/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * 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 and
 * Lawrence Stewart, 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.
 */

/*
 * An implementation of the Vegas congestion control algorithm for FreeBSD,
 * based on L. S. Brakmo and L. L. Peterson, "TCP Vegas: end to end congestion
 * avoidance on a global internet", IEEE J. Sel. Areas Commun., vol. 13, no. 8,
 * pp. 1465-1480, Oct. 1995. The original Vegas duplicate ack policy has not
 * been implemented, since clock ticks are not as coarse as they were (i.e.
 * 500ms) when Vegas was designed. Also, packets are timed once per RTT as in
 * the original paper.
 *
 * Originally released as part of the NewTCP research project at Swinburne
 * University of Technology's Centre for Advanced Internet Architectures,
 * Melbourne, Australia, which was made possible in part by a grant from the
 * Cisco University Research Program Fund at Community Foundation Silicon
 * Valley. More details are available at:
 *   http://caia.swin.edu.au/urp/newtcp/
 */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/khelp.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/queue.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/systm.h>

#include <net/vnet.h>

#include <net/route.h>
#include <net/route/nhop.h>

#include <netinet/in_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/cc/cc.h>
#include <netinet/cc/cc_module.h>

#include <netinet/khelp/h_ertt.h>

/*
 * Private signal type for rate based congestion signal.
 * See <netinet/cc.h> for appropriate bit-range to use for private signals.
 */
#define CC_VEGAS_RATE   0x04000000

static void     vegas_ack_received(struct cc_var *ccv, ccsignal_t ack_type);
static void     vegas_cb_destroy(struct cc_var *ccv);
static int      vegas_cb_init(struct cc_var *ccv, void *ptr);
static void     vegas_cong_signal(struct cc_var *ccv, ccsignal_t signal_type);
static void     vegas_conn_init(struct cc_var *ccv);
static int      vegas_mod_init(void);
static size_t   vegas_data_sz(void);

struct vegas {
        int slow_start_toggle;
};

static int32_t ertt_id;

VNET_DEFINE_STATIC(uint32_t, vegas_alpha) = 1;
VNET_DEFINE_STATIC(uint32_t, vegas_beta) = 3;
#define V_vegas_alpha   VNET(vegas_alpha)
#define V_vegas_beta    VNET(vegas_beta)

struct cc_algo vegas_cc_algo = {
        .name = "vegas",
        .ack_received = vegas_ack_received,
        .cb_destroy = vegas_cb_destroy,
        .cb_init = vegas_cb_init,
        .cong_signal = vegas_cong_signal,
        .conn_init = vegas_conn_init,
        .mod_init = vegas_mod_init,
        .cc_data_sz = vegas_data_sz,
        .after_idle = newreno_cc_after_idle,
        .post_recovery = newreno_cc_post_recovery,
};

/*
 * The vegas window adjustment is done once every RTT, as indicated by the
 * ERTT_NEW_MEASUREMENT flag. This flag is reset once the new measurement data
 * has been used.
 */
static void
vegas_ack_received(struct cc_var *ccv, ccsignal_t ack_type)
{
        struct ertt *e_t;
        struct vegas *vegas_data;
        long actual_tx_rate, expected_tx_rate, ndiff;
        uint32_t mss = tcp_fixed_maxseg(ccv->tp);

        e_t = khelp_get_osd(&CCV(ccv, t_osd), ertt_id);
        vegas_data = ccv->cc_data;

        if (e_t->flags & ERTT_NEW_MEASUREMENT) { /* Once per RTT. */
                if (e_t->minrtt && e_t->markedpkt_rtt) {
                        expected_tx_rate = e_t->marked_snd_cwnd / e_t->minrtt;
                        actual_tx_rate = e_t->bytes_tx_in_marked_rtt /
                            e_t->markedpkt_rtt;
                        ndiff = (expected_tx_rate - actual_tx_rate) *
                            e_t->minrtt / mss;

