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         if (ps_argc > as->argc) {
 557                 dm_put_path_selector(pst);
 558                 ti->error = "not enough arguments for path selector";
 559                 return -EINVAL;
 560         }
 561
 562         r = pst->create(&pg->ps, ps_argc, as->argv);
 563         if (r) {
 564                 dm_put_path_selector(pst);
 565                 ti->error = "path selector constructor failed";
 566                 return r;
 567         }
 568
 569         pg->ps.type = pst;
 570         consume(as, ps_argc);
 571
 572         return 0;
 573 }
 574
 575 static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
 576                                struct dm_target *ti)
 577 {
 578         int r;
 579         struct pgpath *p;
 580         struct multipath *m = ti->private;
 581
 582         /* we need at least a path arg */
 583         if (as->argc < 1) {
 584                 ti->error = "no device given";
 585                 return ERR_PTR(-EINVAL);
 586         }
 587
 588         p = alloc_pgpath();
 589         if (!p)
 590                 return ERR_PTR(-ENOMEM);
 591
 592         r = dm_get_device(ti, shift(as), ti->begin, ti->len,
 593                           dm_table_get_mode(ti->table), &p->path.dev);
 594         if (r) {
 595                 ti->error = "error getting device";
 596                 goto bad;
 597         }
 598
 599         if (m->hw_handler_name) {
 600                 r = scsi_dh_attach(bdev_get_queue(p->path.dev->bdev),
 601                                    m->hw_handler_name);
 602                 if (r < 0) {
 603                         dm_put_device(ti, p->path.dev);
 604                         goto bad;
 605                 }
 606         }
 607
 608         r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
 609         if (r) {
 610                 dm_put_device(ti, p->path.dev);
 611                 goto bad;
 612         }
 613
 614         return p;
 615
 616  bad:
 617         free_pgpath(p);
 618         return ERR_PTR(r);
 619 }
 620
 621 static struct priority_group *parse_priority_group(struct arg_set *as,
 622                                                    struct multipath *m)
 623 {
 624         static struct param _params[] = {
 625                 {1, 1024, "invalid number of paths"},
 626                 {0, 1024, "invalid number of selector args"}
 627         };
 628
 629         int r;
 630         unsigned i, nr_selector_args, nr_params;
 631         struct priority_group *pg;
 632         struct dm_target *ti = m->ti;
 633
 634         if (as->argc < 2) {
 635                 as->argc = 0;
 636                 ti->error = "not enough priority group arguments";
 637                 return ERR_PTR(-EINVAL);
 638         }
 639
 640         pg = alloc_priority_group();
 641         if (!pg) {
 642                 ti->error = "couldn't allocate priority group";
 643                 return ERR_PTR(-ENOMEM);
 644         }
 645         pg->m = m;
 646
 647         r = parse_path_selector(as, pg, ti);
 648         if (r)
 649                 goto bad;
 650
 651         /*
 652          * read the paths
 653          */
 654         r = read_param(_params, shift(as), &pg->nr_pgpaths, &ti->error);
 655         if (r)
 656                 goto bad;
 657
 658         r = read_param(_params + 1, shift(as), &nr_selector_args, &ti->error);
 659         if (r)
 660                 goto bad;
 661
 662         nr_params = 1 + nr_selector_args;
 663         for (i = 0; i < pg->nr_pgpaths; i++) {
 664                 struct pgpath *pgpath;
 665                 struct arg_set path_args;
 666
 667                 if (as->argc < nr_params) {
 668                         ti->error = "not enough path parameters";
 669                         goto bad;
 670                 }
 671
 672                 path_args.argc = nr_params;
 673                 path_args.argv = as->argv;
 674
 675                 pgpath = parse_path(&path_args, &pg->ps, ti);
 676                 if (IS_ERR(pgpath)) {
 677                         r = PTR_ERR(pgpath);
 678                         goto bad;
 679                 }
 680
 681                 pgpath->pg = pg;
