/*
 * net/sched/sch_sfq.c	Stochastic Fairness Queueing discipline.
 *
 *		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>
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/string.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/ipv6.h>
#include <linux/skbuff.h>
#include <linux/jhash.h>
#include <net/ip.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>


/*	Stochastic Fairness Queuing algorithm.
	=======================================

	Source:
	Paul E. McKenney "Stochastic Fairness Queuing",
	IEEE INFOCOMM'90 Proceedings, San Francisco, 1990.

	Paul E. McKenney "Stochastic Fairness Queuing",
	"Interworking: Research and Experience", v.2, 1991, p.113-131.


	See also:
	M. Shreedhar and George Varghese "Efficient Fair
	Queuing using Deficit Round Robin", Proc. SIGCOMM 95.


	This is not the thing that is usually called (W)FQ nowadays.
	It does not use any timestamp mechanism, but instead
	processes queues in round-robin order.

	ADVANTAGE:

	- It is very cheap. Both CPU and memory requirements are minimal.

	DRAWBACKS:

	- "Stochastic" -> It is not 100% fair.
	When hash collisions occur, several flows are considered as one.

	- "Round-robin" -> It introduces larger delays than virtual clock
	based schemes, and should not be used for isolating interactive
	traffic	from non-interactive. It means, that this scheduler
	should be used as leaf of CBQ or P3, which put interactive traffic
	to higher priority band.

	We still need true WFQ for top level CSZ, but using WFQ
	for the best effort traffic is absolutely pointless:
	SFQ is superior for this purpose.

	IMPLEMENTATION:
	This implementation limits maximal queue length to 128;
	maximal mtu to 2^15-1; number of hash buckets to 1024.
	The only goal of this restrictions was that all data
	fit into one 4K page :-). Struct sfq_sched_data is
	organized in anti-cache manner: all the data for a bucket
	are scattered over different locations. This is not good,
	but it allowed me to put it into 4K.

	It is easy to increase these values, but not in flight.  */

#define SFQ_DEPTH		128
#define SFQ_HASH_DIVISOR	1024

/* This type should contain at least SFQ_DEPTH*2 values */
typedef unsigned char sfq_index;

struct sfq_head
{
	sfq_index	next;
	sfq_index	prev;
};

struct sfq_sched_data
{
/* Parameters */
	int		perturb_period;
	unsigned	quantum;	/* Allotment per round: MUST BE >= MTU */
	int		limit;

/* Variables */
	struct timer_list perturb_timer;
	u32		perturbation;
	sfq_index	tail;		/* Index of current slot in round */
	sfq_index	max_depth;	/* Maximal depth */

	sfq_index	ht[SFQ_HASH_DIVISOR];	/* Hash table */
	sfq_index	next[SFQ_DEPTH];	/* Active slots link */
	short		allot[SFQ_DEPTH];	/* Current allotment per slot */
	unsigned short	hash[SFQ_DEPTH];	/* Hash value indexed by slots */
	struct sk_buff_head	qs[SFQ_DEPTH];		/* Slot queue */
	struct sfq_head	dep[SFQ_DEPTH*2];	/* Linked list of slots, indexed by depth */
};

static __inline__ unsigned sfq_fold_hash(struct sfq_sched_data *q, u32 h, u32 h1)
{
	return jhash_2words(h, h1, q->perturbation) & (SFQ_HASH_DIVISOR - 1);
}

static unsigned sfq_hash(struct sfq_sched_data *q, struct sk_buff *skb)
{
	u32 h, h2;

