// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* IPVS: Weighted Round-Robin Scheduling module
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*
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* Authors: Wensong Zhang <wensong@linuxvirtualserver.org>
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*
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* Changes:
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* Wensong Zhang : changed the ip_vs_wrr_schedule to return dest
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* Wensong Zhang : changed some comestics things for debugging
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* Wensong Zhang : changed for the d-linked destination list
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* Wensong Zhang : added the ip_vs_wrr_update_svc
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* Julian Anastasov : fixed the bug of returning destination
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* with weight 0 when all weights are zero
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*/
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#define KMSG_COMPONENT "IPVS"
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#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <linux/net.h>
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#include <linux/gcd.h>
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#include <net/ip_vs.h>
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/* The WRR algorithm depends on some caclulations:
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* - mw: maximum weight
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* - di: weight step, greatest common divisor from all weights
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* - cw: current required weight
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* As result, all weights are in the [di..mw] range with a step=di.
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*
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* First, we start with cw = mw and select dests with weight >= cw.
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* Then cw is reduced with di and all dests are checked again.
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* Last pass should be with cw = di. We have mw/di passes in total:
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*
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* pass 1: cw = max weight
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* pass 2: cw = max weight - di
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* pass 3: cw = max weight - 2 * di
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* ...
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* last pass: cw = di
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*
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* Weights are supposed to be >= di but we run in parallel with
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* weight changes, it is possible some dest weight to be reduced
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* below di, bad if it is the only available dest.
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*
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* So, we modify how mw is calculated, now it is reduced with (di - 1),
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* so that last cw is 1 to catch such dests with weight below di:
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* pass 1: cw = max weight - (di - 1)
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* pass 2: cw = max weight - di - (di - 1)
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* pass 3: cw = max weight - 2 * di - (di - 1)
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* ...
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* last pass: cw = 1
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*
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*/
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/*
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* current destination pointer for weighted round-robin scheduling
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*/
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struct ip_vs_wrr_mark {
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struct ip_vs_dest *cl; /* current dest or head */
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int cw; /* current weight */
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int mw; /* maximum weight */
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int di; /* decreasing interval */
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struct rcu_head rcu_head;
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};
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static int ip_vs_wrr_gcd_weight(struct ip_vs_service *svc)
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{
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struct ip_vs_dest *dest;
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int weight;
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int g = 0;
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list_for_each_entry(dest, &svc->destinations, n_list) {
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weight = atomic_read(&dest->weight);
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if (weight > 0) {
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if (g > 0)
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g = gcd(weight, g);
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else
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g = weight;
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}
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}
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return g ? g : 1;
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}
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/*
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* Get the maximum weight of the service destinations.
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*/
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static int ip_vs_wrr_max_weight(struct ip_vs_service *svc)
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{
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struct ip_vs_dest *dest;
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int new_weight, weight = 0;
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list_for_each_entry(dest, &svc->destinations, n_list) {
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new_weight = atomic_read(&dest->weight);
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if (new_weight > weight)
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weight = new_weight;
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}
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return weight;
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}
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static int ip_vs_wrr_init_svc(struct ip_vs_service *svc)
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{
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struct ip_vs_wrr_mark *mark;
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/*
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* Allocate the mark variable for WRR scheduling
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*/
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mark = kmalloc(sizeof(struct ip_vs_wrr_mark), GFP_KERNEL);
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if (mark == NULL)
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return -ENOMEM;
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mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
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mark->di = ip_vs_wrr_gcd_weight(svc);
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mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
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mark->cw = mark->mw;
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svc->sched_data = mark;
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return 0;
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}
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static void ip_vs_wrr_done_svc(struct ip_vs_service *svc)
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{
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struct ip_vs_wrr_mark *mark = svc->sched_data;
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/*
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* Release the mark variable
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*/
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kfree_rcu(mark, rcu_head);
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}
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static int ip_vs_wrr_dest_changed(struct ip_vs_service *svc,
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struct ip_vs_dest *dest)
