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dm-raid1.c

/*
 * Copyright (C) 2003 Sistina Software Limited.
 *
 * This file is released under the GPL.
 */

#include "dm.h"
#include "dm-bio-list.h"
#include "dm-io.h"
#include "dm-log.h"
#include "kcopyd.h"

#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/log2.h>

#define DM_MSG_PREFIX "raid1"
#define DM_IO_PAGES 64

#define DM_RAID1_HANDLE_ERRORS 0x01
#define errors_handled(p)     ((p)->features & DM_RAID1_HANDLE_ERRORS)

static DECLARE_WAIT_QUEUE_HEAD(_kmirrord_recovery_stopped);

/*-----------------------------------------------------------------
 * 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.  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.  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
 *   'bhs_delayed' fields of the regions.  This is used from irq
 *   context, so all other uses will have to suspend local irqs.
 *---------------------------------------------------------------*/
struct mirror_set;
struct region_hash {
      struct mirror_set *ms;
      uint32_t region_size;
      unsigned region_shift;

      /* holds persistent region state */
      struct dirty_log *log;

      /* hash table */
      rwlock_t hash_lock;
      mempool_t *region_pool;
      unsigned int mask;
      unsigned int nr_buckets;
      struct list_head *buckets;

      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;
};

enum {
      RH_CLEAN,
      RH_DIRTY,
      RH_NOSYNC,
      RH_RECOVERING
};

struct region {
      struct 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;
};


/*-----------------------------------------------------------------
 * Mirror set structures.
 *---------------------------------------------------------------*/
struct mirror {
      struct mirror_set *ms;
      atomic_t error_count;
      struct dm_dev *dev;
      sector_t offset;
};

struct mirror_set {
      struct dm_target *ti;
      struct list_head list;
      struct region_hash rh;
      struct kcopyd_client *kcopyd_client;
      uint64_t features;

      spinlock_t lock;  /* protects the next two lists */
      struct bio_list reads;
      struct bio_list writes;

      struct dm_io_client *io_client;

      /* recovery */
      region_t nr_regions;
      int in_sync;
      int log_failure;

      struct mirror *default_mirror;      /* Default mirror */

      struct workqueue_struct *kmirrord_wq;
      struct work_struct kmirrord_work;

      unsigned int nr_mirrors;
      struct mirror mirror[0];
};

/*
 * Conversion fns
 */
static inline region_t bio_to_region(struct region_hash *rh, struct bio *bio)
{
      return (bio->bi_sector - rh->ms->ti->begin) >> rh->region_shift;
}

static inline sector_t region_to_sector(struct region_hash *rh, region_t region)
{
      return region << rh->region_shift;
}

static void wake(struct mirror_set *ms)
{
      queue_work(ms->kmirrord_wq, &ms->kmirrord_work);
}

/* FIXME move this */
static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw);

#define MIN_REGIONS 64
#define MAX_RECOVERY 1
static int rh_init(struct region_hash *rh, struct mirror_set *ms,
               struct dirty_log *log, uint32_t region_size,
               region_t nr_regions)
{
      unsigned int 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->ms = ms;
      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->buckets = vmalloc(nr_buckets * sizeof(*rh->buckets));
      if (!rh->buckets) {
            DMERR("unable to allocate region hash memory");
            return -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->region_pool = mempool_create_kmalloc_pool(MIN_REGIONS,
                                          sizeof(struct region));
      if (!rh->region_pool) {
            vfree(rh->buckets);
            rh->buckets = NULL;
            return -ENOMEM;
      }

      return 0;
}

static void rh_exit(struct region_hash *rh)
{
      unsigned int h;
      struct 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_destroy_dirty_log(rh->log);
      if (rh->region_pool)
            mempool_destroy(rh->region_pool);
      vfree(rh->buckets);
}

