simple hello.c device driver for 2.6 kernel

blavo · 06-16-2004, 06:49 AM

I'm trying to build a very simple device driver using Mandrake 10 with the 2.6 kernel. Every attempt seems to fail and all the links I'm finding explain the procedure for the previous kernel versions. I found an example on a website that said this should work. Bellow is a cut and past directly from the website.

My source file "helllo2.c" looks like this.

/* hello2.c - Demonstrating the module_init() and module_exit() macros. This is the
* preferred over using init_module() and cleanup_module().
*/
#include <linux/module.h> // Needed by all modules
#include <linux/kernel.h> // Needed for KERN_ALERT
#include <linux/init.h> // Needed for the macros

static int hello_2_init(void)
{
printk(KERN_ALERT "Hello, world 2\n");
return 0;
}

static void hello_2_exit(void)
{
printk(KERN_ALERT "Goodbye, world 2\n");
}

module_init(hello_2_init);
module_exit(hello_2_exit);

The example make file looks like this

TARGET := hello2
WARN := -W -Wall
INCLUDE := -isystem /lib/modules/`uname -r`/build/include
CFLAGS := -O2 -DMODULE -D__KERNEL__ ${WARN} ${INCLUDE}
CC := gcc-3.0

${TARGET}.o: ${TARGET}.c

.PHONY: clean

clean:
rm -rf {TARGET}.o

I've also tried building hello2.c from the command line gcc -c hello2.c and that doesn't work either.

I'm looking for help in getting this very simple driver to build, any help is greatly appreciated.

Thanks

keefaz · 06-16-2004, 12:01 PM

Try this Makefile :

Code:

ifneq ($(KERNELRELEASE),)
obj-m := hello2.o

else
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)

default:
    $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
endif

And look at http://lwn.net/Articles/driver-porting/, there are good stuff here for 2.6 kernel

blavo · 06-17-2004, 09:31 AM

I tried your suggestion and I get a message that says "nothing to do for default".

I have a question on the first line ifneq ($(KERNELRELEASE),) I left this line as is, does something need to go in after the comma?

keefaz · 06-17-2004, 02:24 PM

Don't you get your kernel module helllo2.ko issuing this Makefile ? It need nothing after the comma, I grabbed this Makefile as this from the link I mentioned above (but it seems break today).
For me it's worked, I result with a .ko module which I loads from insmod modulename.ko, when I typed dmesg, it give me expected output messages ( printk(KERN_ALERT "Hello, world 2\n"); )

AMDPwred · 06-18-2004, 12:20 PM

Can anybody help with the make file for a 2.4 kernel? I found the website you are using and I'd really like to try this on a 2.4 kernel. Once you write the make file and get the code compiled, how does it actually get added to the kernel?

http://lwn.net/Articles/21817/

keefaz · 06-18-2004, 12:27 PM

The first Makefile described by blavo at the top of this thread is good for 2.4
It is loaded in the kernel by : insmod yourModuleName.o (for 2.4)

AMDPwred · 06-18-2004, 12:55 PM

Do I need to place my source file anywhere specific to get this to work? I wrote the make file mentioned above and ran "make hellokernel.c" and got the "Nothing to be done for hellokernel.c" message. Then I tried to compile it manually with gcc and got compile errors. It looks like the header files cannot be found.

infamous41md · 06-18-2004, 01:00 PM

i use this makefile daily on 2.4:

Code:

[n00b@localho.outernet] cat devdr/makefile 
KERNELDIR       = /lib/modules/`uname -r`/build/include/
OBJECTS         = usb-skeleton.o cmos.o
WARNINGS        = -Wall
CC      = gcc
OPT     = -O2
CFLAGS  = -D__KERNEL__ -DMODULE -isystem$(KERNELDIR) $(WARNINGS) $(OPT)

all: $(OBJECTS)

clean:
        rm -f $(OBJECTS) *~ core

keefaz · 06-18-2004, 01:56 PM

AMDPwred> Adapt Makefile to suit your project by replacing target value by your module name.
ie for first Makefile:
TARGET := hellokernel
for second Makefile (provided by infamous41md) :
OBJECTS = hellokernel.o

And when invoking make do not use extension after module name. ie:
make hellokernel

AMDPwred · 06-18-2004, 02:05 PM

Ok cool, that got the make piece running. During the compile I still get those errors. Do I need to include a path to these header files in my system PATH?

hellokernel.c

Code:

/*
 * hellokernel.c
 * Demonstrating the init_module() and cleanup_module().
 */

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

int init_module(void)
{
        printk(KERN_INFO "Hello kernel!\n");
        return 0;
}

void cleanup_module(void)
{
        printk(KERN_INFO "Peace out kernel!\n");
}

error during make

Code:

chris@zion kernelmodule $ make hellokernel
gcc     hellokernel.c   -o hellokernel
hellokernel.c: In function `init_module':
hellokernel.c:12: error: `KERN_INFO' undeclared (first use in this function)
hellokernel.c:12: error: (Each undeclared identifier is reported only once
hellokernel.c:12: error: for each function it appears in.)
hellokernel.c:12: error: syntax error before string constant
hellokernel.c: In function `cleanup_module':
hellokernel.c:18: error: `KERN_INFO' undeclared (first use in this function)
hellokernel.c:18: error: syntax error before string constant
make: *** [hellokernel] Error 1

keefaz · 06-18-2004, 02:15 PM

Try

Code:

printk("Hello kernel!\n");

Just remove KERN_INFO and KERN_ALERT, it is for 2.6

AMDPwred · 06-18-2004, 02:28 PM

Here is the error output after removing those two phrases:

Code:

chris@zion kernelmodule $ make hellokernel
gcc     hellokernel.c   -o hellokernel
/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/../../../crt1.o(.text+0x18): In function `_start':
: undefined reference to `main'
/tmp/ccmDnTfs.o(.text+0xe): In function `init_module':
: undefined reference to `printk'
/tmp/ccmDnTfs.o(.text+0x27): In function `cleanup_module':
: undefined reference to `printk'
collect2: ld returned 1 exit status
make: *** [hellokernel] Error 1

keefaz · 06-18-2004, 02:46 PM

verify in your /lib/modules/`uname -r`/build/include/linux directory that module.h and kernel.h exist, if yes verify in your Makefile that you have inclued the directory by parameter -isystem (which make sure that /lib/modules/`uname -r`/build/include/ will be used instead of /usr/include)

AMDPwred · 06-18-2004, 03:05 PM

Those header files don't exist in that directory. Which is weird because I remember seeing them browsing the kernel source tree one day. I can't seem to find them at the moment though.

Update:

I found a directory where they do exist:

Code:

/usr/src/linux/include/linux

I used that in the make file and I'm getting the same error. I also double checked to make sure I'm using -isystem for the include path.

keefaz · 06-18-2004, 03:21 PM

what is the output of :
uname -r
grep RELEASE /usr/src/linux/include/linux/version.h