Hotkey implementation in linux

Linux hotkey implementation-General Linux technology-Linux programming and kernel information. The following is a detailed description. Recently, I was writing a program for the hotkey function. it was required that the system volume could be adjusted by setting the shortcut key. after more than a week, I still did not solve the problem, if it is A single key, you can use the input_event structure and the eventx device file to set the global hot key. However, you do not know how to set the key combination, such as Alt + A or others, linux/input. h. there is only A separate definition for Alt and A, but there is no definition for key combination. could you help me ~! Thank you!