/*
   * Copyright (C) 2003 Sistina Software Limited.
   * Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
   *
   * This file is released under the GPL.
   */
  
  #include <linux/dm-dirty-log.h>
  #include <linux/dm-region-hash.h>
  
  #include <linux/ctype.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/vmalloc.h>
  
  #include "dm.h"
  
  #define	DM_MSG_PREFIX	"region hash"
  
  /*-----------------------------------------------------------------
   * Region hash
   *
   * The mirror splits itself up into discrete regions.  Each
   * region can be in one of three states: clean, dirty,
   * nosync.  There is no need to put clean regions in the hash.
   *
   * In addition to being present in the hash table a region _may_
   * be present on one of three lists.
   *
   *   clean_regions: Regions on this list have no io pending to
   *   them, they are in sync, we are no longer interested in them,
   *   they are dull.  dm_rh_update_states() will remove them from the
   *   hash table.
   *
   *   quiesced_regions: These regions have been spun down, ready
   *   for recovery.  rh_recovery_start() will remove regions from
   *   this list and hand them to kmirrord, which will schedule the
   *   recovery io with kcopyd.
   *
   *   recovered_regions: Regions that kcopyd has successfully
   *   recovered.  dm_rh_update_states() will now schedule any delayed
   *   io, up the recovery_count, and remove the region from the
   *   hash.
   *
   * There are 2 locks:
   *   A rw spin lock 'hash_lock' protects just the hash table,
   *   this is never held in write mode from interrupt context,
   *   which I believe means that we only have to disable irqs when
   *   doing a write lock.
   *
   *   An ordinary spin lock 'region_lock' that protects the three
   *   lists in the region_hash, with the 'state', 'list' and
   *   'delayed_bios' fields of the regions.  This is used from irq
   *   context, so all other uses will have to suspend local irqs.
   *---------------------------------------------------------------*/
  struct dm_region_hash {
  	uint32_t region_size;
  	unsigned region_shift;
  
  	/* holds persistent region state */
  	struct dm_dirty_log *log;
  
  	/* hash table */
  	rwlock_t hash_lock;
  	mempool_t *region_pool;
  	unsigned mask;
  	unsigned nr_buckets;
  	unsigned prime;
  	unsigned shift;
  	struct list_head *buckets;
  
  	unsigned max_recovery; /* Max # of regions to recover in parallel */
  
  	spinlock_t region_lock;
  	atomic_t recovery_in_flight;
  	struct semaphore recovery_count;
  	struct list_head clean_regions;
  	struct list_head quiesced_regions;
  	struct list_head recovered_regions;
  	struct list_head failed_recovered_regions;
  
  	/*
  	 * If there was a flush failure no regions can be marked clean.
  	 */
  	int flush_failure;
  
  	void *context;
  	sector_t target_begin;
  
  	/* Callback function to schedule bios writes */
  	void (*dispatch_bios)(void *context, struct bio_list *bios);
  
  	/* Callback function to wakeup callers worker thread. */
  	void (*wakeup_workers)(void *context);
  
  	/* Callback function to wakeup callers recovery waiters. */
  	void (*wakeup_all_recovery_waiters)(void *context);
  };
  
  struct dm_region {
  	struct dm_region_hash *rh;	/* FIXME: can we get rid of this ? */
  	region_t key;
  	int state;
  
  	struct list_head hash_list;
  	struct list_head list;
  
  	atomic_t pending;
  	struct bio_list delayed_bios;
  };
  
  /*
   * Conversion fns
   */
  static region_t dm_rh_sector_to_region(struct dm_region_hash *rh, sector_t sector)
  {
  	return sector >> rh->region_shift;
  }
  
  sector_t dm_rh_region_to_sector(struct dm_region_hash *rh, region_t region)
  {
  	return region << rh->region_shift;
  }
  EXPORT_SYMBOL_GPL(dm_rh_region_to_sector);
  
  region_t dm_rh_bio_to_region(struct dm_region_hash *rh, struct bio *bio)
  {
  	return dm_rh_sector_to_region(rh, bio->bi_iter.bi_sector -
  				      rh->target_begin);
  }
  EXPORT_SYMBOL_GPL(dm_rh_bio_to_region);
  
  void *dm_rh_region_context(struct dm_region *reg)
  {
  	return reg->rh->context;
  }
  EXPORT_SYMBOL_GPL(dm_rh_region_context);
  
  region_t dm_rh_get_region_key(struct dm_region *reg)
  {
  	return reg->key;
  }
  EXPORT_SYMBOL_GPL(dm_rh_get_region_key);
  
  sector_t dm_rh_get_region_size(struct dm_region_hash *rh)
  {
  	return rh->region_size;
  }
  EXPORT_SYMBOL_GPL(dm_rh_get_region_size);
  
