/*
   * Copyright (C) 2003 Sistina Software Limited.

   * Copyright (C) 2005-2008 Red Hat, Inc. All rights reserved.

   *
   * This file is released under the GPL.
   */

  #include "dm-bio-record.h"

  #include <linux/init.h>
  #include <linux/mempool.h>
  #include <linux/module.h>
  #include <linux/pagemap.h>
  #include <linux/slab.h>

  #include <linux/workqueue.h>

  #include <linux/device-mapper.h>

  #include <linux/dm-io.h>
  #include <linux/dm-dirty-log.h>
  #include <linux/dm-kcopyd.h>

  #include <linux/dm-region-hash.h>

  #define DM_MSG_PREFIX "raid1"

  
  #define MAX_RECOVERY 1	/* Maximum number of regions recovered in parallel. */

  #define MAX_NR_MIRRORS	(DM_KCOPYD_MAX_REGIONS + 1)

  #define DM_RAID1_HANDLE_ERRORS	0x01
  #define DM_RAID1_KEEP_LOG	0x02

  #define errors_handled(p)	((p)->features & DM_RAID1_HANDLE_ERRORS)

  #define keep_log(p)		((p)->features & DM_RAID1_KEEP_LOG)

  static DECLARE_WAIT_QUEUE_HEAD(_kmirrord_recovery_stopped);

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

   * Mirror set structures.
   *---------------------------------------------------------------*/

  enum dm_raid1_error {
  	DM_RAID1_WRITE_ERROR,

  	DM_RAID1_FLUSH_ERROR,

  	DM_RAID1_SYNC_ERROR,
  	DM_RAID1_READ_ERROR
  };

  struct mirror {

  	struct mirror_set *ms;

  	atomic_t error_count;

  	unsigned long error_type;

  	struct dm_dev *dev;
  	sector_t offset;
  };
  
  struct mirror_set {
  	struct dm_target *ti;
  	struct list_head list;

  	uint64_t features;

  	spinlock_t lock;	/* protects the lists */

  	struct bio_list reads;
  	struct bio_list writes;

  	struct bio_list failures;

  	struct bio_list holds;	/* bios are waiting until suspend */

  	struct dm_region_hash *rh;
  	struct dm_kcopyd_client *kcopyd_client;

  	struct dm_io_client *io_client;

  	/* recovery */
  	region_t nr_regions;
  	int in_sync;

  	int log_failure;

  	int leg_failure;

  	atomic_t suspend;

  	atomic_t default_mirror;	/* Default mirror */

  	struct workqueue_struct *kmirrord_wq;
  	struct work_struct kmirrord_work;

  	struct timer_list timer;
  	unsigned long timer_pending;

  	struct work_struct trigger_event;

  	unsigned nr_mirrors;

  	struct mirror mirror[];

  };

  DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(raid1_resync_throttle,
  		"A percentage of time allocated for raid resynchronization");

  static void wakeup_mirrord(void *context)

  {

  	struct mirror_set *ms = context;

  	queue_work(ms->kmirrord_wq, &ms->kmirrord_work);
  }

  static void delayed_wake_fn(struct timer_list *t)

  {

  	struct mirror_set *ms = from_timer(ms, t, timer);

  
  	clear_bit(0, &ms->timer_pending);

  	wakeup_mirrord(ms);

  }
  
  static void delayed_wake(struct mirror_set *ms)
  {
  	if (test_and_set_bit(0, &ms->timer_pending))
  		return;
  
  	ms->timer.expires = jiffies + HZ / 5;

  	add_timer(&ms->timer);
  }

  static void wakeup_all_recovery_waiters(void *context)

  {

  	wake_up_all(&_kmirrord_recovery_stopped);

  }

  static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw)

  {
  	unsigned long flags;

  	int should_wake = 0;

  	struct bio_list *bl;

  	bl = (rw == WRITE) ? &ms->writes : &ms->reads;
  	spin_lock_irqsave(&ms->lock, flags);
  	should_wake = !(bl->head);
  	bio_list_add(bl, bio);
  	spin_unlock_irqrestore(&ms->lock, flags);

  
  	if (should_wake)

  		wakeup_mirrord(ms);

  }

  static void dispatch_bios(void *context, struct bio_list *bio_list)

  {

  	struct mirror_set *ms = context;
  	struct bio *bio;

  	while ((bio = bio_list_pop(bio_list)))
  		queue_bio(ms, bio, WRITE);

  }

  struct dm_raid1_bio_record {

  	struct mirror *m;

  	/* if details->bi_disk == NULL, details were not saved */

  	struct dm_bio_details details;

  	region_t write_region;

  };

  /*
   * Every mirror should look like this one.
   */
  #define DEFAULT_MIRROR 0
  
  /*

   * This is yucky.  We squirrel the mirror struct away inside
   * bi_next for read/write buffers.  This is safe since the bh

   * doesn't get submitted to the lower levels of block layer.
   */

  static struct mirror *bio_get_m(struct bio *bio)

  {

  	return (struct mirror *) bio->bi_next;

  }

  static void bio_set_m(struct bio *bio, struct mirror *m)

  {

  	bio->bi_next = (struct bio *) m;

  }

  static struct mirror *get_default_mirror(struct mirror_set *ms)
  {
  	return &ms->mirror[atomic_read(&ms->default_mirror)];
  }
  
  static void set_default_mirror(struct mirror *m)
  {
  	struct mirror_set *ms = m->ms;
  	struct mirror *m0 = &(ms->mirror[0]);
  
  	atomic_set(&ms->default_mirror, m - m0);
  }

  static struct mirror *get_valid_mirror(struct mirror_set *ms)
  {
  	struct mirror *m;
  
  	for (m = ms->mirror; m < ms->mirror + ms->nr_mirrors; m++)
  		if (!atomic_read(&m->error_count))
  			return m;
  
  	return NULL;
  }

  /* fail_mirror
   * @m: mirror device to fail
   * @error_type: one of the enum's, DM_RAID1_*_ERROR
   *
   * If errors are being handled, record the type of
   * error encountered for this device.  If this type
   * of error has already been recorded, we can return;
   * otherwise, we must signal userspace by triggering
   * an event.  Additionally, if the device is the
   * primary device, we must choose a new primary, but
   * only if the mirror is in-sync.
   *
   * This function must not block.
   */
  static void fail_mirror(struct mirror *m, enum dm_raid1_error error_type)
  {
  	struct mirror_set *ms = m->ms;
  	struct mirror *new;

  	ms->leg_failure = 1;

