linux/net/sched/sch_ets.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * net/sched/sch_ets.c         Enhanced Transmission Selection scheduler
 *
 * Description
 * -----------
 *
 * The Enhanced Transmission Selection scheduler is a classful queuing
 * discipline that merges functionality of PRIO and DRR qdiscs in one scheduler.
 * ETS makes it easy to configure a set of strict and bandwidth-sharing bands to
 * implement the transmission selection described in 802.1Qaz.
 *
 * Although ETS is technically classful, it's not possible to add and remove
 * classes at will. Instead one specifies number of classes, how many are
 * PRIO-like and how many DRR-like, and quanta for the latter.
 *
 * Algorithm
 * ---------
 *
 * The strict classes, if any, are tried for traffic first: first band 0, if it
 * has no traffic then band 1, etc.
 *
 * When there is no traffic in any of the strict queues, the bandwidth-sharing
 * ones are tried next. Each band is assigned a deficit counter, initialized to
 * "quantum" of that band. ETS maintains a list of active bandwidth-sharing
 * bands whose qdiscs are non-empty. A packet is dequeued from the band at the
 * head of the list if the packet size is smaller or equal to the deficit
 * counter. If the counter is too small, it is increased by "quantum" and the
 * scheduler moves on to the next band in the active list.
 */

#include <linux/module.h>
#include <net/gen_stats.h>
#include <net/netlink.h>
#include <net/pkt_cls.h>
#include <net/pkt_sched.h>
#include <net/sch_generic.h>

struct ets_class {
	struct list_head alist; /* In struct ets_sched.active. */
	struct Qdisc *qdisc;
	u32 quantum;
	u32 deficit;
	struct gnet_stats_basic_packed bstats;
	struct gnet_stats_queue qstats;
};

struct ets_sched {
	struct list_head active;
	struct tcf_proto __rcu *filter_list;
	struct tcf_block *block;
	unsigned int nbands;
	unsigned int nstrict;
	u8 prio2band[TC_PRIO_MAX + 1];
	struct ets_class classes[TCQ_ETS_MAX_BANDS];
};

static const struct nla_policy ets_policy[TCA_ETS_MAX + 1] = {
	[TCA_ETS_NBANDS] = { .type = NLA_U8 },
	[TCA_ETS_NSTRICT] = { .type = NLA_U8 },
	[TCA_ETS_QUANTA] = { .type = NLA_NESTED },
	[TCA_ETS_PRIOMAP] = { .type = NLA_NESTED },
};

static const struct nla_policy ets_priomap_policy[TCA_ETS_MAX + 1] = {
	[TCA_ETS_PRIOMAP_BAND] = { .type = NLA_U8 },
};

static const struct nla_policy ets_quanta_policy[TCA_ETS_MAX + 1] = {
	[TCA_ETS_QUANTA_BAND] = { .type = NLA_U32 },
};

static const struct nla_policy ets_class_policy[TCA_ETS_MAX + 1] = {
	[TCA_ETS_QUANTA_BAND] = { .type = NLA_U32 },
};

static int ets_quantum_parse(struct Qdisc *sch, const struct nlattr *attr,
			     unsigned int *quantum,
			     struct netlink_ext_ack *extack)
{
	*quantum = nla_get_u32(attr);
	if (!*quantum) {
		NL_SET_ERR_MSG(extack, "ETS quantum cannot be zero");
		return -EINVAL;
	}
	return 0;
}

static struct ets_class *
ets_class_from_arg(struct Qdisc *sch, unsigned long arg)
{
	struct ets_sched *q = qdisc_priv(sch);

	return &q->classes[arg - 1];
}

static u32 ets_class_id(struct Qdisc *sch, const struct ets_class *cl)
{
	struct ets_sched *q = qdisc_priv(sch);
	int band = cl - q->classes;

	return TC_H_MAKE(sch->handle, band + 1);
}

static bool ets_class_is_strict(struct ets_sched *q, const struct ets_class *cl)
{
	unsigned int band = cl - q->classes;

