different targets were rolling their own data strutures, for example:

- Mikulas Patocka's multisnap implementation
- Heinz Mauelshagen's thin provisioning target
- Another btree based caching target posted to dm-devel
- Another multi-snapshot target based on a design of Daniel Phillips

Maintaining these data structures takes a lot of work, so if possible
we'd like to reduce the number.

The persistent-data library is an attempt to provide a re-usable
framework for people who want to store metadata in device mapper
targets.  It's currently used by the thin-provisioning target and an
upcoming hierarchical storage target.

Please see: Documentation/device-mapper/persistent-data.txt

Signed-off-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 Documentation/device-mapper/persistent-data.txt    |   90 ++
 drivers/md/persistent-data/Kconfig                 |    9 +
 drivers/md/persistent-data/Makefile                |   10 +
 drivers/md/persistent-data/dm-block-manager.c      |  931 ++++++++++++++++++++
 drivers/md/persistent-data/dm-block-manager.h      |  110 +++
 drivers/md/persistent-data/dm-btree-internal.h     |  141 +++
 drivers/md/persistent-data/dm-btree-remove.c       |  540 ++++++++++++
 drivers/md/persistent-data/dm-btree-spine.c        |  192 ++++
 drivers/md/persistent-data/dm-btree.c              |  871 ++++++++++++++++++
 drivers/md/persistent-data/dm-btree.h              |  146 +++
 drivers/md/persistent-data/dm-pd-module.c          |   18 +
 drivers/md/persistent-data/dm-space-map-common.h   |   99 +++
 drivers/md/persistent-data/dm-space-map-disk.c     |  624 +++++++++++++
 drivers/md/persistent-data/dm-space-map-disk.h     |   21 +
 drivers/md/persistent-data/dm-space-map-metadata.c |  878 ++++++++++++++++++
 drivers/md/persistent-data/dm-space-map-metadata.h |   29 +
 drivers/md/persistent-data/dm-space-map.h          |  116 +++
 .../md/persistent-data/dm-transaction-manager.c    |  442 ++++++++++
 .../md/persistent-data/dm-transaction-manager.h    |  139 +++
 19 files changed, 5406 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/device-mapper/persistent-data.txt
 create mode 100644 drivers/md/persistent-data/Kconfig
 create mode 100644 drivers/md/persistent-data/Makefile
 create mode 100644 drivers/md/persistent-data/dm-block-manager.c
 create mode 100644 drivers/md/persistent-data/dm-block-manager.h
 create mode 100644 drivers/md/persistent-data/dm-btree-internal.h
 create mode 100644 drivers/md/persistent-data/dm-btree-remove.c
 create mode 100644 drivers/md/persistent-data/dm-btree-spine.c
 create mode 100644 drivers/md/persistent-data/dm-btree.c
 create mode 100644 drivers/md/persistent-data/dm-btree.h
 create mode 100644 drivers/md/persistent-data/dm-pd-module.c
 create mode 100644 drivers/md/persistent-data/dm-space-map-common.h
 create mode 100644 drivers/md/persistent-data/dm-space-map-disk.c
 create mode 100644 drivers/md/persistent-data/dm-space-map-disk.h
 create mode 100644 drivers/md/persistent-data/dm-space-map-metadata.c
 create mode 100644 drivers/md/persistent-data/dm-space-map-metadata.h
 create mode 100644 drivers/md/persistent-data/dm-space-map.h
 create mode 100644 drivers/md/persistent-data/dm-transaction-manager.c
 create mode 100644 drivers/md/persistent-data/dm-transaction-manager.h

diff --git a/Documentation/device-mapper/persistent-data.txt b/Documentation/device-mapper/persistent-data.txt
new file mode 100644
index 0000000..399c958
--- /dev/null
+++ b/Documentation/device-mapper/persistent-data.txt
@@ -0,0 +1,90 @@
+Introduction
+============
+
+The more sophisticated device mapper targets require complex metadata
+that is managed in kernel.  In late 2010 we were seeing that various
+different targets were rolling their own data strutures, for example:
+
+- Mikulas Patocka's multisnap implementation
+- Heinz Mauelshagen's thin provisioning target
+- Another btree based caching target posted to dm-devel
+- Another multi-snapshot target based on a design of Daniel Phillips
+
+Maintaining these data structures takes a lot of work, so if possible
+we'd like to reduce the number.
+
+The persistent-data library is an attempt to provide a re-usable
+framework for people who want to store metadata in device mapper
+targets.  It's currently used by the thin-provisioning target and an
+upcoming hierarchical storage target.
+
+
+Overview
+========
+
+The main documentation is in the header files, which can all be found
+under drivers/md/persistent-data.  But here is an overview:
+
+The block manager
+-----------------
+
+dm-block-manager.[hc]
+
+This provides access to the data on disk in fixed sized blocks.  There
+is a read/write locking interface to prevent concurrent accesses, and
+keep data that is being used in the cache.
+
+Clients of persistent-data are unlikely to use this directly.
+
+The transaction manager
+-----------------------
+
+dm-transaction-manager.[hc]
+
+This restricts access to blocks and enforces copy-on-write semantics.
+The only way you can get hold of a writable block through the
+transaction manager is by shadowing an existing block (ie. doing
+copy-on-write), or allocating a fresh one.  Shadowing is elided within
+the same transaction, so performance is reasonable.  The commit method
+ensures that all data is flushed, before your superblock, and then the
+superblock written.  On power failure your metadata will be as it was
+when last committed.
+
+Clients will need to be familiar with tm to use persistent-data.
+
+The Space Maps
+--------------
+
+dm-space-map.h
+dm-space-map-metadata.[hc]
+dm-space-map-disk.[hc]
+
+On disk data structures that keep track of reference counts of blocks.
+Also acts as the allocator of new blocks.  Currently two
+implementations, a simpler one for managing blocks on a different
+device (eg. thinly provisioned data blocks), and another for managing
+the metadata space.  The latter is complicated by the need to store
+it's own data within the space it's managing.
+
+Clients do not need to use space maps directly.
+
+The data structures
+-------------------
+
+dm-btree.[hc]
+dm-btree-remove.c
+dm-btree-spine.c
+dm-btree-internal.h
+
+Currently there is only one data structure.  A hierarchical btree.
+There are plans to add more, for example something with an array like
+interface would see a lot of use.
+
+The btree is 'hierarchical' in that you can define it to be composed
+of nested btrees, and take multiple keys.  For example the
+thin-provisioning target uses a btree with two levels of nesting, the
+first mapping a device id to a mapping tree, which in turn maps a
+virtual block to a physical block.
+
+Values stored in the btrees can have arbitrary size.  Keys are always
+64bits (though nesting allows you to use multiple keys).
diff --git a/drivers/md/persistent-data/Kconfig b/drivers/md/persistent-data/Kconfig
new file mode 100644
index 0000000..ee81085
--- /dev/null
+++ b/drivers/md/persistent-data/Kconfig
@@ -0,0 +1,9 @@
+config DM_PERSISTENT_DATA
+       tristate "Persistent data library"
+       depends on BLK_DEV_DM && EXPERIMENTAL
+       select LIBCRC32C
+       ---help---
+         Library of code for metadata support for dm targets.  The
+         term persistent isn't referring to the fact that the data is
+         written to disk (which of course it is).  But that these data
+         structures are immutable.
diff --git a/drivers/md/persistent-data/Makefile b/drivers/md/persistent-data/Makefile
new file mode 100644
index 0000000..8b8455d
--- /dev/null
+++ b/drivers/md/persistent-data/Makefile
@@ -0,0 +1,10 @@
+obj-$(CONFIG_DM_PERSISTENT_DATA) += dm-persistent-data.o
+dm-persistent-data-objs := \
+	dm-block-manager.o \
+	dm-pd-module.o \
+	dm-space-map-disk.o \
+	dm-space-map-metadata.o \
+	dm-transaction-manager.o \
+	dm-btree.o \
+	dm-btree-remove.o \
+	dm-btree-spine.o
diff --git a/drivers/md/persistent-data/dm-block-manager.c b/drivers/md/persistent-data/dm-block-manager.c
new file mode 100644
index 0000000..5fb696d
--- /dev/null
+++ b/drivers/md/persistent-data/dm-block-manager.c
@@ -0,0 +1,931 @@
+#include "dm-block-manager.h"
+
+#include <linux/dm-io.h>
+#include <linux/slab.h>
+#include <linux/device-mapper.h> /* For SECTOR_SHIFT and DMERR */
+
+#define DM_MSG_PREFIX "block manager"
+
+/*----------------------------------------------------------------*/
+
+#define SECTOR_SIZE 512
+
+enum dm_block_state {
+	BS_EMPTY,
+	BS_CLEAN,
+	BS_READING,
+	BS_WRITING,
+	BS_READ_LOCKED,
+	BS_READ_LOCKED_DIRTY,	/* block was dirty before it was read locked */
+	BS_WRITE_LOCKED,
+	BS_DIRTY,
+	BS_ERROR
+};
+
+struct dm_block {
+	struct list_head list;
+	struct hlist_node hlist;
+
+	dm_block_t where;
+	struct dm_block_validator *validator;
+	void *data_actual;
+	void *data;
+	wait_queue_head_t io_q;
+	unsigned read_lock_count;
+	unsigned write_lock_pending;
+	enum dm_block_state state;
+
+	/* Extra flags like REQ_FLUSH and REQ_FUA can be set here.  This is
+	 * mainly as to avoid a race condition in flush_and_unlock() where
+	 * the newly unlocked superblock may have been submitted for a
+	 * write before the write_all_dirty() call is made.
+	 */
+	int io_flags;
+
+	/*
+	 * Sadly we need an up pointer so we can get to the bm on io
+	 * completion.
+	 */
+	struct dm_block_manager *bm;
+};
+
+struct dm_block_manager {
+	struct block_device *bdev;
+	unsigned cache_size; /* in bytes */
+	unsigned block_size; /* in bytes */
+	dm_block_t nr_blocks;
+
+	/* this will trigger everytime an io completes */
+	wait_queue_head_t io_q;
+
+	struct dm_io_client *io;
+
+	/* |lock| protects all the lists and the hash table */
+	spinlock_t lock;
+	struct list_head empty_list; /* no block assigned */
+	struct list_head clean_list; /* unlocked and clean */
+	struct list_head dirty_list; /* unlocked and dirty */
+	struct list_head error_list;
+	unsigned available_count;
+	unsigned reading_count;
+	unsigned writing_count;
+
+	/*
+	 * Hash table of cached blocks, holds everything that isn't in the
+	 * BS_EMPTY state.
+	 */
+	unsigned hash_size;
+	unsigned hash_mask;
+	struct hlist_head buckets[0]; /* must be last member of struct */
+};
+
+dm_block_t dm_block_location(struct dm_block *b)
+{
+	return b->where;
+}
+EXPORT_SYMBOL_GPL(dm_block_location);
+
+void *dm_block_data(struct dm_block *b)
+{
+	return b->data;
+}
+EXPORT_SYMBOL_GPL(dm_block_data);
+
+/*----------------------------------------------------------------
+ * Hash table
+ *--------------------------------------------------------------*/
+static unsigned hash_block(struct dm_block_manager *bm, dm_block_t b)
+{
+	const unsigned BIG_PRIME = 4294967291UL;
+
+	return (((unsigned) b) * BIG_PRIME) & bm->hash_mask;
+}
+
+static struct dm_block *__find_block(struct dm_block_manager *bm, dm_block_t b)
+{
+	unsigned bucket = hash_block(bm, b);
+	struct dm_block *blk;
+	struct hlist_node *n;
+
+	hlist_for_each_entry(blk, n, bm->buckets + bucket, hlist)
+		if (blk->where == b)
+			return blk;
+
+	return NULL;
+}
+
+static void __insert_block(struct dm_block_manager *bm, struct dm_block *b)
+{
+	unsigned bucket = hash_block(bm, b->where);
+
+	hlist_add_head(&b->hlist, bm->buckets + bucket);
+}
+
+/*----------------------------------------------------------------
+ * Block state:
+ * __transition() handles transition of a block between different states.
+ * Study this to understand the state machine.
+ *
+ * Alternatively install graphviz and run:
+ *     grep DOT dm-block-manager.c | grep -v '	' |
+ *	 sed -e 's/.*DOT: //' -e 's/\*\///' |
+ *	 dot -Tps -o states.ps
+ *
+ * Assumes bm->lock is held.
+ *--------------------------------------------------------------*/
+static void __transition(struct dm_block *b, enum dm_block_state new_state)
+{
+	/* DOT: digraph BlockStates { */
+	struct dm_block_manager *bm = b->bm;
+
+	switch (new_state) {
+	case BS_EMPTY:
+		/* DOT: error -> empty */
+		/* DOT: clean -> empty */
+		BUG_ON(!((b->state == BS_ERROR) ||
+			 (b->state == BS_CLEAN)));
+		hlist_del(&b->hlist);
+		list_move(&b->list, &bm->empty_list);
+		b->write_lock_pending = 0;
+		b->read_lock_count = 0;
+		b->io_flags = 0;
+		b->validator = NULL;
+
+		if (b->state == BS_ERROR)
+			bm->available_count++;
+		break;
+
+	case BS_CLEAN:
+		/* DOT: reading -> clean */
+		/* DOT: writing -> clean */
+		/* DOT: read_locked -> clean */
+		BUG_ON(!((b->state == BS_READING) ||
+			 (b->state == BS_WRITING) ||
+			 (b->state == BS_READ_LOCKED)));
+		switch (b->state) {
+		case BS_READING:
+			BUG_ON(bm->reading_count == 0);
+			bm->reading_count--;
+			break;
+
+		case BS_WRITING:
+			BUG_ON(bm->writing_count == 0);
+			bm->writing_count--;
+			b->io_flags = 0;
+			break;
+
+		default:
+			break;
+		}
+		list_add_tail(&b->list, &bm->clean_list);
+		bm->available_count++;
+		break;
+
+	case BS_READING:
+		/* DOT: empty -> reading */
+		BUG_ON(!(b->state == BS_EMPTY));
+		/* FIXME: insert into the hash */
+		__insert_block(bm, b);
+		list_del(&b->list);
+		bm->available_count--;
+		bm->reading_count++;
+		break;
+
+	case BS_WRITING:
+		/* DOT: dirty -> writing */
+		BUG_ON(!(b->state == BS_DIRTY));
+		list_del(&b->list);
+		bm->writing_count++;
+		break;
+
+	case BS_READ_LOCKED:
+		/* DOT: clean -> read_locked */
+		BUG_ON(!(b->state == BS_CLEAN));
+		list_del(&b->list);
+		bm->available_count--;
+		break;
+
+	case BS_READ_LOCKED_DIRTY:
+		/* DOT: dirty -> read_locked_dirty */
+		BUG_ON(!((b->state == BS_DIRTY)));
+		list_del(&b->list);
+		break;
+
+	case BS_WRITE_LOCKED:
+		/* DOT: dirty -> write_locked */
+		/* DOT: clean -> write_locked */
+		BUG_ON(!((b->state == BS_DIRTY) ||
+			 (b->state == BS_CLEAN)));
+		list_del(&b->list);
+
+		if (b->state == BS_CLEAN)
+			bm->available_count--;
+		break;
+
+	case BS_DIRTY:
+		/* DOT: write_locked -> dirty */
+		/* DOT: read_locked_dirty -> dirty */
+		BUG_ON(!((b->state == BS_WRITE_LOCKED) ||
+			 (b->state == BS_READ_LOCKED_DIRTY)));
+		list_add_tail(&b->list, &bm->dirty_list);
+		break;
+
+	case BS_ERROR:
+		/* DOT: writing -> error */
+		/* DOT: reading -> error */
+		BUG_ON(!((b->state == BS_WRITING) ||
+			 (b->state == BS_READING)));
+		list_add_tail(&b->list, &bm->error_list);
+		break;
+	}
+
+	b->state = new_state;
+	/* DOT: } */
+}
+
+/*----------------------------------------------------------------
+ * low level io
+ *--------------------------------------------------------------*/
+typedef void (completion_fn)(unsigned long error, struct dm_block *b);
+
+static void submit_io(struct dm_block *b, int rw,
+		      completion_fn fn)
+{
+	struct dm_block_manager *bm = b->bm;
+	struct dm_io_request req;
+	struct dm_io_region region;
+	unsigned sectors_per_block = bm->block_size >> SECTOR_SHIFT;
+
+	region.bdev = bm->bdev;
+	region.sector = b->where * sectors_per_block;
+	region.count = sectors_per_block;
+
+	req.bi_rw = rw;
+	req.mem.type = DM_IO_KMEM;
+	req.mem.offset = 0;
+	req.mem.ptr.addr = b->data;
+	req.notify.fn = (void (*)(unsigned long, void *)) fn;
+	req.notify.context = b;
+	req.client = bm->io;
+
+	if (dm_io(&req, 1, &region, NULL) < 0)
+		fn(1, b);
+}
+
+/*----------------------------------------------------------------
+ * High level io
+ *--------------------------------------------------------------*/
+static void __complete_io(unsigned long error, struct dm_block *b)
+{
+	struct dm_block_manager *bm = b->bm;
+
+	if (error) {
+		DMERR("io error = %lu, block = %llu",
+		      error , (unsigned long long)b->where);
+		__transition(b, BS_ERROR);
+	} else
+		__transition(b, BS_CLEAN);
+
+	wake_up(&b->io_q);
+	wake_up(&bm->io_q);
+}
+
+static void complete_io(unsigned long error, struct dm_block *b)
+{
+	struct dm_block_manager *bm = b->bm;
+	unsigned long flags;
+
+	spin_lock_irqsave(&bm->lock, flags);
+	__complete_io(error, b);
+	spin_unlock_irqrestore(&bm->lock, flags);
+}
+
+static void read_block(struct dm_block *b)
+{
+	submit_io(b, READ, complete_io);
+}
+
+static void write_block(struct dm_block *b)
+{
+	if (b->validator)
+		b->validator->prepare_for_write(b->validator, b,
+						b->bm->block_size);
+
+	submit_io(b, WRITE | b->io_flags, complete_io);
+}
+
+static void write_dirty(struct dm_block_manager *bm, unsigned count)
+{
+	struct dm_block *b, *tmp;
+	struct list_head dirty;
+	unsigned long flags;
+
+	/* Grab the first |count| entries from the dirty list */
+	INIT_LIST_HEAD(&dirty);
+	spin_lock_irqsave(&bm->lock, flags);
+	list_for_each_entry_safe(b, tmp, &bm->dirty_list, list) {
+		if (count-- == 0)
+			break;
+		__transition(b, BS_WRITING);
+		list_add_tail(&b->list, &dirty);
+	}
+	spin_unlock_irqrestore(&bm->lock, flags);
+
+	list_for_each_entry_safe(b, tmp, &dirty, list) {
+		list_del(&b->list);
+		write_block(b);
+	}
+}
+
+static void write_all_dirty(struct dm_block_manager *bm)
+{
+	write_dirty(bm, bm->cache_size);
+}
+
+static void __clear_errors(struct dm_block_manager *bm)
+{
+	struct dm_block *b, *tmp;
+	list_for_each_entry_safe(b, tmp, &bm->error_list, list)
+		__transition(b, BS_EMPTY);
+}
+
+/*----------------------------------------------------------------
+ * Waiting
+ *--------------------------------------------------------------*/
+#ifdef __CHECKER__
+# define __retains(x)	__attribute__((context(x, 1, 1)))
+#else
+# define __retains(x)
+#endif
+
+#ifdef USE_PLUGGING
+static inline unplug(void)
+{
+	blk_flush_plug(current);
+}
+#else
+static inline void unplug(void) {}
+#endif
+
+#define __wait_block(wq, lock, flags, sched_fn, condition)	\
+do {								\
+	int ret = 0;						\
+								\
+	DEFINE_WAIT(wait);					\
+	add_wait_queue(wq, &wait);				\
+								\
+	for (;;) {						\
+		prepare_to_wait(wq, &wait, TASK_INTERRUPTIBLE); \
+		if (condition)					\
+			break;					\
+								\
+		spin_unlock_irqrestore(lock, flags);		\
+		if (signal_pending(current)) {			\
+			ret = -ERESTARTSYS;			\
+			spin_lock_irqsave(lock, flags);		\
+			break;					\
+		}						\
+								\
+		sched_fn();					\
+		spin_lock_irqsave(lock, flags);			\
+	}							\
+								\
+	finish_wait(wq, &wait);					\
+	return ret;						\
+} while (0)
+
+static int __wait_io(struct dm_block *b, unsigned long *flags)
+	__retains(&b->bm->lock)
+{
+	unplug();
+	__wait_block(&b->io_q, &b->bm->lock, *flags, io_schedule,
+		     ((b->state != BS_READING) && (b->state != BS_WRITING)));
+}
+
+static int __wait_unlocked(struct dm_block *b, unsigned long *flags)
+	__retains(&b->bm->lock)
+{
+	__wait_block(&b->io_q, &b->bm->lock, *flags, schedule,
+		     ((b->state == BS_CLEAN) || (b->state == BS_DIRTY)));
+}
+
+static int __wait_read_lockable(struct dm_block *b, unsigned long *flags)
+	__retains(&b->bm->lock)
+{
+	__wait_block(&b->io_q, &b->bm->lock, *flags, schedule,
+		     (!b->write_lock_pending && (b->state == BS_CLEAN ||
+						 b->state == BS_DIRTY ||
+						 b->state == BS_READ_LOCKED)));
+}
+
+static int __wait_all_writes(struct dm_block_manager *bm, unsigned long *flags)
+	__retains(&bm->lock)
+{
+	unplug();
+	__wait_block(&bm->io_q, &bm->lock, *flags, io_schedule,
+		     !bm->writing_count);
+}
+
+static int __wait_clean(struct dm_block_manager *bm, unsigned long *flags)
+	__retains(&bm->lock)
+{
+	unplug();
+	__wait_block(&bm->io_q, &bm->lock, *flags, io_schedule,
+		     (!list_empty(&bm->clean_list) ||
+		      (bm->writing_count == 0)));
+}
+
+/*----------------------------------------------------------------
+ * Finding a free block to recycle
+ *--------------------------------------------------------------*/
+static int recycle_block(struct dm_block_manager *bm, dm_block_t where,
+			 int need_read, struct dm_block_validator *v,
+			 struct dm_block **result)
+{
+	int ret = 0;
+	struct dm_block *b;
+	unsigned long flags, available;
+
+	/* wait for a block to appear on the empty or clean lists */
+	spin_lock_irqsave(&bm->lock, flags);
+	while (1) {
+		/*
+		 * Once we can lock and do io concurrently then we should
+		 * probably flush at bm->cache_size / 2 and write _all_
+		 * dirty blocks.
