1 files changed, 2191 insertions, 0 deletions

diff --git a/drivers/md/dm-clone-target.c b/drivers/md/dm-clone-target.c
new file mode 100644
index 000000000000..cd6f9e9fc98e
--- /dev/null
+++ b/drivers/md/dm-clone-target.c
@@ -0,0 +1,2191 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2019 Arrikto, Inc. All Rights Reserved.
+ */
+
+#include <linux/mm.h>
+#include <linux/bio.h>
+#include <linux/err.h>
+#include <linux/hash.h>
+#include <linux/list.h>
+#include <linux/log2.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/wait.h>
+#include <linux/dm-io.h>
+#include <linux/mutex.h>
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/blkdev.h>
+#include <linux/kdev_t.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/jiffies.h>
+#include <linux/mempool.h>
+#include <linux/spinlock.h>
+#include <linux/blk_types.h>
+#include <linux/dm-kcopyd.h>
+#include <linux/workqueue.h>
+#include <linux/backing-dev.h>
+#include <linux/device-mapper.h>
+
+#include "dm.h"
+#include "dm-clone-metadata.h"
+
+#define DM_MSG_PREFIX "clone"
+
+/*
+ * Minimum and maximum allowed region sizes
+ */
+#define MIN_REGION_SIZE (1 << 3)  /* 4KB */
+#define MAX_REGION_SIZE (1 << 21) /* 1GB */
+
+#define MIN_HYDRATIONS 256 /* Size of hydration mempool */
+#define DEFAULT_HYDRATION_THRESHOLD 1 /* 1 region */
+#define DEFAULT_HYDRATION_BATCH_SIZE 1 /* Hydrate in batches of 1 region */
+
+#define COMMIT_PERIOD HZ /* 1 sec */
+
+/*
+ * Hydration hash table size: 1 << HASH_TABLE_BITS
+ */
+#define HASH_TABLE_BITS 15
+
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(clone_hydration_throttle,
+        "A percentage of time allocated for hydrating regions");
+
+/* Slab cache for struct dm_clone_region_hydration */
+static struct kmem_cache *_hydration_cache;
+
+/* dm-clone metadata modes */
+enum clone_metadata_mode {
+        CM_WRITE,               /* metadata may be changed */
+        CM_READ_ONLY,           /* metadata may not be changed */
+        CM_FAIL,                /* all metadata I/O fails */
+};
+
+struct hash_table_bucket;
+
+struct clone {
+        struct dm_target *ti;
+        struct dm_target_callbacks callbacks;
+
+        struct dm_dev *metadata_dev;
+        struct dm_dev *dest_dev;
+        struct dm_dev *source_dev;
+
+        unsigned long nr_regions;
+        sector_t region_size;
+        unsigned int region_shift;
+
+        /*
+         * A metadata commit and the actions taken in case it fails should run
+         * as a single atomic step.
+         */
+        struct mutex commit_lock;
+
+        struct dm_clone_metadata *cmd;
+
+        /* Region hydration hash table */
+        struct hash_table_bucket *ht;
+
+        atomic_t ios_in_flight;
+
+        wait_queue_head_t hydration_stopped;
+
+        mempool_t hydration_pool;
+
+        unsigned long last_commit_jiffies;
+
+        /*
+         * We defer incoming WRITE bios for regions that are not hydrated,
+         * until after these regions have been hydrated.
+         *
+         * Also, we defer REQ_FUA and REQ_PREFLUSH bios, until after the
+         * metadata have been committed.
+         */
+        spinlock_t lock;
+        struct bio_list deferred_bios;
+        struct bio_list deferred_discard_bios;
+        struct bio_list deferred_flush_bios;
+        struct bio_list deferred_flush_completions;
+
+        /* Maximum number of regions being copied during background hydration. */
+        unsigned int hydration_threshold;
+
+        /* Number of regions to batch together during background hydration. */
+        unsigned int hydration_batch_size;
+
+        /* Which region to hydrate next */
+        unsigned long hydration_offset;
+
+        atomic_t hydrations_in_flight;
+
+        /*
+         * Save a copy of the table line rather than reconstructing it for the
+         * status.
+         */
+        unsigned int nr_ctr_args;
+        const char **ctr_args;
+
+        struct workqueue_struct *wq;
+        struct work_struct worker;
+        struct delayed_work waker;
+
+        struct dm_kcopyd_client *kcopyd_client;
+
+        enum clone_metadata_mode mode;
+        unsigned long flags;
+};
+
+/*
+ * dm-clone flags
+ */
+#define DM_CLONE_DISCARD_PASSDOWN 0
+#define DM_CLONE_HYDRATION_ENABLED 1
+#define DM_CLONE_HYDRATION_SUSPENDED 2
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Metadata failure handling.
+ */
+static enum clone_metadata_mode get_clone_mode(struct clone *clone)
+{
+        return READ_ONCE(clone->mode);
+}
+
+static const char *clone_device_name(struct clone *clone)
+{
+        return dm_table_device_name(clone->ti->table);
+}
+
+static void __set_clone_mode(struct clone *clone, enum clone_metadata_mode new_mode)
+{
+        const char *descs[] = {
+                "read-write",
+                "read-only",
+                "fail"
+        };
+
+        enum clone_metadata_mode old_mode = get_clone_mode(clone);
+
+        /* Never move out of fail mode */
+        if (old_mode == CM_FAIL)
+                new_mode = CM_FAIL;
+
+        switch (new_mode) {
+        case CM_FAIL:
+        case CM_READ_ONLY:
+                dm_clone_metadata_set_read_only(clone->cmd);
+                break;
+
+        case CM_WRITE:
+                dm_clone_metadata_set_read_write(clone->cmd);
+                break;
+        }
+
+        WRITE_ONCE(clone->mode, new_mode);
+
+        if (new_mode != old_mode) {
+                dm_table_event(clone->ti->table);
+                DMINFO("%s: Switching to %s mode", clone_device_name(clone),
+                       descs[(int)new_mode]);
+        }
+}
+
+static void __abort_transaction(struct clone *clone)
+{
+        const char *dev_name = clone_device_name(clone);
+
+        if (get_clone_mode(clone) >= CM_READ_ONLY)
+                return;
+
+        DMERR("%s: Aborting current metadata transaction", dev_name);
+        if (dm_clone_metadata_abort(clone->cmd)) {
+                DMERR("%s: Failed to abort metadata transaction", dev_name);
+                __set_clone_mode(clone, CM_FAIL);
+        }
+}
+
+static void __reload_in_core_bitset(struct clone *clone)
+{
+        const char *dev_name = clone_device_name(clone);
+
+        if (get_clone_mode(clone) == CM_FAIL)
+                return;
+
+        /* Reload the on-disk bitset */
+        DMINFO("%s: Reloading on-disk bitmap", dev_name);
+        if (dm_clone_reload_in_core_bitset(clone->cmd)) {
+                DMERR("%s: Failed to reload on-disk bitmap", dev_name);
+                __set_clone_mode(clone, CM_FAIL);
+        }
+}
+
+static void __metadata_operation_failed(struct clone *clone, const char *op, int r)
+{
+        DMERR("%s: Metadata operation `%s' failed: error = %d",
+              clone_device_name(clone), op, r);
+
+        __abort_transaction(clone);
+        __set_clone_mode(clone, CM_READ_ONLY);
+
+        /*
+         * dm_clone_reload_in_core_bitset() may run concurrently with either
+         * dm_clone_set_region_hydrated() or dm_clone_cond_set_range(), but
+         * it's safe as we have already set the metadata to read-only mode.
+         */
+        __reload_in_core_bitset(clone);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/* Wake up anyone waiting for region hydrations to stop */
+static inline void wakeup_hydration_waiters(struct clone *clone)
+{
+        wake_up_all(&clone->hydration_stopped);
+}
+
+static inline void wake_worker(struct clone *clone)
+{
+        queue_work(clone->wq, &clone->worker);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * bio helper functions.
