fs_mgr/liblp/reader.cpp - android-core - Git at Google

 /*
  * Copyright (C) 2018 The Android Open Source Project
  *
  * 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
  *
  *      http://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.
  */

 #include "reader.h"

 #include <stddef.h>
 #include <stdlib.h>
 #include <unistd.h>

 #include <functional>

 #include <android-base/file.h>
 #include <android-base/unique_fd.h>

 #include "utility.h"

 namespace android {
 namespace fs_mgr {

 // Helper class for reading descriptors and memory buffers in the same manner.
 class Reader {
   public:
     virtual ~Reader(){};
     virtual bool ReadFully(void* buffer, size_t length) = 0;
 };

 class FileReader final : public Reader {
   public:
     explicit FileReader(int fd) : fd_(fd) {}
     bool ReadFully(void* buffer, size_t length) override {
         return android::base::ReadFully(fd_, buffer, length);
     }

   private:
     int fd_;
 };

 class MemoryReader final : public Reader {
   public:
     MemoryReader(const void* buffer, size_t size)
         : buffer_(reinterpret_cast<const uint8_t*>(buffer)), size_(size), pos_(0) {}
     bool ReadFully(void* out, size_t length) override {
         if (size_ - pos_ < length) {
             errno = EINVAL;
             return false;
         }
         memcpy(out, buffer_ + pos_, length);
         pos_ += length;
         return true;
     }

   private:
     const uint8_t* buffer_;
     size_t size_;
     size_t pos_;
 };

 bool ParseGeometry(const void* buffer, LpMetadataGeometry* geometry) {
     static_assert(sizeof(*geometry) <= LP_METADATA_GEOMETRY_SIZE);
     memcpy(geometry, buffer, sizeof(*geometry));

     // Check the magic signature.
     if (geometry->magic != LP_METADATA_GEOMETRY_MAGIC) {
         LERROR << "Logical partition metadata has invalid geometry magic signature.";
         return false;
     }
     // Reject if the struct size is larger than what we compiled. This is so we
     // can compute a checksum with the |struct_size| field rather than using
     // sizeof.
     if (geometry->struct_size > sizeof(LpMetadataGeometry)) {
         LERROR << "Logical partition metadata has unrecognized fields.";
         return false;
     }
     // Recompute and check the CRC32.
     {
         LpMetadataGeometry temp = *geometry;
         memset(&temp.checksum, 0, sizeof(temp.checksum));
         SHA256(&temp, temp.struct_size, temp.checksum);
         if (memcmp(temp.checksum, geometry->checksum, sizeof(temp.checksum)) != 0) {
             LERROR << "Logical partition metadata has invalid geometry checksum.";
             return false;
         }
     }
     // Check that the struct size is equal (this will have to change if we ever
     // change the struct size in a release).
     if (geometry->struct_size != sizeof(LpMetadataGeometry)) {
         LERROR << "Logical partition metadata has invalid struct size.";
         return false;
     }
     if (geometry->metadata_slot_count == 0) {
         LERROR << "Logical partition metadata has invalid slot count.";
         return false;
     }
     if (geometry->metadata_max_size % LP_SECTOR_SIZE != 0) {
         LERROR << "Metadata max size is not sector-aligned.";
         return false;
     }

     // Check that the metadata area and logical partition areas don't overlap.
     int64_t end_of_metadata =
             GetPrimaryMetadataOffset(*geometry, geometry->metadata_slot_count - 1) +
             geometry->metadata_max_size;
     if (uint64_t(end_of_metadata) > geometry->first_logical_sector * LP_SECTOR_SIZE) {
         LERROR << "Logical partition metadata overlaps with logical partition contents.";
         return false;
     }
     return true;
 }

 // Read and validate geometry information from a block device that holds
 // logical partitions. If the information is corrupted, this will attempt
 // to read it from a secondary backup location.
 bool ReadLogicalPartitionGeometry(int fd, LpMetadataGeometry* geometry) {
     // Read the first 4096 bytes.
     std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(LP_METADATA_GEOMETRY_SIZE);
     if (SeekFile64(fd, 0, SEEK_SET) < 0) {
         PERROR << __PRETTY_FUNCTION__ << "lseek failed";
         return false;
     }
     if (!android::base::ReadFully(fd, buffer.get(), LP_METADATA_GEOMETRY_SIZE)) {
         PERROR << __PRETTY_FUNCTION__ << "read " << LP_METADATA_GEOMETRY_SIZE << " bytes failed";
         return false;
     }
     if (ParseGeometry(buffer.get(), geometry)) {
         return true;
     }

