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// Copyright 2020 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#pragma once
#include <array>
#include <cstddef>
#include <cstdint>
#include <span>
#include <string_view>
#include <type_traits>
#include "pw_containers/vector.h"
#include "pw_kvs/checksum.h"
#include "pw_kvs/flash_memory.h"
#include "pw_kvs/format.h"
#include "pw_kvs/internal/entry.h"
#include "pw_kvs/internal/entry_cache.h"
#include "pw_kvs/internal/key_descriptor.h"
#include "pw_kvs/internal/sectors.h"
#include "pw_kvs/internal/span_traits.h"
#include "pw_status/status.h"
#include "pw_status/status_with_size.h"
namespace pw::kvs {
enum class GargbageCollectOnWrite {
// Disable all automatic garbage collection on write.
kDisabled,
// Allow up to a single sector, if needed, to be garbage collected on write.
kOneSector,
// Allow as many sectors as needed be garbage collected on write.
kAsManySectorsNeeded,
};
enum class ErrorRecovery {
// Immediately do full recovery of any errors that are detected.
kImmediate,
// Recover from errors, but delay time consuming recovery steps until later
// as part of other time consuming operations. Such as waiting to garbage
// collect sectors with corrupt entries until the next garbage collection.
kLazy,
// Only recover from errors when manually triggered as part of maintenance
// operations. This is not recommended for normal use, only for test or
// read-only use.
kManual,
};
struct Options {
// Perform garbage collection if necessary when writing. If not kDisabled,
// garbage collection is attempted if space for an entry cannot be found. This
// is a relatively lengthy operation. If kDisabled, Put calls that would
// require garbage collection fail with RESOURCE_EXHAUSTED.
GargbageCollectOnWrite gc_on_write = GargbageCollectOnWrite::kOneSector;
// When the KVS handles errors that are discovered, such as corrupt entries,
// not enough redundant copys of an entry, etc.
ErrorRecovery recovery = ErrorRecovery::kLazy;
// Verify an entry's checksum after reading it from flash.
bool verify_on_read = true;
// Verify an in-flash entry's checksum after writing it.
bool verify_on_write = true;
};
class KeyValueStore {
public:
// KeyValueStores are declared as instances of
// KeyValueStoreBuffer<MAX_ENTRIES, MAX_SECTORS>, which allocates buffers for
// tracking entries and flash sectors.
// Initializes the key-value store. Must be called before calling other
// functions.
//
// Return values:
//
// OK: KVS successfully initialized.
// DATA_LOSS: KVS initialized and is usable, but contains corrupt data.
// UNKNOWN: Unknown error. KVS is not initialized.
//
Status Init();
bool initialized() const {
return initialized_ == InitializationState::kReady;
}
// Reads the value of an entry in the KVS. The value is read into the provided
// buffer and the number of bytes read is returned. If desired, the read can
// be started at an offset.
//
// If the output buffer is too small for the value, Get returns
// RESOURCE_EXHAUSTED with the number of bytes read. The remainder of the
// value can be read by calling get with an offset.
//
// OK: the entry was successfully read
// NOT_FOUND: the key is not present in the KVS
// DATA_LOSS: found the entry, but the data was corrupted
// RESOURCE_EXHAUSTED: the buffer could not fit the entire value, but as
// many bytes as possible were written to it
// FAILED_PRECONDITION: the KVS is not initialized
// INVALID_ARGUMENT: key is empty or too long or value is too large
//
StatusWithSize Get(std::string_view key,
std::span<std::byte> value,
size_t offset_bytes = 0) const;
// This overload of Get accepts a pointer to a trivially copyable object.
// If the value is an array, call Get with
// std::as_writable_bytes(std::span(array)), or pass a pointer to the array
// instead of the array itself.
template <typename Pointer,
typename = std::enable_if_t<std::is_pointer_v<Pointer>>>
Status Get(const std::string_view& key, const Pointer& pointer) const {
using T = std::remove_reference_t<std::remove_pointer_t<Pointer>>;
CheckThatObjectCanBePutOrGet<T>();
return FixedSizeGet(key, pointer, sizeof(T));
}
// Adds a key-value entry to the KVS. If the key was already present, its
// value is overwritten.
//
// The value may be a std::span of bytes or a trivially copyable object.
//
// In the current implementation, all keys in the KVS must have a unique hash.
// If Put is called with a key whose hash matches an existing key, nothing
// is added and ALREADY_EXISTS is returned.
