block/blk-timeout.c


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/*
 * Functions related to generic timeout handling of requests.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/blkdev.h>
#include <linux/fault-inject.h>

#include "blk.h"
#include "blk-mq.h"

#ifdef CONFIG_FAIL_IO_TIMEOUT

static DECLARE_FAULT_ATTR(fail_io_timeout);

static int __init setup_fail_io_timeout(char *str)
{
	return setup_fault_attr(&fail_io_timeout, str);
}
__setup("fail_io_timeout=", setup_fail_io_timeout);

int blk_should_fake_timeout(struct request_queue *q)
{
	if (!test_bit(QUEUE_FLAG_FAIL_IO, &q->queue_flags))
		return 0;

	return should_fail(&fail_io_timeout, 1);
}

static int __init fail_io_timeout_debugfs(void)
{
	struct dentry *dir = fault_create_debugfs_attr("fail_io_timeout",
						NULL, &fail_io_timeout);

	return PTR_ERR_OR_ZERO(dir);
}

late_initcall(fail_io_timeout_debugfs);

ssize_t part_timeout_show(struct device *dev, struct device_attribute *attr,
			  char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	int set = test_bit(QUEUE_FLAG_FAIL_IO, &disk->queue->queue_flags);

	return sprintf(buf, "%d\n", set != 0);
}

ssize_t part_timeout_store(struct device *dev, struct device_attribute *attr,
			   const char *buf, size_t count)
{
	struct gendisk *disk = dev_to_disk(dev);
	int val;

	if (count) {
		struct request_queue *q = disk->queue;
		char *p = (char *) buf;

		val = simple_strtoul(p, &p, 10);
		spin_lock_irq(q->queue_lock);
		if (val)
			queue_flag_set(QUEUE_FLAG_FAIL_IO, q);
		else
			queue_flag_clear(QUEUE_FLAG_FAIL_IO, q);
		spin_unlock_irq(q->queue_lock);
	}

	return count;
}

#endif /* CONFIG_FAIL_IO_TIMEOUT */

/*
 * blk_delete_timer - Delete/cancel timer for a given function.
 * @req:	request that we are canceling timer for
 *
 */
void blk_delete_timer(struct request *req)
{
	list_del_init(&req->timeout_list);
}

static void blk_rq_timed_out(struct request *req)
{
	struct request_queue *q = req->q;
	enum blk_eh_timer_return ret = BLK_EH_RESET_TIMER;

	if (q->rq_timed_out_fn)
		ret = q->rq_timed_out_fn(req);
	switch (ret) {
	case BLK_EH_HANDLED:
		/* Can we use req->errors here? */
		if (q->mq_ops)
			__blk_mq_complete_request(req);
		else
			__blk_complete_request(req);
		break;
	case BLK_EH_RESET_TIMER:
		if (q->mq_ops)
			blk_mq_add_timer(req);
		else
			blk_add_timer(req);

		blk_clear_rq_complete(req);
		break;
	case BLK_EH_NOT_HANDLED:
		/*
		 * LLD handles this for now but in the future
		 * we can send a request msg to abort the command
		 * and we can move more of the generic scsi eh code to
		 * the blk layer.
		 */
		break;
	default:
		printk(KERN_ERR "block: bad eh return: %d\n", ret);
		break;
	}
}

void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout,
			  unsigned int *next_set)
{
	if (time_after_eq(jiffies, rq->deadline)) {
		list_del_init(&rq->timeout_list);

		/*
		 * Check if we raced with end io completion
		 */
		if (!blk_mark_rq_complete(rq))
			blk_rq_timed_out(rq);
	} else if (!*next_set || time_after(*next_timeout, rq->deadline)) {
		*next_timeout = rq->deadline;
		*next_set = 1;
	}
}

void blk_rq_timed_out_timer(unsigned long data)
{
	struct request_queue *q = (struct request_queue *) data;
	unsigned long flags, next = 0;
	struct request *rq, *tmp;
	int next_set = 0;

	spin_lock_irqsave(q->queue_lock, flags);

	list_for_each_entry_safe(rq, tmp, &q->timeout_list, timeout_list)
		blk_rq_check_expired(rq, &next, &next_set);

	if (next_set)
		mod_timer(&q->timeout, round_jiffies_up(next));

	spin_unlock_irqrestore(q->queue_lock, flags);
}

/**
 * blk_abort_request -- Request request recovery for the specified command
 * @req:	pointer to the request of interest
 *
 * This function requests that the block layer start recovery for the
 * request by deleting the timer and calling the q's timeout function.
 * LLDDs who implement their own error recovery MAY ignore the timeout
 * event if they generated blk_abort_req. Must hold queue lock.
 */
void blk_abort_request(struct request *req)
{
	if (blk_mark_rq_complete(req))
		return;
	blk_delete_timer(req);
	blk_rq_timed_out(req);
}
EXPORT_SYMBOL_GPL(blk_abort_request);

void __blk_add_timer(struct request *req, struct list_head *timeout_list)
{
	struct request_queue *q = req->q;
	unsigned long expiry;

	if (!q->rq_timed_out_fn)
		return;

	BUG_ON(!list_empty(&req->timeout_list));

	/*
	 * Some LLDs, like scsi, peek at the timeout to prevent a
	 * command from being retried forever.
	 */
	if (!req->timeout)
		req->timeout = q->rq_timeout;

	req->deadline = jiffies + req->timeout;
	if (timeout_list)
		list_add_tail(&req->timeout_list, timeout_list);

	/*
	 * If the timer isn't already pending or this timeout is earlier
	 * than an existing one, modify the timer. Round up to next nearest
	 * second.
	 */
	expiry = round_jiffies_up(req->deadline);

	if (!timer_pending(&q->timeout) ||
	    time_before(expiry, q->timeout.expires))
		mod_timer(&q->timeout, expiry);

}

/**
 * blk_add_timer - Start timeout timer for a single request
 * @req:	request that is about to start running.
 *
 * Notes:
 *    Each request has its own timer, and as it is added to the queue, we
 *    set up the timer. When the request completes, we cancel the timer.
 */
void blk_add_timer(struct request *req)
{
	__blk_add_timer(req, &req->q->timeout_list);
}
/*
 * Copyright (C) 2011-2012 Red Hat UK.
 *
 * This file is released under the GPL.
 */

#include "dm-thin-metadata.h"
#include "dm-bio-prison.h"
#include "dm.h"

#include <linux/device-mapper.h>
#include <linux/dm-io.h>
#include <linux/dm-kcopyd.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>

#define	DM_MSG_PREFIX	"thin"

/*
 * Tunable constants
 */
#define ENDIO_HOOK_POOL_SIZE 1024
#define MAPPING_POOL_SIZE 1024
#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.
 */
#define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (64 * 1024 >> SECTOR_SHIFT)
#define DATA_DEV_BLOCK_SIZE_MAX_SECTORS (1024 * 1024 * 1024 >> SECTOR_SHIFT)

/*
 * Device id is restricted to 24 bits.
 */
#define MAX_DEV_ID ((1 << 24) - 1)

/*
 * How do we handle breaking sharing of data blocks?
 * =================================================
 *
 * We use a standard copy-on-write btree to store the mappings for the
 * devices (note I'm talking about copy-on-write of the metadata here, not
 * the data).  When you take an internal snapshot you clone the root node
 * of the origin btree.  After this there is no concept of an origin or a
 * snapshot.  They are just two device trees that happen to point to the
 * same data blocks.
 *
 * When we get a write in we decide if it's to a shared data block using
 * some timestamp magic.  If it is, we have to break sharing.
 *
 * Let's say we write to a shared block in what was the origin.  The
 * steps are:
 *
 * i) plug io further to this physical block. (see bio_prison code).
 *
 * ii) quiesce any read io to that shared data block.  Obviously
 * including all devices that share this block.  (see dm_deferred_set code)
 *
 * iii) copy the data block to a newly allocate block.  This step can be
 * missed out if the io covers the block. (schedule_copy).
 *
 * iv) insert the new mapping into the origin's btree
 * (process_prepared_mapping).  This act of inserting breaks some
 * sharing of btree nodes between the two devices.  Breaking sharing only
 * effects the btree of that specific device.  Btrees for the other
 * devices that share the block never change.  The btree for the origin
 * device as it was after the last commit is untouched, ie. we're using
 * persistent data structures in the functional programming sense.
 *
 * v) unplug io to this physical block, including the io that triggered
 * the breaking of sharing.
 *
 * Steps (ii) and (iii) occur in parallel.
 *
 * The metadata _doesn't_ need to be committed before the io continues.  We
 * get away with this because the io is always written to a _new_ block.
 * If there's a crash, then:
 *
 * - The origin mapping will point to the old origin block (the shared
 * one).  This will contain the data as it was before the io that triggered
 * the breaking of sharing came in.
 *
 * - The snap mapping still points to the old block.  As it would after
 * the commit.
 *
 * The downside of this scheme is the timestamp magic isn't perfect, and
 * will continue to think that data block in the snapshot device is shared
 * even after the write to the origin has broken sharing.  I suspect data
 * blocks will typically be shared by many different devices, so we're
 * breaking sharing n + 1 times, rather than n, where n is the number of
 * devices that reference this data block.  At the moment I think the
 * benefits far, far outweigh the disadvantages.
 */

/*----------------------------------------------------------------*/

/*
 * Key building.
 */
static void build_data_key(struct dm_thin_device *td,
			   dm_block_t b, struct dm_cell_key *key)
{
	key->virtual = 0;
	key->dev = dm_thin_dev_id(td);
	key->block = b;
}

static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
			      struct dm_cell_key *key)
{
	key->virtual = 1;
	key->dev = dm_thin_dev_id(td);
	key->block = b;
}

