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