dm: add persistent data library

The persistent-data library offers a re-usable framework for the storage
and management of on-disk metadata in device-mapper targets.

It's used by the thin-provisioning target in the next patch and in an
upcoming hierarchical storage target.

For further information, please read
Documentation/device-mapper/persistent-data.txt

Signed-off-by: Joe Thornber <[e-mail]>
Signed-off-by: Mike Snitzer <[e-mail]>
Signed-off-by: Alasdair G Kergon <[e-mail]>

Documentation/device-mapper/persistent-data.txt

···
+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.
+
+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 it writes the superblock.
+On power failure your metadata will be as it was when last committed.
+
+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 one for managing
+the metadata space.  The latter is complicated by the need to store
+its own data within the space it's managing.
+
+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 maps a device id to a mapping tree, and that in turn maps a
+virtual block to a physical block.
+
+Values stored in the btrees can have arbitrary size.  Keys are always
+64bits, although nesting allows you to use multiple keys.

drivers/md/persistent-data/Kconfig

···
+config DM_PERSISTENT_DATA
+       tristate
+       depends on BLK_DEV_DM && EXPERIMENTAL
+       select LIBCRC32C
+       select DM_BUFIO
+       ---help---
+	 Library providing immutable on-disk data structure support for
+	 device-mapper targets such as the thin provisioning target.

drivers/md/persistent-data/Makefile

···
+obj-$(CONFIG_DM_PERSISTENT_DATA) += dm-persistent-data.o
+dm-persistent-data-objs := \
+	dm-block-manager.o \
+	dm-space-map-checker.o \
+	dm-space-map-common.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

drivers/md/persistent-data/dm-block-manager.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+#include "dm-block-manager.h"
+#include "dm-persistent-data-internal.h"
+#include "../dm-bufio.h"
+
+#include <linux/crc32c.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/rwsem.h>
+#include <linux/device-mapper.h>
+#include <linux/stacktrace.h>
+
+#define DM_MSG_PREFIX "block manager"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * This is a read/write semaphore with a couple of differences.
+ *
+ * i) There is a restriction on the number of concurrent read locks that
+ * may be held at once.  This is just an implementation detail.
+ *
+ * ii) Recursive locking attempts are detected and return EINVAL.  A stack
+ * trace is also emitted for the previous lock aquisition.
+ *
+ * iii) Priority is given to write locks.
+ */
+#define MAX_HOLDERS 4
+#define MAX_STACK 10
+
+typedef unsigned long stack_entries[MAX_STACK];
+
+struct block_lock {
+	spinlock_t lock;
+	__s32 count;
+	struct list_head waiters;
+	struct task_struct *holders[MAX_HOLDERS];
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	struct stack_trace traces[MAX_HOLDERS];
+	stack_entries entries[MAX_HOLDERS];
+#endif
+};
+
+struct waiter {
+	struct list_head list;
+	struct task_struct *task;
+	int wants_write;
+};
+
+static unsigned __find_holder(struct block_lock *lock,
+			      struct task_struct *task)
+{
+	unsigned i;
+
+	for (i = 0; i < MAX_HOLDERS; i++)
+		if (lock->holders[i] == task)
+			break;
+
+	BUG_ON(i == MAX_HOLDERS);
+	return i;
+}
+
+/* call this *after* you increment lock->count */
+static void __add_holder(struct block_lock *lock, struct task_struct *task)
+{
+	unsigned h = __find_holder(lock, NULL);
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	struct stack_trace *t;
+#endif
+
+	get_task_struct(task);
+	lock->holders[h] = task;
+
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	t = lock->traces + h;
+	t->nr_entries = 0;
+	t->max_entries = MAX_STACK;
+	t->entries = lock->entries[h];
+	t->skip = 2;
+	save_stack_trace(t);
+#endif
+}
+
+/* call this *before* you decrement lock->count */
+static void __del_holder(struct block_lock *lock, struct task_struct *task)
+{
+	unsigned h = __find_holder(lock, task);
+	lock->holders[h] = NULL;
+	put_task_struct(task);
+}
+
+static int __check_holder(struct block_lock *lock)
+{
+	unsigned i;
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+	static struct stack_trace t;
+	static stack_entries entries;
+#endif
+
+	for (i = 0; i < MAX_HOLDERS; i++) {
+		if (lock->holders[i] == current) {
+			DMERR("recursive lock detected in pool metadata");
+#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
+			DMERR("previously held here:");
+			print_stack_trace(lock->traces + i, 4);
+
+			DMERR("subsequent aquisition attempted here:");
+			t.nr_entries = 0;
+			t.max_entries = MAX_STACK;
+			t.entries = entries;
+			t.skip = 3;
+			save_stack_trace(&t);
+			print_stack_trace(&t, 4);
+#endif
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static void __wait(struct waiter *w)
+{
+	for (;;) {
+		set_task_state(current, TASK_UNINTERRUPTIBLE);
+
+		if (!w->task)
+			break;
+
+		schedule();
+	}
+
+	set_task_state(current, TASK_RUNNING);
+}
+
+static void __wake_waiter(struct waiter *w)
+{
+	struct task_struct *task;
+
+	list_del(&w->list);
+	task = w->task;
+	smp_mb();
+	w->task = NULL;
+	wake_up_process(task);
+}
+
+/*
+ * We either wake a few readers or a single writer.
+ */
+static void __wake_many(struct block_lock *lock)
+{
+	struct waiter *w, *tmp;
+
+	BUG_ON(lock->count < 0);
+	list_for_each_entry_safe(w, tmp, &lock->waiters, list) {
+		if (lock->count >= MAX_HOLDERS)
+			return;
+
+		if (w->wants_write) {
+			if (lock->count > 0)
+				return; /* still read locked */
+
+			lock->count = -1;
+			__add_holder(lock, w->task);
+			__wake_waiter(w);
+			return;
+		}
+
+		lock->count++;
+		__add_holder(lock, w->task);
+		__wake_waiter(w);
+	}
+}
+
+static void bl_init(struct block_lock *lock)
+{
+	int i;
+
+	spin_lock_init(&lock->lock);
+	lock->count = 0;
+	INIT_LIST_HEAD(&lock->waiters);
+	for (i = 0; i < MAX_HOLDERS; i++)
+		lock->holders[i] = NULL;
+}
+
+static int __available_for_read(struct block_lock *lock)
+{
+	return lock->count >= 0 &&
+		lock->count < MAX_HOLDERS &&
+		list_empty(&lock->waiters);
+}
+
+static int bl_down_read(struct block_lock *lock)
+{
+	int r;
+	struct waiter w;
+
+	spin_lock(&lock->lock);
+	r = __check_holder(lock);
+	if (r) {
+		spin_unlock(&lock->lock);
+		return r;
+	}
+
+	if (__available_for_read(lock)) {
+		lock->count++;
+		__add_holder(lock, current);
+		spin_unlock(&lock->lock);
+		return 0;
+	}
+
+	get_task_struct(current);
+
+	w.task = current;
+	w.wants_write = 0;
+	list_add_tail(&w.list, &lock->waiters);
+	spin_unlock(&lock->lock);
+
+	__wait(&w);
+	put_task_struct(current);
+	return 0;
+}
+
+static int bl_down_read_nonblock(struct block_lock *lock)
+{
+	int r;
+
+	spin_lock(&lock->lock);
+	r = __check_holder(lock);
+	if (r)
+		goto out;
+
+	if (__available_for_read(lock)) {
+		lock->count++;
+		__add_holder(lock, current);
+		r = 0;
+	} else
+		r = -EWOULDBLOCK;
+
+out:
+	spin_unlock(&lock->lock);
+	return r;
+}
+
+static void bl_up_read(struct block_lock *lock)
+{
+	spin_lock(&lock->lock);
+	BUG_ON(lock->count <= 0);
+	__del_holder(lock, current);
+	--lock->count;
+	if (!list_empty(&lock->waiters))
+		__wake_many(lock);
+	spin_unlock(&lock->lock);
+}
+
+static int bl_down_write(struct block_lock *lock)
+{
+	int r;
+	struct waiter w;
+
+	spin_lock(&lock->lock);
+	r = __check_holder(lock);
+	if (r) {
+		spin_unlock(&lock->lock);
+		return r;
+	}
+
+	if (lock->count == 0 && list_empty(&lock->waiters)) {
+		lock->count = -1;
+		__add_holder(lock, current);
+		spin_unlock(&lock->lock);
+		return 0;
+	}
+
+	get_task_struct(current);
+	w.task = current;
+	w.wants_write = 1;
+
+	/*
+	 * Writers given priority. We know there's only one mutator in the
+	 * system, so ignoring the ordering reversal.
+	 */
+	list_add(&w.list, &lock->waiters);
+	spin_unlock(&lock->lock);
+
+	__wait(&w);
+	put_task_struct(current);
+
+	return 0;
+}
+
+static void bl_up_write(struct block_lock *lock)
+{
+	spin_lock(&lock->lock);
+	__del_holder(lock, current);
+	lock->count = 0;
+	if (!list_empty(&lock->waiters))
+		__wake_many(lock);
+	spin_unlock(&lock->lock);
+}
+
+static void report_recursive_bug(dm_block_t b, int r)
+{
+	if (r == -EINVAL)
+		DMERR("recursive acquisition of block %llu requested.",
+		      (unsigned long long) b);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Block manager is currently implemented using dm-bufio.  struct
+ * dm_block_manager and struct dm_block map directly onto a couple of
+ * structs in the bufio interface.  I want to retain the freedom to move
+ * away from bufio in the future.  So these structs are just cast within
+ * this .c file, rather than making it through to the public interface.
+ */
+static struct dm_buffer *to_buffer(struct dm_block *b)
+{
+	return (struct dm_buffer *) b;
+}
+
+static struct dm_bufio_client *to_bufio(struct dm_block_manager *bm)
+{
+	return (struct dm_bufio_client *) bm;
+}
+
+dm_block_t dm_block_location(struct dm_block *b)
+{
+	return dm_bufio_get_block_number(to_buffer(b));
+}
+EXPORT_SYMBOL_GPL(dm_block_location);
+
+void *dm_block_data(struct dm_block *b)
+{
+	return dm_bufio_get_block_data(to_buffer(b));
+}
+EXPORT_SYMBOL_GPL(dm_block_data);
+
+struct buffer_aux {
+	struct dm_block_validator *validator;
+	struct block_lock lock;
+	int write_locked;
+};
+
+static void dm_block_manager_alloc_callback(struct dm_buffer *buf)
+{
+	struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
+	aux->validator = NULL;
+	bl_init(&aux->lock);
+}
+
+static void dm_block_manager_write_callback(struct dm_buffer *buf)
+{
+	struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
+	if (aux->validator) {
+		aux->validator->prepare_for_write(aux->validator, (struct dm_block *) buf,
+			 dm_bufio_get_block_size(dm_bufio_get_client(buf)));
+	}
+}
+
+/*----------------------------------------------------------------
+ * Public interface
+ *--------------------------------------------------------------*/
+struct dm_block_manager *dm_block_manager_create(struct block_device *bdev,
+						 unsigned block_size,
+						 unsigned cache_size,
+						 unsigned max_held_per_thread)
+{
+	return (struct dm_block_manager *)
+		dm_bufio_client_create(bdev, block_size, max_held_per_thread,
+				       sizeof(struct buffer_aux),
+				       dm_block_manager_alloc_callback,
+				       dm_block_manager_write_callback);
+}
+EXPORT_SYMBOL_GPL(dm_block_manager_create);
+
+void dm_block_manager_destroy(struct dm_block_manager *bm)
+{
+	return dm_bufio_client_destroy(to_bufio(bm));
+}
+EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
+
+unsigned dm_bm_block_size(struct dm_block_manager *bm)
+{
+	return dm_bufio_get_block_size(to_bufio(bm));
+}
+EXPORT_SYMBOL_GPL(dm_bm_block_size);
+
+dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm)
+{
+	return dm_bufio_get_device_size(to_bufio(bm));
+}
+
+static int dm_bm_validate_buffer(struct dm_block_manager *bm,
+				 struct dm_buffer *buf,
+				 struct buffer_aux *aux,
+				 struct dm_block_validator *v)
+{
+	if (unlikely(!aux->validator)) {
+		int r;
+		if (!v)
+			return 0;
+		r = v->check(v, (struct dm_block *) buf, dm_bufio_get_block_size(to_bufio(bm)));
+		if (unlikely(r))
+			return r;
+		aux->validator = v;
+	} else {
+		if (unlikely(aux->validator != v)) {
+			DMERR("validator mismatch (old=%s vs new=%s) for block %llu",
+				aux->validator->name, v ? v->name : "NULL",
+				(unsigned long long)
+					dm_bufio_get_block_number(buf));
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
+		    struct dm_block_validator *v,
+		    struct dm_block **result)
+{
+	struct buffer_aux *aux;
+	void *p;
+	int r;
+
+	p = dm_bufio_read(to_bufio(bm), b, (struct dm_buffer **) result);
+	if (unlikely(IS_ERR(p)))
+		return PTR_ERR(p);
+
+	aux = dm_bufio_get_aux_data(to_buffer(*result));
+	r = bl_down_read(&aux->lock);
+	if (unlikely(r)) {
+		dm_bufio_release(to_buffer(*result));
+		report_recursive_bug(b, r);
+		return r;
+	}
+
+	aux->write_locked = 0;
+
+	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
+	if (unlikely(r)) {
+		bl_up_read(&aux->lock);
+		dm_bufio_release(to_buffer(*result));
+		return r;
+	}
+
+	return 0;
+}
+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)
+{
+	struct buffer_aux *aux;
+	void *p;
+	int r;
+
+	p = dm_bufio_read(to_bufio(bm), b, (struct dm_buffer **) result);
+	if (unlikely(IS_ERR(p)))
+		return PTR_ERR(p);
+
+	aux = dm_bufio_get_aux_data(to_buffer(*result));
+	r = bl_down_write(&aux->lock);
+	if (r) {
+		dm_bufio_release(to_buffer(*result));
+		report_recursive_bug(b, r);
+		return r;
+	}
+
+	aux->write_locked = 1;
+
+	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
+	if (unlikely(r)) {
+		bl_up_write(&aux->lock);
+		dm_bufio_release(to_buffer(*result));
+		return r;
+	}
+
+	return 0;
+}
+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)
+{
+	struct buffer_aux *aux;
+	void *p;
+	int r;
+
+	p = dm_bufio_get(to_bufio(bm), b, (struct dm_buffer **) result);
+	if (unlikely(IS_ERR(p)))
+		return PTR_ERR(p);
+	if (unlikely(!p))
+		return -EWOULDBLOCK;
+
+	aux = dm_bufio_get_aux_data(to_buffer(*result));
+	r = bl_down_read_nonblock(&aux->lock);
+	if (r < 0) {
+		dm_bufio_release(to_buffer(*result));
+		report_recursive_bug(b, r);
+		return r;
+	}
+	aux->write_locked = 0;
+
+	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
+	if (unlikely(r)) {
+		bl_up_read(&aux->lock);
+		dm_bufio_release(to_buffer(*result));
+		return r;
+	}
+
+	return 0;
+}
+
+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;
+	struct buffer_aux *aux;
+	void *p;
+
+	p = dm_bufio_new(to_bufio(bm), b, (struct dm_buffer **) result);
+	if (unlikely(IS_ERR(p)))
+		return PTR_ERR(p);
+
+	memset(p, 0, dm_bm_block_size(bm));
+
+	aux = dm_bufio_get_aux_data(to_buffer(*result));
+	r = bl_down_write(&aux->lock);
+	if (r) {
+		dm_bufio_release(to_buffer(*result));
+		return r;
+	}
+
+	aux->write_locked = 1;
+	aux->validator = v;
+
+	return 0;
+}
+
+int dm_bm_unlock(struct dm_block *b)
+{
+	struct buffer_aux *aux;
+	aux = dm_bufio_get_aux_data(to_buffer(b));
+
+	if (aux->write_locked) {
+		dm_bufio_mark_buffer_dirty(to_buffer(b));
+		bl_up_write(&aux->lock);
+	} else
+		bl_up_read(&aux->lock);
+
+	dm_bufio_release(to_buffer(b));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_bm_unlock);
+
+int dm_bm_unlock_move(struct dm_block *b, dm_block_t n)
+{
+	struct buffer_aux *aux;
+
+	aux = dm_bufio_get_aux_data(to_buffer(b));
+
+	if (aux->write_locked) {
+		dm_bufio_mark_buffer_dirty(to_buffer(b));
+		bl_up_write(&aux->lock);
+	} else
+		bl_up_read(&aux->lock);
+
+	dm_bufio_release_move(to_buffer(b), n);
+	return 0;
+}
+
+int dm_bm_flush_and_unlock(struct dm_block_manager *bm,
+			   struct dm_block *superblock)
+{
+	int r;
+
+	r = dm_bufio_write_dirty_buffers(to_bufio(bm));
+	if (unlikely(r))
+		return r;
+	r = dm_bufio_issue_flush(to_bufio(bm));
+	if (unlikely(r))
+		return r;
+
+	dm_bm_unlock(superblock);
+
+	r = dm_bufio_write_dirty_buffers(to_bufio(bm));
+	if (unlikely(r))
+		return r;
+	r = dm_bufio_issue_flush(to_bufio(bm));
+	if (unlikely(r))
+		return r;
+
+	return 0;
+}
+
+u32 dm_bm_checksum(const void *data, size_t len, u32 init_xor)
+{
+	return crc32c(~(u32) 0, data, len) ^ init_xor;
+}
+EXPORT_SYMBOL_GPL(dm_bm_checksum);
+
+/*----------------------------------------------------------------*/
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Joe Thornber <[e-mail]>");
+MODULE_DESCRIPTION("Immutable metadata library for dm");
+
+/*----------------------------------------------------------------*/

