Moved, renamed, and deleted files

The original directory structure was scattered and unorganized.
Changes are basically to make it look like kernel structure.

1 files changed, 6050 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
new file mode 100644
index 00000000..73a58007
--- /dev/null
+++ b/drivers/md/raid5.c
@@ -0,0 +1,6050 @@
+/*
+ * 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->seq_write is the number of the last batch successfully written.
+ * conf->seq_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 seq_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/module.h>
+#include <linux/async.h>
+#include <linux/seq_file.h>
+#include <linux/cpu.h>
+#include <linux/slab.h>
+#include <linux/ratelimit.h>
+#include "md.h"
+#include "raid5.h"
+#include "raid0.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)
+
+static inline struct hlist_head *stripe_hash(struct r5conf *conf, sector_t sect)
+{
+	int hash = (sect >> STRIPE_SHIFT) & HASH_MASK;
+	return &conf->stripe_hashtbl[hash];
+}
+
+/* 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 function is used to determine the 'next' bio in the list, given the sector
+ * of the current stripe+device
+ */
+static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
+{
+	int sectors = bio->bi_size >> 9;
+	if (bio->bi_sector + sectors < sector + STRIPE_SECTORS)
+		return bio->bi_next;
+	else
+		return NULL;
+}
+
+/*
+ * 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 = *count;
+
+	if (sh->ddf_layout)
+		(*count)++;
+	if (idx == sh->pd_idx)
+		return syndrome_disks;
+	if (idx == sh->qd_idx)
+		return syndrome_disks + 1;
+	if (!sh->ddf_layout)
+		(*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 (struct r5conf *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(struct r5conf *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) &&
+			    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+				list_add_tail(&sh->lru, &conf->delayed_list);
+			else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
+				   sh->bm_seq - conf->seq_write > 0)
+				list_add_tail(&sh->lru, &conf->bitmap_list);
+			else {
+				clear_bit(STRIPE_DELAYED, &sh->state);
+				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))
+				if (atomic_dec_return(&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)
+{
+	struct r5conf *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(struct r5conf *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);
+
+	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(struct r5conf *conf)
+{
+	struct stripe_head *sh = NULL;
+	struct list_head *first;
+
+	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)
+{
+	struct page *p;
+	int i;
+	int num = sh->raid_conf->pool_size;
+
+	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 i;
+	int num = sh->raid_conf->pool_size;
+
+	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, struct r5conf *conf, int previous,
+			    struct stripe_head *sh);
+
+static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
+{
+	struct r5conf *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));
+
+	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));
+			WARN_ON(1);
+		}
+		dev->flags = 0;
+		raid5_build_block(sh, i, previous);
+	}
+	insert_hash(conf, sh);
+}
+
+static struct stripe_head *__find_stripe(struct r5conf *conf, sector_t sector,
+					 short generation)
+{
+	struct stripe_head *sh;
+	struct hlist_node *hn;
+
+	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;
+}
+
+/*
+ * Need to check if array has failed when deciding whether to:
+ *  - start an array
+ *  - remove non-faulty devices
+ *  - add a spare
+ *  - allow a reshape
+ * This determination is simple when no reshape is happening.
+ * However if there is a reshape, we need to carefully check
+ * both the before and after sections.
+ * This is because some failed devices may only affect one
+ * of the two sections, and some non-in_sync devices may
+ * be insync in the section most affected by failed devices.
+ */
+static int calc_degraded(struct r5conf *conf)
+{
+	int degraded, degraded2;
+	int i;
+
+	rcu_read_lock();
+	degraded = 0;
+	for (i = 0; i < conf->previous_raid_disks; i++) {
+		struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
+		if (!rdev || test_bit(Faulty, &rdev->flags))
+			degraded++;
+		else if (test_bit(In_sync, &rdev->flags))
+			;
+		else
+			/* not in-sync or faulty.
+			 * If the reshape increases the number of devices,
+			 * this is being recovered by the reshape, so
+			 * this 'previous' section is not in_sync.
+			 * If the number of devices is being reduced however,
+			 * the device can only be part of the array if
+			 * we are reverting a reshape, so this section will
+			 * be in-sync.
+			 */
+			if (conf->raid_disks >= conf->previous_raid_disks)
+				degraded++;
+	}
+	rcu_read_unlock();
+	if (conf->raid_disks == conf->previous_raid_disks)
+		return degraded;
+	rcu_read_lock();
+	degraded2 = 0;
+	for (i = 0; i < conf->raid_disks; i++) {
+		struct md_rdev *rdev = rcu_dereference(conf->disks[i].rdev);
+		if (!rdev || test_bit(Faulty, &rdev->flags))
+			degraded2++;
+		else if (test_bit(In_sync, &rdev->flags))
+			;
+		else
+			/* not in-sync or faulty.
+			 * If reshape increases the number of devices, this
+			 * section has already been recovered, else it
+			 * almost certainly hasn't.
+			 */
+			if (conf->raid_disks <= conf->previous_raid_disks)
+				degraded2++;
+	}
+	rcu_read_unlock();
+	if (degraded2 > degraded)
+		return degraded2;
+	return degraded;
+}
+
+static int has_failed(struct r5conf *conf)
+{
+	int degraded;
+
+	if (conf->mddev->reshape_position == MaxSector)
+		return conf->mddev->degraded > conf->max_degraded;
+
+	degraded = calc_degraded(conf);
+	if (degraded > conf->max_degraded)
+		return 1;
+	return 0;
+}
+
+static struct stripe_head *
+get_active_stripe(struct r5conf *conf, sector_t sector,
+		  int previous, int noblock, int noquiesce)
+{
+	struct stripe_head *sh;
+
+	pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);
+
+	spin_lock_irq(&conf->device_lock);
+
+	do {
+		wait_event_lock_irq(conf->wait_for_stripe,
+				    conf->quiesce == 0 || noquiesce,
+				    conf->device_lock, /* nothing */);
+		sh = __find_stripe(conf, sector, conf->generation - previous);
+		if (!sh) {
+			if (!conf->inactive_blocked)
+				sh = get_free_stripe(conf);
+			if (noblock && sh == NULL)
+				break;
+			if (!sh) {
+				conf->inactive_blocked = 1;
+				wait_event_lock_irq(conf->wait_for_stripe,
+						    !list_empty(&conf->inactive_list) &&
+						    (atomic_read(&conf->active_stripes)
+						     < (conf->max_nr_stripes *3/4)
+						     || !conf->inactive_blocked),
+						    conf->device_lock,
+						    );
+				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)
+{
+	struct r5conf *conf = sh->raid_conf;
+	int i, disks = sh->disks;
+
+	might_sleep();
+
+	for (i = disks; i--; ) {
+		int rw;
+		int replace_only = 0;
+		struct bio *bi, *rbi;
+		struct md_rdev *rdev, *rrdev = NULL;
+		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags)) {
+			if (test_and_clear_bit(R5_WantFUA, &sh->dev[i].flags))
+				rw = WRITE_FUA;
+			else
+				rw = WRITE;
+		} else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
+			rw = READ;
+		else if (test_and_clear_bit(R5_WantReplace,
+					    &sh->dev[i].flags)) {
+			rw = WRITE;
+			replace_only = 1;
+		} else
+			continue;
+
+		bi = &sh->dev[i].req;
+		rbi = &sh->dev[i].rreq; /* For writing to replacement */
+
+		bi->bi_rw = rw;
+		rbi->bi_rw = rw;
+		if (rw & WRITE) {
+			bi->bi_end_io = raid5_end_write_request;
+			rbi->bi_end_io = raid5_end_write_request;
+		} else
+			bi->bi_end_io = raid5_end_read_request;
+
+		rcu_read_lock();
+		rrdev = rcu_dereference(conf->disks[i].replacement);
+		smp_mb(); /* Ensure that if rrdev is NULL, rdev won't be */
+		rdev = rcu_dereference(conf->disks[i].rdev);
+		if (!rdev) {
+			rdev = rrdev;
+			rrdev = NULL;
+		}
+		if (rw & WRITE) {
+			if (replace_only)
+				rdev = NULL;
+			if (rdev == rrdev)
+				/* We raced and saw duplicates */
+				rrdev = NULL;
+		} else {
+			if (test_bit(R5_ReadRepl, &sh->dev[i].flags) && rrdev)
+				rdev = rrdev;
+			rrdev = NULL;
+		}
+
+		if (rdev && test_bit(Faulty, &rdev->flags))
+			rdev = NULL;
+		if (rdev)
+			atomic_inc(&rdev->nr_pending);
+		if (rrdev && test_bit(Faulty, &rrdev->flags))
+			rrdev = NULL;
+		if (rrdev)
+			atomic_inc(&rrdev->nr_pending);
+		rcu_read_unlock();
+
+		/* We have already checked bad blocks for reads.  Now
+		 * need to check for writes.  We never accept write errors
+		 * on the replacement, so we don't to check rrdev.
+		 */
+		while ((rw & WRITE) && rdev &&
+		       test_bit(WriteErrorSeen, &rdev->flags)) {
+			sector_t first_bad;
+			int bad_sectors;
+			int bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
+					      &first_bad, &bad_sectors);
+			if (!bad)
+				break;
+
+			if (bad < 0) {
+				set_bit(BlockedBadBlocks, &rdev->flags);
+				if (!conf->mddev->external &&
+				    conf->mddev->flags) {
+					/* It is very unlikely, but we might
+					 * still need to write out the
+					 * bad block log - better give it
+					 * a chance*/
+					md_check_recovery(conf->mddev);
+				}
+				/*
+				 * Because md_wait_for_blocked_rdev
+				 * will dec nr_pending, we must
+				 * increment it first.
+				 */
+				atomic_inc(&rdev->nr_pending);
+				md_wait_for_blocked_rdev(rdev, conf->mddev);
+			} else {
+				/* Acknowledged bad block - skip the write */
+				rdev_dec_pending(rdev, conf->mddev);
+				rdev = NULL;
+			}
+		}
+
+		if (rdev) {
+			if (s->syncing || s->expanding || s->expanded
+			    || s->replacing)
+				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_idx = 0;
+			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 (rrdev)
+				set_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags);
+			generic_make_request(bi);
+		}
+		if (rrdev) {
+			if (s->syncing || s->expanding || s->expanded
+			    || s->replacing)
+				md_sync_acct(rrdev->bdev, STRIPE_SECTORS);
+
+			set_bit(STRIPE_IO_STARTED, &sh->state);
+
+			rbi->bi_bdev = rrdev->bdev;
+			pr_debug("%s: for %llu schedule op %ld on "
+				 "replacement disc %d\n",
+				__func__, (unsigned long long)sh->sector,
+				rbi->bi_rw, i);
+			atomic_inc(&sh->count);
+			rbi->bi_sector = sh->sector + rrdev->data_offset;
+			rbi->bi_flags = 1 << BIO_UPTODATE;
+			rbi->bi_idx = 0;
+			rbi->bi_io_vec[0].bv_len = STRIPE_SIZE;
+			rbi->bi_io_vec[0].bv_offset = 0;
+			rbi->bi_size = STRIPE_SIZE;
+			rbi->bi_next = NULL;
+			generic_make_request(rbi);
+		}
+		if (!rdev && !rrdev) {
+			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;
+	enum async_tx_flags flags = 0;
+
+	if (bio->bi_sector >= sector)
+		page_offset = (signed)(bio->bi_sector - sector) * 512;
+	else
+		page_offset = (signed)(sector - bio->bi_sector) * -512;
+
+	if (frombio)
+		flags |= ASYNC_TX_FENCE;
+	init_async_submit(&submit, flags, tx, NULL, NULL, NULL);
+
+	bio_for_each_segment(bvl, bio, i) {
+		int len = bvl->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 += bvl->bv_offset;
+			bio_page = bvl->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;
+	struct r5conf *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;
+	struct r5conf *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 mark_target_uptodate(struct stripe_head *sh, int target)
+{
+	struct r5dev *tgt;
+
+	if (target < 0)
+		return;
+
+	tgt = &sh->dev[target];
+	set_bit(R5_UPTODATE, &tgt->flags);
+	BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
+	clear_bit(R5_Wantcompute, &tgt->flags);
+}
+
+static void ops_complete_compute(void *stripe_head_ref)
+{
+	struct stripe_head *sh = stripe_head_ref;
+
+	pr_debug("%s: stripe %llu\n", __func__,
+		(unsigned long long)sh->sector);
+
+	/* mark the computed target(s) as uptodate */
+	mark_target_uptodate(sh, sh->ops.target);
+	mark_target_uptodate(sh, sh->ops.target2);
+
+	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);
+}
+
+/* return a pointer to the address conversion region of the scribble buffer */
+static addr_conv_t *to_addr_conv(struct stripe_head *sh,
+				 struct raid5_percpu *percpu)
+{
+	return percpu->scribble + sizeof(struct page *) * (sh->disks + 2);
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_compute5(struct stripe_head *sh, struct raid5_percpu *percpu)
+{
+	int disks = sh->disks;
+	struct page **xor_srcs = percpu->scribble;
+	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_FENCE|ASYNC_TX_XOR_ZERO_DST, NULL,
+			  ops_complete_compute, sh, to_addr_conv(sh, percpu));
+	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;
+}
+
+/* set_syndrome_sources - populate source buffers for gen_syndrome
+ * @srcs - (struct page *) array of size sh->disks
+ * @sh - stripe_head to parse
+ *
+ * Populates srcs in proper layout order for the stripe and returns the
+ * 'count' of sources to be used in a call to async_gen_syndrome.  The P
+ * destination buffer is recorded in srcs[count] and the Q destination
+ * is recorded in srcs[count+1]].
