Logo Search packages:      
Sourcecode: linux-fsl-imx51 version File versions  Download package

raid5.c

/*
 * raid5.c : Multiple Devices driver for Linux
 *       Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *       Copyright (C) 1999, 2000 Ingo Molnar
 *       Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-4/5/6 management functions.
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * BITMAP UNPLUGGING:
 *
 * The sequencing for updating the bitmap reliably is a little
 * subtle (and I got it wrong the first time) so it deserves some
 * explanation.
 *
 * We group bitmap updates into batches.  Each batch has a number.
 * We may write out several batches at once, but that isn't very important.
 * conf->bm_write is the number of the last batch successfully written.
 * conf->bm_flush is the number of the last batch that was closed to
 *    new additions.
 * When we discover that we will need to write to any block in a stripe
 * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
 * the number of the batch it will be in. This is bm_flush+1.
 * When we are ready to do a write, if that batch hasn't been written yet,
 *   we plug the array and queue the stripe for later.
 * When an unplug happens, we increment bm_flush, thus closing the current
 *   batch.
 * When we notice that bm_flush > bm_write, we write out all pending updates
 * to the bitmap, and advance bm_write to where bm_flush was.
 * This may occasionally write a bit out twice, but is sure never to
 * miss any bits.
 */

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/raid/pq.h>
#include <linux/async_tx.h>
#include <linux/seq_file.h>
#include "md.h"
#include "raid5.h"
#include "bitmap.h"

/*
 * Stripe cache
 */

#define NR_STRIPES            256
#define STRIPE_SIZE           PAGE_SIZE
#define STRIPE_SHIFT          (PAGE_SHIFT - 9)
#define STRIPE_SECTORS        (STRIPE_SIZE>>9)
#define     IO_THRESHOLD            1
#define BYPASS_THRESHOLD      1
#define NR_HASH               (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK       (NR_HASH - 1)

#define stripe_hash(conf, sect)     (&((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK]))

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This macro is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
/*
 * The following can be used to debug the driver
 */
#define RAID5_PARANOIA  1
#if RAID5_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#ifdef DEBUG
#define inline
#define __inline__
#endif

#define printk_rl(args...) ((void) (printk_ratelimit() && printk(args)))

/*
 * We maintain a biased count of active stripes in the bottom 16 bits of
 * bi_phys_segments, and a count of processed stripes in the upper 16 bits
 */
static inline int raid5_bi_phys_segments(struct bio *bio)
{
      return bio->bi_phys_segments & 0xffff;
}

static inline int raid5_bi_hw_segments(struct bio *bio)
{
      return (bio->bi_phys_segments >> 16) & 0xffff;
}

static inline int raid5_dec_bi_phys_segments(struct bio *bio)
{
      --bio->bi_phys_segments;
      return raid5_bi_phys_segments(bio);
}

static inline int raid5_dec_bi_hw_segments(struct bio *bio)
{
      unsigned short val = raid5_bi_hw_segments(bio);

      --val;
      bio->bi_phys_segments = (val << 16) | raid5_bi_phys_segments(bio);
      return val;
}

static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
{
      bio->bi_phys_segments = raid5_bi_phys_segments(bio) || (cnt << 16);
}

/* Find first data disk in a raid6 stripe */
static inline int raid6_d0(struct stripe_head *sh)
{
      if (sh->ddf_layout)
            /* ddf always start from first device */
            return 0;
      /* md starts just after Q block */
      if (sh->qd_idx == sh->disks - 1)
            return 0;
      else
            return sh->qd_idx + 1;
}
static inline int raid6_next_disk(int disk, int raid_disks)
{
      disk++;
      return (disk < raid_disks) ? disk : 0;
}

/* When walking through the disks in a raid5, starting at raid6_d0,
 * We need to map each disk to a 'slot', where the data disks are slot
 * 0 .. raid_disks-3, the parity disk is raid_disks-2 and the Q disk
 * is raid_disks-1.  This help does that mapping.
 */
static int raid6_idx_to_slot(int idx, struct stripe_head *sh,
                       int *count, int syndrome_disks)
{
      int slot;

      if (idx == sh->pd_idx)
            return syndrome_disks;
      if (idx == sh->qd_idx)
            return syndrome_disks + 1;
      slot = (*count)++;
      return slot;
}

static void return_io(struct bio *return_bi)
{
      struct bio *bi = return_bi;
      while (bi) {

            return_bi = bi->bi_next;
            bi->bi_next = NULL;
            bi->bi_size = 0;
            bio_endio(bi, 0);
            bi = return_bi;
      }
}

static void print_raid5_conf (raid5_conf_t *conf);

static int stripe_operations_active(struct stripe_head *sh)
{
      return sh->check_state || sh->reconstruct_state ||
             test_bit(STRIPE_BIOFILL_RUN, &sh->state) ||
             test_bit(STRIPE_COMPUTE_RUN, &sh->state);
}

static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
{
      if (atomic_dec_and_test(&sh->count)) {
            BUG_ON(!list_empty(&sh->lru));
            BUG_ON(atomic_read(&conf->active_stripes)==0);
            if (test_bit(STRIPE_HANDLE, &sh->state)) {
                  if (test_bit(STRIPE_DELAYED, &sh->state)) {
                        list_add_tail(&sh->lru, &conf->delayed_list);
                        blk_plug_device(conf->mddev->queue);
                  } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                           sh->bm_seq - conf->seq_write > 0) {
                        list_add_tail(&sh->lru, &conf->bitmap_list);
                        blk_plug_device(conf->mddev->queue);
                  } else {
                        clear_bit(STRIPE_BIT_DELAY, &sh->state);
                        list_add_tail(&sh->lru, &conf->handle_list);
                  }
                  md_wakeup_thread(conf->mddev->thread);
            } else {
                  BUG_ON(stripe_operations_active(sh));
                  if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                        atomic_dec(&conf->preread_active_stripes);
                        if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
                              md_wakeup_thread(conf->mddev->thread);
                  }
                  atomic_dec(&conf->active_stripes);
                  if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
                        list_add_tail(&sh->lru, &conf->inactive_list);
                        wake_up(&conf->wait_for_stripe);
                        if (conf->retry_read_aligned)
                              md_wakeup_thread(conf->mddev->thread);
                  }
            }
      }
}

static void release_stripe(struct stripe_head *sh)
{
      raid5_conf_t *conf = sh->raid_conf;
      unsigned long flags;

      spin_lock_irqsave(&conf->device_lock, flags);
      __release_stripe(conf, sh);
      spin_unlock_irqrestore(&conf->device_lock, flags);
}

static inline void remove_hash(struct stripe_head *sh)
{
      pr_debug("remove_hash(), stripe %llu\n",
            (unsigned long long)sh->sector);

      hlist_del_init(&sh->hash);
}

static inline void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
{
      struct hlist_head *hp = stripe_hash(conf, sh->sector);

      pr_debug("insert_hash(), stripe %llu\n",
            (unsigned long long)sh->sector);

      CHECK_DEVLOCK();
      hlist_add_head(&sh->hash, hp);
}


/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(raid5_conf_t *conf)
{
      struct stripe_head *sh = NULL;
      struct list_head *first;

      CHECK_DEVLOCK();
      if (list_empty(&conf->inactive_list))
            goto out;
      first = conf->inactive_list.next;
      sh = list_entry(first, struct stripe_head, lru);
      list_del_init(first);
      remove_hash(sh);
      atomic_inc(&conf->active_stripes);
out:
      return sh;
}

static void shrink_buffers(struct stripe_head *sh, int num)
{
      struct page *p;
      int i;

      for (i=0; i<num ; i++) {
            p = sh->dev[i].page;
            if (!p)
                  continue;
            sh->dev[i].page = NULL;
            put_page(p);
      }
}

static int grow_buffers(struct stripe_head *sh, int num)
{
      int i;

      for (i=0; i<num; i++) {
            struct page *page;

            if (!(page = alloc_page(GFP_KERNEL))) {
                  return 1;
            }
            sh->dev[i].page = page;
      }
      return 0;
}

static void raid5_build_block(struct stripe_head *sh, int i, int previous);
static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                      struct stripe_head *sh);

static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
{
      raid5_conf_t *conf = sh->raid_conf;
      int i;

      BUG_ON(atomic_read(&sh->count) != 0);
      BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
      BUG_ON(stripe_operations_active(sh));

      CHECK_DEVLOCK();
      pr_debug("init_stripe called, stripe %llu\n",
            (unsigned long long)sh->sector);

      remove_hash(sh);

      sh->generation = conf->generation - previous;
      sh->disks = previous ? conf->previous_raid_disks : conf->raid_disks;
      sh->sector = sector;
      stripe_set_idx(sector, conf, previous, sh);
      sh->state = 0;


      for (i = sh->disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];

            if (dev->toread || dev->read || dev->towrite || dev->written ||
                test_bit(R5_LOCKED, &dev->flags)) {
                  printk(KERN_ERR "sector=%llx i=%d %p %p %p %p %d\n",
                         (unsigned long long)sh->sector, i, dev->toread,
                         dev->read, dev->towrite, dev->written,
                         test_bit(R5_LOCKED, &dev->flags));
                  BUG();
            }
            dev->flags = 0;
            raid5_build_block(sh, i, previous);
      }
      insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid5_conf_t *conf, sector_t sector,
                               short generation)
{
      struct stripe_head *sh;
      struct hlist_node *hn;

      CHECK_DEVLOCK();
      pr_debug("__find_stripe, sector %llu\n", (unsigned long long)sector);
      hlist_for_each_entry(sh, hn, stripe_hash(conf, sector), hash)
            if (sh->sector == sector && sh->generation == generation)
                  return sh;
      pr_debug("__stripe %llu not in cache\n", (unsigned long long)sector);
      return NULL;
}

static void unplug_slaves(mddev_t *mddev);
static void raid5_unplug_device(struct request_queue *q);

static struct stripe_head *
get_active_stripe(raid5_conf_t *conf, sector_t sector,
              int previous, int noblock, int noquiesce)
{
      struct stripe_head *sh;

      pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);

      spin_lock_irq(&conf->device_lock);

      do {
            wait_event_lock_irq(conf->wait_for_stripe,
                            conf->quiesce == 0 || noquiesce,
                            conf->device_lock, /* nothing */);
            sh = __find_stripe(conf, sector, conf->generation - previous);
            if (!sh) {
                  if (!conf->inactive_blocked)
                        sh = get_free_stripe(conf);
                  if (noblock && sh == NULL)
                        break;
                  if (!sh) {
                        conf->inactive_blocked = 1;
                        wait_event_lock_irq(conf->wait_for_stripe,
                                        !list_empty(&conf->inactive_list) &&
                                        (atomic_read(&conf->active_stripes)
                                         < (conf->max_nr_stripes *3/4)
                                         || !conf->inactive_blocked),
                                        conf->device_lock,
                                        raid5_unplug_device(conf->mddev->queue)
                              );
                        conf->inactive_blocked = 0;
                  } else
                        init_stripe(sh, sector, previous);
            } else {
                  if (atomic_read(&sh->count)) {
                        BUG_ON(!list_empty(&sh->lru)
                            && !test_bit(STRIPE_EXPANDING, &sh->state));
                  } else {
                        if (!test_bit(STRIPE_HANDLE, &sh->state))
                              atomic_inc(&conf->active_stripes);
                        if (list_empty(&sh->lru) &&
                            !test_bit(STRIPE_EXPANDING, &sh->state))
                              BUG();
                        list_del_init(&sh->lru);
                  }
            }
      } while (sh == NULL);

      if (sh)
            atomic_inc(&sh->count);

      spin_unlock_irq(&conf->device_lock);
      return sh;
}

static void
raid5_end_read_request(struct bio *bi, int error);
static void
raid5_end_write_request(struct bio *bi, int error);

static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
{
      raid5_conf_t *conf = sh->raid_conf;
      int i, disks = sh->disks;

      might_sleep();

      for (i = disks; i--; ) {
            int rw;
            struct bio *bi;
            mdk_rdev_t *rdev;
            if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
                  rw = WRITE;
            else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                  rw = READ;
            else
                  continue;

            bi = &sh->dev[i].req;

            bi->bi_rw = rw;
            if (rw == WRITE)
                  bi->bi_end_io = raid5_end_write_request;
            else
                  bi->bi_end_io = raid5_end_read_request;

            rcu_read_lock();
            rdev = rcu_dereference(conf->disks[i].rdev);
            if (rdev && test_bit(Faulty, &rdev->flags))
                  rdev = NULL;
            if (rdev)
                  atomic_inc(&rdev->nr_pending);
            rcu_read_unlock();

            if (rdev) {
                  if (s->syncing || s->expanding || s->expanded)
                        md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                  set_bit(STRIPE_IO_STARTED, &sh->state);

                  bi->bi_bdev = rdev->bdev;
                  pr_debug("%s: for %llu schedule op %ld on disc %d\n",
                        __func__, (unsigned long long)sh->sector,
                        bi->bi_rw, i);
                  atomic_inc(&sh->count);
                  bi->bi_sector = sh->sector + rdev->data_offset;
                  bi->bi_flags = 1 << BIO_UPTODATE;
                  bi->bi_vcnt = 1;
                  bi->bi_max_vecs = 1;
                  bi->bi_idx = 0;
                  bi->bi_io_vec = &sh->dev[i].vec;
                  bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                  bi->bi_io_vec[0].bv_offset = 0;
                  bi->bi_size = STRIPE_SIZE;
                  bi->bi_next = NULL;
                  if (rw == WRITE &&
                      test_bit(R5_ReWrite, &sh->dev[i].flags))
                        atomic_add(STRIPE_SECTORS,
                              &rdev->corrected_errors);
                  generic_make_request(bi);
            } else {
                  if (rw == WRITE)
                        set_bit(STRIPE_DEGRADED, &sh->state);
                  pr_debug("skip op %ld on disc %d for sector %llu\n",
                        bi->bi_rw, i, (unsigned long long)sh->sector);
                  clear_bit(R5_LOCKED, &sh->dev[i].flags);
                  set_bit(STRIPE_HANDLE, &sh->state);
            }
      }
}

static struct dma_async_tx_descriptor *
async_copy_data(int frombio, struct bio *bio, struct page *page,
      sector_t sector, struct dma_async_tx_descriptor *tx)
{
      struct bio_vec *bvl;
      struct page *bio_page;
      int i;
      int page_offset;

      if (bio->bi_sector >= sector)
            page_offset = (signed)(bio->bi_sector - sector) * 512;
      else
            page_offset = (signed)(sector - bio->bi_sector) * -512;
      bio_for_each_segment(bvl, bio, i) {
            int len = bio_iovec_idx(bio, i)->bv_len;
            int clen;
            int b_offset = 0;

            if (page_offset < 0) {
                  b_offset = -page_offset;
                  page_offset += b_offset;
                  len -= b_offset;
            }

            if (len > 0 && page_offset + len > STRIPE_SIZE)
                  clen = STRIPE_SIZE - page_offset;
            else
                  clen = len;

            if (clen > 0) {
                  b_offset += bio_iovec_idx(bio, i)->bv_offset;
                  bio_page = bio_iovec_idx(bio, i)->bv_page;
                  if (frombio)
                        tx = async_memcpy(page, bio_page, page_offset,
                              b_offset, clen,
                              ASYNC_TX_DEP_ACK,
                              tx, NULL, NULL);
                  else
                        tx = async_memcpy(bio_page, page, b_offset,
                              page_offset, clen,
                              ASYNC_TX_DEP_ACK,
                              tx, NULL, NULL);
            }
            if (clen < len) /* hit end of page */
                  break;
            page_offset +=  len;
      }

      return tx;
}

static void ops_complete_biofill(void *stripe_head_ref)
{
      struct stripe_head *sh = stripe_head_ref;
      struct bio *return_bi = NULL;
      raid5_conf_t *conf = sh->raid_conf;
      int i;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      /* clear completed biofills */
      spin_lock_irq(&conf->device_lock);
      for (i = sh->disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];

            /* acknowledge completion of a biofill operation */
            /* and check if we need to reply to a read request,
             * new R5_Wantfill requests are held off until
             * !STRIPE_BIOFILL_RUN
             */
            if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                  struct bio *rbi, *rbi2;

                  BUG_ON(!dev->read);
                  rbi = dev->read;
                  dev->read = NULL;
                  while (rbi && rbi->bi_sector <
                        dev->sector + STRIPE_SECTORS) {
                        rbi2 = r5_next_bio(rbi, dev->sector);
                        if (!raid5_dec_bi_phys_segments(rbi)) {
                              rbi->bi_next = return_bi;
                              return_bi = rbi;
                        }
                        rbi = rbi2;
                  }
            }
      }
      spin_unlock_irq(&conf->device_lock);
      clear_bit(STRIPE_BIOFILL_RUN, &sh->state);

      return_io(return_bi);

      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}

static void ops_run_biofill(struct stripe_head *sh)
{
      struct dma_async_tx_descriptor *tx = NULL;
      raid5_conf_t *conf = sh->raid_conf;
      int i;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      for (i = sh->disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            if (test_bit(R5_Wantfill, &dev->flags)) {
                  struct bio *rbi;
                  spin_lock_irq(&conf->device_lock);
                  dev->read = rbi = dev->toread;
                  dev->toread = NULL;
                  spin_unlock_irq(&conf->device_lock);
                  while (rbi && rbi->bi_sector <
                        dev->sector + STRIPE_SECTORS) {
                        tx = async_copy_data(0, rbi, dev->page,
                              dev->sector, tx);
                        rbi = r5_next_bio(rbi, dev->sector);
                  }
            }
      }

      atomic_inc(&sh->count);
      async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
            ops_complete_biofill, sh);
}

static void ops_complete_compute5(void *stripe_head_ref)
{
      struct stripe_head *sh = stripe_head_ref;
      int target = sh->ops.target;
      struct r5dev *tgt = &sh->dev[target];

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      set_bit(R5_UPTODATE, &tgt->flags);
      BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
      clear_bit(R5_Wantcompute, &tgt->flags);
      clear_bit(STRIPE_COMPUTE_RUN, &sh->state);
      if (sh->check_state == check_state_compute_run)
            sh->check_state = check_state_compute_result;
      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}

static struct dma_async_tx_descriptor *ops_run_compute5(struct stripe_head *sh)
{
      /* kernel stack size limits the total number of disks */
      int disks = sh->disks;
      struct page *xor_srcs[disks];
      int target = sh->ops.target;
      struct r5dev *tgt = &sh->dev[target];
      struct page *xor_dest = tgt->page;
      int count = 0;
      struct dma_async_tx_descriptor *tx;
      int i;

      pr_debug("%s: stripe %llu block: %d\n",
            __func__, (unsigned long long)sh->sector, target);
      BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));

      for (i = disks; i--; )
            if (i != target)
                  xor_srcs[count++] = sh->dev[i].page;

      atomic_inc(&sh->count);

      if (unlikely(count == 1))
            tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                  0, NULL, ops_complete_compute5, sh);
      else
            tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                  ASYNC_TX_XOR_ZERO_DST, NULL,
                  ops_complete_compute5, sh);

      return tx;
}

static void ops_complete_prexor(void *stripe_head_ref)
{
      struct stripe_head *sh = stripe_head_ref;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);
}

static struct dma_async_tx_descriptor *
ops_run_prexor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
      /* kernel stack size limits the total number of disks */
      int disks = sh->disks;
      struct page *xor_srcs[disks];
      int count = 0, pd_idx = sh->pd_idx, i;

      /* existing parity data subtracted */
      struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            /* Only process blocks that are known to be uptodate */
            if (test_bit(R5_Wantdrain, &dev->flags))
                  xor_srcs[count++] = dev->page;
      }

      tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
            ASYNC_TX_DEP_ACK | ASYNC_TX_XOR_DROP_DST, tx,
            ops_complete_prexor, sh);

      return tx;
}

static struct dma_async_tx_descriptor *
ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
      int disks = sh->disks;
      int i;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            struct bio *chosen;

            if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
                  struct bio *wbi;

                  spin_lock(&sh->lock);
                  chosen = dev->towrite;
                  dev->towrite = NULL;
                  BUG_ON(dev->written);
                  wbi = dev->written = chosen;
                  spin_unlock(&sh->lock);

                  while (wbi && wbi->bi_sector <
                        dev->sector + STRIPE_SECTORS) {
                        tx = async_copy_data(1, wbi, dev->page,
                              dev->sector, tx);
                        wbi = r5_next_bio(wbi, dev->sector);
                  }
            }
      }

      return tx;
}

static void ops_complete_postxor(void *stripe_head_ref)
{
      struct stripe_head *sh = stripe_head_ref;
      int disks = sh->disks, i, pd_idx = sh->pd_idx;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            if (dev->written || i == pd_idx)
                  set_bit(R5_UPTODATE, &dev->flags);
      }

      if (sh->reconstruct_state == reconstruct_state_drain_run)
            sh->reconstruct_state = reconstruct_state_drain_result;
      else if (sh->reconstruct_state == reconstruct_state_prexor_drain_run)
            sh->reconstruct_state = reconstruct_state_prexor_drain_result;
      else {
            BUG_ON(sh->reconstruct_state != reconstruct_state_run);
            sh->reconstruct_state = reconstruct_state_result;
      }

