dm vdo: add the top-level DM target

This adds the dm-vdo target.

The dm-vdo target provides inline deduplication, compression, and
zero-block elimination, allowing applications to consume less actual
storage than a normal target. By layering it with other device mapper
targets, it can add these features to any storage stack. It can also
provide a common deduplication pool for groups of targets. The vdo target
does not protect against data corruption, relying instead on integrity
protection of the storage below it.

Co-developed-by: J. corwin Coburn <corwin@hurlbutnet.net>
Signed-off-by: J. corwin Coburn <corwin@hurlbutnet.net>
Co-developed-by: Michael Sclafani <dm-devel@lists.linux.dev>
Signed-off-by: Michael Sclafani <dm-devel@lists.linux.dev>
Co-developed-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
Co-developed-by: Bruce Johnston <bjohnsto@redhat.com>
Signed-off-by: Bruce Johnston <bjohnsto@redhat.com>
Co-developed-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Ken Raeburn <raeburn@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

1 files changed, 2952 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo-target.c b/drivers/md/dm-vdo-target.c
new file mode 100644
index 00000000000000..72d2291dd93f26
--- /dev/null
+++ b/drivers/md/dm-vdo-target.c
@@ -0,0 +1,2952 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/device-mapper.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+
+#include "dm-vdo/admin-state.h"
+#include "dm-vdo/block-map.h"
+#include "dm-vdo/completion.h"
+#include "dm-vdo/constants.h"
+#include "dm-vdo/data-vio.h"
+#include "dm-vdo/dedupe.h"
+#include "dm-vdo/dump.h"
+#include "dm-vdo/encodings.h"
+#include "dm-vdo/errors.h"
+#include "dm-vdo/flush.h"
+#include "dm-vdo/io-submitter.h"
+#include "dm-vdo/logger.h"
+#include "dm-vdo/memory-alloc.h"
+#include "dm-vdo/message-stats.h"
+#include "dm-vdo/pool-sysfs.h"
+#include "dm-vdo/recovery-journal.h"
+#include "dm-vdo/repair.h"
+#include "dm-vdo/slab-depot.h"
+#include "dm-vdo/status-codes.h"
+#include "dm-vdo/string-utils.h"
+#include "dm-vdo/thread-device.h"
+#include "dm-vdo/thread-registry.h"
+#include "dm-vdo/types.h"
+#include "dm-vdo/uds-sysfs.h"
+#include "dm-vdo/vdo.h"
+#include "dm-vdo/vio.h"
+
+#define	CURRENT_VERSION "8.3.0.65"
+
+enum {
+	GROW_LOGICAL_PHASE_START,
+	GROW_LOGICAL_PHASE_GROW_BLOCK_MAP,
+	GROW_LOGICAL_PHASE_END,
+	GROW_LOGICAL_PHASE_ERROR,
+	GROW_PHYSICAL_PHASE_START,
+	GROW_PHYSICAL_PHASE_COPY_SUMMARY,
+	GROW_PHYSICAL_PHASE_UPDATE_COMPONENTS,
+	GROW_PHYSICAL_PHASE_USE_NEW_SLABS,
+	GROW_PHYSICAL_PHASE_END,
+	GROW_PHYSICAL_PHASE_ERROR,
+	LOAD_PHASE_START,
+	LOAD_PHASE_STATS,
+	LOAD_PHASE_LOAD_DEPOT,
+	LOAD_PHASE_MAKE_DIRTY,
+	LOAD_PHASE_PREPARE_TO_ALLOCATE,
+	LOAD_PHASE_SCRUB_SLABS,
+	LOAD_PHASE_DATA_REDUCTION,
+	LOAD_PHASE_FINISHED,
+	LOAD_PHASE_DRAIN_JOURNAL,
+	LOAD_PHASE_WAIT_FOR_READ_ONLY,
+	PRE_LOAD_PHASE_START,
+	PRE_LOAD_PHASE_LOAD_COMPONENTS,
+	PRE_LOAD_PHASE_END,
+	PREPARE_GROW_PHYSICAL_PHASE_START,
+	RESUME_PHASE_START,
+	RESUME_PHASE_ALLOW_READ_ONLY_MODE,
+	RESUME_PHASE_DEDUPE,
+	RESUME_PHASE_DEPOT,
+	RESUME_PHASE_JOURNAL,
+	RESUME_PHASE_BLOCK_MAP,
+	RESUME_PHASE_LOGICAL_ZONES,
+	RESUME_PHASE_PACKER,
+	RESUME_PHASE_FLUSHER,
+	RESUME_PHASE_DATA_VIOS,
+	RESUME_PHASE_END,
+	SUSPEND_PHASE_START,
+	SUSPEND_PHASE_PACKER,
+	SUSPEND_PHASE_DATA_VIOS,
+	SUSPEND_PHASE_DEDUPE,
+	SUSPEND_PHASE_FLUSHES,
+	SUSPEND_PHASE_LOGICAL_ZONES,
+	SUSPEND_PHASE_BLOCK_MAP,
+	SUSPEND_PHASE_JOURNAL,
+	SUSPEND_PHASE_DEPOT,
+	SUSPEND_PHASE_READ_ONLY_WAIT,
+	SUSPEND_PHASE_WRITE_SUPER_BLOCK,
+	SUSPEND_PHASE_END,
+};
+
+static const char * const ADMIN_PHASE_NAMES[] = {
+	"GROW_LOGICAL_PHASE_START",
+	"GROW_LOGICAL_PHASE_GROW_BLOCK_MAP",
+	"GROW_LOGICAL_PHASE_END",
+	"GROW_LOGICAL_PHASE_ERROR",
+	"GROW_PHYSICAL_PHASE_START",
+	"GROW_PHYSICAL_PHASE_COPY_SUMMARY",
+	"GROW_PHYSICAL_PHASE_UPDATE_COMPONENTS",
+	"GROW_PHYSICAL_PHASE_USE_NEW_SLABS",
+	"GROW_PHYSICAL_PHASE_END",
+	"GROW_PHYSICAL_PHASE_ERROR",
+	"LOAD_PHASE_START",
+	"LOAD_PHASE_STATS",
+	"LOAD_PHASE_LOAD_DEPOT",
+	"LOAD_PHASE_MAKE_DIRTY",
+	"LOAD_PHASE_PREPARE_TO_ALLOCATE",
+	"LOAD_PHASE_SCRUB_SLABS",
+	"LOAD_PHASE_DATA_REDUCTION",
+	"LOAD_PHASE_FINISHED",
+	"LOAD_PHASE_DRAIN_JOURNAL",
+	"LOAD_PHASE_WAIT_FOR_READ_ONLY",
+	"PRE_LOAD_PHASE_START",
+	"PRE_LOAD_PHASE_LOAD_COMPONENTS",
+	"PRE_LOAD_PHASE_END",
+	"PREPARE_GROW_PHYSICAL_PHASE_START",
+	"RESUME_PHASE_START",
+	"RESUME_PHASE_ALLOW_READ_ONLY_MODE",
+	"RESUME_PHASE_DEDUPE",
+	"RESUME_PHASE_DEPOT",
+	"RESUME_PHASE_JOURNAL",
+	"RESUME_PHASE_BLOCK_MAP",
+	"RESUME_PHASE_LOGICAL_ZONES",
+	"RESUME_PHASE_PACKER",
+	"RESUME_PHASE_FLUSHER",
+	"RESUME_PHASE_DATA_VIOS",
+	"RESUME_PHASE_END",
+	"SUSPEND_PHASE_START",
+	"SUSPEND_PHASE_PACKER",
+	"SUSPEND_PHASE_DATA_VIOS",
+	"SUSPEND_PHASE_DEDUPE",
+	"SUSPEND_PHASE_FLUSHES",
+	"SUSPEND_PHASE_LOGICAL_ZONES",
+	"SUSPEND_PHASE_BLOCK_MAP",
+	"SUSPEND_PHASE_JOURNAL",
+	"SUSPEND_PHASE_DEPOT",
+	"SUSPEND_PHASE_READ_ONLY_WAIT",
+	"SUSPEND_PHASE_WRITE_SUPER_BLOCK",
+	"SUSPEND_PHASE_END",
+};
+
+enum {
+	/* If we bump this, update the arrays below */
+	TABLE_VERSION = 4,
+};
+
+/* arrays for handling different table versions */
+static const u8 REQUIRED_ARGC[] = { 10, 12, 9, 7, 6 };
+/* pool name no longer used. only here for verification of older versions */
+static const u8 POOL_NAME_ARG_INDEX[] = { 8, 10, 8 };
+
+/*
+ * Track in-use instance numbers using a flat bit array.
+ *
+ * O(n) run time isn't ideal, but if we have 1000 VDO devices in use simultaneously we still only
+ * need to scan 16 words, so it's not likely to be a big deal compared to other resource usage.
+ */
+
+enum {
+	/*
+	 * This minimum size for the bit array creates a numbering space of 0-999, which allows
+	 * successive starts of the same volume to have different instance numbers in any
+	 * reasonably-sized test. Changing instances on restart allows vdoMonReport to detect that
+	 * the ephemeral stats have reset to zero.
+	 */
+	BIT_COUNT_MINIMUM = 1000,
+	/** Grow the bit array by this many bits when needed */
+	BIT_COUNT_INCREMENT = 100,
+};
+
+struct instance_tracker {
+	unsigned int bit_count;
+	unsigned long *words;
+	unsigned int count;
+	unsigned int next;
+};
+
+static DEFINE_MUTEX(instances_lock);
+static struct instance_tracker instances;
+
+/**
+ * free_device_config() - Free a device config created by parse_device_config().
+ * @config: The config to free.
+ */
+static void free_device_config(struct device_config *config)
+{
+	if (config == NULL)
+		return;
+
+	if (config->owned_device != NULL)
+		dm_put_device(config->owning_target, config->owned_device);
+
+	uds_free(config->parent_device_name);
+	uds_free(config->original_string);
+
+	/* Reduce the chance a use-after-free (as in BZ 1669960) happens to work. */
+	memset(config, 0, sizeof(*config));
+	uds_free(config);
+}
+
+/**
+ * get_version_number() - Decide the version number from argv.
+ *
+ * @argc: The number of table values.
+ * @argv: The array of table values.
+ * @error_ptr: A pointer to return a error string in.
+ * @version_ptr: A pointer to return the version.
+ *
+ * Return: VDO_SUCCESS or an error code.
+ */
+static int get_version_number(int argc, char **argv, char **error_ptr,
+			      unsigned int *version_ptr)
+{
+	/* version, if it exists, is in a form of V<n> */
+	if (sscanf(argv[0], "V%u", version_ptr) == 1) {
+		if (*version_ptr < 1 || *version_ptr > TABLE_VERSION) {
+			*error_ptr = "Unknown version number detected";
+			return VDO_BAD_CONFIGURATION;
+		}
+	} else {
+		/* V0 actually has no version number in the table string */
+		*version_ptr = 0;
+	}
+
+	/*
+	 * V0 and V1 have no optional parameters. There will always be a parameter for thread
+	 * config, even if it's a "." to show it's an empty list.
+	 */
+	if (*version_ptr <= 1) {
+		if (argc != REQUIRED_ARGC[*version_ptr]) {
+			*error_ptr = "Incorrect number of arguments for version";
+			return VDO_BAD_CONFIGURATION;
+		}
+	} else if (argc < REQUIRED_ARGC[*version_ptr]) {
+		*error_ptr = "Incorrect number of arguments for version";
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	if (*version_ptr != TABLE_VERSION) {
+		uds_log_warning("Detected version mismatch between kernel module and tools kernel: %d, tool: %d",
+				TABLE_VERSION, *version_ptr);
+		uds_log_warning("Please consider upgrading management tools to match kernel.");
+	}
+	return VDO_SUCCESS;
+}
+
+/* Free a list of non-NULL string pointers, and then the list itself. */
+static void free_string_array(char **string_array)
+{
+	unsigned int offset;
+
+	for (offset = 0; string_array[offset] != NULL; offset++)
+		uds_free(string_array[offset]);
+	uds_free(string_array);
+}
+
+/*
+ * Split the input string into substrings, separated at occurrences of the indicated character,
+ * returning a null-terminated list of string pointers.
+ *
+ * The string pointers and the pointer array itself should both be freed with uds_free() when no
+ * longer needed. This can be done with vdo_free_string_array (below) if the pointers in the array
+ * are not changed. Since the array and copied strings are allocated by this function, it may only
+ * be used in contexts where allocation is permitted.
+ *
+ * Empty substrings are not ignored; that is, returned substrings may be empty strings if the
+ * separator occurs twice in a row.
+ */
+static int split_string(const char *string, char separator, char ***substring_array_ptr)
+{
+	unsigned int current_substring = 0, substring_count = 1;
+	const char *s;
+	char **substrings;
+	int result;
+	ptrdiff_t length;
+
+	for (s = string; *s != 0; s++) {
+		if (*s == separator)
+			substring_count++;
+	}
+
+	result = uds_allocate(substring_count + 1, char *, "string-splitting array",
+			      &substrings);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	for (s = string; *s != 0; s++) {
+		if (*s == separator) {
+			ptrdiff_t length = s - string;
+
+			result = uds_allocate(length + 1, char, "split string",
+					      &substrings[current_substring]);
+			if (result != UDS_SUCCESS) {
+				free_string_array(substrings);
+				return result;
+			}
+			/*
+			 * Trailing NUL is already in place after allocation; deal with the zero or
+			 * more non-NUL bytes in the string.
