/*
 * net/sched/sch_sfb.c    Stochastic Fair Blue
 *
 * Copyright (c) 2008-2011 Juliusz Chroboczek <jch@pps.jussieu.fr>
 * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * W. Feng, D. Kandlur, D. Saha, K. Shin. Blue:
 * A New Class of Active Queue Management Algorithms.
 * U. Michigan CSE-TR-387-99, April 1999.
 *
 * http://www.thefengs.com/wuchang/blue/CSE-TR-387-99.pdf
 *
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <net/ip.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>

/*
 * SFB uses two B[l][n] : L x N arrays of bins (L levels, N bins per level)
 * This implementation uses L = 8 and N = 16
 * This permits us to split one 32bit hash (provided per packet by rxhash or
 * external classifier) into 8 subhashes of 4 bits.
 */
#define SFB_BUCKET_SHIFT 4
#define SFB_NUMBUCKETS  (1 << SFB_BUCKET_SHIFT) /* N bins per Level */
#define SFB_BUCKET_MASK (SFB_NUMBUCKETS - 1)
#define SFB_LEVELS      (32 / SFB_BUCKET_SHIFT) /* L */

/* SFB algo uses a virtual queue, named "bin" */
struct sfb_bucket {
        u16             qlen; /* length of virtual queue */
        u16             p_mark; /* marking probability */
};

/* We use a double buffering right before hash change
 * (Section 4.4 of SFB reference : moving hash functions)
 */
struct sfb_bins {
        u32               perturbation; /* jhash perturbation */
        struct sfb_bucket bins[SFB_LEVELS][SFB_NUMBUCKETS];
};

struct sfb_sched_data {
        struct Qdisc    *qdisc;
        struct tcf_proto *filter_list;
        unsigned long   rehash_interval;
        unsigned long   warmup_time;    /* double buffering warmup time in jiffies */
        u32             max;
        u32             bin_size;       /* maximum queue length per bin */
        u32             increment;      /* d1 */
        u32             decrement;      /* d2 */
        u32             limit;          /* HARD maximal queue length */
        u32             penalty_rate;
        u32             penalty_burst;
        u32             tokens_avail;
        unsigned long   rehash_time;
        unsigned long   token_time;

        u8              slot;           /* current active bins (0 or 1) */
        bool            double_buffering;
        struct sfb_bins bins[2];

        struct {
                u32     earlydrop;
                u32     penaltydrop;
                u32     bucketdrop;
                u32     queuedrop;
                u32     childdrop;      /* drops in child qdisc */
                u32     marked;         /* ECN mark */
        } stats;
};

/*
 * Each queued skb might be hashed on one or two bins
 * We store in skb_cb the two hash values.
 * (A zero value means double buffering was not used)
 */
struct sfb_skb_cb {
        u32 hashes[2];
};

static inline struct sfb_skb_cb *sfb_skb_cb(const struct sk_buff *skb)
{
        BUILD_BUG_ON(sizeof(skb->cb) <
                sizeof(struct qdisc_skb_cb) + sizeof(struct sfb_skb_cb));
        return (struct sfb_skb_cb *)qdisc_skb_cb(skb)->data;
}

/*
 * If using 'internal' SFB flow classifier, hash comes from skb rxhash
 * If using external classifier, hash comes from the classid.
 */
static u32 sfb_hash(const struct sk_buff *skb, u32 slot)
{
        return sfb_skb_cb(skb)->hashes[slot];
}

/* Probabilities are coded as Q0.16 fixed-point values,
 * with 0xFFFF representing 65535/65536 (almost 1.0)
 * Addition and subtraction are saturating in [0, 65535]
 */
static u32 prob_plus(u32 p1, u32 p2)
{
        u32 res = p1 + p2;

        return min_t(u32, res, SFB_MAX_PROB);
}

static u32 prob_minus(u32 p1, u32 p2)
{
        return p1 > p2 ? p1 - p2 : 0;
}

static void increment_one_qlen(u32 sfbhash, u32 slot, struct sfb_sched_data *q)
{
        int i;
        struct sfb_bucket *b = &q->bins[slot].bins[0][0];

        for (i = 0; i < SFB_LEVELS; i++) {
                u32 hash = sfbhash & SFB_BUCKET_MASK;

                sfbhash >>= SFB_BUCKET_SHIFT;
                if (b[hash].qlen < 0xFFFF)
                        b[hash].qlen++;
                b += SFB_NUMBUCKETS; /* next level */
        }
}