                        if (ndiff < V_vegas_alpha) {
                                if (CCV(ccv, snd_cwnd) <=
                                    CCV(ccv, snd_ssthresh)) {
                                        vegas_data->slow_start_toggle =
                                            vegas_data->slow_start_toggle ?
                                            0 : 1;
                                } else {
                                        vegas_data->slow_start_toggle = 0;
                                        CCV(ccv, snd_cwnd) =
                                            min(CCV(ccv, snd_cwnd) + mss,
                                            TCP_MAXWIN << CCV(ccv, snd_scale));
                                }
                        } else if (ndiff > V_vegas_beta) {
                                /* Rate-based congestion. */
                                vegas_cong_signal(ccv, CC_VEGAS_RATE);
                                vegas_data->slow_start_toggle = 0;
                        }
                }
                e_t->flags &= ~ERTT_NEW_MEASUREMENT;
        }

        if (vegas_data->slow_start_toggle)
                newreno_cc_ack_received(ccv, ack_type);
}

static void
vegas_cb_destroy(struct cc_var *ccv)
{
        free(ccv->cc_data, M_CC_MEM);
}

static size_t
vegas_data_sz(void)
{
        return (sizeof(struct vegas));
}

static int
vegas_cb_init(struct cc_var *ccv, void *ptr)
{
        struct vegas *vegas_data;

        INP_WLOCK_ASSERT(tptoinpcb(ccv->tp));
        if (ptr == NULL) {
                vegas_data = malloc(sizeof(struct vegas), M_CC_MEM, M_NOWAIT);
                if (vegas_data == NULL)
                        return (ENOMEM);
        } else
                vegas_data = ptr;

        vegas_data->slow_start_toggle = 1;
        ccv->cc_data = vegas_data;

        return (0);
}

/*
 * If congestion has been triggered triggered by the Vegas measured rates, it is
 * handled here, otherwise it falls back to newreno's congestion handling.
 */
static void
vegas_cong_signal(struct cc_var *ccv, ccsignal_t signal_type)
{
        struct vegas *vegas_data;
        int presignalrecov;
        uint32_t mss = tcp_fixed_maxseg(ccv->tp);

        vegas_data = ccv->cc_data;

        if (IN_RECOVERY(CCV(ccv, t_flags)))
                presignalrecov = 1;
        else
                presignalrecov = 0;

        switch((int)signal_type) {
        case CC_VEGAS_RATE:
                if (!IN_RECOVERY(CCV(ccv, t_flags))) {
                        CCV(ccv, snd_cwnd) = max(2 * mss,
                            CCV(ccv, snd_cwnd) - mss);
                        if (CCV(ccv, snd_cwnd) < CCV(ccv, snd_ssthresh))
                                /* Exit slow start. */
                                CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
                }
                break;

        default:
                newreno_cc_cong_signal(ccv, signal_type);
                break;
        }

        if (IN_RECOVERY(CCV(ccv, t_flags)) && !presignalrecov)
                vegas_data->slow_start_toggle =
                    (CCV(ccv, snd_cwnd) < CCV(ccv, snd_ssthresh)) ? 1 : 0;
}

static void
vegas_conn_init(struct cc_var *ccv)
{
        struct vegas *vegas_data;

        vegas_data = ccv->cc_data;
        vegas_data->slow_start_toggle = 1;
}

static int
vegas_mod_init(void)
{
        ertt_id = khelp_get_id("ertt");
        if (ertt_id <= 0) {
                printf("%s: h_ertt module not found\n", __func__);
                return (ENOENT);
        }
        return (0);
}

static int
vegas_alpha_handler(SYSCTL_HANDLER_ARGS)
{
        int error;
        uint32_t new;

        new = V_vegas_alpha;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr != NULL) {
                if (new == 0 || new > V_vegas_beta)
                        error = EINVAL;
                else
                        V_vegas_alpha = new;
        }

        return (error);
}

static int
vegas_beta_handler(SYSCTL_HANDLER_ARGS)
{
        int error;
        uint32_t new;

        new = V_vegas_beta;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr != NULL) {
                if (new == 0 || new < V_vegas_alpha)
                         error = EINVAL;
                else
                        V_vegas_beta = new;
        }

        return (error);
}

SYSCTL_DECL(_net_inet_tcp_cc_vegas);
SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, vegas,
    CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
    "Vegas related settings");

SYSCTL_PROC(_net_inet_tcp_cc_vegas, OID_AUTO, alpha,
    CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(vegas_alpha), 1, &vegas_alpha_handler, "IU",
    "vegas alpha, specified as number of \"buffers\" (0 < alpha < beta)");

SYSCTL_PROC(_net_inet_tcp_cc_vegas, OID_AUTO, beta,
    CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(vegas_beta), 3, &vegas_beta_handler, "IU",
    "vegas beta, specified as number of \"buffers\" (0 < alpha < beta)");

DECLARE_CC_MODULE(vegas, &vegas_cc_algo);
MODULE_VERSION(vegas, 2);
MODULE_DEPEND(vegas, ertt, 1, 1, 1);