drivers/md/dm-flakey.c - kernel/msm-4.9 - Gitiles

 /*
  * Copyright (C) 2003 Sistina Software (UK) Limited.
  * Copyright (C) 2004, 2010-2011 Red Hat, Inc. All rights reserved.
  *
  * This file is released under the GPL.
  */

 #include <linux/device-mapper.h>

 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/blkdev.h>
 #include <linux/bio.h>
 #include <linux/slab.h>

 #define DM_MSG_PREFIX "flakey"

 #define all_corrupt_bio_flags_match(bio, fc)	\
 	(((bio)->bi_rw & (fc)->corrupt_bio_flags) == (fc)->corrupt_bio_flags)

 /*
  * Flakey: Used for testing only, simulates intermittent,
  * catastrophic device failure.
  */
 struct flakey_c {
 	struct dm_dev *dev;
 	unsigned long start_time;
 	sector_t start;
 	unsigned up_interval;
 	unsigned down_interval;
 	unsigned long flags;
 	unsigned corrupt_bio_byte;
 	unsigned corrupt_bio_rw;
 	unsigned corrupt_bio_value;
 	unsigned corrupt_bio_flags;
 };

 enum feature_flag_bits {
 	DROP_WRITES
 };

 static int parse_features(struct dm_arg_set *as, struct flakey_c *fc,
 			  struct dm_target *ti)
 {
 	int r;
 	unsigned argc;
 	const char *arg_name;

 	static struct dm_arg _args[] = {
 		{0, 6, "Invalid number of feature args"},
 		{1, UINT_MAX, "Invalid corrupt bio byte"},
 		{0, 255, "Invalid corrupt value to write into bio byte (0-255)"},
 		{0, UINT_MAX, "Invalid corrupt bio flags mask"},
 	};

 	/* No feature arguments supplied. */
 	if (!as->argc)
 		return 0;

 	r = dm_read_arg_group(_args, as, &argc, &ti->error);
 	if (r)
 		return r;

 	while (argc) {
 		arg_name = dm_shift_arg(as);
 		argc--;

 		/*
 		 * drop_writes
 		 */
 		if (!strcasecmp(arg_name, "drop_writes")) {
 			if (test_and_set_bit(DROP_WRITES, &fc->flags)) {
 				ti->error = "Feature drop_writes duplicated";
 				return -EINVAL;
 			}

 			continue;
 		}

 		/*
 		 * corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>
 		 */
 		if (!strcasecmp(arg_name, "corrupt_bio_byte")) {
 			if (!argc) {
 				ti->error = "Feature corrupt_bio_byte requires parameters";
 				return -EINVAL;
 			}

 			r = dm_read_arg(_args + 1, as, &fc->corrupt_bio_byte, &ti->error);
 			if (r)
 				return r;
 			argc--;

 			/*
 			 * Direction r or w?
 			 */
 			arg_name = dm_shift_arg(as);
 			if (!strcasecmp(arg_name, "w"))
 				fc->corrupt_bio_rw = WRITE;
 			else if (!strcasecmp(arg_name, "r"))
 				fc->corrupt_bio_rw = READ;
 			else {
 				ti->error = "Invalid corrupt bio direction (r or w)";
 				return -EINVAL;
 			}
 			argc--;

 			/*
 			 * Value of byte (0-255) to write in place of correct one.
 			 */
 			r = dm_read_arg(_args + 2, as, &fc->corrupt_bio_value, &ti->error);
 			if (r)
 				return r;
 			argc--;

 			/*
 			 * Only corrupt bios with these flags set.
 			 */
 			r = dm_read_arg(_args + 3, as, &fc->corrupt_bio_flags, &ti->error);
 			if (r)
 				return r;
 			argc--;

 			continue;
 		}

 		ti->error = "Unrecognised flakey feature requested";
 		return -EINVAL;
 	}

 	if (test_bit(DROP_WRITES, &fc->flags) && (fc->corrupt_bio_rw == WRITE)) {
 		ti->error = "drop_writes is incompatible with corrupt_bio_byte with the WRITE flag set";
 		return -EINVAL;
 	}