static void increment_qlen(const struct sk_buff *skb, struct sfb_sched_data *q)
{
        u32 sfbhash;

        sfbhash = sfb_hash(skb, 0);
        if (sfbhash)
                increment_one_qlen(sfbhash, 0, q);

        sfbhash = sfb_hash(skb, 1);
        if (sfbhash)
                increment_one_qlen(sfbhash, 1, q);
}

static void decrement_one_qlen(u32 sfbhash, u32 slot,
                               struct sfb_sched_data *q)
{
        int i;
        struct sfb_bucket *b = &q->bins[slot].bins[0][0];

        for (i = 0; i < SFB_LEVELS; i++) {
                u32 hash = sfbhash & SFB_BUCKET_MASK;

                sfbhash >>= SFB_BUCKET_SHIFT;
                if (b[hash].qlen > 0)
                        b[hash].qlen--;
                b += SFB_NUMBUCKETS; /* next level */
        }
}

static void decrement_qlen(const struct sk_buff *skb, struct sfb_sched_data *q)
{
        u32 sfbhash;

        sfbhash = sfb_hash(skb, 0);
        if (sfbhash)
                decrement_one_qlen(sfbhash, 0, q);

        sfbhash = sfb_hash(skb, 1);
        if (sfbhash)
                decrement_one_qlen(sfbhash, 1, q);
}

static void decrement_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
{
        b->p_mark = prob_minus(b->p_mark, q->decrement);
}

static void increment_prob(struct sfb_bucket *b, struct sfb_sched_data *q)
{
        b->p_mark = prob_plus(b->p_mark, q->increment);
}

static void sfb_zero_all_buckets(struct sfb_sched_data *q)
{
        memset(&q->bins, 0, sizeof(q->bins));
}

/*
 * compute max qlen, max p_mark, and avg p_mark
 */
static u32 sfb_compute_qlen(u32 *prob_r, u32 *avgpm_r, const struct sfb_sched_data *q)
{
        int i;
        u32 qlen = 0, prob = 0, totalpm = 0;
        const struct sfb_bucket *b = &q->bins[q->slot].bins[0][0];

        for (i = 0; i < SFB_LEVELS * SFB_NUMBUCKETS; i++) {
                if (qlen < b->qlen)
                        qlen = b->qlen;
                totalpm += b->p_mark;
                if (prob < b->p_mark)
                        prob = b->p_mark;
                b++;
        }
        *prob_r = prob;
        *avgpm_r = totalpm / (SFB_LEVELS * SFB_NUMBUCKETS);
        return qlen;
}


static void sfb_init_perturbation(u32 slot, struct sfb_sched_data *q)
{
        q->bins[slot].perturbation = net_random();
}

static void sfb_swap_slot(struct sfb_sched_data *q)
{
        sfb_init_perturbation(q->slot, q);
        q->slot ^= 1;
        q->double_buffering = false;
}

/* Non elastic flows are allowed to use part of the bandwidth, expressed
 * in "penalty_rate" packets per second, with "penalty_burst" burst
 */
static bool sfb_rate_limit(struct sk_buff *skb, struct sfb_sched_data *q)
{
        if (q->penalty_rate == 0 || q->penalty_burst == 0)
                return true;

        if (q->tokens_avail < 1) {
                unsigned long age = min(10UL * HZ, jiffies - q->token_time);

                q->tokens_avail = (age * q->penalty_rate) / HZ;
                if (q->tokens_avail > q->penalty_burst)
                        q->tokens_avail = q->penalty_burst;
                q->token_time = jiffies;
                if (q->tokens_avail < 1)
                        return true;
        }

        q->tokens_avail--;
        return false;
}

static bool sfb_classify(struct sk_buff *skb, struct sfb_sched_data *q,
                         int *qerr, u32 *salt)
{
        struct tcf_result res;
        int result;

        result = tc_classify(skb, q->filter_list, &res);
        if (result >= 0) {
#ifdef CONFIG_NET_CLS_ACT
                switch (result) {
                case TC_ACT_STOLEN:
                case TC_ACT_QUEUED:
                        *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
                case TC_ACT_SHOT:
                        return false;
                }
#endif
                *salt = TC_H_MIN(res.classid);
                return true;
        }
        return false;
}

