在介紹完了DownloadAction之后，還剩下FilesystemVerifierAction和PostinstallRunnerAction，下面開始對其進行分析。
FilesystemVerifierAction
在數據下載完成后，在DownloadAction中會切換到FilesystemVerifierAction
1 void DownloadAction::TransferComplete(HttpFetcher* fetcher, bool successful) { 2 if (writer_) { 3 ........ 4 // Write the path to the output pipe if we're successful.
5 if (code == ErrorCode::kSuccess && HasOutputPipe()) 6 SetOutputObject(install_plan_); 7 processor_->ActionComplete(this, code); 8 }
最后的ActionComplete會開始執行FilesystemVerifierAction。
src/system/update_engine/payload_consumer/filesystem_verifer_action.cc
1 void FilesystemVerifierAction::PerformAction() { 2 // Will tell the ActionProcessor we've failed if we return.
3 ScopedActionCompleter abort_action_completer(processor_, this); 4
5 if (!HasInputObject()) { 6 LOG(ERROR) << "FilesystemVerifierAction missing input object."; 7 return; 8 } 9 install_plan_ = GetInputObject(); //獲取上一個Action傳過來的install_plan_
10
11 if (install_plan_.partitions.empty()) { 12 LOG(INFO) << "No partitions to verify."; 13 if (HasOutputPipe()) 14 SetOutputObject(install_plan_); 15 abort_action_completer.set_code(ErrorCode::kSuccess); 16 return; 17 } 18
19 StartPartitionHashing(); //開始計算分區的hash
20 abort_action_completer.set_should_complete(false); 21 }
接着看StartPartitionHashing
1 void FilesystemVerifierAction::StartPartitionHashing() { 2 if (partition_index_ == install_plan_.partitions.size()) { //判斷是否驗證到了最后一個分區
3 Cleanup(ErrorCode::kSuccess); 4 return; 5 } 6 InstallPlan::Partition& partition =
7 install_plan_.partitions[partition_index_]; 8
9 string part_path; 10 switch (verifier_step_) { //默認值是KVerifyTargetHash
11 case VerifierStep::kVerifySourceHash: 12 part_path = partition.source_path; 13 remaining_size_ = partition.source_size; 14 break; 15 case VerifierStep::kVerifyTargetHash: 16 part_path = partition.target_path; //分區的路徑
17 remaining_size_ = partition.target_size; //大小
18 break; 19 } 20 LOG(INFO) << "Hashing partition " << partition_index_ << " ("
21 << partition.name << ") on device " << part_path; 22 if (part_path.empty()) 23 return Cleanup(ErrorCode::kFilesystemVerifierError); 24
25 brillo::ErrorPtr error; 26 src_stream_ = brillo::FileStream::Open( //打開對應的分區文件
27 base::FilePath(part_path), 28 brillo::Stream::AccessMode::READ, 29 brillo::FileStream::Disposition::OPEN_EXISTING, 30 &error); 31
32 if (!src_stream_) { 33 LOG(ERROR) << "Unable to open " << part_path << " for reading"; 34 return Cleanup(ErrorCode::kFilesystemVerifierError); 35 } 36
37 buffer_.resize(kReadFileBufferSize); //重置緩存區的大小
38 read_done_ = false; //未被讀取完成
39 hasher_.reset(new HashCalculator()); //設置HashCalculator
40
41 // Start the first read.
42 ScheduleRead(); //開始讀取
43 }
首先判斷是否驗證的分區的所有hash，如果驗證完成了，調用CleanUp做最后的工作。
CleanUp
1 void FilesystemVerifierAction::Cleanup(ErrorCode code) { 2 src_stream_.reset(); 3 // This memory is not used anymore.
