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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/module.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/bitops.h>
#include <linux/kthread.h>
#include <asm/atomic.h>
#include "raid6.h"

#include <linux/raid/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 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_DEBUG     0
#define RAID5_PARANOIA  1
#if RAID5_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#define PRINTK(x...) ((void)(RAID5_DEBUG && printk(x)))
#if RAID5_DEBUG
#define inline
#define __inline__
#endif

#if !RAID6_USE_EMPTY_ZERO_PAGE
/* In .bss so it's zeroed */
const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
#endif

static inline int raid6_next_disk(int disk, int raid_disks)
{
      disk++;
      return (disk < raid_disks) ? disk : 0;
}
static void print_raid5_conf (raid5_conf_t *conf);

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 {
                  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);
                  }
            }
      }
}
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)
{
      PRINTK("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);

      PRINTK("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);

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

      BUG_ON(atomic_read(&sh->count) != 0);
      BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
      
      CHECK_DEVLOCK();
      PRINTK("init_stripe called, stripe %llu\n", 
            (unsigned long long)sh->sector);

      remove_hash(sh);

      sh->sector = sector;
      sh->pd_idx = pd_idx;
      sh->state = 0;

      sh->disks = disks;

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

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

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

      CHECK_DEVLOCK();
      PRINTK("__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->disks == disks)
                  return sh;
      PRINTK("__stripe %llu not in cache\n", (unsigned long long)sector);
      return NULL;
}

static void unplug_slaves(mddev_t *mddev);
static void raid5_unplug_device(request_queue_t *q);

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

      PRINTK("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,
                            conf->device_lock, /* nothing */);
            sh = __find_stripe(conf, sector, disks);
            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, pd_idx, disks);
            } else {
                  if (atomic_read(&sh->count)) {
                    BUG_ON(!list_empty(&sh->lru));
                  } 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 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)
{
      kmem_cache_t *sc;
      int devs = conf->raid_disks;

      sprintf(conf->cache_name[0], "raid5/%s", mdname(conf->mddev));
      sprintf(conf->cache_name[1], "raid5/%s-alt", 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, NULL);
      if (!sc)
            return 1;
      conf->slab_cache = sc;
      conf->pool_size = devs;
      while (num--)
            if (!grow_one_stripe(conf))
                  return 1;
      return 0;
}

#ifdef CONFIG_MD_RAID5_RESHAPE
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 = 0;
      kmem_cache_t *sc;
      int i;

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

      /* 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, 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;
}
#endif

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 int raid5_end_read_request(struct bio * bi, unsigned int bytes_done,
                           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;

      if (bi->bi_size)
            return 1;

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

      PRINTK("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 0;
      }

      if (uptodate) {
#if 0
            struct bio *bio;
            unsigned long flags;
            spin_lock_irqsave(&conf->device_lock, flags);
            /* we can return a buffer if we bypassed the cache or
             * if the top buffer is not in highmem.  If there are
             * multiple buffers, leave the extra work to
             * handle_stripe
             */
            buffer = sh->bh_read[i];
            if (buffer &&
                (!PageHighMem(buffer->b_page)
                 || buffer->b_page == bh->b_page )
                  ) {
                  sh->bh_read[i] = buffer->b_reqnext;
                  buffer->b_reqnext = NULL;
            } else
                  buffer = NULL;
            spin_unlock_irqrestore(&conf->device_lock, flags);
            if (sh->bh_page[i]==bh->b_page)
                  set_buffer_uptodate(bh);
            if (buffer) {
                  if (buffer->b_page != bh->b_page)
                        memcpy(buffer->b_data, bh->b_data, bh->b_size);
                  buffer->b_end_io(buffer, 1);
            }
#else
            set_bit(R5_UPTODATE, &sh->dev[i].flags);
#endif
            if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                  rdev = conf->disks[i].rdev;
                  printk(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(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(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);
#if 0
      /* must restore b_page before unlocking buffer... */
      if (sh->bh_page[i] != bh->b_page) {
            bh->b_page = sh->bh_page[i];
            bh->b_data = page_address(bh->b_page);
            clear_buffer_uptodate(bh);
      }
#endif
      clear_bit(R5_LOCKED, &sh->dev[i].flags);
      set_bit(STRIPE_HANDLE, &sh->state);
      release_stripe(sh);
      return 0;
}

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

      if (bi->bi_size)
            return 1;

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

      PRINTK("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 0;
      }

      spin_lock_irqsave(&conf->device_lock, flags);
      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(conf, sh);
      spin_unlock_irqrestore(&conf->device_lock, flags);
      return 0;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i);
      
static void raid5_build_block (struct stripe_head *sh, int i)
{
      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);
}

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

      if (!test_bit(Faulty, &rdev->flags)) {
            mddev->sb_dirty = 1;
            if (test_bit(In_sync, &rdev->flags)) {
                  conf->working_disks--;
                  mddev->degraded++;
                  conf->failed_disks++;
                  clear_bit(In_sync, &rdev->flags);
                  /*
                   * if recovery was running, make sure it aborts.
                   */
                  set_bit(MD_RECOVERY_ERR, &mddev->recovery);
            }
            set_bit(Faulty, &rdev->flags);
            printk (KERN_ALERT
                  "raid5: Disk failure on %s, disabling device."
                  " Operation continuing on %d devices\n",
                  bdevname(rdev->bdev,b), conf->working_disks);
      }
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(sector_t r_sector, unsigned int raid_disks,
                  unsigned int data_disks, unsigned int * dd_idx,
                  unsigned int * pd_idx, raid5_conf_t *conf)
{
      long stripe;
      unsigned long chunk_number;
      unsigned int chunk_offset;
      sector_t new_sector;
      int sectors_per_chunk = conf->chunk_size >> 9;

      /* 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.
       */
      switch(conf->level) {
      case 4:
            *pd_idx = data_disks;
            break;
      case 5:
            switch (conf->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;
            default:
                  printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                        conf->algorithm);
            }
            break;
      case 6:

