问题：系统在采用差分升级时，因业务要求，需要一部分分区需要差分升级，另一部分特定分区需要整包升级

分析：正常情况下，当使用./build/make/tools/releasetools/ota_from_target_files.py  -i  old.zip  new.zip  cfb.zip命令制作差分包时，所有分区均采用了差分升级。所以要想达到上述业务要求，需修改编译脚本，本次提供2种方式进行修改，均可。

第一种：

修改代码路径：aosp/system/update_engine/payload_generator/delta_diff_utils.cc

bool ReadExtentsToDiff(const string& old_part,
                       const string& new_part,
                       const vector<Extent>& old_extents,
                       const vector<Extent>& new_extents,
                       const vector<puffin::BitExtent>& old_deflates,
                       const vector<puffin::BitExtent>& new_deflates,
                       const PayloadVersion& version,
                       brillo::Blob* out_data,
                       InstallOperation* out_op) {
  InstallOperation operation;

  // We read blocks from old_extents and write blocks to new_extents.
  uint64_t blocks_to_read = utils::BlocksInExtents(old_extents);
  uint64_t blocks_to_write = utils::BlocksInExtents(new_extents);

  // Disable bsdiff, and puffdiff when the data is too big.
  bool bsdiff_allowed =
      version.OperationAllowed(InstallOperation::SOURCE_BSDIFF) ||
      version.OperationAllowed(InstallOperation::BSDIFF);

//此处主要是判断当前遍历的分区bsdiff大小是否大于200mb，若是大于，则不采用差分diff增量升级，从做差分包效率性能考虑

  if (bsdiff_allowed &&
      blocks_to_read * kBlockSize > kMaxBsdiffDestinationSize) {
    LOG(INFO) << "bsdiff blacklisted, data too big: "
              << blocks_to_read * kBlockSize << " bytes";
    bsdiff_allowed = false;
  }

//此处主要是判断当前遍历的分区puffdif大小是否大于100mb，若是大于，则不采用差分puffdiff增量升，
  bool puffdiff_allowed = version.OperationAllowed(InstallOperation::PUFFDIFF);
  if (puffdiff_allowed &&
      blocks_to_read * kBlockSize > kMaxPuffdiffDestinationSize) {
    LOG(INFO) << "puffdiff blacklisted, data too big: "
              << blocks_to_read * kBlockSize << " bytes";
    puffdiff_allowed = false;
  }

/*****修改处******* 将特定分区时，两个Boolean值全部修改为false，跳过差分增量升级/
 if(new_part.find("修改的分区名例如 system") != string::npos ){
	bsdiff_allowed = false;
	puffdiff_allowed = false;
	
 }

  // Make copies of the extents so we can modify them.
  vector<Extent> src_extents = old_extents;
  vector<Extent> dst_extents = new_extents;

第二种：

代码路径：aosp/system/update_engine/payload_generator/delta_diff_generator.cc

bool GenerateUpdatePayloadFile(const PayloadGenerationConfig& config,
                               const string& output_path,
                               const string& private_key_path,
                               uint64_t* metadata_size) {
  if (!config.version.Validate()) {
    LOG(ERROR) << "Unsupported major.minor version: " << config.version.major
               << "." << config.version.minor;
    return false;
  }

  // Create empty payload file object.
  PayloadFile payload;
  TEST_AND_RETURN_FALSE(payload.Init(config));

  const string kTempFileTemplate("CrAU_temp_data.XXXXXX");
  string temp_file_path;
  int data_file_fd;
  TEST_AND_RETURN_FALSE(
      utils::MakeTempFile(kTempFileTemplate, &temp_file_path, &data_file_fd));
  ScopedPathUnlinker temp_file_unlinker(temp_file_path);
  TEST_AND_RETURN_FALSE(data_file_fd >= 0);

  {
    off_t data_file_size = 0;
    ScopedFdCloser data_file_fd_closer(&data_file_fd);
    BlobFileWriter blob_file(data_file_fd, &data_file_size);
    if (config.is_delta) {
      TEST_AND_RETURN_FALSE(config.source.partitions.size() ==
                            config.target.partitions.size());
    }
    PartitionConfig empty_part("");
    for (size_t i = 0; i < config.target.partitions.size(); i++) {
      const PartitionConfig& old_part =
          config.is_delta ? config.source.partitions[i] : empty_part;
      const PartitionConfig& new_part = config.target.partitions[i];
      LOG(INFO) << "Partition name: " << new_part.name;
      LOG(INFO) << "Partition size: " << new_part.size;
      LOG(INFO) << "Block count: " << new_part.size / config.block_size;

      // Select payload generation strategy based on the config.
      unique_ptr<OperationsGenerator> strategy;
      if (!old_part.path.empty()) {
        // Delta update.
   /*******修改处******遍历特定分区时，直接采用FullUpdateGenerator()整分区升级方法****/
    if(new_part.name.find("修改的分区名例如 system") != string::npos ){
	    strategy.reset(new FullUpdateGenerator());
     }else   if (config.version.minor == kInPlaceMinorPayloadVersion) {
          LOG(INFO) << "Using generator InplaceGenerator().";
          strategy.reset(new InplaceGenerator());
        } else {
          LOG(INFO) << "Using generator ABGenerator().";
          strategy.reset(new ABGenerator());
        }
      } else {
        LOG(INFO) << "Using generator FullUpdateGenerator().";
        strategy.reset(new FullUpdateGenerator());
      }

      vector<AnnotatedOperation> aops;
      // Generate the operations using the strategy we selected above.
      TEST_AND_RETURN_FALSE(strategy->GenerateOperations(
          config, old_part, new_part, &blob_file, &aops));

      // Filter the no-operations. OperationsGenerators should not output this
      // kind of operations normally, but this is an extra step to fix that if
      // happened.
      diff_utils::FilterNoopOperations(&aops);

      TEST_AND_RETURN_FALSE(payload.AddPartition(old_part, new_part, aops));
    }
  }

  LOG(INFO) << "Writing payload file...";
  // Write payload file to disk.
  TEST_AND_RETURN_FALSE(payload.WritePayload(
      output_path, temp_file_path, private_key_path, metadata_size));

  LOG(INFO) << "All done. Successfully created delta file with "
            << "metadata size = " << *metadata_size;
  return true;
}

 按照上述两种方式 代码修改后，单编make delta_generator，然后重新执行 差分命令，即可。