4 buffer_.clear(); 5
6 if (cancelled_) 7 return; 8 if (code == ErrorCode::kSuccess && HasOutputPipe()) 9 SetOutputObject(install_plan_); 10 processor_->ActionComplete(this, code); 11 }
可以看到主要就是清空緩存區，設置install_plan_,切換到下一個Action。如果沒有驗證完成，就獲取要驗證的分區路徑和大小，這個大小只是要驗證的大小，不一定是分區的真正大小。對於鏡像文件而言1G的大小能被安裝在2G的分區上。接下來調用ScheduleRead()開始進行驗證。
ScheduleRead()
1 void FilesystemVerifierAction::ScheduleRead() { 2 size_t bytes_to_read = std::min(static_cast<int64_t>(buffer_.size()), 3 remaining_size_); //獲取要讀取數據的大小
4 if (!bytes_to_read) { //讀取完成
5 OnReadDoneCallback(0); 6 return; 7 } 8
9 bool read_async_ok = src_stream_->ReadAsync( 10 buffer_.data(), 11 bytes_to_read, 12 base::Bind(&FilesystemVerifierAction::OnReadDoneCallback, 13 base::Unretained(this)), 14 base::Bind(&FilesystemVerifierAction::OnReadErrorCallback, 15 base::Unretained(this)), 16 nullptr); //開始讀取
17
18 if (!read_async_ok) { 19 LOG(ERROR) << "Unable to schedule an asynchronous read from the stream."; 20 Cleanup(ErrorCode::kError); 21 } 22 }
獲取讀取數據的真實大小，開始讀取數據。
1 void FilesystemVerifierAction::OnReadDoneCallback(size_t bytes_read) { 2 if (bytes_read == 0) { //讀取完成
3 read_done_ = true; 4 } else { 5 remaining_size_ -= bytes_read; 6 CHECK(!read_done_); 7 if (!hasher_->Update(buffer_.data(), bytes_read)) { //計算hash
8 LOG(ERROR) << "Unable to update the hash."; 9 Cleanup(ErrorCode::kError); 10 return; 11 } 12 } 13
14 // We either terminate the current partition or have more data to read.
15 if (cancelled_) 16 return Cleanup(ErrorCode::kError); 17
18 if (read_done_ || remaining_size_ == 0) { 19 if (remaining_size_ != 0) { 20 LOG(ERROR) << "Failed to read the remaining " << remaining_size_ 21 << " bytes from partition "
22 << install_plan_.partitions[partition_index_].name; 23 return Cleanup(ErrorCode::kFilesystemVerifierError); 24 } 25 return FinishPartitionHashing(); //計算完成后
26 } 27 ScheduleRead(); //如果沒有計算完成，繼續計讀取計算
28 }
在這個方法中會對讀取的數據進行hash計算，每次計算其實都是基於前一次的計算結果來進行的，不然就會有太對的數據加載到內存中，導致內存不足。當計算完成后
1 void FilesystemVerifierAction::FinishPartitionHashing() { 2 if (!hasher_->Finalize()) { 3 LOG(ERROR) << "Unable to finalize the hash."; 4 return Cleanup(ErrorCode::kError); 5 } 6 InstallPlan::Partition& partition =
7 install_plan_.partitions[partition_index_]; 8 LOG(INFO) << "Hash of " << partition.name << ": "
9 << Base64Encode(hasher_->raw_hash()); 10
11 switch (verifier_step_) { 12 case VerifierStep::kVerifyTargetHash: 13 if (partition.target_hash != hasher_->raw_hash()) { //對保存的targethash和計算得到的hash進行一個比較
14 LOG(ERROR) << "New '" << partition.name 15 << "' partition verification failed."; 16 if (partition.source_hash.empty()) { 17 // No need to verify source if it is a full payload.
18 return Cleanup(ErrorCode::kNewRootfsVerificationError); 19 } 20 // If we have not verified source partition yet, now that the target
21 // partition does not match, and it's not a full payload, we need to
22 // switch to kVerifySourceHash step to check if it's because the source
23 // partition does not match either.
24 verifier_step_ = VerifierStep::kVerifySourceHash; //計算source hash
25 } else { 26 partition_index_++; //計算下一個分區
27 } 28 break; 29 case VerifierStep::kVerifySourceHash: 30 if (partition.source_hash != hasher_->raw_hash()) { //保存的source hash和計算得到的也不相同
31 LOG(ERROR) << "Old '" << partition.name 32 << "' partition verification failed."; 33 LOG(ERROR) << "This is a server-side error due to mismatched delta"
34 << " update image!"; 35 LOG(ERROR) << "The delta I've been given contains a " << partition.name 36 << " delta update that must be applied over a "
37 << partition.name << " with a specific checksum, but the "
38 << partition.name 39 << " we're starting with doesn't have that checksum! This"
40 " means that the delta I've been given doesn't match my"
41 " existing system. The "
42 << partition.name << " partition I have has hash: "
43 << Base64Encode(hasher_->raw_hash()) 44 << " but the update expected me to have "
45 << Base64Encode(partition.source_hash) << " ."; 46 LOG(INFO) << "To get the checksum of the " << partition.name 47 << " partition run this command: dd if="
48 << partition.source_path 49 << " bs=1M count=" << partition.source_size 50 << " iflag=count_bytes 2>/dev/null | openssl dgst -sha256 "
51 "-binary | openssl base64"; 52 LOG(INFO) << "To get the checksum of partitions in a bin file, "
53 << "run: .../src/scripts/sha256_partitions.sh .../file.bin"; 54 return Cleanup(ErrorCode::kDownloadStateInitializationError); 55 } 56 // The action will skip kVerifySourceHash step if target partition hash
57 // matches, if we are in this step, it means target hash does not match,
58 // and now that the source partition hash matches, we should set the error
59 // code to reflect the error in target partition.