            /**** FIX THIS ****/
            switch (conf->algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
                  *pd_idx = raid_disks - 1 - (stripe % raid_disks);
                  if (*pd_idx == raid_disks-1)
                        (*dd_idx)++;      /* Q D D D P */
                  else if (*dd_idx >= *pd_idx)
                        (*dd_idx) += 2; /* D D P Q D */
                  break;
            case ALGORITHM_RIGHT_ASYMMETRIC:
                  *pd_idx = stripe % raid_disks;
                  if (*pd_idx == raid_disks-1)
                        (*dd_idx)++;      /* Q D D D P */
                  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);
                  *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                  break;
            case ALGORITHM_RIGHT_SYMMETRIC:
                  *pd_idx = stripe % raid_disks;
                  *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                  break;
            default:
                  printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                        conf->algorithm);
            }
            break;
      }

      /*
       * 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)
{
      raid5_conf_t *conf = sh->raid_conf;
      int raid_disks = sh->disks, data_disks = raid_disks - 1;
      sector_t new_sector = sh->sector, check;
      int sectors_per_chunk = conf->chunk_size >> 9;
      sector_t stripe;
      int chunk_offset;
      int chunk_number, dummy1, dummy2, dd_idx = i;
      sector_t r_sector;


      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 (conf->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;
            default:
                  printk(KERN_ERR "raid5: unsupported algorithm %d\n",
                         conf->algorithm);
            }
            break;
      case 6:
            data_disks = raid_disks - 2;
            if (i == raid6_next_disk(sh->pd_idx, raid_disks))
                  return 0; /* It is the Q disk */
            switch (conf->algorithm) {
            case ALGORITHM_LEFT_ASYMMETRIC:
            case ALGORITHM_RIGHT_ASYMMETRIC:
                  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;
            default:
                  printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
                        conf->algorithm);
            }
            break;
      }

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

      check = raid5_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
      if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_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_block(count, STRIPE_SIZE, ptr); \
                        count = 1;                    \
                     }                                \
                  } while(0)


static void compute_block(struct stripe_head *sh, int dd_idx)
{
      int i, count, disks = sh->disks;
      void *ptr[MAX_XOR_BLOCKS], *p;

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

      ptr[0] = page_address(sh->dev[dd_idx].page);
      memset(ptr[0], 0, STRIPE_SIZE);
      count = 1;
      for (i = disks ; i--; ) {
            if (i == dd_idx)
                  continue;
            p = page_address(sh->dev[i].page);
            if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
                  ptr[count++] = p;
            else
                  printk(KERN_ERR "compute_block() %d, stripe %llu, %d"
                        " not present\n", dd_idx,
                        (unsigned long long)sh->sector, i);

            check_xor();
      }
      if (count != 1)
            xor_block(count, STRIPE_SIZE, ptr);
      set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
}

static void compute_parity5(struct stripe_head *sh, int method)
{
      raid5_conf_t *conf = sh->raid_conf;
      int i, pd_idx = sh->pd_idx, disks = sh->disks, count;
      void *ptr[MAX_XOR_BLOCKS];
      struct bio *chosen;

      PRINTK("compute_parity5, stripe %llu, method %d\n",
            (unsigned long long)sh->sector, method);

      count = 1;
      ptr[0] = page_address(sh->dev[pd_idx].page);
      switch(method) {
      case READ_MODIFY_WRITE:
            BUG_ON(!test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags));
            for (i=disks ; i-- ;) {
                  if (i==pd_idx)
                        continue;
                  if (sh->dev[i].towrite &&
                      test_bit(R5_UPTODATE, &sh->dev[i].flags)) {
                        ptr[count++] = page_address(sh->dev[i].page);
                        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;
                        check_xor();
                  }
            }
            break;
      case RECONSTRUCT_WRITE:
            memset(ptr[0], 0, STRIPE_SIZE);
            for (i= disks; i-- ;)
                  if (i!=pd_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:
            break;
      }
      if (count>1) {
            xor_block(count, STRIPE_SIZE, ptr);
            count = 1;
      }
      
      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);
            }

      switch(method) {
      case RECONSTRUCT_WRITE:
      case CHECK_PARITY:
            for (i=disks; i--;)
                  if (i != pd_idx) {
                        ptr[count++] = page_address(sh->dev[i].page);
                        check_xor();
                  }
            break;
      case READ_MODIFY_WRITE:
            for (i = disks; i--;)
                  if (sh->dev[i].written) {
                        ptr[count++] = page_address(sh->dev[i].page);
                        check_xor();
                  }
      }
      if (count != 1)
            xor_block(count, STRIPE_SIZE, ptr);
      
      if (method != CHECK_PARITY) {
            set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
            set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
      } else
            clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
}

static void compute_parity6(struct stripe_head *sh, int method)
{
      raid6_conf_t *conf = sh->raid_conf;
      int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = conf->raid_disks, count;
      struct bio *chosen;
      /**** FIX THIS: This could be very bad if disks is close to 256 ****/
      void *ptrs[disks];

      qd_idx = raid6_next_disk(pd_idx, disks);
      d0_idx = raid6_next_disk(qd_idx, disks);

      PRINTK("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);

                        if (sh->dev[i].written) BUG();
                        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);
            }

//    switch(method) {
//    case RECONSTRUCT_WRITE:
//    case CHECK_PARITY:
//    case UPDATE_PARITY:
            /* Note that unlike RAID-5, the ordering of the disks matters greatly. */
            /* FIX: Is this ordering of drives even remotely optimal? */
            count = 0;
            i = d0_idx;
            do {
                  ptrs[count++] = page_address(sh->dev[i].page);
                  if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                        printk("block %d/%d not uptodate on parity calc\n", i,count);
                  i = raid6_next_disk(i, disks);
            } while ( i != d0_idx );
//          break;
//    }

      raid6_call.gen_syndrome(disks, 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)
{
      raid6_conf_t *conf = sh->raid_conf;
      int i, count, disks = conf->raid_disks;
      void *ptr[MAX_XOR_BLOCKS], *p;
      int pd_idx = sh->pd_idx;
      int qd_idx = raid6_next_disk(pd_idx, disks);

