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    "1.1.0"
  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 };
  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         if (repeat_count > 1) {
 131                 DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
 132                 repeat_count = 1;
 133         }
 134
 135         /* allocate the path */
 136         pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 137         if (!pi) {
 138                 *error = "round-robin ps: Error allocating path context";
 139                 return -ENOMEM;
 140         }
 141
 142         pi->path = path;
 143         pi->repeat_count = repeat_count;
 144
 145         path->pscontext = pi;
 146
 147         list_add_tail(&pi->list, &s->valid_paths);
 148
 149         return 0;
 150 }
 151
 152 static void rr_fail_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->invalid_paths);
 158 }
 159
 160 static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
 161 {
 162         struct selector *s = (struct selector *) ps->context;
 163         struct path_info *pi = p->pscontext;
 164
 165         list_move(&pi->list, &s->valid_paths);
 166
 167         return 0;
 168 }
 169
 170 static struct dm_path *rr_select_path(struct path_selector *ps,
 171                                       unsigned *repeat_count, size_t nr_bytes)
 172 {
 173         struct selector *s = (struct selector *) ps->context;
 174         struct path_info *pi = NULL;
 175
 176         if (!list_empty(&s->valid_paths)) {
 177                 pi = list_entry(s->valid_paths.next, struct path_info, list);
 178                 list_move_tail(&pi->list, &s->valid_paths);
 179                 *repeat_count = pi->repeat_count;
 180         }
 181
 182         return pi ? pi->path : NULL;
 183 }
 184
 185 static struct path_selector_type rr_ps = {
 186         .name = "round-robin",
 187         .module = THIS_MODULE,
 188         .table_args = 1,
 189         .info_args = 0,
 190         .create = rr_create,
 191         .destroy = rr_destroy,
 192         .status = rr_status,
 193         .add_path = rr_add_path,
 194         .fail_path = rr_fail_path,
 195         .reinstate_path = rr_reinstate_path,
 196         .select_path = rr_select_path,
 197 };
 198
 199 static int __init dm_rr_init(void)
 200 {
 201         int r = dm_register_path_selector(&rr_ps);
 202
 203         if (r < 0)
 204                 DMERR("register failed %d", r);
 205
 206         DMINFO("version " RR_VERSION " loaded");
 207
 208         return r;
 209 }
 210
 211 static void __exit dm_rr_exit(void)
 212 {
 213         int r = dm_unregister_path_selector(&rr_ps);
 214
 215         if (r < 0)
 216                 DMERR("unregister failed %d", r);
 217 }
 218
 219 module_init(dm_rr_init);
 220 module_exit(dm_rr_exit);
 221
 222 MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
 223 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
 224 MODULE_LICENSE("GPL");