OS-LAB-xv6

A modified xv6 operating system with some extra features.

1. Introduction to xv6

• Added contributors' names to the system boot message

• Added following keyboard shortcuts to the console:

  i) Ctrl + N : Removing all the digits from the console

  ii) Ctrl + R : Reversing the current line

  iii) Tab : Substituting the current line with a command from the history

• Finding the prime numbers in the range [a, b] with the prime_numbers a b command.

2. System Calls

• find_largest_prime_factor : This system call finds the largest prime factor of a given number. The parameter of this system call is passed in the ebx register.

• change_file_size : This system call changes the size of the file by adding zeros to the end of the file or removing the last bytes of the file

• get_callers : This system call returns the history of the callers of every system call.

• get_parent_pid : This system call returns the parent process id of the current process.

3. CPU Scheduling

• Added 3 different queues:

  i) Round-Robin (with the highest priority)

  ii) Lottery-queue: The chance of each process for being executed is showed with a number.

  iii) Best-Job-First: The process with the lowest rank is executed first.

• Added Aging: If a runnable process has not been executed for 8000 ticks, we move it to the Round-Robin queue. By default all the processes except the init and sh processes are in Lottery queue.

• The following system calls are also added:

  i) int change_scheduling_queue(int pid, int queue): Changes the scheduling queue of a process.

  ii) set_bjf_params_process(int pid, float priority_ratio, float arrival_time_ratio, float executed_cycles_ratio): Sets the Best Job First parameters for a process.

  iii) int set_bjf_params_system(float priority_ratio, float arrival_time_ratio, float executed_cycles_ratio): Sets the Best Job First parameters for a system.

  iv) int set_lottery_tickets(int pid, int tickets): Sets the lottery tickets of a process.

  v) print_process_info(void): Shows the processes information.

4. Synchronization

• System calls which initialize, acquire, and release a semaphore are added.
• The simulation of the Dining-Philosophers is implemented.