VFS

VFS stands for Virtual File System. It is a software abstraction layer used by many operating systems to provide a uniform interface for accessing different types of storage devices and file systems. By exposing a common set of operations for opening, reading, writing, and traversing files, the VFS decouples user-space applications and kernel file system implementations, enabling seamless access to local disks, network shares, or other storage substrates.

In Linux, the VFS sits between system calls and concrete file system implementations. It maps generic operations to specific file systems such as ext4, XFS, Btrfs, or NFS. The VFS defines core objects such as inodes, dentries (directory entries), and superblocks, and it handles mount and unmount operations, as well as file creation, deletion, and permissions checks. It also manages path name resolution and coordinates with the kernel’s caching and I/O subsystems to optimize performance.

The VFS enables runtime mounting of diverse file systems, providing a single namespace for users and processes. This includes traditional local file systems, network file systems, and virtual or pseudo file systems that do not correspond to a physical device. By handling universal concepts like permissions, locking, and caching, the VFS makes it possible to mix and match different storage backends without requiring changes to applications.

Beyond Linux, many other operating systems implement a similar virtualized file system concept. Windows and others use a related architecture to present a unified file access interface, while Plan 9 emphasizes a more uniform, networked approach using the 9P protocol. The general goal is to provide portability, modularity, and transparent access to heterogeneous storage.