/*
 * IPVS:        Locality-Based Least-Connection scheduling module
 *
 * Version:     $Id: ip_vs_lblc.c,v 1.9 2002/03/25 12:44:35 wensong Exp $
 *
 * 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 uninitilized 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.
 */

#include <linux/module.h>
#include <linux/kernel.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)

/*
 *    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
static int sysctl_ip_vs_lblc_expiration = 24*60*60*HZ;


/*
 *     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 list_head        list;
        __u32                   addr;           /* destination IP address */
        struct ip_vs_dest       *dest;          /* real server (cache) */
        unsigned long           lastuse;        /* last used time */
};


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


/*
 *      IPVS LBLC sysctl table
 */
struct ip_vs_lblc_sysctl_table {
        struct ctl_table_header *sysctl_header;
        ctl_table vs_vars[2];
        ctl_table vs_dir[2];
        ctl_table ipv4_dir[2];
        ctl_table root_dir[2];
};


static struct ip_vs_lblc_sysctl_table lblc_sysctl_table = {
        NULL,
        {{NET_IPV4_VS_LBLC_EXPIRE, "lblc_expiration",
          &sysctl_ip_vs_lblc_expiration,
          sizeof(int), 0644, NULL, &proc_dointvec_jiffies},
         {0}},
        {{NET_IPV4_VS, "vs", NULL, 0, 0555, lblc_sysctl_table.vs_vars},
         {0}},
        {{NET_IPV4, "ipv4", NULL, 0, 0555, lblc_sysctl_table.vs_dir},
         {0}},
        {{CTL_NET, "net", NULL, 0, 0555, lblc_sysctl_table.ipv4_dir},
         {0}}
};


/*
 *      new/free a ip_vs_lblc_entry, which is a mapping of a destionation
 *      IP address to a server.
 */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_new(__u32 daddr, struct ip_vs_dest *dest)
{
        struct ip_vs_lblc_entry *en;

        en = kmalloc(sizeof(struct ip_vs_lblc_entry), GFP_ATOMIC);
        if (en == NULL) {
                IP_VS_ERR("ip_vs_lblc_new(): no memory\n");
                return NULL;
        }

        INIT_LIST_HEAD(&en->list);
        en->addr = daddr;

        atomic_inc(&dest->refcnt);
        en->dest = dest;

        return en;
}


static inline void ip_vs_lblc_free(struct ip_vs_lblc_entry *en)
{
        list_del(&en->list);
        /*
         * We don't kfree dest because it is refered either by its service
         * or the trash dest list.
         */
        atomic_dec(&en->dest->refcnt);
        kfree(en);
}


/*
 *      Returns hash value for IPVS LBLC entry
 */
static inline unsigned ip_vs_lblc_hashkey(__u32 addr)
{
        return (ntohl(addr)*2654435761UL) & IP_VS_LBLC_TAB_MASK;
}


/*
 *      Hash an entry in the ip_vs_lblc_table.
 *      returns bool success.
 */
static int
ip_vs_lblc_hash(struct ip_vs_lblc_table *tbl, struct ip_vs_lblc_entry *en)
{
        unsigned hash;

        if (!list_empty(&en->list)) {
                IP_VS_ERR("ip_vs_lblc_hash(): request for already hashed, "
                          "called from %p\n", __builtin_return_address(0));
                return 0;
        }

        /*
         *      Hash by destination IP address
         */
        hash = ip_vs_lblc_hashkey(en->addr);

        write_lock(&tbl->lock);
        list_add(&en->list, &tbl->bucket[hash]);
        atomic_inc(&tbl->entries);
        write_unlock(&tbl->lock);

        return 1;
}


#if 0000
/*
 *      Unhash ip_vs_lblc_entry from ip_vs_lblc_table.
 *      returns bool success.
 */
static int ip_vs_lblc_unhash(struct ip_vs_lblc_table *tbl,
                             struct ip_vs_lblc_entry *en)
{
        if (list_empty(&en->list)) {
                IP_VS_ERR("ip_vs_lblc_unhash(): request for not hashed entry, "
                          "called from %p\n", __builtin_return_address(0));
                return 0;
        }

