drivers/md/dm-least-pending.c

   1 /*
   2  * (C) Copyright 2008 Hewlett-Packard Development Company, L.P
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-path-selector.h"
   8
   9 #include <linux/slab.h>
  10 #include <linux/module.h>
  11
  12 #define DM_MSG_PREFIX "multipath least-pending"
  13
  14 /*-----------------------------------------------------------------
  15 * Path-handling code, paths are held in lists
  16 *---------------------------------------------------------------*/
  17 struct path_info {
  18        struct list_head list;
  19        struct dm_path *path;
  20        unsigned repeat_count;
  21        atomic_t io_count;
  22 };
  23
  24 static void free_paths(struct list_head *paths)
  25 {
  26        struct path_info *pi, *next;
  27
  28        list_for_each_entry_safe(pi, next, paths, list) {
  29                 list_del(&pi->list);
  30                 kfree(pi);
  31        }
  32 }
  33
  34 /*-----------------------------------------------------------------
  35  * Least-pending selector
  36  *---------------------------------------------------------------*/
  37
  38 #define LPP_MIN_IO     1
  39
  40 struct selector {
  41        struct list_head valid_paths;
  42        struct list_head invalid_paths;
  43 };
  44
  45 static struct selector *alloc_selector(void)
  46 {
  47        struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
  48
  49        if (s) {
  50                 INIT_LIST_HEAD(&s->valid_paths);
  51                 INIT_LIST_HEAD(&s->invalid_paths);
  52        }
  53
  54        return s;
  55 }
  56
  57 static int lpp_create(struct path_selector *ps, unsigned argc, char **argv)
  58 {
  59        struct selector *s;
  60
  61        s = alloc_selector();
  62        if (!s)
  63                 return -ENOMEM;
  64
  65        ps->context = s;
  66        return 0;
  67 }
  68
  69 static void lpp_destroy(struct path_selector *ps)
  70 {
  71        struct selector *s = ps->context;
  72
  73        free_paths(&s->valid_paths);
  74        free_paths(&s->invalid_paths);
  75        kfree(s);
  76        ps->context = NULL;
  77 }
  78
  79 static int lpp_status(struct path_selector *ps, struct dm_path *path,
  80                         status_type_t type, char *result, unsigned int maxlen)
  81 {
  82        struct path_info *pi;
  83        int sz = 0;
  84
  85        if (!path)
  86                 switch (type) {
  87                 case STATUSTYPE_INFO:
  88                         DMEMIT("1 ");
  89                 break;
  90                 case STATUSTYPE_TABLE:
  91                         DMEMIT("0 ");
  92                 break;
  93                 }
  94        else {
  95                 pi = path->pscontext;
  96                 switch (type) {
  97                 case STATUSTYPE_INFO:
  98                         DMEMIT("%u:%u ", pi->repeat_count,
  99                                          atomic_read(&pi->io_count));
 100                 break;
 101                 case STATUSTYPE_TABLE:
 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 lpp_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 = LPP_MIN_IO;
 119
 120         if (argc > 1) {
 121                 *error = "least-pending ps: incorrect number of arguments";
 122                 return -EINVAL;
 123         }
 124
 125        /* First path argument is number of I/Os before switching path */
 126        if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
 127                 *error = "least-pending ps: invalid repeat count";
 128                 return -EINVAL;
 129        }
 130
 131        /* allocate the path */
 132        pi = kmalloc(sizeof(*pi), GFP_KERNEL);
 133        if (!pi) {
 134                 *error = "least-pending ps: Error allocating path context";
 135                 return -ENOMEM;
 136        }
 137
 138        pi->path = path;
 139        pi->repeat_count = repeat_count;
 140        atomic_set(&pi->io_count, 0);
 141
 142        path->pscontext = pi;
 143
 144        list_add(&pi->list, &s->valid_paths);
 145
 146        return 0;
 147 }
 148
 149 static void lpp_fail_path(struct path_selector *ps, struct dm_path *p)
 150 {
 151        struct selector *s = ps->context;
 152        struct path_info *pi = p->pscontext;
 153
 154        if (!pi)
 155         return;
 156
 157        atomic_set(&pi->io_count, 0);
 158
 159        list_move(&pi->list, &s->invalid_paths);
 160 }
 161
 162 static int lpp_reinstate_path(struct path_selector *ps, struct dm_path *p)
 163 {
 164        struct selector *s = ps->context;
 165        struct path_info *pi = p->pscontext;
 166
 167        if (!pi)
 168         return 1;
 169
 170        list_move(&pi->list, &s->valid_paths);
 171
 172        return 0;
 173 }
 174
 175 static struct dm_path *lpp_select_path(struct path_selector *ps,
 176                                         unsigned *repeat_count,
 177                                         size_t nr_bytes)
 178 {
 179        struct selector *s = ps->context;
 180        struct path_info *pi, *next, *least_io_path = NULL;
 181        struct list_head *paths;
 182
 183        if (list_empty(&s->valid_paths))
 184                 return NULL;
 185
 186        paths = &s->valid_paths;
 187
 188        list_for_each_entry_safe(pi, next, paths, list) {
 189                 if (!least_io_path || atomic_read(&least_io_path->io_count) < atomic_read(&pi->io_count))
 190                         least_io_path = pi;
 191                 if (!atomic_read(&least_io_path->io_count))
 192                         break;
 193        }
 194
 195        if (!least_io_path)
 196                 return NULL;
 197
 198        atomic_inc(&least_io_path->io_count);
 199        *repeat_count = least_io_path->repeat_count;
 200
 201        return least_io_path->path;
 202 }
 203
 204 static int lpp_end_io(struct path_selector *ps, struct dm_path *path,
 205                       size_t nr_bytes)
 206 {
 207        struct path_info *pi = NULL;
 208
 209        pi = path->pscontext;
 210        if (!pi)
 211         return 1;
 212
 213        atomic_dec(&pi->io_count);
 214
 215        return 0;
 216 }
 217
 218 static struct path_selector_type lpp_ps = {
 219        .name = "least-pending",
 220        .module = THIS_MODULE,
 221        .table_args = 1,
 222        .info_args = 0,
 223        .create = lpp_create,
 224        .destroy = lpp_destroy,
 225        .status = lpp_status,
 226        .add_path = lpp_add_path,
 227        .fail_path = lpp_fail_path,
 228        .reinstate_path = lpp_reinstate_path,
 229        .select_path = lpp_select_path,
 230        .end_io = lpp_end_io,
 231 };
 232
 233 static int __init dm_lpp_init(void)
 234 {
 235        int r = dm_register_path_selector(&lpp_ps);
 236
 237        if (r < 0)
 238                 DMERR("register failed %d", r);
 239
 240        DMINFO("version 1.0.0 loaded");
 241
 242        return r;
 243 }
 244
 245 static void __exit dm_lpp_exit(void)
 246 {
 247        int r = dm_unregister_path_selector(&lpp_ps);
 248
 249        if (r < 0)
 250                 DMERR("unregister failed %d", r);
 251 }
 252
 253 module_init(dm_lpp_init);
 254 module_exit(dm_lpp_exit);
 255
 256 MODULE_DESCRIPTION(DM_NAME " least-pending multipath path selector");
 257 MODULE_AUTHOR("Sakshi Chaitanya Veni <vsakshi@hp.com>");
 258 MODULE_LICENSE("GPL");
 259