      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}

static void
ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
      /* kernel stack size limits the total number of disks */
      int disks = sh->disks;
      struct page *xor_srcs[disks];

      int count = 0, pd_idx = sh->pd_idx, i;
      struct page *xor_dest;
      int prexor = 0;
      unsigned long flags;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      /* check if prexor is active which means only process blocks
       * that are part of a read-modify-write (written)
       */
      if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
            prexor = 1;
            xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (dev->written)
                        xor_srcs[count++] = dev->page;
            }
      } else {
            xor_dest = sh->dev[pd_idx].page;
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (i != pd_idx)
                        xor_srcs[count++] = dev->page;
            }
      }

      /* 1/ if we prexor'd then the dest is reused as a source
       * 2/ if we did not prexor then we are redoing the parity
       * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
       * for the synchronous xor case
       */
      flags = ASYNC_TX_DEP_ACK | ASYNC_TX_ACK |
            (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);

      atomic_inc(&sh->count);

      if (unlikely(count == 1)) {
            flags &= ~(ASYNC_TX_XOR_DROP_DST | ASYNC_TX_XOR_ZERO_DST);
            tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE,
                  flags, tx, ops_complete_postxor, sh);
      } else
            tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                  flags, tx, ops_complete_postxor, sh);
}

static void ops_complete_check(void *stripe_head_ref)
{
      struct stripe_head *sh = stripe_head_ref;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      sh->check_state = check_state_check_result;
      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}

static void ops_run_check(struct stripe_head *sh)
{
      /* kernel stack size limits the total number of disks */
      int disks = sh->disks;
      struct page *xor_srcs[disks];
      struct dma_async_tx_descriptor *tx;

      int count = 0, pd_idx = sh->pd_idx, i;
      struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

      pr_debug("%s: stripe %llu\n", __func__,
            (unsigned long long)sh->sector);

      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            if (i != pd_idx)
                  xor_srcs[count++] = dev->page;
      }

      tx = async_xor_zero_sum(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
            &sh->ops.zero_sum_result, 0, NULL, NULL, NULL);

      atomic_inc(&sh->count);
      tx = async_trigger_callback(ASYNC_TX_DEP_ACK | ASYNC_TX_ACK, tx,
            ops_complete_check, sh);
}

static void raid5_run_ops(struct stripe_head *sh, unsigned long ops_request)
{
      int overlap_clear = 0, i, disks = sh->disks;
      struct dma_async_tx_descriptor *tx = NULL;

      if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
            ops_run_biofill(sh);
            overlap_clear++;
      }

      if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
            tx = ops_run_compute5(sh);
            /* terminate the chain if postxor is not set to be run */
            if (tx && !test_bit(STRIPE_OP_POSTXOR, &ops_request))
                  async_tx_ack(tx);
      }

      if (test_bit(STRIPE_OP_PREXOR, &ops_request))
            tx = ops_run_prexor(sh, tx);

      if (test_bit(STRIPE_OP_BIODRAIN, &ops_request)) {
            tx = ops_run_biodrain(sh, tx);
            overlap_clear++;
      }

      if (test_bit(STRIPE_OP_POSTXOR, &ops_request))
            ops_run_postxor(sh, tx);

      if (test_bit(STRIPE_OP_CHECK, &ops_request))
            ops_run_check(sh);

      if (overlap_clear)
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (test_and_clear_bit(R5_Overlap, &dev->flags))
                        wake_up(&sh->raid_conf->wait_for_overlap);
            }
}

static int grow_one_stripe(raid5_conf_t *conf)
{
      struct stripe_head *sh;
      sh = kmem_cache_alloc(conf->slab_cache, GFP_KERNEL);
      if (!sh)
            return 0;
      memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
      sh->raid_conf = conf;
      spin_lock_init(&sh->lock);

      if (grow_buffers(sh, conf->raid_disks)) {
            shrink_buffers(sh, conf->raid_disks);
            kmem_cache_free(conf->slab_cache, sh);
            return 0;
      }
      sh->disks = conf->raid_disks;
      /* we just created an active stripe so... */
      atomic_set(&sh->count, 1);
      atomic_inc(&conf->active_stripes);
      INIT_LIST_HEAD(&sh->lru);
      release_stripe(sh);
      return 1;
}

static int grow_stripes(raid5_conf_t *conf, int num)
{
      struct kmem_cache *sc;
      int devs = conf->raid_disks;

      sprintf(conf->cache_name[0],
            "raid%d-%s", conf->level, mdname(conf->mddev));
      sprintf(conf->cache_name[1],
            "raid%d-%s-alt", conf->level, mdname(conf->mddev));
      conf->active_name = 0;
      sc = kmem_cache_create(conf->cache_name[conf->active_name],
                         sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                         0, 0, NULL);
      if (!sc)
            return 1;
      conf->slab_cache = sc;
      conf->pool_size = devs;
      while (num--)
            if (!grow_one_stripe(conf))
                  return 1;
      return 0;
}

static int resize_stripes(raid5_conf_t *conf, int newsize)
{
      /* Make all the stripes able to hold 'newsize' devices.
       * New slots in each stripe get 'page' set to a new page.
       *
       * This happens in stages:
       * 1/ create a new kmem_cache and allocate the required number of
       *    stripe_heads.
       * 2/ gather all the old stripe_heads and tranfer the pages across
       *    to the new stripe_heads.  This will have the side effect of
       *    freezing the array as once all stripe_heads have been collected,
       *    no IO will be possible.  Old stripe heads are freed once their
       *    pages have been transferred over, and the old kmem_cache is
       *    freed when all stripes are done.
       * 3/ reallocate conf->disks to be suitable bigger.  If this fails,
       *    we simple return a failre status - no need to clean anything up.
       * 4/ allocate new pages for the new slots in the new stripe_heads.
       *    If this fails, we don't bother trying the shrink the
       *    stripe_heads down again, we just leave them as they are.
       *    As each stripe_head is processed the new one is released into
       *    active service.
       *
       * Once step2 is started, we cannot afford to wait for a write,
       * so we use GFP_NOIO allocations.
       */
      struct stripe_head *osh, *nsh;
      LIST_HEAD(newstripes);
      struct disk_info *ndisks;
      int err;
      struct kmem_cache *sc;
      int i;

      if (newsize <= conf->pool_size)
            return 0; /* never bother to shrink */

      err = md_allow_write(conf->mddev);
      if (err)
            return err;

      /* Step 1 */
      sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                         sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
                         0, 0, NULL);
      if (!sc)
            return -ENOMEM;

      for (i = conf->max_nr_stripes; i; i--) {
            nsh = kmem_cache_alloc(sc, GFP_KERNEL);
            if (!nsh)
                  break;

            memset(nsh, 0, sizeof(*nsh) + (newsize-1)*sizeof(struct r5dev));

            nsh->raid_conf = conf;
            spin_lock_init(&nsh->lock);

            list_add(&nsh->lru, &newstripes);
      }
      if (i) {
            /* didn't get enough, give up */
            while (!list_empty(&newstripes)) {
                  nsh = list_entry(newstripes.next, struct stripe_head, lru);
                  list_del(&nsh->lru);
                  kmem_cache_free(sc, nsh);
            }
            kmem_cache_destroy(sc);
            return -ENOMEM;
      }
      /* Step 2 - Must use GFP_NOIO now.
       * OK, we have enough stripes, start collecting inactive
       * stripes and copying them over
       */
      list_for_each_entry(nsh, &newstripes, lru) {
            spin_lock_irq(&conf->device_lock);
            wait_event_lock_irq(conf->wait_for_stripe,
                            !list_empty(&conf->inactive_list),
                            conf->device_lock,
                            unplug_slaves(conf->mddev)
                  );
            osh = get_free_stripe(conf);
            spin_unlock_irq(&conf->device_lock);
            atomic_set(&nsh->count, 1);
            for(i=0; i<conf->pool_size; i++)
                  nsh->dev[i].page = osh->dev[i].page;
            for( ; i<newsize; i++)
                  nsh->dev[i].page = NULL;
            kmem_cache_free(conf->slab_cache, osh);
      }
      kmem_cache_destroy(conf->slab_cache);

      /* Step 3.
       * At this point, we are holding all the stripes so the array
       * is completely stalled, so now is a good time to resize
       * conf->disks.
       */
      ndisks = kzalloc(newsize * sizeof(struct disk_info), GFP_NOIO);
      if (ndisks) {
            for (i=0; i<conf->raid_disks; i++)
                  ndisks[i] = conf->disks[i];
            kfree(conf->disks);
            conf->disks = ndisks;
      } else
            err = -ENOMEM;

      /* Step 4, return new stripes to service */
      while(!list_empty(&newstripes)) {
            nsh = list_entry(newstripes.next, struct stripe_head, lru);
            list_del_init(&nsh->lru);
            for (i=conf->raid_disks; i < newsize; i++)
                  if (nsh->dev[i].page == NULL) {
                        struct page *p = alloc_page(GFP_NOIO);
                        nsh->dev[i].page = p;
                        if (!p)
                              err = -ENOMEM;
                  }
            release_stripe(nsh);
      }
      /* critical section pass, GFP_NOIO no longer needed */

      conf->slab_cache = sc;
      conf->active_name = 1-conf->active_name;
      conf->pool_size = newsize;
      return err;
}

static int drop_one_stripe(raid5_conf_t *conf)
{
      struct stripe_head *sh;

      spin_lock_irq(&conf->device_lock);
      sh = get_free_stripe(conf);
      spin_unlock_irq(&conf->device_lock);
      if (!sh)
            return 0;
      BUG_ON(atomic_read(&sh->count));
      shrink_buffers(sh, conf->pool_size);
      kmem_cache_free(conf->slab_cache, sh);
      atomic_dec(&conf->active_stripes);
      return 1;
}

static void shrink_stripes(raid5_conf_t *conf)
{
      while (drop_one_stripe(conf))
            ;

      if (conf->slab_cache)
            kmem_cache_destroy(conf->slab_cache);
      conf->slab_cache = NULL;
}

static void raid5_end_read_request(struct bio * bi, int error)
{
      struct stripe_head *sh = bi->bi_private;
      raid5_conf_t *conf = sh->raid_conf;
      int disks = sh->disks, i;
      int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
      char b[BDEVNAME_SIZE];
      mdk_rdev_t *rdev;


      for (i=0 ; i<disks; i++)
            if (bi == &sh->dev[i].req)
                  break;

      pr_debug("end_read_request %llu/%d, count: %d, uptodate %d.\n",
            (unsigned long long)sh->sector, i, atomic_read(&sh->count),
            uptodate);
      if (i == disks) {
            BUG();
            return;
      }

      if (uptodate) {
            set_bit(R5_UPTODATE, &sh->dev[i].flags);
            if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                  rdev = conf->disks[i].rdev;
                  printk_rl(KERN_INFO "raid5:%s: read error corrected"
                          " (%lu sectors at %llu on %s)\n",
                          mdname(conf->mddev), STRIPE_SECTORS,
                          (unsigned long long)(sh->sector
                                           + rdev->data_offset),
                          bdevname(rdev->bdev, b));
                  clear_bit(R5_ReadError, &sh->dev[i].flags);
                  clear_bit(R5_ReWrite, &sh->dev[i].flags);
            }
            if (atomic_read(&conf->disks[i].rdev->read_errors))
                  atomic_set(&conf->disks[i].rdev->read_errors, 0);
      } else {
            const char *bdn = bdevname(conf->disks[i].rdev->bdev, b);
            int retry = 0;
            rdev = conf->disks[i].rdev;

            clear_bit(R5_UPTODATE, &sh->dev[i].flags);
            atomic_inc(&rdev->read_errors);
            if (conf->mddev->degraded)
                  printk_rl(KERN_WARNING
                          "raid5:%s: read error not correctable "
                          "(sector %llu on %s).\n",
                          mdname(conf->mddev),
                          (unsigned long long)(sh->sector
                                           + rdev->data_offset),
                          bdn);
            else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                  /* Oh, no!!! */
                  printk_rl(KERN_WARNING
                          "raid5:%s: read error NOT corrected!! "
                          "(sector %llu on %s).\n",
                          mdname(conf->mddev),
                          (unsigned long long)(sh->sector
                                           + rdev->data_offset),
                          bdn);
            else if (atomic_read(&rdev->read_errors)
                   > conf->max_nr_stripes)
                  printk(KERN_WARNING
                         "raid5:%s: Too many read errors, failing device %s.\n",
                         mdname(conf->mddev), bdn);
            else
                  retry = 1;
            if (retry)
                  set_bit(R5_ReadError, &sh->dev[i].flags);
            else {
                  clear_bit(R5_ReadError, &sh->dev[i].flags);
                  clear_bit(R5_ReWrite, &sh->dev[i].flags);
                  md_error(conf->mddev, rdev);
            }
      }
      rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
      clear_bit(R5_LOCKED, &sh->dev[i].flags);
      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}

static void raid5_end_write_request(struct bio *bi, int error)
{
      struct stripe_head *sh = bi->bi_private;
      raid5_conf_t *conf = sh->raid_conf;
      int disks = sh->disks, i;
      int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);

      for (i=0 ; i<disks; i++)
            if (bi == &sh->dev[i].req)
                  break;

      pr_debug("end_write_request %llu/%d, count %d, uptodate: %d.\n",
            (unsigned long long)sh->sector, i, atomic_read(&sh->count),
            uptodate);
      if (i == disks) {
            BUG();
            return;
      }

      if (!uptodate)
            md_error(conf->mddev, conf->disks[i].rdev);

      rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
      
      clear_bit(R5_LOCKED, &sh->dev[i].flags);
      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous);
      
static void raid5_build_block(struct stripe_head *sh, int i, int previous)
{
      struct r5dev *dev = &sh->dev[i];

      bio_init(&dev->req);
      dev->req.bi_io_vec = &dev->vec;
      dev->req.bi_vcnt++;
      dev->req.bi_max_vecs++;
      dev->vec.bv_page = dev->page;
      dev->vec.bv_len = STRIPE_SIZE;
      dev->vec.bv_offset = 0;

      dev->req.bi_sector = sh->sector;
      dev->req.bi_private = sh;

      dev->flags = 0;
      dev->sector = compute_blocknr(sh, i, previous);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
      char b[BDEVNAME_SIZE];
      raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
      pr_debug("raid5: error called\n");

      if (!test_bit(Faulty, &rdev->flags)) {
            set_bit(MD_CHANGE_DEVS, &mddev->flags);
            if (test_and_clear_bit(In_sync, &rdev->flags)) {
                  unsigned long flags;
                  spin_lock_irqsave(&conf->device_lock, flags);
                  mddev->degraded++;
                  spin_unlock_irqrestore(&conf->device_lock, flags);
                  /*
                   * if recovery was running, make sure it aborts.
                   */
                  set_bit(MD_RECOVERY_INTR, &mddev->recovery);
            }
            set_bit(Faulty, &rdev->flags);
            printk(KERN_ALERT
                   "raid5: Disk failure on %s, disabling device.\n"
                   "raid5: Operation continuing on %d devices.\n",
                   bdevname(rdev->bdev,b), conf->raid_disks - mddev->degraded);
      }
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                             int previous, int *dd_idx,
                             struct stripe_head *sh)
{
      long stripe;
      unsigned long chunk_number;
      unsigned int chunk_offset;
      int pd_idx, qd_idx;
      int ddf_layout = 0;
      sector_t new_sector;
      int algorithm = previous ? conf->prev_algo
                         : conf->algorithm;
      int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                               : conf->chunk_sectors;
      int raid_disks = previous ? conf->previous_raid_disks
                          : conf->raid_disks;
      int data_disks = raid_disks - conf->max_degraded;

      /* First compute the information on this sector */

      /*
       * Compute the chunk number and the sector offset inside the chunk
       */
      chunk_offset = sector_div(r_sector, sectors_per_chunk);
      chunk_number = r_sector;
      BUG_ON(r_sector != chunk_number);

      /*
       * Compute the stripe number
       */
      stripe = chunk_number / data_disks;

      /*
       * Compute the data disk and parity disk indexes inside the stripe
       */
      *dd_idx = chunk_number % data_disks;

      /*
       * Select the parity disk based on the user selected algorithm.
       */
      pd_idx = qd_idx = ~0;
      switch(conf->level) {
      case 4:
            pd_idx = data_disks;
            break;
      case 5:
            switch (algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
                  pd_idx = data_disks - stripe % raid_disks;
                  if (*dd_idx >= pd_idx)
                        (*dd_idx)++;
                  break;
            case ALGORITHM_RIGHT_ASYMMETRIC:
                  pd_idx = stripe % raid_disks;
                  if (*dd_idx >= pd_idx)
                        (*dd_idx)++;
                  break;
            case ALGORITHM_LEFT_SYMMETRIC:
                  pd_idx = data_disks - stripe % raid_disks;
                  *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                  break;
            case ALGORITHM_RIGHT_SYMMETRIC:
                  pd_idx = stripe % raid_disks;
                  *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                  break;
            case ALGORITHM_PARITY_0:
                  pd_idx = 0;
                  (*dd_idx)++;
                  break;
            case ALGORITHM_PARITY_N:
                  pd_idx = data_disks;
                  break;
            default:
                  printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                        algorithm);
                  BUG();
            }
            break;
      case 6:

            switch (algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
                  pd_idx = raid_disks - 1 - (stripe % raid_disks);
                  qd_idx = pd_idx + 1;
                  if (pd_idx == raid_disks-1) {
                        (*dd_idx)++;      /* Q D D D P */
                        qd_idx = 0;
                  } else if (*dd_idx >= pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                  break;
            case ALGORITHM_RIGHT_ASYMMETRIC:
                  pd_idx = stripe % raid_disks;
                  qd_idx = pd_idx + 1;
                  if (pd_idx == raid_disks-1) {
                        (*dd_idx)++;      /* Q D D D P */
                        qd_idx = 0;
                  } else if (*dd_idx >= pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                  break;
            case ALGORITHM_LEFT_SYMMETRIC:
                  pd_idx = raid_disks - 1 - (stripe % raid_disks);
                  qd_idx = (pd_idx + 1) % raid_disks;
                  *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                  break;
            case ALGORITHM_RIGHT_SYMMETRIC:
                  pd_idx = stripe % raid_disks;
                  qd_idx = (pd_idx + 1) % raid_disks;
                  *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                  break;

            case ALGORITHM_PARITY_0:
                  pd_idx = 0;
                  qd_idx = 1;
                  (*dd_idx) += 2;
                  break;
            case ALGORITHM_PARITY_N:
                  pd_idx = data_disks;
                  qd_idx = data_disks + 1;
                  break;

            case ALGORITHM_ROTATING_ZERO_RESTART:
                  /* Exactly the same as RIGHT_ASYMMETRIC, but or
                   * of blocks for computing Q is different.
                   */
                  pd_idx = stripe % raid_disks;
                  qd_idx = pd_idx + 1;
                  if (pd_idx == raid_disks-1) {
                        (*dd_idx)++;      /* Q D D D P */
                        qd_idx = 0;
                  } else if (*dd_idx >= pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                  ddf_layout = 1;
                  break;

            case ALGORITHM_ROTATING_N_RESTART:
                  /* Same a left_asymmetric, by first stripe is
                   * D D D P Q  rather than
                   * Q D D D P
                   */
                  pd_idx = raid_disks - 1 - ((stripe + 1) % raid_disks);
                  qd_idx = pd_idx + 1;
                  if (pd_idx == raid_disks-1) {
                        (*dd_idx)++;      /* Q D D D P */
                        qd_idx = 0;
                  } else if (*dd_idx >= pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                  ddf_layout = 1;
                  break;

            case ALGORITHM_ROTATING_N_CONTINUE:
                  /* Same as left_symmetric but Q is before P */
                  pd_idx = raid_disks - 1 - (stripe % raid_disks);
                  qd_idx = (pd_idx + raid_disks - 1) % raid_disks;
                  *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                  ddf_layout = 1;
                  break;

            case ALGORITHM_LEFT_ASYMMETRIC_6:
                  /* RAID5 left_asymmetric, with Q on last device */
                  pd_idx = data_disks - stripe % (raid_disks-1);
                  if (*dd_idx >= pd_idx)
                        (*dd_idx)++;
                  qd_idx = raid_disks - 1;
                  break;

            case ALGORITHM_RIGHT_ASYMMETRIC_6:
                  pd_idx = stripe % (raid_disks-1);
                  if (*dd_idx >= pd_idx)
                        (*dd_idx)++;
                  qd_idx = raid_disks - 1;
                  break;

            case ALGORITHM_LEFT_SYMMETRIC_6:
                  pd_idx = data_disks - stripe % (raid_disks-1);
                  *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                  qd_idx = raid_disks - 1;
                  break;

            case ALGORITHM_RIGHT_SYMMETRIC_6:
                  pd_idx = stripe % (raid_disks-1);
                  *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                  qd_idx = raid_disks - 1;
                  break;

            case ALGORITHM_PARITY_0_6:
                  pd_idx = 0;
                  (*dd_idx)++;
                  qd_idx = raid_disks - 1;
                  break;


            default:
                  printk(KERN_CRIT "raid6: unsupported algorithm %d\n",
                         algorithm);
                  BUG();
            }
            break;
      }

      if (sh) {
            sh->pd_idx = pd_idx;
            sh->qd_idx = qd_idx;
            sh->ddf_layout = ddf_layout;
      }
      /*
       * Finally, compute the new sector number
       */
      new_sector = (sector_t)stripe * sectors_per_chunk + chunk_offset;
      return new_sector;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous)
{
      raid5_conf_t *conf = sh->raid_conf;
      int raid_disks = sh->disks;
      int data_disks = raid_disks - conf->max_degraded;
      sector_t new_sector = sh->sector, check;
      int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                               : conf->chunk_sectors;
      int algorithm = previous ? conf->prev_algo
                         : conf->algorithm;
      sector_t stripe;
      int chunk_offset;
      int chunk_number, dummy1, dd_idx = i;
      sector_t r_sector;
      struct stripe_head sh2;


