[PATCH] md: merge raid5 and raid6 code

There is a lot of commonality between raid5.c and raid6main.c.  This patches
merges both into one module called raid456.  This saves a lot of code, and
paves the way for online raid5->raid6 migrations.

There is still duplication, e.g.  between handle_stripe5 and handle_stripe6.
This will probably be cleaned up later.

Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

5 files changed, 1003 insertions, 2527 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index ac25a48..f657aa7 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -104,8 +104,8 @@ config MD_RAID10
 
 	  If unsure, say Y.
 
-config MD_RAID5
-	tristate "RAID-4/RAID-5 mode"
+config MD_RAID456
+	tristate "RAID-4/RAID-5/RAID-6 mode"
 	depends on BLK_DEV_MD
 	---help---
 	  A RAID-5 set of N drives with a capacity of C MB per drive provides
@@ -116,14 +116,22 @@ config MD_RAID5
 	  while a RAID-5 set distributes the parity across the drives in one
 	  of the available parity distribution methods.
 
+	  A RAID-6 set of N drives with a capacity of C MB per drive
+	  provides the capacity of C * (N - 2) MB, and protects
+	  against a failure of any two drives. For a given sector
+	  (row) number, (N - 2) drives contain data sectors, and two
+	  drives contains two independent redundancy syndromes.  Like
+	  RAID-5, RAID-6 distributes the syndromes across the drives
+	  in one of the available parity distribution methods.
+
 	  Information about Software RAID on Linux is contained in the
 	  Software-RAID mini-HOWTO, available from
 	  <http://www.tldp.org/docs.html#howto>. There you will also
 	  learn where to get the supporting user space utilities raidtools.
 
-	  If you want to use such a RAID-4/RAID-5 set, say Y.  To
+	  If you want to use such a RAID-4/RAID-5/RAID-6 set, say Y.  To
 	  compile this code as a module, choose M here: the module
-	  will be called raid5.
+	  will be called raid456.
 
 	  If unsure, say Y.
 
@@ -154,28 +162,6 @@ config MD_RAID5_RESHAPE
 	  There should be enough spares already present to make the new
 	  array workable.
 
-config MD_RAID6
-	tristate "RAID-6 mode"
-	depends on BLK_DEV_MD
-	---help---
-	  A RAID-6 set of N drives with a capacity of C MB per drive
-	  provides the capacity of C * (N - 2) MB, and protects
-	  against a failure of any two drives. For a given sector
-	  (row) number, (N - 2) drives contain data sectors, and two
-	  drives contains two independent redundancy syndromes.  Like
-	  RAID-5, RAID-6 distributes the syndromes across the drives
-	  in one of the available parity distribution methods.
-
-	  RAID-6 requires mdadm-1.5.0 or later, available at:
-
-	  ftp://ftp.kernel.org/pub/linux/utils/raid/mdadm/
-
-	  If you want to use such a RAID-6 set, say Y.  To compile
-	  this code as a module, choose M here: the module will be
-	  called raid6.
-
-	  If unsure, say Y.
-
 config MD_MULTIPATH
 	tristate "Multipath I/O support"
 	depends on BLK_DEV_MD
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index d3efedf..34957a6 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -8,7 +8,7 @@ dm-multipath-objs := dm-hw-handler.o dm-path-selector.o dm-mpath.o
 dm-snapshot-objs := dm-snap.o dm-exception-store.o
 dm-mirror-objs	:= dm-log.o dm-raid1.o
 md-mod-objs     := md.o bitmap.o
-raid6-objs	:= raid6main.o raid6algos.o raid6recov.o raid6tables.o \
+raid456-objs	:= raid5.o raid6algos.o raid6recov.o raid6tables.o \
 		   raid6int1.o raid6int2.o raid6int4.o \
 		   raid6int8.o raid6int16.o raid6int32.o \
 		   raid6altivec1.o raid6altivec2.o raid6altivec4.o \
@@ -25,8 +25,7 @@ obj-$(CONFIG_MD_LINEAR)		+= linear.o
 obj-$(CONFIG_MD_RAID0)		+= raid0.o
 obj-$(CONFIG_MD_RAID1)		+= raid1.o
 obj-$(CONFIG_MD_RAID10)		+= raid10.o
-obj-$(CONFIG_MD_RAID5)		+= raid5.o xor.o
-obj-$(CONFIG_MD_RAID6)		+= raid6.o xor.o
+obj-$(CONFIG_MD_RAID456)	+= raid456.o xor.o
 obj-$(CONFIG_MD_MULTIPATH)	+= multipath.o
 obj-$(CONFIG_MD_FAULTY)		+= faulty.o
 obj-$(CONFIG_BLK_DEV_MD)	+= md-mod.o
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 122e64e..9ba7307 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2,8 +2,11 @@
  * 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-5 management functions.
+ * 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
@@ -19,11 +22,11 @@
 #include <linux/config.h>
 #include <linux/module.h>
 #include <linux/slab.h>
-#include <linux/raid/raid5.h>
 #include <linux/highmem.h>
 #include <linux/bitops.h>
 #include <linux/kthread.h>
 #include <asm/atomic.h>
+#include "raid6.h"
 
 #include <linux/raid/bitmap.h>
 
@@ -68,6 +71,16 @@
 #define __inline__
 #endif
 
+#if !RAID6_USE_EMPTY_ZERO_PAGE
+/* In .bss so it's zeroed */
+const char raid6_empty_zero_page[PAGE_SIZE] __attribute__((aligned(256)));
+#endif
+
+static inline int raid6_next_disk(int disk, int raid_disks)
+{
+	disk++;
+	return (disk < raid_disks) ? disk : 0;
+}
 static void print_raid5_conf (raid5_conf_t *conf);
 
 static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
@@ -104,7 +117,7 @@ static void release_stripe(struct stripe_head *sh)
 {
 	raid5_conf_t *conf = sh->raid_conf;
 	unsigned long flags;
-	
+
 	spin_lock_irqsave(&conf->device_lock, flags);
 	__release_stripe(conf, sh);
 	spin_unlock_irqrestore(&conf->device_lock, flags);
@@ -117,7 +130,7 @@ static inline void remove_hash(struct stripe_head *sh)
 	hlist_del_init(&sh->hash);
 }
 
-static void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
+static inline void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
 {
 	struct hlist_head *hp = stripe_hash(conf, sh->sector);
 
@@ -190,7 +203,7 @@ static void init_stripe(struct stripe_head *sh, sector_t sector, int pd_idx, int
 		(unsigned long long)sh->sector);
 
 	remove_hash(sh);
-	
+
 	sh->sector = sector;
 	sh->pd_idx = pd_idx;
 	sh->state = 0;
@@ -269,8 +282,9 @@ static struct stripe_head *get_active_stripe(raid5_conf_t *conf, sector_t sector
 			} else {
 				if (!test_bit(STRIPE_HANDLE, &sh->state))
 					atomic_inc(&conf->active_stripes);
-				if (!list_empty(&sh->lru))
-					list_del_init(&sh->lru);
+				if (list_empty(&sh->lru))
+					BUG();
+				list_del_init(&sh->lru);
 			}
 		}
 	} while (sh == NULL);
@@ -321,10 +335,9 @@ static int grow_stripes(raid5_conf_t *conf, int num)
 		return 1;
 	conf->slab_cache = sc;
 	conf->pool_size = devs;
-	while (num--) {
+	while (num--)
 		if (!grow_one_stripe(conf))
 			return 1;
-	}
 	return 0;
 }
 
@@ -631,8 +644,7 @@ static void raid5_build_block (struct stripe_head *sh, int i)
 	dev->req.bi_private = sh;
 
 	dev->flags = 0;
-	if (i != sh->pd_idx)
-		dev->sector = compute_blocknr(sh, i);
+	dev->sector = compute_blocknr(sh, i);
 }
 
 static void error(mddev_t *mddev, mdk_rdev_t *rdev)
@@ -659,7 +671,7 @@ static void error(mddev_t *mddev, mdk_rdev_t *rdev)
 			" Operation continuing on %d devices\n",
 			bdevname(rdev->bdev,b), conf->working_disks);
 	}
-}	
+}
 
 /*
  * Input: a 'big' sector number,
@@ -697,9 +709,12 @@ static sector_t raid5_compute_sector(sector_t r_sector, unsigned int raid_disks,
 	/*
 	 * Select the parity disk based on the user selected algorithm.
 	 */
-	if (conf->level == 4)
+	switch(conf->level) {
+	case 4:
 		*pd_idx = data_disks;
-	else switch (conf->algorithm) {
+		break;
+	case 5:
+		switch (conf->algorithm) {
 		case ALGORITHM_LEFT_ASYMMETRIC:
 			*pd_idx = data_disks - stripe % raid_disks;
 			if (*dd_idx >= *pd_idx)
@@ -721,6 +736,39 @@ static sector_t raid5_compute_sector(sector_t r_sector, unsigned int raid_disks,
 		default:
 			printk(KERN_ERR "raid5: unsupported algorithm %d\n",
 				conf->algorithm);
+		}
+		break;
+	case 6:
+
+		/**** FIX THIS ****/
+		switch (conf->algorithm) {
+		case ALGORITHM_LEFT_ASYMMETRIC:
+			*pd_idx = raid_disks - 1 - (stripe % raid_disks);
+			if (*pd_idx == raid_disks-1)
+				(*dd_idx)++; 	/* Q D D D P */
+			else if (*dd_idx >= *pd_idx)
+				(*dd_idx) += 2; /* D D P Q D */
+			break;
+		case ALGORITHM_RIGHT_ASYMMETRIC:
+			*pd_idx = stripe % raid_disks;
+			if (*pd_idx == raid_disks-1)
+				(*dd_idx)++; 	/* Q D D D P */
+			else if (*dd_idx >= *pd_idx)
+				(*dd_idx) += 2; /* D D P Q D */
+			break;
+		case ALGORITHM_LEFT_SYMMETRIC:
+			*pd_idx = raid_disks - 1 - (stripe % raid_disks);
+			*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
+			break;
+		case ALGORITHM_RIGHT_SYMMETRIC:
+			*pd_idx = stripe % raid_disks;
+			*dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
+			break;
+		default:
+			printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
+				conf->algorithm);
+		}
+		break;
 	}
 
 	/*
@@ -742,12 +790,17 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
 	int chunk_number, dummy1, dummy2, dd_idx = i;
 	sector_t r_sector;
 
+
 	chunk_offset = sector_div(new_sector, sectors_per_chunk);
 	stripe = new_sector;
 	BUG_ON(new_sector != stripe);
 
-	
-	switch (conf->algorithm) {
+	if (i == sh->pd_idx)
+		return 0;
+	switch(conf->level) {
+	case 4: break;
+	case 5:
+		switch (conf->algorithm) {
 		case ALGORITHM_LEFT_ASYMMETRIC:
 		case ALGORITHM_RIGHT_ASYMMETRIC:
 			if (i > sh->pd_idx)
@@ -761,7 +814,37 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
 			break;
 		default:
 			printk(KERN_ERR "raid5: unsupported algorithm %d\n",
+			       conf->algorithm);
+		}
+		break;
+	case 6:
+		data_disks = raid_disks - 2;
+		if (i == raid6_next_disk(sh->pd_idx, raid_disks))
+			return 0; /* It is the Q disk */
+		switch (conf->algorithm) {
+		case ALGORITHM_LEFT_ASYMMETRIC:
+		case ALGORITHM_RIGHT_ASYMMETRIC:
+		  	if (sh->pd_idx == raid_disks-1)
+				i--; 	/* Q D D D P */
+			else if (i > sh->pd_idx)
+				i -= 2; /* D D P Q D */
+			break;
+		case ALGORITHM_LEFT_SYMMETRIC:
+		case ALGORITHM_RIGHT_SYMMETRIC:
+			if (sh->pd_idx == raid_disks-1)
+				i--; /* Q D D D P */
+			else {
+				/* D D P Q D */
+				if (i < sh->pd_idx)
+					i += raid_disks;
+				i -= (sh->pd_idx + 2);
+			}
+			break;
+		default:
+			printk (KERN_CRIT "raid6: unsupported algorithm %d\n",
 				conf->algorithm);
+		}
+		break;
 	}
 
 	chunk_number = stripe * data_disks + i;
@@ -778,10 +861,11 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
 
 
 /*
- * Copy data between a page in the stripe cache, and a bio.
- * There are no alignment or size guarantees between the page or the
- * bio except that there is some overlap.
- * All iovecs in the bio must be considered.
+ * 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,
@@ -810,7 +894,7 @@ static void copy_data(int frombio, struct bio *bio,
 		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)
@@ -862,14 +946,14 @@ static void compute_block(struct stripe_head *sh, int dd_idx)
 	set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
 }
 
-static void compute_parity(struct stripe_head *sh, int method)
+static void compute_parity5(struct stripe_head *sh, int method)
 {
 	raid5_conf_t *conf = sh->raid_conf;
 	int i, pd_idx = sh->pd_idx, disks = sh->disks, count;
 	void *ptr[MAX_XOR_BLOCKS];
 	struct bio *chosen;
 
-	PRINTK("compute_parity, stripe %llu, method %d\n",
+	PRINTK("compute_parity5, stripe %llu, method %d\n",
 		(unsigned long long)sh->sector, method);
 
 	count = 1;
@@ -956,9 +1040,195 @@ static void compute_parity(struct stripe_head *sh, int method)
 		clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
 }
 