60 // We only need to verify the source partition which the target hash does
61 // not match, the rest of the partitions don't matter.
62 return Cleanup(ErrorCode::kNewRootfsVerificationError); 63 } 64 // Start hashing the next partition, if any.
65 hasher_.reset(); //重置hash計算器
66 buffer_.clear(); //清空緩存
67 src_stream_->CloseBlocking(nullptr); 68 StartPartitionHashing(); //接着計算
69 }
可見當一個分區的hash被計算出來的時候就會根據保存好的進行比較，如果target的hash不一致就會轉向比較該分區的source hash，其實比較source hash主要就是為了確定錯誤的類型，只要target hash不一致，無論source hash是否一致都不會繼續下一個分區的計算了。就這樣一直到最后一個分區驗證完后，執行最后一個Action,PostinstallRunnerAction。
PostinstallRunnerAction
PostinstallRunnerAction執行每個分區更新完后的postinstall script。但是在高通平台的，android8.0上無論是全包還是差分包升級並沒有實質性的postinstall script。在PostinstallRunnerAction中僅僅是將target_slot標記為active狀態。目前只分析於執行相關的代碼。
src/system/update_engine/payload_consumer/postinstall_runner_action.cc
1 void PostinstallRunnerAction::PerformAction() { 2 CHECK(HasInputObject()); 3 install_plan_ = GetInputObject(); //獲取install_plan_
4
5 if (install_plan_.powerwash_required) { //是否需要進行數據的擦除
6 if (hardware_->SchedulePowerwash()) { 7 powerwash_scheduled_ = true; 8 } else { 9 return CompletePostinstall(ErrorCode::kPostinstallPowerwashError); 10 } 11 } 12
13 // Initialize all the partition weights.
14 partition_weight_.resize(install_plan_.partitions.size()); //初始化每個分區的權重
15 total_weight_ = 0; 16 for (size_t i = 0; i < install_plan_.partitions.size(); ++i) { 17 // TODO(deymo): This code sets the weight to all the postinstall commands,
18 // but we could remember how long they took in the past and use those
19 // values.
20 partition_weight_[i] = install_plan_.partitions[i].run_postinstall; 21 total_weight_ += partition_weight_[i]; //計算總的權重
22 } 23 accumulated_weight_ = 0; 24 ReportProgress(0); //更新進度
25
26 PerformPartitionPostinstall(); //開始真正的流程
27 }
來看PerformPartitionPostinstall()
1 void PostinstallRunnerAction::PerformPartitionPostinstall() { 2 if (install_plan_.download_url.empty()) { 3 LOG(INFO) << "Skipping post-install during rollback"; 4 return CompletePostinstall(ErrorCode::kSuccess); 5 } 6
7 // Skip all the partitions that don't have a post-install step.
8 while (current_partition_ < install_plan_.partitions.size() &&
9 !install_plan_.partitions[current_partition_].run_postinstall) { //run_postinstall為false
10 VLOG(1) << "Skipping post-install on partition "
11 << install_plan_.partitions[current_partition_].name; 12 current_partition_++; 13 } 14 if (current_partition_ == install_plan_.partitions.size()) 15 return CompletePostinstall(ErrorCode::kSuccess); 16 ................... 17 ................... 18 ................... 19 }
在當前分析中run_postinstall為false,會跳過post-install。之后會直接執行CompletePostinstall(ErrorCode::kSuccess)
1 void PostinstallRunnerAction::CompletePostinstall(ErrorCode error_code) { 2 // We only attempt to mark the new slot as active if all the postinstall
3 // steps succeeded.
4 if (error_code == ErrorCode::kSuccess &&
5 !boot_control_->SetActiveBootSlot(install_plan_.target_slot)) { //設置target_slot為active
6 error_code = ErrorCode::kPostinstallRunnerError; 7 } 8
9 ScopedActionCompleter completer(processor_, this); 10 completer.set_code(error_code); 11
12 if (error_code != ErrorCode::kSuccess) { 13 LOG(ERROR) << "Postinstall action failed."; 14
15 // Undo any changes done to trigger Powerwash.
16 if (powerwash_scheduled_) 17 hardware_->CancelPowerwash(); 18
19 return; 20 } 21
22 LOG(INFO) << "All post-install commands succeeded"; 23 if (HasOutputPipe()) { //設置輸出的install_plan
24 SetOutputObject(install_plan_); 25 } 26 }
最終將target_slot設置為active在重啟之后就會從target_slot開始啟動了。
分析到這里就算是對update_engine的核心過程有了個大概的了解，除了對升級的知識點的認識，還體會到了它的架構。不足之處就是還有很多的細節未涉及。