A tiny loadable kernel module used for testing and learning. The module implements a simple guest book: by writing on the device, a message can be left, and by reading from the device the latest inserted message can be read.

To read the kernel log:

tail -f /var/log/kern.log

The test.sh script does a quick test compiling and loading the module, and also unloading it and deleting the generated files when it's done.

If you want to do the testing manually:

• To load the kernel module, compile it with make, then a .ko file is produced. Run:

sudo insmod guestbook.ko

• To unload it:

sudo rmmod guestbook

• Once the module is running, you can compile (just run gcc -o tester tester.c) and run tester.c to see how it does.

• If you want to quickly remove the files generated with make, run make clean.

The module now creates (and deletes) its own device file via C code, and we have a tester.c program to test the module, so the section below is not needed anymore. I will keep it there in case anyone finds it useful.

Once it's running we want to create a node for the device in /dev:

cd /dev
#          dev name c is for char device
sudo mknod guestbook c <major_number> 0

To see it in action do for example:

cat /dev/guestbook