Advanced Operating Systems

1
Advanced Operating Systems

• File System Internals

2
UNIX File System Organisation

• The Traditional UNIX organisation from Ed 7
  onwards has been
• Boot Block, Super Block, Inodes, Data

3
UNIX File System Organisation

• Searching and allocation is done through logical
  device and inumber

4
UNIX File System Organisation

• Problems of Traditional UNIX FS
• Fragmentation of disc
• No way to use disc geometry
• Short file names

5
Berkeley Fast File System

• Restructured File System organisation using
  cylinder groups
• 1 or more cylinders per group
• Identical superblocks in cylinder group
• Superblocks offset for each in cylinder group

6
Berkeley Fast File System

• Inode/file allocation
• File inode is allocated in parent directory
  cylinder group
• New directory placed in new cylinder group
• Large and small files are segregated
• Use of 8k byte blocks 1k fragements

7
Berkeley Fast File System

• Filename size changes
• 255 character file names
• Changed directory organisation
• Quota system introduced
• Symbolic links introduced
• File truncation introduced

8
Linux file system

• Added VFS Virtual File System
• Allows other system to be added
• Clean, object orientated, design of system
• 3 parts
• Inode object
• File object
• File system object

9
Virtual File System
10
Virtual File System

• VFS Objects define an action for each file system
• Each object has a pointer into a table of
  functions for each file system implementation
• File system object is the hierarchy
• Files found through fs-inode paring