//
// OK: the entry was successfully added or updated
// DATA_LOSS: checksum validation failed after writing the data
// RESOURCE_EXHAUSTED: there is not enough space to add the entry
// ALREADY_EXISTS: the entry could not be added because a different key
// with the same hash is already in the KVS
// FAILED_PRECONDITION: the KVS is not initialized
// INVALID_ARGUMENT: key is empty or too long or value is too large
//
template <typename T>
Status Put(const std::string_view& key, const T& value) {
if constexpr (ConvertsToSpan<T>::value) {
return PutBytes(key, std::as_bytes(std::span(value)));
} else {
CheckThatObjectCanBePutOrGet<T>();
return PutBytes(key, std::as_bytes(std::span(&value, 1)));
}
}
// Removes a key-value entry from the KVS.
//
// OK: the entry was successfully added or updated
// NOT_FOUND: the key is not present in the KVS
// DATA_LOSS: checksum validation failed after recording the erase
// RESOURCE_EXHAUSTED: insufficient space to mark the entry as deleted
// FAILED_PRECONDITION: the KVS is not initialized
// INVALID_ARGUMENT: key is empty or too long
//
Status Delete(std::string_view key);
// Returns the size of the value corresponding to the key.
//
// OK: the size was returned successfully
// NOT_FOUND: the key is not present in the KVS
// DATA_LOSS: checksum validation failed after reading the entry
// FAILED_PRECONDITION: the KVS is not initialized
// INVALID_ARGUMENT: key is empty or too long
//
StatusWithSize ValueSize(std::string_view key) const;
// Perform all maintenance possible, including all neeeded repairing of
// corruption and garbage collection of all reclaimable space in the KVS. When
// configured for manual recovery, this is the only way KVS repair is
// triggered.
Status FullMaintenance();
// Perform a portion of KVS maintenance. If configured for at least lazy
// recovery, will do any needed repairing of corruption. Does garbage
// collection of part of the KVS, typically a single sector or similar unit
// that makes sense for the KVS implementation.
Status PartialMaintenance();
void LogDebugInfo() const;
// Classes and functions to support STL-style iteration.
class iterator;
class Item {
public:
// The key as a null-terminated string.
const char* key() const { return key_buffer_.data(); }
// Gets the value referred to by this iterator. Equivalent to
// KeyValueStore::Get.
StatusWithSize Get(std::span<std::byte> value_buffer,
size_t offset_bytes = 0) const {
return kvs_.Get(key(), *iterator_, value_buffer, offset_bytes);
}
template <typename Pointer,
typename = std::enable_if_t<std::is_pointer_v<Pointer>>>
Status Get(const Pointer& pointer) const {
using T = std::remove_reference_t<std::remove_pointer_t<Pointer>>;
CheckThatObjectCanBePutOrGet<T>();
return kvs_.FixedSizeGet(key(), *iterator_, pointer, sizeof(T));
}
// Reads the size of the value referred to by this iterator. Equivalent to
// KeyValueStore::ValueSize.
StatusWithSize ValueSize() const { return kvs_.ValueSize(*iterator_); }
private:
friend class iterator;
constexpr Item(const KeyValueStore& kvs,
const internal::EntryCache::const_iterator& item_iterator)
: kvs_(kvs), iterator_(item_iterator), key_buffer_{} {}
void ReadKey();
const KeyValueStore& kvs_;
internal::EntryCache::const_iterator iterator_;
// Buffer large enough for a null-terminated version of any valid key.
std::array<char, internal::Entry::kMaxKeyLength + 1> key_buffer_;
};
class iterator {
public:
iterator& operator++();
iterator& operator++(int) { return operator++(); }
// Reads the entry's key from flash.
const Item& operator*() {
item_.ReadKey();
return item_;
}
const Item* operator->() {
return &operator*(); // Read the key into the Item object.
}
constexpr bool operator==(const iterator& rhs) const {
return item_.iterator_ == rhs.item_.iterator_;
}
constexpr bool operator!=(const iterator& rhs) const {
return item_.iterator_ != rhs.item_.iterator_;
}
private:
friend class KeyValueStore;
constexpr iterator(
const KeyValueStore& kvs,
const internal::EntryCache::const_iterator& item_iterator)
: item_(kvs, item_iterator) {}
Item item_;
};
using const_iterator = iterator; // Standard alias for iterable types.
iterator begin() const;
iterator end() const { return iterator(*this, entry_cache_.end()); }
// Returns the number of valid entries in the KeyValueStore.
size_t size() const { return entry_cache_.present_entries(); }
size_t max_size() const { return entry_cache_.max_entries(); }
size_t empty() const { return size() == 0u; }
// Returns the number of transactions that have occurred since the KVS was
// first used. This value is retained across initializations, but is reset if
// the underlying flash is erased.
uint32_t transaction_count() const { return last_transaction_id_; }
struct StorageStats {
size_t writable_bytes;
size_t in_use_bytes;
size_t reclaimable_bytes;
size_t corrupt_sectors_recovered;
size_t missing_redundant_entries_recovered;
};
StorageStats GetStorageStats() const;
// Level of redundancy to use for writing entries.
size_t redundancy() const { return entry_cache_.redundancy(); }
bool error_detected() const { return error_detected_; }
// Check KVS for any error conditions. Primarily intended for test and
// internal use.
bool CheckForErrors();
protected:
using Address = FlashPartition::Address;
using Entry = internal::Entry;
using KeyDescriptor = internal::KeyDescriptor;
using SectorDescriptor = internal::SectorDescriptor;
// In the future, will be able to provide additional EntryFormats for
// backwards compatibility.
