/*
   * Fair Queue CoDel discipline
   *
   *	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.
   *

   *  Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>

   */
  
  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/jiffies.h>
  #include <linux/string.h>
  #include <linux/in.h>
  #include <linux/errno.h>
  #include <linux/init.h>
  #include <linux/skbuff.h>
  #include <linux/jhash.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  #include <net/netlink.h>
  #include <net/pkt_sched.h>

  #include <net/pkt_cls.h>

  #include <net/codel.h>

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

  
  /*	Fair Queue CoDel.
   *
   * Principles :
   * Packets are classified (internal classifier or external) on flows.
   * This is a Stochastic model (as we use a hash, several flows
   *			       might be hashed on same slot)
   * Each flow has a CoDel managed queue.
   * Flows are linked onto two (Round Robin) lists,
   * so that new flows have priority on old ones.
   *
   * For a given flow, packets are not reordered (CoDel uses a FIFO)
   * head drops only.
   * ECN capability is on by default.
   * Low memory footprint (64 bytes per flow)
   */
  
  struct fq_codel_flow {
  	struct sk_buff	  *head;
  	struct sk_buff	  *tail;
  	struct list_head  flowchain;
  	int		  deficit;
  	u32		  dropped; /* number of drops (or ECN marks) on this flow */
  	struct codel_vars cvars;
  }; /* please try to keep this structure <= 64 bytes */
  
  struct fq_codel_sched_data {

  	struct tcf_proto __rcu *filter_list; /* optional external classifier */

  	struct tcf_block *block;

  	struct fq_codel_flow *flows;	/* Flows table [flows_cnt] */
  	u32		*backlogs;	/* backlog table [flows_cnt] */
  	u32		flows_cnt;	/* number of flows */

  	u32		quantum;	/* psched_mtu(qdisc_dev(sch)); */

  	u32		drop_batch_size;

  	u32		memory_limit;

  	struct codel_params cparams;
  	struct codel_stats cstats;

  	u32		memory_usage;
  	u32		drop_overmemory;

  	u32		drop_overlimit;
  	u32		new_flow_count;
  
  	struct list_head new_flows;	/* list of new flows */
  	struct list_head old_flows;	/* list of old flows */
  };
  
  static unsigned int fq_codel_hash(const struct fq_codel_sched_data *q,

  				  struct sk_buff *skb)

  {

  	return reciprocal_scale(skb_get_hash(skb), q->flows_cnt);

  }
  
  static unsigned int fq_codel_classify(struct sk_buff *skb, struct Qdisc *sch,
  				      int *qerr)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);

  	struct tcf_proto *filter;

  	struct tcf_result res;
  	int result;
  
  	if (TC_H_MAJ(skb->priority) == sch->handle &&
  	    TC_H_MIN(skb->priority) > 0 &&
  	    TC_H_MIN(skb->priority) <= q->flows_cnt)
  		return TC_H_MIN(skb->priority);

  	filter = rcu_dereference_bh(q->filter_list);

  	if (!filter)

  		return fq_codel_hash(q, skb) + 1;
  
  	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;

  	result = tcf_classify(skb, filter, &res, false);

  	if (result >= 0) {
  #ifdef CONFIG_NET_CLS_ACT
  		switch (result) {
  		case TC_ACT_STOLEN:
  		case TC_ACT_QUEUED:

  		case TC_ACT_TRAP:

  			*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
  		case TC_ACT_SHOT:
  			return 0;
  		}
  #endif
  		if (TC_H_MIN(res.classid) <= q->flows_cnt)
  			return TC_H_MIN(res.classid);
  	}
  	return 0;
  }
  
  /* helper functions : might be changed when/if skb use a standard list_head */
  
  /* remove one skb from head of slot queue */
  static inline struct sk_buff *dequeue_head(struct fq_codel_flow *flow)
  {
  	struct sk_buff *skb = flow->head;
  
  	flow->head = skb->next;
  	skb->next = NULL;
  	return skb;
  }
  
  /* add skb to flow queue (tail add) */
  static inline void flow_queue_add(struct fq_codel_flow *flow,
  				  struct sk_buff *skb)
  {
  	if (flow->head == NULL)
  		flow->head = skb;
  	else
  		flow->tail->next = skb;
  	flow->tail = skb;
  	skb->next = NULL;
  }

  static unsigned int fq_codel_drop(struct Qdisc *sch, unsigned int max_packets,
  				  struct sk_buff **to_free)

  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	struct sk_buff *skb;
  	unsigned int maxbacklog = 0, idx = 0, i, len;
  	struct fq_codel_flow *flow;

  	unsigned int threshold;

  	unsigned int mem = 0;

  	/* Queue is full! Find the fat flow and drop packet(s) from it.

