drivers/md/dm-thin-metadata.c

   1 /*
   2  * Copyright (C) 2011-2012 Red Hat, Inc.
   3  *
   4  * This file is released under the GPL.
   5  */
   6
   7 #include "dm-thin-metadata.h"
   8 #include "persistent-data/dm-btree.h"
   9 #include "persistent-data/dm-space-map.h"
  10 #include "persistent-data/dm-space-map-disk.h"
  11 #include "persistent-data/dm-transaction-manager.h"
  12
  13 #include <linux/list.h>
  14 #include <linux/device-mapper.h>
  15 #include <linux/workqueue.h>
  16
  17 /*--------------------------------------------------------------------------
  18  * As far as the metadata goes, there is:
  19  *
  20  * - A superblock in block zero, taking up fewer than 512 bytes for
  21  *   atomic writes.
  22  *
  23  * - A space map managing the metadata blocks.
  24  *
  25  * - A space map managing the data blocks.
  26  *
  27  * - A btree mapping our internal thin dev ids onto struct disk_device_details.
  28  *
  29  * - A hierarchical btree, with 2 levels which effectively maps (thin
  30  *   dev id, virtual block) -> block_time.  Block time is a 64-bit
  31  *   field holding the time in the low 24 bits, and block in the top 40
  32  *   bits.
  33  *
  34  * BTrees consist solely of btree_nodes, that fill a block.  Some are
  35  * internal nodes, as such their values are a __le64 pointing to other
  36  * nodes.  Leaf nodes can store data of any reasonable size (ie. much
  37  * smaller than the block size).  The nodes consist of the header,
  38  * followed by an array of keys, followed by an array of values.  We have
  39  * to binary search on the keys so they're all held together to help the
  40  * cpu cache.
  41  *
  42  * Space maps have 2 btrees:
  43  *
  44  * - One maps a uint64_t onto a struct index_entry.  Which points to a
  45  *   bitmap block, and has some details about how many free entries there
  46  *   are etc.
  47  *
  48  * - The bitmap blocks have a header (for the checksum).  Then the rest
  49  *   of the block is pairs of bits.  With the meaning being:
  50  *
  51  *   0 - ref count is 0
  52  *   1 - ref count is 1
  53  *   2 - ref count is 2
  54  *   3 - ref count is higher than 2
  55  *
  56  * - If the count is higher than 2 then the ref count is entered in a
  57  *   second btree that directly maps the block_address to a uint32_t ref
  58  *   count.
  59  *
  60  * The space map metadata variant doesn't have a bitmaps btree.  Instead
  61  * it has one single blocks worth of index_entries.  This avoids
  62  * recursive issues with the bitmap btree needing to allocate space in
  63  * order to insert.  With a small data block size such as 64k the
  64  * metadata support data devices that are hundreds of terrabytes.
  65  *
  66  * The space maps allocate space linearly from front to back.  Space that
  67  * is freed in a transaction is never recycled within that transaction.
  68  * To try and avoid fragmenting _free_ space the allocator always goes
  69  * back and fills in gaps.
  70  *
  71  * All metadata io is in THIN_METADATA_BLOCK_SIZE sized/aligned chunks
  72  * from the block manager.
  73  *--------------------------------------------------------------------------*/
  74
  75 #define DM_MSG_PREFIX   "thin metadata"
  76
  77 #define THIN_SUPERBLOCK_MAGIC 27022010
  78 #define THIN_SUPERBLOCK_LOCATION 0
  79 #define THIN_VERSION 2
  80 #define SECTOR_TO_BLOCK_SHIFT 3
  81
  82 /*
  83  * For btree insert:
  84  *  3 for btree insert +
  85  *  2 for btree lookup used within space map
  86  * For btree remove:
  87  *  2 for shadow spine +
  88  *  4 for rebalance 3 child node
  89  */
  90 #define THIN_MAX_CONCURRENT_LOCKS 6
  91
  92 /* This should be plenty */
  93 #define SPACE_MAP_ROOT_SIZE 128
  94
  95 /*
  96  * Little endian on-disk superblock and device details.
  97  */
  98 struct thin_disk_superblock {
  99         __le32 csum;    /* Checksum of superblock except for this field. */
 100         __le32 flags;
 101         __le64 blocknr; /* This block number, dm_block_t. */
 102
 103         __u8 uuid[16];
 104         __le64 magic;
 105         __le32 version;
 106         __le32 time;
 107
 108         __le64 trans_id;
 109
 110         /*
 111          * Root held by userspace transactions.
 112          */
 113         __le64 held_root;
 114
 115         __u8 data_space_map_root[SPACE_MAP_ROOT_SIZE];
 116         __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
 117
 118         /*
 119          * 2-level btree mapping (dev_id, (dev block, time)) -> data block
 120          */
 121         __le64 data_mapping_root;
 122
 123         /*
 124          * Device detail root mapping dev_id -> device_details
 125          */
 126         __le64 device_details_root;
 127
 128         __le32 data_block_size;         /* In 512-byte sectors. */
 129
 130         __le32 metadata_block_size;     /* In 512-byte sectors. */
 131         __le64 metadata_nr_blocks;
 132
 133         __le32 compat_flags;
 134         __le32 compat_ro_flags;
 135         __le32 incompat_flags;
 136 } __packed;
 137
 138 struct disk_device_details {
 139         __le64 mapped_blocks;
 140         __le64 transaction_id;          /* When created. */
 141         __le32 creation_time;
 142         __le32 snapshotted_time;
 143 } __packed;
 144
 145 struct dm_pool_metadata {
 146         struct hlist_node hash;
 147
 148         struct block_device *bdev;
 149         struct dm_block_manager *bm;
 150         struct dm_space_map *metadata_sm;
 151         struct dm_space_map *data_sm;
 152         struct dm_transaction_manager *tm;
 153         struct dm_transaction_manager *nb_tm;
 154
 155         /*
 156          * Two-level btree.
 157          * First level holds thin_dev_t.
 158          * Second level holds mappings.
 159          */
 160         struct dm_btree_info info;
 161
 162         /*
 163          * Non-blocking version of the above.
 164          */
 165         struct dm_btree_info nb_info;
 166
 167         /*
 168          * Just the top level for deleting whole devices.
 169          */
 170         struct dm_btree_info tl_info;
 171
 172         /*
 173          * Just the bottom level for creating new devices.
 174          */
 175         struct dm_btree_info bl_info;
 176
 177         /*
 178          * Describes the device details btree.
 179          */
 180         struct dm_btree_info details_info;
 181
 182         struct rw_semaphore root_lock;
 183         uint32_t time;
 184         dm_block_t root;
 185         dm_block_t details_root;
 186         struct list_head thin_devices;
 187         uint64_t trans_id;
 188         unsigned long flags;
 189         sector_t data_block_size;
 190
 191         /*
 192          * Pre-commit callback.
 193          *
 194          * This allows the thin provisioning target to run a callback before
 195          * the metadata are committed.
 196          */
 197         dm_pool_pre_commit_fn pre_commit_fn;
 198         void *pre_commit_context;
 199
 200         /*
 201          * We reserve a section of the metadata for commit overhead.
 202          * All reported space does *not* include this.
 203          */
 204         dm_block_t metadata_reserve;
 205
 206         /*
 207          * Set if a transaction has to be aborted but the attempt to roll back
 208          * to the previous (good) transaction failed.  The only pool metadata
 209          * operation possible in this state is the closing of the device.
 210          */
 211         bool fail_io:1;
 212
 213         /*
 214          * Set once a thin-pool has been accessed through one of the interfaces
 215          * that imply the pool is in-service (e.g. thin devices created/deleted,
 216          * thin-pool message, metadata snapshots, etc).
 217          */
 218         bool in_service:1;
 219
 220         /*
 221          * Reading the space map roots can fail, so we read it into these
 222          * buffers before the superblock is locked and updated.