+		 */
+		available = bm->available_count + bm->writing_count;
+		if (available < bm->cache_size / 4) {
+			spin_unlock_irqrestore(&bm->lock, flags);
+			write_dirty(bm, bm->cache_size / 4);
+			spin_lock_irqsave(&bm->lock, flags);
+		}
+
+		if (!list_empty(&bm->empty_list)) {
+			b = list_first_entry(&bm->empty_list, struct dm_block, list);
+			break;
+
+		} else if (!list_empty(&bm->clean_list)) {
+			b = list_first_entry(&bm->clean_list, struct dm_block, list);
+			__transition(b, BS_EMPTY);
+			break;
+		}
+
+		__wait_clean(bm, &flags);
+	}
+
+	b->where = where;
+	b->validator = v;
+	__transition(b, BS_READING);
+
+	if (!need_read) {
+		memset(b->data, 0, bm->block_size);
+		__transition(b, BS_CLEAN);
+	} else {
+		spin_unlock_irqrestore(&bm->lock, flags);
+		read_block(b);
+		spin_lock_irqsave(&bm->lock, flags);
+		__wait_io(b, &flags);
+
+		/* FIXME: can |b| have been recycled between io completion and here ? */
+
+		/* did the io succeed ? */
+		if (b->state == BS_ERROR) {
+			/* Since this is a read that has failed we can
+			 * clear the error immediately.	 Failed writes are
+			 * revealed during a commit.
+			 */
+			__transition(b, BS_EMPTY);
+			ret = -EIO;
+		}
+
+		if (b->validator) {
+			ret = b->validator->check(b->validator, b, bm->block_size);
+			if (ret) {
+				DMERR("%s validator check failed for block %llu",
+				      b->validator->name, (unsigned long long)b->where);
+				__transition(b, BS_EMPTY);
+			}
+		}
+	}
+	spin_unlock_irqrestore(&bm->lock, flags);
+
+	if (ret == 0)
+		*result = b;
+	return ret;
+}
+
+#ifdef USE_PLUGGING
+static int recycle_block_with_plugging(struct dm_block_manager *bm,
+				       dm_block_t where, int need_read,
+				       struct dm_block_validator *v,
+				       struct dm_block **result)
+{
+	int r;
+	struct blk_plug plug;
+
+	blk_start_plug(&plug);
+	r = recycle_block(bm, where, need_read, v, result);
+	blk_finish_plug(&plug);
+
+	return r;
+}
+#endif
+
+/*----------------------------------------------------------------
+ * Low level block management
+ *--------------------------------------------------------------*/
+static void *align(void *ptr, size_t amount)
+{
+	size_t offset = (uint64_t) ptr & (amount - 1);
+	return offset ? ((unsigned char *) ptr) + (amount - offset) : ptr;
+}
+
+/* Alloc a page if block_size equals PAGE_SIZE or kmalloc it. */
+static void *_alloc_block(struct dm_block_manager *bm)
+{
+	void *r;
+
+	if (bm->block_size == PAGE_SIZE) {
+		struct page *p = alloc_page(GFP_KERNEL);
+		r = p ? page_address(p) : NULL;
+
+	} else
+		r = kmalloc(bm->block_size + SECTOR_SIZE, GFP_KERNEL);
+
+	return r;
+}
+
+static struct dm_block *alloc_block(struct dm_block_manager *bm)
+{
+	struct dm_block *b = kmalloc(sizeof(*b), GFP_KERNEL);
+	if (!b)
+		return NULL;
+
+	INIT_LIST_HEAD(&b->list);
+	INIT_HLIST_NODE(&b->hlist);
+
+	b->data_actual = _alloc_block(bm);
+	if (!b->data_actual) {
+		kfree(b);
+		return NULL;
+	}
+
+	b->validator = NULL;
+	b->data = align(b->data_actual, SECTOR_SIZE);
+	b->state = BS_EMPTY;
+	init_waitqueue_head(&b->io_q);
+	b->read_lock_count = 0;
+	b->write_lock_pending = 0;
+	b->io_flags = 0;
+	b->bm = bm;
+
+	return b;
+}
+
+static void free_block(struct dm_block *b)
+{
+	if (b->bm->block_size == PAGE_SIZE)
+		free_page((unsigned long) b->data_actual);
+	else
+		kfree(b->data_actual);
+
+	kfree(b);
+}
+
+static int populate_bm(struct dm_block_manager *bm, unsigned count)
+{
+	int i;
+	LIST_HEAD(bs);
+
+	for (i = 0; i < count; i++) {
+		struct dm_block *b = alloc_block(bm);
+		if (!b) {
+			struct dm_block *tmp;
+			list_for_each_entry_safe(b, tmp, &bs, list)
+				free_block(b);
+			return -ENOMEM;
+		}
+
+		list_add(&b->list, &bs);
+	}
+
+	list_replace(&bs, &bm->empty_list);
+	bm->available_count = count;
+
+	return 0;
+}
+
+/*----------------------------------------------------------------
+ * Public interface
+ *--------------------------------------------------------------*/
+static unsigned calc_hash_size(unsigned cache_size)
+{
+	unsigned r = 32;	/* minimum size is 16 */
+
+	while (r < cache_size)
+		r <<= 1;
+
+	return r >> 1;
+}
+
+struct dm_block_manager *
+dm_block_manager_create(struct block_device *bdev,
+			unsigned block_size, unsigned cache_size)
+{
+	unsigned i;
+	unsigned hash_size = calc_hash_size(cache_size);
+	size_t len = sizeof(struct dm_block_manager) +
+		sizeof(struct hlist_head) * hash_size;
+	struct dm_block_manager *bm;
+
+	bm = kmalloc(len, GFP_KERNEL);
+	if (!bm)
+		return NULL;
+	bm->bdev = bdev;
+	bm->cache_size = max(16u, cache_size);
+	bm->block_size = block_size;
+	bm->nr_blocks = i_size_read(bdev->bd_inode);
+	do_div(bm->nr_blocks, block_size);
+	init_waitqueue_head(&bm->io_q);
+	spin_lock_init(&bm->lock);
+
+	INIT_LIST_HEAD(&bm->empty_list);
+	INIT_LIST_HEAD(&bm->clean_list);
+	INIT_LIST_HEAD(&bm->dirty_list);
+	INIT_LIST_HEAD(&bm->error_list);
+	bm->available_count = 0;
+	bm->reading_count = 0;
+	bm->writing_count = 0;
+
+	bm->hash_size = hash_size;
+	bm->hash_mask = hash_size - 1;
+	for (i = 0; i < hash_size; i++)
+		INIT_HLIST_HEAD(bm->buckets + i);
+
+	bm->io = dm_io_client_create();
+	if (!bm->io) {
+		kfree(bm);
+		return NULL;
+	}
+
+	if (populate_bm(bm, cache_size) < 0) {
+		dm_io_client_destroy(bm->io);
+		kfree(bm);
+		return NULL;
+	}
+
+	return bm;
+}
+EXPORT_SYMBOL_GPL(dm_block_manager_create);
+
+void dm_block_manager_destroy(struct dm_block_manager *bm)
+{
+	int i;
+	struct dm_block *b, *btmp;
+	struct hlist_node *n, *tmp;
+
+	dm_io_client_destroy(bm->io);
+
+	for (i = 0; i < bm->hash_size; i++)
+		hlist_for_each_entry_safe(b, n, tmp, bm->buckets + i, hlist)
+			free_block(b);
+
+	list_for_each_entry_safe(b, btmp, &bm->empty_list, list)
+		free_block(b);
+
+	kfree(bm);
+}
+EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
+
+unsigned dm_bm_block_size(struct dm_block_manager *bm)
+{
+	return bm->block_size;
+}
+EXPORT_SYMBOL_GPL(dm_bm_block_size);
+
+dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm)
+{
+	return bm->nr_blocks;
+}
+EXPORT_SYMBOL_GPL(dm_bm_nr_blocks);
+
+static int lock_internal(struct dm_block_manager *bm, dm_block_t block,
+			 int how, int need_read, int can_block,
+			 struct dm_block_validator *v,
+			 struct dm_block **result)
+{
+	int r = 0;
+	struct dm_block *b;
+	unsigned long flags;
+
+	spin_lock_irqsave(&bm->lock, flags);
+retry:
+	b = __find_block(bm, block);
+	if (b) {
+		if (need_read) {
+			if (b->validator && (v != b->validator)) {
+				DMERR("validator mismatch (old=%s vs new=%s) for block %llu",
+				      b->validator->name, v->name,
+				      (unsigned long long)b->where);
+				spin_unlock_irqrestore(&bm->lock, flags);
+				return -EINVAL;
+
+			} else if (!b->validator && v) {
+				b->validator = v;
+				r = b->validator->check(b->validator, b, bm->block_size);
+				if (r) {
+					DMERR("%s validator check failed for block %llu",
+					      b->validator->name,
+					      (unsigned long long)b->where);
+					spin_unlock_irqrestore(&bm->lock, flags);
+					return r;
+				}
+			}
+		} else
+			b->validator = v;
+
+		switch (how) {
+		case READ:
+			if (b->write_lock_pending || (b->state != BS_CLEAN &&
+						      b->state != BS_DIRTY &&
+						      b->state != BS_READ_LOCKED)) {
+				if (!can_block) {
+					spin_unlock_irqrestore(&bm->lock, flags);
+					return -EWOULDBLOCK;
+				}
+
+				__wait_read_lockable(b, &flags);
+
+				if (b->where != block)
+					goto retry;
+			}
+			break;
+
+		case WRITE:
+			while (b->state != BS_CLEAN && b->state != BS_DIRTY) {
+				if (!can_block) {
+					spin_unlock_irqrestore(&bm->lock, flags);
+					return -EWOULDBLOCK;
+				}
+
+				b->write_lock_pending++;
+				__wait_unlocked(b, &flags);
+				b->write_lock_pending--;
+				if (b->where != block)
+					goto retry;
+			}
+			break;
+		}
+
+	} else if (!can_block) {
+		r = -EWOULDBLOCK;
+		goto out;
+
+	} else {
+		spin_unlock_irqrestore(&bm->lock, flags);
+#ifdef USE_PLUGGING
+		r = recycle_block_with_plugging(bm, block, need_read, v, &b);
+#else
+		r = recycle_block(bm, block, need_read, v, &b);
+#endif
+		spin_lock_irqsave(&bm->lock, flags);
+	}
+
+	if (r == 0) {
+		switch (how) {
+		case READ:
+			b->read_lock_count++;
+
+			if (b->state == BS_DIRTY)
+				__transition(b, BS_READ_LOCKED_DIRTY);
+			else if (b->state == BS_CLEAN)
+				__transition(b, BS_READ_LOCKED);
+			break;
+
+		case WRITE:
+			__transition(b, BS_WRITE_LOCKED);
+			break;
+		}
+
+		*result = b;
+	}
+
+out:
+	spin_unlock_irqrestore(&bm->lock, flags);
+	return r;
+}
+
+int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
+		    struct dm_block_validator *v,
+		    struct dm_block **result)
+{
+	return lock_internal(bm, b, READ, 1, 1, v, result);
+}
+EXPORT_SYMBOL_GPL(dm_bm_read_lock);
+
+int dm_bm_write_lock(struct dm_block_manager *bm,
+		     dm_block_t b, struct dm_block_validator *v,
+		     struct dm_block **result)
+{
+	return lock_internal(bm, b, WRITE, 1, 1, v, result);
+}
+EXPORT_SYMBOL_GPL(dm_bm_write_lock);
+
+int dm_bm_read_try_lock(struct dm_block_manager *bm,
+			dm_block_t b, struct dm_block_validator *v,
+			struct dm_block **result)
+{
+	return lock_internal(bm, b, READ, 1, 0, v, result);
+}
+EXPORT_SYMBOL_GPL(dm_bm_read_try_lock);
+
+int dm_bm_write_lock_zero(struct dm_block_manager *bm,
+			  dm_block_t b, struct dm_block_validator *v,
+			  struct dm_block **result)
+{
+	int r = lock_internal(bm, b, WRITE, 0, 1, v, result);
+	if (!r)
+		memset((*result)->data, 0, bm->block_size);
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_bm_write_lock_zero);
+
+int dm_bm_unlock(struct dm_block *b)
+{
+	int ret = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&b->bm->lock, flags);
+	switch (b->state) {
+	case BS_WRITE_LOCKED:
+		__transition(b, BS_DIRTY);
+		wake_up(&b->io_q);
+		break;
+
+	case BS_READ_LOCKED:
+		if (!--b->read_lock_count) {
+			__transition(b, BS_CLEAN);
+			wake_up(&b->io_q);
+		}
+		break;
+
+	case BS_READ_LOCKED_DIRTY:
+		if (!--b->read_lock_count) {
+			__transition(b, BS_DIRTY);
+			wake_up(&b->io_q);
+		}
+		break;
+
+	default:
+		DMERR("block = %llu not locked",
+		      (unsigned long long)b->where);
+		ret = -EINVAL;
+		break;
+	}
+	spin_unlock_irqrestore(&b->bm->lock, flags);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dm_bm_unlock);
+
+static int __wait_flush(struct dm_block_manager *bm)
+{
+	int ret = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&bm->lock, flags);
+	__wait_all_writes(bm, &flags);
+
+	if (!list_empty(&bm->error_list)) {
+		ret = -EIO;
+		__clear_errors(bm);
+	}
+	spin_unlock_irqrestore(&bm->lock, flags);
+
+	return ret;
+}
+
+int dm_bm_flush_and_unlock(struct dm_block_manager *bm,
+			   struct dm_block *superblock)
+{
+	int r;
+	unsigned long flags;
+
+	write_all_dirty(bm);
+	r = __wait_flush(bm);
+	if (r)
+		return r;
+
+	spin_lock_irqsave(&bm->lock, flags);
+	superblock->io_flags = REQ_FUA | REQ_FLUSH;
+	spin_unlock_irqrestore(&bm->lock, flags);
+
+	dm_bm_unlock(superblock);
+	write_all_dirty(bm);
+
+	return __wait_flush(bm);
+}
+EXPORT_SYMBOL_GPL(dm_bm_flush_and_unlock);
+
+/*----------------------------------------------------------------*/
diff --git a/drivers/md/persistent-data/dm-block-manager.h b/drivers/md/persistent-data/dm-block-manager.h
new file mode 100644
index 0000000..55b96cb
--- /dev/null
+++ b/drivers/md/persistent-data/dm-block-manager.h
@@ -0,0 +1,110 @@
+#ifndef DM_BLOCK_MANAGER_H
+#define DM_BLOCK_MANAGER_H
+
+#include <linux/blkdev.h>
+#include <linux/types.h>
+#include <linux/crc32c.h>
+
+/*----------------------------------------------------------------*/
+
+typedef uint64_t dm_block_t;
+
+/* An opaque handle to a block of data */
+struct dm_block;
+dm_block_t dm_block_location(struct dm_block *b);
+void *dm_block_data(struct dm_block *b);
+
+static inline __le32 dm_block_csum_data(const void *data, unsigned int length)
+{
+	return __cpu_to_le32(crc32c(~(u32)0, data, length));
+}
+
+/*----------------------------------------------------------------*/
+
+struct dm_block_manager;
+struct dm_block_manager *
+dm_block_manager_create(struct block_device *bdev, unsigned block_size,
+			unsigned cache_size);
+void dm_block_manager_destroy(struct dm_block_manager *bm);
+
+unsigned dm_bm_block_size(struct dm_block_manager *bm);
+dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm);
+
+/*----------------------------------------------------------------*/
+
+/* 4 bytes for CRC32c */
+#define PERSISTENT_DATA_CSUM_SIZE 4
+
+/*
+ * The validator allows the caller to verify newly read data, and modify
+ * the data just before writing.  eg, to calculate checksums.  It's
+ * important to be consistent with your use of validators.  The only time
+ * you can change validators is if you call dm_bm_write_lock_zero.
+ */
+struct dm_block_validator {
+	const char *name;
+	void (*prepare_for_write)(struct dm_block_validator *v, struct dm_block *b, size_t block_size);
+
+	/* return 0 if valid, < 0 on error */
+	int (*check)(struct dm_block_validator *v, struct dm_block *b, size_t block_size);
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * You can have multiple concurrent readers, or a single writer holding a
+ * block lock.
+ */
+
+/*
+ * dm_bm_lock() locks a block, and returns via |data| a pointer to memory that
+ * holds a copy of that block.  If you have write locked the block then any
+ * changes you make to memory pointed to by |data| will be written back to
+ * the disk sometime after dm_bm_unlock is called.
+ */
+int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
+		    struct dm_block_validator *v,
+		    struct dm_block **result);
+
+int dm_bm_write_lock(struct dm_block_manager *bm, dm_block_t b,
+		     struct dm_block_validator *v,
+		     struct dm_block **result);
+
+/*
+ * The *_try_lock variants return -EWOULDBLOCK if the block isn't
+ * immediately available.
+ */
+int dm_bm_read_try_lock(struct dm_block_manager *bm, dm_block_t b,
+			struct dm_block_validator *v,
+			struct dm_block **result);
+
+/*
+ * dm_bm_write_lock_zero() is for use when you know you're going to completely
+ * overwrite the block.  It saves a disk read.
+ */
+int dm_bm_write_lock_zero(struct dm_block_manager *bm, dm_block_t b,
+			  struct dm_block_validator *v,
+			  struct dm_block **result);
+
+int dm_bm_unlock(struct dm_block *b);
+
+/*
+ * It's a common idiom to have a superblock that should be committed last.
+ *
+ * |superblock| should be write locked, it will be unlocked during this
+ * function.  All dirty blocks are guaranteed to be written and flushed
+ * before the superblock.
+ *
+ * This method always blocks.
+ */
+int dm_bm_flush_and_unlock(struct dm_block_manager *bm,
+			   struct dm_block *superblock);
+
+/*
+ * Debug routines.
+ */
+unsigned dm_bm_locks_held(struct dm_block_manager *bm);
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-btree-internal.h b/drivers/md/persistent-data/dm-btree-internal.h
new file mode 100644
index 0000000..be688a1
--- /dev/null
+++ b/drivers/md/persistent-data/dm-btree-internal.h
@@ -0,0 +1,141 @@
+#ifndef DM_BTREE_INTERNAL_H
+#define DM_BTREE_INTERNAL_H
+
+#include "dm-btree.h"
+
+#include <linux/list.h>
+
+/*----------------------------------------------------------------*/
+
+/* TODO: move all this into btree.c */
+/*
+ * We'll need 2 accessor functions for n->csum and n->blocknr
+ * to support dm-btree-spine.c in that case.
+ */
+
+enum node_flags {
+	INTERNAL_NODE = 1,
+	LEAF_NODE = 1 << 1
+};
+
+/*
+ * To ease coding I'm packing all the different node types into one
+ * structure.  We can optimise later.
