git.oblomov.eu Git - linux-2.6/blob - drivers/md/dm-mpath.c

   1 /*
   2  * Copyright (C) 2003 Sistina Software Limited.
   3  * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
   4  *
   5  * This file is released under the GPL.
   6  */
   7
   8 #include <linux/device-mapper.h>
   9
  10 #include "dm-path-selector.h"
  11 #include "dm-bio-record.h"
  12 #include "dm-uevent.h"
  13
  14 #include <linux/ctype.h>
  15 #include <linux/init.h>
  16 #include <linux/mempool.h>
  17 #include <linux/module.h>
  18 #include <linux/pagemap.h>
  19 #include <linux/slab.h>
  20 #include <linux/time.h>
  21 #include <linux/workqueue.h>
  22 #include <scsi/scsi_dh.h>
  23 #include <asm/atomic.h>
  24
  25 #define DM_MSG_PREFIX "multipath"
  26 #define MESG_STR(x) x, sizeof(x)
  27
  28 /* Path properties */
  29 struct pgpath {
  30         struct list_head list;
  31
  32         struct priority_group *pg;      /* Owning PG */
  33         unsigned is_active;             /* Path status */
  34         unsigned fail_count;            /* Cumulative failure count */
  35
  36         struct dm_path path;
  37         struct work_struct deactivate_path;
  38 };
  39
  40 #define path_to_pgpath(__pgp) container_of((__pgp), struct pgpath, path)
  41
  42 /*
  43  * Paths are grouped into Priority Groups and numbered from 1 upwards.
  44  * Each has a path selector which controls which path gets used.
  45  */
  46 struct priority_group {
  47         struct list_head list;
  48
  49         struct multipath *m;            /* Owning multipath instance */
  50         struct path_selector ps;
  51
  52         unsigned pg_num;                /* Reference number */
  53         unsigned bypassed;              /* Temporarily bypass this PG? */
  54
  55         unsigned nr_pgpaths;            /* Number of paths in PG */
  56         struct list_head pgpaths;
  57 };
  58
  59 /* Multipath context */
  60 struct multipath {
  61         struct list_head list;
  62         struct dm_target *ti;
  63
  64         spinlock_t lock;
  65
  66         const char *hw_handler_name;
  67         struct work_struct activate_path;
  68         struct pgpath *pgpath_to_activate;
  69         unsigned nr_priority_groups;
  70         struct list_head priority_groups;
  71         unsigned pg_init_required;      /* pg_init needs calling? */
  72         unsigned pg_init_in_progress;   /* Only one pg_init allowed at once */
  73
  74         unsigned nr_valid_paths;        /* Total number of usable paths */
  75         struct pgpath *current_pgpath;
  76         struct priority_group *current_pg;
  77         struct priority_group *next_pg; /* Switch to this PG if set */
  78         unsigned repeat_count;          /* I/Os left before calling PS again */
  79
  80         unsigned queue_io;              /* Must we queue all I/O? */
  81         unsigned queue_if_no_path;      /* Queue I/O if last path fails? */
  82         unsigned saved_queue_if_no_path;/* Saved state during suspension */
  83         unsigned pg_init_retries;       /* Number of times to retry pg_init */
  84         unsigned pg_init_count;         /* Number of times pg_init called */
  85
  86         struct work_struct process_queued_ios;
  87         struct bio_list queued_ios;
  88         unsigned queue_size;
  89
  90         struct work_struct trigger_event;
  91
  92         /*
  93          * We must use a mempool of dm_mpath_io structs so that we
  94          * can resubmit bios on error.
  95          */
  96         mempool_t *mpio_pool;
  97 };
  98
  99 /*
 100  * Context information attached to each bio we process.
 101  */
 102 struct dm_mpath_io {
 103         struct pgpath *pgpath;
 104         struct dm_bio_details details;
 105 };
 106
 107 typedef int (*action_fn) (struct pgpath *pgpath);
 108
 109 #define MIN_IOS 256     /* Mempool size */
 110
 111 static struct kmem_cache *_mpio_cache;
 112
 113 static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
 114 static void process_queued_ios(struct work_struct *work);
 115 static void trigger_event(struct work_struct *work);
 116 static void activate_path(struct work_struct *work);
 117 static void deactivate_path(struct work_struct *work);
 118
 119
 120 /*-----------------------------------------------
 121  * Allocation routines
 122  *-----------------------------------------------*/
 123
 124 static struct pgpath *alloc_pgpath(void)
 125 {
 126         struct pgpath *pgpath = kzalloc(sizeof(*pgpath), GFP_KERNEL);
 127
 128         if (pgpath) {
 129                 pgpath->is_active = 1;
 130                 INIT_WORK(&pgpath->deactivate_path, deactivate_path);
 131         }
 132
 133         return pgpath;
 134 }
 135
 136 static void free_pgpath(struct pgpath *pgpath)
 137 {
 138         kfree(pgpath);
 139 }
 140
 141 static void deactivate_path(struct work_struct *work)
 142 {
 143         struct pgpath *pgpath =
 144                 container_of(work, struct pgpath, deactivate_path);
 145
 146         blk_abort_queue(pgpath->path.dev->bdev->bd_disk->queue);
 147 }
 148
 149 static struct priority_group *alloc_priority_group(void)
 150 {
 151         struct priority_group *pg;
 152
 153         pg = kzalloc(sizeof(*pg), GFP_KERNEL);
 154
 155         if (pg)
 156                 INIT_LIST_HEAD(&pg->pgpaths);
 157
 158         return pg;
 159 }
 160
 161 static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
 162 {
 163         unsigned long flags;
 164         struct pgpath *pgpath, *tmp;
 165         struct multipath *m = ti->private;
 166
 167         list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
 168                 list_del(&pgpath->list);
 169                 if (m->hw_handler_name)
 170                         scsi_dh_detach(bdev_get_queue(pgpath->path.dev->bdev));
 171                 dm_put_device(ti, pgpath->path.dev);
 172                 spin_lock_irqsave(&m->lock, flags);
 173                 if (m->pgpath_to_activate == pgpath)
 174                         m->pgpath_to_activate = NULL;
 175                 spin_unlock_irqrestore(&m->lock, flags);
 176                 free_pgpath(pgpath);
 177         }
 178 }
 179
 180 static void free_priority_group(struct priority_group *pg,
 181                                 struct dm_target *ti)
