dm: add dust target

dm-dust

=======

This target emulates the behavior of bad sectors at arbitrary

locations, and the ability to enable the emulation of the failures

at an arbitrary time.

This target behaves similarly to a linear target.  At a given time,

the user can send a message to the target to start failing read

requests on specific blocks (to emulate the behavior of a hard disk

drive with bad sectors).

When the failure behavior is enabled (i.e.: when the output of

"dmsetup status" displays "fail_read_on_bad_block"), reads of blocks

in the "bad block list" will fail with EIO ("Input/output error").

Writes of blocks in the "bad block list will result in the following:

1. Remove the block from the "bad block list".

2. Successfully complete the write.

This emulates the "remapped sector" behavior of a drive with bad

sectors.

Normally, a drive that is encountering bad sectors will most likely

encounter more bad sectors, at an unknown time or location.

With dm-dust, the user can use the "addbadblock" and "removebadblock"

messages to add arbitrary bad blocks at new locations, and the

"enable" and "disable" messages to modulate the state of whether the

configured "bad blocks" will be treated as bad, or bypassed.

This allows the pre-writing of test data and metadata prior to

simulating a "failure" event where bad sectors start to appear.

Table parameters:

-----------------

<device_path> <offset> <blksz>

Mandatory parameters:

    <device_path>: path to the block device.

    <offset>: offset to data area from start of device_path

    <blksz>: block size in bytes

	     (minimum 512, maximum 1073741824, must be a power of 2)

Usage instructions:

-------------------

First, find the size (in 512-byte sectors) of the device to be used:

$ sudo blockdev --getsz /dev/vdb1

33552384

Create the dm-dust device:

(For a device with a block size of 512 bytes)

$ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 512'

(For a device with a block size of 4096 bytes)

$ sudo dmsetup create dust1 --table '0 33552384 dust /dev/vdb1 0 4096'

Check the status of the read behavior ("bypass" indicates that all I/O

will be passed through to the underlying device):

$ sudo dmsetup status dust1

0 33552384 dust 252:17 bypass

$ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=128 iflag=direct

128+0 records in

128+0 records out

$ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct

128+0 records in

128+0 records out

Adding and removing bad blocks:

-------------------------------

At any time (i.e.: whether the device has the "bad block" emulation

enabled or disabled), bad blocks may be added or removed from the

device via the "addbadblock" and "removebadblock" messages:

$ sudo dmsetup message dust1 0 addbadblock 60

kernel: device-mapper: dust: badblock added at block 60

$ sudo dmsetup message dust1 0 addbadblock 67

kernel: device-mapper: dust: badblock added at block 67

$ sudo dmsetup message dust1 0 addbadblock 72

kernel: device-mapper: dust: badblock added at block 72

These bad blocks will be stored in the "bad block list".

While the device is in "bypass" mode, reads and writes will succeed:

$ sudo dmsetup status dust1

0 33552384 dust 252:17 bypass

Enabling block read failures:

-----------------------------

To enable the "fail read on bad block" behavior, send the "enable" message:

$ sudo dmsetup message dust1 0 enable

kernel: device-mapper: dust: enabling read failures on bad sectors

$ sudo dmsetup status dust1

0 33552384 dust 252:17 fail_read_on_bad_block

With the device in "fail read on bad block" mode, attempting to read a

block will encounter an "Input/output error":

$ sudo dd if=/dev/mapper/dust1 of=/dev/null bs=512 count=1 skip=67 iflag=direct

dd: error reading '/dev/mapper/dust1': Input/output error

0+0 records in

0+0 records out

0 bytes copied, 0.00040651 s, 0.0 kB/s

...and writing to the bad blocks will remove the blocks from the list,

therefore emulating the "remap" behavior of hard disk drives:

$ sudo dd if=/dev/zero of=/dev/mapper/dust1 bs=512 count=128 oflag=direct

128+0 records in

128+0 records out

kernel: device-mapper: dust: block 60 removed from badblocklist by write

kernel: device-mapper: dust: block 67 removed from badblocklist by write

kernel: device-mapper: dust: block 72 removed from badblocklist by write

kernel: device-mapper: dust: block 87 removed from badblocklist by write

Bad block add/remove error handling:

------------------------------------

Attempting to add a bad block that already exists in the list will

result in an "Invalid argument" error, as well as a helpful message:

$ sudo dmsetup message dust1 0 addbadblock 88

device-mapper: message ioctl on dust1  failed: Invalid argument

kernel: device-mapper: dust: block 88 already in badblocklist

Attempting to remove a bad block that doesn't exist in the list will

result in an "Invalid argument" error, as well as a helpful message:

$ sudo dmsetup message dust1 0 removebadblock 87

device-mapper: message ioctl on dust1  failed: Invalid argument

kernel: device-mapper: dust: block 87 not found in badblocklist

Counting the number of bad blocks in the bad block list:

--------------------------------------------------------

To count the number of bad blocks configured in the device, run the

following message command:

$ sudo dmsetup message dust1 0 countbadblocks

A message will print with the number of bad blocks currently

configured on the device:

kernel: device-mapper: dust: countbadblocks: 895 badblock(s) found

Querying for specific bad blocks:

---------------------------------

To find out if a specific block is in the bad block list, run the

following message command:

$ sudo dmsetup message dust1 0 queryblock 72

The following message will print if the block is in the list:

device-mapper: dust: queryblock: block 72 found in badblocklist

The following message will print if the block is in the list:

device-mapper: dust: queryblock: block 72 not found in badblocklist

The "queryblock" message command will work in both the "enabled"

and "disabled" modes, allowing the verification of whether a block

will be treated as "bad" without having to issue I/O to the device,

or having to "enable" the bad block emulation.

Clearing the bad block list:

----------------------------

To clear the bad block list (without needing to individually run

a "removebadblock" message command for every block), run the

following message command:

$ sudo dmsetup message dust1 0 clearbadblocks

After clearing the bad block list, the following message will appear:

kernel: device-mapper: dust: clearbadblocks: badblocks cleared

If there were no bad blocks to clear, the following message will

appear:

kernel: device-mapper: dust: clearbadblocks: no badblocks found

Message commands list:

----------------------

Below is a list of the messages that can be sent to a dust device:

Operations on blocks (requires a <blknum> argument):

addbadblock <blknum>

queryblock <blknum>

removebadblock <blknum>

...where <blknum> is a block number within range of the device

  (corresponding to the block size of the device.)

Single argument message commands:

countbadblocks

clearbadblocks

disable

enable

quiet

Device removal:

---------------

When finished, remove the device via the "dmsetup remove" command:

$ sudo dmsetup remove dust1

Quiet mode:

-----------

On test runs with many bad blocks, it may be desirable to avoid

excessive logging (from bad blocks added, removed, or "remapped").

This can be done by enabling "quiet mode" via the following message:

$ sudo dmsetup message dust1 0 quiet

This will suppress log messages from add / remove / removed by write

operations.  Log messages from "countbadblocks" or "queryblock"

message commands will still print in quiet mode.

The status of quiet mode can be seen by running "dmsetup status":

$ sudo dmsetup status dust1

0 33552384 dust 252:17 fail_read_on_bad_block quiet

To disable quiet mode, send the "quiet" message again:

$ sudo dmsetup message dust1 0 quiet

$ sudo dmsetup status dust1

0 33552384 dust 252:17 fail_read_on_bad_block verbose

(The presence of "verbose" indicates normal logging.)

"Why not...?"

-------------

scsi_debug has a "medium error" mode that can fail reads on one

specified sector (sector 0x1234, hardcoded in the source code), but

it uses RAM for the persistent storage, which drastically decreases

the potential device size.

dm-flakey fails all I/O from all block locations at a specified time

frequency, and not a given point in time.

