A Simple File System

Description

CS 445/445G Project 1: A Simple File System

(due on the class on 03/03/17)

In this project, you will implement a simple simulated file system. This project will let you get

familiar with important data structures in a file system, including i) volume control block, ii) the directory

structure, iii) open file tables (system-wide and per-process), and iv) File Control Block (FCB). You will

also learn how basic file operations, such as open(), interact with these data structures.

Before we describe the tasks of this project, we make the following assumptions. The simulated file

system is implemented on main memory. More specifically, a slot of main memory of 1M is used to

simulate a disk. We assume that a data block is of 2K. Therefore, the disk has 512 blocks. In this

project, we assume the disk is a data disk, i.e., no OS installed. So the first data block is used as the

volume control block. We assume that the volume control block contains the following items:

number of blocks

size of block

a free-block count

a bit-map of free blocks

Table 1: Volume control block

We assume that the file allocation (i.e., data block allocation) is contiguous allocation. For simplicity,

our file system uses a flat directory structure to manage files. In other words, the directory contains no

subdirectories. With the assumption of contiguous allocations, the content of the directory of our file

the system can be organized as a table as follows:

file name start block number file size

file1 0 2

file3 6 3

Table 2: Flat directory structure.

To be consistent with the contiguous allocation, the FCB contains the following items:

file size

pointer to the first data block

Table 3: File control block (FCB).

A system-wide open file table is a set of FCBs of open files. An example of a system-wide open file

table is shown in Table 4.

Given a specific process, its per-process open file table contains a set of file handles of files opened

by the process. For example, assume that a process has open files: f1 and f4, its per-process table will

be the one shown in Table 5.