Merge tag 'dm-3.9-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm

Pull device-mapper update from Alasdair G Kergon:
"The main addition here is a long-desired target framework to allow an
SSD to be used as a cache in front of a slower device. Cache tuning
is delegated to interchangeable policy modules so these can be
developed independently of the mechanics needed to shuffle the data
around.

Other than that, kcopyd users acquire a throttling parameter, ioctl
buffer usage gets streamlined, more mempool reliance is reduced and
there are a few other bug fixes and tidy-ups."

* tag 'dm-3.9-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/agk/linux-dm: (30 commits)
dm cache: add cleaner policy
dm cache: add mq policy
dm: add cache target
dm persistent data: add bitset
dm persistent data: add transactional array
dm thin: remove cells from stack
dm bio prison: pass cell memory in
dm persistent data: add btree_walk
dm: add target num_write_bios fn
dm kcopyd: introduce configurable throttling
dm ioctl: allow message to return data
dm ioctl: optimize functions without variable params
dm ioctl: introduce ioctl_flags
dm: merge io_pool and tio_pool
dm: remove unused _rq_bio_info_cache
dm: fix limits initialization when there are no data devices
dm snapshot: add missing module aliases
dm persistent data: set some btree fn parms const
dm: refactor bio cloning
dm: rename bio cloning functions
...

Documentation/device-mapper/cache-policies.txt

···
+Guidance for writing policies
+=============================
+
+Try to keep transactionality out of it.  The core is careful to
+avoid asking about anything that is migrating.  This is a pain, but
+makes it easier to write the policies.
+
+Mappings are loaded into the policy at construction time.
+
+Every bio that is mapped by the target is referred to the policy.
+The policy can return a simple HIT or MISS or issue a migration.
+
+Currently there's no way for the policy to issue background work,
+e.g. to start writing back dirty blocks that are going to be evicte
+soon.
+
+Because we map bios, rather than requests it's easy for the policy
+to get fooled by many small bios.  For this reason the core target
+issues periodic ticks to the policy.  It's suggested that the policy
+doesn't update states (eg, hit counts) for a block more than once
+for each tick.  The core ticks by watching bios complete, and so
+trying to see when the io scheduler has let the ios run.
+
+
+Overview of supplied cache replacement policies
+===============================================
+
+multiqueue
+----------
+
+This policy is the default.
+
+The multiqueue policy has two sets of 16 queues: one set for entries
+waiting for the cache and another one for those in the cache.
+Cache entries in the queues are aged based on logical time. Entry into
+the cache is based on variable thresholds and queue selection is based
+on hit count on entry. The policy aims to take different cache miss
+costs into account and to adjust to varying load patterns automatically.
+
+Message and constructor argument pairs are:
+	'sequential_threshold <#nr_sequential_ios>' and
+	'random_threshold <#nr_random_ios>'.
+
+The sequential threshold indicates the number of contiguous I/Os
+required before a stream is treated as sequential.  The random threshold
+is the number of intervening non-contiguous I/Os that must be seen
+before the stream is treated as random again.
+
+The sequential and random thresholds default to 512 and 4 respectively.
+
+Large, sequential ios are probably better left on the origin device
+since spindles tend to have good bandwidth. The io_tracker counts
+contiguous I/Os to try to spot when the io is in one of these sequential
+modes.
+
+cleaner
+-------
+
+The cleaner writes back all dirty blocks in a cache to decommission it.
+
+Examples
+========
+
+The syntax for a table is:
+	cache <metadata dev> <cache dev> <origin dev> <block size>
+	<#feature_args> [<feature arg>]*
+	<policy> <#policy_args> [<policy arg>]*
+
+The syntax to send a message using the dmsetup command is:
+	dmsetup message <mapped device> 0 sequential_threshold 1024
+	dmsetup message <mapped device> 0 random_threshold 8
+
+Using dmsetup:
+	dmsetup create blah --table "0 268435456 cache /dev/sdb /dev/sdc \
+	    /dev/sdd 512 0 mq 4 sequential_threshold 1024 random_threshold 8"
+	creates a 128GB large mapped device named 'blah' with the
+	sequential threshold set to 1024 and the random_threshold set to 8.

Documentation/device-mapper/cache.txt

···
+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'

drivers/md/Kconfig

···
 
 config DM_BUFIO
        tristate
-       depends on BLK_DEV_DM && EXPERIMENTAL
+       depends on BLK_DEV_DM
        ---help---
 	 This interface allows you to do buffered I/O on a device and acts
 	 as a cache, holding recently-read blocks in memory and performing
···
 
 config DM_BIO_PRISON
        tristate
-       depends on BLK_DEV_DM && EXPERIMENTAL
+       depends on BLK_DEV_DM
        ---help---
 	 Some bio locking schemes used by other device-mapper targets
 	 including thin provisioning.
···
          Allow volume managers to take writable snapshots of a device.
 
 config DM_THIN_PROVISIONING
-       tristate "Thin provisioning target (EXPERIMENTAL)"
-       depends on BLK_DEV_DM && EXPERIMENTAL
+       tristate "Thin provisioning target"
+       depends on BLK_DEV_DM
        select DM_PERSISTENT_DATA
        select DM_BIO_PRISON
        ---help---
···
 	  block manager locking used by thin provisioning.
 
 	  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_CACHE_MQ
+       tristate "MQ Cache Policy (EXPERIMENTAL)"
+       depends on DM_CACHE
+       default y
+       ---help---
+         A cache policy that uses a multiqueue ordered by recent hit
+         count to select which blocks should be promoted and demoted.
+         This is meant to be a general purpose policy.  It prioritises
+         reads over writes.
+
+config DM_CACHE_CLEANER
+       tristate "Cleaner Cache Policy (EXPERIMENTAL)"
+       depends on DM_CACHE
+       default y
+       ---help---
+         A simple cache policy that writes back all data to the
+         origin.  Used when decommissioning a dm-cache.
 
 config DM_MIRROR
        tristate "Mirror target"
···
 	 in one of the available parity distribution methods.
 
 config DM_LOG_USERSPACE
-	tristate "Mirror userspace logging (EXPERIMENTAL)"
-	depends on DM_MIRROR && EXPERIMENTAL && NET
+	tristate "Mirror userspace logging"
+	depends on DM_MIRROR && NET
 	select CONNECTOR
 	---help---
 	  The userspace logging module provides a mechanism for
···
 	  If unsure, say N.
 
 config DM_DELAY
-	tristate "I/O delaying target (EXPERIMENTAL)"
-	depends on BLK_DEV_DM && EXPERIMENTAL
+	tristate "I/O delaying target"
+	depends on BLK_DEV_DM
 	---help---
 	A target that delays reads and/or writes and can send
 	them to different devices.  Useful for testing.
···
 	Generate udev events for DM events.
 
 config DM_FLAKEY
-       tristate "Flakey target (EXPERIMENTAL)"
-       depends on BLK_DEV_DM && EXPERIMENTAL
+       tristate "Flakey target"
+       depends on BLK_DEV_DM
        ---help---
          A target that intermittently fails I/O for debugging purposes.
 
 config DM_VERITY
-	tristate "Verity target support (EXPERIMENTAL)"
-	depends on BLK_DEV_DM && EXPERIMENTAL
+	tristate "Verity target support"
+	depends on BLK_DEV_DM
 	select CRYPTO
 	select CRYPTO_HASH
 	select DM_BUFIO

drivers/md/Makefile

···
 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
+dm-cache-mq-y   += dm-cache-policy-mq.o
+dm-cache-cleaner-y += dm-cache-policy-cleaner.o
 md-mod-y	+= md.o bitmap.o
 raid456-y	+= raid5.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
+obj-$(CONFIG_DM_CACHE_MQ)	+= dm-cache-mq.o
+obj-$(CONFIG_DM_CACHE_CLEANER)	+= dm-cache-cleaner.o
 
 ifeq ($(CONFIG_DM_UEVENT),y)
 dm-mod-objs			+= dm-uevent.o

drivers/md/dm-bio-prison.c

···
 
 /*----------------------------------------------------------------*/
 
-struct dm_bio_prison_cell {
-	struct hlist_node list;
-	struct dm_bio_prison *prison;
-	struct dm_cell_key key;
-	struct bio *holder;
-	struct bio_list bios;
-};
-
 struct dm_bio_prison {
 	spinlock_t lock;
 	mempool_t *cell_pool;
···
 }
 EXPORT_SYMBOL_GPL(dm_bio_prison_destroy);
 
+struct dm_bio_prison_cell *dm_bio_prison_alloc_cell(struct dm_bio_prison *prison, gfp_t gfp)
+{
+	return mempool_alloc(prison->cell_pool, gfp);
+}
+EXPORT_SYMBOL_GPL(dm_bio_prison_alloc_cell);
+
+void dm_bio_prison_free_cell(struct dm_bio_prison *prison,
+			     struct dm_bio_prison_cell *cell)
+{
+	mempool_free(cell, prison->cell_pool);
+}
+EXPORT_SYMBOL_GPL(dm_bio_prison_free_cell);
+
 static uint32_t hash_key(struct dm_bio_prison *prison, struct dm_cell_key *key)
 {
 	const unsigned long BIG_PRIME = 4294967291UL;
···
 	return NULL;
 }
 
-/*
- * This may block if a new cell needs allocating.  You must ensure that
- * cells will be unlocked even if the calling thread is blocked.
- *
- * Returns 1 if the cell was already held, 0 if @inmate is the new holder.
- */
-int dm_bio_detain(struct dm_bio_prison *prison, struct dm_cell_key *key,
-		  struct bio *inmate, struct dm_bio_prison_cell **ref)
+static void __setup_new_cell(struct dm_bio_prison *prison,
+			     struct dm_cell_key *key,
+			     struct bio *holder,
+			     uint32_t hash,
+			     struct dm_bio_prison_cell *cell)
 {
-	int r = 1;
-	unsigned long flags;
-	uint32_t hash = hash_key(prison, key);
-	struct dm_bio_prison_cell *cell, *cell2;
-
-	BUG_ON(hash > prison->nr_buckets);
-
-	spin_lock_irqsave(&prison->lock, flags);
-
-	cell = __search_bucket(prison->cells + hash, key);
-	if (cell) {
-		bio_list_add(&cell->bios, inmate);
-		goto out;
-	}
-
-	/*
-	 * Allocate a new cell
-	 */
-	spin_unlock_irqrestore(&prison->lock, flags);
-	cell2 = mempool_alloc(prison->cell_pool, GFP_NOIO);
-	spin_lock_irqsave(&prison->lock, flags);
-
-	/*
-	 * We've been unlocked, so we have to double check that
-	 * nobody else has inserted this cell in the meantime.
-	 */
-	cell = __search_bucket(prison->cells + hash, key);
-	if (cell) {
-		mempool_free(cell2, prison->cell_pool);
-		bio_list_add(&cell->bios, inmate);
-		goto out;
-	}
-
-	/*
-	 * Use new cell.
-	 */
-	cell = cell2;
-
-	cell->prison = prison;
 	memcpy(&cell->key, key, sizeof(cell->key));
-	cell->holder = inmate;
+	cell->holder = holder;
 	bio_list_init(&cell->bios);
 	hlist_add_head(&cell->list, prison->cells + hash);
+}
 
-	r = 0;
+static int __bio_detain(struct dm_bio_prison *prison,
+			struct dm_cell_key *key,
+			struct bio *inmate,
+			struct dm_bio_prison_cell *cell_prealloc,
+			struct dm_bio_prison_cell **cell_result)
+{
+	uint32_t hash = hash_key(prison, key);
+	struct dm_bio_prison_cell *cell;
 
-out:
+	cell = __search_bucket(prison->cells + hash, key);
+	if (cell) {
+		if (inmate)
+			bio_list_add(&cell->bios, inmate);
+		*cell_result = cell;
+		return 1;
+	}
+
+	__setup_new_cell(prison, key, inmate, hash, cell_prealloc);
+	*cell_result = cell_prealloc;
+	return 0;
+}
+
+static int bio_detain(struct dm_bio_prison *prison,
+		      struct dm_cell_key *key,
+		      struct bio *inmate,
+		      struct dm_bio_prison_cell *cell_prealloc,
+		      struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&prison->lock, flags);
+	r = __bio_detain(prison, key, inmate, cell_prealloc, cell_result);
 	spin_unlock_irqrestore(&prison->lock, flags);
-
-	*ref = cell;
 
 	return r;
 }
+
+int dm_bio_detain(struct dm_bio_prison *prison,
+		  struct dm_cell_key *key,
+		  struct bio *inmate,
+		  struct dm_bio_prison_cell *cell_prealloc,
+		  struct dm_bio_prison_cell **cell_result)
+{
+	return bio_detain(prison, key, inmate, cell_prealloc, cell_result);
+}
 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
  */
-static void __cell_release(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+static void __cell_release(struct dm_bio_prison_cell *cell,
+			   struct bio_list *inmates)
 {
-	struct dm_bio_prison *prison = cell->prison;
-
 	hlist_del(&cell->list);
 
 	if (inmates) {
-		bio_list_add(inmates, cell->holder);
+		if (cell->holder)
+			bio_list_add(inmates, cell->holder);
 		bio_list_merge(inmates, &cell->bios);
 	}
-
-	mempool_free(cell, prison->cell_pool);
 }
 
-void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios)
+void dm_cell_release(struct dm_bio_prison *prison,
+		     struct dm_bio_prison_cell *cell,
+		     struct bio_list *bios)
 {
 	unsigned long flags;
-	struct dm_bio_prison *prison = cell->prison;
 
 	spin_lock_irqsave(&prison->lock, flags);
 	__cell_release(cell, bios);
···
 /*
  * Sometimes we don't want the holder, just the additional bios.
  */
-static void __cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+static void __cell_release_no_holder(struct dm_bio_prison_cell *cell,
+				     struct bio_list *inmates)
 {
-	struct dm_bio_prison *prison = cell->prison;
-
 	hlist_del(&cell->list);
 	bio_list_merge(inmates, &cell->bios);
-
-	mempool_free(cell, prison->cell_pool);
 }
 
-void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates)
+void dm_cell_release_no_holder(struct dm_bio_prison *prison,
+			       struct dm_bio_prison_cell *cell,
+			       struct bio_list *inmates)
 {
 	unsigned long flags;
-	struct dm_bio_prison *prison = cell->prison;
 
 	spin_lock_irqsave(&prison->lock, flags);
 	__cell_release_no_holder(cell, inmates);
···
 }
 EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);
 
-void dm_cell_error(struct dm_bio_prison_cell *cell)
+void dm_cell_error(struct dm_bio_prison *prison,
+		   struct dm_bio_prison_cell *cell)
 {
-	struct dm_bio_prison *prison = cell->prison;
 	struct bio_list bios;
 	struct bio *bio;
 	unsigned long flags;

drivers/md/dm-bio-prison.h

···
  * subsequently unlocked the bios become available.
  */
 struct dm_bio_prison;
-struct dm_bio_prison_cell;
 
 /* FIXME: this needs to be more abstract */
 struct dm_cell_key {
···
 	dm_block_t block;
 };
 
+/*
+ * Treat this as opaque, only in header so callers can manage allocation
+ * themselves.
+ */
+struct dm_bio_prison_cell {
+	struct hlist_node list;
+	struct dm_cell_key key;
+	struct bio *holder;
+	struct bio_list bios;
+};
+
 struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells);
 void dm_bio_prison_destroy(struct dm_bio_prison *prison);
 
 /*
- * This may block if a new cell needs allocating.  You must ensure that
- * cells will be unlocked even if the calling thread is blocked.
+ * These two functions just wrap a mempool.  This is a transitory step:
+ * Eventually all bio prison clients should manage their own cell memory.
+ *
+ * Like mempool_alloc(), dm_bio_prison_alloc_cell() can only fail if called
+ * in interrupt context or passed GFP_NOWAIT.
+ */
+struct dm_bio_prison_cell *dm_bio_prison_alloc_cell(struct dm_bio_prison *prison,
+						    gfp_t gfp);
+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.
  */
-int dm_bio_detain(struct dm_bio_prison *prison, struct dm_cell_key *key,
-		  struct bio *inmate, struct dm_bio_prison_cell **ref);
+int dm_bio_detain(struct dm_bio_prison *prison,
+		  struct dm_cell_key *key,
+		  struct bio *inmate,
+		  struct dm_bio_prison_cell *cell_prealloc,
+		  struct dm_bio_prison_cell **cell_result);
 
-void dm_cell_release(struct dm_bio_prison_cell *cell, struct bio_list *bios);
-void dm_cell_release_no_holder(struct dm_bio_prison_cell *cell, struct bio_list *inmates);
-void dm_cell_error(struct dm_bio_prison_cell *cell);
+void dm_cell_release(struct dm_bio_prison *prison,
+		     struct dm_bio_prison_cell *cell,
+		     struct bio_list *bios);
+void dm_cell_release_no_holder(struct dm_bio_prison *prison,
+			       struct dm_bio_prison_cell *cell,
+			       struct bio_list *inmates);
+void dm_cell_error(struct dm_bio_prison *prison,
+		   struct dm_bio_prison_cell *cell);
 
 /*----------------------------------------------------------------*/
 

drivers/md/dm-bufio.c

···
 int dm_bufio_issue_flush(struct dm_bufio_client *c)
 {
 	struct dm_io_request io_req = {
-		.bi_rw = REQ_FLUSH,
+		.bi_rw = WRITE_FLUSH,
 		.mem.type = DM_IO_KMEM,
 		.mem.ptr.addr = NULL,
 		.client = c->dm_io,

drivers/md/dm-cache-block-types.h

···
+/*
+ * 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 */

drivers/md/dm-cache-metadata.c

···
+/*
+ * 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_hint_size;
+	cmd->changed = true;
+
+	r = __create_persistent_data_objects(cmd, may_format_device);
+	if (r) {
+		kfree(cmd);
+		return ERR_PTR(r);
+	}
+
+	r = __begin_transaction_flags(cmd, clear_clean_shutdown);
+	if (r < 0) {
+		dm_cache_metadata_close(cmd);
+		return ERR_PTR(r);
+	}
+
+	return cmd;
+}
+
+void dm_cache_metadata_close(struct dm_cache_metadata *cmd)
+{
+	__destroy_persistent_data_objects(cmd);
+	kfree(cmd);
+}
+
+int dm_cache_resize(struct dm_cache_metadata *cmd, dm_cblock_t new_cache_size)
+{
+	int r;
+	__le64 null_mapping = pack_value(0, 0);
+
+	down_write(&cmd->root_lock);
+	__dm_bless_for_disk(&null_mapping);
+	r = dm_array_resize(&cmd->info, cmd->root, from_cblock(cmd->cache_blocks),
+			    from_cblock(new_cache_size),
+			    &null_mapping, &cmd->root);
+	if (!r)
+		cmd->cache_blocks = new_cache_size;
+	cmd->changed = true;
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+int dm_cache_discard_bitset_resize(struct dm_cache_metadata *cmd,
+				   sector_t discard_block_size,
+				   dm_dblock_t new_nr_entries)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = dm_bitset_resize(&cmd->discard_info,
+			     cmd->discard_root,
+			     from_dblock(cmd->discard_nr_blocks),
+			     from_dblock(new_nr_entries),
+			     false, &cmd->discard_root);
+	if (!r) {
+		cmd->discard_block_size = discard_block_size;
+		cmd->discard_nr_blocks = new_nr_entries;
+	}
+
+	cmd->changed = true;
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+static int __set_discard(struct dm_cache_metadata *cmd, dm_dblock_t b)
+{
+	return dm_bitset_set_bit(&cmd->discard_info, cmd->discard_root,
+				 from_dblock(b), &cmd->discard_root);
+}
+
+static int __clear_discard(struct dm_cache_metadata *cmd, dm_dblock_t b)
+{
+	return dm_bitset_clear_bit(&cmd->discard_info, cmd->discard_root,
+				   from_dblock(b), &cmd->discard_root);
+}
+
+static int __is_discarded(struct dm_cache_metadata *cmd, dm_dblock_t b,
+			  bool *is_discarded)
+{
+	return dm_bitset_test_bit(&cmd->discard_info, cmd->discard_root,
+				  from_dblock(b), &cmd->discard_root,
+				  is_discarded);
+}
+
+static int __discard(struct dm_cache_metadata *cmd,
+		     dm_dblock_t dblock, bool discard)
+{
+	int r;
+
+	r = (discard ? __set_discard : __clear_discard)(cmd, dblock);
+	if (r)
+		return r;
+
+	cmd->changed = true;
+	return 0;
+}
+
+int dm_cache_set_discard(struct dm_cache_metadata *cmd,
+			 dm_dblock_t dblock, bool discard)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = __discard(cmd, dblock, discard);
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+static int __load_discards(struct dm_cache_metadata *cmd,
+			   load_discard_fn fn, void *context)
+{
+	int r = 0;
+	dm_block_t b;
+	bool discard;
+
+	for (b = 0; b < from_dblock(cmd->discard_nr_blocks); b++) {
+		dm_dblock_t dblock = to_dblock(b);
+
+		if (cmd->clean_when_opened) {
+			r = __is_discarded(cmd, dblock, &discard);
+			if (r)
+				return r;
+		} else
+			discard = false;
+
+		r = fn(context, cmd->discard_block_size, dblock, discard);
+		if (r)
+			break;
+	}
+
+	return r;
+}
+
+int dm_cache_load_discards(struct dm_cache_metadata *cmd,
+			   load_discard_fn fn, void *context)
+{
+	int r;
+
+	down_read(&cmd->root_lock);
+	r = __load_discards(cmd, fn, context);
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+dm_cblock_t dm_cache_size(struct dm_cache_metadata *cmd)
+{
+	dm_cblock_t r;
+
+	down_read(&cmd->root_lock);
+	r = cmd->cache_blocks;
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+static int __remove(struct dm_cache_metadata *cmd, dm_cblock_t cblock)
+{
+	int r;
+	__le64 value = pack_value(0, 0);
+
+	__dm_bless_for_disk(&value);
+	r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
+			       &value, &cmd->root);
+	if (r)
+		return r;
+
+	cmd->changed = true;
+	return 0;
+}
+
+int dm_cache_remove_mapping(struct dm_cache_metadata *cmd, dm_cblock_t cblock)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = __remove(cmd, cblock);
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+static int __insert(struct dm_cache_metadata *cmd,
+		    dm_cblock_t cblock, dm_oblock_t oblock)
+{
+	int r;
+	__le64 value = pack_value(oblock, M_VALID);
+	__dm_bless_for_disk(&value);
+
+	r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
+			       &value, &cmd->root);
+	if (r)
+		return r;
+
+	cmd->changed = true;
+	return 0;
+}
+
+int dm_cache_insert_mapping(struct dm_cache_metadata *cmd,
+			    dm_cblock_t cblock, dm_oblock_t oblock)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = __insert(cmd, cblock, oblock);
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+struct thunk {
+	load_mapping_fn fn;
+	void *context;
+
+	struct dm_cache_metadata *cmd;
+	bool respect_dirty_flags;
+	bool hints_valid;
+};
+
+static bool hints_array_initialized(struct dm_cache_metadata *cmd)
+{
+	return cmd->hint_root && cmd->policy_hint_size;
+}
+
+static bool hints_array_available(struct dm_cache_metadata *cmd,
+				  const char *policy_name)
+{
+	bool policy_names_match = !strncmp(cmd->policy_name, policy_name,
+					   sizeof(cmd->policy_name));
+
+	return cmd->clean_when_opened && policy_names_match &&
+		hints_array_initialized(cmd);
+}
+
+static int __load_mapping(void *context, uint64_t cblock, void *leaf)
+{
+	int r = 0;
+	bool dirty;
+	__le64 value;
+	__le32 hint_value = 0;
+	dm_oblock_t oblock;
+	unsigned flags;
+	struct thunk *thunk = context;
+	struct dm_cache_metadata *cmd = thunk->cmd;
+
+	memcpy(&value, leaf, sizeof(value));
+	unpack_value(value, &oblock, &flags);
+
+	if (flags & M_VALID) {
+		if (thunk->hints_valid) {
+			r = dm_array_get_value(&cmd->hint_info, cmd->hint_root,
+					       cblock, &hint_value);
+			if (r && r != -ENODATA)
+				return r;
+		}
+
+		dirty = thunk->respect_dirty_flags ? (flags & M_DIRTY) : true;
+		r = thunk->fn(thunk->context, oblock, to_cblock(cblock),
+			      dirty, le32_to_cpu(hint_value), thunk->hints_valid);
+	}
+
+	return r;
+}
+
+static int __load_mappings(struct dm_cache_metadata *cmd, const char *policy_name,
+			   load_mapping_fn fn, void *context)
+{
+	struct thunk thunk;
+
+	thunk.fn = fn;
+	thunk.context = context;
+
+	thunk.cmd = cmd;
+	thunk.respect_dirty_flags = cmd->clean_when_opened;
+	thunk.hints_valid = hints_array_available(cmd, policy_name);
+
+	return dm_array_walk(&cmd->info, cmd->root, __load_mapping, &thunk);
+}
+
+int dm_cache_load_mappings(struct dm_cache_metadata *cmd, const char *policy_name,
+			   load_mapping_fn fn, void *context)
+{
+	int r;
+
+	down_read(&cmd->root_lock);
+	r = __load_mappings(cmd, policy_name, fn, context);
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+static int __dump_mapping(void *context, uint64_t cblock, void *leaf)
+{
+	int r = 0;
+	__le64 value;
+	dm_oblock_t oblock;
+	unsigned flags;
+
+	memcpy(&value, leaf, sizeof(value));
+	unpack_value(value, &oblock, &flags);
+
+	return r;
+}
+
+static int __dump_mappings(struct dm_cache_metadata *cmd)
+{
+	return dm_array_walk(&cmd->info, cmd->root, __dump_mapping, NULL);
+}
+
+void dm_cache_dump(struct dm_cache_metadata *cmd)
+{
+	down_read(&cmd->root_lock);
+	__dump_mappings(cmd);
+	up_read(&cmd->root_lock);
+}
+
+int dm_cache_changed_this_transaction(struct dm_cache_metadata *cmd)
+{
+	int r;
+
+	down_read(&cmd->root_lock);
+	r = cmd->changed;
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+static int __dirty(struct dm_cache_metadata *cmd, dm_cblock_t cblock, bool dirty)
+{
+	int r;
+	unsigned flags;
+	dm_oblock_t oblock;
+	__le64 value;
+
+	r = dm_array_get_value(&cmd->info, cmd->root, from_cblock(cblock), &value);
+	if (r)
+		return r;
+
+	unpack_value(value, &oblock, &flags);
+
+	if (((flags & M_DIRTY) && dirty) || (!(flags & M_DIRTY) && !dirty))
+		/* nothing to be done */
+		return 0;
+
+	value = pack_value(oblock, flags | (dirty ? M_DIRTY : 0));
+	__dm_bless_for_disk(&value);
+
+	r = dm_array_set_value(&cmd->info, cmd->root, from_cblock(cblock),
+			       &value, &cmd->root);
+	if (r)
+		return r;
+
+	cmd->changed = true;
+	return 0;
+
+}
+
+int dm_cache_set_dirty(struct dm_cache_metadata *cmd,
+		       dm_cblock_t cblock, bool dirty)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = __dirty(cmd, cblock, dirty);
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+void dm_cache_metadata_get_stats(struct dm_cache_metadata *cmd,
+				 struct dm_cache_statistics *stats)
+{
+	down_read(&cmd->root_lock);
+	memcpy(stats, &cmd->stats, sizeof(*stats));
+	up_read(&cmd->root_lock);
+}
+
+void dm_cache_metadata_set_stats(struct dm_cache_metadata *cmd,
+				 struct dm_cache_statistics *stats)
+{
+	down_write(&cmd->root_lock);
+	memcpy(&cmd->stats, stats, sizeof(*stats));
+	up_write(&cmd->root_lock);
+}
+
+int dm_cache_commit(struct dm_cache_metadata *cmd, bool clean_shutdown)
+{
+	int r;
+	flags_mutator mutator = (clean_shutdown ? set_clean_shutdown :
+				 clear_clean_shutdown);
+
+	down_write(&cmd->root_lock);
+	r = __commit_transaction(cmd, mutator);
+	if (r)
+		goto out;
+
+	r = __begin_transaction(cmd);
+
+out:
+	up_write(&cmd->root_lock);
+	return r;
+}
+
+int dm_cache_get_free_metadata_block_count(struct dm_cache_metadata *cmd,
+					   dm_block_t *result)
+{
+	int r = -EINVAL;
+
+	down_read(&cmd->root_lock);
+	r = dm_sm_get_nr_free(cmd->metadata_sm, result);
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+int dm_cache_get_metadata_dev_size(struct dm_cache_metadata *cmd,
+				   dm_block_t *result)
+{
+	int r = -EINVAL;
+
+	down_read(&cmd->root_lock);
+	r = dm_sm_get_nr_blocks(cmd->metadata_sm, result);
+	up_read(&cmd->root_lock);
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+static int begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
+{
+	int r;
+	__le32 value;
+	size_t hint_size;
+	const char *policy_name = dm_cache_policy_get_name(policy);
+
+	if (!policy_name[0] ||
+	    (strlen(policy_name) > sizeof(cmd->policy_name) - 1))
+		return -EINVAL;
+
+	if (strcmp(cmd->policy_name, policy_name)) {
+		strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name));
+
+		hint_size = dm_cache_policy_get_hint_size(policy);
+		if (!hint_size)
+			return 0; /* short-circuit hints initialization */
+		cmd->policy_hint_size = hint_size;
+
+		if (cmd->hint_root) {
+			r = dm_array_del(&cmd->hint_info, cmd->hint_root);
+			if (r)
+				return r;
+		}
+
+		r = dm_array_empty(&cmd->hint_info, &cmd->hint_root);
+		if (r)
+			return r;
+
+		value = cpu_to_le32(0);
+		__dm_bless_for_disk(&value);
+		r = dm_array_resize(&cmd->hint_info, cmd->hint_root, 0,
+				    from_cblock(cmd->cache_blocks),
+				    &value, &cmd->hint_root);
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *policy)
+{
+	int r;
+
+	down_write(&cmd->root_lock);
+	r = begin_hints(cmd, policy);
+	up_write(&cmd->root_lock);
+
+	return r;
+}
+
+static int save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
+		     uint32_t hint)
+{
+	int r;
+	__le32 value = cpu_to_le32(hint);
+	__dm_bless_for_disk(&value);
+
+	r = dm_array_set_value(&cmd->hint_info, cmd->hint_root,
+			       from_cblock(cblock), &value, &cmd->hint_root);
+	cmd->changed = true;
+
+	return r;
+}
+
+int dm_cache_save_hint(struct dm_cache_metadata *cmd, dm_cblock_t cblock,
+		       uint32_t hint)
+{
+	int r;
+
+	if (!hints_array_initialized(cmd))
+		return 0;
+
+	down_write(&cmd->root_lock);
+	r = save_hint(cmd, cblock, hint);
+	up_write(&cmd->root_lock);
+
+	return r;
+}

drivers/md/dm-cache-metadata.h

···
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_METADATA_H
+#define DM_CACHE_METADATA_H
+
+#include "dm-cache-block-types.h"
+#include "dm-cache-policy-internal.h"
+
+/*----------------------------------------------------------------*/
+
+#define DM_CACHE_METADATA_BLOCK_SIZE 4096
+
+/* FIXME: remove this restriction */
+/*
+ * The metadata device is currently limited in size.
+ *
+ * We have one block of index, which can hold 255 index entries.  Each
+ * index entry contains allocation info about 16k metadata blocks.
+ */
+#define DM_CACHE_METADATA_MAX_SECTORS (255 * (1 << 14) * (DM_CACHE_METADATA_BLOCK_SIZE / (1 << SECTOR_SHIFT)))
+
+/*
+ * A metadata device larger than 16GB triggers a warning.
+ */
+#define DM_CACHE_METADATA_MAX_SECTORS_WARNING (16 * (1024 * 1024 * 1024 >> SECTOR_SHIFT))
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Ext[234]-style compat feature flags.
+ *
+ * A new feature which old metadata will still be compatible with should
+ * define a DM_CACHE_FEATURE_COMPAT_* flag (rarely useful).
+ *
+ * A new feature that is not compatible with old code should define a
+ * DM_CACHE_FEATURE_INCOMPAT_* flag and guard the relevant code with
+ * that flag.
+ *
+ * A new feature that is not compatible with old code accessing the
+ * metadata RDWR should define a DM_CACHE_FEATURE_RO_COMPAT_* flag and
+ * guard the relevant code with that flag.
+ *
+ * As these various flags are defined they should be added to the
+ * following masks.
+ */
+#define DM_CACHE_FEATURE_COMPAT_SUPP	  0UL
+#define DM_CACHE_FEATURE_COMPAT_RO_SUPP	  0UL
+#define DM_CACHE_FEATURE_INCOMPAT_SUPP	  0UL
+
+/*
+ * Reopens or creates a new, empty metadata volume.
+ * Returns an ERR_PTR on failure.
+ */
+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);
+
+void dm_cache_metadata_close(struct dm_cache_metadata *cmd);
+
+/*
+ * The metadata needs to know how many cache blocks there are.  We don't
+ * care about the origin, assuming the core target is giving us valid
+ * origin blocks to map to.
+ */
+int dm_cache_resize(struct dm_cache_metadata *cmd, dm_cblock_t new_cache_size);
+dm_cblock_t dm_cache_size(struct dm_cache_metadata *cmd);
+
+int dm_cache_discard_bitset_resize(struct dm_cache_metadata *cmd,
+				   sector_t discard_block_size,
+				   dm_dblock_t new_nr_entries);
+
+typedef int (*load_discard_fn)(void *context, sector_t discard_block_size,
+			       dm_dblock_t dblock, bool discarded);
+int dm_cache_load_discards(struct dm_cache_metadata *cmd,
+			   load_discard_fn fn, void *context);
+
+int dm_cache_set_discard(struct dm_cache_metadata *cmd, dm_dblock_t dblock, bool discard);
+
+int dm_cache_remove_mapping(struct dm_cache_metadata *cmd, dm_cblock_t cblock);
+int dm_cache_insert_mapping(struct dm_cache_metadata *cmd, dm_cblock_t cblock, dm_oblock_t oblock);
+int dm_cache_changed_this_transaction(struct dm_cache_metadata *cmd);
+
+typedef int (*load_mapping_fn)(void *context, dm_oblock_t oblock,
+			       dm_cblock_t cblock, bool dirty,
+			       uint32_t hint, bool hint_valid);
+int dm_cache_load_mappings(struct dm_cache_metadata *cmd,
+			   const char *policy_name,
+			   load_mapping_fn fn,
+			   void *context);
+
+int dm_cache_set_dirty(struct dm_cache_metadata *cmd, dm_cblock_t cblock, bool dirty);
+
+struct dm_cache_statistics {
+	uint32_t read_hits;
+	uint32_t read_misses;
+	uint32_t write_hits;
+	uint32_t write_misses;
+};
+
+void dm_cache_metadata_get_stats(struct dm_cache_metadata *cmd,
+				 struct dm_cache_statistics *stats);
+void dm_cache_metadata_set_stats(struct dm_cache_metadata *cmd,
+				 struct dm_cache_statistics *stats);
+
+int dm_cache_commit(struct dm_cache_metadata *cmd, bool clean_shutdown);
+
+int dm_cache_get_free_metadata_block_count(struct dm_cache_metadata *cmd,
+					   dm_block_t *result);
+
+int dm_cache_get_metadata_dev_size(struct dm_cache_metadata *cmd,
+				   dm_block_t *result);
+
+void dm_cache_dump(struct dm_cache_metadata *cmd);
+
+/*
+ * The policy is invited to save a 32bit hint value for every cblock (eg,
+ * for a hit count).  These are stored against the policy name.  If
+ * policies are changed, then hints will be lost.  If the machine crashes,
+ * hints will be lost.
+ *
+ * The hints are indexed by the cblock, but many policies will not
+ * neccessarily have a fast way of accessing efficiently via cblock.  So
+ * rather than querying the policy for each cblock, we let it walk its data
+ * structures and fill in the hints in whatever order it wishes.
+ */
+
+int dm_cache_begin_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *p);
+
+/*
+ * requests hints for every cblock and stores in the metadata device.
+ */
+int dm_cache_save_hint(struct dm_cache_metadata *cmd,
+		       dm_cblock_t cblock, uint32_t hint);
+
+/*----------------------------------------------------------------*/
+
+#endif /* DM_CACHE_METADATA_H */