+ */
+struct node_header {
+	__le32 csum;
+	__le32 flags;
+	__le64 blocknr; /* which block this node is supposed to live in */
+
+	__le32 nr_entries;
+	__le32 max_entries;
+} __packed;
+
+struct node {
+	struct node_header header;
+	__le64 keys[0];
+} __packed;
+
+
+/*
+ * Based on the ideas in ["B-trees, Shadowing, and Clones" Ohad Rodeh]
+ */
+
+/* FIXME: enable close packing for on disk structures */
+
+void inc_children(struct dm_transaction_manager *tm, struct node *n,
+		  struct dm_btree_value_type *vt);
+
+/* FIXME: change bn_ prefix for these, refers to an old struct block_node */
+int bn_read_lock(struct dm_btree_info *info, dm_block_t b,
+		 struct dm_block **result);
+int bn_shadow(struct dm_btree_info *info, dm_block_t orig,
+	      struct dm_btree_value_type *vt, struct dm_block **result, int *inc);
+int bn_new_block(struct dm_btree_info *info, struct dm_block **result);
+int bn_unlock(struct dm_btree_info *info, struct dm_block *b);
+
+/*
+ * Spines keep track of the rolling locks.  There are 2 variants, read-only
+ * and one that uses shadowing.  These are separate structs to allow the
+ * type checker to spot misuse, for example accidentally calling read_lock
+ * on a shadow spine.
+ */
+struct ro_spine {
+	struct dm_btree_info *info;
+
+	int count;
+	struct dm_block *nodes[2];
+};
+
+void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info);
+int exit_ro_spine(struct ro_spine *s);
+int ro_step(struct ro_spine *s, dm_block_t new_child);
+struct node *ro_node(struct ro_spine *s);
+
+struct shadow_spine {
+	struct dm_btree_info *info;
+
+	int count;
+	struct dm_block *nodes[2];
+
+	dm_block_t root;
+};
+
+void init_shadow_spine(struct shadow_spine *s, struct dm_btree_info *info);
+int exit_shadow_spine(struct shadow_spine *s);
+
+int shadow_step(struct shadow_spine *s, dm_block_t b,
+		struct dm_btree_value_type *vt, int *inc);
+
+struct dm_block *shadow_current(struct shadow_spine *s);
+
+struct dm_block *shadow_parent(struct shadow_spine *s);
+
+int shadow_root(struct shadow_spine *s);
+
+/*
+ * Some inlines.
+ */
+static inline __le64 *key_ptr(struct node *n, uint32_t index)
+{
+	return n->keys + index;
+}
+
+static inline void *value_base(struct node *n)
+{
+	return &n->keys[__le32_to_cpu(n->header.max_entries)];
+}
+
+static inline void *value_ptr(struct node *n, uint32_t index, size_t value_size)
+{
+	return value_base(n) + (value_size * index);
+}
+
+/* assumes the values are suitably aligned and converts to core format */
+static inline uint64_t value64(struct node *n, uint32_t index)
+{
+	__le64 *values = value_base(n);
+	return __le64_to_cpu(values[index]);
+}
+
+/* searching for a key within a single node */
+int lower_bound(struct node *n, uint64_t key);
+
+int upper_bound(struct node *n, uint64_t key);
+
+/*
+ * Exported for testing.
+ */
+uint32_t calc_max_entries(size_t value_size, size_t block_size);
+
+void insert_at(size_t value_size, struct node *node,
+	       unsigned index, uint64_t key, void *value);
+
+int dm_btree_merge(struct shadow_spine *s, unsigned parent_index,
+		   size_t value_size);
+
+extern struct dm_block_validator btree_node_validator;
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c
new file mode 100644
index 0000000..4b616e3
--- /dev/null
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -0,0 +1,540 @@
+#include "dm-btree.h"
+#include "dm-btree-internal.h"
+
+/*
+ * Removing an entry from a btree
+ * ==============================
+ *
+ * A very important constraint for our btree is that no node, except the
+ * root, may have fewer than a certain number of entries.
+ * (MIN_ENTRIES <= nr_entries <= MAX_ENTRIES).
+ *
+ * Ensuring this is complicated by the way we want to only ever hold the
+ * locks on 2 nodes concurrently, and only change nodes in a top to bottom
+ * fashion.
+ *
+ * Each node may have a left or right sibling.  When decending the spine,
+ * if a node contains only MIN_ENTRIES then we try and increase this to at
+ * least MIN_ENTRIES + 1.  We do this in the following ways:
+ *
+ * [A] No siblings => this can only happen if the node is the root, in which
+ *     case we copy the childs contents over the root.
+ *
+ * [B] No left sibling
+ *     ==> rebalance(node, right sibling)
+ *
+ * [C] No right sibling
+ *     ==> rebalance(left sibling, node)
+ *
+ * [D] Both siblings, total_entries(left, node, right) <= DEL_THRESHOLD
+ *     ==> delete node adding it's contents to left and right
+ *
+ * [E] Both siblings, total_entries(left, node, right) > DEL_THRESHOLD
+ *     ==> rebalance(left, node, right)
+ *
+ * After these operations it's possible that the our original node no
+ * longer contains the desired sub tree.  For this reason this rebalancing
+ * is performed on the children of the current node.  This also avoids
+ * having a special case for the root.
+ *
+ * Once this rebalancing has occurred we can then step into the child node
+ * for internal nodes.  Or delete the entry for leaf nodes.
+ */
+
+/*
+ * Some little utilities for moving node data around.
+ */
+static void node_shift(struct node *n, int shift)
+{
+	uint32_t nr_entries = __le32_to_cpu(n->header.nr_entries);
+
+	if (shift < 0) {
+		shift = -shift;
+		memmove(key_ptr(n, 0),
+			key_ptr(n, shift),
+			(nr_entries - shift) * sizeof(__le64));
+		memmove(value_ptr(n, 0, sizeof(__le64)),
+			value_ptr(n, shift, sizeof(__le64)),
+			(nr_entries - shift) * sizeof(__le64));
+	} else {
+		memmove(key_ptr(n, shift),
+			key_ptr(n, 0),
+			nr_entries * sizeof(__le64));
+		memmove(value_ptr(n, shift, sizeof(__le64)),
+			value_ptr(n, 0, sizeof(__le64)),
+			nr_entries * sizeof(__le64));
+	}
+}
+
+static void node_copy(struct node *left, struct node *right, int shift)
+{
+	uint32_t nr_left = __le32_to_cpu(left->header.nr_entries);
+
+	if (shift < 0) {
+		shift = -shift;
+		memcpy(key_ptr(left, nr_left),
+		       key_ptr(right, 0),
+		       shift * sizeof(__le64));
+		memcpy(value_ptr(left, nr_left, sizeof(__le64)),
+		       value_ptr(right, 0, sizeof(__le64)),
+		       shift * sizeof(__le64));
+	} else {
+		memcpy(key_ptr(right, 0),
+		       key_ptr(left, nr_left - shift),
+		       shift * sizeof(__le64));
+		memcpy(value_ptr(right, 0, sizeof(__le64)),
+		       value_ptr(left, nr_left - shift, sizeof(__le64)),
+		       shift * sizeof(__le64));
+	}
+}
+
+/*
+ * Delete a specific entry from a leaf node.
+ */
+static void delete_at(struct node *n, unsigned index, size_t value_size)
+{
+	unsigned nr_entries = __le32_to_cpu(n->header.nr_entries);
+	unsigned nr_to_copy = nr_entries - (index + 1);
+
+	if (nr_to_copy) {
+		memmove(key_ptr(n, index),
+			key_ptr(n, index + 1),
+			nr_to_copy * sizeof(__le64));
+
+		memmove(value_ptr(n, index, value_size),
+			value_ptr(n, index + 1, value_size),
+			nr_to_copy * value_size);
+	}
+
+	n->header.nr_entries = __cpu_to_le32(nr_entries - 1);
+}
+
+static unsigned del_threshold(struct node *n)
+{
+	return __le32_to_cpu(n->header.max_entries) / 3;
+}
+
+static unsigned merge_threshold(struct node *n)
+{
+	/*
+	 * The extra one is because we know we're potentially going to
+	 * delete an entry.
+	 */
+	return 2 * (__le32_to_cpu(n->header.max_entries) / 3) + 1;
+}
+
+struct child {
+	unsigned index;
+	struct dm_block *block;
+	struct node *n;
+};
+
+static struct dm_btree_value_type le64_type_ = {
+	.context = NULL,
+	.size = sizeof(__le64),
+	.inc = NULL,
+	.dec = NULL,
+	.equal = NULL
+};
+
+static int init_child(struct dm_btree_info *info, struct node *parent,
+		      unsigned index, struct child *result)
+{
+	int r, inc;
+	dm_block_t root;
+
+	result->index = index;
+	root = value64(parent, index);
+
+	r = dm_tm_shadow_block(info->tm, root, &btree_node_validator,
+			       &result->block, &inc);
+	if (r)
+		return r;
+
+	result->n = dm_block_data(result->block);
+	if (inc)
+		inc_children(info->tm, result->n, &le64_type_);
+	return 0;
+}
+
+static int exit_child(struct dm_btree_info *info, struct child *c)
+{
+	return dm_tm_unlock(info->tm, c->block);
+}
+
+static void shift(struct node *left, struct node *right, int count)
+{
+	if (count == 0)
+		return;
+
+	if (count > 0) {
+		node_shift(right, count);
+		node_copy(left, right, count);
+
+	} else {
+		node_copy(left, right, count);
+		node_shift(right, count);
+	}
+
+	left->header.nr_entries =
+		__cpu_to_le32(__le32_to_cpu(left->header.nr_entries) - count);
+	right->header.nr_entries =
+		__cpu_to_le32(__le32_to_cpu(right->header.nr_entries) + count);
+}
+
+static void __rebalance2(struct dm_btree_info *info, struct node *parent,
+			 struct child *l, struct child *r)
+{
+	struct node *left = l->n;
+	struct node *right = r->n;
+	uint32_t nr_left = __le32_to_cpu(left->header.nr_entries);
+	uint32_t nr_right = __le32_to_cpu(right->header.nr_entries);
+
+	if (nr_left + nr_right <= merge_threshold(left)) {
+		/* merge */
+		node_copy(left, right, -nr_right);
+		left->header.nr_entries = __cpu_to_le32(nr_left + nr_right);
+
+		*((__le64 *) value_ptr(parent, l->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(l->block));
+		delete_at(parent, r->index, sizeof(__le64));
+
+		/*
+		 * We need to decrement the right block, but not it's
+		 * children, since they're still referenced by @left
+		 */
+		dm_tm_dec(info->tm, dm_block_location(r->block));
+
+	} else {
+		/* rebalance */
+		unsigned target_left = (nr_left + nr_right) / 2;
+		shift(left, right, nr_left - target_left);
+		*((__le64 *) value_ptr(parent, l->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(l->block));
+		*((__le64 *) value_ptr(parent, r->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(r->block));
+		*key_ptr(parent, r->index) = right->keys[0];
+	}
+}
+
+static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
+		      unsigned left_index)
+{
+	int r;
+	struct node *parent;
+	struct child left, right;
+
+	parent = dm_block_data(shadow_current(s));
+
+	r = init_child(info, parent, left_index, &left);
+	if (r)
+		return r;
+
+	r = init_child(info, parent, left_index + 1, &right);
+	if (r) {
+		exit_child(info, &left);
+		return r;
+	}
+
+	__rebalance2(info, parent, &left, &right);
+
+	r = exit_child(info, &left);
+	if (r) {
+		exit_child(info, &right);
+		return r;
+	}
+
+	r = exit_child(info, &right);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+static void __rebalance3(struct dm_btree_info *info, struct node *parent,
+			 struct child *l, struct child *c, struct child *r)
+{
+	struct node *left = l->n;
+	struct node *center = c->n;
+	struct node *right = r->n;
+
+	uint32_t nr_left = __le32_to_cpu(left->header.nr_entries);
+	uint32_t nr_center = __le32_to_cpu(center->header.nr_entries);
+	uint32_t nr_right = __le32_to_cpu(right->header.nr_entries);
+	uint32_t max_entries = __le32_to_cpu(left->header.max_entries);
+
+	if (((nr_left + nr_center + nr_right) / 2) < merge_threshold(center)) {
+		/* delete center node:
+		 *
+		 * We dump as many entries from center as possible into
+		 * left, then the rest in right, then rebalance2.  This
+		 * wastes some cpu, but I want something simple atm.
+		 */
+
+		unsigned shift = min(max_entries - nr_left, nr_center);
+		node_copy(left, center, -shift);
+		left->header.nr_entries = __cpu_to_le32(nr_left + shift);
+
+		if (shift != nr_center) {
+			shift = nr_center - shift;
+			node_shift(right, shift);
+			node_copy(center, right, shift);
+			right->header.nr_entries = __cpu_to_le32(nr_right + shift);
+		}
+
+		*((__le64 *) value_ptr(parent, l->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(l->block));
+		*((__le64 *) value_ptr(parent, r->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(r->block));
+		*key_ptr(parent, r->index) = right->keys[0];
+
+		delete_at(parent, c->index, sizeof(__le64));
+		r->index--;
+
+		dm_tm_dec(info->tm, dm_block_location(c->block));
+		__rebalance2(info, parent, l, r);
+
+	} else {
+		/* rebalance */
+		unsigned target = (nr_left + nr_center + nr_right) / 3;
+		BUG_ON(target == nr_center);
+
+		/* adjust the left node */
+		shift(left, center, nr_left - target);
+
+		/* adjust the right node */
+		shift(center, right, target - nr_right);
+
+		*((__le64 *) value_ptr(parent, l->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(l->block));
+		*((__le64 *) value_ptr(parent, c->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(c->block));
+		*((__le64 *) value_ptr(parent, r->index, sizeof(__le64))) =
+			__cpu_to_le64(dm_block_location(r->block));
+
+		*key_ptr(parent, c->index) = center->keys[0];
+		*key_ptr(parent, r->index) = right->keys[0];
+	}
+}
+
+static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
+		      unsigned left_index)
+{
+	int r;
+	struct node *parent = dm_block_data(shadow_current(s));
+	struct child left, center, right;
+
+	/* FIXME: fill out an array? */
+	r = init_child(info, parent, left_index, &left);
+	if (r)
+		return r;
+
+	r = init_child(info, parent, left_index + 1, &center);
+	if (r) {
+		exit_child(info, &left);
+		return r;
+	}
+
+	r = init_child(info, parent, left_index + 2, &right);
+	if (r) {
+		exit_child(info, &left);
+		exit_child(info, &center);
+		return r;
+	}
+
+	__rebalance3(info, parent, &left, &center, &right);
+
+	r = exit_child(info, &left);
+	if (r) {
+		exit_child(info, &center);
+		exit_child(info, &right);
+		return r;
+	}
+
+	r = exit_child(info, &center);
+	if (r) {
+		exit_child(info, &right);
+		return r;
+	}
+
+	r = exit_child(info, &right);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+static int get_nr_entries(struct dm_transaction_manager *tm,
+			  dm_block_t b, uint32_t *result)
+{
+	int r;
+	struct dm_block *block;
+	struct node *c;
+
+	r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
+	if (r)
+		return r;
+
+	c = dm_block_data(block);
+	*result = __le32_to_cpu(c->header.nr_entries);
+
+	return dm_tm_unlock(tm, block);
+}
+
+static int rebalance_children(struct shadow_spine *s,
+			      struct dm_btree_info *info, uint64_t key)
+{
+	int i, r, has_left_sibling, has_right_sibling;
+	uint32_t child_entries;
+	struct node *n;
+
+	n = dm_block_data(shadow_current(s));
+
+	if (__le32_to_cpu(n->header.nr_entries) == 1) {
+		struct dm_block *child;
+		dm_block_t b = value64(n, 0);
+
+		r = dm_tm_read_lock(info->tm, b, &btree_node_validator, &child);
+		if (r)
+			return r;
+
+		memcpy(n, dm_block_data(child),
+		       dm_bm_block_size(dm_tm_get_bm(info->tm)));
+		r = dm_tm_unlock(info->tm, child);
+		dm_tm_dec(info->tm, dm_block_location(child));
+
+	} else {
+		i = lower_bound(n, key);
+
+		if (i < 0)
+			return -ENODATA;
+
+		r = get_nr_entries(info->tm, value64(n, i), &child_entries);
+		if (r)
+			return r;
+
+		if (child_entries > del_threshold(n))
+			return 0;
+
+		has_left_sibling = i > 0 ? 1 : 0;
+		has_right_sibling =
+			(i >= (__le32_to_cpu(n->header.nr_entries) - 1)) ? 0 : 1;
+
+		if (!has_left_sibling)
+			r = rebalance2(s, info, i);
+
+		else if (!has_right_sibling)
+			r = rebalance2(s, info, i - 1);
+
+		else
+			r = rebalance3(s, info, i - 1);
+	}
+
+	return r;
+}
+
+static int do_leaf(struct node *n, uint64_t key, unsigned *index)
+{
+	int i = lower_bound(n, key);
+
+	if ((i < 0) ||
+	    (i >= __le32_to_cpu(n->header.nr_entries)) ||
+	    (__le64_to_cpu(n->keys[i]) != key))
+		return -ENODATA;
+
+	*index = i;
+	return 0;
+}
+
+/*
+ * Prepares for removal from one level of the hierarchy.  The caller must
+ * actually call delete_at() to remove the entry at index.
+ */
+static int remove_raw(struct shadow_spine *s, struct dm_btree_info *info,
+		      struct dm_btree_value_type *vt, dm_block_t root,
+		      uint64_t key, unsigned *index)
+{
+	int i = *index, inc, r;
+	struct node *n;
+
+	for (;;) {
+		r = shadow_step(s, root, vt, &inc);
+		if (r < 0)
+			break;
+
+		/* We have to patch up the parent node, ugly, but I don't
+		 * see a way to do this automatically as part of the spine
+		 * op. */
+		if (shadow_parent(s)) {
+			__le64 location = __cpu_to_le64(dm_block_location(shadow_current(s)));
+			memcpy(value_ptr(dm_block_data(shadow_parent(s)), i, sizeof(uint64_t)),
+			       &location, sizeof(__le64));
+		}
+
+		n = dm_block_data(shadow_current(s));
+		if (inc)
+			inc_children(info->tm, n, vt);
+
+		if (__le32_to_cpu(n->header.flags) & LEAF_NODE)
+			return do_leaf(n, key, index);
+
+		else {
+			r = rebalance_children(s, info, key);
+			if (r)
+				break;
+
+			n = dm_block_data(shadow_current(s));
+			if (__le32_to_cpu(n->header.flags) & LEAF_NODE)
+				return do_leaf(n, key, index);
+
+			i = lower_bound(n, key);
+
+			/* We know the key is present, or else
+			 * rebalance_children would have returned
+			 * -ENODATA
+			 */
+			root = value64(n, i);
+		}
+	}
+
+	return r;
+}
+
+int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, dm_block_t *new_root)
+{
+	unsigned level, last_level = info->levels - 1;
+	int index = 0, r = 0;
+	struct shadow_spine spine;
+	struct node *n;
+
+	init_shadow_spine(&spine, info);
+	for (level = 0; level < info->levels; level++) {
+		r = remove_raw(&spine, info,
+			       (level == last_level ?
