13 files changed, 4718 insertions, 0 deletions

diff --git a/Documentation/device-mapper/cache.txt b/Documentation/device-mapper/cache.txt
new file mode 100644
index 00000000000..f50470abe24
--- /dev/null
+++ b/Documentation/device-mapper/cache.txt
@@ -0,0 +1,243 @@
+Introduction
+============
+
+dm-cache is a device mapper target written by Joe Thornber, Heinz
+Mauelshagen, and Mike Snitzer.
+
+It aims to improve performance of a block device (eg, a spindle) by
+dynamically migrating some of its data to a faster, smaller device
+(eg, an SSD).
+
+This device-mapper solution allows us to insert this caching at
+different levels of the dm stack, for instance above the data device for
+a thin-provisioning pool.  Caching solutions that are integrated more
+closely with the virtual memory system should give better performance.
+
+The target reuses the metadata library used in the thin-provisioning
+library.
+
+The decision as to what data to migrate and when is left to a plug-in
+policy module.  Several of these have been written as we experiment,
+and we hope other people will contribute others for specific io
+scenarios (eg. a vm image server).
+
+Glossary
+========
+
+  Migration -  Movement of the primary copy of a logical block from one
+	       device to the other.
+  Promotion -  Migration from slow device to fast device.
+  Demotion  -  Migration from fast device to slow device.
+
+The origin device always contains a copy of the logical block, which
+may be out of date or kept in sync with the copy on the cache device
+(depending on policy).
+
+Design
+======
+
+Sub-devices
+-----------
+
+The target is constructed by passing three devices to it (along with
+other parameters detailed later):
+
+1. An origin device - the big, slow one.
+
+2. A cache device - the small, fast one.
+
+3. A small metadata device - records which blocks are in the cache,
+   which are dirty, and extra hints for use by the policy object.
+   This information could be put on the cache device, but having it
+   separate allows the volume manager to configure it differently,
+   e.g. as a mirror for extra robustness.
+
+Fixed block size
+----------------
+
+The origin is divided up into blocks of a fixed size.  This block size
+is configurable when you first create the cache.  Typically we've been
+using block sizes of 256k - 1024k.
+
+Having a fixed block size simplifies the target a lot.  But it is
+something of a compromise.  For instance, a small part of a block may be
+getting hit a lot, yet the whole block will be promoted to the cache.
+So large block sizes are bad because they waste cache space.  And small
+block sizes are bad because they increase the amount of metadata (both
+in core and on disk).
+
+Writeback/writethrough
+----------------------
+
+The cache has two modes, writeback and writethrough.
+
+If writeback, the default, is selected then a write to a block that is
+cached will go only to the cache and the block will be marked dirty in
+the metadata.
+
+If writethrough is selected then a write to a cached block will not
+complete until it has hit both the origin and cache devices.  Clean
+blocks should remain clean.
+
+A simple cleaner policy is provided, which will clean (write back) all
+dirty blocks in a cache.  Useful for decommissioning a cache.
+
+Migration throttling
+--------------------
+
+Migrating data between the origin and cache device uses bandwidth.
+The user can set a throttle to prevent more than a certain amount of
+migration occuring at any one time.  Currently we're not taking any
+account of normal io traffic going to the devices.  More work needs
+doing here to avoid migrating during those peak io moments.
+
+For the time being, a message "migration_threshold <#sectors>"
+can be used to set the maximum number of sectors being migrated,
+the default being 204800 sectors (or 100MB).
+
+Updating on-disk metadata
+-------------------------
+
+On-disk metadata is committed every time a REQ_SYNC or REQ_FUA bio is
+written.  If no such requests are made then commits will occur every
+second.  This means the cache behaves like a physical disk that has a
+write cache (the same is true of the thin-provisioning target).  If
+power is lost you may lose some recent writes.  The metadata should
+always be consistent in spite of any crash.
+
+The 'dirty' state for a cache block changes far too frequently for us
+to keep updating it on the fly.  So we treat it as a hint.  In normal
+operation it will be written when the dm device is suspended.  If the
+system crashes all cache blocks will be assumed dirty when restarted.
+
+Per-block policy hints
+----------------------
+
+Policy plug-ins can store a chunk of data per cache block.  It's up to
+the policy how big this chunk is, but it should be kept small.  Like the
+dirty flags this data is lost if there's a crash so a safe fallback
+value should always be possible.
+
+For instance, the 'mq' policy, which is currently the default policy,
+uses this facility to store the hit count of the cache blocks.  If
+there's a crash this information will be lost, which means the cache
+may be less efficient until those hit counts are regenerated.