 182 {
 183         struct path_selector *ps = &pg->ps;
 184
 185         if (ps->type) {
 186                 ps->type->destroy(ps);
 187                 dm_put_path_selector(ps->type);
 188         }
 189
 190         free_pgpaths(&pg->pgpaths, ti);
 191         kfree(pg);
 192 }
 193
 194 static struct multipath *alloc_multipath(struct dm_target *ti)
 195 {
 196         struct multipath *m;
 197
 198         m = kzalloc(sizeof(*m), GFP_KERNEL);
 199         if (m) {
 200                 INIT_LIST_HEAD(&m->priority_groups);
 201                 spin_lock_init(&m->lock);
 202                 m->queue_io = 1;
 203                 INIT_WORK(&m->process_queued_ios, process_queued_ios);
 204                 INIT_WORK(&m->trigger_event, trigger_event);
 205                 INIT_WORK(&m->activate_path, activate_path);
 206                 m->mpio_pool = mempool_create_slab_pool(MIN_IOS, _mpio_cache);
 207                 if (!m->mpio_pool) {
 208                         kfree(m);
 209                         return NULL;
 210                 }
 211                 m->ti = ti;
 212                 ti->private = m;
 213         }
 214
 215         return m;
 216 }
 217
 218 static void free_multipath(struct multipath *m)
 219 {
 220         struct priority_group *pg, *tmp;
 221
 222         list_for_each_entry_safe(pg, tmp, &m->priority_groups, list) {
 223                 list_del(&pg->list);
 224                 free_priority_group(pg, m->ti);
 225         }
 226
 227         kfree(m->hw_handler_name);
 228         mempool_destroy(m->mpio_pool);
 229         kfree(m);
 230 }
 231
 232
 233 /*-----------------------------------------------
 234  * Path selection
 235  *-----------------------------------------------*/
 236
 237 static void __switch_pg(struct multipath *m, struct pgpath *pgpath)
 238 {
 239         m->current_pg = pgpath->pg;
 240
 241         /* Must we initialise the PG first, and queue I/O till it's ready? */
 242         if (m->hw_handler_name) {
 243                 m->pg_init_required = 1;
 244                 m->queue_io = 1;
 245         } else {
 246                 m->pg_init_required = 0;
 247                 m->queue_io = 0;
 248         }
 249
 250         m->pg_init_count = 0;
 251 }
 252
 253 static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
 254 {
 255         struct dm_path *path;
 256
 257         path = pg->ps.type->select_path(&pg->ps, &m->repeat_count);
 258         if (!path)
 259                 return -ENXIO;
 260
 261         m->current_pgpath = path_to_pgpath(path);
 262
 263         if (m->current_pg != pg)
 264                 __switch_pg(m, m->current_pgpath);
 265
 266         return 0;
 267 }
 268
 269 static void __choose_pgpath(struct multipath *m)
 270 {
 271         struct priority_group *pg;
 272         unsigned bypassed = 1;
 273
 274         if (!m->nr_valid_paths)
 275                 goto failed;
 276
 277         /* Were we instructed to switch PG? */
 278         if (m->next_pg) {
 279                 pg = m->next_pg;
 280                 m->next_pg = NULL;
 281                 if (!__choose_path_in_pg(m, pg))
 282                         return;
 283         }
 284
 285         /* Don't change PG until it has no remaining paths */
 286         if (m->current_pg && !__choose_path_in_pg(m, m->current_pg))
 287                 return;
 288
 289         /*
 290          * Loop through priority groups until we find a valid path.
 291          * First time we skip PGs marked 'bypassed'.
 292          * Second time we only try the ones we skipped.
 293          */
 294         do {
 295                 list_for_each_entry(pg, &m->priority_groups, list) {
 296                         if (pg->bypassed == bypassed)
 297                                 continue;
 298                         if (!__choose_path_in_pg(m, pg))
 299                                 return;
 300                 }
 301         } while (bypassed--);
 302
 303 failed:
 304         m->current_pgpath = NULL;
 305         m->current_pg = NULL;
 306 }
 307
 308 /*
 309  * Check whether bios must be queued in the device-mapper core rather
 310  * than here in the target.
 311  *
 312  * m->lock must be held on entry.
 313  *
 314  * If m->queue_if_no_path and m->saved_queue_if_no_path hold the
 315  * same value then we are not between multipath_presuspend()
 316  * and multipath_resume() calls and we have no need to check
 317  * for the DMF_NOFLUSH_SUSPENDING flag.
 318  */
 319 static int __must_push_back(struct multipath *m)
 320 {
 321         return (m->queue_if_no_path != m->saved_queue_if_no_path &&
 322                 dm_noflush_suspending(m->ti));
 323 }
 324
 325 static int map_io(struct multipath *m, struct bio *bio,
 326                   struct dm_mpath_io *mpio, unsigned was_queued)
 327 {
 328         int r = DM_MAPIO_REMAPPED;
 329         unsigned long flags;
 330         struct pgpath *pgpath;
 331
 332         spin_lock_irqsave(&m->lock, flags);
 333
 334         /* Do we need to select a new pgpath? */
 335         if (!m->current_pgpath ||
 336             (!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
 337                 __choose_pgpath(m);
 338
 339         pgpath = m->current_pgpath;
 340
 341         if (was_queued)
 342                 m->queue_size--;
 343
 344         if ((pgpath && m->queue_io) ||
 345             (!pgpath && m->queue_if_no_path)) {
 346                 /* Queue for the daemon to resubmit */
 347                 bio_list_add(&m->queued_ios, bio);
 348                 m->queue_size++;
 349                 if ((m->pg_init_required && !m->pg_init_in_progress) ||
 350                     !m->queue_io)
 351                         queue_work(kmultipathd, &m->process_queued_ios);
 352                 pgpath = NULL;
 353                 r = DM_MAPIO_SUBMITTED;
 354         } else if (pgpath)
 355                 bio->bi_bdev = pgpath->path.dev->bdev;
 356         else if (__must_push_back(m))
 357                 r = DM_MAPIO_REQUEUE;
 358         else
 359                 r = -EIO;       /* Failed */
 360
 361         mpio->pgpath = pgpath;
 362
 363         spin_unlock_irqrestore(&m->lock, flags);
 364
 365         return r;
 366 }
 367
 368 /*
 369  * If we run out of usable paths, should we queue I/O or error it?
