drivers/md/dm-snap.c

   1 /*
   2  * dm-snapshot.c
   3  *
   4  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
   5  *
   6  * This file is released under the GPL.
   7  */
   8
   9 #include <linux/blkdev.h>
  10 #include <linux/device-mapper.h>
  11 #include <linux/delay.h>
  12 #include <linux/fs.h>
  13 #include <linux/init.h>
  14 #include <linux/kdev_t.h>
  15 #include <linux/list.h>
  16 #include <linux/mempool.h>
  17 #include <linux/module.h>
  18 #include <linux/slab.h>
  19 #include <linux/vmalloc.h>
  20 #include <linux/log2.h>
  21 #include <linux/dm-kcopyd.h>
  22 #include <linux/workqueue.h>
  23
  24 #include "dm-exception-store.h"
  25
  26 #define DM_MSG_PREFIX "snapshots"
  27
  28 static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
  29
  30 #define dm_target_is_snapshot_merge(ti) \
  31         ((ti)->type->name == dm_snapshot_merge_target_name)
  32
  33 /*
  34  * The percentage increment we will wake up users at
  35  */
  36 #define WAKE_UP_PERCENT 5
  37
  38 /*
  39  * kcopyd priority of snapshot operations
  40  */
  41 #define SNAPSHOT_COPY_PRIORITY 2
  42
  43 /*
  44  * Reserve 1MB for each snapshot initially (with minimum of 1 page).
  45  */
  46 #define SNAPSHOT_PAGES (((1UL << 20) >> PAGE_SHIFT) ? : 1)
  47
  48 /*
  49  * The size of the mempool used to track chunks in use.
  50  */
  51 #define MIN_IOS 256
  52
  53 #define DM_TRACKED_CHUNK_HASH_SIZE      16
  54 #define DM_TRACKED_CHUNK_HASH(x)        ((unsigned long)(x) & \
  55                                          (DM_TRACKED_CHUNK_HASH_SIZE - 1))
  56
  57 struct dm_exception_table {
  58         uint32_t hash_mask;
  59         unsigned hash_shift;
  60         struct list_head *table;
  61 };
  62
  63 struct dm_snapshot {
  64         struct rw_semaphore lock;
  65
  66         struct dm_dev *origin;
  67         struct dm_dev *cow;
  68
  69         struct dm_target *ti;
  70
  71         /* List of snapshots per Origin */
  72         struct list_head list;
  73
  74         /*
  75          * You can't use a snapshot if this is 0 (e.g. if full).
  76          * A snapshot-merge target never clears this.
  77          */
  78         int valid;
  79
  80         /* Origin writes don't trigger exceptions until this is set */
  81         int active;
  82
  83         /* Whether or not owning mapped_device is suspended */
  84         int suspended;
  85
  86         mempool_t *pending_pool;
  87
  88         atomic_t pending_exceptions_count;
  89
  90         struct dm_exception_table pending;
  91         struct dm_exception_table complete;
  92
  93         /*
  94          * pe_lock protects all pending_exception operations and access
  95          * as well as the snapshot_bios list.
  96          */
  97         spinlock_t pe_lock;
  98
  99         /* The on disk metadata handler */
 100         struct dm_exception_store *store;
 101
 102         struct dm_kcopyd_client *kcopyd_client;
 103
 104         /* Queue of snapshot writes for ksnapd to flush */
 105         struct bio_list queued_bios;
 106         struct work_struct queued_bios_work;
 107
 108         /* Chunks with outstanding reads */
 109         mempool_t *tracked_chunk_pool;
 110         spinlock_t tracked_chunk_lock;
 111         struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
 112
 113         /*
 114          * The merge operation failed if this flag is set.
 115          * Failure modes are handled as follows:
 116          * - I/O error reading the header
 117          *      => don't load the target; abort.
 118          * - Header does not have "valid" flag set
 119          *      => use the origin; forget about the snapshot.
 120          * - I/O error when reading exceptions
 121          *      => don't load the target; abort.
 122          *         (We can't use the intermediate origin state.)
 123          * - I/O error while merging
 124          *      => stop merging; set merge_failed; process I/O normally.
 125          */
 126         int merge_failed;
 127
 128         /* Wait for events based on state_bits */
 129         unsigned long state_bits;
 130
 131         /* Range of chunks currently being merged. */
 132         chunk_t first_merging_chunk;
 133         int num_merging_chunks;
 134
 135         /*
 136          * Incoming bios that overlap with chunks being merged must wait
 137          * for them to be committed.
 138          */
 139         struct bio_list bios_queued_during_merge;
 140 };
 141
 142 /*
 143  * state_bits:
 144  *   RUNNING_MERGE  - Merge operation is in progress.
 145  *   SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
 146  *                    cleared afterwards.
 147  */
 148 #define RUNNING_MERGE          0
 149 #define SHUTDOWN_MERGE         1
 150
 151 struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
 152 {
 153         return s->cow;
 154 }
 155 EXPORT_SYMBOL(dm_snap_cow);
 156
 157 static struct workqueue_struct *ksnapd;
 158 static void flush_queued_bios(struct work_struct *work);
 159
 160 static sector_t chunk_to_sector(struct dm_exception_store *store,
 161                                 chunk_t chunk)
 162 {
 163         return chunk << store->chunk_shift;
 164 }
 165
 166 static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
 167 {
 168         /*
 169          * There is only ever one instance of a particular block
 170          * device so we can compare pointers safely.
 171          */
 172         return lhs == rhs;
 173 }
 174
 175 struct dm_snap_pending_exception {
 176         struct dm_exception e;
 177
 178         /*
 179          * Origin buffers waiting for this to complete are held
 180          * in a bio list
 181          */
 182         struct bio_list origin_bios;
 183         struct bio_list snapshot_bios;
 184
 185         /* Pointer back to snapshot context */
 186         struct dm_snapshot *snap;
 187
 188         /*
 189          * 1 indicates the exception has already been sent to
 190          * kcopyd.
 191          */
 192         int started;
 193 };
 194
 195 /*
 196  * Hash table mapping origin volumes to lists of snapshots and
 197  * a lock to protect it
 198  */
 199 static struct kmem_cache *exception_cache;
 200 static struct kmem_cache *pending_cache;
 201
 202 struct dm_snap_tracked_chunk {
 203         struct hlist_node node;
 204         chunk_t chunk;
 205 };
 206
 207 static struct kmem_cache *tracked_chunk_cache;
 208
 209 static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s,
 210                                                  chunk_t chunk)
 211 {
 212         struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool,
 213                                                         GFP_NOIO);
 214         unsigned long flags;
 215
 216         c->chunk = chunk;
 217
 218         spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 219         hlist_add_head(&c->node,
 220                        &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
 221         spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
 222
 223         return c;
 224 }
 225
 226 static void stop_tracking_chunk(struct dm_snapshot *s,
 227                                 struct dm_snap_tracked_chunk *c)
 228 {
 229         unsigned long flags;
 230
 231         spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 232         hlist_del(&c->node);
 233         spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
 234
 235         mempool_free(c, s->tracked_chunk_pool);
 236 }
 237
 238 static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
 239 {
 240         struct dm_snap_tracked_chunk *c;
 241         struct hlist_node *hn;
 242         int found = 0;
 243
 244         spin_lock_irq(&s->tracked_chunk_lock);
 245
 246         hlist_for_each_entry(c, hn,
 247             &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
 248                 if (c->chunk == chunk) {
 249                         found = 1;
 250                         break;
 251                 }
 252         }
 253
 254         spin_unlock_irq(&s->tracked_chunk_lock);
 255
 256         return found;
 257 }
 258
 259 /*
 260  * This conflicting I/O is extremely improbable in the caller,
 261  * so msleep(1) is sufficient and there is no need for a wait queue.
 262  */
 263 static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
 264 {
 265         while (__chunk_is_tracked(s, chunk))
 266                 msleep(1);
 267 }
 268
 269 /*
 270  * One of these per registered origin, held in the snapshot_origins hash
 271  */
 272 struct origin {
 273         /* The origin device */
 274         struct block_device *bdev;
 275
 276         struct list_head hash_list;
 277
 278         /* List of snapshots for this origin */
 279         struct list_head snapshots;
 280 };
 281
 282 /*
 283  * Size of the hash table for origin volumes. If we make this
 284  * the size of the minors list then it should be nearly perfect
 285  */
 286 #define ORIGIN_HASH_SIZE 256
 287 #define ORIGIN_MASK      0xFF
 288 static struct list_head *_origins;
 289 static struct rw_semaphore _origins_lock;
 290
 291 static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
 292 static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
 293 static uint64_t _pending_exceptions_done_count;
 294
 295 static int init_origin_hash(void)
 296 {
 297         int i;
 298
 299         _origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
 300                            GFP_KERNEL);
 301         if (!_origins) {
 302                 DMERR("unable to allocate memory");
 303                 return -ENOMEM;
 304         }
 305
 306         for (i = 0; i < ORIGIN_HASH_SIZE; i++)
 307                 INIT_LIST_HEAD(_origins + i);
 308         init_rwsem(&_origins_lock);
 309
 310         return 0;
 311 }
 312
 313 static void exit_origin_hash(void)
 314 {
 315         kfree(_origins);
 316 }
 317
 318 static unsigned origin_hash(struct block_device *bdev)
 319 {
 320         return bdev->bd_dev & ORIGIN_MASK;
 321 }
 322
 323 static struct origin *__lookup_origin(struct block_device *origin)
 324 {
 325         struct list_head *ol;
 326         struct origin *o;
 327
 328         ol = &_origins[origin_hash(origin)];
 329         list_for_each_entry (o, ol, hash_list)
 330                 if (bdev_equal(o->bdev, origin))
 331                         return o;
 332
 333         return NULL;
 334 }
 335
 336 static void __insert_origin(struct origin *o)
 337 {
 338         struct list_head *sl = &_origins[origin_hash(o->bdev)];
 339         list_add_tail(&o->hash_list, sl);
 340 }
 341
 342 /*
 343  * _origins_lock must be held when calling this function.