      chunk_offset = sector_div(new_sector, sectors_per_chunk);
      stripe = new_sector;
      BUG_ON(new_sector != stripe);

      if (i == sh->pd_idx)
            return 0;
      switch(conf->level) {
      case 4: break;
      case 5:
            switch (algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
            case ALGORITHM_RIGHT_ASYMMETRIC:
                  if (i > sh->pd_idx)
                        i--;
                  break;
            case ALGORITHM_LEFT_SYMMETRIC:
            case ALGORITHM_RIGHT_SYMMETRIC:
                  if (i < sh->pd_idx)
                        i += raid_disks;
                  i -= (sh->pd_idx + 1);
                  break;
            case ALGORITHM_PARITY_0:
                  i -= 1;
                  break;
            case ALGORITHM_PARITY_N:
                  break;
            default:
                  printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                         algorithm);
                  BUG();
            }
            break;
      case 6:
            if (i == sh->qd_idx)
                  return 0; /* It is the Q disk */
            switch (algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
            case ALGORITHM_RIGHT_ASYMMETRIC:
            case ALGORITHM_ROTATING_ZERO_RESTART:
            case ALGORITHM_ROTATING_N_RESTART:
                  if (sh->pd_idx == raid_disks-1)
                        i--;  /* Q D D D P */
                  else if (i > sh->pd_idx)
                        i -= 2; /* D D P Q D */
                  break;
            case ALGORITHM_LEFT_SYMMETRIC:
            case ALGORITHM_RIGHT_SYMMETRIC:
                  if (sh->pd_idx == raid_disks-1)
                        i--; /* Q D D D P */
                  else {
                        /* D D P Q D */
                        if (i < sh->pd_idx)
                              i += raid_disks;
                        i -= (sh->pd_idx + 2);
                  }
                  break;
            case ALGORITHM_PARITY_0:
                  i -= 2;
                  break;
            case ALGORITHM_PARITY_N:
                  break;
            case ALGORITHM_ROTATING_N_CONTINUE:
                  if (sh->pd_idx == 0)
                        i--;  /* P D D D Q */
                  else if (i > sh->pd_idx)
                        i -= 2; /* D D Q P D */
                  break;
            case ALGORITHM_LEFT_ASYMMETRIC_6:
            case ALGORITHM_RIGHT_ASYMMETRIC_6:
                  if (i > sh->pd_idx)
                        i--;
                  break;
            case ALGORITHM_LEFT_SYMMETRIC_6:
            case ALGORITHM_RIGHT_SYMMETRIC_6:
                  if (i < sh->pd_idx)
                        i += data_disks + 1;
                  i -= (sh->pd_idx + 1);
                  break;
            case ALGORITHM_PARITY_0_6:
                  i -= 1;
                  break;
            default:
                  printk(KERN_CRIT "raid6: unsupported algorithm %d\n",
                         algorithm);
                  BUG();
            }
            break;
      }

      chunk_number = stripe * data_disks + i;
      r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;

      check = raid5_compute_sector(conf, r_sector,
                             previous, &dummy1, &sh2);
      if (check != sh->sector || dummy1 != dd_idx || sh2.pd_idx != sh->pd_idx
            || sh2.qd_idx != sh->qd_idx) {
            printk(KERN_ERR "compute_blocknr: map not correct\n");
            return 0;
      }
      return r_sector;
}



/*
 * Copy data between a page in the stripe cache, and one or more bion
 * The page could align with the middle of the bio, or there could be
 * several bion, each with several bio_vecs, which cover part of the page
 * Multiple bion are linked together on bi_next.  There may be extras
 * at the end of this list.  We ignore them.
 */
static void copy_data(int frombio, struct bio *bio,
                 struct page *page,
                 sector_t sector)
{
      char *pa = page_address(page);
      struct bio_vec *bvl;
      int i;
      int page_offset;

      if (bio->bi_sector >= sector)
            page_offset = (signed)(bio->bi_sector - sector) * 512;
      else
            page_offset = (signed)(sector - bio->bi_sector) * -512;
      bio_for_each_segment(bvl, bio, i) {
            int len = bio_iovec_idx(bio,i)->bv_len;
            int clen;
            int b_offset = 0;

            if (page_offset < 0) {
                  b_offset = -page_offset;
                  page_offset += b_offset;
                  len -= b_offset;
            }

            if (len > 0 && page_offset + len > STRIPE_SIZE)
                  clen = STRIPE_SIZE - page_offset;
            else clen = len;

            if (clen > 0) {
                  char *ba = __bio_kmap_atomic(bio, i, KM_USER0);
                  if (frombio)
                        memcpy(pa+page_offset, ba+b_offset, clen);
                  else
                        memcpy(ba+b_offset, pa+page_offset, clen);
                  __bio_kunmap_atomic(ba, KM_USER0);
            }
            if (clen < len) /* hit end of page */
                  break;
            page_offset +=  len;
      }
}

#define check_xor()     do {                                  \
                        if (count == MAX_XOR_BLOCKS) {              \
                        xor_blocks(count, STRIPE_SIZE, dest, ptr);\
                        count = 0;                      \
                     }                                  \
                  } while(0)

static void compute_parity6(struct stripe_head *sh, int method)
{
      raid5_conf_t *conf = sh->raid_conf;
      int i, pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
      int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
      struct bio *chosen;
      /**** FIX THIS: This could be very bad if disks is close to 256 ****/
      void *ptrs[syndrome_disks+2];

      pd_idx = sh->pd_idx;
      qd_idx = sh->qd_idx;
      d0_idx = raid6_d0(sh);

      pr_debug("compute_parity, stripe %llu, method %d\n",
            (unsigned long long)sh->sector, method);

      switch(method) {
      case READ_MODIFY_WRITE:
            BUG();            /* READ_MODIFY_WRITE N/A for RAID-6 */
      case RECONSTRUCT_WRITE:
            for (i= disks; i-- ;)
                  if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
                        chosen = sh->dev[i].towrite;
                        sh->dev[i].towrite = NULL;

                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                              wake_up(&conf->wait_for_overlap);

                        BUG_ON(sh->dev[i].written);
                        sh->dev[i].written = chosen;
                  }
            break;
      case CHECK_PARITY:
            BUG();            /* Not implemented yet */
      }

      for (i = disks; i--;)
            if (sh->dev[i].written) {
                  sector_t sector = sh->dev[i].sector;
                  struct bio *wbi = sh->dev[i].written;
                  while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
                        copy_data(1, wbi, sh->dev[i].page, sector);
                        wbi = r5_next_bio(wbi, sector);
                  }

                  set_bit(R5_LOCKED, &sh->dev[i].flags);
                  set_bit(R5_UPTODATE, &sh->dev[i].flags);
            }

      /* Note that unlike RAID-5, the ordering of the disks matters greatly.*/

      for (i = 0; i < disks; i++)
            ptrs[i] = (void *)raid6_empty_zero_page;

      count = 0;
      i = d0_idx;
      do {
            int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

            ptrs[slot] = page_address(sh->dev[i].page);
            if (slot < syndrome_disks &&
                !test_bit(R5_UPTODATE, &sh->dev[i].flags)) {
                  printk(KERN_ERR "block %d/%d not uptodate "
                         "on parity calc\n", i, count);
                  BUG();
            }

            i = raid6_next_disk(i, disks);
      } while (i != d0_idx);
      BUG_ON(count != syndrome_disks);

      raid6_call.gen_syndrome(syndrome_disks+2, STRIPE_SIZE, ptrs);

      switch(method) {
      case RECONSTRUCT_WRITE:
            set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
            set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
            set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
            set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
            break;
      case UPDATE_PARITY:
            set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
            set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
            break;
      }
}


/* Compute one missing block */
static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
{
      int i, count, disks = sh->disks;
      void *ptr[MAX_XOR_BLOCKS], *dest, *p;
      int qd_idx = sh->qd_idx;

      pr_debug("compute_block_1, stripe %llu, idx %d\n",
            (unsigned long long)sh->sector, dd_idx);

      if ( dd_idx == qd_idx ) {
            /* We're actually computing the Q drive */
            compute_parity6(sh, UPDATE_PARITY);
      } else {
            dest = page_address(sh->dev[dd_idx].page);
            if (!nozero) memset(dest, 0, STRIPE_SIZE);
            count = 0;
            for (i = disks ; i--; ) {
                  if (i == dd_idx || i == qd_idx)
                        continue;
                  p = page_address(sh->dev[i].page);
                  if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
                        ptr[count++] = p;
                  else
                        printk("compute_block() %d, stripe %llu, %d"
                               " not present\n", dd_idx,
                               (unsigned long long)sh->sector, i);

                  check_xor();
            }
            if (count)
                  xor_blocks(count, STRIPE_SIZE, dest, ptr);
            if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
            else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
      }
}

/* Compute two missing blocks */
static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
{
      int i, count, disks = sh->disks;
      int syndrome_disks = sh->ddf_layout ? disks : disks-2;
      int d0_idx = raid6_d0(sh);
      int faila = -1, failb = -1;
      /**** FIX THIS: This could be very bad if disks is close to 256 ****/
      void *ptrs[syndrome_disks+2];

      for (i = 0; i < disks ; i++)
            ptrs[i] = (void *)raid6_empty_zero_page;
      count = 0;
      i = d0_idx;
      do {
            int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

            ptrs[slot] = page_address(sh->dev[i].page);

            if (i == dd_idx1)
                  faila = slot;
            if (i == dd_idx2)
                  failb = slot;
            i = raid6_next_disk(i, disks);
      } while (i != d0_idx);
      BUG_ON(count != syndrome_disks);

      BUG_ON(faila == failb);
      if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }

      pr_debug("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
             (unsigned long long)sh->sector, dd_idx1, dd_idx2,
             faila, failb);

      if (failb == syndrome_disks+1) {
            /* Q disk is one of the missing disks */
            if (faila == syndrome_disks) {
                  /* Missing P+Q, just recompute */
                  compute_parity6(sh, UPDATE_PARITY);
                  return;
            } else {
                  /* We're missing D+Q; recompute D from P */
                  compute_block_1(sh, ((dd_idx1 == sh->qd_idx) ?
                                   dd_idx2 : dd_idx1),
                              0);
                  compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
                  return;
            }
      }

      /* We're missing D+P or D+D; */
      if (failb == syndrome_disks) {
            /* We're missing D+P. */
            raid6_datap_recov(syndrome_disks+2, STRIPE_SIZE, faila, ptrs);
      } else {
            /* We're missing D+D. */
            raid6_2data_recov(syndrome_disks+2, STRIPE_SIZE, faila, failb,
                          ptrs);
      }

      /* Both the above update both missing blocks */
      set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
      set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
}

static void
schedule_reconstruction5(struct stripe_head *sh, struct stripe_head_state *s,
                   int rcw, int expand)
{
      int i, pd_idx = sh->pd_idx, disks = sh->disks;

      if (rcw) {
            /* if we are not expanding this is a proper write request, and
             * there will be bios with new data to be drained into the
             * stripe cache
             */
            if (!expand) {
                  sh->reconstruct_state = reconstruct_state_drain_run;
                  set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
            } else
                  sh->reconstruct_state = reconstruct_state_run;

            set_bit(STRIPE_OP_POSTXOR, &s->ops_request);

            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];

                  if (dev->towrite) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantdrain, &dev->flags);
                        if (!expand)
                              clear_bit(R5_UPTODATE, &dev->flags);
                        s->locked++;
                  }
            }
            if (s->locked + 1 == disks)
                  if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                        atomic_inc(&sh->raid_conf->pending_full_writes);
      } else {
            BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
                  test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));

            sh->reconstruct_state = reconstruct_state_prexor_drain_run;
            set_bit(STRIPE_OP_PREXOR, &s->ops_request);
            set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
            set_bit(STRIPE_OP_POSTXOR, &s->ops_request);

            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (i == pd_idx)
                        continue;

                  if (dev->towrite &&
                      (test_bit(R5_UPTODATE, &dev->flags) ||
                       test_bit(R5_Wantcompute, &dev->flags))) {
                        set_bit(R5_Wantdrain, &dev->flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        clear_bit(R5_UPTODATE, &dev->flags);
                        s->locked++;
                  }
            }
      }

      /* keep the parity disk locked while asynchronous operations
       * are in flight
       */
      set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
      clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
      s->locked++;

      pr_debug("%s: stripe %llu locked: %d ops_request: %lx\n",
            __func__, (unsigned long long)sh->sector,
            s->locked, s->ops_request);
}

/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
      struct bio **bip;
      raid5_conf_t *conf = sh->raid_conf;
      int firstwrite=0;

      pr_debug("adding bh b#%llu to stripe s#%llu\n",
            (unsigned long long)bi->bi_sector,
            (unsigned long long)sh->sector);


      spin_lock(&sh->lock);
      spin_lock_irq(&conf->device_lock);
      if (forwrite) {
            bip = &sh->dev[dd_idx].towrite;
            if (*bip == NULL && sh->dev[dd_idx].written == NULL)
                  firstwrite = 1;
      } else
            bip = &sh->dev[dd_idx].toread;
      while (*bip && (*bip)->bi_sector < bi->bi_sector) {
            if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
                  goto overlap;
            bip = & (*bip)->bi_next;
      }
      if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
            goto overlap;

      BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
      if (*bip)
            bi->bi_next = *bip;
      *bip = bi;
      bi->bi_phys_segments++;
      spin_unlock_irq(&conf->device_lock);
      spin_unlock(&sh->lock);

      pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
            (unsigned long long)bi->bi_sector,
            (unsigned long long)sh->sector, dd_idx);

      if (conf->mddev->bitmap && firstwrite) {
            bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                          STRIPE_SECTORS, 0);
            sh->bm_seq = conf->seq_flush+1;
            set_bit(STRIPE_BIT_DELAY, &sh->state);
      }

      if (forwrite) {
            /* check if page is covered */
            sector_t sector = sh->dev[dd_idx].sector;
            for (bi=sh->dev[dd_idx].towrite;
                 sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
                       bi && bi->bi_sector <= sector;
                 bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
                  if (bi->bi_sector + (bi->bi_size>>9) >= sector)
                        sector = bi->bi_sector + (bi->bi_size>>9);
            }
            if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                  set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
      }
      return 1;

 overlap:
      set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
      spin_unlock_irq(&conf->device_lock);
      spin_unlock(&sh->lock);
      return 0;
}

static void end_reshape(raid5_conf_t *conf);

static int page_is_zero(struct page *p)
{
      char *a = page_address(p);
      return ((*(u32*)a) == 0 &&
            memcmp(a, a+4, STRIPE_SIZE-4)==0);
}

static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                      struct stripe_head *sh)
{
      int sectors_per_chunk =
            previous ? conf->prev_chunk_sectors : conf->chunk_sectors;
      int dd_idx;
      int chunk_offset = sector_div(stripe, sectors_per_chunk);
      int disks = previous ? conf->previous_raid_disks : conf->raid_disks;

      raid5_compute_sector(conf,
                       stripe * (disks - conf->max_degraded)
                       *sectors_per_chunk + chunk_offset,
                       previous,
                       &dd_idx, sh);
}

static void
handle_failed_stripe(raid5_conf_t *conf, struct stripe_head *sh,
                        struct stripe_head_state *s, int disks,
                        struct bio **return_bi)
{
      int i;
      for (i = disks; i--; ) {
            struct bio *bi;
            int bitmap_end = 0;

            if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                  mdk_rdev_t *rdev;
                  rcu_read_lock();
                  rdev = rcu_dereference(conf->disks[i].rdev);
                  if (rdev && test_bit(In_sync, &rdev->flags))
                        /* multiple read failures in one stripe */
                        md_error(conf->mddev, rdev);
                  rcu_read_unlock();
            }
            spin_lock_irq(&conf->device_lock);
            /* fail all writes first */
            bi = sh->dev[i].towrite;
            sh->dev[i].towrite = NULL;
            if (bi) {
                  s->to_write--;
                  bitmap_end = 1;
            }

            if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                  wake_up(&conf->wait_for_overlap);

            while (bi && bi->bi_sector <
                  sh->dev[i].sector + STRIPE_SECTORS) {
                  struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
                  clear_bit(BIO_UPTODATE, &bi->bi_flags);
                  if (!raid5_dec_bi_phys_segments(bi)) {
                        md_write_end(conf->mddev);
                        bi->bi_next = *return_bi;
                        *return_bi = bi;
                  }
                  bi = nextbi;
            }
            /* and fail all 'written' */
            bi = sh->dev[i].written;
            sh->dev[i].written = NULL;
            if (bi) bitmap_end = 1;
            while (bi && bi->bi_sector <
                   sh->dev[i].sector + STRIPE_SECTORS) {
                  struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
                  clear_bit(BIO_UPTODATE, &bi->bi_flags);
                  if (!raid5_dec_bi_phys_segments(bi)) {
                        md_write_end(conf->mddev);
                        bi->bi_next = *return_bi;
                        *return_bi = bi;
                  }
                  bi = bi2;
            }

            /* fail any reads if this device is non-operational and
             * the data has not reached the cache yet.
             */
            if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
                (!test_bit(R5_Insync, &sh->dev[i].flags) ||
                  test_bit(R5_ReadError, &sh->dev[i].flags))) {
                  bi = sh->dev[i].toread;
                  sh->dev[i].toread = NULL;
                  if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        wake_up(&conf->wait_for_overlap);
                  if (bi) s->to_read--;
                  while (bi && bi->bi_sector <
                         sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *nextbi =
                              r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (!raid5_dec_bi_phys_segments(bi)) {
                              bi->bi_next = *return_bi;
                              *return_bi = bi;
                        }
                        bi = nextbi;
                  }
            }
            spin_unlock_irq(&conf->device_lock);
            if (bitmap_end)
                  bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                              STRIPE_SECTORS, 0, 0);
      }

      if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
            if (atomic_dec_and_test(&conf->pending_full_writes))
                  md_wakeup_thread(conf->mddev->thread);
}

/* fetch_block5 - checks the given member device to see if its data needs
 * to be read or computed to satisfy a request.
 *
 * Returns 1 when no more member devices need to be checked, otherwise returns
 * 0 to tell the loop in handle_stripe_fill5 to continue
 */
static int fetch_block5(struct stripe_head *sh, struct stripe_head_state *s,
                  int disk_idx, int disks)
{
      struct r5dev *dev = &sh->dev[disk_idx];
      struct r5dev *failed_dev = &sh->dev[s->failed_num];

      /* is the data in this block needed, and can we get it? */
      if (!test_bit(R5_LOCKED, &dev->flags) &&
          !test_bit(R5_UPTODATE, &dev->flags) &&
          (dev->toread ||
           (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
           s->syncing || s->expanding ||
           (s->failed &&
            (failed_dev->toread ||
             (failed_dev->towrite &&
            !test_bit(R5_OVERWRITE, &failed_dev->flags)))))) {
            /* We would like to get this block, possibly by computing it,
             * otherwise read it if the backing disk is insync
             */
            if ((s->uptodate == disks - 1) &&
                (s->failed && disk_idx == s->failed_num)) {
                  set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                  set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                  set_bit(R5_Wantcompute, &dev->flags);
                  sh->ops.target = disk_idx;
                  s->req_compute = 1;
                  /* Careful: from this point on 'uptodate' is in the eye
                   * of raid5_run_ops which services 'compute' operations
                   * before writes. R5_Wantcompute flags a block that will
                   * be R5_UPTODATE by the time it is needed for a
                   * subsequent operation.
                   */
                  s->uptodate++;
                  return 1; /* uptodate + compute == disks */
            } else if (test_bit(R5_Insync, &dev->flags)) {
                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantread, &dev->flags);
                  s->locked++;
                  pr_debug("Reading block %d (sync=%d)\n", disk_idx,
                        s->syncing);
            }
      }

      return 0;
}

/**
 * handle_stripe_fill5 - read or compute data to satisfy pending requests.
 */
static void handle_stripe_fill5(struct stripe_head *sh,
                  struct stripe_head_state *s, int disks)
{
      int i;

