diff --git a/drivers/md/md.c b/drivers/md/md.c
index d169bc9..b9dfdfc 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -662,7 +662,8 @@
 	}
 
 	if (sb->major_version != 0 ||
-	    sb->minor_version != 90) {
+	    sb->minor_version < 90 ||
+	    sb->minor_version > 91) {
 		printk(KERN_WARNING "Bad version number %d.%d on %s\n",
 			sb->major_version, sb->minor_version,
 			b);
@@ -747,6 +748,20 @@
 		mddev->bitmap_offset = 0;
 		mddev->default_bitmap_offset = MD_SB_BYTES >> 9;
 
+		if (mddev->minor_version >= 91) {
+			mddev->reshape_position = sb->reshape_position;
+			mddev->delta_disks = sb->delta_disks;
+			mddev->new_level = sb->new_level;
+			mddev->new_layout = sb->new_layout;
+			mddev->new_chunk = sb->new_chunk;
+		} else {
+			mddev->reshape_position = MaxSector;
+			mddev->delta_disks = 0;
+			mddev->new_level = mddev->level;
+			mddev->new_layout = mddev->layout;
+			mddev->new_chunk = mddev->chunk_size;
+		}
+
 		if (sb->state & (1<<MD_SB_CLEAN))
 			mddev->recovery_cp = MaxSector;
 		else {
@@ -841,7 +856,6 @@
 
 	sb->md_magic = MD_SB_MAGIC;
 	sb->major_version = mddev->major_version;
-	sb->minor_version = mddev->minor_version;
 	sb->patch_version = mddev->patch_version;
 	sb->gvalid_words  = 0; /* ignored */
 	memcpy(&sb->set_uuid0, mddev->uuid+0, 4);
@@ -860,6 +874,17 @@
 	sb->events_hi = (mddev->events>>32);
 	sb->events_lo = (u32)mddev->events;
 
+	if (mddev->reshape_position == MaxSector)
+		sb->minor_version = 90;
+	else {
+		sb->minor_version = 91;
+		sb->reshape_position = mddev->reshape_position;
+		sb->new_level = mddev->new_level;
+		sb->delta_disks = mddev->delta_disks;
+		sb->new_layout = mddev->new_layout;
+		sb->new_chunk = mddev->new_chunk;
+	}
+	mddev->minor_version = sb->minor_version;
 	if (mddev->in_sync)
 	{
 		sb->recovery_cp = mddev->recovery_cp;
@@ -1104,6 +1129,20 @@
 			}
 			mddev->bitmap_offset = (__s32)le32_to_cpu(sb->bitmap_offset);
 		}
+		if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RESHAPE_ACTIVE)) {
+			mddev->reshape_position = le64_to_cpu(sb->reshape_position);
+			mddev->delta_disks = le32_to_cpu(sb->delta_disks);
+			mddev->new_level = le32_to_cpu(sb->new_level);
+			mddev->new_layout = le32_to_cpu(sb->new_layout);
+			mddev->new_chunk = le32_to_cpu(sb->new_chunk)<<9;
+		} else {
+			mddev->reshape_position = MaxSector;
+			mddev->delta_disks = 0;
+			mddev->new_level = mddev->level;
+			mddev->new_layout = mddev->layout;
+			mddev->new_chunk = mddev->chunk_size;
+		}
+
 	} else if (mddev->pers == NULL) {
 		/* Insist of good event counter while assembling */
 		__u64 ev1 = le64_to_cpu(sb->events);
@@ -1175,6 +1214,14 @@
 		sb->bitmap_offset = cpu_to_le32((__u32)mddev->bitmap_offset);
 		sb->feature_map = cpu_to_le32(MD_FEATURE_BITMAP_OFFSET);
 	}
+	if (mddev->reshape_position != MaxSector) {
+		sb->feature_map |= cpu_to_le32(MD_FEATURE_RESHAPE_ACTIVE);
+		sb->reshape_position = cpu_to_le64(mddev->reshape_position);
+		sb->new_layout = cpu_to_le32(mddev->new_layout);
+		sb->delta_disks = cpu_to_le32(mddev->delta_disks);
+		sb->new_level = cpu_to_le32(mddev->new_level);
+		sb->new_chunk = cpu_to_le32(mddev->new_chunk>>9);
+	}
 
 	max_dev = 0;
 	ITERATE_RDEV(mddev,rdev2,tmp)
@@ -1497,7 +1544,7 @@
 	}
 }
 
-static void md_update_sb(mddev_t * mddev)
+void md_update_sb(mddev_t * mddev)
 {
 	int err;
 	struct list_head *tmp;
@@ -1574,6 +1621,7 @@
 	wake_up(&mddev->sb_wait);
 
