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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /*
  * Copyright (C) 2011-2012 Red Hat UK.
  *
  * This file is released under the GPL.
  */
 
 #include "dm-thin-metadata.h"
 #include "dm-bio-prison-v1.h"
 #include "dm.h"
 
 #include <linux/device-mapper.h>
 #include <linux/dm-io.h>
 #include <linux/dm-kcopyd.h>
 #include <linux/jiffies.h>
 #include <linux/log2.h>
 #include <linux/list.h>
 #include <linux/rculist.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/sort.h>
 #include <linux/rbtree.h>
 
 #define DM_MSG_PREFIX   "thin"
 
 /*
  * Tunable constants
  */
 #define ENDIO_HOOK_POOL_SIZE 1024
 #define MAPPING_POOL_SIZE 1024
 #define COMMIT_PERIOD HZ
 #define NO_SPACE_TIMEOUT_SECS 60
 
 static unsigned no_space_timeout_secs = NO_SPACE_TIMEOUT_SECS;
 
 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.
  */
 enum lock_space {
     VIRTUAL,
     PHYSICAL
 };
 
 static void build_key(struct dm_thin_device *td, enum lock_space ls,
               dm_block_t b, dm_block_t e, struct dm_cell_key *key)
 {
     key->virtual = (ls == VIRTUAL);
     key->dev = dm_thin_dev_id(td);
     key->block_begin = b;
     key->block_end = e;
 }
 
 static void build_data_key(struct dm_thin_device *td, dm_block_t b,
                struct dm_cell_key *key)
 {
     build_key(td, PHYSICAL, b, b + 1llu, key);
 }
 
 static void build_virtual_key(struct dm_thin_device *td, dm_block_t b,
                   struct dm_cell_key *key)
 {
     build_key(td, VIRTUAL, b, b + 1llu, key);
 }
 
 /*----------------------------------------------------------------*/
 
 #define THROTTLE_THRESHOLD (1 * HZ)
 
 struct throttle {
     struct rw_semaphore lock;
     unsigned long threshold;
     bool throttle_applied;
 };
 
 static void throttle_init(struct throttle *t)
 {
     init_rwsem(&t->lock);
     t->throttle_applied = false;
 }
 
 static void throttle_work_start(struct throttle *t)
 {
     t->threshold = jiffies + THROTTLE_THRESHOLD;
 }
 
 static void throttle_work_update(struct throttle *t)
 {
     if (!t->throttle_applied && time_is_before_jiffies(t->threshold)) {
         down_write(&t->lock);
         t->throttle_applied = true;
     }
 }
 
 static void throttle_work_complete(struct throttle *t)
 {
     if (t->throttle_applied) {
         t->throttle_applied = false;
         up_write(&t->lock);
     }
 }
 
 static void throttle_lock(struct throttle *t)
 {
     down_read(&t->lock);
 }
 
 static void throttle_unlock(struct throttle *t)
 {
     up_read(&t->lock);
 }
 
 /*----------------------------------------------------------------*/
 
 /*
  * 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 various 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 */
 
     /*
      * Like READ_ONLY, except may switch back to WRITE on metadata resize. Reported as READ_ONLY.
      */
     PM_OUT_OF_METADATA_SPACE,
     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_cell_fn)(struct thin_c *tc, struct dm_bio_prison_cell *cell);
 typedef void (*process_mapping_fn)(struct dm_thin_new_mapping *m);
 
 #define CELL_SORT_ARRAY_SIZE 8192
 
 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 *data_dev;
     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 */
     bool suspended:1;
     bool out_of_data_space:1;
 
     struct dm_bio_prison *prison;
     struct dm_kcopyd_client *copier;
 
     struct work_struct worker;
     struct workqueue_struct *wq;
     struct throttle throttle;
     struct delayed_work waker;
     struct delayed_work no_space_timeout;
 
     unsigned long last_commit_jiffies;
     unsigned ref_count;
 
     spinlock_t lock;
     struct bio_list deferred_flush_bios;
     struct bio_list deferred_flush_completions;
     struct list_head prepared_mappings;
     struct list_head prepared_discards;
     struct list_head prepared_discards_pt2;
     struct list_head active_thins;
 
     struct dm_deferred_set *shared_read_ds;
     struct dm_deferred_set *all_io_ds;
 
     struct dm_thin_new_mapping *next_mapping;
 
     process_bio_fn process_bio;
     process_bio_fn process_discard;
 
     process_cell_fn process_cell;
     process_cell_fn process_discard_cell;
 
     process_mapping_fn process_prepared_mapping;
     process_mapping_fn process_prepared_discard;
     process_mapping_fn process_prepared_discard_pt2;
 
     struct dm_bio_prison_cell **cell_sort_array;
 
     mempool_t mapping_pool;
 };
 
 static void metadata_operation_failed(struct pool *pool, const char *op, int r);
 
 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 *descs[] = {
         "write",
         "out-of-data-space",
         "read-only",
         "read-only",
         "fail"
     };
     const char *extra_desc = NULL;
     enum pool_mode mode = get_pool_mode(pool);
 
     if (mode == PM_OUT_OF_DATA_SPACE) {
         if (!pool->pf.error_if_no_space)
             extra_desc = " (queue IO)";
         else
             extra_desc = " (error IO)";
     }
 
     dm_table_event(pool->ti->table);
     DMINFO("%s: switching pool to %s%s mode",
            dm_device_name(pool->pool_md),
            descs[(int)mode], extra_desc ? : "");
 }
 
 /*
  * 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;
 
     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 list_head list;
     struct dm_dev *pool_dev;
     struct dm_dev *origin_dev;
     sector_t origin_size;
     dm_thin_id dev_id;
 
     struct pool *pool;
     struct dm_thin_device *td;
     struct mapped_device *thin_md;
 
     bool requeue_mode:1;
     spinlock_t lock;
     struct list_head deferred_cells;
     struct bio_list deferred_bio_list;
     struct bio_list retry_on_resume_list;
     struct rb_root sort_bio_list; /* sorted list of deferred bios */
 
     /*
      * Ensures the thin is not destroyed until the worker has finished
      * iterating the active_thins list.
      */
     refcount_t refcount;
     struct completion can_destroy;
 };
 
 /*----------------------------------------------------------------*/
 
 static bool block_size_is_power_of_two(struct pool *pool)
 {
     return pool->sectors_per_block_shift >= 0;
 }
 
 static sector_t block_to_sectors(struct pool *pool, dm_block_t b)
 {
     return block_size_is_power_of_two(pool) ?
         (b << pool->sectors_per_block_shift) :
         (b * pool->sectors_per_block);
 }
 
 /*----------------------------------------------------------------*/
 
 struct discard_op {
     struct thin_c *tc;
     struct blk_plug plug;
     struct bio *parent_bio;
     struct bio *bio;
 };
 
 static void begin_discard(struct discard_op *op, struct thin_c *tc, struct bio *parent)
 {
     BUG_ON(!parent);
 
     op->tc = tc;
     blk_start_plug(&op->plug);
     op->parent_bio = parent;
     op->bio = NULL;
 }
 
 static int issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
 {
     struct thin_c *tc = op->tc;
     sector_t s = block_to_sectors(tc->pool, data_b);
     sector_t len = block_to_sectors(tc->pool, data_e - data_b);
 
     return __blkdev_issue_discard(tc->pool_dev->bdev, s, len, GFP_NOWAIT,
                       &op->bio);
 }
 
 static void end_discard(struct discard_op *op, int r)
 {
     if (op->bio) {
         /*
          * Even if one of the calls to issue_discard failed, we
          * need to wait for the chain to complete.
          */
         bio_chain(op->bio, op->parent_bio);
         bio_set_op_attrs(op->bio, REQ_OP_DISCARD, 0);
         submit_bio(op->bio);
     }
 
     blk_finish_plug(&op->plug);
 
     /*
      * Even if r is set, there could be sub discards in flight that we
      * need to wait for.
      */
     if (r && !op->parent_bio->bi_status)
         op->parent_bio->bi_status = errno_to_blk_status(r);
     bio_endio(op->parent_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);
 }
 
 /*----------------------------------------------------------------*/
 
 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_visit_release(struct pool *pool,
                    void (*fn)(void *, struct dm_bio_prison_cell *),
                    void *context,
                    struct dm_bio_prison_cell *cell)
 {
     dm_cell_visit_release(pool->prison, fn, context, cell);
     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_error_with_code(struct pool *pool,
         struct dm_bio_prison_cell *cell, blk_status_t error_code)
 {
     dm_cell_error(pool->prison, cell, error_code);
     dm_bio_prison_free_cell(pool->prison, cell);
 }
 
 static blk_status_t get_pool_io_error_code(struct pool *pool)
 {
     return pool->out_of_data_space ? BLK_STS_NOSPC : BLK_STS_IOERR;
 }
 
 static void cell_error(struct pool *pool, struct dm_bio_prison_cell *cell)
 {
     cell_error_with_code(pool, cell, get_pool_io_error_code(pool));
 }
 
 static void cell_success(struct pool *pool, struct dm_bio_prison_cell *cell)
 {
     cell_error_with_code(pool, cell, 0);
 }
 
 static void cell_requeue(struct pool *pool, struct dm_bio_prison_cell *cell)
 {
     cell_error_with_code(pool, cell, BLK_STS_DM_REQUEUE);
 }
 
 /*----------------------------------------------------------------*/
 
 /*
  * 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_exit(void)
 {
     mutex_destroy(&dm_thin_pool_table.mutex);
 }
 
 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;
     struct rb_node rb_node;
     struct dm_bio_prison_cell *cell;
 };
 
 static void __merge_bio_list(struct bio_list *bios, struct bio_list *master)
 {
     bio_list_merge(bios, master);
     bio_list_init(master);
 }
 
 static void error_bio_list(struct bio_list *bios, blk_status_t error)
 {
     struct bio *bio;
 
     while ((bio = bio_list_pop(bios))) {
         bio->bi_status = error;
         bio_endio(bio);
     }
 }
 
 static void error_thin_bio_list(struct thin_c *tc, struct bio_list *master,
         blk_status_t error)
 {
     struct bio_list bios;
 
     bio_list_init(&bios);
 
     spin_lock_irq(&tc->lock);
     __merge_bio_list(&bios, master);
     spin_unlock_irq(&tc->lock);
 
     error_bio_list(&bios, error);
 }
 
 static void requeue_deferred_cells(struct thin_c *tc)
 {
     struct pool *pool = tc->pool;
     struct list_head cells;
     struct dm_bio_prison_cell *cell, *tmp;
 
