Error in building hello world module in kernel - linux

Question

/*
* hello-1.c - The simplest kernel module.
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
int init_module(void)
{
printk(KERN_INFO "Hello world 1.\n");
/*
* A non 0 return means init_module failed; module can't be loaded.
*/
return 0;
}
void cleanup_module(void)
{
printk(KERN_INFO "Goodbye world 1.\n");
}
MAKEFILE
obj-m += hello.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
After the make command I am getting the following error. What is the reason for this error and how can i resolve this?
make -C /lib/modules/2.6.32-358.el6.x86_64/build M=/home/hello modules
make: *** /lib/modules/2.6.32-358.el6.x86_64/build: No such file or directory. Stop.
make: *** [all] Error 2

Answer 1

-C option in make command instruct to change directory to one provided with -C. In your case, it is /lib/modules/2.6.32-358.el6.x86_64/build. But when it tries to change to that directory, compilation gives error with "No such file or directory", which means that you don't have build directory at /lib/modules/2.6.32-358.el6.x86_64/.
A lot of time it happens that build in the given path may not be a directory, but it may be a soft link pointing to a kernel source code directory.
So you need to check either there should be build directory at the required path which contains kernel source or it should be a soft link to kernel source.

Answer 2

Apart from all those build related comments, there are few things you have to follow while writing a kernel module. Your code will not work as you expect even after you fix those build issues. Why? you have the init and cleanup routines built, but you haven't specified/directed which one is your init routine and which is cleanup.
You have to do that this way,
at the end of the file add these two line.
module_init ( foo_init_fn);
module_exit ( bar_exit_fn);
Also, you have to specify the module license details etc. like below
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Copyright (c) 2006 by xxxx xxxxx, Inc.");
MODULE_DESCRIPTION("klm_vdc");