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