text: /*
   * Copyright (C) 2011-2012 Red Hat, Inc.
   *
   * This file is released under the GPL.
   */
  
  #include "dm-thin-metadata.h"
  #include "persistent-data/dm-btree.h"
  #include "persistent-data/dm-space-map.h"
  #include "persistent-data/dm-space-map-disk.h"
  #include "persistent-data/dm-transaction-manager.h"
  
  #include <linux/list.h>
  #include <linux/device-mapper.h>
  #include <linux/workqueue.h>
  
  /*--------------------------------------------------------------------------
   * As far as the metadata goes, there is:
   *
   * - A superblock in block zero, taking up fewer than 512 bytes for
   *   atomic writes.
   *
   * - A space map managing the metadata blocks.
   *
   * - A space map managing the data blocks.
   *
   * - A btree mapping our internal thin dev ids onto struct disk_device_details.
   *
   * - A hierarchical btree, with 2 levels which effectively maps (thin
   *   dev id, virtual block) -> block_time.  Block time is a 64-bit
   *   field holding the time in the low 24 bits, and block in the top 48
   *   bits.
   *
   * BTrees consist solely of btree_nodes, that fill a block.  Some are
   * internal nodes, as such their values are a __le64 pointing to other
   * nodes.  Leaf nodes can store data of any reasonable size (ie. much
   * smaller than the block size).  The nodes consist of the header,
   * followed by an array of keys, followed by an array of values.  We have
   * to binary search on the keys so they're all held together to help the
   * cpu cache.
   *
   * Space maps have 2 btrees:
   *
   * - One maps a uint64_t onto a struct index_entry.  Which points to a
   *   bitmap block, and has some details about how many free entries there
   *   are etc.
   *
   * - The bitmap blocks have a header (for the checksum).  Then the rest
   *   of the block is pairs of bits.  With the meaning being:
   *
   *   0 - ref count is 0
   *   1 - ref count is 1
   *   2 - ref count is 2
   *   3 - ref count is higher than 2
   *
   * - If the count is higher than 2 then the ref count is entered in a
   *   second btree that directly maps the block_address to a uint32_t ref
   *   count.
   *
   * The space map metadata variant doesn't have a bitmaps btree.  Instead
   * it has one single blocks worth of index_entries.  This avoids
   * recursive issues with the bitmap btree needing to allocate space in
   * order to insert.  With a small data block size such as 64k the
   * metadata support data devices that are hundreds of terrabytes.
   *
   * The space maps allocate space linearly from front to back.  Space that
   * is freed in a transaction is never recycled within that transaction.
   * To try and avoid fragmenting _free_ space the allocator always goes
   * back and fills in gaps.
   *
   * All metadata io is in THIN_METADATA_BLOCK_SIZE sized/aligned chunks
   * from the block manager.
   *--------------------------------------------------------------------------*/
  
  #define DM_MSG_PREFIX   "thin metadata"
  
  #define THIN_SUPERBLOCK_MAGIC 27022010
  #define THIN_SUPERBLOCK_LOCATION 0
  #define THIN_VERSION 2
  #define THIN_METADATA_CACHE_SIZE 64
  #define SECTOR_TO_BLOCK_SHIFT 3
  
  /*
   *  3 for btree insert +
   *  2 for btree lookup used within space map
   */
  #define THIN_MAX_CONCURRENT_LOCKS 5
  
  /* This should be plenty */
  #define SPACE_MAP_ROOT_SIZE 128
  
  /*
   * Little endian on-disk superblock and device details.
   */
  struct thin_disk_superblock {
  	__le32 csum;	/* Checksum of superblock except for this field. */
  	__le32 flags;
  	__le64 blocknr;	/* This block number, dm_block_t. */
  
  	__u8 uuid[16];
  	__le64 magic;
  	__le32 version;
  	__le32 time;
  
  	__le64 trans_id;
  
  	/*
  	 * Root held by userspace transactions.
  	 */
  	__le64 held_root;
  
  	__u8 data_space_map_root[SPACE_MAP_ROOT_SIZE];
  	__u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
  
  	/*
  	 * 2-level btree mapping (dev_id, (dev block, time)) -> data block
  	 */
  	__le64 data_mapping_root;
  
  	/*
  	 * Device detail root mapping dev_id -> device_details
  	 */
  	__le64 device_details_root;
  
  	__le32 data_block_size;		/* In 512-byte sectors. */
  
  	__le32 metadata_block_size;	/* In 512-byte sectors. */
  	__le64 metadata_nr_blocks;
  
  	__le32 compat_flags;
  	__le32 compat_ro_flags;
  	__le32 incompat_flags;
  } __packed;
  
  struct disk_device_details {
  	__le64 mapped_blocks;
  	__le64 transaction_id;		/* When created. */
  	__le32 creation_time;
  	__le32 snapshotted_time;
  } __packed;
  
  struct dm_pool_metadata {
  	struct hlist_node hash;
  
  	struct block_device *bdev;
  	struct dm_block_manager *bm;
  	struct dm_space_map *metadata_sm;
  	struct dm_space_map *data_sm;
  	struct dm_transaction_manager *tm;
  	struct dm_transaction_manager *nb_tm;
  
  	/*
  	 * Two-level btree.
  	 * First level holds thin_dev_t.
  	 * Second level holds mappings.
  	 */
  	struct dm_btree_info info;
  
  	/*
  	 * Non-blocking version of the above.
  	 */
  	struct dm_btree_info nb_info;
  
  	/*
  	 * Just the top level for deleting whole devices.
  	 */
  	struct dm_btree_info tl_info;
  
  	/*
  	 * Just the bottom level for creating new devices.
  	 */
  	struct dm_btree_info bl_info;
  
  	/*
  	 * Describes the device details btree.
  	 */
  	struct dm_btree_info details_info;
  
  	struct rw_semaphore root_lock;
  	uint32_t time;
  	dm_block_t root;
  	dm_block_t details_root;
  	struct list_head thin_devices;
  	uint64_t trans_id;
  	unsigned long flags;
  	sector_t data_block_size;
  	bool read_only:1;
  
  	/*
  	 * Set if a transaction has to be aborted but the attempt to roll back
  	 * to the previous (good) transaction failed.  The only pool metadata
  	 * operation possible in this state is the closing of the device.
  	 */
  	bool fail_io:1;
  
