File System Architecture of Linux

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File System Architecture of Linux

• By Alireza Fathi

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VFS

• What is VFS?!!!

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VFS is stable!!!

• Not many changes during 5-7 passed years.
• The idea is a common file model
• Every registered file system represents its self
  in the VFS model.
• The structure is Object Oriented with
  performance enhancement

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Object Oriented view of VFS

• There are 4 main Objects
• 1- Superblock Object
• 2- Inode Object
• 3- File Object
• 4- Dentry Object

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Superblock Object

• The doubled link list structure in Linux
• Super blocks are stored in a doubled link list
• Each superblock has a pointer to a structure
  containing superblock operations

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Fields of the super block object
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Inode Object

• A hash table contains in-use and dirty inodes
• every inode is hashed via its superblock number
  and its inode number
• Three linked lists exist which contain inodes of
  different type
• 1- A list of unused inodes ( i_count 0)
• 2- A list of in use inodes ( i_count gt 0) (
  i_nlink gt 0)
• 3- For every super block a list of dirty inodes
  (in s_dirty)

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Fields of the inode object
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File Object

• There are two double linked lists for holding the
  file objects
• 1- Unused files list
• 2- In use file list

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Fields of File Object
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Implementing consistency for Directories

• Every Directory is a file!
• Usage of i_version field of inode-object and
  f_version field of file-object in implementing
  consistency!

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Files associated with a process
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EXT2 Filesystem

• The extension of minix filesystem but claims
  robustness and flexibility .
• Better performance from EXT1.
• Inode based filesystem.

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Layout of an EXT2 partition
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Stored superblock on disk
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Stored group descriptor on disk
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Stored inode on disk
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Directory structure