fs_mgr/liblp/images.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 "images.h"

 #include <limits.h>

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

 #include "reader.h"
 #include "utility.h"
 #include "writer.h"

 namespace android {
 namespace fs_mgr {

 std::unique_ptr<LpMetadata> ReadFromImageFile(int fd) {
     LpMetadataGeometry geometry;
     if (!ReadLogicalPartitionGeometry(fd, &geometry)) {
         return nullptr;
     }
     if (SeekFile64(fd, LP_METADATA_GEOMETRY_SIZE, SEEK_SET) < 0) {
         PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << LP_METADATA_GEOMETRY_SIZE;
         return nullptr;
     }
     return ParseMetadata(geometry, fd);
 }

 std::unique_ptr<LpMetadata> ReadFromImageBlob(const void* data, size_t bytes) {
     if (bytes < LP_METADATA_GEOMETRY_SIZE) {
         LERROR << __PRETTY_FUNCTION__ << ": " << bytes << " is smaller than geometry header";
         return nullptr;
     }

     LpMetadataGeometry geometry;
     if (!ParseGeometry(data, &geometry)) {
         return nullptr;
     }

     const uint8_t* metadata_buffer =
             reinterpret_cast<const uint8_t*>(data) + LP_METADATA_GEOMETRY_SIZE;
     size_t metadata_buffer_size = bytes - LP_METADATA_GEOMETRY_SIZE;
     return ParseMetadata(geometry, metadata_buffer, metadata_buffer_size);
 }

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

 bool WriteToImageFile(int fd, const LpMetadata& input) {
     std::string geometry = SerializeGeometry(input.geometry);
     std::string metadata = SerializeMetadata(input);

     std::string everything = geometry + metadata;

     if (!android::base::WriteFully(fd, everything.data(), everything.size())) {
         PERROR << __PRETTY_FUNCTION__ << "write " << everything.size() << " bytes failed";
         return false;
     }
     return true;
 }

 bool WriteToImageFile(const char* file, const LpMetadata& input) {
     android::base::unique_fd fd(open(file, O_CREAT | O_RDWR | O_TRUNC, 0644));
     if (fd < 0) {
         PERROR << __PRETTY_FUNCTION__ << "open failed: " << file;
         return false;
     }
     return WriteToImageFile(fd, input);
 }

 // We use an object to build the sparse file since it requires that data
 // pointers be held alive until the sparse file is destroyed. It's easier
 // to do this when the data pointers are all in one place.
 class SparseBuilder {
   public:
     SparseBuilder(const LpMetadata& metadata, uint32_t block_size,
                   const std::map<std::string, std::string>& images);

     bool Build();
     bool Export(const char* file);
     bool IsValid() const { return file_ != nullptr; }

   private:
     bool AddData(const std::string& blob, uint64_t sector);
     bool AddPartitionImage(const LpMetadataPartition& partition, const std::string& file);
     int OpenImageFile(const std::string& file);
     bool SectorToBlock(uint64_t sector, uint32_t* block);

     const LpMetadata& metadata_;
     const LpMetadataGeometry& geometry_;
     uint32_t block_size_;
     std::unique_ptr<sparse_file, decltype(&sparse_file_destroy)> file_;
     std::string primary_blob_;
     std::string backup_blob_;
     std::map<std::string, std::string> images_;
     std::vector<android::base::unique_fd> temp_fds_;
 };

 SparseBuilder::SparseBuilder(const LpMetadata& metadata, uint32_t block_size,
                              const std::map<std::string, std::string>& images)
     : metadata_(metadata),
       geometry_(metadata.geometry),
       block_size_(block_size),
       file_(sparse_file_new(block_size_, geometry_.block_device_size), sparse_file_destroy),
       images_(images) {}

 bool SparseBuilder::Export(const char* file) {
     android::base::unique_fd fd(open(file, O_CREAT | O_RDWR | O_TRUNC, 0644));
     if (fd < 0) {
         PERROR << "open failed: " << file;
         return false;
     }
     // No gzip compression; sparseify; no checksum.
     int ret = sparse_file_write(file_.get(), fd, false, true, false);
     if (ret != 0) {
         LERROR << "sparse_file_write failed (error code " << ret << ")";
         return false;
     }
     return true;
 }