+				&info->value_type : &le64_type_),
+			       root, keys[level], &index);
+		if (r < 0)
+			break;
+
+		n = dm_block_data(shadow_current(&spine));
+		if (level == last_level) {
+			BUG_ON(index < 0 ||
+			       index >= __le32_to_cpu(n->header.nr_entries));
+			if (info->value_type.dec)
+				info->value_type.dec(info->value_type.context,
+						     value_ptr(n, index, info->value_type.size));
+			delete_at(n, index, info->value_type.size);
+			r = 0;
+			*new_root = shadow_root(&spine);
+
+		} else
+			root = value64(n, index);
+	}
+	exit_shadow_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_remove);
+
+/*----------------------------------------------------------------*/
diff --git a/drivers/md/persistent-data/dm-btree-spine.c b/drivers/md/persistent-data/dm-btree-spine.c
new file mode 100644
index 0000000..cacdfda
--- /dev/null
+++ b/drivers/md/persistent-data/dm-btree-spine.c
@@ -0,0 +1,192 @@
+#include "dm-btree-internal.h"
+
+#include <linux/device-mapper.h> /* For DMERR */
+
+#define DM_MSG_PREFIX "btree spine"
+
+/*----------------------------------------------------------------*/
+
+static void node_prepare_for_write(struct dm_block_validator *v,
+				   struct dm_block *b,
+				   size_t block_size)
+{
+	struct node_header *node = dm_block_data(b);
+
+	node->blocknr = __cpu_to_le64(dm_block_location(b));
+	node->csum = dm_block_csum_data(&node->flags,
+					block_size - sizeof(u32));
+}
+
+static int node_check(struct dm_block_validator *v,
+		      struct dm_block *b,
+		      size_t block_size)
+{
+	struct node_header *node = dm_block_data(b);
+	__le32 csum;
+
+	if (dm_block_location(b) != __le64_to_cpu(node->blocknr)) {
+		DMERR("node_check failed blocknr %llu wanted %llu",
+		      __le64_to_cpu(node->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum = dm_block_csum_data(&node->flags,
+				  block_size - sizeof(u32));
+	if (csum != node->csum) {
+		DMERR("node_check failed csum %u wanted %u",
+		      __le32_to_cpu(csum), __le32_to_cpu(node->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+struct dm_block_validator btree_node_validator = {
+	.name = "btree_node",
+	.prepare_for_write = node_prepare_for_write,
+	.check = node_check
+};
+
+/*----------------------------------------------------------------*/
+
+int bn_read_lock(struct dm_btree_info *info, dm_block_t b,
+		 struct dm_block **result)
+{
+	return dm_tm_read_lock(info->tm, b, &btree_node_validator, result);
+}
+
+int bn_shadow(struct dm_btree_info *info, dm_block_t orig,
+	      struct dm_btree_value_type *vt,
+	      struct dm_block **result, int *inc)
+{
+	int r;
+
+	r = dm_tm_shadow_block(info->tm, orig, &btree_node_validator,
+			       result, inc);
+	if (r == 0 && *inc)
+		inc_children(info->tm, dm_block_data(*result), vt);
+
+	return r;
+}
+
+int bn_new_block(struct dm_btree_info *info, struct dm_block **result)
+{
+	return dm_tm_new_block(info->tm, &btree_node_validator, result);
+}
+
+int bn_unlock(struct dm_btree_info *info, struct dm_block *b)
+{
+	return dm_tm_unlock(info->tm, b);
+}
+
+/*----------------------------------------------------------------*/
+
+void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info)
+{
+	s->info = info;
+	s->count = 0;
+	s->nodes[0] = NULL;
+	s->nodes[1] = NULL;
+}
+
+int exit_ro_spine(struct ro_spine *s)
+{
+	int r = 0, i;
+
+	for (i = 0; i < s->count; i++) {
+		int r2 = bn_unlock(s->info, s->nodes[i]);
+		if (r2 < 0)
+			r = r2;
+	}
+
+	return r;
+}
+
+int ro_step(struct ro_spine *s, dm_block_t new_child)
+{
+	int r;
+
+	if (s->count == 2) {
+		r = bn_unlock(s->info, s->nodes[0]);
+		if (r < 0)
+			return r;
+		s->nodes[0] = s->nodes[1];
+		s->count--;
+	}
+
+	r = bn_read_lock(s->info, new_child, s->nodes + s->count);
+	if (r == 0)
+		s->count++;
+
+	return r;
+}
+
+struct node *ro_node(struct ro_spine *s)
+{
+	struct dm_block *n;
+	BUG_ON(!s->count);
+	n = s->nodes[s->count - 1];
+	return dm_block_data(n);
+}
+
+/*----------------------------------------------------------------*/
+
+void init_shadow_spine(struct shadow_spine *s, struct dm_btree_info *info)
+{
+	s->info = info;
+	s->count = 0;
+}
+
+int exit_shadow_spine(struct shadow_spine *s)
+{
+	int r = 0, i;
+
+	for (i = 0; i < s->count; i++) {
+		int r2 = bn_unlock(s->info, s->nodes[i]);
+		if (r2 < 0)
+			r = r2;
+	}
+
+	return r;
+}
+
+int shadow_step(struct shadow_spine *s, dm_block_t b,
+		struct dm_btree_value_type *vt, int *inc)
+{
+	int r;
+
+	if (s->count == 2) {
+		r = bn_unlock(s->info, s->nodes[0]);
+		if (r < 0)
+			return r;
+		s->nodes[0] = s->nodes[1];
+		s->count--;
+	}
+
+	r = bn_shadow(s->info, b, vt, s->nodes + s->count, inc);
+	if (r == 0) {
+		if (s->count == 0)
+			s->root = dm_block_location(s->nodes[0]);
+
+		s->count++;
+	}
+
+	return r;
+}
+
+struct dm_block *shadow_current(struct shadow_spine *s)
+{
+	return s->nodes[s->count - 1];
+}
+
+struct dm_block *shadow_parent(struct shadow_spine *s)
+{
+	return s->count == 2 ? s->nodes[0] : NULL;
+}
+
+int shadow_root(struct shadow_spine *s)
+{
+	return s->root;
+}
+
+/*----------------------------------------------------------------*/
diff --git a/drivers/md/persistent-data/dm-btree.c b/drivers/md/persistent-data/dm-btree.c
new file mode 100644
index 0000000..7ec3dcd
--- /dev/null
+++ b/drivers/md/persistent-data/dm-btree.c
@@ -0,0 +1,871 @@
+#include "dm-btree-internal.h"
+#include "dm-space-map.h"
+
+/*----------------------------------------------------------------
+ * Array manipulation
+ *--------------------------------------------------------------*/
+static void array_insert(void *base, size_t elt_size, unsigned nr_elts,
+			 unsigned index, void *elt)
+{
+	if (index < nr_elts)
+		memmove(base + (elt_size * (index + 1)),
+			base + (elt_size * index),
+			(nr_elts - index) * elt_size);
+	memcpy(base + (elt_size * index), elt, elt_size);
+}
+
+/*----------------------------------------------------------------*/
+
+/* makes the assumption that no two keys are the same. */
+static int bsearch(struct node *n, uint64_t key, int want_hi)
+{
+	int lo = -1, hi = __le32_to_cpu(n->header.nr_entries);
+
+	while (hi - lo > 1) {
+		int mid = lo + ((hi - lo) / 2);
+		uint64_t mid_key = __le64_to_cpu(n->keys[mid]);
+
+		if (mid_key == key)
+			return mid;
+
+		if (mid_key < key)
+			lo = mid;
+		else
+			hi = mid;
+	}
+
+	return want_hi ? hi : lo;
+}
+
+int lower_bound(struct node *n, uint64_t key)
+{
+	return bsearch(n, key, 0);
+}
+
+int upper_bound(struct node *n, uint64_t key)
+{
+	return bsearch(n, key, 1);
+}
+
+void inc_children(struct dm_transaction_manager *tm, struct node *n,
+		  struct dm_btree_value_type *vt)
+{
+	unsigned i;
+	uint32_t nr_entries = __le32_to_cpu(n->header.nr_entries);
+
+	if (__le32_to_cpu(n->header.flags) & INTERNAL_NODE)
+		for (i = 0; i < nr_entries; i++)
+			dm_tm_inc(tm, value64(n, i));
+	else if (vt->inc)
+		for (i = 0; i < nr_entries; i++)
+			vt->inc(vt->context,
+				value_ptr(n, i, vt->size));
+}
+
+void insert_at(size_t value_size, struct node *node, unsigned index,
+	       uint64_t key, void *value)
+{
+	uint32_t nr_entries = __le32_to_cpu(node->header.nr_entries);
+
+	BUG_ON(index > nr_entries ||
+	       index >= __le32_to_cpu(node->header.max_entries));
+
+	array_insert(node->keys, sizeof(*node->keys), nr_entries, index, &key);
+	array_insert(value_base(node), value_size, nr_entries, index, value);
+	node->header.nr_entries = __cpu_to_le32(nr_entries + 1);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * We want 3n entries (for some n).  This works more nicely for repeated
+ * insert remove loops than (2n + 1).
+ */
+uint32_t calc_max_entries(size_t value_size, size_t block_size)
+{
+	uint32_t total, n;
+	size_t elt_size = sizeof(uint64_t) + value_size; /* key + value */
+
+	block_size -= sizeof(struct node_header);
+	total = block_size / elt_size;
+	n = total / 3;		/* rounds down */
+
+	return 3 * n;
+}
+
+int dm_btree_empty(struct dm_btree_info *info, dm_block_t *root)
+{
+	int r;
+	struct dm_block *b;
+	struct node *n;
+	size_t block_size;
+	uint32_t max_entries;
+
+	r = bn_new_block(info, &b);
+	if (r < 0)
+		return r;
+
+	block_size = dm_bm_block_size(dm_tm_get_bm(info->tm));
+	max_entries = calc_max_entries(info->value_type.size, block_size);
+
+	n = (struct node *) dm_block_data(b);
+	memset(n, 0, block_size);
+	n->header.flags = __cpu_to_le32(LEAF_NODE);
+	n->header.nr_entries = __cpu_to_le32(0);
+	n->header.max_entries =	__cpu_to_le32(max_entries);
+
+	*root = dm_block_location(b);
+	return bn_unlock(info, b);
+}
+EXPORT_SYMBOL_GPL(dm_btree_empty);
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Deletion uses a recursive algorithm, since we have limited stack space
+ * we explicitly manage our own stack on the heap.
+ */
+#define MAX_SPINE_DEPTH 64
+struct frame {
+	struct dm_block *b;
+	struct node *n;
+	unsigned level;
+	unsigned nr_children;
+	unsigned current_child;
+};
+
+struct del_stack {
+	struct dm_transaction_manager *tm;
+	int top;
+	struct frame spine[MAX_SPINE_DEPTH];
+};
+
+static void top_frame(struct del_stack *s, struct frame **f)
+{
+	BUG_ON(s->top < 0);
+	*f = s->spine + s->top;
+}
+
+static int unprocessed_frames(struct del_stack *s)
+{
+	return s->top >= 0;
+}
+
+static int push_frame(struct del_stack *s, dm_block_t b, unsigned level)
+{
+	int r;
+	uint32_t ref_count;
+
+	BUG_ON(s->top >= MAX_SPINE_DEPTH);
+
+	r = dm_tm_ref(s->tm, b, &ref_count);
+	if (r)
+		return r;
+
+	if (ref_count > 1)
+		/*
+		 * This is a shared node, so we can just decrement it's
+		 * reference counter and leave the children.
+		 */
+		dm_tm_dec(s->tm, b);
+
+	else {
+		struct frame *f = s->spine + ++s->top;
+
+		r = dm_tm_read_lock(s->tm, b, &btree_node_validator, &f->b);
+		if (r) {
+			s->top--;
+			return r;
+		}
+
+		f->n = dm_block_data(f->b);
+		f->level = level;
+		f->nr_children = __le32_to_cpu(f->n->header.nr_entries);
+		f->current_child = 0;
+	}
+
+	return 0;
+}
+
+static void pop_frame(struct del_stack *s)
+{
+	struct frame *f = s->spine + s->top--;
+
+	dm_tm_dec(s->tm, dm_block_location(f->b));
+	dm_tm_unlock(s->tm, f->b);
+}
+
+int dm_btree_del(struct dm_btree_info *info, dm_block_t root)
+{
+	struct del_stack *s;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+	s->tm = info->tm;
+	s->top = -1;
+
+	push_frame(s, root, 1);
+	while (unprocessed_frames(s)) {
+		int r;
+		uint32_t flags;
+		struct frame *f;
+		dm_block_t b;
+
+		top_frame(s, &f);
+
+		if (f->current_child >= f->nr_children) {
+			pop_frame(s);
+			continue;
+		}
+
+		flags = __le32_to_cpu(f->n->header.flags);
+		if (flags & INTERNAL_NODE) {
+			b = value64(f->n, f->current_child);
+			f->current_child++;
+			r = push_frame(s, b, f->level);
+			if (r)
+				goto bad;
+
+		} else if (f->level != (info->levels - 1)) {
+			b = value64(f->n, f->current_child);
+			f->current_child++;
+			r = push_frame(s, b, f->level + 1);
+			if (r)
+				goto bad;
+
+		} else {
+			if (info->value_type.dec) {
+				unsigned i;
+
+				for (i = 0; i < f->nr_children; i++)
+					info->value_type.dec(info->value_type.context,
+							     value_ptr(f->n, i, info->value_type.size));
+			}
+			f->current_child = f->nr_children;
+		}
+	}
+
+	return 0;
+
+bad:
+	/* what happens if we've deleted half a tree? */
+	return -1; /* FIXME: return error code rather than -1? */
+}
+EXPORT_SYMBOL_GPL(dm_btree_del);
+
+int dm_btree_del_gt(struct dm_btree_info *info, dm_block_t root, uint64_t *key,
+		    dm_block_t *new_root)
+{
+	/* FIXME: implement */
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_btree_del_gt);
+
+/*----------------------------------------------------------------*/
+
+static int btree_lookup_raw(struct ro_spine *s, dm_block_t block, uint64_t key,
+			    int (*search_fn)(struct node *, uint64_t),
+			    uint64_t *result_key, void *v, size_t value_size)
+{
+	int i, r;
+	uint32_t flags, nr_entries;
+
+	do {
+		r = ro_step(s, block);
+		if (r < 0)
+			return r;
+
+		i = search_fn(ro_node(s), key);
+
+		flags = __le32_to_cpu(ro_node(s)->header.flags);
+		nr_entries = __le32_to_cpu(ro_node(s)->header.nr_entries);
+		if (i < 0 || i >= nr_entries)
+			return -ENODATA;
+
+		if (flags & INTERNAL_NODE)
+			block = value64(ro_node(s), i);
+
+	} while (!(flags & LEAF_NODE));
+
+	*result_key = __le64_to_cpu(ro_node(s)->keys[i]);
+	memcpy(v, value_ptr(ro_node(s), i, value_size), value_size);
+
+	return 0;
+}
+
+int dm_btree_lookup(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, void *value)
+{
+	unsigned level, last_level = info->levels - 1;
+	int r;
+	uint64_t rkey;
+	__le64 internal_value;
+	struct ro_spine spine;
+
+	init_ro_spine(&spine, info);
+	for (level = 0; level < info->levels; level++) {
+		size_t size;
+		void *value_p;
+
+		if (level == last_level) {
+			value_p = value;
+			size = info->value_type.size;
+
+		} else {
+			value_p = &internal_value;
+			size = sizeof(uint64_t);
+		}
+
+		r = btree_lookup_raw(&spine, root, keys[level],
+				     lower_bound, &rkey,
+				     value_p, size);
+
+		if (r == 0) {
+			if (rkey != keys[level]) {
+				exit_ro_spine(&spine);
+				return -ENODATA;
+			}
+		} else {
+			exit_ro_spine(&spine);
+			return r;
+		}
+
+		root = __le64_to_cpu(internal_value);
+	}
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_lookup);
+
+int dm_btree_lookup_le(struct dm_btree_info *info, dm_block_t root,
+		       uint64_t *keys, uint64_t *key, void *value)
+{
+	unsigned level, last_level = info->levels - 1;
+	int r;
+	__le64 internal_value;
+	struct ro_spine spine;
+
+	init_ro_spine(&spine, info);
+	for (level = 0; level < info->levels; level++) {
+		size_t size;
+		void *value_p;
+
+		if (level == last_level) {
+			value_p = value;
+			size = info->value_type.size;
+
+		} else {
+			value_p = &internal_value;
+			size = sizeof(uint64_t);
+		}
+
+		r = btree_lookup_raw(&spine, root, keys[level],
+				     lower_bound, key,
+				     value_p, size);
+
+		if (r != 0) {
+			exit_ro_spine(&spine);
+			return r;
+		}
+
+		root = __le64_to_cpu(internal_value);
+	}
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_lookup_le);
+
+int dm_btree_lookup_ge(struct dm_btree_info *info, dm_block_t root,
+		       uint64_t *keys, uint64_t *key, void *value)
+{
+	unsigned level, last_level = info->levels - 1;
+	int r;
+	__le64 internal_value;
+	struct ro_spine spine;
+
+	init_ro_spine(&spine, info);
+	for (level = 0; level < info->levels; level++) {
+		size_t size;
+		void *value_p;
+
+		if (level == last_level) {
+			value_p = value;
+			size = info->value_type.size;
+
+		} else {
+			value_p = &internal_value;
+			size = sizeof(uint64_t);
+		}
+
+		r = btree_lookup_raw(&spine, root, keys[level],
+				     upper_bound, key,
+				     value_p, size);
+
+		if (r != 0) {
+			exit_ro_spine(&spine);
+			return r;
+		}
+
+		root = __le64_to_cpu(internal_value);
+	}
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_lookup_ge);
+
+/*
+ * Splits a node by creating a sibling node and shifting half the nodes
+ * contents across.  Assumes there is a parent node, and it has room for
+ * another child.
+ *
+ * Before:
+ *	  +--------+
+ *	  | Parent |
+ *	  +--------+
+ *	     |
+ *	     v
+ *	+----------+
+ *	| A ++++++ |
+ *	+----------+
+ *
+ *
+ * After:
+ *		+--------+
+ *		| Parent |
+ *		+--------+
+ *		  |	|
+ *		  v	+------+
+ *	    +---------+	       |
+ *	    | A* +++  |	       v
+ *	    +---------+	  +-------+
+ *			  | B +++ |
+ *			  +-------+
+ *
+ * Where A* is a shadow of A.
+ */
+static int btree_split_sibling(struct shadow_spine *s, dm_block_t root,
+			       unsigned parent_index, uint64_t key)
+{
+	int ret;
+	size_t size;
+	unsigned nr_left, nr_right;
+	struct dm_block *left, *right, *parent;
+	struct node *l, *r, *p;
+	__le64 location;
+
+	left = shadow_current(s);
+	BUG_ON(!left);
+
+	ret = bn_new_block(s->info, &right);
+	if (ret < 0)
+		return ret;
+
+	l = dm_block_data(left);
+	r = (struct node *) dm_block_data(right);
+
+	nr_left = __le32_to_cpu(l->header.nr_entries) / 2;
+	nr_right = __le32_to_cpu(l->header.nr_entries) - nr_left;
+
+	l->header.nr_entries = __cpu_to_le32(nr_left);
+
+	r->header.flags = l->header.flags;
+	r->header.nr_entries = __cpu_to_le32(nr_right);
+	r->header.max_entries = l->header.max_entries;
+	memcpy(r->keys, l->keys + nr_left, nr_right * sizeof(r->keys[0]));
+
+	size = __le32_to_cpu(l->header.flags) & INTERNAL_NODE ?
+		sizeof(uint64_t) : s->info->value_type.size;
+	memcpy(value_ptr(r, 0, size), value_ptr(l, nr_left, size),
+	       size * nr_right);
+
+	/* Patch up the parent */
+	parent = shadow_parent(s);
+	BUG_ON(!parent);
+
+	p = dm_block_data(parent);
+	location = __cpu_to_le64(dm_block_location(left));
+	memcpy(value_ptr(p, parent_index, sizeof(__le64)),
+	       &location, sizeof(__le64));
+
+	location = __cpu_to_le64(dm_block_location(right));
+	insert_at(sizeof(__le64), p, parent_index + 1,
+		  __le64_to_cpu(r->keys[0]), &location);
+
+	if (key < __le64_to_cpu(r->keys[0])) {
+		bn_unlock(s->info, right);
+		s->nodes[1] = left;
+	} else {
+		bn_unlock(s->info, left);
+		s->nodes[1] = right;
+	}
+
+	return 0;
+}
+
+/*
+ * Splits a node by creating two new children beneath the given node.
+ *
+ * Before:
+ *	  +----------+
+ *	  | A ++++++ |
+ *	  +----------+
+ *
+ *
+ * After:
+ *	+------------+
+ *	| A (shadow) |
+ *	+------------+
+ *	    |	|
+ *   +------+	+----+
+ *   |		     |
+ *   v		     v
+ * +-------+	 +-------+
+ * | B +++ |	 | C +++ |
+ * +-------+	 +-------+
+ */
+static int btree_split_beneath(struct shadow_spine *s, uint64_t key)
+{
+	int ret;
+	size_t size;
+	unsigned nr_left, nr_right;
+	struct dm_block *left, *right, *new_parent;
+	struct node *p, *l, *r;
+	__le64 val;
+
+	new_parent = shadow_current(s);
+	BUG_ON(!new_parent);
+
+	ret = bn_new_block(s->info, &left);
+	if (ret < 0)
+		return ret;
+
+	ret = bn_new_block(s->info, &right);
+	if (ret < 0) {
+		/* FIXME: put left */
+		return ret;
+	}
+
+	p = dm_block_data(new_parent);
+	l = (struct node *) dm_block_data(left);
+	r = (struct node *) dm_block_data(right);
+
+	nr_left = __le32_to_cpu(p->header.nr_entries) / 2;
+	nr_right = __le32_to_cpu(p->header.nr_entries) - nr_left;
+
+	l->header.flags = p->header.flags;
+	l->header.nr_entries = __cpu_to_le32(nr_left);
+	l->header.max_entries = p->header.max_entries;
+
+	r->header.flags = p->header.flags;
+	r->header.nr_entries = __cpu_to_le32(nr_right);
+	r->header.max_entries = p->header.max_entries;
+
+	memcpy(l->keys, p->keys, nr_left * sizeof(p->keys[0]));
+	memcpy(r->keys, p->keys + nr_left, nr_right * sizeof(p->keys[0]));
+
+	size = __le32_to_cpu(p->header.flags) & INTERNAL_NODE ?
