Module with more then one file

[Sascha Effert <fermat@xxxxxxxxxxxxxxxx>]

Hello,

I am trying to port a module written for the 2.4 Kernels to 2.6 Kernels. 
 One of my first step was to use the kernel-build system. Following the 
Documentation of the makefiles in Documentation/kbuild/makefiles.txt I 
wrote following Makefile:

----start Makefile----
  ifneq ($(KERNELRELEASE),)
  obj-m   := module.o
  module-objs += extra.o

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

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

  endif
----end Makefile----

This Makefile should compile module.c and extra.c and link them to one 
object. So I wrote two .c-files. First the module.c:

----start module.c----
  #include <linux/version.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/config.h>
  #include <linux/sysctl.h>
  #include <linux/devfs_fs_kernel.h>
  #include <linux/proc_fs.h>

  int test_int = 0;

  void test_function(void) {
    return ;
  }

  static int __init mymodule_init (void) {
    printk (KERN_INFO "module starts\n");
    return (0);
  }

  static void __exit mymodule_exit (void) {
    printk(KERN_INFO "module ends\n");
    return;
  }

  module_init(mymodule_init);
  module_exit(mymodule_exit);

  MODULE_LICENSE("GPL");

  EXPORT_SYMBOL (test_function);
  EXPORT_SYMBOL (test_int);
----end module.c----

and a extra.c which uses the test_function and test_int defined and 
exportet in module.c:

----start extra.c----
  extern void test_function(void);
  extern int test_int;

  void try_this(void) {
    test_function();
    test_int++;
    return;
  }
----end extra.c----

So I thought that try_this would use the test_function defined and 
exportet in module.c. But compiling the function results in following 
output:

----start output----
  formate@albana:~/imt/VDrive/test> make
    make -C /lib/modules/2.6.8-24.10-default/build
      SUBDIRS=/afs/uni-paderborn.de/user/f/fermat/VDrive/test modules
    make[1]: Entering directory
      `/usr/src/linux-2.6.8-24.10-obj/i386/default'
    make -C ../../../linux-2.6.8-24.10
      O=../linux-2.6.8-24.10-obj/i386/default modules
      CC [M]  /afs/uni-paderborn.de/user/f/fermat/VDrive/test/extra.o
      LD [M]  /afs/uni-paderborn.de/user/f/fermat/VDrive/test/module.o
      Building modules, stage 2.
      MODPOST
    *** Warning: "test_function"
      [/afs/uni-paderborn.de/user/f/fermat/VDrive/test/module.ko]
      undefined!
    *** Warning: "test_int"
      [/afs/uni-paderborn.de/user/f/fermat/VDrive/test/module.ko]
      undefined!
      LD [M]  /afs/uni-paderborn.de/user/f/fermat/VDrive/test/module.ko
    make[1]: Leaving directory
      `/usr/src/linux-2.6.8-24.10-obj/i386/default'
  formate@albana:~/imt/VDrive/test>
----end output----

I do not understand the two Warnings. Why are test_function and 
test_init undefined? What is wrong?

I would be pleased if someone could help me.



thanks for your time,


Sascha Effert


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