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         /* You can't use a snapshot if this is 0 (e.g. if full) */
  75         int valid;
  76
  77         /* Origin writes don't trigger exceptions until this is set */
  78         int active;
  79
  80         /* Whether or not owning mapped_device is suspended */
  81         int suspended;
  82
  83         mempool_t *pending_pool;
  84
  85         atomic_t pending_exceptions_count;
  86
  87         struct dm_exception_table pending;
  88         struct dm_exception_table complete;
  89
  90         /*
  91          * pe_lock protects all pending_exception operations and access
  92          * as well as the snapshot_bios list.
  93          */
  94         spinlock_t pe_lock;
  95
  96         /* The on disk metadata handler */
  97         struct dm_exception_store *store;
  98
  99         struct dm_kcopyd_client *kcopyd_client;
 100
 101         /* Queue of snapshot writes for ksnapd to flush */
 102         struct bio_list queued_bios;
 103         struct work_struct queued_bios_work;
 104
 105         /* Chunks with outstanding reads */
 106         mempool_t *tracked_chunk_pool;
 107         spinlock_t tracked_chunk_lock;
 108         struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
 109 };
 110
 111 struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
 112 {
 113         return s->cow;
 114 }
 115 EXPORT_SYMBOL(dm_snap_cow);
 116
 117 static struct workqueue_struct *ksnapd;
 118 static void flush_queued_bios(struct work_struct *work);
 119
 120 static sector_t chunk_to_sector(struct dm_exception_store *store,
 121                                 chunk_t chunk)
 122 {
 123         return chunk << store->chunk_shift;
 124 }
 125
 126 static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
 127 {
 128         /*
 129          * There is only ever one instance of a particular block
 130          * device so we can compare pointers safely.
 131          */
 132         return lhs == rhs;
 133 }
 134
 135 struct dm_snap_pending_exception {
 136         struct dm_exception e;
 137
 138         /*
 139          * Origin buffers waiting for this to complete are held
 140          * in a bio list
 141          */
 142         struct bio_list origin_bios;
 143         struct bio_list snapshot_bios;
 144
 145         /* Pointer back to snapshot context */
 146         struct dm_snapshot *snap;
 147
 148         /*
 149          * 1 indicates the exception has already been sent to
 150          * kcopyd.
 151          */
 152         int started;
 153 };
 154
 155 /*
 156  * Hash table mapping origin volumes to lists of snapshots and
 157  * a lock to protect it
 158  */
 159 static struct kmem_cache *exception_cache;
 160 static struct kmem_cache *pending_cache;
 161
 162 struct dm_snap_tracked_chunk {
 163         struct hlist_node node;
 164         chunk_t chunk;
 165 };
 166
 167 static struct kmem_cache *tracked_chunk_cache;
 168
 169 static struct dm_snap_tracked_chunk *track_chunk(struct dm_snapshot *s,
 170                                                  chunk_t chunk)
 171 {
 172         struct dm_snap_tracked_chunk *c = mempool_alloc(s->tracked_chunk_pool,
 173                                                         GFP_NOIO);
 174         unsigned long flags;
 175
 176         c->chunk = chunk;
 177
 178         spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 179         hlist_add_head(&c->node,
 180                        &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
 181         spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
 182
 183         return c;
 184 }
 185
 186 static void stop_tracking_chunk(struct dm_snapshot *s,
 187                                 struct dm_snap_tracked_chunk *c)
 188 {
 189         unsigned long flags;
 190
 191         spin_lock_irqsave(&s->tracked_chunk_lock, flags);
 192         hlist_del(&c->node);
 193         spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
 194
 195         mempool_free(c, s->tracked_chunk_pool);
 196 }
 197
 198 static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
 199 {
 200         struct dm_snap_tracked_chunk *c;
 201         struct hlist_node *hn;
 202         int found = 0;
 203
 204         spin_lock_irq(&s->tracked_chunk_lock);
 205
 206         hlist_for_each_entry(c, hn,
 207             &s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
 208                 if (c->chunk == chunk) {
 209                         found = 1;
 210                         break;
 211                 }
 212         }
 213
 214         spin_unlock_irq(&s->tracked_chunk_lock);
 215
 216         return found;
 217 }
 218
 219 /*
 220  * This conflicting I/O is extremely improbable in the caller,
 221  * so msleep(1) is sufficient and there is no need for a wait queue.
 222  */
 223 static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
 224 {
 225         while (__chunk_is_tracked(s, chunk))
 226                 msleep(1);
 227 }
 228
 229 /*
 230  * One of these per registered origin, held in the snapshot_origins hash
 231  */
 232 struct origin {
 233         /* The origin device */
 234         struct block_device *bdev;
 235
 236         struct list_head hash_list;
 237
 238         /* List of snapshots for this origin */
 239         struct list_head snapshots;
 240 };
 241
 242 /*
 243  * Size of the hash table for origin volumes. If we make this
 244  * the size of the minors list then it should be nearly perfect
 245  */
 246 #define ORIGIN_HASH_SIZE 256
 247 #define ORIGIN_MASK      0xFF
 248 static struct list_head *_origins;
 249 static struct rw_semaphore _origins_lock;
 250
 251 static int init_origin_hash(void)
 252 {
 253         int i;
 254
 255         _origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
 256                            GFP_KERNEL);
 257         if (!_origins) {
 258                 DMERR("unable to allocate memory");
 259                 return -ENOMEM;
 260         }
 261
 262         for (i = 0; i < ORIGIN_HASH_SIZE; i++)
 263                 INIT_LIST_HEAD(_origins + i);
 264         init_rwsem(&_origins_lock);
 265
 266         return 0;
 267 }
 268
 269 static void exit_origin_hash(void)
 270 {
 271         kfree(_origins);
 272 }
 273
 274 static unsigned origin_hash(struct block_device *bdev)
 275 {
 276         return bdev->bd_dev & ORIGIN_MASK;
 277 }
 278
 279 static struct origin *__lookup_origin(struct block_device *origin)
 280 {
 281         struct list_head *ol;
 282         struct origin *o;
 283
 284         ol = &_origins[origin_hash(origin)];
 285         list_for_each_entry (o, ol, hash_list)
 286                 if (bdev_equal(o->bdev, origin))
 287                         return o;
 288
 289         return NULL;
 290 }
 291
 292 static void __insert_origin(struct origin *o)
 293 {
 294         struct list_head *sl = &_origins[origin_hash(o->bdev)];
 295         list_add_tail(&o->hash_list, sl);
 296 }
 297
 298 /*
 299  * _origins_lock must be held when calling this function.
 300  * Returns number of snapshots registered using the supplied cow device, plus:
 301  * snap_src - a snapshot suitable for use as a source of exception handover
 302  * snap_dest - a snapshot capable of receiving exception handover.
 303  * snap_merge - an existing snapshot-merge target linked to the same origin.
 304  *   There can be at most one snapshot-merge target. The parameter is optional.
 305  *
 306  * Possible return values and states of snap_src and snap_dest.
