sch_fifo.c

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/*
 * net/sched/sch_fifo.c The simplest FIFO 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, <[email protected]>
 */

#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 <net/pkt_sched.h>

/* 1 band FIFO pseudo-"scheduler" */

static int bfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
    if (likely(sch->qstats.backlog + qdisc_pkt_len(skb) <= sch->limit))
        return qdisc_enqueue_tail(skb, sch);

    return qdisc_reshape_fail(skb, sch);
}

static int pfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
    if (likely(skb_queue_len(&sch->q) < sch->limit))
        return qdisc_enqueue_tail(skb, sch);

    return qdisc_reshape_fail(skb, sch);
}

static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
    if (likely(skb_queue_len(&sch->q) < sch->limit))
        return qdisc_enqueue_tail(skb, sch);

    /* queue full, remove one skb to fulfill the limit */
    __qdisc_queue_drop_head(sch, &sch->q);
    sch->qstats.drops++;
    qdisc_enqueue_tail(skb, sch);

    return NET_XMIT_CN;
}

static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
{
    bool bypass;
    bool is_bfifo = sch->ops == &bfifo_qdisc_ops;

    if (opt == NULL) {
        u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;

        if (is_bfifo)
            limit *= psched_mtu(qdisc_dev(sch));

        sch->limit = limit;
    } else {
        struct tc_fifo_qopt *ctl = nla_data(opt);

        if (nla_len(opt) < sizeof(*ctl))
            return -EINVAL;

        sch->limit = ctl->limit;
    }

    if (is_bfifo)
        bypass = sch->limit >= psched_mtu(qdisc_dev(sch));
    else
        bypass = sch->limit >= 1;

    if (bypass)
        sch->flags |= TCQ_F_CAN_BYPASS;
    else
        sch->flags &= ~TCQ_F_CAN_BYPASS;
    return 0;
}

static int fifo_dump(struct Qdisc *sch, struct sk_buff *skb)
{
    struct tc_fifo_qopt opt = { .limit = sch->limit };

    if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
        goto nla_put_failure;
    return skb->len;

nla_put_failure:
    return -1;
}

struct Qdisc_ops pfifo_qdisc_ops __read_mostly = {
    .id     =   "pfifo",
    .priv_size  =   0,
    .enqueue    =   pfifo_enqueue,
    .dequeue    =   qdisc_dequeue_head,
    .peek       =   qdisc_peek_head,
    .drop       =   qdisc_queue_drop,
    .init       =   fifo_init,
    .reset      =   qdisc_reset_queue,
    .change     =   fifo_init,
    .dump       =   fifo_dump,
    .owner      =   THIS_MODULE,
};
EXPORT_SYMBOL(pfifo_qdisc_ops);

struct Qdisc_ops bfifo_qdisc_ops __read_mostly = {
    .id     =   "bfifo",
    .priv_size  =   0,
    .enqueue    =   bfifo_enqueue,
    .dequeue    =   qdisc_dequeue_head,
    .peek       =   qdisc_peek_head,
    .drop       =   qdisc_queue_drop,
    .init       =   fifo_init,
    .reset      =   qdisc_reset_queue,
    .change     =   fifo_init,
    .dump       =   fifo_dump,
    .owner      =   THIS_MODULE,
};
EXPORT_SYMBOL(bfifo_qdisc_ops);

struct Qdisc_ops pfifo_head_drop_qdisc_ops __read_mostly = {
    .id     =   "pfifo_head_drop",
    .priv_size  =   0,
    .enqueue    =   pfifo_tail_enqueue,
    .dequeue    =   qdisc_dequeue_head,
    .peek       =   qdisc_peek_head,
    .drop       =   qdisc_queue_drop_head,
    .init       =   fifo_init,
    .reset      =   qdisc_reset_queue,
    .change     =   fifo_init,
    .dump       =   fifo_dump,
    .owner      =   THIS_MODULE,
};

/* Pass size change message down to embedded FIFO */
int fifo_set_limit(struct Qdisc *q, unsigned int limit)
{
    struct nlattr *nla;
    int ret = -ENOMEM;

    /* Hack to avoid sending change message to non-FIFO */
    if (strncmp(q->ops->id + 1, "fifo", 4) != 0)
        return 0;

    nla = kmalloc(nla_attr_size(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
    if (nla) {
        nla->nla_type = RTM_NEWQDISC;
        nla->nla_len = nla_attr_size(sizeof(struct tc_fifo_qopt));
        ((struct tc_fifo_qopt *)nla_data(nla))->limit = limit;

        ret = q->ops->change(q, nla);
        kfree(nla);
    }
    return ret;
}
EXPORT_SYMBOL(fifo_set_limit);

struct Qdisc *fifo_create_dflt(struct Qdisc *sch, struct Qdisc_ops *ops,
                   unsigned int limit)
{
    struct Qdisc *q;
    int err = -ENOMEM;

    q = qdisc_create_dflt(sch->dev_queue, ops, TC_H_MAKE(sch->handle, 1));
    if (q) {
        err = fifo_set_limit(q, limit);
        if (err < 0) {
            qdisc_destroy(q);
            q = NULL;
        }
    }

    return q ? : ERR_PTR(err);
}
EXPORT_SYMBOL(fifo_create_dflt);