drivers/md/dm-cache-policy-cleaner.c

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * writeback cache policy supporting flushing out dirty cache blocks.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-policy.h"
+#include "dm.h"
+
+#include <linux/hash.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX "cache cleaner"
+#define CLEANER_VERSION "1.0.0"
+
+/* Cache entry struct. */
+struct wb_cache_entry {
+	struct list_head list;
+	struct hlist_node hlist;
+
+	dm_oblock_t oblock;
+	dm_cblock_t cblock;
+	bool dirty:1;
+	bool pending:1;
+};
+
+struct hash {
+	struct hlist_head *table;
+	dm_block_t hash_bits;
+	unsigned nr_buckets;
+};
+
+struct policy {
+	struct dm_cache_policy policy;
+	spinlock_t lock;
+
+	struct list_head free;
+	struct list_head clean;
+	struct list_head clean_pending;
+	struct list_head dirty;
+
+	/*
+	 * We know exactly how many cblocks will be needed,
+	 * so we can allocate them up front.
+	 */
+	dm_cblock_t cache_size, nr_cblocks_allocated;
+	struct wb_cache_entry *cblocks;
+	struct hash chash;
+};
+
+/*----------------------------------------------------------------------------*/
+
+/*
+ * Low-level functions.
+ */
+static unsigned next_power(unsigned n, unsigned min)
+{
+	return roundup_pow_of_two(max(n, min));
+}
+
+static struct policy *to_policy(struct dm_cache_policy *p)
+{
+	return container_of(p, struct policy, policy);
+}
+
+static struct list_head *list_pop(struct list_head *q)
+{
+	struct list_head *r = q->next;
+
+	list_del(r);
+
+	return r;
+}
+
+/*----------------------------------------------------------------------------*/
+
+/* Allocate/free various resources. */
+static int alloc_hash(struct hash *hash, unsigned elts)
+{
+	hash->nr_buckets = next_power(elts >> 4, 16);
+	hash->hash_bits = ffs(hash->nr_buckets) - 1;
+	hash->table = vzalloc(sizeof(*hash->table) * hash->nr_buckets);
+
+	return hash->table ? 0 : -ENOMEM;
+}
+
+static void free_hash(struct hash *hash)
+{
+	vfree(hash->table);
+}
+
+static int alloc_cache_blocks_with_hash(struct policy *p, dm_cblock_t cache_size)
+{
+	int r = -ENOMEM;
+
+	p->cblocks = vzalloc(sizeof(*p->cblocks) * from_cblock(cache_size));
+	if (p->cblocks) {
+		unsigned u = from_cblock(cache_size);
+
+		while (u--)
+			list_add(&p->cblocks[u].list, &p->free);
+
+		p->nr_cblocks_allocated = 0;
+
+		/* Cache entries hash. */
+		r = alloc_hash(&p->chash, from_cblock(cache_size));
+		if (r)
+			vfree(p->cblocks);
+	}
+
+	return r;
+}
+
+static void free_cache_blocks_and_hash(struct policy *p)
+{
+	free_hash(&p->chash);
+	vfree(p->cblocks);
+}
+
+static struct wb_cache_entry *alloc_cache_entry(struct policy *p)
+{
+	struct wb_cache_entry *e;
+
+	BUG_ON(from_cblock(p->nr_cblocks_allocated) >= from_cblock(p->cache_size));
+
+	e = list_entry(list_pop(&p->free), struct wb_cache_entry, list);
+	p->nr_cblocks_allocated = to_cblock(from_cblock(p->nr_cblocks_allocated) + 1);
+
+	return e;
+}
+
+/*----------------------------------------------------------------------------*/
+
+/* Hash functions (lookup, insert, remove). */
+static struct wb_cache_entry *lookup_cache_entry(struct policy *p, dm_oblock_t oblock)
+{
+	struct hash *hash = &p->chash;
+	unsigned h = hash_64(from_oblock(oblock), hash->hash_bits);
+	struct wb_cache_entry *cur;
+	struct hlist_head *bucket = &hash->table[h];
+
+	hlist_for_each_entry(cur, bucket, hlist) {
+		if (cur->oblock == oblock) {
+			/* Move upfront bucket for faster access. */
+			hlist_del(&cur->hlist);
+			hlist_add_head(&cur->hlist, bucket);
+			return cur;
+		}
+	}
+
+	return NULL;
+}
+
+static void insert_cache_hash_entry(struct policy *p, struct wb_cache_entry *e)
+{
+	unsigned h = hash_64(from_oblock(e->oblock), p->chash.hash_bits);
+
+	hlist_add_head(&e->hlist, &p->chash.table[h]);
+}
+
+static void remove_cache_hash_entry(struct wb_cache_entry *e)
+{
+	hlist_del(&e->hlist);
+}
+
+/* Public interface (see dm-cache-policy.h */
+static int wb_map(struct dm_cache_policy *pe, dm_oblock_t oblock,
+		  bool can_block, bool can_migrate, bool discarded_oblock,
+		  struct bio *bio, struct policy_result *result)
+{
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+	unsigned long flags;
+
+	result->op = POLICY_MISS;
+
+	if (can_block)
+		spin_lock_irqsave(&p->lock, flags);
+
+	else if (!spin_trylock_irqsave(&p->lock, flags))
+		return -EWOULDBLOCK;
+
+	e = lookup_cache_entry(p, oblock);
+	if (e) {
+		result->op = POLICY_HIT;
+		result->cblock = e->cblock;
+
+	}
+
+	spin_unlock_irqrestore(&p->lock, flags);
+
+	return 0;
+}
+
+static int wb_lookup(struct dm_cache_policy *pe, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+	int r;
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+	unsigned long flags;
+
+	if (!spin_trylock_irqsave(&p->lock, flags))
+		return -EWOULDBLOCK;
+
+	e = lookup_cache_entry(p, oblock);
+	if (e) {
+		*cblock = e->cblock;
+		r = 0;
+
+	} else
+		r = -ENOENT;
+
+	spin_unlock_irqrestore(&p->lock, flags);
+
+	return r;
+}
+
+static void __set_clear_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock, bool set)
+{
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+
+	e = lookup_cache_entry(p, oblock);
+	BUG_ON(!e);
+
+	if (set) {
+		if (!e->dirty) {
+			e->dirty = true;
+			list_move(&e->list, &p->dirty);
+		}
+
+	} else {
+		if (e->dirty) {
+			e->pending = false;
+			e->dirty = false;
+			list_move(&e->list, &p->clean);
+		}
+	}
+}
+
+static void wb_set_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+	struct policy *p = to_policy(pe);
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->lock, flags);
+	__set_clear_dirty(pe, oblock, true);
+	spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void wb_clear_dirty(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+	struct policy *p = to_policy(pe);
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->lock, flags);
+	__set_clear_dirty(pe, oblock, false);
+	spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void add_cache_entry(struct policy *p, struct wb_cache_entry *e)
+{
+	insert_cache_hash_entry(p, e);
+	if (e->dirty)
+		list_add(&e->list, &p->dirty);
+	else
+		list_add(&e->list, &p->clean);
+}
+
+static int wb_load_mapping(struct dm_cache_policy *pe,
+			   dm_oblock_t oblock, dm_cblock_t cblock,
+			   uint32_t hint, bool hint_valid)
+{
+	int r;
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e = alloc_cache_entry(p);
+
+	if (e) {
+		e->cblock = cblock;
+		e->oblock = oblock;
+		e->dirty = false; /* blocks default to clean */
+		add_cache_entry(p, e);
+		r = 0;
+
+	} else
+		r = -ENOMEM;
+
+	return r;
+}
+
+static void wb_destroy(struct dm_cache_policy *pe)
+{
+	struct policy *p = to_policy(pe);
+
+	free_cache_blocks_and_hash(p);
+	kfree(p);
+}
+
+static struct wb_cache_entry *__wb_force_remove_mapping(struct policy *p, dm_oblock_t oblock)
+{
+	struct wb_cache_entry *r = lookup_cache_entry(p, oblock);
+
+	BUG_ON(!r);
+
+	remove_cache_hash_entry(r);
+	list_del(&r->list);
+
+	return r;
+}
+
+static void wb_remove_mapping(struct dm_cache_policy *pe, dm_oblock_t oblock)
+{
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->lock, flags);
+	e = __wb_force_remove_mapping(p, oblock);
+	list_add_tail(&e->list, &p->free);
+	BUG_ON(!from_cblock(p->nr_cblocks_allocated));
+	p->nr_cblocks_allocated = to_cblock(from_cblock(p->nr_cblocks_allocated) - 1);
+	spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static void wb_force_mapping(struct dm_cache_policy *pe,
+				dm_oblock_t current_oblock, dm_oblock_t oblock)
+{
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->lock, flags);
+	e = __wb_force_remove_mapping(p, current_oblock);
+	e->oblock = oblock;
+	add_cache_entry(p, e);
+	spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static struct wb_cache_entry *get_next_dirty_entry(struct policy *p)
+{
+	struct list_head *l;
+	struct wb_cache_entry *r;
+
+	if (list_empty(&p->dirty))
+		return NULL;
+
+	l = list_pop(&p->dirty);
+	r = container_of(l, struct wb_cache_entry, list);
+	list_add(l, &p->clean_pending);
+
+	return r;
+}
+
+static int wb_writeback_work(struct dm_cache_policy *pe,
+			     dm_oblock_t *oblock,
+			     dm_cblock_t *cblock)
+{
+	int r = -ENOENT;
+	struct policy *p = to_policy(pe);
+	struct wb_cache_entry *e;
+	unsigned long flags;
+
+	spin_lock_irqsave(&p->lock, flags);
+
+	e = get_next_dirty_entry(p);
+	if (e) {
+		*oblock = e->oblock;
+		*cblock = e->cblock;
+		r = 0;
+	}
+
+	spin_unlock_irqrestore(&p->lock, flags);
+
+	return r;
+}
+
+static dm_cblock_t wb_residency(struct dm_cache_policy *pe)
+{
+	return to_policy(pe)->nr_cblocks_allocated;
+}
+
+/* Init the policy plugin interface function pointers. */
+static void init_policy_functions(struct policy *p)
+{
+	p->policy.destroy = wb_destroy;
+	p->policy.map = wb_map;
+	p->policy.lookup = wb_lookup;
+	p->policy.set_dirty = wb_set_dirty;
+	p->policy.clear_dirty = wb_clear_dirty;
+	p->policy.load_mapping = wb_load_mapping;
+	p->policy.walk_mappings = NULL;
+	p->policy.remove_mapping = wb_remove_mapping;
+	p->policy.writeback_work = wb_writeback_work;
+	p->policy.force_mapping = wb_force_mapping;
+	p->policy.residency = wb_residency;
+	p->policy.tick = NULL;
+}
+
+static struct dm_cache_policy *wb_create(dm_cblock_t cache_size,
+					 sector_t origin_size,
+					 sector_t cache_block_size)
+{
+	int r;
+	struct policy *p = kzalloc(sizeof(*p), GFP_KERNEL);
+
+	if (!p)
+		return NULL;
+
+	init_policy_functions(p);
+	INIT_LIST_HEAD(&p->free);
+	INIT_LIST_HEAD(&p->clean);
+	INIT_LIST_HEAD(&p->clean_pending);
+	INIT_LIST_HEAD(&p->dirty);
+
+	p->cache_size = cache_size;
+	spin_lock_init(&p->lock);
+
+	/* Allocate cache entry structs and add them to free list. */
+	r = alloc_cache_blocks_with_hash(p, cache_size);
+	if (!r)
+		return &p->policy;
+
+	kfree(p);
+
+	return NULL;
+}
+/*----------------------------------------------------------------------------*/
+
+static struct dm_cache_policy_type wb_policy_type = {
+	.name = "cleaner",
+	.hint_size = 0,
+	.owner = THIS_MODULE,
+	.create = wb_create
+};
+
+static int __init wb_init(void)
+{
+	int r = dm_cache_policy_register(&wb_policy_type);
+
+	if (r < 0)
+		DMERR("register failed %d", r);
+	else
+		DMINFO("version " CLEANER_VERSION " loaded");
+
+	return r;
+}
+
+static void __exit wb_exit(void)
+{
+	dm_cache_policy_unregister(&wb_policy_type);
+}
+
+module_init(wb_init);
+module_exit(wb_exit);
+
+MODULE_AUTHOR("Heinz Mauelshagen <[e-mail]>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("cleaner cache policy");

drivers/md/dm-cache-policy-internal.h

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_POLICY_INTERNAL_H
+#define DM_CACHE_POLICY_INTERNAL_H
+
+#include "dm-cache-policy.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Little inline functions that simplify calling the policy methods.
+ */
+static inline int policy_map(struct dm_cache_policy *p, dm_oblock_t oblock,
+			     bool can_block, bool can_migrate, bool discarded_oblock,
+			     struct bio *bio, struct policy_result *result)
+{
+	return p->map(p, oblock, can_block, can_migrate, discarded_oblock, bio, result);
+}
+
+static inline int policy_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+	BUG_ON(!p->lookup);
+	return p->lookup(p, oblock, cblock);
+}
+
+static inline void policy_set_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	if (p->set_dirty)
+		p->set_dirty(p, oblock);
+}
+
+static inline void policy_clear_dirty(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	if (p->clear_dirty)
+		p->clear_dirty(p, oblock);
+}
+
+static inline int policy_load_mapping(struct dm_cache_policy *p,
+				      dm_oblock_t oblock, dm_cblock_t cblock,
+				      uint32_t hint, bool hint_valid)
+{
+	return p->load_mapping(p, oblock, cblock, hint, hint_valid);
+}
+
+static inline int policy_walk_mappings(struct dm_cache_policy *p,
+				      policy_walk_fn fn, void *context)
+{
+	return p->walk_mappings ? p->walk_mappings(p, fn, context) : 0;
+}
+
+static inline int policy_writeback_work(struct dm_cache_policy *p,
+					dm_oblock_t *oblock,
+					dm_cblock_t *cblock)
+{
+	return p->writeback_work ? p->writeback_work(p, oblock, cblock) : -ENOENT;
+}
+
+static inline void policy_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	return p->remove_mapping(p, oblock);
+}
+
+static inline void policy_force_mapping(struct dm_cache_policy *p,
+					dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	return p->force_mapping(p, current_oblock, new_oblock);
+}
+
+static inline dm_cblock_t policy_residency(struct dm_cache_policy *p)
+{
+	return p->residency(p);
+}
+
+static inline void policy_tick(struct dm_cache_policy *p)
+{
+	if (p->tick)
+		return p->tick(p);
+}
+
+static inline int policy_emit_config_values(struct dm_cache_policy *p, char *result, unsigned maxlen)
+{
+	ssize_t sz = 0;
+	if (p->emit_config_values)
+		return p->emit_config_values(p, result, maxlen);
+
+	DMEMIT("0");
+	return 0;
+}
+
+static inline int policy_set_config_value(struct dm_cache_policy *p,
+					  const char *key, const char *value)
+{
+	return p->set_config_value ? p->set_config_value(p, key, value) : -EINVAL;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Creates a new cache policy given a policy name, a cache size, an origin size and the block size.
+ */
+struct dm_cache_policy *dm_cache_policy_create(const char *name, dm_cblock_t cache_size,
+					       sector_t origin_size, sector_t block_size);
+
+/*
+ * Destroys the policy.  This drops references to the policy module as well
+ * as calling it's destroy method.  So always use this rather than calling
+ * the policy->destroy method directly.
+ */
+void dm_cache_policy_destroy(struct dm_cache_policy *p);
+
+/*
+ * In case we've forgotten.
+ */
+const char *dm_cache_policy_get_name(struct dm_cache_policy *p);
+
+size_t dm_cache_policy_get_hint_size(struct dm_cache_policy *p);
+
+/*----------------------------------------------------------------*/
+
+#endif /* DM_CACHE_POLICY_INTERNAL_H */

drivers/md/dm-cache-policy-mq.c

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-policy.h"
+#include "dm.h"
+
+#include <linux/hash.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#define DM_MSG_PREFIX "cache-policy-mq"
+#define MQ_VERSION	"1.0.0"
+
+static struct kmem_cache *mq_entry_cache;
+
+/*----------------------------------------------------------------*/
+
+static unsigned next_power(unsigned n, unsigned min)
+{
+	return roundup_pow_of_two(max(n, min));
+}
+
+/*----------------------------------------------------------------*/
+
+static unsigned long *alloc_bitset(unsigned nr_entries)
+{
+	size_t s = sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
+	return vzalloc(s);
+}
+
+static void free_bitset(unsigned long *bits)
+{
+	vfree(bits);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Large, sequential ios are probably better left on the origin device since
+ * spindles tend to have good bandwidth.
+ *
+ * The io_tracker tries to spot when the io is in one of these sequential
+ * modes.
+ *
+ * Two thresholds to switch between random and sequential io mode are defaulting
+ * as follows and can be adjusted via the constructor and message interfaces.
+ */
+#define RANDOM_THRESHOLD_DEFAULT 4
+#define SEQUENTIAL_THRESHOLD_DEFAULT 512
+
+enum io_pattern {
+	PATTERN_SEQUENTIAL,
+	PATTERN_RANDOM
+};
+
+struct io_tracker {
+	enum io_pattern pattern;
+
+	unsigned nr_seq_samples;
+	unsigned nr_rand_samples;
+	unsigned thresholds[2];
+
+	dm_oblock_t last_end_oblock;
+};
+
+static void iot_init(struct io_tracker *t,
+		     int sequential_threshold, int random_threshold)
+{
+	t->pattern = PATTERN_RANDOM;
+	t->nr_seq_samples = 0;
+	t->nr_rand_samples = 0;
+	t->last_end_oblock = 0;
+	t->thresholds[PATTERN_RANDOM] = random_threshold;
+	t->thresholds[PATTERN_SEQUENTIAL] = sequential_threshold;
+}
+
+static enum io_pattern iot_pattern(struct io_tracker *t)
+{
+	return t->pattern;
+}
+
+static void iot_update_stats(struct io_tracker *t, struct bio *bio)
+{
+	if (bio->bi_sector == from_oblock(t->last_end_oblock) + 1)
+		t->nr_seq_samples++;
+	else {
+		/*
+		 * Just one non-sequential IO is enough to reset the
+		 * counters.
+		 */
+		if (t->nr_seq_samples) {
+			t->nr_seq_samples = 0;
+			t->nr_rand_samples = 0;
+		}
+
+		t->nr_rand_samples++;
+	}
+
+	t->last_end_oblock = to_oblock(bio->bi_sector + bio_sectors(bio) - 1);
+}
+
+static void iot_check_for_pattern_switch(struct io_tracker *t)
+{
+	switch (t->pattern) {
+	case PATTERN_SEQUENTIAL:
+		if (t->nr_rand_samples >= t->thresholds[PATTERN_RANDOM]) {
+			t->pattern = PATTERN_RANDOM;
+			t->nr_seq_samples = t->nr_rand_samples = 0;
+		}
+		break;
+
+	case PATTERN_RANDOM:
+		if (t->nr_seq_samples >= t->thresholds[PATTERN_SEQUENTIAL]) {
+			t->pattern = PATTERN_SEQUENTIAL;
+			t->nr_seq_samples = t->nr_rand_samples = 0;
+		}
+		break;
+	}
+}
+
+static void iot_examine_bio(struct io_tracker *t, struct bio *bio)
+{
+	iot_update_stats(t, bio);
+	iot_check_for_pattern_switch(t);
+}
+
+/*----------------------------------------------------------------*/
+
+
+/*
+ * This queue is divided up into different levels.  Allowing us to push
+ * entries to the back of any of the levels.  Think of it as a partially
+ * sorted queue.
+ */
+#define NR_QUEUE_LEVELS 16u
+
+struct queue {
+	struct list_head qs[NR_QUEUE_LEVELS];
+};
+
+static void queue_init(struct queue *q)
+{
+	unsigned i;
+
+	for (i = 0; i < NR_QUEUE_LEVELS; i++)
+		INIT_LIST_HEAD(q->qs + i);
+}
+
+/*
+ * Insert an entry to the back of the given level.
+ */
+static void queue_push(struct queue *q, unsigned level, struct list_head *elt)
+{
+	list_add_tail(elt, q->qs + level);
+}
+
+static void queue_remove(struct list_head *elt)
+{
+	list_del(elt);
+}
+
+/*
+ * Shifts all regions down one level.  This has no effect on the order of
+ * the queue.
+ */
+static void queue_shift_down(struct queue *q)
+{
+	unsigned level;
+
+	for (level = 1; level < NR_QUEUE_LEVELS; level++)
+		list_splice_init(q->qs + level, q->qs + level - 1);
+}
+
+/*
+ * Gives us the oldest entry of the lowest popoulated level.  If the first
+ * level is emptied then we shift down one level.
+ */
+static struct list_head *queue_pop(struct queue *q)
+{
+	unsigned level;
+	struct list_head *r;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		if (!list_empty(q->qs + level)) {
+			r = q->qs[level].next;
+			list_del(r);
+
+			/* have we just emptied the bottom level? */
+			if (level == 0 && list_empty(q->qs))
+				queue_shift_down(q);
+
+			return r;
+		}
+
+	return NULL;
+}
+
+static struct list_head *list_pop(struct list_head *lh)
+{
+	struct list_head *r = lh->next;
+
+	BUG_ON(!r);
+	list_del_init(r);
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Describes a cache entry.  Used in both the cache and the pre_cache.
+ */
+struct entry {
+	struct hlist_node hlist;
+	struct list_head list;
+	dm_oblock_t oblock;
+	dm_cblock_t cblock;	/* valid iff in_cache */
+
+	/*
+	 * FIXME: pack these better
+	 */
+	bool in_cache:1;
+	unsigned hit_count;
+	unsigned generation;
+	unsigned tick;
+};
+
+struct mq_policy {
+	struct dm_cache_policy policy;
+
+	/* protects everything */
+	struct mutex lock;
+	dm_cblock_t cache_size;
+	struct io_tracker tracker;
+
+	/*
+	 * We maintain two queues of entries.  The cache proper contains
+	 * the currently active mappings.  Whereas the pre_cache tracks
+	 * blocks that are being hit frequently and potential candidates
+	 * for promotion to the cache.
+	 */
+	struct queue pre_cache;
+	struct queue cache;
+
+	/*
+	 * Keeps track of time, incremented by the core.  We use this to
+	 * avoid attributing multiple hits within the same tick.
+	 *
+	 * Access to tick_protected should be done with the spin lock held.
+	 * It's copied to tick at the start of the map function (within the
+	 * mutex).
+	 */
+	spinlock_t tick_lock;
+	unsigned tick_protected;
+	unsigned tick;
+
+	/*
+	 * A count of the number of times the map function has been called
+	 * and found an entry in the pre_cache or cache.  Currently used to
+	 * calculate the generation.
+	 */
+	unsigned hit_count;
+
+	/*
+	 * A generation is a longish period that is used to trigger some
+	 * book keeping effects.  eg, decrementing hit counts on entries.
+	 * This is needed to allow the cache to evolve as io patterns
+	 * change.
+	 */
+	unsigned generation;
+	unsigned generation_period; /* in lookups (will probably change) */
+
+	/*
+	 * Entries in the pre_cache whose hit count passes the promotion
+	 * threshold move to the cache proper.  Working out the correct
+	 * value for the promotion_threshold is crucial to this policy.
+	 */
+	unsigned promote_threshold;
+
+	/*
+	 * We need cache_size entries for the cache, and choose to have
+	 * cache_size entries for the pre_cache too.  One motivation for
+	 * using the same size is to make the hit counts directly
+	 * comparable between pre_cache and cache.
+	 */
+	unsigned nr_entries;
+	unsigned nr_entries_allocated;
+	struct list_head free;
+
+	/*
+	 * Cache blocks may be unallocated.  We store this info in a
+	 * bitset.
+	 */
+	unsigned long *allocation_bitset;
+	unsigned nr_cblocks_allocated;
+	unsigned find_free_nr_words;
+	unsigned find_free_last_word;
+
+	/*
+	 * The hash table allows us to quickly find an entry by origin
+	 * block.  Both pre_cache and cache entries are in here.
+	 */
+	unsigned nr_buckets;
+	dm_block_t hash_bits;
+	struct hlist_head *table;
+};
+
+/*----------------------------------------------------------------*/
+/* Free/alloc mq cache entry structures. */
+static void takeout_queue(struct list_head *lh, struct queue *q)
+{
+	unsigned level;
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_splice(q->qs + level, lh);
+}
+
+static void free_entries(struct mq_policy *mq)
+{
+	struct entry *e, *tmp;
+
+	takeout_queue(&mq->free, &mq->pre_cache);
+	takeout_queue(&mq->free, &mq->cache);
+
+	list_for_each_entry_safe(e, tmp, &mq->free, list)
+		kmem_cache_free(mq_entry_cache, e);
+}
+
+static int alloc_entries(struct mq_policy *mq, unsigned elts)
+{
+	unsigned u = mq->nr_entries;
+
+	INIT_LIST_HEAD(&mq->free);
+	mq->nr_entries_allocated = 0;
+
+	while (u--) {
+		struct entry *e = kmem_cache_zalloc(mq_entry_cache, GFP_KERNEL);
+
+		if (!e) {
+			free_entries(mq);
+			return -ENOMEM;
+		}
+
+
+		list_add(&e->list, &mq->free);
+	}
+
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Simple hash table implementation.  Should replace with the standard hash
+ * table that's making its way upstream.
+ */
+static void hash_insert(struct mq_policy *mq, struct entry *e)
+{
+	unsigned h = hash_64(from_oblock(e->oblock), mq->hash_bits);
+
+	hlist_add_head(&e->hlist, mq->table + h);
+}
+
+static struct entry *hash_lookup(struct mq_policy *mq, dm_oblock_t oblock)
+{
+	unsigned h = hash_64(from_oblock(oblock), mq->hash_bits);
+	struct hlist_head *bucket = mq->table + h;
+	struct entry *e;
+
+	hlist_for_each_entry(e, bucket, hlist)
+		if (e->oblock == oblock) {
+			hlist_del(&e->hlist);
+			hlist_add_head(&e->hlist, bucket);
+			return e;
+		}
+
+	return NULL;
+}
+
+static void hash_remove(struct entry *e)
+{
+	hlist_del(&e->hlist);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Allocates a new entry structure.  The memory is allocated in one lump,
+ * so we just handing it out here.  Returns NULL if all entries have
+ * already been allocated.  Cannot fail otherwise.
+ */
+static struct entry *alloc_entry(struct mq_policy *mq)
+{
+	struct entry *e;
+
+	if (mq->nr_entries_allocated >= mq->nr_entries) {
+		BUG_ON(!list_empty(&mq->free));
+		return NULL;
+	}
+
+	e = list_entry(list_pop(&mq->free), struct entry, list);
+	INIT_LIST_HEAD(&e->list);
+	INIT_HLIST_NODE(&e->hlist);
+
+	mq->nr_entries_allocated++;
+	return e;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Mark cache blocks allocated or not in the bitset.
+ */
+static void alloc_cblock(struct mq_policy *mq, dm_cblock_t cblock)
+{
+	BUG_ON(from_cblock(cblock) > from_cblock(mq->cache_size));
+	BUG_ON(test_bit(from_cblock(cblock), mq->allocation_bitset));
+
+	set_bit(from_cblock(cblock), mq->allocation_bitset);
+	mq->nr_cblocks_allocated++;
+}
+
+static void free_cblock(struct mq_policy *mq, dm_cblock_t cblock)
+{
+	BUG_ON(from_cblock(cblock) > from_cblock(mq->cache_size));
+	BUG_ON(!test_bit(from_cblock(cblock), mq->allocation_bitset));
+
+	clear_bit(from_cblock(cblock), mq->allocation_bitset);
+	mq->nr_cblocks_allocated--;
+}
+
+static bool any_free_cblocks(struct mq_policy *mq)
+{
+	return mq->nr_cblocks_allocated < from_cblock(mq->cache_size);
+}
+
+/*
+ * Fills result out with a cache block that isn't in use, or return
+ * -ENOSPC.  This does _not_ mark the cblock as allocated, the caller is
+ * reponsible for that.
+ */
+static int __find_free_cblock(struct mq_policy *mq, unsigned begin, unsigned end,
+			      dm_cblock_t *result, unsigned *last_word)
+{
+	int r = -ENOSPC;
+	unsigned w;
+
+	for (w = begin; w < end; w++) {
+		/*
+		 * ffz is undefined if no zero exists
+		 */
+		if (mq->allocation_bitset[w] != ~0UL) {
+			*last_word = w;
+			*result = to_cblock((w * BITS_PER_LONG) + ffz(mq->allocation_bitset[w]));
+			if (from_cblock(*result) < from_cblock(mq->cache_size))
+				r = 0;
+
+			break;
+		}
+	}
+
+	return r;
+}
+
+static int find_free_cblock(struct mq_policy *mq, dm_cblock_t *result)
+{
+	int r;
+
+	if (!any_free_cblocks(mq))
+		return -ENOSPC;
+
+	r = __find_free_cblock(mq, mq->find_free_last_word, mq->find_free_nr_words, result, &mq->find_free_last_word);
+	if (r == -ENOSPC && mq->find_free_last_word)
+		r = __find_free_cblock(mq, 0, mq->find_free_last_word, result, &mq->find_free_last_word);
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Now we get to the meat of the policy.  This section deals with deciding
+ * when to to add entries to the pre_cache and cache, and move between
+ * them.
+ */
+
+/*
+ * The queue level is based on the log2 of the hit count.
+ */
+static unsigned queue_level(struct entry *e)
+{
+	return min((unsigned) ilog2(e->hit_count), NR_QUEUE_LEVELS - 1u);
+}
+
+/*
+ * Inserts the entry into the pre_cache or the cache.  Ensures the cache
+ * block is marked as allocated if necc.  Inserts into the hash table.  Sets the
+ * tick which records when the entry was last moved about.
+ */
+static void push(struct mq_policy *mq, struct entry *e)
+{
+	e->tick = mq->tick;
+	hash_insert(mq, e);
+
+	if (e->in_cache) {
+		alloc_cblock(mq, e->cblock);
+		queue_push(&mq->cache, queue_level(e), &e->list);
+	} else
+		queue_push(&mq->pre_cache, queue_level(e), &e->list);
+}
+
+/*
+ * Removes an entry from pre_cache or cache.  Removes from the hash table.
+ * Frees off the cache block if necc.
+ */
+static void del(struct mq_policy *mq, struct entry *e)
+{
+	queue_remove(&e->list);
+	hash_remove(e);
+	if (e->in_cache)
+		free_cblock(mq, e->cblock);
+}
+
+/*
+ * Like del, except it removes the first entry in the queue (ie. the least
+ * recently used).
+ */
+static struct entry *pop(struct mq_policy *mq, struct queue *q)
+{
+	struct entry *e = container_of(queue_pop(q), struct entry, list);
+
+	if (e) {
+		hash_remove(e);
+
+		if (e->in_cache)
+			free_cblock(mq, e->cblock);
+	}
+
+	return e;
+}
+
+/*
+ * Has this entry already been updated?
+ */
+static bool updated_this_tick(struct mq_policy *mq, struct entry *e)
+{
+	return mq->tick == e->tick;
+}
+
+/*
+ * The promotion threshold is adjusted every generation.  As are the counts
+ * of the entries.
+ *
+ * At the moment the threshold is taken by averaging the hit counts of some
+ * of the entries in the cache (the first 20 entries of the first level).
+ *
+ * We can be much cleverer than this though.  For example, each promotion
+ * could bump up the threshold helping to prevent churn.  Much more to do
+ * here.
+ */
+
+#define MAX_TO_AVERAGE 20
+
+static void check_generation(struct mq_policy *mq)
+{
+	unsigned total = 0, nr = 0, count = 0, level;
+	struct list_head *head;
+	struct entry *e;
+
+	if ((mq->hit_count >= mq->generation_period) &&
+	    (mq->nr_cblocks_allocated == from_cblock(mq->cache_size))) {
+
+		mq->hit_count = 0;
+		mq->generation++;
+
+		for (level = 0; level < NR_QUEUE_LEVELS && count < MAX_TO_AVERAGE; level++) {
+			head = mq->cache.qs + level;
+			list_for_each_entry(e, head, list) {
+				nr++;
+				total += e->hit_count;
+
+				if (++count >= MAX_TO_AVERAGE)
+					break;
+			}
+		}
+
+		mq->promote_threshold = nr ? total / nr : 1;
+		if (mq->promote_threshold * nr < total)
+			mq->promote_threshold++;
+	}
+}
+
+/*
+ * Whenever we use an entry we bump up it's hit counter, and push it to the
+ * back to it's current level.
+ */
+static void requeue_and_update_tick(struct mq_policy *mq, struct entry *e)
+{
+	if (updated_this_tick(mq, e))
+		return;
+
+	e->hit_count++;
+	mq->hit_count++;
+	check_generation(mq);
+
+	/* generation adjustment, to stop the counts increasing forever. */
+	/* FIXME: divide? */
+	/* e->hit_count -= min(e->hit_count - 1, mq->generation - e->generation); */
+	e->generation = mq->generation;
+
+	del(mq, e);
+	push(mq, e);
+}
+
+/*
+ * Demote the least recently used entry from the cache to the pre_cache.
+ * Returns the new cache entry to use, and the old origin block it was
+ * mapped to.
+ *
+ * We drop the hit count on the demoted entry back to 1 to stop it bouncing
+ * straight back into the cache if it's subsequently hit.  There are
+ * various options here, and more experimentation would be good:
+ *
+ * - just forget about the demoted entry completely (ie. don't insert it
+     into the pre_cache).
+ * - divide the hit count rather that setting to some hard coded value.
+ * - set the hit count to a hard coded value other than 1, eg, is it better
+ *   if it goes in at level 2?
+ */
+static dm_cblock_t demote_cblock(struct mq_policy *mq, dm_oblock_t *oblock)
+{
+	dm_cblock_t result;
+	struct entry *demoted = pop(mq, &mq->cache);
+
+	BUG_ON(!demoted);
+	result = demoted->cblock;
+	*oblock = demoted->oblock;
+	demoted->in_cache = false;
+	demoted->hit_count = 1;
+	push(mq, demoted);
+
+	return result;
+}
+
+/*
+ * We modify the basic promotion_threshold depending on the specific io.
+ *
+ * If the origin block has been discarded then there's no cost to copy it
+ * to the cache.
+ *
+ * We bias towards reads, since they can be demoted at no cost if they
+ * haven't been dirtied.
+ */
+#define DISCARDED_PROMOTE_THRESHOLD 1
+#define READ_PROMOTE_THRESHOLD 4
+#define WRITE_PROMOTE_THRESHOLD 8
+
+static unsigned adjusted_promote_threshold(struct mq_policy *mq,
+					   bool discarded_oblock, int data_dir)
+{
+	if (discarded_oblock && any_free_cblocks(mq) && data_dir == WRITE)
+		/*
+		 * We don't need to do any copying at all, so give this a
+		 * very low threshold.  In practice this only triggers
+		 * during initial population after a format.
+		 */
+		return DISCARDED_PROMOTE_THRESHOLD;
+
+	return data_dir == READ ?
+		(mq->promote_threshold + READ_PROMOTE_THRESHOLD) :
+		(mq->promote_threshold + WRITE_PROMOTE_THRESHOLD);
+}
+
+static bool should_promote(struct mq_policy *mq, struct entry *e,
+			   bool discarded_oblock, int data_dir)
+{
+	return e->hit_count >=
+		adjusted_promote_threshold(mq, discarded_oblock, data_dir);
+}
+
+static int cache_entry_found(struct mq_policy *mq,
+			     struct entry *e,
+			     struct policy_result *result)
+{
+	requeue_and_update_tick(mq, e);
+
+	if (e->in_cache) {
+		result->op = POLICY_HIT;
+		result->cblock = e->cblock;
+	}
+
+	return 0;
+}
+
+/*
+ * Moves and entry from the pre_cache to the cache.  The main work is
+ * finding which cache block to use.
+ */
+static int pre_cache_to_cache(struct mq_policy *mq, struct entry *e,
+			      struct policy_result *result)
+{
+	dm_cblock_t cblock;
+
+	if (find_free_cblock(mq, &cblock) == -ENOSPC) {
+		result->op = POLICY_REPLACE;
+		cblock = demote_cblock(mq, &result->old_oblock);
+	} else
+		result->op = POLICY_NEW;
+
+	result->cblock = e->cblock = cblock;
+
+	del(mq, e);
+	e->in_cache = true;
+	push(mq, e);
+
+	return 0;
+}
+
+static int pre_cache_entry_found(struct mq_policy *mq, struct entry *e,
+				 bool can_migrate, bool discarded_oblock,
+				 int data_dir, struct policy_result *result)
+{
+	int r = 0;
+	bool updated = updated_this_tick(mq, e);
+
+	requeue_and_update_tick(mq, e);
+
+	if ((!discarded_oblock && updated) ||
+	    !should_promote(mq, e, discarded_oblock, data_dir))
+		result->op = POLICY_MISS;
+	else if (!can_migrate)
+		r = -EWOULDBLOCK;
+	else
+		r = pre_cache_to_cache(mq, e, result);
+
+	return r;
+}
+
+static void insert_in_pre_cache(struct mq_policy *mq,
+				dm_oblock_t oblock)
+{
+	struct entry *e = alloc_entry(mq);
+
+	if (!e)
+		/*
+		 * There's no spare entry structure, so we grab the least
+		 * used one from the pre_cache.
+		 */
+		e = pop(mq, &mq->pre_cache);
+
+	if (unlikely(!e)) {
+		DMWARN("couldn't pop from pre cache");
+		return;
+	}
+
+	e->in_cache = false;
+	e->oblock = oblock;
+	e->hit_count = 1;
+	e->generation = mq->generation;
+	push(mq, e);
+}
+
+static void insert_in_cache(struct mq_policy *mq, dm_oblock_t oblock,
+			    struct policy_result *result)
+{
+	struct entry *e;
+	dm_cblock_t cblock;
+
+	if (find_free_cblock(mq, &cblock) == -ENOSPC) {
+		result->op = POLICY_MISS;
+		insert_in_pre_cache(mq, oblock);
+		return;
+	}
+
+	e = alloc_entry(mq);
+	if (unlikely(!e)) {
+		result->op = POLICY_MISS;
+		return;
+	}
+
+	e->oblock = oblock;
+	e->cblock = cblock;
+	e->in_cache = true;
+	e->hit_count = 1;
+	e->generation = mq->generation;
+	push(mq, e);
+
+	result->op = POLICY_NEW;
+	result->cblock = e->cblock;
+}
+
+static int no_entry_found(struct mq_policy *mq, dm_oblock_t oblock,
+			  bool can_migrate, bool discarded_oblock,
+			  int data_dir, struct policy_result *result)
+{
+	if (adjusted_promote_threshold(mq, discarded_oblock, data_dir) == 1) {
+		if (can_migrate)
+			insert_in_cache(mq, oblock, result);
+		else
+			return -EWOULDBLOCK;
+	} else {
+		insert_in_pre_cache(mq, oblock);
+		result->op = POLICY_MISS;
+	}
+
+	return 0;
+}
+
+/*
+ * Looks the oblock up in the hash table, then decides whether to put in
+ * pre_cache, or cache etc.
+ */
+static int map(struct mq_policy *mq, dm_oblock_t oblock,
+	       bool can_migrate, bool discarded_oblock,
+	       int data_dir, struct policy_result *result)
+{
+	int r = 0;
+	struct entry *e = hash_lookup(mq, oblock);
+
+	if (e && e->in_cache)
+		r = cache_entry_found(mq, e, result);
+	else if (iot_pattern(&mq->tracker) == PATTERN_SEQUENTIAL)
+		result->op = POLICY_MISS;
+	else if (e)
+		r = pre_cache_entry_found(mq, e, can_migrate, discarded_oblock,
+					  data_dir, result);
+	else
+		r = no_entry_found(mq, oblock, can_migrate, discarded_oblock,
+				   data_dir, result);
+
+	if (r == -EWOULDBLOCK)
+		result->op = POLICY_MISS;
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Public interface, via the policy struct.  See dm-cache-policy.h for a
+ * description of these.
+ */
+
+static struct mq_policy *to_mq_policy(struct dm_cache_policy *p)
+{
+	return container_of(p, struct mq_policy, policy);
+}
+
+static void mq_destroy(struct dm_cache_policy *p)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	free_bitset(mq->allocation_bitset);
+	kfree(mq->table);
+	free_entries(mq);
+	kfree(mq);
+}
+
+static void copy_tick(struct mq_policy *mq)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&mq->tick_lock, flags);
+	mq->tick = mq->tick_protected;
+	spin_unlock_irqrestore(&mq->tick_lock, flags);
+}
+
+static int mq_map(struct dm_cache_policy *p, dm_oblock_t oblock,
+		  bool can_block, bool can_migrate, bool discarded_oblock,
+		  struct bio *bio, struct policy_result *result)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	result->op = POLICY_MISS;
+
+	if (can_block)
+		mutex_lock(&mq->lock);
+	else if (!mutex_trylock(&mq->lock))
+		return -EWOULDBLOCK;
+
+	copy_tick(mq);
+
+	iot_examine_bio(&mq->tracker, bio);
+	r = map(mq, oblock, can_migrate, discarded_oblock,
+		bio_data_dir(bio), result);
+
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static int mq_lookup(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock)
+{
+	int r;
+	struct mq_policy *mq = to_mq_policy(p);
+	struct entry *e;
+
+	if (!mutex_trylock(&mq->lock))
+		return -EWOULDBLOCK;
+
+	e = hash_lookup(mq, oblock);
+	if (e && e->in_cache) {
+		*cblock = e->cblock;
+		r = 0;
+	} else
+		r = -ENOENT;
+
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static int mq_load_mapping(struct dm_cache_policy *p,
+			   dm_oblock_t oblock, dm_cblock_t cblock,
+			   uint32_t hint, bool hint_valid)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	struct entry *e;
+
+	e = alloc_entry(mq);
+	if (!e)
+		return -ENOMEM;
+
+	e->cblock = cblock;
+	e->oblock = oblock;
+	e->in_cache = true;
+	e->hit_count = hint_valid ? hint : 1;
+	e->generation = mq->generation;
+	push(mq, e);
+
+	return 0;
+}
+
+static int mq_walk_mappings(struct dm_cache_policy *p, policy_walk_fn fn,
+			    void *context)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	int r = 0;
+	struct entry *e;
+	unsigned level;
+
+	mutex_lock(&mq->lock);
+
+	for (level = 0; level < NR_QUEUE_LEVELS; level++)
+		list_for_each_entry(e, &mq->cache.qs[level], list) {
+			r = fn(context, e->cblock, e->oblock, e->hit_count);
+			if (r)
+				goto out;
+		}
+
+out:
+	mutex_unlock(&mq->lock);
+
+	return r;
+}
+
+static void remove_mapping(struct mq_policy *mq, dm_oblock_t oblock)
+{
+	struct entry *e = hash_lookup(mq, oblock);
+
+	BUG_ON(!e || !e->in_cache);
+
+	del(mq, e);
+	e->in_cache = false;
+	push(mq, e);
+}
+
+static void mq_remove_mapping(struct dm_cache_policy *p, dm_oblock_t oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	remove_mapping(mq, oblock);
+	mutex_unlock(&mq->lock);
+}
+
+static void force_mapping(struct mq_policy *mq,
+			  dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	struct entry *e = hash_lookup(mq, current_oblock);
+
+	BUG_ON(!e || !e->in_cache);
+
+	del(mq, e);
+	e->oblock = new_oblock;
+	push(mq, e);
+}
+
+static void mq_force_mapping(struct dm_cache_policy *p,
+			     dm_oblock_t current_oblock, dm_oblock_t new_oblock)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	mutex_lock(&mq->lock);
+	force_mapping(mq, current_oblock, new_oblock);
+	mutex_unlock(&mq->lock);
+}
+
+static dm_cblock_t mq_residency(struct dm_cache_policy *p)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+
+	/* FIXME: lock mutex, not sure we can block here */
+	return to_cblock(mq->nr_cblocks_allocated);
+}
+
+static void mq_tick(struct dm_cache_policy *p)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	unsigned long flags;
+
+	spin_lock_irqsave(&mq->tick_lock, flags);
+	mq->tick_protected++;
+	spin_unlock_irqrestore(&mq->tick_lock, flags);
+}
+
+static int mq_set_config_value(struct dm_cache_policy *p,
+			       const char *key, const char *value)
+{
+	struct mq_policy *mq = to_mq_policy(p);
+	enum io_pattern pattern;
+	unsigned long tmp;
+
+	if (!strcasecmp(key, "random_threshold"))
+		pattern = PATTERN_RANDOM;
+	else if (!strcasecmp(key, "sequential_threshold"))
+		pattern = PATTERN_SEQUENTIAL;
+	else
+		return -EINVAL;
+
+	if (kstrtoul(value, 10, &tmp))
+		return -EINVAL;
+
+	mq->tracker.thresholds[pattern] = tmp;
+
+	return 0;
+}
+
+static int mq_emit_config_values(struct dm_cache_policy *p, char *result, unsigned maxlen)
+{
+	ssize_t sz = 0;
+	struct mq_policy *mq = to_mq_policy(p);
+
+	DMEMIT("4 random_threshold %u sequential_threshold %u",
+	       mq->tracker.thresholds[PATTERN_RANDOM],
+	       mq->tracker.thresholds[PATTERN_SEQUENTIAL]);
+
+	return 0;
+}
+
+/* Init the policy plugin interface function pointers. */
+static void init_policy_functions(struct mq_policy *mq)
+{
+	mq->policy.destroy = mq_destroy;
+	mq->policy.map = mq_map;
+	mq->policy.lookup = mq_lookup;
+	mq->policy.load_mapping = mq_load_mapping;
+	mq->policy.walk_mappings = mq_walk_mappings;
+	mq->policy.remove_mapping = mq_remove_mapping;
+	mq->policy.writeback_work = NULL;
+	mq->policy.force_mapping = mq_force_mapping;
+	mq->policy.residency = mq_residency;
+	mq->policy.tick = mq_tick;
+	mq->policy.emit_config_values = mq_emit_config_values;
+	mq->policy.set_config_value = mq_set_config_value;
+}
+
+static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
+					 sector_t origin_size,
+					 sector_t cache_block_size)
+{
+	int r;
+	struct mq_policy *mq = kzalloc(sizeof(*mq), GFP_KERNEL);
+
+	if (!mq)
+		return NULL;
+
+	init_policy_functions(mq);
+	iot_init(&mq->tracker, SEQUENTIAL_THRESHOLD_DEFAULT, RANDOM_THRESHOLD_DEFAULT);
+
+	mq->cache_size = cache_size;
+	mq->tick_protected = 0;
+	mq->tick = 0;
+	mq->hit_count = 0;
+	mq->generation = 0;
+	mq->promote_threshold = 0;
+	mutex_init(&mq->lock);
+	spin_lock_init(&mq->tick_lock);
+	mq->find_free_nr_words = dm_div_up(from_cblock(mq->cache_size), BITS_PER_LONG);
+	mq->find_free_last_word = 0;
+
+	queue_init(&mq->pre_cache);
+	queue_init(&mq->cache);
+	mq->generation_period = max((unsigned) from_cblock(cache_size), 1024U);
+
+	mq->nr_entries = 2 * from_cblock(cache_size);
+	r = alloc_entries(mq, mq->nr_entries);
+	if (r)
+		goto bad_cache_alloc;
+
+	mq->nr_entries_allocated = 0;
+	mq->nr_cblocks_allocated = 0;
+
+	mq->nr_buckets = next_power(from_cblock(cache_size) / 2, 16);
+	mq->hash_bits = ffs(mq->nr_buckets) - 1;
+	mq->table = kzalloc(sizeof(*mq->table) * mq->nr_buckets, GFP_KERNEL);
+	if (!mq->table)
+		goto bad_alloc_table;
+
+	mq->allocation_bitset = alloc_bitset(from_cblock(cache_size));
+	if (!mq->allocation_bitset)
+		goto bad_alloc_bitset;
+
+	return &mq->policy;
+
+bad_alloc_bitset:
+	kfree(mq->table);
+bad_alloc_table:
+	free_entries(mq);
+bad_cache_alloc:
+	kfree(mq);
+
+	return NULL;
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_cache_policy_type mq_policy_type = {
+	.name = "mq",
+	.hint_size = 4,
+	.owner = THIS_MODULE,
+	.create = mq_create
+};
+
+static struct dm_cache_policy_type default_policy_type = {
+	.name = "default",
+	.hint_size = 4,
+	.owner = THIS_MODULE,
+	.create = mq_create
+};
+
+static int __init mq_init(void)
+{
+	int r;
+
+	mq_entry_cache = kmem_cache_create("dm_mq_policy_cache_entry",
+					   sizeof(struct entry),
+					   __alignof__(struct entry),
+					   0, NULL);
+	if (!mq_entry_cache)
+		goto bad;
+
+	r = dm_cache_policy_register(&mq_policy_type);
+	if (r) {
+		DMERR("register failed %d", r);
+		goto bad_register_mq;
+	}
+
+	r = dm_cache_policy_register(&default_policy_type);
+	if (!r) {
+		DMINFO("version " MQ_VERSION " loaded");
+		return 0;
+	}
+
+	DMERR("register failed (as default) %d", r);
+
+	dm_cache_policy_unregister(&mq_policy_type);
+bad_register_mq:
+	kmem_cache_destroy(mq_entry_cache);
+bad:
+	return -ENOMEM;
+}
+
+static void __exit mq_exit(void)
+{
+	dm_cache_policy_unregister(&mq_policy_type);
+	dm_cache_policy_unregister(&default_policy_type);
+
+	kmem_cache_destroy(mq_entry_cache);
+}
+
+module_init(mq_init);
+module_exit(mq_exit);
+
+MODULE_AUTHOR("Joe Thornber <[e-mail]>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("mq cache policy");
+
+MODULE_ALIAS("dm-cache-default");

