/*
 * IPVS:        Locality-Based Least-Connection scheduling module
 *
 * Authors:     Wensong Zhang <wensong@gnuchina.org>
 *
 *              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.
 *
 * Changes:
 *     Martin Hamilton         :    fixed the terrible locking bugs
 *                                   *lock(tbl->lock) ==> *lock(&tbl->lock)
 *     Wensong Zhang           :    fixed the uninitialized tbl->lock bug
 *     Wensong Zhang           :    added doing full expiration check to
 *                                   collect stale entries of 24+ hours when
 *                                   no partial expire check in a half hour
 *     Julian Anastasov        :    replaced del_timer call with del_timer_sync
 *                                   to avoid the possible race between timer
 *                                   handler and del_timer thread in SMP
 *
 */

/*
 * The lblc algorithm is as follows (pseudo code):
 *
 *       if cachenode[dest_ip] is null then
 *               n, cachenode[dest_ip] <- {weighted least-conn node};
 *       else
 *               n <- cachenode[dest_ip];
 *               if (n is dead) OR
 *                  (n.conns>n.weight AND
 *                   there is a node m with m.conns<m.weight/2) then
 *                 n, cachenode[dest_ip] <- {weighted least-conn node};
 *
 *       return n;
 *
 * Thanks must go to Wenzhuo Zhang for talking WCCP to me and pushing
 * me to write this module.
 */

#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 <linux/jiffies.h>

/* for sysctl */
#include <linux/fs.h>
#include <linux/sysctl.h>

#include <net/ip_vs.h>


/*
 *    It is for garbage collection of stale IPVS lblc entries,
 *    when the table is full.
 */
#define CHECK_EXPIRE_INTERVAL   (60*HZ)
#define ENTRY_TIMEOUT           (6*60*HZ)

#define DEFAULT_EXPIRATION      (24*60*60*HZ)

/*
 *    It is for full expiration check.
 *    When there is no partial expiration check (garbage collection)
 *    in a half hour, do a full expiration check to collect stale
 *    entries that haven't been touched for a day.
 */
#define COUNT_FOR_FULL_EXPIRATION   30


/*
 *     for IPVS lblc entry hash table
 */
#ifndef CONFIG_IP_VS_LBLC_TAB_BITS
#define CONFIG_IP_VS_LBLC_TAB_BITS      10
#endif
#define IP_VS_LBLC_TAB_BITS     CONFIG_IP_VS_LBLC_TAB_BITS
#define IP_VS_LBLC_TAB_SIZE     (1 << IP_VS_LBLC_TAB_BITS)
#define IP_VS_LBLC_TAB_MASK     (IP_VS_LBLC_TAB_SIZE - 1)


/*
 *      IPVS lblc entry represents an association between destination
 *      IP address and its destination server
 */
struct ip_vs_lblc_entry {
        struct hlist_node       list;
        int                     af;             /* address family */
        union nf_inet_addr      addr;           /* destination IP address */
        struct ip_vs_dest __rcu *dest;          /* real server (cache) */
        unsigned long           lastuse;        /* last used time */
        struct rcu_head         rcu_head;
};


/*
 *      IPVS lblc hash table
 */
struct ip_vs_lblc_table {
        struct rcu_head         rcu_head;
        struct hlist_head       bucket[IP_VS_LBLC_TAB_SIZE];  /* hash bucket */
        struct timer_list       periodic_timer; /* collect stale entries */
        atomic_t                entries;        /* number of entries */
        int                     max_size;       /* maximum size of entries */
        int                     rover;          /* rover for expire check */
        int                     counter;        /* counter for no expire */
        bool                    dead;
};


