/*
 * IPVS:        Weighted Round-Robin Scheduling module
 *
 * Version:     $Id: ip_vs_wrr.c,v 1.12 2002/09/15 08:14:08 wensong Exp $
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.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:
 *     Wensong Zhang            :     changed the ip_vs_wrr_schedule to return dest
 *     Wensong Zhang            :     changed some comestics things for debugging
 *     Wensong Zhang            :     changed for the d-linked destination list
 *     Wensong Zhang            :     added the ip_vs_wrr_update_svc
 *     Julian Anastasov         :     fixed the bug of returning destination
 *                                    with weight 0 when all weights are zero
 *
 */

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

#include <net/ip_vs.h>

/*
 * current destination pointer for weighted round-robin scheduling
 */
struct ip_vs_wrr_mark {
        struct list_head *cl;   /* current list head */
        int cw;                 /* current weight */
        int mw;                 /* maximum weight */
        int di;                 /* decreasing interval */
};


/*
 *    Get the gcd of server weights
 */
static int gcd(int a, int b)
{
        int c;

        while ((c = a % b)) {
                a = b;
                b = c;
        }
        return b;
}

static int ip_vs_wrr_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->weight);
                if (weight > 0) {
                        if (g > 0)
                                g = gcd(weight, g);
                        else
                                g = weight;
                }
        }
        return g ? g : 1;
}


/*
 *    Get the maximum weight of the service destinations.
 */
static int ip_vs_wrr_max_weight(struct ip_vs_service *svc)
{
        struct ip_vs_dest *dest;
        int weight = 0;

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

        return weight;
}


static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
{
        struct ip_vs_wrr_mark *mark;

        /*
         *    Allocate the mark variable for WRR scheduling
         */
        mark = kmalloc(sizeof(struct ip_vs_wrr_mark), GFP_ATOMIC);
        if (mark == NULL) {
                IP_VS_ERR("ip_vs_wrr_init_svc(): no memory\n");
                return -ENOMEM;
        }
        mark->cl = &svc->destinations;
        mark->cw = 0;
        mark->mw = ip_vs_wrr_max_weight(svc);
        mark->di = ip_vs_wrr_gcd_weight(svc);
        svc->sched_data = mark;

        return 0;
}


static int ip_vs_wrr_done_svc(struct ip_vs_service *svc)
{
        /*
         *    Release the mark variable
         */
        kfree(svc->sched_data);

        return 0;
}


static int ip_vs_wrr_update_svc(struct ip_vs_service *svc)
{
        struct ip_vs_wrr_mark *mark = svc->sched_data;

        mark->cl = &svc->destinations;
        mark->mw = ip_vs_wrr_max_weight(svc);
        mark->di = ip_vs_wrr_gcd_weight(svc);
        if (mark->cw > mark->mw)
                mark->cw = 0;
        return 0;
}


/*
 *    Weighted Round-Robin Scheduling
 */
static struct ip_vs_dest *
ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb)
{
        struct ip_vs_dest *dest;
        struct ip_vs_wrr_mark *mark = svc->sched_data;
        struct list_head *p;

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

        /*
         * This loop will always terminate, because mark->cw in (0, max_weight]
         * and at least one server has its weight equal to max_weight.
         */
        write_lock(&svc->sched_lock);
        p = mark->cl;
        while (1) {
                if (mark->cl == &svc->destinations) {
                        /* it is at the head of the destination list */

                        if (mark->cl == mark->cl->next) {
                                /* no dest entry */
                                dest = NULL;
                                goto out;
                        }

                        mark->cl = svc->destinations.next;
                        mark->cw -= mark->di;
                        if (mark->cw <= 0) {
                                mark->cw = mark->mw;
                                /*
                                 * Still zero, which means no available servers.
                                 */
                                if (mark->cw == 0) {
                                        mark->cl = &svc->destinations;
                                        IP_VS_ERR_RL("ip_vs_wrr_schedule(): "
                                                   "no available servers\n");
                                        dest = NULL;
                                        goto out;
                                }
                        }
                } else
                        mark->cl = mark->cl->next;

                if (mark->cl != &svc->destinations) {
                        /* not at the head of the list */
                        dest = list_entry(mark->cl, struct ip_vs_dest, n_list);
                        if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
                            atomic_read(&dest->weight) >= mark->cw) {
                                /* got it */
                                break;
                        }
                }

                if (mark->cl == p && mark->cw == mark->di) {
                        /* back to the start, and no dest is found.
                           It is only possible when all dests are OVERLOADED */
                        dest = NULL;
                        goto out;
                }
        }

        IP_VS_DBG(6, "WRR: server %u.%u.%u.%u:%u "
                  "activeconns %d refcnt %d weight %d\n",
                  NIPQUAD(dest->addr), ntohs(dest->port),
                  atomic_read(&dest->activeconns),
                  atomic_read(&dest->refcnt),
                  atomic_read(&dest->weight));

  out:
        write_unlock(&svc->sched_lock);
        return dest;
}


static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
        .name =                 "wrr",
        .refcnt =               ATOMIC_INIT(0),
        .module =               THIS_MODULE,
        .init_service =         ip_vs_wrr_init_svc,
        .done_service =         ip_vs_wrr_done_svc,
        .update_service =       ip_vs_wrr_update_svc,
        .schedule =             ip_vs_wrr_schedule,
};

static int __init ip_vs_wrr_init(void)
{
        INIT_LIST_HEAD(&ip_vs_wrr_scheduler.n_list);
        return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ;
}

static void __exit ip_vs_wrr_cleanup(void)
{
        unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler);
}

module_init(ip_vs_wrr_init);
module_exit(ip_vs_wrr_cleanup);
MODULE_LICENSE("GPL");