+
+Policy hints affect performance, not correctness.
+
+Policy messaging
+----------------
+
+Policies will have different tunables, specific to each one, so we
+need a generic way of getting and setting these.  Device-mapper
+messages are used.  Refer to cache-policies.txt.
+
+Discard bitset resolution
+-------------------------
+
+We can avoid copying data during migration if we know the block has
+been discarded.  A prime example of this is when mkfs discards the
+whole block device.  We store a bitset tracking the discard state of
+blocks.  However, we allow this bitset to have a different block size
+from the cache blocks.  This is because we need to track the discard
+state for all of the origin device (compare with the dirty bitset
+which is just for the smaller cache device).
+
+Target interface
+================
+
+Constructor
+-----------
+
+ cache <metadata dev> <cache dev> <origin dev> <block size>
+       <#feature args> [<feature arg>]*
+       <policy> <#policy args> [policy args]*
+
+ metadata dev    : fast device holding the persistent metadata
+ cache dev	 : fast device holding cached data blocks
+ origin dev	 : slow device holding original data blocks
+ block size      : cache unit size in sectors
+
+ #feature args   : number of feature arguments passed
+ feature args    : writethrough.  (The default is writeback.)
+
+ policy          : the replacement policy to use
+ #policy args    : an even number of arguments corresponding to
+                   key/value pairs passed to the policy
+ policy args     : key/value pairs passed to the policy
+		   E.g. 'sequential_threshold 1024'
+		   See cache-policies.txt for details.
+
+Optional feature arguments are:
+   writethrough  : write through caching that prohibits cache block
+		   content from being different from origin block content.
+		   Without this argument, the default behaviour is to write
+		   back cache block contents later for performance reasons,
+		   so they may differ from the corresponding origin blocks.
+
+A policy called 'default' is always registered.  This is an alias for
+the policy we currently think is giving best all round performance.
+
+As the default policy could vary between kernels, if you are relying on
+the characteristics of a specific policy, always request it by name.
+
+Status
+------
+
+<#used metadata blocks>/<#total metadata blocks> <#read hits> <#read misses>
+<#write hits> <#write misses> <#demotions> <#promotions> <#blocks in cache>
+<#dirty> <#features> <features>* <#core args> <core args>* <#policy args>
+<policy args>*
+
+#used metadata blocks    : Number of metadata blocks used
+#total metadata blocks   : Total number of metadata blocks
+#read hits               : Number of times a READ bio has been mapped
+			     to the cache
+#read misses             : Number of times a READ bio has been mapped
+			     to the origin
+#write hits              : Number of times a WRITE bio has been mapped
+			     to the cache
+#write misses            : Number of times a WRITE bio has been
+			     mapped to the origin
+#demotions               : Number of times a block has been removed
+			     from the cache
+#promotions              : Number of times a block has been moved to
+			     the cache
+#blocks in cache         : Number of blocks resident in the cache
+#dirty                   : Number of blocks in the cache that differ
+			     from the origin
+#feature args            : Number of feature args to follow
+feature args             : 'writethrough' (optional)
+#core args               : Number of core arguments (must be even)
+core args                : Key/value pairs for tuning the core
+			     e.g. migration_threshold
+#policy args             : Number of policy arguments to follow (must be even)
+policy args              : Key/value pairs
+			     e.g. 'sequential_threshold 1024
+
+Messages
+--------
+
+Policies will have different tunables, specific to each one, so we
+need a generic way of getting and setting these.  Device-mapper
+messages are used.  (A sysfs interface would also be possible.)
+
+The message format is:
+
+   <key> <value>
+
+E.g.
+   dmsetup message my_cache 0 sequential_threshold 1024
+
+Examples
+========
+
+The test suite can be found here:
+
+https://github.com/jthornber/thinp-test-suite
+
+dmsetup create my_cache --table '0 41943040 cache /dev/mapper/metadata \
+	/dev/mapper/ssd /dev/mapper/origin 512 1 writeback default 0'
+dmsetup create my_cache --table '0 41943040 cache /dev/mapper/metadata \
+	/dev/mapper/ssd /dev/mapper/origin 1024 1 writeback \
+	mq 4 sequential_threshold 1024 random_threshold 8'
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 7cdf359d6b2..1a4fbcdb5ca 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -268,6 +268,19 @@ config DM_DEBUG_BLOCK_STACK_TRACING
 
 	  If unsure, say N.