     INIT_LIST_HEAD(&cells);
 
     spin_lock_irq(&tc->lock);
     list_splice_init(&tc->deferred_cells, &cells);
     spin_unlock_irq(&tc->lock);
 
     list_for_each_entry_safe(cell, tmp, &cells, user_list)
         cell_requeue(pool, cell);
 }
 
 static void requeue_io(struct thin_c *tc)
 {
     struct bio_list bios;
 
     bio_list_init(&bios);
 
     spin_lock_irq(&tc->lock);
     __merge_bio_list(&bios, &tc->deferred_bio_list);
     __merge_bio_list(&bios, &tc->retry_on_resume_list);
     spin_unlock_irq(&tc->lock);
 
     error_bio_list(&bios, BLK_STS_DM_REQUEUE);
     requeue_deferred_cells(tc);
 }
 
 static void error_retry_list_with_code(struct pool *pool, blk_status_t error)
 {
     struct thin_c *tc;
 
     rcu_read_lock();
     list_for_each_entry_rcu(tc, &pool->active_thins, list)
         error_thin_bio_list(tc, &tc->retry_on_resume_list, error);
     rcu_read_unlock();
 }
 
 static void error_retry_list(struct pool *pool)
 {
     error_retry_list_with_code(pool, get_pool_io_error_code(pool));
 }
 
 /*
  * 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 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;
 }
 
 /*
  * Returns the _complete_ blocks that this bio covers.
  */
 static void get_bio_block_range(struct thin_c *tc, struct bio *bio,
                 dm_block_t *begin, dm_block_t *end)
 {
     struct pool *pool = tc->pool;
     sector_t b = bio->bi_iter.bi_sector;
     sector_t e = b + (bio->bi_iter.bi_size >> SECTOR_SHIFT);
 
     b += pool->sectors_per_block - 1ull; /* so we round up */
 
     if (block_size_is_power_of_two(pool)) {
         b >>= pool->sectors_per_block_shift;
         e >>= pool->sectors_per_block_shift;
     } else {
         (void) sector_div(b, pool->sectors_per_block);
         (void) sector_div(e, pool->sectors_per_block);
     }
 
     if (e < b)
         /* Can happen if the bio is within a single block. */
         e = b;
 
     *begin = b;
     *end = e;
 }
 
 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_set_dev(bio, 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_set_dev(bio, tc->origin_dev->bdev);
 }
 
 static int bio_triggers_commit(struct thin_c *tc, struct bio *bio)
 {
     return op_is_flush(bio->bi_opf) &&
         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_op(bio) == REQ_OP_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;
 
     if (!bio_triggers_commit(tc, bio)) {
         dm_submit_bio_remap(bio, NULL);
         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_irq(&pool->lock);
     bio_list_add(&pool->deferred_flush_bios, bio);
     spin_unlock_irq(&pool->lock);
 }
 
 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 pass_discard:1;
     bool maybe_shared:1;
 
     /*
      * Track quiescing, copying and zeroing preparation actions.  When this
      * counter hits zero the block is prepared and can be inserted into the
      * btree.
      */
     atomic_t prepare_actions;
 
     blk_status_t status;
     struct thin_c *tc;
     dm_block_t virt_begin, virt_end;
     dm_block_t data_block;
     struct dm_bio_prison_cell *cell;
 
     /*
      * 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 __complete_mapping_preparation(struct dm_thin_new_mapping *m)
 {
     struct pool *pool = m->tc->pool;
 
     if (atomic_dec_and_test(&m->prepare_actions)) {
         list_add_tail(&m->list, &pool->prepared_mappings);
         wake_worker(pool);
     }
 }
 
 static void complete_mapping_preparation(struct dm_thin_new_mapping *m)
 {
     unsigned long flags;
     struct pool *pool = m->tc->pool;
 
     spin_lock_irqsave(&pool->lock, flags);
     __complete_mapping_preparation(m);
     spin_unlock_irqrestore(&pool->lock, flags);
 }
 
 static void copy_complete(int read_err, unsigned long write_err, void *context)
 {
     struct dm_thin_new_mapping *m = context;
 
     m->status = read_err || write_err ? BLK_STS_IOERR : 0;
     complete_mapping_preparation(m);
 }
 
 static void overwrite_endio(struct bio *bio)
 {
     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;
 
     bio->bi_end_io = m->saved_bi_end_io;
 
     m->status = bio->bi_status;
     complete_mapping_preparation(m);
 }
 
 /*----------------------------------------------------------------*/
 
 /*
  * Workqueue.
  */
 
 /*
  * Prepared mapping jobs.
  */
 
 /*
  * This sends the bios in the cell, except the original holder, back
  * to the deferred_bios list.
  */
 static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     struct pool *pool = tc->pool;
     unsigned long flags;
     int has_work;
 
     spin_lock_irqsave(&tc->lock, flags);
     cell_release_no_holder(pool, cell, &tc->deferred_bio_list);
     has_work = !bio_list_empty(&tc->deferred_bio_list);
     spin_unlock_irqrestore(&tc->lock, flags);
 
     if (has_work)
         wake_worker(pool);
 }
 
 static void thin_defer_bio(struct thin_c *tc, struct bio *bio);
 
 struct remap_info {
     struct thin_c *tc;
     struct bio_list defer_bios;
     struct bio_list issue_bios;
 };
 
 static void __inc_remap_and_issue_cell(void *context,
                        struct dm_bio_prison_cell *cell)
 {
     struct remap_info *info = context;
     struct bio *bio;
 
     while ((bio = bio_list_pop(&cell->bios))) {
         if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD)
             bio_list_add(&info->defer_bios, bio);
         else {
             inc_all_io_entry(info->tc->pool, bio);
 
             /*
              * We can't issue the bios with the bio prison lock
              * held, so we add them to a list to issue on
              * return from this function.
              */
             bio_list_add(&info->issue_bios, bio);
         }
     }
 }
 
 static void inc_remap_and_issue_cell(struct thin_c *tc,
                      struct dm_bio_prison_cell *cell,
                      dm_block_t block)
 {
     struct bio *bio;
     struct remap_info info;
 
     info.tc = tc;
     bio_list_init(&info.defer_bios);
     bio_list_init(&info.issue_bios);
 
     /*
      * We have to be careful to inc any bios we're about to issue
      * before the cell is released, and avoid a race with new bios
      * being added to the cell.
      */
     cell_visit_release(tc->pool, __inc_remap_and_issue_cell,
                &info, cell);
 
     while ((bio = bio_list_pop(&info.defer_bios)))
         thin_defer_bio(tc, bio);
 
     while ((bio = bio_list_pop(&info.issue_bios)))
         remap_and_issue(info.tc, bio, block);
 }
 
 static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
 {
     cell_error(m->tc->pool, m->cell);
     list_del(&m->list);
     mempool_free(m, &m->tc->pool->mapping_pool);
 }
 
 static void complete_overwrite_bio(struct thin_c *tc, struct bio *bio)
 {
     struct pool *pool = tc->pool;
 
     /*
      * If the bio has the REQ_FUA flag set we must commit the metadata
      * before signaling its completion.
      */
     if (!bio_triggers_commit(tc, bio)) {
         bio_endio(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_irq(&pool->lock);
     bio_list_add(&pool->deferred_flush_completions, bio);
     spin_unlock_irq(&pool->lock);
 }
 
 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 = m->bio;
     int r;
 
     if (m->status) {
         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_begin, 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) {
         inc_remap_and_issue_cell(tc, m->cell, m->data_block);
         complete_overwrite_bio(tc, bio);
     } else {
         inc_all_io_entry(tc->pool, m->cell->holder);
         remap_and_issue(tc, m->cell->holder, m->data_block);
         inc_remap_and_issue_cell(tc, m->cell, m->data_block);
     }
 
 out:
     list_del(&m->list);
     mempool_free(m, &pool->mapping_pool);
 }
 
 /*----------------------------------------------------------------*/
 
 static void free_discard_mapping(struct dm_thin_new_mapping *m)
 {
     struct thin_c *tc = m->tc;
     if (m->cell)
         cell_defer_no_holder(tc, m->cell);
     mempool_free(m, &tc->pool->mapping_pool);
 }
 
 static void process_prepared_discard_fail(struct dm_thin_new_mapping *m)
 {
     bio_io_error(m->bio);
     free_discard_mapping(m);
 }
 
 static void process_prepared_discard_success(struct dm_thin_new_mapping *m)
 {
     bio_endio(m->bio);
     free_discard_mapping(m);
 }
 
 static void process_prepared_discard_no_passdown(struct dm_thin_new_mapping *m)
 {
     int r;
     struct thin_c *tc = m->tc;
 
     r = dm_thin_remove_range(tc->td, m->cell->key.block_begin, m->cell->key.block_end);
     if (r) {
         metadata_operation_failed(tc->pool, "dm_thin_remove_range", r);
         bio_io_error(m->bio);
     } else
         bio_endio(m->bio);
 
     cell_defer_no_holder(tc, m->cell);
     mempool_free(m, &tc->pool->mapping_pool);
 }
 
 /*----------------------------------------------------------------*/
 
 static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m,
                            struct bio *discard_parent)
 {
     /*
      * We've already unmapped this range of blocks, but before we
      * passdown we have to check that these blocks are now unused.
      */
     int r = 0;
     bool shared = true;
     struct thin_c *tc = m->tc;
     struct pool *pool = tc->pool;
     dm_block_t b = m->data_block, e, end = m->data_block + m->virt_end - m->virt_begin;
     struct discard_op op;
 
     begin_discard(&op, tc, discard_parent);
     while (b != end) {
         /* find start of unmapped run */
         for (; b < end; b++) {
             r = dm_pool_block_is_shared(pool->pmd, b, &shared);
             if (r)
                 goto out;
 
             if (!shared)
                 break;
         }
 
         if (b == end)
             break;
 
         /* find end of run */
         for (e = b + 1; e != end; e++) {
             r = dm_pool_block_is_shared(pool->pmd, e, &shared);
             if (r)
                 goto out;
 
             if (shared)
                 break;
         }
 
         r = issue_discard(&op, b, e);
         if (r)
             goto out;
 
         b = e;
     }
 out:
     end_discard(&op, r);
 }
 
 static void queue_passdown_pt2(struct dm_thin_new_mapping *m)
 {
     unsigned long flags;
     struct pool *pool = m->tc->pool;
 
     spin_lock_irqsave(&pool->lock, flags);
     list_add_tail(&m->list, &pool->prepared_discards_pt2);
     spin_unlock_irqrestore(&pool->lock, flags);
     wake_worker(pool);
 }
 
 static void passdown_endio(struct bio *bio)
 {
     /*
      * It doesn't matter if the passdown discard failed, we still want
      * to unmap (we ignore err).
      */
     queue_passdown_pt2(bio->bi_private);
     bio_put(bio);
 }
 
 static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m)
 {
     int r;
     struct thin_c *tc = m->tc;
     struct pool *pool = tc->pool;
     struct bio *discard_parent;
     dm_block_t data_end = m->data_block + (m->virt_end - m->virt_begin);
 
     /*
      * Only this thread allocates blocks, so we can be sure that the
      * newly unmapped blocks will not be allocated before the end of
      * the function.
      */
     r = dm_thin_remove_range(tc->td, m->virt_begin, m->virt_end);
     if (r) {
         metadata_operation_failed(pool, "dm_thin_remove_range", r);
         bio_io_error(m->bio);
         cell_defer_no_holder(tc, m->cell);
         mempool_free(m, &pool->mapping_pool);
         return;
     }
 
