Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 2136 insertions, 0 deletions

diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
new file mode 100644
index 000000000000..7e30ab29691a
--- /dev/null
+++ b/drivers/md/raid6main.c
@@ -0,0 +1,2136 @@
+/*
+ * raid6main.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-6 management functions.  This code is derived from raid5.c.
+ * Last merge from raid5.c bkcvs version 1.79 (kernel 2.6.1).
+ *
+ * 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.
+ */
+
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/highmem.h>
+#include <linux/bitops.h>
+#include <asm/atomic.h>
+#include "raid6.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 HASH_PAGES		1
+#define HASH_PAGES_ORDER	0
+#define NR_HASH			(HASH_PAGES * PAGE_SIZE / sizeof(struct stripe_head *))
+#define HASH_MASK		(NR_HASH - 1)
+
+#define stripe_hash(conf, sect)	((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK])
+
+/* bio's attached to a stripe+device for I/O are linked together in bi_sector
+ * order without overlap.  There may be several bio's per stripe+device, and
+ * a bio could span several devices.
+ * When walking this list for a particular stripe+device, we must never proceed
+ * beyond a bio that extends past this device, as the next bio might no longer
+ * be valid.
+ * This macro is used to determine the 'next' bio in the list, given the sector
+ * of the current stripe+device
+ */
+#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
+/*
+ * The following can be used to debug the driver
+ */
+#define RAID6_DEBUG	0	/* Extremely verbose printk */
+#define RAID6_PARANOIA	1	/* Check spinlocks */
+#define RAID6_DUMPSTATE 0	/* Include stripe cache state in /proc/mdstat */
+#if RAID6_PARANOIA && defined(CONFIG_SMP)
+# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
+#else
+# define CHECK_DEVLOCK()
+#endif
+
+#define PRINTK(x...) ((void)(RAID6_DEBUG && printk(KERN_DEBUG x)))
+#if RAID6_DEBUG
+#undef inline
+#undef __inline__
+#define inline
+#define __inline__
+#endif
+
+#if !RAID6_USE_EMPTY_ZERO_PAGE
+/* In .bss so it's zeroed */
+const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
+#endif
+
+static inline int raid6_next_disk(int disk, int raid_disks)
+{
+	disk++;
+	return (disk < raid_disks) ? disk : 0;
+}
+
+static void print_raid6_conf (raid6_conf_t *conf);
+
+static inline void __release_stripe(raid6_conf_t *conf, struct stripe_head *sh)
+{
+	if (atomic_dec_and_test(&sh->count)) {
+		if (!list_empty(&sh->lru))
+			BUG();
+		if (atomic_read(&conf->active_stripes)==0)
+			BUG();
+		if (test_bit(STRIPE_HANDLE, &sh->state)) {
+			if (test_bit(STRIPE_DELAYED, &sh->state))
+				list_add_tail(&sh->lru, &conf->delayed_list);
+			else
+				list_add_tail(&sh->lru, &conf->handle_list);
+			md_wakeup_thread(conf->mddev->thread);
+		} else {
+			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+				atomic_dec(&conf->preread_active_stripes);
+				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
+					md_wakeup_thread(conf->mddev->thread);
+			}
+			list_add_tail(&sh->lru, &conf->inactive_list);
+			atomic_dec(&conf->active_stripes);
+			if (!conf->inactive_blocked ||
+			    atomic_read(&conf->active_stripes) < (NR_STRIPES*3/4))
+				wake_up(&conf->wait_for_stripe);
+		}
+	}
+}
+static void release_stripe(struct stripe_head *sh)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	unsigned long flags;
+
+	spin_lock_irqsave(&conf->device_lock, flags);
+	__release_stripe(conf, sh);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+}
+
+static void remove_hash(struct stripe_head *sh)
+{
+	PRINTK("remove_hash(), stripe %llu\n", (unsigned long long)sh->sector);
+
+	if (sh->hash_pprev) {
+		if (sh->hash_next)
+			sh->hash_next->hash_pprev = sh->hash_pprev;
+		*sh->hash_pprev = sh->hash_next;
+		sh->hash_pprev = NULL;
+	}
+}
+
+static __inline__ void insert_hash(raid6_conf_t *conf, struct stripe_head *sh)
+{
+	struct stripe_head **shp = &stripe_hash(conf, sh->sector);
+
+	PRINTK("insert_hash(), stripe %llu\n", (unsigned long long)sh->sector);
+
+	CHECK_DEVLOCK();
+	if ((sh->hash_next = *shp) != NULL)
+		(*shp)->hash_pprev = &sh->hash_next;
+	*shp = sh;
+	sh->hash_pprev = shp;
+}
+
+
+/* find an idle stripe, make sure it is unhashed, and return it. */
+static struct stripe_head *get_free_stripe(raid6_conf_t *conf)
+{
+	struct stripe_head *sh = NULL;
+	struct list_head *first;
+
+	CHECK_DEVLOCK();
+	if (list_empty(&conf->inactive_list))
+		goto out;
+	first = conf->inactive_list.next;
+	sh = list_entry(first, struct stripe_head, lru);
+	list_del_init(first);
+	remove_hash(sh);
+	atomic_inc(&conf->active_stripes);
+out:
+	return sh;
+}
+
+static void shrink_buffers(struct stripe_head *sh, int num)
+{
+	struct page *p;
+	int i;
+
+	for (i=0; i<num ; i++) {
+		p = sh->dev[i].page;
+		if (!p)
+			continue;
+		sh->dev[i].page = NULL;
+		page_cache_release(p);
+	}
+}
+
+static int grow_buffers(struct stripe_head *sh, int num)
+{
+	int i;
+
+	for (i=0; i<num; i++) {
+		struct page *page;
+
+		if (!(page = alloc_page(GFP_KERNEL))) {
+			return 1;
+		}
+		sh->dev[i].page = page;
+	}
+	return 0;
+}
+
+static void raid6_build_block (struct stripe_head *sh, int i);
+
+static inline void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int disks = conf->raid_disks, i;
+
+	if (atomic_read(&sh->count) != 0)
+		BUG();
+	if (test_bit(STRIPE_HANDLE, &sh->state))
+		BUG();
+
+	CHECK_DEVLOCK();
+	PRINTK("init_stripe called, stripe %llu\n",
+		(unsigned long long)sh->sector);
+
+	remove_hash(sh);
+
+	sh->sector = sector;
+	sh->pd_idx = pd_idx;
+	sh->state = 0;
+
+	for (i=disks; i--; ) {
+		struct r5dev *dev = &sh->dev[i];
+
+		if (dev->toread || dev->towrite || dev->written ||
+		    test_bit(R5_LOCKED, &dev->flags)) {
+			PRINTK("sector=%llx i=%d %p %p %p %d\n",
+			       (unsigned long long)sh->sector, i, dev->toread,
+			       dev->towrite, dev->written,
+			       test_bit(R5_LOCKED, &dev->flags));
+			BUG();
+		}
+		dev->flags = 0;
+		raid6_build_block(sh, i);
+	}
+	insert_hash(conf, sh);
+}
+
+static struct stripe_head *__find_stripe(raid6_conf_t *conf, sector_t sector)
+{
+	struct stripe_head *sh;
+
+	CHECK_DEVLOCK();
+	PRINTK("__find_stripe, sector %llu\n", (unsigned long long)sector);
+	for (sh = stripe_hash(conf, sector); sh; sh = sh->hash_next)
+		if (sh->sector == sector)
+			return sh;
+	PRINTK("__stripe %llu not in cache\n", (unsigned long long)sector);
+	return NULL;
+}
+
+static void unplug_slaves(mddev_t *mddev);
+
+static struct stripe_head *get_active_stripe(raid6_conf_t *conf, sector_t sector,
+					     int pd_idx, int noblock)
+{
+	struct stripe_head *sh;
+
+	PRINTK("get_stripe, sector %llu\n", (unsigned long long)sector);
+
+	spin_lock_irq(&conf->device_lock);
+
+	do {
+		sh = __find_stripe(conf, sector);
+		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) < (NR_STRIPES *3/4)
+						     || !conf->inactive_blocked),
+						    conf->device_lock,
+						    unplug_slaves(conf->mddev);
+					);
+				conf->inactive_blocked = 0;
+			} else