+ */
+static inline void remap_to_source(struct clone *clone, struct bio *bio)
+{
+        bio_set_dev(bio, clone->source_dev->bdev);
+}
+
+static inline void remap_to_dest(struct clone *clone, struct bio *bio)
+{
+        bio_set_dev(bio, clone->dest_dev->bdev);
+}
+
+static bool bio_triggers_commit(struct clone *clone, struct bio *bio)
+{
+        return op_is_flush(bio->bi_opf) &&
+                dm_clone_changed_this_transaction(clone->cmd);
+}
+
+/* Get the address of the region in sectors */
+static inline sector_t region_to_sector(struct clone *clone, unsigned long region_nr)
+{
+        return (region_nr << clone->region_shift);
+}
+
+/* Get the region number of the bio */
+static inline unsigned long bio_to_region(struct clone *clone, struct bio *bio)
+{
+        return (bio->bi_iter.bi_sector >> clone->region_shift);
+}
+
+/* Get the region range covered by the bio */
+static void bio_region_range(struct clone *clone, struct bio *bio,
+                             unsigned long *rs, unsigned long *re)
+{
+        *rs = dm_sector_div_up(bio->bi_iter.bi_sector, clone->region_size);
+        *re = bio_end_sector(bio) >> clone->region_shift;
+}
+
+/* Check whether a bio overwrites a region */
+static inline bool is_overwrite_bio(struct clone *clone, struct bio *bio)
+{
+        return (bio_data_dir(bio) == WRITE && bio_sectors(bio) == clone->region_size);
+}
+
+static void fail_bios(struct bio_list *bios, blk_status_t status)
+{
+        struct bio *bio;
+
+        while ((bio = bio_list_pop(bios))) {
+                bio->bi_status = status;
+                bio_endio(bio);
+        }
+}
+
+static void submit_bios(struct bio_list *bios)
+{
+        struct bio *bio;
+        struct blk_plug plug;
+
+        blk_start_plug(&plug);
+
+        while ((bio = bio_list_pop(bios)))
+                generic_make_request(bio);
+
+        blk_finish_plug(&plug);
+}
+
+/*
+ * Submit bio to the underlying device.
+ *
+ * If the bio triggers a commit, delay it, until after the metadata have been
+ * committed.
+ *
+ * NOTE: The bio remapping must be performed by the caller.
+ */
+static void issue_bio(struct clone *clone, struct bio *bio)
+{
+        unsigned long flags;
+
+        if (!bio_triggers_commit(clone, bio)) {
+                generic_make_request(bio);
+                return;
+        }
+
+        /*
+         * If the metadata mode is RO or FAIL we won't be able to commit the
+         * metadata, so we complete the bio with an error.
+         */
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
+                bio_io_error(bio);
+                return;
+        }
+
+        /*
+         * Batch together any bios that trigger commits and then issue a single
+         * commit for them in process_deferred_flush_bios().
+         */
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_add(&clone->deferred_flush_bios, bio);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        wake_worker(clone);
+}
+
+/*
+ * Remap bio to the destination device and submit it.
+ *
+ * If the bio triggers a commit, delay it, until after the metadata have been
+ * committed.
+ */
+static void remap_and_issue(struct clone *clone, struct bio *bio)
+{
+        remap_to_dest(clone, bio);
+        issue_bio(clone, bio);
+}
+
+/*
+ * Issue bios that have been deferred until after their region has finished
+ * hydrating.
+ *
+ * We delegate the bio submission to the worker thread, so this is safe to call
+ * from interrupt context.
+ */
+static void issue_deferred_bios(struct clone *clone, struct bio_list *bios)
+{
+        struct bio *bio;
+        unsigned long flags;
+        struct bio_list flush_bios = BIO_EMPTY_LIST;
+        struct bio_list normal_bios = BIO_EMPTY_LIST;
+
+        if (bio_list_empty(bios))
+                return;
+
+        while ((bio = bio_list_pop(bios))) {
+                if (bio_triggers_commit(clone, bio))
+                        bio_list_add(&flush_bios, bio);
+                else
+                        bio_list_add(&normal_bios, bio);
+        }
+
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_merge(&clone->deferred_bios, &normal_bios);
+        bio_list_merge(&clone->deferred_flush_bios, &flush_bios);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        wake_worker(clone);
+}
+
+static void complete_overwrite_bio(struct clone *clone, struct bio *bio)
+{
+        unsigned long flags;
+
+        /*
+         * If the bio has the REQ_FUA flag set we must commit the metadata
+         * before signaling its completion.
+         *
+         * complete_overwrite_bio() is only called by hydration_complete(),
+         * after having successfully updated the metadata. This means we don't
+         * need to call dm_clone_changed_this_transaction() to check if the
+         * metadata has changed and thus we can avoid taking the metadata spin
+         * lock.
+         */
+        if (!(bio->bi_opf & REQ_FUA)) {
+                bio_endio(bio);
+                return;
+        }
+
+        /*
+         * If the metadata mode is RO or FAIL we won't be able to commit the
+         * metadata, so we complete the bio with an error.
+         */
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
+                bio_io_error(bio);
+                return;
+        }
+
+        /*
+         * Batch together any bios that trigger commits and then issue a single
+         * commit for them in process_deferred_flush_bios().
+         */
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_add(&clone->deferred_flush_completions, bio);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        wake_worker(clone);
+}
+
+static void trim_bio(struct bio *bio, sector_t sector, unsigned int len)
+{
+        bio->bi_iter.bi_sector = sector;
+        bio->bi_iter.bi_size = to_bytes(len);
+}
+
+static void complete_discard_bio(struct clone *clone, struct bio *bio, bool success)
+{
+        unsigned long rs, re;
+
+        /*
+         * If the destination device supports discards, remap and trim the
+         * discard bio and pass it down. Otherwise complete the bio
+         * immediately.
+         */
+        if (test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags) && success) {
+                remap_to_dest(clone, bio);
+                bio_region_range(clone, bio, &rs, &re);
+                trim_bio(bio, rs << clone->region_shift,
+                         (re - rs) << clone->region_shift);
+                generic_make_request(bio);
+        } else
+                bio_endio(bio);
+}
+
+static void process_discard_bio(struct clone *clone, struct bio *bio)
+{
+        unsigned long rs, re, flags;
+
+        bio_region_range(clone, bio, &rs, &re);
+        BUG_ON(re > clone->nr_regions);
+
+        if (unlikely(rs == re)) {
+                bio_endio(bio);
+                return;
+        }
+
+        /*
+         * The covered regions are already hydrated so we just need to pass
+         * down the discard.
+         */
+        if (dm_clone_is_range_hydrated(clone->cmd, rs, re - rs)) {
+                complete_discard_bio(clone, bio, true);
+                return;
+        }
+
+        /*
+         * If the metadata mode is RO or FAIL we won't be able to update the
+         * metadata for the regions covered by the discard so we just ignore
+         * it.
+         */
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
+                bio_endio(bio);
+                return;
+        }
+
+        /*
+         * Defer discard processing.
+         */
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_add(&clone->deferred_discard_bios, bio);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        wake_worker(clone);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * dm-clone region hydrations.
+ */
+struct dm_clone_region_hydration {
+        struct clone *clone;
+        unsigned long region_nr;
+
+        struct bio *overwrite_bio;
+        bio_end_io_t *overwrite_bio_end_io;
+
+        struct bio_list deferred_bios;
+
+        blk_status_t status;
+
+        /* Used by hydration batching */
+        struct list_head list;
+
+        /* Used by hydration hash table */
+        struct hlist_node h;
+};
+
+/*
+ * Hydration hash table implementation.
+ *
+ * Ideally we would like to use list_bl, which uses bit spin locks and employs
+ * the least significant bit of the list head to lock the corresponding bucket,
+ * reducing the memory overhead for the locks. But, currently, list_bl and bit
+ * spin locks don't support IRQ safe versions. Since we have to take the lock
+ * in both process and interrupt context, we must fall back to using regular
+ * spin locks; one per hash table bucket.