  	/*
  	 * error_count is used for nothing more than a
  	 * simple way to tell if a device has encountered
  	 * errors.
  	 */
  	atomic_inc(&m->error_count);
  
  	if (test_and_set_bit(error_type, &m->error_type))
  		return;

  	if (!errors_handled(ms))
  		return;

  	if (m != get_default_mirror(ms))
  		goto out;

  	if (!ms->in_sync && !keep_log(ms)) {

  		/*
  		 * Better to issue requests to same failing device
  		 * than to risk returning corrupt data.
  		 */
  		DMERR("Primary mirror (%s) failed while out-of-sync: "
  		      "Reads may fail.", m->dev->name);
  		goto out;
  	}

  	new = get_valid_mirror(ms);
  	if (new)
  		set_default_mirror(new);
  	else

  		DMWARN("All sides of mirror have failed.");
  
  out:
  	schedule_work(&ms->trigger_event);
  }

  static int mirror_flush(struct dm_target *ti)
  {
  	struct mirror_set *ms = ti->private;
  	unsigned long error_bits;
  
  	unsigned int i;

  	struct dm_io_region io[MAX_NR_MIRRORS];

  	struct mirror *m;
  	struct dm_io_request io_req = {

  		.bi_op = REQ_OP_WRITE,

  		.bi_op_flags = REQ_PREFLUSH | REQ_SYNC,

  		.mem.type = DM_IO_KMEM,

  		.mem.ptr.addr = NULL,

  		.client = ms->io_client,
  	};
  
  	for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++) {
  		io[i].bdev = m->dev->bdev;
  		io[i].sector = 0;
  		io[i].count = 0;
  	}
  
  	error_bits = -1;
  	dm_io(&io_req, ms->nr_mirrors, io, &error_bits);
  	if (unlikely(error_bits != 0)) {
  		for (i = 0; i < ms->nr_mirrors; i++)
  			if (test_bit(i, &error_bits))
  				fail_mirror(ms->mirror + i,

  					    DM_RAID1_FLUSH_ERROR);

  		return -EIO;
  	}
  
  	return 0;
  }

  /*-----------------------------------------------------------------
   * Recovery.
   *
   * When a mirror is first activated we may find that some regions
   * are in the no-sync state.  We have to recover these by
   * recopying from the default mirror to all the others.
   *---------------------------------------------------------------*/

  static void recovery_complete(int read_err, unsigned long write_err,

  			      void *context)
  {

  	struct dm_region *reg = context;
  	struct mirror_set *ms = dm_rh_region_context(reg);

  	int m, bit = 0;

  	if (read_err) {

  		/* Read error means the failure of default mirror. */
  		DMERR_LIMIT("Unable to read primary mirror during recovery");

  		fail_mirror(get_default_mirror(ms), DM_RAID1_SYNC_ERROR);
  	}

  	if (write_err) {

  		DMERR_LIMIT("Write error during recovery (error = 0x%lx)",

  			    write_err);

  		/*
  		 * Bits correspond to devices (excluding default mirror).
  		 * The default mirror cannot change during recovery.
  		 */
  		for (m = 0; m < ms->nr_mirrors; m++) {
  			if (&ms->mirror[m] == get_default_mirror(ms))
  				continue;
  			if (test_bit(bit, &write_err))
  				fail_mirror(ms->mirror + m,
  					    DM_RAID1_SYNC_ERROR);
  			bit++;
  		}
  	}

  	dm_rh_recovery_end(reg, !(read_err || write_err));

  }

  static void recover(struct mirror_set *ms, struct dm_region *reg)

  {

  	unsigned i;

  	struct dm_io_region from, to[DM_KCOPYD_MAX_REGIONS], *dest;

  	struct mirror *m;
  	unsigned long flags = 0;

  	region_t key = dm_rh_get_region_key(reg);
  	sector_t region_size = dm_rh_get_region_size(ms->rh);

  
  	/* fill in the source */

  	m = get_default_mirror(ms);

  	from.bdev = m->dev->bdev;

  	from.sector = m->offset + dm_rh_region_to_sector(ms->rh, key);
  	if (key == (ms->nr_regions - 1)) {

  		/*
  		 * The final region may be smaller than
  		 * region_size.
  		 */

  		from.count = ms->ti->len & (region_size - 1);

  		if (!from.count)

  			from.count = region_size;

  	} else

  		from.count = region_size;

  
  	/* fill in the destinations */
  	for (i = 0, dest = to; i < ms->nr_mirrors; i++) {

  		if (&ms->mirror[i] == get_default_mirror(ms))

  			continue;
  
  		m = ms->mirror + i;
  		dest->bdev = m->dev->bdev;

  		dest->sector = m->offset + dm_rh_region_to_sector(ms->rh, key);

  		dest->count = from.count;
  		dest++;
  	}
  
  	/* hand to kcopyd */

  	if (!errors_handled(ms))
  		set_bit(DM_KCOPYD_IGNORE_ERROR, &flags);

  	dm_kcopyd_copy(ms->kcopyd_client, &from, ms->nr_mirrors - 1, to,
  		       flags, recovery_complete, reg);

  }

  static void reset_ms_flags(struct mirror_set *ms)
  {
  	unsigned int m;
  
  	ms->leg_failure = 0;
  	for (m = 0; m < ms->nr_mirrors; m++) {
  		atomic_set(&(ms->mirror[m].error_count), 0);
  		ms->mirror[m].error_type = 0;
  	}
  }

  static void do_recovery(struct mirror_set *ms)
  {

  	struct dm_region *reg;
  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  
  	/*
  	 * Start quiescing some regions.
  	 */

  	dm_rh_recovery_prepare(ms->rh);