 682                 list_add_tail(&pgpath->list, &pg->pgpaths);
 683                 consume(as, nr_params);
 684         }
 685
 686         return pg;
 687
 688  bad:
 689         free_priority_group(pg, ti);
 690         return ERR_PTR(r);
 691 }
 692
 693 static int parse_hw_handler(struct arg_set *as, struct multipath *m)
 694 {
 695         unsigned hw_argc;
 696         struct dm_target *ti = m->ti;
 697
 698         static struct param _params[] = {
 699                 {0, 1024, "invalid number of hardware handler args"},
 700         };
 701
 702         if (read_param(_params, shift(as), &hw_argc, &ti->error))
 703                 return -EINVAL;
 704
 705         if (!hw_argc)
 706                 return 0;
 707
 708         m->hw_handler_name = kstrdup(shift(as), GFP_KERNEL);
 709         request_module("scsi_dh_%s", m->hw_handler_name);
 710         if (scsi_dh_handler_exist(m->hw_handler_name) == 0) {
 711                 ti->error = "unknown hardware handler type";
 712                 kfree(m->hw_handler_name);
 713                 m->hw_handler_name = NULL;
 714                 return -EINVAL;
 715         }
 716
 717         if (hw_argc > 1)
 718                 DMWARN("Ignoring user-specified arguments for "
 719                        "hardware handler \"%s\"", m->hw_handler_name);
 720         consume(as, hw_argc - 1);
 721
 722         return 0;
 723 }
 724
 725 static int parse_features(struct arg_set *as, struct multipath *m)
 726 {
 727         int r;
 728         unsigned argc;
 729         struct dm_target *ti = m->ti;
 730         const char *param_name;
 731
 732         static struct param _params[] = {
 733                 {0, 3, "invalid number of feature args"},
 734                 {1, 50, "pg_init_retries must be between 1 and 50"},
 735         };
 736
 737         r = read_param(_params, shift(as), &argc, &ti->error);
 738         if (r)
 739                 return -EINVAL;
 740
 741         if (!argc)
 742                 return 0;
 743
 744         do {
 745                 param_name = shift(as);
 746                 argc--;
 747
 748                 if (!strnicmp(param_name, MESG_STR("queue_if_no_path"))) {
 749                         r = queue_if_no_path(m, 1, 0);
 750                         continue;
 751                 }
 752
 753                 if (!strnicmp(param_name, MESG_STR("pg_init_retries")) &&
 754                     (argc >= 1)) {
 755                         r = read_param(_params + 1, shift(as),
 756                                        &m->pg_init_retries, &ti->error);
 757                         argc--;
 758                         continue;
 759                 }
 760
 761                 ti->error = "Unrecognised multipath feature request";
 762                 r = -EINVAL;
 763         } while (argc && !r);
 764
 765         return r;
 766 }
 767
 768 static int multipath_ctr(struct dm_target *ti, unsigned int argc,
 769                          char **argv)
 770 {
 771         /* target parameters */
 772         static struct param _params[] = {
 773                 {1, 1024, "invalid number of priority groups"},
 774                 {1, 1024, "invalid initial priority group number"},
 775         };
 776
 777         int r;
 778         struct multipath *m;
 779         struct arg_set as;
 780         unsigned pg_count = 0;
 781         unsigned next_pg_num;
 782
 783         as.argc = argc;
 784         as.argv = argv;
 785
 786         m = alloc_multipath(ti);
 787         if (!m) {
 788                 ti->error = "can't allocate multipath";
 789                 return -EINVAL;
 790         }
 791
 792         r = parse_features(&as, m);
 793         if (r)
 794                 goto bad;
 795
 796         r = parse_hw_handler(&as, m);
 797         if (r)
 798                 goto bad;
 799
 800         r = read_param(_params, shift(&as), &m->nr_priority_groups, &ti->error);
 801         if (r)
 802                 goto bad;
 803
 804         r = read_param(_params + 1, shift(&as), &next_pg_num, &ti->error);
 805         if (r)
 806                 goto bad;
 807
 808         /* parse the priority groups */
 809         while (as.argc) {
 810                 struct priority_group *pg;
 811