  	/*
  	 * Reading the space map roots can fail, so we read it into these
  	 * buffers before the superblock is locked and updated.
  	 */
  	__u8 data_space_map_root[SPACE_MAP_ROOT_SIZE];
  	__u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
  };
  
  struct dm_thin_device {
  	struct list_head list;
  	struct dm_pool_metadata *pmd;
  	dm_thin_id id;
  
  	int open_count;
  	bool changed:1;
  	bool aborted_with_changes:1;
  	uint64_t mapped_blocks;
  	uint64_t transaction_id;
  	uint32_t creation_time;
  	uint32_t snapshotted_time;
  };
  
  /*----------------------------------------------------------------
   * superblock validator
   *--------------------------------------------------------------*/
  
  #define SUPERBLOCK_CSUM_XOR 160774
  
  static void sb_prepare_for_write(struct dm_block_validator *v,
  				 struct dm_block *b,
  				 size_t block_size)
  {
  	struct thin_disk_superblock *disk_super = dm_block_data(b);
  
  	disk_super->blocknr = cpu_to_le64(dm_block_location(b));
  	disk_super->csum = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
  						      block_size - sizeof(__le32),
  						      SUPERBLOCK_CSUM_XOR));
  }
  
  static int sb_check(struct dm_block_validator *v,
  		    struct dm_block *b,
  		    size_t block_size)
  {
  	struct thin_disk_superblock *disk_super = dm_block_data(b);
  	__le32 csum_le;
  
  	if (dm_block_location(b) != le64_to_cpu(disk_super->blocknr)) {
  		DMERR("sb_check failed: blocknr %llu: "
  		      "wanted %llu", le64_to_cpu(disk_super->blocknr),
  		      (unsigned long long)dm_block_location(b));
  		return -ENOTBLK;
  	}
  
  	if (le64_to_cpu(disk_super->magic) != THIN_SUPERBLOCK_MAGIC) {
  		DMERR("sb_check failed: magic %llu: "
  		      "wanted %llu", le64_to_cpu(disk_super->magic),
  		      (unsigned long long)THIN_SUPERBLOCK_MAGIC);
  		return -EILSEQ;
  	}
  
  	csum_le = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
  					     block_size - sizeof(__le32),
  					     SUPERBLOCK_CSUM_XOR));
  	if (csum_le != disk_super->csum) {
  		DMERR("sb_check failed: csum %u: wanted %u",
  		      le32_to_cpu(csum_le), le32_to_cpu(disk_super->csum));
  		return -EILSEQ;
  	}
  
  	return 0;
  }
  
  static struct dm_block_validator sb_validator = {
  	.name = "superblock",
  	.prepare_for_write = sb_prepare_for_write,
  	.check = sb_check
  };
  
  /*----------------------------------------------------------------
   * Methods for the btree value types
   *--------------------------------------------------------------*/
  
  static uint64_t pack_block_time(dm_block_t b, uint32_t t)
  {
  	return (b << 24) | t;
  }
  
  static void unpack_block_time(uint64_t v, dm_block_t *b, uint32_t *t)
  {
  	*b = v >> 24;
  	*t = v & ((1 << 24) - 1);
  }
  
  static void data_block_inc(void *context, const void *value_le)
  {
  	struct dm_space_map *sm = context;
  	__le64 v_le;
  	uint64_t b;
  	uint32_t t;
  
  	memcpy(&v_le, value_le, sizeof(v_le));
  	unpack_block_time(le64_to_cpu(v_le), &b, &t);
  	dm_sm_inc_block(sm, b);
  }
  
  static void data_block_dec(void *context, const void *value_le)
  {
  	struct dm_space_map *sm = context;
  	__le64 v_le;
  	uint64_t b;
  	uint32_t t;
  
  	memcpy(&v_le, value_le, sizeof(v_le));
  	unpack_block_time(le64_to_cpu(v_le), &b, &t);
  	dm_sm_dec_block(sm, b);
  }
  
  static int data_block_equal(void *context, const void *value1_le, const void *value2_le)
  {
  	__le64 v1_le, v2_le;
  	uint64_t b1, b2;
  	uint32_t t;
  
  	memcpy(&v1_le, value1_le, sizeof(v1_le));
  	memcpy(&v2_le, value2_le, sizeof(v2_le));
  	unpack_block_time(le64_to_cpu(v1_le), &b1, &t);
  	unpack_block_time(le64_to_cpu(v2_le), &b2, &t);
  
  	return b1 == b2;
  }
  
  static void subtree_inc(void *context, const void *value)
  {
  	struct dm_btree_info *info = context;
  	__le64 root_le;
  	uint64_t root;
  
  	memcpy(&root_le, value, sizeof(root_le));
  	root = le64_to_cpu(root_le);
  	dm_tm_inc(info->tm, root);
  }
  
  static void subtree_dec(void *context, const void *value)
  {
  	struct dm_btree_info *info = context;
  	__le64 root_le;
  	uint64_t root;
  
  	memcpy(&root_le, value, sizeof(root_le));
  	root = le64_to_cpu(root_le);
  	if (dm_btree_del(info, root))
  		DMERR("btree delete failed\n");
  }
  
  static int subtree_equal(void *context, const void *value1_le, const void *value2_le)
  {
  	__le64 v1_le, v2_le;
  	memcpy(&v1_le, value1_le, sizeof(v1_le));
  	memcpy(&v2_le, value2_le, sizeof(v2_le));
  
  	return v1_le == v2_le;
  }
  
  /*----------------------------------------------------------------*/
  
  static int superblock_lock_zero(struct dm_pool_metadata *pmd,
  				struct dm_block **sblock)
  {
  	return dm_bm_write_lock_zero(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  				     &sb_validator, sblock);
  }
  
  static int superblock_lock(struct dm_pool_metadata *pmd,
  			   struct dm_block **sblock)
  {
  	return dm_bm_write_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  				&sb_validator, sblock);
  }
  
  static int __superblock_all_zeroes(struct dm_block_manager *bm, int *result)
  {
  	int r;
  	unsigned i;
  	struct dm_block *b;
  	__le64 *data_le, zero = cpu_to_le64(0);
  	unsigned block_size = dm_bm_block_size(bm) / sizeof(__le64);
  