+			 */
+			if (length > 0)
+				memcpy(substrings[current_substring], string, length);
+			string = s + 1;
+			current_substring++;
+			BUG_ON(current_substring >= substring_count);
+		}
+	}
+	/* Process final string, with no trailing separator. */
+	BUG_ON(current_substring != (substring_count - 1));
+	length = strlen(string);
+
+	result = uds_allocate(length + 1, char, "split string",
+			      &substrings[current_substring]);
+	if (result != UDS_SUCCESS) {
+		free_string_array(substrings);
+		return result;
+	}
+	memcpy(substrings[current_substring], string, length);
+	current_substring++;
+	/* substrings[current_substring] is NULL already */
+	*substring_array_ptr = substrings;
+	return UDS_SUCCESS;
+}
+
+/*
+ * Join the input substrings into one string, joined with the indicated character, returning a
+ * string. array_length is a bound on the number of valid elements in substring_array, in case it
+ * is not NULL-terminated.
+ */
+static int join_strings(char **substring_array, size_t array_length, char separator,
+			char **string_ptr)
+{
+	size_t string_length = 0;
+	size_t i;
+	int result;
+	char *output, *current_position;
+
+	for (i = 0; (i < array_length) && (substring_array[i] != NULL); i++)
+		string_length += strlen(substring_array[i]) + 1;
+
+	result = uds_allocate(string_length, char, __func__, &output);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	current_position = &output[0];
+
+	for (i = 0; (i < array_length) && (substring_array[i] != NULL); i++) {
+		current_position = uds_append_to_buffer(current_position,
+							output + string_length, "%s",
+							substring_array[i]);
+		*current_position = separator;
+		current_position++;
+	}
+
+	/* We output one too many separators; replace the last with a zero byte. */
+	if (current_position != output)
+		*(current_position - 1) = '\0';
+
+	*string_ptr = output;
+	return UDS_SUCCESS;
+}
+
+/**
+ * parse_bool() - Parse a two-valued option into a bool.
+ * @bool_str: The string value to convert to a bool.
+ * @true_str: The string value which should be converted to true.
+ * @false_str: The string value which should be converted to false.
+ * @bool_ptr: A pointer to return the bool value in.
+ *
+ * Return: VDO_SUCCESS or an error if bool_str is neither true_str nor false_str.
+ */
+static inline int __must_check parse_bool(const char *bool_str, const char *true_str,
+					  const char *false_str, bool *bool_ptr)
+{
+	bool value = false;
+
+	if (strcmp(bool_str, true_str) == 0)
+		value = true;
+	else if (strcmp(bool_str, false_str) == 0)
+		value = false;
+	else
+		return VDO_BAD_CONFIGURATION;
+
+	*bool_ptr = value;
+	return VDO_SUCCESS;
+}
+
+/**
+ * process_one_thread_config_spec() - Process one component of a thread parameter configuration
+ *				      string and update the configuration data structure.
+ * @thread_param_type: The type of thread specified.
+ * @count: The thread count requested.
+ * @config: The configuration data structure to update.
+ *
+ * If the thread count requested is invalid, a message is logged and -EINVAL returned. If the
+ * thread name is unknown, a message is logged but no error is returned.
+ *
+ * Return: VDO_SUCCESS or -EINVAL
+ */
+static int process_one_thread_config_spec(const char *thread_param_type,
+					  unsigned int count,
+					  struct thread_count_config *config)
+{
+	/* Handle limited thread parameters */
+	if (strcmp(thread_param_type, "bioRotationInterval") == 0) {
+		if (count == 0) {
+			uds_log_error("thread config string error:  'bioRotationInterval' of at least 1 is required");
+			return -EINVAL;
+		} else if (count > VDO_BIO_ROTATION_INTERVAL_LIMIT) {
+			uds_log_error("thread config string error: 'bioRotationInterval' cannot be higher than %d",
+				      VDO_BIO_ROTATION_INTERVAL_LIMIT);
+			return -EINVAL;
+		}
+		config->bio_rotation_interval = count;
+		return VDO_SUCCESS;
+	}
+	if (strcmp(thread_param_type, "logical") == 0) {
+		if (count > MAX_VDO_LOGICAL_ZONES) {
+			uds_log_error("thread config string error: at most %d 'logical' threads are allowed",
+				      MAX_VDO_LOGICAL_ZONES);
+			return -EINVAL;
+		}
+		config->logical_zones = count;
+		return VDO_SUCCESS;
+	}
+	if (strcmp(thread_param_type, "physical") == 0) {
+		if (count > MAX_VDO_PHYSICAL_ZONES) {
+			uds_log_error("thread config string error: at most %d 'physical' threads are allowed",
+				      MAX_VDO_PHYSICAL_ZONES);
+			return -EINVAL;
+		}
+		config->physical_zones = count;
+		return VDO_SUCCESS;
+	}
+	/* Handle other thread count parameters */
+	if (count > MAXIMUM_VDO_THREADS) {
+		uds_log_error("thread config string error: at most %d '%s' threads are allowed",
+			      MAXIMUM_VDO_THREADS, thread_param_type);
+		return -EINVAL;
+	}
+	if (strcmp(thread_param_type, "hash") == 0) {
+		config->hash_zones = count;
+		return VDO_SUCCESS;
+	}
+	if (strcmp(thread_param_type, "cpu") == 0) {
+		if (count == 0) {
+			uds_log_error("thread config string error: at least one 'cpu' thread required");
+			return -EINVAL;
+		}
+		config->cpu_threads = count;
+		return VDO_SUCCESS;
+	}
+	if (strcmp(thread_param_type, "ack") == 0) {
+		config->bio_ack_threads = count;
+		return VDO_SUCCESS;
+	}
+	if (strcmp(thread_param_type, "bio") == 0) {
+		if (count == 0) {
+			uds_log_error("thread config string error: at least one 'bio' thread required");
+			return -EINVAL;
+		}
+		config->bio_threads = count;
+		return VDO_SUCCESS;
+	}
+
+	/*
+	 * Don't fail, just log. This will handle version mismatches between user mode tools and
+	 * kernel.
+	 */
+	uds_log_info("unknown thread parameter type \"%s\"", thread_param_type);
+	return VDO_SUCCESS;
+}
+
+/**
+ * parse_one_thread_config_spec() - Parse one component of a thread parameter configuration string
+ *				    and update the configuration data structure.
+ * @spec: The thread parameter specification string.
+ * @config: The configuration data to be updated.
+ */
+static int parse_one_thread_config_spec(const char *spec,
+					struct thread_count_config *config)
+{
+	unsigned int count;
+	char **fields;
+	int result;
+
+	result = split_string(spec, '=', &fields);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	if ((fields[0] == NULL) || (fields[1] == NULL) || (fields[2] != NULL)) {
+		uds_log_error("thread config string error: expected thread parameter assignment, saw \"%s\"",
+			      spec);
+		free_string_array(fields);
+		return -EINVAL;
+	}
+
+	result = kstrtouint(fields[1], 10, &count);
+	if (result != UDS_SUCCESS) {
+		uds_log_error("thread config string error: integer value needed, found \"%s\"",
+			      fields[1]);
+		free_string_array(fields);
+		return result;
+	}
+
+	result = process_one_thread_config_spec(fields[0], count, config);
+	free_string_array(fields);
+	return result;
+}
+
+/**
+ * parse_thread_config_string() - Parse the configuration string passed and update the specified
+ *				  counts and other parameters of various types of threads to be
+ *				  created.
+ * @string: Thread parameter configuration string.
+ * @config: The thread configuration data to update.
+ *
+ * The configuration string should contain one or more comma-separated specs of the form
+ * "typename=number"; the supported type names are "cpu", "ack", "bio", "bioRotationInterval",
+ * "logical", "physical", and "hash".
+ *
+ * If an error occurs during parsing of a single key/value pair, we deem it serious enough to stop
+ * further parsing.
+ *
+ * This function can't set the "reason" value the caller wants to pass back, because we'd want to
+ * format it to say which field was invalid, and we can't allocate the "reason" strings
+ * dynamically. So if an error occurs, we'll log the details and pass back an error.
+ *
+ * Return: VDO_SUCCESS or -EINVAL or -ENOMEM
+ */
+static int parse_thread_config_string(const char *string,
+				      struct thread_count_config *config)
+{
+	int result = VDO_SUCCESS;
+	char **specs;
+
+	if (strcmp(".", string) != 0) {
+		unsigned int i;
+
+		result = split_string(string, ',', &specs);
+		if (result != UDS_SUCCESS)
+			return result;
+
+		for (i = 0; specs[i] != NULL; i++) {
+			result = parse_one_thread_config_spec(specs[i], config);
+			if (result != VDO_SUCCESS)
+				break;
+		}
+		free_string_array(specs);
+	}
+	return result;
+}
+
+/**
+ * process_one_key_value_pair() - Process one component of an optional parameter string and update
+ *				  the configuration data structure.
+ * @key: The optional parameter key name.
+ * @value: The optional parameter value.
+ * @config: The configuration data structure to update.
+ *
+ * If the value requested is invalid, a message is logged and -EINVAL returned. If the key is
+ * unknown, a message is logged but no error is returned.
+ *
+ * Return: VDO_SUCCESS or -EINVAL
+ */
+static int process_one_key_value_pair(const char *key, unsigned int value,
+				      struct device_config *config)
+{
+	/* Non thread optional parameters */
+	if (strcmp(key, "maxDiscard") == 0) {
+		if (value == 0) {
+			uds_log_error("optional parameter error: at least one max discard block required");
+			return -EINVAL;
+		}
+		/* Max discard sectors in blkdev_issue_discard is UINT_MAX >> 9 */
+		if (value > (UINT_MAX / VDO_BLOCK_SIZE)) {
+			uds_log_error("optional parameter error: at most %d max discard	 blocks are allowed",
+				      UINT_MAX / VDO_BLOCK_SIZE);
+			return -EINVAL;
+		}
+		config->max_discard_blocks = value;
+		return VDO_SUCCESS;
+	}
+	/* Handles unknown key names */
+	return process_one_thread_config_spec(key, value, &config->thread_counts);
+}
+
+/**
+ * parse_one_key_value_pair() - Parse one key/value pair and update the configuration data
+ *				structure.
+ * @key: The optional key name.
+ * @value: The optional value.
+ * @config: The configuration data to be updated.
+ *
+ * Return: VDO_SUCCESS or error.
+ */
+static int parse_one_key_value_pair(const char *key, const char *value,
+				    struct device_config *config)
+{
+	unsigned int count;
+	int result;
+
+	if (strcmp(key, "deduplication") == 0)
+		return parse_bool(value, "on", "off", &config->deduplication);
+
+	if (strcmp(key, "compression") == 0)
+		return parse_bool(value, "on", "off", &config->compression);
+
+	/* The remaining arguments must have integral values. */
+	result = kstrtouint(value, 10, &count);
+	if (result != UDS_SUCCESS) {
+		uds_log_error("optional config string error: integer value needed, found \"%s\"",
+			      value);
+		return result;
+	}
+	return process_one_key_value_pair(key, count, config);
+}
+
+/**
+ * parse_key_value_pairs() - Parse all key/value pairs from a list of arguments.
+ * @argc: The total number of arguments in list.
+ * @argv: The list of key/value pairs.
+ * @config: The device configuration data to update.
+ *
+ * If an error occurs during parsing of a single key/value pair, we deem it serious enough to stop
+ * further parsing.
+ *
+ * This function can't set the "reason" value the caller wants to pass back, because we'd want to
+ * format it to say which field was invalid, and we can't allocate the "reason" strings
+ * dynamically. So if an error occurs, we'll log the details and return the error.
+ *
+ * Return: VDO_SUCCESS or error
+ */
+static int parse_key_value_pairs(int argc, char **argv, struct device_config *config)
+{
+	int result = VDO_SUCCESS;
+
+	while (argc) {
+		result = parse_one_key_value_pair(argv[0], argv[1], config);
+		if (result != VDO_SUCCESS)
+			break;
+
+		argc -= 2;
+		argv += 2;
+	}
+
+	return result;
+}
+
+/**
+ * parse_optional_arguments() - Parse the configuration string passed in for optional arguments.
+ * @arg_set: The structure holding the arguments to parse.
+ * @error_ptr: Pointer to a buffer to hold the error string.
+ * @config: Pointer to device configuration data to update.
+ *
+ * For V0/V1 configurations, there will only be one optional parameter; the thread configuration.
+ * The configuration string should contain one or more comma-separated specs of the form
+ * "typename=number"; the supported type names are "cpu", "ack", "bio", "bioRotationInterval",
+ * "logical", "physical", and "hash".
+ *
+ * For V2 configurations and beyond, there could be any number of arguments. They should contain
+ * one or more key/value pairs separated by a space.