drivers/md/persistent-data/dm-block-manager.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _LINUX_DM_BLOCK_MANAGER_H
+#define _LINUX_DM_BLOCK_MANAGER_H
+
+#include <linux/types.h>
+#include <linux/blkdev.h>
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Block number.
+ */
+typedef uint64_t dm_block_t;
+struct dm_block;
+
+dm_block_t dm_block_location(struct dm_block *b);
+void *dm_block_data(struct dm_block *b);
+
+/*----------------------------------------------------------------*/
+
+/*
+ * @name should be a unique identifier for the block manager, no longer
+ * than 32 chars.
+ *
+ * @max_held_per_thread should be the maximum number of locks, read or
+ * write, that an individual thread holds at any one time.
+ */
+struct dm_block_manager;
+struct dm_block_manager *dm_block_manager_create(
+	struct block_device *bdev, unsigned block_size,
+	unsigned cache_size, unsigned max_held_per_thread);
+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);
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The validator allows the caller to verify newly-read data and modify
+ * the data just before writing, e.g. 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 the checksum is valid or < 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 through @result 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 @result 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
+ * available immediately.
+ */
+int dm_bm_read_try_lock(struct dm_block_manager *bm, dm_block_t b,
+			struct dm_block_validator *v,
+			struct dm_block **result);
+
+/*
+ * Use dm_bm_write_lock_zero() when you know you're going to
+ * overwrite the block completely.  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);
+
+/*
+ * An optimisation; we often want to copy a block's contents to a new
+ * block.  eg, as part of the shadowing operation.  It's far better for
+ * bufio to do this move behind the scenes than hold 2 locks and memcpy the
+ * data.
+ */
+int dm_bm_unlock_move(struct dm_block *b, dm_block_t n);
+
+/*
+ * It's a common idiom to have a superblock that should be committed last.
+ *
+ * @superblock should be write-locked on entry. 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);
+
+u32 dm_bm_checksum(const void *data, size_t len, u32 init_xor);
+
+/*----------------------------------------------------------------*/
+
+#endif	/* _LINUX_DM_BLOCK_MANAGER_H */

drivers/md/persistent-data/dm-btree-internal.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_BTREE_INTERNAL_H
+#define DM_BTREE_INTERNAL_H
+
+#include "dm-btree.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * 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
+};
+
+/*
+ * Every btree node begins with this structure.  Make sure it's a multiple
+ * of 8-bytes in size, otherwise the 64bit keys will be mis-aligned.
+ */
+struct node_header {
+	__le32 csum;
+	__le32 flags;
+	__le64 blocknr; /* Block this node is supposed to live in. */
+
+	__le32 nr_entries;
+	__le32 max_entries;
+	__le32 value_size;
+	__le32 padding;
+} __packed;
+
+struct node {
+	struct node_header header;
+	__le64 keys[0];
+} __packed;
+
+
+void inc_children(struct dm_transaction_manager *tm, struct node *n,
+		  struct dm_btree_value_type *vt);
+
+int new_block(struct dm_btree_info *info, struct dm_block **result);
+int unlock_block(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);
+
+/*
+ * The spine must have at least one entry before calling this.
+ */
+struct dm_block *shadow_current(struct shadow_spine *s);
+
+/*
+ * The spine must have at least two entries before calling this.
+ */
+struct dm_block *shadow_parent(struct shadow_spine *s);
+
+int shadow_has_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)];
+}
+
+/*
+ * FIXME: Now that value size is stored in node we don't need the third parm.
+ */
+static inline void *value_ptr(struct node *n, uint32_t index, size_t value_size)
+{
+	BUG_ON(value_size != le32_to_cpu(n->header.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_le = value_base(n);
+
+	return le64_to_cpu(values_le[index]);
+}
+
+/*
+ * Searching for a key within a single node.
+ */
+int lower_bound(struct node *n, uint64_t key);
+
+extern struct dm_block_validator btree_node_validator;
+
+#endif	/* DM_BTREE_INTERNAL_H */

drivers/md/persistent-data/dm-btree-remove.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-btree.h"
+#include "dm-btree-internal.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/module.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);
+	uint32_t value_size = le32_to_cpu(n->header.value_size);
+
+	if (shift < 0) {
+		shift = -shift;
+		BUG_ON(shift > nr_entries);
+		BUG_ON((void *) key_ptr(n, shift) >= value_ptr(n, shift, value_size));
+		memmove(key_ptr(n, 0),
+			key_ptr(n, shift),
+			(nr_entries - shift) * sizeof(__le64));
+		memmove(value_ptr(n, 0, value_size),
+			value_ptr(n, shift, value_size),
+			(nr_entries - shift) * value_size);
+	} else {
+		BUG_ON(nr_entries + shift > le32_to_cpu(n->header.max_entries));
+		memmove(key_ptr(n, shift),
+			key_ptr(n, 0),
+			nr_entries * sizeof(__le64));
+		memmove(value_ptr(n, shift, value_size),
+			value_ptr(n, 0, value_size),
+			nr_entries * value_size);
+	}
+}
+
+static void node_copy(struct node *left, struct node *right, int shift)
+{
+	uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
+	uint32_t value_size = le32_to_cpu(left->header.value_size);
+	BUG_ON(value_size != le32_to_cpu(right->header.value_size));
+
+	if (shift < 0) {
+		shift = -shift;
+		BUG_ON(nr_left + shift > le32_to_cpu(left->header.max_entries));
+		memcpy(key_ptr(left, nr_left),
+		       key_ptr(right, 0),
+		       shift * sizeof(__le64));
+		memcpy(value_ptr(left, nr_left, value_size),
+		       value_ptr(right, 0, value_size),
+		       shift * value_size);
+	} else {
+		BUG_ON(shift > le32_to_cpu(right->header.max_entries));
+		memcpy(key_ptr(right, 0),
+		       key_ptr(left, nr_left - shift),
+		       shift * sizeof(__le64));
+		memcpy(value_ptr(right, 0, value_size),
+		       value_ptr(left, nr_left - shift, value_size),
+		       shift * value_size);
+	}
+}
+
+/*
+ * Delete a specific entry from a leaf node.
+ */
+static void delete_at(struct node *n, unsigned index)
+{
+	unsigned nr_entries = le32_to_cpu(n->header.nr_entries);
+	unsigned nr_to_copy = nr_entries - (index + 1);
+	uint32_t value_size = le32_to_cpu(n->header.value_size);
+	BUG_ON(index >= nr_entries);
+
+	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);
+
+	*((__le64 *) value_ptr(parent, index, sizeof(__le64))) =
+		cpu_to_le64(dm_block_location(result->block));
+
+	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)
+		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);
+	BUG_ON(le32_to_cpu(left->header.nr_entries) > le32_to_cpu(left->header.max_entries));
+
+	right->header.nr_entries =
+		cpu_to_le32(le32_to_cpu(right->header.nr_entries) + count);
+	BUG_ON(le32_to_cpu(right->header.nr_entries) > le32_to_cpu(right->header.max_entries));
+}
+
+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);
+		delete_at(parent, r->index);
+
+		/*
+		 * 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;
+		unsigned shift_ = nr_left - target_left;
+		BUG_ON(le32_to_cpu(left->header.max_entries) <= nr_left - shift_);
+		BUG_ON(le32_to_cpu(right->header.max_entries) <= nr_right + shift_);
+		shift(left, right, nr_left - target_left);
+		*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;
+	}
+
+	return exit_child(info, &right);
+}
+
+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);
+
+	unsigned target;
+
+	BUG_ON(left->header.max_entries != center->header.max_entries);
+	BUG_ON(center->header.max_entries != right->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);
+
+		BUG_ON(nr_left + shift > max_entries);
+		node_copy(left, center, -shift);
+		left->header.nr_entries = cpu_to_le32(nr_left + shift);
+
+		if (shift != nr_center) {
+			shift = nr_center - shift;
+			BUG_ON((nr_right + shift) >= max_entries);
+			node_shift(right, shift);
+			node_copy(center, right, shift);
+			right->header.nr_entries = cpu_to_le32(nr_right + shift);
+		}
+		*key_ptr(parent, r->index) = right->keys[0];
+
+		delete_at(parent, c->index);
+		r->index--;
+
+		dm_tm_dec(info->tm, dm_block_location(c->block));
+		__rebalance2(info, parent, l, r);
+
+		return;
+	}
+
+	/*
+	 * Rebalance
+	 */
+	target = (nr_left + nr_center + nr_right) / 3;
+	BUG_ON(target > max_entries);
+
+	/*
+	 * Adjust the left node
+	 */
+	shift(left, center, nr_left - target);
+
+	/*
+	 * Adjust the right node
+	 */
+	shift(center, right, target - nr_right);
+	*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 *n;
+
+	r = dm_tm_read_lock(tm, b, &btree_node_validator, &block);
+	if (r)
+		return r;
+
+	n = dm_block_data(block);
+	*result = le32_to_cpu(n->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);
+		if (r)
+			return r;
+
+		dm_tm_dec(info->tm, dm_block_location(child));
+		return 0;
+	}
+
+	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;
+	has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 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
+ * 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, r;
+	struct node *n;
+
+	for (;;) {
+		r = shadow_step(s, root, vt);
+		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_has_parent(s)) {
+			__le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
+			memcpy(value_ptr(dm_block_data(shadow_parent(s)), i, sizeof(__le64)),
+			       &location, sizeof(__le64));
+		}
+
+		n = dm_block_data(shadow_current(s));
+
+		if (le32_to_cpu(n->header.flags) & LEAF_NODE)
+			return do_leaf(n, key, index);
+
+		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], (unsigned *)&index);
+		if (r < 0)
+			break;
+
+		n = dm_block_data(shadow_current(&spine));
+		if (level != last_level) {
+			root = value64(n, index);
+			continue;
+		}
+
+		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);
+	}
+
+	*new_root = shadow_root(&spine);
+	exit_shadow_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_remove);