+static void compute_parity6(struct stripe_head *sh, int method)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = conf->raid_disks, count;
+	struct bio *chosen;
+	/**** FIX THIS: This could be very bad if disks is close to 256 ****/
+	void *ptrs[disks];
+
+	qd_idx = raid6_next_disk(pd_idx, disks);
+	d0_idx = raid6_next_disk(qd_idx, disks);
+
+	PRINTK("compute_parity, stripe %llu, method %d\n",
+		(unsigned long long)sh->sector, method);
+
+	switch(method) {
+	case READ_MODIFY_WRITE:
+		BUG();		/* READ_MODIFY_WRITE N/A for RAID-6 */
+	case RECONSTRUCT_WRITE:
+		for (i= disks; i-- ;)
+			if ( i != pd_idx && i != qd_idx && sh->dev[i].towrite ) {
+				chosen = sh->dev[i].towrite;
+				sh->dev[i].towrite = NULL;
+
+				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+					wake_up(&conf->wait_for_overlap);
+
+				if (sh->dev[i].written) BUG();
+				sh->dev[i].written = chosen;
+			}
+		break;
+	case CHECK_PARITY:
+		BUG();		/* Not implemented yet */
+	}
+
+	for (i = disks; i--;)
+		if (sh->dev[i].written) {
+			sector_t sector = sh->dev[i].sector;
+			struct bio *wbi = sh->dev[i].written;
+			while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
+				copy_data(1, wbi, sh->dev[i].page, sector);
+				wbi = r5_next_bio(wbi, sector);
+			}
+
+			set_bit(R5_LOCKED, &sh->dev[i].flags);
+			set_bit(R5_UPTODATE, &sh->dev[i].flags);
+		}
+
+//	switch(method) {
+//	case RECONSTRUCT_WRITE:
+//	case CHECK_PARITY:
+//	case UPDATE_PARITY:
+		/* Note that unlike RAID-5, the ordering of the disks matters greatly. */
+		/* FIX: Is this ordering of drives even remotely optimal? */
+		count = 0;
+		i = d0_idx;
+		do {
+			ptrs[count++] = page_address(sh->dev[i].page);
+			if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				printk("block %d/%d not uptodate on parity calc\n", i,count);
+			i = raid6_next_disk(i, disks);
+		} while ( i != d0_idx );
+//		break;
+//	}
+
+	raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);
+
+	switch(method) {
+	case RECONSTRUCT_WRITE:
+		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
+		set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
+		set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
+		break;
+	case UPDATE_PARITY:
+		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
+		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
+		break;
+	}
+}
+
+
+/* Compute one missing block */
+static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, count, disks = conf->raid_disks;
+	void *ptr[MAX_XOR_BLOCKS], *p;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+
+	PRINTK("compute_block_1, stripe %llu, idx %d\n",
+		(unsigned long long)sh->sector, dd_idx);
+
+	if ( dd_idx == qd_idx ) {
+		/* We're actually computing the Q drive */
+		compute_parity6(sh, UPDATE_PARITY);
+	} else {
+		ptr[0] = page_address(sh->dev[dd_idx].page);
+		if (!nozero) memset(ptr[0], 0, STRIPE_SIZE);
+		count = 1;
+		for (i = disks ; i--; ) {
+			if (i == dd_idx || i == qd_idx)
+				continue;
+			p = page_address(sh->dev[i].page);
+			if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				ptr[count++] = p;
+			else
+				printk("compute_block() %d, stripe %llu, %d"
+				       " not present\n", dd_idx,
+				       (unsigned long long)sh->sector, i);
+
+			check_xor();
+		}
+		if (count != 1)
+			xor_block(count, STRIPE_SIZE, ptr);
+		if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
+		else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
+	}
+}
+
+/* Compute two missing blocks */
+static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int i, count, disks = conf->raid_disks;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+	int d0_idx = raid6_next_disk(qd_idx, disks);
+	int faila, failb;
+
+	/* faila and failb are disk numbers relative to d0_idx */
+	/* pd_idx become disks-2 and qd_idx become disks-1 */
+	faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
+	failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;
+
+	BUG_ON(faila == failb);
+	if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }
+
+	PRINTK("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
+	       (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);
+
+	if ( failb == disks-1 ) {
+		/* Q disk is one of the missing disks */
+		if ( faila == disks-2 ) {
+			/* Missing P+Q, just recompute */
+			compute_parity6(sh, UPDATE_PARITY);
+			return;
+		} else {
+			/* We're missing D+Q; recompute D from P */
+			compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1, 0);
+			compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
+			return;
+		}
+	}
+
+	/* We're missing D+P or D+D; build pointer table */
+	{
+		/**** FIX THIS: This could be very bad if disks is close to 256 ****/
+		void *ptrs[disks];
+
+		count = 0;
+		i = d0_idx;
+		do {
+			ptrs[count++] = page_address(sh->dev[i].page);
+			i = raid6_next_disk(i, disks);
+			if (i != dd_idx1 && i != dd_idx2 &&
+			    !test_bit(R5_UPTODATE, &sh->dev[i].flags))
+				printk("compute_2 with missing block %d/%d\n", count, i);
+		} while ( i != d0_idx );
+
+		if ( failb == disks-2 ) {
+			/* We're missing D+P. */
+			raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
+		} else {
+			/* We're missing D+D. */
+			raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
+		}
+
+		/* Both the above update both missing blocks */
+		set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
+		set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
+	}
+}
+
+
+
 /*
  * Each stripe/dev can have one or more bion attached.
- * toread/towrite point to the first in a chain. 
+ * 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)
@@ -1031,6 +1301,13 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
 
 static void end_reshape(raid5_conf_t *conf);
 
+static int page_is_zero(struct page *p)
+{
+	char *a = page_address(p);
+	return ((*(u32*)a) == 0 &&
+		memcmp(a, a+4, STRIPE_SIZE-4)==0);
+}
+
 static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int disks)
 {
 	int sectors_per_chunk = conf->chunk_size >> 9;
@@ -1062,7 +1339,7 @@ static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int disks)
  *
  */
  
-static void handle_stripe(struct stripe_head *sh)
+static void handle_stripe5(struct stripe_head *sh)
 {
 	raid5_conf_t *conf = sh->raid_conf;
 	int disks = sh->disks;
@@ -1394,7 +1671,7 @@ static void handle_stripe(struct stripe_head *sh)
 		if (locked == 0 && (rcw == 0 ||rmw == 0) &&
 		    !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
 			PRINTK("Computing parity...\n");
-			compute_parity(sh, rcw==0 ? RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
+			compute_parity5(sh, rcw==0 ? RECONSTRUCT_WRITE : READ_MODIFY_WRITE);
 			/* now every locked buffer is ready to be written */
 			for (i=disks; i--;)
 				if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
@@ -1421,13 +1698,10 @@ static void handle_stripe(struct stripe_head *sh)
 	    !test_bit(STRIPE_INSYNC, &sh->state)) {
 		set_bit(STRIPE_HANDLE, &sh->state);
 		if (failed == 0) {
-			char *pagea;
 			BUG_ON(uptodate != disks);
-			compute_parity(sh, CHECK_PARITY);
+			compute_parity5(sh, CHECK_PARITY);
 			uptodate--;
-			pagea = page_address(sh->dev[sh->pd_idx].page);
-			if ((*(u32*)pagea) == 0 &&
-			    !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
+			if (page_is_zero(sh->dev[sh->pd_idx].page)) {
 				/* parity is correct (on disc, not in buffer any more) */
 				set_bit(STRIPE_INSYNC, &sh->state);
 			} else {
@@ -1487,7 +1761,7 @@ static void handle_stripe(struct stripe_head *sh)
 		/* Need to write out all blocks after computing parity */
 		sh->disks = conf->raid_disks;
 		sh->pd_idx = stripe_to_pdidx(sh->sector, conf, conf->raid_disks);
-		compute_parity(sh, RECONSTRUCT_WRITE);
+		compute_parity5(sh, RECONSTRUCT_WRITE);
 		for (i= conf->raid_disks; i--;) {
 			set_bit(R5_LOCKED, &sh->dev[i].flags);
 			locked++;
@@ -1615,6 +1889,569 @@ static void handle_stripe(struct stripe_head *sh)
 	}
 }
 