/*----------------------------------------------------------------*/

/*
 * A pool device ties together a metadata device and a data device.  It
 * also provides the interface for creating and destroying internal
 * devices.
 */
struct dm_thin_new_mapping;

/*
 * The pool runs in 4 modes.  Ordered in degraded order for comparisons.
 */
enum pool_mode {
	PM_WRITE,		/* metadata may be changed */
	PM_OUT_OF_DATA_SPACE,	/* metadata may be changed, though data may not be allocated */
	PM_READ_ONLY,		/* metadata may not be changed */
	PM_FAIL,		/* all I/O fails */
};

struct pool_features {
	enum pool_mode mode;

	bool zero_new_blocks:1;
	bool discard_enabled:1;
	bool discard_passdown:1;
	bool error_if_no_space:1;
};

struct thin_c;
typedef void (*process_bio_fn)(struct thin_c *tc, struct bio *bio);
typedef void (*process_mapping_fn)(struct dm_thin_new_mapping *m);

struct pool {
	struct list_head list;
	struct dm_target *ti;	/* Only set if a pool target is bound */

	struct mapped_device *pool_md;
	struct block_device *md_dev;
	struct dm_pool_metadata *pmd;

	dm_block_t low_water_blocks;
	uint32_t sectors_per_block;
	int sectors_per_block_shift;

	struct pool_features pf;
	bool low_water_triggered:1;	/* A dm event has been sent */

	struct dm_bio_prison *prison;
	struct dm_kcopyd_client *copier;

	struct workqueue_struct *wq;
	struct work_struct worker;
	struct delayed_work waker;

	unsigned long last_commit_jiffies;
	unsigned ref_count;

	spinlock_t lock;
	struct bio_list deferred_bios;
	struct bio_list deferred_flush_bios;
	struct list_head prepared_mappings;
	struct list_head prepared_discards;

	struct bio_list retry_on_resume_list;

	struct dm_deferred_set *shared_read_ds;
	struct dm_deferred_set *all_io_ds;

	struct dm_thin_new_mapping *next_mapping;
	mempool_t *mapping_pool;

	process_bio_fn process_bio;
	process_bio_fn process_discard;

	process_mapping_fn process_prepared_mapping;
	process_mapping_fn process_prepared_discard;
};

static enum pool_mode get_pool_mode(struct pool *pool);
static void metadata_operation_failed(struct pool *pool, const char *op, int r);

/*
 * Target context for a pool.
 */
struct pool_c {
	struct dm_target *ti;
	struct pool *pool;
	struct dm_dev *data_dev;
	struct dm_dev *metadata_dev;
	struct dm_target_callbacks callbacks;

	dm_block_t low_water_blocks;
	struct pool_features requested_pf; /* Features requested during table load */
	struct pool_features adjusted_pf;  /* Features used after adjusting for constituent devices */
};

/*
 * Target context for a thin.
 */
struct thin_c {
	struct dm_dev *pool_dev;
	struct dm_dev *origin_dev;
	dm_thin_id dev_id;

	struct pool *pool;
	struct dm_thin_device *td;
	bool requeue_mode:1;
};

/*----------------------------------------------------------------*/

/*
 * 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 {
	struct mutex mutex;
	struct list_head pools;
} dm_thin_pool_table;

static void pool_table_init(void)
{
	mutex_init(&dm_thin_pool_table.mutex);
	INIT_LIST_HEAD(&dm_thin_pool_table.pools);
}

static void __pool_table_insert(struct pool *pool)
{
	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
	list_add(&pool->list, &dm_thin_pool_table.pools);
}

static void __pool_table_remove(struct pool *pool)
{
	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
	list_del(&pool->list);
}

static struct pool *__pool_table_lookup(struct mapped_device *md)
{
	struct pool *pool = NULL, *tmp;

	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));

	list_for_each_entry(tmp, &dm_thin_pool_table.pools, list) {
		if (tmp->pool_md == md) {
			pool = tmp;
			break;
		}
	}

	return pool;
}

static struct pool *__pool_table_lookup_metadata_dev(struct block_device *md_dev)
{
	struct pool *pool = NULL, *tmp;

	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));

	list_for_each_entry(tmp, &dm_thin_pool_table.pools, list) {
		if (tmp->md_dev == md_dev) {
			pool = tmp;
			break;
		}
	}

	return pool;
}

/*----------------------------------------------------------------*/

struct dm_thin_endio_hook {
	struct thin_c *tc;
	struct dm_deferred_entry *shared_read_entry;
	struct dm_deferred_entry *all_io_entry;
	struct dm_thin_new_mapping *overwrite_mapping;
};

static void requeue_bio_list(struct thin_c *tc, struct bio_list *master)
{
	struct bio *bio;
	struct bio_list bios;
	unsigned long flags;

	bio_list_init(&bios);

	spin_lock_irqsave(&tc->pool->lock, flags);
	bio_list_merge(&bios, master);
	bio_list_init(master);
	spin_unlock_irqrestore(&tc->pool->lock, flags);

	while ((bio = bio_list_pop(&bios))) {
		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

		if (h->tc == tc)
			bio_endio(bio, DM_ENDIO_REQUEUE);
		else
			bio_list_add(master, bio);
	}
}

static void requeue_io(struct thin_c *tc)
{
	struct pool *pool = tc->pool;

	requeue_bio_list(tc, &pool->deferred_bios);
	requeue_bio_list(tc, &pool->retry_on_resume_list);
}

static void error_retry_list(struct pool *pool)
{
	struct bio *bio;
	unsigned long flags;
	struct bio_list bios;

	bio_list_init(&bios);

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_merge(&bios, &pool->retry_on_resume_list);
	bio_list_init(&pool->retry_on_resume_list);
	spin_unlock_irqrestore(&pool->lock, flags);

	while ((bio = bio_list_pop(&bios)))
		bio_io_error(bio);
}

/*
 * This section of code contains the logic for processing a thin device's IO.
 * Much of the code depends on pool object resources (lists, workqueues, etc)
 * but most is exclusively called from the thin target rather than the thin-pool
 * 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_iter.bi_sector;

	if (block_size_is_power_of_two(pool))
		block_nr >>= pool->sectors_per_block_shift;
	else
		(void) sector_div(block_nr, pool->sectors_per_block);

	return block_nr;
}

static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
{
	struct pool *pool = tc->pool;
	sector_t bi_sector = bio->bi_iter.bi_sector;

	bio->bi_bdev = tc->pool_dev->bdev;
	if (block_size_is_power_of_two(pool))
		bio->bi_iter.bi_sector =
			(block << pool->sectors_per_block_shift) |
			(bi_sector & (pool->sectors_per_block - 1));
	else
		bio->bi_iter.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)
{
	bio->bi_bdev = tc->origin_dev->bdev;
}

static int bio_triggers_commit(struct thin_c *tc, struct bio *bio)
{
	return (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) &&
		dm_thin_changed_this_transaction(tc->td);
}

static void inc_all_io_entry(struct pool *pool, struct bio *bio)
{
	struct dm_thin_endio_hook *h;

	if (bio->bi_rw & REQ_DISCARD)
		return;

	h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
	h->all_io_entry = dm_deferred_entry_inc(pool->all_io_ds);
}

static void issue(struct thin_c *tc, struct bio *bio)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	if (!bio_triggers_commit(tc, bio)) {
		generic_make_request(bio);
		return;
	}

	/*
	 * Complete bio with an error if earlier I/O caused changes to
	 * the metadata that can't be committed e.g, due to I/O errors
	 * on the metadata device.
	 */
	if (dm_thin_aborted_changes(tc->td)) {
		bio_io_error(bio);
		return;
	}

	/*
	 * Batch together any bios that trigger commits and then issue a
	 * single commit for them in process_deferred_bios().
	 */
	spin_lock_irqsave(&pool->lock, flags);
	bio_list_add(&pool->deferred_flush_bios, bio);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static void remap_to_origin_and_issue(struct thin_c *tc, struct bio *bio)
{
	remap_to_origin(tc, bio);
	issue(tc, bio);
}

static void remap_and_issue(struct thin_c *tc, struct bio *bio,
			    dm_block_t block)
{
	remap(tc, bio, block);
	issue(tc, bio);
}

/*----------------------------------------------------------------*/

/*
 * Bio endio functions.
 */
struct dm_thin_new_mapping {
	struct list_head list;

	bool quiesced:1;
	bool prepared:1;
	bool pass_discard:1;
	bool definitely_not_shared:1;

	int err;
	struct thin_c *tc;
	dm_block_t virt_block;
	dm_block_t data_block;
	struct dm_bio_prison_cell *cell, *cell2;

	/*
	 * If the bio covers the whole area of a block then we can avoid
	 * zeroing or copying.  Instead this bio is hooked.  The bio will
	 * still be in the cell, so care has to be taken to avoid issuing
	 * the bio twice.
	 */
	struct bio *bio;
	bio_end_io_t *saved_bi_end_io;
};

static void __maybe_add_mapping(struct dm_thin_new_mapping *m)
{
	struct pool *pool = m->tc->pool;

	if (m->quiesced && m->prepared) {
		list_add_tail(&m->list, &pool->prepared_mappings);
		wake_worker(pool);
	}
}

static void copy_complete(int read_err, unsigned long write_err, void *context)
{
	unsigned long flags;
	struct dm_thin_new_mapping *m = context;
	struct pool *pool = m->tc->pool;

	m->err = read_err || write_err ? -EIO : 0;

	spin_lock_irqsave(&pool->lock, flags);
	m->prepared = true;
	__maybe_add_mapping(m);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static void overwrite_endio(struct bio *bio, int err)
{
	unsigned long flags;
	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
	struct dm_thin_new_mapping *m = h->overwrite_mapping;
	struct pool *pool = m->tc->pool;

	m->err = err;

	spin_lock_irqsave(&pool->lock, flags);
	m->prepared = true;
	__maybe_add_mapping(m);
	spin_unlock_irqrestore(&pool->lock, flags);
}