      PRINTK("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 {
            ptr[0] = page_address(sh->dev[dd_idx].page);
            if (!nozero) memset(ptr[0], 0, STRIPE_SIZE);
            count = 1;
            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 != 1)
                  xor_block(count, STRIPE_SIZE, 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)
{
      raid6_conf_t *conf = sh->raid_conf;
      int i, count, disks = conf->raid_disks;
      int pd_idx = sh->pd_idx;
      int qd_idx = raid6_next_disk(pd_idx, disks);
      int d0_idx = raid6_next_disk(qd_idx, disks);
      int faila, failb;

      /* faila and failb are disk numbers relative to d0_idx */
      /* pd_idx become disks-2 and qd_idx become disks-1 */
      faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
      failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;

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

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

      if ( failb == disks-1 ) {
            /* Q disk is one of the missing disks */
            if ( faila == disks-2 ) {
                  /* 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 == qd_idx) ? dd_idx2 : dd_idx1, 0);
                  compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
                  return;
            }
      }

      /* We're missing D+P or D+D; build pointer table */
      {
            /**** FIX THIS: This could be very bad if disks is close to 256 ****/
            void *ptrs[disks];

            count = 0;
            i = d0_idx;
            do {
                  ptrs[count++] = page_address(sh->dev[i].page);
                  i = raid6_next_disk(i, disks);
                  if (i != dd_idx1 && i != dd_idx2 &&
                      !test_bit(R5_UPTODATE, &sh->dev[i].flags))
                        printk("compute_2 with missing block %d/%d\n", count, i);
            } while ( i != d0_idx );

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



/*
 * 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;

      PRINTK("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);

      PRINTK("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 int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int disks)
{
      int sectors_per_chunk = conf->chunk_size >> 9;
      sector_t x = stripe;
      int pd_idx, dd_idx;
      int chunk_offset = sector_div(x, sectors_per_chunk);
      stripe = x;
      raid5_compute_sector(stripe*(disks-1)*sectors_per_chunk
                       + chunk_offset, disks, disks-1, &dd_idx, &pd_idx, conf);
      return pd_idx;
}


/*
 * 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
 *
 * Parity calculations are done inside the stripe lock
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */
 
static void handle_stripe5(struct stripe_head *sh)
{
      raid5_conf_t *conf = sh->raid_conf;
      int disks = sh->disks;
      struct bio *return_bi= NULL;
      struct bio *bi;
      int i;
      int syncing, expanding, expanded;
      int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
      int non_overwrite = 0;
      int failed_num=0;
      struct r5dev *dev;

      PRINTK("handling stripe %llu, cnt=%d, pd_idx=%d\n",
            (unsigned long long)sh->sector, atomic_read(&sh->count),
            sh->pd_idx);

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

      syncing = test_bit(STRIPE_SYNCING, &sh->state);
      expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
      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);

            PRINTK("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;
                  PRINTK("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 (--rbi->bi_phys_segments == 0) {
                              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)) locked++;
            if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;

            
            if (dev->toread) to_read++;
            if (dev->towrite) {
                  to_write++;
                  if (!test_bit(R5_OVERWRITE, &dev->flags))
                        non_overwrite++;
            }
            if (dev->written) written++;
            rdev = rcu_dereference(conf->disks[i].rdev);
            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)) {
                  failed++;
                  failed_num = i;
            } else
                  set_bit(R5_Insync, &dev->flags);
      }
      rcu_read_unlock();
      PRINTK("locked=%d uptodate=%d to_read=%d"
            " to_write=%d failed=%d failed_num=%d\n",
            locked, uptodate, to_read, to_write, failed, failed_num);
      /* check if the array has lost two devices and, if so, some requests might
       * need to be failed
       */
      if (failed > 1 && to_read+to_write+written) {
            for (i=disks; i--; ) {
                  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) { 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 (--bi->bi_phys_segments == 0) {
                              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 (--bi->bi_phys_segments == 0) {
                              md_write_end(conf->mddev);
                              bi->bi_next = return_bi;
                              return_bi = bi;
                        }
                        bi = bi2;
                  }

                  /* fail any reads if this device is non-operational */
                  if (!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) 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 (--bi->bi_phys_segments == 0) {
                                    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 (failed > 1 && syncing) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,0);
            clear_bit(STRIPE_SYNCING, &sh->state);
            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 ( written &&
           ( (test_bit(R5_Insync, &dev->flags) && !test_bit(R5_LOCKED, &dev->flags) &&
            test_bit(R5_UPTODATE, &dev->flags))
             || (failed == 1 && failed_num == sh->pd_idx))
          ) {
          /* 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.
           */
          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;
                      PRINTK("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 (--wbi->bi_phys_segments == 0) {
                                  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);
                }
            }
      }

      /* 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 (to_read || non_overwrite || (syncing && (uptodate < disks)) || expanding) {
            for (i=disks; i--;) {
                  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)) ||
                       syncing ||
                       expanding ||
                       (failed && (sh->dev[failed_num].toread ||
                               (sh->dev[failed_num].towrite && !test_bit(R5_OVERWRITE, &sh->dev[failed_num].flags))))
                            )
                        ) {
                        /* we would like to get this block, possibly
                         * by computing it, but we might not be able to
                         */
                        if (uptodate == disks-1) {
                              PRINTK("Computing block %d\n", i);
                              compute_block(sh, i);
                              uptodate++;
                        } else if (test_bit(R5_Insync, &dev->flags)) {
                              set_bit(R5_LOCKED, &dev->flags);
                              set_bit(R5_Wantread, &dev->flags);
#if 0
                              /* if I am just reading this block and we don't have
                                 a failed drive, or any pending writes then sidestep the cache */
                              if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
                                  ! syncing && !failed && !to_write) {
                                    sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
                                    sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
                              }
#endif
                              locked++;
                              PRINTK("Reading block %d (sync=%d)\n", 
                                    i, syncing);
                        }
                  }
            }
            set_bit(STRIPE_HANDLE, &sh->state);
      }

