// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * net/sched/sch_fifo.c The simplest FIFO queue.
 *
 * Authors:     Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 */

#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>
#include <net/pkt_cls.h>

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

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

        return qdisc_drop(skb, sch, to_free);
}

static int pfifo_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                         struct sk_buff **to_free)
{
        if (likely(sch->q.qlen < READ_ONCE(sch->limit)))
                return qdisc_enqueue_tail(skb, sch);

        return qdisc_drop(skb, sch, to_free);
}

static int pfifo_tail_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                              struct sk_buff **to_free)
{
        unsigned int prev_backlog;

        if (unlikely(READ_ONCE(sch->limit) == 0))
                return qdisc_drop(skb, sch, to_free);

        if (likely(sch->q.qlen < READ_ONCE(sch->limit)))
                return qdisc_enqueue_tail(skb, sch);

        prev_backlog = sch->qstats.backlog;
        /* queue full, remove one skb to fulfill the limit */
        __qdisc_queue_drop_head(sch, &sch->q, to_free);
        qdisc_qstats_drop(sch);
        qdisc_enqueue_tail(skb, sch);

        qdisc_tree_reduce_backlog(sch, 0, prev_backlog - sch->qstats.backlog);
        return NET_XMIT_CN;
}

static void fifo_offload_init(struct Qdisc *sch)
{
        struct net_device *dev = qdisc_dev(sch);
        struct tc_fifo_qopt_offload qopt;

        if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
                return;

        qopt.command = TC_FIFO_REPLACE;
        qopt.handle = sch->handle;
        qopt.parent = sch->parent;
        dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_FIFO, &qopt);
}

static void fifo_offload_destroy(struct Qdisc *sch)
{
        struct net_device *dev = qdisc_dev(sch);
        struct tc_fifo_qopt_offload qopt;

        if (!tc_can_offload(dev) || !dev->netdev_ops->ndo_setup_tc)
                return;

        qopt.command = TC_FIFO_DESTROY;
        qopt.handle = sch->handle;
        qopt.parent = sch->parent;
        dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_FIFO, &qopt);
}

static int fifo_offload_dump(struct Qdisc *sch)
{
        struct tc_fifo_qopt_offload qopt;

        qopt.command = TC_FIFO_STATS;
        qopt.handle = sch->handle;
        qopt.parent = sch->parent;
        qopt.stats.bstats = &sch->bstats;
        qopt.stats.qstats = &sch->qstats;

        return qdisc_offload_dump_helper(sch, TC_SETUP_QDISC_FIFO, &qopt);
}

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

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

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

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

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

                WRITE_ONCE(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_init(struct Qdisc *sch, struct nlattr *opt,
                     struct netlink_ext_ack *extack)
{
        int err;

        err = __fifo_init(sch, opt, extack);
        if (err)
                return err;

        fifo_offload_init(sch);
        return 0;
}

static int fifo_hd_init(struct Qdisc *sch, struct nlattr *opt,
                        struct netlink_ext_ack *extack)
{
        return __fifo_init(sch, opt, extack);
}

static void fifo_destroy(struct Qdisc *sch)
{
        fifo_offload_destroy(sch);
}

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

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

nla_put_failure:
        return -1;
}

static int fifo_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        int err;

        err = fifo_offload_dump(sch);
        if (err)
                return err;

        return __fifo_dump(sch, skb);
}

static int fifo_hd_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        return __fifo_dump(sch, skb);
}

struct Qdisc_ops pfifo_qdisc_ops __read_mostly = {
        .id             =       "pfifo",
        .priv_size      =       0,
        .enqueue        =       pfifo_enqueue,
        .dequeue        =       qdisc_dequeue_head,
        .peek           =       qdisc_peek_head,
        .init           =       fifo_init,
        .destroy        =       fifo_destroy,
        .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,
        .init           =       fifo_init,
        .destroy        =       fifo_destroy,
        .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,
        .init           =       fifo_hd_init,
        .reset          =       qdisc_reset_queue,
        .change         =       fifo_hd_init,
        .dump           =       fifo_hd_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;

        if (!q->ops->change)
                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, NULL);
                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 netlink_ext_ack *extack)
{
        struct Qdisc *q;
        int err = -ENOMEM;

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

        return q ? : ERR_PTR(err);
}
EXPORT_SYMBOL(fifo_create_dflt);
MODULE_DESCRIPTION("Single queue packet and byte based First In First Out(P/BFIFO) scheduler");