 
+config DM_CACHE
+       tristate "Cache target (EXPERIMENTAL)"
+       depends on BLK_DEV_DM
+       default n
+       select DM_PERSISTENT_DATA
+       select DM_BIO_PRISON
+       ---help---
+         dm-cache attempts to improve performance of a block device by
+         moving frequently used data to a smaller, higher performance
+         device.  Different 'policy' plugins can be used to change the
+         algorithms used to select which blocks are promoted, demoted,
+         cleaned etc.  It supports writeback and writethrough modes.
+
 config DM_MIRROR
        tristate "Mirror target"
        depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 94dce8b4932..24b52560f4d 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -11,6 +11,7 @@ dm-mirror-y	+= dm-raid1.o
 dm-log-userspace-y \
 		+= dm-log-userspace-base.o dm-log-userspace-transfer.o
 dm-thin-pool-y	+= dm-thin.o dm-thin-metadata.o
+dm-cache-y	+= dm-cache-target.o dm-cache-metadata.o dm-cache-policy.o
 md-mod-y	+= md.o bitmap.o
 raid456-y	+= raid5.o
 
@@ -44,6 +45,7 @@ obj-$(CONFIG_DM_ZERO)		+= dm-zero.o
 obj-$(CONFIG_DM_RAID)	+= dm-raid.o
 obj-$(CONFIG_DM_THIN_PROVISIONING)	+= dm-thin-pool.o
 obj-$(CONFIG_DM_VERITY)		+= dm-verity.o
+obj-$(CONFIG_DM_CACHE)		+= dm-cache.o
 
 ifeq ($(CONFIG_DM_UEVENT),y)
 dm-mod-objs			+= dm-uevent.o
diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index 144067c95ab..85f0b707425 100644
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -179,6 +179,15 @@ int dm_bio_detain(struct dm_bio_prison *prison,
 }
 EXPORT_SYMBOL_GPL(dm_bio_detain);
 
+int dm_get_cell(struct dm_bio_prison *prison,
+		struct dm_cell_key *key,
+		struct dm_bio_prison_cell *cell_prealloc,
+		struct dm_bio_prison_cell **cell_result)
+{
+	return bio_detain(prison, key, NULL, cell_prealloc, cell_result);
+}
+EXPORT_SYMBOL_GPL(dm_get_cell);
+
 /*
  * @inmates must have been initialised prior to this call
  */
diff --git a/drivers/md/dm-bio-prison.h b/drivers/md/dm-bio-prison.h
index 981a02d3a05..3f833190ead 100644
--- a/drivers/md/dm-bio-prison.h
+++ b/drivers/md/dm-bio-prison.h
@@ -57,6 +57,17 @@ void dm_bio_prison_free_cell(struct dm_bio_prison *prison,
 			     struct dm_bio_prison_cell *cell);
 
 /*
+ * Creates, or retrieves a cell for the given key.
+ *
+ * Returns 1 if pre-existing cell returned, zero if new cell created using
+ * @cell_prealloc.
+ */
+int dm_get_cell(struct dm_bio_prison *prison,
+		struct dm_cell_key *key,
+		struct dm_bio_prison_cell *cell_prealloc,
+		struct dm_bio_prison_cell **cell_result);
+
+/*
  * An atomic op that combines retrieving a cell, and adding a bio to it.
  *
  * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
diff --git a/drivers/md/dm-cache-block-types.h b/drivers/md/dm-cache-block-types.h
new file mode 100644
index 00000000000..bed4ad4e1b7
--- /dev/null
+++ b/drivers/md/dm-cache-block-types.h
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_BLOCK_TYPES_H
+#define DM_CACHE_BLOCK_TYPES_H
+
+#include "persistent-data/dm-block-manager.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * It's helpful to get sparse to differentiate between indexes into the
+ * origin device, indexes into the cache device, and indexes into the
+ * discard bitset.