drivers/md/persistent-data/dm-btree-spine.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-btree-internal.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "btree spine"
+
+/*----------------------------------------------------------------*/
+
+#define BTREE_CSUM_XOR 121107
+
+static int node_check(struct dm_block_validator *v,
+		      struct dm_block *b,
+		      size_t block_size);
+
+static void node_prepare_for_write(struct dm_block_validator *v,
+				   struct dm_block *b,
+				   size_t block_size)
+{
+	struct node *n = dm_block_data(b);
+	struct node_header *h = &n->header;
+
+	h->blocknr = cpu_to_le64(dm_block_location(b));
+	h->csum = cpu_to_le32(dm_bm_checksum(&h->flags,
+					     block_size - sizeof(__le32),
+					     BTREE_CSUM_XOR));
+
+	BUG_ON(node_check(v, b, 4096));
+}
+
+static int node_check(struct dm_block_validator *v,
+		      struct dm_block *b,
+		      size_t block_size)
+{
+	struct node *n = dm_block_data(b);
+	struct node_header *h = &n->header;
+	size_t value_size;
+	__le32 csum_disk;
+	uint32_t flags;
+
+	if (dm_block_location(b) != le64_to_cpu(h->blocknr)) {
+		DMERR("node_check failed blocknr %llu wanted %llu",
+		      le64_to_cpu(h->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum_disk = cpu_to_le32(dm_bm_checksum(&h->flags,
+					       block_size - sizeof(__le32),
+					       BTREE_CSUM_XOR));
+	if (csum_disk != h->csum) {
+		DMERR("node_check failed csum %u wanted %u",
+		      le32_to_cpu(csum_disk), le32_to_cpu(h->csum));
+		return -EILSEQ;
+	}
+
+	value_size = le32_to_cpu(h->value_size);
+
+	if (sizeof(struct node_header) +
+	    (sizeof(__le64) + value_size) * le32_to_cpu(h->max_entries) > block_size) {
+		DMERR("node_check failed: max_entries too large");
+		return -EILSEQ;
+	}
+
+	if (le32_to_cpu(h->nr_entries) > le32_to_cpu(h->max_entries)) {
+		DMERR("node_check failed, too many entries");
+		return -EILSEQ;
+	}
+
+	/*
+	 * The node must be either INTERNAL or LEAF.
+	 */
+	flags = le32_to_cpu(h->flags);
+	if (!(flags & INTERNAL_NODE) && !(flags & LEAF_NODE)) {
+		DMERR("node_check failed, node is neither INTERNAL or LEAF");
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+struct dm_block_validator btree_node_validator = {
+	.name = "btree_node",
+	.prepare_for_write = node_prepare_for_write,
+	.check = node_check
+};
+
+/*----------------------------------------------------------------*/
+
+static 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);
+}
+
+static int bn_shadow(struct dm_btree_info *info, dm_block_t orig,
+	      struct dm_btree_value_type *vt,
+	      struct dm_block **result)
+{
+	int r, inc;
+
+	r = dm_tm_shadow_block(info->tm, orig, &btree_node_validator,
+			       result, &inc);
+	if (!r && inc)
+		inc_children(info->tm, dm_block_data(*result), vt);
+
+	return r;
+}
+
+int new_block(struct dm_btree_info *info, struct dm_block **result)
+{
+	return dm_tm_new_block(info->tm, &btree_node_validator, result);
+}
+
+int unlock_block(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 = unlock_block(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 = unlock_block(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)
+		s->count++;
+
+	return r;
+}
+
+struct node *ro_node(struct ro_spine *s)
+{
+	struct dm_block *block;
+
+	BUG_ON(!s->count);
+	block = s->nodes[s->count - 1];
+
+	return dm_block_data(block);
+}
+
+/*----------------------------------------------------------------*/
+
+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 = unlock_block(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 r;
+
+	if (s->count == 2) {
+		r = unlock_block(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);
+	if (!r) {
+		if (!s->count)
+			s->root = dm_block_location(s->nodes[0]);
+
+		s->count++;
+	}
+
+	return r;
+}
+
+struct dm_block *shadow_current(struct shadow_spine *s)
+{
+	BUG_ON(!s->count);
+
+	return s->nodes[s->count - 1];
+}
+
+struct dm_block *shadow_parent(struct shadow_spine *s)
+{
+	BUG_ON(s->count != 2);
+
+	return s->count == 2 ? s->nodes[0] : NULL;
+}
+
+int shadow_has_parent(struct shadow_spine *s)
+{
+	return s->count >= 2;
+}
+
+int shadow_root(struct shadow_spine *s)
+{
+	return s->root;
+}

