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+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef UDS_DELTA_INDEX_H
+#define UDS_DELTA_INDEX_H
+
+#include <linux/cache.h>
+
+#include "numeric.h"
+#include "time-utils.h"
+
+#include "config.h"
+#include "io-factory.h"
+
+/*
+ * A delta index is a key-value store, where each entry maps an address (the key) to a payload (the
+ * value). The entries are sorted by address, and only the delta between successive addresses is
+ * stored in the entry. The addresses are assumed to be uniformly distributed, and the deltas are
+ * therefore exponentially distributed.
+ *
+ * A delta_index can either be mutable or immutable depending on its expected use. The immutable
+ * form of a delta index is used for the indexes of closed chapters committed to the volume. The
+ * mutable form of a delta index is used by the volume index, and also by the chapter index in an
+ * open chapter. Like the index as a whole, each mutable delta index is divided into a number of
+ * independent zones.
+ */
+
+struct delta_list {
+ /* The offset of the delta list start, in bits */
+ u64 start;
+ /* The number of bits in the delta list */
+ u16 size;
+ /* Where the last search "found" the key, in bits */
+ u16 save_offset;
+ /* The key for the record just before save_offset */
+ u32 save_key;
+};
+
+struct delta_zone {
+ /* The delta list memory */
+ u8 *memory;
+ /* The delta list headers */
+ struct delta_list *delta_lists;
+ /* Temporary starts of delta lists */
+ u64 *new_offsets;
+ /* Buffered writer for saving an index */
+ struct buffered_writer *buffered_writer;
+ /* The size of delta list memory */
+ size_t size;
+ /* Nanoseconds spent rebalancing */
+ ktime_t rebalance_time;
+ /* Number of memory rebalances */
+ u32 rebalance_count;
+ /* The number of bits in a stored value */
+ u8 value_bits;
+ /* The number of bits in the minimal key code */
+ u16 min_bits;
+ /* The number of keys used in a minimal code */
+ u32 min_keys;
+ /* The number of keys used for another code bit */
+ u32 incr_keys;
+ /* The number of records in the index */
+ u64 record_count;
+ /* The number of collision records */
+ u64 collision_count;
+ /* The number of records removed */
+ u64 discard_count;
+ /* The number of UDS_OVERFLOW errors detected */
+ u64 overflow_count;
+ /* The index of the first delta list */
+ u32 first_list;
+ /* The number of delta lists */
+ u32 list_count;
+ /* Tag belonging to this delta index */
+ u8 tag;
+} __aligned(L1_CACHE_BYTES);
+
+struct delta_list_save_info {
+ /* Tag identifying which delta index this list is in */
+ u8 tag;
+ /* Bit offset of the start of the list data */
+ u8 bit_offset;
+ /* Number of bytes of list data */
+ u16 byte_count;
+ /* The delta list number within the delta index */
+ u32 index;
+} __packed;
+
+struct delta_index {
+ /* The zones */
+ struct delta_zone *delta_zones;
+ /* The number of zones */
+ unsigned int zone_count;
+ /* The number of delta lists */
+ u32 list_count;
+ /* Maximum lists per zone */
+ u32 lists_per_zone;
+ /* Total memory allocated to this index */
+ size_t memory_size;
+ /* The number of non-empty lists at load time per zone */
+ u32 load_lists[MAX_ZONES];
+ /* True if this index is mutable */
+ bool mutable;
+ /* Tag belonging to this delta index */
+ u8 tag;
+};
+
+/*
+ * A delta_index_page describes a single page of a chapter index. The delta_index field allows the
+ * page to be treated as an immutable delta_index. We use the delta_zone field to treat the chapter
+ * index page as a single zone index, and without the need to do an additional memory allocation.
+ */
+struct delta_index_page {
+ struct delta_index delta_index;
+ /* These values are loaded from the delta_page_header */
+ u32 lowest_list_number;
+ u32 highest_list_number;
+ u64 virtual_chapter_number;
+ /* This structure describes the single zone of a delta index page. */
+ struct delta_zone delta_zone;
+};
+
+/*
+ * Notes on the delta_index_entries:
+ *
+ * The fields documented as "public" can be read by any code that uses a delta_index. The fields
+ * documented as "private" carry information between delta_index method calls and should not be
+ * used outside the delta_index module.
+ *
+ * (1) The delta_index_entry is used like an iterator when searching a delta list.
+ *
+ * (2) It is also the result of a successful search and can be used to refer to the element found
+ * by the search.
+ *
+ * (3) It is also the result of an unsuccessful search and can be used to refer to the insertion
+ * point for a new record.
+ *
+ * (4) If at_end is true, the delta_list entry can only be used as the insertion point for a new
+ * record at the end of the list.
+ *
+ * (5) If at_end is false and is_collision is true, the delta_list entry fields refer to a
+ * collision entry in the list, and the delta_list entry can be used as a reference to this
+ * entry.
+ *
+ * (6) If at_end is false and is_collision is false, the delta_list entry fields refer to a
+ * non-collision entry in the list. Such delta_list entries can be used as a reference to a
+ * found entry, or an insertion point for a non-collision entry before this entry, or an
+ * insertion point for a collision entry that collides with this entry.