  
  	/*
  	 * Copy any already quiesced regions.
  	 */

  	while ((reg = dm_rh_recovery_start(ms->rh)))
  		recover(ms, reg);

  
  	/*
  	 * Update the in sync flag.
  	 */
  	if (!ms->in_sync &&
  	    (log->type->get_sync_count(log) == ms->nr_regions)) {
  		/* the sync is complete */
  		dm_table_event(ms->ti->table);
  		ms->in_sync = 1;

  		reset_ms_flags(ms);

  	}
  }
  
  /*-----------------------------------------------------------------
   * Reads
   *---------------------------------------------------------------*/
  static struct mirror *choose_mirror(struct mirror_set *ms, sector_t sector)
  {

  	struct mirror *m = get_default_mirror(ms);
  
  	do {
  		if (likely(!atomic_read(&m->error_count)))
  			return m;
  
  		if (m-- == ms->mirror)
  			m += ms->nr_mirrors;
  	} while (m != get_default_mirror(ms));
  
  	return NULL;
  }
  
  static int default_ok(struct mirror *m)
  {
  	struct mirror *default_mirror = get_default_mirror(m->ms);
  
  	return !atomic_read(&default_mirror->error_count);
  }
  
  static int mirror_available(struct mirror_set *ms, struct bio *bio)
  {

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
  	region_t region = dm_rh_bio_to_region(ms->rh, bio);

  	if (log->type->in_sync(log, region, 0))

  		return choose_mirror(ms,  bio->bi_iter.bi_sector) ? 1 : 0;

  
  	return 0;

  }
  
  /*
   * remap a buffer to a particular mirror.
   */

  static sector_t map_sector(struct mirror *m, struct bio *bio)
  {

  	if (unlikely(!bio->bi_iter.bi_size))

  		return 0;

  	return m->offset + dm_target_offset(m->ms->ti, bio->bi_iter.bi_sector);

  }
  
  static void map_bio(struct mirror *m, struct bio *bio)

  {

  	bio_set_dev(bio, m->dev->bdev);

  	bio->bi_iter.bi_sector = map_sector(m, bio);

  }

  static void map_region(struct dm_io_region *io, struct mirror *m,

  		       struct bio *bio)
  {
  	io->bdev = m->dev->bdev;
  	io->sector = map_sector(m, bio);

  	io->count = bio_sectors(bio);

  }

  static void hold_bio(struct mirror_set *ms, struct bio *bio)
  {
  	/*

  	 * Lock is required to avoid race condition during suspend
  	 * process.

  	 */

  	spin_lock_irq(&ms->lock);

  	if (atomic_read(&ms->suspend)) {

  		spin_unlock_irq(&ms->lock);
  
  		/*
  		 * If device is suspended, complete the bio.
  		 */

  		if (dm_noflush_suspending(ms->ti))

  			bio->bi_status = BLK_STS_DM_REQUEUE;

  		else

  			bio->bi_status = BLK_STS_IOERR;

  
  		bio_endio(bio);

  		return;
  	}
  
  	/*
  	 * Hold bio until the suspend is complete.
  	 */

  	bio_list_add(&ms->holds, bio);
  	spin_unlock_irq(&ms->lock);
  }

  /*-----------------------------------------------------------------
   * Reads
   *---------------------------------------------------------------*/
  static void read_callback(unsigned long error, void *context)
  {
  	struct bio *bio = context;
  	struct mirror *m;
  
  	m = bio_get_m(bio);
  	bio_set_m(bio, NULL);
  
  	if (likely(!error)) {

  		bio_endio(bio);

  		return;
  	}
  
  	fail_mirror(m, DM_RAID1_READ_ERROR);
  
  	if (likely(default_ok(m)) || mirror_available(m->ms, bio)) {
  		DMWARN_LIMIT("Read failure on mirror device %s.  "
  			     "Trying alternative device.",
  			     m->dev->name);

  		queue_bio(m->ms, bio, bio_data_dir(bio));

  		return;
  	}
  
  	DMERR_LIMIT("Read failure on mirror device %s.  Failing I/O.",
  		    m->dev->name);

  	bio_io_error(bio);

  }
  
  /* Asynchronous read. */
  static void read_async_bio(struct mirror *m, struct bio *bio)
  {

  	struct dm_io_region io;

  	struct dm_io_request io_req = {

  		.bi_op = REQ_OP_READ,
  		.bi_op_flags = 0,

  		.mem.type = DM_IO_BIO,
  		.mem.ptr.bio = bio,

  		.notify.fn = read_callback,
  		.notify.context = bio,
  		.client = m->ms->io_client,
  	};
  
  	map_region(&io, m, bio);
  	bio_set_m(bio, m);

  	BUG_ON(dm_io(&io_req, 1, &io, NULL));
  }
  
  static inline int region_in_sync(struct mirror_set *ms, region_t region,
  				 int may_block)
  {
  	int state = dm_rh_get_state(ms->rh, region, may_block);
  	return state == DM_RH_CLEAN || state == DM_RH_DIRTY;

  }
  
  static void do_reads(struct mirror_set *ms, struct bio_list *reads)
  {
  	region_t region;
  	struct bio *bio;
  	struct mirror *m;
  
  	while ((bio = bio_list_pop(reads))) {

  		region = dm_rh_bio_to_region(ms->rh, bio);

  		m = get_default_mirror(ms);

  
  		/*
  		 * We can only read balance if the region is in sync.
  		 */

  		if (likely(region_in_sync(ms, region, 1)))

  			m = choose_mirror(ms, bio->bi_iter.bi_sector);

  		else if (m && atomic_read(&m->error_count))
  			m = NULL;

  		if (likely(m))
  			read_async_bio(m, bio);
  		else

  			bio_io_error(bio);

