libsnapshot: Off-line tool for converting OTA payloads to COWs.

The A/B version of this tool takes in a payload.bin file (from an OTA
package), and converts it into COWs in the new format. It uses the
CowWriter API to do this. This tool can be used to precisely see the
size of a COW relative to an OTA. Since there is one COW per partition,
it also takes an output folder:

    make_cow_from_ab_ota payload.bin ./ota-cows/

If the payload is incremental, a source target-files package is needed.
It must be the exact package used to build the OTA, otherwise, the
conversion is likely to fail. Example:

    make_cow_from_ab_ota -source_tf target-files-XYZ.zip \
                         payload.bin ./ota-cows/

Bug: 162274240
Test: manual tests
Change-Id: I22c86546f4166ee9df99165399646b7daa3519d5

fs_mgr/libsnapshot/Android.bp

@@ -403,3 +403,30 @@ cc_test {
     auto_gen_config: true,
     require_root: false,
 }
+
+cc_binary {
+    name: "make_cow_from_ab_ota",
+    host_supported: true,
+    device_supported: false,
+    static_libs: [
+        "libbase",
+        "libbspatch",
+        "libbrotli",
+        "libbz",
+        "libchrome",
+        "libcrypto",
+        "libgflags",
+        "liblog",
+        "libprotobuf-cpp-lite",
+        "libpuffpatch",
+        "libsnapshot_cow",
+        "libsparse",
+        "libxz",
+        "libz",
+        "libziparchive",
+        "update_metadata-protos",
+    ],
+    srcs: [
+        "make_cow_from_ab_ota.cpp",
+    ],
+}

fs_mgr/libsnapshot/make_cow_from_ab_ota.cpp

@@ -0,0 +1,690 @@
+//
+// Copyright (C) 2020 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 <arpa/inet.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <iostream>
+#include <limits>
+#include <string>
+#include <unordered_set>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/unique_fd.h>
+#include <bsdiff/bspatch.h>
+#include <bzlib.h>
+#include <gflags/gflags.h>
+#include <libsnapshot/cow_writer.h>
+#include <puffin/puffpatch.h>
+#include <sparse/sparse.h>
+#include <update_engine/update_metadata.pb.h>
+#include <xz.h>
+#include <ziparchive/zip_archive.h>
+
+namespace android {
+namespace snapshot {
+
+using android::base::borrowed_fd;
+using android::base::unique_fd;
+using chromeos_update_engine::DeltaArchiveManifest;
+using chromeos_update_engine::Extent;
+using chromeos_update_engine::InstallOperation;
+using chromeos_update_engine::PartitionUpdate;
+
+static constexpr uint64_t kBlockSize = 4096;
+
+DEFINE_string(source_tf, "", "Source target files (dir or zip file) for incremental payloads");
+DEFINE_string(compression, "gz", "Compression type to use (none or gz)");
+
+void MyLogger(android::base::LogId, android::base::LogSeverity severity, const char*, const char*,
+              unsigned int, const char* message) {
+    if (severity == android::base::ERROR) {
+        fprintf(stderr, "%s\n", message);
+    } else {
+        fprintf(stdout, "%s\n", message);
+    }
+}
+
+uint64_t ToLittleEndian(uint64_t value) {
+    union {
+        uint64_t u64;
+        char bytes[8];
+    } packed;
+    packed.u64 = value;
+    std::swap(packed.bytes[0], packed.bytes[7]);
+    std::swap(packed.bytes[1], packed.bytes[6]);
+    std::swap(packed.bytes[2], packed.bytes[5]);
+    std::swap(packed.bytes[3], packed.bytes[4]);
+    return packed.u64;
+}
+
+class PayloadConverter final {
+  public:
+    PayloadConverter(const std::string& in_file, const std::string& out_dir)
+        : in_file_(in_file), out_dir_(out_dir), source_tf_zip_(nullptr, &CloseArchive) {}
+
+    bool Run();
+
+  private:
+    bool OpenPayload();
+    bool OpenSourceTargetFiles();
+    bool ProcessPartition(const PartitionUpdate& update);
+    bool ProcessOperation(const InstallOperation& op);
+    bool ProcessZero(const InstallOperation& op);
+    bool ProcessCopy(const InstallOperation& op);
+    bool ProcessReplace(const InstallOperation& op);
+    bool ProcessDiff(const InstallOperation& op);
+    borrowed_fd OpenSourceImage();
+
+    std::string in_file_;
+    std::string out_dir_;
+    unique_fd in_fd_;
+    uint64_t payload_offset_ = 0;
+    DeltaArchiveManifest manifest_;
+    std::unordered_set<std::string> dap_;
+    unique_fd source_tf_fd_;
+    std::unique_ptr<ZipArchive, decltype(&CloseArchive)> source_tf_zip_;
+
+    // Updated during ProcessPartition().