 	return 0;
 }

 /*
  * Construct a flakey mapping:
  * <dev_path> <offset> <up interval> <down interval> [<#feature args> [<arg>]*]
  *
  *   Feature args:
  *     [drop_writes]
  *     [corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>]
  *
  *   Nth_byte starts from 1 for the first byte.
  *   Direction is r for READ or w for WRITE.
  *   bio_flags is ignored if 0.
  */
 static int flakey_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
 	static struct dm_arg _args[] = {
 		{0, UINT_MAX, "Invalid up interval"},
 		{0, UINT_MAX, "Invalid down interval"},
 	};

 	int r;
 	struct flakey_c *fc;
 	unsigned long long tmpll;
 	struct dm_arg_set as;
 	const char *devname;

 	as.argc = argc;
 	as.argv = argv;

 	if (argc < 4) {
 		ti->error = "Invalid argument count";
 		return -EINVAL;
 	}

 	fc = kzalloc(sizeof(*fc), GFP_KERNEL);
 	if (!fc) {
 		ti->error = "Cannot allocate linear context";
 		return -ENOMEM;
 	}
 	fc->start_time = jiffies;

 	devname = dm_shift_arg(&as);

 	if (sscanf(dm_shift_arg(&as), "%llu", &tmpll) != 1) {
 		ti->error = "Invalid device sector";
 		goto bad;
 	}
 	fc->start = tmpll;

 	r = dm_read_arg(_args, &as, &fc->up_interval, &ti->error);
 	if (r)
 		goto bad;

 	r = dm_read_arg(_args, &as, &fc->down_interval, &ti->error);
 	if (r)
 		goto bad;

 	if (!(fc->up_interval + fc->down_interval)) {
 		ti->error = "Total (up + down) interval is zero";
 		goto bad;
 	}

 	if (fc->up_interval + fc->down_interval < fc->up_interval) {
 		ti->error = "Interval overflow";
 		goto bad;
 	}

 	r = parse_features(&as, fc, ti);
 	if (r)
 		goto bad;

 	if (dm_get_device(ti, devname, dm_table_get_mode(ti->table), &fc->dev)) {
 		ti->error = "Device lookup failed";
 		goto bad;
 	}

 	ti->num_flush_requests = 1;
 	ti->num_discard_requests = 1;
 	ti->private = fc;
 	return 0;

 bad:
 	kfree(fc);
 	return -EINVAL;
 }

 static void flakey_dtr(struct dm_target *ti)
 {
 	struct flakey_c *fc = ti->private;

 	dm_put_device(ti, fc->dev);
 	kfree(fc);
 }

 static sector_t flakey_map_sector(struct dm_target *ti, sector_t bi_sector)
 {
 	struct flakey_c *fc = ti->private;

 	return fc->start + dm_target_offset(ti, bi_sector);
 }

 static void flakey_map_bio(struct dm_target *ti, struct bio *bio)
 {
 	struct flakey_c *fc = ti->private;

 	bio->bi_bdev = fc->dev->bdev;
 	if (bio_sectors(bio))
 		bio->bi_sector = flakey_map_sector(ti, bio->bi_sector);
 }

 static void corrupt_bio_data(struct bio *bio, struct flakey_c *fc)
 {
 	unsigned bio_bytes = bio_cur_bytes(bio);
 	char *data = bio_data(bio);

 	/*
 	 * Overwrite the Nth byte of the data returned.
 	 */
 	if (data && bio_bytes >= fc->corrupt_bio_byte) {
 		data[fc->corrupt_bio_byte - 1] = fc->corrupt_bio_value;

 		DMDEBUG("Corrupting data bio=%p by writing %u to byte %u "
 			"(rw=%c bi_rw=%lu bi_sector=%llu cur_bytes=%u)\n",
 			bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
 			(bio_data_dir(bio) == WRITE) ? 'w' : 'r',
 			bio->bi_rw, (unsigned long long)bio->bi_sector, bio_bytes);
 	}
 }

 static int flakey_map(struct dm_target *ti, struct bio *bio,
 		      union map_info *map_context)
 {
 	struct flakey_c *fc = ti->private;
 	unsigned elapsed;

 	/* Are we alive ? */
 	elapsed = (jiffies - fc->start_time) / HZ;
 	if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval) {
 		/*
 		 * Flag this bio as submitted while down.
 		 */
 		map_context->ll = 1;

 		/*
 		 * Map reads as normal.
 		 */
 		if (bio_data_dir(bio) == READ)
 			goto map_bio;