     // Try the backup copy in the last 4096 bytes.
     if (SeekFile64(fd, -LP_METADATA_GEOMETRY_SIZE, SEEK_END) < 0) {
         PERROR << __PRETTY_FUNCTION__ << "lseek failed, offset " << -LP_METADATA_GEOMETRY_SIZE;
         return false;
     }
     if (!android::base::ReadFully(fd, buffer.get(), LP_METADATA_GEOMETRY_SIZE)) {
         PERROR << __PRETTY_FUNCTION__ << "backup read " << LP_METADATA_GEOMETRY_SIZE
                << " bytes failed";
         return false;
     }
     return ParseGeometry(buffer.get(), geometry);
 }

 static bool ValidateTableBounds(const LpMetadataHeader& header,
                                 const LpMetadataTableDescriptor& table) {
     if (table.offset > header.tables_size) {
         return false;
     }
     uint64_t table_size = uint64_t(table.num_entries) * table.entry_size;
     if (header.tables_size - table.offset < table_size) {
         return false;
     }
     return true;
 }

 static bool ValidateMetadataHeader(const LpMetadataHeader& header) {
     // To compute the header's checksum, we have to temporarily set its checksum
     // field to 0.
     {
         LpMetadataHeader temp = header;
         memset(&temp.header_checksum, 0, sizeof(temp.header_checksum));
         SHA256(&temp, sizeof(temp), temp.header_checksum);
         if (memcmp(temp.header_checksum, header.header_checksum, sizeof(temp.header_checksum)) != 0) {
             LERROR << "Logical partition metadata has invalid checksum.";
             return false;
         }
     }

     // Do basic validation of key metadata bits.
     if (header.magic != LP_METADATA_HEADER_MAGIC) {
         LERROR << "Logical partition metadata has invalid magic value.";
         return false;
     }
     // Check that the version is compatible.
     if (header.major_version != LP_METADATA_MAJOR_VERSION ||
         header.minor_version > LP_METADATA_MINOR_VERSION) {
         LERROR << "Logical partition metadata has incompatible version.";
         return false;
     }
     if (!ValidateTableBounds(header, header.partitions) ||
         !ValidateTableBounds(header, header.extents)) {
         LERROR << "Logical partition metadata has invalid table bounds.";
         return false;
     }
     // Check that table entry sizes can accomodate their respective structs. If
     // table sizes change, these checks will have to be adjusted.
     if (header.partitions.entry_size != sizeof(LpMetadataPartition)) {
         LERROR << "Logical partition metadata has invalid partition table entry size.";
         return false;
     }
     if (header.extents.entry_size != sizeof(LpMetadataExtent)) {
         LERROR << "Logical partition metadata has invalid extent table entry size.";
         return false;
     }
     return true;
 }

 // Parse and validate all metadata at the current position in the given file
 // descriptor.
 static std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry,
                                                  Reader* reader) {
     // First read and validate the header.
     std::unique_ptr<LpMetadata> metadata = std::make_unique<LpMetadata>();
     if (!reader->ReadFully(&metadata->header, sizeof(metadata->header))) {
         PERROR << __PRETTY_FUNCTION__ << "read " << sizeof(metadata->header) << "bytes failed";
         return nullptr;
     }
     if (!ValidateMetadataHeader(metadata->header)) {
         return nullptr;
     }
     metadata->geometry = geometry;

     LpMetadataHeader& header = metadata->header;

     // Read the metadata payload. Allocation is fallible in case the metadata is
     // corrupt and has some huge value.
     std::unique_ptr<uint8_t[]> buffer(new (std::nothrow) uint8_t[header.tables_size]);
     if (!buffer) {
         LERROR << "Out of memory reading logical partition tables.";
         return nullptr;
     }
     if (!reader->ReadFully(buffer.get(), header.tables_size)) {
         PERROR << __PRETTY_FUNCTION__ << "read " << header.tables_size << "bytes failed";
         return nullptr;
     }

     uint8_t checksum[32];
     SHA256(buffer.get(), header.tables_size, checksum);
     if (memcmp(checksum, header.tables_checksum, sizeof(checksum)) != 0) {
         LERROR << "Logical partition metadata has invalid table checksum.";
         return nullptr;
     }