      /* look for blocks to read/compute, skip this if a compute
       * is already in flight, or if the stripe contents are in the
       * midst of changing due to a write
       */
      if (!test_bit(STRIPE_COMPUTE_RUN, &sh->state) && !sh->check_state &&
          !sh->reconstruct_state)
            for (i = disks; i--; )
                  if (fetch_block5(sh, s, i, disks))
                        break;
      set_bit(STRIPE_HANDLE, &sh->state);
}

static void handle_stripe_fill6(struct stripe_head *sh,
                  struct stripe_head_state *s, struct r6_state *r6s,
                  int disks)
{
      int i;
      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            if (!test_bit(R5_LOCKED, &dev->flags) &&
                !test_bit(R5_UPTODATE, &dev->flags) &&
                (dev->toread || (dev->towrite &&
                 !test_bit(R5_OVERWRITE, &dev->flags)) ||
                 s->syncing || s->expanding ||
                 (s->failed >= 1 &&
                  (sh->dev[r6s->failed_num[0]].toread ||
                   s->to_write)) ||
                 (s->failed >= 2 &&
                  (sh->dev[r6s->failed_num[1]].toread ||
                   s->to_write)))) {
                  /* we would like to get this block, possibly
                   * by computing it, but we might not be able to
                   */
                  if ((s->uptodate == disks - 1) &&
                      (s->failed && (i == r6s->failed_num[0] ||
                                 i == r6s->failed_num[1]))) {
                        pr_debug("Computing stripe %llu block %d\n",
                               (unsigned long long)sh->sector, i);
                        compute_block_1(sh, i, 0);
                        s->uptodate++;
                  } else if ( s->uptodate == disks-2 && s->failed >= 2 ) {
                        /* Computing 2-failure is *very* expensive; only
                         * do it if failed >= 2
                         */
                        int other;
                        for (other = disks; other--; ) {
                              if (other == i)
                                    continue;
                              if (!test_bit(R5_UPTODATE,
                                    &sh->dev[other].flags))
                                    break;
                        }
                        BUG_ON(other < 0);
                        pr_debug("Computing stripe %llu blocks %d,%d\n",
                               (unsigned long long)sh->sector,
                               i, other);
                        compute_block_2(sh, i, other);
                        s->uptodate += 2;
                  } else if (test_bit(R5_Insync, &dev->flags)) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantread, &dev->flags);
                        s->locked++;
                        pr_debug("Reading block %d (sync=%d)\n",
                              i, s->syncing);
                  }
            }
      }
      set_bit(STRIPE_HANDLE, &sh->state);
}


/* handle_stripe_clean_event
 * any written block on an uptodate or failed drive can be returned.
 * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
 * never LOCKED, so we don't need to test 'failed' directly.
 */
static void handle_stripe_clean_event(raid5_conf_t *conf,
      struct stripe_head *sh, int disks, struct bio **return_bi)
{
      int i;
      struct r5dev *dev;

      for (i = disks; i--; )
            if (sh->dev[i].written) {
                  dev = &sh->dev[i];
                  if (!test_bit(R5_LOCKED, &dev->flags) &&
                        test_bit(R5_UPTODATE, &dev->flags)) {
                        /* We can return any write requests */
                        struct bio *wbi, *wbi2;
                        int bitmap_end = 0;
                        pr_debug("Return write for disc %d\n", i);
                        spin_lock_irq(&conf->device_lock);
                        wbi = dev->written;
                        dev->written = NULL;
                        while (wbi && wbi->bi_sector <
                              dev->sector + STRIPE_SECTORS) {
                              wbi2 = r5_next_bio(wbi, dev->sector);
                              if (!raid5_dec_bi_phys_segments(wbi)) {
                                    md_write_end(conf->mddev);
                                    wbi->bi_next = *return_bi;
                                    *return_bi = wbi;
                              }
                              wbi = wbi2;
                        }
                        if (dev->towrite == NULL)
                              bitmap_end = 1;
                        spin_unlock_irq(&conf->device_lock);
                        if (bitmap_end)
                              bitmap_endwrite(conf->mddev->bitmap,
                                          sh->sector,
                                          STRIPE_SECTORS,
                               !test_bit(STRIPE_DEGRADED, &sh->state),
                                          0);
                  }
            }

      if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
            if (atomic_dec_and_test(&conf->pending_full_writes))
                  md_wakeup_thread(conf->mddev->thread);
}

static void handle_stripe_dirtying5(raid5_conf_t *conf,
            struct stripe_head *sh, struct stripe_head_state *s, int disks)
{
      int rmw = 0, rcw = 0, i;
      for (i = disks; i--; ) {
            /* would I have to read this buffer for read_modify_write */
            struct r5dev *dev = &sh->dev[i];
            if ((dev->towrite || i == sh->pd_idx) &&
                !test_bit(R5_LOCKED, &dev->flags) &&
                !(test_bit(R5_UPTODATE, &dev->flags) ||
                  test_bit(R5_Wantcompute, &dev->flags))) {
                  if (test_bit(R5_Insync, &dev->flags))
                        rmw++;
                  else
                        rmw += 2*disks;  /* cannot read it */
            }
            /* Would I have to read this buffer for reconstruct_write */
            if (!test_bit(R5_OVERWRITE, &dev->flags) && i != sh->pd_idx &&
                !test_bit(R5_LOCKED, &dev->flags) &&
                !(test_bit(R5_UPTODATE, &dev->flags) ||
                test_bit(R5_Wantcompute, &dev->flags))) {
                  if (test_bit(R5_Insync, &dev->flags)) rcw++;
                  else
                        rcw += 2*disks;
            }
      }
      pr_debug("for sector %llu, rmw=%d rcw=%d\n",
            (unsigned long long)sh->sector, rmw, rcw);
      set_bit(STRIPE_HANDLE, &sh->state);
      if (rmw < rcw && rmw > 0)
            /* prefer read-modify-write, but need to get some data */
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if ((dev->towrite || i == sh->pd_idx) &&
                      !test_bit(R5_LOCKED, &dev->flags) &&
                      !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags)) &&
                      test_bit(R5_Insync, &dev->flags)) {
                        if (
                          test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                              pr_debug("Read_old block "
                                    "%d for r-m-w\n", i);
                              set_bit(R5_LOCKED, &dev->flags);
                              set_bit(R5_Wantread, &dev->flags);
                              s->locked++;
                        } else {
                              set_bit(STRIPE_DELAYED, &sh->state);
                              set_bit(STRIPE_HANDLE, &sh->state);
                        }
                  }
            }
      if (rcw <= rmw && rcw > 0)
            /* want reconstruct write, but need to get some data */
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                      i != sh->pd_idx &&
                      !test_bit(R5_LOCKED, &dev->flags) &&
                      !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags)) &&
                      test_bit(R5_Insync, &dev->flags)) {
                        if (
                          test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                              pr_debug("Read_old block "
                                    "%d for Reconstruct\n", i);
                              set_bit(R5_LOCKED, &dev->flags);
                              set_bit(R5_Wantread, &dev->flags);
                              s->locked++;
                        } else {
                              set_bit(STRIPE_DELAYED, &sh->state);
                              set_bit(STRIPE_HANDLE, &sh->state);
                        }
                  }
            }
      /* now if nothing is locked, and if we have enough data,
       * we can start a write request
       */
      /* since handle_stripe can be called at any time we need to handle the
       * case where a compute block operation has been submitted and then a
       * subsequent call wants to start a write request.  raid5_run_ops only
       * handles the case where compute block and postxor are requested
       * simultaneously.  If this is not the case then new writes need to be
       * held off until the compute completes.
       */
      if ((s->req_compute || !test_bit(STRIPE_COMPUTE_RUN, &sh->state)) &&
          (s->locked == 0 && (rcw == 0 || rmw == 0) &&
          !test_bit(STRIPE_BIT_DELAY, &sh->state)))
            schedule_reconstruction5(sh, s, rcw == 0, 0);
}

static void handle_stripe_dirtying6(raid5_conf_t *conf,
            struct stripe_head *sh, struct stripe_head_state *s,
            struct r6_state *r6s, int disks)
{
      int rcw = 0, must_compute = 0, pd_idx = sh->pd_idx, i;
      int qd_idx = sh->qd_idx;
      for (i = disks; i--; ) {
            struct r5dev *dev = &sh->dev[i];
            /* Would I have to read this buffer for reconstruct_write */
            if (!test_bit(R5_OVERWRITE, &dev->flags)
                && i != pd_idx && i != qd_idx
                && (!test_bit(R5_LOCKED, &dev->flags)
                      ) &&
                !test_bit(R5_UPTODATE, &dev->flags)) {
                  if (test_bit(R5_Insync, &dev->flags)) rcw++;
                  else {
                        pr_debug("raid6: must_compute: "
                              "disk %d flags=%#lx\n", i, dev->flags);
                        must_compute++;
                  }
            }
      }
      pr_debug("for sector %llu, rcw=%d, must_compute=%d\n",
             (unsigned long long)sh->sector, rcw, must_compute);
      set_bit(STRIPE_HANDLE, &sh->state);

      if (rcw > 0)
            /* want reconstruct write, but need to get some data */
            for (i = disks; i--; ) {
                  struct r5dev *dev = &sh->dev[i];
                  if (!test_bit(R5_OVERWRITE, &dev->flags)
                      && !(s->failed == 0 && (i == pd_idx || i == qd_idx))
                      && !test_bit(R5_LOCKED, &dev->flags) &&
                      !test_bit(R5_UPTODATE, &dev->flags) &&
                      test_bit(R5_Insync, &dev->flags)) {
                        if (
                          test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                              pr_debug("Read_old stripe %llu "
                                    "block %d for Reconstruct\n",
                                   (unsigned long long)sh->sector, i);
                              set_bit(R5_LOCKED, &dev->flags);
                              set_bit(R5_Wantread, &dev->flags);
                              s->locked++;
                        } else {
                              pr_debug("Request delayed stripe %llu "
                                    "block %d for Reconstruct\n",
                                   (unsigned long long)sh->sector, i);
                              set_bit(STRIPE_DELAYED, &sh->state);
                              set_bit(STRIPE_HANDLE, &sh->state);
                        }
                  }
            }
      /* now if nothing is locked, and if we have enough data, we can start a
       * write request
       */
      if (s->locked == 0 && rcw == 0 &&
          !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
            if (must_compute > 0) {
                  /* We have failed blocks and need to compute them */
                  switch (s->failed) {
                  case 0:
                        BUG();
                  case 1:
                        compute_block_1(sh, r6s->failed_num[0], 0);
                        break;
                  case 2:
                        compute_block_2(sh, r6s->failed_num[0],
                                    r6s->failed_num[1]);
                        break;
                  default: /* This request should have been failed? */
                        BUG();
                  }
            }

            pr_debug("Computing parity for stripe %llu\n",
                  (unsigned long long)sh->sector);
            compute_parity6(sh, RECONSTRUCT_WRITE);
            /* now every locked buffer is ready to be written */
            for (i = disks; i--; )
                  if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
                        pr_debug("Writing stripe %llu block %d\n",
                               (unsigned long long)sh->sector, i);
                        s->locked++;
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
                  }
            if (s->locked == disks)
                  if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                        atomic_inc(&conf->pending_full_writes);
            /* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
            set_bit(STRIPE_INSYNC, &sh->state);

            if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                  atomic_dec(&conf->preread_active_stripes);
                  if (atomic_read(&conf->preread_active_stripes) <
                      IO_THRESHOLD)
                        md_wakeup_thread(conf->mddev->thread);
            }
      }
}

static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
                        struct stripe_head_state *s, int disks)
{
      struct r5dev *dev = NULL;

      set_bit(STRIPE_HANDLE, &sh->state);

      switch (sh->check_state) {
      case check_state_idle:
            /* start a new check operation if there are no failures */
            if (s->failed == 0) {
                  BUG_ON(s->uptodate != disks);
                  sh->check_state = check_state_run;
                  set_bit(STRIPE_OP_CHECK, &s->ops_request);
                  clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                  s->uptodate--;
                  break;
            }
            dev = &sh->dev[s->failed_num];
            /* fall through */
      case check_state_compute_result:
            sh->check_state = check_state_idle;
            if (!dev)
                  dev = &sh->dev[sh->pd_idx];

            /* check that a write has not made the stripe insync */
            if (test_bit(STRIPE_INSYNC, &sh->state))
                  break;

            /* either failed parity check, or recovery is happening */
            BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
            BUG_ON(s->uptodate != disks);

            set_bit(R5_LOCKED, &dev->flags);
            s->locked++;
            set_bit(R5_Wantwrite, &dev->flags);

            clear_bit(STRIPE_DEGRADED, &sh->state);
            set_bit(STRIPE_INSYNC, &sh->state);
            break;
      case check_state_run:
            break; /* we will be called again upon completion */
      case check_state_check_result:
            sh->check_state = check_state_idle;

            /* if a failure occurred during the check operation, leave
             * STRIPE_INSYNC not set and let the stripe be handled again
             */
            if (s->failed)
                  break;

            /* handle a successful check operation, if parity is correct
             * we are done.  Otherwise update the mismatch count and repair
             * parity if !MD_RECOVERY_CHECK
             */
            if (sh->ops.zero_sum_result == 0)
                  /* parity is correct (on disc,
                   * not in buffer any more)
                   */
                  set_bit(STRIPE_INSYNC, &sh->state);
            else {
                  conf->mddev->resync_mismatches += STRIPE_SECTORS;
                  if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                        /* don't try to repair!! */
                        set_bit(STRIPE_INSYNC, &sh->state);
                  else {
                        sh->check_state = check_state_compute_run;
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute,
                              &sh->dev[sh->pd_idx].flags);
                        sh->ops.target = sh->pd_idx;
                        s->uptodate++;
                  }
            }
            break;
      case check_state_compute_run:
            break;
      default:
            printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                   __func__, sh->check_state,
                   (unsigned long long) sh->sector);
            BUG();
      }
}


static void handle_parity_checks6(raid5_conf_t *conf, struct stripe_head *sh,
                        struct stripe_head_state *s,
                        struct r6_state *r6s, struct page *tmp_page,
                        int disks)
{
      int update_p = 0, update_q = 0;
      struct r5dev *dev;
      int pd_idx = sh->pd_idx;
      int qd_idx = sh->qd_idx;

      set_bit(STRIPE_HANDLE, &sh->state);

      BUG_ON(s->failed > 2);
      BUG_ON(s->uptodate < disks);
      /* Want to check and possibly repair P and Q.
       * However there could be one 'failed' device, in which
       * case we can only check one of them, possibly using the
       * other to generate missing data
       */

      /* If !tmp_page, we cannot do the calculations,
       * but as we have set STRIPE_HANDLE, we will soon be called
       * by stripe_handle with a tmp_page - just wait until then.
       */
      if (tmp_page) {
            if (s->failed == r6s->q_failed) {
                  /* The only possible failed device holds 'Q', so it
                   * makes sense to check P (If anything else were failed,
                   * we would have used P to recreate it).
                   */
                  compute_block_1(sh, pd_idx, 1);
                  if (!page_is_zero(sh->dev[pd_idx].page)) {
                        compute_block_1(sh, pd_idx, 0);
                        update_p = 1;
                  }
            }
            if (!r6s->q_failed && s->failed < 2) {
                  /* q is not failed, and we didn't use it to generate
                   * anything, so it makes sense to check it
                   */
                  memcpy(page_address(tmp_page),
                         page_address(sh->dev[qd_idx].page),
                         STRIPE_SIZE);
                  compute_parity6(sh, UPDATE_PARITY);
                  if (memcmp(page_address(tmp_page),
                           page_address(sh->dev[qd_idx].page),
                           STRIPE_SIZE) != 0) {
                        clear_bit(STRIPE_INSYNC, &sh->state);
                        update_q = 1;
                  }
            }
            if (update_p || update_q) {
                  conf->mddev->resync_mismatches += STRIPE_SECTORS;
                  if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                        /* don't try to repair!! */
                        update_p = update_q = 0;
            }

            /* now write out any block on a failed drive,
             * or P or Q if they need it
             */

            if (s->failed == 2) {
                  dev = &sh->dev[r6s->failed_num[1]];
                  s->locked++;
                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantwrite, &dev->flags);
            }
            if (s->failed >= 1) {
                  dev = &sh->dev[r6s->failed_num[0]];
                  s->locked++;
                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantwrite, &dev->flags);
            }

            if (update_p) {
                  dev = &sh->dev[pd_idx];
                  s->locked++;
                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantwrite, &dev->flags);
            }
            if (update_q) {
                  dev = &sh->dev[qd_idx];
                  s->locked++;
                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantwrite, &dev->flags);
            }
            clear_bit(STRIPE_DEGRADED, &sh->state);

            set_bit(STRIPE_INSYNC, &sh->state);
      }
}

static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh,
                        struct r6_state *r6s)
{
      int i;

      /* We have read all the blocks in this stripe and now we need to
       * copy some of them into a target stripe for expand.
       */
      struct dma_async_tx_descriptor *tx = NULL;
      clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
      for (i = 0; i < sh->disks; i++)
            if (i != sh->pd_idx && i != sh->qd_idx) {
                  int dd_idx, j;
                  struct stripe_head *sh2;

                  sector_t bn = compute_blocknr(sh, i, 1);
                  sector_t s = raid5_compute_sector(conf, bn, 0,
                                            &dd_idx, NULL);
                  sh2 = get_active_stripe(conf, s, 0, 1, 1);
                  if (sh2 == NULL)
                        /* so far only the early blocks of this stripe
                         * have been requested.  When later blocks
                         * get requested, we will try again
                         */
                        continue;
                  if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
                     test_bit(R5_Expanded, &sh2->dev[dd_idx].flags)) {
                        /* must have already done this block */
                        release_stripe(sh2);
                        continue;
                  }

                  /* place all the copies on one channel */
                  tx = async_memcpy(sh2->dev[dd_idx].page,
                        sh->dev[i].page, 0, 0, STRIPE_SIZE,
                        ASYNC_TX_DEP_ACK, tx, NULL, NULL);

                  set_bit(R5_Expanded, &sh2->dev[dd_idx].flags);
                  set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                  for (j = 0; j < conf->raid_disks; j++)
                        if (j != sh2->pd_idx &&
                            (!r6s || j != sh2->qd_idx) &&
                            !test_bit(R5_Expanded, &sh2->dev[j].flags))
                              break;
                  if (j == conf->raid_disks) {
                        set_bit(STRIPE_EXPAND_READY, &sh2->state);
                        set_bit(STRIPE_HANDLE, &sh2->state);
                  }
                  release_stripe(sh2);

            }
      /* done submitting copies, wait for them to complete */
      if (tx) {
            async_tx_ack(tx);
            dma_wait_for_async_tx(tx);
      }
}


/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe and then examine the state of various bits
 * to see what needs to be done.
 * Possible results:
 *    return some read request which now have data
 *    return some write requests which are safely on disc
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static bool handle_stripe5(struct stripe_head *sh)
{
      raid5_conf_t *conf = sh->raid_conf;
      int disks = sh->disks, i;
      struct bio *return_bi = NULL;
      struct stripe_head_state s;
      struct r5dev *dev;
      mdk_rdev_t *blocked_rdev = NULL;
      int prexor;

      memset(&s, 0, sizeof(s));
      pr_debug("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d check:%d "
             "reconstruct:%d\n", (unsigned long long)sh->sector, sh->state,
             atomic_read(&sh->count), sh->pd_idx, sh->check_state,
             sh->reconstruct_state);

      spin_lock(&sh->lock);
      clear_bit(STRIPE_HANDLE, &sh->state);
      clear_bit(STRIPE_DELAYED, &sh->state);

      s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
      s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
      s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);

      /* Now to look around and see what can be done */
      rcu_read_lock();
      for (i=disks; i--; ) {
            mdk_rdev_t *rdev;
            struct r5dev *dev = &sh->dev[i];
            clear_bit(R5_Insync, &dev->flags);

            pr_debug("check %d: state 0x%lx toread %p read %p write %p "
                  "written %p\n",   i, dev->flags, dev->toread, dev->read,
                  dev->towrite, dev->written);

            /* maybe we can request a biofill operation
             *
             * new wantfill requests are only permitted while
             * ops_complete_biofill is guaranteed to be inactive
             */
            if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread &&
                !test_bit(STRIPE_BIOFILL_RUN, &sh->state))
                  set_bit(R5_Wantfill, &dev->flags);

            /* now count some things */
            if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
            if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;
            if (test_bit(R5_Wantcompute, &dev->flags)) s.compute++;

            if (test_bit(R5_Wantfill, &dev->flags))
                  s.to_fill++;
            else if (dev->toread)
                  s.to_read++;
            if (dev->towrite) {
                  s.to_write++;
                  if (!test_bit(R5_OVERWRITE, &dev->flags))
                        s.non_overwrite++;
            }
            if (dev->written)
                  s.written++;
            rdev = rcu_dereference(conf->disks[i].rdev);
            if (blocked_rdev == NULL &&
                rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                  blocked_rdev = rdev;
                  atomic_inc(&rdev->nr_pending);
            }
            if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                  /* The ReadError flag will just be confusing now */
                  clear_bit(R5_ReadError, &dev->flags);
                  clear_bit(R5_ReWrite, &dev->flags);
            }
            if (!rdev || !test_bit(In_sync, &rdev->flags)
                || test_bit(R5_ReadError, &dev->flags)) {
                  s.failed++;
                  s.failed_num = i;
            } else
                  set_bit(R5_Insync, &dev->flags);
      }
      rcu_read_unlock();

      if (unlikely(blocked_rdev)) {
            if (s.syncing || s.expanding || s.expanded ||
                s.to_write || s.written) {
                  set_bit(STRIPE_HANDLE, &sh->state);
                  goto unlock;
            }
            /* There is nothing for the blocked_rdev to block */
            rdev_dec_pending(blocked_rdev, conf->mddev);
            blocked_rdev = NULL;
      }

      if (s.to_fill && !test_bit(STRIPE_BIOFILL_RUN, &sh->state)) {
            set_bit(STRIPE_OP_BIOFILL, &s.ops_request);
            set_bit(STRIPE_BIOFILL_RUN, &sh->state);
      }

      pr_debug("locked=%d uptodate=%d to_read=%d"
            " to_write=%d failed=%d failed_num=%d\n",
            s.locked, s.uptodate, s.to_read, s.to_write,
            s.failed, s.failed_num);
      /* check if the array has lost two devices and, if so, some requests might
       * need to be failed
       */
      if (s.failed > 1 && s.to_read+s.to_write+s.written)
            handle_failed_stripe(conf, sh, &s, disks, &return_bi);
      if (s.failed > 1 && s.syncing) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,0);
            clear_bit(STRIPE_SYNCING, &sh->state);
            s.syncing = 0;
      }

