Driver porting: hello world

I appeciate the series in modernizing modules, but just FYI, I don't think the old-style init_module/cleanup_module stuff will break any time soon: there are still a large number of drivers which use it, and there's not much point making such changes.

However, this "new" scheme (introduced by Linus in 2.3 IIRC) has the advantage that your module will work correctly when built into the kernel: you want that initialization routine called, even then.

So I hope that clarifies,
Rusty.

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

static int hello_init(void)
{
printk("<1> Hello, world\n");
return 0;
}

static void hello_exit(void)
{
printk("<1> Goodbye, cruel world\n");
}

module_init(hello_init);
module_exit(hello_exit);

The Makefile for this is:

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

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

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

so the problem is once I type the command "make" at the shell prompt it gives the following message :

$ make: Nothing to be done for 'default'

I dont know whats the problem. Can any1 please help me out here. Your help will be appreciated.

I'm new to "Linux Device Drivers". When I try to compile the given example as shown above, I get the following error messages. The only difference is that I named the file "hello-driver2.c".
Anyone who knows what I did wrong?

*/usr/include/linux/jiffies.h:16: error: parse error before "jiffies_64"
*/usr/include/linux/jiffies.h:20: error: parse error before "get_jiffies_64"
*/usr/include/asm/mmu.h:13: error: field `sem' has incomplete type
*/usr/include/linux/list.h:604:2: warning: #warning "don't include kernel headers in userspace"
*/usr/include/asm-generic/siginfo.h:53: error: size of array `_pad' is too large
*/usr/include/linux/fs_struct.h:9: error: parse error before "rwlock_t"
*/usr/include/linux/fs_struct.h:13: error: parse error before '}' token
*/usr/include/linux/completion.h:15: error: parse error before "wait_queue_head_t"
*/usr/include/linux/completion.h:26: error: dereferencing pointer to incomplete type
*/usr/include/linux/completion.h:27: error: dereferencing pointer to incomplete type
*/usr/include/linux/pid.h:18: error: field `task_list' has incomplete type
*/usr/include/linux/pid.h:19: error: field `hash_chain' has incomplete type
*/usr/include/linux/pid.h:24: error: field `pid_chain' has incomplete type
*/usr/include/linux/sched.h:93: error: parse error before "process_counts"
*/usr/include/linux/timer.h:10: error: field `entry' has incomplete type
*hello-driver2.c:6: error: `KERN_ALERT' undeclared (first use in this function)
*hello-driver2.c:6: error: parse error before string constant
*hello-driver2.c:11: error: `KERN_ALERT' undeclared (first use in this function)
*hello-driver2.c:11: error: parse error before string constant
*hello-driver2.c:14: error: parse error before "__attribute_used__"
*hello-driver2.c:14: warning: initialization makes integer from pointer without a cast
*hello-driver2.c:14: warning: data definition has no type or storage class
*hello-driver2.c:15: error: parse error before "__attribute_used__"
*hello-driver2.c:15: error: redefinition of `__attribute_used__'
*hello-driver2.c:14: error: `__attribute_used__' previously defined here
*hello-driver2.c:15: warning: initialization makes integer from pointer without a cast
*hello-driver2.c:15: warning: data definition has no type or storage class
**** Beëindigd met status: 2 ***

Here is the small hello.c program.
----------------------------------

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

MODULE_LICENSE("Dual BSD/GPL");

static int hello_init(void)
{
printk("Hello World!\n");
return 0;
}

static void hello_exit(void)
{
printk("Good bye!\n");
}

module_init(hello_init);
module_exit(hello_exit);

Here is the Makefile.
---------------------

#
# Makefile for hello.c file
#
KDIR:=/lib/modules/$(shell uname -r)/build

obj-m:=hello.o

default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
clean:
$(RM) .*.cmd *.mod.c *.o *.ko -r .tmp*

#####################################################

It got compiled and inserted with out any errors, but dmesg says "unsupported module, tainting kernel".

