Merging upstream version 6.9.7.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1693 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/indexer/volume.c b/drivers/md/dm-vdo/indexer/volume.c
new file mode 100644
index 0000000000..655453bb27
--- /dev/null
+++ b/drivers/md/dm-vdo/indexer/volume.c
@@ -0,0 +1,1693 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "volume.h"
+
+#include <linux/atomic.h>
+#include <linux/dm-bufio.h>
+#include <linux/err.h>
+
+#include "errors.h"
+#include "logger.h"
+#include "memory-alloc.h"
+#include "permassert.h"
+#include "string-utils.h"
+#include "thread-utils.h"
+
+#include "chapter-index.h"
+#include "config.h"
+#include "geometry.h"
+#include "hash-utils.h"
+#include "index.h"
+#include "sparse-cache.h"
+
+/*
+ * The first block of the volume layout is reserved for the volume header, which is no longer used.
+ * The remainder of the volume is divided into chapters consisting of several pages of records, and
+ * several pages of static index to use to find those records. The index pages are recorded first,
+ * followed by the record pages. The chapters are written in order as they are filled, so the
+ * volume storage acts as a circular log of the most recent chapters, with each new chapter
+ * overwriting the oldest saved one.
+ *
+ * When a new chapter is filled and closed, the records from that chapter are sorted and
+ * interleaved in approximate temporal order, and assigned to record pages. Then a static delta
+ * index is generated to store which record page contains each record. The in-memory index page map
+ * is also updated to indicate which delta lists fall on each chapter index page. This means that
+ * when a record is read, the volume only has to load a single index page and a single record page,
+ * rather than search the entire chapter. These index and record pages are written to storage, and
+ * the index pages are transferred to the page cache under the theory that the most recently
+ * written chapter is likely to be accessed again soon.
+ *
+ * When reading a record, the volume index will indicate which chapter should contain it. The
+ * volume uses the index page map to determine which chapter index page needs to be loaded, and
+ * then reads the relevant record page number from the chapter index. Both index and record pages
+ * are stored in a page cache when read for the common case that subsequent records need the same
+ * pages. The page cache evicts the least recently accessed entries when caching new pages. In
+ * addition, the volume uses dm-bufio to manage access to the storage, which may allow for
+ * additional caching depending on available system resources.
+ *
+ * Record requests are handled from cached pages when possible. If a page needs to be read, it is
+ * placed on a queue along with the request that wants to read it. Any requests for the same page
+ * that arrive while the read is pending are added to the queue entry. A separate reader thread
+ * handles the queued reads, adding the page to the cache and updating any requests queued with it
+ * so they can continue processing. This allows the index zone threads to continue processing new
+ * requests rather than wait for the storage reads.
+ *
+ * When an index rebuild is necessary, the volume reads each stored chapter to determine which
+ * range of chapters contain valid records, so that those records can be used to reconstruct the
+ * in-memory volume index.
+ */
+
+/* The maximum allowable number of contiguous bad chapters */
+#define MAX_BAD_CHAPTERS 100
+#define VOLUME_CACHE_MAX_ENTRIES (U16_MAX >> 1)
+#define VOLUME_CACHE_QUEUED_FLAG (1 << 15)
+#define VOLUME_CACHE_MAX_QUEUED_READS 4096
+
+static const u64 BAD_CHAPTER = U64_MAX;
+
+/*
+ * The invalidate counter is two 32 bits fields stored together atomically. The low order 32 bits
+ * are the physical page number of the cached page being read. The high order 32 bits are a
+ * sequence number. This value is written when the zone that owns it begins or completes a cache
+ * search. Any other thread will only read the counter in wait_for_pending_searches() while waiting
+ * to update the cache contents.
+ */
+union invalidate_counter {
+	u64 value;
+	struct {
+		u32 page;
+		u32 counter;
+	};
+};
+
+static inline u32 map_to_page_number(struct index_geometry *geometry, u32 physical_page)
+{
+	return (physical_page - HEADER_PAGES_PER_VOLUME) % geometry->pages_per_chapter;
+}
+
+static inline u32 map_to_chapter_number(struct index_geometry *geometry, u32 physical_page)
+{
+	return (physical_page - HEADER_PAGES_PER_VOLUME) / geometry->pages_per_chapter;
+}
+
+static inline bool is_record_page(struct index_geometry *geometry, u32 physical_page)
+{
+	return map_to_page_number(geometry, physical_page) >= geometry->index_pages_per_chapter;
+}
+
+static u32 map_to_physical_page(const struct index_geometry *geometry, u32 chapter, u32 page)
+{
+	/* Page zero is the header page, so the first chapter index page is page one. */
+	return HEADER_PAGES_PER_VOLUME + (geometry->pages_per_chapter * chapter) + page;
+}
+
+static inline union invalidate_counter get_invalidate_counter(struct page_cache *cache,
+							      unsigned int zone_number)
+{
+	return (union invalidate_counter) {
+		.value = READ_ONCE(cache->search_pending_counters[zone_number].atomic_value),
+	};
+}
+
+static inline void set_invalidate_counter(struct page_cache *cache,
+					  unsigned int zone_number,
+					  union invalidate_counter invalidate_counter)
+{
+	WRITE_ONCE(cache->search_pending_counters[zone_number].atomic_value,
+		   invalidate_counter.value);
+}
+
+static inline bool search_pending(union invalidate_counter invalidate_counter)
+{
+	return (invalidate_counter.counter & 1) != 0;
+}
+
+/* Lock the cache for a zone in order to search for a page. */
+static void begin_pending_search(struct page_cache *cache, u32 physical_page,
+				 unsigned int zone_number)
+{
+	union invalidate_counter invalidate_counter =
+		get_invalidate_counter(cache, zone_number);
+
+	invalidate_counter.page = physical_page;
+	invalidate_counter.counter++;
+	set_invalidate_counter(cache, zone_number, invalidate_counter);
+	VDO_ASSERT_LOG_ONLY(search_pending(invalidate_counter),
+			    "Search is pending for zone %u", zone_number);
+	/*
+	 * This memory barrier ensures that the write to the invalidate counter is seen by other
+	 * threads before this thread accesses the cached page. The corresponding read memory
+	 * barrier is in wait_for_pending_searches().
+	 */
+	smp_mb();
+}
+
+/* Unlock the cache for a zone by clearing its invalidate counter. */
+static void end_pending_search(struct page_cache *cache, unsigned int zone_number)
+{
+	union invalidate_counter invalidate_counter;
+
+	/*
+	 * This memory barrier ensures that this thread completes reads of the
+	 * cached page before other threads see the write to the invalidate
+	 * counter.
+	 */
+	smp_mb();
+
+	invalidate_counter = get_invalidate_counter(cache, zone_number);
+	VDO_ASSERT_LOG_ONLY(search_pending(invalidate_counter),
+			    "Search is pending for zone %u", zone_number);
+	invalidate_counter.counter++;
+	set_invalidate_counter(cache, zone_number, invalidate_counter);
+}
+
+static void wait_for_pending_searches(struct page_cache *cache, u32 physical_page)
+{
+	union invalidate_counter initial_counters[MAX_ZONES];
+	unsigned int i;
+
+	/*
+	 * We hold the read_threads_mutex. We are waiting for threads that do not hold the
+	 * read_threads_mutex. Those threads have "locked" their targeted page by setting the
+	 * search_pending_counter. The corresponding write memory barrier is in
+	 * begin_pending_search().
+	 */
+	smp_mb();
+
+	for (i = 0; i < cache->zone_count; i++)
+		initial_counters[i] = get_invalidate_counter(cache, i);
+	for (i = 0; i < cache->zone_count; i++) {
+		if (search_pending(initial_counters[i]) &&
+		    (initial_counters[i].page == physical_page)) {
+			/*
+			 * There is an active search using the physical page. We need to wait for
+			 * the search to finish.
