// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
/*
 * 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>
 */

#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;

        qdisc_dequeue_drop(sch, skb, SKB_DROP_REASON_QDISC_CONGESTED);
        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);

        if (q->stats.drop_count) {
                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_reason(skb, sch, to_free,
                                 SKB_DROP_REASON_QDISC_OVERLIMIT);
}

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 netlink_ext_ack *extack)
{
        unsigned int dropped_pkts = 0, dropped_bytes = 0;
        struct codel_sched_data *q = qdisc_priv(sch);
        struct nlattr *tb[TCA_CODEL_MAX + 1];
        int err;

        err = nla_parse_nested_deprecated(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]);

                WRITE_ONCE(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]);

                WRITE_ONCE(q->params.ce_threshold,
                           (val * NSEC_PER_USEC) >> CODEL_SHIFT);
        }

        if (tb[TCA_CODEL_INTERVAL]) {
                u32 interval = nla_get_u32(tb[TCA_CODEL_INTERVAL]);

                WRITE_ONCE(q->params.interval,
                           ((u64)interval * NSEC_PER_USEC) >> CODEL_SHIFT);
        }

        if (tb[TCA_CODEL_LIMIT])
                WRITE_ONCE(sch->limit,
                           nla_get_u32(tb[TCA_CODEL_LIMIT]));

        if (tb[TCA_CODEL_ECN])
                WRITE_ONCE(q->params.ecn,
                           !!nla_get_u32(tb[TCA_CODEL_ECN]));

        while (sch->q.qlen > sch->limit) {
                struct sk_buff *skb = qdisc_dequeue_internal(sch, true);

                if (!skb)
                        break;

                dropped_pkts++;
                dropped_bytes += qdisc_pkt_len(skb);
                rtnl_qdisc_drop(skb, sch);
        }
        qdisc_tree_reduce_backlog(sch, dropped_pkts, dropped_bytes);

        sch_tree_unlock(sch);
        return 0;
}

static int codel_init(struct Qdisc *sch, struct nlattr *opt,
                      struct netlink_ext_ack *extack)
{
        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, extack);

                if (err)
                        return err;
        }

        if (sch->limit >= 1)
                sch->flags |= TCQ_F_CAN_BYPASS;
        else
                sch->flags &= ~TCQ_F_CAN_BYPASS;

        sch->flags |= TCQ_F_DEQUEUE_DROPS;

        return 0;
}

static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        struct codel_sched_data *q = qdisc_priv(sch);
        codel_time_t ce_threshold;
        struct nlattr *opts;

        opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
        if (opts == NULL)
                goto nla_put_failure;

        if (nla_put_u32(skb, TCA_CODEL_TARGET,
                        codel_time_to_us(READ_ONCE(q->params.target))) ||
            nla_put_u32(skb, TCA_CODEL_LIMIT,
                        READ_ONCE(sch->limit)) ||
            nla_put_u32(skb, TCA_CODEL_INTERVAL,
                        codel_time_to_us(READ_ONCE(q->params.interval))) ||
            nla_put_u32(skb, TCA_CODEL_ECN,
                        READ_ONCE(q->params.ecn)))
                goto nla_put_failure;
        ce_threshold = READ_ONCE(q->params.ce_threshold);
        if (ce_threshold != CODEL_DISABLED_THRESHOLD &&
            nla_put_u32(skb, TCA_CODEL_CE_THRESHOLD,
                        codel_time_to_us(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,
};
MODULE_ALIAS_NET_SCH("codel");

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");