      /* now to consider writing and what else, if anything should be read */
      if (to_write) {
            int rmw=0, rcw=0;
            for (i=disks ; i--;) {
                  /* would I have to read this buffer for read_modify_write */
                  dev = &sh->dev[i];
                  if ((dev->towrite || i == sh->pd_idx) &&
                      (!test_bit(R5_LOCKED, &dev->flags) 
#if 0
|| sh->bh_page[i]!=bh->b_page
#endif
                            ) &&
                      !test_bit(R5_UPTODATE, &dev->flags)) {
                        if (test_bit(R5_Insync, &dev->flags)
/*                          && !(!mddev->insync && i == sh->pd_idx) */
                              )
                              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) 
#if 0
|| sh->bh_page[i] != bh->b_page
#endif
                            ) &&
                      !test_bit(R5_UPTODATE, &dev->flags)) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else rcw += 2*disks;
                  }
            }
            PRINTK("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--;) {
                        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_Insync, &dev->flags)) {
                              if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                              {
                                    PRINTK("Read_old block %d for r-m-w\n", i);
                                    set_bit(R5_LOCKED, &dev->flags);
                                    set_bit(R5_Wantread, &dev->flags);
                                    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--;) {
                        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_Insync, &dev->flags)) {
                              if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                              {
                                    PRINTK("Read_old block %d for Reconstruct\n", i);
                                    set_bit(R5_LOCKED, &dev->flags);
                                    set_bit(R5_Wantread, &dev->flags);
                                    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 */
            if (locked == 0 && (rcw == 0 ||rmw == 0) &&
                !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
                  PRINTK("Computing parity...\n");
                  compute_parity5(sh, rcw==0 ? RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
                  /* now every locked buffer is ready to be written */
                  for (i=disks; i--;)
                        if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
                              PRINTK("Writing block %d\n", i);
                              locked++;
                              set_bit(R5_Wantwrite, &sh->dev[i].flags);
                              if (!test_bit(R5_Insync, &sh->dev[i].flags)
                                  || (i==sh->pd_idx && 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);
                  }
            }
      }

      /* 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 (syncing && locked == 0 &&
          !test_bit(STRIPE_INSYNC, &sh->state)) {
            set_bit(STRIPE_HANDLE, &sh->state);
            if (failed == 0) {
                  BUG_ON(uptodate != disks);
                  compute_parity5(sh, CHECK_PARITY);
                  uptodate--;
                  if (page_is_zero(sh->dev[sh->pd_idx].page)) {
                        /* 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 {
                              compute_block(sh, sh->pd_idx);
                              uptodate++;
                        }
                  }
            }
            if (!test_bit(STRIPE_INSYNC, &sh->state)) {
                  /* either failed parity check, or recovery is happening */
                  if (failed==0)
                        failed_num = sh->pd_idx;
                  dev = &sh->dev[failed_num];
                  BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
                  BUG_ON(uptodate != disks);

                  set_bit(R5_LOCKED, &dev->flags);
                  set_bit(R5_Wantwrite, &dev->flags);
                  clear_bit(STRIPE_DEGRADED, &sh->state);
                  locked++;
                  set_bit(STRIPE_INSYNC, &sh->state);
            }
      }
      if (syncing && 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 (failed == 1 && ! conf->mddev->ro &&
          test_bit(R5_ReadError, &sh->dev[failed_num].flags)
          && !test_bit(R5_LOCKED, &sh->dev[failed_num].flags)
          && test_bit(R5_UPTODATE, &sh->dev[failed_num].flags)
            ) {
            dev = &sh->dev[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);
                  locked++;
            } else {
                  /* let's read it back */
                  set_bit(R5_Wantread, &dev->flags);
                  set_bit(R5_LOCKED, &dev->flags);
                  locked++;
            }
      }

      if (expanded && test_bit(STRIPE_EXPANDING, &sh->state)) {
            /* Need to write out all blocks after computing parity */
            sh->disks = conf->raid_disks;
            sh->pd_idx = stripe_to_pdidx(sh->sector, conf, conf->raid_disks);
            compute_parity5(sh, RECONSTRUCT_WRITE);
            for (i= conf->raid_disks; i--;) {
                  set_bit(R5_LOCKED, &sh->dev[i].flags);
                  locked++;
                  set_bit(R5_Wantwrite, &sh->dev[i].flags);
            }
            clear_bit(STRIPE_EXPANDING, &sh->state);
      } else if (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 (expanding && locked == 0) {
            /* We have read all the blocks in this stripe and now we need to
             * copy some of them into a target stripe for expand.
             */
            clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
            for (i=0; i< sh->disks; i++)
                  if (i != sh->pd_idx) {
                        int dd_idx, pd_idx, j;
                        struct stripe_head *sh2;

                        sector_t bn = compute_blocknr(sh, i);
                        sector_t s = raid5_compute_sector(bn, conf->raid_disks,
                                                  conf->raid_disks-1,
                                                  &dd_idx, &pd_idx, conf);
                        sh2 = get_active_stripe(conf, s, conf->raid_disks, pd_idx, 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;
                        }
                        memcpy(page_address(sh2->dev[dd_idx].page),
                               page_address(sh->dev[i].page),
                               STRIPE_SIZE);
                        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 &&
                                  !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);
                  }
      }

      spin_unlock(&sh->lock);

      while ((bi=return_bi)) {
            int bytes = bi->bi_size;

            return_bi = bi->bi_next;
            bi->bi_next = NULL;
            bi->bi_size = 0;
            bi->bi_end_io(bi, bytes, 0);
      }
      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 = 1;
            else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                  rw = 0;
            else
                  continue;
 
            bi = &sh->dev[i].req;
 
            bi->bi_rw = rw;
            if (rw)
                  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 (syncing || expanding || expanded)
                        md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                  bi->bi_bdev = rdev->bdev;
                  PRINTK("for %llu schedule op %ld on disc %d\n",
                        (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 == 1)
                        set_bit(STRIPE_DEGRADED, &sh->state);
                  PRINTK("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 void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
{
      raid6_conf_t *conf = sh->raid_conf;
      int disks = conf->raid_disks;
      struct bio *return_bi= NULL;
      struct bio *bi;
      int i;
      int syncing;
      int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
      int non_overwrite = 0;
      int failed_num[2] = {0, 0};
      struct r5dev *dev, *pdev, *qdev;
      int pd_idx = sh->pd_idx;
      int qd_idx = raid6_next_disk(pd_idx, disks);
      int p_failed, q_failed;

