Description
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.
Please consult the freely available O’Reilly book “Linux Device Drivers, 3rd 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 <linux/init.h>
#include <linux/module.h>
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).
In addition, you may also need to slightly modify the Make file provided in the book to suit your setup.
Modify this module 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,
2) The exit function prints a goodbye message and the time 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
(HINT Hint: Search for “jiffies” and “HZ” in the O’Reilly book)
b. Using the time difference obtained by reading the timer (Hint: use ktime_get_boottime(void),
more documentation may be found at https://www.kernel.org/doc/html/latest/coreapi/timekeeping.html).
Hints:
• 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/coreapi/printk-basics.html
• Unless the message level you pass to printk() is of higher priority (i.e. lower value) than the console’s log
level (i.e. threshold), printk()will print to a log buffer instead of your shell’s console.
o In such a case, you shall use dmesg shell command to view messages printed by printk(), e.g.:
dmesg
o You may clear the log using:
dmesg -C
• You may modify the printk() behavior by either changing the message log level (i.e. the first byte you
pass to printk() ) OR by changing the console’s threshold using:
dmesg – n 8 // prints everything to console
• You may use the Makefile provided in the O’Reilly book, but you may need to install the kernel headers prior
to using it if not already installed:
sudo apt-get install linux-headers-$(uname -r)
Submission file structure:
Please submit a single .zip file named [Your Netid]_lab#.zip. It shall have the following structure (replace # with
the actual assignment number):
└── [Your Netid] hw# (Single folder includes all your submissions)
├── lab#_1.c (Source code for problem 1)
├── lab#_2a.c (Source code for problem 2a, and so on)
├── lab#_1.h (Source code header file, if any)
├── Makefile (makefile used to build your program, if any)
├── lab#.pdf (images + Report/answers to short-answer questions)
What to hand in (using Brightspace):
• Source files (.c or .h) with appropriate comments.
• Your Makefile if any.
• A .pdf file named “lab#.pdf” (# is replaced by the assignment number), containing:
o 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.
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.