+static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
+{
+	raid6_conf_t *conf = sh->raid_conf;
+	int disks = conf->raid_disks;
+	struct bio *return_bi= NULL;
+	struct bio *bi;
+	int i;
+	int syncing;
+	int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
+	int non_overwrite = 0;
+	int failed_num[2] = {0, 0};
+	struct r5dev *dev, *pdev, *qdev;
+	int pd_idx = sh->pd_idx;
+	int qd_idx = raid6_next_disk(pd_idx, disks);
+	int p_failed, q_failed;
+
+	PRINTK("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d, qd_idx=%d\n",
+	       (unsigned long long)sh->sector, sh->state, atomic_read(&sh->count),
+	       pd_idx, qd_idx);
+
+	spin_lock(&sh->lock);
+	clear_bit(STRIPE_HANDLE, &sh->state);
+	clear_bit(STRIPE_DELAYED, &sh->state);
+
+	syncing = test_bit(STRIPE_SYNCING, &sh->state);
+	/* Now to look around and see what can be done */
+
+	rcu_read_lock();
+	for (i=disks; i--; ) {
+		mdk_rdev_t *rdev;
+		dev = &sh->dev[i];
+		clear_bit(R5_Insync, &dev->flags);
+
+		PRINTK("check %d: state 0x%lx read %p write %p written %p\n",
+			i, dev->flags, dev->toread, dev->towrite, dev->written);
+		/* maybe we can reply to a read */
+		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
+			struct bio *rbi, *rbi2;
+			PRINTK("Return read for disc %d\n", i);
+			spin_lock_irq(&conf->device_lock);
+			rbi = dev->toread;
+			dev->toread = NULL;
+			if (test_and_clear_bit(R5_Overlap, &dev->flags))
+				wake_up(&conf->wait_for_overlap);
+			spin_unlock_irq(&conf->device_lock);
+			while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
+				copy_data(0, rbi, dev->page, dev->sector);
+				rbi2 = r5_next_bio(rbi, dev->sector);
+				spin_lock_irq(&conf->device_lock);
+				if (--rbi->bi_phys_segments == 0) {
+					rbi->bi_next = return_bi;
+					return_bi = rbi;
+				}
+				spin_unlock_irq(&conf->device_lock);
+				rbi = rbi2;
+			}
+		}
+
+		/* now count some things */
+		if (test_bit(R5_LOCKED, &dev->flags)) locked++;
+		if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;
+
+
+		if (dev->toread) to_read++;
+		if (dev->towrite) {
+			to_write++;
+			if (!test_bit(R5_OVERWRITE, &dev->flags))
+				non_overwrite++;
+		}
+		if (dev->written) written++;
+		rdev = rcu_dereference(conf->disks[i].rdev);
+		if (!rdev || !test_bit(In_sync, &rdev->flags)) {
+			/* The ReadError flag will just be confusing now */
+			clear_bit(R5_ReadError, &dev->flags);
+			clear_bit(R5_ReWrite, &dev->flags);
+		}
+		if (!rdev || !test_bit(In_sync, &rdev->flags)
+		    || test_bit(R5_ReadError, &dev->flags)) {
+			if ( failed < 2 )
+				failed_num[failed] = i;
+			failed++;
+		} else
+			set_bit(R5_Insync, &dev->flags);
+	}
+	rcu_read_unlock();
+	PRINTK("locked=%d uptodate=%d to_read=%d"
+	       " to_write=%d failed=%d failed_num=%d,%d\n",
+	       locked, uptodate, to_read, to_write, failed,
+	       failed_num[0], failed_num[1]);
+	/* check if the array has lost >2 devices and, if so, some requests might
+	 * need to be failed
+	 */
+	if (failed > 2 && to_read+to_write+written) {
+		for (i=disks; i--; ) {
+			int bitmap_end = 0;
+
+			if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
+				mdk_rdev_t *rdev;
+				rcu_read_lock();
+				rdev = rcu_dereference(conf->disks[i].rdev);
+				if (rdev && test_bit(In_sync, &rdev->flags))
+					/* multiple read failures in one stripe */
+					md_error(conf->mddev, rdev);
+				rcu_read_unlock();
+			}
+
+			spin_lock_irq(&conf->device_lock);
+			/* fail all writes first */
+			bi = sh->dev[i].towrite;
+			sh->dev[i].towrite = NULL;
+			if (bi) { to_write--; bitmap_end = 1; }
+
+			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+				wake_up(&conf->wait_for_overlap);
+
+			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
+				struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
+				clear_bit(BIO_UPTODATE, &bi->bi_flags);
+				if (--bi->bi_phys_segments == 0) {
+					md_write_end(conf->mddev);
+					bi->bi_next = return_bi;
+					return_bi = bi;
+				}
+				bi = nextbi;
+			}
+			/* and fail all 'written' */
+			bi = sh->dev[i].written;
+			sh->dev[i].written = NULL;
+			if (bi) bitmap_end = 1;
+			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS) {
+				struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
+				clear_bit(BIO_UPTODATE, &bi->bi_flags);
+				if (--bi->bi_phys_segments == 0) {
+					md_write_end(conf->mddev);
+					bi->bi_next = return_bi;
+					return_bi = bi;
+				}
+				bi = bi2;
+			}
+
+			/* fail any reads if this device is non-operational */
+			if (!test_bit(R5_Insync, &sh->dev[i].flags) ||
+			    test_bit(R5_ReadError, &sh->dev[i].flags)) {
+				bi = sh->dev[i].toread;
+				sh->dev[i].toread = NULL;
+				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
+					wake_up(&conf->wait_for_overlap);
+				if (bi) to_read--;
+				while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
+					struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
+					clear_bit(BIO_UPTODATE, &bi->bi_flags);
+					if (--bi->bi_phys_segments == 0) {
+						bi->bi_next = return_bi;
+						return_bi = bi;
+					}
+					bi = nextbi;
+				}
+			}
+			spin_unlock_irq(&conf->device_lock);
+			if (bitmap_end)
+				bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+						STRIPE_SECTORS, 0, 0);
+		}
+	}
+	if (failed > 2 && syncing) {
+		md_done_sync(conf->mddev, STRIPE_SECTORS,0);
+		clear_bit(STRIPE_SYNCING, &sh->state);
+		syncing = 0;
+	}
+
+	/*
+	 * might be able to return some write requests if the parity blocks
+	 * are safe, or on a failed drive
+	 */
+	pdev = &sh->dev[pd_idx];
+	p_failed = (failed >= 1 && failed_num[0] == pd_idx)
+		|| (failed >= 2 && failed_num[1] == pd_idx);
+	qdev = &sh->dev[qd_idx];
+	q_failed = (failed >= 1 && failed_num[0] == qd_idx)
+		|| (failed >= 2 && failed_num[1] == qd_idx);
+
+	if ( written &&
+	     ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
+			     && !test_bit(R5_LOCKED, &pdev->flags)
+			     && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
+	     ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
+			     && !test_bit(R5_LOCKED, &qdev->flags)
+			     && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
+		/* any written block on an uptodate or failed drive can be
+		 * returned.  Note that if we 'wrote' to a failed drive,
+		 * it will be UPTODATE, but never LOCKED, so we don't need
+		 * to test 'failed' directly.
+		 */
+		for (i=disks; i--; )
+			if (sh->dev[i].written) {
+				dev = &sh->dev[i];
+				if (!test_bit(R5_LOCKED, &dev->flags) &&
+				    test_bit(R5_UPTODATE, &dev->flags) ) {
+					/* We can return any write requests */
+					int bitmap_end = 0;
+					struct bio *wbi, *wbi2;
+					PRINTK("Return write for stripe %llu disc %d\n",
+					       (unsigned long long)sh->sector, i);
+					spin_lock_irq(&conf->device_lock);
+					wbi = dev->written;
+					dev->written = NULL;
+					while (wbi && wbi->bi_sector < dev->sector + STRIPE_SECTORS) {
+						wbi2 = r5_next_bio(wbi, dev->sector);
+						if (--wbi->bi_phys_segments == 0) {
+							md_write_end(conf->mddev);
+							wbi->bi_next = return_bi;
+							return_bi = wbi;
+						}
+						wbi = wbi2;
+					}
+					if (dev->towrite == NULL)
+						bitmap_end = 1;
+					spin_unlock_irq(&conf->device_lock);
+					if (bitmap_end)
+						bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+								STRIPE_SECTORS,
+								!test_bit(STRIPE_DEGRADED, &sh->state), 0);
+				}
+			}
+	}
+
+	/* Now we might consider reading some blocks, either to check/generate
+	 * parity, or to satisfy requests
+	 * or to load a block that is being partially written.
+	 */
+	if (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
+		for (i=disks; i--;) {
+			dev = &sh->dev[i];
+			if (!test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
+			    (dev->toread ||
+			     (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
+			     syncing ||
+			     (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
+			     (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
+				    )
+				) {
+				/* we would like to get this block, possibly
+				 * by computing it, but we might not be able to
+				 */
+				if (uptodate == disks-1) {
+					PRINTK("Computing stripe %llu block %d\n",
+					       (unsigned long long)sh->sector, i);
+					compute_block_1(sh, i, 0);
+					uptodate++;
+				} else if ( uptodate == disks-2 && failed >= 2 ) {
+					/* Computing 2-failure is *very* expensive; only do it if failed >= 2 */
+					int other;
+					for (other=disks; other--;) {
+						if ( other == i )
+							continue;
+						if ( !test_bit(R5_UPTODATE, &sh->dev[other].flags) )
+							break;
+					}
+					BUG_ON(other < 0);
+					PRINTK("Computing stripe %llu blocks %d,%d\n",
+					       (unsigned long long)sh->sector, i, other);
+					compute_block_2(sh, i, other);
+					uptodate += 2;
+				} else if (test_bit(R5_Insync, &dev->flags)) {
+					set_bit(R5_LOCKED, &dev->flags);
+					set_bit(R5_Wantread, &dev->flags);
+#if 0
+					/* if I am just reading this block and we don't have
+					   a failed drive, or any pending writes then sidestep the cache */
+					if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
+					    ! syncing && !failed && !to_write) {
+						sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
+						sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
+					}
+#endif
+					locked++;
+					PRINTK("Reading block %d (sync=%d)\n",
+						i, syncing);
+				}
+			}
+		}
+		set_bit(STRIPE_HANDLE, &sh->state);
+	}
+
+	/* now to consider writing and what else, if anything should be read */
+	if (to_write) {
+		int rcw=0, must_compute=0;
+		for (i=disks ; i--;) {
+			dev = &sh->dev[i];
+			/* Would I have to read this buffer for reconstruct_write */
+			if (!test_bit(R5_OVERWRITE, &dev->flags)
+			    && i != pd_idx && i != qd_idx
+			    && (!test_bit(R5_LOCKED, &dev->flags)
+#if 0
+				|| sh->bh_page[i] != bh->b_page
+#endif
+				    ) &&
+			    !test_bit(R5_UPTODATE, &dev->flags)) {
+				if (test_bit(R5_Insync, &dev->flags)) rcw++;
+				else {
+					PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
+					must_compute++;
+				}
+			}
+		}
+		PRINTK("for sector %llu, rcw=%d, must_compute=%d\n",
+		       (unsigned long long)sh->sector, rcw, must_compute);
+		set_bit(STRIPE_HANDLE, &sh->state);
+
+		if (rcw > 0)
+			/* want reconstruct write, but need to get some data */
+			for (i=disks; i--;) {
+				dev = &sh->dev[i];
+				if (!test_bit(R5_OVERWRITE, &dev->flags)
+				    && !(failed == 0 && (i == pd_idx || i == qd_idx))
+				    && !test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
+				    test_bit(R5_Insync, &dev->flags)) {
+					if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+					{
+						PRINTK("Read_old stripe %llu block %d for Reconstruct\n",
+						       (unsigned long long)sh->sector, i);
+						set_bit(R5_LOCKED, &dev->flags);
+						set_bit(R5_Wantread, &dev->flags);
+						locked++;
+					} else {
+						PRINTK("Request delayed stripe %llu block %d for Reconstruct\n",
+						       (unsigned long long)sh->sector, i);
+						set_bit(STRIPE_DELAYED, &sh->state);
+						set_bit(STRIPE_HANDLE, &sh->state);
+					}
+				}
+			}
+		/* now if nothing is locked, and if we have enough data, we can start a write request */
+		if (locked == 0 && rcw == 0 &&
+		    !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
+			if ( must_compute > 0 ) {
+				/* We have failed blocks and need to compute them */
+				switch ( failed ) {
+				case 0:	BUG();
+				case 1: compute_block_1(sh, failed_num[0], 0); break;
+				case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
+				default: BUG();	/* This request should have been failed? */
+				}
+			}
+
+			PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
+			compute_parity6(sh, RECONSTRUCT_WRITE);
+			/* now every locked buffer is ready to be written */
+			for (i=disks; i--;)
+				if (test_bit(R5_LOCKED, &sh->dev[i].flags)) {
+					PRINTK("Writing stripe %llu block %d\n",
+					       (unsigned long long)sh->sector, i);
+					locked++;
+					set_bit(R5_Wantwrite, &sh->dev[i].flags);
+				}
+			/* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
+			set_bit(STRIPE_INSYNC, &sh->state);
+
+			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
+				atomic_dec(&conf->preread_active_stripes);
+				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
+					md_wakeup_thread(conf->mddev->thread);
+			}
+		}
+	}
+
+	/* maybe we need to check and possibly fix the parity for this stripe
+	 * Any reads will already have been scheduled, so we just see if enough data
+	 * is available
+	 */
+	if (syncing && locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state)) {
+		int update_p = 0, update_q = 0;
+		struct r5dev *dev;
+
+		set_bit(STRIPE_HANDLE, &sh->state);
+
+		BUG_ON(failed>2);
+		BUG_ON(uptodate < disks);
+		/* Want to check and possibly repair P and Q.
+		 * However there could be one 'failed' device, in which
+		 * case we can only check one of them, possibly using the
+		 * other to generate missing data
+		 */
+
+		/* If !tmp_page, we cannot do the calculations,
+		 * but as we have set STRIPE_HANDLE, we will soon be called
+		 * by stripe_handle with a tmp_page - just wait until then.
+		 */
+		if (tmp_page) {
+			if (failed == q_failed) {
+				/* The only possible failed device holds 'Q', so it makes
+				 * sense to check P (If anything else were failed, we would
+				 * have used P to recreate it).
+				 */
+				compute_block_1(sh, pd_idx, 1);
+				if (!page_is_zero(sh->dev[pd_idx].page)) {
+					compute_block_1(sh,pd_idx,0);
+					update_p = 1;
+				}
+			}
+			if (!q_failed && failed < 2) {
+				/* q is not failed, and we didn't use it to generate
+				 * anything, so it makes sense to check it
+				 */
+				memcpy(page_address(tmp_page),
+				       page_address(sh->dev[qd_idx].page),
+				       STRIPE_SIZE);
+				compute_parity6(sh, UPDATE_PARITY);
+				if (memcmp(page_address(tmp_page),
+					   page_address(sh->dev[qd_idx].page),
+					   STRIPE_SIZE)!= 0) {
+					clear_bit(STRIPE_INSYNC, &sh->state);
+					update_q = 1;
+				}
+			}
+			if (update_p || update_q) {
+				conf->mddev->resync_mismatches += STRIPE_SECTORS;
+				if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
+					/* don't try to repair!! */
+					update_p = update_q = 0;
+			}
+
+			/* now write out any block on a failed drive,
+			 * or P or Q if they need it
+			 */
+
+			if (failed == 2) {
+				dev = &sh->dev[failed_num[1]];
+				locked++;
+				set_bit(R5_LOCKED, &dev->flags);
+				set_bit(R5_Wantwrite, &dev->flags);
+			}
+			if (failed >= 1) {
+				dev = &sh->dev[failed_num[0]];
+				locked++;
+				set_bit(R5_LOCKED, &dev->flags);
+				set_bit(R5_Wantwrite, &dev->flags);
+			}
+
+			if (update_p) {
+				dev = &sh->dev[pd_idx];
+				locked ++;
+				set_bit(R5_LOCKED, &dev->flags);
+				set_bit(R5_Wantwrite, &dev->flags);
+			}
+			if (update_q) {
+				dev = &sh->dev[qd_idx];
+				locked++;
+				set_bit(R5_LOCKED, &dev->flags);
+				set_bit(R5_Wantwrite, &dev->flags);
+			}
+			clear_bit(STRIPE_DEGRADED, &sh->state);
+
+			set_bit(STRIPE_INSYNC, &sh->state);
+		}
+	}
+
+	if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
+		md_done_sync(conf->mddev, STRIPE_SECTORS,1);
+		clear_bit(STRIPE_SYNCING, &sh->state);
+	}
+
+	/* If the failed drives are just a ReadError, then we might need
+	 * to progress the repair/check process
+	 */
+	if (failed <= 2 && ! conf->mddev->ro)
+		for (i=0; i<failed;i++) {
+			dev = &sh->dev[failed_num[i]];
+			if (test_bit(R5_ReadError, &dev->flags)
+			    && !test_bit(R5_LOCKED, &dev->flags)
+			    && test_bit(R5_UPTODATE, &dev->flags)
+				) {
+				if (!test_bit(R5_ReWrite, &dev->flags)) {
+					set_bit(R5_Wantwrite, &dev->flags);
+					set_bit(R5_ReWrite, &dev->flags);
+					set_bit(R5_LOCKED, &dev->flags);
+				} else {
+					/* let's read it back */
+					set_bit(R5_Wantread, &dev->flags);
+					set_bit(R5_LOCKED, &dev->flags);
+				}
+			}
+		}
+	spin_unlock(&sh->lock);
+
+	while ((bi=return_bi)) {
+		int bytes = bi->bi_size;
+
+		return_bi = bi->bi_next;
+		bi->bi_next = NULL;
+		bi->bi_size = 0;
+		bi->bi_end_io(bi, bytes, 0);
+	}
+	for (i=disks; i-- ;) {
+		int rw;
+		struct bio *bi;
+		mdk_rdev_t *rdev;
+		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
+			rw = 1;
+		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
+			rw = 0;
+		else
+			continue;
+
+		bi = &sh->dev[i].req;
+
+		bi->bi_rw = rw;
+		if (rw)
+			bi->bi_end_io = raid5_end_write_request;
+		else
+			bi->bi_end_io = raid5_end_read_request;
+
+		rcu_read_lock();
+		rdev = rcu_dereference(conf->disks[i].rdev);
+		if (rdev && test_bit(Faulty, &rdev->flags))
+			rdev = NULL;
+		if (rdev)
+			atomic_inc(&rdev->nr_pending);
+		rcu_read_unlock();
+
+		if (rdev) {
+			if (syncing)
+				md_sync_acct(rdev->bdev, STRIPE_SECTORS);
+
+			bi->bi_bdev = rdev->bdev;
+			PRINTK("for %llu schedule op %ld on disc %d\n",
+				(unsigned long long)sh->sector, bi->bi_rw, i);
+			atomic_inc(&sh->count);
+			bi->bi_sector = sh->sector + rdev->data_offset;
+			bi->bi_flags = 1 << BIO_UPTODATE;
+			bi->bi_vcnt = 1;
+			bi->bi_max_vecs = 1;
+			bi->bi_idx = 0;
+			bi->bi_io_vec = &sh->dev[i].vec;
+			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
+			bi->bi_io_vec[0].bv_offset = 0;
+			bi->bi_size = STRIPE_SIZE;
+			bi->bi_next = NULL;
+			if (rw == WRITE &&
+			    test_bit(R5_ReWrite, &sh->dev[i].flags))
+				atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
+			generic_make_request(bi);
+		} else {
+			if (rw == 1)
+				set_bit(STRIPE_DEGRADED, &sh->state);
+			PRINTK("skip op %ld on disc %d for sector %llu\n",
+				bi->bi_rw, i, (unsigned long long)sh->sector);
+			clear_bit(R5_LOCKED, &sh->dev[i].flags);
+			set_bit(STRIPE_HANDLE, &sh->state);
+		}
+	}
+}
+
+static void handle_stripe(struct stripe_head *sh, struct page *tmp_page)
+{
+	if (sh->raid_conf->level == 6)
+		handle_stripe6(sh, tmp_page);
+	else
+		handle_stripe5(sh);
+}
+
+
+
 static void raid5_activate_delayed(raid5_conf_t *conf)
 {
 	if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD) {
@@ -1753,7 +2590,7 @@ static int make_request(request_queue_t *q, struct bio * bi)
 