  	/*
  	 * We can't use a validator here - it may be all zeroes.
  	 */
  	r = dm_bm_read_lock(bm, THIN_SUPERBLOCK_LOCATION, NULL, &b);
  	if (r)
  		return r;
  
  	data_le = dm_block_data(b);
  	*result = 1;
  	for (i = 0; i < block_size; i++) {
  		if (data_le[i] != zero) {
  			*result = 0;
  			break;
  		}
  	}
  
  	return dm_bm_unlock(b);
  }
  
  static void __setup_btree_details(struct dm_pool_metadata *pmd)
  {
  	pmd->info.tm = pmd->tm;
  	pmd->info.levels = 2;
  	pmd->info.value_type.context = pmd->data_sm;
  	pmd->info.value_type.size = sizeof(__le64);
  	pmd->info.value_type.inc = data_block_inc;
  	pmd->info.value_type.dec = data_block_dec;
  	pmd->info.value_type.equal = data_block_equal;
  
  	memcpy(&pmd->nb_info, &pmd->info, sizeof(pmd->nb_info));
  	pmd->nb_info.tm = pmd->nb_tm;
  
  	pmd->tl_info.tm = pmd->tm;
  	pmd->tl_info.levels = 1;
  	pmd->tl_info.value_type.context = &pmd->bl_info;
  	pmd->tl_info.value_type.size = sizeof(__le64);
  	pmd->tl_info.value_type.inc = subtree_inc;
  	pmd->tl_info.value_type.dec = subtree_dec;
  	pmd->tl_info.value_type.equal = subtree_equal;
  
  	pmd->bl_info.tm = pmd->tm;
  	pmd->bl_info.levels = 1;
  	pmd->bl_info.value_type.context = pmd->data_sm;
  	pmd->bl_info.value_type.size = sizeof(__le64);
  	pmd->bl_info.value_type.inc = data_block_inc;
  	pmd->bl_info.value_type.dec = data_block_dec;
  	pmd->bl_info.value_type.equal = data_block_equal;
  
  	pmd->details_info.tm = pmd->tm;
  	pmd->details_info.levels = 1;
  	pmd->details_info.value_type.context = NULL;
  	pmd->details_info.value_type.size = sizeof(struct disk_device_details);
  	pmd->details_info.value_type.inc = NULL;
  	pmd->details_info.value_type.dec = NULL;
  	pmd->details_info.value_type.equal = NULL;
  }
  
  static int save_sm_roots(struct dm_pool_metadata *pmd)
  {
  	int r;
  	size_t len;
  
  	r = dm_sm_root_size(pmd->metadata_sm, &len);
  	if (r < 0)
  		return r;
  
  	r = dm_sm_copy_root(pmd->metadata_sm, &pmd->metadata_space_map_root, len);
  	if (r < 0)
  		return r;
  
  	r = dm_sm_root_size(pmd->data_sm, &len);
  	if (r < 0)
  		return r;
  
  	return dm_sm_copy_root(pmd->data_sm, &pmd->data_space_map_root, len);
  }
  
  static void copy_sm_roots(struct dm_pool_metadata *pmd,
  			  struct thin_disk_superblock *disk)
  {
  	memcpy(&disk->metadata_space_map_root,
  	       &pmd->metadata_space_map_root,
  	       sizeof(pmd->metadata_space_map_root));
  
  	memcpy(&disk->data_space_map_root,
  	       &pmd->data_space_map_root,
  	       sizeof(pmd->data_space_map_root));
  }
  
  static int __write_initial_superblock(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct dm_block *sblock;
  	struct thin_disk_superblock *disk_super;
  	sector_t bdev_size = i_size_read(pmd->bdev->bd_inode) >> SECTOR_SHIFT;
  
  	if (bdev_size > THIN_METADATA_MAX_SECTORS)
  		bdev_size = THIN_METADATA_MAX_SECTORS;
  
  	r = dm_sm_commit(pmd->data_sm);
  	if (r < 0)
  		return r;
  
  	r = save_sm_roots(pmd);
  	if (r < 0)
  		return r;
  
  	r = dm_tm_pre_commit(pmd->tm);
  	if (r < 0)
  		return r;
  
  	r = superblock_lock_zero(pmd, &sblock);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(sblock);
  	disk_super->flags = 0;
  	memset(disk_super->uuid, 0, sizeof(disk_super->uuid));
  	disk_super->magic = cpu_to_le64(THIN_SUPERBLOCK_MAGIC);
  	disk_super->version = cpu_to_le32(THIN_VERSION);
  	disk_super->time = 0;
  	disk_super->trans_id = 0;
  	disk_super->held_root = 0;
  
  	copy_sm_roots(pmd, disk_super);
  
  	disk_super->data_mapping_root = cpu_to_le64(pmd->root);
  	disk_super->device_details_root = cpu_to_le64(pmd->details_root);
  	disk_super->metadata_block_size = cpu_to_le32(THIN_METADATA_BLOCK_SIZE);
  	disk_super->metadata_nr_blocks = cpu_to_le64(bdev_size >> SECTOR_TO_BLOCK_SHIFT);
  	disk_super->data_block_size = cpu_to_le32(pmd->data_block_size);
  
  	return dm_tm_commit(pmd->tm, sblock);
  }
  
  static int __format_metadata(struct dm_pool_metadata *pmd)
  {
  	int r;
  
  	r = dm_tm_create_with_sm(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  				 &pmd->tm, &pmd->metadata_sm);
  	if (r < 0) {
  		DMERR("tm_create_with_sm failed");
  		return r;
  	}
  
  	pmd->data_sm = dm_sm_disk_create(pmd->tm, 0);
  	if (IS_ERR(pmd->data_sm)) {
  		DMERR("sm_disk_create failed");
  		r = PTR_ERR(pmd->data_sm);
  		goto bad_cleanup_tm;
  	}
  
  	pmd->nb_tm = dm_tm_create_non_blocking_clone(pmd->tm);
  	if (!pmd->nb_tm) {
  		DMERR("could not create non-blocking clone tm");
  		r = -ENOMEM;
  		goto bad_cleanup_data_sm;
  	}
  
  	__setup_btree_details(pmd);
  
  	r = dm_btree_empty(&pmd->info, &pmd->root);
  	if (r < 0)
  		goto bad_cleanup_nb_tm;
  
  	r = dm_btree_empty(&pmd->details_info, &pmd->details_root);
  	if (r < 0) {
  		DMERR("couldn't create devices root");
  		goto bad_cleanup_nb_tm;
  	}
  
  	r = __write_initial_superblock(pmd);
  	if (r)
  		goto bad_cleanup_nb_tm;
  
  	return 0;
  
  bad_cleanup_nb_tm:
  	dm_tm_destroy(pmd->nb_tm);
  bad_cleanup_data_sm:
  	dm_sm_destroy(pmd->data_sm);
  bad_cleanup_tm:
  	dm_tm_destroy(pmd->tm);
  	dm_sm_destroy(pmd->metadata_sm);
  
  	return r;
  }
  
  static int __check_incompat_features(struct thin_disk_superblock *disk_super,
  				     struct dm_pool_metadata *pmd)
  {
  	uint32_t features;
  
  	features = le32_to_cpu(disk_super->incompat_flags) & ~THIN_FEATURE_INCOMPAT_SUPP;
  	if (features) {
  		DMERR("could not access metadata due to unsupported optional features (%lx).",
  		      (unsigned long)features);
  		return -EINVAL;
  	}
  
