#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_to_ns(ktime_get());
  
  	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