KRFFS

A FUSE userspace single-level file system in a file based on the first-fit linked list memory allocator presented in the book The C Programming Language by Brian Kernighan and Dennis Ritchie.

Prerequisites

• FUSE libraries, headers, and utilities
• GCC or Clang compilers with pkg-config and GNU Make installed
• dd to generate empty file system files

Fuse Installation

Linux

Use a package manager of your OS distribution and install FUSE libraries, development files, and utilities.

Mac OS X

Download and install the FUSE for macOS package.

Windows

Download and install the latest version of Dokany, a user mode file system library for Windows with a FUSE wrapper.

Support for Windows is lackluster. You need to generate a VS project on your own.

Compilation

To compile the FUSE KRFFS program and all supporting utilities (to create, check, and defragment the file system), use the following

make

To remove compiled files

make clean

Usage

1. Create an empty 10-megabyte file file_system.krffs and initialize a new KRFFS file system on it with the compiled mkfs.krffs utility.

    dd if=/dev/zero of=file_system.krffs bs=1048576 count=1
    mkfs.krffs file_system.krffs
   

   You can do the same by calling a helper script

    ./create_krffs_file_system.sh
   

2. Mount the file system from the file_system.krffs file into an empty directory mount_point.

    krffs file_system.krffs mount_point
   

   One useful option is to tell the program to print debug information for each file system operation with the -d flag.

    krffs file_system.krffs mount_point -d
   

   You can also check the list of all FUSE options by passing just the -h flag.

    krffs -h
   

3. Go inside the directory mount_point, experiment with the file system by creating files and writing or reading data from them. Attempt to rename or remove files. Try to use unsupported operations by attempting to create a new directory.

   Sample commands

    cd mount_point
    touch hello.txt
    echo "hello, world" > hello.txt
    cat hello.txt
    echo "#include <stdio.h>" > test.c
    echo "bye" > hello.txt
    rm hello.txt
    mv test.c hello.c
    cp hello.c hello_backup.c
    mkdir sample_directory
    nano hello_backup.c
    ...
   

4. Leave the mount_point directory and unmount it.

    cd ..
    sudo umount mount_point
   

   On some systems, a fusermount command can be used to unmount FUSE mount points without administrative privileges.

    fusermount -u mount_point
   

Tasks

Option #1 (+10 points)

Use the provided template fsck.krffs.c and finish writing the file system check utility. The application should go through the file system structure and report about any data inconsistencies.

Option #2 (+15 points)

Use the provided template defrag.krffs.c and finish writing the file defragmentation utility that rearranges file nodes with their data to the beginning of the disk file one by one. You can also sort the entries by their file size or usage attributes.

In both cases, you need to research the allocation and deallocation algorithm utilized by the file system. The structure and the algorithms can be found throughout the sources of the project.

Resources

• FUSE, Filesystem in Userspace
• FUSE for OS X
• Dokany

Documentation

man fuse
man mount
man umount
man fusermount
man pkg-config