+ */
+
+typedef dm_block_t __bitwise__ dm_oblock_t;
+typedef uint32_t __bitwise__ dm_cblock_t;
+typedef dm_block_t __bitwise__ dm_dblock_t;
+
+static inline dm_oblock_t to_oblock(dm_block_t b)
+{
+	return (__force dm_oblock_t) b;
+}
+
+static inline dm_block_t from_oblock(dm_oblock_t b)
+{
+	return (__force dm_block_t) b;
+}
+
+static inline dm_cblock_t to_cblock(uint32_t b)
+{
+	return (__force dm_cblock_t) b;
+}
+
+static inline uint32_t from_cblock(dm_cblock_t b)
+{
+	return (__force uint32_t) b;
+}
+
+static inline dm_dblock_t to_dblock(dm_block_t b)
+{
+	return (__force dm_dblock_t) b;
+}
+
+static inline dm_block_t from_dblock(dm_dblock_t b)
+{
+	return (__force dm_block_t) b;
+}
+
+#endif /* DM_CACHE_BLOCK_TYPES_H */
diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
new file mode 100644
index 00000000000..fbd3625f274
--- /dev/null
+++ b/drivers/md/dm-cache-metadata.c
@@ -0,0 +1,1146 @@
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-metadata.h"
+
+#include "persistent-data/dm-array.h"
+#include "persistent-data/dm-bitset.h"
+#include "persistent-data/dm-space-map.h"
+#include "persistent-data/dm-space-map-disk.h"
+#include "persistent-data/dm-transaction-manager.h"
+
+#include <linux/device-mapper.h>
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX   "cache metadata"
+
+#define CACHE_SUPERBLOCK_MAGIC 06142003
+#define CACHE_SUPERBLOCK_LOCATION 0
+#define CACHE_VERSION 1
+#define CACHE_METADATA_CACHE_SIZE 64
+
+/*
+ *  3 for btree insert +
+ *  2 for btree lookup used within space map
+ */
+#define CACHE_MAX_CONCURRENT_LOCKS 5
+#define SPACE_MAP_ROOT_SIZE 128
+
+enum superblock_flag_bits {
+	/* for spotting crashes that would invalidate the dirty bitset */
+	CLEAN_SHUTDOWN,
+};
+
+/*
+ * Each mapping from cache block -> origin block carries a set of flags.
+ */
+enum mapping_bits {
+	/*
+	 * A valid mapping.  Because we're using an array we clear this
+	 * flag for an non existant mapping.
+	 */
+	M_VALID = 1,
+
+	/*
+	 * The data on the cache is different from that on the origin.
+	 */
+	M_DIRTY = 2
+};
+
+struct cache_disk_superblock {
+	__le32 csum;
+	__le32 flags;
+	__le64 blocknr;
+
+	__u8 uuid[16];
+	__le64 magic;
+	__le32 version;
+
+	__u8 policy_name[CACHE_POLICY_NAME_SIZE];
+	__le32 policy_hint_size;
+
+	__u8 metadata_space_map_root[SPACE_MAP_ROOT_SIZE];
+	__le64 mapping_root;
+	__le64 hint_root;
+
+	__le64 discard_root;
+	__le64 discard_block_size;
+	__le64 discard_nr_blocks;
+
+	__le32 data_block_size;
+	__le32 metadata_block_size;
+	__le32 cache_blocks;
+
+	__le32 compat_flags;
+	__le32 compat_ro_flags;
+	__le32 incompat_flags;
+
+	__le32 read_hits;
+	__le32 read_misses;
+	__le32 write_hits;
+	__le32 write_misses;
+} __packed;
+
+struct dm_cache_metadata {
+	struct block_device *bdev;
+	struct dm_block_manager *bm;
+	struct dm_space_map *metadata_sm;
+	struct dm_transaction_manager *tm;
+
+	struct dm_array_info info;
+	struct dm_array_info hint_info;
+	struct dm_disk_bitset discard_info;
+
+	struct rw_semaphore root_lock;
+	dm_block_t root;
+	dm_block_t hint_root;
+	dm_block_t discard_root;
+
+	sector_t discard_block_size;
+	dm_dblock_t discard_nr_blocks;
+
+	sector_t data_block_size;
+	dm_cblock_t cache_blocks;
+	bool changed:1;
+	bool clean_when_opened:1;
+
+	char policy_name[CACHE_POLICY_NAME_SIZE];
+	size_t policy_hint_size;
+	struct dm_cache_statistics stats;