 307  *   0: NULL, NULL  - first new snapshot
 308  *   1: snap_src, NULL - normal snapshot
 309  *   2: snap_src, snap_dest  - waiting for handover
 310  *   2: snap_src, NULL - handed over, waiting for old to be deleted
 311  *   1: NULL, snap_dest - source got destroyed without handover
 312  */
 313 static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
 314                                         struct dm_snapshot **snap_src,
 315                                         struct dm_snapshot **snap_dest,
 316                                         struct dm_snapshot **snap_merge)
 317 {
 318         struct dm_snapshot *s;
 319         struct origin *o;
 320         int count = 0;
 321         int active;
 322
 323         o = __lookup_origin(snap->origin->bdev);
 324         if (!o)
 325                 goto out;
 326
 327         list_for_each_entry(s, &o->snapshots, list) {
 328                 if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
 329                         *snap_merge = s;
 330                 if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
 331                         continue;
 332
 333                 down_read(&s->lock);
 334                 active = s->active;
 335                 up_read(&s->lock);
 336
 337                 if (active) {
 338                         if (snap_src)
 339                                 *snap_src = s;
 340                 } else if (snap_dest)
 341                         *snap_dest = s;
 342
 343                 count++;
 344         }
 345
 346 out:
 347         return count;
 348 }
 349
 350 /*
 351  * On success, returns 1 if this snapshot is a handover destination,
 352  * otherwise returns 0.
 353  */
 354 static int __validate_exception_handover(struct dm_snapshot *snap)
 355 {
 356         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
 357         struct dm_snapshot *snap_merge = NULL;
 358
 359         /* Does snapshot need exceptions handed over to it? */
 360         if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
 361                                           &snap_merge) == 2) ||
 362             snap_dest) {
 363                 snap->ti->error = "Snapshot cow pairing for exception "
 364                                   "table handover failed";
 365                 return -EINVAL;
 366         }
 367
 368         /*
 369          * If no snap_src was found, snap cannot become a handover
 370          * destination.
 371          */
 372         if (!snap_src)
 373                 return 0;
 374
 375         /*
 376          * Non-snapshot-merge handover?
 377          */
 378         if (!dm_target_is_snapshot_merge(snap->ti))
 379                 return 1;
 380
 381         /*
 382          * Do not allow more than one merging snapshot.
 383          */
 384         if (snap_merge) {
 385                 snap->ti->error = "A snapshot is already merging.";
 386                 return -EINVAL;
 387         }
 388
 389         return 1;
 390 }
 391
 392 static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
 393 {
 394         struct dm_snapshot *l;
 395
 396         /* Sort the list according to chunk size, largest-first smallest-last */
 397         list_for_each_entry(l, &o->snapshots, list)
 398                 if (l->store->chunk_size < s->store->chunk_size)
 399                         break;
 400         list_add_tail(&s->list, &l->list);
 401 }
 402
 403 /*
 404  * Make a note of the snapshot and its origin so we can look it
 405  * up when the origin has a write on it.
 406  *
 407  * Also validate snapshot exception store handovers.
 408  * On success, returns 1 if this registration is a handover destination,
 409  * otherwise returns 0.
 410  */
 411 static int register_snapshot(struct dm_snapshot *snap)
 412 {
 413         struct origin *o, *new_o = NULL;
 414         struct block_device *bdev = snap->origin->bdev;
 415         int r = 0;
 416
 417         new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
 418         if (!new_o)
 419                 return -ENOMEM;
 420
 421         down_write(&_origins_lock);
 422
 423         r = __validate_exception_handover(snap);
 424         if (r < 0) {
 425                 kfree(new_o);
 426                 goto out;
 427         }
 428
 429         o = __lookup_origin(bdev);
 430         if (o)
 431                 kfree(new_o);
 432         else {
 433                 /* New origin */
 434                 o = new_o;
 435
 436                 /* Initialise the struct */
 437                 INIT_LIST_HEAD(&o->snapshots);
 438                 o->bdev = bdev;
 439
 440                 __insert_origin(o);
 441         }
 442
 443         __insert_snapshot(o, snap);
 444
 445 out:
 446         up_write(&_origins_lock);
 447
 448         return r;
 449 }
 450
 451 /*
 452  * Move snapshot to correct place in list according to chunk size.
 453  */
 454 static void reregister_snapshot(struct dm_snapshot *s)
 455 {
 456         struct block_device *bdev = s->origin->bdev;
 457
 458         down_write(&_origins_lock);
 459
 460         list_del(&s->list);
 461         __insert_snapshot(__lookup_origin(bdev), s);
 462
 463         up_write(&_origins_lock);
 464 }
 465
 466 static void unregister_snapshot(struct dm_snapshot *s)
 467 {
 468         struct origin *o;
 469
 470         down_write(&_origins_lock);
 471         o = __lookup_origin(s->origin->bdev);
 472
 473         list_del(&s->list);
 474         if (o && list_empty(&o->snapshots)) {
 475                 list_del(&o->hash_list);
 476                 kfree(o);
 477         }
 478
 479         up_write(&_origins_lock);
 480 }
 481
 482 /*
 483  * Implementation of the exception hash tables.
 484  * The lowest hash_shift bits of the chunk number are ignored, allowing
 485  * some consecutive chunks to be grouped together.
 486  */
 487 static int dm_exception_table_init(struct dm_exception_table *et,
 488                                    uint32_t size, unsigned hash_shift)
 489 {
 490         unsigned int i;
 491
 492         et->hash_shift = hash_shift;
 493         et->hash_mask = size - 1;
 494         et->table = dm_vcalloc(size, sizeof(struct list_head));
 495         if (!et->table)
 496                 return -ENOMEM;
 497
 498         for (i = 0; i < size; i++)
 499                 INIT_LIST_HEAD(et->table + i);
 500
 501         return 0;
 502 }
 503
 504 static void dm_exception_table_exit(struct dm_exception_table *et,
 505                                     struct kmem_cache *mem)
 506 {
 507         struct list_head *slot;
 508         struct dm_exception *ex, *next;
 509         int i, size;
 510
 511         size = et->hash_mask + 1;
 512         for (i = 0; i < size; i++) {
 513                 slot = et->table + i;
 514
 515                 list_for_each_entry_safe (ex, next, slot, hash_list)
 516                         kmem_cache_free(mem, ex);
 517         }
 518
 519         vfree(et->table);
 520 }
 521
 522 static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
 523 {
 524         return (chunk >> et->hash_shift) & et->hash_mask;
 525 }
 526
 527 static void dm_remove_exception(struct dm_exception *e)
 528 {
 529         list_del(&e->hash_list);
 530 }
 531
 532 /*
 533  * Return the exception data for a sector, or NULL if not
 534  * remapped.