 	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
 		DEFINE_WAIT(w);
-		int disks;
+		int disks, data_disks;
 
 	retry:
 		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
@@ -1781,7 +2618,9 @@ static int make_request(request_queue_t *q, struct bio * bi)
 			}
 			spin_unlock_irq(&conf->device_lock);
 		}
- 		new_sector = raid5_compute_sector(logical_sector, disks, disks - 1,
+		data_disks = disks - conf->max_degraded;
+
+ 		new_sector = raid5_compute_sector(logical_sector, disks, data_disks,
 						  &dd_idx, &pd_idx, conf);
 		PRINTK("raid5: make_request, sector %llu logical %llu\n",
 			(unsigned long long)new_sector, 
@@ -1833,7 +2672,7 @@ static int make_request(request_queue_t *q, struct bio * bi)
 			}
 			finish_wait(&conf->wait_for_overlap, &w);
 			raid5_plug_device(conf);
-			handle_stripe(sh);
+			handle_stripe(sh, NULL);
 			release_stripe(sh);
 		} else {
 			/* cannot get stripe for read-ahead, just give-up */
@@ -1849,7 +2688,7 @@ static int make_request(request_queue_t *q, struct bio * bi)
 	if (remaining == 0) {
 		int bytes = bi->bi_size;
 
-		if ( bio_data_dir(bi) == WRITE )
+		if ( rw == WRITE )
 			md_write_end(mddev);
 		bi->bi_size = 0;
 		bi->bi_end_io(bi, bytes, 0);
@@ -1865,9 +2704,11 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 	int pd_idx;
 	sector_t first_sector, last_sector;
 	int raid_disks = conf->raid_disks;
-	int data_disks = raid_disks-1;
+	int data_disks = raid_disks - conf->max_degraded;
 	sector_t max_sector = mddev->size << 1;
 	int sync_blocks;
+	int still_degraded = 0;
+	int i;
 
 	if (sector_nr >= max_sector) {
 		/* just being told to finish up .. nothing much to do */
@@ -1880,7 +2721,7 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 		if (mddev->curr_resync < max_sector) /* aborted */
 			bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
 					&sync_blocks, 1);
-		else /* compelted sync */
+		else /* completed sync */
 			conf->fullsync = 0;
 		bitmap_close_sync(mddev->bitmap);
 
@@ -2003,11 +2844,12 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 		}
 		return conf->chunk_size>>9;
 	}
-	/* if there is 1 or more failed drives and we are trying
+	/* 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 >= 1 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
+	if (mddev->degraded >= (data_disks - raid_disks) &&
+	    test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
 		sector_t rv = (mddev->size << 1) - sector_nr;
 		*skipped = 1;
 		return rv;
@@ -2026,17 +2868,26 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
 	if (sh == NULL) {
 		sh = get_active_stripe(conf, sector_nr, raid_disks, pd_idx, 0);
 		/* make sure we don't swamp the stripe cache if someone else
-		 * is trying to get access 
+		 * is trying to get access
 		 */
 		schedule_timeout_uninterruptible(1);
 	}
-	bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 0);
-	spin_lock(&sh->lock);	
+	/* Need to check if array will still be degraded after recovery/resync
+	 * We don't need to check the 'failed' flag as when that gets set,
+	 * recovery aborts.
+	 */
+	for (i=0; i<mddev->raid_disks; i++)
+		if (conf->disks[i].rdev == NULL)
+			still_degraded = 1;
+
+	bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);
+
+	spin_lock(&sh->lock);
 	set_bit(STRIPE_SYNCING, &sh->state);
 	clear_bit(STRIPE_INSYNC, &sh->state);
 	spin_unlock(&sh->lock);
 
-	handle_stripe(sh);
+	handle_stripe(sh, NULL);
 	release_stripe(sh);
 
 	return STRIPE_SECTORS;
@@ -2091,7 +2942,7 @@ static void raid5d (mddev_t *mddev)
 		spin_unlock_irq(&conf->device_lock);
 		
 		handled++;
-		handle_stripe(sh);
+		handle_stripe(sh, conf->spare_page);
 		release_stripe(sh);
 
 		spin_lock_irq(&conf->device_lock);
@@ -2181,8 +3032,8 @@ static int run(mddev_t *mddev)
 	struct disk_info *disk;
 	struct list_head *tmp;
 
-	if (mddev->level != 5 && mddev->level != 4) {
-		printk(KERN_ERR "raid5: %s: raid level not set to 4/5 (%d)\n",
+	if (mddev->level != 5 && mddev->level != 4 && mddev->level != 6) {
+		printk(KERN_ERR "raid5: %s: raid level not set to 4/5/6 (%d)\n",
 		       mdname(mddev), mddev->level);
 		return -EIO;
 	}
@@ -2251,6 +3102,11 @@ static int run(mddev_t *mddev)
 	if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
 		goto abort;
 
+	if (mddev->level == 6) {
+		conf->spare_page = alloc_page(GFP_KERNEL);
+		if (!conf->spare_page)
+			goto abort;
+	}
 	spin_lock_init(&conf->device_lock);
 	init_waitqueue_head(&conf->wait_for_stripe);
 	init_waitqueue_head(&conf->wait_for_overlap);
@@ -2282,12 +3138,16 @@ static int run(mddev_t *mddev)
 	}
 
 	/*
-	 * 0 for a fully functional array, 1 for a degraded array.
+	 * 0 for a fully functional array, 1 or 2 for a degraded array.
 	 */
 	mddev->degraded = conf->failed_disks = conf->raid_disks - conf->working_disks;
 	conf->mddev = mddev;
 	conf->chunk_size = mddev->chunk_size;
 	conf->level = mddev->level;
+	if (conf->level == 6)
+		conf->max_degraded = 2;
+	else
+		conf->max_degraded = 1;
 	conf->algorithm = mddev->layout;
 	conf->max_nr_stripes = NR_STRIPES;
 	conf->expand_progress = mddev->reshape_position;
@@ -2296,6 +3156,11 @@ static int run(mddev_t *mddev)
 	mddev->size &= ~(mddev->chunk_size/1024 -1);
 	mddev->resync_max_sectors = mddev->size << 1;
 
+	if (conf->level == 6 && conf->raid_disks < 4) {
+		printk(KERN_ERR "raid6: not enough configured devices for %s (%d, minimum 4)\n",
+		       mdname(mddev), conf->raid_disks);
+		goto abort;
+	}
 	if (!conf->chunk_size || conf->chunk_size % 4) {
 		printk(KERN_ERR "raid5: invalid chunk size %d for %s\n",
 			conf->chunk_size, mdname(mddev));
@@ -2307,14 +3172,14 @@ static int run(mddev_t *mddev)
 			conf->algorithm, mdname(mddev));
 		goto abort;
 	}
-	if (mddev->degraded > 1) {
+	if (mddev->degraded > conf->max_degraded) {
 		printk(KERN_ERR "raid5: not enough operational devices for %s"
 			" (%d/%d failed)\n",
 			mdname(mddev), conf->failed_disks, conf->raid_disks);
 		goto abort;
 	}
 
-	if (mddev->degraded == 1 &&
+	if (mddev->degraded > 0 &&
 	    mddev->recovery_cp != MaxSector) {
 		if (mddev->ok_start_degraded)
 			printk(KERN_WARNING
@@ -2379,10 +3244,11 @@ static int run(mddev_t *mddev)
 	}
 
 	/* read-ahead size must cover two whole stripes, which is
-	 * 2 * (n-1) * chunksize where 'n' is the number of raid devices
+	 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
 	 */
 	{
-		int stripe = (mddev->raid_disks-1) *
+		int data_disks = conf->previous_raid_disks - conf->max_degraded;
+		int stripe = data_disks *
 			(mddev->chunk_size / PAGE_SIZE);
 		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
 			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
@@ -2393,12 +3259,14 @@ static int run(mddev_t *mddev)
 
 	mddev->queue->unplug_fn = raid5_unplug_device;
 	mddev->queue->issue_flush_fn = raid5_issue_flush;
-	mddev->array_size =  mddev->size * (conf->previous_raid_disks - 1);
+	mddev->array_size =  mddev->size * (conf->previous_raid_disks -
+					    conf->max_degraded);
 
 	return 0;
 abort:
 	if (conf) {
 		print_raid5_conf(conf);
+		safe_put_page(conf->spare_page);
 		kfree(conf->disks);
 		kfree(conf->stripe_hashtbl);
 		kfree(conf);
@@ -2427,23 +3295,23 @@ static int stop(mddev_t *mddev)
 }
 
 #if RAID5_DEBUG
-static void print_sh (struct stripe_head *sh)
+static void print_sh (struct seq_file *seq, struct stripe_head *sh)
 {
 	int i;
 
-	printk("sh %llu, pd_idx %d, state %ld.\n",
-		(unsigned long long)sh->sector, sh->pd_idx, sh->state);
-	printk("sh %llu,  count %d.\n",
-		(unsigned long long)sh->sector, atomic_read(&sh->count));
-	printk("sh %llu, ", (unsigned long long)sh->sector);
+	seq_printf(seq, "sh %llu, pd_idx %d, state %ld.\n",
+		   (unsigned long long)sh->sector, sh->pd_idx, sh->state);
+	seq_printf(seq, "sh %llu,  count %d.\n",
+		   (unsigned long long)sh->sector, atomic_read(&sh->count));
+	seq_printf(seq, "sh %llu, ", (unsigned long long)sh->sector);
 	for (i = 0; i < sh->disks; i++) {
-		printk("(cache%d: %p %ld) ", 
-			i, sh->dev[i].page, sh->dev[i].flags);
+		seq_printf(seq, "(cache%d: %p %ld) ",
+			   i, sh->dev[i].page, sh->dev[i].flags);
 	}
-	printk("\n");
+	seq_printf(seq, "\n");
 }
 
-static void printall (raid5_conf_t *conf)
+static void printall (struct seq_file *seq, raid5_conf_t *conf)
 {
 	struct stripe_head *sh;
 	struct hlist_node *hn;
@@ -2454,7 +3322,7 @@ static void printall (raid5_conf_t *conf)
 		hlist_for_each_entry(sh, hn, &conf->stripe_hashtbl[i], hash) {
 			if (sh->raid_conf != conf)
 				continue;
-			print_sh(sh);
+			print_sh(seq, sh);
 		}
 	}
 	spin_unlock_irq(&conf->device_lock);
@@ -2474,9 +3342,8 @@ static void status (struct seq_file *seq, mddev_t *mddev)
 			       test_bit(In_sync, &conf->disks[i].rdev->flags) ? "U" : "_");
 	seq_printf (seq, "]");
 #if RAID5_DEBUG
-#define D(x) \
-	seq_printf (seq, "<"#x":%d>", atomic_read(&conf->x))
-	printall(conf);
+	seq_printf (seq, "\n");
+	printall(seq, conf);
 #endif
 }
 
@@ -2560,14 +3427,20 @@ static int raid5_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
 	int disk;
 	struct disk_info *p;
 
-	if (mddev->degraded > 1)
+	if (mddev->degraded > conf->max_degraded)
 		/* no point adding a device */
 		return 0;
 