      PRINTK("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);

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

      syncing = test_bit(STRIPE_SYNCING, &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);

            PRINTK("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;
                  PRINTK("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 (--rbi->bi_phys_segments == 0) {
                              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)) locked++;
            if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;


            if (dev->toread) to_read++;
            if (dev->towrite) {
                  to_write++;
                  if (!test_bit(R5_OVERWRITE, &dev->flags))
                        non_overwrite++;
            }
            if (dev->written) written++;
            rdev = rcu_dereference(conf->disks[i].rdev);
            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 ( failed < 2 )
                        failed_num[failed] = i;
                  failed++;
            } else
                  set_bit(R5_Insync, &dev->flags);
      }
      rcu_read_unlock();
      PRINTK("locked=%d uptodate=%d to_read=%d"
             " to_write=%d failed=%d failed_num=%d,%d\n",
             locked, uptodate, to_read, to_write, failed,
             failed_num[0], failed_num[1]);
      /* check if the array has lost >2 devices and, if so, some requests might
       * need to be failed
       */
      if (failed > 2 && to_read+to_write+written) {
            for (i=disks; i--; ) {
                  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) { 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 (--bi->bi_phys_segments == 0) {
                              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 (--bi->bi_phys_segments == 0) {
                              md_write_end(conf->mddev);
                              bi->bi_next = return_bi;
                              return_bi = bi;
                        }
                        bi = bi2;
                  }

                  /* fail any reads if this device is non-operational */
                  if (!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) 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 (--bi->bi_phys_segments == 0) {
                                    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 (failed > 2 && syncing) {
            md_done_sync(conf->mddev, STRIPE_SECTORS,0);
            clear_bit(STRIPE_SYNCING, &sh->state);
            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];
      p_failed = (failed >= 1 && failed_num[0] == pd_idx)
            || (failed >= 2 && failed_num[1] == pd_idx);
      qdev = &sh->dev[qd_idx];
      q_failed = (failed >= 1 && failed_num[0] == qd_idx)
            || (failed >= 2 && failed_num[1] == qd_idx);

      if ( written &&
           ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
                       && !test_bit(R5_LOCKED, &pdev->flags)
                       && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
           ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
                       && !test_bit(R5_LOCKED, &qdev->flags)
                       && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
            /* 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.
             */
            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 */
                              int bitmap_end = 0;
                              struct bio *wbi, *wbi2;
                              PRINTK("Return write for stripe %llu disc %d\n",
                                     (unsigned long long)sh->sector, 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 (--wbi->bi_phys_segments == 0) {
                                          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);
                        }
                  }
      }

      /* 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 (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
            for (i=disks; i--;) {
                  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)) ||
                       syncing ||
                       (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
                       (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
                            )
                        ) {
                        /* we would like to get this block, possibly
                         * by computing it, but we might not be able to
                         */
                        if (uptodate == disks-1) {
                              PRINTK("Computing stripe %llu block %d\n",
                                     (unsigned long long)sh->sector, i);
                              compute_block_1(sh, i, 0);
                              uptodate++;
                        } else if ( uptodate == disks-2 && 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);
                              PRINTK("Computing stripe %llu blocks %d,%d\n",
                                     (unsigned long long)sh->sector, i, other);
                              compute_block_2(sh, i, other);
                              uptodate += 2;
                        } else if (test_bit(R5_Insync, &dev->flags)) {
                              set_bit(R5_LOCKED, &dev->flags);
                              set_bit(R5_Wantread, &dev->flags);
#if 0
                              /* if I am just reading this block and we don't have
                                 a failed drive, or any pending writes then sidestep the cache */
                              if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
                                  ! syncing && !failed && !to_write) {
                                    sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
                                    sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
                              }
#endif
                              locked++;
                              PRINTK("Reading block %d (sync=%d)\n",
                                    i, syncing);
                        }
                  }
            }
            set_bit(STRIPE_HANDLE, &sh->state);
      }

      /* now to consider writing and what else, if anything should be read */
      if (to_write) {
            int rcw=0, must_compute=0;
            for (i=disks ; i--;) {
                  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)
#if 0
                        || sh->bh_page[i] != bh->b_page
#endif
                            ) &&
                      !test_bit(R5_UPTODATE, &dev->flags)) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else {
                              PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
                              must_compute++;
                        }
                  }
            }
            PRINTK("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--;) {
                        dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags)
                            && !(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))
                              {
                                    PRINTK("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);
                                    locked++;
                              } else {
                                    PRINTK("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 (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 ( failed ) {
                        case 0:     BUG();
                        case 1: compute_block_1(sh, failed_num[0], 0); break;
                        case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
                        default: BUG();   /* This request should have been failed? */
                        }
                  }

                  PRINTK("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)) {
                              PRINTK("Writing stripe %llu block %d\n",
                                     (unsigned long long)sh->sector, i);
                              locked++;
                              set_bit(R5_Wantwrite, &sh->dev[i].flags);
                        }
                  /* 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);
                  }
            }
      }

      /* 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 (syncing && locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state)) {
            int update_p = 0, update_q = 0;
            struct r5dev *dev;

            set_bit(STRIPE_HANDLE, &sh->state);

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

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

      if (syncing && 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 (failed <= 2 && ! conf->mddev->ro)
            for (i=0; i<failed;i++) {
                  dev = &sh->dev[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);
                        }
                  }
            }
      spin_unlock(&sh->lock);

      while ((bi=return_bi)) {
            int bytes = bi->bi_size;

            return_bi = bi->bi_next;
            bi->bi_next = NULL;
            bi->bi_size = 0;
            bi->bi_end_io(bi, bytes, 0);
      }
      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 = 1;
            else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                  rw = 0;
            else
                  continue;

