稀疏镜像在OpenHarmony上的应用

开源项目 OpenHarmony是每个人的 OpenHarmony

陈甲印

鸿湖万联高级技术专家

鸿湖万联产品推荐官

一、稀疏镜像升级背景

常用系统镜像格式为原始镜像，即RAW格式。镜像体积比较大，在烧录固件或者升级固件时比较耗时，而且在移动设备升级过程时比较耗费流量。为此，将原始镜像用稀疏描述，可以大大地缩减镜像体积，省时省流量。

二、稀疏镜像原理

1、稀疏镜像的概念 原始镜像：即raw image，完整的ext4分区镜像，包含很多全零的无效填充区 稀疏镜像：即sparse image，将raw ext4进行稀疏描述，因此尺寸比较小，制作目录有多少文件就计算多少，没有全零填充2、稀疏镜像格式   稀疏镜像数据格式：首先是sparse_header占用28byte，然后是12byte的chunk_header，同样这chunk_header的类型决定了后面跟着的数据，如果读到数据是0xCAC1意味着后面是本身的raw_data，如果是0xCAC3，则后面num为0，接着再0xCAC2意味着后面填充4byte的内容。  

三、实现稀疏镜像升级方案

版本基线：

OpenAtom OpenHarmony（以下简称“OpenHarmony”） 3.1 Release

代码路径：

https://gitee.com/openharmony/docs/blob/master/zh-cn/release-notes/OpenHarmony-v3.1-release.md

1、稀疏镜像烧录（1）生成稀疏格式镜像有2种方法可以生成稀疏镜像：1）修改文件build/ohos_var.gni中，sparse_image=true  2）编译命令增加--sparse-image字段，如./build.sh --product-name=xxx --sparse-image（2）增加稀疏格式转换工具在目录build/ohos/images/mkimage中增加文件img2simg，该工具用于编译完成后将raw镜像转换为sparse格式，并设置权限为777。（3）编译后的镜像对比  编译出的镜像格式为sparse格式，镜像大小相比raw格式明显变小。（4）烧录稀疏镜像烧录稀疏镜像方法和烧录原始镜像方法一致。稀疏镜像本身是不能直接挂载的，在烧录过程中通过uboot将稀疏格式镜像还原为原始镜像，然后写到磁盘中，系统启动后可挂载对应的镜像。 2、稀疏镜像升级升级包采用稀疏镜像制作。（1）修改升级包制作工具官方升级包工具不支持生成稀疏镜像的升级包，修改升级包工具，生成稀疏格式的升级包。.aseupdatepackaging_toolsimage_class.py  按照上图所示注释代码（2）生成稀疏镜像升级包和全量镜像升级包制作方法一致。

参考：

https://gitee.com/openharmony/docs/blob/master/zh-cn/device-dev/subsystems/subsys-ota-guide.md#%E6%A0%87%E5%87%86%E7%B3%BB%E7%BB%9F%E5%8D%87%E7%BA%A7%E5%8C%85%E5%88%B6%E4%BD%9C

（3）适配updater组件中稀疏镜像功能●增加写稀疏镜像分支.aseupdateupdaterservicesapplypatchdata_writer.cpp写数据函数CreateDataWriter增加写稀疏镜像分支

case WRITE_SPARSE:
{
    std::unique_ptr writer(std::make_unique(partitionName));
    return std::move(writer);
}

●增加稀疏镜像类声明.aseupdateupdaterservicesapplypatch aw_writer.h增加稀疏镜像类声明及相关变量定义

typedefstructsparse_header{
 uint32_tmagic;  /* 0xed26ff3a */
 uint16_tmajor_version;/* (0x1) - reject images with higher major versions */
 uint16_tminor_version;/* (0x0) - allow images with higer minor versions */
 uint16_tfile_hdr_sz; /* 28 bytes for first revision of the file format */
 uint16_tchunk_hdr_sz; /* 12 bytes for first revision of the file format */
 uint32_tblk_sz;  /* block size in bytes, must be a multiple of 4 (4096) */
 uint32_ttotal_blks;/* total blocks in the non-sparse output image */
 uint32_ttotal_chunks; /* total chunks in the sparse input image */
 uint32_timage_checksum;/* CRC32 checksum of the original data, counting "don't care" */
        /* as 0. Standard 802.3 polynomial, use a Public Domain */
        /* table implementation */
} sparse_header_t;