+			 *
+			 * FIXME: Investigate using wait_event() to wait for the search to finish.
+			 */
+			while (initial_counters[i].value ==
+			       get_invalidate_counter(cache, i).value)
+				cond_resched();
+		}
+	}
+}
+
+static void release_page_buffer(struct cached_page *page)
+{
+	if (page->buffer != NULL)
+		dm_bufio_release(vdo_forget(page->buffer));
+}
+
+static void clear_cache_page(struct page_cache *cache, struct cached_page *page)
+{
+	/* Do not clear read_pending because the read queue relies on it. */
+	release_page_buffer(page);
+	page->physical_page = cache->indexable_pages;
+	WRITE_ONCE(page->last_used, 0);
+}
+
+static void make_page_most_recent(struct page_cache *cache, struct cached_page *page)
+{
+	/*
+	 * ASSERTION: We are either a zone thread holding a search_pending_counter, or we are any
+	 * thread holding the read_threads_mutex.
+	 */
+	if (atomic64_read(&cache->clock) != READ_ONCE(page->last_used))
+		WRITE_ONCE(page->last_used, atomic64_inc_return(&cache->clock));
+}
+
+/* Select a page to remove from the cache to make space for a new entry. */
+static struct cached_page *select_victim_in_cache(struct page_cache *cache)
+{
+	struct cached_page *page;
+	int oldest_index = 0;
+	s64 oldest_time = S64_MAX;
+	s64 last_used;
+	u16 i;
+
+	/* Find the oldest unclaimed page. We hold the read_threads_mutex. */
+	for (i = 0; i < cache->cache_slots; i++) {
+		/* A page with a pending read must not be replaced. */
+		if (cache->cache[i].read_pending)
+			continue;
+
+		last_used = READ_ONCE(cache->cache[i].last_used);
+		if (last_used <= oldest_time) {
+			oldest_time = last_used;
+			oldest_index = i;
+		}
+	}
+
+	page = &cache->cache[oldest_index];
+	if (page->physical_page != cache->indexable_pages) {
+		WRITE_ONCE(cache->index[page->physical_page], cache->cache_slots);
+		wait_for_pending_searches(cache, page->physical_page);
+	}
+
+	page->read_pending = true;
+	clear_cache_page(cache, page);
+	return page;
+}
+
+/* Make a newly filled cache entry available to other threads. */
+static int put_page_in_cache(struct page_cache *cache, u32 physical_page,
+			     struct cached_page *page)
+{
+	int result;
+
+	/* We hold the read_threads_mutex. */
+	result = VDO_ASSERT((page->read_pending), "page to install has a pending read");
+	if (result != VDO_SUCCESS)
+		return result;
+
+	page->physical_page = physical_page;
+	make_page_most_recent(cache, page);
+	page->read_pending = false;
+
+	/*
+	 * We hold the read_threads_mutex, but we must have a write memory barrier before making
+	 * the cached_page available to the readers that do not hold the mutex. The corresponding
+	 * read memory barrier is in get_page_and_index().
+	 */
+	smp_wmb();
+
+	/* This assignment also clears the queued flag. */
+	WRITE_ONCE(cache->index[physical_page], page - cache->cache);
+	return UDS_SUCCESS;
+}
+
+static void cancel_page_in_cache(struct page_cache *cache, u32 physical_page,
+				 struct cached_page *page)
+{
+	int result;
+
+	/* We hold the read_threads_mutex. */
+	result = VDO_ASSERT((page->read_pending), "page to install has a pending read");
+	if (result != VDO_SUCCESS)
+		return;
+
+	clear_cache_page(cache, page);
+	page->read_pending = false;
+
+	/* Clear the mapping and the queued flag for the new page. */
+	WRITE_ONCE(cache->index[physical_page], cache->cache_slots);
+}
+
+static inline u16 next_queue_position(u16 position)
+{
+	return (position + 1) % VOLUME_CACHE_MAX_QUEUED_READS;
+}
+
+static inline void advance_queue_position(u16 *position)
+{
+	*position = next_queue_position(*position);
+}
+
+static inline bool read_queue_is_full(struct page_cache *cache)
+{
+	return cache->read_queue_first == next_queue_position(cache->read_queue_last);
+}
+
+static bool enqueue_read(struct page_cache *cache, struct uds_request *request,
+			 u32 physical_page)
+{
+	struct queued_read *queue_entry;
+	u16 last = cache->read_queue_last;
+	u16 read_queue_index;
+
+	/* We hold the read_threads_mutex. */
+	if ((cache->index[physical_page] & VOLUME_CACHE_QUEUED_FLAG) == 0) {
+		/* This page has no existing entry in the queue. */
+		if (read_queue_is_full(cache))
+			return false;
+
+		/* Fill in the read queue entry. */
+		cache->read_queue[last].physical_page = physical_page;
+		cache->read_queue[last].invalid = false;
+		cache->read_queue[last].first_request = NULL;
+		cache->read_queue[last].last_request = NULL;
+
+		/* Point the cache index to the read queue entry. */
+		read_queue_index = last;
+		WRITE_ONCE(cache->index[physical_page],
+			   read_queue_index | VOLUME_CACHE_QUEUED_FLAG);
+
+		advance_queue_position(&cache->read_queue_last);
+	} else {
+		/* It's already queued, so add this request to the existing entry. */
+		read_queue_index = cache->index[physical_page] & ~VOLUME_CACHE_QUEUED_FLAG;
+	}
+
+	request->next_request = NULL;
+	queue_entry = &cache->read_queue[read_queue_index];
+	if (queue_entry->first_request == NULL)
+		queue_entry->first_request = request;
+	else
+		queue_entry->last_request->next_request = request;
+	queue_entry->last_request = request;
+
+	return true;
+}
+
+static void enqueue_page_read(struct volume *volume, struct uds_request *request,
+			      u32 physical_page)
+{
+	/* Mark the page as queued, so that chapter invalidation knows to cancel a read. */
+	while (!enqueue_read(&volume->page_cache, request, physical_page)) {
+		vdo_log_debug("Read queue full, waiting for reads to finish");
+		uds_wait_cond(&volume->read_threads_read_done_cond,
+			      &volume->read_threads_mutex);
+	}
+
+	uds_signal_cond(&volume->read_threads_cond);
+}
+
+/*
+ * Reserve the next read queue entry for processing, but do not actually remove it from the queue.
+ * Must be followed by release_queued_requests().
+ */
+static struct queued_read *reserve_read_queue_entry(struct page_cache *cache)
+{
+	/* We hold the read_threads_mutex. */
+	struct queued_read *entry;
+	u16 index_value;
+	bool queued;
+
+	/* No items to dequeue */
+	if (cache->read_queue_next_read == cache->read_queue_last)
+		return NULL;
+
+	entry = &cache->read_queue[cache->read_queue_next_read];
+	index_value = cache->index[entry->physical_page];
+	queued = (index_value & VOLUME_CACHE_QUEUED_FLAG) != 0;
+	/* Check to see if it's still queued before resetting. */
+	if (entry->invalid && queued)
+		WRITE_ONCE(cache->index[entry->physical_page], cache->cache_slots);
+
+	/*
+	 * If a synchronous read has taken this page, set invalid to true so it doesn't get
+	 * overwritten. Requests will just be requeued.