+ *
+ * Return: VDO_SUCCESS or error
+ */
+static int parse_optional_arguments(struct dm_arg_set *arg_set, char **error_ptr,
+				    struct device_config *config)
+{
+	int result = VDO_SUCCESS;
+
+	if (config->version == 0 || config->version == 1) {
+		result = parse_thread_config_string(arg_set->argv[0],
+						    &config->thread_counts);
+		if (result != VDO_SUCCESS) {
+			*error_ptr = "Invalid thread-count configuration";
+			return VDO_BAD_CONFIGURATION;
+		}
+	} else {
+		if ((arg_set->argc % 2) != 0) {
+			*error_ptr = "Odd number of optional arguments given but they should be <key> <value> pairs";
+			return VDO_BAD_CONFIGURATION;
+		}
+		result = parse_key_value_pairs(arg_set->argc, arg_set->argv, config);
+		if (result != VDO_SUCCESS) {
+			*error_ptr = "Invalid optional argument configuration";
+			return VDO_BAD_CONFIGURATION;
+		}
+	}
+	return result;
+}
+
+/**
+ * handle_parse_error() - Handle a parsing error.
+ * @config: The config to free.
+ * @error_ptr: A place to store a constant string about the error.
+ * @error_str: A constant string to store in error_ptr.
+ */
+static void handle_parse_error(struct device_config *config, char **error_ptr,
+			       char *error_str)
+{
+	free_device_config(config);
+	*error_ptr = error_str;
+}
+
+/**
+ * parse_device_config() - Convert the dmsetup table into a struct device_config.
+ * @argc: The number of table values.
+ * @argv: The array of table values.
+ * @ti: The target structure for this table.
+ * @config_ptr: A pointer to return the allocated config.
+ *
+ * Return: VDO_SUCCESS or an error code.
+ */
+static int parse_device_config(int argc, char **argv, struct dm_target *ti,
+			       struct device_config **config_ptr)
+{
+	bool enable_512e;
+	size_t logical_bytes = to_bytes(ti->len);
+	struct dm_arg_set arg_set;
+	char **error_ptr = &ti->error;
+	struct device_config *config = NULL;
+	int result;
+
+	if ((logical_bytes % VDO_BLOCK_SIZE) != 0) {
+		handle_parse_error(config, error_ptr,
+				   "Logical size must be a multiple of 4096");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	if (argc == 0) {
+		handle_parse_error(config, error_ptr, "Incorrect number of arguments");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	result = uds_allocate(1, struct device_config, "device_config", &config);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr,
+				   "Could not allocate config structure");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	config->owning_target = ti;
+	config->logical_blocks = logical_bytes / VDO_BLOCK_SIZE;
+	INIT_LIST_HEAD(&config->config_list);
+
+	/* Save the original string. */
+	result = join_strings(argv, argc, ' ', &config->original_string);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr, "Could not populate string");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	uds_log_info("table line: %s", config->original_string);
+
+	config->thread_counts = (struct thread_count_config) {
+		.bio_ack_threads = 1,
+		.bio_threads = DEFAULT_VDO_BIO_SUBMIT_QUEUE_COUNT,
+		.bio_rotation_interval = DEFAULT_VDO_BIO_SUBMIT_QUEUE_ROTATE_INTERVAL,
+		.cpu_threads = 1,
+		.logical_zones = 0,
+		.physical_zones = 0,
+		.hash_zones = 0,
+	};
+	config->max_discard_blocks = 1;
+	config->deduplication = true;
+	config->compression = false;
+
+	arg_set.argc = argc;
+	arg_set.argv = argv;
+
+	result = get_version_number(argc, argv, error_ptr, &config->version);
+	if (result != VDO_SUCCESS) {
+		/* get_version_number sets error_ptr itself. */
+		handle_parse_error(config, error_ptr, *error_ptr);
+		return result;
+	}
+	/* Move the arg pointer forward only if the argument was there. */
+	if (config->version >= 1)
+		dm_shift_arg(&arg_set);
+
+	result = uds_duplicate_string(dm_shift_arg(&arg_set), "parent device name",
+				      &config->parent_device_name);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr,
+				   "Could not copy parent device name");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	/* Get the physical blocks, if known. */
+	if (config->version >= 1) {
+		result = kstrtoull(dm_shift_arg(&arg_set), 10, &config->physical_blocks);
+		if (result != VDO_SUCCESS) {
+			handle_parse_error(config, error_ptr,
+					   "Invalid physical block count");
+			return VDO_BAD_CONFIGURATION;
+		}
+	}
+
+	/* Get the logical block size and validate */
+	result = parse_bool(dm_shift_arg(&arg_set), "512", "4096", &enable_512e);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr, "Invalid logical block size");
+		return VDO_BAD_CONFIGURATION;
+	}
+	config->logical_block_size = (enable_512e ? 512 : 4096);
+
+	/* Skip past the two no longer used read cache options. */
+	if (config->version <= 1)
+		dm_consume_args(&arg_set, 2);
+
+	/* Get the page cache size. */
+	result = kstrtouint(dm_shift_arg(&arg_set), 10, &config->cache_size);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr,
+				   "Invalid block map page cache size");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	/* Get the block map era length. */
+	result = kstrtouint(dm_shift_arg(&arg_set), 10, &config->block_map_maximum_age);
+	if (result != VDO_SUCCESS) {
+		handle_parse_error(config, error_ptr, "Invalid block map maximum age");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	/* Skip past the no longer used MD RAID5 optimization mode */
+	if (config->version <= 2)
+		dm_consume_args(&arg_set, 1);
+
+	/* Skip past the no longer used write policy setting */
+	if (config->version <= 3)
+		dm_consume_args(&arg_set, 1);
+
+	/* Skip past the no longer used pool name for older table lines */
+	if (config->version <= 2) {
+		/*
+		 * Make sure the enum to get the pool name from argv directly is still in sync with
+		 * the parsing of the table line.
+		 */
+		if (&arg_set.argv[0] != &argv[POOL_NAME_ARG_INDEX[config->version]]) {
+			handle_parse_error(config, error_ptr,
+					   "Pool name not in expected location");
+			return VDO_BAD_CONFIGURATION;
+		}
+		dm_shift_arg(&arg_set);
+	}
+
+	/* Get the optional arguments and validate. */
+	result = parse_optional_arguments(&arg_set, error_ptr, config);
+	if (result != VDO_SUCCESS) {
+		/* parse_optional_arguments sets error_ptr itself. */
+		handle_parse_error(config, error_ptr, *error_ptr);
+		return result;
+	}
+
+	/*
+	 * Logical, physical, and hash zone counts can all be zero; then we get one thread doing
+	 * everything, our older configuration. If any zone count is non-zero, the others must be
+	 * as well.
+	 */
+	if (((config->thread_counts.logical_zones == 0) !=
+	     (config->thread_counts.physical_zones == 0)) ||
+	    ((config->thread_counts.physical_zones == 0) !=
+	     (config->thread_counts.hash_zones == 0))) {
+		handle_parse_error(config, error_ptr,
+				   "Logical, physical, and hash zones counts must all be zero or all non-zero");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	if (config->cache_size <
+	    (2 * MAXIMUM_VDO_USER_VIOS * config->thread_counts.logical_zones)) {
+		handle_parse_error(config, error_ptr,
+				   "Insufficient block map cache for logical zones");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	result = dm_get_device(ti, config->parent_device_name,
+			       dm_table_get_mode(ti->table), &config->owned_device);
+	if (result != 0) {
+		uds_log_error("couldn't open device \"%s\": error %d",
+			      config->parent_device_name, result);
+		handle_parse_error(config, error_ptr, "Unable to open storage device");
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	if (config->version == 0) {
+		u64 device_size = i_size_read(config->owned_device->bdev->bd_inode);
+
+		config->physical_blocks = device_size / VDO_BLOCK_SIZE;
+	}
+
+	*config_ptr = config;
+	return result;
+}
+
+static struct vdo *get_vdo_for_target(struct dm_target *ti)
+{
+	return ((struct device_config *) ti->private)->vdo;
+}
+
+
+static int vdo_map_bio(struct dm_target *ti, struct bio *bio)
+{
+	struct vdo *vdo = get_vdo_for_target(ti);
+	struct vdo_work_queue *current_work_queue;
+	const struct admin_state_code *code = vdo_get_admin_state_code(&vdo->admin.state);
+
+	ASSERT_LOG_ONLY(code->normal, "vdo should not receive bios while in state %s",
+			code->name);
+
+	/* Count all incoming bios. */
+	vdo_count_bios(&vdo->stats.bios_in, bio);
+
+
+	/* Handle empty bios.  Empty flush bios are not associated with a vio. */
+	if ((bio_op(bio) == REQ_OP_FLUSH) || ((bio->bi_opf & REQ_PREFLUSH) != 0)) {
+		vdo_launch_flush(vdo, bio);
+		return DM_MAPIO_SUBMITTED;
+	}
+
+	/* This could deadlock, */
+	current_work_queue = vdo_get_current_work_queue();
+	BUG_ON((current_work_queue != NULL) &&
+	       (vdo == vdo_get_work_queue_owner(current_work_queue)->vdo));
+	vdo_launch_bio(vdo->data_vio_pool, bio);
+	return DM_MAPIO_SUBMITTED;
+}
+
+static void vdo_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct vdo *vdo = get_vdo_for_target(ti);
+
+	limits->logical_block_size = vdo->device_config->logical_block_size;
+	limits->physical_block_size = VDO_BLOCK_SIZE;
+
+	/* The minimum io size for random io */
+	blk_limits_io_min(limits, VDO_BLOCK_SIZE);
+	/* The optimal io size for streamed/sequential io */
+	blk_limits_io_opt(limits, VDO_BLOCK_SIZE);
+
+	/*
+	 * Sets the maximum discard size that will be passed into VDO. This value comes from a
+	 * table line value passed in during dmsetup create.
+	 *
+	 * The value 1024 is the largest usable value on HD systems.  A 2048 sector discard on a
+	 * busy HD system takes 31 seconds.  We should use a value no higher than 1024, which takes
+	 * 15 to 16 seconds on a busy HD system.
+	 *
+	 * But using large values results in 120 second blocked task warnings in /var/log/kern.log.
+	 * In order to avoid these warnings, we choose to use the smallest reasonable value.  See
+	 * VDO-3062 and VDO-3087.
+	 *
+	 * The value is displayed in sysfs, and also used by dm-thin to determine whether to pass
+	 * down discards. The block layer splits large discards on this boundary when this is set.
+	 */
+	limits->max_discard_sectors =
+		(vdo->device_config->max_discard_blocks * VDO_SECTORS_PER_BLOCK);
+
+	/*
+	 * Force discards to not begin or end with a partial block by stating the granularity is
+	 * 4k.
+	 */
+	limits->discard_granularity = VDO_BLOCK_SIZE;
+}
+
+static int vdo_iterate_devices(struct dm_target *ti, iterate_devices_callout_fn fn,
+			       void *data)
+{
+	struct device_config *config = get_vdo_for_target(ti)->device_config;
+
+	return fn(ti, config->owned_device, 0,
+		  config->physical_blocks * VDO_SECTORS_PER_BLOCK, data);
+}
+
+/*
+ * Status line is:
+ *    <device> <operating mode> <in recovery> <index state> <compression state>
+ *    <used physical blocks> <total physical blocks>
+ */
+
+static void vdo_status(struct dm_target *ti, status_type_t status_type,
+		       unsigned int status_flags, char *result, unsigned int maxlen)
+{
+	struct vdo *vdo = get_vdo_for_target(ti);
+	struct vdo_statistics *stats;
+	struct device_config *device_config;
+	/* N.B.: The DMEMIT macro uses the variables named "sz", "result", "maxlen". */
+	int sz = 0;
+
+	switch (status_type) {
+	case STATUSTYPE_INFO:
+		/* Report info for dmsetup status */
+		mutex_lock(&vdo->stats_mutex);
+		vdo_fetch_statistics(vdo, &vdo->stats_buffer);
+		stats = &vdo->stats_buffer;
+
+		DMEMIT("/dev/%pg %s %s %s %s %llu %llu",
+		       vdo_get_backing_device(vdo), stats->mode,
+		       stats->in_recovery_mode ? "recovering" : "-",
+		       vdo_get_dedupe_index_state_name(vdo->hash_zones),
+		       vdo_get_compressing(vdo) ? "online" : "offline",
+		       stats->data_blocks_used + stats->overhead_blocks_used,
+		       stats->physical_blocks);
+		mutex_unlock(&vdo->stats_mutex);
+		break;
+
+	case STATUSTYPE_TABLE:
+		/* Report the string actually specified in the beginning. */
+		device_config = (struct device_config *) ti->private;
+		DMEMIT("%s", device_config->original_string);
+		break;
+
+	case STATUSTYPE_IMA:
+		/* FIXME: We ought to be more detailed here, but this is what thin does. */
+		*result = '\0';
+		break;
+	}
+}
+
+static block_count_t __must_check get_underlying_device_block_count(const struct vdo *vdo)
+{
+	return i_size_read(vdo_get_backing_device(vdo)->bd_inode) / VDO_BLOCK_SIZE;
+}
+
+static int __must_check process_vdo_message_locked(struct vdo *vdo, unsigned int argc,
+						   char **argv)
+{
+	if ((argc == 2) && (strcasecmp(argv[0], "compression") == 0)) {
+		if (strcasecmp(argv[1], "on") == 0) {
+			vdo_set_compressing(vdo, true);
+			return 0;
+		}
+
+		if (strcasecmp(argv[1], "off") == 0) {
+			vdo_set_compressing(vdo, false);
+			return 0;
+		}
+
+		uds_log_warning("invalid argument '%s' to dmsetup compression message",
+				argv[1]);
+		return -EINVAL;
+	}
+
+	uds_log_warning("unrecognized dmsetup message '%s' received", argv[0]);
+	return -EINVAL;
+}
+
+/*
+ * If the message is a dump, just do it. Otherwise, check that no other message is being processed,
+ * and only proceed if so.