	switch (skb->protocol) {
	case __constant_htons(ETH_P_IP):
	{
		const struct iphdr *iph = ip_hdr(skb);
		h = iph->daddr;
		h2 = iph->saddr^iph->protocol;
		if (!(iph->frag_off&htons(IP_MF|IP_OFFSET)) &&
		    (iph->protocol == IPPROTO_TCP ||
		     iph->protocol == IPPROTO_UDP ||
		     iph->protocol == IPPROTO_UDPLITE ||
		     iph->protocol == IPPROTO_SCTP ||
		     iph->protocol == IPPROTO_DCCP ||
		     iph->protocol == IPPROTO_ESP))
			h2 ^= *(((u32*)iph) + iph->ihl);
		break;
	}
	case __constant_htons(ETH_P_IPV6):
	{
		struct ipv6hdr *iph = ipv6_hdr(skb);
		h = iph->daddr.s6_addr32[3];
		h2 = iph->saddr.s6_addr32[3]^iph->nexthdr;
		if (iph->nexthdr == IPPROTO_TCP ||
		    iph->nexthdr == IPPROTO_UDP ||
		    iph->nexthdr == IPPROTO_UDPLITE ||
		    iph->nexthdr == IPPROTO_SCTP ||
		    iph->nexthdr == IPPROTO_DCCP ||
		    iph->nexthdr == IPPROTO_ESP)
			h2 ^= *(u32*)&iph[1];
		break;
	}
	default:
		h = (u32)(unsigned long)skb->dst^skb->protocol;
		h2 = (u32)(unsigned long)skb->sk;
	}
	return sfq_fold_hash(q, h, h2);
}

static inline void sfq_link(struct sfq_sched_data *q, sfq_index x)
{
	sfq_index p, n;
	int d = q->qs[x].qlen + SFQ_DEPTH;

	p = d;
	n = q->dep[d].next;
	q->dep[x].next = n;
	q->dep[x].prev = p;
	q->dep[p].next = q->dep[n].prev = x;
}

static inline void sfq_dec(struct sfq_sched_data *q, sfq_index x)
{
	sfq_index p, n;

	n = q->dep[x].next;
	p = q->dep[x].prev;
	q->dep[p].next = n;
	q->dep[n].prev = p;

	if (n == p && q->max_depth == q->qs[x].qlen + 1)
		q->max_depth--;

	sfq_link(q, x);
}

static inline void sfq_inc(struct sfq_sched_data *q, sfq_index x)
{
	sfq_index p, n;
	int d;

	n = q->dep[x].next;
	p = q->dep[x].prev;
	q->dep[p].next = n;
	q->dep[n].prev = p;
	d = q->qs[x].qlen;
	if (q->max_depth < d)
		q->max_depth = d;

	sfq_link(q, x);
}

static unsigned int sfq_drop(struct Qdisc *sch)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	sfq_index d = q->max_depth;
	struct sk_buff *skb;
	unsigned int len;

	/* Queue is full! Find the longest slot and
	   drop a packet from it */

	if (d > 1) {
		sfq_index x = q->dep[d+SFQ_DEPTH].next;
		skb = q->qs[x].prev;
		len = skb->len;
		__skb_unlink(skb, &q->qs[x]);
		kfree_skb(skb);
		sfq_dec(q, x);
		sch->q.qlen--;
		sch->qstats.drops++;
		sch->qstats.backlog -= len;
		return len;
	}

	if (d == 1) {
		/* It is difficult to believe, but ALL THE SLOTS HAVE LENGTH 1. */
		d = q->next[q->tail];
		q->next[q->tail] = q->next[d];
		q->allot[q->next[d]] += q->quantum;
		skb = q->qs[d].prev;
		len = skb->len;
		__skb_unlink(skb, &q->qs[d]);
		kfree_skb(skb);
		sfq_dec(q, d);
		sch->q.qlen--;
		q->ht[q->hash[d]] = SFQ_DEPTH;
		sch->qstats.drops++;
		sch->qstats.backlog -= len;
		return len;
	}

	return 0;
}

static int
sfq_enqueue(struct sk_buff *skb, struct Qdisc* sch)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	unsigned hash = sfq_hash(q, skb);
	sfq_index x;