 344  * Returns number of snapshots registered using the supplied cow device, plus:
 345  * snap_src - a snapshot suitable for use as a source of exception handover
 346  * snap_dest - a snapshot capable of receiving exception handover.
 347  * snap_merge - an existing snapshot-merge target linked to the same origin.
 348  *   There can be at most one snapshot-merge target. The parameter is optional.
 349  *
 350  * Possible return values and states of snap_src and snap_dest.
 351  *   0: NULL, NULL  - first new snapshot
 352  *   1: snap_src, NULL - normal snapshot
 353  *   2: snap_src, snap_dest  - waiting for handover
 354  *   2: snap_src, NULL - handed over, waiting for old to be deleted
 355  *   1: NULL, snap_dest - source got destroyed without handover
 356  */
 357 static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
 358                                         struct dm_snapshot **snap_src,
 359                                         struct dm_snapshot **snap_dest,
 360                                         struct dm_snapshot **snap_merge)
 361 {
 362         struct dm_snapshot *s;
 363         struct origin *o;
 364         int count = 0;
 365         int active;
 366
 367         o = __lookup_origin(snap->origin->bdev);
 368         if (!o)
 369                 goto out;
 370
 371         list_for_each_entry(s, &o->snapshots, list) {
 372                 if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
 373                         *snap_merge = s;
 374                 if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
 375                         continue;
 376
 377                 down_read(&s->lock);
 378                 active = s->active;
 379                 up_read(&s->lock);
 380
 381                 if (active) {
 382                         if (snap_src)
 383                                 *snap_src = s;
 384                 } else if (snap_dest)
 385                         *snap_dest = s;
 386
 387                 count++;
 388         }
 389
 390 out:
 391         return count;
 392 }
 393
 394 /*
 395  * On success, returns 1 if this snapshot is a handover destination,
 396  * otherwise returns 0.
 397  */
 398 static int __validate_exception_handover(struct dm_snapshot *snap)
 399 {
 400         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
 401         struct dm_snapshot *snap_merge = NULL;
 402
 403         /* Does snapshot need exceptions handed over to it? */
 404         if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
 405                                           &snap_merge) == 2) ||
 406             snap_dest) {
 407                 snap->ti->error = "Snapshot cow pairing for exception "
 408                                   "table handover failed";
 409                 return -EINVAL;
 410         }
 411
 412         /*
 413          * If no snap_src was found, snap cannot become a handover
 414          * destination.
 415          */
 416         if (!snap_src)
 417                 return 0;
 418
 419         /*
 420          * Non-snapshot-merge handover?
 421          */
 422         if (!dm_target_is_snapshot_merge(snap->ti))
 423                 return 1;
 424
 425         /*
 426          * Do not allow more than one merging snapshot.
 427          */
 428         if (snap_merge) {
 429                 snap->ti->error = "A snapshot is already merging.";
 430                 return -EINVAL;
 431         }
 432
 433         if (!snap_src->store->type->prepare_merge ||
 434             !snap_src->store->type->commit_merge) {
 435                 snap->ti->error = "Snapshot exception store does not "
 436                                   "support snapshot-merge.";
 437                 return -EINVAL;
 438         }
 439
 440         return 1;
 441 }
 442
 443 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
 444 {
 445         struct dm_snapshot *l;
 446
 447         /* Sort the list according to chunk size, largest-first smallest-last */
 448         list_for_each_entry(l, &o->snapshots, list)
 449                 if (l->store->chunk_size < s->store->chunk_size)
 450                         break;
 451         list_add_tail(&s->list, &l->list);
 452 }
 453
 454 /*
 455  * Make a note of the snapshot and its origin so we can look it
 456  * up when the origin has a write on it.
 457  *
 458  * Also validate snapshot exception store handovers.
 459  * On success, returns 1 if this registration is a handover destination,
 460  * otherwise returns 0.
 461  */
 462 static int register_snapshot(struct dm_snapshot *snap)
 463 {
 464         struct origin *o, *new_o = NULL;
 465         struct block_device *bdev = snap->origin->bdev;
 466         int r = 0;
 467
 468         new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
 469         if (!new_o)
 470                 return -ENOMEM;
 471
 472         down_write(&_origins_lock);
 473
 474         r = __validate_exception_handover(snap);
 475         if (r < 0) {
 476                 kfree(new_o);
 477                 goto out;
 478         }
 479
 480         o = __lookup_origin(bdev);
 481         if (o)
 482                 kfree(new_o);
 483         else {
 484                 /* New origin */
 485                 o = new_o;
 486
 487                 /* Initialise the struct */
 488                 INIT_LIST_HEAD(&o->snapshots);
 489                 o->bdev = bdev;
 490
 491                 __insert_origin(o);
 492         }
 493
 494         __insert_snapshot(o, snap);
 495
 496 out:
 497         up_write(&_origins_lock);
 498
 499         return r;
 500 }
 501
 502 /*
 503  * Move snapshot to correct place in list according to chunk size.
 504  */
 505 static void reregister_snapshot(struct dm_snapshot *s)
 506 {
 507         struct block_device *bdev = s->origin->bdev;
 508
 509         down_write(&_origins_lock);
 510
 511         list_del(&s->list);
 512         __insert_snapshot(__lookup_origin(bdev), s);
 513
 514         up_write(&_origins_lock);
 515 }
 516
 517 static void unregister_snapshot(struct dm_snapshot *s)
 518 {
 519         struct origin *o;
 520
 521         down_write(&_origins_lock);
 522         o = __lookup_origin(s->origin->bdev);
 523
 524         list_del(&s->list);
 525         if (o && list_empty(&o->snapshots)) {
 526                 list_del(&o->hash_list);
 527                 kfree(o);
 528         }
 529
 530         up_write(&_origins_lock);
 531 }
 532
 533 /*
 534  * Implementation of the exception hash tables.
 535  * The lowest hash_shift bits of the chunk number are ignored, allowing
 536  * some consecutive chunks to be grouped together.
 537  */
 538 static int dm_exception_table_init(struct dm_exception_table *et,
 539                                    uint32_t size, unsigned hash_shift)
 540 {
 541         unsigned int i;
 542
 543         et->hash_shift = hash_shift;
 544         et->hash_mask = size - 1;
 545         et->table = dm_vcalloc(size, sizeof(struct list_head));
 546         if (!et->table)
 547                 return -ENOMEM;
 548
 549         for (i = 0; i < size; i++)
 550                 INIT_LIST_HEAD(et->table + i);
 551
 552         return 0;
 553 }
 554
 555 static void dm_exception_table_exit(struct dm_exception_table *et,
 556                                     struct kmem_cache *mem)
 557 {
 558         struct list_head *slot;
 559         struct dm_exception *ex, *next;
 560         int i, size;
 561
 562         size = et->hash_mask + 1;
 563         for (i = 0; i < size; i++) {
 564                 slot = et->table + i;
 565
 566                 list_for_each_entry_safe (ex, next, slot, hash_list)
 567                         kmem_cache_free(mem, ex);
 568         }
 569
 570         vfree(et->table);
 571 }
 572
 573 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
 574 {
 575         return (chunk >> et->hash_shift) & et->hash_mask;
 576 }
 577
 578 static void dm_remove_exception(struct dm_exception *e)
 579 {
 580         list_del(&e->hash_list);
 581 }
 582
 583 /*
 584  * Return the exception data for a sector, or NULL if not
 585  * remapped.
