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 "dm.h"
   9 #include "dm-path-selector.h"
  10 #include "dm-bio-list.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         m->pgpath_to_activate = m->current_pgpath;
 444
 445         if ((pgpath && !m->queue_io) ||
 446             (!pgpath && !m->queue_if_no_path))
 447                 must_queue = 0;
 448
 449         if (m->pg_init_required && !m->pg_init_in_progress) {
 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         consume(as, hw_argc - 1);
 711
 712         return 0;
 713 }
 714
 715 static int parse_features(struct arg_set *as, struct multipath *m)
 716 {
 717         int r;
 718         unsigned argc;
 719         struct dm_target *ti = m->ti;
 720         const char *param_name;
 721
 722         static struct param _params[] = {
 723                 {0, 3, "invalid number of feature args"},
 724                 {1, 50, "pg_init_retries must be between 1 and 50"},
 725         };
 726
 727         r = read_param(_params, shift(as), &argc, &ti->error);
 728         if (r)
 729                 return -EINVAL;
 730
 731         if (!argc)
 732                 return 0;
 733
 734         do {
 735                 param_name = shift(as);
 736                 argc--;
 737
 738                 if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
 739                         r = queue_if_no_path(m, 1, 0);
 740                         continue;
 741                 }
 742
 743                 if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
 744                     (argc >= 1)) {
 745                         r = read_param(_params + 1, shift(as),
 746                                        &m->pg_init_retries, &ti->error);
 747                         argc--;
 748                         continue;
 749                 }
 750
 751                 ti->error = "Unrecognised multipath feature request";
 752                 r = -EINVAL;
 753         } while (argc && !r);
 754
 755         return r;
 756 }
 757
 758 static int multipath_ctr(struct dm_target *ti, unsigned int argc,
 759                          char **argv)
 760 {
 761         /* target parameters */
 762         static struct param _params[] = {
 763                 {1, 1024, "invalid number of priority groups"},
 764                 {1, 1024, "invalid initial priority group number"},
 765         };
 766
 767         int r;
 768         struct multipath *m;
 769         struct arg_set as;
 770         unsigned pg_count = 0;
 771         unsigned next_pg_num;
 772
 773         as.argc = argc;
 774         as.argv = argv;
 775
 776         m = alloc_multipath(ti);
 777         if (!m) {
 778                 ti->error = "can't allocate multipath";
 779                 return -EINVAL;
 780         }
 781
 782         r = parse_features(&as, m);
 783         if (r)
 784                 goto bad;
 785
 786         r = parse_hw_handler(&as, m);
 787         if (r)
 788                 goto bad;
 789
 790         r = read_param(_params, shift(&as), &m->nr_priority_groups, &ti->error);
 791         if (r)
 792                 goto bad;
 793
 794         r = read_param(_params + 1, shift(&as), &next_pg_num, &ti->error);
 795         if (r)
 796                 goto bad;
 797
 798         /* parse the priority groups */
 799         while (as.argc) {
 800                 struct priority_group *pg;
 801
 802                 pg = parse_priority_group(&as, m);
 803                 if (IS_ERR(pg)) {
 804                         r = PTR_ERR(pg);
 805                         goto bad;
 806                 }
 807
 808                 m->nr_valid_paths += pg->nr_pgpaths;
 809                 list_add_tail(&pg->list, &m->priority_groups);
 810                 pg_count++;
 811                 pg->pg_num = pg_count;
 812                 if (!--next_pg_num)
 813                         m->next_pg = pg;
 814         }
 815
 816         if (pg_count != m->nr_priority_groups) {
 817                 ti->error = "priority group count mismatch";
 818                 r = -EINVAL;
 819                 goto bad;
 820         }
 821
 822         return 0;
 823
 824  bad:
 825         free_multipath(m);
 826         return r;
 827 }
 828
 829 static void multipath_dtr(struct dm_target *ti)
 830 {
 831         struct multipath *m = (struct multipath *) ti->private;
 832
 833         flush_workqueue(kmpath_handlerd);
 834         flush_workqueue(kmultipathd);
 835         free_multipath(m);
 836 }
 837
 838 /*
 839  * Map bios, recording original fields for later in case we have to resubmit
 840  */
 841 static int multipath_map(struct dm_target *ti, struct bio *bio,
 842                          union map_info *map_context)
 843 {
 844         int r;
 845         struct dm_mpath_io *mpio;
 846         struct multipath *m = (struct multipath *) ti->private;
 847
 848         mpio = mempool_alloc(m->mpio_pool, GFP_NOIO);
 849         dm_bio_record(&mpio->details, bio);
 850
 851         map_context->ptr = mpio;
 852         bio->bi_rw |= (1 << BIO_RW_FAILFAST_TRANSPORT);
 853         r = map_io(m, bio, mpio, 0);
 854         if (r < 0 || r == DM_MAPIO_REQUEUE)
 855                 mempool_free(mpio, m->mpio_pool);
 856
 857         return r;
 858 }
 859
 860 /*
 861  * Take a path out of use.