drivers/md/persistent-data/dm-btree.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-btree-internal.h"
+#include "dm-space-map.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/module.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "btree"
+
+/*----------------------------------------------------------------
+ * Array manipulation
+ *--------------------------------------------------------------*/
+static void memcpy_disk(void *dest, const void *src, size_t len)
+	__dm_written_to_disk(src)
+{
+	memcpy(dest, src, len);
+	__dm_unbless_for_disk(src);
+}
+
+static void array_insert(void *base, size_t elt_size, unsigned nr_elts,
+			 unsigned index, void *elt)
+	__dm_written_to_disk(elt)
+{
+	if (index < nr_elts)
+		memmove(base + (elt_size * (index + 1)),
+			base + (elt_size * index),
+			(nr_elts - index) * elt_size);
+
+	memcpy_disk(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);
+}
+
+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));
+}
+
+static int insert_at(size_t value_size, struct node *node, unsigned index,
+		      uint64_t key, void *value)
+		      __dm_written_to_disk(value)
+{
+	uint32_t nr_entries = le32_to_cpu(node->header.nr_entries);
+	__le64 key_le = cpu_to_le64(key);
+
+	if (index > nr_entries ||
+	    index >= le32_to_cpu(node->header.max_entries)) {
+		DMERR("too many entries in btree node for insert");
+		__dm_unbless_for_disk(value);
+		return -ENOMEM;
+	}
+
+	__dm_bless_for_disk(&key_le);
+
+	array_insert(node->keys, sizeof(*node->keys), nr_entries, index, &key_le);
+	array_insert(value_base(node), value_size, nr_entries, index, value);
+	node->header.nr_entries = cpu_to_le32(nr_entries + 1);
+
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * We want 3n entries (for some n).  This works more nicely for repeated
+ * insert remove loops than (2n + 1).
+ */
+static 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 = 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 = 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);
+	n->header.value_size = cpu_to_le32(info->value_type.size);
+
+	*root = dm_block_location(b);
+	return unlock_block(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 int top_frame(struct del_stack *s, struct frame **f)
+{
+	if (s->top < 0) {
+		DMERR("btree deletion stack empty");
+		return -EINVAL;
+	}
+
+	*f = s->spine + s->top;
+
+	return 0;
+}
+
+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;
+
+	if (s->top >= MAX_SPINE_DEPTH - 1) {
+		DMERR("btree deletion stack out of memory");
+		return -ENOMEM;
+	}
+
+	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)
+{
+	int r;
+	struct del_stack *s;
+
+	s = kmalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+	s->tm = info->tm;
+	s->top = -1;
+
+	r = push_frame(s, root, 1);
+	if (r)
+		goto out;
+
+	while (unprocessed_frames(s)) {
+		uint32_t flags;
+		struct frame *f;
+		dm_block_t b;
+
+		r = top_frame(s, &f);
+		if (r)
+			goto out;
+
+		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 out;
+
+		} 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 out;
+
+		} 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;
+		}
+	}
+
+out:
+	kfree(s);
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_del);
+
+/*----------------------------------------------------------------*/
+
+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_le)
+{
+	unsigned level, last_level = info->levels - 1;
+	int r = -ENODATA;
+	uint64_t rkey;
+	__le64 internal_value_le;
+	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_le;
+			size = info->value_type.size;
+
+		} else {
+			value_p = &internal_value_le;
+			size = sizeof(uint64_t);
+		}
+
+		r = btree_lookup_raw(&spine, root, keys[level],
+				     lower_bound, &rkey,
+				     value_p, size);
+
+		if (!r) {
+			if (rkey != keys[level]) {
+				exit_ro_spine(&spine);
+				return -ENODATA;
+			}
+		} else {
+			exit_ro_spine(&spine);
+			return r;
+		}
+
+		root = le64_to_cpu(internal_value_le);
+	}
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_lookup);
+
+/*
+ * 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 r;
+	size_t size;
+	unsigned nr_left, nr_right;
+	struct dm_block *left, *right, *parent;
+	struct node *ln, *rn, *pn;
+	__le64 location;
+
+	left = shadow_current(s);
+
+	r = new_block(s->info, &right);
+	if (r < 0)
+		return r;
+
+	ln = dm_block_data(left);
+	rn = dm_block_data(right);
+
+	nr_left = le32_to_cpu(ln->header.nr_entries) / 2;
+	nr_right = le32_to_cpu(ln->header.nr_entries) - nr_left;
+
+	ln->header.nr_entries = cpu_to_le32(nr_left);
+
+	rn->header.flags = ln->header.flags;
+	rn->header.nr_entries = cpu_to_le32(nr_right);
+	rn->header.max_entries = ln->header.max_entries;
+	rn->header.value_size = ln->header.value_size;
+	memcpy(rn->keys, ln->keys + nr_left, nr_right * sizeof(rn->keys[0]));
+
+	size = le32_to_cpu(ln->header.flags) & INTERNAL_NODE ?
+		sizeof(uint64_t) : s->info->value_type.size;
+	memcpy(value_ptr(rn, 0, size), value_ptr(ln, nr_left, size),
+	       size * nr_right);
+
+	/*
+	 * Patch up the parent
+	 */
+	parent = shadow_parent(s);
+
+	pn = dm_block_data(parent);
+	location = cpu_to_le64(dm_block_location(left));
+	__dm_bless_for_disk(&location);
+	memcpy_disk(value_ptr(pn, parent_index, sizeof(__le64)),
+		    &location, sizeof(__le64));
+
+	location = cpu_to_le64(dm_block_location(right));
+	__dm_bless_for_disk(&location);
+
+	r = insert_at(sizeof(__le64), pn, parent_index + 1,
+		      le64_to_cpu(rn->keys[0]), &location);
+	if (r)
+		return r;
+
+	if (key < le64_to_cpu(rn->keys[0])) {
+		unlock_block(s->info, right);
+		s->nodes[1] = left;
+	} else {
+		unlock_block(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 r;
+	size_t size;
+	unsigned nr_left, nr_right;
+	struct dm_block *left, *right, *new_parent;
+	struct node *pn, *ln, *rn;
+	__le64 val;
+
+	new_parent = shadow_current(s);
+
+	r = new_block(s->info, &left);
+	if (r < 0)
+		return r;
+
+	r = new_block(s->info, &right);
+	if (r < 0) {
+		/* FIXME: put left */
+		return r;
+	}
+
+	pn = dm_block_data(new_parent);
+	ln = dm_block_data(left);
+	rn = dm_block_data(right);
+
+	nr_left = le32_to_cpu(pn->header.nr_entries) / 2;
+	nr_right = le32_to_cpu(pn->header.nr_entries) - nr_left;
+
+	ln->header.flags = pn->header.flags;
+	ln->header.nr_entries = cpu_to_le32(nr_left);
+	ln->header.max_entries = pn->header.max_entries;
+	ln->header.value_size = pn->header.value_size;
+
+	rn->header.flags = pn->header.flags;
+	rn->header.nr_entries = cpu_to_le32(nr_right);
+	rn->header.max_entries = pn->header.max_entries;
+	rn->header.value_size = pn->header.value_size;
+
+	memcpy(ln->keys, pn->keys, nr_left * sizeof(pn->keys[0]));
+	memcpy(rn->keys, pn->keys + nr_left, nr_right * sizeof(pn->keys[0]));
+
+	size = le32_to_cpu(pn->header.flags) & INTERNAL_NODE ?
+		sizeof(__le64) : s->info->value_type.size;
+	memcpy(value_ptr(ln, 0, size), value_ptr(pn, 0, size), nr_left * size);
+	memcpy(value_ptr(rn, 0, size), value_ptr(pn, nr_left, size),
+	       nr_right * size);
+
+	/* new_parent should just point to l and r now */
+	pn->header.flags = cpu_to_le32(INTERNAL_NODE);
+	pn->header.nr_entries = cpu_to_le32(2);
+	pn->header.max_entries = cpu_to_le32(
+		calc_max_entries(sizeof(__le64),
+				 dm_bm_block_size(
+					 dm_tm_get_bm(s->info->tm))));
+	pn->header.value_size = cpu_to_le32(sizeof(__le64));
+
+	val = cpu_to_le64(dm_block_location(left));
+	__dm_bless_for_disk(&val);
+	pn->keys[0] = ln->keys[0];
+	memcpy_disk(value_ptr(pn, 0, sizeof(__le64)), &val, sizeof(__le64));
+
+	val = cpu_to_le64(dm_block_location(right));
+	__dm_bless_for_disk(&val);
+	pn->keys[1] = rn->keys[0];
+	memcpy_disk(value_ptr(pn, 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) {
+		unlock_block(s->info, s->nodes[0]);
+		s->nodes[0] = new_parent;
+	}
+	if (key < le64_to_cpu(rn->keys[0])) {
+		unlock_block(s->info, right);
+		s->nodes[1] = left;
+	} else {
+		unlock_block(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, top = 1;
+	struct node *node;
+
+	for (;;) {
+		r = shadow_step(s, root, vt);
+		if (r < 0)
+			return r;
+
+		node = dm_block_data(shadow_current(s));
+
+		/*
+		 * 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_has_parent(s) && i >= 0) { /* FIXME: second clause unness. */
+			__le64 location = cpu_to_le64(dm_block_location(shadow_current(s)));
+
+			__dm_bless_for_disk(&location);
+			memcpy_disk(value_ptr(dm_block_data(shadow_parent(s)), i, sizeof(uint64_t)),
+				    &location, sizeof(__le64));
+		}
+
+		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;
+		}
+
+		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++;
+
+	*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)
+		  __dm_written_to_disk(value)
+{
+	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 - 1); level++) {
+		r = btree_insert_raw(&spine, block, &le64_type, keys[level], &index);
+		if (r < 0)
+			goto bad;
+
+		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 (need_insert) {
+			dm_block_t new_tree;
+			__le64 new_le;
+
+			r = dm_btree_empty(info, &new_tree);
+			if (r < 0)
+				goto bad;
+
+			new_le = cpu_to_le64(new_tree);
+			__dm_bless_for_disk(&new_le);
+
+			r = insert_at(sizeof(uint64_t), n, index,
+				      keys[level], &new_le);
+			if (r)
+				goto bad;
+		}
+
+		if (level < last_level)
+			block = value64(n, index);
+	}
+
+	r = btree_insert_raw(&spine, block, &info->value_type,
+			     keys[level], &index);
+	if (r < 0)
+		goto bad;
+
+	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 (need_insert) {
+		if (inserted)
+			*inserted = 1;
+
+		r = insert_at(info->value_type.size, n, index,
+			      keys[level], value);
+		if (r)
+			goto bad_unblessed;
+	} 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_disk(value_ptr(n, index, info->value_type.size),
+			    value, info->value_type.size);
+	}
+
+	*new_root = shadow_root(&spine);
+	exit_shadow_spine(&spine);
+
+	return 0;
+
+bad:
+	__dm_unbless_for_disk(value);
+bad_unblessed:
+	exit_shadow_spine(&spine);
+	return r;
+}
+
+int dm_btree_insert(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, void *value, dm_block_t *new_root)
+		    __dm_written_to_disk(value)
+{
+	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)
+			   __dm_written_to_disk(value)
+{
+	return insert(info, root, keys, value, new_root, inserted);
+}
+EXPORT_SYMBOL_GPL(dm_btree_insert_notify);
+
+/*----------------------------------------------------------------*/
+
+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)
+			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);

drivers/md/persistent-data/dm-btree.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+#ifndef _LINUX_DM_BTREE_H
+#define _LINUX_DM_BTREE_H
+
+#include "dm-block-manager.h"
+
+struct dm_transaction_manager;
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Annotations used to check on-disk metadata is handled as little-endian.
+ */
+#ifdef __CHECKER__
+#  define __dm_written_to_disk(x) __releases(x)
+#  define __dm_reads_from_disk(x) __acquires(x)
+#  define __dm_bless_for_disk(x) __acquire(x)
+#  define __dm_unbless_for_disk(x) __release(x)
+#else
+#  define __dm_written_to_disk(x)
+#  define __dm_reads_from_disk(x)
+#  define __dm_bless_for_disk(x)
+#  define __dm_unbless_for_disk(x)
+#endif
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Manipulates hierarchical B+ trees with 64-bit keys and arbitrary-sized
+ * values.
+ */
+
+/*
+ * Infomation about the values stored within the btree.
+ */
+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 the corresponding feature.
+	 */
+
+	/*
+	 * The btree is making a duplicate of the value, for instance
+	 * because previously-shared btree nodes have now diverged.
+	 * @value argument is the new copy that the copy function may modify.
+	 * (Probably it just wants to increment a reference count
+	 * somewhere.) This method is _not_ called for insertion of a new
+	 * value: It is 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);
+
+	/*
+	 * A 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 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);
+
+/*
+ * 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_le);
+
+/*
+ * 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)
+		    __dm_written_to_disk(value);
+
+/*
+ * 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)
+			   __dm_written_to_disk(value);
+
+/*
+ * 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)).
+ */
+int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
+		    uint64_t *keys, dm_block_t *new_root);
+
+/*
+ * 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	/* _LINUX_DM_BTREE_H */

drivers/md/persistent-data/dm-persistent-data-internal.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _DM_PERSISTENT_DATA_INTERNAL_H
+#define _DM_PERSISTENT_DATA_INTERNAL_H
+
+#include "dm-block-manager.h"
+
+static inline unsigned dm_hash_block(dm_block_t b, unsigned hash_mask)
+{
+	const unsigned BIG_PRIME = 4294967291UL;
+
+	return (((unsigned) b) * BIG_PRIME) & hash_mask;
+}
+
+#endif	/* _PERSISTENT_DATA_INTERNAL_H */