/*
 *      IPVS LBLC sysctl table
 */
#ifdef CONFIG_SYSCTL
static ctl_table vs_vars_table[] = {
        {
                .procname       = "lblc_expiration",
                .data           = NULL,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};
#endif

static inline void ip_vs_lblc_free(struct ip_vs_lblc_entry *en)
{
        struct ip_vs_dest *dest;

        hlist_del_rcu(&en->list);
        /*
         * We don't kfree dest because it is referred either by its service
         * or the trash dest list.
         */
        dest = rcu_dereference_protected(en->dest, 1);
        ip_vs_dest_put(dest);
        kfree_rcu(en, rcu_head);
}


/*
 *      Returns hash value for IPVS LBLC entry
 */
static inline unsigned int
ip_vs_lblc_hashkey(int af, const union nf_inet_addr *addr)
{
        __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
        return (ntohl(addr_fold)*2654435761UL) & IP_VS_LBLC_TAB_MASK;
}


/*
 *      Hash an entry in the ip_vs_lblc_table.
 *      returns bool success.
 */
static void
ip_vs_lblc_hash(struct ip_vs_lblc_table *tbl, struct ip_vs_lblc_entry *en)
{
        unsigned int hash = ip_vs_lblc_hashkey(en->af, &en->addr);

        hlist_add_head_rcu(&en->list, &tbl->bucket[hash]);
        atomic_inc(&tbl->entries);
}


/* Get ip_vs_lblc_entry associated with supplied parameters. */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_get(int af, struct ip_vs_lblc_table *tbl,
               const union nf_inet_addr *addr)
{
        unsigned int hash = ip_vs_lblc_hashkey(af, addr);
        struct ip_vs_lblc_entry *en;

        hlist_for_each_entry_rcu(en, &tbl->bucket[hash], list)
                if (ip_vs_addr_equal(af, &en->addr, addr))
                        return en;

        return NULL;
}


/*
 * Create or update an ip_vs_lblc_entry, which is a mapping of a destination IP
 * address to a server. Called under spin lock.
 */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_new(struct ip_vs_lblc_table *tbl, const union nf_inet_addr *daddr,
               struct ip_vs_dest *dest)
{
        struct ip_vs_lblc_entry *en;

        en = ip_vs_lblc_get(dest->af, tbl, daddr);
        if (!en) {
                en = kmalloc(sizeof(*en), GFP_ATOMIC);
                if (!en)
                        return NULL;

                en->af = dest->af;
                ip_vs_addr_copy(dest->af, &en->addr, daddr);
                en->lastuse = jiffies;

                ip_vs_dest_hold(dest);
                RCU_INIT_POINTER(en->dest, dest);

                ip_vs_lblc_hash(tbl, en);
        } else {
                struct ip_vs_dest *old_dest;

                old_dest = rcu_dereference_protected(en->dest, 1);
                if (old_dest != dest) {
                        ip_vs_dest_put(old_dest);
                        ip_vs_dest_hold(dest);
                        /* No ordering constraints for refcnt */
                        RCU_INIT_POINTER(en->dest, dest);
                }
        }

        return en;
}


/*
 *      Flush all the entries of the specified table.
 */
static void ip_vs_lblc_flush(struct ip_vs_service *svc)
{
        struct ip_vs_lblc_table *tbl = svc->sched_data;
        struct ip_vs_lblc_entry *en;
        struct hlist_node *next;
        int i;

        spin_lock_bh(&svc->sched_lock);
        tbl->dead = 1;
        for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
                hlist_for_each_entry_safe(en, next, &tbl->bucket[i], list) {
                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
        }
        spin_unlock_bh(&svc->sched_lock);
}

static int sysctl_lblc_expiration(struct ip_vs_service *svc)
{
#ifdef CONFIG_SYSCTL
        struct netns_ipvs *ipvs = net_ipvs(svc->net);
        return ipvs->sysctl_lblc_expiration;
#else
        return DEFAULT_EXPIRATION;
#endif
}

static inline void ip_vs_lblc_full_check(struct ip_vs_service *svc)
{
        struct ip_vs_lblc_table *tbl = svc->sched_data;
        struct ip_vs_lblc_entry *en;
        struct hlist_node *next;
        unsigned long now = jiffies;
        int i, j;

        for (i=0, j=tbl->rover; i<IP_VS_LBLC_TAB_SIZE; i++) {
                j = (j + 1) & IP_VS_LBLC_TAB_MASK;

                spin_lock(&svc->sched_lock);
                hlist_for_each_entry_safe(en, next, &tbl->bucket[j], list) {
                        if (time_before(now,
                                        en->lastuse +
                                        sysctl_lblc_expiration(svc)))
                                continue;