  	 * This might sound expensive, but with 1024 flows, we scan
  	 * 4KB of memory, and we dont need to handle a complex tree
  	 * in fast path (packet queue/enqueue) with many cache misses.

  	 * In stress mode, we'll try to drop 64 packets from the flow,
  	 * amortizing this linear lookup to one cache line per drop.

  	 */
  	for (i = 0; i < q->flows_cnt; i++) {
  		if (q->backlogs[i] > maxbacklog) {
  			maxbacklog = q->backlogs[i];
  			idx = i;
  		}
  	}

  
  	/* Our goal is to drop half of this fat flow backlog */
  	threshold = maxbacklog >> 1;

  	flow = &q->flows[idx];

  	len = 0;
  	i = 0;
  	do {
  		skb = dequeue_head(flow);
  		len += qdisc_pkt_len(skb);

  		mem += get_codel_cb(skb)->mem_usage;

  		__qdisc_drop(skb, to_free);

  	} while (++i < max_packets && len < threshold);
  
  	flow->dropped += i;

  	q->backlogs[idx] -= len;

  	q->memory_usage -= mem;

  	sch->qstats.drops += i;
  	sch->qstats.backlog -= len;
  	sch->q.qlen -= i;

  	return idx;
  }

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

  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);

  	unsigned int idx, prev_backlog, prev_qlen;

  	struct fq_codel_flow *flow;
  	int uninitialized_var(ret);

  	unsigned int pkt_len;

  	bool memory_limited;

  
  	idx = fq_codel_classify(skb, sch, &ret);
  	if (idx == 0) {
  		if (ret & __NET_XMIT_BYPASS)

  			qdisc_qstats_drop(sch);

  		__qdisc_drop(skb, to_free);

  		return ret;
  	}
  	idx--;
  
  	codel_set_enqueue_time(skb);
  	flow = &q->flows[idx];
  	flow_queue_add(flow, skb);
  	q->backlogs[idx] += qdisc_pkt_len(skb);

  	qdisc_qstats_backlog_inc(sch, skb);

  
  	if (list_empty(&flow->flowchain)) {
  		list_add_tail(&flow->flowchain, &q->new_flows);

  		q->new_flow_count++;
  		flow->deficit = q->quantum;
  		flow->dropped = 0;
  	}

  	get_codel_cb(skb)->mem_usage = skb->truesize;
  	q->memory_usage += get_codel_cb(skb)->mem_usage;

  	memory_limited = q->memory_usage > q->memory_limit;
  	if (++sch->q.qlen <= sch->limit && !memory_limited)

  		return NET_XMIT_SUCCESS;

  	prev_backlog = sch->qstats.backlog;

  	prev_qlen = sch->q.qlen;

  	/* save this packet length as it might be dropped by fq_codel_drop() */
  	pkt_len = qdisc_pkt_len(skb);

  	/* fq_codel_drop() is quite expensive, as it performs a linear search
  	 * in q->backlogs[] to find a fat flow.
  	 * So instead of dropping a single packet, drop half of its backlog
  	 * with a 64 packets limit to not add a too big cpu spike here.