 }
+EXPORT_SYMBOL_GPL(md_update_sb);
 
 /* words written to sysfs files may, or my not, be \n terminated.
  * We want to accept with case. For this we use cmd_match.
@@ -2545,6 +2593,14 @@
 	mddev->level = pers->level;
 	strlcpy(mddev->clevel, pers->name, sizeof(mddev->clevel));
 
+	if (mddev->reshape_position != MaxSector &&
+	    pers->reshape == NULL) {
+		/* This personality cannot handle reshaping... */
+		mddev->pers = NULL;
+		module_put(pers->owner);
+		return -EINVAL;
+	}
+
 	mddev->recovery = 0;
 	mddev->resync_max_sectors = mddev->size << 1; /* may be over-ridden by personality */
 	mddev->barriers_work = 1;
@@ -3433,11 +3489,18 @@
 	mddev->default_bitmap_offset = MD_SB_BYTES >> 9;
 	mddev->bitmap_offset = 0;
 
+	mddev->reshape_position = MaxSector;
+
 	/*
 	 * Generate a 128 bit UUID
 	 */
 	get_random_bytes(mddev->uuid, 16);
 
+	mddev->new_level = mddev->level;
+	mddev->new_chunk = mddev->chunk_size;
+	mddev->new_layout = mddev->layout;
+	mddev->delta_disks = 0;
+
 	return 0;
 }
 
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 5d88329..b65b8cf 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1789,6 +1789,11 @@
 		       mdname(mddev), mddev->level);
 		goto out;
 	}
+	if (mddev->reshape_position != MaxSector) {
+		printk("raid1: %s: reshape_position set but not supported\n",
+		       mdname(mddev));
+		goto out;
+	}
 	/*
 	 * copy the already verified devices into our private RAID1
 	 * bookkeeping area. [whatever we allocate in run(),
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index b29135a..20ae32d6 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -22,6 +22,7 @@
 #include <linux/raid/raid5.h>
 #include <linux/highmem.h>
 #include <linux/bitops.h>
+#include <linux/kthread.h>
 #include <asm/atomic.h>
 
 #include <linux/raid/bitmap.h>
@@ -1504,6 +1505,7 @@
 		clear_bit(STRIPE_EXPANDING, &sh->state);
 	} else if (expanded) {
 		clear_bit(STRIPE_EXPAND_READY, &sh->state);
+		atomic_dec(&conf->reshape_stripes);
 		wake_up(&conf->wait_for_overlap);
 		md_done_sync(conf->mddev, STRIPE_SECTORS, 1);
 	}
@@ -1875,6 +1877,26 @@
 		 */
 		int i;
 		int dd_idx;
+
+		if (sector_nr == 0 &&
+		    conf->expand_progress != 0) {
+			/* restarting in the middle, skip the initial sectors */
+			sector_nr = conf->expand_progress;
+			sector_div(sector_nr, conf->raid_disks-1);
+			*skipped = 1;
+			return sector_nr;
+		}
+
+		/* Cannot proceed until we've updated the superblock... */
+		wait_event(conf->wait_for_overlap,
+			   atomic_read(&conf->reshape_stripes)==0);
+		mddev->reshape_position = conf->expand_progress;
+
+		mddev->sb_dirty = 1;
+		md_wakeup_thread(mddev->thread);
+		wait_event(mddev->sb_wait, mddev->sb_dirty == 0 ||
+			kthread_should_stop());
+
 		for (i=0; i < conf->chunk_size/512; i+= STRIPE_SECTORS) {
 			int j;
 			int skipped = 0;
@@ -1882,6 +1904,7 @@
 			sh = get_active_stripe(conf, sector_nr+i,
 					       conf->raid_disks, pd_idx, 0);
 			set_bit(STRIPE_EXPANDING, &sh->state);
+			atomic_inc(&conf->reshape_stripes);
 			/* If any of this stripe is beyond the end of the old
 			 * array, then we need to zero those blocks
 			 */
@@ -2121,10 +2144,61 @@
 		return -EIO;
 	}
 