+				init_stripe(sh, sector, pd_idx);
+		} else {
+			if (atomic_read(&sh->count)) {
+				if (!list_empty(&sh->lru))
+					BUG();
+			} else {
+				if (!test_bit(STRIPE_HANDLE, &sh->state))
+					atomic_inc(&conf->active_stripes);
+				if (list_empty(&sh->lru))
+					BUG();
+				list_del_init(&sh->lru);
+			}
+		}
+	} while (sh == NULL);
+
+	if (sh)
+		atomic_inc(&sh->count);
+
+	spin_unlock_irq(&conf->device_lock);
+	return sh;
+}
+
+static int grow_stripes(raid6_conf_t *conf, int num)
+{
+	struct stripe_head *sh;
+	kmem_cache_t *sc;
+	int devs = conf->raid_disks;
+
+	sprintf(conf->cache_name, "raid6/%s", mdname(conf->mddev));
+
+	sc = kmem_cache_create(conf->cache_name,
+			       sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
+			       0, 0, NULL, NULL);
+	if (!sc)
+		return 1;
+	conf->slab_cache = sc;
+	while (num--) {
+		sh = kmem_cache_alloc(sc, GFP_KERNEL);
+		if (!sh)
+			return 1;
+		memset(sh, 0, sizeof(*sh) + (devs-1)*sizeof(struct r5dev));
+		sh->raid_conf = conf;
+		spin_lock_init(&sh->lock);
+
+		if (grow_buffers(sh, conf->raid_disks)) {
+			shrink_buffers(sh, conf->raid_disks);
+			kmem_cache_free(sc, sh);
+			return 1;
+		}
+		/* 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 0;
+}
+
+static void shrink_stripes(raid6_conf_t *conf)
+{
+	struct stripe_head *sh;
+
+	while (1) {
+		spin_lock_irq(&conf->device_lock);
+		sh = get_free_stripe(conf);
+		spin_unlock_irq(&conf->device_lock);
+		if (!sh)
+			break;
+		if (atomic_read(&sh->count))
+			BUG();
+		shrink_buffers(sh, conf->raid_disks);
+		kmem_cache_free(conf->slab_cache, sh);
+		atomic_dec(&conf->active_stripes);
+	}
+	kmem_cache_destroy(conf->slab_cache);
+	conf->slab_cache = NULL;
+}
+
+static int raid6_end_read_request (struct bio * bi, unsigned int bytes_done,
+				   int error)
+{
+ 	struct stripe_head *sh = bi->bi_private;
+	raid6_conf_t *conf = sh->raid_conf;
+	int disks = conf->raid_disks, i;
+	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+
+	if (bi->bi_size)
+		return 1;
+
+	for (i=0 ; i<disks; i++)
+		if (bi == &sh->dev[i].req)
+			break;
+
+	PRINTK("end_read_request %llu/%d, count: %d, uptodate %d.\n",
+		(unsigned long long)sh->sector, i, atomic_read(&sh->count),
+		uptodate);
+	if (i == disks) {
+		BUG();
+		return 0;
+	}
+
+	if (uptodate) {
+#if 0
+		struct bio *bio;
+		unsigned long flags;
+		spin_lock_irqsave(&conf->device_lock, flags);
+		/* we can return a buffer if we bypassed the cache or
+		 * if the top buffer is not in highmem.  If there are
+		 * multiple buffers, leave the extra work to
+		 * handle_stripe
+		 */
+		buffer = sh->bh_read[i];
+		if (buffer &&
+		    (!PageHighMem(buffer->b_page)
+		     || buffer->b_page == bh->b_page )
+			) {
+			sh->bh_read[i] = buffer->b_reqnext;
+			buffer->b_reqnext = NULL;
+		} else
+			buffer = NULL;
+		spin_unlock_irqrestore(&conf->device_lock, flags);
+		if (sh->bh_page[i]==bh->b_page)
+			set_buffer_uptodate(bh);
+		if (buffer) {
+			if (buffer->b_page != bh->b_page)
+				memcpy(buffer->b_data, bh->b_data, bh->b_size);
+			buffer->b_end_io(buffer, 1);
+		}
+#else
+		set_bit(R5_UPTODATE, &sh->dev[i].flags);
+#endif
+	} else {
+		md_error(conf->mddev, conf->disks[i].rdev);
+		clear_bit(R5_UPTODATE, &sh->dev[i].flags);
+	}
+	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
+#if 0
+	/* must restore b_page before unlocking buffer... */
+	if (sh->bh_page[i] != bh->b_page) {
+		bh->b_page = sh->bh_page[i];
+		bh->b_data = page_address(bh->b_page);
+		clear_buffer_uptodate(bh);
+	}
+#endif
+	clear_bit(R5_LOCKED, &sh->dev[i].flags);
+	set_bit(STRIPE_HANDLE, &sh->state);
+	release_stripe(sh);
+	return 0;
+}
+
+static int raid6_end_write_request (struct bio *bi, unsigned int bytes_done,
+				    int error)
+{
+ 	struct stripe_head *sh = bi->bi_private;
+	raid6_conf_t *conf = sh->raid_conf;
+	int disks = conf->raid_disks, i;
+	unsigned long flags;
+	int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
+
+	if (bi->bi_size)
+		return 1;
+
+	for (i=0 ; i<disks; i++)
+		if (bi == &sh->dev[i].req)
+			break;
+
+	PRINTK("end_write_request %llu/%d, count %d, uptodate: %d.\n",
+		(unsigned long long)sh->sector, i, atomic_read(&sh->count),
+		uptodate);
+	if (i == disks) {
+		BUG();
+		return 0;
+	}
+
+	spin_lock_irqsave(&conf->device_lock, flags);
+	if (!uptodate)
+		md_error(conf->mddev, conf->disks[i].rdev);
+
+	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
+
+	clear_bit(R5_LOCKED, &sh->dev[i].flags);
+	set_bit(STRIPE_HANDLE, &sh->state);
+	__release_stripe(conf, sh);
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+	return 0;
+}
+
+
+static sector_t compute_blocknr(struct stripe_head *sh, int i);
+
+static void raid6_build_block (struct stripe_head *sh, int i)
+{
+	struct r5dev *dev = &sh->dev[i];
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, sh->raid_conf->raid_disks);
+
+	bio_init(&dev->req);
+	dev->req.bi_io_vec = &dev->vec;
+	dev->req.bi_vcnt++;
+	dev->req.bi_max_vecs++;
+	dev->vec.bv_page = dev->page;
+	dev->vec.bv_len = STRIPE_SIZE;
+	dev->vec.bv_offset = 0;
+
+	dev->req.bi_sector = sh->sector;
+	dev->req.bi_private = sh;
+
+	dev->flags = 0;
+	if (i != pd_idx && i != qd_idx)
+		dev->sector = compute_blocknr(sh, i);
+}
+
+static void error(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+	char b[BDEVNAME_SIZE];
+	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+	PRINTK("raid6: error called\n");
+
+	if (!rdev->faulty) {
+		mddev->sb_dirty = 1;
+		if (rdev->in_sync) {
+			conf->working_disks--;
+			mddev->degraded++;
+			conf->failed_disks++;
+			rdev->in_sync = 0;
+			/*
+			 * if recovery was running, make sure it aborts.
+			 */
+			set_bit(MD_RECOVERY_ERR, &mddev->recovery);
+		}
+		rdev->faulty = 1;
+		printk (KERN_ALERT
+			"raid6: Disk failure on %s, disabling device."
+			" Operation continuing on %d devices\n",
+			bdevname(rdev->bdev,b), conf->working_disks);
+	}
+}
+
+/*
+ * Input: a 'big' sector number,
+ * Output: index of the data and parity disk, and the sector # in them.
+ */
+static sector_t raid6_compute_sector(sector_t r_sector, unsigned int raid_disks,
+			unsigned int data_disks, unsigned int * dd_idx,
+			unsigned int * pd_idx, raid6_conf_t *conf)
+{
+	long stripe;
+	unsigned long chunk_number;
+	unsigned int chunk_offset;
+	sector_t new_sector;
+	int sectors_per_chunk = conf->chunk_size >> 9;
+
+	/* First compute the information on this sector */
+
+	/*
+	 * Compute the chunk number and the sector offset inside the chunk
+	 */
+	chunk_offset = sector_div(r_sector, sectors_per_chunk);
+	chunk_number = r_sector;
+	if ( r_sector != chunk_number ) {
+		printk(KERN_CRIT "raid6: ERROR: r_sector = %llu, chunk_number = %lu\n",
+		       (unsigned long long)r_sector, (unsigned long)chunk_number);
+		BUG();
+	}
+
+	/*
+	 * Compute the stripe number
+	 */
+	stripe = chunk_number / data_disks;
+
+	/*
+	 * Compute the data disk and parity disk indexes inside the stripe
+	 */
+	*dd_idx = chunk_number % data_disks;
+
+	/*
+	 * Select the parity disk based on the user selected algorithm.