 bool SparseBuilder::AddData(const std::string& blob, uint64_t sector) {
     uint32_t block;
     if (!SectorToBlock(sector, &block)) {
         return false;
     }
     void* data = const_cast<char*>(blob.data());
     int ret = sparse_file_add_data(file_.get(), data, blob.size(), block);
     if (ret != 0) {
         LERROR << "sparse_file_add_data failed (error code " << ret << ")";
         return false;
     }
     return true;
 }

 bool SparseBuilder::SectorToBlock(uint64_t sector, uint32_t* block) {
     // The caller must ensure that the metadata has an alignment that is a
     // multiple of the block size. liblp will take care of the rest, ensuring
     // that all partitions are on an aligned boundary. Therefore all writes
     // should be block-aligned, and if they are not, the table was misconfigured.
     // Note that the default alignment is 1MiB, which is a multiple of the
     // default block size (4096).
     if ((sector * LP_SECTOR_SIZE) % block_size_ != 0) {
         LERROR << "sector " << sector << " is not aligned to block size " << block_size_;
         return false;
     }
     *block = (sector * LP_SECTOR_SIZE) / block_size_;
     return true;
 }

 bool SparseBuilder::Build() {
     std::string geometry_blob = SerializeGeometry(geometry_);
     std::string metadata_blob = SerializeMetadata(metadata_);
     metadata_blob.resize(geometry_.metadata_max_size);

     std::string all_metadata;
     for (size_t i = 0; i < geometry_.metadata_slot_count; i++) {
         all_metadata += metadata_blob;
     }

     // Metadata immediately follows geometry, and we write the same metadata
     // to all slots. Note that we don't bother trying to write skip chunks
     // here since it's a small amount of data.
     primary_blob_ = geometry_blob + all_metadata;
     if (!AddData(primary_blob_, 0)) {
         return false;
     }

     for (const auto& partition : metadata_.partitions) {
         auto iter = images_.find(GetPartitionName(partition));
         if (iter == images_.end()) {
             continue;
         }
         if (!AddPartitionImage(partition, iter->second)) {
             return false;
         }
         images_.erase(iter);
     }

     if (!images_.empty()) {
         LERROR << "Partition image was specified but no partition was found.";
         return false;
     }

     // The backup area contains all metadata slots, and then geometry. Similar
     // to before we write the metadata to every slot.
     int64_t backup_offset = GetBackupMetadataOffset(geometry_, 0);
     uint64_t backups_start = geometry_.block_device_size + backup_offset;
     uint64_t backup_sector = backups_start / LP_SECTOR_SIZE;

     backup_blob_ = all_metadata + geometry_blob;
     if (!AddData(backup_blob_, backup_sector)) {
         return false;
     }
     return true;
 }

 static inline bool HasFillValue(uint32_t* buffer, size_t count) {
     uint32_t fill_value = buffer[0];
     for (size_t i = 1; i < count; i++) {
         if (fill_value != buffer[i]) {
             return false;
         }
     }
     return true;
 }

 bool SparseBuilder::AddPartitionImage(const LpMetadataPartition& partition,
                                       const std::string& file) {
     if (partition.num_extents != 1) {
         LERROR << "Partition for new tables should not have more than one extent: "
                << GetPartitionName(partition);
         return false;
     }

     const LpMetadataExtent& extent = metadata_.extents[partition.first_extent_index];
     if (extent.target_type != LP_TARGET_TYPE_LINEAR) {
         LERROR << "Partition should only have linear extents: " << GetPartitionName(partition);
         return false;
     }

     int fd = OpenImageFile(file);
     if (fd < 0) {
         LERROR << "Could not open image for partition: " << GetPartitionName(partition);
         return false;
     }

