Operating Systems - 

New York University

Tandon School of Engineering

Department of Computer Science and Engineering

Introduction to Operating Systems

Spring 2025


Assignment 3

(10 points)


Develop a simple Linux kernel module that runs on your virtual machine. The only functionality required of your

module is to be able to load and unload, printing a debug message while doing so.

When a Linux kernel module is loaded, it invokes an init function, and when it is removed (or unloaded), it

invokes an exit function.

A) (0 points) Read chapter 2 of the freely available O’Reilly book “Linux Device Drivers, 3

rd

Edition”

(https://lwn.net/Kernel/LDD3/), in particular p.16, as well as your text book p.96 to get you started. Note that

even though the LDD3 book is written for kernel version 2.6, most mechanisms are applicable with minor or

no changes. The relevant example code is copied below as a starting point.

#include

#include

MODULE_LICENSE("Dual BSD/GPL");

static int hello_init(void)

{

printk(KERN_ALERT "Hello, world\n");

return 0;

}

static void hello_exit(void)

{

printk(KERN_ALERT "Goodbye, cruel world\n");

}

module_init(hello_init);

module_exit(hello_exit);

The hello_init() function is invoked when you insert your module (using the insmod shell command),

whereas the hello_exit() is called when you unload your module (using the rmmod shell command).

B) (0 points) Read the description of the global kernel variable jiffies and the macro HZ in the O’Reilly book

(search in the searchable pdf). Then read about the ktime_get_boottime() routine in

https://www.kernel.org/doc/html/latest/core-api/timekeeping.html


C) (0 points) You may need to install the kernel headers if not already installed. Type:


sudo apt-get install linux-headers-$(uname -r)


D) (10 points) Modify the c code given above (which becomes your lab3.c) such that:

1) The init function prints the tick time in milliseconds (i.e. the timer interval, as we defined it in weeks 1/2)

after the hello message.

The init function shall also save the value of jiffies and the current time.

Operating Systems - Prof. Omar Mansour

2) The exit function prints a goodbye message and the time in milliseconds between the insertion and

removal of the module i.e. between init and exit functions) using two different methods:

a. Using the difference in the value of jiffies from inserting the module to removing the module.

b. Using the time difference obtained by reading the timer (Hint: use ktime_get_boottime().

You shall use the Makefile provided with the assignment (In some cases, you may need to slightly modify the

Makefile provided to suit your setup). You should place it in the same directory as your .c file (lab3.c)

Hints:

E) Your module should use printk() to print messages. You will use this print facility to also debug your

code if needed ( ). More information may be found on https://www.kernel.org/doc/html/latest/core-

api/printk-basics.html

F) Use dmesg shell command to view messages printed by printk(), e.g. type:

dmesg

You may clear the log using:

dmesg -C

What to submit to gradescope:

Please submit the following files individually:

1) Source file(s) with appropriate comments.

The naming should be similar to “lab#_$.c” (# is replaced with the assignment number and $ with the

question number within the assignment, e.g. lab4_b.c, for lab 4, question b OR lab5_1a for lab 5, question

1a).

2) A single pdf file (for images + report/answers to questions), named “lab#.pdf” (# is replaced by the

assignment number), containing:

 Screen shot(s) of your terminal window showing the current directory, the command used to

compile your program, the command used to run your program and the output of your program.

3) Your Makefile, if any. This is applicable only to kernel modules.


RULES:

 You shall use kernel version 4.x.x or above. You shall not use kernel version 3.x.x.

 You may consult with other students about GENERAL concepts or methods but copying code (or code

fragments) or algorithms is NOT ALLOWED and is considered cheating (whether copied form other

students, the internet or any other source).

 If you are having trouble, please ask your teaching assistant for help.

 You must submit your assignment prior to the deadline.

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