+ */
+static int set_syndrome_sources(struct page **srcs, struct stripe_head *sh)
+{
+	int disks = sh->disks;
+	int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
+	int d0_idx = raid6_d0(sh);
+	int count;
+	int i;
+
+	for (i = 0; i < disks; i++)
+		srcs[i] = NULL;
+
+	count = 0;
+	i = d0_idx;
+	do {
+		int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);
+
+		srcs[slot] = sh->dev[i].page;
+		i = raid6_next_disk(i, disks);
+	} while (i != d0_idx);
+
+	return syndrome_disks;
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_compute6_1(struct stripe_head *sh, struct raid5_percpu *percpu)
+{
+	int disks = sh->disks;
+	struct page **blocks = percpu->scribble;
+	int target;
+	int qd_idx = sh->qd_idx;
+	struct dma_async_tx_descriptor *tx;
+	struct async_submit_ctl submit;
+	struct r5dev *tgt;
+	struct page *dest;
+	int i;
+	int count;
+
+	if (sh->ops.target < 0)
+		target = sh->ops.target2;
+	else if (sh->ops.target2 < 0)
+		target = sh->ops.target;
+	else
+		/* we should only have one valid target */
+		BUG();
+	BUG_ON(target < 0);
+	pr_debug("%s: stripe %llu block: %d\n",
+		__func__, (unsigned long long)sh->sector, target);
+
+	tgt = &sh->dev[target];
+	BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
+	dest = tgt->page;
+
+	atomic_inc(&sh->count);
+
+	if (target == qd_idx) {
+		count = set_syndrome_sources(blocks, sh);
+		blocks[count] = NULL; /* regenerating p is not necessary */
+		BUG_ON(blocks[count+1] != dest); /* q should already be set */
+		init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
+				  ops_complete_compute, sh,
+				  to_addr_conv(sh, percpu));
+		tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE, &submit);
+	} else {
+		/* Compute any data- or p-drive using XOR */
+		count = 0;
+		for (i = disks; i-- ; ) {
+			if (i == target || i == qd_idx)
+				continue;
+			blocks[count++] = sh->dev[i].page;
+		}
+
+		init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
+				  NULL, ops_complete_compute, sh,
+				  to_addr_conv(sh, percpu));
+		tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE, &submit);
+	}
+
+	return tx;
+}
+
+static struct dma_async_tx_descriptor *
+ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
+{
+	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;
+	int target = sh->ops.target;
+	int target2 = sh->ops.target2;
+	struct r5dev *tgt = &sh->dev[target];
+	struct r5dev *tgt2 = &sh->dev[target2];
+	struct dma_async_tx_descriptor *tx;
+	struct page **blocks = percpu->scribble;
+	struct async_submit_ctl submit;
+
+	pr_debug("%s: stripe %llu block1: %d block2: %d\n",
+		 __func__, (unsigned long long)sh->sector, target, target2);
+	BUG_ON(target < 0 || target2 < 0);
+	BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
+	BUG_ON(!test_bit(R5_Wantcompute, &tgt2->flags));
+
+	/* we need to open-code set_syndrome_sources to handle the
+	 * slot number conversion for 'faila' and 'failb'
+	 */
+	for (i = 0; i < disks ; i++)
+		blocks[i] = NULL;
+	count = 0;
+	i = d0_idx;
+	do {
+		int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);
+
+		blocks[slot] = sh->dev[i].page;
+
+		if (i == target)
+			faila = slot;
+		if (i == target2)
+			failb = slot;
+		i = raid6_next_disk(i, disks);
+	} while (i != d0_idx);
+
+	BUG_ON(faila == failb);
+	if (failb < faila)
+		swap(faila, failb);
+	pr_debug("%s: stripe: %llu faila: %d failb: %d\n",
+		 __func__, (unsigned long long)sh->sector, faila, failb);
+
+	atomic_inc(&sh->count);
+
+	if (failb == syndrome_disks+1) {
+		/* Q disk is one of the missing disks */
+		if (faila == syndrome_disks) {
+			/* Missing P+Q, just recompute */
+			init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
+					  ops_complete_compute, sh,
+					  to_addr_conv(sh, percpu));
+			return async_gen_syndrome(blocks, 0, syndrome_disks+2,
+						  STRIPE_SIZE, &submit);
+		} else {
+			struct page *dest;
+			int data_target;
+			int qd_idx = sh->qd_idx;
+
+			/* Missing D+Q: recompute D from P, then recompute Q */
+			if (target == qd_idx)
+				data_target = target2;
+			else
+				data_target = target;
+
+			count = 0;
+			for (i = disks; i-- ; ) {
+				if (i == data_target || i == qd_idx)
+					continue;
+				blocks[count++] = sh->dev[i].page;
+			}
+			dest = sh->dev[data_target].page;
+			init_async_submit(&submit,
+					  ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
+					  NULL, NULL, NULL,
+					  to_addr_conv(sh, percpu));
+			tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE,
+				       &submit);
+
+			count = set_syndrome_sources(blocks, sh);
+			init_async_submit(&submit, ASYNC_TX_FENCE, tx,
+					  ops_complete_compute, sh,
+					  to_addr_conv(sh, percpu));
+			return async_gen_syndrome(blocks, 0, count+2,
+						  STRIPE_SIZE, &submit);
+		}
+	} else {
+		init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
+				  ops_complete_compute, sh,
+				  to_addr_conv(sh, percpu));
+		if (failb == syndrome_disks) {
+			/* We're missing D+P. */
+			return async_raid6_datap_recov(syndrome_disks+2,
+						       STRIPE_SIZE, faila,
+						       blocks, &submit);
+		} else {
+			/* We're missing D+D. */
+			return async_raid6_2data_recov(syndrome_disks+2,
+						       STRIPE_SIZE, faila, failb,
+						       blocks, &submit);
+		}
+	}
+}
+
+
+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 raid5_percpu *percpu,
+	       struct dma_async_tx_descriptor *tx)
+{
+	int disks = sh->disks;
+	struct page **xor_srcs = percpu->scribble;
+	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_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  ops_complete_prexor, sh, to_addr_conv(sh, percpu));
+	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_irq(&sh->raid_conf->device_lock);
+			chosen = dev->towrite;
+			dev->towrite = NULL;
+			BUG_ON(dev->written);
+			wbi = dev->written = chosen;
+			spin_unlock_irq(&sh->raid_conf->device_lock);
+
+			while (wbi && wbi->bi_sector <
+				dev->sector + STRIPE_SECTORS) {
+				if (wbi->bi_rw & REQ_FUA)
+					set_bit(R5_WantFUA, &dev->flags);
+				tx = async_copy_data(1, wbi, dev->page,
+					dev->sector, tx);
+				wbi = r5_next_bio(wbi, dev->sector);
+			}
+		}
+	}
+
+	return tx;
+}
+
+static void ops_complete_reconstruct(void *stripe_head_ref)
+{
+	struct stripe_head *sh = stripe_head_ref;
+	int disks = sh->disks;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = sh->qd_idx;
+	int i;
+	bool fua = false;
+
+	pr_debug("%s: stripe %llu\n", __func__,
+		(unsigned long long)sh->sector);
+
+	for (i = disks; i--; )
+		fua |= test_bit(R5_WantFUA, &sh->dev[i].flags);
+
+	for (i = disks; i--; ) {
+		struct r5dev *dev = &sh->dev[i];
+
+		if (dev->written || i == pd_idx || i == qd_idx) {
+			set_bit(R5_UPTODATE, &dev->flags);
+			if (fua)
+				set_bit(R5_WantFUA, &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_reconstruct5(struct stripe_head *sh, struct raid5_percpu *percpu,
+		     struct dma_async_tx_descriptor *tx)
+{
+	int disks = sh->disks;
+	struct page **xor_srcs = percpu->scribble;
+	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_reconstruct, sh,
+			  to_addr_conv(sh, percpu));
+	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_run_reconstruct6(struct stripe_head *sh, struct raid5_percpu *percpu,
+		     struct dma_async_tx_descriptor *tx)
+{
+	struct async_submit_ctl submit;
+	struct page **blocks = percpu->scribble;
+	int count;
+
+	pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);
+
+	count = set_syndrome_sources(blocks, sh);
+
+	atomic_inc(&sh->count);
+
+	init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_reconstruct,
+			  sh, to_addr_conv(sh, percpu));
+	async_gen_syndrome(blocks, 0, count+2, 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_p(struct stripe_head *sh, struct raid5_percpu *percpu)
+{
+	int disks = sh->disks;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = sh->qd_idx;
+	struct page *xor_dest;
+	struct page **xor_srcs = percpu->scribble;
+	struct dma_async_tx_descriptor *tx;
+	struct async_submit_ctl submit;
+	int count;
+	int i;
+
+	pr_debug("%s: stripe %llu\n", __func__,
+		(unsigned long long)sh->sector);
+
+	count = 0;
+	xor_dest = sh->dev[pd_idx].page;
+	xor_srcs[count++] = xor_dest;
+	for (i = disks; i--; ) {
+		if (i == pd_idx || i == qd_idx)
+			continue;
+		xor_srcs[count++] = sh->dev[i].page;
+	}
+
+	init_async_submit(&submit, 0, NULL, NULL, NULL,
+			  to_addr_conv(sh, percpu));
+	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 ops_run_check_pq(struct stripe_head *sh, struct raid5_percpu *percpu, int checkp)
+{
+	struct page **srcs = percpu->scribble;
+	struct async_submit_ctl submit;
+	int count;
+
+	pr_debug("%s: stripe %llu checkp: %d\n", __func__,
+		(unsigned long long)sh->sector, checkp);
+
+	count = set_syndrome_sources(srcs, sh);
+	if (!checkp)
+		srcs[count] = NULL;
+
+	atomic_inc(&sh->count);
+	init_async_submit(&submit, ASYNC_TX_ACK, NULL, ops_complete_check,
+			  sh, to_addr_conv(sh, percpu));
+	async_syndrome_val(srcs, 0, count+2, STRIPE_SIZE,
+			   &sh->ops.zero_sum_result, percpu->spare_page, &submit);
+}
+
+static void __raid_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;
+	struct r5conf *conf = sh->raid_conf;
+	int level = conf->level;
+	struct raid5_percpu *percpu;
+	unsigned long cpu;
+
+	cpu = get_cpu();
+	percpu = per_cpu_ptr(conf->percpu, cpu);
+	if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
+		ops_run_biofill(sh);
+		overlap_clear++;
+	}
+
+	if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
+		if (level < 6)
+			tx = ops_run_compute5(sh, percpu);
+		else {
+			if (sh->ops.target2 < 0 || sh->ops.target < 0)
+				tx = ops_run_compute6_1(sh, percpu);
+			else
+				tx = ops_run_compute6_2(sh, percpu);
+		}
+		/* terminate the chain if reconstruct is not set to be run */
+		if (tx && !test_bit(STRIPE_OP_RECONSTRUCT, &ops_request))
+			async_tx_ack(tx);
+	}
+
+	if (test_bit(STRIPE_OP_PREXOR, &ops_request))
+		tx = ops_run_prexor(sh, percpu, tx);
+
+	if (test_bit(STRIPE_OP_BIODRAIN, &ops_request)) {
+		tx = ops_run_biodrain(sh, tx);
+		overlap_clear++;
+	}
+
+	if (test_bit(STRIPE_OP_RECONSTRUCT, &ops_request)) {
+		if (level < 6)
+			ops_run_reconstruct5(sh, percpu, tx);
+		else
+			ops_run_reconstruct6(sh, percpu, tx);
+	}
+
+	if (test_bit(STRIPE_OP_CHECK, &ops_request)) {
+		if (sh->check_state == check_state_run)
+			ops_run_check_p(sh, percpu);
+		else if (sh->check_state == check_state_run_q)
+			ops_run_check_pq(sh, percpu, 0);
+		else if (sh->check_state == check_state_run_pq)
+			ops_run_check_pq(sh, percpu, 1);
+		else
+			BUG();
+	}
+
+	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);
+		}
+	put_cpu();
+}
+
+#ifdef CONFIG_MULTICORE_RAID456
+static void async_run_ops(void *param, async_cookie_t cookie)
+{
+	struct stripe_head *sh = param;
+	unsigned long ops_request = sh->ops.request;
+
+	clear_bit_unlock(STRIPE_OPS_REQ_PENDING, &sh->state);
+	wake_up(&sh->ops.wait_for_ops);
+
+	__raid_run_ops(sh, ops_request);
+	release_stripe(sh);
+}
+
+static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
+{
+	/* since handle_stripe can be called outside of raid5d context
+	 * we need to ensure sh->ops.request is de-staged before another
+	 * request arrives
+	 */
+	wait_event(sh->ops.wait_for_ops,
+		   !test_and_set_bit_lock(STRIPE_OPS_REQ_PENDING, &sh->state));
+	sh->ops.request = ops_request;
+
+	atomic_inc(&sh->count);
+	async_schedule(async_run_ops, sh);
+}
+#else
+#define raid_run_ops __raid_run_ops
+#endif
+
+static int grow_one_stripe(struct r5conf *conf)
+{
+	struct stripe_head *sh;
+	sh = kmem_cache_zalloc(conf->slab_cache, GFP_KERNEL);
+	if (!sh)
+		return 0;
+
+	sh->raid_conf = conf;
+	#ifdef CONFIG_MULTICORE_RAID456
+	init_waitqueue_head(&sh->ops.wait_for_ops);
+	#endif
+
+	if (grow_buffers(sh)) {
+		shrink_buffers(sh);
+		kmem_cache_free(conf->slab_cache, sh);
+		return 0;
+	}
+	/* 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(struct r5conf *conf, int num)
+{
+	struct kmem_cache *sc;
+	int devs = max(conf->raid_disks, conf->previous_raid_disks);
+
+	if (conf->mddev->gendisk)
+		sprintf(conf->cache_name[0],
+			"raid%d-%s", conf->level, mdname(conf->mddev));
+	else
+		sprintf(conf->cache_name[0],
+			"raid%d-%p", conf->level, conf->mddev);
+	sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);
+
+	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;
+}
+
+/**
+ * scribble_len - return the required size of the scribble region
+ * @num - total number of disks in the array
+ *
+ * The size must be enough to contain:
+ * 1/ a struct page pointer for each device in the array +2
+ * 2/ room to convert each entry in (1) to its corresponding dma
+ *    (dma_map_page()) or page (page_address()) address.
+ *
+ * Note: the +2 is for the destination buffers of the ddf/raid6 case where we
+ * calculate over all devices (not just the data blocks), using zeros in place
+ * of the P and Q blocks.
+ */
+static size_t scribble_len(int num)
+{
+	size_t len;
+
+	len = sizeof(struct page *) * (num+2) + sizeof(addr_conv_t) * (num+2);
+
+	return len;
+}
+
+static int resize_stripes(struct r5conf *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;
+	unsigned long cpu;
+	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_zalloc(sc, GFP_KERNEL);
+		if (!nsh)
+			break;
+
+		nsh->raid_conf = conf;
+		#ifdef CONFIG_MULTICORE_RAID456
+		init_waitqueue_head(&nsh->ops.wait_for_ops);
+		#endif
+
+		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,
+				    );
+		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 and the scribble region
+	 */
+	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;
+
+	get_online_cpus();
+	conf->scribble_len = scribble_len(newsize);
+	for_each_present_cpu(cpu) {
+		struct raid5_percpu *percpu;
+		void *scribble;
+
+		percpu = per_cpu_ptr(conf->percpu, cpu);
+		scribble = kmalloc(conf->scribble_len, GFP_NOIO);
+
+		if (scribble) {
+			kfree(percpu->scribble);
+			percpu->scribble = scribble;
+		} else {
+			err = -ENOMEM;
+			break;
+		}
+	}
+	put_online_cpus();
+
+	/* 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(struct r5conf *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);
+	kmem_cache_free(conf->slab_cache, sh);
+	atomic_dec(&conf->active_stripes);
+	return 1;
+}
+
+static void shrink_stripes(struct r5conf *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;
+	struct r5conf *conf = sh->raid_conf;
+	int disks = sh->disks, i;
+	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+	char b[BDEVNAME_SIZE];
+	struct md_rdev *rdev = NULL;
+
+
+	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 (test_bit(R5_ReadRepl, &sh->dev[i].flags))
+		/* If replacement finished while this request was outstanding,
+		 * 'replacement' might be NULL already.
+		 * In that case it moved down to 'rdev'.
+		 * rdev is not removed until all requests are finished.
+		 */
+		rdev = conf->disks[i].replacement;
+	if (!rdev)
+		rdev = conf->disks[i].rdev;
+
+	if (uptodate) {
+		set_bit(R5_UPTODATE, &sh->dev[i].flags);
+		if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
+			/* Note that this cannot happen on a
+			 * replacement device.  We just fail those on
+			 * any error
+			 */
+			printk_ratelimited(
+				KERN_INFO
+				"md/raid:%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));
+			atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
+			clear_bit(R5_ReadError, &sh->dev[i].flags);
+			clear_bit(R5_ReWrite, &sh->dev[i].flags);
+		}
+		if (atomic_read(&rdev->read_errors))
+			atomic_set(&rdev->read_errors, 0);
+	} else {
+		const char *bdn = bdevname(rdev->bdev, b);
+		int retry = 0;
+
+		clear_bit(R5_UPTODATE, &sh->dev[i].flags);
+		atomic_inc(&rdev->read_errors);
+		if (test_bit(R5_ReadRepl, &sh->dev[i].flags))
+			printk_ratelimited(
+				KERN_WARNING
+				"md/raid:%s: read error on replacement device "
+				"(sector %llu on %s).\n",
+				mdname(conf->mddev),
+				(unsigned long long)(sh->sector
+						     + rdev->data_offset),
+				bdn);
+		else if (conf->mddev->degraded >= conf->max_degraded)
+			printk_ratelimited(
+				KERN_WARNING
+				"md/raid:%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_ratelimited(
+				KERN_WARNING
+				"md/raid:%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
+			       "md/raid:%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(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;
+	struct r5conf *conf = sh->raid_conf;
+	int disks = sh->disks, i;
+	struct md_rdev *uninitialized_var(rdev);
+	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+	sector_t first_bad;
+	int bad_sectors;
+	int replacement = 0;
+
+	for (i = 0 ; i < disks; i++) {
+		if (bi == &sh->dev[i].req) {
+			rdev = conf->disks[i].rdev;
+			break;
+		}
+		if (bi == &sh->dev[i].rreq) {
+			rdev = conf->disks[i].replacement;
+			if (rdev)
+				replacement = 1;
+			else
+				/* rdev was removed and 'replacement'
+				 * replaced it.  rdev is not removed
+				 * until all requests are finished.