      /* might be able to return some write requests if the parity block
       * is safe, or on a failed drive
       */
      dev = &sh->dev[sh->pd_idx];
      if ( s.written &&
           ((test_bit(R5_Insync, &dev->flags) &&
             !test_bit(R5_LOCKED, &dev->flags) &&
             test_bit(R5_UPTODATE, &dev->flags)) ||
             (s.failed == 1 && s.failed_num == sh->pd_idx)))
            handle_stripe_clean_event(conf, sh, disks, &return_bi);

      /* Now we might consider reading some blocks, either to check/generate
       * parity, or to satisfy requests
       * or to load a block that is being partially written.
       */
      if (s.to_read || s.non_overwrite ||
          (s.syncing && (s.uptodate + s.compute < disks)) || s.expanding)
            handle_stripe_fill5(sh, &s, disks);

      /* Now we check to see if any write operations have recently
       * completed
       */
      prexor = 0;
      if (sh->reconstruct_state == reconstruct_state_prexor_drain_result)
            prexor = 1;
      if (sh->reconstruct_state == reconstruct_state_drain_result ||
          sh->reconstruct_state == reconstruct_state_prexor_drain_result) {
            sh->reconstruct_state = reconstruct_state_idle;

            /* All the 'written' buffers and the parity block are ready to
             * be written back to disk
             */
            BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags));
            for (i = disks; i--; ) {
                  dev = &sh->dev[i];
                  if (test_bit(R5_LOCKED, &dev->flags) &&
                        (i == sh->pd_idx || dev->written)) {
                        pr_debug("Writing block %d\n", i);
                        set_bit(R5_Wantwrite, &dev->flags);
                        if (prexor)
                              continue;
                        if (!test_bit(R5_Insync, &dev->flags) ||
                            (i == sh->pd_idx && s.failed == 0))
                              set_bit(STRIPE_INSYNC, &sh->state);
                  }
            }
            if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                  atomic_dec(&conf->preread_active_stripes);
                  if (atomic_read(&conf->preread_active_stripes) <
                        IO_THRESHOLD)
                        md_wakeup_thread(conf->mddev->thread);
            }
      }

      /* Now to consider new write requests and what else, if anything
       * should be read.  We do not handle new writes when:
       * 1/ A 'write' operation (copy+xor) is already in flight.
       * 2/ A 'check' operation is in flight, as it may clobber the parity
       *    block.
       */
      if (s.to_write && !sh->reconstruct_state && !sh->check_state)
            handle_stripe_dirtying5(conf, sh, &s, disks);

      /* maybe we need to check and possibly fix the parity for this stripe
       * Any reads will already have been scheduled, so we just see if enough
       * data is available.  The parity check is held off while parity
       * dependent operations are in flight.
       */
      if (sh->check_state ||
          (s.syncing && s.locked == 0 &&
           !test_bit(STRIPE_COMPUTE_RUN, &sh->state) &&
           !test_bit(STRIPE_INSYNC, &sh->state)))
            handle_parity_checks5(conf, sh, &s, disks);

      if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,1);
            clear_bit(STRIPE_SYNCING, &sh->state);
      }

      /* If the failed drive is just a ReadError, then we might need to progress
       * the repair/check process
       */
      if (s.failed == 1 && !conf->mddev->ro &&
          test_bit(R5_ReadError, &sh->dev[s.failed_num].flags)
          && !test_bit(R5_LOCKED, &sh->dev[s.failed_num].flags)
          && test_bit(R5_UPTODATE, &sh->dev[s.failed_num].flags)
            ) {
            dev = &sh->dev[s.failed_num];
            if (!test_bit(R5_ReWrite, &dev->flags)) {
                  set_bit(R5_Wantwrite, &dev->flags);
                  set_bit(R5_ReWrite, &dev->flags);
                  set_bit(R5_LOCKED, &dev->flags);
                  s.locked++;
            } else {
                  /* let's read it back */
                  set_bit(R5_Wantread, &dev->flags);
                  set_bit(R5_LOCKED, &dev->flags);
                  s.locked++;
            }
      }

      /* Finish reconstruct operations initiated by the expansion process */
      if (sh->reconstruct_state == reconstruct_state_result) {
            struct stripe_head *sh2
                  = get_active_stripe(conf, sh->sector, 1, 1, 1);
            if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) {
                  /* sh cannot be written until sh2 has been read.
                   * so arrange for sh to be delayed a little
                   */
                  set_bit(STRIPE_DELAYED, &sh->state);
                  set_bit(STRIPE_HANDLE, &sh->state);
                  if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE,
                                    &sh2->state))
                        atomic_inc(&conf->preread_active_stripes);
                  release_stripe(sh2);
                  goto unlock;
            }
            if (sh2)
                  release_stripe(sh2);

            sh->reconstruct_state = reconstruct_state_idle;
            clear_bit(STRIPE_EXPANDING, &sh->state);
            for (i = conf->raid_disks; i--; ) {
                  set_bit(R5_Wantwrite, &sh->dev[i].flags);
                  set_bit(R5_LOCKED, &sh->dev[i].flags);
                  s.locked++;
            }
      }

      if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state) &&
          !sh->reconstruct_state) {
            /* Need to write out all blocks after computing parity */
            sh->disks = conf->raid_disks;
            stripe_set_idx(sh->sector, conf, 0, sh);
            schedule_reconstruction5(sh, &s, 1, 1);
      } else if (s.expanded && !sh->reconstruct_state && s.locked == 0) {
            clear_bit(STRIPE_EXPAND_READY, &sh->state);
            atomic_dec(&conf->reshape_stripes);
            wake_up(&conf->wait_for_overlap);
            md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
      }

      if (s.expanding && s.locked == 0 &&
          !test_bit(STRIPE_COMPUTE_RUN, &sh->state))
            handle_stripe_expansion(conf, sh, NULL);

 unlock:
      spin_unlock(&sh->lock);

      /* wait for this device to become unblocked */
      if (unlikely(blocked_rdev))
            md_wait_for_blocked_rdev(blocked_rdev, conf->mddev);

      if (s.ops_request)
            raid5_run_ops(sh, s.ops_request);

      ops_run_io(sh, &s);

      return_io(return_bi);

      return blocked_rdev == NULL;
}

static bool handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
{
      raid5_conf_t *conf = sh->raid_conf;
      int disks = sh->disks;
      struct bio *return_bi = NULL;
      int i, pd_idx = sh->pd_idx, qd_idx = sh->qd_idx;
      struct stripe_head_state s;
      struct r6_state r6s;
      struct r5dev *dev, *pdev, *qdev;
      mdk_rdev_t *blocked_rdev = NULL;

      pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
            "pd_idx=%d, qd_idx=%d\n",
             (unsigned long long)sh->sector, sh->state,
             atomic_read(&sh->count), pd_idx, qd_idx);
      memset(&s, 0, sizeof(s));

      spin_lock(&sh->lock);
      clear_bit(STRIPE_HANDLE, &sh->state);
      clear_bit(STRIPE_DELAYED, &sh->state);

      s.syncing = test_bit(STRIPE_SYNCING, &sh->state);
      s.expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
      s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
      /* Now to look around and see what can be done */

      rcu_read_lock();
      for (i=disks; i--; ) {
            mdk_rdev_t *rdev;
            dev = &sh->dev[i];
            clear_bit(R5_Insync, &dev->flags);

            pr_debug("check %d: state 0x%lx read %p write %p written %p\n",
                  i, dev->flags, dev->toread, dev->towrite, dev->written);
            /* maybe we can reply to a read */
            if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
                  struct bio *rbi, *rbi2;
                  pr_debug("Return read for disc %d\n", i);
                  spin_lock_irq(&conf->device_lock);
                  rbi = dev->toread;
                  dev->toread = NULL;
                  if (test_and_clear_bit(R5_Overlap, &dev->flags))
                        wake_up(&conf->wait_for_overlap);
                  spin_unlock_irq(&conf->device_lock);
                  while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
                        copy_data(0, rbi, dev->page, dev->sector);
                        rbi2 = r5_next_bio(rbi, dev->sector);
                        spin_lock_irq(&conf->device_lock);
                        if (!raid5_dec_bi_phys_segments(rbi)) {
                              rbi->bi_next = return_bi;
                              return_bi = rbi;
                        }
                        spin_unlock_irq(&conf->device_lock);
                        rbi = rbi2;
                  }
            }

            /* now count some things */
            if (test_bit(R5_LOCKED, &dev->flags)) s.locked++;
            if (test_bit(R5_UPTODATE, &dev->flags)) s.uptodate++;


            if (dev->toread)
                  s.to_read++;
            if (dev->towrite) {
                  s.to_write++;
                  if (!test_bit(R5_OVERWRITE, &dev->flags))
                        s.non_overwrite++;
            }
            if (dev->written)
                  s.written++;
            rdev = rcu_dereference(conf->disks[i].rdev);
            if (blocked_rdev == NULL &&
                rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                  blocked_rdev = rdev;
                  atomic_inc(&rdev->nr_pending);
            }
            if (!rdev || !test_bit(In_sync, &rdev->flags)) {
                  /* The ReadError flag will just be confusing now */
                  clear_bit(R5_ReadError, &dev->flags);
                  clear_bit(R5_ReWrite, &dev->flags);
            }
            if (!rdev || !test_bit(In_sync, &rdev->flags)
                || test_bit(R5_ReadError, &dev->flags)) {
                  if (s.failed < 2)
                        r6s.failed_num[s.failed] = i;
                  s.failed++;
            } else
                  set_bit(R5_Insync, &dev->flags);
      }
      rcu_read_unlock();

      if (unlikely(blocked_rdev)) {
            if (s.syncing || s.expanding || s.expanded ||
                s.to_write || s.written) {
                  set_bit(STRIPE_HANDLE, &sh->state);
                  goto unlock;
            }
            /* There is nothing for the blocked_rdev to block */
            rdev_dec_pending(blocked_rdev, conf->mddev);
            blocked_rdev = NULL;
      }

      pr_debug("locked=%d uptodate=%d to_read=%d"
             " to_write=%d failed=%d failed_num=%d,%d\n",
             s.locked, s.uptodate, s.to_read, s.to_write, s.failed,
             r6s.failed_num[0], r6s.failed_num[1]);
      /* check if the array has lost >2 devices and, if so, some requests
       * might need to be failed
       */
      if (s.failed > 2 && s.to_read+s.to_write+s.written)
            handle_failed_stripe(conf, sh, &s, disks, &return_bi);
      if (s.failed > 2 && s.syncing) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,0);
            clear_bit(STRIPE_SYNCING, &sh->state);
            s.syncing = 0;
      }

      /*
       * might be able to return some write requests if the parity blocks
       * are safe, or on a failed drive
       */
      pdev = &sh->dev[pd_idx];
      r6s.p_failed = (s.failed >= 1 && r6s.failed_num[0] == pd_idx)
            || (s.failed >= 2 && r6s.failed_num[1] == pd_idx);
      qdev = &sh->dev[qd_idx];
      r6s.q_failed = (s.failed >= 1 && r6s.failed_num[0] == qd_idx)
            || (s.failed >= 2 && r6s.failed_num[1] == qd_idx);

      if ( s.written &&
           ( r6s.p_failed || ((test_bit(R5_Insync, &pdev->flags)
                       && !test_bit(R5_LOCKED, &pdev->flags)
                       && test_bit(R5_UPTODATE, &pdev->flags)))) &&
           ( r6s.q_failed || ((test_bit(R5_Insync, &qdev->flags)
                       && !test_bit(R5_LOCKED, &qdev->flags)
                       && test_bit(R5_UPTODATE, &qdev->flags)))))
            handle_stripe_clean_event(conf, sh, disks, &return_bi);

      /* Now we might consider reading some blocks, either to check/generate
       * parity, or to satisfy requests
       * or to load a block that is being partially written.
       */
      if (s.to_read || s.non_overwrite || (s.to_write && s.failed) ||
          (s.syncing && (s.uptodate < disks)) || s.expanding)
            handle_stripe_fill6(sh, &s, &r6s, disks);

      /* now to consider writing and what else, if anything should be read */
      if (s.to_write)
            handle_stripe_dirtying6(conf, sh, &s, &r6s, disks);

      /* maybe we need to check and possibly fix the parity for this stripe
       * Any reads will already have been scheduled, so we just see if enough
       * data is available
       */
      if (s.syncing && s.locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state))
            handle_parity_checks6(conf, sh, &s, &r6s, tmp_page, disks);

      if (s.syncing && s.locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,1);
            clear_bit(STRIPE_SYNCING, &sh->state);
      }

      /* If the failed drives are just a ReadError, then we might need
       * to progress the repair/check process
       */
      if (s.failed <= 2 && !conf->mddev->ro)
            for (i = 0; i < s.failed; i++) {
                  dev = &sh->dev[r6s.failed_num[i]];
                  if (test_bit(R5_ReadError, &dev->flags)
                      && !test_bit(R5_LOCKED, &dev->flags)
                      && test_bit(R5_UPTODATE, &dev->flags)
                        ) {
                        if (!test_bit(R5_ReWrite, &dev->flags)) {
                              set_bit(R5_Wantwrite, &dev->flags);
                              set_bit(R5_ReWrite, &dev->flags);
                              set_bit(R5_LOCKED, &dev->flags);
                        } else {
                              /* let's read it back */
                              set_bit(R5_Wantread, &dev->flags);
                              set_bit(R5_LOCKED, &dev->flags);
                        }
                  }
            }

      if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state)) {
            struct stripe_head *sh2
                  = get_active_stripe(conf, sh->sector, 1, 1, 1);
            if (sh2 && test_bit(STRIPE_EXPAND_SOURCE, &sh2->state)) {
                  /* sh cannot be written until sh2 has been read.
                   * so arrange for sh to be delayed a little
                   */
                  set_bit(STRIPE_DELAYED, &sh->state);
                  set_bit(STRIPE_HANDLE, &sh->state);
                  if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE,
                                    &sh2->state))
                        atomic_inc(&conf->preread_active_stripes);
                  release_stripe(sh2);
                  goto unlock;
            }
            if (sh2)
                  release_stripe(sh2);

            /* Need to write out all blocks after computing P&Q */
            sh->disks = conf->raid_disks;
            stripe_set_idx(sh->sector, conf, 0, sh);
            compute_parity6(sh, RECONSTRUCT_WRITE);
            for (i = conf->raid_disks ; i-- ;  ) {
                  set_bit(R5_LOCKED, &sh->dev[i].flags);
                  s.locked++;
                  set_bit(R5_Wantwrite, &sh->dev[i].flags);
            }
            clear_bit(STRIPE_EXPANDING, &sh->state);
      } else if (s.expanded) {
            clear_bit(STRIPE_EXPAND_READY, &sh->state);
            atomic_dec(&conf->reshape_stripes);
            wake_up(&conf->wait_for_overlap);
            md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
      }

      if (s.expanding && s.locked == 0 &&
          !test_bit(STRIPE_COMPUTE_RUN, &sh->state))
            handle_stripe_expansion(conf, sh, &r6s);

 unlock:
      spin_unlock(&sh->lock);

      /* wait for this device to become unblocked */
      if (unlikely(blocked_rdev))
            md_wait_for_blocked_rdev(blocked_rdev, conf->mddev);

      ops_run_io(sh, &s);

      return_io(return_bi);

      return blocked_rdev == NULL;
}

/* returns true if the stripe was handled */
static bool handle_stripe(struct stripe_head *sh, struct page *tmp_page)
{
      if (sh->raid_conf->level == 6)
            return handle_stripe6(sh, tmp_page);
      else
            return handle_stripe5(sh);
}



static void raid5_activate_delayed(raid5_conf_t *conf)
{
      if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
            while (!list_empty(&conf->delayed_list)) {
                  struct list_head *l = conf->delayed_list.next;
                  struct stripe_head *sh;
                  sh = list_entry(l, struct stripe_head, lru);
                  list_del_init(l);
                  clear_bit(STRIPE_DELAYED, &sh->state);
                  if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                        atomic_inc(&conf->preread_active_stripes);
                  list_add_tail(&sh->lru, &conf->hold_list);
            }
      } else
            blk_plug_device(conf->mddev->queue);
}

static void activate_bit_delay(raid5_conf_t *conf)
{
      /* device_lock is held */
      struct list_head head;
      list_add(&head, &conf->bitmap_list);
      list_del_init(&conf->bitmap_list);
      while (!list_empty(&head)) {
            struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
            list_del_init(&sh->lru);
            atomic_inc(&sh->count);
            __release_stripe(conf, sh);
      }
}

static void unplug_slaves(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev->private;
      int i;

      rcu_read_lock();
      for (i = 0; i < conf->raid_disks; i++) {
            mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
            if (rdev && !test_bit(Faulty, &rdev->flags) && atomic_read(&rdev->nr_pending)) {
                  struct request_queue *r_queue = bdev_get_queue(rdev->bdev);

                  atomic_inc(&rdev->nr_pending);
                  rcu_read_unlock();

                  blk_unplug(r_queue);

                  rdev_dec_pending(rdev, mddev);
                  rcu_read_lock();
            }
      }
      rcu_read_unlock();
}

static void raid5_unplug_device(struct request_queue *q)
{
      mddev_t *mddev = q->queuedata;
      raid5_conf_t *conf = mddev->private;
      unsigned long flags;

      spin_lock_irqsave(&conf->device_lock, flags);

      if (blk_remove_plug(q)) {
            conf->seq_flush++;
            raid5_activate_delayed(conf);
      }
      md_wakeup_thread(mddev->thread);

      spin_unlock_irqrestore(&conf->device_lock, flags);

      unplug_slaves(mddev);
}

static int raid5_congested(void *data, int bits)
{
      mddev_t *mddev = data;
      raid5_conf_t *conf = mddev->private;

      /* No difference between reads and writes.  Just check
       * how busy the stripe_cache is
       */
      if (conf->inactive_blocked)
            return 1;
      if (conf->quiesce)
            return 1;
      if (list_empty_careful(&conf->inactive_list))
            return 1;

      return 0;
}

/* We want read requests to align with chunks where possible,
 * but write requests don't need to.
 */
static int raid5_mergeable_bvec(struct request_queue *q,
                        struct bvec_merge_data *bvm,
                        struct bio_vec *biovec)
{
      mddev_t *mddev = q->queuedata;
      sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
      int max;
      unsigned int chunk_sectors = mddev->chunk_sectors;
      unsigned int bio_sectors = bvm->bi_size >> 9;

      if ((bvm->bi_rw & 1) == WRITE)
            return biovec->bv_len; /* always allow writes to be mergeable */

      if (mddev->new_chunk_sectors < mddev->chunk_sectors)
            chunk_sectors = mddev->new_chunk_sectors;
      max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
      if (max < 0) max = 0;
      if (max <= biovec->bv_len && bio_sectors == 0)
            return biovec->bv_len;
      else
            return max;
}


static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
{
      sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
      unsigned int chunk_sectors = mddev->chunk_sectors;
      unsigned int bio_sectors = bio->bi_size >> 9;

      if (mddev->new_chunk_sectors < mddev->chunk_sectors)
            chunk_sectors = mddev->new_chunk_sectors;
      return  chunk_sectors >=
            ((sector & (chunk_sectors - 1)) + bio_sectors);
}

