dm: add clone target

Add the dm-clone target, which allows cloning of arbitrary block
devices.

dm-clone produces a one-to-one copy of an existing, read-only source
device into a writable destination device: It presents a virtual block
device which makes all data appear immediately, and redirects reads and
writes accordingly.

The main use case of dm-clone is to clone a potentially remote,
high-latency, read-only, archival-type block device into a writable,
fast, primary-type device for fast, low-latency I/O. The cloned device
is visible/mountable immediately and the copy of the source device to
the destination device happens in the background, in parallel with user
I/O.

When the cloning completes, the dm-clone table can be removed altogether
and be replaced, e.g., by a linear table, mapping directly to the
destination device.

For further information and examples of how to use dm-clone, please read
Documentation/admin-guide/device-mapper/dm-clone.rst

Suggested-by: Vangelis Koukis <vkoukis@arrikto.com>
Co-developed-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 964 insertions, 0 deletions

diff --git a/drivers/md/dm-clone-metadata.c b/drivers/md/dm-clone-metadata.c
new file mode 100644
index 000000000000..6bc8c1d1c351
--- /dev/null
+++ b/drivers/md/dm-clone-metadata.c
@@ -0,0 +1,964 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2019 Arrikto, Inc. All Rights Reserved.
+ */
+
+#include <linux/mm.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/rwsem.h>
+#include <linux/bitops.h>
+#include <linux/bitmap.h>
+#include <linux/device-mapper.h>
+
+#include "persistent-data/dm-bitset.h"
+#include "persistent-data/dm-space-map.h"
+#include "persistent-data/dm-block-manager.h"
+#include "persistent-data/dm-transaction-manager.h"
+
+#include "dm-clone-metadata.h"
+
+#define DM_MSG_PREFIX "clone metadata"
+
+#define SUPERBLOCK_LOCATION 0
+#define SUPERBLOCK_MAGIC 0x8af27f64
+#define SUPERBLOCK_CSUM_XOR 257649492
+
+#define DM_CLONE_MAX_CONCURRENT_LOCKS 5
+
+#define UUID_LEN 16
+
+/* Min and max dm-clone metadata versions supported */
+#define DM_CLONE_MIN_METADATA_VERSION 1
+#define DM_CLONE_MAX_METADATA_VERSION 1
+
+/*
+ * On-disk metadata layout
+ */
+struct superblock_disk {
+	__le32 csum;
+	__le32 flags;
+	__le64 blocknr;
+
+	__u8 uuid[UUID_LEN];
+	__le64 magic;
+	__le32 version;
+
+	__u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
+
+	__le64 region_size;
+	__le64 target_size;
+
+	__le64 bitset_root;
+} __packed;
+
+/*
+ * Region and Dirty bitmaps.
+ *
+ * dm-clone logically splits the source and destination devices in regions of
+ * fixed size. The destination device's regions are gradually hydrated, i.e.,
+ * we copy (clone) the source's regions to the destination device. Eventually,
+ * all regions will get hydrated and all I/O will be served from the
+ * destination device.
+ *
+ * We maintain an on-disk bitmap which tracks the state of each of the
+ * destination device's regions, i.e., whether they are hydrated or not.
+ *
+ * To save constantly doing look ups on disk we keep an in core copy of the
+ * on-disk bitmap, the region_map.
+ *
+ * To further reduce metadata I/O overhead we use a second bitmap, the dmap
+ * (dirty bitmap), which tracks the dirty words, i.e. longs, of the region_map.
+ *
+ * When a region finishes hydrating dm-clone calls
+ * dm_clone_set_region_hydrated(), or for discard requests
+ * dm_clone_cond_set_range(), which sets the corresponding bits in region_map
+ * and dmap.
+ *
+ * During a metadata commit we scan the dmap for dirty region_map words (longs)
+ * and update accordingly the on-disk metadata. Thus, we don't have to flush to
+ * disk the whole region_map. We can just flush the dirty region_map words.
