md/dm-vdo/vdo.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2023 Red Hat
 */

/*
 * This file contains the main entry points for normal operations on a vdo as well as functions for
 * constructing and destroying vdo instances (in memory).
 */

/**
 * DOC:
 *
 * A read_only_notifier has a single completion which is used to perform read-only notifications,
 * however, vdo_enter_read_only_mode() may be called from any thread. A pair of fields, protected
 * by a spinlock, are used to control the read-only mode entry process. The first field holds the
 * read-only error. The second is the state field, which may hold any of the four special values
 * enumerated here.
 *
 * When vdo_enter_read_only_mode() is called from some vdo thread, if the read_only_error field
 * already contains an error (i.e. its value is not VDO_SUCCESS), then some other error has already
 * initiated the read-only process, and nothing more is done. Otherwise, the new error is stored in
 * the read_only_error field, and the state field is consulted. If the state is MAY_NOTIFY, it is
 * set to NOTIFYING, and the notification process begins. If the state is MAY_NOT_NOTIFY, then
 * notifications are currently disallowed, generally due to the vdo being suspended. In this case,
 * the nothing more will be done until the vdo is resumed, at which point the notification will be
 * performed. In any other case, the vdo is already read-only, and there is nothing more to do.
 */

#include "vdo.h"

#include <linux/completion.h>
#include <linux/device-mapper.h>
#include <linux/kernel.h>
#include <linux/lz4.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/spinlock.h>
#include <linux/types.h>

#include "logger.h"
#include "memory-alloc.h"
#include "permassert.h"
#include "string-utils.h"

#include "block-map.h"
#include "completion.h"
#include "data-vio.h"
#include "dedupe.h"
#include "encodings.h"
#include "funnel-workqueue.h"
#include "io-submitter.h"
#include "logical-zone.h"
#include "packer.h"
#include "physical-zone.h"
#include "recovery-journal.h"
#include "slab-depot.h"
#include "statistics.h"
#include "status-codes.h"
#include "vio.h"

#define PARANOID_THREAD_CONSISTENCY_CHECKS 0

struct sync_completion {
	struct vdo_completion vdo_completion;
	struct completion completion;
};

/* A linked list is adequate for the small number of entries we expect. */
struct device_registry {
	struct list_head links;
	/* TODO: Convert to rcu per kernel recommendation. */
	rwlock_t lock;
};

static struct device_registry registry;

/**
 * vdo_initialize_device_registry_once() - Initialize the necessary structures for the device
 *                                         registry.
 */
void vdo_initialize_device_registry_once(void)
{
	INIT_LIST_HEAD(&registry.links);
	rwlock_init(&registry.lock);
}

/** vdo_is_equal() - Implements vdo_filter_fn. */
static bool vdo_is_equal(struct vdo *vdo, const void *context)
{
	return (vdo == context);
}

/**
 * filter_vdos_locked() - Find a vdo in the registry if it exists there.
 * @filter: The filter function to apply to devices.
 * @context: A bit of context to provide the filter.
 *
 * Context: Must be called holding the lock.
 *
 * Return: the vdo object found, if any.
 */
static struct vdo * __must_check filter_vdos_locked(vdo_filter_fn filter,
						    const void *context)
{
	struct vdo *vdo;

	list_for_each_entry(vdo, &registry.links, registration) {
		if (filter(vdo, context))
			return vdo;
	}

	return NULL;
}

/**
 * vdo_find_matching() - Find and return the first (if any) vdo matching a given filter function.
 * @filter: The filter function to apply to vdos.
 * @context: A bit of context to provide the filter.
 */
struct vdo *vdo_find_matching(vdo_filter_fn filter, const void *context)
{
	struct vdo *vdo;

	read_lock(&registry.lock);
	vdo = filter_vdos_locked(filter, context);
	read_unlock(&registry.lock);

	return vdo;
}

static void start_vdo_request_queue(void *ptr)
{
	struct vdo_thread *thread = vdo_get_work_queue_owner(vdo_get_current_work_queue());

	vdo_register_allocating_thread(&thread->allocating_thread,
				       &thread->vdo->allocations_allowed);
}

static void finish_vdo_request_queue(void *ptr)
{
	vdo_unregister_allocating_thread();
}

#ifdef MODULE
#define MODULE_NAME THIS_MODULE->name
#else
#define MODULE_NAME "dm-vdo"
#endif  /* MODULE */

static const struct vdo_work_queue_type default_queue_type = {
	.start = start_vdo_request_queue,
	.finish = finish_vdo_request_queue,
	.max_priority = VDO_DEFAULT_Q_MAX_PRIORITY,
	.default_priority = VDO_DEFAULT_Q_COMPLETION_PRIORITY,
};

static const struct vdo_work_queue_type bio_ack_q_type = {
	.start = NULL,
	.finish = NULL,
	.max_priority = BIO_ACK_Q_MAX_PRIORITY,
	.default_priority = BIO_ACK_Q_ACK_PRIORITY,
};

static const struct vdo_work_queue_type cpu_q_type = {
	.start = NULL,
	.finish = NULL,
	.max_priority = CPU_Q_MAX_PRIORITY,
	.default_priority = CPU_Q_MAX_PRIORITY,
};

static void uninitialize_thread_config(struct thread_config *config)
{
	vdo_free(vdo_forget(config->logical_threads));
	vdo_free(vdo_forget(config->physical_threads));
	vdo_free(vdo_forget(config->hash_zone_threads));
	vdo_free(vdo_forget(config->bio_threads));
	memset(config, 0, sizeof(struct thread_config));
}

static void assign_thread_ids(struct thread_config *config,
			      thread_id_t thread_ids[], zone_count_t count)
{
	zone_count_t zone;

	for (zone = 0; zone < count; zone++)
		thread_ids[zone] = config->thread_count++;
}

/**
 * initialize_thread_config() - Initialize the thread mapping
 *
 * If the logical, physical, and hash zone counts are all 0, a single thread will be shared by all
 * three plus the packer and recovery journal. Otherwise, there must be at least one of each type,
 * and each will have its own thread, as will the packer and recovery journal.
 *
 * Return: VDO_SUCCESS or an error.
 */
static int __must_check initialize_thread_config(struct thread_count_config counts,
						 struct thread_config *config)
{
	int result;
	bool single = ((counts.logical_zones + counts.physical_zones + counts.hash_zones) == 0);

	config->bio_thread_count = counts.bio_threads;
	if (single) {
		config->logical_zone_count = 1;
		config->physical_zone_count = 1;
		config->hash_zone_count = 1;
	} else {
		config->logical_zone_count = counts.logical_zones;
		config->physical_zone_count = counts.physical_zones;
		config->hash_zone_count = counts.hash_zones;
	}

	result = vdo_allocate(config->logical_zone_count, thread_id_t,
			      "logical thread array", &config->logical_threads);
	if (result != VDO_SUCCESS) {
		uninitialize_thread_config(config);
		return result;
	}

	result = vdo_allocate(config->physical_zone_count, thread_id_t,
			      "physical thread array", &config->physical_threads);
	if (result != VDO_SUCCESS) {
		uninitialize_thread_config(config);
		return result;
	}

	result = vdo_allocate(config->hash_zone_count, thread_id_t,
			      "hash thread array", &config->hash_zone_threads);
	if (result != VDO_SUCCESS) {
		uninitialize_thread_config(config);
		return result;
	}

	result = vdo_allocate(config->bio_thread_count, thread_id_t,
			      "bio thread array", &config->bio_threads);
	if (result != VDO_SUCCESS) {
		uninitialize_thread_config(config);
		return result;
	}

	if (single) {
		config->logical_threads[0] = config->thread_count;
		config->physical_threads[0] = config->thread_count;
		config->hash_zone_threads[0] = config->thread_count++;
	} else {
		config->admin_thread = config->thread_count;
		config->journal_thread = config->thread_count++;
		config->packer_thread = config->thread_count++;
		assign_thread_ids(config, config->logical_threads, counts.logical_zones);
		assign_thread_ids(config, config->physical_threads, counts.physical_zones);
		assign_thread_ids(config, config->hash_zone_threads, counts.hash_zones);
	}

	config->dedupe_thread = config->thread_count++;
	config->bio_ack_thread =
		((counts.bio_ack_threads > 0) ? config->thread_count++ : VDO_INVALID_THREAD_ID);
	config->cpu_thread = config->thread_count++;
	assign_thread_ids(config, config->bio_threads, counts.bio_threads);
	return VDO_SUCCESS;
}