+				 */
+				rdev = conf->disks[i].rdev;
+			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 (replacement) {
+		if (!uptodate)
+			md_error(conf->mddev, rdev);
+		else if (is_badblock(rdev, sh->sector,
+				     STRIPE_SECTORS,
+				     &first_bad, &bad_sectors))
+			set_bit(R5_MadeGoodRepl, &sh->dev[i].flags);
+	} else {
+		if (!uptodate) {
+			set_bit(WriteErrorSeen, &rdev->flags);
+			set_bit(R5_WriteError, &sh->dev[i].flags);
+			if (!test_and_set_bit(WantReplacement, &rdev->flags))
+				set_bit(MD_RECOVERY_NEEDED,
+					&rdev->mddev->recovery);
+		} else if (is_badblock(rdev, sh->sector,
+				       STRIPE_SECTORS,
+				       &first_bad, &bad_sectors))
+			set_bit(R5_MadeGood, &sh->dev[i].flags);
+	}
+	rdev_dec_pending(rdev, conf->mddev);
+
+	if (!test_and_clear_bit(R5_DOUBLE_LOCKED, &sh->dev[i].flags))
+		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->req.bi_private = sh;
+	dev->vec.bv_page = dev->page;
+
+	bio_init(&dev->rreq);
+	dev->rreq.bi_io_vec = &dev->rvec;
+	dev->rreq.bi_vcnt++;
+	dev->rreq.bi_max_vecs++;
+	dev->rreq.bi_private = sh;
+	dev->rvec.bv_page = dev->page;
+
+	dev->flags = 0;
+	dev->sector = compute_blocknr(sh, i, previous);
+}
+
+static void error(struct mddev *mddev, struct md_rdev *rdev)
+{
+	char b[BDEVNAME_SIZE];
+	struct r5conf *conf = mddev->private;
+	unsigned long flags;
+	pr_debug("raid456: error called\n");
+
+	spin_lock_irqsave(&conf->device_lock, flags);
+	clear_bit(In_sync, &rdev->flags);
+	mddev->degraded = calc_degraded(conf);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+	set_bit(MD_RECOVERY_INTR, &mddev->recovery);
+
+	set_bit(Blocked, &rdev->flags);
+	set_bit(Faulty, &rdev->flags);
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
+	printk(KERN_ALERT
+	       "md/raid:%s: Disk failure on %s, disabling device.\n"
+	       "md/raid:%s: Operation continuing on %d devices.\n",
+	       mdname(mddev),
+	       bdevname(rdev->bdev, b),
+	       mdname(mddev),
+	       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(struct r5conf *conf, sector_t r_sector,
+				     int previous, int *dd_idx,
+				     struct stripe_head *sh)
+{
+	sector_t stripe, stripe2;
+	sector_t chunk_number;
+	unsigned int chunk_offset;
+	int pd_idx, qd_idx;
+	int ddf_layout = 0;
+	sector_t new_sector;
+	int algorithm = previous ? conf->prev_algo
+				 : conf->algorithm;
+	int sectors_per_chunk = previous ? conf->prev_chunk_sectors
+					 : conf->chunk_sectors;
+	int raid_disks = previous ? conf->previous_raid_disks
+				  : conf->raid_disks;
+	int data_disks = raid_disks - conf->max_degraded;
+
+	/* First compute the information on this sector */
+
+	/*
+	 * Compute the chunk number and the sector offset inside the chunk
+	 */
+	chunk_offset = sector_div(r_sector, sectors_per_chunk);
+	chunk_number = r_sector;
+
+	/*
+	 * Compute the stripe number
+	 */
+	stripe = chunk_number;
+	*dd_idx = sector_div(stripe, data_disks);
+	stripe2 = stripe;
+	/*
+	 * Select the parity disk based on the user selected algorithm.
+	 */
+	pd_idx = qd_idx = -1;
+	switch(conf->level) {
+	case 4:
+		pd_idx = data_disks;
+		break;
+	case 5:
+		switch (algorithm) {
+		case ALGORITHM_LEFT_ASYMMETRIC:
+			pd_idx = data_disks - sector_div(stripe2, raid_disks);
+			if (*dd_idx >= pd_idx)
+				(*dd_idx)++;
+			break;
+		case ALGORITHM_RIGHT_ASYMMETRIC:
+			pd_idx = sector_div(stripe2, raid_disks);
+			if (*dd_idx >= pd_idx)
+				(*dd_idx)++;
+			break;
+		case ALGORITHM_LEFT_SYMMETRIC:
+			pd_idx = data_disks - sector_div(stripe2, raid_disks);
+			*dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
+			break;
+		case ALGORITHM_RIGHT_SYMMETRIC:
+			pd_idx = sector_div(stripe2, 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:
+			BUG();
+		}
+		break;
+	case 6:
+
+		switch (algorithm) {
+		case ALGORITHM_LEFT_ASYMMETRIC:
+			pd_idx = raid_disks - 1 - sector_div(stripe2, 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 = sector_div(stripe2, 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 - sector_div(stripe2, 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 = sector_div(stripe2, 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 = sector_div(stripe2, 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
+			 */
+			stripe2 += 1;
+			pd_idx = raid_disks - 1 - sector_div(stripe2, 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 - sector_div(stripe2, 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 - sector_div(stripe2, raid_disks-1);
+			if (*dd_idx >= pd_idx)
+				(*dd_idx)++;
+			qd_idx = raid_disks - 1;
+			break;
+
+		case ALGORITHM_RIGHT_ASYMMETRIC_6:
+			pd_idx = sector_div(stripe2, 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 - sector_div(stripe2, 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 = sector_div(stripe2, 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:
+			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)
+{
+	struct r5conf *conf = sh->raid_conf;
+	int raid_disks = sh->disks;
+	int data_disks = raid_disks - conf->max_degraded;
+	sector_t new_sector = sh->sector, check;
+	int sectors_per_chunk = previous ? conf->prev_chunk_sectors
+					 : conf->chunk_sectors;
+	int algorithm = previous ? conf->prev_algo
+				 : conf->algorithm;
+	sector_t stripe;
+	int chunk_offset;
+	sector_t chunk_number;
+	int dummy1, dd_idx = i;
+	sector_t r_sector;
+	struct stripe_head sh2;
+
+
+	chunk_offset = sector_div(new_sector, sectors_per_chunk);
+	stripe = new_sector;
+
+	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:
+			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:
+			/* Like left_symmetric, but P is before Q */
+			if (sh->pd_idx == 0)
+				i--;	/* P D D D Q */
+			else {
+				/* D D Q P D */
+				if (i < sh->pd_idx)
+					i += raid_disks;
+				i -= (sh->pd_idx + 1);
+			}
+			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:
+			BUG();
+		}
+		break;
+	}
+
+	chunk_number = stripe * data_disks + i;
+	r_sector = 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 "md/raid:%s: compute_blocknr: map not correct\n",
+		       mdname(conf->mddev));
+		return 0;
+	}
+	return r_sector;
+}
+
+
+static void
+schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
+			 int rcw, int expand)
+{
+	int i, pd_idx = sh->pd_idx, disks = sh->disks;
+	struct r5conf *conf = sh->raid_conf;
+	int level = conf->level;
+
+	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_RECONSTRUCT, &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 + conf->max_degraded == disks)
+			if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
+				atomic_inc(&conf->pending_full_writes);
+	} else {
+		BUG_ON(level == 6);
+		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_RECONSTRUCT, &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(s) 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++;
+
+	if (level == 6) {
+		int qd_idx = sh->qd_idx;
+		struct r5dev *dev = &sh->dev[qd_idx];
+
+		set_bit(R5_LOCKED, &dev->flags);
+		clear_bit(R5_UPTODATE, &dev->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;
+	struct r5conf *conf = sh->raid_conf;
+	int firstwrite=0;
+
+	pr_debug("adding bi b#%llu to stripe s#%llu\n",
+		(unsigned long long)bi->bi_sector,
+		(unsigned long long)sh->sector);
+
+
+	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++;
+
+	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);
+	}
+	spin_unlock_irq(&conf->device_lock);
+
+	pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
+		(unsigned long long)(*bip)->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);
+	}
+	return 1;
+
+ overlap:
+	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
+	spin_unlock_irq(&conf->device_lock);
+	return 0;
+}
+
+static void end_reshape(struct r5conf *conf);
+
+static void stripe_set_idx(sector_t stripe, struct r5conf *conf, int previous,
+			    struct stripe_head *sh)
+{
+	int sectors_per_chunk =
+		previous ? conf->prev_chunk_sectors : conf->chunk_sectors;
+	int dd_idx;
+	int chunk_offset = sector_div(stripe, sectors_per_chunk);
+	int disks = previous ? conf->previous_raid_disks : conf->raid_disks;
+
+	raid5_compute_sector(conf,
+			     stripe * (disks - conf->max_degraded)
+			     *sectors_per_chunk + chunk_offset,
+			     previous,
+			     &dd_idx, sh);
+}
+
+static void
+handle_failed_stripe(struct r5conf *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)) {
+			struct md_rdev *rdev;
+			rcu_read_lock();
+			rdev = rcu_dereference(conf->disks[i].rdev);
+			if (rdev && test_bit(In_sync, &rdev->flags))
+				atomic_inc(&rdev->nr_pending);
+			else
+				rdev = NULL;
+			rcu_read_unlock();
+			if (rdev) {
+				if (!rdev_set_badblocks(
+					    rdev,
+					    sh->sector,
+					    STRIPE_SECTORS, 0))
+					md_error(conf->mddev, rdev);
+				rdev_dec_pending(rdev, conf->mddev);
+			}
+		}
+		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 we were in the middle of a write the parity block might
+		 * still be locked - so just clear all R5_LOCKED flags
+		 */
+		clear_bit(R5_LOCKED, &sh->dev[i].flags);
+	}
+
+	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_failed_sync(struct r5conf *conf, struct stripe_head *sh,
+		   struct stripe_head_state *s)
+{
+	int abort = 0;
+	int i;
+
+	clear_bit(STRIPE_SYNCING, &sh->state);
+	s->syncing = 0;
+	s->replacing = 0;
+	/* There is nothing more to do for sync/check/repair.
+	 * Don't even need to abort as that is handled elsewhere
+	 * if needed, and not always wanted e.g. if there is a known
+	 * bad block here.
+	 * For recover/replace we need to record a bad block on all
+	 * non-sync devices, or abort the recovery
+	 */
+	if (test_bit(MD_RECOVERY_RECOVER, &conf->mddev->recovery)) {
+		/* During recovery devices cannot be removed, so
+		 * locking and refcounting of rdevs is not needed
+		 */
+		for (i = 0; i < conf->raid_disks; i++) {
+			struct md_rdev *rdev = conf->disks[i].rdev;
+			if (rdev
+			    && !test_bit(Faulty, &rdev->flags)
+			    && !test_bit(In_sync, &rdev->flags)
+			    && !rdev_set_badblocks(rdev, sh->sector,
+						   STRIPE_SECTORS, 0))
+				abort = 1;
+			rdev = conf->disks[i].replacement;
+			if (rdev
+			    && !test_bit(Faulty, &rdev->flags)
+			    && !test_bit(In_sync, &rdev->flags)
+			    && !rdev_set_badblocks(rdev, sh->sector,
+						   STRIPE_SECTORS, 0))
+				abort = 1;
+		}
+		if (abort)
+			conf->recovery_disabled =
+				conf->mddev->recovery_disabled;
+	}
+	md_done_sync(conf->mddev, STRIPE_SECTORS, !abort);
+}
+
+static int want_replace(struct stripe_head *sh, int disk_idx)
+{
+	struct md_rdev *rdev;
+	int rv = 0;
+	/* Doing recovery so rcu locking not required */
+	rdev = sh->raid_conf->disks[disk_idx].replacement;
+	if (rdev
+	    && !test_bit(Faulty, &rdev->flags)
+	    && !test_bit(In_sync, &rdev->flags)
+	    && (rdev->recovery_offset <= sh->sector
+		|| rdev->mddev->recovery_cp <= sh->sector))
+		rv = 1;
+
+	return rv;
+}
+
+/* fetch_block - 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_fill to continue
+ */
+static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s,
+		       int disk_idx, int disks)
+{
+	struct r5dev *dev = &sh->dev[disk_idx];
+	struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
+				  &sh->dev[s->failed_num[1]] };
+
+	/* 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->replacing && want_replace(sh, disk_idx)) ||
+	     (s->failed >= 1 && fdev[0]->toread) ||
+	     (s->failed >= 2 && fdev[1]->toread) ||
+	     (sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
+	      !test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
+	     (sh->raid_conf->level == 6 && s->failed && s->to_write))) {
+		/* we would like to get this block, possibly by computing it,
+		 * otherwise read it if the backing disk is insync
+		 */
+		BUG_ON(test_bit(R5_Wantcompute, &dev->flags));
+		BUG_ON(test_bit(R5_Wantread, &dev->flags));
+		if ((s->uptodate == disks - 1) &&
+		    (s->failed && (disk_idx == s->failed_num[0] ||
+				   disk_idx == s->failed_num[1]))) {
+			/* have disk failed, and we're requested to fetch it;
+			 * do compute it
+			 */
+			pr_debug("Computing stripe %llu block %d\n",
+			       (unsigned long long)sh->sector, disk_idx);
+			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;
+			sh->ops.target2 = -1; /* no 2nd target */
+			s->req_compute = 1;
+			/* Careful: from this point on 'uptodate' is in the eye
+			 * of raid_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;
+		} 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 == disk_idx)
+					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,
+			       disk_idx, other);
+			set_bit(STRIPE_COMPUTE_RUN, &sh->state);
+			set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
+			set_bit(R5_Wantcompute, &sh->dev[disk_idx].flags);
+			set_bit(R5_Wantcompute, &sh->dev[other].flags);
+			sh->ops.target = disk_idx;
+			sh->ops.target2 = other;
+			s->uptodate += 2;
+			s->req_compute = 1;
+			return 1;
+		} 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_fill - read or compute data to satisfy pending requests.
+ */
+static void handle_stripe_fill(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_block(sh, s, i, disks))
+				break;
+	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(struct r5conf *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_dirtying(struct r5conf *conf,
+				   struct stripe_head *sh,
+				   struct stripe_head_state *s,
+				   int disks)
+{
+	int rmw = 0, rcw = 0, i;
+	if (conf->max_degraded == 2) {
+		/* RAID6 requires 'rcw' in current implementation
+		 * Calculate the real rcw later - for now fake it
+		 * look like rcw is cheaper
+		 */
+		rcw = 1; rmw = 2;
+	} else 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 */
+		rcw = 0;
+		for (i = disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
+			if (!test_bit(R5_OVERWRITE, &dev->flags) &&
+			    i != sh->pd_idx && i != sh->qd_idx &&
+			    !test_bit(R5_LOCKED, &dev->flags) &&
+			    !(test_bit(R5_UPTODATE, &dev->flags) ||
+			      test_bit(R5_Wantcompute, &dev->flags))) {
+				rcw++;
+				if (!test_bit(R5_Insync, &dev->flags))
+					continue; /* it's a failed drive */
+				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.  raid_run_ops only
+	 * handles the case where compute block and reconstruct 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_reconstruction(sh, s, rcw == 0, 0);
+}
+
+static void handle_parity_checks5(struct r5conf *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[0]];
+		/* 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 & SUM_CHECK_P_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;
+				sh->ops.target2 = -1;
+				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(struct r5conf *conf, struct stripe_head *sh,
+				  struct stripe_head_state *s,
+				  int disks)
+{
+	int pd_idx = sh->pd_idx;
+	int qd_idx = sh->qd_idx;
+	struct r5dev *dev;
+
+	set_bit(STRIPE_HANDLE, &sh->state);
+
+	BUG_ON(s->failed > 2);
+
+	/* 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
+	 */
+
+	switch (sh->check_state) {
+	case check_state_idle:
+		/* start a new check operation if there are < 2 failures */
+		if (s->failed == s->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).