KeyValueStore(FlashPartition* partition,
std::span<const EntryFormat> formats,
const Options& options,
size_t redundancy,
Vector<SectorDescriptor>& sector_descriptor_list,
const SectorDescriptor** temp_sectors_to_skip,
Vector<KeyDescriptor>& key_descriptor_list,
Address* addresses);
private:
using EntryMetadata = internal::EntryMetadata;
using EntryState = internal::EntryState;
template <typename T>
static constexpr void CheckThatObjectCanBePutOrGet() {
static_assert(
std::is_trivially_copyable_v<T> && !std::is_pointer_v<T>,
"Only trivially copyable, non-pointer objects may be Put and Get by "
"value. Any value may be stored by converting it to a byte std::span "
"with std::as_bytes(std::span(&value, 1)) or "
"std::as_writable_bytes(std::span(&value, 1)).");
}
Status InitializeMetadata();
Status LoadEntry(Address entry_address, Address* next_entry_address);
Status ScanForEntry(const SectorDescriptor& sector,
Address start_address,
Address* next_entry_address);
Status PutBytes(std::string_view key, std::span<const std::byte> value);
StatusWithSize ValueSize(const EntryMetadata& metadata) const;
Status ReadEntry(const EntryMetadata& metadata, Entry& entry) const;
// Finds the metadata for an entry matching a particular key. Searches for a
// KeyDescriptor that matches this key and sets *metadata to point to it if
// one is found.
//
// OK: there is a matching descriptor and *metadata is set
// NOT_FOUND: there is no descriptor that matches this key, but this key
// has a unique hash (and could potentially be added to the
// KVS)
// ALREADY_EXISTS: there is no descriptor that matches this key, but the
// key's hash collides with the hash for an existing
// descriptor
//
Status FindEntry(std::string_view key, EntryMetadata* metadata) const;
// Searches for a KeyDescriptor that matches this key and sets *metadata to
// point to it if one is found.
//
// OK: there is a matching descriptor and *metadata is set
// NOT_FOUND: there is no descriptor that matches this key
//
Status FindExisting(std::string_view key, EntryMetadata* metadata) const;
StatusWithSize Get(std::string_view key,
const EntryMetadata& metadata,
std::span<std::byte> value_buffer,
size_t offset_bytes) const;
Status FixedSizeGet(std::string_view key,
void* value,
size_t size_bytes) const;
Status FixedSizeGet(std::string_view key,
const EntryMetadata& descriptor,
void* value,
size_t size_bytes) const;
Status CheckWriteOperation(std::string_view key) const;
Status CheckReadOperation(std::string_view key) const;
Status WriteEntryForExistingKey(EntryMetadata& metadata,
EntryState new_state,
std::string_view key,
std::span<const std::byte> value);
Status WriteEntryForNewKey(std::string_view key,
std::span<const std::byte> value);
Status WriteEntry(std::string_view key,
std::span<const std::byte> value,
EntryState new_state,
EntryMetadata* prior_metadata = nullptr,
const internal::Entry* prior_entry = nullptr);
EntryMetadata CreateOrUpdateKeyDescriptor(const Entry& new_entry,
std::string_view key,
EntryMetadata* prior_metadata,
size_t prior_size);
EntryMetadata UpdateKeyDescriptor(const Entry& entry,
Address new_address,
EntryMetadata* prior_metadata,
size_t prior_size);
Status GetAddressesForWrite(Address* write_addresses, size_t write_size);
Status GetSectorForWrite(SectorDescriptor** sector,
size_t entry_size,
std::span<const Address> addresses_to_skip);
Status MarkSectorCorruptIfNotOk(Status status, SectorDescriptor* sector);
Status AppendEntry(const Entry& entry,
std::string_view key,
std::span<const std::byte> value);
StatusWithSize CopyEntryToSector(Entry& entry,
SectorDescriptor* new_sector,
Address new_address);
Status RelocateEntry(const EntryMetadata& metadata,
KeyValueStore::Address& address,
std::span<const Address> addresses_to_skip);
// Find and garbage collect a singe sector that does not include an address to
// skip.
