insmod: Unknown symbol in module or no symbol version for

char * vdisk[VHDD_MAX_DEVICE]={NULL,};
EXPORT_SYMBOL(vdisk);

extern char *vdisk[VHDD_MAX_DEVICE];

obj-m	:=vhdd.o
export-objs :=vdisk.o
KDIR	:=/lib/modules/$(shell uname -r)/build
PWD	:=$(shell pwd)
default:
$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
clean:
rm -rf *.ko
rm -rf *.mod.*
rm -rf .*.cmd
rm -rf *.o