#ifndef __NET_SCHED_CODEL_H
#define __NET_SCHED_CODEL_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 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.
 *
 */

#include <linux/types.h>
#include <linux/ktime.h>
#include <linux/skbuff.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>

/* 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
 */


/* CoDel uses a 1024 nsec clock, encoded in u32
 * This gives a range of 2199 seconds, because of signed compares
 */
typedef u32 codel_time_t;
typedef s32 codel_tdiff_t;
#define CODEL_SHIFT 10
#define MS2TIME(a) ((a * NSEC_PER_MSEC) >> CODEL_SHIFT)

static inline codel_time_t codel_get_time(void)
{
        u64 ns = ktime_get_ns();

        return ns >> CODEL_SHIFT;
}

/* Dealing with timer wrapping, according to RFC 1982, as desc in wikipedia:
 *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
 * codel_time_after(a,b) returns true if the time a is after time b.
 */
#define codel_time_after(a, b)                                          \
        (typecheck(codel_time_t, a) &&                                  \
         typecheck(codel_time_t, b) &&                                  \
         ((s32)((a) - (b)) > 0))
#define codel_time_before(a, b)         codel_time_after(b, a)

#define codel_time_after_eq(a, b)                                       \
        (typecheck(codel_time_t, a) &&                                  \
         typecheck(codel_time_t, b) &&                                  \
         ((s32)((a) - (b)) >= 0))
#define codel_time_before_eq(a, b)      codel_time_after_eq(b, a)

/* Qdiscs using codel plugin must use codel_skb_cb in their own cb[] */
struct codel_skb_cb {
        codel_time_t enqueue_time;
};

static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
{
        qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
        return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
}

static codel_time_t codel_get_enqueue_time(const struct sk_buff *skb)
{
        return get_codel_cb(skb)->enqueue_time;
}

static void codel_set_enqueue_time(struct sk_buff *skb)
{
        get_codel_cb(skb)->enqueue_time = codel_get_time();
}

static inline u32 codel_time_to_us(codel_time_t val)
{
        u64 valns = ((u64)val << CODEL_SHIFT);

        do_div(valns, NSEC_PER_USEC);
        return (u32)valns;
}

/**
 * struct codel_params - contains codel parameters
 * @target:     target queue size (in time units)
 * @interval:   width of moving time window
 * @ecn:        is Explicit Congestion Notification enabled
 */
struct codel_params {
        codel_time_t    target;
        codel_time_t    interval;
        bool            ecn;
};

/**
 * struct codel_vars - contains codel variables
 * @count:              how many drops we've done since the last time we
 *                      entered dropping state
 * @lastcount:          count at entry to dropping state
 * @dropping:           set to true if in dropping state
 * @rec_inv_sqrt:       reciprocal value of sqrt(count) >> 1
 * @first_above_time:   when we went (or will go) continuously above target
 *                      for interval
 * @drop_next:          time to drop next packet, or when we dropped last
 * @ldelay:             sojourn time of last dequeued packet
 */
struct codel_vars {
        u32             count;
        u32             lastcount;
        bool            dropping;
        u16             rec_inv_sqrt;
        codel_time_t    first_above_time;
        codel_time_t    drop_next;
        codel_time_t    ldelay;
};

#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
/* needed shift to get a Q0.32 number from rec_inv_sqrt */
#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)

/**
 * struct codel_stats - contains codel shared variables and stats
 * @maxpacket:  largest packet we've seen so far
 * @drop_count: temp count of dropped packets in dequeue()
 * ecn_mark:    number of packets we ECN marked instead of dropping
 */
struct codel_stats {
        u32             maxpacket;
        u32             drop_count;
        u32             ecn_mark;
};

static void codel_params_init(struct codel_params *params)
{
        params->interval = MS2TIME(100);
        params->target = MS2TIME(5);
        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 = 256;
}

/*
 * 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,
                              struct Qdisc *sch,
                              struct codel_vars *vars,
                              struct codel_params *params,
                              struct codel_stats *stats,
                              codel_time_t now)
{
        bool ok_to_drop;

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

        vars->ldelay = now - codel_get_enqueue_time(skb);
        sch->qstats.backlog -= qdisc_pkt_len(skb);

        if (unlikely(qdisc_pkt_len(skb) > stats->maxpacket))
                stats->maxpacket = qdisc_pkt_len(skb);

        if (codel_time_before(vars->ldelay, params->target) ||
            sch->qstats.backlog <= stats->maxpacket) {
                /* 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;
}

typedef struct sk_buff * (*codel_skb_dequeue_t)(struct codel_vars *vars,
                                                struct Qdisc *sch);

static struct sk_buff *codel_dequeue(struct Qdisc *sch,
                                     struct codel_params *params,
                                     struct codel_vars *vars,
                                     struct codel_stats *stats,
                                     codel_skb_dequeue_t dequeue_func)
{
        struct sk_buff *skb = dequeue_func(vars, sch);
        codel_time_t now;
        bool drop;

        if (!skb) {
                vars->dropping = false;
                return skb;
        }
        now = codel_get_time();
        drop = codel_should_drop(skb, sch, vars, params, stats, 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;
                                }
                                qdisc_drop(skb, sch);
                                stats->drop_count++;
                                skb = dequeue_func(vars, sch);
                                if (!codel_should_drop(skb, sch,
                                                       vars, params, stats, 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 {
                        qdisc_drop(skb, sch);
                        stats->drop_count++;

                        skb = dequeue_func(vars, sch);
                        drop = codel_should_drop(skb, sch, vars, params,
                                                 stats, 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:
        return skb;
}
#endif