+			 */
+			sh->check_state = check_state_run;
+		}
+		if (!s->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
+			 */
+			if (sh->check_state == check_state_run)
+				sh->check_state = check_state_run_pq;
+			else
+				sh->check_state = check_state_run_q;
+		}
+
+		/* discard potentially stale zero_sum_result */
+		sh->ops.zero_sum_result = 0;
+
+		if (sh->check_state == check_state_run) {
+			/* async_xor_zero_sum destroys the contents of P */
+			clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+			s->uptodate--;
+		}
+		if (sh->check_state >= check_state_run &&
+		    sh->check_state <= check_state_run_pq) {
+			/* async_syndrome_zero_sum preserves P and Q, so
+			 * no need to mark them !uptodate here
+			 */
+			set_bit(STRIPE_OP_CHECK, &s->ops_request);
+			break;
+		}
+
+		/* we have 2-disk failure */
+		BUG_ON(s->failed != 2);
+		/* fall through */
+	case check_state_compute_result:
+		sh->check_state = check_state_idle;
+
+		/* check that a write has not made the stripe insync */
+		if (test_bit(STRIPE_INSYNC, &sh->state))
+			break;
+
+		/* now write out any block on a failed drive,
+		 * or P or Q if they were recomputed
+		 */
+		BUG_ON(s->uptodate < disks - 1); /* We don't need Q to recover */
+		if (s->failed == 2) {
+			dev = &sh->dev[s->failed_num[1]];
+			s->locked++;
+			set_bit(R5_LOCKED, &dev->flags);
+			set_bit(R5_Wantwrite, &dev->flags);
+		}
+		if (s->failed >= 1) {
+			dev = &sh->dev[s->failed_num[0]];
+			s->locked++;
+			set_bit(R5_LOCKED, &dev->flags);
+			set_bit(R5_Wantwrite, &dev->flags);
+		}
+		if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
+			dev = &sh->dev[pd_idx];
+			s->locked++;
+			set_bit(R5_LOCKED, &dev->flags);
+			set_bit(R5_Wantwrite, &dev->flags);
+		}
+		if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
+			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);
+		break;
+	case check_state_run:
+	case check_state_run_q:
+	case check_state_run_pq:
+		break; /* we will be called again upon completion */
+	case check_state_check_result:
+		sh->check_state = check_state_idle;
+
+		/* 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) {
+			/* both parities are correct */
+			if (!s->failed)
+				set_bit(STRIPE_INSYNC, &sh->state);
+			else {
+				/* in contrast to the raid5 case we can validate
+				 * parity, but still have a failure to write
+				 * back
+				 */
+				sh->check_state = check_state_compute_result;
+				/* Returning at this point means that we may go
+				 * off and bring p and/or q uptodate again so
+				 * we make sure to check zero_sum_result again
+				 * to verify if p or q need writeback
+				 */
+			}
+		} 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 {
+				int *target = &sh->ops.target;
+
+				sh->ops.target = -1;
+				sh->ops.target2 = -1;
+				sh->check_state = check_state_compute_run;
+				set_bit(STRIPE_COMPUTE_RUN, &sh->state);
+				set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
+				if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
+					set_bit(R5_Wantcompute,
+						&sh->dev[pd_idx].flags);
+					*target = pd_idx;
+					target = &sh->ops.target2;
+					s->uptodate++;
+				}
+				if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
+					set_bit(R5_Wantcompute,
+						&sh->dev[qd_idx].flags);
+					*target = qd_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_stripe_expansion(struct r5conf *conf, struct stripe_head *sh)
+{
+	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, 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 &&
+				    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 by setting STRIPE_ACTIVE and then examine the
+ * state of various bits to see what needs to be done.
+ * Possible results:
+ *    return some read requests which now have data
+ *    return some write requests which are safely on storage
+ *    schedule a read on some buffers
+ *    schedule a write of some buffers
+ *    return confirmation of parity correctness
+ *
+ */
+
+static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
+{
+	struct r5conf *conf = sh->raid_conf;
+	int disks = sh->disks;
+	struct r5dev *dev;
+	int i;
+	int do_recovery = 0;
+
+	memset(s, 0, sizeof(*s));
+
+	s->expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
+	s->expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
+	s->failed_num[0] = -1;
+	s->failed_num[1] = -1;
+
+	/* Now to look around and see what can be done */
+	rcu_read_lock();
+	spin_lock_irq(&conf->device_lock);
+	for (i=disks; i--; ) {
+		struct md_rdev *rdev;
+		sector_t first_bad;
+		int bad_sectors;
+		int is_bad = 0;
+
+		dev = &sh->dev[i];
+
+		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
+		 *
+		 * 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++;
+			BUG_ON(s->compute > 2);
+		}
+
+		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++;
+		/* Prefer to use the replacement for reads, but only
+		 * if it is recovered enough and has no bad blocks.
+		 */
+		rdev = rcu_dereference(conf->disks[i].replacement);
+		if (rdev && !test_bit(Faulty, &rdev->flags) &&
+		    rdev->recovery_offset >= sh->sector + STRIPE_SECTORS &&
+		    !is_badblock(rdev, sh->sector, STRIPE_SECTORS,
+				 &first_bad, &bad_sectors))
+			set_bit(R5_ReadRepl, &dev->flags);
+		else {
+			if (rdev)
+				set_bit(R5_NeedReplace, &dev->flags);
+			rdev = rcu_dereference(conf->disks[i].rdev);
+			clear_bit(R5_ReadRepl, &dev->flags);
+		}
+		if (rdev && test_bit(Faulty, &rdev->flags))
+			rdev = NULL;
+		if (rdev) {
+			is_bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
+					     &first_bad, &bad_sectors);
+			if (s->blocked_rdev == NULL
+			    && (test_bit(Blocked, &rdev->flags)
+				|| is_bad < 0)) {
+				if (is_bad < 0)
+					set_bit(BlockedBadBlocks,
+						&rdev->flags);
+				s->blocked_rdev = rdev;
+				atomic_inc(&rdev->nr_pending);
+			}
+		}
+		clear_bit(R5_Insync, &dev->flags);
+		if (!rdev)
+			/* Not in-sync */;
+		else if (is_bad) {
+			/* also not in-sync */
+			if (!test_bit(WriteErrorSeen, &rdev->flags) &&
+			    test_bit(R5_UPTODATE, &dev->flags)) {
+				/* treat as in-sync, but with a read error
+				 * which we can now try to correct
+				 */
+				set_bit(R5_Insync, &dev->flags);
+				set_bit(R5_ReadError, &dev->flags);
+			}
+		} else if (test_bit(In_sync, &rdev->flags))
+			set_bit(R5_Insync, &dev->flags);
+		else if (sh->sector + STRIPE_SECTORS <= rdev->recovery_offset)
+			/* in sync if before recovery_offset */
+			set_bit(R5_Insync, &dev->flags);
+		else if (test_bit(R5_UPTODATE, &dev->flags) &&
+			 test_bit(R5_Expanded, &dev->flags))
+			/* If we've reshaped into here, we assume it is Insync.
+			 * We will shortly update recovery_offset to make
+			 * it official.
+			 */
+			set_bit(R5_Insync, &dev->flags);
+
+		if (rdev && test_bit(R5_WriteError, &dev->flags)) {
+			/* This flag does not apply to '.replacement'
+			 * only to .rdev, so make sure to check that*/
+			struct md_rdev *rdev2 = rcu_dereference(
+				conf->disks[i].rdev);
+			if (rdev2 == rdev)
+				clear_bit(R5_Insync, &dev->flags);
+			if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
+				s->handle_bad_blocks = 1;
+				atomic_inc(&rdev2->nr_pending);
+			} else
+				clear_bit(R5_WriteError, &dev->flags);
+		}
+		if (rdev && test_bit(R5_MadeGood, &dev->flags)) {
+			/* This flag does not apply to '.replacement'
+			 * only to .rdev, so make sure to check that*/
+			struct md_rdev *rdev2 = rcu_dereference(
+				conf->disks[i].rdev);
+			if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
+				s->handle_bad_blocks = 1;
+				atomic_inc(&rdev2->nr_pending);
+			} else
+				clear_bit(R5_MadeGood, &dev->flags);
+		}
+		if (test_bit(R5_MadeGoodRepl, &dev->flags)) {
+			struct md_rdev *rdev2 = rcu_dereference(
+				conf->disks[i].replacement);
+			if (rdev2 && !test_bit(Faulty, &rdev2->flags)) {
+				s->handle_bad_blocks = 1;
+				atomic_inc(&rdev2->nr_pending);
+			} else
+				clear_bit(R5_MadeGoodRepl, &dev->flags);
+		}
+		if (!test_bit(R5_Insync, &dev->flags)) {
+			/* The ReadError flag will just be confusing now */
+			clear_bit(R5_ReadError, &dev->flags);
+			clear_bit(R5_ReWrite, &dev->flags);
+		}
+		if (test_bit(R5_ReadError, &dev->flags))
+			clear_bit(R5_Insync, &dev->flags);
+		if (!test_bit(R5_Insync, &dev->flags)) {
+			if (s->failed < 2)
+				s->failed_num[s->failed] = i;
+			s->failed++;
+			if (rdev && !test_bit(Faulty, &rdev->flags))
+				do_recovery = 1;
+		}
+	}
+	spin_unlock_irq(&conf->device_lock);
+	if (test_bit(STRIPE_SYNCING, &sh->state)) {
+		/* If there is a failed device being replaced,
+		 *     we must be recovering.
+		 * else if we are after recovery_cp, we must be syncing
+		 * else if MD_RECOVERY_REQUESTED is set, we also are syncing.
+		 * else we can only be replacing
+		 * sync and recovery both need to read all devices, and so
+		 * use the same flag.
+		 */
+		if (do_recovery ||
+		    sh->sector >= conf->mddev->recovery_cp ||
+		    test_bit(MD_RECOVERY_REQUESTED, &(conf->mddev->recovery)))
+			s->syncing = 1;
+		else
+			s->replacing = 1;
+	}
+	rcu_read_unlock();
+}
+
+static void handle_stripe(struct stripe_head *sh)
+{
+	struct stripe_head_state s;
+	struct r5conf *conf = sh->raid_conf;
+	int i;
+	int prexor;
+	int disks = sh->disks;
+	struct r5dev *pdev, *qdev;
+
+	clear_bit(STRIPE_HANDLE, &sh->state);
+	if (test_and_set_bit_lock(STRIPE_ACTIVE, &sh->state)) {
+		/* already being handled, ensure it gets handled
+		 * again when current action finishes */
+		set_bit(STRIPE_HANDLE, &sh->state);
+		return;
+	}
+
+	if (test_and_clear_bit(STRIPE_SYNC_REQUESTED, &sh->state)) {
+		set_bit(STRIPE_SYNCING, &sh->state);
+		clear_bit(STRIPE_INSYNC, &sh->state);
+	}
+	clear_bit(STRIPE_DELAYED, &sh->state);
+
+	pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
+		"pd_idx=%d, qd_idx=%d\n, check:%d, reconstruct:%d\n",
+	       (unsigned long long)sh->sector, sh->state,
+	       atomic_read(&sh->count), sh->pd_idx, sh->qd_idx,
+	       sh->check_state, sh->reconstruct_state);
+
+	analyse_stripe(sh, &s);
+
+	if (s.handle_bad_blocks) {
+		set_bit(STRIPE_HANDLE, &sh->state);
+		goto finish;
+	}
+
+	if (unlikely(s.blocked_rdev)) {
+		if (s.syncing || s.expanding || s.expanded ||
+		    s.replacing || s.to_write || s.written) {
+			set_bit(STRIPE_HANDLE, &sh->state);
+			goto finish;
+		}
+		/* There is nothing for the blocked_rdev to block */
+		rdev_dec_pending(s.blocked_rdev, conf->mddev);
+		s.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,%d\n",
+	       s.locked, s.uptodate, s.to_read, s.to_write, s.failed,
+	       s.failed_num[0], s.failed_num[1]);
+	/* check if the array has lost more than max_degraded devices and,
+	 * if so, some requests might need to be failed.
+	 */
+	if (s.failed > conf->max_degraded) {
+		sh->check_state = 0;
+		sh->reconstruct_state = 0;
+		if (s.to_read+s.to_write+s.written)
+			handle_failed_stripe(conf, sh, &s, disks, &s.return_bi);
+		if (s.syncing + s.replacing)
+			handle_failed_sync(conf, sh, &s);
+	}
+
+	/*
+	 * might be able to return some write requests if the parity blocks
+	 * are safe, or on a failed drive
+	 */
+	pdev = &sh->dev[sh->pd_idx];
+	s.p_failed = (s.failed >= 1 && s.failed_num[0] == sh->pd_idx)
+		|| (s.failed >= 2 && s.failed_num[1] == sh->pd_idx);
+	qdev = &sh->dev[sh->qd_idx];
+	s.q_failed = (s.failed >= 1 && s.failed_num[0] == sh->qd_idx)
+		|| (s.failed >= 2 && s.failed_num[1] == sh->qd_idx)
+		|| conf->level < 6;
+
+	if (s.written &&
+	    (s.p_failed || ((test_bit(R5_Insync, &pdev->flags)
+			     && !test_bit(R5_LOCKED, &pdev->flags)
+			     && test_bit(R5_UPTODATE, &pdev->flags)))) &&
+	    (s.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, &s.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
+	    || (conf->level == 6 && s.to_write && s.failed)
+	    || (s.syncing && (s.uptodate + s.compute < disks))
+	    || s.replacing
+	    || s.expanding)
+		handle_stripe_fill(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));
+		BUG_ON(sh->qd_idx >= 0 &&
+		       !test_bit(R5_UPTODATE, &sh->dev[sh->qd_idx].flags));
+		for (i = disks; i--; ) {
+			struct r5dev *dev = &sh->dev[i];
+			if (test_bit(R5_LOCKED, &dev->flags) &&
+				(i == sh->pd_idx || i == sh->qd_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 || i == sh->qd_idx)  &&
+				     s.failed == 0))
+					set_bit(STRIPE_INSYNC, &sh->state);
+			}
+		}
+		if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+			s.dec_preread_active = 1;
+	}
+
+	/* 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_dirtying(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))) {
+		if (conf->level == 6)
+			handle_parity_checks6(conf, sh, &s, disks);
+		else
+			handle_parity_checks5(conf, sh, &s, disks);
+	}
+
+	if (s.replacing && s.locked == 0
+	    && !test_bit(STRIPE_INSYNC, &sh->state)) {
+		/* Write out to replacement devices where possible */
+		for (i = 0; i < conf->raid_disks; i++)
+			if (test_bit(R5_UPTODATE, &sh->dev[i].flags) &&
+			    test_bit(R5_NeedReplace, &sh->dev[i].flags)) {
+				set_bit(R5_WantReplace, &sh->dev[i].flags);
+				set_bit(R5_LOCKED, &sh->dev[i].flags);
+				s.locked++;
+			}
+		set_bit(STRIPE_INSYNC, &sh->state);
+	}
+	if ((s.syncing || s.replacing) && 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 <= conf->max_degraded && !conf->mddev->ro)
+		for (i = 0; i < s.failed; i++) {
+			struct r5dev *dev = &sh->dev[s.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);
+					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 *sh_src
+			= get_active_stripe(conf, sh->sector, 1, 1, 1);
+		if (sh_src && test_bit(STRIPE_EXPAND_SOURCE, &sh_src->state)) {
+			/* sh cannot be written until sh_src 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,
+					      &sh_src->state))
+				atomic_inc(&conf->preread_active_stripes);
+			release_stripe(sh_src);
+			goto finish;
+		}
+		if (sh_src)
+			release_stripe(sh_src);
+
+		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_reconstruction(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);
+
+finish:
+	/* wait for this device to become unblocked */
+	if (conf->mddev->external && unlikely(s.blocked_rdev))
+		md_wait_for_blocked_rdev(s.blocked_rdev, conf->mddev);
+
+	if (s.handle_bad_blocks)
+		for (i = disks; i--; ) {
+			struct md_rdev *rdev;
+			struct r5dev *dev = &sh->dev[i];
+			if (test_and_clear_bit(R5_WriteError, &dev->flags)) {
+				/* We own a safe reference to the rdev */
+				rdev = conf->disks[i].rdev;
+				if (!rdev_set_badblocks(rdev, sh->sector,
+							STRIPE_SECTORS, 0))
+					md_error(conf->mddev, rdev);
+				rdev_dec_pending(rdev, conf->mddev);
+			}
+			if (test_and_clear_bit(R5_MadeGood, &dev->flags)) {
+				rdev = conf->disks[i].rdev;
+				rdev_clear_badblocks(rdev, sh->sector,
+						     STRIPE_SECTORS);
+				rdev_dec_pending(rdev, conf->mddev);
+			}
+			if (test_and_clear_bit(R5_MadeGoodRepl, &dev->flags)) {
+				rdev = conf->disks[i].replacement;
+				if (!rdev)
+					/* rdev have been moved down */
+					rdev = conf->disks[i].rdev;
+				rdev_clear_badblocks(rdev, sh->sector,
+						     STRIPE_SECTORS);
+				rdev_dec_pending(rdev, conf->mddev);
+			}
+		}
+
+	if (s.ops_request)
+		raid_run_ops(sh, s.ops_request);
+
+	ops_run_io(sh, &s);
+
+	if (s.dec_preread_active) {
+		/* We delay this until after ops_run_io so that if make_request
+		 * is waiting on a flush, it won't continue until the writes
+		 * have actually been submitted.
