Kernel Space communication with User Space:
1. System calls.
2. Proc file system.
3. Sysfs file system.
4. Netlink Socket.
5. Mmap(Memory map).
6. (Device)File and Signal.
BTW. For more infomation please look up kernel development book ULK/LKD/LDD/ELDD.
Reference Blog: https://www.cnblogs.com/dchipnau/p/5043591.html