 812                 pg = parse_priority_group(&as, m);
 813                 if (IS_ERR(pg)) {
 814                         r = PTR_ERR(pg);
 815                         goto bad;
 816                 }
 817
 818                 m->nr_valid_paths += pg->nr_pgpaths;
 819                 list_add_tail(&pg->list, &m->priority_groups);
 820                 pg_count++;
 821                 pg->pg_num = pg_count;
 822                 if (!--next_pg_num)
 823                         m->next_pg = pg;
 824         }
 825
 826         if (pg_count != m->nr_priority_groups) {
 827                 ti->error = "priority group count mismatch";
 828                 r = -EINVAL;
 829                 goto bad;
 830         }
 831
 832         return 0;
 833
 834  bad:
 835         free_multipath(m);
 836         return r;
 837 }
 838
 839 static void multipath_dtr(struct dm_target *ti)
 840 {
 841         struct multipath *m = (struct multipath *) ti->private;
 842
 843         flush_workqueue(kmpath_handlerd);
 844         flush_workqueue(kmultipathd);
 845         free_multipath(m);
 846 }
 847
 848 /*
 849  * Map bios, recording original fields for later in case we have to resubmit
 850  */
 851 static int multipath_map(struct dm_target *ti, struct bio *bio,
 852                          union map_info *map_context)
 853 {
 854         int r;
 855         struct dm_mpath_io *mpio;
 856         struct multipath *m = (struct multipath *) ti->private;
 857
 858         mpio = mempool_alloc(m->mpio_pool, GFP_NOIO);
 859         dm_bio_record(&mpio->details, bio);
 860
 861         map_context->ptr = mpio;
 862         bio->bi_rw |= (1 << BIO_RW_FAILFAST_TRANSPORT);
 863         r = map_io(m, bio, mpio, 0);
 864         if (r < 0 || r == DM_MAPIO_REQUEUE)
 865                 mempool_free(mpio, m->mpio_pool);
 866
 867         return r;
 868 }
 869
 870 /*
 871  * Take a path out of use.
 872  */
 873 static int fail_path(struct pgpath *pgpath)
 874 {
 875         unsigned long flags;
 876         struct multipath *m = pgpath->pg->m;
 877
 878         spin_lock_irqsave(&m->lock, flags);
 879
 880         if (!pgpath->is_active)
 881                 goto out;
 882
 883         DMWARN("Failing path %s.", pgpath->path.dev->name);
 884
 885         pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
 886         pgpath->is_active = 0;
 887         pgpath->fail_count++;
 888
 889         m->nr_valid_paths--;
 890
 891         if (pgpath == m->current_pgpath)
 892                 m->current_pgpath = NULL;
 893
 894         dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
 895                       pgpath->path.dev->name, m->nr_valid_paths);
 896
 897         schedule_work(&m->trigger_event);
 898         queue_work(kmultipathd, &pgpath->deactivate_path);
 899
 900 out:
 901         spin_unlock_irqrestore(&m->lock, flags);
 902
 903         return 0;
 904 }
 905
 906 /*
 907  * Reinstate a previously-failed path
 908  */
 909 static int reinstate_path(struct pgpath *pgpath)
 910 {
 911         int r = 0;
 912         unsigned long flags;
 913         struct multipath *m = pgpath->pg->m;
 914
 915         spin_lock_irqsave(&m->lock, flags);
 916
 917         if (pgpath->is_active)
 918                 goto out;
 919
 920         if (!pgpath->pg->ps.type->reinstate_path) {
 921                 DMWARN("Reinstate path not supported by path selector %s",
 922                        pgpath->pg->ps.type->name);
 923                 r = -EINVAL;
 924                 goto out;
 925         }
 926
 927         r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
 928         if (r)
 929                 goto out;
 930
 931         pgpath->is_active = 1;
 932
 933         m->current_pgpath = NULL;
 934         if (!m->nr_valid_paths++ && m->queue_size)
 935                 queue_work(kmultipathd, &m->process_queued_ios);
 936
 937         dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
 938                       pgpath->path.dev->name, m->nr_valid_paths);
 939
 940         schedule_work(&m->trigger_event);
 941
 942 out:
 943         spin_unlock_irqrestore(&m->lock, flags);
 944
 945         return r;
 946 }
 947
 948 /*
 949  * Fail or reinstate all paths that match the provided struct dm_dev.