  /*
   * FIXME: shall we pass in a structure instead of all these args to
   * dm_region_hash_create()????
   */
  #define RH_HASH_MULT 2654435387U
  #define RH_HASH_SHIFT 12
  
  #define MIN_REGIONS 64
  struct dm_region_hash *dm_region_hash_create(
  		void *context, void (*dispatch_bios)(void *context,
  						     struct bio_list *bios),
  		void (*wakeup_workers)(void *context),
  		void (*wakeup_all_recovery_waiters)(void *context),
  		sector_t target_begin, unsigned max_recovery,
  		struct dm_dirty_log *log, uint32_t region_size,
  		region_t nr_regions)
  {
  	struct dm_region_hash *rh;
  	unsigned nr_buckets, max_buckets;
  	size_t i;
  
  	/*
  	 * Calculate a suitable number of buckets for our hash
  	 * table.
  	 */
  	max_buckets = nr_regions >> 6;
  	for (nr_buckets = 128u; nr_buckets < max_buckets; nr_buckets <<= 1)
  		;
  	nr_buckets >>= 1;
  
  	rh = kmalloc(sizeof(*rh), GFP_KERNEL);
  	if (!rh) {
  		DMERR("unable to allocate region hash memory");
  		return ERR_PTR(-ENOMEM);
  	}
  
  	rh->context = context;
  	rh->dispatch_bios = dispatch_bios;
  	rh->wakeup_workers = wakeup_workers;
  	rh->wakeup_all_recovery_waiters = wakeup_all_recovery_waiters;
  	rh->target_begin = target_begin;
  	rh->max_recovery = max_recovery;
  	rh->log = log;
  	rh->region_size = region_size;
  	rh->region_shift = ffs(region_size) - 1;
  	rwlock_init(&rh->hash_lock);
  	rh->mask = nr_buckets - 1;
  	rh->nr_buckets = nr_buckets;
  
  	rh->shift = RH_HASH_SHIFT;
  	rh->prime = RH_HASH_MULT;
  
  	rh->buckets = vmalloc(nr_buckets * sizeof(*rh->buckets));
  	if (!rh->buckets) {
  		DMERR("unable to allocate region hash bucket memory");
  		kfree(rh);
  		return ERR_PTR(-ENOMEM);
  	}
  
  	for (i = 0; i < nr_buckets; i++)
  		INIT_LIST_HEAD(rh->buckets + i);
  
  	spin_lock_init(&rh->region_lock);
  	sema_init(&rh->recovery_count, 0);
  	atomic_set(&rh->recovery_in_flight, 0);
  	INIT_LIST_HEAD(&rh->clean_regions);
  	INIT_LIST_HEAD(&rh->quiesced_regions);
  	INIT_LIST_HEAD(&rh->recovered_regions);
  	INIT_LIST_HEAD(&rh->failed_recovered_regions);
  	rh->flush_failure = 0;
  
  	rh->region_pool = mempool_create_kmalloc_pool(MIN_REGIONS,
  						      sizeof(struct dm_region));
  	if (!rh->region_pool) {
  		vfree(rh->buckets);
  		kfree(rh);
  		rh = ERR_PTR(-ENOMEM);
  	}
  
  	return rh;
  }
  EXPORT_SYMBOL_GPL(dm_region_hash_create);
  
  void dm_region_hash_destroy(struct dm_region_hash *rh)
  {
  	unsigned h;
  	struct dm_region *reg, *nreg;
  
