COMP3891

Virtual File System

Overview

Aim is to provide a framework that separates file system independent and file system dependent code.

• Provides single syscall interface for many file systems.
  • E.g. UFS, Ext2, ….
• Transparent handling of network file systems
  • E.g. NFS, AFS, CODA.
• File-based interface to arbitrary device drivers.
• File-based interface to kernel data structures.
• Provides an indirection layer for system calls.
  • File operation table set up at file open time.
  • Points to actual handling code for particular type.
  • Further file operations redirected to those functions.

Interface

• VFS
  • Represents all file system types.
  • Contains pointers to functions to manipualte each file system as a whole (e.g. mount and unmount).
    • Form a standard interface to the file system.
• Vnode
  • Represents a file (inode) in the underlying filesystem.
  • Points to the real inode.
  • Contains pointers to functiosn to manipulate files/inodes (e.g. open, close, read, write….).