When a bad sector occurs on a hard disk drive, reads to that sector

are failed by the device, usually resulting in an error code of EIO

("I/O error") or ENODATA ("No data available").  However, a write to

the sector may succeed, and result in the sector becoming readable

after the device controller no longer experiences errors reading the

sector (or after a reallocation of the sector).  However, there may

be bad sectors that occur on the device in the future, in a different,

unpredictable location.

This target seeks to provide a device that can exhibit the behavior

of a bad sector at a known sector location, at a known time, based

on a large storage device (at least tens of gigabytes, not occupying

system memory).

	If unsure, say N.

config DM_DUST

	tristate "Bad sector simulation target"

	depends on BLK_DEV_DM

	---help---

	A target that simulates bad sector behavior.

	Useful for testing.

	If unsure, say N.

config DM_INIT

	bool "DM \"dm-mod.create=\" parameter support"

	depends on BLK_DEV_DM=y

obj-$(CONFIG_DM_BIO_PRISON)	+= dm-bio-prison.o

obj-$(CONFIG_DM_CRYPT)		+= dm-crypt.o

obj-$(CONFIG_DM_DELAY)		+= dm-delay.o

obj-$(CONFIG_DM_DUST)		+= dm-dust.o

obj-$(CONFIG_DM_FLAKEY)		+= dm-flakey.o

obj-$(CONFIG_DM_MULTIPATH)	+= dm-multipath.o dm-round-robin.o

obj-$(CONFIG_DM_MULTIPATH_QL)	+= dm-queue-length.o

// SPDX-License-Identifier: GPL-2.0

/*

 * Copyright (c) 2018 Red Hat, Inc.

 *

 * This is a test "dust" device, which fails reads on specified

 * sectors, emulating the behavior of a hard disk drive sending

 * a "Read Medium Error" sense.

 *

 */

#include <linux/device-mapper.h>

#include <linux/module.h>

#include <linux/rbtree.h>

#define DM_MSG_PREFIX "dust"

struct badblock {

	struct rb_node node;

	sector_t bb;

};

struct dust_device {

	struct dm_dev *dev;

	struct rb_root badblocklist;

	unsigned long long badblock_count;

	spinlock_t dust_lock;

	unsigned int blksz;

	unsigned int sect_per_block;

	sector_t start;

	bool fail_read_on_bb:1;

	bool quiet_mode:1;

};

static struct badblock *dust_rb_search(struct rb_root *root, sector_t blk)

{

	struct rb_node *node = root->rb_node;

	while (node) {

		struct badblock *bblk = rb_entry(node, struct badblock, node);

		if (bblk->bb > blk)

			node = node->rb_left;

		else if (bblk->bb < blk)

			node = node->rb_right;

		else

			return bblk;

	}

	return NULL;

}

static bool dust_rb_insert(struct rb_root *root, struct badblock *new)

{

	struct badblock *bblk;

	struct rb_node **link = &root->rb_node, *parent = NULL;

	sector_t value = new->bb;

	while (*link) {

		parent = *link;

		bblk = rb_entry(parent, struct badblock, node);

		if (bblk->bb > value)

			link = &(*link)->rb_left;

		else if (bblk->bb < value)

			link = &(*link)->rb_right;

		else

			return false;

	}

	rb_link_node(&new->node, parent, link);

	rb_insert_color(&new->node, root);

	return true;

}

static int dust_remove_block(struct dust_device *dd, unsigned long long block)

{

	struct badblock *bblock;

	unsigned long flags;

	spin_lock_irqsave(&dd->dust_lock, flags);

	bblock = dust_rb_search(&dd->badblocklist, block * dd->sect_per_block);

	if (bblock == NULL) {

		if (!dd->quiet_mode) {

			DMERR("%s: block %llu not found in badblocklist",

			      __func__, block);

		}

		spin_unlock_irqrestore(&dd->dust_lock, flags);

		return -EINVAL;