  	}
  }
  
  /*-----------------------------------------------------------------
   * Writes.
   *
   * We do different things with the write io depending on the
   * state of the region that it's in:
   *
   * SYNC: 	increment pending, use kcopyd to write to *all* mirrors
   * RECOVERING:	delay the io until recovery completes
   * NOSYNC:	increment pending, just write to the default mirror
   *---------------------------------------------------------------*/

  static void write_callback(unsigned long error, void *context)
  {

  	unsigned i;

  	struct bio *bio = (struct bio *) context;
  	struct mirror_set *ms;

  	int should_wake = 0;
  	unsigned long flags;

  	ms = bio_get_m(bio)->ms;
  	bio_set_m(bio, NULL);

  
  	/*
  	 * NOTE: We don't decrement the pending count here,
  	 * instead it is done by the targets endio function.
  	 * This way we handle both writes to SYNC and NOSYNC
  	 * regions with the same code.
  	 */

  	if (likely(!error)) {

  		bio_endio(bio);

  		return;
  	}

  	/*
  	 * If the bio is discard, return an error, but do not
  	 * degrade the array.
  	 */

  	if (bio_op(bio) == REQ_OP_DISCARD) {

  		bio->bi_status = BLK_STS_NOTSUPP;

  		bio_endio(bio);

  		return;
  	}

  	for (i = 0; i < ms->nr_mirrors; i++)
  		if (test_bit(i, &error))
  			fail_mirror(ms->mirror + i, DM_RAID1_WRITE_ERROR);

  	/*
  	 * Need to raise event.  Since raising
  	 * events can block, we need to do it in
  	 * the main thread.
  	 */
  	spin_lock_irqsave(&ms->lock, flags);
  	if (!ms->failures.head)
  		should_wake = 1;
  	bio_list_add(&ms->failures, bio);
  	spin_unlock_irqrestore(&ms->lock, flags);
  	if (should_wake)
  		wakeup_mirrord(ms);

  }
  
  static void do_write(struct mirror_set *ms, struct bio *bio)
  {
  	unsigned int i;

  	struct dm_io_region io[MAX_NR_MIRRORS], *dest = io;

  	struct mirror *m;

  	struct dm_io_request io_req = {

  		.bi_op = REQ_OP_WRITE,

  		.bi_op_flags = bio->bi_opf & (REQ_FUA | REQ_PREFLUSH),

  		.mem.type = DM_IO_BIO,
  		.mem.ptr.bio = bio,

  		.notify.fn = write_callback,
  		.notify.context = bio,
  		.client = ms->io_client,
  	};

  	if (bio_op(bio) == REQ_OP_DISCARD) {
  		io_req.bi_op = REQ_OP_DISCARD;

  		io_req.mem.type = DM_IO_KMEM;
  		io_req.mem.ptr.addr = NULL;
  	}

  	for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++)
  		map_region(dest++, m, bio);

  	/*
  	 * Use default mirror because we only need it to retrieve the reference
  	 * to the mirror set in write_callback().
  	 */
  	bio_set_m(bio, get_default_mirror(ms));

  	BUG_ON(dm_io(&io_req, ms->nr_mirrors, io, NULL));

  }
  
  static void do_writes(struct mirror_set *ms, struct bio_list *writes)
  {
  	int state;
  	struct bio *bio;
  	struct bio_list sync, nosync, recover, *this_list = NULL;

  	struct bio_list requeue;
  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);
  	region_t region;

  
  	if (!writes->head)
  		return;
  
  	/*
  	 * Classify each write.
  	 */
  	bio_list_init(&sync);
  	bio_list_init(&nosync);
  	bio_list_init(&recover);

  	bio_list_init(&requeue);

  
  	while ((bio = bio_list_pop(writes))) {

  		if ((bio->bi_opf & REQ_PREFLUSH) ||

  		    (bio_op(bio) == REQ_OP_DISCARD)) {

  			bio_list_add(&sync, bio);
  			continue;
  		}

  		region = dm_rh_bio_to_region(ms->rh, bio);
  
  		if (log->type->is_remote_recovering &&
  		    log->type->is_remote_recovering(log, region)) {
  			bio_list_add(&requeue, bio);
  			continue;
  		}
  
  		state = dm_rh_get_state(ms->rh, region, 1);

  		switch (state) {

  		case DM_RH_CLEAN:
  		case DM_RH_DIRTY:

  			this_list = &sync;
  			break;

  		case DM_RH_NOSYNC:

  			this_list = &nosync;
  			break;

  		case DM_RH_RECOVERING:

  			this_list = &recover;
  			break;
  		}
  
  		bio_list_add(this_list, bio);
  	}
  
  	/*

  	 * Add bios that are delayed due to remote recovery
  	 * back on to the write queue
  	 */
  	if (unlikely(requeue.head)) {
  		spin_lock_irq(&ms->lock);
  		bio_list_merge(&ms->writes, &requeue);
  		spin_unlock_irq(&ms->lock);

  		delayed_wake(ms);

  	}
  
  	/*

  	 * Increment the pending counts for any regions that will
  	 * be written to (writes to recover regions are going to
  	 * be delayed).
  	 */

  	dm_rh_inc_pending(ms->rh, &sync);
  	dm_rh_inc_pending(ms->rh, &nosync);

  
  	/*
  	 * If the flush fails on a previous call and succeeds here,
  	 * we must not reset the log_failure variable.  We need
  	 * userspace interaction to do that.
  	 */
  	ms->log_failure = dm_rh_flush(ms->rh) ? 1 : ms->log_failure;

  
  	/*
  	 * Dispatch io.
  	 */

  	if (unlikely(ms->log_failure) && errors_handled(ms)) {

  		spin_lock_irq(&ms->lock);
  		bio_list_merge(&ms->failures, &sync);
  		spin_unlock_irq(&ms->lock);

  		wakeup_mirrord(ms);