+ *
+ * We use a dirty bitmap, which is smaller than the original region_map, to
+ * reduce the amount of memory accesses during a metadata commit. As dm-bitset
+ * accesses the on-disk bitmap in 64-bit word granularity, there is no
+ * significant benefit in tracking the dirty region_map bits with a smaller
+ * granularity.
+ *
+ * We could update directly the on-disk bitmap, when dm-clone calls either
+ * dm_clone_set_region_hydrated() or dm_clone_cond_set_range(), buts this
+ * inserts significant metadata I/O overhead in dm-clone's I/O path. Also, as
+ * these two functions don't block, we can call them in interrupt context,
+ * e.g., in a hooked overwrite bio's completion routine, and further reduce the
+ * I/O completion latency.
+ *
+ * We maintain two dirty bitmaps. During a metadata commit we atomically swap
+ * the currently used dmap with the unused one. This allows the metadata update
+ * functions to run concurrently with an ongoing commit.
+ */
+struct dirty_map {
+	unsigned long *dirty_words;
+	unsigned int changed;
+};
+
+struct dm_clone_metadata {
+	/* The metadata block device */
+	struct block_device *bdev;
+
+	sector_t target_size;
+	sector_t region_size;
+	unsigned long nr_regions;
+	unsigned long nr_words;
+
+	/* Spinlock protecting the region and dirty bitmaps. */
+	spinlock_t bitmap_lock;
+	struct dirty_map dmap[2];
+	struct dirty_map *current_dmap;
+
+	/*
+	 * In core copy of the on-disk bitmap to save constantly doing look ups
+	 * on disk.
+	 */
+	unsigned long *region_map;
+
+	/* Protected by bitmap_lock */
+	unsigned int read_only;
+
+	struct dm_block_manager *bm;
+	struct dm_space_map *sm;
+	struct dm_transaction_manager *tm;
+
+	struct rw_semaphore lock;
+
+	struct dm_disk_bitset bitset_info;
+	dm_block_t bitset_root;
+
+	/*
+	 * Reading the space map root can fail, so we read it into this
+	 * buffer before the superblock is locked and updated.
+	 */
+	__u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
+
+	bool hydration_done:1;
+	bool fail_io:1;
+};
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Superblock validation.
+ */
+static void sb_prepare_for_write(struct dm_block_validator *v,
+				 struct dm_block *b, size_t sb_block_size)
+{
+	struct superblock_disk *sb;
+	u32 csum;
+
+	sb = dm_block_data(b);
+	sb->blocknr = cpu_to_le64(dm_block_location(b));
+
+	csum = dm_bm_checksum(&sb->flags, sb_block_size - sizeof(__le32),
+			      SUPERBLOCK_CSUM_XOR);
+	sb->csum = cpu_to_le32(csum);
+}
+
+static int sb_check(struct dm_block_validator *v, struct dm_block *b,
+		    size_t sb_block_size)
+{
+	struct superblock_disk *sb;
+	u32 csum, metadata_version;
+
+	sb = dm_block_data(b);
+
+	if (dm_block_location(b) != le64_to_cpu(sb->blocknr)) {
+		DMERR("Superblock check failed: blocknr %llu, expected %llu",
+		      le64_to_cpu(sb->blocknr),
+		      (unsigned long long)dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	if (le64_to_cpu(sb->magic) != SUPERBLOCK_MAGIC) {
+		DMERR("Superblock check failed: magic %llu, expected %llu",
+		      le64_to_cpu(sb->magic),
+		      (unsigned long long)SUPERBLOCK_MAGIC);
+		return -EILSEQ;
+	}
+
+	csum = dm_bm_checksum(&sb->flags, sb_block_size - sizeof(__le32),
+			      SUPERBLOCK_CSUM_XOR);
+	if (sb->csum != cpu_to_le32(csum)) {
+		DMERR("Superblock check failed: checksum %u, expected %u",
+		      csum, le32_to_cpu(sb->csum));
+		return -EILSEQ;
+	}
+
+	/* Check metadata version */
+	metadata_version = le32_to_cpu(sb->version);
+	if (metadata_version < DM_CLONE_MIN_METADATA_VERSION ||
+	    metadata_version > DM_CLONE_MAX_METADATA_VERSION) {
+		DMERR("Clone metadata version %u found, but only versions between %u and %u supported.",
+		      metadata_version, DM_CLONE_MIN_METADATA_VERSION,
+		      DM_CLONE_MAX_METADATA_VERSION);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static struct dm_block_validator sb_validator = {
+	.name = "superblock",
+	.prepare_for_write = sb_prepare_for_write,
+	.check = sb_check
+};
+
+/*
+ * Check if the superblock is formatted or not. We consider the superblock to
+ * be formatted in case we find non-zero bytes in it.