 862  */
 863 static int fail_path(struct pgpath *pgpath)
 864 {
 865         unsigned long flags;
 866         struct multipath *m = pgpath->pg->m;
 867
 868         spin_lock_irqsave(&m->lock, flags);
 869
 870         if (!pgpath->is_active)
 871                 goto out;
 872
 873         DMWARN("Failing path %s.", pgpath->path.dev->name);
 874
 875         pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
 876         pgpath->is_active = 0;
 877         pgpath->fail_count++;
 878
 879         m->nr_valid_paths--;
 880
 881         if (pgpath == m->current_pgpath)
 882                 m->current_pgpath = NULL;
 883
 884         dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
 885                       pgpath->path.dev->name, m->nr_valid_paths);
 886
 887         queue_work(kmultipathd, &m->trigger_event);
 888         queue_work(kmultipathd, &pgpath->deactivate_path);
 889
 890 out:
 891         spin_unlock_irqrestore(&m->lock, flags);
 892
 893         return 0;
 894 }
 895
 896 /*
 897  * Reinstate a previously-failed path
 898  */
 899 static int reinstate_path(struct pgpath *pgpath)
 900 {
 901         int r = 0;
 902         unsigned long flags;
 903         struct multipath *m = pgpath->pg->m;
 904
 905         spin_lock_irqsave(&m->lock, flags);
 906
 907         if (pgpath->is_active)
 908                 goto out;
 909
 910         if (!pgpath->pg->ps.type->reinstate_path) {
 911                 DMWARN("Reinstate path not supported by path selector %s",
 912                        pgpath->pg->ps.type->name);
 913                 r = -EINVAL;
 914                 goto out;
 915         }
 916
 917         r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
 918         if (r)
 919                 goto out;
 920
 921         pgpath->is_active = 1;
 922
 923         m->current_pgpath = NULL;
 924         if (!m->nr_valid_paths++ && m->queue_size)
 925                 queue_work(kmultipathd, &m->process_queued_ios);
 926
 927         dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
 928                       pgpath->path.dev->name, m->nr_valid_paths);
 929
 930         queue_work(kmultipathd, &m->trigger_event);
 931
 932 out:
 933         spin_unlock_irqrestore(&m->lock, flags);
 934
 935         return r;
 936 }
 937
 938 /*
 939  * Fail or reinstate all paths that match the provided struct dm_dev.