     /*
      * Increment the unmapped blocks.  This prevents a race between the
      * passdown io and reallocation of freed blocks.
      */
     r = dm_pool_inc_data_range(pool->pmd, m->data_block, data_end);
     if (r) {
         metadata_operation_failed(pool, "dm_pool_inc_data_range", r);
         bio_io_error(m->bio);
         cell_defer_no_holder(tc, m->cell);
         mempool_free(m, &pool->mapping_pool);
         return;
     }
 
     discard_parent = bio_alloc(NULL, 1, 0, GFP_NOIO);
     discard_parent->bi_end_io = passdown_endio;
     discard_parent->bi_private = m;
     if (m->maybe_shared)
         passdown_double_checking_shared_status(m, discard_parent);
     else {
         struct discard_op op;
 
         begin_discard(&op, tc, discard_parent);
         r = issue_discard(&op, m->data_block, data_end);
         end_discard(&op, r);
     }
 }
 
 static void process_prepared_discard_passdown_pt2(struct dm_thin_new_mapping *m)
 {
     int r;
     struct thin_c *tc = m->tc;
     struct pool *pool = tc->pool;
 
     /*
      * The passdown has completed, so now we can decrement all those
      * unmapped blocks.
      */
     r = dm_pool_dec_data_range(pool->pmd, m->data_block,
                    m->data_block + (m->virt_end - m->virt_begin));
     if (r) {
         metadata_operation_failed(pool, "dm_pool_dec_data_range", r);
         bio_io_error(m->bio);
     } else
         bio_endio(m->bio);
 
     cell_defer_no_holder(tc, m->cell);
     mempool_free(m, &pool->mapping_pool);
 }
 
 static void process_prepared(struct pool *pool, struct list_head *head,
                  process_mapping_fn *fn)
 {
     struct list_head maps;
     struct dm_thin_new_mapping *m, *tmp;
 
     INIT_LIST_HEAD(&maps);
     spin_lock_irq(&pool->lock);
     list_splice_init(head, &maps);
     spin_unlock_irq(&pool->lock);
 
     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 ll_zero(struct thin_c *tc, struct dm_thin_new_mapping *m,
             sector_t begin, sector_t end)
 {
     struct dm_io_region to;
 
     to.bdev = tc->pool_dev->bdev;
     to.sector = begin;
     to.count = end - begin;
 
     dm_kcopyd_zero(tc->pool->copier, 1, &to, 0, copy_complete, m);
 }
 
 static void remap_and_issue_overwrite(struct thin_c *tc, struct bio *bio,
                       dm_block_t data_begin,
                       struct dm_thin_new_mapping *m)
 {
     struct pool *pool = tc->pool;
     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_begin);
 }
 
 /*
  * A partial copy also needs to zero the uncopied region.
  */
 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,
               sector_t len)
 {
     struct pool *pool = tc->pool;
     struct dm_thin_new_mapping *m = get_next_mapping(pool);
 
     m->tc = tc;
     m->virt_begin = virt_block;
     m->virt_end = virt_block + 1u;
     m->data_block = data_dest;
     m->cell = cell;
 
     /*
      * quiesce action + copy action + an extra reference held for the
      * duration of this function (we may need to inc later for a
      * partial zero).
      */
     atomic_set(&m->prepare_actions, 3);
 
     if (!dm_deferred_set_add_work(pool->shared_read_ds, &m->list))
         complete_mapping_preparation(m); /* already quiesced */
 
     /*
      * 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))
         remap_and_issue_overwrite(tc, bio, data_dest, m);
     else {
         struct dm_io_region from, to;
 
         from.bdev = origin->bdev;
         from.sector = data_origin * pool->sectors_per_block;
         from.count = len;
 
         to.bdev = tc->pool_dev->bdev;
         to.sector = data_dest * pool->sectors_per_block;
         to.count = len;
 
         dm_kcopyd_copy(pool->copier, &from, 1, &to,
                    0, copy_complete, m);
 
         /*
          * Do we need to zero a tail region?
          */
         if (len < pool->sectors_per_block && pool->pf.zero_new_blocks) {
             atomic_inc(&m->prepare_actions);
             ll_zero(tc, m,
                 data_dest * pool->sectors_per_block + len,
                 (data_dest + 1) * pool->sectors_per_block);
         }
     }
 
     complete_mapping_preparation(m); /* drop our ref */
 }
 
 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,
               tc->pool->sectors_per_block);
 }
 
 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);
 
     atomic_set(&m->prepare_actions, 1); /* no need to quiesce */
     m->tc = tc;
     m->virt_begin = virt_block;
     m->virt_end = virt_block + 1u;
     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) {
         if (io_overwrites_block(pool, bio))
             remap_and_issue_overwrite(tc, bio, data_block, m);
         else
             ll_zero(tc, m, data_block * pool->sectors_per_block,
                 (data_block + 1) * pool->sectors_per_block);
     } else
         process_prepared_mapping(m);
 }
 
 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)
 {
     struct pool *pool = tc->pool;
     sector_t virt_block_begin = virt_block * pool->sectors_per_block;
     sector_t virt_block_end = (virt_block + 1) * pool->sectors_per_block;
 
     if (virt_block_end <= tc->origin_size)
         schedule_copy(tc, virt_block, tc->origin_dev,
                   virt_block, data_dest, cell, bio,
                   pool->sectors_per_block);
 
     else if (virt_block_begin < tc->origin_size)
         schedule_copy(tc, virt_block, tc->origin_dev,
                   virt_block, data_dest, cell, bio,
                   tc->origin_size - virt_block_begin);
 
     else
         schedule_zero(tc, virt_block, data_dest, cell, bio);
 }
 
 static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);
 
 static void requeue_bios(struct pool *pool);
 
 static bool is_read_only_pool_mode(enum pool_mode mode)
 {
     return (mode == PM_OUT_OF_METADATA_SPACE || mode == PM_READ_ONLY);
 }
 
 static bool is_read_only(struct pool *pool)
 {
     return is_read_only_pool_mode(get_pool_mode(pool));
 }
 
 static void check_for_metadata_space(struct pool *pool)
 {
     int r;
     const char *ooms_reason = NULL;
     dm_block_t nr_free;
 
     r = dm_pool_get_free_metadata_block_count(pool->pmd, &nr_free);
     if (r)
         ooms_reason = "Could not get free metadata blocks";
     else if (!nr_free)
         ooms_reason = "No free metadata blocks";
 
     if (ooms_reason && !is_read_only(pool)) {
         DMERR("%s", ooms_reason);
         set_pool_mode(pool, PM_OUT_OF_METADATA_SPACE);
     }
 }
 
 static void check_for_data_space(struct pool *pool)
 {
     int r;
     dm_block_t nr_free;
 
     if (get_pool_mode(pool) != PM_OUT_OF_DATA_SPACE)
         return;
 
     r = dm_pool_get_free_block_count(pool->pmd, &nr_free);
     if (r)
         return;
 
     if (nr_free) {
         set_pool_mode(pool, PM_WRITE);
         requeue_bios(pool);
     }
 }
 
 /*
  * 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_OUT_OF_METADATA_SPACE)
         return -EINVAL;
 
     r = dm_pool_commit_metadata(pool->pmd);
     if (r)
         metadata_operation_failed(pool, "dm_pool_commit_metadata", r);
     else {
         check_for_metadata_space(pool);
         check_for_data_space(pool);
     }
 
     return r;
 }
 
 static void check_low_water_mark(struct pool *pool, dm_block_t free_blocks)
 {
     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_irq(&pool->lock);
         pool->low_water_triggered = true;
         spin_unlock_irq(&pool->lock);
         dm_table_event(pool->ti->table);
     }
 }
 
 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) {
         if (r == -ENOSPC)
             set_pool_mode(pool, PM_OUT_OF_DATA_SPACE);
         else
             metadata_operation_failed(pool, "dm_pool_alloc_data_block", r);
         return r;
     }
 
     r = dm_pool_get_free_metadata_block_count(pool->pmd, &free_blocks);
     if (r) {
         metadata_operation_failed(pool, "dm_pool_get_free_metadata_block_count", r);
         return r;
     }
 
     if (!free_blocks) {
         /* Let's commit before we use up the metadata reserve. */
         r = commit(pool);
         if (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;
 
     spin_lock_irq(&tc->lock);
     bio_list_add(&tc->retry_on_resume_list, bio);
     spin_unlock_irq(&tc->lock);
 }
 
 static blk_status_t 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 BLK_STS_IOERR;
 
     case PM_OUT_OF_DATA_SPACE:
         return pool->pf.error_if_no_space ? BLK_STS_NOSPC : 0;
 
     case PM_OUT_OF_METADATA_SPACE:
     case PM_READ_ONLY:
     case PM_FAIL:
         return BLK_STS_IOERR;
     default:
         /* Shouldn't get here */
         DMERR_LIMIT("bio unserviceable, yet pool has an unknown mode");
         return BLK_STS_IOERR;
     }
 }
 
 static void handle_unserviceable_bio(struct pool *pool, struct bio *bio)
 {
     blk_status_t error = should_error_unserviceable_bio(pool);
 
     if (error) {
         bio->bi_status = error;
         bio_endio(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;
     blk_status_t error;
 
     error = should_error_unserviceable_bio(pool);
     if (error) {
         cell_error_with_code(pool, cell, error);
         return;
     }
 
     bio_list_init(&bios);
     cell_release(pool, cell, &bios);
 
     while ((bio = bio_list_pop(&bios)))
         retry_on_resume(bio);
 }
 
 static void process_discard_cell_no_passdown(struct thin_c *tc,
                          struct dm_bio_prison_cell *virt_cell)
 {
     struct pool *pool = tc->pool;
     struct dm_thin_new_mapping *m = get_next_mapping(pool);
 
     /*
      * We don't need to lock the data blocks, since there's no
      * passdown.  We only lock data blocks for allocation and breaking sharing.
      */
     m->tc = tc;
     m->virt_begin = virt_cell->key.block_begin;
     m->virt_end = virt_cell->key.block_end;
     m->cell = virt_cell;
     m->bio = virt_cell->holder;
 
     if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list))
         pool->process_prepared_discard(m);
 }
 
 static void break_up_discard_bio(struct thin_c *tc, dm_block_t begin, dm_block_t end,
                  struct bio *bio)
 {
     struct pool *pool = tc->pool;
 
     int r;
     bool maybe_shared;
     struct dm_cell_key data_key;
     struct dm_bio_prison_cell *data_cell;
     struct dm_thin_new_mapping *m;
     dm_block_t virt_begin, virt_end, data_begin;
 
     while (begin != end) {
         r = ensure_next_mapping(pool);
         if (r)
             /* we did our best */
             return;
 
         r = dm_thin_find_mapped_range(tc->td, begin, end, &virt_begin, &virt_end,
                           &data_begin, &maybe_shared);
         if (r)
             /*
              * Silently fail, letting any mappings we've
              * created complete.
              */
             break;
 
         build_key(tc->td, PHYSICAL, data_begin, data_begin + (virt_end - virt_begin), &data_key);
         if (bio_detain(tc->pool, &data_key, NULL, &data_cell)) {
             /* contention, we'll give up with this range */
             begin = virt_end;
             continue;
         }
 