#define RH_HASH_MULT 2654435387U

static inline unsigned int rh_hash(struct region_hash *rh, region_t region)
{
      return (unsigned int) ((region * RH_HASH_MULT) >> 12) & rh->mask;
}

static struct region *__rh_lookup(struct region_hash *rh, region_t region)
{
      struct region *reg;

      list_for_each_entry (reg, rh->buckets + rh_hash(rh, region), hash_list)
            if (reg->key == region)
                  return reg;

      return NULL;
}

static void __rh_insert(struct region_hash *rh, struct region *reg)
{
      unsigned int h = rh_hash(rh, reg->key);
      list_add(&reg->hash_list, rh->buckets + h);
}

static struct region *__rh_alloc(struct region_hash *rh, region_t region)
{
      struct region *reg, *nreg;

      read_unlock(&rh->hash_lock);
      nreg = mempool_alloc(rh->region_pool, GFP_ATOMIC);
      if (unlikely(!nreg))
            nreg = kmalloc(sizeof(struct region), GFP_NOIO);
      nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
            RH_CLEAN : 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 == 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);
      read_lock(&rh->hash_lock);

      return reg;
}

static inline struct region *__rh_find(struct region_hash *rh, region_t region)
{
      struct region *reg;

      reg = __rh_lookup(rh, region);
      if (!reg)
            reg = __rh_alloc(rh, region);

      return reg;
}

static int rh_state(struct region_hash *rh, region_t region, int may_block)
{
      int r;
      struct 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 RH_NOSYNC
       */
      return r == 1 ? RH_CLEAN : RH_NOSYNC;
}

static inline int rh_in_sync(struct region_hash *rh,
                       region_t region, int may_block)
{
      int state = rh_state(rh, region, may_block);
      return state == RH_CLEAN || state == RH_DIRTY;
}

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

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

static void complete_resync_work(struct region *reg, int success)
{
      struct region_hash *rh = reg->rh;

      rh->log->type->set_region_sync(rh->log, reg->key, success);
      dispatch_bios(rh->ms, &reg->delayed_bios);
      if (atomic_dec_and_test(&rh->recovery_in_flight))
            wake_up_all(&_kmirrord_recovery_stopped);
      up(&rh->recovery_count);
}

static void rh_update_states(struct region_hash *rh)
{
      struct 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(&rh->clean_regions, &clean);
            INIT_LIST_HEAD(&rh->clean_regions);

            list_for_each_entry(reg, &clean, list)
                  list_del(&reg->hash_list);
      }

      if (!list_empty(&rh->recovered_regions)) {
            list_splice(&rh->recovered_regions, &recovered);
            INIT_LIST_HEAD(&rh->recovered_regions);

            list_for_each_entry (reg, &recovered, list)
                  list_del(&reg->hash_list);
      }

      if (!list_empty(&rh->failed_recovered_regions)) {
            list_splice(&rh->failed_recovered_regions, &failed_recovered);
            INIT_LIST_HEAD(&rh->failed_recovered_regions);

            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(rh->ms) ? 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);
}

static void rh_inc(struct region_hash *rh, region_t region)
{
      struct 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 == RH_CLEAN) {
            reg->state = 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);
}

static void rh_inc_pending(struct region_hash *rh, struct bio_list *bios)
{
      struct bio *bio;

      for (bio = bios->head; bio; bio = bio->bi_next)
            rh_inc(rh, bio_to_region(rh, bio));
}

static void rh_dec(struct region_hash *rh, region_t region)
{
      unsigned long flags;
      struct 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 RH_NOSYNC, the region should be kept off
             * from clean list.
             * The hash entry for RH_NOSYNC will remain in memory
             * until the region is recovered or the map is reloaded.
             */

            /* do nothing for RH_NOSYNC */
            if (reg->state == RH_RECOVERING) {
                  list_add_tail(&reg->list, &rh->quiesced_regions);
            } else if (reg->state == RH_DIRTY) {
                  reg->state = RH_CLEAN;
                  list_add(&reg->list, &rh->clean_regions);
            }
            should_wake = 1;
      }
      spin_unlock_irqrestore(&rh->region_lock, flags);

      if (should_wake)
            wake(rh->ms);
}

/*
 * Starts quiescing a region in preparation for recovery.
 */
static int __rh_recovery_prepare(struct region_hash *rh)
{
      int r;
      struct region *reg;
      region_t region;

      /*
       * 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 = 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;
}

static void rh_recovery_prepare(struct region_hash *rh)
{
      /* Extra reference to avoid race with 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))
            wake_up_all(&_kmirrord_recovery_stopped);
}