 535  */
 536 static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
 537                                                 chunk_t chunk)
 538 {
 539         struct list_head *slot;
 540         struct dm_exception *e;
 541
 542         slot = &et->table[exception_hash(et, chunk)];
 543         list_for_each_entry (e, slot, hash_list)
 544                 if (chunk >= e->old_chunk &&
 545                     chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
 546                         return e;
 547
 548         return NULL;
 549 }
 550
 551 static struct dm_exception *alloc_completed_exception(void)
 552 {
 553         struct dm_exception *e;
 554
 555         e = kmem_cache_alloc(exception_cache, GFP_NOIO);
 556         if (!e)
 557                 e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
 558
 559         return e;
 560 }
 561
 562 static void free_completed_exception(struct dm_exception *e)
 563 {
 564         kmem_cache_free(exception_cache, e);
 565 }
 566
 567 static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
 568 {
 569         struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
 570                                                              GFP_NOIO);
 571
 572         atomic_inc(&s->pending_exceptions_count);
 573         pe->snap = s;
 574
 575         return pe;
 576 }
 577
 578 static void free_pending_exception(struct dm_snap_pending_exception *pe)
 579 {
 580         struct dm_snapshot *s = pe->snap;
 581
 582         mempool_free(pe, s->pending_pool);
 583         smp_mb__before_atomic_dec();
 584         atomic_dec(&s->pending_exceptions_count);
 585 }
 586
 587 static void dm_insert_exception(struct dm_exception_table *eh,
 588                                 struct dm_exception *new_e)
 589 {
 590         struct list_head *l;
 591         struct dm_exception *e = NULL;
 592
 593         l = &eh->table[exception_hash(eh, new_e->old_chunk)];
 594
 595         /* Add immediately if this table doesn't support consecutive chunks */
 596         if (!eh->hash_shift)
 597                 goto out;
 598
 599         /* List is ordered by old_chunk */
 600         list_for_each_entry_reverse(e, l, hash_list) {
 601                 /* Insert after an existing chunk? */
 602                 if (new_e->old_chunk == (e->old_chunk +
 603                                          dm_consecutive_chunk_count(e) + 1) &&
 604                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
 605                                          dm_consecutive_chunk_count(e) + 1)) {
 606                         dm_consecutive_chunk_count_inc(e);
 607                         free_completed_exception(new_e);
 608                         return;
 609                 }
 610
 611                 /* Insert before an existing chunk? */
 612                 if (new_e->old_chunk == (e->old_chunk - 1) &&
 613                     new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
 614                         dm_consecutive_chunk_count_inc(e);
 615                         e->old_chunk--;
 616                         e->new_chunk--;
 617                         free_completed_exception(new_e);
 618                         return;
 619                 }
 620
 621                 if (new_e->old_chunk > e->old_chunk)
 622                         break;
 623         }
 624
 625 out:
 626         list_add(&new_e->hash_list, e ? &e->hash_list : l);
 627 }
 628
 629 /*
 630  * Callback used by the exception stores to load exceptions when
 631  * initialising.
 632  */
 633 static int dm_add_exception(void *context, chunk_t old, chunk_t new)
 634 {
 635         struct dm_snapshot *s = context;
 636         struct dm_exception *e;
 637
 638         e = alloc_completed_exception();
 639         if (!e)
 640                 return -ENOMEM;
 641
 642         e->old_chunk = old;
 643
 644         /* Consecutive_count is implicitly initialised to zero */
 645         e->new_chunk = new;
 646
 647         dm_insert_exception(&s->complete, e);
 648
 649         return 0;
 650 }
 651
 652 #define min_not_zero(l, r) (((l) == 0) ? (r) : (((r) == 0) ? (l) : min(l, r)))
 653
 654 /*
 655  * Return a minimum chunk size of all snapshots that have the specified origin.
 656  * Return zero if the origin has no snapshots.
 657  */
 658 static sector_t __minimum_chunk_size(struct origin *o)
 659 {
 660         struct dm_snapshot *snap;
 661         unsigned chunk_size = 0;
 662
 663         if (o)
 664                 list_for_each_entry(snap, &o->snapshots, list)
 665                         chunk_size = min_not_zero(chunk_size,
 666                                                   snap->store->chunk_size);
 667
 668         return chunk_size;
 669 }
 670
 671 /*
 672  * Hard coded magic.
 673  */
 674 static int calc_max_buckets(void)
 675 {
 676         /* use a fixed size of 2MB */
 677         unsigned long mem = 2 * 1024 * 1024;
 678         mem /= sizeof(struct list_head);
 679
 680         return mem;
 681 }
 682
 683 /*
 684  * Allocate room for a suitable hash table.
 685  */
 686 static int init_hash_tables(struct dm_snapshot *s)
 687 {
 688         sector_t hash_size, cow_dev_size, origin_dev_size, max_buckets;
 689
 690         /*
 691          * Calculate based on the size of the original volume or
 692          * the COW volume...
 693          */
 694         cow_dev_size = get_dev_size(s->cow->bdev);
 695         origin_dev_size = get_dev_size(s->origin->bdev);
 696         max_buckets = calc_max_buckets();
 697
 698         hash_size = min(origin_dev_size, cow_dev_size) >> s->store->chunk_shift;
 699         hash_size = min(hash_size, max_buckets);
 700
 701         if (hash_size < 64)
 702                 hash_size = 64;
 703         hash_size = rounddown_pow_of_two(hash_size);
 704         if (dm_exception_table_init(&s->complete, hash_size,
 705                                     DM_CHUNK_CONSECUTIVE_BITS))
 706                 return -ENOMEM;
 707
 708         /*
 709          * Allocate hash table for in-flight exceptions
 710          * Make this smaller than the real hash table
 711          */
 712         hash_size >>= 3;
 713         if (hash_size < 64)
 714                 hash_size = 64;
 715
 716         if (dm_exception_table_init(&s->pending, hash_size, 0)) {
 717                 dm_exception_table_exit(&s->complete, exception_cache);
 718                 return -ENOMEM;
 719         }
 720
 721         return 0;
 722 }
 723
 724 /*
 725  * Construct a snapshot mapping: <origin_dev> <COW-dev> <p/n> <chunk-size>
 726  */
 727 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 728 {
 729         struct dm_snapshot *s;
 730         int i;
 731         int r = -EINVAL;
 732         char *origin_path, *cow_path;
 733         unsigned args_used, num_flush_requests = 1;
 734         fmode_t origin_mode = FMODE_READ;
 735
 736         if (argc != 4) {
 737                 ti->error = "requires exactly 4 arguments";
 738                 r = -EINVAL;
 739                 goto bad;
 740         }
 741
 742         if (dm_target_is_snapshot_merge(ti)) {
 743                 num_flush_requests = 2;
 744                 origin_mode = FMODE_WRITE;
 745         }
 746
 747         origin_path = argv[0];
 748         argv++;
 749         argc--;
 750
 751         s = kmalloc(sizeof(*s), GFP_KERNEL);
 752         if (!s) {
 753                 ti->error = "Cannot allocate snapshot context private "
 754                     "structure";
 755                 r = -ENOMEM;
 756                 goto bad;
 757         }
 758
 759         cow_path = argv[0];
 760         argv++;
 761         argc--;
 762
 763         r = dm_get_device(ti, cow_path, 0, 0,
 764                           FMODE_READ | FMODE_WRITE, &s->cow);
 765         if (r) {
 766                 ti->error = "Cannot get COW device";
 767                 goto bad_cow;
 768         }
 769
 770         r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
 771         if (r) {
 772                 ti->error = "Couldn't create exception store";
 773                 r = -EINVAL;
 774                 goto bad_store;
 775         }
 776
 777         argv += args_used;
 778         argc -= args_used;
 779
 780         r = dm_get_device(ti, origin_path, 0, ti->len, origin_mode, &s->origin);
 781         if (r) {
 782                 ti->error = "Cannot get origin device";
 783                 goto bad_origin;
 784         }
 785
 786         s->ti = ti;
 787         s->valid = 1;
 788         s->active = 0;
 789         s->suspended = 0;
 790         atomic_set(&s->pending_exceptions_count, 0);
 791         init_rwsem(&s->lock);
 792         INIT_LIST_HEAD(&s->list);
 793         spin_lock_init(&s->pe_lock);
 794
 795         /* Allocate hash table for COW data */
 796         if (init_hash_tables(s)) {
 797                 ti->error = "Unable to allocate hash table space";
 798                 r = -ENOMEM;
 799                 goto bad_hash_tables;
 800         }
 801
 802         r = dm_kcopyd_client_create(SNAPSHOT_PAGES, &s->kcopyd_client);
 803         if (r) {
 804                 ti->error = "Could not create kcopyd client";
 805                 goto bad_kcopyd;
 806         }
 807
 808         s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
 809         if (!s->pending_pool) {
 810                 ti->error = "Could not allocate mempool for pending exceptions";
 811                 goto bad_pending_pool;
 812         }
 813
 814         s->tracked_chunk_pool = mempool_create_slab_pool(MIN_IOS,
 815                                                          tracked_chunk_cache);
 816         if (!s->tracked_chunk_pool) {
 817                 ti->error = "Could not allocate tracked_chunk mempool for "
 818                             "tracking reads";
 819                 goto bad_tracked_chunk_pool;
 820         }
 821
 822         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
 823                 INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
 824
 825         spin_lock_init(&s->tracked_chunk_lock);
 826
 827         bio_list_init(&s->queued_bios);
 828         INIT_WORK(&s->queued_bios_work, flush_queued_bios);
 829
 830         ti->private = s;
 831         ti->num_flush_requests = num_flush_requests;
 832
 833         /* Add snapshot to the list of snapshots for this origin */
 834         /* Exceptions aren't triggered till snapshot_resume() is called */
 835         r = register_snapshot(s);
 836         if (r == -ENOMEM) {
 837                 ti->error = "Snapshot origin struct allocation failed";
 838                 goto bad_load_and_register;
 839         } else if (r < 0) {
 840                 /* invalid handover, register_snapshot has set ti->error */
 841                 goto bad_load_and_register;
 842         }
 843
 844         /*
 845          * Metadata must only be loaded into one table at once, so skip this
 846          * if metadata will be handed over during resume.