+		 */
+		atomic_dec(&conf->preread_active_stripes);
+		if (atomic_read(&conf->preread_active_stripes) <
+		    IO_THRESHOLD)
+			md_wakeup_thread(conf->mddev->thread);
+	}
+
+	return_io(s.return_bi);
+
+	clear_bit_unlock(STRIPE_ACTIVE, &sh->state);
+}
+
+static void raid5_activate_delayed(struct r5conf *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);
+		}
+	}
+}
+
+static void activate_bit_delay(struct r5conf *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);
+	}
+}
+
+int md_raid5_congested(struct mddev *mddev, int bits)
+{
+	struct r5conf *conf = mddev->private;
+
+	/* No difference between reads and writes.  Just check
+	 * how busy the stripe_cache is
+	 */
+
+	if (conf->inactive_blocked)
+		return 1;
+	if (conf->quiesce)
+		return 1;
+	if (list_empty_careful(&conf->inactive_list))
+		return 1;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(md_raid5_congested);
+
+static int raid5_congested(void *data, int bits)
+{
+	struct mddev *mddev = data;
+
+	return mddev_congested(mddev, bits) ||
+		md_raid5_congested(mddev, bits);
+}
+
+/* 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)
+{
+	struct mddev *mddev = q->queuedata;
+	sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
+	int max;
+	unsigned int chunk_sectors = mddev->chunk_sectors;
+	unsigned int bio_sectors = bvm->bi_size >> 9;
+
+	if ((bvm->bi_rw & 1) == WRITE)
+		return biovec->bv_len; /* always allow writes to be mergeable */
+
+	if (mddev->new_chunk_sectors < mddev->chunk_sectors)
+		chunk_sectors = mddev->new_chunk_sectors;
+	max =  (chunk_sectors - ((sector & (chunk_sectors - 1)) + bio_sectors)) << 9;
+	if (max < 0) max = 0;
+	if (max <= biovec->bv_len && bio_sectors == 0)
+		return biovec->bv_len;
+	else
+		return max;
+}
+
+
+static int in_chunk_boundary(struct mddev *mddev, struct bio *bio)
+{
+	sector_t sector = bio->bi_sector + get_start_sect(bio->bi_bdev);
+	unsigned int chunk_sectors = mddev->chunk_sectors;
+	unsigned int bio_sectors = bio->bi_size >> 9;
+
+	if (mddev->new_chunk_sectors < mddev->chunk_sectors)
+		chunk_sectors = mddev->new_chunk_sectors;
+	return  chunk_sectors >=
+		((sector & (chunk_sectors - 1)) + bio_sectors);
+}
+
+/*
+ *  add bio to the retry LIFO  ( in O(1) ... we are in interrupt )
+ *  later sampled by raid5d.
+ */
+static void add_bio_to_retry(struct bio *bi,struct r5conf *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(struct r5conf *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;
+	struct mddev *mddev;
+	struct r5conf *conf;
+	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+	struct md_rdev *rdev;
+
+	bio_put(bi);
+
+	rdev = (void*)raid_bi->bi_next;
+	raid_bi->bi_next = NULL;
+	mddev = rdev->mddev;
+	conf = mddev->private;
+
+	rdev_dec_pending(rdev, conf->mddev);
+
+	if (!error && uptodate) {
+		bio_endio(raid_bi, 0);
+		if (atomic_dec_and_test(&conf->active_aligned_reads))
+			wake_up(&conf->wait_for_stripe);
+		return;
+	}
+
+
+	pr_debug("raid5_align_endio : io error...handing IO for a retry\n");
+
+	add_bio_to_retry(raid_bi, conf);
+}
+
+static int bio_fits_rdev(struct bio *bi)
+{
+	struct request_queue *q = bdev_get_queue(bi->bi_bdev);
+
+	if ((bi->bi_size>>9) > queue_max_sectors(q))
+		return 0;
+	blk_recount_segments(q, bi);
+	if (bi->bi_phys_segments > queue_max_segments(q))
+		return 0;
+
+	if (q->merge_bvec_fn)
+		/* it's too hard to apply the merge_bvec_fn at this stage,
+		 * just just give up
+		 */
+		return 0;
+
+	return 1;
+}
+
+
+static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
+{
+	struct r5conf *conf = mddev->private;
+	int dd_idx;
+	struct bio* align_bi;
+	struct md_rdev *rdev;
+	sector_t end_sector;
+
+	if (!in_chunk_boundary(mddev, raid_bio)) {
+		pr_debug("chunk_aligned_read : non aligned\n");
+		return 0;
+	}
+	/*
+	 * use bio_clone_mddev to make a copy of the bio
+	 */
+	align_bi = bio_clone_mddev(raid_bio, GFP_NOIO, mddev);
+	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);
+
+	end_sector = align_bi->bi_sector + (align_bi->bi_size >> 9);
+	rcu_read_lock();
+	rdev = rcu_dereference(conf->disks[dd_idx].replacement);
+	if (!rdev || test_bit(Faulty, &rdev->flags) ||
+	    rdev->recovery_offset < end_sector) {
+		rdev = rcu_dereference(conf->disks[dd_idx].rdev);
+		if (rdev &&
+		    (test_bit(Faulty, &rdev->flags) ||
+		    !(test_bit(In_sync, &rdev->flags) ||
+		      rdev->recovery_offset >= end_sector)))
+			rdev = NULL;
+	}
+	if (rdev) {
+		sector_t first_bad;
+		int bad_sectors;
+
+		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);
+
+		if (!bio_fits_rdev(align_bi) ||
+		    is_badblock(rdev, align_bi->bi_sector, align_bi->bi_size>>9,
+				&first_bad, &bad_sectors)) {
+			/* too big in some way, or has a known bad block */
+			bio_put(align_bi);
+			rdev_dec_pending(rdev, mddev);
+			return 0;
+		}
+
+		/* No reshape active, so we can trust rdev->data_offset */
+		align_bi->bi_sector += rdev->data_offset;
+
+		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(struct r5conf *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 void make_request(struct mddev *mddev, struct bio * bi)
+{
+	struct r5conf *conf = mddev->private;
+	int dd_idx;
+	sector_t new_sector;
+	sector_t logical_sector, last_sector;
+	struct stripe_head *sh;
+	const int rw = bio_data_dir(bi);
+	int remaining;
+	int plugged;
+
+	if (unlikely(bi->bi_rw & REQ_FLUSH)) {
+		md_flush_request(mddev, bi);
+		return;
+	}
+
+	md_write_start(mddev, bi);
+
+	if (rw == READ &&
+	     mddev->reshape_position == MaxSector &&
+	     chunk_aligned_read(mddev,bi))
+		return;
+
+	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 */
+
+	plugged = mddev_check_plugged(mddev);
+	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
+			 * Of course 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("raid456: make_request, sector %llu logical %llu\n",
+			(unsigned long long)new_sector, 
+			(unsigned long long)logical_sector);
+
+		sh = get_active_stripe(conf, new_sector, previous,
+				       (bi->bi_rw&RWA_MASK), 0);
+		if (sh) {
+			if (unlikely(previous)) {
+				/* expansion might have moved on while waiting for a
+				 * stripe, so we must do the range check again.
+				 * Expansion could still move past after this
+				 * test, but as we are holding a reference to
+				 * 'sh', we know that if that happens,
+				 *  STRIPE_EXPANDING will get set and the expansion
+				 * won't proceed until we finish with the stripe.
+				 */
+				int must_retry = 0;
+				spin_lock_irq(&conf->device_lock);
+				if (mddev->delta_disks < 0
+				    ? logical_sector >= conf->reshape_progress
+				    : logical_sector < conf->reshape_progress)
+					/* mismatch, need to try again */
+					must_retry = 1;
+				spin_unlock_irq(&conf->device_lock);
+				if (must_retry) {
+					release_stripe(sh);
+					schedule();
+					goto retry;
+				}
+			}
+
+			if (rw == WRITE &&
+			    logical_sector >= mddev->suspend_lo &&
+			    logical_sector < mddev->suspend_hi) {
+				release_stripe(sh);
+				/* As the suspend_* range is controlled by
+				 * userspace, we want an interruptible
+				 * wait.
+				 */
+				flush_signals(current);
+				prepare_to_wait(&conf->wait_for_overlap,
+						&w, TASK_INTERRUPTIBLE);
+				if (logical_sector >= mddev->suspend_lo &&
+				    logical_sector < mddev->suspend_hi)
+					schedule();
+				goto retry;
+			}
+
+			if (test_bit(STRIPE_EXPANDING, &sh->state) ||
+			    !add_stripe_bio(sh, bi, dd_idx, rw)) {
+				/* Stripe is busy expanding or
+				 * add failed due to overlap.  Flush everything
+				 * and wait a while
+				 */
+				md_wakeup_thread(mddev->thread);
+				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);
+			if ((bi->bi_rw & REQ_SYNC) &&
+			    !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+				atomic_inc(&conf->preread_active_stripes);
+			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;
+		}
+			
+	}
+	if (!plugged)
+		md_wakeup_thread(mddev->thread);
+
+	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);
+	}
+}
+
+static sector_t raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks);
+
+static sector_t reshape_request(struct mddev *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.
+	 */
+	struct r5conf *conf = 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) {
+			mddev->curr_resync_completed = sector_nr;
+			sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+			*skipped = 1;
+			return sector_nr;
+		}
+	}
+
+	/* We need to process a full chunk at a time.
+	 * If old and new chunk sizes differ, we need to process the
+	 * largest of these
+	 */
+	if (mddev->new_chunk_sectors > mddev->chunk_sectors)
+		reshape_sectors = mddev->new_chunk_sectors;
+	else
+		reshape_sectors = mddev->chunk_sectors;
+
+	/* we update the metadata when there is more than 3Meg
+	 * in the block range (that is rather arbitrary, should
+	 * probably be time based) or when the data about to be
+	 * copied would over-write the source of the data at
+	 * the front of the range.
+	 * i.e. one new_stripe along from reshape_progress new_maps
+	 * to after where reshape_safe old_maps to
+	 */
+	writepos = conf->reshape_progress;
+	sector_div(writepos, new_data_disks);
+	readpos = conf->reshape_progress;
+	sector_div(readpos, data_disks);
+	safepos = conf->reshape_safe;
+	sector_div(safepos, data_disks);
+	if (mddev->delta_disks < 0) {
+		writepos -= min_t(sector_t, reshape_sectors, writepos);
+		readpos += reshape_sectors;
+		safepos += reshape_sectors;
+	} else {
+		writepos += reshape_sectors;
+		readpos -= min_t(sector_t, reshape_sectors, readpos);
+		safepos -= min_t(sector_t, reshape_sectors, safepos);
+	}
+
+	/* 'writepos' is the most advanced device address we might write.
+	 * 'readpos' is the least advanced device address we might read.
+	 * 'safepos' is the least address recorded in the metadata as having
+	 *     been reshaped.
+	 * If 'readpos' is behind 'writepos', then there is no way that we can
+	 * ensure safety in the face of a crash - that must be done by userspace
+	 * making a backup of the data.  So in that case there is no particular
+	 * rush to update metadata.
+	 * Otherwise if 'safepos' is behind 'writepos', then we really need to
+	 * update the metadata to advance 'safepos' to match 'readpos' so that
+	 * we can be safe in the event of a crash.
+	 * So we insist on updating metadata if safepos is behind writepos and
+	 * readpos is beyond writepos.
+	 * In any case, update the metadata every 10 seconds.
+	 * Maybe that number should be configurable, but I'm not sure it is
+	 * worth it.... maybe it could be a multiple of safemode_delay???
+	 */
+	if ((mddev->delta_disks < 0
+	     ? (safepos > writepos && readpos < writepos)
+	     : (safepos < writepos && readpos > writepos)) ||
+	    time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
+		/* Cannot proceed until we've updated the superblock... */
+		wait_event(conf->wait_for_overlap,
+			   atomic_read(&conf->reshape_stripes)==0);
+		mddev->reshape_position = conf->reshape_progress;
+		mddev->curr_resync_completed = sector_nr;
+		conf->reshape_checkpoint = jiffies;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
+		md_wakeup_thread(mddev->thread);
+		wait_event(mddev->sb_wait, mddev->flags == 0 ||
+			   kthread_should_stop());
+		spin_lock_irq(&conf->device_lock);
+		conf->reshape_safe = mddev->reshape_position;
+		spin_unlock_irq(&conf->device_lock);
+		wake_up(&conf->wait_for_overlap);
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+	}
+
+	if (mddev->delta_disks < 0) {
+		BUG_ON(conf->reshape_progress == 0);
+		stripe_addr = writepos;
+		BUG_ON((mddev->dev_sectors &
+			~((sector_t)reshape_sectors - 1))
+		       - reshape_sectors - stripe_addr
+		       != sector_nr);
+	} else {
+		BUG_ON(writepos != sector_nr + reshape_sectors);
+		stripe_addr = sector_nr;
+	}
+	INIT_LIST_HEAD(&stripes);
+	for (i = 0; i < reshape_sectors; i += STRIPE_SECTORS) {
+		int j;
+		int skipped_disk = 0;
+		sh = get_active_stripe(conf, stripe_addr+i, 0, 0, 1);
+		set_bit(STRIPE_EXPANDING, &sh->state);
+		atomic_inc(&conf->reshape_stripes);
+		/* If any of this stripe is beyond the end of the old
+		 * array, then we need to zero those blocks
+		 */
+		for (j=sh->disks; j--;) {
+			sector_t s;
+			if (j == sh->pd_idx)
+				continue;
+			if (conf->level == 6 &&
+			    j == sh->qd_idx)
+				continue;
+			s = compute_blocknr(sh, j, 0);
+			if (s < raid5_size(mddev, 0, 0)) {
+				skipped_disk = 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_disk) {
+			set_bit(STRIPE_EXPAND_READY, &sh->state);
+			set_bit(STRIPE_HANDLE, &sh->state);
+		}
+		list_add(&sh->lru, &stripes);
+	}
+	spin_lock_irq(&conf->device_lock);
+	if (mddev->delta_disks < 0)
+		conf->reshape_progress -= reshape_sectors * new_data_disks;
+	else
+		conf->reshape_progress += reshape_sectors * new_data_disks;
+	spin_unlock_irq(&conf->device_lock);
+	/* Ok, those stripe are ready. We can start scheduling
+	 * reads on the source stripes.
+	 * The source stripes are determined by mapping the first and last
+	 * block on the destination stripes.
+	 */
+	first_sector =
+		raid5_compute_sector(conf, stripe_addr*(new_data_disks),
+				     1, &dd_idx, NULL);
+	last_sector =
+		raid5_compute_sector(conf, ((stripe_addr+reshape_sectors)
+					    * new_data_disks - 1),
+				     1, &dd_idx, NULL);
+	if (last_sector >= mddev->dev_sectors)
+		last_sector = mddev->dev_sectors - 1;
+	while (first_sector <= last_sector) {
+		sh = get_active_stripe(conf, first_sector, 1, 0, 1);
+		set_bit(STRIPE_EXPAND_SOURCE, &sh->state);
+		set_bit(STRIPE_HANDLE, &sh->state);
+		release_stripe(sh);
+		first_sector += STRIPE_SECTORS;
+	}
+	/* Now that the sources are clearly marked, we can release
+	 * the destination stripes
+	 */
+	while (!list_empty(&stripes)) {
+		sh = list_entry(stripes.next, struct stripe_head, lru);
+		list_del_init(&sh->lru);
+		release_stripe(sh);
+	}
+	/* If this takes us to the resync_max point where we have to pause,
+	 * then we need to write out the superblock.