 		/*
 		 * Drop writes?
 		 */
 		if (test_bit(DROP_WRITES, &fc->flags)) {
 			bio_endio(bio, 0);
 			return DM_MAPIO_SUBMITTED;
 		}

 		/*
 		 * Corrupt matching writes.
 		 */
 		if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == WRITE)) {
 			if (all_corrupt_bio_flags_match(bio, fc))
 				corrupt_bio_data(bio, fc);
 			goto map_bio;
 		}

 		/*
 		 * By default, error all I/O.
 		 */
 		return -EIO;
 	}

 map_bio:
 	flakey_map_bio(ti, bio);

 	return DM_MAPIO_REMAPPED;
 }

 static int flakey_end_io(struct dm_target *ti, struct bio *bio,
 			 int error, union map_info *map_context)
 {
 	struct flakey_c *fc = ti->private;
 	unsigned bio_submitted_while_down = map_context->ll;

 	/*
 	 * Corrupt successful READs while in down state.
 	 * If flags were specified, only corrupt those that match.
 	 */
 	if (!error && bio_submitted_while_down &&
 	    (bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw == READ) &&
 	    all_corrupt_bio_flags_match(bio, fc))
 		corrupt_bio_data(bio, fc);

 	return error;
 }

 static int flakey_status(struct dm_target *ti, status_type_t type,
 			 char *result, unsigned int maxlen)
 {
 	unsigned sz = 0;
 	struct flakey_c *fc = ti->private;
 	unsigned drop_writes;

 	switch (type) {
 	case STATUSTYPE_INFO:
 		result[0] = '\0';
 		break;

 	case STATUSTYPE_TABLE:
 		DMEMIT("%s %llu %u %u ", fc->dev->name,
 		       (unsigned long long)fc->start, fc->up_interval,
 		       fc->down_interval);

 		drop_writes = test_bit(DROP_WRITES, &fc->flags);
 		DMEMIT("%u ", drop_writes + (fc->corrupt_bio_byte > 0) * 5);

 		if (drop_writes)
 			DMEMIT("drop_writes ");

 		if (fc->corrupt_bio_byte)
 			DMEMIT("corrupt_bio_byte %u %c %u %u ",
 			       fc->corrupt_bio_byte,
 			       (fc->corrupt_bio_rw == WRITE) ? 'w' : 'r',
 			       fc->corrupt_bio_value, fc->corrupt_bio_flags);

 		break;
 	}
 	return 0;
 }

 static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
 {
 	struct flakey_c *fc = ti->private;
 	struct dm_dev *dev = fc->dev;
 	int r = 0;

 	/*
 	 * Only pass ioctls through if the device sizes match exactly.
 	 */
 	if (fc->start ||
 	    ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
 		r = scsi_verify_blk_ioctl(NULL, cmd);

 	return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
 }

 static int flakey_merge(struct dm_target *ti, struct bvec_merge_data *bvm,
 			struct bio_vec *biovec, int max_size)
 {
 	struct flakey_c *fc = ti->private;
 	struct request_queue *q = bdev_get_queue(fc->dev->bdev);

 	if (!q->merge_bvec_fn)
 		return max_size;

 	bvm->bi_bdev = fc->dev->bdev;
 	bvm->bi_sector = flakey_map_sector(ti, bvm->bi_sector);

 	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
 }

 static int flakey_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn, void *data)
 {
 	struct flakey_c *fc = ti->private;

 	return fn(ti, fc->dev, fc->start, ti->len, data);
 }

 static struct target_type flakey_target = {
 	.name   = "flakey",
 	.version = {1, 2, 0},
 	.module = THIS_MODULE,
 	.ctr    = flakey_ctr,
 	.dtr    = flakey_dtr,
 	.map    = flakey_map,
 	.end_io = flakey_end_io,
 	.status = flakey_status,
 	.ioctl	= flakey_ioctl,
 	.merge	= flakey_merge,
 	.iterate_devices = flakey_iterate_devices,
 };

 static int __init dm_flakey_init(void)
 {
 	int r = dm_register_target(&flakey_target);

 	if (r < 0)
 		DMERR("register failed %d", r);

 	return r;
 }

 static void __exit dm_flakey_exit(void)
 {
 	dm_unregister_target(&flakey_target);
 }

 /* Module hooks */
 module_init(dm_flakey_init);
 module_exit(dm_flakey_exit);

