The file access tests that the kernel performs each time

本文详细介绍了操作系统内核如何根据文件所有者、进程的有效用户ID和组ID以及补充组ID来确定文件访问权限。具体步骤包括超级用户直接授权、文件所有者的权限检查、所属组的权限检查以及其他用户的权限检查。

The file access tests that the kernel performs each time a process opens, creates, or deletes a file depend on the owners of the file (st_uidand st_gid), the effective IDs of the process (effective user ID and effective group ID), and the supplementary group IDs of the process, if supported. The two owner IDs are properties of the file, whereas the two effective IDs and the supplementary group IDs are properties of the process. The tests performed by the kernel are as follows.

  1. If the effective user ID of the process is 0 (the superuser), access is allowed. This gives the superuser free rein throughout the entire file system.

  2. If the effective user ID of the process equals the owner ID of the file (i.e., the process owns the file), access is allowed if the appropriate user access permission bit is set. Otherwise, permission is denied. By appropriate access permission bit, we mean that if the process is opening the file for reading, the user-read bit must be on. If the process is opening the file for writing, the user-write bit must be on. If the process is executing the file, the user-execute bit must be on.

  3. If the effective group ID of the process or one of the supplementary group IDs of the process equals the group ID of the file, access is allowed if the appropriate group access permission bit is set. Otherwise, permission is denied.

  4. If the appropriate other access permission bit is set, access is allowed. Otherwise, permission is denied.

These four steps are tried in sequence. Note that if the process owns the file (step 2), access is granted or denied based only on the user access permissions; the group permissions are never looked at. Similarly, if the process does not own the file, but belongs to an appropriate group, access is granted or denied based only on the group access permissions; the other permissions are not looked at. 
在处理测试用例时,如果遇到 **"No tests found in the selected file or folder"** 的提示,通常意味着测试运行器未能识别出指定文件或目录中的测试用例。以下是常见的原因及解决方法: ### 1. 测试类或方法未正确命名 许多测试框架(如 JUnit、pytest、unittest)依赖特定的命名约定来识别测试用例。例如: - **JUnit (Java)** 要求测试类以 `Test` 结尾,或使用 `@Test` 注解标记方法。 - **pytest (Python)** 要求测试函数以 `test_` 开头,测试类以 `Test` 开头且不带 `__init__` 方法。 ```python # 示例:符合 pytest 命名规范的测试函数 def test_addition(): assert 1 + 1 == 2 ``` ### 2. 测试文件未放置在正确的目录中 根据项目结构,测试代码应与生产代码分离,并放置在专门的目录中。例如: - **Maven/Java** 项目通常将测试代码放在 `src/test/java`。 - **Python** 项目通常将测试文件放在 `tests/` 或 `test_*.py` 文件中。 确保测试运行器配置正确,能够扫描到这些目录[^1]。 ### 3. 测试框架未正确配置 确保项目中已安装并配置了相应的测试框架。例如: - **Pytest** 需要安装 `pytest` 包,并在 `pytest.ini` 中配置搜索路径。 - **JUnit** 需要添加 `junit-platform-runner` 和 `junit-jupiter-api` 依赖。 ```bash # 安装 pytest pip install pytest ``` ### 4. IDE 缓存问题 有时 IDE(如 PyCharm、IntelliJ IDEA、VS Code)可能未能正确识别测试文件,导致提示未找到测试用例。尝试以下操作: - **刷新项目索引**:在 IDE 中重新加载项目。 - **重新配置测试运行器**:在设置中指定正确的测试框架。 - **清除缓存并重启 IDE**。 ### 5. 使用命令行运行测试 如果 IDE 无法识别测试,尝试使用命令行运行测试,以确认是否为 IDE 问题: ```bash # 使用 pytest 运行所有测试 pytest # 使用 unittest 运行特定测试文件 python -m unittest tests/test_example.py ``` ### 6. 检查测试文件是否被忽略 某些项目使用 `.gitignore` 或 `.pytest_cache/` 等机制排除测试文件,确保测试文件未被意外忽略。 ---
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