+	 */
+	sector_nr += reshape_sectors;
+	if ((sector_nr - mddev->curr_resync_completed) * 2
+	    >= mddev->resync_max - mddev->curr_resync_completed) {
+		/* Cannot proceed until we've updated the superblock... */
+		wait_event(conf->wait_for_overlap,
+			   atomic_read(&conf->reshape_stripes) == 0);
+		mddev->reshape_position = conf->reshape_progress;
+		mddev->curr_resync_completed = sector_nr;
+		conf->reshape_checkpoint = jiffies;
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
+		md_wakeup_thread(mddev->thread);
+		wait_event(mddev->sb_wait,
+			   !test_bit(MD_CHANGE_DEVS, &mddev->flags)
+			   || kthread_should_stop());
+		spin_lock_irq(&conf->device_lock);
+		conf->reshape_safe = mddev->reshape_position;
+		spin_unlock_irq(&conf->device_lock);
+		wake_up(&conf->wait_for_overlap);
+		sysfs_notify(&mddev->kobj, NULL, "sync_completed");
+	}
+	return reshape_sectors;
+}
+
+/* FIXME go_faster isn't used */
+static inline sector_t sync_request(struct mddev *mddev, sector_t sector_nr, int *skipped, int go_faster)
+{
+	struct r5conf *conf = mddev->private;
+	struct stripe_head *sh;
+	sector_t max_sector = mddev->dev_sectors;
+	sector_t sync_blocks;
+	int still_degraded = 0;
+	int i;
+
+	if (sector_nr >= max_sector) {
+		/* just being told to finish up .. nothing much to do */
+
+		if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
+			end_reshape(conf);
+			return 0;
+		}
+
+		if (mddev->curr_resync < max_sector) /* aborted */
+			bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
+					&sync_blocks, 1);
+		else /* completed sync */
+			conf->fullsync = 0;
+		bitmap_close_sync(mddev->bitmap);
+
+		return 0;
+	}
+
+	/* Allow raid5_quiesce to complete */
+	wait_event(conf->wait_for_overlap, conf->quiesce != 2);
+
+	if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
+		return reshape_request(mddev, sector_nr, skipped);
+
+	/* No need to check resync_max as we never do more than one
+	 * stripe, and as resync_max will always be on a chunk boundary,
+	 * if the check in md_do_sync didn't fire, there is no chance
+	 * of overstepping resync_max here
+	 */
+
+	/* if there is too many failed drives and we are trying
+	 * to resync, then assert that we are finished, because there is
+	 * nothing we can do.
+	 */
+	if (mddev->degraded >= conf->max_degraded &&
+	    test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
+		sector_t rv = mddev->dev_sectors - sector_nr;
+		*skipped = 1;
+		return rv;
+	}
+	if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
+	    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
+	    !conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
+		/* we can skip this block, and probably more */
+		sync_blocks /= STRIPE_SECTORS;
+		*skipped = 1;
+		return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
+	}
+
+	bitmap_cond_end_sync(mddev->bitmap, sector_nr);
+
+	sh = get_active_stripe(conf, sector_nr, 0, 1, 0);
+	if (sh == NULL) {
+		sh = get_active_stripe(conf, sector_nr, 0, 0, 0);
+		/* make sure we don't swamp the stripe cache if someone else
+		 * is trying to get access
+		 */
+		schedule_timeout_uninterruptible(1);
+	}
+	/* Need to check if array will still be degraded after recovery/resync
+	 * We don't need to check the 'failed' flag as when that gets set,
+	 * recovery aborts.
+	 */
+	for (i = 0; i < conf->raid_disks; i++)
+		if (conf->disks[i].rdev == NULL)
+			still_degraded = 1;
+
+	bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);
+
+	set_bit(STRIPE_SYNC_REQUESTED, &sh->state);
+
+	handle_stripe(sh);
+	release_stripe(sh);
+
+	return STRIPE_SECTORS;
+}
+
+static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
+{
+	/* We may not be able to submit a whole bio at once as there
+	 * may not be enough stripe_heads available.
+	 * We cannot pre-allocate enough stripe_heads as we may need
+	 * more than exist in the cache (if we allow ever large chunks).
+	 * So we do one stripe head at a time and record in
+	 * ->bi_hw_segments how many have been done.
+	 *
+	 * We *know* that this entire raid_bio is in one chunk, so
+	 * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
+	 */
+	struct stripe_head *sh;
+	int dd_idx;
+	sector_t sector, logical_sector, last_sector;
+	int scnt = 0;
+	int remaining;
+	int handled = 0;
+
+	logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
+	sector = raid5_compute_sector(conf, logical_sector,
+				      0, &dd_idx, NULL);
+	last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
+
+	for (; logical_sector < last_sector;
+	     logical_sector += STRIPE_SECTORS,
+		     sector += STRIPE_SECTORS,
+		     scnt++) {
+
+		if (scnt < raid5_bi_hw_segments(raid_bio))
+			/* already done this stripe */
+			continue;
+
+		sh = get_active_stripe(conf, sector, 0, 1, 0);
+
+		if (!sh) {
+			/* failed to get a stripe - must wait */
+			raid5_set_bi_hw_segments(raid_bio, scnt);
+			conf->retry_read_aligned = raid_bio;
+			return handled;
+		}
+
+		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(struct mddev *mddev)
+{
+	struct stripe_head *sh;
+	struct r5conf *conf = mddev->private;
+	int handled;
+	struct blk_plug plug;
+
+	pr_debug("+++ raid5d active\n");
+
+	md_check_recovery(mddev);
+
+	blk_start_plug(&plug);
+	handled = 0;
+	spin_lock_irq(&conf->device_lock);
+	while (1) {
+		struct bio *bio;
+
+		if (atomic_read(&mddev->plug_cnt) == 0 &&
+		    !list_empty(&conf->bitmap_list)) {
+			/* Now is a good time to flush some bitmap updates */
+			conf->seq_flush++;
+			spin_unlock_irq(&conf->device_lock);
+			bitmap_unplug(mddev->bitmap);
+			spin_lock_irq(&conf->device_lock);
+			conf->seq_write = conf->seq_flush;
+			activate_bit_delay(conf);
+		}
+		if (atomic_read(&mddev->plug_cnt) == 0)
+			raid5_activate_delayed(conf);
+
+		while ((bio = remove_bio_from_retry(conf))) {
+			int ok;
+			spin_unlock_irq(&conf->device_lock);
+			ok = retry_aligned_read(conf, bio);
+			spin_lock_irq(&conf->device_lock);
+			if (!ok)
+				break;
+			handled++;
+		}
+
+		sh = __get_priority_stripe(conf);
+
+		if (!sh)
+			break;
+		spin_unlock_irq(&conf->device_lock);
+		
+		handled++;
+		handle_stripe(sh);
+		release_stripe(sh);
+		cond_resched();
+
+		if (mddev->flags & ~(1<<MD_CHANGE_PENDING))
+			md_check_recovery(mddev);
+
+		spin_lock_irq(&conf->device_lock);
+	}
+	pr_debug("%d stripes handled\n", handled);
+
+	spin_unlock_irq(&conf->device_lock);
+
+	async_tx_issue_pending_all();
+	blk_finish_plug(&plug);
+
+	pr_debug("--- raid5d inactive\n");
+}
+
+static ssize_t
+raid5_show_stripe_cache_size(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	if (conf)
+		return sprintf(page, "%d\n", conf->max_nr_stripes);
+	else
+		return 0;
+}
+
+int
+raid5_set_cache_size(struct mddev *mddev, int size)
+{
+	struct r5conf *conf = mddev->private;
+	int err;
+
+	if (size <= 16 || size > 32768)
+		return -EINVAL;
+	while (size < 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 (size > conf->max_nr_stripes) {
+		if (grow_one_stripe(conf))
+			conf->max_nr_stripes++;
+		else break;
+	}
+	return 0;
+}
+EXPORT_SYMBOL(raid5_set_cache_size);
+
+static ssize_t
+raid5_store_stripe_cache_size(struct mddev *mddev, const char *page, size_t len)
+{
+	struct r5conf *conf = mddev->private;
+	unsigned long new;
+	int err;
+
+	if (len >= PAGE_SIZE)
+		return -EINVAL;
+	if (!conf)
+		return -ENODEV;
+
+	if (strict_strtoul(page, 10, &new))
+		return -EINVAL;
+	err = raid5_set_cache_size(mddev, new);
+	if (err)
+		return err;
+	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(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	if (conf)
+		return sprintf(page, "%d\n", conf->bypass_threshold);
+	else
+		return 0;
+}
+
+static ssize_t
+raid5_store_preread_threshold(struct mddev *mddev, const char *page, size_t len)
+{
+	struct r5conf *conf = mddev->private;
+	unsigned long new;
+	if (len >= PAGE_SIZE)
+		return -EINVAL;
+	if (!conf)
+		return -ENODEV;
+
+	if (strict_strtoul(page, 10, &new))
+		return -EINVAL;
+	if (new > conf->max_nr_stripes)
+		return -EINVAL;
+	conf->bypass_threshold = new;
+	return len;
+}
+
+static struct md_sysfs_entry
+raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,
+					S_IRUGO | S_IWUSR,
+					raid5_show_preread_threshold,
+					raid5_store_preread_threshold);
+
+static ssize_t
+stripe_cache_active_show(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	if (conf)
+		return sprintf(page, "%d\n", atomic_read(&conf->active_stripes));
+	else
+		return 0;
+}
+
+static struct md_sysfs_entry
+raid5_stripecache_active = __ATTR_RO(stripe_cache_active);
+
+static struct attribute *raid5_attrs[] =  {
+	&raid5_stripecache_size.attr,
+	&raid5_stripecache_active.attr,
+	&raid5_preread_bypass_threshold.attr,
+	NULL,
+};
+static struct attribute_group raid5_attrs_group = {
+	.name = NULL,
+	.attrs = raid5_attrs,
+};
+
+static sector_t
+raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks)
+{
+	struct r5conf *conf = mddev->private;
+
+	if (!sectors)
+		sectors = mddev->dev_sectors;
+	if (!raid_disks)
+		/* size is defined by the smallest of previous and new size */
+		raid_disks = min(conf->raid_disks, conf->previous_raid_disks);
+
+	sectors &= ~((sector_t)mddev->chunk_sectors - 1);
+	sectors &= ~((sector_t)mddev->new_chunk_sectors - 1);
+	return sectors * (raid_disks - conf->max_degraded);
+}
+
+static void raid5_free_percpu(struct r5conf *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);
+		kfree(percpu->scribble);
+	}
+#ifdef CONFIG_HOTPLUG_CPU
+	unregister_cpu_notifier(&conf->cpu_notify);
+#endif
+	put_online_cpus();
+
+	free_percpu(conf->percpu);
+}
+
+static void free_conf(struct r5conf *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)
+{
+	struct r5conf *conf = container_of(nfb, struct r5conf, 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 (conf->level == 6 && !percpu->spare_page)
+			percpu->spare_page = alloc_page(GFP_KERNEL);
+		if (!percpu->scribble)
+			percpu->scribble = kmalloc(conf->scribble_len, GFP_KERNEL);
+
+		if (!percpu->scribble ||
+		    (conf->level == 6 && !percpu->spare_page)) {
+			safe_put_page(percpu->spare_page);
+			kfree(percpu->scribble);
+			pr_err("%s: failed memory allocation for cpu%ld\n",
+			       __func__, cpu);
+			return notifier_from_errno(-ENOMEM);
+		}
+		break;
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		safe_put_page(percpu->spare_page);
+		kfree(percpu->scribble);
+		percpu->spare_page = NULL;
+		percpu->scribble = NULL;
+		break;
+	default:
+		break;
+	}
+	return NOTIFY_OK;
+}
+#endif
+
+static int raid5_alloc_percpu(struct r5conf *conf)
+{
+	unsigned long cpu;
+	struct page *spare_page;
+	struct raid5_percpu __percpu *allcpus;
+	void *scribble;
+	int err;
+
+	allcpus = alloc_percpu(struct raid5_percpu);
+	if (!allcpus)
+		return -ENOMEM;
+	conf->percpu = allcpus;
+
+	get_online_cpus();
+	err = 0;
+	for_each_present_cpu(cpu) {
+		if (conf->level == 6) {
+			spare_page = alloc_page(GFP_KERNEL);
+			if (!spare_page) {
+				err = -ENOMEM;
+				break;
+			}
+			per_cpu_ptr(conf->percpu, cpu)->spare_page = spare_page;
+		}
+		scribble = kmalloc(conf->scribble_len, GFP_KERNEL);
+		if (!scribble) {
+			err = -ENOMEM;
+			break;
+		}
+		per_cpu_ptr(conf->percpu, cpu)->scribble = scribble;
+	}
+#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 struct r5conf *setup_conf(struct mddev *mddev)
+{
+	struct r5conf *conf;
+	int raid_disk, memory, max_disks;
+	struct md_rdev *rdev;
+	struct disk_info *disk;
+
+	if (mddev->new_level != 5
+	    && mddev->new_level != 4
+	    && mddev->new_level != 6) {
+		printk(KERN_ERR "md/raid:%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 "md/raid:%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 "md/raid:%s: not enough configured devices (%d, minimum 4)\n",
+		       mdname(mddev), mddev->raid_disks);
+		return ERR_PTR(-EINVAL);
+	}
+
+	if (!mddev->new_chunk_sectors ||
+	    (mddev->new_chunk_sectors << 9) % PAGE_SIZE ||
+	    !is_power_of_2(mddev->new_chunk_sectors)) {
+		printk(KERN_ERR "md/raid:%s: invalid chunk size %d\n",
+		       mdname(mddev), mddev->new_chunk_sectors << 9);
+		return ERR_PTR(-EINVAL);
+	}
+
+	conf = kzalloc(sizeof(struct r5conf), GFP_KERNEL);
+	if (conf == NULL)
+		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;
+	conf->recovery_disabled = mddev->recovery_disabled - 1;
+
+	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;
+	max_disks = max(conf->raid_disks, conf->previous_raid_disks);
+	conf->scribble_len = scribble_len(max_disks);
+
+	conf->disks = kzalloc(max_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;
+
+	pr_debug("raid456: run(%s) called.\n", mdname(mddev));
+
+	rdev_for_each(rdev, mddev) {
+		raid_disk = rdev->raid_disk;
+		if (raid_disk >= max_disks
+		    || raid_disk < 0)
+			continue;
+		disk = conf->disks + raid_disk;
+
+		if (test_bit(Replacement, &rdev->flags)) {
+			if (disk->replacement)
+				goto abort;
+			disk->replacement = rdev;
+		} else {
+			if (disk->rdev)
+				goto abort;
+			disk->rdev = rdev;
+		}
+
+		if (test_bit(In_sync, &rdev->flags)) {
+			char b[BDEVNAME_SIZE];
+			printk(KERN_INFO "md/raid:%s: device %s operational as raid"
+			       " disk %d\n",
+			       mdname(mddev), bdevname(rdev->bdev, b), raid_disk);
+		} else if (rdev->saved_raid_disk != raid_disk)
+			/* Cannot rely on bitmap to complete recovery */
+			conf->fullsync = 1;
+	}
+
+	conf->chunk_sectors = mddev->new_chunk_sectors;
+	conf->level = mddev->new_level;
+	if (conf->level == 6)
+		conf->max_degraded = 2;
+	else
+		conf->max_degraded = 1;
+	conf->algorithm = mddev->new_layout;
+	conf->max_nr_stripes = NR_STRIPES;
+	conf->reshape_progress = mddev->reshape_position;
+	if (conf->reshape_progress != MaxSector) {
+		conf->prev_chunk_sectors = mddev->chunk_sectors;
+		conf->prev_algo = mddev->layout;
+	}
+
+	memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
+		 max_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
+	if (grow_stripes(conf, conf->max_nr_stripes)) {
+		printk(KERN_ERR
+		       "md/raid:%s: couldn't allocate %dkB for buffers\n",
+		       mdname(mddev), memory);
+		goto abort;
+	} else
+		printk(KERN_INFO "md/raid:%s: allocated %dkB\n",
+		       mdname(mddev), memory);
+
+	conf->thread = md_register_thread(raid5d, mddev, NULL);
+	if (!conf->thread) {
+		printk(KERN_ERR
+		       "md/raid:%s: couldn't allocate thread.\n",
+		       mdname(mddev));
+		goto abort;
+	}
+
+	return conf;
+
+ abort:
+	if (conf) {
+		free_conf(conf);
+		return ERR_PTR(-EIO);
+	} else
+		return ERR_PTR(-ENOMEM);
+}
+
+
+static int only_parity(int raid_disk, int algo, int raid_disks, int max_degraded)
+{
+	switch (algo) {
+	case ALGORITHM_PARITY_0:
+		if (raid_disk < max_degraded)
+			return 1;
+		break;
+	case ALGORITHM_PARITY_N:
+		if (raid_disk >= raid_disks - max_degraded)
+			return 1;
+		break;
+	case ALGORITHM_PARITY_0_6:
+		if (raid_disk == 0 || 
+		    raid_disk == raid_disks - 1)
+			return 1;
+		break;
+	case ALGORITHM_LEFT_ASYMMETRIC_6:
+	case ALGORITHM_RIGHT_ASYMMETRIC_6:
+	case ALGORITHM_LEFT_SYMMETRIC_6:
+	case ALGORITHM_RIGHT_SYMMETRIC_6:
+		if (raid_disk == raid_disks - 1)
+			return 1;
+	}
+	return 0;
+}
+
+static int run(struct mddev *mddev)
+{
+	struct r5conf *conf;
+	int working_disks = 0;
+	int dirty_parity_disks = 0;
+	struct md_rdev *rdev;
+	sector_t reshape_offset = 0;
+	int i;
+
+	if (mddev->recovery_cp != MaxSector)
+		printk(KERN_NOTICE "md/raid:%s: not clean"
+		       " -- starting background reconstruction\n",
+		       mdname(mddev));
+	if (mddev->reshape_position != MaxSector) {
+		/* Check that we can continue the reshape.