     // Make sure the image does not exceed the partition size.
     uint64_t file_length;
     if (!GetDescriptorSize(fd, &file_length)) {
         LERROR << "Could not compute image size";
         return false;
     }
     if (file_length > extent.num_sectors * LP_SECTOR_SIZE) {
         LERROR << "Image for partition '" << GetPartitionName(partition)
                << "' is greater than its size";
         return false;
     }
     if (SeekFile64(fd, 0, SEEK_SET)) {
         PERROR << "lseek failed";
         return false;
     }

     uint32_t output_block;
     if (!SectorToBlock(extent.target_data, &output_block)) {
         return false;
     }

     uint64_t pos = 0;
     uint64_t remaining = file_length;
     while (remaining) {
         uint32_t buffer[block_size_ / sizeof(uint32_t)];
         size_t read_size = remaining >= sizeof(buffer) ? sizeof(buffer) : size_t(remaining);
         if (!android::base::ReadFully(fd, buffer, sizeof(buffer))) {
             PERROR << "read failed";
             return false;
         }
         if (read_size != sizeof(buffer) || !HasFillValue(buffer, read_size / sizeof(uint32_t))) {
             int rv = sparse_file_add_fd(file_.get(), fd, pos, read_size, output_block);
             if (rv) {
                 LERROR << "sparse_file_add_fd failed with code: " << rv;
                 return false;
             }
         } else {
             int rv = sparse_file_add_fill(file_.get(), buffer[0], read_size, output_block);
             if (rv) {
                 LERROR << "sparse_file_add_fill failed with code: " << rv;
                 return false;
             }
         }
         pos += read_size;
         remaining -= read_size;
         output_block++;
     }

     return true;
 }

 int SparseBuilder::OpenImageFile(const std::string& file) {
     android::base::unique_fd source_fd(open(file.c_str(), O_RDONLY));
     if (source_fd < 0) {
         PERROR << "open image file failed: " << file;
         return -1;
     }

     std::unique_ptr<sparse_file, decltype(&sparse_file_destroy)> source(
             sparse_file_import(source_fd, true, true), sparse_file_destroy);
     if (!source) {
         int fd = source_fd.get();
         temp_fds_.push_back(std::move(source_fd));
         return fd;
     }

     char temp_file[PATH_MAX];
     snprintf(temp_file, sizeof(temp_file), "%s/imageXXXXXX", P_tmpdir);
     android::base::unique_fd temp_fd(mkstemp(temp_file));
     if (temp_fd < 0) {
         PERROR << "mkstemp failed";
         return -1;
     }
     if (unlink(temp_file) < 0) {
         PERROR << "unlink failed";
         return -1;
     }

     // We temporarily unsparse the file, rather than try to merge its chunks.
     int rv = sparse_file_write(source.get(), temp_fd, false, false, false);
     if (rv) {
         LERROR << "sparse_file_write failed with code: " << rv;
         return -1;
     }
     temp_fds_.push_back(std::move(temp_fd));
     return temp_fds_.back().get();
 }

 bool WriteToSparseFile(const char* file, const LpMetadata& metadata, uint32_t block_size,
                        const std::map<std::string, std::string>& images) {
     if (block_size % LP_SECTOR_SIZE != 0) {
         LERROR << "Block size must be a multiple of the sector size, " << LP_SECTOR_SIZE;
         return false;
     }
     if (metadata.geometry.block_device_size % block_size != 0) {
         LERROR << "Device size must be a multiple of the block size, " << block_size;
         return false;
     }
     uint64_t num_blocks = metadata.geometry.block_device_size % block_size;
     if (num_blocks >= UINT_MAX) {
         // libsparse counts blocks in unsigned 32-bit integers, so we check to
         // make sure we're not going to overflow.
         LERROR << "Block device is too large to encode with libsparse.";
         return false;
     }

     SparseBuilder builder(metadata, block_size, images);
     if (!builder.IsValid()) {
         LERROR << "Could not allocate sparse file of size " << metadata.geometry.block_device_size;
         return false;
     }
     if (!builder.Build()) {
         return false;
     }
     return builder.Export(file);
 }

 }  // 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 "images.h"

