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/*

 * IPVS:        Destination Hashing scheduling module

 *

 * Version:     $Id: ip_vs_dh.c,v 1.1.1.1 2004-04-15 01:14:07 phoenix Exp $

 *

 * Authors:     Wensong Zhang <wensong@gnuchina.org>

 *

 *              Inspired by the consistent hashing scheduler patch from

 *              Thomas Proell <proellt@gmx.de>

 *

 *              This program is free software; you can redistribute it and/or

 *              modify it under the terms of the GNU General Public License

 *              as published by the Free Software Foundation; either version

 *              2 of the License, or (at your option) any later version.

 *

 * Changes:

 *

 */

/*

 * The dh algorithm is to select server by the hash key of destination IP

 * address. The pseudo code is as follows:

 *

 *       n <- servernode[dest_ip];

 *       if (n is dead) OR

 *          (n is overloaded, such as n.conns>2*n.weight) then

 *                 return NULL;

 *

 *       return n;

 *

 * Notes that servernode is a 256-bucket hash table that maps the hash

 * index derived from packet destination IP address to the current server

 * array. If the dh scheduler is used in cache cluster, it is good to

 * combine it with cache_bypass feature. When the statically assigned

 * server is dead or overloaded, the load balancer can bypass the cache

 * server and send requests to the original server directly.

 *

 */

#include <linux/module.h>

#include <linux/kernel.h>

#include <net/ip_vs.h>

/*

 *      IPVS DH bucket

 */

struct ip_vs_dh_bucket {

        struct ip_vs_dest       *dest;          /* real server (cache) */

};

/*

 *     for IPVS DH entry hash table

 */

#ifndef CONFIG_IP_VS_DH_TAB_BITS

#define CONFIG_IP_VS_DH_TAB_BITS        8

#endif

#define IP_VS_DH_TAB_BITS               CONFIG_IP_VS_DH_TAB_BITS

#define IP_VS_DH_TAB_SIZE               (1 << IP_VS_DH_TAB_BITS)

#define IP_VS_DH_TAB_MASK               (IP_VS_DH_TAB_SIZE - 1)

/*

 *      Returns hash value for IPVS DH entry

 */

static inline unsigned ip_vs_dh_hashkey(__u32 addr)

{

        return (ntohl(addr)*2654435761UL) & IP_VS_DH_TAB_MASK;

}

/*

 *      Get ip_vs_dest associated with supplied parameters.

 */

static inline struct ip_vs_dest *

ip_vs_dh_get(struct ip_vs_dh_bucket *tbl, __u32 addr)

{

        return (tbl[ip_vs_dh_hashkey(addr)]).dest;

}

/*

 *      Assign all the hash buckets of the specified table with the service.

 */

static int

ip_vs_dh_assign(struct ip_vs_dh_bucket *tbl, struct ip_vs_service *svc)

{

        int i;

        struct ip_vs_dh_bucket *b;

        struct list_head *p;

        struct ip_vs_dest *dest;

        b = tbl;

        p = &svc->destinations;

        for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {

                if (list_empty(p)) {

                        b->dest = NULL;

                } else {

                        if (p == &svc->destinations)

                                p = p->next;

                        dest = list_entry(p, struct ip_vs_dest, n_list);

                        atomic_inc(&dest->refcnt);

                        b->dest = dest;

                        p = p->next;

                }

                b++;

        }

        return 0;

}

/*

 *      Flush all the hash buckets of the specified table.

 */

static void ip_vs_dh_flush(struct ip_vs_dh_bucket *tbl)

{

        int i;

        struct ip_vs_dh_bucket *b;

        b = tbl;

        for (i=0; i<IP_VS_DH_TAB_SIZE; i++) {

                if (b->dest) {

                        atomic_dec(&b->dest->refcnt);

                        b->dest = NULL;

                }

                b++;

        }

}

static int ip_vs_dh_init_svc(struct ip_vs_service *svc)

{

        struct ip_vs_dh_bucket *tbl;

        /* allocate the DH table for this service */

        tbl = kmalloc(sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE,

                      GFP_ATOMIC);

        if (tbl == NULL) {

                IP_VS_ERR("ip_vs_dh_init_svc(): no memory\n");

                return -ENOMEM;

        }

        svc->sched_data = tbl;

        IP_VS_DBG(6, "DH hash table (memory=%dbytes) allocated for "

                  "current service\n",

                  sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);

        /* assign the hash buckets with the updated service */

        ip_vs_dh_assign(tbl, svc);

        return 0;

}

static int ip_vs_dh_done_svc(struct ip_vs_service *svc)

{

        struct ip_vs_dh_bucket *tbl = svc->sched_data;

        /* got to clean up hash buckets here */

        ip_vs_dh_flush(tbl);

        /* release the table itself */

        kfree(svc->sched_data);

        IP_VS_DBG(6, "DH hash table (memory=%dbytes) released\n",

                  sizeof(struct ip_vs_dh_bucket)*IP_VS_DH_TAB_SIZE);

        return 0;

}

static int ip_vs_dh_update_svc(struct ip_vs_service *svc)

{

        struct ip_vs_dh_bucket *tbl = svc->sched_data;

        /* got to clean up hash buckets here */

        ip_vs_dh_flush(tbl);

        /* assign the hash buckets with the updated service */

        ip_vs_dh_assign(tbl, svc);

        return 0;

}

/*

 *      If the number of active connections is twice larger than its weight,

 *      consider that the server is overloaded here.

 */

static inline int is_overloaded(struct ip_vs_dest *dest)

{

        if (atomic_read(&dest->activeconns) > atomic_read(&dest->weight)*2) {

                return 1;

        }

        return 0;

}

/*

 *      Destination hashing scheduling

 */

static struct ip_vs_dest *

ip_vs_dh_schedule(struct ip_vs_service *svc, struct iphdr *iph)

{

        struct ip_vs_dest *dest;

        struct ip_vs_dh_bucket *tbl;

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

        tbl = (struct ip_vs_dh_bucket *)svc->sched_data;

        dest = ip_vs_dh_get(tbl, iph->daddr);

        if (!dest

            || !(dest->flags & IP_VS_DEST_F_AVAILABLE)

            || atomic_read(&dest->weight) <= 0

            || is_overloaded(dest)) {

                return NULL;

        }

        IP_VS_DBG(6, "DH: destination IP address %u.%u.%u.%u "

                  "--> server %u.%u.%u.%u:%d\n",

                  NIPQUAD(iph->daddr),

                  NIPQUAD(dest->addr),

                  ntohs(dest->port));

        return dest;

}

/*

 *      IPVS DH Scheduler structure

 */

static struct ip_vs_scheduler ip_vs_dh_scheduler =

{

        {0},                    /* n_list */

        "dh",                   /* name */

        ATOMIC_INIT(0),         /* refcnt */

        THIS_MODULE,            /* this module */

        ip_vs_dh_init_svc,      /* service initializer */

        ip_vs_dh_done_svc,      /* service done */

        ip_vs_dh_update_svc,    /* service updater */

        ip_vs_dh_schedule,      /* select a server from the destination list */

};

static int __init ip_vs_dh_init(void)

{

        INIT_LIST_HEAD(&ip_vs_dh_scheduler.n_list);

        return register_ip_vs_scheduler(&ip_vs_dh_scheduler);

}

static void __exit ip_vs_dh_cleanup(void)

{

        unregister_ip_vs_scheduler(&ip_vs_dh_scheduler);

}

module_init(ip_vs_dh_init);

module_exit(ip_vs_dh_cleanup);

MODULE_LICENSE("GPL");