	return band < q->nstrict;
}

static int ets_class_change(struct Qdisc *sch, u32 classid, u32 parentid,
			    struct nlattr **tca, unsigned long *arg,
			    struct netlink_ext_ack *extack)
{
	struct ets_class *cl = ets_class_from_arg(sch, *arg);
	struct ets_sched *q = qdisc_priv(sch);
	struct nlattr *opt = tca[TCA_OPTIONS];
	struct nlattr *tb[TCA_ETS_MAX + 1];
	unsigned int quantum;
	int err;

	/* Classes can be added and removed only through Qdisc_ops.change
	 * interface.
	 */
	if (!cl) {
		NL_SET_ERR_MSG(extack, "Fine-grained class addition and removal is not supported");
		return -EOPNOTSUPP;
	}

	if (!opt) {
		NL_SET_ERR_MSG(extack, "ETS options are required for this operation");
		return -EINVAL;
	}

	err = nla_parse_nested(tb, TCA_ETS_MAX, opt, ets_class_policy, extack);
	if (err < 0)
		return err;

	if (!tb[TCA_ETS_QUANTA_BAND])
		/* Nothing to configure. */
		return 0;

	if (ets_class_is_strict(q, cl)) {
		NL_SET_ERR_MSG(extack, "Strict bands do not have a configurable quantum");
		return -EINVAL;
	}

	err = ets_quantum_parse(sch, tb[TCA_ETS_QUANTA_BAND], &quantum,
				extack);
	if (err)
		return err;

	sch_tree_lock(sch);
	cl->quantum = quantum;
	sch_tree_unlock(sch);
	return 0;
}

static int ets_class_graft(struct Qdisc *sch, unsigned long arg,
			   struct Qdisc *new, struct Qdisc **old,
			   struct netlink_ext_ack *extack)
{
	struct ets_class *cl = ets_class_from_arg(sch, arg);

	if (!new) {
		new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
					ets_class_id(sch, cl), NULL);
		if (!new)
			new = &noop_qdisc;
		else
			qdisc_hash_add(new, true);
	}

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

static struct Qdisc *ets_class_leaf(struct Qdisc *sch, unsigned long arg)
{
	struct ets_class *cl = ets_class_from_arg(sch, arg);

	return cl->qdisc;
}

static unsigned long ets_class_find(struct Qdisc *sch, u32 classid)
{
	unsigned long band = TC_H_MIN(classid);
	struct ets_sched *q = qdisc_priv(sch);

	if (band - 1 >= q->nbands)
		return 0;
	return band;
}

static void ets_class_qlen_notify(struct Qdisc *sch, unsigned long arg)
{
	struct ets_class *cl = ets_class_from_arg(sch, arg);
	struct ets_sched *q = qdisc_priv(sch);

	/* We get notified about zero-length child Qdiscs as well if they are
	 * offloaded. Those aren't on the active list though, so don't attempt
	 * to remove them.
	 */
	if (!ets_class_is_strict(q, cl) && sch->q.qlen)
		list_del(&cl->alist);
}

static int ets_class_dump(struct Qdisc *sch, unsigned long arg,
			  struct sk_buff *skb, struct tcmsg *tcm)
{
	struct ets_class *cl = ets_class_from_arg(sch, arg);
	struct ets_sched *q = qdisc_priv(sch);
	struct nlattr *nest;

	tcm->tcm_parent = TC_H_ROOT;
	tcm->tcm_handle = ets_class_id(sch, cl);
	tcm->tcm_info = cl->qdisc->handle;

	nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
	if (!nest)
		goto nla_put_failure;
	if (!ets_class_is_strict(q, cl)) {
		if (nla_put_u32(skb, TCA_ETS_QUANTA_BAND, cl->quantum))
			goto nla_put_failure;
	}
	return nla_nest_end(skb, nest);