 586  */
 587 static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
 588                                                 chunk_t chunk)
 589 {
 590         struct list_head *slot;
 591         struct dm_exception *e;
 592
 593         slot = &et->table[exception_hash(et, chunk)];
 594         list_for_each_entry (e, slot, hash_list)
 595                 if (chunk >= e->old_chunk &&
 596                     chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
 597                         return e;
 598
 599         return NULL;
 600 }
 601
 602 static struct dm_exception *alloc_completed_exception(void)
 603 {
 604         struct dm_exception *e;
 605
 606         e = kmem_cache_alloc(exception_cache, GFP_NOIO);
 607         if (!e)
 608                 e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
 609
 610         return e;
 611 }
 612
 613 static void free_completed_exception(struct dm_exception *e)
 614 {
 615         kmem_cache_free(exception_cache, e);
 616 }
 617
 618 static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
 619 {
 620         struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
 621                                                              GFP_NOIO);
 622
 623         atomic_inc(&s->pending_exceptions_count);
 624         pe->snap = s;
 625
 626         return pe;
 627 }
 628
 629 static void free_pending_exception(struct dm_snap_pending_exception *pe)
 630 {
 631         struct dm_snapshot *s = pe->snap;
 632
 633         mempool_free(pe, s->pending_pool);
 634         smp_mb__before_atomic_dec();
 635         atomic_dec(&s->pending_exceptions_count);
 636 }
 637
 638 static void dm_insert_exception(struct dm_exception_table *eh,
 639                                 struct dm_exception *new_e)
 640 {
 641         struct list_head *l;
 642         struct dm_exception *e = NULL;
 643
 644         l = &eh->table[exception_hash(eh, new_e->old_chunk)];
 645
 646         /* Add immediately if this table doesn't support consecutive chunks */
 647         if (!eh->hash_shift)
 648                 goto out;
 649
 650         /* List is ordered by old_chunk */
 651         list_for_each_entry_reverse(e, l, hash_list) {
 652                 /* Insert after an existing chunk? */
 653                 if (new_e->old_chunk == (e->old_chunk +
 654                                          dm_consecutive_chunk_count(e) + 1) &&
 655                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
 656                                          dm_consecutive_chunk_count(e) + 1)) {
 657                         dm_consecutive_chunk_count_inc(e);
 658                         free_completed_exception(new_e);
 659                         return;
 660                 }
 661
 662                 /* Insert before an existing chunk? */
 663                 if (new_e->old_chunk == (e->old_chunk - 1) &&
 664                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
 665                         dm_consecutive_chunk_count_inc(e);
 666                         e->old_chunk--;
 667                         e->new_chunk--;
 668                         free_completed_exception(new_e);
 669                         return;
 670                 }
 671
 672                 if (new_e->old_chunk > e->old_chunk)
 673                         break;
 674         }
 675
 676 out:
 677         list_add(&new_e->hash_list, e ? &e->hash_list : l);
 678 }
 679
 680 /*
 681  * Callback used by the exception stores to load exceptions when
 682  * initialising.
 683  */
 684 static int dm_add_exception(void *context, chunk_t old, chunk_t new)
 685 {
 686         struct dm_snapshot *s = context;
 687         struct dm_exception *e;
 688
 689         e = alloc_completed_exception();
 690         if (!e)
 691                 return -ENOMEM;
 692
 693         e->old_chunk = old;
 694
 695         /* Consecutive_count is implicitly initialised to zero */
 696         e->new_chunk = new;
 697
 698         dm_insert_exception(&s->complete, e);
 699
 700         return 0;
 701 }
 702
 703 #define min_not_zero(l, r) (((l) == 0) ? (r) : (((r) == 0) ? (l) : min(l, r)))
 704
 705 /*
 706  * Return a minimum chunk size of all snapshots that have the specified origin.
 707  * Return zero if the origin has no snapshots.
 708  */
 709 static sector_t __minimum_chunk_size(struct origin *o)
 710 {
 711         struct dm_snapshot *snap;
 712         unsigned chunk_size = 0;
 713
 714         if (o)
 715                 list_for_each_entry(snap, &o->snapshots, list)
 716                         chunk_size = min_not_zero(chunk_size,
 717                                                   snap->store->chunk_size);
 718
 719         return chunk_size;
 720 }
 721
 722 /*
 723  * Hard coded magic.
 724  */
 725 static int calc_max_buckets(void)
 726 {
 727         /* use a fixed size of 2MB */
 728         unsigned long mem = 2 * 1024 * 1024;
 729         mem /= sizeof(struct list_head);
 730
 731         return mem;
 732 }
 733
 734 /*
 735  * Allocate room for a suitable hash table.
 736  */
 737 static int init_hash_tables(struct dm_snapshot *s)
 738 {
 739         sector_t hash_size, cow_dev_size, origin_dev_size, max_buckets;
 740
 741         /*
 742          * Calculate based on the size of the original volume or
 743          * the COW volume...
 744          */
 745         cow_dev_size = get_dev_size(s->cow->bdev);
 746         origin_dev_size = get_dev_size(s->origin->bdev);
 747         max_buckets = calc_max_buckets();
 748
 749         hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift;
 750         hash_size = min(hash_size, max_buckets);
 751
 752         if (hash_size < 64)
 753                 hash_size = 64;
 754         hash_size = rounddown_pow_of_two(hash_size);
 755         if (dm_exception_table_init(&s->complete, hash_size,
 756                                     DM_CHUNK_CONSECUTIVE_BITS))
 757                 return -ENOMEM;
 758
 759         /*
 760          * Allocate hash table for in-flight exceptions
 761          * Make this smaller than the real hash table
 762          */
 763         hash_size >>= 3;
 764         if (hash_size < 64)
 765                 hash_size = 64;
 766
 767         if (dm_exception_table_init(&s->pending, hash_size, 0)) {
 768                 dm_exception_table_exit(&s->complete, exception_cache);
 769                 return -ENOMEM;
 770         }
 771
 772         return 0;
 773 }
 774
 775 static void merge_shutdown(struct dm_snapshot *s)
 776 {
 777         clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
 778         smp_mb__after_clear_bit();
 779         wake_up_bit(&s->state_bits, RUNNING_MERGE);
 780 }
 781
 782 static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
 783 {
 784         s->first_merging_chunk = 0;
 785         s->num_merging_chunks = 0;
 786
 787         return bio_list_get(&s->bios_queued_during_merge);
 788 }
 789
 790 /*
 791  * Remove one chunk from the index of completed exceptions.
 792  */
 793 static int __remove_single_exception_chunk(struct dm_snapshot *s,
 794                                            chunk_t old_chunk)
 795 {
 796         struct dm_exception *e;
 797
 798         e = dm_lookup_exception(&s->complete, old_chunk);
 799         if (!e) {
 800                 DMERR("Corruption detected: exception for block %llu is "
 801                       "on disk but not in memory",
 802                       (unsigned long long)old_chunk);
 803                 return -EINVAL;
 804         }
 805
 806         /*
 807          * If this is the only chunk using this exception, remove exception.
 808          */
 809         if (!dm_consecutive_chunk_count(e)) {
 810                 dm_remove_exception(e);
 811                 free_completed_exception(e);
 812                 return 0;
 813         }
 814
 815         /*
 816          * The chunk may be either at the beginning or the end of a
 817          * group of consecutive chunks - never in the middle.  We are
 818          * removing chunks in the opposite order to that in which they
 819          * were added, so this should always be true.
 820          * Decrement the consecutive chunk counter and adjust the
 821          * starting point if necessary.
 822          */
 823         if (old_chunk == e->old_chunk) {
 824                 e->old_chunk++;
 825                 e->new_chunk++;
 826         } else if (old_chunk != e->old_chunk +
 827                    dm_consecutive_chunk_count(e)) {
 828                 DMERR("Attempt to merge block %llu from the "
 829                       "middle of a chunk range [%llu - %llu]",
 830                       (unsigned long long)old_chunk,
 831                       (unsigned long long)e->old_chunk,
 832                       (unsigned long long)
 833                       e->old_chunk + dm_consecutive_chunk_count(e));
 834                 return -EINVAL;
 835         }
 836
 837         dm_consecutive_chunk_count_dec(e);
 838
 839         return 0;
 840 }
 841
 842 static void flush_bios(struct bio *bio);
 843
 844 static int remove_single_exception_chunk(struct dm_snapshot *s)
 845 {
 846         struct bio *b = NULL;
 847         int r;
 848         chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
 849
 850         down_write(&s->lock);
 851
 852         /*
 853          * Process chunks (and associated exceptions) in reverse order
 854          * so that dm_consecutive_chunk_count_dec() accounting works.
 855          */
 856         do {
 857                 r = __remove_single_exception_chunk(s, old_chunk);
 858                 if (r)
 859                         goto out;
 860         } while (old_chunk-- > s->first_merging_chunk);
 861
 862         b = __release_queued_bios_after_merge(s);
 863
 864 out:
 865         up_write(&s->lock);
 866         if (b)
 867                 flush_bios(b);
 868
 869         return r;
 870 }
 871
 872 static int origin_write_extent(struct dm_snapshot *merging_snap,
 873                                sector_t sector, unsigned chunk_size);
 874
 875 static void merge_callback(int read_err, unsigned long write_err,
 876                            void *context);
 877
 878 static uint64_t read_pending_exceptions_done_count(void)
 879 {
 880         uint64_t pending_exceptions_done;
 881
 882         spin_lock(&_pending_exceptions_done_spinlock);
 883         pending_exceptions_done = _pending_exceptions_done_count;
 884         spin_unlock(&_pending_exceptions_done_spinlock);
 885
 886         return pending_exceptions_done;
 887 }
 888
 889 static void increment_pending_exceptions_done_count(void)
 890 {
 891         spin_lock(&_pending_exceptions_done_spinlock);
 892         _pending_exceptions_done_count++;
 893         spin_unlock(&_pending_exceptions_done_spinlock);
 894
 895         wake_up_all(&_pending_exceptions_done);
 896 }
 897
 898 static void snapshot_merge_next_chunks(struct dm_snapshot *s)
 899 {
 900         int i, linear_chunks;
 901         chunk_t old_chunk, new_chunk;
 902         struct dm_io_region src, dest;
 903         sector_t io_size;
 904         uint64_t previous_count;
 905
 906         BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
 907         if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
 908                 goto shut;
 909
 910         /*
 911          * valid flag never changes during merge, so no lock required.