/**
 * read_geometry_block() - Synchronously read the geometry block from a vdo's underlying block
 *                         device.
 * @vdo: The vdo whose geometry is to be read.
 *
 * Return: VDO_SUCCESS or an error code.
 */
static int __must_check read_geometry_block(struct vdo *vdo)
{
	struct vio *vio;
	char *block;
	int result;

	result = vdo_allocate(VDO_BLOCK_SIZE, u8, __func__, &block);
	if (result != VDO_SUCCESS)
		return result;

	result = create_metadata_vio(vdo, VIO_TYPE_GEOMETRY, VIO_PRIORITY_HIGH, NULL,
				     block, &vio);
	if (result != VDO_SUCCESS) {
		vdo_free(block);
		return result;
	}

	/*
	 * This is only safe because, having not already loaded the geometry, the vdo's geometry's
	 * bio_offset field is 0, so the fact that vio_reset_bio() will subtract that offset from
	 * the supplied pbn is not a problem.
	 */
	result = vio_reset_bio(vio, block, NULL, REQ_OP_READ,
			       VDO_GEOMETRY_BLOCK_LOCATION);
	if (result != VDO_SUCCESS) {
		free_vio(vdo_forget(vio));
		vdo_free(block);
		return result;
	}

	bio_set_dev(vio->bio, vdo_get_backing_device(vdo));
	submit_bio_wait(vio->bio);
	result = blk_status_to_errno(vio->bio->bi_status);
	free_vio(vdo_forget(vio));
	if (result != 0) {
		vdo_log_error_strerror(result, "synchronous read failed");
		vdo_free(block);
		return -EIO;
	}

	result = vdo_parse_geometry_block((u8 *) block, &vdo->geometry);
	vdo_free(block);
	return result;
}

static bool get_zone_thread_name(const thread_id_t thread_ids[], zone_count_t count,
				 thread_id_t id, const char *prefix,
				 char *buffer, size_t buffer_length)
{
	if (id >= thread_ids[0]) {
		thread_id_t index = id - thread_ids[0];

		if (index < count) {
			snprintf(buffer, buffer_length, "%s%d", prefix, index);
			return true;
		}
	}

	return false;
}

/**
 * get_thread_name() - Format the name of the worker thread desired to support a given work queue.
 * @thread_config: The thread configuration.
 * @thread_id: The thread id.
 * @buffer: Where to put the formatted name.
 * @buffer_length: Size of the output buffer.
 *
 * The physical layer may add a prefix identifying the product; the output from this function
 * should just identify the thread.
 */
static void get_thread_name(const struct thread_config *thread_config,
			    thread_id_t thread_id, char *buffer, size_t buffer_length)
{
	if (thread_id == thread_config->journal_thread) {
		if (thread_config->packer_thread == thread_id) {
			/*
			 * This is the "single thread" config where one thread is used for the
			 * journal, packer, logical, physical, and hash zones. In that case, it is
			 * known as the "request queue."
			 */
			snprintf(buffer, buffer_length, "reqQ");
			return;
		}

		snprintf(buffer, buffer_length, "journalQ");
		return;
	} else if (thread_id == thread_config->admin_thread) {
		/* Theoretically this could be different from the journal thread. */
		snprintf(buffer, buffer_length, "adminQ");
		return;
	} else if (thread_id == thread_config->packer_thread) {
		snprintf(buffer, buffer_length, "packerQ");
		return;
	} else if (thread_id == thread_config->dedupe_thread) {
		snprintf(buffer, buffer_length, "dedupeQ");
		return;
	} else if (thread_id == thread_config->bio_ack_thread) {
		snprintf(buffer, buffer_length, "ackQ");
		return;
	} else if (thread_id == thread_config->cpu_thread) {
		snprintf(buffer, buffer_length, "cpuQ");
		return;
	}

	if (get_zone_thread_name(thread_config->logical_threads,
				 thread_config->logical_zone_count,
				 thread_id, "logQ", buffer, buffer_length))
		return;

	if (get_zone_thread_name(thread_config->physical_threads,
				 thread_config->physical_zone_count,
				 thread_id, "physQ", buffer, buffer_length))
		return;

	if (get_zone_thread_name(thread_config->hash_zone_threads,
				 thread_config->hash_zone_count,
				 thread_id, "hashQ", buffer, buffer_length))
		return;

	if (get_zone_thread_name(thread_config->bio_threads,
				 thread_config->bio_thread_count,
				 thread_id, "bioQ", buffer, buffer_length))
		return;

	/* Some sort of misconfiguration? */
	snprintf(buffer, buffer_length, "reqQ%d", thread_id);
}

/**
 * vdo_make_thread() - Construct a single vdo work_queue and its associated thread (or threads for
 *                     round-robin queues).
 * @vdo: The vdo which owns the thread.
 * @thread_id: The id of the thread to create (as determined by the thread_config).
 * @type: The description of the work queue for this thread.
 * @queue_count: The number of actual threads/queues contained in the "thread".
 * @contexts: An array of queue_count contexts, one for each individual queue; may be NULL.
 *
 * Each "thread" constructed by this method is represented by a unique thread id in the thread
 * config, and completions can be enqueued to the queue and run on the threads comprising this
 * entity.
 *
 * Return: VDO_SUCCESS or an error.
 */
int vdo_make_thread(struct vdo *vdo, thread_id_t thread_id,
		    const struct vdo_work_queue_type *type,
		    unsigned int queue_count, void *contexts[])
{
	struct vdo_thread *thread = &vdo->threads[thread_id];
	char queue_name[MAX_VDO_WORK_QUEUE_NAME_LEN];

	if (type == NULL)
		type = &default_queue_type;

	if (thread->queue != NULL) {
		return VDO_ASSERT(vdo_work_queue_type_is(thread->queue, type),
				  "already constructed vdo thread %u is of the correct type",
				  thread_id);
	}

	thread->vdo = vdo;
	thread->thread_id = thread_id;
	get_thread_name(&vdo->thread_config, thread_id, queue_name, sizeof(queue_name));
	return vdo_make_work_queue(vdo->thread_name_prefix, queue_name, thread,
				   type, queue_count, contexts, &thread->queue);
}