Status GarbageCollect(std::span<const Address> addresses_to_skip);
Status RelocateKeyAddressesInSector(
SectorDescriptor& sector_to_gc,
const EntryMetadata& descriptor,
std::span<const Address> addresses_to_skip);
Status GarbageCollectSector(SectorDescriptor& sector_to_gc,
std::span<const Address> addresses_to_skip);
// Ensure that all entries are on the primary (first) format. Entries that are
// not on the primary format are rewritten.
//
// Return: status + number of entries updated.
StatusWithSize UpdateEntriesToPrimaryFormat();
Status AddRedundantEntries(EntryMetadata& metadata);
Status RepairCorruptSectors();
Status EnsureFreeSectorExists();
Status EnsureEntryRedundancy();
Status FixErrors();
Status Repair();
internal::Entry CreateEntry(Address address,
std::string_view key,
std::span<const std::byte> value,
EntryState state);
void LogSectors() const;
void LogKeyDescriptor() const;
FlashPartition& partition_;
const internal::EntryFormats formats_;
// List of sectors used by this KVS.
internal::Sectors sectors_;
// Unordered list of KeyDescriptors. Finding a key requires scanning and
// verifying a match by reading the actual entry.
internal::EntryCache entry_cache_;
Options options_;
// Threshold value for when to garbage collect all stale data. Above the
// threshold, GC all reclaimable bytes regardless of if valid data is in
// sector. Below the threshold, only GC sectors with reclaimable bytes and no
// valid bytes. The threshold is based on the portion of KVS capacity used by
// valid bytes.
static constexpr size_t kGcUsageThresholdPercentage = 70;
enum class InitializationState {
// KVS Init() has not been called and KVS is not usable.
kNotInitialized,
// KVS Init() run but not all the needed invariants are met for an operating
// KVS. KVS is not writable, but read operaions are possible.
kNeedsMaintenance,
// KVS is fully ready for use.
kReady,
};
InitializationState initialized_;
// error_detected_ needs to be set from const KVS methods (such as Get), so
// make it mutable.
mutable bool error_detected_;
struct ErrorStats {
size_t corrupt_sectors_recovered;
size_t missing_redundant_entries_recovered;
};
ErrorStats error_stats_;
uint32_t last_transaction_id_;
};
template <size_t kMaxEntries,
size_t kMaxUsableSectors,
size_t kRedundancy = 1,
size_t kEntryFormats = 1>
class KeyValueStoreBuffer : public KeyValueStore {
public:
// Constructs a KeyValueStore on the partition, with support for one
// EntryFormat (kEntryFormats must be 1).
KeyValueStoreBuffer(FlashPartition* partition,
const EntryFormat& format,
const Options& options = {})
: KeyValueStoreBuffer(
partition,
std::span(reinterpret_cast<const EntryFormat (&)[1]>(format)),
options) {
static_assert(kEntryFormats == 1,
"kEntryFormats EntryFormats must be specified");
}
// Constructs a KeyValueStore on the partition. Supports multiple entry
// formats. The first EntryFormat is used for new entries.
KeyValueStoreBuffer(FlashPartition* partition,
std::span<const EntryFormat, kEntryFormats> formats,
const Options& options = {})
: KeyValueStore(partition,
formats_,
options,
kRedundancy,
sectors_,
temp_sectors_to_skip_,
key_descriptors_,
addresses_) {
std::copy(formats.begin(), formats.end(), formats_.begin());
}
private:
static_assert(kMaxEntries > 0u);
static_assert(kMaxUsableSectors > 0u);
static_assert(kRedundancy > 0u);
static_assert(kEntryFormats > 0u);
Vector<SectorDescriptor, kMaxUsableSectors> sectors_;
// Allocate space for an list of SectorDescriptors to avoid while searching
// for space to write entries. This is used to avoid changing sectors that are
// reserved for a new entry or marked as having other redundant copies of an
// entry. Up to kRedundancy sectors are reserved for a new entry, and up to
// kRedundancy - 1 sectors can have redundant copies of an entry, giving a
// maximum of 2 * kRedundancy - 1 sectors to avoid.
const SectorDescriptor* temp_sectors_to_skip_[2 * kRedundancy - 1];
// KeyDescriptors for use by the KVS's EntryCache.
Vector<KeyDescriptor, kMaxEntries> key_descriptors_;
// An array of addresses associated with the KeyDescriptors for use with the
// EntryCache. To support having KeyValueStores with different redundancies,
// the addresses are stored in a parallel array instead of inside
// KeyDescriptors.
internal::EntryCache::AddressList<kRedundancy, kMaxEntries> addresses_;
// EntryFormats that can be read by this KeyValueStore.
std::array<EntryFormat, kEntryFormats> formats_;
};
} // namespace pw::kvs