+		 * Currently only disks can change, it must
+		 * increase, and we must be past the point where
+		 * a stripe over-writes itself
+		 */
+		sector_t here_new, here_old;
+		int old_disks;
+		int max_degraded = (mddev->level == 6 ? 2 : 1);
+
+		if (mddev->new_level != mddev->level) {
+			printk(KERN_ERR "md/raid:%s: unsupported reshape "
+			       "required - aborting.\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+		old_disks = mddev->raid_disks - mddev->delta_disks;
+		/* reshape_position must be on a new-stripe boundary, and one
+		 * further up in new geometry must map after here in old
+		 * geometry.
+		 */
+		here_new = mddev->reshape_position;
+		if (sector_div(here_new, mddev->new_chunk_sectors *
+			       (mddev->raid_disks - max_degraded))) {
+			printk(KERN_ERR "md/raid:%s: reshape_position not "
+			       "on a stripe boundary\n", mdname(mddev));
+			return -EINVAL;
+		}
+		reshape_offset = here_new * mddev->new_chunk_sectors;
+		/* here_new is the stripe we will write to */
+		here_old = mddev->reshape_position;
+		sector_div(here_old, mddev->chunk_sectors *
+			   (old_disks-max_degraded));
+		/* here_old is the first stripe that we might need to read
+		 * from */
+		if (mddev->delta_disks == 0) {
+			/* We cannot be sure it is safe to start an in-place
+			 * reshape.  It is only safe if user-space if monitoring
+			 * and taking constant backups.
+			 * mdadm always starts a situation like this in
+			 * readonly mode so it can take control before
+			 * allowing any writes.  So just check for that.
+			 */
+			if ((here_new * mddev->new_chunk_sectors != 
+			     here_old * mddev->chunk_sectors) ||
+			    mddev->ro == 0) {
+				printk(KERN_ERR "md/raid:%s: in-place reshape must be started"
+				       " in read-only mode - aborting\n",
+				       mdname(mddev));
+				return -EINVAL;
+			}
+		} else if (mddev->delta_disks < 0
+		    ? (here_new * mddev->new_chunk_sectors <=
+		       here_old * mddev->chunk_sectors)
+		    : (here_new * mddev->new_chunk_sectors >=
+		       here_old * mddev->chunk_sectors)) {
+			/* Reading from the same stripe as writing to - bad */
+			printk(KERN_ERR "md/raid:%s: reshape_position too early for "
+			       "auto-recovery - aborting.\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+		printk(KERN_INFO "md/raid:%s: reshape will continue\n",
+		       mdname(mddev));
+		/* OK, we should be able to continue; */
+	} else {
+		BUG_ON(mddev->level != mddev->new_level);
+		BUG_ON(mddev->layout != mddev->new_layout);
+		BUG_ON(mddev->chunk_sectors != mddev->new_chunk_sectors);
+		BUG_ON(mddev->delta_disks != 0);
+	}
+
+	if (mddev->private == NULL)
+		conf = setup_conf(mddev);
+	else
+		conf = mddev->private;
+
+	if (IS_ERR(conf))
+		return PTR_ERR(conf);
+
+	mddev->thread = conf->thread;
+	conf->thread = NULL;
+	mddev->private = conf;
+
+	for (i = 0; i < conf->raid_disks && conf->previous_raid_disks;
+	     i++) {
+		rdev = conf->disks[i].rdev;
+		if (!rdev && conf->disks[i].replacement) {
+			/* The replacement is all we have yet */
+			rdev = conf->disks[i].replacement;
+			conf->disks[i].replacement = NULL;
+			clear_bit(Replacement, &rdev->flags);
+			conf->disks[i].rdev = rdev;
+		}
+		if (!rdev)
+			continue;
+		if (conf->disks[i].replacement &&
+		    conf->reshape_progress != MaxSector) {
+			/* replacements and reshape simply do not mix. */
+			printk(KERN_ERR "md: cannot handle concurrent "
+			       "replacement and reshape.\n");
+			goto abort;
+		}
+		if (test_bit(In_sync, &rdev->flags)) {
+			working_disks++;
+			continue;
+		}
+		/* This disc is not fully in-sync.  However if it
+		 * just stored parity (beyond the recovery_offset),
+		 * when we don't need to be concerned about the
+		 * array being dirty.
+		 * When reshape goes 'backwards', we never have
+		 * partially completed devices, so we only need
+		 * to worry about reshape going forwards.
+		 */
+		/* Hack because v0.91 doesn't store recovery_offset properly. */
+		if (mddev->major_version == 0 &&
+		    mddev->minor_version > 90)
+			rdev->recovery_offset = reshape_offset;
+			
+		if (rdev->recovery_offset < reshape_offset) {
+			/* We need to check old and new layout */
+			if (!only_parity(rdev->raid_disk,
+					 conf->algorithm,
+					 conf->raid_disks,
+					 conf->max_degraded))
+				continue;
+		}
+		if (!only_parity(rdev->raid_disk,
+				 conf->prev_algo,
+				 conf->previous_raid_disks,
+				 conf->max_degraded))
+			continue;
+		dirty_parity_disks++;
+	}
+
+	/*
+	 * 0 for a fully functional array, 1 or 2 for a degraded array.
+	 */
+	mddev->degraded = calc_degraded(conf);
+
+	if (has_failed(conf)) {
+		printk(KERN_ERR "md/raid:%s: not enough operational devices"
+			" (%d/%d failed)\n",
+			mdname(mddev), mddev->degraded, conf->raid_disks);
+		goto abort;
+	}
+
+	/* device size must be a multiple of chunk size */
+	mddev->dev_sectors &= ~(mddev->chunk_sectors - 1);
+	mddev->resync_max_sectors = mddev->dev_sectors;
+
+	if (mddev->degraded > dirty_parity_disks &&
+	    mddev->recovery_cp != MaxSector) {
+		if (mddev->ok_start_degraded)
+			printk(KERN_WARNING
+			       "md/raid:%s: starting dirty degraded array"
+			       " - data corruption possible.\n",
+			       mdname(mddev));
+		else {
+			printk(KERN_ERR
+			       "md/raid:%s: cannot start dirty degraded array.\n",
+			       mdname(mddev));
+			goto abort;
+		}
+	}
+
+	if (mddev->degraded == 0)
+		printk(KERN_INFO "md/raid:%s: raid level %d active with %d out of %d"
+		       " devices, algorithm %d\n", mdname(mddev), conf->level,
+		       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
+		       mddev->new_layout);
+	else
+		printk(KERN_ALERT "md/raid:%s: raid level %d active with %d"
+		       " out of %d devices, algorithm %d\n",
+		       mdname(mddev), conf->level,
+		       mddev->raid_disks - mddev->degraded,
+		       mddev->raid_disks, mddev->new_layout);
+
+	print_raid5_conf(conf);
+
+	if (conf->reshape_progress != MaxSector) {
+		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,
+							"reshape");
+	}
+
+
+	/* Ok, everything is just fine now */
+	if (mddev->to_remove == &raid5_attrs_group)
+		mddev->to_remove = NULL;
+	else if (mddev->kobj.sd &&
+	    sysfs_create_group(&mddev->kobj, &raid5_attrs_group))
+		printk(KERN_WARNING
+		       "raid5: failed to create sysfs attributes for %s\n",
+		       mdname(mddev));
+	md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
+
+	if (mddev->queue) {
+		int chunk_size;
+		/* read-ahead size must cover two whole stripes, which
+		 * is 2 * (datadisks) * chunksize where 'n' is the
+		 * number of raid devices
+		 */
+		int data_disks = conf->previous_raid_disks - conf->max_degraded;
+		int stripe = data_disks *
+			((mddev->chunk_sectors << 9) / PAGE_SIZE);
+		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+
+		blk_queue_merge_bvec(mddev->queue, raid5_mergeable_bvec);
+
+		mddev->queue->backing_dev_info.congested_data = mddev;
+		mddev->queue->backing_dev_info.congested_fn = raid5_congested;
+
+		chunk_size = mddev->chunk_sectors << 9;
+		blk_queue_io_min(mddev->queue, chunk_size);
+		blk_queue_io_opt(mddev->queue, chunk_size *
+				 (conf->raid_disks - conf->max_degraded));
+
+		rdev_for_each(rdev, mddev)
+			disk_stack_limits(mddev->gendisk, rdev->bdev,
+					  rdev->data_offset << 9);
+	}
+
+	return 0;
+abort:
+	md_unregister_thread(&mddev->thread);
+	print_raid5_conf(conf);
+	free_conf(conf);
+	mddev->private = NULL;
+	printk(KERN_ALERT "md/raid:%s: failed to run raid set.\n", mdname(mddev));
+	return -EIO;
+}
+
+static int stop(struct mddev *mddev)
+{
+	struct r5conf *conf = mddev->private;
+
+	md_unregister_thread(&mddev->thread);
+	if (mddev->queue)
+		mddev->queue->backing_dev_info.congested_fn = NULL;
+	free_conf(conf);
+	mddev->private = NULL;
+	mddev->to_remove = &raid5_attrs_group;
+	return 0;
+}
+
+static void status(struct seq_file *seq, struct mddev *mddev)
+{
+	struct r5conf *conf = mddev->private;
+	int i;
+
+	seq_printf(seq, " level %d, %dk chunk, algorithm %d", mddev->level,
+		mddev->chunk_sectors / 2, mddev->layout);
+	seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->raid_disks - mddev->degraded);
+	for (i = 0; i < conf->raid_disks; i++)
+		seq_printf (seq, "%s",
+			       conf->disks[i].rdev &&
+			       test_bit(In_sync, &conf->disks[i].rdev->flags) ? "U" : "_");
+	seq_printf (seq, "]");
+}
+
+static void print_raid5_conf (struct r5conf *conf)
+{
+	int i;
+	struct disk_info *tmp;
+
+	printk(KERN_DEBUG "RAID conf printout:\n");
+	if (!conf) {
+		printk("(conf==NULL)\n");
+		return;
+	}
+	printk(KERN_DEBUG " --- level:%d rd:%d wd:%d\n", conf->level,
+	       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(KERN_DEBUG " disk %d, o:%d, dev:%s\n",
+			       i, !test_bit(Faulty, &tmp->rdev->flags),
+			       bdevname(tmp->rdev->bdev, b));
+	}
+}
+
+static int raid5_spare_active(struct mddev *mddev)
+{
+	int i;
+	struct r5conf *conf = mddev->private;
+	struct disk_info *tmp;
+	int count = 0;
+	unsigned long flags;
+
+	for (i = 0; i < conf->raid_disks; i++) {
+		tmp = conf->disks + i;
+		if (tmp->replacement
+		    && tmp->replacement->recovery_offset == MaxSector
+		    && !test_bit(Faulty, &tmp->replacement->flags)
+		    && !test_and_set_bit(In_sync, &tmp->replacement->flags)) {
+			/* Replacement has just become active. */
+			if (!tmp->rdev
+			    || !test_and_clear_bit(In_sync, &tmp->rdev->flags))
+				count++;
+			if (tmp->rdev) {
+				/* Replaced device not technically faulty,
+				 * but we need to be sure it gets removed
+				 * and never re-added.
+				 */
+				set_bit(Faulty, &tmp->rdev->flags);
+				sysfs_notify_dirent_safe(
+					tmp->rdev->sysfs_state);
+			}
+			sysfs_notify_dirent_safe(tmp->replacement->sysfs_state);
+		} else if (tmp->rdev
+		    && tmp->rdev->recovery_offset == MaxSector
+		    && !test_bit(Faulty, &tmp->rdev->flags)
+		    && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
+			count++;
+			sysfs_notify_dirent_safe(tmp->rdev->sysfs_state);
+		}
+	}
+	spin_lock_irqsave(&conf->device_lock, flags);
+	mddev->degraded = calc_degraded(conf);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+	print_raid5_conf(conf);
+	return count;
+}
+
+static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
+{
+	struct r5conf *conf = mddev->private;
+	int err = 0;
+	int number = rdev->raid_disk;
+	struct md_rdev **rdevp;
+	struct disk_info *p = conf->disks + number;
+
+	print_raid5_conf(conf);
+	if (rdev == p->rdev)
+		rdevp = &p->rdev;
+	else if (rdev == p->replacement)
+		rdevp = &p->replacement;
+	else
+		return 0;
+
+	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->recovery_disabled != conf->recovery_disabled &&
+	    !has_failed(conf) &&
+	    (!p->replacement || p->replacement == rdev) &&
+	    number < conf->raid_disks) {
+		err = -EBUSY;
+		goto abort;
+	}
+	*rdevp = NULL;
+	synchronize_rcu();
+	if (atomic_read(&rdev->nr_pending)) {
+		/* lost the race, try later */
+		err = -EBUSY;
+		*rdevp = rdev;
+	} else if (p->replacement) {
+		/* We must have just cleared 'rdev' */
+		p->rdev = p->replacement;
+		clear_bit(Replacement, &p->replacement->flags);
+		smp_mb(); /* Make sure other CPUs may see both as identical
+			   * but will never see neither - if they are careful
+			   */
+		p->replacement = NULL;
+		clear_bit(WantReplacement, &rdev->flags);
+	} else
+		/* We might have just removed the Replacement as faulty-
+		 * clear the bit just in case
+		 */
+		clear_bit(WantReplacement, &rdev->flags);
+abort:
+
+	print_raid5_conf(conf);
+	return err;
+}
+
+static int raid5_add_disk(struct mddev *mddev, struct md_rdev *rdev)
+{
+	struct r5conf *conf = mddev->private;
+	int err = -EEXIST;
+	int disk;
+	struct disk_info *p;
+	int first = 0;
+	int last = conf->raid_disks - 1;
+
+	if (mddev->recovery_disabled == conf->recovery_disabled)
+		return -EBUSY;
+
+	if (rdev->saved_raid_disk < 0 && has_failed(conf))
+		/* 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++) {
+		p = conf->disks + disk;
+		if (p->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;
+		}
+		if (test_bit(WantReplacement, &p->rdev->flags) &&
+		    p->replacement == NULL) {
+			clear_bit(In_sync, &rdev->flags);
+			set_bit(Replacement, &rdev->flags);
+			rdev->raid_disk = disk;
+			err = 0;
+			conf->fullsync = 1;
+			rcu_assign_pointer(p->replacement, rdev);
+			break;
+		}
+	}
+	print_raid5_conf(conf);
+	return err;
+}
+
+static int raid5_resize(struct mddev *mddev, sector_t sectors)
+{
+	/* no resync is happening, and there is enough space
+	 * on all devices, so we can resize.
+	 * We need to make sure resync covers any new space.
+	 * If the array is shrinking we should possibly wait until
+	 * any io in the removed space completes, but it hardly seems
+	 * worth it.
+	 */
+	sectors &= ~((sector_t)mddev->chunk_sectors - 1);
+	md_set_array_sectors(mddev, raid5_size(mddev, sectors,
+					       mddev->raid_disks));
+	if (mddev->array_sectors >
+	    raid5_size(mddev, sectors, mddev->raid_disks))
+		return -EINVAL;
+	set_capacity(mddev->gendisk, mddev->array_sectors);
+	revalidate_disk(mddev->gendisk);
+	if (sectors > mddev->dev_sectors &&
+	    mddev->recovery_cp > mddev->dev_sectors) {
+		mddev->recovery_cp = mddev->dev_sectors;
+		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+	}
+	mddev->dev_sectors = sectors;
+	mddev->resync_max_sectors = sectors;
+	return 0;
+}
+
+static int check_stripe_cache(struct mddev *mddev)
+{
+	/* Can only proceed if there are plenty of stripe_heads.
