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 #define RR_MIN_IO     1
  21 #define RR_VERSION    "1.2.0"
  22
  23 /*-----------------------------------------------------------------
  24  * Path-handling code, paths are held in lists
  25  *---------------------------------------------------------------*/
  26 struct path_info {
  27         struct list_head list;
  28         struct dm_path *path;
  29         unsigned repeat_count;
  30 };
  31
  32 static void free_paths(struct list_head *paths)
  33 {
  34         struct path_info *pi, *next;
  35
  36         list_for_each_entry_safe(pi, next, paths, list) {
  37                 list_del(&pi->list);
  38                 kfree(pi);
  39         }
  40 }
  41
  42 /*-----------------------------------------------------------------
  43  * Round-robin selector
  44  *---------------------------------------------------------------*/
  45
  46 struct selector {
  47         struct list_head valid_paths;
  48         struct list_head invalid_paths;
  49         spinlock_t lock;
  50 };
  51
  52 static struct selector *alloc_selector(void)
  53 {
  54         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  55
  56         if (s) {
  57                 INIT_LIST_HEAD(&s->valid_paths);
  58                 INIT_LIST_HEAD(&s->invalid_paths);
  59                 spin_lock_init(&s->lock);
  60         }
  61
  62         return s;
  63 }
  64
  65 static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
  66 {
  67         struct selector *s;
  68
  69         s = alloc_selector();
  70         if (!s)
  71                 return -ENOMEM;
  72
  73         ps->context = s;
  74         return 0;
  75 }
  76
  77 static void rr_destroy(struct path_selector *ps)
  78 {
  79         struct selector *s = ps->context;
  80
  81         free_paths(&s->valid_paths);
  82         free_paths(&s->invalid_paths);
  83         kfree(s);
  84         ps->context = NULL;
  85 }
  86
  87 static int rr_status(struct path_selector *ps, struct dm_path *path,
  88                      status_type_t type, char *result, unsigned int maxlen)
  89 {
  90         struct path_info *pi;
  91         int sz = 0;
  92
  93         if (!path)
  94                 DMEMIT("0 ");
  95         else {
  96                 switch(type) {
  97                 case STATUSTYPE_INFO:
  98                         break;
  99                 case STATUSTYPE_TABLE:
 100                         pi = path->pscontext;
 101                         DMEMIT("%u ", pi->repeat_count);
 102                         break;
 103                 }
 104         }
 105
 106         return sz;
 107 }
 108
 109 /*
 110  * Called during initialisation to register each path with an
 111  * optional repeat_count.
 112  */
 113 static int rr_add_path(struct path_selector *ps, struct dm_path *path,
 114                        int argc, char **argv, char **error)
 115 {
 116         struct selector *s = ps->context;
 117         struct path_info *pi;
 118         unsigned repeat_count = RR_MIN_IO;
 119         char dummy;
 120         unsigned long flags;
 121
 122         if (argc > 1) {
 123                 *error = "round-robin ps: incorrect number of arguments";
 124                 return -EINVAL;
 125         }
 126
 127         /* First path argument is number of I/Os before switching path */
 128         if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 129                 *error = "round-robin ps: invalid repeat count";
 130                 return -EINVAL;
 131         }
 132
 133         if (repeat_count > 1) {
 134                 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
 135                 repeat_count = 1;
 136         }
 137
 138         /* allocate the path */
 139         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 140         if (!pi) {
 141                 *error = "round-robin ps: Error allocating path context";
 142                 return -ENOMEM;
 143         }
 144
 145         pi->path = path;
 146         pi->repeat_count = repeat_count;
 147
 148         path->pscontext = pi;
 149
 150         spin_lock_irqsave(&s->lock, flags);
 151         list_add_tail(&pi->list, &s->valid_paths);
 152         spin_unlock_irqrestore(&s->lock, flags);
 153
 154         return 0;
 155 }
 156
 157 static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
 158 {
 159         unsigned long flags;
 160         struct selector *s = ps->context;
 161         struct path_info *pi = p->pscontext;
 162
 163         spin_lock_irqsave(&s->lock, flags);
 164         list_move(&pi->list, &s->invalid_paths);
 165         spin_unlock_irqrestore(&s->lock, flags);
 166 }
 167
 168 static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 169 {
 170         unsigned long flags;
 171         struct selector *s = ps->context;
 172         struct path_info *pi = p->pscontext;
 173
 174         spin_lock_irqsave(&s->lock, flags);
 175         list_move(&pi->list, &s->valid_paths);
 176         spin_unlock_irqrestore(&s->lock, flags);
 177
 178         return 0;
 179 }
 180
 181 static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
 182 {
 183         unsigned long flags;
 184         struct selector *s = ps->context;
 185         struct path_info *pi = NULL;
 186
 187         spin_lock_irqsave(&s->lock, flags);
 188         if (!list_empty(&s->valid_paths)) {
 189                 pi = list_entry(s->valid_paths.next, struct path_info, list);
 190                 list_move_tail(&pi->list, &s->valid_paths);
 191         }
 192         spin_unlock_irqrestore(&s->lock, flags);
 193
 194         return pi ? pi->path : NULL;
 195 }
 196
 197 static struct path_selector_type rr_ps = {
 198         .name = "round-robin",
 199         .module = THIS_MODULE,
 200         .table_args = 1,
 201         .info_args = 0,
 202         .create = rr_create,
 203         .destroy = rr_destroy,
 204         .status = rr_status,
 205         .add_path = rr_add_path,
 206         .fail_path = rr_fail_path,
 207         .reinstate_path = rr_reinstate_path,
 208         .select_path = rr_select_path,
 209 };
 210
 211 static int __init dm_rr_init(void)
 212 {
 213         int r = dm_register_path_selector(&rr_ps);
 214
 215         if (r < 0)
 216                 DMERR("register failed %d", r);
 217
 218         DMINFO("version " RR_VERSION " loaded");
 219
 220         return r;
 221 }
 222
 223 static void __exit dm_rr_exit(void)
 224 {
 225         int r = dm_unregister_path_selector(&rr_ps);
 226
 227         if (r < 0)
 228                 DMERR("unregister failed %d", r);
 229 }
 230
 231 module_init(dm_rr_init);
 232 module_exit(dm_rr_exit);
 233
 234 MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
 235 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
 236 MODULE_LICENSE("GPL");