md/raid6: move the spare page to a percpu allocation

[net-next-2.6.git] / drivers / md / raid5.c

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

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

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

/*
 * Stripe cache
 */

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

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

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

#ifdef DEBUG
#define inline
#define __inline__
#endif

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

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

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

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

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

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

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

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

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

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

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

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

static void print_raid5_conf (raid5_conf_t *conf);

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

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

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

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

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

	hlist_del_init(&sh->hash);
}

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

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

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


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

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

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

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

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

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

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

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

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

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

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

	remove_hash(sh);

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


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

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

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

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

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

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

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

	spin_lock_irq(&conf->device_lock);

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

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

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

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

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

	might_sleep();

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

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

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

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

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

			set_bit(STRIPE_IO_STARTED, &sh->state);

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

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

	if (bio->bi_sector >= sector)
		page_offset = (signed)(bio->bi_sector - sector) * 512;
	else
		page_offset = (signed)(sector - bio->bi_sector) * -512;

	init_async_submit(&submit, 0, tx, NULL, NULL, NULL);
	bio_for_each_segment(bvl, bio, i) {
		int len = bio_iovec_idx(bio, i)->bv_len;
		int clen;
		int b_offset = 0;

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

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

		if (clen > 0) {
			b_offset += bio_iovec_idx(bio, i)->bv_offset;
			bio_page = bio_iovec_idx(bio, i)->bv_page;
			if (frombio)
				tx = async_memcpy(page, bio_page, page_offset,
						  b_offset, clen, &submit);
			else
				tx = async_memcpy(bio_page, page, b_offset,
						  page_offset, clen, &submit);
		}
		/* chain the operations */
		submit.depend_tx = tx;

		if (clen < len) /* hit end of page */
			break;
		page_offset +=  len;
	}

	return tx;
}

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

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

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

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

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

	return_io(return_bi);

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

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

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

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

	atomic_inc(&sh->count);
	init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_biofill, sh, NULL);
	async_trigger_callback(&submit);
}

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

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

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

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

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

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

	atomic_inc(&sh->count);

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

	return tx;
}

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

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

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

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

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

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

	init_async_submit(&submit, ASYNC_TX_XOR_DROP_DST, tx,
			  ops_complete_prexor, sh, NULL);
	tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);

	return tx;
}

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

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

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

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

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

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

	return tx;
}

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

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

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

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

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

static void
ops_run_postxor(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
	/* kernel stack size limits the total number of disks */
	int disks = sh->disks;
	struct page *xor_srcs[disks];
	struct async_submit_ctl submit;
	int count = 0, pd_idx = sh->pd_idx, i;
	struct page *xor_dest;
	int prexor = 0;
	unsigned long flags;

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

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

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

	atomic_inc(&sh->count);

	init_async_submit(&submit, flags, tx, ops_complete_postxor, sh, NULL);
	if (unlikely(count == 1))
		tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
	else
		tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);
}

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

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

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

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

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

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

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

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

	atomic_inc(&sh->count);
	init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_check, sh, NULL);
	tx = async_trigger_callback(&submit);
}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
				     int previous, int *dd_idx,
				     struct stripe_head *sh)
{
	long stripe;
	unsigned long chunk_number;
	unsigned int chunk_offset;
	int pd_idx, qd_idx;
	int ddf_layout = 0;
	sector_t new_sector;
	int algorithm = previous ? conf->prev_algo
				 : conf->algorithm;
	int sectors_per_chunk = previous ? (conf->prev_chunk >> 9)
					 : (conf->chunk_size >> 9);
	int raid_disks = previous ? conf->previous_raid_disks
				  : conf->raid_disks;
	int data_disks = raid_disks - conf->max_degraded;

	/* First compute the information on this sector */

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous)
{
	raid5_conf_t *conf = sh->raid_conf;
	int raid_disks = sh->disks;
	int data_disks = raid_disks - conf->max_degraded;
	sector_t new_sector = sh->sector, check;
	int sectors_per_chunk = previous ? (conf->prev_chunk >> 9)
					 : (conf->chunk_size >> 9);
	int algorithm = previous ? conf->prev_algo
				 : conf->algorithm;
	sector_t stripe;
	int chunk_offset;
	int chunk_number, dummy1, dd_idx = i;
	sector_t r_sector;
	struct stripe_head sh2;