  	 */

  	ret = fq_codel_drop(sch, q->drop_batch_size, to_free);

  	prev_qlen -= sch->q.qlen;
  	prev_backlog -= sch->qstats.backlog;
  	q->drop_overlimit += prev_qlen;

  	if (memory_limited)

  		q->drop_overmemory += prev_qlen;

  	/* As we dropped packet(s), better let upper stack know this.
  	 * If we dropped a packet for this flow, return NET_XMIT_CN,
  	 * but in this case, our parents wont increase their backlogs.
  	 */
  	if (ret == idx) {
  		qdisc_tree_reduce_backlog(sch, prev_qlen - 1,
  					  prev_backlog - pkt_len);
  		return NET_XMIT_CN;
  	}
  	qdisc_tree_reduce_backlog(sch, prev_qlen, prev_backlog);
  	return NET_XMIT_SUCCESS;

  }
  
  /* 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 fq_codel_sched_data *q = qdisc_priv(sch);

  	struct fq_codel_flow *flow;
  	struct sk_buff *skb = NULL;
  
  	flow = container_of(vars, struct fq_codel_flow, cvars);
  	if (flow->head) {
  		skb = dequeue_head(flow);

  		q->backlogs[flow - q->flows] -= qdisc_pkt_len(skb);

  		q->memory_usage -= get_codel_cb(skb)->mem_usage;

  		sch->q.qlen--;

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

  	}
  	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 *fq_codel_dequeue(struct Qdisc *sch)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	struct sk_buff *skb;
  	struct fq_codel_flow *flow;
  	struct list_head *head;
  	u32 prev_drop_count, prev_ecn_mark;
  
  begin:
  	head = &q->new_flows;
  	if (list_empty(head)) {
  		head = &q->old_flows;
  		if (list_empty(head))
  			return NULL;
  	}
  	flow = list_first_entry(head, struct fq_codel_flow, flowchain);
  
  	if (flow->deficit <= 0) {
  		flow->deficit += q->quantum;
  		list_move_tail(&flow->flowchain, &q->old_flows);
  		goto begin;
  	}
  
  	prev_drop_count = q->cstats.drop_count;
  	prev_ecn_mark = q->cstats.ecn_mark;

  	skb = codel_dequeue(sch, &sch->qstats.backlog, &q->cparams,
  			    &flow->cvars, &q->cstats, qdisc_pkt_len,
  			    codel_get_enqueue_time, drop_func, dequeue_func);

  
  	flow->dropped += q->cstats.drop_count - prev_drop_count;
  	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
  
  	if (!skb) {
  		/* force a pass through old_flows to prevent starvation */
  		if ((head == &q->new_flows) && !list_empty(&q->old_flows))
  			list_move_tail(&flow->flowchain, &q->old_flows);
  		else
  			list_del_init(&flow->flowchain);
  		goto begin;
  	}
  	qdisc_bstats_update(sch, skb);
  	flow->deficit -= qdisc_pkt_len(skb);

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

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

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

  		q->cstats.drop_count = 0;

  		q->cstats.drop_len = 0;

  	}
  	return skb;
  }

  static void fq_codel_flow_purge(struct fq_codel_flow *flow)
  {
  	rtnl_kfree_skbs(flow->head, flow->tail);
  	flow->head = NULL;
  }

  static void fq_codel_reset(struct Qdisc *sch)
  {

  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	int i;

  	INIT_LIST_HEAD(&q->new_flows);
  	INIT_LIST_HEAD(&q->old_flows);
  	for (i = 0; i < q->flows_cnt; i++) {
  		struct fq_codel_flow *flow = q->flows + i;

  		fq_codel_flow_purge(flow);

  		INIT_LIST_HEAD(&flow->flowchain);
  		codel_vars_init(&flow->cvars);
  	}
  	memset(q->backlogs, 0, q->flows_cnt * sizeof(u32));
  	sch->q.qlen = 0;

  	sch->qstats.backlog = 0;

  	q->memory_usage = 0;

  }
  
  static const struct nla_policy fq_codel_policy[TCA_FQ_CODEL_MAX + 1] = {
  	[TCA_FQ_CODEL_TARGET]	= { .type = NLA_U32 },
  	[TCA_FQ_CODEL_LIMIT]	= { .type = NLA_U32 },
  	[TCA_FQ_CODEL_INTERVAL]	= { .type = NLA_U32 },
  	[TCA_FQ_CODEL_ECN]	= { .type = NLA_U32 },
  	[TCA_FQ_CODEL_FLOWS]	= { .type = NLA_U32 },
  	[TCA_FQ_CODEL_QUANTUM]	= { .type = NLA_U32 },