  	BUG_ON(!list_empty(&rh->quiesced_regions));
  	for (h = 0; h < rh->nr_buckets; h++) {
  		list_for_each_entry_safe(reg, nreg, rh->buckets + h,
  					 hash_list) {
  			BUG_ON(atomic_read(&reg->pending));
  			mempool_free(reg, rh->region_pool);
  		}
  	}
  
  	if (rh->log)
  		dm_dirty_log_destroy(rh->log);
  
  	if (rh->region_pool)
  		mempool_destroy(rh->region_pool);
  
  	vfree(rh->buckets);
  	kfree(rh);
  }
  EXPORT_SYMBOL_GPL(dm_region_hash_destroy);
  
  struct dm_dirty_log *dm_rh_dirty_log(struct dm_region_hash *rh)
  {
  	return rh->log;
  }
  EXPORT_SYMBOL_GPL(dm_rh_dirty_log);
  
  static unsigned rh_hash(struct dm_region_hash *rh, region_t region)
  {
  	return (unsigned) ((region * rh->prime) >> rh->shift) & rh->mask;
  }
  
  static struct dm_region *__rh_lookup(struct dm_region_hash *rh, region_t region)
  {
  	struct dm_region *reg;
  	struct list_head *bucket = rh->buckets + rh_hash(rh, region);
  
  	list_for_each_entry(reg, bucket, hash_list)
  		if (reg->key == region)
  			return reg;
  
  	return NULL;
  }
  
  static void __rh_insert(struct dm_region_hash *rh, struct dm_region *reg)
  {
  	list_add(&reg->hash_list, rh->buckets + rh_hash(rh, reg->key));
  }
  
  static struct dm_region *__rh_alloc(struct dm_region_hash *rh, region_t region)
  {
  	struct dm_region *reg, *nreg;
  
  	nreg = mempool_alloc(rh->region_pool, GFP_ATOMIC);
  	if (unlikely(!nreg))
  		nreg = kmalloc(sizeof(*nreg), GFP_NOIO | __GFP_NOFAIL);
  
  	nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
  		      DM_RH_CLEAN : DM_RH_NOSYNC;
  	nreg->rh = rh;
  	nreg->key = region;
  	INIT_LIST_HEAD(&nreg->list);
  	atomic_set(&nreg->pending, 0);
  	bio_list_init(&nreg->delayed_bios);
  
  	write_lock_irq(&rh->hash_lock);
  	reg = __rh_lookup(rh, region);
  	if (reg)
  		/* We lost the race. */
  		mempool_free(nreg, rh->region_pool);
  	else {
  		__rh_insert(rh, nreg);
  		if (nreg->state == DM_RH_CLEAN) {
  			spin_lock(&rh->region_lock);
  			list_add(&nreg->list, &rh->clean_regions);
  			spin_unlock(&rh->region_lock);
  		}
  
  		reg = nreg;
  	}
  	write_unlock_irq(&rh->hash_lock);
  
  	return reg;
  }
  
  static struct dm_region *__rh_find(struct dm_region_hash *rh, region_t region)
  {
  	struct dm_region *reg;
  
  	reg = __rh_lookup(rh, region);
  	if (!reg) {
  		read_unlock(&rh->hash_lock);
  		reg = __rh_alloc(rh, region);
  		read_lock(&rh->hash_lock);
  	}
  
  	return reg;
  }
  
  int dm_rh_get_state(struct dm_region_hash *rh, region_t region, int may_block)
  {
  	int r;
  	struct dm_region *reg;
  
  	read_lock(&rh->hash_lock);
  	reg = __rh_lookup(rh, region);
  	read_unlock(&rh->hash_lock);
  
  	if (reg)
  		return reg->state;
  
  	/*
  	 * The region wasn't in the hash, so we fall back to the
  	 * dirty log.
  	 */
  	r = rh->log->type->in_sync(rh->log, region, may_block);
  
  	/*
  	 * Any error from the dirty log (eg. -EWOULDBLOCK) gets
  	 * taken as a DM_RH_NOSYNC
  	 */
  	return r == 1 ? DM_RH_CLEAN : DM_RH_NOSYNC;
  }
  EXPORT_SYMBOL_GPL(dm_rh_get_state);
  
  static void complete_resync_work(struct dm_region *reg, int success)
  {
  	struct dm_region_hash *rh = reg->rh;
  
  	rh->log->type->set_region_sync(rh->log, reg->key, success);
  