         /*
          * 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->maybe_shared = maybe_shared;
         m->virt_begin = virt_begin;
         m->virt_end = virt_end;
         m->data_block = data_begin;
         m->cell = data_cell;
         m->bio = bio;
 
         /*
          * The parent bio must not complete before sub discard bios are
          * chained to it (see end_discard's bio_chain)!
          *
          * This per-mapping bi_remaining increment is paired with
          * the implicit decrement that occurs via bio_endio() in
          * end_discard().
          */
         bio_inc_remaining(bio);
         if (!dm_deferred_set_add_work(pool->all_io_ds, &m->list))
             pool->process_prepared_discard(m);
 
         begin = virt_end;
     }
 }
 
 static void process_discard_cell_passdown(struct thin_c *tc, struct dm_bio_prison_cell *virt_cell)
 {
     struct bio *bio = virt_cell->holder;
     struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
 
     /*
      * The virt_cell will only get freed once the origin bio completes.
      * This means it will remain locked while all the individual
      * passdown bios are in flight.
      */
     h->cell = virt_cell;
     break_up_discard_bio(tc, virt_cell->key.block_begin, virt_cell->key.block_end, bio);
 
     /*
      * We complete the bio now, knowing that the bi_remaining field
      * will prevent completion until the sub range discards have
      * completed.
      */
     bio_endio(bio);
 }
 
 static void process_discard_bio(struct thin_c *tc, struct bio *bio)
 {
     dm_block_t begin, end;
     struct dm_cell_key virt_key;
     struct dm_bio_prison_cell *virt_cell;
 
     get_bio_block_range(tc, bio, &begin, &end);
     if (begin == end) {
         /*
          * The discard covers less than a block.
          */
         bio_endio(bio);
         return;
     }
 
     build_key(tc->td, VIRTUAL, begin, end, &virt_key);
     if (bio_detain(tc->pool, &virt_key, bio, &virt_cell))
         /*
          * Potential starvation issue: We're relying on the
          * fs/application being well behaved, and not trying to
          * send IO to a region at the same time as discarding it.
          * If they do this persistently then it's possible this
          * cell will never be granted.
          */
         return;
 
     tc->pool->process_discard_cell(tc, virt_cell);
 }
 
 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 __remap_and_issue_shared_cell(void *context,
                       struct dm_bio_prison_cell *cell)
 {
     struct remap_info *info = context;
     struct bio *bio;
 
     while ((bio = bio_list_pop(&cell->bios))) {
         if (bio_data_dir(bio) == WRITE || op_is_flush(bio->bi_opf) ||
             bio_op(bio) == REQ_OP_DISCARD)
             bio_list_add(&info->defer_bios, bio);
         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(info->tc->pool->shared_read_ds);
             inc_all_io_entry(info->tc->pool, bio);
             bio_list_add(&info->issue_bios, bio);
         }
     }
 }
 
 static void remap_and_issue_shared_cell(struct thin_c *tc,
                     struct dm_bio_prison_cell *cell,
                     dm_block_t block)
 {
     struct bio *bio;
     struct remap_info info;
 
     info.tc = tc;
     bio_list_init(&info.defer_bios);
     bio_list_init(&info.issue_bios);
 
     cell_visit_release(tc->pool, __remap_and_issue_shared_cell,
                &info, cell);
 
     while ((bio = bio_list_pop(&info.defer_bios)))
         thin_defer_bio(tc, bio);
 
     while ((bio = bio_list_pop(&info.issue_bios)))
         remap_and_issue(tc, bio, block);
 }
 
 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 *virt_cell)
 {
     struct dm_bio_prison_cell *data_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, &data_cell)) {
         cell_defer_no_holder(tc, virt_cell);
         return;
     }
 
     if (bio_data_dir(bio) == WRITE && bio->bi_iter.bi_size) {
         break_sharing(tc, bio, block, &key, lookup_result, data_cell);
         cell_defer_no_holder(tc, virt_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);
         remap_and_issue(tc, bio, lookup_result->block);
 
         remap_and_issue_shared_cell(tc, data_cell, lookup_result->block);
         remap_and_issue_shared_cell(tc, virt_cell, 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);
         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_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     int r;
     struct pool *pool = tc->pool;
     struct bio *bio = cell->holder;
     dm_block_t block = get_bio_block(tc, bio);
     struct dm_thin_lookup_result lookup_result;
 
     if (tc->requeue_mode) {
         cell_requeue(pool, 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);
         else {
             inc_all_io_entry(pool, bio);
             remap_and_issue(tc, bio, lookup_result.block);
             inc_remap_and_issue_cell(tc, cell, 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);
 
             if (bio_end_sector(bio) <= tc->origin_size)
                 remap_to_origin_and_issue(tc, bio);
 
             else if (bio->bi_iter.bi_sector < tc->origin_size) {
                 zero_fill_bio(bio);
                 bio->bi_iter.bi_size = (tc->origin_size - bio->bi_iter.bi_sector) << SECTOR_SHIFT;
                 remap_to_origin_and_issue(tc, bio);
 
             } else {
                 zero_fill_bio(bio);
                 bio_endio(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(struct thin_c *tc, struct bio *bio)
 {
     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;
 
     /*
      * 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;
 
     process_cell(tc, cell);
 }
 
 static void __process_bio_read_only(struct thin_c *tc, struct bio *bio,
                     struct dm_bio_prison_cell *cell)
 {
     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);
             if (cell)
                 cell_defer_no_holder(tc, cell);
         } else {
             inc_all_io_entry(tc->pool, bio);
             remap_and_issue(tc, bio, lookup_result.block);
             if (cell)
                 inc_remap_and_issue_cell(tc, cell, lookup_result.block);
         }
         break;
 
     case -ENODATA:
         if (cell)
             cell_defer_no_holder(tc, cell);
         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);
         break;
 
     default:
         DMERR_LIMIT("%s: dm_thin_find_block() failed: error = %d",
                 __func__, r);
         if (cell)
             cell_defer_no_holder(tc, cell);
         bio_io_error(bio);
         break;
     }
 }
 
 static void process_bio_read_only(struct thin_c *tc, struct bio *bio)
 {
     __process_bio_read_only(tc, bio, NULL);
 }
 
 static void process_cell_read_only(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     __process_bio_read_only(tc, cell->holder, cell);
 }
 
 static void process_bio_success(struct thin_c *tc, struct bio *bio)
 {
     bio_endio(bio);
 }
 
 static void process_bio_fail(struct thin_c *tc, struct bio *bio)
 {
     bio_io_error(bio);
 }
 
 static void process_cell_success(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     cell_success(tc->pool, cell);
 }
 
 static void process_cell_fail(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     cell_error(tc->pool, cell);
 }
 
 /*
  * 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 !time_in_range(jiffies, pool->last_commit_jiffies,
                   pool->last_commit_jiffies + COMMIT_PERIOD);
 }
 
 #define thin_pbd(node) rb_entry((node), struct dm_thin_endio_hook, rb_node)
 #define thin_bio(pbd) dm_bio_from_per_bio_data((pbd), sizeof(struct dm_thin_endio_hook))
 
 static void __thin_bio_rb_add(struct thin_c *tc, struct bio *bio)
 {
     struct rb_node **rbp, *parent;
     struct dm_thin_endio_hook *pbd;
     sector_t bi_sector = bio->bi_iter.bi_sector;
 
     rbp = &tc->sort_bio_list.rb_node;
     parent = NULL;
     while (*rbp) {
         parent = *rbp;
         pbd = thin_pbd(parent);
 
         if (bi_sector < thin_bio(pbd)->bi_iter.bi_sector)
             rbp = &(*rbp)->rb_left;
         else
             rbp = &(*rbp)->rb_right;
     }
 
     pbd = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
     rb_link_node(&pbd->rb_node, parent, rbp);
     rb_insert_color(&pbd->rb_node, &tc->sort_bio_list);
 }
 
 static void __extract_sorted_bios(struct thin_c *tc)
 {
     struct rb_node *node;
     struct dm_thin_endio_hook *pbd;
     struct bio *bio;
 
     for (node = rb_first(&tc->sort_bio_list); node; node = rb_next(node)) {
         pbd = thin_pbd(node);
         bio = thin_bio(pbd);
 
         bio_list_add(&tc->deferred_bio_list, bio);
         rb_erase(&pbd->rb_node, &tc->sort_bio_list);
     }
 
     WARN_ON(!RB_EMPTY_ROOT(&tc->sort_bio_list));
 }
 
 static void __sort_thin_deferred_bios(struct thin_c *tc)
 {
     struct bio *bio;
     struct bio_list bios;
 
     bio_list_init(&bios);
     bio_list_merge(&bios, &tc->deferred_bio_list);
     bio_list_init(&tc->deferred_bio_list);
 
     /* Sort deferred_bio_list using rb-tree */
     while ((bio = bio_list_pop(&bios)))
         __thin_bio_rb_add(tc, bio);
 
     /*
      * Transfer the sorted bios in sort_bio_list back to
      * deferred_bio_list to allow lockless submission of
      * all bios.
      */
     __extract_sorted_bios(tc);
 }
 
 static void process_thin_deferred_bios(struct thin_c *tc)
 {
     struct pool *pool = tc->pool;
     struct bio *bio;
     struct bio_list bios;
     struct blk_plug plug;
     unsigned count = 0;
 
     if (tc->requeue_mode) {
         error_thin_bio_list(tc, &tc->deferred_bio_list,
                 BLK_STS_DM_REQUEUE);
         return;
     }
 
     bio_list_init(&bios);
 
     spin_lock_irq(&tc->lock);
 
     if (bio_list_empty(&tc->deferred_bio_list)) {
         spin_unlock_irq(&tc->lock);
         return;
     }
 
     __sort_thin_deferred_bios(tc);
 
     bio_list_merge(&bios, &tc->deferred_bio_list);
     bio_list_init(&tc->deferred_bio_list);
 
     spin_unlock_irq(&tc->lock);
 
     blk_start_plug(&plug);
     while ((bio = bio_list_pop(&bios))) {
         /*
          * 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_irq(&tc->lock);
             bio_list_add(&tc->deferred_bio_list, bio);
             bio_list_merge(&tc->deferred_bio_list, &bios);
             spin_unlock_irq(&tc->lock);
             break;
         }
 
         if (bio_op(bio) == REQ_OP_DISCARD)
             pool->process_discard(tc, bio);
         else
             pool->process_bio(tc, bio);
 
         if ((count++ & 127) == 0) {
             throttle_work_update(&pool->throttle);
             dm_pool_issue_prefetches(pool->pmd);
         }
     }
     blk_finish_plug(&plug);
 }
 
 static int cmp_cells(const void *lhs, const void *rhs)
 {
     struct dm_bio_prison_cell *lhs_cell = *((struct dm_bio_prison_cell **) lhs);
     struct dm_bio_prison_cell *rhs_cell = *((struct dm_bio_prison_cell **) rhs);
 