 223          */
 224         __u8 data_space_map_root[SPACE_MAP_ROOT_SIZE];
 225         __u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
 226 };
 227
 228 struct dm_thin_device {
 229         struct list_head list;
 230         struct dm_pool_metadata *pmd;
 231         dm_thin_id id;
 232
 233         int open_count;
 234         bool changed:1;
 235         bool aborted_with_changes:1;
 236         uint64_t mapped_blocks;
 237         uint64_t transaction_id;
 238         uint32_t creation_time;
 239         uint32_t snapshotted_time;
 240 };
 241
 242 /*----------------------------------------------------------------
 243  * superblock validator
 244  *--------------------------------------------------------------*/
 245
 246 #define SUPERBLOCK_CSUM_XOR 160774
 247
 248 static void sb_prepare_for_write(struct dm_block_validator *v,
 249                                  struct dm_block *b,
 250                                  size_t block_size)
 251 {
 252         struct thin_disk_superblock *disk_super = dm_block_data(b);
 253
 254         disk_super->blocknr = cpu_to_le64(dm_block_location(b));
 255         disk_super->csum = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
 256                                                       block_size - sizeof(__le32),
 257                                                       SUPERBLOCK_CSUM_XOR));
 258 }
 259
 260 static int sb_check(struct dm_block_validator *v,
 261                     struct dm_block *b,
 262                     size_t block_size)
 263 {
 264         struct thin_disk_superblock *disk_super = dm_block_data(b);
 265         __le32 csum_le;
 266
 267         if (dm_block_location(b) != le64_to_cpu(disk_super->blocknr)) {
 268                 DMERR("sb_check failed: blocknr %llu: "
 269                       "wanted %llu", le64_to_cpu(disk_super->blocknr),
 270                       (unsigned long long)dm_block_location(b));
 271                 return -ENOTBLK;
 272         }
 273
 274         if (le64_to_cpu(disk_super->magic) != THIN_SUPERBLOCK_MAGIC) {
 275                 DMERR("sb_check failed: magic %llu: "
 276                       "wanted %llu", le64_to_cpu(disk_super->magic),
 277                       (unsigned long long)THIN_SUPERBLOCK_MAGIC);
 278                 return -EILSEQ;
 279         }
 280
 281         csum_le = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
 282                                              block_size - sizeof(__le32),
 283                                              SUPERBLOCK_CSUM_XOR));
 284         if (csum_le != disk_super->csum) {
 285                 DMERR("sb_check failed: csum %u: wanted %u",
 286                       le32_to_cpu(csum_le), le32_to_cpu(disk_super->csum));
 287                 return -EILSEQ;
 288         }
 289
 290         return 0;
 291 }
 292
 293 static struct dm_block_validator sb_validator = {
 294         .name = "superblock",
 295         .prepare_for_write = sb_prepare_for_write,
 296         .check = sb_check
 297 };
 298
 299 /*----------------------------------------------------------------
 300  * Methods for the btree value types
 301  *--------------------------------------------------------------*/
 302
 303 static uint64_t pack_block_time(dm_block_t b, uint32_t t)
 304 {
 305         return (b << 24) | t;
 306 }
 307
 308 static void unpack_block_time(uint64_t v, dm_block_t *b, uint32_t *t)
 309 {
 310         *b = v >> 24;
 311         *t = v & ((1 << 24) - 1);
 312 }
 313
 314 /*
 315  * It's more efficient to call dm_sm_{inc,dec}_blocks as few times as
 316  * possible.  'with_runs' reads contiguous runs of blocks, and calls the
 317  * given sm function.
 318  */
 319 typedef int (*run_fn)(struct dm_space_map *, dm_block_t, dm_block_t);
 320
 321 static void with_runs(struct dm_space_map *sm, const __le64 *value_le, unsigned count, run_fn fn)
 322 {
 323         uint64_t b, begin, end;
 324         uint32_t t;
 325         bool in_run = false;
 326         unsigned i;
 327
 328         for (i = 0; i < count; i++, value_le++) {
 329                 /* We know value_le is 8 byte aligned */
 330                 unpack_block_time(le64_to_cpu(*value_le), &b, &t);
 331
 332                 if (in_run) {
 333                         if (b == end) {
 334                                 end++;
 335                         } else {
 336                                 fn(sm, begin, end);
 337                                 begin = b;
 338                                 end = b + 1;
 339                         }
 340                 } else {
 341                         in_run = true;
 342                         begin = b;
 343                         end = b + 1;
 344                 }
 345         }
 346
 347         if (in_run)
 348                 fn(sm, begin, end);
 349 }
 350
 351 static void data_block_inc(void *context, const void *value_le, unsigned count)
 352 {
 353         with_runs((struct dm_space_map *) context,
 354                   (const __le64 *) value_le, count, dm_sm_inc_blocks);
 355 }
 356
 357 static void data_block_dec(void *context, const void *value_le, unsigned count)
 358 {
 359         with_runs((struct dm_space_map *) context,
 360                   (const __le64 *) value_le, count, dm_sm_dec_blocks);
 361 }
 362
 363 static int data_block_equal(void *context, const void *value1_le, const void *value2_le)
 364 {
 365         __le64 v1_le, v2_le;
 366         uint64_t b1, b2;
 367         uint32_t t;
 368
 369         memcpy(&v1_le, value1_le, sizeof(v1_le));
 370         memcpy(&v2_le, value2_le, sizeof(v2_le));
 371         unpack_block_time(le64_to_cpu(v1_le), &b1, &t);
 372         unpack_block_time(le64_to_cpu(v2_le), &b2, &t);
 373
 374         return b1 == b2;
 375 }
 376
 377 static void subtree_inc(void *context, const void *value, unsigned count)
 378 {
 379         struct dm_btree_info *info = context;
 380         const __le64 *root_le = value;
 381         unsigned i;
 382
 383         for (i = 0; i < count; i++, root_le++)
 384                 dm_tm_inc(info->tm, le64_to_cpu(*root_le));
 385 }
 386
 387 static void subtree_dec(void *context, const void *value, unsigned count)
 388 {
 389         struct dm_btree_info *info = context;
 390         const __le64 *root_le = value;
 391         unsigned i;
 392
 393         for (i = 0; i < count; i++, root_le++)
 394                 if (dm_btree_del(info, le64_to_cpu(*root_le)))
 395                         DMERR("btree delete failed");
 396 }
 397
 398 static int subtree_equal(void *context, const void *value1_le, const void *value2_le)
 399 {
 400         __le64 v1_le, v2_le;
 401         memcpy(&v1_le, value1_le, sizeof(v1_le));
 402         memcpy(&v2_le, value2_le, sizeof(v2_le));
 403
 404         return v1_le == v2_le;
 405 }
 406
 407 /*----------------------------------------------------------------*/
 408
 409 /*
 410  * Variant that is used for in-core only changes or code that
 411  * shouldn't put the pool in service on its own (e.g. commit).
 412  */
 413 static inline void pmd_write_lock_in_core(struct dm_pool_metadata *pmd)
 414         __acquires(pmd->root_lock)
 415 {
 416         down_write(&pmd->root_lock);
 417 }
 418
 419 static inline void pmd_write_lock(struct dm_pool_metadata *pmd)
 420 {
 421         pmd_write_lock_in_core(pmd);
 422         if (unlikely(!pmd->in_service))
 423                 pmd->in_service = true;
 424 }
 425
 426 static inline void pmd_write_unlock(struct dm_pool_metadata *pmd)
 427         __releases(pmd->root_lock)
 428 {
 429         up_write(&pmd->root_lock);
 430 }
 431
 432 /*----------------------------------------------------------------*/
 433
 434 static int superblock_lock_zero(struct dm_pool_metadata *pmd,
 435                                 struct dm_block **sblock)
 436 {
 437         return dm_bm_write_lock_zero(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 438                                      &sb_validator, sblock);
 439 }
 440
 441 static int superblock_lock(struct dm_pool_metadata *pmd,
 442                            struct dm_block **sblock)
 443 {
 444         return dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 445                                 &sb_validator, sblock);
 446 }
 447
 448 static int __superblock_all_zeroes(struct dm_block_manager *bm, int *result)
 449 {
 450         int r;
 451         unsigned i;
 452         struct dm_block *b;
 453         __le64 *data_le, zero = cpu_to_le64(0);
 454         unsigned block_size = dm_bm_block_size(bm) / sizeof(__le64);
 455
 456         /*
 457          * We can't use a validator here - it may be all zeroes.