 940  */
 941 static int action_dev(struct multipath *m, struct dm_dev *dev,
 942                       action_fn action)
 943 {
 944         int r = 0;
 945         struct pgpath *pgpath;
 946         struct priority_group *pg;
 947
 948         list_for_each_entry(pg, &m->priority_groups, list) {
 949                 list_for_each_entry(pgpath, &pg->pgpaths, list) {
 950                         if (pgpath->path.dev == dev)
 951                                 r = action(pgpath);
 952                 }
 953         }
 954
 955         return r;
 956 }
 957
 958 /*
 959  * Temporarily try to avoid having to use the specified PG
 960  */
 961 static void bypass_pg(struct multipath *m, struct priority_group *pg,
 962                       int bypassed)
 963 {
 964         unsigned long flags;
 965
 966         spin_lock_irqsave(&m->lock, flags);
 967
 968         pg->bypassed = bypassed;
 969         m->current_pgpath = NULL;
 970         m->current_pg = NULL;
 971
 972         spin_unlock_irqrestore(&m->lock, flags);
 973
 974         queue_work(kmultipathd, &m->trigger_event);
 975 }
 976
 977 /*
 978  * Switch to using the specified PG from the next I/O that gets mapped
 979  */
 980 static int switch_pg_num(struct multipath *m, const char *pgstr)
 981 {
 982         struct priority_group *pg;
 983         unsigned pgnum;
 984         unsigned long flags;
 985
 986         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
 987             (pgnum > m->nr_priority_groups)) {
 988                 DMWARN("invalid PG number supplied to switch_pg_num");
 989                 return -EINVAL;
 990         }
 991
 992         spin_lock_irqsave(&m->lock, flags);
 993         list_for_each_entry(pg, &m->priority_groups, list) {
 994                 pg->bypassed = 0;
 995                 if (--pgnum)
 996                         continue;
 997
 998                 m->current_pgpath = NULL;
 999                 m->current_pg = NULL;
1000                 m->next_pg = pg;
1001         }
1002         spin_unlock_irqrestore(&m->lock, flags);
1003
1004         queue_work(kmultipathd, &m->trigger_event);
1005         return 0;
1006 }
1007
1008 /*
1009  * Set/clear bypassed status of a PG.
1010  * PGs are numbered upwards from 1 in the order they were declared.
1011  */
1012 static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypassed)
1013 {
1014         struct priority_group *pg;
1015         unsigned pgnum;
1016
1017         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
1018             (pgnum > m->nr_priority_groups)) {
1019                 DMWARN("invalid PG number supplied to bypass_pg");
1020                 return -EINVAL;
1021         }
1022
1023         list_for_each_entry(pg, &m->priority_groups, list) {
1024                 if (!--pgnum)
1025                         break;
1026         }
1027
1028         bypass_pg(m, pg, bypassed);
1029         return 0;
1030 }
1031
1032 /*
1033  * Should we retry pg_init immediately?
1034  */
1035 static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
1036 {
1037         unsigned long flags;
1038         int limit_reached = 0;
1039
1040         spin_lock_irqsave(&m->lock, flags);
1041
1042         if (m->pg_init_count <= m->pg_init_retries)
1043                 m->pg_init_required = 1;
1044         else
1045                 limit_reached = 1;
1046
1047         spin_unlock_irqrestore(&m->lock, flags);
1048
1049         return limit_reached;
1050 }
1051
1052 static void pg_init_done(struct dm_path *path, int errors)
1053 {
1054         struct pgpath *pgpath = path_to_pgpath(path);
1055         struct priority_group *pg = pgpath->pg;
1056         struct multipath *m = pg->m;
1057         unsigned long flags;
1058
1059         /* device or driver problems */
1060         switch (errors) {
1061         case SCSI_DH_OK:
1062                 break;
1063         case SCSI_DH_NOSYS:
1064                 if (!m->hw_handler_name) {
1065                         errors = 0;
1066                         break;
1067                 }
1068                 DMERR("Cannot failover device because scsi_dh_%s was not "
1069                       "loaded.", m->hw_handler_name);
1070                 /*
1071                  * Fail path for now, so we do not ping pong
1072                  */
1073                 fail_path(pgpath);
1074                 break;
1075         case SCSI_DH_DEV_TEMP_BUSY:
1076                 /*
1077                  * Probably doing something like FW upgrade on the
1078                  * controller so try the other pg.