+		sizeof(__le64) : s->info->value_type.size;
+	memcpy(value_ptr(l, 0, size), value_ptr(p, 0, size), nr_left * size);
+	memcpy(value_ptr(r, 0, size), value_ptr(p, nr_left, size),
+	       nr_right * size);
+
+	/* new_parent should just point to l and r now */
+	p->header.flags = __cpu_to_le32(INTERNAL_NODE);
+	p->header.nr_entries = __cpu_to_le32(2);
+
+	val = __cpu_to_le64(dm_block_location(left));
+	p->keys[0] = l->keys[0];
+	memcpy(value_ptr(p, 0, sizeof(__le64)), &val, sizeof(__le64));
+
+	val = __cpu_to_le64(dm_block_location(right));
+	p->keys[1] = r->keys[0];
+	memcpy(value_ptr(p, 1, sizeof(__le64)), &val, sizeof(__le64));
+
+	/*
+	 * rejig the spine.  This is ugly, since it knows too
+	 * much about the spine
+	 */
+	if (s->nodes[0] != new_parent) {
+		bn_unlock(s->info, s->nodes[0]);
+		s->nodes[0] = new_parent;
+	}
+	if (key < __le64_to_cpu(r->keys[0])) {
+		bn_unlock(s->info, right);
+		s->nodes[1] = left;
+	} else {
+		bn_unlock(s->info, left);
+		s->nodes[1] = right;
+	}
+	s->count = 2;
+
+	return 0;
+}
+
+static int btree_insert_raw(struct shadow_spine *s, dm_block_t root,
+			    struct dm_btree_value_type *vt,
+			    uint64_t key, unsigned *index)
+{
+	int r, i = *index, inc, top = 1;
+	struct node *node;
+
+	for (;;) {
+		r = shadow_step(s, root, vt, &inc);
+		if (r < 0) {
+			/* FIXME: unpick any allocations */
+			return r;
+		}
+
+		node = dm_block_data(shadow_current(s));
+		if (inc)
+			inc_children(s->info->tm, node, vt);
+
+		/*
+		 * We have to patch up the parent node, ugly, but I don't
+		 * see a way to do this automatically as part of the spine
+		 * op.
+		 */
+		if (shadow_parent(s) && i >= 0) { /* FIXME: second clause unness. */
+			__le64 location = __cpu_to_le64(dm_block_location(shadow_current(s)));
+			memcpy(value_ptr(dm_block_data(shadow_parent(s)), i, sizeof(uint64_t)),
+			       &location, sizeof(__le64));
+		}
+
+		BUG_ON(!shadow_current(s));
+		node = dm_block_data(shadow_current(s));
+
+		if (node->header.nr_entries == node->header.max_entries) {
+			if (top)
+				r = btree_split_beneath(s, key);
+			else
+				r = btree_split_sibling(s, root, i, key);
+
+			if (r < 0)
+				return r;
+		}
+
+		BUG_ON(!shadow_current(s));
+		node = dm_block_data(shadow_current(s));
+
+		i = lower_bound(node, key);
+
+		if (__le32_to_cpu(node->header.flags) & LEAF_NODE)
+			break;
+
+		if (i < 0) {
+			/* change the bounds on the lowest key */
+			node->keys[0] = __cpu_to_le64(key);
+			i = 0;
+		}
+
+		root = value64(node, i);
+		top = 0;
+	}
+
+	if (i < 0 || __le64_to_cpu(node->keys[i]) != key)
+		i++;
+
+	/* we're about to overwrite this value, so undo the increment for it */
+	/* FIXME: shame that inc information is leaking outside the spine.
+	 * Plus inc is just plain wrong in the event of a split */
+	if (__le64_to_cpu(node->keys[i]) == key && inc)
+		if (vt->dec)
+			vt->dec(vt->context, value_ptr(node, i, vt->size));
+
+	*index = i;
+	return 0;
+}
+
+static int insert(struct dm_btree_info *info, dm_block_t root,
+		  uint64_t *keys, void *value, dm_block_t *new_root,
+		  int *inserted)
+{
+	int r, need_insert;
+	unsigned level, index = -1, last_level = info->levels - 1;
+	dm_block_t *block = &root;
+	struct shadow_spine spine;
+	struct node *n;
+	struct dm_btree_value_type le64_type;
+
+	le64_type.context = NULL;
+	le64_type.size = sizeof(__le64);
+	le64_type.inc = NULL;
+	le64_type.dec = NULL;
+	le64_type.equal = NULL;
+
+	init_shadow_spine(&spine, info);
+
+	for (level = 0; level < info->levels; level++) {
+		r = btree_insert_raw(&spine, *block,
+				     (level == last_level ?
+				      &info->value_type : &le64_type),
+				     keys[level], &index);
+		if (r < 0) {
+			exit_shadow_spine(&spine);
+			/* FIXME: avoid block leaks */
+			return r;
+		}
+
+		BUG_ON(!shadow_current(&spine));
+		n = dm_block_data(shadow_current(&spine));
+		need_insert = ((index >= __le32_to_cpu(n->header.nr_entries)) ||
+			       (__le64_to_cpu(n->keys[index]) != keys[level]));
+
+		if (level == last_level) {
+			if (need_insert) {
+				if (inserted)
+					*inserted = 1;
+
+				insert_at(info->value_type.size, n, index,
+					  keys[level], value);
+			} else {
+				if (inserted)
+					*inserted = 0;
+
+				if (info->value_type.dec &&
+				    (!info->value_type.equal ||
+				     !info->value_type.equal(
+					     info->value_type.context,
+					     value_ptr(n, index, info->value_type.size),
+					     value))) {
+					info->value_type.dec(info->value_type.context,
+					     value_ptr(n, index, info->value_type.size));
+				}
+				memcpy(value_ptr(n, index, info->value_type.size),
+				       value, info->value_type.size);
+			}
+		} else {
+			if (need_insert) {
+				dm_block_t new_tree;
+				r = dm_btree_empty(info, &new_tree);
+				if (r < 0) {
+					/* FIXME: avoid block leaks */
+					exit_shadow_spine(&spine);
+					return r;
+				}
+
+				insert_at(sizeof(uint64_t), n, index,
+					  keys[level], &new_tree);
+			}
+		}
+
+		if (level < last_level)
+			block = value_ptr(n, index, sizeof(uint64_t));
+	}
+
+	*new_root = shadow_root(&spine);
+	exit_shadow_spine(&spine);
+
+	return 0;
+}
+
+
+int dm_btree_insert(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, void *value, dm_block_t *new_root)
+{
+	return insert(info, root, keys, value, new_root, NULL);
+}
+EXPORT_SYMBOL_GPL(dm_btree_insert);
+
+int dm_btree_insert_notify(struct dm_btree_info *info, dm_block_t root,
+			   uint64_t *keys, void *value, dm_block_t *new_root,
+			   int *inserted)
+{
+	return insert(info, root, keys, value, new_root, inserted);
+}
+EXPORT_SYMBOL_GPL(dm_btree_insert_notify);
+
+/*----------------------------------------------------------------*/
+
+int dm_btree_clone(struct dm_btree_info *info, dm_block_t root,
+		   dm_block_t *clone)
+{
+	int r;
+	struct dm_block *b, *orig_b;
+	struct node *b_node, *orig_node;
+
+	/* Copy the root node */
+	r = bn_new_block(info, &b);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_read_lock(info->tm, root, &btree_node_validator, &orig_b);
+	if (r < 0) {
+		dm_block_t location = dm_block_location(b);
+
+		bn_unlock(info, b);
+		dm_tm_dec(info->tm, location);
+	}
+
+	*clone = dm_block_location(b);
+	b_node = (struct node *) dm_block_data(b);
+	orig_node = dm_block_data(orig_b);
+
+	memcpy(b_node, orig_node,
+	       dm_bm_block_size(dm_tm_get_bm(info->tm)));
+	dm_tm_unlock(info->tm, orig_b);
+	inc_children(info->tm, b_node, &info->value_type);
+	dm_tm_unlock(info->tm, b);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_btree_clone);
+
+/*----------------------------------------------------------------*/
+
+static int find_highest_key(struct ro_spine *s, dm_block_t block,
+			    uint64_t *result_key, dm_block_t *next_block)
+{
+	int i, r;
+	uint32_t flags;
+
+	do {
+		r = ro_step(s, block);
+		if (r < 0)
+			return r;
+
+		flags = __le32_to_cpu(ro_node(s)->header.flags);
+		i = __le32_to_cpu(ro_node(s)->header.nr_entries);
+		if (i == 0)
+			return -ENODATA;
+		else
+			i--;
+
+		*result_key = __le64_to_cpu(ro_node(s)->keys[i]);
+		if (next_block || flags & INTERNAL_NODE)
+			block = value64(ro_node(s), i);
+
+	} while (flags & INTERNAL_NODE);
+
+	if (next_block)
+		*next_block = block;
+	return 0;
+}
+
+int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
+			      uint64_t *result_keys)
+{
+	int r = 0, count = 0, level;
+	struct ro_spine spine;
+
+	init_ro_spine(&spine, info);
+	for (level = 0; level < info->levels; level++) {
+		r = find_highest_key(&spine, root, result_keys + level,
+				     level == info->levels - 1 ? NULL : &root);
+		if (r == -ENODATA) {
+			r = 0;
+			break;
+
+		} else if (r)
+			break;
+
+		count++;
+	}
+	exit_ro_spine(&spine);
+
+	return r ? r : count;
+}
+EXPORT_SYMBOL_GPL(dm_btree_find_highest_key);
diff --git a/drivers/md/persistent-data/dm-btree.h b/drivers/md/persistent-data/dm-btree.h
new file mode 100644
index 0000000..3128382
--- /dev/null
+++ b/drivers/md/persistent-data/dm-btree.h
@@ -0,0 +1,146 @@
+#ifndef DM_BTREE_H
+#define DM_BTREE_H
+
+#include "dm-transaction-manager.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Manipulates hierarchical B+ trees with 64bit keys and arbitrary sized
+ * values.
+ */
+
+/*
+ * The btree needs some knowledge about the values stored within it.  This
+ * is provided by a |btree_value_type| structure.
+ */
+struct dm_btree_value_type {
+	void *context;
+
+	/*
+	 * The size in bytes of each value.
+	 */
+	uint32_t size;
+
+	/*
+	 * Any of these methods can be safely set to NULL if you do not
+	 * need this feature.
+	 */
+
+	/*
+	 * The btree is making a duplicate of the value, for instance
+	 * because previously shared btree nodes have now diverged.  The
+	 * |value| argument is the new copy, the copy function may modify
+	 * it.  Probably it just wants to increment a reference count
+	 * somewhere.  This method is _not_ called for insertion of a new
+	 * value, it's assumed the ref count is already 1.
+	 */
+	void (*inc)(void *context, void *value);
+
+	/*
+	 * This value is being deleted.  The btree takes care of freeing
+	 * the memory pointed to by |value|.  Often the |del| function just
+	 * needs to decrement a reference count somewhere.
+	 */
+	void (*dec)(void *context, void *value);
+
+	/*
+	 * An test for equality between two values.  When a value is
+	 * overwritten with a new one the old one has the |dec| method
+	 * called, _unless_ the new and old value are deemed equal.
+	 */
+	int (*equal)(void *context, void *value1, void *value2);
+};
+
+/*
+ * The |btree_info| structure describes the shape and contents of a btree.
+ */
+struct dm_btree_info {
+	struct dm_transaction_manager *tm;
+
+	/* number of nested btrees (not the depth of a single tree). */
+	unsigned levels;
+	struct dm_btree_value_type value_type;
+};
+
+/* Set up an empty tree.  O(1). */
+int dm_btree_empty(struct dm_btree_info *info, dm_block_t *root);
+
+/*
+ * Delete a tree.  O(n) - this is the slow one!  It can also block, so
+ * please don't call it on an io path.
+ */
+int dm_btree_del(struct dm_btree_info *info, dm_block_t root);
+
+/*
+ * Delete part of a tree.  This is really specific to truncation of
+ * multisnap devs.  It only removes keys from the bottom level btree that
+ * are greater than key[info->levels - 1].
+ */
+int dm_btree_del_gt(struct dm_btree_info *info, dm_block_t root, uint64_t *key,
+		    dm_block_t *new_root);
+
+/*
+ * All the lookup functions return -ENODATA if the key cannot be found.
+ */
+
+/* Tries to find a key that matches exactly.  O(ln(n)) */
+int dm_btree_lookup(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, void *value);
+
+/*
+ * Find the greatest key that is less than or equal to that requested.  A
+ * ENODATA result indicates the key would appear in front of all (possibly
+ * zero) entries.  O(ln(n))
+ */
+int dm_btree_lookup_le(struct dm_btree_info *info, dm_block_t root,
+		       uint64_t *keys, uint64_t *rkey, void *value);
+
+/*
+ * Find the least key that is greater than or equal to that requested.
+ * ENODATA indicates all the keys are below.  O(ln(n))
+ */
+int dm_btree_lookup_ge(struct dm_btree_info *info, dm_block_t root,
+		       uint64_t *keys, uint64_t *rkey, void *value);
+
+/*
+ * Insertion (or overwrite an existing value).
+ * O(ln(n))
+ */
+int dm_btree_insert(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, void *value, dm_block_t *new_root);
+
+/*
+ * A variant of insert that indicates whether it actually inserted or just
+ * overwrote.  Useful if you're keeping track of the number of entries in a
+ * tree.
+ */
+int dm_btree_insert_notify(struct dm_btree_info *info, dm_block_t root,
+			   uint64_t *keys, void *value, dm_block_t *new_root,
+			   int *inserted);
+
+/*
+ * Remove a key if present.  This doesn't remove empty sub trees.  Normally
+ * subtrees represent a separate entity, like a snapshot map, so this is
+ * correct behaviour.
+ * O(ln(n)).
+ * Returns ENODATA if the key isn't present.
+ */
+int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, dm_block_t *new_root);
+
+/* Clone a tree. O(1) */
+int dm_btree_clone(struct dm_btree_info *info, dm_block_t root,
+		   dm_block_t *clone);
+
+/*
+ * Returns < 0 on failure.  Otherwise the number of key entries that have
+ * been filled out.  Remember trees can have zero entries, and as such have
+ * no highest key.
+ */
+int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
+			      uint64_t *result_keys);
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-pd-module.c b/drivers/md/persistent-data/dm-pd-module.c
new file mode 100644
index 0000000..eac6083
--- /dev/null
+++ b/drivers/md/persistent-data/dm-pd-module.c
@@ -0,0 +1,18 @@
+#include <linux/init.h>
+#include <linux/module.h>
+
+static int dm_persistent_data_init(void)
+{
+	return 0;
+}
+
+static void dm_persistent_data_exit(void)
+{
+}
+
+module_init(dm_persistent_data_init);
+module_exit(dm_persistent_data_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Joe Thornber");
+MODULE_DESCRIPTION("Immutable metadata library for dm");
diff --git a/drivers/md/persistent-data/dm-space-map-common.h b/drivers/md/persistent-data/dm-space-map-common.h
new file mode 100644
index 0000000..6635d5b
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map-common.h
@@ -0,0 +1,99 @@
+#ifndef DM_SPACE_MAP_COMMON_H
+#define DM_SPACE_MAP_COMMON_H
+
+#include "dm-transaction-manager.h"
+#include "dm-btree.h"
+
+/*----------------------------------------------------------------
+ * Low level disk format
+ *
+ * Bitmap btree
+ * ------------
+ *
+ * Each value stored in the btree is an index_entry.  This points to a
+ * block that is used as a bitmap.  Within the bitmap hold 2 bits per
+ * entry, which represent UNUSED = 0, REF_COUNT = 1, REF_COUNT = 2 and
+ * REF_COUNT = many.
+ *
+ * Refcount btree
+ * --------------
+ *
+ * Any entry that has a ref count higher than 2 gets entered in the ref
+ * count tree.  The leaf values for this tree is the 32bit ref count.
+ *--------------------------------------------------------------*/
+struct index_entry {
+	__le64 blocknr;
+	__le32 nr_free;
+	__le32 none_free_before;
+} __packed;
+
+
+#define MAX_METADATA_BITMAPS 255
+struct metadata_index {
+	__le32 csum;
+	__le32 padding;
+	__le64 blocknr;
+
+	struct index_entry index[MAX_METADATA_BITMAPS];
+} __packed;
+
+struct ll_disk {
+	struct dm_transaction_manager *tm;
+	struct dm_btree_info bitmap_info;
+	struct dm_btree_info ref_count_info;
+
+	uint32_t block_size;
+	uint32_t entries_per_block;
+	dm_block_t nr_blocks;
+	dm_block_t nr_allocated;
+	dm_block_t bitmap_root;	/* sometimes a btree root,
+				 * sometimes a simple index */
+	dm_block_t ref_count_root;
+
+	struct metadata_index mi;
+};
+
+struct sm_root {
+	__le64 nr_blocks;
+	__le64 nr_allocated;
+	__le64 bitmap_root;
+	__le64 ref_count_root;
+} __packed;
+
+#define ENTRIES_PER_BYTE 4
+
+struct bitmap_header {
+	__le32 csum;
+	__le32 not_used;
+	__le64 blocknr;
+} __packed;
+
+/*
+ * These bitops work on a blocks worth of bits.
+ */
+unsigned sm_lookup_bitmap(void *addr, unsigned b);
+void sm_set_bitmap(void *addr, unsigned b, unsigned val);
+int sm_find_free(void *addr, unsigned begin, unsigned end,
+		 unsigned *result);
+
+void *dm_bitmap_data(struct dm_block *b);
+
+extern struct dm_block_validator dm_sm_bitmap_validator;
+
+/*----------------------------------------------------------------*/
+
+static inline uint64_t div_up(uint64_t v, uint64_t n)
+{
+	uint64_t t = v;
+	uint64_t rem = do_div(t, n);
+	return t + (rem > 0 ? 1 : 0);
+}
+
+static inline uint64_t mod64(uint64_t n, uint64_t d)
+{
+	return do_div(n, d);
+}
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-space-map-disk.c b/drivers/md/persistent-data/dm-space-map-disk.c
new file mode 100644
index 0000000..a2f1b37
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map-disk.c
@@ -0,0 +1,624 @@
+#include "dm-space-map-common.h"
+#include "dm-space-map-disk.h"
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <asm-generic/bitops/le.h>
+#include <linux/device-mapper.h> /* For DMERR */
+
+#define DM_MSG_PREFIX "space map disk"
+
+/*----------------------------------------------------------------
+ * bitmap validator
+ *--------------------------------------------------------------*/
+static void bitmap_prepare_for_write(struct dm_block_validator *v,
+				     struct dm_block *b,
+				     size_t block_size)
+{
+	struct bitmap_header *header = dm_block_data(b);
+
+	header->blocknr = __cpu_to_le64(dm_block_location(b));
+	header->csum = dm_block_csum_data(&header->not_used,
+					  block_size - sizeof(u32));
+}
+
+static int bitmap_check(struct dm_block_validator *v,
+			struct dm_block *b,
+			size_t block_size)
+{
+	struct bitmap_header *header = dm_block_data(b);
+	__le32 csum;
+
+	if (dm_block_location(b) != __le64_to_cpu(header->blocknr)) {
+		DMERR("bitmap check failed blocknr %llu wanted %llu",
+		      __le64_to_cpu(header->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum = dm_block_csum_data(&header->not_used,
+				  block_size - sizeof(u32));
+	if (csum != header->csum) {
+		DMERR("bitmap check failed csum %u wanted %u",
+		      __le32_to_cpu(csum), __le32_to_cpu(header->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+struct dm_block_validator dm_sm_bitmap_validator = {
+	.name = "sm_bitmap",
+	.prepare_for_write = bitmap_prepare_for_write,
+	.check = bitmap_check
+};
+
+/*----------------------------------------------------------------*/
+
+#define ENTRIES_PER_WORD 32
+#define ENTRIES_SHIFT	5
+
+void *dm_bitmap_data(struct dm_block *b)
+{
+	return dm_block_data(b) + sizeof(struct bitmap_header);
+}
+
+#define WORD_MASK_LOW 0x5555555555555555ULL
+#define WORD_MASK_HIGH 0xAAAAAAAAAAAAAAAAULL
+#define WORD_MASK_ALL 0xFFFFFFFFFFFFFFFFULL
+
+static unsigned bitmap_word_used(void *addr, unsigned b)
+{
+	__le64 *words = (__le64 *) addr;
+	__le64 *w = words + (b >> ENTRIES_SHIFT);
+
+	uint64_t bits = __le64_to_cpu(*w);
+	return ((bits & WORD_MASK_LOW) == WORD_MASK_LOW ||
+		(bits & WORD_MASK_HIGH) == WORD_MASK_HIGH ||
+		(bits & WORD_MASK_ALL) == WORD_MASK_ALL);
+}
+
+unsigned sm_lookup_bitmap(void *addr, unsigned b)
+{
+	__le64 *words = (__le64 *) addr;
+	__le64 *w = words + (b >> ENTRIES_SHIFT);
+
+	b = (b & (ENTRIES_PER_WORD - 1)) << 1;
+	return ((!!test_bit_le(b, (void *) w) << 1)) |
+		(!!test_bit_le(b + 1, (void *) w));
+}
+
+
+void sm_set_bitmap(void *addr, unsigned b, unsigned val)
+{
+	__le64 *words = (__le64 *) addr;
+	__le64 *w = words + (b >> ENTRIES_SHIFT);
+
+	b = (b & (ENTRIES_PER_WORD - 1)) << 1;
+
+	if (val & 2)
+		__set_bit_le(b, (void *) w);
+	else
+		__clear_bit_le(b, (void *) w);
+
+	if (val & 1)
+		__set_bit_le(b + 1, (void *) w);
+	else
+		__clear_bit_le(b + 1, (void *) w);
+}
+
+int sm_find_free(void *addr, unsigned begin, unsigned end,
+		 unsigned *result)
+{
+	while (begin < end) {
+		if (!(begin & (ENTRIES_PER_WORD - 1)) &&
+		    bitmap_word_used(addr, begin)) {
+			begin += ENTRIES_PER_WORD;
+			continue;
+		}
+
+		if (sm_lookup_bitmap(addr, begin))
+			begin++;
+		else {
+			*result = begin;
+			return 0;
+		}
+	}
+
+	return -ENOSPC;
+}
+
+static int ll_init(struct ll_disk *io, struct dm_transaction_manager *tm)
+{
+	io->tm = tm;
+	io->bitmap_info.tm = tm;
+	io->bitmap_info.levels = 1;
+
+	/*
+	 * Because the new bitmap blocks are created via a shadow
+	 * operation, the old entry has already had it's reference count
+	 * decremented.	 So we don't need the btree to do any book
+	 * keeping.