  	/*
  	 * Check for read-only metadata to skip the following RDWR checks.
  	 */
  	if (get_disk_ro(pmd->bdev->bd_disk))
  		return 0;
  
  	features = le32_to_cpu(disk_super->compat_ro_flags) & ~THIN_FEATURE_COMPAT_RO_SUPP;
  	if (features) {
  		DMERR("could not access metadata RDWR due to unsupported optional features (%lx).",
  		      (unsigned long)features);
  		return -EINVAL;
  	}
  
  	return 0;
  }
  
  static int __open_metadata(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct dm_block *sblock;
  	struct thin_disk_superblock *disk_super;
  
  	r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  			    &sb_validator, &sblock);
  	if (r < 0) {
  		DMERR("couldn't read superblock");
  		return r;
  	}
  
  	disk_super = dm_block_data(sblock);
  
  	/* Verify the data block size hasn't changed */
  	if (le32_to_cpu(disk_super->data_block_size) != pmd->data_block_size) {
  		DMERR("changing the data block size (from %u to %llu) is not supported",
  		      le32_to_cpu(disk_super->data_block_size),
  		      (unsigned long long)pmd->data_block_size);
  		r = -EINVAL;
  		goto bad_unlock_sblock;
  	}
  
  	r = __check_incompat_features(disk_super, pmd);
  	if (r < 0)
  		goto bad_unlock_sblock;
  
  	r = dm_tm_open_with_sm(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  			       disk_super->metadata_space_map_root,
  			       sizeof(disk_super->metadata_space_map_root),
  			       &pmd->tm, &pmd->metadata_sm);
  	if (r < 0) {
  		DMERR("tm_open_with_sm failed");
  		goto bad_unlock_sblock;
  	}
  
  	pmd->data_sm = dm_sm_disk_open(pmd->tm, disk_super->data_space_map_root,
  				       sizeof(disk_super->data_space_map_root));
  	if (IS_ERR(pmd->data_sm)) {
  		DMERR("sm_disk_open failed");
  		r = PTR_ERR(pmd->data_sm);
  		goto bad_cleanup_tm;
  	}
  
  	pmd->nb_tm = dm_tm_create_non_blocking_clone(pmd->tm);
  	if (!pmd->nb_tm) {
  		DMERR("could not create non-blocking clone tm");
  		r = -ENOMEM;
  		goto bad_cleanup_data_sm;
  	}
  
  	__setup_btree_details(pmd);
  	return dm_bm_unlock(sblock);
  
  bad_cleanup_data_sm:
  	dm_sm_destroy(pmd->data_sm);
  bad_cleanup_tm:
  	dm_tm_destroy(pmd->tm);
  	dm_sm_destroy(pmd->metadata_sm);
  bad_unlock_sblock:
  	dm_bm_unlock(sblock);
  
  	return r;
  }
  
  static int __open_or_format_metadata(struct dm_pool_metadata *pmd, bool format_device)
  {
  	int r, unformatted;
  
  	r = __superblock_all_zeroes(pmd->bm, &unformatted);
  	if (r)
  		return r;
  
  	if (unformatted)
  		return format_device ? __format_metadata(pmd) : -EPERM;
  
  	return __open_metadata(pmd);
  }
  
  static int __create_persistent_data_objects(struct dm_pool_metadata *pmd, bool format_device)
  {
  	int r;
  
  	pmd->bm = dm_block_manager_create(pmd->bdev, THIN_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
  					  THIN_METADATA_CACHE_SIZE,
  					  THIN_MAX_CONCURRENT_LOCKS);
  	if (IS_ERR(pmd->bm)) {
  		DMERR("could not create block manager");
  		return PTR_ERR(pmd->bm);
  	}
  
  	r = __open_or_format_metadata(pmd, format_device);
  	if (r)
  		dm_block_manager_destroy(pmd->bm);
  
  	return r;
  }
  
  static void __destroy_persistent_data_objects(struct dm_pool_metadata *pmd)
  {
  	dm_sm_destroy(pmd->data_sm);
  	dm_sm_destroy(pmd->metadata_sm);
  	dm_tm_destroy(pmd->nb_tm);
  	dm_tm_destroy(pmd->tm);
  	dm_block_manager_destroy(pmd->bm);
  }
  
  static int __begin_transaction(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct thin_disk_superblock *disk_super;
  	struct dm_block *sblock;
  
  	/*
  	 * We re-read the superblock every time.  Shouldn't need to do this
  	 * really.
  	 */
  	r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  			    &sb_validator, &sblock);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(sblock);
  	pmd->time = le32_to_cpu(disk_super->time);
  	pmd->root = le64_to_cpu(disk_super->data_mapping_root);
  	pmd->details_root = le64_to_cpu(disk_super->device_details_root);
  	pmd->trans_id = le64_to_cpu(disk_super->trans_id);
  	pmd->flags = le32_to_cpu(disk_super->flags);
  	pmd->data_block_size = le32_to_cpu(disk_super->data_block_size);
  
  	dm_bm_unlock(sblock);
  	return 0;
  }
  
  static int __write_changed_details(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct dm_thin_device *td, *tmp;
  	struct disk_device_details details;
  	uint64_t key;
  
  	list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
  		if (!td->changed)
  			continue;
  
  		key = td->id;
  
  		details.mapped_blocks = cpu_to_le64(td->mapped_blocks);
  		details.transaction_id = cpu_to_le64(td->transaction_id);
  		details.creation_time = cpu_to_le32(td->creation_time);
  		details.snapshotted_time = cpu_to_le32(td->snapshotted_time);
  		__dm_bless_for_disk(&details);
  
  		r = dm_btree_insert(&pmd->details_info, pmd->details_root,
  				    &key, &details, &pmd->details_root);
  		if (r)
  			return r;
  
  		if (td->open_count)
  			td->changed = 0;
  		else {
  			list_del(&td->list);
  			kfree(td);
  		}
  	}
  
  	return 0;
  }
  
  static int __commit_transaction(struct dm_pool_metadata *pmd)
  {
  	int r;
  	size_t metadata_len, data_len;
  	struct thin_disk_superblock *disk_super;
  	struct dm_block *sblock;
  
