netlink_test

Example of communication between kernel module and user application

Workflow:

1. Kernel module invokes user application by calling call_usermodehelper
2. User app sends some message to kernel
3. Kernel receives message and sends response
4. User app receives kernel-response and sends something back

First of all prepare a testing environment (maybe a virtual machine), because kernel modules may be very dangerous

1. make

All build artifacts (kernel module and user app) will be placed into the 'build' directory

Now insert the module

2. cd build
3. sudo insmod kernel_mod.ko

Show last ten log messages

4. dmesg -T | tail

If everything's fine you will receive something like this:

[19:39:05 2020] User app path: /home/owl/my/cpp/test_module/build/user_app
[19:39:05 2020] Launch with option: Wake up!
[19:39:05 2020] Message from user(pid 7187) : Hello kernel, you heartless bitch!
[19:39:05 2020] Send message back: Goodbye!
[19:39:05 2020] Message from user(pid 7187) : Goodbye kernel!

There is an additional logfile from user app in build directory.

Do cleanup

5. make clean
6. sudo rmmod kernel_mod.ko

Tested on 5.4.0