+ * Returns -EBUSY if another message is being processed
+ */
+static int __must_check process_vdo_message(struct vdo *vdo, unsigned int argc,
+					    char **argv)
+{
+	int result;
+
+	/*
+	 * All messages which may be processed in parallel with other messages should be handled
+	 * here before the atomic check below. Messages which should be exclusive should be
+	 * processed in process_vdo_message_locked().
+	 */
+
+	/* Dump messages should always be processed */
+	if (strcasecmp(argv[0], "dump") == 0)
+		return vdo_dump(vdo, argc, argv, "dmsetup message");
+
+	if (argc == 1) {
+		if (strcasecmp(argv[0], "dump-on-shutdown") == 0) {
+			vdo->dump_on_shutdown = true;
+			return 0;
+		}
+
+		/* Index messages should always be processed */
+		if ((strcasecmp(argv[0], "index-close") == 0) ||
+		    (strcasecmp(argv[0], "index-create") == 0) ||
+		    (strcasecmp(argv[0], "index-disable") == 0) ||
+		    (strcasecmp(argv[0], "index-enable") == 0))
+			return vdo_message_dedupe_index(vdo->hash_zones, argv[0]);
+	}
+
+	if (atomic_cmpxchg(&vdo->processing_message, 0, 1) != 0)
+		return -EBUSY;
+
+	result = process_vdo_message_locked(vdo, argc, argv);
+
+	/* Pairs with the implicit barrier in cmpxchg just above */
+	smp_wmb();
+	atomic_set(&vdo->processing_message, 0);
+	return result;
+}
+
+static int vdo_message(struct dm_target *ti, unsigned int argc, char **argv,
+		       char *result_buffer, unsigned int maxlen)
+{
+	struct registered_thread allocating_thread, instance_thread;
+	struct vdo *vdo;
+	int result;
+
+	if (argc == 0) {
+		uds_log_warning("unspecified dmsetup message");
+		return -EINVAL;
+	}
+
+	vdo = get_vdo_for_target(ti);
+	uds_register_allocating_thread(&allocating_thread, NULL);
+	uds_register_thread_device_id(&instance_thread, &vdo->instance);
+
+	/*
+	 * Must be done here so we don't map return codes. The code in dm-ioctl expects a 1 for a
+	 * return code to look at the buffer and see if it is full or not.
+	 */
+	if ((argc == 1) && (strcasecmp(argv[0], "stats") == 0)) {
+		vdo_write_stats(vdo, result_buffer, maxlen);
+		result = 1;
+	} else {
+		result = vdo_map_to_system_error(process_vdo_message(vdo, argc, argv));
+	}
+
+	uds_unregister_thread_device_id();
+	uds_unregister_allocating_thread();
+	return result;
+}
+
+static void configure_target_capabilities(struct dm_target *ti)
+{
+	ti->discards_supported = 1;
+	ti->flush_supported = true;
+	ti->num_discard_bios = 1;
+	ti->num_flush_bios = 1;
+
+	/*
+	 * If this value changes, please make sure to update the value for max_discard_sectors
+	 * accordingly.
+	 */
+	BUG_ON(dm_set_target_max_io_len(ti, VDO_SECTORS_PER_BLOCK) != 0);
+}
+
+/*
+ * Implements vdo_filter_fn.
+ */
+static bool vdo_uses_device(struct vdo *vdo, const void *context)
+{
+	const struct device_config *config = context;
+
+	return vdo_get_backing_device(vdo)->bd_dev == config->owned_device->bdev->bd_dev;
+}
+
+/**
+ * get_thread_id_for_phase() - Get the thread id for the current phase of the admin operation in
+ *                             progress.
+ */
+static thread_id_t __must_check get_thread_id_for_phase(struct vdo *vdo)
+{
+	switch (vdo->admin.phase) {
+	case RESUME_PHASE_PACKER:
+	case RESUME_PHASE_FLUSHER:
+	case SUSPEND_PHASE_PACKER:
+	case SUSPEND_PHASE_FLUSHES:
+		return vdo->thread_config.packer_thread;
+
+	case RESUME_PHASE_DATA_VIOS:
+	case SUSPEND_PHASE_DATA_VIOS:
+		return vdo->thread_config.cpu_thread;
+
+	case LOAD_PHASE_DRAIN_JOURNAL:
+	case RESUME_PHASE_JOURNAL:
+	case SUSPEND_PHASE_JOURNAL:
+		return vdo->thread_config.journal_thread;
+
+	default:
+		return vdo->thread_config.admin_thread;
+	}
+}
+
+static struct vdo_completion *prepare_admin_completion(struct vdo *vdo,
+						       vdo_action_fn callback,
+						       vdo_action_fn error_handler)
+{
+	struct vdo_completion *completion = &vdo->admin.completion;
+
+	/*
+	 * We can't use vdo_prepare_completion_for_requeue() here because we don't want to reset
+	 * any error in the completion.
+	 */
+	completion->callback = callback;
+	completion->error_handler = error_handler;
+	completion->callback_thread_id = get_thread_id_for_phase(vdo);
+	completion->requeue = true;
+	return completion;
+}
+
+/**
+ * advance_phase() - Increment the phase of the current admin operation and prepare the admin
+ *                   completion to run on the thread for the next phase.
+ * @vdo: The on which an admin operation is being performed
+ *
+ * Return: The current phase
+ */
+static u32 advance_phase(struct vdo *vdo)
+{
+	u32 phase = vdo->admin.phase++;
+
+	vdo->admin.completion.callback_thread_id = get_thread_id_for_phase(vdo);
+	vdo->admin.completion.requeue = true;
+	return phase;
+}
+
+/*
+ * Perform an administrative operation (load, suspend, grow logical, or grow physical). This method
+ * should not be called from vdo threads.
+ */
+static int perform_admin_operation(struct vdo *vdo, u32 starting_phase,
+				   vdo_action_fn callback, vdo_action_fn error_handler,
+				   const char *type)
+{
+	int result;
+	struct vdo_administrator *admin = &vdo->admin;
+
+	if (atomic_cmpxchg(&admin->busy, 0, 1) != 0) {
+		return uds_log_error_strerror(VDO_COMPONENT_BUSY,
+					      "Can't start %s operation, another operation is already in progress",
+					      type);
+	}
+
+	admin->phase = starting_phase;
+	reinit_completion(&admin->callback_sync);
+	vdo_reset_completion(&admin->completion);
+	vdo_launch_completion(prepare_admin_completion(vdo, callback, error_handler));
+
+	/*
+	 * Using the "interruptible" interface means that Linux will not log a message when we wait
+	 * for more than 120 seconds.
+	 */
+	while (wait_for_completion_interruptible(&admin->callback_sync) != 0)
+		/* * However, if we get a signal in a user-mode process, we could spin... */
+		fsleep(1000);
+
+	result = admin->completion.result;
+	/* pairs with implicit barrier in cmpxchg above */
+	smp_wmb();
+	atomic_set(&admin->busy, 0);
+	return result;
+}
+
+/* Assert that we are operating on the correct thread for the current phase. */
+static void assert_admin_phase_thread(struct vdo *vdo, const char *what)
+{
+	ASSERT_LOG_ONLY(vdo_get_callback_thread_id() == get_thread_id_for_phase(vdo),
+			"%s on correct thread for %s", what,
+			ADMIN_PHASE_NAMES[vdo->admin.phase]);
+}
+
+/**
+ * finish_operation_callback() - Callback to finish an admin operation.
+ * @completion: The admin_completion.
+ */
+static void finish_operation_callback(struct vdo_completion *completion)
+{
+	struct vdo_administrator *admin = &completion->vdo->admin;
+
+	vdo_finish_operation(&admin->state, completion->result);
+	complete(&admin->callback_sync);
+}
+
+/**
+ * decode_from_super_block() - Decode the VDO state from the super block and validate that it is
+ *                             correct.
+ * @vdo: The vdo being loaded.
+ *
+ * On error from this method, the component states must be destroyed explicitly. If this method
+ * returns successfully, the component states must not be destroyed.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int __must_check decode_from_super_block(struct vdo *vdo)
+{
+	const struct device_config *config = vdo->device_config;
+	int result;
+
+	result = vdo_decode_component_states(vdo->super_block.buffer, &vdo->geometry,
+					     &vdo->states);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	vdo_set_state(vdo, vdo->states.vdo.state);
+	vdo->load_state = vdo->states.vdo.state;
+
+	/*
+	 * If the device config specifies a larger logical size than was recorded in the super
+	 * block, just accept it.
+	 */
+	if (vdo->states.vdo.config.logical_blocks < config->logical_blocks) {
+		uds_log_warning("Growing logical size: a logical size of %llu blocks was specified, but that differs from the %llu blocks configured in the vdo super block",
+				(unsigned long long) config->logical_blocks,
+				(unsigned long long) vdo->states.vdo.config.logical_blocks);
+		vdo->states.vdo.config.logical_blocks = config->logical_blocks;
+	}
+
+	result = vdo_validate_component_states(&vdo->states, vdo->geometry.nonce,
+					       config->physical_blocks,
+					       config->logical_blocks);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	vdo->layout = vdo->states.layout;
+	return VDO_SUCCESS;
+}
+
+/**
+ * decode_vdo() - Decode the component data portion of a super block and fill in the corresponding
+ *                portions of the vdo being loaded.
+ * @vdo: The vdo being loaded.
+ *
+ * This will also allocate the recovery journal and slab depot. If this method is called with an
+ * asynchronous layer (i.e. a thread config which specifies at least one base thread), the block
+ * map and packer will be constructed as well.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int __must_check decode_vdo(struct vdo *vdo)
+{
+	block_count_t maximum_age, journal_length;
+	struct partition *partition;
+	int result;
+
+	result = decode_from_super_block(vdo);
+	if (result != VDO_SUCCESS) {
+		vdo_destroy_component_states(&vdo->states);
+		return result;
+	}
+
+	maximum_age = vdo_convert_maximum_age(vdo->device_config->block_map_maximum_age);
+	journal_length =
+		vdo_get_recovery_journal_length(vdo->states.vdo.config.recovery_journal_size);
+	if (maximum_age > (journal_length / 2)) {
+		return uds_log_error_strerror(VDO_BAD_CONFIGURATION,
+					      "maximum age: %llu exceeds limit %llu",
+					      (unsigned long long) maximum_age,
+					      (unsigned long long) (journal_length / 2));
+	}
+
+	if (maximum_age == 0) {
+		return uds_log_error_strerror(VDO_BAD_CONFIGURATION,
+					      "maximum age must be greater than 0");
+	}
+
+	result = vdo_enable_read_only_entry(vdo);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	partition = vdo_get_known_partition(&vdo->layout,
+					    VDO_RECOVERY_JOURNAL_PARTITION);
+	result = vdo_decode_recovery_journal(vdo->states.recovery_journal,
+					     vdo->states.vdo.nonce, vdo, partition,
+					     vdo->states.vdo.complete_recoveries,
+					     vdo->states.vdo.config.recovery_journal_size,
+					     &vdo->recovery_journal);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	partition = vdo_get_known_partition(&vdo->layout, VDO_SLAB_SUMMARY_PARTITION);
+	result = vdo_decode_slab_depot(vdo->states.slab_depot, vdo, partition,
+				       &vdo->depot);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_decode_block_map(vdo->states.block_map,
+				      vdo->states.vdo.config.logical_blocks, vdo,
+				      vdo->recovery_journal, vdo->states.vdo.nonce,
+				      vdo->device_config->cache_size, maximum_age,
+				      &vdo->block_map);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_make_physical_zones(vdo, &vdo->physical_zones);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	/* The logical zones depend on the physical zones already existing. */
+	result = vdo_make_logical_zones(vdo, &vdo->logical_zones);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	return vdo_make_hash_zones(vdo, &vdo->hash_zones);
+}
+
+/**
+ * pre_load_callback() - Callback to initiate a pre-load, registered in vdo_initialize().
+ * @completion: The admin completion.