     // ValidateTableSize ensured that |cursor| is valid for the number of
     // entries in the table.
     uint8_t* cursor = buffer.get() + header.partitions.offset;
     for (size_t i = 0; i < header.partitions.num_entries; i++) {
         LpMetadataPartition partition;
         memcpy(&partition, cursor, sizeof(partition));
         cursor += header.partitions.entry_size;

         if (partition.attributes & ~LP_PARTITION_ATTRIBUTE_MASK) {
             LERROR << "Logical partition has invalid attribute set.";
             return nullptr;
         }
         if (partition.first_extent_index + partition.num_extents > header.extents.num_entries) {
             LERROR << "Logical partition has invalid extent list.";
             return nullptr;
         }

         metadata->partitions.push_back(partition);
     }

     cursor = buffer.get() + header.extents.offset;
     for (size_t i = 0; i < header.extents.num_entries; i++) {
         LpMetadataExtent extent;
         memcpy(&extent, cursor, sizeof(extent));
         cursor += header.extents.entry_size;

         metadata->extents.push_back(extent);
     }
     return metadata;
 }

 std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry, const void* buffer,
                                           size_t size) {
     MemoryReader reader(buffer, size);
     return ParseMetadata(geometry, &reader);
 }

 std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry, int fd) {
     FileReader reader(fd);
     return ParseMetadata(geometry, &reader);
 }

 std::unique_ptr<LpMetadata> ReadPrimaryMetadata(int fd, const LpMetadataGeometry& geometry,
                                                 uint32_t slot_number) {
     int64_t offset = GetPrimaryMetadataOffset(geometry, slot_number);
     if (SeekFile64(fd, offset, SEEK_SET) < 0) {
         PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << offset;
         return nullptr;
     }
     return ParseMetadata(geometry, fd);
 }

 std::unique_ptr<LpMetadata> ReadBackupMetadata(int fd, const LpMetadataGeometry& geometry,
                                                uint32_t slot_number) {
     int64_t offset = GetBackupMetadataOffset(geometry, slot_number);
     if (SeekFile64(fd, offset, SEEK_END) < 0) {
         PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << offset;
         return nullptr;
     }
     return ParseMetadata(geometry, fd);
 }

 std::unique_ptr<LpMetadata> ReadMetadata(int fd, uint32_t slot_number) {
     LpMetadataGeometry geometry;
     if (!ReadLogicalPartitionGeometry(fd, &geometry)) {
         return nullptr;
     }

     if (slot_number >= geometry.metadata_slot_count) {
         LERROR << __PRETTY_FUNCTION__ << "invalid metadata slot number";
         return nullptr;
     }

     // Read the primary copy, and if that fails, try the backup.
     std::unique_ptr<LpMetadata> metadata = ReadPrimaryMetadata(fd, geometry, slot_number);
     if (metadata) {
         return metadata;
     }
     return ReadBackupMetadata(fd, geometry, slot_number);
 }

 std::unique_ptr<LpMetadata> ReadMetadata(const char* block_device, uint32_t slot_number) {
     android::base::unique_fd fd(open(block_device, O_RDONLY));
     if (fd < 0) {
         PERROR << __PRETTY_FUNCTION__ << "open failed: " << block_device;
         return nullptr;
     }
     return ReadMetadata(fd, slot_number);
 }

 static std::string NameFromFixedArray(const char* name, size_t buffer_size) {
     // If the end of the buffer has a null character, it's safe to assume the
     // buffer is null terminated. Otherwise, we cap the string to the input
     // buffer size.
     if (name[buffer_size - 1] == '\0') {
         return std::string(name);
     }
     return std::string(name, buffer_size);
 }

 std::string GetPartitionName(const LpMetadataPartition& partition) {
     return NameFromFixedArray(partition.name, sizeof(partition.name));
 }

