// SPDX-License-Identifier: GPL-2.0
/* IPVS:	Maglev Hashing scheduling module
 *
 * Authors:	Inju Song <inju.song@navercorp.com>
 *
 */

/* The mh algorithm is to assign a preference list of all the lookup
 * table positions to each destination and populate the table with
 * the most-preferred position of destinations. Then it is to select
 * destination with the hash key of source IP address through looking
 * up a the lookup table.
 *
 * The algorithm is detailed in:
 * [3.4 Consistent Hasing]
https://www.usenix.org/system/files/conference/nsdi16/nsdi16-paper-eisenbud.pdf
 *
 */

#define KMSG_COMPONENT "IPVS"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/ip.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>

#include <net/ip_vs.h>

#include <linux/siphash.h>
#include <linux/bitops.h>
#include <linux/gcd.h>

#define IP_VS_SVC_F_SCHED_MH_FALLBACK	IP_VS_SVC_F_SCHED1 /* MH fallback */
#define IP_VS_SVC_F_SCHED_MH_PORT	IP_VS_SVC_F_SCHED2 /* MH use port */

struct ip_vs_mh_lookup {
	struct ip_vs_dest __rcu	*dest;	/* real server (cache) */
};

struct ip_vs_mh_dest_setup {
	unsigned int	offset; /* starting offset */
	unsigned int	skip;	/* skip */
	unsigned int	perm;	/* next_offset */
	int		turns;	/* weight / gcd() and rshift */
};

/* Available prime numbers for MH table */
static int primes[] = {251, 509, 1021, 2039, 4093,
		       8191, 16381, 32749, 65521, 131071};

/* For IPVS MH entry hash table */
#ifndef CONFIG_IP_VS_MH_TAB_INDEX
#define CONFIG_IP_VS_MH_TAB_INDEX	12
#endif
#define IP_VS_MH_TAB_BITS		(CONFIG_IP_VS_MH_TAB_INDEX / 2)
#define IP_VS_MH_TAB_INDEX		(CONFIG_IP_VS_MH_TAB_INDEX - 8)
#define IP_VS_MH_TAB_SIZE               primes[IP_VS_MH_TAB_INDEX]

struct ip_vs_mh_state {
	struct rcu_head			rcu_head;
	struct ip_vs_mh_lookup		*lookup;
	struct ip_vs_mh_dest_setup	*dest_setup;
	hsiphash_key_t			hash1, hash2;
	int				gcd;
	int				rshift;
};

static inline void generate_hash_secret(hsiphash_key_t *hash1,
					hsiphash_key_t *hash2)
{
	hash1->key[0] = 2654435761UL;
	hash1->key[1] = 2654435761UL;

	hash2->key[0] = 2654446892UL;
	hash2->key[1] = 2654446892UL;
}

/* Helper function to determine if server is unavailable */
static inline bool is_unavailable(struct ip_vs_dest *dest)
{
	return atomic_read(&dest->weight) <= 0 ||
	       dest->flags & IP_VS_DEST_F_OVERLOAD;
}

/* Returns hash value for IPVS MH entry */
static inline unsigned int
ip_vs_mh_hashkey(int af, const union nf_inet_addr *addr,
		 __be16 port, hsiphash_key_t *key, unsigned int offset)
{
	unsigned int v;
	__be32 addr_fold = addr->ip;

#ifdef CONFIG_IP_VS_IPV6
	if (af == AF_INET6)
		addr_fold = addr->ip6[0] ^ addr->ip6[1] ^
			    addr->ip6[2] ^ addr->ip6[3];
#endif
	v = (offset + ntohs(port) + ntohl(addr_fold));
	return hsiphash(&v, sizeof(v), key);
}

/* Reset all the hash buckets of the specified table. */
static void ip_vs_mh_reset(struct ip_vs_mh_state *s)
{
	int i;
	struct ip_vs_mh_lookup *l;
	struct ip_vs_dest *dest;

	l = &s->lookup[0];
	for (i = 0; i < IP_VS_MH_TAB_SIZE; i++) {
		dest = rcu_dereference_protected(l->dest, 1);
		if (dest) {
			ip_vs_dest_put(dest);
			RCU_INIT_POINTER(l->dest, NULL);
		}
		l++;
	}
}

static int ip_vs_mh_permutate(struct ip_vs_mh_state *s,
			      struct ip_vs_service *svc)
{
	struct list_head *p;
	struct ip_vs_mh_dest_setup *ds;
	struct ip_vs_dest *dest;
	int lw;