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

            bi->bi_rw = rw;
            if (rw)
                  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 (syncing)
                        md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                  bi->bi_bdev = rdev->bdev;
                  PRINTK("for %llu schedule op %ld on disc %d\n",
                        (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 == 1)
                        set_bit(STRIPE_DEGRADED, &sh->state);
                  PRINTK("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 void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
{
      if (sh->raid_conf->level == 6)
            handle_stripe6(sh, tmp_page);
      else
            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->handle_list);
            }
      }
}

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_to_conf(mddev);
      int i;

      rcu_read_lock();
      for (i=0; i<mddev->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)) {
                  request_queue_t *r_queue = bdev_get_queue(rdev->bdev);

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

                  if (r_queue->unplug_fn)
                        r_queue->unplug_fn(r_queue);

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

static void raid5_unplug_device(request_queue_t *q)
{
      mddev_t *mddev = q->queuedata;
      raid5_conf_t *conf = mddev_to_conf(mddev);
      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_issue_flush(request_queue_t *q, struct gendisk *disk,
                       sector_t *error_sector)
{
      mddev_t *mddev = q->queuedata;
      raid5_conf_t *conf = mddev_to_conf(mddev);
      int i, ret = 0;

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

                  if (!r_queue->issue_flush_fn)
                        ret = -EOPNOTSUPP;
                  else {
                        atomic_inc(&rdev->nr_pending);
                        rcu_read_unlock();
                        ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
                                                error_sector);
                        rdev_dec_pending(rdev, mddev);
                        rcu_read_lock();
                  }
            }
      }
      rcu_read_unlock();
      return ret;
}

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

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

      md_write_start(mddev, bi);

      disk_stat_inc(mddev->gendisk, ios[rw]);
      disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));

      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;

      retry:
            prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
            if (likely(conf->expand_progress == MaxSector))
                  disks = conf->raid_disks;
            else {
                  /* spinlock is needed as expand_progress may be
                   * 64bit on a 32bit platform, and so it might be
                   * possible to see a half-updated value
                   * Ofcourse expand_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);
                  disks = conf->raid_disks;
                  if (logical_sector >= conf->expand_progress)
                        disks = conf->previous_raid_disks;
                  else {
                        if (logical_sector >= conf->expand_lo) {
                              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(logical_sector, disks, data_disks,
                                      &dd_idx, &pd_idx, conf);
            PRINTK("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, disks, pd_idx, (bi->bi_rw&RWA_MASK));
            if (sh) {
                  if (unlikely(conf->expand_progress != MaxSector)) {
                        /* 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 (logical_sector <  conf->expand_progress &&
                            disks == conf->previous_raid_disks)
                              /* mismatch, need to try again */
                              must_retry = 1;
                        spin_unlock_irq(&conf->device_lock);
                        if (must_retry) {
                              release_stripe(sh);
                              goto retry;
                        }
                  }
                  /* FIXME what if we get a false positive because these
                   * are being updated.
                   */
                  if (logical_sector >= mddev->suspend_lo &&
                      logical_sector < mddev->suspend_hi) {
                        release_stripe(sh);
                        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);
                  handle_stripe(sh, NULL);
                  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 = --bi->bi_phys_segments;
      spin_unlock_irq(&conf->device_lock);
      if (remaining == 0) {
            int bytes = bi->bi_size;

            if ( rw == WRITE )
                  md_write_end(mddev);
            bi->bi_size = 0;
            bi->bi_end_io(bi, bytes, 0);
      }
      return 0;
}

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;
      int pd_idx;
      sector_t first_sector, last_sector;
      int raid_disks;
      int data_disks;
      int i;
      int dd_idx;
      sector_t writepos, safepos, gap;

      if (sector_nr == 0 &&
          conf->expand_progress != 0) {
            /* restarting in the middle, skip the initial sectors */
            sector_nr = conf->expand_progress;
            sector_div(sector_nr, conf->raid_disks-1);
            *skipped = 1;
            return sector_nr;
      }

      /* 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 forward from expand_progress new_maps
       * to after where expand_lo old_maps to
       */
      writepos = conf->expand_progress +
            conf->chunk_size/512*(conf->raid_disks-1);
      sector_div(writepos, conf->raid_disks-1);
      safepos = conf->expand_lo;
      sector_div(safepos, conf->previous_raid_disks-1);
      gap = conf->expand_progress - conf->expand_lo;

      if (writepos >= safepos ||
          gap > (conf->raid_disks-1)*3000*2 /*3Meg*/) {
            /* Cannot proceed until we've updated the superblock... */
            wait_event(conf->wait_for_overlap,
                     atomic_read(&conf->reshape_stripes)==0);
            mddev->reshape_position = conf->expand_progress;
            mddev->sb_dirty = 1;
            md_wakeup_thread(mddev->thread);
            wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
                     kthread_should_stop());
            spin_lock_irq(&conf->device_lock);
            conf->expand_lo = mddev->reshape_position;
            spin_unlock_irq(&conf->device_lock);
            wake_up(&conf->wait_for_overlap);
      }

      for (i=0; i < conf->chunk_size/512; i+= STRIPE_SECTORS) {
            int j;
            int skipped = 0;
            pd_idx = stripe_to_pdidx(sector_nr+i, conf, conf->raid_disks);
            sh = get_active_stripe(conf, sector_nr+i,
                               conf->raid_disks, pd_idx, 0);
            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;
                  s = compute_blocknr(sh, j);
                  if (s < (mddev->array_size<<1)) {
                        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);
            }
            release_stripe(sh);
      }
      spin_lock_irq(&conf->device_lock);
      conf->expand_progress = (sector_nr + i)*(conf->raid_disks-1);
      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.
       */
      raid_disks = conf->previous_raid_disks;
      data_disks = raid_disks - 1;
      first_sector =
            raid5_compute_sector(sector_nr*(conf->raid_disks-1),
                             raid_disks, data_disks,
                             &dd_idx, &pd_idx, conf);
      last_sector =
            raid5_compute_sector((sector_nr+conf->chunk_size/512)
                             *(conf->raid_disks-1) -1,
                             raid_disks, data_disks,
                             &dd_idx, &pd_idx, conf);
      if (last_sector >= (mddev->size<<1))
            last_sector = (mddev->size<<1)-1;
      while (first_sector <= last_sector) {
            pd_idx = stripe_to_pdidx(first_sector, conf, conf->previous_raid_disks);
            sh = get_active_stripe(conf, first_sector,
                               conf->previous_raid_disks, pd_idx, 0);
            set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
            set_bit(STRIPE_HANDLE, &sh->state);
            release_stripe(sh);
            first_sector += STRIPE_SECTORS;
      }
      return conf->chunk_size>>9;
}