	#include <limits.h>

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

	#include "reader.h"
	#include "utility.h"
	#include "writer.h"

	namespace android {
	namespace fs_mgr {

	std::unique_ptr<LpMetadata> ReadFromImageFile(int fd) {
	LpMetadataGeometry geometry;
	if (!ReadLogicalPartitionGeometry(fd, &geometry)) {
	return nullptr;
	}
	if (SeekFile64(fd, LP_METADATA_GEOMETRY_SIZE, SEEK_SET) < 0) {
	PERROR << __PRETTY_FUNCTION__ << "lseek failed: offset " << LP_METADATA_GEOMETRY_SIZE;
	return nullptr;
	}
	return ParseMetadata(geometry, fd);
	}

	std::unique_ptr<LpMetadata> ReadFromImageBlob(const void* data, size_t bytes) {
	if (bytes < LP_METADATA_GEOMETRY_SIZE) {
	LERROR << __PRETTY_FUNCTION__ << ": " << bytes << " is smaller than geometry header";
	return nullptr;
	}

	LpMetadataGeometry geometry;
	if (!ParseGeometry(data, &geometry)) {
	return nullptr;
	}

	const uint8_t* metadata_buffer =
	reinterpret_cast<const uint8_t*>(data) + LP_METADATA_GEOMETRY_SIZE;
	size_t metadata_buffer_size = bytes - LP_METADATA_GEOMETRY_SIZE;
	return ParseMetadata(geometry, metadata_buffer, metadata_buffer_size);
	}

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

	bool WriteToImageFile(int fd, const LpMetadata& input) {
	std::string geometry = SerializeGeometry(input.geometry);
	std::string metadata = SerializeMetadata(input);

	std::string everything = geometry + metadata;

	if (!android::base::WriteFully(fd, everything.data(), everything.size())) {
	PERROR << __PRETTY_FUNCTION__ << "write " << everything.size() << " bytes failed";
	return false;
	}
	return true;
	}

	bool WriteToImageFile(const char* file, const LpMetadata& input) {
	android::base::unique_fd fd(open(file, O_CREAT \| O_RDWR \| O_TRUNC, 0644));
	if (fd < 0) {
	PERROR << __PRETTY_FUNCTION__ << "open failed: " << file;
	return false;
	}
	return WriteToImageFile(fd, input);
	}

	// We use an object to build the sparse file since it requires that data
	// pointers be held alive until the sparse file is destroyed. It's easier
	// to do this when the data pointers are all in one place.
	class SparseBuilder {
	public:
	SparseBuilder(const LpMetadata& metadata, uint32_t block_size,
	const std::map<std::string, std::string>& images);

	bool Build();
	bool Export(const char* file);
	bool IsValid() const { return file_ != nullptr; }

	private:
	bool AddData(const std::string& blob, uint64_t sector);
	bool AddPartitionImage(const LpMetadataPartition& partition, const std::string& file);
	int OpenImageFile(const std::string& file);
	bool SectorToBlock(uint64_t sector, uint32_t* block);

	const LpMetadata& metadata_;
	const LpMetadataGeometry& geometry_;
	uint32_t block_size_;
	std::unique_ptr<sparse_file, decltype(&sparse_file_destroy)> file_;
	std::string primary_blob_;
	std::string backup_blob_;
	std::map<std::string, std::string> images_;
	std::vector<android::base::unique_fd> temp_fds_;
	};

	SparseBuilder::SparseBuilder(const LpMetadata& metadata, uint32_t block_size,
	const std::map<std::string, std::string>& images)
	: metadata_(metadata),
	geometry_(metadata.geometry),
	block_size_(block_size),
	file_(sparse_file_new(block_size_, geometry_.block_device_size), sparse_file_destroy),
	images_(images) {}

	bool SparseBuilder::Export(const char* file) {
	android::base::unique_fd fd(open(file, O_CREAT \| O_RDWR \| O_TRUNC, 0644));
	if (fd < 0) {
	PERROR << "open failed: " << file;
	return false;
	}
	// No gzip compression; sparseify; no checksum.
	int ret = sparse_file_write(file_.get(), fd, false, true, false);
	if (ret != 0) {
	LERROR << "sparse_file_write failed (error code " << ret << ")";
	return false;
	}
	return true;
	}