  	} else

  		while ((bio = bio_list_pop(&sync)))

  			do_write(ms, bio);

  
  	while ((bio = bio_list_pop(&recover)))

  		dm_rh_delay(ms->rh, bio);

  
  	while ((bio = bio_list_pop(&nosync))) {

  		if (unlikely(ms->leg_failure) && errors_handled(ms) && !keep_log(ms)) {

  			spin_lock_irq(&ms->lock);
  			bio_list_add(&ms->failures, bio);
  			spin_unlock_irq(&ms->lock);
  			wakeup_mirrord(ms);
  		} else {

  			map_bio(get_default_mirror(ms), bio);

  			submit_bio_noacct(bio);

  		}

  	}
  }

  static void do_failures(struct mirror_set *ms, struct bio_list *failures)
  {
  	struct bio *bio;

  	if (likely(!failures->head))

  		return;

  	/*
  	 * If the log has failed, unattempted writes are being

  	 * put on the holds list.  We can't issue those writes

  	 * until a log has been marked, so we must store them.
  	 *
  	 * If a 'noflush' suspend is in progress, we can requeue
  	 * the I/O's to the core.  This give userspace a chance
  	 * to reconfigure the mirror, at which point the core
  	 * will reissue the writes.  If the 'noflush' flag is
  	 * not set, we have no choice but to return errors.
  	 *
  	 * Some writes on the failures list may have been
  	 * submitted before the log failure and represent a
  	 * failure to write to one of the devices.  It is ok
  	 * for us to treat them the same and requeue them
  	 * as well.
  	 */

  	while ((bio = bio_list_pop(failures))) {

  		if (!ms->log_failure) {

  			ms->in_sync = 0;

  			dm_rh_mark_nosync(ms->rh, bio);

  		}

  
  		/*
  		 * If all the legs are dead, fail the I/O.

  		 * If the device has failed and keep_log is enabled,
  		 * fail the I/O.
  		 *
  		 * If we have been told to handle errors, and keep_log
  		 * isn't enabled, hold the bio and wait for userspace to
  		 * deal with the problem.
  		 *

  		 * Otherwise pretend that the I/O succeeded. (This would
  		 * be wrong if the failed leg returned after reboot and
  		 * got replicated back to the good legs.)
  		 */

  		if (unlikely(!get_valid_mirror(ms) || (keep_log(ms) && ms->log_failure)))

  			bio_io_error(bio);

  		else if (errors_handled(ms) && !keep_log(ms))

  			hold_bio(ms, bio);
  		else

  			bio_endio(bio);

  	}

  }
  
  static void trigger_event(struct work_struct *work)
  {
  	struct mirror_set *ms =
  		container_of(work, struct mirror_set, trigger_event);
  
  	dm_table_event(ms->ti->table);
  }

  /*-----------------------------------------------------------------
   * kmirrord
   *---------------------------------------------------------------*/

  static void do_mirror(struct work_struct *work)

  {

  	struct mirror_set *ms = container_of(work, struct mirror_set,
  					     kmirrord_work);

  	struct bio_list reads, writes, failures;
  	unsigned long flags;

  	spin_lock_irqsave(&ms->lock, flags);

  	reads = ms->reads;
  	writes = ms->writes;

  	failures = ms->failures;

  	bio_list_init(&ms->reads);
  	bio_list_init(&ms->writes);

  	bio_list_init(&ms->failures);
  	spin_unlock_irqrestore(&ms->lock, flags);

  	dm_rh_update_states(ms->rh, errors_handled(ms));

  	do_recovery(ms);
  	do_reads(ms, &reads);
  	do_writes(ms, &writes);

  	do_failures(ms, &failures);

  }

  /*-----------------------------------------------------------------
   * Target functions
   *---------------------------------------------------------------*/
  static struct mirror_set *alloc_context(unsigned int nr_mirrors,
  					uint32_t region_size,
  					struct dm_target *ti,

  					struct dm_dirty_log *dl)

  {

  	struct mirror_set *ms =
  		kzalloc(struct_size(ms, mirror, nr_mirrors), GFP_KERNEL);

  	if (!ms) {

  		ti->error = "Cannot allocate mirror context";

  		return NULL;
  	}

  	spin_lock_init(&ms->lock);

  	bio_list_init(&ms->reads);
  	bio_list_init(&ms->writes);
  	bio_list_init(&ms->failures);
  	bio_list_init(&ms->holds);

  
  	ms->ti = ti;
  	ms->nr_mirrors = nr_mirrors;
  	ms->nr_regions = dm_sector_div_up(ti->len, region_size);
  	ms->in_sync = 0;

  	ms->log_failure = 0;

  	ms->leg_failure = 0;

  	atomic_set(&ms->suspend, 0);

  	atomic_set(&ms->default_mirror, DEFAULT_MIRROR);

  	ms->io_client = dm_io_client_create();

  	if (IS_ERR(ms->io_client)) {
  		ti->error = "Error creating dm_io client";
  		kfree(ms);
   		return NULL;
  	}

  	ms->rh = dm_region_hash_create(ms, dispatch_bios, wakeup_mirrord,
  				       wakeup_all_recovery_waiters,
  				       ms->ti->begin, MAX_RECOVERY,
  				       dl, region_size, ms->nr_regions);
  	if (IS_ERR(ms->rh)) {

  		ti->error = "Error creating dirty region hash";

  		dm_io_client_destroy(ms->io_client);

  		kfree(ms);
  		return NULL;
  	}
  
  	return ms;
  }
  
  static void free_context(struct mirror_set *ms, struct dm_target *ti,
  			 unsigned int m)
  {
  	while (m--)
  		dm_put_device(ti, ms->mirror[m].dev);

  	dm_io_client_destroy(ms->io_client);

  	dm_region_hash_destroy(ms->rh);

  	kfree(ms);
  }

  static int get_mirror(struct mirror_set *ms, struct dm_target *ti,
  		      unsigned int mirror, char **argv)
  {

  	unsigned long long offset;

  	char dummy;

  	int ret;

  	if (sscanf(argv[1], "%llu%c", &offset, &dummy) != 1 ||
  	    offset != (sector_t)offset) {

  		ti->error = "Invalid offset";

  		return -EINVAL;
  	}

  	ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
  			    &ms->mirror[mirror].dev);
  	if (ret) {

  		ti->error = "Device lookup failure";

  		return ret;