 458          */
 459         r = dm_bm_read_lock(bm, THIN_SUPERBLOCK_LOCATION, NULL, &b);
 460         if (r)
 461                 return r;
 462
 463         data_le = dm_block_data(b);
 464         *result = 1;
 465         for (i = 0; i < block_size; i++) {
 466                 if (data_le[i] != zero) {
 467                         *result = 0;
 468                         break;
 469                 }
 470         }
 471
 472         dm_bm_unlock(b);
 473
 474         return 0;
 475 }
 476
 477 static void __setup_btree_details(struct dm_pool_metadata *pmd)
 478 {
 479         pmd->info.tm = pmd->tm;
 480         pmd->info.levels = 2;
 481         pmd->info.value_type.context = pmd->data_sm;
 482         pmd->info.value_type.size = sizeof(__le64);
 483         pmd->info.value_type.inc = data_block_inc;
 484         pmd->info.value_type.dec = data_block_dec;
 485         pmd->info.value_type.equal = data_block_equal;
 486
 487         memcpy(&pmd->nb_info, &pmd->info, sizeof(pmd->nb_info));
 488         pmd->nb_info.tm = pmd->nb_tm;
 489
 490         pmd->tl_info.tm = pmd->tm;
 491         pmd->tl_info.levels = 1;
 492         pmd->tl_info.value_type.context = &pmd->bl_info;
 493         pmd->tl_info.value_type.size = sizeof(__le64);
 494         pmd->tl_info.value_type.inc = subtree_inc;
 495         pmd->tl_info.value_type.dec = subtree_dec;
 496         pmd->tl_info.value_type.equal = subtree_equal;
 497
 498         pmd->bl_info.tm = pmd->tm;
 499         pmd->bl_info.levels = 1;
 500         pmd->bl_info.value_type.context = pmd->data_sm;
 501         pmd->bl_info.value_type.size = sizeof(__le64);
 502         pmd->bl_info.value_type.inc = data_block_inc;
 503         pmd->bl_info.value_type.dec = data_block_dec;
 504         pmd->bl_info.value_type.equal = data_block_equal;
 505
 506         pmd->details_info.tm = pmd->tm;
 507         pmd->details_info.levels = 1;
 508         pmd->details_info.value_type.context = NULL;
 509         pmd->details_info.value_type.size = sizeof(struct disk_device_details);
 510         pmd->details_info.value_type.inc = NULL;
 511         pmd->details_info.value_type.dec = NULL;
 512         pmd->details_info.value_type.equal = NULL;
 513 }
 514
 515 static int save_sm_roots(struct dm_pool_metadata *pmd)
 516 {
 517         int r;
 518         size_t len;
 519
 520         r = dm_sm_root_size(pmd->metadata_sm, &len);
 521         if (r < 0)
 522                 return r;
 523
 524         r = dm_sm_copy_root(pmd->metadata_sm, &pmd->metadata_space_map_root, len);
 525         if (r < 0)
 526                 return r;
 527
 528         r = dm_sm_root_size(pmd->data_sm, &len);
 529         if (r < 0)
 530                 return r;
 531
 532         return dm_sm_copy_root(pmd->data_sm, &pmd->data_space_map_root, len);
 533 }
 534
 535 static void copy_sm_roots(struct dm_pool_metadata *pmd,
 536                           struct thin_disk_superblock *disk)
 537 {
 538         memcpy(&disk->metadata_space_map_root,
 539                &pmd->metadata_space_map_root,
 540                sizeof(pmd->metadata_space_map_root));
 541
 542         memcpy(&disk->data_space_map_root,
 543                &pmd->data_space_map_root,
 544                sizeof(pmd->data_space_map_root));
 545 }
 546
 547 static int __write_initial_superblock(struct dm_pool_metadata *pmd)
 548 {
 549         int r;
 550         struct dm_block *sblock;
 551         struct thin_disk_superblock *disk_super;
 552         sector_t bdev_size = bdev_nr_sectors(pmd->bdev);
 553
 554         if (bdev_size > THIN_METADATA_MAX_SECTORS)
 555                 bdev_size = THIN_METADATA_MAX_SECTORS;
 556
 557         r = dm_sm_commit(pmd->data_sm);
 558         if (r < 0)
 559                 return r;
 560
 561         r = dm_tm_pre_commit(pmd->tm);
 562         if (r < 0)
 563                 return r;
 564
 565         r = save_sm_roots(pmd);
 566         if (r < 0)
 567                 return r;
 568
 569         r = superblock_lock_zero(pmd, &sblock);
 570         if (r)
 571                 return r;
 572
 573         disk_super = dm_block_data(sblock);
 574         disk_super->flags = 0;
 575         memset(disk_super->uuid, 0, sizeof(disk_super->uuid));
 576         disk_super->magic = cpu_to_le64(THIN_SUPERBLOCK_MAGIC);
 577         disk_super->version = cpu_to_le32(THIN_VERSION);
 578         disk_super->time = 0;
 579         disk_super->trans_id = 0;
 580         disk_super->held_root = 0;
 581
 582         copy_sm_roots(pmd, disk_super);
 583
 584         disk_super->data_mapping_root = cpu_to_le64(pmd->root);
 585         disk_super->device_details_root = cpu_to_le64(pmd->details_root);
 586         disk_super->metadata_block_size = cpu_to_le32(THIN_METADATA_BLOCK_SIZE);
 587         disk_super->metadata_nr_blocks = cpu_to_le64(bdev_size >> SECTOR_TO_BLOCK_SHIFT);
 588         disk_super->data_block_size = cpu_to_le32(pmd->data_block_size);
 589
 590         return dm_tm_commit(pmd->tm, sblock);
 591 }
 592
 593 static int __format_metadata(struct dm_pool_metadata *pmd)
 594 {
 595         int r;
 596
 597         r = dm_tm_create_with_sm(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 598                                  &pmd->tm, &pmd->metadata_sm);
 599         if (r < 0) {
 600                 DMERR("tm_create_with_sm failed");
 601                 return r;
 602         }
 603
 604         pmd->data_sm = dm_sm_disk_create(pmd->tm, 0);
 605         if (IS_ERR(pmd->data_sm)) {
 606                 DMERR("sm_disk_create failed");
 607                 r = PTR_ERR(pmd->data_sm);
 608                 goto bad_cleanup_tm;
 609         }
 610
 611         pmd->nb_tm = dm_tm_create_non_blocking_clone(pmd->tm);
 612         if (!pmd->nb_tm) {
 613                 DMERR("could not create non-blocking clone tm");
 614                 r = -ENOMEM;
 615                 goto bad_cleanup_data_sm;
 616         }
 617
 618         __setup_btree_details(pmd);
 619
 620         r = dm_btree_empty(&pmd->info, &pmd->root);
 621         if (r < 0)
 622                 goto bad_cleanup_nb_tm;
 623
 624         r = dm_btree_empty(&pmd->details_info, &pmd->details_root);
 625         if (r < 0) {
 626                 DMERR("couldn't create devices root");
 627                 goto bad_cleanup_nb_tm;
 628         }
 629
 630         r = __write_initial_superblock(pmd);
 631         if (r)
 632                 goto bad_cleanup_nb_tm;
 633
 634         return 0;
 635
 636 bad_cleanup_nb_tm:
 637         dm_tm_destroy(pmd->nb_tm);
 638 bad_cleanup_data_sm:
 639         dm_sm_destroy(pmd->data_sm);
 640 bad_cleanup_tm:
 641         dm_tm_destroy(pmd->tm);
 642         dm_sm_destroy(pmd->metadata_sm);
 643
 644         return r;
 645 }
 646
 647 static int __check_incompat_features(struct thin_disk_superblock *disk_super,
 648                                      struct dm_pool_metadata *pmd)
 649 {
 650         uint32_t features;
 651
 652         features = le32_to_cpu(disk_super->incompat_flags) & ~THIN_FEATURE_INCOMPAT_SUPP;
 653         if (features) {
 654                 DMERR("could not access metadata due to unsupported optional features (%lx).",
 655                       (unsigned long)features);
 656                 return -EINVAL;
 657         }
 658
 659         /*
 660          * Check for read-only metadata to skip the following RDWR checks.
 661          */
 662         if (bdev_read_only(pmd->bdev))
 663                 return 0;
 664
 665         features = le32_to_cpu(disk_super->compat_ro_flags) & ~THIN_FEATURE_COMPAT_RO_SUPP;
 666         if (features) {
 667                 DMERR("could not access metadata RDWR due to unsupported optional features (%lx).",
 668                       (unsigned long)features);
 669                 return -EINVAL;
 670         }
 671
 672         return 0;
 673 }
 674
 675 static int __open_metadata(struct dm_pool_metadata *pmd)
 676 {
 677         int r;
 678         struct dm_block *sblock;
 679         struct thin_disk_superblock *disk_super;
 680
 681         r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 682                             &sb_validator, &sblock);
 683         if (r < 0) {
 684                 DMERR("couldn't read superblock");
 685                 return r;
 686         }
 687
 688         disk_super = dm_block_data(sblock);
 689
 690         /* Verify the data block size hasn't changed */
 691         if (le32_to_cpu(disk_super->data_block_size) != pmd->data_block_size) {
 692                 DMERR("changing the data block size (from %u to %llu) is not supported",
 693                       le32_to_cpu(disk_super->data_block_size),
 694                       (unsigned long long)pmd->data_block_size);
 695                 r = -EINVAL;
 696                 goto bad_unlock_sblock;
 697         }
 698
 699         r = __check_incompat_features(disk_super, pmd);
 700         if (r < 0)
 701                 goto bad_unlock_sblock;
 702
 703         r = dm_tm_open_with_sm(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 704                                disk_super->metadata_space_map_root,
 705                                sizeof(disk_super->metadata_space_map_root),
 706                                &pmd->tm, &pmd->metadata_sm);
 707         if (r < 0) {
 708                 DMERR("tm_open_with_sm failed");
 709                 goto bad_unlock_sblock;
 710         }
 711
 712         pmd->data_sm = dm_sm_disk_open(pmd->tm, disk_super->data_space_map_root,
 713                                        sizeof(disk_super->data_space_map_root));
 714         if (IS_ERR(pmd->data_sm)) {
 715                 DMERR("sm_disk_open failed");
 716                 r = PTR_ERR(pmd->data_sm);
 717                 goto bad_cleanup_tm;
 718         }
 719
 720         pmd->nb_tm = dm_tm_create_non_blocking_clone(pmd->tm);
 721         if (!pmd->nb_tm) {
 722                 DMERR("could not create non-blocking clone tm");
 723                 r = -ENOMEM;
 724                 goto bad_cleanup_data_sm;
 725         }
 726
 727         /*
 728          * For pool metadata opening process, root setting is redundant
 729          * because it will be set again in __begin_transaction(). But dm
 730          * pool aborting process really needs to get last transaction's
 731          * root to avoid accessing broken btree.