drivers/md/persistent-data/dm-space-map-checker.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-space-map-checker.h"
+
+#include <linux/device-mapper.h>
+
+#ifdef CONFIG_DM_DEBUG_SPACE_MAPS
+
+#define DM_MSG_PREFIX "space map checker"
+
+/*----------------------------------------------------------------*/
+
+struct count_array {
+	dm_block_t nr;
+	dm_block_t nr_free;
+
+	uint32_t *counts;
+};
+
+static int ca_get_count(struct count_array *ca, dm_block_t b, uint32_t *count)
+{
+	if (b >= ca->nr)
+		return -EINVAL;
+
+	*count = ca->counts[b];
+	return 0;
+}
+
+static int ca_count_more_than_one(struct count_array *ca, dm_block_t b, int *r)
+{
+	if (b >= ca->nr)
+		return -EINVAL;
+
+	*r = ca->counts[b] > 1;
+	return 0;
+}
+
+static int ca_set_count(struct count_array *ca, dm_block_t b, uint32_t count)
+{
+	uint32_t old_count;
+
+	if (b >= ca->nr)
+		return -EINVAL;
+
+	old_count = ca->counts[b];
+
+	if (!count && old_count)
+		ca->nr_free++;
+
+	else if (count && !old_count)
+		ca->nr_free--;
+
+	ca->counts[b] = count;
+	return 0;
+}
+
+static int ca_inc_block(struct count_array *ca, dm_block_t b)
+{
+	if (b >= ca->nr)
+		return -EINVAL;
+
+	ca_set_count(ca, b, ca->counts[b] + 1);
+	return 0;
+}
+
+static int ca_dec_block(struct count_array *ca, dm_block_t b)
+{
+	if (b >= ca->nr)
+		return -EINVAL;
+
+	BUG_ON(ca->counts[b] == 0);
+	ca_set_count(ca, b, ca->counts[b] - 1);
+	return 0;
+}
+
+static int ca_create(struct count_array *ca, struct dm_space_map *sm)
+{
+	int r;
+	dm_block_t nr_blocks;
+
+	r = dm_sm_get_nr_blocks(sm, &nr_blocks);
+	if (r)
+		return r;
+
+	ca->nr = nr_blocks;
+	ca->nr_free = nr_blocks;
+	ca->counts = kzalloc(sizeof(*ca->counts) * nr_blocks, GFP_KERNEL);
+	if (!ca->counts)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int ca_load(struct count_array *ca, struct dm_space_map *sm)
+{
+	int r;
+	uint32_t count;
+	dm_block_t nr_blocks, i;
+
+	r = dm_sm_get_nr_blocks(sm, &nr_blocks);
+	if (r)
+		return r;
+
+	BUG_ON(ca->nr != nr_blocks);
+
+	DMWARN("Loading debug space map from disk.  This may take some time");
+	for (i = 0; i < nr_blocks; i++) {
+		r = dm_sm_get_count(sm, i, &count);
+		if (r) {
+			DMERR("load failed");
+			return r;
+		}
+
+		ca_set_count(ca, i, count);
+	}
+	DMWARN("Load complete");
+
+	return 0;
+}
+
+static int ca_extend(struct count_array *ca, dm_block_t extra_blocks)
+{
+	dm_block_t nr_blocks = ca->nr + extra_blocks;
+	uint32_t *counts = kzalloc(sizeof(*counts) * nr_blocks, GFP_KERNEL);
+	if (!counts)
+		return -ENOMEM;
+
+	memcpy(counts, ca->counts, sizeof(*counts) * ca->nr);
+	kfree(ca->counts);
+	ca->nr = nr_blocks;
+	ca->nr_free += extra_blocks;
+	ca->counts = counts;
+	return 0;
+}
+
+static int ca_commit(struct count_array *old, struct count_array *new)
+{
+	if (old->nr != new->nr) {
+		BUG_ON(old->nr > new->nr);
+		ca_extend(old, new->nr - old->nr);
+	}
+
+	BUG_ON(old->nr != new->nr);
+	old->nr_free = new->nr_free;
+	memcpy(old->counts, new->counts, sizeof(*old->counts) * old->nr);
+	return 0;
+}
+
+static void ca_destroy(struct count_array *ca)
+{
+	kfree(ca->counts);
+}
+
+/*----------------------------------------------------------------*/
+
+struct sm_checker {
+	struct dm_space_map sm;
+
+	struct count_array old_counts;
+	struct count_array counts;
+
+	struct dm_space_map *real_sm;
+};
+
+static void sm_checker_destroy(struct dm_space_map *sm)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+
+	dm_sm_destroy(smc->real_sm);
+	ca_destroy(&smc->old_counts);
+	ca_destroy(&smc->counts);
+	kfree(smc);
+}
+
+static int sm_checker_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_get_nr_blocks(smc->real_sm, count);
+	if (!r)
+		BUG_ON(smc->old_counts.nr != *count);
+	return r;
+}
+
+static int sm_checker_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_get_nr_free(smc->real_sm, count);
+	if (!r) {
+		/*
+		 * Slow, but we know it's correct.
+		 */
+		dm_block_t b, n = 0;
+		for (b = 0; b < smc->old_counts.nr; b++)
+			if (smc->old_counts.counts[b] == 0 &&
+			    smc->counts.counts[b] == 0)
+				n++;
+
+		if (n != *count)
+			DMERR("free block counts differ, checker %u, sm-disk:%u",
+			      (unsigned) n, (unsigned) *count);
+	}
+	return r;
+}
+
+static int sm_checker_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_new_block(smc->real_sm, b);
+
+	if (!r) {
+		BUG_ON(*b >= smc->old_counts.nr);
+		BUG_ON(smc->old_counts.counts[*b] != 0);
+		BUG_ON(*b >= smc->counts.nr);
+		BUG_ON(smc->counts.counts[*b] != 0);
+		ca_set_count(&smc->counts, *b, 1);
+	}
+
+	return r;
+}
+
+static int sm_checker_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_inc_block(smc->real_sm, b);
+	int r2 = ca_inc_block(&smc->counts, b);
+	BUG_ON(r != r2);
+	return r;
+}
+
+static int sm_checker_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_dec_block(smc->real_sm, b);
+	int r2 = ca_dec_block(&smc->counts, b);
+	BUG_ON(r != r2);
+	return r;
+}
+
+static int sm_checker_get_count(struct dm_space_map *sm, dm_block_t b, uint32_t *result)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	uint32_t result2 = 0;
+	int r = dm_sm_get_count(smc->real_sm, b, result);
+	int r2 = ca_get_count(&smc->counts, b, &result2);
+
+	BUG_ON(r != r2);
+	if (!r)
+		BUG_ON(*result != result2);
+	return r;
+}
+
+static int sm_checker_count_more_than_one(struct dm_space_map *sm, dm_block_t b, int *result)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int result2 = 0;
+	int r = dm_sm_count_is_more_than_one(smc->real_sm, b, result);
+	int r2 = ca_count_more_than_one(&smc->counts, b, &result2);
+
+	BUG_ON(r != r2);
+	if (!r)
+		BUG_ON(!(*result) && result2);
+	return r;
+}
+
+static int sm_checker_set_count(struct dm_space_map *sm, dm_block_t b, uint32_t count)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	uint32_t old_rc;
+	int r = dm_sm_set_count(smc->real_sm, b, count);
+	int r2;
+
+	BUG_ON(b >= smc->counts.nr);
+	old_rc = smc->counts.counts[b];
+	r2 = ca_set_count(&smc->counts, b, count);
+	BUG_ON(r != r2);
+
+	return r;
+}
+
+static int sm_checker_commit(struct dm_space_map *sm)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r;
+
+	r = dm_sm_commit(smc->real_sm);
+	if (r)
+		return r;
+
+	r = ca_commit(&smc->old_counts, &smc->counts);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+static int sm_checker_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	int r = dm_sm_extend(smc->real_sm, extra_blocks);
+	if (r)
+		return r;
+
+	return ca_extend(&smc->counts, extra_blocks);
+}
+
+static int sm_checker_root_size(struct dm_space_map *sm, size_t *result)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	return dm_sm_root_size(smc->real_sm, result);
+}
+
+static int sm_checker_copy_root(struct dm_space_map *sm, void *copy_to_here_le, size_t len)
+{
+	struct sm_checker *smc = container_of(sm, struct sm_checker, sm);
+	return dm_sm_copy_root(smc->real_sm, copy_to_here_le, len);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_space_map ops_ = {
+	.destroy = sm_checker_destroy,
+	.get_nr_blocks = sm_checker_get_nr_blocks,
+	.get_nr_free = sm_checker_get_nr_free,
+	.inc_block = sm_checker_inc_block,
+	.dec_block = sm_checker_dec_block,
+	.new_block = sm_checker_new_block,
+	.get_count = sm_checker_get_count,
+	.count_is_more_than_one = sm_checker_count_more_than_one,
+	.set_count = sm_checker_set_count,
+	.commit = sm_checker_commit,
+	.extend = sm_checker_extend,
+	.root_size = sm_checker_root_size,
+	.copy_root = sm_checker_copy_root
+};
+
+struct dm_space_map *dm_sm_checker_create(struct dm_space_map *sm)
+{
+	int r;
+	struct sm_checker *smc;
+
+	if (!sm)
+		return NULL;
+
+	smc = kmalloc(sizeof(*smc), GFP_KERNEL);
+	if (!smc)
+		return NULL;
+
+	memcpy(&smc->sm, &ops_, sizeof(smc->sm));
+	r = ca_create(&smc->old_counts, sm);
+	if (r) {
+		kfree(smc);
+		return NULL;
+	}
+
+	r = ca_create(&smc->counts, sm);
+	if (r) {
+		ca_destroy(&smc->old_counts);
+		kfree(smc);
+		return NULL;
+	}
+
+	smc->real_sm = sm;
+
+	r = ca_load(&smc->counts, sm);
+	if (r) {
+		ca_destroy(&smc->counts);
+		ca_destroy(&smc->old_counts);
+		kfree(smc);
+		return NULL;
+	}
+
+	r = ca_commit(&smc->old_counts, &smc->counts);
+	if (r) {
+		ca_destroy(&smc->counts);
+		ca_destroy(&smc->old_counts);
+		kfree(smc);
+		return NULL;
+	}
+
+	return &smc->sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_checker_create);
+
+struct dm_space_map *dm_sm_checker_create_fresh(struct dm_space_map *sm)
+{
+	int r;
+	struct sm_checker *smc;
+
+	if (!sm)
+		return NULL;
+
+	smc = kmalloc(sizeof(*smc), GFP_KERNEL);
+	if (!smc)
+		return NULL;
+
+	memcpy(&smc->sm, &ops_, sizeof(smc->sm));
+	r = ca_create(&smc->old_counts, sm);
+	if (r) {
+		kfree(smc);
+		return NULL;
+	}
+
+	r = ca_create(&smc->counts, sm);
+	if (r) {
+		ca_destroy(&smc->old_counts);
+		kfree(smc);
+		return NULL;
+	}
+
+	smc->real_sm = sm;
+	return &smc->sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_checker_create_fresh);
+
+/*----------------------------------------------------------------*/
+
+#else
+
+struct dm_space_map *dm_sm_checker_create(struct dm_space_map *sm)
+{
+	return sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_checker_create);
+
+struct dm_space_map *dm_sm_checker_create_fresh(struct dm_space_map *sm)
+{
+	return sm;
+}
+EXPORT_SYMBOL_GPL(dm_sm_checker_create_fresh);
+
+/*----------------------------------------------------------------*/
+
+#endif

drivers/md/persistent-data/dm-space-map-checker.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef SNAPSHOTS_SPACE_MAP_CHECKER_H
+#define SNAPSHOTS_SPACE_MAP_CHECKER_H
+
+#include "dm-space-map.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * This space map wraps a real on-disk space map, and verifies all of its
+ * operations.  It uses a lot of memory, so only use if you have a specific
+ * problem that you're debugging.
+ *
+ * Ownership of @sm passes.
+ */
+struct dm_space_map *dm_sm_checker_create(struct dm_space_map *sm);
+struct dm_space_map *dm_sm_checker_create_fresh(struct dm_space_map *sm);
+
+/*----------------------------------------------------------------*/
+
+#endif