#defineSPARSE_HEADER_MAGIC 0xed26ff3a

#defineCHUNK_TYPE_RAW   0xCAC1
#defineCHUNK_TYPE_FILL   0xCAC2
#defineCHUNK_TYPE_DONT_CARE  0xCAC3
#defineCHUNK_TYPE_CRC32  0xCAC4

typedefstructchunk_header{
 uint16_tchunk_type;/* 0xCAC1 -> raw; 0xCAC2 -> fill; 0xCAC3 -> don't care */
 uint16_treserved1;
 uint32_tchunk_sz; /* in blocks in output image */
 uint32_ttotal_sz; /* in bytes of chunk input file including chunk header and data */
} chunk_header_t;

classSparseWriter: publicDataWriter{
public:
  virtualboolWrite(constuint8_t*addr, size_tlen, WriteModemode, conststd::string&partitionName);

  explicitSparseWriter(conststd::stringpartitionName) : offset_(0), fd_(-1), partitionName_(partitionName) {}

  virtual~SparseWriter()
  {
    offset_= 0;
    if(fd_> 0) {
      fsync(fd_);
      close(fd_);
    }
    fd_= -1;
  }
private:
  intWriteInternal(intfd, constuint8_t*data, size_tlen, conststd::string&partitionName);

  SparseWriter(constSparseWriter&) = delete;

  constSparseWriter&operator=(constSparseWriter&) = delete;
  off64_toffset_;
  intfd_;
  std::string partitionName_;
};

●增加稀疏镜像类实现.aseupdateupdaterservicesapplypatch aw_writer.cpp增加稀疏镜像类实现及相关变量定义，原有代码不变

bool SparseWriter::Write(const uint8_t *addr, size_t len, WriteMode mode, const std::string &partitionName)
{
  if (addr == nullptr) {
    LOG(ERROR) << "SparseWriter: invalid address.";
    return false;
  }
  if (len == 0) {
    LOG(INFO) << "SparseWriter: write length is 0, skip.";
    return false;
  }
  if (fd_ < 0) {
    fd_ = OpenPartition(partitionName_);
    if (fd_ < 0) {
      return false;
    }
  }

  UPDATER_CHECK_ONLY_RETURN(WriteInternal(fd_, addr, len, partitionName_) >= 0, return false);
  return true;
}


int SparseWriter::WriteInternal(int fd, const uint8_t *data, size_t len, const std::string &partitionName)
{
  uint32_t written = 0;
  sparse_header_t *sparse_header;
  chunk_header_t *chunk_header;
  unsigned int chunk;
  void *membuf = NULL;
  uint32_t *fill_buf = NULL;
  uint32_t fill_val;
  uint32_t bytes_written = 0;
  uint32_t total_bytes = 0;
  uint32_t blk = 0;
  uint32_t chunk_data_sz = 0;
  uint32_t blkcnt = 0;
  uint32_t blks = 0;
  uint32_t total_blocks = 0;
  uint32_t addr_offset = 0;
  uint32_t fill_buf_num_blks = 0;


  uint32_t block_size = 4096;
  uint32_t block_count = 524288;
  uint32_t i;
  uint32_t j;
  int ret = lseek64(fd, offset_, SEEK_SET);
  UPDATER_FILE_CHECK(ret != -1, "RawWriter: failed to seek file to " << offset_, return -1);
  fill_buf_num_blks = CONFIG_FASTBOOT_FLASH_FILLBUF_SIZE / block_size;
  LOG(INFO) << "WriteInternal offset_ " << offset_;
  /* Read and skip over sparse image header */
  sparse_header = (sparse_header_t *)data;
  data += sparse_header->file_hdr_sz;
  if (sparse_header->file_hdr_sz > sizeof(sparse_header_t)) {
    /*
    * Skip the remaining bytes in a header that is longer than
    * we expected.
    */
    data += (sparse_header->file_hdr_sz - sizeof(sparse_header_t));
  }
  LOG(INFO) << "=== Sparse Image Header ===";
  LOG(INFO) << "magic: "  << sparse_header->magic;
  LOG(INFO) << "major_version: " << sparse_header->major_version;
  LOG(INFO) << "minor_version: " << sparse_header->minor_version;
  LOG(INFO) << "file_hdr_sz: " << sparse_header->file_hdr_sz;
  LOG(INFO) << "chunk_hdr_sz: " << sparse_header->chunk_hdr_sz;
  LOG(INFO) << "blk_sz: " << sparse_header->blk_sz;
  LOG(INFO) << "total_blks: " << sparse_header->total_blks;
  LOG(INFO) << "total_chunks: " << sparse_header->total_chunks;