+	 */
+
+	/**** FIX THIS ****/
+	switch (conf->algorithm) {
+	case ALGORITHM_LEFT_ASYMMETRIC:
+		*pd_idx = raid_disks - 1 - (stripe % raid_disks);
+		if (*pd_idx == raid_disks-1)
+		  	(*dd_idx)++; 	/* Q D D D P */
+		else if (*dd_idx >= *pd_idx)
+		  	(*dd_idx) += 2; /* D D P Q D */
+		break;
+	case ALGORITHM_RIGHT_ASYMMETRIC:
+		*pd_idx = stripe % raid_disks;
+		if (*pd_idx == raid_disks-1)
+		  	(*dd_idx)++; 	/* Q D D D P */
+		else if (*dd_idx >= *pd_idx)
+		  	(*dd_idx) += 2; /* D D P Q D */
+		break;
+	case ALGORITHM_LEFT_SYMMETRIC:
+		*pd_idx = raid_disks - 1 - (stripe % raid_disks);
+		*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
+		break;
+	case ALGORITHM_RIGHT_SYMMETRIC:
+		*pd_idx = stripe % raid_disks;
+		*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
+		break;
+	default:
+		printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
+			conf->algorithm);
+	}
+
+	PRINTK("raid6: chunk_number = %lu, pd_idx = %u, dd_idx = %u\n",
+	       chunk_number, *pd_idx, *dd_idx);
+
+	/*
+	 * 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)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int raid_disks = conf->raid_disks, data_disks = raid_disks - 2;
+	sector_t new_sector = sh->sector, check;
+	int sectors_per_chunk = conf->chunk_size >> 9;
+	sector_t stripe;
+	int chunk_offset;
+	int chunk_number, dummy1, dummy2, dd_idx = i;
+	sector_t r_sector;
+	int i0 = i;
+
+	chunk_offset = sector_div(new_sector, sectors_per_chunk);
+	stripe = new_sector;
+	if ( new_sector != stripe ) {
+		printk(KERN_CRIT "raid6: ERROR: new_sector = %llu, stripe = %lu\n",
+		       (unsigned long long)new_sector, (unsigned long)stripe);
+		BUG();
+	}
+
+	switch (conf->algorithm) {
+		case ALGORITHM_LEFT_ASYMMETRIC:
+		case ALGORITHM_RIGHT_ASYMMETRIC:
+		  	if (sh->pd_idx == raid_disks-1)
+				i--; 	/* Q D D D P */
+			else if (i > sh->pd_idx)
+				i -= 2; /* D D P Q D */
+			break;
+		case ALGORITHM_LEFT_SYMMETRIC:
+		case ALGORITHM_RIGHT_SYMMETRIC:
+			if (sh->pd_idx == raid_disks-1)
+				i--; /* Q D D D P */
+			else {
+				/* D D P Q D */
+				if (i < sh->pd_idx)
+					i += raid_disks;
+				i -= (sh->pd_idx + 2);
+			}
+			break;
+		default:
+			printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
+				conf->algorithm);
+	}
+
+	PRINTK("raid6: compute_blocknr: pd_idx = %u, i0 = %u, i = %u\n", sh->pd_idx, i0, i);
+
+	chunk_number = stripe * data_disks + i;
+	r_sector = (sector_t)chunk_number * sectors_per_chunk + chunk_offset;
+
+	check = raid6_compute_sector (r_sector, raid_disks, data_disks, &dummy1, &dummy2, conf);
+	if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
+		printk(KERN_CRIT "raid6: compute_blocknr: map not correct\n");
+		return 0;
+	}
+	return r_sector;
+}
+
+
+
+/*
+ * Copy data between a page in the stripe cache, and one or more bion
+ * The page could align with the middle of the bio, or there could be
+ * several bion, each with several bio_vecs, which cover part of the page
+ * Multiple bion are linked together on bi_next.  There may be extras
+ * at the end of this list.  We ignore them.
+ */
+static void copy_data(int frombio, struct bio *bio,
+		     struct page *page,
+		     sector_t sector)
+{
+	char *pa = page_address(page);
+	struct bio_vec *bvl;
+	int i;
+	int page_offset;
+
+	if (bio->bi_sector >= sector)
+		page_offset = (signed)(bio->bi_sector - sector) * 512;
+	else
+		page_offset = (signed)(sector - bio->bi_sector) * -512;
+	bio_for_each_segment(bvl, bio, i) {
+		int len = bio_iovec_idx(bio,i)->bv_len;
+		int clen;
+		int b_offset = 0;
+
+		if (page_offset < 0) {
+			b_offset = -page_offset;
+			page_offset += b_offset;
+			len -= b_offset;
+		}
+
+		if (len > 0 && page_offset + len > STRIPE_SIZE)
+			clen = STRIPE_SIZE - page_offset;
+		else clen = len;
+
+		if (clen > 0) {
+			char *ba = __bio_kmap_atomic(bio, i, KM_USER0);
+			if (frombio)
+				memcpy(pa+page_offset, ba+b_offset, clen);
+			else
+				memcpy(ba+b_offset, pa+page_offset, clen);
+			__bio_kunmap_atomic(ba, KM_USER0);
+		}
+		if (clen < len) /* hit end of page */
+			break;
+		page_offset +=  len;
+	}
+}
+
+#define check_xor() 	do { 						\
+			   if (count == MAX_XOR_BLOCKS) {		\
+				xor_block(count, STRIPE_SIZE, ptr);	\
+				count = 1;				\
+			   }						\
+			} while(0)
+
+/* Compute P and Q syndromes */
+static void compute_parity(struct stripe_head *sh, int method)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = conf->raid_disks, count;
+	struct bio *chosen;
+	/**** FIX THIS: This could be very bad if disks is close to 256 ****/
+	void *ptrs[disks];
+
+	qd_idx = raid6_next_disk(pd_idx, disks);
+	d0_idx = raid6_next_disk(qd_idx, disks);
+
+	PRINTK("compute_parity, stripe %llu, method %d\n",
+		(unsigned long long)sh->sector, method);
+
+	switch(method) {
+	case READ_MODIFY_WRITE:
+		BUG();		/* READ_MODIFY_WRITE N/A for RAID-6 */
+	case RECONSTRUCT_WRITE:
+		for (i= disks; i-- ;)
+			if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
+				chosen = sh->dev[i].towrite;
+				sh->dev[i].towrite = NULL;
+
+				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+					wake_up(&conf->wait_for_overlap);
+
+				if (sh->dev[i].written) BUG();
+				sh->dev[i].written = chosen;
+			}
+		break;
+	case CHECK_PARITY:
+		BUG();		/* Not implemented yet */
+	}
+
+	for (i = disks; i--;)
+		if (sh->dev[i].written) {
+			sector_t sector = sh->dev[i].sector;
+			struct bio *wbi = sh->dev[i].written;
+			while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
+				copy_data(1, wbi, sh->dev[i].page, sector);
+				wbi = r5_next_bio(wbi, sector);
+			}
+
+			set_bit(R5_LOCKED, &sh->dev[i].flags);
+			set_bit(R5_UPTODATE, &sh->dev[i].flags);
+		}
+
+//	switch(method) {
+//	case RECONSTRUCT_WRITE:
+//	case CHECK_PARITY:
+//	case UPDATE_PARITY:
+		/* Note that unlike RAID-5, the ordering of the disks matters greatly. */
+		/* FIX: Is this ordering of drives even remotely optimal? */
+		count = 0;
+		i = d0_idx;
+		do {
+			ptrs[count++] = page_address(sh->dev[i].page);
+			if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				printk("block %d/%d not uptodate on parity calc\n", i,count);
+			i = raid6_next_disk(i, disks);
+		} while ( i != d0_idx );
+//		break;
+//	}
+
+	raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);
+
+	switch(method) {
+	case RECONSTRUCT_WRITE:
+		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
+		set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
+		set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
+		break;
+	case UPDATE_PARITY:
+		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
+		break;
+	}
+}
+
+/* Compute one missing block */
+static void compute_block_1(struct stripe_head *sh, int dd_idx)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, count, disks = conf->raid_disks;
+	void *ptr[MAX_XOR_BLOCKS], *p;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+
+	PRINTK("compute_block_1, stripe %llu, idx %d\n",
+		(unsigned long long)sh->sector, dd_idx);
+
+	if ( dd_idx == qd_idx ) {
+		/* We're actually computing the Q drive */
+		compute_parity(sh, UPDATE_PARITY);
+	} else {
+		ptr[0] = page_address(sh->dev[dd_idx].page);
+		memset(ptr[0], 0, STRIPE_SIZE);
+		count = 1;
+		for (i = disks ; i--; ) {
+			if (i == dd_idx || i == qd_idx)
+				continue;
+			p = page_address(sh->dev[i].page);
+			if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				ptr[count++] = p;
+			else
+				printk("compute_block() %d, stripe %llu, %d"
+				       " not present\n", dd_idx,
+				       (unsigned long long)sh->sector, i);
+
+			check_xor();
+		}
+		if (count != 1)
+			xor_block(count, STRIPE_SIZE, ptr);
+		set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
+	}
+}
+
+/* Compute two missing blocks */
+static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, count, disks = conf->raid_disks;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+	int d0_idx = raid6_next_disk(qd_idx, disks);
+	int faila, failb;
+
+	/* faila and failb are disk numbers relative to d0_idx */
+	/* pd_idx become disks-2 and qd_idx become disks-1 */
+	faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
+	failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;
+
+	BUG_ON(faila == failb);
+	if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }
+
+	PRINTK("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
+	       (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);
+
+	if ( failb == disks-1 ) {
+		/* Q disk is one of the missing disks */
+		if ( faila == disks-2 ) {
+			/* Missing P+Q, just recompute */
+			compute_parity(sh, UPDATE_PARITY);
+			return;
+		} else {
+			/* We're missing D+Q; recompute D from P */
+			compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1);
+			compute_parity(sh, UPDATE_PARITY); /* Is this necessary? */
+			return;
+		}
+	}
+
+	/* We're missing D+P or D+D; build pointer table */
+	{
+		/**** FIX THIS: This could be very bad if disks is close to 256 ****/
+		void *ptrs[disks];
+
+		count = 0;
+		i = d0_idx;
+		do {
+			ptrs[count++] = page_address(sh->dev[i].page);
+			i = raid6_next_disk(i, disks);
+			if (i != dd_idx1 && i != dd_idx2 &&
+			    !test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				printk("compute_2 with missing block %d/%d\n", count, i);
+		} while ( i != d0_idx );
+
+		if ( failb == disks-2 ) {
+			/* We're missing D+P. */
+			raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
+		} else {
+			/* We're missing D+D. */
+			raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
+		}
+
+		/* Both the above update both missing blocks */
+		set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
+		set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
+	}
+}
+
+
+/*
+ * Each stripe/dev can have one or more bion attached.