 370  */
 371 static int queue_if_no_path(struct multipath *m, unsigned queue_if_no_path,
 372                             unsigned save_old_value)
 373 {
 374         unsigned long flags;
 375
 376         spin_lock_irqsave(&m->lock, flags);
 377
 378         if (save_old_value)
 379                 m->saved_queue_if_no_path = m->queue_if_no_path;
 380         else
 381                 m->saved_queue_if_no_path = queue_if_no_path;
 382         m->queue_if_no_path = queue_if_no_path;
 383         if (!m->queue_if_no_path && m->queue_size)
 384                 queue_work(kmultipathd, &m->process_queued_ios);
 385
 386         spin_unlock_irqrestore(&m->lock, flags);
 387
 388         return 0;
 389 }
 390
 391 /*-----------------------------------------------------------------
 392  * The multipath daemon is responsible for resubmitting queued ios.
 393  *---------------------------------------------------------------*/
 394
 395 static void dispatch_queued_ios(struct multipath *m)
 396 {
 397         int r;
 398         unsigned long flags;
 399         struct bio *bio = NULL, *next;
 400         struct dm_mpath_io *mpio;
 401         union map_info *info;
 402
 403         spin_lock_irqsave(&m->lock, flags);
 404         bio = bio_list_get(&m->queued_ios);
 405         spin_unlock_irqrestore(&m->lock, flags);
 406
 407         while (bio) {
 408                 next = bio->bi_next;
 409                 bio->bi_next = NULL;
 410
 411                 info = dm_get_mapinfo(bio);
 412                 mpio = info->ptr;
 413
 414                 r = map_io(m, bio, mpio, 1);
 415                 if (r < 0)
 416                         bio_endio(bio, r);
 417                 else if (r == DM_MAPIO_REMAPPED)
 418                         generic_make_request(bio);
 419                 else if (r == DM_MAPIO_REQUEUE)
 420                         bio_endio(bio, -EIO);
 421
 422                 bio = next;
 423         }
 424 }
 425
 426 static void process_queued_ios(struct work_struct *work)
 427 {
 428         struct multipath *m =
 429                 container_of(work, struct multipath, process_queued_ios);
 430         struct pgpath *pgpath = NULL;
 431         unsigned init_required = 0, must_queue = 1;
 432         unsigned long flags;
 433
 434         spin_lock_irqsave(&m->lock, flags);
 435
 436         if (!m->queue_size)
 437                 goto out;
 438
 439         if (!m->current_pgpath)
 440                 __choose_pgpath(m);
 441
 442         pgpath = m->current_pgpath;
 443
 444         if ((pgpath && !m->queue_io) ||
 445             (!pgpath && !m->queue_if_no_path))
 446                 must_queue = 0;
 447
 448         if (m->pg_init_required && !m->pg_init_in_progress && pgpath) {
 449                 m->pgpath_to_activate = pgpath;
 450                 m->pg_init_count++;
 451                 m->pg_init_required = 0;
 452                 m->pg_init_in_progress = 1;
 453                 init_required = 1;
 454         }
 455
 456 out:
 457         spin_unlock_irqrestore(&m->lock, flags);
 458
 459         if (init_required)
 460                 queue_work(kmpath_handlerd, &m->activate_path);
 461
 462         if (!must_queue)
 463                 dispatch_queued_ios(m);
 464 }
 465
 466 /*
 467  * An event is triggered whenever a path is taken out of use.
 468  * Includes path failure and PG bypass.
 469  */
 470 static void trigger_event(struct work_struct *work)
 471 {
 472         struct multipath *m =
 473                 container_of(work, struct multipath, trigger_event);
 474
 475         dm_table_event(m->ti->table);
 476 }
 477
 478 /*-----------------------------------------------------------------
 479  * Constructor/argument parsing:
 480  * <#multipath feature args> [<arg>]*
 481  * <#hw_handler args> [hw_handler [<arg>]*]
 482  * <#priority groups>
 483  * <initial priority group>
 484  *     [<selector> <#selector args> [<arg>]*
 485  *      <#paths> <#per-path selector args>
 486  *         [<path> [<arg>]* ]+ ]+
 487  *---------------------------------------------------------------*/
 488 struct param {
 489         unsigned min;
 490         unsigned max;
 491         char *error;
 492 };
 493
 494 static int read_param(struct param *param, char *str, unsigned *v, char **error)
 495 {
 496         if (!str ||
 497             (sscanf(str, "%u", v) != 1) ||
 498             (*v < param->min) ||
 499             (*v > param->max)) {
 500                 *error = param->error;
 501                 return -EINVAL;
 502         }
 503
 504         return 0;
 505 }
 506
 507 struct arg_set {
 508         unsigned argc;
 509         char **argv;
 510 };
 511
 512 static char *shift(struct arg_set *as)
 513 {
 514         char *r;
 515
 516         if (as->argc) {
 517                 as->argc--;
 518                 r = *as->argv;
 519                 as->argv++;
 520                 return r;
 521         }
 522
 523         return NULL;
 524 }
 525
 526 static void consume(struct arg_set *as, unsigned n)
 527 {
 528         BUG_ON (as->argc < n);
 529         as->argc -= n;
 530         as->argv += n;
 531 }
 532
 533 static int parse_path_selector(struct arg_set *as, struct priority_group *pg,
 534                                struct dm_target *ti)
 535 {
 536         int r;
 537         struct path_selector_type *pst;
 538         unsigned ps_argc;
 539
 540         static struct param _params[] = {
 541                 {0, 1024, "invalid number of path selector args"},
 542         };
 543
 544         pst = dm_get_path_selector(shift(as));
 545         if (!pst) {
 546                 ti->error = "unknown path selector type";
 547                 return -EINVAL;
 548         }
 549
 550         r = read_param(_params, shift(as), &ps_argc, &ti->error);
 551         if (r) {
 552                 dm_put_path_selector(pst);
 553                 return -EINVAL;
 554         }
 555
 556         r = pst->create(&pg->ps, ps_argc, as->argv);
 557         if (r) {
 558                 dm_put_path_selector(pst);
 559                 ti->error = "path selector constructor failed";
