text: /*
   * 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);
  				if (conf->retry_read_aligned)
  					md_wakeup_thread(conf->mddev->thread);
  			}
  		}
  	}
  }
  static void release_stripe(struct stripe_head *sh)
  {
  	raid5_conf_t *conf = sh->raid_conf;
  	unsigned long flags;
  
  	spin_lock_irqsave(&conf->device_lock, flags);
  	__release_stripe(conf, sh);
  	spin_unlock_irqrestore(&conf->device_lock, flags);
  }
  
  static inline void remove_hash(struct stripe_head *sh)
  {
  	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)
  {
  	struct kmem_cache *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;
  	struct kmem_cache *sc;
  	int i;
  
  	if (newsize <= conf->pool_size)
  		return 0; /* never bother to shrink */
  
  	md_allow_write(conf->mddev);
  
  	/* 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) {
  		set_bit(R5_UPTODATE, &sh->dev[i].flags);
  		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);
  	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;
  	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;
  	}
  
  	if (!uptodate)
  		md_error(conf->mddev, conf->disks[i].rdev);
  
  	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
  	
  	clear_bit(R5_LOCKED, &sh->dev[i].flags);
  	set_bit(STRIPE_HANDLE, &sh->state);
  	release_stripe(sh);
  	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)) {
  		set_bit(MD_CHANGE_DEVS, &mddev->flags);
  		if (test_and_clear_bit(In_sync, &rdev->flags)) {
  			unsigned long flags;
  			spin_lock_irqsave(&conf->device_lock, flags);
  			mddev->degraded++;
  			spin_unlock_irqrestore(&conf->device_lock, flags);
  			/*
  			 * if recovery was running, make sure it aborts.
  			 */
  			set_bit(MD_RECOVERY_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->raid_disks - mddev->degraded);
  	}
  }
  
  /*
   * Input: a 'big' sector number,
   * Output: index of the data and parity disk, and the sector # in them.
   */
  static sector_t raid5_compute_sector(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;
  	int data_disks = raid_disks - conf->max_degraded;
  	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:
  		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 = sh->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);
  
  				BUG_ON(sh->dev[i].written);
  				sh->dev[i].written = chosen;
  			}
  		break;
  	case CHECK_PARITY:
  		BUG();		/* Not implemented yet */
  	}
  
  	for (i = disks; i--;)
  		if (sh->dev[i].written) {
  			sector_t sector = sh->dev[i].sector;
  			struct bio *wbi = sh->dev[i].written;
  			while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
  				copy_data(1, wbi, sh->dev[i].page, sector);
  				wbi = r5_next_bio(wbi, sector);
  			}
  
  			set_bit(R5_LOCKED, &sh->dev[i].flags);
  			set_bit(R5_UPTODATE, &sh->dev[i].flags);
  		}
  
  //	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)
  {
  	int i, count, disks = sh->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)
  {
  	int i, count, disks = sh->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;
  	int pd_idx, dd_idx;
  	int chunk_offset = sector_div(stripe, sectors_per_chunk);
  
  	raid5_compute_sector(stripe * (disks - conf->max_degraded)
  			     *sectors_per_chunk + chunk_offset,
  			     disks, disks - conf->max_degraded,
  			     &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);
  					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) 
  				    ) &&
  			    !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) 
  				    ) &&
  			    !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,
  			      test_bit(BIO_UPTODATE, &bi->bi_flags)
  			        ? 0 : -EIO);
  	}
  	for (i=disks; i-- ;) {
  		int rw;
  		struct bio *bi;
  		mdk_rdev_t *rdev;
  		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
  			rw = WRITE;
  		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
  			rw = READ;
  		else
  			continue;
   
  		bi = &sh->dev[i].req;
   
  		bi->bi_rw = rw;
  		if (rw == WRITE)
  			bi->bi_end_io = raid5_end_write_request;
  		else
  			bi->bi_end_io = raid5_end_read_request;
   
  		rcu_read_lock();
  		rdev = rcu_dereference(conf->disks[i].rdev);
  		if (rdev && test_bit(Faulty, &rdev->flags))
  			rdev = NULL;
  		if (rdev)
  			atomic_inc(&rdev->nr_pending);
  		rcu_read_unlock();
   
