#ifndef __NET_SCHED_CODEL_IMPL_H
#define __NET_SCHED_CODEL_IMPL_H

/*
 * Codel - The Controlled-Delay Active Queue Management algorithm
 *
 *  Copyright (C) 2011-2012 Kathleen Nichols <nichols@pollere.com>
 *  Copyright (C) 2011-2012 Van Jacobson <van@pollere.net>
 *  Copyright (C) 2012 Michael D. Taht <dave.taht@bufferbloat.net>
 *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
 *
 * 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,
 *    without modification.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The names of the authors may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
 * OWNER 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.
 *
 */

/* Controlling Queue Delay (CoDel) algorithm
 * =========================================
 * Source : Kathleen Nichols and Van Jacobson
 * http://queue.acm.org/detail.cfm?id=2209336
 *
 * Implemented on linux by Dave Taht and Eric Dumazet
 */

#include <net/inet_ecn.h>

static void codel_params_init(struct codel_params *params)
{
        params->interval = MS2TIME(100);
        params->target = MS2TIME(5);
        params->ce_threshold = CODEL_DISABLED_THRESHOLD;
        params->ce_threshold_mask = 0;
        params->ce_threshold_selector = 0;
        params->ecn = false;
}

static void codel_vars_init(struct codel_vars *vars)
{
        memset(vars, 0, sizeof(*vars));
}

static void codel_stats_init(struct codel_stats *stats)
{
        stats->maxpacket = 0;
}

/*
 * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
 * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
 *
 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
 */
static void codel_Newton_step(struct codel_vars *vars)
{
        u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
        u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
        u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);

        val >>= 2; /* avoid overflow in following multiply */
        val = (val * invsqrt) >> (32 - 2 + 1);

        vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
}

/*
 * CoDel control_law is t + interval/sqrt(count)
 * We maintain in rec_inv_sqrt the reciprocal value of sqrt(count) to avoid
 * both sqrt() and divide operation.
 */
static codel_time_t codel_control_law(codel_time_t t,
                                      codel_time_t interval,
                                      u32 rec_inv_sqrt)
{
        return t + reciprocal_scale(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
}

static bool codel_should_drop(const struct sk_buff *skb,
                              void *ctx,
                              struct codel_vars *vars,
                              struct codel_params *params,
                              struct codel_stats *stats,
                              codel_skb_len_t skb_len_func,
                              codel_skb_time_t skb_time_func,
                              u32 *backlog,
                              codel_time_t now)
{
        bool ok_to_drop;
        u32 skb_len;

        if (!skb) {
                vars->first_above_time = 0;
                return false;
        }

        skb_len = skb_len_func(skb);
        vars->ldelay = now - skb_time_func(skb);

        if (unlikely(skb_len > stats->maxpacket))
                stats->maxpacket = skb_len;

        if (codel_time_before(vars->ldelay, params->target) ||
            *backlog <= params->mtu) {
                /* went below - stay below for at least interval */
                vars->first_above_time = 0;
                return false;
        }
        ok_to_drop = false;
        if (vars->first_above_time == 0) {
                /* just went above from below. If we stay above
                 * for at least interval we'll say it's ok to drop
                 */
                vars->first_above_time = now + params->interval;
        } else if (codel_time_after(now, vars->first_above_time)) {
                ok_to_drop = true;
        }
        return ok_to_drop;
}

static struct sk_buff *codel_dequeue(void *ctx,
                                     u32 *backlog,
                                     struct codel_params *params,
                                     struct codel_vars *vars,
                                     struct codel_stats *stats,
                                     codel_skb_len_t skb_len_func,
                                     codel_skb_time_t skb_time_func,
                                     codel_skb_drop_t drop_func,
                                     codel_skb_dequeue_t dequeue_func)
{
        struct sk_buff *skb = dequeue_func(vars, ctx);
        codel_time_t now;
        bool drop;

        if (!skb) {
                vars->first_above_time = 0;
                vars->dropping = false;
                return skb;
        }
        now = codel_get_time();
        drop = codel_should_drop(skb, ctx, vars, params, stats,
                                 skb_len_func, skb_time_func, backlog, now);
        if (vars->dropping) {
                if (!drop) {
                        /* sojourn time below target - leave dropping state */
                        vars->dropping = false;
                } else if (codel_time_after_eq(now, vars->drop_next)) {
                        /* It's time for the next drop. Drop the current
                         * packet and dequeue the next. The dequeue might
                         * take us out of dropping state.
                         * If not, schedule the next drop.
                         * A large backlog might result in drop rates so high
                         * that the next drop should happen now,
                         * hence the while loop.
                         */
                        while (vars->dropping &&
                               codel_time_after_eq(now, vars->drop_next)) {
                                vars->count++; /* dont care of possible wrap
                                                * since there is no more divide
                                                */
                                codel_Newton_step(vars);
                                if (params->ecn && INET_ECN_set_ce(skb)) {
                                        stats->ecn_mark++;
                                        vars->drop_next =
                                                codel_control_law(vars->drop_next,
                                                                  params->interval,
                                                                  vars->rec_inv_sqrt);
                                        goto end;
                                }
                                stats->drop_len += skb_len_func(skb);
                                drop_func(skb, ctx);
                                stats->drop_count++;
                                skb = dequeue_func(vars, ctx);
                                if (!codel_should_drop(skb, ctx,
                                                       vars, params, stats,
                                                       skb_len_func,
                                                       skb_time_func,
                                                       backlog, now)) {
                                        /* leave dropping state */
                                        vars->dropping = false;
                                } else {
                                        /* and schedule the next drop */
                                        vars->drop_next =
                                                codel_control_law(vars->drop_next,
                                                                  params->interval,
                                                                  vars->rec_inv_sqrt);
                                }
                        }
                }
        } else if (drop) {
                u32 delta;

                if (params->ecn && INET_ECN_set_ce(skb)) {
                        stats->ecn_mark++;
                } else {
                        stats->drop_len += skb_len_func(skb);
                        drop_func(skb, ctx);
                        stats->drop_count++;

                        skb = dequeue_func(vars, ctx);
                        drop = codel_should_drop(skb, ctx, vars, params,
                                                 stats, skb_len_func,
                                                 skb_time_func, backlog, now);
                }
                vars->dropping = true;
                /* if min went above target close to when we last went below it
                 * assume that the drop rate that controlled the queue on the
                 * last cycle is a good starting point to control it now.
                 */
                delta = vars->count - vars->lastcount;
                if (delta > 1 &&
                    codel_time_before(now - vars->drop_next,
                                      16 * params->interval)) {
                        vars->count = delta;
                        /* we dont care if rec_inv_sqrt approximation
                         * is not very precise :
                         * Next Newton steps will correct it quadratically.
                         */
                        codel_Newton_step(vars);
                } else {
                        vars->count = 1;
                        vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
                }
                vars->lastcount = vars->count;
                vars->drop_next = codel_control_law(now, params->interval,
                                                    vars->rec_inv_sqrt);
        }
end:
        if (skb && codel_time_after(vars->ldelay, params->ce_threshold)) {
                bool set_ce = true;

                if (params->ce_threshold_mask) {
                        int dsfield = skb_get_dsfield(skb);

                        set_ce = (dsfield >= 0 &&
                                  (((u8)dsfield & params->ce_threshold_mask) ==
                                   params->ce_threshold_selector));
                }
                if (set_ce && INET_ECN_set_ce(skb))
                        stats->ce_mark++;
        }
        return skb;
}

#endif