 950  */
 951 static int action_dev(struct multipath *m, struct dm_dev *dev,
 952                       action_fn action)
 953 {
 954         int r = 0;
 955         struct pgpath *pgpath;
 956         struct priority_group *pg;
 957
 958         list_for_each_entry(pg, &m->priority_groups, list) {
 959                 list_for_each_entry(pgpath, &pg->pgpaths, list) {
 960                         if (pgpath->path.dev == dev)
 961                                 r = action(pgpath);
 962                 }
 963         }
 964
 965         return r;
 966 }
 967
 968 /*
 969  * Temporarily try to avoid having to use the specified PG
 970  */
 971 static void bypass_pg(struct multipath *m, struct priority_group *pg,
 972                       int bypassed)
 973 {
 974         unsigned long flags;
 975
 976         spin_lock_irqsave(&m->lock, flags);
 977
 978         pg->bypassed = bypassed;
 979         m->current_pgpath = NULL;
 980         m->current_pg = NULL;
 981
 982         spin_unlock_irqrestore(&m->lock, flags);
 983
 984         schedule_work(&m->trigger_event);
 985 }
 986
 987 /*
 988  * Switch to using the specified PG from the next I/O that gets mapped
 989  */
 990 static int switch_pg_num(struct multipath *m, const char *pgstr)
 991 {
 992         struct priority_group *pg;
 993         unsigned pgnum;
 994         unsigned long flags;
 995
 996         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
 997             (pgnum > m->nr_priority_groups)) {
 998                 DMWARN("invalid PG number supplied to switch_pg_num");
 999                 return -EINVAL;
1000         }
1001
1002         spin_lock_irqsave(&m->lock, flags);
1003         list_for_each_entry(pg, &m->priority_groups, list) {
1004                 pg->bypassed = 0;
1005                 if (--pgnum)
1006                         continue;
1007
1008                 m->current_pgpath = NULL;
1009                 m->current_pg = NULL;
1010                 m->next_pg = pg;
1011         }
1012         spin_unlock_irqrestore(&m->lock, flags);
1013
1014         schedule_work(&m->trigger_event);
1015         return 0;
1016 }
1017
1018 /*
1019  * Set/clear bypassed status of a PG.
1020  * PGs are numbered upwards from 1 in the order they were declared.
1021  */
1022 static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypassed)
1023 {
1024         struct priority_group *pg;
1025         unsigned pgnum;
1026
1027         if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum ||
1028             (pgnum > m->nr_priority_groups)) {
1029                 DMWARN("invalid PG number supplied to bypass_pg");
1030                 return -EINVAL;
1031         }
1032
1033         list_for_each_entry(pg, &m->priority_groups, list) {
1034                 if (!--pgnum)
1035                         break;
1036         }
1037
1038         bypass_pg(m, pg, bypassed);
1039         return 0;
1040 }
1041
1042 /*
1043  * Should we retry pg_init immediately?
1044  */
1045 static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
1046 {
1047         unsigned long flags;
1048         int limit_reached = 0;
1049
1050         spin_lock_irqsave(&m->lock, flags);
1051
1052         if (m->pg_init_count <= m->pg_init_retries)
1053                 m->pg_init_required = 1;
1054         else
1055                 limit_reached = 1;
1056
1057         spin_unlock_irqrestore(&m->lock, flags);
1058
1059         return limit_reached;
1060 }
1061
1062 static void pg_init_done(struct dm_path *path, int errors)
1063 {
1064         struct pgpath *pgpath = path_to_pgpath(path);
1065         struct priority_group *pg = pgpath->pg;
1066         struct multipath *m = pg->m;
1067         unsigned long flags;
1068
1069         /* device or driver problems */
1070         switch (errors) {
1071         case SCSI_DH_OK:
1072                 break;
1073         case SCSI_DH_NOSYS:
1074                 if (!m->hw_handler_name) {
1075                         errors = 0;
1076                         break;
1077                 }
1078                 DMERR("Cannot failover device because scsi_dh_%s was not "
1079                       "loaded.", m->hw_handler_name);
1080                 /*
1081                  * Fail path for now, so we do not ping pong
1082                  */
1083                 fail_path(pgpath);
1084                 break;
1085         case SCSI_DH_DEV_TEMP_BUSY:
1086                 /*
1087                  * Probably doing something like FW upgrade on the
1088                  * controller so try the other pg.
