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