     BUG_ON(!lhs_cell->holder);
     BUG_ON(!rhs_cell->holder);
 
     if (lhs_cell->holder->bi_iter.bi_sector < rhs_cell->holder->bi_iter.bi_sector)
         return -1;
 
     if (lhs_cell->holder->bi_iter.bi_sector > rhs_cell->holder->bi_iter.bi_sector)
         return 1;
 
     return 0;
 }
 
 static unsigned sort_cells(struct pool *pool, struct list_head *cells)
 {
     unsigned count = 0;
     struct dm_bio_prison_cell *cell, *tmp;
 
     list_for_each_entry_safe(cell, tmp, cells, user_list) {
         if (count >= CELL_SORT_ARRAY_SIZE)
             break;
 
         pool->cell_sort_array[count++] = cell;
         list_del(&cell->user_list);
     }
 
     sort(pool->cell_sort_array, count, sizeof(cell), cmp_cells, NULL);
 
     return count;
 }
 
 static void process_thin_deferred_cells(struct thin_c *tc)
 {
     struct pool *pool = tc->pool;
     struct list_head cells;
     struct dm_bio_prison_cell *cell;
     unsigned i, j, count;
 
     INIT_LIST_HEAD(&cells);
 
     spin_lock_irq(&tc->lock);
     list_splice_init(&tc->deferred_cells, &cells);
     spin_unlock_irq(&tc->lock);
 
     if (list_empty(&cells))
         return;
 
     do {
         count = sort_cells(tc->pool, &cells);
 
         for (i = 0; i < count; i++) {
             cell = pool->cell_sort_array[i];
             BUG_ON(!cell->holder);
 
             /*
              * 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)) {
                 for (j = i; j < count; j++)
                     list_add(&pool->cell_sort_array[j]->user_list, &cells);
 
                 spin_lock_irq(&tc->lock);
                 list_splice(&cells, &tc->deferred_cells);
                 spin_unlock_irq(&tc->lock);
                 return;
             }
 
             if (bio_op(cell->holder) == REQ_OP_DISCARD)
                 pool->process_discard_cell(tc, cell);
             else
                 pool->process_cell(tc, cell);
         }
     } while (!list_empty(&cells));
 }
 
 static void thin_get(struct thin_c *tc);
 static void thin_put(struct thin_c *tc);
 
 /*
  * We can't hold rcu_read_lock() around code that can block.  So we
  * find a thin with the rcu lock held; bump a refcount; then drop
  * the lock.
  */
 static struct thin_c *get_first_thin(struct pool *pool)
 {
     struct thin_c *tc = NULL;
 
     rcu_read_lock();
     if (!list_empty(&pool->active_thins)) {
         tc = list_entry_rcu(pool->active_thins.next, struct thin_c, list);
         thin_get(tc);
     }
     rcu_read_unlock();
 
     return tc;
 }
 
 static struct thin_c *get_next_thin(struct pool *pool, struct thin_c *tc)
 {
     struct thin_c *old_tc = tc;
 
     rcu_read_lock();
     list_for_each_entry_continue_rcu(tc, &pool->active_thins, list) {
         thin_get(tc);
         thin_put(old_tc);
         rcu_read_unlock();
         return tc;
     }
     thin_put(old_tc);
     rcu_read_unlock();
 
     return NULL;
 }
 
 static void process_deferred_bios(struct pool *pool)
 {
     struct bio *bio;
     struct bio_list bios, bio_completions;
     struct thin_c *tc;
 
     tc = get_first_thin(pool);
     while (tc) {
         process_thin_deferred_cells(tc);
         process_thin_deferred_bios(tc);
         tc = get_next_thin(pool, tc);
     }
 
     /*
      * If there are any deferred flush bios, we must commit the metadata
      * before issuing them or signaling their completion.
      */
     bio_list_init(&bios);
     bio_list_init(&bio_completions);
 
     spin_lock_irq(&pool->lock);
     bio_list_merge(&bios, &pool->deferred_flush_bios);
     bio_list_init(&pool->deferred_flush_bios);
 
     bio_list_merge(&bio_completions, &pool->deferred_flush_completions);
     bio_list_init(&pool->deferred_flush_completions);
     spin_unlock_irq(&pool->lock);
 
     if (bio_list_empty(&bios) && bio_list_empty(&bio_completions) &&
         !(dm_pool_changed_this_transaction(pool->pmd) && need_commit_due_to_time(pool)))
         return;
 
     if (commit(pool)) {
         bio_list_merge(&bios, &bio_completions);
 
         while ((bio = bio_list_pop(&bios)))
             bio_io_error(bio);
         return;
     }
     pool->last_commit_jiffies = jiffies;
 
     while ((bio = bio_list_pop(&bio_completions)))
         bio_endio(bio);
 
     while ((bio = bio_list_pop(&bios))) {
         /*
          * The data device was flushed as part of metadata commit,
          * so complete redundant flushes immediately.
          */
         if (bio->bi_opf & REQ_PREFLUSH)
             bio_endio(bio);
         else
             dm_submit_bio_remap(bio, NULL);
     }
 }
 
 static void do_worker(struct work_struct *ws)
 {
     struct pool *pool = container_of(ws, struct pool, worker);
 
     throttle_work_start(&pool->throttle);
     dm_pool_issue_prefetches(pool->pmd);
     throttle_work_update(&pool->throttle);
     process_prepared(pool, &pool->prepared_mappings, &pool->process_prepared_mapping);
     throttle_work_update(&pool->throttle);
     process_prepared(pool, &pool->prepared_discards, &pool->process_prepared_discard);
     throttle_work_update(&pool->throttle);
     process_prepared(pool, &pool->prepared_discards_pt2, &pool->process_prepared_discard_pt2);
     throttle_work_update(&pool->throttle);
     process_deferred_bios(pool);
     throttle_work_complete(&pool->throttle);
 }
 
 /*
  * 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);
 }
 
 /*
  * We're holding onto IO to allow userland time to react.  After the
  * timeout either the pool will have been resized (and thus back in
  * PM_WRITE mode), or we degrade to PM_OUT_OF_DATA_SPACE w/ error_if_no_space.
  */
 static void do_no_space_timeout(struct work_struct *ws)
 {
     struct pool *pool = container_of(to_delayed_work(ws), struct pool,
                      no_space_timeout);
 
     if (get_pool_mode(pool) == PM_OUT_OF_DATA_SPACE && !pool->pf.error_if_no_space) {
         pool->pf.error_if_no_space = true;
         notify_of_pool_mode_change(pool);
         error_retry_list_with_code(pool, BLK_STS_NOSPC);
     }
 }
 
 /*----------------------------------------------------------------*/
 
 struct pool_work {
     struct work_struct worker;
     struct completion complete;
 };
 
 static struct pool_work *to_pool_work(struct work_struct *ws)
 {
     return container_of(ws, struct pool_work, worker);
 }
 
 static void pool_work_complete(struct pool_work *pw)
 {
     complete(&pw->complete);
 }
 
 static void pool_work_wait(struct pool_work *pw, struct pool *pool,
                void (*fn)(struct work_struct *))
 {
     INIT_WORK_ONSTACK(&pw->worker, fn);
     init_completion(&pw->complete);
     queue_work(pool->wq, &pw->worker);
     wait_for_completion(&pw->complete);
 }
 
 /*----------------------------------------------------------------*/
 
 struct noflush_work {
     struct pool_work pw;
     struct thin_c *tc;
 };
 
 static struct noflush_work *to_noflush(struct work_struct *ws)
 {
     return container_of(to_pool_work(ws), struct noflush_work, pw);
 }
 
 static void do_noflush_start(struct work_struct *ws)
 {
     struct noflush_work *w = to_noflush(ws);
     w->tc->requeue_mode = true;
     requeue_io(w->tc);
     pool_work_complete(&w->pw);
 }
 
 static void do_noflush_stop(struct work_struct *ws)
 {
     struct noflush_work *w = to_noflush(ws);
     w->tc->requeue_mode = false;
     pool_work_complete(&w->pw);
 }
 
 static void noflush_work(struct thin_c *tc, void (*fn)(struct work_struct *))
 {
     struct noflush_work w;
 
     w.tc = tc;
     pool_work_wait(&w.pw, tc->pool, fn);
 }
 
 /*----------------------------------------------------------------*/
 
 static bool passdown_enabled(struct pool_c *pt)
 {
     return pt->adjusted_pf.discard_passdown;
 }
 
 static void set_discard_callbacks(struct pool *pool)
 {
     struct pool_c *pt = pool->ti->private;
 
     if (passdown_enabled(pt)) {
         pool->process_discard_cell = process_discard_cell_passdown;
         pool->process_prepared_discard = process_prepared_discard_passdown_pt1;
         pool->process_prepared_discard_pt2 = process_prepared_discard_passdown_pt2;
     } else {
         pool->process_discard_cell = process_discard_cell_no_passdown;
         pool->process_prepared_discard = process_prepared_discard_no_passdown;
     }
 }
 
 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);
     unsigned long no_space_timeout = READ_ONCE(no_space_timeout_secs) * HZ;
 
     /*
      * 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:
         dm_pool_metadata_read_only(pool->pmd);
         pool->process_bio = process_bio_fail;
         pool->process_discard = process_bio_fail;
         pool->process_cell = process_cell_fail;
         pool->process_discard_cell = process_cell_fail;
         pool->process_prepared_mapping = process_prepared_mapping_fail;
         pool->process_prepared_discard = process_prepared_discard_fail;
 
         error_retry_list(pool);
         break;
 
     case PM_OUT_OF_METADATA_SPACE:
     case PM_READ_ONLY:
         dm_pool_metadata_read_only(pool->pmd);
         pool->process_bio = process_bio_read_only;
         pool->process_discard = process_bio_success;
         pool->process_cell = process_cell_read_only;
         pool->process_discard_cell = process_cell_success;
         pool->process_prepared_mapping = process_prepared_mapping_fail;
         pool->process_prepared_discard = process_prepared_discard_success;
 
         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.
          */
         pool->out_of_data_space = true;
         pool->process_bio = process_bio_read_only;
         pool->process_discard = process_discard_bio;
         pool->process_cell = process_cell_read_only;
         pool->process_prepared_mapping = process_prepared_mapping;
         set_discard_callbacks(pool);
 
         if (!pool->pf.error_if_no_space && no_space_timeout)
             queue_delayed_work(pool->wq, &pool->no_space_timeout, no_space_timeout);
         break;
 
     case PM_WRITE:
         if (old_mode == PM_OUT_OF_DATA_SPACE)
             cancel_delayed_work_sync(&pool->no_space_timeout);
         pool->out_of_data_space = false;
         pool->pf.error_if_no_space = pt->requested_pf.error_if_no_space;
         dm_pool_metadata_read_write(pool->pmd);
         pool->process_bio = process_bio;
         pool->process_discard = process_discard_bio;
         pool->process_cell = process_cell;
         pool->process_prepared_mapping = process_prepared_mapping;
         set_discard_callbacks(pool);
         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;
 
     if (old_mode != new_mode)
         notify_of_pool_mode_change(pool);
 }
 
 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)
 {
     struct pool *pool = tc->pool;
 
     spin_lock_irq(&tc->lock);
     bio_list_add(&tc->deferred_bio_list, bio);
     spin_unlock_irq(&tc->lock);
 
     wake_worker(pool);
 }
 
 static void thin_defer_bio_with_throttle(struct thin_c *tc, struct bio *bio)
 {
     struct pool *pool = tc->pool;
 
     throttle_lock(&pool->throttle);
     thin_defer_bio(tc, bio);
     throttle_unlock(&pool->throttle);
 }
 
 static void thin_defer_cell(struct thin_c *tc, struct dm_bio_prison_cell *cell)
 {
     struct pool *pool = tc->pool;
 
     throttle_lock(&pool->throttle);
     spin_lock_irq(&tc->lock);
     list_add_tail(&cell->user_list, &tc->deferred_cells);
     spin_unlock_irq(&tc->lock);
     throttle_unlock(&pool->throttle);
 