+ */
+struct hash_table_bucket {
+        struct hlist_head head;
+
+        /* Spinlock protecting the bucket */
+        spinlock_t lock;
+};
+
+#define bucket_lock_irqsave(bucket, flags) \
+        spin_lock_irqsave(&(bucket)->lock, flags)
+
+#define bucket_unlock_irqrestore(bucket, flags) \
+        spin_unlock_irqrestore(&(bucket)->lock, flags)
+
+static int hash_table_init(struct clone *clone)
+{
+        unsigned int i, sz;
+        struct hash_table_bucket *bucket;
+
+        sz = 1 << HASH_TABLE_BITS;
+
+        clone->ht = kvmalloc(sz * sizeof(struct hash_table_bucket), GFP_KERNEL);
+        if (!clone->ht)
+                return -ENOMEM;
+
+        for (i = 0; i < sz; i++) {
+                bucket = clone->ht + i;
+
+                INIT_HLIST_HEAD(&bucket->head);
+                spin_lock_init(&bucket->lock);
+        }
+
+        return 0;
+}
+
+static void hash_table_exit(struct clone *clone)
+{
+        kvfree(clone->ht);
+}
+
+static struct hash_table_bucket *get_hash_table_bucket(struct clone *clone,
+                                                       unsigned long region_nr)
+{
+        return &clone->ht[hash_long(region_nr, HASH_TABLE_BITS)];
+}
+
+/*
+ * Search hash table for a hydration with hd->region_nr == region_nr
+ *
+ * NOTE: Must be called with the bucket lock held
+ */
+struct dm_clone_region_hydration *__hash_find(struct hash_table_bucket *bucket,
+                                              unsigned long region_nr)
+{
+        struct dm_clone_region_hydration *hd;
+
+        hlist_for_each_entry(hd, &bucket->head, h) {
+                if (hd->region_nr == region_nr)
+                        return hd;
+        }
+
+        return NULL;
+}
+
+/*
+ * Insert a hydration into the hash table.
+ *
+ * NOTE: Must be called with the bucket lock held.
+ */
+static inline void __insert_region_hydration(struct hash_table_bucket *bucket,
+                                             struct dm_clone_region_hydration *hd)
+{
+        hlist_add_head(&hd->h, &bucket->head);
+}
+
+/*
+ * This function inserts a hydration into the hash table, unless someone else
+ * managed to insert a hydration for the same region first. In the latter case
+ * it returns the existing hydration descriptor for this region.
+ *
+ * NOTE: Must be called with the hydration hash table lock held.
+ */
+static struct dm_clone_region_hydration *
+__find_or_insert_region_hydration(struct hash_table_bucket *bucket,
+                                  struct dm_clone_region_hydration *hd)
+{
+        struct dm_clone_region_hydration *hd2;
+
+        hd2 = __hash_find(bucket, hd->region_nr);
+        if (hd2)
+                return hd2;
+
+        __insert_region_hydration(bucket, hd);
+
+        return hd;
+}
+
+/*---------------------------------------------------------------------------*/
+
+/* Allocate a hydration */
+static struct dm_clone_region_hydration *alloc_hydration(struct clone *clone)
+{
+        struct dm_clone_region_hydration *hd;
+
+        /*
+         * Allocate a hydration from the hydration mempool.
+         * This might block but it can't fail.
+         */
+        hd = mempool_alloc(&clone->hydration_pool, GFP_NOIO);
+        hd->clone = clone;
+
+        return hd;
+}
+
+static inline void free_hydration(struct dm_clone_region_hydration *hd)
+{
+        mempool_free(hd, &hd->clone->hydration_pool);
+}
+
+/* Initialize a hydration */
+static void hydration_init(struct dm_clone_region_hydration *hd, unsigned long region_nr)
+{
+        hd->region_nr = region_nr;
+        hd->overwrite_bio = NULL;
+        bio_list_init(&hd->deferred_bios);
+        hd->status = 0;
+
+        INIT_LIST_HEAD(&hd->list);
+        INIT_HLIST_NODE(&hd->h);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Update dm-clone's metadata after a region has finished hydrating and remove
+ * hydration from the hash table.
+ */
+static int hydration_update_metadata(struct dm_clone_region_hydration *hd)
+{
+        int r = 0;
+        unsigned long flags;
+        struct hash_table_bucket *bucket;
+        struct clone *clone = hd->clone;
+
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
+                r = -EPERM;
+
+        /* Update the metadata */
+        if (likely(!r) && hd->status == BLK_STS_OK)
+                r = dm_clone_set_region_hydrated(clone->cmd, hd->region_nr);
+
+        bucket = get_hash_table_bucket(clone, hd->region_nr);
+
+        /* Remove hydration from hash table */
+        bucket_lock_irqsave(bucket, flags);
+        hlist_del(&hd->h);
+        bucket_unlock_irqrestore(bucket, flags);
+
+        return r;
+}
+
+/*
+ * Complete a region's hydration:
+ *
+ *      1. Update dm-clone's metadata.
+ *      2. Remove hydration from hash table.
+ *      3. Complete overwrite bio.
+ *      4. Issue deferred bios.
+ *      5. If this was the last hydration, wake up anyone waiting for
+ *         hydrations to finish.
+ */
+static void hydration_complete(struct dm_clone_region_hydration *hd)
+{
+        int r;
+        blk_status_t status;
+        struct clone *clone = hd->clone;
+
+        r = hydration_update_metadata(hd);
+
+        if (hd->status == BLK_STS_OK && likely(!r)) {
+                if (hd->overwrite_bio)
+                        complete_overwrite_bio(clone, hd->overwrite_bio);
+
+                issue_deferred_bios(clone, &hd->deferred_bios);
+        } else {
+                status = r ? BLK_STS_IOERR : hd->status;
+
+                if (hd->overwrite_bio)
+                        bio_list_add(&hd->deferred_bios, hd->overwrite_bio);
+
+                fail_bios(&hd->deferred_bios, status);
+        }
+
+        free_hydration(hd);
+
+        if (atomic_dec_and_test(&clone->hydrations_in_flight))
+                wakeup_hydration_waiters(clone);
+}
+
+static void hydration_kcopyd_callback(int read_err, unsigned long write_err, void *context)
+{
+        blk_status_t status;
+
+        struct dm_clone_region_hydration *tmp, *hd = context;
+        struct clone *clone = hd->clone;
+
+        LIST_HEAD(batched_hydrations);
+
+        if (read_err || write_err) {
+                DMERR_LIMIT("%s: hydration failed", clone_device_name(clone));
+                status = BLK_STS_IOERR;
+        } else {
+                status = BLK_STS_OK;
+        }
+        list_splice_tail(&hd->list, &batched_hydrations);
+
+        hd->status = status;
+        hydration_complete(hd);
+
+        /* Complete batched hydrations */
+        list_for_each_entry_safe(hd, tmp, &batched_hydrations, list) {
+                hd->status = status;
+                hydration_complete(hd);
+        }
+
+        /* Continue background hydration, if there is no I/O in-flight */
+        if (test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags) &&
+            !atomic_read(&clone->ios_in_flight))
+                wake_worker(clone);
+}
+
+static void hydration_copy(struct dm_clone_region_hydration *hd, unsigned int nr_regions)
+{
+        unsigned long region_start, region_end;
+        sector_t tail_size, region_size, total_size;
+        struct dm_io_region from, to;
+        struct clone *clone = hd->clone;
+
+        region_size = clone->region_size;
+        region_start = hd->region_nr;
+        region_end = region_start + nr_regions - 1;
+
+        total_size = (nr_regions - 1) << clone->region_shift;
+
+        if (region_end == clone->nr_regions - 1) {
+                /*
+                 * The last region of the target might be smaller than
+                 * region_size.
+                 */
+                tail_size = clone->ti->len & (region_size - 1);
+                if (!tail_size)
+                        tail_size = region_size;
+        } else {
+                tail_size = region_size;
+        }
+
+        total_size += tail_size;
+
+        from.bdev = clone->source_dev->bdev;
+        from.sector = region_to_sector(clone, region_start);
+        from.count = total_size;
+
+        to.bdev = clone->dest_dev->bdev;
+        to.sector = from.sector;
+        to.count = from.count;
+
+        /* Issue copy */
+        atomic_add(nr_regions, &clone->hydrations_in_flight);
+        dm_kcopyd_copy(clone->kcopyd_client, &from, 1, &to, 0,
+                       hydration_kcopyd_callback, hd);
+}
+
+static void overwrite_endio(struct bio *bio)
+{
+        struct dm_clone_region_hydration *hd = bio->bi_private;
+
+        bio->bi_end_io = hd->overwrite_bio_end_io;
+        hd->status = bio->bi_status;
+
+        hydration_complete(hd);
+}
+
+static void hydration_overwrite(struct dm_clone_region_hydration *hd, struct bio *bio)
+{
+        /*
+         * We don't need to save and restore bio->bi_private because device
+         * mapper core generates a new bio for us to use, with clean
+         * bi_private.
+         */
+        hd->overwrite_bio = bio;
+        hd->overwrite_bio_end_io = bio->bi_end_io;
+
+        bio->bi_end_io = overwrite_endio;
+        bio->bi_private = hd;
+
+        atomic_inc(&hd->clone->hydrations_in_flight);
+        generic_make_request(bio);
+}
+
+/*
+ * Hydrate bio's region.
