Keun young Park | b734226 | 2021-10-25 08:09:27 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (C) 2021 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | #ifndef ANDROID_INSTALLD_RESTORABLE_FILE_H |
| 18 | #define ANDROID_INSTALLD_RESTORABLE_FILE_H |
| 19 | |
| 20 | #include <functional> |
| 21 | #include <string> |
| 22 | |
| 23 | #include "unique_file.h" |
| 24 | |
| 25 | namespace android { |
| 26 | namespace installd { |
| 27 | |
| 28 | // This is a file abstraction which allows restoring to the original file while temporary work |
| 29 | // file is updated. |
| 30 | // |
| 31 | // Typical flow for this API will be: |
| 32 | // RestorableFile rf = RestorableFile::CreateWritableFile(...) |
| 33 | // write to file using file descriptor acquired from: rf.fd() |
| 34 | // Make work file into a regular file with: rf.CommitWorkFile() |
| 35 | // Or throw away the work file by destroying the instance without calling CommitWorkFile(). |
| 36 | // The temporary work file is closed / removed when an instance is destroyed without calling |
| 37 | // CommitWorkFile(). The original file, if CommitWorkFile() is not called, will be kept. |
| 38 | // |
| 39 | // For safer restoration of original file when commit fails, following 3 steps can be taken: |
| 40 | // 1. CreateBackupFile(): This renames an existing regular file into a separate backup file. |
| 41 | // 2. CommitWorkFile(): Rename the work file into the regular file. |
| 42 | // 3. RemoveBackupFile(): Removes the backup file |
| 43 | // If CommitWorkFile fails, client can call RestoreBackupFile() which will restore regular file from |
| 44 | // the backup. |
| 45 | class RestorableFile { |
| 46 | public: |
| 47 | // Creates invalid instance with no fd (=-1) and empty path. |
| 48 | RestorableFile(); |
| 49 | RestorableFile(RestorableFile&& other) = default; |
| 50 | ~RestorableFile(); |
| 51 | |
| 52 | // Passes all contents of other file into the current file. |
| 53 | // Files kept for the current file will be either deleted or committed depending on |
| 54 | // CommitWorkFile() and DisableCleanUp() calls made before this. |
| 55 | RestorableFile& operator=(RestorableFile&& other) = default; |
| 56 | |
| 57 | // Gets file descriptor for backing work (=temporary) file. If work file does not exist, it will |
| 58 | // return -1. |
| 59 | int fd() const { return unique_file_.fd(); } |
| 60 | |
| 61 | // Gets the path name for the regular file (not temporary file). |
| 62 | const std::string& path() const { return unique_file_.path(); } |
| 63 | |
| 64 | // Closes work file, deletes it and resets all internal states into default states. |
| 65 | void reset(); |
| 66 | |
| 67 | // Closes work file and closes all files including work file, backup file and regular file. |
| 68 | void ResetAndRemoveAllFiles(); |
| 69 | |
| 70 | // Creates a backup file by renaming existing regular file. This will return false if renaming |
| 71 | // fails. If regular file for renaming does not exist, it will return true. |
| 72 | bool CreateBackupFile(); |
| 73 | |
| 74 | // Closes existing work file and makes it a regular file. |
| 75 | // Note that the work file is closed and fd() will return -1 after this. path() will still |
| 76 | // return the original path. |
| 77 | // This will return false when committing fails (=cannot rename). Both the regular file and tmp |
| 78 | // file will be deleted when it fails. |
| 79 | bool CommitWorkFile(); |
| 80 | |
| 81 | // Cancels the commit and restores the backup file into the regular one. If renaming fails, |
| 82 | // it will return false. This returns true if the backup file does not exist. |
| 83 | bool RestoreBackupFile(); |
| 84 | |
| 85 | // Removes the backup file. |
| 86 | void RemoveBackupFile(); |
| 87 | |
| 88 | // Gets UniqueFile with the same path and fd() pointing to the work file. |
| 89 | const UniqueFile& GetUniqueFile() const; |
| 90 | |
| 91 | // Creates writable RestorableFile. This involves creating tmp file for writing. |
| 92 | static RestorableFile CreateWritableFile(const std::string& path, int permissions); |
| 93 | |
| 94 | // Removes the specified file together with tmp file generated as RestorableFile. |
| 95 | static void RemoveAllFiles(const std::string& path); |
| 96 | |
| 97 | private: |
| 98 | RestorableFile(int value, const std::string& path); |
| 99 | |
| 100 | // Used as a storage for work file fd and path string. |
| 101 | UniqueFile unique_file_; |
| 102 | }; |
| 103 | |
| 104 | } // namespace installd |
| 105 | } // namespace android |
| 106 | |
| 107 | #endif // ANDROID_INSTALLD_RESTORABLE_FILE_H |