  		if (rdev) {
  			if (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 == WRITE)
  				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 = 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[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);
  	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)) {
  			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)) || 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 >= 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);
  					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)
  				    ) &&
  			    !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);
  				}
  			}
  		}
  
  	if (expanded && test_bit(STRIPE_EXPANDING, &sh->state)) {
  		/* Need to write out all blocks after computing P&Q */
  		sh->disks = conf->raid_disks;
  		sh->pd_idx = stripe_to_pdidx(sh->sector, conf,
  					     conf->raid_disks);
  		compute_parity6(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 != pd_idx && i != qd_idx) {
  				int dd_idx2, pd_idx2, 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 - conf->max_degraded,
  					&dd_idx2, &pd_idx2, conf);
  				sh2 = get_active_stripe(conf, s,
  							conf->raid_disks,
  						       pd_idx2, 1);
  				if (sh2 == NULL)
  					/* so for only the early blocks of
  					 * this stripe have been requests.
  					 * When later blocks get requests, we
  					 * will try again
  					 */
  					continue;
  				if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
  				    test_bit(R5_Expanded,
  					     &sh2->dev[dd_idx2].flags)) {
  					/* must have already done this block */
  					release_stripe(sh2);
  					continue;
  				}
  				memcpy(page_address(sh2->dev[dd_idx2].page),
  				       page_address(sh->dev[i].page),
  				       STRIPE_SIZE);
  				set_bit(R5_Expanded, &sh2->dev[dd_idx2].flags);
  				set_bit(R5_UPTODATE, &sh2->dev[dd_idx2].flags);
  				for (j = 0 ; j < conf->raid_disks ; j++)
  					if (j != sh2->pd_idx &&
  					    j != raid6_next_disk(sh2->pd_idx,
  							   sh2->disks) &&
  					    !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,
  			      test_bit(BIO_UPTODATE, &bi->bi_flags)
  			        ? 0 : -EIO);
  	}
  	for (i=disks; i-- ;) {
  		int rw;
  		struct bio *bi;
  		mdk_rdev_t *rdev;
  		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
  			rw = WRITE;
  		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
  			rw = READ;
  		else
  			continue;
  
  		bi = &sh->dev[i].req;
  
  		bi->bi_rw = rw;
  		if (rw == WRITE)
  			bi->bi_end_io = raid5_end_write_request;
  		else
  			bi->bi_end_io = raid5_end_read_request;
  
  		rcu_read_lock();
  		rdev = rcu_dereference(conf->disks[i].rdev);
  		if (rdev && test_bit(Faulty, &rdev->flags))
  			rdev = NULL;
  		if (rdev)
  			atomic_inc(&rdev->nr_pending);
  		rcu_read_unlock();
  
  		if (rdev) {
  			if (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 == WRITE)
  				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 raid5_congested(void *data, int bits)
  {
  	mddev_t *mddev = data;
  	raid5_conf_t *conf = mddev_to_conf(mddev);
  
  	/* No difference between reads and writes.  Just check
  	 * how busy the stripe_cache is
  	 */
  	if (conf->inactive_blocked)
  		return 1;
  	if (conf->quiesce)
  		return 1;
  	if (list_empty_careful(&conf->inactive_list))
  		return 1;
  
  	return 0;
  }
  
  /* We want read requests to align with chunks where possible,
   * but write requests don't need to.
   */
  static int raid5_mergeable_bvec(request_queue_t *q, struct bio *bio, struct bio_vec *biovec)
  {
  	mddev_t *mddev = q->queuedata;
  	sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
  	int max;
  	unsigned int chunk_sectors = mddev->chunk_size >> 9;
  	unsigned int bio_sectors = bio->bi_size >> 9;
  
  	if (bio_data_dir(bio) == WRITE)
  		return biovec->bv_len; /* always allow writes to be mergeable */
  
  	max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
  	if (max < 0) max = 0;
  	if (max <= biovec->bv_len && bio_sectors == 0)
  		return biovec->bv_len;
  	else
  		return max;
  }
  
  
  static int in_chunk_boundary(mddev_t *mddev, struct bio *bio)
  {
  	sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
  	unsigned int chunk_sectors = mddev->chunk_size >> 9;
  	unsigned int bio_sectors = bio->bi_size >> 9;
  