+ * toread/towrite point to the first in a chain.
+ * The bi_next chain must be in order.
+ */
+static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
+{
+	struct bio **bip;
+	raid6_conf_t *conf = sh->raid_conf;
+
+	PRINTK("adding bh b#%llu to stripe s#%llu\n",
+		(unsigned long long)bi->bi_sector,
+		(unsigned long long)sh->sector);
+
+
+	spin_lock(&sh->lock);
+	spin_lock_irq(&conf->device_lock);
+	if (forwrite)
+		bip = &sh->dev[dd_idx].towrite;
+	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;
+
+	if (*bip && bi->bi_next && (*bip) != bi->bi_next)
+		BUG();
+	if (*bip)
+		bi->bi_next = *bip;
+	*bip = bi;
+	bi->bi_phys_segments ++;
+	spin_unlock_irq(&conf->device_lock);
+	spin_unlock(&sh->lock);
+
+	PRINTK("added bi b#%llu to stripe s#%llu, disk %d.\n",
+		(unsigned long long)bi->bi_sector,
+		(unsigned long long)sh->sector, dd_idx);
+
+	if (forwrite) {
+		/* check if page is covered */
+		sector_t sector = sh->dev[dd_idx].sector;
+		for (bi=sh->dev[dd_idx].towrite;
+		     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
+			     bi && bi->bi_sector <= sector;
+		     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
+			if (bi->bi_sector + (bi->bi_size>>9) >= sector)
+				sector = bi->bi_sector + (bi->bi_size>>9);
+		}
+		if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
+			set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
+	}
+	return 1;
+
+ overlap:
+	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
+	spin_unlock_irq(&conf->device_lock);
+	spin_unlock(&sh->lock);
+	return 0;
+}
+
+
+/*
+ * handle_stripe - do things to a stripe.
+ *
+ * We lock the stripe and then examine the state of various bits
+ * to see what needs to be done.
+ * Possible results:
+ *    return some read request which now have data
+ *    return some write requests which are safely on disc
+ *    schedule a read on some buffers
+ *    schedule a write of some buffers
+ *    return confirmation of parity correctness
+ *
+ * Parity calculations are done inside the stripe lock
+ * buffers are taken off read_list or write_list, and bh_cache buffers
+ * get BH_Lock set before the stripe lock is released.
+ *
+ */
+
+static void handle_stripe(struct stripe_head *sh)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int disks = conf->raid_disks;
+	struct bio *return_bi= NULL;
+	struct bio *bi;
+	int i;
+	int syncing;
+	int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
+	int non_overwrite = 0;
+	int failed_num[2] = {0, 0};
+	struct r5dev *dev, *pdev, *qdev;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+	int p_failed, q_failed;
+
+	PRINTK("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d, qd_idx=%d\n",
+	       (unsigned long long)sh->sector, sh->state, atomic_read(&sh->count),
+	       pd_idx, qd_idx);
+
+	spin_lock(&sh->lock);
+	clear_bit(STRIPE_HANDLE, &sh->state);
+	clear_bit(STRIPE_DELAYED, &sh->state);
+
+	syncing = test_bit(STRIPE_SYNCING, &sh->state);
+	/* Now to look around and see what can be done */
+
+	for (i=disks; i--; ) {
+		mdk_rdev_t *rdev;
+		dev = &sh->dev[i];
+		clear_bit(R5_Insync, &dev->flags);
+		clear_bit(R5_Syncio, &dev->flags);
+
+		PRINTK("check %d: state 0x%lx read %p write %p written %p\n",
+			i, dev->flags, dev->toread, dev->towrite, dev->written);
+		/* maybe we can reply to a read */
+		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
+			struct bio *rbi, *rbi2;
+			PRINTK("Return read for disc %d\n", i);
+			spin_lock_irq(&conf->device_lock);
+			rbi = dev->toread;
+			dev->toread = NULL;
+			if (test_and_clear_bit(R5_Overlap, &dev->flags))
+				wake_up(&conf->wait_for_overlap);
+			spin_unlock_irq(&conf->device_lock);
+			while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
+				copy_data(0, rbi, dev->page, dev->sector);
+				rbi2 = r5_next_bio(rbi, dev->sector);
+				spin_lock_irq(&conf->device_lock);
+				if (--rbi->bi_phys_segments == 0) {
+					rbi->bi_next = return_bi;
+					return_bi = rbi;
+				}
+				spin_unlock_irq(&conf->device_lock);
+				rbi = rbi2;
+			}
+		}
+
+		/* now count some things */
+		if (test_bit(R5_LOCKED, &dev->flags)) locked++;
+		if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;
+
+
+		if (dev->toread) to_read++;
+		if (dev->towrite) {
+			to_write++;
+			if (!test_bit(R5_OVERWRITE, &dev->flags))
+				non_overwrite++;
+		}
+		if (dev->written) written++;
+		rdev = conf->disks[i].rdev; /* FIXME, should I be looking rdev */
+		if (!rdev || !rdev->in_sync) {
+			if ( failed < 2 )
+				failed_num[failed] = i;
+			failed++;
+		} else
+			set_bit(R5_Insync, &dev->flags);
+	}
+	PRINTK("locked=%d uptodate=%d to_read=%d"
+	       " to_write=%d failed=%d failed_num=%d,%d\n",
+	       locked, uptodate, to_read, to_write, failed,
+	       failed_num[0], failed_num[1]);
+	/* check if the array has lost >2 devices and, if so, some requests might
+	 * need to be failed
+	 */
+	if (failed > 2 && to_read+to_write+written) {
+		spin_lock_irq(&conf->device_lock);
+		for (i=disks; i--; ) {
+			/* fail all writes first */
+			bi = sh->dev[i].towrite;
+			sh->dev[i].towrite = NULL;
+			if (bi) to_write--;
+
+			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+				wake_up(&conf->wait_for_overlap);
+
+			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
+				struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
+				clear_bit(BIO_UPTODATE, &bi->bi_flags);
+				if (--bi->bi_phys_segments == 0) {
+					md_write_end(conf->mddev);
+					bi->bi_next = return_bi;
+					return_bi = bi;
+				}
+				bi = nextbi;
+			}
+			/* and fail all 'written' */
+			bi = sh->dev[i].written;
+			sh->dev[i].written = NULL;
+			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS) {
+				struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
+				clear_bit(BIO_UPTODATE, &bi->bi_flags);
+				if (--bi->bi_phys_segments == 0) {
+					md_write_end(conf->mddev);
+					bi->bi_next = return_bi;
+					return_bi = bi;
+				}
+				bi = bi2;
+			}
+
+			/* fail any reads if this device is non-operational */
+			if (!test_bit(R5_Insync, &sh->dev[i].flags)) {
+				bi = sh->dev[i].toread;
+				sh->dev[i].toread = NULL;
+				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+					wake_up(&conf->wait_for_overlap);
+				if (bi) to_read--;
+				while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
+					struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
+					clear_bit(BIO_UPTODATE, &bi->bi_flags);
+					if (--bi->bi_phys_segments == 0) {
+						bi->bi_next = return_bi;
+						return_bi = bi;
+					}
+					bi = nextbi;
+				}
+			}
+		}
+		spin_unlock_irq(&conf->device_lock);
+	}
+	if (failed > 2 && syncing) {
+		md_done_sync(conf->mddev, STRIPE_SECTORS,0);
+		clear_bit(STRIPE_SYNCING, &sh->state);
+		syncing = 0;
+	}
+
+	/*
+	 * might be able to return some write requests if the parity blocks
+	 * are safe, or on a failed drive
+	 */
+	pdev = &sh->dev[pd_idx];
+	p_failed = (failed >= 1 && failed_num[0] == pd_idx)
+		|| (failed >= 2 && failed_num[1] == pd_idx);
+	qdev = &sh->dev[qd_idx];
+	q_failed = (failed >= 1 && failed_num[0] == qd_idx)
+		|| (failed >= 2 && failed_num[1] == qd_idx);
+
+	if ( written &&
+	     ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
+			     && !test_bit(R5_LOCKED, &pdev->flags)
+			     && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
+	     ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
+			     && !test_bit(R5_LOCKED, &qdev->flags)
+			     && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
+		/* any written block on an uptodate or failed drive can be
+		 * returned.  Note that if we 'wrote' to a failed drive,
+		 * it will be UPTODATE, but never LOCKED, so we don't need
+		 * to test 'failed' directly.
