linux/drivers/md/dm-raid.c

/*
 * Copyright (C) 2010-2011 Neil Brown
 * Copyright (C) 2010-2011 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include <linux/slab.h>

#include "md.h"
#include "raid1.h"
#include "raid5.h"
#include "bitmap.h"

#include <linux/device-mapper.h>

#define DM_MSG_PREFIX "raid"

/*
 * The following flags are used by dm-raid.c to set up the array state.
 * They must be cleared before md_run is called.
 */
#define FirstUse 10             /* rdev flag */

struct raid_dev {
	/*
	 * Two DM devices, one to hold metadata and one to hold the
	 * actual data/parity.  The reason for this is to not confuse
	 * ti->len and give more flexibility in altering size and
	 * characteristics.
	 *
	 * While it is possible for this device to be associated
	 * with a different physical device than the data_dev, it
	 * is intended for it to be the same.
	 *    |--------- Physical Device ---------|
	 *    |- meta_dev -|------ data_dev ------|
	 */
	struct dm_dev *meta_dev;
	struct dm_dev *data_dev;
	struct mdk_rdev_s rdev;
};

/*
 * Flags for rs->print_flags field.
 */
#define DMPF_SYNC              0x1
#define DMPF_NOSYNC            0x2
#define DMPF_REBUILD           0x4
#define DMPF_DAEMON_SLEEP      0x8
#define DMPF_MIN_RECOVERY_RATE 0x10
#define DMPF_MAX_RECOVERY_RATE 0x20
#define DMPF_MAX_WRITE_BEHIND  0x40
#define DMPF_STRIPE_CACHE      0x80
#define DMPF_REGION_SIZE       0X100
struct raid_set {
	struct dm_target *ti;

	uint64_t print_flags;

	struct mddev_s md;
	struct raid_type *raid_type;
	struct dm_target_callbacks callbacks;

	struct raid_dev dev[0];
};

/* Supported raid types and properties. */
static struct raid_type {
	const char *name;		/* RAID algorithm. */
	const char *descr;		/* Descriptor text for logging. */
	const unsigned parity_devs;	/* # of parity devices. */
	const unsigned minimal_devs;	/* minimal # of devices in set. */
	const unsigned level;		/* RAID level. */
	const unsigned algorithm;	/* RAID algorithm. */
} raid_types[] = {
	{"raid1",    "RAID1 (mirroring)",               0, 2, 1, 0 /* NONE */},
	{"raid4",    "RAID4 (dedicated parity disk)",	1, 2, 5, ALGORITHM_PARITY_0},
	{"raid5_la", "RAID5 (left asymmetric)",		1, 2, 5, ALGORITHM_LEFT_ASYMMETRIC},
	{"raid5_ra", "RAID5 (right asymmetric)",	1, 2, 5, ALGORITHM_RIGHT_ASYMMETRIC},
	{"raid5_ls", "RAID5 (left symmetric)",		1, 2, 5, ALGORITHM_LEFT_SYMMETRIC},
	{"raid5_rs", "RAID5 (right symmetric)",		1, 2, 5, ALGORITHM_RIGHT_SYMMETRIC},
	{"raid6_zr", "RAID6 (zero restart)",		2, 4, 6, ALGORITHM_ROTATING_ZERO_RESTART},
	{"raid6_nr", "RAID6 (N restart)",		2, 4, 6, ALGORITHM_ROTATING_N_RESTART},
	{"raid6_nc", "RAID6 (N continue)",		2, 4, 6, ALGORITHM_ROTATING_N_CONTINUE}
};

static struct raid_type *get_raid_type(char *name)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(raid_types); i++)
		if (!strcmp(raid_types[i].name, name))
			return &raid_types[i];

	return NULL;
}

static struct raid_set *context_alloc(struct dm_target *ti, struct raid_type *raid_type, unsigned raid_devs)
{
	unsigned i;
	struct raid_set *rs;
	sector_t sectors_per_dev;

	if (raid_devs <= raid_type->parity_devs) {
		ti->error = "Insufficient number of devices";
		return ERR_PTR(-EINVAL);
	}

	sectors_per_dev = ti->len;
	if ((raid_type->level > 1) &&
	    sector_div(sectors_per_dev, (raid_devs - raid_type->parity_devs))) {
		ti->error = "Target length not divisible by number of data devices";
		return ERR_PTR(-EINVAL);
	}

	rs = kzalloc(sizeof(*rs) + raid_devs * sizeof(rs->dev[0]), GFP_KERNEL);
	if (!rs) {
		ti->error = "Cannot allocate raid context";
		return ERR_PTR(-ENOMEM);
	}

	mddev_init(&rs->md);

	rs->ti = ti;
	rs->raid_type = raid_type;
	rs->md.raid_disks = raid_devs;
	rs->md.level = raid_type->level;
	rs->md.new_level = rs->md.level;
	rs->md.dev_sectors = sectors_per_dev;
	rs->md.layout = raid_type->algorithm;
	rs->md.new_layout = rs->md.layout;
	rs->md.delta_disks = 0;
	rs->md.recovery_cp = 0;

	for (i = 0; i < raid_devs; i++)
		md_rdev_init(&rs->dev[i].rdev);