+	if (mddev->reshape_position != MaxSector) {
+		/* Check that we can continue the reshape.
+		 * Currently only disks can change, it must
+		 * increase, and we must be past the point where
+		 * a stripe over-writes itself
+		 */
+		sector_t here_new, here_old;
+		int old_disks;
+
+		if (mddev->new_level != mddev->level ||
+		    mddev->new_layout != mddev->layout ||
+		    mddev->new_chunk != mddev->chunk_size) {
+			printk(KERN_ERR "raid5: %s: unsupported reshape required - aborting.\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+		if (mddev->delta_disks <= 0) {
+			printk(KERN_ERR "raid5: %s: unsupported reshape (reduce disks) required - aborting.\n",
+			       mdname(mddev));
+			return -EINVAL;
+		}
+		old_disks = mddev->raid_disks - mddev->delta_disks;
+		/* reshape_position must be on a new-stripe boundary, and one
+		 * further up in new geometry must map after here in old geometry.
+		 */
+		here_new = mddev->reshape_position;
+		if (sector_div(here_new, (mddev->chunk_size>>9)*(mddev->raid_disks-1))) {
+			printk(KERN_ERR "raid5: reshape_position not on a stripe boundary\n");
+			return -EINVAL;
+		}
+		/* here_new is the stripe we will write to */
+		here_old = mddev->reshape_position;
+		sector_div(here_old, (mddev->chunk_size>>9)*(old_disks-1));
+		/* here_old is the first stripe that we might need to read from */
+		if (here_new >= here_old) {
+			/* Reading from the same stripe as writing to - bad */
+			printk(KERN_ERR "raid5: reshape_position too early for auto-recovery - aborting.\n");
+			return -EINVAL;
+		}
+		printk(KERN_INFO "raid5: reshape will continue\n");
+		/* OK, we should be able to continue; */
+	}
+
+
 	mddev->private = kzalloc(sizeof (raid5_conf_t), GFP_KERNEL);
 	if ((conf = mddev->private) == NULL)
 		goto abort;
-	conf->disks = kzalloc(mddev->raid_disks * sizeof(struct disk_info),
+	if (mddev->reshape_position == MaxSector) {
+		conf->previous_raid_disks = conf->raid_disks = mddev->raid_disks;
+	} else {
+		conf->raid_disks = mddev->raid_disks;
+		conf->previous_raid_disks = mddev->raid_disks - mddev->delta_disks;
+	}
+
+	conf->disks = kzalloc(conf->raid_disks * sizeof(struct disk_info),
 			      GFP_KERNEL);
 	if (!conf->disks)
 		goto abort;
@@ -2148,7 +2222,7 @@
 
 	ITERATE_RDEV(mddev,rdev,tmp) {
 		raid_disk = rdev->raid_disk;
-		if (raid_disk >= mddev->raid_disks
+		if (raid_disk >= conf->raid_disks
 		    || raid_disk < 0)
 			continue;
 		disk = conf->disks + raid_disk;
@@ -2164,7 +2238,6 @@
 		}
 	}
 
-	conf->raid_disks = mddev->raid_disks;
 	/*
 	 * 0 for a fully functional array, 1 for a degraded array.
 	 */
@@ -2174,7 +2247,7 @@
 	conf->level = mddev->level;
 	conf->algorithm = mddev->layout;
 	conf->max_nr_stripes = NR_STRIPES;
-	conf->expand_progress = MaxSector;
+	conf->expand_progress = mddev->reshape_position;
 
 	/* device size must be a multiple of chunk size */
 	mddev->size &= ~(mddev->chunk_size/1024 -1);
@@ -2247,6 +2320,20 @@
 
 	print_raid5_conf(conf);
 
+	if (conf->expand_progress != MaxSector) {
+		printk("...ok start reshape thread\n");
+		atomic_set(&conf->reshape_stripes, 0);
+		clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
+		clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+		set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
+		set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+		mddev->sync_thread = md_register_thread(md_do_sync, mddev,
+							"%s_reshape");
+		/* FIXME if md_register_thread fails?? */
+		md_wakeup_thread(mddev->sync_thread);
+
+	}
+
 	/* read-ahead size must cover two whole stripes, which is
 	 * 2 * (n-1) * chunksize where 'n' is the number of raid devices
 	 */
@@ -2262,8 +2349,8 @@
 