 912          */
 913         if (!s->valid) {
 914                 DMERR("Snapshot is invalid: can't merge");
 915                 goto shut;
 916         }
 917
 918         linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
 919                                                       &new_chunk);
 920         if (linear_chunks <= 0) {
 921                 if (linear_chunks < 0) {
 922                         DMERR("Read error in exception store: "
 923                               "shutting down merge");
 924                         down_write(&s->lock);
 925                         s->merge_failed = 1;
 926                         up_write(&s->lock);
 927                 }
 928                 goto shut;
 929         }
 930
 931         /* Adjust old_chunk and new_chunk to reflect start of linear region */
 932         old_chunk = old_chunk + 1 - linear_chunks;
 933         new_chunk = new_chunk + 1 - linear_chunks;
 934
 935         /*
 936          * Use one (potentially large) I/O to copy all 'linear_chunks'
 937          * from the exception store to the origin
 938          */
 939         io_size = linear_chunks * s->store->chunk_size;
 940
 941         dest.bdev = s->origin->bdev;
 942         dest.sector = chunk_to_sector(s->store, old_chunk);
 943         dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
 944
 945         src.bdev = s->cow->bdev;
 946         src.sector = chunk_to_sector(s->store, new_chunk);
 947         src.count = dest.count;
 948
 949         /*
 950          * Reallocate any exceptions needed in other snapshots then
 951          * wait for the pending exceptions to complete.
 952          * Each time any pending exception (globally on the system)
 953          * completes we are woken and repeat the process to find out
 954          * if we can proceed.  While this may not seem a particularly
 955          * efficient algorithm, it is not expected to have any
 956          * significant impact on performance.
 957          */
 958         previous_count = read_pending_exceptions_done_count();
 959         while (origin_write_extent(s, dest.sector, io_size)) {
 960                 wait_event(_pending_exceptions_done,
 961                            (read_pending_exceptions_done_count() !=
 962                             previous_count));
 963                 /* Retry after the wait, until all exceptions are done. */
 964                 previous_count = read_pending_exceptions_done_count();
 965         }
 966
 967         down_write(&s->lock);
 968         s->first_merging_chunk = old_chunk;
 969         s->num_merging_chunks = linear_chunks;
 970         up_write(&s->lock);
 971
 972         /* Wait until writes to all 'linear_chunks' drain */
 973         for (i = 0; i < linear_chunks; i++)
 974                 __check_for_conflicting_io(s, old_chunk + i);
 975
 976         dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
 977         return;
 978
 979 shut:
 980         merge_shutdown(s);
 981 }
 982
 983 static void error_bios(struct bio *bio);
 984
 985 static void merge_callback(int read_err, unsigned long write_err, void *context)
 986 {
 987         struct dm_snapshot *s = context;
 988         struct bio *b = NULL;
 989
 990         if (read_err || write_err) {
 991                 if (read_err)
 992                         DMERR("Read error: shutting down merge.");
 993                 else
 994                         DMERR("Write error: shutting down merge.");
 995                 goto shut;
 996         }
 997
 998         if (s->store->type->commit_merge(s->store,
 999                                          s->num_merging_chunks) < 0) {
1000                 DMERR("Write error in exception store: shutting down merge");
1001                 goto shut;
1002         }
1003
1004         if (remove_single_exception_chunk(s) < 0)
1005                 goto shut;
1006
1007         snapshot_merge_next_chunks(s);
1008
1009         return;
1010
1011 shut:
1012         down_write(&s->lock);
1013         s->merge_failed = 1;
1014         b = __release_queued_bios_after_merge(s);
1015         up_write(&s->lock);
1016         error_bios(b);
1017
1018         merge_shutdown(s);
1019 }
1020
1021 static void start_merge(struct dm_snapshot *s)
1022 {
1023         if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
1024                 snapshot_merge_next_chunks(s);
1025 }
1026
1027 static int wait_schedule(void *ptr)
1028 {
1029         schedule();
1030
1031         return 0;
1032 }
1033
1034 /*
1035  * Stop the merging process and wait until it finishes.
1036  */
1037 static void stop_merge(struct dm_snapshot *s)
1038 {
1039         set_bit(SHUTDOWN_MERGE, &s->state_bits);
1040         wait_on_bit(&s->state_bits, RUNNING_MERGE, wait_schedule,
1041                     TASK_UNINTERRUPTIBLE);
1042         clear_bit(SHUTDOWN_MERGE, &s->state_bits);
1043 }
1044
1045 /*
1046  * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
1047  */
1048 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1049 {
1050         struct dm_snapshot *s;
1051         int i;
1052         int r = -EINVAL;
1053         char *origin_path, *cow_path;
1054         unsigned args_used, num_flush_requests = 1;
1055         fmode_t origin_mode = FMODE_READ;
1056
1057         if (argc != 4) {
1058                 ti->error = "requires exactly 4 arguments";
1059                 r = -EINVAL;
1060                 goto bad;
1061         }
1062
1063         if (dm_target_is_snapshot_merge(ti)) {
1064                 num_flush_requests = 2;
1065                 origin_mode = FMODE_WRITE;
1066         }
1067
1068         origin_path = argv[0];
1069         argv++;
1070         argc--;
1071
1072         s = kmalloc(sizeof(*s), GFP_KERNEL);
1073         if (!s) {
1074                 ti->error = "Cannot allocate snapshot context private "
1075                     "structure";
1076                 r = -ENOMEM;
1077                 goto bad;
1078         }
1079
1080         cow_path = argv[0];
1081         argv++;
1082         argc--;
1083
1084         r = dm_get_device(ti, cow_path, 0, 0,
1085                           FMODE_READ | FMODE_WRITE, &s->cow);
1086         if (r) {
1087                 ti->error = "Cannot get COW device";
1088                 goto bad_cow;
1089         }
1090
1091         r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
1092         if (r) {
1093                 ti->error = "Couldn't create exception store";
1094                 r = -EINVAL;
1095                 goto bad_store;
1096         }
1097
1098         argv += args_used;
1099         argc -= args_used;
1100
1101         r = dm_get_device(ti, origin_path, 0, ti->len, origin_mode, &s->origin);
1102         if (r) {
1103                 ti->error = "Cannot get origin device";
1104                 goto bad_origin;
1105         }
1106
1107         s->ti = ti;
1108         s->valid = 1;
1109         s->active = 0;
1110         s->suspended = 0;
1111         atomic_set(&s->pending_exceptions_count, 0);
1112         init_rwsem(&s->lock);
1113         INIT_LIST_HEAD(&s->list);
1114         spin_lock_init(&s->pe_lock);
1115         s->state_bits = 0;
1116         s->merge_failed = 0;
1117         s->first_merging_chunk = 0;
1118         s->num_merging_chunks = 0;
1119         bio_list_init(&s->bios_queued_during_merge);
1120
1121         /* Allocate hash table for COW data */
1122         if (init_hash_tables(s)) {
1123                 ti->error = "Unable to allocate hash table space";
1124                 r = -ENOMEM;
1125                 goto bad_hash_tables;
1126         }
1127
1128         r = dm_kcopyd_client_create(SNAPSHOT_PAGES, &s->kcopyd_client);
1129         if (r) {
1130                 ti->error = "Could not create kcopyd client";
1131                 goto bad_kcopyd;
1132         }
1133
1134         s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
1135         if (!s->pending_pool) {
1136                 ti->error = "Could not allocate mempool for pending exceptions";
1137                 goto bad_pending_pool;
1138         }
1139
1140         s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS,
1141                                                          tracked_chunk_cache);
1142         if (!s->tracked_chunk_pool) {
1143                 ti->error = "Could not allocate tracked_chunk mempool for "
1144                             "tracking reads";
1145                 goto bad_tracked_chunk_pool;
1146         }
1147
1148         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1149                 INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
1150
1151         spin_lock_init(&s->tracked_chunk_lock);
1152
1153         bio_list_init(&s->queued_bios);
1154         INIT_WORK(&s->queued_bios_work, flush_queued_bios);
1155
1156         ti->private = s;
1157         ti->num_flush_requests = num_flush_requests;
1158
1159         /* Add snapshot to the list of snapshots for this origin */
1160         /* Exceptions aren't triggered till snapshot_resume() is called */
1161         r = register_snapshot(s);
1162         if (r == -ENOMEM) {
1163                 ti->error = "Snapshot origin struct allocation failed";
1164                 goto bad_load_and_register;
1165         } else if (r < 0) {
1166                 /* invalid handover, register_snapshot has set ti->error */
1167                 goto bad_load_and_register;
1168         }
1169
1170         /*
1171          * Metadata must only be loaded into one table at once, so skip this
1172          * if metadata will be handed over during resume.
1173          * Chunk size will be set during the handover - set it to zero to
1174          * ensure it's ignored.