	/*
	 * Remaining items to be initialized by further RAID params:
	 *  rs->md.persistent
	 *  rs->md.external
	 *  rs->md.chunk_sectors
	 *  rs->md.new_chunk_sectors
	 */

	return rs;
}

static void context_free(struct raid_set *rs)
{
	int i;

	for (i = 0; i < rs->md.raid_disks; i++) {
		if (rs->dev[i].meta_dev)
			dm_put_device(rs->ti, rs->dev[i].meta_dev);
		if (rs->dev[i].rdev.sb_page)
			put_page(rs->dev[i].rdev.sb_page);
		rs->dev[i].rdev.sb_page = NULL;
		rs->dev[i].rdev.sb_loaded = 0;
		if (rs->dev[i].data_dev)
			dm_put_device(rs->ti, rs->dev[i].data_dev);
	}

	kfree(rs);
}

/*
 * For every device we have two words
 *  <meta_dev>: meta device name or '-' if missing
 *  <data_dev>: data device name or '-' if missing
 *
 * The following are permitted:
 *    - -
 *    - <data_dev>
 *    <meta_dev> <data_dev>
 *
 * The following is not allowed:
 *    <meta_dev> -
 *
 * This code parses those words.  If there is a failure,
 * the caller must use context_free to unwind the operations.
 */
static int dev_parms(struct raid_set *rs, char **argv)
{
	int i;
	int rebuild = 0;
	int metadata_available = 0;
	int ret = 0;

	for (i = 0; i < rs->md.raid_disks; i++, argv += 2) {
		rs->dev[i].rdev.raid_disk = i;

		rs->dev[i].meta_dev = NULL;
		rs->dev[i].data_dev = NULL;

		/*
		 * There are no offsets, since there is a separate device
		 * for data and metadata.
		 */
		rs->dev[i].rdev.data_offset = 0;
		rs->dev[i].rdev.mddev = &rs->md;

		if (strcmp(argv[0], "-")) {
			ret = dm_get_device(rs->ti, argv[0],
					    dm_table_get_mode(rs->ti->table),
					    &rs->dev[i].meta_dev);
			rs->ti->error = "RAID metadata device lookup failure";
			if (ret)
				return ret;

			rs->dev[i].rdev.sb_page = alloc_page(GFP_KERNEL);
			if (!rs->dev[i].rdev.sb_page)
				return -ENOMEM;
		}

		if (!strcmp(argv[1], "-")) {
			if (!test_bit(In_sync, &rs->dev[i].rdev.flags) &&
			    (!rs->dev[i].rdev.recovery_offset)) {
				rs->ti->error = "Drive designated for rebuild not specified";
				return -EINVAL;
			}

			rs->ti->error = "No data device supplied with metadata device";
			if (rs->dev[i].meta_dev)
				return -EINVAL;

			continue;
		}

		ret = dm_get_device(rs->ti, argv[1],
				    dm_table_get_mode(rs->ti->table),
				    &rs->dev[i].data_dev);
		if (ret) {
			rs->ti->error = "RAID device lookup failure";
			return ret;
		}

		if (rs->dev[i].meta_dev) {
			metadata_available = 1;
			rs->dev[i].rdev.meta_bdev = rs->dev[i].meta_dev->bdev;
		}
		rs->dev[i].rdev.bdev = rs->dev[i].data_dev->bdev;
		list_add(&rs->dev[i].rdev.same_set, &rs->md.disks);
		if (!test_bit(In_sync, &rs->dev[i].rdev.flags))
			rebuild++;
	}

	if (metadata_available) {
		rs->md.external = 0;
		rs->md.persistent = 1;
		rs->md.major_version = 2;
	} else if (rebuild && !rs->md.recovery_cp) {
		/*
		 * Without metadata, we will not be able to tell if the array
		 * is in-sync or not - we must assume it is not.  Therefore,
		 * it is impossible to rebuild a drive.
		 *
		 * Even if there is metadata, the on-disk information may
		 * indicate that the array is not in-sync and it will then
		 * fail at that time.
		 *
		 * User could specify 'nosync' option if desperate.
		 */
		DMERR("Unable to rebuild drive while array is not in-sync");
		rs->ti->error = "RAID device lookup failure";
		return -EINVAL;
	}

	return 0;
}

/*
 * validate_region_size
 * @rs
 * @region_size:  region size in sectors.  If 0, pick a size (4MiB default).
 *
 * Set rs->md.bitmap_info.chunksize (which really refers to 'region size').
 * Ensure that (ti->len/region_size < 2^21) - required by MD bitmap.
 *
 * Returns: 0 on success, -EINVAL on failure.
 */
static int validate_region_size(struct raid_set *rs, unsigned long region_size)
{
	unsigned long min_region_size = rs->ti->len / (1 << 21);

