;
			e_t->bytes_tx_in_marked_rtt = e_t->bytes_tx_in_rtt -
			    *prtt_bytes_adjust;
		}
		e_t->marked_snd_cwnd = tp->snd_cwnd;

		/*
		 * Reset the ERTT_MEASUREMENT_IN_PROGRESS flag to indicate to
		 * add_tx_segment_info that a new measurement should be started.
		 */
		e_t->flags &= ~ERTT_MEASUREMENT_IN_PROGRESS;
		/*
		 * Set ERTT_NEW_MEASUREMENT to tell the congestion control
		 * algorithm that a new marked RTT measurement has has been made
		 * and is available for use.
		 */
		e_t->flags |= ERTT_NEW_MEASUREMENT;

		if (tp->t_flags & TF_TSO) {
			/* Temporarily disable TSO to aid a new measurment. */
			tp->t_flags &= ~TF_TSO;
			/* Keep track that we've disabled it. */
			e_t->flags |= ERTT_TSO_DISABLED;
		}
	}
}

/*
 * Ertt_packet_measurements uses a small amount of state kept on each packet
 * sent to match incoming acknowledgements. This enables more accurate and
 * secure round trip time measurements. The resulting measurement is used for
 * congestion control algorithms which require a more accurate time.
 * Ertt_packet_measurements is called via the helper hook in tcp_input.c
 */
static int
ertt_packet_measurement_hook(int hhook_type, int hhook_id, void *udata,
    void *ctx_data, void *hdata, struct osd *hosd)
{
	struct ertt *e_t;
	struct tcpcb *tp;
	struct tcphdr *th;
	struct tcpopt *to;
	struct tcp_hhook_data *thdp;
	struct txseginfo *txsi;
	int acked, measurenext_len, multiack, new_sacked_bytes, rtt_bytes_adjust;
	uint32_t measurenext, rts;
	tcp_seq ack;

	KASSERT(ctx_data != NULL, ("%s: ctx_data is NULL!", __func__));
	KASSERT(hdata != NULL, ("%s: hdata is NULL!", __func__));

	e_t = (struct ertt *)hdata;
	thdp = ctx_data;
	tp = thdp->tp;
	th = thdp->th;
	to = thdp->to;
	new_sacked_bytes = (tp->sackhint.last_sack_ack != 0);
	measurenext = measurenext_len = multiack = rts = rtt_bytes_adjust = 0;
	acked = th->th_ack - tp->snd_una;

	INP_WLOCK_ASSERT(tp->t_inpcb);

	/* Packet has provided new acknowledgements. */
	if (acked > 0 || new_sacked_bytes) {
		if (acked == 0 && new_sacked_bytes) {
			/* Use last sacked data. */
			ack = tp->sackhint.last_sack_ack;
		} else
			ack = th->th_ack;

		txsi = TAILQ_FIRST(&e_t->txsegi_q);
		while (txsi != NULL) {
			rts = 0;

			/* Acknowledgement is acking more than this txsi. */
			if (SEQ_GT(ack, txsi->seq + txsi->len)) {
				if (txsi->flags & TXSI_RTT_MEASURE_START ||
				    measurenext) {
					marked_packet_rtt(txsi, e_t, tp,
					    &measurenext, &measurenext_len,
					    &rtt_bytes_adjust, MULTI_ACK);
				}
				TAILQ_REMOVE(&e_t->txsegi_q, txsi, txsegi_lnk);
				uma_zfree(txseginfo_zone, txsi);
				txsi = TAILQ_FIRST(&e_t->txsegi_q);
				continue;
			}

			/*
			 * Guess if delayed acks are being used by the receiver.
			 *
			 * XXXDH: A simple heuristic that could be improved
			 */
			if (!new_sacked_bytes) {
				if (acked > tp->t_maxseg) {
					e_t->dlyack_rx +=
					    (e_t->dlyack_rx < DLYACK_SMOOTH) ?
					    1 : 0;
					multiack = 1;
				} else if (acked > txsi->len) {
					multiack = 1;
					e_t->dlyack_rx +=
					    (e_t->dlyack_rx < DLYACK_SMOOTH) ?
					    1 : 0;
				} else if (acked == tp->t_maxseg ||
					   acked == txsi->len) {
					e_t->dlyack_rx -=
					    (e_t->dlyack_rx > 0) ? 1 : 0;
				}
				/* Otherwise leave dlyack_rx the way it was. */
			}