                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
                spin_unlock(&svc->sched_lock);
        }
        tbl->rover = j;
}


/*
 *      Periodical timer handler for IPVS lblc table
 *      It is used to collect stale entries when the number of entries
 *      exceeds the maximum size of the table.
 *
 *      Fixme: we probably need more complicated algorithm to collect
 *             entries that have not been used for a long time even
 *             if the number of entries doesn't exceed the maximum size
 *             of the table.
 *      The full expiration check is for this purpose now.
 */
static void ip_vs_lblc_check_expire(unsigned long data)
{
        struct ip_vs_service *svc = (struct ip_vs_service *) data;
        struct ip_vs_lblc_table *tbl = svc->sched_data;
        unsigned long now = jiffies;
        int goal;
        int i, j;
        struct ip_vs_lblc_entry *en;
        struct hlist_node *next;

        if ((tbl->counter % COUNT_FOR_FULL_EXPIRATION) == 0) {
                /* do full expiration check */
                ip_vs_lblc_full_check(svc);
                tbl->counter = 1;
                goto out;
        }

        if (atomic_read(&tbl->entries) <= tbl->max_size) {
                tbl->counter++;
                goto out;
        }

        goal = (atomic_read(&tbl->entries) - tbl->max_size)*4/3;
        if (goal > tbl->max_size/2)
                goal = tbl->max_size/2;

        for (i=0, j=tbl->rover; i<IP_VS_LBLC_TAB_SIZE; i++) {
                j = (j + 1) & IP_VS_LBLC_TAB_MASK;

                spin_lock(&svc->sched_lock);
                hlist_for_each_entry_safe(en, next, &tbl->bucket[j], list) {
                        if (time_before(now, en->lastuse + ENTRY_TIMEOUT))
                                continue;

                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                        goal--;
                }
                spin_unlock(&svc->sched_lock);
                if (goal <= 0)
                        break;
        }
        tbl->rover = j;

  out:
        mod_timer(&tbl->periodic_timer, jiffies+CHECK_EXPIRE_INTERVAL);
}


static int ip_vs_lblc_init_svc(struct ip_vs_service *svc)
{
        int i;
        struct ip_vs_lblc_table *tbl;

        /*
         *    Allocate the ip_vs_lblc_table for this service
         */
        tbl = kmalloc(sizeof(*tbl), GFP_KERNEL);
        if (tbl == NULL)
                return -ENOMEM;

        svc->sched_data = tbl;
        IP_VS_DBG(6, "LBLC hash table (memory=%Zdbytes) allocated for "
                  "current service\n", sizeof(*tbl));

        /*
         *    Initialize the hash buckets
         */
        for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
                INIT_HLIST_HEAD(&tbl->bucket[i]);
        }
        tbl->max_size = IP_VS_LBLC_TAB_SIZE*16;
        tbl->rover = 0;
        tbl->counter = 1;
        tbl->dead = 0;

        /*
         *    Hook periodic timer for garbage collection
         */
        setup_timer(&tbl->periodic_timer, ip_vs_lblc_check_expire,
                        (unsigned long)svc);
        mod_timer(&tbl->periodic_timer, jiffies + CHECK_EXPIRE_INTERVAL);

        return 0;
}


static void ip_vs_lblc_done_svc(struct ip_vs_service *svc)
{
        struct ip_vs_lblc_table *tbl = svc->sched_data;

        /* remove periodic timer */
        del_timer_sync(&tbl->periodic_timer);