+	 * We need a minimum of one full stripe,, and for sensible progress
+	 * it is best to have about 4 times that.
+	 * If we require 4 times, then the default 256 4K stripe_heads will
+	 * allow for chunk sizes up to 256K, which is probably OK.
+	 * If the chunk size is greater, user-space should request more
+	 * stripe_heads first.
+	 */
+	struct r5conf *conf = mddev->private;
+	if (((mddev->chunk_sectors << 9) / STRIPE_SIZE) * 4
+	    > conf->max_nr_stripes ||
+	    ((mddev->new_chunk_sectors << 9) / STRIPE_SIZE) * 4
+	    > conf->max_nr_stripes) {
+		printk(KERN_WARNING "md/raid:%s: reshape: not enough stripes.  Needed %lu\n",
+		       mdname(mddev),
+		       ((max(mddev->chunk_sectors, mddev->new_chunk_sectors) << 9)
+			/ STRIPE_SIZE)*4);
+		return 0;
+	}
+	return 1;
+}
+
+static int check_reshape(struct mddev *mddev)
+{
+	struct r5conf *conf = mddev->private;
+
+	if (mddev->delta_disks == 0 &&
+	    mddev->new_layout == mddev->layout &&
+	    mddev->new_chunk_sectors == mddev->chunk_sectors)
+		return 0; /* nothing to do */
+	if (mddev->bitmap)
+		/* Cannot grow a bitmap yet */
+		return -EBUSY;
+	if (has_failed(conf))
+		return -EINVAL;
+	if (mddev->delta_disks < 0) {
+		/* We might be able to shrink, but the devices must
+		 * be made bigger first.
+		 * For raid6, 4 is the minimum size.
+		 * Otherwise 2 is the minimum
+		 */
+		int min = 2;
+		if (mddev->level == 6)
+			min = 4;
+		if (mddev->raid_disks + mddev->delta_disks < min)
+			return -EINVAL;
+	}
+
+	if (!check_stripe_cache(mddev))
+		return -ENOSPC;
+
+	return resize_stripes(conf, conf->raid_disks + mddev->delta_disks);
+}
+
+static int raid5_start_reshape(struct mddev *mddev)
+{
+	struct r5conf *conf = mddev->private;
+	struct md_rdev *rdev;
+	int spares = 0;
+	unsigned long flags;
+
+	if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+		return -EBUSY;
+
+	if (!check_stripe_cache(mddev))
+		return -ENOSPC;
+
+	rdev_for_each(rdev, mddev)
+		if (!test_bit(In_sync, &rdev->flags)
+		    && !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/raid:%s: array size must be reduced "
+		       "before number of disks\n", mdname(mddev));
+		return -EINVAL;
+	}
+
+	atomic_set(&conf->reshape_stripes, 0);
+	spin_lock_irq(&conf->device_lock);
+	conf->previous_raid_disks = conf->raid_disks;
+	conf->raid_disks += mddev->delta_disks;
+	conf->prev_chunk_sectors = conf->chunk_sectors;
+	conf->chunk_sectors = mddev->new_chunk_sectors;
+	conf->prev_algo = conf->algorithm;
+	conf->algorithm = mddev->new_layout;
+	if (mddev->delta_disks < 0)
+		conf->reshape_progress = raid5_size(mddev, 0, 0);
+	else
+		conf->reshape_progress = 0;
+	conf->reshape_safe = conf->reshape_progress;
+	conf->generation++;
+	spin_unlock_irq(&conf->device_lock);
+
+	/* Add some new drives, as many as will fit.
+	 * We know there are enough to make the newly sized array work.
+	 * Don't add devices if we are reducing the number of
+	 * devices in the array.  This is because it is not possible
+	 * to correctly record the "partially reconstructed" state of
+	 * such devices during the reshape and confusion could result.
+	 */
+	if (mddev->delta_disks >= 0) {
+		rdev_for_each(rdev, mddev)
+			if (rdev->raid_disk < 0 &&
+			    !test_bit(Faulty, &rdev->flags)) {
+				if (raid5_add_disk(mddev, rdev) == 0) {
+					if (rdev->raid_disk
+					    >= conf->previous_raid_disks)
+						set_bit(In_sync, &rdev->flags);
+					else
+						rdev->recovery_offset = 0;
+
+					if (sysfs_link_rdev(mddev, rdev))
+						/* Failure here is OK */;
+				}
+			} else if (rdev->raid_disk >= conf->previous_raid_disks
+				   && !test_bit(Faulty, &rdev->flags)) {
+				/* This is a spare that was manually added */
+				set_bit(In_sync, &rdev->flags);
+			}
+
+		/* When a reshape changes the number of devices,
+		 * ->degraded is measured against the larger of the
+		 * pre and post number of devices.
+		 */
+		spin_lock_irqsave(&conf->device_lock, flags);
+		mddev->degraded = calc_degraded(conf);
+		spin_unlock_irqrestore(&conf->device_lock, flags);
+	}
+	mddev->raid_disks = conf->raid_disks;
+	mddev->reshape_position = conf->reshape_progress;
+	set_bit(MD_CHANGE_DEVS, &mddev->flags);
+
+	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
+	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
+	set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+	mddev->sync_thread = md_register_thread(md_do_sync, mddev,
+						"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;
+		mddev->reshape_position = 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(struct r5conf *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
+		 */
+		if (conf->mddev->queue) {
+			int data_disks = conf->raid_disks - conf->max_degraded;
+			int stripe = data_disks * ((conf->chunk_sectors << 9)
+						   / PAGE_SIZE);
+			if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+				conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+		}
+	}
+}
+
+/* This is called from the raid5d thread with mddev_lock held.
+ * It makes config changes to the device.
+ */
+static void raid5_finish_reshape(struct mddev *mddev)
+{
+	struct r5conf *conf = mddev->private;
+
+	if (!test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
+
+		if (mddev->delta_disks > 0) {
+			md_set_array_sectors(mddev, raid5_size(mddev, 0, 0));
+			set_capacity(mddev->gendisk, mddev->array_sectors);
+			revalidate_disk(mddev->gendisk);
+		} else {
+			int d;
+			spin_lock_irq(&conf->device_lock);
+			mddev->degraded = calc_degraded(conf);
+			spin_unlock_irq(&conf->device_lock);
+			for (d = conf->raid_disks ;
+			     d < conf->raid_disks - mddev->delta_disks;
+			     d++) {
+				struct md_rdev *rdev = conf->disks[d].rdev;
+				if (rdev &&
+				    raid5_remove_disk(mddev, rdev) == 0) {
+					sysfs_unlink_rdev(mddev, rdev);
+					rdev->raid_disk = -1;
+				}
+			}
+		}
+		mddev->layout = conf->algorithm;
+		mddev->chunk_sectors = conf->chunk_sectors;
+		mddev->reshape_position = MaxSector;
+		mddev->delta_disks = 0;
+	}
+}
+
+static void raid5_quiesce(struct mddev *mddev, int state)
+{
+	struct r5conf *conf = mddev->private;
+
+	switch(state) {
+	case 2: /* resume for a suspend */
+		wake_up(&conf->wait_for_overlap);
+		break;
+
+	case 1: /* stop all writes */
+		spin_lock_irq(&conf->device_lock);
+		/* '2' tells resync/reshape to pause so that all
+		 * active stripes can drain
+		 */
+		conf->quiesce = 2;
+		wait_event_lock_irq(conf->wait_for_stripe,
+				    atomic_read(&conf->active_stripes) == 0 &&
+				    atomic_read(&conf->active_aligned_reads) == 0,
+				    conf->device_lock, /* nothing */);
+		conf->quiesce = 1;
+		spin_unlock_irq(&conf->device_lock);
+		/* allow reshape to continue */
+		wake_up(&conf->wait_for_overlap);
+		break;
+
+	case 0: /* re-enable writes */
+		spin_lock_irq(&conf->device_lock);
+		conf->quiesce = 0;
+		wake_up(&conf->wait_for_stripe);
+		wake_up(&conf->wait_for_overlap);
+		spin_unlock_irq(&conf->device_lock);
+		break;
+	}
+}
+
+
+static void *raid45_takeover_raid0(struct mddev *mddev, int level)
+{
+	struct r0conf *raid0_conf = mddev->private;
+	sector_t sectors;
+
+	/* for raid0 takeover only one zone is supported */
+	if (raid0_conf->nr_strip_zones > 1) {
+		printk(KERN_ERR "md/raid:%s: cannot takeover raid0 with more than one zone.\n",
+		       mdname(mddev));
+		return ERR_PTR(-EINVAL);
+	}
+
+	sectors = raid0_conf->strip_zone[0].zone_end;
+	sector_div(sectors, raid0_conf->strip_zone[0].nb_dev);
+	mddev->dev_sectors = sectors;
+	mddev->new_level = level;
+	mddev->new_layout = ALGORITHM_PARITY_N;
+	mddev->new_chunk_sectors = mddev->chunk_sectors;
+	mddev->raid_disks += 1;
+	mddev->delta_disks = 1;
+	/* make sure it will be not marked as dirty */
+	mddev->recovery_cp = MaxSector;
+
+	return setup_conf(mddev);
+}
+
+
+static void *raid5_takeover_raid1(struct mddev *mddev)
+{
+	int chunksect;
+
+	if (mddev->raid_disks != 2 ||
+	    mddev->degraded > 1)
+		return ERR_PTR(-EINVAL);
+
+	/* Should check if there are write-behind devices? */
+
+	chunksect = 64*2; /* 64K by default */
+
+	/* The array must be an exact multiple of chunksize */
+	while (chunksect && (mddev->array_sectors & (chunksect-1)))
+		chunksect >>= 1;
+
+	if ((chunksect<<9) < STRIPE_SIZE)
+		/* array size does not allow a suitable chunk size */
+		return ERR_PTR(-EINVAL);
+
+	mddev->new_level = 5;
+	mddev->new_layout = ALGORITHM_LEFT_SYMMETRIC;
+	mddev->new_chunk_sectors = chunksect;
+
+	return setup_conf(mddev);
+}
+
+static void *raid5_takeover_raid6(struct mddev *mddev)
+{
+	int new_layout;
+
+	switch (mddev->layout) {
+	case ALGORITHM_LEFT_ASYMMETRIC_6:
+		new_layout = ALGORITHM_LEFT_ASYMMETRIC;
+		break;
+	case ALGORITHM_RIGHT_ASYMMETRIC_6:
+		new_layout = ALGORITHM_RIGHT_ASYMMETRIC;
+		break;
+	case ALGORITHM_LEFT_SYMMETRIC_6:
+		new_layout = ALGORITHM_LEFT_SYMMETRIC;
+		break;
+	case ALGORITHM_RIGHT_SYMMETRIC_6:
+		new_layout = ALGORITHM_RIGHT_SYMMETRIC;
+		break;
+	case ALGORITHM_PARITY_0_6:
+		new_layout = ALGORITHM_PARITY_0;
+		break;
+	case ALGORITHM_PARITY_N:
+		new_layout = ALGORITHM_PARITY_N;
+		break;
+	default:
+		return ERR_PTR(-EINVAL);
+	}
+	mddev->new_level = 5;
+	mddev->new_layout = new_layout;
+	mddev->delta_disks = -1;
+	mddev->raid_disks -= 1;
+	return setup_conf(mddev);
+}
+
+
+static int raid5_check_reshape(struct mddev *mddev)
+{
+	/* For a 2-drive array, the layout and chunk size can be changed
+	 * immediately as not restriping is needed.
+	 * For larger arrays we record the new value - after validation
+	 * to be used by a reshape pass.
+	 */
+	struct r5conf *conf = mddev->private;
+	int new_chunk = mddev->new_chunk_sectors;
+
+	if (mddev->new_layout >= 0 && !algorithm_valid_raid5(mddev->new_layout))
+		return -EINVAL;
+	if (new_chunk > 0) {
+		if (!is_power_of_2(new_chunk))
+			return -EINVAL;
+		if (new_chunk < (PAGE_SIZE>>9))
+			return -EINVAL;
+		if (mddev->array_sectors & (new_chunk-1))
+			/* not factor of array size */
+			return -EINVAL;
+	}
+
+	/* They look valid */
+
+	if (mddev->raid_disks == 2) {
+		/* can make the change immediately */
+		if (mddev->new_layout >= 0) {
+			conf->algorithm = mddev->new_layout;
+			mddev->layout = mddev->new_layout;
+		}
+		if (new_chunk > 0) {
+			conf->chunk_sectors = new_chunk ;
+			mddev->chunk_sectors = new_chunk;
+		}
+		set_bit(MD_CHANGE_DEVS, &mddev->flags);
+		md_wakeup_thread(mddev->thread);
+	}
+	return check_reshape(mddev);
+}
+
+static int raid6_check_reshape(struct mddev *mddev)
+{
+	int new_chunk = mddev->new_chunk_sectors;
+
+	if (mddev->new_layout >= 0 && !algorithm_valid_raid6(mddev->new_layout))
+		return -EINVAL;
+	if (new_chunk > 0) {
+		if (!is_power_of_2(new_chunk))
+			return -EINVAL;
+		if (new_chunk < (PAGE_SIZE >> 9))
+			return -EINVAL;
+		if (mddev->array_sectors & (new_chunk-1))
+			/* not factor of array size */
+			return -EINVAL;
+	}
+
+	/* They look valid */
+	return check_reshape(mddev);
+}
+
+static void *raid5_takeover(struct mddev *mddev)
+{
+	/* raid5 can take over:
+	 *  raid0 - if there is only one strip zone - make it a raid4 layout
+	 *  raid1 - if there are two drives.  We need to know the chunk size
+	 *  raid4 - trivial - just use a raid4 layout.
+	 *  raid6 - Providing it is a *_6 layout
+	 */
+	if (mddev->level == 0)
+		return raid45_takeover_raid0(mddev, 5);
+	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 void *raid4_takeover(struct mddev *mddev)
+{
+	/* raid4 can take over:
+	 *  raid0 - if there is only one strip zone
+	 *  raid5 - if layout is right
+	 */
+	if (mddev->level == 0)
+		return raid45_takeover_raid0(mddev, 4);
+	if (mddev->level == 5 &&
+	    mddev->layout == ALGORITHM_PARITY_N) {
+		mddev->new_layout = 0;
+		mddev->new_level = 4;
+		return setup_conf(mddev);
+	}
+	return ERR_PTR(-EINVAL);
+}
+
+static struct md_personality raid5_personality;
+
+static void *raid6_takeover(struct mddev *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 md_personality raid6_personality =
+{
+	.name		= "raid6",
+	.level		= 6,
+	.owner		= THIS_MODULE,
+	.make_request	= make_request,
+	.run		= run,
+	.stop		= stop,
+	.status		= status,
+	.error_handler	= error,
+	.hot_add_disk	= raid5_add_disk,
+	.hot_remove_disk= raid5_remove_disk,
+	.spare_active	= raid5_spare_active,
+	.sync_request	= sync_request,
+	.resize		= raid5_resize,
+	.size		= raid5_size,
+	.check_reshape	= raid6_check_reshape,
+	.start_reshape  = raid5_start_reshape,
+	.finish_reshape = raid5_finish_reshape,
+	.quiesce	= raid5_quiesce,
+	.takeover	= raid6_takeover,
+};
+static struct md_personality raid5_personality =
+{
+	.name		= "raid5",
+	.level		= 5,
+	.owner		= THIS_MODULE,
+	.make_request	= make_request,
+	.run		= run,
+	.stop		= stop,
+	.status		= status,
+	.error_handler	= error,
+	.hot_add_disk	= raid5_add_disk,
+	.hot_remove_disk= raid5_remove_disk,
+	.spare_active	= raid5_spare_active,
+	.sync_request	= sync_request,
+	.resize		= raid5_resize,
+	.size		= raid5_size,
+	.check_reshape	= raid5_check_reshape,
+	.start_reshape  = raid5_start_reshape,
+	.finish_reshape = raid5_finish_reshape,
+	.quiesce	= raid5_quiesce,
+	.takeover	= raid5_takeover,
+};
+
+static struct md_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,
+	.takeover	= raid4_takeover,
+};
+
+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_DESCRIPTION("RAID4/5/6 (striping with parity) personality for MD");
+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");