xv6 Operating System Projects
This repository contains implementations for five projects that extend the xv6 operating system, covering fundamental operating systems concepts including system calls, concurrency, scheduling, memory management, and file systems.

Course Information
Course: CSEN283 - Operating Systems Platform: xv6-riscv operating system Architecture: RISC-V

Project Overview
Project 1 - System Calls (proj1/)
Focus: Introduction to system call implementation and kernel-user space communication
Implementation:

System Call: calculate(int x, int y, char* op, int* result)
Performs arithmetic operations (+, -, *, /) in kernel space.

Handles error cases (invalid operators, division by zero).

Demonstrates parameter passing between user and kernel space using copyin() and copyout()

Key Learning: System call implementation, kernel-user space transitions, argument handling

Project 2 - Concurrency and Synchronization (proj2/)
Focus: Inter-process communication and priority-based task management
Parts:

Part 1: Basic pipe-based IPC with parent server and multiple child clients
Part 2: Prioritized pipe implementation with new pipe_rt() system call
Part 3: Priority queue using linked lists for task scheduling
Key Features:
Tasks include priority field (higher number = higher priority)
Linked list implementation for O(n) insertion, O(1) removal
Server processes client requests in priority order
Key Learning: IPC mechanisms, priority queues, synchronization, producer-consumer patterns

Project 3 - Timer, Trap and Scheduling (proj3/)
Focus: Timer interrupts, scheduling algorithms, and real-time systems.
Parts:
Part 1: CPU affinity with set_cpu_affinity(int cpu_mask) system call
Part 2: Custom timer implementation with callback functions
Part 3: Periodic tasks using setperiod() and wait_until_next_period() system calls
Part 4: Rate Monotonic Scheduling (RMS) implementation
Key Features:
Custom timer structure with expiry times and callbacks
Periodic task support for real-time applications
RMS scheduler (shorter period = higher priority)
Falls back to round-robin when no real-time tasks available
Supports up to 4 concurrent periodic tasks
Key Learning: Timer interrupts, scheduling algorithms, real-time systems, trap handling

Project 4 - Memory Management (proj4/)
Focus: Virtual memory management and shared memory IPC
Parts:
Part 1: Memory mapping visualization with show_vm_areas() system call
Part 2: Shared memory IPC using shmget(int key, uint64 size) system call
Key Features:
Displays process memory layout (start/end addresses, page counts)
Shared memory implementation for efficient IPC
Improves on Project 2 by eliminating multiple pipes
Supports at least 10 concurrent clients
Memory allocated in high virtual addresses near MAXVA
Key Learning: Page tables, virtual memory, shared memory, memory management

Project 5 - File Systems (proj5/)
Focus: File system internals and inode operations
Parts:

Part 1: File size retrieval with getfilesize(int* size, char* filepath) system call
Part 2: File append mode implementation with O_APPEND flag support
Key Features:
Direct inode access for file size information
Append mode ensures all writes occur at end of file
Compatible with existing open() system call interface
Key Learning: File system structures, inodes, file operations, file control flags