 	/*
-	 * find the disk ...
+	 * find the disk ... but prefer rdev->saved_raid_disk
+	 * if possible.
 	 */
-	for (disk=0; disk < conf->raid_disks; disk++)
+	if (rdev->saved_raid_disk >= 0 &&
+	    conf->disks[rdev->saved_raid_disk].rdev == NULL)
+		disk = rdev->saved_raid_disk;
+	else
+		disk = 0;
+	for ( ; disk < conf->raid_disks; disk++)
 		if ((p=conf->disks + disk)->rdev == NULL) {
 			clear_bit(In_sync, &rdev->flags);
 			rdev->raid_disk = disk;
@@ -2590,8 +3463,10 @@ static int raid5_resize(mddev_t *mddev, sector_t sectors)
 	 * any io in the removed space completes, but it hardly seems
 	 * worth it.
 	 */
+	raid5_conf_t *conf = mddev_to_conf(mddev);
+
 	sectors &= ~((sector_t)mddev->chunk_size/512 - 1);
-	mddev->array_size = (sectors * (mddev->raid_disks-1))>>1;
+	mddev->array_size = (sectors * (mddev->raid_disks-conf->max_degraded))>>1;
 	set_capacity(mddev->gendisk, mddev->array_size << 1);
 	mddev->changed = 1;
 	if (sectors/2  > mddev->size && mddev->recovery_cp == MaxSector) {
@@ -2731,6 +3606,17 @@ static void end_reshape(raid5_conf_t *conf)
 		conf->expand_progress = MaxSector;
 		spin_unlock_irq(&conf->device_lock);
 		conf->mddev->reshape_position = MaxSector;
+
+		/* read-ahead size must cover two whole stripes, which is
+		 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
+		 */
+		{
+			int data_disks = conf->previous_raid_disks - conf->max_degraded;
+			int stripe = data_disks *
+				(conf->mddev->chunk_size / PAGE_SIZE);
+			if (conf->mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
+				conf->mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
+		}
 	}
 }
 
@@ -2762,6 +3648,23 @@ static void raid5_quiesce(mddev_t *mddev, int state)
 	}
 }
 
+static struct mdk_personality raid6_personality =
+{
+	.name		= "raid6",
+	.level		= 6,
+	.owner		= THIS_MODULE,
+	.make_request	= make_request,
+	.run		= run,
+	.stop		= stop,
+	.status		= status,
+	.error_handler	= error,
+	.hot_add_disk	= raid5_add_disk,
+	.hot_remove_disk= raid5_remove_disk,
+	.spare_active	= raid5_spare_active,
+	.sync_request	= sync_request,
+	.resize		= raid5_resize,
+	.quiesce	= raid5_quiesce,
+};
 static struct mdk_personality raid5_personality =
 {
 	.name		= "raid5",
@@ -2804,6 +3707,12 @@ static struct mdk_personality raid4_personality =
 
 static int __init raid5_init(void)
 {
+	int e;
+
+	e = raid6_select_algo();
+	if ( e )
+		return e;
+	register_md_personality(&raid6_personality);
 	register_md_personality(&raid5_personality);
 	register_md_personality(&raid4_personality);
 	return 0;
@@ -2811,6 +3720,7 @@ static int __init raid5_init(void)
 
