module compilation
 

i am trying to compile a simple hello module but when i write

gcc -c -Wall hello.c

then i get

warning: implicit declaration of function "printk"

so where is the wrong , thanx for helps

/* hello.c */

#define MODULE
#include <linux/module.h>

int init_module(void) {printk("<1>hello\n"); return 0; }

void cleanup_module(void) {printk("<1>goodbye\n");}