1175          */
1176         if (r > 0) {
1177                 s->store->chunk_size = 0;
1178                 return 0;
1179         }
1180
1181         r = s->store->type->read_metadata(s->store, dm_add_exception,
1182                                           (void *)s);
1183         if (r < 0) {
1184                 ti->error = "Failed to read snapshot metadata";
1185                 goto bad_read_metadata;
1186         } else if (r > 0) {
1187                 s->valid = 0;
1188                 DMWARN("Snapshot is marked invalid.");
1189         }
1190
1191         if (!s->store->chunk_size) {
1192                 ti->error = "Chunk size not set";
1193                 goto bad_read_metadata;
1194         }
1195         ti->split_io = s->store->chunk_size;
1196
1197         return 0;
1198
1199 bad_read_metadata:
1200         unregister_snapshot(s);
1201
1202 bad_load_and_register:
1203         mempool_destroy(s->tracked_chunk_pool);
1204
1205 bad_tracked_chunk_pool:
1206         mempool_destroy(s->pending_pool);
1207
1208 bad_pending_pool:
1209         dm_kcopyd_client_destroy(s->kcopyd_client);
1210
1211 bad_kcopyd:
1212         dm_exception_table_exit(&s->pending, pending_cache);
1213         dm_exception_table_exit(&s->complete, exception_cache);
1214
1215 bad_hash_tables:
1216         dm_put_device(ti, s->origin);
1217
1218 bad_origin:
1219         dm_exception_store_destroy(s->store);
1220
1221 bad_store:
1222         dm_put_device(ti, s->cow);
1223
1224 bad_cow:
1225         kfree(s);
1226
1227 bad:
1228         return r;
1229 }
1230
1231 static void __free_exceptions(struct dm_snapshot *s)
1232 {
1233         dm_kcopyd_client_destroy(s->kcopyd_client);
1234         s->kcopyd_client = NULL;
1235
1236         dm_exception_table_exit(&s->pending, pending_cache);
1237         dm_exception_table_exit(&s->complete, exception_cache);
1238 }
1239
1240 static void __handover_exceptions(struct dm_snapshot *snap_src,
1241                                   struct dm_snapshot *snap_dest)
1242 {
1243         union {
1244                 struct dm_exception_table table_swap;
1245                 struct dm_exception_store *store_swap;
1246         } u;
1247
1248         /*
1249          * Swap all snapshot context information between the two instances.
1250          */
1251         u.table_swap = snap_dest->complete;
1252         snap_dest->complete = snap_src->complete;
1253         snap_src->complete = u.table_swap;
1254
1255         u.store_swap = snap_dest->store;
1256         snap_dest->store = snap_src->store;
1257         snap_src->store = u.store_swap;
1258
1259         snap_dest->store->snap = snap_dest;
1260         snap_src->store->snap = snap_src;
1261
1262         snap_dest->ti->split_io = snap_dest->store->chunk_size;
1263         snap_dest->valid = snap_src->valid;
1264
1265         /*
1266          * Set source invalid to ensure it receives no further I/O.
1267          */
1268         snap_src->valid = 0;
1269 }
1270
1271 static void snapshot_dtr(struct dm_target *ti)
1272 {
1273 #ifdef CONFIG_DM_DEBUG
1274         int i;
1275 #endif
1276         struct dm_snapshot *s = ti->private;
1277         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1278
1279         flush_workqueue(ksnapd);
1280
1281         down_read(&_origins_lock);
1282         /* Check whether exception handover must be cancelled */
1283         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1284         if (snap_src && snap_dest && (s == snap_src)) {
1285                 down_write(&snap_dest->lock);
1286                 snap_dest->valid = 0;
1287                 up_write(&snap_dest->lock);
1288                 DMERR("Cancelling snapshot handover.");
1289         }
1290         up_read(&_origins_lock);
1291
1292         if (dm_target_is_snapshot_merge(ti))
1293                 stop_merge(s);
1294
1295         /* Prevent further origin writes from using this snapshot. */
1296         /* After this returns there can be no new kcopyd jobs. */
1297         unregister_snapshot(s);
1298
1299         while (atomic_read(&s->pending_exceptions_count))
1300                 msleep(1);
1301         /*
1302          * Ensure instructions in mempool_destroy aren't reordered
1303          * before atomic_read.
1304          */
1305         smp_mb();
1306
1307 #ifdef CONFIG_DM_DEBUG
1308         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
1309                 BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
1310 #endif
1311
1312         mempool_destroy(s->tracked_chunk_pool);
1313
1314         __free_exceptions(s);
1315
1316         mempool_destroy(s->pending_pool);
1317
1318         dm_put_device(ti, s->origin);
1319
1320         dm_exception_store_destroy(s->store);
1321
1322         dm_put_device(ti, s->cow);
1323
1324         kfree(s);
1325 }
1326
1327 /*
1328  * Flush a list of buffers.
1329  */
1330 static void flush_bios(struct bio *bio)
1331 {
1332         struct bio *n;
1333
1334         while (bio) {
1335                 n = bio->bi_next;
1336                 bio->bi_next = NULL;
1337                 generic_make_request(bio);
1338                 bio = n;
1339         }
1340 }
1341
1342 static void flush_queued_bios(struct work_struct *work)
1343 {
1344         struct dm_snapshot *s =
1345                 container_of(work, struct dm_snapshot, queued_bios_work);
1346         struct bio *queued_bios;
1347         unsigned long flags;
1348
1349         spin_lock_irqsave(&s->pe_lock, flags);
1350         queued_bios = bio_list_get(&s->queued_bios);
1351         spin_unlock_irqrestore(&s->pe_lock, flags);
1352
1353         flush_bios(queued_bios);
1354 }
1355
1356 static int do_origin(struct dm_dev *origin, struct bio *bio);
1357
1358 /*
1359  * Flush a list of buffers.
1360  */
1361 static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1362 {
1363         struct bio *n;
1364         int r;
1365
1366         while (bio) {
1367                 n = bio->bi_next;
1368                 bio->bi_next = NULL;
1369                 r = do_origin(s->origin, bio);
1370                 if (r == DM_MAPIO_REMAPPED)
1371                         generic_make_request(bio);
1372                 bio = n;
1373         }
1374 }
1375
1376 /*
1377  * Error a list of buffers.
1378  */
1379 static void error_bios(struct bio *bio)
1380 {
1381         struct bio *n;
1382
1383         while (bio) {
1384                 n = bio->bi_next;
1385                 bio->bi_next = NULL;
1386                 bio_io_error(bio);
1387                 bio = n;
1388         }
1389 }
1390
1391 static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1392 {
1393         if (!s->valid)
1394                 return;
1395
1396         if (err == -EIO)
1397                 DMERR("Invalidating snapshot: Error reading/writing.");
1398         else if (err == -ENOMEM)
1399                 DMERR("Invalidating snapshot: Unable to allocate exception.");
1400
1401         if (s->store->type->drop_snapshot)
1402                 s->store->type->drop_snapshot(s->store);
1403
1404         s->valid = 0;
1405
1406         dm_table_event(s->ti->table);
1407 }
1408
1409 static void pending_complete(struct dm_snap_pending_exception *pe, int success)
1410 {
1411         struct dm_exception *e;
1412         struct dm_snapshot *s = pe->snap;
1413         struct bio *origin_bios = NULL;
1414         struct bio *snapshot_bios = NULL;
1415         int error = 0;
1416
1417         if (!success) {
1418                 /* Read/write error - snapshot is unusable */
1419                 down_write(&s->lock);
1420                 __invalidate_snapshot(s, -EIO);
1421                 error = 1;
1422                 goto out;
1423         }
1424
1425         e = alloc_completed_exception();
1426         if (!e) {
1427                 down_write(&s->lock);
1428                 __invalidate_snapshot(s, -ENOMEM);
1429                 error = 1;
1430                 goto out;
1431         }
1432         *e = pe->e;
1433
1434         down_write(&s->lock);
1435         if (!s->valid) {
1436                 free_completed_exception(e);
1437                 error = 1;
1438                 goto out;
1439         }
1440
1441         /* Check for conflicting reads */
1442         __check_for_conflicting_io(s, pe->e.old_chunk);
1443
1444         /*
1445          * Add a proper exception, and remove the
1446          * in-flight exception from the list.
1447          */
1448         dm_insert_exception(&s->complete, e);
1449
1450  out:
1451         dm_remove_exception(&pe->e);
1452         snapshot_bios = bio_list_get(&pe->snapshot_bios);
1453         origin_bios = bio_list_get(&pe->origin_bios);
1454         free_pending_exception(pe);
1455
1456         increment_pending_exceptions_done_count();
1457
1458         up_write(&s->lock);
1459
1460         /* Submit any pending write bios */
1461         if (error)
1462                 error_bios(snapshot_bios);
1463         else
1464                 flush_bios(snapshot_bios);
1465
1466         retry_origin_bios(s, origin_bios);
1467 }
1468
1469 static void commit_callback(void *context, int success)
1470 {
1471         struct dm_snap_pending_exception *pe = context;
1472
1473         pending_complete(pe, success);
1474 }
1475
1476 /*
1477  * Called when the copy I/O has finished.  kcopyd actually runs
1478  * this code so don't block.