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

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

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

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



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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

		set_bit(STRIPE_OP_POSTXOR, &s->ops_request);

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

static void end_reshape(raid5_conf_t *conf);

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

static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
			    struct stripe_head *sh)
{
	int sectors_per_chunk =
		previous ? (conf->prev_chunk >> 9)
			 : (conf->chunk_size >> 9);
	int dd_idx;
	int chunk_offset = sector_div(stripe, sectors_per_chunk);
	int disks = previous ? conf->previous_raid_disks : conf->raid_disks;

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

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

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

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

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

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

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

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

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

	return 0;
}

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

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

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


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

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

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

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

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

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

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

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

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

	set_bit(STRIPE_HANDLE, &sh->state);

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

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

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

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

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

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

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


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

	set_bit(STRIPE_HANDLE, &sh->state);

	BUG_ON(s->failed > 2);
	BUG_ON(s->uptodate < disks);
	/* Want to check and possibly repair P and Q.
	 * However there could be one 'failed' device, in which
	 * case we can only check one of them, possibly using the
	 * other to generate missing data
	 */
	cpu = get_cpu();
	tmp_page = per_cpu_ptr(conf->percpu, cpu)->spare_page;
	if (s->failed == r6s->q_failed) {
		/* The only possible failed device holds 'Q', so it
		 * makes sense to check P (If anything else were failed,
		 * we would have used P to recreate it).
		 */
		compute_block_1(sh, pd_idx, 1);
		if (!page_is_zero(sh->dev[pd_idx].page)) {
			compute_block_1(sh, pd_idx, 0);
			update_p = 1;
		}
	}
	if (!r6s->q_failed && s->failed < 2) {
		/* q is not failed, and we didn't use it to generate
		 * anything, so it makes sense to check it
		 */
		memcpy(page_address(tmp_page),
		       page_address(sh->dev[qd_idx].page),
		       STRIPE_SIZE);
		compute_parity6(sh, UPDATE_PARITY);
		if (memcmp(page_address(tmp_page),
			   page_address(sh->dev[qd_idx].page),
			   STRIPE_SIZE) != 0) {
			clear_bit(STRIPE_INSYNC, &sh->state);
			update_q = 1;
		}
	}
	put_cpu();

	if (update_p || update_q) {
		conf->mddev->resync_mismatches += STRIPE_SECTORS;
		if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
			/* don't try to repair!! */
			update_p = update_q = 0;
	}

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

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 unlock:
	spin_unlock(&sh->lock);

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

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

	ops_run_io(sh, &s);

	return_io(return_bi);

	return blocked_rdev == NULL;
}

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

 unlock:
	spin_unlock(&sh->lock);

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

	ops_run_io(sh, &s);

	return_io(return_bi);

	return blocked_rdev == NULL;
}

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

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

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

static void unplug_slaves(mddev_t *mddev)
{
	raid5_conf_t *conf = mddev_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)) {
			struct request_queue *r_queue = bdev_get_queue(rdev->bdev);

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

			blk_unplug(r_queue);

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

static void raid5_unplug_device(struct request_queue *q)
{
	mddev_t *mddev = q->queuedata;
	raid5_conf_t *conf = mddev_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_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(struct request_queue *q,
				struct bvec_merge_data *bvm,
				struct bio_vec *biovec)
{
	mddev_t *mddev = q->queuedata;
	sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
	int max;
	unsigned int chunk_sectors = mddev->chunk_size >> 9;
	unsigned int bio_sectors = bvm->bi_size >> 9;

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

	if (mddev->new_chunk < mddev->chunk_size)
		chunk_sectors = mddev->new_chunk >> 9;
	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;

	if (mddev->new_chunk < mddev->chunk_size)
		chunk_sectors = mddev->new_chunk >> 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;
		/*
		 * this sets the active strip count to 1 and the processed
		 * strip count to zero (upper 8 bits)
		 */
		bi->bi_phys_segments = 1; /* biased count of active stripes */
	}

	return bi;
}


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

	bio_put(bi);

	mddev = raid_bi->bi_bdev->bd_disk->queue->queuedata;
	conf = mddev_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, 0);
		if (atomic_dec_and_test(&conf->active_aligned_reads))
			wake_up(&conf->wait_for_stripe);
		return;
	}