drivers/md/dm-cache-policy.c

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-policy-internal.h"
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/slab.h>
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX "cache-policy"
+
+static DEFINE_SPINLOCK(register_lock);
+static LIST_HEAD(register_list);
+
+static struct dm_cache_policy_type *__find_policy(const char *name)
+{
+	struct dm_cache_policy_type *t;
+
+	list_for_each_entry(t, &register_list, list)
+		if (!strcmp(t->name, name))
+			return t;
+
+	return NULL;
+}
+
+static struct dm_cache_policy_type *__get_policy_once(const char *name)
+{
+	struct dm_cache_policy_type *t = __find_policy(name);
+
+	if (t && !try_module_get(t->owner)) {
+		DMWARN("couldn't get module %s", name);
+		t = ERR_PTR(-EINVAL);
+	}
+
+	return t;
+}
+
+static struct dm_cache_policy_type *get_policy_once(const char *name)
+{
+	struct dm_cache_policy_type *t;
+
+	spin_lock(&register_lock);
+	t = __get_policy_once(name);
+	spin_unlock(&register_lock);
+
+	return t;
+}
+
+static struct dm_cache_policy_type *get_policy(const char *name)
+{
+	struct dm_cache_policy_type *t;
+
+	t = get_policy_once(name);
+	if (IS_ERR(t))
+		return NULL;
+
+	if (t)
+		return t;
+
+	request_module("dm-cache-%s", name);
+
+	t = get_policy_once(name);
+	if (IS_ERR(t))
+		return NULL;
+
+	return t;
+}
+
+static void put_policy(struct dm_cache_policy_type *t)
+{
+	module_put(t->owner);
+}
+
+int dm_cache_policy_register(struct dm_cache_policy_type *type)
+{
+	int r;
+
+	/* One size fits all for now */
+	if (type->hint_size != 0 && type->hint_size != 4) {
+		DMWARN("hint size must be 0 or 4 but %llu supplied.", (unsigned long long) type->hint_size);
+		return -EINVAL;
+	}
+
+	spin_lock(&register_lock);
+	if (__find_policy(type->name)) {
+		DMWARN("attempt to register policy under duplicate name %s", type->name);
+		r = -EINVAL;
+	} else {
+		list_add(&type->list, &register_list);
+		r = 0;
+	}
+	spin_unlock(&register_lock);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_register);
+
+void dm_cache_policy_unregister(struct dm_cache_policy_type *type)
+{
+	spin_lock(&register_lock);
+	list_del_init(&type->list);
+	spin_unlock(&register_lock);
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_unregister);
+
+struct dm_cache_policy *dm_cache_policy_create(const char *name,
+					       dm_cblock_t cache_size,
+					       sector_t origin_size,
+					       sector_t cache_block_size)
+{
+	struct dm_cache_policy *p = NULL;
+	struct dm_cache_policy_type *type;
+
+	type = get_policy(name);
+	if (!type) {
+		DMWARN("unknown policy type");
+		return NULL;
+	}
+
+	p = type->create(cache_size, origin_size, cache_block_size);
+	if (!p) {
+		put_policy(type);
+		return NULL;
+	}
+	p->private = type;
+
+	return p;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_create);
+
+void dm_cache_policy_destroy(struct dm_cache_policy *p)
+{
+	struct dm_cache_policy_type *t = p->private;
+
+	p->destroy(p);
+	put_policy(t);
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_destroy);
+
+const char *dm_cache_policy_get_name(struct dm_cache_policy *p)
+{
+	struct dm_cache_policy_type *t = p->private;
+
+	return t->name;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_get_name);
+
+size_t dm_cache_policy_get_hint_size(struct dm_cache_policy *p)
+{
+	struct dm_cache_policy_type *t = p->private;
+
+	return t->hint_size;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_get_hint_size);
+
+/*----------------------------------------------------------------*/

drivers/md/dm-cache-policy.h

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_CACHE_POLICY_H
+#define DM_CACHE_POLICY_H
+
+#include "dm-cache-block-types.h"
+
+#include <linux/device-mapper.h>
+
+/*----------------------------------------------------------------*/
+
+/* FIXME: make it clear which methods are optional.  Get debug policy to
+ * double check this at start.
+ */
+
+/*
+ * The cache policy makes the important decisions about which blocks get to
+ * live on the faster cache device.
+ *
+ * When the core target has to remap a bio it calls the 'map' method of the
+ * policy.  This returns an instruction telling the core target what to do.
+ *
+ * POLICY_HIT:
+ *   That block is in the cache.  Remap to the cache and carry on.
+ *
+ * POLICY_MISS:
+ *   This block is on the origin device.  Remap and carry on.
+ *
+ * POLICY_NEW:
+ *   This block is currently on the origin device, but the policy wants to
+ *   move it.  The core should:
+ *
+ *   - hold any further io to this origin block
+ *   - copy the origin to the given cache block
+ *   - release all the held blocks
+ *   - remap the original block to the cache
+ *
+ * POLICY_REPLACE:
+ *   This block is currently on the origin device.  The policy wants to
+ *   move it to the cache, with the added complication that the destination
+ *   cache block needs a writeback first.  The core should:
+ *
+ *   - hold any further io to this origin block
+ *   - hold any further io to the origin block that's being written back
+ *   - writeback
+ *   - copy new block to cache
+ *   - release held blocks
+ *   - remap bio to cache and reissue.
+ *
+ * Should the core run into trouble while processing a POLICY_NEW or
+ * POLICY_REPLACE instruction it will roll back the policies mapping using
+ * remove_mapping() or force_mapping().  These methods must not fail.  This
+ * approach avoids having transactional semantics in the policy (ie, the
+ * core informing the policy when a migration is complete), and hence makes
+ * it easier to write new policies.
+ *
+ * In general policy methods should never block, except in the case of the
+ * map function when can_migrate is set.  So be careful to implement using
+ * bounded, preallocated memory.
+ */
+enum policy_operation {
+	POLICY_HIT,
+	POLICY_MISS,
+	POLICY_NEW,
+	POLICY_REPLACE
+};
+
+/*
+ * This is the instruction passed back to the core target.
+ */
+struct policy_result {
+	enum policy_operation op;
+	dm_oblock_t old_oblock;	/* POLICY_REPLACE */
+	dm_cblock_t cblock;	/* POLICY_HIT, POLICY_NEW, POLICY_REPLACE */
+};
+
+typedef int (*policy_walk_fn)(void *context, dm_cblock_t cblock,
+			      dm_oblock_t oblock, uint32_t hint);
+
+/*
+ * The cache policy object.  Just a bunch of methods.  It is envisaged that
+ * this structure will be embedded in a bigger, policy specific structure
+ * (ie. use container_of()).
+ */
+struct dm_cache_policy {
+
+	/*
+	 * FIXME: make it clear which methods are optional, and which may
+	 * block.
+	 */
+
+	/*
+	 * Destroys this object.
+	 */
+	void (*destroy)(struct dm_cache_policy *p);
+
+	/*
+	 * See large comment above.
+	 *
+	 * oblock      - the origin block we're interested in.
+	 *
+	 * can_block - indicates whether the current thread is allowed to
+	 *             block.  -EWOULDBLOCK returned if it can't and would.
+	 *
+	 * can_migrate - gives permission for POLICY_NEW or POLICY_REPLACE
+	 *               instructions.  If denied and the policy would have
+	 *               returned one of these instructions it should
+	 *               return -EWOULDBLOCK.
+	 *
+	 * discarded_oblock - indicates whether the whole origin block is
+	 *               in a discarded state (FIXME: better to tell the
+	 *               policy about this sooner, so it can recycle that
+	 *               cache block if it wants.)
+	 * bio         - the bio that triggered this call.
+	 * result      - gets filled in with the instruction.
+	 *
+	 * May only return 0, or -EWOULDBLOCK (if !can_migrate)
+	 */
+	int (*map)(struct dm_cache_policy *p, dm_oblock_t oblock,
+		   bool can_block, bool can_migrate, bool discarded_oblock,
+		   struct bio *bio, struct policy_result *result);
+
+	/*
+	 * Sometimes we want to see if a block is in the cache, without
+	 * triggering any update of stats.  (ie. it's not a real hit).
+	 *
+	 * Must not block.
+	 *
+	 * Returns 1 iff in cache, 0 iff not, < 0 on error (-EWOULDBLOCK
+	 * would be typical).
+	 */
+	int (*lookup)(struct dm_cache_policy *p, dm_oblock_t oblock, dm_cblock_t *cblock);
+
+	/*
+	 * oblock must be a mapped block.  Must not block.
+	 */
+	void (*set_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
+	void (*clear_dirty)(struct dm_cache_policy *p, dm_oblock_t oblock);
+
+	/*
+	 * Called when a cache target is first created.  Used to load a
+	 * mapping from the metadata device into the policy.
+	 */
+	int (*load_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock,
+			    dm_cblock_t cblock, uint32_t hint, bool hint_valid);
+
+	int (*walk_mappings)(struct dm_cache_policy *p, policy_walk_fn fn,
+			     void *context);
+
+	/*
+	 * Override functions used on the error paths of the core target.
+	 * They must succeed.
+	 */
+	void (*remove_mapping)(struct dm_cache_policy *p, dm_oblock_t oblock);
+	void (*force_mapping)(struct dm_cache_policy *p, dm_oblock_t current_oblock,
+			      dm_oblock_t new_oblock);
+
+	int (*writeback_work)(struct dm_cache_policy *p, dm_oblock_t *oblock, dm_cblock_t *cblock);
+
+
+	/*
+	 * How full is the cache?
+	 */
+	dm_cblock_t (*residency)(struct dm_cache_policy *p);
+
+	/*
+	 * Because of where we sit in the block layer, we can be asked to
+	 * map a lot of little bios that are all in the same block (no
+	 * queue merging has occurred).  To stop the policy being fooled by
+	 * these the core target sends regular tick() calls to the policy.
+	 * The policy should only count an entry as hit once per tick.
+	 */
+	void (*tick)(struct dm_cache_policy *p);
+
+	/*
+	 * Configuration.
+	 */
+	int (*emit_config_values)(struct dm_cache_policy *p,
+				  char *result, unsigned maxlen);
+	int (*set_config_value)(struct dm_cache_policy *p,
+				const char *key, const char *value);
+
+	/*
+	 * Book keeping ptr for the policy register, not for general use.
+	 */
+	void *private;
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * We maintain a little register of the different policy types.
+ */
+#define CACHE_POLICY_NAME_SIZE 16
+
+struct dm_cache_policy_type {
+	/* For use by the register code only. */
+	struct list_head list;
+
+	/*
+	 * Policy writers should fill in these fields.  The name field is
+	 * what gets passed on the target line to select your policy.
+	 */
+	char name[CACHE_POLICY_NAME_SIZE];
+
+	/*
+	 * Policies may store a hint for each each cache block.
+	 * Currently the size of this hint must be 0 or 4 bytes but we
+	 * expect to relax this in future.
+	 */
+	size_t hint_size;
+
+	struct module *owner;
+	struct dm_cache_policy *(*create)(dm_cblock_t cache_size,
+					  sector_t origin_size,
+					  sector_t block_size);
+};
+
+int dm_cache_policy_register(struct dm_cache_policy_type *type);
+void dm_cache_policy_unregister(struct dm_cache_policy_type *type);
+
+/*----------------------------------------------------------------*/
+
+#endif	/* DM_CACHE_POLICY_H */