/*----------------------------------------------------------------*/

/*
 * Workqueue.
 */

/*
 * Prepared mapping jobs.
 */

/*
 * This sends the bios in the cell back to the deferred_bios list.
 */
static void cell_defer(struct thin_c *tc, struct dm_bio_prison_cell *cell)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	cell_release(pool, cell, &pool->deferred_bios);
	spin_unlock_irqrestore(&tc->pool->lock, flags);

	wake_worker(pool);
}

/*
 * 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)
{
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	cell_release_no_holder(pool, cell, &pool->deferred_bios);
	spin_unlock_irqrestore(&pool->lock, flags);

	wake_worker(pool);
}

static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
{
	if (m->bio) {
		m->bio->bi_end_io = m->saved_bi_end_io;
		atomic_inc(&m->bio->bi_remaining);
	}
	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 = m->bio;
	if (bio) {
		bio->bi_end_io = m->saved_bi_end_io;
		atomic_inc(&bio->bi_remaining);
	}

	if (m->err) {
		cell_error(pool, m->cell);
		goto out;
	}

	/*
	 * Commit the prepared block into the mapping btree.
	 * Any I/O for this block arriving after this point will get
	 * remapped to it directly.
	 */
	r = dm_thin_insert_block(tc->td, m->virt_block, m->data_block);
	if (r) {
		metadata_operation_failed(pool, "dm_thin_insert_block", r);
		cell_error(pool, m->cell);
		goto out;
	}

	/*
	 * Release any bios held while the block was being provisioned.
	 * If we are processing a write bio that completely covers the block,
	 * we already processed it so can ignore it now when processing
	 * the bios in the cell.
	 */
	if (bio) {
		cell_defer_no_holder(tc, m->cell);
		bio_endio(bio, 0);
	} else
		cell_defer(tc, m->cell);

out:
	list_del(&m->list);
	mempool_free(m, pool->mapping_pool);
}

static void process_prepared_discard_fail(struct dm_thin_new_mapping *m)
{
	struct thin_c *tc = m->tc;

	bio_io_error(m->bio);
	cell_defer_no_holder(tc, m->cell);
	cell_defer_no_holder(tc, m->cell2);
	mempool_free(m, tc->pool->mapping_pool);
}

static void process_prepared_discard_passdown(struct dm_thin_new_mapping *m)
{
	struct thin_c *tc = m->tc;

	inc_all_io_entry(tc->pool, m->bio);
	cell_defer_no_holder(tc, m->cell);
	cell_defer_no_holder(tc, m->cell2);

	if (m->pass_discard)
		if (m->definitely_not_shared)
			remap_and_issue(tc, m->bio, m->data_block);
		else {
			bool used = false;
			if (dm_pool_block_is_used(tc->pool->pmd, m->data_block, &used) || used)
				bio_endio(m->bio, 0);
			else
				remap_and_issue(tc, m->bio, m->data_block);
		}
	else
		bio_endio(m->bio, 0);

	mempool_free(m, tc->pool->mapping_pool);
}

static void process_prepared_discard(struct dm_thin_new_mapping *m)
{
	int r;
	struct thin_c *tc = m->tc;

	r = dm_thin_remove_block(tc->td, m->virt_block);
	if (r)
		DMERR_LIMIT("dm_thin_remove_block() failed");

	process_prepared_discard_passdown(m);
}

static void process_prepared(struct pool *pool, struct list_head *head,
			     process_mapping_fn *fn)
{
	unsigned long flags;
	struct list_head maps;
	struct dm_thin_new_mapping *m, *tmp;

	INIT_LIST_HEAD(&maps);
	spin_lock_irqsave(&pool->lock, flags);
	list_splice_init(head, &maps);
	spin_unlock_irqrestore(&pool->lock, flags);

	list_for_each_entry_safe(m, tmp, &maps, list)
		(*fn)(m);
}

/*
 * Deferred bio jobs.
 */
static int io_overlaps_block(struct pool *pool, struct bio *bio)
{
	return bio->bi_iter.bi_size ==
		(pool->sectors_per_block << SECTOR_SHIFT);
}

static int io_overwrites_block(struct pool *pool, struct bio *bio)
{
	return (bio_data_dir(bio) == WRITE) &&
		io_overlaps_block(pool, bio);
}

static void save_and_set_endio(struct bio *bio, bio_end_io_t **save,
			       bio_end_io_t *fn)
{
	*save = bio->bi_end_io;
	bio->bi_end_io = fn;
}

static int ensure_next_mapping(struct pool *pool)
{
	if (pool->next_mapping)
		return 0;

	pool->next_mapping = mempool_alloc(pool->mapping_pool, GFP_ATOMIC);

	return pool->next_mapping ? 0 : -ENOMEM;
}

static struct dm_thin_new_mapping *get_next_mapping(struct pool *pool)
{
	struct dm_thin_new_mapping *m = pool->next_mapping;

	BUG_ON(!pool->next_mapping);

	memset(m, 0, sizeof(struct dm_thin_new_mapping));
	INIT_LIST_HEAD(&m->list);
	m->bio = NULL;

	pool->next_mapping = NULL;

	return m;
}

static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
			  struct dm_dev *origin, dm_block_t data_origin,
			  dm_block_t data_dest,
			  struct dm_bio_prison_cell *cell, struct bio *bio)
{
	int r;
	struct pool *pool = tc->pool;
	struct dm_thin_new_mapping *m = get_next_mapping(pool);

	m->tc = tc;
	m->virt_block = virt_block;
	m->data_block = data_dest;
	m->cell = cell;

	if (!dm_deferred_set_add_work(pool->shared_read_ds, &m->list))
		m->quiesced = true;

	/*
	 * IO to pool_dev remaps to the pool target's data_dev.
	 *
	 * If the whole block of data is being overwritten, we can issue the
	 * bio immediately. Otherwise we use kcopyd to clone the data first.
	 */
	if (io_overwrites_block(pool, bio)) {
		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

		h->overwrite_mapping = m;
		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		inc_all_io_entry(pool, bio);
		remap_and_issue(tc, bio, data_dest);
	} else {
		struct dm_io_region from, to;

		from.bdev = origin->bdev;
		from.sector = data_origin * pool->sectors_per_block;
		from.count = pool->sectors_per_block;

		to.bdev = tc->pool_dev->bdev;
		to.sector = data_dest * pool->sectors_per_block;
		to.count = pool->sectors_per_block;

		r = dm_kcopyd_copy(pool->copier, &from, 1, &to,
				   0, copy_complete, m);
		if (r < 0) {
			mempool_free(m, pool->mapping_pool);
			DMERR_LIMIT("dm_kcopyd_copy() failed");
			cell_error(pool, cell);
		}
	}
}

static void schedule_internal_copy(struct thin_c *tc, dm_block_t virt_block,
				   dm_block_t data_origin, dm_block_t data_dest,
				   struct dm_bio_prison_cell *cell, struct bio *bio)
{
	schedule_copy(tc, virt_block, tc->pool_dev,
		      data_origin, data_dest, cell, bio);
}

static void schedule_external_copy(struct thin_c *tc, dm_block_t virt_block,
				   dm_block_t data_dest,
				   struct dm_bio_prison_cell *cell, struct bio *bio)
{
	schedule_copy(tc, virt_block, tc->origin_dev,
		      virt_block, data_dest, cell, bio);
}

static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
			  dm_block_t data_block, struct dm_bio_prison_cell *cell,
			  struct bio *bio)
{
	struct pool *pool = tc->pool;
	struct dm_thin_new_mapping *m = get_next_mapping(pool);

	m->quiesced = true;
	m->prepared = false;
	m->tc = tc;
	m->virt_block = virt_block;
	m->data_block = data_block;
	m->cell = cell;

	/*
	 * If the whole block of data is being overwritten or we are not
	 * zeroing pre-existing data, we can issue the bio immediately.
	 * Otherwise we use kcopyd to zero the data first.
	 */
	if (!pool->pf.zero_new_blocks)
		process_prepared_mapping(m);

	else if (io_overwrites_block(pool, bio)) {
		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

		h->overwrite_mapping = m;
		m->bio = bio;
		save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
		inc_all_io_entry(pool, bio);
		remap_and_issue(tc, bio, data_block);
	} else {
		int r;
		struct dm_io_region to;

		to.bdev = tc->pool_dev->bdev;
		to.sector = data_block * pool->sectors_per_block;
		to.count = pool->sectors_per_block;

		r = dm_kcopyd_zero(pool->copier, 1, &to, 0, copy_complete, m);
		if (r < 0) {
			mempool_free(m, pool->mapping_pool);
			DMERR_LIMIT("dm_kcopyd_zero() failed");
			cell_error(pool, cell);
		}
	}
}

