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/*

 * net/sched/sch_red.c  Random Early Detection 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>

 *

 * Changes:

 * J Hadi Salim <hadi@nortel.com> 980914:       computation fixes

 * Alexey Makarenko <makar@phoenix.kharkov.ua> 990814: qave on idle link was calculated incorrectly.

 * J Hadi Salim <hadi@nortelnetworks.com> 980816:  ECN support

 */

#include <linux/config.h>

#include <linux/module.h>

#include <asm/uaccess.h>

#include <asm/system.h>

#include <asm/bitops.h>

#include <linux/types.h>

#include <linux/kernel.h>

#include <linux/sched.h>

#include <linux/string.h>

#include <linux/mm.h>

#include <linux/socket.h>

#include <linux/sockios.h>

#include <linux/in.h>

#include <linux/errno.h>

#include <linux/interrupt.h>

#include <linux/if_ether.h>

#include <linux/inet.h>

#include <linux/netdevice.h>

#include <linux/etherdevice.h>

#include <linux/notifier.h>

#include <net/ip.h>

#include <net/route.h>

#include <linux/skbuff.h>

#include <net/sock.h>

#include <net/pkt_sched.h>

#include <net/inet_ecn.h>

/*      Random Early Detection (RED) algorithm.

        =======================================

        Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways

        for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.

        This file codes a "divisionless" version of RED algorithm

        as written down in Fig.17 of the paper.

Short description.

------------------

        When a new packet arrives we calculate the average queue length:

        avg = (1-W)*avg + W*current_queue_len,

        W is the filter time constant (choosen as 2^(-Wlog)), it controls

        the inertia of the algorithm. To allow larger bursts, W should be

        decreased.

        if (avg > th_max) -> packet marked (dropped).

        if (avg < th_min) -> packet passes.

        if (th_min < avg < th_max) we calculate probability:

        Pb = max_P * (avg - th_min)/(th_max-th_min)

        and mark (drop) packet with this probability.

        Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).

        max_P should be small (not 1), usually 0.01..0.02 is good value.

        max_P is chosen as a number, so that max_P/(th_max-th_min)

        is a negative power of two in order arithmetics to contain

        only shifts.

        Parameters, settable by user:

        -----------------------------

        limit           - bytes (must be > qth_max + burst)

        Hard limit on queue length, should be chosen >qth_max

        to allow packet bursts. This parameter does not

        affect the algorithms behaviour and can be chosen

        arbitrarily high (well, less than ram size)

        Really, this limit will never be reached

        if RED works correctly.

        qth_min         - bytes (should be < qth_max/2)

        qth_max         - bytes (should be at least 2*qth_min and less limit)

        Wlog            - bits (<32) log(1/W).

        Plog            - bits (<32)

        Plog is related to max_P by formula:

        max_P = (qth_max-qth_min)/2^Plog;

        F.e. if qth_max=128K and qth_min=32K, then Plog=22

        corresponds to max_P=0.02

        Scell_log

        Stab

        Lookup table for log((1-W)^(t/t_ave).

NOTES:

Upper bound on W.

-----------------

        If you want to allow bursts of L packets of size S,

        you should choose W:

        L + 1 - th_min/S < (1-(1-W)^L)/W

        th_min/S = 32         th_min/S = 4

        log(W)  L

        -1      33

        -2      35

        -3      39

        -4      46

        -5      57

        -6      75

        -7      101

        -8      135

        -9      190

        etc.

 */

struct red_sched_data

{

/* Parameters */

        u32             limit;          /* HARD maximal queue length    */

        u32             qth_min;        /* Min average length threshold: A scaled */

        u32             qth_max;        /* Max average length threshold: A scaled */

        u32             Rmask;

        u32             Scell_max;

        unsigned char   flags;

        char            Wlog;           /* log(W)               */

        char            Plog;           /* random number bits   */

        char            Scell_log;

        u8              Stab[256];

/* Variables */

        unsigned long   qave;           /* Average queue length: A scaled */

        int             qcount;         /* Packets since last random number generation */

        u32             qR;             /* Cached random number */

        psched_time_t   qidlestart;     /* Start of idle period         */

        struct tc_red_xstats st;

};

static int red_ecn_mark(struct sk_buff *skb)

{

        if (skb->nh.raw + 20 > skb->tail)

                return 0;

        switch (skb->protocol) {

        case __constant_htons(ETH_P_IP):

                if (!INET_ECN_is_capable(skb->nh.iph->tos))

                        return 0;

                if (INET_ECN_is_not_ce(skb->nh.iph->tos))