+ */
+static int __superblock_all_zeroes(struct dm_block_manager *bm, bool *formatted)
+{
+	int r;
+	unsigned int i, nr_words;
+	struct dm_block *sblock;
+	__le64 *data_le, zero = cpu_to_le64(0);
+
+	/*
+	 * We don't use a validator here because the superblock could be all
+	 * zeroes.
+	 */
+	r = dm_bm_read_lock(bm, SUPERBLOCK_LOCATION, NULL, &sblock);
+	if (r) {
+		DMERR("Failed to read_lock superblock");
+		return r;
+	}
+
+	data_le = dm_block_data(sblock);
+	*formatted = false;
+
+	/* This assumes that the block size is a multiple of 8 bytes */
+	BUG_ON(dm_bm_block_size(bm) % sizeof(__le64));
+	nr_words = dm_bm_block_size(bm) / sizeof(__le64);
+	for (i = 0; i < nr_words; i++) {
+		if (data_le[i] != zero) {
+			*formatted = true;
+			break;
+		}
+	}
+
+	dm_bm_unlock(sblock);
+
+	return 0;
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Low-level metadata handling.
+ */
+static inline int superblock_read_lock(struct dm_clone_metadata *cmd,
+				       struct dm_block **sblock)
+{
+	return dm_bm_read_lock(cmd->bm, SUPERBLOCK_LOCATION, &sb_validator, sblock);
+}
+
+static inline int superblock_write_lock(struct dm_clone_metadata *cmd,
+					struct dm_block **sblock)
+{
+	return dm_bm_write_lock(cmd->bm, SUPERBLOCK_LOCATION, &sb_validator, sblock);
+}
+
+static inline int superblock_write_lock_zero(struct dm_clone_metadata *cmd,
+					     struct dm_block **sblock)
+{
+	return dm_bm_write_lock_zero(cmd->bm, SUPERBLOCK_LOCATION, &sb_validator, sblock);
+}
+
+static int __copy_sm_root(struct dm_clone_metadata *cmd)
+{
+	int r;
+	size_t root_size;
+
+	r = dm_sm_root_size(cmd->sm, &root_size);
+	if (r)
+		return r;
+
+	return dm_sm_copy_root(cmd->sm, &cmd->metadata_space_map_root, root_size);
+}
+
+/* Save dm-clone metadata in superblock */
+static void __prepare_superblock(struct dm_clone_metadata *cmd,
+				 struct superblock_disk *sb)
+{
+	sb->flags = cpu_to_le32(0UL);
+
+	/* FIXME: UUID is currently unused */
+	memset(sb->uuid, 0, sizeof(sb->uuid));
+
+	sb->magic = cpu_to_le64(SUPERBLOCK_MAGIC);
+	sb->version = cpu_to_le32(DM_CLONE_MAX_METADATA_VERSION);
+
+	/* Save the metadata space_map root */
+	memcpy(&sb->metadata_space_map_root, &cmd->metadata_space_map_root,
+	       sizeof(cmd->metadata_space_map_root));
+
+	sb->region_size = cpu_to_le64(cmd->region_size);
+	sb->target_size = cpu_to_le64(cmd->target_size);
+	sb->bitset_root = cpu_to_le64(cmd->bitset_root);
+}
+
+static int __open_metadata(struct dm_clone_metadata *cmd)
+{
+	int r;
+	struct dm_block *sblock;
+	struct superblock_disk *sb;
+
+	r = superblock_read_lock(cmd, &sblock);
+
+	if (r) {
+		DMERR("Failed to read_lock superblock");