 MODULE_DESCRIPTION(DM_NAME " flakey target");
 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
 MODULE_LICENSE("GPL");
	/*
	* Copyright (C) 2003 Sistina Software (UK) Limited.
	* Copyright (C) 2004, 2010-2011 Red Hat, Inc. All rights reserved.
	*
	* This file is released under the GPL.
	*/

	#include <linux/device-mapper.h>

	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/blkdev.h>
	#include <linux/bio.h>
	#include <linux/slab.h>

	#define DM_MSG_PREFIX "flakey"

	#define all_corrupt_bio_flags_match(bio, fc) \
	(((bio)->bi_rw & (fc)->corrupt_bio_flags) == (fc)->corrupt_bio_flags)

	/*
	* Flakey: Used for testing only, simulates intermittent,
	* catastrophic device failure.
	*/
	struct flakey_c {
	struct dm_dev *dev;
	unsigned long start_time;
	sector_t start;
	unsigned up_interval;
	unsigned down_interval;
	unsigned long flags;
	unsigned corrupt_bio_byte;
	unsigned corrupt_bio_rw;
	unsigned corrupt_bio_value;
	unsigned corrupt_bio_flags;
	};

	enum feature_flag_bits {
	DROP_WRITES
	};

	static int parse_features(struct dm_arg_set as, struct flakey_c fc,
	struct dm_target *ti)
	{
	int r;
	unsigned argc;
	const char *arg_name;

	static struct dm_arg _args[] = {
	{0, 6, "Invalid number of feature args"},
	{1, UINT_MAX, "Invalid corrupt bio byte"},
	{0, 255, "Invalid corrupt value to write into bio byte (0-255)"},
	{0, UINT_MAX, "Invalid corrupt bio flags mask"},
	};

	/* No feature arguments supplied. */
	if (!as->argc)
	return 0;

	r = dm_read_arg_group(_args, as, &argc, &ti->error);
	if (r)
	return r;

	while (argc) {
	arg_name = dm_shift_arg(as);
	argc--;

	/*
	* drop_writes
	*/
	if (!strcasecmp(arg_name, "drop_writes")) {
	if (test_and_set_bit(DROP_WRITES, &fc->flags)) {
	ti->error = "Feature drop_writes duplicated";
	return -EINVAL;
	}

	continue;
	}

	/*
	* corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>
	*/
	if (!strcasecmp(arg_name, "corrupt_bio_byte")) {
	if (!argc) {
	ti->error = "Feature corrupt_bio_byte requires parameters";
	return -EINVAL;
	}

	r = dm_read_arg(_args + 1, as, &fc->corrupt_bio_byte, &ti->error);
	if (r)
	return r;
	argc--;

	/*
	* Direction r or w?
	*/
	arg_name = dm_shift_arg(as);
	if (!strcasecmp(arg_name, "w"))
	fc->corrupt_bio_rw = WRITE;
	else if (!strcasecmp(arg_name, "r"))
	fc->corrupt_bio_rw = READ;
	else {
	ti->error = "Invalid corrupt bio direction (r or w)";
	return -EINVAL;
	}
	argc--;

	/*
	* Value of byte (0-255) to write in place of correct one.
	*/
	r = dm_read_arg(_args + 2, as, &fc->corrupt_bio_value, &ti->error);
	if (r)
	return r;
	argc--;

	/*
	* Only corrupt bios with these flags set.
	*/
	r = dm_read_arg(_args + 3, as, &fc->corrupt_bio_flags, &ti->error);
	if (r)
	return r;
	argc--;

	continue;
	}

	ti->error = "Unrecognised flakey feature requested";
	return -EINVAL;
	}

	if (test_bit(DROP_WRITES, &fc->flags) && (fc->corrupt_bio_rw == WRITE)) {
	ti->error = "drop_writes is incompatible with corrupt_bio_byte with the WRITE flag set";
	return -EINVAL;
	}

	return 0;
	}

	/*
	* Construct a flakey mapping:
	* <dev_path> <offset> <up interval> <down interval> [<#feature args> [<arg>]*]
	*
	* Feature args:
	* [drop_writes]
	* [corrupt_bio_byte <Nth_byte> <direction> <value> <bio_flags>]
	*
	* Nth_byte starts from 1 for the first byte.
	* Direction is r for READ or w for WRITE.
	* bio_flags is ignored if 0.
	*/
	static int flakey_ctr(struct dm_target ti, unsigned int argc, char *argv)
	{
	static struct dm_arg _args[] = {
	{0, UINT_MAX, "Invalid up interval"},
	{0, UINT_MAX, "Invalid down interval"},
	};