/* 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;
      int pd_idx;
      int raid_disks = conf->raid_disks;
      sector_t max_sector = mddev->size << 1;
      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;
      }

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

      /* 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->size << 1) - 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 */
      }

      pd_idx = stripe_to_pdidx(sector_nr, conf, raid_disks);
      sh = get_active_stripe(conf, sector_nr, raid_disks, pd_idx, 1);
      if (sh == NULL) {
            sh = get_active_stripe(conf, sector_nr, raid_disks, pd_idx, 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<mddev->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);

      handle_stripe(sh, NULL);
      release_stripe(sh);

      return STRIPE_SECTORS;
}

/*
 * 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_to_conf(mddev);
      int handled;

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

      md_check_recovery(mddev);

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

            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);
            }

            if (list_empty(&conf->handle_list) &&
                atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
                !blk_queue_plugged(mddev->queue) &&
                !list_empty(&conf->delayed_list))
                  raid5_activate_delayed(conf);

            if (list_empty(&conf->handle_list))
                  break;

            first = conf->handle_list.next;
            sh = list_entry(first, struct stripe_head, lru);

            list_del_init(first);
            atomic_inc(&sh->count);
            BUG_ON(atomic_read(&sh->count)!= 1);
            spin_unlock_irq(&conf->device_lock);
            
            handled++;
            handle_stripe(sh, conf->spare_page);
            release_stripe(sh);

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

      spin_unlock_irq(&conf->device_lock);

      unplug_slaves(mddev);

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

static ssize_t
raid5_show_stripe_cache_size(mddev_t *mddev, char *page)
{
      raid5_conf_t *conf = mddev_to_conf(mddev);
      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_to_conf(mddev);
      char *end;
      int new;
      if (len >= PAGE_SIZE)
            return -EINVAL;
      if (!conf)
            return -ENODEV;

      new = simple_strtoul(page, &end, 10);
      if (!*page || (*end && *end != '\n') )
            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;
      }
      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
stripe_cache_active_show(mddev_t *mddev, char *page)
{
      raid5_conf_t *conf = mddev_to_conf(mddev);
      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,
      NULL,
};
static struct attribute_group raid5_attrs_group = {
      .name = NULL,
      .attrs = raid5_attrs,
};

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

      if (mddev->level != 5 && mddev->level != 4 && mddev->level != 6) {
            printk(KERN_ERR "raid5: %s: raid level not set to 4/5/6 (%d)\n",
                   mdname(mddev), mddev->level);
            return -EIO;
      }

      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;

            if (mddev->new_level != mddev->level ||
                mddev->new_layout != mddev->layout ||
                mddev->new_chunk != mddev->chunk_size) {
                  printk(KERN_ERR "raid5: %s: unsupported reshape required - aborting.\n",
                         mdname(mddev));
                  return -EINVAL;
            }
            if (mddev->delta_disks <= 0) {
                  printk(KERN_ERR "raid5: %s: unsupported reshape (reduce disks) 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->chunk_size>>9)*(mddev->raid_disks-1))) {
                  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_size>>9)*(old_disks-1));
            /* here_old is the first stripe that we might need to read from */
            if (here_new >= here_old) {
                  /* 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; */
      }


      mddev->private = kzalloc(sizeof (raid5_conf_t), GFP_KERNEL);
      if ((conf = mddev->private) == NULL)
            goto abort;
      if (mddev->reshape_position == MaxSector) {
            conf->previous_raid_disks = conf->raid_disks = mddev->raid_disks;
      } else {
            conf->raid_disks = mddev->raid_disks;
            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->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->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);

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

      ITERATE_RDEV(mddev,rdev,tmp) {
            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);
                  conf->working_disks++;
            }
      }

      /*
       * 0 for a fully functional array, 1 or 2 for a degraded array.
       */
      mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
      conf->mddev = mddev;
      conf->chunk_size = mddev->chunk_size;
      conf->level = mddev->level;
      if (conf->level == 6)
            conf->max_degraded = 2;
      else
            conf->max_degraded = 1;
      conf->algorithm = mddev->layout;
      conf->max_nr_stripes = NR_STRIPES;
      conf->expand_progress = mddev->reshape_position;

      /* device size must be a multiple of chunk size */
      mddev->size &= ~(mddev->chunk_size/1024 -1);
      mddev->resync_max_sectors = mddev->size << 1;

      if (conf->level == 6 && conf->raid_disks < 4) {
            printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
                   mdname(mddev), conf->raid_disks);
            goto abort;
      }
      if (!conf->chunk_size || conf->chunk_size % 4) {
            printk(KERN_ERR "raid5: invalid chunk size %d for %s\n",
                  conf->chunk_size, mdname(mddev));
            goto abort;
      }
      if (conf->algorithm > ALGORITHM_RIGHT_SYMMETRIC) {
            printk(KERN_ERR 
                  "raid5: unsupported parity algorithm %d for %s\n",
                  conf->algorithm, mdname(mddev));
            goto abort;
      }
      if (mddev->degraded > conf->max_degraded) {
            printk(KERN_ERR "raid5: not enough operational devices for %s"
                  " (%d/%d failed)\n",
                  mdname(mddev), conf->failed_disks, conf->raid_disks);
            goto abort;
      }