+	 */
+	io->bitmap_info.value_type.size = sizeof(struct index_entry);
+	io->bitmap_info.value_type.inc = NULL;
+	io->bitmap_info.value_type.dec = NULL;
+	io->bitmap_info.value_type.equal = NULL;
+
+	io->ref_count_info.tm = tm;
+	io->ref_count_info.levels = 1;
+	io->ref_count_info.value_type.size = sizeof(uint32_t);
+	io->ref_count_info.value_type.inc = NULL;
+	io->ref_count_info.value_type.dec = NULL;
+	io->ref_count_info.value_type.equal = NULL;
+
+	io->block_size = dm_bm_block_size(dm_tm_get_bm(tm));
+
+	if (io->block_size > (1 << 30)) {
+		DMERR("block size too big to hold bitmaps");
+		return -EINVAL;
+	}
+	io->entries_per_block = (io->block_size - sizeof(struct bitmap_header)) *
+		ENTRIES_PER_BYTE;
+	io->nr_blocks = 0;
+	io->bitmap_root = 0;
+	io->ref_count_root = 0;
+
+	return 0;
+}
+
+static int ll_new(struct ll_disk *io, struct dm_transaction_manager *tm)
+{
+	int r;
+
+	r = ll_init(io, tm);
+	if (r < 0)
+		return r;
+
+	io->nr_blocks = 0;
+	io->nr_allocated = 0;
+	r = dm_btree_empty(&io->bitmap_info, &io->bitmap_root);
+	if (r < 0)
+		return r;
+
+	r = dm_btree_empty(&io->ref_count_info, &io->ref_count_root);
+	if (r < 0) {
+		dm_btree_del(&io->bitmap_info, io->bitmap_root);
+		return r;
+	}
+
+	return 0;
+}
+
+static int ll_extend(struct ll_disk *io, dm_block_t extra_blocks)
+{
+	int r;
+	dm_block_t i, nr_blocks;
+	unsigned old_blocks, blocks;
+
+	nr_blocks = io->nr_blocks + extra_blocks;
+	old_blocks = div_up(io->nr_blocks, io->entries_per_block);
+	blocks = div_up(nr_blocks, io->entries_per_block);
+	for (i = old_blocks; i < blocks; i++) {
+		struct dm_block *b;
+		struct index_entry idx;
+
+		r = dm_tm_new_block(io->tm, &dm_sm_bitmap_validator, &b);
+		if (r < 0)
+			return r;
+		idx.blocknr = __cpu_to_le64(dm_block_location(b));
+
+		r = dm_tm_unlock(io->tm, b);
+		if (r < 0)
+			return r;
+
+		idx.nr_free = __cpu_to_le32(io->entries_per_block);
+		idx.none_free_before = 0;
+
+		r = dm_btree_insert(&io->bitmap_info, io->bitmap_root,
+				    &i, &idx, &io->bitmap_root);
+		if (r < 0)
+			return r;
+	}
+
+	io->nr_blocks = nr_blocks;
+	return 0;
+}
+
+static int ll_open(struct ll_disk *ll, struct dm_transaction_manager *tm,
+		   void *root, size_t len)
+{
+	int r;
+	struct sm_root *smr = (struct sm_root *) root;
+
+	if (len < sizeof(struct sm_root)) {
+		DMERR("sm_disk root too small");
+		return -ENOMEM;
+	}
+
+	r = ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->nr_blocks = __le64_to_cpu(smr->nr_blocks);
+	ll->nr_allocated = __le64_to_cpu(smr->nr_allocated);
+	ll->bitmap_root = __le64_to_cpu(smr->bitmap_root);
+	ll->ref_count_root = __le64_to_cpu(smr->ref_count_root);
+
+	return 0;
+}
+
+static int ll_lookup_bitmap(struct ll_disk *io, dm_block_t b, uint32_t *result)
+{
+	int r;
+	dm_block_t index = b;
+	struct index_entry ie;
+	struct dm_block *blk;
+
+	do_div(index, io->entries_per_block);
+	r = dm_btree_lookup(&io->bitmap_info, io->bitmap_root, &index, &ie);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_read_lock(io->tm, __le64_to_cpu(ie.blocknr),
+			    &dm_sm_bitmap_validator, &blk);
+	if (r < 0)
+		return r;
+	*result = sm_lookup_bitmap(dm_bitmap_data(blk),
+				   mod64(b, io->entries_per_block));
+	return dm_tm_unlock(io->tm, blk);
+}
+
+static int ll_lookup(struct ll_disk *io, dm_block_t b, uint32_t *result)
+{
+	int r = ll_lookup_bitmap(io, b, result);
+
+	if (r)
+		return r;
+
+	if (*result == 3) {
+		__le32 le_rc;
+		r = dm_btree_lookup(&io->ref_count_info, io->ref_count_root,
+				    &b, &le_rc);
+		if (r < 0)
+			return r;
+
+		*result = __le32_to_cpu(le_rc);
+	}
+
+	return r;
+}
+
+static int ll_find_free_block(struct ll_disk *io, dm_block_t begin,
+			      dm_block_t end, dm_block_t *result)
+{
+	int r;
+	struct index_entry ie;
+	dm_block_t i, index_begin = begin;
+	dm_block_t index_end = div_up(end, io->entries_per_block);
+
+	begin = do_div(index_begin, io->entries_per_block);
+	for (i = index_begin; i < index_end; i++, begin = 0) {
+		r = dm_btree_lookup(&io->bitmap_info, io->bitmap_root, &i, &ie);
+		if (r < 0)
+			return r;
+
+		if (__le32_to_cpu(ie.nr_free) > 0) {
+			struct dm_block *blk;
+			unsigned position;
+			uint32_t bit_end;
+
+			r = dm_tm_read_lock(io->tm, __le64_to_cpu(ie.blocknr),
+					    &dm_sm_bitmap_validator, &blk);
+			if (r < 0)
+				return r;
+
+			bit_end = (i == index_end - 1) ?
+				mod64(end, io->entries_per_block) : io->entries_per_block;
+
+			r = sm_find_free(dm_bitmap_data(blk),
+					 max((unsigned)begin,
+					     (unsigned)__le32_to_cpu(ie.none_free_before)),
+					 bit_end, &position);
+			if (r < 0) {
+				dm_tm_unlock(io->tm, blk);
+				continue;
+			}
+
+			r = dm_tm_unlock(io->tm, blk);
+			if (r < 0)
+				return r;
+
+			*result = i * io->entries_per_block + (dm_block_t) position;
+			return 0;
+		}
+	}
+
+	return -ENOSPC;
+}
+
+static int ll_insert(struct ll_disk *io, dm_block_t b, uint32_t ref_count)
+{
+	int r;
+	uint32_t bit, old;
+	struct dm_block *nb;
+	dm_block_t index = b;
+	struct index_entry ie;
+	void *bm;
+	int inc;
+
+	do_div(index, io->entries_per_block);
+	r = dm_btree_lookup(&io->bitmap_info, io->bitmap_root, &index, &ie);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_shadow_block(io->tm, __le64_to_cpu(ie.blocknr),
+			       &dm_sm_bitmap_validator, &nb, &inc);
+	if (r < 0) {
+		DMERR("dm_tm_shadow_block() failed");
+		return r;
+	}
+	ie.blocknr = __cpu_to_le64(dm_block_location(nb));
+
+	bm = dm_bitmap_data(nb);
+	bit = mod64(b, io->entries_per_block);
+	old = sm_lookup_bitmap(bm, bit);
+
+	if (ref_count <= 2) {
+		sm_set_bitmap(bm, bit, ref_count);
+
+		if (old > 2) {
+			r = dm_btree_remove(&io->ref_count_info, io->ref_count_root,
+					    &b, &io->ref_count_root);
+			if (r) {
+				dm_tm_unlock(io->tm, nb);
+				return r;
+			}
+		}
+	} else {
+		__le32 le_rc = __cpu_to_le32(ref_count);
+		sm_set_bitmap(bm, bit, 3);
+		r = dm_btree_insert(&io->ref_count_info, io->ref_count_root,
+				    &b, &le_rc, &io->ref_count_root);
+		if (r < 0) {
+			dm_tm_unlock(io->tm, nb);
+			DMERR("ref count insert failed");
+			return r;
+		}
+	}
+
+	r = dm_tm_unlock(io->tm, nb);
+	if (r < 0)
+		return r;
+
+	if (ref_count && !old) {
+		io->nr_allocated++;
+		ie.nr_free = __cpu_to_le32(__le32_to_cpu(ie.nr_free) - 1);
+		if (__le32_to_cpu(ie.none_free_before) == b)
+			ie.none_free_before = __cpu_to_le32(b + 1);
+
+	} else if (old && !ref_count) {
+		io->nr_allocated--;
+		ie.nr_free = __cpu_to_le32(__le32_to_cpu(ie.nr_free) + 1);
+		ie.none_free_before = __cpu_to_le32(min((dm_block_t) __le32_to_cpu(ie.none_free_before), b));
+	}
+
+	r = dm_btree_insert(&io->bitmap_info, io->bitmap_root,
+			    &index, &ie, &io->bitmap_root);
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+
+static int ll_inc(struct ll_disk *ll, dm_block_t b)
+{
+	int r;
+	uint32_t rc;
+
+	r = ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	return ll_insert(ll, b, rc + 1);
+}
+
+static int ll_dec(struct ll_disk *ll, dm_block_t b)
+{
+	int r;
+	uint32_t rc;
+
+	r = ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	if (!rc)
+		return -EINVAL;
+
+	return ll_insert(ll, b, rc - 1);
+}
+
+/*----------------------------------------------------------------
+ * Space map interface.
+ *--------------------------------------------------------------*/
+struct sm_disk {
+	struct dm_space_map sm;
+
+	struct ll_disk ll;
+};
+
+static void sm_disk_destroy(struct dm_space_map *sm)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	kfree(smd);
+}
+
+static int sm_disk_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	return ll_extend(&smd->ll, extra_blocks);
+}
+
+static int sm_disk_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	*count = smd->ll.nr_blocks;
+	return 0;
+}
+
+static int sm_disk_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	*count = smd->ll.nr_blocks - smd->ll.nr_allocated;
+	return 0;
+}
+
+static int sm_disk_get_count(struct dm_space_map *sm, dm_block_t b,
+			     uint32_t *result)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	return ll_lookup(&smd->ll, b, result);
+}
+
+static int sm_disk_count_is_more_than_one(struct dm_space_map *sm, dm_block_t b,
+					  int *result)
+{
+	int r;
+	uint32_t count;
+
+	r = sm_disk_get_count(sm, b, &count);
+	if (r)
+		return r;
+
+	return count > 1;
+}
+
+static int sm_disk_set_count(struct dm_space_map *sm, dm_block_t b,
+			     uint32_t count)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	return ll_insert(&smd->ll, b, count);
+}
+
+static int sm_disk_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	return ll_inc(&smd->ll, b);
+}
+
+static int sm_disk_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	return ll_dec(&smd->ll, b);
+}
+
+static int sm_disk_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	int r;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	/* FIXME: we should start the search where we left off */
+	r = ll_find_free_block(&smd->ll, 0, smd->ll.nr_blocks, b);
+	if (r)
+		return r;
+
+	return ll_inc(&smd->ll, *b);
+}
+
+static int sm_disk_commit(struct dm_space_map *sm)
+{
+	return 0;
+}
+
+static int sm_disk_root_size(struct dm_space_map *sm, size_t *result)
+{
+	*result = sizeof(struct sm_root);
+	return 0;
+}
+
+static int sm_disk_copy_root(struct dm_space_map *sm, void *where, size_t max)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	struct sm_root root;
+
+	root.nr_blocks = __cpu_to_le64(smd->ll.nr_blocks);
+	root.nr_allocated = __cpu_to_le64(smd->ll.nr_allocated);
+	root.bitmap_root = __cpu_to_le64(smd->ll.bitmap_root);
+	root.ref_count_root = __cpu_to_le64(smd->ll.ref_count_root);
+
+	if (max < sizeof(root))
+		return -ENOSPC;
+
+	memcpy(where, &root, sizeof(root));
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_space_map ops_ = {
+	.destroy = sm_disk_destroy,
+	.extend = sm_disk_extend,
+	.get_nr_blocks = sm_disk_get_nr_blocks,
+	.get_nr_free = sm_disk_get_nr_free,
+	.get_count = sm_disk_get_count,
+	.count_is_more_than_one = sm_disk_count_is_more_than_one,
+	.set_count = sm_disk_set_count,
+	.inc_block = sm_disk_inc_block,
+	.dec_block = sm_disk_dec_block,
+	.new_block = sm_disk_new_block,
+	.commit = sm_disk_commit,
+	.root_size = sm_disk_root_size,
+	.copy_root = sm_disk_copy_root
+};
+
+struct dm_space_map *dm_sm_disk_create(struct dm_transaction_manager *tm,
+				       dm_block_t nr_blocks)
+{
+	int r;
+	struct sm_disk *smd;
+
+	smd = kmalloc(sizeof(*smd), GFP_KERNEL);
+	if (!smd)
+		return ERR_PTR(-ENOMEM);
+
+	memcpy(&smd->sm, &ops_, sizeof(smd->sm));
+
+	r = ll_new(&smd->ll, tm);
+	if (r)
+		return ERR_PTR(r);
+
+	r = ll_extend(&smd->ll, nr_blocks);
+	if (r)
+		return ERR_PTR(r);
+
+	r = sm_disk_commit(&smd->sm);
+	if (r)
+		return ERR_PTR(r);
+
+	return &smd->sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_disk_create);
+
+struct dm_space_map *dm_sm_disk_open(struct dm_transaction_manager *tm,
+				     void *root, size_t len)
+{
+	int r;
+	struct sm_disk *smd;
+
+	smd = kmalloc(sizeof(*smd), GFP_KERNEL);
+	if (!smd)
+		return ERR_PTR(-ENOMEM);
+
+	memcpy(&smd->sm, &ops_, sizeof(smd->sm));
+
+	r = ll_open(&smd->ll, tm, root, len);
+	if (r)
+		return ERR_PTR(r);
+
+	r = sm_disk_commit(&smd->sm);
+	if (r)
+		return ERR_PTR(r);
+
+	return &smd->sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_disk_open);
diff --git a/drivers/md/persistent-data/dm-space-map-disk.h b/drivers/md/persistent-data/dm-space-map-disk.h
new file mode 100644
index 0000000..d13450d
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map-disk.h
@@ -0,0 +1,21 @@
+#ifndef DM_SPACE_MAP_DISK_H
+#define DM_SPACE_MAP_DISK_H
+
+#include "dm-transaction-manager.h"
+#include "dm-space-map.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Unfortunately we have to use 2 phase construction due to the cycle
+ * between the tm and sm.
+ */
+struct dm_space_map *dm_sm_disk_create(struct dm_transaction_manager *tm,
+				       dm_block_t nr_blocks);
+
+struct dm_space_map *dm_sm_disk_open(struct dm_transaction_manager *tm,
+				     void *root, size_t len);
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-space-map-metadata.c b/drivers/md/persistent-data/dm-space-map-metadata.c
new file mode 100644
index 0000000..6263601
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map-metadata.c
@@ -0,0 +1,878 @@
+#include "dm-space-map-common.h"
+#include "dm-space-map-metadata.h"
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <asm-generic/bitops/le.h>
+#include <linux/device-mapper.h> /* For DMERR */
+
+#define DM_MSG_PREFIX "space map metadata"
+
+/*----------------------------------------------------------------
+ * index validator
+ *--------------------------------------------------------------*/
+static void index_prepare_for_write(struct dm_block_validator *v,
+				    struct dm_block *b,
+				    size_t block_size)
+{
+	struct metadata_index *mi = dm_block_data(b);
+	mi->blocknr = __cpu_to_le64(dm_block_location(b));
+	mi->csum = dm_block_csum_data(&mi->padding,
+				      block_size - sizeof(__le32));
+}
+
+static int index_check(struct dm_block_validator *v,
+		       struct dm_block *b,
+		       size_t block_size)
+{
+	struct metadata_index *mi = dm_block_data(b);
+	__le32 csum;
+
+	if (dm_block_location(b) != __le64_to_cpu(mi->blocknr)) {
+		DMERR("index_check failed blocknr %llu wanted %llu",
+		      __le64_to_cpu(mi->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum = dm_block_csum_data(&mi->padding,
+				  block_size - sizeof(__le32));
+	if (csum != mi->csum) {
+		DMERR("index_check failed csum %u wanted %u",
+		      __le32_to_cpu(csum), __le32_to_cpu(mi->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+static struct dm_block_validator index_validator_ = {
+	.name = "index",
+	.prepare_for_write = index_prepare_for_write,
+	.check = index_check
+};
+
+/*----------------------------------------------------------------
+ * low level disk ops
+ *--------------------------------------------------------------*/
+static int ll_init(struct ll_disk *ll, struct dm_transaction_manager *tm)
+{
+	ll->tm = tm;
+
+	ll->ref_count_info.tm = tm;
+	ll->ref_count_info.levels = 1;
+	ll->ref_count_info.value_type.size = sizeof(uint32_t);
+	ll->ref_count_info.value_type.inc = NULL;
+	ll->ref_count_info.value_type.dec = NULL;
+	ll->ref_count_info.value_type.equal = NULL;
+
+	ll->block_size = dm_bm_block_size(dm_tm_get_bm(tm));
+
+	if (ll->block_size > (1 << 30)) {
+		DMERR("block size too big to hold bitmaps");
+		return -EINVAL;
+	}
+	ll->entries_per_block = (ll->block_size - sizeof(struct bitmap_header)) *
+		ENTRIES_PER_BYTE;
+	ll->nr_blocks = 0;
+	ll->bitmap_root = 0;
+	ll->ref_count_root = 0;
+
+	return 0;
+}
+
+static int ll_new(struct ll_disk *ll, struct dm_transaction_manager *tm,
+		  dm_block_t nr_blocks)
+{
+	int r;
+	dm_block_t i;
+	unsigned blocks;
+	struct dm_block *index_block;
+
+	r = ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->nr_blocks = nr_blocks;
+	ll->nr_allocated = 0;
+
+	blocks = div_up(nr_blocks, ll->entries_per_block);
+	for (i = 0; i < blocks; i++) {
+		struct dm_block *b;
+		struct index_entry *idx = ll->mi.index + i;
+
+		r = dm_tm_new_block(tm, &dm_sm_bitmap_validator, &b);
+		if (r < 0)
+			return r;
+		idx->blocknr = __cpu_to_le64(dm_block_location(b));
+
+		r = dm_tm_unlock(tm, b);
+		if (r < 0)
+			return r;
+
+		idx->nr_free = __cpu_to_le32(ll->entries_per_block);
+		idx->none_free_before = 0;
+	}
+
+	/* write the index */
+	r = dm_tm_new_block(tm, &index_validator_, &index_block);
+	if (r)
+		return r;
+	ll->bitmap_root = dm_block_location(index_block);
+	memcpy(dm_block_data(index_block), &ll->mi, sizeof(ll->mi));
+	r = dm_tm_unlock(tm, index_block);
+	if (r)
+		return r;
+
+	r = dm_btree_empty(&ll->ref_count_info, &ll->ref_count_root);
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+
+static int ll_open(struct ll_disk *ll, struct dm_transaction_manager *tm,
+		   void *root, size_t len)
+{
+	int r;
+	struct sm_root *smr = (struct sm_root *) root;
+	struct dm_block *block;
+
+	if (len < sizeof(struct sm_root)) {
+		DMERR("sm_disk root too small");
+		return -ENOMEM;
+	}
+
+	r = ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->nr_blocks = __le64_to_cpu(smr->nr_blocks);
+	ll->nr_allocated = __le64_to_cpu(smr->nr_allocated);
+	ll->bitmap_root = __le64_to_cpu(smr->bitmap_root);
+
+	r = dm_tm_read_lock(tm, __le64_to_cpu(smr->bitmap_root),
+			    &index_validator_, &block);
+	if (r)
+		return r;
+	memcpy(&ll->mi, dm_block_data(block), sizeof(ll->mi));
+	r = dm_tm_unlock(tm, block);
+	if (r)
+		return r;
+
+	ll->ref_count_root = __le64_to_cpu(smr->ref_count_root);
+	return 0;
+}
+
+static int ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+{
+	int r;
+	dm_block_t index = b;
+	struct index_entry *ie;
+	struct dm_block *blk;
+
+	b = do_div(index, ll->entries_per_block);
+	ie = ll->mi.index + index;
+
+	r = dm_tm_read_lock(ll->tm, __le64_to_cpu(ie->blocknr),
+			    &dm_sm_bitmap_validator, &blk);
+	if (r < 0)
+		return r;
+	*result = sm_lookup_bitmap(dm_bitmap_data(blk), b);
+	return dm_tm_unlock(ll->tm, blk);
+}
+
+static int ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+{
+	int r = ll_lookup_bitmap(ll, b, result);
+
+	if (r)
+		return r;
+
+	if (*result == 3) {
+		__le32 le_rc;
+		r = dm_btree_lookup(&ll->ref_count_info, ll->ref_count_root,
+				    &b, &le_rc);
+		if (r < 0)
+			return r;
+
+		*result = __le32_to_cpu(le_rc);
+	}
+
+	return r;
+}
+
+static int ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
+			      dm_block_t end, dm_block_t *result)
+{
+	int r;
+	struct index_entry *ie;
+	dm_block_t i, index_begin = begin;
+	dm_block_t index_end = div_up(end, ll->entries_per_block);
+
+	/* FIXME: use shifts */
+	begin = do_div(index_begin, ll->entries_per_block);
+	end = do_div(end, ll->entries_per_block);
+
+	for (i = index_begin; i < index_end; i++, begin = 0) {
+		ie = ll->mi.index + i;
+
+		if (__le32_to_cpu(ie->nr_free) > 0) {
+			struct dm_block *blk;
+			unsigned position;
+			uint32_t bit_end;
+
+			r = dm_tm_read_lock(ll->tm, __le64_to_cpu(ie->blocknr),
+					    &dm_sm_bitmap_validator, &blk);
+			if (r < 0)
+				return r;
+
+			bit_end = (i == index_end - 1) ?