	if (!region_size) {
		/*
		 * Choose a reasonable default.  All figures in sectors.
		 */
		if (min_region_size > (1 << 13)) {
			DMINFO("Choosing default region size of %lu sectors",
			       region_size);
			region_size = min_region_size;
		} else {
			DMINFO("Choosing default region size of 4MiB");
			region_size = 1 << 13; /* sectors */
		}
	} else {
		/*
		 * Validate user-supplied value.
		 */
		if (region_size > rs->ti->len) {
			rs->ti->error = "Supplied region size is too large";
			return -EINVAL;
		}

		if (region_size < min_region_size) {
			DMERR("Supplied region_size (%lu sectors) below minimum (%lu)",
			      region_size, min_region_size);
			rs->ti->error = "Supplied region size is too small";
			return -EINVAL;
		}

		if (!is_power_of_2(region_size)) {
			rs->ti->error = "Region size is not a power of 2";
			return -EINVAL;
		}

		if (region_size < rs->md.chunk_sectors) {
			rs->ti->error = "Region size is smaller than the chunk size";
			return -EINVAL;
		}
	}

	/*
	 * Convert sectors to bytes.
	 */
	rs->md.bitmap_info.chunksize = (region_size << 9);

	return 0;
}

/*
 * Possible arguments are...
 *	<chunk_size> [optional_args]
 *
 * Argument definitions
 *    <chunk_size>			The number of sectors per disk that
 *                                      will form the "stripe"
 *    [[no]sync]			Force or prevent recovery of the
 *                                      entire array
 *    [rebuild <idx>]			Rebuild the drive indicated by the index
 *    [daemon_sleep <ms>]		Time between bitmap daemon work to
 *                                      clear bits
 *    [min_recovery_rate <kB/sec/disk>]	Throttle RAID initialization
 *    [max_recovery_rate <kB/sec/disk>]	Throttle RAID initialization
 *    [write_mostly <idx>]		Indicate a write mostly drive via index
 *    [max_write_behind <sectors>]	See '-write-behind=' (man mdadm)
 *    [stripe_cache <sectors>]		Stripe cache size for higher RAIDs
 *    [region_size <sectors>]           Defines granularity of bitmap
 */
static int parse_raid_params(struct raid_set *rs, char **argv,
			     unsigned num_raid_params)
{
	unsigned i, rebuild_cnt = 0;
	unsigned long value, region_size = 0;
	char *key;

	/*
	 * First, parse the in-order required arguments
	 * "chunk_size" is the only argument of this type.
	 */
	if ((strict_strtoul(argv[0], 10, &value) < 0)) {
		rs->ti->error = "Bad chunk size";
		return -EINVAL;
	} else if (rs->raid_type->level == 1) {
		if (value)
			DMERR("Ignoring chunk size parameter for RAID 1");
		value = 0;
	} else if (!is_power_of_2(value)) {
		rs->ti->error = "Chunk size must be a power of 2";
		return -EINVAL;
	} else if (value < 8) {
		rs->ti->error = "Chunk size value is too small";
		return -EINVAL;
	}

	rs->md.new_chunk_sectors = rs->md.chunk_sectors = value;
	argv++;
	num_raid_params--;

	/*
	 * We set each individual device as In_sync with a completed
	 * 'recovery_offset'.  If there has been a device failure or
	 * replacement then one of the following cases applies:
	 *
	 *   1) User specifies 'rebuild'.
	 *      - Device is reset when param is read.
	 *   2) A new device is supplied.
	 *      - No matching superblock found, resets device.
	 *   3) Device failure was transient and returns on reload.
	 *      - Failure noticed, resets device for bitmap replay.
	 *   4) Device hadn't completed recovery after previous failure.
	 *      - Superblock is read and overrides recovery_offset.
	 *
	 * What is found in the superblocks of the devices is always
	 * authoritative, unless 'rebuild' or '[no]sync' was specified.
	 */
	for (i = 0; i < rs->md.raid_disks; i++) {
		set_bit(In_sync, &rs->dev[i].rdev.flags);
		rs->dev[i].rdev.recovery_offset = MaxSector;
	}

	/*
	 * Second, parse the unordered optional arguments
	 */
	for (i = 0; i < num_raid_params; i++) {
		if (!strcasecmp(argv[i], "nosync")) {
			rs->md.recovery_cp = MaxSector;
			rs->print_flags |= DMPF_NOSYNC;
			continue;
		}
		if (!strcasecmp(argv[i], "sync")) {
			rs->md.recovery_cp = 0;
			rs->print_flags |= DMPF_SYNC;
			continue;
		}