+    std::string partition_name_;
+    std::unique_ptr<CowWriter> writer_;
+    unique_fd source_image_;
+};
+
+bool PayloadConverter::Run() {
+    if (!OpenPayload()) {
+        return false;
+    }
+
+    if (manifest_.has_dynamic_partition_metadata()) {
+        const auto& dpm = manifest_.dynamic_partition_metadata();
+        for (const auto& group : dpm.groups()) {
+            for (const auto& partition : group.partition_names()) {
+                dap_.emplace(partition);
+            }
+        }
+    }
+
+    if (dap_.empty()) {
+        LOG(ERROR) << "No dynamic partitions found.";
+        return false;
+    }
+
+    if (!OpenSourceTargetFiles()) {
+        return false;
+    }
+
+    for (const auto& update : manifest_.partitions()) {
+        if (!ProcessPartition(update)) {
+            return false;
+        }
+        writer_ = nullptr;
+        source_image_.reset();
+    }
+    return true;
+}
+
+bool PayloadConverter::OpenSourceTargetFiles() {
+    if (FLAGS_source_tf.empty()) {
+        return true;
+    }
+
+    source_tf_fd_.reset(open(FLAGS_source_tf.c_str(), O_RDONLY));
+    if (source_tf_fd_ < 0) {
+        LOG(ERROR) << "open failed: " << FLAGS_source_tf;
+        return false;
+    }
+
+    struct stat s;
+    if (fstat(source_tf_fd_.get(), &s) < 0) {
+        LOG(ERROR) << "fstat failed: " << FLAGS_source_tf;
+        return false;
+    }
+    if (S_ISDIR(s.st_mode)) {
+        return true;
+    }
+
+    // Otherwise, assume it's a zip file.
+    ZipArchiveHandle handle;
+    if (OpenArchiveFd(source_tf_fd_.get(), FLAGS_source_tf.c_str(), &handle, false)) {
+        LOG(ERROR) << "Could not open " << FLAGS_source_tf << " as a zip archive.";
+        return false;
+    }
+    source_tf_zip_.reset(handle);
+    return true;
+}
+
+bool PayloadConverter::ProcessPartition(const PartitionUpdate& update) {
+    auto partition_name = update.partition_name();
+    if (dap_.find(partition_name) == dap_.end()) {
+        // Skip non-DAP partitions.
+        return true;
+    }
+
+    auto path = out_dir_ + "/" + partition_name + ".cow";
+    unique_fd fd(open(path.c_str(), O_RDWR | O_CREAT | O_TRUNC | O_CLOEXEC, 0644));
+    if (fd < 0) {
+        PLOG(ERROR) << "open failed: " << path;
+        return false;
+    }
+
+    CowOptions options;
+    options.block_size = kBlockSize;
+    options.compression = FLAGS_compression;
+
+    writer_ = std::make_unique<CowWriter>(options);
+    if (!writer_->Initialize(std::move(fd))) {
+        LOG(ERROR) << "Unable to initialize COW writer";
+        return false;
+    }
+
+    partition_name_ = partition_name;
+
+    for (const auto& op : update.operations()) {
+        if (!ProcessOperation(op)) {
+            return false;
+        }
+    }
+
+    if (!writer_->Finalize()) {
+        LOG(ERROR) << "Unable to finalize COW for " << partition_name;
+        return false;
+    }
+    return true;
+}
+
+bool PayloadConverter::ProcessOperation(const InstallOperation& op) {
+    switch (op.type()) {
+        case InstallOperation::SOURCE_COPY:
+            return ProcessCopy(op);
+        case InstallOperation::BROTLI_BSDIFF:
+        case InstallOperation::PUFFDIFF:
+            return ProcessDiff(op);
+        case InstallOperation::REPLACE:
+        case InstallOperation::REPLACE_XZ:
+        case InstallOperation::REPLACE_BZ:
+            return ProcessReplace(op);
+        case InstallOperation::ZERO:
+            return ProcessZero(op);
+        default:
+            LOG(ERROR) << "Unsupported op: " << (int)op.type();
+            return false;
+    }
+    return true;
+}
+
+bool PayloadConverter::ProcessZero(const InstallOperation& op) {