+				end : ll->entries_per_block;
+
+			r = sm_find_free(dm_bitmap_data(blk), begin,
+					 bit_end, &position);
+			if (r < 0) {
+				dm_tm_unlock(ll->tm, blk);
+				return r; /* avoiding retry (FIXME: explain why) */
+			}
+
+			r = dm_tm_unlock(ll->tm, blk);
+			if (r < 0)
+				return r;
+
+			*result = i * ll->entries_per_block +
+				(dm_block_t) position;
+			return 0;
+		}
+	}
+
+	return -ENOSPC;
+}
+
+static int ll_insert(struct ll_disk *ll, dm_block_t b, uint32_t ref_count)
+{
+	int r;
+	uint32_t bit, old;
+	struct dm_block *nb;
+	dm_block_t index = b;
+	struct index_entry *ie;
+	void *bm;
+	int inc;
+
+	bit = do_div(index, ll->entries_per_block);
+	ie = ll->mi.index + index;
+
+	r = dm_tm_shadow_block(ll->tm, __le64_to_cpu(ie->blocknr),
+			       &dm_sm_bitmap_validator, &nb, &inc);
+	if (r < 0) {
+		DMERR("dm_tm_shadow_block() failed");
+		return r;
+	}
+	ie->blocknr = __cpu_to_le64(dm_block_location(nb));
+
+	bm = dm_bitmap_data(nb);
+	old = sm_lookup_bitmap(bm, bit);
+
+	if (ref_count <= 2) {
+		sm_set_bitmap(bm, bit, ref_count);
+
+		r = dm_tm_unlock(ll->tm, nb);
+		if (r < 0)
+			return r;
+
+		if (old > 2) {
+			r = dm_btree_remove(&ll->ref_count_info,
+					    ll->ref_count_root,
+					    &b, &ll->ref_count_root);
+			if (r) {
+				sm_set_bitmap(bm, bit, old);
+				return r;
+			}
+		}
+	} else {
+		__le32 le_rc = __cpu_to_le32(ref_count);
+		sm_set_bitmap(bm, bit, 3);
+		r = dm_tm_unlock(ll->tm, nb);
+		if (r < 0)
+			return r;
+
+		r = dm_btree_insert(&ll->ref_count_info, ll->ref_count_root,
+				    &b, &le_rc, &ll->ref_count_root);
+		if (r < 0) {
+			/* FIXME: release shadow? or assume the whole transaction will be ditched */
+			DMERR("ref count insert failed");
+			return r;
+		}
+	}
+
+	if (ref_count && !old) {
+		ll->nr_allocated++;
+		ie->nr_free = __cpu_to_le32(__le32_to_cpu(ie->nr_free) - 1);
+		if (__le32_to_cpu(ie->none_free_before) == b)
+			ie->none_free_before = __cpu_to_le32(b + 1);
+
+	} else if (old && !ref_count) {
+		ll->nr_allocated--;
+		ie->nr_free = __cpu_to_le32(__le32_to_cpu(ie->nr_free) + 1);
+		ie->none_free_before = __cpu_to_le32(min((dm_block_t) __le32_to_cpu(ie->none_free_before), b));
+	}
+
+	return 0;
+}
+
+static int ll_inc(struct ll_disk *ll, dm_block_t b)
+{
+	int r;
+	uint32_t rc;
+
+	r = ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	return ll_insert(ll, b, rc + 1);
+}
+
+static int ll_dec(struct ll_disk *ll, dm_block_t b)
+{
+	int r;
+	uint32_t rc;
+
+	r = ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	if (!rc)
+		return -EINVAL;
+
+	return ll_insert(ll, b, rc - 1);
+}
+
+static int ll_commit(struct ll_disk *ll)
+{
+	int r, inc;
+	struct dm_block *b;
+
+	r = dm_tm_shadow_block(ll->tm, ll->bitmap_root,
+			       &index_validator_, &b, &inc);
+	if (r)
+		return r;
+
+	memcpy(dm_block_data(b), &ll->mi, sizeof(ll->mi));
+	ll->bitmap_root = dm_block_location(b);
+	return dm_tm_unlock(ll->tm, b);
+}
+
+/*----------------------------------------------------------------
+ * Space map interface.
+ *
+ * The low level disk format is written using the standard btree and
+ * transaction manager.  This means that performing disk operations may
+ * cause us to recurse into the space map in order to allocate new blocks.
+ * For this reason we have a pool of pre-allocated blocks large enough to
+ * service any ll_disk operation.
+ *--------------------------------------------------------------*/
+
+/*
+ * FIXME: we should calculate this based on the size of the device.
+ * Only the metadata space map needs this functionality.
+ */
+#define MAX_RECURSIVE_ALLOCATIONS 1024
+
+enum block_op_type {
+	BOP_INC,
+	BOP_DEC
+};
+
+struct block_op {
+	enum block_op_type type;
+	dm_block_t block;
+};
+
+struct sm_metadata {
+	struct dm_space_map sm;
+
+	struct ll_disk ll;
+	struct ll_disk old_ll;
+
+	dm_block_t begin;
+
+	unsigned recursion_count;
+	unsigned allocated_this_transaction;
+	unsigned nr_uncommitted;
+	struct block_op uncommitted[MAX_RECURSIVE_ALLOCATIONS];
+};
+
+static int add_bop(struct sm_metadata *smm, enum block_op_type type, dm_block_t b)
+{
+	struct block_op *op;
+
+	if (smm->nr_uncommitted == MAX_RECURSIVE_ALLOCATIONS) {
+		BUG();
+		return -1;
+	}
+
+	op = smm->uncommitted + smm->nr_uncommitted++;
+	op->type = type;
+	op->block = b;
+	return 0;
+}
+
+static int commit_bop(struct sm_metadata *smm, struct block_op *op)
+{
+	int r = 0;
+
+	switch (op->type) {
+	case BOP_INC:
+		r = ll_inc(&smm->ll, op->block);
+		break;
+
+	case BOP_DEC:
+		r = ll_dec(&smm->ll, op->block);
+		break;
+	}
+
+	return r;
+}
+
+static void in(struct sm_metadata *smm)
+{
+	smm->recursion_count++;
+}
+
+static void out(struct sm_metadata *smm)
+{
+	int r = 0;
+	BUG_ON(!smm->recursion_count);
+
+	if (smm->recursion_count == 1 && smm->nr_uncommitted) {
+		while (smm->nr_uncommitted && !r) {
+			smm->nr_uncommitted--;
+			r = commit_bop(smm, smm->uncommitted +
+				       smm->nr_uncommitted);
+		}
+	}
+
+	smm->recursion_count--;
+}
+
+static void no_recurse(struct sm_metadata *smm)
+{
+	BUG_ON(smm->recursion_count);
+}
+
+static int recursing(struct sm_metadata *smm)
+{
+	return smm->recursion_count;
+}
+
+static void sm_metadata_destroy(struct dm_space_map *sm)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	kfree(smm);
+}
+
+static int sm_metadata_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	BUG();
+	return -1;
+}
+
+static int sm_metadata_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	*count = smm->ll.nr_blocks;
+	return 0;
+}
+
+static int sm_metadata_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	*count = smm->old_ll.nr_blocks - smm->old_ll.nr_allocated -
+		smm->allocated_this_transaction;
+	return 0;
+}
+
+static int sm_metadata_get_count(struct dm_space_map *sm, dm_block_t b,
+				 uint32_t *result)
+{
+	int r, i;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	unsigned adjustment = 0;
+
+	/*
+	 * we may have some uncommitted adjustments to add.  This list
+	 * should always be really short.
+	 */
+	for (i = 0; i < smm->nr_uncommitted; i++) {
+		struct block_op *op = smm->uncommitted + i;
+		if (op->block == b)
+			switch (op->type) {
+			case BOP_INC:
+				adjustment++;
+				break;
+
+			case BOP_DEC:
+				adjustment--;
+				break;
+			}
+	}
+
+	r = ll_lookup(&smm->ll, b, result);
+	if (r)
+		return r;
+	*result += adjustment;
+
+	return 0;
+}
+
+static int sm_metadata_count_is_more_than_one(struct dm_space_map *sm,
+					      dm_block_t b, int *result)
+{
+	int r, i, adjustment = 0;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	uint32_t rc;
+
+	/*
+	 * we may have some uncommitted adjustments to add.  This list
+	 * should always be really short.
+	 */
+	for (i = 0; i < smm->nr_uncommitted; i++) {
+		struct block_op *op = smm->uncommitted + i;
+		if (op->block == b)
+			switch (op->type) {
+			case BOP_INC:
+				adjustment++;
+				break;
+
+			case BOP_DEC:
+				adjustment--;
+				break;
+			}
+	}
+
+	if (adjustment > 1) {
+		*result = 1;
+		return 0;
+	}
+
+	r = ll_lookup_bitmap(&smm->ll, b, &rc);
+	if (r)
+		return r;
+
+	if (rc == 3)
+		/* we err on the side of caution, and always return true */
+		*result = 1;
+	else
+		*result = rc + adjustment > 1;
+
+	return 0;
+}
+
+static int sm_metadata_set_count(struct dm_space_map *sm, dm_block_t b,
+				 uint32_t count)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	no_recurse(smm);
+
+	in(smm);
+	r = ll_insert(&smm->ll, b, count);
+	out(smm);
+	return r;
+}
+
+static int sm_metadata_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	if (recursing(smm))
+		r = add_bop(smm, BOP_INC, b);
+
+	else {
+		in(smm);
+		r = ll_inc(&smm->ll, b);
+		out(smm);
+	}
+	return r;
+}
+
+static int sm_metadata_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	if (recursing(smm))
+		r = add_bop(smm, BOP_DEC, b);
+
+	else {
+		in(smm);
+		r = ll_dec(&smm->ll, b);
+		out(smm);
+	}
+	return r;
+}
+
+static int sm_metadata_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	r = ll_find_free_block(&smm->old_ll, smm->begin, smm->old_ll.nr_blocks, b);
+	if (r)
+		return r;
+
+	smm->begin = *b + 1;
+
+	if (recursing(smm))
+		r = add_bop(smm, BOP_INC, *b);
+
+	else {
+		in(smm);
+		r = ll_inc(&smm->ll, *b);
+		out(smm);
+	}
+
+	if (!r)
+		smm->allocated_this_transaction++;
+	return r;
+}
+
+static int sm_metadata_commit(struct dm_space_map *sm)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
+
+	r = ll_commit(&smm->ll);
+	if (r)
+		return r;
+
+	memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
+	smm->begin = 0;
+	smm->allocated_this_transaction = 0;
+	return 0;
+}
+
+static int sm_metadata_root_size(struct dm_space_map *sm, size_t *result)
+{
+	*result = sizeof(struct sm_root);
+	return 0;
+}
+
+static int sm_metadata_copy_root(struct dm_space_map *sm, void *where, size_t max)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	struct sm_root root;
+
+	root.nr_blocks = __cpu_to_le64(smm->ll.nr_blocks);
+	root.nr_allocated = __cpu_to_le64(smm->ll.nr_allocated);
+	root.bitmap_root = __cpu_to_le64(smm->ll.bitmap_root);
+	root.ref_count_root = __cpu_to_le64(smm->ll.ref_count_root);
+
+	if (max < sizeof(root))
+		return -ENOSPC;
+
+	memcpy(where, &root, sizeof(root));
+
+	return 0;
+}
+
+static struct dm_space_map ops_ = {
+	.destroy = sm_metadata_destroy,
+	.extend = sm_metadata_extend,
+	.get_nr_blocks = sm_metadata_get_nr_blocks,
+	.get_nr_free = sm_metadata_get_nr_free,
+	.get_count = sm_metadata_get_count,
+	.count_is_more_than_one = sm_metadata_count_is_more_than_one,
+	.set_count = sm_metadata_set_count,
+	.inc_block = sm_metadata_inc_block,
+	.dec_block = sm_metadata_dec_block,
+	.new_block = sm_metadata_new_block,
+	.commit = sm_metadata_commit,
+	.root_size = sm_metadata_root_size,
+	.copy_root = sm_metadata_copy_root
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * When a new space map is created, that manages it's own space.  We use
+ * this tiny bootstrap allocator.
+ */
+static void sm_bootstrap_destroy(struct dm_space_map *sm)
+{
+	BUG();
+}
+
+static int sm_bootstrap_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	BUG();
+	return -1;
+}
+
+static int sm_bootstrap_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	return smm->ll.nr_blocks;
+}
+
+static int sm_bootstrap_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	*count = smm->ll.nr_blocks - smm->begin;
+	return 0;
+}
+
+static int sm_bootstrap_get_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t *result)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	return b < smm->begin ? 1 : 0;
+}
+
+static int sm_bootstrap_count_is_more_than_one(struct dm_space_map *sm,
+					       dm_block_t b, int *result)
+{
+	*result = 0;
+	return 0;
+}
+
+static int sm_bootstrap_set_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t count)
+{
+	BUG();
+	return -1;
+}
+
+static int sm_bootstrap_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	/*
+	 * We know the entire device is unused.
+	 */
+	if (smm->begin == smm->ll.nr_blocks)
+		return -ENOSPC;
+
+	*b = smm->begin++;
+	return 0;
+}
+
+static int sm_bootstrap_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	return add_bop(smm, BOP_INC, b);
+}
+
+static int sm_bootstrap_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	return add_bop(smm, BOP_DEC, b);
+}
+
+static int sm_bootstrap_commit(struct dm_space_map *sm)
+{
+	return 0;
+}
+
+static int sm_bootstrap_root_size(struct dm_space_map *sm, size_t *result)
+{
+	BUG();
+	return -1;
+}
+
+static int sm_bootstrap_copy_root(struct dm_space_map *sm, void *where,
+				  size_t max)
+{
+	BUG();
+	return -1;
+}
+
+static struct dm_space_map bootstrap_ops_ = {
+	.destroy = sm_bootstrap_destroy,
+	.extend = sm_bootstrap_extend,
+	.get_nr_blocks = sm_bootstrap_get_nr_blocks,
+	.get_nr_free = sm_bootstrap_get_nr_free,
+	.get_count = sm_bootstrap_get_count,
+	.count_is_more_than_one = sm_bootstrap_count_is_more_than_one,
+	.set_count = sm_bootstrap_set_count,
+	.inc_block = sm_bootstrap_inc_block,
+	.dec_block = sm_bootstrap_dec_block,
+	.new_block = sm_bootstrap_new_block,
+	.commit = sm_bootstrap_commit,
+	.root_size = sm_bootstrap_root_size,
+	.copy_root = sm_bootstrap_copy_root
+};
+
+/*----------------------------------------------------------------*/
+
+struct dm_space_map *dm_sm_metadata_init(void)
+{
+	struct sm_metadata *smm;
+
+	smm = kmalloc(sizeof(*smm), GFP_KERNEL);
+	if (!smm)
+		return ERR_PTR(-ENOMEM);
+
+	memcpy(&smm->sm, &ops_, sizeof(smm->sm));
+	return &smm->sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_metadata_init);
+
+int dm_sm_metadata_create(struct dm_space_map *sm,
+			  struct dm_transaction_manager *tm,
+			  dm_block_t nr_blocks,
+			  dm_block_t superblock)
+{
+	int r;
+	dm_block_t i;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	smm->begin = superblock + 1;
+	smm->recursion_count = 0;
+	smm->allocated_this_transaction = 0;
+	smm->nr_uncommitted = 0;
+
+	memcpy(&smm->sm, &bootstrap_ops_, sizeof(smm->sm));
+	r = ll_new(&smm->ll, tm, nr_blocks);
+	if (r)
+		return r;
+	memcpy(&smm->sm, &ops_, sizeof(smm->sm));
+
+	/*
+	 * Now we need to update the newly created data structures with the
+	 * allocated blocks that they were built from.
+	 */
+	for (i = superblock; !r && i < smm->begin; i++)
+		r = ll_inc(&smm->ll, i);
+
+	if (r)
+		return r;
+
+	return sm_metadata_commit(sm);
+}
+EXPORT_SYMBOL_GPL(dm_sm_metadata_create);
+
+int dm_sm_metadata_open(struct dm_space_map *sm,
+			struct dm_transaction_manager *tm,
+			void *root, size_t len)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	r = ll_open(&smm->ll, tm, root, len);
+	if (r)
+		return r;
+
+	smm->begin = 0;
+	smm->recursion_count = 0;
+	smm->allocated_this_transaction = 0;
+	smm->nr_uncommitted = 0;
+
+	return sm_metadata_commit(sm);
+}
+EXPORT_SYMBOL_GPL(dm_sm_metadata_open);
diff --git a/drivers/md/persistent-data/dm-space-map-metadata.h b/drivers/md/persistent-data/dm-space-map-metadata.h
new file mode 100644
index 0000000..412c196
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map-metadata.h
@@ -0,0 +1,29 @@
+#ifndef DM_SPACE_MAP_METADATA_H
+#define DM_SPACE_MAP_METADATA_H
+
+#include "dm-transaction-manager.h"
+#include "dm-space-map.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Unfortunately we have to use 2 phase construction due to the cycle
+ * between the tm and sm.