	bool SparseBuilder::AddData(const std::string& blob, uint64_t sector) {
	uint32_t block;
	if (!SectorToBlock(sector, &block)) {
	return false;
	}
	void* data = const_cast<char*>(blob.data());
	int ret = sparse_file_add_data(file_.get(), data, blob.size(), block);
	if (ret != 0) {
	LERROR << "sparse_file_add_data failed (error code " << ret << ")";
	return false;
	}
	return true;
	}

	bool SparseBuilder::SectorToBlock(uint64_t sector, uint32_t* block) {
	// The caller must ensure that the metadata has an alignment that is a
	// multiple of the block size. liblp will take care of the rest, ensuring
	// that all partitions are on an aligned boundary. Therefore all writes
	// should be block-aligned, and if they are not, the table was misconfigured.
	// Note that the default alignment is 1MiB, which is a multiple of the
	// default block size (4096).
	if ((sector * LP_SECTOR_SIZE) % block_size_ != 0) {
	LERROR << "sector " << sector << " is not aligned to block size " << block_size_;
	return false;
	}
	block = (sector LP_SECTOR_SIZE) / block_size_;
	return true;
	}

	bool SparseBuilder::Build() {
	std::string geometry_blob = SerializeGeometry(geometry_);
	std::string metadata_blob = SerializeMetadata(metadata_);
	metadata_blob.resize(geometry_.metadata_max_size);

	std::string all_metadata;
	for (size_t i = 0; i < geometry_.metadata_slot_count; i++) {
	all_metadata += metadata_blob;
	}

	// Metadata immediately follows geometry, and we write the same metadata
	// to all slots. Note that we don't bother trying to write skip chunks
	// here since it's a small amount of data.
	primary_blob_ = geometry_blob + all_metadata;
	if (!AddData(primary_blob_, 0)) {
	return false;
	}

	for (const auto& partition : metadata_.partitions) {
	auto iter = images_.find(GetPartitionName(partition));
	if (iter == images_.end()) {
	continue;
	}
	if (!AddPartitionImage(partition, iter->second)) {
	return false;
	}
	images_.erase(iter);
	}

	if (!images_.empty()) {
	LERROR << "Partition image was specified but no partition was found.";
	return false;
	}

	// The backup area contains all metadata slots, and then geometry. Similar
	// to before we write the metadata to every slot.
	int64_t backup_offset = GetBackupMetadataOffset(geometry_, 0);
	uint64_t backups_start = geometry_.block_device_size + backup_offset;
	uint64_t backup_sector = backups_start / LP_SECTOR_SIZE;

	backup_blob_ = all_metadata + geometry_blob;
	if (!AddData(backup_blob_, backup_sector)) {
	return false;
	}
	return true;
	}

	static inline bool HasFillValue(uint32_t* buffer, size_t count) {
	uint32_t fill_value = buffer[0];
	for (size_t i = 1; i < count; i++) {
	if (fill_value != buffer[i]) {
	return false;
	}
	}
	return true;
	}

	bool SparseBuilder::AddPartitionImage(const LpMetadataPartition& partition,
	const std::string& file) {
	if (partition.num_extents != 1) {
	LERROR << "Partition for new tables should not have more than one extent: "
	<< GetPartitionName(partition);
	return false;
	}

	const LpMetadataExtent& extent = metadata_.extents[partition.first_extent_index];
	if (extent.target_type != LP_TARGET_TYPE_LINEAR) {
	LERROR << "Partition should only have linear extents: " << GetPartitionName(partition);
	return false;
	}

	int fd = OpenImageFile(file);
	if (fd < 0) {
	LERROR << "Could not open image for partition: " << GetPartitionName(partition);
	return false;
	}