 560                 return r;
 561         }
 562
 563         pg->ps.type = pst;
 564         consume(as, ps_argc);
 565
 566         return 0;
 567 }
 568
 569 static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
 570                                struct dm_target *ti)
 571 {
 572         int r;
 573         struct pgpath *p;
 574         struct multipath *m = ti->private;
 575
 576         /* we need at least a path arg */
 577         if (as->argc < 1) {
 578                 ti->error = "no device given";
 579                 return ERR_PTR(-EINVAL);
 580         }
 581
 582         p = alloc_pgpath();
 583         if (!p)
 584                 return ERR_PTR(-ENOMEM);
 585
 586         r = dm_get_device(ti, shift(as), ti->begin, ti->len,
 587                           dm_table_get_mode(ti->table), &p->path.dev);
 588         if (r) {
 589                 ti->error = "error getting device";
 590                 goto bad;
 591         }
 592
 593         if (m->hw_handler_name) {
 594                 r = scsi_dh_attach(bdev_get_queue(p->path.dev->bdev),
 595                                    m->hw_handler_name);
 596                 if (r < 0) {
 597                         dm_put_device(ti, p->path.dev);
 598                         goto bad;
 599                 }
 600         }
 601
 602         r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
 603         if (r) {
 604                 dm_put_device(ti, p->path.dev);
 605                 goto bad;
 606         }
 607
 608         return p;
 609
 610  bad:
 611         free_pgpath(p);
 612         return ERR_PTR(r);
 613 }
 614
 615 static struct priority_group *parse_priority_group(struct arg_set *as,
 616                                                    struct multipath *m)
 617 {
 618         static struct param _params[] = {
 619                 {1, 1024, "invalid number of paths"},
 620                 {0, 1024, "invalid number of selector args"}
 621         };
 622
 623         int r;
 624         unsigned i, nr_selector_args, nr_params;
 625         struct priority_group *pg;
 626         struct dm_target *ti = m->ti;
 627
 628         if (as->argc < 2) {
 629                 as->argc = 0;
 630                 ti->error = "not enough priority group arguments";
 631                 return ERR_PTR(-EINVAL);
 632         }
 633
 634         pg = alloc_priority_group();
 635         if (!pg) {
 636                 ti->error = "couldn't allocate priority group";
 637                 return ERR_PTR(-ENOMEM);
 638         }
 639         pg->m = m;
 640
 641         r = parse_path_selector(as, pg, ti);
 642         if (r)
 643                 goto bad;
 644
 645         /*
 646          * read the paths
 647          */
 648         r = read_param(_params, shift(as), &pg->nr_pgpaths, &ti->error);
 649         if (r)
 650                 goto bad;
 651
 652         r = read_param(_params + 1, shift(as), &nr_selector_args, &ti->error);
 653         if (r)
 654                 goto bad;
 655
 656         nr_params = 1 + nr_selector_args;
 657         for (i = 0; i < pg->nr_pgpaths; i++) {
 658                 struct pgpath *pgpath;
 659                 struct arg_set path_args;
 660
 661                 if (as->argc < nr_params) {
 662                         ti->error = "not enough path parameters";
 663                         goto bad;
 664                 }
 665
 666                 path_args.argc = nr_params;
 667                 path_args.argv = as->argv;
 668
 669                 pgpath = parse_path(&path_args, &pg->ps, ti);
 670                 if (IS_ERR(pgpath)) {
 671                         r = PTR_ERR(pgpath);
 672                         goto bad;
 673                 }
 674
 675                 pgpath->pg = pg;
 676                 list_add_tail(&pgpath->list, &pg->pgpaths);
 677                 consume(as, nr_params);
 678         }
 679
 680         return pg;
 681
 682  bad:
 683         free_priority_group(pg, ti);
 684         return ERR_PTR(r);
 685 }
 686
 687 static int parse_hw_handler(struct arg_set *as, struct multipath *m)
 688 {
 689         unsigned hw_argc;
 690         struct dm_target *ti = m->ti;
 691
 692         static struct param _params[] = {
 693                 {0, 1024, "invalid number of hardware handler args"},
 694         };
 695
 696         if (read_param(_params, shift(as), &hw_argc, &ti->error))
 697                 return -EINVAL;
 698
 699         if (!hw_argc)
 700                 return 0;
 701
 702         m->hw_handler_name = kstrdup(shift(as), GFP_KERNEL);
 703         request_module("scsi_dh_%s", m->hw_handler_name);
 704         if (scsi_dh_handler_exist(m->hw_handler_name) == 0) {
 705                 ti->error = "unknown hardware handler type";
 706                 kfree(m->hw_handler_name);
 707                 m->hw_handler_name = NULL;
 708                 return -EINVAL;
 709         }
 710
 711         if (hw_argc > 1)
 712                 DMWARN("Ignoring user-specified arguments for "
 713                        "hardware handler \"%s\"", m->hw_handler_name);
 714         consume(as, hw_argc - 1);
 715
 716         return 0;
 717 }
 718
 719 static int parse_features(struct arg_set *as, struct multipath *m)
 720 {
 721         int r;
 722         unsigned argc;
 723         struct dm_target *ti = m->ti;
 724         const char *param_name;
 725
 726         static struct param _params[] = {
 727                 {0, 3, "invalid number of feature args"},
 728                 {1, 50, "pg_init_retries must be between 1 and 50"},
 729         };
 730
 731         r = read_param(_params, shift(as), &argc, &ti->error);
 732         if (r)
 733                 return -EINVAL;
 734
 735         if (!argc)
 736                 return 0;
 737
 738         do {
 739                 param_name = shift(as);
 740                 argc--;
 741
 742                 if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
 743                         r = queue_if_no_path(m, 1, 0);
 744                         continue;
 745                 }
 746
 747                 if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