/*
 *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
 *  later sampled by raid5d.
 */
static void add_bio_to_retry(struct bio *bi,raid5_conf_t *conf)
{
      unsigned long flags;

      spin_lock_irqsave(&conf->device_lock, flags);

      bi->bi_next = conf->retry_read_aligned_list;
      conf->retry_read_aligned_list = bi;

      spin_unlock_irqrestore(&conf->device_lock, flags);
      md_wakeup_thread(conf->mddev->thread);
}


static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
{
      struct bio *bi;

      bi = conf->retry_read_aligned;
      if (bi) {
            conf->retry_read_aligned = NULL;
            return bi;
      }
      bi = conf->retry_read_aligned_list;
      if(bi) {
            conf->retry_read_aligned_list = bi->bi_next;
            bi->bi_next = NULL;
            /*
             * this sets the active strip count to 1 and the processed
             * strip count to zero (upper 8 bits)
             */
            bi->bi_phys_segments = 1; /* biased count of active stripes */
      }

      return bi;
}


/*
 *  The "raid5_align_endio" should check if the read succeeded and if it
 *  did, call bio_endio on the original bio (having bio_put the new bio
 *  first).
 *  If the read failed..
 */
static void raid5_align_endio(struct bio *bi, int error)
{
      struct bio* raid_bi  = bi->bi_private;
      mddev_t *mddev;
      raid5_conf_t *conf;
      int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
      mdk_rdev_t *rdev;

      bio_put(bi);

      mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
      conf = mddev->private;
      rdev = (void*)raid_bi->bi_next;
      raid_bi->bi_next = NULL;

      rdev_dec_pending(rdev, conf->mddev);

      if (!error && uptodate) {
            bio_endio(raid_bi, 0);
            if (atomic_dec_and_test(&conf->active_aligned_reads))
                  wake_up(&conf->wait_for_stripe);
            return;
      }


      pr_debug("raid5_align_endio : io error...handing IO for a retry\n");

      add_bio_to_retry(raid_bi, conf);
}

static int bio_fits_rdev(struct bio *bi)
{
      struct request_queue *q = bdev_get_queue(bi->bi_bdev);

      if ((bi->bi_size>>9) > queue_max_sectors(q))
            return 0;
      blk_recount_segments(q, bi);
      if (bi->bi_phys_segments > queue_max_phys_segments(q))
            return 0;

      if (q->merge_bvec_fn)
            /* it's too hard to apply the merge_bvec_fn at this stage,
             * just just give up
             */
            return 0;

      return 1;
}


static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio)
{
      mddev_t *mddev = q->queuedata;
      raid5_conf_t *conf = mddev->private;
      unsigned int dd_idx;
      struct bio* align_bi;
      mdk_rdev_t *rdev;

      if (!in_chunk_boundary(mddev, raid_bio)) {
            pr_debug("chunk_aligned_read : non aligned\n");
            return 0;
      }
      /*
       * use bio_clone to make a copy of the bio
       */
      align_bi = bio_clone(raid_bio, GFP_NOIO);
      if (!align_bi)
            return 0;
      /*
       *   set bi_end_io to a new function, and set bi_private to the
       *     original bio.
       */
      align_bi->bi_end_io  = raid5_align_endio;
      align_bi->bi_private = raid_bio;
      /*
       *    compute position
       */
      align_bi->bi_sector =  raid5_compute_sector(conf, raid_bio->bi_sector,
                                        0,
                                        &dd_idx, NULL);

      rcu_read_lock();
      rdev = rcu_dereference(conf->disks[dd_idx].rdev);
      if (rdev && test_bit(In_sync, &rdev->flags)) {
            atomic_inc(&rdev->nr_pending);
            rcu_read_unlock();
            raid_bio->bi_next = (void*)rdev;
            align_bi->bi_bdev =  rdev->bdev;
            align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
            align_bi->bi_sector += rdev->data_offset;

            if (!bio_fits_rdev(align_bi)) {
                  /* too big in some way */
                  bio_put(align_bi);
                  rdev_dec_pending(rdev, mddev);
                  return 0;
            }

            spin_lock_irq(&conf->device_lock);
            wait_event_lock_irq(conf->wait_for_stripe,
                            conf->quiesce == 0,
                            conf->device_lock, /* nothing */);
            atomic_inc(&conf->active_aligned_reads);
            spin_unlock_irq(&conf->device_lock);

            generic_make_request(align_bi);
            return 1;
      } else {
            rcu_read_unlock();
            bio_put(align_bi);
            return 0;
      }
}

/* __get_priority_stripe - get the next stripe to process
 *
 * Full stripe writes are allowed to pass preread active stripes up until
 * the bypass_threshold is exceeded.  In general the bypass_count
 * increments when the handle_list is handled before the hold_list; however, it
 * will not be incremented when STRIPE_IO_STARTED is sampled set signifying a
 * stripe with in flight i/o.  The bypass_count will be reset when the
 * head of the hold_list has changed, i.e. the head was promoted to the
 * handle_list.
 */
static struct stripe_head *__get_priority_stripe(raid5_conf_t *conf)
{
      struct stripe_head *sh;

      pr_debug("%s: handle: %s hold: %s full_writes: %d bypass_count: %d\n",
              __func__,
              list_empty(&conf->handle_list) ? "empty" : "busy",
              list_empty(&conf->hold_list) ? "empty" : "busy",
              atomic_read(&conf->pending_full_writes), conf->bypass_count);

      if (!list_empty(&conf->handle_list)) {
            sh = list_entry(conf->handle_list.next, typeof(*sh), lru);

            if (list_empty(&conf->hold_list))
                  conf->bypass_count = 0;
            else if (!test_bit(STRIPE_IO_STARTED, &sh->state)) {
                  if (conf->hold_list.next == conf->last_hold)
                        conf->bypass_count++;
                  else {
                        conf->last_hold = conf->hold_list.next;
                        conf->bypass_count -= conf->bypass_threshold;
                        if (conf->bypass_count < 0)
                              conf->bypass_count = 0;
                  }
            }
      } else if (!list_empty(&conf->hold_list) &&
               ((conf->bypass_threshold &&
                 conf->bypass_count > conf->bypass_threshold) ||
                atomic_read(&conf->pending_full_writes) == 0)) {
            sh = list_entry(conf->hold_list.next,
                        typeof(*sh), lru);
            conf->bypass_count -= conf->bypass_threshold;
            if (conf->bypass_count < 0)
                  conf->bypass_count = 0;
      } else
            return NULL;

      list_del_init(&sh->lru);
      atomic_inc(&sh->count);
      BUG_ON(atomic_read(&sh->count) != 1);
      return sh;
}

static int make_request(struct request_queue *q, struct bio * bi)
{
      mddev_t *mddev = q->queuedata;
      raid5_conf_t *conf = mddev->private;
      int dd_idx;
      sector_t new_sector;
      sector_t logical_sector, last_sector;
      struct stripe_head *sh;
      const int rw = bio_data_dir(bi);
      int cpu, remaining;

      if (unlikely(bio_barrier(bi))) {
            bio_endio(bi, -EOPNOTSUPP);
            return 0;
      }

      md_write_start(mddev, bi);

      cpu = part_stat_lock();
      part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
      part_stat_add(cpu, &mddev->gendisk->part0, sectors[rw],
                  bio_sectors(bi));
      part_stat_unlock();

      if (rw == READ &&
           mddev->reshape_position == MaxSector &&
           chunk_aligned_read(q,bi))
            return 0;

      logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
      last_sector = bi->bi_sector + (bi->bi_size>>9);
      bi->bi_next = NULL;
      bi->bi_phys_segments = 1;     /* over-loaded to count active stripes */

      for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
            DEFINE_WAIT(w);
            int disks, data_disks;
            int previous;

      retry:
            previous = 0;
            disks = conf->raid_disks;
            prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
            if (unlikely(conf->reshape_progress != MaxSector)) {
                  /* spinlock is needed as reshape_progress may be
                   * 64bit on a 32bit platform, and so it might be
                   * possible to see a half-updated value
                   * Ofcourse reshape_progress could change after
                   * the lock is dropped, so once we get a reference
                   * to the stripe that we think it is, we will have
                   * to check again.
                   */
                  spin_lock_irq(&conf->device_lock);
                  if (mddev->delta_disks < 0
                      ? logical_sector < conf->reshape_progress
                      : logical_sector >= conf->reshape_progress) {
                        disks = conf->previous_raid_disks;
                        previous = 1;
                  } else {
                        if (mddev->delta_disks < 0
                            ? logical_sector < conf->reshape_safe
                            : logical_sector >= conf->reshape_safe) {
                              spin_unlock_irq(&conf->device_lock);
                              schedule();
                              goto retry;
                        }
                  }
                  spin_unlock_irq(&conf->device_lock);
            }
            data_disks = disks - conf->max_degraded;

            new_sector = raid5_compute_sector(conf, logical_sector,
                                      previous,
                                      &dd_idx, NULL);
            pr_debug("raid5: make_request, sector %llu logical %llu\n",
                  (unsigned long long)new_sector, 
                  (unsigned long long)logical_sector);

            sh = get_active_stripe(conf, new_sector, previous,
                               (bi->bi_rw&RWA_MASK), 0);
            if (sh) {
                  if (unlikely(previous)) {
                        /* expansion might have moved on while waiting for a
                         * stripe, so we must do the range check again.
                         * Expansion could still move past after this
                         * test, but as we are holding a reference to
                         * 'sh', we know that if that happens,
                         *  STRIPE_EXPANDING will get set and the expansion
                         * won't proceed until we finish with the stripe.
                         */
                        int must_retry = 0;
                        spin_lock_irq(&conf->device_lock);
                        if (mddev->delta_disks < 0
                            ? logical_sector >= conf->reshape_progress
                            : logical_sector < conf->reshape_progress)
                              /* mismatch, need to try again */
                              must_retry = 1;
                        spin_unlock_irq(&conf->device_lock);
                        if (must_retry) {
                              release_stripe(sh);
                              schedule();
                              goto retry;
                        }
                  }

                  if (bio_data_dir(bi) == WRITE &&
                      logical_sector >= mddev->suspend_lo &&
                      logical_sector < mddev->suspend_hi) {
                        release_stripe(sh);
                        /* As the suspend_* range is controlled by
                         * userspace, we want an interruptible
                         * wait.
                         */
                        flush_signals(current);
                        prepare_to_wait(&conf->wait_for_overlap,
                                    &w, TASK_INTERRUPTIBLE);
                        if (logical_sector >= mddev->suspend_lo &&
                            logical_sector < mddev->suspend_hi)
                              schedule();
                        goto retry;
                  }

                  if (test_bit(STRIPE_EXPANDING, &sh->state) ||
                      !add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
                        /* Stripe is busy expanding or
                         * add failed due to overlap.  Flush everything
                         * and wait a while
                         */
                        raid5_unplug_device(mddev->queue);
                        release_stripe(sh);
                        schedule();
                        goto retry;
                  }
                  finish_wait(&conf->wait_for_overlap, &w);
                  set_bit(STRIPE_HANDLE, &sh->state);
                  clear_bit(STRIPE_DELAYED, &sh->state);
                  release_stripe(sh);
            } else {
                  /* cannot get stripe for read-ahead, just give-up */
                  clear_bit(BIO_UPTODATE, &bi->bi_flags);
                  finish_wait(&conf->wait_for_overlap, &w);
                  break;
            }
                  
      }
      spin_lock_irq(&conf->device_lock);
      remaining = raid5_dec_bi_phys_segments(bi);
      spin_unlock_irq(&conf->device_lock);
      if (remaining == 0) {

            if ( rw == WRITE )
                  md_write_end(mddev);

            bio_endio(bi, 0);
      }
      return 0;
}

static sector_t raid5_size(mddev_t *mddev, sector_t sectors, int raid_disks);

static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped)
{
      /* reshaping is quite different to recovery/resync so it is
       * handled quite separately ... here.
       *
       * On each call to sync_request, we gather one chunk worth of
       * destination stripes and flag them as expanding.
       * Then we find all the source stripes and request reads.
       * As the reads complete, handle_stripe will copy the data
       * into the destination stripe and release that stripe.
       */
      raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
      struct stripe_head *sh;
      sector_t first_sector, last_sector;
      int raid_disks = conf->previous_raid_disks;
      int data_disks = raid_disks - conf->max_degraded;
      int new_data_disks = conf->raid_disks - conf->max_degraded;
      int i;
      int dd_idx;
      sector_t writepos, readpos, safepos;
      sector_t stripe_addr;
      int reshape_sectors;
      struct list_head stripes;

      if (sector_nr == 0) {
            /* If restarting in the middle, skip the initial sectors */
            if (mddev->delta_disks < 0 &&
                conf->reshape_progress < raid5_size(mddev, 0, 0)) {
                  sector_nr = raid5_size(mddev, 0, 0)
                        - conf->reshape_progress;
            } else if (mddev->delta_disks >= 0 &&
                     conf->reshape_progress > 0)
                  sector_nr = conf->reshape_progress;
            sector_div(sector_nr, new_data_disks);
            if (sector_nr) {
                  *skipped = 1;
                  return sector_nr;
            }
      }

      /* We need to process a full chunk at a time.
       * If old and new chunk sizes differ, we need to process the
       * largest of these
       */
      if (mddev->new_chunk_sectors > mddev->chunk_sectors)
            reshape_sectors = mddev->new_chunk_sectors;
      else
            reshape_sectors = mddev->chunk_sectors;

      /* we update the metadata when there is more than 3Meg
       * in the block range (that is rather arbitrary, should
       * probably be time based) or when the data about to be
       * copied would over-write the source of the data at
       * the front of the range.
       * i.e. one new_stripe along from reshape_progress new_maps
       * to after where reshape_safe old_maps to
       */
      writepos = conf->reshape_progress;
      sector_div(writepos, new_data_disks);
      readpos = conf->reshape_progress;
      sector_div(readpos, data_disks);
      safepos = conf->reshape_safe;
      sector_div(safepos, data_disks);
      if (mddev->delta_disks < 0) {
            writepos -= min_t(sector_t, reshape_sectors, writepos);
            readpos += reshape_sectors;
            safepos += reshape_sectors;
      } else {
            writepos += reshape_sectors;
            readpos -= min_t(sector_t, reshape_sectors, readpos);
            safepos -= min_t(sector_t, reshape_sectors, safepos);
      }

      /* 'writepos' is the most advanced device address we might write.
       * 'readpos' is the least advanced device address we might read.
       * 'safepos' is the least address recorded in the metadata as having
       *     been reshaped.
       * If 'readpos' is behind 'writepos', then there is no way that we can
       * ensure safety in the face of a crash - that must be done by userspace
       * making a backup of the data.  So in that case there is no particular
       * rush to update metadata.
       * Otherwise if 'safepos' is behind 'writepos', then we really need to
       * update the metadata to advance 'safepos' to match 'readpos' so that
       * we can be safe in the event of a crash.
       * So we insist on updating metadata if safepos is behind writepos and
       * readpos is beyond writepos.
       * In any case, update the metadata every 10 seconds.
       * Maybe that number should be configurable, but I'm not sure it is
       * worth it.... maybe it could be a multiple of safemode_delay???
       */
      if ((mddev->delta_disks < 0
           ? (safepos > writepos && readpos < writepos)
           : (safepos < writepos && readpos > writepos)) ||
          time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
            /* Cannot proceed until we've updated the superblock... */
            wait_event(conf->wait_for_overlap,
                     atomic_read(&conf->reshape_stripes)==0);
            mddev->reshape_position = conf->reshape_progress;
            mddev->curr_resync_completed = mddev->curr_resync;
            conf->reshape_checkpoint = jiffies;
            set_bit(MD_CHANGE_DEVS, &mddev->flags);
            md_wakeup_thread(mddev->thread);
            wait_event(mddev->sb_wait, mddev->flags == 0 ||
                     kthread_should_stop());
            spin_lock_irq(&conf->device_lock);
            conf->reshape_safe = mddev->reshape_position;
            spin_unlock_irq(&conf->device_lock);
            wake_up(&conf->wait_for_overlap);
            sysfs_notify(&mddev->kobj, NULL, "sync_completed");
      }

      if (mddev->delta_disks < 0) {
            BUG_ON(conf->reshape_progress == 0);
            stripe_addr = writepos;
            BUG_ON((mddev->dev_sectors &
                  ~((sector_t)reshape_sectors - 1))
                   - reshape_sectors - stripe_addr
                   != sector_nr);
      } else {
            BUG_ON(writepos != sector_nr + reshape_sectors);
            stripe_addr = sector_nr;
      }
      INIT_LIST_HEAD(&stripes);
      for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
            int j;
            int skipped = 0;
            sh = get_active_stripe(conf, stripe_addr+i, 0, 0, 1);
            set_bit(STRIPE_EXPANDING, &sh->state);
            atomic_inc(&conf->reshape_stripes);
            /* If any of this stripe is beyond the end of the old
             * array, then we need to zero those blocks
             */
            for (j=sh->disks; j--;) {
                  sector_t s;
                  if (j == sh->pd_idx)
                        continue;
                  if (conf->level == 6 &&
                      j == sh->qd_idx)
                        continue;
                  s = compute_blocknr(sh, j, 0);
                  if (s < raid5_size(mddev, 0, 0)) {
                        skipped = 1;
                        continue;
                  }
                  memset(page_address(sh->dev[j].page), 0, STRIPE_SIZE);
                  set_bit(R5_Expanded, &sh->dev[j].flags);
                  set_bit(R5_UPTODATE, &sh->dev[j].flags);
            }
            if (!skipped) {
                  set_bit(STRIPE_EXPAND_READY, &sh->state);
                  set_bit(STRIPE_HANDLE, &sh->state);
            }
            list_add(&sh->lru, &stripes);
      }
      spin_lock_irq(&conf->device_lock);
      if (mddev->delta_disks < 0)
            conf->reshape_progress -= reshape_sectors * new_data_disks;
      else
            conf->reshape_progress += reshape_sectors * new_data_disks;
      spin_unlock_irq(&conf->device_lock);
      /* Ok, those stripe are ready. We can start scheduling
       * reads on the source stripes.
       * The source stripes are determined by mapping the first and last
       * block on the destination stripes.
       */
      first_sector =
            raid5_compute_sector(conf, stripe_addr*(new_data_disks),
                             1, &dd_idx, NULL);
      last_sector =
            raid5_compute_sector(conf, ((stripe_addr+reshape_sectors)
                                  * new_data_disks - 1),
                             1, &dd_idx, NULL);
      if (last_sector >= mddev->dev_sectors)
            last_sector = mddev->dev_sectors - 1;
      while (first_sector <= last_sector) {
            sh = get_active_stripe(conf, first_sector, 1, 0, 1);
            set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
            set_bit(STRIPE_HANDLE, &sh->state);
            release_stripe(sh);
            first_sector += STRIPE_SECTORS;
      }
      /* Now that the sources are clearly marked, we can release
       * the destination stripes
       */
      while (!list_empty(&stripes)) {
            sh = list_entry(stripes.next, struct stripe_head, lru);
            list_del_init(&sh->lru);
            release_stripe(sh);
      }
      /* If this takes us to the resync_max point where we have to pause,
       * then we need to write out the superblock.
       */
      sector_nr += reshape_sectors;
      if ((sector_nr - mddev->curr_resync_completed) * 2
          >= mddev->resync_max - mddev->curr_resync_completed) {
            /* Cannot proceed until we've updated the superblock... */
            wait_event(conf->wait_for_overlap,
                     atomic_read(&conf->reshape_stripes) == 0);
            mddev->reshape_position = conf->reshape_progress;
            mddev->curr_resync_completed = mddev->curr_resync + reshape_sectors;
            conf->reshape_checkpoint = jiffies;
            set_bit(MD_CHANGE_DEVS, &mddev->flags);
            md_wakeup_thread(mddev->thread);
            wait_event(mddev->sb_wait,
                     !test_bit(MD_CHANGE_DEVS, &mddev->flags)
                     || kthread_should_stop());
            spin_lock_irq(&conf->device_lock);
            conf->reshape_safe = mddev->reshape_position;
            spin_unlock_irq(&conf->device_lock);
            wake_up(&conf->wait_for_overlap);
            sysfs_notify(&mddev->kobj, NULL, "sync_completed");
      }
      return reshape_sectors;
}

/* FIXME go_faster isn't used */
static inline sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, int go_faster)
{
      raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
      struct stripe_head *sh;
      sector_t max_sector = mddev->dev_sectors;
      int sync_blocks;
      int still_degraded = 0;
      int i;

      if (sector_nr >= max_sector) {
            /* just being told to finish up .. nothing much to do */
            unplug_slaves(mddev);

            if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
                  end_reshape(conf);
                  return 0;
            }

            if (mddev->curr_resync < max_sector) /* aborted */
                  bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                              &sync_blocks, 1);
            else /* completed sync */
                  conf->fullsync = 0;
            bitmap_close_sync(mddev->bitmap);

            return 0;
      }

      /* Allow raid5_quiesce to complete */
      wait_event(conf->wait_for_overlap, conf->quiesce != 2);

      if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
            return reshape_request(mddev, sector_nr, skipped);

      /* No need to check resync_max as we never do more than one
       * stripe, and as resync_max will always be on a chunk boundary,
       * if the check in md_do_sync didn't fire, there is no chance
       * of overstepping resync_max here
       */

      /* if there is too many failed drives and we are trying
       * to resync, then assert that we are finished, because there is
       * nothing we can do.
       */
      if (mddev->degraded >= conf->max_degraded &&
          test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
            sector_t rv = mddev->dev_sectors - sector_nr;
            *skipped = 1;
            return rv;
      }
      if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
          !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
          !conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
            /* we can skip this block, and probably more */
            sync_blocks /= STRIPE_SECTORS;
            *skipped = 1;
            return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
      }


      bitmap_cond_end_sync(mddev->bitmap, sector_nr);

      sh = get_active_stripe(conf, sector_nr, 0, 1, 0);
      if (sh == NULL) {
            sh = get_active_stripe(conf, sector_nr, 0, 0, 0);
            /* make sure we don't swamp the stripe cache if someone else
             * is trying to get access
             */
            schedule_timeout_uninterruptible(1);
      }
      /* Need to check if array will still be degraded after recovery/resync
       * We don't need to check the 'failed' flag as when that gets set,
       * recovery aborts.
       */
      for (i = 0; i < conf->raid_disks; i++)
            if (conf->disks[i].rdev == NULL)
                  still_degraded = 1;

      bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);

      spin_lock(&sh->lock);
      set_bit(STRIPE_SYNCING, &sh->state);
      clear_bit(STRIPE_INSYNC, &sh->state);
      spin_unlock(&sh->lock);

