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     1000
  21 #define RR_VERSION    "1.1.0"
  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         struct dm_path * __percpu *current_path;
  51         struct percpu_counter repeat_count;
  52 };
  53
  54 static void set_percpu_current_path(struct selector *s, struct dm_path *path)
  55 {
  56         int cpu;
  57
  58         for_each_possible_cpu(cpu)
  59                 *per_cpu_ptr(s->current_path, cpu) = path;
  60 }
  61
  62 static struct selector *alloc_selector(void)
  63 {
  64         struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  65
  66         if (!s)
  67                 return NULL;
  68
  69         INIT_LIST_HEAD(&s->valid_paths);
  70         INIT_LIST_HEAD(&s->invalid_paths);
  71         spin_lock_init(&s->lock);
  72
  73         s->current_path = alloc_percpu(struct dm_path *);
  74         if (!s->current_path)
  75                 goto out_current_path;
  76         set_percpu_current_path(s, NULL);
  77
  78         if (percpu_counter_init(&s->repeat_count, 0, GFP_KERNEL))
  79                 goto out_repeat_count;
  80
  81         return s;
  82
  83 out_repeat_count:
  84         free_percpu(s->current_path);
  85 out_current_path:
  86         kfree(s);
  87         return NULL;;
  88 }
  89
  90 static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
  91 {
  92         struct selector *s;
  93
  94         s = alloc_selector();
  95         if (!s)
  96                 return -ENOMEM;
  97
  98         ps->context = s;
  99         return 0;
 100 }
 101
 102 static void rr_destroy(struct path_selector *ps)
 103 {
 104         struct selector *s = ps->context;
 105
 106         free_paths(&s->valid_paths);
 107         free_paths(&s->invalid_paths);
 108         free_percpu(s->current_path);
 109         percpu_counter_destroy(&s->repeat_count);
 110         kfree(s);
 111         ps->context = NULL;
 112 }
 113
 114 static int rr_status(struct path_selector *ps, struct dm_path *path,
 115                      status_type_t type, char *result, unsigned int maxlen)
 116 {
 117         struct path_info *pi;
 118         int sz = 0;
 119
 120         if (!path)
 121                 DMEMIT("0 ");
 122         else {
 123                 switch(type) {
 124                 case STATUSTYPE_INFO:
 125                         break;
 126                 case STATUSTYPE_TABLE:
 127                         pi = path->pscontext;
 128                         DMEMIT("%u ", pi->repeat_count);
 129                         break;
 130                 }
 131         }
 132
 133         return sz;
 134 }
 135
 136 /*
 137  * Called during initialisation to register each path with an
 138  * optional repeat_count.
 139  */
 140 static int rr_add_path(struct path_selector *ps, struct dm_path *path,
 141                        int argc, char **argv, char **error)
 142 {
 143         struct selector *s = ps->context;
 144         struct path_info *pi;
 145         unsigned repeat_count = RR_MIN_IO;
 146         char dummy;
 147         unsigned long flags;
 148
 149         if (argc > 1) {
 150                 *error = "round-robin ps: incorrect number of arguments";
 151                 return -EINVAL;
 152         }
 153
 154         /* First path argument is number of I/Os before switching path */
 155         if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 156                 *error = "round-robin ps: invalid repeat count";
 157                 return -EINVAL;
 158         }
 159
 160         /* allocate the path */
 161         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 162         if (!pi) {
 163                 *error = "round-robin ps: Error allocating path context";
 164                 return -ENOMEM;
 165         }
 166
 167         pi->path = path;
 168         pi->repeat_count = repeat_count;
 169
 170         path->pscontext = pi;
 171
 172         spin_lock_irqsave(&s->lock, flags);
 173         list_add_tail(&pi->list, &s->valid_paths);
 174         spin_unlock_irqrestore(&s->lock, flags);
 175
 176         return 0;
 177 }
 178
 179 static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
 180 {
 181         unsigned long flags;
 182         struct selector *s = ps->context;
 183         struct path_info *pi = p->pscontext;
 184
 185         spin_lock_irqsave(&s->lock, flags);
 186         if (p == *this_cpu_ptr(s->current_path))
 187                 set_percpu_current_path(s, NULL);
 188
 189         list_move(&pi->list, &s->invalid_paths);
 190         spin_unlock_irqrestore(&s->lock, flags);
 191 }
 192
 193 static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 194 {
 195         unsigned long flags;
 196         struct selector *s = ps->context;
 197         struct path_info *pi = p->pscontext;
 198
 199         spin_lock_irqsave(&s->lock, flags);
 200         list_move(&pi->list, &s->valid_paths);
 201         spin_unlock_irqrestore(&s->lock, flags);
 202
 203         return 0;
 204 }
 205
 206 static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
 207 {
 208         unsigned long flags;
 209         struct selector *s = ps->context;
 210         struct path_info *pi = NULL;
 211         struct dm_path *current_path = NULL;
 212
 213         current_path = *this_cpu_ptr(s->current_path);
 214         if (current_path) {
 215                 percpu_counter_dec(&s->repeat_count);
 216                 if (percpu_counter_read_positive(&s->repeat_count) > 0)
 217                         return current_path;
 218         }
 219
 220         spin_lock_irqsave(&s->lock, flags);
 221         if (!list_empty(&s->valid_paths)) {
 222                 pi = list_entry(s->valid_paths.next, struct path_info, list);
 223                 list_move_tail(&pi->list, &s->valid_paths);
 224                 percpu_counter_set(&s->repeat_count, pi->repeat_count);
 225                 set_percpu_current_path(s, pi->path);
 226                 current_path = pi->path;
 227         }
 228         spin_unlock_irqrestore(&s->lock, flags);
 229
 230         return current_path;
 231 }
 232
 233 static struct path_selector_type rr_ps = {
 234         .name = "round-robin",
 235         .module = THIS_MODULE,
 236         .table_args = 1,
 237         .info_args = 0,
 238         .create = rr_create,
 239         .destroy = rr_destroy,
 240         .status = rr_status,
 241         .add_path = rr_add_path,
 242         .fail_path = rr_fail_path,
 243         .reinstate_path = rr_reinstate_path,
 244         .select_path = rr_select_path,
 245 };
 246
 247 static int __init dm_rr_init(void)
 248 {
 249         int r = dm_register_path_selector(&rr_ps);
 250
 251         if (r < 0)
 252                 DMERR("register failed %d", r);
 253
 254         DMINFO("version " RR_VERSION " loaded");
 255
 256         return r;
 257 }
 258
 259 static void __exit dm_rr_exit(void)
 260 {
 261         int r = dm_unregister_path_selector(&rr_ps);
 262
 263         if (r < 0)
 264                 DMERR("unregister failed %d", r);
 265 }
 266
 267 module_init(dm_rr_init);
 268 module_exit(dm_rr_exit);
 269
 270 MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
 271 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
 272 MODULE_LICENSE("GPL");