  	[TCA_FQ_CODEL_CE_THRESHOLD] = { .type = NLA_U32 },

  	[TCA_FQ_CODEL_DROP_BATCH_SIZE] = { .type = NLA_U32 },

  	[TCA_FQ_CODEL_MEMORY_LIMIT] = { .type = NLA_U32 },

  };
  
  static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	struct nlattr *tb[TCA_FQ_CODEL_MAX + 1];
  	int err;
  
  	if (!opt)
  		return -EINVAL;

  	err = nla_parse_nested(tb, TCA_FQ_CODEL_MAX, opt, fq_codel_policy,
  			       NULL);

  	if (err < 0)
  		return err;
  	if (tb[TCA_FQ_CODEL_FLOWS]) {
  		if (q->flows)
  			return -EINVAL;
  		q->flows_cnt = nla_get_u32(tb[TCA_FQ_CODEL_FLOWS]);
  		if (!q->flows_cnt ||
  		    q->flows_cnt > 65536)
  			return -EINVAL;
  	}
  	sch_tree_lock(sch);
  
  	if (tb[TCA_FQ_CODEL_TARGET]) {
  		u64 target = nla_get_u32(tb[TCA_FQ_CODEL_TARGET]);
  
  		q->cparams.target = (target * NSEC_PER_USEC) >> CODEL_SHIFT;
  	}

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

  	if (tb[TCA_FQ_CODEL_INTERVAL]) {
  		u64 interval = nla_get_u32(tb[TCA_FQ_CODEL_INTERVAL]);
  
  		q->cparams.interval = (interval * NSEC_PER_USEC) >> CODEL_SHIFT;
  	}
  
  	if (tb[TCA_FQ_CODEL_LIMIT])
  		sch->limit = nla_get_u32(tb[TCA_FQ_CODEL_LIMIT]);
  
  	if (tb[TCA_FQ_CODEL_ECN])
  		q->cparams.ecn = !!nla_get_u32(tb[TCA_FQ_CODEL_ECN]);
  
  	if (tb[TCA_FQ_CODEL_QUANTUM])
  		q->quantum = max(256U, nla_get_u32(tb[TCA_FQ_CODEL_QUANTUM]));

  	if (tb[TCA_FQ_CODEL_DROP_BATCH_SIZE])
  		q->drop_batch_size = min(1U, nla_get_u32(tb[TCA_FQ_CODEL_DROP_BATCH_SIZE]));

  	if (tb[TCA_FQ_CODEL_MEMORY_LIMIT])
  		q->memory_limit = min(1U << 31, nla_get_u32(tb[TCA_FQ_CODEL_MEMORY_LIMIT]));
  
  	while (sch->q.qlen > sch->limit ||
  	       q->memory_usage > q->memory_limit) {

  		struct sk_buff *skb = fq_codel_dequeue(sch);

  		q->cstats.drop_len += qdisc_pkt_len(skb);

  		rtnl_kfree_skbs(skb, skb);

  		q->cstats.drop_count++;
  	}

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

  	q->cstats.drop_count = 0;

  	q->cstats.drop_len = 0;

  
  	sch_tree_unlock(sch);
  	return 0;
  }

  static void fq_codel_destroy(struct Qdisc *sch)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);

  	tcf_block_put(q->block);

  	kvfree(q->backlogs);
  	kvfree(q->flows);

  }
  
  static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	int i;

  	int err;

  
  	sch->limit = 10*1024;
  	q->flows_cnt = 1024;

  	q->memory_limit = 32 << 20; /* 32 MBytes */

  	q->drop_batch_size = 64;

  	q->quantum = psched_mtu(qdisc_dev(sch));

  	INIT_LIST_HEAD(&q->new_flows);
  	INIT_LIST_HEAD(&q->old_flows);

  	codel_params_init(&q->cparams);

  	codel_stats_init(&q->cstats);
  	q->cparams.ecn = true;