/*
 * A non-zero return indicates read_only or fail_io mode.
 * Many callers don't care about the return value.
 */
static int commit(struct pool *pool)
{
	int r;

	if (get_pool_mode(pool) != PM_WRITE)
		return -EINVAL;

	r = dm_pool_commit_metadata(pool->pmd);
	if (r)
		metadata_operation_failed(pool, "dm_pool_commit_metadata", r);

	return r;
}

static void check_low_water_mark(struct pool *pool, dm_block_t free_blocks)
{
	unsigned long flags;

	if (free_blocks <= pool->low_water_blocks && !pool->low_water_triggered) {
		DMWARN("%s: reached low water mark for data device: sending event.",
		       dm_device_name(pool->pool_md));
		spin_lock_irqsave(&pool->lock, flags);
		pool->low_water_triggered = true;
		spin_unlock_irqrestore(&pool->lock, flags);
		dm_table_event(pool->ti->table);
	}
}

static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);

static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
{
	int r;
	dm_block_t free_blocks;
	struct pool *pool = tc->pool;

	if (WARN_ON(get_pool_mode(pool) != PM_WRITE))
		return -EINVAL;

	r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
	if (r) {
		metadata_operation_failed(pool, "dm_pool_get_free_block_count", r);
		return r;
	}

	check_low_water_mark(pool, free_blocks);

	if (!free_blocks) {
		/*
		 * Try to commit to see if that will free up some
		 * more space.
		 */
		r = commit(pool);
		if (r)
			return r;

		r = dm_pool_get_free_block_count(pool->pmd, &free_blocks);
		if (r) {
			metadata_operation_failed(pool, "dm_pool_get_free_block_count", r);
			return r;
		}

		if (!free_blocks) {
			set_pool_mode(pool, PM_OUT_OF_DATA_SPACE);
			return -ENOSPC;
		}
	}

	r = dm_pool_alloc_data_block(pool->pmd, result);
	if (r) {
		metadata_operation_failed(pool, "dm_pool_alloc_data_block", r);
		return r;
	}

	return 0;
}

/*
 * If we have run out of space, queue bios until the device is
 * resumed, presumably after having been reloaded with more space.
 */
static void retry_on_resume(struct bio *bio)
{
	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
	struct thin_c *tc = h->tc;
	struct pool *pool = tc->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_add(&pool->retry_on_resume_list, bio);
	spin_unlock_irqrestore(&pool->lock, flags);
}

static bool should_error_unserviceable_bio(struct pool *pool)
{
	enum pool_mode m = get_pool_mode(pool);

	switch (m) {
	case PM_WRITE:
		/* Shouldn't get here */
		DMERR_LIMIT("bio unserviceable, yet pool is in PM_WRITE mode");
		return true;

	case PM_OUT_OF_DATA_SPACE:
		return pool->pf.error_if_no_space;

	case PM_READ_ONLY:
	case PM_FAIL:
		return true;
	default:
		/* Shouldn't get here */
		DMERR_LIMIT("bio unserviceable, yet pool has an unknown mode");
		return true;
	}
}

static void handle_unserviceable_bio(struct pool *pool, struct bio *bio)
{
	if (should_error_unserviceable_bio(pool))
		bio_io_error(bio);
	else
		retry_on_resume(bio);
}

static void retry_bios_on_resume(struct pool *pool, struct dm_bio_prison_cell *cell)
{
	struct bio *bio;
	struct bio_list bios;

	if (should_error_unserviceable_bio(pool)) {
		cell_error(pool, cell);
		return;
	}

	bio_list_init(&bios);
	cell_release(pool, cell, &bios);

	if (should_error_unserviceable_bio(pool))
		while ((bio = bio_list_pop(&bios)))
			bio_io_error(bio);
	else
		while ((bio = bio_list_pop(&bios)))
			retry_on_resume(bio);
}

static void process_discard(struct thin_c *tc, struct bio *bio)
{
	int r;
	unsigned long flags;
	struct pool *pool = tc->pool;
	struct dm_bio_prison_cell *cell, *cell2;
	struct dm_cell_key key, key2;
	dm_block_t block = get_bio_block(tc, bio);
	struct dm_thin_lookup_result lookup_result;
	struct dm_thin_new_mapping *m;

	build_virtual_key(tc->td, block, &key);
	if (bio_detain(tc->pool, &key, bio, &cell))
		return;

	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
	switch (r) {
	case 0:
		/*
		 * Check nobody is fiddling with this pool block.  This can
		 * happen if someone's in the process of breaking sharing
		 * on this block.
		 */
		build_data_key(tc->td, lookup_result.block, &key2);
		if (bio_detain(tc->pool, &key2, bio, &cell2)) {
			cell_defer_no_holder(tc, cell);
			break;
		}

		if (io_overlaps_block(pool, bio)) {
			/*
			 * IO may still be going to the destination block.  We must
			 * quiesce before we can do the removal.
			 */
			m = get_next_mapping(pool);
			m->tc = tc;
			m->pass_discard = pool->pf.discard_passdown;
			m->definitely_not_shared = !lookup_result.shared;
			m->virt_block = block;
			m->data_block = lookup_result.block;
			m->cell = cell;
			m->cell2 = cell2;
			m->bio = bio;

			if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list)) {
				spin_lock_irqsave(&pool->lock, flags);
				list_add_tail(&m->list, &pool->prepared_discards);
				spin_unlock_irqrestore(&pool->lock, flags);
				wake_worker(pool);
			}
		} else {
			inc_all_io_entry(pool, bio);
			cell_defer_no_holder(tc, cell);
			cell_defer_no_holder(tc, cell2);

			/*
			 * The DM core makes sure that the discard doesn't span
			 * a block boundary.  So we submit the discard of a
			 * partial block appropriately.
			 */
			if ((!lookup_result.shared) && pool->pf.discard_passdown)
				remap_and_issue(tc, bio, lookup_result.block);
			else
				bio_endio(bio, 0);
		}
		break;

	case -ENODATA:
		/*
		 * It isn't provisioned, just forget it.
		 */
		cell_defer_no_holder(tc, cell);
		bio_endio(bio, 0);
		break;

	default:
		DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
			    __func__, r);
		cell_defer_no_holder(tc, cell);
		bio_io_error(bio);
		break;
	}
}

static void break_sharing(struct thin_c *tc, struct bio *bio, dm_block_t block,
			  struct dm_cell_key *key,
			  struct dm_thin_lookup_result *lookup_result,
			  struct dm_bio_prison_cell *cell)
{
	int r;
	dm_block_t data_block;
	struct pool *pool = tc->pool;

	r = alloc_data_block(tc, &data_block);
	switch (r) {
	case 0:
		schedule_internal_copy(tc, block, lookup_result->block,
				       data_block, cell, bio);
		break;

	case -ENOSPC:
		retry_bios_on_resume(pool, cell);
		break;

	default:
		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
			    __func__, r);
		cell_error(pool, cell);
		break;
	}
}

static void process_shared_bio(struct thin_c *tc, struct bio *bio,
			       dm_block_t block,
			       struct dm_thin_lookup_result *lookup_result)
{
	struct dm_bio_prison_cell *cell;
	struct pool *pool = tc->pool;
	struct dm_cell_key key;

	/*
	 * If cell is already occupied, then sharing is already in the process
	 * of being broken so we have nothing further to do here.
	 */
	build_data_key(tc->td, lookup_result->block, &key);
	if (bio_detain(pool, &key, bio, &cell))
		return;

	if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size)
		break_sharing(tc, bio, block, &key, lookup_result, cell);
	else {
		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

		h->shared_read_entry = dm_deferred_entry_inc(pool->shared_read_ds);
		inc_all_io_entry(pool, bio);
		cell_defer_no_holder(tc, cell);

		remap_and_issue(tc, bio, lookup_result->block);
	}
}

static void provision_block(struct thin_c *tc, struct bio *bio, dm_block_t block,
			    struct dm_bio_prison_cell *cell)
{
	int r;
	dm_block_t data_block;
	struct pool *pool = tc->pool;

	/*
	 * Remap empty bios (flushes) immediately, without provisioning.
	 */
	if (!bio->bi_iter.bi_size) {
		inc_all_io_entry(pool, bio);
		cell_defer_no_holder(tc, cell);

		remap_and_issue(tc, bio, 0);
		return;
	}

	/*
	 * Fill read bios with zeroes and complete them immediately.
	 */
	if (bio_data_dir(bio) == READ) {
		zero_fill_bio(bio);
		cell_defer_no_holder(tc, cell);
		bio_endio(bio, 0);
		return;
	}

	r = alloc_data_block(tc, &data_block);
	switch (r) {
	case 0:
		if (tc->origin_dev)
			schedule_external_copy(tc, block, data_block, cell, bio);
		else
			schedule_zero(tc, block, data_block, cell, bio);
		break;

	case -ENOSPC:
		retry_bios_on_resume(pool, cell);
		break;

	default:
		DMERR_LIMIT("%s: alloc_data_block() failed: error = %d",
			    __func__, r);
		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;
	struct dm_thin_lookup_result lookup_result;

	/*
	 * If cell is already occupied, then the block is already
	 * being provisioned so we have nothing further to do here.
	 */
	build_virtual_key(tc->td, block, &key);
	if (bio_detain(pool, &key, bio, &cell))
		return;