		/* The rest of the optional arguments come in key/value pairs */
		if ((i + 1) >= num_raid_params) {
			rs->ti->error = "Wrong number of raid parameters given";
			return -EINVAL;
		}

		key = argv[i++];
		if (strict_strtoul(argv[i], 10, &value) < 0) {
			rs->ti->error = "Bad numerical argument given in raid params";
			return -EINVAL;
		}

		if (!strcasecmp(key, "rebuild")) {
			rebuild_cnt++;
			if (((rs->raid_type->level != 1) &&
			     (rebuild_cnt > rs->raid_type->parity_devs)) ||
			    ((rs->raid_type->level == 1) &&
			     (rebuild_cnt > (rs->md.raid_disks - 1)))) {
				rs->ti->error = "Too many rebuild devices specified for given RAID type";
				return -EINVAL;
			}
			if (value > rs->md.raid_disks) {
				rs->ti->error = "Invalid rebuild index given";
				return -EINVAL;
			}
			clear_bit(In_sync, &rs->dev[value].rdev.flags);
			rs->dev[value].rdev.recovery_offset = 0;
			rs->print_flags |= DMPF_REBUILD;
		} else if (!strcasecmp(key, "write_mostly")) {
			if (rs->raid_type->level != 1) {
				rs->ti->error = "write_mostly option is only valid for RAID1";
				return -EINVAL;
			}
			if (value > rs->md.raid_disks) {
				rs->ti->error = "Invalid write_mostly drive index given";
				return -EINVAL;
			}
			set_bit(WriteMostly, &rs->dev[value].rdev.flags);
		} else if (!strcasecmp(key, "max_write_behind")) {
			if (rs->raid_type->level != 1) {
				rs->ti->error = "max_write_behind option is only valid for RAID1";
				return -EINVAL;
			}
			rs->print_flags |= DMPF_MAX_WRITE_BEHIND;

			/*
			 * In device-mapper, we specify things in sectors, but
			 * MD records this value in kB
			 */
			value /= 2;
			if (value > COUNTER_MAX) {
				rs->ti->error = "Max write-behind limit out of range";
				return -EINVAL;
			}
			rs->md.bitmap_info.max_write_behind = value;
		} else if (!strcasecmp(key, "daemon_sleep")) {
			rs->print_flags |= DMPF_DAEMON_SLEEP;
			if (!value || (value > MAX_SCHEDULE_TIMEOUT)) {
				rs->ti->error = "daemon sleep period out of range";
				return -EINVAL;
			}
			rs->md.bitmap_info.daemon_sleep = value;
		} else if (!strcasecmp(key, "stripe_cache")) {
			rs->print_flags |= DMPF_STRIPE_CACHE;

			/*
			 * In device-mapper, we specify things in sectors, but
			 * MD records this value in kB
			 */
			value /= 2;

			if (rs->raid_type->level < 5) {
				rs->ti->error = "Inappropriate argument: stripe_cache";
				return -EINVAL;
			}
			if (raid5_set_cache_size(&rs->md, (int)value)) {
				rs->ti->error = "Bad stripe_cache size";
				return -EINVAL;
			}
		} else if (!strcasecmp(key, "min_recovery_rate")) {
			rs->print_flags |= DMPF_MIN_RECOVERY_RATE;
			if (value > INT_MAX) {
				rs->ti->error = "min_recovery_rate out of range";
				return -EINVAL;
			}
			rs->md.sync_speed_min = (int)value;
		} else if (!strcasecmp(key, "max_recovery_rate")) {
			rs->print_flags |= DMPF_MAX_RECOVERY_RATE;
			if (value > INT_MAX) {
				rs->ti->error = "max_recovery_rate out of range";
				return -EINVAL;
			}
			rs->md.sync_speed_max = (int)value;
		} else if (!strcasecmp(key, "region_size")) {
			rs->print_flags |= DMPF_REGION_SIZE;
			region_size = value;
		} else {
			DMERR("Unable to parse RAID parameter: %s", key);
			rs->ti->error = "Unable to parse RAID parameters";
			return -EINVAL;
		}
	}

	if (validate_region_size(rs, region_size))
		return -EINVAL;

	if (rs->md.chunk_sectors)
		rs->ti->split_io = rs->md.chunk_sectors;
	else
		rs->ti->split_io = region_size;

	if (rs->md.chunk_sectors)
		rs->ti->split_io = rs->md.chunk_sectors;
	else
		rs->ti->split_io = region_size;

	/* Assume there are no metadata devices until the drives are parsed */
	rs->md.persistent = 0;
	rs->md.external = 1;

	return 0;
}

static void do_table_event(struct work_struct *ws)
{
	struct raid_set *rs = container_of(ws, struct raid_set, md.event_work);

	dm_table_event(rs->ti->table);
}

static int raid_is_congested(struct dm_target_callbacks *cb, int bits)
{
	struct raid_set *rs = container_of(cb, struct raid_set, callbacks);

	if (rs->raid_type->level == 1)
		return md_raid1_congested(&rs->md, bits);

	return md_raid5_congested(&rs->md, bits);
}

/*
 * This structure is never routinely used by userspace, unlike md superblocks.
 * Devices with this superblock should only ever be accessed via device-mapper.
 */
#define DM_RAID_MAGIC 0x64526D44
struct dm_raid_superblock {
	__le32 magic;		/* "DmRd" */
	__le32 features;	/* Used to indicate possible future changes */

	__le32 num_devices;	/* Number of devices in this array. (Max 64) */
	__le32 array_position;	/* The position of this drive in the array */

	__le64 events;		/* Incremented by md when superblock updated */
	__le64 failed_devices;	/* Bit field of devices to indicate failures */

