1. Review and Q/A

2. Demonstration (1) We use doodle
(2) Half hour for one group, most time in evening
(3) I will post the link once I create it

3. Partner? Does everyone has a partner?
If you haven’t sent me your team info, please do it
Make sure both of you understand the other’s work

4. Review In general, simulation of a shuttle in the kernel Basic steps
Add three system calls
Implement the system call function in a module
Create a kernel thread to simulate the shuttle
Data structure, Lock, schedule algorithm

5. System calls Follow the steps in the slides and video
Make sure whether is 32 bit or 64 bit
Wrapper

6. Wrapper system call What is this STUB thing Used in our module
User space program
system call
int sys_start_shuttle(void) {
if (STUB_start_shuttle)
STUB_start_shuttle();
else
return -ENOSYS; }
What is this STUB thing
Used in our module

7. Benefit At this stage, all the work can be done in your module
Does not need to compile the kernel again
Use the Makefile example for compiling the module

8. Module
Kernel
(a giant process)
Module

9. When module is loaded STUB_start_shuttle Module Kernel
(a giant process)
Module
STUB_start_shuttle

10. Module module_init, module_exit In module_init, set function pointers
It will go to the “if” part
In module_exit, re-set function pointers
It will go to the “else” part

11. Kernel thread One process, multiple threads Module Kernel
(a giant process)
Module

12. Create a thread kthread_run(threadfn, data, name)
threadfn — the name of the thread function
data — here it is NULL
name — whatever you want to name this thread, e.g “ShuttleSimulation”

13. Stop a thread kthread_stop() Where to use it?
Once receive the stop_shuttle() system call
After deliver all the passenger
In module_exit()

14. In the kernel thread Review previous slides
No more to tell (Don’t hate me :()

15. Data Structure Linked List(Recommend) Use the kernel linked list
Use your own defined list
Integers
Be careful with array
Still need to use lock

16. Lock Where to use lock All the places that need protection
All the places that can be modified by two different processes/threads
Passenger information at each terminal

17. Schedule algorithm One-way scan 1,2,3,4,5,1,2,3,4,5,… Two-way scan
1,2,3,4,5,4,3,2,1,2,3,…
Greedy
Potential issue?
Priority-weight (Recommend)

18. Priority
Children > Adult > Adult with luggage
Close > Far …

19. Reminder Allocate memory for pointers parameter check
correctness check
real time <=> clock time

20. Question 1
Can not get a new kernel following the slides and video, tried several times?
Start over entirely.
See me in my office.

21. Question 2 Can not see my kernel when I boot on machines in lab?
Use fixgrub.sh from website.

22. Question 3
Already used the fixgrub.sh, but still want to make some changes to the kernel?
Don’t try to modify the grub yourself. Let me know.

23. Question 4 Can get my new kernel, but system call does not work?
Things to check: 32bit or 64bit, system call number, system call function, log.

24. Question 5 What is wrapper? Where to wrap? How to wrap?
Previous slides.
Meet me in my office or in the lab.

25. Question 6 Where to implement the system calls? In your module.
How does the system know the implementation is in the module?
Wrapper.

26. Question 7 How to create a kernel thread? Where?
kthread_run(threadfn, data, name).
In module_init function, after all the preparation.

27. Question 8 How to stop the thread? Where to stop the thread?
kthread_stop()
Either after it deliver the last passenger, or in module_exit function.

28. Question 9
Everytime I start the shuttle(add one passenger, stop the shuttle, do xxx), it crashes, why?
Something is wrong in your program.
Reboot.
Things to look: your code, system log

29. Question 10
Can you debug for me?
No.

30. Question 11
Can, or should it be able to add passengers before shuttle started?
Yes.
Can, or should it be able to add passengers after shuttle stopped?

31. Question 12
Is it possible for a passenger whose initial_terminal and dest_terminal are the same?
Yes. One case for you to optimize you schedule algorithm.

32. Question 13 Can I use float/double variables?
No. There is no float/double variables in kernel programming. All variables are either integers or characters.

33. Question 14 Then how do I indicate that the child takes half seat?
(1) Double all the numbers, make the capacity 50, and each type of passengers takes 4, 2, 1.
(2) Use odd/even number to determine.

34. Question 15
How to print a decimal number if float/double is not allowed?
Use odd/even and manually append the decimal point if necessary.

35. Question 16 May we have some extensions for this project?
Let’s discuss about this.