+    for (const auto& extent : op.dst_extents()) {
+        if (!writer_->AddZeroBlocks(extent.start_block(), extent.num_blocks())) {
+            LOG(ERROR) << "Could not add zero operation";
+            return false;
+        }
+    }
+    return true;
+}
+
+template <typename T>
+static uint64_t SizeOfAllExtents(const T& extents) {
+    uint64_t total = 0;
+    for (const auto& extent : extents) {
+        total += extent.num_blocks() * kBlockSize;
+    }
+    return total;
+}
+
+class PuffInputStream final : public puffin::StreamInterface {
+  public:
+    PuffInputStream(uint8_t* buffer, size_t length) : buffer_(buffer), length_(length) {}
+
+    bool GetSize(uint64_t* size) const override {
+        *size = length_;
+        return true;
+    }
+    bool GetOffset(uint64_t* offset) const override {
+        *offset = pos_;
+        return true;
+    }
+    bool Seek(uint64_t offset) override {
+        if (offset > length_) return false;
+        pos_ = offset;
+        return true;
+    }
+    bool Read(void* buffer, size_t length) override {
+        if (length_ - pos_ < length) return false;
+        memcpy(buffer, buffer_ + pos_, length);
+        pos_ += length;
+        return true;
+    }
+    bool Write(const void*, size_t) override { return false; }
+    bool Close() override { return true; }
+
+  private:
+    uint8_t* buffer_;
+    size_t length_;
+    size_t pos_;
+};
+
+class PuffOutputStream final : public puffin::StreamInterface {
+  public:
+    PuffOutputStream(std::vector<uint8_t>& stream) : stream_(stream), pos_(0) {}
+
+    bool GetSize(uint64_t* size) const override {
+        *size = stream_.size();
+        return true;
+    }
+    bool GetOffset(uint64_t* offset) const override {
+        *offset = pos_;
+        return true;
+    }
+    bool Seek(uint64_t offset) override {
+        if (offset > stream_.size()) {
+            return false;
+        }
+        pos_ = offset;
+        return true;
+    }
+    bool Read(void* buffer, size_t length) override {
+        if (stream_.size() - pos_ < length) {
+            return false;
+        }
+        memcpy(buffer, &stream_[0] + pos_, length);
+        pos_ += length;
+        return true;
+    }
+    bool Write(const void* buffer, size_t length) override {
+        auto remaining = stream_.size() - pos_;
+        if (remaining < length) {
+            stream_.resize(stream_.size() + (length - remaining));
+        }
+        memcpy(&stream_[0] + pos_, buffer, length);
+        pos_ += length;
+        return true;
+    }
+    bool Close() override { return true; }
+
+  private:
+    std::vector<uint8_t>& stream_;
+    size_t pos_;
+};
+
+bool PayloadConverter::ProcessDiff(const InstallOperation& op) {
+    auto source_image = OpenSourceImage();
+    if (source_image < 0) {
+        return false;
+    }
+
+    uint64_t src_length = SizeOfAllExtents(op.src_extents());
+    auto src = std::make_unique<uint8_t[]>(src_length);
+    size_t src_pos = 0;
+
+    // Read source bytes.
+    for (const auto& extent : op.src_extents()) {
+        uint64_t offset = extent.start_block() * kBlockSize;
+        if (lseek(source_image.get(), offset, SEEK_SET) < 0) {
+            PLOG(ERROR) << "lseek source image failed";
+            return false;
+        }
+
+        uint64_t size = extent.num_blocks() * kBlockSize;
+        CHECK(src_length - src_pos >= size);
+        if (!android::base::ReadFully(source_image, src.get() + src_pos, size)) {
+            PLOG(ERROR) << "read source image failed";
+            return false;
+        }
+        src_pos += size;
+    }
+    CHECK(src_pos == src_length);
+
+    // Read patch bytes.