  	return  chunk_sectors >=
  		((sector & (chunk_sectors - 1)) + bio_sectors);
  }
  
  /*
   *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
   *  later sampled by raid5d.
   */
  static void add_bio_to_retry(struct bio *bi,raid5_conf_t *conf)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&conf->device_lock, flags);
  
  	bi->bi_next = conf->retry_read_aligned_list;
  	conf->retry_read_aligned_list = bi;
  
  	spin_unlock_irqrestore(&conf->device_lock, flags);
  	md_wakeup_thread(conf->mddev->thread);
  }
  
  
  static struct bio *remove_bio_from_retry(raid5_conf_t *conf)
  {
  	struct bio *bi;
  
  	bi = conf->retry_read_aligned;
  	if (bi) {
  		conf->retry_read_aligned = NULL;
  		return bi;
  	}
  	bi = conf->retry_read_aligned_list;
  	if(bi) {
  		conf->retry_read_aligned_list = bi->bi_next;
  		bi->bi_next = NULL;
  		bi->bi_phys_segments = 1; /* biased count of active stripes */
  		bi->bi_hw_segments = 0; /* count of processed stripes */
  	}
  
  	return bi;
  }
  
  
  /*
   *  The "raid5_align_endio" should check if the read succeeded and if it
   *  did, call bio_endio on the original bio (having bio_put the new bio
   *  first).
   *  If the read failed..
   */
  static int raid5_align_endio(struct bio *bi, unsigned int bytes, int error)
  {
  	struct bio* raid_bi  = bi->bi_private;
  	mddev_t *mddev;
  	raid5_conf_t *conf;
  	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
  	mdk_rdev_t *rdev;
  
  	if (bi->bi_size)
  		return 1;
  	bio_put(bi);
  
  	mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
  	conf = mddev_to_conf(mddev);
  	rdev = (void*)raid_bi->bi_next;
  	raid_bi->bi_next = NULL;
  
  	rdev_dec_pending(rdev, conf->mddev);
  
  	if (!error && uptodate) {
  		bio_endio(raid_bi, bytes, 0);
  		if (atomic_dec_and_test(&conf->active_aligned_reads))
  			wake_up(&conf->wait_for_stripe);
  		return 0;
  	}
  
  
  	PRINTK("raid5_align_endio : io error...handing IO for a retry\n");
  
  	add_bio_to_retry(raid_bi, conf);
  	return 0;
  }
  
  static int bio_fits_rdev(struct bio *bi)
  {
  	request_queue_t *q = bdev_get_queue(bi->bi_bdev);
  
  	if ((bi->bi_size>>9) > q->max_sectors)
  		return 0;
  	blk_recount_segments(q, bi);
  	if (bi->bi_phys_segments > q->max_phys_segments ||
  	    bi->bi_hw_segments > q->max_hw_segments)
  		return 0;
  
  	if (q->merge_bvec_fn)
  		/* it's too hard to apply the merge_bvec_fn at this stage,
  		 * just just give up
  		 */
  		return 0;
  
  	return 1;
  }
  
  
  static int chunk_aligned_read(request_queue_t *q, struct bio * raid_bio)
  {
  	mddev_t *mddev = q->queuedata;
  	raid5_conf_t *conf = mddev_to_conf(mddev);
  	const unsigned int raid_disks = conf->raid_disks;
  	const unsigned int data_disks = raid_disks - conf->max_degraded;
  	unsigned int dd_idx, pd_idx;
  	struct bio* align_bi;
  	mdk_rdev_t *rdev;
  
  	if (!in_chunk_boundary(mddev, raid_bio)) {
  		PRINTK("chunk_aligned_read : non aligned\n");
  		return 0;
  	}
  	/*
   	 * use bio_clone to make a copy of the bio
  	 */
  	align_bi = bio_clone(raid_bio, GFP_NOIO);
  	if (!align_bi)
  		return 0;
  	/*
  	 *   set bi_end_io to a new function, and set bi_private to the
  	 *     original bio.
  	 */
  	align_bi->bi_end_io  = raid5_align_endio;
  	align_bi->bi_private = raid_bio;
  	/*
  	 *	compute position
  	 */
  	align_bi->bi_sector =  raid5_compute_sector(raid_bio->bi_sector,
  					raid_disks,
  					data_disks,
  					&dd_idx,
  					&pd_idx,
  					conf);
  