	/* If gcd is smaller then 1, number of dests or
	 * all last_weight of dests are zero. So, skip
	 * permutation for the dests.
	 */
	if (s->gcd < 1)
		return 0;

	/* Set dest_setup for the dests permutation */
	p = &svc->destinations;
	ds = &s->dest_setup[0];
	while ((p = p->next) != &svc->destinations) {
		dest = list_entry(p, struct ip_vs_dest, n_list);

		ds->offset = ip_vs_mh_hashkey(svc->af, &dest->addr,
					      dest->port, &s->hash1, 0) %
					      IP_VS_MH_TAB_SIZE;
		ds->skip = ip_vs_mh_hashkey(svc->af, &dest->addr,
					    dest->port, &s->hash2, 0) %
					    (IP_VS_MH_TAB_SIZE - 1) + 1;
		ds->perm = ds->offset;

		lw = atomic_read(&dest->last_weight);
		ds->turns = ((lw / s->gcd) >> s->rshift) ? : (lw != 0);
		ds++;
	}

	return 0;
}

static int ip_vs_mh_populate(struct ip_vs_mh_state *s,
			     struct ip_vs_service *svc)
{
	int n, c, dt_count;
	unsigned long *table;
	struct list_head *p;
	struct ip_vs_mh_dest_setup *ds;
	struct ip_vs_dest *dest, *new_dest;

	/* If gcd is smaller then 1, number of dests or
	 * all last_weight of dests are zero. So, skip
	 * the population for the dests and reset lookup table.
	 */
	if (s->gcd < 1) {
		ip_vs_mh_reset(s);
		return 0;
	}

	table =  kcalloc(BITS_TO_LONGS(IP_VS_MH_TAB_SIZE),
			 sizeof(unsigned long), GFP_KERNEL);
	if (!table)
		return -ENOMEM;

	p = &svc->destinations;
	n = 0;
	dt_count = 0;
	while (n < IP_VS_MH_TAB_SIZE) {
		if (p == &svc->destinations)
			p = p->next;

		ds = &s->dest_setup[0];
		while (p != &svc->destinations) {
			/* Ignore added server with zero weight */
			if (ds->turns < 1) {
				p = p->next;
				ds++;
				continue;
			}

			c = ds->perm;
			while (test_bit(c, table)) {
				/* Add skip, mod IP_VS_MH_TAB_SIZE */
				ds->perm += ds->skip;
				if (ds->perm >= IP_VS_MH_TAB_SIZE)
					ds->perm -= IP_VS_MH_TAB_SIZE;
				c = ds->perm;
			}

			__set_bit(c, table);

			dest = rcu_dereference_protected(s->lookup[c].dest, 1);
			new_dest = list_entry(p, struct ip_vs_dest, n_list);
			if (dest != new_dest) {
				if (dest)
					ip_vs_dest_put(dest);
				ip_vs_dest_hold(new_dest);
				RCU_INIT_POINTER(s->lookup[c].dest, new_dest);
			}

			if (++n == IP_VS_MH_TAB_SIZE)
				goto out;

			if (++dt_count >= ds->turns) {
				dt_count = 0;
				p = p->next;
				ds++;
			}
		}
	}

out:
	kfree(table);
	return 0;
}

/* Get ip_vs_dest associated with supplied parameters. */
static inline struct ip_vs_dest *
ip_vs_mh_get(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
	     const union nf_inet_addr *addr, __be16 port)
{
	unsigned int hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1, 0)
					     % IP_VS_MH_TAB_SIZE;
	struct ip_vs_dest *dest = rcu_dereference(s->lookup[hash].dest);

	return (!dest || is_unavailable(dest)) ? NULL : dest;
}

/* As ip_vs_mh_get, but with fallback if selected server is unavailable */
static inline struct ip_vs_dest *
ip_vs_mh_get_fallback(struct ip_vs_service *svc, struct ip_vs_mh_state *s,
		      const union nf_inet_addr *addr, __be16 port)
{
	unsigned int offset, roffset;
	unsigned int hash, ihash;
	struct ip_vs_dest *dest;

	/* First try the dest it's supposed to go to */
	ihash = ip_vs_mh_hashkey(svc->af, addr, port,
				 &s->hash1, 0) % IP_VS_MH_TAB_SIZE;
	dest = rcu_dereference(s->lookup[ihash].dest);
	if (!dest)
		return NULL;
	if (!is_unavailable(dest))
		return dest;

	IP_VS_DBG_BUF(6, "MH: selected unavailable server %s:%u, reselecting",
		      IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port));