+    auto patch = std::make_unique<uint8_t[]>(op.data_length());
+    if (lseek(in_fd_.get(), payload_offset_ + op.data_offset(), SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek payload failed";
+        return false;
+    }
+    if (!android::base::ReadFully(in_fd_, patch.get(), op.data_length())) {
+        PLOG(ERROR) << "read payload failed";
+        return false;
+    }
+
+    std::vector<uint8_t> dest(SizeOfAllExtents(op.dst_extents()));
+
+    // Apply the diff.
+    if (op.type() == InstallOperation::BROTLI_BSDIFF) {
+        size_t dest_pos = 0;
+        auto sink = [&](const uint8_t* data, size_t length) -> size_t {
+            CHECK(dest.size() - dest_pos >= length);
+            memcpy(&dest[dest_pos], data, length);
+            dest_pos += length;
+            return length;
+        };
+        if (int rv = bsdiff::bspatch(src.get(), src_pos, patch.get(), op.data_length(), sink)) {
+            LOG(ERROR) << "bspatch failed, error code " << rv;
+            return false;
+        }
+    } else if (op.type() == InstallOperation::PUFFDIFF) {
+        auto src_stream = std::make_unique<PuffInputStream>(src.get(), src_length);
+        auto dest_stream = std::make_unique<PuffOutputStream>(dest);
+        bool ok = PuffPatch(std::move(src_stream), std::move(dest_stream), patch.get(),
+                            op.data_length());
+        if (!ok) {
+            LOG(ERROR) << "puffdiff operation failed to apply";
+            return false;
+        }
+    } else {
+        LOG(ERROR) << "unsupported diff operation: " << op.type();
+        return false;
+    }
+
+    // Write the final blocks to the COW.
+    size_t dest_pos = 0;
+    for (const auto& extent : op.dst_extents()) {
+        uint64_t size = extent.num_blocks() * kBlockSize;
+        CHECK(dest.size() - dest_pos >= size);
+
+        if (!writer_->AddRawBlocks(extent.start_block(), &dest[dest_pos], size)) {
+            return false;
+        }
+        dest_pos += size;
+    }
+    return true;
+}
+
+borrowed_fd PayloadConverter::OpenSourceImage() {
+    if (source_image_ >= 0) {
+        return source_image_;
+    }
+
+    unique_fd unzip_fd;
+
+    auto local_path = "IMAGES/" + partition_name_ + ".img";
+    if (source_tf_zip_) {
+        {
+            TemporaryFile tmp;
+            if (tmp.fd < 0) {
+                PLOG(ERROR) << "mkstemp failed";
+                return -1;
+            }
+            unzip_fd.reset(tmp.release());
+        }
+
+        ZipEntry64 entry;
+        if (FindEntry(source_tf_zip_.get(), local_path, &entry)) {
+            LOG(ERROR) << "not found in archive: " << local_path;
+            return -1;
+        }
+        if (ExtractEntryToFile(source_tf_zip_.get(), &entry, unzip_fd.get())) {
+            LOG(ERROR) << "could not extract " << local_path;
+            return -1;
+        }
+        if (lseek(unzip_fd.get(), 0, SEEK_SET) < 0) {
+            PLOG(ERROR) << "lseek failed";
+            return -1;
+        }
+    } else if (source_tf_fd_ >= 0) {
+        unzip_fd.reset(openat(source_tf_fd_.get(), local_path.c_str(), O_RDONLY));
+        if (unzip_fd < 0) {
+            PLOG(ERROR) << "open failed: " << FLAGS_source_tf << "/" << local_path;
+            return -1;
+        }
+    } else {
+        LOG(ERROR) << "No source target files package was specified; need -source_tf";
+        return -1;
+    }
+
+    std::unique_ptr<struct sparse_file, decltype(&sparse_file_destroy)> s(
+            sparse_file_import(unzip_fd.get(), false, false), &sparse_file_destroy);
+    if (s) {
+        TemporaryFile tmp;
+        if (tmp.fd < 0) {
+            PLOG(ERROR) << "mkstemp failed";
+            return -1;
+        }
+        if (sparse_file_write(s.get(), tmp.fd, false, false, false) < 0) {