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

  
  	if (opt) {
  		int err = fq_codel_change(sch, opt);
  		if (err)
  			return err;
  	}

  	err = tcf_block_get(&q->block, &q->filter_list);
  	if (err)
  		return err;

  	if (!q->flows) {

  		q->flows = kvzalloc(q->flows_cnt *
  					   sizeof(struct fq_codel_flow), GFP_KERNEL);

  		if (!q->flows)
  			return -ENOMEM;

  		q->backlogs = kvzalloc(q->flows_cnt * sizeof(u32), GFP_KERNEL);

  		if (!q->backlogs)

  			return -ENOMEM;

  		for (i = 0; i < q->flows_cnt; i++) {
  			struct fq_codel_flow *flow = q->flows + i;
  
  			INIT_LIST_HEAD(&flow->flowchain);

  			codel_vars_init(&flow->cvars);

  		}
  	}
  	if (sch->limit >= 1)
  		sch->flags |= TCQ_F_CAN_BYPASS;
  	else
  		sch->flags &= ~TCQ_F_CAN_BYPASS;
  	return 0;
  }
  
  static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
  {
  	struct fq_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_FQ_CODEL_TARGET,
  			codel_time_to_us(q->cparams.target)) ||
  	    nla_put_u32(skb, TCA_FQ_CODEL_LIMIT,
  			sch->limit) ||
  	    nla_put_u32(skb, TCA_FQ_CODEL_INTERVAL,
  			codel_time_to_us(q->cparams.interval)) ||
  	    nla_put_u32(skb, TCA_FQ_CODEL_ECN,
  			q->cparams.ecn) ||
  	    nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM,
  			q->quantum) ||

  	    nla_put_u32(skb, TCA_FQ_CODEL_DROP_BATCH_SIZE,
  			q->drop_batch_size) ||

  	    nla_put_u32(skb, TCA_FQ_CODEL_MEMORY_LIMIT,
  			q->memory_limit) ||

  	    nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
  			q->flows_cnt))
  		goto nla_put_failure;

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

  	return nla_nest_end(skb, opts);

  
  nla_put_failure:
  	return -1;
  }
  
  static int fq_codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	struct tc_fq_codel_xstats st = {
  		.type				= TCA_FQ_CODEL_XSTATS_QDISC,

  	};
  	struct list_head *pos;

  	st.qdisc_stats.maxpacket = q->cstats.maxpacket;
  	st.qdisc_stats.drop_overlimit = q->drop_overlimit;
  	st.qdisc_stats.ecn_mark = q->cstats.ecn_mark;
  	st.qdisc_stats.new_flow_count = q->new_flow_count;

  	st.qdisc_stats.ce_mark = q->cstats.ce_mark;

  	st.qdisc_stats.memory_usage  = q->memory_usage;
  	st.qdisc_stats.drop_overmemory = q->drop_overmemory;

  	sch_tree_lock(sch);

  	list_for_each(pos, &q->new_flows)
  		st.qdisc_stats.new_flows_len++;
  
  	list_for_each(pos, &q->old_flows)
  		st.qdisc_stats.old_flows_len++;

  	sch_tree_unlock(sch);

  
  	return gnet_stats_copy_app(d, &st, sizeof(st));
  }
  
  static struct Qdisc *fq_codel_leaf(struct Qdisc *sch, unsigned long arg)
  {
  	return NULL;
  }

  static unsigned long fq_codel_find(struct Qdisc *sch, u32 classid)

  {
  	return 0;
  }
  
  static unsigned long fq_codel_bind(struct Qdisc *sch, unsigned long parent,
  			      u32 classid)
  {
  	/* we cannot bypass queue discipline anymore */
  	sch->flags &= ~TCQ_F_CAN_BYPASS;
  	return 0;
  }

  static void fq_codel_unbind(struct Qdisc *q, unsigned long cl)

  {
  }

  static struct tcf_block *fq_codel_tcf_block(struct Qdisc *sch, unsigned long cl)

  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  
  	if (cl)
  		return NULL;

  	return q->block;