  	/*
  	 * Dispatch the bios before we call 'wake_up_all'.
  	 * This is important because if we are suspending,
  	 * we want to know that recovery is complete and
  	 * the work queue is flushed.  If we wake_up_all
  	 * before we dispatch_bios (queue bios and call wake()),
  	 * then we risk suspending before the work queue
  	 * has been properly flushed.
  	 */
  	rh->dispatch_bios(rh->context, &reg->delayed_bios);
  	if (atomic_dec_and_test(&rh->recovery_in_flight))
  		rh->wakeup_all_recovery_waiters(rh->context);
  	up(&rh->recovery_count);
  }
  
  /* dm_rh_mark_nosync
   * @ms
   * @bio
   *
   * The bio was written on some mirror(s) but failed on other mirror(s).
   * We can successfully endio the bio but should avoid the region being
   * marked clean by setting the state DM_RH_NOSYNC.
   *
   * This function is _not_ safe in interrupt context!
   */
  void dm_rh_mark_nosync(struct dm_region_hash *rh, struct bio *bio)
  {
  	unsigned long flags;
  	struct dm_dirty_log *log = rh->log;
  	struct dm_region *reg;
  	region_t region = dm_rh_bio_to_region(rh, bio);
  	int recovering = 0;
  
  	if (bio->bi_rw & REQ_FLUSH) {
  		rh->flush_failure = 1;
  		return;
  	}
  
  	if (bio->bi_rw & REQ_DISCARD)
  		return;
  
  	/* We must inform the log that the sync count has changed. */
  	log->type->set_region_sync(log, region, 0);
  
  	read_lock(&rh->hash_lock);
  	reg = __rh_find(rh, region);
  	read_unlock(&rh->hash_lock);
  
  	/* region hash entry should exist because write was in-flight */
  	BUG_ON(!reg);
  	BUG_ON(!list_empty(&reg->list));
  
  	spin_lock_irqsave(&rh->region_lock, flags);
  	/*
  	 * Possible cases:
  	 *   1) DM_RH_DIRTY
  	 *   2) DM_RH_NOSYNC: was dirty, other preceding writes failed
  	 *   3) DM_RH_RECOVERING: flushing pending writes
  	 * Either case, the region should have not been connected to list.
  	 */
  	recovering = (reg->state == DM_RH_RECOVERING);
  	reg->state = DM_RH_NOSYNC;
  	BUG_ON(!list_empty(&reg->list));
  	spin_unlock_irqrestore(&rh->region_lock, flags);
  
  	if (recovering)
  		complete_resync_work(reg, 0);
  }
  EXPORT_SYMBOL_GPL(dm_rh_mark_nosync);
  
  void dm_rh_update_states(struct dm_region_hash *rh, int errors_handled)
  {
  	struct dm_region *reg, *next;
  
  	LIST_HEAD(clean);
  	LIST_HEAD(recovered);
  	LIST_HEAD(failed_recovered);
  
  	/*
  	 * Quickly grab the lists.
  	 */
  	write_lock_irq(&rh->hash_lock);
  	spin_lock(&rh->region_lock);
  	if (!list_empty(&rh->clean_regions)) {
  		list_splice_init(&rh->clean_regions, &clean);
  
  		list_for_each_entry(reg, &clean, list)
  			list_del(&reg->hash_list);
  	}
  
  	if (!list_empty(&rh->recovered_regions)) {
  		list_splice_init(&rh->recovered_regions, &recovered);
  
  		list_for_each_entry(reg, &recovered, list)
  			list_del(&reg->hash_list);
  	}
  
  	if (!list_empty(&rh->failed_recovered_regions)) {
  		list_splice_init(&rh->failed_recovered_regions,
  				 &failed_recovered);
  
  		list_for_each_entry(reg, &failed_recovered, list)
  			list_del(&reg->hash_list);
  	}
  
  	spin_unlock(&rh->region_lock);
  	write_unlock_irq(&rh->hash_lock);
  