	/* If the original dest is unavailable, loop around the table
	 * starting from ihash to find a new dest
	 */
	for (offset = 0; offset < IP_VS_MH_TAB_SIZE; offset++) {
		roffset = (offset + ihash) % IP_VS_MH_TAB_SIZE;
		hash = ip_vs_mh_hashkey(svc->af, addr, port, &s->hash1,
					roffset) % IP_VS_MH_TAB_SIZE;
		dest = rcu_dereference(s->lookup[hash].dest);
		if (!dest)
			break;
		if (!is_unavailable(dest))
			return dest;
		IP_VS_DBG_BUF(6,
			      "MH: selected unavailable server %s:%u (offset %u), reselecting",
			      IP_VS_DBG_ADDR(dest->af, &dest->addr),
			      ntohs(dest->port), roffset);
	}

	return NULL;
}

/* Assign all the hash buckets of the specified table with the service. */
static int ip_vs_mh_reassign(struct ip_vs_mh_state *s,
			     struct ip_vs_service *svc)
{
	int ret;

	if (svc->num_dests > IP_VS_MH_TAB_SIZE)
		return -EINVAL;

	if (svc->num_dests >= 1) {
		s->dest_setup = kcalloc(svc->num_dests,
					sizeof(struct ip_vs_mh_dest_setup),
					GFP_KERNEL);
		if (!s->dest_setup)
			return -ENOMEM;
	}

	ip_vs_mh_permutate(s, svc);

	ret = ip_vs_mh_populate(s, svc);
	if (ret < 0)
		goto out;

	IP_VS_DBG_BUF(6, "MH: reassign lookup table of %s:%u\n",
		      IP_VS_DBG_ADDR(svc->af, &svc->addr),
		      ntohs(svc->port));

out:
	if (svc->num_dests >= 1) {
		kfree(s->dest_setup);
		s->dest_setup = NULL;
	}
	return ret;
}

static int ip_vs_mh_gcd_weight(struct ip_vs_service *svc)
{
	struct ip_vs_dest *dest;
	int weight;
	int g = 0;

	list_for_each_entry(dest, &svc->destinations, n_list) {
		weight = atomic_read(&dest->last_weight);
		if (weight > 0) {
			if (g > 0)
				g = gcd(weight, g);
			else
				g = weight;
		}
	}
	return g;
}

/* To avoid assigning huge weight for the MH table,
 * calculate shift value with gcd.
 */
static int ip_vs_mh_shift_weight(struct ip_vs_service *svc, int gcd)
{
	struct ip_vs_dest *dest;
	int new_weight, weight = 0;
	int mw, shift;

	/* If gcd is smaller then 1, number of dests or
	 * all last_weight of dests are zero. So, return
	 * shift value as zero.
	 */
	if (gcd < 1)
		return 0;

	list_for_each_entry(dest, &svc->destinations, n_list) {
		new_weight = atomic_read(&dest->last_weight);
		if (new_weight > weight)
			weight = new_weight;
	}

	/* Because gcd is greater than zero,
	 * the maximum weight and gcd are always greater than zero
	 */
	mw = weight / gcd;

	/* shift = occupied bits of weight/gcd - MH highest bits */
	shift = fls(mw) - IP_VS_MH_TAB_BITS;
	return (shift >= 0) ? shift : 0;
}

static void ip_vs_mh_state_free(struct rcu_head *head)
{
	struct ip_vs_mh_state *s;

	s = container_of(head, struct ip_vs_mh_state, rcu_head);
	kfree(s->lookup);
	kfree(s);
}

static int ip_vs_mh_init_svc(struct ip_vs_service *svc)
{
	int ret;
	struct ip_vs_mh_state *s;

	/* Allocate the MH table for this service */
	s = kzalloc(sizeof(*s), GFP_KERNEL);
	if (!s)
		return -ENOMEM;

	s->lookup = kcalloc(IP_VS_MH_TAB_SIZE, sizeof(struct ip_vs_mh_lookup),
			    GFP_KERNEL);
	if (!s->lookup) {
		kfree(s);
		return -ENOMEM;
	}

	generate_hash_secret(&s->hash1, &s->hash2);
	s->gcd = ip_vs_mh_gcd_weight(svc);
	s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);

	IP_VS_DBG(6,
		  "MH lookup table (memory=%zdbytes) allocated for current service\n",
		  sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);

	/* Assign the lookup table with current dests */
	ret = ip_vs_mh_reassign(s, svc);
	if (ret < 0) {
		ip_vs_mh_reset(s);
		ip_vs_mh_state_free(&s->rcu_head);
		return ret;
	}