+	 */
+	if (!queued)
+		entry->invalid = true;
+
+	entry->reserved = true;
+	advance_queue_position(&cache->read_queue_next_read);
+	return entry;
+}
+
+static inline struct queued_read *wait_to_reserve_read_queue_entry(struct volume *volume)
+{
+	struct queued_read *queue_entry = NULL;
+
+	while (!volume->read_threads_exiting) {
+		queue_entry = reserve_read_queue_entry(&volume->page_cache);
+		if (queue_entry != NULL)
+			break;
+
+		uds_wait_cond(&volume->read_threads_cond, &volume->read_threads_mutex);
+	}
+
+	return queue_entry;
+}
+
+static int init_chapter_index_page(const struct volume *volume, u8 *index_page,
+				   u32 chapter, u32 index_page_number,
+				   struct delta_index_page *chapter_index_page)
+{
+	u64 ci_virtual;
+	u32 ci_chapter;
+	u32 lowest_list;
+	u32 highest_list;
+	struct index_geometry *geometry = volume->geometry;
+	int result;
+
+	result = uds_initialize_chapter_index_page(chapter_index_page, geometry,
+						   index_page, volume->nonce);
+	if (volume->lookup_mode == LOOKUP_FOR_REBUILD)
+		return result;
+
+	if (result != UDS_SUCCESS) {
+		return vdo_log_error_strerror(result,
+					      "Reading chapter index page for chapter %u page %u",
+					      chapter, index_page_number);
+	}
+
+	uds_get_list_number_bounds(volume->index_page_map, chapter, index_page_number,
+				   &lowest_list, &highest_list);
+	ci_virtual = chapter_index_page->virtual_chapter_number;
+	ci_chapter = uds_map_to_physical_chapter(geometry, ci_virtual);
+	if ((chapter == ci_chapter) &&
+	    (lowest_list == chapter_index_page->lowest_list_number) &&
+	    (highest_list == chapter_index_page->highest_list_number))
+		return UDS_SUCCESS;
+
+	vdo_log_warning("Index page map updated to %llu",
+			(unsigned long long) volume->index_page_map->last_update);
+	vdo_log_warning("Page map expects that chapter %u page %u has range %u to %u, but chapter index page has chapter %llu with range %u to %u",
+			chapter, index_page_number, lowest_list, highest_list,
+			(unsigned long long) ci_virtual,
+			chapter_index_page->lowest_list_number,
+			chapter_index_page->highest_list_number);
+	return vdo_log_error_strerror(UDS_CORRUPT_DATA,
+				      "index page map mismatch with chapter index");
+}
+
+static int initialize_index_page(const struct volume *volume, u32 physical_page,
+				 struct cached_page *page)
+{
+	u32 chapter = map_to_chapter_number(volume->geometry, physical_page);
+	u32 index_page_number = map_to_page_number(volume->geometry, physical_page);
+
+	return init_chapter_index_page(volume, dm_bufio_get_block_data(page->buffer),
+				       chapter, index_page_number, &page->index_page);
+}
+
+static bool search_record_page(const u8 record_page[],
+			       const struct uds_record_name *name,
+			       const struct index_geometry *geometry,
+			       struct uds_record_data *metadata)
+{
+	/*
+	 * The array of records is sorted by name and stored as a binary tree in heap order, so the
+	 * root of the tree is the first array element.
+	 */
+	u32 node = 0;
+	const struct uds_volume_record *records = (const struct uds_volume_record *) record_page;
+
+	while (node < geometry->records_per_page) {
+		int result;
+		const struct uds_volume_record *record = &records[node];
+
+		result = memcmp(name, &record->name, UDS_RECORD_NAME_SIZE);
+		if (result == 0) {
+			if (metadata != NULL)
+				*metadata = record->data;
+			return true;
+		}
+
+		/* The children of node N are at indexes 2N+1 and 2N+2. */
+		node = ((2 * node) + ((result < 0) ? 1 : 2));
+	}
+
+	return false;
+}
+
+/*
+ * If we've read in a record page, we're going to do an immediate search, to speed up processing by
+ * avoiding get_record_from_zone(), and to ensure that requests make progress even when queued. If
+ * we've read in an index page, we save the record page number so we don't have to resolve the
+ * index page again. We use the location, virtual_chapter, and old_metadata fields in the request
+ * to allow the index code to know where to begin processing the request again.
+ */
+static int search_page(struct cached_page *page, const struct volume *volume,
+		       struct uds_request *request, u32 physical_page)
+{
+	int result;
+	enum uds_index_region location;
+	u16 record_page_number;
+
+	if (is_record_page(volume->geometry, physical_page)) {
+		if (search_record_page(dm_bufio_get_block_data(page->buffer),
+				       &request->record_name, volume->geometry,
+				       &request->old_metadata))
+			location = UDS_LOCATION_RECORD_PAGE_LOOKUP;
+		else
+			location = UDS_LOCATION_UNAVAILABLE;
+	} else {
+		result = uds_search_chapter_index_page(&page->index_page,
+						       volume->geometry,
+						       &request->record_name,
+						       &record_page_number);
+		if (result != UDS_SUCCESS)
+			return result;
+
+		if (record_page_number == NO_CHAPTER_INDEX_ENTRY) {
+			location = UDS_LOCATION_UNAVAILABLE;
+		} else {
+			location = UDS_LOCATION_INDEX_PAGE_LOOKUP;
+			*((u16 *) &request->old_metadata) = record_page_number;
+		}
+	}
+
+	request->location = location;
+	request->found = false;
+	return UDS_SUCCESS;
+}
+
+static int process_entry(struct volume *volume, struct queued_read *entry)
+{
+	u32 page_number = entry->physical_page;
+	struct uds_request *request;
+	struct cached_page *page = NULL;
+	u8 *page_data;
+	int result;
+
+	if (entry->invalid) {
+		vdo_log_debug("Requeuing requests for invalid page");
+		return UDS_SUCCESS;
+	}
+
+	page = select_victim_in_cache(&volume->page_cache);
+
+	mutex_unlock(&volume->read_threads_mutex);
+	page_data = dm_bufio_read(volume->client, page_number, &page->buffer);
+	mutex_lock(&volume->read_threads_mutex);
+	if (IS_ERR(page_data)) {
+		result = -PTR_ERR(page_data);
+		vdo_log_warning_strerror(result,
+					 "error reading physical page %u from volume",
+					 page_number);
+		cancel_page_in_cache(&volume->page_cache, page_number, page);
+		return result;
+	}
+
+	if (entry->invalid) {
+		vdo_log_warning("Page %u invalidated after read", page_number);
+		cancel_page_in_cache(&volume->page_cache, page_number, page);
+		return UDS_SUCCESS;
+	}
+
+	if (!is_record_page(volume->geometry, page_number)) {
+		result = initialize_index_page(volume, page_number, page);
+		if (result != UDS_SUCCESS) {
+			vdo_log_warning("Error initializing chapter index page");
+			cancel_page_in_cache(&volume->page_cache, page_number, page);
+			return result;
+		}
+	}
+
+	result = put_page_in_cache(&volume->page_cache, page_number, page);
+	if (result != UDS_SUCCESS) {
+		vdo_log_warning("Error putting page %u in cache", page_number);
+		cancel_page_in_cache(&volume->page_cache, page_number, page);
+		return result;
+	}
+
+	request = entry->first_request;
+	while ((request != NULL) && (result == UDS_SUCCESS)) {
+		result = search_page(page, volume, request, page_number);
+		request = request->next_request;
+	}
+
+	return result;
+}
+
+static void release_queued_requests(struct volume *volume, struct queued_read *entry,
+				    int result)
+{
+	struct page_cache *cache = &volume->page_cache;
+	u16 next_read = cache->read_queue_next_read;
+	struct uds_request *request;
+	struct uds_request *next;
+
+	for (request = entry->first_request; request != NULL; request = next) {
+		next = request->next_request;
+		request->status = result;
+		request->requeued = true;
+		uds_enqueue_request(request, STAGE_INDEX);
+	}
+
+	entry->reserved = false;
+
+	/* Move the read_queue_first pointer as far as we can. */
+	while ((cache->read_queue_first != next_read) &&
+	       (!cache->read_queue[cache->read_queue_first].reserved))
+		advance_queue_position(&cache->read_queue_first);
+	uds_broadcast_cond(&volume->read_threads_read_done_cond);
+}
+
+static void read_thread_function(void *arg)
+{
+	struct volume *volume = arg;
+
+	vdo_log_debug("reader starting");
+	mutex_lock(&volume->read_threads_mutex);
+	while (true) {
+		struct queued_read *queue_entry;
+		int result;
+
+		queue_entry = wait_to_reserve_read_queue_entry(volume);
+		if (volume->read_threads_exiting)
+			break;
+
+		result = process_entry(volume, queue_entry);
+		release_queued_requests(volume, queue_entry, result);
+	}
+	mutex_unlock(&volume->read_threads_mutex);
+	vdo_log_debug("reader done");
+}
+
+static void get_page_and_index(struct page_cache *cache, u32 physical_page,
+			       int *queue_index, struct cached_page **page_ptr)
+{
+	u16 index_value;
+	u16 index;
+	bool queued;
+
+	/*
+	 * ASSERTION: We are either a zone thread holding a search_pending_counter, or we are any
+	 * thread holding the read_threads_mutex.