 	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 * (mddev->raid_disks - 1);
 	return 0;
 abort:
 	if (conf) {
@@ -2436,7 +2523,7 @@
 	/*
 	 * find the disk ...
 	 */
-	for (disk=0; disk < mddev->raid_disks; disk++)
+	for (disk=0; disk < conf->raid_disks; disk++)
 		if ((p=conf->disks + disk)->rdev == NULL) {
 			clear_bit(In_sync, &rdev->flags);
 			rdev->raid_disk = disk;
@@ -2518,9 +2605,10 @@
 	if (err)
 		return err;
 
+	atomic_set(&conf->reshape_stripes, 0);
 	spin_lock_irq(&conf->device_lock);
 	conf->previous_raid_disks = conf->raid_disks;
-	mddev->raid_disks = conf->raid_disks = raid_disks;
+	conf->raid_disks = raid_disks;
 	conf->expand_progress = 0;
 	spin_unlock_irq(&conf->device_lock);
 
@@ -2542,6 +2630,14 @@
 		}
 
 	mddev->degraded = (raid_disks - conf->previous_raid_disks) - added_devices;
+	mddev->new_chunk = mddev->chunk_size;
+	mddev->new_layout = mddev->layout;
+	mddev->new_level = mddev->level;
+	mddev->raid_disks = raid_disks;
+	mddev->delta_disks = raid_disks - conf->previous_raid_disks;
+	mddev->reshape_position = 0;
+	mddev->sb_dirty = 1;
+
 	clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
 	clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
 	set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
@@ -2552,6 +2648,7 @@
 		mddev->recovery = 0;
 		spin_lock_irq(&conf->device_lock);
 		mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
+		mddev->delta_disks = 0;
 		conf->expand_progress = MaxSector;
 		spin_unlock_irq(&conf->device_lock);
 		return -EAGAIN;
@@ -2566,20 +2663,23 @@
 {
 	struct block_device *bdev;
 
-	conf->mddev->array_size = conf->mddev->size * (conf->mddev->raid_disks-1);
-	set_capacity(conf->mddev->gendisk, conf->mddev->array_size << 1);
-	conf->mddev->changed = 1;
+	if (!test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery)) {
+		conf->mddev->array_size = conf->mddev->size * (conf->raid_disks-1);
+		set_capacity(conf->mddev->gendisk, conf->mddev->array_size << 1);
+		conf->mddev->changed = 1;
 
-	bdev = bdget_disk(conf->mddev->gendisk, 0);
-	if (bdev) {
-		mutex_lock(&bdev->bd_inode->i_mutex);
-		i_size_write(bdev->bd_inode, conf->mddev->array_size << 10);
-		mutex_unlock(&bdev->bd_inode->i_mutex);
-		bdput(bdev);
+		bdev = bdget_disk(conf->mddev->gendisk, 0);
+		if (bdev) {
+			mutex_lock(&bdev->bd_inode->i_mutex);
+			i_size_write(bdev->bd_inode, conf->mddev->array_size << 10);
+			mutex_unlock(&bdev->bd_inode->i_mutex);
+			bdput(bdev);
+		}
+		spin_lock_irq(&conf->device_lock);
+		conf->expand_progress = MaxSector;
+		spin_unlock_irq(&conf->device_lock);
+		conf->mddev->reshape_position = MaxSector;
 	}
-	spin_lock_irq(&conf->device_lock);
-	conf->expand_progress = MaxSector;
-	spin_unlock_irq(&conf->device_lock);
 }
 
 static void raid5_quiesce(mddev_t *mddev, int state)
diff --git a/include/linux/raid/md.h b/include/linux/raid/md.h
index 9c77cde..66b44e5 100644
--- a/include/linux/raid/md.h
+++ b/include/linux/raid/md.h
@@ -95,6 +95,8 @@
 extern void md_do_sync(mddev_t *mddev);
 extern void md_new_event(mddev_t *mddev);
 