drivers/md/dm-cache-target.c

···
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm.h"
+#include "dm-bio-prison.h"
+#include "dm-cache-metadata.h"
+
+#include <linux/dm-io.h>
+#include <linux/dm-kcopyd.h>
+#include <linux/init.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#define DM_MSG_PREFIX "cache"
+
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(cache_copy_throttle,
+	"A percentage of time allocated for copying to and/or from cache");
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Glossary:
+ *
+ * oblock: index of an origin block
+ * cblock: index of a cache block
+ * promotion: movement of a block from origin to cache
+ * demotion: movement of a block from cache to origin
+ * migration: movement of a block between the origin and cache device,
+ *	      either direction
+ */
+
+/*----------------------------------------------------------------*/
+
+static size_t bitset_size_in_bytes(unsigned nr_entries)
+{
+	return sizeof(unsigned long) * dm_div_up(nr_entries, BITS_PER_LONG);
+}
+
+static unsigned long *alloc_bitset(unsigned nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+	return vzalloc(s);
+}
+
+static void clear_bitset(void *bitset, unsigned nr_entries)
+{
+	size_t s = bitset_size_in_bytes(nr_entries);
+	memset(bitset, 0, s);
+}
+
+static void free_bitset(unsigned long *bits)
+{
+	vfree(bits);
+}
+
+/*----------------------------------------------------------------*/
+
+#define PRISON_CELLS 1024
+#define MIGRATION_POOL_SIZE 128
+#define COMMIT_PERIOD HZ
+#define MIGRATION_COUNT_WINDOW 10
+
+/*
+ * The block size of the device holding cache data must be >= 32KB
+ */
+#define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (32 * 1024 >> SECTOR_SHIFT)
+
+/*
+ * FIXME: the cache is read/write for the time being.
+ */
+enum cache_mode {
+	CM_WRITE,		/* metadata may be changed */
+	CM_READ_ONLY,		/* metadata may not be changed */
+};
+
+struct cache_features {
+	enum cache_mode mode;
+	bool write_through:1;
+};
+
+struct cache_stats {
+	atomic_t read_hit;
+	atomic_t read_miss;
+	atomic_t write_hit;
+	atomic_t write_miss;
+	atomic_t demotion;
+	atomic_t promotion;
+	atomic_t copies_avoided;
+	atomic_t cache_cell_clash;
+	atomic_t commit_count;
+	atomic_t discard_count;
+};
+
+struct cache {
+	struct dm_target *ti;
+	struct dm_target_callbacks callbacks;
+
+	/*
+	 * Metadata is written to this device.
+	 */
+	struct dm_dev *metadata_dev;
+
+	/*
+	 * The slower of the two data devices.  Typically a spindle.
+	 */
+	struct dm_dev *origin_dev;
+
+	/*
+	 * The faster of the two data devices.  Typically an SSD.
+	 */
+	struct dm_dev *cache_dev;
+
+	/*
+	 * Cache features such as write-through.
+	 */
+	struct cache_features features;
+
+	/*
+	 * Size of the origin device in _complete_ blocks and native sectors.
+	 */
+	dm_oblock_t origin_blocks;
+	sector_t origin_sectors;
+
+	/*
+	 * Size of the cache device in blocks.
+	 */
+	dm_cblock_t cache_size;
+
+	/*
+	 * Fields for converting from sectors to blocks.
+	 */
+	uint32_t sectors_per_block;
+	int sectors_per_block_shift;
+
+	struct dm_cache_metadata *cmd;
+
+	spinlock_t lock;
+	struct bio_list deferred_bios;
+	struct bio_list deferred_flush_bios;
+	struct list_head quiesced_migrations;
+	struct list_head completed_migrations;
+	struct list_head need_commit_migrations;
+	sector_t migration_threshold;
+	atomic_t nr_migrations;
+	wait_queue_head_t migration_wait;
+
+	/*
+	 * cache_size entries, dirty if set
+	 */
+	dm_cblock_t nr_dirty;
+	unsigned long *dirty_bitset;
+
+	/*
+	 * origin_blocks entries, discarded if set.
+	 */
+	sector_t discard_block_size; /* a power of 2 times sectors per block */
+	dm_dblock_t discard_nr_blocks;
+	unsigned long *discard_bitset;
+
+	struct dm_kcopyd_client *copier;
+	struct workqueue_struct *wq;
+	struct work_struct worker;
+
+	struct delayed_work waker;
+	unsigned long last_commit_jiffies;
+
+	struct dm_bio_prison *prison;
+	struct dm_deferred_set *all_io_ds;
+
+	mempool_t *migration_pool;
+	struct dm_cache_migration *next_migration;
+
+	struct dm_cache_policy *policy;
+	unsigned policy_nr_args;
+
+	bool need_tick_bio:1;
+	bool sized:1;
+	bool quiescing:1;
+	bool commit_requested:1;
+	bool loaded_mappings:1;
+	bool loaded_discards:1;
+
+	struct cache_stats stats;
+
+	/*
+	 * Rather than reconstructing the table line for the status we just
+	 * save it and regurgitate.
+	 */
+	unsigned nr_ctr_args;
+	const char **ctr_args;
+};
+
+struct per_bio_data {
+	bool tick:1;
+	unsigned req_nr:2;
+	struct dm_deferred_entry *all_io_entry;
+};
+
+struct dm_cache_migration {
+	struct list_head list;
+	struct cache *cache;
+
+	unsigned long start_jiffies;
+	dm_oblock_t old_oblock;
+	dm_oblock_t new_oblock;
+	dm_cblock_t cblock;
+
+	bool err:1;
+	bool writeback:1;
+	bool demote:1;
+	bool promote:1;
+
+	struct dm_bio_prison_cell *old_ocell;
+	struct dm_bio_prison_cell *new_ocell;
+};
+
+/*
+ * Processing a bio in the worker thread may require these memory
+ * allocations.  We prealloc to avoid deadlocks (the same worker thread
+ * frees them back to the mempool).
+ */
+struct prealloc {
+	struct dm_cache_migration *mg;
+	struct dm_bio_prison_cell *cell1;
+	struct dm_bio_prison_cell *cell2;
+};
+
+static void wake_worker(struct cache *cache)
+{
+	queue_work(cache->wq, &cache->worker);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct dm_bio_prison_cell *alloc_prison_cell(struct cache *cache)
+{
+	/* FIXME: change to use a local slab. */
+	return dm_bio_prison_alloc_cell(cache->prison, GFP_NOWAIT);
+}
+
+static void free_prison_cell(struct cache *cache, struct dm_bio_prison_cell *cell)
+{
+	dm_bio_prison_free_cell(cache->prison, cell);
+}
+
+static int prealloc_data_structs(struct cache *cache, struct prealloc *p)
+{
+	if (!p->mg) {
+		p->mg = mempool_alloc(cache->migration_pool, GFP_NOWAIT);
+		if (!p->mg)
+			return -ENOMEM;
+	}
+
+	if (!p->cell1) {
+		p->cell1 = alloc_prison_cell(cache);
+		if (!p->cell1)
+			return -ENOMEM;
+	}
+
+	if (!p->cell2) {
+		p->cell2 = alloc_prison_cell(cache);
+		if (!p->cell2)
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void prealloc_free_structs(struct cache *cache, struct prealloc *p)
+{
+	if (p->cell2)
+		free_prison_cell(cache, p->cell2);
+
+	if (p->cell1)
+		free_prison_cell(cache, p->cell1);
+
+	if (p->mg)
+		mempool_free(p->mg, cache->migration_pool);
+}
+
+static struct dm_cache_migration *prealloc_get_migration(struct prealloc *p)
+{
+	struct dm_cache_migration *mg = p->mg;
+
+	BUG_ON(!mg);
+	p->mg = NULL;
+
+	return mg;
+}
+
+/*
+ * You must have a cell within the prealloc struct to return.  If not this
+ * function will BUG() rather than returning NULL.
+ */
+static struct dm_bio_prison_cell *prealloc_get_cell(struct prealloc *p)
+{
+	struct dm_bio_prison_cell *r = NULL;
+
+	if (p->cell1) {
+		r = p->cell1;
+		p->cell1 = NULL;
+
+	} else if (p->cell2) {
+		r = p->cell2;
+		p->cell2 = NULL;
+	} else
+		BUG();
+
+	return r;
+}
+
+/*
+ * You can't have more than two cells in a prealloc struct.  BUG() will be
+ * called if you try and overfill.
+ */
+static void prealloc_put_cell(struct prealloc *p, struct dm_bio_prison_cell *cell)
+{
+	if (!p->cell2)
+		p->cell2 = cell;
+
+	else if (!p->cell1)
+		p->cell1 = cell;
+
+	else
+		BUG();
+}
+
+/*----------------------------------------------------------------*/
+
+static void build_key(dm_oblock_t oblock, struct dm_cell_key *key)
+{
+	key->virtual = 0;
+	key->dev = 0;
+	key->block = from_oblock(oblock);
+}
+
+/*
+ * The caller hands in a preallocated cell, and a free function for it.
+ * The cell will be freed if there's an error, or if it wasn't used because
+ * a cell with that key already exists.
+ */
+typedef void (*cell_free_fn)(void *context, struct dm_bio_prison_cell *cell);
+
+static int bio_detain(struct cache *cache, dm_oblock_t oblock,
+		      struct bio *bio, struct dm_bio_prison_cell *cell_prealloc,
+		      cell_free_fn free_fn, void *free_context,
+		      struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	struct dm_cell_key key;
+
+	build_key(oblock, &key);
+	r = dm_bio_detain(cache->prison, &key, bio, cell_prealloc, cell_result);
+	if (r)
+		free_fn(free_context, cell_prealloc);
+
+	return r;
+}
+
+static int get_cell(struct cache *cache,
+		    dm_oblock_t oblock,
+		    struct prealloc *structs,
+		    struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	struct dm_cell_key key;
+	struct dm_bio_prison_cell *cell_prealloc;
+
+	cell_prealloc = prealloc_get_cell(structs);
+
+	build_key(oblock, &key);
+	r = dm_get_cell(cache->prison, &key, cell_prealloc, cell_result);
+	if (r)
+		prealloc_put_cell(structs, cell_prealloc);
+
+	return r;
+}
+
+ /*----------------------------------------------------------------*/
+
+static bool is_dirty(struct cache *cache, dm_cblock_t b)
+{
+	return test_bit(from_cblock(b), cache->dirty_bitset);
+}
+
+static void set_dirty(struct cache *cache, dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	if (!test_and_set_bit(from_cblock(cblock), cache->dirty_bitset)) {
+		cache->nr_dirty = to_cblock(from_cblock(cache->nr_dirty) + 1);
+		policy_set_dirty(cache->policy, oblock);
+	}
+}
+
+static void clear_dirty(struct cache *cache, dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	if (test_and_clear_bit(from_cblock(cblock), cache->dirty_bitset)) {
+		policy_clear_dirty(cache->policy, oblock);
+		cache->nr_dirty = to_cblock(from_cblock(cache->nr_dirty) - 1);
+		if (!from_cblock(cache->nr_dirty))
+			dm_table_event(cache->ti->table);
+	}
+}
+
+/*----------------------------------------------------------------*/
+static bool block_size_is_power_of_two(struct cache *cache)
+{
+	return cache->sectors_per_block_shift >= 0;
+}
+
+static dm_dblock_t oblock_to_dblock(struct cache *cache, dm_oblock_t oblock)
+{
+	sector_t discard_blocks = cache->discard_block_size;
+	dm_block_t b = from_oblock(oblock);
+
+	if (!block_size_is_power_of_two(cache))
+		(void) sector_div(discard_blocks, cache->sectors_per_block);
+	else
+		discard_blocks >>= cache->sectors_per_block_shift;
+
+	(void) sector_div(b, discard_blocks);
+
+	return to_dblock(b);
+}
+
+static void set_discard(struct cache *cache, dm_dblock_t b)
+{
+	unsigned long flags;
+
+	atomic_inc(&cache->stats.discard_count);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	set_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void clear_discard(struct cache *cache, dm_dblock_t b)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	clear_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static bool is_discarded(struct cache *cache, dm_dblock_t b)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	r = test_bit(from_dblock(b), cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return r;
+}
+
+static bool is_discarded_oblock(struct cache *cache, dm_oblock_t b)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	r = test_bit(from_dblock(oblock_to_dblock(cache, b)),
+		     cache->discard_bitset);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return r;
+}
+
+/*----------------------------------------------------------------*/
+
+static void load_stats(struct cache *cache)
+{
+	struct dm_cache_statistics stats;
+
+	dm_cache_metadata_get_stats(cache->cmd, &stats);
+	atomic_set(&cache->stats.read_hit, stats.read_hits);
+	atomic_set(&cache->stats.read_miss, stats.read_misses);
+	atomic_set(&cache->stats.write_hit, stats.write_hits);
+	atomic_set(&cache->stats.write_miss, stats.write_misses);
+}
+
+static void save_stats(struct cache *cache)
+{
+	struct dm_cache_statistics stats;
+
+	stats.read_hits = atomic_read(&cache->stats.read_hit);
+	stats.read_misses = atomic_read(&cache->stats.read_miss);
+	stats.write_hits = atomic_read(&cache->stats.write_hit);
+	stats.write_misses = atomic_read(&cache->stats.write_miss);
+
+	dm_cache_metadata_set_stats(cache->cmd, &stats);
+}
+
+/*----------------------------------------------------------------
+ * Per bio data
+ *--------------------------------------------------------------*/
+static struct per_bio_data *get_per_bio_data(struct bio *bio)
+{
+	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));
+	BUG_ON(!pb);
+	return pb;
+}
+
+static struct per_bio_data *init_per_bio_data(struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	pb->tick = false;
+	pb->req_nr = dm_bio_get_target_bio_nr(bio);
+	pb->all_io_entry = NULL;
+
+	return pb;
+}
+
+/*----------------------------------------------------------------
+ * Remapping
+ *--------------------------------------------------------------*/
+static void remap_to_origin(struct cache *cache, struct bio *bio)
+{
+	bio->bi_bdev = cache->origin_dev->bdev;
+}
+
+static void remap_to_cache(struct cache *cache, struct bio *bio,
+			   dm_cblock_t cblock)
+{
+	sector_t bi_sector = bio->bi_sector;
+
+	bio->bi_bdev = cache->cache_dev->bdev;
+	if (!block_size_is_power_of_two(cache))
+		bio->bi_sector = (from_cblock(cblock) * cache->sectors_per_block) +
+				sector_div(bi_sector, cache->sectors_per_block);
+	else
+		bio->bi_sector = (from_cblock(cblock) << cache->sectors_per_block_shift) |
+				(bi_sector & (cache->sectors_per_block - 1));
+}
+
+static void check_if_tick_bio_needed(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	if (cache->need_tick_bio &&
+	    !(bio->bi_rw & (REQ_FUA | REQ_FLUSH | REQ_DISCARD))) {
+		pb->tick = true;
+		cache->need_tick_bio = false;
+	}
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
+				  dm_oblock_t oblock)
+{
+	check_if_tick_bio_needed(cache, bio);
+	remap_to_origin(cache, bio);
+	if (bio_data_dir(bio) == WRITE)
+		clear_discard(cache, oblock_to_dblock(cache, oblock));
+}
+
+static void remap_to_cache_dirty(struct cache *cache, struct bio *bio,
+				 dm_oblock_t oblock, dm_cblock_t cblock)
+{
+	remap_to_cache(cache, bio, cblock);
+	if (bio_data_dir(bio) == WRITE) {
+		set_dirty(cache, oblock, cblock);
+		clear_discard(cache, oblock_to_dblock(cache, oblock));
+	}
+}
+
+static dm_oblock_t get_bio_block(struct cache *cache, struct bio *bio)
+{
+	sector_t block_nr = bio->bi_sector;
+
+	if (!block_size_is_power_of_two(cache))
+		(void) sector_div(block_nr, cache->sectors_per_block);
+	else
+		block_nr >>= cache->sectors_per_block_shift;
+
+	return to_oblock(block_nr);
+}
+
+static int bio_triggers_commit(struct cache *cache, struct bio *bio)
+{
+	return bio->bi_rw & (REQ_FLUSH | REQ_FUA);
+}
+
+static void issue(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+
+	if (!bio_triggers_commit(cache, bio)) {
+		generic_make_request(bio);
+		return;
+	}
+
+	/*
+	 * Batch together any bios that trigger commits and then issue a
+	 * single commit for them in do_worker().
+	 */
+	spin_lock_irqsave(&cache->lock, flags);
+	cache->commit_requested = true;
+	bio_list_add(&cache->deferred_flush_bios, bio);
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+/*----------------------------------------------------------------
+ * Migration processing
+ *
+ * Migration covers moving data from the origin device to the cache, or
+ * vice versa.
+ *--------------------------------------------------------------*/
+static void free_migration(struct dm_cache_migration *mg)
+{
+	mempool_free(mg, mg->cache->migration_pool);
+}
+
+static void inc_nr_migrations(struct cache *cache)
+{
+	atomic_inc(&cache->nr_migrations);
+}
+
+static void dec_nr_migrations(struct cache *cache)
+{
+	atomic_dec(&cache->nr_migrations);
+
+	/*
+	 * Wake the worker in case we're suspending the target.
+	 */
+	wake_up(&cache->migration_wait);
+}
+
+static void __cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
+			 bool holder)
+{
+	(holder ? dm_cell_release : dm_cell_release_no_holder)
+		(cache->prison, cell, &cache->deferred_bios);
+	free_prison_cell(cache, cell);
+}
+
+static void cell_defer(struct cache *cache, struct dm_bio_prison_cell *cell,
+		       bool holder)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	__cell_defer(cache, cell, holder);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void cleanup_migration(struct dm_cache_migration *mg)
+{
+	dec_nr_migrations(mg->cache);
+	free_migration(mg);
+}
+
+static void migration_failure(struct dm_cache_migration *mg)
+{
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		DMWARN_LIMIT("writeback failed; couldn't copy block");
+		set_dirty(cache, mg->old_oblock, mg->cblock);
+		cell_defer(cache, mg->old_ocell, false);
+
+	} else if (mg->demote) {
+		DMWARN_LIMIT("demotion failed; couldn't copy block");
+		policy_force_mapping(cache->policy, mg->new_oblock, mg->old_oblock);
+
+		cell_defer(cache, mg->old_ocell, mg->promote ? 0 : 1);
+		if (mg->promote)
+			cell_defer(cache, mg->new_ocell, 1);
+	} else {
+		DMWARN_LIMIT("promotion failed; couldn't copy block");
+		policy_remove_mapping(cache->policy, mg->new_oblock);
+		cell_defer(cache, mg->new_ocell, 1);
+	}
+
+	cleanup_migration(mg);
+}
+
+static void migration_success_pre_commit(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		cell_defer(cache, mg->old_ocell, false);
+		clear_dirty(cache, mg->old_oblock, mg->cblock);
+		cleanup_migration(mg);
+		return;
+
+	} else if (mg->demote) {
+		if (dm_cache_remove_mapping(cache->cmd, mg->cblock)) {
+			DMWARN_LIMIT("demotion failed; couldn't update on disk metadata");
+			policy_force_mapping(cache->policy, mg->new_oblock,
+					     mg->old_oblock);
+			if (mg->promote)
+				cell_defer(cache, mg->new_ocell, true);
+			cleanup_migration(mg);
+			return;
+		}
+	} else {
+		if (dm_cache_insert_mapping(cache->cmd, mg->cblock, mg->new_oblock)) {
+			DMWARN_LIMIT("promotion failed; couldn't update on disk metadata");
+			policy_remove_mapping(cache->policy, mg->new_oblock);
+			cleanup_migration(mg);
+			return;
+		}
+	}
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_add_tail(&mg->list, &cache->need_commit_migrations);
+	cache->commit_requested = true;
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void migration_success_post_commit(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback) {
+		DMWARN("writeback unexpectedly triggered commit");
+		return;
+
+	} else if (mg->demote) {
+		cell_defer(cache, mg->old_ocell, mg->promote ? 0 : 1);
+
+		if (mg->promote) {
+			mg->demote = false;
+
+			spin_lock_irqsave(&cache->lock, flags);
+			list_add_tail(&mg->list, &cache->quiesced_migrations);
+			spin_unlock_irqrestore(&cache->lock, flags);
+
+		} else
+			cleanup_migration(mg);
+
+	} else {
+		cell_defer(cache, mg->new_ocell, true);
+		clear_dirty(cache, mg->new_oblock, mg->cblock);
+		cleanup_migration(mg);
+	}
+}
+
+static void copy_complete(int read_err, unsigned long write_err, void *context)
+{
+	unsigned long flags;
+	struct dm_cache_migration *mg = (struct dm_cache_migration *) context;
+	struct cache *cache = mg->cache;
+
+	if (read_err || write_err)
+		mg->err = true;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_add_tail(&mg->list, &cache->completed_migrations);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void issue_copy_real(struct dm_cache_migration *mg)
+{
+	int r;
+	struct dm_io_region o_region, c_region;
+	struct cache *cache = mg->cache;
+
+	o_region.bdev = cache->origin_dev->bdev;
+	o_region.count = cache->sectors_per_block;
+
+	c_region.bdev = cache->cache_dev->bdev;
+	c_region.sector = from_cblock(mg->cblock) * cache->sectors_per_block;
+	c_region.count = cache->sectors_per_block;
+
+	if (mg->writeback || mg->demote) {
+		/* demote */
+		o_region.sector = from_oblock(mg->old_oblock) * cache->sectors_per_block;
+		r = dm_kcopyd_copy(cache->copier, &c_region, 1, &o_region, 0, copy_complete, mg);
+	} else {
+		/* promote */
+		o_region.sector = from_oblock(mg->new_oblock) * cache->sectors_per_block;
+		r = dm_kcopyd_copy(cache->copier, &o_region, 1, &c_region, 0, copy_complete, mg);
+	}
+
+	if (r < 0)
+		migration_failure(mg);
+}
+
+static void avoid_copy(struct dm_cache_migration *mg)
+{
+	atomic_inc(&mg->cache->stats.copies_avoided);
+	migration_success_pre_commit(mg);
+}
+
+static void issue_copy(struct dm_cache_migration *mg)
+{
+	bool avoid;
+	struct cache *cache = mg->cache;
+
+	if (mg->writeback || mg->demote)
+		avoid = !is_dirty(cache, mg->cblock) ||
+			is_discarded_oblock(cache, mg->old_oblock);
+	else
+		avoid = is_discarded_oblock(cache, mg->new_oblock);
+
+	avoid ? avoid_copy(mg) : issue_copy_real(mg);
+}
+
+static void complete_migration(struct dm_cache_migration *mg)
+{
+	if (mg->err)
+		migration_failure(mg);
+	else
+		migration_success_pre_commit(mg);
+}
+
+static void process_migrations(struct cache *cache, struct list_head *head,
+			       void (*fn)(struct dm_cache_migration *))
+{
+	unsigned long flags;
+	struct list_head list;
+	struct dm_cache_migration *mg, *tmp;
+
+	INIT_LIST_HEAD(&list);
+	spin_lock_irqsave(&cache->lock, flags);
+	list_splice_init(head, &list);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	list_for_each_entry_safe(mg, tmp, &list, list)
+		fn(mg);
+}
+
+static void __queue_quiesced_migration(struct dm_cache_migration *mg)
+{
+	list_add_tail(&mg->list, &mg->cache->quiesced_migrations);
+}
+
+static void queue_quiesced_migration(struct dm_cache_migration *mg)
+{
+	unsigned long flags;
+	struct cache *cache = mg->cache;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	__queue_quiesced_migration(mg);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void queue_quiesced_migrations(struct cache *cache, struct list_head *work)
+{
+	unsigned long flags;
+	struct dm_cache_migration *mg, *tmp;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	list_for_each_entry_safe(mg, tmp, work, list)
+		__queue_quiesced_migration(mg);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void check_for_quiesced_migrations(struct cache *cache,
+					  struct per_bio_data *pb)
+{
+	struct list_head work;
+
+	if (!pb->all_io_entry)
+		return;
+
+	INIT_LIST_HEAD(&work);
+	if (pb->all_io_entry)
+		dm_deferred_entry_dec(pb->all_io_entry, &work);
+
+	if (!list_empty(&work))
+		queue_quiesced_migrations(cache, &work);
+}
+
+static void quiesce_migration(struct dm_cache_migration *mg)
+{
+	if (!dm_deferred_set_add_work(mg->cache->all_io_ds, &mg->list))
+		queue_quiesced_migration(mg);
+}
+
+static void promote(struct cache *cache, struct prealloc *structs,
+		    dm_oblock_t oblock, dm_cblock_t cblock,
+		    struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->writeback = false;
+	mg->demote = false;
+	mg->promote = true;
+	mg->cache = cache;
+	mg->new_oblock = oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = NULL;
+	mg->new_ocell = cell;
+	mg->start_jiffies = jiffies;
+
+	inc_nr_migrations(cache);
+	quiesce_migration(mg);
+}
+
+static void writeback(struct cache *cache, struct prealloc *structs,
+		      dm_oblock_t oblock, dm_cblock_t cblock,
+		      struct dm_bio_prison_cell *cell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->writeback = true;
+	mg->demote = false;
+	mg->promote = false;
+	mg->cache = cache;
+	mg->old_oblock = oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = cell;
+	mg->new_ocell = NULL;
+	mg->start_jiffies = jiffies;
+
+	inc_nr_migrations(cache);
+	quiesce_migration(mg);
+}
+
+static void demote_then_promote(struct cache *cache, struct prealloc *structs,
+				dm_oblock_t old_oblock, dm_oblock_t new_oblock,
+				dm_cblock_t cblock,
+				struct dm_bio_prison_cell *old_ocell,
+				struct dm_bio_prison_cell *new_ocell)
+{
+	struct dm_cache_migration *mg = prealloc_get_migration(structs);
+
+	mg->err = false;
+	mg->writeback = false;
+	mg->demote = true;
+	mg->promote = true;
+	mg->cache = cache;
+	mg->old_oblock = old_oblock;
+	mg->new_oblock = new_oblock;
+	mg->cblock = cblock;
+	mg->old_ocell = old_ocell;
+	mg->new_ocell = new_ocell;
+	mg->start_jiffies = jiffies;
+
+	inc_nr_migrations(cache);
+	quiesce_migration(mg);
+}
+
+/*----------------------------------------------------------------
+ * bio processing
+ *--------------------------------------------------------------*/
+static void defer_bio(struct cache *cache, struct bio *bio)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_add(&cache->deferred_bios, bio);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	wake_worker(cache);
+}
+
+static void process_flush_bio(struct cache *cache, struct bio *bio)
+{
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	BUG_ON(bio->bi_size);
+	if (!pb->req_nr)
+		remap_to_origin(cache, bio);
+	else
+		remap_to_cache(cache, bio, 0);
+
+	issue(cache, bio);
+}
+
+/*
+ * People generally discard large parts of a device, eg, the whole device
+ * when formatting.  Splitting these large discards up into cache block
+ * sized ios and then quiescing (always neccessary for discard) takes too
+ * long.
+ *
+ * We keep it simple, and allow any size of discard to come in, and just
+ * mark off blocks on the discard bitset.  No passdown occurs!
+ *
+ * To implement passdown we need to change the bio_prison such that a cell
+ * can have a key that spans many blocks.
+ */
+static void process_discard_bio(struct cache *cache, struct bio *bio)
+{
+	dm_block_t start_block = dm_sector_div_up(bio->bi_sector,
+						  cache->discard_block_size);
+	dm_block_t end_block = bio->bi_sector + bio_sectors(bio);
+	dm_block_t b;
+
+	(void) sector_div(end_block, cache->discard_block_size);
+
+	for (b = start_block; b < end_block; b++)
+		set_discard(cache, to_dblock(b));
+
+	bio_endio(bio, 0);
+}
+
+static bool spare_migration_bandwidth(struct cache *cache)
+{
+	sector_t current_volume = (atomic_read(&cache->nr_migrations) + 1) *
+		cache->sectors_per_block;
+	return current_volume < cache->migration_threshold;
+}
+
+static bool is_writethrough_io(struct cache *cache, struct bio *bio,
+			       dm_cblock_t cblock)
+{
+	return bio_data_dir(bio) == WRITE &&
+		cache->features.write_through && !is_dirty(cache, cblock);
+}
+
+static void inc_hit_counter(struct cache *cache, struct bio *bio)
+{
+	atomic_inc(bio_data_dir(bio) == READ ?
+		   &cache->stats.read_hit : &cache->stats.write_hit);
+}
+
+static void inc_miss_counter(struct cache *cache, struct bio *bio)
+{
+	atomic_inc(bio_data_dir(bio) == READ ?
+		   &cache->stats.read_miss : &cache->stats.write_miss);
+}
+
+static void process_bio(struct cache *cache, struct prealloc *structs,
+			struct bio *bio)
+{
+	int r;
+	bool release_cell = true;
+	dm_oblock_t block = get_bio_block(cache, bio);
+	struct dm_bio_prison_cell *cell_prealloc, *old_ocell, *new_ocell;
+	struct policy_result lookup_result;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+	bool discarded_block = is_discarded_oblock(cache, block);
+	bool can_migrate = discarded_block || spare_migration_bandwidth(cache);
+
+	/*
+	 * Check to see if that block is currently migrating.
+	 */
+	cell_prealloc = prealloc_get_cell(structs);
+	r = bio_detain(cache, block, bio, cell_prealloc,
+		       (cell_free_fn) prealloc_put_cell,
+		       structs, &new_ocell);
+	if (r > 0)
+		return;
+
+	r = policy_map(cache->policy, block, true, can_migrate, discarded_block,
+		       bio, &lookup_result);
+
+	if (r == -EWOULDBLOCK)
+		/* migration has been denied */
+		lookup_result.op = POLICY_MISS;
+
+	switch (lookup_result.op) {
+	case POLICY_HIT:
+		inc_hit_counter(cache, bio);
+		pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+
+		if (is_writethrough_io(cache, bio, lookup_result.cblock)) {
+			/*
+			 * No need to mark anything dirty in write through mode.
+			 */
+			pb->req_nr == 0 ?
+				remap_to_cache(cache, bio, lookup_result.cblock) :
+				remap_to_origin_clear_discard(cache, bio, block);
+		} else
+			remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+
+		issue(cache, bio);
+		break;
+
+	case POLICY_MISS:
+		inc_miss_counter(cache, bio);
+		pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+
+		if (pb->req_nr != 0) {
+			/*
+			 * This is a duplicate writethrough io that is no
+			 * longer needed because the block has been demoted.
+			 */
+			bio_endio(bio, 0);
+		} else {
+			remap_to_origin_clear_discard(cache, bio, block);
+			issue(cache, bio);
+		}
+		break;
+
+	case POLICY_NEW:
+		atomic_inc(&cache->stats.promotion);
+		promote(cache, structs, block, lookup_result.cblock, new_ocell);
+		release_cell = false;
+		break;
+
+	case POLICY_REPLACE:
+		cell_prealloc = prealloc_get_cell(structs);
+		r = bio_detain(cache, lookup_result.old_oblock, bio, cell_prealloc,
+			       (cell_free_fn) prealloc_put_cell,
+			       structs, &old_ocell);
+		if (r > 0) {
+			/*
+			 * We have to be careful to avoid lock inversion of
+			 * the cells.  So we back off, and wait for the
+			 * old_ocell to become free.
+			 */
+			policy_force_mapping(cache->policy, block,
+					     lookup_result.old_oblock);
+			atomic_inc(&cache->stats.cache_cell_clash);
+			break;
+		}
+		atomic_inc(&cache->stats.demotion);
+		atomic_inc(&cache->stats.promotion);
+
+		demote_then_promote(cache, structs, lookup_result.old_oblock,
+				    block, lookup_result.cblock,
+				    old_ocell, new_ocell);
+		release_cell = false;
+		break;
+
+	default:
+		DMERR_LIMIT("%s: erroring bio, unknown policy op: %u", __func__,
+			    (unsigned) lookup_result.op);
+		bio_io_error(bio);
+	}
+
+	if (release_cell)
+		cell_defer(cache, new_ocell, false);
+}
+
+static int need_commit_due_to_time(struct cache *cache)
+{
+	return jiffies < cache->last_commit_jiffies ||
+	       jiffies > cache->last_commit_jiffies + COMMIT_PERIOD;
+}
+
+static int commit_if_needed(struct cache *cache)
+{
+	if (dm_cache_changed_this_transaction(cache->cmd) &&
+	    (cache->commit_requested || need_commit_due_to_time(cache))) {
+		atomic_inc(&cache->stats.commit_count);
+		cache->last_commit_jiffies = jiffies;
+		cache->commit_requested = false;
+		return dm_cache_commit(cache->cmd, false);
+	}
+
+	return 0;
+}
+
+static void process_deferred_bios(struct cache *cache)
+{
+	unsigned long flags;
+	struct bio_list bios;
+	struct bio *bio;
+	struct prealloc structs;
+
+	memset(&structs, 0, sizeof(structs));
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_merge(&bios, &cache->deferred_bios);
+	bio_list_init(&cache->deferred_bios);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	while (!bio_list_empty(&bios)) {
+		/*
+		 * If we've got no free migration structs, and processing
+		 * this bio might require one, we pause until there are some
+		 * prepared mappings to process.
+		 */
+		if (prealloc_data_structs(cache, &structs)) {
+			spin_lock_irqsave(&cache->lock, flags);
+			bio_list_merge(&cache->deferred_bios, &bios);
+			spin_unlock_irqrestore(&cache->lock, flags);
+			break;
+		}
+
+		bio = bio_list_pop(&bios);
+
+		if (bio->bi_rw & REQ_FLUSH)
+			process_flush_bio(cache, bio);
+		else if (bio->bi_rw & REQ_DISCARD)
+			process_discard_bio(cache, bio);
+		else
+			process_bio(cache, &structs, bio);
+	}
+
+	prealloc_free_structs(cache, &structs);
+}
+
+static void process_deferred_flush_bios(struct cache *cache, bool submit_bios)
+{
+	unsigned long flags;
+	struct bio_list bios;
+	struct bio *bio;
+
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&cache->lock, flags);
+	bio_list_merge(&bios, &cache->deferred_flush_bios);
+	bio_list_init(&cache->deferred_flush_bios);
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	while ((bio = bio_list_pop(&bios)))
+		submit_bios ? generic_make_request(bio) : bio_io_error(bio);
+}
+
+static void writeback_some_dirty_blocks(struct cache *cache)
+{
+	int r = 0;
+	dm_oblock_t oblock;
+	dm_cblock_t cblock;
+	struct prealloc structs;
+	struct dm_bio_prison_cell *old_ocell;
+
+	memset(&structs, 0, sizeof(structs));
+
+	while (spare_migration_bandwidth(cache)) {
+		if (prealloc_data_structs(cache, &structs))
+			break;
+
+		r = policy_writeback_work(cache->policy, &oblock, &cblock);
+		if (r)
+			break;
+
+		r = get_cell(cache, oblock, &structs, &old_ocell);
+		if (r) {
+			policy_set_dirty(cache->policy, oblock);
+			break;
+		}
+
+		writeback(cache, &structs, oblock, cblock, old_ocell);
+	}
+
+	prealloc_free_structs(cache, &structs);
+}
+
+/*----------------------------------------------------------------
+ * Main worker loop
+ *--------------------------------------------------------------*/
+static void start_quiescing(struct cache *cache)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	cache->quiescing = 1;
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static void stop_quiescing(struct cache *cache)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	cache->quiescing = 0;
+	spin_unlock_irqrestore(&cache->lock, flags);
+}
+
+static bool is_quiescing(struct cache *cache)
+{
+	int r;
+	unsigned long flags;
+
+	spin_lock_irqsave(&cache->lock, flags);
+	r = cache->quiescing;
+	spin_unlock_irqrestore(&cache->lock, flags);
+
+	return r;
+}
+
+static void wait_for_migrations(struct cache *cache)
+{
+	wait_event(cache->migration_wait, !atomic_read(&cache->nr_migrations));
+}
+
+static void stop_worker(struct cache *cache)
+{
+	cancel_delayed_work(&cache->waker);
+	flush_workqueue(cache->wq);
+}
+
+static void requeue_deferred_io(struct cache *cache)
+{
+	struct bio *bio;
+	struct bio_list bios;
+
+	bio_list_init(&bios);
+	bio_list_merge(&bios, &cache->deferred_bios);
+	bio_list_init(&cache->deferred_bios);
+
+	while ((bio = bio_list_pop(&bios)))
+		bio_endio(bio, DM_ENDIO_REQUEUE);
+}
+
+static int more_work(struct cache *cache)
+{
+	if (is_quiescing(cache))
+		return !list_empty(&cache->quiesced_migrations) ||
+			!list_empty(&cache->completed_migrations) ||
+			!list_empty(&cache->need_commit_migrations);
+	else
+		return !bio_list_empty(&cache->deferred_bios) ||
+			!bio_list_empty(&cache->deferred_flush_bios) ||
+			!list_empty(&cache->quiesced_migrations) ||
+			!list_empty(&cache->completed_migrations) ||
+			!list_empty(&cache->need_commit_migrations);
+}
+
+static void do_worker(struct work_struct *ws)
+{
+	struct cache *cache = container_of(ws, struct cache, worker);
+
+	do {
+		if (!is_quiescing(cache))
+			process_deferred_bios(cache);
+
+		process_migrations(cache, &cache->quiesced_migrations, issue_copy);
+		process_migrations(cache, &cache->completed_migrations, complete_migration);
+
+		writeback_some_dirty_blocks(cache);
+
+		if (commit_if_needed(cache)) {
+			process_deferred_flush_bios(cache, false);
+
+			/*
+			 * FIXME: rollback metadata or just go into a
+			 * failure mode and error everything
+			 */
+		} else {
+			process_deferred_flush_bios(cache, true);
+			process_migrations(cache, &cache->need_commit_migrations,
+					   migration_success_post_commit);
+		}
+	} while (more_work(cache));
+}
+
+/*
+ * We want to commit periodically so that not too much
+ * unwritten metadata builds up.
+ */
+static void do_waker(struct work_struct *ws)
+{
+	struct cache *cache = container_of(to_delayed_work(ws), struct cache, waker);
+	wake_worker(cache);
+	queue_delayed_work(cache->wq, &cache->waker, COMMIT_PERIOD);
+}
+
+/*----------------------------------------------------------------*/
+
+static int is_congested(struct dm_dev *dev, int bdi_bits)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+	return bdi_congested(&q->backing_dev_info, bdi_bits);
+}
+
+static int cache_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
+{
+	struct cache *cache = container_of(cb, struct cache, callbacks);
+
+	return is_congested(cache->origin_dev, bdi_bits) ||
+		is_congested(cache->cache_dev, bdi_bits);
+}
+
+/*----------------------------------------------------------------
+ * Target methods
+ *--------------------------------------------------------------*/
+
+/*
+ * This function gets called on the error paths of the constructor, so we
+ * have to cope with a partially initialised struct.
+ */
+static void destroy(struct cache *cache)
+{
+	unsigned i;
+
+	if (cache->next_migration)
+		mempool_free(cache->next_migration, cache->migration_pool);
+
+	if (cache->migration_pool)
+		mempool_destroy(cache->migration_pool);
+
+	if (cache->all_io_ds)
+		dm_deferred_set_destroy(cache->all_io_ds);
+
+	if (cache->prison)
+		dm_bio_prison_destroy(cache->prison);
+
+	if (cache->wq)
+		destroy_workqueue(cache->wq);
+
+	if (cache->dirty_bitset)
+		free_bitset(cache->dirty_bitset);
+
+	if (cache->discard_bitset)
+		free_bitset(cache->discard_bitset);
+
+	if (cache->copier)
+		dm_kcopyd_client_destroy(cache->copier);
+
+	if (cache->cmd)
+		dm_cache_metadata_close(cache->cmd);
+
+	if (cache->metadata_dev)
+		dm_put_device(cache->ti, cache->metadata_dev);
+
+	if (cache->origin_dev)
+		dm_put_device(cache->ti, cache->origin_dev);
+
+	if (cache->cache_dev)
+		dm_put_device(cache->ti, cache->cache_dev);
+
+	if (cache->policy)
+		dm_cache_policy_destroy(cache->policy);
+
+	for (i = 0; i < cache->nr_ctr_args ; i++)
+		kfree(cache->ctr_args[i]);
+	kfree(cache->ctr_args);
+
+	kfree(cache);
+}
+
+static void cache_dtr(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	destroy(cache);
+}
+
+static sector_t get_dev_size(struct dm_dev *dev)
+{
+	return i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT;
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Construct a cache device mapping.
+ *
+ * cache <metadata dev> <cache dev> <origin dev> <block size>
+ *       <#feature args> [<feature arg>]*
+ *       <policy> <#policy args> [<policy arg>]*
+ *
+ * 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 policy 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.
+ */
+struct cache_args {
+	struct dm_target *ti;
+
+	struct dm_dev *metadata_dev;
+
+	struct dm_dev *cache_dev;
+	sector_t cache_sectors;
+
+	struct dm_dev *origin_dev;
+	sector_t origin_sectors;
+
+	uint32_t block_size;
+
+	const char *policy_name;
+	int policy_argc;
+	const char **policy_argv;
+
+	struct cache_features features;
+};
+
+static void destroy_cache_args(struct cache_args *ca)
+{
+	if (ca->metadata_dev)
+		dm_put_device(ca->ti, ca->metadata_dev);
+
+	if (ca->cache_dev)
+		dm_put_device(ca->ti, ca->cache_dev);
+
+	if (ca->origin_dev)
+		dm_put_device(ca->ti, ca->origin_dev);
+
+	kfree(ca);
+}
+
+static bool at_least_one_arg(struct dm_arg_set *as, char **error)
+{
+	if (!as->argc) {
+		*error = "Insufficient args";
+		return false;
+	}
+
+	return true;
+}
+
+static int parse_metadata_dev(struct cache_args *ca, struct dm_arg_set *as,
+			      char **error)
+{
+	int r;
+	sector_t metadata_dev_size;
+	char b[BDEVNAME_SIZE];
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->metadata_dev);
+	if (r) {
+		*error = "Error opening metadata device";
+		return r;
+	}
+
+	metadata_dev_size = get_dev_size(ca->metadata_dev);
+	if (metadata_dev_size > DM_CACHE_METADATA_MAX_SECTORS_WARNING)
+		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
+		       bdevname(ca->metadata_dev->bdev, b), THIN_METADATA_MAX_SECTORS);
+
+	return 0;
+}
+
+static int parse_cache_dev(struct cache_args *ca, struct dm_arg_set *as,
+			   char **error)
+{
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->cache_dev);
+	if (r) {
+		*error = "Error opening cache device";
+		return r;
+	}
+	ca->cache_sectors = get_dev_size(ca->cache_dev);
+
+	return 0;
+}
+
+static int parse_origin_dev(struct cache_args *ca, struct dm_arg_set *as,
+			    char **error)
+{
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	r = dm_get_device(ca->ti, dm_shift_arg(as), FMODE_READ | FMODE_WRITE,
+			  &ca->origin_dev);
+	if (r) {
+		*error = "Error opening origin device";
+		return r;
+	}
+
+	ca->origin_sectors = get_dev_size(ca->origin_dev);
+	if (ca->ti->len > ca->origin_sectors) {
+		*error = "Device size larger than cached device";
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int parse_block_size(struct cache_args *ca, struct dm_arg_set *as,
+			    char **error)
+{
+	unsigned long tmp;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	if (kstrtoul(dm_shift_arg(as), 10, &tmp) || !tmp ||
+	    tmp < DATA_DEV_BLOCK_SIZE_MIN_SECTORS ||
+	    tmp & (DATA_DEV_BLOCK_SIZE_MIN_SECTORS - 1)) {
+		*error = "Invalid data block size";
+		return -EINVAL;
+	}
+
+	if (tmp > ca->cache_sectors) {
+		*error = "Data block size is larger than the cache device";
+		return -EINVAL;
+	}
+
+	ca->block_size = tmp;
+
+	return 0;
+}
+
+static void init_features(struct cache_features *cf)
+{
+	cf->mode = CM_WRITE;
+	cf->write_through = false;
+}
+
+static int parse_features(struct cache_args *ca, struct dm_arg_set *as,
+			  char **error)
+{
+	static struct dm_arg _args[] = {
+		{0, 1, "Invalid number of cache feature arguments"},
+	};
+
+	int r;
+	unsigned argc;
+	const char *arg;
+	struct cache_features *cf = &ca->features;
+
+	init_features(cf);
+
+	r = dm_read_arg_group(_args, as, &argc, error);
+	if (r)
+		return -EINVAL;
+
+	while (argc--) {
+		arg = dm_shift_arg(as);
+
+		if (!strcasecmp(arg, "writeback"))
+			cf->write_through = false;
+
+		else if (!strcasecmp(arg, "writethrough"))
+			cf->write_through = true;
+
+		else {
+			*error = "Unrecognised cache feature requested";
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int parse_policy(struct cache_args *ca, struct dm_arg_set *as,
+			char **error)
+{
+	static struct dm_arg _args[] = {
+		{0, 1024, "Invalid number of policy arguments"},
+	};
+
+	int r;
+
+	if (!at_least_one_arg(as, error))
+		return -EINVAL;
+
+	ca->policy_name = dm_shift_arg(as);
+
+	r = dm_read_arg_group(_args, as, &ca->policy_argc, error);
+	if (r)
+		return -EINVAL;
+
+	ca->policy_argv = (const char **)as->argv;
+	dm_consume_args(as, ca->policy_argc);
+
+	return 0;
+}
+
+static int parse_cache_args(struct cache_args *ca, int argc, char **argv,
+			    char **error)
+{
+	int r;
+	struct dm_arg_set as;
+
+	as.argc = argc;
+	as.argv = argv;
+
+	r = parse_metadata_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_cache_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_origin_dev(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_block_size(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_features(ca, &as, error);
+	if (r)
+		return r;
+
+	r = parse_policy(ca, &as, error);
+	if (r)
+		return r;
+
+	return 0;
+}
+
+/*----------------------------------------------------------------*/
+
+static struct kmem_cache *migration_cache;
+
+static int set_config_values(struct dm_cache_policy *p, int argc, const char **argv)
+{
+	int r = 0;
+
+	if (argc & 1) {
+		DMWARN("Odd number of policy arguments given but they should be <key> <value> pairs.");
+		return -EINVAL;
+	}
+
+	while (argc) {
+		r = policy_set_config_value(p, argv[0], argv[1]);
+		if (r) {
+			DMWARN("policy_set_config_value failed: key = '%s', value = '%s'",
+			       argv[0], argv[1]);
+			return r;
+		}
+
+		argc -= 2;
+		argv += 2;
+	}
+
+	return r;
+}
+
+static int create_cache_policy(struct cache *cache, struct cache_args *ca,
+			       char **error)
+{
+	int r;
+
+	cache->policy =	dm_cache_policy_create(ca->policy_name,
+					       cache->cache_size,
+					       cache->origin_sectors,
+					       cache->sectors_per_block);
+	if (!cache->policy) {
+		*error = "Error creating cache's policy";
+		return -ENOMEM;
+	}
+
+	r = set_config_values(cache->policy, ca->policy_argc, ca->policy_argv);
+	if (r)
+		dm_cache_policy_destroy(cache->policy);
+
+	return r;
+}
+
+/*
+ * We want the discard block size to be a power of two, at least the size
+ * of the cache block size, and have no more than 2^14 discard blocks
+ * across the origin.
+ */
+#define MAX_DISCARD_BLOCKS (1 << 14)
+
+static bool too_many_discard_blocks(sector_t discard_block_size,
+				    sector_t origin_size)
+{
+	(void) sector_div(origin_size, discard_block_size);
+
+	return origin_size > MAX_DISCARD_BLOCKS;
+}
+
+static sector_t calculate_discard_block_size(sector_t cache_block_size,
+					     sector_t origin_size)
+{
+	sector_t discard_block_size;
+
+	discard_block_size = roundup_pow_of_two(cache_block_size);
+
+	if (origin_size)
+		while (too_many_discard_blocks(discard_block_size, origin_size))
+			discard_block_size *= 2;
+
+	return discard_block_size;
+}
+
+#define DEFAULT_MIGRATION_THRESHOLD (2048 * 100)
+
+static unsigned cache_num_write_bios(struct dm_target *ti, struct bio *bio);
+
+static int cache_create(struct cache_args *ca, struct cache **result)
+{
+	int r = 0;
+	char **error = &ca->ti->error;
+	struct cache *cache;
+	struct dm_target *ti = ca->ti;
+	dm_block_t origin_blocks;
+	struct dm_cache_metadata *cmd;
+	bool may_format = ca->features.mode == CM_WRITE;
+
+	cache = kzalloc(sizeof(*cache), GFP_KERNEL);
+	if (!cache)
+		return -ENOMEM;
+
+	cache->ti = ca->ti;
+	ti->private = cache;
+	ti->per_bio_data_size = sizeof(struct per_bio_data);
+	ti->num_flush_bios = 2;
+	ti->flush_supported = true;
+
+	ti->num_discard_bios = 1;
+	ti->discards_supported = true;
+	ti->discard_zeroes_data_unsupported = true;
+
+	memcpy(&cache->features, &ca->features, sizeof(cache->features));
+
+	if (cache->features.write_through)
+		ti->num_write_bios = cache_num_write_bios;
+
+	cache->callbacks.congested_fn = cache_is_congested;
+	dm_table_add_target_callbacks(ti->table, &cache->callbacks);
+
+	cache->metadata_dev = ca->metadata_dev;
+	cache->origin_dev = ca->origin_dev;
+	cache->cache_dev = ca->cache_dev;
+
+	ca->metadata_dev = ca->origin_dev = ca->cache_dev = NULL;
+
+	/* FIXME: factor out this whole section */
+	origin_blocks = cache->origin_sectors = ca->origin_sectors;
+	(void) sector_div(origin_blocks, ca->block_size);
+	cache->origin_blocks = to_oblock(origin_blocks);
+
+	cache->sectors_per_block = ca->block_size;
+	if (dm_set_target_max_io_len(ti, cache->sectors_per_block)) {
+		r = -EINVAL;
+		goto bad;
+	}
+
+	if (ca->block_size & (ca->block_size - 1)) {
+		dm_block_t cache_size = ca->cache_sectors;
+
+		cache->sectors_per_block_shift = -1;
+		(void) sector_div(cache_size, ca->block_size);
+		cache->cache_size = to_cblock(cache_size);
+	} else {
+		cache->sectors_per_block_shift = __ffs(ca->block_size);
+		cache->cache_size = to_cblock(ca->cache_sectors >> cache->sectors_per_block_shift);
+	}
+
+	r = create_cache_policy(cache, ca, error);
+	if (r)
+		goto bad;
+	cache->policy_nr_args = ca->policy_argc;
+
+	cmd = dm_cache_metadata_open(cache->metadata_dev->bdev,
+				     ca->block_size, may_format,
+				     dm_cache_policy_get_hint_size(cache->policy));
+	if (IS_ERR(cmd)) {
+		*error = "Error creating metadata object";
+		r = PTR_ERR(cmd);
+		goto bad;
+	}
+	cache->cmd = cmd;
+
+	spin_lock_init(&cache->lock);
+	bio_list_init(&cache->deferred_bios);
+	bio_list_init(&cache->deferred_flush_bios);
+	INIT_LIST_HEAD(&cache->quiesced_migrations);
+	INIT_LIST_HEAD(&cache->completed_migrations);
+	INIT_LIST_HEAD(&cache->need_commit_migrations);
+	cache->migration_threshold = DEFAULT_MIGRATION_THRESHOLD;
+	atomic_set(&cache->nr_migrations, 0);
+	init_waitqueue_head(&cache->migration_wait);
+
+	cache->nr_dirty = 0;
+	cache->dirty_bitset = alloc_bitset(from_cblock(cache->cache_size));
+	if (!cache->dirty_bitset) {
+		*error = "could not allocate dirty bitset";
+		goto bad;
+	}
+	clear_bitset(cache->dirty_bitset, from_cblock(cache->cache_size));
+
+	cache->discard_block_size =
+		calculate_discard_block_size(cache->sectors_per_block,
+					     cache->origin_sectors);
+	cache->discard_nr_blocks = oblock_to_dblock(cache, cache->origin_blocks);
+	cache->discard_bitset = alloc_bitset(from_dblock(cache->discard_nr_blocks));
+	if (!cache->discard_bitset) {
+		*error = "could not allocate discard bitset";
+		goto bad;
+	}
+	clear_bitset(cache->discard_bitset, from_dblock(cache->discard_nr_blocks));
+
+	cache->copier = dm_kcopyd_client_create(&dm_kcopyd_throttle);
+	if (IS_ERR(cache->copier)) {
+		*error = "could not create kcopyd client";
+		r = PTR_ERR(cache->copier);
+		goto bad;
+	}
+
+	cache->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
+	if (!cache->wq) {
+		*error = "could not create workqueue for metadata object";
+		goto bad;
+	}
+	INIT_WORK(&cache->worker, do_worker);
+	INIT_DELAYED_WORK(&cache->waker, do_waker);
+	cache->last_commit_jiffies = jiffies;
+
+	cache->prison = dm_bio_prison_create(PRISON_CELLS);
+	if (!cache->prison) {
+		*error = "could not create bio prison";
+		goto bad;
+	}
+
+	cache->all_io_ds = dm_deferred_set_create();
+	if (!cache->all_io_ds) {
+		*error = "could not create all_io deferred set";
+		goto bad;
+	}
+
+	cache->migration_pool = mempool_create_slab_pool(MIGRATION_POOL_SIZE,
+							 migration_cache);
+	if (!cache->migration_pool) {
+		*error = "Error creating cache's migration mempool";
+		goto bad;
+	}
+
+	cache->next_migration = NULL;
+
+	cache->need_tick_bio = true;
+	cache->sized = false;
+	cache->quiescing = false;
+	cache->commit_requested = false;
+	cache->loaded_mappings = false;
+	cache->loaded_discards = false;
+
+	load_stats(cache);
+
+	atomic_set(&cache->stats.demotion, 0);
+	atomic_set(&cache->stats.promotion, 0);
+	atomic_set(&cache->stats.copies_avoided, 0);
+	atomic_set(&cache->stats.cache_cell_clash, 0);
+	atomic_set(&cache->stats.commit_count, 0);
+	atomic_set(&cache->stats.discard_count, 0);
+
+	*result = cache;
+	return 0;
+
+bad:
+	destroy(cache);
+	return r;
+}
+
+static int copy_ctr_args(struct cache *cache, int argc, const char **argv)
+{
+	unsigned i;
+	const char **copy;
+
+	copy = kcalloc(argc, sizeof(*copy), GFP_KERNEL);
+	if (!copy)
+		return -ENOMEM;
+	for (i = 0; i < argc; i++) {
+		copy[i] = kstrdup(argv[i], GFP_KERNEL);
+		if (!copy[i]) {
+			while (i--)
+				kfree(copy[i]);
+			kfree(copy);
+			return -ENOMEM;
+		}
+	}
+
+	cache->nr_ctr_args = argc;
+	cache->ctr_args = copy;
+
+	return 0;
+}
+
+static int cache_ctr(struct dm_target *ti, unsigned argc, char **argv)
+{
+	int r = -EINVAL;
+	struct cache_args *ca;
+	struct cache *cache = NULL;
+
+	ca = kzalloc(sizeof(*ca), GFP_KERNEL);
+	if (!ca) {
+		ti->error = "Error allocating memory for cache";
+		return -ENOMEM;
+	}
+	ca->ti = ti;
+
+	r = parse_cache_args(ca, argc, argv, &ti->error);
+	if (r)
+		goto out;
+
+	r = cache_create(ca, &cache);
+
+	r = copy_ctr_args(cache, argc - 3, (const char **)argv + 3);
+	if (r) {
+		destroy(cache);
+		goto out;
+	}
+
+	ti->private = cache;
+
+out:
+	destroy_cache_args(ca);
+	return r;
+}
+
+static unsigned cache_num_write_bios(struct dm_target *ti, struct bio *bio)
+{
+	int r;
+	struct cache *cache = ti->private;
+	dm_oblock_t block = get_bio_block(cache, bio);
+	dm_cblock_t cblock;
+
+	r = policy_lookup(cache->policy, block, &cblock);
+	if (r < 0)
+		return 2;	/* assume the worst */
+
+	return (!r && !is_dirty(cache, cblock)) ? 2 : 1;
+}
+
+static int cache_map(struct dm_target *ti, struct bio *bio)
+{
+	struct cache *cache = ti->private;
+
+	int r;
+	dm_oblock_t block = get_bio_block(cache, bio);
+	bool can_migrate = false;
+	bool discarded_block;
+	struct dm_bio_prison_cell *cell;
+	struct policy_result lookup_result;
+	struct per_bio_data *pb;
+
+	if (from_oblock(block) > from_oblock(cache->origin_blocks)) {
+		/*
+		 * This can only occur if the io goes to a partial block at
+		 * the end of the origin device.  We don't cache these.
+		 * Just remap to the origin and carry on.
+		 */
+		remap_to_origin_clear_discard(cache, bio, block);
+		return DM_MAPIO_REMAPPED;
+	}
+
+	pb = init_per_bio_data(bio);
+
+	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA | REQ_DISCARD)) {
+		defer_bio(cache, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	/*
+	 * Check to see if that block is currently migrating.
+	 */
+	cell = alloc_prison_cell(cache);
+	if (!cell) {
+		defer_bio(cache, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	r = bio_detain(cache, block, bio, cell,
+		       (cell_free_fn) free_prison_cell,
+		       cache, &cell);
+	if (r) {
+		if (r < 0)
+			defer_bio(cache, bio);
+
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	discarded_block = is_discarded_oblock(cache, block);
+
+	r = policy_map(cache->policy, block, false, can_migrate, discarded_block,
+		       bio, &lookup_result);
+	if (r == -EWOULDBLOCK) {
+		cell_defer(cache, cell, true);
+		return DM_MAPIO_SUBMITTED;
+
+	} else if (r) {
+		DMERR_LIMIT("Unexpected return from cache replacement policy: %d", r);
+		bio_io_error(bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	switch (lookup_result.op) {
+	case POLICY_HIT:
+		inc_hit_counter(cache, bio);
+		pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+
+		if (is_writethrough_io(cache, bio, lookup_result.cblock)) {
+			/*
+			 * No need to mark anything dirty in write through mode.
+			 */
+			pb->req_nr == 0 ?
+				remap_to_cache(cache, bio, lookup_result.cblock) :
+				remap_to_origin_clear_discard(cache, bio, block);
+			cell_defer(cache, cell, false);
+		} else {
+			remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+			cell_defer(cache, cell, false);
+		}
+		break;
+
+	case POLICY_MISS:
+		inc_miss_counter(cache, bio);
+		pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+
+		if (pb->req_nr != 0) {
+			/*
+			 * This is a duplicate writethrough io that is no
+			 * longer needed because the block has been demoted.
+			 */
+			bio_endio(bio, 0);
+			cell_defer(cache, cell, false);
+			return DM_MAPIO_SUBMITTED;
+		} else {
+			remap_to_origin_clear_discard(cache, bio, block);
+			cell_defer(cache, cell, false);
+		}
+		break;
+
+	default:
+		DMERR_LIMIT("%s: erroring bio: unknown policy op: %u", __func__,
+			    (unsigned) lookup_result.op);
+		bio_io_error(bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	return DM_MAPIO_REMAPPED;
+}
+
+static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
+{
+	struct cache *cache = ti->private;
+	unsigned long flags;
+	struct per_bio_data *pb = get_per_bio_data(bio);
+
+	if (pb->tick) {
+		policy_tick(cache->policy);
+
+		spin_lock_irqsave(&cache->lock, flags);
+		cache->need_tick_bio = true;
+		spin_unlock_irqrestore(&cache->lock, flags);
+	}
+
+	check_for_quiesced_migrations(cache, pb);
+
+	return 0;
+}
+
+static int write_dirty_bitset(struct cache *cache)
+{
+	unsigned i, r;
+
+	for (i = 0; i < from_cblock(cache->cache_size); i++) {
+		r = dm_cache_set_dirty(cache->cmd, to_cblock(i),
+				       is_dirty(cache, to_cblock(i)));
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+static int write_discard_bitset(struct cache *cache)
+{
+	unsigned i, r;
+
+	r = dm_cache_discard_bitset_resize(cache->cmd, cache->discard_block_size,
+					   cache->discard_nr_blocks);
+	if (r) {
+		DMERR("could not resize on-disk discard bitset");
+		return r;
+	}
+
+	for (i = 0; i < from_dblock(cache->discard_nr_blocks); i++) {
+		r = dm_cache_set_discard(cache->cmd, to_dblock(i),
+					 is_discarded(cache, to_dblock(i)));
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+static int save_hint(void *context, dm_cblock_t cblock, dm_oblock_t oblock,
+		     uint32_t hint)
+{
+	struct cache *cache = context;
+	return dm_cache_save_hint(cache->cmd, cblock, hint);
+}
+
+static int write_hints(struct cache *cache)
+{
+	int r;
+
+	r = dm_cache_begin_hints(cache->cmd, cache->policy);
+	if (r) {
+		DMERR("dm_cache_begin_hints failed");
+		return r;
+	}
+
+	r = policy_walk_mappings(cache->policy, save_hint, cache);
+	if (r)
+		DMERR("policy_walk_mappings failed");
+
+	return r;
+}
+
+/*
+ * returns true on success
+ */
+static bool sync_metadata(struct cache *cache)
+{
+	int r1, r2, r3, r4;
+
+	r1 = write_dirty_bitset(cache);
+	if (r1)
+		DMERR("could not write dirty bitset");
+
+	r2 = write_discard_bitset(cache);
+	if (r2)
+		DMERR("could not write discard bitset");
+
+	save_stats(cache);
+
+	r3 = write_hints(cache);
+	if (r3)
+		DMERR("could not write hints");
+
+	/*
+	 * If writing the above metadata failed, we still commit, but don't
+	 * set the clean shutdown flag.  This will effectively force every
+	 * dirty bit to be set on reload.
+	 */
+	r4 = dm_cache_commit(cache->cmd, !r1 && !r2 && !r3);
+	if (r4)
+		DMERR("could not write cache metadata.  Data loss may occur.");
+
+	return !r1 && !r2 && !r3 && !r4;
+}
+
+static void cache_postsuspend(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	start_quiescing(cache);
+	wait_for_migrations(cache);
+	stop_worker(cache);
+	requeue_deferred_io(cache);
+	stop_quiescing(cache);
+
+	(void) sync_metadata(cache);
+}
+
+static int load_mapping(void *context, dm_oblock_t oblock, dm_cblock_t cblock,
+			bool dirty, uint32_t hint, bool hint_valid)
+{
+	int r;
+	struct cache *cache = context;
+
+	r = policy_load_mapping(cache->policy, oblock, cblock, hint, hint_valid);
+	if (r)
+		return r;
+
+	if (dirty)
+		set_dirty(cache, oblock, cblock);
+	else
+		clear_dirty(cache, oblock, cblock);
+
+	return 0;
+}
+
+static int load_discard(void *context, sector_t discard_block_size,
+			dm_dblock_t dblock, bool discard)
+{
+	struct cache *cache = context;
+
+	/* FIXME: handle mis-matched block size */
+
+	if (discard)
+		set_discard(cache, dblock);
+	else
+		clear_discard(cache, dblock);
+
+	return 0;
+}
+
+static int cache_preresume(struct dm_target *ti)
+{
+	int r = 0;
+	struct cache *cache = ti->private;
+	sector_t actual_cache_size = get_dev_size(cache->cache_dev);
+	(void) sector_div(actual_cache_size, cache->sectors_per_block);
+
+	/*
+	 * Check to see if the cache has resized.
+	 */
+	if (from_cblock(cache->cache_size) != actual_cache_size || !cache->sized) {
+		cache->cache_size = to_cblock(actual_cache_size);
+
+		r = dm_cache_resize(cache->cmd, cache->cache_size);
+		if (r) {
+			DMERR("could not resize cache metadata");
+			return r;
+		}
+
+		cache->sized = true;
+	}
+
+	if (!cache->loaded_mappings) {
+		r = dm_cache_load_mappings(cache->cmd,
+					   dm_cache_policy_get_name(cache->policy),
+					   load_mapping, cache);
+		if (r) {
+			DMERR("could not load cache mappings");
+			return r;
+		}
+
+		cache->loaded_mappings = true;
+	}
+
+	if (!cache->loaded_discards) {
+		r = dm_cache_load_discards(cache->cmd, load_discard, cache);
+		if (r) {
+			DMERR("could not load origin discards");
+			return r;
+		}
+
+		cache->loaded_discards = true;
+	}
+
+	return r;
+}
+
+static void cache_resume(struct dm_target *ti)
+{
+	struct cache *cache = ti->private;
+
+	cache->need_tick_bio = true;
+	do_waker(&cache->waker.work);
+}
+
+/*
+ * Status format:
+ *
+ * <#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>*
+ */
+static void cache_status(struct dm_target *ti, status_type_t type,
+			 unsigned status_flags, char *result, unsigned maxlen)
+{
+	int r = 0;
+	unsigned i;
+	ssize_t sz = 0;
+	dm_block_t nr_free_blocks_metadata = 0;
+	dm_block_t nr_blocks_metadata = 0;
+	char buf[BDEVNAME_SIZE];
+	struct cache *cache = ti->private;
+	dm_cblock_t residency;
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		/* Commit to ensure statistics aren't out-of-date */
+		if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti)) {
+			r = dm_cache_commit(cache->cmd, false);
+			if (r)
+				DMERR("could not commit metadata for accurate status");
+		}
+
+		r = dm_cache_get_free_metadata_block_count(cache->cmd,
+							   &nr_free_blocks_metadata);
+		if (r) {
+			DMERR("could not get metadata free block count");
+			goto err;
+		}
+
+		r = dm_cache_get_metadata_dev_size(cache->cmd, &nr_blocks_metadata);
+		if (r) {
+			DMERR("could not get metadata device size");
+			goto err;
+		}
+
+		residency = policy_residency(cache->policy);
+
+		DMEMIT("%llu/%llu %u %u %u %u %u %u %llu %u ",
+		       (unsigned long long)(nr_blocks_metadata - nr_free_blocks_metadata),
+		       (unsigned long long)nr_blocks_metadata,
+		       (unsigned) atomic_read(&cache->stats.read_hit),
+		       (unsigned) atomic_read(&cache->stats.read_miss),
+		       (unsigned) atomic_read(&cache->stats.write_hit),
+		       (unsigned) atomic_read(&cache->stats.write_miss),
+		       (unsigned) atomic_read(&cache->stats.demotion),
+		       (unsigned) atomic_read(&cache->stats.promotion),
+		       (unsigned long long) from_cblock(residency),
+		       cache->nr_dirty);
+
+		if (cache->features.write_through)
+			DMEMIT("1 writethrough ");
+		else
+			DMEMIT("0 ");
+
+		DMEMIT("2 migration_threshold %llu ", (unsigned long long) cache->migration_threshold);
+		if (sz < maxlen) {
+			r = policy_emit_config_values(cache->policy, result + sz, maxlen - sz);
+			if (r)
+				DMERR("policy_emit_config_values returned %d", r);
+		}
+
+		break;
+
+	case STATUSTYPE_TABLE:
+		format_dev_t(buf, cache->metadata_dev->bdev->bd_dev);
+		DMEMIT("%s ", buf);
+		format_dev_t(buf, cache->cache_dev->bdev->bd_dev);
+		DMEMIT("%s ", buf);
+		format_dev_t(buf, cache->origin_dev->bdev->bd_dev);
+		DMEMIT("%s", buf);
+
+		for (i = 0; i < cache->nr_ctr_args - 1; i++)
+			DMEMIT(" %s", cache->ctr_args[i]);
+		if (cache->nr_ctr_args)
+			DMEMIT(" %s", cache->ctr_args[cache->nr_ctr_args - 1]);
+	}
+
+	return;
+
+err:
+	DMEMIT("Error");
+}
+
+#define NOT_CORE_OPTION 1
+
+static int process_config_option(struct cache *cache, char **argv)
+{
+	unsigned long tmp;
+
+	if (!strcasecmp(argv[0], "migration_threshold")) {
+		if (kstrtoul(argv[1], 10, &tmp))
+			return -EINVAL;
+
+		cache->migration_threshold = tmp;
+		return 0;
+	}
+
+	return NOT_CORE_OPTION;
+}
+
+/*
+ * Supports <key> <value>.
+ *
+ * The key migration_threshold is supported by the cache target core.
+ */
+static int cache_message(struct dm_target *ti, unsigned argc, char **argv)
+{
+	int r;
+	struct cache *cache = ti->private;
+
+	if (argc != 2)
+		return -EINVAL;
+
+	r = process_config_option(cache, argv);
+	if (r == NOT_CORE_OPTION)
+		return policy_set_config_value(cache->policy, argv[0], argv[1]);
+
+	return r;
+}
+
+static int cache_iterate_devices(struct dm_target *ti,
+				 iterate_devices_callout_fn fn, void *data)
+{
+	int r = 0;
+	struct cache *cache = ti->private;
+
+	r = fn(ti, cache->cache_dev, 0, get_dev_size(cache->cache_dev), data);
+	if (!r)
+		r = fn(ti, cache->origin_dev, 0, ti->len, data);
+
+	return r;
+}
+
+/*
+ * We assume I/O is going to the origin (which is the volume
+ * more likely to have restrictions e.g. by being striped).
+ * (Looking up the exact location of the data would be expensive
+ * and could always be out of date by the time the bio is submitted.)
+ */
+static int cache_bvec_merge(struct dm_target *ti,
+			    struct bvec_merge_data *bvm,
+			    struct bio_vec *biovec, int max_size)
+{
+	struct cache *cache = ti->private;
+	struct request_queue *q = bdev_get_queue(cache->origin_dev->bdev);
+
+	if (!q->merge_bvec_fn)
+		return max_size;
+
+	bvm->bi_bdev = cache->origin_dev->bdev;
+	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
+}
+
+static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
+{
+	/*
+	 * FIXME: these limits may be incompatible with the cache device
+	 */
+	limits->max_discard_sectors = cache->discard_block_size * 1024;
+	limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
+}
+
+static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct cache *cache = ti->private;
+
+	blk_limits_io_min(limits, 0);
+	blk_limits_io_opt(limits, cache->sectors_per_block << SECTOR_SHIFT);
+	set_discard_limits(cache, limits);
+}
+
+/*----------------------------------------------------------------*/
+
+static struct target_type cache_target = {
+	.name = "cache",
+	.version = {1, 0, 0},
+	.module = THIS_MODULE,
+	.ctr = cache_ctr,
+	.dtr = cache_dtr,
+	.map = cache_map,
+	.end_io = cache_end_io,
+	.postsuspend = cache_postsuspend,
+	.preresume = cache_preresume,
+	.resume = cache_resume,
+	.status = cache_status,
+	.message = cache_message,
+	.iterate_devices = cache_iterate_devices,
+	.merge = cache_bvec_merge,
+	.io_hints = cache_io_hints,
+};
+
+static int __init dm_cache_init(void)
+{
+	int r;
+
+	r = dm_register_target(&cache_target);
+	if (r) {
+		DMERR("cache target registration failed: %d", r);
+		return r;
+	}
+
+	migration_cache = KMEM_CACHE(dm_cache_migration, 0);
+	if (!migration_cache) {
+		dm_unregister_target(&cache_target);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void __exit dm_cache_exit(void)
+{
+	dm_unregister_target(&cache_target);
+	kmem_cache_destroy(migration_cache);
+}
+
+module_init(dm_cache_init);
+module_exit(dm_cache_exit);
+
+MODULE_DESCRIPTION(DM_NAME " cache target");
+MODULE_AUTHOR("Joe Thornber <[e-mail]>");
+MODULE_LICENSE("GPL");

