This design provided for code reuse among file system types with differing but similar semantics ( e.g., an encrypting file system could reuse all of the naming and storage-management code of a non-encrypting file system). John Heidemann developed a stacking VFS under SunOS 4.0 for the experimental Ficus file system. The SunOS implementation was the basis of the VFS mechanism in System V Release 4. Other file systems could be plugged into it also: there was an implementation of the MS-DOS FAT file system developed at Sun that plugged into the SunOS VFS, although it wasn't shipped as a product until SunOS 4.1. For this reason, Unix vendors who licensed the NFS code from Sun often copied the design of Sun's VFS. It allowed Unix system calls to access local UFS file systems and remote NFS file systems transparently. One of the first virtual file system mechanisms on Unix-like systems was introduced by Sun Microsystems in SunOS 2.0 in 1985. The position of the VFS layer within various parts of the Linux kernel's storage stack. The terms of the contract might change incompatibly from release to release, which would require that concrete file system support be recompiled, and possibly modified before recompilation, to allow it to work with a new release of the operating system or the supplier of the operating system might make only backward-compatible changes to the contract, so that concrete file system support built for a given release of the operating system would work with future versions of the operating system.

Therefore, it is easy to add support for new file system types to the kernel simply by fulfilling the contract. It can be used to bridge the differences in Windows, classic Mac OS/ macOS and Unix filesystems, so that applications can access files on local file systems of those types without having to know what type of file system they are accessing.Ī VFS specifies an interface (or a 'contract') between the kernel and a concrete file system. A VFS can, for example, be used to access local and network storage devices transparently without the client application noticing the difference.

The purpose of a VFS is to allow client applications to access different types of concrete file systems in a uniform way. A virtual file system ( VFS) or virtual filesystem switch is an abstract layer on top of a more concrete file system.

Mac os system files emulator