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

static int ets_class_dump_stats(struct Qdisc *sch, unsigned long arg,
				struct gnet_dump *d)
{
	struct ets_class *cl = ets_class_from_arg(sch, arg);
	struct Qdisc *cl_q = cl->qdisc;

	if (gnet_stats_copy_basic(qdisc_root_sleeping_running(sch),
				  d, NULL, &cl_q->bstats) < 0 ||
	    qdisc_qstats_copy(d, cl_q) < 0)
		return -1;

	return 0;
}

static void ets_qdisc_walk(struct Qdisc *sch, struct qdisc_walker *arg)
{
	struct ets_sched *q = qdisc_priv(sch);
	int i;

	if (arg->stop)
		return;

	for (i = 0; i < q->nbands; i++) {
		if (arg->count < arg->skip) {
			arg->count++;
			continue;
		}
		if (arg->fn(sch, i + 1, arg) < 0) {
			arg->stop = 1;
			break;
		}
		arg->count++;
	}
}

static struct tcf_block *
ets_qdisc_tcf_block(struct Qdisc *sch, unsigned long cl,
		    struct netlink_ext_ack *extack)
{
	struct ets_sched *q = qdisc_priv(sch);

	if (cl) {
		NL_SET_ERR_MSG(extack, "ETS classid must be zero");
		return NULL;
	}

	return q->block;
}

static unsigned long ets_qdisc_bind_tcf(struct Qdisc *sch, unsigned long parent,
					u32 classid)
{
	return ets_class_find(sch, classid);
}

static void ets_qdisc_unbind_tcf(struct Qdisc *sch, unsigned long arg)
{
}

static struct ets_class *ets_classify(struct sk_buff *skb, struct Qdisc *sch,
				      int *qerr)
{
	struct ets_sched *q = qdisc_priv(sch);
	u32 band = skb->priority;
	struct tcf_result res;
	struct tcf_proto *fl;
	int err;

	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
	if (TC_H_MAJ(skb->priority) != sch->handle) {
		fl = rcu_dereference_bh(q->filter_list);
		err = tcf_classify(skb, fl, &res, false);
#ifdef CONFIG_NET_CLS_ACT
		switch (err) {
		case TC_ACT_STOLEN:
		case TC_ACT_QUEUED:
		case TC_ACT_TRAP:
			*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
			/* fall through */
		case TC_ACT_SHOT:
			return NULL;
		}
#endif
		if (!fl || err < 0) {
			if (TC_H_MAJ(band))
				band = 0;
			return &q->classes[q->prio2band[band & TC_PRIO_MAX]];
		}
		band = res.classid;
	}
	band = TC_H_MIN(band) - 1;
	if (band >= q->nbands)
		return &q->classes[q->prio2band[0]];
	return &q->classes[band];
}

static int ets_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
			     struct sk_buff **to_free)
{
	unsigned int len = qdisc_pkt_len(skb);
	struct ets_sched *q = qdisc_priv(sch);
	struct ets_class *cl;
	int err = 0;
	bool first;

	cl = ets_classify(skb, sch, &err);
	if (!cl) {
		if (err & __NET_XMIT_BYPASS)
			qdisc_qstats_drop(sch);
		__qdisc_drop(skb, to_free);
		return err;
	}

	first = !cl->qdisc->q.qlen;
	err = qdisc_enqueue(skb, cl->qdisc, to_free);
	if (unlikely(err != NET_XMIT_SUCCESS)) {
		if (net_xmit_drop_count(err)) {
			cl->qstats.drops++;
			qdisc_qstats_drop(sch);
		}
		return err;
	}

	if (first && !ets_class_is_strict(q, cl)) {
		list_add_tail(&cl->alist, &q->active);
		cl->deficit = cl->quantum;
	}

