Virtual File System (VFS)

 

Virtual File System (VFS) — Brief Explanation

🧠 What is VFS?

The Virtual File System (VFS) is an abstraction layer in UNIX that provides a uniform interface to different types of file systems.

👉 It allows the OS to handle:

• Local file systems (like disk-based)

• Network file systems (like NFS)

• Other special file systems

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🎯 Purpose of VFS

• Provide a common API for file operations (open, read, write, close)

• Hide differences between file system implementations

• Enable multiple file systems to coexist

👉 Key idea:
User programs don’t need to know which file system they are using.

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🧩 Key Components of VFS

1. Vnode (Virtual Node)

• Represents a file in a file-system-independent way

• Similar to an inode, but generic

📌 Contains:

• File type

• Pointer to actual file system data

• Operations (read, write, etc.)

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2. File Object

• Represents an open file

• Stores:

  • File offset (current position)

  • Access mode (read/write)

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3. Mount Table

• Keeps track of all mounted file systems

• Links directories to file systems

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4. File System Switch (FSS)

• Table of function pointers

• Chooses correct implementation for each file system

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⚙️ How VFS Works (Flow)

1. User calls:

   open("/home/file.txt")
   

2. VFS:

   • Parses pathname

   • Locates corresponding vnode

3. VFS uses:

   • File System Switch → selects correct file system

4. Actual file system performs operation

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🔄 Mounting in VFS

• VFS combines multiple file systems into one tree

• Uses mount points to attach file systems

👉 Example:

/home → local disk
/net  → network file system

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📌 Advantages of VFS

• ✔ Uniform interface

• ✔ Extensibility (new file systems easily added)

• ✔ Transparency to users

• ✔ Supports distributed systems

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Summary

👉 VFS acts as a bridge between user programs and multiple file systems, providing a single unified interface while internally handling different implementations.

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👉 VFS is an abstraction layer in UNIX that provides a uniform interface to access different file systems using common operations like open, read, and write.