+		return r;
+	}
+
+	sb = dm_block_data(sblock);
+
+	/* Verify that target_size and region_size haven't changed. */
+	if (cmd->region_size != le64_to_cpu(sb->region_size) ||
+	    cmd->target_size != le64_to_cpu(sb->target_size)) {
+		DMERR("Region and/or target size don't match the ones in metadata");
+		r = -EINVAL;
+		goto out_with_lock;
+	}
+
+	r = dm_tm_open_with_sm(cmd->bm, SUPERBLOCK_LOCATION,
+			       sb->metadata_space_map_root,
+			       sizeof(sb->metadata_space_map_root),
+			       &cmd->tm, &cmd->sm);
+
+	if (r) {
+		DMERR("dm_tm_open_with_sm failed");
+		goto out_with_lock;
+	}
+
+	dm_disk_bitset_init(cmd->tm, &cmd->bitset_info);
+	cmd->bitset_root = le64_to_cpu(sb->bitset_root);
+
+out_with_lock:
+	dm_bm_unlock(sblock);
+
+	return r;
+}
+
+static int __format_metadata(struct dm_clone_metadata *cmd)
+{
+	int r;
+	struct dm_block *sblock;
+	struct superblock_disk *sb;
+
+	r = dm_tm_create_with_sm(cmd->bm, SUPERBLOCK_LOCATION, &cmd->tm, &cmd->sm);
+	if (r) {
+		DMERR("Failed to create transaction manager");
+		return r;
+	}
+
+	dm_disk_bitset_init(cmd->tm, &cmd->bitset_info);
+
+	r = dm_bitset_empty(&cmd->bitset_info, &cmd->bitset_root);
+	if (r) {
+		DMERR("Failed to create empty on-disk bitset");
+		goto err_with_tm;
+	}
+
+	r = dm_bitset_resize(&cmd->bitset_info, cmd->bitset_root, 0,
+			     cmd->nr_regions, false, &cmd->bitset_root);
+	if (r) {
+		DMERR("Failed to resize on-disk bitset to %lu entries", cmd->nr_regions);
+		goto err_with_tm;
+	}
+
+	/* Flush to disk all blocks, except the superblock */
+	r = dm_tm_pre_commit(cmd->tm);
+	if (r) {
+		DMERR("dm_tm_pre_commit failed");
+		goto err_with_tm;
+	}
+
+	r = __copy_sm_root(cmd);
+	if (r) {
+		DMERR("__copy_sm_root failed");
+		goto err_with_tm;
+	}
+
+	r = superblock_write_lock_zero(cmd, &sblock);
+	if (r) {
+		DMERR("Failed to write_lock superblock");
+		goto err_with_tm;
+	}
+
+	sb = dm_block_data(sblock);
+	__prepare_superblock(cmd, sb);
+	r = dm_tm_commit(cmd->tm, sblock);
+	if (r) {
+		DMERR("Failed to commit superblock");
+		goto err_with_tm;
+	}
+
+	return 0;
+
+err_with_tm:
+	dm_sm_destroy(cmd->sm);
+	dm_tm_destroy(cmd->tm);
+
+	return r;
+}
+
+static int __open_or_format_metadata(struct dm_clone_metadata *cmd, bool may_format_device)
+{
+	int r;
+	bool formatted = false;
+
+	r = __superblock_all_zeroes(cmd->bm, &formatted);
+	if (r)
+		return r;
+
+	if (!formatted)
+		return may_format_device ? __format_metadata(cmd) : -EPERM;
+
+	return __open_metadata(cmd);
+}
+
+static int __create_persistent_data_structures(struct dm_clone_metadata *cmd,
+					       bool may_format_device)
+{
+	int r;
+
+	/* Create block manager */