+ *
+ * This function starts the hydration of the bio's region and puts the bio in
+ * the list of deferred bios for this region. In case, by the time this
+ * function is called, the region has finished hydrating it's submitted to the
+ * destination device.
+ *
+ * NOTE: The bio remapping must be performed by the caller.
+ */
+static void hydrate_bio_region(struct clone *clone, struct bio *bio)
+{
+        unsigned long flags;
+        unsigned long region_nr;
+        struct hash_table_bucket *bucket;
+        struct dm_clone_region_hydration *hd, *hd2;
+
+        region_nr = bio_to_region(clone, bio);
+        bucket = get_hash_table_bucket(clone, region_nr);
+
+        bucket_lock_irqsave(bucket, flags);
+
+        hd = __hash_find(bucket, region_nr);
+        if (hd) {
+                /* Someone else is hydrating the region */
+                bio_list_add(&hd->deferred_bios, bio);
+                bucket_unlock_irqrestore(bucket, flags);
+                return;
+        }
+
+        if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
+                /* The region has been hydrated */
+                bucket_unlock_irqrestore(bucket, flags);
+                issue_bio(clone, bio);
+                return;
+        }
+
+        /*
+         * We must allocate a hydration descriptor and start the hydration of
+         * the corresponding region.
+         */
+        bucket_unlock_irqrestore(bucket, flags);
+
+        hd = alloc_hydration(clone);
+        hydration_init(hd, region_nr);
+
+        bucket_lock_irqsave(bucket, flags);
+
+        /* Check if the region has been hydrated in the meantime. */
+        if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
+                bucket_unlock_irqrestore(bucket, flags);
+                free_hydration(hd);
+                issue_bio(clone, bio);
+                return;
+        }
+
+        hd2 = __find_or_insert_region_hydration(bucket, hd);
+        if (hd2 != hd) {
+                /* Someone else started the region's hydration. */
+                bio_list_add(&hd2->deferred_bios, bio);
+                bucket_unlock_irqrestore(bucket, flags);
+                free_hydration(hd);
+                return;
+        }
+
+        /*
+         * If the metadata mode is RO or FAIL then there is no point starting a
+         * hydration, since we will not be able to update the metadata when the
+         * hydration finishes.
+         */
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
+                hlist_del(&hd->h);
+                bucket_unlock_irqrestore(bucket, flags);
+                free_hydration(hd);
+                bio_io_error(bio);
+                return;
+        }
+
+        /*
+         * Start region hydration.
+         *
+         * If a bio overwrites a region, i.e., its size is equal to the
+         * region's size, then we don't need to copy the region from the source
+         * to the destination device.
+         */
+        if (is_overwrite_bio(clone, bio)) {
+                bucket_unlock_irqrestore(bucket, flags);
+                hydration_overwrite(hd, bio);
+        } else {
+                bio_list_add(&hd->deferred_bios, bio);
+                bucket_unlock_irqrestore(bucket, flags);
+                hydration_copy(hd, 1);
+        }
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Background hydrations.
+ */
+
+/*
+ * Batch region hydrations.
+ *
+ * To better utilize device bandwidth we batch together the hydration of
+ * adjacent regions. This allows us to use small region sizes, e.g., 4KB, which
+ * is good for small, random write performance (because of the overwriting of
+ * un-hydrated regions) and at the same time issue big copy requests to kcopyd
+ * to achieve high hydration bandwidth.
+ */
+struct batch_info {
+        struct dm_clone_region_hydration *head;
+        unsigned int nr_batched_regions;
+};
+
+static void __batch_hydration(struct batch_info *batch,
+                              struct dm_clone_region_hydration *hd)
+{
+        struct clone *clone = hd->clone;
+        unsigned int max_batch_size = READ_ONCE(clone->hydration_batch_size);
+
+        if (batch->head) {
+                /* Try to extend the current batch */
+                if (batch->nr_batched_regions < max_batch_size &&
+                    (batch->head->region_nr + batch->nr_batched_regions) == hd->region_nr) {
+                        list_add_tail(&hd->list, &batch->head->list);
+                        batch->nr_batched_regions++;
+                        hd = NULL;
+                }
+
+                /* Check if we should issue the current batch */
+                if (batch->nr_batched_regions >= max_batch_size || hd) {
+                        hydration_copy(batch->head, batch->nr_batched_regions);
+                        batch->head = NULL;
+                        batch->nr_batched_regions = 0;
+                }
+        }
+
+        if (!hd)
+                return;
+
+        /* We treat max batch sizes of zero and one equivalently */
+        if (max_batch_size <= 1) {
+                hydration_copy(hd, 1);
+                return;
+        }
+
+        /* Start a new batch */
+        BUG_ON(!list_empty(&hd->list));
+        batch->head = hd;
+        batch->nr_batched_regions = 1;
+}
+
+static unsigned long __start_next_hydration(struct clone *clone,
+                                            unsigned long offset,
+                                            struct batch_info *batch)
+{
+        unsigned long flags;
+        struct hash_table_bucket *bucket;
+        struct dm_clone_region_hydration *hd;
+        unsigned long nr_regions = clone->nr_regions;
+
+        hd = alloc_hydration(clone);
+
+        /* Try to find a region to hydrate. */
+        do {
+                offset = dm_clone_find_next_unhydrated_region(clone->cmd, offset);
+                if (offset == nr_regions)
+                        break;
+
+                bucket = get_hash_table_bucket(clone, offset);
+                bucket_lock_irqsave(bucket, flags);
+
+                if (!dm_clone_is_region_hydrated(clone->cmd, offset) &&
+                    !__hash_find(bucket, offset)) {
+                        hydration_init(hd, offset);
+                        __insert_region_hydration(bucket, hd);
+                        bucket_unlock_irqrestore(bucket, flags);
+
+                        /* Batch hydration */
+                        __batch_hydration(batch, hd);
+
+                        return (offset + 1);
+                }
+
+                bucket_unlock_irqrestore(bucket, flags);
+
+        } while (++offset < nr_regions);
+
+        if (hd)
+                free_hydration(hd);
+
+        return offset;
+}
+
+/*
+ * This function searches for regions that still reside in the source device
+ * and starts their hydration.
+ */
+static void do_hydration(struct clone *clone)
+{
+        unsigned int current_volume;
+        unsigned long offset, nr_regions = clone->nr_regions;
+
+        struct batch_info batch = {
+                .head = NULL,
+                .nr_batched_regions = 0,
+        };
+
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
+                return;
+
+        if (dm_clone_is_hydration_done(clone->cmd))
+                return;
+
+        /*
+         * Avoid race with device suspension.
+         */
+        atomic_inc(&clone->hydrations_in_flight);
+
+        /*
+         * Make sure atomic_inc() is ordered before test_bit(), otherwise we
+         * might race with clone_postsuspend() and start a region hydration
+         * after the target has been suspended.
+         *
+         * This is paired with the smp_mb__after_atomic() in
+         * clone_postsuspend().
+         */
+        smp_mb__after_atomic();
+
+        offset = clone->hydration_offset;
+        while (likely(!test_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags)) &&
+               !atomic_read(&clone->ios_in_flight) &&
+               test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags) &&
+               offset < nr_regions) {
+                current_volume = atomic_read(&clone->hydrations_in_flight);
+                current_volume += batch.nr_batched_regions;
+
+                if (current_volume > READ_ONCE(clone->hydration_threshold))
+                        break;
+
+                offset = __start_next_hydration(clone, offset, &batch);
+        }
+
+        if (batch.head)
+                hydration_copy(batch.head, batch.nr_batched_regions);
+
+        if (offset >= nr_regions)
+                offset = 0;
+
+        clone->hydration_offset = offset;
+
+        if (atomic_dec_and_test(&clone->hydrations_in_flight))
+                wakeup_hydration_waiters(clone);
+}
+
+/*---------------------------------------------------------------------------*/
+
+static bool need_commit_due_to_time(struct clone *clone)
+{
+        return !time_in_range(jiffies, clone->last_commit_jiffies,
+                              clone->last_commit_jiffies + COMMIT_PERIOD);
+}
+
+/*
+ * A non-zero return indicates read-only or fail mode.