1089                  */
1090                 bypass_pg(m, pg, 1);
1091                 break;
1092         /* TODO: For SCSI_DH_RETRY we should wait a couple seconds */
1093         case SCSI_DH_RETRY:
1094         case SCSI_DH_IMM_RETRY:
1095         case SCSI_DH_RES_TEMP_UNAVAIL:
1096                 if (pg_init_limit_reached(m, pgpath))
1097                         fail_path(pgpath);
1098                 errors = 0;
1099                 break;
1100         default:
1101                 /*
1102                  * We probably do not want to fail the path for a device
1103                  * error, but this is what the old dm did. In future
1104                  * patches we can do more advanced handling.
1105                  */
1106                 fail_path(pgpath);
1107         }
1108
1109         spin_lock_irqsave(&m->lock, flags);
1110         if (errors) {
1111                 DMERR("Could not failover device. Error %d.", errors);
1112                 m->current_pgpath = NULL;
1113                 m->current_pg = NULL;
1114         } else if (!m->pg_init_required) {
1115                 m->queue_io = 0;
1116                 pg->bypassed = 0;
1117         }
1118
1119         m->pg_init_in_progress = 0;
1120         queue_work(kmultipathd, &m->process_queued_ios);
1121         spin_unlock_irqrestore(&m->lock, flags);
1122 }
1123
1124 static void activate_path(struct work_struct *work)
1125 {
1126         int ret;
1127         struct multipath *m =
1128                 container_of(work, struct multipath, activate_path);
1129         struct dm_path *path;
1130         unsigned long flags;
1131
1132         spin_lock_irqsave(&m->lock, flags);
1133         path = &m->pgpath_to_activate->path;
1134         m->pgpath_to_activate = NULL;
1135         spin_unlock_irqrestore(&m->lock, flags);
1136         if (!path)
1137                 return;
1138         ret = scsi_dh_activate(bdev_get_queue(path->dev->bdev));
1139         pg_init_done(path, ret);
1140 }
1141
1142 /*
1143  * end_io handling
1144  */
1145 static int do_end_io(struct multipath *m, struct bio *bio,
1146                      int error, struct dm_mpath_io *mpio)
1147 {
1148         unsigned long flags;
1149
1150         if (!error)
1151                 return 0;       /* I/O complete */
1152
1153         if ((error == -EWOULDBLOCK) && bio_rw_ahead(bio))
1154                 return error;
1155
1156         if (error == -EOPNOTSUPP)
1157                 return error;
1158
1159         spin_lock_irqsave(&m->lock, flags);
1160         if (!m->nr_valid_paths) {
1161                 if (__must_push_back(m)) {
1162                         spin_unlock_irqrestore(&m->lock, flags);
1163                         return DM_ENDIO_REQUEUE;
1164                 } else if (!m->queue_if_no_path) {
1165                         spin_unlock_irqrestore(&m->lock, flags);
1166                         return -EIO;
1167                 } else {
1168                         spin_unlock_irqrestore(&m->lock, flags);
1169                         goto requeue;
1170                 }
1171         }
1172         spin_unlock_irqrestore(&m->lock, flags);
1173
1174         if (mpio->pgpath)
1175                 fail_path(mpio->pgpath);
1176
1177       requeue:
1178         dm_bio_restore(&mpio->details, bio);
1179
1180         /* queue for the daemon to resubmit or fail */
1181         spin_lock_irqsave(&m->lock, flags);
1182         bio_list_add(&m->queued_ios, bio);
1183         m->queue_size++;
1184         if (!m->queue_io)
1185                 queue_work(kmultipathd, &m->process_queued_ios);
1186         spin_unlock_irqrestore(&m->lock, flags);
1187
1188         return DM_ENDIO_INCOMPLETE;     /* io not complete */
1189 }
1190
1191 static int multipath_end_io(struct dm_target *ti, struct bio *bio,
1192                             int error, union map_info *map_context)
1193 {
1194         struct multipath *m = ti->private;
1195         struct dm_mpath_io *mpio = map_context->ptr;
1196         struct pgpath *pgpath = mpio->pgpath;
1197         struct path_selector *ps;
1198         int r;
1199
1200         r  = do_end_io(m, bio, error, mpio);
1201         if (pgpath) {
1202                 ps = &pgpath->pg->ps;
1203                 if (ps->type->end_io)
1204                         ps->type->end_io(ps, &pgpath->path);
1205         }
1206         if (r != DM_ENDIO_INCOMPLETE)
1207                 mempool_free(mpio, m->mpio_pool);
1208
1209         return r;
1210 }
1211
1212 /*
1213  * Suspend can't complete until all the I/O is processed so if
1214  * the last path fails we must error any remaining I/O.
