Summary

The Linux storage stack is a complex design and consists of multiple layers, all of which work in coordination. Like other hardware resources, storage lies in the kernel space. When a user space program wants to access any of these resources, it has to invoke a system call. The system call interface in Linux allows user space programs to access resources in the kernel space. When a user space program wants to access something on the disk, the first component it interacts with is the VFS subsystem. The VFS provides an abstraction of filesystem-related interfaces and is responsible for accommodating multiple filesystems in the kernel. Through its common filesystem interface, the VFS intercepts the generic system calls (such as read() and write()) from the user space programs and redirects them to their appropriate interfaces in the filesystem layer. Because of this approach, the user space programs do not need to worry about the underlying filesystems being used, and they can uniformly perform filesystem operations.

This chapter served as an introduction to the major Linux kernel subsystem Virtual Filesystem and its primary functions in the Linux kernel. The VFS provides a common interface for all filesystems through data structures, such as inodes, superblocks, and directory entries. In the next chapter, we will take a look at these data structures and explain how they all help the VFS to manage multiple filesystems.