/*
 * Returns any quiesced regions.
 */
static struct region *rh_recovery_start(struct region_hash *rh)
{
      struct region *reg = NULL;

      spin_lock_irq(&rh->region_lock);
      if (!list_empty(&rh->quiesced_regions)) {
            reg = list_entry(rh->quiesced_regions.next,
                         struct region, list);
            list_del_init(&reg->list);    /* remove from the quiesced list */
      }
      spin_unlock_irq(&rh->region_lock);

      return reg;
}

static void rh_recovery_end(struct region *reg, int success)
{
      struct region_hash *rh = reg->rh;

      spin_lock_irq(&rh->region_lock);
      if (success)
            list_add(&reg->list, &reg->rh->recovered_regions);
      else {
            reg->state = RH_NOSYNC;
            list_add(&reg->list, &reg->rh->failed_recovered_regions);
      }
      spin_unlock_irq(&rh->region_lock);

      wake(rh->ms);
}

static int rh_flush(struct region_hash *rh)
{
      return rh->log->type->flush(rh->log);
}

static void rh_delay(struct region_hash *rh, struct bio *bio)
{
      struct region *reg;

      read_lock(&rh->hash_lock);
      reg = __rh_find(rh, bio_to_region(rh, bio));
      bio_list_add(&reg->delayed_bios, bio);
      read_unlock(&rh->hash_lock);
}

static void rh_stop_recovery(struct region_hash *rh)
{
      int i;

      /* wait for any recovering regions */
      for (i = 0; i < MAX_RECOVERY; i++)
            down(&rh->recovery_count);
}

static void rh_start_recovery(struct region_hash *rh)
{
      int i;

      for (i = 0; i < MAX_RECOVERY; i++)
            up(&rh->recovery_count);

      wake(rh->ms);
}

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

/*
 * This is yucky.  We squirrel the mirror_set struct away inside
 * bi_next for write buffers.  This is safe since the bh
 * doesn't get submitted to the lower levels of block layer.
 */
static struct mirror_set *bio_get_ms(struct bio *bio)
{
      return (struct mirror_set *) bio->bi_next;
}

static void bio_set_ms(struct bio *bio, struct mirror_set *ms)
{
      bio->bi_next = (struct bio *) ms;
}

/*-----------------------------------------------------------------
 * 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 int write_err,
                        void *context)
{
      struct region *reg = (struct region *) context;

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

      if (write_err)
            DMERR_LIMIT("Write error during recovery (error = 0x%x)",
                      write_err);

      rh_recovery_end(reg, !(read_err || write_err));
}

static int recover(struct mirror_set *ms, struct region *reg)
{
      int r;
      unsigned int i;
      struct io_region from, to[KCOPYD_MAX_REGIONS], *dest;
      struct mirror *m;
      unsigned long flags = 0;

      /* fill in the source */
      m = ms->default_mirror;
      from.bdev = m->dev->bdev;
      from.sector = m->offset + region_to_sector(reg->rh, reg->key);
      if (reg->key == (ms->nr_regions - 1)) {
            /*
             * The final region may be smaller than
             * region_size.
             */
            from.count = ms->ti->len & (reg->rh->region_size - 1);
            if (!from.count)
                  from.count = reg->rh->region_size;
      } else
            from.count = reg->rh->region_size;

      /* fill in the destinations */
      for (i = 0, dest = to; i < ms->nr_mirrors; i++) {
            if (&ms->mirror[i] == ms->default_mirror)
                  continue;

            m = ms->mirror + i;
            dest->bdev = m->dev->bdev;
            dest->sector = m->offset + region_to_sector(reg->rh, reg->key);
            dest->count = from.count;
            dest++;
      }

      /* hand to kcopyd */
      set_bit(KCOPYD_IGNORE_ERROR, &flags);
      r = kcopyd_copy(ms->kcopyd_client, &from, ms->nr_mirrors - 1, to, flags,
                  recovery_complete, reg);

      return r;
}

static void do_recovery(struct mirror_set *ms)
{
      int r;
      struct region *reg;
      struct dirty_log *log = ms->rh.log;

      /*
       * Start quiescing some regions.
       */
      rh_recovery_prepare(&ms->rh);

      /*
       * Copy any already quiesced regions.
       */
      while ((reg = rh_recovery_start(&ms->rh))) {
            r = recover(ms, reg);
            if (r)
                  rh_recovery_end(reg, 0);
      }

