OSLab-xv6

A modified xv6 operating system with several extra features.

1. Introduction to xv6

• Added contributors names to boot message.

• Shell features:

  1. CTRL + K: Cursor jumps left one word
  2. CTRL + L: Cursor jumps right one word
  3. CTRL + I: Line is deleted upto current char above cursor

• Comparing two string by adding strdiff command.

2. System calls

• calculate_biggest_perfect_square(int n): returns the biggest perfect square smaller than
• get_ancestors(int pid): prints all the ancestors of the process associated with pid
• get_descendants(int pid): prints all the descendants of the process associated with pid
• set_sleep(int n): sleeps the process for n seconds

3. CPU Scheduling

Modified the scheduler by adding 4 different levels for processes.

0. Level 0: Round Robin
1. Level 1: Minimum Priority
2. Level 2: Best Job First (BJF)
3. Level 3: First Come First Served (FCFS)

Some system calls added:

• set_queue(int pid, int queue): Sets the level for the process
• set_priority(int pid, int priority): Sets the priority value for those processes in Level 1
• set_bjf_params(int pid, int priority_ratio, int arrival_time_ratio, int executed_cycle_ratio): Sets the parameters needed to chose the best job

View all processes in a beautiful table with ps command.

4. Synchronization

1. Allowing to acquire a lock multiple times. The user program multiple_acquire is added for test.

2. Reader/Writer problem:

• Reader Priority: rwtest <num> 0
• Writer Priority: rwtest <num> 1

where num in binary, represents a queue of readers (0) and writers (1) waiting to enter a space.