Character driver finished

LKM/hello.c

@@ -0,0 +1,43 @@
+#include <linux/module.h>   // included for all kernel module
+#include <linux/kernel.h>   // included for KERN_INFO
+#include <linux/init.h>     // included for __init and __exit macros
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Junet Hossain");
+MODULE_DESCRIPTION("A Simple Hello World module");
+
+static int __init hello_init(void){
+    printk(KERN_INFO "Hello world!\n");
+    return 0; // Non-zero return means that the module couldn't be loaded.
+}
+
+static void  __exit hello_cleanup(void){
+    printk(KERN_INFO "Cleaning up hello module.\n");
+}
+
+module_init(hello_init);
+module_exit(hello_cleanup);
+
+/**
+ *  Use these macros for efficient and optimized kernel modules.
+ *  
+ *  __init: It's a macro which is used for marking
+ *          the function which is executed when the
+ *          kernel is loaded. After execution, its memory
+ *          is freed (for built-in modules). For module
+ *          compiled as a loadable kernel module (LKM),
+ *          __init has no effect (because the memory
+ *          is allocated dynamically). If not used for built
+ *          -in kernel, the memory for the init function
+ *          remains allocated even after module initializaiton
+ *          (wasted memory)
+ * 
+ *  __exit: It's a macro which is used to mark the function
+ *          which is executed when the module is unloaded
+ *          from the kernel. It is ignored for built-in kernel modules
+ *          (since they can't be removed at runtime). For
+ *          dynamically loaded modules, it ensures proper
+ *          cleanup. If __exit is not used, the function will
+ *          still run when removing the module, but marking
+ *          it properly makes the code cleaner and optimized.
+ */