      /*
       * 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;
      }
}

/*-----------------------------------------------------------------
 * Reads
 *---------------------------------------------------------------*/
static struct mirror *choose_mirror(struct mirror_set *ms, sector_t sector)
{
      /* FIXME: add read balancing */
      return ms->default_mirror;
}

/*
 * remap a buffer to a particular mirror.
 */
static void map_bio(struct mirror_set *ms, struct mirror *m, struct bio *bio)
{
      bio->bi_bdev = m->dev->bdev;
      bio->bi_sector = m->offset + (bio->bi_sector - ms->ti->begin);
}

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 = bio_to_region(&ms->rh, bio);

            /*
             * We can only read balance if the region is in sync.
             */
            if (rh_in_sync(&ms->rh, region, 1))
                  m = choose_mirror(ms, bio->bi_sector);
            else
                  m = ms->default_mirror;

            map_bio(ms, m, bio);
            generic_make_request(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 int i;
      int uptodate = 1;
      struct bio *bio = (struct bio *) context;
      struct mirror_set *ms;

      ms = bio_get_ms(bio);
      bio_set_ms(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 (error) {
            /*
             * only error the io if all mirrors failed.
             * FIXME: bogus
             */
            uptodate = 0;
            for (i = 0; i < ms->nr_mirrors; i++)
                  if (!test_bit(i, &error)) {
                        uptodate = 1;
                        break;
                  }
      }
      bio_endio(bio, 0);
}

static void do_write(struct mirror_set *ms, struct bio *bio)
{
      unsigned int i;
      struct io_region io[KCOPYD_MAX_REGIONS+1];
      struct mirror *m;
      struct dm_io_request io_req = {
            .bi_rw = WRITE,
            .mem.type = DM_IO_BVEC,
            .mem.ptr.bvec = bio->bi_io_vec + bio->bi_idx,
            .notify.fn = write_callback,
            .notify.context = bio,
            .client = ms->io_client,
      };

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

            io[i].bdev = m->dev->bdev;
            io[i].sector = m->offset + (bio->bi_sector - ms->ti->begin);
            io[i].count = bio->bi_size >> 9;
      }

      bio_set_ms(bio, ms);

      (void) 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;

      if (!writes->head)
            return;

      /*
       * Classify each write.
       */
      bio_list_init(&sync);
      bio_list_init(&nosync);
      bio_list_init(&recover);

      while ((bio = bio_list_pop(writes))) {
            state = rh_state(&ms->rh, bio_to_region(&ms->rh, bio), 1);
            switch (state) {
            case RH_CLEAN:
            case RH_DIRTY:
                  this_list = &sync;
                  break;

            case RH_NOSYNC:
                  this_list = &nosync;
                  break;

            case RH_RECOVERING:
                  this_list = &recover;
                  break;
            }

            bio_list_add(this_list, bio);
      }

      /*
       * Increment the pending counts for any regions that will
       * be written to (writes to recover regions are going to
       * be delayed).
       */
      rh_inc_pending(&ms->rh, &sync);
      rh_inc_pending(&ms->rh, &nosync);
      ms->log_failure = rh_flush(&ms->rh) ? 1 : 0;

      /*
       * Dispatch io.
       */
      if (unlikely(ms->log_failure))
            while ((bio = bio_list_pop(&sync)))
                  bio_endio(bio, -EIO);
      else while ((bio = bio_list_pop(&sync)))
            do_write(ms, bio);

      while ((bio = bio_list_pop(&recover)))
            rh_delay(&ms->rh, bio);

      while ((bio = bio_list_pop(&nosync))) {
            map_bio(ms, ms->default_mirror, bio);
            generic_make_request(bio);
      }
}

/*-----------------------------------------------------------------
 * 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;

      spin_lock(&ms->lock);
      reads = ms->reads;
      writes = ms->writes;
      bio_list_init(&ms->reads);
      bio_list_init(&ms->writes);
      spin_unlock(&ms->lock);

      rh_update_states(&ms->rh);
      do_recovery(ms);
      do_reads(ms, &reads);
      do_writes(ms, &writes);
}