	/*
	 * This offset tracks the progress of the repair or replacement of
	 * an individual drive.
	 */
	__le64 disk_recovery_offset;

	/*
	 * This offset tracks the progress of the initial array
	 * synchronisation/parity calculation.
	 */
	__le64 array_resync_offset;

	/*
	 * RAID characteristics
	 */
	__le32 level;
	__le32 layout;
	__le32 stripe_sectors;

	__u8 pad[452];		/* Round struct to 512 bytes. */
				/* Always set to 0 when writing. */
} __packed;

static int read_disk_sb(mdk_rdev_t *rdev, int size)
{
	BUG_ON(!rdev->sb_page);

	if (rdev->sb_loaded)
		return 0;

	if (!sync_page_io(rdev, 0, size, rdev->sb_page, READ, 1)) {
		DMERR("Failed to read device superblock");
		return -EINVAL;
	}

	rdev->sb_loaded = 1;

	return 0;
}

static void super_sync(mddev_t *mddev, mdk_rdev_t *rdev)
{
	mdk_rdev_t *r, *t;
	uint64_t failed_devices;
	struct dm_raid_superblock *sb;

	sb = page_address(rdev->sb_page);
	failed_devices = le64_to_cpu(sb->failed_devices);

	rdev_for_each(r, t, mddev)
		if ((r->raid_disk >= 0) && test_bit(Faulty, &r->flags))
			failed_devices |= (1ULL << r->raid_disk);

	memset(sb, 0, sizeof(*sb));

	sb->magic = cpu_to_le32(DM_RAID_MAGIC);
	sb->features = cpu_to_le32(0);	/* No features yet */

	sb->num_devices = cpu_to_le32(mddev->raid_disks);
	sb->array_position = cpu_to_le32(rdev->raid_disk);

	sb->events = cpu_to_le64(mddev->events);
	sb->failed_devices = cpu_to_le64(failed_devices);

	sb->disk_recovery_offset = cpu_to_le64(rdev->recovery_offset);
	sb->array_resync_offset = cpu_to_le64(mddev->recovery_cp);

	sb->level = cpu_to_le32(mddev->level);
	sb->layout = cpu_to_le32(mddev->layout);
	sb->stripe_sectors = cpu_to_le32(mddev->chunk_sectors);
}

/*
 * super_load
 *
 * This function creates a superblock if one is not found on the device
 * and will decide which superblock to use if there's a choice.
 *
 * Return: 1 if use rdev, 0 if use refdev, -Exxx otherwise
 */
static int super_load(mdk_rdev_t *rdev, mdk_rdev_t *refdev)
{
	int ret;
	struct dm_raid_superblock *sb;
	struct dm_raid_superblock *refsb;
	uint64_t events_sb, events_refsb;

	rdev->sb_start = 0;
	rdev->sb_size = sizeof(*sb);

	ret = read_disk_sb(rdev, rdev->sb_size);
	if (ret)
		return ret;

	sb = page_address(rdev->sb_page);
	if (sb->magic != cpu_to_le32(DM_RAID_MAGIC)) {
		super_sync(rdev->mddev, rdev);

		set_bit(FirstUse, &rdev->flags);

		/* Force writing of superblocks to disk */
		set_bit(MD_CHANGE_DEVS, &rdev->mddev->flags);

		/* Any superblock is better than none, choose that if given */
		return refdev ? 0 : 1;
	}

	if (!refdev)
		return 1;

	events_sb = le64_to_cpu(sb->events);

	refsb = page_address(refdev->sb_page);
	events_refsb = le64_to_cpu(refsb->events);

	return (events_sb > events_refsb) ? 1 : 0;
}

static int super_init_validation(mddev_t *mddev, mdk_rdev_t *rdev)
{
	int role;
	struct raid_set *rs = container_of(mddev, struct raid_set, md);
	uint64_t events_sb;
	uint64_t failed_devices;
	struct dm_raid_superblock *sb;
	uint32_t new_devs = 0;
	uint32_t rebuilds = 0;
	mdk_rdev_t *r, *t;
	struct dm_raid_superblock *sb2;

	sb = page_address(rdev->sb_page);
	events_sb = le64_to_cpu(sb->events);
	failed_devices = le64_to_cpu(sb->failed_devices);

	/*
	 * Initialise to 1 if this is a new superblock.
	 */
	mddev->events = events_sb ? : 1;

	/*
	 * Reshaping is not currently allowed
	 */
	if ((le32_to_cpu(sb->level) != mddev->level) ||
	    (le32_to_cpu(sb->layout) != mddev->layout) ||
	    (le32_to_cpu(sb->stripe_sectors) != mddev->chunk_sectors)) {
		DMERR("Reshaping arrays not yet supported.");
		return -EINVAL;
	}

	/* We can only change the number of devices in RAID1 right now */
	if ((rs->raid_type->level != 1) &&
	    (le32_to_cpu(sb->num_devices) != mddev->raid_disks)) {
		DMERR("Reshaping arrays not yet supported.");
		return -EINVAL;
	}

	if (!(rs->print_flags & (DMPF_SYNC | DMPF_NOSYNC)))
		mddev->recovery_cp = le64_to_cpu(sb->array_resync_offset);