	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
	switch (r) {
	case 0:
		if (lookup_result.shared) {
			process_shared_bio(tc, bio, block, &lookup_result);
			cell_defer_no_holder(tc, cell); /* FIXME: pass this cell into process_shared? */
		} else {
			inc_all_io_entry(pool, bio);
			cell_defer_no_holder(tc, cell);

			remap_and_issue(tc, bio, lookup_result.block);
		}
		break;

	case -ENODATA:
		if (bio_data_dir(bio) == READ && tc->origin_dev) {
			inc_all_io_entry(pool, bio);
			cell_defer_no_holder(tc, cell);

			remap_to_origin_and_issue(tc, bio);
		} else
			provision_block(tc, bio, block, cell);
		break;

	default:
		DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
			    __func__, r);
		cell_defer_no_holder(tc, cell);
		bio_io_error(bio);
		break;
	}
}

static void process_bio_read_only(struct thin_c *tc, struct bio *bio)
{
	int r;
	int rw = bio_data_dir(bio);
	dm_block_t block = get_bio_block(tc, bio);
	struct dm_thin_lookup_result lookup_result;

	r = dm_thin_find_block(tc->td, block, 1, &lookup_result);
	switch (r) {
	case 0:
		if (lookup_result.shared && (rw == WRITE) && bio->bi_iter.bi_size)
			handle_unserviceable_bio(tc->pool, bio);
		else {
			inc_all_io_entry(tc->pool, bio);
			remap_and_issue(tc, bio, lookup_result.block);
		}
		break;

	case -ENODATA:
		if (rw != READ) {
			handle_unserviceable_bio(tc->pool, bio);
			break;
		}

		if (tc->origin_dev) {
			inc_all_io_entry(tc->pool, bio);
			remap_to_origin_and_issue(tc, bio);
			break;
		}

		zero_fill_bio(bio);
		bio_endio(bio, 0);
		break;

	default:
		DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
			    __func__, r);
		bio_io_error(bio);
		break;
	}
}

static void process_bio_success(struct thin_c *tc, struct bio *bio)
{
	bio_endio(bio, 0);
}

static void process_bio_fail(struct thin_c *tc, struct bio *bio)
{
	bio_io_error(bio);
}

/*
 * FIXME: should we also commit due to size of transaction, measured in
 * metadata blocks?
 */
static int need_commit_due_to_time(struct pool *pool)
{
	return jiffies < pool->last_commit_jiffies ||
	       jiffies > pool->last_commit_jiffies + COMMIT_PERIOD;
}

static void process_deferred_bios(struct pool *pool)
{
	unsigned long flags;
	struct bio *bio;
	struct bio_list bios;

	bio_list_init(&bios);

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_merge(&bios, &pool->deferred_bios);
	bio_list_init(&pool->deferred_bios);
	spin_unlock_irqrestore(&pool->lock, flags);

	while ((bio = bio_list_pop(&bios))) {
		struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
		struct thin_c *tc = h->tc;

		if (tc->requeue_mode) {
			bio_endio(bio, DM_ENDIO_REQUEUE);
			continue;
		}

		/*
		 * If we've got no free new_mapping structs, and processing
		 * this bio might require one, we pause until there are some
		 * prepared mappings to process.
		 */
		if (ensure_next_mapping(pool)) {
			spin_lock_irqsave(&pool->lock, flags);
			bio_list_merge(&pool->deferred_bios, &bios);
			spin_unlock_irqrestore(&pool->lock, flags);

			break;
		}

		if (bio->bi_rw & REQ_DISCARD)
			pool->process_discard(tc, bio);
		else
			pool->process_bio(tc, bio);
	}

	/*
	 * If there are any deferred flush bios, we must commit
	 * the metadata before issuing them.
	 */
	bio_list_init(&bios);
	spin_lock_irqsave(&pool->lock, flags);
	bio_list_merge(&bios, &pool->deferred_flush_bios);
	bio_list_init(&pool->deferred_flush_bios);
	spin_unlock_irqrestore(&pool->lock, flags);

	if (bio_list_empty(&bios) &&
	    !(dm_pool_changed_this_transaction(pool->pmd) && need_commit_due_to_time(pool)))
		return;

	if (commit(pool)) {
		while ((bio = bio_list_pop(&bios)))
			bio_io_error(bio);
		return;
	}
	pool->last_commit_jiffies = jiffies;

	while ((bio = bio_list_pop(&bios)))
		generic_make_request(bio);
}

static void do_worker(struct work_struct *ws)
{
	struct pool *pool = container_of(ws, struct pool, worker);

	process_prepared(pool, &pool->prepared_mappings, &pool->process_prepared_mapping);
	process_prepared(pool, &pool->prepared_discards, &pool->process_prepared_discard);
	process_deferred_bios(pool);
}

/*
 * We want to commit periodically so that not too much
 * unwritten data builds up.
 */
static void do_waker(struct work_struct *ws)
{
	struct pool *pool = container_of(to_delayed_work(ws), struct pool, waker);
	wake_worker(pool);
	queue_delayed_work(pool->wq, &pool->waker, COMMIT_PERIOD);
}

/*----------------------------------------------------------------*/

struct noflush_work {
	struct work_struct worker;
	struct thin_c *tc;

	atomic_t complete;
	wait_queue_head_t wait;
};

static void complete_noflush_work(struct noflush_work *w)
{
	atomic_set(&w->complete, 1);
	wake_up(&w->wait);
}

static void do_noflush_start(struct work_struct *ws)
{
	struct noflush_work *w = container_of(ws, struct noflush_work, worker);
	w->tc->requeue_mode = true;
	requeue_io(w->tc);
	complete_noflush_work(w);
}

static void do_noflush_stop(struct work_struct *ws)
{
	struct noflush_work *w = container_of(ws, struct noflush_work, worker);
	w->tc->requeue_mode = false;
	complete_noflush_work(w);
}

static void noflush_work(struct thin_c *tc, void (*fn)(struct work_struct *))
{
	struct noflush_work w;

	INIT_WORK(&w.worker, fn);
	w.tc = tc;
	atomic_set(&w.complete, 0);
	init_waitqueue_head(&w.wait);

	queue_work(tc->pool->wq, &w.worker);

	wait_event(w.wait, atomic_read(&w.complete));
}

/*----------------------------------------------------------------*/

static enum pool_mode get_pool_mode(struct pool *pool)
{
	return pool->pf.mode;
}

static void notify_of_pool_mode_change(struct pool *pool, const char *new_mode)
{
	dm_table_event(pool->ti->table);
	DMINFO("%s: switching pool to %s mode",
	       dm_device_name(pool->pool_md), new_mode);
}

static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
{
	struct pool_c *pt = pool->ti->private;
	bool needs_check = dm_pool_metadata_needs_check(pool->pmd);
	enum pool_mode old_mode = get_pool_mode(pool);

	/*
	 * Never allow the pool to transition to PM_WRITE mode if user
	 * intervention is required to verify metadata and data consistency.
	 */
	if (new_mode == PM_WRITE && needs_check) {
		DMERR("%s: unable to switch pool to write mode until repaired.",
		      dm_device_name(pool->pool_md));
		if (old_mode != new_mode)
			new_mode = old_mode;
		else
			new_mode = PM_READ_ONLY;
	}
	/*
	 * If we were in PM_FAIL mode, rollback of metadata failed.  We're
	 * not going to recover without a thin_repair.	So we never let the
	 * pool move out of the old mode.
	 */
	if (old_mode == PM_FAIL)
		new_mode = old_mode;

	switch (new_mode) {
	case PM_FAIL:
		if (old_mode != new_mode)
			notify_of_pool_mode_change(pool, "failure");
		dm_pool_metadata_read_only(pool->pmd);
		pool->process_bio = process_bio_fail;
		pool->process_discard = process_bio_fail;
		pool->process_prepared_mapping = process_prepared_mapping_fail;
		pool->process_prepared_discard = process_prepared_discard_fail;

		error_retry_list(pool);
		break;

	case PM_READ_ONLY:
		if (old_mode != new_mode)
			notify_of_pool_mode_change(pool, "read-only");
		dm_pool_metadata_read_only(pool->pmd);
		pool->process_bio = process_bio_read_only;
		pool->process_discard = process_bio_success;
		pool->process_prepared_mapping = process_prepared_mapping_fail;
		pool->process_prepared_discard = process_prepared_discard_passdown;

		error_retry_list(pool);
		break;

	case PM_OUT_OF_DATA_SPACE:
		/*
		 * Ideally we'd never hit this state; the low water mark
		 * would trigger userland to extend the pool before we
		 * completely run out of data space.  However, many small
		 * IOs to unprovisioned space can consume data space at an
		 * alarming rate.  Adjust your low water mark if you're
		 * frequently seeing this mode.
		 */
		if (old_mode != new_mode)
			notify_of_pool_mode_change(pool, "out-of-data-space");
		pool->process_bio = process_bio_read_only;
		pool->process_discard = process_discard;
		pool->process_prepared_mapping = process_prepared_mapping;
		pool->process_prepared_discard = process_prepared_discard_passdown;
		break;

	case PM_WRITE:
		if (old_mode != new_mode)
			notify_of_pool_mode_change(pool, "write");
		dm_pool_metadata_read_write(pool->pmd);
		pool->process_bio = process_bio;
		pool->process_discard = process_discard;
		pool->process_prepared_mapping = process_prepared_mapping;
		pool->process_prepared_discard = process_prepared_discard;
		break;
	}

	pool->pf.mode = new_mode;
	/*
	 * The pool mode may have changed, sync it so bind_control_target()
	 * doesn't cause an unexpected mode transition on resume.
	 */
	pt->adjusted_pf.mode = new_mode;
}

static void abort_transaction(struct pool *pool)
{
	const char *dev_name = dm_device_name(pool->pool_md);