 732          */
 733         pmd->root = le64_to_cpu(disk_super->data_mapping_root);
 734         pmd->details_root = le64_to_cpu(disk_super->device_details_root);
 735
 736         __setup_btree_details(pmd);
 737         dm_bm_unlock(sblock);
 738
 739         return 0;
 740
 741 bad_cleanup_data_sm:
 742         dm_sm_destroy(pmd->data_sm);
 743 bad_cleanup_tm:
 744         dm_tm_destroy(pmd->tm);
 745         dm_sm_destroy(pmd->metadata_sm);
 746 bad_unlock_sblock:
 747         dm_bm_unlock(sblock);
 748
 749         return r;
 750 }
 751
 752 static int __open_or_format_metadata(struct dm_pool_metadata *pmd, bool format_device)
 753 {
 754         int r, unformatted;
 755
 756         r = __superblock_all_zeroes(pmd->bm, &unformatted);
 757         if (r)
 758                 return r;
 759
 760         if (unformatted)
 761                 return format_device ? __format_metadata(pmd) : -EPERM;
 762
 763         return __open_metadata(pmd);
 764 }
 765
 766 static int __create_persistent_data_objects(struct dm_pool_metadata *pmd, bool format_device)
 767 {
 768         int r;
 769
 770         pmd->bm = dm_block_manager_create(pmd->bdev, THIN_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
 771                                           THIN_MAX_CONCURRENT_LOCKS);
 772         if (IS_ERR(pmd->bm)) {
 773                 DMERR("could not create block manager");
 774                 r = PTR_ERR(pmd->bm);
 775                 pmd->bm = NULL;
 776                 return r;
 777         }
 778
 779         r = __open_or_format_metadata(pmd, format_device);
 780         if (r) {
 781                 dm_block_manager_destroy(pmd->bm);
 782                 pmd->bm = NULL;
 783         }
 784
 785         return r;
 786 }
 787
 788 static void __destroy_persistent_data_objects(struct dm_pool_metadata *pmd,
 789                                               bool destroy_bm)
 790 {
 791         dm_sm_destroy(pmd->data_sm);
 792         dm_sm_destroy(pmd->metadata_sm);
 793         dm_tm_destroy(pmd->nb_tm);
 794         dm_tm_destroy(pmd->tm);
 795         if (destroy_bm)
 796                 dm_block_manager_destroy(pmd->bm);
 797 }
 798
 799 static int __begin_transaction(struct dm_pool_metadata *pmd)
 800 {
 801         int r;
 802         struct thin_disk_superblock *disk_super;
 803         struct dm_block *sblock;
 804
 805         /*
 806          * We re-read the superblock every time.  Shouldn't need to do this
 807          * really.
 808          */
 809         r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
 810                             &sb_validator, &sblock);
 811         if (r)
 812                 return r;
 813
 814         disk_super = dm_block_data(sblock);
 815         pmd->time = le32_to_cpu(disk_super->time);
 816         pmd->root = le64_to_cpu(disk_super->data_mapping_root);
 817         pmd->details_root = le64_to_cpu(disk_super->device_details_root);
 818         pmd->trans_id = le64_to_cpu(disk_super->trans_id);
 819         pmd->flags = le32_to_cpu(disk_super->flags);
 820         pmd->data_block_size = le32_to_cpu(disk_super->data_block_size);
 821
 822         dm_bm_unlock(sblock);
 823         return 0;
 824 }
 825
 826 static int __write_changed_details(struct dm_pool_metadata *pmd)
 827 {
 828         int r;
 829         struct dm_thin_device *td, *tmp;
 830         struct disk_device_details details;
 831         uint64_t key;
 832
 833         list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
 834                 if (!td->changed)
 835                         continue;
 836
 837                 key = td->id;
 838
 839                 details.mapped_blocks = cpu_to_le64(td->mapped_blocks);
 840                 details.transaction_id = cpu_to_le64(td->transaction_id);
 841                 details.creation_time = cpu_to_le32(td->creation_time);
 842                 details.snapshotted_time = cpu_to_le32(td->snapshotted_time);
 843                 __dm_bless_for_disk(&details);
 844
 845                 r = dm_btree_insert(&pmd->details_info, pmd->details_root,
 846                                     &key, &details, &pmd->details_root);
 847                 if (r)
 848                         return r;
 849
 850                 if (td->open_count)
 851                         td->changed = false;
 852                 else {
 853                         list_del(&td->list);
 854                         kfree(td);
 855                 }
 856         }
 857
 858         return 0;
 859 }
 860
 861 static int __commit_transaction(struct dm_pool_metadata *pmd)
 862 {
 863         int r;
 864         struct thin_disk_superblock *disk_super;
 865         struct dm_block *sblock;
 866
 867         /*
 868          * We need to know if the thin_disk_superblock exceeds a 512-byte sector.
 869          */
 870         BUILD_BUG_ON(sizeof(struct thin_disk_superblock) > 512);
 871         BUG_ON(!rwsem_is_locked(&pmd->root_lock));
 872
 873         if (unlikely(!pmd->in_service))
 874                 return 0;
 875
 876         if (pmd->pre_commit_fn) {
 877                 r = pmd->pre_commit_fn(pmd->pre_commit_context);
 878                 if (r < 0) {
 879                         DMERR("pre-commit callback failed");
 880                         return r;
 881                 }
 882         }
 883
 884         r = __write_changed_details(pmd);
 885         if (r < 0)
 886                 return r;
 887
 888         r = dm_sm_commit(pmd->data_sm);
 889         if (r < 0)
 890                 return r;
 891
 892         r = dm_tm_pre_commit(pmd->tm);
 893         if (r < 0)
 894                 return r;
 895
 896         r = save_sm_roots(pmd);
 897         if (r < 0)
 898                 return r;
 899
 900         r = superblock_lock(pmd, &sblock);
 901         if (r)
 902                 return r;
 903
 904         disk_super = dm_block_data(sblock);
 905         disk_super->time = cpu_to_le32(pmd->time);
 906         disk_super->data_mapping_root = cpu_to_le64(pmd->root);
 907         disk_super->device_details_root = cpu_to_le64(pmd->details_root);
 908         disk_super->trans_id = cpu_to_le64(pmd->trans_id);
 909         disk_super->flags = cpu_to_le32(pmd->flags);
 910
 911         copy_sm_roots(pmd, disk_super);
 912
 913         return dm_tm_commit(pmd->tm, sblock);
 914 }
 915
 916 static void __set_metadata_reserve(struct dm_pool_metadata *pmd)
 917 {
 918         int r;
 919         dm_block_t total;
 920         dm_block_t max_blocks = 4096; /* 16M */
 921
 922         r = dm_sm_get_nr_blocks(pmd->metadata_sm, &total);
 923         if (r) {
 924                 DMERR("could not get size of metadata device");
 925                 pmd->metadata_reserve = max_blocks;
 926         } else
 927                 pmd->metadata_reserve = min(max_blocks, div_u64(total, 10));
 928 }
 929
 930 struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
 931                                                sector_t data_block_size,
 932                                                bool format_device)
 933 {
 934         int r;
 935         struct dm_pool_metadata *pmd;
 936
 937         pmd = kmalloc(sizeof(*pmd), GFP_KERNEL);
 938         if (!pmd) {
 939                 DMERR("could not allocate metadata struct");
 940                 return ERR_PTR(-ENOMEM);
 941         }
 942
 943         init_rwsem(&pmd->root_lock);
 944         pmd->time = 0;
 945         INIT_LIST_HEAD(&pmd->thin_devices);
 946         pmd->fail_io = false;
 947         pmd->in_service = false;
 948         pmd->bdev = bdev;
 949         pmd->data_block_size = data_block_size;
 950         pmd->pre_commit_fn = NULL;
 951         pmd->pre_commit_context = NULL;
 952
 953         r = __create_persistent_data_objects(pmd, format_device);
 954         if (r) {
 955                 kfree(pmd);
 956                 return ERR_PTR(r);
 957         }
 958
 959         r = __begin_transaction(pmd);
 960         if (r < 0) {
 961                 if (dm_pool_metadata_close(pmd) < 0)
 962                         DMWARN("%s: dm_pool_metadata_close() failed.", __func__);
 963                 return ERR_PTR(r);
 964         }
 965
 966         __set_metadata_reserve(pmd);
 967
 968         return pmd;
 969 }
 970
 971 int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
 972 {
 973         int r;
 974         unsigned open_devices = 0;
 975         struct dm_thin_device *td, *tmp;
 976
 977         down_read(&pmd->root_lock);
 978         list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
 979                 if (td->open_count)
 980                         open_devices++;
 981                 else {
 982                         list_del(&td->list);
 983                         kfree(td);
 984                 }
 985         }
 986         up_read(&pmd->root_lock);
 987
 988         if (open_devices) {
 989                 DMERR("attempt to close pmd when %u device(s) are still open",
 990                        open_devices);
 991                 return -EBUSY;
 992         }
 993
 994         pmd_write_lock_in_core(pmd);
 995         if (!pmd->fail_io && !dm_bm_is_read_only(pmd->bm)) {
 996                 r = __commit_transaction(pmd);
 997                 if (r < 0)
 998                         DMWARN("%s: __commit_transaction() failed, error = %d",
 999                                __func__, r);
1000         }
1001         pmd_write_unlock(pmd);
1002         if (!pmd->fail_io)
1003                 __destroy_persistent_data_objects(pmd, true);
1004
1005         kfree(pmd);
1006         return 0;
1007 }
1008
1009 /*
1010  * __open_device: Returns @td corresponding to device with id @dev,
1011  * creating it if @create is set and incrementing @td->open_count.