 }  // namespace fs_mgr
 }  // namespace android
	/*
	* Copyright (C) 2018 The Android Open Source Project
	*
	* 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
	*
	* http://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.
	*/

	#include "reader.h"

	#include <stddef.h>
	#include <stdlib.h>
	#include <unistd.h>

	#include <functional>

	#include <android-base/file.h>
	#include <android-base/unique_fd.h>

	#include "utility.h"

	namespace android {
	namespace fs_mgr {

	// Helper class for reading descriptors and memory buffers in the same manner.
	class Reader {
	public:
	virtual ~Reader(){};
	virtual bool ReadFully(void* buffer, size_t length) = 0;
	};

	class FileReader final : public Reader {
	public:
	explicit FileReader(int fd) : fd_(fd) {}
	bool ReadFully(void* buffer, size_t length) override {
	return android::base::ReadFully(fd_, buffer, length);
	}

	private:
	int fd_;
	};

	class MemoryReader final : public Reader {
	public:
	MemoryReader(const void* buffer, size_t size)
	: buffer_(reinterpret_cast<const uint8_t*>(buffer)), size_(size), pos_(0) {}
	bool ReadFully(void* out, size_t length) override {
	if (size_ - pos_ < length) {
	errno = EINVAL;
	return false;
	}
	memcpy(out, buffer_ + pos_, length);
	pos_ += length;
	return true;
	}

	private:
	const uint8_t* buffer_;
	size_t size_;
	size_t pos_;
	};

	bool ParseGeometry(const void* buffer, LpMetadataGeometry* geometry) {
	static_assert(sizeof(*geometry) <= LP_METADATA_GEOMETRY_SIZE);
	memcpy(geometry, buffer, sizeof(*geometry));

	// Check the magic signature.
	if (geometry->magic != LP_METADATA_GEOMETRY_MAGIC) {
	LERROR << "Logical partition metadata has invalid geometry magic signature.";
	return false;
	}
	// Reject if the struct size is larger than what we compiled. This is so we
	// can compute a checksum with the \|struct_size\| field rather than using
	// sizeof.
	if (geometry->struct_size > sizeof(LpMetadataGeometry)) {
	LERROR << "Logical partition metadata has unrecognized fields.";
	return false;
	}
	// Recompute and check the CRC32.
	{
	LpMetadataGeometry temp = *geometry;
	memset(&temp.checksum, 0, sizeof(temp.checksum));
	SHA256(&temp, temp.struct_size, temp.checksum);
	if (memcmp(temp.checksum, geometry->checksum, sizeof(temp.checksum)) != 0) {
	LERROR << "Logical partition metadata has invalid geometry checksum.";
	return false;
	}
	}
	// Check that the struct size is equal (this will have to change if we ever
	// change the struct size in a release).
	if (geometry->struct_size != sizeof(LpMetadataGeometry)) {
	LERROR << "Logical partition metadata has invalid struct size.";
	return false;
	}
	if (geometry->metadata_slot_count == 0) {
	LERROR << "Logical partition metadata has invalid slot count.";
	return false;
	}
	if (geometry->metadata_max_size % LP_SECTOR_SIZE != 0) {
	LERROR << "Metadata max size is not sector-aligned.";
	return false;
	}

	// Check that the metadata area and logical partition areas don't overlap.
	int64_t end_of_metadata =
	GetPrimaryMetadataOffset(*geometry, geometry->metadata_slot_count - 1) +
	geometry->metadata_max_size;
	if (uint64_t(end_of_metadata) > geometry->first_logical_sector * LP_SECTOR_SIZE) {
	LERROR << "Logical partition metadata overlaps with logical partition contents.";
	return false;
	}
	return true;
	}

	// Read and validate geometry information from a block device that holds
	// logical partitions. If the information is corrupted, this will attempt
	// to read it from a secondary backup location.
	bool ReadLogicalPartitionGeometry(int fd, LpMetadataGeometry* geometry) {
	// Read the first 4096 bytes.
	std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(LP_METADATA_GEOMETRY_SIZE);
	if (SeekFile64(fd, 0, SEEK_SET) < 0) {
	PERROR << __PRETTY_FUNCTION__ << "lseek failed";
	return false;
	}
	if (!android::base::ReadFully(fd, buffer.get(), LP_METADATA_GEOMETRY_SIZE)) {
	PERROR << __PRETTY_FUNCTION__ << "read " << LP_METADATA_GEOMETRY_SIZE << " bytes failed";
	return false;
	}
	if (ParseGeometry(buffer.get(), geometry)) {
	return true;
	}

