// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * IPVS:        Round-Robin Scheduling module
 *
 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
 *              Peter Kese <peter.kese@ijs.si>
 *
 * Fixes/Changes:
 *     Wensong Zhang            :     changed the ip_vs_rr_schedule to return dest
 *     Julian Anastasov         :     fixed the NULL pointer access bug in debugging
 *     Wensong Zhang            :     changed some comestics things for debugging
 *     Wensong Zhang            :     changed for the d-linked destination list
 *     Wensong Zhang            :     added the ip_vs_rr_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>


static int ip_vs_rr_init_svc(struct ip_vs_service *svc)
{
        svc->sched_data = &svc->destinations;
        return 0;
}


static int ip_vs_rr_del_dest(struct ip_vs_service *svc, struct ip_vs_dest *dest)
{
        struct list_head *p;

        spin_lock_bh(&svc->sched_lock);
        p = (struct list_head *) svc->sched_data;
        /* dest is already unlinked, so p->prev is not valid but
         * p->next is valid, use it to reach previous entry.
         */
        if (p == &dest->n_list)
                svc->sched_data = p->next->prev;
        spin_unlock_bh(&svc->sched_lock);
        return 0;
}


/*
 * Round-Robin Scheduling
 */
static struct ip_vs_dest *
ip_vs_rr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
                  struct ip_vs_iphdr *iph)
{
        struct list_head *p;
        struct ip_vs_dest *dest, *last;
        int pass = 0;

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

        spin_lock_bh(&svc->sched_lock);
        p = (struct list_head *) svc->sched_data;
        last = dest = list_entry(p, struct ip_vs_dest, n_list);

        do {
                list_for_each_entry_continue_rcu(dest,
                                                 &svc->destinations,
                                                 n_list) {
                        if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
                            atomic_read(&dest->weight) > 0)
                                /* HIT */
                                goto out;
                        if (dest == last)
                                goto stop;
                }
                pass++;
                /* Previous dest could be unlinked, do not loop forever.
                 * If we stay at head there is no need for 2nd pass.
                 */
        } while (pass < 2 && p != &svc->destinations);

stop:
        spin_unlock_bh(&svc->sched_lock);
        ip_vs_scheduler_err(svc, "no destination available");
        return NULL;

  out:
        svc->sched_data = &dest->n_list;
        spin_unlock_bh(&svc->sched_lock);
        IP_VS_DBG_BUF(6, "RR: server %s:%u "
                      "activeconns %d refcnt %d weight %d\n",
                      IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
                      atomic_read(&dest->activeconns),
                      refcount_read(&dest->refcnt), atomic_read(&dest->weight));

        return dest;
}


static struct ip_vs_scheduler ip_vs_rr_scheduler = {
        .name =                 "rr",                   /* name */
        .refcnt =               ATOMIC_INIT(0),
        .module =               THIS_MODULE,
        .n_list =               LIST_HEAD_INIT(ip_vs_rr_scheduler.n_list),
        .init_service =         ip_vs_rr_init_svc,
        .add_dest =             NULL,
        .del_dest =             ip_vs_rr_del_dest,
        .schedule =             ip_vs_rr_schedule,
};

static int __init ip_vs_rr_init(void)
{
        return register_ip_vs_scheduler(&ip_vs_rr_scheduler);
}

static void __exit ip_vs_rr_cleanup(void)
{
        unregister_ip_vs_scheduler(&ip_vs_rr_scheduler);
        synchronize_rcu();
}

module_init(ip_vs_rr_init);
module_exit(ip_vs_rr_cleanup);
MODULE_DESCRIPTION("ipvs round-robin scheduler");
MODULE_LICENSE("GPL");