+ */
+static void pre_load_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case PRE_LOAD_PHASE_START:
+		result = vdo_start_operation(&vdo->admin.state,
+					     VDO_ADMIN_STATE_PRE_LOADING);
+		if (result != VDO_SUCCESS) {
+			vdo_continue_completion(completion, result);
+			return;
+		}
+
+		vdo_load_super_block(vdo, completion);
+		return;
+
+	case PRE_LOAD_PHASE_LOAD_COMPONENTS:
+		vdo_continue_completion(completion, decode_vdo(vdo));
+		return;
+
+	case PRE_LOAD_PHASE_END:
+		break;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	finish_operation_callback(completion);
+}
+
+static void release_instance(unsigned int instance)
+{
+	mutex_lock(&instances_lock);
+	if (instance >= instances.bit_count) {
+		ASSERT_LOG_ONLY(false,
+				"instance number %u must be less than bit count %u",
+				instance, instances.bit_count);
+	} else if (test_bit(instance, instances.words) == 0) {
+		ASSERT_LOG_ONLY(false, "instance number %u must be allocated", instance);
+	} else {
+		__clear_bit(instance, instances.words);
+		instances.count -= 1;
+	}
+	mutex_unlock(&instances_lock);
+}
+
+static void set_device_config(struct dm_target *ti, struct vdo *vdo,
+			      struct device_config *config)
+{
+	list_del_init(&config->config_list);
+	list_add_tail(&config->config_list, &vdo->device_config_list);
+	config->vdo = vdo;
+	ti->private = config;
+	configure_target_capabilities(ti);
+}
+
+static int vdo_initialize(struct dm_target *ti, unsigned int instance,
+			  struct device_config *config)
+{
+	struct vdo *vdo;
+	int result;
+	u64 block_size = VDO_BLOCK_SIZE;
+	u64 logical_size = to_bytes(ti->len);
+	block_count_t logical_blocks = logical_size / block_size;
+
+	uds_log_info("loading device '%s'", vdo_get_device_name(ti));
+	uds_log_debug("Logical block size     = %llu", (u64) config->logical_block_size);
+	uds_log_debug("Logical blocks         = %llu", logical_blocks);
+	uds_log_debug("Physical block size    = %llu", (u64) block_size);
+	uds_log_debug("Physical blocks        = %llu", config->physical_blocks);
+	uds_log_debug("Block map cache blocks = %u", config->cache_size);
+	uds_log_debug("Block map maximum age  = %u", config->block_map_maximum_age);
+	uds_log_debug("Deduplication          = %s", (config->deduplication ? "on" : "off"));
+	uds_log_debug("Compression            = %s", (config->compression ? "on" : "off"));
+
+	vdo = vdo_find_matching(vdo_uses_device, config);
+	if (vdo != NULL) {
+		uds_log_error("Existing vdo already uses device %s",
+			      vdo->device_config->parent_device_name);
+		ti->error = "Cannot share storage device with already-running VDO";
+		return VDO_BAD_CONFIGURATION;
+	}
+
+	result = vdo_make(instance, config, &ti->error, &vdo);
+	if (result != VDO_SUCCESS) {
+		uds_log_error("Could not create VDO device. (VDO error %d, message %s)",
+			      result, ti->error);
+		vdo_destroy(vdo);
+		return result;
+	}
+
+	result = perform_admin_operation(vdo, PRE_LOAD_PHASE_START, pre_load_callback,
+					 finish_operation_callback, "pre-load");
+	if (result != VDO_SUCCESS) {
+		ti->error = ((result == VDO_INVALID_ADMIN_STATE) ?
+			     "Pre-load is only valid immediately after initialization" :
+			     "Cannot load metadata from device");
+		uds_log_error("Could not start VDO device. (VDO error %d, message %s)",
+			      result, ti->error);
+		vdo_destroy(vdo);
+		return result;
+	}
+
+	set_device_config(ti, vdo, config);
+	vdo->device_config = config;
+	return VDO_SUCCESS;
+}
+
+/* Implements vdo_filter_fn. */
+static bool __must_check vdo_is_named(struct vdo *vdo, const void *context)
+{
+	struct dm_target *ti = vdo->device_config->owning_target;
+	const char *device_name = vdo_get_device_name(ti);
+
+	return strcmp(device_name, context) == 0;
+}
+
+/**
+ * get_bit_array_size() - Return the number of bytes needed to store a bit array of the specified
+ *                        capacity in an array of unsigned longs.
+ * @bit_count: The number of bits the array must hold.
+ *
+ * Return: the number of bytes needed for the array representation.
+ */
+static size_t get_bit_array_size(unsigned int bit_count)
+{
+	/* Round up to a multiple of the word size and convert to a byte count. */
+	return (BITS_TO_LONGS(bit_count) * sizeof(unsigned long));
+}
+
+/**
+ * grow_bit_array() - Re-allocate the bitmap word array so there will more instance numbers that
+ *                    can be allocated.
+ *
+ * Since the array is initially NULL, this also initializes the array the first time we allocate an
+ * instance number.
+ *
+ * Return: UDS_SUCCESS or an error code from the allocation
+ */
+static int grow_bit_array(void)
+{
+	unsigned int new_count = max(instances.bit_count + BIT_COUNT_INCREMENT,
+				     (unsigned int) BIT_COUNT_MINIMUM);
+	unsigned long *new_words;
+	int result;
+
+	result = uds_reallocate_memory(instances.words,
+				       get_bit_array_size(instances.bit_count),
+				       get_bit_array_size(new_count),
+				       "instance number bit array", &new_words);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	instances.bit_count = new_count;
+	instances.words = new_words;
+	return UDS_SUCCESS;
+}
+
+/**
+ * allocate_instance() - Allocate an instance number.
+ * @instance_ptr: A point to hold the instance number
+ *
+ * Return: UDS_SUCCESS or an error code
+ *
+ * This function must be called while holding the instances lock.
+ */
+static int allocate_instance(unsigned int *instance_ptr)
+{
+	unsigned int instance;
+	int result;
+
+	/* If there are no unallocated instances, grow the bit array. */
+	if (instances.count >= instances.bit_count) {
+		result = grow_bit_array();
+		if (result != UDS_SUCCESS)
+			return result;
+	}
+
+	/*
+	 * There must be a zero bit somewhere now. Find it, starting just after the last instance
+	 * allocated.
+	 */
+	instance = find_next_zero_bit(instances.words, instances.bit_count,
+				      instances.next);
+	if (instance >= instances.bit_count) {
+		/* Nothing free after next, so wrap around to instance zero. */
+		instance = find_first_zero_bit(instances.words, instances.bit_count);
+		result = ASSERT(instance < instances.bit_count,
+				"impossibly, no zero bit found");
+		if (result != UDS_SUCCESS)
+			return result;
+	}
+
+	__set_bit(instance, instances.words);
+	instances.count++;
+	instances.next = instance + 1;
+	*instance_ptr = instance;
+	return UDS_SUCCESS;
+}
+
+static int construct_new_vdo_registered(struct dm_target *ti, unsigned int argc,
+					char **argv, unsigned int instance)
+{
+	int result;
+	struct device_config *config;
+
+	result = parse_device_config(argc, argv, ti, &config);
+	if (result != VDO_SUCCESS) {
+		uds_log_error_strerror(result, "parsing failed: %s", ti->error);
+		release_instance(instance);
+		return -EINVAL;
+	}
+
+	/* Beyond this point, the instance number will be cleaned up for us if needed */
+	result = vdo_initialize(ti, instance, config);
+	if (result != VDO_SUCCESS) {
+		release_instance(instance);
+		free_device_config(config);
+		return vdo_map_to_system_error(result);
+	}
+
+	return VDO_SUCCESS;
+}
+
+static int construct_new_vdo(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	int result;
+	unsigned int instance;
+	struct registered_thread instance_thread;
+
+	mutex_lock(&instances_lock);
+	result = allocate_instance(&instance);
+	mutex_unlock(&instances_lock);
+	if (result != VDO_SUCCESS)
+		return -ENOMEM;
+
+	uds_register_thread_device_id(&instance_thread, &instance);
+	result = construct_new_vdo_registered(ti, argc, argv, instance);
+	uds_unregister_thread_device_id();
+	return result;
+}
+
+/**
+ * check_may_grow_physical() - Callback to check that we're not in recovery mode, used in
+ *                             vdo_prepare_to_grow_physical().
+ * @completion: The admin completion.
+ */
+static void check_may_grow_physical(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	/* These checks can only be done from a vdo thread. */
+	if (vdo_is_read_only(vdo))
+		vdo_set_completion_result(completion, VDO_READ_ONLY);
+
+	if (vdo_in_recovery_mode(vdo))
+		vdo_set_completion_result(completion, VDO_RETRY_AFTER_REBUILD);
+
+	finish_operation_callback(completion);
+}
+
+static block_count_t get_partition_size(struct layout *layout, enum partition_id id)
+{
+	return vdo_get_known_partition(layout, id)->count;
+}
+
+/**
+ * grow_layout() - Make the layout for growing a vdo.
+ * @vdo: The vdo preparing to grow.
+ * @old_size: The current size of the vdo.
+ * @new_size: The size to which the vdo will be grown.
+ *
+ * Return: VDO_SUCCESS or an error code.
+ */
+static int grow_layout(struct vdo *vdo, block_count_t old_size, block_count_t new_size)
+{
+	int result;
+	block_count_t min_new_size;
+
+	if (vdo->next_layout.size == new_size) {
+		/* We are already prepared to grow to the new size, so we're done. */
+		return VDO_SUCCESS;
+	}
+
+	/* Make a copy completion if there isn't one */
+	if (vdo->partition_copier == NULL) {
+		vdo->partition_copier = dm_kcopyd_client_create(NULL);
+		if (vdo->partition_copier == NULL)
+			return -ENOMEM;
+	}
+
+	/* Free any unused preparation. */
+	vdo_uninitialize_layout(&vdo->next_layout);
+
+	/*
+	 * Make a new layout with the existing partition sizes for everything but the slab depot
+	 * partition.
+	 */
+	result = vdo_initialize_layout(new_size, vdo->layout.start,
+				       get_partition_size(&vdo->layout,
+							  VDO_BLOCK_MAP_PARTITION),
+				       get_partition_size(&vdo->layout,
+							  VDO_RECOVERY_JOURNAL_PARTITION),
+				       get_partition_size(&vdo->layout,
+							  VDO_SLAB_SUMMARY_PARTITION),
+				       &vdo->next_layout);
+	if (result != VDO_SUCCESS) {
+		dm_kcopyd_client_destroy(uds_forget(vdo->partition_copier));
+		return result;
+	}
+
+	/* Ensure the new journal and summary are entirely within the added blocks. */
+	min_new_size = (old_size +
+			get_partition_size(&vdo->next_layout,
+					   VDO_SLAB_SUMMARY_PARTITION) +
+			get_partition_size(&vdo->next_layout,
+					   VDO_RECOVERY_JOURNAL_PARTITION));
+	if (min_new_size > new_size) {
+		/* Copying the journal and summary would destroy some old metadata. */
+		vdo_uninitialize_layout(&vdo->next_layout);
+		dm_kcopyd_client_destroy(uds_forget(vdo->partition_copier));
+		return VDO_INCREMENT_TOO_SMALL;
+	}
+
+	return VDO_SUCCESS;
+}
+
+static int prepare_to_grow_physical(struct vdo *vdo, block_count_t new_physical_blocks)
+{
+	int result;
+	block_count_t current_physical_blocks = vdo->states.vdo.config.physical_blocks;
+
+	uds_log_info("Preparing to resize physical to %llu",
+		     (unsigned long long) new_physical_blocks);
+	ASSERT_LOG_ONLY((new_physical_blocks > current_physical_blocks),
+			"New physical size is larger than current physical size");
+	result = perform_admin_operation(vdo, PREPARE_GROW_PHYSICAL_PHASE_START,
+					 check_may_grow_physical,
+					 finish_operation_callback,
+					 "prepare grow-physical");
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = grow_layout(vdo, current_physical_blocks, new_physical_blocks);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_prepare_to_grow_slab_depot(vdo->depot,
+						vdo_get_known_partition(&vdo->next_layout,
+									VDO_SLAB_DEPOT_PARTITION));
+	if (result != VDO_SUCCESS) {
+		vdo_uninitialize_layout(&vdo->next_layout);
+		return result;
+	}
+
+	uds_log_info("Done preparing to resize physical");
+	return VDO_SUCCESS;
+}
+
+/**
+ * validate_new_device_config() - Check whether a new device config represents a valid modification
+ *				  to an existing config.
+ * @to_validate: The new config to validate.
+ * @config: The existing config.
+ * @may_grow: Set to true if growing the logical and physical size of the vdo is currently
+ *	      permitted.