	x = q->ht[hash];
	if (x == SFQ_DEPTH) {
		q->ht[hash] = x = q->dep[SFQ_DEPTH].next;
		q->hash[x] = hash;
	}
	/* If selected queue has length q->limit, this means that
	 * all another queues are empty and that we do simple tail drop,
	 * i.e. drop _this_ packet.
	 */
	if (q->qs[x].qlen >= q->limit)
		return qdisc_drop(skb, sch);

	sch->qstats.backlog += skb->len;
	__skb_queue_tail(&q->qs[x], skb);
	sfq_inc(q, x);
	if (q->qs[x].qlen == 1) {		/* The flow is new */
		if (q->tail == SFQ_DEPTH) {	/* It is the first flow */
			q->tail = x;
			q->next[x] = x;
			q->allot[x] = q->quantum;
		} else {
			q->next[x] = q->next[q->tail];
			q->next[q->tail] = x;
			q->tail = x;
		}
	}
	if (++sch->q.qlen <= q->limit) {
		sch->bstats.bytes += skb->len;
		sch->bstats.packets++;
		return 0;
	}

	sfq_drop(sch);
	return NET_XMIT_CN;
}

static int
sfq_requeue(struct sk_buff *skb, struct Qdisc* sch)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	unsigned hash = sfq_hash(q, skb);
	sfq_index x;

	x = q->ht[hash];
	if (x == SFQ_DEPTH) {
		q->ht[hash] = x = q->dep[SFQ_DEPTH].next;
		q->hash[x] = hash;
	}
	sch->qstats.backlog += skb->len;
	__skb_queue_head(&q->qs[x], skb);
	/* If selected queue has length q->limit+1, this means that
	 * all another queues are empty and we do simple tail drop.
	 * This packet is still requeued at head of queue, tail packet
	 * is dropped.
	 */
	if (q->qs[x].qlen > q->limit) {
		skb = q->qs[x].prev;
		__skb_unlink(skb, &q->qs[x]);
		sch->qstats.drops++;
		sch->qstats.backlog -= skb->len;
		kfree_skb(skb);
		return NET_XMIT_CN;
	}
	sfq_inc(q, x);
	if (q->qs[x].qlen == 1) {		/* The flow is new */
		if (q->tail == SFQ_DEPTH) {	/* It is the first flow */
			q->tail = x;
			q->next[x] = x;
			q->allot[x] = q->quantum;
		} else {
			q->next[x] = q->next[q->tail];
			q->next[q->tail] = x;
			q->tail = x;
		}
	}
	if (++sch->q.qlen <= q->limit) {
		sch->qstats.requeues++;
		return 0;
	}

	sch->qstats.drops++;
	sfq_drop(sch);
	return NET_XMIT_CN;
}


static struct sk_buff *
sfq_dequeue(struct Qdisc* sch)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	struct sk_buff *skb;
	sfq_index a, old_a;

	/* No active slots */
	if (q->tail == SFQ_DEPTH)
		return NULL;

	a = old_a = q->next[q->tail];

	/* Grab packet */
	skb = __skb_dequeue(&q->qs[a]);
	sfq_dec(q, a);
	sch->q.qlen--;
	sch->qstats.backlog -= skb->len;

	/* Is the slot empty? */
	if (q->qs[a].qlen == 0) {
		q->ht[q->hash[a]] = SFQ_DEPTH;
		a = q->next[a];
		if (a == old_a) {
			q->tail = SFQ_DEPTH;
			return skb;
		}
		q->next[q->tail] = a;
		q->allot[a] += q->quantum;
	} else if ((q->allot[a] -= skb->len) <= 0) {
		q->tail = a;
		a = q->next[a];
		q->allot[a] += q->quantum;
	}
	return skb;
}

static void
sfq_reset(struct Qdisc* sch)
{
	struct sk_buff *skb;

	while ((skb = sfq_dequeue(sch)) != NULL)
		kfree_skb(skb);
}

static void sfq_perturbation(unsigned long arg)
{
	struct Qdisc *sch = (struct Qdisc*)arg;
	struct sfq_sched_data *q = qdisc_priv(sch);

