Educational Operating System Project (FOS – OS’25)

This repository contains the implementation of an educational operating system developed as part of the OS’25 course project at Ain Shams University.
The project provides a hands-on exploration of core operating system concepts through kernel-level programming, modular design, and rigorous testing.

The system is built incrementally, where each module depends on previously implemented components. A strong emphasis is placed on correctness by design, safe synchronization, and full compliance with provided testing frameworks.

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📌 Project Overview

The objective of this project is to design and implement the essential components of an operating system, including:

• Memory management (kernel & user space)
• Page fault handling and replacement strategies
• Process scheduling
• Inter-process communication
• Kernel protection and synchronization

All components are validated using predefined and unseen test cases that simulate realistic execution scenarios.

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🎯 Project Objectives

• Apply operating system theory in real kernel implementations
• Understand virtual memory and paging mechanisms
• Implement and compare multiple page replacement algorithms
• Design a priority-based CPU scheduler with starvation prevention
• Build safe kernel synchronization primitives
• Gain experience in debugging and testing low-level systems code

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🧩 System Architecture

The system is divided into Group Modules (prerequisites) and Individual Modules to allow structured development and testing.

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🔹 Group Modules (Prerequisites)

1. Dynamic Allocator

• Block-based dynamic memory allocation
• Allocation, deallocation, and block management

2. Kernel Heap

• Page allocator and block allocator
• Virtual to physical address translation
• Custom fit allocation strategy

3. Page Fault Handler I (Placement)

• Demand paging
• Stack growth handling
• Invalid memory access detection

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🔹 Individual Modules

🧠 1. Page Fault Handler II & III (Replacement)

Implements multiple page replacement algorithms with full working set management:

• Optimal (OPT) – theoretical benchmark
• Clock (Second Chance)
• LRU (Aging-based approximation)
• Modified Clock

Responsibilities include:

• Tracking page reference streams
• Managing working sets
• Handling page eviction and disk interaction
• Maintaining used and modified bits

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💾 2. User Heap Management

Provides dynamic memory allocation for user processes:

• Block allocator for small allocations
• Page allocator for large allocations
• Custom Fit allocation strategy
• Lazy allocation through page faults

User-level APIs:

• malloc()
• free()

Kernel support:

• allocate_user_mem()
• free_user_mem()

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🔗 3. Shared Memory

Enables inter-process communication through shared memory objects:

• Runtime creation and sharing of memory objects
• Reference counting and permission control
• Frame tracking for safe sharing
• Full kernel-level synchronization using locks

User-level APIs:

• smalloc()
• sget()

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⏱️ 4. CPU Scheduling

Implements a Priority-Based Round Robin Scheduler:

• Multiple ready queues per priority level
• Preemptive scheduling
• Configurable quantum
• Starvation prevention via priority promotion
• Runtime priority modification using system calls

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🔐 5. Kernel Protection & Synchronization

Ensures safe concurrent execution inside the kernel using:

• Sleep Locks
• Semaphores
• Channel-based sleep/wakeup mechanisms

Used for:

• Console I/O protection
• Disk I/O synchronization
• Inter-process coordination

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🧪 Testing & Validation

The project follows a logic-driven design approach rather than test-driven development.

Testing includes:

• Individual module testing
• Group module testing
• Full system integration testing
• Execution of real user programs (sorting, Fibonacci, shared memory workloads)

Each test has strict time limits and must complete without kernel panics or errors to be considered successful.

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▶️ How to Run & Test

1. Enable or disable kernel heap when required:

   • Modify USE_KHEAP in inc/memlayout.h

2. Switch scheduling or replacement policies from the FOS prompt:

   • optimal, clock, lru, modclock
   • schedPRIRR, schedRR

3. Run a single program:

   FOS> run <program_name> <working_set_size> [priority]
   

4. Load and execute multiple programs:

   FOS> load <program_name> <working_set_size> [priority]
   FOS> runall
   

🛠 Technologies & Environment

• Programming Language: C
• Domain: Operating Systems / Kernel Development
• Environment: Educational OS Framework (FOS)
• Execution Model: Monolithic Kernel
• Memory Model: Paging & Virtual Memory
• Scheduling Model: Priority-Based Round Robin

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📚 Learning Outcomes

Through this project, the developer gained practical experience in:

• Kernel-level memory management
• Page placement and replacement strategies
• Working set management
• CPU scheduling and starvation handling
• Synchronization and concurrency control
• Inter-process communication using shared memory
• Debugging and testing low-level operating system code

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⚠️ Disclaimer

This project was developed strictly for educational purposes as part of an academic Operating Systems course at FCIS.
It is not intended to be a production-ready operating system.

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🤝 Team Acknowledgment

Special thanks to my amazing teammates for their collaboration, dedication, and continuous support throughout the development of this project.

Team Members:

• Omnia Mostafa
• Tag Eldeen
• Meshkat Zaki
• Sohila Mohamed
• Sama Waleed

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🙏 Acknowledgment

Special thanks to Dr. Ahmed Salah for his guidance and support throughout the semester.