	DMERR_LIMIT("%s: aborting current metadata transaction", dev_name);
	if (dm_pool_abort_metadata(pool->pmd)) {
		DMERR("%s: failed to abort metadata transaction", dev_name);
		set_pool_mode(pool, PM_FAIL);
	}

	if (dm_pool_metadata_set_needs_check(pool->pmd)) {
		DMERR("%s: failed to set 'needs_check' flag in metadata", dev_name);
		set_pool_mode(pool, PM_FAIL);
	}
}

static void metadata_operation_failed(struct pool *pool, const char *op, int r)
{
	DMERR_LIMIT("%s: metadata operation '%s' failed: error = %d",
		    dm_device_name(pool->pool_md), op, r);

	abort_transaction(pool);
	set_pool_mode(pool, PM_READ_ONLY);
}

/*----------------------------------------------------------------*/

/*
 * Mapping functions.
 */

/*
 * Called only while mapping a thin bio to hand it over to the workqueue.
 */
static void thin_defer_bio(struct thin_c *tc, struct bio *bio)
{
	unsigned long flags;
	struct pool *pool = tc->pool;

	spin_lock_irqsave(&pool->lock, flags);
	bio_list_add(&pool->deferred_bios, bio);
	spin_unlock_irqrestore(&pool->lock, flags);

	wake_worker(pool);
}

static void thin_hook_bio(struct thin_c *tc, struct bio *bio)
{
	struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));

	h->tc = tc;
	h->shared_read_entry = NULL;
	h->all_io_entry = NULL;
	h->overwrite_mapping = NULL;
}

/*
 * Non-blocking function called from the thin target's map function.
 */
static int thin_bio_map(struct dm_target *ti, struct bio *bio)
{
	int r;
	struct thin_c *tc = ti->private;
	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 *cell_result;
	struct dm_cell_key key;

	thin_hook_bio(tc, bio);

	if (tc->requeue_mode) {
		bio_endio(bio, DM_ENDIO_REQUEUE);
		return DM_MAPIO_SUBMITTED;
	}

	if (get_pool_mode(tc->pool) == PM_FAIL) {
		bio_io_error(bio);
		return DM_MAPIO_SUBMITTED;
	}

	if (bio->bi_rw & (REQ_DISCARD | REQ_FLUSH | REQ_FUA)) {
		thin_defer_bio(tc, bio);
		return DM_MAPIO_SUBMITTED;
	}

	r = dm_thin_find_block(td, block, 0, &result);

	/*
	 * Note that we defer readahead too.
	 */
	switch (r) {
	case 0:
		if (unlikely(result.shared)) {
			/*
			 * We have a race condition here between the
			 * result.shared value returned by the lookup and
			 * snapshot creation, which may cause new
			 * sharing.
			 *
			 * To avoid this always quiesce the origin before
			 * taking the snap.  You want to do this anyway to
			 * ensure a consistent application view
			 * (i.e. lockfs).
			 *
			 * More distant ancestors are irrelevant. The
			 * shared flag will be set in their case.
			 */
			thin_defer_bio(tc, bio);
			return DM_MAPIO_SUBMITTED;
		}

		build_virtual_key(tc->td, block, &key);
		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_result)) {
			cell_defer_no_holder_no_free(tc, &cell1);
			return DM_MAPIO_SUBMITTED;
		}

		inc_all_io_entry(tc->pool, bio);
		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;

	case -ENODATA:
		if (get_pool_mode(tc->pool) == PM_READ_ONLY) {
			/*
			 * This block isn't provisioned, and we have no way
			 * of doing so.
			 */
			handle_unserviceable_bio(tc->pool, bio);
			return DM_MAPIO_SUBMITTED;
		}
		/* fall through */

	case -EWOULDBLOCK:
		/*
		 * In future, the failed dm_thin_find_block above could
		 * provide the hint to load the metadata into cache.
		 */
		thin_defer_bio(tc, bio);
		return DM_MAPIO_SUBMITTED;

	default:
		/*
		 * Must always call bio_io_error on failure.
		 * dm_thin_find_block can fail with -EINVAL if the
		 * pool is switched to fail-io mode.
		 */
		bio_io_error(bio);
		return DM_MAPIO_SUBMITTED;
	}
}

static int pool_is_congested(struct dm_target_callbacks *cb, int bdi_bits)
{
	int r;
	unsigned long flags;
	struct pool_c *pt = container_of(cb, struct pool_c, callbacks);

	spin_lock_irqsave(&pt->pool->lock, flags);
	r = !bio_list_empty(&pt->pool->retry_on_resume_list);
	spin_unlock_irqrestore(&pt->pool->lock, flags);

	if (!r) {
		struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);
		r = bdi_congested(&q->backing_dev_info, bdi_bits);
	}

	return r;
}

static void __requeue_bios(struct pool *pool)
{
	bio_list_merge(&pool->deferred_bios, &pool->retry_on_resume_list);
	bio_list_init(&pool->retry_on_resume_list);
}

/*----------------------------------------------------------------
 * Binding of control targets to a pool object
 *--------------------------------------------------------------*/
static bool data_dev_supports_discard(struct pool_c *pt)
{
	struct request_queue *q = bdev_get_queue(pt->data_dev->bdev);

	return q && blk_queue_discard(q);
}

static bool is_factor(sector_t block_size, uint32_t n)
{
	return !sector_div(block_size, n);
}

/*
 * If discard_passdown was enabled verify that the data device
 * supports discards.  Disable discard_passdown if not.
 */
static void disable_passdown_if_not_supported(struct pool_c *pt)
{
	struct pool *pool = pt->pool;
	struct block_device *data_bdev = pt->data_dev->bdev;
	struct queue_limits *data_limits = &bdev_get_queue(data_bdev)->limits;
	sector_t block_size = pool->sectors_per_block << SECTOR_SHIFT;
	const char *reason = NULL;
	char buf[BDEVNAME_SIZE];

	if (!pt->adjusted_pf.discard_passdown)
		return;

	if (!data_dev_supports_discard(pt))
		reason = "discard unsupported";

	else if (data_limits->max_discard_sectors < pool->sectors_per_block)
		reason = "max discard sectors smaller than a block";

	else if (data_limits->discard_granularity > block_size)
		reason = "discard granularity larger than a block";

	else if (!is_factor(block_size, data_limits->discard_granularity))
		reason = "discard granularity not a factor of block size";

	if (reason) {
		DMWARN("Data device (%s) %s: Disabling discard passdown.", bdevname(data_bdev, buf), reason);
		pt->adjusted_pf.discard_passdown = false;
	}
}

static int bind_control_target(struct pool *pool, struct dm_target *ti)
{
	struct pool_c *pt = ti->private;

	/*
	 * We want to make sure that a pool in PM_FAIL mode is never upgraded.
	 */
	enum pool_mode old_mode = get_pool_mode(pool);
	enum pool_mode new_mode = pt->adjusted_pf.mode;

	/*
	 * Don't change the pool's mode until set_pool_mode() below.
	 * Otherwise the pool's process_* function pointers may
	 * not match the desired pool mode.
	 */
	pt->adjusted_pf.mode = old_mode;

	pool->ti = ti;
	pool->pf = pt->adjusted_pf;
	pool->low_water_blocks = pt->low_water_blocks;

	set_pool_mode(pool, new_mode);

	return 0;
}

static void unbind_control_target(struct pool *pool, struct dm_target *ti)
{
	if (pool->ti == ti)
		pool->ti = NULL;
}

/*----------------------------------------------------------------
 * Pool creation
 *--------------------------------------------------------------*/
/* Initialize pool features. */
static void pool_features_init(struct pool_features *pf)
{
	pf->mode = PM_WRITE;
	pf->zero_new_blocks = true;
	pf->discard_enabled = true;
	pf->discard_passdown = true;
	pf->error_if_no_space = false;
}

static void __pool_destroy(struct pool *pool)
{
	__pool_table_remove(pool);

	if (dm_pool_metadata_close(pool->pmd) < 0)
		DMWARN("%s: dm_pool_metadata_close() failed.", __func__);

	dm_bio_prison_destroy(pool->prison);
	dm_kcopyd_client_destroy(pool->copier);

	if (pool->wq)
		destroy_workqueue(pool->wq);

	if (pool->next_mapping)
		mempool_free(pool->next_mapping, pool->mapping_pool);
	mempool_destroy(pool->mapping_pool);
	dm_deferred_set_destroy(pool->shared_read_ds);
	dm_deferred_set_destroy(pool->all_io_ds);
	kfree(pool);
}

static struct kmem_cache *_new_mapping_cache;

static struct pool *pool_create(struct mapped_device *pool_md,
				struct block_device *metadata_dev,
				unsigned long block_size,
				int read_only, char **error)
{
	int r;
	void *err_p;
	struct pool *pool;
	struct dm_pool_metadata *pmd;
	bool format_device = read_only ? false : true;

	pmd = dm_pool_metadata_open(metadata_dev, block_size, format_device);
	if (IS_ERR(pmd)) {
		*error = "Error creating metadata object";
		return (struct pool *)pmd;
	}

	pool = kmalloc(sizeof(*pool), GFP_KERNEL);
	if (!pool) {
		*error = "Error allocating memory for pool";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_pool;
	}

	pool->pmd = pmd;
	pool->sectors_per_block = block_size;
	if (block_size & (block_size - 1))
		pool->sectors_per_block_shift = -1;
	else
		pool->sectors_per_block_shift = __ffs(block_size);
	pool->low_water_blocks = 0;
	pool_features_init(&pool->pf);
	pool->prison = dm_bio_prison_create(PRISON_CELLS);
	if (!pool->prison) {
		*error = "Error creating pool's bio prison";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_prison;
	}

	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";
		err_p = ERR_PTR(r);
		goto bad_kcopyd_client;
	}