+extern void md_update_sb(mddev_t * mddev);
+
 #define MD_BUG(x...) { printk("md: bug in file %s, line %d\n", __FILE__, __LINE__); md_print_devices(); }
 
 #endif 
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 4e26ef2..1a6f9f2 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -132,6 +132,14 @@
 
 	char				uuid[16];
 
+	/* If the array is being reshaped, we need to record the
+	 * new shape and an indication of where we are up to.
+	 * This is written to the superblock.
+	 * If reshape_position is MaxSector, then no reshape is happening (yet).
+	 */
+	sector_t			reshape_position;
+	int				delta_disks, new_level, new_layout, new_chunk;
+
 	struct mdk_thread_s		*thread;	/* management thread */
 	struct mdk_thread_s		*sync_thread;	/* doing resync or reconstruct */
 	sector_t			curr_resync;	/* blocks scheduled */
diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index c100fa5..774e1ac 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -102,6 +102,18 @@
 #define MD_SB_ERRORS		1
 
 #define	MD_SB_BITMAP_PRESENT	8 /* bitmap may be present nearby */
+
+/*
+ * Notes:
+ * - if an array is being reshaped (restriped) in order to change the
+ *   the number of active devices in the array, 'raid_disks' will be
+ *   the larger of the old and new numbers.  'delta_disks' will
+ *   be the "new - old".  So if +ve, raid_disks is the new value, and
+ *   "raid_disks-delta_disks" is the old.  If -ve, raid_disks is the
+ *   old value and "raid_disks+delta_disks" is the new (smaller) value.
+ */
+
+
 typedef struct mdp_superblock_s {
 	/*
 	 * Constant generic information
@@ -146,7 +158,13 @@
 	__u32 cp_events_hi;	/* 10 high-order of checkpoint update count   */
 #endif
 	__u32 recovery_cp;	/* 11 recovery checkpoint sector count	      */
-	__u32 gstate_sreserved[MD_SB_GENERIC_STATE_WORDS - 12];
+	/* There are only valid for minor_version > 90 */
+	__u64 reshape_position;	/* 12,13 next address in array-space for reshape */
+	__u32 new_level;	/* 14 new level we are reshaping to	      */
+	__u32 delta_disks;	/* 15 change in number of raid_disks	      */
+	__u32 new_layout;	/* 16 new layout			      */
+	__u32 new_chunk;	/* 17 new chunk size (bytes)		      */
+	__u32 gstate_sreserved[MD_SB_GENERIC_STATE_WORDS - 18];
 
 	/*
 	 * Personality information
@@ -207,7 +225,14 @@
 				 * NOTE: signed, so bitmap can be before superblock
 				 * only meaningful of feature_map[0] is set.
 				 */
-	__u8	pad1[128-100];	/* set to 0 when written */
+
+	/* These are only valid with feature bit '4' */
+	__u64	reshape_position;	/* next address in array-space for reshape */
+	__u32	new_level;	/* new level we are reshaping to		*/
+	__u32	delta_disks;	/* change in number of raid_disks		*/
+	__u32	new_layout;	/* new layout					*/
+	__u32	new_chunk;	/* new chunk size (bytes)			*/
+	__u8	pad1[128-124];	/* set to 0 when written */
 
 	/* constant this-device information - 64 bytes */
 	__u64	data_offset;	/* sector start of data, often 0 */
@@ -240,8 +265,9 @@
 
 /* feature_map bits */
 #define MD_FEATURE_BITMAP_OFFSET	1
+#define	MD_FEATURE_RESHAPE_ACTIVE	4
 
-#define	MD_FEATURE_ALL			1
+#define	MD_FEATURE_ALL			5
 
 #endif 
 
diff --git a/include/linux/raid/raid5.h b/include/linux/raid/raid5.h
index 55c738d..abcdf0d 100644
--- a/include/linux/raid/raid5.h
+++ b/include/linux/raid/raid5.h
@@ -224,6 +224,7 @@
 	struct list_head	bitmap_list; /* stripes delaying awaiting bitmap update */
 	atomic_t		preread_active_stripes; /* stripes with scheduled io */
 
+	atomic_t		reshape_stripes; /* stripes with pending writes for reshape */
 	/* unfortunately we need two cache names as we temporarily have
 	 * two caches.
 	 */