+	 *
+	 * Holding only a search_pending_counter is the most frequent case.
+	 */
+	/*
+	 * It would be unlikely for the compiler to turn the usage of index_value into two reads of
+	 * cache->index, but it would be possible and very bad if those reads did not return the
+	 * same bits.
+	 */
+	index_value = READ_ONCE(cache->index[physical_page]);
+	queued = (index_value & VOLUME_CACHE_QUEUED_FLAG) != 0;
+	index = index_value & ~VOLUME_CACHE_QUEUED_FLAG;
+
+	if (!queued && (index < cache->cache_slots)) {
+		*page_ptr = &cache->cache[index];
+		/*
+		 * We have acquired access to the cached page, but unless we hold the
+		 * read_threads_mutex, we need a read memory barrier now. The corresponding write
+		 * memory barrier is in put_page_in_cache().
+		 */
+		smp_rmb();
+	} else {
+		*page_ptr = NULL;
+	}
+
+	*queue_index = queued ? index : -1;
+}
+
+static void get_page_from_cache(struct page_cache *cache, u32 physical_page,
+				struct cached_page **page)
+{
+	/*
+	 * ASSERTION: We are in a zone thread.
+	 * ASSERTION: We holding a search_pending_counter or the read_threads_mutex.
+	 */
+	int queue_index = -1;
+
+	get_page_and_index(cache, physical_page, &queue_index, page);
+}
+
+static int read_page_locked(struct volume *volume, u32 physical_page,
+			    struct cached_page **page_ptr)
+{
+	int result = UDS_SUCCESS;
+	struct cached_page *page = NULL;
+	u8 *page_data;
+
+	page = select_victim_in_cache(&volume->page_cache);
+	page_data = dm_bufio_read(volume->client, physical_page, &page->buffer);
+	if (IS_ERR(page_data)) {
+		result = -PTR_ERR(page_data);
+		vdo_log_warning_strerror(result,
+					 "error reading physical page %u from volume",
+					 physical_page);
+		cancel_page_in_cache(&volume->page_cache, physical_page, page);
+		return result;
+	}
+
+	if (!is_record_page(volume->geometry, physical_page)) {
+		result = initialize_index_page(volume, physical_page, page);
+		if (result != UDS_SUCCESS) {
+			if (volume->lookup_mode != LOOKUP_FOR_REBUILD)
+				vdo_log_warning("Corrupt index page %u", physical_page);
+			cancel_page_in_cache(&volume->page_cache, physical_page, page);
+			return result;
+		}
+	}
+
+	result = put_page_in_cache(&volume->page_cache, physical_page, page);
+	if (result != UDS_SUCCESS) {
+		vdo_log_warning("Error putting page %u in cache", physical_page);
+		cancel_page_in_cache(&volume->page_cache, physical_page, page);
+		return result;
+	}
+
+	*page_ptr = page;
+	return UDS_SUCCESS;
+}
+
+/* Retrieve a page from the cache while holding the read threads mutex. */
+static int get_volume_page_locked(struct volume *volume, u32 physical_page,
+				  struct cached_page **page_ptr)
+{
+	int result;
+	struct cached_page *page = NULL;
+
+	get_page_from_cache(&volume->page_cache, physical_page, &page);
+	if (page == NULL) {
+		result = read_page_locked(volume, physical_page, &page);
+		if (result != UDS_SUCCESS)
+			return result;
+	} else {
+		make_page_most_recent(&volume->page_cache, page);
+	}
+
+	*page_ptr = page;
+	return UDS_SUCCESS;
+}
+
+/* Retrieve a page from the cache while holding a search_pending lock. */
+static int get_volume_page_protected(struct volume *volume, struct uds_request *request,
+				     u32 physical_page, struct cached_page **page_ptr)
+{
+	struct cached_page *page;
+
+	get_page_from_cache(&volume->page_cache, physical_page, &page);
+	if (page != NULL) {
+		if (request->zone_number == 0) {
+			/* Only one zone is allowed to update the LRU. */
+			make_page_most_recent(&volume->page_cache, page);
+		}
+
+		*page_ptr = page;
+		return UDS_SUCCESS;
+	}
+
+	/* Prepare to enqueue a read for the page. */
+	end_pending_search(&volume->page_cache, request->zone_number);
+	mutex_lock(&volume->read_threads_mutex);
+
+	/*
+	 * Do the lookup again while holding the read mutex (no longer the fast case so this should
+	 * be fine to repeat). We need to do this because a page may have been added to the cache
+	 * by a reader thread between the time we searched above and the time we went to actually
+	 * try to enqueue it below. This could result in us enqueuing another read for a page which
+	 * is already in the cache, which would mean we end up with two entries in the cache for
+	 * the same page.
+	 */
+	get_page_from_cache(&volume->page_cache, physical_page, &page);
+	if (page == NULL) {
+		enqueue_page_read(volume, request, physical_page);
+		/*
+		 * The performance gain from unlocking first, while "search pending" mode is off,
+		 * turns out to be significant in some cases. The page is not available yet so
+		 * the order does not matter for correctness as it does below.
+		 */
+		mutex_unlock(&volume->read_threads_mutex);
+		begin_pending_search(&volume->page_cache, physical_page,
+				     request->zone_number);
+		return UDS_QUEUED;
+	}
+
+	/*
+	 * Now that the page is loaded, the volume needs to switch to "reader thread unlocked" and
+	 * "search pending" state in careful order so no other thread can mess with the data before
+	 * the caller gets to look at it.
+	 */
+	begin_pending_search(&volume->page_cache, physical_page, request->zone_number);
+	mutex_unlock(&volume->read_threads_mutex);
+	*page_ptr = page;
+	return UDS_SUCCESS;
+}
+
+static int get_volume_page(struct volume *volume, u32 chapter, u32 page_number,
+			   struct cached_page **page_ptr)
+{
+	int result;
+	u32 physical_page = map_to_physical_page(volume->geometry, chapter, page_number);
+
+	mutex_lock(&volume->read_threads_mutex);
+	result = get_volume_page_locked(volume, physical_page, page_ptr);
+	mutex_unlock(&volume->read_threads_mutex);
+	return result;
+}
+
+int uds_get_volume_record_page(struct volume *volume, u32 chapter, u32 page_number,
+			       u8 **data_ptr)
+{
+	int result;
+	struct cached_page *page = NULL;
+
+	result = get_volume_page(volume, chapter, page_number, &page);
+	if (result == UDS_SUCCESS)
+		*data_ptr = dm_bufio_get_block_data(page->buffer);
+	return result;
+}
+
+int uds_get_volume_index_page(struct volume *volume, u32 chapter, u32 page_number,
+			      struct delta_index_page **index_page_ptr)
+{
+	int result;
+	struct cached_page *page = NULL;
+
+	result = get_volume_page(volume, chapter, page_number, &page);
+	if (result == UDS_SUCCESS)
+		*index_page_ptr = &page->index_page;
+	return result;
+}
+
+/*
+ * Find the record page associated with a name in a given index page. This will return UDS_QUEUED
+ * if the page in question must be read from storage.