1079                  */
1080                 bypass_pg(m, pg, 1);
1081                 break;
1082         /* TODO: For SCSI_DH_RETRY we should wait a couple seconds */
1083         case SCSI_DH_RETRY:
1084         case SCSI_DH_IMM_RETRY:
1085         case SCSI_DH_RES_TEMP_UNAVAIL:
1086                 if (pg_init_limit_reached(m, pgpath))
1087                         fail_path(pgpath);
1088                 errors = 0;
1089                 break;
1090         default:
1091                 /*
1092                  * We probably do not want to fail the path for a device
1093                  * error, but this is what the old dm did. In future
1094                  * patches we can do more advanced handling.
1095                  */
1096                 fail_path(pgpath);
1097         }
1098
1099         spin_lock_irqsave(&m->lock, flags);
1100         if (errors) {
1101                 DMERR("Could not failover device. Error %d.", errors);
1102                 m->current_pgpath = NULL;
1103                 m->current_pg = NULL;
1104         } else if (!m->pg_init_required) {
1105                 m->queue_io = 0;
1106                 pg->bypassed = 0;
1107         }
1108
1109         m->pg_init_in_progress = 0;
1110         queue_work(kmultipathd, &m->process_queued_ios);
1111         spin_unlock_irqrestore(&m->lock, flags);
1112 }
1113
1114 static void activate_path(struct work_struct *work)
1115 {
1116         int ret;
1117         struct multipath *m =
1118                 container_of(work, struct multipath, activate_path);
1119         struct dm_path *path;
1120         unsigned long flags;
1121
1122         spin_lock_irqsave(&m->lock, flags);
1123         path = &m->pgpath_to_activate->path;
1124         m->pgpath_to_activate = NULL;
1125         spin_unlock_irqrestore(&m->lock, flags);
1126         if (!path)
1127                 return;
1128         ret = scsi_dh_activate(bdev_get_queue(path->dev->bdev));
1129         pg_init_done(path, ret);
1130 }
1131
1132 /*
1133  * end_io handling
1134  */
1135 static int do_end_io(struct multipath *m, struct bio *bio,
1136                      int error, struct dm_mpath_io *mpio)
1137 {
1138         unsigned long flags;
1139
1140         if (!error)
1141                 return 0;       /* I/O complete */
1142
1143         if ((error == -EWOULDBLOCK) && bio_rw_ahead(bio))
1144                 return error;
1145
1146         if (error == -EOPNOTSUPP)
1147                 return error;
1148
1149         spin_lock_irqsave(&m->lock, flags);
1150         if (!m->nr_valid_paths) {
1151                 if (__must_push_back(m)) {
1152                         spin_unlock_irqrestore(&m->lock, flags);
1153                         return DM_ENDIO_REQUEUE;
1154                 } else if (!m->queue_if_no_path) {
1155                         spin_unlock_irqrestore(&m->lock, flags);
1156                         return -EIO;
1157                 } else {
1158                         spin_unlock_irqrestore(&m->lock, flags);
1159                         goto requeue;
1160                 }
1161         }
1162         spin_unlock_irqrestore(&m->lock, flags);
1163
1164         if (mpio->pgpath)
1165                 fail_path(mpio->pgpath);
1166
1167       requeue:
1168         dm_bio_restore(&mpio->details, bio);
1169
1170         /* queue for the daemon to resubmit or fail */
1171         spin_lock_irqsave(&m->lock, flags);
1172         bio_list_add(&m->queued_ios, bio);
1173         m->queue_size++;
1174         if (!m->queue_io)
1175                 queue_work(kmultipathd, &m->process_queued_ios);
1176         spin_unlock_irqrestore(&m->lock, flags);
1177
1178         return DM_ENDIO_INCOMPLETE;     /* io not complete */
1179 }
1180
1181 static int multipath_end_io(struct dm_target *ti, struct bio *bio,
1182                             int error, union map_info *map_context)
1183 {
1184         struct multipath *m = ti->private;
1185         struct dm_mpath_io *mpio = map_context->ptr;
1186         struct pgpath *pgpath = mpio->pgpath;
1187         struct path_selector *ps;
1188         int r;
1189
1190         r  = do_end_io(m, bio, error, mpio);
1191         if (pgpath) {
1192                 ps = &pgpath->pg->ps;
1193                 if (ps->type->end_io)
1194                         ps->type->end_io(ps, &pgpath->path);
1195         }
1196         if (r != DM_ENDIO_INCOMPLETE)
1197                 mempool_free(mpio, m->mpio_pool);
1198
1199         return r;
1200 }
1201
1202 /*
1203  * Suspend can't complete until all the I/O is processed so if
1204  * the last path fails we must error any remaining I/O.
