// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * net/sched/sch_cbs.c  Credit Based Shaper
 *
 * Authors:     Vinicius Costa Gomes <vinicius.gomes@intel.com>
 */

/* Credit Based Shaper (CBS)
 * =========================
 *
 * This is a simple rate-limiting shaper aimed at TSN applications on
 * systems with known traffic workloads.
 *
 * Its algorithm is defined by the IEEE 802.1Q-2014 Specification,
 * Section 8.6.8.2, and explained in more detail in the Annex L of the
 * same specification.
 *
 * There are four tunables to be considered:
 *
 *      'idleslope': Idleslope is the rate of credits that is
 *      accumulated (in kilobits per second) when there is at least
 *      one packet waiting for transmission. Packets are transmitted
 *      when the current value of credits is equal or greater than
 *      zero. When there is no packet to be transmitted the amount of
 *      credits is set to zero. This is the main tunable of the CBS
 *      algorithm.
 *
 *      'sendslope':
 *      Sendslope is the rate of credits that is depleted (it should be a
 *      negative number of kilobits per second) when a transmission is
 *      ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
 *      8.6.8.2 item g):
 *
 *      sendslope = idleslope - port_transmit_rate
 *
 *      'hicredit': Hicredit defines the maximum amount of credits (in
 *      bytes) that can be accumulated. Hicredit depends on the
 *      characteristics of interfering traffic,
 *      'max_interference_size' is the maximum size of any burst of
 *      traffic that can delay the transmission of a frame that is
 *      available for transmission for this traffic class, (IEEE
 *      802.1Q-2014 Annex L, Equation L-3):
 *
 *      hicredit = max_interference_size * (idleslope / port_transmit_rate)
 *
 *      'locredit': Locredit is the minimum amount of credits that can
 *      be reached. It is a function of the traffic flowing through
 *      this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2):
 *
 *      locredit = max_frame_size * (sendslope / port_transmit_rate)
 */

#include <linux/ethtool.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/units.h>

#include <net/netevent.h>
#include <net/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>

static LIST_HEAD(cbs_list);
static DEFINE_SPINLOCK(cbs_list_lock);

struct cbs_sched_data {
        bool offload;
        int queue;
        atomic64_t port_rate; /* in bytes/s */
        s64 last; /* timestamp in ns */
        s64 credits; /* in bytes */
        s32 locredit; /* in bytes */
        s32 hicredit; /* in bytes */
        s64 sendslope; /* in bytes/s */
        s64 idleslope; /* in bytes/s */
        struct qdisc_watchdog watchdog;
        int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch,
                       struct sk_buff **to_free);
        struct sk_buff *(*dequeue)(struct Qdisc *sch);
        struct Qdisc *qdisc;
        struct list_head cbs_list;
};

static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                             struct Qdisc *child,
                             struct sk_buff **to_free)
{
        unsigned int len = qdisc_pkt_len(skb);
        int err;

        err = child->ops->enqueue(skb, child, to_free);
        if (err != NET_XMIT_SUCCESS)
                return err;

        sch->qstats.backlog += len;
        sch->q.qlen++;

        return NET_XMIT_SUCCESS;
}

static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch,
                               struct sk_buff **to_free)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct Qdisc *qdisc = q->qdisc;

        return cbs_child_enqueue(skb, sch, qdisc, to_free);
}

static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch,
                            struct sk_buff **to_free)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct Qdisc *qdisc = q->qdisc;

        if (sch->q.qlen == 0 && q->credits > 0) {
                /* We need to stop accumulating credits when there's
                 * no enqueued packets and q->credits is positive.
                 */
                q->credits = 0;
                q->last = ktime_get_ns();
        }

        return cbs_child_enqueue(skb, sch, qdisc, to_free);
}

static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
                       struct sk_buff **to_free)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        return q->enqueue(skb, sch, to_free);
}

/* timediff is in ns, slope is in bytes/s */
static s64 timediff_to_credits(s64 timediff, s64 slope)
{
        return div64_s64(timediff * slope, NSEC_PER_SEC);
}

static s64 delay_from_credits(s64 credits, s64 slope)
{
        if (unlikely(slope == 0))
                return S64_MAX;

        return div64_s64(-credits * NSEC_PER_SEC, slope);
}

static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
{
        if (unlikely(port_rate == 0))
                return S64_MAX;

        return div64_s64(len * slope, port_rate);
}

static struct sk_buff *cbs_child_dequeue(struct Qdisc *sch, struct Qdisc *child)
{
        struct sk_buff *skb;

        skb = child->ops->dequeue(child);
        if (!skb)
                return NULL;

        qdisc_qstats_backlog_dec(sch, skb);
        qdisc_bstats_update(sch, skb);
        sch->q.qlen--;

        return skb;
}

static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct Qdisc *qdisc = q->qdisc;
        s64 now = ktime_get_ns();
        struct sk_buff *skb;
        s64 credits;
        int len;

