// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * IPVS:        Least-Connection Scheduling module
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *
 * Changes:
 *     Wensong Zhang            :     added the ip_vs_lc_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>

/*
 *      Least Connection scheduling
 */
static struct ip_vs_dest *
ip_vs_lc_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
                  struct ip_vs_iphdr *iph)
{
        struct ip_vs_dest *dest, *least = NULL;
        unsigned int loh = 0, doh;

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

        /*
         * Simply select the server with the least number of
         *        (activeconns<<5) + inactconns
         * Except whose weight is equal to zero.
         * If the weight is equal to zero, it means that the server is
         * quiesced, the existing connections to the server still get
         * served, but no new connection is assigned to the server.
         */

        list_for_each_entry_rcu(dest, &svc->destinations, n_list) {
                if ((dest->flags & IP_VS_DEST_F_OVERLOAD) ||
                    atomic_read(&dest->weight) == 0)
                        continue;
                doh = ip_vs_dest_conn_overhead(dest);
                if (!least || doh < loh) {
                        least = dest;
                        loh = doh;
                }
        }

        if (!least)
                ip_vs_scheduler_err(svc, "no destination available");
        else
                IP_VS_DBG_BUF(6, "LC: server %s:%u activeconns %d "
                              "inactconns %d\n",
                              IP_VS_DBG_ADDR(least->af, &least->addr),
                              ntohs(least->port),
                              atomic_read(&least->activeconns),
                              atomic_read(&least->inactconns));

        return least;
}


static struct ip_vs_scheduler ip_vs_lc_scheduler = {
        .name =                 "lc",
        .refcnt =               ATOMIC_INIT(0),
        .module =               THIS_MODULE,
        .n_list =               LIST_HEAD_INIT(ip_vs_lc_scheduler.n_list),
        .schedule =             ip_vs_lc_schedule,
};


static int __init ip_vs_lc_init(void)
{
        return register_ip_vs_scheduler(&ip_vs_lc_scheduler) ;
}

static void __exit ip_vs_lc_cleanup(void)
{
        unregister_ip_vs_scheduler(&ip_vs_lc_scheduler);
        synchronize_rcu();
}

module_init(ip_vs_lc_init);
module_exit(ip_vs_lc_cleanup);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ipvs least connection scheduler");