 748                     (argc >= 1)) {
 749                         r = read_param(_params + 1, shift(as),
 750                                        &m->pg_init_retries, &ti->error);
 751                         argc--;
 752                         continue;
 753                 }
 754
 755                 ti->error = "Unrecognised multipath feature request";
 756                 r = -EINVAL;
 757         } while (argc && !r);
 758
 759         return r;
 760 }
 761
 762 static int multipath_ctr(struct dm_target *ti, unsigned int argc,
 763                          char **argv)
 764 {
 765         /* target parameters */
 766         static struct param _params[] = {
 767                 {1, 1024, "invalid number of priority groups"},
 768                 {1, 1024, "invalid initial priority group number"},
 769         };
 770
 771         int r;
 772         struct multipath *m;
 773         struct arg_set as;
 774         unsigned pg_count = 0;
 775         unsigned next_pg_num;
 776
 777         as.argc = argc;
 778         as.argv = argv;
 779
 780         m = alloc_multipath(ti);
 781         if (!m) {
 782                 ti->error = "can't allocate multipath";
 783                 return -EINVAL;
 784         }
 785
 786         r = parse_features(&as, m);
 787         if (r)
 788                 goto bad;
 789
 790         r = parse_hw_handler(&as, m);
 791         if (r)
 792                 goto bad;
 793
 794         r = read_param(_params, shift(&as), &m->nr_priority_groups, &ti->error);
 795         if (r)
 796                 goto bad;
 797
 798         r = read_param(_params + 1, shift(&as), &next_pg_num, &ti->error);
 799         if (r)
 800                 goto bad;
 801
 802         /* parse the priority groups */
 803         while (as.argc) {
 804                 struct priority_group *pg;
 805
 806                 pg = parse_priority_group(&as, m);
 807                 if (IS_ERR(pg)) {
 808                         r = PTR_ERR(pg);
 809                         goto bad;
 810                 }
 811
 812                 m->nr_valid_paths += pg->nr_pgpaths;
 813                 list_add_tail(&pg->list, &m->priority_groups);
 814                 pg_count++;
 815                 pg->pg_num = pg_count;
 816                 if (!--next_pg_num)
 817                         m->next_pg = pg;
 818         }
 819
 820         if (pg_count != m->nr_priority_groups) {
 821                 ti->error = "priority group count mismatch";
 822                 r = -EINVAL;
 823                 goto bad;
 824         }
 825
 826         return 0;
 827
 828  bad:
 829         free_multipath(m);
 830         return r;
 831 }
 832
 833 static void multipath_dtr(struct dm_target *ti)
 834 {
 835         struct multipath *m = (struct multipath *) ti->private;
 836
 837         flush_workqueue(kmpath_handlerd);
 838         flush_workqueue(kmultipathd);
 839         free_multipath(m);
 840 }
 841
 842 /*
 843  * Map bios, recording original fields for later in case we have to resubmit
 844  */
 845 static int multipath_map(struct dm_target *ti, struct bio *bio,
 846                          union map_info *map_context)
 847 {
 848         int r;
 849         struct dm_mpath_io *mpio;
 850         struct multipath *m = (struct multipath *) ti->private;
 851
 852         mpio = mempool_alloc(m->mpio_pool, GFP_NOIO);
 853         dm_bio_record(&mpio->details, bio);
 854
 855         map_context->ptr = mpio;
 856         bio->bi_rw |= (1 << BIO_RW_FAILFAST_TRANSPORT);
 857         r = map_io(m, bio, mpio, 0);
 858         if (r < 0 || r == DM_MAPIO_REQUEUE)
 859                 mempool_free(mpio, m->mpio_pool);
 860
 861         return r;
 862 }
 863
 864 /*
 865  * Take a path out of use.
 866  */
 867 static int fail_path(struct pgpath *pgpath)
 868 {
 869         unsigned long flags;
 870         struct multipath *m = pgpath->pg->m;
 871
 872         spin_lock_irqsave(&m->lock, flags);
 873
 874         if (!pgpath->is_active)
 875                 goto out;
 876
 877         DMWARN("Failing path %s.", pgpath->path.dev->name);
 878
 879         pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
 880         pgpath->is_active = 0;
 881         pgpath->fail_count++;
 882
 883         m->nr_valid_paths--;
 884
 885         if (pgpath == m->current_pgpath)
 886                 m->current_pgpath = NULL;
 887
 888         dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
 889                       pgpath->path.dev->name, m->nr_valid_paths);
 890
 891         schedule_work(&m->trigger_event);
 892         queue_work(kmultipathd, &pgpath->deactivate_path);
 893
 894 out:
 895         spin_unlock_irqrestore(&m->lock, flags);
 896
 897         return 0;
 898 }
 899
 900 /*
 901  * Reinstate a previously-failed path
 902  */
 903 static int reinstate_path(struct pgpath *pgpath)
 904 {
 905         int r = 0;
 906         unsigned long flags;
 907         struct multipath *m = pgpath->pg->m;
 908
 909         spin_lock_irqsave(&m->lock, flags);
 910
 911         if (pgpath->is_active)
 912                 goto out;
 913
 914         if (!pgpath->pg->ps.type->reinstate_path) {
 915                 DMWARN("Reinstate path not supported by path selector %s",
 916                        pgpath->pg->ps.type->name);
 917                 r = -EINVAL;
 918                 goto out;
 919         }
 920
 921         r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
 922         if (r)
 923                 goto out;
 924
 925         pgpath->is_active = 1;
 926
 927         m->current_pgpath = NULL;
 928         if (!m->nr_valid_paths++ && m->queue_size)
 929                 queue_work(kmultipathd, &m->process_queued_ios);
 930
 931         dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
 932                       pgpath->path.dev->name, m->nr_valid_paths);
 933
 934         schedule_work(&m->trigger_event);
 935
 936 out:
 937         spin_unlock_irqrestore(&m->lock, flags);
 938
 939         return r;
 940 }
 941
 942 /*
 943  * Fail or reinstate all paths that match the provided struct dm_dev.