	int r;
	struct flakey_c *fc;
	unsigned long long tmpll;
	struct dm_arg_set as;
	const char *devname;

	as.argc = argc;
	as.argv = argv;

	if (argc < 4) {
	ti->error = "Invalid argument count";
	return -EINVAL;
	}

	fc = kzalloc(sizeof(*fc), GFP_KERNEL);
	if (!fc) {
	ti->error = "Cannot allocate linear context";
	return -ENOMEM;
	}
	fc->start_time = jiffies;

	devname = dm_shift_arg(&as);

	if (sscanf(dm_shift_arg(&as), "%llu", &tmpll) != 1) {
	ti->error = "Invalid device sector";
	goto bad;
	}
	fc->start = tmpll;

	r = dm_read_arg(_args, &as, &fc->up_interval, &ti->error);
	if (r)
	goto bad;

	r = dm_read_arg(_args, &as, &fc->down_interval, &ti->error);
	if (r)
	goto bad;

	if (!(fc->up_interval + fc->down_interval)) {
	ti->error = "Total (up + down) interval is zero";
	goto bad;
	}

	if (fc->up_interval + fc->down_interval < fc->up_interval) {
	ti->error = "Interval overflow";
	goto bad;
	}

	r = parse_features(&as, fc, ti);
	if (r)
	goto bad;

	if (dm_get_device(ti, devname, dm_table_get_mode(ti->table), &fc->dev)) {
	ti->error = "Device lookup failed";
	goto bad;
	}

	ti->num_flush_requests = 1;
	ti->num_discard_requests = 1;
	ti->private = fc;
	return 0;

	bad:
	kfree(fc);
	return -EINVAL;
	}

	static void flakey_dtr(struct dm_target *ti)
	{
	struct flakey_c *fc = ti->private;

	dm_put_device(ti, fc->dev);
	kfree(fc);
	}

	static sector_t flakey_map_sector(struct dm_target *ti, sector_t bi_sector)
	{
	struct flakey_c *fc = ti->private;

	return fc->start + dm_target_offset(ti, bi_sector);
	}

	static void flakey_map_bio(struct dm_target ti, struct bio bio)
	{
	struct flakey_c *fc = ti->private;

	bio->bi_bdev = fc->dev->bdev;
	if (bio_sectors(bio))
	bio->bi_sector = flakey_map_sector(ti, bio->bi_sector);
	}

	static void corrupt_bio_data(struct bio bio, struct flakey_c fc)
	{
	unsigned bio_bytes = bio_cur_bytes(bio);
	char *data = bio_data(bio);

	/*
	* Overwrite the Nth byte of the data returned.
	*/
	if (data && bio_bytes >= fc->corrupt_bio_byte) {
	data[fc->corrupt_bio_byte - 1] = fc->corrupt_bio_value;

	DMDEBUG("Corrupting data bio=%p by writing %u to byte %u "
	"(rw=%c bi_rw=%lu bi_sector=%llu cur_bytes=%u)\n",
	bio, fc->corrupt_bio_value, fc->corrupt_bio_byte,
	(bio_data_dir(bio) == WRITE) ? 'w' : 'r',
	bio->bi_rw, (unsigned long long)bio->bi_sector, bio_bytes);
	}
	}

	static int flakey_map(struct dm_target ti, struct bio bio,
	union map_info *map_context)
	{
	struct flakey_c *fc = ti->private;
	unsigned elapsed;

	/* Are we alive ? */
	elapsed = (jiffies - fc->start_time) / HZ;
	if (elapsed % (fc->up_interval + fc->down_interval) >= fc->up_interval) {
	/*
	* Flag this bio as submitted while down.
	*/
	map_context->ll = 1;

	/*
	* Map reads as normal.
	*/
	if (bio_data_dir(bio) == READ)
	goto map_bio;

	/*
	* Drop writes?
	*/
	if (test_bit(DROP_WRITES, &fc->flags)) {
	bio_endio(bio, 0);
	return DM_MAPIO_SUBMITTED;
	}