  	/*
  	 * All the regions on the recovered and clean lists have
  	 * now been pulled out of the system, so no need to do
  	 * any more locking.
  	 */
  	list_for_each_entry_safe(reg, next, &recovered, list) {
  		rh->log->type->clear_region(rh->log, reg->key);
  		complete_resync_work(reg, 1);
  		mempool_free(reg, rh->region_pool);
  	}
  
  	list_for_each_entry_safe(reg, next, &failed_recovered, list) {
  		complete_resync_work(reg, errors_handled ? 0 : 1);
  		mempool_free(reg, rh->region_pool);
  	}
  
  	list_for_each_entry_safe(reg, next, &clean, list) {
  		rh->log->type->clear_region(rh->log, reg->key);
  		mempool_free(reg, rh->region_pool);
  	}
  
  	rh->log->type->flush(rh->log);
  }
  EXPORT_SYMBOL_GPL(dm_rh_update_states);
  
  static void rh_inc(struct dm_region_hash *rh, region_t region)
  {
  	struct dm_region *reg;
  
  	read_lock(&rh->hash_lock);
  	reg = __rh_find(rh, region);
  
  	spin_lock_irq(&rh->region_lock);
  	atomic_inc(&reg->pending);
  
  	if (reg->state == DM_RH_CLEAN) {
  		reg->state = DM_RH_DIRTY;
  		list_del_init(&reg->list);	/* take off the clean list */
  		spin_unlock_irq(&rh->region_lock);
  
  		rh->log->type->mark_region(rh->log, reg->key);
  	} else
  		spin_unlock_irq(&rh->region_lock);
  
  
  	read_unlock(&rh->hash_lock);
  }
  
  void dm_rh_inc_pending(struct dm_region_hash *rh, struct bio_list *bios)
  {
  	struct bio *bio;
  
  	for (bio = bios->head; bio; bio = bio->bi_next) {
  		if (bio->bi_rw & (REQ_FLUSH | REQ_DISCARD))
  			continue;
  		rh_inc(rh, dm_rh_bio_to_region(rh, bio));
  	}
  }
  EXPORT_SYMBOL_GPL(dm_rh_inc_pending);
  
  void dm_rh_dec(struct dm_region_hash *rh, region_t region)
  {
  	unsigned long flags;
  	struct dm_region *reg;
  	int should_wake = 0;
  
  	read_lock(&rh->hash_lock);
  	reg = __rh_lookup(rh, region);
  	read_unlock(&rh->hash_lock);
  
  	spin_lock_irqsave(&rh->region_lock, flags);
  	if (atomic_dec_and_test(&reg->pending)) {
  		/*
  		 * There is no pending I/O for this region.
  		 * We can move the region to corresponding list for next action.
  		 * At this point, the region is not yet connected to any list.
  		 *
  		 * If the state is DM_RH_NOSYNC, the region should be kept off
  		 * from clean list.
  		 * The hash entry for DM_RH_NOSYNC will remain in memory
  		 * until the region is recovered or the map is reloaded.
  		 */
  
  		/* do nothing for DM_RH_NOSYNC */
  		if (unlikely(rh->flush_failure)) {
  			/*
  			 * If a write flush failed some time ago, we
  			 * don't know whether or not this write made it
  			 * to the disk, so we must resync the device.
  			 */
  			reg->state = DM_RH_NOSYNC;
  		} else if (reg->state == DM_RH_RECOVERING) {
  			list_add_tail(&reg->list, &rh->quiesced_regions);
  		} else if (reg->state == DM_RH_DIRTY) {
  			reg->state = DM_RH_CLEAN;
  			list_add(&reg->list, &rh->clean_regions);
  		}
  		should_wake = 1;
  	}
  	spin_unlock_irqrestore(&rh->region_lock, flags);
  
  	if (should_wake)
  		rh->wakeup_workers(rh->context);
  }
  EXPORT_SYMBOL_GPL(dm_rh_dec);
  
  /*
   * Starts quiescing a region in preparation for recovery.
   */
  static int __rh_recovery_prepare(struct dm_region_hash *rh)
  {
  	int r;
  	region_t region;
  	struct dm_region *reg;
  
  	/*
  	 * Ask the dirty log what's next.
  	 */
  	r = rh->log->type->get_resync_work(rh->log, &region);
  	if (r <= 0)
  		return r;
  
  	/*
  	 * Get this region, and start it quiescing by setting the
  	 * recovering flag.
  	 */
  	read_lock(&rh->hash_lock);
  	reg = __rh_find(rh, region);
  	read_unlock(&rh->hash_lock);
  
  	spin_lock_irq(&rh->region_lock);
  	reg->state = DM_RH_RECOVERING;
  