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

static struct sk_buff *
ets_qdisc_dequeue_skb(struct Qdisc *sch, struct sk_buff *skb)
{
	qdisc_bstats_update(sch, skb);
	qdisc_qstats_backlog_dec(sch, skb);
	sch->q.qlen--;
	return skb;
}

static struct sk_buff *ets_qdisc_dequeue(struct Qdisc *sch)
{
	struct ets_sched *q = qdisc_priv(sch);
	struct ets_class *cl;
	struct sk_buff *skb;
	unsigned int band;
	unsigned int len;

	while (1) {
		for (band = 0; band < q->nstrict; band++) {
			cl = &q->classes[band];
			skb = qdisc_dequeue_peeked(cl->qdisc);
			if (skb)
				return ets_qdisc_dequeue_skb(sch, skb);
		}

		if (list_empty(&q->active))
			goto out;

		cl = list_first_entry(&q->active, struct ets_class, alist);
		skb = cl->qdisc->ops->peek(cl->qdisc);
		if (!skb) {
			qdisc_warn_nonwc(__func__, cl->qdisc);
			goto out;
		}

		len = qdisc_pkt_len(skb);
		if (len <= cl->deficit) {
			cl->deficit -= len;
			skb = qdisc_dequeue_peeked(cl->qdisc);
			if (unlikely(!skb))
				goto out;
			if (cl->qdisc->q.qlen == 0)
				list_del(&cl->alist);
			return ets_qdisc_dequeue_skb(sch, skb);
		}

		cl->deficit += cl->quantum;
		list_move_tail(&cl->alist, &q->active);
	}
out:
	return NULL;
}

static int ets_qdisc_priomap_parse(struct nlattr *priomap_attr,
				   unsigned int nbands, u8 *priomap,
				   struct netlink_ext_ack *extack)
{
	const struct nlattr *attr;
	int prio = 0;
	u8 band;
	int rem;
	int err;

	err = __nla_validate_nested(priomap_attr, TCA_ETS_MAX,
				    ets_priomap_policy, NL_VALIDATE_STRICT,
				    extack);
	if (err)
		return err;

	nla_for_each_nested(attr, priomap_attr, rem) {
		switch (nla_type(attr)) {
		case TCA_ETS_PRIOMAP_BAND:
			if (prio > TC_PRIO_MAX) {
				NL_SET_ERR_MSG_MOD(extack, "Too many priorities in ETS priomap");
				return -EINVAL;
			}
			band = nla_get_u8(attr);
			if (band >= nbands) {
				NL_SET_ERR_MSG_MOD(extack, "Invalid band number in ETS priomap");
				return -EINVAL;
			}
			priomap[prio++] = band;
			break;
		default:
			WARN_ON_ONCE(1); /* Validate should have caught this. */
			return -EINVAL;
		}
	}

	return 0;
}

static int ets_qdisc_quanta_parse(struct Qdisc *sch, struct nlattr *quanta_attr,
				  unsigned int nbands, unsigned int nstrict,
				  unsigned int *quanta,
				  struct netlink_ext_ack *extack)
{
	const struct nlattr *attr;
	int band = nstrict;
	int rem;
	int err;

	err = __nla_validate_nested(quanta_attr, TCA_ETS_MAX,
				    ets_quanta_policy, NL_VALIDATE_STRICT,
				    extack);
	if (err < 0)
		return err;

	nla_for_each_nested(attr, quanta_attr, rem) {
		switch (nla_type(attr)) {
		case TCA_ETS_QUANTA_BAND:
			if (band >= nbands) {
				NL_SET_ERR_MSG_MOD(extack, "ETS quanta has more values than bands");
				return -EINVAL;
			}
			err = ets_quantum_parse(sch, attr, &quanta[band++],
						extack);
			if (err)
				return err;
			break;
		default:
			WARN_ON_ONCE(1); /* Validate should have caught this. */
			return -EINVAL;
		}
	}