+ * @error_ptr: A pointer to hold the reason for any error.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int validate_new_device_config(struct device_config *to_validate,
+				      struct device_config *config, bool may_grow,
+				      char **error_ptr)
+{
+	if (to_validate->owning_target->begin != config->owning_target->begin) {
+		*error_ptr = "Starting sector cannot change";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (to_validate->logical_block_size != config->logical_block_size) {
+		*error_ptr = "Logical block size cannot change";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (to_validate->logical_blocks < config->logical_blocks) {
+		*error_ptr = "Can't shrink VDO logical size";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (to_validate->cache_size != config->cache_size) {
+		*error_ptr = "Block map cache size cannot change";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (to_validate->block_map_maximum_age != config->block_map_maximum_age) {
+		*error_ptr = "Block map maximum age cannot change";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (memcmp(&to_validate->thread_counts, &config->thread_counts,
+		   sizeof(struct thread_count_config)) != 0) {
+		*error_ptr = "Thread configuration cannot change";
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	if (to_validate->physical_blocks < config->physical_blocks) {
+		*error_ptr = "Removing physical storage from a VDO is not supported";
+		return VDO_NOT_IMPLEMENTED;
+	}
+
+	if (!may_grow && (to_validate->physical_blocks > config->physical_blocks)) {
+		*error_ptr = "VDO physical size may not grow in current state";
+		return VDO_NOT_IMPLEMENTED;
+	}
+
+	return VDO_SUCCESS;
+}
+
+static int prepare_to_modify(struct dm_target *ti, struct device_config *config,
+			     struct vdo *vdo)
+{
+	int result;
+	bool may_grow = (vdo_get_admin_state(vdo) != VDO_ADMIN_STATE_PRE_LOADED);
+
+	result = validate_new_device_config(config, vdo->device_config, may_grow,
+					    &ti->error);
+	if (result != VDO_SUCCESS)
+		return -EINVAL;
+
+	if (config->logical_blocks > vdo->device_config->logical_blocks) {
+		block_count_t logical_blocks = vdo->states.vdo.config.logical_blocks;
+
+		uds_log_info("Preparing to resize logical to %llu",
+			     (unsigned long long) config->logical_blocks);
+		ASSERT_LOG_ONLY((config->logical_blocks > logical_blocks),
+				"New logical size is larger than current size");
+
+		result = vdo_prepare_to_grow_block_map(vdo->block_map,
+						       config->logical_blocks);
+		if (result != VDO_SUCCESS) {
+			ti->error = "Device vdo_prepare_to_grow_logical failed";
+			return result;
+		}
+
+		uds_log_info("Done preparing to resize logical");
+	}
+
+	if (config->physical_blocks > vdo->device_config->physical_blocks) {
+		result = prepare_to_grow_physical(vdo, config->physical_blocks);
+		if (result != VDO_SUCCESS) {
+			if (result == VDO_PARAMETER_MISMATCH) {
+				/*
+				 * If we don't trap this case, vdo_map_to_system_error() will remap
+				 * it to -EIO, which is misleading and ahistorical.
+				 */
+				result = -EINVAL;
+			}
+
+			if (result == VDO_TOO_MANY_SLABS)
+				ti->error = "Device vdo_prepare_to_grow_physical failed (specified physical size too big based on formatted slab size)";
+			else
+				ti->error = "Device vdo_prepare_to_grow_physical failed";
+
+			return result;
+		}
+	}
+
+	if (strcmp(config->parent_device_name, vdo->device_config->parent_device_name) != 0) {
+		const char *device_name = vdo_get_device_name(config->owning_target);
+
+		uds_log_info("Updating backing device of %s from %s to %s", device_name,
+			     vdo->device_config->parent_device_name,
+			     config->parent_device_name);
+	}
+
+	return VDO_SUCCESS;
+}
+
+static int update_existing_vdo(const char *device_name, struct dm_target *ti,
+			       unsigned int argc, char **argv, struct vdo *vdo)
+{
+	int result;
+	struct device_config *config;
+
+	result = parse_device_config(argc, argv, ti, &config);
+	if (result != VDO_SUCCESS)
+		return -EINVAL;
+
+	uds_log_info("preparing to modify device '%s'", device_name);
+	result = prepare_to_modify(ti, config, vdo);
+	if (result != VDO_SUCCESS) {
+		free_device_config(config);
+		return vdo_map_to_system_error(result);
+	}
+
+	set_device_config(ti, vdo, config);
+	return VDO_SUCCESS;
+}
+
+static int vdo_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	int result;
+	struct registered_thread allocating_thread, instance_thread;
+	const char *device_name;
+	struct vdo *vdo;
+
+	uds_register_allocating_thread(&allocating_thread, NULL);
+	device_name = vdo_get_device_name(ti);
+	vdo = vdo_find_matching(vdo_is_named, device_name);
+	if (vdo == NULL) {
+		result = construct_new_vdo(ti, argc, argv);
+	} else {
+		uds_register_thread_device_id(&instance_thread, &vdo->instance);
+		result = update_existing_vdo(device_name, ti, argc, argv, vdo);
+		uds_unregister_thread_device_id();
+	}
+
+	uds_unregister_allocating_thread();
+	return result;
+}
+
+static void vdo_dtr(struct dm_target *ti)
+{
+	struct device_config *config = ti->private;
+	struct vdo *vdo = uds_forget(config->vdo);
+
+	list_del_init(&config->config_list);
+	if (list_empty(&vdo->device_config_list)) {
+		const char *device_name;
+
+		/* This was the last config referencing the VDO. Free it. */
+		unsigned int instance = vdo->instance;
+		struct registered_thread allocating_thread, instance_thread;
+
+		uds_register_thread_device_id(&instance_thread, &instance);
+		uds_register_allocating_thread(&allocating_thread, NULL);
+
+		device_name = vdo_get_device_name(ti);
+		uds_log_info("stopping device '%s'", device_name);
+		if (vdo->dump_on_shutdown)
+			vdo_dump_all(vdo, "device shutdown");
+
+		vdo_destroy(uds_forget(vdo));
+		uds_log_info("device '%s' stopped", device_name);
+		uds_unregister_thread_device_id();
+		uds_unregister_allocating_thread();
+		release_instance(instance);
+	} else if (config == vdo->device_config) {
+		/*
+		 * The VDO still references this config. Give it a reference to a config that isn't
+		 * being destroyed.
+		 */
+		vdo->device_config = list_first_entry(&vdo->device_config_list,
+						      struct device_config, config_list);
+	}
+
+	free_device_config(config);
+	ti->private = NULL;
+}
+
+static void vdo_presuspend(struct dm_target *ti)
+{
+	get_vdo_for_target(ti)->suspend_type =
+		(dm_noflush_suspending(ti) ? VDO_ADMIN_STATE_SUSPENDING : VDO_ADMIN_STATE_SAVING);
+}
+
+/**
+ * write_super_block_for_suspend() - Update the VDO state and save the super block.
+ * @completion: The admin completion
+ */
+static void write_super_block_for_suspend(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+
+	switch (vdo_get_state(vdo)) {
+	case VDO_DIRTY:
+	case VDO_NEW:
+		vdo_set_state(vdo, VDO_CLEAN);
+		break;
+
+	case VDO_CLEAN:
+	case VDO_READ_ONLY_MODE:
+	case VDO_FORCE_REBUILD:
+	case VDO_RECOVERING:
+	case VDO_REBUILD_FOR_UPGRADE:
+		break;
+
+	case VDO_REPLAYING:
+	default:
+		vdo_continue_completion(completion, UDS_BAD_STATE);
+		return;
+	}
+
+	vdo_save_components(vdo, completion);
+}
+
+/**
+ * suspend_callback() - Callback to initiate a suspend, registered in vdo_postsuspend().
+ * @completion: The sub-task completion.
+ */
+static void suspend_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	struct admin_state *state = &vdo->admin.state;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case SUSPEND_PHASE_START:
+		if (vdo_get_admin_state_code(state)->quiescent) {
+			/* Already suspended */
+			break;
+		}
+
+		vdo_continue_completion(completion,
+					vdo_start_operation(state, vdo->suspend_type));
+		return;
+
+	case SUSPEND_PHASE_PACKER:
+		/*
+		 * If the VDO was already resumed from a prior suspend while read-only, some of the
+		 * components may not have been resumed. By setting a read-only error here, we
+		 * guarantee that the result of this suspend will be VDO_READ_ONLY and not
+		 * VDO_INVALID_ADMIN_STATE in that case.
+		 */
+		if (vdo_in_read_only_mode(vdo))
+			vdo_set_completion_result(completion, VDO_READ_ONLY);
+
+		vdo_drain_packer(vdo->packer, completion);
+		return;
+
+	case SUSPEND_PHASE_DATA_VIOS:
+		drain_data_vio_pool(vdo->data_vio_pool, completion);
+		return;
+
+	case SUSPEND_PHASE_DEDUPE:
+		vdo_drain_hash_zones(vdo->hash_zones, completion);
+		return;
+
+	case SUSPEND_PHASE_FLUSHES:
+		vdo_drain_flusher(vdo->flusher, completion);
+		return;
+
+	case SUSPEND_PHASE_LOGICAL_ZONES:
+		/*
+		 * Attempt to flush all I/O before completing post suspend work. We believe a
+		 * suspended device is expected to have persisted all data written before the
+		 * suspend, even if it hasn't been flushed yet.
+		 */
+		result = vdo_synchronous_flush(vdo);
+		if (result != VDO_SUCCESS)
+			vdo_enter_read_only_mode(vdo, result);
+
+		vdo_drain_logical_zones(vdo->logical_zones,
+					vdo_get_admin_state_code(state), completion);
+		return;
+
+	case SUSPEND_PHASE_BLOCK_MAP:
+		vdo_drain_block_map(vdo->block_map, vdo_get_admin_state_code(state),
+				    completion);
+		return;
+
+	case SUSPEND_PHASE_JOURNAL:
+		vdo_drain_recovery_journal(vdo->recovery_journal,
+					   vdo_get_admin_state_code(state), completion);
+		return;
+
+	case SUSPEND_PHASE_DEPOT:
+		vdo_drain_slab_depot(vdo->depot, vdo_get_admin_state_code(state),
+				     completion);
+		return;
+
+	case SUSPEND_PHASE_READ_ONLY_WAIT:
+		vdo_wait_until_not_entering_read_only_mode(completion);
+		return;
+
+	case SUSPEND_PHASE_WRITE_SUPER_BLOCK:
+		if (vdo_is_state_suspending(state) || (completion->result != VDO_SUCCESS)) {
+			/* If we didn't save the VDO or there was an error, we're done. */
+			break;
+		}
+
+		write_super_block_for_suspend(completion);
+		return;
+
+	case SUSPEND_PHASE_END:
+		break;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	finish_operation_callback(completion);
+}
+
+static void vdo_postsuspend(struct dm_target *ti)
+{
+	struct vdo *vdo = get_vdo_for_target(ti);
+	struct registered_thread instance_thread;
+	const char *device_name;
+	int result;
+
+	uds_register_thread_device_id(&instance_thread, &vdo->instance);
+	device_name = vdo_get_device_name(vdo->device_config->owning_target);
+	uds_log_info("suspending device '%s'", device_name);
+
+	/*
+	 * It's important to note any error here does not actually stop device-mapper from
+	 * suspending the device. All this work is done post suspend.
+	 */
+	result = perform_admin_operation(vdo, SUSPEND_PHASE_START, suspend_callback,
+					 suspend_callback, "suspend");
+
+	if ((result == VDO_SUCCESS) || (result == VDO_READ_ONLY)) {
+		/*
+		 * Treat VDO_READ_ONLY as a success since a read-only suspension still leaves the
+		 * VDO suspended.
+		 */
+		uds_log_info("device '%s' suspended", device_name);
+	} else if (result == VDO_INVALID_ADMIN_STATE) {
+		uds_log_error("Suspend invoked while in unexpected state: %s",
+			      vdo_get_admin_state(vdo)->name);
+	} else {
+		uds_log_error_strerror(result, "Suspend of device '%s' failed",
+				       device_name);
+	}
+
+	uds_unregister_thread_device_id();
+}
+
+/**
+ * was_new() - Check whether the vdo was new when it was loaded.
+ * @vdo: The vdo to query.
+ *
+ * Return: true if the vdo was new.
+ */
+static bool was_new(const struct vdo *vdo)
+{
+	return (vdo->load_state == VDO_NEW);
+}
+
+/**
+ * requires_repair() - Check whether a vdo requires recovery or rebuild.
+ * @vdo: The vdo to query.
+ *
+ * Return: true if the vdo must be repaired.
+ */
+static bool __must_check requires_repair(const struct vdo *vdo)
+{
+	switch (vdo_get_state(vdo)) {
+	case VDO_DIRTY:
+	case VDO_FORCE_REBUILD:
+	case VDO_REPLAYING:
+	case VDO_REBUILD_FOR_UPGRADE:
+		return true;
+
+	default:
+		return false;
+	}
+}
+
+/**
+ * get_load_type() - Determine how the slab depot was loaded.
+ * @vdo: The vdo.
+ *
+ * Return: How the depot was loaded.
+ */
+static enum slab_depot_load_type get_load_type(struct vdo *vdo)
+{
+	if (vdo_state_requires_read_only_rebuild(vdo->load_state))
+		return VDO_SLAB_DEPOT_REBUILD_LOAD;
+
+	if (vdo_state_requires_recovery(vdo->load_state))
+		return VDO_SLAB_DEPOT_RECOVERY_LOAD;
+
+	return VDO_SLAB_DEPOT_NORMAL_LOAD;
+}
+
+/**
+ * vdo_initialize_kobjects() - Initialize the vdo sysfs directory.