  	}

  	ms->mirror[mirror].ms = ms;

  	atomic_set(&(ms->mirror[mirror].error_count), 0);
  	ms->mirror[mirror].error_type = 0;

  	ms->mirror[mirror].offset = offset;
  
  	return 0;
  }

  /*
   * Create dirty log: log_type #log_params <log_params>
   */

  static struct dm_dirty_log *create_dirty_log(struct dm_target *ti,

  					     unsigned argc, char **argv,
  					     unsigned *args_used)

  {

  	unsigned param_count;

  	struct dm_dirty_log *dl;

  	char dummy;

  
  	if (argc < 2) {

  		ti->error = "Insufficient mirror log arguments";

  		return NULL;
  	}

  	if (sscanf(argv[1], "%u%c", &param_count, &dummy) != 1) {

  		ti->error = "Invalid mirror log argument count";

  		return NULL;
  	}
  
  	*args_used = 2 + param_count;
  
  	if (argc < *args_used) {

  		ti->error = "Insufficient mirror log arguments";

  		return NULL;
  	}

  	dl = dm_dirty_log_create(argv[0], ti, mirror_flush, param_count,
  				 argv + 2);

  	if (!dl) {

  		ti->error = "Error creating mirror dirty log";

  		return NULL;
  	}

  	return dl;
  }

  static int parse_features(struct mirror_set *ms, unsigned argc, char **argv,
  			  unsigned *args_used)
  {
  	unsigned num_features;
  	struct dm_target *ti = ms->ti;

  	char dummy;

  	int i;

  
  	*args_used = 0;
  
  	if (!argc)
  		return 0;

  	if (sscanf(argv[0], "%u%c", &num_features, &dummy) != 1) {

  		ti->error = "Invalid number of features";
  		return -EINVAL;
  	}
  
  	argc--;
  	argv++;
  	(*args_used)++;
  
  	if (num_features > argc) {
  		ti->error = "Not enough arguments to support feature count";
  		return -EINVAL;
  	}

  	for (i = 0; i < num_features; i++) {
  		if (!strcmp("handle_errors", argv[0]))
  			ms->features |= DM_RAID1_HANDLE_ERRORS;
  		else if (!strcmp("keep_log", argv[0]))
  			ms->features |= DM_RAID1_KEEP_LOG;
  		else {
  			ti->error = "Unrecognised feature requested";
  			return -EINVAL;
  		}
  
  		argc--;
  		argv++;
  		(*args_used)++;
  	}
  	if (!errors_handled(ms) && keep_log(ms)) {
  		ti->error = "keep_log feature requires the handle_errors feature";

  		return -EINVAL;
  	}

  	return 0;
  }

  /*
   * Construct a mirror mapping:
   *
   * log_type #log_params <log_params>
   * #mirrors [mirror_path offset]{2,}

   * [#features <features>]

   *
   * log_type is "core" or "disk"
   * #log_params is between 1 and 3

   *

   * If present, supported features are "handle_errors" and "keep_log".

   */

  static int mirror_ctr(struct dm_target *ti, unsigned int argc, char **argv)
  {
  	int r;
  	unsigned int nr_mirrors, m, args_used;
  	struct mirror_set *ms;

  	struct dm_dirty_log *dl;

  	char dummy;

  
  	dl = create_dirty_log(ti, argc, argv, &args_used);
  	if (!dl)
  		return -EINVAL;
  
  	argv += args_used;
  	argc -= args_used;

  	if (!argc || sscanf(argv[0], "%u%c", &nr_mirrors, &dummy) != 1 ||

  	    nr_mirrors < 2 || nr_mirrors > MAX_NR_MIRRORS) {

  		ti->error = "Invalid number of mirrors";

  		dm_dirty_log_destroy(dl);

  		return -EINVAL;
  	}
  
  	argv++, argc--;

  	if (argc < nr_mirrors * 2) {
  		ti->error = "Too few mirror arguments";

  		dm_dirty_log_destroy(dl);

  		return -EINVAL;
  	}
  
  	ms = alloc_context(nr_mirrors, dl->type->get_region_size(dl), ti, dl);
  	if (!ms) {

  		dm_dirty_log_destroy(dl);

  		return -ENOMEM;
  	}
  
  	/* Get the mirror parameter sets */
  	for (m = 0; m < nr_mirrors; m++) {
  		r = get_mirror(ms, ti, m, argv);
  		if (r) {
  			free_context(ms, ti, m);
  			return r;
  		}
  		argv += 2;
  		argc -= 2;
  	}
  
  	ti->private = ms;

  
  	r = dm_set_target_max_io_len(ti, dm_rh_get_region_size(ms->rh));
  	if (r)
  		goto err_free_context;

  	ti->num_flush_bios = 1;
  	ti->num_discard_bios = 1;

  	ti->per_io_data_size = sizeof(struct dm_raid1_bio_record);

  	ms->kmirrord_wq = alloc_workqueue("kmirrord", WQ_MEM_RECLAIM, 0);

  	if (!ms->kmirrord_wq) {
  		DMERR("couldn't start kmirrord");

  		r = -ENOMEM;
  		goto err_free_context;

  	}
  	INIT_WORK(&ms->kmirrord_work, do_mirror);

  	timer_setup(&ms->timer, delayed_wake_fn, 0);

  	ms->timer_pending = 0;

  	INIT_WORK(&ms->trigger_event, trigger_event);

  	r = parse_features(ms, argc, argv, &args_used);

  	if (r)
  		goto err_destroy_wq;

  
  	argv += args_used;
  	argc -= args_used;