+};
+
+/*-------------------------------------------------------------------
+ * superblock validator
+ *-----------------------------------------------------------------*/
+
+#define SUPERBLOCK_CSUM_XOR 9031977
+
+static void sb_prepare_for_write(struct dm_block_validator *v,
+				 struct dm_block *b,
+				 size_t sb_block_size)
+{
+	struct cache_disk_superblock *disk_super = dm_block_data(b);
+
+	disk_super->blocknr = cpu_to_le64(dm_block_location(b));
+	disk_super->csum = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
+						      sb_block_size - sizeof(__le32),
+						      SUPERBLOCK_CSUM_XOR));
+}
+
+static int sb_check(struct dm_block_validator *v,
+		    struct dm_block *b,
+		    size_t sb_block_size)
+{
+	struct cache_disk_superblock *disk_super = dm_block_data(b);
+	__le32 csum_le;
+
+	if (dm_block_location(b) != le64_to_cpu(disk_super->blocknr)) {
+		DMERR("sb_check failed: blocknr %llu: wanted %llu",
+		      le64_to_cpu(disk_super->blocknr),
+		      (unsigned long long)dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	if (le64_to_cpu(disk_super->magic) != CACHE_SUPERBLOCK_MAGIC) {
+		DMERR("sb_check failed: magic %llu: wanted %llu",
+		      le64_to_cpu(disk_super->magic),
+		      (unsigned long long)CACHE_SUPERBLOCK_MAGIC);
+		return -EILSEQ;
+	}
+
+	csum_le = cpu_to_le32(dm_bm_checksum(&disk_super->flags,
+					     sb_block_size - sizeof(__le32),
+					     SUPERBLOCK_CSUM_XOR));
+	if (csum_le != disk_super->csum) {
+		DMERR("sb_check failed: csum %u: wanted %u",
+		      le32_to_cpu(csum_le), le32_to_cpu(disk_super->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+static struct dm_block_validator sb_validator = {
+	.name = "superblock",
+	.prepare_for_write = sb_prepare_for_write,
+	.check = sb_check
+};
+
+/*----------------------------------------------------------------*/
+
+static int superblock_read_lock(struct dm_cache_metadata *cmd,
+				struct dm_block **sblock)
+{
+	return dm_bm_read_lock(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
+			       &sb_validator, sblock);
+}
+
+static int superblock_lock_zero(struct dm_cache_metadata *cmd,
+				struct dm_block **sblock)
+{
+	return dm_bm_write_lock_zero(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
+				     &sb_validator, sblock);
+}
+
+static int superblock_lock(struct dm_cache_metadata *cmd,
+			   struct dm_block **sblock)
+{
+	return dm_bm_write_lock(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
+				&sb_validator, sblock);
+}
+
+/*----------------------------------------------------------------*/
+
+static int __superblock_all_zeroes(struct dm_block_manager *bm, int *result)
+{
+	int r;
+	unsigned i;
+	struct dm_block *b;
+	__le64 *data_le, zero = cpu_to_le64(0);
+	unsigned sb_block_size = dm_bm_block_size(bm) / sizeof(__le64);
+
+	/*
+	 * We can't use a validator here - it may be all zeroes.
+	 */
+	r = dm_bm_read_lock(bm, CACHE_SUPERBLOCK_LOCATION, NULL, &b);
+	if (r)
+		return r;
+
+	data_le = dm_block_data(b);
+	*result = 1;
+	for (i = 0; i < sb_block_size; i++) {
+		if (data_le[i] != zero) {
+			*result = 0;
+			break;
+		}
+	}
+
+	return dm_bm_unlock(b);
+}
+
+static void __setup_mapping_info(struct dm_cache_metadata *cmd)
+{
+	struct dm_btree_value_type vt;
+
+	vt.context = NULL;
+	vt.size = sizeof(__le64);
+	vt.inc = NULL;
+	vt.dec = NULL;
+	vt.equal = NULL;