+ */
+struct dm_space_map *dm_sm_metadata_init(void);
+
+/* create a fresh space map */
+int dm_sm_metadata_create(struct dm_space_map *sm,
+			  struct dm_transaction_manager *tm,
+			  dm_block_t nr_blocks,
+			  dm_block_t superblock);
+
+
+/* Open from a previously recorded root */
+int dm_sm_metadata_open(struct dm_space_map *sm,
+			struct dm_transaction_manager *tm,
+			void *root, size_t len);
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-space-map.h b/drivers/md/persistent-data/dm-space-map.h
new file mode 100644
index 0000000..8e73daa
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map.h
@@ -0,0 +1,116 @@
+#ifndef DM_SPACE_MAP_H
+#define DM_SPACE_MAP_H
+
+#include "dm-block-manager.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * This structure keeps a record of how many times each block in a device
+ * is referenced.  It needs to be persisted to disk as part of the
+ * transaction.
+ */
+struct dm_space_map {
+	void (*destroy)(struct dm_space_map *sm);
+
+	int (*extend)(struct dm_space_map *sm, dm_block_t extra_blocks);
+
+	int (*get_nr_blocks)(struct dm_space_map *sm, dm_block_t *count);
+	int (*get_nr_free)(struct dm_space_map *sm, dm_block_t *count);
+
+	int (*get_count)(struct dm_space_map *sm, dm_block_t b, uint32_t *result);
+	int (*count_is_more_than_one)(struct dm_space_map *sm, dm_block_t b,
+				      int *result);
+	int (*set_count)(struct dm_space_map *sm, dm_block_t b, uint32_t count);
+
+	int (*commit)(struct dm_space_map *sm);
+
+	int (*inc_block)(struct dm_space_map *sm, dm_block_t b);
+	int (*dec_block)(struct dm_space_map *sm, dm_block_t b);
+
+	/* new_block will increment the returned block */
+	int (*new_block)(struct dm_space_map *sm, dm_block_t *b);
+
+	/*
+	 * The root contains all the information needed to persist the
+	 * space map.  Generally this info is small, squirrel it away in a
+	 * disk block along with other info.
+	 */
+	int (*root_size)(struct dm_space_map *sm, size_t *result);
+	int (*copy_root)(struct dm_space_map *sm, void *copy_to_here, size_t len);
+};
+
+/*----------------------------------------------------------------*/
+
+static inline void dm_sm_destroy(struct dm_space_map *sm)
+{
+	sm->destroy(sm);
+}
+
+static inline int dm_sm_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	return sm->extend(sm, extra_blocks);
+}
+
+static inline int dm_sm_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	return sm->get_nr_blocks(sm, count);
+}
+
+static inline int dm_sm_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	return sm->get_nr_free(sm, count);
+}
+
+static inline int dm_sm_get_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t *result)
+{
+	return sm->get_count(sm, b, result);
+}
+
+static inline int dm_sm_count_is_more_than_one(struct dm_space_map *sm,
+					       dm_block_t b, int *result)
+{
+	return sm->count_is_more_than_one(sm, b, result);
+}
+
+static inline int dm_sm_set_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t count)
+{
+	return sm->set_count(sm, b, count);
+}
+
+static inline int dm_sm_commit(struct dm_space_map *sm)
+{
+	return sm->commit(sm);
+}
+
+static inline int dm_sm_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	return sm->inc_block(sm, b);
+}
+
+static inline int dm_sm_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	return sm->dec_block(sm, b);
+}
+
+static inline int dm_sm_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	return sm->new_block(sm, b);
+}
+
+static inline int dm_sm_root_size(struct dm_space_map *sm, size_t *result)
+{
+	return sm->root_size(sm, result);
+}
+
+static inline int dm_sm_copy_root(struct dm_space_map *sm,
+				  void *copy_to_here, size_t len)
+{
+	return sm->copy_root(sm, copy_to_here, len);
+}
+
+/*----------------------------------------------------------------*/
+
+#endif
diff --git a/drivers/md/persistent-data/dm-transaction-manager.c b/drivers/md/persistent-data/dm-transaction-manager.c
new file mode 100644
index 0000000..28042a9
--- /dev/null
+++ b/drivers/md/persistent-data/dm-transaction-manager.c
@@ -0,0 +1,442 @@
+#include "dm-transaction-manager.h"
+#include "dm-space-map-disk.h"
+#include "dm-space-map-metadata.h"
+
+#include <linux/slab.h>
+#include <linux/device-mapper.h> /* For DMERR */
+
+#define DM_MSG_PREFIX "transaction manager"
+
+/*----------------------------------------------------------------*/
+
+struct shadow_info {
+	struct hlist_node hlist;
+	dm_block_t where;
+};
+
+/* it would be nice if we scaled with the size of transaction */
+#define HASH_SIZE 256
+#define HASH_MASK (HASH_SIZE - 1)
+struct dm_transaction_manager {
+	int is_clone;
+	struct dm_transaction_manager *real;
+
+	struct dm_block_manager *bm;
+	struct dm_space_map *sm;
+
+	struct hlist_head buckets[HASH_SIZE];
+
+	/* stats */
+	unsigned shadow_count;
+};
+
+/*----------------------------------------------------------------*/
+
+/* FIXME: similar code in block-manager */
+static unsigned hash_block(dm_block_t b)
+{
+	const unsigned BIG_PRIME = 4294967291UL;
+	return (((unsigned) b) * BIG_PRIME) & HASH_MASK;
+}
+
+static int is_shadow(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	unsigned bucket = hash_block(b);
+	struct shadow_info *si;
+	struct hlist_node *n;
+
+	hlist_for_each_entry(si, n, tm->buckets + bucket, hlist)
+		if (si->where == b)
+			return 1;
+
+	return 0;
+}
+
+/*
+ * This can silently fail if there's no memory.  We're ok with this since
+ * creating redundant shadows causes no harm.
+ */
+static void insert_shadow(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	unsigned bucket;
+	struct shadow_info *si;
+
+	si = kmalloc(sizeof(*si), GFP_NOIO);
+	if (si) {
+		si->where = b;
+		bucket = hash_block(b);
+		hlist_add_head(&si->hlist, tm->buckets + bucket);
+	}
+}
+
+static void wipe_shadow_table(struct dm_transaction_manager *tm)
+{
+	int i;
+	for (i = 0; i < HASH_SIZE; i++) {
+		struct shadow_info *si;
+		struct hlist_node *n, *tmp;
+		struct hlist_head *bucket = tm->buckets + i;
+		hlist_for_each_entry_safe(si, n, tmp, bucket, hlist)
+			kfree(si);
+
+		INIT_HLIST_HEAD(bucket);
+	}
+
+	tm->shadow_count = 0;
+}
+
+/*----------------------------------------------------------------*/
+
+struct dm_transaction_manager *dm_tm_create(struct dm_block_manager *bm,
+					    struct dm_space_map *sm)
+{
+	int i;
+	struct dm_transaction_manager *tm;
+
+	tm = kmalloc(sizeof(*tm), GFP_KERNEL);
+	if (!tm)
+		return ERR_PTR(-ENOMEM);
+
+	tm->is_clone = 0;
+	tm->real = NULL;
+	tm->bm = bm;
+	tm->sm = sm;
+
+	for (i = 0; i < HASH_SIZE; i++)
+		INIT_HLIST_HEAD(tm->buckets + i);
+
+	tm->shadow_count = 0;
+
+	return tm;
+}
+EXPORT_SYMBOL_GPL(dm_tm_create);
+
+struct dm_transaction_manager *
+dm_tm_create_non_blocking_clone(struct dm_transaction_manager *real)
+{
+	struct dm_transaction_manager *tm;
+
+	tm = kmalloc(sizeof(*tm), GFP_KERNEL);
+	if (tm) {
+		tm->is_clone = 1;
+		tm->real = real;
+	}
+
+	return tm;
+}
+EXPORT_SYMBOL_GPL(dm_tm_create_non_blocking_clone);
+
+void dm_tm_destroy(struct dm_transaction_manager *tm)
+{
+	kfree(tm);
+}
+EXPORT_SYMBOL_GPL(dm_tm_destroy);
+
+int dm_tm_reserve_block(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	return dm_sm_inc_block(tm->sm, b);
+}
+EXPORT_SYMBOL_GPL(dm_tm_reserve_block);
+
+int dm_tm_begin(struct dm_transaction_manager *tm)
+{
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_tm_begin);
+
+int dm_tm_pre_commit(struct dm_transaction_manager *tm)
+{
+	int r;
+
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	r = dm_sm_commit(tm->sm);
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_tm_pre_commit);
+
+int dm_tm_commit(struct dm_transaction_manager *tm, struct dm_block *root)
+{
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	wipe_shadow_table(tm);
+	return dm_bm_flush_and_unlock(tm->bm, root);
+}
+EXPORT_SYMBOL_GPL(dm_tm_commit);
+
+int dm_tm_alloc_block(struct dm_transaction_manager *tm, dm_block_t *new_block)
+{
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	return dm_sm_new_block(tm->sm, new_block);
+}
+EXPORT_SYMBOL_GPL(dm_tm_alloc_block);
+
+int dm_tm_new_block(struct dm_transaction_manager *tm,
+		    struct dm_block_validator *v,
+		    struct dm_block **result)
+{
+	int r;
+	dm_block_t new_block;
+
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	r = dm_sm_new_block(tm->sm, &new_block);
+	if (r < 0)
+		return r;
+
+	r = dm_bm_write_lock_zero(tm->bm, new_block, v, result);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new_block);
+		return r;
+	}
+
+	/*
+	 * New blocks count as shadows, in that they don't need to be
+	 * shadowed again.
+	 */
+	insert_shadow(tm, new_block);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_tm_new_block);
+
+static int __shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
+			  struct dm_block_validator *v,
+			  struct dm_block **result, int *inc_children)
+{
+	int r;
+	dm_block_t new;
+	uint32_t count;
+	struct dm_block *orig_block;
+
+	r = dm_sm_new_block(tm->sm, &new);
+	if (r < 0)
+		return r;
+
+	r = dm_bm_write_lock_zero(tm->bm, new, v, result);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new);
+		return r;
+	}
+
+	r = dm_bm_read_lock(tm->bm, orig, v, &orig_block);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new);
+		return r;
+	}
+	memcpy(dm_block_data(*result), dm_block_data(orig_block),
+	       dm_bm_block_size(tm->bm));
+	r = dm_bm_unlock(orig_block);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new);
+		return r;
+	}
+
+	r = dm_sm_get_count(tm->sm, orig, &count);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new);
+		dm_bm_unlock(*result);
+		return r;
+	}
+
+	r = dm_sm_dec_block(tm->sm, orig);
+	if (r < 0) {
+		dm_sm_dec_block(tm->sm, new);
+		dm_bm_unlock(*result);
+		return r;
+	}
+
+	*inc_children = count > 1;
+	return 0;
+}
+
+int dm_tm_shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
+		       struct dm_block_validator *v, struct dm_block **result,
+		       int *inc_children)
+{
+	int r, more_than_one;
+
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	if (is_shadow(tm, orig)) {
+		r = dm_sm_count_is_more_than_one(tm->sm, orig, &more_than_one);
+		if (r < 0)
+			return r;
+
+		if (!more_than_one) {
+			*inc_children = 0;
+			return dm_bm_write_lock(tm->bm, orig, v, result);
+		}
+		/* fall through */
+	}
+
+	r = __shadow_block(tm, orig, v, result, inc_children);
+	if (r < 0)
+		return r;
+	tm->shadow_count++;
+	insert_shadow(tm, dm_block_location(*result));
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_tm_shadow_block);
+
+int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
+		    struct dm_block_validator *v,
+		    struct dm_block **blk)
+{
+	if (tm->is_clone)
+		return dm_bm_read_try_lock(tm->real->bm, b, v, blk);
+
+	return dm_bm_read_lock(tm->bm, b, v, blk);
+}
+EXPORT_SYMBOL_GPL(dm_tm_read_lock);
+
+int dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b)
+{
+	return dm_bm_unlock(b);
+}
+EXPORT_SYMBOL_GPL(dm_tm_unlock);
+
+void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	BUG_ON(tm->is_clone);
+	dm_sm_inc_block(tm->sm, b);
+}
+EXPORT_SYMBOL_GPL(dm_tm_inc);
+
+void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	BUG_ON(tm->is_clone);
+	dm_sm_dec_block(tm->sm, b);
+}
+EXPORT_SYMBOL_GPL(dm_tm_dec);
+
+int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
+	      uint32_t *result)
+{
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	return dm_sm_get_count(tm->sm, b, result);
+}
+EXPORT_SYMBOL_GPL(dm_tm_ref);
+
+struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm)
+{
+	BUG_ON(tm->is_clone);
+	return tm->bm;
+}
+EXPORT_SYMBOL_GPL(dm_tm_get_bm);
+
+/*----------------------------------------------------------------*/
+
+static int dm_tm_create_internal(struct dm_block_manager *bm,
+				 dm_block_t sb_location,
+				 struct dm_block_validator *sb_validator,
+				 size_t root_offset, size_t root_max_len,
+				 struct dm_transaction_manager **tm,
+				 struct dm_space_map **sm,
+				 struct dm_block **sblock,
+				 int create)
+{
+	int r;
+
+	*sm = dm_sm_metadata_init();
+	if (IS_ERR(*sm))
+		return PTR_ERR(*sm);
+
+	*tm = dm_tm_create(bm, *sm);
+	if (IS_ERR(*tm)) {
+		dm_sm_destroy(*sm);
+		return -1;
+	}
+
+	r = dm_tm_begin(*tm);
+	if (r < 0)
+		goto bad1;
+
+	if (create) {
+		r = dm_bm_write_lock_zero(dm_tm_get_bm(*tm), sb_location,
+					  sb_validator, sblock);
+		if (r < 0) {
+			DMERR("couldn't lock superblock");
+			goto bad1;
+		}
+
+		r = dm_sm_metadata_create(*sm, *tm, dm_bm_nr_blocks(bm),
+					  sb_location);
+		if (r) {
+			DMERR("couldn't create metadata space map");
+			goto bad2;
+		}
+
+	} else {
+		r = dm_bm_write_lock(dm_tm_get_bm(*tm), sb_location,
+				     sb_validator, sblock);
+		if (r < 0) {
+			DMERR("couldn't lock superblock");
+			goto bad1;
+		}
+
+		r = dm_sm_metadata_open(*sm, *tm,
+					dm_block_data(*sblock) + root_offset,
+					root_max_len);
+		if (IS_ERR(*sm)) {
+			DMERR("couldn't open metadata space map");
+			goto bad2;
+		}
+	}
+
+	r = dm_tm_begin(*tm);
+	if (r < 0)
+		goto bad2;
+
+	return 0;
+
+bad2:
+	dm_tm_unlock(*tm, *sblock);
+bad1:
+	dm_tm_destroy(*tm);
+	dm_sm_destroy(*sm);
+	return r;
+}
+
+int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
+			 struct dm_block_validator *sb_validator,
+			 struct dm_transaction_manager **tm,
+			 struct dm_space_map **sm, struct dm_block **sblock)
+{
+	return dm_tm_create_internal(bm, sb_location, sb_validator,
+				     0, 0, tm, sm, sblock, 1);
+}
+EXPORT_SYMBOL_GPL(dm_tm_create_with_sm);
+
+int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
+		       struct dm_block_validator *sb_validator,
+		       size_t root_offset, size_t root_max_len,
+		       struct dm_transaction_manager **tm,
+		       struct dm_space_map **sm, struct dm_block **sblock)
+{
+	return dm_tm_create_internal(bm, sb_location, sb_validator, root_offset,
+				     root_max_len, tm, sm, sblock, 0);
+}
+EXPORT_SYMBOL_GPL(dm_tm_open_with_sm);
+
+unsigned dm_tm_shadow_count(struct dm_transaction_manager *tm)
+{
+	return tm->shadow_count;
+}
+EXPORT_SYMBOL_GPL(dm_tm_shadow_count);
+/*----------------------------------------------------------------*/
diff --git a/drivers/md/persistent-data/dm-transaction-manager.h b/drivers/md/persistent-data/dm-transaction-manager.h
new file mode 100644
index 0000000..90c9d1f
--- /dev/null
+++ b/drivers/md/persistent-data/dm-transaction-manager.h
@@ -0,0 +1,139 @@
+#ifndef DM_TRANSACTION_MANAGER_H
+#define DM_TRANSACTION_MANAGER_H
+
+#include "dm-block-manager.h"
+#include "dm-space-map.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * This manages the scope of a transaction.  It also enforces immutability
+ * of the on-disk data structures by limiting access to writeable blocks.
+ *
+ * Clients should not fiddle with the block manager directly.
+ */
+struct dm_transaction_manager;
+
+struct dm_transaction_manager *
+dm_tm_create(struct dm_block_manager *bm, struct dm_space_map *sm);
+
+void dm_tm_destroy(struct dm_transaction_manager *tm);
+
+/*
+ * The non-blocking version of a transaction manager is intended for use in
+ * fast path code that needs to do lookups.  eg, a dm mapping function.
+ * You create the non-blocking variant from a normal tm.  The interface is
+ * the same, except that most functions will just return -EWOULDBLOCK.
+ * Call tm_destroy() as you would with a normal tm when you've finished
+ * with it.  You may not destroy the original prior to clones.
+ */
+struct dm_transaction_manager *
+dm_tm_create_non_blocking_clone(struct dm_transaction_manager *real);
+
+/*
+ * The client may want to manage some blocks directly (eg, the
+ * superblocks).  Call this immediately after construction to reserve
+ * blocks.
+ */
+int dm_tm_reserve_block(struct dm_transaction_manager *tm, dm_block_t b);
+
+int dm_tm_begin(struct dm_transaction_manager *tm);
+
+/*
+ * We use a 2 phase commit here.
+ *
+ * i) In the first phase the block manager is told to start flushing, and
+ * the changes to the space map are written to disk.  You should interogate
+ * your particular space map to get detail of its root node etc. to be
+ * included in your superblock.
+ *
+ * ii) |root| will be committed last.  You shouldn't use more than the
+ * first 512 bytes of |root| if you wish the transaction to survive a power
+ * failure.  You *must* have a write lock held on |root| for both stage (i)
+ * and (ii).  The commit will drop the write lock.
+ */
+int dm_tm_pre_commit(struct dm_transaction_manager *tm);
+int dm_tm_commit(struct dm_transaction_manager *tm, struct dm_block *root);
+
+/*
+ * These methods are the only way to get hold of a writeable block.
+ *
+ * tm_new_block() is pretty self explanatory.  Make sure you do actually
+ * write to the whole of |data| before you unlock, otherwise you could get
+ * a data leak.  (The other option is for tm_new_block() to zero new blocks
+ * before handing them out, which will be redundant in most if not all
+ * cases).
+ *
+ * tm_shadow_block() will allocate a new block and copy the data from orig
+ * to it.  It then decrements the reference count on original block.  Use
+ * this to update the contents of a block in a data structure, don't
+ * confuse this with a clone - you shouldn't access the orig block after
+ * this operation.  Because the tm knows the scope of the transaction it
+ * can optimise requests for a shadow of a shadow to a no-op.  Don't forget
+ * to unlock when you've finished with the shadow.
+ *
+ * The |inc_children| flag is used to tell the caller whether they need to
+ * adjust reference counts for children (data in the block may refer to
+ * other blocks).
+ */
+int dm_tm_alloc_block(struct dm_transaction_manager *tm, dm_block_t *new);
+
+/* zeroes the new block at returns with write lock held */
+int dm_tm_new_block(struct dm_transaction_manager *tm,
+		    struct dm_block_validator *v,
+		    struct dm_block **result);
+
+/*
+ * Shadowing implicitly drops a reference on |orig|, so you must not have
+ * it locked when you call this.
+ */
+int dm_tm_shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
+		       struct dm_block_validator *v,
+		       struct dm_block **result, int *inc_children);
+
+/*
+ * Read access.  You can lock any block you want, if there's a write lock
+ * on it outstanding then it'll block.
+ */
+int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
+		    struct dm_block_validator *v,
+		    struct dm_block **result);
+
+int dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b);
+
+/*
+ * Functions for altering the reference count of a block directly.
+ */
+void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b);
+
+void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b);
+
+int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
+	      uint32_t *result);
+
+struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm);
+
+/*
+ * A little utility that ties the knot by producing a transaction manager
+ * that has a space map managed by the transaction manager ...
+ *
+ * Returns a tm that has an open transaction to write the new disk sm.
+ * Caller should store the new sm root and commit.
+ */
+int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
+			 struct dm_block_validator *sb_validator,
+			 struct dm_transaction_manager **tm,
+			 struct dm_space_map **sm, struct dm_block **sblock);
+
+int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
+		       struct dm_block_validator *sb_validator,
+		       size_t root_offset, size_t root_max_len,
+		       struct dm_transaction_manager **tm,
+		       struct dm_space_map **sm, struct dm_block **sblock);
+
+/* useful for debugging performance */
+unsigned dm_tm_shadow_count(struct dm_transaction_manager *tm);
+
+/*----------------------------------------------------------------*/
+
+#endif