+            LOG(ERROR) << "sparse_file_write failed";
+            return -1;
+        }
+        source_image_.reset(tmp.release());
+    } else {
+        source_image_ = std::move(unzip_fd);
+    }
+    return source_image_;
+}
+
+template <typename ContainerType>
+class ExtentIter final {
+  public:
+    ExtentIter(const ContainerType& container)
+        : iter_(container.cbegin()), end_(container.cend()) {}
+
+    bool GetNext(uint64_t* block) {
+        while (iter_ != end_) {
+            if (dst_index_ < iter_->num_blocks()) {
+                break;
+            }
+            iter_++;
+            dst_index_ = 0;
+        }
+        if (iter_ == end_) {
+            return false;
+        }
+        *block = iter_->start_block() + dst_index_;
+        dst_index_++;
+        return true;
+    }
+
+  private:
+    typename ContainerType::const_iterator iter_;
+    typename ContainerType::const_iterator end_;
+    uint64_t dst_index_;
+};
+
+bool PayloadConverter::ProcessCopy(const InstallOperation& op) {
+    ExtentIter dst_blocks(op.dst_extents());
+
+    for (const auto& extent : op.src_extents()) {
+        for (uint64_t i = 0; i < extent.num_blocks(); i++) {
+            uint64_t src_block = extent.start_block() + i;
+            uint64_t dst_block;
+            if (!dst_blocks.GetNext(&dst_block)) {
+                LOG(ERROR) << "SOURCE_COPY contained mismatching extents";
+                return false;
+            }
+            if (src_block == dst_block) continue;
+            if (!writer_->AddCopy(dst_block, src_block)) {
+                LOG(ERROR) << "Could not add copy operation";
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
+bool PayloadConverter::ProcessReplace(const InstallOperation& op) {
+    auto buffer_size = op.data_length();
+    auto buffer = std::make_unique<char[]>(buffer_size);
+    uint64_t offs = payload_offset_ + op.data_offset();
+    if (lseek(in_fd_.get(), offs, SEEK_SET) < 0) {
+        PLOG(ERROR) << "lseek " << offs << " failed";
+        return false;
+    }
+    if (!android::base::ReadFully(in_fd_, buffer.get(), buffer_size)) {
+        PLOG(ERROR) << "read " << buffer_size << " bytes from offset " << offs << "failed";
+        return false;
+    }
+
+    uint64_t dst_size = 0;
+    for (const auto& extent : op.dst_extents()) {
+        dst_size += extent.num_blocks() * kBlockSize;
+    }
+
+    if (op.type() == InstallOperation::REPLACE_BZ) {
+        auto tmp = std::make_unique<char[]>(dst_size);
+
+        uint32_t actual_size;
+        if (dst_size > std::numeric_limits<typeof(actual_size)>::max()) {
+            LOG(ERROR) << "too many bytes to decompress: " << dst_size;
+            return false;
+        }
+        actual_size = static_cast<uint32_t>(dst_size);
+
+        auto rv = BZ2_bzBuffToBuffDecompress(tmp.get(), &actual_size, buffer.get(), buffer_size, 0,
+                                             0);
+        if (rv) {
+            LOG(ERROR) << "bz2 decompress failed: " << rv;
+            return false;
+        }
+        if (actual_size != dst_size) {
+            LOG(ERROR) << "bz2 returned " << actual_size << " bytes, expected " << dst_size;
+            return false;
+        }
+        buffer = std::move(tmp);
+        buffer_size = dst_size;
+    } else if (op.type() == InstallOperation::REPLACE_XZ) {
+        constexpr uint32_t kXzMaxDictSize = 64 * 1024 * 1024;
+
+        if (dst_size > std::numeric_limits<size_t>::max()) {
+            LOG(ERROR) << "too many bytes to decompress: " << dst_size;
+            return false;
+        }
+
+        std::unique_ptr<struct xz_dec, decltype(&xz_dec_end)> s(
+                xz_dec_init(XZ_DYNALLOC, kXzMaxDictSize), xz_dec_end);
+        if (!s) {
+            LOG(ERROR) << "xz_dec_init failed";
+            return false;