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

	add_bio_to_retry(raid_bi, conf);
}

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

	if ((bi->bi_size>>9) > q->max_sectors)
		return 0;
	blk_recount_segments(q, bi);
	if (bi->bi_phys_segments > q->max_phys_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(struct request_queue *q, struct bio * raid_bio)
{
	mddev_t *mddev = q->queuedata;
	raid5_conf_t *conf = mddev_to_conf(mddev);
	unsigned int dd_idx;
	struct bio* align_bi;
	mdk_rdev_t *rdev;

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

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

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

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

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

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

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

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

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

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

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

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

	md_write_start(mddev, bi);

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

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

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

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

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

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

		sh = get_active_stripe(conf, new_sector, previous,
				       (bi->bi_rw&RWA_MASK));
		if (sh) {
			if (unlikely(previous)) {
				/* expansion might have moved on while waiting for a
				 * stripe, so we must do the range check again.
				 * Expansion could still move past after this
				 * test, but as we are holding a reference to
				 * 'sh', we know that if that happens,
				 *  STRIPE_EXPANDING will get set and the expansion
				 * won't proceed until we finish with the stripe.
				 */
				int must_retry = 0;
				spin_lock_irq(&conf->device_lock);
				if (mddev->delta_disks < 0
				    ? logical_sector >= conf->reshape_progress
				    : logical_sector < conf->reshape_progress)
					/* mismatch, need to try again */
					must_retry = 1;
				spin_unlock_irq(&conf->device_lock);
				if (must_retry) {
					release_stripe(sh);
					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);
			set_bit(STRIPE_HANDLE, &sh->state);
			clear_bit(STRIPE_DELAYED, &sh->state);
			release_stripe(sh);
		} else {
			/* cannot get stripe for read-ahead, just give-up */
			clear_bit(BIO_UPTODATE, &bi->bi_flags);
			finish_wait(&conf->wait_for_overlap, &w);
			break;
		}
			
	}
	spin_lock_irq(&conf->device_lock);
	remaining = raid5_dec_bi_phys_segments(bi);
	spin_unlock_irq(&conf->device_lock);
	if (remaining == 0) {

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

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

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

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

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

	/* We need to process a full chunk at a time.
	 * If old and new chunk sizes differ, we need to process the
	 * largest of these
	 */
	if (mddev->new_chunk > mddev->chunk_size)
		reshape_sectors = mddev->new_chunk / 512;
	else
		reshape_sectors = mddev->chunk_size / 512;