	}

	rb_erase(&bblock->node, &dd->badblocklist);

	dd->badblock_count--;

	if (!dd->quiet_mode)

		DMINFO("%s: badblock removed at block %llu", __func__, block);

	kfree(bblock);

	spin_unlock_irqrestore(&dd->dust_lock, flags);

	return 0;

}

static int dust_add_block(struct dust_device *dd, unsigned long long block)

{

	struct badblock *bblock;

	unsigned long flags;

	bblock = kmalloc(sizeof(*bblock), GFP_KERNEL);

	if (bblock == NULL) {

		if (!dd->quiet_mode)

			DMERR("%s: badblock allocation failed", __func__);

		return -ENOMEM;

	}

	spin_lock_irqsave(&dd->dust_lock, flags);

	bblock->bb = block * dd->sect_per_block;

	if (!dust_rb_insert(&dd->badblocklist, bblock)) {

		if (!dd->quiet_mode) {

			DMERR("%s: block %llu already in badblocklist",

			      __func__, block);

		}

		spin_unlock_irqrestore(&dd->dust_lock, flags);

		kfree(bblock);

		return -EINVAL;

	}

	dd->badblock_count++;

	if (!dd->quiet_mode)

		DMINFO("%s: badblock added at block %llu", __func__, block);

	spin_unlock_irqrestore(&dd->dust_lock, flags);

	return 0;

}

static int dust_query_block(struct dust_device *dd, unsigned long long block)

{

	struct badblock *bblock;

	unsigned long flags;

	spin_lock_irqsave(&dd->dust_lock, flags);

	bblock = dust_rb_search(&dd->badblocklist, block * dd->sect_per_block);

	if (bblock != NULL)

		DMINFO("%s: block %llu found in badblocklist", __func__, block);

	else

		DMINFO("%s: block %llu not found in badblocklist", __func__, block);

	spin_unlock_irqrestore(&dd->dust_lock, flags);

	return 0;

}

static int __dust_map_read(struct dust_device *dd, sector_t thisblock)

{

	struct badblock *bblk = dust_rb_search(&dd->badblocklist, thisblock);

	if (bblk)

		return DM_MAPIO_KILL;

	return DM_MAPIO_REMAPPED;

}

static int dust_map_read(struct dust_device *dd, sector_t thisblock,

			 bool fail_read_on_bb)

{

	unsigned long flags;

	int ret = DM_MAPIO_REMAPPED;

	if (fail_read_on_bb) {

		spin_lock_irqsave(&dd->dust_lock, flags);

		ret = __dust_map_read(dd, thisblock);

		spin_unlock_irqrestore(&dd->dust_lock, flags);

	}

	return ret;

}

static void __dust_map_write(struct dust_device *dd, sector_t thisblock)

{

	struct badblock *bblk = dust_rb_search(&dd->badblocklist, thisblock);

	if (bblk) {

		rb_erase(&bblk->node, &dd->badblocklist);

		dd->badblock_count--;

		kfree(bblk);

		if (!dd->quiet_mode) {

			sector_div(thisblock, dd->sect_per_block);

			DMINFO("block %llu removed from badblocklist by write",

			       (unsigned long long)thisblock);

		}

	}

}

static int dust_map_write(struct dust_device *dd, sector_t thisblock,

			  bool fail_read_on_bb)

{

	unsigned long flags;

	if (fail_read_on_bb) {

		spin_lock_irqsave(&dd->dust_lock, flags);

		__dust_map_write(dd, thisblock);

		spin_unlock_irqrestore(&dd->dust_lock, flags);

	}

	return DM_MAPIO_REMAPPED;

}

static int dust_map(struct dm_target *ti, struct bio *bio)