      /* wait for any blocked device to be handled */
      while(unlikely(!handle_stripe(sh, NULL)))
            ;
      release_stripe(sh);

      return STRIPE_SECTORS;
}

static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
{
      /* We may not be able to submit a whole bio at once as there
       * may not be enough stripe_heads available.
       * We cannot pre-allocate enough stripe_heads as we may need
       * more than exist in the cache (if we allow ever large chunks).
       * So we do one stripe head at a time and record in
       * ->bi_hw_segments how many have been done.
       *
       * We *know* that this entire raid_bio is in one chunk, so
       * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
       */
      struct stripe_head *sh;
      int dd_idx;
      sector_t sector, logical_sector, last_sector;
      int scnt = 0;
      int remaining;
      int handled = 0;

      logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
      sector = raid5_compute_sector(conf, logical_sector,
                              0, &dd_idx, NULL);
      last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);

      for (; logical_sector < last_sector;
           logical_sector += STRIPE_SECTORS,
                 sector += STRIPE_SECTORS,
                 scnt++) {

            if (scnt < raid5_bi_hw_segments(raid_bio))
                  /* already done this stripe */
                  continue;

            sh = get_active_stripe(conf, sector, 0, 1, 0);

            if (!sh) {
                  /* failed to get a stripe - must wait */
                  raid5_set_bi_hw_segments(raid_bio, scnt);
                  conf->retry_read_aligned = raid_bio;
                  return handled;
            }

            set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
            if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {
                  release_stripe(sh);
                  raid5_set_bi_hw_segments(raid_bio, scnt);
                  conf->retry_read_aligned = raid_bio;
                  return handled;
            }

            handle_stripe(sh, NULL);
            release_stripe(sh);
            handled++;
      }
      spin_lock_irq(&conf->device_lock);
      remaining = raid5_dec_bi_phys_segments(raid_bio);
      spin_unlock_irq(&conf->device_lock);
      if (remaining == 0)
            bio_endio(raid_bio, 0);
      if (atomic_dec_and_test(&conf->active_aligned_reads))
            wake_up(&conf->wait_for_stripe);
      return handled;
}



/*
 * This is our raid5 kernel thread.
 *
 * We scan the hash table for stripes which can be handled now.
 * During the scan, completed stripes are saved for us by the interrupt
 * handler, so that they will not have to wait for our next wakeup.
 */
static void raid5d(mddev_t *mddev)
{
      struct stripe_head *sh;
      raid5_conf_t *conf = mddev->private;
      int handled;

      pr_debug("+++ raid5d active\n");

      md_check_recovery(mddev);

      handled = 0;
      spin_lock_irq(&conf->device_lock);
      while (1) {
            struct bio *bio;

            if (conf->seq_flush != conf->seq_write) {
                  int seq = conf->seq_flush;
                  spin_unlock_irq(&conf->device_lock);
                  bitmap_unplug(mddev->bitmap);
                  spin_lock_irq(&conf->device_lock);
                  conf->seq_write = seq;
                  activate_bit_delay(conf);
            }

            while ((bio = remove_bio_from_retry(conf))) {
                  int ok;
                  spin_unlock_irq(&conf->device_lock);
                  ok = retry_aligned_read(conf, bio);
                  spin_lock_irq(&conf->device_lock);
                  if (!ok)
                        break;
                  handled++;
            }

            sh = __get_priority_stripe(conf);

            if (!sh)
                  break;
            spin_unlock_irq(&conf->device_lock);
            
            handled++;
            handle_stripe(sh, conf->spare_page);
            release_stripe(sh);

            spin_lock_irq(&conf->device_lock);
      }
      pr_debug("%d stripes handled\n", handled);

      spin_unlock_irq(&conf->device_lock);

      async_tx_issue_pending_all();
      unplug_slaves(mddev);

      pr_debug("--- raid5d inactive\n");
}

static ssize_t
raid5_show_stripe_cache_size(mddev_t *mddev, char *page)
{
      raid5_conf_t *conf = mddev->private;
      if (conf)
            return sprintf(page, "%d\n", conf->max_nr_stripes);
      else
            return 0;
}

static ssize_t
raid5_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
{
      raid5_conf_t *conf = mddev->private;
      unsigned long new;
      int err;

      if (len >= PAGE_SIZE)
            return -EINVAL;
      if (!conf)
            return -ENODEV;

      if (strict_strtoul(page, 10, &new))
            return -EINVAL;
      if (new <= 16 || new > 32768)
            return -EINVAL;
      while (new < conf->max_nr_stripes) {
            if (drop_one_stripe(conf))
                  conf->max_nr_stripes--;
            else
                  break;
      }
      err = md_allow_write(mddev);
      if (err)
            return err;
      while (new > conf->max_nr_stripes) {
            if (grow_one_stripe(conf))
                  conf->max_nr_stripes++;
            else break;
      }
      return len;
}

static struct md_sysfs_entry
raid5_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR,
                        raid5_show_stripe_cache_size,
                        raid5_store_stripe_cache_size);

static ssize_t
raid5_show_preread_threshold(mddev_t *mddev, char *page)
{
      raid5_conf_t *conf = mddev->private;
      if (conf)
            return sprintf(page, "%d\n", conf->bypass_threshold);
      else
            return 0;
}

static ssize_t
raid5_store_preread_threshold(mddev_t *mddev, const char *page, size_t len)
{
      raid5_conf_t *conf = mddev->private;
      unsigned long new;
      if (len >= PAGE_SIZE)
            return -EINVAL;
      if (!conf)
            return -ENODEV;

      if (strict_strtoul(page, 10, &new))
            return -EINVAL;
      if (new > conf->max_nr_stripes)
            return -EINVAL;
      conf->bypass_threshold = new;
      return len;
}

static struct md_sysfs_entry
raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,
                              S_IRUGO | S_IWUSR,
                              raid5_show_preread_threshold,
                              raid5_store_preread_threshold);

static ssize_t
stripe_cache_active_show(mddev_t *mddev, char *page)
{
      raid5_conf_t *conf = mddev->private;
      if (conf)
            return sprintf(page, "%d\n", atomic_read(&conf->active_stripes));
      else
            return 0;
}

static struct md_sysfs_entry
raid5_stripecache_active = __ATTR_RO(stripe_cache_active);

static struct attribute *raid5_attrs[] =  {
      &raid5_stripecache_size.attr,
      &raid5_stripecache_active.attr,
      &raid5_preread_bypass_threshold.attr,
      NULL,
};
static struct attribute_group raid5_attrs_group = {
      .name = NULL,
      .attrs = raid5_attrs,
};

static sector_t
raid5_size(mddev_t *mddev, sector_t sectors, int raid_disks)
{
      raid5_conf_t *conf = mddev->private;

      if (!sectors)
            sectors = mddev->dev_sectors;
      if (!raid_disks) {
            /* size is defined by the smallest of previous and new size */
            if (conf->raid_disks < conf->previous_raid_disks)
                  raid_disks = conf->raid_disks;
            else
                  raid_disks = conf->previous_raid_disks;
      }

      sectors &= ~((sector_t)mddev->chunk_sectors - 1);
      sectors &= ~((sector_t)mddev->new_chunk_sectors - 1);
      return sectors * (raid_disks - conf->max_degraded);
}

static void free_conf(raid5_conf_t *conf)
{
      shrink_stripes(conf);
      safe_put_page(conf->spare_page);
      kfree(conf->disks);
      kfree(conf->stripe_hashtbl);
      kfree(conf);
}

static raid5_conf_t *setup_conf(mddev_t *mddev)
{
      raid5_conf_t *conf;
      int raid_disk, memory;
      mdk_rdev_t *rdev;
      struct disk_info *disk;

      if (mddev->new_level != 5
          && mddev->new_level != 4
          && mddev->new_level != 6) {
            printk(KERN_ERR "raid5: %s: raid level not set to 4/5/6 (%d)\n",
                   mdname(mddev), mddev->new_level);
            return ERR_PTR(-EIO);
      }
      if ((mddev->new_level == 5
           && !algorithm_valid_raid5(mddev->new_layout)) ||
          (mddev->new_level == 6
           && !algorithm_valid_raid6(mddev->new_layout))) {
            printk(KERN_ERR "raid5: %s: layout %d not supported\n",
                   mdname(mddev), mddev->new_layout);
            return ERR_PTR(-EIO);
      }
      if (mddev->new_level == 6 && mddev->raid_disks < 4) {
            printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
                   mdname(mddev), mddev->raid_disks);
            return ERR_PTR(-EINVAL);
      }

      if (!mddev->new_chunk_sectors ||
          (mddev->new_chunk_sectors << 9) % PAGE_SIZE ||
          !is_power_of_2(mddev->new_chunk_sectors)) {
            printk(KERN_ERR "raid5: invalid chunk size %d for %s\n",
                   mddev->new_chunk_sectors << 9, mdname(mddev));
            return ERR_PTR(-EINVAL);
      }

      conf = kzalloc(sizeof(raid5_conf_t), GFP_KERNEL);
      if (conf == NULL)
            goto abort;

      conf->raid_disks = mddev->raid_disks;
      if (mddev->reshape_position == MaxSector)
            conf->previous_raid_disks = mddev->raid_disks;
      else
            conf->previous_raid_disks = mddev->raid_disks - mddev->delta_disks;

      conf->disks = kzalloc(conf->raid_disks * sizeof(struct disk_info),
                        GFP_KERNEL);
      if (!conf->disks)
            goto abort;

      conf->mddev = mddev;

      if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
            goto abort;

      if (mddev->new_level == 6) {
            conf->spare_page = alloc_page(GFP_KERNEL);
            if (!conf->spare_page)
                  goto abort;
      }
      spin_lock_init(&conf->device_lock);
      init_waitqueue_head(&conf->wait_for_stripe);
      init_waitqueue_head(&conf->wait_for_overlap);
      INIT_LIST_HEAD(&conf->handle_list);
      INIT_LIST_HEAD(&conf->hold_list);
      INIT_LIST_HEAD(&conf->delayed_list);
      INIT_LIST_HEAD(&conf->bitmap_list);
      INIT_LIST_HEAD(&conf->inactive_list);
      atomic_set(&conf->active_stripes, 0);
      atomic_set(&conf->preread_active_stripes, 0);
      atomic_set(&conf->active_aligned_reads, 0);
      conf->bypass_threshold = BYPASS_THRESHOLD;

      pr_debug("raid5: run(%s) called.\n", mdname(mddev));

      list_for_each_entry(rdev, &mddev->disks, same_set) {
            raid_disk = rdev->raid_disk;
            if (raid_disk >= conf->raid_disks
                || raid_disk < 0)
                  continue;
            disk = conf->disks + raid_disk;

            disk->rdev = rdev;

            if (test_bit(In_sync, &rdev->flags)) {
                  char b[BDEVNAME_SIZE];
                  printk(KERN_INFO "raid5: device %s operational as raid"
                        " disk %d\n", bdevname(rdev->bdev,b),
                        raid_disk);
            } else
                  /* Cannot rely on bitmap to complete recovery */
                  conf->fullsync = 1;
      }

      conf->chunk_sectors = mddev->new_chunk_sectors;
      conf->level = mddev->new_level;
      if (conf->level == 6)
            conf->max_degraded = 2;
      else
            conf->max_degraded = 1;
      conf->algorithm = mddev->new_layout;
      conf->max_nr_stripes = NR_STRIPES;
      conf->reshape_progress = mddev->reshape_position;
      if (conf->reshape_progress != MaxSector) {
            conf->prev_chunk_sectors = mddev->chunk_sectors;
            conf->prev_algo = mddev->layout;
      }

      memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
             conf->raid_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
      if (grow_stripes(conf, conf->max_nr_stripes)) {
            printk(KERN_ERR
                  "raid5: couldn't allocate %dkB for buffers\n", memory);
            goto abort;
      } else
            printk(KERN_INFO "raid5: allocated %dkB for %s\n",
                  memory, mdname(mddev));

      conf->thread = md_register_thread(raid5d, mddev, "%s_raid5");
      if (!conf->thread) {
            printk(KERN_ERR
                   "raid5: couldn't allocate thread for %s\n",
                   mdname(mddev));
            goto abort;
      }

      return conf;

 abort:
      if (conf) {
            free_conf(conf);
            return ERR_PTR(-EIO);
      } else
            return ERR_PTR(-ENOMEM);
}

static int run(mddev_t *mddev)
{
      raid5_conf_t *conf;
      int working_disks = 0, chunk_size;
      mdk_rdev_t *rdev;

      if (mddev->recovery_cp != MaxSector)
            printk(KERN_NOTICE "raid5: %s is not clean"
                   " -- starting background reconstruction\n",
                   mdname(mddev));
      if (mddev->reshape_position != MaxSector) {
            /* Check that we can continue the reshape.
             * Currently only disks can change, it must
             * increase, and we must be past the point where
             * a stripe over-writes itself
             */
            sector_t here_new, here_old;
            int old_disks;
            int max_degraded = (mddev->level == 6 ? 2 : 1);

            if (mddev->new_level != mddev->level) {
                  printk(KERN_ERR "raid5: %s: unsupported reshape "
                         "required - aborting.\n",
                         mdname(mddev));
                  return -EINVAL;
            }
            old_disks = mddev->raid_disks - mddev->delta_disks;
            /* reshape_position must be on a new-stripe boundary, and one
             * further up in new geometry must map after here in old
             * geometry.
             */
            here_new = mddev->reshape_position;
            if (sector_div(here_new, mddev->new_chunk_sectors *
                         (mddev->raid_disks - max_degraded))) {
                  printk(KERN_ERR "raid5: reshape_position not "
                         "on a stripe boundary\n");
                  return -EINVAL;
            }
            /* here_new is the stripe we will write to */
            here_old = mddev->reshape_position;
            sector_div(here_old, mddev->chunk_sectors *
                     (old_disks-max_degraded));
            /* here_old is the first stripe that we might need to read
             * from */
            if (mddev->delta_disks == 0) {
                  /* We cannot be sure it is safe to start an in-place
                   * reshape.  It is only safe if user-space if monitoring
                   * and taking constant backups.
                   * mdadm always starts a situation like this in
                   * readonly mode so it can take control before
                   * allowing any writes.  So just check for that.
                   */
                  if ((here_new * mddev->new_chunk_sectors != 
                       here_old * mddev->chunk_sectors) ||
                      mddev->ro == 0) {
                        printk(KERN_ERR "raid5: in-place reshape must be started"
                               " in read-only mode - aborting\n");
                        return -EINVAL;
                  }
            } else if (mddev->delta_disks < 0
                ? (here_new * mddev->new_chunk_sectors <=
                   here_old * mddev->chunk_sectors)
                : (here_new * mddev->new_chunk_sectors >=
                   here_old * mddev->chunk_sectors)) {
                  /* Reading from the same stripe as writing to - bad */
                  printk(KERN_ERR "raid5: reshape_position too early for "
                         "auto-recovery - aborting.\n");
                  return -EINVAL;
            }
            printk(KERN_INFO "raid5: reshape will continue\n");
            /* OK, we should be able to continue; */
      } else {
            BUG_ON(mddev->level != mddev->new_level);
            BUG_ON(mddev->layout != mddev->new_layout);
            BUG_ON(mddev->chunk_sectors != mddev->new_chunk_sectors);
            BUG_ON(mddev->delta_disks != 0);
      }

      if (mddev->private == NULL)
            conf = setup_conf(mddev);
      else
            conf = mddev->private;

      if (IS_ERR(conf))
            return PTR_ERR(conf);

      mddev->thread = conf->thread;
      conf->thread = NULL;
      mddev->private = conf;

      /*
       * 0 for a fully functional array, 1 or 2 for a degraded array.
       */
      list_for_each_entry(rdev, &mddev->disks, same_set)
            if (rdev->raid_disk >= 0 &&
                test_bit(In_sync, &rdev->flags))
                  working_disks++;

      mddev->degraded = conf->raid_disks - working_disks;

      if (mddev->degraded > conf->max_degraded) {
            printk(KERN_ERR "raid5: not enough operational devices for %s"
                  " (%d/%d failed)\n",
                  mdname(mddev), mddev->degraded, conf->raid_disks);
            goto abort;
      }

      /* device size must be a multiple of chunk size */
      mddev->dev_sectors &= ~(mddev->chunk_sectors - 1);
      mddev->resync_max_sectors = mddev->dev_sectors;

      if (mddev->degraded > 0 &&
          mddev->recovery_cp != MaxSector) {
            if (mddev->ok_start_degraded)
                  printk(KERN_WARNING
                         "raid5: starting dirty degraded array: %s"
                         "- data corruption possible.\n",
                         mdname(mddev));
            else {
                  printk(KERN_ERR
                         "raid5: cannot start dirty degraded array for %s\n",
                         mdname(mddev));
                  goto abort;
            }
      }

      if (mddev->degraded == 0)
            printk("raid5: raid level %d set %s active with %d out of %d"
                   " devices, algorithm %d\n", conf->level, mdname(mddev),
                   mddev->raid_disks-mddev->degraded, mddev->raid_disks,
                   mddev->new_layout);
      else
            printk(KERN_ALERT "raid5: raid level %d set %s active with %d"
                  " out of %d devices, algorithm %d\n", conf->level,
                  mdname(mddev), mddev->raid_disks - mddev->degraded,
                  mddev->raid_disks, mddev->new_layout);

      print_raid5_conf(conf);

      if (conf->reshape_progress != MaxSector) {
            printk("...ok start reshape thread\n");
            conf->reshape_safe = conf->reshape_progress;
            atomic_set(&conf->reshape_stripes, 0);
            clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
            clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
            set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
            set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
            mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                          "%s_reshape");
      }

      /* read-ahead size must cover two whole stripes, which is
       * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
       */
      {
            int data_disks = conf->previous_raid_disks - conf->max_degraded;
            int stripe = data_disks *
                  ((mddev->chunk_sectors << 9) / PAGE_SIZE);
            if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                  mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
      }

      /* Ok, everything is just fine now */
      if (sysfs_create_group(&mddev->kobj, &raid5_attrs_group))
            printk(KERN_WARNING
                   "raid5: failed to create sysfs attributes for %s\n",
                   mdname(mddev));

      mddev->queue->queue_lock = &conf->device_lock;

      mddev->queue->unplug_fn = raid5_unplug_device;
      mddev->queue->backing_dev_info.congested_data = mddev;
      mddev->queue->backing_dev_info.congested_fn = raid5_congested;

      md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));

      blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);
      chunk_size = mddev->chunk_sectors << 9;
      blk_queue_io_min(mddev->queue, chunk_size);
      blk_queue_io_opt(mddev->queue, chunk_size *
                   (conf->raid_disks - conf->max_degraded));

      list_for_each_entry(rdev, &mddev->disks, same_set)
            disk_stack_limits(mddev->gendisk, rdev->bdev,
                          rdev->data_offset << 9);

      return 0;
abort:
      md_unregister_thread(mddev->thread);
      mddev->thread = NULL;
      if (conf) {
            print_raid5_conf(conf);
            free_conf(conf);
      }
      mddev->private = NULL;
      printk(KERN_ALERT "raid5: failed to run raid set %s\n", mdname(mddev));
      return -EIO;
}



static int stop(mddev_t *mddev)
{
      raid5_conf_t *conf = (raid5_conf_t *) mddev->private;

      md_unregister_thread(mddev->thread);
      mddev->thread = NULL;
      mddev->queue->backing_dev_info.congested_fn = NULL;
      blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
      sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
      free_conf(conf);
      mddev->private = NULL;
      return 0;
}

#ifdef DEBUG
static void print_sh(struct seq_file *seq, struct stripe_head *sh)
{
      int i;

      seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
               (unsigned long long)sh->sector, sh->pd_idx, sh->state);
      seq_printf(seq, "sh %llu,  count %d.\n",
               (unsigned long long)sh->sector, atomic_read(&sh->count));
      seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
      for (i = 0; i < sh->disks; i++) {
            seq_printf(seq, "(cache%d: %p %ld) ",
                     i, sh->dev[i].page, sh->dev[i].flags);
      }
      seq_printf(seq, "\n");
}

static void printall(struct seq_file *seq, raid5_conf_t *conf)
{
      struct stripe_head *sh;
      struct hlist_node *hn;
      int i;

      spin_lock_irq(&conf->device_lock);
      for (i = 0; i < NR_HASH; i++) {
            hlist_for_each_entry(sh, hn, &conf->stripe_hashtbl[i], hash) {
                  if (sh->raid_conf != conf)
                        continue;
                  print_sh(seq, sh);
            }
      }
      spin_unlock_irq(&conf->device_lock);
}
#endif

static void status(struct seq_file *seq, mddev_t *mddev)
{
      raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
      int i;

      seq_printf(seq, " level %d, %dk chunk, algorithm %d", mddev->level,
            mddev->chunk_sectors / 2, mddev->layout);
      seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->raid_disks - mddev->degraded);
      for (i = 0; i < conf->raid_disks; i++)
            seq_printf (seq, "%s",
                         conf->disks[i].rdev &&
                         test_bit(In_sync, &conf->disks[i].rdev->flags) ? "U" : "_");
      seq_printf (seq, "]");
#ifdef DEBUG
      seq_printf (seq, "\n");
      printall(seq, conf);
#endif
}

static void print_raid5_conf (raid5_conf_t *conf)
{
      int i;
      struct disk_info *tmp;

      printk("RAID5 conf printout:\n");
      if (!conf) {
            printk("(conf==NULL)\n");
            return;
      }
      printk(" --- rd:%d wd:%d\n", conf->raid_disks,
             conf->raid_disks - conf->mddev->degraded);

      for (i = 0; i < conf->raid_disks; i++) {
            char b[BDEVNAME_SIZE];
            tmp = conf->disks + i;
            if (tmp->rdev)
            printk(" disk %d, o:%d, dev:%s\n",
                  i, !test_bit(Faulty, &tmp->rdev->flags),
                  bdevname(tmp->rdev->bdev,b));
      }
}

static int raid5_spare_active(mddev_t *mddev)
{
      int i;
      raid5_conf_t *conf = mddev->private;
      struct disk_info *tmp;

      for (i = 0; i < conf->raid_disks; i++) {
            tmp = conf->disks + i;
            if (tmp->rdev
                && !test_bit(Faulty, &tmp->rdev->flags)
                && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
                  unsigned long flags;
                  spin_lock_irqsave(&conf->device_lock, flags);
                  mddev->degraded--;
                  spin_unlock_irqrestore(&conf->device_lock, flags);
            }
      }
      print_raid5_conf(conf);
      return 0;
}

static int raid5_remove_disk(mddev_t *mddev, int number)
{
      raid5_conf_t *conf = mddev->private;
      int err = 0;
      mdk_rdev_t *rdev;
      struct disk_info *p = conf->disks + number;

      print_raid5_conf(conf);
      rdev = p->rdev;
      if (rdev) {
            if (number >= conf->raid_disks &&
                conf->reshape_progress == MaxSector)
                  clear_bit(In_sync, &rdev->flags);

            if (test_bit(In_sync, &rdev->flags) ||
                atomic_read(&rdev->nr_pending)) {
                  err = -EBUSY;
                  goto abort;
            }
            /* Only remove non-faulty devices if recovery
             * isn't possible.
             */
            if (!test_bit(Faulty, &rdev->flags) &&
                mddev->degraded <= conf->max_degraded &&
                number < conf->raid_disks) {
                  err = -EBUSY;
                  goto abort;
            }
            p->rdev = NULL;
            synchronize_rcu();
            if (atomic_read(&rdev->nr_pending)) {
                  /* lost the race, try later */
                  err = -EBUSY;
                  p->rdev = rdev;
            }
      }
abort:

      print_raid5_conf(conf);
      return err;
}

static int raid5_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
{
      raid5_conf_t *conf = mddev->private;
      int err = -EEXIST;
      int disk;
      struct disk_info *p;
      int first = 0;
      int last = conf->raid_disks - 1;

      if (mddev->degraded > conf->max_degraded)
            /* no point adding a device */
            return -EINVAL;

      if (rdev->raid_disk >= 0)
            first = last = rdev->raid_disk;