 847          * Chunk size will be set during the handover - set it to zero to
 848          * ensure it's ignored.
 849          */
 850         if (r > 0) {
 851                 s->store->chunk_size = 0;
 852                 return 0;
 853         }
 854
 855         r = s->store->type->read_metadata(s->store, dm_add_exception,
 856                                           (void *)s);
 857         if (r < 0) {
 858                 ti->error = "Failed to read snapshot metadata";
 859                 goto bad_read_metadata;
 860         } else if (r > 0) {
 861                 s->valid = 0;
 862                 DMWARN("Snapshot is marked invalid.");
 863         }
 864
 865         if (!s->store->chunk_size) {
 866                 ti->error = "Chunk size not set";
 867                 goto bad_read_metadata;
 868         }
 869         ti->split_io = s->store->chunk_size;
 870
 871         return 0;
 872
 873 bad_read_metadata:
 874         unregister_snapshot(s);
 875
 876 bad_load_and_register:
 877         mempool_destroy(s->tracked_chunk_pool);
 878
 879 bad_tracked_chunk_pool:
 880         mempool_destroy(s->pending_pool);
 881
 882 bad_pending_pool:
 883         dm_kcopyd_client_destroy(s->kcopyd_client);
 884
 885 bad_kcopyd:
 886         dm_exception_table_exit(&s->pending, pending_cache);
 887         dm_exception_table_exit(&s->complete, exception_cache);
 888
 889 bad_hash_tables:
 890         dm_put_device(ti, s->origin);
 891
 892 bad_origin:
 893         dm_exception_store_destroy(s->store);
 894
 895 bad_store:
 896         dm_put_device(ti, s->cow);
 897
 898 bad_cow:
 899         kfree(s);
 900
 901 bad:
 902         return r;
 903 }
 904
 905 static void __free_exceptions(struct dm_snapshot *s)
 906 {
 907         dm_kcopyd_client_destroy(s->kcopyd_client);
 908         s->kcopyd_client = NULL;
 909
 910         dm_exception_table_exit(&s->pending, pending_cache);
 911         dm_exception_table_exit(&s->complete, exception_cache);
 912 }
 913
 914 static void __handover_exceptions(struct dm_snapshot *snap_src,
 915                                   struct dm_snapshot *snap_dest)
 916 {
 917         union {
 918                 struct dm_exception_table table_swap;
 919                 struct dm_exception_store *store_swap;
 920         } u;
 921
 922         /*
 923          * Swap all snapshot context information between the two instances.
 924          */
 925         u.table_swap = snap_dest->complete;
 926         snap_dest->complete = snap_src->complete;
 927         snap_src->complete = u.table_swap;
 928
 929         u.store_swap = snap_dest->store;
 930         snap_dest->store = snap_src->store;
 931         snap_src->store = u.store_swap;
 932
 933         snap_dest->store->snap = snap_dest;
 934         snap_src->store->snap = snap_src;
 935
 936         snap_dest->ti->split_io = snap_dest->store->chunk_size;
 937         snap_dest->valid = snap_src->valid;
 938
 939         /*
 940          * Set source invalid to ensure it receives no further I/O.
 941          */
 942         snap_src->valid = 0;
 943 }
 944
 945 static void snapshot_dtr(struct dm_target *ti)
 946 {
 947 #ifdef CONFIG_DM_DEBUG
 948         int i;
 949 #endif
 950         struct dm_snapshot *s = ti->private;
 951         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
 952
 953         flush_workqueue(ksnapd);
 954
 955         down_read(&_origins_lock);
 956         /* Check whether exception handover must be cancelled */
 957         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
 958         if (snap_src && snap_dest && (s == snap_src)) {
 959                 down_write(&snap_dest->lock);
 960                 snap_dest->valid = 0;
 961                 up_write(&snap_dest->lock);
 962                 DMERR("Cancelling snapshot handover.");
 963         }
 964         up_read(&_origins_lock);
 965
 966         /* Prevent further origin writes from using this snapshot. */
 967         /* After this returns there can be no new kcopyd jobs. */
 968         unregister_snapshot(s);
 969
 970         while (atomic_read(&s->pending_exceptions_count))
 971                 msleep(1);
 972         /*
 973          * Ensure instructions in mempool_destroy aren't reordered
 974          * before atomic_read.
 975          */
 976         smp_mb();
 977
 978 #ifdef CONFIG_DM_DEBUG
 979         for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
 980                 BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
 981 #endif
 982
 983         mempool_destroy(s->tracked_chunk_pool);
 984
 985         __free_exceptions(s);
 986
 987         mempool_destroy(s->pending_pool);
 988
 989         dm_put_device(ti, s->origin);
 990
 991         dm_exception_store_destroy(s->store);
 992
 993         dm_put_device(ti, s->cow);
 994
 995         kfree(s);
 996 }
 997
 998 /*
 999  * Flush a list of buffers.