        /* The previous packet is still being sent */
        if (now < q->last) {
                qdisc_watchdog_schedule_ns(&q->watchdog, q->last);
                return NULL;
        }
        if (q->credits < 0) {
                credits = timediff_to_credits(now - q->last, q->idleslope);

                credits = q->credits + credits;
                q->credits = min_t(s64, credits, q->hicredit);

                if (q->credits < 0) {
                        s64 delay;

                        delay = delay_from_credits(q->credits, q->idleslope);
                        qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);

                        q->last = now;

                        return NULL;
                }
        }
        skb = cbs_child_dequeue(sch, qdisc);
        if (!skb)
                return NULL;

        len = qdisc_pkt_len(skb);

        /* As sendslope is a negative number, this will decrease the
         * amount of q->credits.
         */
        credits = credits_from_len(len, q->sendslope,
                                   atomic64_read(&q->port_rate));
        credits += q->credits;

        q->credits = max_t(s64, credits, q->locredit);
        /* Estimate of the transmission of the last byte of the packet in ns */
        if (unlikely(atomic64_read(&q->port_rate) == 0))
                q->last = now;
        else
                q->last = now + div64_s64(len * NSEC_PER_SEC,
                                          atomic64_read(&q->port_rate));

        return skb;
}

static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct Qdisc *qdisc = q->qdisc;

        return cbs_child_dequeue(sch, qdisc);
}

static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        return q->dequeue(sch);
}

static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
        [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
};

static void cbs_disable_offload(struct net_device *dev,
                                struct cbs_sched_data *q)
{
        struct tc_cbs_qopt_offload cbs = { };
        const struct net_device_ops *ops;
        int err;

        if (!q->offload)
                return;

        q->enqueue = cbs_enqueue_soft;
        q->dequeue = cbs_dequeue_soft;

        ops = dev->netdev_ops;
        if (!ops->ndo_setup_tc)
                return;

        cbs.queue = q->queue;
        cbs.enable = 0;

        err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
        if (err < 0)
                pr_warn("Couldn't disable CBS offload for queue %d\n",
                        cbs.queue);
}

static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
                              const struct tc_cbs_qopt *opt,
                              struct netlink_ext_ack *extack)
{
        const struct net_device_ops *ops = dev->netdev_ops;
        struct tc_cbs_qopt_offload cbs = { };
        int err;

        if (!ops->ndo_setup_tc) {
                NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
                return -EOPNOTSUPP;
        }

        cbs.queue = q->queue;

        cbs.enable = 1;
        cbs.hicredit = opt->hicredit;
        cbs.locredit = opt->locredit;
        cbs.idleslope = opt->idleslope;
        cbs.sendslope = opt->sendslope;

        err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
        if (err < 0) {
                NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload");
                return err;
        }

        q->enqueue = cbs_enqueue_offload;
        q->dequeue = cbs_dequeue_offload;

        return 0;
}

static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
{
        struct ethtool_link_ksettings ecmd;
        int speed = SPEED_10;
        s64 port_rate;
        int err;

        err = __ethtool_get_link_ksettings(dev, &ecmd);
        if (err < 0)
                goto skip;

        if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
                speed = ecmd.base.speed;

skip:
        port_rate = speed * 1000 * BYTES_PER_KBIT;

        atomic64_set(&q->port_rate, port_rate);
        netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
                   dev->name, (long long)atomic64_read(&q->port_rate),
                   ecmd.base.speed);
}

static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event,
                            void *ptr)
{
        struct net_device *dev = netdev_notifier_info_to_dev(ptr);
        struct cbs_sched_data *q;
        struct net_device *qdev;
        bool found = false;

        ASSERT_RTNL();

        if (event != NETDEV_UP && event != NETDEV_CHANGE)
                return NOTIFY_DONE;

        spin_lock(&cbs_list_lock);
        list_for_each_entry(q, &cbs_list, cbs_list) {
                qdev = qdisc_dev(q->qdisc);
                if (qdev == dev) {
                        found = true;
                        break;
                }
        }
        spin_unlock(&cbs_list_lock);

        if (found)
                cbs_set_port_rate(dev, q);

        return NOTIFY_DONE;
}

static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
                      struct netlink_ext_ack *extack)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);
        struct nlattr *tb[TCA_CBS_MAX + 1];
        struct tc_cbs_qopt *qopt;
        int err;

        err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy,
                                          extack);
        if (err < 0)
                return err;

        if (!tb[TCA_CBS_PARMS]) {
                NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory");
                return -EINVAL;
        }

        qopt = nla_data(tb[TCA_CBS_PARMS]);

        if (!qopt->offload) {
                cbs_set_port_rate(dev, q);
                cbs_disable_offload(dev, q);
        } else {
                err = cbs_enable_offload(dev, q, qopt, extack);
                if (err < 0)
                        return err;
        }

