net/ipv4/multipath_random.c

   1 /*
   2  *              Random policy for multipath.
   3  *
   4  *
   5  * Version:     $Id: multipath_random.c,v 1.1.2.3 2004/09/21 08:42:11 elueck Exp $
   6  *
   7  * Authors:     Einar Lueck <elueck@de.ibm.com><lkml@einar-lueck.de>
   8  *
   9  *              This program is free software; you can redistribute it and/or
  10  *              modify it under the terms of the GNU General Public License
  11  *              as published by the Free Software Foundation; either version
  12  *              2 of the License, or (at your option) any later version.
  13  */
  14
  15 #include <linux/config.h>
  16 #include <asm/system.h>
  17 #include <asm/uaccess.h>
  18 #include <linux/types.h>
  19 #include <linux/sched.h>
  20 #include <linux/errno.h>
  21 #include <linux/timer.h>
  22 #include <linux/mm.h>
  23 #include <linux/kernel.h>
  24 #include <linux/fcntl.h>
  25 #include <linux/stat.h>
  26 #include <linux/socket.h>
  27 #include <linux/in.h>
  28 #include <linux/inet.h>
  29 #include <linux/netdevice.h>
  30 #include <linux/inetdevice.h>
  31 #include <linux/igmp.h>
  32 #include <linux/proc_fs.h>
  33 #include <linux/seq_file.h>
  34 #include <linux/mroute.h>
  35 #include <linux/init.h>
  36 #include <net/ip.h>
  37 #include <net/protocol.h>
  38 #include <linux/skbuff.h>
  39 #include <net/sock.h>
  40 #include <net/icmp.h>
  41 #include <net/udp.h>
  42 #include <net/raw.h>
  43 #include <linux/notifier.h>
  44 #include <linux/if_arp.h>
  45 #include <linux/netfilter_ipv4.h>
  46 #include <net/ipip.h>
  47 #include <net/checksum.h>
  48 #include <net/ip_mp_alg.h>
  49
  50 #define MULTIPATH_MAX_CANDIDATES 40
  51
  52 /* interface to random number generation */
  53 static unsigned int RANDOM_SEED = 93186752;
  54
  55 static inline unsigned int random(unsigned int ubound)
  56 {
  57         static unsigned int a = 1588635695,
  58                 q = 2,
  59                 r = 1117695901;
  60
  61         RANDOM_SEED = a*(RANDOM_SEED % q) - r*(RANDOM_SEED / q);
  62
  63         return RANDOM_SEED % ubound;
  64 }
  65
  66
  67 static void random_select_route(const struct flowi *flp,
  68                                 struct rtable *first,
  69                                 struct rtable **rp)
  70 {
  71         struct rtable *rt;
  72         struct rtable *decision;
  73         unsigned char candidate_count = 0;
  74
  75         /* count all candidate */
  76         for (rt = rcu_dereference(first); rt;
  77              rt = rcu_dereference(rt->u.rt_next)) {
  78                 if ((rt->u.dst.flags & DST_BALANCED) != 0 &&
  79                     multipath_comparekeys(&rt->fl, flp))
  80                         ++candidate_count;
  81         }
  82
  83         /* choose a random candidate */
  84         decision = first;
  85         if (candidate_count > 1) {
  86                 unsigned char i = 0;
  87                 unsigned char candidate_no = (unsigned char)
  88                         random(candidate_count);
  89
  90                 /* find chosen candidate and adjust GC data for all candidates
  91                  * to ensure they stay in cache
  92                  */
  93                 for (rt = first; rt; rt = rt->u.rt_next) {
  94                         if ((rt->u.dst.flags & DST_BALANCED) != 0 &&
  95                             multipath_comparekeys(&rt->fl, flp)) {
  96                                 rt->u.dst.lastuse = jiffies;
  97
  98                                 if (i == candidate_no)
  99                                         decision = rt;
 100
 101                                 if (i >= candidate_count)
 102                                         break;
 103
 104                                 i++;
 105                         }
 106                 }
 107         }
 108
 109         decision->u.dst.__use++;
 110         *rp = decision;
 111 }
 112
 113 static struct ip_mp_alg_ops random_ops = {
 114         .mp_alg_select_route    =       random_select_route,
 115 };
 116
 117 static int __init random_init(void)
 118 {
 119         return multipath_alg_register(&random_ops, IP_MP_ALG_RANDOM);
 120 }
 121
 122 static void __exit random_exit(void)
 123 {
 124         multipath_alg_unregister(&random_ops, IP_MP_ALG_RANDOM);
 125 }
 126
 127 module_init(random_init);
 128 module_exit(random_exit);