Operating System - xv6

This repository contains several patch files that modify the xv6 operating system. These modifications were made for CSE314 (Operating System Sessional) course at BUET. The detailed specifications for patches can be found in the corresponding folders.

• Added system calls and !! command
• Implemented multi-level feedback queue scheduling
• Implemented threading and synchronization support

How to Run

Repository

This is the repo on which patches have to be applied:

git clone https://github.com/shuaibw/xv6-riscv --depth=1

Alternatively:

git clone https://github.com/mit-pdos/xv6-riscv
cd xv6-riscv
git reset --hard dd2574bc1097a912e799340172b8b6ef42ac5ceb

Quick commands:

make qemu

make clean

git add --all; git diff HEAD > <patch file name>

git apply --whitespace=fix <patch file name>

git clean -fdx; git reset --hard

patch-1: System Calls

• trace: This system call monitors traces the system call (whose id was provided as an argument) made by a process

  trace 5 grep hello README
  pid: 4, syscall: read, args: (3, 0x0000000000001010, 1023), return: 1023
  pid: 4, syscall: read, args: (3, 0x000000000000103a, 981), return: 981
  pid: 4, syscall: read, args: (3, 0x0000000000001023, 1004), return: 350
  pid: 4, syscall: read, args: (3, 0x0000000000001010, 1023), return: 0
  

• System call named info that returns the aggregated information of currently running processes as struct procInfo; design of a load user program that creates some processes, allocates memory and uses info.

  struct procInfo {
      int activeProcess; // # of processes in RUNNABLE and RUNNING state
      int totalProcess; // # of total possible processes
      int memsize; // in bytes; summation of all active process
      int totalMemSize; // in bytes; all available physical Memory
  };

• Implementation of !! command and !! n command where n is a positive integer. Implemented by storing previously executed commands in kernel space. Used system calls to set and get the desired command.

patch-2: Scheduling

• Multi Level Feedback Queue
• 2 queues
• Round Robin Scheduling in lower priority queue
• Lottery Scheduling in higher priority queue

patch-3: Threading

• Implemented threading support and relevant system calls.
• Implemented synchronization primitives: spinlock and mutex.