+	cmd->bm = dm_block_manager_create(cmd->bdev,
+					 DM_CLONE_METADATA_BLOCK_SIZE << SECTOR_SHIFT,
+					 DM_CLONE_MAX_CONCURRENT_LOCKS);
+	if (IS_ERR(cmd->bm)) {
+		DMERR("Failed to create block manager");
+		return PTR_ERR(cmd->bm);
+	}
+
+	r = __open_or_format_metadata(cmd, may_format_device);
+	if (r)
+		dm_block_manager_destroy(cmd->bm);
+
+	return r;
+}
+
+static void __destroy_persistent_data_structures(struct dm_clone_metadata *cmd)
+{
+	dm_sm_destroy(cmd->sm);
+	dm_tm_destroy(cmd->tm);
+	dm_block_manager_destroy(cmd->bm);
+}
+
+/*---------------------------------------------------------------------------*/
+
+static size_t bitmap_size(unsigned long nr_bits)
+{
+	return BITS_TO_LONGS(nr_bits) * sizeof(long);
+}
+
+static int dirty_map_init(struct dm_clone_metadata *cmd)
+{
+	cmd->dmap[0].changed = 0;
+	cmd->dmap[0].dirty_words = kvzalloc(bitmap_size(cmd->nr_words), GFP_KERNEL);
+
+	if (!cmd->dmap[0].dirty_words) {
+		DMERR("Failed to allocate dirty bitmap");
+		return -ENOMEM;
+	}
+
+	cmd->dmap[1].changed = 0;
+	cmd->dmap[1].dirty_words = kvzalloc(bitmap_size(cmd->nr_words), GFP_KERNEL);
+
+	if (!cmd->dmap[1].dirty_words) {
+		DMERR("Failed to allocate dirty bitmap");
+		kvfree(cmd->dmap[0].dirty_words);
+		return -ENOMEM;
+	}
+
+	cmd->current_dmap = &cmd->dmap[0];
+
+	return 0;
+}
+
+static void dirty_map_exit(struct dm_clone_metadata *cmd)
+{
+	kvfree(cmd->dmap[0].dirty_words);
+	kvfree(cmd->dmap[1].dirty_words);
+}
+
+static int __load_bitset_in_core(struct dm_clone_metadata *cmd)
+{
+	int r;
+	unsigned long i;
+	struct dm_bitset_cursor c;
+
+	/* Flush bitset cache */
+	r = dm_bitset_flush(&cmd->bitset_info, cmd->bitset_root, &cmd->bitset_root);
+	if (r)
+		return r;
+
+	r = dm_bitset_cursor_begin(&cmd->bitset_info, cmd->bitset_root, cmd->nr_regions, &c);
+	if (r)
+		return r;
+
+	for (i = 0; ; i++) {
+		if (dm_bitset_cursor_get_value(&c))
+			__set_bit(i, cmd->region_map);
+		else
+			__clear_bit(i, cmd->region_map);
+
+		if (i >= (cmd->nr_regions - 1))
+			break;
+
+		r = dm_bitset_cursor_next(&c);
+
+		if (r)
+			break;
+	}
+
+	dm_bitset_cursor_end(&c);
+
+	return r;
+}
+
+struct dm_clone_metadata *dm_clone_metadata_open(struct block_device *bdev,
+						 sector_t target_size,
+						 sector_t region_size)
+{
+	int r;
+	struct dm_clone_metadata *cmd;
+
+	cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
+	if (!cmd) {
+		DMERR("Failed to allocate memory for dm-clone metadata");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	cmd->bdev = bdev;
+	cmd->target_size = target_size;
+	cmd->region_size = region_size;
+	cmd->nr_regions = dm_sector_div_up(cmd->target_size, cmd->region_size);