  	/* Already quiesced ? */
  	if (atomic_read(&reg->pending))
  		list_del_init(&reg->list);
  	else
  		list_move(&reg->list, &rh->quiesced_regions);
  
  	spin_unlock_irq(&rh->region_lock);
  
  	return 1;
  }
  
  void dm_rh_recovery_prepare(struct dm_region_hash *rh)
  {
  	/* Extra reference to avoid race with dm_rh_stop_recovery */
  	atomic_inc(&rh->recovery_in_flight);
  
  	while (!down_trylock(&rh->recovery_count)) {
  		atomic_inc(&rh->recovery_in_flight);
  		if (__rh_recovery_prepare(rh) <= 0) {
  			atomic_dec(&rh->recovery_in_flight);
  			up(&rh->recovery_count);
  			break;
  		}
  	}
  
  	/* Drop the extra reference */
  	if (atomic_dec_and_test(&rh->recovery_in_flight))
  		rh->wakeup_all_recovery_waiters(rh->context);
  }
  EXPORT_SYMBOL_GPL(dm_rh_recovery_prepare);
  
  /*
   * Returns any quiesced regions.
   */
  struct dm_region *dm_rh_recovery_start(struct dm_region_hash *rh)
  {
  	struct dm_region *reg = NULL;
  
  	spin_lock_irq(&rh->region_lock);
  	if (!list_empty(&rh->quiesced_regions)) {
  		reg = list_entry(rh->quiesced_regions.next,
  				 struct dm_region, list);
  		list_del_init(&reg->list);  /* remove from the quiesced list */
  	}
  	spin_unlock_irq(&rh->region_lock);
  
  	return reg;
  }
  EXPORT_SYMBOL_GPL(dm_rh_recovery_start);
  
  void dm_rh_recovery_end(struct dm_region *reg, int success)
  {
  	struct dm_region_hash *rh = reg->rh;
  
  	spin_lock_irq(&rh->region_lock);
  	if (success)
  		list_add(&reg->list, &reg->rh->recovered_regions);
  	else
  		list_add(&reg->list, &reg->rh->failed_recovered_regions);
  
  	spin_unlock_irq(&rh->region_lock);
  
  	rh->wakeup_workers(rh->context);
  }
  EXPORT_SYMBOL_GPL(dm_rh_recovery_end);
  
  /* Return recovery in flight count. */
  int dm_rh_recovery_in_flight(struct dm_region_hash *rh)
  {
  	return atomic_read(&rh->recovery_in_flight);
  }
  EXPORT_SYMBOL_GPL(dm_rh_recovery_in_flight);
  
  int dm_rh_flush(struct dm_region_hash *rh)
  {
  	return rh->log->type->flush(rh->log);
  }
  EXPORT_SYMBOL_GPL(dm_rh_flush);
  
  void dm_rh_delay(struct dm_region_hash *rh, struct bio *bio)
  {
  	struct dm_region *reg;
  
  	read_lock(&rh->hash_lock);
  	reg = __rh_find(rh, dm_rh_bio_to_region(rh, bio));
  	bio_list_add(&reg->delayed_bios, bio);
  	read_unlock(&rh->hash_lock);
  }
  EXPORT_SYMBOL_GPL(dm_rh_delay);
  
  void dm_rh_stop_recovery(struct dm_region_hash *rh)
  {
  	int i;
  
  	/* wait for any recovering regions */
  	for (i = 0; i < rh->max_recovery; i++)
  		down(&rh->recovery_count);
  }
  EXPORT_SYMBOL_GPL(dm_rh_stop_recovery);
  
  void dm_rh_start_recovery(struct dm_region_hash *rh)
  {
  	int i;
  
  	for (i = 0; i < rh->max_recovery; i++)
  		up(&rh->recovery_count);
  
  	rh->wakeup_workers(rh->context);
  }
  EXPORT_SYMBOL_GPL(dm_rh_start_recovery);
  
  MODULE_DESCRIPTION(DM_NAME " region hash");
  MODULE_AUTHOR("Joe Thornber/Heinz Mauelshagen <dm-devel@redhat.com>");
  MODULE_LICENSE("GPL");