static int sfb_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{

        struct sfb_sched_data *q = qdisc_priv(sch);
        struct Qdisc *child = q->qdisc;
        int i;
        u32 p_min = ~0;
        u32 minqlen = ~0;
        u32 r, slot, salt, sfbhash;
        int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;

        if (q->rehash_interval > 0) {
                unsigned long limit = q->rehash_time + q->rehash_interval;

                if (unlikely(time_after(jiffies, limit))) {
                        sfb_swap_slot(q);
                        q->rehash_time = jiffies;
                } else if (unlikely(!q->double_buffering && q->warmup_time > 0 &&
                                    time_after(jiffies, limit - q->warmup_time))) {
                        q->double_buffering = true;
                }
        }

        if (q->filter_list) {
                /* If using external classifiers, get result and record it. */
                if (!sfb_classify(skb, q, &ret, &salt))
                        goto other_drop;
        } else {
                salt = skb_get_rxhash(skb);
        }

        slot = q->slot;

        sfbhash = jhash_1word(salt, q->bins[slot].perturbation);
        if (!sfbhash)
                sfbhash = 1;
        sfb_skb_cb(skb)->hashes[slot] = sfbhash;

        for (i = 0; i < SFB_LEVELS; i++) {
                u32 hash = sfbhash & SFB_BUCKET_MASK;
                struct sfb_bucket *b = &q->bins[slot].bins[i][hash];

                sfbhash >>= SFB_BUCKET_SHIFT;
                if (b->qlen == 0)
                        decrement_prob(b, q);
                else if (b->qlen >= q->bin_size)
                        increment_prob(b, q);
                if (minqlen > b->qlen)
                        minqlen = b->qlen;
                if (p_min > b->p_mark)
                        p_min = b->p_mark;
        }

        slot ^= 1;
        sfb_skb_cb(skb)->hashes[slot] = 0;

        if (unlikely(minqlen >= q->max || sch->q.qlen >= q->limit)) {
                sch->qstats.overlimits++;
                if (minqlen >= q->max)
                        q->stats.bucketdrop++;
                else
                        q->stats.queuedrop++;
                goto drop;
        }

        if (unlikely(p_min >= SFB_MAX_PROB)) {
                /* Inelastic flow */
                if (q->double_buffering) {
                        sfbhash = jhash_1word(salt, q->bins[slot].perturbation);
                        if (!sfbhash)
                                sfbhash = 1;
                        sfb_skb_cb(skb)->hashes[slot] = sfbhash;

                        for (i = 0; i < SFB_LEVELS; i++) {
                                u32 hash = sfbhash & SFB_BUCKET_MASK;
                                struct sfb_bucket *b = &q->bins[slot].bins[i][hash];

                                sfbhash >>= SFB_BUCKET_SHIFT;
                                if (b->qlen == 0)
                                        decrement_prob(b, q);
                                else if (b->qlen >= q->bin_size)
                                        increment_prob(b, q);
                        }
                }
                if (sfb_rate_limit(skb, q)) {
                        sch->qstats.overlimits++;
                        q->stats.penaltydrop++;
                        goto drop;
                }
                goto enqueue;
        }

        r = net_random() & SFB_MAX_PROB;

        if (unlikely(r < p_min)) {
                if (unlikely(p_min > SFB_MAX_PROB / 2)) {
                        /* If we're marking that many packets, then either
                         * this flow is unresponsive, or we're badly congested.
                         * In either case, we want to start dropping packets.
                         */
                        if (r < (p_min - SFB_MAX_PROB / 2) * 2) {
                                q->stats.earlydrop++;
                                goto drop;
                        }
                }
                if (INET_ECN_set_ce(skb)) {
                        q->stats.marked++;
                } else {
                        q->stats.earlydrop++;
                        goto drop;
                }
        }

enqueue:
        ret = qdisc_enqueue(skb, child);
        if (likely(ret == NET_XMIT_SUCCESS)) {
                sch->q.qlen++;
                increment_qlen(skb, q);
        } else if (net_xmit_drop_count(ret)) {
                q->stats.childdrop++;
                sch->qstats.drops++;
        }
        return ret;

drop:
        qdisc_drop(skb, sch);
        return NET_XMIT_CN;
other_drop:
        if (ret & __NET_XMIT_BYPASS)
                sch->qstats.drops++;
        kfree_skb(skb);
        return ret;
}

static struct sk_buff *sfb_dequeue(struct Qdisc *sch)
{
        struct sfb_sched_data *q = qdisc_priv(sch);
        struct Qdisc *child = q->qdisc;
        struct sk_buff *skb;