 static void raid5_exit(void)
 {
+	unregister_md_personality(&raid6_personality);
 	unregister_md_personality(&raid5_personality);
 	unregister_md_personality(&raid4_personality);
 }
@@ -2823,3 +3733,10 @@ 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");
diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
deleted file mode 100644
index e53d2d9..0000000
--- a/drivers/md/raid6main.c
+++ /dev/null
@@ -1,2427 +0,0 @@
-/*
- * 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"
-
-#include <linux/raid/bitmap.h>
-
-/*
- * Stripe cache
- */
-
-#define NR_STRIPES		256
-#define STRIPE_SIZE		PAGE_SIZE
-#define STRIPE_SHIFT		(PAGE_SHIFT - 9)
-#define STRIPE_SECTORS		(STRIPE_SIZE>>9)
-#define	IO_THRESHOLD		1
-#define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))
-#define HASH_MASK		(NR_HASH - 1)
-
-#define stripe_hash(conf, sect)	(&((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK]))
-
-/* bio's attached to a stripe+device for I/O are linked together in bi_sector
- * order without overlap.  There may be several bio's per stripe+device, and
- * a bio could span several devices.
- * When walking this list for a particular stripe+device, we must never proceed
- * beyond a bio that extends past this device, as the next bio might no longer
- * be valid.
- * This macro is used to determine the 'next' bio in the list, given the sector
- * of the current stripe+device
- */
-#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
-/*
- * The following can be used to debug the driver
- */
-#define 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 void __release_stripe(raid6_conf_t *conf, struct stripe_head *sh)
-{
-	if (atomic_dec_and_test(&sh->count)) {
-		BUG_ON(!list_empty(&sh->lru));
-		BUG_ON(atomic_read(&conf->active_stripes)==0);
-		if (test_bit(STRIPE_HANDLE, &sh->state)) {
-			if (test_bit(STRIPE_DELAYED, &sh->state))
-				list_add_tail(&sh->lru, &conf->delayed_list);
-			else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
-				 conf->seq_write == sh->bm_seq)
-				list_add_tail(&sh->lru, &conf->bitmap_list);
-			else {
-				clear_bit(STRIPE_BIT_DELAY, &sh->state);
-				list_add_tail(&sh->lru, &conf->handle_list);
-			}
-			md_wakeup_thread(conf->mddev->thread);
-		} else {
-			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
-				atomic_dec(&conf->preread_active_stripes);
-				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
-					md_wakeup_thread(conf->mddev->thread);
-			}
-			list_add_tail(&sh->lru, &conf->inactive_list);
-			atomic_dec(&conf->active_stripes);
-			if (!conf->inactive_blocked ||
-			    atomic_read(&conf->active_stripes) < (conf->max_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 inline void remove_hash(struct stripe_head *sh)
-{
-	PRINTK("remove_hash(), stripe %llu\n", (unsigned long long)sh->sector);
-
-	hlist_del_init(&sh->hash);
-}
-
-static inline void insert_hash(raid6_conf_t *conf, struct stripe_head *sh)
-{
-	struct hlist_head *hp = stripe_hash(conf, sh->sector);
-
-	PRINTK("insert_hash(), stripe %llu\n", (unsigned long long)sh->sector);
-
-	CHECK_DEVLOCK();
-	hlist_add_head(&sh->hash, hp);
-}
-
-
-/* find an idle stripe, make sure it is unhashed, and return it. */
-static struct stripe_head *get_free_stripe(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;
-		put_page(p);
-	}
-}
-
-static int grow_buffers(struct stripe_head *sh, int num)
-{
-	int i;
-
-	for (i=0; i<num; i++) {
-		struct page *page;
-
-		if (!(page = alloc_page(GFP_KERNEL))) {
-			return 1;
-		}
-		sh->dev[i].page = page;
-	}
-	return 0;
-}
-
-static void raid6_build_block (struct stripe_head *sh, int i);
-
-static 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;
-
-	BUG_ON(atomic_read(&sh->count) != 0);
-	BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
-
-	CHECK_DEVLOCK();
-	PRINTK("init_stripe called, stripe %llu\n",
-		(unsigned long long)sh->sector);
-
-	remove_hash(sh);
-
-	sh->sector = sector;
-	sh->pd_idx = pd_idx;
-	sh->state = 0;
-
-	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;
-	struct hlist_node *hn;
-
-	CHECK_DEVLOCK();
-	PRINTK("__find_stripe, sector %llu\n", (unsigned long long)sector);
-	hlist_for_each_entry (sh, hn,  stripe_hash(conf, sector), hash)
-		if (sh->sector == sector)
-			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 {
-		wait_event_lock_irq(conf->wait_for_stripe,
-				    conf->quiesce == 0,
-				    conf->device_lock, /* nothing */);
-		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)
-						     < (conf->max_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)) {
-				BUG_ON(!list_empty(&sh->lru));
-			} else {
-				if (!test_bit(STRIPE_HANDLE, &sh->state))
-					atomic_inc(&conf->active_stripes);
-				BUG_ON(list_empty(&sh->lru));
-				list_del_init(&sh->lru);
-			}
-		}
-	} while (sh == NULL);
-
-	if (sh)
-		atomic_inc(&sh->count);
-
-	spin_unlock_irq(&conf->device_lock);
-	return sh;
-}
-
-static int grow_one_stripe(raid6_conf_t *conf)
-{
-	struct stripe_head *sh;
-	sh = kmem_cache_alloc(conf->slab_cache, GFP_KERNEL);
-	if (!sh)
-		return 0;
-	memset(sh, 0, sizeof(*sh) + (conf->raid_disks-1)*sizeof(struct r5dev));
-	sh->raid_conf = conf;
-	spin_lock_init(&sh->lock);
-
-	if (grow_buffers(sh, conf->raid_disks)) {
-		shrink_buffers(sh, conf->raid_disks);
-		kmem_cache_free(conf->slab_cache, sh);
-		return 0;
-	}
-	/* 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(raid6_conf_t *conf, int num)
-{
-	kmem_cache_t *sc;
-	int devs = conf->raid_disks;
-
-	sprintf(conf->cache_name[0], "raid6/%s", mdname(conf->mddev));
-
-	sc = kmem_cache_create(conf->cache_name[0],
-			       sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
-			       0, 0, NULL, NULL);
-	if (!sc)
-		return 1;
-	conf->slab_cache = sc;
-	while (num--)
-		if (!grow_one_stripe(conf))
-			return 1;
-	return 0;
-}
-
-static int drop_one_stripe(raid6_conf_t *conf)
-{
-	struct stripe_head *sh;
-	spin_lock_irq(&conf->device_lock);
-	sh = get_free_stripe(conf);
-	spin_unlock_irq(&conf->device_lock);
-	if (!sh)
-		return 0;
-	BUG_ON(atomic_read(&sh->count));
-	shrink_buffers(sh, conf->raid_disks);
-	kmem_cache_free(conf->slab_cache, sh);
-	atomic_dec(&conf->active_stripes);
-	return 1;
-}
-
-static void shrink_stripes(raid6_conf_t *conf)
-{
-	while (drop_one_stripe(conf))
-		;
-
-	if (conf->slab_cache)
-		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
-		if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
-			printk(KERN_INFO "raid6: read error corrected!!\n");
-			clear_bit(R5_ReadError, &sh->dev[i].flags);
-			clear_bit(R5_ReWrite, &sh->dev[i].flags);
-		}
-		if (atomic_read(&conf->disks[i].rdev->read_errors))
-			atomic_set(&conf->disks[i].rdev->read_errors, 0);
-	} else {
-		int retry = 0;
-		clear_bit(R5_UPTODATE, &sh->dev[i].flags);
-		atomic_inc(&conf->disks[i].rdev->read_errors);
-		if (conf->mddev->degraded)
-			printk(KERN_WARNING "raid6: read error not correctable.\n");
-		else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
-			/* Oh, no!!! */
-			printk(KERN_WARNING "raid6: read error NOT corrected!!\n");
-		else if (atomic_read(&conf->disks[i].rdev->read_errors)
-			 > conf->max_nr_stripes)
-			printk(KERN_WARNING
-			       "raid6: Too many read errors, failing device.\n");
-		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, conf->disks[i].rdev);
-		}
-	}
-	rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
-#if 0
-	/* must restore b_page before unlocking buffer... */
-	if (sh->bh_page[i] != bh->b_page) {
-		bh->b_page = sh->bh_page[i];
-		bh->b_data = page_address(bh->b_page);
-		clear_buffer_uptodate(bh);
-	}
-#endif
-	clear_bit(R5_LOCKED, &sh->dev[i].flags);
-	set_bit(STRIPE_HANDLE, &sh->state);
-	release_stripe(sh);
-	return 0;
-}
-
-static int 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 (!test_bit(Faulty, &rdev->flags)) {
-		mddev->sb_dirty = 1;
-		if (test_bit(In_sync, &rdev->flags)) {
-			conf->working_disks--;
-			mddev->degraded++;
-			conf->failed_disks++;
-			clear_bit(In_sync, &rdev->flags);
-			/*
-			 * if recovery was running, make sure it aborts.
-			 */
-			set_bit(MD_RECOVERY_ERR, &mddev->recovery);
-		}
-		set_bit(Faulty, &rdev->flags);
-		printk (KERN_ALERT
-			"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);
-
-				BUG_ON(sh->dev[i].written);
-				sh->dev[i].written = chosen;
-			}
-		break;
-	case CHECK_PARITY:
-		BUG();		/* Not implemented yet */
-	}
-
-	for (i = disks; i--;)
-		if (sh->dev[i].written) {
-			sector_t sector = sh->dev[i].sector;
-			struct bio *wbi = sh->dev[i].written;
-			while (wbi && wbi->bi_sector < sector + STRIPE_SECTORS) {
-				copy_data(1, wbi, sh->dev[i].page, sector);
-				wbi = r5_next_bio(wbi, sector);
-			}
-
-			set_bit(R5_LOCKED, &sh->dev[i].flags);
-			set_bit(R5_UPTODATE, &sh->dev[i].flags);
-		}
-
-//	switch(method) {
-//	case RECONSTRUCT_WRITE:
-//	case CHECK_PARITY:
-//	case UPDATE_PARITY:
-		/* Note that unlike RAID-5, the ordering of the disks matters greatly. */
-		/* FIX: Is this ordering of drives even remotely optimal? */
-		count = 0;
-		i = d0_idx;
-		do {
-			ptrs[count++] = page_address(sh->dev[i].page);
-			if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
-				printk("block %d/%d not uptodate on parity calc\n", i,count);
-			i = raid6_next_disk(i, disks);
-		} while ( i != d0_idx );
-//		break;
-//	}
-
-	raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);
-
-	switch(method) {
-	case RECONSTRUCT_WRITE:
-		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
-		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
-		set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
-		set_bit(R5_LOCKED,   &sh->dev[qd_idx].flags);
-		break;
-	case UPDATE_PARITY:
-		set_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
-		set_bit(R5_UPTODATE, &sh->dev[qd_idx].flags);
-		break;
-	}
-}
-
-/* Compute one missing block */
-static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
-{
-	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);
-		if (!nozero) memset(ptr[0], 0, STRIPE_SIZE);
-		count = 1;
-		for (i = disks ; i--; ) {
-			if (i == dd_idx || i == qd_idx)
-				continue;
-			p = page_address(sh->dev[i].page);
-			if (test_bit(R5_UPTODATE, &sh->dev[i].flags))
-				ptr[count++] = p;
-			else
-				printk("compute_block() %d, stripe %llu, %d"
-				       " not present\n", dd_idx,
-				       (unsigned long long)sh->sector, i);
-
-			check_xor();
-		}
-		if (count != 1)
-			xor_block(count, STRIPE_SIZE, ptr);
-		if (!nozero) set_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
-		else clear_bit(R5_UPTODATE, &sh->dev[dd_idx].flags);
-	}
-}
-
-/* Compute two missing blocks */
-static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
-{
-	raid6_conf_t *conf = sh->raid_conf;
-	int i, count, disks = conf->raid_disks;
-	int pd_idx = sh->pd_idx;
-	int qd_idx = raid6_next_disk(pd_idx, disks);
-	int d0_idx = raid6_next_disk(qd_idx, disks);
-	int faila, failb;
-
-	/* faila and failb are disk numbers relative to d0_idx */
-	/* pd_idx become disks-2 and qd_idx become disks-1 */
-	faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
-	failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;
-
-	BUG_ON(faila == failb);
-	if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }
-
-	PRINTK("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
-	       (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);
-
-	if ( failb == disks-1 ) {
-		/* Q disk is one of the missing disks */
-		if ( faila == disks-2 ) {
-			/* Missing P+Q, just recompute */
-			compute_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, 0);
-			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;
-	int firstwrite=0;
-
-	PRINTK("adding bh b#%llu to stripe s#%llu\n",
-		(unsigned long long)bi->bi_sector,
-		(unsigned long long)sh->sector);
-
-
-	spin_lock(&sh->lock);
-	spin_lock_irq(&conf->device_lock);
-	if (forwrite) {
-		bip = &sh->dev[dd_idx].towrite;
-		if (*bip == NULL && sh->dev[dd_idx].written == NULL)
-			firstwrite = 1;
-	} else
-		bip = &sh->dev[dd_idx].toread;
-	while (*bip && (*bip)->bi_sector < bi->bi_sector) {
-		if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
-			goto overlap;
-		bip = &(*bip)->bi_next;
-	}
-	if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
-		goto overlap;
-
-	BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
-	if (*bip)
-		bi->bi_next = *bip;
-	*bip = bi;
-	bi->bi_phys_segments ++;
-	spin_unlock_irq(&conf->device_lock);
-	spin_unlock(&sh->lock);
-
-	PRINTK("added bi b#%llu to stripe s#%llu, disk %d.\n",
-		(unsigned long long)bi->bi_sector,
-		(unsigned long long)sh->sector, dd_idx);
-
-	if (conf->mddev->bitmap && firstwrite) {
-		sh->bm_seq = conf->seq_write;
-		bitmap_startwrite(conf->mddev->bitmap, sh->sector,
-				  STRIPE_SECTORS, 0);
-		set_bit(STRIPE_BIT_DELAY, &sh->state);
-	}
-
-	if (forwrite) {
-		/* check if page is covered */
-		sector_t sector = sh->dev[dd_idx].sector;
-		for (bi=sh->dev[dd_idx].towrite;
-		     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
-			     bi && bi->bi_sector <= sector;
-		     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
-			if (bi->bi_sector + (bi->bi_size>>9) >= sector)
-				sector = bi->bi_sector + (bi->bi_size>>9);
-		}
-		if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
-			set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
-	}
-	return 1;
-
- overlap:
-	set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
-	spin_unlock_irq(&conf->device_lock);
-	spin_unlock(&sh->lock);
-	return 0;
-}
-
-
-static int page_is_zero(struct page *p)
-{
-	char *a = page_address(p);
-	return ((*(u32*)a) == 0 &&
-		memcmp(a, a+4, STRIPE_SIZE-4)==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, struct page *tmp_page)
-{
-	raid6_conf_t *conf = sh->raid_conf;
-	int disks = conf->raid_disks;
-	struct bio *return_bi= NULL;
-	struct bio *bi;
-	int i;
-	int syncing;
-	int locked=0, uptodate=0, to_read=0, to_write=0, failed=0, written=0;
-	int non_overwrite = 0;
-	int failed_num[2] = {0, 0};
-	struct r5dev *dev, *pdev, *qdev;
-	int pd_idx = sh->pd_idx;
-	int qd_idx = raid6_next_disk(pd_idx, disks);
-	int p_failed, q_failed;
-
-	PRINTK("handling stripe %llu, state=%#lx cnt=%d, pd_idx=%d, qd_idx=%d\n",
-	       (unsigned long long)sh->sector, sh->state, atomic_read(&sh->count),
-	       pd_idx, qd_idx);
-
-	spin_lock(&sh->lock);
-	clear_bit(STRIPE_HANDLE, &sh->state);
-	clear_bit(STRIPE_DELAYED, &sh->state);
-
-	syncing = test_bit(STRIPE_SYNCING, &sh->state);
-	/* Now to look around and see what can be done */
-
-	rcu_read_lock();
-	for (i=disks; i--; ) {
-		mdk_rdev_t *rdev;
-		dev = &sh->dev[i];
-		clear_bit(R5_Insync, &dev->flags);
-
-		PRINTK("check %d: state 0x%lx read %p write %p written %p\n",
-			i, dev->flags, dev->toread, dev->towrite, dev->written);
-		/* maybe we can reply to a read */
