/*
 * 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)

/*
 *    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;
        int                     af;             /* address family */
        union nf_inet_addr      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 {
        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
 */

static ctl_table vs_vars_table[] = {
        {
                .procname       = "lblc_expiration",
                .data           = &sysctl_ip_vs_lblc_expiration,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        { }
};

static struct ctl_table_header * sysctl_header;

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(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 hash = ip_vs_lblc_hashkey(en->af, &en->addr);

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


/*
 *  Get ip_vs_lblc_entry associated with supplied parameters. Called under read
 *  lock
 */
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 hash = ip_vs_lblc_hashkey(af, addr);
        struct ip_vs_lblc_entry *en;

        list_for_each_entry(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 write 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) {
                        pr_err("%s(): no memory\n", __func__);
                        return NULL;
                }

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

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

                ip_vs_lblc_hash(tbl, en);
        } else if (en->dest != dest) {
                atomic_dec(&en->dest->refcnt);
                atomic_inc(&dest->refcnt);
                en->dest = dest;
        }

        return en;
}


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

        for (i=0; i<IP_VS_LBLC_TAB_SIZE; i++) {
                list_for_each_entry_safe(en, nxt, &tbl->bucket[i], list) {
                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
        }
}


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, *nxt;
        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;

                write_lock(&svc->sched_lock);
                list_for_each_entry_safe(en, nxt, &tbl->bucket[j], list) {
                        if (time_before(now,
                                        en->lastuse + sysctl_ip_vs_lblc_expiration))
                                continue;

                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                }
                write_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, *nxt;

        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;

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

                        ip_vs_lblc_free(en);
                        atomic_dec(&tbl->entries);
                        goal--;
                }
                write_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_ATOMIC);
        if (tbl == NULL) {
                pr_err("%s(): no memory\n", __func__);
                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_LIST_HEAD(&tbl->bucket[i]);
        }
        tbl->max_size = IP_VS_LBLC_TAB_SIZE*16;
        tbl->rover = 0;
        tbl->counter = 1;

        /*
         *    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 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(tbl);
        IP_VS_DBG(6, "LBLC hash table (memory=%Zdbytes) released\n",
                  sizeof(*tbl));

        return 0;
}


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 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.
         */
        list_for_each_entry(dest, &svc->destinations, n_list) {
                if (dest->flags & IP_VS_DEST_F_OVERLOAD)
                        continue;
                if (atomic_read(&dest->weight) > 0) {
                        least = dest;
                        loh = atomic_read(&least->activeconns) * 50
                                + atomic_read(&least->inactconns);
                        goto nextstage;
                }
        }
        return NULL;

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

                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_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(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_iphdr(svc->af, skb_network_header(skb), &iph);

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

        /* First look in our cache */
        read_lock(&svc->sched_lock);
        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.
                 */

                if (en->dest->flags & IP_VS_DEST_F_AVAILABLE)
                        dest = en->dest;
        }
        read_unlock(&svc->sched_lock);

        /* If the destination has a weight and is not overloaded, use it */
        if (dest && 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_ERR_RL("LBLC: no destination available\n");
                return NULL;
        }

        /* If we fail to create a cache entry, we'll just use the valid dest */
        write_lock(&svc->sched_lock);
        ip_vs_lblc_new(tbl, &iph.daddr, dest);
        write_unlock(&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,
};


static int __init ip_vs_lblc_init(void)
{
        int ret;

        sysctl_header = register_sysctl_paths(net_vs_ctl_path, vs_vars_table);
        ret = register_ip_vs_scheduler(&ip_vs_lblc_scheduler);
        if (ret)
                unregister_sysctl_table(sysctl_header);
        return ret;
}


static void __exit ip_vs_lblc_cleanup(void)
{
        unregister_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");