  	/*
  	 * Any read-balancing addition depends on the
  	 * DM_RAID1_HANDLE_ERRORS flag being present.
  	 * This is because the decision to balance depends
  	 * on the sync state of a region.  If the above
  	 * flag is not present, we ignore errors; and
  	 * the sync state may be inaccurate.
  	 */

  	if (argc) {
  		ti->error = "Too many mirror arguments";

  		r = -EINVAL;
  		goto err_destroy_wq;

  	}

  	ms->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);

  	if (IS_ERR(ms->kcopyd_client)) {
  		r = PTR_ERR(ms->kcopyd_client);

  		goto err_destroy_wq;

  	}

  	wakeup_mirrord(ms);

  	return 0;

  
  err_destroy_wq:
  	destroy_workqueue(ms->kmirrord_wq);
  err_free_context:
  	free_context(ms, ti, ms->nr_mirrors);
  	return r;

  }
  
  static void mirror_dtr(struct dm_target *ti)
  {
  	struct mirror_set *ms = (struct mirror_set *) ti->private;

  	del_timer_sync(&ms->timer);

  	flush_workqueue(ms->kmirrord_wq);

  	flush_work(&ms->trigger_event);

  	dm_kcopyd_client_destroy(ms->kcopyd_client);

  	destroy_workqueue(ms->kmirrord_wq);

  	free_context(ms, ti, ms->nr_mirrors);
  }

  /*
   * Mirror mapping function
   */

  static int mirror_map(struct dm_target *ti, struct bio *bio)

  {

  	int r, rw = bio_data_dir(bio);

  	struct mirror *m;
  	struct mirror_set *ms = ti->private;

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  	struct dm_raid1_bio_record *bio_record =
  	  dm_per_bio_data(bio, sizeof(struct dm_raid1_bio_record));

  	bio_record->details.bi_disk = NULL;

  	if (rw == WRITE) {

  		/* Save region for mirror_end_io() handler */

  		bio_record->write_region = dm_rh_bio_to_region(ms->rh, bio);

  		queue_bio(ms, bio, rw);

  		return DM_MAPIO_SUBMITTED;

  	}

  	r = log->type->in_sync(log, dm_rh_bio_to_region(ms->rh, bio), 0);

  	if (r < 0 && r != -EWOULDBLOCK)

  		return DM_MAPIO_KILL;

  	/*

  	 * If region is not in-sync queue the bio.

  	 */

  	if (!r || (r == -EWOULDBLOCK)) {

  		if (bio->bi_opf & REQ_RAHEAD)

  			return DM_MAPIO_KILL;

  		queue_bio(ms, bio, rw);

  		return DM_MAPIO_SUBMITTED;

  	}

  	/*
  	 * The region is in-sync and we can perform reads directly.
  	 * Store enough information so we can retry if it fails.
  	 */

  	m = choose_mirror(ms, bio->bi_iter.bi_sector);

  	if (unlikely(!m))

  		return DM_MAPIO_KILL;

  	dm_bio_record(&bio_record->details, bio);

  	bio_record->m = m;

  
  	map_bio(m, bio);

  	return DM_MAPIO_REMAPPED;

  }

  static int mirror_end_io(struct dm_target *ti, struct bio *bio,
  		blk_status_t *error)

  {

  	int rw = bio_data_dir(bio);

  	struct mirror_set *ms = (struct mirror_set *) ti->private;

  	struct mirror *m = NULL;
  	struct dm_bio_details *bd = NULL;

  	struct dm_raid1_bio_record *bio_record =
  	  dm_per_bio_data(bio, sizeof(struct dm_raid1_bio_record));

  
  	/*
  	 * We need to dec pending if this was a write.
  	 */

  	if (rw == WRITE) {

  		if (!(bio->bi_opf & REQ_PREFLUSH) &&

  		    bio_op(bio) != REQ_OP_DISCARD)

  			dm_rh_dec(ms->rh, bio_record->write_region);

  		return DM_ENDIO_DONE;

  	}

  	if (*error == BLK_STS_NOTSUPP)

  		goto out;

  	if (bio->bi_opf & REQ_RAHEAD)

  		goto out;

  	if (unlikely(*error)) {

  		if (!bio_record->details.bi_disk) {

  			/*
  			 * There wasn't enough memory to record necessary
  			 * information for a retry or there was no other
  			 * mirror in-sync.
  			 */
  			DMERR_LIMIT("Mirror read failed.");

  			return DM_ENDIO_DONE;

  		}

  		m = bio_record->m;

  		DMERR("Mirror read failed from %s. Trying alternative device.",
  		      m->dev->name);

  		fail_mirror(m, DM_RAID1_READ_ERROR);
  
  		/*
  		 * A failed read is requeued for another attempt using an intact
  		 * mirror.
  		 */
  		if (default_ok(m) || mirror_available(ms, bio)) {

  			bd = &bio_record->details;

  
  			dm_bio_restore(bd, bio);

  			bio_record->details.bi_disk = NULL;

  			bio->bi_status = 0;

  			queue_bio(ms, bio, rw);

  			return DM_ENDIO_INCOMPLETE;

  		}
  		DMERR("All replicated volumes dead, failing I/O");
  	}

  out:

  	bio_record->details.bi_disk = NULL;

  	return DM_ENDIO_DONE;

  }

  static void mirror_presuspend(struct dm_target *ti)

  {
  	struct mirror_set *ms = (struct mirror_set *) ti->private;

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  	struct bio_list holds;
  	struct bio *bio;

  	atomic_set(&ms->suspend, 1);
  
  	/*

  	 * Process bios in the hold list to start recovery waiting
  	 * for bios in the hold list. After the process, no bio has
  	 * a chance to be added in the hold list because ms->suspend
  	 * is set.
  	 */
  	spin_lock_irq(&ms->lock);
  	holds = ms->holds;
  	bio_list_init(&ms->holds);
  	spin_unlock_irq(&ms->lock);
  
  	while ((bio = bio_list_pop(&holds)))
  		hold_bio(ms, bio);
  