	/*
	 * During load, we set FirstUse if a new superblock was written.
	 * There are two reasons we might not have a superblock:
	 * 1) The array is brand new - in which case, all of the
	 *    devices must have their In_sync bit set.  Also,
	 *    recovery_cp must be 0, unless forced.
	 * 2) This is a new device being added to an old array
	 *    and the new device needs to be rebuilt - in which
	 *    case the In_sync bit will /not/ be set and
	 *    recovery_cp must be MaxSector.
	 */
	rdev_for_each(r, t, mddev) {
		if (!test_bit(In_sync, &r->flags)) {
			if (!test_bit(FirstUse, &r->flags))
				DMERR("Superblock area of "
				      "rebuild device %d should have been "
				      "cleared.", r->raid_disk);
			set_bit(FirstUse, &r->flags);
			rebuilds++;
		} else if (test_bit(FirstUse, &r->flags))
			new_devs++;
	}

	if (!rebuilds) {
		if (new_devs == mddev->raid_disks) {
			DMINFO("Superblocks created for new array");
			set_bit(MD_ARRAY_FIRST_USE, &mddev->flags);
		} else if (new_devs) {
			DMERR("New device injected "
			      "into existing array without 'rebuild' "
			      "parameter specified");
			return -EINVAL;
		}
	} else if (new_devs) {
		DMERR("'rebuild' devices cannot be "
		      "injected into an array with other first-time devices");
		return -EINVAL;
	} else if (mddev->recovery_cp != MaxSector) {
		DMERR("'rebuild' specified while array is not in-sync");
		return -EINVAL;
	}

	/*
	 * Now we set the Faulty bit for those devices that are
	 * recorded in the superblock as failed.
	 */
	rdev_for_each(r, t, mddev) {
		if (!r->sb_page)
			continue;
		sb2 = page_address(r->sb_page);
		sb2->failed_devices = 0;

		/*
		 * Check for any device re-ordering.
		 */
		if (!test_bit(FirstUse, &r->flags) && (r->raid_disk >= 0)) {
			role = le32_to_cpu(sb2->array_position);
			if (role != r->raid_disk) {
				if (rs->raid_type->level != 1) {
					rs->ti->error = "Cannot change device "
						"positions in RAID array";
					return -EINVAL;
				}
				DMINFO("RAID1 device #%d now at position #%d",
				       role, r->raid_disk);
			}

			/*
			 * Partial recovery is performed on
			 * returning failed devices.
			 */
			if (failed_devices & (1 << role))
				set_bit(Faulty, &r->flags);
		}
	}

	return 0;
}

static int super_validate(mddev_t *mddev, mdk_rdev_t *rdev)
{
	struct dm_raid_superblock *sb = page_address(rdev->sb_page);

	/*
	 * If mddev->events is not set, we know we have not yet initialized
	 * the array.
	 */
	if (!mddev->events && super_init_validation(mddev, rdev))
		return -EINVAL;

	mddev->bitmap_info.offset = 4096 >> 9; /* Enable bitmap creation */
	rdev->mddev->bitmap_info.default_offset = 4096 >> 9;
	if (!test_bit(FirstUse, &rdev->flags)) {
		rdev->recovery_offset = le64_to_cpu(sb->disk_recovery_offset);
		if (rdev->recovery_offset != MaxSector)
			clear_bit(In_sync, &rdev->flags);
	}

	/*
	 * If a device comes back, set it as not In_sync and no longer faulty.
	 */
	if (test_bit(Faulty, &rdev->flags)) {
		clear_bit(Faulty, &rdev->flags);
		clear_bit(In_sync, &rdev->flags);
		rdev->saved_raid_disk = rdev->raid_disk;
		rdev->recovery_offset = 0;
	}

	clear_bit(FirstUse, &rdev->flags);

	return 0;
}

/*
 * Analyse superblocks and select the freshest.
 */
static int analyse_superblocks(struct dm_target *ti, struct raid_set *rs)
{
	int ret;
	mdk_rdev_t *rdev, *freshest, *tmp;
	mddev_t *mddev = &rs->md;

	freshest = NULL;
	rdev_for_each(rdev, tmp, mddev) {
		if (!rdev->meta_bdev)
			continue;

		ret = super_load(rdev, freshest);

		switch (ret) {
		case 1:
			freshest = rdev;
			break;
		case 0:
			break;
		default:
			ti->error = "Failed to load superblock";
			return ret;
		}
	}

	if (!freshest)
		return 0;

	/*
	 * Validation of the freshest device provides the source of
	 * validation for the remaining devices.
	 */
	ti->error = "Unable to assemble array: Invalid superblocks";
	if (super_validate(mddev, freshest))
		return -EINVAL;

	rdev_for_each(rdev, tmp, mddev)
		if ((rdev != freshest) && super_validate(mddev, rdev))
			return -EINVAL;

	return 0;
}

/*
 * Construct a RAID4/5/6 mapping:
 * Args:
 *	<raid_type> <#raid_params> <raid_params>		\
 *	<#raid_devs> { <meta_dev1> <dev1> .. <meta_devN> <devN> }
 *
 * <raid_params> varies by <raid_type>.  See 'parse_raid_params' for
 * details on possible <raid_params>.
 */
static int raid_ctr(struct dm_target *ti, unsigned argc, char **argv)
{
	int ret;
	struct raid_type *rt;
	unsigned long num_raid_params, num_raid_devs;
	struct raid_set *rs = NULL;