        skb = child->dequeue(q->qdisc);

        if (skb) {
                qdisc_bstats_update(sch, skb);
                sch->q.qlen--;
                decrement_qlen(skb, q);
        }

        return skb;
}

static struct sk_buff *sfb_peek(struct Qdisc *sch)
{
        struct sfb_sched_data *q = qdisc_priv(sch);
        struct Qdisc *child = q->qdisc;

        return child->ops->peek(child);
}

/* No sfb_drop -- impossible since the child doesn't return the dropped skb. */

static void sfb_reset(struct Qdisc *sch)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        qdisc_reset(q->qdisc);
        sch->q.qlen = 0;
        q->slot = 0;
        q->double_buffering = false;
        sfb_zero_all_buckets(q);
        sfb_init_perturbation(0, q);
}

static void sfb_destroy(struct Qdisc *sch)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        tcf_destroy_chain(&q->filter_list);
        qdisc_destroy(q->qdisc);
}

static const struct nla_policy sfb_policy[TCA_SFB_MAX + 1] = {
        [TCA_SFB_PARMS] = { .len = sizeof(struct tc_sfb_qopt) },
};

static const struct tc_sfb_qopt sfb_default_ops = {
        .rehash_interval = 600 * MSEC_PER_SEC,
        .warmup_time = 60 * MSEC_PER_SEC,
        .limit = 0,
        .max = 25,
        .bin_size = 20,
        .increment = (SFB_MAX_PROB + 500) / 1000, /* 0.1 % */
        .decrement = (SFB_MAX_PROB + 3000) / 6000,
        .penalty_rate = 10,
        .penalty_burst = 20,
};

static int sfb_change(struct Qdisc *sch, struct nlattr *opt)
{
        struct sfb_sched_data *q = qdisc_priv(sch);
        struct Qdisc *child;
        struct nlattr *tb[TCA_SFB_MAX + 1];
        const struct tc_sfb_qopt *ctl = &sfb_default_ops;
        u32 limit;
        int err;

        if (opt) {
                err = nla_parse_nested(tb, TCA_SFB_MAX, opt, sfb_policy);
                if (err < 0)
                        return -EINVAL;

                if (tb[TCA_SFB_PARMS] == NULL)
                        return -EINVAL;

                ctl = nla_data(tb[TCA_SFB_PARMS]);
        }

        limit = ctl->limit;
        if (limit == 0)
                limit = max_t(u32, qdisc_dev(sch)->tx_queue_len, 1);

        child = fifo_create_dflt(sch, &pfifo_qdisc_ops, limit);
        if (IS_ERR(child))
                return PTR_ERR(child);

        sch_tree_lock(sch);

        qdisc_tree_decrease_qlen(q->qdisc, q->qdisc->q.qlen);
        qdisc_destroy(q->qdisc);
        q->qdisc = child;

        q->rehash_interval = msecs_to_jiffies(ctl->rehash_interval);
        q->warmup_time = msecs_to_jiffies(ctl->warmup_time);
        q->rehash_time = jiffies;
        q->limit = limit;
        q->increment = ctl->increment;
        q->decrement = ctl->decrement;
        q->max = ctl->max;
        q->bin_size = ctl->bin_size;
        q->penalty_rate = ctl->penalty_rate;
        q->penalty_burst = ctl->penalty_burst;
        q->tokens_avail = ctl->penalty_burst;
        q->token_time = jiffies;

        q->slot = 0;
        q->double_buffering = false;
        sfb_zero_all_buckets(q);
        sfb_init_perturbation(0, q);
        sfb_init_perturbation(1, q);

        sch_tree_unlock(sch);

        return 0;
}

static int sfb_init(struct Qdisc *sch, struct nlattr *opt)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        q->qdisc = &noop_qdisc;
        return sfb_change(sch, opt);
}

static int sfb_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        struct sfb_sched_data *q = qdisc_priv(sch);
        struct nlattr *opts;
        struct tc_sfb_qopt opt = {
                .rehash_interval = jiffies_to_msecs(q->rehash_interval),
                .warmup_time = jiffies_to_msecs(q->warmup_time),
                .limit = q->limit,
                .max = q->max,
                .bin_size = q->bin_size,
                .increment = q->increment,
                .decrement = q->decrement,
                .penalty_rate = q->penalty_rate,
                .penalty_burst = q->penalty_burst,
        };