+		 */
+		for (i=disks; i--; )
+			if (sh->dev[i].written) {
+				dev = &sh->dev[i];
+				if (!test_bit(R5_LOCKED, &dev->flags) &&
+				    test_bit(R5_UPTODATE, &dev->flags) ) {
+					/* We can return any write requests */
+					struct bio *wbi, *wbi2;
+					PRINTK("Return write for stripe %llu disc %d\n",
+					       (unsigned long long)sh->sector, i);
+					spin_lock_irq(&conf->device_lock);
+					wbi = dev->written;
+					dev->written = NULL;
+					while (wbi && wbi->bi_sector < dev->sector + STRIPE_SECTORS) {
+						wbi2 = r5_next_bio(wbi, dev->sector);
+						if (--wbi->bi_phys_segments == 0) {
+							md_write_end(conf->mddev);
+							wbi->bi_next = return_bi;
+							return_bi = wbi;
+						}
+						wbi = wbi2;
+					}
+					spin_unlock_irq(&conf->device_lock);
+				}
+			}
+	}
+
+	/* Now we might consider reading some blocks, either to check/generate
+	 * parity, or to satisfy requests
+	 * or to load a block that is being partially written.
+	 */
+	if (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
+		for (i=disks; i--;) {
+			dev = &sh->dev[i];
+			if (!test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
+			    (dev->toread ||
+			     (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
+			     syncing ||
+			     (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
+			     (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
+				    )
+				) {
+				/* we would like to get this block, possibly
+				 * by computing it, but we might not be able to
+				 */
+				if (uptodate == disks-1) {
+					PRINTK("Computing stripe %llu block %d\n",
+					       (unsigned long long)sh->sector, i);
+					compute_block_1(sh, i);
+					uptodate++;
+				} else if ( uptodate == disks-2 && failed >= 2 ) {
+					/* Computing 2-failure is *very* expensive; only do it if failed >= 2 */
+					int other;
+					for (other=disks; other--;) {
+						if ( other == i )
+							continue;
+						if ( !test_bit(R5_UPTODATE, &sh->dev[other].flags) )
+							break;
+					}
+					BUG_ON(other < 0);
+					PRINTK("Computing stripe %llu blocks %d,%d\n",
+					       (unsigned long long)sh->sector, i, other);
+					compute_block_2(sh, i, other);
+					uptodate += 2;
+				} else if (test_bit(R5_Insync, &dev->flags)) {
+					set_bit(R5_LOCKED, &dev->flags);
+					set_bit(R5_Wantread, &dev->flags);
+#if 0
+					/* if I am just reading this block and we don't have
+					   a failed drive, or any pending writes then sidestep the cache */
+					if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
+					    ! syncing && !failed && !to_write) {
+						sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
+						sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
+					}
+#endif
+					locked++;
+					PRINTK("Reading block %d (sync=%d)\n",
+						i, syncing);
+					if (syncing)
+						md_sync_acct(conf->disks[i].rdev->bdev,
+							     STRIPE_SECTORS);
+				}
+			}
+		}
+		set_bit(STRIPE_HANDLE, &sh->state);
+	}
+
+	/* now to consider writing and what else, if anything should be read */
+	if (to_write) {
+		int rcw=0, must_compute=0;
+		for (i=disks ; i--;) {
+			dev = &sh->dev[i];
+			/* Would I have to read this buffer for reconstruct_write */
+			if (!test_bit(R5_OVERWRITE, &dev->flags)
+			    && i != pd_idx && i != qd_idx
+			    && (!test_bit(R5_LOCKED, &dev->flags)
+#if 0
+				|| sh->bh_page[i] != bh->b_page
+#endif
+				    ) &&
+			    !test_bit(R5_UPTODATE, &dev->flags)) {
+				if (test_bit(R5_Insync, &dev->flags)) rcw++;
+				else {
+					PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
+					must_compute++;
+				}
+			}
+		}
+		PRINTK("for sector %llu, rcw=%d, must_compute=%d\n",
+		       (unsigned long long)sh->sector, rcw, must_compute);
+		set_bit(STRIPE_HANDLE, &sh->state);
+
+		if (rcw > 0)
+			/* want reconstruct write, but need to get some data */
+			for (i=disks; i--;) {
+				dev = &sh->dev[i];
+				if (!test_bit(R5_OVERWRITE, &dev->flags)
+				    && !(failed == 0 && (i == pd_idx || i == qd_idx))
+				    && !test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
+				    test_bit(R5_Insync, &dev->flags)) {
+					if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+					{
+						PRINTK("Read_old stripe %llu block %d for Reconstruct\n",
+						       (unsigned long long)sh->sector, i);
+						set_bit(R5_LOCKED, &dev->flags);
+						set_bit(R5_Wantread, &dev->flags);
+						locked++;
+					} else {
+						PRINTK("Request delayed stripe %llu block %d for Reconstruct\n",
+						       (unsigned long long)sh->sector, i);
+						set_bit(STRIPE_DELAYED, &sh->state);
+						set_bit(STRIPE_HANDLE, &sh->state);
+					}
+				}
+			}
+		/* now if nothing is locked, and if we have enough data, we can start a write request */
+		if (locked == 0 && rcw == 0) {
+			if ( must_compute > 0 ) {
+				/* We have failed blocks and need to compute them */
+				switch ( failed ) {
+				case 0:	BUG();
+				case 1: compute_block_1(sh, failed_num[0]); break;
+				case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
+				default: BUG();	/* This request should have been failed? */
+				}
+			}
+
+			PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
+			compute_parity(sh, RECONSTRUCT_WRITE);
+			/* now every locked buffer is ready to be written */
+			for (i=disks; i--;)
+				if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
+					PRINTK("Writing stripe %llu block %d\n",
+					       (unsigned long long)sh->sector, i);
+					locked++;
+					set_bit(R5_Wantwrite, &sh->dev[i].flags);
+#if 0 /**** FIX: I don't understand the logic here... ****/
+					if (!test_bit(R5_Insync, &sh->dev[i].flags)
+					    || ((i==pd_idx || i==qd_idx) && failed == 0)) /* FIX? */
+						set_bit(STRIPE_INSYNC, &sh->state);
+#endif
+				}
+			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+				atomic_dec(&conf->preread_active_stripes);
+				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
+					md_wakeup_thread(conf->mddev->thread);
+			}
+		}
+	}
+
+	/* maybe we need to check and possibly fix the parity for this stripe
+	 * Any reads will already have been scheduled, so we just see if enough data
+	 * is available
+	 */
+	if (syncing && locked == 0 &&
+	    !test_bit(STRIPE_INSYNC, &sh->state) && failed <= 2) {
+		set_bit(STRIPE_HANDLE, &sh->state);
+#if 0 /* RAID-6: Don't support CHECK PARITY yet */
+		if (failed == 0) {
+			char *pagea;
+			if (uptodate != disks)
+				BUG();
+			compute_parity(sh, CHECK_PARITY);
+			uptodate--;
+			pagea = page_address(sh->dev[pd_idx].page);
+			if ((*(u32*)pagea) == 0 &&
+			    !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
+				/* parity is correct (on disc, not in buffer any more) */
+				set_bit(STRIPE_INSYNC, &sh->state);
+			}
+		}
+#endif
+		if (!test_bit(STRIPE_INSYNC, &sh->state)) {
+			int failed_needupdate[2];
+			struct r5dev *adev, *bdev;
+
+			if ( failed < 1 )
+				failed_num[0] = pd_idx;
+			if ( failed < 2 )
+				failed_num[1] = (failed_num[0] == qd_idx) ? pd_idx : qd_idx;
+
+			failed_needupdate[0] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[0]].flags);
+			failed_needupdate[1] = !test_bit(R5_UPTODATE, &sh->dev[failed_num[1]].flags);
+
+			PRINTK("sync: failed=%d num=%d,%d fnu=%u%u\n",
+			       failed, failed_num[0], failed_num[1], failed_needupdate[0], failed_needupdate[1]);
+
+#if 0  /* RAID-6: This code seems to require that CHECK_PARITY destroys the uptodateness of the parity */
+			/* should be able to compute the missing block(s) and write to spare */
+			if ( failed_needupdate[0] ^ failed_needupdate[1] ) {
+				if (uptodate+1 != disks)
+					BUG();
+				compute_block_1(sh, failed_needupdate[0] ? failed_num[0] : failed_num[1]);
+				uptodate++;
+			} else if ( failed_needupdate[0] & failed_needupdate[1] ) {
+				if (uptodate+2 != disks)
+					BUG();
+				compute_block_2(sh, failed_num[0], failed_num[1]);
+				uptodate += 2;
+			}
+#else
+			compute_block_2(sh, failed_num[0], failed_num[1]);
