Abstract
The Virtual File system (VFS) is an abstraction layer over the file system im-
plementations in the operating system. It handles all system calls related to the
file system and allows for client applications to access different types of file sys-
tems in a uniform way. It also provides a common interface to several kinds of file
system implementations. The VFS layer was introduced first in the SunOS and it
is present in many modern operating systems.
MINIX 3 is a microkernel based POSIX compliant operating system designed
to be highly reliable, flexible, and secure. A minimal kernel provides interrupt
handlers, a mechanism for starting and stopping processes, a scheduler, and inter-
process communication. Standard operating system functionality that is present
in a monolithic kernel is moved to user space, and no longer runs at the highest
privilege level. Device drivers, the file system, the network server and high-level
memory management run as separate user processes that are encapsulated in their
private address space.
By splitting an operating system into small, independent modules, the sys-
tem becomes less complex and more robust, because the smaller parts are more
manageable and help to isolate faults.
This thesis describes the Virtual File system design and implementation in the
MINIX 3 operating system. It also gives a comparison to other VFS designs. Ex-
ploiting modularity is a key idea behind MINIX, therefore the design of the Virtual
File system layer is also driven by this idea. The result is a substantially differ-
ent architecture from the Virtual File system layer in other UNIX-like operating
systems.
The main contribution of this work is that the MINIX FS server was fully
revised in order to divide it into an abstract layer and the actual MINIX file sys-
tem driver. New data structures and methods were added to the virtual layer and
modifications were realized in the actual file system implementation.