  	/*
  	 * We need to know if the thin_disk_superblock exceeds a 512-byte sector.
  	 */
  	BUILD_BUG_ON(sizeof(struct thin_disk_superblock) > 512);
  
  	r = __write_changed_details(pmd);
  	if (r < 0)
  		return r;
  
  	r = dm_sm_commit(pmd->data_sm);
  	if (r < 0)
  		return r;
  
  	r = dm_tm_pre_commit(pmd->tm);
  	if (r < 0)
  		return r;
  
  	r = dm_sm_root_size(pmd->metadata_sm, &metadata_len);
  	if (r < 0)
  		return r;
  
  	r = dm_sm_root_size(pmd->data_sm, &data_len);
  	if (r < 0)
  		return r;
  
  	r = save_sm_roots(pmd);
  	if (r < 0)
  		return r;
  
  	r = superblock_lock(pmd, &sblock);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(sblock);
  	disk_super->time = cpu_to_le32(pmd->time);
  	disk_super->data_mapping_root = cpu_to_le64(pmd->root);
  	disk_super->device_details_root = cpu_to_le64(pmd->details_root);
  	disk_super->trans_id = cpu_to_le64(pmd->trans_id);
  	disk_super->flags = cpu_to_le32(pmd->flags);
  
  	copy_sm_roots(pmd, disk_super);
  
  	return dm_tm_commit(pmd->tm, sblock);
  }
  
  struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev,
  					       sector_t data_block_size,
  					       bool format_device)
  {
  	int r;
  	struct dm_pool_metadata *pmd;
  
  	pmd = kmalloc(sizeof(*pmd), GFP_KERNEL);
  	if (!pmd) {
  		DMERR("could not allocate metadata struct");
  		return ERR_PTR(-ENOMEM);
  	}
  
  	init_rwsem(&pmd->root_lock);
  	pmd->time = 0;
  	INIT_LIST_HEAD(&pmd->thin_devices);
  	pmd->read_only = false;
  	pmd->fail_io = false;
  	pmd->bdev = bdev;
  	pmd->data_block_size = data_block_size;
  
  	r = __create_persistent_data_objects(pmd, format_device);
  	if (r) {
  		kfree(pmd);
  		return ERR_PTR(r);
  	}
  
  	r = __begin_transaction(pmd);
  	if (r < 0) {
  		if (dm_pool_metadata_close(pmd) < 0)
  			DMWARN("%s: dm_pool_metadata_close() failed.", __func__);
  		return ERR_PTR(r);
  	}
  
  	return pmd;
  }
  
  int dm_pool_metadata_close(struct dm_pool_metadata *pmd)
  {
  	int r;
  	unsigned open_devices = 0;
  	struct dm_thin_device *td, *tmp;
  
  	down_read(&pmd->root_lock);
  	list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
  		if (td->open_count)
  			open_devices++;
  		else {
  			list_del(&td->list);
  			kfree(td);
  		}
  	}
  	up_read(&pmd->root_lock);
  
  	if (open_devices) {
  		DMERR("attempt to close pmd when %u device(s) are still open",
  		       open_devices);
  		return -EBUSY;
  	}
  
  	if (!pmd->read_only && !pmd->fail_io) {
  		r = __commit_transaction(pmd);
  		if (r < 0)
  			DMWARN("%s: __commit_transaction() failed, error = %d",
  			       __func__, r);
  	}
  
  	if (!pmd->fail_io)
  		__destroy_persistent_data_objects(pmd);
  
  	kfree(pmd);
  	return 0;
  }
  
  /*
   * __open_device: Returns @td corresponding to device with id @dev,
   * creating it if @create is set and incrementing @td->open_count.
   * On failure, @td is undefined.
   */
  static int __open_device(struct dm_pool_metadata *pmd,
  			 dm_thin_id dev, int create,
  			 struct dm_thin_device **td)
  {
  	int r, changed = 0;
  	struct dm_thin_device *td2;
  	uint64_t key = dev;
  	struct disk_device_details details_le;
  
  	/*
  	 * If the device is already open, return it.
  	 */
  	list_for_each_entry(td2, &pmd->thin_devices, list)
  		if (td2->id == dev) {
  			/*
  			 * May not create an already-open device.
  			 */
  			if (create)
  				return -EEXIST;
  
  			td2->open_count++;
  			*td = td2;
  			return 0;
  		}
  
  	/*
  	 * Check the device exists.
  	 */
  	r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
  			    &key, &details_le);
  	if (r) {
  		if (r != -ENODATA || !create)
  			return r;
  
  		/*
  		 * Create new device.
  		 */
  		changed = 1;
  		details_le.mapped_blocks = 0;
  		details_le.transaction_id = cpu_to_le64(pmd->trans_id);
  		details_le.creation_time = cpu_to_le32(pmd->time);
  		details_le.snapshotted_time = cpu_to_le32(pmd->time);
  	}
  
  	*td = kmalloc(sizeof(**td), GFP_NOIO);
  	if (!*td)
  		return -ENOMEM;
  
  	(*td)->pmd = pmd;
  	(*td)->id = dev;
  	(*td)->open_count = 1;
  	(*td)->changed = changed;
  	(*td)->aborted_with_changes = false;
  	(*td)->mapped_blocks = le64_to_cpu(details_le.mapped_blocks);
  	(*td)->transaction_id = le64_to_cpu(details_le.transaction_id);
  	(*td)->creation_time = le32_to_cpu(details_le.creation_time);
  	(*td)->snapshotted_time = le32_to_cpu(details_le.snapshotted_time);
  
  	list_add(&(*td)->list, &pmd->thin_devices);
  
  	return 0;
  }
  
  static void __close_device(struct dm_thin_device *td)
  {
  	--td->open_count;
  }
  
  static int __create_thin(struct dm_pool_metadata *pmd,
  			 dm_thin_id dev)
  {
  	int r;
  	dm_block_t dev_root;
  	uint64_t key = dev;
  	struct disk_device_details details_le;
  	struct dm_thin_device *td;
  	__le64 value;
  
  	r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
  			    &key, &details_le);
  	if (!r)
  		return -EEXIST;
  