+	dm_array_info_init(&cmd->info, cmd->tm, &vt);
+
+	if (cmd->policy_hint_size) {
+		vt.size = sizeof(__le32);
+		dm_array_info_init(&cmd->hint_info, cmd->tm, &vt);
+	}
+}
+
+static int __write_initial_superblock(struct dm_cache_metadata *cmd)
+{
+	int r;
+	struct dm_block *sblock;
+	size_t metadata_len;
+	struct cache_disk_superblock *disk_super;
+	sector_t bdev_size = i_size_read(cmd->bdev->bd_inode) >> SECTOR_SHIFT;
+
+	/* FIXME: see if we can lose the max sectors limit */
+	if (bdev_size > DM_CACHE_METADATA_MAX_SECTORS)
+		bdev_size = DM_CACHE_METADATA_MAX_SECTORS;
+
+	r = dm_sm_root_size(cmd->metadata_sm, &metadata_len);
+	if (r < 0)
+		return r;
+
+	r = dm_tm_pre_commit(cmd->tm);
+	if (r < 0)
+		return r;
+
+	r = superblock_lock_zero(cmd, &sblock);
+	if (r)
+		return r;
+
+	disk_super = dm_block_data(sblock);
+	disk_super->flags = 0;
+	memset(disk_super->uuid, 0, sizeof(disk_super->uuid));
+	disk_super->magic = cpu_to_le64(CACHE_SUPERBLOCK_MAGIC);
+	disk_super->version = cpu_to_le32(CACHE_VERSION);
+	memset(disk_super->policy_name, 0, CACHE_POLICY_NAME_SIZE);
+	disk_super->policy_hint_size = 0;
+
+	r = dm_sm_copy_root(cmd->metadata_sm, &disk_super->metadata_space_map_root,
+			    metadata_len);
+	if (r < 0)
+		goto bad_locked;
+
+	disk_super->mapping_root = cpu_to_le64(cmd->root);
+	disk_super->hint_root = cpu_to_le64(cmd->hint_root);
+	disk_super->discard_root = cpu_to_le64(cmd->discard_root);
+	disk_super->discard_block_size = cpu_to_le64(cmd->discard_block_size);
+	disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks));
+	disk_super->metadata_block_size = cpu_to_le32(DM_CACHE_METADATA_BLOCK_SIZE >> SECTOR_SHIFT);
+	disk_super->data_block_size = cpu_to_le32(cmd->data_block_size);
+	disk_super->cache_blocks = cpu_to_le32(0);
+	memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name));
+
+	disk_super->read_hits = cpu_to_le32(0);
+	disk_super->read_misses = cpu_to_le32(0);
+	disk_super->write_hits = cpu_to_le32(0);
+	disk_super->write_misses = cpu_to_le32(0);
+
+	return dm_tm_commit(cmd->tm, sblock);
+
+bad_locked:
+	dm_bm_unlock(sblock);
+	return r;
+}
+
+static int __format_metadata(struct dm_cache_metadata *cmd)
+{
+	int r;
+
+	r = dm_tm_create_with_sm(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
+				 &cmd->tm, &cmd->metadata_sm);
+	if (r < 0) {
+		DMERR("tm_create_with_sm failed");
+		return r;
+	}
+
+	__setup_mapping_info(cmd);
+
+	r = dm_array_empty(&cmd->info, &cmd->root);
+	if (r < 0)
+		goto bad;
+
+	dm_disk_bitset_init(cmd->tm, &cmd->discard_info);
+
+	r = dm_bitset_empty(&cmd->discard_info, &cmd->discard_root);
+	if (r < 0)
+		goto bad;
+
+	cmd->discard_block_size = 0;
+	cmd->discard_nr_blocks = 0;
+
+	r = __write_initial_superblock(cmd);
+	if (r)
+		goto bad;
+
+	cmd->clean_when_opened = true;
+	return 0;
+
+bad:
+	dm_tm_destroy(cmd->tm);
+	dm_sm_destroy(cmd->metadata_sm);
+
+	return r;
+}
+
+static int __check_incompat_features(struct cache_disk_superblock *disk_super,
+				     struct dm_cache_metadata *cmd)
+{
+	uint32_t features;
+
+	features = le32_to_cpu(disk_super->incompat_flags) & ~DM_CACHE_FEATURE_INCOMPAT_SUPP;
+	if (features) {
+		DMERR("could not access metadata due to unsupported optional features (%lx).",
+		      (unsigned long)features);
+		return -EINVAL;
+	}
+
+	/*
+	 * Check for read-only metadata to skip the following RDWR checks.
