File Management Overview

File management is an important functional module in modern operating systems, mainly responsible for managing user information, including storage, retrieval, update, sharing and protection.

Files and file systems

File is the basic unit for storing information in the operating system. Files have the following main attributes:
Basic attributes: file name, file size, creation time, etc.
Type attributes: file type, such as text files, binary files, etc.
Protection attributes: permission settings, such as read-only, readable and writable, executable, etc.
Management attributes: file path, owner, group, etc.
Control attributes: Access control list (ACL), lock status, etc.
File system is a software system in the operating system responsible for accessing and managing file information. Its main functions include:
System function: manage file storage, retrieval, and update. Provide a safe and reliable sharing and protection mechanism. Provide users with a convenient operation interface.
System perspective: The function of the file system is to manage the storage of files, and retrieve, protect, organize and allocate storage space for files.
User perspective: The function of the file system is to achieve "access by name", that is, users can access files through file names.

File classification

Classification by nature and purpose:
System files: operating system core files and configuration files.
Library files: shared program libraries or dynamic link libraries (DLLs).
User files: files created by users, such as documents, pictures, etc.
Classification by protection level:
Read-only files: only reading is allowed, not modification.
Read-write files: reading and modification are allowed.
Executable files: executable program files.
Unprotected files: files without permission protection.
Classification by information flow:
Input files: files that obtain input data from external devices or systems.
Output files: files that output data to external devices or systems.
Input and output files: files used for both input and output.
Classification by storage time limit:
Temporary files: used to temporarily store data, with a short life cycle.
Permanent files: files that are stored for a long time.
Archive files: important files used for archiving and storage.
Classification by data form:
Ordinary files: Contains text, binary data, etc.
Directory files: used to store organizational information of files and directories.
Special files: files that represent devices, pipes, etc.

Functions of the file system

Directory management: Organize files through directory structure to achieve access by name.
File organization:
Logical structure: File structure from the user's perspective, such as flat files and tree files.
Physical structure: File layout on storage devices, such as continuous allocation and chain allocation.
File storage space management: responsible for the allocation and release of auxiliary storage space (disk, etc.).
File operations: including basic operations such as creating, opening, reading, writing, closing, and deleting files.
File sharing, protection, and confidentiality: Provide permission control and encryption mechanisms to ensure the security and privacy of files.

Hierarchical structure of file system

File system is usually divided into the following three levels:

Description layer: responsible for describing the usage status of all files and storage media in the system. For example, metadata of the file system, file directory structure, etc.
Management layer: the core part of the file system, mainly including:
Device driver management: manage drivers related to storage devices.
Physical I/O control: handle low-level input/output operations.
File storage organization: manage the organization of files on physical storage media.
Logical I/O management: provide a logical view of files and shield the low-level storage details.
Interface layer: provide users with interfaces for operating file systems, including command interfaces (such as CLI commands) and program interfaces (such as API calls).