-		if (test_bit(R5_UPTODATE, &dev->flags) && dev->toread) {
-			struct bio *rbi, *rbi2;
-			PRINTK("Return read for disc %d\n", i);
-			spin_lock_irq(&conf->device_lock);
-			rbi = dev->toread;
-			dev->toread = NULL;
-			if (test_and_clear_bit(R5_Overlap, &dev->flags))
-				wake_up(&conf->wait_for_overlap);
-			spin_unlock_irq(&conf->device_lock);
-			while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
-				copy_data(0, rbi, dev->page, dev->sector);
-				rbi2 = r5_next_bio(rbi, dev->sector);
-				spin_lock_irq(&conf->device_lock);
-				if (--rbi->bi_phys_segments == 0) {
-					rbi->bi_next = return_bi;
-					return_bi = rbi;
-				}
-				spin_unlock_irq(&conf->device_lock);
-				rbi = rbi2;
-			}
-		}
-
-		/* now count some things */
-		if (test_bit(R5_LOCKED, &dev->flags)) locked++;
-		if (test_bit(R5_UPTODATE, &dev->flags)) uptodate++;
-
-
-		if (dev->toread) to_read++;
-		if (dev->towrite) {
-			to_write++;
-			if (!test_bit(R5_OVERWRITE, &dev->flags))
-				non_overwrite++;
-		}
-		if (dev->written) written++;
-		rdev = rcu_dereference(conf->disks[i].rdev);
-		if (!rdev || !test_bit(In_sync, &rdev->flags)) {
-			/* The ReadError flag will just be confusing now */
-			clear_bit(R5_ReadError, &dev->flags);
-			clear_bit(R5_ReWrite, &dev->flags);
-		}
-		if (!rdev || !test_bit(In_sync, &rdev->flags)
-		    || test_bit(R5_ReadError, &dev->flags)) {
-			if ( failed < 2 )
-				failed_num[failed] = i;
-			failed++;
-		} else
-			set_bit(R5_Insync, &dev->flags);
-	}
-	rcu_read_unlock();
-	PRINTK("locked=%d uptodate=%d to_read=%d"
-	       " to_write=%d failed=%d failed_num=%d,%d\n",
-	       locked, uptodate, to_read, to_write, failed,
-	       failed_num[0], failed_num[1]);
-	/* check if the array has lost >2 devices and, if so, some requests might
-	 * need to be failed
-	 */
-	if (failed > 2 && to_read+to_write+written) {
-		for (i=disks; i--; ) {
-			int bitmap_end = 0;
-
-			if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
-				mdk_rdev_t *rdev;
-				rcu_read_lock();
-				rdev = rcu_dereference(conf->disks[i].rdev);
-				if (rdev && test_bit(In_sync, &rdev->flags))
-					/* multiple read failures in one stripe */
-					md_error(conf->mddev, rdev);
-				rcu_read_unlock();
-			}
-
-			spin_lock_irq(&conf->device_lock);
-			/* fail all writes first */
-			bi = sh->dev[i].towrite;
-			sh->dev[i].towrite = NULL;
-			if (bi) { to_write--; bitmap_end = 1; }
-
-			if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
-				wake_up(&conf->wait_for_overlap);
-
-			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
-				struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
-				clear_bit(BIO_UPTODATE, &bi->bi_flags);
-				if (--bi->bi_phys_segments == 0) {
-					md_write_end(conf->mddev);
-					bi->bi_next = return_bi;
-					return_bi = bi;
-				}
-				bi = nextbi;
-			}
-			/* and fail all 'written' */
-			bi = sh->dev[i].written;
-			sh->dev[i].written = NULL;
-			if (bi) bitmap_end = 1;
-			while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS) {
-				struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
-				clear_bit(BIO_UPTODATE, &bi->bi_flags);
-				if (--bi->bi_phys_segments == 0) {
-					md_write_end(conf->mddev);
-					bi->bi_next = return_bi;
-					return_bi = bi;
-				}
-				bi = bi2;
-			}
-
-			/* fail any reads if this device is non-operational */
-			if (!test_bit(R5_Insync, &sh->dev[i].flags) ||
-			    test_bit(R5_ReadError, &sh->dev[i].flags)) {
-				bi = sh->dev[i].toread;
-				sh->dev[i].toread = NULL;
-				if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
-					wake_up(&conf->wait_for_overlap);
-				if (bi) to_read--;
-				while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
-					struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
-					clear_bit(BIO_UPTODATE, &bi->bi_flags);
-					if (--bi->bi_phys_segments == 0) {
-						bi->bi_next = return_bi;
-						return_bi = bi;
-					}
-					bi = nextbi;
-				}
-			}
-			spin_unlock_irq(&conf->device_lock);
-			if (bitmap_end)
-				bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-						STRIPE_SECTORS, 0, 0);
-		}
-	}
-	if (failed > 2 && syncing) {
-		md_done_sync(conf->mddev, STRIPE_SECTORS,0);
-		clear_bit(STRIPE_SYNCING, &sh->state);
-		syncing = 0;
-	}
-
-	/*
-	 * might be able to return some write requests if the parity blocks
-	 * are safe, or on a failed drive
-	 */
-	pdev = &sh->dev[pd_idx];
-	p_failed = (failed >= 1 && failed_num[0] == pd_idx)
-		|| (failed >= 2 && failed_num[1] == pd_idx);
-	qdev = &sh->dev[qd_idx];
-	q_failed = (failed >= 1 && failed_num[0] == qd_idx)
-		|| (failed >= 2 && failed_num[1] == qd_idx);
-
-	if ( written &&
-	     ( p_failed || ((test_bit(R5_Insync, &pdev->flags)
-			     && !test_bit(R5_LOCKED, &pdev->flags)
-			     && test_bit(R5_UPTODATE, &pdev->flags))) ) &&
-	     ( q_failed || ((test_bit(R5_Insync, &qdev->flags)
-			     && !test_bit(R5_LOCKED, &qdev->flags)
-			     && test_bit(R5_UPTODATE, &qdev->flags))) ) ) {
-		/* any written block on an uptodate or failed drive can be
-		 * returned.  Note that if we 'wrote' to a failed drive,
-		 * it will be UPTODATE, but never LOCKED, so we don't need
-		 * to test 'failed' directly.
-		 */
-		for (i=disks; i--; )
-			if (sh->dev[i].written) {
-				dev = &sh->dev[i];
-				if (!test_bit(R5_LOCKED, &dev->flags) &&
-				    test_bit(R5_UPTODATE, &dev->flags) ) {
-					/* We can return any write requests */
-					int bitmap_end = 0;
-					struct bio *wbi, *wbi2;
-					PRINTK("Return write for stripe %llu disc %d\n",
-					       (unsigned long long)sh->sector, i);
-					spin_lock_irq(&conf->device_lock);
-					wbi = dev->written;
-					dev->written = NULL;
-					while (wbi && wbi->bi_sector < dev->sector + STRIPE_SECTORS) {
-						wbi2 = r5_next_bio(wbi, dev->sector);
-						if (--wbi->bi_phys_segments == 0) {
-							md_write_end(conf->mddev);
-							wbi->bi_next = return_bi;
-							return_bi = wbi;
-						}
-						wbi = wbi2;
-					}
-					if (dev->towrite == NULL)
-						bitmap_end = 1;
-					spin_unlock_irq(&conf->device_lock);
-					if (bitmap_end)
-						bitmap_endwrite(conf->mddev->bitmap, sh->sector,
-								STRIPE_SECTORS,
-								!test_bit(STRIPE_DEGRADED, &sh->state), 0);
-				}
-			}
-	}
-
-	/* Now we might consider reading some blocks, either to check/generate
-	 * parity, or to satisfy requests
-	 * or to load a block that is being partially written.
-	 */
-	if (to_read || non_overwrite || (to_write && failed) || (syncing && (uptodate < disks))) {
-		for (i=disks; i--;) {
-			dev = &sh->dev[i];
-			if (!test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
-			    (dev->toread ||
-			     (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
-			     syncing ||
-			     (failed >= 1 && (sh->dev[failed_num[0]].toread || to_write)) ||
-			     (failed >= 2 && (sh->dev[failed_num[1]].toread || to_write))
-				    )
-				) {
-				/* we would like to get this block, possibly
-				 * by computing it, but we might not be able to
-				 */
-				if (uptodate == disks-1) {
-					PRINTK("Computing stripe %llu block %d\n",
-					       (unsigned long long)sh->sector, i);
-					compute_block_1(sh, i, 0);
-					uptodate++;
-				} else if ( uptodate == disks-2 && failed >= 2 ) {
-					/* Computing 2-failure is *very* expensive; only do it if failed >= 2 */
-					int other;
-					for (other=disks; other--;) {
-						if ( other == i )
-							continue;
-						if ( !test_bit(R5_UPTODATE, &sh->dev[other].flags) )
-							break;
-					}
-					BUG_ON(other < 0);
-					PRINTK("Computing stripe %llu blocks %d,%d\n",
-					       (unsigned long long)sh->sector, i, other);
-					compute_block_2(sh, i, other);
-					uptodate += 2;
-				} else if (test_bit(R5_Insync, &dev->flags)) {
-					set_bit(R5_LOCKED, &dev->flags);
-					set_bit(R5_Wantread, &dev->flags);
-#if 0
-					/* if I am just reading this block and we don't have
-					   a failed drive, or any pending writes then sidestep the cache */
-					if (sh->bh_read[i] && !sh->bh_read[i]->b_reqnext &&
-					    ! syncing && !failed && !to_write) {
-						sh->bh_cache[i]->b_page =  sh->bh_read[i]->b_page;
-						sh->bh_cache[i]->b_data =  sh->bh_read[i]->b_data;
-					}
-#endif
-					locked++;
-					PRINTK("Reading block %d (sync=%d)\n",
-						i, syncing);
-				}
-			}
-		}
-		set_bit(STRIPE_HANDLE, &sh->state);
-	}
-
-	/* now to consider writing and what else, if anything should be read */
-	if (to_write) {
-		int rcw=0, must_compute=0;
-		for (i=disks ; i--;) {
-			dev = &sh->dev[i];
-			/* Would I have to read this buffer for reconstruct_write */
-			if (!test_bit(R5_OVERWRITE, &dev->flags)
-			    && i != pd_idx && i != qd_idx
-			    && (!test_bit(R5_LOCKED, &dev->flags)
-#if 0
-				|| sh->bh_page[i] != bh->b_page
-#endif
-				    ) &&
-			    !test_bit(R5_UPTODATE, &dev->flags)) {
-				if (test_bit(R5_Insync, &dev->flags)) rcw++;
-				else {
-					PRINTK("raid6: must_compute: disk %d flags=%#lx\n", i, dev->flags);
-					must_compute++;
-				}
-			}
-		}
-		PRINTK("for sector %llu, rcw=%d, must_compute=%d\n",
-		       (unsigned long long)sh->sector, rcw, must_compute);
-		set_bit(STRIPE_HANDLE, &sh->state);
-
-		if (rcw > 0)
-			/* want reconstruct write, but need to get some data */
-			for (i=disks; i--;) {
-				dev = &sh->dev[i];
-				if (!test_bit(R5_OVERWRITE, &dev->flags)
-				    && !(failed == 0 && (i == pd_idx || i == qd_idx))
-				    && !test_bit(R5_LOCKED, &dev->flags) && !test_bit(R5_UPTODATE, &dev->flags) &&
-				    test_bit(R5_Insync, &dev->flags)) {
-					if (test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
-					{
-						PRINTK("Read_old stripe %llu block %d for Reconstruct\n",
-						       (unsigned long long)sh->sector, i);
-						set_bit(R5_LOCKED, &dev->flags);
-						set_bit(R5_Wantread, &dev->flags);
-						locked++;
-					} else {
-						PRINTK("Request delayed stripe %llu block %d for Reconstruct\n",
-						       (unsigned long long)sh->sector, i);
-						set_bit(STRIPE_DELAYED, &sh->state);
-						set_bit(STRIPE_HANDLE, &sh->state);
-					}
-				}
-			}
-		/* now if nothing is locked, and if we have enough data, we can start a write request */
-		if (locked == 0 && rcw == 0 &&
-		    !test_bit(STRIPE_BIT_DELAY, &sh->state)) {
-			if ( must_compute > 0 ) {
-				/* We have failed blocks and need to compute them */
-				switch ( failed ) {
-				case 0:	BUG();
-				case 1: compute_block_1(sh, failed_num[0], 0); break;
-				case 2: compute_block_2(sh, failed_num[0], failed_num[1]); break;
-				default: BUG();	/* This request should have been failed? */
-				}
-			}
-
-			PRINTK("Computing parity for stripe %llu\n", (unsigned long long)sh->sector);
-			compute_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);
-				}
-			/* after a RECONSTRUCT_WRITE, the stripe MUST be in-sync */
-			set_bit(STRIPE_INSYNC, &sh->state);
-
-			if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
-				atomic_dec(&conf->preread_active_stripes);
-				if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
-					md_wakeup_thread(conf->mddev->thread);
-			}
-		}
-	}
-
-	/* maybe we need to check and possibly fix the parity for this stripe
-	 * Any reads will already have been scheduled, so we just see if enough data
-	 * is available
-	 */
-	if (syncing && locked == 0 && !test_bit(STRIPE_INSYNC, &sh->state)) {
-		int update_p = 0, update_q = 0;
-		struct r5dev *dev;
-
-		set_bit(STRIPE_HANDLE, &sh->state);
-
-		BUG_ON(failed>2);
-		BUG_ON(uptodate < disks);
-		/* Want to check and possibly repair P and Q.
-		 * However there could be one 'failed' device, in which
-		 * case we can only check one of them, possibly using the
-		 * other to generate missing data
-		 */
-
-		/* If !tmp_page, we cannot do the calculations,
-		 * but as we have set STRIPE_HANDLE, we will soon be called
-		 * by stripe_handle with a tmp_page - just wait until then.
-		 */
-		if (tmp_page) {
-			if (failed == q_failed) {
-				/* The only possible failed device holds 'Q', so it makes
-				 * sense to check P (If anything else were failed, we would
-				 * have used P to recreate it).
-				 */
-				compute_block_1(sh, pd_idx, 1);
-				if (!page_is_zero(sh->dev[pd_idx].page)) {
-					compute_block_1(sh,pd_idx,0);
-					update_p = 1;
-				}
-			}
-			if (!q_failed && failed < 2) {
-				/* q is not failed, and we didn't use it to generate
-				 * anything, so it makes sense to check it
-				 */
-				memcpy(page_address(tmp_page),
-				       page_address(sh->dev[qd_idx].page),
-				       STRIPE_SIZE);
-				compute_parity(sh, UPDATE_PARITY);
-				if (memcmp(page_address(tmp_page),
-					   page_address(sh->dev[qd_idx].page),
-					   STRIPE_SIZE)!= 0) {
-					clear_bit(STRIPE_INSYNC, &sh->state);
-					update_q = 1;
-				}
-			}
-			if (update_p || update_q) {
-				conf->mddev->resync_mismatches += STRIPE_SECTORS;
-				if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
-					/* don't try to repair!! */
-					update_p = update_q = 0;
-			}
-
-			/* now write out any block on a failed drive,
-			 * or P or Q if they need it
-			 */
-
-			if (failed == 2) {
-				dev = &sh->dev[failed_num[1]];
-				locked++;
-				set_bit(R5_LOCKED, &dev->flags);
-				set_bit(R5_Wantwrite, &dev->flags);
-			}
-			if (failed >= 1) {
-				dev = &sh->dev[failed_num[0]];
-				locked++;
-				set_bit(R5_LOCKED, &dev->flags);
-				set_bit(R5_Wantwrite, &dev->flags);
-			}
-
-			if (update_p) {
-				dev = &sh->dev[pd_idx];
-				locked ++;
-				set_bit(R5_LOCKED, &dev->flags);
-				set_bit(R5_Wantwrite, &dev->flags);
-			}
-			if (update_q) {
-				dev = &sh->dev[qd_idx];
-				locked++;
-				set_bit(R5_LOCKED, &dev->flags);
-				set_bit(R5_Wantwrite, &dev->flags);
-			}
-			clear_bit(STRIPE_DEGRADED, &sh->state);
-
-			set_bit(STRIPE_INSYNC, &sh->state);
-		}
-	}
-
-	if (syncing && locked == 0 && test_bit(STRIPE_INSYNC, &sh->state)) {
-		md_done_sync(conf->mddev, STRIPE_SECTORS,1);
-		clear_bit(STRIPE_SYNCING, &sh->state);
-	}
-
-	/* If the failed drives are just a ReadError, then we might need
-	 * to progress the repair/check process
-	 */
-	if (failed <= 2 && ! conf->mddev->ro)
-		for (i=0; i<failed;i++) {
-			dev = &sh->dev[failed_num[i]];
-			if (test_bit(R5_ReadError, &dev->flags)
-			    && !test_bit(R5_LOCKED, &dev->flags)
-			    && test_bit(R5_UPTODATE, &dev->flags)
-				) {
-				if (!test_bit(R5_ReWrite, &dev->flags)) {
-					set_bit(R5_Wantwrite, &dev->flags);
-					set_bit(R5_ReWrite, &dev->flags);
-					set_bit(R5_LOCKED, &dev->flags);
-				} else {
-					/* let's read it back */
-					set_bit(R5_Wantread, &dev->flags);
-					set_bit(R5_LOCKED, &dev->flags);
-				}
-			}
-		}
-	spin_unlock(&sh->lock);
-
-	while ((bi=return_bi)) {
-		int bytes = bi->bi_size;
-
-		return_bi = bi->bi_next;
-		bi->bi_next = NULL;
-		bi->bi_size = 0;
-		bi->bi_end_io(bi, bytes, 0);
-	}