	/*
	 * Create singlethreaded workqueue that will service all devices
	 * that use this metadata.
	 */
	pool->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
	if (!pool->wq) {
		*error = "Error creating pool's workqueue";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_wq;
	}

	INIT_WORK(&pool->worker, do_worker);
	INIT_DELAYED_WORK(&pool->waker, do_waker);
	spin_lock_init(&pool->lock);
	bio_list_init(&pool->deferred_bios);
	bio_list_init(&pool->deferred_flush_bios);
	INIT_LIST_HEAD(&pool->prepared_mappings);
	INIT_LIST_HEAD(&pool->prepared_discards);
	pool->low_water_triggered = false;
	bio_list_init(&pool->retry_on_resume_list);

	pool->shared_read_ds = dm_deferred_set_create();
	if (!pool->shared_read_ds) {
		*error = "Error creating pool's shared read deferred set";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_shared_read_ds;
	}

	pool->all_io_ds = dm_deferred_set_create();
	if (!pool->all_io_ds) {
		*error = "Error creating pool's all io deferred set";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_all_io_ds;
	}

	pool->next_mapping = NULL;
	pool->mapping_pool = mempool_create_slab_pool(MAPPING_POOL_SIZE,
						      _new_mapping_cache);
	if (!pool->mapping_pool) {
		*error = "Error creating pool's mapping mempool";
		err_p = ERR_PTR(-ENOMEM);
		goto bad_mapping_pool;
	}

	pool->ref_count = 1;
	pool->last_commit_jiffies = jiffies;
	pool->pool_md = pool_md;
	pool->md_dev = metadata_dev;
	__pool_table_insert(pool);

	return pool;

bad_mapping_pool:
	dm_deferred_set_destroy(pool->all_io_ds);
bad_all_io_ds:
	dm_deferred_set_destroy(pool->shared_read_ds);
bad_shared_read_ds:
	destroy_workqueue(pool->wq);
bad_wq:
	dm_kcopyd_client_destroy(pool->copier);
bad_kcopyd_client:
	dm_bio_prison_destroy(pool->prison);
bad_prison:
	kfree(pool);
bad_pool:
	if (dm_pool_metadata_close(pmd))
		DMWARN("%s: dm_pool_metadata_close() failed.", __func__);

	return err_p;
}

static void __pool_inc(struct pool *pool)
{
	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
	pool->ref_count++;
}

static void __pool_dec(struct pool *pool)
{
	BUG_ON(!mutex_is_locked(&dm_thin_pool_table.mutex));
	BUG_ON(!pool->ref_count);
	if (!--pool->ref_count)
		__pool_destroy(pool);
}

static struct pool *__pool_find(struct mapped_device *pool_md,
				struct block_device *metadata_dev,
				unsigned long block_size, int read_only,
				char **error, int *created)
{
	struct pool *pool = __pool_table_lookup_metadata_dev(metadata_dev);

	if (pool) {
		if (pool->pool_md != pool_md) {
			*error = "metadata device already in use by a pool";
			return ERR_PTR(-EBUSY);
		}
		__pool_inc(pool);

	} else {
		pool = __pool_table_lookup(pool_md);
		if (pool) {
			if (pool->md_dev != metadata_dev) {
				*error = "different pool cannot replace a pool";
				return ERR_PTR(-EINVAL);
			}
			__pool_inc(pool);

		} else {
			pool = pool_create(pool_md, metadata_dev, block_size, read_only, error);
			*created = 1;
		}
	}

	return pool;
}

/*----------------------------------------------------------------
 * Pool target methods
 *--------------------------------------------------------------*/
static void pool_dtr(struct dm_target *ti)
{
	struct pool_c *pt = ti->private;

	mutex_lock(&dm_thin_pool_table.mutex);

	unbind_control_target(pt->pool, ti);
	__pool_dec(pt->pool);
	dm_put_device(ti, pt->metadata_dev);
	dm_put_device(ti, pt->data_dev);
	kfree(pt);

	mutex_unlock(&dm_thin_pool_table.mutex);
}

static int parse_pool_features(struct dm_arg_set *as, struct pool_features *pf,
			       struct dm_target *ti)
{
	int r;
	unsigned argc;
	const char *arg_name;

	static struct dm_arg _args[] = {
		{0, 4, "Invalid number of pool feature arguments"},
	};

	/*
	 * No feature arguments supplied.
	 */
	if (!as->argc)
		return 0;

	r = dm_read_arg_group(_args, as, &argc, &ti->error);
	if (r)
		return -EINVAL;

	while (argc && !r) {
		arg_name = dm_shift_arg(as);
		argc--;

		if (!strcasecmp(arg_name, "skip_block_zeroing"))
			pf->zero_new_blocks = false;

		else if (!strcasecmp(arg_name, "ignore_discard"))
			pf->discard_enabled = false;

		else if (!strcasecmp(arg_name, "no_discard_passdown"))
			pf->discard_passdown = false;

		else if (!strcasecmp(arg_name, "read_only"))
			pf->mode = PM_READ_ONLY;

		else if (!strcasecmp(arg_name, "error_if_no_space"))
			pf->error_if_no_space = true;

		else {
			ti->error = "Unrecognised pool feature requested";
			r = -EINVAL;
			break;
		}
	}

	return r;
}

static void metadata_low_callback(void *context)
{
	struct pool *pool = context;

	DMWARN("%s: reached low water mark for metadata device: sending event.",
	       dm_device_name(pool->pool_md));

	dm_table_event(pool->ti->table);
}

static sector_t get_dev_size(struct block_device *bdev)
{
	return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
}

static void warn_if_metadata_device_too_big(struct block_device *bdev)
{
	sector_t metadata_dev_size = get_dev_size(bdev);
	char buffer[BDEVNAME_SIZE];

	if (metadata_dev_size > THIN_METADATA_MAX_SECTORS_WARNING)
		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",
		       bdevname(bdev, buffer), THIN_METADATA_MAX_SECTORS);
}

static sector_t get_metadata_dev_size(struct block_device *bdev)
{
	sector_t metadata_dev_size = get_dev_size(bdev);

	if (metadata_dev_size > THIN_METADATA_MAX_SECTORS)
		metadata_dev_size = THIN_METADATA_MAX_SECTORS;

	return metadata_dev_size;
}

static dm_block_t get_metadata_dev_size_in_blocks(struct block_device *bdev)
{
	sector_t metadata_dev_size = get_metadata_dev_size(bdev);

	sector_div(metadata_dev_size, THIN_METADATA_BLOCK_SIZE);

	return metadata_dev_size;
}

/*
 * When a metadata threshold is crossed a dm event is triggered, and
 * userland should respond by growing the metadata device.  We could let
 * userland set the threshold, like we do with the data threshold, but I'm
 * not sure they know enough to do this well.
 */
static dm_block_t calc_metadata_threshold(struct pool_c *pt)
{
	/*
	 * 4M is ample for all ops with the possible exception of thin
	 * device deletion which is harmless if it fails (just retry the
	 * delete after you've grown the device).
	 */
	dm_block_t quarter = get_metadata_dev_size_in_blocks(pt->metadata_dev->bdev) / 4;
	return min((dm_block_t)1024ULL /* 4M */, quarter);
}

/*
 * thin-pool <metadata dev> <data dev>
 *	     <data block size (sectors)>
 *	     <low water mark (blocks)>
 *	     [<#feature args> [<arg>]*]
 *
 * Optional feature arguments are:
 *	     skip_block_zeroing: skips the zeroing of newly-provisioned blocks.
 *	     ignore_discard: disable discard
 *	     no_discard_passdown: don't pass discards down to the data device
 *	     read_only: Don't allow any changes to be made to the pool metadata.
 *	     error_if_no_space: error IOs, instead of queueing, if no space.
 */
static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	int r, pool_created = 0;
	struct pool_c *pt;
	struct pool *pool;
	struct pool_features pf;
	struct dm_arg_set as;
	struct dm_dev *data_dev;
	unsigned long block_size;
	dm_block_t low_water_blocks;
	struct dm_dev *metadata_dev;
	fmode_t metadata_mode;

	/*
	 * FIXME Remove validation from scope of lock.
	 */
	mutex_lock(&dm_thin_pool_table.mutex);

	if (argc < 4) {
		ti->error = "Invalid argument count";
		r = -EINVAL;
		goto out_unlock;
	}

	as.argc = argc;
	as.argv = argv;

	/*
	 * Set default pool features.
	 */
	pool_features_init(&pf);

	dm_consume_args(&as, 4);
	r = parse_pool_features(&as, &pf, ti);
	if (r)
		goto out_unlock;

	metadata_mode = FMODE_READ | ((pf.mode == PM_READ_ONLY) ? 0 : FMODE_WRITE);
	r = dm_get_device(ti, argv[0], metadata_mode, &metadata_dev);
	if (r) {
		ti->error = "Error opening metadata block device";
		goto out_unlock;
	}
	warn_if_metadata_device_too_big(metadata_dev->bdev);

	r = dm_get_device(ti, argv[1], FMODE_READ | FMODE_WRITE, &data_dev);
	if (r) {
		ti->error = "Error getting data device";
		goto out_metadata;
	}

	if (kstrtoul(argv[2], 10, &block_size) || !block_size ||
	    block_size < DATA_DEV_BLOCK_SIZE_MIN_SECTORS ||
	    block_size > DATA_DEV_BLOCK_SIZE_MAX_SECTORS ||
	    block_size & (DATA_DEV_BLOCK_SIZE_MIN_SECTORS - 1)) {
		ti->error = "Invalid block size";
		r = -EINVAL;
		goto out;
	}

	if (kstrtoull(argv[3], 10, (unsigned long long *)&low_water_blocks)) {
		ti->error = "Invalid low water mark";
		r = -EINVAL;
		goto out;
	}

	pt = kzalloc(sizeof(*pt), GFP_KERNEL);
	if (!pt) {
		r = -ENOMEM;
		goto out;
	}

	pool = __pool_find(dm_table_get_md(ti->table), metadata_dev->bdev,
			   block_size, pf.mode == PM_READ_ONLY, &ti->error, &pool_created);
	if (IS_ERR(pool)) {
		r = PTR_ERR(pool);
		goto out_free_pt;
	}