	/*
	* Corrupt matching writes.
	*/
	if (fc->corrupt_bio_byte && (fc->corrupt_bio_rw == WRITE)) {
	if (all_corrupt_bio_flags_match(bio, fc))
	corrupt_bio_data(bio, fc);
	goto map_bio;
	}

	/*
	* By default, error all I/O.
	*/
	return -EIO;
	}

	map_bio:
	flakey_map_bio(ti, bio);

	return DM_MAPIO_REMAPPED;
	}

	static int flakey_end_io(struct dm_target ti, struct bio bio,
	int error, union map_info *map_context)
	{
	struct flakey_c *fc = ti->private;
	unsigned bio_submitted_while_down = map_context->ll;

	/*
	* Corrupt successful READs while in down state.
	* If flags were specified, only corrupt those that match.
	*/
	if (!error && bio_submitted_while_down &&
	(bio_data_dir(bio) == READ) && (fc->corrupt_bio_rw == READ) &&
	all_corrupt_bio_flags_match(bio, fc))
	corrupt_bio_data(bio, fc);

	return error;
	}

	static int flakey_status(struct dm_target *ti, status_type_t type,
	char *result, unsigned int maxlen)
	{
	unsigned sz = 0;
	struct flakey_c *fc = ti->private;
	unsigned drop_writes;

	switch (type) {
	case STATUSTYPE_INFO:
	result[0] = '\0';
	break;

	case STATUSTYPE_TABLE:
	DMEMIT("%s %llu %u %u ", fc->dev->name,
	(unsigned long long)fc->start, fc->up_interval,
	fc->down_interval);

	drop_writes = test_bit(DROP_WRITES, &fc->flags);
	DMEMIT("%u ", drop_writes + (fc->corrupt_bio_byte > 0) * 5);

	if (drop_writes)
	DMEMIT("drop_writes ");

	if (fc->corrupt_bio_byte)
	DMEMIT("corrupt_bio_byte %u %c %u %u ",
	fc->corrupt_bio_byte,
	(fc->corrupt_bio_rw == WRITE) ? 'w' : 'r',
	fc->corrupt_bio_value, fc->corrupt_bio_flags);

	break;
	}
	return 0;
	}

	static int flakey_ioctl(struct dm_target *ti, unsigned int cmd, unsigned long arg)
	{
	struct flakey_c *fc = ti->private;
	struct dm_dev *dev = fc->dev;
	int r = 0;

	/*
	* Only pass ioctls through if the device sizes match exactly.
	*/
	if (fc->start \|\|
	ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)
	r = scsi_verify_blk_ioctl(NULL, cmd);

	return r ? : __blkdev_driver_ioctl(dev->bdev, dev->mode, cmd, arg);
	}

	static int flakey_merge(struct dm_target ti, struct bvec_merge_data bvm,
	struct bio_vec *biovec, int max_size)
	{
	struct flakey_c *fc = ti->private;
	struct request_queue *q = bdev_get_queue(fc->dev->bdev);

	if (!q->merge_bvec_fn)
	return max_size;

	bvm->bi_bdev = fc->dev->bdev;
	bvm->bi_sector = flakey_map_sector(ti, bvm->bi_sector);

	return min(max_size, q->merge_bvec_fn(q, bvm, biovec));
	}

	static int flakey_iterate_devices(struct dm_target ti, iterate_devices_callout_fn fn, void data)
	{
	struct flakey_c *fc = ti->private;

	return fn(ti, fc->dev, fc->start, ti->len, data);
	}

	static struct target_type flakey_target = {
	.name = "flakey",
	.version = {1, 2, 0},
	.module = THIS_MODULE,
	.ctr = flakey_ctr,
	.dtr = flakey_dtr,
	.map = flakey_map,
	.end_io = flakey_end_io,
	.status = flakey_status,
	.ioctl = flakey_ioctl,
	.merge = flakey_merge,
	.iterate_devices = flakey_iterate_devices,
	};

	static int __init dm_flakey_init(void)
	{
	int r = dm_register_target(&flakey_target);

	if (r < 0)
	DMERR("register failed %d", r);

	return r;
	}

	static void __exit dm_flakey_exit(void)
	{
	dm_unregister_target(&flakey_target);
	}

	/* Module hooks */
	module_init(dm_flakey_init);
	module_exit(dm_flakey_exit);

	MODULE_DESCRIPTION(DM_NAME " flakey target");
	MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
	MODULE_LICENSE("GPL");