  	/*
  	 * Create an empty btree for the mappings.
  	 */
  	r = dm_btree_empty(&pmd->bl_info, &dev_root);
  	if (r)
  		return r;
  
  	/*
  	 * Insert it into the main mapping tree.
  	 */
  	value = cpu_to_le64(dev_root);
  	__dm_bless_for_disk(&value);
  	r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
  	if (r) {
  		dm_btree_del(&pmd->bl_info, dev_root);
  		return r;
  	}
  
  	r = __open_device(pmd, dev, 1, &td);
  	if (r) {
  		dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
  		dm_btree_del(&pmd->bl_info, dev_root);
  		return r;
  	}
  	__close_device(td);
  
  	return r;
  }
  
  int dm_pool_create_thin(struct dm_pool_metadata *pmd, dm_thin_id dev)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __create_thin(pmd, dev);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  static int __set_snapshot_details(struct dm_pool_metadata *pmd,
  				  struct dm_thin_device *snap,
  				  dm_thin_id origin, uint32_t time)
  {
  	int r;
  	struct dm_thin_device *td;
  
  	r = __open_device(pmd, origin, 0, &td);
  	if (r)
  		return r;
  
  	td->changed = 1;
  	td->snapshotted_time = time;
  
  	snap->mapped_blocks = td->mapped_blocks;
  	snap->snapshotted_time = time;
  	__close_device(td);
  
  	return 0;
  }
  
  static int __create_snap(struct dm_pool_metadata *pmd,
  			 dm_thin_id dev, dm_thin_id origin)
  {
  	int r;
  	dm_block_t origin_root;
  	uint64_t key = origin, dev_key = dev;
  	struct dm_thin_device *td;
  	struct disk_device_details details_le;
  	__le64 value;
  
  	/* check this device is unused */
  	r = dm_btree_lookup(&pmd->details_info, pmd->details_root,
  			    &dev_key, &details_le);
  	if (!r)
  		return -EEXIST;
  
  	/* find the mapping tree for the origin */
  	r = dm_btree_lookup(&pmd->tl_info, pmd->root, &key, &value);
  	if (r)
  		return r;
  	origin_root = le64_to_cpu(value);
  
  	/* clone the origin, an inc will do */
  	dm_tm_inc(pmd->tm, origin_root);
  
  	/* insert into the main mapping tree */
  	value = cpu_to_le64(origin_root);
  	__dm_bless_for_disk(&value);
  	key = dev;
  	r = dm_btree_insert(&pmd->tl_info, pmd->root, &key, &value, &pmd->root);
  	if (r) {
  		dm_tm_dec(pmd->tm, origin_root);
  		return r;
  	}
  
  	pmd->time++;
  
  	r = __open_device(pmd, dev, 1, &td);
  	if (r)
  		goto bad;
  
  	r = __set_snapshot_details(pmd, td, origin, pmd->time);
  	__close_device(td);
  
  	if (r)
  		goto bad;
  
  	return 0;
  
  bad:
  	dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
  	dm_btree_remove(&pmd->details_info, pmd->details_root,
  			&key, &pmd->details_root);
  	return r;
  }
  
  int dm_pool_create_snap(struct dm_pool_metadata *pmd,
  				 dm_thin_id dev,
  				 dm_thin_id origin)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __create_snap(pmd, dev, origin);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  static int __delete_device(struct dm_pool_metadata *pmd, dm_thin_id dev)
  {
  	int r;
  	uint64_t key = dev;
  	struct dm_thin_device *td;
  
  	/* TODO: failure should mark the transaction invalid */
  	r = __open_device(pmd, dev, 0, &td);
  	if (r)
  		return r;
  
  	if (td->open_count > 1) {
  		__close_device(td);
  		return -EBUSY;
  	}
  
  	list_del(&td->list);
  	kfree(td);
  	r = dm_btree_remove(&pmd->details_info, pmd->details_root,
  			    &key, &pmd->details_root);
  	if (r)
  		return r;
  
  	r = dm_btree_remove(&pmd->tl_info, pmd->root, &key, &pmd->root);
  	if (r)
  		return r;
  
  	return 0;
  }
  
  int dm_pool_delete_thin_device(struct dm_pool_metadata *pmd,
  			       dm_thin_id dev)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __delete_device(pmd, dev);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_set_metadata_transaction_id(struct dm_pool_metadata *pmd,
  					uint64_t current_id,
  					uint64_t new_id)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  
  	if (pmd->fail_io)
  		goto out;
  
  	if (pmd->trans_id != current_id) {
  		DMERR("mismatched transaction id");
  		goto out;
  	}
  
  	pmd->trans_id = new_id;
  	r = 0;
  
  out:
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_get_metadata_transaction_id(struct dm_pool_metadata *pmd,
  					uint64_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io) {
  		*result = pmd->trans_id;
  		r = 0;
  	}
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  static int __reserve_metadata_snap(struct dm_pool_metadata *pmd)
  {
  	int r, inc;
  	struct thin_disk_superblock *disk_super;
  	struct dm_block *copy, *sblock;
  	dm_block_t held_root;
  
  	/*
  	 * Copy the superblock.
  	 */
  	dm_sm_inc_block(pmd->metadata_sm, THIN_SUPERBLOCK_LOCATION);
  	r = dm_tm_shadow_block(pmd->tm, THIN_SUPERBLOCK_LOCATION,
  			       &sb_validator, &copy, &inc);
  	if (r)
  		return r;
  
  	BUG_ON(!inc);
  
  	held_root = dm_block_location(copy);
  	disk_super = dm_block_data(copy);
  
  	if (le64_to_cpu(disk_super->held_root)) {
  		DMWARN("Pool metadata snapshot already exists: release this before taking another.");
  
  		dm_tm_dec(pmd->tm, held_root);
  		dm_tm_unlock(pmd->tm, copy);
  		return -EBUSY;
  	}
  
  	/*
  	 * Wipe the spacemap since we're not publishing this.
  	 */
  	memset(&disk_super->data_space_map_root, 0,
  	       sizeof(disk_super->data_space_map_root));
  	memset(&disk_super->metadata_space_map_root, 0,
  	       sizeof(disk_super->metadata_space_map_root));
  
  	/*
  	 * Increment the data structures that need to be preserved.
  	 */
  	dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->data_mapping_root));
  	dm_tm_inc(pmd->tm, le64_to_cpu(disk_super->device_details_root));
  	dm_tm_unlock(pmd->tm, copy);
  