+			uptodate += failed_needupdate[0] + failed_needupdate[1];
+#endif
+
+			if (uptodate != disks)
+				BUG();
+
+			PRINTK("Marking for sync stripe %llu blocks %d,%d\n",
+			       (unsigned long long)sh->sector, failed_num[0], failed_num[1]);
+
+			/**** FIX: Should we really do both of these unconditionally? ****/
+			adev = &sh->dev[failed_num[0]];
+			locked += !test_bit(R5_LOCKED, &adev->flags);
+			set_bit(R5_LOCKED, &adev->flags);
+			set_bit(R5_Wantwrite, &adev->flags);
+			bdev = &sh->dev[failed_num[1]];
+			locked += !test_bit(R5_LOCKED, &bdev->flags);
+			set_bit(R5_LOCKED, &bdev->flags);
+			set_bit(R5_Wantwrite, &bdev->flags);
+
+			set_bit(STRIPE_INSYNC, &sh->state);
+			set_bit(R5_Syncio, &adev->flags);
+			set_bit(R5_Syncio, &bdev->flags);
+		}
+	}
+	if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
+		md_done_sync(conf->mddev, STRIPE_SECTORS,1);
+		clear_bit(STRIPE_SYNCING, &sh->state);
+	}
+
+	spin_unlock(&sh->lock);
+
+	while ((bi=return_bi)) {
+		int bytes = bi->bi_size;
+
+		return_bi = bi->bi_next;
+		bi->bi_next = NULL;
+		bi->bi_size = 0;
+		bi->bi_end_io(bi, bytes, 0);
+	}
+	for (i=disks; i-- ;) {
+		int rw;
+		struct bio *bi;
+		mdk_rdev_t *rdev;
+		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
+			rw = 1;
+		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
+			rw = 0;
+		else
+			continue;
+
+		bi = &sh->dev[i].req;
+
+		bi->bi_rw = rw;
+		if (rw)
+			bi->bi_end_io = raid6_end_write_request;
+		else
+			bi->bi_end_io = raid6_end_read_request;
+
+		rcu_read_lock();
+		rdev = conf->disks[i].rdev;
+		if (rdev && rdev->faulty)
+			rdev = NULL;
+		if (rdev)
+			atomic_inc(&rdev->nr_pending);
+		rcu_read_unlock();
+
+		if (rdev) {
+			if (test_bit(R5_Syncio, &sh->dev[i].flags))
+				md_sync_acct(rdev->bdev, STRIPE_SECTORS);
+
+			bi->bi_bdev = rdev->bdev;
+			PRINTK("for %llu schedule op %ld on disc %d\n",
+				(unsigned long long)sh->sector, bi->bi_rw, i);
+			atomic_inc(&sh->count);
+			bi->bi_sector = sh->sector + rdev->data_offset;
+			bi->bi_flags = 1 << BIO_UPTODATE;
+			bi->bi_vcnt = 1;
+			bi->bi_max_vecs = 1;
+			bi->bi_idx = 0;
+			bi->bi_io_vec = &sh->dev[i].vec;
+			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
+			bi->bi_io_vec[0].bv_offset = 0;
+			bi->bi_size = STRIPE_SIZE;
+			bi->bi_next = NULL;
+			generic_make_request(bi);
+		} else {
+			PRINTK("skip op %ld on disc %d for sector %llu\n",
+				bi->bi_rw, i, (unsigned long long)sh->sector);
+			clear_bit(R5_LOCKED, &sh->dev[i].flags);
+			set_bit(STRIPE_HANDLE, &sh->state);
+		}
+	}
+}
+
+static inline void raid6_activate_delayed(raid6_conf_t *conf)
+{
+	if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
+		while (!list_empty(&conf->delayed_list)) {
+			struct list_head *l = conf->delayed_list.next;
+			struct stripe_head *sh;
+			sh = list_entry(l, struct stripe_head, lru);
+			list_del_init(l);
+			clear_bit(STRIPE_DELAYED, &sh->state);
+			if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+				atomic_inc(&conf->preread_active_stripes);
+			list_add_tail(&sh->lru, &conf->handle_list);
+		}
+	}
+}
+
+static void unplug_slaves(mddev_t *mddev)
+{
+	raid6_conf_t *conf = mddev_to_conf(mddev);
+	int i;
+
+	rcu_read_lock();
+	for (i=0; i<mddev->raid_disks; i++) {
+		mdk_rdev_t *rdev = conf->disks[i].rdev;
+		if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) {
+			request_queue_t *r_queue = bdev_get_queue(rdev->bdev);
+
+			atomic_inc(&rdev->nr_pending);
+			rcu_read_unlock();
+
+			if (r_queue->unplug_fn)
+				r_queue->unplug_fn(r_queue);
+
+			rdev_dec_pending(rdev, mddev);
+			rcu_read_lock();
+		}
+	}
+	rcu_read_unlock();
+}
+
+static void raid6_unplug_device(request_queue_t *q)
+{
+	mddev_t *mddev = q->queuedata;
+	raid6_conf_t *conf = mddev_to_conf(mddev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&conf->device_lock, flags);
+
+	if (blk_remove_plug(q))
+		raid6_activate_delayed(conf);
+	md_wakeup_thread(mddev->thread);
+
+	spin_unlock_irqrestore(&conf->device_lock, flags);
+
+	unplug_slaves(mddev);
+}
+
+static int raid6_issue_flush(request_queue_t *q, struct gendisk *disk,
+			     sector_t *error_sector)
+{
+	mddev_t *mddev = q->queuedata;
+	raid6_conf_t *conf = mddev_to_conf(mddev);
+	int i, ret = 0;
+
+	rcu_read_lock();
+	for (i=0; i<mddev->raid_disks && ret == 0; i++) {
+		mdk_rdev_t *rdev = conf->disks[i].rdev;
+		if (rdev && !rdev->faulty) {
+			struct block_device *bdev = rdev->bdev;
+			request_queue_t *r_queue = bdev_get_queue(bdev);
+
+			if (!r_queue->issue_flush_fn)
+				ret = -EOPNOTSUPP;
+			else {
+				atomic_inc(&rdev->nr_pending);
+				rcu_read_unlock();
+				ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
+							      error_sector);
+				rdev_dec_pending(rdev, mddev);
+				rcu_read_lock();
+			}
+		}
+	}
+	rcu_read_unlock();
+	return ret;
+}
+
+static inline void raid6_plug_device(raid6_conf_t *conf)
+{
+	spin_lock_irq(&conf->device_lock);
+	blk_plug_device(conf->mddev->queue);
+	spin_unlock_irq(&conf->device_lock);
+}
+
+static int make_request (request_queue_t *q, struct bio * bi)
+{
+	mddev_t *mddev = q->queuedata;
+	raid6_conf_t *conf = mddev_to_conf(mddev);
+	const unsigned int raid_disks = conf->raid_disks;
+	const unsigned int data_disks = raid_disks - 2;
+	unsigned int dd_idx, pd_idx;
+	sector_t new_sector;
+	sector_t logical_sector, last_sector;
+	struct stripe_head *sh;
+
+	if (bio_data_dir(bi)==WRITE) {
+		disk_stat_inc(mddev->gendisk, writes);
+		disk_stat_add(mddev->gendisk, write_sectors, bio_sectors(bi));
+	} else {
+		disk_stat_inc(mddev->gendisk, reads);
+		disk_stat_add(mddev->gendisk, read_sectors, bio_sectors(bi));
+	}
+
+	logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
+	last_sector = bi->bi_sector + (bi->bi_size>>9);
+
+	bi->bi_next = NULL;
+	bi->bi_phys_segments = 1;	/* over-loaded to count active stripes */
+	if ( bio_data_dir(bi) == WRITE )
+		md_write_start(mddev);
+	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
+		DEFINE_WAIT(w);
+
+		new_sector = raid6_compute_sector(logical_sector,
+						  raid_disks, data_disks, &dd_idx, &pd_idx, conf);
+
+		PRINTK("raid6: make_request, sector %llu logical %llu\n",
+		       (unsigned long long)new_sector,
+		       (unsigned long long)logical_sector);
+
+	retry:
+		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
+		sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
+		if (sh) {
+			if (!add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
+				/* Add failed due to overlap.  Flush everything
+				 * and wait a while
+				 */
+				raid6_unplug_device(mddev->queue);
+				release_stripe(sh);
+				schedule();
+				goto retry;
+			}
+			finish_wait(&conf->wait_for_overlap, &w);
+			raid6_plug_device(conf);
+			handle_stripe(sh);
+			release_stripe(sh);
+		} else {
+			/* cannot get stripe for read-ahead, just give-up */
+			clear_bit(BIO_UPTODATE, &bi->bi_flags);
+			finish_wait(&conf->wait_for_overlap, &w);
+			break;
+		}
+
+	}
+	spin_lock_irq(&conf->device_lock);
+	if (--bi->bi_phys_segments == 0) {
+		int bytes = bi->bi_size;
+
+		if ( bio_data_dir(bi) == WRITE )
+			md_write_end(mddev);
+		bi->bi_size = 0;
+		bi->bi_end_io(bi, bytes, 0);
+	}
+	spin_unlock_irq(&conf->device_lock);
+	return 0;
+}
+
+/* FIXME go_faster isn't used */
+static int sync_request (mddev_t *mddev, sector_t sector_nr, int go_faster)
+{
+	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+	struct stripe_head *sh;
+	int sectors_per_chunk = conf->chunk_size >> 9;
+	sector_t x;
+	unsigned long stripe;
+	int chunk_offset;
+	int dd_idx, pd_idx;
+	sector_t first_sector;
+	int raid_disks = conf->raid_disks;
+	int data_disks = raid_disks - 2;
+
+	if (sector_nr >= mddev->size <<1) {
+		/* just being told to finish up .. nothing much to do */
+		unplug_slaves(mddev);
+		return 0;
+	}
+	/* if there are 2 or more failed drives and we are trying
+	 * to resync, then assert that we are finished, because there is
+	 * nothing we can do.