1215  * Note that if the freeze_bdev fails while suspending, the
1216  * queue_if_no_path state is lost - userspace should reset it.
1217  */
1218 static void multipath_presuspend(struct dm_target *ti)
1219 {
1220         struct multipath *m = (struct multipath *) ti->private;
1221
1222         queue_if_no_path(m, 0, 1);
1223 }
1224
1225 /*
1226  * Restore the queue_if_no_path setting.
1227  */
1228 static void multipath_resume(struct dm_target *ti)
1229 {
1230         struct multipath *m = (struct multipath *) ti->private;
1231         unsigned long flags;
1232
1233         spin_lock_irqsave(&m->lock, flags);
1234         m->queue_if_no_path = m->saved_queue_if_no_path;
1235         spin_unlock_irqrestore(&m->lock, flags);
1236 }
1237
1238 /*
1239  * Info output has the following format:
1240  * num_multipath_feature_args [multipath_feature_args]*
1241  * num_handler_status_args [handler_status_args]*
1242  * num_groups init_group_number
1243  *            [A|D|E num_ps_status_args [ps_status_args]*
1244  *             num_paths num_selector_args
1245  *             [path_dev A|F fail_count [selector_args]* ]+ ]+
1246  *
1247  * Table output has the following format (identical to the constructor string):
1248  * num_feature_args [features_args]*
1249  * num_handler_args hw_handler [hw_handler_args]*
1250  * num_groups init_group_number
1251  *     [priority selector-name num_ps_args [ps_args]*
1252  *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
1253  */
1254 static int multipath_status(struct dm_target *ti, status_type_t type,
1255                             char *result, unsigned int maxlen)
1256 {
1257         int sz = 0;
1258         unsigned long flags;
1259         struct multipath *m = (struct multipath *) ti->private;
1260         struct priority_group *pg;
1261         struct pgpath *p;
1262         unsigned pg_num;
1263         char state;
1264
1265         spin_lock_irqsave(&m->lock, flags);
1266
1267         /* Features */
1268         if (type == STATUSTYPE_INFO)
1269                 DMEMIT("2 %u %u ", m->queue_size, m->pg_init_count);
1270         else {
1271                 DMEMIT("%u ", m->queue_if_no_path +
1272                               (m->pg_init_retries > 0) * 2);
1273                 if (m->queue_if_no_path)
1274                         DMEMIT("queue_if_no_path ");
1275                 if (m->pg_init_retries)
1276                         DMEMIT("pg_init_retries %u ", m->pg_init_retries);
1277         }
1278
1279         if (!m->hw_handler_name || type == STATUSTYPE_INFO)
1280                 DMEMIT("0 ");
1281         else
1282                 DMEMIT("1 %s ", m->hw_handler_name);
1283
1284         DMEMIT("%u ", m->nr_priority_groups);
1285
1286         if (m->next_pg)
1287                 pg_num = m->next_pg->pg_num;
1288         else if (m->current_pg)
1289                 pg_num = m->current_pg->pg_num;
1290         else
1291                         pg_num = 1;
1292
1293         DMEMIT("%u ", pg_num);
1294
1295         switch (type) {
1296         case STATUSTYPE_INFO:
1297                 list_for_each_entry(pg, &m->priority_groups, list) {
1298                         if (pg->bypassed)
1299                                 state = 'D';    /* Disabled */
1300                         else if (pg == m->current_pg)
1301                                 state = 'A';    /* Currently Active */
1302                         else
1303                                 state = 'E';    /* Enabled */
1304
1305                         DMEMIT("%c ", state);
1306
1307                         if (pg->ps.type->status)
1308                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1309                                                           result + sz,
1310                                                           maxlen - sz);
1311                         else
1312                                 DMEMIT("0 ");