	// Try the backup copy in the last 4096 bytes.
	if (SeekFile64(fd, -LP_METADATA_GEOMETRY_SIZE, SEEK_END) < 0) {
	PERROR << __PRETTY_FUNCTION__ << "lseek failed, offset " << -LP_METADATA_GEOMETRY_SIZE;
	return false;
	}
	if (!android::base::ReadFully(fd, buffer.get(), LP_METADATA_GEOMETRY_SIZE)) {
	PERROR << __PRETTY_FUNCTION__ << "backup read " << LP_METADATA_GEOMETRY_SIZE
	<< " bytes failed";
	return false;
	}
	return ParseGeometry(buffer.get(), geometry);
	}

	static bool ValidateTableBounds(const LpMetadataHeader& header,
	const LpMetadataTableDescriptor& table) {
	if (table.offset > header.tables_size) {
	return false;
	}
	uint64_t table_size = uint64_t(table.num_entries) * table.entry_size;
	if (header.tables_size - table.offset < table_size) {
	return false;
	}
	return true;
	}

	static bool ValidateMetadataHeader(const LpMetadataHeader& header) {
	// To compute the header's checksum, we have to temporarily set its checksum
	// field to 0.
	{
	LpMetadataHeader temp = header;
	memset(&temp.header_checksum, 0, sizeof(temp.header_checksum));
	SHA256(&temp, sizeof(temp), temp.header_checksum);
	if (memcmp(temp.header_checksum, header.header_checksum, sizeof(temp.header_checksum)) != 0) {
	LERROR << "Logical partition metadata has invalid checksum.";
	return false;
	}
	}

	// Do basic validation of key metadata bits.
	if (header.magic != LP_METADATA_HEADER_MAGIC) {
	LERROR << "Logical partition metadata has invalid magic value.";
	return false;
	}
	// Check that the version is compatible.
	if (header.major_version != LP_METADATA_MAJOR_VERSION \|\|
	header.minor_version > LP_METADATA_MINOR_VERSION) {
	LERROR << "Logical partition metadata has incompatible version.";
	return false;
	}
	if (!ValidateTableBounds(header, header.partitions) \|\|
	!ValidateTableBounds(header, header.extents)) {
	LERROR << "Logical partition metadata has invalid table bounds.";
	return false;
	}
	// Check that table entry sizes can accomodate their respective structs. If
	// table sizes change, these checks will have to be adjusted.
	if (header.partitions.entry_size != sizeof(LpMetadataPartition)) {
	LERROR << "Logical partition metadata has invalid partition table entry size.";
	return false;
	}
	if (header.extents.entry_size != sizeof(LpMetadataExtent)) {
	LERROR << "Logical partition metadata has invalid extent table entry size.";
	return false;
	}
	return true;
	}

	// Parse and validate all metadata at the current position in the given file
	// descriptor.
	static std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry,
	Reader* reader) {
	// First read and validate the header.
	std::unique_ptr<LpMetadata> metadata = std::make_unique<LpMetadata>();
	if (!reader->ReadFully(&metadata->header, sizeof(metadata->header))) {
	PERROR << __PRETTY_FUNCTION__ << "read " << sizeof(metadata->header) << "bytes failed";
	return nullptr;
	}
	if (!ValidateMetadataHeader(metadata->header)) {
	return nullptr;
	}
	metadata->geometry = geometry;

	LpMetadataHeader& header = metadata->header;

	// Read the metadata payload. Allocation is fallible in case the metadata is
	// corrupt and has some huge value.
	std::unique_ptr<uint8_t[]> buffer(new (std::nothrow) uint8_t[header.tables_size]);
	if (!buffer) {
	LERROR << "Out of memory reading logical partition tables.";
	return nullptr;
	}
	if (!reader->ReadFully(buffer.get(), header.tables_size)) {
	PERROR << __PRETTY_FUNCTION__ << "read " << header.tables_size << "bytes failed";
	return nullptr;
	}

	uint8_t checksum[32];
	SHA256(buffer.get(), header.tables_size, checksum);
	if (memcmp(checksum, header.tables_checksum, sizeof(checksum)) != 0) {
	LERROR << "Logical partition metadata has invalid table checksum.";
	return nullptr;
	}