+	 */
+	if (mddev->degraded >= 2 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
+		int rv = (mddev->size << 1) - sector_nr;
+		md_done_sync(mddev, rv, 1);
+		return rv;
+	}
+
+	x = sector_nr;
+	chunk_offset = sector_div(x, sectors_per_chunk);
+	stripe = x;
+	BUG_ON(x != stripe);
+
+	first_sector = raid6_compute_sector((sector_t)stripe*data_disks*sectors_per_chunk
+		+ chunk_offset, raid_disks, data_disks, &dd_idx, &pd_idx, conf);
+	sh = get_active_stripe(conf, sector_nr, pd_idx, 1);
+	if (sh == NULL) {
+		sh = get_active_stripe(conf, sector_nr, pd_idx, 0);
+		/* make sure we don't swamp the stripe cache if someone else
+		 * is trying to get access
+		 */
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		schedule_timeout(1);
+	}
+	spin_lock(&sh->lock);
+	set_bit(STRIPE_SYNCING, &sh->state);
+	clear_bit(STRIPE_INSYNC, &sh->state);
+	spin_unlock(&sh->lock);
+
+	handle_stripe(sh);
+	release_stripe(sh);
+
+	return STRIPE_SECTORS;
+}
+
+/*
+ * This is our raid6 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 raid6d (mddev_t *mddev)
+{
+	struct stripe_head *sh;
+	raid6_conf_t *conf = mddev_to_conf(mddev);
+	int handled;
+
+	PRINTK("+++ raid6d active\n");
+
+	md_check_recovery(mddev);
+	md_handle_safemode(mddev);
+
+	handled = 0;
+	spin_lock_irq(&conf->device_lock);
+	while (1) {
+		struct list_head *first;
+
+		if (list_empty(&conf->handle_list) &&
+		    atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
+		    !blk_queue_plugged(mddev->queue) &&
+		    !list_empty(&conf->delayed_list))
+			raid6_activate_delayed(conf);
+
+		if (list_empty(&conf->handle_list))
+			break;
+
+		first = conf->handle_list.next;
+		sh = list_entry(first, struct stripe_head, lru);
+
+		list_del_init(first);
+		atomic_inc(&sh->count);
+		if (atomic_read(&sh->count)!= 1)
+			BUG();
+		spin_unlock_irq(&conf->device_lock);
+
+		handled++;
+		handle_stripe(sh);
+		release_stripe(sh);
+
+		spin_lock_irq(&conf->device_lock);
+	}
+	PRINTK("%d stripes handled\n", handled);
+
+	spin_unlock_irq(&conf->device_lock);
+
+	unplug_slaves(mddev);
+
+	PRINTK("--- raid6d inactive\n");
+}
+
+static int run (mddev_t *mddev)
+{
+	raid6_conf_t *conf;
+	int raid_disk, memory;
+	mdk_rdev_t *rdev;
+	struct disk_info *disk;
+	struct list_head *tmp;
+
+	if (mddev->level != 6) {
+		PRINTK("raid6: %s: raid level not set to 6 (%d)\n", mdname(mddev), mddev->level);
+		return -EIO;
+	}
+
+	mddev->private = kmalloc (sizeof (raid6_conf_t)
+				  + mddev->raid_disks * sizeof(struct disk_info),
+				  GFP_KERNEL);
+	if ((conf = mddev->private) == NULL)
+		goto abort;
+	memset (conf, 0, sizeof (*conf) + mddev->raid_disks * sizeof(struct disk_info) );
+	conf->mddev = mddev;
+
+	if ((conf->stripe_hashtbl = (struct stripe_head **) __get_free_pages(GFP_ATOMIC, HASH_PAGES_ORDER)) == NULL)
+		goto abort;
+	memset(conf->stripe_hashtbl, 0, HASH_PAGES * PAGE_SIZE);
+
+	spin_lock_init(&conf->device_lock);
+	init_waitqueue_head(&conf->wait_for_stripe);
+	init_waitqueue_head(&conf->wait_for_overlap);
+	INIT_LIST_HEAD(&conf->handle_list);
+	INIT_LIST_HEAD(&conf->delayed_list);
+	INIT_LIST_HEAD(&conf->inactive_list);
+	atomic_set(&conf->active_stripes, 0);
+	atomic_set(&conf->preread_active_stripes, 0);
+
+	mddev->queue->unplug_fn = raid6_unplug_device;
+	mddev->queue->issue_flush_fn = raid6_issue_flush;
+
+	PRINTK("raid6: run(%s) called.\n", mdname(mddev));
+
+	ITERATE_RDEV(mddev,rdev,tmp) {
+		raid_disk = rdev->raid_disk;
+		if (raid_disk >= mddev->raid_disks
+		    || raid_disk < 0)
+			continue;
+		disk = conf->disks + raid_disk;
+
+		disk->rdev = rdev;
+
+		if (rdev->in_sync) {
+			char b[BDEVNAME_SIZE];
+			printk(KERN_INFO "raid6: device %s operational as raid"
+			       " disk %d\n", bdevname(rdev->bdev,b),
+			       raid_disk);
+			conf->working_disks++;
+		}
+	}
+
+	conf->raid_disks = mddev->raid_disks;
+
+	/*
+	 * 0 for a fully functional array, 1 or 2 for a degraded array.