/**
 * register_vdo() - Register a VDO; it must not already be registered.
 * @vdo: The vdo to register.
 *
 * Return: VDO_SUCCESS or an error.
 */
static int register_vdo(struct vdo *vdo)
{
	int result;

	write_lock(&registry.lock);
	result = VDO_ASSERT(filter_vdos_locked(vdo_is_equal, vdo) == NULL,
			    "VDO not already registered");
	if (result == VDO_SUCCESS) {
		INIT_LIST_HEAD(&vdo->registration);
		list_add_tail(&vdo->registration, &registry.links);
	}
	write_unlock(&registry.lock);

	return result;
}

/**
 * initialize_vdo() - Do the portion of initializing a vdo which will clean up after itself on
 *                    error.
 * @vdo: The vdo being initialized
 * @config: The configuration of the vdo
 * @instance: The instance number of the vdo
 * @reason: The buffer to hold the failure reason on error
 */
static int initialize_vdo(struct vdo *vdo, struct device_config *config,
			  unsigned int instance, char **reason)
{
	int result;
	zone_count_t i;

	vdo->device_config = config;
	vdo->starting_sector_offset = config->owning_target->begin;
	vdo->instance = instance;
	vdo->allocations_allowed = true;
	vdo_set_admin_state_code(&vdo->admin.state, VDO_ADMIN_STATE_NEW);
	INIT_LIST_HEAD(&vdo->device_config_list);
	vdo_initialize_completion(&vdo->admin.completion, vdo, VDO_ADMIN_COMPLETION);
	init_completion(&vdo->admin.callback_sync);
	mutex_init(&vdo->stats_mutex);
	result = read_geometry_block(vdo);
	if (result != VDO_SUCCESS) {
		*reason = "Could not load geometry block";
		return result;
	}

	result = initialize_thread_config(config->thread_counts, &vdo->thread_config);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot create thread configuration";
		return result;
	}

	vdo_log_info("zones: %d logical, %d physical, %d hash; total threads: %d",
		     config->thread_counts.logical_zones,
		     config->thread_counts.physical_zones,
		     config->thread_counts.hash_zones, vdo->thread_config.thread_count);

	/* Compression context storage */
	result = vdo_allocate(config->thread_counts.cpu_threads, char *, "LZ4 context",
			      &vdo->compression_context);
	if (result != VDO_SUCCESS) {
		*reason = "cannot allocate LZ4 context";
		return result;
	}

	for (i = 0; i < config->thread_counts.cpu_threads; i++) {
		result = vdo_allocate(LZ4_MEM_COMPRESS, char, "LZ4 context",
				      &vdo->compression_context[i]);
		if (result != VDO_SUCCESS) {
			*reason = "cannot allocate LZ4 context";
			return result;
		}
	}

	result = register_vdo(vdo);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot add VDO to device registry";
		return result;
	}

	vdo_set_admin_state_code(&vdo->admin.state, VDO_ADMIN_STATE_INITIALIZED);
	return result;
}

/**
 * vdo_make() - Allocate and initialize a vdo.
 * @instance: Device instantiation counter.
 * @config: The device configuration.
 * @reason: The reason for any failure during this call.
 * @vdo_ptr: A pointer to hold the created vdo.
 *
 * Return: VDO_SUCCESS or an error.
 */
int vdo_make(unsigned int instance, struct device_config *config, char **reason,
	     struct vdo **vdo_ptr)
{
	int result;
	struct vdo *vdo;

	/* Initialize with a generic failure reason to prevent returning garbage. */
	*reason = "Unspecified error";

	result = vdo_allocate(1, struct vdo, __func__, &vdo);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot allocate VDO";
		return result;
	}

	result = initialize_vdo(vdo, config, instance, reason);
	if (result != VDO_SUCCESS) {
		vdo_destroy(vdo);
		return result;
	}

	/* From here on, the caller will clean up if there is an error. */
	*vdo_ptr = vdo;

	snprintf(vdo->thread_name_prefix, sizeof(vdo->thread_name_prefix),
		 "%s%u", MODULE_NAME, instance);
	BUG_ON(vdo->thread_name_prefix[0] == '\0');
	result = vdo_allocate(vdo->thread_config.thread_count,
			      struct vdo_thread, __func__, &vdo->threads);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot allocate thread structures";
		return result;
	}

	result = vdo_make_thread(vdo, vdo->thread_config.admin_thread,
				 &default_queue_type, 1, NULL);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot make admin thread";
		return result;
	}

	result = vdo_make_flusher(vdo);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot make flusher zones";
		return result;
	}

	result = vdo_make_packer(vdo, DEFAULT_PACKER_BINS, &vdo->packer);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot make packer zones";
		return result;
	}

	BUG_ON(vdo->device_config->logical_block_size <= 0);
	BUG_ON(vdo->device_config->owned_device == NULL);
	result = make_data_vio_pool(vdo, MAXIMUM_VDO_USER_VIOS,
				    MAXIMUM_VDO_USER_VIOS * 3 / 4,
				    &vdo->data_vio_pool);
	if (result != VDO_SUCCESS) {
		*reason = "Cannot allocate data_vio pool";
		return result;
	}

	result = vdo_make_io_submitter(config->thread_counts.bio_threads,
				       config->thread_counts.bio_rotation_interval,
				       get_data_vio_pool_request_limit(vdo->data_vio_pool),
				       vdo, &vdo->io_submitter);
	if (result != VDO_SUCCESS) {
		*reason = "bio submission initialization failed";
		return result;
	}

	if (vdo_uses_bio_ack_queue(vdo)) {
		result = vdo_make_thread(vdo, vdo->thread_config.bio_ack_thread,
					 &bio_ack_q_type,
					 config->thread_counts.bio_ack_threads, NULL);
		if (result != VDO_SUCCESS) {
			*reason = "bio ack queue initialization failed";
			return result;
		}
	}

	result = vdo_make_thread(vdo, vdo->thread_config.cpu_thread, &cpu_q_type,
				 config->thread_counts.cpu_threads,
				 (void **) vdo->compression_context);
	if (result != VDO_SUCCESS) {
		*reason = "CPU queue initialization failed";
		return result;
	}

	return VDO_SUCCESS;
}

static void finish_vdo(struct vdo *vdo)
{
	int i;

	if (vdo->threads == NULL)
		return;

	vdo_cleanup_io_submitter(vdo->io_submitter);
	vdo_finish_dedupe_index(vdo->hash_zones);

	for (i = 0; i < vdo->thread_config.thread_count; i++)
		vdo_finish_work_queue(vdo->threads[i].queue);
}

/**
 * free_listeners() - Free the list of read-only listeners associated with a thread.
 * @thread_data: The thread holding the list to free.
 */
static void free_listeners(struct vdo_thread *thread)
{
	struct read_only_listener *listener, *next;

	for (listener = vdo_forget(thread->listeners); listener != NULL; listener = next) {
		next = vdo_forget(listener->next);
		vdo_free(listener);
	}
}

static void uninitialize_super_block(struct vdo_super_block *super_block)
{
	free_vio_components(&super_block->vio);
	vdo_free(super_block->buffer);
}

/**
 * unregister_vdo() - Remove a vdo from the device registry.
 * @vdo: The vdo to remove.
 */
static void unregister_vdo(struct vdo *vdo)
{
	write_lock(&registry.lock);
	if (filter_vdos_locked(vdo_is_equal, vdo) == vdo)
		list_del_init(&vdo->registration);

	write_unlock(&registry.lock);
}

/**
 * vdo_destroy() - Destroy a vdo instance.
 * @vdo: The vdo to destroy (may be NULL).
 */
void vdo_destroy(struct vdo *vdo)
{
	unsigned int i;

	if (vdo == NULL)
		return;

