I'm newbie in LKM and I use Ubuntu (9.04). I have problems compiling a module. I want to access to xtime variable.

This is the source code:

 *  acumulador.c - Example kernel module.
#include <linux/module.h>
#include <linux/kernel.h>

int init_module(void)
	printk("<1>Acumulador iniciado %ld\n", xtime.tv_sec);
	return 0;

void cleanup_module(void)
	printk("<1>Acumulador terminado\n");
And it's my Makefile:
obj-m += acumulador.o

	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
and it's the result :

$ make
make -C /lib/modules/2.6.28-8-generic/build M=/home/uve/Escritorio/DSO modules
make[1]: se ingresa al directorio `/usr/src/linux-headers-2.6.28-8-generic'
  CC [M]  /home/uve/Escritorio/DSO/acumulador.o
  Building modules, stage 2.
  MODPOST 2 modules
  CC      /home/uve/Escritorio/DSO/acumulador.mod.o
  LD [M]  /home/uve/Escritorio/DSO/acumulador.ko
make[1]: se sale del directorio `/usr/src/linux-headers-2.6.28-8-generic'
$ sudo insmod acumulador.ko
insmod: error inserting 'acumulador.ko': -1 Unknown symbol in module
$ dmesg
[ 3761.483358] acumulador: Unknown symbol xtime

$ grep xtime /proc/kallsyms 
ffffffff80270340 T update_xtime_cache
ffffffff80910280 D xtime_lock
ffffffff809a6500 D inet_peer_gc_maxtime
ffffffff80add180 B xtime
ffffffff80add1b0 b xtime_cache
What's the problem?

I apologise for my english! Thanks!