Programming Assignment 4 - File Management

Table of Contents

• Due Date
• Introduction
• Files
• File Operations
• The File System
• System Calls
• Interrupt Handlers
• Notes

This assignment is due on Wednesday, 13 December, no later than 2:00 p.m..

In this fourth and last assignment, you will be implementing a simple file system.

A file is a sequence of zero or more words; the size of a file is the number of words contained in the file. An empty file contains no words and has size zero. A file has no predefined maximum size; it may grow until there's no more disk space.

The words in a file of size n are addressed by the numbers 0 to n - 1. The first (or leftmost) word in the file is word 0; the last (or rightmost) word in the file is word n - 1. If two words are adjacent in a file and the first word is word i, then the second word is word i + 1; that is, word address increase consecutively and sequentially from the start of the file.

A file pointer is a reference to a word in the file, or to the location just past the last word in the file, which is known as the end-of-file location.

When a file is opened, the file pointer references the first word in the file, or end of file if the file is empty. Read and write operations take place relative to the file pointer, and move the file pointer to reference the word after the data read or written, or the end of file.

There is one file pointer per opened file. If a file is opened more than once, it will have more than one file pointer; for example, a file opened three times will have three file pointers. File pointers are independent of one another; an operation affecting one of a file's file pointers doesn't affect any of the other file pointers.

The file system is a simple, flat file system. A file name must contain one character and can contain no more than 5 characters. A character can be a letter, of either case, or a decimal digit; case is significant.

This assignment implements two new system calls - the seek system call and the delete system call - and extends the interpretation of the device system calls to cover files.

This assignment does not require any changes to the interrupt handlers.

• Make sure you are working with the most recent copies of the include files and simulator library. The new include files and simulator library contain functions and features you will need to implement this assignment.

  Don't forget to recompile and relink your code against the new files.

• Review the new system.h to familiarize yourself with the new features it provides.

• The free space for each disk is located immediately after the paging area and consists of the rest of the disk. Batch disks have fixed size, and the amount of free space varies from disk to disk depending on the amount of space taken up by programs.

• When reading a disk block that's never been written, the block returned contains all zeros. You can use this to tell if a batch disk contains a file system.

• The simulator calls the externally defined function

  void file_system_shutdown(void);
  

  before exiting. Your file system code should define and export this routine.

• Strings are stored one character per word, terminated with a null byte. For example, the string "Hi!" would be stored as

  

This page last modified on 29 November 2000.