1313
1314                         DMEMIT("%u %u ", pg->nr_pgpaths,
1315                                pg->ps.type->info_args);
1316
1317                         list_for_each_entry(p, &pg->pgpaths, list) {
1318                                 DMEMIT("%s %s %u ", p->path.dev->name,
1319                                        p->is_active ? "A" : "F",
1320                                        p->fail_count);
1321                                 if (pg->ps.type->status)
1322                                         sz += pg->ps.type->status(&pg->ps,
1323                                               &p->path, type, result + sz,
1324                                               maxlen - sz);
1325                         }
1326                 }
1327                 break;
1328
1329         case STATUSTYPE_TABLE:
1330                 list_for_each_entry(pg, &m->priority_groups, list) {
1331                         DMEMIT("%s ", pg->ps.type->name);
1332
1333                         if (pg->ps.type->status)
1334                                 sz += pg->ps.type->status(&pg->ps, NULL, type,
1335                                                           result + sz,
1336                                                           maxlen - sz);
1337                         else
1338                                 DMEMIT("0 ");
1339
1340                         DMEMIT("%u %u ", pg->nr_pgpaths,
1341                                pg->ps.type->table_args);
1342
1343                         list_for_each_entry(p, &pg->pgpaths, list) {
1344                                 DMEMIT("%s ", p->path.dev->name);
1345                                 if (pg->ps.type->status)
1346                                         sz += pg->ps.type->status(&pg->ps,
1347                                               &p->path, type, result + sz,
1348                                               maxlen - sz);
1349                         }
1350                 }
1351                 break;
1352         }
1353
1354         spin_unlock_irqrestore(&m->lock, flags);
1355
1356         return 0;
1357 }
1358
1359 static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
1360 {
1361         int r;
1362         struct dm_dev *dev;
1363         struct multipath *m = (struct multipath *) ti->private;
1364         action_fn action;
1365
1366         if (argc == 1) {
1367                 if (!strnicmp(argv[0], MESG_STR("queue_if_no_path")))
1368                         return queue_if_no_path(m, 1, 0);
1369                 else if (!strnicmp(argv[0], MESG_STR("fail_if_no_path")))
1370                         return queue_if_no_path(m, 0, 0);
1371         }
1372
1373         if (argc != 2)
1374                 goto error;
1375
1376         if (!strnicmp(argv[0], MESG_STR("disable_group")))
1377                 return bypass_pg_num(m, argv[1], 1);
1378         else if (!strnicmp(argv[0], MESG_STR("enable_group")))
1379                 return bypass_pg_num(m, argv[1], 0);
1380         else if (!strnicmp(argv[0], MESG_STR("switch_group")))
1381                 return switch_pg_num(m, argv[1]);
1382         else if (!strnicmp(argv[0], MESG_STR("reinstate_path")))
1383                 action = reinstate_path;
1384         else if (!strnicmp(argv[0], MESG_STR("fail_path")))
1385                 action = fail_path;
1386         else
1387                 goto error;
1388
1389         r = dm_get_device(ti, argv[1], ti->begin, ti->len,
1390                           dm_table_get_mode(ti->table), &dev);
1391         if (r) {
1392                 DMWARN("message: error getting device %s",
1393                        argv[1]);
1394                 return -EINVAL;
1395         }
1396
1397         r = action_dev(m, dev, action);
1398
1399         dm_put_device(ti, dev);
1400
1401         return r;
1402
1403 error:
1404         DMWARN("Unrecognised multipath message received.");
1405         return -EINVAL;