 944  */
 945 static int action_dev(struct multipath *m, struct dm_dev *dev,
 946                       action_fn action)
 947 {
 948         int r = 0;
 949         struct pgpath *pgpath;
 950         struct priority_group *pg;
 951
 952         list_for_each_entry(pg, &m->priority_groups, list) {
 953                 list_for_each_entry(pgpath, &pg->pgpaths, list) {
 954                         if (pgpath->path.dev == dev)
 955                                 r = action(pgpath);
 956                 }
 957         }
 958
 959         return r;
 960 }
 961
 962 /*
 963  * Temporarily try to avoid having to use the specified PG
 964  */
 965 static void bypass_pg(struct multipath *m, struct priority_group *pg,
 966                       int bypassed)
 967 {
 968         unsigned long flags;
 969
 970         spin_lock_irqsave(&m->lock, flags);
 971
 972         pg->bypassed = bypassed;
 973         m->current_pgpath = NULL;
 974         m->current_pg = NULL;
 975
 976         spin_unlock_irqrestore(&m->lock, flags);
 977
 978         schedule_work(&m->trigger_event);
 979 }
 980
 981 /*
 982  * Switch to using the specified PG from the next I/O that gets mapped
 983  */
 984 static int switch_pg_num(struct multipath *m, const char *pgstr)
 985 {
 986         struct priority_group *pg;
 987         unsigned pgnum;
 988         unsigned long flags;
 989
 990         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
 991             (pgnum > m->nr_priority_groups)) {
 992                 DMWARN("invalid PG number supplied to switch_pg_num");
 993                 return -EINVAL;
 994         }
 995
 996         spin_lock_irqsave(&m->lock, flags);
 997         list_for_each_entry(pg, &m->priority_groups, list) {
 998                 pg->bypassed = 0;
 999                 if (--pgnum)
1000                         continue;
1001
1002                 m->current_pgpath = NULL;
1003                 m->current_pg = NULL;
1004                 m->next_pg = pg;
1005         }
1006         spin_unlock_irqrestore(&m->lock, flags);
1007
1008         schedule_work(&m->trigger_event);
1009         return 0;
1010 }
1011
1012 /*
1013  * Set/clear bypassed status of a PG.
1014  * PGs are numbered upwards from 1 in the order they were declared.
1015  */
1016 static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypassed)
1017 {
1018         struct priority_group *pg;
1019         unsigned pgnum;
1020
1021         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
1022             (pgnum > m->nr_priority_groups)) {
1023                 DMWARN("invalid PG number supplied to bypass_pg");
1024                 return -EINVAL;
1025         }
1026
1027         list_for_each_entry(pg, &m->priority_groups, list) {
1028                 if (!--pgnum)
1029                         break;
1030         }
1031
1032         bypass_pg(m, pg, bypassed);
1033         return 0;
1034 }
1035
1036 /*
1037  * Should we retry pg_init immediately?
1038  */
1039 static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
1040 {
1041         unsigned long flags;
1042         int limit_reached = 0;
1043
1044         spin_lock_irqsave(&m->lock, flags);
1045
1046         if (m->pg_init_count <= m->pg_init_retries)
1047                 m->pg_init_required = 1;
1048         else
1049                 limit_reached = 1;
1050
1051         spin_unlock_irqrestore(&m->lock, flags);
1052
1053         return limit_reached;
1054 }
1055
1056 static void pg_init_done(struct dm_path *path, int errors)
1057 {
1058         struct pgpath *pgpath = path_to_pgpath(path);
1059         struct priority_group *pg = pgpath->pg;
1060         struct multipath *m = pg->m;
1061         unsigned long flags;
1062
1063         /* device or driver problems */
1064         switch (errors) {
1065         case SCSI_DH_OK:
1066                 break;
1067         case SCSI_DH_NOSYS:
1068                 if (!m->hw_handler_name) {
1069                         errors = 0;
1070                         break;
1071                 }
1072                 DMERR("Cannot failover device because scsi_dh_%s was not "
1073                       "loaded.", m->hw_handler_name);
1074                 /*
1075                  * Fail path for now, so we do not ping pong
1076                  */
1077                 fail_path(pgpath);
1078                 break;
1079         case SCSI_DH_DEV_TEMP_BUSY:
1080                 /*
1081                  * Probably doing something like FW upgrade on the
1082                  * controller so try the other pg.
1083                  */
1084                 bypass_pg(m, pg, 1);
1085                 break;
1086         /* TODO: For SCSI_DH_RETRY we should wait a couple seconds */
1087         case SCSI_DH_RETRY:
1088         case SCSI_DH_IMM_RETRY:
1089         case SCSI_DH_RES_TEMP_UNAVAIL:
1090                 if (pg_init_limit_reached(m, pgpath))
1091                         fail_path(pgpath);
1092                 errors = 0;
1093                 break;
1094         default:
1095                 /*
1096                  * We probably do not want to fail the path for a device
1097                  * error, but this is what the old dm did. In future
1098                  * patches we can do more advanced handling.
1099                  */
1100                 fail_path(pgpath);
1101         }
1102
1103         spin_lock_irqsave(&m->lock, flags);
1104         if (errors) {
1105                 DMERR("Could not failover device. Error %d.", errors);
1106                 m->current_pgpath = NULL;
1107                 m->current_pg = NULL;
1108         } else if (!m->pg_init_required) {
1109                 m->queue_io = 0;
1110                 pg->bypassed = 0;
1111         }
1112
1113         m->pg_init_in_progress = 0;
1114         queue_work(kmultipathd, &m->process_queued_ios);
1115         spin_unlock_irqrestore(&m->lock, flags);
1116 }
1117
1118 static void activate_path(struct work_struct *work)
1119 {
1120         int ret;
1121         struct multipath *m =
1122                 container_of(work, struct multipath, activate_path);
1123         struct dm_path *path;
1124         unsigned long flags;
1125
1126         spin_lock_irqsave(&m->lock, flags);
1127         path = &m->pgpath_to_activate->path;
1128         m->pgpath_to_activate = NULL;
1129         spin_unlock_irqrestore(&m->lock, flags);
1130         if (!path)
1131                 return;
1132         ret = scsi_dh_activate(bdev_get_queue(path->dev->bdev));
1133         pg_init_done(path, ret);
1134 }
1135
1136 /*
1137  * end_io handling
1138  */
1139 static int do_end_io(struct multipath *m, struct bio *bio,
1140                      int error, struct dm_mpath_io *mpio)
1141 {
1142         unsigned long flags;
1143
1144         if (!error)
1145                 return 0;       /* I/O complete */
1146
1147         if ((error == -EWOULDBLOCK) && bio_rw_ahead(bio))
1148                 return error;
1149
1150         if (error == -EOPNOTSUPP)
1151                 return error;
1152
1153         spin_lock_irqsave(&m->lock, flags);
1154         if (!m->nr_valid_paths) {
1155                 if (__must_push_back(m)) {
1156                         spin_unlock_irqrestore(&m->lock, flags);
1157                         return DM_ENDIO_REQUEUE;
1158                 } else if (!m->queue_if_no_path) {
1159                         spin_unlock_irqrestore(&m->lock, flags);
1160                         return -EIO;
1161                 } else {
1162                         spin_unlock_irqrestore(&m->lock, flags);
1163                         goto requeue;
1164                 }
1165         }
1166         spin_unlock_irqrestore(&m->lock, flags);
1167
1168         if (mpio->pgpath)
1169                 fail_path(mpio->pgpath);
1170
1171       requeue:
1172         dm_bio_restore(&mpio->details, bio);
1173
1174         /* queue for the daemon to resubmit or fail */
1175         spin_lock_irqsave(&m->lock, flags);
1176         bio_list_add(&m->queued_ios, bio);
1177         m->queue_size++;
1178         if (!m->queue_io)
1179                 queue_work(kmultipathd, &m->process_queued_ios);
1180         spin_unlock_irqrestore(&m->lock, flags);
1181
1182         return DM_ENDIO_INCOMPLETE;     /* io not complete */
1183 }
1184
1185 static int multipath_end_io(struct dm_target *ti, struct bio *bio,
1186                             int error, union map_info *map_context)
1187 {
1188         struct multipath *m = ti->private;
1189         struct dm_mpath_io *mpio = map_context->ptr;
1190         struct pgpath *pgpath = mpio->pgpath;
1191         struct path_selector *ps;
1192         int r;
1193
1194         r  = do_end_io(m, bio, error, mpio);
1195         if (pgpath) {
1196                 ps = &pgpath->pg->ps;
1197                 if (ps->type->end_io)
1198                         ps->type->end_io(ps, &pgpath->path);
1199         }
1200         if (r != DM_ENDIO_INCOMPLETE)
1201                 mempool_free(mpio, m->mpio_pool);
1202
1203         return r;
1204 }
1205
1206 /*
1207  * Suspend can't complete until all the I/O is processed so if
1208  * the last path fails we must error any remaining I/O.