+ */
+static int search_cached_index_page(struct volume *volume, struct uds_request *request,
+				    u32 chapter, u32 index_page_number,
+				    u16 *record_page_number)
+{
+	int result;
+	struct cached_page *page = NULL;
+	u32 physical_page = map_to_physical_page(volume->geometry, chapter,
+						 index_page_number);
+
+	/*
+	 * Make sure the invalidate counter is updated before we try and read the mapping. This
+	 * prevents this thread from reading a page in the cache which has already been marked for
+	 * invalidation by the reader thread, before the reader thread has noticed that the
+	 * invalidate_counter has been incremented.
+	 */
+	begin_pending_search(&volume->page_cache, physical_page, request->zone_number);
+
+	result = get_volume_page_protected(volume, request, physical_page, &page);
+	if (result != UDS_SUCCESS) {
+		end_pending_search(&volume->page_cache, request->zone_number);
+		return result;
+	}
+
+	result = uds_search_chapter_index_page(&page->index_page, volume->geometry,
+					       &request->record_name,
+					       record_page_number);
+	end_pending_search(&volume->page_cache, request->zone_number);
+	return result;
+}
+
+/*
+ * Find the metadata associated with a name in a given record page. This will return UDS_QUEUED if
+ * the page in question must be read from storage.
+ */
+int uds_search_cached_record_page(struct volume *volume, struct uds_request *request,
+				  u32 chapter, u16 record_page_number, bool *found)
+{
+	struct cached_page *record_page;
+	struct index_geometry *geometry = volume->geometry;
+	int result;
+	u32 physical_page, page_number;
+
+	*found = false;
+	if (record_page_number == NO_CHAPTER_INDEX_ENTRY)
+		return UDS_SUCCESS;
+
+	result = VDO_ASSERT(record_page_number < geometry->record_pages_per_chapter,
+			    "0 <= %d < %u", record_page_number,
+			    geometry->record_pages_per_chapter);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	page_number = geometry->index_pages_per_chapter + record_page_number;
+
+	physical_page = map_to_physical_page(volume->geometry, chapter, page_number);
+
+	/*
+	 * Make sure the invalidate counter is updated before we try and read the mapping. This
+	 * prevents this thread from reading a page in the cache which has already been marked for
+	 * invalidation by the reader thread, before the reader thread has noticed that the
+	 * invalidate_counter has been incremented.
+	 */
+	begin_pending_search(&volume->page_cache, physical_page, request->zone_number);
+
+	result = get_volume_page_protected(volume, request, physical_page, &record_page);
+	if (result != UDS_SUCCESS) {
+		end_pending_search(&volume->page_cache, request->zone_number);
+		return result;
+	}
+
+	if (search_record_page(dm_bufio_get_block_data(record_page->buffer),
+			       &request->record_name, geometry, &request->old_metadata))
+		*found = true;
+
+	end_pending_search(&volume->page_cache, request->zone_number);
+	return UDS_SUCCESS;
+}
+
+void uds_prefetch_volume_chapter(const struct volume *volume, u32 chapter)
+{
+	const struct index_geometry *geometry = volume->geometry;
+	u32 physical_page = map_to_physical_page(geometry, chapter, 0);
+
+	dm_bufio_prefetch(volume->client, physical_page, geometry->pages_per_chapter);
+}
+
+int uds_read_chapter_index_from_volume(const struct volume *volume, u64 virtual_chapter,
+				       struct dm_buffer *volume_buffers[],
+				       struct delta_index_page index_pages[])
+{
+	int result;
+	u32 i;
+	const struct index_geometry *geometry = volume->geometry;
+	u32 physical_chapter = uds_map_to_physical_chapter(geometry, virtual_chapter);
+	u32 physical_page = map_to_physical_page(geometry, physical_chapter, 0);
+
+	dm_bufio_prefetch(volume->client, physical_page, geometry->index_pages_per_chapter);
+	for (i = 0; i < geometry->index_pages_per_chapter; i++) {
+		u8 *index_page;
+
+		index_page = dm_bufio_read(volume->client, physical_page + i,
+					   &volume_buffers[i]);
+		if (IS_ERR(index_page)) {
+			result = -PTR_ERR(index_page);
+			vdo_log_warning_strerror(result,
+						 "error reading physical page %u",
+						 physical_page);
+			return result;
+		}
+
+		result = init_chapter_index_page(volume, index_page, physical_chapter, i,
+						 &index_pages[i]);
+		if (result != UDS_SUCCESS)
+			return result;
+	}
+
+	return UDS_SUCCESS;
+}
+
+int uds_search_volume_page_cache(struct volume *volume, struct uds_request *request,
+				 bool *found)
+{
+	int result;
+	u32 physical_chapter =
+		uds_map_to_physical_chapter(volume->geometry, request->virtual_chapter);
+	u32 index_page_number;
+	u16 record_page_number;
+
+	index_page_number = uds_find_index_page_number(volume->index_page_map,
+						       &request->record_name,
+						       physical_chapter);
+
+	if (request->location == UDS_LOCATION_INDEX_PAGE_LOOKUP) {
+		record_page_number = *((u16 *) &request->old_metadata);
+	} else {
+		result = search_cached_index_page(volume, request, physical_chapter,
+						  index_page_number,
+						  &record_page_number);
+		if (result != UDS_SUCCESS)
+			return result;
+	}
+
+	return uds_search_cached_record_page(volume, request, physical_chapter,
+					     record_page_number, found);
+}
+
+int uds_search_volume_page_cache_for_rebuild(struct volume *volume,
+					     const struct uds_record_name *name,
+					     u64 virtual_chapter, bool *found)
+{
+	int result;
+	struct index_geometry *geometry = volume->geometry;
+	struct cached_page *page;
+	u32 physical_chapter = uds_map_to_physical_chapter(geometry, virtual_chapter);
+	u32 index_page_number;
+	u16 record_page_number;
+	u32 page_number;
+
+	*found = false;
+	index_page_number =
+		uds_find_index_page_number(volume->index_page_map, name,
+					   physical_chapter);
+	result = get_volume_page(volume, physical_chapter, index_page_number, &page);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	result = uds_search_chapter_index_page(&page->index_page, geometry, name,
+					       &record_page_number);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	if (record_page_number == NO_CHAPTER_INDEX_ENTRY)
+		return UDS_SUCCESS;
+
+	page_number = geometry->index_pages_per_chapter + record_page_number;
+	result = get_volume_page(volume, physical_chapter, page_number, &page);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	*found = search_record_page(dm_bufio_get_block_data(page->buffer), name,
+				    geometry, NULL);
+	return UDS_SUCCESS;
+}
+
+static void invalidate_page(struct page_cache *cache, u32 physical_page)
+{
+	struct cached_page *page;
+	int queue_index = -1;
+
+	/* We hold the read_threads_mutex. */
+	get_page_and_index(cache, physical_page, &queue_index, &page);
+	if (page != NULL) {
+		WRITE_ONCE(cache->index[page->physical_page], cache->cache_slots);
+		wait_for_pending_searches(cache, page->physical_page);
+		clear_cache_page(cache, page);
+	} else if (queue_index > -1) {
+		vdo_log_debug("setting pending read to invalid");
+		cache->read_queue[queue_index].invalid = true;
+	}
+}
+
+void uds_forget_chapter(struct volume *volume, u64 virtual_chapter)
+{
+	u32 physical_chapter =
+		uds_map_to_physical_chapter(volume->geometry, virtual_chapter);
+	u32 first_page = map_to_physical_page(volume->geometry, physical_chapter, 0);
+	u32 i;
+
+	vdo_log_debug("forgetting chapter %llu", (unsigned long long) virtual_chapter);
+	mutex_lock(&volume->read_threads_mutex);
+	for (i = 0; i < volume->geometry->pages_per_chapter; i++)
+		invalidate_page(&volume->page_cache, first_page + i);
+	mutex_unlock(&volume->read_threads_mutex);
+}
+
+/*
+ * Donate an index pages from a newly written chapter to the page cache since it is likely to be
+ * used again soon. The caller must already hold the reader thread mutex.