  LOG(INFO) << "Flashing Sparse Image";
  blk = 0;
  for (chunk = 0; chunk < sparse_header->total_chunks; chunk++) {
    /* Read and skip over chunk header */
    chunk_header = (chunk_header_t *)data;
    data += sizeof(chunk_header_t);
    if (chunk_header->chunk_type != CHUNK_TYPE_RAW) 
    {
      LOG(INFO) << "=== Chunk Header ===";
      LOG(INFO) << "chunk_type: " << chunk_header->chunk_type;
      LOG(INFO) << "chunk_sz: " << chunk_header->chunk_sz;
      LOG(INFO) << "total_sz: " << chunk_header->total_sz;
    }
    if (sparse_header->chunk_hdr_sz > sizeof(chunk_header_t)) {
      /*
      * Skip the remaining bytes in a header that is longer
      * than we expected.
      */
      data += (sparse_header->chunk_hdr_sz -
        sizeof(chunk_header_t));
    }
    chunk_data_sz = sparse_header->blk_sz * chunk_header->chunk_sz;
    blkcnt = chunk_data_sz / block_size;
    switch (chunk_header->chunk_type) {
    case CHUNK_TYPE_RAW:
      if (chunk_header->total_sz !=
        (sparse_header->chunk_hdr_sz + chunk_data_sz)) {
        LOG(ERROR) << "Bogus chunk size for chunk type Raw";
        return -1;
      }
      if (blk + blkcnt > 0 + block_count) {
        LOG(ERROR) << "Request would exceed partition size!";
        return -1;
      }
      addr_offset = blk * block_size;
      ret = lseek64(fd, offset_ + addr_offset, SEEK_SET);
      if (ret < 0) {
        LOG(ERROR) << "failed to seek file to " << addr_offset << " error=" << strerror(errno);
        return -1;
      }
      written = write(fd, data, blkcnt * block_size);
      if (written < 0) {
        LOG(ERROR) << "SparseWriter: failed to write data of len ";
        return -1;
      }
      total_bytes = total_bytes + blkcnt * block_size;
      blks = written / block_size;
      blk += blks;
      bytes_written += blkcnt * block_size;
      total_blocks += chunk_header->chunk_sz;
      data += chunk_data_sz;
      break;
    case CHUNK_TYPE_FILL:
      if (chunk_header->total_sz !=
        (sparse_header->chunk_hdr_sz + sizeof(uint32_t))) {
        LOG(ERROR) << "Bogus chunk size for chunk type FILL total_sz err " << chunk_header->total_sz << "
";
        return -1;
      }
      ret = posix_memalign (&membuf, 64, 
            ROUNDUP(
            block_size * fill_buf_num_blks,
            64));
      if (ret) {
        LOG(ERROR) << "posix_memalign:" << strerror (errno);
        return -1;
      }
      fill_buf = (uint32_t *)membuf;
      if (!fill_buf) {
        LOG(ERROR) << "Malloc failed for: CHUNK_TYPE_FILL";
        return -1;
      }
      fill_val = *(uint32_t *)data;
      data = data + sizeof(uint32_t);
      for (i = 0;
        i < (block_size * fill_buf_num_blks /
         sizeof(fill_val));
        i++)
        fill_buf[i] = fill_val;
      if (blk + blkcnt > 0 + block_count) {
        LOG(ERROR) << "Request would exceed partition size!";
        return -1;
      }
      for (i = 0; i < blkcnt;) {
        j = blkcnt - i;
        if (j > fill_buf_num_blks)
          j = fill_buf_num_blks;
        addr_offset = blk * block_size;
        ret = lseek64(fd, offset_ + addr_offset, SEEK_SET);
        if (ret < 0) {
          LOG(ERROR) << "failed to lseek file to " << addr_offset << " error=" << strerror(errno);
          return -1;
        }
        written = write(fd, fill_buf, j * block_size);
        if (written < 0) {
          LOG(ERROR) << "SparseWriter: failed to write data of len ";
          return -1;
        }
        total_bytes = total_bytes + j * block_size;
        blks = written / block_size;
        if (blks < j) {
          LOG(ERROR) << "Write failed, block";
          free(fill_buf);
          return -1;
        }
        blk += blks;
        i += j;
      }
      bytes_written += blkcnt * block_size;
      total_blocks += chunk_data_sz / sparse_header->blk_sz;
      free(fill_buf);
      break;
    case CHUNK_TYPE_DONT_CARE:
      blk += blkcnt;
      total_blocks += chunk_header->chunk_sz;
      break;
    case CHUNK_TYPE_CRC32:
      if (chunk_header->total_sz !=
        sparse_header->chunk_hdr_sz) {
        LOG(ERROR) << "Bogus chunk size for chunk type CRC32 total_sz err " << chunk_header->total_sz;
        return -1;
      }
      total_blocks += chunk_header->chunk_sz;
      data += chunk_data_sz;
      break;
    default:
      LOG(INFO) << __func__ << ": Unknown chunk type: " << chunk_header->chunk_type;
      return -1;
    }
  }
  LOG(INFO) << "Wrote "<< chunk <<"blocks, expected to write " << sparse_header->total_blks << "blocks
";
  LOG(INFO) << "........ wrote "<< bytes_written <<"bytes to " << partitionName << "
";
  LOG(INFO) << "total_bytes=" << total_bytes;
  return 0;
}

3、验证稀疏镜像升级（1）拷贝升级包将制作的稀疏镜像升级包通过HDC工具推进系统data目录，并修改文件名为updater.zip，路径如下：/data/updater/updater.zip（2）启动升级系统启动后，在命令行工具输入如下命令启动升级reboot updater:--update_package=/data/updater/updater.zip输入命令后，系统重启，进入升级页面，等待升级完成。 本文介绍了OpenHarmony系统中实现稀疏镜像升级的方法，理解稀疏镜像原理及稀疏镜像还原方法可以快速在自己的系统中应用稀疏镜像升级，提高系统升级速度。