Linux Kernel Development, Third Edition

13. The Virtual Filesystem

The Virtual Filesystem (sometimes called the Virtual File Switch or more commonly simply the VFS) is the subsystem of the kernel that implements the file and filesystem-related interfaces provided to user-space programs. All filesystems rely on the VFS to enable them not only to coexist, but also to interoperate. This enables programs to use standard Unix system calls to read and write to different filesystems, even on different media, as shown in Figure 13.1.

Figure 13.1. The VFS in action: Using the cp(1) utility to move data from a hard disk mounted as ext3 to a removable disk mounted as ext2. Two different filesystems, two different media, one VFS.

Common Filesystem Interface

The VFS is the glue that enables ...