+ * @vdo: The vdo being initialized.
+ *
+ * Return: VDO_SUCCESS or an error code.
+ */
+static int vdo_initialize_kobjects(struct vdo *vdo)
+{
+	int result;
+	struct dm_target *target = vdo->device_config->owning_target;
+	struct mapped_device *md = dm_table_get_md(target->table);
+
+	kobject_init(&vdo->vdo_directory, &vdo_directory_type);
+	vdo->sysfs_added = true;
+	result = kobject_add(&vdo->vdo_directory, &disk_to_dev(dm_disk(md))->kobj,
+			     "vdo");
+	if (result != 0)
+		return VDO_CANT_ADD_SYSFS_NODE;
+
+	result = vdo_add_dedupe_index_sysfs(vdo->hash_zones);
+	if (result != 0)
+		return VDO_CANT_ADD_SYSFS_NODE;
+
+	return vdo_add_sysfs_stats_dir(vdo);
+}
+
+/**
+ * load_callback() - Callback to do the destructive parts of loading a VDO.
+ * @completion: The sub-task completion.
+ */
+static void load_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case LOAD_PHASE_START:
+		result = vdo_start_operation(&vdo->admin.state, VDO_ADMIN_STATE_LOADING);
+		if (result != VDO_SUCCESS) {
+			vdo_continue_completion(completion, result);
+			return;
+		}
+
+		/* Prepare the recovery journal for new entries. */
+		vdo_open_recovery_journal(vdo->recovery_journal, vdo->depot,
+					  vdo->block_map);
+		vdo_allow_read_only_mode_entry(completion);
+		return;
+
+	case LOAD_PHASE_STATS:
+		vdo_continue_completion(completion, vdo_initialize_kobjects(vdo));
+		return;
+
+	case LOAD_PHASE_LOAD_DEPOT:
+		if (vdo_is_read_only(vdo)) {
+			/*
+			 * In read-only mode we don't use the allocator and it may not even be
+			 * readable, so don't bother trying to load it.
+			 */
+			vdo_set_completion_result(completion, VDO_READ_ONLY);
+			break;
+		}
+
+		if (requires_repair(vdo)) {
+			vdo_repair(completion);
+			return;
+		}
+
+		vdo_load_slab_depot(vdo->depot,
+				    (was_new(vdo) ? VDO_ADMIN_STATE_FORMATTING :
+				     VDO_ADMIN_STATE_LOADING),
+				    completion, NULL);
+		return;
+
+	case LOAD_PHASE_MAKE_DIRTY:
+		vdo_set_state(vdo, VDO_DIRTY);
+		vdo_save_components(vdo, completion);
+		return;
+
+	case LOAD_PHASE_PREPARE_TO_ALLOCATE:
+		vdo_initialize_block_map_from_journal(vdo->block_map,
+						      vdo->recovery_journal);
+		vdo_prepare_slab_depot_to_allocate(vdo->depot, get_load_type(vdo),
+						   completion);
+		return;
+
+	case LOAD_PHASE_SCRUB_SLABS:
+		if (vdo_state_requires_recovery(vdo->load_state))
+			vdo_enter_recovery_mode(vdo);
+
+		vdo_scrub_all_unrecovered_slabs(vdo->depot, completion);
+		return;
+
+	case LOAD_PHASE_DATA_REDUCTION:
+		WRITE_ONCE(vdo->compressing, vdo->device_config->compression);
+		if (vdo->device_config->deduplication) {
+			/*
+			 * Don't try to load or rebuild the index first (and log scary error
+			 * messages) if this is known to be a newly-formatted volume.
+			 */
+			vdo_start_dedupe_index(vdo->hash_zones, was_new(vdo));
+		}
+
+		vdo->allocations_allowed = false;
+		fallthrough;
+
+	case LOAD_PHASE_FINISHED:
+		break;
+
+	case LOAD_PHASE_DRAIN_JOURNAL:
+		vdo_drain_recovery_journal(vdo->recovery_journal, VDO_ADMIN_STATE_SAVING,
+					   completion);
+		return;
+
+	case LOAD_PHASE_WAIT_FOR_READ_ONLY:
+		/* Avoid an infinite loop */
+		completion->error_handler = NULL;
+		vdo->admin.phase = LOAD_PHASE_FINISHED;
+		vdo_wait_until_not_entering_read_only_mode(completion);
+		return;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	finish_operation_callback(completion);
+}
+
+/**
+ * handle_load_error() - Handle an error during the load operation.
+ * @completion: The admin completion.
+ *
+ * If at all possible, brings the vdo online in read-only mode. This handler is registered in
+ * vdo_preresume_registered().
+ */
+static void handle_load_error(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+
+	if (vdo_requeue_completion_if_needed(completion,
+					     vdo->thread_config.admin_thread))
+		return;
+
+	if (vdo_state_requires_read_only_rebuild(vdo->load_state) &&
+	    (vdo->admin.phase == LOAD_PHASE_MAKE_DIRTY)) {
+		uds_log_error_strerror(completion->result, "aborting load");
+		vdo->admin.phase = LOAD_PHASE_DRAIN_JOURNAL;
+		load_callback(uds_forget(completion));
+		return;
+	}
+
+	uds_log_error_strerror(completion->result,
+			       "Entering read-only mode due to load error");
+	vdo->admin.phase = LOAD_PHASE_WAIT_FOR_READ_ONLY;
+	vdo_enter_read_only_mode(vdo, completion->result);
+	completion->result = VDO_READ_ONLY;
+	load_callback(completion);
+}
+
+/**
+ * write_super_block_for_resume() - Update the VDO state and save the super block.
+ * @completion: The admin completion
+ */
+static void write_super_block_for_resume(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+
+	switch (vdo_get_state(vdo)) {
+	case VDO_CLEAN:
+	case VDO_NEW:
+		vdo_set_state(vdo, VDO_DIRTY);
+		vdo_save_components(vdo, completion);
+		return;
+
+	case VDO_DIRTY:
+	case VDO_READ_ONLY_MODE:
+	case VDO_FORCE_REBUILD:
+	case VDO_RECOVERING:
+	case VDO_REBUILD_FOR_UPGRADE:
+		/* No need to write the super block in these cases */
+		vdo_launch_completion(completion);
+		return;
+
+	case VDO_REPLAYING:
+	default:
+		vdo_continue_completion(completion, UDS_BAD_STATE);
+	}
+}
+
+/**
+ * resume_callback() - Callback to resume a VDO.
+ * @completion: The admin completion.
+ */
+static void resume_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case RESUME_PHASE_START:
+		result = vdo_start_operation(&vdo->admin.state,
+					     VDO_ADMIN_STATE_RESUMING);
+		if (result != VDO_SUCCESS) {
+			vdo_continue_completion(completion, result);
+			return;
+		}
+
+		write_super_block_for_resume(completion);
+		return;
+
+	case RESUME_PHASE_ALLOW_READ_ONLY_MODE:
+		vdo_allow_read_only_mode_entry(completion);
+		return;
+
+	case RESUME_PHASE_DEDUPE:
+		vdo_resume_hash_zones(vdo->hash_zones, completion);
+		return;
+
+	case RESUME_PHASE_DEPOT:
+		vdo_resume_slab_depot(vdo->depot, completion);
+		return;
+
+	case RESUME_PHASE_JOURNAL:
+		vdo_resume_recovery_journal(vdo->recovery_journal, completion);
+		return;
+
+	case RESUME_PHASE_BLOCK_MAP:
+		vdo_resume_block_map(vdo->block_map, completion);
+		return;
+
+	case RESUME_PHASE_LOGICAL_ZONES:
+		vdo_resume_logical_zones(vdo->logical_zones, completion);
+		return;
+
+	case RESUME_PHASE_PACKER:
+	{
+		bool was_enabled = vdo_get_compressing(vdo);
+		bool enable = vdo->device_config->compression;
+
+		if (enable != was_enabled)
+			WRITE_ONCE(vdo->compressing, enable);
+		uds_log_info("compression is %s", (enable ? "enabled" : "disabled"));
+
+		vdo_resume_packer(vdo->packer, completion);
+		return;
+	}
+
+	case RESUME_PHASE_FLUSHER:
+		vdo_resume_flusher(vdo->flusher, completion);
+		return;
+
+	case RESUME_PHASE_DATA_VIOS:
+		resume_data_vio_pool(vdo->data_vio_pool, completion);
+		return;
+
+	case RESUME_PHASE_END:
+		break;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	finish_operation_callback(completion);
+}
+
+/**
+ * grow_logical_callback() - Callback to initiate a grow logical.
+ * @completion: The admin completion.
+ *
+ * Registered in perform_grow_logical().
+ */
+static void grow_logical_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case GROW_LOGICAL_PHASE_START:
+		if (vdo_is_read_only(vdo)) {
+			uds_log_error_strerror(VDO_READ_ONLY,
+					       "Can't grow logical size of a read-only VDO");
+			vdo_set_completion_result(completion, VDO_READ_ONLY);
+			break;
+		}
+
+		result = vdo_start_operation(&vdo->admin.state,
+					     VDO_ADMIN_STATE_SUSPENDED_OPERATION);
+		if (result != VDO_SUCCESS) {
+			vdo_continue_completion(completion, result);
+			return;
+		}
+
+		vdo->states.vdo.config.logical_blocks = vdo->block_map->next_entry_count;
+		vdo_save_components(vdo, completion);
+		return;
+
+	case GROW_LOGICAL_PHASE_GROW_BLOCK_MAP:
+		vdo_grow_block_map(vdo->block_map, completion);
+		return;
+
+	case GROW_LOGICAL_PHASE_END:
+		break;
+
+	case GROW_LOGICAL_PHASE_ERROR:
+		vdo_enter_read_only_mode(vdo, completion->result);
+		break;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	finish_operation_callback(completion);
+}
+
+/**
+ * handle_logical_growth_error() - Handle an error during the grow physical process.
+ * @completion: The admin completion.
+ */
+static void handle_logical_growth_error(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+
+	if (vdo->admin.phase == GROW_LOGICAL_PHASE_GROW_BLOCK_MAP) {
+		/*
+		 * We've failed to write the new size in the super block, so set our in memory
+		 * config back to the old size.
+		 */
+		vdo->states.vdo.config.logical_blocks = vdo->block_map->entry_count;
+		vdo_abandon_block_map_growth(vdo->block_map);
+	}
+
+	vdo->admin.phase = GROW_LOGICAL_PHASE_ERROR;
+	grow_logical_callback(completion);
+}
+
+/**
+ * perform_grow_logical() - Grow the logical size of the vdo.
+ * @vdo: The vdo to grow.
+ * @new_logical_blocks: The size to which the vdo should be grown.
+ *
+ * Context: This method may only be called when the vdo has been suspended and must not be called
+ * from a base thread.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int perform_grow_logical(struct vdo *vdo, block_count_t new_logical_blocks)
+{
+	int result;
+
+	if (vdo->device_config->logical_blocks == new_logical_blocks) {
+		/*
+		 * A table was loaded for which we prepared to grow, but a table without that
+		 * growth was what we are resuming with.
+		 */
+		vdo_abandon_block_map_growth(vdo->block_map);
+		return VDO_SUCCESS;
+	}
+
+	uds_log_info("Resizing logical to %llu",
+		     (unsigned long long) new_logical_blocks);
+	if (vdo->block_map->next_entry_count != new_logical_blocks)
+		return VDO_PARAMETER_MISMATCH;
+
+	result = perform_admin_operation(vdo, GROW_LOGICAL_PHASE_START,
+					 grow_logical_callback,
+					 handle_logical_growth_error, "grow logical");
+	if (result != VDO_SUCCESS)
+		return result;
+
+	uds_log_info("Logical blocks now %llu", (unsigned long long) new_logical_blocks);
+	return VDO_SUCCESS;
+}
+
+static void copy_callback(int read_err, unsigned long write_err, void *context)
+{
+	struct vdo_completion *completion = context;
+	int result = (((read_err == 0) && (write_err == 0)) ? VDO_SUCCESS : -EIO);
+
+	vdo_continue_completion(completion, result);
+}
+
+static void partition_to_region(struct partition *partition, struct vdo *vdo,
+				struct dm_io_region *region)
+{
+	physical_block_number_t pbn = partition->offset - vdo->geometry.bio_offset;
+
+	*region = (struct dm_io_region) {
+		.bdev = vdo_get_backing_device(vdo),
+		.sector = pbn * VDO_SECTORS_PER_BLOCK,
+		.count = partition->count * VDO_SECTORS_PER_BLOCK,
+	};
+}
+
+/**
+ * copy_partition() - Copy a partition from the location specified in the current layout to that in
+ *                    the next layout.
+ * @vdo: The vdo preparing to grow.
+ * @id: The ID of the partition to copy.
+ * @parent: The completion to notify when the copy is complete.