1012  * On failure, @td is undefined.
1013  */
1014 static int __open_device(struct dm_pool_metadata *pmd,
1015                          dm_thin_id dev, int create,
1016                          struct dm_thin_device **td)
1017 {
1018         int r, changed = 0;
1019         struct dm_thin_device *td2;
1020         uint64_t key = dev;
1021         struct disk_device_details details_le;
1022
1023         /*
1024          * If the device is already open, return it.
1025          */
1026         list_for_each_entry(td2, &pmd->thin_devices, list)
1027                 if (td2->id == dev) {
1028                         /*
1029                          * May not create an already-open device.
1030                          */
1031                         if (create)
1032                                 return -EEXIST;
1033
1034                         td2->open_count++;
1035                         *td = td2;
1036                         return 0;
1037                 }
1038
1039         /*
1040          * Check the device exists.
1041          */
1042         r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
1043                             &key, &details_le);
1044         if (r) {
1045                 if (r != -ENODATA || !create)
1046                         return r;
1047
1048                 /*
1049                  * Create new device.
1050                  */
1051                 changed = 1;
1052                 details_le.mapped_blocks = 0;
1053                 details_le.transaction_id = cpu_to_le64(pmd->trans_id);
1054                 details_le.creation_time = cpu_to_le32(pmd->time);
1055                 details_le.snapshotted_time = cpu_to_le32(pmd->time);
1056         }
1057
1058         *td = kmalloc(sizeof(**td), GFP_NOIO);
1059         if (!*td)
1060                 return -ENOMEM;
1061
1062         (*td)->pmd = pmd;
1063         (*td)->id = dev;
1064         (*td)->open_count = 1;
1065         (*td)->changed = changed;
1066         (*td)->aborted_with_changes = false;
1067         (*td)->mapped_blocks = le64_to_cpu(details_le.mapped_blocks);
1068         (*td)->transaction_id = le64_to_cpu(details_le.transaction_id);
1069         (*td)->creation_time = le32_to_cpu(details_le.creation_time);
1070         (*td)->snapshotted_time = le32_to_cpu(details_le.snapshotted_time);
1071
1072         list_add(&(*td)->list, &pmd->thin_devices);
1073
1074         return 0;
1075 }
1076
1077 static void __close_device(struct dm_thin_device *td)
1078 {
1079         --td->open_count;
1080 }
1081
1082 static int __create_thin(struct dm_pool_metadata *pmd,
1083                          dm_thin_id dev)
1084 {
1085         int r;
1086         dm_block_t dev_root;
1087         uint64_t key = dev;
1088         struct dm_thin_device *td;
1089         __le64 value;
1090
1091         r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
1092                             &key, NULL);
1093         if (!r)
1094                 return -EEXIST;
1095
1096         /*
1097          * Create an empty btree for the mappings.
1098          */
1099         r = dm_btree_empty(&pmd->bl_info, &dev_root);
1100         if (r)
1101                 return r;
1102
1103         /*
1104          * Insert it into the main mapping tree.
1105          */
1106         value = cpu_to_le64(dev_root);
1107         __dm_bless_for_disk(&value);
1108         r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
1109         if (r) {
1110                 dm_btree_del(&pmd->bl_info, dev_root);
1111                 return r;
1112         }
1113
1114         r = __open_device(pmd, dev, 1, &td);
1115         if (r) {
1116                 dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
1117                 dm_btree_del(&pmd->bl_info, dev_root);
1118                 return r;
1119         }
1120         __close_device(td);
1121
1122         return r;
1123 }
1124
1125 int dm_pool_create_thin(struct dm_pool_metadata *pmd, dm_thin_id dev)
1126 {
1127         int r = -EINVAL;
1128
1129         pmd_write_lock(pmd);
1130         if (!pmd->fail_io)
1131                 r = __create_thin(pmd, dev);
1132         pmd_write_unlock(pmd);
1133
1134         return r;
1135 }
1136
1137 static int __set_snapshot_details(struct dm_pool_metadata *pmd,
1138                                   struct dm_thin_device *snap,
1139                                   dm_thin_id origin, uint32_t time)
1140 {
1141         int r;
1142         struct dm_thin_device *td;
1143
1144         r = __open_device(pmd, origin, 0, &td);
1145         if (r)
1146                 return r;
1147
1148         td->changed = true;
1149         td->snapshotted_time = time;
1150
1151         snap->mapped_blocks = td->mapped_blocks;
1152         snap->snapshotted_time = time;
1153         __close_device(td);
1154
1155         return 0;
1156 }
1157
1158 static int __create_snap(struct dm_pool_metadata *pmd,
1159                          dm_thin_id dev, dm_thin_id origin)
1160 {
1161         int r;
1162         dm_block_t origin_root;
1163         uint64_t key = origin, dev_key = dev;
1164         struct dm_thin_device *td;
1165         __le64 value;
1166
1167         /* check this device is unused */
1168         r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
1169                             &dev_key, NULL);
1170         if (!r)
1171                 return -EEXIST;
1172
1173         /* find the mapping tree for the origin */
1174         r = dm_btree_lookup(&pmd->tl_info, pmd->root, &key, &value);
1175         if (r)
1176                 return r;
1177         origin_root = le64_to_cpu(value);
1178
1179         /* clone the origin, an inc will do */
1180         dm_tm_inc(pmd->tm, origin_root);
1181
1182         /* insert into the main mapping tree */
1183         value = cpu_to_le64(origin_root);
1184         __dm_bless_for_disk(&value);
1185         key = dev;
1186         r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
1187         if (r) {
1188                 dm_tm_dec(pmd->tm, origin_root);
1189                 return r;
1190         }
1191
1192         pmd->time++;
1193
1194         r = __open_device(pmd, dev, 1, &td);
1195         if (r)
1196                 goto bad;
1197
1198         r = __set_snapshot_details(pmd, td, origin, pmd->time);
1199         __close_device(td);
1200
1201         if (r)
1202                 goto bad;
1203
1204         return 0;
1205
1206 bad:
1207         dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
1208         dm_btree_remove(&pmd->details_info, pmd->details_root,
1209                         &key, &pmd->details_root);
1210         return r;
1211 }
1212
1213 int dm_pool_create_snap(struct dm_pool_metadata *pmd,
1214                                  dm_thin_id dev,
1215                                  dm_thin_id origin)
1216 {
1217         int r = -EINVAL;
1218
1219         pmd_write_lock(pmd);
1220         if (!pmd->fail_io)
1221                 r = __create_snap(pmd, dev, origin);
1222         pmd_write_unlock(pmd);
1223
1224         return r;
1225 }
1226
1227 static int __delete_device(struct dm_pool_metadata *pmd, dm_thin_id dev)
1228 {
1229         int r;
1230         uint64_t key = dev;
1231         struct dm_thin_device *td;
1232
1233         /* TODO: failure should mark the transaction invalid */
1234         r = __open_device(pmd, dev, 0, &td);
1235         if (r)
1236                 return r;
1237
1238         if (td->open_count > 1) {
1239                 __close_device(td);
1240                 return -EBUSY;
1241         }
1242
1243         list_del(&td->list);
1244         kfree(td);
1245         r = dm_btree_remove(&pmd->details_info, pmd->details_root,
1246                             &key, &pmd->details_root);
1247         if (r)
1248                 return r;
1249
1250         r = dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
1251         if (r)
1252                 return r;
1253
1254         return 0;
1255 }
1256
1257 int dm_pool_delete_thin_device(struct dm_pool_metadata *pmd,
1258                                dm_thin_id dev)
1259 {
1260         int r = -EINVAL;
1261
1262         pmd_write_lock(pmd);
1263         if (!pmd->fail_io)
1264                 r = __delete_device(pmd, dev);
1265         pmd_write_unlock(pmd);
1266
1267         return r;
1268 }
1269
1270 int dm_pool_set_metadata_transaction_id(struct dm_pool_metadata *pmd,
1271                                         uint64_t current_id,
1272                                         uint64_t new_id)
1273 {
1274         int r = -EINVAL;
1275
1276         pmd_write_lock(pmd);
1277
1278         if (pmd->fail_io)
1279                 goto out;
1280
1281         if (pmd->trans_id != current_id) {
1282                 DMERR("mismatched transaction id");
1283                 goto out;
1284         }
1285
1286         pmd->trans_id = new_id;
1287         r = 0;
1288
1289 out:
1290         pmd_write_unlock(pmd);
1291
1292         return r;
1293 }
1294
1295 int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd,
1296                                         uint64_t *result)
1297 {
1298         int r = -EINVAL;
1299
1300         down_read(&pmd->root_lock);
1301         if (!pmd->fail_io) {
1302                 *result = pmd->trans_id;
1303                 r = 0;
1304         }
1305         up_read(&pmd->root_lock);
1306
1307         return r;
1308 }
1309
1310 static int __reserve_metadata_snap(struct dm_pool_metadata *pmd)
1311 {
1312         int r, inc;
1313         struct thin_disk_superblock *disk_super;
1314         struct dm_block *copy, *sblock;
1315         dm_block_t held_root;
1316
1317         /*
1318          * We commit to ensure the btree roots which we increment in a
1319          * moment are up to date.