	/* Must have at least <raid_type> <#raid_params> */
	if (argc < 2) {
		ti->error = "Too few arguments";
		return -EINVAL;
	}

	/* raid type */
	rt = get_raid_type(argv[0]);
	if (!rt) {
		ti->error = "Unrecognised raid_type";
		return -EINVAL;
	}
	argc--;
	argv++;

	/* number of RAID parameters */
	if (strict_strtoul(argv[0], 10, &num_raid_params) < 0) {
		ti->error = "Cannot understand number of RAID parameters";
		return -EINVAL;
	}
	argc--;
	argv++;

	/* Skip over RAID params for now and find out # of devices */
	if (num_raid_params + 1 > argc) {
		ti->error = "Arguments do not agree with counts given";
		return -EINVAL;
	}

	if ((strict_strtoul(argv[num_raid_params], 10, &num_raid_devs) < 0) ||
	    (num_raid_devs >= INT_MAX)) {
		ti->error = "Cannot understand number of raid devices";
		return -EINVAL;
	}

	rs = context_alloc(ti, rt, (unsigned)num_raid_devs);
	if (IS_ERR(rs))
		return PTR_ERR(rs);

	ret = parse_raid_params(rs, argv, (unsigned)num_raid_params);
	if (ret)
		goto bad;

	ret = -EINVAL;

	argc -= num_raid_params + 1; /* +1: we already have num_raid_devs */
	argv += num_raid_params + 1;

	if (argc != (num_raid_devs * 2)) {
		ti->error = "Supplied RAID devices does not match the count given";
		goto bad;
	}

	ret = dev_parms(rs, argv);
	if (ret)
		goto bad;

	rs->md.sync_super = super_sync;
	ret = analyse_superblocks(ti, rs);
	if (ret)
		goto bad;

	INIT_WORK(&rs->md.event_work, do_table_event);
	ti->private = rs;

	mutex_lock(&rs->md.reconfig_mutex);
	ret = md_run(&rs->md);
	rs->md.in_sync = 0; /* Assume already marked dirty */
	mutex_unlock(&rs->md.reconfig_mutex);

	if (ret) {
		ti->error = "Fail to run raid array";
		goto bad;
	}

	rs->callbacks.congested_fn = raid_is_congested;
	dm_table_add_target_callbacks(ti->table, &rs->callbacks);

	mddev_suspend(&rs->md);
	return 0;

bad:
	context_free(rs);

	return ret;
}

static void raid_dtr(struct dm_target *ti)
{
	struct raid_set *rs = ti->private;

	list_del_init(&rs->callbacks.list);
	md_stop(&rs->md);
	context_free(rs);
}

static int raid_map(struct dm_target *ti, struct bio *bio, union map_info *map_context)
{
	struct raid_set *rs = ti->private;
	mddev_t *mddev = &rs->md;

	mddev->pers->make_request(mddev, bio);

	return DM_MAPIO_SUBMITTED;
}

static int raid_status(struct dm_target *ti, status_type_t type,
		       char *result, unsigned maxlen)
{
	struct raid_set *rs = ti->private;
	unsigned raid_param_cnt = 1; /* at least 1 for chunksize */
	unsigned sz = 0;
	int i;
	sector_t sync;

	switch (type) {
	case STATUSTYPE_INFO:
		DMEMIT("%s %d ", rs->raid_type->name, rs->md.raid_disks);

		for (i = 0; i < rs->md.raid_disks; i++) {
			if (test_bit(Faulty, &rs->dev[i].rdev.flags))
				DMEMIT("D");
			else if (test_bit(In_sync, &rs->dev[i].rdev.flags))
				DMEMIT("A");
			else
				DMEMIT("a");
		}

		if (test_bit(MD_RECOVERY_RUNNING, &rs->md.recovery))
			sync = rs->md.curr_resync_completed;
		else
			sync = rs->md.recovery_cp;

		if (sync > rs->md.resync_max_sectors)
			sync = rs->md.resync_max_sectors;

		DMEMIT(" %llu/%llu",
		       (unsigned long long) sync,
		       (unsigned long long) rs->md.resync_max_sectors);

		break;
	case STATUSTYPE_TABLE:
		/* The string you would use to construct this array */
		for (i = 0; i < rs->md.raid_disks; i++) {
			if ((rs->print_flags & DMPF_REBUILD) &&
			    rs->dev[i].data_dev &&
			    !test_bit(In_sync, &rs->dev[i].rdev.flags))
				raid_param_cnt += 2; /* for rebuilds */
			if (rs->dev[i].data_dev &&
			    test_bit(WriteMostly, &rs->dev[i].rdev.flags))
				raid_param_cnt += 2;
		}

		raid_param_cnt += (hweight64(rs->print_flags & ~DMPF_REBUILD) * 2);
		if (rs->print_flags & (DMPF_SYNC | DMPF_NOSYNC))
			raid_param_cnt--;