{

	struct dust_device *dd = ti->private;

	int ret;

	bio_set_dev(bio, dd->dev->bdev);

	bio->bi_iter.bi_sector = dd->start + dm_target_offset(ti, bio->bi_iter.bi_sector);

	if (bio_data_dir(bio) == READ)

		ret = dust_map_read(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);

	else

		ret = dust_map_write(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);

	return ret;

}

static bool __dust_clear_badblocks(struct rb_root *tree,

				   unsigned long long count)

{

	struct rb_node *node = NULL, *nnode = NULL;

	nnode = rb_first(tree);

	if (nnode == NULL) {

		BUG_ON(count != 0);

		return false;

	}

	while (nnode) {

		node = nnode;

		nnode = rb_next(node);

		rb_erase(node, tree);

		count--;

		kfree(node);

	}

	BUG_ON(count != 0);

	BUG_ON(tree->rb_node != NULL);

	return true;

}

static int dust_clear_badblocks(struct dust_device *dd)

{

	unsigned long flags;

	struct rb_root badblocklist;

	unsigned long long badblock_count;

	spin_lock_irqsave(&dd->dust_lock, flags);

	badblocklist = dd->badblocklist;

	badblock_count = dd->badblock_count;

	dd->badblocklist = RB_ROOT;

	dd->badblock_count = 0;

	spin_unlock_irqrestore(&dd->dust_lock, flags);

	if (!__dust_clear_badblocks(&badblocklist, badblock_count))

		DMINFO("%s: no badblocks found", __func__);

	else

		DMINFO("%s: badblocks cleared", __func__);

	return 0;

}

/*

 * Target parameters:

 *

 * <device_path> <offset> <blksz>

 *

 * device_path: path to the block device

 * offset: offset to data area from start of device_path

 * blksz: block size (minimum 512, maximum 1073741824, must be a power of 2)

 */

static int dust_ctr(struct dm_target *ti, unsigned int argc, char **argv)

{

	struct dust_device *dd;

	unsigned long long tmp;

	char dummy;

	unsigned int blksz;

	unsigned int sect_per_block;

	sector_t DUST_MAX_BLKSZ_SECTORS = 2097152;

	sector_t max_block_sectors = min(ti->len, DUST_MAX_BLKSZ_SECTORS);

	if (argc != 3) {

		ti->error = "Invalid argument count";

		return -EINVAL;

	}

	if (kstrtouint(argv[2], 10, &blksz) || !blksz) {

		ti->error = "Invalid block size parameter";

		return -EINVAL;

	}

	if (blksz < 512) {

		ti->error = "Block size must be at least 512";

		return -EINVAL;

	}

	if (!is_power_of_2(blksz)) {

		ti->error = "Block size must be a power of 2";

		return -EINVAL;

	}

	if (to_sector(blksz) > max_block_sectors) {

		ti->error = "Block size is too large";

		return -EINVAL;

	}

	sect_per_block = (blksz >> SECTOR_SHIFT);

	if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 || tmp != (sector_t)tmp) {

		ti->error = "Invalid device offset sector";

		return -EINVAL;

	}

	dd = kzalloc(sizeof(struct dust_device), GFP_KERNEL);

	if (dd == NULL) {

		ti->error = "Cannot allocate context";

		return -ENOMEM;

	}

	if (dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &dd->dev)) {

		ti->error = "Device lookup failed";

		kfree(dd);

		return -EINVAL;

	}

	dd->sect_per_block = sect_per_block;

	dd->blksz = blksz;

	dd->start = tmp;

	/*

	 * Whether to fail a read on a "bad" block.

	 * Defaults to false; enabled later by message.

	 */

	dd->fail_read_on_bb = false;

	/*

	 * Initialize bad block list rbtree.