        /*
         * Remove it from the table
         */
        write_lock(&tbl->lock);
        list_del(&en->list);
        INIT_LIST_HEAD(&en->list);
        write_unlock(&tbl->lock);

        return 1;
}
#endif


/*
 *  Get ip_vs_lblc_entry associated with supplied parameters.
 */
static inline struct ip_vs_lblc_entry *
ip_vs_lblc_get(struct ip_vs_lblc_table *tbl, __u32 addr)
{
        unsigned hash;
        struct ip_vs_lblc_entry *en;
        struct list_head *l,*e;

        hash = ip_vs_lblc_hashkey(addr);
        l = &tbl->bucket[hash];

        read_lock(&tbl->lock);

        for (e=l->next; e!=l; e=e->next) {
                en = list_entry(e, struct ip_vs_lblc_entry, list);
                if (en->addr == addr) {
                        /* HIT */
                        read_unlock(&tbl->lock);
                        return en;
                }
        }

        read_unlock(&tbl->lock);

        return NULL;
}


/*
 *      Flush all the entries of the specified table.
 */
static void ip_vs_lblc_flush(struct ip_vs_lblc_table *tbl)
{
        int i;
        struct list_head *l;
        struct ip_vs_lblc_entry *en;

        for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
                write_lock(&tbl->lock);
                for (l=&tbl->bucket[i]; l->next!=l; ) {
                        en = list_entry(l->next,
                                        struct ip_vs_lblc_entry, list);
                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
                write_unlock(&tbl->lock);
        }
}


static inline void ip_vs_lblc_full_check(struct ip_vs_lblc_table *tbl)
{
        unsigned long now = jiffies;
        int i, j;
        struct list_head *l, *e;
        struct ip_vs_lblc_entry *en;

        for (i=0, j=tbl->rover; i<IP_VS_LBLC_TAB_SIZE; i++) {
                j = (j + 1) & IP_VS_LBLC_TAB_MASK;
                e = l = &tbl->bucket[j];
                write_lock(&tbl->lock);
                while (e->next != l) {
                        en = list_entry(e->next,
                                        struct ip_vs_lblc_entry, list);
                        if ((now - en->lastuse) <
                            sysctl_ip_vs_lblc_expiration) {
                                e = e->next;
                                continue;
                        }
                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
                write_unlock(&tbl->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_lblc_table *tbl;
        unsigned long now = jiffies;
        int goal;
        int i, j;
        struct list_head *l, *e;
        struct ip_vs_lblc_entry *en;

        tbl = (struct ip_vs_lblc_table *)data;

        if ((tbl->counter % COUNT_FOR_FULL_EXPIRATION) == 0) {
                /* do full expiration check */
                ip_vs_lblc_full_check(tbl);
                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;
                e = l = &tbl->bucket[j];
                write_lock(&tbl->lock);
                while (e->next != l) {
                        en = list_entry(e->next,
                                        struct ip_vs_lblc_entry, list);
                        if ((now - en->lastuse) < ENTRY_TIMEOUT) {
                                e = e->next;
                                continue;
                        }
                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                        goal--;
                }
                write_unlock(&tbl->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(struct ip_vs_lblc_table), GFP_ATOMIC);
        if (tbl == NULL) {
                IP_VS_ERR("ip_vs_lblc_init_svc(): no memory\n");
                return -ENOMEM;
        }
        svc->sched_data = tbl;
        IP_VS_DBG(6, "LBLC hash table (memory=%dbytes) allocated for "
                  "current service\n",
                  sizeof(struct ip_vs_lblc_table));

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

        /*
         *    Hook periodic timer for garbage collection
         */
        init_timer(&tbl->periodic_timer);
        tbl->periodic_timer.data = (unsigned long)tbl;
        tbl->periodic_timer.function = ip_vs_lblc_check_expire;
        tbl->periodic_timer.expires = jiffies+CHECK_EXPIRE_INTERVAL;
        add_timer(&tbl->periodic_timer);

        return 0;
}


static int 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(tbl);

        /* release the table itself */
        kfree(svc->sched_data);
        IP_VS_DBG(6, "LBLC hash table (memory=%dbytes) released\n",
                  sizeof(struct ip_vs_lblc_table));

        return 0;
}


static int ip_vs_lblc_update_svc(struct ip_vs_service *svc)
{
        return 0;
}


static inline struct ip_vs_dest *
__ip_vs_wlc_schedule(struct ip_vs_service *svc, struct iphdr *iph)
{
        register struct list_head *l, *e;
        struct ip_vs_dest *dest, *least;
        int loh, doh;