     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;
     h->cell = 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 *virt_cell, *data_cell;
     struct dm_cell_key key;
 
     thin_hook_bio(tc, bio);
 
     if (tc->requeue_mode) {
         bio->bi_status = BLK_STS_DM_REQUEUE;
         bio_endio(bio);
         return DM_MAPIO_SUBMITTED;
     }
 
     if (get_pool_mode(tc->pool) == PM_FAIL) {
         bio_io_error(bio);
         return DM_MAPIO_SUBMITTED;
     }
 
     if (op_is_flush(bio->bi_opf) || bio_op(bio) == REQ_OP_DISCARD) {
         thin_defer_bio_with_throttle(tc, bio);
         return DM_MAPIO_SUBMITTED;
     }
 
     /*
      * We must hold the virtual cell before doing the lookup, otherwise
      * there's a race with discard.
      */
     build_virtual_key(tc->td, block, &key);
     if (bio_detain(tc->pool, &key, bio, &virt_cell))
         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_cell(tc, virt_cell);
             return DM_MAPIO_SUBMITTED;
         }
 
         build_data_key(tc->td, result.block, &key);
         if (bio_detain(tc->pool, &key, bio, &data_cell)) {
             cell_defer_no_holder(tc, virt_cell);
             return DM_MAPIO_SUBMITTED;
         }
 
         inc_all_io_entry(tc->pool, bio);
         cell_defer_no_holder(tc, data_cell);
         cell_defer_no_holder(tc, virt_cell);
 
         remap(tc, bio, result.block);
         return DM_MAPIO_REMAPPED;
 
     case -ENODATA:
     case -EWOULDBLOCK:
         thin_defer_cell(tc, virt_cell);
         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);
         cell_defer_no_holder(tc, virt_cell);
         return DM_MAPIO_SUBMITTED;
     }
 }
 
 static void requeue_bios(struct pool *pool)
 {
     struct thin_c *tc;
 
     rcu_read_lock();
     list_for_each_entry_rcu(tc, &pool->active_thins, list) {
         spin_lock_irq(&tc->lock);
         bio_list_merge(&tc->deferred_bio_list, &tc->retry_on_resume_list);
         bio_list_init(&tc->retry_on_resume_list);
         spin_unlock_irq(&tc->lock);
     }
     rcu_read_unlock();
 }
 
 /*----------------------------------------------------------------
  * Binding of control targets to a pool object
  *--------------------------------------------------------------*/
 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;
     const char *reason = NULL;
 
     if (!pt->adjusted_pf.discard_passdown)
         return;
 
     if (!bdev_max_discard_sectors(pt->data_dev->bdev))
         reason = "discard unsupported";
 
     else if (data_limits->max_discard_sectors < pool->sectors_per_block)
         reason = "max discard sectors smaller than a block";
 
     if (reason) {
         DMWARN("Data device (%pg) %s: Disabling discard passdown.", data_bdev, 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);
 
     vfree(pool->cell_sort_array);
     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_exit(&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,
                 struct block_device *data_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 = kzalloc(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();
     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;
     }
 
     throttle_init(&pool->throttle);
     INIT_WORK(&pool->worker, do_worker);
     INIT_DELAYED_WORK(&pool->waker, do_waker);
     INIT_DELAYED_WORK(&pool->no_space_timeout, do_no_space_timeout);
     spin_lock_init(&pool->lock);
     bio_list_init(&pool->deferred_flush_bios);
     bio_list_init(&pool->deferred_flush_completions);
     INIT_LIST_HEAD(&pool->prepared_mappings);
     INIT_LIST_HEAD(&pool->prepared_discards);
     INIT_LIST_HEAD(&pool->prepared_discards_pt2);
     INIT_LIST_HEAD(&pool->active_thins);
     pool->low_water_triggered = false;
     pool->suspended = true;
     pool->out_of_data_space = false;
 
     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;
     r = mempool_init_slab_pool(&pool->mapping_pool, MAPPING_POOL_SIZE,
                    _new_mapping_cache);
     if (r) {
         *error = "Error creating pool's mapping mempool";
         err_p = ERR_PTR(r);
         goto bad_mapping_pool;
     }
 
     pool->cell_sort_array =
         vmalloc(array_size(CELL_SORT_ARRAY_SIZE,
                    sizeof(*pool->cell_sort_array)));
     if (!pool->cell_sort_array) {
         *error = "Error allocating cell sort array";
         err_p = ERR_PTR(-ENOMEM);
         goto bad_sort_array;
     }
 
     pool->ref_count = 1;
     pool->last_commit_jiffies = jiffies;
     pool->pool_md = pool_md;
     pool->md_dev = metadata_dev;
     pool->data_dev = data_dev;
     __pool_table_insert(pool);
 
     return pool;
 
 bad_sort_array:
     mempool_exit(&pool->mapping_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,
                 struct block_device *data_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);
         }
         if (pool->data_dev != data_dev) {
             *error = "data 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 || pool->data_dev != data_dev) {
                 *error = "different pool cannot replace a pool";
                 return ERR_PTR(-EINVAL);
             }
             __pool_inc(pool);
 
         } else {
             pool = pool_create(pool_md, metadata_dev, data_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 const 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);
 }
 
 /*
  * We need to flush the data device **before** committing the metadata.
  *
  * This ensures that the data blocks of any newly inserted mappings are
  * properly written to non-volatile storage and won't be lost in case of a
  * crash.
  *
  * Failure to do so can result in data corruption in the case of internal or
  * external snapshots and in the case of newly provisioned blocks, when block
  * zeroing is enabled.
  */
 static int metadata_pre_commit_callback(void *context)
 {
     struct pool *pool = context;
 
     return blkdev_issue_flush(pool->data_dev);
 }
 
 static sector_t get_dev_size(struct block_device *bdev)
 {
     return bdev_nr_sectors(bdev);
 }
 
 static void warn_if_metadata_device_too_big(struct block_device *bdev)
 {
     sector_t metadata_dev_size = get_dev_size(bdev);
 
     if (metadata_dev_size > THIN_METADATA_MAX_SECTORS_WARNING)
         DMWARN("Metadata device %pg is larger than %u sectors: excess space will not be used.",
                bdev, 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;
 
     /* make sure metadata and data are different devices */
     if (!strcmp(argv[0], argv[1])) {
         ti->error = "Error setting metadata or data device";
         r = -EINVAL;
         goto out_unlock;
     }
 
     /*
      * 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, data_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.
      */
     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) {
         ti->error = "Error registering metadata threshold";
         goto out_flags_changed;
     }
 
     dm_pool_register_pre_commit_callback(pool->pmd,
                          metadata_pre_commit_callback, pool);
 
     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;
 
     /*
      * As this is a singleton target, ti->begin is always zero.
      */
     spin_lock_irq(&pool->lock);
     bio_set_dev(bio, pt->data_dev->bdev);
     r = DM_MAPIO_REMAPPED;
     spin_unlock_irq(&pool->lock);
 
     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);
 
         if (get_pool_mode(pool) == PM_OUT_OF_METADATA_SPACE)
             set_pool_mode(pool, PM_WRITE);
 
         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_suspend_active_thins(struct pool *pool)
 {
     struct thin_c *tc;
 
     /* Suspend all active thin devices */
     tc = get_first_thin(pool);
     while (tc) {
         dm_internal_suspend_noflush(tc->thin_md);
         tc = get_next_thin(pool, tc);
     }
 }
 
 static void pool_resume_active_thins(struct pool *pool)
 {
     struct thin_c *tc;
 
     /* Resume all active thin devices */
     tc = get_first_thin(pool);
     while (tc) {
         dm_internal_resume(tc->thin_md);
         tc = get_next_thin(pool, tc);
     }
 }
 
 static void pool_resume(struct dm_target *ti)
 {
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     /*
      * Must requeue active_thins' bios and then resume
      * active_thins _before_ clearing 'suspend' flag.
      */
     requeue_bios(pool);
     pool_resume_active_thins(pool);
 
     spin_lock_irq(&pool->lock);
     pool->low_water_triggered = false;
     pool->suspended = false;
     spin_unlock_irq(&pool->lock);
 
     do_waker(&pool->waker.work);
 }
 
 static void pool_presuspend(struct dm_target *ti)
 {
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     spin_lock_irq(&pool->lock);
     pool->suspended = true;
     spin_unlock_irq(&pool->lock);
 
     pool_suspend_active_thins(pool);
 }
 
 static void pool_presuspend_undo(struct dm_target *ti)
 {
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     pool_resume_active_thins(pool);
 
     spin_lock_irq(&pool->lock);
     pool->suspended = false;
     spin_unlock_irq(&pool->lock);
 }
 
 static void pool_postsuspend(struct dm_target *ti)
 {
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     cancel_delayed_work_sync(&pool->waker);
     cancel_delayed_work_sync(&pool->no_space_timeout);
     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);
     if (r)
         return r;
 
     r = dm_pool_delete_thin_device(pool->pmd, dev_id);
     if (r)
         DMWARN("Deletion of thin device %s failed.", argv[1]);
 
     return r;
 }
 
 static int process_set_transaction_id_mesg(unsigned argc, char **argv, struct pool *pool)
 {
     dm_thin_id old_id, new_id;
     int r;
 
     r = check_arg_count(argc, 3);
     if (r)
         return r;
 
     if (kstrtoull(argv[1], 10, (unsigned long long *)&old_id)) {
         DMWARN("set_transaction_id message: Unrecognised id %s.", argv[1]);
         return -EINVAL;
     }
 
     if (kstrtoull(argv[2], 10, (unsigned long long *)&new_id)) {
         DMWARN("set_transaction_id message: Unrecognised new id %s.", argv[2]);
         return -EINVAL;
     }
 
     r = dm_pool_set_metadata_transaction_id(pool->pmd, old_id, new_id);
     if (r) {
         DMWARN("Failed to change transaction id from %s to %s.",
                argv[1], argv[2]);
         return r;
     }
 
     return 0;
 }
 
 static int process_reserve_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
 {
     int r;
 
     r = check_arg_count(argc, 1);
     if (r)
         return r;
 