+	 */
+	mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
+	conf->mddev = mddev;
+	conf->chunk_size = mddev->chunk_size;
+	conf->level = mddev->level;
+	conf->algorithm = mddev->layout;
+	conf->max_nr_stripes = NR_STRIPES;
+
+	/* device size must be a multiple of chunk size */
+	mddev->size &= ~(mddev->chunk_size/1024 -1);
+
+	if (conf->raid_disks < 4) {
+		printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
+		       mdname(mddev), conf->raid_disks);
+		goto abort;
+	}
+	if (!conf->chunk_size || conf->chunk_size % 4) {
+		printk(KERN_ERR "raid6: invalid chunk size %d for %s\n",
+		       conf->chunk_size, mdname(mddev));
+		goto abort;
+	}
+	if (conf->algorithm > ALGORITHM_RIGHT_SYMMETRIC) {
+		printk(KERN_ERR
+		       "raid6: unsupported parity algorithm %d for %s\n",
+		       conf->algorithm, mdname(mddev));
+		goto abort;
+	}
+	if (mddev->degraded > 2) {
+		printk(KERN_ERR "raid6: not enough operational devices for %s"
+		       " (%d/%d failed)\n",
+		       mdname(mddev), conf->failed_disks, conf->raid_disks);
+		goto abort;
+	}
+
+#if 0				/* FIX: For now */
+	if (mddev->degraded > 0 &&
+	    mddev->recovery_cp != MaxSector) {
+		printk(KERN_ERR "raid6: cannot start dirty degraded array for %s\n", mdname(mddev));
+		goto abort;
+	}
+#endif
+
+	{
+		mddev->thread = md_register_thread(raid6d, mddev, "%s_raid6");
+		if (!mddev->thread) {
+			printk(KERN_ERR
+			       "raid6: couldn't allocate thread for %s\n",
+			       mdname(mddev));
+			goto abort;
+		}
+	}
+
+	memory = conf->max_nr_stripes * (sizeof(struct stripe_head) +
+		 conf->raid_disks * ((sizeof(struct bio) + PAGE_SIZE))) / 1024;
+	if (grow_stripes(conf, conf->max_nr_stripes)) {
+		printk(KERN_ERR
+		       "raid6: couldn't allocate %dkB for buffers\n", memory);
+		shrink_stripes(conf);
+		md_unregister_thread(mddev->thread);
+		goto abort;
+	} else
+		printk(KERN_INFO "raid6: allocated %dkB for %s\n",
+		       memory, mdname(mddev));
+
+	if (mddev->degraded == 0)
+		printk(KERN_INFO "raid6: raid level %d set %s active with %d out of %d"
+		       " devices, algorithm %d\n", conf->level, mdname(mddev),
+		       mddev->raid_disks-mddev->degraded, mddev->raid_disks,
+		       conf->algorithm);
+	else
+		printk(KERN_ALERT "raid6: raid level %d set %s active with %d"
+		       " out of %d devices, algorithm %d\n", conf->level,
+		       mdname(mddev), mddev->raid_disks - mddev->degraded,
+		       mddev->raid_disks, conf->algorithm);
+
+	print_raid6_conf(conf);
+
+	/* read-ahead size must cover two whole stripes, which is
+	 * 2 * (n-2) * chunksize where 'n' is the number of raid devices
+	 */
+	{
+		int stripe = (mddev->raid_disks-2) * mddev->chunk_size
+			/ PAGE_CACHE_SIZE;
+		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+	}
+
+	/* Ok, everything is just fine now */
+	mddev->array_size =  mddev->size * (mddev->raid_disks - 2);
+	return 0;
+abort:
+	if (conf) {
+		print_raid6_conf(conf);
+		if (conf->stripe_hashtbl)
+			free_pages((unsigned long) conf->stripe_hashtbl,
+							HASH_PAGES_ORDER);
+		kfree(conf);
+	}
+	mddev->private = NULL;
+	printk(KERN_ALERT "raid6: failed to run raid set %s\n", mdname(mddev));
+	return -EIO;
+}
+
+
+
+static int stop (mddev_t *mddev)
+{
+	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+
+	md_unregister_thread(mddev->thread);
+	mddev->thread = NULL;
+	shrink_stripes(conf);
+	free_pages((unsigned long) conf->stripe_hashtbl, HASH_PAGES_ORDER);
+	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
+	kfree(conf);
+	mddev->private = NULL;
+	return 0;
+}
+
+#if RAID6_DUMPSTATE
+static void print_sh (struct seq_file *seq, struct stripe_head *sh)
+{
+	int i;
+
+	seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
+		   (unsigned long long)sh->sector, sh->pd_idx, sh->state);
+	seq_printf(seq, "sh %llu,  count %d.\n",
+		   (unsigned long long)sh->sector, atomic_read(&sh->count));
+	seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
+	for (i = 0; i < sh->raid_conf->raid_disks; i++) {
+		seq_printf(seq, "(cache%d: %p %ld) ",
+			   i, sh->dev[i].page, sh->dev[i].flags);
+	}
+	seq_printf(seq, "\n");
+}
+
+static void printall (struct seq_file *seq, raid6_conf_t *conf)
+{
+	struct stripe_head *sh;
+	int i;
+
+	spin_lock_irq(&conf->device_lock);
+	for (i = 0; i < NR_HASH; i++) {
+		sh = conf->stripe_hashtbl[i];
+		for (; sh; sh = sh->hash_next) {
+			if (sh->raid_conf != conf)
+				continue;
+			print_sh(seq, sh);
+		}
+	}
+	spin_unlock_irq(&conf->device_lock);
+}
+#endif
+
+static void status (struct seq_file *seq, mddev_t *mddev)
+{
+	raid6_conf_t *conf = (raid6_conf_t *) mddev->private;
+	int i;
+
+	seq_printf (seq, " level %d, %dk chunk, algorithm %d", mddev->level, mddev->chunk_size >> 10, mddev->layout);
+	seq_printf (seq, " [%d/%d] [", conf->raid_disks, conf->working_disks);
+	for (i = 0; i < conf->raid_disks; i++)
+ 		seq_printf (seq, "%s",
+			    conf->disks[i].rdev &&
+			    conf->disks[i].rdev->in_sync ? "U" : "_");
+	seq_printf (seq, "]");
+#if RAID6_DUMPSTATE
+	seq_printf (seq, "\n");
+	printall(seq, conf);
+#endif
+}
+
+static void print_raid6_conf (raid6_conf_t *conf)
+{
+	int i;
+	struct disk_info *tmp;
+
+	printk("RAID6 conf printout:\n");
+	if (!conf) {
+		printk("(conf==NULL)\n");
+		return;
+	}
+	printk(" --- rd:%d wd:%d fd:%d\n", conf->raid_disks,
+		 conf->working_disks, conf->failed_disks);
+
+	for (i = 0; i < conf->raid_disks; i++) {
+		char b[BDEVNAME_SIZE];
+		tmp = conf->disks + i;
+		if (tmp->rdev)
+		printk(" disk %d, o:%d, dev:%s\n",
+			i, !tmp->rdev->faulty,
+			bdevname(tmp->rdev->bdev,b));
+	}
+}
+
+static int raid6_spare_active(mddev_t *mddev)
+{
+	int i;
+	raid6_conf_t *conf = mddev->private;
+	struct disk_info *tmp;
+
+	for (i = 0; i < conf->raid_disks; i++) {
+		tmp = conf->disks + i;
+		if (tmp->rdev
+		    && !tmp->rdev->faulty
+		    && !tmp->rdev->in_sync) {
+			mddev->degraded--;
+			conf->failed_disks--;
+			conf->working_disks++;
+			tmp->rdev->in_sync = 1;
+		}
+	}
+	print_raid6_conf(conf);
+	return 0;
+}
+
+static int raid6_remove_disk(mddev_t *mddev, int number)
+{
+	raid6_conf_t *conf = mddev->private;
+	int err = 0;
+	mdk_rdev_t *rdev;
+	struct disk_info *p = conf->disks + number;
+
+	print_raid6_conf(conf);
+	rdev = p->rdev;
+	if (rdev) {
+		if (rdev->in_sync ||
+		    atomic_read(&rdev->nr_pending)) {
+			err = -EBUSY;
+			goto abort;
+		}
+		p->rdev = NULL;
+		synchronize_kernel();
+		if (atomic_read(&rdev->nr_pending)) {
+			/* lost the race, try later */
+			err = -EBUSY;
+			p->rdev = rdev;
+		}
+	}
+
+abort:
+
+	print_raid6_conf(conf);
+	return err;
+}
+
+static int raid6_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
+{
+	raid6_conf_t *conf = mddev->private;
+	int found = 0;
+	int disk;
+	struct disk_info *p;
+
+	if (mddev->degraded > 2)
+		/* no point adding a device */
+		return 0;
+	/*
+	 * find the disk ...
+	 */
+	for (disk=0; disk < mddev->raid_disks; disk++)
+		if ((p=conf->disks + disk)->rdev == NULL) {
+			rdev->in_sync = 0;
+			rdev->raid_disk = disk;
+			found = 1;
+			p->rdev = rdev;
+			break;
+		}
+	print_raid6_conf(conf);
+	return found;
+}
+
+static int raid6_resize(mddev_t *mddev, sector_t sectors)
+{
+	/* no resync is happening, and there is enough space
+	 * on all devices, so we can resize.
+	 * We need to make sure resync covers any new space.
+	 * If the array is shrinking we should possibly wait until
+	 * any io in the removed space completes, but it hardly seems
+	 * worth it.
+	 */
+	sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
+	mddev->array_size = (sectors * (mddev->raid_disks-2))>>1;
+	set_capacity(mddev->gendisk, mddev->array_size << 1);
+	mddev->changed = 1;
+	if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
+		mddev->recovery_cp = mddev->size << 1;
+		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+	}
+	mddev->size = sectors /2;
+	return 0;
+}
+
+static mdk_personality_t raid6_personality=
+{
+	.name		= "raid6",
+	.owner		= THIS_MODULE,
+	.make_request	= make_request,
+	.run		= run,
+	.stop		= stop,
+	.status		= status,
+	.error_handler	= error,
+	.hot_add_disk	= raid6_add_disk,
+	.hot_remove_disk= raid6_remove_disk,
+	.spare_active	= raid6_spare_active,
+	.sync_request	= sync_request,
+	.resize		= raid6_resize,
+};
+
+static int __init raid6_init (void)
+{
+	int e;
+
+	e = raid6_select_algo();
+	if ( e )
+		return e;
+
+	return register_md_personality (RAID6, &raid6_personality);
+}
+
+static void raid6_exit (void)
+{
+	unregister_md_personality (RAID6);
+}
+
+module_init(raid6_init);
+module_exit(raid6_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("md-personality-8"); /* RAID6 */