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{
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struct ip_vs_wrr_mark *mark = svc->sched_data;
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spin_lock_bh(&svc->sched_lock);
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mark->cl = list_entry(&svc->destinations, struct ip_vs_dest, n_list);
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mark->di = ip_vs_wrr_gcd_weight(svc);
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mark->mw = ip_vs_wrr_max_weight(svc) - (mark->di - 1);
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if (mark->cw > mark->mw || !mark->cw)
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mark->cw = mark->mw;
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else if (mark->di > 1)
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mark->cw = (mark->cw / mark->di) * mark->di + 1;
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spin_unlock_bh(&svc->sched_lock);
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return 0;
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}
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/*
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* Weighted Round-Robin Scheduling
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*/
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static struct ip_vs_dest *
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ip_vs_wrr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
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struct ip_vs_iphdr *iph)
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{
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struct ip_vs_dest *dest, *last, *stop = NULL;
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struct ip_vs_wrr_mark *mark = svc->sched_data;
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bool last_pass = false, restarted = false;
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IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
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spin_lock_bh(&svc->sched_lock);
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dest = mark->cl;
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/* No available dests? */
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if (mark->mw == 0)
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goto err_noavail;
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last = dest;
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/* Stop only after all dests were checked for weight >= 1 (last pass) */
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while (1) {
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list_for_each_entry_continue_rcu(dest,
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&svc->destinations,
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n_list) {
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if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
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atomic_read(&dest->weight) >= mark->cw)
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goto found;
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if (dest == stop)
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goto err_over;
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}
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mark->cw -= mark->di;
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if (mark->cw <= 0) {
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mark->cw = mark->mw;
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/* Stop if we tried last pass from first dest:
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* 1. last_pass: we started checks when cw > di but
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* then all dests were checked for w >= 1
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* 2. last was head: the first and only traversal
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* was for weight >= 1, for all dests.
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*/
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if (last_pass ||
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&last->n_list == &svc->destinations)
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goto err_over;
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restarted = true;
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}
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last_pass = mark->cw <= mark->di;
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if (last_pass && restarted &&
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&last->n_list != &svc->destinations) {
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/* First traversal was for w >= 1 but only
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* for dests after 'last', now do the same
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* for all dests up to 'last'.
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*/
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stop = last;
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}
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}
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found:
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IP_VS_DBG_BUF(6, "WRR: server %s:%u "
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"activeconns %d refcnt %d weight %d\n",
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IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
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atomic_read(&dest->activeconns),
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refcount_read(&dest->refcnt),
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atomic_read(&dest->weight));
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mark->cl = dest;
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out:
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spin_unlock_bh(&svc->sched_lock);
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return dest;
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err_noavail:
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mark->cl = dest;
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dest = NULL;
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ip_vs_scheduler_err(svc, "no destination available");
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goto out;
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err_over:
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mark->cl = dest;
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dest = NULL;
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ip_vs_scheduler_err(svc, "no destination available: "
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"all destinations are overloaded");
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goto out;
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}
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static struct ip_vs_scheduler ip_vs_wrr_scheduler = {
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.name = "wrr",
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.refcnt = ATOMIC_INIT(0),
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.module = THIS_MODULE,
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.n_list = LIST_HEAD_INIT(ip_vs_wrr_scheduler.n_list),
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.init_service = ip_vs_wrr_init_svc,
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.done_service = ip_vs_wrr_done_svc,
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.add_dest = ip_vs_wrr_dest_changed,
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.del_dest = ip_vs_wrr_dest_changed,
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.upd_dest = ip_vs_wrr_dest_changed,
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.schedule = ip_vs_wrr_schedule,
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};
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static int __init ip_vs_wrr_init(void)
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{
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return register_ip_vs_scheduler(&ip_vs_wrr_scheduler) ;
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}
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static void __exit ip_vs_wrr_cleanup(void)
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{
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unregister_ip_vs_scheduler(&ip_vs_wrr_scheduler);
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synchronize_rcu();
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}
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module_init(ip_vs_wrr_init);
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module_exit(ip_vs_wrr_cleanup);
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MODULE_LICENSE("GPL");
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