			/*
			 * Time stamps are only to help match the txsi with the
			 * received acknowledgements.
			 */
			if (e_t->timestamp_errors < MAX_TS_ERR &&
			    (to->to_flags & TOF_TS) != 0 && to->to_tsecr) {
				/*
				 * Note: All packets sent with the offload will
				 * have the same time stamp. If we are sending
				 * on a fast interface and the t_maxseg is much
				 * smaller than one tick, this will be fine. The
				 * time stamp would be the same whether we were
				 * using tso or not. However, if the interface
				 * is slow, this will cause problems with the
				 * calculations. If the interface is slow, there
				 * is not reason to be using tso, and it should
				 * be turned off.
				 */
				/*
				 * If there are too many time stamp errors, time
				 * stamps won't be trusted
				 */
				rts = to->to_tsecr;
				/* Before this packet. */
				if (!e_t->dlyack_rx && TSTMP_LT(rts, txsi->tx_ts))
					/* When delayed acking is used, the
					 * reflected time stamp is of the first
					 * packet and thus may be before
					 * txsi->tx_ts.
					 */
					break;
				if (TSTMP_GT(rts, txsi->tx_ts)) {
					/*
					 * If reflected time stamp is later than
					 * tx_tsi, then this txsi is old.
					 */
					if (txsi->flags & TXSI_RTT_MEASURE_START
					    || measurenext) {
						marked_packet_rtt(txsi, e_t, tp,
						    &measurenext, &measurenext_len,
						    &rtt_bytes_adjust, OLD_TXSI);
					}
					TAILQ_REMOVE(&e_t->txsegi_q, txsi,
					    txsegi_lnk);
					uma_zfree(txseginfo_zone, txsi);
					txsi = TAILQ_FIRST(&e_t->txsegi_q);
					continue;
				}
				if (rts == txsi->tx_ts &&
				    TSTMP_LT(to->to_tsval, txsi->rx_ts)) {
					/*
					 * Segment received before sent!
					 * Something is wrong with the received
					 * timestamps so increment errors. If
					 * this keeps up we will ignore
					 * timestamps.
					 */
					e_t->timestamp_errors++;
				}
			}
			/*
			 * Acknowledging a sequence number before this txsi.
			 * If it is an old txsi that may have had the same seq
			 * numbers, it should have been removed if time stamps
			 * are being used.
			 */
			if (SEQ_LEQ(ack, txsi->seq))
				break; /* Before first packet in txsi. */

			/*
			 * Only ack > txsi->seq and ack <= txsi->seq+txsi->len
			 * past this point.
			 *
			 * If delayed acks are being used, an acknowledgement
			 * for a single segment will have been delayed by the
			 * receiver and will yield an inaccurate measurement. In
			 * this case, we only make the measurement if more than
			 * one segment is being acknowledged or sack is
			 * currently being used.
			 */
			if (!e_t->dlyack_rx || multiack || new_sacked_bytes) {
				/* Make an accurate new measurement. */
				e_t->rtt = tcp_ts_getticks() - txsi->tx_ts + 1;

				if (e_t->rtt < e_t->minrtt || e_t->minrtt == 0)
					e_t->minrtt = e_t->rtt;

				if (e_t->rtt > e_t->maxrtt || e_t->maxrtt == 0)
					e_t->maxrtt = e_t->rtt;
			}

			if (txsi->flags & TXSI_RTT_MEASURE_START || measurenext)
				marked_packet_rtt(txsi, e_t, tp,
				    &measurenext, &measurenext_len,
				    &rtt_bytes_adjust, CORRECT_ACK);

			if (txsi->flags & TXSI_TSO) {
				if (txsi->len > acked) {
					txsi->len -= acked;
					/*
					 * This presumes ack for first bytes in
					 * txsi, this may not be true but it
					 * shouldn't cause problems for the
					 * timing.
					 *
					 * We remeasure RTT even though we only
					 * have a single txsi. The rationale
					 * behind this is that it is better to
					 * have a slightly inaccurate
					 * measurement than no additional
					 * measurement for the rest of the bulk
					 * transfer. Since TSO is only used on
					 * high speed interface cards, so the
					 * packets should be transmitted at line
					 * rate back to back with little
					 * difference in transmission times (in
					 * ticks).
					 */
					txsi->seq += acked;
					/*
					 * Reset txsi measure flag so we don't
					 * use it for another RTT measurement.
					 */
					txsi->flags &= ~TXSI_RTT_MEASURE_START;
					/*
					 * There is still more data to be acked
					 * from tso bulk transmission, so we
					 * won't remove it from the TAILQ yet.
					 */
					break;
				}
				txsi->len = 0;
			}