        /* got to clean up table entries here */
        ip_vs_lblc_flush(svc);

        /* release the table itself */
        kfree_rcu(tbl, rcu_head);
        IP_VS_DBG(6, "LBLC hash table (memory=%Zdbytes) released\n",
                  sizeof(*tbl));
}


static inline struct ip_vs_dest *
__ip_vs_lblc_schedule(struct ip_vs_service *svc)
{
        struct ip_vs_dest *dest, *least;
        int loh, doh;

        /*
         * We use the following formula to estimate the load:
         *                (dest overhead) / dest->weight
         *
         * Remember -- no floats in kernel mode!!!
         * The comparison of h1*w2 > h2*w1 is equivalent to that of
         *                h1/w1 > h2/w2
         * if every weight is larger than zero.
         *
         * The server with weight=0 is quiesced and will not receive any
         * new connection.
         */
        list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
                if (dest->flags & IP_VS_DEST_F_OVERLOAD)
                        continue;
                if (atomic_read(&dest->weight) > 0) {
                        least = dest;
                        loh = ip_vs_dest_conn_overhead(least);
                        goto nextstage;
                }
        }
        return NULL;

        /*
         *    Find the destination with the least load.
         */
  nextstage:
        list_for_each_entry_continue_rcu(dest, &svc->destinations, n_list) {
                if (dest->flags & IP_VS_DEST_F_OVERLOAD)
                        continue;

                doh = ip_vs_dest_conn_overhead(dest);
                if (loh * atomic_read(&dest->weight) >
                    doh * atomic_read(&least->weight)) {
                        least = dest;
                        loh = doh;
                }
        }

        IP_VS_DBG_BUF(6, "LBLC: server %s:%d "
                      "activeconns %d refcnt %d weight %d overhead %d\n",
                      IP_VS_DBG_ADDR(least->af, &least->addr),
                      ntohs(least->port),
                      atomic_read(&least->activeconns),
                      atomic_read(&least->refcnt),
                      atomic_read(&least->weight), loh);

        return least;
}


/*
 *   If this destination server is overloaded and there is a less loaded
 *   server, then return true.
 */
static inline int
is_overloaded(struct ip_vs_dest *dest, struct ip_vs_service *svc)
{
        if (atomic_read(&dest->activeconns) > atomic_read(&dest->weight)) {
                struct ip_vs_dest *d;

                list_for_each_entry_rcu(d, &svc->destinations, n_list) {
                        if (atomic_read(&d->activeconns)*2
                            < atomic_read(&d->weight)) {
                                return 1;
                        }
                }
        }
        return 0;
}


/*
 *    Locality-Based (weighted) Least-Connection scheduling
 */
static struct ip_vs_dest *
ip_vs_lblc_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
        struct ip_vs_lblc_table *tbl = svc->sched_data;
        struct ip_vs_iphdr iph;
        struct ip_vs_dest *dest = NULL;
        struct ip_vs_lblc_entry *en;

        ip_vs_fill_iph_addr_only(svc->af, skb, &iph);

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

        /* First look in our cache */
        en = ip_vs_lblc_get(svc->af, tbl, &iph.daddr);
        if (en) {
                /* We only hold a read lock, but this is atomic */
                en->lastuse = jiffies;

                /*
                 * If the destination is not available, i.e. it's in the trash,
                 * we must ignore it, as it may be removed from under our feet,
                 * if someone drops our reference count. Our caller only makes
                 * sure that destinations, that are not in the trash, are not
                 * moved to the trash, while we are scheduling. But anyone can
                 * free up entries from the trash at any time.
                 */

                dest = rcu_dereference(en->dest);
                if ((dest->flags & IP_VS_DEST_F_AVAILABLE) &&
                    atomic_read(&dest->weight) > 0 && !is_overloaded(dest, svc))
                        goto out;
        }

        /* No cache entry or it is invalid, time to schedule */
        dest = __ip_vs_lblc_schedule(svc);
        if (!dest) {
                ip_vs_scheduler_err(svc, "no destination available");
                return NULL;
        }