        sch->qstats.backlog = q->qdisc->qstats.backlog;
        opts = nla_nest_start(skb, TCA_OPTIONS);
        NLA_PUT(skb, TCA_SFB_PARMS, sizeof(opt), &opt);
        return nla_nest_end(skb, opts);

nla_put_failure:
        nla_nest_cancel(skb, opts);
        return -EMSGSIZE;
}

static int sfb_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
        struct sfb_sched_data *q = qdisc_priv(sch);
        struct tc_sfb_xstats st = {
                .earlydrop = q->stats.earlydrop,
                .penaltydrop = q->stats.penaltydrop,
                .bucketdrop = q->stats.bucketdrop,
                .queuedrop = q->stats.queuedrop,
                .childdrop = q->stats.childdrop,
                .marked = q->stats.marked,
        };

        st.maxqlen = sfb_compute_qlen(&st.maxprob, &st.avgprob, q);

        return gnet_stats_copy_app(d, &st, sizeof(st));
}

static int sfb_dump_class(struct Qdisc *sch, unsigned long cl,
                          struct sk_buff *skb, struct tcmsg *tcm)
{
        return -ENOSYS;
}

static int sfb_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
                     struct Qdisc **old)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        if (new == NULL)
                new = &noop_qdisc;

        sch_tree_lock(sch);
        *old = q->qdisc;
        q->qdisc = new;
        qdisc_tree_decrease_qlen(*old, (*old)->q.qlen);
        qdisc_reset(*old);
        sch_tree_unlock(sch);
        return 0;
}

static struct Qdisc *sfb_leaf(struct Qdisc *sch, unsigned long arg)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        return q->qdisc;
}

static unsigned long sfb_get(struct Qdisc *sch, u32 classid)
{
        return 1;
}

static void sfb_put(struct Qdisc *sch, unsigned long arg)
{
}

static int sfb_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
                            struct nlattr **tca, unsigned long *arg)
{
        return -ENOSYS;
}

static int sfb_delete(struct Qdisc *sch, unsigned long cl)
{
        return -ENOSYS;
}

static void sfb_walk(struct Qdisc *sch, struct qdisc_walker *walker)
{
        if (!walker->stop) {
                if (walker->count >= walker->skip)
                        if (walker->fn(sch, 1, walker) < 0) {
                                walker->stop = 1;
                                return;
                        }
                walker->count++;
        }
}

static struct tcf_proto **sfb_find_tcf(struct Qdisc *sch, unsigned long cl)
{
        struct sfb_sched_data *q = qdisc_priv(sch);

        if (cl)
                return NULL;
        return &q->filter_list;
}

static unsigned long sfb_bind(struct Qdisc *sch, unsigned long parent,
                              u32 classid)
{
        return 0;
}


static const struct Qdisc_class_ops sfb_class_ops = {
        .graft          =       sfb_graft,
        .leaf           =       sfb_leaf,
        .get            =       sfb_get,
        .put            =       sfb_put,
        .change         =       sfb_change_class,
        .delete         =       sfb_delete,
        .walk           =       sfb_walk,
        .tcf_chain      =       sfb_find_tcf,
        .bind_tcf       =       sfb_bind,
        .unbind_tcf     =       sfb_put,
        .dump           =       sfb_dump_class,
};

static struct Qdisc_ops sfb_qdisc_ops __read_mostly = {
        .id             =       "sfb",
        .priv_size      =       sizeof(struct sfb_sched_data),
        .cl_ops         =       &sfb_class_ops,
        .enqueue        =       sfb_enqueue,
        .dequeue        =       sfb_dequeue,
        .peek           =       sfb_peek,
        .init           =       sfb_init,
        .reset          =       sfb_reset,
        .destroy        =       sfb_destroy,
        .change         =       sfb_change,
        .dump           =       sfb_dump,
        .dump_stats     =       sfb_dump_stats,
        .owner          =       THIS_MODULE,
};

static int __init sfb_module_init(void)
{
        return register_qdisc(&sfb_qdisc_ops);
}

static void __exit sfb_module_exit(void)
{
        unregister_qdisc(&sfb_qdisc_ops);
}

module_init(sfb_module_init)
module_exit(sfb_module_exit)

MODULE_DESCRIPTION("Stochastic Fair Blue queue discipline");
MODULE_AUTHOR("Juliusz Chroboczek");
MODULE_AUTHOR("Eric Dumazet");
MODULE_LICENSE("GPL");