fs_mgr/libsnapshot/libsnapshot_cow/create_cow.cpp

#include <linux/types.h>
#include <stdint.h>
#include <stdlib.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

#include <condition_variable>
#include <cstring>
#include <future>
#include <iostream>
#include <limits>
#include <mutex>
#include <string>
#include <thread>
#include <unordered_map>
#include <vector>

#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <android-base/unique_fd.h>
#include <ext4_utils/ext4_utils.h>
#include <storage_literals/storage_literals.h>

#include <android-base/chrono_utils.h>
#include <android-base/scopeguard.h>
#include <android-base/strings.h>

#include <gflags/gflags.h>
#include <libsnapshot/cow_writer.h>

#include <openssl/sha.h>

DEFINE_string(source, "", "Source partition image");
DEFINE_string(target, "", "Target partition image");
DEFINE_string(compression, "lz4",
              "Compression algorithm. Default is set to lz4. Available options: lz4, zstd, gz");

namespace android {
namespace snapshot {

using namespace android::storage_literals;
using namespace android;
using android::base::unique_fd;

using android::snapshot::CreateCowWriter;
using android::snapshot::ICowWriter;

class CreateSnapshot {
  public:
    CreateSnapshot(const std::string& src_file, const std::string& target_file,
                   const std::string& patch_file, const std::string& compression);
    bool CreateSnapshotPatch();

  private:
    /* source.img */
    std::string src_file_;
    /* target.img */
    std::string target_file_;
    /* snapshot-patch generated */
    std::string patch_file_;

    /*
     * Active file which is being parsed by this instance.
     * It will either be source.img or target.img.
     */
    std::string parsing_file_;
    bool create_snapshot_patch_ = false;

    const int kNumThreads = 6;
    const size_t kBlockSizeToRead = 1_MiB;

    std::unordered_map<std::string, int> source_block_hash_;
    std::mutex source_block_hash_lock_;

    std::unique_ptr<ICowWriter> writer_;
    std::mutex write_lock_;

    std::unique_ptr<uint8_t[]> zblock_;

    std::string compression_ = "lz4";
    unique_fd fd_;

    const int BLOCK_SZ = 4_KiB;
    void SHA256(const void* data, size_t length, uint8_t out[32]);
    bool IsBlockAligned(uint64_t read_size) { return ((read_size & (BLOCK_SZ - 1)) == 0); }
    bool ReadBlocks(off_t offset, const int skip_blocks, const uint64_t dev_sz);
    std::string ToHexString(const uint8_t* buf, size_t len);

    bool CreateSnapshotFile();
    bool FindSourceBlockHash();
    bool PrepareParse(std::string& parsing_file, const bool createSnapshot);
    bool ParsePartition();
    bool WriteSnapshot(const void* buffer, uint64_t block, std::string& block_hash);
};

void CreateSnapshotLogger(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);
    }
}

CreateSnapshot::CreateSnapshot(const std::string& src_file, const std::string& target_file,
                               const std::string& patch_file, const std::string& compression)
    : src_file_(src_file), target_file_(target_file), patch_file_(patch_file) {
    if (!compression.empty()) {
        compression_ = compression;
    }
}

bool CreateSnapshot::PrepareParse(std::string& parsing_file, const bool createSnapshot) {
    parsing_file_ = parsing_file;
    create_snapshot_patch_ = createSnapshot;

    if (createSnapshot) {
        fd_.reset(open(patch_file_.c_str(), O_RDWR | O_CREAT | O_TRUNC, 0666));
        if (fd_ < 0) {
            PLOG(ERROR) << "Failed to open the snapshot-patch file: " << patch_file_;
            return false;
        }

        zblock_ = std::make_unique<uint8_t[]>(BLOCK_SZ);
        std::memset(zblock_.get(), 0, BLOCK_SZ);

        CowOptions options;
        options.compression = compression_;
        options.num_compress_threads = 2;
        options.batch_write = true;
        options.cluster_ops = 600;
        writer_ = CreateCowWriter(2, options, std::move(fd_));
    }
    return true;
}

/*
 * Create per-block sha256 hash of source partition
 */
bool CreateSnapshot::FindSourceBlockHash() {
    if (!PrepareParse(src_file_, false)) {
        return false;
    }
    return ParsePartition();
}

/*
 * Create snapshot file by comparing sha256 per block
 * of target.img with the constructed per-block sha256 hash
 * of source partition.
 */
bool CreateSnapshot::CreateSnapshotFile() {
    if (!PrepareParse(target_file_, true)) {
        return false;
    }
    return ParsePartition();
}

/*
 * Creates snapshot patch file by comparing source.img and target.img
 */
bool CreateSnapshot::CreateSnapshotPatch() {
    if (!FindSourceBlockHash()) {
        return false;
    }
    return CreateSnapshotFile();
}

void CreateSnapshot::SHA256(const void* data, size_t length, uint8_t out[32]) {
    SHA256_CTX c;
    SHA256_Init(&c);
    SHA256_Update(&c, data, length);
    SHA256_Final(out, &c);
}

std::string CreateSnapshot::ToHexString(const uint8_t* buf, size_t len) {
    char lookup[] = "0123456789abcdef";
    std::string out(len * 2 + 1, '\0');
    char* outp = out.data();
    for (; len > 0; len--, buf++) {
        *outp++ = (char)lookup[*buf >> 4];
        *outp++ = (char)lookup[*buf & 0xf];
    }
    return out;
}

bool CreateSnapshot::WriteSnapshot(const void* buffer, uint64_t block, std::string& block_hash) {
    if (std::memcmp(zblock_.get(), buffer, BLOCK_SZ) == 0) {
        std::lock_guard<std::mutex> lock(write_lock_);
        return writer_->AddZeroBlocks(block, 1);
    }

