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