1000  */
1001 static void flush_bios(struct bio *bio)
1002 {
1003         struct bio *n;
1004
1005         while (bio) {
1006                 n = bio->bi_next;
1007                 bio->bi_next = NULL;
1008                 generic_make_request(bio);
1009                 bio = n;
1010         }
1011 }
1012
1013 static void flush_queued_bios(struct work_struct *work)
1014 {
1015         struct dm_snapshot *s =
1016                 container_of(work, struct dm_snapshot, queued_bios_work);
1017         struct bio *queued_bios;
1018         unsigned long flags;
1019
1020         spin_lock_irqsave(&s->pe_lock, flags);
1021         queued_bios = bio_list_get(&s->queued_bios);
1022         spin_unlock_irqrestore(&s->pe_lock, flags);
1023
1024         flush_bios(queued_bios);
1025 }
1026
1027 static int do_origin(struct dm_dev *origin, struct bio *bio);
1028
1029 /*
1030  * Flush a list of buffers.
1031  */
1032 static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
1033 {
1034         struct bio *n;
1035         int r;
1036
1037         while (bio) {
1038                 n = bio->bi_next;
1039                 bio->bi_next = NULL;
1040                 r = do_origin(s->origin, bio);
1041                 if (r == DM_MAPIO_REMAPPED)
1042                         generic_make_request(bio);
1043                 bio = n;
1044         }
1045 }
1046
1047 /*
1048  * Error a list of buffers.
1049  */
1050 static void error_bios(struct bio *bio)
1051 {
1052         struct bio *n;
1053
1054         while (bio) {
1055                 n = bio->bi_next;
1056                 bio->bi_next = NULL;
1057                 bio_io_error(bio);
1058                 bio = n;
1059         }
1060 }
1061
1062 static void __invalidate_snapshot(struct dm_snapshot *s, int err)
1063 {
1064         if (!s->valid)
1065                 return;
1066
1067         if (err == -EIO)
1068                 DMERR("Invalidating snapshot: Error reading/writing.");
1069         else if (err == -ENOMEM)
1070                 DMERR("Invalidating snapshot: Unable to allocate exception.");
1071
1072         if (s->store->type->drop_snapshot)
1073                 s->store->type->drop_snapshot(s->store);
1074
1075         s->valid = 0;
1076
1077         dm_table_event(s->ti->table);
1078 }
1079
1080 static void pending_complete(struct dm_snap_pending_exception *pe, int success)
1081 {
1082         struct dm_exception *e;
1083         struct dm_snapshot *s = pe->snap;
1084         struct bio *origin_bios = NULL;
1085         struct bio *snapshot_bios = NULL;
1086         int error = 0;
1087
1088         if (!success) {
1089                 /* Read/write error - snapshot is unusable */
1090                 down_write(&s->lock);
1091                 __invalidate_snapshot(s, -EIO);
1092                 error = 1;
1093                 goto out;
1094         }
1095
1096         e = alloc_completed_exception();
1097         if (!e) {
1098                 down_write(&s->lock);
1099                 __invalidate_snapshot(s, -ENOMEM);
1100                 error = 1;
1101                 goto out;
1102         }
1103         *e = pe->e;
1104
1105         down_write(&s->lock);
1106         if (!s->valid) {
1107                 free_completed_exception(e);
1108                 error = 1;
1109                 goto out;
1110         }
1111
1112         /* Check for conflicting reads */
1113         __check_for_conflicting_io(s, pe->e.old_chunk);
1114
1115         /*
1116          * Add a proper exception, and remove the
1117          * in-flight exception from the list.
1118          */
1119         dm_insert_exception(&s->complete, e);
1120
1121  out:
1122         dm_remove_exception(&pe->e);
1123         snapshot_bios = bio_list_get(&pe->snapshot_bios);
1124         origin_bios = bio_list_get(&pe->origin_bios);
1125         free_pending_exception(pe);
1126
1127         up_write(&s->lock);
1128
1129         /* Submit any pending write bios */
1130         if (error)
1131                 error_bios(snapshot_bios);
1132         else
1133                 flush_bios(snapshot_bios);
1134
1135         retry_origin_bios(s, origin_bios);
1136 }
1137
1138 static void commit_callback(void *context, int success)
1139 {
1140         struct dm_snap_pending_exception *pe = context;
1141
1142         pending_complete(pe, success);
1143 }
1144
1145 /*
1146  * Called when the copy I/O has finished.  kcopyd actually runs
1147  * this code so don't block.
1148  */
1149 static void copy_callback(int read_err, unsigned long write_err, void *context)
1150 {
1151         struct dm_snap_pending_exception *pe = context;
1152         struct dm_snapshot *s = pe->snap;
1153
1154         if (read_err || write_err)
1155                 pending_complete(pe, 0);
1156
1157         else
1158                 /* Update the metadata if we are persistent */
1159                 s->store->type->commit_exception(s->store, &pe->e,
1160                                                  commit_callback, pe);
1161 }
1162
1163 /*
1164  * Dispatches the copy operation to kcopyd.
1165  */
1166 static void start_copy(struct dm_snap_pending_exception *pe)
1167 {
1168         struct dm_snapshot *s = pe->snap;
1169         struct dm_io_region src, dest;
1170         struct block_device *bdev = s->origin->bdev;
1171         sector_t dev_size;
1172
1173         dev_size = get_dev_size(bdev);
1174
1175         src.bdev = bdev;
1176         src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
1177         src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
1178
1179         dest.bdev = s->cow->bdev;
1180         dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
1181         dest.count = src.count;
1182
1183         /* Hand over to kcopyd */
1184         dm_kcopyd_copy(s->kcopyd_client,
1185                     &src, 1, &dest, 0, copy_callback, pe);
1186 }
1187
1188 static struct dm_snap_pending_exception *
1189 __lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
1190 {
1191         struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
1192
1193         if (!e)
1194                 return NULL;
1195
1196         return container_of(e, struct dm_snap_pending_exception, e);
1197 }
1198
1199 /*
1200  * Looks to see if this snapshot already has a pending exception
1201  * for this chunk, otherwise it allocates a new one and inserts
1202  * it into the pending table.
1203  *
1204  * NOTE: a write lock must be held on snap->lock before calling
1205  * this.