1479  */
1480 static void copy_callback(int read_err, unsigned long write_err, void *context)
1481 {
1482         struct dm_snap_pending_exception *pe = context;
1483         struct dm_snapshot *s = pe->snap;
1484
1485         if (read_err || write_err)
1486                 pending_complete(pe, 0);
1487
1488         else
1489                 /* Update the metadata if we are persistent */
1490                 s->store->type->commit_exception(s->store, &pe->e,
1491                                                  commit_callback, pe);
1492 }
1493
1494 /*
1495  * Dispatches the copy operation to kcopyd.
1496  */
1497 static void start_copy(struct dm_snap_pending_exception *pe)
1498 {
1499         struct dm_snapshot *s = pe->snap;
1500         struct dm_io_region src, dest;
1501         struct block_device *bdev = s->origin->bdev;
1502         sector_t dev_size;
1503
1504         dev_size = get_dev_size(bdev);
1505
1506         src.bdev = bdev;
1507         src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1508         src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1509
1510         dest.bdev = s->cow->bdev;
1511         dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1512         dest.count = src.count;
1513
1514         /* Hand over to kcopyd */
1515         dm_kcopyd_copy(s->kcopyd_client,
1516                     &src, 1, &dest, 0, copy_callback, pe);
1517 }
1518
1519 static struct dm_snap_pending_exception *
1520 __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1521 {
1522         struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1523
1524         if (!e)
1525                 return NULL;
1526
1527         return container_of(e, struct dm_snap_pending_exception, e);
1528 }
1529
1530 /*
1531  * Looks to see if this snapshot already has a pending exception
1532  * for this chunk, otherwise it allocates a new one and inserts
1533  * it into the pending table.
1534  *
1535  * NOTE: a write lock must be held on snap->lock before calling
1536  * this.
1537  */
1538 static struct dm_snap_pending_exception *
1539 __find_pending_exception(struct dm_snapshot *s,
1540                          struct dm_snap_pending_exception *pe, chunk_t chunk)
1541 {
1542         struct dm_snap_pending_exception *pe2;
1543
1544         pe2 = __lookup_pending_exception(s, chunk);
1545         if (pe2) {
1546                 free_pending_exception(pe);
1547                 return pe2;
1548         }
1549
1550         pe->e.old_chunk = chunk;
1551         bio_list_init(&pe->origin_bios);
1552         bio_list_init(&pe->snapshot_bios);
1553         pe->started = 0;
1554
1555         if (s->store->type->prepare_exception(s->store, &pe->e)) {
1556                 free_pending_exception(pe);
1557                 return NULL;
1558         }
1559
1560         dm_insert_exception(&s->pending, &pe->e);
1561
1562         return pe;
1563 }
1564
1565 static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1566                             struct bio *bio, chunk_t chunk)
1567 {
1568         bio->bi_bdev = s->cow->bdev;
1569         bio->bi_sector = chunk_to_sector(s->store,
1570                                          dm_chunk_number(e->new_chunk) +
1571                                          (chunk - e->old_chunk)) +
1572                                          (bio->bi_sector &
1573                                           s->store->chunk_mask);
1574 }
1575
1576 static int snapshot_map(struct dm_target *ti, struct bio *bio,
1577                         union map_info *map_context)
1578 {
1579         struct dm_exception *e;
1580         struct dm_snapshot *s = ti->private;
1581         int r = DM_MAPIO_REMAPPED;
1582         chunk_t chunk;
1583         struct dm_snap_pending_exception *pe = NULL;
1584
1585         if (unlikely(bio_empty_barrier(bio))) {
1586                 bio->bi_bdev = s->cow->bdev;
1587                 return DM_MAPIO_REMAPPED;
1588         }
1589
1590         chunk = sector_to_chunk(s->store, bio->bi_sector);
1591
1592         /* Full snapshots are not usable */
1593         /* To get here the table must be live so s->active is always set. */
1594         if (!s->valid)
1595                 return -EIO;
1596
1597         /* FIXME: should only take write lock if we need
1598          * to copy an exception */
1599         down_write(&s->lock);
1600
1601         if (!s->valid) {
1602                 r = -EIO;
1603                 goto out_unlock;
1604         }
1605
1606         /* If the block is already remapped - use that, else remap it */
1607         e = dm_lookup_exception(&s->complete, chunk);
1608         if (e) {
1609                 remap_exception(s, e, bio, chunk);
1610                 goto out_unlock;
1611         }
1612
1613         /*
1614          * Write to snapshot - higher level takes care of RW/RO
1615          * flags so we should only get this if we are
1616          * writeable.
1617          */
1618         if (bio_rw(bio) == WRITE) {
1619                 pe = __lookup_pending_exception(s, chunk);
1620                 if (!pe) {
1621                         up_write(&s->lock);
1622                         pe = alloc_pending_exception(s);
1623                         down_write(&s->lock);
1624
1625                         if (!s->valid) {
1626                                 free_pending_exception(pe);
1627                                 r = -EIO;
1628                                 goto out_unlock;
1629                         }
1630
1631                         e = dm_lookup_exception(&s->complete, chunk);
1632                         if (e) {
1633                                 free_pending_exception(pe);
1634                                 remap_exception(s, e, bio, chunk);
1635                                 goto out_unlock;
1636                         }
1637
1638                         pe = __find_pending_exception(s, pe, chunk);
1639                         if (!pe) {
1640                                 __invalidate_snapshot(s, -ENOMEM);
1641                                 r = -EIO;
1642                                 goto out_unlock;
1643                         }
1644                 }
1645
1646                 remap_exception(s, &pe->e, bio, chunk);
1647                 bio_list_add(&pe->snapshot_bios, bio);
1648
1649                 r = DM_MAPIO_SUBMITTED;
1650
1651                 if (!pe->started) {
1652                         /* this is protected by snap->lock */
1653                         pe->started = 1;
1654                         up_write(&s->lock);
1655                         start_copy(pe);
1656                         goto out;
1657                 }
1658         } else {
1659                 bio->bi_bdev = s->origin->bdev;
1660                 map_context->ptr = track_chunk(s, chunk);
1661         }
1662
1663  out_unlock:
1664         up_write(&s->lock);
1665  out:
1666         return r;
1667 }
1668
1669 /*
1670  * A snapshot-merge target behaves like a combination of a snapshot
1671  * target and a snapshot-origin target.  It only generates new
1672  * exceptions in other snapshots and not in the one that is being
1673  * merged.
1674  *
1675  * For each chunk, if there is an existing exception, it is used to
1676  * redirect I/O to the cow device.  Otherwise I/O is sent to the origin,
1677  * which in turn might generate exceptions in other snapshots.
1678  * If merging is currently taking place on the chunk in question, the
1679  * I/O is deferred by adding it to s->bios_queued_during_merge.
1680  */
1681 static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
1682                               union map_info *map_context)
1683 {
1684         struct dm_exception *e;
1685         struct dm_snapshot *s = ti->private;
1686         int r = DM_MAPIO_REMAPPED;
1687         chunk_t chunk;
1688
1689         if (unlikely(bio_empty_barrier(bio))) {
1690                 if (!map_context->flush_request)
1691                         bio->bi_bdev = s->origin->bdev;
1692                 else
1693                         bio->bi_bdev = s->cow->bdev;
1694                 map_context->ptr = NULL;
1695                 return DM_MAPIO_REMAPPED;
1696         }
1697
1698         chunk = sector_to_chunk(s->store, bio->bi_sector);
1699
1700         down_write(&s->lock);
1701
1702         /* Full merging snapshots are redirected to the origin */
1703         if (!s->valid)
1704                 goto redirect_to_origin;
1705
1706         /* If the block is already remapped - use that */
1707         e = dm_lookup_exception(&s->complete, chunk);
1708         if (e) {
1709                 /* Queue writes overlapping with chunks being merged */
1710                 if (bio_rw(bio) == WRITE &&
1711                     chunk >= s->first_merging_chunk &&
1712                     chunk < (s->first_merging_chunk +
1713                              s->num_merging_chunks)) {
1714                         bio->bi_bdev = s->origin->bdev;
1715                         bio_list_add(&s->bios_queued_during_merge, bio);
1716                         r = DM_MAPIO_SUBMITTED;
1717                         goto out_unlock;
1718                 }
1719
1720                 remap_exception(s, e, bio, chunk);
1721
1722                 if (bio_rw(bio) == WRITE)
1723                         map_context->ptr = track_chunk(s, chunk);
1724                 goto out_unlock;
1725         }
1726
1727 redirect_to_origin:
1728         bio->bi_bdev = s->origin->bdev;
1729
1730         if (bio_rw(bio) == WRITE) {
1731                 up_write(&s->lock);
1732                 return do_origin(s->origin, bio);
1733         }
1734
1735 out_unlock:
1736         up_write(&s->lock);
1737
1738         return r;
1739 }
1740
1741 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
1742                            int error, union map_info *map_context)
1743 {
1744         struct dm_snapshot *s = ti->private;
1745         struct dm_snap_tracked_chunk *c = map_context->ptr;
1746
1747         if (c)
1748                 stop_tracking_chunk(s, c);
1749
1750         return 0;
1751 }
1752
1753 static void snapshot_merge_presuspend(struct dm_target *ti)
1754 {
1755         struct dm_snapshot *s = ti->private;
1756
1757         stop_merge(s);
1758 }
1759
1760 static void snapshot_postsuspend(struct dm_target *ti)
1761 {
1762         struct dm_snapshot *s = ti->private;
1763
1764         down_write(&s->lock);
1765         s->suspended = 1;
1766         up_write(&s->lock);
1767 }
1768
1769 static int snapshot_preresume(struct dm_target *ti)
1770 {
1771         int r = 0;
1772         struct dm_snapshot *s = ti->private;
1773         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1774
1775         down_read(&_origins_lock);
1776         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1777         if (snap_src && snap_dest) {
1778                 down_read(&snap_src->lock);
1779                 if (s == snap_src) {
1780                         DMERR("Unable to resume snapshot source until "
1781                               "handover completes.");
1782                         r = -EINVAL;
1783                 } else if (!snap_src->suspended) {
1784                         DMERR("Unable to perform snapshot handover until "
1785                               "source is suspended.");
1786                         r = -EINVAL;
1787                 }
1788                 up_read(&snap_src->lock);
1789         }
1790         up_read(&_origins_lock);
1791
1792         return r;
1793 }
1794
1795 static void snapshot_resume(struct dm_target *ti)
1796 {
1797         struct dm_snapshot *s = ti->private;
1798         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1799
1800         down_read(&_origins_lock);
1801         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1802         if (snap_src && snap_dest) {
1803                 down_write(&snap_src->lock);
1804                 down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
1805                 __handover_exceptions(snap_src, snap_dest);
1806                 up_write(&snap_dest->lock);
1807                 up_write(&snap_src->lock);
1808         }
1809         up_read(&_origins_lock);
1810
1811         /* Now we have correct chunk size, reregister */
1812         reregister_snapshot(s);
1813
1814         down_write(&s->lock);
1815         s->active = 1;
1816         s->suspended = 0;
1817         up_write(&s->lock);
1818 }
1819
1820 static sector_t get_origin_minimum_chunksize(struct block_device *bdev)
1821 {
1822         sector_t min_chunksize;
1823
1824         down_read(&_origins_lock);
1825         min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
1826         up_read(&_origins_lock);
1827
1828         return min_chunksize;
1829 }
1830
1831 static void snapshot_merge_resume(struct dm_target *ti)
1832 {
1833         struct dm_snapshot *s = ti->private;
1834
1835         /*
1836          * Handover exceptions from existing snapshot.
