drivers/md/dm-round-robin.c

   1 /*
   2  * Copyright (C) 2003 Sistina Software.
   3  * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
   4  *
   5  * Module Author: Heinz Mauelshagen
   6  *
   7  * This file is released under the GPL.
   8  *
   9  * Round-robin path selector.
  10  */
  11
  12 #include <linux/device-mapper.h>
  13
  14 #include "dm-path-selector.h"
  15
  16 #include <linux/slab.h>
  17 #include <linux/module.h>
  18
  19 #define DM_MSG_PREFIX "multipath round-robin"
  20
  21 /*-----------------------------------------------------------------
  22  * Path-handling code, paths are held in lists
  23  *---------------------------------------------------------------*/
  24 struct path_info {
  25         struct list_head list;
  26         struct dm_path *path;
  27         unsigned repeat_count;
  28 };
  29
  30 static void free_paths(struct list_head *paths)
  31 {
  32         struct path_info *pi, *next;
  33
  34         list_for_each_entry_safe(pi, next, paths, list) {
  35                 list_del(&pi->list);
  36                 kfree(pi);
  37         }
  38 }
  39
  40 /*-----------------------------------------------------------------
  41  * Round-robin selector
  42  *---------------------------------------------------------------*/
  43
  44 #define RR_MIN_IO               1000
  45
  46 struct selector {
  47         struct list_head valid_paths;
  48         struct list_head invalid_paths;
  49 };
  50
  51 static struct selector *alloc_selector(void)
  52 {
  53         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  54
  55         if (s) {
  56                 INIT_LIST_HEAD(&s->valid_paths);
  57                 INIT_LIST_HEAD(&s->invalid_paths);
  58         }
  59
  60         return s;
  61 }
  62
  63 static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
  64 {
  65         struct selector *s;
  66
  67         s = alloc_selector();
  68         if (!s)
  69                 return -ENOMEM;
  70
  71         ps->context = s;
  72         return 0;
  73 }
  74
  75 static void rr_destroy(struct path_selector *ps)
  76 {
  77         struct selector *s = (struct selector *) ps->context;
  78
  79         free_paths(&s->valid_paths);
  80         free_paths(&s->invalid_paths);
  81         kfree(s);
  82         ps->context = NULL;
  83 }
  84
  85 static int rr_status(struct path_selector *ps, struct dm_path *path,
  86                      status_type_t type, char *result, unsigned int maxlen)
  87 {
  88         struct path_info *pi;
  89         int sz = 0;
  90
  91         if (!path)
  92                 DMEMIT("0 ");
  93         else {
  94                 switch(type) {
  95                 case STATUSTYPE_INFO:
  96                         break;
  97                 case STATUSTYPE_TABLE:
  98                         pi = path->pscontext;
  99                         DMEMIT("%u ", pi->repeat_count);
 100                         break;
 101                 }
 102         }
 103
 104         return sz;
 105 }
 106
 107 /*
 108  * Called during initialisation to register each path with an
 109  * optional repeat_count.
 110  */
 111 static int rr_add_path(struct path_selector *ps, struct dm_path *path,
 112                        int argc, char **argv, char **error)
 113 {
 114         struct selector *s = (struct selector *) ps->context;
 115         struct path_info *pi;
 116         unsigned repeat_count = RR_MIN_IO;
 117
 118         if (argc > 1) {
 119                 *error = "round-robin ps: incorrect number of arguments";
 120                 return -EINVAL;
 121         }
 122
 123         /* First path argument is number of I/Os before switching path */
 124         if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
 125                 *error = "round-robin ps: invalid repeat count";
 126                 return -EINVAL;
 127         }
 128
 129         /* allocate the path */
 130         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 131         if (!pi) {
 132                 *error = "round-robin ps: Error allocating path context";
 133                 return -ENOMEM;
 134         }
 135
 136         pi->path = path;
 137         pi->repeat_count = repeat_count;
 138
 139         path->pscontext = pi;
 140
 141         list_add_tail(&pi->list, &s->valid_paths);
 142
 143         return 0;
 144 }
 145
 146 static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
 147 {
 148         struct selector *s = (struct selector *) ps->context;
 149         struct path_info *pi = p->pscontext;
 150
 151         list_move(&pi->list, &s->invalid_paths);
 152 }
 153
 154 static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 155 {
 156         struct selector *s = (struct selector *) ps->context;
 157         struct path_info *pi = p->pscontext;
 158
 159         list_move(&pi->list, &s->valid_paths);
 160
 161         return 0;
 162 }
 163
 164 static struct dm_path *rr_select_path(struct path_selector *ps,
 165                                       unsigned *repeat_count, size_t nr_bytes)
 166 {
 167         struct selector *s = (struct selector *) ps->context;
 168         struct path_info *pi = NULL;
 169
 170         if (!list_empty(&s->valid_paths)) {
 171                 pi = list_entry(s->valid_paths.next, struct path_info, list);
 172                 list_move_tail(&pi->list, &s->valid_paths);
 173                 *repeat_count = pi->repeat_count;
 174         }
 175
 176         return pi ? pi->path : NULL;
 177 }
 178
 179 static struct path_selector_type rr_ps = {
 180         .name = "round-robin",
 181         .module = THIS_MODULE,
 182         .table_args = 1,
 183         .info_args = 0,
 184         .create = rr_create,
 185         .destroy = rr_destroy,
 186         .status = rr_status,
 187         .add_path = rr_add_path,
 188         .fail_path = rr_fail_path,
 189         .reinstate_path = rr_reinstate_path,
 190         .select_path = rr_select_path,
 191 };
 192
 193 static int __init dm_rr_init(void)
 194 {
 195         int r = dm_register_path_selector(&rr_ps);
 196
 197         if (r < 0)
 198                 DMERR("register failed %d", r);
 199
 200         DMINFO("version 1.0.0 loaded");
 201
 202         return r;
 203 }
 204
 205 static void __exit dm_rr_exit(void)
 206 {
 207         int r = dm_unregister_path_selector(&rr_ps);
 208
 209         if (r < 0)
 210                 DMERR("unregister failed %d", r);
 211 }
 212
 213 module_init(dm_rr_init);
 214 module_exit(dm_rr_exit);
 215
 216 MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
 217 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
 218 MODULE_LICENSE("GPL");