/*-----------------------------------------------------------------
 * Target functions
 *---------------------------------------------------------------*/
static struct mirror_set *alloc_context(unsigned int nr_mirrors,
                              uint32_t region_size,
                              struct dm_target *ti,
                              struct dirty_log *dl)
{
      size_t len;
      struct mirror_set *ms = NULL;

      if (array_too_big(sizeof(*ms), sizeof(ms->mirror[0]), nr_mirrors))
            return NULL;

      len = sizeof(*ms) + (sizeof(ms->mirror[0]) * nr_mirrors);

      ms = kzalloc(len, GFP_KERNEL);
      if (!ms) {
            ti->error = "Cannot allocate mirror context";
            return NULL;
      }

      spin_lock_init(&ms->lock);

      ms->ti = ti;
      ms->nr_mirrors = nr_mirrors;
      ms->nr_regions = dm_sector_div_up(ti->len, region_size);
      ms->in_sync = 0;
      ms->default_mirror = &ms->mirror[DEFAULT_MIRROR];

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

      if (rh_init(&ms->rh, ms, dl, region_size, ms->nr_regions)) {
            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);
      rh_exit(&ms->rh);
      kfree(ms);
}

static inline int _check_region_size(struct dm_target *ti, uint32_t size)
{
      return !(size % (PAGE_SIZE >> 9) || !is_power_of_2(size) ||
             size > ti->len);
}

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

      if (sscanf(argv[1], "%llu", &offset) != 1) {
            ti->error = "Invalid offset";
            return -EINVAL;
      }

      if (dm_get_device(ti, argv[0], offset, ti->len,
                    dm_table_get_mode(ti->table),
                    &ms->mirror[mirror].dev)) {
            ti->error = "Device lookup failure";
            return -ENXIO;
      }

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

      return 0;
}

/*
 * Create dirty log: log_type #log_params <log_params>
 */
static struct dirty_log *create_dirty_log(struct dm_target *ti,
                                unsigned int argc, char **argv,
                                unsigned int *args_used)
{
      unsigned int param_count;
      struct dirty_log *dl;

      if (argc < 2) {
            ti->error = "Insufficient mirror log arguments";
            return NULL;
      }

      if (sscanf(argv[1], "%u", &param_count) != 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_create_dirty_log(argv[0], ti, param_count, argv + 2);
      if (!dl) {
            ti->error = "Error creating mirror dirty log";
            return NULL;
      }

      if (!_check_region_size(ti, dl->type->get_region_size(dl))) {
            ti->error = "Invalid region size";
            dm_destroy_dirty_log(dl);
            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;

      *args_used = 0;

      if (!argc)
            return 0;

      if (sscanf(argv[0], "%u", &num_features) != 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;
      }

      if (!strcmp("handle_errors", argv[0]))
            ms->features |= DM_RAID1_HANDLE_ERRORS;
      else {
            ti->error = "Unrecognised feature requested";
            return -EINVAL;
      }

      (*args_used)++;

      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, features must be "handle_errors".
 */
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 dirty_log *dl;

      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", &nr_mirrors) != 1 ||
          nr_mirrors < 2 || nr_mirrors > KCOPYD_MAX_REGIONS + 1) {
            ti->error = "Invalid number of mirrors";
            dm_destroy_dirty_log(dl);
            return -EINVAL;
      }

      argv++, argc--;

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

      ms = alloc_context(nr_mirrors, dl->type->get_region_size(dl), ti, dl);
      if (!ms) {
            dm_destroy_dirty_log(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;
      ti->split_io = ms->rh.region_size;

      ms->kmirrord_wq = create_singlethread_workqueue("kmirrord");
      if (!ms->kmirrord_wq) {
            DMERR("couldn't start kmirrord");
            r = -ENOMEM;
            goto err_free_context;
      }
      INIT_WORK(&ms->kmirrord_work, do_mirror);

      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;
      }

      r = kcopyd_client_create(DM_IO_PAGES, &ms->kcopyd_client);
      if (r)
            goto err_destroy_wq;

      wake(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;

      flush_workqueue(ms->kmirrord_wq);
      kcopyd_client_destroy(ms->kcopyd_client);
      destroy_workqueue(ms->kmirrord_wq);
      free_context(ms, ti, ms->nr_mirrors);
}

static void queue_bio(struct mirror_set *ms, struct bio *bio, int rw)
{
      int should_wake = 0;
      struct bio_list *bl;