	/* A running VDO should never be destroyed without suspending first. */
	BUG_ON(vdo_get_admin_state(vdo)->normal);

	vdo->allocations_allowed = true;

	finish_vdo(vdo);
	unregister_vdo(vdo);
	free_data_vio_pool(vdo->data_vio_pool);
	vdo_free_io_submitter(vdo_forget(vdo->io_submitter));
	vdo_free_flusher(vdo_forget(vdo->flusher));
	vdo_free_packer(vdo_forget(vdo->packer));
	vdo_free_recovery_journal(vdo_forget(vdo->recovery_journal));
	vdo_free_slab_depot(vdo_forget(vdo->depot));
	vdo_uninitialize_layout(&vdo->layout);
	vdo_uninitialize_layout(&vdo->next_layout);
	if (vdo->partition_copier)
		dm_kcopyd_client_destroy(vdo_forget(vdo->partition_copier));
	uninitialize_super_block(&vdo->super_block);
	vdo_free_block_map(vdo_forget(vdo->block_map));
	vdo_free_hash_zones(vdo_forget(vdo->hash_zones));
	vdo_free_physical_zones(vdo_forget(vdo->physical_zones));
	vdo_free_logical_zones(vdo_forget(vdo->logical_zones));

	if (vdo->threads != NULL) {
		for (i = 0; i < vdo->thread_config.thread_count; i++) {
			free_listeners(&vdo->threads[i]);
			vdo_free_work_queue(vdo_forget(vdo->threads[i].queue));
		}
		vdo_free(vdo_forget(vdo->threads));
	}

	uninitialize_thread_config(&vdo->thread_config);

	if (vdo->compression_context != NULL) {
		for (i = 0; i < vdo->device_config->thread_counts.cpu_threads; i++)
			vdo_free(vdo_forget(vdo->compression_context[i]));

		vdo_free(vdo_forget(vdo->compression_context));
	}
	vdo_free(vdo);
}

static int initialize_super_block(struct vdo *vdo, struct vdo_super_block *super_block)
{
	int result;

	result = vdo_allocate(VDO_BLOCK_SIZE, char, "encoded super block",
			      (char **) &vdo->super_block.buffer);
	if (result != VDO_SUCCESS)
		return result;

	return allocate_vio_components(vdo, VIO_TYPE_SUPER_BLOCK,
				       VIO_PRIORITY_METADATA, NULL, 1,
				       (char *) super_block->buffer,
				       &vdo->super_block.vio);
}

/**
 * finish_reading_super_block() - Continue after loading the super block.
 * @completion: The super block vio.
 *
 * This callback is registered in vdo_load_super_block().
 */
static void finish_reading_super_block(struct vdo_completion *completion)
{
	struct vdo_super_block *super_block =
		container_of(as_vio(completion), struct vdo_super_block, vio);

	vdo_continue_completion(vdo_forget(completion->parent),
				vdo_decode_super_block(super_block->buffer));
}

/**
 * handle_super_block_read_error() - Handle an error reading the super block.
 * @completion: The super block vio.
 *
 * This error handler is registered in vdo_load_super_block().
 */
static void handle_super_block_read_error(struct vdo_completion *completion)
{
	vio_record_metadata_io_error(as_vio(completion));
	finish_reading_super_block(completion);
}

static void read_super_block_endio(struct bio *bio)
{
	struct vio *vio = bio->bi_private;
	struct vdo_completion *parent = vio->completion.parent;

	continue_vio_after_io(vio, finish_reading_super_block,
			      parent->callback_thread_id);
}

/**
 * vdo_load_super_block() - Allocate a super block and read its contents from storage.
 * @vdo: The vdo containing the super block on disk.
 * @parent: The completion to notify after loading the super block.
 */
void vdo_load_super_block(struct vdo *vdo, struct vdo_completion *parent)
{
	int result;

	result = initialize_super_block(vdo, &vdo->super_block);
	if (result != VDO_SUCCESS) {
		vdo_continue_completion(parent, result);
		return;
	}

	vdo->super_block.vio.completion.parent = parent;
	vdo_submit_metadata_vio(&vdo->super_block.vio,
				vdo_get_data_region_start(vdo->geometry),
				read_super_block_endio,
				handle_super_block_read_error,
				REQ_OP_READ);
}

/**
 * vdo_get_backing_device() - Get the block device object underlying a vdo.
 * @vdo: The vdo.
 *
 * Return: The vdo's current block device.
 */
struct block_device *vdo_get_backing_device(const struct vdo *vdo)
{
	return vdo->device_config->owned_device->bdev;
}

/**
 * vdo_get_device_name() - Get the device name associated with the vdo target.
 * @target: The target device interface.
 *
 * Return: The block device name.
 */
const char *vdo_get_device_name(const struct dm_target *target)
{
	return dm_device_name(dm_table_get_md(target->table));
}

/**
 * vdo_synchronous_flush() - Issue a flush request and wait for it to complete.
 * @vdo: The vdo.
 *
 * Return: VDO_SUCCESS or an error.
 */
int vdo_synchronous_flush(struct vdo *vdo)
{
	int result;
	struct bio bio;

	bio_init(&bio, vdo_get_backing_device(vdo), NULL, 0,
		 REQ_OP_WRITE | REQ_PREFLUSH);
	submit_bio_wait(&bio);
	result = blk_status_to_errno(bio.bi_status);

	atomic64_inc(&vdo->stats.flush_out);
	if (result != 0) {
		vdo_log_error_strerror(result, "synchronous flush failed");
		result = -EIO;
	}

	bio_uninit(&bio);
	return result;
}

/**
 * vdo_get_state() - Get the current state of the vdo.
 * @vdo: The vdo.

 * Context: This method may be called from any thread.
 *
 * Return: The current state of the vdo.
 */
enum vdo_state vdo_get_state(const struct vdo *vdo)
{
	enum vdo_state state = atomic_read(&vdo->state);

	/* pairs with barriers where state field is changed */
	smp_rmb();
	return state;
}

/**
 * vdo_set_state() - Set the current state of the vdo.
 * @vdo: The vdo whose state is to be set.
 * @state: The new state of the vdo.
 *
 * Context: This method may be called from any thread.
 */
void vdo_set_state(struct vdo *vdo, enum vdo_state state)
{
	/* pairs with barrier in vdo_get_state */
	smp_wmb();
	atomic_set(&vdo->state, state);
}

/**
 * vdo_get_admin_state() - Get the admin state of the vdo.
 * @vdo: The vdo.
 *
 * Return: The code for the vdo's current admin state.
 */
const struct admin_state_code *vdo_get_admin_state(const struct vdo *vdo)
{
	return vdo_get_admin_state_code(&vdo->admin.state);
}

/**
 * record_vdo() - Record the state of the VDO for encoding in the super block.
 */
static void record_vdo(struct vdo *vdo)
{
	/* This is for backwards compatibility. */
	vdo->states.unused = vdo->geometry.unused;
	vdo->states.vdo.state = vdo_get_state(vdo);
	vdo->states.block_map = vdo_record_block_map(vdo->block_map);
	vdo->states.recovery_journal = vdo_record_recovery_journal(vdo->recovery_journal);
	vdo->states.slab_depot = vdo_record_slab_depot(vdo->depot);
	vdo->states.layout = vdo->layout;
}