	get_random_bytes(&q->perturbation, 4);

	if (q->perturb_period)
		mod_timer(&q->perturb_timer, jiffies + q->perturb_period);
}

static int sfq_change(struct Qdisc *sch, struct rtattr *opt)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	struct tc_sfq_qopt *ctl = RTA_DATA(opt);
	unsigned int qlen;

	if (opt->rta_len < RTA_LENGTH(sizeof(*ctl)))
		return -EINVAL;

	sch_tree_lock(sch);
	q->quantum = ctl->quantum ? : psched_mtu(sch->dev);
	q->perturb_period = ctl->perturb_period*HZ;
	if (ctl->limit)
		q->limit = min_t(u32, ctl->limit, SFQ_DEPTH - 1);

	qlen = sch->q.qlen;
	while (sch->q.qlen > q->limit)
		sfq_drop(sch);
	qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);

	del_timer(&q->perturb_timer);
	if (q->perturb_period) {
		mod_timer(&q->perturb_timer, jiffies + q->perturb_period);
		get_random_bytes(&q->perturbation, 4);
	}
	sch_tree_unlock(sch);
	return 0;
}

static int sfq_init(struct Qdisc *sch, struct rtattr *opt)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	int i;

	init_timer(&q->perturb_timer);
	q->perturb_timer.data = (unsigned long)sch;
	q->perturb_timer.function = sfq_perturbation;

	for (i=0; i<SFQ_HASH_DIVISOR; i++)
		q->ht[i] = SFQ_DEPTH;
	for (i=0; i<SFQ_DEPTH; i++) {
		skb_queue_head_init(&q->qs[i]);
		q->dep[i+SFQ_DEPTH].next = i+SFQ_DEPTH;
		q->dep[i+SFQ_DEPTH].prev = i+SFQ_DEPTH;
	}
	q->limit = SFQ_DEPTH - 1;
	q->max_depth = 0;
	q->tail = SFQ_DEPTH;
	if (opt == NULL) {
		q->quantum = psched_mtu(sch->dev);
		q->perturb_period = 0;
		get_random_bytes(&q->perturbation, 4);
	} else {
		int err = sfq_change(sch, opt);
		if (err)
			return err;
	}
	for (i=0; i<SFQ_DEPTH; i++)
		sfq_link(q, i);
	return 0;
}

static void sfq_destroy(struct Qdisc *sch)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	del_timer(&q->perturb_timer);
}

static int sfq_dump(struct Qdisc *sch, struct sk_buff *skb)
{
	struct sfq_sched_data *q = qdisc_priv(sch);
	unsigned char *b = skb_tail_pointer(skb);
	struct tc_sfq_qopt opt;

	opt.quantum = q->quantum;
	opt.perturb_period = q->perturb_period/HZ;

	opt.limit = q->limit;
	opt.divisor = SFQ_HASH_DIVISOR;
	opt.flows = q->limit;

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

	return skb->len;

rtattr_failure:
	nlmsg_trim(skb, b);
	return -1;
}

static struct Qdisc_ops sfq_qdisc_ops = {
	.next		=	NULL,
	.cl_ops		=	NULL,
	.id		=	"sfq",
	.priv_size	=	sizeof(struct sfq_sched_data),
	.enqueue	=	sfq_enqueue,
	.dequeue	=	sfq_dequeue,
	.requeue	=	sfq_requeue,
	.drop		=	sfq_drop,
	.init		=	sfq_init,
	.reset		=	sfq_reset,
	.destroy	=	sfq_destroy,
	.change		=	NULL,
	.dump		=	sfq_dump,
	.owner		=	THIS_MODULE,
};

static int __init sfq_module_init(void)
{
	return register_qdisc(&sfq_qdisc_ops);
}
static void __exit sfq_module_exit(void)
{
	unregister_qdisc(&sfq_qdisc_ops);
}
module_init(sfq_module_init)
module_exit(sfq_module_exit)
MODULE_LICENSE("GPL");