drivers/md/persistent-data/dm-space-map-common.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-space-map-common.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/bitops.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "space map common"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Index validator.
+ */
+#define INDEX_CSUM_XOR 160478
+
+static void index_prepare_for_write(struct dm_block_validator *v,
+				    struct dm_block *b,
+				    size_t block_size)
+{
+	struct disk_metadata_index *mi_le = dm_block_data(b);
+
+	mi_le->blocknr = cpu_to_le64(dm_block_location(b));
+	mi_le->csum = cpu_to_le32(dm_bm_checksum(&mi_le->padding,
+						 block_size - sizeof(__le32),
+						 INDEX_CSUM_XOR));
+}
+
+static int index_check(struct dm_block_validator *v,
+		       struct dm_block *b,
+		       size_t block_size)
+{
+	struct disk_metadata_index *mi_le = dm_block_data(b);
+	__le32 csum_disk;
+
+	if (dm_block_location(b) != le64_to_cpu(mi_le->blocknr)) {
+		DMERR("index_check failed blocknr %llu wanted %llu",
+		      le64_to_cpu(mi_le->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum_disk = cpu_to_le32(dm_bm_checksum(&mi_le->padding,
+					       block_size - sizeof(__le32),
+					       INDEX_CSUM_XOR));
+	if (csum_disk != mi_le->csum) {
+		DMERR("index_check failed csum %u wanted %u",
+		      le32_to_cpu(csum_disk), le32_to_cpu(mi_le->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+static struct dm_block_validator index_validator = {
+	.name = "index",
+	.prepare_for_write = index_prepare_for_write,
+	.check = index_check
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Bitmap validator
+ */
+#define BITMAP_CSUM_XOR 240779
+
+static void bitmap_prepare_for_write(struct dm_block_validator *v,
+				     struct dm_block *b,
+				     size_t block_size)
+{
+	struct disk_bitmap_header *disk_header = dm_block_data(b);
+
+	disk_header->blocknr = cpu_to_le64(dm_block_location(b));
+	disk_header->csum = cpu_to_le32(dm_bm_checksum(&disk_header->not_used,
+						       block_size - sizeof(__le32),
+						       BITMAP_CSUM_XOR));
+}
+
+static int bitmap_check(struct dm_block_validator *v,
+			struct dm_block *b,
+			size_t block_size)
+{
+	struct disk_bitmap_header *disk_header = dm_block_data(b);
+	__le32 csum_disk;
+
+	if (dm_block_location(b) != le64_to_cpu(disk_header->blocknr)) {
+		DMERR("bitmap check failed blocknr %llu wanted %llu",
+		      le64_to_cpu(disk_header->blocknr), dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum_disk = cpu_to_le32(dm_bm_checksum(&disk_header->not_used,
+					       block_size - sizeof(__le32),
+					       BITMAP_CSUM_XOR));
+	if (csum_disk != disk_header->csum) {
+		DMERR("bitmap check failed csum %u wanted %u",
+		      le32_to_cpu(csum_disk), le32_to_cpu(disk_header->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+static 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
+
+static void *dm_bitmap_data(struct dm_block *b)
+{
+	return dm_block_data(b) + sizeof(struct disk_bitmap_header);
+}
+
+#define WORD_MASK_HIGH 0xAAAAAAAAAAAAAAAAULL
+
+static unsigned bitmap_word_used(void *addr, unsigned b)
+{
+	__le64 *words_le = addr;
+	__le64 *w_le = words_le + (b >> ENTRIES_SHIFT);
+
+	uint64_t bits = le64_to_cpu(*w_le);
+	uint64_t mask = (bits + WORD_MASK_HIGH + 1) & WORD_MASK_HIGH;
+
+	return !(~bits & mask);
+}
+
+static unsigned sm_lookup_bitmap(void *addr, unsigned b)
+{
+	__le64 *words_le = addr;
+	__le64 *w_le = words_le + (b >> ENTRIES_SHIFT);
+	unsigned hi, lo;
+
+	b = (b & (ENTRIES_PER_WORD - 1)) << 1;
+	hi = !!test_bit_le(b, (void *) w_le);
+	lo = !!test_bit_le(b + 1, (void *) w_le);
+	return (hi << 1) | lo;
+}
+
+static void sm_set_bitmap(void *addr, unsigned b, unsigned val)
+{
+	__le64 *words_le = addr;
+	__le64 *w_le = words_le + (b >> ENTRIES_SHIFT);
+
+	b = (b & (ENTRIES_PER_WORD - 1)) << 1;
+
+	if (val & 2)
+		__set_bit_le(b, (void *) w_le);
+	else
+		__clear_bit_le(b, (void *) w_le);
+
+	if (val & 1)
+		__set_bit_le(b + 1, (void *) w_le);
+	else
+		__clear_bit_le(b + 1, (void *) w_le);
+}
+
+static 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)) {
+			*result = begin;
+			return 0;
+		}
+
+		begin++;
+	}
+
+	return -ENOSPC;
+}
+
+/*----------------------------------------------------------------*/
+
+static int sm_ll_init(struct ll_disk *ll, struct dm_transaction_manager *tm)
+{
+	ll->tm = tm;
+
+	ll->bitmap_info.tm = tm;
+	ll->bitmap_info.levels = 1;
+
+	/*
+	 * Because the new bitmap blocks are created via a shadow
+	 * operation, the old entry has already had its reference count
+	 * decremented and we don't need the btree to do any bookkeeping.
+	 */
+	ll->bitmap_info.value_type.size = sizeof(struct disk_index_entry);
+	ll->bitmap_info.value_type.inc = NULL;
+	ll->bitmap_info.value_type.dec = NULL;
+	ll->bitmap_info.value_type.equal = NULL;
+
+	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 disk_bitmap_header)) *
+		ENTRIES_PER_BYTE;
+	ll->nr_blocks = 0;
+	ll->bitmap_root = 0;
+	ll->ref_count_root = 0;
+
+	return 0;
+}
+
+int sm_ll_extend(struct ll_disk *ll, dm_block_t extra_blocks)
+{
+	int r;
+	dm_block_t i, nr_blocks, nr_indexes;
+	unsigned old_blocks, blocks;
+
+	nr_blocks = ll->nr_blocks + extra_blocks;
+	old_blocks = dm_sector_div_up(ll->nr_blocks, ll->entries_per_block);
+	blocks = dm_sector_div_up(nr_blocks, ll->entries_per_block);
+
+	nr_indexes = dm_sector_div_up(nr_blocks, ll->entries_per_block);
+	if (nr_indexes > ll->max_entries(ll)) {
+		DMERR("space map too large");
+		return -EINVAL;
+	}
+
+	for (i = old_blocks; i < blocks; i++) {
+		struct dm_block *b;
+		struct disk_index_entry idx;
+
+		r = dm_tm_new_block(ll->tm, &dm_sm_bitmap_validator, &b);
+		if (r < 0)
+			return r;
+		idx.blocknr = cpu_to_le64(dm_block_location(b));
+
+		r = dm_tm_unlock(ll->tm, b);
+		if (r < 0)
+			return r;
+
+		idx.nr_free = cpu_to_le32(ll->entries_per_block);
+		idx.none_free_before = 0;
+
+		r = ll->save_ie(ll, i, &idx);
+		if (r < 0)
+			return r;
+	}
+
+	ll->nr_blocks = nr_blocks;
+	return 0;
+}
+
+int sm_ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+{
+	int r;
+	dm_block_t index = b;
+	struct disk_index_entry ie_disk;
+	struct dm_block *blk;
+
+	b = do_div(index, ll->entries_per_block);
+	r = ll->load_ie(ll, index, &ie_disk);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_read_lock(ll->tm, le64_to_cpu(ie_disk.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);
+}
+
+int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result)
+{
+	__le32 le_rc;
+	int r = sm_ll_lookup_bitmap(ll, b, result);
+
+	if (r)
+		return r;
+
+	if (*result != 3)
+		return r;
+
+	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;
+}
+
+int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
+			  dm_block_t end, dm_block_t *result)
+{
+	int r;
+	struct disk_index_entry ie_disk;
+	dm_block_t i, index_begin = begin;
+	dm_block_t index_end = dm_sector_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) {
+		struct dm_block *blk;
+		unsigned position;
+		uint32_t bit_end;
+
+		r = ll->load_ie(ll, i, &ie_disk);
+		if (r < 0)
+			return r;
+
+		if (le32_to_cpu(ie_disk.nr_free) == 0)
+			continue;
+
+		r = dm_tm_read_lock(ll->tm, le64_to_cpu(ie_disk.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),
+				 max_t(unsigned, begin, le32_to_cpu(ie_disk.none_free_before)),
+				 bit_end, &position);
+		if (r == -ENOSPC) {
+			/*
+			 * This might happen because we started searching
+			 * part way through the bitmap.
+			 */
+			dm_tm_unlock(ll->tm, blk);
+			continue;
+
+		} else if (r < 0) {
+			dm_tm_unlock(ll->tm, blk);
+			return r;
+		}
+
+		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;
+}
+
+int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
+		 uint32_t ref_count, enum allocation_event *ev)
+{
+	int r;
+	uint32_t bit, old;
+	struct dm_block *nb;
+	dm_block_t index = b;
+	struct disk_index_entry ie_disk;
+	void *bm_le;
+	int inc;
+
+	bit = do_div(index, ll->entries_per_block);
+	r = ll->load_ie(ll, index, &ie_disk);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_shadow_block(ll->tm, le64_to_cpu(ie_disk.blocknr),
+			       &dm_sm_bitmap_validator, &nb, &inc);
+	if (r < 0) {
+		DMERR("dm_tm_shadow_block() failed");
+		return r;
+	}
+	ie_disk.blocknr = cpu_to_le64(dm_block_location(nb));
+
+	bm_le = dm_bitmap_data(nb);
+	old = sm_lookup_bitmap(bm_le, bit);
+
+	if (ref_count <= 2) {
+		sm_set_bitmap(bm_le, bit, ref_count);
+
+		r = dm_tm_unlock(ll->tm, nb);
+		if (r < 0)
+			return r;
+
+#if 0
+		/* FIXME: dm_btree_remove doesn't handle this yet */
+		if (old > 2) {
+			r = dm_btree_remove(&ll->ref_count_info,
+					    ll->ref_count_root,
+					    &b, &ll->ref_count_root);
+			if (r)
+				return r;
+		}
+#endif
+
+	} else {
+		__le32 le_rc = cpu_to_le32(ref_count);
+
+		sm_set_bitmap(bm_le, bit, 3);
+		r = dm_tm_unlock(ll->tm, nb);
+		if (r < 0)
+			return r;
+
+		__dm_bless_for_disk(&le_rc);
+		r = dm_btree_insert(&ll->ref_count_info, ll->ref_count_root,
+				    &b, &le_rc, &ll->ref_count_root);
+		if (r < 0) {
+			DMERR("ref count insert failed");
+			return r;
+		}
+	}
+
+	if (ref_count && !old) {
+		*ev = SM_ALLOC;
+		ll->nr_allocated++;
+		ie_disk.nr_free = cpu_to_le32(le32_to_cpu(ie_disk.nr_free) - 1);
+		if (le32_to_cpu(ie_disk.none_free_before) == bit)
+			ie_disk.none_free_before = cpu_to_le32(bit + 1);
+
+	} else if (old && !ref_count) {
+		*ev = SM_FREE;
+		ll->nr_allocated--;
+		ie_disk.nr_free = cpu_to_le32(le32_to_cpu(ie_disk.nr_free) + 1);
+		ie_disk.none_free_before = cpu_to_le32(min(le32_to_cpu(ie_disk.none_free_before), bit));
+	}
+
+	return ll->save_ie(ll, index, &ie_disk);
+}
+
+int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+{
+	int r;
+	uint32_t rc;
+
+	r = sm_ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	return sm_ll_insert(ll, b, rc + 1, ev);
+}
+
+int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
+{
+	int r;
+	uint32_t rc;
+
+	r = sm_ll_lookup(ll, b, &rc);
+	if (r)
+		return r;
+
+	if (!rc)
+		return -EINVAL;
+
+	return sm_ll_insert(ll, b, rc - 1, ev);
+}
+
+int sm_ll_commit(struct ll_disk *ll)
+{
+	return ll->commit(ll);
+}
+
+/*----------------------------------------------------------------*/
+
+static int metadata_ll_load_ie(struct ll_disk *ll, dm_block_t index,
+			       struct disk_index_entry *ie)
+{
+	memcpy(ie, ll->mi_le.index + index, sizeof(*ie));
+	return 0;
+}
+
+static int metadata_ll_save_ie(struct ll_disk *ll, dm_block_t index,
+			       struct disk_index_entry *ie)
+{
+	memcpy(ll->mi_le.index + index, ie, sizeof(*ie));
+	return 0;
+}
+
+static int metadata_ll_init_index(struct ll_disk *ll)
+{
+	int r;
+	struct dm_block *b;
+
+	r = dm_tm_new_block(ll->tm, &index_validator, &b);
+	if (r < 0)
+		return r;
+
+	memcpy(dm_block_data(b), &ll->mi_le, sizeof(ll->mi_le));
+	ll->bitmap_root = dm_block_location(b);
+
+	return dm_tm_unlock(ll->tm, b);
+}
+
+static int metadata_ll_open(struct ll_disk *ll)
+{
+	int r;
+	struct dm_block *block;
+
+	r = dm_tm_read_lock(ll->tm, ll->bitmap_root,
+			    &index_validator, &block);
+	if (r)
+		return r;
+
+	memcpy(&ll->mi_le, dm_block_data(block), sizeof(ll->mi_le));
+	return dm_tm_unlock(ll->tm, block);
+}
+
+static dm_block_t metadata_ll_max_entries(struct ll_disk *ll)
+{
+	return MAX_METADATA_BITMAPS;
+}
+
+static int metadata_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_le, sizeof(ll->mi_le));
+	ll->bitmap_root = dm_block_location(b);
+
+	return dm_tm_unlock(ll->tm, b);
+}
+
+int sm_ll_new_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm)
+{
+	int r;
+
+	r = sm_ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->load_ie = metadata_ll_load_ie;
+	ll->save_ie = metadata_ll_save_ie;
+	ll->init_index = metadata_ll_init_index;
+	ll->open_index = metadata_ll_open;
+	ll->max_entries = metadata_ll_max_entries;
+	ll->commit = metadata_ll_commit;
+
+	ll->nr_blocks = 0;
+	ll->nr_allocated = 0;
+
+	r = ll->init_index(ll);
+	if (r < 0)
+		return r;
+
+	r = dm_btree_empty(&ll->ref_count_info, &ll->ref_count_root);
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+
+int sm_ll_open_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm,
+			void *root_le, size_t len)
+{
+	int r;
+	struct disk_sm_root *smr = root_le;
+
+	if (len < sizeof(struct disk_sm_root)) {
+		DMERR("sm_metadata root too small");
+		return -ENOMEM;
+	}
+
+	r = sm_ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->load_ie = metadata_ll_load_ie;
+	ll->save_ie = metadata_ll_save_ie;
+	ll->init_index = metadata_ll_init_index;
+	ll->open_index = metadata_ll_open;
+	ll->max_entries = metadata_ll_max_entries;
+	ll->commit = metadata_ll_commit;
+
+	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 ll->open_index(ll);
+}
+
+/*----------------------------------------------------------------*/
+
+static int disk_ll_load_ie(struct ll_disk *ll, dm_block_t index,
+			   struct disk_index_entry *ie)
+{
+	return dm_btree_lookup(&ll->bitmap_info, ll->bitmap_root, &index, ie);
+}
+
+static int disk_ll_save_ie(struct ll_disk *ll, dm_block_t index,
+			   struct disk_index_entry *ie)
+{
+	__dm_bless_for_disk(ie);
+	return dm_btree_insert(&ll->bitmap_info, ll->bitmap_root,
+			       &index, ie, &ll->bitmap_root);
+}
+
+static int disk_ll_init_index(struct ll_disk *ll)
+{
+	return dm_btree_empty(&ll->bitmap_info, &ll->bitmap_root);
+}
+
+static int disk_ll_open(struct ll_disk *ll)
+{
+	/* nothing to do */
+	return 0;
+}
+
+static dm_block_t disk_ll_max_entries(struct ll_disk *ll)
+{
+	return -1ULL;
+}
+
+static int disk_ll_commit(struct ll_disk *ll)
+{
+	return 0;
+}
+
+int sm_ll_new_disk(struct ll_disk *ll, struct dm_transaction_manager *tm)
+{
+	int r;
+
+	r = sm_ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->load_ie = disk_ll_load_ie;
+	ll->save_ie = disk_ll_save_ie;
+	ll->init_index = disk_ll_init_index;
+	ll->open_index = disk_ll_open;
+	ll->max_entries = disk_ll_max_entries;
+	ll->commit = disk_ll_commit;
+
+	ll->nr_blocks = 0;
+	ll->nr_allocated = 0;
+
+	r = ll->init_index(ll);
+	if (r < 0)
+		return r;
+
+	r = dm_btree_empty(&ll->ref_count_info, &ll->ref_count_root);
+	if (r < 0)
+		return r;
+
+	return 0;
+}
+
+int sm_ll_open_disk(struct ll_disk *ll, struct dm_transaction_manager *tm,
+		    void *root_le, size_t len)
+{
+	int r;
+	struct disk_sm_root *smr = root_le;
+
+	if (len < sizeof(struct disk_sm_root)) {
+		DMERR("sm_metadata root too small");
+		return -ENOMEM;
+	}
+
+	r = sm_ll_init(ll, tm);
+	if (r < 0)
+		return r;
+
+	ll->load_ie = disk_ll_load_ie;
+	ll->save_ie = disk_ll_save_ie;
+	ll->init_index = disk_ll_init_index;
+	ll->open_index = disk_ll_open;
+	ll->max_entries = disk_ll_max_entries;
+	ll->commit = disk_ll_commit;
+
+	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 ll->open_index(ll);
+}
+
+/*----------------------------------------------------------------*/