  	rcu_read_lock();
  	rdev = rcu_dereference(conf->disks[dd_idx].rdev);
  	if (rdev && test_bit(In_sync, &rdev->flags)) {
  		atomic_inc(&rdev->nr_pending);
  		rcu_read_unlock();
  		raid_bio->bi_next = (void*)rdev;
  		align_bi->bi_bdev =  rdev->bdev;
  		align_bi->bi_flags &= ~(1 << BIO_SEG_VALID);
  		align_bi->bi_sector += rdev->data_offset;
  
  		if (!bio_fits_rdev(align_bi)) {
  			/* too big in some way */
  			bio_put(align_bi);
  			rdev_dec_pending(rdev, mddev);
  			return 0;
  		}
  
  		spin_lock_irq(&conf->device_lock);
  		wait_event_lock_irq(conf->wait_for_stripe,
  				    conf->quiesce == 0,
  				    conf->device_lock, /* nothing */);
  		atomic_inc(&conf->active_aligned_reads);
  		spin_unlock_irq(&conf->device_lock);
  
  		generic_make_request(align_bi);
  		return 1;
  	} else {
  		rcu_read_unlock();
  		bio_put(align_bi);
  		return 0;
  	}
  }
  
  
  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));
  
  	if (rw == READ &&
  	     mddev->reshape_position == MaxSector &&
  	     chunk_aligned_read(q,bi))
              	return 0;
  
  	logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
  	last_sector = bi->bi_sector + (bi->bi_size>>9);
  	bi->bi_next = NULL;
  	bi->bi_phys_segments = 1;	/* over-loaded to count active stripes */
  
  	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
  		DEFINE_WAIT(w);
  		int disks, data_disks;
  
  	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,
  			      test_bit(BIO_UPTODATE, &bi->bi_flags)
  			        ? 0 : -EIO);
  	}
  	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 = conf->previous_raid_disks;
  	int data_disks = raid_disks - conf->max_degraded;
  	int new_data_disks = conf->raid_disks - conf->max_degraded;
  	int i;
  	int dd_idx;
  	sector_t writepos, 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, new_data_disks);
  		*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*(new_data_disks);
  	sector_div(writepos, new_data_disks);
  	safepos = conf->expand_lo;
  	sector_div(safepos, data_disks);
  	gap = conf->expand_progress - conf->expand_lo;
  
  	if (writepos >= safepos ||
  	    gap > (new_data_disks)*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;
  		set_bit(MD_CHANGE_DEVS, &mddev->flags);
  		md_wakeup_thread(mddev->thread);
  		wait_event(mddev->sb_wait, mddev->flags == 0 ||
  			   kthread_should_stop());
  		spin_lock_irq(&conf->device_lock);
  		conf->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;
  			if (conf->level == 6 &&
  			    j == raid6_next_disk(sh->pd_idx, sh->disks))
  				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) * new_data_disks;
  	spin_unlock_irq(&conf->device_lock);
  	/* Ok, those stripe are ready. We can start scheduling
  	 * reads on the source stripes.
  	 * The source stripes are determined by mapping the first and last
  	 * block on the destination stripes.
  	 */
  	first_sector =
  		raid5_compute_sector(sector_nr*(new_data_disks),
  				     raid_disks, data_disks,
  				     &dd_idx, &pd_idx, conf);
  	last_sector =
  		raid5_compute_sector((sector_nr+conf->chunk_size/512)
  				     *(new_data_disks) -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;
  }
  
  static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
  {
  	/* We may not be able to submit a whole bio at once as there
  	 * may not be enough stripe_heads available.
  	 * We cannot pre-allocate enough stripe_heads as we may need
  	 * more than exist in the cache (if we allow ever large chunks).
  	 * So we do one stripe head at a time and record in
  	 * ->bi_hw_segments how many have been done.
  	 *
  	 * We *know* that this entire raid_bio is in one chunk, so
  	 * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
  	 */
  	struct stripe_head *sh;
  	int dd_idx, pd_idx;
  	sector_t sector, logical_sector, last_sector;
  	int scnt = 0;
  	int remaining;
  	int handled = 0;
  
