Hello World for linux Kernel Module

01_hello/Makefile

@@ -0,0 +1,21 @@
+
+#This variable is used to specify all the object file
+#which will be loaded and compile as kernel module for
+#usage. And the compilation for obj file from .c file
+#is done automatically.
+
+obj-m += hello.o
+
+# M variable used here tells the "make" to look in
+# current path to build bootable kernel module from
+# .c files in specified current path.
+
+# modules: It is the target that is used to build the kernel
+# 			modules.
+# clean: It is used to clean the build targets, compile and 
+#			generated files which would be created.
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

01_hello/hello.c

@@ -0,0 +1,58 @@
+#include <linux/module.h>
+#include <linux/init.h>
+
+
+/*
+*   insmod: It's the command to insert the
+*           loadable kernel module to the
+*           kernel.
+*
+*   rmmod:  It's the command to remove the
+*           loadable kernel module from the
+*           kernel.
+*/
+
+/*
+*   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.
+*/
+int
+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
+*/
+
+void
+my_exit(void){
+    
+    printk("hello - Goodbye, kernel!\n");
+}
+
+module_init(my_init);
+module_exit(my_exit);
+
+
+MODULE_LICENSE("GPL");