🖥️ Os-Fos

A lightweight educational operating system built for learning systems programming concepts from the ground up.
We started with a template OS and gradually added advanced features such as semaphores, nth chance clock page replacement, dynamic memory allocation, user/kernel heap, system calls, fault handling, and more.

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📖 About

Os-Fos is designed as a hands-on kernel project where new OS features are implemented iteratively.
It emphasizes memory management, scheduling, concurrency primitives, and system calls, offering a practical way to understand how modern operating systems function under the hood.

This project was developed as part of coursework and self-learning, where each milestone introduced a new concept (allocators, schedulers, synchronization tools, etc.) and was tested through structured test cases.

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✨ Features

🔹 Memory Management

• Kernel Heap:

  • kmalloc, kfree, krealloc (First-Fit strategy)
  • sbrk for dynamic heap expansion
  • Virtual ↔ Physical address mapping

• User Heap:

  • malloc, free, realloc (First-Fit)
  • sys_sbrk for user space heap management

• Dynamic Allocator:

  • Block allocation with First-Fit (FF) and Best-Fit (BF)
  • Block freeing and reallocation support

• Shared Memory:

  • smalloc, sget, sfree for inter-process shared objects
  • Kernel-side shared memory manager for tracking allocations

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🔹 Process Management & Scheduling

• Priority Round-Robin Scheduler:
  • Set process priority & thresholds
  • Timer tick–based scheduling decisions
• System Calls:
  • User–Kernel communication layer
  • Parameter validation and trap handling

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🔹 Synchronization

• Semaphores (user-level):
  • Create, Get, Wait, Signal
  • Tested with producer-consumer & barber shop scenarios
• Sleep Locks:
  • Sleep, Wakeup-One, Wakeup-All mechanisms

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🔹 Page Replacement & Fault Handling

• Nth-Chance Clock Algorithm:
  • Normal and Modified versions implemented
  • Page replacement testing with custom workloads
• Fault Handler:
  • Page fault detection and recovery
  • Invalid pointer checks

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📂 Project Structure

Copy code
kern/
 ├── cmd/                # Command prompt & kernel commands
 ├── conc/               # Concurrency: semaphores, locks, channels
 ├── cpu/                # Scheduling helpers
 ├── mem/                # Kernel/User heap, allocators, shared memory
 ├── proc/               # User environment mgmt
 ├── sched/              # Schedulers
 ├── tests/              # Module-specific tests
 └── trap/               # Syscalls, trap handling, fault handler

lib/
 ├── syscall.c           # Syscall wrappers
 ├── dynamic_allocator.c # Block allocators (FF, BF)
 ├── uheap.c             # User heap
 └── semaphore.c         # User-level semaphores

inc/
 ├── syscall.h           # Syscall definitions
 ├── environment_definitions.h
 └── ...

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🚀 Getting Started Clone the repository:

git clone https://github.com/Os-Creators/Os-Fos.git
cd Os-Fos

Build and run inside your environment.

Use FOS> prompt to run tests and commands.

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📌 Topics

• Operating Systems
• Kernel Development
• Memory Management (Heap, Allocators, Shared Memory)
• Concurrency & Synchronization (Semaphores, Locks)
• Scheduling (Priority Round Robin)
• Page Replacement Algorithms (Nth Chance Clock)
• System Calls & Traps