1837          */
1838         snapshot_resume(ti);
1839
1840         /*
1841          * snapshot-merge acts as an origin, so set ti->split_io
1842          */
1843         ti->split_io = get_origin_minimum_chunksize(s->origin->bdev);
1844
1845         start_merge(s);
1846 }
1847
1848 static int snapshot_status(struct dm_target *ti, status_type_t type,
1849                            char *result, unsigned int maxlen)
1850 {
1851         unsigned sz = 0;
1852         struct dm_snapshot *snap = ti->private;
1853
1854         switch (type) {
1855         case STATUSTYPE_INFO:
1856
1857                 down_write(&snap->lock);
1858
1859                 if (!snap->valid)
1860                         DMEMIT("Invalid");
1861                 else if (snap->merge_failed)
1862                         DMEMIT("Merge failed");
1863                 else {
1864                         if (snap->store->type->usage) {
1865                                 sector_t total_sectors, sectors_allocated,
1866                                          metadata_sectors;
1867                                 snap->store->type->usage(snap->store,
1868                                                          &total_sectors,
1869                                                          &sectors_allocated,
1870                                                          &metadata_sectors);
1871                                 DMEMIT("%llu/%llu %llu",
1872                                        (unsigned long long)sectors_allocated,
1873                                        (unsigned long long)total_sectors,
1874                                        (unsigned long long)metadata_sectors);
1875                         }
1876                         else
1877                                 DMEMIT("Unknown");
1878                 }
1879
1880                 up_write(&snap->lock);
1881
1882                 break;
1883
1884         case STATUSTYPE_TABLE:
1885                 /*
1886                  * kdevname returns a static pointer so we need
1887                  * to make private copies if the output is to
1888                  * make sense.
1889                  */
1890                 DMEMIT("%s %s", snap->origin->name, snap->cow->name);
1891                 snap->store->type->status(snap->store, type, result + sz,
1892                                           maxlen - sz);
1893                 break;
1894         }
1895
1896         return 0;
1897 }
1898
1899 static int snapshot_iterate_devices(struct dm_target *ti,
1900                                     iterate_devices_callout_fn fn, void *data)
1901 {
1902         struct dm_snapshot *snap = ti->private;
1903
1904         return fn(ti, snap->origin, 0, ti->len, data);
1905 }
1906
1907
1908 /*-----------------------------------------------------------------
1909  * Origin methods
1910  *---------------------------------------------------------------*/
1911
1912 /*
1913  * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
1914  * supplied bio was ignored.  The caller may submit it immediately.
1915  * (No remapping actually occurs as the origin is always a direct linear
1916  * map.)
1917  *
1918  * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
1919  * and any supplied bio is added to a list to be submitted once all
1920  * the necessary exceptions exist.
1921  */
1922 static int __origin_write(struct list_head *snapshots, sector_t sector,
1923                           struct bio *bio)
1924 {
1925         int r = DM_MAPIO_REMAPPED;
1926         struct dm_snapshot *snap;
1927         struct dm_exception *e;
1928         struct dm_snap_pending_exception *pe;
1929         struct dm_snap_pending_exception *pe_to_start_now = NULL;
1930         struct dm_snap_pending_exception *pe_to_start_last = NULL;
1931         chunk_t chunk;
1932
1933         /* Do all the snapshots on this origin */
1934         list_for_each_entry (snap, snapshots, list) {
1935                 /*
1936                  * Don't make new exceptions in a merging snapshot
1937                  * because it has effectively been deleted
1938                  */
1939                 if (dm_target_is_snapshot_merge(snap->ti))
1940                         continue;
1941
1942                 down_write(&snap->lock);
1943
1944                 /* Only deal with valid and active snapshots */
1945                 if (!snap->valid || !snap->active)
1946                         goto next_snapshot;
1947
1948                 /* Nothing to do if writing beyond end of snapshot */
1949                 if (sector >= dm_table_get_size(snap->ti->table))
1950                         goto next_snapshot;
1951
1952                 /*
1953                  * Remember, different snapshots can have
1954                  * different chunk sizes.
1955                  */
1956                 chunk = sector_to_chunk(snap->store, sector);
1957
1958                 /*
1959                  * Check exception table to see if block
1960                  * is already remapped in this snapshot
1961                  * and trigger an exception if not.
1962                  */
1963                 e = dm_lookup_exception(&snap->complete, chunk);
1964                 if (e)
1965                         goto next_snapshot;
1966
1967                 pe = __lookup_pending_exception(snap, chunk);
1968                 if (!pe) {
1969                         up_write(&snap->lock);
1970                         pe = alloc_pending_exception(snap);
1971                         down_write(&snap->lock);
1972
1973                         if (!snap->valid) {
1974                                 free_pending_exception(pe);
1975                                 goto next_snapshot;
1976                         }
1977
1978                         e = dm_lookup_exception(&snap->complete, chunk);
1979                         if (e) {
1980                                 free_pending_exception(pe);
1981                                 goto next_snapshot;
1982                         }
1983
1984                         pe = __find_pending_exception(snap, pe, chunk);
1985                         if (!pe) {
1986                                 __invalidate_snapshot(snap, -ENOMEM);
1987                                 goto next_snapshot;
1988                         }
1989                 }
1990
1991                 r = DM_MAPIO_SUBMITTED;
1992
1993                 /*
1994                  * If an origin bio was supplied, queue it to wait for the
1995                  * completion of this exception, and start this one last,
1996                  * at the end of the function.
1997                  */
1998                 if (bio) {
1999                         bio_list_add(&pe->origin_bios, bio);
2000                         bio = NULL;
2001
2002                         if (!pe->started) {
2003                                 pe->started = 1;
2004                                 pe_to_start_last = pe;
2005                         }
2006                 }
2007
2008                 if (!pe->started) {
2009                         pe->started = 1;
2010                         pe_to_start_now = pe;
2011                 }
2012
2013  next_snapshot:
2014                 up_write(&snap->lock);
2015
2016                 if (pe_to_start_now) {
2017                         start_copy(pe_to_start_now);
2018                         pe_to_start_now = NULL;
2019                 }
2020         }
2021
2022         /*
2023          * Submit the exception against which the bio is queued last,
2024          * to give the other exceptions a head start.
2025          */
2026         if (pe_to_start_last)
2027                 start_copy(pe_to_start_last);
2028
2029         return r;
2030 }
2031
2032 /*
2033  * Called on a write from the origin driver.
2034  */
2035 static int do_origin(struct dm_dev *origin, struct bio *bio)
2036 {
2037         struct origin *o;
2038         int r = DM_MAPIO_REMAPPED;
2039
2040         down_read(&_origins_lock);
2041         o = __lookup_origin(origin->bdev);
2042         if (o)
2043                 r = __origin_write(&o->snapshots, bio->bi_sector, bio);
2044         up_read(&_origins_lock);
2045
2046         return r;
2047 }
2048
2049 /*
2050  * Trigger exceptions in all non-merging snapshots.