      /*
       * find the disk ... but prefer rdev->saved_raid_disk
       * if possible.
       */
      if (rdev->saved_raid_disk >= 0 &&
          rdev->saved_raid_disk >= first &&
          conf->disks[rdev->saved_raid_disk].rdev == NULL)
            disk = rdev->saved_raid_disk;
      else
            disk = first;
      for ( ; disk <= last ; disk++)
            if ((p=conf->disks + disk)->rdev == NULL) {
                  clear_bit(In_sync, &rdev->flags);
                  rdev->raid_disk = disk;
                  err = 0;
                  if (rdev->saved_raid_disk != disk)
                        conf->fullsync = 1;
                  rcu_assign_pointer(p->rdev, rdev);
                  break;
            }
      print_raid5_conf(conf);
      return err;
}

static int raid5_resize(mddev_t *mddev, sector_t sectors)
{
      /* no resync is happening, and there is enough space
       * on all devices, so we can resize.
       * We need to make sure resync covers any new space.
       * If the array is shrinking we should possibly wait until
       * any io in the removed space completes, but it hardly seems
       * worth it.
       */
      sectors &= ~((sector_t)mddev->chunk_sectors - 1);
      md_set_array_sectors(mddev, raid5_size(mddev, sectors,
                                     mddev->raid_disks));
      if (mddev->array_sectors >
          raid5_size(mddev, sectors, mddev->raid_disks))
            return -EINVAL;
      set_capacity(mddev->gendisk, mddev->array_sectors);
      mddev->changed = 1;
      revalidate_disk(mddev->gendisk);
      if (sectors > mddev->dev_sectors && mddev->recovery_cp == MaxSector) {
            mddev->recovery_cp = mddev->dev_sectors;
            set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
      }
      mddev->dev_sectors = sectors;
      mddev->resync_max_sectors = sectors;
      return 0;
}

static int check_stripe_cache(mddev_t *mddev)
{
      /* Can only proceed if there are plenty of stripe_heads.
       * We need a minimum of one full stripe,, and for sensible progress
       * it is best to have about 4 times that.
       * If we require 4 times, then the default 256 4K stripe_heads will
       * allow for chunk sizes up to 256K, which is probably OK.
       * If the chunk size is greater, user-space should request more
       * stripe_heads first.
       */
      raid5_conf_t *conf = mddev->private;
      if (((mddev->chunk_sectors << 9) / STRIPE_SIZE) * 4
          > conf->max_nr_stripes ||
          ((mddev->new_chunk_sectors << 9) / STRIPE_SIZE) * 4
          > conf->max_nr_stripes) {
            printk(KERN_WARNING "raid5: reshape: not enough stripes.  Needed %lu\n",
                   ((max(mddev->chunk_sectors, mddev->new_chunk_sectors) << 9)
                  / STRIPE_SIZE)*4);
            return 0;
      }
      return 1;
}

static int check_reshape(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev->private;

      if (mddev->delta_disks == 0 &&
          mddev->new_layout == mddev->layout &&
          mddev->new_chunk_sectors == mddev->chunk_sectors)
            return 0; /* nothing to do */
      if (mddev->bitmap)
            /* Cannot grow a bitmap yet */
            return -EBUSY;
      if (mddev->degraded > conf->max_degraded)
            return -EINVAL;
      if (mddev->delta_disks < 0) {
            /* We might be able to shrink, but the devices must
             * be made bigger first.
             * For raid6, 4 is the minimum size.
             * Otherwise 2 is the minimum
             */
            int min = 2;
            if (mddev->level == 6)
                  min = 4;
            if (mddev->raid_disks + mddev->delta_disks < min)
                  return -EINVAL;
      }

      if (!check_stripe_cache(mddev))
            return -ENOSPC;

      return resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
}

static int raid5_start_reshape(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev->private;
      mdk_rdev_t *rdev;
      int spares = 0;
      int added_devices = 0;
      unsigned long flags;

      if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
            return -EBUSY;

      if (!check_stripe_cache(mddev))
            return -ENOSPC;

      list_for_each_entry(rdev, &mddev->disks, same_set)
            if (rdev->raid_disk < 0 &&
                !test_bit(Faulty, &rdev->flags))
                  spares++;

      if (spares - mddev->degraded < mddev->delta_disks - conf->max_degraded)
            /* Not enough devices even to make a degraded array
             * of that size
             */
            return -EINVAL;

      /* Refuse to reduce size of the array.  Any reductions in
       * array size must be through explicit setting of array_size
       * attribute.
       */
      if (raid5_size(mddev, 0, conf->raid_disks + mddev->delta_disks)
          < mddev->array_sectors) {
            printk(KERN_ERR "md: %s: array size must be reduced "
                   "before number of disks\n", mdname(mddev));
            return -EINVAL;
      }

      atomic_set(&conf->reshape_stripes, 0);
      spin_lock_irq(&conf->device_lock);
      conf->previous_raid_disks = conf->raid_disks;
      conf->raid_disks += mddev->delta_disks;
      conf->prev_chunk_sectors = conf->chunk_sectors;
      conf->chunk_sectors = mddev->new_chunk_sectors;
      conf->prev_algo = conf->algorithm;
      conf->algorithm = mddev->new_layout;
      if (mddev->delta_disks < 0)
            conf->reshape_progress = raid5_size(mddev, 0, 0);
      else
            conf->reshape_progress = 0;
      conf->reshape_safe = conf->reshape_progress;
      conf->generation++;
      spin_unlock_irq(&conf->device_lock);

      /* Add some new drives, as many as will fit.
       * We know there are enough to make the newly sized array work.
       */
      list_for_each_entry(rdev, &mddev->disks, same_set)
            if (rdev->raid_disk < 0 &&
                !test_bit(Faulty, &rdev->flags)) {
                  if (raid5_add_disk(mddev, rdev) == 0) {
                        char nm[20];
                        set_bit(In_sync, &rdev->flags);
                        added_devices++;
                        rdev->recovery_offset = 0;
                        sprintf(nm, "rd%d", rdev->raid_disk);
                        if (sysfs_create_link(&mddev->kobj,
                                          &rdev->kobj, nm))
                              printk(KERN_WARNING
                                     "raid5: failed to create "
                                     " link %s for %s\n",
                                     nm, mdname(mddev));
                  } else
                        break;
            }

      if (mddev->delta_disks > 0) {
            spin_lock_irqsave(&conf->device_lock, flags);
            mddev->degraded = (conf->raid_disks - conf->previous_raid_disks)
                  - added_devices;
            spin_unlock_irqrestore(&conf->device_lock, flags);
      }
      mddev->raid_disks = conf->raid_disks;
      mddev->reshape_position = conf->reshape_progress;
      set_bit(MD_CHANGE_DEVS, &mddev->flags);

      clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
      clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
      set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
      set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
      mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                                    "%s_reshape");
      if (!mddev->sync_thread) {
            mddev->recovery = 0;
            spin_lock_irq(&conf->device_lock);
            mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
            conf->reshape_progress = MaxSector;
            spin_unlock_irq(&conf->device_lock);
            return -EAGAIN;
      }
      conf->reshape_checkpoint = jiffies;
      md_wakeup_thread(mddev->sync_thread);
      md_new_event(mddev);
      return 0;
}

/* This is called from the reshape thread and should make any
 * changes needed in 'conf'
 */
static void end_reshape(raid5_conf_t *conf)
{

      if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {

            spin_lock_irq(&conf->device_lock);
            conf->previous_raid_disks = conf->raid_disks;
            conf->reshape_progress = MaxSector;
            spin_unlock_irq(&conf->device_lock);
            wake_up(&conf->wait_for_overlap);

            /* read-ahead size must cover two whole stripes, which is
             * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
             */
            {
                  int data_disks = conf->raid_disks - conf->max_degraded;
                  int stripe = data_disks * ((conf->chunk_sectors << 9)
                                       / PAGE_SIZE);
                  if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
            }
      }
}

/* This is called from the raid5d thread with mddev_lock held.
 * It makes config changes to the device.
 */
static void raid5_finish_reshape(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev->private;

      if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {

            if (mddev->delta_disks > 0) {
                  md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
                  set_capacity(mddev->gendisk, mddev->array_sectors);
                  mddev->changed = 1;
                  revalidate_disk(mddev->gendisk);
            } else {
                  int d;
                  mddev->degraded = conf->raid_disks;
                  for (d = 0; d < conf->raid_disks ; d++)
                        if (conf->disks[d].rdev &&
                            test_bit(In_sync,
                                   &conf->disks[d].rdev->flags))
                              mddev->degraded--;
                  for (d = conf->raid_disks ;
                       d < conf->raid_disks - mddev->delta_disks;
                       d++) {
                        mdk_rdev_t *rdev = conf->disks[d].rdev;
                        if (rdev && raid5_remove_disk(mddev, d) == 0) {
                              char nm[20];
                              sprintf(nm, "rd%d", rdev->raid_disk);
                              sysfs_remove_link(&mddev->kobj, nm);
                              rdev->raid_disk = -1;
                        }
                  }
            }
            mddev->layout = conf->algorithm;
            mddev->chunk_sectors = conf->chunk_sectors;
            mddev->reshape_position = MaxSector;
            mddev->delta_disks = 0;
      }
}

static void raid5_quiesce(mddev_t *mddev, int state)
{
      raid5_conf_t *conf = mddev->private;

      switch(state) {
      case 2: /* resume for a suspend */
            wake_up(&conf->wait_for_overlap);
            break;

      case 1: /* stop all writes */
            spin_lock_irq(&conf->device_lock);
            /* '2' tells resync/reshape to pause so that all
             * active stripes can drain
             */
            conf->quiesce = 2;
            wait_event_lock_irq(conf->wait_for_stripe,
                            atomic_read(&conf->active_stripes) == 0 &&
                            atomic_read(&conf->active_aligned_reads) == 0,
                            conf->device_lock, /* nothing */);
            conf->quiesce = 1;
            spin_unlock_irq(&conf->device_lock);
            /* allow reshape to continue */
            wake_up(&conf->wait_for_overlap);
            break;

      case 0: /* re-enable writes */
            spin_lock_irq(&conf->device_lock);
            conf->quiesce = 0;
            wake_up(&conf->wait_for_stripe);
            wake_up(&conf->wait_for_overlap);
            spin_unlock_irq(&conf->device_lock);
            break;
      }
}


static void *raid5_takeover_raid1(mddev_t *mddev)
{
      int chunksect;

      if (mddev->raid_disks != 2 ||
          mddev->degraded > 1)
            return ERR_PTR(-EINVAL);

      /* Should check if there are write-behind devices? */

      chunksect = 64*2; /* 64K by default */

      /* The array must be an exact multiple of chunksize */
      while (chunksect && (mddev->array_sectors & (chunksect-1)))
            chunksect >>= 1;

      if ((chunksect<<9) < STRIPE_SIZE)
            /* array size does not allow a suitable chunk size */
            return ERR_PTR(-EINVAL);

      mddev->new_level = 5;
      mddev->new_layout = ALGORITHM_LEFT_SYMMETRIC;
      mddev->new_chunk_sectors = chunksect;

      return setup_conf(mddev);
}

static void *raid5_takeover_raid6(mddev_t *mddev)
{
      int new_layout;

      switch (mddev->layout) {
      case ALGORITHM_LEFT_ASYMMETRIC_6:
            new_layout = ALGORITHM_LEFT_ASYMMETRIC;
            break;
      case ALGORITHM_RIGHT_ASYMMETRIC_6:
            new_layout = ALGORITHM_RIGHT_ASYMMETRIC;
            break;
      case ALGORITHM_LEFT_SYMMETRIC_6:
            new_layout = ALGORITHM_LEFT_SYMMETRIC;
            break;
      case ALGORITHM_RIGHT_SYMMETRIC_6:
            new_layout = ALGORITHM_RIGHT_SYMMETRIC;
            break;
      case ALGORITHM_PARITY_0_6:
            new_layout = ALGORITHM_PARITY_0;
            break;
      case ALGORITHM_PARITY_N:
            new_layout = ALGORITHM_PARITY_N;
            break;
      default:
            return ERR_PTR(-EINVAL);
      }
      mddev->new_level = 5;
      mddev->new_layout = new_layout;
      mddev->delta_disks = -1;
      mddev->raid_disks -= 1;
      return setup_conf(mddev);
}


static int raid5_check_reshape(mddev_t *mddev)
{
      /* For a 2-drive array, the layout and chunk size can be changed
       * immediately as not restriping is needed.
       * For larger arrays we record the new value - after validation
       * to be used by a reshape pass.
       */
      raid5_conf_t *conf = mddev->private;
      int new_chunk = mddev->new_chunk_sectors;

      if (mddev->new_layout >= 0 && !algorithm_valid_raid5(mddev->new_layout))
            return -EINVAL;
      if (new_chunk > 0) {
            if (!is_power_of_2(new_chunk))
                  return -EINVAL;
            if (new_chunk < (PAGE_SIZE>>9))
                  return -EINVAL;
            if (mddev->array_sectors & (new_chunk-1))
                  /* not factor of array size */
                  return -EINVAL;
      }

      /* They look valid */

      if (mddev->raid_disks == 2) {
            /* can make the change immediately */
            if (mddev->new_layout >= 0) {
                  conf->algorithm = mddev->new_layout;
                  mddev->layout = mddev->new_layout;
            }
            if (new_chunk > 0) {
                  conf->chunk_sectors = new_chunk ;
                  mddev->chunk_sectors = new_chunk;
            }
            set_bit(MD_CHANGE_DEVS, &mddev->flags);
            md_wakeup_thread(mddev->thread);
      }
      return check_reshape(mddev);
}

static int raid6_check_reshape(mddev_t *mddev)
{
      int new_chunk = mddev->new_chunk_sectors;

      if (mddev->new_layout >= 0 && !algorithm_valid_raid6(mddev->new_layout))
            return -EINVAL;
      if (new_chunk > 0) {
            if (!is_power_of_2(new_chunk))
                  return -EINVAL;
            if (new_chunk < (PAGE_SIZE >> 9))
                  return -EINVAL;
            if (mddev->array_sectors & (new_chunk-1))
                  /* not factor of array size */
                  return -EINVAL;
      }

      /* They look valid */
      return check_reshape(mddev);
}

static void *raid5_takeover(mddev_t *mddev)
{
      /* raid5 can take over:
       *  raid0 - if all devices are the same - make it a raid4 layout
       *  raid1 - if there are two drives.  We need to know the chunk size
       *  raid4 - trivial - just use a raid4 layout.
       *  raid6 - Providing it is a *_6 layout
       */

      if (mddev->level == 1)
            return raid5_takeover_raid1(mddev);
      if (mddev->level == 4) {
            mddev->new_layout = ALGORITHM_PARITY_N;
            mddev->new_level = 5;
            return setup_conf(mddev);
      }
      if (mddev->level == 6)
            return raid5_takeover_raid6(mddev);

      return ERR_PTR(-EINVAL);
}


static struct mdk_personality raid5_personality;

static void *raid6_takeover(mddev_t *mddev)
{
      /* Currently can only take over a raid5.  We map the
       * personality to an equivalent raid6 personality
       * with the Q block at the end.
       */
      int new_layout;

      if (mddev->pers != &raid5_personality)
            return ERR_PTR(-EINVAL);
      if (mddev->degraded > 1)
            return ERR_PTR(-EINVAL);
      if (mddev->raid_disks > 253)
            return ERR_PTR(-EINVAL);
      if (mddev->raid_disks < 3)
            return ERR_PTR(-EINVAL);

      switch (mddev->layout) {
      case ALGORITHM_LEFT_ASYMMETRIC:
            new_layout = ALGORITHM_LEFT_ASYMMETRIC_6;
            break;
      case ALGORITHM_RIGHT_ASYMMETRIC:
            new_layout = ALGORITHM_RIGHT_ASYMMETRIC_6;
            break;
      case ALGORITHM_LEFT_SYMMETRIC:
            new_layout = ALGORITHM_LEFT_SYMMETRIC_6;
            break;
      case ALGORITHM_RIGHT_SYMMETRIC:
            new_layout = ALGORITHM_RIGHT_SYMMETRIC_6;
            break;
      case ALGORITHM_PARITY_0:
            new_layout = ALGORITHM_PARITY_0_6;
            break;
      case ALGORITHM_PARITY_N:
            new_layout = ALGORITHM_PARITY_N;
            break;
      default:
            return ERR_PTR(-EINVAL);
      }
      mddev->new_level = 6;
      mddev->new_layout = new_layout;
      mddev->delta_disks = 1;
      mddev->raid_disks += 1;
      return setup_conf(mddev);
}


static struct mdk_personality raid6_personality =
{
      .name       = "raid6",
      .level            = 6,
      .owner            = THIS_MODULE,
      .make_request     = make_request,
      .run        = run,
      .stop       = stop,
      .status           = status,
      .error_handler    = error,
      .hot_add_disk     = raid5_add_disk,
      .hot_remove_disk= raid5_remove_disk,
      .spare_active     = raid5_spare_active,
      .sync_request     = sync_request,
      .resize           = raid5_resize,
      .size       = raid5_size,
      .check_reshape    = raid6_check_reshape,
      .start_reshape  = raid5_start_reshape,
      .finish_reshape = raid5_finish_reshape,
      .quiesce    = raid5_quiesce,
      .takeover   = raid6_takeover,
};
static struct mdk_personality raid5_personality =
{
      .name       = "raid5",
      .level            = 5,
      .owner            = THIS_MODULE,
      .make_request     = make_request,
      .run        = run,
      .stop       = stop,
      .status           = status,
      .error_handler    = error,
      .hot_add_disk     = raid5_add_disk,
      .hot_remove_disk= raid5_remove_disk,
      .spare_active     = raid5_spare_active,
      .sync_request     = sync_request,
      .resize           = raid5_resize,
      .size       = raid5_size,
      .check_reshape    = raid5_check_reshape,
      .start_reshape  = raid5_start_reshape,
      .finish_reshape = raid5_finish_reshape,
      .quiesce    = raid5_quiesce,
      .takeover   = raid5_takeover,
};

static struct mdk_personality raid4_personality =
{
      .name       = "raid4",
      .level            = 4,
      .owner            = THIS_MODULE,
      .make_request     = make_request,
      .run        = run,
      .stop       = stop,
      .status           = status,
      .error_handler    = error,
      .hot_add_disk     = raid5_add_disk,
      .hot_remove_disk= raid5_remove_disk,
      .spare_active     = raid5_spare_active,
      .sync_request     = sync_request,
      .resize           = raid5_resize,
      .size       = raid5_size,
      .check_reshape    = raid5_check_reshape,
      .start_reshape  = raid5_start_reshape,
      .finish_reshape = raid5_finish_reshape,
      .quiesce    = raid5_quiesce,
};

static int __init raid5_init(void)
{
      register_md_personality(&raid6_personality);
      register_md_personality(&raid5_personality);
      register_md_personality(&raid4_personality);
      return 0;
}

static void raid5_exit(void)
{
      unregister_md_personality(&raid6_personality);
      unregister_md_personality(&raid5_personality);
      unregister_md_personality(&raid4_personality);
}

module_init(raid5_init);
module_exit(raid5_exit);
MODULE_LICENSE("GPL");
MODULE_ALIAS("md-personality-4"); /* RAID5 */
MODULE_ALIAS("md-raid5");
MODULE_ALIAS("md-raid4");
MODULE_ALIAS("md-level-5");
MODULE_ALIAS("md-level-4");
MODULE_ALIAS("md-personality-8"); /* RAID6 */
MODULE_ALIAS("md-raid6");
MODULE_ALIAS("md-level-6");

/* This used to be two separate modules, they were: */
MODULE_ALIAS("raid5");
MODULE_ALIAS("raid6");

Generated by  Doxygen 1.6.0   Back to index