/**
 * continue_super_block_parent() - Continue the parent of a super block save operation.
 * @completion: The super block vio.
 *
 * This callback is registered in vdo_save_components().
 */
static void continue_super_block_parent(struct vdo_completion *completion)
{
	vdo_continue_completion(vdo_forget(completion->parent), completion->result);
}

/**
 * handle_save_error() - Log a super block save error.
 * @completion: The super block vio.
 *
 * This error handler is registered in vdo_save_components().
 */
static void handle_save_error(struct vdo_completion *completion)
{
	struct vdo_super_block *super_block =
		container_of(as_vio(completion), struct vdo_super_block, vio);

	vio_record_metadata_io_error(&super_block->vio);
	vdo_log_error_strerror(completion->result, "super block save failed");
	/*
	 * Mark the super block as unwritable so that we won't attempt to write it again. This
	 * avoids the case where a growth attempt fails writing the super block with the new size,
	 * but the subsequent attempt to write out the read-only state succeeds. In this case,
	 * writes which happened just before the suspend would not be visible if the VDO is
	 * restarted without rebuilding, but, after a read-only rebuild, the effects of those
	 * writes would reappear.
	 */
	super_block->unwritable = true;
	completion->callback(completion);
}

static void super_block_write_endio(struct bio *bio)
{
	struct vio *vio = bio->bi_private;
	struct vdo_completion *parent = vio->completion.parent;

	continue_vio_after_io(vio, continue_super_block_parent,
			      parent->callback_thread_id);
}

/**
 * vdo_save_components() - Encode the vdo and save the super block asynchronously.
 * @vdo: The vdo whose state is being saved.
 * @parent: The completion to notify when the save is complete.
 */
void vdo_save_components(struct vdo *vdo, struct vdo_completion *parent)
{
	struct vdo_super_block *super_block = &vdo->super_block;

	if (super_block->unwritable) {
		vdo_continue_completion(parent, VDO_READ_ONLY);
		return;
	}

	if (super_block->vio.completion.parent != NULL) {
		vdo_continue_completion(parent, VDO_COMPONENT_BUSY);
		return;
	}

	record_vdo(vdo);

	vdo_encode_super_block(super_block->buffer, &vdo->states);
	super_block->vio.completion.parent = parent;
	super_block->vio.completion.callback_thread_id = parent->callback_thread_id;
	vdo_submit_metadata_vio(&super_block->vio,
				vdo_get_data_region_start(vdo->geometry),
				super_block_write_endio, handle_save_error,
				REQ_OP_WRITE | REQ_PREFLUSH | REQ_FUA);
}

/**
 * vdo_register_read_only_listener() - Register a listener to be notified when the VDO goes
 *                                     read-only.
 * @vdo: The vdo to register with.
 * @listener: The object to notify.
 * @notification: The function to call to send the notification.
 * @thread_id: The id of the thread on which to send the notification.
 *
 * Return: VDO_SUCCESS or an error.
 */
int vdo_register_read_only_listener(struct vdo *vdo, void *listener,
				    vdo_read_only_notification_fn notification,
				    thread_id_t thread_id)
{
	struct vdo_thread *thread = &vdo->threads[thread_id];
	struct read_only_listener *read_only_listener;
	int result;

	result = VDO_ASSERT(thread_id != vdo->thread_config.dedupe_thread,
			    "read only listener not registered on dedupe thread");
	if (result != VDO_SUCCESS)
		return result;

	result = vdo_allocate(1, struct read_only_listener, __func__,
			      &read_only_listener);
	if (result != VDO_SUCCESS)
		return result;

	*read_only_listener = (struct read_only_listener) {
		.listener = listener,
		.notify = notification,
		.next = thread->listeners,
	};

	thread->listeners = read_only_listener;
	return VDO_SUCCESS;
}

/**
 * notify_vdo_of_read_only_mode() - Notify a vdo that it is going read-only.
 * @listener: The vdo.
 * @parent: The completion to notify in order to acknowledge the notification.
 *
 * This will save the read-only state to the super block.
 *
 * Implements vdo_read_only_notification_fn.
 */
static void notify_vdo_of_read_only_mode(void *listener, struct vdo_completion *parent)
{
	struct vdo *vdo = listener;

	if (vdo_in_read_only_mode(vdo))
		vdo_finish_completion(parent);

	vdo_set_state(vdo, VDO_READ_ONLY_MODE);
	vdo_save_components(vdo, parent);
}

/**
 * vdo_enable_read_only_entry() - Enable a vdo to enter read-only mode on errors.
 * @vdo: The vdo to enable.
 *
 * Return: VDO_SUCCESS or an error.
 */
int vdo_enable_read_only_entry(struct vdo *vdo)
{
	thread_id_t id;
	bool is_read_only = vdo_in_read_only_mode(vdo);
	struct read_only_notifier *notifier = &vdo->read_only_notifier;

	if (is_read_only) {
		notifier->read_only_error = VDO_READ_ONLY;
		notifier->state = NOTIFIED;
	} else {
		notifier->state = MAY_NOT_NOTIFY;
	}

	spin_lock_init(&notifier->lock);
	vdo_initialize_completion(&notifier->completion, vdo,
				  VDO_READ_ONLY_MODE_COMPLETION);

	for (id = 0; id < vdo->thread_config.thread_count; id++)
		vdo->threads[id].is_read_only = is_read_only;

	return vdo_register_read_only_listener(vdo, vdo, notify_vdo_of_read_only_mode,
					       vdo->thread_config.admin_thread);
}

/**
 * vdo_wait_until_not_entering_read_only_mode() - Wait until no read-only notifications are in
 *                                                progress and prevent any subsequent
 *                                                notifications.
 * @parent: The completion to notify when no threads are entering read-only mode.
 *
 * Notifications may be re-enabled by calling vdo_allow_read_only_mode_entry().
 */
void vdo_wait_until_not_entering_read_only_mode(struct vdo_completion *parent)
{
	struct vdo *vdo = parent->vdo;
	struct read_only_notifier *notifier = &vdo->read_only_notifier;

	vdo_assert_on_admin_thread(vdo, __func__);

	if (notifier->waiter != NULL) {
		vdo_continue_completion(parent, VDO_COMPONENT_BUSY);
		return;
	}

	spin_lock(&notifier->lock);
	if (notifier->state == NOTIFYING)
		notifier->waiter = parent;
	else if (notifier->state == MAY_NOTIFY)
		notifier->state = MAY_NOT_NOTIFY;
	spin_unlock(&notifier->lock);

	if (notifier->waiter == NULL) {
		/*
		 * A notification was not in progress, and now they are
		 * disallowed.
		 */
		vdo_launch_completion(parent);
		return;
	}
}

/**
 * as_notifier() - Convert a generic vdo_completion to a read_only_notifier.
 * @completion: The completion to convert.
 *
 * Return: The completion as a read_only_notifier.
 */
static inline struct read_only_notifier *as_notifier(struct vdo_completion *completion)
{
	vdo_assert_completion_type(completion, VDO_READ_ONLY_MODE_COMPLETION);
	return container_of(completion, struct read_only_notifier, completion);
}