+ */
+static int donate_index_page_locked(struct volume *volume, u32 physical_chapter,
+				    u32 index_page_number, struct dm_buffer *page_buffer)
+{
+	int result;
+	struct cached_page *page = NULL;
+	u32 physical_page =
+		map_to_physical_page(volume->geometry, physical_chapter,
+				     index_page_number);
+
+	page = select_victim_in_cache(&volume->page_cache);
+	page->buffer = page_buffer;
+	result = init_chapter_index_page(volume, dm_bufio_get_block_data(page_buffer),
+					 physical_chapter, index_page_number,
+					 &page->index_page);
+	if (result != UDS_SUCCESS) {
+		vdo_log_warning("Error initialize chapter index page");
+		cancel_page_in_cache(&volume->page_cache, physical_page, page);
+		return result;
+	}
+
+	result = put_page_in_cache(&volume->page_cache, physical_page, page);
+	if (result != UDS_SUCCESS) {
+		vdo_log_warning("Error putting page %u in cache", physical_page);
+		cancel_page_in_cache(&volume->page_cache, physical_page, page);
+		return result;
+	}
+
+	return UDS_SUCCESS;
+}
+
+static int write_index_pages(struct volume *volume, u32 physical_chapter_number,
+			     struct open_chapter_index *chapter_index)
+{
+	struct index_geometry *geometry = volume->geometry;
+	struct dm_buffer *page_buffer;
+	u32 first_index_page = map_to_physical_page(geometry, physical_chapter_number, 0);
+	u32 delta_list_number = 0;
+	u32 index_page_number;
+
+	for (index_page_number = 0;
+	     index_page_number < geometry->index_pages_per_chapter;
+	     index_page_number++) {
+		u8 *page_data;
+		u32 physical_page = first_index_page + index_page_number;
+		u32 lists_packed;
+		bool last_page;
+		int result;
+
+		page_data = dm_bufio_new(volume->client, physical_page, &page_buffer);
+		if (IS_ERR(page_data)) {
+			return vdo_log_warning_strerror(-PTR_ERR(page_data),
+							"failed to prepare index page");
+		}
+
+		last_page = ((index_page_number + 1) == geometry->index_pages_per_chapter);
+		result = uds_pack_open_chapter_index_page(chapter_index, page_data,
+							  delta_list_number, last_page,
+							  &lists_packed);
+		if (result != UDS_SUCCESS) {
+			dm_bufio_release(page_buffer);
+			return vdo_log_warning_strerror(result,
+							"failed to pack index page");
+		}
+
+		dm_bufio_mark_buffer_dirty(page_buffer);
+
+		if (lists_packed == 0) {
+			vdo_log_debug("no delta lists packed on chapter %u page %u",
+				      physical_chapter_number, index_page_number);
+		} else {
+			delta_list_number += lists_packed;
+		}
+
+		uds_update_index_page_map(volume->index_page_map,
+					  chapter_index->virtual_chapter_number,
+					  physical_chapter_number, index_page_number,
+					  delta_list_number - 1);
+
+		mutex_lock(&volume->read_threads_mutex);
+		result = donate_index_page_locked(volume, physical_chapter_number,
+						  index_page_number, page_buffer);
+		mutex_unlock(&volume->read_threads_mutex);
+		if (result != UDS_SUCCESS) {
+			dm_bufio_release(page_buffer);
+			return result;
+		}
+	}
+
+	return UDS_SUCCESS;
+}
+
+static u32 encode_tree(u8 record_page[],
+		       const struct uds_volume_record *sorted_pointers[],
+		       u32 next_record, u32 node, u32 node_count)
+{
+	if (node < node_count) {
+		u32 child = (2 * node) + 1;
+
+		next_record = encode_tree(record_page, sorted_pointers, next_record,
+					  child, node_count);
+
+		/*
+		 * In-order traversal: copy the contents of the next record into the page at the
+		 * node offset.
+		 */
+		memcpy(&record_page[node * BYTES_PER_RECORD],
+		       sorted_pointers[next_record++], BYTES_PER_RECORD);
+
+		next_record = encode_tree(record_page, sorted_pointers, next_record,
+					  child + 1, node_count);
+	}
+
+	return next_record;
+}
+
+static int encode_record_page(const struct volume *volume,
+			      const struct uds_volume_record records[], u8 record_page[])
+{
+	int result;
+	u32 i;
+	u32 records_per_page = volume->geometry->records_per_page;
+	const struct uds_volume_record **record_pointers = volume->record_pointers;
+
+	for (i = 0; i < records_per_page; i++)
+		record_pointers[i] = &records[i];
+
+	/*
+	 * Sort the record pointers by using just the names in the records, which is less work than
+	 * sorting the entire record values.