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

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

	if (mddev->delta_disks < 0) {
		BUG_ON(conf->reshape_progress == 0);
		stripe_addr = writepos;
		BUG_ON((mddev->dev_sectors &
			~((sector_t)reshape_sectors - 1))
		       - reshape_sectors - stripe_addr
		       != sector_nr);
	} else {
		BUG_ON(writepos != sector_nr + reshape_sectors);
		stripe_addr = sector_nr;
	}
	INIT_LIST_HEAD(&stripes);
	for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
		int j;
		int skipped = 0;
		sh = get_active_stripe(conf, stripe_addr+i, 0, 0);
		set_bit(STRIPE_EXPANDING, &sh->state);
		atomic_inc(&conf->reshape_stripes);
		/* If any of this stripe is beyond the end of the old
		 * array, then we need to zero those blocks
		 */
		for (j=sh->disks; j--;) {
			sector_t s;
			if (j == sh->pd_idx)
				continue;
			if (conf->level == 6 &&
			    j == sh->qd_idx)
				continue;
			s = compute_blocknr(sh, j, 0);
			if (s < raid5_size(mddev, 0, 0)) {
				skipped = 1;
				continue;
			}
			memset(page_address(sh->dev[j].page), 0, STRIPE_SIZE);
			set_bit(R5_Expanded, &sh->dev[j].flags);
			set_bit(R5_UPTODATE, &sh->dev[j].flags);
		}
		if (!skipped) {
			set_bit(STRIPE_EXPAND_READY, &sh->state);
			set_bit(STRIPE_HANDLE, &sh->state);
		}
		list_add(&sh->lru, &stripes);
	}
	spin_lock_irq(&conf->device_lock);
	if (mddev->delta_disks < 0)
		conf->reshape_progress -= reshape_sectors * new_data_disks;
	else
		conf->reshape_progress += reshape_sectors * new_data_disks;
	spin_unlock_irq(&conf->device_lock);
	/* Ok, those stripe are ready. We can start scheduling
	 * reads on the source stripes.
	 * The source stripes are determined by mapping the first and last
	 * block on the destination stripes.
	 */
	first_sector =
		raid5_compute_sector(conf, stripe_addr*(new_data_disks),
				     1, &dd_idx, NULL);
	last_sector =
		raid5_compute_sector(conf, ((stripe_addr+conf->chunk_size/512)
					    *(new_data_disks) - 1),
				     1, &dd_idx, NULL);
	if (last_sector >= mddev->dev_sectors)
		last_sector = mddev->dev_sectors - 1;
	while (first_sector <= last_sector) {
		sh = get_active_stripe(conf, first_sector, 1, 0);
		set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
		set_bit(STRIPE_HANDLE, &sh->state);
		release_stripe(sh);
		first_sector += STRIPE_SECTORS;
	}
	/* Now that the sources are clearly marked, we can release
	 * the destination stripes
	 */
	while (!list_empty(&stripes)) {
		sh = list_entry(stripes.next, struct stripe_head, lru);
		list_del_init(&sh->lru);
		release_stripe(sh);
	}
	/* If this takes us to the resync_max point where we have to pause,
	 * then we need to write out the superblock.
	 */
	sector_nr += reshape_sectors;
	if (sector_nr >= mddev->resync_max) {
		/* Cannot proceed until we've updated the superblock... */
		wait_event(conf->wait_for_overlap,
			   atomic_read(&conf->reshape_stripes) == 0);
		mddev->reshape_position = conf->reshape_progress;
		conf->reshape_checkpoint = jiffies;
		set_bit(MD_CHANGE_DEVS, &mddev->flags);
		md_wakeup_thread(mddev->thread);
		wait_event(mddev->sb_wait,
			   !test_bit(MD_CHANGE_DEVS, &mddev->flags)
			   || kthread_should_stop());
		spin_lock_irq(&conf->device_lock);
		conf->reshape_safe = mddev->reshape_position;
		spin_unlock_irq(&conf->device_lock);
		wake_up(&conf->wait_for_overlap);
	}
	return reshape_sectors;
}

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

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

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

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

		return 0;
	}

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

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

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


	bitmap_cond_end_sync(mddev->bitmap, sector_nr);

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

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

	return STRIPE_SECTORS;
}

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

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

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

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

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

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

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

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



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

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

	md_check_recovery(mddev);

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

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

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

		sh = __get_priority_stripe(conf);

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

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

	spin_unlock_irq(&conf->device_lock);

	async_tx_issue_pending_all();
	unplug_slaves(mddev);

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

static ssize_t
raid5_show_stripe_cache_size(mddev_t *mddev, char *page)
{
	raid5_conf_t *conf = mddev_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);
	unsigned long new;
	int err;

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

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

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

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

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

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

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

static ssize_t
stripe_cache_active_show(mddev_t *mddev, char *page)
{
	raid5_conf_t *conf = mddev_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,
	&raid5_preread_bypass_threshold.attr,
	NULL,
};
static struct attribute_group raid5_attrs_group = {
	.name = NULL,
	.attrs = raid5_attrs,
};

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

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

	sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
	sectors &= ~((sector_t)mddev->new_chunk/512 - 1);
	return sectors * (raid_disks - conf->max_degraded);
}

static void raid5_free_percpu(raid5_conf_t *conf)
{
	struct raid5_percpu *percpu;
	unsigned long cpu;

	if (!conf->percpu)
		return;

	get_online_cpus();
	for_each_possible_cpu(cpu) {
		percpu = per_cpu_ptr(conf->percpu, cpu);
		safe_put_page(percpu->spare_page);
	}
#ifdef CONFIG_HOTPLUG_CPU
	unregister_cpu_notifier(&conf->cpu_notify);
#endif
	put_online_cpus();

	free_percpu(conf->percpu);
}

static void free_conf(raid5_conf_t *conf)
{
	shrink_stripes(conf);
	raid5_free_percpu(conf);
	kfree(conf->disks);
	kfree(conf->stripe_hashtbl);
	kfree(conf);
}