     (void) commit(pool);
 
     r = dm_pool_reserve_metadata_snap(pool->pmd);
     if (r)
         DMWARN("reserve_metadata_snap message failed.");
 
     return r;
 }
 
 static int process_release_metadata_snap_mesg(unsigned argc, char **argv, struct pool *pool)
 {
     int r;
 
     r = check_arg_count(argc, 1);
     if (r)
         return r;
 
     r = dm_pool_release_metadata_snap(pool->pmd);
     if (r)
         DMWARN("release_metadata_snap message failed.");
 
     return r;
 }
 
 /*
  * Messages supported:
  *   create_thin    <dev_id>
  *   create_snap    <dev_id> <origin_id>
  *   delete     <dev_id>
  *   set_transaction_id <current_trans_id> <new_trans_id>
  *   reserve_metadata_snap
  *   release_metadata_snap
  */
 static int pool_message(struct dm_target *ti, unsigned argc, char **argv,
             char *result, unsigned maxlen)
 {
     int r = -EINVAL;
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     if (get_pool_mode(pool) >= PM_OUT_OF_METADATA_SPACE) {
         DMERR("%s: unable to service pool target messages in READ_ONLY or FAIL mode",
               dm_device_name(pool->pool_md));
         return -EOPNOTSUPP;
     }
 
     if (!strcasecmp(argv[0], "create_thin"))
         r = process_create_thin_mesg(argc, argv, pool);
 
     else if (!strcasecmp(argv[0], "create_snap"))
         r = process_create_snap_mesg(argc, argv, pool);
 
     else if (!strcasecmp(argv[0], "delete"))
         r = process_delete_mesg(argc, argv, pool);
 
     else if (!strcasecmp(argv[0], "set_transaction_id"))
         r = process_set_transaction_id_mesg(argc, argv, pool);
 
     else if (!strcasecmp(argv[0], "reserve_metadata_snap"))
         r = process_reserve_metadata_snap_mesg(argc, argv, pool);
 
     else if (!strcasecmp(argv[0], "release_metadata_snap"))
         r = process_release_metadata_snap_mesg(argc, argv, pool);
 
     else
         DMWARN("Unrecognised thin pool target message received: %s", argv[0]);
 
     if (!r)
         (void) commit(pool);
 
     return r;
 }
 
 static void emit_flags(struct pool_features *pf, char *result,
                unsigned sz, unsigned maxlen)
 {
     unsigned count = !pf->zero_new_blocks + !pf->discard_enabled +
         !pf->discard_passdown + (pf->mode == PM_READ_ONLY) +
         pf->error_if_no_space;
     DMEMIT("%u ", count);
 
     if (!pf->zero_new_blocks)
         DMEMIT("skip_block_zeroing ");
 
     if (!pf->discard_enabled)
         DMEMIT("ignore_discard ");
 
     if (!pf->discard_passdown)
         DMEMIT("no_discard_passdown ");
 
     if (pf->mode == PM_READ_ONLY)
         DMEMIT("read_only ");
 
     if (pf->error_if_no_space)
         DMEMIT("error_if_no_space ");
 }
 
 /*
  * Status line is:
  *    <transaction id> <used metadata sectors>/<total metadata sectors>
  *    <used data sectors>/<total data sectors> <held metadata root>
  *    <pool mode> <discard config> <no space config> <needs_check>
  */
 static void pool_status(struct dm_target *ti, status_type_t type,
             unsigned status_flags, char *result, unsigned maxlen)
 {
     int r;
     unsigned sz = 0;
     uint64_t transaction_id;
     dm_block_t nr_free_blocks_data;
     dm_block_t nr_free_blocks_metadata;
     dm_block_t nr_blocks_data;
     dm_block_t nr_blocks_metadata;
     dm_block_t held_root;
     enum pool_mode mode;
     char buf[BDEVNAME_SIZE];
     char buf2[BDEVNAME_SIZE];
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
 
     switch (type) {
     case STATUSTYPE_INFO:
         if (get_pool_mode(pool) == PM_FAIL) {
             DMEMIT("Fail");
             break;
         }
 
         /* Commit to ensure statistics aren't out-of-date */
         if (!(status_flags & DM_STATUS_NOFLUSH_FLAG) && !dm_suspended(ti))
             (void) commit(pool);
 
         r = dm_pool_get_metadata_transaction_id(pool->pmd, &transaction_id);
         if (r) {
             DMERR("%s: dm_pool_get_metadata_transaction_id returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         r = dm_pool_get_free_metadata_block_count(pool->pmd, &nr_free_blocks_metadata);
         if (r) {
             DMERR("%s: dm_pool_get_free_metadata_block_count returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         r = dm_pool_get_metadata_dev_size(pool->pmd, &nr_blocks_metadata);
         if (r) {
             DMERR("%s: dm_pool_get_metadata_dev_size returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         r = dm_pool_get_free_block_count(pool->pmd, &nr_free_blocks_data);
         if (r) {
             DMERR("%s: dm_pool_get_free_block_count returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         r = dm_pool_get_data_dev_size(pool->pmd, &nr_blocks_data);
         if (r) {
             DMERR("%s: dm_pool_get_data_dev_size returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         r = dm_pool_get_metadata_snap(pool->pmd, &held_root);
         if (r) {
             DMERR("%s: dm_pool_get_metadata_snap returned %d",
                   dm_device_name(pool->pool_md), r);
             goto err;
         }
 
         DMEMIT("%llu %llu/%llu %llu/%llu ",
                (unsigned long long)transaction_id,
                (unsigned long long)(nr_blocks_metadata - nr_free_blocks_metadata),
                (unsigned long long)nr_blocks_metadata,
                (unsigned long long)(nr_blocks_data - nr_free_blocks_data),
                (unsigned long long)nr_blocks_data);
 
         if (held_root)
             DMEMIT("%llu ", held_root);
         else
             DMEMIT("- ");
 
         mode = get_pool_mode(pool);
         if (mode == PM_OUT_OF_DATA_SPACE)
             DMEMIT("out_of_data_space ");
         else if (is_read_only_pool_mode(mode))
             DMEMIT("ro ");
         else
             DMEMIT("rw ");
 
         if (!pool->pf.discard_enabled)
             DMEMIT("ignore_discard ");
         else if (pool->pf.discard_passdown)
             DMEMIT("discard_passdown ");
         else
             DMEMIT("no_discard_passdown ");
 
         if (pool->pf.error_if_no_space)
             DMEMIT("error_if_no_space ");
         else
             DMEMIT("queue_if_no_space ");
 
         if (dm_pool_metadata_needs_check(pool->pmd))
             DMEMIT("needs_check ");
         else
             DMEMIT("- ");
 
         DMEMIT("%llu ", (unsigned long long)calc_metadata_threshold(pt));
 
         break;
 
     case STATUSTYPE_TABLE:
         DMEMIT("%s %s %lu %llu ",
                format_dev_t(buf, pt->metadata_dev->bdev->bd_dev),
                format_dev_t(buf2, pt->data_dev->bdev->bd_dev),
                (unsigned long)pool->sectors_per_block,
                (unsigned long long)pt->low_water_blocks);
         emit_flags(&pt->requested_pf, result, sz, maxlen);
         break;
 
     case STATUSTYPE_IMA:
         *result = '\0';
         break;
     }
     return;
 
 err:
     DMEMIT("Error");
 }
 
 static int pool_iterate_devices(struct dm_target *ti,
                 iterate_devices_callout_fn fn, void *data)
 {
     struct pool_c *pt = ti->private;
 
     return fn(ti, pt->data_dev, 0, ti->len, data);
 }
 
 static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
     struct pool_c *pt = ti->private;
     struct pool *pool = pt->pool;
     sector_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
 
     /*
      * If max_sectors is smaller than pool->sectors_per_block adjust it
      * to the highest possible power-of-2 factor of pool->sectors_per_block.
      * This is especially beneficial when the pool's data device is a RAID
      * device that has a full stripe width that matches pool->sectors_per_block
      * -- because even though partial RAID stripe-sized IOs will be issued to a
      *    single RAID stripe; when aggregated they will end on a full RAID stripe
      *    boundary.. which avoids additional partial RAID stripe writes cascading
      */
     if (limits->max_sectors < pool->sectors_per_block) {
         while (!is_factor(pool->sectors_per_block, limits->max_sectors)) {
             if ((limits->max_sectors & (limits->max_sectors - 1)) == 0)
                 limits->max_sectors--;
             limits->max_sectors = rounddown_pow_of_two(limits->max_sectors);
         }
     }
 
     /*
      * If the system-determined stacked limits are compatible with the
      * pool's blocksize (io_opt is a factor) do not override them.
      */
     if (io_opt_sectors < pool->sectors_per_block ||
         !is_factor(io_opt_sectors, pool->sectors_per_block)) {
         if (is_factor(pool->sectors_per_block, limits->max_sectors))
             blk_limits_io_min(limits, limits->max_sectors << SECTOR_SHIFT);
         else
             blk_limits_io_min(limits, pool->sectors_per_block << SECTOR_SHIFT);
         blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
     }
 
     /*
      * pt->adjusted_pf is a staging area for the actual features to use.
      * They get transferred to the live pool in bind_control_target()
      * called from pool_preresume().
      */
     if (!pt->adjusted_pf.discard_enabled) {
         /*
          * Must explicitly disallow stacking discard limits otherwise the
          * block layer will stack them if pool's data device has support.
          */
         limits->discard_granularity = 0;
         return;
     }
 
     disable_passdown_if_not_supported(pt);
 
     /*
      * The pool uses the same discard limits as the underlying data
      * device.  DM core has already set this up.
      */
 }
 
 static struct target_type pool_target = {
     .name = "thin-pool",
     .features = DM_TARGET_SINGLETON | DM_TARGET_ALWAYS_WRITEABLE |
             DM_TARGET_IMMUTABLE,
     .version = {1, 22, 0},
     .module = THIS_MODULE,
     .ctr = pool_ctr,
     .dtr = pool_dtr,
     .map = pool_map,
     .presuspend = pool_presuspend,
     .presuspend_undo = pool_presuspend_undo,
     .postsuspend = pool_postsuspend,
     .preresume = pool_preresume,
     .resume = pool_resume,
     .message = pool_message,
     .status = pool_status,
     .iterate_devices = pool_iterate_devices,
     .io_hints = pool_io_hints,
 };
 
 /*----------------------------------------------------------------
  * Thin target methods
  *--------------------------------------------------------------*/
 static void thin_get(struct thin_c *tc)
 {
     refcount_inc(&tc->refcount);
 }
 
 static void thin_put(struct thin_c *tc)
 {
     if (refcount_dec_and_test(&tc->refcount))
         complete(&tc->can_destroy);
 }
 
 static void thin_dtr(struct dm_target *ti)
 {
     struct thin_c *tc = ti->private;
 
     spin_lock_irq(&tc->pool->lock);
     list_del_rcu(&tc->list);
     spin_unlock_irq(&tc->pool->lock);
     synchronize_rcu();
 
     thin_put(tc);
     wait_for_completion(&tc->can_destroy);
 
     mutex_lock(&dm_thin_pool_table.mutex);
 