+ */
+static int commit_metadata(struct clone *clone)
+{
+        int r = 0;
+
+        mutex_lock(&clone->commit_lock);
+
+        if (!dm_clone_changed_this_transaction(clone->cmd))
+                goto out;
+
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY)) {
+                r = -EPERM;
+                goto out;
+        }
+
+        r = dm_clone_metadata_commit(clone->cmd);
+
+        if (unlikely(r)) {
+                __metadata_operation_failed(clone, "dm_clone_metadata_commit", r);
+                goto out;
+        }
+
+        if (dm_clone_is_hydration_done(clone->cmd))
+                dm_table_event(clone->ti->table);
+out:
+        mutex_unlock(&clone->commit_lock);
+
+        return r;
+}
+
+static void process_deferred_discards(struct clone *clone)
+{
+        int r = -EPERM;
+        struct bio *bio;
+        struct blk_plug plug;
+        unsigned long rs, re, flags;
+        struct bio_list discards = BIO_EMPTY_LIST;
+
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_merge(&discards, &clone->deferred_discard_bios);
+        bio_list_init(&clone->deferred_discard_bios);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        if (bio_list_empty(&discards))
+                return;
+
+        if (unlikely(get_clone_mode(clone) >= CM_READ_ONLY))
+                goto out;
+
+        /* Update the metadata */
+        bio_list_for_each(bio, &discards) {
+                bio_region_range(clone, bio, &rs, &re);
+                /*
+                 * A discard request might cover regions that have been already
+                 * hydrated. There is no need to update the metadata for these
+                 * regions.
+                 */
+                r = dm_clone_cond_set_range(clone->cmd, rs, re - rs);
+
+                if (unlikely(r))
+                        break;
+        }
+out:
+        blk_start_plug(&plug);
+        while ((bio = bio_list_pop(&discards)))
+                complete_discard_bio(clone, bio, r == 0);
+        blk_finish_plug(&plug);
+}
+
+static void process_deferred_bios(struct clone *clone)
+{
+        unsigned long flags;
+        struct bio_list bios = BIO_EMPTY_LIST;
+
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_merge(&bios, &clone->deferred_bios);
+        bio_list_init(&clone->deferred_bios);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        if (bio_list_empty(&bios))
+                return;
+
+        submit_bios(&bios);
+}
+
+static void process_deferred_flush_bios(struct clone *clone)
+{
+        struct bio *bio;
+        unsigned long flags;
+        struct bio_list bios = BIO_EMPTY_LIST;
+        struct bio_list bio_completions = BIO_EMPTY_LIST;
+
+        /*
+         * If there are any deferred flush bios, we must commit the metadata
+         * before issuing them or signaling their completion.
+         */
+        spin_lock_irqsave(&clone->lock, flags);
+        bio_list_merge(&bios, &clone->deferred_flush_bios);
+        bio_list_init(&clone->deferred_flush_bios);
+
+        bio_list_merge(&bio_completions, &clone->deferred_flush_completions);
+        bio_list_init(&clone->deferred_flush_completions);
+        spin_unlock_irqrestore(&clone->lock, flags);
+
+        if (bio_list_empty(&bios) && bio_list_empty(&bio_completions) &&
+            !(dm_clone_changed_this_transaction(clone->cmd) && need_commit_due_to_time(clone)))
+                return;
+
+        if (commit_metadata(clone)) {
+                bio_list_merge(&bios, &bio_completions);
+
+                while ((bio = bio_list_pop(&bios)))
+                        bio_io_error(bio);
+
+                return;
+        }
+
+        clone->last_commit_jiffies = jiffies;
+
+        while ((bio = bio_list_pop(&bio_completions)))
+                bio_endio(bio);
+
+        while ((bio = bio_list_pop(&bios)))
+                generic_make_request(bio);
+}
+
+static void do_worker(struct work_struct *work)
+{
+        struct clone *clone = container_of(work, typeof(*clone), worker);
+
+        process_deferred_bios(clone);
+        process_deferred_discards(clone);
+
+        /*
+         * process_deferred_flush_bios():
+         *
+         *   - Commit metadata
+         *
+         *   - Process deferred REQ_FUA completions
+         *
+         *   - Process deferred REQ_PREFLUSH bios
+         */
+        process_deferred_flush_bios(clone);
+
+        /* Background hydration */
+        do_hydration(clone);
+}
+
+/*
+ * Commit periodically so that not too much unwritten data builds up.
+ *
+ * Also, restart background hydration, if it has been stopped by in-flight I/O.
+ */
+static void do_waker(struct work_struct *work)
+{
+        struct clone *clone = container_of(to_delayed_work(work), struct clone, waker);
+
+        wake_worker(clone);
+        queue_delayed_work(clone->wq, &clone->waker, COMMIT_PERIOD);
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Target methods
+ */
+static int clone_map(struct dm_target *ti, struct bio *bio)
+{
+        struct clone *clone = ti->private;
+        unsigned long region_nr;
+
+        atomic_inc(&clone->ios_in_flight);
+
+        if (unlikely(get_clone_mode(clone) == CM_FAIL))
+                return DM_MAPIO_KILL;
+
+        /*
+         * REQ_PREFLUSH bios carry no data:
+         *
+         * - Commit metadata, if changed
+         *
+         * - Pass down to destination device
+         */
+        if (bio->bi_opf & REQ_PREFLUSH) {
+                remap_and_issue(clone, bio);
+                return DM_MAPIO_SUBMITTED;
+        }
+
+        bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
+
+        /*
+         * dm-clone interprets discards and performs a fast hydration of the
+         * discarded regions, i.e., we skip the copy from the source device and
+         * just mark the regions as hydrated.
+         */
+        if (bio_op(bio) == REQ_OP_DISCARD) {
+                process_discard_bio(clone, bio);
+                return DM_MAPIO_SUBMITTED;
+        }
+
+        /*
+         * If the bio's region is hydrated, redirect it to the destination
+         * device.
+         *
+         * If the region is not hydrated and the bio is a READ, redirect it to
+         * the source device.
+         *
+         * Else, defer WRITE bio until after its region has been hydrated and
+         * start the region's hydration immediately.