        /*
         * We think the overhead of processing active connections is fifty
         * times higher than that of inactive connections in average. (This
         * fifty times might not be accurate, we will change it later.) We
         * use the following formula to estimate the overhead:
         *                dest->activeconns*50 + dest->inactconns
         * and 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.
         */

        l = &svc->destinations;
        for (e=l->next; e!=l; e=e->next) {
                least = list_entry(e, struct ip_vs_dest, n_list);
                if (atomic_read(&least->weight) > 0) {
                        loh = atomic_read(&least->activeconns) * 50
                                + atomic_read(&least->inactconns);
                        goto nextstage;
                }
        }
        return NULL;

        /*
         *    Find the destination with the least load.
         */
  nextstage:
        for (e=e->next; e!=l; e=e->next) {
                dest = list_entry(e, struct ip_vs_dest, n_list);
                doh = atomic_read(&dest->activeconns) * 50
                        + atomic_read(&dest->inactconns);
                if (loh * atomic_read(&dest->weight) >
                    doh * atomic_read(&least->weight)) {
                        least = dest;
                        loh = doh;
                }
        }

        IP_VS_DBG(6, "LBLC: server %d.%d.%d.%d:%d "
                  "activeconns %d refcnt %d weight %d overhead %d\n",
                  NIPQUAD(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)) {
                register struct list_head *l, *e;
                struct ip_vs_dest *d;

                l = &svc->destinations;
                for (e=l->next; e!=l; e=e->next) {
                        d = list_entry(e, struct ip_vs_dest, 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, struct iphdr *iph)
{
        struct ip_vs_dest *dest;
        struct ip_vs_lblc_table *tbl;
        struct ip_vs_lblc_entry *en;

        IP_VS_DBG(6, "ip_vs_lblc_schedule(): Scheduling...\n");

        tbl = (struct ip_vs_lblc_table *)svc->sched_data;
        en = ip_vs_lblc_get(tbl, iph->daddr);
        if (en == NULL) {
                dest = __ip_vs_wlc_schedule(svc, iph);
                if (dest == NULL) {
                        IP_VS_DBG(1, "no destination available\n");
                        return NULL;
                }
                en = ip_vs_lblc_new(iph->daddr, dest);
                if (en == NULL) {
                        return NULL;
                }
                ip_vs_lblc_hash(tbl, en);
        } else {
                dest = en->dest;
                if (!(dest->flags & IP_VS_DEST_F_AVAILABLE)
                    || atomic_read(&dest->weight) <= 0
                    || is_overloaded(dest, svc)) {
                        dest = __ip_vs_wlc_schedule(svc, iph);
                        if (dest == NULL) {
                                IP_VS_DBG(1, "no destination available\n");
                                return NULL;
                        }
                        atomic_dec(&en->dest->refcnt);
                        atomic_inc(&dest->refcnt);
                        en->dest = dest;
                }
        }
        en->lastuse = jiffies;

        IP_VS_DBG(6, "LBLC: destination IP address %u.%u.%u.%u "
                  "--> server %u.%u.%u.%u:%d\n",
                  NIPQUAD(en->addr),
                  NIPQUAD(dest->addr),
                  ntohs(dest->port));

        return dest;
}


/*
 *      IPVS LBLC Scheduler structure
 */
static struct ip_vs_scheduler ip_vs_lblc_scheduler =
{
        {0},                    /* n_list */
        "lblc",                 /* name */
        ATOMIC_INIT(0),         /* refcnt */
        THIS_MODULE,            /* this module */
        ip_vs_lblc_init_svc,    /* service initializer */
        ip_vs_lblc_done_svc,    /* service done */
        ip_vs_lblc_update_svc,  /* service updater */
        ip_vs_lblc_schedule,    /* select a server from the destination list */
};


static int __init ip_vs_lblc_init(void)
{
        INIT_LIST_HEAD(&ip_vs_lblc_scheduler.n_list);
        lblc_sysctl_table.sysctl_header =
                register_sysctl_table(lblc_sysctl_table.root_dir, 0);
        return register_ip_vs_scheduler(&ip_vs_lblc_scheduler);
}


static void __exit ip_vs_lblc_cleanup(void)
{
        unregister_sysctl_table(lblc_sysctl_table.sysctl_header);
        unregister_ip_vs_scheduler(&ip_vs_lblc_scheduler);
}


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