1205  * Note that if the freeze_bdev fails while suspending, the
1206  * queue_if_no_path state is lost - userspace should reset it.
1207  */
1208 static void multipath_presuspend(struct dm_target *ti)
1209 {
1210         struct multipath *m = (struct multipath *) ti->private;
1211
1212         queue_if_no_path(m, 0, 1);
1213 }
1214
1215 /*
1216  * Restore the queue_if_no_path setting.
1217  */
1218 static void multipath_resume(struct dm_target *ti)
1219 {
1220         struct multipath *m = (struct multipath *) ti->private;
1221         unsigned long flags;
1222
1223         spin_lock_irqsave(&m->lock, flags);
1224         m->queue_if_no_path = m->saved_queue_if_no_path;
1225         spin_unlock_irqrestore(&m->lock, flags);
1226 }
1227
1228 /*
1229  * Info output has the following format:
1230  * num_multipath_feature_args [multipath_feature_args]*
1231  * num_handler_status_args [handler_status_args]*
1232  * num_groups init_group_number
1233  *            [A|D|E num_ps_status_args [ps_status_args]*
1234  *             num_paths num_selector_args
1235  *             [path_dev A|F fail_count [selector_args]* ]+ ]+
1236  *
1237  * Table output has the following format (identical to the constructor string):
1238  * num_feature_args [features_args]*
1239  * num_handler_args hw_handler [hw_handler_args]*
1240  * num_groups init_group_number
1241  *     [priority selector-name num_ps_args [ps_args]*
1242  *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
1243  */
1244 static int multipath_status(struct dm_target *ti, status_type_t type,
1245                             char *result, unsigned int maxlen)
1246 {
1247         int sz = 0;
1248         unsigned long flags;
1249         struct multipath *m = (struct multipath *) ti->private;
1250         struct priority_group *pg;
1251         struct pgpath *p;
1252         unsigned pg_num;
1253         char state;
1254
1255         spin_lock_irqsave(&m->lock, flags);
1256
1257         /* Features */
1258         if (type == STATUSTYPE_INFO)
1259                 DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
1260         else {
1261                 DMEMIT("%u ", m->queue_if_no_path +
1262                               (m->pg_init_retries > 0) * 2);
1263                 if (m->queue_if_no_path)
1264                         DMEMIT("queue_if_no_path ");
1265                 if (m->pg_init_retries)
1266                         DMEMIT("pg_init_retries %u ", m->pg_init_retries);
1267         }
1268
1269         if (!m->hw_handler_name || type == STATUSTYPE_INFO)
1270                 DMEMIT("0 ");
1271         else
1272                 DMEMIT("1 %s ", m->hw_handler_name);
1273
1274         DMEMIT("%u ", m->nr_priority_groups);
1275
1276         if (m->next_pg)
1277                 pg_num = m->next_pg->pg_num;
1278         else if (m->current_pg)
1279                 pg_num = m->current_pg->pg_num;
1280         else
1281                         pg_num = 1;
1282
1283         DMEMIT("%u ", pg_num);
1284
1285         switch (type) {
1286         case STATUSTYPE_INFO:
1287                 list_for_each_entry(pg, &m->priority_groups, list) {
1288                         if (pg->bypassed)
1289                                 state = 'D';    /* Disabled */
1290                         else if (pg == m->current_pg)
1291                                 state = 'A';    /* Currently Active */
1292                         else
1293                                 state = 'E';    /* Enabled */
1294
1295                         DMEMIT("%c ", state);
1296
1297                         if (pg->ps.type->status)
1298                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1299                                                           result + sz,
1300                                                           maxlen - sz);
1301                         else
1302                                 DMEMIT("0 ");
1303