drivers/md/dm-crypt.c

···
 	return 0;
 }
 
-/*
- * Encode key into its hex representation
- */
-static void crypt_encode_key(char *hex, u8 *key, unsigned int size)
-{
-	unsigned int i;
-
-	for (i = 0; i < size; i++) {
-		sprintf(hex, "%02x", *key);
-		hex += 2;
-		key++;
-	}
-}
-
 static void crypt_free_tfms(struct crypt_config *cc)
 {
 	unsigned i;
···
 
 		if (opt_params == 1 && opt_string &&
 		    !strcasecmp(opt_string, "allow_discards"))
-			ti->num_discard_requests = 1;
+			ti->num_discard_bios = 1;
 		else if (opt_params) {
 			ret = -EINVAL;
 			ti->error = "Invalid feature arguments";
···
 		goto bad;
 	}
 
-	ti->num_flush_requests = 1;
+	ti->num_flush_bios = 1;
 	ti->discard_zeroes_data_unsupported = true;
 
 	return 0;
···
 	return DM_MAPIO_SUBMITTED;
 }
 
-static int crypt_status(struct dm_target *ti, status_type_t type,
-			unsigned status_flags, char *result, unsigned maxlen)
+static void crypt_status(struct dm_target *ti, status_type_t type,
+			 unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct crypt_config *cc = ti->private;
-	unsigned int sz = 0;
+	unsigned i, sz = 0;
 
 	switch (type) {
 	case STATUSTYPE_INFO:
···
 	case STATUSTYPE_TABLE:
 		DMEMIT("%s ", cc->cipher_string);
 
-		if (cc->key_size > 0) {
-			if ((maxlen - sz) < ((cc->key_size << 1) + 1))
-				return -ENOMEM;
-
-			crypt_encode_key(result + sz, cc->key, cc->key_size);
-			sz += cc->key_size << 1;
-		} else {
-			if (sz >= maxlen)
-				return -ENOMEM;
-			result[sz++] = '-';
-		}
+		if (cc->key_size > 0)
+			for (i = 0; i < cc->key_size; i++)
+				DMEMIT("%02x", cc->key[i]);
+		else
+			DMEMIT("-");
 
 		DMEMIT(" %llu %s %llu", (unsigned long long)cc->iv_offset,
 				cc->dev->name, (unsigned long long)cc->start);
 
-		if (ti->num_discard_requests)
+		if (ti->num_discard_bios)
 			DMEMIT(" 1 allow_discards");
 
 		break;
 	}
-	return 0;
 }
 
 static void crypt_postsuspend(struct dm_target *ti)
···
 
 static struct target_type crypt_target = {
 	.name   = "crypt",
-	.version = {1, 12, 0},
+	.version = {1, 12, 1},
 	.module = THIS_MODULE,
 	.ctr    = crypt_ctr,
 	.dtr    = crypt_dtr,

drivers/md/dm-delay.c

···
 	mutex_init(&dc->timer_lock);
 	atomic_set(&dc->may_delay, 1);
 
-	ti->num_flush_requests = 1;
-	ti->num_discard_requests = 1;
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
 	ti->private = dc;
 	return 0;
 
···
 	return delay_bio(dc, dc->read_delay, bio);
 }
 
-static int delay_status(struct dm_target *ti, status_type_t type,
-			unsigned status_flags, char *result, unsigned maxlen)
+static void delay_status(struct dm_target *ti, status_type_t type,
+			 unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct delay_c *dc = ti->private;
 	int sz = 0;
···
 			       dc->write_delay);
 		break;
 	}
-
-	return 0;
 }
 
 static int delay_iterate_devices(struct dm_target *ti,
···
 
 static struct target_type delay_target = {
 	.name	     = "delay",
-	.version     = {1, 2, 0},
+	.version     = {1, 2, 1},
 	.module      = THIS_MODULE,
 	.ctr	     = delay_ctr,
 	.dtr	     = delay_dtr,

drivers/md/dm-flakey.c

···
 		goto bad;
 	}
 
-	ti->num_flush_requests = 1;
-	ti->num_discard_requests = 1;
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
 	ti->per_bio_data_size = sizeof(struct per_bio_data);
 	ti->private = fc;
 	return 0;
···
 	return error;
 }
 
-static int flakey_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void flakey_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	unsigned sz = 0;
 	struct flakey_c *fc = ti->private;
···
 
 		break;
 	}
-	return 0;
 }
 
 static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
···
 
 static struct target_type flakey_target = {
 	.name   = "flakey",
-	.version = {1, 3, 0},
+	.version = {1, 3, 1},
 	.module = THIS_MODULE,
 	.ctr    = flakey_ctr,
 	.dtr    = flakey_dtr,

drivers/md/dm-ioctl.c

···
 	num_targets = dm_table_get_num_targets(table);
 	for (i = 0; i < num_targets; i++) {
 		struct dm_target *ti = dm_table_get_target(table, i);
+		size_t l;
 
 		remaining = len - (outptr - outbuf);
 		if (remaining <= sizeof(struct dm_target_spec)) {
···
 		if (ti->type->status) {
 			if (param->flags & DM_NOFLUSH_FLAG)
 				status_flags |= DM_STATUS_NOFLUSH_FLAG;
-			if (ti->type->status(ti, type, status_flags, outptr, remaining)) {
-				param->flags |= DM_BUFFER_FULL_FLAG;
-				break;
-			}
+			ti->type->status(ti, type, status_flags, outptr, remaining);
 		} else
 			outptr[0] = '\0';
 
-		outptr += strlen(outptr) + 1;
+		l = strlen(outptr) + 1;
+		if (l == remaining) {
+			param->flags |= DM_BUFFER_FULL_FLAG;
+			break;
+		}
+
+		outptr += l;
 		used = param->data_start + (outptr - outbuf);
 
 		outptr = align_ptr(outptr);
···
 	return 0;
 }
 
+static bool buffer_test_overflow(char *result, unsigned maxlen)
+{
+	return !maxlen || strlen(result) + 1 >= maxlen;
+}
+
+/*
+ * Process device-mapper dependent messages.
+ * Returns a number <= 1 if message was processed by device mapper.
+ * Returns 2 if message should be delivered to the target.
+ */
+static int message_for_md(struct mapped_device *md, unsigned argc, char **argv,
+			  char *result, unsigned maxlen)
+{
+	return 2;
+}
+
 /*
  * Pass a message to the target that's at the supplied device offset.
  */
···
 	struct dm_table *table;
 	struct dm_target *ti;
 	struct dm_target_msg *tmsg = (void *) param + param->data_start;
+	size_t maxlen;
+	char *result = get_result_buffer(param, param_size, &maxlen);
 
 	md = find_device(param);
 	if (!md)
···
 		DMWARN("Empty message received.");
 		goto out_argv;
 	}
+
+	r = message_for_md(md, argc, argv, result, maxlen);
+	if (r <= 1)
+		goto out_argv;
 
 	table = dm_get_live_table(md);
 	if (!table)
···
  out_argv:
 	kfree(argv);
  out:
-	param->data_size = 0;
+	if (r >= 0)
+		__dev_status(md, param);
+
+	if (r == 1) {
+		param->flags |= DM_DATA_OUT_FLAG;
+		if (buffer_test_overflow(result, maxlen))
+			param->flags |= DM_BUFFER_FULL_FLAG;
+		else
+			param->data_size = param->data_start + strlen(result) + 1;
+		r = 0;
+	}
+
 	dm_put(md);
 	return r;
 }
+
+/*
+ * The ioctl parameter block consists of two parts, a dm_ioctl struct
+ * followed by a data buffer.  This flag is set if the second part,
+ * which has a variable size, is not used by the function processing
+ * the ioctl.
+ */
+#define IOCTL_FLAGS_NO_PARAMS	1
 
 /*-----------------------------------------------------------------
  * Implementation of open/close/ioctl on the special char
  * device.
  *---------------------------------------------------------------*/
-static ioctl_fn lookup_ioctl(unsigned int cmd)
+static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
 {
 	static struct {
 		int cmd;
+		int flags;
 		ioctl_fn fn;
 	} _ioctls[] = {
-		{DM_VERSION_CMD, NULL},	/* version is dealt with elsewhere */
-		{DM_REMOVE_ALL_CMD, remove_all},
-		{DM_LIST_DEVICES_CMD, list_devices},
+		{DM_VERSION_CMD, 0, NULL}, /* version is dealt with elsewhere */
+		{DM_REMOVE_ALL_CMD, IOCTL_FLAGS_NO_PARAMS, remove_all},
+		{DM_LIST_DEVICES_CMD, 0, list_devices},
 
-		{DM_DEV_CREATE_CMD, dev_create},
-		{DM_DEV_REMOVE_CMD, dev_remove},
-		{DM_DEV_RENAME_CMD, dev_rename},
-		{DM_DEV_SUSPEND_CMD, dev_suspend},
-		{DM_DEV_STATUS_CMD, dev_status},
-		{DM_DEV_WAIT_CMD, dev_wait},
+		{DM_DEV_CREATE_CMD, IOCTL_FLAGS_NO_PARAMS, dev_create},
+		{DM_DEV_REMOVE_CMD, IOCTL_FLAGS_NO_PARAMS, dev_remove},
+		{DM_DEV_RENAME_CMD, 0, dev_rename},
+		{DM_DEV_SUSPEND_CMD, IOCTL_FLAGS_NO_PARAMS, dev_suspend},
+		{DM_DEV_STATUS_CMD, IOCTL_FLAGS_NO_PARAMS, dev_status},
+		{DM_DEV_WAIT_CMD, 0, dev_wait},
 
-		{DM_TABLE_LOAD_CMD, table_load},
-		{DM_TABLE_CLEAR_CMD, table_clear},
-		{DM_TABLE_DEPS_CMD, table_deps},
-		{DM_TABLE_STATUS_CMD, table_status},
+		{DM_TABLE_LOAD_CMD, 0, table_load},
+		{DM_TABLE_CLEAR_CMD, IOCTL_FLAGS_NO_PARAMS, table_clear},
+		{DM_TABLE_DEPS_CMD, 0, table_deps},
+		{DM_TABLE_STATUS_CMD, 0, table_status},
 
-		{DM_LIST_VERSIONS_CMD, list_versions},
+		{DM_LIST_VERSIONS_CMD, 0, list_versions},
 
-		{DM_TARGET_MSG_CMD, target_message},
-		{DM_DEV_SET_GEOMETRY_CMD, dev_set_geometry}
+		{DM_TARGET_MSG_CMD, 0, target_message},
+		{DM_DEV_SET_GEOMETRY_CMD, 0, dev_set_geometry}
 	};
 
-	return (cmd >= ARRAY_SIZE(_ioctls)) ? NULL : _ioctls[cmd].fn;
+	if (unlikely(cmd >= ARRAY_SIZE(_ioctls)))
+		return NULL;
+
+	*ioctl_flags = _ioctls[cmd].flags;
+	return _ioctls[cmd].fn;
 }
 
 /*
···
 	return r;
 }
 
-#define DM_PARAMS_VMALLOC	0x0001	/* Params alloced with vmalloc not kmalloc */
+#define DM_PARAMS_KMALLOC	0x0001	/* Params alloced with kmalloc */
+#define DM_PARAMS_VMALLOC	0x0002	/* Params alloced with vmalloc */
 #define DM_WIPE_BUFFER		0x0010	/* Wipe input buffer before returning from ioctl */
 
 static void free_params(struct dm_ioctl *param, size_t param_size, int param_flags)
···
 	if (param_flags & DM_WIPE_BUFFER)
 		memset(param, 0, param_size);
 
+	if (param_flags & DM_PARAMS_KMALLOC)
+		kfree(param);
 	if (param_flags & DM_PARAMS_VMALLOC)
 		vfree(param);
-	else
-		kfree(param);
 }
 
-static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param, int *param_flags)
+static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kernel,
+		       int ioctl_flags,
+		       struct dm_ioctl **param, int *param_flags)
 {
-	struct dm_ioctl tmp, *dmi;
+	struct dm_ioctl *dmi;
 	int secure_data;
+	const size_t minimum_data_size = sizeof(*param_kernel) - sizeof(param_kernel->data);
 
-	if (copy_from_user(&tmp, user, sizeof(tmp) - sizeof(tmp.data)))
+	if (copy_from_user(param_kernel, user, minimum_data_size))
 		return -EFAULT;
 
-	if (tmp.data_size < (sizeof(tmp) - sizeof(tmp.data)))
+	if (param_kernel->data_size < minimum_data_size)
 		return -EINVAL;
 
-	secure_data = tmp.flags & DM_SECURE_DATA_FLAG;
+	secure_data = param_kernel->flags & DM_SECURE_DATA_FLAG;
 
 	*param_flags = secure_data ? DM_WIPE_BUFFER : 0;
+
+	if (ioctl_flags & IOCTL_FLAGS_NO_PARAMS) {
+		dmi = param_kernel;
+		dmi->data_size = minimum_data_size;
+		goto data_copied;
+	}
 
 	/*
 	 * Try to avoid low memory issues when a device is suspended.
 	 * Use kmalloc() rather than vmalloc() when we can.
 	 */
 	dmi = NULL;
-	if (tmp.data_size <= KMALLOC_MAX_SIZE)
-		dmi = kmalloc(tmp.data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
-
-	if (!dmi) {
-		dmi = __vmalloc(tmp.data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH, PAGE_KERNEL);
-		*param_flags |= DM_PARAMS_VMALLOC;
+	if (param_kernel->data_size <= KMALLOC_MAX_SIZE) {
+		dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+		if (dmi)
+			*param_flags |= DM_PARAMS_KMALLOC;
 	}
 
 	if (!dmi) {
-		if (secure_data && clear_user(user, tmp.data_size))
+		dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH, PAGE_KERNEL);
+		if (dmi)
+			*param_flags |= DM_PARAMS_VMALLOC;
+	}
+
+	if (!dmi) {
+		if (secure_data && clear_user(user, param_kernel->data_size))
 			return -EFAULT;
 		return -ENOMEM;
 	}
 
-	if (copy_from_user(dmi, user, tmp.data_size))
+	if (copy_from_user(dmi, user, param_kernel->data_size))
 		goto bad;
 
+data_copied:
 	/*
 	 * Abort if something changed the ioctl data while it was being copied.
 	 */
-	if (dmi->data_size != tmp.data_size) {
+	if (dmi->data_size != param_kernel->data_size) {
 		DMERR("rejecting ioctl: data size modified while processing parameters");
 		goto bad;
 	}
 
 	/* Wipe the user buffer so we do not return it to userspace */
-	if (secure_data && clear_user(user, tmp.data_size))
+	if (secure_data && clear_user(user, param_kernel->data_size))
 		goto bad;
 
 	*param = dmi;
 	return 0;
 
 bad:
-	free_params(dmi, tmp.data_size, *param_flags);
+	free_params(dmi, param_kernel->data_size, *param_flags);
 
 	return -EFAULT;
 }
···
 	param->flags &= ~DM_BUFFER_FULL_FLAG;
 	param->flags &= ~DM_UEVENT_GENERATED_FLAG;
 	param->flags &= ~DM_SECURE_DATA_FLAG;
+	param->flags &= ~DM_DATA_OUT_FLAG;
 
 	/* Ignores parameters */
 	if (cmd == DM_REMOVE_ALL_CMD ||
···
 static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 {
 	int r = 0;
+	int ioctl_flags;
 	int param_flags;
 	unsigned int cmd;
 	struct dm_ioctl *uninitialized_var(param);
 	ioctl_fn fn = NULL;
 	size_t input_param_size;
+	struct dm_ioctl param_kernel;
 
 	/* only root can play with this */
 	if (!capable(CAP_SYS_ADMIN))
···
 	if (cmd == DM_VERSION_CMD)
 		return 0;
 
-	fn = lookup_ioctl(cmd);
+	fn = lookup_ioctl(cmd, &ioctl_flags);
 	if (!fn) {
 		DMWARN("dm_ctl_ioctl: unknown command 0x%x", command);
 		return -ENOTTY;
···
 	/*
 	 * Copy the parameters into kernel space.
 	 */
-	r = copy_params(user, &param, &param_flags);
+	r = copy_params(user, &param_kernel, ioctl_flags, &param, &param_flags);
 
 	if (r)
 		return r;
···
 
 	param->data_size = sizeof(*param);
 	r = fn(param, input_param_size);
+
+	if (unlikely(param->flags & DM_BUFFER_FULL_FLAG) &&
+	    unlikely(ioctl_flags & IOCTL_FLAGS_NO_PARAMS))
+		DMERR("ioctl %d tried to output some data but has IOCTL_FLAGS_NO_PARAMS set", cmd);
 
