跳转至

Lecture 14 - File System

  • CPU is abstract to processes
  • Memory is abstracted to address space
  • Storage is abstracted to file system

There are different types of file:

  • data: character, binary, and application-specific program 1. character: text files like .txt, .c. 2. binary: executable files like .exe, .elf, .out 3. application-specific: configuration files, like .pptx, .docx, .xlsx
  • special one: proc file system - use file-system interface to retrieve system information

pie: position independent executable - can be loaded anywhere in memory

File Control Block (FCB) - inode.

File System Interface

  • Magic number : saved in the header of the file, to identify the file type.

Access Methods

Sequential access

  • a group of elements is access in a predetermined order
  • for some media types, the only access mode (e.g., tape)

Direct access

  • access an element at an arbitrary position in a sequence in(roughly) equal time, independent of sequence size
  • it is possible to emulate random access in a tape, but access time varies
  • sometime called random access
  • Add index to the file to access it directly

Directory structure

  • Disk can be subdivided into partitions
  • A partition containing file system is known as a volume
  • Each volume tracks file system info in the volume’s table of contents
  • Disk or partition can be used raw (without a file system)

Directory is a collection of nodes containing information about all files

  • Both the directory structure and the files reside on disk

Tree-Structured Directories

1

Acyclic-Graph Directories

  • Dangling pointer problem: Because a file can be pointed by multiple directories, if one directory is deleted, the file is still there, but the pointer is lost.

Solution: back pointers/reference counter

  • Back pointers record all the pointers to the entity, a variable size record
  • Or count # of links to it and only (physically) delete it when counter is zero -- Hard Link

2

General Graph Directory

File System Mounting

A file system must be mounted before it can be accessed

  • mounting links a file system to the system, usually forms a single name space
  • the location of the file system being mounted is call the mount point
  • a mounted file system makes the old directory at the mount point invisible

Protection

  • ACL: Access Control List

File System Implementation

[TODO]

File System In Practice

[TODO]

最后更新: 2025年1月6日 21:18:56
创建日期: 2024年12月27日 21:05:43