Help: My first kernel module

[kvorion]

I am trying to compile my first hello world kernel module. I realized that I did not have the linux kernel source, so I downloaded it.



#define MODULE
#include <linux/module.h>
int init_module(void) { printk("<1>Hello, world\n"); return 0; }
void cleanup_module(void) { printk("<1>Goodbye cruel world\n"); }


The problem is that gcc is not able to find linux/module.h file inside /usr/include/iinux folder (which I believe is the default path). How do I like gcc to the file inside the /usr/src/linux-source-2.6.15-2.6.15/include/linux folder where the file actually is? (I created this folder by extracting from the source archive that I downloaded). Where should I extract this so that gcc can actually find it?

[CptPicard]

Would be easier for you to download the sources using apt from the repositories, and in particular, install the kernel-headers package.

[kvorion]

I also used the makefile method of compiling the code, but I got the following error:

make: Nothing to be done for 'all'. I checked out this page: http://www.captain.at/programming/kernel-2.6/

and it said that the kernel source has to be installed. What does that mean? Is there a guide that lists the exact steps to be done before I can start compiling kernel modules? The dont seem to be able to figure out what exactly the pre-requisites are.

[gnusci]

first of all make sure you did download the kernel source according to you actual kernel:

> uname -a

Now if you gcc is looking for the libraries in:

/usr/include/linux

just make a symbolic link to the right path:

> ln -s /usr/src/linux-source-2.6.15-2.6.15/include/linux /usr/include/linux

make sure that there is not a:

/usr/include/linux

symbolic link first.

EDIT: maybe you will need to compile a new kernel if you want to use a new one, but I will suggest you to take CptPicard advising.

[fct]

You don't need to compile a new kernel. Just the kernel-headers package of your current kernel is enough.

And the linked tutorial doesn't seem right to me, specially the KDIR part. I compile my modules like this:

Makefile:

obj-m := modulename.o

Command:

$ make -C /usr/src/linux-headers-`uname -r` SUBDIRS=$PWD modules