			TAILQ_REMOVE(&e_t->txsegi_q, txsi, txsegi_lnk);
			uma_zfree(txseginfo_zone, txsi);
			break;
		}

		if (measurenext) {
			/*
			 * We need to do a RTT measurement. It won't be the best
			 * if we do it here.
			 */
			marked_packet_rtt(txsi, e_t, tp,
			    &measurenext, &measurenext_len,
			    &rtt_bytes_adjust, FORCED_MEASUREMENT);
		}
	}

	return (0);
}

/*
 * Add information about a transmitted segment to a list.
 * This is called via the helper hook in tcp_output.c
 */
static int
ertt_add_tx_segment_info_hook(int hhook_type, int hhook_id, void *udata,
    void *ctx_data, void *hdata, struct osd *hosd)
{
	struct ertt *e_t;
	struct tcpcb *tp;
	struct tcphdr *th;
	struct tcpopt *to;
	struct tcp_hhook_data *thdp;
	struct txseginfo *txsi;
	uint32_t len;
	int tso;

	KASSERT(ctx_data != NULL, ("%s: ctx_data is NULL!", __func__));
	KASSERT(hdata != NULL, ("%s: hdata is NULL!", __func__));

	e_t = (struct ertt *)hdata;
	thdp = ctx_data;
	tp = thdp->tp;
	th = thdp->th;
	to = thdp->to;
	len = thdp->len;
	tso = thdp->tso;

	INP_WLOCK_ASSERT(tp->t_inpcb);

	if (len > 0) {
		txsi = uma_zalloc(txseginfo_zone, M_NOWAIT);
		if (txsi != NULL) {
			/* Construct txsi setting the necessary flags. */
			txsi->flags = 0; /* Needs to be initialised. */
			txsi->seq = ntohl(th->th_seq);
			txsi->len = len;
			if (tso)
				txsi->flags |= TXSI_TSO;
			else if (e_t->flags & ERTT_TSO_DISABLED) {
				tp->t_flags |= TF_TSO;
				e_t->flags &= ~ERTT_TSO_DISABLED;
			}

			if (e_t->flags & ERTT_MEASUREMENT_IN_PROGRESS) {
				e_t->bytes_tx_in_rtt += len;
			} else {
				txsi->flags |= TXSI_RTT_MEASURE_START;
				e_t->flags |= ERTT_MEASUREMENT_IN_PROGRESS;
				e_t->bytes_tx_in_rtt = len;
			}

			if (((tp->t_flags & TF_NOOPT) == 0) &&
			    (to->to_flags & TOF_TS)) {
				txsi->tx_ts = ntohl(to->to_tsval) -
				    tp->ts_offset;
				txsi->rx_ts = ntohl(to->to_tsecr);
			} else {
				txsi->tx_ts = tcp_ts_getticks();
				txsi->rx_ts = 0; /* No received time stamp. */
			}
			TAILQ_INSERT_TAIL(&e_t->txsegi_q, txsi, txsegi_lnk);
		}
	}

	return (0);
}

static int
ertt_mod_init(void)
{

	txseginfo_zone = uma_zcreate("ertt_txseginfo", sizeof(struct txseginfo),
	    NULL, NULL, NULL, NULL, 0, 0);

	return (0);
}

static int
ertt_mod_destroy(void)
{

	uma_zdestroy(txseginfo_zone);

	return (0);
}

static int
ertt_uma_ctor(void *mem, int size, void *arg, int flags)
{
	struct ertt *e_t;

	e_t = mem;

	TAILQ_INIT(&e_t->txsegi_q);
	e_t->timestamp_errors = 0;
	e_t->minrtt = 0;
	e_t->maxrtt = 0;
	e_t->rtt = 0;
	e_t->flags = 0;
	e_t->dlyack_rx = 0;
	e_t->bytes_tx_in_rtt = 0;
	e_t->markedpkt_rtt = 0;

	return (0);
}

static void
ertt_uma_dtor(void *mem, int size, void *arg)
{
	struct ertt *e_t;
	struct txseginfo *n_txsi, *txsi;

	e_t = mem;
	txsi = TAILQ_FIRST(&e_t->txsegi_q);
	while (txsi != NULL) {
		n_txsi = TAILQ_NEXT(txsi, txsegi_lnk);
		uma_zfree(txseginfo_zone, txsi);
		txsi = n_txsi;
	}
}

KHELP_DECLARE_MOD_UMA(ertt, &ertt_helper, ertt_hooks, 1, sizeof(struct ertt),
    ertt_uma_ctor, ertt_uma_dtor);