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

      if (should_wake)
            wake(ms);
}

/*
 * Mirror mapping function
 */
static int mirror_map(struct dm_target *ti, struct bio *bio,
                  union map_info *map_context)
{
      int r, rw = bio_rw(bio);
      struct mirror *m;
      struct mirror_set *ms = ti->private;

      map_context->ll = bio_to_region(&ms->rh, bio);

      if (rw == WRITE) {
            queue_bio(ms, bio, rw);
            return DM_MAPIO_SUBMITTED;
      }

      r = ms->rh.log->type->in_sync(ms->rh.log,
                              bio_to_region(&ms->rh, bio), 0);
      if (r < 0 && r != -EWOULDBLOCK)
            return r;

      if (r == -EWOULDBLOCK)  /* FIXME: ugly */
            r = DM_MAPIO_SUBMITTED;

      /*
       * We don't want to fast track a recovery just for a read
       * ahead.  So we just let it silently fail.
       * FIXME: get rid of this.
       */
      if (!r && rw == READA)
            return -EIO;

      if (!r) {
            /* Pass this io over to the daemon */
            queue_bio(ms, bio, rw);
            return DM_MAPIO_SUBMITTED;
      }

      m = choose_mirror(ms, bio->bi_sector);
      if (!m)
            return -EIO;

      map_bio(ms, m, bio);
      return DM_MAPIO_REMAPPED;
}

static int mirror_end_io(struct dm_target *ti, struct bio *bio,
                   int error, union map_info *map_context)
{
      int rw = bio_rw(bio);
      struct mirror_set *ms = (struct mirror_set *) ti->private;
      region_t region = map_context->ll;

      /*
       * We need to dec pending if this was a write.
       */
      if (rw == WRITE)
            rh_dec(&ms->rh, region);

      return 0;
}

static void mirror_postsuspend(struct dm_target *ti)
{
      struct mirror_set *ms = (struct mirror_set *) ti->private;
      struct dirty_log *log = ms->rh.log;

      rh_stop_recovery(&ms->rh);

      /* Wait for all I/O we generated to complete */
      wait_event(_kmirrord_recovery_stopped,
               !atomic_read(&ms->rh.recovery_in_flight));

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

static void mirror_resume(struct dm_target *ti)
{
      struct mirror_set *ms = (struct mirror_set *) ti->private;
      struct dirty_log *log = ms->rh.log;
      if (log->type->resume && log->type->resume(log))
            /* FIXME: need better error handling */
            DMWARN("log resume failed");
      rh_start_recovery(&ms->rh);
}

static int mirror_status(struct dm_target *ti, status_type_t type,
                   char *result, unsigned int maxlen)
{
      unsigned int m, sz = 0;
      struct mirror_set *ms = (struct mirror_set *) ti->private;

      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);

            DMEMIT("%llu/%llu 0 ",
                  (unsigned long long)ms->rh.log->type->
                        get_sync_count(ms->rh.log),
                  (unsigned long long)ms->nr_regions);

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

            break;

      case STATUSTYPE_TABLE:
            sz = ms->rh.log->type->status(ms->rh.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);

            if (ms->features & DM_RAID1_HANDLE_ERRORS)
                  DMEMIT(" 1 handle_errors");
      }

      return 0;
}

static struct target_type mirror_target = {
      .name  = "mirror",
      .version = {1, 0, 3},
      .module      = THIS_MODULE,
      .ctr   = mirror_ctr,
      .dtr   = mirror_dtr,
      .map   = mirror_map,
      .end_io      = mirror_end_io,
      .postsuspend = mirror_postsuspend,
      .resume      = mirror_resume,
      .status      = mirror_status,
};

static int __init dm_mirror_init(void)
{
      int r;

      r = dm_dirty_log_init();
      if (r)
            return r;

      r = dm_register_target(&mirror_target);
      if (r < 0) {
            DMERR("Failed to register mirror target");
            dm_dirty_log_exit();
      }

      return r;
}

static void __exit dm_mirror_exit(void)
{
      int r;

      r = dm_unregister_target(&mirror_target);
      if (r < 0)
            DMERR("unregister failed %d", r);

      dm_dirty_log_exit();
}

/* 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");

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