Simple Linux driver

The tutorial is located here: https://www.apriorit.com/dev-blog/195-simple-driver-for-linux-os

On a fresh system, to get the module to build, we have to make sure that the kernel headers are installed. Under Fedora, the command is dnf install -y kernel-devel dwarves. On Debian based systems the command is apt install -y linux-headers-`uname -r` dwarves. The dwarves package is required to mitigate a "BTF" error, which is required to allow the module to load and be recognized.

Also, the built kernel needs to be present in the module build directory. This can be done with a symbolic link using the command ln -s /sys/kernel/btf/vmlinux /usr/lib/modules/`uname -r`/build/

The module is installed using the command sudo make load and uninstalled using the command sudo make unload.

Monitor the kernel messages with the command sudo dmesg -w. Type CTRL-C to exit.

Creating the dev file in the dev directory:

• First find the major device number that was assigned by the kernel using the command grep imple-dri /proc/devices. I get a line such as 239 Simple-driver.
• Then make the node using the command sudo mknod /dev/simple-driver c 239 0.
• Prove it works with the command sudo cat /dev/simple-driver.

Then one may unload the driver and delete the node as root.