// 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*256) + totalconns
	 * 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),
			      ip_vs_dest_inactconns(least));

	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");