1206  */
1207 static struct dm_snap_pending_exception *
1208 __find_pending_exception(struct dm_snapshot *s,
1209                          struct dm_snap_pending_exception *pe, chunk_t chunk)
1210 {
1211         struct dm_snap_pending_exception *pe2;
1212
1213         pe2 = __lookup_pending_exception(s, chunk);
1214         if (pe2) {
1215                 free_pending_exception(pe);
1216                 return pe2;
1217         }
1218
1219         pe->e.old_chunk = chunk;
1220         bio_list_init(&pe->origin_bios);
1221         bio_list_init(&pe->snapshot_bios);
1222         pe->started = 0;
1223
1224         if (s->store->type->prepare_exception(s->store, &pe->e)) {
1225                 free_pending_exception(pe);
1226                 return NULL;
1227         }
1228
1229         dm_insert_exception(&s->pending, &pe->e);
1230
1231         return pe;
1232 }
1233
1234 static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
1235                             struct bio *bio, chunk_t chunk)
1236 {
1237         bio->bi_bdev = s->cow->bdev;
1238         bio->bi_sector = chunk_to_sector(s->store,
1239                                          dm_chunk_number(e->new_chunk) +
1240                                          (chunk - e->old_chunk)) +
1241                                          (bio->bi_sector &
1242                                           s->store->chunk_mask);
1243 }
1244
1245 static int snapshot_map(struct dm_target *ti, struct bio *bio,
1246                         union map_info *map_context)
1247 {
1248         struct dm_exception *e;
1249         struct dm_snapshot *s = ti->private;
1250         int r = DM_MAPIO_REMAPPED;
1251         chunk_t chunk;
1252         struct dm_snap_pending_exception *pe = NULL;
1253
1254         if (unlikely(bio_empty_barrier(bio))) {
1255                 bio->bi_bdev = s->cow->bdev;
1256                 return DM_MAPIO_REMAPPED;
1257         }
1258
1259         chunk = sector_to_chunk(s->store, bio->bi_sector);
1260
1261         /* Full snapshots are not usable */
1262         /* To get here the table must be live so s->active is always set. */
1263         if (!s->valid)
1264                 return -EIO;
1265
1266         /* FIXME: should only take write lock if we need
1267          * to copy an exception */
1268         down_write(&s->lock);
1269
1270         if (!s->valid) {
1271                 r = -EIO;
1272                 goto out_unlock;
1273         }
1274
1275         /* If the block is already remapped - use that, else remap it */
1276         e = dm_lookup_exception(&s->complete, chunk);
1277         if (e) {
1278                 remap_exception(s, e, bio, chunk);
1279                 goto out_unlock;
1280         }
1281
1282         /*
1283          * Write to snapshot - higher level takes care of RW/RO
1284          * flags so we should only get this if we are
1285          * writeable.
1286          */
1287         if (bio_rw(bio) == WRITE) {
1288                 pe = __lookup_pending_exception(s, chunk);
1289                 if (!pe) {
1290                         up_write(&s->lock);
1291                         pe = alloc_pending_exception(s);
1292                         down_write(&s->lock);
1293
1294                         if (!s->valid) {
1295                                 free_pending_exception(pe);
1296                                 r = -EIO;
1297                                 goto out_unlock;
1298                         }
1299
1300                         e = dm_lookup_exception(&s->complete, chunk);
1301                         if (e) {
1302                                 free_pending_exception(pe);
1303                                 remap_exception(s, e, bio, chunk);
1304                                 goto out_unlock;
1305                         }
1306
1307                         pe = __find_pending_exception(s, pe, chunk);
1308                         if (!pe) {
1309                                 __invalidate_snapshot(s, -ENOMEM);
1310                                 r = -EIO;
1311                                 goto out_unlock;
1312                         }
1313                 }
1314
1315                 remap_exception(s, &pe->e, bio, chunk);
1316                 bio_list_add(&pe->snapshot_bios, bio);
1317
1318                 r = DM_MAPIO_SUBMITTED;
1319
1320                 if (!pe->started) {
1321                         /* this is protected by snap->lock */
1322                         pe->started = 1;
1323                         up_write(&s->lock);
1324                         start_copy(pe);
1325                         goto out;
1326                 }
1327         } else {
1328                 bio->bi_bdev = s->origin->bdev;
1329                 map_context->ptr = track_chunk(s, chunk);
1330         }
1331
1332  out_unlock:
1333         up_write(&s->lock);
1334  out:
1335         return r;
1336 }
1337
1338 /*
1339  * A snapshot-merge target behaves like a combination of a snapshot
1340  * target and a snapshot-origin target.  It only generates new
1341  * exceptions in other snapshots and not in the one that is being
1342  * merged.
1343  *
1344  * For each chunk, if there is an existing exception, it is used to
1345  * redirect I/O to the cow device.  Otherwise I/O is sent to the origin,
1346  * which in turn might generate exceptions in other snapshots.
1347  */
1348 static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
1349                               union map_info *map_context)
1350 {
1351         struct dm_exception *e;
1352         struct dm_snapshot *s = ti->private;
1353         int r = DM_MAPIO_REMAPPED;
1354         chunk_t chunk;
1355
1356         if (unlikely(bio_empty_barrier(bio))) {
1357                 if (!map_context->flush_request)
1358                         bio->bi_bdev = s->origin->bdev;
1359                 else
1360                         bio->bi_bdev = s->cow->bdev;
1361                 map_context->ptr = NULL;
1362                 return DM_MAPIO_REMAPPED;
1363         }
1364
1365         chunk = sector_to_chunk(s->store, bio->bi_sector);
1366
1367         down_read(&s->lock);
1368
1369         /* Full snapshots are not usable */
1370         if (!s->valid) {
1371                 r = -EIO;
1372                 goto out_unlock;
1373         }
1374
1375         /* If the block is already remapped - use that */
1376         e = dm_lookup_exception(&s->complete, chunk);
1377         if (e) {
1378                 remap_exception(s, e, bio, chunk);
1379                 goto out_unlock;
1380         }
1381
1382         bio->bi_bdev = s->origin->bdev;
1383
1384         if (bio_rw(bio) == WRITE) {
1385                 up_read(&s->lock);
1386                 return do_origin(s->origin, bio);
1387         }
1388
1389 out_unlock:
1390         up_read(&s->lock);
1391
1392         return r;
1393 }
1394
1395 static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
1396                            int error, union map_info *map_context)
1397 {
1398         struct dm_snapshot *s = ti->private;
1399         struct dm_snap_tracked_chunk *c = map_context->ptr;
1400
1401         if (c)
1402                 stop_tracking_chunk(s, c);
1403
1404         return 0;
1405 }
1406
1407 static void snapshot_postsuspend(struct dm_target *ti)
1408 {
1409         struct dm_snapshot *s = ti->private;
1410
1411         down_write(&s->lock);
1412         s->suspended = 1;
1413         up_write(&s->lock);
1414 }
1415
1416 static int snapshot_preresume(struct dm_target *ti)
1417 {
1418         int r = 0;
1419         struct dm_snapshot *s = ti->private;
1420         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1421
1422         down_read(&_origins_lock);
1423         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1424         if (snap_src && snap_dest) {
1425                 down_read(&snap_src->lock);
1426                 if (s == snap_src) {
1427                         DMERR("Unable to resume snapshot source until "
1428                               "handover completes.");
1429                         r = -EINVAL;
1430                 } else if (!snap_src->suspended) {
1431                         DMERR("Unable to perform snapshot handover until "
1432                               "source is suspended.");
1433                         r = -EINVAL;
1434                 }
1435                 up_read(&snap_src->lock);
1436         }
1437         up_read(&_origins_lock);
1438
1439         return r;
1440 }
1441
1442 static void snapshot_resume(struct dm_target *ti)
1443 {
1444         struct dm_snapshot *s = ti->private;
1445         struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
1446
1447         down_read(&_origins_lock);
1448         (void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
1449         if (snap_src && snap_dest) {
1450                 down_write(&snap_src->lock);
1451                 down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
1452                 __handover_exceptions(snap_src, snap_dest);
1453                 up_write(&snap_dest->lock);
1454                 up_write(&snap_src->lock);
1455         }
1456         up_read(&_origins_lock);
1457
1458         /* Now we have correct chunk size, reregister */
1459         reregister_snapshot(s);
1460
1461         down_write(&s->lock);
1462         s->active = 1;
1463         s->suspended = 0;
1464         up_write(&s->lock);
1465 }
1466
1467 static int snapshot_status(struct dm_target *ti, status_type_t type,
1468                            char *result, unsigned int maxlen)
1469 {
1470         unsigned sz = 0;
1471         struct dm_snapshot *snap = ti->private;
1472
1473         switch (type) {
1474         case STATUSTYPE_INFO:
1475
1476                 down_write(&snap->lock);
1477
1478                 if (!snap->valid)
1479                         DMEMIT("Invalid");
1480                 else {
1481                         if (snap->store->type->usage) {
1482                                 sector_t total_sectors, sectors_allocated,
1483                                          metadata_sectors;
1484                                 snap->store->type->usage(snap->store,
1485                                                          &total_sectors,
1486                                                          &sectors_allocated,
1487                                                          &metadata_sectors);
1488                                 DMEMIT("%llu/%llu %llu",
1489                                        (unsigned long long)sectors_allocated,
1490                                        (unsigned long long)total_sectors,
1491                                        (unsigned long long)metadata_sectors);
1492                         }
1493                         else
1494                                 DMEMIT("Unknown");
1495                 }
1496
1497                 up_write(&snap->lock);
1498
1499                 break;
1500
1501         case STATUSTYPE_TABLE:
1502                 /*
1503                  * kdevname returns a static pointer so we need
1504                  * to make private copies if the output is to
1505                  * make sense.