#ifdef CONFIG_HOTPLUG_CPU
static int raid456_cpu_notify(struct notifier_block *nfb, unsigned long action,
			      void *hcpu)
{
	raid5_conf_t *conf = container_of(nfb, raid5_conf_t, cpu_notify);
	long cpu = (long)hcpu;
	struct raid5_percpu *percpu = per_cpu_ptr(conf->percpu, cpu);

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
		if (!percpu->spare_page)
			percpu->spare_page = alloc_page(GFP_KERNEL);
		if (!percpu->spare_page) {
			pr_err("%s: failed memory allocation for cpu%ld\n",
			       __func__, cpu);
			return NOTIFY_BAD;
		}
		break;
	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
		safe_put_page(percpu->spare_page);
		percpu->spare_page = NULL;
		break;
	default:
		break;
	}
	return NOTIFY_OK;
}
#endif

static int raid5_alloc_percpu(raid5_conf_t *conf)
{
	unsigned long cpu;
	struct page *spare_page;
	struct raid5_percpu *allcpus;
	int err;

	/* the only percpu data is the raid6 spare page */
	if (conf->level != 6)
		return 0;

	allcpus = alloc_percpu(struct raid5_percpu);
	if (!allcpus)
		return -ENOMEM;
	conf->percpu = allcpus;

	get_online_cpus();
	err = 0;
	for_each_present_cpu(cpu) {
		spare_page = alloc_page(GFP_KERNEL);
		if (!spare_page) {
			err = -ENOMEM;
			break;
		}
		per_cpu_ptr(conf->percpu, cpu)->spare_page = spare_page;
	}
#ifdef CONFIG_HOTPLUG_CPU
	conf->cpu_notify.notifier_call = raid456_cpu_notify;
	conf->cpu_notify.priority = 0;
	if (err == 0)
		err = register_cpu_notifier(&conf->cpu_notify);
#endif
	put_online_cpus();

	return err;
}

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

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

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

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

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

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

	conf->mddev = mddev;

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

	conf->level = mddev->new_level;
	if (raid5_alloc_percpu(conf) != 0)
		goto abort;

	spin_lock_init(&conf->device_lock);
	init_waitqueue_head(&conf->wait_for_stripe);
	init_waitqueue_head(&conf->wait_for_overlap);
	INIT_LIST_HEAD(&conf->handle_list);
	INIT_LIST_HEAD(&conf->hold_list);
	INIT_LIST_HEAD(&conf->delayed_list);
	INIT_LIST_HEAD(&conf->bitmap_list);
	INIT_LIST_HEAD(&conf->inactive_list);
	atomic_set(&conf->active_stripes, 0);
	atomic_set(&conf->preread_active_stripes, 0);
	atomic_set(&conf->active_aligned_reads, 0);
	conf->bypass_threshold = BYPASS_THRESHOLD;

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

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

		disk->rdev = rdev;

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

	conf->chunk_size = mddev->new_chunk;
	if (conf->level == 6)
		conf->max_degraded = 2;
	else
		conf->max_degraded = 1;
	conf->algorithm = mddev->new_layout;
	conf->max_nr_stripes = NR_STRIPES;
	conf->reshape_progress = mddev->reshape_position;
	if (conf->reshape_progress != MaxSector) {
		conf->prev_chunk = mddev->chunk_size;
		conf->prev_algo = mddev->layout;
	}

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

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

	return conf;

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

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

	if (mddev->reshape_position != MaxSector) {
		/* Check that we can continue the reshape.
		 * Currently only disks can change, it must
		 * increase, and we must be past the point where
		 * a stripe over-writes itself
		 */
		sector_t here_new, here_old;
		int old_disks;
		int max_degraded = (mddev->level == 6 ? 2 : 1);

		if (mddev->new_level != mddev->level) {
			printk(KERN_ERR "raid5: %s: unsupported reshape "
			       "required - aborting.\n",
			       mdname(mddev));
			return -EINVAL;
		}
		old_disks = mddev->raid_disks - mddev->delta_disks;
		/* reshape_position must be on a new-stripe boundary, and one
		 * further up in new geometry must map after here in old
		 * geometry.
		 */
		here_new = mddev->reshape_position;
		if (sector_div(here_new, (mddev->new_chunk>>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; */
	} else {
		BUG_ON(mddev->level != mddev->new_level);
		BUG_ON(mddev->layout != mddev->new_layout);
		BUG_ON(mddev->chunk_size != mddev->new_chunk);
		BUG_ON(mddev->delta_disks != 0);
	}