2051  *
2052  * The chunk size of the merging snapshot may be larger than the chunk
2053  * size of some other snapshot so we may need to reallocate multiple
2054  * chunks in other snapshots.
2055  *
2056  * We scan all the overlapping exceptions in the other snapshots.
2057  * Returns 1 if anything was reallocated and must be waited for,
2058  * otherwise returns 0.
2059  *
2060  * size must be a multiple of merging_snap's chunk_size.
2061  */
2062 static int origin_write_extent(struct dm_snapshot *merging_snap,
2063                                sector_t sector, unsigned size)
2064 {
2065         int must_wait = 0;
2066         sector_t n;
2067         struct origin *o;
2068
2069         /*
2070          * The origin's __minimum_chunk_size() got stored in split_io
2071          * by snapshot_merge_resume().
2072          */
2073         down_read(&_origins_lock);
2074         o = __lookup_origin(merging_snap->origin->bdev);
2075         for (n = 0; n < size; n += merging_snap->ti->split_io)
2076                 if (__origin_write(&o->snapshots, sector + n, NULL) ==
2077                     DM_MAPIO_SUBMITTED)
2078                         must_wait = 1;
2079         up_read(&_origins_lock);
2080
2081         return must_wait;
2082 }
2083
2084 /*
2085  * Origin: maps a linear range of a device, with hooks for snapshotting.
2086  */
2087
2088 /*
2089  * Construct an origin mapping: <dev_path>
2090  * The context for an origin is merely a 'struct dm_dev *'
2091  * pointing to the real device.
2092  */
2093 static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
2094 {
2095         int r;
2096         struct dm_dev *dev;
2097
2098         if (argc != 1) {
2099                 ti->error = "origin: incorrect number of arguments";
2100                 return -EINVAL;
2101         }
2102
2103         r = dm_get_device(ti, argv[0], 0, ti->len,
2104                           dm_table_get_mode(ti->table), &dev);
2105         if (r) {
2106                 ti->error = "Cannot get target device";
2107                 return r;
2108         }
2109
2110         ti->private = dev;
2111         ti->num_flush_requests = 1;
2112
2113         return 0;
2114 }
2115
2116 static void origin_dtr(struct dm_target *ti)
2117 {
2118         struct dm_dev *dev = ti->private;
2119         dm_put_device(ti, dev);
2120 }
2121
2122 static int origin_map(struct dm_target *ti, struct bio *bio,
2123                       union map_info *map_context)
2124 {
2125         struct dm_dev *dev = ti->private;
2126         bio->bi_bdev = dev->bdev;
2127
2128         if (unlikely(bio_empty_barrier(bio)))
2129                 return DM_MAPIO_REMAPPED;
2130
2131         /* Only tell snapshots if this is a write */
2132         return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
2133 }
2134
2135 /*
2136  * Set the target "split_io" field to the minimum of all the snapshots'
2137  * chunk sizes.
2138  */
2139 static void origin_resume(struct dm_target *ti)
2140 {
2141         struct dm_dev *dev = ti->private;
2142
2143         ti->split_io = get_origin_minimum_chunksize(dev->bdev);
2144 }
2145
2146 static int origin_status(struct dm_target *ti, status_type_t type, char *result,
2147                          unsigned int maxlen)
2148 {
2149         struct dm_dev *dev = ti->private;
2150
2151         switch (type) {
2152         case STATUSTYPE_INFO:
2153                 result[0] = '\0';
2154                 break;
2155
2156         case STATUSTYPE_TABLE:
2157                 snprintf(result, maxlen, "%s", dev->name);
2158                 break;
2159         }
2160
2161         return 0;
2162 }
2163
2164 static int origin_iterate_devices(struct dm_target *ti,
2165                                   iterate_devices_callout_fn fn, void *data)
2166 {
2167         struct dm_dev *dev = ti->private;
2168
2169         return fn(ti, dev, 0, ti->len, data);
2170 }
2171
2172 static struct target_type origin_target = {
2173         .name    = "snapshot-origin",
2174         .version = {1, 7, 0},
2175         .module  = THIS_MODULE,
2176         .ctr     = origin_ctr,
2177         .dtr     = origin_dtr,
2178         .map     = origin_map,
2179         .resume  = origin_resume,
2180         .status  = origin_status,
2181         .iterate_devices = origin_iterate_devices,
2182 };
2183
2184 static struct target_type snapshot_target = {
2185         .name    = "snapshot",
2186         .version = {1, 9, 0},
2187         .module  = THIS_MODULE,
2188         .ctr     = snapshot_ctr,
2189         .dtr     = snapshot_dtr,
2190         .map     = snapshot_map,
2191         .end_io  = snapshot_end_io,
2192         .postsuspend = snapshot_postsuspend,
2193         .preresume  = snapshot_preresume,
2194         .resume  = snapshot_resume,
2195         .status  = snapshot_status,
2196         .iterate_devices = snapshot_iterate_devices,
2197 };
2198
2199 static struct target_type merge_target = {
2200         .name    = dm_snapshot_merge_target_name,
2201         .version = {1, 0, 0},
2202         .module  = THIS_MODULE,
2203         .ctr     = snapshot_ctr,
2204         .dtr     = snapshot_dtr,
2205         .map     = snapshot_merge_map,
2206         .end_io  = snapshot_end_io,
2207         .presuspend = snapshot_merge_presuspend,
2208         .postsuspend = snapshot_postsuspend,
2209         .preresume  = snapshot_preresume,
2210         .resume  = snapshot_merge_resume,
2211         .status  = snapshot_status,
2212         .iterate_devices = snapshot_iterate_devices,
2213 };
2214
2215 static int __init dm_snapshot_init(void)
2216 {
2217         int r;
2218
2219         r = dm_exception_store_init();
2220         if (r) {
2221                 DMERR("Failed to initialize exception stores");
2222                 return r;
2223         }
2224
2225         r = dm_register_target(&snapshot_target);
2226         if (r < 0) {
2227                 DMERR("snapshot target register failed %d", r);
2228                 goto bad_register_snapshot_target;
2229         }
2230
2231         r = dm_register_target(&origin_target);
2232         if (r < 0) {
2233                 DMERR("Origin target register failed %d", r);
2234                 goto bad_register_origin_target;
2235         }
2236
2237         r = dm_register_target(&merge_target);
2238         if (r < 0) {
2239                 DMERR("Merge target register failed %d", r);
2240                 goto bad_register_merge_target;
2241         }
2242
2243         r = init_origin_hash();
2244         if (r) {
2245                 DMERR("init_origin_hash failed.");
2246                 goto bad_origin_hash;
2247         }
2248
2249         exception_cache = KMEM_CACHE(dm_exception, 0);
2250         if (!exception_cache) {
2251                 DMERR("Couldn't create exception cache.");
2252                 r = -ENOMEM;
2253                 goto bad_exception_cache;
2254         }
2255
2256         pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
2257         if (!pending_cache) {
2258                 DMERR("Couldn't create pending cache.");
2259                 r = -ENOMEM;
2260                 goto bad_pending_cache;
2261         }
2262
2263         tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
2264         if (!tracked_chunk_cache) {
2265                 DMERR("Couldn't create cache to track chunks in use.");
2266                 r = -ENOMEM;
2267                 goto bad_tracked_chunk_cache;
2268         }
2269
2270         ksnapd = create_singlethread_workqueue("ksnapd");
2271         if (!ksnapd) {
2272                 DMERR("Failed to create ksnapd workqueue.");
2273                 r = -ENOMEM;
2274                 goto bad_pending_pool;
2275         }
2276
2277         return 0;
2278
2279 bad_pending_pool:
2280         kmem_cache_destroy(tracked_chunk_cache);
2281 bad_tracked_chunk_cache:
2282         kmem_cache_destroy(pending_cache);
2283 bad_pending_cache:
2284         kmem_cache_destroy(exception_cache);
2285 bad_exception_cache:
2286         exit_origin_hash();
2287 bad_origin_hash:
2288         dm_unregister_target(&merge_target);
2289 bad_register_merge_target:
2290         dm_unregister_target(&origin_target);
2291 bad_register_origin_target:
2292         dm_unregister_target(&snapshot_target);
2293 bad_register_snapshot_target:
2294         dm_exception_store_exit();
2295
2296         return r;
2297 }
2298
2299 static void __exit dm_snapshot_exit(void)
2300 {
2301         destroy_workqueue(ksnapd);
2302
2303         dm_unregister_target(&snapshot_target);
2304         dm_unregister_target(&origin_target);
2305         dm_unregister_target(&merge_target);
2306
2307         exit_origin_hash();
2308         kmem_cache_destroy(pending_cache);
2309         kmem_cache_destroy(exception_cache);
2310         kmem_cache_destroy(tracked_chunk_cache);
2311
2312         dm_exception_store_exit();
2313 }
2314
2315 /* Module hooks */
2316 module_init(dm_snapshot_init);
2317 module_exit(dm_snapshot_exit);
2318
2319 MODULE_DESCRIPTION(DM_NAME " snapshot target");
2320 MODULE_AUTHOR("Joe Thornber");
2321 MODULE_LICENSE("GPL");