 	/*
 	 * Copy the results back to userland.

drivers/md/dm-kcopyd.c

···
 #include <linux/vmalloc.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
+#include <linux/delay.h>
 #include <linux/device-mapper.h>
 #include <linux/dm-kcopyd.h>
 
···
 	struct workqueue_struct *kcopyd_wq;
 	struct work_struct kcopyd_work;
 
+	struct dm_kcopyd_throttle *throttle;
+
 /*
  * We maintain three lists of jobs:
  *
···
 };
 
 static struct page_list zero_page_list;
+
+static DEFINE_SPINLOCK(throttle_spinlock);
+
+/*
+ * IO/IDLE accounting slowly decays after (1 << ACCOUNT_INTERVAL_SHIFT) period.
+ * When total_period >= (1 << ACCOUNT_INTERVAL_SHIFT) the counters are divided
+ * by 2.
+ */
+#define ACCOUNT_INTERVAL_SHIFT		SHIFT_HZ
+
+/*
+ * Sleep this number of milliseconds.
+ *
+ * The value was decided experimentally.
+ * Smaller values seem to cause an increased copy rate above the limit.
+ * The reason for this is unknown but possibly due to jiffies rounding errors
+ * or read/write cache inside the disk.
+ */
+#define SLEEP_MSEC			100
+
+/*
+ * Maximum number of sleep events. There is a theoretical livelock if more
+ * kcopyd clients do work simultaneously which this limit avoids.
+ */
+#define MAX_SLEEPS			10
+
+static void io_job_start(struct dm_kcopyd_throttle *t)
+{
+	unsigned throttle, now, difference;
+	int slept = 0, skew;
+
+	if (unlikely(!t))
+		return;
+
+try_again:
+	spin_lock_irq(&throttle_spinlock);
+
+	throttle = ACCESS_ONCE(t->throttle);
+
+	if (likely(throttle >= 100))
+		goto skip_limit;
+
+	now = jiffies;
+	difference = now - t->last_jiffies;
+	t->last_jiffies = now;
+	if (t->num_io_jobs)
+		t->io_period += difference;
+	t->total_period += difference;
+
+	/*
+	 * Maintain sane values if we got a temporary overflow.
+	 */
+	if (unlikely(t->io_period > t->total_period))
+		t->io_period = t->total_period;
+
+	if (unlikely(t->total_period >= (1 << ACCOUNT_INTERVAL_SHIFT))) {
+		int shift = fls(t->total_period >> ACCOUNT_INTERVAL_SHIFT);
+		t->total_period >>= shift;
+		t->io_period >>= shift;
+	}
+
+	skew = t->io_period - throttle * t->total_period / 100;
+
+	if (unlikely(skew > 0) && slept < MAX_SLEEPS) {
+		slept++;
+		spin_unlock_irq(&throttle_spinlock);
+		msleep(SLEEP_MSEC);
+		goto try_again;
+	}
+
+skip_limit:
+	t->num_io_jobs++;
+
+	spin_unlock_irq(&throttle_spinlock);
+}
+
+static void io_job_finish(struct dm_kcopyd_throttle *t)
+{
+	unsigned long flags;
+
+	if (unlikely(!t))
+		return;
+
+	spin_lock_irqsave(&throttle_spinlock, flags);
+
+	t->num_io_jobs--;
+
+	if (likely(ACCESS_ONCE(t->throttle) >= 100))
+		goto skip_limit;
+
+	if (!t->num_io_jobs) {
+		unsigned now, difference;
+
+		now = jiffies;
+		difference = now - t->last_jiffies;
+		t->last_jiffies = now;
+
+		t->io_period += difference;
+		t->total_period += difference;
+
+		/*
+		 * Maintain sane values if we got a temporary overflow.
+		 */
+		if (unlikely(t->io_period > t->total_period))
+			t->io_period = t->total_period;
+	}
+
+skip_limit:
+	spin_unlock_irqrestore(&throttle_spinlock, flags);
+}
+
 
 static void wake(struct dm_kcopyd_client *kc)
 {
···
 	struct kcopyd_job *job = (struct kcopyd_job *) context;
 	struct dm_kcopyd_client *kc = job->kc;
 
+	io_job_finish(kc->throttle);
+
 	if (error) {
 		if (job->rw & WRITE)
 			job->write_err |= error;
···
 		.notify.context = job,
 		.client = job->kc->io_client,
 	};
+
+	io_job_start(job->kc->throttle);
 
 	if (job->rw == READ)
 		r = dm_io(&io_req, 1, &job->source, NULL);
···
 /*-----------------------------------------------------------------
  * Client setup
  *---------------------------------------------------------------*/
-struct dm_kcopyd_client *dm_kcopyd_client_create(void)
+struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle)
 {
 	int r = -ENOMEM;
 	struct dm_kcopyd_client *kc;
···
 	INIT_LIST_HEAD(&kc->complete_jobs);
 	INIT_LIST_HEAD(&kc->io_jobs);
 	INIT_LIST_HEAD(&kc->pages_jobs);
+	kc->throttle = throttle;
 
 	kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
 	if (!kc->job_pool)

drivers/md/dm-linear.c

···
 		goto bad;
 	}
 
-	ti->num_flush_requests = 1;
-	ti->num_discard_requests = 1;
-	ti->num_write_same_requests = 1;
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
+	ti->num_write_same_bios = 1;
 	ti->private = lc;
 	return 0;
 
···
 	return DM_MAPIO_REMAPPED;
 }
 
-static int linear_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void linear_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct linear_c *lc = (struct linear_c *) ti->private;
 
···
 				(unsigned long long)lc->start);
 		break;
 	}
-	return 0;
 }
 
 static int linear_ioctl(struct dm_target *ti, unsigned int cmd,
···
 
 static struct target_type linear_target = {
 	.name   = "linear",
-	.version = {1, 2, 0},
+	.version = {1, 2, 1},
 	.module = THIS_MODULE,
 	.ctr    = linear_ctr,
 	.dtr    = linear_dtr,

drivers/md/dm-mpath.c

···
 		goto bad;
 	}
 
-	ti->num_flush_requests = 1;
-	ti->num_discard_requests = 1;
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
 
 	return 0;
 
···
  *     [priority selector-name num_ps_args [ps_args]*
  *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
  */
-static int multipath_status(struct dm_target *ti, status_type_t type,
-			    unsigned status_flags, char *result, unsigned maxlen)
+static void multipath_status(struct dm_target *ti, status_type_t type,
+			     unsigned status_flags, char *result, unsigned maxlen)
 {
 	int sz = 0;
 	unsigned long flags;
···
 	}
 
 	spin_unlock_irqrestore(&m->lock, flags);
-
-	return 0;
 }
 
 static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
···
  *---------------------------------------------------------------*/
 static struct target_type multipath_target = {
 	.name = "multipath",
-	.version = {1, 5, 0},
+	.version = {1, 5, 1},
 	.module = THIS_MODULE,
 	.ctr = multipath_ctr,
 	.dtr = multipath_dtr,

drivers/md/dm-raid.c

···
 
 	INIT_WORK(&rs->md.event_work, do_table_event);
 	ti->private = rs;
-	ti->num_flush_requests = 1;
+	ti->num_flush_bios = 1;
 
 	mutex_lock(&rs->md.reconfig_mutex);
 	ret = md_run(&rs->md);
···
 	return DM_MAPIO_SUBMITTED;
 }
 
-static int raid_status(struct dm_target *ti, status_type_t type,
-		       unsigned status_flags, char *result, unsigned maxlen)
+static void raid_status(struct dm_target *ti, status_type_t type,
+			unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct raid_set *rs = ti->private;
 	unsigned raid_param_cnt = 1; /* at least 1 for chunksize */
···
 				DMEMIT(" -");
 		}
 	}
-
-	return 0;
 }
 
 static int raid_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
···
 
 static struct target_type raid_target = {
 	.name = "raid",
-	.version = {1, 4, 1},
+	.version = {1, 4, 2},
 	.module = THIS_MODULE,
 	.ctr = raid_ctr,
 	.dtr = raid_dtr,

drivers/md/dm-raid1.c

···
 	struct mirror mirror[0];
 };
 
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,
+		"A percentage of time allocated for raid resynchronization");
+
 static void wakeup_mirrord(void *context)
 {
 	struct mirror_set *ms = context;
···
 	if (r)
 		goto err_free_context;
 
-	ti->num_flush_requests = 1;
-	ti->num_discard_requests = 1;
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
 	ti->per_bio_data_size = sizeof(struct dm_raid1_bio_record);
 	ti->discard_zeroes_data_unsupported = true;
 
···
 		goto err_destroy_wq;
 	}
 
-	ms->kcopyd_client = dm_kcopyd_client_create();
+	ms->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
 	if (IS_ERR(ms->kcopyd_client)) {
 		r = PTR_ERR(ms->kcopyd_client);
 		goto err_destroy_wq;
···
 }
 
 
-static int mirror_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void mirror_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	unsigned int m, sz = 0;
 	struct mirror_set *ms = (struct mirror_set *) ti->private;
···
 		if (ms->features & DM_RAID1_HANDLE_ERRORS)
 			DMEMIT(" 1 handle_errors");
 	}
-
-	return 0;
 }
 
 static int mirror_iterate_devices(struct dm_target *ti,
···
 
 static struct target_type mirror_target = {
 	.name	 = "mirror",
-	.version = {1, 13, 1},
+	.version = {1, 13, 2},
 	.module	 = THIS_MODULE,
 	.ctr	 = mirror_ctr,
 	.dtr	 = mirror_dtr,

drivers/md/dm-snap.c

···
 #define RUNNING_MERGE          0
 #define SHUTDOWN_MERGE         1
 
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
+		"A percentage of time allocated for copy on write");
+
 struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
 {
 	return s->origin;
···
 	int i;
 	int r = -EINVAL;
 	char *origin_path, *cow_path;
-	unsigned args_used, num_flush_requests = 1;
+	unsigned args_used, num_flush_bios = 1;
 	fmode_t origin_mode = FMODE_READ;
 
 	if (argc != 4) {
···
 	}
 
 	if (dm_target_is_snapshot_merge(ti)) {
-		num_flush_requests = 2;
+		num_flush_bios = 2;
 		origin_mode = FMODE_WRITE;
 	}
 
···
 		goto bad_hash_tables;
 	}
 
-	s->kcopyd_client = dm_kcopyd_client_create();
+	s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
 	if (IS_ERR(s->kcopyd_client)) {
 		r = PTR_ERR(s->kcopyd_client);
 		ti->error = "Could not create kcopyd client";
···
 	spin_lock_init(&s->tracked_chunk_lock);
 
 	ti->private = s;
-	ti->num_flush_requests = num_flush_requests;
+	ti->num_flush_bios = num_flush_bios;
 	ti->per_bio_data_size = sizeof(struct dm_snap_tracked_chunk);
 
 	/* Add snapshot to the list of snapshots for this origin */
···
 	init_tracked_chunk(bio);
 
 	if (bio->bi_rw & REQ_FLUSH) {
-		if (!dm_bio_get_target_request_nr(bio))
+		if (!dm_bio_get_target_bio_nr(bio))
 			bio->bi_bdev = s->origin->bdev;
 		else
 			bio->bi_bdev = s->cow->bdev;
···
 	start_merge(s);
 }
 
-static int snapshot_status(struct dm_target *ti, status_type_t type,
-			   unsigned status_flags, char *result, unsigned maxlen)
+static void snapshot_status(struct dm_target *ti, status_type_t type,
+			    unsigned status_flags, char *result, unsigned maxlen)
 {
 	unsigned sz = 0;
 	struct dm_snapshot *snap = ti->private;
···
 					  maxlen - sz);
 		break;
 	}
-
-	return 0;
 }
 
 static int snapshot_iterate_devices(struct dm_target *ti,
···
 	}
 
 	ti->private = dev;
-	ti->num_flush_requests = 1;
+	ti->num_flush_bios = 1;
 
 	return 0;
 }
···
 	ti->max_io_len = get_origin_minimum_chunksize(dev->bdev);
 }
 
-static int origin_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void origin_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct dm_dev *dev = ti->private;
 
···
 		snprintf(result, maxlen, "%s", dev->name);
 		break;
 	}
-
-	return 0;
 }
 
 static int origin_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
···
 
 static struct target_type origin_target = {
 	.name    = "snapshot-origin",
-	.version = {1, 8, 0},
+	.version = {1, 8, 1},
 	.module  = THIS_MODULE,
 	.ctr     = origin_ctr,
 	.dtr     = origin_dtr,
···
 
 static struct target_type snapshot_target = {
 	.name    = "snapshot",
-	.version = {1, 11, 0},
+	.version = {1, 11, 1},
 	.module  = THIS_MODULE,
 	.ctr     = snapshot_ctr,
 	.dtr     = snapshot_dtr,
···
 MODULE_DESCRIPTION(DM_NAME " snapshot target");
 MODULE_AUTHOR("Joe Thornber");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS("dm-snapshot-origin");
+MODULE_ALIAS("dm-snapshot-merge");

drivers/md/dm-stripe.c

···
 	if (r)
 		return r;
 
-	ti->num_flush_requests = stripes;
-	ti->num_discard_requests = stripes;
-	ti->num_write_same_requests = stripes;
+	ti->num_flush_bios = stripes;
+	ti->num_discard_bios = stripes;
+	ti->num_write_same_bios = stripes;
 
 	sc->chunk_size = chunk_size;
 	if (chunk_size & (chunk_size - 1))
···
 {
 	struct stripe_c *sc = ti->private;
 	uint32_t stripe;
-	unsigned target_request_nr;
+	unsigned target_bio_nr;
 
 	if (bio->bi_rw & REQ_FLUSH) {
-		target_request_nr = dm_bio_get_target_request_nr(bio);
-		BUG_ON(target_request_nr >= sc->stripes);
-		bio->bi_bdev = sc->stripe[target_request_nr].dev->bdev;
+		target_bio_nr = dm_bio_get_target_bio_nr(bio);
+		BUG_ON(target_bio_nr >= sc->stripes);
+		bio->bi_bdev = sc->stripe[target_bio_nr].dev->bdev;
 		return DM_MAPIO_REMAPPED;
 	}
 	if (unlikely(bio->bi_rw & REQ_DISCARD) ||
 	    unlikely(bio->bi_rw & REQ_WRITE_SAME)) {
-		target_request_nr = dm_bio_get_target_request_nr(bio);
-		BUG_ON(target_request_nr >= sc->stripes);
-		return stripe_map_range(sc, bio, target_request_nr);
+		target_bio_nr = dm_bio_get_target_bio_nr(bio);
+		BUG_ON(target_bio_nr >= sc->stripes);
+		return stripe_map_range(sc, bio, target_bio_nr);
 	}
 
 	stripe_map_sector(sc, bio->bi_sector, &stripe, &bio->bi_sector);
···
  *
  */
 
-static int stripe_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void stripe_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct stripe_c *sc = (struct stripe_c *) ti->private;
 	char buffer[sc->stripes + 1];
···
 			    (unsigned long long)sc->stripe[i].physical_start);
 		break;
 	}
-	return 0;
 }
 
 static int stripe_end_io(struct dm_target *ti, struct bio *bio, int error)
···
 
 static struct target_type stripe_target = {
 	.name   = "striped",
-	.version = {1, 5, 0},
+	.version = {1, 5, 1},
 	.module = THIS_MODULE,
 	.ctr    = stripe_ctr,
 	.dtr    = stripe_dtr,

drivers/md/dm-table.c

···
 
 	if (alloc_targets(t, num_targets)) {
 		kfree(t);
-		t = NULL;
 		return -ENOMEM;
 	}
 
···
 
 	t->highs[t->num_targets++] = tgt->begin + tgt->len - 1;
 
-	if (!tgt->num_discard_requests && tgt->discards_supported)
-		DMWARN("%s: %s: ignoring discards_supported because num_discard_requests is zero.",
+	if (!tgt->num_discard_bios && tgt->discards_supported)
+		DMWARN("%s: %s: ignoring discards_supported because num_discard_bios is zero.",
 		       dm_device_name(t->md), type);
 
 	return 0;
···
 	while (i < dm_table_get_num_targets(t)) {
 		ti = dm_table_get_target(t, i++);
 
-		if (!ti->num_flush_requests)
+		if (!ti->num_flush_bios)
 			continue;
 
 		if (ti->flush_supported)
···
 	while (i < dm_table_get_num_targets(t)) {
 		ti = dm_table_get_target(t, i++);
 
-		if (!ti->num_write_same_requests)
+		if (!ti->num_write_same_bios)
 			return false;
 
 		if (!ti->type->iterate_devices ||
···
 	while (i < dm_table_get_num_targets(t)) {
 		ti = dm_table_get_target(t, i++);
 
-		if (!ti->num_discard_requests)
+		if (!ti->num_discard_bios)
 			continue;
 
 		if (ti->discards_supported)

drivers/md/dm-target.c

···
 	/*
 	 * Return error for discards instead of -EOPNOTSUPP
 	 */
-	tt->num_discard_requests = 1;
+	tt->num_discard_bios = 1;
 
 	return 0;
 }

drivers/md/dm-thin-metadata.c

···
 	*t = v & ((1 << 24) - 1);
 }
 
-static void data_block_inc(void *context, void *value_le)
+static void data_block_inc(void *context, const void *value_le)
 {
 	struct dm_space_map *sm = context;
 	__le64 v_le;
···
 	dm_sm_inc_block(sm, b);
 }
 
-static void data_block_dec(void *context, void *value_le)
+static void data_block_dec(void *context, const void *value_le)
 {
 	struct dm_space_map *sm = context;
 	__le64 v_le;
···
 	dm_sm_dec_block(sm, b);
 }
 
-static int data_block_equal(void *context, void *value1_le, void *value2_le)
+static int data_block_equal(void *context, const void *value1_le, const void *value2_le)
 {
 	__le64 v1_le, v2_le;
 	uint64_t b1, b2;
···
 	return b1 == b2;
 }
 
-static void subtree_inc(void *context, void *value)
+static void subtree_inc(void *context, const void *value)
 {
 	struct dm_btree_info *info = context;
 	__le64 root_le;
···
 	dm_tm_inc(info->tm, root);
 }
 
-static void subtree_dec(void *context, void *value)
+static void subtree_dec(void *context, const void *value)
 {
 	struct dm_btree_info *info = context;
 	__le64 root_le;
···
 		DMERR("btree delete failed\n");
 }
 
-static int subtree_equal(void *context, void *value1_le, void *value2_le)
+static int subtree_equal(void *context, const void *value1_le, const void *value2_le)
 {
 	__le64 v1_le, v2_le;
 	memcpy(&v1_le, value1_le, sizeof(v1_le));

drivers/md/dm-thin.c

···
 #define PRISON_CELLS 1024
 #define COMMIT_PERIOD HZ
 
+DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
+		"A percentage of time allocated for copy on write");
+
 /*
  * The block size of the device holding pool data must be
  * between 64KB and 1GB.
···
 /*----------------------------------------------------------------*/
 
 /*
+ * wake_worker() is used when new work is queued and when pool_resume is
+ * ready to continue deferred IO processing.
+ */
+static void wake_worker(struct pool *pool)
+{
+	queue_work(pool->wq, &pool->worker);
+}
+
+/*----------------------------------------------------------------*/
+
+static int bio_detain(struct pool *pool, struct dm_cell_key *key, struct bio *bio,
+		      struct dm_bio_prison_cell **cell_result)
+{
+	int r;
+	struct dm_bio_prison_cell *cell_prealloc;
+
+	/*
+	 * Allocate a cell from the prison's mempool.
+	 * This might block but it can't fail.
+	 */
+	cell_prealloc = dm_bio_prison_alloc_cell(pool->prison, GFP_NOIO);
+
+	r = dm_bio_detain(pool->prison, key, bio, cell_prealloc, cell_result);
+	if (r)
+		/*
+		 * We reused an old cell; we can get rid of
+		 * the new one.
+		 */
+		dm_bio_prison_free_cell(pool->prison, cell_prealloc);
+
+	return r;
+}
+
+static void cell_release(struct pool *pool,
+			 struct dm_bio_prison_cell *cell,
+			 struct bio_list *bios)
+{
+	dm_cell_release(pool->prison, cell, bios);
+	dm_bio_prison_free_cell(pool->prison, cell);
+}
+
+static void cell_release_no_holder(struct pool *pool,
+				   struct dm_bio_prison_cell *cell,
+				   struct bio_list *bios)
+{
+	dm_cell_release_no_holder(pool->prison, cell, bios);
+	dm_bio_prison_free_cell(pool->prison, cell);
+}
+
+static void cell_defer_no_holder_no_free(struct thin_c *tc,
+					 struct dm_bio_prison_cell *cell)
+{
+	struct pool *pool = tc->pool;
+	unsigned long flags;
+
+	spin_lock_irqsave(&pool->lock, flags);
+	dm_cell_release_no_holder(pool->prison, cell, &pool->deferred_bios);
+	spin_unlock_irqrestore(&pool->lock, flags);
+
+	wake_worker(pool);
+}
+
+static void cell_error(struct pool *pool,
+		       struct dm_bio_prison_cell *cell)
+{
+	dm_cell_error(pool->prison, cell);
+	dm_bio_prison_free_cell(pool->prison, cell);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
  * A global list of pools that uses a struct mapped_device as a key.
  */
 static struct dm_thin_pool_table {
···
  * target.
  */
 
+static bool block_size_is_power_of_two(struct pool *pool)
+{
+	return pool->sectors_per_block_shift >= 0;
+}
+
 static dm_block_t get_bio_block(struct thin_c *tc, struct bio *bio)
 {
+	struct pool *pool = tc->pool;
 	sector_t block_nr = bio->bi_sector;
 
-	if (tc->pool->sectors_per_block_shift < 0)
-		(void) sector_div(block_nr, tc->pool->sectors_per_block);
+	if (block_size_is_power_of_two(pool))
+		block_nr >>= pool->sectors_per_block_shift;
 	else
-		block_nr >>= tc->pool->sectors_per_block_shift;
+		(void) sector_div(block_nr, pool->sectors_per_block);
 
 	return block_nr;
 }
···
 	sector_t bi_sector = bio->bi_sector;
 
 	bio->bi_bdev = tc->pool_dev->bdev;
-	if (tc->pool->sectors_per_block_shift < 0)
-		bio->bi_sector = (block * pool->sectors_per_block) +
-				 sector_div(bi_sector, pool->sectors_per_block);
-	else
+	if (block_size_is_power_of_two(pool))
 		bio->bi_sector = (block << pool->sectors_per_block_shift) |
 				(bi_sector & (pool->sectors_per_block - 1));
+	else
+		bio->bi_sector = (block * pool->sectors_per_block) +
+				 sector_div(bi_sector, pool->sectors_per_block);
 }
 
 static void remap_to_origin(struct thin_c *tc, struct bio *bio)
···
 {
 	remap(tc, bio, block);
 	issue(tc, bio);
-}
-
-/*
- * wake_worker() is used when new work is queued and when pool_resume is
- * ready to continue deferred IO processing.
- */
-static void wake_worker(struct pool *pool)
-{
-	queue_work(pool->wq, &pool->worker);
 }
 
 /*----------------------------------------------------------------*/
···
 	unsigned long flags;
 
 	spin_lock_irqsave(&pool->lock, flags);
-	dm_cell_release(cell, &pool->deferred_bios);
+	cell_release(pool, cell, &pool->deferred_bios);
 	spin_unlock_irqrestore(&tc->pool->lock, flags);
 
 	wake_worker(pool);
 }
 
 /*
- * Same as cell_defer except it omits the original holder of the cell.
+ * Same as cell_defer above, except it omits the original holder of the cell.
  */
 static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
···
 	unsigned long flags;
 
 	spin_lock_irqsave(&pool->lock, flags);
-	dm_cell_release_no_holder(cell, &pool->deferred_bios);
+	cell_release_no_holder(pool, cell, &pool->deferred_bios);
 	spin_unlock_irqrestore(&pool->lock, flags);
 
 	wake_worker(pool);
···
 {
 	if (m->bio)
 		m->bio->bi_end_io = m->saved_bi_end_io;
-	dm_cell_error(m->cell);
+	cell_error(m->tc->pool, m->cell);
 	list_del(&m->list);
 	mempool_free(m, m->tc->pool->mapping_pool);
 }
+
 static void process_prepared_mapping(struct dm_thin_new_mapping *m)
 {
 	struct thin_c *tc = m->tc;
+	struct pool *pool = tc->pool;
 	struct bio *bio;
 	int r;
 
···
 		bio->bi_end_io = m->saved_bi_end_io;
 
 	if (m->err) {
-		dm_cell_error(m->cell);
+		cell_error(pool, m->cell);
 		goto out;
 	}
 
···
 	r = dm_thin_insert_block(tc->td, m->virt_block, m->data_block);
 	if (r) {
 		DMERR_LIMIT("dm_thin_insert_block() failed");
-		dm_cell_error(m->cell);
+		cell_error(pool, m->cell);
 		goto out;
 	}
 
···
 
 out:
 	list_del(&m->list);
-	mempool_free(m, tc->pool->mapping_pool);
+	mempool_free(m, pool->mapping_pool);
 }
 
 static void process_prepared_discard_fail(struct dm_thin_new_mapping *m)
···
 		if (r < 0) {
 			mempool_free(m, pool->mapping_pool);
 			DMERR_LIMIT("dm_kcopyd_copy() failed");
-			dm_cell_error(cell);
+			cell_error(pool, cell);
 		}
 	}
 }
···
 		if (r < 0) {
 			mempool_free(m, pool->mapping_pool);
 			DMERR_LIMIT("dm_kcopyd_zero() failed");
-			dm_cell_error(cell);
+			cell_error(pool, cell);
 		}
 	}
 }
···
 	spin_unlock_irqrestore(&pool->lock, flags);
 }
 
-static void no_space(struct dm_bio_prison_cell *cell)
+static void no_space(struct pool *pool, struct dm_bio_prison_cell *cell)
 {
 	struct bio *bio;
 	struct bio_list bios;
 
 	bio_list_init(&bios);
-	dm_cell_release(cell, &bios);
+	cell_release(pool, cell, &bios);
 
 	while ((bio = bio_list_pop(&bios)))
 		retry_on_resume(bio);
···
 	struct dm_thin_new_mapping *m;
 
 	build_virtual_key(tc->td, block, &key);
-	if (dm_bio_detain(tc->pool->prison, &key, bio, &cell))
+	if (bio_detain(tc->pool, &key, bio, &cell))
 		return;
 
 	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
···
 		 * on this block.
 		 */
 		build_data_key(tc->td, lookup_result.block, &key2);
-		if (dm_bio_detain(tc->pool->prison, &key2, bio, &cell2)) {
+		if (bio_detain(tc->pool, &key2, bio, &cell2)) {
 			cell_defer_no_holder(tc, cell);
 			break;
 		}
···
 		break;
 
 	case -ENOSPC:
-		no_space(cell);
+		no_space(tc->pool, cell);
 		break;
 
 	default:
 		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
 			    __func__, r);
-		dm_cell_error(cell);
+		cell_error(tc->pool, cell);
 		break;
 	}
 }
···
 	 * of being broken so we have nothing further to do here.
 	 */
 	build_data_key(tc->td, lookup_result->block, &key);
-	if (dm_bio_detain(pool->prison, &key, bio, &cell))
+	if (bio_detain(pool, &key, bio, &cell))
 		return;
 
 	if (bio_data_dir(bio) == WRITE && bio->bi_size)
···
 {
 	int r;
 	dm_block_t data_block;
+	struct pool *pool = tc->pool;
 
 	/*
 	 * Remap empty bios (flushes) immediately, without provisioning.
 	 */
 	if (!bio->bi_size) {
-		inc_all_io_entry(tc->pool, bio);
+		inc_all_io_entry(pool, bio);
 		cell_defer_no_holder(tc, cell);
 
 		remap_and_issue(tc, bio, 0);
···
 		break;
 
 	case -ENOSPC:
-		no_space(cell);
+		no_space(pool, cell);
 		break;
 
 	default:
 		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
 			    __func__, r);
-		set_pool_mode(tc->pool, PM_READ_ONLY);
-		dm_cell_error(cell);
+		set_pool_mode(pool, PM_READ_ONLY);
+		cell_error(pool, cell);
 		break;
 	}
 }
···
 static void process_bio(struct thin_c *tc, struct bio *bio)
 {
 	int r;
+	struct pool *pool = tc->pool;
 	dm_block_t block = get_bio_block(tc, bio);
 	struct dm_bio_prison_cell *cell;
 	struct dm_cell_key key;
···
 	 * being provisioned so we have nothing further to do here.
 	 */
 	build_virtual_key(tc->td, block, &key);
-	if (dm_bio_detain(tc->pool->prison, &key, bio, &cell))
+	if (bio_detain(pool, &key, bio, &cell))
 		return;
 
 	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
···
 	case 0:
 		if (lookup_result.shared) {
 			process_shared_bio(tc, bio, block, &lookup_result);
-			cell_defer_no_holder(tc, cell);
+			cell_defer_no_holder(tc, cell); /* FIXME: pass this cell into process_shared? */
 		} else {
-			inc_all_io_entry(tc->pool, bio);
+			inc_all_io_entry(pool, bio);
 			cell_defer_no_holder(tc, cell);
 
 			remap_and_issue(tc, bio, lookup_result.block);
···
 
 	case -ENODATA:
 		if (bio_data_dir(bio) == READ && tc->origin_dev) {
-			inc_all_io_entry(tc->pool, bio);
+			inc_all_io_entry(pool, bio);
 			cell_defer_no_holder(tc, cell);
 
 			remap_to_origin_and_issue(tc, bio);
···
 	dm_block_t block = get_bio_block(tc, bio);
 	struct dm_thin_device *td = tc->td;
 	struct dm_thin_lookup_result result;
-	struct dm_bio_prison_cell *cell1, *cell2;
+	struct dm_bio_prison_cell cell1, cell2;
+	struct dm_bio_prison_cell *cell_result;
 	struct dm_cell_key key;
 
 	thin_hook_bio(tc, bio);
···
 		}
 
 		build_virtual_key(tc->td, block, &key);
-		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1))
+		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
 			return DM_MAPIO_SUBMITTED;
 
 		build_data_key(tc->td, result.block, &key);
-		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2)) {
-			cell_defer_no_holder(tc, cell1);
+		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2, &cell_result)) {
+			cell_defer_no_holder_no_free(tc, &cell1);
 			return DM_MAPIO_SUBMITTED;
 		}
 
 		inc_all_io_entry(tc->pool, bio);
-		cell_defer_no_holder(tc, cell2);
-		cell_defer_no_holder(tc, cell1);
+		cell_defer_no_holder_no_free(tc, &cell2);
+		cell_defer_no_holder_no_free(tc, &cell1);
 
 		remap(tc, bio, result.block);
 		return DM_MAPIO_REMAPPED;
···
 		goto bad_prison;
 	}
 
-	pool->copier = dm_kcopyd_client_create();
+	pool->copier = dm_kcopyd_client_create(&dm_kcopyd_throttle);
 	if (IS_ERR(pool->copier)) {
 		r = PTR_ERR(pool->copier);
 		*error = "Error creating pool's kcopyd client";
···
 	pt->data_dev = data_dev;
 	pt->low_water_blocks = low_water_blocks;
 	pt->adjusted_pf = pt->requested_pf = pf;
-	ti->num_flush_requests = 1;
+	ti->num_flush_bios = 1;
 
 	/*
 	 * Only need to enable discards if the pool should pass
···
 	 * processing will cause mappings to be removed from the btree.
 	 */
 	if (pf.discard_enabled && pf.discard_passdown) {
-		ti->num_discard_requests = 1;
+		ti->num_discard_bios = 1;
 
 		/*
 		 * Setting 'discards_supported' circumvents the normal
···
  *    <transaction id> <used metadata sectors>/<total metadata sectors>
  *    <used data sectors>/<total data sectors> <held metadata root>
  */
-static int pool_status(struct dm_target *ti, status_type_t type,
-		       unsigned status_flags, char *result, unsigned maxlen)
+static void pool_status(struct dm_target *ti, status_type_t type,
+			unsigned status_flags, char *result, unsigned maxlen)
 {
 	int r;
 	unsigned sz = 0;
···
 		if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
 			(void) commit_or_fallback(pool);
 
-		r = dm_pool_get_metadata_transaction_id(pool->pmd,
-							&transaction_id);
-		if (r)
-			return r;
+		r = dm_pool_get_metadata_transaction_id(pool->pmd, &transaction_id);
+		if (r) {
+			DMERR("dm_pool_get_metadata_transaction_id returned %d", r);
+			goto err;
+		}
 
-		r = dm_pool_get_free_metadata_block_count(pool->pmd,
-							  &nr_free_blocks_metadata);
-		if (r)
-			return r;
+		r = dm_pool_get_free_metadata_block_count(pool->pmd, &nr_free_blocks_metadata);
+		if (r) {
+			DMERR("dm_pool_get_free_metadata_block_count returned %d", r);
+			goto err;
+		}
 
 		r = dm_pool_get_metadata_dev_size(pool->pmd, &nr_blocks_metadata);
-		if (r)
-			return r;
+		if (r) {
+			DMERR("dm_pool_get_metadata_dev_size returned %d", r);
+			goto err;
+		}
 
-		r = dm_pool_get_free_block_count(pool->pmd,
-						 &nr_free_blocks_data);
-		if (r)
-			return r;
+		r = dm_pool_get_free_block_count(pool->pmd, &nr_free_blocks_data);
+		if (r) {
+			DMERR("dm_pool_get_free_block_count returned %d", r);
+			goto err;
+		}
 
 		r = dm_pool_get_data_dev_size(pool->pmd, &nr_blocks_data);
-		if (r)
-			return r;
+		if (r) {
+			DMERR("dm_pool_get_data_dev_size returned %d", r);
+			goto err;
+		}
 
 		r = dm_pool_get_metadata_snap(pool->pmd, &held_root);
-		if (r)
-			return r;
+		if (r) {
+			DMERR("dm_pool_get_metadata_snap returned %d", r);
+			goto err;
+		}
 
 		DMEMIT("%llu %llu/%llu %llu/%llu ",
 		       (unsigned long long)transaction_id,
···
 		emit_flags(&pt->requested_pf, result, sz, maxlen);
 		break;
 	}
+	return;
 
-	return 0;
+err:
+	DMEMIT("Error");
 }
 
 static int pool_iterate_devices(struct dm_target *ti,
···
 	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
 }
 
-static bool block_size_is_power_of_two(struct pool *pool)
-{
-	return pool->sectors_per_block_shift >= 0;
-}
-
 static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits)
 {
 	struct pool *pool = pt->pool;
···
 	if (pt->adjusted_pf.discard_passdown) {
 		data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits;
 		limits->discard_granularity = data_limits->discard_granularity;
-	} else if (block_size_is_power_of_two(pool))
+	} else
 		limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
-	else
-		/*
-		 * Use largest power of 2 that is a factor of sectors_per_block
-		 * but at least DATA_DEV_BLOCK_SIZE_MIN_SECTORS.
-		 */
-		limits->discard_granularity = max(1 << (ffs(pool->sectors_per_block) - 1),
-						  DATA_DEV_BLOCK_SIZE_MIN_SECTORS) << SECTOR_SHIFT;
 }
 
 static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
···
 	.name = "thin-pool",
 	.features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
 		    DM_TARGET_IMMUTABLE,
-	.version = {1, 6, 0},
+	.version = {1, 6, 1},
 	.module = THIS_MODULE,
 	.ctr = pool_ctr,
 	.dtr = pool_dtr,
···
 	if (r)
 		goto bad_thin_open;
 
-	ti->num_flush_requests = 1;
+	ti->num_flush_bios = 1;
 	ti->flush_supported = true;
 	ti->per_bio_data_size = sizeof(struct dm_thin_endio_hook);
 
 	/* In case the pool supports discards, pass them on. */
 	if (tc->pool->pf.discard_enabled) {
 		ti->discards_supported = true;
-		ti->num_discard_requests = 1;
+		ti->num_discard_bios = 1;
 		ti->discard_zeroes_data_unsupported = true;
-		/* Discard requests must be split on a block boundary */
-		ti->split_discard_requests = true;
+		/* Discard bios must be split on a block boundary */
+		ti->split_discard_bios = true;
 	}
 
 	dm_put(pool_md);
···
 /*
  * <nr mapped sectors> <highest mapped sector>
  */
-static int thin_status(struct dm_target *ti, status_type_t type,
-		       unsigned status_flags, char *result, unsigned maxlen)
+static void thin_status(struct dm_target *ti, status_type_t type,
+			unsigned status_flags, char *result, unsigned maxlen)
 {
 	int r;
 	ssize_t sz = 0;
···
 
 	if (get_pool_mode(tc->pool) == PM_FAIL) {
 		DMEMIT("Fail");
-		return 0;
+		return;
 	}
 
 	if (!tc->td)
···
 		switch (type) {
 		case STATUSTYPE_INFO:
 			r = dm_thin_get_mapped_count(tc->td, &mapped);
-			if (r)
-				return r;
+			if (r) {
+				DMERR("dm_thin_get_mapped_count returned %d", r);
+				goto err;
+			}
 
 			r = dm_thin_get_highest_mapped_block(tc->td, &highest);
-			if (r < 0)
-				return r;
+			if (r < 0) {
+				DMERR("dm_thin_get_highest_mapped_block returned %d", r);
+				goto err;
+			}
 