	// Make sure the image does not exceed the partition size.
	uint64_t file_length;
	if (!GetDescriptorSize(fd, &file_length)) {
	LERROR << "Could not compute image size";
	return false;
	}
	if (file_length > extent.num_sectors * LP_SECTOR_SIZE) {
	LERROR << "Image for partition '" << GetPartitionName(partition)
	<< "' is greater than its size";
	return false;
	}
	if (SeekFile64(fd, 0, SEEK_SET)) {
	PERROR << "lseek failed";
	return false;
	}

	uint32_t output_block;
	if (!SectorToBlock(extent.target_data, &output_block)) {
	return false;
	}

	uint64_t pos = 0;
	uint64_t remaining = file_length;
	while (remaining) {
	uint32_t buffer[block_size_ / sizeof(uint32_t)];
	size_t read_size = remaining >= sizeof(buffer) ? sizeof(buffer) : size_t(remaining);
	if (!android::base::ReadFully(fd, buffer, sizeof(buffer))) {
	PERROR << "read failed";
	return false;
	}
	if (read_size != sizeof(buffer) \|\| !HasFillValue(buffer, read_size / sizeof(uint32_t))) {
	int rv = sparse_file_add_fd(file_.get(), fd, pos, read_size, output_block);
	if (rv) {
	LERROR << "sparse_file_add_fd failed with code: " << rv;
	return false;
	}
	} else {
	int rv = sparse_file_add_fill(file_.get(), buffer[0], read_size, output_block);
	if (rv) {
	LERROR << "sparse_file_add_fill failed with code: " << rv;
	return false;
	}
	}
	pos += read_size;
	remaining -= read_size;
	output_block++;
	}

	return true;
	}

	int SparseBuilder::OpenImageFile(const std::string& file) {
	android::base::unique_fd source_fd(open(file.c_str(), O_RDONLY));
	if (source_fd < 0) {
	PERROR << "open image file failed: " << file;
	return -1;
	}

	std::unique_ptr<sparse_file, decltype(&sparse_file_destroy)> source(
	sparse_file_import(source_fd, true, true), sparse_file_destroy);
	if (!source) {
	int fd = source_fd.get();
	temp_fds_.push_back(std::move(source_fd));
	return fd;
	}

	char temp_file[PATH_MAX];
	snprintf(temp_file, sizeof(temp_file), "%s/imageXXXXXX", P_tmpdir);
	android::base::unique_fd temp_fd(mkstemp(temp_file));
	if (temp_fd < 0) {
	PERROR << "mkstemp failed";
	return -1;
	}
	if (unlink(temp_file) < 0) {
	PERROR << "unlink failed";
	return -1;
	}

	// We temporarily unsparse the file, rather than try to merge its chunks.
	int rv = sparse_file_write(source.get(), temp_fd, false, false, false);
	if (rv) {
	LERROR << "sparse_file_write failed with code: " << rv;
	return -1;
	}
	temp_fds_.push_back(std::move(temp_fd));
	return temp_fds_.back().get();
	}

	bool WriteToSparseFile(const char* file, const LpMetadata& metadata, uint32_t block_size,
	const std::map<std::string, std::string>& images) {
	if (block_size % LP_SECTOR_SIZE != 0) {
	LERROR << "Block size must be a multiple of the sector size, " << LP_SECTOR_SIZE;
	return false;
	}
	if (metadata.geometry.block_device_size % block_size != 0) {
	LERROR << "Device size must be a multiple of the block size, " << block_size;
	return false;
	}
	uint64_t num_blocks = metadata.geometry.block_device_size % block_size;
	if (num_blocks >= UINT_MAX) {
	// libsparse counts blocks in unsigned 32-bit integers, so we check to
	// make sure we're not going to overflow.
	LERROR << "Block device is too large to encode with libsparse.";
	return false;
	}

	SparseBuilder builder(metadata, block_size, images);
	if (!builder.IsValid()) {
	LERROR << "Could not allocate sparse file of size " << metadata.geometry.block_device_size;
	return false;
	}
	if (!builder.Build()) {
	return false;
	}
	return builder.Export(file);
	}

	} // namespace fs_mgr
	} // namespace android