        /* Everything went OK, save the parameters used. */
        WRITE_ONCE(q->hicredit, qopt->hicredit);
        WRITE_ONCE(q->locredit, qopt->locredit);
        WRITE_ONCE(q->idleslope, qopt->idleslope * BYTES_PER_KBIT);
        WRITE_ONCE(q->sendslope, qopt->sendslope * BYTES_PER_KBIT);
        WRITE_ONCE(q->offload, qopt->offload);

        return 0;
}

static int cbs_init(struct Qdisc *sch, struct nlattr *opt,
                    struct netlink_ext_ack *extack)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);

        if (!opt) {
                NL_SET_ERR_MSG(extack, "Missing CBS qdisc options  which are mandatory");
                return -EINVAL;
        }

        q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
                                     sch->handle, extack);
        if (!q->qdisc)
                return -ENOMEM;

        spin_lock(&cbs_list_lock);
        list_add(&q->cbs_list, &cbs_list);
        spin_unlock(&cbs_list_lock);

        qdisc_hash_add(q->qdisc, false);

        q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);

        q->enqueue = cbs_enqueue_soft;
        q->dequeue = cbs_dequeue_soft;

        qdisc_watchdog_init(&q->watchdog, sch);

        return cbs_change(sch, opt, extack);
}

static void cbs_destroy(struct Qdisc *sch)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct net_device *dev = qdisc_dev(sch);

        /* Nothing to do if we couldn't create the underlying qdisc */
        if (!q->qdisc)
                return;

        qdisc_watchdog_cancel(&q->watchdog);
        cbs_disable_offload(dev, q);

        spin_lock(&cbs_list_lock);
        list_del(&q->cbs_list);
        spin_unlock(&cbs_list_lock);

        qdisc_put(q->qdisc);
}

static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
{
        struct cbs_sched_data *q = qdisc_priv(sch);
        struct tc_cbs_qopt opt = { };
        struct nlattr *nest;

        nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
        if (!nest)
                goto nla_put_failure;

        opt.hicredit = READ_ONCE(q->hicredit);
        opt.locredit = READ_ONCE(q->locredit);
        opt.sendslope = div64_s64(READ_ONCE(q->sendslope), BYTES_PER_KBIT);
        opt.idleslope = div64_s64(READ_ONCE(q->idleslope), BYTES_PER_KBIT);
        opt.offload = READ_ONCE(q->offload);

        if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
                goto nla_put_failure;

        return nla_nest_end(skb, nest);

nla_put_failure:
        nla_nest_cancel(skb, nest);
        return -1;
}

static int cbs_dump_class(struct Qdisc *sch, unsigned long cl,
                          struct sk_buff *skb, struct tcmsg *tcm)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        if (cl != 1 || !q->qdisc)       /* only one class */
                return -ENOENT;

        tcm->tcm_handle |= TC_H_MIN(1);
        tcm->tcm_info = q->qdisc->handle;

        return 0;
}

static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
                     struct Qdisc **old, struct netlink_ext_ack *extack)
{
        struct cbs_sched_data *q = qdisc_priv(sch);

        if (!new) {
                new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
                                        sch->handle, NULL);
                if (!new)
                        new = &noop_qdisc;
        }

        *old = qdisc_replace(sch, new, &q->qdisc);
        return 0;
}

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

        return q->qdisc;
}

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

static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker)
{
        if (!walker->stop) {
                tc_qdisc_stats_dump(sch, 1, walker);
        }
}

static const struct Qdisc_class_ops cbs_class_ops = {
        .graft          =       cbs_graft,
        .leaf           =       cbs_leaf,
        .find           =       cbs_find,
        .walk           =       cbs_walk,
        .dump           =       cbs_dump_class,
};

static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
        .id             =       "cbs",
        .cl_ops         =       &cbs_class_ops,
        .priv_size      =       sizeof(struct cbs_sched_data),
        .enqueue        =       cbs_enqueue,
        .dequeue        =       cbs_dequeue,
        .peek           =       qdisc_peek_dequeued,
        .init           =       cbs_init,
        .reset          =       qdisc_reset_queue,
        .destroy        =       cbs_destroy,
        .change         =       cbs_change,
        .dump           =       cbs_dump,
        .owner          =       THIS_MODULE,
};
MODULE_ALIAS_NET_SCH("cbs");

static struct notifier_block cbs_device_notifier = {
        .notifier_call = cbs_dev_notifier,
};

static int __init cbs_module_init(void)
{
        int err;

        err = register_netdevice_notifier(&cbs_device_notifier);
        if (err)
                return err;

        err = register_qdisc(&cbs_qdisc_ops);
        if (err)
                unregister_netdevice_notifier(&cbs_device_notifier);

        return err;
}

static void __exit cbs_module_exit(void)
{
        unregister_qdisc(&cbs_qdisc_ops);
        unregister_netdevice_notifier(&cbs_device_notifier);
}
module_init(cbs_module_init)
module_exit(cbs_module_exit)
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Credit Based shaper");