1209  * Note that if the freeze_bdev fails while suspending, the
1210  * queue_if_no_path state is lost - userspace should reset it.
1211  */
1212 static void multipath_presuspend(struct dm_target *ti)
1213 {
1214         struct multipath *m = (struct multipath *) ti->private;
1215
1216         queue_if_no_path(m, 0, 1);
1217 }
1218
1219 /*
1220  * Restore the queue_if_no_path setting.
1221  */
1222 static void multipath_resume(struct dm_target *ti)
1223 {
1224         struct multipath *m = (struct multipath *) ti->private;
1225         unsigned long flags;
1226
1227         spin_lock_irqsave(&m->lock, flags);
1228         m->queue_if_no_path = m->saved_queue_if_no_path;
1229         spin_unlock_irqrestore(&m->lock, flags);
1230 }
1231
1232 /*
1233  * Info output has the following format:
1234  * num_multipath_feature_args [multipath_feature_args]*
1235  * num_handler_status_args [handler_status_args]*
1236  * num_groups init_group_number
1237  *            [A|D|E num_ps_status_args [ps_status_args]*
1238  *             num_paths num_selector_args
1239  *             [path_dev A|F fail_count [selector_args]* ]+ ]+
1240  *
1241  * Table output has the following format (identical to the constructor string):
1242  * num_feature_args [features_args]*
1243  * num_handler_args hw_handler [hw_handler_args]*
1244  * num_groups init_group_number
1245  *     [priority selector-name num_ps_args [ps_args]*
1246  *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
1247  */
1248 static int multipath_status(struct dm_target *ti, status_type_t type,
1249                             char *result, unsigned int maxlen)
1250 {
1251         int sz = 0;
1252         unsigned long flags;
1253         struct multipath *m = (struct multipath *) ti->private;
1254         struct priority_group *pg;
1255         struct pgpath *p;
1256         unsigned pg_num;
1257         char state;
1258
1259         spin_lock_irqsave(&m->lock, flags);
1260
1261         /* Features */
1262         if (type == STATUSTYPE_INFO)
1263                 DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
1264         else {
1265                 DMEMIT("%u ", m->queue_if_no_path +
1266                               (m->pg_init_retries > 0) * 2);
1267                 if (m->queue_if_no_path)
1268                         DMEMIT("queue_if_no_path ");
1269                 if (m->pg_init_retries)
1270                         DMEMIT("pg_init_retries %u ", m->pg_init_retries);
1271         }
1272
1273         if (!m->hw_handler_name || type == STATUSTYPE_INFO)
1274                 DMEMIT("0 ");
1275         else
1276                 DMEMIT("1 %s ", m->hw_handler_name);
1277
1278         DMEMIT("%u ", m->nr_priority_groups);
1279
1280         if (m->next_pg)
1281                 pg_num = m->next_pg->pg_num;
1282         else if (m->current_pg)
1283                 pg_num = m->current_pg->pg_num;
1284         else
1285                         pg_num = 1;
1286
1287         DMEMIT("%u ", pg_num);
1288
1289         switch (type) {
1290         case STATUSTYPE_INFO:
1291                 list_for_each_entry(pg, &m->priority_groups, list) {
1292                         if (pg->bypassed)
1293                                 state = 'D';    /* Disabled */
1294                         else if (pg == m->current_pg)
1295                                 state = 'A';    /* Currently Active */
1296                         else
1297                                 state = 'E';    /* Enabled */
1298
1299                         DMEMIT("%c ", state);
1300
1301                         if (pg->ps.type->status)
1302                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1303                                                           result + sz,
1304                                                           maxlen - sz);
1305                         else
1306                                 DMEMIT("0 ");
1307
1308                         DMEMIT("%u %u ", pg->nr_pgpaths,
1309                                pg->ps.type->info_args);
1310
1311                         list_for_each_entry(p, &pg->pgpaths, list) {
1312                                 DMEMIT("%s %s %u ", p->path.dev->name,
1313                                        p->is_active ? "A" : "F",
1314                                        p->fail_count);
1315                                 if (pg->ps.type->status)
1316                                         sz += pg->ps.type->status(&pg->ps,
1317                                               &p->path, type, result + sz,
1318                                               maxlen - sz);
1319                         }
1320                 }
1321                 break;
1322
1323         case STATUSTYPE_TABLE:
1324                 list_for_each_entry(pg, &m->priority_groups, list) {
1325                         DMEMIT("%s ", pg->ps.type->name);
1326
1327                         if (pg->ps.type->status)
1328                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1329                                                           result + sz,
1330                                                           maxlen - sz);
1331                         else
1332                                 DMEMIT("0 ");
1333
1334                         DMEMIT("%u %u ", pg->nr_pgpaths,
1335                                pg->ps.type->table_args);
1336
1337                         list_for_each_entry(p, &pg->pgpaths, list) {
1338                                 DMEMIT("%s ", p->path.dev->name);
1339                                 if (pg->ps.type->status)
1340                                         sz += pg->ps.type->status(&pg->ps,
1341                                               &p->path, type, result + sz,
1342                                               maxlen - sz);
1343                         }
1344                 }