  	/*

  	 * We must finish up all the work that we've
  	 * generated (i.e. recovery work).
  	 */

  	dm_rh_stop_recovery(ms->rh);

  	wait_event(_kmirrord_recovery_stopped,

  		   !dm_rh_recovery_in_flight(ms->rh));

  	if (log->type->presuspend && log->type->presuspend(log))
  		/* FIXME: need better error handling */
  		DMWARN("log presuspend failed");
  
  	/*
  	 * Now that recovery is complete/stopped and the
  	 * delayed bios are queued, we need to wait for
  	 * the worker thread to complete.  This way,
  	 * we know that all of our I/O has been pushed.
  	 */
  	flush_workqueue(ms->kmirrord_wq);
  }
  
  static void mirror_postsuspend(struct dm_target *ti)
  {
  	struct mirror_set *ms = ti->private;

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  	if (log->type->postsuspend && log->type->postsuspend(log))

  		/* FIXME: need better error handling */

  		DMWARN("log postsuspend failed");

  }
  
  static void mirror_resume(struct dm_target *ti)
  {

  	struct mirror_set *ms = ti->private;

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  
  	atomic_set(&ms->suspend, 0);

  	if (log->type->resume && log->type->resume(log))
  		/* FIXME: need better error handling */
  		DMWARN("log resume failed");

  	dm_rh_start_recovery(ms->rh);

  }

  /*
   * device_status_char
   * @m: mirror device/leg we want the status of
   *
   * We return one character representing the most severe error
   * we have encountered.
   *    A => Alive - No failures
   *    D => Dead - A write failure occurred leaving mirror out-of-sync
   *    S => Sync - A sychronization failure occurred, mirror out-of-sync
   *    R => Read - A read failure occurred, mirror data unaffected
   *
   * Returns: <char>
   */
  static char device_status_char(struct mirror *m)
  {
  	if (!atomic_read(&(m->error_count)))
  		return 'A';

  	return (test_bit(DM_RAID1_FLUSH_ERROR, &(m->error_type))) ? 'F' :
  		(test_bit(DM_RAID1_WRITE_ERROR, &(m->error_type))) ? 'D' :

  		(test_bit(DM_RAID1_SYNC_ERROR, &(m->error_type))) ? 'S' :
  		(test_bit(DM_RAID1_READ_ERROR, &(m->error_type))) ? 'R' : 'U';
  }

  static void mirror_status(struct dm_target *ti, status_type_t type,
  			  unsigned status_flags, char *result, unsigned maxlen)

  {

  	unsigned int m, sz = 0;

  	int num_feature_args = 0;

  	struct mirror_set *ms = (struct mirror_set *) ti->private;

  	struct dm_dirty_log *log = dm_rh_dirty_log(ms->rh);

  	char buffer[MAX_NR_MIRRORS + 1];

  	switch (type) {
  	case STATUSTYPE_INFO:
  		DMEMIT("%d ", ms->nr_mirrors);

  		for (m = 0; m < ms->nr_mirrors; m++) {

  			DMEMIT("%s ", ms->mirror[m].dev->name);

  			buffer[m] = device_status_char(&(ms->mirror[m]));
  		}
  		buffer[m] = '\0';

  		DMEMIT("%llu/%llu 1 %s ",

  		      (unsigned long long)log->type->get_sync_count(log),

  		      (unsigned long long)ms->nr_regions, buffer);

  		sz += log->type->status(log, type, result+sz, maxlen-sz);

  		break;
  
  	case STATUSTYPE_TABLE:

  		sz = log->type->status(log, type, result, maxlen);

  		DMEMIT("%d", ms->nr_mirrors);

  		for (m = 0; m < ms->nr_mirrors; m++)

  			DMEMIT(" %s %llu", ms->mirror[m].dev->name,

  			       (unsigned long long)ms->mirror[m].offset);

  		num_feature_args += !!errors_handled(ms);
  		num_feature_args += !!keep_log(ms);
  		if (num_feature_args) {
  			DMEMIT(" %d", num_feature_args);
  			if (errors_handled(ms))
  				DMEMIT(" handle_errors");
  			if (keep_log(ms))
  				DMEMIT(" keep_log");
  		}
  
  		break;

  	}

  }

  static int mirror_iterate_devices(struct dm_target *ti,
  				  iterate_devices_callout_fn fn, void *data)
  {
  	struct mirror_set *ms = ti->private;
  	int ret = 0;
  	unsigned i;
  
  	for (i = 0; !ret && i < ms->nr_mirrors; i++)
  		ret = fn(ti, ms->mirror[i].dev,

  			 ms->mirror[i].offset, ti->len, data);

  
  	return ret;
  }

  static struct target_type mirror_target = {
  	.name	 = "mirror",

  	.version = {1, 14, 0},

  	.module	 = THIS_MODULE,
  	.ctr	 = mirror_ctr,
  	.dtr	 = mirror_dtr,
  	.map	 = mirror_map,
  	.end_io	 = mirror_end_io,

  	.presuspend = mirror_presuspend,

  	.postsuspend = mirror_postsuspend,
  	.resume	 = mirror_resume,
  	.status	 = mirror_status,

  	.iterate_devices = mirror_iterate_devices,

  };
  
  static int __init dm_mirror_init(void)
  {
  	int r;

  	r = dm_register_target(&mirror_target);

  	if (r < 0) {

  		DMERR("Failed to register mirror target");

  		goto bad_target;
  	}
  
  	return 0;

  bad_target:

  	return r;
  }
  
  static void __exit dm_mirror_exit(void)
  {

  	dm_unregister_target(&mirror_target);

  }
  
  /* Module hooks */
  module_init(dm_mirror_init);
  module_exit(dm_mirror_exit);
  
  MODULE_DESCRIPTION(DM_NAME " mirror target");
  MODULE_AUTHOR("Joe Thornber");
  MODULE_LICENSE("GPL");