drivers/md/persistent-data/dm-space-map-common.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_SPACE_MAP_COMMON_H
+#define DM_SPACE_MAP_COMMON_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 32-bit ref count.
+ */
+
+struct disk_index_entry {
+	__le64 blocknr;
+	__le32 nr_free;
+	__le32 none_free_before;
+} __packed;
+
+
+#define MAX_METADATA_BITMAPS 255
+struct disk_metadata_index {
+	__le32 csum;
+	__le32 padding;
+	__le64 blocknr;
+
+	struct disk_index_entry index[MAX_METADATA_BITMAPS];
+} __packed;
+
+struct ll_disk;
+
+typedef int (*load_ie_fn)(struct ll_disk *ll, dm_block_t index, struct disk_index_entry *result);
+typedef int (*save_ie_fn)(struct ll_disk *ll, dm_block_t index, struct disk_index_entry *ie);
+typedef int (*init_index_fn)(struct ll_disk *ll);
+typedef int (*open_index_fn)(struct ll_disk *ll);
+typedef dm_block_t (*max_index_entries_fn)(struct ll_disk *ll);
+typedef int (*commit_fn)(struct ll_disk *ll);
+
+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;
+
+	/*
+	 * bitmap_root may be a btree root or a simple index.
+	 */
+	dm_block_t bitmap_root;
+
+	dm_block_t ref_count_root;
+
+	struct disk_metadata_index mi_le;
+	load_ie_fn load_ie;
+	save_ie_fn save_ie;
+	init_index_fn init_index;
+	open_index_fn open_index;
+	max_index_entries_fn max_entries;
+	commit_fn commit;
+};
+
+struct disk_sm_root {
+	__le64 nr_blocks;
+	__le64 nr_allocated;
+	__le64 bitmap_root;
+	__le64 ref_count_root;
+} __packed;
+
+#define ENTRIES_PER_BYTE 4
+
+struct disk_bitmap_header {
+	__le32 csum;
+	__le32 not_used;
+	__le64 blocknr;
+} __packed;
+
+enum allocation_event {
+	SM_NONE,
+	SM_ALLOC,
+	SM_FREE,
+};
+
+/*----------------------------------------------------------------*/
+
+int sm_ll_extend(struct ll_disk *ll, dm_block_t extra_blocks);
+int sm_ll_lookup_bitmap(struct ll_disk *ll, dm_block_t b, uint32_t *result);
+int sm_ll_lookup(struct ll_disk *ll, dm_block_t b, uint32_t *result);
+int sm_ll_find_free_block(struct ll_disk *ll, dm_block_t begin,
+			  dm_block_t end, dm_block_t *result);
+int sm_ll_insert(struct ll_disk *ll, dm_block_t b, uint32_t ref_count, enum allocation_event *ev);
+int sm_ll_inc(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev);
+int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev);
+int sm_ll_commit(struct ll_disk *ll);
+
+int sm_ll_new_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm);
+int sm_ll_open_metadata(struct ll_disk *ll, struct dm_transaction_manager *tm,
+			void *root_le, size_t len);
+
+int sm_ll_new_disk(struct ll_disk *ll, struct dm_transaction_manager *tm);
+int sm_ll_open_disk(struct ll_disk *ll, struct dm_transaction_manager *tm,
+		    void *root_le, size_t len);
+
+/*----------------------------------------------------------------*/
+
+#endif	/* DM_SPACE_MAP_COMMON_H */

drivers/md/persistent-data/dm-space-map-disk.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-space-map-checker.h"
+#include "dm-space-map-common.h"
+#include "dm-space-map-disk.h"
+#include "dm-space-map.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "space map disk"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Space map interface.
+ */
+struct sm_disk {
+	struct dm_space_map sm;
+
+	struct ll_disk ll;
+	struct ll_disk old_ll;
+
+	dm_block_t begin;
+	dm_block_t nr_allocated_this_transaction;
+};
+
+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 sm_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->old_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->old_ll.nr_blocks - smd->old_ll.nr_allocated) - smd->nr_allocated_this_transaction;
+
+	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 sm_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)
+{
+	int r;
+	uint32_t old_count;
+	enum allocation_event ev;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	r = sm_ll_insert(&smd->ll, b, count, &ev);
+	if (!r) {
+		switch (ev) {
+		case SM_NONE:
+			break;
+
+		case SM_ALLOC:
+			/*
+			 * This _must_ be free in the prior transaction
+			 * otherwise we've lost atomicity.
+			 */
+			smd->nr_allocated_this_transaction++;
+			break;
+
+		case SM_FREE:
+			/*
+			 * It's only free if it's also free in the last
+			 * transaction.
+			 */
+			r = sm_ll_lookup(&smd->old_ll, b, &old_count);
+			if (r)
+				return r;
+
+			if (!old_count)
+				smd->nr_allocated_this_transaction--;
+			break;
+		}
+	}
+
+	return r;
+}
+
+static int sm_disk_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r;
+	enum allocation_event ev;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	r = sm_ll_inc(&smd->ll, b, &ev);
+	if (!r && (ev == SM_ALLOC))
+		/*
+		 * This _must_ be free in the prior transaction
+		 * otherwise we've lost atomicity.
+		 */
+		smd->nr_allocated_this_transaction++;
+
+	return r;
+}
+
+static int sm_disk_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r;
+	uint32_t old_count;
+	enum allocation_event ev;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	r = sm_ll_dec(&smd->ll, b, &ev);
+	if (!r && (ev == SM_FREE)) {
+		/*
+		 * It's only free if it's also free in the last
+		 * transaction.
+		 */
+		r = sm_ll_lookup(&smd->old_ll, b, &old_count);
+		if (r)
+			return r;
+
+		if (!old_count)
+			smd->nr_allocated_this_transaction--;
+	}
+
+	return r;
+}
+
+static int sm_disk_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	int r;
+	enum allocation_event ev;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	/* FIXME: we should loop round a couple of times */
+	r = sm_ll_find_free_block(&smd->old_ll, smd->begin, smd->old_ll.nr_blocks, b);
+	if (r)
+		return r;
+
+	smd->begin = *b + 1;
+	r = sm_ll_inc(&smd->ll, *b, &ev);
+	if (!r) {
+		BUG_ON(ev != SM_ALLOC);
+		smd->nr_allocated_this_transaction++;
+	}
+
+	return r;
+}
+
+static int sm_disk_commit(struct dm_space_map *sm)
+{
+	int r;
+	dm_block_t nr_free;
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+
+	r = sm_disk_get_nr_free(sm, &nr_free);
+	if (r)
+		return r;
+
+	r = sm_ll_commit(&smd->ll);
+	if (r)
+		return r;
+
+	memcpy(&smd->old_ll, &smd->ll, sizeof(smd->old_ll));
+	smd->begin = 0;
+	smd->nr_allocated_this_transaction = 0;
+
+	r = sm_disk_get_nr_free(sm, &nr_free);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+static int sm_disk_root_size(struct dm_space_map *sm, size_t *result)
+{
+	*result = sizeof(struct disk_sm_root);
+
+	return 0;
+}
+
+static int sm_disk_copy_root(struct dm_space_map *sm, void *where_le, size_t max)
+{
+	struct sm_disk *smd = container_of(sm, struct sm_disk, sm);
+	struct disk_sm_root root_le;
+
+	root_le.nr_blocks = cpu_to_le64(smd->ll.nr_blocks);
+	root_le.nr_allocated = cpu_to_le64(smd->ll.nr_allocated);
+	root_le.bitmap_root = cpu_to_le64(smd->ll.bitmap_root);
+	root_le.ref_count_root = cpu_to_le64(smd->ll.ref_count_root);
+
+	if (max < sizeof(root_le))
+		return -ENOSPC;
+
+	memcpy(where_le, &root_le, sizeof(root_le));
+
+	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
+};
+
+static struct dm_space_map *dm_sm_disk_create_real(
+	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);
+
+	smd->begin = 0;
+	smd->nr_allocated_this_transaction = 0;
+	memcpy(&smd->sm, &ops, sizeof(smd->sm));
+
+	r = sm_ll_new_disk(&smd->ll, tm);
+	if (r)
+		goto bad;
+
+	r = sm_ll_extend(&smd->ll, nr_blocks);
+	if (r)
+		goto bad;
+
+	r = sm_disk_commit(&smd->sm);
+	if (r)
+		goto bad;
+
+	return &smd->sm;
+
+bad:
+	kfree(smd);
+	return ERR_PTR(r);
+}
+
+struct dm_space_map *dm_sm_disk_create(struct dm_transaction_manager *tm,
+				       dm_block_t nr_blocks)
+{
+	struct dm_space_map *sm = dm_sm_disk_create_real(tm, nr_blocks);
+	return dm_sm_checker_create_fresh(sm);
+}
+EXPORT_SYMBOL_GPL(dm_sm_disk_create);
+
+static struct dm_space_map *dm_sm_disk_open_real(
+	struct dm_transaction_manager *tm,
+	void *root_le, size_t len)
+{
+	int r;
+	struct sm_disk *smd;
+
+	smd = kmalloc(sizeof(*smd), GFP_KERNEL);
+	if (!smd)
+		return ERR_PTR(-ENOMEM);
+
+	smd->begin = 0;
+	smd->nr_allocated_this_transaction = 0;
+	memcpy(&smd->sm, &ops, sizeof(smd->sm));
+
+	r = sm_ll_open_disk(&smd->ll, tm, root_le, len);
+	if (r)
+		goto bad;
+
+	r = sm_disk_commit(&smd->sm);
+	if (r)
+		goto bad;
+
+	return &smd->sm;
+
+bad:
+	kfree(smd);
+	return ERR_PTR(r);
+}
+
+struct dm_space_map *dm_sm_disk_open(struct dm_transaction_manager *tm,
+				     void *root_le, size_t len)
+{
+	return dm_sm_checker_create(
+		dm_sm_disk_open_real(tm, root_le, len));
+}
+EXPORT_SYMBOL_GPL(dm_sm_disk_open);
+
+/*----------------------------------------------------------------*/

drivers/md/persistent-data/dm-space-map-disk.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _LINUX_DM_SPACE_MAP_DISK_H
+#define _LINUX_DM_SPACE_MAP_DISK_H
+
+#include "dm-block-manager.h"
+
+struct dm_space_map;
+struct dm_transaction_manager;
+
+/*
+ * Unfortunately we have to use two-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 /* _LINUX_DM_SPACE_MAP_DISK_H */