1320          */
1321         r = __commit_transaction(pmd);
1322         if (r < 0) {
1323                 DMWARN("%s: __commit_transaction() failed, error = %d",
1324                        __func__, r);
1325                 return r;
1326         }
1327
1328         /*
1329          * Copy the superblock.
1330          */
1331         dm_sm_inc_block(pmd->metadata_sm, THIN_SUPERBLOCK_LOCATION);
1332         r = dm_tm_shadow_block(pmd->tm, THIN_SUPERBLOCK_LOCATION,
1333                                &sb_validator, &copy, &inc);
1334         if (r)
1335                 return r;
1336
1337         BUG_ON(!inc);
1338
1339         held_root = dm_block_location(copy);
1340         disk_super = dm_block_data(copy);
1341
1342         if (le64_to_cpu(disk_super->held_root)) {
1343                 DMWARN("Pool metadata snapshot already exists: release this before taking another.");
1344
1345                 dm_tm_dec(pmd->tm, held_root);
1346                 dm_tm_unlock(pmd->tm, copy);
1347                 return -EBUSY;
1348         }
1349
1350         /*
1351          * Wipe the spacemap since we're not publishing this.
1352          */
1353         memset(&disk_super->data_space_map_root, 0,
1354                sizeof(disk_super->data_space_map_root));
1355         memset(&disk_super->metadata_space_map_root, 0,
1356                sizeof(disk_super->metadata_space_map_root));
1357
1358         /*
1359          * Increment the data structures that need to be preserved.
1360          */
1361         dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->data_mapping_root));
1362         dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->device_details_root));
1363         dm_tm_unlock(pmd->tm, copy);
1364
1365         /*
1366          * Write the held root into the superblock.
1367          */
1368         r = superblock_lock(pmd, &sblock);
1369         if (r) {
1370                 dm_tm_dec(pmd->tm, held_root);
1371                 return r;
1372         }
1373
1374         disk_super = dm_block_data(sblock);
1375         disk_super->held_root = cpu_to_le64(held_root);
1376         dm_bm_unlock(sblock);
1377         return 0;
1378 }
1379
1380 int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd)
1381 {
1382         int r = -EINVAL;
1383
1384         pmd_write_lock(pmd);
1385         if (!pmd->fail_io)
1386                 r = __reserve_metadata_snap(pmd);
1387         pmd_write_unlock(pmd);
1388
1389         return r;
1390 }
1391
1392 static int __release_metadata_snap(struct dm_pool_metadata *pmd)
1393 {
1394         int r;
1395         struct thin_disk_superblock *disk_super;
1396         struct dm_block *sblock, *copy;
1397         dm_block_t held_root;
1398
1399         r = superblock_lock(pmd, &sblock);
1400         if (r)
1401                 return r;
1402
1403         disk_super = dm_block_data(sblock);
1404         held_root = le64_to_cpu(disk_super->held_root);
1405         disk_super->held_root = cpu_to_le64(0);
1406
1407         dm_bm_unlock(sblock);
1408
1409         if (!held_root) {
1410                 DMWARN("No pool metadata snapshot found: nothing to release.");
1411                 return -EINVAL;
1412         }
1413
1414         r = dm_tm_read_lock(pmd->tm, held_root, &sb_validator, &copy);
1415         if (r)
1416                 return r;
1417
1418         disk_super = dm_block_data(copy);
1419         dm_btree_del(&pmd->info, le64_to_cpu(disk_super->data_mapping_root));
1420         dm_btree_del(&pmd->details_info, le64_to_cpu(disk_super->device_details_root));
1421         dm_sm_dec_block(pmd->metadata_sm, held_root);
1422
1423         dm_tm_unlock(pmd->tm, copy);
1424
1425         return 0;
1426 }
1427
1428 int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd)
1429 {
1430         int r = -EINVAL;
1431
1432         pmd_write_lock(pmd);
1433         if (!pmd->fail_io)
1434                 r = __release_metadata_snap(pmd);
1435         pmd_write_unlock(pmd);
1436
1437         return r;
1438 }
1439
1440 static int __get_metadata_snap(struct dm_pool_metadata *pmd,
1441                                dm_block_t *result)
1442 {
1443         int r;
1444         struct thin_disk_superblock *disk_super;
1445         struct dm_block *sblock;
1446
1447         r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
1448                             &sb_validator, &sblock);
1449         if (r)
1450                 return r;
1451
1452         disk_super = dm_block_data(sblock);
1453         *result = le64_to_cpu(disk_super->held_root);
1454
1455         dm_bm_unlock(sblock);
1456
1457         return 0;
1458 }
1459
1460 int dm_pool_get_metadata_snap(struct dm_pool_metadata *pmd,
1461                               dm_block_t *result)
1462 {
1463         int r = -EINVAL;
1464
1465         down_read(&pmd->root_lock);
1466         if (!pmd->fail_io)
1467                 r = __get_metadata_snap(pmd, result);
1468         up_read(&pmd->root_lock);
1469
1470         return r;
1471 }
1472
1473 int dm_pool_open_thin_device(struct dm_pool_metadata *pmd, dm_thin_id dev,
1474                              struct dm_thin_device **td)
1475 {
1476         int r = -EINVAL;
1477
1478         pmd_write_lock_in_core(pmd);
1479         if (!pmd->fail_io)
1480                 r = __open_device(pmd, dev, 0, td);
1481         pmd_write_unlock(pmd);
1482
1483         return r;
1484 }
1485
1486 int dm_pool_close_thin_device(struct dm_thin_device *td)
1487 {
1488         pmd_write_lock_in_core(td->pmd);
1489         __close_device(td);
1490         pmd_write_unlock(td->pmd);
1491
1492         return 0;
1493 }
1494
1495 dm_thin_id dm_thin_dev_id(struct dm_thin_device *td)
1496 {
1497         return td->id;
1498 }
1499
1500 /*
1501  * Check whether @time (of block creation) is older than @td's last snapshot.
1502  * If so then the associated block is shared with the last snapshot device.
1503  * Any block on a device created *after* the device last got snapshotted is
1504  * necessarily not shared.
1505  */
1506 static bool __snapshotted_since(struct dm_thin_device *td, uint32_t time)
1507 {
1508         return td->snapshotted_time > time;
1509 }
1510
1511 static void unpack_lookup_result(struct dm_thin_device *td, __le64 value,
1512                                  struct dm_thin_lookup_result *result)
1513 {
1514         uint64_t block_time = 0;
1515         dm_block_t exception_block;
1516         uint32_t exception_time;
1517
1518         block_time = le64_to_cpu(value);
1519         unpack_block_time(block_time, &exception_block, &exception_time);
1520         result->block = exception_block;
1521         result->shared = __snapshotted_since(td, exception_time);
1522 }
1523
1524 static int __find_block(struct dm_thin_device *td, dm_block_t block,
1525                         int can_issue_io, struct dm_thin_lookup_result *result)
1526 {
1527         int r;
1528         __le64 value;
1529         struct dm_pool_metadata *pmd = td->pmd;
1530         dm_block_t keys[2] = { td->id, block };
1531         struct dm_btree_info *info;
1532
1533         if (can_issue_io) {
1534                 info = &pmd->info;
1535         } else
1536                 info = &pmd->nb_info;
1537
1538         r = dm_btree_lookup(info, pmd->root, keys, &value);
1539         if (!r)
1540                 unpack_lookup_result(td, value, result);
1541
1542         return r;
1543 }
1544
1545 int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
1546                        int can_issue_io, struct dm_thin_lookup_result *result)
1547 {
1548         int r;
1549         struct dm_pool_metadata *pmd = td->pmd;
1550
1551         down_read(&pmd->root_lock);
1552         if (pmd->fail_io) {
1553                 up_read(&pmd->root_lock);
1554                 return -EINVAL;
1555         }
1556
1557         r = __find_block(td, block, can_issue_io, result);
1558
1559         up_read(&pmd->root_lock);
1560         return r;
1561 }
1562
1563 static int __find_next_mapped_block(struct dm_thin_device *td, dm_block_t block,
1564                                           dm_block_t *vblock,
1565                                           struct dm_thin_lookup_result *result)
1566 {
1567         int r;
1568         __le64 value;
1569         struct dm_pool_metadata *pmd = td->pmd;
1570         dm_block_t keys[2] = { td->id, block };
1571
1572         r = dm_btree_lookup_next(&pmd->info, pmd->root, keys, vblock, &value);
1573         if (!r)
1574                 unpack_lookup_result(td, value, result);
1575
1576         return r;
1577 }
1578
1579 static int __find_mapped_range(struct dm_thin_device *td,
1580                                dm_block_t begin, dm_block_t end,
1581                                dm_block_t *thin_begin, dm_block_t *thin_end,
1582                                dm_block_t *pool_begin, bool *maybe_shared)
1583 {
1584         int r;
1585         dm_block_t pool_end;
1586         struct dm_thin_lookup_result lookup;
1587
1588         if (end < begin)
1589                 return -ENODATA;
1590
1591         r = __find_next_mapped_block(td, begin, &begin, &lookup);