+	 */
+	if (get_disk_ro(cmd->bdev->bd_disk))
+		return 0;
+
+	features = le32_to_cpu(disk_super->compat_ro_flags) & ~DM_CACHE_FEATURE_COMPAT_RO_SUPP;
+	if (features) {
+		DMERR("could not access metadata RDWR due to unsupported optional features (%lx).",
+		      (unsigned long)features);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int __open_metadata(struct dm_cache_metadata *cmd)
+{
+	int r;
+	struct dm_block *sblock;
+	struct cache_disk_superblock *disk_super;
+	unsigned long sb_flags;
+
+	r = superblock_read_lock(cmd, &sblock);
+	if (r < 0) {
+		DMERR("couldn't read lock superblock");
+		return r;
+	}
+
+	disk_super = dm_block_data(sblock);
+
+	r = __check_incompat_features(disk_super, cmd);
+	if (r < 0)
+		goto bad;
+
+	r = dm_tm_open_with_sm(cmd->bm, CACHE_SUPERBLOCK_LOCATION,
+			       disk_super->metadata_space_map_root,
+			       sizeof(disk_super->metadata_space_map_root),
+			       &cmd->tm, &cmd->metadata_sm);
+	if (r < 0) {
+		DMERR("tm_open_with_sm failed");
+		goto bad;
+	}
+
+	__setup_mapping_info(cmd);
+	dm_disk_bitset_init(cmd->tm, &cmd->discard_info);
+	sb_flags = le32_to_cpu(disk_super->flags);
+	cmd->clean_when_opened = test_bit(CLEAN_SHUTDOWN, &sb_flags);
+	return dm_bm_unlock(sblock);
+
+bad:
+	dm_bm_unlock(sblock);
+	return r;
+}
+
+static int __open_or_format_metadata(struct dm_cache_metadata *cmd,
+				     bool format_device)
+{
+	int r, unformatted;
+
+	r = __superblock_all_zeroes(cmd->bm, &unformatted);
+	if (r)
+		return r;
+
+	if (unformatted)
+		return format_device ? __format_metadata(cmd) : -EPERM;
+
+	return __open_metadata(cmd);
+}
+
+static int __create_persistent_data_objects(struct dm_cache_metadata *cmd,
+					    bool may_format_device)
+{
+	int r;
+	cmd->bm = dm_block_manager_create(cmd->bdev, DM_CACHE_METADATA_BLOCK_SIZE,
+					  CACHE_METADATA_CACHE_SIZE,
+					  CACHE_MAX_CONCURRENT_LOCKS);
+	if (IS_ERR(cmd->bm)) {
+		DMERR("could not create block manager");
+		return PTR_ERR(cmd->bm);
+	}
+
+	r = __open_or_format_metadata(cmd, may_format_device);
+	if (r)
+		dm_block_manager_destroy(cmd->bm);
+
+	return r;
+}
+
+static void __destroy_persistent_data_objects(struct dm_cache_metadata *cmd)
+{
+	dm_sm_destroy(cmd->metadata_sm);
+	dm_tm_destroy(cmd->tm);
+	dm_block_manager_destroy(cmd->bm);
+}
+
+typedef unsigned long (*flags_mutator)(unsigned long);
+
+static void update_flags(struct cache_disk_superblock *disk_super,
+			 flags_mutator mutator)
+{
+	uint32_t sb_flags = mutator(le32_to_cpu(disk_super->flags));
+	disk_super->flags = cpu_to_le32(sb_flags);
+}
+
+static unsigned long set_clean_shutdown(unsigned long flags)
+{
+	set_bit(CLEAN_SHUTDOWN, &flags);
+	return flags;
+}
+
+static unsigned long clear_clean_shutdown(unsigned long flags)
+{
+	clear_bit(CLEAN_SHUTDOWN, &flags);
+	return flags;
+}
+
+static void read_superblock_fields(struct dm_cache_metadata *cmd,
+				   struct cache_disk_superblock *disk_super)
+{
+	cmd->root = le64_to_cpu(disk_super->mapping_root);
+	cmd->hint_root = le64_to_cpu(disk_super->hint_root);
+	cmd->discard_root = le64_to_cpu(disk_super->discard_root);
+	cmd->discard_block_size = le64_to_cpu(disk_super->discard_block_size);
+	cmd->discard_nr_blocks = to_dblock(le64_to_cpu(disk_super->discard_nr_blocks));
+	cmd->data_block_size = le32_to_cpu(disk_super->data_block_size);
+	cmd->cache_blocks = to_cblock(le32_to_cpu(disk_super->cache_blocks));
+	strncpy(cmd->policy_name, disk_super->policy_name, sizeof(cmd->policy_name));
+	cmd->policy_hint_size = le32_to_cpu(disk_super->policy_hint_size);
+
+	cmd->stats.read_hits = le32_to_cpu(disk_super->read_hits);
+	cmd->stats.read_misses = le32_to_cpu(disk_super->read_misses);
+	cmd->stats.write_hits = le32_to_cpu(disk_super->write_hits);
+	cmd->stats.write_misses = le32_to_cpu(disk_super->write_misses);
+
+	cmd->changed = false;
+}
+
+/*
+ * The mutator updates the superblock flags.
+ */
+static int __begin_transaction_flags(struct dm_cache_metadata *cmd,
+				     flags_mutator mutator)
+{
+	int r;
+	struct cache_disk_superblock *disk_super;
+	struct dm_block *sblock;
+
+	r = superblock_lock(cmd, &sblock);
+	if (r)
+		return r;
+
+	disk_super = dm_block_data(sblock);
+	update_flags(disk_super, mutator);
+	read_superblock_fields(cmd, disk_super);
+
+	return dm_bm_flush_and_unlock(cmd->bm, sblock);
+}
+
+static int __begin_transaction(struct dm_cache_metadata *cmd)
+{
+	int r;
+	struct cache_disk_superblock *disk_super;
+	struct dm_block *sblock;
+
+	/*
+	 * We re-read the superblock every time.  Shouldn't need to do this
+	 * really.