+	cmd->nr_words = BITS_TO_LONGS(cmd->nr_regions);
+
+	init_rwsem(&cmd->lock);
+	spin_lock_init(&cmd->bitmap_lock);
+	cmd->read_only = 0;
+	cmd->fail_io = false;
+	cmd->hydration_done = false;
+
+	cmd->region_map = kvmalloc(bitmap_size(cmd->nr_regions), GFP_KERNEL);
+	if (!cmd->region_map) {
+		DMERR("Failed to allocate memory for region bitmap");
+		r = -ENOMEM;
+		goto out_with_md;
+	}
+
+	r = __create_persistent_data_structures(cmd, true);
+	if (r)
+		goto out_with_region_map;
+
+	r = __load_bitset_in_core(cmd);
+	if (r) {
+		DMERR("Failed to load on-disk region map");
+		goto out_with_pds;
+	}
+
+	r = dirty_map_init(cmd);
+	if (r)
+		goto out_with_pds;
+
+	if (bitmap_full(cmd->region_map, cmd->nr_regions))
+		cmd->hydration_done = true;
+
+	return cmd;
+
+out_with_pds:
+	__destroy_persistent_data_structures(cmd);
+
+out_with_region_map:
+	kvfree(cmd->region_map);
+
+out_with_md:
+	kfree(cmd);
+
+	return ERR_PTR(r);
+}
+
+void dm_clone_metadata_close(struct dm_clone_metadata *cmd)
+{
+	if (!cmd->fail_io)
+		__destroy_persistent_data_structures(cmd);
+
+	dirty_map_exit(cmd);
+	kvfree(cmd->region_map);
+	kfree(cmd);
+}
+
+bool dm_clone_is_hydration_done(struct dm_clone_metadata *cmd)
+{
+	return cmd->hydration_done;
+}
+
+bool dm_clone_is_region_hydrated(struct dm_clone_metadata *cmd, unsigned long region_nr)
+{
+	return dm_clone_is_hydration_done(cmd) || test_bit(region_nr, cmd->region_map);
+}
+
+bool dm_clone_is_range_hydrated(struct dm_clone_metadata *cmd,
+				unsigned long start, unsigned long nr_regions)
+{
+	unsigned long bit;
+
+	if (dm_clone_is_hydration_done(cmd))
+		return true;
+
+	bit = find_next_zero_bit(cmd->region_map, cmd->nr_regions, start);
+
+	return (bit >= (start + nr_regions));
+}
+
+unsigned long dm_clone_nr_of_hydrated_regions(struct dm_clone_metadata *cmd)
+{
+	return bitmap_weight(cmd->region_map, cmd->nr_regions);
+}
+
+unsigned long dm_clone_find_next_unhydrated_region(struct dm_clone_metadata *cmd,
+						   unsigned long start)
+{
+	return find_next_zero_bit(cmd->region_map, cmd->nr_regions, start);
+}
+
+static int __update_metadata_word(struct dm_clone_metadata *cmd, unsigned long word)
+{
+	int r;
+	unsigned long index = word * BITS_PER_LONG;
+	unsigned long max_index = min(cmd->nr_regions, (word + 1) * BITS_PER_LONG);
+
+	while (index < max_index) {
+		if (test_bit(index, cmd->region_map)) {
+			r = dm_bitset_set_bit(&cmd->bitset_info, cmd->bitset_root,
+					      index, &cmd->bitset_root);
+
+			if (r) {
+				DMERR("dm_bitset_set_bit failed");
+				return r;
+			}
+		}
+		index++;
+	}
+
+	return 0;
+}
+
+static int __metadata_commit(struct dm_clone_metadata *cmd)
