hi All

i was trying to insert a module ..but it is giving compilation error ..

[root@localhost test]# gcc -D__KERNEL__ -I/usr/src/linux/include -O -Wall -c hello1.c
In file included from /usr/src/linux/include/asm/thread_info.h:16,
from /usr/src/linux/include/linux/thread_info.h:21,
from /usr/src/linux/include/linux/preempt.h:9,
from /usr/src/linux/include/linux/spinlock.h:49,
from /usr/src/linux/include/linux/module.h:9,
from hello1.c:1:
/usr/src/linux/include/asm/processor.h:83: error: `CONFIG_X86_L1_CACHE_SHIFT' undeclared here (not in a function)
/usr/src/linux/include/asm/processor.h:83: error: requested alignment is not a constant
In file included from /usr/src/linux/include/linux/module.h:21,
from hello1.c:1:
/usr/src/linux/include/asm/module.h:64:2: #error unknown processor family

i am using linux-2.6.22.5/ from linux.org ..

please help me out guys ... this is my first linux kernel level program

It would seem to me you need to #include /usr/src/linux/.config so that CONFIG_X86_L1_CACHE_SHIFT is defined properly. Naturally this assumes you've configured first.

As a general rule you don't want to compile as root, and especially not in /usr/src/linux - you ought to copy the source to some other location (like ~/src/linux) and build there, only installing as root.

It seems like you are using an older (2.4) method on newer (2.6) kernels. Moreover, you are including your header files from /usr/src/linux instead of those matching to your particular kernel (this may point to your actual kernel sources, but this is not the recommended way).

First off, please don’t do this:
Basically, on newer kernels, everyone is advised to use the kernel make system. This means you will change directory to your kernel build tree, run “make” from there with some magical options which make the make system compile and link your module. If you just want to use this without all the explanation, skip down to the Makefile at the end.

<EXPLANATION>
First, we need the kernel build tree: If you compiled your kernel from source and installed modules with “make modules_install” (on your 2.6 kernel), it should have created a directory “/lib/modules/`uname -r`” which has a two symlinks: “source” points to the kernel source tree, and “build” points to the kernel build tree (note, that in most cases, they are the same).

The build tree is needed intact for this to work. Next, we need to know some of the magical variables we pass to the make system. The first such option tells the make system you want to compile external module(s) which reside in the directory you specify. This is “M” variable (alternatively, you could use the older “SUBDIRS” variable).

The other variable will tell the make system what to compile (in this case, your one file: hello1.c) and how to link it (in this case, as a module). To specify linkage as a module, you use the variable “obj-m” (the value of this variable is the same name as the source file except the suffix is “.o” rather than “.c”).

Now, we should be set for making your module. Basically, this is what you do (replace “/path/to/your/source” with the location of “hello1.c”):
You should end up with (among other new files) a file named “hello1.ko” in the directory you specified. This is your module which you can insert with “insmod hello1.ko” (as root). Alternatively, you can install the module like this:
and insert it with “modprobe hello1” (as root).
</EXPLANATION>

If you don’t want to do this by hand each time, you can create a Makefile that looks something like this:
Place this file in the same directory that contains hello1.c, and just run “make” to build your module.