linux/module.h: No such file or directory

Question

i'm a beginner and i'm trying out some basics of kernel programming in linux. Today morning i've opened the module.h file in VIM, and closed without saving any changes as well. After that i'm not able to compile any of my codes. I'm getting the following error message

[root@localhost helloworld]# cc helloworld.c
helloworld.c:1:25: error: linux/module.h: No such file or directory
[root@localhost helloworld]# 

Here is a sample code which was running successfully till the last day.

#include<linux/module.h>
#include<linux/kernel.h>

int init_module(void)
{
        printk("HELLO WORLD");
        return 0;
}

void cleanup_module(void)
{
        printk("GOODBYE");
}

I searched for the module.h file like the following and it do exist

[root@localhost usr]# find . -name module.h
./src/kernels/2.6.18-194.el5-i686/include/asm-x86_64/module.h
./src/kernels/2.6.18-194.el5-i686/include/asm-i386/module.h
./src/kernels/2.6.18-194.el5-i686/include/linux/module.h
./include/sepol/policydb/module.h
./include/sepol/module.h
./include/kde/kunittest/module.h
[root@localhost usr]# 

Please help me out. I'm using CentOS in virtual box.

Answer 1

You're trying to compile your module with plain gcc with none of the surrounding kbuild framework. You might have gotten something to work in the past with this approach, but it is painful horrible awful to try to maintain a module using anything other than pure-kbuild Makefile approaches. I've wasted too much of my life fighting against kbuild and I don't want the same to happen with you -- embrace kbuild and let it help you build your module. Please read Documentation/kbuild/modules.txt before writing another line of code.

What you need to do is create a Makefile for your module. Its contents should look like this:

ifneq ($(KERNELRELEASE),)
# kbuild part of makefile
obj-m  := modulename.o

else
# normal makefile
    KDIR ?= /lib/modules/`uname -r`/build

default:
$(MAKE) -C $(KDIR) M=$$PWD

endif

I know it's a lot more complicated than most Makefiles you're used to seeing, but it serves a dual-purpose. If you just run make in your directory, it'll re-invoke make to use the kbuild mechanism from the currently-running kernel (assumed to at least have a symlink from /lib/modules/.../build to the correct location).

The re-invoked make command ($(MAKE)) will properly build your module and save you more time than you can ever appreciate. (Really.)

Keep Documentation/kbuild/modules.txt by your side while making this work.

Note: Documentation/kbuild/modules.txt may be available at your linux system at /usr/share/linux-headers-$(uname -r)/Documentation/kbuild/modules.txt