1506                  */
1507                 DMEMIT("%s %s", snap->origin->name, snap->cow->name);
1508                 snap->store->type->status(snap->store, type, result + sz,
1509                                           maxlen - sz);
1510                 break;
1511         }
1512
1513         return 0;
1514 }
1515
1516 static int snapshot_iterate_devices(struct dm_target *ti,
1517                                     iterate_devices_callout_fn fn, void *data)
1518 {
1519         struct dm_snapshot *snap = ti->private;
1520
1521         return fn(ti, snap->origin, 0, ti->len, data);
1522 }
1523
1524
1525 /*-----------------------------------------------------------------
1526  * Origin methods
1527  *---------------------------------------------------------------*/
1528
1529 /*
1530  * If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
1531  * supplied bio was ignored.  The caller may submit it immediately.
1532  * (No remapping actually occurs as the origin is always a direct linear
1533  * map.)
1534  *
1535  * If further exceptions are required, DM_MAPIO_SUBMITTED is returned
1536  * and any supplied bio is added to a list to be submitted once all
1537  * the necessary exceptions exist.
1538  */
1539 static int __origin_write(struct list_head *snapshots, sector_t sector,
1540                           struct bio *bio)
1541 {
1542         int r = DM_MAPIO_REMAPPED;
1543         struct dm_snapshot *snap;
1544         struct dm_exception *e;
1545         struct dm_snap_pending_exception *pe;
1546         struct dm_snap_pending_exception *pe_to_start_now = NULL;
1547         struct dm_snap_pending_exception *pe_to_start_last = NULL;
1548         chunk_t chunk;
1549
1550         /* Do all the snapshots on this origin */
1551         list_for_each_entry (snap, snapshots, list) {
1552                 /*
1553                  * Don't make new exceptions in a merging snapshot
1554                  * because it has effectively been deleted
1555                  */
1556                 if (dm_target_is_snapshot_merge(snap->ti))
1557                         continue;
1558
1559                 down_write(&snap->lock);
1560
1561                 /* Only deal with valid and active snapshots */
1562                 if (!snap->valid || !snap->active)
1563                         goto next_snapshot;
1564
1565                 /* Nothing to do if writing beyond end of snapshot */
1566                 if (sector >= dm_table_get_size(snap->ti->table))
1567                         goto next_snapshot;
1568
1569                 /*
1570                  * Remember, different snapshots can have
1571                  * different chunk sizes.
1572                  */
1573                 chunk = sector_to_chunk(snap->store, sector);
1574
1575                 /*
1576                  * Check exception table to see if block
1577                  * is already remapped in this snapshot
1578                  * and trigger an exception if not.
1579                  */
1580                 e = dm_lookup_exception(&snap->complete, chunk);
1581                 if (e)
1582                         goto next_snapshot;
1583
1584                 pe = __lookup_pending_exception(snap, chunk);
1585                 if (!pe) {
1586                         up_write(&snap->lock);
1587                         pe = alloc_pending_exception(snap);
1588                         down_write(&snap->lock);
1589
1590                         if (!snap->valid) {
1591                                 free_pending_exception(pe);
1592                                 goto next_snapshot;
1593                         }
1594
1595                         e = dm_lookup_exception(&snap->complete, chunk);
1596                         if (e) {
1597                                 free_pending_exception(pe);
1598                                 goto next_snapshot;
1599                         }
1600
1601                         pe = __find_pending_exception(snap, pe, chunk);
1602                         if (!pe) {
1603                                 __invalidate_snapshot(snap, -ENOMEM);
1604                                 goto next_snapshot;
1605                         }
1606                 }
1607
1608                 r = DM_MAPIO_SUBMITTED;
1609
1610                 /*
1611                  * If an origin bio was supplied, queue it to wait for the
1612                  * completion of this exception, and start this one last,
1613                  * at the end of the function.
1614                  */
1615                 if (bio) {
1616                         bio_list_add(&pe->origin_bios, bio);
1617                         bio = NULL;
1618
1619                         if (!pe->started) {
1620                                 pe->started = 1;
1621                                 pe_to_start_last = pe;
1622                         }
1623                 }
1624
1625                 if (!pe->started) {
1626                         pe->started = 1;
1627                         pe_to_start_now = pe;
1628                 }
1629
1630  next_snapshot:
1631                 up_write(&snap->lock);
1632
1633                 if (pe_to_start_now) {
1634                         start_copy(pe_to_start_now);
1635                         pe_to_start_now = NULL;
1636                 }
1637         }
1638
1639         /*
1640          * Submit the exception against which the bio is queued last,
1641          * to give the other exceptions a head start.
1642          */
1643         if (pe_to_start_last)
1644                 start_copy(pe_to_start_last);
1645
1646         return r;
1647 }
1648
1649 /*
1650  * Called on a write from the origin driver.
1651  */
1652 static int do_origin(struct dm_dev *origin, struct bio *bio)
1653 {
1654         struct origin *o;
1655         int r = DM_MAPIO_REMAPPED;
1656
1657         down_read(&_origins_lock);
1658         o = __lookup_origin(origin->bdev);
1659         if (o)
1660                 r = __origin_write(&o->snapshots, bio->bi_sector, bio);
1661         up_read(&_origins_lock);
1662
1663         return r;
1664 }
1665
1666 /*
1667  * Origin: maps a linear range of a device, with hooks for snapshotting.
1668  */
1669
1670 /*
1671  * Construct an origin mapping: <dev_path>
1672  * The context for an origin is merely a 'struct dm_dev *'
1673  * pointing to the real device.