  }
  
  static int fq_codel_dump_class(struct Qdisc *sch, unsigned long cl,
  			  struct sk_buff *skb, struct tcmsg *tcm)
  {
  	tcm->tcm_handle |= TC_H_MIN(cl);
  	return 0;
  }
  
  static int fq_codel_dump_class_stats(struct Qdisc *sch, unsigned long cl,
  				     struct gnet_dump *d)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	u32 idx = cl - 1;
  	struct gnet_stats_queue qs = { 0 };
  	struct tc_fq_codel_xstats xstats;
  
  	if (idx < q->flows_cnt) {
  		const struct fq_codel_flow *flow = &q->flows[idx];

  		const struct sk_buff *skb;

  
  		memset(&xstats, 0, sizeof(xstats));
  		xstats.type = TCA_FQ_CODEL_XSTATS_CLASS;
  		xstats.class_stats.deficit = flow->deficit;
  		xstats.class_stats.ldelay =
  			codel_time_to_us(flow->cvars.ldelay);
  		xstats.class_stats.count = flow->cvars.count;
  		xstats.class_stats.lastcount = flow->cvars.lastcount;
  		xstats.class_stats.dropping = flow->cvars.dropping;
  		if (flow->cvars.dropping) {
  			codel_tdiff_t delta = flow->cvars.drop_next -
  					      codel_get_time();
  
  			xstats.class_stats.drop_next = (delta >= 0) ?
  				codel_time_to_us(delta) :
  				-codel_time_to_us(-delta);
  		}

  		if (flow->head) {
  			sch_tree_lock(sch);
  			skb = flow->head;
  			while (skb) {
  				qs.qlen++;
  				skb = skb->next;
  			}
  			sch_tree_unlock(sch);

  		}
  		qs.backlog = q->backlogs[idx];
  		qs.drops = flow->dropped;
  	}

  	if (gnet_stats_copy_queue(d, NULL, &qs, qs.qlen) < 0)

  		return -1;
  	if (idx < q->flows_cnt)
  		return gnet_stats_copy_app(d, &xstats, sizeof(xstats));
  	return 0;
  }
  
  static void fq_codel_walk(struct Qdisc *sch, struct qdisc_walker *arg)
  {
  	struct fq_codel_sched_data *q = qdisc_priv(sch);
  	unsigned int i;
  
  	if (arg->stop)
  		return;
  
  	for (i = 0; i < q->flows_cnt; i++) {
  		if (list_empty(&q->flows[i].flowchain) ||
  		    arg->count < arg->skip) {
  			arg->count++;
  			continue;
  		}
  		if (arg->fn(sch, i + 1, arg) < 0) {
  			arg->stop = 1;
  			break;
  		}
  		arg->count++;
  	}
  }
  
  static const struct Qdisc_class_ops fq_codel_class_ops = {
  	.leaf		=	fq_codel_leaf,

  	.find		=	fq_codel_find,

  	.tcf_block	=	fq_codel_tcf_block,

  	.bind_tcf	=	fq_codel_bind,

  	.unbind_tcf	=	fq_codel_unbind,

  	.dump		=	fq_codel_dump_class,
  	.dump_stats	=	fq_codel_dump_class_stats,
  	.walk		=	fq_codel_walk,
  };
  
  static struct Qdisc_ops fq_codel_qdisc_ops __read_mostly = {
  	.cl_ops		=	&fq_codel_class_ops,
  	.id		=	"fq_codel",
  	.priv_size	=	sizeof(struct fq_codel_sched_data),
  	.enqueue	=	fq_codel_enqueue,
  	.dequeue	=	fq_codel_dequeue,
  	.peek		=	qdisc_peek_dequeued,

  	.init		=	fq_codel_init,
  	.reset		=	fq_codel_reset,
  	.destroy	=	fq_codel_destroy,
  	.change		=	fq_codel_change,
  	.dump		=	fq_codel_dump,
  	.dump_stats =	fq_codel_dump_stats,
  	.owner		=	THIS_MODULE,
  };
  
  static int __init fq_codel_module_init(void)
  {
  	return register_qdisc(&fq_codel_qdisc_ops);
  }
  
  static void __exit fq_codel_module_exit(void)
  {
  	unregister_qdisc(&fq_codel_qdisc_ops);
  }
  
  module_init(fq_codel_module_init)
  module_exit(fq_codel_module_exit)
  MODULE_AUTHOR("Eric Dumazet");
  MODULE_LICENSE("GPL");