     __pool_dec(tc->pool);
     dm_pool_close_thin_device(tc->td);
     dm_put_device(ti, tc->pool_dev);
     if (tc->origin_dev)
         dm_put_device(ti, tc->origin_dev);
     kfree(tc);
 
     mutex_unlock(&dm_thin_pool_table.mutex);
 }
 
 /*
  * Thin target parameters:
  *
  * <pool_dev> <dev_id> [origin_dev]
  *
  * pool_dev: the path to the pool (eg, /dev/mapper/my_pool)
  * dev_id: the internal device identifier
  * origin_dev: a device external to the pool that should act as the origin
  *
  * If the pool device has discards disabled, they get disabled for the thin
  * device as well.
  */
 static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
 {
     int r;
     struct thin_c *tc;
     struct dm_dev *pool_dev, *origin_dev;
     struct mapped_device *pool_md;
 
     mutex_lock(&dm_thin_pool_table.mutex);
 
     if (argc != 2 && argc != 3) {
         ti->error = "Invalid argument count";
         r = -EINVAL;
         goto out_unlock;
     }
 
     tc = ti->private = kzalloc(sizeof(*tc), GFP_KERNEL);
     if (!tc) {
         ti->error = "Out of memory";
         r = -ENOMEM;
         goto out_unlock;
     }
     tc->thin_md = dm_table_get_md(ti->table);
     spin_lock_init(&tc->lock);
     INIT_LIST_HEAD(&tc->deferred_cells);
     bio_list_init(&tc->deferred_bio_list);
     bio_list_init(&tc->retry_on_resume_list);
     tc->sort_bio_list = RB_ROOT;
 
     if (argc == 3) {
         if (!strcmp(argv[0], argv[2])) {
             ti->error = "Error setting origin device";
             r = -EINVAL;
             goto bad_origin_dev;
         }
 
         r = dm_get_device(ti, argv[2], FMODE_READ, &origin_dev);
         if (r) {
             ti->error = "Error opening origin device";
             goto bad_origin_dev;
         }
         tc->origin_dev = origin_dev;
     }
 
     r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &pool_dev);
     if (r) {
         ti->error = "Error opening pool device";
         goto bad_pool_dev;
     }
     tc->pool_dev = pool_dev;
 
     if (read_dev_id(argv[1], (unsigned long long *)&tc->dev_id, 0)) {
         ti->error = "Invalid device id";
         r = -EINVAL;
         goto bad_common;
     }
 
     pool_md = dm_get_md(tc->pool_dev->bdev->bd_dev);
     if (!pool_md) {
         ti->error = "Couldn't get pool mapped device";
         r = -EINVAL;
         goto bad_common;
     }
 
     tc->pool = __pool_table_lookup(pool_md);
     if (!tc->pool) {
         ti->error = "Couldn't find pool object";
         r = -EINVAL;
         goto bad_pool_lookup;
     }
     __pool_inc(tc->pool);
 
     if (get_pool_mode(tc->pool) == PM_FAIL) {
         ti->error = "Couldn't open thin device, Pool is in fail mode";
         r = -EINVAL;
         goto bad_pool;
     }
 
     r = dm_pool_open_thin_device(tc->pool->pmd, tc->dev_id, &tc->td);
     if (r) {
         ti->error = "Couldn't open thin internal device";
         goto bad_pool;
     }
 
     r = dm_set_target_max_io_len(ti, tc->pool->sectors_per_block);
     if (r)
         goto bad;
 
     ti->num_flush_bios = 1;
     ti->flush_supported = true;
     ti->accounts_remapped_io = true;
     ti->per_io_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_bios = 1;
     }
 
     mutex_unlock(&dm_thin_pool_table.mutex);
 
     spin_lock_irq(&tc->pool->lock);
     if (tc->pool->suspended) {
         spin_unlock_irq(&tc->pool->lock);
         mutex_lock(&dm_thin_pool_table.mutex); /* reacquire for __pool_dec */
         ti->error = "Unable to activate thin device while pool is suspended";
         r = -EINVAL;
         goto bad;
     }
     refcount_set(&tc->refcount, 1);
     init_completion(&tc->can_destroy);
     list_add_tail_rcu(&tc->list, &tc->pool->active_thins);
     spin_unlock_irq(&tc->pool->lock);
     /*
      * This synchronize_rcu() call is needed here otherwise we risk a
      * wake_worker() call finding no bios to process (because the newly
      * added tc isn't yet visible).  So this reduces latency since we
      * aren't then dependent on the periodic commit to wake_worker().
      */
     synchronize_rcu();
 
     dm_put(pool_md);
 
     return 0;
 
 bad:
     dm_pool_close_thin_device(tc->td);
 bad_pool:
     __pool_dec(tc->pool);
 bad_pool_lookup:
     dm_put(pool_md);
 bad_common:
     dm_put_device(ti, tc->pool_dev);
 bad_pool_dev:
     if (tc->origin_dev)
         dm_put_device(ti, tc->origin_dev);
 bad_origin_dev:
     kfree(tc);
 out_unlock:
     mutex_unlock(&dm_thin_pool_table.mutex);
 
     return r;
 }
 
 static int thin_map(struct dm_target *ti, struct bio *bio)
 {
     bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
 
     return thin_bio_map(ti, bio);
 }
 
 static int thin_endio(struct dm_target *ti, struct bio *bio,
         blk_status_t *err)
 {
     unsigned long flags;
     struct dm_thin_endio_hook *h = dm_per_bio_data(bio, sizeof(struct dm_thin_endio_hook));
     struct list_head work;
     struct dm_thin_new_mapping *m, *tmp;
     struct pool *pool = h->tc->pool;
 
     if (h->shared_read_entry) {
         INIT_LIST_HEAD(&work);
         dm_deferred_entry_dec(h->shared_read_entry, &work);
 
         spin_lock_irqsave(&pool->lock, flags);
         list_for_each_entry_safe(m, tmp, &work, list) {
             list_del(&m->list);
             __complete_mapping_preparation(m);
         }
         spin_unlock_irqrestore(&pool->lock, flags);
     }
 
     if (h->all_io_entry) {
         INIT_LIST_HEAD(&work);
         dm_deferred_entry_dec(h->all_io_entry, &work);
         if (!list_empty(&work)) {
             spin_lock_irqsave(&pool->lock, flags);
             list_for_each_entry_safe(m, tmp, &work, list)
                 list_add_tail(&m->list, &pool->prepared_discards);
             spin_unlock_irqrestore(&pool->lock, flags);
             wake_worker(pool);
         }
     }
 
     if (h->cell)
         cell_defer_no_holder(h->tc, h->cell);
 
     return DM_ENDIO_DONE;
 }
 
 static void thin_presuspend(struct dm_target *ti)
 {
     struct thin_c *tc = ti->private;
 
     if (dm_noflush_suspending(ti))
         noflush_work(tc, do_noflush_start);
 }
 
 static void thin_postsuspend(struct dm_target *ti)
 {
     struct thin_c *tc = ti->private;
 
     /*
      * The dm_noflush_suspending flag has been cleared by now, so
      * unfortunately we must always run this.
      */
     noflush_work(tc, do_noflush_stop);
 }
 
 static int thin_preresume(struct dm_target *ti)
 {
     struct thin_c *tc = ti->private;
 
     if (tc->origin_dev)
         tc->origin_size = get_dev_size(tc->origin_dev->bdev);
 
     return 0;
 }
 
 /*
  * <nr mapped sectors> <highest mapped sector>
  */
 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;
     dm_block_t mapped, highest;
     char buf[BDEVNAME_SIZE];
     struct thin_c *tc = ti->private;
 
     if (get_pool_mode(tc->pool) == PM_FAIL) {
         DMEMIT("Fail");
         return;
     }
 
     if (!tc->td)
         DMEMIT("-");
     else {
         switch (type) {
         case STATUSTYPE_INFO:
             r = dm_thin_get_mapped_count(tc->td, &mapped);
             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) {
                 DMERR("dm_thin_get_highest_mapped_block returned %d", r);
                 goto err;
             }
 
             DMEMIT("%llu ", mapped * tc->pool->sectors_per_block);
             if (r)
                 DMEMIT("%llu", ((highest + 1) *
                         tc->pool->sectors_per_block) - 1);
             else
                 DMEMIT("-");
             break;
 
         case STATUSTYPE_TABLE:
             DMEMIT("%s %lu",
                    format_dev_t(buf, tc->pool_dev->bdev->bd_dev),
                    (unsigned long) tc->dev_id);
             if (tc->origin_dev)
                 DMEMIT(" %s", format_dev_t(buf, tc->origin_dev->bdev->bd_dev));
             break;
 
         case STATUSTYPE_IMA:
             *result = '\0';
             break;
         }
     }
 
     return;
 
 err:
     DMEMIT("Error");
 }
 
 static int thin_iterate_devices(struct dm_target *ti,
                 iterate_devices_callout_fn fn, void *data)
 {
     sector_t blocks;
     struct thin_c *tc = ti->private;
     struct pool *pool = tc->pool;
 
     /*
      * We can't call dm_pool_get_data_dev_size() since that blocks.  So
      * we follow a more convoluted path through to the pool's target.
      */
     if (!pool->ti)
         return 0;   /* nothing is bound */
 
     blocks = pool->ti->len;
     (void) sector_div(blocks, pool->sectors_per_block);
     if (blocks)
         return fn(ti, tc->pool_dev, 0, pool->sectors_per_block * blocks, data);
 
     return 0;
 }
 
 static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
     struct thin_c *tc = ti->private;
     struct pool *pool = tc->pool;
 
     if (!pool->pf.discard_enabled)
         return;
 
     limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
     limits->max_discard_sectors = 2048 * 1024 * 16; /* 16G */
 }
 
 static struct target_type thin_target = {
     .name = "thin",
     .version = {1, 22, 0},
     .module = THIS_MODULE,
     .ctr = thin_ctr,
     .dtr = thin_dtr,
     .map = thin_map,
     .end_io = thin_endio,
     .preresume = thin_preresume,
     .presuspend = thin_presuspend,
     .postsuspend = thin_postsuspend,
     .status = thin_status,
     .iterate_devices = thin_iterate_devices,
     .io_hints = thin_io_hints,
 };
 
 /*----------------------------------------------------------------*/
 
 static int __init dm_thin_init(void)
 {
     int r = -ENOMEM;
 
     pool_table_init();
 
     _new_mapping_cache = KMEM_CACHE(dm_thin_new_mapping, 0);
     if (!_new_mapping_cache)
         return r;
 
     r = dm_register_target(&thin_target);
     if (r)
         goto bad_new_mapping_cache;
 
     r = dm_register_target(&pool_target);
     if (r)
         goto bad_thin_target;
 
     return 0;
 
 bad_thin_target:
     dm_unregister_target(&thin_target);
 bad_new_mapping_cache:
     kmem_cache_destroy(_new_mapping_cache);
 
     return r;
 }
 
 static void dm_thin_exit(void)
 {
     dm_unregister_target(&thin_target);
     dm_unregister_target(&pool_target);
 
     kmem_cache_destroy(_new_mapping_cache);
 
     pool_table_exit();
 }
 
 module_init(dm_thin_init);
 module_exit(dm_thin_exit);
 
 module_param_named(no_space_timeout, no_space_timeout_secs, uint, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(no_space_timeout, "Out of data space queue IO timeout in seconds");
 
 MODULE_DESCRIPTION(DM_NAME " thin provisioning target");
 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
 MODULE_LICENSE("GPL");