 			DMEMIT("%llu ", mapped * tc->pool->sectors_per_block);
 			if (r)
···
 		}
 	}
 
-	return 0;
+	return;
+
+err:
+	DMEMIT("Error");
 }
 
 static int thin_iterate_devices(struct dm_target *ti,
···
 
 static struct target_type thin_target = {
 	.name = "thin",
-	.version = {1, 7, 0},
+	.version = {1, 7, 1},
 	.module	= THIS_MODULE,
 	.ctr = thin_ctr,
 	.dtr = thin_dtr,

drivers/md/dm-verity.c

···
 /*
  * Status: V (valid) or C (corruption found)
  */
-static int verity_status(struct dm_target *ti, status_type_t type,
-			 unsigned status_flags, char *result, unsigned maxlen)
+static void verity_status(struct dm_target *ti, status_type_t type,
+			  unsigned status_flags, char *result, unsigned maxlen)
 {
 	struct dm_verity *v = ti->private;
 	unsigned sz = 0;
···
 				DMEMIT("%02x", v->salt[x]);
 		break;
 	}
-
-	return 0;
 }
 
 static int verity_ioctl(struct dm_target *ti, unsigned cmd,
···
 
 static struct target_type verity_target = {
 	.name		= "verity",
-	.version	= {1, 1, 0},
+	.version	= {1, 1, 1},
 	.module		= THIS_MODULE,
 	.ctr		= verity_ctr,
 	.dtr		= verity_dtr,

drivers/md/dm-zero.c

···
 	/*
 	 * Silently drop discards, avoiding -EOPNOTSUPP.
 	 */
-	ti->num_discard_requests = 1;
+	ti->num_discard_bios = 1;
 
 	return 0;
 }

drivers/md/dm.c

···
 	 * io objects are allocated from here.
 	 */
 	mempool_t *io_pool;
-	mempool_t *tio_pool;
 
 	struct bio_set *bs;
 
···
  */
 struct dm_md_mempools {
 	mempool_t *io_pool;
-	mempool_t *tio_pool;
 	struct bio_set *bs;
 };
 
 #define MIN_IOS 256
 static struct kmem_cache *_io_cache;
 static struct kmem_cache *_rq_tio_cache;
-
-/*
- * Unused now, and needs to be deleted. But since io_pool is overloaded and it's
- * still used for _io_cache, I'm leaving this for a later cleanup
- */
-static struct kmem_cache *_rq_bio_info_cache;
 
 static int __init local_init(void)
 {
···
 	if (!_rq_tio_cache)
 		goto out_free_io_cache;
 
-	_rq_bio_info_cache = KMEM_CACHE(dm_rq_clone_bio_info, 0);
-	if (!_rq_bio_info_cache)
-		goto out_free_rq_tio_cache;
-
 	r = dm_uevent_init();
 	if (r)
-		goto out_free_rq_bio_info_cache;
+		goto out_free_rq_tio_cache;
 
 	_major = major;
 	r = register_blkdev(_major, _name);
···
 
 out_uevent_exit:
 	dm_uevent_exit();
-out_free_rq_bio_info_cache:
-	kmem_cache_destroy(_rq_bio_info_cache);
 out_free_rq_tio_cache:
 	kmem_cache_destroy(_rq_tio_cache);
 out_free_io_cache:
···
 
 static void local_exit(void)
 {
-	kmem_cache_destroy(_rq_bio_info_cache);
 	kmem_cache_destroy(_rq_tio_cache);
 	kmem_cache_destroy(_io_cache);
 	unregister_blkdev(_major, _name);
···
 static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md,
 					    gfp_t gfp_mask)
 {
-	return mempool_alloc(md->tio_pool, gfp_mask);
+	return mempool_alloc(md->io_pool, gfp_mask);
 }
 
 static void free_rq_tio(struct dm_rq_target_io *tio)
 {
-	mempool_free(tio, tio->md->tio_pool);
+	mempool_free(tio, tio->md->io_pool);
 }
 
 static int md_in_flight(struct mapped_device *md)
···
 }
 EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);
 
-static void __map_bio(struct dm_target *ti, struct dm_target_io *tio)
+static void __map_bio(struct dm_target_io *tio)
 {
 	int r;
 	sector_t sector;
 	struct mapped_device *md;
 	struct bio *clone = &tio->clone;
+	struct dm_target *ti = tio->ti;
 
 	clone->bi_end_io = clone_endio;
 	clone->bi_private = tio;
···
 	unsigned short idx;
 };
 
+static void bio_setup_sector(struct bio *bio, sector_t sector, sector_t len)
+{
+	bio->bi_sector = sector;
+	bio->bi_size = to_bytes(len);
+}
+
+static void bio_setup_bv(struct bio *bio, unsigned short idx, unsigned short bv_count)
+{
+	bio->bi_idx = idx;
+	bio->bi_vcnt = idx + bv_count;
+	bio->bi_flags &= ~(1 << BIO_SEG_VALID);
+}
+
+static void clone_bio_integrity(struct bio *bio, struct bio *clone,
+				unsigned short idx, unsigned len, unsigned offset,
+				unsigned trim)
+{
+	if (!bio_integrity(bio))
+		return;
+
+	bio_integrity_clone(clone, bio, GFP_NOIO);
+
+	if (trim)
+		bio_integrity_trim(clone, bio_sector_offset(bio, idx, offset), len);
+}
+
 /*
  * Creates a little bio that just does part of a bvec.
  */
-static void split_bvec(struct dm_target_io *tio, struct bio *bio,
-		       sector_t sector, unsigned short idx, unsigned int offset,
-		       unsigned int len, struct bio_set *bs)
+static void clone_split_bio(struct dm_target_io *tio, struct bio *bio,
+			    sector_t sector, unsigned short idx,
+			    unsigned offset, unsigned len)
 {
 	struct bio *clone = &tio->clone;
 	struct bio_vec *bv = bio->bi_io_vec + idx;
 
 	*clone->bi_io_vec = *bv;
 
-	clone->bi_sector = sector;
+	bio_setup_sector(clone, sector, len);
+
 	clone->bi_bdev = bio->bi_bdev;
 	clone->bi_rw = bio->bi_rw;
 	clone->bi_vcnt = 1;
-	clone->bi_size = to_bytes(len);
 	clone->bi_io_vec->bv_offset = offset;
 	clone->bi_io_vec->bv_len = clone->bi_size;
 	clone->bi_flags |= 1 << BIO_CLONED;
 
-	if (bio_integrity(bio)) {
-		bio_integrity_clone(clone, bio, GFP_NOIO);
-		bio_integrity_trim(clone,
-				   bio_sector_offset(bio, idx, offset), len);
-	}
+	clone_bio_integrity(bio, clone, idx, len, offset, 1);
 }
 
 /*
···
  */
 static void clone_bio(struct dm_target_io *tio, struct bio *bio,
 		      sector_t sector, unsigned short idx,
-		      unsigned short bv_count, unsigned int len,
-		      struct bio_set *bs)
+		      unsigned short bv_count, unsigned len)
 {
 	struct bio *clone = &tio->clone;
+	unsigned trim = 0;
 
 	__bio_clone(clone, bio);
-	clone->bi_sector = sector;
-	clone->bi_idx = idx;
-	clone->bi_vcnt = idx + bv_count;
-	clone->bi_size = to_bytes(len);
-	clone->bi_flags &= ~(1 << BIO_SEG_VALID);
+	bio_setup_sector(clone, sector, len);
+	bio_setup_bv(clone, idx, bv_count);
 
-	if (bio_integrity(bio)) {
-		bio_integrity_clone(clone, bio, GFP_NOIO);
-
-		if (idx != bio->bi_idx || clone->bi_size < bio->bi_size)
-			bio_integrity_trim(clone,
-					   bio_sector_offset(bio, idx, 0), len);
-	}
+	if (idx != bio->bi_idx || clone->bi_size < bio->bi_size)
+		trim = 1;
+	clone_bio_integrity(bio, clone, idx, len, 0, trim);
 }
 
 static struct dm_target_io *alloc_tio(struct clone_info *ci,
-				      struct dm_target *ti, int nr_iovecs)
+				      struct dm_target *ti, int nr_iovecs,
+				      unsigned target_bio_nr)
 {
 	struct dm_target_io *tio;
 	struct bio *clone;
···
 	tio->io = ci->io;
 	tio->ti = ti;
 	memset(&tio->info, 0, sizeof(tio->info));
-	tio->target_request_nr = 0;
+	tio->target_bio_nr = target_bio_nr;
 
 	return tio;
 }
 
-static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
-				   unsigned request_nr, sector_t len)
+static void __clone_and_map_simple_bio(struct clone_info *ci,
+				       struct dm_target *ti,
+				       unsigned target_bio_nr, sector_t len)
 {
-	struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs);
+	struct dm_target_io *tio = alloc_tio(ci, ti, ci->bio->bi_max_vecs, target_bio_nr);
 	struct bio *clone = &tio->clone;
-
-	tio->target_request_nr = request_nr;
 
 	/*
 	 * Discard requests require the bio's inline iovecs be initialized.
 	 * ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
 	 * and discard, so no need for concern about wasted bvec allocations.
 	 */
-
 	 __bio_clone(clone, ci->bio);
-	if (len) {
-		clone->bi_sector = ci->sector;
-		clone->bi_size = to_bytes(len);
-	}
+	if (len)
+		bio_setup_sector(clone, ci->sector, len);
 
-	__map_bio(ti, tio);
+	__map_bio(tio);
 }
 
-static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
-				    unsigned num_requests, sector_t len)
+static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
+				  unsigned num_bios, sector_t len)
 {
-	unsigned request_nr;
+	unsigned target_bio_nr;
 
-	for (request_nr = 0; request_nr < num_requests; request_nr++)
-		__issue_target_request(ci, ti, request_nr, len);
+	for (target_bio_nr = 0; target_bio_nr < num_bios; target_bio_nr++)
+		__clone_and_map_simple_bio(ci, ti, target_bio_nr, len);
 }
 
-static int __clone_and_map_empty_flush(struct clone_info *ci)
+static int __send_empty_flush(struct clone_info *ci)
 {
 	unsigned target_nr = 0;
 	struct dm_target *ti;
 
 	BUG_ON(bio_has_data(ci->bio));
 	while ((ti = dm_table_get_target(ci->map, target_nr++)))
-		__issue_target_requests(ci, ti, ti->num_flush_requests, 0);
+		__send_duplicate_bios(ci, ti, ti->num_flush_bios, 0);
 
 	return 0;
 }
 
-/*
- * Perform all io with a single clone.
- */
-static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
+static void __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
+				     sector_t sector, int nr_iovecs,
+				     unsigned short idx, unsigned short bv_count,
+				     unsigned offset, unsigned len,
+				     unsigned split_bvec)
 {
 	struct bio *bio = ci->bio;
 	struct dm_target_io *tio;
+	unsigned target_bio_nr;
+	unsigned num_target_bios = 1;
 
-	tio = alloc_tio(ci, ti, bio->bi_max_vecs);
-	clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,
-		  ci->sector_count, ci->md->bs);
-	__map_bio(ti, tio);
-	ci->sector_count = 0;
+	/*
+	 * Does the target want to receive duplicate copies of the bio?
+	 */
+	if (bio_data_dir(bio) == WRITE && ti->num_write_bios)
+		num_target_bios = ti->num_write_bios(ti, bio);
+
+	for (target_bio_nr = 0; target_bio_nr < num_target_bios; target_bio_nr++) {
+		tio = alloc_tio(ci, ti, nr_iovecs, target_bio_nr);
+		if (split_bvec)
+			clone_split_bio(tio, bio, sector, idx, offset, len);
+		else
+			clone_bio(tio, bio, sector, idx, bv_count, len);
+		__map_bio(tio);
+	}
 }
 
-typedef unsigned (*get_num_requests_fn)(struct dm_target *ti);
+typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);
 
-static unsigned get_num_discard_requests(struct dm_target *ti)
+static unsigned get_num_discard_bios(struct dm_target *ti)
 {
-	return ti->num_discard_requests;
+	return ti->num_discard_bios;
 }
 
-static unsigned get_num_write_same_requests(struct dm_target *ti)
+static unsigned get_num_write_same_bios(struct dm_target *ti)
 {
-	return ti->num_write_same_requests;
+	return ti->num_write_same_bios;
 }
 
 typedef bool (*is_split_required_fn)(struct dm_target *ti);
 
 static bool is_split_required_for_discard(struct dm_target *ti)
 {
-	return ti->split_discard_requests;
+	return ti->split_discard_bios;
 }
 
-static int __clone_and_map_changing_extent_only(struct clone_info *ci,
-						get_num_requests_fn get_num_requests,
-						is_split_required_fn is_split_required)
+static int __send_changing_extent_only(struct clone_info *ci,
+				       get_num_bios_fn get_num_bios,
+				       is_split_required_fn is_split_required)
 {
 	struct dm_target *ti;
 	sector_t len;
-	unsigned num_requests;
+	unsigned num_bios;
 
 	do {
 		ti = dm_table_find_target(ci->map, ci->sector);
···
 		 * reconfiguration might also have changed that since the
 		 * check was performed.
 		 */
-		num_requests = get_num_requests ? get_num_requests(ti) : 0;
-		if (!num_requests)
+		num_bios = get_num_bios ? get_num_bios(ti) : 0;
+		if (!num_bios)
 			return -EOPNOTSUPP;
 
 		if (is_split_required && !is_split_required(ti))
···
 		else
 			len = min(ci->sector_count, max_io_len(ci->sector, ti));
 
-		__issue_target_requests(ci, ti, num_requests, len);
+		__send_duplicate_bios(ci, ti, num_bios, len);
 
 		ci->sector += len;
 	} while (ci->sector_count -= len);
···
 	return 0;
 }
 
-static int __clone_and_map_discard(struct clone_info *ci)
+static int __send_discard(struct clone_info *ci)
 {
-	return __clone_and_map_changing_extent_only(ci, get_num_discard_requests,
-						    is_split_required_for_discard);
+	return __send_changing_extent_only(ci, get_num_discard_bios,
+					   is_split_required_for_discard);
 }
 
-static int __clone_and_map_write_same(struct clone_info *ci)
+static int __send_write_same(struct clone_info *ci)
 {
-	return __clone_and_map_changing_extent_only(ci, get_num_write_same_requests, NULL);
+	return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);
 }
 
-static int __clone_and_map(struct clone_info *ci)
+/*
+ * Find maximum number of sectors / bvecs we can process with a single bio.
+ */
+static sector_t __len_within_target(struct clone_info *ci, sector_t max, int *idx)
+{
+	struct bio *bio = ci->bio;
+	sector_t bv_len, total_len = 0;
+
+	for (*idx = ci->idx; max && (*idx < bio->bi_vcnt); (*idx)++) {
+		bv_len = to_sector(bio->bi_io_vec[*idx].bv_len);
+
+		if (bv_len > max)
+			break;
+
+		max -= bv_len;
+		total_len += bv_len;
+	}
+
+	return total_len;
+}
+
+static int __split_bvec_across_targets(struct clone_info *ci,
+				       struct dm_target *ti, sector_t max)
+{
+	struct bio *bio = ci->bio;
+	struct bio_vec *bv = bio->bi_io_vec + ci->idx;
+	sector_t remaining = to_sector(bv->bv_len);
+	unsigned offset = 0;
+	sector_t len;
+
+	do {
+		if (offset) {
+			ti = dm_table_find_target(ci->map, ci->sector);
+			if (!dm_target_is_valid(ti))
+				return -EIO;
+
+			max = max_io_len(ci->sector, ti);
+		}
+
+		len = min(remaining, max);
+
+		__clone_and_map_data_bio(ci, ti, ci->sector, 1, ci->idx, 0,
+					 bv->bv_offset + offset, len, 1);
+
+		ci->sector += len;
+		ci->sector_count -= len;
+		offset += to_bytes(len);
+	} while (remaining -= len);
+
+	ci->idx++;
+
+	return 0;
+}
+
+/*
+ * Select the correct strategy for processing a non-flush bio.
+ */
+static int __split_and_process_non_flush(struct clone_info *ci)
 {
 	struct bio *bio = ci->bio;
 	struct dm_target *ti;
-	sector_t len = 0, max;
-	struct dm_target_io *tio;
+	sector_t len, max;
+	int idx;
 
 	if (unlikely(bio->bi_rw & REQ_DISCARD))
-		return __clone_and_map_discard(ci);
+		return __send_discard(ci);
 	else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))
-		return __clone_and_map_write_same(ci);
+		return __send_write_same(ci);
 
 	ti = dm_table_find_target(ci->map, ci->sector);
 	if (!dm_target_is_valid(ti))
···
 
 	max = max_io_len(ci->sector, ti);
 
+	/*
+	 * Optimise for the simple case where we can do all of
+	 * the remaining io with a single clone.
+	 */
 	if (ci->sector_count <= max) {
-		/*
-		 * Optimise for the simple case where we can do all of
-		 * the remaining io with a single clone.
-		 */
-		__clone_and_map_simple(ci, ti);
+		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
+					 ci->idx, bio->bi_vcnt - ci->idx, 0,
+					 ci->sector_count, 0);
+		ci->sector_count = 0;
+		return 0;
+	}
 
-	} else if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
-		/*
-		 * There are some bvecs that don't span targets.
-		 * Do as many of these as possible.
-		 */
-		int i;
-		sector_t remaining = max;
-		sector_t bv_len;
+	/*
+	 * There are some bvecs that don't span targets.
+	 * Do as many of these as possible.
+	 */
+	if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {
+		len = __len_within_target(ci, max, &idx);
 
-		for (i = ci->idx; remaining && (i < bio->bi_vcnt); i++) {
-			bv_len = to_sector(bio->bi_io_vec[i].bv_len);
-
-			if (bv_len > remaining)
-				break;
-
-			remaining -= bv_len;
-			len += bv_len;
-		}
-
-		tio = alloc_tio(ci, ti, bio->bi_max_vecs);
-		clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len,
-			  ci->md->bs);
-		__map_bio(ti, tio);
+		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,
+					 ci->idx, idx - ci->idx, 0, len, 0);
 
 		ci->sector += len;
 		ci->sector_count -= len;
-		ci->idx = i;
+		ci->idx = idx;
 
-	} else {
-		/*
-		 * Handle a bvec that must be split between two or more targets.
-		 */
-		struct bio_vec *bv = bio->bi_io_vec + ci->idx;
-		sector_t remaining = to_sector(bv->bv_len);
-		unsigned int offset = 0;
-
-		do {
-			if (offset) {
-				ti = dm_table_find_target(ci->map, ci->sector);
-				if (!dm_target_is_valid(ti))
-					return -EIO;
-
-				max = max_io_len(ci->sector, ti);
-			}
-
-			len = min(remaining, max);
-
-			tio = alloc_tio(ci, ti, 1);
-			split_bvec(tio, bio, ci->sector, ci->idx,
-				   bv->bv_offset + offset, len, ci->md->bs);
-
-			__map_bio(ti, tio);
-
-			ci->sector += len;
-			ci->sector_count -= len;
-			offset += to_bytes(len);
-		} while (remaining -= len);
-
-		ci->idx++;
+		return 0;
 	}
 
-	return 0;
+	/*
+	 * Handle a bvec that must be split between two or more targets.
+	 */
+	return __split_bvec_across_targets(ci, ti, max);
 }
 
 /*
- * Split the bio into several clones and submit it to targets.
+ * Entry point to split a bio into clones and submit them to the targets.
  */
 static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
 {
···
 	ci.idx = bio->bi_idx;
 
 	start_io_acct(ci.io);
+
 	if (bio->bi_rw & REQ_FLUSH) {
 		ci.bio = &ci.md->flush_bio;
 		ci.sector_count = 0;
-		error = __clone_and_map_empty_flush(&ci);
+		error = __send_empty_flush(&ci);
 		/* dec_pending submits any data associated with flush */
 	} else {
 		ci.bio = bio;
 		ci.sector_count = bio_sectors(bio);
 		while (ci.sector_count && !error)
-			error = __clone_and_map(&ci);
+			error = __split_and_process_non_flush(&ci);
 	}
 
 	/* drop the extra reference count */
···
 	unlock_fs(md);
 	bdput(md->bdev);
 	destroy_workqueue(md->wq);
-	if (md->tio_pool)
-		mempool_destroy(md->tio_pool);
 	if (md->io_pool)
 		mempool_destroy(md->io_pool);
 	if (md->bs)
···
 {
 	struct dm_md_mempools *p = dm_table_get_md_mempools(t);
 
-	if (md->io_pool && (md->tio_pool || dm_table_get_type(t) == DM_TYPE_BIO_BASED) && md->bs) {
-		/*
-		 * The md already has necessary mempools. Reload just the
-		 * bioset because front_pad may have changed because
-		 * a different table was loaded.
-		 */
-		bioset_free(md->bs);
-		md->bs = p->bs;
-		p->bs = NULL;
+	if (md->io_pool && md->bs) {
+		/* The md already has necessary mempools. */
+		if (dm_table_get_type(t) == DM_TYPE_BIO_BASED) {
+			/*
+			 * Reload bioset because front_pad may have changed
+			 * because a different table was loaded.
+			 */
+			bioset_free(md->bs);
+			md->bs = p->bs;
+			p->bs = NULL;
+		} else if (dm_table_get_type(t) == DM_TYPE_REQUEST_BASED) {
+			/*
+			 * There's no need to reload with request-based dm
+			 * because the size of front_pad doesn't change.
+			 * Note for future: If you are to reload bioset,
+			 * prep-ed requests in the queue may refer
+			 * to bio from the old bioset, so you must walk
+			 * through the queue to unprep.
+			 */
+		}
 		goto out;
 	}
 
-	BUG_ON(!p || md->io_pool || md->tio_pool || md->bs);
+	BUG_ON(!p || md->io_pool || md->bs);
 
 	md->io_pool = p->io_pool;
 	p->io_pool = NULL;
-	md->tio_pool = p->tio_pool;
-	p->tio_pool = NULL;
 	md->bs = p->bs;
 	p->bs = NULL;
 
···
  */
 struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
 {
-	struct dm_table *live_map, *map = ERR_PTR(-EINVAL);
+	struct dm_table *live_map = NULL, *map = ERR_PTR(-EINVAL);
 	struct queue_limits limits;
 	int r;
 
···
 		dm_table_put(live_map);
 	}
 
-	r = dm_calculate_queue_limits(table, &limits);
-	if (r) {
-		map = ERR_PTR(r);
-		goto out;
+	if (!live_map) {
+		r = dm_calculate_queue_limits(table, &limits);
+		if (r) {
+			map = ERR_PTR(r);
+			goto out;
+		}
 	}
 
 	map = __bind(md, table, &limits);
···
 
 struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity, unsigned per_bio_data_size)
 {
-	struct dm_md_mempools *pools = kmalloc(sizeof(*pools), GFP_KERNEL);
-	unsigned int pool_size = (type == DM_TYPE_BIO_BASED) ? 16 : MIN_IOS;
+	struct dm_md_mempools *pools = kzalloc(sizeof(*pools), GFP_KERNEL);
+	struct kmem_cache *cachep;
+	unsigned int pool_size;
+	unsigned int front_pad;
 
 	if (!pools)
 		return NULL;
 
-	per_bio_data_size = roundup(per_bio_data_size, __alignof__(struct dm_target_io));
+	if (type == DM_TYPE_BIO_BASED) {
+		cachep = _io_cache;
+		pool_size = 16;
+		front_pad = roundup(per_bio_data_size, __alignof__(struct dm_target_io)) + offsetof(struct dm_target_io, clone);
+	} else if (type == DM_TYPE_REQUEST_BASED) {
+		cachep = _rq_tio_cache;
+		pool_size = MIN_IOS;
+		front_pad = offsetof(struct dm_rq_clone_bio_info, clone);
+		/* per_bio_data_size is not used. See __bind_mempools(). */
+		WARN_ON(per_bio_data_size != 0);
+	} else
+		goto out;
 
-	pools->io_pool = (type == DM_TYPE_BIO_BASED) ?
-			 mempool_create_slab_pool(MIN_IOS, _io_cache) :
-			 mempool_create_slab_pool(MIN_IOS, _rq_bio_info_cache);
+	pools->io_pool = mempool_create_slab_pool(MIN_IOS, cachep);
 	if (!pools->io_pool)
-		goto free_pools_and_out;
+		goto out;
 
-	pools->tio_pool = NULL;
-	if (type == DM_TYPE_REQUEST_BASED) {
-		pools->tio_pool = mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
-		if (!pools->tio_pool)
-			goto free_io_pool_and_out;
-	}
-
-	pools->bs = (type == DM_TYPE_BIO_BASED) ?
-		bioset_create(pool_size,
-			      per_bio_data_size + offsetof(struct dm_target_io, clone)) :
-		bioset_create(pool_size,
-			      offsetof(struct dm_rq_clone_bio_info, clone));
+	pools->bs = bioset_create(pool_size, front_pad);
 	if (!pools->bs)
-		goto free_tio_pool_and_out;
+		goto out;
 
 	if (integrity && bioset_integrity_create(pools->bs, pool_size))
-		goto free_bioset_and_out;
+		goto out;
 
 	return pools;
 
-free_bioset_and_out:
-	bioset_free(pools->bs);
-
-free_tio_pool_and_out:
-	if (pools->tio_pool)
-		mempool_destroy(pools->tio_pool);
-
-free_io_pool_and_out:
-	mempool_destroy(pools->io_pool);
-
-free_pools_and_out:
-	kfree(pools);
+out:
+	dm_free_md_mempools(pools);
 
 	return NULL;
 }
···
 
 	if (pools->io_pool)
 		mempool_destroy(pools->io_pool);
-
-	if (pools->tio_pool)
-		mempool_destroy(pools->tio_pool);
 
 	if (pools->bs)
 		bioset_free(pools->bs);

drivers/md/persistent-data/Kconfig

···
 config DM_PERSISTENT_DATA
        tristate
-       depends on BLK_DEV_DM && EXPERIMENTAL
+       depends on BLK_DEV_DM
        select LIBCRC32C
        select DM_BUFIO
        ---help---