/**
 * finish_entering_read_only_mode() - Complete the process of entering read only mode.
 * @completion: The read-only mode completion.
 */
static void finish_entering_read_only_mode(struct vdo_completion *completion)
{
	struct read_only_notifier *notifier = as_notifier(completion);

	vdo_assert_on_admin_thread(completion->vdo, __func__);

	spin_lock(&notifier->lock);
	notifier->state = NOTIFIED;
	spin_unlock(&notifier->lock);

	if (notifier->waiter != NULL)
		vdo_continue_completion(vdo_forget(notifier->waiter),
					completion->result);
}

/**
 * make_thread_read_only() - Inform each thread that the VDO is in read-only mode.
 * @completion: The read-only mode completion.
 */
static void make_thread_read_only(struct vdo_completion *completion)
{
	struct vdo *vdo = completion->vdo;
	thread_id_t thread_id = completion->callback_thread_id;
	struct read_only_notifier *notifier = as_notifier(completion);
	struct read_only_listener *listener = completion->parent;

	if (listener == NULL) {
		/* This is the first call on this thread */
		struct vdo_thread *thread = &vdo->threads[thread_id];

		thread->is_read_only = true;
		listener = thread->listeners;
		if (thread_id == 0)
			vdo_log_error_strerror(READ_ONCE(notifier->read_only_error),
					       "Unrecoverable error, entering read-only mode");
	} else {
		/* We've just finished notifying a listener */
		listener = listener->next;
	}

	if (listener != NULL) {
		/* We have a listener to notify */
		vdo_prepare_completion(completion, make_thread_read_only,
				       make_thread_read_only, thread_id,
				       listener);
		listener->notify(listener->listener, completion);
		return;
	}

	/* We're done with this thread */
	if (++thread_id == vdo->thread_config.dedupe_thread) {
		/*
		 * We don't want to notify the dedupe thread since it may be
		 * blocked rebuilding the index.
		 */
		thread_id++;
	}

	if (thread_id >= vdo->thread_config.thread_count) {
		/* There are no more threads */
		vdo_prepare_completion(completion, finish_entering_read_only_mode,
				       finish_entering_read_only_mode,
				       vdo->thread_config.admin_thread, NULL);
	} else {
		vdo_prepare_completion(completion, make_thread_read_only,
				       make_thread_read_only, thread_id, NULL);
	}

	vdo_launch_completion(completion);
}

/**
 * vdo_allow_read_only_mode_entry() - Allow the notifier to put the VDO into read-only mode,
 *                                    reversing the effects of
 *                                    vdo_wait_until_not_entering_read_only_mode().
 * @parent: The object to notify once the operation is complete.
 *
 * If some thread tried to put the vdo into read-only mode while notifications were disallowed, it
 * will be done when this method is called. If that happens, the parent will not be notified until
 * the vdo has actually entered read-only mode and attempted to save the super block.
 *
 * Context: This method may only be called from the admin thread.
 */
void vdo_allow_read_only_mode_entry(struct vdo_completion *parent)
{
	struct vdo *vdo = parent->vdo;
	struct read_only_notifier *notifier = &vdo->read_only_notifier;

	vdo_assert_on_admin_thread(vdo, __func__);

	if (notifier->waiter != NULL) {
		vdo_continue_completion(parent, VDO_COMPONENT_BUSY);
		return;
	}

	spin_lock(&notifier->lock);
	if (notifier->state == MAY_NOT_NOTIFY) {
		if (notifier->read_only_error == VDO_SUCCESS) {
			notifier->state = MAY_NOTIFY;
		} else {
			notifier->state = NOTIFYING;
			notifier->waiter = parent;
		}
	}
	spin_unlock(&notifier->lock);

	if (notifier->waiter == NULL) {
		/* We're done */
		vdo_launch_completion(parent);
		return;
	}

	/* Do the pending notification. */
	make_thread_read_only(&notifier->completion);
}

/**
 * vdo_enter_read_only_mode() - Put a VDO into read-only mode and save the read-only state in the
 *                              super block.
 * @vdo: The vdo.
 * @error_code: The error which caused the VDO to enter read-only mode.
 *
 * This method is a no-op if the VDO is already read-only.
 */
void vdo_enter_read_only_mode(struct vdo *vdo, int error_code)
{
	bool notify = false;
	thread_id_t thread_id = vdo_get_callback_thread_id();
	struct read_only_notifier *notifier = &vdo->read_only_notifier;
	struct vdo_thread *thread;

	if (thread_id != VDO_INVALID_THREAD_ID) {
		thread = &vdo->threads[thread_id];
		if (thread->is_read_only) {
			/* This thread has already gone read-only. */
			return;
		}

		/* Record for this thread that the VDO is read-only. */
		thread->is_read_only = true;
	}

	spin_lock(&notifier->lock);
	if (notifier->read_only_error == VDO_SUCCESS) {
		WRITE_ONCE(notifier->read_only_error, error_code);
		if (notifier->state == MAY_NOTIFY) {
			notifier->state = NOTIFYING;
			notify = true;
		}
	}
	spin_unlock(&notifier->lock);

	if (!notify) {
		/* The notifier is already aware of a read-only error */
		return;
	}

	/* Initiate a notification starting on the lowest numbered thread. */
	vdo_launch_completion_callback(&notifier->completion, make_thread_read_only, 0);
}

/**
 * vdo_is_read_only() - Check whether the VDO is read-only.
 * @vdo: The vdo.
 *
 * Return: true if the vdo is read-only.
 *
 * This method may be called from any thread, as opposed to examining the VDO's state field which
 * is only safe to check from the admin thread.
 */
bool vdo_is_read_only(struct vdo *vdo)
{
	return vdo->threads[vdo_get_callback_thread_id()].is_read_only;
}

/**
 * vdo_in_read_only_mode() - Check whether a vdo is in read-only mode.
 * @vdo: The vdo to query.
 *
 * Return: true if the vdo is in read-only mode.
 */
bool vdo_in_read_only_mode(const struct vdo *vdo)
{
	return (vdo_get_state(vdo) == VDO_READ_ONLY_MODE);
}

/**
 * vdo_in_recovery_mode() - Check whether the vdo is in recovery mode.
 * @vdo: The vdo to query.
 *
 * Return: true if the vdo is in recovery mode.
 */
bool vdo_in_recovery_mode(const struct vdo *vdo)
{
	return (vdo_get_state(vdo) == VDO_RECOVERING);
}

/**
 * vdo_enter_recovery_mode() - Put the vdo into recovery mode.
 * @vdo: The vdo.
 */
void vdo_enter_recovery_mode(struct vdo *vdo)
{
	vdo_assert_on_admin_thread(vdo, __func__);

	if (vdo_in_read_only_mode(vdo))
		return;

	vdo_log_info("Entering recovery mode");
	vdo_set_state(vdo, VDO_RECOVERING);
}

/**
 * complete_synchronous_action() - Signal the waiting thread that a synchronous action is complete.
 * @completion: The sync completion.
 */
static void complete_synchronous_action(struct vdo_completion *completion)
{
	vdo_assert_completion_type(completion, VDO_SYNC_COMPLETION);
	complete(&(container_of(completion, struct sync_completion,
				vdo_completion)->completion));
}

/**
 * perform_synchronous_action() - Launch an action on a VDO thread and wait for it to complete.
 * @vdo: The vdo.
 * @action: The callback to launch.
 * @thread_id: The thread on which to run the action.
 * @parent: The parent of the sync completion (may be NULL).
 */
static int perform_synchronous_action(struct vdo *vdo, vdo_action_fn action,
				      thread_id_t thread_id, void *parent)
{
	struct sync_completion sync;

	vdo_initialize_completion(&sync.vdo_completion, vdo, VDO_SYNC_COMPLETION);
	init_completion(&sync.completion);
	sync.vdo_completion.parent = parent;
	vdo_launch_completion_callback(&sync.vdo_completion, action, thread_id);
	wait_for_completion(&sync.completion);
	return sync.vdo_completion.result;
}