+         */
+        region_nr = bio_to_region(clone, bio);
+        if (dm_clone_is_region_hydrated(clone->cmd, region_nr)) {
+                remap_and_issue(clone, bio);
+                return DM_MAPIO_SUBMITTED;
+        } else if (bio_data_dir(bio) == READ) {
+                remap_to_source(clone, bio);
+                return DM_MAPIO_REMAPPED;
+        }
+
+        remap_to_dest(clone, bio);
+        hydrate_bio_region(clone, bio);
+
+        return DM_MAPIO_SUBMITTED;
+}
+
+static int clone_endio(struct dm_target *ti, struct bio *bio, blk_status_t *error)
+{
+        struct clone *clone = ti->private;
+
+        atomic_dec(&clone->ios_in_flight);
+
+        return DM_ENDIO_DONE;
+}
+
+static void emit_flags(struct clone *clone, char *result, unsigned int maxlen,
+                       ssize_t *sz_ptr)
+{
+        ssize_t sz = *sz_ptr;
+        unsigned int count;
+
+        count = !test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
+        count += !test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
+
+        DMEMIT("%u ", count);
+
+        if (!test_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags))
+                DMEMIT("no_hydration ");
+
+        if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags))
+                DMEMIT("no_discard_passdown ");
+
+        *sz_ptr = sz;
+}
+
+static void emit_core_args(struct clone *clone, char *result,
+                           unsigned int maxlen, ssize_t *sz_ptr)
+{
+        ssize_t sz = *sz_ptr;
+        unsigned int count = 4;
+
+        DMEMIT("%u hydration_threshold %u hydration_batch_size %u ", count,
+               READ_ONCE(clone->hydration_threshold),
+               READ_ONCE(clone->hydration_batch_size));
+
+        *sz_ptr = sz;
+}
+
+/*
+ * Status format:
+ *
+ * <metadata block size> <#used metadata blocks>/<#total metadata blocks>
+ * <clone region size> <#hydrated regions>/<#total regions> <#hydrating regions>
+ * <#features> <features>* <#core args> <core args>* <clone metadata mode>
+ */
+static void clone_status(struct dm_target *ti, status_type_t type,
+                         unsigned int status_flags, char *result,
+                         unsigned int maxlen)
+{
+        int r;
+        unsigned int i;
+        ssize_t sz = 0;
+        dm_block_t nr_free_metadata_blocks = 0;
+        dm_block_t nr_metadata_blocks = 0;
+        char buf[BDEVNAME_SIZE];
+        struct clone *clone = ti->private;
+
+        switch (type) {
+        case STATUSTYPE_INFO:
+                if (get_clone_mode(clone) == CM_FAIL) {
+                        DMEMIT("Fail");
+                        break;
+                }
+
+                /* Commit to ensure statistics aren't out-of-date */
+                if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
+                        (void) commit_metadata(clone);
+
+                r = dm_clone_get_free_metadata_block_count(clone->cmd, &nr_free_metadata_blocks);
+
+                if (r) {
+                        DMERR("%s: dm_clone_get_free_metadata_block_count returned %d",
+                              clone_device_name(clone), r);
+                        goto error;
+                }
+
+                r = dm_clone_get_metadata_dev_size(clone->cmd, &nr_metadata_blocks);
+
+                if (r) {
+                        DMERR("%s: dm_clone_get_metadata_dev_size returned %d",
+                              clone_device_name(clone), r);
+                        goto error;
+                }
+
+                DMEMIT("%u %llu/%llu %llu %lu/%lu %u ",
+                       DM_CLONE_METADATA_BLOCK_SIZE,
+                       (unsigned long long)(nr_metadata_blocks - nr_free_metadata_blocks),
+                       (unsigned long long)nr_metadata_blocks,
+                       (unsigned long long)clone->region_size,
+                       dm_clone_nr_of_hydrated_regions(clone->cmd),
+                       clone->nr_regions,
+                       atomic_read(&clone->hydrations_in_flight));
+
+                emit_flags(clone, result, maxlen, &sz);
+                emit_core_args(clone, result, maxlen, &sz);
+
+                switch (get_clone_mode(clone)) {
+                case CM_WRITE:
+                        DMEMIT("rw");
+                        break;
+                case CM_READ_ONLY:
+                        DMEMIT("ro");
+                        break;
+                case CM_FAIL:
+                        DMEMIT("Fail");
+                }
+
+                break;
+
+        case STATUSTYPE_TABLE:
+                format_dev_t(buf, clone->metadata_dev->bdev->bd_dev);
+                DMEMIT("%s ", buf);
+
+                format_dev_t(buf, clone->dest_dev->bdev->bd_dev);
+                DMEMIT("%s ", buf);
+
+                format_dev_t(buf, clone->source_dev->bdev->bd_dev);
+                DMEMIT("%s", buf);
+
+                for (i = 0; i < clone->nr_ctr_args; i++)
+                        DMEMIT(" %s", clone->ctr_args[i]);
+        }
+
+        return;
+
+error:
+        DMEMIT("Error");
+}
+
+static int clone_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
+{
+        struct request_queue *dest_q, *source_q;
+        struct clone *clone = container_of(cb, struct clone, callbacks);
+
+        source_q = bdev_get_queue(clone->source_dev->bdev);
+        dest_q = bdev_get_queue(clone->dest_dev->bdev);
+
+        return (bdi_congested(dest_q->backing_dev_info, bdi_bits) |
+                bdi_congested(source_q->backing_dev_info, bdi_bits));
+}
+
+static sector_t get_dev_size(struct dm_dev *dev)
+{
+        return i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT;
+}
+
+/*---------------------------------------------------------------------------*/
+
+/*
+ * Construct a clone device mapping:
+ *
+ * clone <metadata dev> <destination dev> <source dev> <region size>
+ *      [<#feature args> [<feature arg>]* [<#core args> [key value]*]]
+ *
+ * metadata dev: Fast device holding the persistent metadata
+ * destination dev: The destination device, which will become a clone of the
+ *                  source device
+ * source dev: The read-only source device that gets cloned
+ * region size: dm-clone unit size in sectors
+ *
+ * #feature args: Number of feature arguments passed
+ * feature args: E.g. no_hydration, no_discard_passdown
+ *
+ * #core arguments: An even number of core arguments
+ * core arguments: Key/value pairs for tuning the core
+ *                 E.g. 'hydration_threshold 256'
+ */
+static int parse_feature_args(struct dm_arg_set *as, struct clone *clone)
+{
+        int r;
+        unsigned int argc;
+        const char *arg_name;
+        struct dm_target *ti = clone->ti;
+
+        const struct dm_arg args = {
+                .min = 0,
+                .max = 2,
+                .error = "Invalid number of feature arguments"
+        };
+
+        /* No feature arguments supplied */
+        if (!as->argc)
+                return 0;
+
+        r = dm_read_arg_group(&args, as, &argc, &ti->error);
+        if (r)
+                return r;
+
+        while (argc) {
+                arg_name = dm_shift_arg(as);
+                argc--;
+
+                if (!strcasecmp(arg_name, "no_hydration")) {
+                        __clear_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
+                } else if (!strcasecmp(arg_name, "no_discard_passdown")) {
+                        __clear_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
+                } else {
+                        ti->error = "Invalid feature argument";
+                        return -EINVAL;
+                }
+        }
+
+        return 0;
+}
+
+static int parse_core_args(struct dm_arg_set *as, struct clone *clone)
+{
+        int r;
+        unsigned int argc;
+        unsigned int value;
+        const char *arg_name;
+        struct dm_target *ti = clone->ti;
+
+        const struct dm_arg args = {
+                .min = 0,
+                .max = 4,
+                .error = "Invalid number of core arguments"
+        };
+
+        /* Initialize core arguments */
+        clone->hydration_batch_size = DEFAULT_HYDRATION_BATCH_SIZE;
+        clone->hydration_threshold = DEFAULT_HYDRATION_THRESHOLD;
+
+        /* No core arguments supplied */
+        if (!as->argc)
+                return 0;
+
+        r = dm_read_arg_group(&args, as, &argc, &ti->error);
+        if (r)
+                return r;
+
+        if (argc & 1) {
+                ti->error = "Number of core arguments must be even";
+                return -EINVAL;
+        }
+
+        while (argc) {
+                arg_name = dm_shift_arg(as);
+                argc -= 2;
+
+                if (!strcasecmp(arg_name, "hydration_threshold")) {
+                        if (kstrtouint(dm_shift_arg(as), 10, &value)) {
+                                ti->error = "Invalid value for argument `hydration_threshold'";
+                                return -EINVAL;
+                        }
+                        clone->hydration_threshold = value;
+                } else if (!strcasecmp(arg_name, "hydration_batch_size")) {
+                        if (kstrtouint(dm_shift_arg(as), 10, &value)) {
+                                ti->error = "Invalid value for argument `hydration_batch_size'";
+                                return -EINVAL;
+                        }
+                        clone->hydration_batch_size = value;
+                } else {
+                        ti->error = "Invalid core argument";
+                        return -EINVAL;
+                }
+        }
+
+        return 0;
+}
+
+static int parse_region_size(struct clone *clone, struct dm_arg_set *as, char **error)
+{
+        int r;
+        unsigned int region_size;
+        struct dm_arg arg;
+
+        arg.min = MIN_REGION_SIZE;
+        arg.max = MAX_REGION_SIZE;
+        arg.error = "Invalid region size";
+
+        r = dm_read_arg(&arg, as, &region_size, error);
+        if (r)
+                return r;
+
+        /* Check region size is a power of 2 */
+        if (!is_power_of_2(region_size)) {
+                *error = "Region size is not a power of 2";
+                return -EINVAL;
+        }
+
+        /* Validate the region size against the device logical block size */
+        if (region_size % (bdev_logical_block_size(clone->source_dev->bdev) >> 9) ||
+            region_size % (bdev_logical_block_size(clone->dest_dev->bdev) >> 9)) {
+                *error = "Region size is not a multiple of device logical block size";
+                return -EINVAL;
+        }
+
+        clone->region_size = region_size;
+
+        return 0;
+}
+
+static int validate_nr_regions(unsigned long n, char **error)
+{
+        /*
+         * dm_bitset restricts us to 2^32 regions. test_bit & co. restrict us
+         * further to 2^31 regions.