	return 0;
}

static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt,
			    struct netlink_ext_ack *extack)
{
	unsigned int quanta[TCQ_ETS_MAX_BANDS] = {0};
	struct Qdisc *queues[TCQ_ETS_MAX_BANDS];
	struct ets_sched *q = qdisc_priv(sch);
	struct nlattr *tb[TCA_ETS_MAX + 1];
	unsigned int oldbands = q->nbands;
	u8 priomap[TC_PRIO_MAX + 1];
	unsigned int nstrict = 0;
	unsigned int nbands;
	unsigned int i;
	int err;

	if (!opt) {
		NL_SET_ERR_MSG(extack, "ETS options are required for this operation");
		return -EINVAL;
	}

	err = nla_parse_nested(tb, TCA_ETS_MAX, opt, ets_policy, extack);
	if (err < 0)
		return err;

	if (!tb[TCA_ETS_NBANDS]) {
		NL_SET_ERR_MSG_MOD(extack, "Number of bands is a required argument");
		return -EINVAL;
	}
	nbands = nla_get_u8(tb[TCA_ETS_NBANDS]);
	if (nbands < 1 || nbands > TCQ_ETS_MAX_BANDS) {
		NL_SET_ERR_MSG_MOD(extack, "Invalid number of bands");
		return -EINVAL;
	}
	/* Unless overridden, traffic goes to the last band. */
	memset(priomap, nbands - 1, sizeof(priomap));

	if (tb[TCA_ETS_NSTRICT]) {
		nstrict = nla_get_u8(tb[TCA_ETS_NSTRICT]);
		if (nstrict > nbands) {
			NL_SET_ERR_MSG_MOD(extack, "Invalid number of strict bands");
			return -EINVAL;
		}
	}

	if (tb[TCA_ETS_PRIOMAP]) {
		err = ets_qdisc_priomap_parse(tb[TCA_ETS_PRIOMAP],
					      nbands, priomap, extack);
		if (err)
			return err;
	}

	if (tb[TCA_ETS_QUANTA]) {
		err = ets_qdisc_quanta_parse(sch, tb[TCA_ETS_QUANTA],
					     nbands, nstrict, quanta, extack);
		if (err)
			return err;
	}
	/* If there are more bands than strict + quanta provided, the remaining
	 * ones are ETS with quantum of MTU. Initialize the missing values here.
	 */
	for (i = nstrict; i < nbands; i++) {
		if (!quanta[i])
			quanta[i] = psched_mtu(qdisc_dev(sch));
	}

	/* Before commit, make sure we can allocate all new qdiscs */
	for (i = oldbands; i < nbands; i++) {
		queues[i] = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
					      ets_class_id(sch, &q->classes[i]),
					      extack);
		if (!queues[i]) {
			while (i > oldbands)
				qdisc_put(queues[--i]);
			return -ENOMEM;
		}
	}

	sch_tree_lock(sch);

	q->nbands = nbands;
	q->nstrict = nstrict;
	memcpy(q->prio2band, priomap, sizeof(priomap));

	for (i = q->nbands; i < oldbands; i++)
		qdisc_tree_flush_backlog(q->classes[i].qdisc);

	for (i = 0; i < q->nbands; i++)
		q->classes[i].quantum = quanta[i];

	for (i = oldbands; i < q->nbands; i++) {
		q->classes[i].qdisc = queues[i];
		if (q->classes[i].qdisc != &noop_qdisc)
			qdisc_hash_add(q->classes[i].qdisc, true);
	}

	sch_tree_unlock(sch);

	for (i = q->nbands; i < oldbands; i++) {
		qdisc_put(q->classes[i].qdisc);
		memset(&q->classes[i], 0, sizeof(q->classes[i]));
	}
	return 0;
}

static int ets_qdisc_init(struct Qdisc *sch, struct nlattr *opt,
			  struct netlink_ext_ack *extack)
{
	struct ets_sched *q = qdisc_priv(sch);
	int err;

	if (!opt)
		return -EINVAL;

	err = tcf_block_get(&q->block, &q->filter_list, sch, extack);
	if (err)
		return err;