  	/*
  	 * Write the held root into the superblock.
  	 */
  	r = superblock_lock(pmd, &sblock);
  	if (r) {
  		dm_tm_dec(pmd->tm, held_root);
  		return r;
  	}
  
  	disk_super = dm_block_data(sblock);
  	disk_super->held_root = cpu_to_le64(held_root);
  	dm_bm_unlock(sblock);
  	return 0;
  }
  
  int dm_pool_reserve_metadata_snap(struct dm_pool_metadata *pmd)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __reserve_metadata_snap(pmd);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  static int __release_metadata_snap(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct thin_disk_superblock *disk_super;
  	struct dm_block *sblock, *copy;
  	dm_block_t held_root;
  
  	r = superblock_lock(pmd, &sblock);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(sblock);
  	held_root = le64_to_cpu(disk_super->held_root);
  	disk_super->held_root = cpu_to_le64(0);
  
  	dm_bm_unlock(sblock);
  
  	if (!held_root) {
  		DMWARN("No pool metadata snapshot found: nothing to release.");
  		return -EINVAL;
  	}
  
  	r = dm_tm_read_lock(pmd->tm, held_root, &sb_validator, &copy);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(copy);
  	dm_btree_del(&pmd->info, le64_to_cpu(disk_super->data_mapping_root));
  	dm_btree_del(&pmd->details_info, le64_to_cpu(disk_super->device_details_root));
  	dm_sm_dec_block(pmd->metadata_sm, held_root);
  
  	return dm_tm_unlock(pmd->tm, copy);
  }
  
  int dm_pool_release_metadata_snap(struct dm_pool_metadata *pmd)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __release_metadata_snap(pmd);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  static int __get_metadata_snap(struct dm_pool_metadata *pmd,
  			       dm_block_t *result)
  {
  	int r;
  	struct thin_disk_superblock *disk_super;
  	struct dm_block *sblock;
  
  	r = dm_bm_read_lock(pmd->bm, THIN_SUPERBLOCK_LOCATION,
  			    &sb_validator, &sblock);
  	if (r)
  		return r;
  
  	disk_super = dm_block_data(sblock);
  	*result = le64_to_cpu(disk_super->held_root);
  
  	return dm_bm_unlock(sblock);
  }
  
  int dm_pool_get_metadata_snap(struct dm_pool_metadata *pmd,
  			      dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __get_metadata_snap(pmd, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_open_thin_device(struct dm_pool_metadata *pmd, dm_thin_id dev,
  			     struct dm_thin_device **td)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __open_device(pmd, dev, 0, td);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_close_thin_device(struct dm_thin_device *td)
  {
  	down_write(&td->pmd->root_lock);
  	__close_device(td);
  	up_write(&td->pmd->root_lock);
  
  	return 0;
  }
  
  dm_thin_id dm_thin_dev_id(struct dm_thin_device *td)
  {
  	return td->id;
  }
  
  /*
   * Check whether @time (of block creation) is older than @td's last snapshot.
   * If so then the associated block is shared with the last snapshot device.
   * Any block on a device created *after* the device last got snapshotted is
   * necessarily not shared.
   */
  static bool __snapshotted_since(struct dm_thin_device *td, uint32_t time)
  {
  	return td->snapshotted_time > time;
  }
  
  int dm_thin_find_block(struct dm_thin_device *td, dm_block_t block,
  		       int can_issue_io, struct dm_thin_lookup_result *result)
  {
  	int r;
  	__le64 value;
  	struct dm_pool_metadata *pmd = td->pmd;
  	dm_block_t keys[2] = { td->id, block };
  	struct dm_btree_info *info;
  
  	if (pmd->fail_io)
  		return -EINVAL;
  
  	down_read(&pmd->root_lock);
  
  	if (can_issue_io) {
  		info = &pmd->info;
  	} else
  		info = &pmd->nb_info;
  
  	r = dm_btree_lookup(info, pmd->root, keys, &value);
  	if (!r) {
  		uint64_t block_time = 0;
  		dm_block_t exception_block;
  		uint32_t exception_time;
  
  		block_time = le64_to_cpu(value);
  		unpack_block_time(block_time, &exception_block,
  				  &exception_time);
  		result->block = exception_block;
  		result->shared = __snapshotted_since(td, exception_time);
  	}
  
  	up_read(&pmd->root_lock);
  	return r;
  }
  
  static int __insert(struct dm_thin_device *td, dm_block_t block,
  		    dm_block_t data_block)
  {
  	int r, inserted;
  	__le64 value;
  	struct dm_pool_metadata *pmd = td->pmd;
  	dm_block_t keys[2] = { td->id, block };
  
  	value = cpu_to_le64(pack_block_time(data_block, pmd->time));
  	__dm_bless_for_disk(&value);
  
  	r = dm_btree_insert_notify(&pmd->info, pmd->root, keys, &value,
  				   &pmd->root, &inserted);
  	if (r)
  		return r;
  
  	td->changed = 1;
  	if (inserted)
  		td->mapped_blocks++;
  
  	return 0;
  }
  
  int dm_thin_insert_block(struct dm_thin_device *td, dm_block_t block,
  			 dm_block_t data_block)
  {
  	int r = -EINVAL;
  
  	down_write(&td->pmd->root_lock);
  	if (!td->pmd->fail_io)
  		r = __insert(td, block, data_block);
  	up_write(&td->pmd->root_lock);
  
  	return r;
  }
  
  static int __remove(struct dm_thin_device *td, dm_block_t block)
  {
  	int r;
  	struct dm_pool_metadata *pmd = td->pmd;
  	dm_block_t keys[2] = { td->id, block };
  
  	r = dm_btree_remove(&pmd->info, pmd->root, keys, &pmd->root);
  	if (r)
  		return r;
  
  	td->mapped_blocks--;
  	td->changed = 1;
  
  	return 0;
  }
  
  int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block)
  {
  	int r = -EINVAL;
  
  	down_write(&td->pmd->root_lock);
  	if (!td->pmd->fail_io)
  		r = __remove(td, block);
  	up_write(&td->pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_block_is_used(struct dm_pool_metadata *pmd, dm_block_t b, bool *result)
  {
  	int r;
  	uint32_t ref_count;
  
  	down_read(&pmd->root_lock);
  	r = dm_sm_get_count(pmd->data_sm, b, &ref_count);
  	if (!r)
  		*result = (ref_count != 0);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  bool dm_thin_changed_this_transaction(struct dm_thin_device *td)
  {
  	int r;
  
  	down_read(&td->pmd->root_lock);
  	r = td->changed;
  	up_read(&td->pmd->root_lock);
  
  	return r;
  }
  
  bool dm_pool_changed_this_transaction(struct dm_pool_metadata *pmd)
  {
  	bool r = false;
  	struct dm_thin_device *td, *tmp;
  
  	down_read(&pmd->root_lock);
  	list_for_each_entry_safe(td, tmp, &pmd->thin_devices, list) {
  		if (td->changed) {
  			r = td->changed;
  			break;
  		}
  	}
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  bool dm_thin_aborted_changes(struct dm_thin_device *td)
  {
  	bool r;
  
  	down_read(&td->pmd->root_lock);
  	r = td->aborted_with_changes;
  	up_read(&td->pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = dm_sm_new_block(pmd->data_sm, result);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_commit_metadata(struct dm_pool_metadata *pmd)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (pmd->fail_io)
  		goto out;
  
  	r = __commit_transaction(pmd);
  	if (r <= 0)
  		goto out;
  
