/*
   * 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>
   *
   *  Implemented on linux by :
   *  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.
   *
   */
  
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/errno.h>
  #include <linux/skbuff.h>

  #include <linux/prefetch.h>

  #include <net/pkt_sched.h>
  #include <net/codel.h>

  #include <net/codel_impl.h>
  #include <net/codel_qdisc.h>

  
  
  #define DEFAULT_CODEL_LIMIT 1000
  
  struct codel_sched_data {
  	struct codel_params	params;
  	struct codel_vars	vars;
  	struct codel_stats	stats;
  	u32			drop_overlimit;
  };
  
  /* This is the specific function called from codel_dequeue()
   * to dequeue a packet from queue. Note: backlog is handled in
   * codel, we dont need to reduce it here.
   */

  static struct sk_buff *dequeue_func(struct codel_vars *vars, void *ctx)

  {

  	struct Qdisc *sch = ctx;

  	struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);

  	if (skb)
  		sch->qstats.backlog -= qdisc_pkt_len(skb);

  	prefetch(&skb->end); /* we'll need skb_shinfo() */
  	return skb;
  }

  static void drop_func(struct sk_buff *skb, void *ctx)
  {
  	struct Qdisc *sch = ctx;

  	kfree_skb(skb);
  	qdisc_qstats_drop(sch);

  }

  static struct sk_buff *codel_qdisc_dequeue(struct Qdisc *sch)
  {
  	struct codel_sched_data *q = qdisc_priv(sch);
  	struct sk_buff *skb;

  	skb = codel_dequeue(sch, &sch->qstats.backlog, &q->params, &q->vars,
  			    &q->stats, qdisc_pkt_len, codel_get_enqueue_time,
  			    drop_func, dequeue_func);

  	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,

  	 * or HTB crashes. Defer it for next round.
  	 */
  	if (q->stats.drop_count && sch->q.qlen) {

  		qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);

  		q->stats.drop_count = 0;

  		q->stats.drop_len = 0;

  	}
  	if (skb)
  		qdisc_bstats_update(sch, skb);
  	return skb;
  }

  static int codel_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
  			       struct sk_buff **to_free)

  {
  	struct codel_sched_data *q;
  
  	if (likely(qdisc_qlen(sch) < sch->limit)) {
  		codel_set_enqueue_time(skb);
  		return qdisc_enqueue_tail(skb, sch);
  	}
  	q = qdisc_priv(sch);
  	q->drop_overlimit++;

  	return qdisc_drop(skb, sch, to_free);

  }
  
  static const struct nla_policy codel_policy[TCA_CODEL_MAX + 1] = {
  	[TCA_CODEL_TARGET]	= { .type = NLA_U32 },
  	[TCA_CODEL_LIMIT]	= { .type = NLA_U32 },
  	[TCA_CODEL_INTERVAL]	= { .type = NLA_U32 },
  	[TCA_CODEL_ECN]		= { .type = NLA_U32 },

  	[TCA_CODEL_CE_THRESHOLD]= { .type = NLA_U32 },

  };
  
  static int codel_change(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct codel_sched_data *q = qdisc_priv(sch);
  	struct nlattr *tb[TCA_CODEL_MAX + 1];

  	unsigned int qlen, dropped = 0;

  	int err;
  
  	if (!opt)
  		return -EINVAL;

  	err = nla_parse_nested(tb, TCA_CODEL_MAX, opt, codel_policy, NULL);

  	if (err < 0)
  		return err;
  
  	sch_tree_lock(sch);
  
  	if (tb[TCA_CODEL_TARGET]) {
  		u32 target = nla_get_u32(tb[TCA_CODEL_TARGET]);
  
  		q->params.target = ((u64)target * NSEC_PER_USEC) >> CODEL_SHIFT;
  	}

  	if (tb[TCA_CODEL_CE_THRESHOLD]) {
  		u64 val = nla_get_u32(tb[TCA_CODEL_CE_THRESHOLD]);
  
  		q->params.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
  	}

  	if (tb[TCA_CODEL_INTERVAL]) {
  		u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);
  
  		q->params.interval = ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT;
  	}
  
  	if (tb[TCA_CODEL_LIMIT])
  		sch->limit = nla_get_u32(tb[TCA_CODEL_LIMIT]);
  
  	if (tb[TCA_CODEL_ECN])
  		q->params.ecn = !!nla_get_u32(tb[TCA_CODEL_ECN]);
  
  	qlen = sch->q.qlen;
  	while (sch->q.qlen > sch->limit) {

  		struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);

  		dropped += qdisc_pkt_len(skb);

  		qdisc_qstats_backlog_dec(sch, skb);

  		rtnl_qdisc_drop(skb, sch);