/**
 * set_compression_callback() - Callback to turn compression on or off.
 * @completion: The completion.
 */
static void set_compression_callback(struct vdo_completion *completion)
{
	struct vdo *vdo = completion->vdo;
	bool *enable = completion->parent;
	bool was_enabled = vdo_get_compressing(vdo);

	if (*enable != was_enabled) {
		WRITE_ONCE(vdo->compressing, *enable);
		if (was_enabled) {
			/* Signal the packer to flush since compression has been disabled. */
			vdo_flush_packer(vdo->packer);
		}
	}

	vdo_log_info("compression is %s", (*enable ? "enabled" : "disabled"));
	*enable = was_enabled;
	complete_synchronous_action(completion);
}

/**
 * vdo_set_compressing() - Turn compression on or off.
 * @vdo: The vdo.
 * @enable: Whether to enable or disable compression.
 *
 * Return: Whether compression was previously on or off.
 */
bool vdo_set_compressing(struct vdo *vdo, bool enable)
{
	perform_synchronous_action(vdo, set_compression_callback,
				   vdo->thread_config.packer_thread,
				   &enable);
	return enable;
}

/**
 * vdo_get_compressing() - Get whether compression is enabled in a vdo.
 * @vdo: The vdo.
 *
 * Return: State of compression.
 */
bool vdo_get_compressing(struct vdo *vdo)
{
	return READ_ONCE(vdo->compressing);
}

static size_t get_block_map_cache_size(const struct vdo *vdo)
{
	return ((size_t) vdo->device_config->cache_size) * VDO_BLOCK_SIZE;
}

static struct error_statistics __must_check get_vdo_error_statistics(const struct vdo *vdo)
{
	/*
	 * The error counts can be incremented from arbitrary threads and so must be incremented
	 * atomically, but they are just statistics with no semantics that could rely on memory
	 * order, so unfenced reads are sufficient.
	 */
	const struct atomic_statistics *atoms = &vdo->stats;

	return (struct error_statistics) {
		.invalid_advice_pbn_count = atomic64_read(&atoms->invalid_advice_pbn_count),
		.no_space_error_count = atomic64_read(&atoms->no_space_error_count),
		.read_only_error_count = atomic64_read(&atoms->read_only_error_count),
	};
}

static void copy_bio_stat(struct bio_stats *b, const struct atomic_bio_stats *a)
{
	b->read = atomic64_read(&a->read);
	b->write = atomic64_read(&a->write);
	b->discard = atomic64_read(&a->discard);
	b->flush = atomic64_read(&a->flush);
	b->empty_flush = atomic64_read(&a->empty_flush);
	b->fua = atomic64_read(&a->fua);
}

static struct bio_stats subtract_bio_stats(struct bio_stats minuend,
					   struct bio_stats subtrahend)
{
	return (struct bio_stats) {
		.read = minuend.read - subtrahend.read,
		.write = minuend.write - subtrahend.write,
		.discard = minuend.discard - subtrahend.discard,
		.flush = minuend.flush - subtrahend.flush,
		.empty_flush = minuend.empty_flush - subtrahend.empty_flush,
		.fua = minuend.fua - subtrahend.fua,
	};
}

/**
 * vdo_get_physical_blocks_allocated() - Get the number of physical blocks in use by user data.
 * @vdo: The vdo.
 *
 * Return: The number of blocks allocated for user data.
 */
static block_count_t __must_check vdo_get_physical_blocks_allocated(const struct vdo *vdo)
{
	return (vdo_get_slab_depot_allocated_blocks(vdo->depot) -
		vdo_get_journal_block_map_data_blocks_used(vdo->recovery_journal));
}

/**
 * vdo_get_physical_blocks_overhead() - Get the number of physical blocks used by vdo metadata.
 * @vdo: The vdo.
 *
 * Return: The number of overhead blocks.
 */
static block_count_t __must_check vdo_get_physical_blocks_overhead(const struct vdo *vdo)
{
	/*
	 * config.physical_blocks is mutated during resize and is in a packed structure,
	 * but resize runs on admin thread.
	 * TODO: Verify that this is always safe.
	 */
	return (vdo->states.vdo.config.physical_blocks -
		vdo_get_slab_depot_data_blocks(vdo->depot) +
		vdo_get_journal_block_map_data_blocks_used(vdo->recovery_journal));
}

static const char *vdo_describe_state(enum vdo_state state)
{
	/* These strings should all fit in the 15 chars of VDOStatistics.mode. */
	switch (state) {
	case VDO_RECOVERING:
		return "recovering";

	case VDO_READ_ONLY_MODE:
		return "read-only";

	default:
		return "normal";
	}
}

/**
 * get_vdo_statistics() - Populate a vdo_statistics structure on the admin thread.
 * @vdo: The vdo.
 * @stats: The statistics structure to populate.
 */
static void get_vdo_statistics(const struct vdo *vdo, struct vdo_statistics *stats)
{
	struct recovery_journal *journal = vdo->recovery_journal;
	enum vdo_state state = vdo_get_state(vdo);

	vdo_assert_on_admin_thread(vdo, __func__);

	/* start with a clean slate */
	memset(stats, 0, sizeof(struct vdo_statistics));

	/*
	 * These are immutable properties of the vdo object, so it is safe to query them from any
	 * thread.
	 */
	stats->version = STATISTICS_VERSION;
	stats->logical_blocks = vdo->states.vdo.config.logical_blocks;
	/*
	 * config.physical_blocks is mutated during resize and is in a packed structure, but resize
	 * runs on the admin thread.
	 * TODO: verify that this is always safe
	 */
	stats->physical_blocks = vdo->states.vdo.config.physical_blocks;
	stats->block_size = VDO_BLOCK_SIZE;
	stats->complete_recoveries = vdo->states.vdo.complete_recoveries;
	stats->read_only_recoveries = vdo->states.vdo.read_only_recoveries;
	stats->block_map_cache_size = get_block_map_cache_size(vdo);

	/* The callees are responsible for thread-safety. */
	stats->data_blocks_used = vdo_get_physical_blocks_allocated(vdo);
	stats->overhead_blocks_used = vdo_get_physical_blocks_overhead(vdo);
	stats->logical_blocks_used = vdo_get_recovery_journal_logical_blocks_used(journal);
	vdo_get_slab_depot_statistics(vdo->depot, stats);
	stats->journal = vdo_get_recovery_journal_statistics(journal);
	stats->packer = vdo_get_packer_statistics(vdo->packer);
	stats->block_map = vdo_get_block_map_statistics(vdo->block_map);
	vdo_get_dedupe_statistics(vdo->hash_zones, stats);
	stats->errors = get_vdo_error_statistics(vdo);
	stats->in_recovery_mode = (state == VDO_RECOVERING);
	snprintf(stats->mode, sizeof(stats->mode), "%s", vdo_describe_state(state));

	stats->instance = vdo->instance;
	stats->current_vios_in_progress = get_data_vio_pool_active_requests(vdo->data_vio_pool);
	stats->max_vios = get_data_vio_pool_maximum_requests(vdo->data_vio_pool);