	/*
	 * 'pool_created' reflects whether this is the first table load.
	 * Top level discard support is not allowed to be changed after
	 * initial load.  This would require a pool reload to trigger thin
	 * device changes.
	 */
	if (!pool_created && pf.discard_enabled != pool->pf.discard_enabled) {
		ti->error = "Discard support cannot be disabled once enabled";
		r = -EINVAL;
		goto out_flags_changed;
	}

	pt->pool = pool;
	pt->ti = ti;
	pt->metadata_dev = metadata_dev;
	pt->data_dev = data_dev;
	pt->low_water_blocks = low_water_blocks;
	pt->adjusted_pf = pt->requested_pf = pf;
	ti->num_flush_bios = 1;

	/*
	 * Only need to enable discards if the pool should pass
	 * them down to the data device.  The thin device's discard
	 * processing will cause mappings to be removed from the btree.
	 */
	ti->discard_zeroes_data_unsupported = true;
	if (pf.discard_enabled && pf.discard_passdown) {
		ti->num_discard_bios = 1;

		/*
		 * Setting 'discards_supported' circumvents the normal
		 * stacking of discard limits (this keeps the pool and
		 * thin devices' discard limits consistent).
		 */
		ti->discards_supported = true;
	}
	ti->private = pt;

	r = dm_pool_register_metadata_threshold(pt->pool->pmd,
						calc_metadata_threshold(pt),
						metadata_low_callback,
						pool);
	if (r)
		goto out_free_pt;

	pt->callbacks.congested_fn = pool_is_congested;
	dm_table_add_target_callbacks(ti->table, &pt->callbacks);

	mutex_unlock(&dm_thin_pool_table.mutex);

	return 0;

out_flags_changed:
	__pool_dec(pool);
out_free_pt:
	kfree(pt);
out:
	dm_put_device(ti, data_dev);
out_metadata:
	dm_put_device(ti, metadata_dev);
out_unlock:
	mutex_unlock(&dm_thin_pool_table.mutex);

	return r;
}

static int pool_map(struct dm_target *ti, struct bio *bio)
{
	int r;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;
	unsigned long flags;

	/*
	 * As this is a singleton target, ti->begin is always zero.
	 */
	spin_lock_irqsave(&pool->lock, flags);
	bio->bi_bdev = pt->data_dev->bdev;
	r = DM_MAPIO_REMAPPED;
	spin_unlock_irqrestore(&pool->lock, flags);

	return r;
}

static int maybe_resize_data_dev(struct dm_target *ti, bool *need_commit)
{
	int r;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;
	sector_t data_size = ti->len;
	dm_block_t sb_data_size;

	*need_commit = false;

	(void) sector_div(data_size, pool->sectors_per_block);

	r = dm_pool_get_data_dev_size(pool->pmd, &sb_data_size);
	if (r) {
		DMERR("%s: failed to retrieve data device size",
		      dm_device_name(pool->pool_md));
		return r;
	}

	if (data_size < sb_data_size) {
		DMERR("%s: pool target (%llu blocks) too small: expected %llu",
		      dm_device_name(pool->pool_md),
		      (unsigned long long)data_size, sb_data_size);
		return -EINVAL;

	} else if (data_size > sb_data_size) {
		if (dm_pool_metadata_needs_check(pool->pmd)) {
			DMERR("%s: unable to grow the data device until repaired.",
			      dm_device_name(pool->pool_md));
			return 0;
		}

		if (sb_data_size)
			DMINFO("%s: growing the data device from %llu to %llu blocks",
			       dm_device_name(pool->pool_md),
			       sb_data_size, (unsigned long long)data_size);
		r = dm_pool_resize_data_dev(pool->pmd, data_size);
		if (r) {
			metadata_operation_failed(pool, "dm_pool_resize_data_dev", r);
			return r;
		}

		*need_commit = true;
	}

	return 0;
}

static int maybe_resize_metadata_dev(struct dm_target *ti, bool *need_commit)
{
	int r;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;
	dm_block_t metadata_dev_size, sb_metadata_dev_size;

	*need_commit = false;

	metadata_dev_size = get_metadata_dev_size_in_blocks(pool->md_dev);

	r = dm_pool_get_metadata_dev_size(pool->pmd, &sb_metadata_dev_size);
	if (r) {
		DMERR("%s: failed to retrieve metadata device size",
		      dm_device_name(pool->pool_md));
		return r;
	}

	if (metadata_dev_size < sb_metadata_dev_size) {
		DMERR("%s: metadata device (%llu blocks) too small: expected %llu",
		      dm_device_name(pool->pool_md),
		      metadata_dev_size, sb_metadata_dev_size);
		return -EINVAL;

	} else if (metadata_dev_size > sb_metadata_dev_size) {
		if (dm_pool_metadata_needs_check(pool->pmd)) {
			DMERR("%s: unable to grow the metadata device until repaired.",
			      dm_device_name(pool->pool_md));
			return 0;
		}

		warn_if_metadata_device_too_big(pool->md_dev);
		DMINFO("%s: growing the metadata device from %llu to %llu blocks",
		       dm_device_name(pool->pool_md),
		       sb_metadata_dev_size, metadata_dev_size);
		r = dm_pool_resize_metadata_dev(pool->pmd, metadata_dev_size);
		if (r) {
			metadata_operation_failed(pool, "dm_pool_resize_metadata_dev", r);
			return r;
		}

		*need_commit = true;
	}

	return 0;
}

/*
 * Retrieves the number of blocks of the data device from
 * the superblock and compares it to the actual device size,
 * thus resizing the data device in case it has grown.
 *
 * This both copes with opening preallocated data devices in the ctr
 * being followed by a resume
 * -and-
 * calling the resume method individually after userspace has
 * grown the data device in reaction to a table event.
 */
static int pool_preresume(struct dm_target *ti)
{
	int r;
	bool need_commit1, need_commit2;
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;

	/*
	 * Take control of the pool object.
	 */
	r = bind_control_target(pool, ti);
	if (r)
		return r;

	r = maybe_resize_data_dev(ti, &need_commit1);
	if (r)
		return r;

	r = maybe_resize_metadata_dev(ti, &need_commit2);
	if (r)
		return r;

	if (need_commit1 || need_commit2)
		(void) commit(pool);

	return 0;
}

static void pool_resume(struct dm_target *ti)
{
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;
	unsigned long flags;

	spin_lock_irqsave(&pool->lock, flags);
	pool->low_water_triggered = false;
	__requeue_bios(pool);
	spin_unlock_irqrestore(&pool->lock, flags);

	do_waker(&pool->waker.work);
}

static void pool_postsuspend(struct dm_target *ti)
{
	struct pool_c *pt = ti->private;
	struct pool *pool = pt->pool;

	cancel_delayed_work(&pool->waker);
	flush_workqueue(pool->wq);
	(void) commit(pool);
}

static int check_arg_count(unsigned argc, unsigned args_required)
{
	if (argc != args_required) {
		DMWARN("Message received with %u arguments instead of %u.",
		       argc, args_required);
		return -EINVAL;
	}

	return 0;
}

static int read_dev_id(char *arg, dm_thin_id *dev_id, int warning)
{
	if (!kstrtoull(arg, 10, (unsigned long long *)dev_id) &&
	    *dev_id <= MAX_DEV_ID)
		return 0;

	if (warning)
		DMWARN("Message received with invalid device id: %s", arg);

	return -EINVAL;
}

static int process_create_thin_mesg(unsigned argc, char **argv, struct pool *pool)
{
	dm_thin_id dev_id;
	int r;

	r = check_arg_count(argc, 2);
	if (r)
		return r;

	r = read_dev_id(argv[1], &dev_id, 1);
	if (r)
		return r;

	r = dm_pool_create_thin(pool->pmd, dev_id);
	if (r) {
		DMWARN("Creation of new thinly-provisioned device with id %s failed.",
		       argv[1]);
		return r;
	}

	return 0;
}

static int process_create_snap_mesg(unsigned argc, char **argv, struct pool *pool)
{
	dm_thin_id dev_id;
	dm_thin_id origin_dev_id;
	int r;

	r = check_arg_count(argc, 3);
	if (r)
		return r;

	r = read_dev_id(argv[1], &dev_id, 1);
	if (r)
		return r;

	r = read_dev_id(argv[2], &origin_dev_id, 1);
	if (r)
		return r;

	r = dm_pool_create_snap(pool->pmd, dev_id, origin_dev_id);
	if (r) {
		DMWARN("Creation of new snapshot %s of device %s failed.",
		       argv[1], argv[2]);
		return r;
	}

	return 0;
}

static int process_delete_mesg(unsigned argc, char **argv, struct pool *pool)
{
	dm_thin_id dev_id;
	int r;

	r = check_arg_count(argc, 2);
	if (r)
		return r;

	r = read_dev_id(argv[1], &dev_id, 1);