	 */

	dd->badblocklist = RB_ROOT;

	dd->badblock_count = 0;

	spin_lock_init(&dd->dust_lock);

	dd->quiet_mode = false;

	BUG_ON(dm_set_target_max_io_len(ti, dd->sect_per_block) != 0);

	ti->num_discard_bios = 1;

	ti->num_flush_bios = 1;

	ti->private = dd;

	return 0;

}

static void dust_dtr(struct dm_target *ti)

{

	struct dust_device *dd = ti->private;

	__dust_clear_badblocks(&dd->badblocklist, dd->badblock_count);

	dm_put_device(ti, dd->dev);

	kfree(dd);

}

static int dust_message(struct dm_target *ti, unsigned int argc, char **argv,

			char *result_buf, unsigned int maxlen)

{

	struct dust_device *dd = ti->private;

	sector_t size = i_size_read(dd->dev->bdev->bd_inode) >> SECTOR_SHIFT;

	bool invalid_msg = false;

	int result = -EINVAL;

	unsigned long long tmp, block;

	unsigned long flags;

	char dummy;

	if (argc == 1) {

		if (!strcasecmp(argv[0], "addbadblock") ||

		    !strcasecmp(argv[0], "removebadblock") ||

		    !strcasecmp(argv[0], "queryblock")) {

			DMERR("%s requires an additional argument", argv[0]);

		} else if (!strcasecmp(argv[0], "disable")) {

			DMINFO("disabling read failures on bad sectors");

			dd->fail_read_on_bb = false;

			result = 0;

		} else if (!strcasecmp(argv[0], "enable")) {

			DMINFO("enabling read failures on bad sectors");

			dd->fail_read_on_bb = true;

			result = 0;

		} else if (!strcasecmp(argv[0], "countbadblocks")) {

			spin_lock_irqsave(&dd->dust_lock, flags);

			DMINFO("countbadblocks: %llu badblock(s) found",

			       dd->badblock_count);

			spin_unlock_irqrestore(&dd->dust_lock, flags);

			result = 0;

		} else if (!strcasecmp(argv[0], "clearbadblocks")) {

			result = dust_clear_badblocks(dd);

		} else if (!strcasecmp(argv[0], "quiet")) {

			if (!dd->quiet_mode)

				dd->quiet_mode = true;

			else

				dd->quiet_mode = false;

			result = 0;

		} else {

			invalid_msg = true;

		}

	} else if (argc == 2) {

		if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1)

			return result;

		block = tmp;

		sector_div(size, dd->sect_per_block);

		if (block > size || block < 0) {

			DMERR("selected block value out of range");

			return result;

		}

		if (!strcasecmp(argv[0], "addbadblock"))

			result = dust_add_block(dd, block);

		else if (!strcasecmp(argv[0], "removebadblock"))

			result = dust_remove_block(dd, block);

		else if (!strcasecmp(argv[0], "queryblock"))

			result = dust_query_block(dd, block);

		else

			invalid_msg = true;

	} else

		DMERR("invalid number of arguments '%d'", argc);

	if (invalid_msg)

		DMERR("unrecognized message '%s' received", argv[0]);

	return result;

}

static void dust_status(struct dm_target *ti, status_type_t type,

			unsigned int status_flags, char *result, unsigned int maxlen)

{

	struct dust_device *dd = ti->private;

	unsigned int sz = 0;

	switch (type) {

	case STATUSTYPE_INFO:

		DMEMIT("%s %s %s", dd->dev->name,

		       dd->fail_read_on_bb ? "fail_read_on_bad_block" : "bypass",

		       dd->quiet_mode ? "quiet" : "verbose");

		break;

	case STATUSTYPE_TABLE:

		DMEMIT("%s %llu %u", dd->dev->name,

		       (unsigned long long)dd->start, dd->blksz);

		break;

	}

}

static int dust_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)

{

	struct dust_device *dd = ti->private;

	struct dm_dev *dev = dd->dev;

	*bdev = dev->bdev;

	/*

	 * Only pass ioctls through if the device sizes match exactly.

	 */

	if (dd->start ||

	    ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT)

		return 1;

	return 0;

}

static int dust_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn,

				void *data)

{

	struct dust_device *dd = ti->private;

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