// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * IPVS:        Weighted Least-Connection Scheduling module
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Peter Kese <peter.kese@ijs.si>
 *
 * Changes:
 *     Wensong Zhang            :     changed the ip_vs_wlc_schedule to return dest
 *     Wensong Zhang            :     changed to use the inactconns in scheduling
 *     Wensong Zhang            :     changed some comestics things for debugging
 *     Wensong Zhang            :     changed for the d-linked destination list
 *     Wensong Zhang            :     added the ip_vs_wlc_update_svc
 *     Wensong Zhang            :     added any dest with weight=0 is quiesced
 */

#define pr_fmt(fmt) "IPVS: " fmt

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

#include <net/ip_vs.h>

/*
 *      Weighted Least Connection scheduling
 */
static struct ip_vs_dest *
ip_vs_wlc_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
                   struct ip_vs_iphdr *iph)
{
        struct ip_vs_dest *dest, *least;
        int loh, doh;

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

        /*
         * We calculate the load of each dest server as follows:
         *                (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 connections.
         */

        list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
                if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
                    atomic_read(&dest->weight) > 0) {
                        least = dest;
                        loh = ip_vs_dest_conn_overhead(least);
                        goto nextstage;
                }
        }
        ip_vs_scheduler_err(svc, "no destination available");
        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 ((__s64)loh * atomic_read(&dest->weight) >
                    (__s64)doh * atomic_read(&least->weight)) {
                        least = dest;
                        loh = doh;
                }
        }

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

        return least;
}


static struct ip_vs_scheduler ip_vs_wlc_scheduler =
{
        .name =                 "wlc",
        .refcnt =               ATOMIC_INIT(0),
        .module =               THIS_MODULE,
        .n_list =               LIST_HEAD_INIT(ip_vs_wlc_scheduler.n_list),
        .schedule =             ip_vs_wlc_schedule,
};


static int __init ip_vs_wlc_init(void)
{
        return register_ip_vs_scheduler(&ip_vs_wlc_scheduler);
}

static void __exit ip_vs_wlc_cleanup(void)
{
        unregister_ip_vs_scheduler(&ip_vs_wlc_scheduler);
        synchronize_rcu();
}

module_init(ip_vs_wlc_init);
module_exit(ip_vs_wlc_cleanup);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ipvs weighted least connection scheduler");