+	 */
+	BUILD_BUG_ON(offsetof(struct uds_volume_record, name) != 0);
+	result = uds_radix_sort(volume->radix_sorter, (const u8 **) record_pointers,
+				records_per_page, UDS_RECORD_NAME_SIZE);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	encode_tree(record_page, record_pointers, 0, 0, records_per_page);
+	return UDS_SUCCESS;
+}
+
+static int write_record_pages(struct volume *volume, u32 physical_chapter_number,
+			      const struct uds_volume_record *records)
+{
+	u32 record_page_number;
+	struct index_geometry *geometry = volume->geometry;
+	struct dm_buffer *page_buffer;
+	const struct uds_volume_record *next_record = records;
+	u32 first_record_page = map_to_physical_page(geometry, physical_chapter_number,
+						     geometry->index_pages_per_chapter);
+
+	for (record_page_number = 0;
+	     record_page_number < geometry->record_pages_per_chapter;
+	     record_page_number++) {
+		u8 *page_data;
+		u32 physical_page = first_record_page + record_page_number;
+		int result;
+
+		page_data = dm_bufio_new(volume->client, physical_page, &page_buffer);
+		if (IS_ERR(page_data)) {
+			return vdo_log_warning_strerror(-PTR_ERR(page_data),
+							"failed to prepare record page");
+		}
+
+		result = encode_record_page(volume, next_record, page_data);
+		if (result != UDS_SUCCESS) {
+			dm_bufio_release(page_buffer);
+			return vdo_log_warning_strerror(result,
+							"failed to encode record page %u",
+							record_page_number);
+		}
+
+		next_record += geometry->records_per_page;
+		dm_bufio_mark_buffer_dirty(page_buffer);
+		dm_bufio_release(page_buffer);
+	}
+
+	return UDS_SUCCESS;
+}
+
+int uds_write_chapter(struct volume *volume, struct open_chapter_index *chapter_index,
+		      const struct uds_volume_record *records)
+{
+	int result;
+	u32 physical_chapter_number =
+		uds_map_to_physical_chapter(volume->geometry,
+					    chapter_index->virtual_chapter_number);
+
+	result = write_index_pages(volume, physical_chapter_number, chapter_index);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	result = write_record_pages(volume, physical_chapter_number, records);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	result = -dm_bufio_write_dirty_buffers(volume->client);
+	if (result != UDS_SUCCESS)
+		vdo_log_error_strerror(result, "cannot sync chapter to volume");
+
+	return result;
+}
+
+static void probe_chapter(struct volume *volume, u32 chapter_number,
+			  u64 *virtual_chapter_number)
+{
+	const struct index_geometry *geometry = volume->geometry;
+	u32 expected_list_number = 0;
+	u32 i;
+	u64 vcn = BAD_CHAPTER;
+
+	*virtual_chapter_number = BAD_CHAPTER;
+	dm_bufio_prefetch(volume->client,
+			  map_to_physical_page(geometry, chapter_number, 0),
+			  geometry->index_pages_per_chapter);
+
+	for (i = 0; i < geometry->index_pages_per_chapter; i++) {
+		struct delta_index_page *page;
+		int result;
+
+		result = uds_get_volume_index_page(volume, chapter_number, i, &page);
+		if (result != UDS_SUCCESS)
+			return;
+
+		if (page->virtual_chapter_number == BAD_CHAPTER) {
+			vdo_log_error("corrupt index page in chapter %u",
+				      chapter_number);
+			return;
+		}
+
+		if (vcn == BAD_CHAPTER) {
+			vcn = page->virtual_chapter_number;
+		} else if (page->virtual_chapter_number != vcn) {
+			vdo_log_error("inconsistent chapter %u index page %u: expected vcn %llu, got vcn %llu",
+				      chapter_number, i, (unsigned long long) vcn,
+				      (unsigned long long) page->virtual_chapter_number);
+			return;
+		}
+
+		if (expected_list_number != page->lowest_list_number) {
+			vdo_log_error("inconsistent chapter %u index page %u: expected list number %u, got list number %u",
+				      chapter_number, i, expected_list_number,
+				      page->lowest_list_number);
+			return;
+		}
+		expected_list_number = page->highest_list_number + 1;
+
+		result = uds_validate_chapter_index_page(page, geometry);
+		if (result != UDS_SUCCESS)
+			return;
+	}
+
+	if (chapter_number != uds_map_to_physical_chapter(geometry, vcn)) {
+		vdo_log_error("chapter %u vcn %llu is out of phase (%u)", chapter_number,
+			      (unsigned long long) vcn, geometry->chapters_per_volume);
+		return;
+	}
+
+	*virtual_chapter_number = vcn;
+}
+
+/* Find the last valid physical chapter in the volume. */
+static void find_real_end_of_volume(struct volume *volume, u32 limit, u32 *limit_ptr)
+{
+	u32 span = 1;
+	u32 tries = 0;
+
+	while (limit > 0) {
+		u32 chapter = (span > limit) ? 0 : limit - span;
+		u64 vcn = 0;
+
+		probe_chapter(volume, chapter, &vcn);
+		if (vcn == BAD_CHAPTER) {
+			limit = chapter;
+			if (++tries > 1)
+				span *= 2;
+		} else {
+			if (span == 1)
+				break;
+			span /= 2;
+			tries = 0;
+		}
+	}
+
+	*limit_ptr = limit;
+}
+
+static int find_chapter_limits(struct volume *volume, u32 chapter_limit, u64 *lowest_vcn,
+			       u64 *highest_vcn)
+{
+	struct index_geometry *geometry = volume->geometry;
+	u64 zero_vcn;
+	u64 lowest = BAD_CHAPTER;
+	u64 highest = BAD_CHAPTER;
+	u64 moved_chapter = BAD_CHAPTER;
+	u32 left_chapter = 0;
+	u32 right_chapter = 0;
+	u32 bad_chapters = 0;
+
+	/*
+	 * This method assumes there is at most one run of contiguous bad chapters caused by
+	 * unflushed writes. Either the bad spot is at the beginning and end, or somewhere in the
+	 * middle. Wherever it is, the highest and lowest VCNs are adjacent to it. Otherwise the
+	 * volume is cleanly saved and somewhere in the middle of it the highest VCN immediately
+	 * precedes the lowest one.
+	 */
+
+	/* It doesn't matter if this results in a bad spot (BAD_CHAPTER). */
+	probe_chapter(volume, 0, &zero_vcn);
+
+	/*
+	 * Binary search for end of the discontinuity in the monotonically increasing virtual
+	 * chapter numbers; bad spots are treated as a span of BAD_CHAPTER values. In effect we're
+	 * searching for the index of the smallest value less than zero_vcn. In the case we go off
+	 * the end it means that chapter 0 has the lowest vcn.
+	 *
+	 * If a virtual chapter is out-of-order, it will be the one moved by conversion. Always
+	 * skip over the moved chapter when searching, adding it to the range at the end if
+	 * necessary.
+	 */
+	if (geometry->remapped_physical > 0) {
+		u64 remapped_vcn;
+
+		probe_chapter(volume, geometry->remapped_physical, &remapped_vcn);
+		if (remapped_vcn == geometry->remapped_virtual)
+			moved_chapter = geometry->remapped_physical;
+	}
+
+	left_chapter = 0;
+	right_chapter = chapter_limit;
+
+	while (left_chapter < right_chapter) {
+		u64 probe_vcn;
+		u32 chapter = (left_chapter + right_chapter) / 2;
+
+		if (chapter == moved_chapter)
+			chapter--;
+
+		probe_chapter(volume, chapter, &probe_vcn);
+		if (zero_vcn <= probe_vcn) {
+			left_chapter = chapter + 1;
+			if (left_chapter == moved_chapter)
+				left_chapter++;
+		} else {
+			right_chapter = chapter;
+		}
+	}
+
+	/* If left_chapter goes off the end, chapter 0 has the lowest virtual chapter number.*/
+	if (left_chapter >= chapter_limit)
+		left_chapter = 0;
+
+	/* At this point, left_chapter is the chapter with the lowest virtual chapter number. */
+	probe_chapter(volume, left_chapter, &lowest);
+
+	/* The moved chapter might be the lowest in the range. */
+	if ((moved_chapter != BAD_CHAPTER) && (lowest == geometry->remapped_virtual + 1))
+		lowest = geometry->remapped_virtual;
+
+	/*
+	 * Circularly scan backwards, moving over any bad chapters until encountering a good one,
+	 * which is the chapter with the highest vcn.
+	 */
+	while (highest == BAD_CHAPTER) {
+		right_chapter = (right_chapter + chapter_limit - 1) % chapter_limit;
+		if (right_chapter == moved_chapter)
+			continue;
+
+		probe_chapter(volume, right_chapter, &highest);
+		if (bad_chapters++ >= MAX_BAD_CHAPTERS) {
+			vdo_log_error("too many bad chapters in volume: %u",
+				      bad_chapters);
+			return UDS_CORRUPT_DATA;
+		}
+	}
+
+	*lowest_vcn = lowest;
+	*highest_vcn = highest;
+	return UDS_SUCCESS;
+}
+
+/*
+ * Find the highest and lowest contiguous chapters present in the volume and determine their
+ * virtual chapter numbers. This is used by rebuild.