1304                         DMEMIT("%u %u ", pg->nr_pgpaths,
1305                                pg->ps.type->info_args);
1306
1307                         list_for_each_entry(p, &pg->pgpaths, list) {
1308                                 DMEMIT("%s %s %u ", p->path.dev->name,
1309                                        p->is_active ? "A" : "F",
1310                                        p->fail_count);
1311                                 if (pg->ps.type->status)
1312                                         sz += pg->ps.type->status(&pg->ps,
1313                                               &p->path, type, result + sz,
1314                                               maxlen - sz);
1315                         }
1316                 }
1317                 break;
1318
1319         case STATUSTYPE_TABLE:
1320                 list_for_each_entry(pg, &m->priority_groups, list) {
1321                         DMEMIT("%s ", pg->ps.type->name);
1322
1323                         if (pg->ps.type->status)
1324                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1325                                                           result + sz,
1326                                                           maxlen - sz);
1327                         else
1328                                 DMEMIT("0 ");
1329
1330                         DMEMIT("%u %u ", pg->nr_pgpaths,
1331                                pg->ps.type->table_args);
1332
1333                         list_for_each_entry(p, &pg->pgpaths, list) {
1334                                 DMEMIT("%s ", p->path.dev->name);
1335                                 if (pg->ps.type->status)
1336                                         sz += pg->ps.type->status(&pg->ps,
1337                                               &p->path, type, result + sz,
1338                                               maxlen - sz);
1339                         }
1340                 }
1341                 break;
1342         }
1343
1344         spin_unlock_irqrestore(&m->lock, flags);
1345
1346         return 0;
1347 }
1348
1349 static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
1350 {
1351         int r;
1352         struct dm_dev *dev;
1353         struct multipath *m = (struct multipath *) ti->private;
1354         action_fn action;
1355
1356         if (argc == 1) {
1357                 if (!strnicmp(argv[0], MESG_STR("queue_if_no_path")))
1358                         return queue_if_no_path(m, 1, 0);
1359                 else if (!strnicmp(argv[0], MESG_STR("fail_if_no_path")))
1360                         return queue_if_no_path(m, 0, 0);
1361         }
1362
1363         if (argc != 2)
1364                 goto error;
1365
1366         if (!strnicmp(argv[0], MESG_STR("disable_group")))
1367                 return bypass_pg_num(m, argv[1], 1);
1368         else if (!strnicmp(argv[0], MESG_STR("enable_group")))
1369                 return bypass_pg_num(m, argv[1], 0);
1370         else if (!strnicmp(argv[0], MESG_STR("switch_group")))
1371                 return switch_pg_num(m, argv[1]);
1372         else if (!strnicmp(argv[0], MESG_STR("reinstate_path")))
1373                 action = reinstate_path;
1374         else if (!strnicmp(argv[0], MESG_STR("fail_path")))
1375                 action = fail_path;
1376         else
1377                 goto error;
1378
1379         r = dm_get_device(ti, argv[1], ti->begin, ti->len,
1380                           dm_table_get_mode(ti->table), &dev);
1381         if (r) {
1382                 DMWARN("message: error getting device %s",
1383                        argv[1]);
1384                 return -EINVAL;
1385         }
1386
1387         r = action_dev(m, dev, action);
1388
1389         dm_put_device(ti, dev);
1390
1391         return r;
1392
1393 error:
1394         DMWARN("Unrecognised multipath message received.");
1395         return -EINVAL;
1396 }
1397
1398 static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