  	}

  	qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);

  
  	sch_tree_unlock(sch);
  	return 0;
  }
  
  static int codel_init(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct codel_sched_data *q = qdisc_priv(sch);
  
  	sch->limit = DEFAULT_CODEL_LIMIT;

  	codel_params_init(&q->params);

  	codel_vars_init(&q->vars);
  	codel_stats_init(&q->stats);

  	q->params.mtu = psched_mtu(qdisc_dev(sch));

  
  	if (opt) {
  		int err = codel_change(sch, opt);
  
  		if (err)
  			return err;
  	}
  
  	if (sch->limit >= 1)
  		sch->flags |= TCQ_F_CAN_BYPASS;
  	else
  		sch->flags &= ~TCQ_F_CAN_BYPASS;
  
  	return 0;
  }
  
  static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
  {
  	struct codel_sched_data *q = qdisc_priv(sch);
  	struct nlattr *opts;
  
  	opts = nla_nest_start(skb, TCA_OPTIONS);
  	if (opts == NULL)
  		goto nla_put_failure;
  
  	if (nla_put_u32(skb, TCA_CODEL_TARGET,
  			codel_time_to_us(q->params.target)) ||
  	    nla_put_u32(skb, TCA_CODEL_LIMIT,
  			sch->limit) ||
  	    nla_put_u32(skb, TCA_CODEL_INTERVAL,
  			codel_time_to_us(q->params.interval)) ||
  	    nla_put_u32(skb, TCA_CODEL_ECN,
  			q->params.ecn))
  		goto nla_put_failure;

  	if (q->params.ce_threshold != CODEL_DISABLED_THRESHOLD &&
  	    nla_put_u32(skb, TCA_CODEL_CE_THRESHOLD,
  			codel_time_to_us(q->params.ce_threshold)))
  		goto nla_put_failure;

  	return nla_nest_end(skb, opts);
  
  nla_put_failure:
  	nla_nest_cancel(skb, opts);
  	return -1;
  }
  
  static int codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
  {
  	const struct codel_sched_data *q = qdisc_priv(sch);
  	struct tc_codel_xstats st = {
  		.maxpacket	= q->stats.maxpacket,
  		.count		= q->vars.count,
  		.lastcount	= q->vars.lastcount,
  		.drop_overlimit = q->drop_overlimit,
  		.ldelay		= codel_time_to_us(q->vars.ldelay),
  		.dropping	= q->vars.dropping,
  		.ecn_mark	= q->stats.ecn_mark,

  		.ce_mark	= q->stats.ce_mark,

  	};
  
  	if (q->vars.dropping) {
  		codel_tdiff_t delta = q->vars.drop_next - codel_get_time();
  
  		if (delta >= 0)
  			st.drop_next = codel_time_to_us(delta);
  		else
  			st.drop_next = -codel_time_to_us(-delta);
  	}
  
  	return gnet_stats_copy_app(d, &st, sizeof(st));
  }
  
  static void codel_reset(struct Qdisc *sch)
  {
  	struct codel_sched_data *q = qdisc_priv(sch);
  
  	qdisc_reset_queue(sch);
  	codel_vars_init(&q->vars);
  }
  
  static struct Qdisc_ops codel_qdisc_ops __read_mostly = {
  	.id		=	"codel",
  	.priv_size	=	sizeof(struct codel_sched_data),
  
  	.enqueue	=	codel_qdisc_enqueue,
  	.dequeue	=	codel_qdisc_dequeue,
  	.peek		=	qdisc_peek_dequeued,
  	.init		=	codel_init,
  	.reset		=	codel_reset,
  	.change 	=	codel_change,
  	.dump		=	codel_dump,
  	.dump_stats	=	codel_dump_stats,
  	.owner		=	THIS_MODULE,
  };
  
  static int __init codel_module_init(void)
  {
  	return register_qdisc(&codel_qdisc_ops);
  }
  
  static void __exit codel_module_exit(void)
  {
  	unregister_qdisc(&codel_qdisc_ops);
  }
  
  module_init(codel_module_init)
  module_exit(codel_module_exit)
  
  MODULE_DESCRIPTION("Controlled Delay queue discipline");
  MODULE_AUTHOR("Dave Taht");
  MODULE_AUTHOR("Eric Dumazet");
  MODULE_LICENSE("Dual BSD/GPL");