Kernel Module programming...

[guestgulkan]

I have just had a first attempt at this, using the simple 'Hello World' module :

#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");
}

Now this is the 'standard' example used in just about all ttutorials and books (some have a few extra bits like #include <linux/hernel.h> and such - but the much the same).

When i try to compile with the command
gcc -c hello.c as suggested in one book - I get a huge list of errors (mostly about things not being declared, or defined.. etc.)

Any pointers?

[fernape]

You tried the old way to compile modules, now in 2.6 series this is do in this way:

obj-m += hello-1.o

all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

Best regards!

[guestgulkan]

Thanks for your reply.
I also came across this link which proved useful.. (says the same thing that you said..)
http://www.captain.at/programming/kernel-2.6/

[bharathbv]

Adding a module to Linux Kernel

module name:hello.c

This is a simple module that will be inserted into the kernel.
when it is inserted into Kernel it display a message Hello world
When it is removed from the Kernel it display a message Goodbye, world

-----------------------------------------------------------------
#ifndef __MODULE__
#define __MODULE__
#endif

#ifndef __KERNEL__
#define __KERNEL__
#endif

#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include <linux/init.h> /* Needed for the macros */

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

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

module_init(hello_2_init);
module_exit(hello_2_exit);

-------------------------------------------------------------------

Compilation steps:

1.Create a Makefile ( it will be used bu make command)
contents in make file
-------------------------------------------------------------------
KDIR:=/lib/modules/$(shell uname -r)/build

obj-m:=hello.o
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
clean:
$(RM) *.ko *.mod.c *.mod.o *.o
--------------------------------------------------------------------


Once the makefile is ready, use the following command to compile

1.make
2.lsmod|less
3.dmesg
4.rmmod
5.dmesg


Message on the console after each command is executed

1.make
--------------------------------------------------------------------------
[root@localhost new]# make
make -C /lib/modules/2.6.18-1.2798.fc6/build SUBDIRS=/root/Desktop/new modules
make[1]: Entering directory `/usr/src/kernels/2.6.18-1.2798.fc6-i586'
CC [M] /root/Desktop/new/hello.o
Building modules, stage 2.
MODPOST
CC /root/Desktop/new/hello.mod.o
LD [M] /root/Desktop/new/hello.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.18-1.2798.fc6-i586'
[root@localhost new]#
---------------------------------------------------------------------------

2.insmod hello.ko
---------------------------------------------------------------
[root@localhost new]# insmod hello.ko
[root@localhost new]#
Message from syslogd@localhost at Tue Aug 28 12:38:12 2007 ...
localhost kernel: Hello, world 2
---------------------------------------------------------------


-----------------------------------------------------------------------------

4.lsmod | less
---------------------------------------------------------------------
Module Size Used by
hello 5632 0
autofs4 25413 2
hidp 24129 2
rfcomm 45912 0
l2cap 31681 10 hidp,rfcomm
bluetooth 58917 5 hidp,rfcomm,l2cap
sunrpc 158333 1
ip_conntrack_ftp 12081 0
ip_conntrack_netbios_ns 7105 0
ipt_REJECT 9665 1
xt_state 6337 6
ip_conntrack 56993 3 ip_conntrack_ftp,ip_conntrack_netbios_ns,xt_stat
e
nfnetlink 11353 1 ip_conntrack
iptable_filter 7233 1
ip_tables 17669 1 iptable_filter
ip6t_REJECT 9537 1
xt_tcpudp 7361 21
ip6table_filter 7105 1
ip6_tables 18821 1 ip6table_filter
x_tables 18501 6 ipt_REJECT,xt_state,ip_tables,ip6t_REJECT,xt_tcp
udp,ip6_tables
-----------------------------------------------------------------------

5.rmmod
------------------------------------------------------------
[root@localhost new]# rmmod hello
[root@localhost new]#
Message from syslogd@localhost at Tue Aug 28 12:43:51 2007 ...
localhost kernel: Goodbye, world 2
--------------------------------------------------------------

6.make clean
----------------------------------------------------------
[root@localhost new]# make clean
rm -f *.ko *.mod.c *.mod.o *.o
-----------------------------------------------------------