Lab 04

NCTU OSDI Lab 4: Multitasking

Documentation: Lab 4

Lab 4 Demo Release

Required

• Required 1
  • Design your own task struct with at least one field called task id. Task ids should be unique.
  • Implement privilege_task_create.
  • Implement context_switch.
  • In the end of privilege_task_create, put the task into the runqueue.
  • Replace context_switch withschedule in the privilege tasks, you should be able to create more than 2 tasks and switch between them.
• Requried 2
  • Reimplement the core timer handler, it updates the current task’s reschedule flag.
  • Create more than 2 privilege tasks. Each of them keeps checking the reschedule flag. If the flag is set, it prints some message, clears reschedule flag and issue schedule .
• Required 3
  • Implement do_exec.
  • Implement user tasks preemption.
• Required 4
  • Implement uart_read and uart_write.
  • Implement exec.
  • Implement fork.
  • Implement exit and zombie reaper by one of the above methods.

Elective

In the elective part, you should enable interrupt except some critical regions in EL1. Otherwise, you won’t get any score.

• Implement kill and signal handler for SIGKILL.
• Implement a priority based scheduler.
• Implement a wait queue for uart reading.interrupt after top half of ISR.
• Implement mutex_lock, mutex_unlock. If task fail to acquire the lock, it would go to sleep and context switch to other tasks.
• Let kernel could be preempted without explicit calling schedule.

Questions

• Consider the following POSIX signal example code. Can you elaborate how to design the kernel to support it?

  #include <stdio.h>
  #include <signal.h>
  #include <unistd.h>
  
  void handler(int sig) {
    printf("Hello\n");
  }
  
  int main()
  {
    signal(SIGINT, handler);
    char buf[256];
    int n = read(0, buf, 256);
    buf[n] = '\0';
    printf("Bye %s\n", buf);
  }
  

• Can you prevent all possible context switch by disabling interrupt?
• Do you think microkernel need to be preemptive kernel or not? Why or why not?