    auto iter = source_block_hash_.find(block_hash);
    if (iter != source_block_hash_.end()) {
        std::lock_guard<std::mutex> lock(write_lock_);
        return writer_->AddCopy(block, iter->second, 1);
    }
    std::lock_guard<std::mutex> lock(write_lock_);
    return writer_->AddRawBlocks(block, buffer, BLOCK_SZ);
}

bool CreateSnapshot::ReadBlocks(off_t offset, const int skip_blocks, const uint64_t dev_sz) {
    unique_fd fd(TEMP_FAILURE_RETRY(open(parsing_file_.c_str(), O_RDONLY)));
    if (fd < 0) {
        LOG(ERROR) << "open failed: " << parsing_file_;
        return false;
    }

    loff_t file_offset = offset;
    const uint64_t read_sz = kBlockSizeToRead;
    std::unique_ptr<uint8_t[]> buffer = std::make_unique<uint8_t[]>(read_sz);

    while (true) {
        size_t to_read = std::min((dev_sz - file_offset), read_sz);

        if (!android::base::ReadFullyAtOffset(fd.get(), buffer.get(), to_read, file_offset)) {
            LOG(ERROR) << "Failed to read block from block device: " << parsing_file_
                       << " at offset: " << file_offset << " read-size: " << to_read
                       << " block-size: " << dev_sz;
            return false;
        }

        if (!IsBlockAligned(to_read)) {
            LOG(ERROR) << "unable to parse the un-aligned request: " << to_read;
            return false;
        }

        size_t num_blocks = to_read / BLOCK_SZ;
        uint64_t buffer_offset = 0;
        off_t foffset = file_offset;

        while (num_blocks) {
            const void* bufptr = (char*)buffer.get() + buffer_offset;
            uint64_t blkindex = foffset / BLOCK_SZ;

            uint8_t checksum[32];
            SHA256(bufptr, BLOCK_SZ, checksum);
            std::string hash = ToHexString(checksum, sizeof(checksum));

            if (create_snapshot_patch_) {
                if (!WriteSnapshot(bufptr, blkindex, hash)) {
                    LOG(ERROR) << "WriteSnapshot failed for block: " << blkindex;
                    return false;
                }
            } else {
                std::lock_guard<std::mutex> lock(source_block_hash_lock_);
                {
                    if (source_block_hash_.count(hash) == 0) {
                        source_block_hash_[hash] = blkindex;
                    }
                }
            }
            buffer_offset += BLOCK_SZ;
            foffset += BLOCK_SZ;
            num_blocks -= 1;
        }

        file_offset += (skip_blocks * to_read);
        if (file_offset >= dev_sz) {
            break;
        }
    }

    return true;
}

bool CreateSnapshot::ParsePartition() {
    unique_fd fd(TEMP_FAILURE_RETRY(open(parsing_file_.c_str(), O_RDONLY)));
    if (fd < 0) {
        LOG(ERROR) << "open failed: " << parsing_file_;
        return false;
    }

    uint64_t dev_sz = lseek(fd.get(), 0, SEEK_END);
    if (!dev_sz) {
        LOG(ERROR) << "Could not determine block device size: " << parsing_file_;
        return false;
    }

    if (!IsBlockAligned(dev_sz)) {
        LOG(ERROR) << "dev_sz: " << dev_sz << " is not block aligned";
        return false;
    }

    int num_threads = kNumThreads;

    std::vector<std::future<bool>> threads;
    off_t start_offset = 0;
    const int skip_blocks = num_threads;

    while (num_threads) {
        threads.emplace_back(std::async(std::launch::async, &CreateSnapshot::ReadBlocks, this,
                                        start_offset, skip_blocks, dev_sz));
        start_offset += kBlockSizeToRead;
        num_threads -= 1;
        if (start_offset >= dev_sz) {
            break;
        }
    }

    bool ret = true;
    for (auto& t : threads) {
        ret = t.get() && ret;
    }

    if (ret && create_snapshot_patch_ && !writer_->Finalize()) {
        LOG(ERROR) << "Finzalize failed";
        return false;
    }

    return ret;
}

}  // namespace snapshot
}  // namespace android

constexpr char kUsage[] = R"(
NAME
    create_snapshot - Create snapshot patches by comparing two partition images

SYNOPSIS
    create_snapshot --source=<source.img> --target=<target.img> --compression="<compression-algorithm"

    source.img -> Source partition image
    target.img -> Target partition image
    compressoin -> compression algorithm. Default set to lz4. Supported types are gz, lz4, zstd.

EXAMPLES

   $ create_snapshot $SOURCE_BUILD/system.img $TARGET_BUILD/system.img
   $ create_snapshot $SOURCE_BUILD/product.img $TARGET_BUILD/product.img --compression="zstd"

)";

int main(int argc, char* argv[]) {
    android::base::InitLogging(argv, &android::snapshot::CreateSnapshotLogger);
    ::gflags::SetUsageMessage(kUsage);
    ::gflags::ParseCommandLineFlags(&argc, &argv, true);

    if (FLAGS_source.empty() || FLAGS_target.empty()) {
        LOG(INFO) << kUsage;
        return 0;
    }

    std::string fname = android::base::Basename(FLAGS_target.c_str());
    auto parts = android::base::Split(fname, ".");
    std::string snapshotfile = parts[0] + ".patch";
    android::snapshot::CreateSnapshot snapshot(FLAGS_source, FLAGS_target, snapshotfile,
                                               FLAGS_compression);

    if (!snapshot.CreateSnapshotPatch()) {
        LOG(ERROR) << "Snapshot creation failed";
        return -1;
    }

    LOG(INFO) << "Snapshot patch: " << snapshotfile << " created successfully";
    return 0;
}