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

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

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

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

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

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

	/* device size must be a multiple of chunk size */
	mddev->dev_sectors &= ~(mddev->chunk_size / 512 - 1);
	mddev->resync_max_sectors = mddev->dev_sectors;

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

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

	print_raid5_conf(conf);

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

	/* read-ahead size must cover two whole stripes, which is
	 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
	 */
	{
		int data_disks = conf->previous_raid_disks - conf->max_degraded;
		int stripe = data_disks *
			(mddev->chunk_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->queue_lock = &conf->device_lock;

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

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

	blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);

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



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

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

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

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

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

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

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

	seq_printf (seq, " level %d, %dk chunk, algorithm %d", mddev->level, mddev->chunk_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, "]");
#ifdef DEBUG
	seq_printf (seq, "\n");
	printall(seq, conf);
#endif
}

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

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

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

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

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

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

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

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

	print_raid5_conf(conf);
	return err;
}

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

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

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

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

static int raid5_resize(mddev_t *mddev, sector_t sectors)
{
	/* no resync is happening, and there is enough space
	 * on all devices, so we can resize.
	 * We need to make sure resync covers any new space.
	 * If the array is shrinking we should possibly wait until
	 * any io in the removed space completes, but it hardly seems
	 * worth it.
	 */
	sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
	md_set_array_sectors(mddev, raid5_size(mddev, sectors,
					       mddev->raid_disks));
	if (mddev->array_sectors >
	    raid5_size(mddev, sectors, mddev->raid_disks))
		return -EINVAL;
	set_capacity(mddev->gendisk, mddev->array_sectors);
	mddev->changed = 1;
	if (sectors > mddev->dev_sectors && mddev->recovery_cp == MaxSector) {
		mddev->recovery_cp = mddev->dev_sectors;
		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
	}
	mddev->dev_sectors = sectors;
	mddev->resync_max_sectors = sectors;
	return 0;
}

static int raid5_check_reshape(mddev_t *mddev)
{
	raid5_conf_t *conf = mddev_to_conf(mddev);

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

	/* 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",
		       (max(mddev->chunk_size, mddev->new_chunk)
			/ STRIPE_SIZE)*4);
		return -ENOSPC;
	}

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

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

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

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

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

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

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

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

	if (mddev->delta_disks > 0) {
		spin_lock_irqsave(&conf->device_lock, flags);
		mddev->degraded = (conf->raid_disks - conf->previous_raid_disks)
			- added_devices;
		spin_unlock_irqrestore(&conf->device_lock, flags);
	}
	mddev->raid_disks = conf->raid_disks;
	mddev->reshape_position = 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->reshape_progress = MaxSector;
		spin_unlock_irq(&conf->device_lock);
		return -EAGAIN;
	}
	conf->reshape_checkpoint = jiffies;
	md_wakeup_thread(mddev->sync_thread);
	md_new_event(mddev);
	return 0;
}

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

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

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

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

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

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

		if (mddev->delta_disks > 0) {
			md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
			set_capacity(mddev->gendisk, mddev->array_sectors);
			mddev->changed = 1;

			bdev = bdget_disk(mddev->gendisk, 0);
			if (bdev) {
				mutex_lock(&bdev->bd_inode->i_mutex);
				i_size_write(bdev->bd_inode,
					     (loff_t)mddev->array_sectors << 9);
				mutex_unlock(&bdev->bd_inode->i_mutex);
				bdput(bdev);
			}
		} else {
			int d;
			mddev->degraded = conf->raid_disks;
			for (d = 0; d < conf->raid_disks ; d++)
				if (conf->disks[d].rdev &&
				    test_bit(In_sync,
					     &conf->disks[d].rdev->flags))
					mddev->degraded--;
			for (d = conf->raid_disks ;
			     d < conf->raid_disks - mddev->delta_disks;
			     d++)
				raid5_remove_disk(mddev, d);
		}
		mddev->layout = conf->algorithm;
		mddev->chunk_size = conf->chunk_size;
		mddev->reshape_position = MaxSector;
		mddev->delta_disks = 0;
	}
}