1399                            unsigned long arg)
1400 {
1401         struct multipath *m = (struct multipath *) ti->private;
1402         struct block_device *bdev = NULL;
1403         unsigned long flags;
1404         struct file fake_file = {};
1405         struct dentry fake_dentry = {};
1406         int r = 0;
1407
1408         fake_file.f_path.dentry = &fake_dentry;
1409
1410         spin_lock_irqsave(&m->lock, flags);
1411
1412         if (!m->current_pgpath)
1413                 __choose_pgpath(m);
1414
1415         if (m->current_pgpath) {
1416                 bdev = m->current_pgpath->path.dev->bdev;
1417                 fake_dentry.d_inode = bdev->bd_inode;
1418                 fake_file.f_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->bd_inode, &fake_file,
1429                                          bdev->bd_disk, cmd, arg);
1430 }
1431
1432 /*-----------------------------------------------------------------
1433  * Module setup
1434  *---------------------------------------------------------------*/
1435 static struct target_type multipath_target = {
1436         .name = "multipath",
1437         .version = {1, 0, 5},
1438         .module = THIS_MODULE,
1439         .ctr = multipath_ctr,
1440         .dtr = multipath_dtr,
1441         .map = multipath_map,
1442         .end_io = multipath_end_io,
1443         .presuspend = multipath_presuspend,
1444         .resume = multipath_resume,
1445         .status = multipath_status,
1446         .message = multipath_message,
1447         .ioctl  = multipath_ioctl,
1448 };
1449
1450 static int __init dm_multipath_init(void)
1451 {
1452         int r;
1453
1454         /* allocate a slab for the dm_ios */
1455         _mpio_cache = KMEM_CACHE(dm_mpath_io, 0);
1456         if (!_mpio_cache)
1457                 return -ENOMEM;
1458
1459         r = dm_register_target(&multipath_target);
1460         if (r < 0) {
1461                 DMERR("register failed %d", r);
1462                 kmem_cache_destroy(_mpio_cache);
1463                 return -EINVAL;
1464         }
1465
1466         kmultipathd = create_workqueue("kmpathd");
1467         if (!kmultipathd) {
1468                 DMERR("failed to create workqueue kmpathd");
1469                 dm_unregister_target(&multipath_target);
1470                 kmem_cache_destroy(_mpio_cache);
1471                 return -ENOMEM;
1472         }
1473
1474         /*
1475          * A separate workqueue is used to handle the device handlers
1476          * to avoid overloading existing workqueue. Overloading the
1477          * old workqueue would also create a bottleneck in the
1478          * path of the storage hardware device activation.
1479          */
1480         kmpath_handlerd = create_singlethread_workqueue("kmpath_handlerd");
1481         if (!kmpath_handlerd) {
1482                 DMERR("failed to create workqueue kmpath_handlerd");
1483                 destroy_workqueue(kmultipathd);
1484                 dm_unregister_target(&multipath_target);
1485                 kmem_cache_destroy(_mpio_cache);
1486                 return -ENOMEM;
1487         }
1488
1489         DMINFO("version %u.%u.%u loaded",
1490                multipath_target.version[0], multipath_target.version[1],
1491                multipath_target.version[2]);
1492
1493         return r;
1494 }
1495
1496 static void __exit dm_multipath_exit(void)
1497 {
1498         int r;
1499
1500         destroy_workqueue(kmpath_handlerd);
1501         destroy_workqueue(kmultipathd);
1502
1503         r = dm_unregister_target(&multipath_target);
1504         if (r < 0)
1505                 DMERR("target unregister failed %d", r);
1506         kmem_cache_destroy(_mpio_cache);
1507 }
1508
1509 module_init(dm_multipath_init);
1510 module_exit(dm_multipath_exit);
1511
1512 MODULE_DESCRIPTION(DM_NAME " multipath target");
1513 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
1514 MODULE_LICENSE("GPL");