+ */
+static void copy_partition(struct vdo *vdo, enum partition_id id,
+			   struct vdo_completion *parent)
+{
+	struct dm_io_region read_region, write_regions[1];
+	struct partition *from = vdo_get_known_partition(&vdo->layout, id);
+	struct partition *to = vdo_get_known_partition(&vdo->next_layout, id);
+
+	partition_to_region(from, vdo, &read_region);
+	partition_to_region(to, vdo, &write_regions[0]);
+	dm_kcopyd_copy(vdo->partition_copier, &read_region, 1, write_regions, 0,
+		       copy_callback, parent);
+}
+
+/**
+ * grow_physical_callback() - Callback to initiate a grow physical.
+ * @completion: The admin completion.
+ *
+ * Registered in perform_grow_physical().
+ */
+static void grow_physical_callback(struct vdo_completion *completion)
+{
+	struct vdo *vdo = completion->vdo;
+	int result;
+
+	assert_admin_phase_thread(vdo, __func__);
+
+	switch (advance_phase(vdo)) {
+	case GROW_PHYSICAL_PHASE_START:
+		if (vdo_is_read_only(vdo)) {
+			uds_log_error_strerror(VDO_READ_ONLY,
+					       "Can't grow physical size of a read-only VDO");
+			vdo_set_completion_result(completion, VDO_READ_ONLY);
+			break;
+		}
+
+		result = vdo_start_operation(&vdo->admin.state,
+					     VDO_ADMIN_STATE_SUSPENDED_OPERATION);
+		if (result != VDO_SUCCESS) {
+			vdo_continue_completion(completion, result);
+			return;
+		}
+
+		/* Copy the journal into the new layout. */
+		copy_partition(vdo, VDO_RECOVERY_JOURNAL_PARTITION, completion);
+		return;
+
+	case GROW_PHYSICAL_PHASE_COPY_SUMMARY:
+		copy_partition(vdo, VDO_SLAB_SUMMARY_PARTITION, completion);
+		return;
+
+	case GROW_PHYSICAL_PHASE_UPDATE_COMPONENTS:
+		vdo_uninitialize_layout(&vdo->layout);
+		vdo->layout = vdo->next_layout;
+		uds_forget(vdo->next_layout.head);
+		vdo->states.vdo.config.physical_blocks = vdo->layout.size;
+		vdo_update_slab_depot_size(vdo->depot);
+		vdo_save_components(vdo, completion);
+		return;
+
+	case GROW_PHYSICAL_PHASE_USE_NEW_SLABS:
+		vdo_use_new_slabs(vdo->depot, completion);
+		return;
+
+	case GROW_PHYSICAL_PHASE_END:
+		vdo->depot->summary_origin =
+			vdo_get_known_partition(&vdo->layout,
+						VDO_SLAB_SUMMARY_PARTITION)->offset;
+		vdo->recovery_journal->origin =
+			vdo_get_known_partition(&vdo->layout,
+						VDO_RECOVERY_JOURNAL_PARTITION)->offset;
+		break;
+
+	case GROW_PHYSICAL_PHASE_ERROR:
+		vdo_enter_read_only_mode(vdo, completion->result);
+		break;
+
+	default:
+		vdo_set_completion_result(completion, UDS_BAD_STATE);
+	}
+
+	vdo_uninitialize_layout(&vdo->next_layout);
+	finish_operation_callback(completion);
+}
+
+/**
+ * handle_physical_growth_error() - Handle an error during the grow physical process.
+ * @completion: The sub-task completion.
+ */
+static void handle_physical_growth_error(struct vdo_completion *completion)
+{
+	completion->vdo->admin.phase = GROW_PHYSICAL_PHASE_ERROR;
+	grow_physical_callback(completion);
+}
+
+/**
+ * perform_grow_physical() - Grow the physical size of the vdo.
+ * @vdo: The vdo to resize.
+ * @new_physical_blocks: The new physical size in blocks.
+ *
+ * Context: This method may only be called when the vdo has been suspended and must not be called
+ * from a base thread.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int perform_grow_physical(struct vdo *vdo, block_count_t new_physical_blocks)
+{
+	int result;
+	block_count_t new_depot_size, prepared_depot_size;
+	block_count_t old_physical_blocks = vdo->states.vdo.config.physical_blocks;
+
+	/* Skip any noop grows. */
+	if (old_physical_blocks == new_physical_blocks)
+		return VDO_SUCCESS;
+
+	if (new_physical_blocks != vdo->next_layout.size) {
+		/*
+		 * Either the VDO isn't prepared to grow, or it was prepared to grow to a different
+		 * size. Doing this check here relies on the fact that the call to this method is
+		 * done under the dmsetup message lock.
+		 */
+		vdo_uninitialize_layout(&vdo->next_layout);
+		vdo_abandon_new_slabs(vdo->depot);
+		return VDO_PARAMETER_MISMATCH;
+	}
+
+	/* Validate that we are prepared to grow appropriately. */
+	new_depot_size =
+		vdo_get_known_partition(&vdo->next_layout, VDO_SLAB_DEPOT_PARTITION)->count;
+	prepared_depot_size = (vdo->depot->new_slabs == NULL) ? 0 : vdo->depot->new_size;
+	if (prepared_depot_size != new_depot_size)
+		return VDO_PARAMETER_MISMATCH;
+
+	result = perform_admin_operation(vdo, GROW_PHYSICAL_PHASE_START,
+					 grow_physical_callback,
+					 handle_physical_growth_error, "grow physical");
+	if (result != VDO_SUCCESS)
+		return result;
+
+	uds_log_info("Physical block count was %llu, now %llu",
+		     (unsigned long long) old_physical_blocks,
+		     (unsigned long long) new_physical_blocks);
+	return VDO_SUCCESS;
+}
+
+/**
+ * apply_new_vdo_configuration() - Attempt to make any configuration changes from the table being
+ *                                 resumed.
+ * @vdo: The vdo being resumed.
+ * @config: The new device configuration derived from the table with which the vdo is being
+ *          resumed.
+ *
+ * Return: VDO_SUCCESS or an error.
+ */
+static int __must_check apply_new_vdo_configuration(struct vdo *vdo,
+						    struct device_config *config)
+{
+	int result;
+
+	result = perform_grow_logical(vdo, config->logical_blocks);
+	if (result != VDO_SUCCESS) {
+		uds_log_error("grow logical operation failed, result = %d", result);
+		return result;
+	}
+
+	result = perform_grow_physical(vdo, config->physical_blocks);
+	if (result != VDO_SUCCESS)
+		uds_log_error("resize operation failed, result = %d", result);
+
+	return result;
+}
+
+static int vdo_preresume_registered(struct dm_target *ti, struct vdo *vdo)
+{
+	struct device_config *config = ti->private;
+	const char *device_name = vdo_get_device_name(ti);
+	block_count_t backing_blocks;
+	int result;
+
+	backing_blocks = get_underlying_device_block_count(vdo);
+	if (backing_blocks < config->physical_blocks) {
+		/* FIXME: can this still happen? */
+		uds_log_error("resume of device '%s' failed: backing device has %llu blocks but VDO physical size is %llu blocks",
+			      device_name, (unsigned long long) backing_blocks,
+			      (unsigned long long) config->physical_blocks);
+		return -EINVAL;
+	}
+
+	if (vdo_get_admin_state(vdo) == VDO_ADMIN_STATE_PRE_LOADED) {
+		uds_log_info("starting device '%s'", device_name);
+		result = perform_admin_operation(vdo, LOAD_PHASE_START, load_callback,
+						 handle_load_error, "load");
+		if ((result != VDO_SUCCESS) && (result != VDO_READ_ONLY)) {
+			/*
+			 * Something has gone very wrong. Make sure everything has drained and
+			 * leave the device in an unresumable state.
+			 */
+			uds_log_error_strerror(result,
+					       "Start failed, could not load VDO metadata");
+			vdo->suspend_type = VDO_ADMIN_STATE_STOPPING;
+			perform_admin_operation(vdo, SUSPEND_PHASE_START,
+						suspend_callback, suspend_callback,
+						"suspend");
+			return result;
+		}
+
+		/* Even if the VDO is read-only, it is now able to handle read requests. */
+		uds_log_info("device '%s' started", device_name);
+	}
+
+	uds_log_info("resuming device '%s'", device_name);
+
+	/* If this fails, the VDO was not in a state to be resumed. This should never happen. */
+	result = apply_new_vdo_configuration(vdo, config);
+	BUG_ON(result == VDO_INVALID_ADMIN_STATE);
+
+	/*
+	 * Now that we've tried to modify the vdo, the new config *is* the config, whether the
+	 * modifications worked or not.
+	 */
+	vdo->device_config = config;
+
+	/*
+	 * Any error here is highly unexpected and the state of the vdo is questionable, so we mark
+	 * it read-only in memory. Because we are suspended, the read-only state will not be
+	 * written to disk.
+	 */
+	if (result != VDO_SUCCESS) {
+		uds_log_error_strerror(result,
+				       "Commit of modifications to device '%s' failed",
+				       device_name);
+		vdo_enter_read_only_mode(vdo, result);
+		return result;
+	}
+
+	if (vdo_get_admin_state(vdo)->normal) {
+		/* The VDO was just started, so we don't need to resume it. */
+		return VDO_SUCCESS;
+	}
+
+	result = perform_admin_operation(vdo, RESUME_PHASE_START, resume_callback,
+					 resume_callback, "resume");
+	BUG_ON(result == VDO_INVALID_ADMIN_STATE);
+	if (result == VDO_READ_ONLY) {
+		/* Even if the vdo is read-only, it has still resumed. */
+		result = VDO_SUCCESS;
+	}
+
+	if (result != VDO_SUCCESS)
+		uds_log_error("resume of device '%s' failed with error: %d", device_name,
+			      result);
+
+	return result;
+}
+
+static int vdo_preresume(struct dm_target *ti)
+{
+	struct registered_thread instance_thread;
+	struct vdo *vdo = get_vdo_for_target(ti);
+	int result;
+
+	uds_register_thread_device_id(&instance_thread, &vdo->instance);
+	result = vdo_preresume_registered(ti, vdo);
+	if ((result == VDO_PARAMETER_MISMATCH) || (result == VDO_INVALID_ADMIN_STATE))
+		result = -EINVAL;
+	uds_unregister_thread_device_id();
+	return vdo_map_to_system_error(result);
+}
+
+static void vdo_resume(struct dm_target *ti)
+{
+	struct registered_thread instance_thread;
+
+	uds_register_thread_device_id(&instance_thread,
+				      &get_vdo_for_target(ti)->instance);
+	uds_log_info("device '%s' resumed", vdo_get_device_name(ti));
+	uds_unregister_thread_device_id();
+}
+
+/*
+ * If anything changes that affects how user tools will interact with vdo, update the version
+ * number and make sure documentation about the change is complete so tools can properly update
+ * their management code.
+ */
+static struct target_type vdo_target_bio = {
+	.features = DM_TARGET_SINGLETON,
+	.name = "vdo",
+	.version = { 8, 2, 0 },
+	.module = THIS_MODULE,
+	.ctr = vdo_ctr,
+	.dtr = vdo_dtr,
+	.io_hints = vdo_io_hints,
+	.iterate_devices = vdo_iterate_devices,
+	.map = vdo_map_bio,
+	.message = vdo_message,
+	.status = vdo_status,
+	.presuspend = vdo_presuspend,
+	.postsuspend = vdo_postsuspend,
+	.preresume = vdo_preresume,
+	.resume = vdo_resume,
+};
+
+static bool dm_registered;
+
+static void vdo_module_destroy(void)
+{
+	uds_log_debug("unloading");
+
+	if (dm_registered)
+		dm_unregister_target(&vdo_target_bio);
+
+	ASSERT_LOG_ONLY(instances.count == 0,
+			"should have no instance numbers still in use, but have %u",
+			instances.count);
+	uds_free(instances.words);
+	memset(&instances, 0, sizeof(struct instance_tracker));
+
+	uds_log_info("unloaded version %s", CURRENT_VERSION);
+}
+
+static int __init vdo_init(void)
+{
+	int result = 0;
+
+	/*
+	 * UDS module level initialization must be done first, as VDO initialization depends on it
+	 */
+	uds_initialize_thread_device_registry();
+	uds_memory_init();
+	uds_init_sysfs();
+
+	vdo_initialize_device_registry_once();
+	uds_log_info("loaded version %s", CURRENT_VERSION);
+
+	/* Add VDO errors to the already existing set of errors in UDS. */
+	result = vdo_register_status_codes();
+	if (result != UDS_SUCCESS) {
+		uds_log_error("vdo_register_status_codes failed %d", result);
+		vdo_module_destroy();
+		return result;
+	}
+
+	result = dm_register_target(&vdo_target_bio);
+	if (result < 0) {
+		uds_log_error("dm_register_target failed %d", result);
+		vdo_module_destroy();
+		return result;
+	}
+	dm_registered = true;
+
+	return result;
+}
+
+static void __exit vdo_exit(void)
+{
+	vdo_module_destroy();
+	/*
+	 * UDS module level exit processing must be done after all VDO module exit processing is
+	 * complete.
+	 */
+	uds_put_sysfs();
+	uds_memory_exit();
+}
+
+module_init(vdo_init);
+module_exit(vdo_exit);
+
+MODULE_DESCRIPTION(DM_NAME " target for transparent deduplication");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");