+{
+	int r;
+	struct dm_block *sblock;
+	struct superblock_disk *sb;
+
+	/* Flush bitset cache */
+	r = dm_bitset_flush(&cmd->bitset_info, cmd->bitset_root, &cmd->bitset_root);
+	if (r) {
+		DMERR("dm_bitset_flush failed");
+		return r;
+	}
+
+	/* Flush to disk all blocks, except the superblock */
+	r = dm_tm_pre_commit(cmd->tm);
+	if (r) {
+		DMERR("dm_tm_pre_commit failed");
+		return r;
+	}
+
+	/* Save the space map root in cmd->metadata_space_map_root */
+	r = __copy_sm_root(cmd);
+	if (r) {
+		DMERR("__copy_sm_root failed");
+		return r;
+	}
+
+	/* Lock the superblock */
+	r = superblock_write_lock_zero(cmd, &sblock);
+	if (r) {
+		DMERR("Failed to write_lock superblock");
+		return r;
+	}
+
+	/* Save the metadata in superblock */
+	sb = dm_block_data(sblock);
+	__prepare_superblock(cmd, sb);
+
+	/* Unlock superblock and commit it to disk */
+	r = dm_tm_commit(cmd->tm, sblock);
+	if (r) {
+		DMERR("Failed to commit superblock");
+		return r;
+	}
+
+	/*
+	 * FIXME: Find a more efficient way to check if the hydration is done.
+	 */
+	if (bitmap_full(cmd->region_map, cmd->nr_regions))
+		cmd->hydration_done = true;
+
+	return 0;
+}
+
+static int __flush_dmap(struct dm_clone_metadata *cmd, struct dirty_map *dmap)
+{
+	int r;
+	unsigned long word, flags;
+
+	word = 0;
+	do {
+		word = find_next_bit(dmap->dirty_words, cmd->nr_words, word);
+
+		if (word == cmd->nr_words)
+			break;
+
+		r = __update_metadata_word(cmd, word);
+
+		if (r)
+			return r;
+
+		__clear_bit(word, dmap->dirty_words);
+		word++;
+	} while (word < cmd->nr_words);
+
+	r = __metadata_commit(cmd);
+
+	if (r)
+		return r;
+
+	/* Update the changed flag */
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+	dmap->changed = 0;
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	return 0;
+}
+
+int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
+{
+	int r = -EPERM;
+	unsigned long flags;
+	struct dirty_map *dmap, *next_dmap;
+
+	down_write(&cmd->lock);
+
+	if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+		goto out;
+
+	/* Get current dirty bitmap */
+	dmap = cmd->current_dmap;
+
+	/* Get next dirty bitmap */
+	next_dmap = (dmap == &cmd->dmap[0]) ? &cmd->dmap[1] : &cmd->dmap[0];
+
+	/*
+	 * The last commit failed, so we don't have a clean dirty-bitmap to
+	 * use.
+	 */
+	if (WARN_ON(next_dmap->changed)) {
+		r = -EINVAL;
+		goto out;
+	}
+
+	/* Swap dirty bitmaps */
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+	cmd->current_dmap = next_dmap;
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	/*
+	 * No one is accessing the old dirty bitmap anymore, so we can flush
+	 * it.