1592         if (r)
1593                 return r;
1594
1595         if (begin >= end)
1596                 return -ENODATA;
1597
1598         *thin_begin = begin;
1599         *pool_begin = lookup.block;
1600         *maybe_shared = lookup.shared;
1601
1602         begin++;
1603         pool_end = *pool_begin + 1;
1604         while (begin != end) {
1605                 r = __find_block(td, begin, true, &lookup);
1606                 if (r) {
1607                         if (r == -ENODATA)
1608                                 break;
1609                         else
1610                                 return r;
1611                 }
1612
1613                 if ((lookup.block != pool_end) ||
1614                     (lookup.shared != *maybe_shared))
1615                         break;
1616
1617                 pool_end++;
1618                 begin++;
1619         }
1620
1621         *thin_end = begin;
1622         return 0;
1623 }
1624
1625 int dm_thin_find_mapped_range(struct dm_thin_device *td,
1626                               dm_block_t begin, dm_block_t end,
1627                               dm_block_t *thin_begin, dm_block_t *thin_end,
1628                               dm_block_t *pool_begin, bool *maybe_shared)
1629 {
1630         int r = -EINVAL;
1631         struct dm_pool_metadata *pmd = td->pmd;
1632
1633         down_read(&pmd->root_lock);
1634         if (!pmd->fail_io) {
1635                 r = __find_mapped_range(td, begin, end, thin_begin, thin_end,
1636                                         pool_begin, maybe_shared);
1637         }
1638         up_read(&pmd->root_lock);
1639
1640         return r;
1641 }
1642
1643 static int __insert(struct dm_thin_device *td, dm_block_t block,
1644                     dm_block_t data_block)
1645 {
1646         int r, inserted;
1647         __le64 value;
1648         struct dm_pool_metadata *pmd = td->pmd;
1649         dm_block_t keys[2] = { td->id, block };
1650
1651         value = cpu_to_le64(pack_block_time(data_block, pmd->time));
1652         __dm_bless_for_disk(&value);
1653
1654         r = dm_btree_insert_notify(&pmd->info, pmd->root, keys, &value,
1655                                    &pmd->root, &inserted);
1656         if (r)
1657                 return r;
1658
1659         td->changed = true;
1660         if (inserted)
1661                 td->mapped_blocks++;
1662
1663         return 0;
1664 }
1665
1666 int dm_thin_insert_block(struct dm_thin_device *td, dm_block_t block,
1667                          dm_block_t data_block)
1668 {
1669         int r = -EINVAL;
1670
1671         pmd_write_lock(td->pmd);
1672         if (!td->pmd->fail_io)
1673                 r = __insert(td, block, data_block);
1674         pmd_write_unlock(td->pmd);
1675
1676         return r;
1677 }
1678
1679 static int __remove_range(struct dm_thin_device *td, dm_block_t begin, dm_block_t end)
1680 {
1681         int r;
1682         unsigned count, total_count = 0;
1683         struct dm_pool_metadata *pmd = td->pmd;
1684         dm_block_t keys[1] = { td->id };
1685         __le64 value;
1686         dm_block_t mapping_root;
1687
1688         /*
1689          * Find the mapping tree
1690          */
1691         r = dm_btree_lookup(&pmd->tl_info, pmd->root, keys, &value);
1692         if (r)
1693                 return r;
1694
1695         /*
1696          * Remove from the mapping tree, taking care to inc the
1697          * ref count so it doesn't get deleted.
1698          */
1699         mapping_root = le64_to_cpu(value);
1700         dm_tm_inc(pmd->tm, mapping_root);
1701         r = dm_btree_remove(&pmd->tl_info, pmd->root, keys, &pmd->root);
1702         if (r)
1703                 return r;
1704
1705         /*
1706          * Remove leaves stops at the first unmapped entry, so we have to
1707          * loop round finding mapped ranges.
1708          */
1709         while (begin < end) {
1710                 r = dm_btree_lookup_next(&pmd->bl_info, mapping_root, &begin, &begin, &value);
1711                 if (r == -ENODATA)
1712                         break;
1713
1714                 if (r)
1715                         return r;
1716
1717                 if (begin >= end)
1718                         break;
1719
1720                 r = dm_btree_remove_leaves(&pmd->bl_info, mapping_root, &begin, end, &mapping_root, &count);
1721                 if (r)
1722                         return r;
1723
1724                 total_count += count;
1725         }
1726
1727         td->mapped_blocks -= total_count;
1728         td->changed = true;
1729
1730         /*
1731          * Reinsert the mapping tree.
1732          */
1733         value = cpu_to_le64(mapping_root);
1734         __dm_bless_for_disk(&value);
1735         return dm_btree_insert(&pmd->tl_info, pmd->root, keys, &value, &pmd->root);
1736 }
1737
1738 int dm_thin_remove_range(struct dm_thin_device *td,
1739                          dm_block_t begin, dm_block_t end)
1740 {
1741         int r = -EINVAL;
1742
1743         pmd_write_lock(td->pmd);
1744         if (!td->pmd->fail_io)
1745                 r = __remove_range(td, begin, end);
1746         pmd_write_unlock(td->pmd);
1747
1748         return r;
1749 }
1750
1751 int dm_pool_block_is_shared(struct dm_pool_metadata *pmd, dm_block_t b, bool *result)
1752 {
1753         int r;
1754         uint32_t ref_count;
1755
1756         down_read(&pmd->root_lock);
1757         r = dm_sm_get_count(pmd->data_sm, b, &ref_count);
1758         if (!r)
1759                 *result = (ref_count > 1);
1760         up_read(&pmd->root_lock);
1761
1762         return r;
1763 }
1764
1765 int dm_pool_inc_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e)
1766 {
1767         int r = 0;
1768
1769         pmd_write_lock(pmd);
1770         r = dm_sm_inc_blocks(pmd->data_sm, b, e);
1771         pmd_write_unlock(pmd);
1772
1773         return r;
1774 }
1775
1776 int dm_pool_dec_data_range(struct dm_pool_metadata *pmd, dm_block_t b, dm_block_t e)
1777 {
1778         int r = 0;
1779
1780         pmd_write_lock(pmd);
1781         r = dm_sm_dec_blocks(pmd->data_sm, b, e);
1782         pmd_write_unlock(pmd);
1783
1784         return r;
1785 }
1786
1787 bool dm_thin_changed_this_transaction(struct dm_thin_device *td)
1788 {
1789         int r;
1790
1791         down_read(&td->pmd->root_lock);
1792         r = td->changed;
1793         up_read(&td->pmd->root_lock);
1794
1795         return r;
1796 }
1797
1798 bool dm_pool_changed_this_transaction(struct dm_pool_metadata *pmd)
1799 {
1800         bool r = false;
1801         struct dm_thin_device *td, *tmp;
1802
1803         down_read(&pmd->root_lock);
1804         list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
1805                 if (td->changed) {
1806                         r = td->changed;
1807                         break;
1808                 }
1809         }
1810         up_read(&pmd->root_lock);
1811
1812         return r;
1813 }
1814
1815 bool dm_thin_aborted_changes(struct dm_thin_device *td)
1816 {
1817         bool r;
1818
1819         down_read(&td->pmd->root_lock);
1820         r = td->aborted_with_changes;
1821         up_read(&td->pmd->root_lock);
1822
1823         return r;
1824 }
1825
1826 int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result)
1827 {
1828         int r = -EINVAL;
1829
1830         pmd_write_lock(pmd);
1831         if (!pmd->fail_io)
1832                 r = dm_sm_new_block(pmd->data_sm, result);
1833         pmd_write_unlock(pmd);
1834
1835         return r;
1836 }
1837
1838 int dm_pool_commit_metadata(struct dm_pool_metadata *pmd)
1839 {
1840         int r = -EINVAL;
1841
1842         /*
1843          * Care is taken to not have commit be what
1844          * triggers putting the thin-pool in-service.
1845          */
1846         pmd_write_lock_in_core(pmd);
1847         if (pmd->fail_io)
1848                 goto out;
1849
1850         r = __commit_transaction(pmd);
1851         if (r < 0)
1852                 goto out;
1853
1854         /*
1855          * Open the next transaction.
1856          */
1857         r = __begin_transaction(pmd);
1858 out:
1859         pmd_write_unlock(pmd);
1860         return r;
1861 }
1862
1863 static void __set_abort_with_changes_flags(struct dm_pool_metadata *pmd)
1864 {
1865         struct dm_thin_device *td;
1866
1867         list_for_each_entry(td, &pmd->thin_devices, list)
1868                 td->aborted_with_changes = td->changed;
1869 }
1870
1871 int dm_pool_abort_metadata(struct dm_pool_metadata *pmd)
1872 {
1873         int r = -EINVAL;
1874         struct dm_block_manager *old_bm = NULL, *new_bm = NULL;
1875
1876         /* fail_io is double-checked with pmd->root_lock held below */
1877         if (unlikely(pmd->fail_io))
1878                 return r;
1879
1880         /*
1881          * Replacement block manager (new_bm) is created and old_bm destroyed outside of
1882          * pmd root_lock to avoid ABBA deadlock that would result (due to life-cycle of
1883          * shrinker associated with the block manager's bufio client vs pmd root_lock).