	INIT_LIST_HEAD(&q->active);
	return ets_qdisc_change(sch, opt, extack);
}

static void ets_qdisc_reset(struct Qdisc *sch)
{
	struct ets_sched *q = qdisc_priv(sch);
	int band;

	for (band = q->nstrict; band < q->nbands; band++) {
		if (q->classes[band].qdisc->q.qlen)
			list_del(&q->classes[band].alist);
	}
	for (band = 0; band < q->nbands; band++)
		qdisc_reset(q->classes[band].qdisc);
	sch->qstats.backlog = 0;
	sch->q.qlen = 0;
}

static void ets_qdisc_destroy(struct Qdisc *sch)
{
	struct ets_sched *q = qdisc_priv(sch);
	int band;

	tcf_block_put(q->block);
	for (band = 0; band < q->nbands; band++)
		qdisc_put(q->classes[band].qdisc);
}

static int ets_qdisc_dump(struct Qdisc *sch, struct sk_buff *skb)
{
	struct ets_sched *q = qdisc_priv(sch);
	struct nlattr *opts;
	struct nlattr *nest;
	int band;
	int prio;

	opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
	if (!opts)
		goto nla_err;

	if (nla_put_u8(skb, TCA_ETS_NBANDS, q->nbands))
		goto nla_err;

	if (q->nstrict &&
	    nla_put_u8(skb, TCA_ETS_NSTRICT, q->nstrict))
		goto nla_err;

	if (q->nbands > q->nstrict) {
		nest = nla_nest_start(skb, TCA_ETS_QUANTA);
		if (!nest)
			goto nla_err;

		for (band = q->nstrict; band < q->nbands; band++) {
			if (nla_put_u32(skb, TCA_ETS_QUANTA_BAND,
					q->classes[band].quantum))
				goto nla_err;
		}

		nla_nest_end(skb, nest);
	}

	nest = nla_nest_start(skb, TCA_ETS_PRIOMAP);
	if (!nest)
		goto nla_err;

	for (prio = 0; prio <= TC_PRIO_MAX; prio++) {
		if (nla_put_u8(skb, TCA_ETS_PRIOMAP_BAND, q->prio2band[prio]))
			goto nla_err;
	}

	nla_nest_end(skb, nest);

	return nla_nest_end(skb, opts);

nla_err:
	nla_nest_cancel(skb, opts);
	return -EMSGSIZE;
}

static const struct Qdisc_class_ops ets_class_ops = {
	.change		= ets_class_change,
	.graft		= ets_class_graft,
	.leaf		= ets_class_leaf,
	.find		= ets_class_find,
	.qlen_notify	= ets_class_qlen_notify,
	.dump		= ets_class_dump,
	.dump_stats	= ets_class_dump_stats,
	.walk		= ets_qdisc_walk,
	.tcf_block	= ets_qdisc_tcf_block,
	.bind_tcf	= ets_qdisc_bind_tcf,
	.unbind_tcf	= ets_qdisc_unbind_tcf,
};

static struct Qdisc_ops ets_qdisc_ops __read_mostly = {
	.cl_ops		= &ets_class_ops,
	.id		= "ets",
	.priv_size	= sizeof(struct ets_sched),
	.enqueue	= ets_qdisc_enqueue,
	.dequeue	= ets_qdisc_dequeue,
	.peek		= qdisc_peek_dequeued,
	.change		= ets_qdisc_change,
	.init		= ets_qdisc_init,
	.reset		= ets_qdisc_reset,
	.destroy	= ets_qdisc_destroy,
	.dump		= ets_qdisc_dump,
	.owner		= THIS_MODULE,
};

static int __init ets_init(void)
{
	return register_qdisc(&ets_qdisc_ops);
}

static void __exit ets_exit(void)
{
	unregister_qdisc(&ets_qdisc_ops);
}

module_init(ets_init);
module_exit(ets_exit);
MODULE_LICENSE("GPL");