1674  */
1675 static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
1676 {
1677         int r;
1678         struct dm_dev *dev;
1679
1680         if (argc != 1) {
1681                 ti->error = "origin: incorrect number of arguments";
1682                 return -EINVAL;
1683         }
1684
1685         r = dm_get_device(ti, argv[0], 0, ti->len,
1686                           dm_table_get_mode(ti->table), &dev);
1687         if (r) {
1688                 ti->error = "Cannot get target device";
1689                 return r;
1690         }
1691
1692         ti->private = dev;
1693         ti->num_flush_requests = 1;
1694
1695         return 0;
1696 }
1697
1698 static void origin_dtr(struct dm_target *ti)
1699 {
1700         struct dm_dev *dev = ti->private;
1701         dm_put_device(ti, dev);
1702 }
1703
1704 static int origin_map(struct dm_target *ti, struct bio *bio,
1705                       union map_info *map_context)
1706 {
1707         struct dm_dev *dev = ti->private;
1708         bio->bi_bdev = dev->bdev;
1709
1710         if (unlikely(bio_empty_barrier(bio)))
1711                 return DM_MAPIO_REMAPPED;
1712
1713         /* Only tell snapshots if this is a write */
1714         return (bio_rw(bio) == WRITE) ? do_origin(dev, bio) : DM_MAPIO_REMAPPED;
1715 }
1716
1717 /*
1718  * Set the target "split_io" field to the minimum of all the snapshots'
1719  * chunk sizes.
1720  */
1721 static void origin_resume(struct dm_target *ti)
1722 {
1723         struct dm_dev *dev = ti->private;
1724
1725         down_read(&_origins_lock);
1726
1727         ti->split_io = __minimum_chunk_size(__lookup_origin(dev->bdev));
1728
1729         up_read(&_origins_lock);
1730 }
1731
1732 static int origin_status(struct dm_target *ti, status_type_t type, char *result,
1733                          unsigned int maxlen)
1734 {
1735         struct dm_dev *dev = ti->private;
1736
1737         switch (type) {
1738         case STATUSTYPE_INFO:
1739                 result[0] = '\0';
1740                 break;
1741
1742         case STATUSTYPE_TABLE:
1743                 snprintf(result, maxlen, "%s", dev->name);
1744                 break;
1745         }
1746
1747         return 0;
1748 }
1749
1750 static int origin_iterate_devices(struct dm_target *ti,
1751                                   iterate_devices_callout_fn fn, void *data)
1752 {
1753         struct dm_dev *dev = ti->private;
1754
1755         return fn(ti, dev, 0, ti->len, data);
1756 }
1757
1758 static struct target_type origin_target = {
1759         .name    = "snapshot-origin",
1760         .version = {1, 7, 0},
1761         .module  = THIS_MODULE,
1762         .ctr     = origin_ctr,
1763         .dtr     = origin_dtr,
1764         .map     = origin_map,
1765         .resume  = origin_resume,
1766         .status  = origin_status,
1767         .iterate_devices = origin_iterate_devices,
1768 };
1769
1770 static struct target_type snapshot_target = {
1771         .name    = "snapshot",
1772         .version = {1, 9, 0},
1773         .module  = THIS_MODULE,
1774         .ctr     = snapshot_ctr,
1775         .dtr     = snapshot_dtr,
1776         .map     = snapshot_map,
1777         .end_io  = snapshot_end_io,
1778         .postsuspend = snapshot_postsuspend,
1779         .preresume  = snapshot_preresume,
1780         .resume  = snapshot_resume,
1781         .status  = snapshot_status,
1782         .iterate_devices = snapshot_iterate_devices,
1783 };
1784
1785 static struct target_type merge_target = {
1786         .name    = dm_snapshot_merge_target_name,
1787         .version = {1, 0, 0},
1788         .module  = THIS_MODULE,
1789         .ctr     = snapshot_ctr,
1790         .dtr     = snapshot_dtr,
1791         .map     = snapshot_merge_map,
1792         .end_io  = snapshot_end_io,
1793         .postsuspend = snapshot_postsuspend,
1794         .preresume  = snapshot_preresume,
1795         .resume  = snapshot_resume,
1796         .status  = snapshot_status,
1797         .iterate_devices = snapshot_iterate_devices,
1798 };
1799
1800 static int __init dm_snapshot_init(void)
1801 {
1802         int r;
1803
1804         r = dm_exception_store_init();
1805         if (r) {
1806                 DMERR("Failed to initialize exception stores");
1807                 return r;
1808         }
1809
1810         r = dm_register_target(&snapshot_target);
1811         if (r < 0) {
1812                 DMERR("snapshot target register failed %d", r);
1813                 goto bad_register_snapshot_target;
1814         }
1815
1816         r = dm_register_target(&origin_target);
1817         if (r < 0) {
1818                 DMERR("Origin target register failed %d", r);
1819                 goto bad_register_origin_target;
1820         }
1821
1822         r = dm_register_target(&merge_target);
1823         if (r < 0) {
1824                 DMERR("Merge target register failed %d", r);
1825                 goto bad_register_merge_target;
1826         }
1827
1828         r = init_origin_hash();
1829         if (r) {
1830                 DMERR("init_origin_hash failed.");
1831                 goto bad_origin_hash;
1832         }
1833
1834         exception_cache = KMEM_CACHE(dm_exception, 0);
1835         if (!exception_cache) {
1836                 DMERR("Couldn't create exception cache.");
1837                 r = -ENOMEM;
1838                 goto bad_exception_cache;
1839         }
1840
1841         pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
1842         if (!pending_cache) {
1843                 DMERR("Couldn't create pending cache.");
1844                 r = -ENOMEM;
1845                 goto bad_pending_cache;
1846         }
1847
1848         tracked_chunk_cache = KMEM_CACHE(dm_snap_tracked_chunk, 0);
1849         if (!tracked_chunk_cache) {
1850                 DMERR("Couldn't create cache to track chunks in use.");
1851                 r = -ENOMEM;
1852                 goto bad_tracked_chunk_cache;
1853         }
1854
1855         ksnapd = create_singlethread_workqueue("ksnapd");
1856         if (!ksnapd) {
1857                 DMERR("Failed to create ksnapd workqueue.");
1858                 r = -ENOMEM;
1859                 goto bad_pending_pool;
1860         }
1861
1862         return 0;
1863
1864 bad_pending_pool:
1865         kmem_cache_destroy(tracked_chunk_cache);
1866 bad_tracked_chunk_cache:
1867         kmem_cache_destroy(pending_cache);
1868 bad_pending_cache:
1869         kmem_cache_destroy(exception_cache);
1870 bad_exception_cache:
1871         exit_origin_hash();
1872 bad_origin_hash:
1873         dm_unregister_target(&merge_target);
1874 bad_register_merge_target:
1875         dm_unregister_target(&origin_target);
1876 bad_register_origin_target:
1877         dm_unregister_target(&snapshot_target);
1878 bad_register_snapshot_target:
1879         dm_exception_store_exit();
1880
1881         return r;
1882 }
1883
1884 static void __exit dm_snapshot_exit(void)
1885 {
1886         destroy_workqueue(ksnapd);
1887
1888         dm_unregister_target(&snapshot_target);
1889         dm_unregister_target(&origin_target);
1890         dm_unregister_target(&merge_target);
1891
1892         exit_origin_hash();
1893         kmem_cache_destroy(pending_cache);
1894         kmem_cache_destroy(exception_cache);
1895         kmem_cache_destroy(tracked_chunk_cache);
1896
1897         dm_exception_store_exit();
1898 }
1899
1900 /* Module hooks */
1901 module_init(dm_snapshot_init);
1902 module_exit(dm_snapshot_exit);
1903
1904 MODULE_DESCRIPTION(DM_NAME " snapshot target");
1905 MODULE_AUTHOR("Joe Thornber");
1906 MODULE_LICENSE("GPL");