+	 */
+	r = __flush_dmap(cmd, dmap);
+out:
+	up_write(&cmd->lock);
+
+	return r;
+}
+
+int dm_clone_set_region_hydrated(struct dm_clone_metadata *cmd, unsigned long region_nr)
+{
+	int r = 0;
+	struct dirty_map *dmap;
+	unsigned long word, flags;
+
+	word = region_nr / BITS_PER_LONG;
+
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+
+	if (cmd->read_only) {
+		r = -EPERM;
+		goto out;
+	}
+
+	dmap = cmd->current_dmap;
+
+	__set_bit(word, dmap->dirty_words);
+	__set_bit(region_nr, cmd->region_map);
+	dmap->changed = 1;
+
+out:
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	return r;
+}
+
+int dm_clone_cond_set_range(struct dm_clone_metadata *cmd, unsigned long start,
+			    unsigned long nr_regions)
+{
+	int r = 0;
+	struct dirty_map *dmap;
+	unsigned long word, region_nr, flags;
+
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+
+	if (cmd->read_only) {
+		r = -EPERM;
+		goto out;
+	}
+
+	dmap = cmd->current_dmap;
+	for (region_nr = start; region_nr < (start + nr_regions); region_nr++) {
+		if (!test_bit(region_nr, cmd->region_map)) {
+			word = region_nr / BITS_PER_LONG;
+			__set_bit(word, dmap->dirty_words);
+			__set_bit(region_nr, cmd->region_map);
+			dmap->changed = 1;
+		}
+	}
+out:
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	return r;
+}
+
+/*
+ * WARNING: This must not be called concurrently with either
+ * dm_clone_set_region_hydrated() or dm_clone_cond_set_range(), as it changes
+ * cmd->region_map without taking the cmd->bitmap_lock spinlock. The only
+ * exception is after setting the metadata to read-only mode, using
+ * dm_clone_metadata_set_read_only().
+ *
+ * We don't take the spinlock because __load_bitset_in_core() does I/O, so it
+ * may block.
+ */
+int dm_clone_reload_in_core_bitset(struct dm_clone_metadata *cmd)
+{
+	int r = -EINVAL;
+
+	down_write(&cmd->lock);
+
+	if (cmd->fail_io)
+		goto out;
+
+	r = __load_bitset_in_core(cmd);
+out:
+	up_write(&cmd->lock);
+
+	return r;
+}
+
+bool dm_clone_changed_this_transaction(struct dm_clone_metadata *cmd)
+{
+	bool r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+	r = cmd->dmap[0].changed || cmd->dmap[1].changed;
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	return r;
+}
+
+int dm_clone_metadata_abort(struct dm_clone_metadata *cmd)
+{
+	int r = -EPERM;
+
+	down_write(&cmd->lock);
+
+	if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+		goto out;
+
+	__destroy_persistent_data_structures(cmd);
+
+	r = __create_persistent_data_structures(cmd, false);
+	if (r) {
+		/* If something went wrong we can neither write nor read the metadata */
+		cmd->fail_io = true;
+	}
+out:
+	up_write(&cmd->lock);
+
+	return r;
+}
+
+void dm_clone_metadata_set_read_only(struct dm_clone_metadata *cmd)
+{
+	unsigned long flags;
+
+	down_write(&cmd->lock);
+
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+	cmd->read_only = 1;
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	if (!cmd->fail_io)
+		dm_bm_set_read_only(cmd->bm);
+
+	up_write(&cmd->lock);
+}
+
+void dm_clone_metadata_set_read_write(struct dm_clone_metadata *cmd)
+{
+	unsigned long flags;
+
+	down_write(&cmd->lock);
+
+	spin_lock_irqsave(&cmd->bitmap_lock, flags);
+	cmd->read_only = 0;
+	spin_unlock_irqrestore(&cmd->bitmap_lock, flags);
+
+	if (!cmd->fail_io)
+		dm_bm_set_read_write(cmd->bm);
+
+	up_write(&cmd->lock);
+}
+
+int dm_clone_get_free_metadata_block_count(struct dm_clone_metadata *cmd,
+					   dm_block_t *result)
+{
+	int r = -EINVAL;
+
+	down_read(&cmd->lock);
+
+	if (!cmd->fail_io)
+		r = dm_sm_get_nr_free(cmd->sm, result);
+
+	up_read(&cmd->lock);
+
+	return r;
+}
+
+int dm_clone_get_metadata_dev_size(struct dm_clone_metadata *cmd,
+				   dm_block_t *result)
+{
+	int r = -EINVAL;
+
+	down_read(&cmd->lock);
+
+	if (!cmd->fail_io)
+		r = dm_sm_get_nr_blocks(cmd->sm, result);
+
+	up_read(&cmd->lock);
+
+	return r;
+}