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         char dummy;
 118
 119         if (argc > 1) {
 120                 *error = "round-robin ps: incorrect number of arguments";
 121                 return -EINVAL;
 122         }
 123
 124         /* First path argument is number of I/Os before switching path */
 125         if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
 126                 *error = "round-robin ps: invalid repeat count";
 127                 return -EINVAL;
 128         }
 129
 130         /* allocate the path */
 131         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 132         if (!pi) {
 133                 *error = "round-robin ps: Error allocating path context";
 134                 return -ENOMEM;
 135         }
 136
 137         pi->path = path;
 138         pi->repeat_count = repeat_count;
 139
 140         path->pscontext = pi;
 141
 142         list_add_tail(&pi->list, &s->valid_paths);
 143
 144         return 0;
 145 }
 146
 147 static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
 148 {
 149         struct selector *s = (struct selector *) ps->context;
 150         struct path_info *pi = p->pscontext;
 151
 152         list_move(&pi->list, &s->invalid_paths);
 153 }
 154
 155 static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 156 {
 157         struct selector *s = (struct selector *) ps->context;
 158         struct path_info *pi = p->pscontext;
 159
 160         list_move(&pi->list, &s->valid_paths);
 161
 162         return 0;
 163 }
 164
 165 static struct dm_path *rr_select_path(struct path_selector *ps,
 166                                       unsigned *repeat_count, size_t nr_bytes)
 167 {
 168         struct selector *s = (struct selector *) ps->context;
 169         struct path_info *pi = NULL;
 170
 171         if (!list_empty(&s->valid_paths)) {
 172                 pi = list_entry(s->valid_paths.next, struct path_info, list);
 173                 list_move_tail(&pi->list, &s->valid_paths);
 174                 *repeat_count = pi->repeat_count;
 175         }
 176
 177         return pi ? pi->path : NULL;
 178 }
 179
 180 static struct path_selector_type rr_ps = {
 181         .name = "round-robin",
 182         .module = THIS_MODULE,
 183         .table_args = 1,
 184         .info_args = 0,
 185         .create = rr_create,
 186         .destroy = rr_destroy,
 187         .status = rr_status,
 188         .add_path = rr_add_path,
 189         .fail_path = rr_fail_path,
 190         .reinstate_path = rr_reinstate_path,
 191         .select_path = rr_select_path,
 192 };
 193
 194 static int __init dm_rr_init(void)
 195 {
 196         int r = dm_register_path_selector(&rr_ps);
 197
 198         if (r < 0)
 199                 DMERR("register failed %d", r);
 200
 201         DMINFO("version 1.0.0 loaded");
 202
 203         return r;
 204 }
 205
 206 static void __exit dm_rr_exit(void)
 207 {
 208         int r = dm_unregister_path_selector(&rr_ps);
 209
 210         if (r < 0)
 211                 DMERR("unregister failed %d", r);
 212 }
 213
 214 module_init(dm_rr_init);
 215 module_exit(dm_rr_exit);
 216
 217 MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
 218 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
 219 MODULE_LICENSE("GPL");