		DMEMIT("%s %u %u", rs->raid_type->name,
		       raid_param_cnt, rs->md.chunk_sectors);

		if ((rs->print_flags & DMPF_SYNC) &&
		    (rs->md.recovery_cp == MaxSector))
			DMEMIT(" sync");
		if (rs->print_flags & DMPF_NOSYNC)
			DMEMIT(" nosync");

		for (i = 0; i < rs->md.raid_disks; i++)
			if ((rs->print_flags & DMPF_REBUILD) &&
			    rs->dev[i].data_dev &&
			    !test_bit(In_sync, &rs->dev[i].rdev.flags))
				DMEMIT(" rebuild %u", i);

		if (rs->print_flags & DMPF_DAEMON_SLEEP)
			DMEMIT(" daemon_sleep %lu",
			       rs->md.bitmap_info.daemon_sleep);

		if (rs->print_flags & DMPF_MIN_RECOVERY_RATE)
			DMEMIT(" min_recovery_rate %d", rs->md.sync_speed_min);

		if (rs->print_flags & DMPF_MAX_RECOVERY_RATE)
			DMEMIT(" max_recovery_rate %d", rs->md.sync_speed_max);

		for (i = 0; i < rs->md.raid_disks; i++)
			if (rs->dev[i].data_dev &&
			    test_bit(WriteMostly, &rs->dev[i].rdev.flags))
				DMEMIT(" write_mostly %u", i);

		if (rs->print_flags & DMPF_MAX_WRITE_BEHIND)
			DMEMIT(" max_write_behind %lu",
			       rs->md.bitmap_info.max_write_behind);

		if (rs->print_flags & DMPF_STRIPE_CACHE) {
			raid5_conf_t *conf = rs->md.private;

			/* convert from kiB to sectors */
			DMEMIT(" stripe_cache %d",
			       conf ? conf->max_nr_stripes * 2 : 0);
		}

		if (rs->print_flags & DMPF_REGION_SIZE)
			DMEMIT(" region_size %lu",
			       rs->md.bitmap_info.chunksize >> 9);

		DMEMIT(" %d", rs->md.raid_disks);
		for (i = 0; i < rs->md.raid_disks; i++) {
			if (rs->dev[i].meta_dev)
				DMEMIT(" %s", rs->dev[i].meta_dev->name);
			else
				DMEMIT(" -");

			if (rs->dev[i].data_dev)
				DMEMIT(" %s", rs->dev[i].data_dev->name);
			else
				DMEMIT(" -");
		}
	}

	return 0;
}

static int raid_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
{
	struct raid_set *rs = ti->private;
	unsigned i;
	int ret = 0;

	for (i = 0; !ret && i < rs->md.raid_disks; i++)
		if (rs->dev[i].data_dev)
			ret = fn(ti,
				 rs->dev[i].data_dev,
				 0, /* No offset on data devs */
				 rs->md.dev_sectors,
				 data);

	return ret;
}

static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
{
	struct raid_set *rs = ti->private;
	unsigned chunk_size = rs->md.chunk_sectors << 9;
	raid5_conf_t *conf = rs->md.private;

	blk_limits_io_min(limits, chunk_size);
	blk_limits_io_opt(limits, chunk_size * (conf->raid_disks - conf->max_degraded));
}

static void raid_presuspend(struct dm_target *ti)
{
	struct raid_set *rs = ti->private;

	md_stop_writes(&rs->md);
}

static void raid_postsuspend(struct dm_target *ti)
{
	struct raid_set *rs = ti->private;

	mddev_suspend(&rs->md);
}

static void raid_resume(struct dm_target *ti)
{
	struct raid_set *rs = ti->private;

	bitmap_load(&rs->md);
	mddev_resume(&rs->md);
}

static struct target_type raid_target = {
	.name = "raid",
	.version = {1, 1, 0},
	.module = THIS_MODULE,
	.ctr = raid_ctr,
	.dtr = raid_dtr,
	.map = raid_map,
	.status = raid_status,
	.iterate_devices = raid_iterate_devices,
	.io_hints = raid_io_hints,
	.presuspend = raid_presuspend,
	.postsuspend = raid_postsuspend,
	.resume = raid_resume,
};

static int __init dm_raid_init(void)
{
	return dm_register_target(&raid_target);
}

static void __exit dm_raid_exit(void)
{
	dm_unregister_target(&raid_target);
}

module_init(dm_raid_init);
module_exit(dm_raid_exit);

MODULE_DESCRIPTION(DM_NAME " raid4/5/6 target");
MODULE_ALIAS("dm-raid4");
MODULE_ALIAS("dm-raid5");
MODULE_ALIAS("dm-raid6");
MODULE_AUTHOR("Neil Brown <dm-devel@redhat.com>");
MODULE_LICENSE("GPL");