-	for (i=disks; i-- ;) {
-		int rw;
-		struct bio *bi;
-		mdk_rdev_t *rdev;
-		if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags))
-			rw = 1;
-		else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
-			rw = 0;
-		else
-			continue;
-
-		bi = &sh->dev[i].req;
-
-		bi->bi_rw = rw;
-		if (rw)
-			bi->bi_end_io = raid6_end_write_request;
-		else
-			bi->bi_end_io = raid6_end_read_request;
-
-		rcu_read_lock();
-		rdev = rcu_dereference(conf->disks[i].rdev);
-		if (rdev && test_bit(Faulty, &rdev->flags))
-			rdev = NULL;
-		if (rdev)
-			atomic_inc(&rdev->nr_pending);
-		rcu_read_unlock();
-
-		if (rdev) {
-			if (syncing)
-				md_sync_acct(rdev->bdev, STRIPE_SECTORS);
-
-			bi->bi_bdev = rdev->bdev;
-			PRINTK("for %llu schedule op %ld on disc %d\n",
-				(unsigned long long)sh->sector, bi->bi_rw, i);
-			atomic_inc(&sh->count);
-			bi->bi_sector = sh->sector + rdev->data_offset;
-			bi->bi_flags = 1 << BIO_UPTODATE;
-			bi->bi_vcnt = 1;
-			bi->bi_max_vecs = 1;
-			bi->bi_idx = 0;
-			bi->bi_io_vec = &sh->dev[i].vec;
-			bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
-			bi->bi_io_vec[0].bv_offset = 0;
-			bi->bi_size = STRIPE_SIZE;
-			bi->bi_next = NULL;
-			if (rw == WRITE &&
-			    test_bit(R5_ReWrite, &sh->dev[i].flags))
-				atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
-			generic_make_request(bi);
-		} else {
-			if (rw == 1)
-				set_bit(STRIPE_DEGRADED, &sh->state);
-			PRINTK("skip op %ld on disc %d for sector %llu\n",
-				bi->bi_rw, i, (unsigned long long)sh->sector);
-			clear_bit(R5_LOCKED, &sh->dev[i].flags);
-			set_bit(STRIPE_HANDLE, &sh->state);
-		}
-	}
-}
-
-static void 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 activate_bit_delay(raid6_conf_t *conf)
-{
-	/* device_lock is held */
-	struct list_head head;
-	list_add(&head, &conf->bitmap_list);
-	list_del_init(&conf->bitmap_list);
-	while (!list_empty(&head)) {
-		struct stripe_head *sh = list_entry(head.next, struct stripe_head, lru);
-		list_del_init(&sh->lru);
-		atomic_inc(&sh->count);
-		__release_stripe(conf, sh);
-	}
-}
-
-static void unplug_slaves(mddev_t *mddev)
-{
-	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 = rcu_dereference(conf->disks[i].rdev);
-		if (rdev && !test_bit(Faulty, &rdev->flags) && atomic_read(&rdev->nr_pending)) {
-			request_queue_t *r_queue = bdev_get_queue(rdev->bdev);
-
-			atomic_inc(&rdev->nr_pending);
-			rcu_read_unlock();
-
-			if (r_queue->unplug_fn)
-				r_queue->unplug_fn(r_queue);
-
-			rdev_dec_pending(rdev, mddev);
-			rcu_read_lock();
-		}
-	}
-	rcu_read_unlock();
-}
-
-static void 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)) {
-		conf->seq_flush++;
-		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 = rcu_dereference(conf->disks[i].rdev);
-		if (rdev && !test_bit(Faulty, &rdev->flags)) {
-			struct block_device *bdev = rdev->bdev;
-			request_queue_t *r_queue = bdev_get_queue(bdev);
-
-			if (!r_queue->issue_flush_fn)
-				ret = -EOPNOTSUPP;
-			else {
-				atomic_inc(&rdev->nr_pending);
-				rcu_read_unlock();
-				ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk,
-							      error_sector);
-				rdev_dec_pending(rdev, mddev);
-				rcu_read_lock();
-			}
-		}
-	}
-	rcu_read_unlock();
-	return ret;
-}
-
-static 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;
-	const int rw = bio_data_dir(bi);
-
-	if (unlikely(bio_barrier(bi))) {
-		bio_endio(bi, bi->bi_size, -EOPNOTSUPP);
-		return 0;
-	}
-
-	md_write_start(mddev, bi);
-
-	disk_stat_inc(mddev->gendisk, ios[rw]);
-	disk_stat_add(mddev->gendisk, sectors[rw], bio_sectors(bi));
-
-	logical_sector = bi->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
-	last_sector = bi->bi_sector + (bi->bi_size>>9);
-
-	bi->bi_next = NULL;
-	bi->bi_phys_segments = 1;	/* over-loaded to count active stripes */
-
-	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
-		DEFINE_WAIT(w);
-
-		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, NULL);
-			release_stripe(sh);
-		} else {
-			/* cannot get stripe for read-ahead, just give-up */
-			clear_bit(BIO_UPTODATE, &bi->bi_flags);
-			finish_wait(&conf->wait_for_overlap, &w);
-			break;
-		}
-
-	}
-	spin_lock_irq(&conf->device_lock);
-	if (--bi->bi_phys_segments == 0) {
-		int bytes = bi->bi_size;
-
-		if (rw == 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 sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, 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;
-	sector_t max_sector = mddev->size << 1;
-	int sync_blocks;
-	int still_degraded = 0;
-	int i;
-
-	if (sector_nr >= max_sector) {
-		/* just being told to finish up .. nothing much to do */
-		unplug_slaves(mddev);
-
-		if (mddev->curr_resync < max_sector) /* aborted */
-			bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
-					&sync_blocks, 1);
-		else /* completed sync */
-			conf->fullsync = 0;
-		bitmap_close_sync(mddev->bitmap);
-
-		return 0;
-	}
-	/* if 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)) {
-		sector_t rv = (mddev->size << 1) - sector_nr;
-		*skipped = 1;
-		return rv;
-	}
-	if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
-	    !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
-	    !conf->fullsync && sync_blocks >= STRIPE_SECTORS) {
-		/* we can skip this block, and probably more */
-		sync_blocks /= STRIPE_SECTORS;
-		*skipped = 1;
-		return sync_blocks * STRIPE_SECTORS; /* keep things rounded to whole stripes */
-	}
-
-	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
-		 */
-		schedule_timeout_uninterruptible(1);
-	}
-	/* Need to check if array will still be degraded after recovery/resync
-	 * We don't need to check the 'failed' flag as when that gets set,
-	 * recovery aborts.
-	 */
-	for (i=0; i<mddev->raid_disks; i++)
-		if (conf->disks[i].rdev == NULL)
-			still_degraded = 1;
-
-	bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, still_degraded);
-
-	spin_lock(&sh->lock);
-	set_bit(STRIPE_SYNCING, &sh->state);
-	clear_bit(STRIPE_INSYNC, &sh->state);
-	spin_unlock(&sh->lock);
-
-	handle_stripe(sh, NULL);
-	release_stripe(sh);
-
-	return STRIPE_SECTORS;
-}
-
-/*
- * This is our 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);
-
-	handled = 0;
-	spin_lock_irq(&conf->device_lock);
-	while (1) {
-		struct list_head *first;
-
-		if (conf->seq_flush - conf->seq_write > 0) {
-			int seq = conf->seq_flush;
-			spin_unlock_irq(&conf->device_lock);
-			bitmap_unplug(mddev->bitmap);
-			spin_lock_irq(&conf->device_lock);
-			conf->seq_write = seq;
-			activate_bit_delay(conf);
-		}
-
-		if (list_empty(&conf->handle_list) &&
-		    atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD &&
-		    !blk_queue_plugged(mddev->queue) &&
-		    !list_empty(&conf->delayed_list))
-			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);
-		BUG_ON(atomic_read(&sh->count)!= 1);
-		spin_unlock_irq(&conf->device_lock);
-
-		handled++;
-		handle_stripe(sh, conf->spare_page);
-		release_stripe(sh);
-
-		spin_lock_irq(&conf->device_lock);
-	}
-	PRINTK("%d stripes handled\n", handled);
-
-	spin_unlock_irq(&conf->device_lock);
-
-	unplug_slaves(mddev);
-
-	PRINTK("--- raid6d inactive\n");
-}
-
-static ssize_t
-raid6_show_stripe_cache_size(mddev_t *mddev, char *page)
-{
-	raid6_conf_t *conf = mddev_to_conf(mddev);
-	if (conf)
-		return sprintf(page, "%d\n", conf->max_nr_stripes);
-	else
-		return 0;
-}
-
-static ssize_t
-raid6_store_stripe_cache_size(mddev_t *mddev, const char *page, size_t len)
-{
-	raid6_conf_t *conf = mddev_to_conf(mddev);
-	char *end;
-	int new;
-	if (len >= PAGE_SIZE)
-		return -EINVAL;
-	if (!conf)
-		return -ENODEV;
-
-	new = simple_strtoul(page, &end, 10);
-	if (!*page || (*end && *end != '\n') )
-		return -EINVAL;
-	if (new <= 16 || new > 32768)
-		return -EINVAL;
-	while (new < conf->max_nr_stripes) {
-		if (drop_one_stripe(conf))
-			conf->max_nr_stripes--;
-		else
-			break;
-	}
-	while (new > conf->max_nr_stripes) {
-		if (grow_one_stripe(conf))
-			conf->max_nr_stripes++;
-		else break;
-	}
-	return len;
-}
-
-static struct md_sysfs_entry
-raid6_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR,
-				raid6_show_stripe_cache_size,
-				raid6_store_stripe_cache_size);
-
-static ssize_t
-stripe_cache_active_show(mddev_t *mddev, char *page)
-{
-	raid6_conf_t *conf = mddev_to_conf(mddev);
-	if (conf)
-		return sprintf(page, "%d\n", atomic_read(&conf->active_stripes));
-	else
-		return 0;
-}
-
-static struct md_sysfs_entry
-raid6_stripecache_active = __ATTR_RO(stripe_cache_active);
-
-static struct attribute *raid6_attrs[] =  {
-	&raid6_stripecache_size.attr,
-	&raid6_stripecache_active.attr,
-	NULL,
-};
-static struct attribute_group raid6_attrs_group = {
-	.name = NULL,
-	.attrs = raid6_attrs,
-};
-
-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 = kzalloc(sizeof (raid6_conf_t), GFP_KERNEL);
-	if ((conf = mddev->private) == NULL)
-		goto abort;
-	conf->disks = kzalloc(mddev->raid_disks * sizeof(struct disk_info),
-				 GFP_KERNEL);
-	if (!conf->disks)
-		goto abort;
-
-	conf->mddev = mddev;
-
-	if ((conf->stripe_hashtbl = kzalloc(PAGE_SIZE, GFP_KERNEL)) == NULL)
-		goto abort;
-
-	conf->spare_page = alloc_page(GFP_KERNEL);
-	if (!conf->spare_page)
-		goto abort;
-
-	spin_lock_init(&conf->device_lock);
-	init_waitqueue_head(&conf->wait_for_stripe);
-	init_waitqueue_head(&conf->wait_for_overlap);
-	INIT_LIST_HEAD(&conf->handle_list);
-	INIT_LIST_HEAD(&conf->delayed_list);
-	INIT_LIST_HEAD(&conf->bitmap_list);
-	INIT_LIST_HEAD(&conf->inactive_list);
-	atomic_set(&conf->active_stripes, 0);
-	atomic_set(&conf->preread_active_stripes, 0);
-
-	PRINTK("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 (test_bit(In_sync, &rdev->flags)) {
-			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);
-	mddev->resync_max_sectors = mddev->size << 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 (mddev->degraded > 0 &&
-	    mddev->recovery_cp != MaxSector) {
-		if (mddev->ok_start_degraded)
-			printk(KERN_WARNING "raid6: starting dirty degraded array:%s"
-			       "- data corruption possible.\n",
-			       mdname(mddev));
-		else {
-			printk(KERN_ERR "raid6: cannot start dirty degraded array"
-			       " for %s\n", mdname(mddev));
-			goto abort;
-		}
-	}
-
-	{
-		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_SIZE);
-		if (mddev->queue->backing_dev_info.ra_pages < 2 * stripe)
-			mddev->queue->backing_dev_info.ra_pages = 2 * stripe;
-	}
-
-	/* Ok, everything is just fine now */
-	sysfs_create_group(&mddev->kobj, &raid6_attrs_group);
-
-	mddev->array_size =  mddev->size * (mddev->raid_disks - 2);
-
-	mddev->queue->unplug_fn = raid6_unplug_device;
-	mddev->queue->issue_flush_fn = raid6_issue_flush;
-	return 0;
-abort:
-	if (conf) {
-		print_raid6_conf(conf);
-		safe_put_page(conf->spare_page);
-		kfree(conf->stripe_hashtbl);
-		kfree(conf->disks);
-		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);
-	kfree(conf->stripe_hashtbl);
-	blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
-	sysfs_remove_group(&mddev->kobj, &raid6_attrs_group);
-	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;
-	struct hlist_node *hn;
-	int i;
-
-	spin_lock_irq(&conf->device_lock);
-	for (i = 0; i < NR_HASH; i++) {
-		sh = conf->stripe_hashtbl[i];
-		hlist_for_each_entry(sh, hn, &conf->stripe_hashtbl[i], hash) {
-			if (sh->raid_conf != conf)
-				continue;
-			print_sh(seq, sh);
-		}
-	}
-	spin_unlock_irq(&conf->device_lock);
-}
-#endif
-
-static void status (struct seq_file *seq, mddev_t *mddev)
-{
-	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 &&
-			    test_bit(In_sync, &conf->disks[i].rdev->flags) ? "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, !test_bit(Faulty, &tmp->rdev->flags),
-			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
-		    && !test_bit(Faulty, &tmp->rdev->flags)
-		    && !test_bit(In_sync, &tmp->rdev->flags)) {
-			mddev->degraded--;
-			conf->failed_disks--;
-			conf->working_disks++;
-			set_bit(In_sync, &tmp->rdev->flags);
-		}
-	}
-	print_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 (test_bit(In_sync, &rdev->flags) ||
-		    atomic_read(&rdev->nr_pending)) {
-			err = -EBUSY;
-			goto abort;
-		}
-		p->rdev = NULL;
-		synchronize_rcu();
-		if (atomic_read(&rdev->nr_pending)) {
-			/* lost the race, try later */
-			err = -EBUSY;
-			p->rdev = rdev;
-		}
-	}
-
-abort:
-
-	print_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 ... but prefer rdev->saved_raid_disk
-	 * if possible.
-	 */
-	if (rdev->saved_raid_disk >= 0 &&
-	    conf->disks[rdev->saved_raid_disk].rdev == NULL)
-		disk = rdev->saved_raid_disk;
-	else
-		disk = 0;
-	for ( ; disk < mddev->raid_disks; disk++)
-		if ((p=conf->disks + disk)->rdev == NULL) {
-			clear_bit(In_sync, &rdev->flags);
-			rdev->raid_disk = disk;
-			found = 1;
-			if (rdev->saved_raid_disk != disk)
-				conf->fullsync = 1;
-			rcu_assign_pointer(p->rdev, rdev);
-			break;
-		}
-	print_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;
-	mddev->resync_max_sectors = sectors;
-	return 0;
-}
-
-static void raid6_quiesce(mddev_t *mddev, int state)
-{
-	raid6_conf_t *conf = mddev_to_conf(mddev);
-
-	switch(state) {
-	case 1: /* stop all writes */
-		spin_lock_irq(&conf->device_lock);
-		conf->quiesce = 1;
-		wait_event_lock_irq(conf->wait_for_stripe,
-				    atomic_read(&conf->active_stripes) == 0,
-				    conf->device_lock, /* nothing */);
-		spin_unlock_irq(&conf->device_lock);
-		break;
-
-	case 0: /* re-enable writes */
-		spin_lock_irq(&conf->device_lock);
-		conf->quiesce = 0;
-		wake_up(&conf->wait_for_stripe);
-		spin_unlock_irq(&conf->device_lock);
-		break;
-	}
-}
-
-static struct mdk_personality raid6_personality =
-{
-	.name		= "raid6",
-	.level		= 6,
-	.owner		= THIS_MODULE,
-	.make_request	= make_request,
-	.run		= run,
-	.stop		= stop,
-	.status		= status,
-	.error_handler	= error,
-	.hot_add_disk	= raid6_add_disk,
-	.hot_remove_disk= raid6_remove_disk,
-	.spare_active	= raid6_spare_active,
-	.sync_request	= sync_request,
-	.resize		= raid6_resize,
-	.quiesce	= raid6_quiesce,
-};
-
-static int __init raid6_init(void)
-{
-	int e;
-
-	e = raid6_select_algo();
-	if ( e )
-		return e;
-
-	return register_md_personality(&raid6_personality);
-}
-
-static void raid6_exit (void)
-{
-	unregister_md_personality(&raid6_personality);
-}
-
-module_init(raid6_init);
-module_exit(raid6_exit);
-MODULE_LICENSE("GPL");
-MODULE_ALIAS("md-personality-8"); /* RAID6 */
-MODULE_ALIAS("md-raid6");
-MODULE_ALIAS("md-level-6");
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index 914af66..20ed4c9 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -212,6 +212,7 @@ struct raid5_private_data {
 	mddev_t			*mddev;
 	struct disk_info	*spare;
 	int			chunk_size, level, algorithm;
+	int			max_degraded;
 	int			raid_disks, working_disks, failed_disks;
 	int			max_nr_stripes;