                        IP_ECN_set_ce(skb->nh.iph);

                return 1;

        case __constant_htons(ETH_P_IPV6):

                if (!INET_ECN_is_capable(ip6_get_dsfield(skb->nh.ipv6h)))

                        return 0;

                IP6_ECN_set_ce(skb->nh.ipv6h);

                return 1;

        default:

                return 0;

        }

}

static int

red_enqueue(struct sk_buff *skb, struct Qdisc* sch)

{

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        psched_time_t now;

        if (!PSCHED_IS_PASTPERFECT(q->qidlestart)) {

                long us_idle;

                int  shift;

                PSCHED_GET_TIME(now);

                us_idle = PSCHED_TDIFF_SAFE(now, q->qidlestart, q->Scell_max, 0);

                PSCHED_SET_PASTPERFECT(q->qidlestart);

/*

   The problem: ideally, average length queue recalcultion should

   be done over constant clock intervals. This is too expensive, so that

   the calculation is driven by outgoing packets.

   When the queue is idle we have to model this clock by hand.

   SF+VJ proposed to "generate" m = idletime/(average_pkt_size/bandwidth)

   dummy packets as a burst after idle time, i.e.

          q->qave *= (1-W)^m

   This is an apparently overcomplicated solution (f.e. we have to precompute

   a table to make this calculation in reasonable time)

   I believe that a simpler model may be used here,

   but it is field for experiments.

*/

                shift = q->Stab[us_idle>>q->Scell_log];

                if (shift) {

                        q->qave >>= shift;

                } else {

                        /* Approximate initial part of exponent

                           with linear function:

                           (1-W)^m ~= 1-mW + ...

                           Seems, it is the best solution to

                           problem of too coarce exponent tabulation.

                         */

                        us_idle = (q->qave * us_idle)>>q->Scell_log;

                        if (us_idle < q->qave/2)

                                q->qave -= us_idle;

                        else

                                q->qave >>= 1;

                }

        } else {

                q->qave += sch->stats.backlog - (q->qave >> q->Wlog);

                /* NOTE:

                   q->qave is fixed point number with point at Wlog.

                   The formulae above is equvalent to floating point

                   version:

                   qave = qave*(1-W) + sch->stats.backlog*W;

                                                           --ANK (980924)

                 */

        }

        if (q->qave < q->qth_min) {

                q->qcount = -1;

enqueue:

                if (sch->stats.backlog + skb->len <= q->limit) {

                        __skb_queue_tail(&sch->q, skb);

                        sch->stats.backlog += skb->len;

                        sch->stats.bytes += skb->len;

                        sch->stats.packets++;

                        return NET_XMIT_SUCCESS;

                } else {

                        q->st.pdrop++;

                }

                kfree_skb(skb);

                sch->stats.drops++;

                return NET_XMIT_DROP;

        }

        if (q->qave >= q->qth_max) {

                q->qcount = -1;

                sch->stats.overlimits++;

mark:

                if  (!(q->flags&TC_RED_ECN) || !red_ecn_mark(skb)) {

                        q->st.early++;

                        goto drop;

                }

                q->st.marked++;

                goto enqueue;

        }

        if (++q->qcount) {

                /* The formula used below causes questions.

                   OK. qR is random number in the interval 0..Rmask

                   i.e. 0..(2^Plog). If we used floating point

                   arithmetics, it would be: (2^Plog)*rnd_num,

                   where rnd_num is less 1.

                   Taking into account, that qave have fixed

                   point at Wlog, and Plog is related to max_P by

                   max_P = (qth_max-qth_min)/2^Plog; two lines

                   below have the following floating point equivalent:

                   max_P*(qave - qth_min)/(qth_max-qth_min) < rnd/qcount

                   Any questions? --ANK (980924)

                 */

                if (((q->qave - q->qth_min)>>q->Wlog)*q->qcount < q->qR)

                        goto enqueue;

                q->qcount = 0;

                q->qR = net_random()&q->Rmask;

                sch->stats.overlimits++;

                goto mark;

        }

        q->qR = net_random()&q->Rmask;

        goto enqueue;

drop:

        kfree_skb(skb);

        sch->stats.drops++;

        return NET_XMIT_CN;

}

static int

red_requeue(struct sk_buff *skb, struct Qdisc* sch)

{

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        PSCHED_SET_PASTPERFECT(q->qidlestart);

        __skb_queue_head(&sch->q, skb);

        sch->stats.backlog += skb->len;

        return 0;

}

static struct sk_buff *

red_dequeue(struct Qdisc* sch)

{

        struct sk_buff *skb;

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        skb = __skb_dequeue(&sch->q);

        if (skb) {

                sch->stats.backlog -= skb->len;

                return skb;