+ */
+int uds_find_volume_chapter_boundaries(struct volume *volume, u64 *lowest_vcn,
+				       u64 *highest_vcn, bool *is_empty)
+{
+	u32 chapter_limit = volume->geometry->chapters_per_volume;
+
+	find_real_end_of_volume(volume, chapter_limit, &chapter_limit);
+	if (chapter_limit == 0) {
+		*lowest_vcn = 0;
+		*highest_vcn = 0;
+		*is_empty = true;
+		return UDS_SUCCESS;
+	}
+
+	*is_empty = false;
+	return find_chapter_limits(volume, chapter_limit, lowest_vcn, highest_vcn);
+}
+
+int __must_check uds_replace_volume_storage(struct volume *volume,
+					    struct index_layout *layout,
+					    struct block_device *bdev)
+{
+	int result;
+	u32 i;
+
+	result = uds_replace_index_layout_storage(layout, bdev);
+	if (result != UDS_SUCCESS)
+		return result;
+
+	/* Release all outstanding dm_bufio objects */
+	for (i = 0; i < volume->page_cache.indexable_pages; i++)
+		volume->page_cache.index[i] = volume->page_cache.cache_slots;
+	for (i = 0; i < volume->page_cache.cache_slots; i++)
+		clear_cache_page(&volume->page_cache, &volume->page_cache.cache[i]);
+	if (volume->sparse_cache != NULL)
+		uds_invalidate_sparse_cache(volume->sparse_cache);
+	if (volume->client != NULL)
+		dm_bufio_client_destroy(vdo_forget(volume->client));
+
+	return uds_open_volume_bufio(layout, volume->geometry->bytes_per_page,
+				     volume->reserved_buffers, &volume->client);
+}
+
+static int __must_check initialize_page_cache(struct page_cache *cache,
+					      const struct index_geometry *geometry,
+					      u32 chapters_in_cache,
+					      unsigned int zone_count)
+{
+	int result;
+	u32 i;
+
+	cache->indexable_pages = geometry->pages_per_volume + 1;
+	cache->cache_slots = chapters_in_cache * geometry->record_pages_per_chapter;
+	cache->zone_count = zone_count;
+	atomic64_set(&cache->clock, 1);
+
+	result = VDO_ASSERT((cache->cache_slots <= VOLUME_CACHE_MAX_ENTRIES),
+			    "requested cache size, %u, within limit %u",
+			    cache->cache_slots, VOLUME_CACHE_MAX_ENTRIES);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_allocate(VOLUME_CACHE_MAX_QUEUED_READS, struct queued_read,
+			      "volume read queue", &cache->read_queue);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_allocate(cache->zone_count, struct search_pending_counter,
+			      "Volume Cache Zones", &cache->search_pending_counters);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_allocate(cache->indexable_pages, u16, "page cache index",
+			      &cache->index);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	result = vdo_allocate(cache->cache_slots, struct cached_page, "page cache cache",
+			      &cache->cache);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	/* Initialize index values to invalid values. */
+	for (i = 0; i < cache->indexable_pages; i++)
+		cache->index[i] = cache->cache_slots;
+
+	for (i = 0; i < cache->cache_slots; i++)
+		clear_cache_page(cache, &cache->cache[i]);
+
+	return UDS_SUCCESS;
+}
+
+int uds_make_volume(const struct uds_configuration *config, struct index_layout *layout,
+		    struct volume **new_volume)
+{
+	unsigned int i;
+	struct volume *volume = NULL;
+	struct index_geometry *geometry;
+	unsigned int reserved_buffers;
+	int result;
+
+	result = vdo_allocate(1, struct volume, "volume", &volume);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	volume->nonce = uds_get_volume_nonce(layout);
+
+	result = uds_copy_index_geometry(config->geometry, &volume->geometry);
+	if (result != UDS_SUCCESS) {
+		uds_free_volume(volume);
+		return vdo_log_warning_strerror(result,
+						"failed to allocate geometry: error");
+	}
+	geometry = volume->geometry;
+
+	/*
+	 * Reserve a buffer for each entry in the page cache, one for the chapter writer, and one
+	 * for each entry in the sparse cache.
+	 */
+	reserved_buffers = config->cache_chapters * geometry->record_pages_per_chapter;
+	reserved_buffers += 1;
+	if (uds_is_sparse_index_geometry(geometry))
+		reserved_buffers += (config->cache_chapters * geometry->index_pages_per_chapter);
+	volume->reserved_buffers = reserved_buffers;
+	result = uds_open_volume_bufio(layout, geometry->bytes_per_page,
+				       volume->reserved_buffers, &volume->client);
+	if (result != UDS_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	result = uds_make_radix_sorter(geometry->records_per_page,
+				       &volume->radix_sorter);
+	if (result != UDS_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	result = vdo_allocate(geometry->records_per_page,
+			      const struct uds_volume_record *, "record pointers",
+			      &volume->record_pointers);
+	if (result != VDO_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	if (uds_is_sparse_index_geometry(geometry)) {
+		size_t page_size = sizeof(struct delta_index_page) + geometry->bytes_per_page;
+
+		result = uds_make_sparse_cache(geometry, config->cache_chapters,
+					       config->zone_count,
+					       &volume->sparse_cache);
+		if (result != UDS_SUCCESS) {
+			uds_free_volume(volume);
+			return result;
+		}
+
+		volume->cache_size =
+			page_size * geometry->index_pages_per_chapter * config->cache_chapters;
+	}
+
+	result = initialize_page_cache(&volume->page_cache, geometry,
+				       config->cache_chapters, config->zone_count);
+	if (result != UDS_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	volume->cache_size += volume->page_cache.cache_slots * sizeof(struct delta_index_page);
+	result = uds_make_index_page_map(geometry, &volume->index_page_map);
+	if (result != UDS_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	mutex_init(&volume->read_threads_mutex);
+	uds_init_cond(&volume->read_threads_read_done_cond);
+	uds_init_cond(&volume->read_threads_cond);
+
+	result = vdo_allocate(config->read_threads, struct thread *, "reader threads",
+			      &volume->reader_threads);
+	if (result != VDO_SUCCESS) {
+		uds_free_volume(volume);
+		return result;
+	}
+
+	for (i = 0; i < config->read_threads; i++) {
+		result = vdo_create_thread(read_thread_function, (void *) volume,
+					   "reader", &volume->reader_threads[i]);
+		if (result != VDO_SUCCESS) {
+			uds_free_volume(volume);
+			return result;
+		}
+
+		volume->read_thread_count = i + 1;
+	}
+
+	*new_volume = volume;
+	return UDS_SUCCESS;
+}
+
+static void uninitialize_page_cache(struct page_cache *cache)
+{
+	u16 i;
+
+	if (cache->cache != NULL) {
+		for (i = 0; i < cache->cache_slots; i++)
+			release_page_buffer(&cache->cache[i]);
+	}
+	vdo_free(cache->index);
+	vdo_free(cache->cache);
+	vdo_free(cache->search_pending_counters);
+	vdo_free(cache->read_queue);
+}
+
+void uds_free_volume(struct volume *volume)
+{
+	if (volume == NULL)
+		return;
+
+	if (volume->reader_threads != NULL) {
+		unsigned int i;
+
+		/* This works even if some threads weren't started. */
+		mutex_lock(&volume->read_threads_mutex);
+		volume->read_threads_exiting = true;
+		uds_broadcast_cond(&volume->read_threads_cond);
+		mutex_unlock(&volume->read_threads_mutex);
+		for (i = 0; i < volume->read_thread_count; i++)
+			vdo_join_threads(volume->reader_threads[i]);
+		vdo_free(volume->reader_threads);
+		volume->reader_threads = NULL;
+	}
+
+	/* Must destroy the client AFTER freeing the cached pages. */
+	uninitialize_page_cache(&volume->page_cache);
+	uds_free_sparse_cache(volume->sparse_cache);
+	if (volume->client != NULL)
+		dm_bufio_client_destroy(vdo_forget(volume->client));
+
+	uds_free_index_page_map(volume->index_page_map);
+	uds_free_radix_sorter(volume->radix_sorter);
+	vdo_free(volume->geometry);
+	vdo_free(volume->record_pointers);
+	vdo_free(volume);
+}