Laboratory 2

Due Date: Monday, February 21, 2000

Points: 100



These problems ask you to make small modifications to the MINIX kernel.  You will be modifying the kernel's source 
code, recompiling and assembling it, using make(1) to link the various executable files, and then produce a new 
MINIX boot "disk." 

These programs require only rather minor modifications to MINIX.  The key is locating the current code that should 
be modified;  surely, there are many acceptable solutions.

To receive credit for your solutions, show the TAs the modifications you have made to the kernel source code. Also 
demonstrate your new kernel running programs that show that your new kernel meets the requirements of the prob-
lem. Think carefully to come up with programs that demonstrate your new kernel.

Submit a boot disk with your new Minix system to the homework box by the deadline. Put your sources for your 
changes to the MINIX kernel, and the program(s) you wish to run to demonstrate your new kernel, onto a second 
disk, and submit that disk as well.

1.	(30 points) Modify the MINIX kernel to print the word "OUCH!" on the console whenever the user generates an 
interrupt by pressing the interrupt key on the keyboard. For example, if you type ^C to terminate your program, 
the kernel should write "OUCH!" on the screen. After printing the "OUCH!", the kernel should proceed to han-
dle the interrupt in the usual way.

2.	(70 points) Modify the MINIX process scheduler so that user processes are scheduled by a multilevel feedback 
queue with two levels, both scheduled using round robin. The quantum at the first level is the quantum that 
MINIX currently uses in its round robin scheduling algorithm for user processes. The quantum at the second 
level is twice that. At the first level, each process gets 2 quanta before being moved into the second level.

	Pick a keystroke (like control-T) that when struck will print the total CPU time used and the current level (first or 
second) of the currently-running process.

	You will be asked to demonstrate that your new MINIX kernel properly schedules processes.  To do this, you 
might want to have a number of long-running CPU-bound processes around, and then create a few I/O-bound 
processes and demonstrate that these get scheduled as you would expect.