      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;
            }
      }

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

      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,
                  conf->algorithm);
      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, conf->algorithm);

      print_raid5_conf(conf);

      if (conf->expand_progress != MaxSector) {
            printk("...ok start reshape thread\n");
            conf->expand_lo = conf->expand_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_size / 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 */
      sysfs_create_group(&mddev->kobj, &raid5_attrs_group);

      mddev->queue->unplug_fn = raid5_unplug_device;
      mddev->queue->issue_flush_fn = raid5_issue_flush;
      mddev->array_size =  mddev->size * (conf->previous_raid_disks -
                                  conf->max_degraded);

      return 0;
abort:
      if (conf) {
            print_raid5_conf(conf);
            safe_put_page(conf->spare_page);
            kfree(conf->disks);
            kfree(conf->stripe_hashtbl);
            kfree(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;
      shrink_stripes(conf);
      kfree(conf->stripe_hashtbl);
      blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
      sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
      kfree(conf->disks);
      kfree(conf);
      mddev->private = NULL;
      return 0;
}

#if RAID5_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_size >> 10, mddev->layout);
      seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->working_disks);
      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, "]");
#if RAID5_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 fd:%d\n", conf->raid_disks,
             conf->working_disks, conf->failed_disks);

      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_bit(In_sync, &tmp->rdev->flags)) {
                  mddev->degraded--;
                  conf->failed_disks--;
                  conf->working_disks++;
                  set_bit(In_sync, &tmp->rdev->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 (test_bit(In_sync, &rdev->flags) ||
                atomic_read(&rdev->nr_pending)) {
                  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 found = 0;
      int disk;
      struct disk_info *p;

      if (mddev->degraded > conf->max_degraded)
            /* no point adding a device */
            return 0;

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

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.
       */
      raid5_conf_t *conf = mddev_to_conf(mddev);

      sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
      mddev->array_size = (sectors * (mddev->raid_disks-conf->max_degraded))>>1;
      set_capacity(mddev->gendisk, mddev->array_size << 1);
      mddev->changed = 1;
      if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
            mddev->recovery_cp = mddev->size << 1;
            set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
      }
      mddev->size = sectors /2;
      mddev->resync_max_sectors = sectors;
      return 0;
}

#ifdef CONFIG_MD_RAID5_RESHAPE
static int raid5_check_reshape(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev_to_conf(mddev);
      int err;

      if (mddev->delta_disks < 0 ||
          mddev->new_level != mddev->level)
            return -EINVAL; /* Cannot shrink array or change level yet */
      if (mddev->delta_disks == 0)
            return 0; /* nothing to do */

      /* 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.
       */
      if ((mddev->chunk_size / STRIPE_SIZE) * 4 > conf->max_nr_stripes ||
          (mddev->new_chunk / STRIPE_SIZE) * 4 > conf->max_nr_stripes) {
            printk(KERN_WARNING "raid5: reshape: not enough stripes.  Needed %lu\n",
                   (mddev->chunk_size / STRIPE_SIZE)*4);
            return -ENOSPC;
      }

      err = resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
      if (err)
            return err;

      /* looks like we might be able to manage this */
      return 0;
}

static int raid5_start_reshape(mddev_t *mddev)
{
      raid5_conf_t *conf = mddev_to_conf(mddev);
      mdk_rdev_t *rdev;
      struct list_head *rtmp;
      int spares = 0;
      int added_devices = 0;

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

      ITERATE_RDEV(mddev, rdev, rtmp)
            if (rdev->raid_disk < 0 &&
                !test_bit(Faulty, &rdev->flags))
                  spares++;

      if (spares < mddev->delta_disks-1)
            /* Not enough devices even to make a degraded array
             * of that size
             */
            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->expand_progress = 0;
      conf->expand_lo = 0;
      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.
       */
      ITERATE_RDEV(mddev, rdev, rtmp)
            if (rdev->raid_disk < 0 &&
                !test_bit(Faulty, &rdev->flags)) {
                  if (raid5_add_disk(mddev, rdev)) {
                        char nm[20];
                        set_bit(In_sync, &rdev->flags);
                        conf->working_disks++;
                        added_devices++;
                        rdev->recovery_offset = 0;
                        sprintf(nm, "rd%d", rdev->raid_disk);
                        sysfs_create_link(&mddev->kobj, &rdev->kobj, nm);
                  } else
                        break;
            }

      mddev->degraded = (conf->raid_disks - conf->previous_raid_disks) - added_devices;
      mddev->raid_disks = conf->raid_disks;
      mddev->reshape_position = 0;
      mddev->sb_dirty = 1;

      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->expand_progress = MaxSector;
            spin_unlock_irq(&conf->device_lock);
            return -EAGAIN;
      }
      md_wakeup_thread(mddev->sync_thread);
      md_new_event(mddev);
      return 0;
}
#endif

static void end_reshape(raid5_conf_t *conf)
{
      struct block_device *bdev;

      if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {
            conf->mddev->array_size = conf->mddev->size * (conf->raid_disks-1);
            set_capacity(conf->mddev->gendisk, conf->mddev->array_size << 1);
            conf->mddev->changed = 1;

            bdev = bdget_disk(conf->mddev->gendisk, 0);
            if (bdev) {
                  mutex_lock(&bdev->bd_inode->i_mutex);
                  i_size_write(bdev->bd_inode, conf->mddev->array_size << 10);
                  mutex_unlock(&bdev->bd_inode->i_mutex);
                  bdput(bdev);
            }
            spin_lock_irq(&conf->device_lock);
            conf->expand_progress = MaxSector;
            spin_unlock_irq(&conf->device_lock);
            conf->mddev->reshape_position = MaxSector;

            /* 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 *
                        (conf->mddev->chunk_size / PAGE_SIZE);
                  if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
                        conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
            }
      }
}

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

      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);
            conf->quiesce = 1;
            wait_event_lock_irq(conf->wait_for_stripe,
                            atomic_read(&conf->active_stripes) == 0,
                            conf->device_lock, /* nothing */);
            spin_unlock_irq(&conf->device_lock);
            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 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,
      .quiesce    = raid5_quiesce,
};
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,
#ifdef CONFIG_MD_RAID5_RESHAPE
      .check_reshape    = raid5_check_reshape,
      .start_reshape  = raid5_start_reshape,
#endif
      .quiesce    = raid5_quiesce,
};

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,
      .quiesce    = raid5_quiesce,
};

static int __init raid5_init(void)
{
      int e;

      e = raid6_select_algo();
      if ( e )
            return e;
      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");

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