	// ValidateTableSize ensured that \|cursor\| is valid for the number of
	// entries in the table.
	uint8_t* cursor = buffer.get() + header.partitions.offset;
	for (size_t i = 0; i < header.partitions.num_entries; i++) {
	LpMetadataPartition partition;
	memcpy(&partition, cursor, sizeof(partition));
	cursor += header.partitions.entry_size;

	if (partition.attributes & ~LP_PARTITION_ATTRIBUTE_MASK) {
	LERROR << "Logical partition has invalid attribute set.";
	return nullptr;
	}
	if (partition.first_extent_index + partition.num_extents > header.extents.num_entries) {
	LERROR << "Logical partition has invalid extent list.";
	return nullptr;
	}

	metadata->partitions.push_back(partition);
	}

	cursor = buffer.get() + header.extents.offset;
	for (size_t i = 0; i < header.extents.num_entries; i++) {
	LpMetadataExtent extent;
	memcpy(&extent, cursor, sizeof(extent));
	cursor += header.extents.entry_size;

	metadata->extents.push_back(extent);
	}
	return metadata;
	}

	std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry, const void* buffer,
	size_t size) {
	MemoryReader reader(buffer, size);
	return ParseMetadata(geometry, &reader);
	}

	std::unique_ptr<LpMetadata> ParseMetadata(const LpMetadataGeometry& geometry, int fd) {
	FileReader reader(fd);
	return ParseMetadata(geometry, &reader);
	}

	std::unique_ptr<LpMetadata> ReadPrimaryMetadata(int fd, const LpMetadataGeometry& geometry,
	uint32_t slot_number) {
	int64_t offset = GetPrimaryMetadataOffset(geometry, slot_number);
	if (SeekFile64(fd, offset, SEEK_SET) < 0) {
	PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << offset;
	return nullptr;
	}
	return ParseMetadata(geometry, fd);
	}

	std::unique_ptr<LpMetadata> ReadBackupMetadata(int fd, const LpMetadataGeometry& geometry,
	uint32_t slot_number) {
	int64_t offset = GetBackupMetadataOffset(geometry, slot_number);
	if (SeekFile64(fd, offset, SEEK_END) < 0) {
	PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << offset;
	return nullptr;
	}
	return ParseMetadata(geometry, fd);
	}

	std::unique_ptr<LpMetadata> ReadMetadata(int fd, uint32_t slot_number) {
	LpMetadataGeometry geometry;
	if (!ReadLogicalPartitionGeometry(fd, &geometry)) {
	return nullptr;
	}

	if (slot_number >= geometry.metadata_slot_count) {
	LERROR << __PRETTY_FUNCTION__ << "invalid metadata slot number";
	return nullptr;
	}

	// Read the primary copy, and if that fails, try the backup.
	std::unique_ptr<LpMetadata> metadata = ReadPrimaryMetadata(fd, geometry, slot_number);
	if (metadata) {
	return metadata;
	}
	return ReadBackupMetadata(fd, geometry, slot_number);
	}

	std::unique_ptr<LpMetadata> ReadMetadata(const char* block_device, uint32_t slot_number) {
	android::base::unique_fd fd(open(block_device, O_RDONLY));
	if (fd < 0) {
	PERROR << __PRETTY_FUNCTION__ << "open failed: " << block_device;
	return nullptr;
	}
	return ReadMetadata(fd, slot_number);
	}

	static std::string NameFromFixedArray(const char* name, size_t buffer_size) {
	// If the end of the buffer has a null character, it's safe to assume the
	// buffer is null terminated. Otherwise, we cap the string to the input
	// buffer size.
	if (name[buffer_size - 1] == '\0') {
	return std::string(name);
	}
	return std::string(name, buffer_size);
	}

	std::string GetPartitionName(const LpMetadataPartition& partition) {
	return NameFromFixedArray(partition.name, sizeof(partition.name));
	}

	} // namespace fs_mgr
	} // namespace android