+         */
+        if (n > (1UL << 31)) {
+                *error = "Too many regions. Consider increasing the region size";
+                return -EINVAL;
+        }
+
+        return 0;
+}
+
+static int parse_metadata_dev(struct clone *clone, struct dm_arg_set *as, char **error)
+{
+        int r;
+        sector_t metadata_dev_size;
+        char b[BDEVNAME_SIZE];
+
+        r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+                          &clone->metadata_dev);
+        if (r) {
+                *error = "Error opening metadata device";
+                return r;
+        }
+
+        metadata_dev_size = get_dev_size(clone->metadata_dev);
+        if (metadata_dev_size > DM_CLONE_METADATA_MAX_SECTORS_WARNING)
+                DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
+                       bdevname(clone->metadata_dev->bdev, b), DM_CLONE_METADATA_MAX_SECTORS);
+
+        return 0;
+}
+
+static int parse_dest_dev(struct clone *clone, struct dm_arg_set *as, char **error)
+{
+        int r;
+        sector_t dest_dev_size;
+
+        r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+                          &clone->dest_dev);
+        if (r) {
+                *error = "Error opening destination device";
+                return r;
+        }
+
+        dest_dev_size = get_dev_size(clone->dest_dev);
+        if (dest_dev_size < clone->ti->len) {
+                dm_put_device(clone->ti, clone->dest_dev);
+                *error = "Device size larger than destination device";
+                return -EINVAL;
+        }
+
+        return 0;
+}
+
+static int parse_source_dev(struct clone *clone, struct dm_arg_set *as, char **error)
+{
+        int r;
+        sector_t source_dev_size;
+
+        r = dm_get_device(clone->ti, dm_shift_arg(as), FMODE_READ,
+                          &clone->source_dev);
+        if (r) {
+                *error = "Error opening source device";
+                return r;
+        }
+
+        source_dev_size = get_dev_size(clone->source_dev);
+        if (source_dev_size < clone->ti->len) {
+                dm_put_device(clone->ti, clone->source_dev);
+                *error = "Device size larger than source device";
+                return -EINVAL;
+        }
+
+        return 0;
+}
+
+static int copy_ctr_args(struct clone *clone, int argc, const char **argv, char **error)
+{
+        unsigned int i;
+        const char **copy;
+
+        copy = kcalloc(argc, sizeof(*copy), GFP_KERNEL);
+        if (!copy)
+                goto error;
+
+        for (i = 0; i < argc; i++) {
+                copy[i] = kstrdup(argv[i], GFP_KERNEL);
+
+                if (!copy[i]) {
+                        while (i--)
+                                kfree(copy[i]);
+                        kfree(copy);
+                        goto error;
+                }
+        }
+
+        clone->nr_ctr_args = argc;
+        clone->ctr_args = copy;
+        return 0;
+
+error:
+        *error = "Failed to allocate memory for table line";
+        return -ENOMEM;
+}
+
+static int clone_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+        int r;
+        struct clone *clone;
+        struct dm_arg_set as;
+
+        if (argc < 4) {
+                ti->error = "Invalid number of arguments";
+                return -EINVAL;
+        }
+
+        as.argc = argc;
+        as.argv = argv;
+
+        clone = kzalloc(sizeof(*clone), GFP_KERNEL);
+        if (!clone) {
+                ti->error = "Failed to allocate clone structure";
+                return -ENOMEM;
+        }
+
+        clone->ti = ti;
+
+        /* Initialize dm-clone flags */
+        __set_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
+        __set_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
+        __set_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
+
+        r = parse_metadata_dev(clone, &as, &ti->error);
+        if (r)
+                goto out_with_clone;
+
+        r = parse_dest_dev(clone, &as, &ti->error);
+        if (r)
+                goto out_with_meta_dev;
+
+        r = parse_source_dev(clone, &as, &ti->error);
+        if (r)
+                goto out_with_dest_dev;
+
+        r = parse_region_size(clone, &as, &ti->error);
+        if (r)
+                goto out_with_source_dev;
+
+        clone->region_shift = __ffs(clone->region_size);
+        clone->nr_regions = dm_sector_div_up(ti->len, clone->region_size);
+
+        r = validate_nr_regions(clone->nr_regions, &ti->error);
+        if (r)
+                goto out_with_source_dev;
+
+        r = dm_set_target_max_io_len(ti, clone->region_size);
+        if (r) {
+                ti->error = "Failed to set max io len";
+                goto out_with_source_dev;
+        }
+
+        r = parse_feature_args(&as, clone);
+        if (r)
+                goto out_with_source_dev;
+
+        r = parse_core_args(&as, clone);
+        if (r)
+                goto out_with_source_dev;
+
+        /* Load metadata */
+        clone->cmd = dm_clone_metadata_open(clone->metadata_dev->bdev, ti->len,
+                                            clone->region_size);
+        if (IS_ERR(clone->cmd)) {
+                ti->error = "Failed to load metadata";
+                r = PTR_ERR(clone->cmd);
+                goto out_with_source_dev;
+        }
+
+        __set_clone_mode(clone, CM_WRITE);
+
+        if (get_clone_mode(clone) != CM_WRITE) {
+                ti->error = "Unable to get write access to metadata, please check/repair metadata";
+                r = -EPERM;
+                goto out_with_metadata;
+        }
+
+        clone->last_commit_jiffies = jiffies;
+
+        /* Allocate hydration hash table */
+        r = hash_table_init(clone);
+        if (r) {
+                ti->error = "Failed to allocate hydration hash table";
+                goto out_with_metadata;
+        }
+
+        atomic_set(&clone->ios_in_flight, 0);
+        init_waitqueue_head(&clone->hydration_stopped);
+        spin_lock_init(&clone->lock);
+        bio_list_init(&clone->deferred_bios);
+        bio_list_init(&clone->deferred_discard_bios);
+        bio_list_init(&clone->deferred_flush_bios);
+        bio_list_init(&clone->deferred_flush_completions);
+        clone->hydration_offset = 0;
+        atomic_set(&clone->hydrations_in_flight, 0);
+
+        clone->wq = alloc_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM, 0);
+        if (!clone->wq) {
+                ti->error = "Failed to allocate workqueue";
+                r = -ENOMEM;
+                goto out_with_ht;
+        }
+
+        INIT_WORK(&clone->worker, do_worker);
+        INIT_DELAYED_WORK(&clone->waker, do_waker);
+
+        clone->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
+        if (IS_ERR(clone->kcopyd_client)) {
+                r = PTR_ERR(clone->kcopyd_client);
+                goto out_with_wq;
+        }
+
+        r = mempool_init_slab_pool(&clone->hydration_pool, MIN_HYDRATIONS,
+                                   _hydration_cache);
+        if (r) {
+                ti->error = "Failed to create dm_clone_region_hydration memory pool";
+                goto out_with_kcopyd;
+        }
+
+        /* Save a copy of the table line */
+        r = copy_ctr_args(clone, argc - 3, (const char **)argv + 3, &ti->error);
+        if (r)
+                goto out_with_mempool;
+
+        mutex_init(&clone->commit_lock);
+        clone->callbacks.congested_fn = clone_is_congested;
+        dm_table_add_target_callbacks(ti->table, &clone->callbacks);
+
+        /* Enable flushes */
+        ti->num_flush_bios = 1;
+        ti->flush_supported = true;
+
+        /* Enable discards */
+        ti->discards_supported = true;
+        ti->num_discard_bios = 1;
+
+        ti->private = clone;
+
+        return 0;
+
+out_with_mempool:
+        mempool_exit(&clone->hydration_pool);
+out_with_kcopyd:
+        dm_kcopyd_client_destroy(clone->kcopyd_client);
+out_with_wq:
+        destroy_workqueue(clone->wq);
+out_with_ht:
+        hash_table_exit(clone);
+out_with_metadata:
+        dm_clone_metadata_close(clone->cmd);
+out_with_source_dev:
+        dm_put_device(ti, clone->source_dev);
+out_with_dest_dev:
+        dm_put_device(ti, clone->dest_dev);
+out_with_meta_dev:
+        dm_put_device(ti, clone->metadata_dev);
+out_with_clone:
+        kfree(clone);
+
+        return r;
+}
+
+static void clone_dtr(struct dm_target *ti)
+{
+        unsigned int i;
+        struct clone *clone = ti->private;
+
+        mutex_destroy(&clone->commit_lock);
+
+        for (i = 0; i < clone->nr_ctr_args; i++)
+                kfree(clone->ctr_args[i]);
+        kfree(clone->ctr_args);
+
+        mempool_exit(&clone->hydration_pool);
+        dm_kcopyd_client_destroy(clone->kcopyd_client);
+        destroy_workqueue(clone->wq);
+        hash_table_exit(clone);
+        dm_clone_metadata_close(clone->cmd);
+        dm_put_device(ti, clone->source_dev);
+        dm_put_device(ti, clone->dest_dev);
+        dm_put_device(ti, clone->metadata_dev);
+
+        kfree(clone);
+}
+
+/*---------------------------------------------------------------------------*/
+
+static void clone_postsuspend(struct dm_target *ti)
+{
+        struct clone *clone = ti->private;
+
+        /*
+         * To successfully suspend the device:
+         *
+         *      - We cancel the delayed work for periodic commits and wait for
+         *        it to finish.