+	 */
+	r = superblock_read_lock(cmd, &sblock);
+	if (r)
+		return r;
+
+	disk_super = dm_block_data(sblock);
+	read_superblock_fields(cmd, disk_super);
+	dm_bm_unlock(sblock);
+
+	return 0;
+}
+
+static int __commit_transaction(struct dm_cache_metadata *cmd,
+				flags_mutator mutator)
+{
+	int r;
+	size_t metadata_len;
+	struct cache_disk_superblock *disk_super;
+	struct dm_block *sblock;
+
+	/*
+	 * We need to know if the cache_disk_superblock exceeds a 512-byte sector.
+	 */
+	BUILD_BUG_ON(sizeof(struct cache_disk_superblock) > 512);
+
+	r = dm_bitset_flush(&cmd->discard_info, cmd->discard_root,
+			    &cmd->discard_root);
+	if (r)
+		return r;
+
+	r = dm_tm_pre_commit(cmd->tm);
+	if (r < 0)
+		return r;
+
+	r = dm_sm_root_size(cmd->metadata_sm, &metadata_len);
+	if (r < 0)
+		return r;
+
+	r = superblock_lock(cmd, &sblock);
+	if (r)
+		return r;
+
+	disk_super = dm_block_data(sblock);
+
+	if (mutator)
+		update_flags(disk_super, mutator);
+
+	disk_super->mapping_root = cpu_to_le64(cmd->root);
+	disk_super->hint_root = cpu_to_le64(cmd->hint_root);
+	disk_super->discard_root = cpu_to_le64(cmd->discard_root);
+	disk_super->discard_block_size = cpu_to_le64(cmd->discard_block_size);
+	disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks));
+	disk_super->cache_blocks = cpu_to_le32(from_cblock(cmd->cache_blocks));
+	strncpy(disk_super->policy_name, cmd->policy_name, sizeof(disk_super->policy_name));
+
+	disk_super->read_hits = cpu_to_le32(cmd->stats.read_hits);
+	disk_super->read_misses = cpu_to_le32(cmd->stats.read_misses);
+	disk_super->write_hits = cpu_to_le32(cmd->stats.write_hits);
+	disk_super->write_misses = cpu_to_le32(cmd->stats.write_misses);
+
+	r = dm_sm_copy_root(cmd->metadata_sm, &disk_super->metadata_space_map_root,
+			    metadata_len);
+	if (r < 0) {
+		dm_bm_unlock(sblock);
+		return r;
+	}
+
+	return dm_tm_commit(cmd->tm, sblock);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The mappings are held in a dm-array that has 64-bit values stored in
+ * little-endian format.  The index is the cblock, the high 48bits of the
+ * value are the oblock and the low 16 bit the flags.
+ */
+#define FLAGS_MASK ((1 << 16) - 1)
+
+static __le64 pack_value(dm_oblock_t block, unsigned flags)
+{
+	uint64_t value = from_oblock(block);
+	value <<= 16;
+	value = value | (flags & FLAGS_MASK);
+	return cpu_to_le64(value);
+}
+
+static void unpack_value(__le64 value_le, dm_oblock_t *block, unsigned *flags)
+{
+	uint64_t value = le64_to_cpu(value_le);
+	uint64_t b = value >> 16;
+	*block = to_oblock(b);
+	*flags = value & FLAGS_MASK;
+}
+
+/*----------------------------------------------------------------*/
+
+struct dm_cache_metadata *dm_cache_metadata_open(struct block_device *bdev,
+						 sector_t data_block_size,
+						 bool may_format_device,
+						 size_t policy_hint_size)
+{
+	int r;
+	struct dm_cache_metadata *cmd;
+
+	cmd = kzalloc(sizeof(*cmd), GFP_KERNEL);
+	if (!cmd) {
+		DMERR("could not allocate metadata struct");
+		return NULL;
+	}
+
+	init_rwsem(&cmd->root_lock);
+	cmd->bdev = bdev;
+	cmd->data_block_size = data_block_size;
+	cmd->cache_blocks = 0;
+	cmd->policy_hint_size = policy