1345                 break;
1346         }
1347
1348         spin_unlock_irqrestore(&m->lock, flags);
1349
1350         return 0;
1351 }
1352
1353 static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
1354 {
1355         int r;
1356         struct dm_dev *dev;
1357         struct multipath *m = (struct multipath *) ti->private;
1358         action_fn action;
1359
1360         if (argc == 1) {
1361                 if (!strnicmp(argv[0], MESG_STR("queue_if_no_path")))
1362                         return queue_if_no_path(m, 1, 0);
1363                 else if (!strnicmp(argv[0], MESG_STR("fail_if_no_path")))
1364                         return queue_if_no_path(m, 0, 0);
1365         }
1366
1367         if (argc != 2)
1368                 goto error;
1369
1370         if (!strnicmp(argv[0], MESG_STR("disable_group")))
1371                 return bypass_pg_num(m, argv[1], 1);
1372         else if (!strnicmp(argv[0], MESG_STR("enable_group")))
1373                 return bypass_pg_num(m, argv[1], 0);
1374         else if (!strnicmp(argv[0], MESG_STR("switch_group")))
1375                 return switch_pg_num(m, argv[1]);
1376         else if (!strnicmp(argv[0], MESG_STR("reinstate_path")))
1377                 action = reinstate_path;
1378         else if (!strnicmp(argv[0], MESG_STR("fail_path")))
1379                 action = fail_path;
1380         else
1381                 goto error;
1382
1383         r = dm_get_device(ti, argv[1], ti->begin, ti->len,
1384                           dm_table_get_mode(ti->table), &dev);
1385         if (r) {
1386                 DMWARN("message: error getting device %s",
1387                        argv[1]);
1388                 return -EINVAL;
1389         }
1390
1391         r = action_dev(m, dev, action);
1392
1393         dm_put_device(ti, dev);
1394
1395         return r;
1396
1397 error:
1398         DMWARN("Unrecognised multipath message received.");
1399         return -EINVAL;
1400 }
1401
1402 static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
1403                            unsigned long arg)
1404 {
1405         struct multipath *m = (struct multipath *) ti->private;
1406         struct block_device *bdev = NULL;
1407         fmode_t mode = 0;
1408         unsigned long flags;
1409         int r = 0;
1410
1411         spin_lock_irqsave(&m->lock, flags);
1412
1413         if (!m->current_pgpath)
1414                 __choose_pgpath(m);
1415
1416         if (m->current_pgpath) {
1417                 bdev = m->current_pgpath->path.dev->bdev;
1418                 mode = m->current_pgpath->path.dev->mode;
1419         }
1420
1421         if (m->queue_io)
1422                 r = -EAGAIN;
1423         else if (!bdev)
1424                 r = -EIO;
1425
1426         spin_unlock_irqrestore(&m->lock, flags);
1427
1428         return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);
1429 }
1430
1431 /*-----------------------------------------------------------------
1432  * Module setup
1433  *---------------------------------------------------------------*/
1434 static struct target_type multipath_target = {
1435         .name = "multipath",
1436         .version = {1, 0, 5},
1437         .module = THIS_MODULE,
1438         .ctr = multipath_ctr,
1439         .dtr = multipath_dtr,
1440         .map = multipath_map,
1441         .end_io = multipath_end_io,
1442         .presuspend = multipath_presuspend,
1443         .resume = multipath_resume,
1444         .status = multipath_status,
1445         .message = multipath_message,
1446         .ioctl  = multipath_ioctl,
1447 };
1448
1449 static int __init dm_multipath_init(void)
1450 {
1451         int r;
1452
1453         /* allocate a slab for the dm_ios */
1454         _mpio_cache = KMEM_CACHE(dm_mpath_io, 0);
1455         if (!_mpio_cache)
1456                 return -ENOMEM;
1457
1458         r = dm_register_target(&multipath_target);
1459         if (r < 0) {
1460                 DMERR("register failed %d", r);
1461                 kmem_cache_destroy(_mpio_cache);
1462                 return -EINVAL;
1463         }
1464
1465         kmultipathd = create_workqueue("kmpathd");
1466         if (!kmultipathd) {
1467                 DMERR("failed to create workqueue kmpathd");
1468                 dm_unregister_target(&multipath_target);
1469                 kmem_cache_destroy(_mpio_cache);
1470                 return -ENOMEM;
1471         }
1472
1473         /*
1474          * A separate workqueue is used to handle the device handlers
1475          * to avoid overloading existing workqueue. Overloading the
1476          * old workqueue would also create a bottleneck in the
1477          * path of the storage hardware device activation.
1478          */
1479         kmpath_handlerd = create_singlethread_workqueue("kmpath_handlerd");
1480         if (!kmpath_handlerd) {
1481                 DMERR("failed to create workqueue kmpath_handlerd");
1482                 destroy_workqueue(kmultipathd);
1483                 dm_unregister_target(&multipath_target);
1484                 kmem_cache_destroy(_mpio_cache);
1485                 return -ENOMEM;
1486         }
1487
1488         DMINFO("version %u.%u.%u loaded",
1489                multipath_target.version[0], multipath_target.version[1],
1490                multipath_target.version[2]);
1491
1492         return r;
1493 }
1494
1495 static void __exit dm_multipath_exit(void)
1496 {
1497         destroy_workqueue(kmpath_handlerd);
1498         destroy_workqueue(kmultipathd);
1499
1500         dm_unregister_target(&multipath_target);
1501         kmem_cache_destroy(_mpio_cache);
1502 }
1503
1504 module_init(dm_multipath_init);
1505 module_exit(dm_multipath_exit);
1506
1507 MODULE_DESCRIPTION(DM_NAME " multipath target");
1508 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
1509 MODULE_LICENSE("GPL");