/*
 * 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/codel.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 fq_codel_flow *flows;    /* Flows table [flows_cnt] */
        u32             *backlogs;      /* backlog table [flows_cnt] */
        u32             flows_cnt;      /* number of flows */
        u32             perturbation;   /* hash perturbation */
        u32             quantum;        /* psched_mtu(qdisc_dev(sch)); */
        struct codel_params cparams;
        struct codel_stats cstats;
        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)
{
        u32 hash = skb_get_hash_perturb(skb, q->perturbation);

        return reciprocal_scale(hash, 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 = tc_classify(skb, filter, &res, false);
        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 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)
{
        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;

        /* Queue is full! Find the fat flow and drop packet 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.
         */
        for (i = 0; i < q->flows_cnt; i++) {
                if (q->backlogs[i] > maxbacklog) {
                        maxbacklog = q->backlogs[i];
                        idx = i;
                }
        }
        flow = &q->flows[idx];
        skb = dequeue_head(flow);
        len = qdisc_pkt_len(skb);
        q->backlogs[idx] -= len;
        sch->q.qlen--;
        qdisc_qstats_drop(sch);
        qdisc_qstats_backlog_dec(sch, skb);
        kfree_skb(skb);
        flow->dropped++;
        return idx;
}

static unsigned int fq_codel_qdisc_drop(struct Qdisc *sch)
{
        unsigned int prev_backlog;

        prev_backlog = sch->qstats.backlog;
        fq_codel_drop(sch);
        return prev_backlog - sch->qstats.backlog;
}

static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
        struct fq_codel_sched_data *q = qdisc_priv(sch);
        unsigned int idx, prev_backlog;
        struct fq_codel_flow *flow;
        int uninitialized_var(ret);

        idx = fq_codel_classify(skb, sch, &ret);
        if (idx == 0) {
                if (ret & __NET_XMIT_BYPASS)
                        qdisc_qstats_drop(sch);
                kfree_skb(skb);
                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;
        }
        if (++sch->q.qlen <= sch->limit)
                return NET_XMIT_SUCCESS;

        prev_backlog = sch->qstats.backlog;
        q->drop_overlimit++;
        /* Return Congestion Notification only if we dropped a packet
         * from this flow.
         */
        if (fq_codel_drop(sch) == idx)
                return NET_XMIT_CN;

        /* As we dropped a packet, better let upper stack know this */
        qdisc_tree_reduce_backlog(sch, 1, prev_backlog - sch->qstats.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(struct codel_vars *vars, struct Qdisc *sch)
{
        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);
                sch->q.qlen--;
        }
        return skb;
}

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;
        unsigned int prev_backlog;

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;
        prev_backlog = sch->qstats.backlog;

        skb = codel_dequeue(sch, &q->cparams, &flow->cvars, &q->cstats,
                            dequeue);

        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_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;

                while (flow->head) {
                        struct sk_buff *skb = dequeue_head(flow);

                        qdisc_qstats_backlog_dec(sch, skb);
                        kfree_skb(skb);
                }

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

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);
        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]));

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

                q->cstats.drop_len += qdisc_pkt_len(skb);
                kfree_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_zalloc(size_t sz)
{
        void *ptr = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN);

        if (!ptr)
                ptr = vzalloc(sz);
        return ptr;
}

static void fq_codel_free(void *addr)
{
        kvfree(addr);
}

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

        tcf_destroy_chain(&q->filter_list);
        fq_codel_free(q->backlogs);
        fq_codel_free(q->flows);
}

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

        sch->limit = 10*1024;
        q->flows_cnt = 1024;
        q->quantum = psched_mtu(qdisc_dev(sch));
        q->perturbation = prandom_u32();
        INIT_LIST_HEAD(&q->new_flows);
        INIT_LIST_HEAD(&q->old_flows);
        codel_params_init(&q->cparams, sch);
        codel_stats_init(&q->cstats);
        q->cparams.ecn = true;

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

        if (!q->flows) {
                q->flows = fq_codel_zalloc(q->flows_cnt *
                                           sizeof(struct fq_codel_flow));
                if (!q->flows)
                        return -ENOMEM;
                q->backlogs = fq_codel_zalloc(q->flows_cnt * sizeof(u32));
                if (!q->backlogs) {
                        fq_codel_free(q->flows);
                        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_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;

        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++;

        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_get(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_put(struct Qdisc *q, unsigned long cl)
{
}

static struct tcf_proto __rcu **fq_codel_find_tcf(struct Qdisc *sch,
                                                  unsigned long cl)
{
        struct fq_codel_sched_data *q = qdisc_priv(sch);

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

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 = flow->head;

                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);
                }
                while (skb) {
                        qs.qlen++;
                        skb = skb->next;
                }
                qs.backlog = q->backlogs[idx];
                qs.drops = flow->dropped;
        }
        if (gnet_stats_copy_queue(d, NULL, &qs, 0) < 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,
        .get            =       fq_codel_get,
        .put            =       fq_codel_put,
        .tcf_chain      =       fq_codel_find_tcf,
        .bind_tcf       =       fq_codel_bind,
        .unbind_tcf     =       fq_codel_put,
        .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,
        .drop           =       fq_codel_qdisc_drop,
        .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");