System Configuration: x86, SuSE 9.1 with 2.6.5-7.71 kernel version.

What can I do to get rid of that message?

Thanks for any hints.

Regards,
Srinivas G

My code is
>>>>>
#include<linux/module.h>
#include<linux/kernel.h>
int init_module()
{printk("welcome to the world of kernel programming");
return 0;
}
void init_module()
{printk("removing from kernel space");
}

MODULE_LICENCE("GPL");
>>>>>>
i have named this source file as hello.c

Now the problem is i dont know how to insert this module in the kernel space. I have tried gcc -c hello.c to generate hello.o. And then i tried insmod hello.o but to my luck no go . i know this method works with kernel 2.4. But with 2.6 i am not much sure
So i tried modprobe hello.o and i got the message module format not supported.

Finally i tried gcc -I/usr/src/linux-2.6.5-1.358/include -c hello.o
But first it gave me some linker error
then i tried gcc -c hello.0 hello.c
and i got the following errors.

************
/usr/lib/gcc-lib/i386-redhat-linux/3.3.3/../../../crt1.o(.text+0x18): In function `_start':
: undefined reference to `main'
/tmp/cckOZLS5.o(.text+0xf): In function `init_module':
: undefined reference to `printk'
/tmp/cckOZLS5.o(.text+0x2c): In function `cleanup_module':
: undefined reference to `printk'
collect2: ld returned 1 exit status
************

I really dont know what i am doing wrong please suggest me as it is really very important for me.

Thank you in advance
Regards
Vikas Vasudev

in the code snippet, you dont have a cleanup_module (both are init_module functions) and in
the compilation log, you are getting cleanup_module...Seems you have not copied the correct
code...

Ferrari

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

static int hello_init(void)
{
printk( "<1>Hello World 1.\n" );

return 0;
}

static void hello_exit(void)
{
printk( KERN_ALERT "Goodbye 1.\n" );
}

module_init(hello_init);
module_exit(hello_exit);

MODULE_LICENSE("Dual BSD/GPL");
// end of source

the Makefile is

ifneq ($ (KERNELRELEASE), )
obj-m := mod1.o

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

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

endif

# end of Makefile

And executing a command like:

make -C /usr/src/linux SUBDIRS=$PWD modules

I get a response:

make: Entering directory `/usr/src/linux-2.6.11.4-20a'

WARNING: Symbol version dump /usr/src/linux-2.6.11.4-20a/Module.symvers is missing; modules will have no modversions.

Building modules, stage 2.
MODPOST
/bin/sh: scripts/mod/modpost: No such file or directory
make[1]: *** [__modpost] Error 127
make: *** [modules] Error 2
make: Leaving directory `/usr/src/linux-2.6.11.4-20a'

What's the problem? And what should I do? Help me please.

[root@localhost dp-c]# insmod modul.ko
insmod: error inserting 'modul.ko': -1 Invalid module format
[root@localhost dp-c]#

[root@localhost dp-c]# uname -a
Linux localhost.localdomain 2.6.16.20 #1 Sun Jun 25 23:05:31 EDT 2006 i686
i686 i386 GNU/Linux

The program is given below and the Makefile

obj-m += modul.o

Program

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

MODULE_LICENSE("Dual BSD/GPL");

static int hello_init (void) {
printk("Hello World!\n");
return 0;
}

static void hello_exit(void) {
printk("Bye world\n");
}

module_init(hello_init);
module_exit(hello_exit);

Please help me out. I want to be a device driver. None of the online help
regarding invalid format helps.

Thanks,

Alex

I'm new to fedora core 5 and using it. I tried to compile a very simple memory driver and got
the error message 
"memory: module license 'unspecified' taints kernel." when I check log file with dmesg
command.
But I already put 
"MODULE_LICENSE("Dual BSD/GPL");"
on my memory.c code.
Can someone pls expain me why I got that message.

It's ok.Found the bug.It is on my makefile.