Driver skeletons

Let's consider the following helloworld module. It will be the basis for our work during the rest of this chapter.

The helloworld.c file is as follows:

#include <linux/init.h> 
#include <linux/module.h> 
#include <linux/kernel.h> 
 
static int __init helloworld_init(void) { 
    pr_info("Hello world!\n"); 
    return 0; 
} 
 
static void __exit helloworld_exit(void) { 
    pr_info("End of the world\n"); 
} 
 
module_init(helloworld_init); 
module_exit(helloworld_exit); 
MODULE_AUTHOR("John Madieu <[email protected]>"); 
MODULE_LICENSE("GPL"); 

Module entry and exit point

Kernel drivers all have entry and exit points: the former correspond to the function called when the module is loaded (modprobe, insmod) and the latter are the function executed at module unloading (at rmmod or modprobe -r).

We all remember the main() function, which is the entry point for every user space program written in C/C++; it exits when that same function returns. With kernel...