  	/*
  	 * Open the next transaction.
  	 */
  	r = __begin_transaction(pmd);
  out:
  	up_write(&pmd->root_lock);
  	return r;
  }
  
  static void __set_abort_with_changes_flags(struct dm_pool_metadata *pmd)
  {
  	struct dm_thin_device *td;
  
  	list_for_each_entry(td, &pmd->thin_devices, list)
  		td->aborted_with_changes = td->changed;
  }
  
  int dm_pool_abort_metadata(struct dm_pool_metadata *pmd)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (pmd->fail_io)
  		goto out;
  
  	__set_abort_with_changes_flags(pmd);
  	__destroy_persistent_data_objects(pmd);
  	r = __create_persistent_data_objects(pmd, false);
  	if (r)
  		pmd->fail_io = true;
  
  out:
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_get_free_block_count(struct dm_pool_metadata *pmd, dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = dm_sm_get_nr_free(pmd->data_sm, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_get_free_metadata_block_count(struct dm_pool_metadata *pmd,
  					  dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = dm_sm_get_nr_free(pmd->metadata_sm, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_get_metadata_dev_size(struct dm_pool_metadata *pmd,
  				  dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = dm_sm_get_nr_blocks(pmd->metadata_sm, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_get_data_dev_size(struct dm_pool_metadata *pmd, dm_block_t *result)
  {
  	int r = -EINVAL;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = dm_sm_get_nr_blocks(pmd->data_sm, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_thin_get_mapped_count(struct dm_thin_device *td, dm_block_t *result)
  {
  	int r = -EINVAL;
  	struct dm_pool_metadata *pmd = td->pmd;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io) {
  		*result = td->mapped_blocks;
  		r = 0;
  	}
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  static int __highest_block(struct dm_thin_device *td, dm_block_t *result)
  {
  	int r;
  	__le64 value_le;
  	dm_block_t thin_root;
  	struct dm_pool_metadata *pmd = td->pmd;
  
  	r = dm_btree_lookup(&pmd->tl_info, pmd->root, &td->id, &value_le);
  	if (r)
  		return r;
  
  	thin_root = le64_to_cpu(value_le);
  
  	return dm_btree_find_highest_key(&pmd->bl_info, thin_root, result);
  }
  
  int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
  				     dm_block_t *result)
  {
  	int r = -EINVAL;
  	struct dm_pool_metadata *pmd = td->pmd;
  
  	down_read(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __highest_block(td, result);
  	up_read(&pmd->root_lock);
  
  	return r;
  }
  
  static int __resize_space_map(struct dm_space_map *sm, dm_block_t new_count)
  {
  	int r;
  	dm_block_t old_count;
  
  	r = dm_sm_get_nr_blocks(sm, &old_count);
  	if (r)
  		return r;
  
  	if (new_count == old_count)
  		return 0;
  
  	if (new_count < old_count) {
  		DMERR("cannot reduce size of space map");
  		return -EINVAL;
  	}
  
  	return dm_sm_extend(sm, new_count - old_count);
  }
  
  int dm_pool_resize_data_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __resize_space_map(pmd->data_sm, new_count);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_resize_metadata_dev(struct dm_pool_metadata *pmd, dm_block_t new_count)
  {
  	int r = -EINVAL;
  
  	down_write(&pmd->root_lock);
  	if (!pmd->fail_io)
  		r = __resize_space_map(pmd->metadata_sm, new_count);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  void dm_pool_metadata_read_only(struct dm_pool_metadata *pmd)
  {
  	down_write(&pmd->root_lock);
  	pmd->read_only = true;
  	dm_bm_set_read_only(pmd->bm);
  	up_write(&pmd->root_lock);
  }
  
  void dm_pool_metadata_read_write(struct dm_pool_metadata *pmd)
  {
  	down_write(&pmd->root_lock);
  	pmd->read_only = false;
  	dm_bm_set_read_write(pmd->bm);
  	up_write(&pmd->root_lock);
  }
  
  int dm_pool_register_metadata_threshold(struct dm_pool_metadata *pmd,
  					dm_block_t threshold,
  					dm_sm_threshold_fn fn,
  					void *context)
  {
  	int r;
  
  	down_write(&pmd->root_lock);
  	r = dm_sm_register_threshold_callback(pmd->metadata_sm, threshold, fn, context);
  	up_write(&pmd->root_lock);
  
  	return r;
  }
  
  int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd)
  {
  	int r;
  	struct dm_block *sblock;
  	struct thin_disk_superblock *disk_super;
  
  	down_write(&pmd->root_lock);
  	pmd->flags |= THIN_METADATA_NEEDS_CHECK_FLAG;
  
  	r = superblock_lock(pmd, &sblock);
  	if (r) {
  		DMERR("couldn't read superblock");
  		goto out;
  	}
  
  	disk_super = dm_block_data(sblock);
  	disk_super->flags = cpu_to_le32(pmd->flags);
  
  	dm_bm_unlock(sblock);
  out:
  	up_write(&pmd->root_lock);
  	return r;
  }
  
  bool dm_pool_metadata_needs_check(struct dm_pool_metadata *pmd)
  {
  	bool needs_check;
  
  	down_read(&pmd->root_lock);
  	needs_check = pmd->flags & THIN_METADATA_NEEDS_CHECK_FLAG;
  	up_read(&pmd->root_lock);
  
  	return needs_check;
  }
  
  void dm_pool_issue_prefetches(struct dm_pool_metadata *pmd)
  {
  	dm_tm_issue_prefetches(pmd->tm);
  }
  