        }

        PSCHED_GET_TIME(q->qidlestart);

        return NULL;

}

static unsigned int red_drop(struct Qdisc* sch)

{

        struct sk_buff *skb;

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        skb = __skb_dequeue_tail(&sch->q);

        if (skb) {

                unsigned int len = skb->len;

                sch->stats.backlog -= len;

                sch->stats.drops++;

                q->st.other++;

                kfree_skb(skb);

                return len;

        }

        PSCHED_GET_TIME(q->qidlestart);

        return 0;

}

static void red_reset(struct Qdisc* sch)

{

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        __skb_queue_purge(&sch->q);

        sch->stats.backlog = 0;

        PSCHED_SET_PASTPERFECT(q->qidlestart);

        q->qave = 0;

        q->qcount = -1;

}

static int red_change(struct Qdisc *sch, struct rtattr *opt)

{

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        struct rtattr *tb[TCA_RED_STAB];

        struct tc_red_qopt *ctl;

        if (opt == NULL ||

            rtattr_parse(tb, TCA_RED_STAB, RTA_DATA(opt), RTA_PAYLOAD(opt)) ||

            tb[TCA_RED_PARMS-1] == 0 || tb[TCA_RED_STAB-1] == 0 ||

            RTA_PAYLOAD(tb[TCA_RED_PARMS-1]) < sizeof(*ctl) ||

            RTA_PAYLOAD(tb[TCA_RED_STAB-1]) < 256)

                return -EINVAL;

        ctl = RTA_DATA(tb[TCA_RED_PARMS-1]);

        sch_tree_lock(sch);

        q->flags = ctl->flags;

        q->Wlog = ctl->Wlog;

        q->Plog = ctl->Plog;

        q->Rmask = ctl->Plog < 32 ? ((1<<ctl->Plog) - 1) : ~0UL;

        q->Scell_log = ctl->Scell_log;

        q->Scell_max = (255<<q->Scell_log);

        q->qth_min = ctl->qth_min<<ctl->Wlog;

        q->qth_max = ctl->qth_max<<ctl->Wlog;

        q->limit = ctl->limit;

        memcpy(q->Stab, RTA_DATA(tb[TCA_RED_STAB-1]), 256);

        q->qcount = -1;

        if (skb_queue_len(&sch->q) == 0)

                PSCHED_SET_PASTPERFECT(q->qidlestart);

        sch_tree_unlock(sch);

        return 0;

}

static int red_init(struct Qdisc* sch, struct rtattr *opt)

{

        int err;

        MOD_INC_USE_COUNT;

        if ((err = red_change(sch, opt)) != 0) {

                MOD_DEC_USE_COUNT;

        }

        return err;

}

int red_copy_xstats(struct sk_buff *skb, struct tc_red_xstats *st)

{

        RTA_PUT(skb, TCA_XSTATS, sizeof(*st), st);

        return 0;

rtattr_failure:

        return 1;

}

static int red_dump(struct Qdisc *sch, struct sk_buff *skb)

{

        struct red_sched_data *q = (struct red_sched_data *)sch->data;

        unsigned char    *b = skb->tail;

        struct rtattr *rta;

        struct tc_red_qopt opt;

        rta = (struct rtattr*)b;

        RTA_PUT(skb, TCA_OPTIONS, 0, NULL);

        opt.limit = q->limit;

        opt.qth_min = q->qth_min>>q->Wlog;

        opt.qth_max = q->qth_max>>q->Wlog;

        opt.Wlog = q->Wlog;

        opt.Plog = q->Plog;

        opt.Scell_log = q->Scell_log;

        opt.flags = q->flags;

        RTA_PUT(skb, TCA_RED_PARMS, sizeof(opt), &opt);

        rta->rta_len = skb->tail - b;

        if (red_copy_xstats(skb, &q->st))

                goto rtattr_failure;

        return skb->len;

rtattr_failure:

        skb_trim(skb, b - skb->data);

        return -1;

}

static void red_destroy(struct Qdisc *sch)

{

        MOD_DEC_USE_COUNT;

}

struct Qdisc_ops red_qdisc_ops =

{

        NULL,

        NULL,

        "red",

        sizeof(struct red_sched_data),

        red_enqueue,

        red_dequeue,

        red_requeue,

        red_drop,

        red_init,

        red_reset,

        red_destroy,

        red_change,

        red_dump,

};

#ifdef MODULE

int init_module(void)

{

        return register_qdisc(&red_qdisc_ops);

}

void cleanup_module(void)

{

        unregister_qdisc(&red_qdisc_ops);

}

#endif

MODULE_LICENSE("GPL");