1884          * - must take shrinker_rwsem without holding pmd->root_lock
1885          */
1886         new_bm = dm_block_manager_create(pmd->bdev, THIN_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
1887                                          THIN_MAX_CONCURRENT_LOCKS);
1888
1889         pmd_write_lock(pmd);
1890         if (pmd->fail_io) {
1891                 pmd_write_unlock(pmd);
1892                 goto out;
1893         }
1894
1895         __set_abort_with_changes_flags(pmd);
1896         __destroy_persistent_data_objects(pmd, false);
1897         old_bm = pmd->bm;
1898         if (IS_ERR(new_bm)) {
1899                 DMERR("could not create block manager during abort");
1900                 pmd->bm = NULL;
1901                 r = PTR_ERR(new_bm);
1902                 goto out_unlock;
1903         }
1904
1905         pmd->bm = new_bm;
1906         r = __open_or_format_metadata(pmd, false);
1907         if (r) {
1908                 pmd->bm = NULL;
1909                 goto out_unlock;
1910         }
1911         new_bm = NULL;
1912 out_unlock:
1913         if (r)
1914                 pmd->fail_io = true;
1915         pmd_write_unlock(pmd);
1916         dm_block_manager_destroy(old_bm);
1917 out:
1918         if (new_bm && !IS_ERR(new_bm))
1919                 dm_block_manager_destroy(new_bm);
1920
1921         return r;
1922 }
1923
1924 int dm_pool_get_free_block_count(struct dm_pool_metadata *pmd, dm_block_t *result)
1925 {
1926         int r = -EINVAL;
1927
1928         down_read(&pmd->root_lock);
1929         if (!pmd->fail_io)
1930                 r = dm_sm_get_nr_free(pmd->data_sm, result);
1931         up_read(&pmd->root_lock);
1932
1933         return r;
1934 }
1935
1936 int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
1937                                           dm_block_t *result)
1938 {
1939         int r = -EINVAL;
1940
1941         down_read(&pmd->root_lock);
1942         if (!pmd->fail_io)
1943                 r = dm_sm_get_nr_free(pmd->metadata_sm, result);
1944
1945         if (!r) {
1946                 if (*result < pmd->metadata_reserve)
1947                         *result = 0;
1948                 else
1949                         *result -= pmd->metadata_reserve;
1950         }
1951         up_read(&pmd->root_lock);
1952
1953         return r;
1954 }
1955
1956 int dm_pool_get_metadata_dev_size(struct dm_pool_metadata *pmd,
1957                                   dm_block_t *result)
1958 {
1959         int r = -EINVAL;
1960
1961         down_read(&pmd->root_lock);
1962         if (!pmd->fail_io)
1963                 r = dm_sm_get_nr_blocks(pmd->metadata_sm, result);
1964         up_read(&pmd->root_lock);
1965
1966         return r;
1967 }
1968
1969 int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result)
1970 {
1971         int r = -EINVAL;
1972
1973         down_read(&pmd->root_lock);
1974         if (!pmd->fail_io)
1975                 r = dm_sm_get_nr_blocks(pmd->data_sm, result);
1976         up_read(&pmd->root_lock);
1977
1978         return r;
1979 }
1980
1981 int dm_thin_get_mapped_count(struct dm_thin_device *td, dm_block_t *result)
1982 {
1983         int r = -EINVAL;
1984         struct dm_pool_metadata *pmd = td->pmd;
1985
1986         down_read(&pmd->root_lock);
1987         if (!pmd->fail_io) {
1988                 *result = td->mapped_blocks;
1989                 r = 0;
1990         }
1991         up_read(&pmd->root_lock);
1992
1993         return r;
1994 }
1995
1996 static int __highest_block(struct dm_thin_device *td, dm_block_t *result)
1997 {
1998         int r;
1999         __le64 value_le;
2000         dm_block_t thin_root;
2001         struct dm_pool_metadata *pmd = td->pmd;
2002
2003         r = dm_btree_lookup(&pmd->tl_info, pmd->root, &td->id, &value_le);
2004         if (r)
2005                 return r;
2006
2007         thin_root = le64_to_cpu(value_le);
2008
2009         return dm_btree_find_highest_key(&pmd->bl_info, thin_root, result);
2010 }
2011
2012 int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
2013                                      dm_block_t *result)
2014 {
2015         int r = -EINVAL;
2016         struct dm_pool_metadata *pmd = td->pmd;
2017
2018         down_read(&pmd->root_lock);
2019         if (!pmd->fail_io)
2020                 r = __highest_block(td, result);
2021         up_read(&pmd->root_lock);
2022
2023         return r;
2024 }
2025
2026 static int __resize_space_map(struct dm_space_map *sm, dm_block_t new_count)
2027 {
2028         int r;
2029         dm_block_t old_count;
2030
2031         r = dm_sm_get_nr_blocks(sm, &old_count);
2032         if (r)
2033                 return r;
2034
2035         if (new_count == old_count)
2036                 return 0;
2037
2038         if (new_count < old_count) {
2039                 DMERR("cannot reduce size of space map");
2040                 return -EINVAL;
2041         }
2042
2043         return dm_sm_extend(sm, new_count - old_count);
2044 }
2045
2046 int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
2047 {
2048         int r = -EINVAL;
2049
2050         pmd_write_lock(pmd);
2051         if (!pmd->fail_io)
2052                 r = __resize_space_map(pmd->data_sm, new_count);
2053         pmd_write_unlock(pmd);
2054
2055         return r;
2056 }
2057
2058 int dm_pool_resize_metadata_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
2059 {
2060         int r = -EINVAL;
2061
2062         pmd_write_lock(pmd);
2063         if (!pmd->fail_io) {
2064                 r = __resize_space_map(pmd->metadata_sm, new_count);
2065                 if (!r)
2066                         __set_metadata_reserve(pmd);
2067         }
2068         pmd_write_unlock(pmd);
2069
2070         return r;
2071 }
2072
2073 void dm_pool_metadata_read_only(struct dm_pool_metadata *pmd)
2074 {
2075         pmd_write_lock_in_core(pmd);
2076         dm_bm_set_read_only(pmd->bm);
2077         pmd_write_unlock(pmd);
2078 }
2079
2080 void dm_pool_metadata_read_write(struct dm_pool_metadata *pmd)
2081 {
2082         pmd_write_lock_in_core(pmd);
2083         dm_bm_set_read_write(pmd->bm);
2084         pmd_write_unlock(pmd);
2085 }
2086
2087 int dm_pool_register_metadata_threshold(struct dm_pool_metadata *pmd,
2088                                         dm_block_t threshold,
2089                                         dm_sm_threshold_fn fn,
2090                                         void *context)
2091 {
2092         int r = -EINVAL;
2093
2094         pmd_write_lock_in_core(pmd);
2095         if (!pmd->fail_io) {
2096                 r = dm_sm_register_threshold_callback(pmd->metadata_sm,
2097                                                       threshold, fn, context);
2098         }
2099         pmd_write_unlock(pmd);
2100
2101         return r;
2102 }
2103
2104 void dm_pool_register_pre_commit_callback(struct dm_pool_metadata *pmd,
2105                                           dm_pool_pre_commit_fn fn,
2106                                           void *context)
2107 {
2108         pmd_write_lock_in_core(pmd);
2109         pmd->pre_commit_fn = fn;
2110         pmd->pre_commit_context = context;
2111         pmd_write_unlock(pmd);
2112 }
2113
2114 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd)
2115 {
2116         int r = -EINVAL;
2117         struct dm_block *sblock;
2118         struct thin_disk_superblock *disk_super;
2119
2120         pmd_write_lock(pmd);
2121         if (pmd->fail_io)
2122                 goto out;
2123
2124         pmd->flags |= THIN_METADATA_NEEDS_CHECK_FLAG;
2125
2126         r = superblock_lock(pmd, &sblock);
2127         if (r) {
2128                 DMERR("couldn't lock superblock");
2129                 goto out;
2130         }
2131
2132         disk_super = dm_block_data(sblock);
2133         disk_super->flags = cpu_to_le32(pmd->flags);
2134
2135         dm_bm_unlock(sblock);
2136 out:
2137         pmd_write_unlock(pmd);
2138         return r;
2139 }
2140
2141 bool dm_pool_metadata_needs_check(struct dm_pool_metadata *pmd)
2142 {
2143         bool needs_check;
2144
2145         down_read(&pmd->root_lock);
2146         needs_check = pmd->flags & THIN_METADATA_NEEDS_CHECK_FLAG;
2147         up_read(&pmd->root_lock);
2148
2149         return needs_check;
2150 }
2151
2152 void dm_pool_issue_prefetches(struct dm_pool_metadata *pmd)
2153 {
2154         down_read(&pmd->root_lock);
2155         if (!pmd->fail_io)
2156                 dm_tm_issue_prefetches(pmd->tm);
2157         up_read(&pmd->root_lock);
2158 }