+         *
+         *      - We stop the background hydration, i.e. we prevent new region
+         *        hydrations from starting.
+         *
+         *      - We wait for any in-flight hydrations to finish.
+         *
+         *      - We flush the workqueue.
+         *
+         *      - We commit the metadata.
+         */
+        cancel_delayed_work_sync(&clone->waker);
+
+        set_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
+
+        /*
+         * Make sure set_bit() is ordered before atomic_read(), otherwise we
+         * might race with do_hydration() and miss some started region
+         * hydrations.
+         *
+         * This is paired with smp_mb__after_atomic() in do_hydration().
+         */
+        smp_mb__after_atomic();
+
+        wait_event(clone->hydration_stopped, !atomic_read(&clone->hydrations_in_flight));
+        flush_workqueue(clone->wq);
+
+        (void) commit_metadata(clone);
+}
+
+static void clone_resume(struct dm_target *ti)
+{
+        struct clone *clone = ti->private;
+
+        clear_bit(DM_CLONE_HYDRATION_SUSPENDED, &clone->flags);
+        do_waker(&clone->waker.work);
+}
+
+static bool bdev_supports_discards(struct block_device *bdev)
+{
+        struct request_queue *q = bdev_get_queue(bdev);
+
+        return (q && blk_queue_discard(q));
+}
+
+/*
+ * If discard_passdown was enabled verify that the destination device supports
+ * discards. Disable discard_passdown if not.
+ */
+static void disable_passdown_if_not_supported(struct clone *clone)
+{
+        struct block_device *dest_dev = clone->dest_dev->bdev;
+        struct queue_limits *dest_limits = &bdev_get_queue(dest_dev)->limits;
+        const char *reason = NULL;
+        char buf[BDEVNAME_SIZE];
+
+        if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags))
+                return;
+
+        if (!bdev_supports_discards(dest_dev))
+                reason = "discard unsupported";
+        else if (dest_limits->max_discard_sectors < clone->region_size)
+                reason = "max discard sectors smaller than a region";
+
+        if (reason) {
+                DMWARN("Destination device (%s) %s: Disabling discard passdown.",
+                       bdevname(dest_dev, buf), reason);
+                clear_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags);
+        }
+}
+
+static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
+{
+        struct block_device *dest_bdev = clone->dest_dev->bdev;
+        struct queue_limits *dest_limits = &bdev_get_queue(dest_bdev)->limits;
+
+        if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags)) {
+                /* No passdown is done so we set our own virtual limits */
+                limits->discard_granularity = clone->region_size << SECTOR_SHIFT;
+                limits->max_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT, clone->region_size);
+                return;
+        }
+
+        /*
+         * clone_iterate_devices() is stacking both the source and destination
+         * device limits but discards aren't passed to the source device, so
+         * inherit destination's limits.
+         */
+        limits->max_discard_sectors = dest_limits->max_discard_sectors;
+        limits->max_hw_discard_sectors = dest_limits->max_hw_discard_sectors;
+        limits->discard_granularity = dest_limits->discard_granularity;
+        limits->discard_alignment = dest_limits->discard_alignment;
+        limits->discard_misaligned = dest_limits->discard_misaligned;
+        limits->max_discard_segments = dest_limits->max_discard_segments;
+}
+
+static void clone_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+        struct clone *clone = ti->private;
+        u64 io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
+
+        /*
+         * If the system-determined stacked limits are compatible with
+         * dm-clone's region size (io_opt is a factor) do not override them.
+         */
+        if (io_opt_sectors < clone->region_size ||
+            do_div(io_opt_sectors, clone->region_size)) {
+                blk_limits_io_min(limits, clone->region_size << SECTOR_SHIFT);
+                blk_limits_io_opt(limits, clone->region_size << SECTOR_SHIFT);
+        }
+
+        disable_passdown_if_not_supported(clone);
+        set_discard_limits(clone, limits);
+}
+
+static int clone_iterate_devices(struct dm_target *ti,
+                                 iterate_devices_callout_fn fn, void *data)
+{
+        int ret;
+        struct clone *clone = ti->private;
+        struct dm_dev *dest_dev = clone->dest_dev;
+        struct dm_dev *source_dev = clone->source_dev;
+
+        ret = fn(ti, source_dev, 0, ti->len, data);
+        if (!ret)
+                ret = fn(ti, dest_dev, 0, ti->len, data);
+        return ret;
+}
+
+/*
+ * dm-clone message functions.
+ */
+static void set_hydration_threshold(struct clone *clone, unsigned int nr_regions)
+{
+        WRITE_ONCE(clone->hydration_threshold, nr_regions);
+
+        /*
+         * If user space sets hydration_threshold to zero then the hydration
+         * will stop. If at a later time the hydration_threshold is increased
+         * we must restart the hydration process by waking up the worker.
+         */
+        wake_worker(clone);
+}
+
+static void set_hydration_batch_size(struct clone *clone, unsigned int nr_regions)
+{
+        WRITE_ONCE(clone->hydration_batch_size, nr_regions);
+}
+
+static void enable_hydration(struct clone *clone)
+{
+        if (!test_and_set_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags))
+                wake_worker(clone);
+}
+
+static void disable_hydration(struct clone *clone)
+{
+        clear_bit(DM_CLONE_HYDRATION_ENABLED, &clone->flags);
+}
+
+static int clone_message(struct dm_target *ti, unsigned int argc, char **argv,
+                         char *result, unsigned int maxlen)
+{
+        struct clone *clone = ti->private;
+        unsigned int value;
+
+        if (!argc)
+                return -EINVAL;
+
+        if (!strcasecmp(argv[0], "enable_hydration")) {
+                enable_hydration(clone);
+                return 0;
+        }
+
+        if (!strcasecmp(argv[0], "disable_hydration")) {
+                disable_hydration(clone);
+                return 0;
+        }
+
+        if (argc != 2)
+                return -EINVAL;
+
+        if (!strcasecmp(argv[0], "hydration_threshold")) {
+                if (kstrtouint(argv[1], 10, &value))
+                        return -EINVAL;
+
+                set_hydration_threshold(clone, value);
+
+                return 0;
+        }
+
+        if (!strcasecmp(argv[0], "hydration_batch_size")) {
+                if (kstrtouint(argv[1], 10, &value))
+                        return -EINVAL;
+
+                set_hydration_batch_size(clone, value);
+
+                return 0;
+        }
+
+        DMERR("%s: Unsupported message `%s'", clone_device_name(clone), argv[0]);
+        return -EINVAL;
+}
+
+static struct target_type clone_target = {
+        .name = "clone",
+        .version = {1, 0, 0},
+        .module = THIS_MODULE,
+        .ctr = clone_ctr,
+        .dtr =  clone_dtr,
+        .map = clone_map,
+        .end_io = clone_endio,
+        .postsuspend = clone_postsuspend,
+        .resume = clone_resume,
+        .status = clone_status,
+        .message = clone_message,
+        .io_hints = clone_io_hints,
+        .iterate_devices = clone_iterate_devices,
+};
+
+/*---------------------------------------------------------------------------*/
+
+/* Module functions */
+static int __init dm_clone_init(void)
+{
+        int r;
+
+        _hydration_cache = KMEM_CACHE(dm_clone_region_hydration, 0);
+        if (!_hydration_cache)
+                return -ENOMEM;
+
+        r = dm_register_target(&clone_target);
+        if (r < 0) {
+                DMERR("Failed to register clone target");
+                return r;
+        }
+
+        return 0;
+}
+
+static void __exit dm_clone_exit(void)
+{
+        dm_unregister_target(&clone_target);
+
+        kmem_cache_destroy(_hydration_cache);
+        _hydration_cache = NULL;
+}
+
+/* Module hooks */
+module_init(dm_clone_init);
+module_exit(dm_clone_exit);
+
+MODULE_DESCRIPTION(DM_NAME " clone target");
+MODULE_AUTHOR("Nikos Tsironis <ntsironis@arrikto.com>");
+MODULE_LICENSE("GPL");