The Virtual Filesystem Linux

  One of Linux’s keys to success is its ability to coexist comfortably with other sys-

tems. You can transparently mount disks or partitions that host file formats used by

Windows, other Unix systems, or even systems with tiny market shares like the

Amiga. Linux manages to support multiple filesystem types in the same way other

Unix variants do, through a concept called the Virtual Filesystem.

The idea behind the Virtual Filesystem is to put a wide range of information in the

kernel to represent many different types of filesystems; there is a field or function to

support each operation provided by all real filesystems supported by Linux. For each

read, write, or other function called, the kernel substitutes the actual function that

supports a native Linux filesystem, the NTFS filesystem, or whatever other filesys-

tem the file is on.

This chapter discusses the aims, structure, and implementation of Linux’s Virtual

Filesystem. It focuses on three of the five standard Unix file types—namely, regular

files, directories, and symbolic links. Device files are covered in Chapter 13, while

pipes are discussed in Chapter 19. To show how a real filesystem works, Chapter 18

covers the Second Extended Filesystem that appears on nearly all Linux systems.