	/* No more failures, attach state */
	svc->sched_data = s;
	return 0;
}

static void ip_vs_mh_done_svc(struct ip_vs_service *svc)
{
	struct ip_vs_mh_state *s = svc->sched_data;

	/* Got to clean up lookup entry here */
	ip_vs_mh_reset(s);

	call_rcu(&s->rcu_head, ip_vs_mh_state_free);
	IP_VS_DBG(6, "MH lookup table (memory=%zdbytes) released\n",
		  sizeof(struct ip_vs_mh_lookup) * IP_VS_MH_TAB_SIZE);
}

static int ip_vs_mh_dest_changed(struct ip_vs_service *svc,
				 struct ip_vs_dest *dest)
{
	struct ip_vs_mh_state *s = svc->sched_data;

	s->gcd = ip_vs_mh_gcd_weight(svc);
	s->rshift = ip_vs_mh_shift_weight(svc, s->gcd);

	/* Assign the lookup table with the updated service */
	return ip_vs_mh_reassign(s, svc);
}

/* Helper function to get port number */
static inline __be16
ip_vs_mh_get_port(const struct sk_buff *skb, struct ip_vs_iphdr *iph)
{
	__be16 _ports[2], *ports;

	/* At this point we know that we have a valid packet of some kind.
	 * Because ICMP packets are only guaranteed to have the first 8
	 * bytes, let's just grab the ports.  Fortunately they're in the
	 * same position for all three of the protocols we care about.
	 */
	switch (iph->protocol) {
	case IPPROTO_TCP:
	case IPPROTO_UDP:
	case IPPROTO_SCTP:
		ports = skb_header_pointer(skb, iph->len, sizeof(_ports),
					   &_ports);
		if (unlikely(!ports))
			return 0;

		if (likely(!ip_vs_iph_inverse(iph)))
			return ports[0];
		else
			return ports[1];
	default:
		return 0;
	}
}

/* Maglev Hashing scheduling */
static struct ip_vs_dest *
ip_vs_mh_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
		  struct ip_vs_iphdr *iph)
{
	struct ip_vs_dest *dest;
	struct ip_vs_mh_state *s;
	__be16 port = 0;
	const union nf_inet_addr *hash_addr;

	hash_addr = ip_vs_iph_inverse(iph) ? &iph->daddr : &iph->saddr;

	IP_VS_DBG(6, "%s : Scheduling...\n", __func__);

	if (svc->flags & IP_VS_SVC_F_SCHED_MH_PORT)
		port = ip_vs_mh_get_port(skb, iph);

	s = (struct ip_vs_mh_state *)svc->sched_data;

	if (svc->flags & IP_VS_SVC_F_SCHED_MH_FALLBACK)
		dest = ip_vs_mh_get_fallback(svc, s, hash_addr, port);
	else
		dest = ip_vs_mh_get(svc, s, hash_addr, port);

	if (!dest) {
		ip_vs_scheduler_err(svc, "no destination available");
		return NULL;
	}

	IP_VS_DBG_BUF(6, "MH: source IP address %s:%u --> server %s:%u\n",
		      IP_VS_DBG_ADDR(svc->af, hash_addr),
		      ntohs(port),
		      IP_VS_DBG_ADDR(dest->af, &dest->addr),
		      ntohs(dest->port));

	return dest;
}

/* IPVS MH Scheduler structure */
static struct ip_vs_scheduler ip_vs_mh_scheduler = {
	.name =			"mh",
	.refcnt =		ATOMIC_INIT(0),
	.module =		THIS_MODULE,
	.n_list	 =		LIST_HEAD_INIT(ip_vs_mh_scheduler.n_list),
	.init_service =		ip_vs_mh_init_svc,
	.done_service =		ip_vs_mh_done_svc,
	.add_dest =		ip_vs_mh_dest_changed,
	.del_dest =		ip_vs_mh_dest_changed,
	.upd_dest =		ip_vs_mh_dest_changed,
	.schedule =		ip_vs_mh_schedule,
};

static int __init ip_vs_mh_init(void)
{
	return register_ip_vs_scheduler(&ip_vs_mh_scheduler);
}

static void __exit ip_vs_mh_cleanup(void)
{
	unregister_ip_vs_scheduler(&ip_vs_mh_scheduler);
	rcu_barrier();
}

module_init(ip_vs_mh_init);
module_exit(ip_vs_mh_cleanup);
MODULE_DESCRIPTION("Maglev hashing ipvs scheduler");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Inju Song <inju.song@navercorp.com>");