	stats->flush_out = atomic64_read(&vdo->stats.flush_out);
	stats->logical_block_size = vdo->device_config->logical_block_size;
	copy_bio_stat(&stats->bios_in, &vdo->stats.bios_in);
	copy_bio_stat(&stats->bios_in_partial, &vdo->stats.bios_in_partial);
	copy_bio_stat(&stats->bios_out, &vdo->stats.bios_out);
	copy_bio_stat(&stats->bios_meta, &vdo->stats.bios_meta);
	copy_bio_stat(&stats->bios_journal, &vdo->stats.bios_journal);
	copy_bio_stat(&stats->bios_page_cache, &vdo->stats.bios_page_cache);
	copy_bio_stat(&stats->bios_out_completed, &vdo->stats.bios_out_completed);
	copy_bio_stat(&stats->bios_meta_completed, &vdo->stats.bios_meta_completed);
	copy_bio_stat(&stats->bios_journal_completed,
		      &vdo->stats.bios_journal_completed);
	copy_bio_stat(&stats->bios_page_cache_completed,
		      &vdo->stats.bios_page_cache_completed);
	copy_bio_stat(&stats->bios_acknowledged, &vdo->stats.bios_acknowledged);
	copy_bio_stat(&stats->bios_acknowledged_partial, &vdo->stats.bios_acknowledged_partial);
	stats->bios_in_progress =
		subtract_bio_stats(stats->bios_in, stats->bios_acknowledged);
	vdo_get_memory_stats(&stats->memory_usage.bytes_used,
			     &stats->memory_usage.peak_bytes_used);
}

/**
 * vdo_fetch_statistics_callback() - Action to populate a vdo_statistics
 *                                   structure on the admin thread.
 * @completion: The completion.
 *
 * This callback is registered in vdo_fetch_statistics().
 */
static void vdo_fetch_statistics_callback(struct vdo_completion *completion)
{
	get_vdo_statistics(completion->vdo, completion->parent);
	complete_synchronous_action(completion);
}

/**
 * vdo_fetch_statistics() - Fetch statistics on the correct thread.
 * @vdo: The vdo.
 * @stats: The vdo statistics are returned here.
 */
void vdo_fetch_statistics(struct vdo *vdo, struct vdo_statistics *stats)
{
	perform_synchronous_action(vdo, vdo_fetch_statistics_callback,
				   vdo->thread_config.admin_thread, stats);
}

/**
 * vdo_get_callback_thread_id() - Get the id of the callback thread on which a completion is
 *                                currently running.
 *
 * Return: The current thread ID, or -1 if no such thread.
 */
thread_id_t vdo_get_callback_thread_id(void)
{
	struct vdo_work_queue *queue = vdo_get_current_work_queue();
	struct vdo_thread *thread;
	thread_id_t thread_id;

	if (queue == NULL)
		return VDO_INVALID_THREAD_ID;

	thread = vdo_get_work_queue_owner(queue);
	thread_id = thread->thread_id;

	if (PARANOID_THREAD_CONSISTENCY_CHECKS) {
		BUG_ON(thread_id >= thread->vdo->thread_config.thread_count);
		BUG_ON(thread != &thread->vdo->threads[thread_id]);
	}

	return thread_id;
}

/**
 * vdo_dump_status() - Dump status information about a vdo to the log for debugging.
 * @vdo: The vdo to dump.
 */
void vdo_dump_status(const struct vdo *vdo)
{
	zone_count_t zone;

	vdo_dump_flusher(vdo->flusher);
	vdo_dump_recovery_journal_statistics(vdo->recovery_journal);
	vdo_dump_packer(vdo->packer);
	vdo_dump_slab_depot(vdo->depot);

	for (zone = 0; zone < vdo->thread_config.logical_zone_count; zone++)
		vdo_dump_logical_zone(&vdo->logical_zones->zones[zone]);

	for (zone = 0; zone < vdo->thread_config.physical_zone_count; zone++)
		vdo_dump_physical_zone(&vdo->physical_zones->zones[zone]);

	vdo_dump_hash_zones(vdo->hash_zones);
}

/**
 * vdo_assert_on_admin_thread() - Assert that we are running on the admin thread.
 * @vdo: The vdo.
 * @name: The name of the function which should be running on the admin thread (for logging).
 */
void vdo_assert_on_admin_thread(const struct vdo *vdo, const char *name)
{
	VDO_ASSERT_LOG_ONLY((vdo_get_callback_thread_id() == vdo->thread_config.admin_thread),
			    "%s called on admin thread", name);
}

/**
 * vdo_assert_on_logical_zone_thread() - Assert that this function was called on the specified
 *                                       logical zone thread.
 * @vdo: The vdo.
 * @logical_zone: The number of the logical zone.
 * @name: The name of the calling function.
 */
void vdo_assert_on_logical_zone_thread(const struct vdo *vdo, zone_count_t logical_zone,
				       const char *name)
{
	VDO_ASSERT_LOG_ONLY((vdo_get_callback_thread_id() ==
			     vdo->thread_config.logical_threads[logical_zone]),
			    "%s called on logical thread", name);
}

/**
 * vdo_assert_on_physical_zone_thread() - Assert that this function was called on the specified
 *                                        physical zone thread.
 * @vdo: The vdo.
 * @physical_zone: The number of the physical zone.
 * @name: The name of the calling function.
 */
void vdo_assert_on_physical_zone_thread(const struct vdo *vdo,
					zone_count_t physical_zone, const char *name)
{
	VDO_ASSERT_LOG_ONLY((vdo_get_callback_thread_id() ==
			     vdo->thread_config.physical_threads[physical_zone]),
			    "%s called on physical thread", name);
}

/**
 * vdo_get_physical_zone() - Get the physical zone responsible for a given physical block number.
 * @vdo: The vdo containing the physical zones.
 * @pbn: The PBN of the data block.
 * @zone_ptr: A pointer to return the physical zone.
 *
 * Gets the physical zone responsible for a given physical block number of a data block in this vdo
 * instance, or of the zero block (for which a NULL zone is returned). For any other block number
 * that is not in the range of valid data block numbers in any slab, an error will be returned.
 * This function is safe to call on invalid block numbers; it will not put the vdo into read-only
 * mode.
 *
 * Return: VDO_SUCCESS or VDO_OUT_OF_RANGE if the block number is invalid or an error code for any
 *         other failure.
 */
int vdo_get_physical_zone(const struct vdo *vdo, physical_block_number_t pbn,
			  struct physical_zone **zone_ptr)
{
	struct vdo_slab *slab;
	int result;

	if (pbn == VDO_ZERO_BLOCK) {
		*zone_ptr = NULL;
		return VDO_SUCCESS;
	}

	/*
	 * Used because it does a more restrictive bounds check than vdo_get_slab(), and done first
	 * because it won't trigger read-only mode on an invalid PBN.
	 */
	if (!vdo_is_physical_data_block(vdo->depot, pbn))
		return VDO_OUT_OF_RANGE;

	/* With the PBN already checked, we should always succeed in finding a slab. */
	slab = vdo_get_slab(vdo->depot, pbn);
	result = VDO_ASSERT(slab != NULL, "vdo_get_slab must succeed on all valid PBNs");
	if (result != VDO_SUCCESS)
		return result;

	*zone_ptr = &vdo->physical_zones->zones[slab->allocator->zone_number];
	return VDO_SUCCESS;
}