Hello World for linux Kernel Module

02_better_hello/hello.c

@@ -0,0 +1,102 @@
+#include <linux/module.h>
+#include <linux/init.h>
+
+
+/*
+*   insmod: It's the command to insert the
+*           loadable kernel module to the
+*           kernel.
+*
+*           Usage:
+*           insmod ./<Module_name>.ko
+*
+*   rmmod:  It's the command to remove the
+*           loadable kernel module from the
+*           kernel.
+*           
+*           Usage:
+*           rmmod ./<Module_name>.ko
+*   
+*   modinfo:    It's the command to see the
+*               description of the kernel module.
+*
+*           Usage:
+*           modinfo <Module_name>.ko
+*
+*   lsmod:  It's the command to see all the loaded
+*           module of the linux kernel.
+*
+*           Usage:
+*           lsmod
+*
+*   modprobe:   It's the command to load module with
+*               all its dependencies. For using modprobe
+*               kernel module need to be present in 
+*               /lib/modules path so our custom build
+*               kernel module on different path cannot
+*               use modprobe.
+*           
+*           Usage:
+*           modprobe <Module_name>
+*/
+
+/*
+*   There are two imp. events for linux driver
+*   The loading of driver on kernel and unloading
+*   of driver from kernel.
+*/
+
+/*
+*   Function to use when this is
+*   module is loaded to the kernel.
+*   __init-> It's a macro which does nothing
+*               but only increase the readibility
+*               of kernel module.
+*           We just have to search for this macro
+*           to see what are the modules which execute
+*           at the starting of the driver.
+*           This is helpful when module is very big.
+*/
+static int
+__init my_init(void){
+
+
+    /*
+    *   We don't use printf for linux driver
+    *   because printf writes to standard IO
+    *   and there is no standard IO for kernel
+    *   There is only kernel's log. Kernel's log
+    *   is buffer which stores whatever is written
+    *   onto that buffer. It can me printed using
+    *   command: dmesg
+    */
+
+    printk("hello - Hello, Kernel!\n");
+    return 0;
+}
+
+/*
+*   Function to execute when module
+*   is unloaded from the kernel
+*   __exit-> It's a macro which does nothing
+*               but only increase the readibility
+*               of kernel module.
+*           We just have to search for this macro
+*           to see what are the modules which execute
+*           at the exiting of the driver.
+*           This is helpful when module is very big.
+*/
+
+static void
+__exit my_exit(void){
+    
+    printk("hello - Goodbye, kernel!\n");
+}
+
+module_init(my_init);
+module_exit(my_exit);
+
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Junet Hossain <mail@jhossain.online");
+MODULE_DESCRIPTION("A simple Hello World Linux Kernel Module");