1406 }
1407
1408 static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
1409                            unsigned long arg)
1410 {
1411         struct multipath *m = (struct multipath *) ti->private;
1412         struct block_device *bdev = NULL;
1413         fmode_t mode = 0;
1414         unsigned long flags;
1415         int r = 0;
1416
1417         spin_lock_irqsave(&m->lock, flags);
1418
1419         if (!m->current_pgpath)
1420                 __choose_pgpath(m);
1421
1422         if (m->current_pgpath) {
1423                 bdev = m->current_pgpath->path.dev->bdev;
1424                 mode = m->current_pgpath->path.dev->mode;
1425         }
1426
1427         if (m->queue_io)
1428                 r = -EAGAIN;
1429         else if (!bdev)
1430                 r = -EIO;
1431
1432         spin_unlock_irqrestore(&m->lock, flags);
1433
1434         return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);
1435 }
1436
1437 /*-----------------------------------------------------------------
1438  * Module setup
1439  *---------------------------------------------------------------*/
1440 static struct target_type multipath_target = {
1441         .name = "multipath",
1442         .version = {1, 0, 5},
1443         .module = THIS_MODULE,
1444         .ctr = multipath_ctr,
1445         .dtr = multipath_dtr,
1446         .map = multipath_map,
1447         .end_io = multipath_end_io,
1448         .presuspend = multipath_presuspend,
1449         .resume = multipath_resume,
1450         .status = multipath_status,
1451         .message = multipath_message,
1452         .ioctl  = multipath_ioctl,
1453 };
1454
1455 static int __init dm_multipath_init(void)
1456 {
1457         int r;
1458
1459         /* allocate a slab for the dm_ios */
1460         _mpio_cache = KMEM_CACHE(dm_mpath_io, 0);
1461         if (!_mpio_cache)
1462                 return -ENOMEM;
1463
1464         r = dm_register_target(&multipath_target);
1465         if (r < 0) {
1466                 DMERR("register failed %d", r);
1467                 kmem_cache_destroy(_mpio_cache);
1468                 return -EINVAL;
1469         }
1470
1471         kmultipathd = create_workqueue("kmpathd");
1472         if (!kmultipathd) {
1473                 DMERR("failed to create workqueue kmpathd");
1474                 dm_unregister_target(&multipath_target);
1475                 kmem_cache_destroy(_mpio_cache);
1476                 return -ENOMEM;
1477         }
1478
1479         /*
1480          * A separate workqueue is used to handle the device handlers
1481          * to avoid overloading existing workqueue. Overloading the
1482          * old workqueue would also create a bottleneck in the
1483          * path of the storage hardware device activation.
1484          */
1485         kmpath_handlerd = create_singlethread_workqueue("kmpath_handlerd");
1486         if (!kmpath_handlerd) {
1487                 DMERR("failed to create workqueue kmpath_handlerd");
1488                 destroy_workqueue(kmultipathd);
1489                 dm_unregister_target(&multipath_target);
1490                 kmem_cache_destroy(_mpio_cache);
1491                 return -ENOMEM;
1492         }
1493
1494         DMINFO("version %u.%u.%u loaded",
1495                multipath_target.version[0], multipath_target.version[1],
1496                multipath_target.version[2]);
1497
1498         return r;
1499 }
1500
1501 static void __exit dm_multipath_exit(void)
1502 {
1503         destroy_workqueue(kmpath_handlerd);
1504         destroy_workqueue(kmultipathd);
1505
1506         dm_unregister_target(&multipath_target);
1507         kmem_cache_destroy(_mpio_cache);
1508 }
1509
1510 module_init(dm_multipath_init);
1511 module_exit(dm_multipath_exit);
1512
1513 MODULE_DESCRIPTION(DM_NAME " multipath target");
1514 MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
1515 MODULE_LICENSE("GPL");