  	logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
  	sector = raid5_compute_sector(	logical_sector,
  					conf->raid_disks,
  					conf->raid_disks - conf->max_degraded,
  					&dd_idx,
  					&pd_idx,
  					conf);
  	last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
  
  	for (; logical_sector < last_sector;
  	     logical_sector += STRIPE_SECTORS,
  		     sector += STRIPE_SECTORS,
  		     scnt++) {
  
  		if (scnt < raid_bio->bi_hw_segments)
  			/* already done this stripe */
  			continue;
  
  		sh = get_active_stripe(conf, sector, conf->raid_disks, pd_idx, 1);
  
  		if (!sh) {
  			/* failed to get a stripe - must wait */
  			raid_bio->bi_hw_segments = scnt;
  			conf->retry_read_aligned = raid_bio;
  			return handled;
  		}
  
  		set_bit(R5_ReadError, &sh->dev[dd_idx].flags);
  		if (!add_stripe_bio(sh, raid_bio, dd_idx, 0)) {
  			release_stripe(sh);
  			raid_bio->bi_hw_segments = scnt;
  			conf->retry_read_aligned = raid_bio;
  			return handled;
  		}
  
  		handle_stripe(sh, NULL);
  		release_stripe(sh);
  		handled++;
  	}
  	spin_lock_irq(&conf->device_lock);
  	remaining = --raid_bio->bi_phys_segments;
  	spin_unlock_irq(&conf->device_lock);
  	if (remaining == 0) {
  		int bytes = raid_bio->bi_size;
  
  		raid_bio->bi_size = 0;
  		raid_bio->bi_end_io(raid_bio, bytes,
  			      test_bit(BIO_UPTODATE, &raid_bio->bi_flags)
  			        ? 0 : -EIO);
  	}
  	if (atomic_dec_and_test(&conf->active_aligned_reads))
  		wake_up(&conf->wait_for_stripe);
  	return handled;
  }
  
  
  
  /*
   * This is our raid5 kernel thread.
   *
   * We scan the hash table for stripes which can be handled now.
   * During the scan, completed stripes are saved for us by the interrupt
   * handler, so that they will not have to wait for our next wakeup.
   */
  static void raid5d (mddev_t *mddev)
  {
  	struct stripe_head *sh;
  	raid5_conf_t *conf = mddev_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;
  		struct bio *bio;
  
  		if (conf->seq_flush != conf->seq_write) {
  			int seq = conf->seq_flush;
  			spin_unlock_irq(&conf->device_lock);
  			bitmap_unplug(mddev->bitmap);
  			spin_lock_irq(&conf->device_lock);
  			conf->seq_write = seq;
  			activate_bit_delay(conf);
  		}
  
  		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);
  
  		while ((bio = remove_bio_from_retry(conf))) {
  			int ok;
  			spin_unlock_irq(&conf->device_lock);
  			ok = retry_aligned_read(conf, bio);
  			spin_lock_irq(&conf->device_lock);
  			if (!ok)
  				break;
  			handled++;
  		}
  
  		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;
  	}
  	md_allow_write(mddev);
  	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;
  	int working_disks = 0;
  
  	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;
  		int max_degraded = (mddev->level == 5 ? 1 : 2);
  
  		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 - max_degraded))) {
  			printk(KERN_ERR "raid5: reshape_position not "
  			       "on a stripe boundary\n");
  			return -EINVAL;
  		}
  		/* here_new is the stripe we will write to */
  		here_old = mddev->reshape_position;
  		sector_div(here_old, (mddev->chunk_size>>9)*
  			   (old_disks-max_degraded));
  		/* 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);
  	atomic_set(&conf->active_aligned_reads, 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);
  			working_disks++;
  		}
  	}
  
  	/*
  	 * 0 for a fully functional array, 1 or 2 for a degraded array.
  	 */
  	mddev->degraded = conf->raid_disks - 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), mddev->degraded, 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 */
  	if (sysfs_create_group(&mddev->kobj, &raid5_attrs_group))
  		printk(KERN_WARNING
  		       "raid5: failed to create sysfs attributes for %s\n",
  		       mdname(mddev));
  
  	mddev->queue->unplug_fn = raid5_unplug_device;
  	mddev->queue->issue_flush_fn = raid5_issue_flush;
  	mddev->queue->backing_dev_info.congested_data = mddev;
  	mddev->queue->backing_dev_info.congested_fn = raid5_congested;
  
  	mddev->array_size =  mddev->size * (conf->previous_raid_disks -
  					    conf->max_degraded);
  
  	blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);
  