+ */
+struct delta_index_entry {
+ /* Public fields */
+ /* The key for this entry */
+ u32 key;
+ /* We are after the last list entry */
+ bool at_end;
+ /* This record is a collision */
+ bool is_collision;
+
+ /* Private fields */
+ /* This delta list overflowed */
+ bool list_overflow;
+ /* The number of bits used for the value */
+ u8 value_bits;
+ /* The number of bits used for the entire entry */
+ u16 entry_bits;
+ /* The delta index zone */
+ struct delta_zone *delta_zone;
+ /* The delta list containing the entry */
+ struct delta_list *delta_list;
+ /* The delta list number */
+ u32 list_number;
+ /* Bit offset of this entry within the list */
+ u16 offset;
+ /* The delta between this and previous entry */
+ u32 delta;
+ /* Temporary delta list for immutable indices */
+ struct delta_list temp_delta_list;
+};
+
+struct delta_index_stats {
+ /* Number of bytes allocated */
+ size_t memory_allocated;
+ /* Nanoseconds spent rebalancing */
+ ktime_t rebalance_time;
+ /* Number of memory rebalances */
+ u32 rebalance_count;
+ /* The number of records in the index */
+ u64 record_count;
+ /* The number of collision records */
+ u64 collision_count;
+ /* The number of records removed */
+ u64 discard_count;
+ /* The number of UDS_OVERFLOW errors detected */
+ u64 overflow_count;
+ /* The number of delta lists */
+ u32 list_count;
+};
+
+int __must_check uds_initialize_delta_index(struct delta_index *delta_index,
+ unsigned int zone_count, u32 list_count,
+ u32 mean_delta, u32 payload_bits,
+ size_t memory_size, u8 tag);
+
+int __must_check uds_initialize_delta_index_page(struct delta_index_page *delta_index_page,
+ u64 expected_nonce, u32 mean_delta,
+ u32 payload_bits, u8 *memory,
+ size_t memory_size);
+
+void uds_uninitialize_delta_index(struct delta_index *delta_index);
+
+void uds_reset_delta_index(const struct delta_index *delta_index);
+
+int __must_check uds_pack_delta_index_page(const struct delta_index *delta_index,
+ u64 header_nonce, u8 *memory,
+ size_t memory_size,
+ u64 virtual_chapter_number, u32 first_list,
+ u32 *list_count);
+
+int __must_check uds_start_restoring_delta_index(struct delta_index *delta_index,
+ struct buffered_reader **buffered_readers,
+ unsigned int reader_count);
+
+int __must_check uds_finish_restoring_delta_index(struct delta_index *delta_index,
+ struct buffered_reader **buffered_readers,
+ unsigned int reader_count);
+
+int __must_check uds_check_guard_delta_lists(struct buffered_reader **buffered_readers,
+ unsigned int reader_count);
+
+int __must_check uds_start_saving_delta_index(const struct delta_index *delta_index,
+ unsigned int zone_number,
+ struct buffered_writer *buffered_writer);
+
+int __must_check uds_finish_saving_delta_index(const struct delta_index *delta_index,
+ unsigned int zone_number);
+
+int __must_check uds_write_guard_delta_list(struct buffered_writer *buffered_writer);
+
+size_t __must_check uds_compute_delta_index_save_bytes(u32 list_count,
+ size_t memory_size);
+
+int __must_check uds_start_delta_index_search(const struct delta_index *delta_index,
+ u32 list_number, u32 key,
+ struct delta_index_entry *iterator);
+
+int __must_check uds_next_delta_index_entry(struct delta_index_entry *delta_entry);
+
+int __must_check uds_remember_delta_index_offset(const struct delta_index_entry *delta_entry);
+
+int __must_check uds_get_delta_index_entry(const struct delta_index *delta_index,
+ u32 list_number, u32 key, const u8 *name,
+ struct delta_index_entry *delta_entry);
+
+int __must_check uds_get_delta_entry_collision(const struct delta_index_entry *delta_entry,
+ u8 *name);
+
+u32 __must_check uds_get_delta_entry_value(const struct delta_index_entry *delta_entry);
+
+int __must_check uds_set_delta_entry_value(const struct delta_index_entry *delta_entry, u32 value);
+
+int __must_check uds_put_delta_index_entry(struct delta_index_entry *delta_entry, u32 key,
+ u32 value, const u8 *name);
+
+int __must_check uds_remove_delta_index_entry(struct delta_index_entry *delta_entry);
+
+void uds_get_delta_index_stats(const struct delta_index *delta_index,
+ struct delta_index_stats *stats);
+
+size_t __must_check uds_compute_delta_index_size(u32 entry_count, u32 mean_delta,
+ u32 payload_bits);
+
+u32 uds_get_delta_index_page_count(u32 entry_count, u32 list_count, u32 mean_delta,
+ u32 payload_bits, size_t bytes_per_page);
+
+void uds_log_delta_index_entry(struct delta_index_entry *delta_entry);
+
+#endif /* UDS_DELTA_INDEX_H */