payload_consumer/vabc_partition_writer.cc

//
// 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 "update_engine/payload_consumer/vabc_partition_writer.h"

#include <memory>
#include <string>
#include <vector>

#include <libsnapshot/cow_writer.h>

#include "update_engine/common/cow_operation_convert.h"
#include "update_engine/common/utils.h"
#include "update_engine/payload_consumer/extent_writer.h"
#include "update_engine/payload_consumer/file_descriptor.h"
#include "update_engine/payload_consumer/install_plan.h"
#include "update_engine/payload_consumer/partition_writer.h"
#include "update_engine/payload_consumer/snapshot_extent_writer.h"

namespace chromeos_update_engine {
// Expected layout of COW file:
// === Beginning of Cow Image ===
// All Source Copy Operations
// ========== Label 0 ==========
// Operation 0 in PartitionUpdate
// ========== Label 1 ==========
// Operation 1 in PartitionUpdate
// ========== label 2 ==========
// Operation 2 in PartitionUpdate
// ========== label 3 ==========
// .
// .
// .

// When resuming, pass |next_op_index_| as label to
// |InitializeWithAppend|.
// For example, suppose we finished writing SOURCE_COPY, and we finished writing
// operation 2 completely. Update is suspended when we are half way through
// operation 3.
// |cnext_op_index_| would be 3, so we pass 3 as
// label to |InitializeWithAppend|. The CowWriter will retain all data before
// label 3, Which contains all operation 2's data, but none of operation 3's
// data.

bool VABCPartitionWriter::Init(const InstallPlan* install_plan,
                               bool source_may_exist,
                               size_t next_op_index) {
  TEST_AND_RETURN_FALSE(install_plan != nullptr);
  TEST_AND_RETURN_FALSE(
      OpenSourcePartition(install_plan->source_slot, source_may_exist));
  std::optional<std::string> source_path;
  if (!install_part_.source_path.empty()) {
    // TODO(zhangkelvin) Make |source_path| a std::optional<std::string>
    source_path = install_part_.source_path;
  }
  cow_writer_ = dynamic_control_->OpenCowWriter(
      install_part_.name, source_path, install_plan->is_resume);
  TEST_AND_RETURN_FALSE(cow_writer_ != nullptr);

  // ===== Resume case handling code goes here ====
  // It is possible that the SOURCE_COPY are already written but
  // |next_op_index_| is still 0. In this case we discard previously written
  // SOURCE_COPY, and start over.
  if (install_plan->is_resume && next_op_index > 0) {
    LOG(INFO) << "Resuming update on partition `"
              << partition_update_.partition_name() << "` op index "
              << next_op_index;
    TEST_AND_RETURN_FALSE(cow_writer_->InitializeAppend(next_op_index));
    return true;
  } else {
    TEST_AND_RETURN_FALSE(cow_writer_->Initialize());
  }

  // ==============================================

  // TODO(zhangkelvin) Rewrite this in C++20 coroutine once that's available.
  auto converted = ConvertToCowOperations(partition_update_.operations(),
                                          partition_update_.merge_operations());

  if (!converted.empty()) {
    // Use source fd directly. Ideally we want to verify all extents used in
    // source copy, but then what do we do if some extents contain correct
    // hashes and some don't?
    auto source_fd = std::make_shared<EintrSafeFileDescriptor>();
    TEST_AND_RETURN_FALSE_ERRNO(
        source_fd->Open(install_part_.source_path.c_str(), O_RDONLY));
    WriteAllCowOps(block_size_, converted, cow_writer_.get(), source_fd);
  }
  return true;
}

bool VABCPartitionWriter::WriteAllCowOps(
    size_t block_size,
    const std::vector<CowOperation>& converted,
    android::snapshot::ICowWriter* cow_writer,
    FileDescriptorPtr source_fd) {
  std::vector<uint8_t> buffer(block_size);

  for (const auto& cow_op : converted) {
    switch (cow_op.op) {
      case CowOperation::CowCopy:
        if (cow_op.src_block == cow_op.dst_block) {
          continue;
        }
        TEST_AND_RETURN_FALSE(
            cow_writer->AddCopy(cow_op.dst_block, cow_op.src_block));
        break;
      case CowOperation::CowReplace:
        ssize_t bytes_read = 0;
        TEST_AND_RETURN_FALSE(utils::ReadAll(source_fd,
                                             buffer.data(),
                                             block_size,
                                             cow_op.src_block * block_size,
                                             &bytes_read));
        if (bytes_read <= 0 || static_cast<size_t>(bytes_read) != block_size) {
          LOG(ERROR) << "source_fd->Read failed: " << bytes_read;
          return false;
        }
        TEST_AND_RETURN_FALSE(cow_writer->AddRawBlocks(
            cow_op.dst_block, buffer.data(), block_size));
        break;
    }
  }

  return true;
}

std::unique_ptr<ExtentWriter> VABCPartitionWriter::CreateBaseExtentWriter() {
  return std::make_unique<SnapshotExtentWriter>(cow_writer_.get());
}

[[nodiscard]] bool VABCPartitionWriter::PerformZeroOrDiscardOperation(
    const InstallOperation& operation) {
  for (const auto& extent : operation.dst_extents()) {
    TEST_AND_RETURN_FALSE(
        cow_writer_->AddZeroBlocks(extent.start_block(), extent.num_blocks()));
  }
  return true;
}

[[nodiscard]] bool VABCPartitionWriter::PerformSourceCopyOperation(
    const InstallOperation& operation, ErrorCode* error) {
  // TODO(zhangkelvin) Probably just ignore SOURCE_COPY? They should be taken
  // care of during Init();
  return true;
}

void VABCPartitionWriter::CheckpointUpdateProgress(size_t next_op_index) {
  // No need to call fsync/sync, as CowWriter flushes after a label is added
  // added.
  // if cow_writer_ failed, that means Init() failed. This function shouldn't be
  // called if Init() fails.
  TEST_AND_RETURN(cow_writer_ != nullptr);
  cow_writer_->AddLabel(next_op_index);
}

[[nodiscard]] bool VABCPartitionWriter::FinishedInstallOps() {
  // Add a hardcoded magic label to indicate end of all install ops. This label
  // is needed by filesystem verification, don't remove.
  TEST_AND_RETURN_FALSE(cow_writer_ != nullptr);
  return cow_writer_->AddLabel(kEndOfInstallLabel);
}

VABCPartitionWriter::~VABCPartitionWriter() {
  if (cow_writer_) {
    cow_writer_->Finalize();
  }
}

}  // namespace chromeos_update_engine