        /* If we fail to create a cache entry, we'll just use the valid dest */
        spin_lock_bh(&svc->sched_lock);
        if (!tbl->dead)
                ip_vs_lblc_new(tbl, &iph.daddr, dest);
        spin_unlock_bh(&svc->sched_lock);

out:
        IP_VS_DBG_BUF(6, "LBLC: destination IP address %s --> server %s:%d\n",
                      IP_VS_DBG_ADDR(svc->af, &iph.daddr),
                      IP_VS_DBG_ADDR(svc->af, &dest->addr), ntohs(dest->port));

        return dest;
}


/*
 *      IPVS LBLC Scheduler structure
 */
static struct ip_vs_scheduler ip_vs_lblc_scheduler =
{
        .name =                 "lblc",
        .refcnt =               ATOMIC_INIT(0),
        .module =               THIS_MODULE,
        .n_list =               LIST_HEAD_INIT(ip_vs_lblc_scheduler.n_list),
        .init_service =         ip_vs_lblc_init_svc,
        .done_service =         ip_vs_lblc_done_svc,
        .schedule =             ip_vs_lblc_schedule,
};

/*
 *  per netns init.
 */
#ifdef CONFIG_SYSCTL
static int __net_init __ip_vs_lblc_init(struct net *net)
{
        struct netns_ipvs *ipvs = net_ipvs(net);

        if (!ipvs)
                return -ENOENT;

        if (!net_eq(net, &init_net)) {
                ipvs->lblc_ctl_table = kmemdup(vs_vars_table,
                                                sizeof(vs_vars_table),
                                                GFP_KERNEL);
                if (ipvs->lblc_ctl_table == NULL)
                        return -ENOMEM;

                /* Don't export sysctls to unprivileged users */
                if (net->user_ns != &init_user_ns)
                        ipvs->lblc_ctl_table[0].procname = NULL;

        } else
                ipvs->lblc_ctl_table = vs_vars_table;
        ipvs->sysctl_lblc_expiration = DEFAULT_EXPIRATION;
        ipvs->lblc_ctl_table[0].data = &ipvs->sysctl_lblc_expiration;

        ipvs->lblc_ctl_header =
                register_net_sysctl(net, "net/ipv4/vs", ipvs->lblc_ctl_table);
        if (!ipvs->lblc_ctl_header) {
                if (!net_eq(net, &init_net))
                        kfree(ipvs->lblc_ctl_table);
                return -ENOMEM;
        }

        return 0;
}

static void __net_exit __ip_vs_lblc_exit(struct net *net)
{
        struct netns_ipvs *ipvs = net_ipvs(net);

        unregister_net_sysctl_table(ipvs->lblc_ctl_header);

        if (!net_eq(net, &init_net))
                kfree(ipvs->lblc_ctl_table);
}

#else

static int __net_init __ip_vs_lblc_init(struct net *net) { return 0; }
static void __net_exit __ip_vs_lblc_exit(struct net *net) { }

#endif

static struct pernet_operations ip_vs_lblc_ops = {
        .init = __ip_vs_lblc_init,
        .exit = __ip_vs_lblc_exit,
};

static int __init ip_vs_lblc_init(void)
{
        int ret;

        ret = register_pernet_subsys(&ip_vs_lblc_ops);
        if (ret)
                return ret;

        ret = register_ip_vs_scheduler(&ip_vs_lblc_scheduler);
        if (ret)
                unregister_pernet_subsys(&ip_vs_lblc_ops);
        return ret;
}

static void __exit ip_vs_lblc_cleanup(void)
{
        unregister_ip_vs_scheduler(&ip_vs_lblc_scheduler);
        unregister_pernet_subsys(&ip_vs_lblc_ops);
        synchronize_rcu();
}


module_init(ip_vs_lblc_init);
module_exit(ip_vs_lblc_cleanup);
MODULE_LICENSE("GPL");