  	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);
  	mddev->queue->backing_dev_info.congested_fn = NULL;
  	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
  	sysfs_remove_group(&mddev->kobj, &raid5_attrs_group);
  	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->raid_disks - mddev->degraded);
  	for (i = 0; i < conf->raid_disks; i++)
  		seq_printf (seq, "%s",
  			       conf->disks[i].rdev &&
  			       test_bit(In_sync, &conf->disks[i].rdev->flags) ? "U" : "_");
  	seq_printf (seq, "]");
  #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\n", conf->raid_disks,
  		 conf->raid_disks - conf->mddev->degraded);
  
  	for (i = 0; i < conf->raid_disks; i++) {
  		char b[BDEVNAME_SIZE];
  		tmp = conf->disks + i;
  		if (tmp->rdev)
  		printk(" disk %d, o:%d, dev:%s\n",
  			i, !test_bit(Faulty, &tmp->rdev->flags),
  			bdevname(tmp->rdev->bdev,b));
  	}
  }
  
  static int raid5_spare_active(mddev_t *mddev)
  {
  	int i;
  	raid5_conf_t *conf = mddev->private;
  	struct disk_info *tmp;
  
  	for (i = 0; i < conf->raid_disks; i++) {
  		tmp = conf->disks + i;
  		if (tmp->rdev
  		    && !test_bit(Faulty, &tmp->rdev->flags)
  		    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
  			unsigned long flags;
  			spin_lock_irqsave(&conf->device_lock, flags);
  			mddev->degraded--;
  			spin_unlock_irqrestore(&conf->device_lock, flags);
  		}
  	}
  	print_raid5_conf(conf);
  	return 0;
  }
  
  static int raid5_remove_disk(mddev_t *mddev, int number)
  {
  	raid5_conf_t *conf = mddev->private;
  	int err = 0;
  	mdk_rdev_t *rdev;
  	struct disk_info *p = conf->disks + number;
  
  	print_raid5_conf(conf);
  	rdev = p->rdev;
  	if (rdev) {
  		if (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;
  
  	if (mddev->degraded > conf->max_degraded)
  		return -EINVAL;
  	/* 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;
  	unsigned long flags;
  
  	if (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->degraded < mddev->delta_disks - conf->max_degraded)
  		/* 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);
  				added_devices++;
  				rdev->recovery_offset = 0;
  				sprintf(nm, "rd%d", rdev->raid_disk);
  				if (sysfs_create_link(&mddev->kobj,
  						      &rdev->kobj, nm))
  					printk(KERN_WARNING
  					       "raid5: failed to create "
  					       " link %s for %s\n",
  					       nm, mdname(mddev));
  			} else
  				break;
  		}
  
  	spin_lock_irqsave(&conf->device_lock, flags);
  	mddev->degraded = (conf->raid_disks - conf->previous_raid_disks) - added_devices;
  	spin_unlock_irqrestore(&conf->device_lock, flags);
  	mddev->raid_disks = conf->raid_disks;
  	mddev->reshape_position = 0;
  	set_bit(MD_CHANGE_DEVS, &mddev->flags);
  
  	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
  	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
  	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
  	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
  	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
  						"%s_reshape");
  	if (!mddev->sync_thread) {
  		mddev->recovery = 0;
  		spin_lock_irq(&conf->device_lock);
  		mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
  		conf->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 - conf->max_degraded);
  		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, (loff_t)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 &&
  				    atomic_read(&conf->active_aligned_reads) == 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,
  #ifdef CONFIG_MD_RAID5_RESHAPE
  	.check_reshape	= raid5_check_reshape,
  	.start_reshape  = raid5_start_reshape,
  #endif
  	.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,
  #ifdef CONFIG_MD_RAID5_RESHAPE
  	.check_reshape	= raid5_check_reshape,
  	.start_reshape  = raid5_start_reshape,
  #endif
  	.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");
  