/*
   * net/sched/sch_fifo.c	The simplest FIFO queue.
   *
   *		This program is free software; you can redistribute it and/or
   *		modify it under the terms of the GNU General Public License
   *		as published by the Free Software Foundation; either version
   *		2 of the License, or (at your option) any later version.
   *
   * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   */

  #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 <net/pkt_sched.h>
  
  /* 1 band FIFO pseudo-"scheduler" */

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

  {

  	if (likely(sch->qstats.backlog + qdisc_pkt_len(skb) <= sch->limit))

  		return qdisc_enqueue_tail(skb, sch);

  	return qdisc_drop(skb, sch, to_free);

  }

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

  {

  	if (likely(sch->q.qlen < sch->limit))

  		return qdisc_enqueue_tail(skb, sch);

  	return qdisc_drop(skb, sch, to_free);

  }

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

  {

  	unsigned int prev_backlog;

  	if (likely(sch->q.qlen < sch->limit))

  		return qdisc_enqueue_tail(skb, sch);

  	prev_backlog = sch->qstats.backlog;

  	/* queue full, remove one skb to fulfill the limit */

  	__qdisc_queue_drop_head(sch, &sch->q, to_free);

  	qdisc_qstats_drop(sch);

  	qdisc_enqueue_tail(skb, sch);

  	qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);

  	return NET_XMIT_CN;
  }

  static int fifo_init(struct Qdisc *sch, struct nlattr *opt)

  {

  	bool bypass;
  	bool is_bfifo = sch->ops == &bfifo_qdisc_ops;

  
  	if (opt == NULL) {

  		u32 limit = qdisc_dev(sch)->tx_queue_len;

  		if (is_bfifo)

  			limit *= psched_mtu(qdisc_dev(sch));

  		sch->limit = limit;

  	} else {

  		struct tc_fifo_qopt *ctl = nla_data(opt);

  		if (nla_len(opt) < sizeof(*ctl))

  			return -EINVAL;

  		sch->limit = ctl->limit;

  	}

  	if (is_bfifo)

  		bypass = sch->limit >= psched_mtu(qdisc_dev(sch));

  	else

  		bypass = sch->limit >= 1;

  
  	if (bypass)
  		sch->flags |= TCQ_F_CAN_BYPASS;
  	else
  		sch->flags &= ~TCQ_F_CAN_BYPASS;

  	return 0;
  }
  
  static int fifo_dump(struct Qdisc *sch, struct sk_buff *skb)
  {

  	struct tc_fifo_qopt opt = { .limit = sch->limit };

  	if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
  		goto nla_put_failure;

  	return skb->len;

  nla_put_failure:

  	return -1;
  }

  struct Qdisc_ops pfifo_qdisc_ops __read_mostly = {

  	.id		=	"pfifo",

  	.priv_size	=	0,

  	.enqueue	=	pfifo_enqueue,

  	.dequeue	=	qdisc_dequeue_head,

  	.peek		=	qdisc_peek_head,

  	.init		=	fifo_init,

  	.reset		=	qdisc_reset_queue,

  	.change		=	fifo_init,
  	.dump		=	fifo_dump,
  	.owner		=	THIS_MODULE,
  };

  EXPORT_SYMBOL(pfifo_qdisc_ops);

  struct Qdisc_ops bfifo_qdisc_ops __read_mostly = {

  	.id		=	"bfifo",

  	.priv_size	=	0,

  	.enqueue	=	bfifo_enqueue,

  	.dequeue	=	qdisc_dequeue_head,

  	.peek		=	qdisc_peek_head,

  	.init		=	fifo_init,

  	.reset		=	qdisc_reset_queue,

  	.change		=	fifo_init,
  	.dump		=	fifo_dump,
  	.owner		=	THIS_MODULE,
  };

  EXPORT_SYMBOL(bfifo_qdisc_ops);

  struct Qdisc_ops pfifo_head_drop_qdisc_ops __read_mostly = {
  	.id		=	"pfifo_head_drop",

  	.priv_size	=	0,

  	.enqueue	=	pfifo_tail_enqueue,
  	.dequeue	=	qdisc_dequeue_head,
  	.peek		=	qdisc_peek_head,

  	.init		=	fifo_init,
  	.reset		=	qdisc_reset_queue,
  	.change		=	fifo_init,
  	.dump		=	fifo_dump,
  	.owner		=	THIS_MODULE,
  };

  /* Pass size change message down to embedded FIFO */
  int fifo_set_limit(struct Qdisc *q, unsigned int limit)
  {
  	struct nlattr *nla;
  	int ret = -ENOMEM;
  
  	/* Hack to avoid sending change message to non-FIFO */
  	if (strncmp(q->ops->id + 1, "fifo", 4) != 0)
  		return 0;
  
  	nla = kmalloc(nla_attr_size(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
  	if (nla) {
  		nla->nla_type = RTM_NEWQDISC;
  		nla->nla_len = nla_attr_size(sizeof(struct tc_fifo_qopt));
  		((struct tc_fifo_qopt *)nla_data(nla))->limit = limit;
  
  		ret = q->ops->change(q, nla);
  		kfree(nla);
  	}
  	return ret;
  }
  EXPORT_SYMBOL(fifo_set_limit);
  
  struct Qdisc *fifo_create_dflt(struct Qdisc *sch, struct Qdisc_ops *ops,
  			       unsigned int limit)
  {
  	struct Qdisc *q;
  	int err = -ENOMEM;

  	q = qdisc_create_dflt(sch->dev_queue, ops, TC_H_MAKE(sch->handle, 1));

  	if (q) {
  		err = fifo_set_limit(q, limit);
  		if (err < 0) {
  			qdisc_destroy(q);
  			q = NULL;
  		}
  	}
  
  	return q ? : ERR_PTR(err);
  }
  EXPORT_SYMBOL(fifo_create_dflt);