drivers/md/persistent-data/Makefile

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

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

···
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-array.h"
+#include "dm-space-map.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/export.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "array"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The array is implemented as a fully populated btree, which points to
+ * blocks that contain the packed values.  This is more space efficient
+ * than just using a btree since we don't store 1 key per value.
+ */
+struct array_block {
+	__le32 csum;
+	__le32 max_entries;
+	__le32 nr_entries;
+	__le32 value_size;
+	__le64 blocknr; /* Block this node is supposed to live in. */
+} __packed;
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Validator methods.  As usual we calculate a checksum, and also write the
+ * block location into the header (paranoia about ssds remapping areas by
+ * mistake).
+ */
+#define CSUM_XOR 595846735
+
+static void array_block_prepare_for_write(struct dm_block_validator *v,
+					  struct dm_block *b,
+					  size_t size_of_block)
+{
+	struct array_block *bh_le = dm_block_data(b);
+
+	bh_le->blocknr = cpu_to_le64(dm_block_location(b));
+	bh_le->csum = cpu_to_le32(dm_bm_checksum(&bh_le->max_entries,
+						 size_of_block - sizeof(__le32),
+						 CSUM_XOR));
+}
+
+static int array_block_check(struct dm_block_validator *v,
+			     struct dm_block *b,
+			     size_t size_of_block)
+{
+	struct array_block *bh_le = dm_block_data(b);
+	__le32 csum_disk;
+
+	if (dm_block_location(b) != le64_to_cpu(bh_le->blocknr)) {
+		DMERR_LIMIT("array_block_check failed: blocknr %llu != wanted %llu",
+			    (unsigned long long) le64_to_cpu(bh_le->blocknr),
+			    (unsigned long long) dm_block_location(b));
+		return -ENOTBLK;
+	}
+
+	csum_disk = cpu_to_le32(dm_bm_checksum(&bh_le->max_entries,
+					       size_of_block - sizeof(__le32),
+					       CSUM_XOR));
+	if (csum_disk != bh_le->csum) {
+		DMERR_LIMIT("array_block_check failed: csum %u != wanted %u",
+			    (unsigned) le32_to_cpu(csum_disk),
+			    (unsigned) le32_to_cpu(bh_le->csum));
+		return -EILSEQ;
+	}
+
+	return 0;
+}
+
+static struct dm_block_validator array_validator = {
+	.name = "array",
+	.prepare_for_write = array_block_prepare_for_write,
+	.check = array_block_check
+};
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Functions for manipulating the array blocks.
+ */
+
+/*
+ * Returns a pointer to a value within an array block.
+ *
+ * index - The index into _this_ specific block.
+ */
+static void *element_at(struct dm_array_info *info, struct array_block *ab,
+			unsigned index)
+{
+	unsigned char *entry = (unsigned char *) (ab + 1);
+
+	entry += index * info->value_type.size;
+
+	return entry;
+}
+
+/*
+ * Utility function that calls one of the value_type methods on every value
+ * in an array block.
+ */
+static void on_entries(struct dm_array_info *info, struct array_block *ab,
+		       void (*fn)(void *, const void *))
+{
+	unsigned i, nr_entries = le32_to_cpu(ab->nr_entries);
+
+	for (i = 0; i < nr_entries; i++)
+		fn(info->value_type.context, element_at(info, ab, i));
+}
+
+/*
+ * Increment every value in an array block.
+ */
+static void inc_ablock_entries(struct dm_array_info *info, struct array_block *ab)
+{
+	struct dm_btree_value_type *vt = &info->value_type;
+
+	if (vt->inc)
+		on_entries(info, ab, vt->inc);
+}
+
+/*
+ * Decrement every value in an array block.
+ */
+static void dec_ablock_entries(struct dm_array_info *info, struct array_block *ab)
+{
+	struct dm_btree_value_type *vt = &info->value_type;
+
+	if (vt->dec)
+		on_entries(info, ab, vt->dec);
+}
+
+/*
+ * Each array block can hold this many values.
+ */
+static uint32_t calc_max_entries(size_t value_size, size_t size_of_block)
+{
+	return (size_of_block - sizeof(struct array_block)) / value_size;
+}
+
+/*
+ * Allocate a new array block.  The caller will need to unlock block.
+ */
+static int alloc_ablock(struct dm_array_info *info, size_t size_of_block,
+			uint32_t max_entries,
+			struct dm_block **block, struct array_block **ab)
+{
+	int r;
+
+	r = dm_tm_new_block(info->btree_info.tm, &array_validator, block);
+	if (r)
+		return r;
+
+	(*ab) = dm_block_data(*block);
+	(*ab)->max_entries = cpu_to_le32(max_entries);
+	(*ab)->nr_entries = cpu_to_le32(0);
+	(*ab)->value_size = cpu_to_le32(info->value_type.size);
+
+	return 0;
+}
+
+/*
+ * Pad an array block out with a particular value.  Every instance will
+ * cause an increment of the value_type.  new_nr must always be more than
+ * the current number of entries.
+ */
+static void fill_ablock(struct dm_array_info *info, struct array_block *ab,
+			const void *value, unsigned new_nr)
+{
+	unsigned i;
+	uint32_t nr_entries;
+	struct dm_btree_value_type *vt = &info->value_type;
+
+	BUG_ON(new_nr > le32_to_cpu(ab->max_entries));
+	BUG_ON(new_nr < le32_to_cpu(ab->nr_entries));
+
+	nr_entries = le32_to_cpu(ab->nr_entries);
+	for (i = nr_entries; i < new_nr; i++) {
+		if (vt->inc)
+			vt->inc(vt->context, value);
+		memcpy(element_at(info, ab, i), value, vt->size);
+	}
+	ab->nr_entries = cpu_to_le32(new_nr);
+}
+
+/*
+ * Remove some entries from the back of an array block.  Every value
+ * removed will be decremented.  new_nr must be <= the current number of
+ * entries.
+ */
+static void trim_ablock(struct dm_array_info *info, struct array_block *ab,
+			unsigned new_nr)
+{
+	unsigned i;
+	uint32_t nr_entries;
+	struct dm_btree_value_type *vt = &info->value_type;
+
+	BUG_ON(new_nr > le32_to_cpu(ab->max_entries));
+	BUG_ON(new_nr > le32_to_cpu(ab->nr_entries));
+
+	nr_entries = le32_to_cpu(ab->nr_entries);
+	for (i = nr_entries; i > new_nr; i--)
+		if (vt->dec)
+			vt->dec(vt->context, element_at(info, ab, i - 1));
+	ab->nr_entries = cpu_to_le32(new_nr);
+}
+
+/*
+ * Read locks a block, and coerces it to an array block.  The caller must
+ * unlock 'block' when finished.
+ */
+static int get_ablock(struct dm_array_info *info, dm_block_t b,
+		      struct dm_block **block, struct array_block **ab)
+{
+	int r;
+
+	r = dm_tm_read_lock(info->btree_info.tm, b, &array_validator, block);
+	if (r)
+		return r;
+
+	*ab = dm_block_data(*block);
+	return 0;
+}
+
+/*
+ * Unlocks an array block.
+ */
+static int unlock_ablock(struct dm_array_info *info, struct dm_block *block)
+{
+	return dm_tm_unlock(info->btree_info.tm, block);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * Btree manipulation.
+ */
+
+/*
+ * Looks up an array block in the btree, and then read locks it.
+ *
+ * index is the index of the index of the array_block, (ie. the array index
+ * / max_entries).
+ */
+static int lookup_ablock(struct dm_array_info *info, dm_block_t root,
+			 unsigned index, struct dm_block **block,
+			 struct array_block **ab)
+{
+	int r;
+	uint64_t key = index;
+	__le64 block_le;
+
+	r = dm_btree_lookup(&info->btree_info, root, &key, &block_le);
+	if (r)
+		return r;
+
+	return get_ablock(info, le64_to_cpu(block_le), block, ab);
+}
+
+/*
+ * Insert an array block into the btree.  The block is _not_ unlocked.
+ */
+static int insert_ablock(struct dm_array_info *info, uint64_t index,
+			 struct dm_block *block, dm_block_t *root)
+{
+	__le64 block_le = cpu_to_le64(dm_block_location(block));
+
+	__dm_bless_for_disk(block_le);
+	return dm_btree_insert(&info->btree_info, *root, &index, &block_le, root);
+}
+
+/*
+ * Looks up an array block in the btree.  Then shadows it, and updates the
+ * btree to point to this new shadow.  'root' is an input/output parameter
+ * for both the current root block, and the new one.
+ */
+static int shadow_ablock(struct dm_array_info *info, dm_block_t *root,
+			 unsigned index, struct dm_block **block,
+			 struct array_block **ab)
+{
+	int r, inc;
+	uint64_t key = index;
+	dm_block_t b;
+	__le64 block_le;
+
+	/*
+	 * lookup
+	 */
+	r = dm_btree_lookup(&info->btree_info, *root, &key, &block_le);
+	if (r)
+		return r;
+	b = le64_to_cpu(block_le);
+
+	/*
+	 * shadow
+	 */
+	r = dm_tm_shadow_block(info->btree_info.tm, b,
+			       &array_validator, block, &inc);
+	if (r)
+		return r;
+
+	*ab = dm_block_data(*block);
+	if (inc)
+		inc_ablock_entries(info, *ab);
+
+	/*
+	 * Reinsert.
+	 *
+	 * The shadow op will often be a noop.  Only insert if it really
+	 * copied data.
+	 */
+	if (dm_block_location(*block) != b)
+		r = insert_ablock(info, index, *block, root);
+
+	return r;
+}
+
+/*
+ * Allocate an new array block, and fill it with some values.
+ */
+static int insert_new_ablock(struct dm_array_info *info, size_t size_of_block,
+			     uint32_t max_entries,
+			     unsigned block_index, uint32_t nr,
+			     const void *value, dm_block_t *root)
+{
+	int r;
+	struct dm_block *block;
+	struct array_block *ab;
+
+	r = alloc_ablock(info, size_of_block, max_entries, &block, &ab);
+	if (r)
+		return r;
+
+	fill_ablock(info, ab, value, nr);
+	r = insert_ablock(info, block_index, block, root);
+	unlock_ablock(info, block);
+
+	return r;
+}
+
+static int insert_full_ablocks(struct dm_array_info *info, size_t size_of_block,
+			       unsigned begin_block, unsigned end_block,
+			       unsigned max_entries, const void *value,
+			       dm_block_t *root)
+{
+	int r = 0;
+
+	for (; !r && begin_block != end_block; begin_block++)
+		r = insert_new_ablock(info, size_of_block, max_entries, begin_block, max_entries, value, root);
+
+	return r;
+}
+
+/*
+ * There are a bunch of functions involved with resizing an array.  This
+ * structure holds information that commonly needed by them.  Purely here
+ * to reduce parameter count.
+ */
+struct resize {
+	/*
+	 * Describes the array.
+	 */
+	struct dm_array_info *info;
+
+	/*
+	 * The current root of the array.  This gets updated.
+	 */
+	dm_block_t root;
+
+	/*
+	 * Metadata block size.  Used to calculate the nr entries in an
+	 * array block.
+	 */
+	size_t size_of_block;
+
+	/*
+	 * Maximum nr entries in an array block.
+	 */
+	unsigned max_entries;
+
+	/*
+	 * nr of completely full blocks in the array.
+	 *
+	 * 'old' refers to before the resize, 'new' after.
+	 */
+	unsigned old_nr_full_blocks, new_nr_full_blocks;
+
+	/*
+	 * Number of entries in the final block.  0 iff only full blocks in
+	 * the array.
+	 */
+	unsigned old_nr_entries_in_last_block, new_nr_entries_in_last_block;
+
+	/*
+	 * The default value used when growing the array.
+	 */
+	const void *value;
+};
+
+/*
+ * Removes a consecutive set of array blocks from the btree.  The values
+ * in block are decremented as a side effect of the btree remove.
+ *
+ * begin_index - the index of the first array block to remove.
+ * end_index - the one-past-the-end value.  ie. this block is not removed.
+ */
+static int drop_blocks(struct resize *resize, unsigned begin_index,
+		       unsigned end_index)
+{
+	int r;
+
+	while (begin_index != end_index) {
+		uint64_t key = begin_index++;
+		r = dm_btree_remove(&resize->info->btree_info, resize->root,
+				    &key, &resize->root);
+		if (r)
+			return r;
+	}
+
+	return 0;
+}
+
+/*
+ * Calculates how many blocks are needed for the array.
+ */
+static unsigned total_nr_blocks_needed(unsigned nr_full_blocks,
+				       unsigned nr_entries_in_last_block)
+{
+	return nr_full_blocks + (nr_entries_in_last_block ? 1 : 0);
+}
+
+/*
+ * Shrink an array.
+ */
+static int shrink(struct resize *resize)
+{
+	int r;
+	unsigned begin, end;
+	struct dm_block *block;
+	struct array_block *ab;
+
+	/*
+	 * Lose some blocks from the back?
+	 */
+	if (resize->new_nr_full_blocks < resize->old_nr_full_blocks) {
+		begin = total_nr_blocks_needed(resize->new_nr_full_blocks,
+					       resize->new_nr_entries_in_last_block);
+		end = total_nr_blocks_needed(resize->old_nr_full_blocks,
+					     resize->old_nr_entries_in_last_block);
+
+		r = drop_blocks(resize, begin, end);
+		if (r)
+			return r;
+	}
+
+	/*
+	 * Trim the new tail block
+	 */
+	if (resize->new_nr_entries_in_last_block) {
+		r = shadow_ablock(resize->info, &resize->root,
+				  resize->new_nr_full_blocks, &block, &ab);
+		if (r)
+			return r;
+
+		trim_ablock(resize->info, ab, resize->new_nr_entries_in_last_block);
+		unlock_ablock(resize->info, block);
+	}
+
+	return 0;
+}
+
+/*
+ * Grow an array.
+ */
+static int grow_extend_tail_block(struct resize *resize, uint32_t new_nr_entries)
+{
+	int r;
+	struct dm_block *block;
+	struct array_block *ab;
+
+	r = shadow_ablock(resize->info, &resize->root,
+			  resize->old_nr_full_blocks, &block, &ab);
+	if (r)
+		return r;
+
+	fill_ablock(resize->info, ab, resize->value, new_nr_entries);
+	unlock_ablock(resize->info, block);
+
+	return r;
+}
+
+static int grow_add_tail_block(struct resize *resize)
+{
+	return insert_new_ablock(resize->info, resize->size_of_block,
+				 resize->max_entries,
+				 resize->new_nr_full_blocks,
+				 resize->new_nr_entries_in_last_block,
+				 resize->value, &resize->root);
+}
+
+static int grow_needs_more_blocks(struct resize *resize)
+{
+	int r;
+
+	if (resize->old_nr_entries_in_last_block > 0) {
+		r = grow_extend_tail_block(resize, resize->max_entries);
+		if (r)
+			return r;
+	}
+
+	r = insert_full_ablocks(resize->info, resize->size_of_block,
+				resize->old_nr_full_blocks,
+				resize->new_nr_full_blocks,
+				resize->max_entries, resize->value,
+				&resize->root);
+	if (r)
+		return r;
+
+	if (resize->new_nr_entries_in_last_block)
+		r = grow_add_tail_block(resize);
+
+	return r;
+}
+
+static int grow(struct resize *resize)
+{
+	if (resize->new_nr_full_blocks > resize->old_nr_full_blocks)
+		return grow_needs_more_blocks(resize);
+
+	else if (resize->old_nr_entries_in_last_block)
+		return grow_extend_tail_block(resize, resize->new_nr_entries_in_last_block);
+
+	else
+		return grow_add_tail_block(resize);
+}
+
+/*----------------------------------------------------------------*/
+
+/*
+ * These are the value_type functions for the btree elements, which point
+ * to array blocks.
+ */
+static void block_inc(void *context, const void *value)
+{
+	__le64 block_le;
+	struct dm_array_info *info = context;
+
+	memcpy(&block_le, value, sizeof(block_le));
+	dm_tm_inc(info->btree_info.tm, le64_to_cpu(block_le));
+}
+
+static void block_dec(void *context, const void *value)
+{
+	int r;
+	uint64_t b;
+	__le64 block_le;
+	uint32_t ref_count;
+	struct dm_block *block;
+	struct array_block *ab;
+	struct dm_array_info *info = context;
+
+	memcpy(&block_le, value, sizeof(block_le));
+	b = le64_to_cpu(block_le);
+
+	r = dm_tm_ref(info->btree_info.tm, b, &ref_count);
+	if (r) {
+		DMERR_LIMIT("couldn't get reference count for block %llu",
+			    (unsigned long long) b);
+		return;
+	}
+
+	if (ref_count == 1) {
+		/*
+		 * We're about to drop the last reference to this ablock.
+		 * So we need to decrement the ref count of the contents.
+		 */
+		r = get_ablock(info, b, &block, &ab);
+		if (r) {
+			DMERR_LIMIT("couldn't get array block %llu",
+				    (unsigned long long) b);
+			return;
+		}
+
+		dec_ablock_entries(info, ab);
+		unlock_ablock(info, block);
+	}
+
+	dm_tm_dec(info->btree_info.tm, b);
+}
+
+static int block_equal(void *context, const void *value1, const void *value2)
+{
+	return !memcmp(value1, value2, sizeof(__le64));
+}
+
+/*----------------------------------------------------------------*/
+
+void dm_array_info_init(struct dm_array_info *info,
+			struct dm_transaction_manager *tm,
+			struct dm_btree_value_type *vt)
+{
+	struct dm_btree_value_type *bvt = &info->btree_info.value_type;
+
+	memcpy(&info->value_type, vt, sizeof(info->value_type));
+	info->btree_info.tm = tm;
+	info->btree_info.levels = 1;
+
+	bvt->context = info;
+	bvt->size = sizeof(__le64);
+	bvt->inc = block_inc;
+	bvt->dec = block_dec;
+	bvt->equal = block_equal;
+}
+EXPORT_SYMBOL_GPL(dm_array_info_init);
+
+int dm_array_empty(struct dm_array_info *info, dm_block_t *root)
+{
+	return dm_btree_empty(&info->btree_info, root);
+}
+EXPORT_SYMBOL_GPL(dm_array_empty);
+
+static int array_resize(struct dm_array_info *info, dm_block_t root,
+			uint32_t old_size, uint32_t new_size,
+			const void *value, dm_block_t *new_root)
+{
+	int r;
+	struct resize resize;
+
+	if (old_size == new_size)
+		return 0;
+
+	resize.info = info;
+	resize.root = root;
+	resize.size_of_block = dm_bm_block_size(dm_tm_get_bm(info->btree_info.tm));
+	resize.max_entries = calc_max_entries(info->value_type.size,
+					      resize.size_of_block);
+
+	resize.old_nr_full_blocks = old_size / resize.max_entries;
+	resize.old_nr_entries_in_last_block = old_size % resize.max_entries;
+	resize.new_nr_full_blocks = new_size / resize.max_entries;
+	resize.new_nr_entries_in_last_block = new_size % resize.max_entries;
+	resize.value = value;
+
+	r = ((new_size > old_size) ? grow : shrink)(&resize);
+	if (r)
+		return r;
+
+	*new_root = resize.root;
+	return 0;
+}
+
+int dm_array_resize(struct dm_array_info *info, dm_block_t root,
+		    uint32_t old_size, uint32_t new_size,
+		    const void *value, dm_block_t *new_root)
+		    __dm_written_to_disk(value)
+{
+	int r = array_resize(info, root, old_size, new_size, value, new_root);
+	__dm_unbless_for_disk(value);
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_array_resize);
+
+int dm_array_del(struct dm_array_info *info, dm_block_t root)
+{
+	return dm_btree_del(&info->btree_info, root);
+}
+EXPORT_SYMBOL_GPL(dm_array_del);
+
+int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
+		       uint32_t index, void *value_le)
+{
+	int r;
+	struct dm_block *block;
+	struct array_block *ab;
+	size_t size_of_block;
+	unsigned entry, max_entries;
+
+	size_of_block = dm_bm_block_size(dm_tm_get_bm(info->btree_info.tm));
+	max_entries = calc_max_entries(info->value_type.size, size_of_block);
+
+	r = lookup_ablock(info, root, index / max_entries, &block, &ab);
+	if (r)
+		return r;
+
+	entry = index % max_entries;
+	if (entry >= le32_to_cpu(ab->nr_entries))
+		r = -ENODATA;
+	else
+		memcpy(value_le, element_at(info, ab, entry),
+		       info->value_type.size);
+
+	unlock_ablock(info, block);
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_array_get_value);
+
+static int array_set_value(struct dm_array_info *info, dm_block_t root,
+			   uint32_t index, const void *value, dm_block_t *new_root)
+{
+	int r;
+	struct dm_block *block;
+	struct array_block *ab;
+	size_t size_of_block;
+	unsigned max_entries;
+	unsigned entry;
+	void *old_value;
+	struct dm_btree_value_type *vt = &info->value_type;
+
+	size_of_block = dm_bm_block_size(dm_tm_get_bm(info->btree_info.tm));
+	max_entries = calc_max_entries(info->value_type.size, size_of_block);
+
+	r = shadow_ablock(info, &root, index / max_entries, &block, &ab);
+	if (r)
+		return r;
+	*new_root = root;
+
+	entry = index % max_entries;
+	if (entry >= le32_to_cpu(ab->nr_entries)) {
+		r = -ENODATA;
+		goto out;
+	}
+
+	old_value = element_at(info, ab, entry);
+	if (vt->dec &&
+	    (!vt->equal || !vt->equal(vt->context, old_value, value))) {
+		vt->dec(vt->context, old_value);
+		if (vt->inc)
+			vt->inc(vt->context, value);
+	}
+
+	memcpy(old_value, value, info->value_type.size);
+
+out:
+	unlock_ablock(info, block);
+	return r;
+}
+
+int dm_array_set_value(struct dm_array_info *info, dm_block_t root,
+		 uint32_t index, const void *value, dm_block_t *new_root)
+		 __dm_written_to_disk(value)
+{
+	int r;
+
+	r = array_set_value(info, root, index, value, new_root);
+	__dm_unbless_for_disk(value);
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_array_set_value);
+
+struct walk_info {
+	struct dm_array_info *info;
+	int (*fn)(void *context, uint64_t key, void *leaf);
+	void *context;
+};
+
+static int walk_ablock(void *context, uint64_t *keys, void *leaf)
+{
+	struct walk_info *wi = context;
+
+	int r;
+	unsigned i;
+	__le64 block_le;
+	unsigned nr_entries, max_entries;
+	struct dm_block *block;
+	struct array_block *ab;
+
+	memcpy(&block_le, leaf, sizeof(block_le));
+	r = get_ablock(wi->info, le64_to_cpu(block_le), &block, &ab);
+	if (r)
+		return r;
+
+	max_entries = le32_to_cpu(ab->max_entries);
+	nr_entries = le32_to_cpu(ab->nr_entries);
+	for (i = 0; i < nr_entries; i++) {
+		r = wi->fn(wi->context, keys[0] * max_entries + i,
+			   element_at(wi->info, ab, i));
+
+		if (r)
+			break;
+	}
+
+	unlock_ablock(wi->info, block);
+	return r;
+}
+
+int dm_array_walk(struct dm_array_info *info, dm_block_t root,
+		  int (*fn)(void *, uint64_t key, void *leaf),
+		  void *context)
+{
+	struct walk_info wi;
+
+	wi.info = info;
+	wi.fn = fn;
+	wi.context = context;
+
+	return dm_btree_walk(&info->btree_info, root, walk_ablock, &wi);
+}
+EXPORT_SYMBOL_GPL(dm_array_walk);
+
+/*----------------------------------------------------------------*/

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

···
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+#ifndef _LINUX_DM_ARRAY_H
+#define _LINUX_DM_ARRAY_H
+
+#include "dm-btree.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * The dm-array is a persistent version of an array.  It packs the data
+ * more efficiently than a btree which will result in less disk space use,
+ * and a performance boost.  The element get and set operations are still
+ * O(ln(n)), but with a much smaller constant.
+ *
+ * The value type structure is reused from the btree type to support proper
+ * reference counting of values.
+ *
+ * The arrays implicitly know their length, and bounds are checked for
+ * lookups and updated.  It doesn't store this in an accessible place
+ * because it would waste a whole metadata block.  Make sure you store the
+ * size along with the array root in your encompassing data.
+ *
+ * Array entries are indexed via an unsigned integer starting from zero.
+ * Arrays are not sparse; if you resize an array to have 'n' entries then
+ * 'n - 1' will be the last valid index.
+ *
+ * Typical use:
+ *
+ * a) initialise a dm_array_info structure.  This describes the array
+ *    values and ties it into a specific transaction manager.  It holds no
+ *    instance data; the same info can be used for many similar arrays if
+ *    you wish.
+ *
+ * b) Get yourself a root.  The root is the index of a block of data on the
+ *    disk that holds a particular instance of an array.  You may have a
+ *    pre existing root in your metadata that you wish to use, or you may
+ *    want to create a brand new, empty array with dm_array_empty().
+ *
+ * Like the other data structures in this library, dm_array objects are
+ * immutable between transactions.  Update functions will return you the
+ * root for a _new_ array.  If you've incremented the old root, via
+ * dm_tm_inc(), before calling the update function you may continue to use
+ * it in parallel with the new root.
+ *
+ * c) resize an array with dm_array_resize().
+ *
+ * d) Get a value from the array with dm_array_get_value().
+ *
+ * e) Set a value in the array with dm_array_set_value().
+ *
+ * f) Walk an array of values in index order with dm_array_walk().  More
+ *    efficient than making many calls to dm_array_get_value().
+ *
+ * g) Destroy the array with dm_array_del().  This tells the transaction
+ *    manager that you're no longer using this data structure so it can
+ *    recycle it's blocks.  (dm_array_dec() would be a better name for it,
+ *    but del is in keeping with dm_btree_del()).
+ */
+
+/*
+ * Describes an array.  Don't initialise this structure yourself, use the
+ * init function below.
+ */
+struct dm_array_info {
+	struct dm_transaction_manager *tm;
+	struct dm_btree_value_type value_type;
+	struct dm_btree_info btree_info;
+};
+
+/*
+ * Sets up a dm_array_info structure.  You don't need to do anything with
+ * this structure when you finish using it.
+ *
+ * info - the structure being filled in.
+ * tm   - the transaction manager that should supervise this structure.
+ * vt   - describes the leaf values.
+ */
+void dm_array_info_init(struct dm_array_info *info,
+			struct dm_transaction_manager *tm,
+			struct dm_btree_value_type *vt);
+
+/*
+ * Create an empty, zero length array.
+ *
+ * info - describes the array
+ * root - on success this will be filled out with the root block
+ */
+int dm_array_empty(struct dm_array_info *info, dm_block_t *root);
+
+/*
+ * Resizes the array.
+ *
+ * info - describes the array
+ * root - the root block of the array on disk
+ * old_size - the caller is responsible for remembering the size of
+ *            the array
+ * new_size - can be bigger or smaller than old_size
+ * value - if we're growing the array the new entries will have this value
+ * new_root - on success, points to the new root block
+ *
+ * If growing the inc function for 'value' will be called the appropriate
+ * number of times.  So if the caller is holding a reference they may want
+ * to drop it.
+ */
+int dm_array_resize(struct dm_array_info *info, dm_block_t root,
+		    uint32_t old_size, uint32_t new_size,
+		    const void *value, dm_block_t *new_root)
+	__dm_written_to_disk(value);
+
+/*
+ * Frees a whole array.  The value_type's decrement operation will be called
+ * for all values in the array
+ */
+int dm_array_del(struct dm_array_info *info, dm_block_t root);
+
+/*
+ * Lookup a value in the array
+ *
+ * info - describes the array
+ * root - root block of the array
+ * index - array index
+ * value - the value to be read.  Will be in on-disk format of course.
+ *
+ * -ENODATA will be returned if the index is out of bounds.
+ */
+int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
+		       uint32_t index, void *value);
+
+/*
+ * Set an entry in the array.
+ *
+ * info - describes the array
+ * root - root block of the array
+ * index - array index
+ * value - value to be written to disk.  Make sure you confirm the value is
+ *         in on-disk format with__dm_bless_for_disk() before calling.
+ * new_root - the new root block
+ *
+ * The old value being overwritten will be decremented, the new value
+ * incremented.
+ *
+ * -ENODATA will be returned if the index is out of bounds.
+ */
+int dm_array_set_value(struct dm_array_info *info, dm_block_t root,
+		       uint32_t index, const void *value, dm_block_t *new_root)
+	__dm_written_to_disk(value);
+
+/*
+ * Walk through all the entries in an array.
+ *
+ * info - describes the array
+ * root - root block of the array
+ * fn - called back for every element
+ * context - passed to the callback
+ */
+int dm_array_walk(struct dm_array_info *info, dm_block_t root,
+		  int (*fn)(void *context, uint64_t key, void *leaf),
+		  void *context);
+
+/*----------------------------------------------------------------*/
+
+#endif	/* _LINUX_DM_ARRAY_H */

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

···
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-bitset.h"
+#include "dm-transaction-manager.h"
+
+#include <linux/export.h>
+#include <linux/device-mapper.h>
+
+#define DM_MSG_PREFIX "bitset"
+#define BITS_PER_ARRAY_ENTRY 64
+
+/*----------------------------------------------------------------*/
+
+static struct dm_btree_value_type bitset_bvt = {
+	.context = NULL,
+	.size = sizeof(__le64),
+	.inc = NULL,
+	.dec = NULL,
+	.equal = NULL,
+};
+
+/*----------------------------------------------------------------*/
+
+void dm_disk_bitset_init(struct dm_transaction_manager *tm,
+			 struct dm_disk_bitset *info)
+{
+	dm_array_info_init(&info->array_info, tm, &bitset_bvt);
+	info->current_index_set = false;
+}
+EXPORT_SYMBOL_GPL(dm_disk_bitset_init);
+
+int dm_bitset_empty(struct dm_disk_bitset *info, dm_block_t *root)
+{
+	return dm_array_empty(&info->array_info, root);
+}
+EXPORT_SYMBOL_GPL(dm_bitset_empty);
+
+int dm_bitset_resize(struct dm_disk_bitset *info, dm_block_t root,
+		     uint32_t old_nr_entries, uint32_t new_nr_entries,
+		     bool default_value, dm_block_t *new_root)
+{
+	uint32_t old_blocks = dm_div_up(old_nr_entries, BITS_PER_ARRAY_ENTRY);
+	uint32_t new_blocks = dm_div_up(new_nr_entries, BITS_PER_ARRAY_ENTRY);
+	__le64 value = default_value ? cpu_to_le64(~0) : cpu_to_le64(0);
+
+	__dm_bless_for_disk(&value);
+	return dm_array_resize(&info->array_info, root, old_blocks, new_blocks,
+			       &value, new_root);
+}
+EXPORT_SYMBOL_GPL(dm_bitset_resize);
+
+int dm_bitset_del(struct dm_disk_bitset *info, dm_block_t root)
+{
+	return dm_array_del(&info->array_info, root);
+}
+EXPORT_SYMBOL_GPL(dm_bitset_del);
+
+int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
+		    dm_block_t *new_root)
+{
+	int r;
+	__le64 value;
+
+	if (!info->current_index_set)
+		return 0;
+
+	value = cpu_to_le64(info->current_bits);
+
+	__dm_bless_for_disk(&value);
+	r = dm_array_set_value(&info->array_info, root, info->current_index,
+			       &value, new_root);
+	if (r)
+		return r;
+
+	info->current_index_set = false;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_bitset_flush);
+
+static int read_bits(struct dm_disk_bitset *info, dm_block_t root,
+		     uint32_t array_index)
+{
+	int r;
+	__le64 value;
+
+	r = dm_array_get_value(&info->array_info, root, array_index, &value);
+	if (r)
+		return r;
+
+	info->current_bits = le64_to_cpu(value);
+	info->current_index_set = true;
+	info->current_index = array_index;
+	return 0;
+}
+
+static int get_array_entry(struct dm_disk_bitset *info, dm_block_t root,
+			   uint32_t index, dm_block_t *new_root)
+{
+	int r;
+	unsigned array_index = index / BITS_PER_ARRAY_ENTRY;
+
+	if (info->current_index_set) {
+		if (info->current_index == array_index)
+			return 0;
+
+		r = dm_bitset_flush(info, root, new_root);
+		if (r)
+			return r;
+	}
+
+	return read_bits(info, root, array_index);
+}
+
+int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
+		      uint32_t index, dm_block_t *new_root)
+{
+	int r;
+	unsigned b = index % BITS_PER_ARRAY_ENTRY;
+
+	r = get_array_entry(info, root, index, new_root);
+	if (r)
+		return r;
+
+	set_bit(b, (unsigned long *) &info->current_bits);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_bitset_set_bit);
+
+int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
+			uint32_t index, dm_block_t *new_root)
+{
+	int r;
+	unsigned b = index % BITS_PER_ARRAY_ENTRY;
+
+	r = get_array_entry(info, root, index, new_root);
+	if (r)
+		return r;
+
+	clear_bit(b, (unsigned long *) &info->current_bits);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_bitset_clear_bit);
+
+int dm_bitset_test_bit(struct dm_disk_bitset *info, dm_block_t root,
+		       uint32_t index, dm_block_t *new_root, bool *result)
+{
+	int r;
+	unsigned b = index % BITS_PER_ARRAY_ENTRY;
+
+	r = get_array_entry(info, root, index, new_root);
+	if (r)
+		return r;
+
+	*result = test_bit(b, (unsigned long *) &info->current_bits);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dm_bitset_test_bit);
+
+/*----------------------------------------------------------------*/

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

···
+/*
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+#ifndef _LINUX_DM_BITSET_H
+#define _LINUX_DM_BITSET_H
+
+#include "dm-array.h"
+
+/*----------------------------------------------------------------*/
+
+/*
+ * This bitset type is a thin wrapper round a dm_array of 64bit words.  It
+ * uses a tiny, one word cache to reduce the number of array lookups and so
+ * increase performance.
+ *
+ * Like the dm-array that it's based on, the caller needs to keep track of
+ * the size of the bitset separately.  The underlying dm-array implicitly
+ * knows how many words it's storing and will return -ENODATA if you try
+ * and access an out of bounds word.  However, an out of bounds bit in the
+ * final word will _not_ be detected, you have been warned.
+ *
+ * Bits are indexed from zero.
+
+ * Typical use:
+ *
+ * a) Initialise a dm_disk_bitset structure with dm_disk_bitset_init().
+ *    This describes the bitset and includes the cache.  It's not called it
+ *    dm_bitset_info in line with other data structures because it does
+ *    include instance data.
+ *
+ * b) Get yourself a root.  The root is the index of a block of data on the
+ *    disk that holds a particular instance of an bitset.  You may have a
+ *    pre existing root in your metadata that you wish to use, or you may
+ *    want to create a brand new, empty bitset with dm_bitset_empty().
+ *
+ * Like the other data structures in this library, dm_bitset objects are
+ * immutable between transactions.  Update functions will return you the
+ * root for a _new_ array.  If you've incremented the old root, via
+ * dm_tm_inc(), before calling the update function you may continue to use
+ * it in parallel with the new root.
+ *
+ * Even read operations may trigger the cache to be flushed and as such
+ * return a root for a new, updated bitset.
+ *
+ * c) resize a bitset with dm_bitset_resize().
+ *
+ * d) Set a bit with dm_bitset_set_bit().
+ *
+ * e) Clear a bit with dm_bitset_clear_bit().
+ *
+ * f) Test a bit with dm_bitset_test_bit().
+ *
+ * g) Flush all updates from the cache with dm_bitset_flush().
+ *
+ * h) Destroy the bitset with dm_bitset_del().  This tells the transaction
+ *    manager that you're no longer using this data structure so it can
+ *    recycle it's blocks.  (dm_bitset_dec() would be a better name for it,
+ *    but del is in keeping with dm_btree_del()).
+ */
+
+/*
+ * Opaque object.  Unlike dm_array_info, you should have one of these per
+ * bitset.  Initialise with dm_disk_bitset_init().
+ */
+struct dm_disk_bitset {
+	struct dm_array_info array_info;
+
+	uint32_t current_index;
+	uint64_t current_bits;
+
+	bool current_index_set:1;
+};
+
+/*
+ * Sets up a dm_disk_bitset structure.  You don't need to do anything with
+ * this structure when you finish using it.
+ *
+ * tm - the transaction manager that should supervise this structure
+ * info - the structure being initialised
+ */
+void dm_disk_bitset_init(struct dm_transaction_manager *tm,
+			 struct dm_disk_bitset *info);
+
+/*
+ * Create an empty, zero length bitset.
+ *
+ * info - describes the bitset
+ * new_root - on success, points to the new root block
+ */
+int dm_bitset_empty(struct dm_disk_bitset *info, dm_block_t *new_root);
+
+/*
+ * Resize the bitset.
+ *
+ * info - describes the bitset
+ * old_root - the root block of the array on disk
+ * old_nr_entries - the number of bits in the old bitset
+ * new_nr_entries - the number of bits you want in the new bitset
+ * default_value - the value for any new bits
+ * new_root - on success, points to the new root block
+ */
+int dm_bitset_resize(struct dm_disk_bitset *info, dm_block_t old_root,
+		     uint32_t old_nr_entries, uint32_t new_nr_entries,
+		     bool default_value, dm_block_t *new_root);
+
+/*
+ * Frees the bitset.
+ */
+int dm_bitset_del(struct dm_disk_bitset *info, dm_block_t root);
+
+/*
+ * Set a bit.
+ *
+ * info - describes the bitset
+ * root - the root block of the bitset
+ * index - the bit index
+ * new_root - on success, points to the new root block
+ *
+ * -ENODATA will be returned if the index is out of bounds.
+ */
+int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
+		      uint32_t index, dm_block_t *new_root);
+
+/*
+ * Clears a bit.
+ *
+ * info - describes the bitset
+ * root - the root block of the bitset
+ * index - the bit index
+ * new_root - on success, points to the new root block
+ *
+ * -ENODATA will be returned if the index is out of bounds.
+ */
+int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
+			uint32_t index, dm_block_t *new_root);
+
+/*
+ * Tests a bit.
+ *
+ * info - describes the bitset
+ * root - the root block of the bitset
+ * index - the bit index
+ * new_root - on success, points to the new root block (cached values may have been written)
+ * result - the bit value you're after
+ *
+ * -ENODATA will be returned if the index is out of bounds.
+ */
+int dm_bitset_test_bit(struct dm_disk_bitset *info, dm_block_t root,
+		       uint32_t index, dm_block_t *new_root, bool *result);
+
+/*
+ * Flush any cached changes to disk.
+ *
+ * info - describes the bitset
+ * root - the root block of the bitset
+ * new_root - on success, points to the new root block
+ */
+int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
+		    dm_block_t *new_root);
+
+/*----------------------------------------------------------------*/
+
+#endif /* _LINUX_DM_BITSET_H */

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

···
 
 	return dm_bufio_write_dirty_buffers(bm->bufio);
 }
+EXPORT_SYMBOL_GPL(dm_bm_flush_and_unlock);
 
 void dm_bm_set_read_only(struct dm_block_manager *bm)
 {

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

···
 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);
+void ro_pop(struct ro_spine *s);
 struct btree_node *ro_node(struct ro_spine *s);
 
 struct shadow_spine {

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

···
 	return r;
 }
 
+void ro_pop(struct ro_spine *s)
+{
+	BUG_ON(!s->count);
+	--s->count;
+	unlock_block(s->info, s->nodes[s->count]);
+}
+
 struct btree_node *ro_node(struct ro_spine *s)
 {
 	struct dm_block *block;

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

···
 	return r ? r : count;
 }
 EXPORT_SYMBOL_GPL(dm_btree_find_highest_key);
+
+/*
+ * FIXME: We shouldn't use a recursive algorithm when we have limited stack
+ * space.  Also this only works for single level trees.
+ */
+static int walk_node(struct ro_spine *s, dm_block_t block,
+		     int (*fn)(void *context, uint64_t *keys, void *leaf),
+		     void *context)
+{
+	int r;
+	unsigned i, nr;
+	struct btree_node *n;
+	uint64_t keys;
+
+	r = ro_step(s, block);
+	n = ro_node(s);
+
+	nr = le32_to_cpu(n->header.nr_entries);
+	for (i = 0; i < nr; i++) {
+		if (le32_to_cpu(n->header.flags) & INTERNAL_NODE) {
+			r = walk_node(s, value64(n, i), fn, context);
+			if (r)
+				goto out;
+		} else {
+			keys = le64_to_cpu(*key_ptr(n, i));
+			r = fn(context, &keys, value_ptr(n, i));
+			if (r)
+				goto out;
+		}
+	}
+
+out:
+	ro_pop(s);
+	return r;
+}
+
+int dm_btree_walk(struct dm_btree_info *info, dm_block_t root,
+		  int (*fn)(void *context, uint64_t *keys, void *leaf),
+		  void *context)
+{
+	int r;
+	struct ro_spine spine;
+
+	BUG_ON(info->levels > 1);
+
+	init_ro_spine(&spine, info);
+	r = walk_node(&spine, root, fn, context);
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_walk);

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

···
 	 * 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);
+	void (*inc)(void *context, const 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);
+	void (*dec)(void *context, const 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);
+	int (*equal)(void *context, const void *value1, const void *value2);
 };
 
 /*
···
  */
 int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
 			      uint64_t *result_keys);
+
+/*
+ * Iterate through the a btree, calling fn() on each entry.
+ * It only works for single level trees and is internally recursive, so
+ * monitor stack usage carefully.
+ */
+int dm_btree_walk(struct dm_btree_info *info, dm_block_t root,
+		  int (*fn)(void *context, uint64_t *keys, void *leaf),
+		  void *context);
 
 #endif	/* _LINUX_DM_BTREE_H */

include/linux/device-mapper.h

···
 typedef int (*dm_preresume_fn) (struct dm_target *ti);
 typedef void (*dm_resume_fn) (struct dm_target *ti);
 
-typedef int (*dm_status_fn) (struct dm_target *ti, status_type_t status_type,
-			     unsigned status_flags, char *result, unsigned maxlen);
+typedef void (*dm_status_fn) (struct dm_target *ti, status_type_t status_type,
+			      unsigned status_flags, char *result, unsigned maxlen);
 
 typedef int (*dm_message_fn) (struct dm_target *ti, unsigned argc, char **argv);
 
···
 #define DM_TARGET_IMMUTABLE		0x00000004
 #define dm_target_is_immutable(type)	((type)->features & DM_TARGET_IMMUTABLE)
 
+/*
+ * Some targets need to be sent the same WRITE bio severals times so
+ * that they can send copies of it to different devices.  This function
+ * examines any supplied bio and returns the number of copies of it the
+ * target requires.
+ */
+typedef unsigned (*dm_num_write_bios_fn) (struct dm_target *ti, struct bio *bio);
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;
···
 	uint32_t max_io_len;
 
 	/*
-	 * A number of zero-length barrier requests that will be submitted
+	 * A number of zero-length barrier bios that will be submitted
 	 * to the target for the purpose of flushing cache.
 	 *
-	 * The request number can be accessed with dm_bio_get_target_request_nr.
-	 * It is a responsibility of the target driver to remap these requests
+	 * The bio number can be accessed with dm_bio_get_target_bio_nr.
+	 * It is a responsibility of the target driver to remap these bios
 	 * to the real underlying devices.
 	 */
-	unsigned num_flush_requests;
+	unsigned num_flush_bios;
 
 	/*
-	 * The number of discard requests that will be submitted to the target.
-	 * The request number can be accessed with dm_bio_get_target_request_nr.
+	 * The number of discard bios that will be submitted to the target.
+	 * The bio number can be accessed with dm_bio_get_target_bio_nr.
 	 */
-	unsigned num_discard_requests;
+	unsigned num_discard_bios;
 
 	/*
-	 * The number of WRITE SAME requests that will be submitted to the target.
-	 * The request number can be accessed with dm_bio_get_target_request_nr.
+	 * The number of WRITE SAME bios that will be submitted to the target.
+	 * The bio number can be accessed with dm_bio_get_target_bio_nr.
 	 */
-	unsigned num_write_same_requests;
+	unsigned num_write_same_bios;
 
 	/*
 	 * The minimum number of extra bytes allocated in each bio for the
 	 * target to use.  dm_per_bio_data returns the data location.
 	 */
 	unsigned per_bio_data_size;
+
+	/*
+	 * If defined, this function is called to find out how many
+	 * duplicate bios should be sent to the target when writing
+	 * data.
+	 */
+	dm_num_write_bios_fn num_write_bios;
 
 	/* target specific data */
 	void *private;
···
 	bool discards_supported:1;
 
 	/*
-	 * Set if the target required discard request to be split
+	 * Set if the target required discard bios to be split
 	 * on max_io_len boundary.
 	 */
-	bool split_discard_requests:1;
+	bool split_discard_bios:1;
 
 	/*
 	 * Set if this target does not return zeroes on discarded blocks.
···
 	struct dm_io *io;
 	struct dm_target *ti;
 	union map_info info;
-	unsigned target_request_nr;
+	unsigned target_bio_nr;
 	struct bio clone;
 };
 
···
 	return (struct bio *)((char *)data + data_size + offsetof(struct dm_target_io, clone));
 }
 
-static inline unsigned dm_bio_get_target_request_nr(const struct bio *bio)
+static inline unsigned dm_bio_get_target_bio_nr(const struct bio *bio)
 {
-	return container_of(bio, struct dm_target_io, clone)->target_request_nr;
+	return container_of(bio, struct dm_target_io, clone)->target_bio_nr;
 }
 
 int dm_register_target(struct target_type *t);

include/linux/dm-kcopyd.h

···
 
 #define DM_KCOPYD_IGNORE_ERROR 1
 
+struct dm_kcopyd_throttle {
+	unsigned throttle;
+	unsigned num_io_jobs;
+	unsigned io_period;
+	unsigned total_period;
+	unsigned last_jiffies;
+};
+
+/*
+ * kcopyd clients that want to support throttling must pass an initialised
+ * dm_kcopyd_throttle struct into dm_kcopyd_client_create().
+ * Two or more clients may share the same instance of this struct between
+ * them if they wish to be throttled as a group.
+ *
+ * This macro also creates a corresponding module parameter to configure
+ * the amount of throttling.
+ */
+#define DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(name, description)	\
+static struct dm_kcopyd_throttle dm_kcopyd_throttle = { 100, 0, 0, 0, 0 }; \
+module_param_named(name, dm_kcopyd_throttle.throttle, uint, 0644); \
+MODULE_PARM_DESC(name, description)
+
 /*
  * To use kcopyd you must first create a dm_kcopyd_client object.
+ * throttle can be NULL if you don't want any throttling.
  */
 struct dm_kcopyd_client;
-struct dm_kcopyd_client *dm_kcopyd_client_create(void);
+struct dm_kcopyd_client *dm_kcopyd_client_create(struct dm_kcopyd_throttle *throttle);
 void dm_kcopyd_client_destroy(struct dm_kcopyd_client *kc);
 
 /*

include/uapi/linux/dm-ioctl.h

···
 #define DM_DEV_SET_GEOMETRY	_IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
-#define DM_VERSION_MINOR	23
-#define DM_VERSION_PATCHLEVEL	1
-#define DM_VERSION_EXTRA	"-ioctl (2012-12-18)"
+#define DM_VERSION_MINOR	24
+#define DM_VERSION_PATCHLEVEL	0
+#define DM_VERSION_EXTRA	"-ioctl (2013-01-15)"
 
 /* Status bits */
 #define DM_READONLY_FLAG	(1 << 0) /* In/Out */
···
  * or requesting sensitive data such as an encryption key.
  */
 #define DM_SECURE_DATA_FLAG		(1 << 15) /* In */
+
+/*
+ * If set, a message generated output data.
+ */
+#define DM_DATA_OUT_FLAG		(1 << 16) /* Out */
 
 #endif				/* _LINUX_DM_IOCTL_H */