drivers/md/persistent-data/dm-space-map-metadata.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-space-map.h"
+#include "dm-space-map-common.h"
+#include "dm-space-map-metadata.h"
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "space map metadata"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * 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 metadata_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) {
+		DMERR("too many recursive allocations");
+		return -ENOMEM;
+	}
+
+	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;
+	enum allocation_event ev;
+
+	switch (op->type) {
+	case BOP_INC:
+		r = sm_ll_inc(&smm->ll, op->block, &ev);
+		break;
+
+	case BOP_DEC:
+		r = sm_ll_dec(&smm->ll, op->block, &ev);
+		break;
+	}
+
+	return r;
+}
+
+static void in(struct sm_metadata *smm)
+{
+	smm->recursion_count++;
+}
+
+static int out(struct sm_metadata *smm)
+{
+	int r = 0;
+
+	/*
+	 * If we're not recursing then very bad things are happening.
+	 */
+	if (!smm->recursion_count) {
+		DMERR("lost track of recursion depth");
+		return -ENOMEM;
+	}
+
+	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);
+			if (r)
+				break;
+		}
+	}
+
+	smm->recursion_count--;
+
+	return r;
+}
+
+/*
+ * When using the out() function above, we often want to combine an error
+ * code for the operation run in the recursive context with that from
+ * out().
+ */
+static int combine_errors(int r1, int r2)
+{
+	return r1 ? r1 : r2;
+}
+
+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)
+{
+	DMERR("doesn't support extend");
+	return -EINVAL;
+}
+
+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)
+			continue;
+
+		switch (op->type) {
+		case BOP_INC:
+			adjustment++;
+			break;
+
+		case BOP_DEC:
+			adjustment--;
+			break;
+		}
+	}
+
+	r = sm_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)
+			continue;
+
+		switch (op->type) {
+		case BOP_INC:
+			adjustment++;
+			break;
+
+		case BOP_DEC:
+			adjustment--;
+			break;
+		}
+	}
+
+	if (adjustment > 1) {
+		*result = 1;
+		return 0;
+	}
+
+	r = sm_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, r2;
+	enum allocation_event ev;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	if (smm->recursion_count) {
+		DMERR("cannot recurse set_count()");
+		return -EINVAL;
+	}
+
+	in(smm);
+	r = sm_ll_insert(&smm->ll, b, count, &ev);
+	r2 = out(smm);
+
+	return combine_errors(r, r2);
+}
+
+static int sm_metadata_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r, r2 = 0;
+	enum allocation_event ev;
+	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 = sm_ll_inc(&smm->ll, b, &ev);
+		r2 = out(smm);
+	}
+
+	return combine_errors(r, r2);
+}
+
+static int sm_metadata_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	int r, r2 = 0;
+	enum allocation_event ev;
+	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 = sm_ll_dec(&smm->ll, b, &ev);
+		r2 = out(smm);
+	}
+
+	return combine_errors(r, r2);
+}
+
+static int sm_metadata_new_block_(struct dm_space_map *sm, dm_block_t *b)
+{
+	int r, r2 = 0;
+	enum allocation_event ev;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	r = sm_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 = sm_ll_inc(&smm->ll, *b, &ev);
+		r2 = out(smm);
+	}
+
+	if (!r)
+		smm->allocated_this_transaction++;
+
+	return combine_errors(r, r2);
+}
+
+static int sm_metadata_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	int r = sm_metadata_new_block_(sm, b);
+	if (r)
+		DMERR("out of metadata space");
+	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);
+
+	r = sm_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 disk_sm_root);
+
+	return 0;
+}
+
+static int sm_metadata_copy_root(struct dm_space_map *sm, void *where_le, size_t max)
+{
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+	struct disk_sm_root root_le;
+
+	root_le.nr_blocks = cpu_to_le64(smm->ll.nr_blocks);
+	root_le.nr_allocated = cpu_to_le64(smm->ll.nr_allocated);
+	root_le.bitmap_root = cpu_to_le64(smm->ll.bitmap_root);
+	root_le.ref_count_root = cpu_to_le64(smm->ll.ref_count_root);
+
+	if (max < sizeof(root_le))
+		return -ENOSPC;
+
+	memcpy(where_le, &root_le, sizeof(root_le));
+
+	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 its own space.  We use
+ * this tiny bootstrap allocator.
+ */
+static void sm_bootstrap_destroy(struct dm_space_map *sm)
+{
+}
+
+static int sm_bootstrap_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	DMERR("boostrap doesn't support extend");
+
+	return -EINVAL;
+}
+
+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)
+{
+	DMERR("boostrap doesn't support set_count");
+
+	return -EINVAL;
+}
+
+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)
+{
+	DMERR("boostrap doesn't support root_size");
+
+	return -EINVAL;
+}
+
+static int sm_bootstrap_copy_root(struct dm_space_map *sm, void *where,
+				  size_t max)
+{
+	DMERR("boostrap doesn't support copy_root");
+
+	return -EINVAL;
+}
+
+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;
+}
+
+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;
+	enum allocation_event ev;
+	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 = sm_ll_new_metadata(&smm->ll, tm);
+	if (r)
+		return r;
+
+	r = sm_ll_extend(&smm->ll, 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 = sm_ll_inc(&smm->ll, i, &ev);
+
+	if (r)
+		return r;
+
+	return sm_metadata_commit(sm);
+}
+
+int dm_sm_metadata_open(struct dm_space_map *sm,
+			struct dm_transaction_manager *tm,
+			void *root_le, size_t len)
+{
+	int r;
+	struct sm_metadata *smm = container_of(sm, struct sm_metadata, sm);
+
+	r = sm_ll_open_metadata(&smm->ll, tm, root_le, len);
+	if (r)
+		return r;
+
+	smm->begin = 0;
+	smm->recursion_count = 0;
+	smm->allocated_this_transaction = 0;
+	smm->nr_uncommitted = 0;
+
+	memcpy(&smm->old_ll, &smm->ll, sizeof(smm->old_ll));
+	return 0;
+}

drivers/md/persistent-data/dm-space-map-metadata.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_SPACE_MAP_METADATA_H
+#define DM_SPACE_MAP_METADATA_H
+
+#include "dm-transaction-manager.h"
+
+/*
+ * Unfortunately we have to use two-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_le, size_t len);
+
+#endif	/* DM_SPACE_MAP_METADATA_H */

drivers/md/persistent-data/dm-space-map.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _LINUX_DM_SPACE_MAP_H
+#define _LINUX_DM_SPACE_MAP_H
+
+#include "dm-block-manager.h"
+
+/*
+ * struct dm_space_map keeps a record of how many times each block in a device
+ * is referenced.  It needs to be fixed on disk as part of the transaction.
+ */
+struct dm_space_map {
+	void (*destroy)(struct dm_space_map *sm);
+
+	/*
+	 * You must commit before allocating the newly added space.
+	 */
+	int (*extend)(struct dm_space_map *sm, dm_block_t extra_blocks);
+
+	/*
+	 * Extensions do not appear in this count until after commit has
+	 * been called.
+	 */
+	int (*get_nr_blocks)(struct dm_space_map *sm, dm_block_t *count);
+
+	/*
+	 * Space maps must never allocate a block from the previous
+	 * transaction, in case we need to rollback.  This complicates the
+	 * semantics of get_nr_free(), it should return the number of blocks
+	 * that are available for allocation _now_.  For instance you may
+	 * have blocks with a zero reference count that will not be
+	 * available for allocation until after the next commit.
+	 */
+	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 fix the space map.
+	 * Generally this info is small, so 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_le, 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_le, size_t len)
+{
+	return sm->copy_root(sm, copy_to_here_le, len);
+}
+
+#endif	/* _LINUX_DM_SPACE_MAP_H */

drivers/md/persistent-data/dm-transaction-manager.c

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+#include "dm-transaction-manager.h"
+#include "dm-space-map.h"
+#include "dm-space-map-checker.h"
+#include "dm-space-map-disk.h"
+#include "dm-space-map-metadata.h"
+#include "dm-persistent-data-internal.h"
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/device-mapper.h>
+
+#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;
+
+	spinlock_t lock;
+	struct hlist_head buckets[HASH_SIZE];
+};
+
+/*----------------------------------------------------------------*/
+
+static int is_shadow(struct dm_transaction_manager *tm, dm_block_t b)
+{
+	int r = 0;
+	unsigned bucket = dm_hash_block(b, HASH_MASK);
+	struct shadow_info *si;
+	struct hlist_node *n;
+
+	spin_lock(&tm->lock);
+	hlist_for_each_entry(si, n, tm->buckets + bucket, hlist)
+		if (si->where == b) {
+			r = 1;
+			break;
+		}
+	spin_unlock(&tm->lock);
+
+	return r;
+}
+
+/*
+ * 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 = dm_hash_block(b, HASH_MASK);
+		spin_lock(&tm->lock);
+		hlist_add_head(&si->hlist, tm->buckets + bucket);
+		spin_unlock(&tm->lock);
+	}
+}
+
+static void wipe_shadow_table(struct dm_transaction_manager *tm)
+{
+	struct shadow_info *si;
+	struct hlist_node *n, *tmp;
+	struct hlist_head *bucket;
+	int i;
+
+	spin_lock(&tm->lock);
+	for (i = 0; i < HASH_SIZE; i++) {
+		bucket = tm->buckets + i;
+		hlist_for_each_entry_safe(si, n, tmp, bucket, hlist)
+			kfree(si);
+
+		INIT_HLIST_HEAD(bucket);
+	}
+
+	spin_unlock(&tm->lock);
+}
+
+/*----------------------------------------------------------------*/
+
+static 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;
+
+	spin_lock_init(&tm->lock);
+	for (i = 0; i < HASH_SIZE; i++)
+		INIT_HLIST_HEAD(tm->buckets + i);
+
+	return tm;
+}
+
+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_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_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;
+}
+
+static int __shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
+			  struct dm_block_validator *v,
+			  struct dm_block **result)
+{
+	int r;
+	dm_block_t new;
+	struct dm_block *orig_block;
+
+	r = dm_sm_new_block(tm->sm, &new);
+	if (r < 0)
+		return r;
+
+	r = dm_sm_dec_block(tm->sm, orig);
+	if (r < 0)
+		return r;
+
+	r = dm_bm_read_lock(tm->bm, orig, v, &orig_block);
+	if (r < 0)
+		return r;
+
+	r = dm_bm_unlock_move(orig_block, new);
+	if (r < 0) {
+		dm_bm_unlock(orig_block);
+		return r;
+	}
+
+	return dm_bm_write_lock(tm->bm, new, v, result);
+}
+
+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;
+
+	if (tm->is_clone)
+		return -EWOULDBLOCK;
+
+	r = dm_sm_count_is_more_than_one(tm->sm, orig, inc_children);
+	if (r < 0)
+		return r;
+
+	if (is_shadow(tm, orig) && !*inc_children)
+		return dm_bm_write_lock(tm->bm, orig, v, result);
+
+	r = __shadow_block(tm, orig, v, result);
+	if (r < 0)
+		return r;
+	insert_shadow(tm, dm_block_location(*result));
+
+	return r;
+}
+
+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);
+}
+
+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)
+{
+	/*
+	 * The non-blocking clone doesn't support this.
+	 */
+	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)
+{
+	/*
+	 * The non-blocking clone doesn't support this.
+	 */
+	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);
+}
+
+struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm)
+{
+	return tm->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;
+	struct dm_space_map *inner;
+
+	inner = dm_sm_metadata_init();
+	if (IS_ERR(inner))
+		return PTR_ERR(inner);
+
+	*tm = dm_tm_create(bm, inner);
+	if (IS_ERR(*tm)) {
+		dm_sm_destroy(inner);
+		return PTR_ERR(*tm);
+	}
+
+	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(inner, *tm, dm_bm_nr_blocks(bm),
+					  sb_location);
+		if (r) {
+			DMERR("couldn't create metadata space map");
+			goto bad2;
+		}
+
+		*sm = dm_sm_checker_create(inner);
+		if (!*sm)
+			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(inner, *tm,
+					dm_block_data(*sblock) + root_offset,
+					root_max_len);
+		if (r) {
+			DMERR("couldn't open metadata space map");
+			goto bad2;
+		}
+
+		*sm = dm_sm_checker_create(inner);
+		if (!*sm)
+			goto bad2;
+	}
+
+	return 0;
+
+bad2:
+	dm_tm_unlock(*tm, *sblock);
+bad1:
+	dm_tm_destroy(*tm);
+	dm_sm_destroy(inner);
+	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);
+
+/*----------------------------------------------------------------*/

drivers/md/persistent-data/dm-transaction-manager.h

···
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _LINUX_DM_TRANSACTION_MANAGER_H
+#define _LINUX_DM_TRANSACTION_MANAGER_H
+
+#include "dm-block-manager.h"
+
+struct dm_transaction_manager;
+struct dm_space_map;
+
+/*----------------------------------------------------------------*/
+
+/*
+ * 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.
+ */
+
+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 e.g. 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.
+ * Methods that return void yet may block should not be called on a clone
+ * viz. dm_tm_inc, dm_tm_dec.  Call dm_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);
+
+/*
+ * 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 interrogate
+ * 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.
+ */
+
+/*
+ * dm_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).
+ * Zeroes the new block and returns with write lock held.
+ */
+int dm_tm_new_block(struct dm_transaction_manager *tm,
+		    struct dm_block_validator *v,
+		    struct dm_block **result);
+
+/*
+ * dm_tm_shadow_block() allocates a new block and copies 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 it needs to
+ * adjust reference counts for children.  (Data in the block may refer to
+ * other blocks.)
+ *
+ * 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);
+
+#endif	/* _LINUX_DM_TRANSACTION_MANAGER_H */