+        }
+
+        auto tmp = std::make_unique<char[]>(dst_size);
+
+        struct xz_buf args;
+        args.in = reinterpret_cast<const uint8_t*>(buffer.get());
+        args.in_pos = 0;
+        args.in_size = buffer_size;
+        args.out = reinterpret_cast<uint8_t*>(tmp.get());
+        args.out_pos = 0;
+        args.out_size = dst_size;
+
+        auto rv = xz_dec_run(s.get(), &args);
+        if (rv != XZ_STREAM_END) {
+            LOG(ERROR) << "xz decompress failed: " << (int)rv;
+            return false;
+        }
+        buffer = std::move(tmp);
+        buffer_size = dst_size;
+    }
+
+    uint64_t buffer_pos = 0;
+    for (const auto& extent : op.dst_extents()) {
+        uint64_t extent_size = extent.num_blocks() * kBlockSize;
+        if (buffer_size - buffer_pos < extent_size) {
+            LOG(ERROR) << "replace op ran out of input buffer";
+            return false;
+        }
+        if (!writer_->AddRawBlocks(extent.start_block(), buffer.get() + buffer_pos, extent_size)) {
+            LOG(ERROR) << "failed to add raw blocks from replace op";
+            return false;
+        }
+        buffer_pos += extent_size;
+    }
+    return true;
+}
+
+bool PayloadConverter::OpenPayload() {
+    in_fd_.reset(open(in_file_.c_str(), O_RDONLY));
+    if (in_fd_ < 0) {
+        PLOG(ERROR) << "open " << in_file_;
+        return false;
+    }
+
+    char magic[4];
+    if (!android::base::ReadFully(in_fd_, magic, sizeof(magic))) {
+        PLOG(ERROR) << "read magic";
+        return false;
+    }
+    if (std::string(magic, sizeof(magic)) != "CrAU") {
+        LOG(ERROR) << "Invalid magic in " << in_file_;
+        return false;
+    }
+
+    uint64_t version;
+    uint64_t manifest_size;
+    uint32_t manifest_signature_size = 0;
+    if (!android::base::ReadFully(in_fd_, &version, sizeof(version))) {
+        PLOG(ERROR) << "read version";
+        return false;
+    }
+    version = ToLittleEndian(version);
+    if (version < 2) {
+        LOG(ERROR) << "Only payload version 2 or higher is supported.";
+        return false;
+    }
+
+    if (!android::base::ReadFully(in_fd_, &manifest_size, sizeof(manifest_size))) {
+        PLOG(ERROR) << "read manifest_size";
+        return false;
+    }
+    manifest_size = ToLittleEndian(manifest_size);
+    if (!android::base::ReadFully(in_fd_, &manifest_signature_size,
+                                  sizeof(manifest_signature_size))) {
+        PLOG(ERROR) << "read manifest_signature_size";
+        return false;
+    }
+    manifest_signature_size = ntohl(manifest_signature_size);
+
+    auto manifest = std::make_unique<uint8_t[]>(manifest_size);
+    if (!android::base::ReadFully(in_fd_, manifest.get(), manifest_size)) {
+        PLOG(ERROR) << "read manifest";
+        return false;
+    }
+
+    // Skip past manifest signature.
+    auto offs = lseek(in_fd_, manifest_signature_size, SEEK_CUR);
+    if (offs < 0) {
+        PLOG(ERROR) << "lseek failed";
+        return false;
+    }
+    payload_offset_ = offs;
+
+    if (!manifest_.ParseFromArray(manifest.get(), manifest_size)) {
+        LOG(ERROR) << "could not parse manifest";
+        return false;
+    }
+    return true;
+}
+
+}  // namespace snapshot
+}  // namespace android
+
+int main(int argc, char** argv) {
+    android::base::InitLogging(argv, android::snapshot::MyLogger);
+    gflags::SetUsageMessage("Convert OTA payload to a Virtual A/B COW");
+    int arg_start = gflags::ParseCommandLineFlags(&argc, &argv, false);
+
+    xz_crc32_init();
+
+    if (argc - arg_start != 2) {
+        std::cerr << "Usage: [options] <payload.bin> <out-dir>\n";
+        return 1;
+    }
+
+    android::snapshot::PayloadConverter pc(argv[arg_start], argv[arg_start + 1]);
+    return pc.Run() ? 0 : 1;
+}