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

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

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

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

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

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

	mddev->new_level = 5;
	mddev->new_layout = ALGORITHM_LEFT_SYMMETRIC;
	mddev->new_chunk = chunksect << 9;

	return setup_conf(mddev);
}

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

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


static int raid5_reconfig(mddev_t *mddev, int new_layout, int new_chunk)
{
	/* For a 2-drive array, the layout and chunk size can be changed
	 * immediately as not restriping is needed.
	 * For larger arrays we record the new value - after validation
	 * to be used by a reshape pass.
	 */
	raid5_conf_t *conf = mddev_to_conf(mddev);

	if (new_layout >= 0 && !algorithm_valid_raid5(new_layout))
		return -EINVAL;
	if (new_chunk > 0) {
		if (new_chunk & (new_chunk-1))
			/* not a power of 2 */
			return -EINVAL;
		if (new_chunk < PAGE_SIZE)
			return -EINVAL;
		if (mddev->array_sectors & ((new_chunk>>9)-1))
			/* not factor of array size */
			return -EINVAL;
	}

	/* They look valid */

	if (mddev->raid_disks == 2) {

		if (new_layout >= 0) {
			conf->algorithm = new_layout;
			mddev->layout = mddev->new_layout = new_layout;
		}
		if (new_chunk > 0) {
			conf->chunk_size = new_chunk;
			mddev->chunk_size = mddev->new_chunk = new_chunk;
		}
		set_bit(MD_CHANGE_DEVS, &mddev->flags);
		md_wakeup_thread(mddev->thread);
	} else {
		if (new_layout >= 0)
			mddev->new_layout = new_layout;
		if (new_chunk > 0)
			mddev->new_chunk = new_chunk;
	}
	return 0;
}

static int raid6_reconfig(mddev_t *mddev, int new_layout, int new_chunk)
{
	if (new_layout >= 0 && !algorithm_valid_raid6(new_layout))
		return -EINVAL;
	if (new_chunk > 0) {
		if (new_chunk & (new_chunk-1))
			/* not a power of 2 */
			return -EINVAL;
		if (new_chunk < PAGE_SIZE)
			return -EINVAL;
		if (mddev->array_sectors & ((new_chunk>>9)-1))
			/* not factor of array size */
			return -EINVAL;
	}

	/* They look valid */

	if (new_layout >= 0)
		mddev->new_layout = new_layout;
	if (new_chunk > 0)
		mddev->new_chunk = new_chunk;

	return 0;
}

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

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

	return ERR_PTR(-EINVAL);
}


static struct mdk_personality raid5_personality;

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

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

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


static struct mdk_personality raid6_personality =
{
	.name		= "raid6",
	.level		= 6,
	.owner		= THIS_MODULE,
	.make_request	= make_request,
	.run		= run,
	.stop		= stop,
	.status		= status,
	.error_handler	= error,
	.hot_add_disk	= raid5_add_disk,
	.hot_remove_disk= raid5_remove_disk,
	.spare_active	= raid5_spare_active,
	.sync_request	= sync_request,
	.resize		= raid5_resize,
	.size		= raid5_size,
	.check_reshape	= raid5_check_reshape,
	.start_reshape  = raid5_start_reshape,
	.finish_reshape = raid5_finish_reshape,
	.quiesce	= raid5_quiesce,
	.takeover	= raid6_takeover,
	.reconfig	= raid6_reconfig,
};
static struct mdk_personality raid5_personality =
{
	.name		= "raid5",
	.level		= 5,
	.owner		= THIS_MODULE,
	.make_request	= make_request,
	.run		= run,
	.stop		= stop,
	.status		= status,
	.error_handler	= error,
	.hot_add_disk	= raid5_add_disk,
	.hot_remove_disk= raid5_remove_disk,
	.spare_active	= raid5_spare_active,
	.sync_request	= sync_request,
	.resize		= raid5_resize,
	.size		= raid5_size,
	.check_reshape	= raid5_check_reshape,
	.start_reshape  = raid5_start_reshape,
	.finish_reshape = raid5_finish_reshape,
	.quiesce	= raid5_quiesce,
	.takeover	= raid5_takeover,
	.reconfig	= raid5_reconfig,
};

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

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

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

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

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