fs5600 — A Unix-Style File System Built with FUSE

A fully functional Unix-like file system implemented from scratch in user space using FUSE (Filesystem in Userspace).

This project demonstrates deep understanding of operating systems, file system design, and low-level systems programming.

Built as part of an advanced OS curriculum, but engineered to production-quality standards.

This filesystem implements real OS concepts that production systems rely on:

• Inodes and directory entries
• Block allocation with bitmaps
• Path traversal and name resolution
• File metadata (permissions, ownership, timestamps)
• Correct POSIX error handling
• Read/write consistency through disk-backed storage
• Integration with the Linux VFS layer via FUSE

You can mount this filesystem and use it like ext4:

ls
cat
mkdir
touch
mv
rm

Architecture Overview

Linux VFS
   ↓
FUSE Kernel Module
   ↓
User-Space FUSE Driver (fs5600)
   ↓
Disk Image File (test.img)

The filesystem runs as a user-space process, while Linux transparently forwards file operations to it through FUSE.

Disk Layout

Each disk is divided into 4KB blocks:

Block	Purpose
0	Superblock
1	Block bitmap
2	Root directory inode
3+	Inodes and data blocks

Key Design Decisions

• Block size: 4096 bytes
• Inode size: 1 block (4096 bytes)
• Max filesystem size: 128MB
• Directories: Fixed-size (128 entries)
• No hard/soft links (intentional simplification)

Implemented Features

Metadata & Navigation

• stat, getattr
• readdir
• Permission bits (chmod)
• Ownership (uid / gid)
• POSIX timestamps (ctime, mtime)

File Operations

• Create / delete files
• Read & write arbitrary byte ranges
• Rename within directory
• Truncate files
• Persistent storage backed by disk image

Directory Operations

• Create & remove directories
• Enforce empty-directory deletion rules
• Name validation & path resolution

Error Handling

Fully POSIX-compliant error codes:

• ENOENT, ENOTDIR, EISDIR
• EINVAL, ENOMEM, EIO, ENOTEMPTY

Technology Stack

• C (low-level systems programming)
• Linux FUSE
• POSIX filesystem semantics
• Bitmap-based block allocation
• Unit testing (Check framework)

Example Usage

make
mkdir fs
./lab5fuse -image test.img fs
cd fs
mkdir demo
echo "hello world" > demo/file.txt
cat demo/file.txt
fusermount -u fs

The filesystem behaves exactly like a native Linux filesystem.

Testing & Validation

39+ unit tests covering:

• Path resolution
• Metadata correctness
• File and directory semantics
• Error handling edge cases
• Deterministic disk images for reproducibility
• Verified against reference filesystem behavior