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1. #include <linux/module.h>
2. #include <linux/init.h>
3. #include <linux/kernel.h>
4. MODULE_LICENSE("GPL");
5. int myprint(void)
6. {
7. printk("c");
8. return 0;
9. }
10. static int darren_init(void)
11. {
12. return 0;
13. }
14. static void darren_exit(void)
15. {
16. }
17. module_init(darren_init);
18. module_exit(darren_exit);
19. EXPORT_SYMBOL(myprint);

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1. #include <linux/seq_file.h>
2. #include <linux/cdev.h>
3. #include <asm/system.h>
4. MODULE_LICENSE("GPL");
5. extern int print(void);
6. static int darren_init(void)
7. {
8. int i=0;
9. printk("b module init\n");
10. for(;i<10;i++)print();
11. return 0;
12. }
13. static void darren_exit(void)
14. {
15. }
16. module_init(darren_init);
17. module_exit(darren_exit);

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1. Sometimes, an external module uses exported symbols from
2. another external module. kbuild needs to have full knowledge of
3. all symbols to avoid spitting out warnings about undefined
4. symbols. Three solutions exist for this situation.
5. NOTE: The method with a top-level kbuild file is recommended
6. but may be impractical in certain situations.
7. Use a top-level kbuild file
8. If you have two modules, foo.ko and bar.ko, where
9. foo.ko needs symbols from bar.ko, you can use a
10. common top-level kbuild file so both modules are
11. compiled in the same build. Consider the following
12. directory layout:
13. ./foo/ <= contains foo.ko
14. ./bar/ <= contains bar.ko
15. The top-level kbuild file would then look like:
16. #./Kbuild (or ./Makefile):
17. obj-y := foo/ bar/
18. And executing
19. $ make -C $KDIR M=$PWD
20. will then do the expected and compile both modules with
21. full knowledge of symbols from either module.
22. Use an extra Module.symvers file
23. When an external module is built, a Module.symvers file
24. is generated containing all exported symbols which are
25. not defined in the kernel. To get access to symbols
26. from bar.ko, copy the Module.symvers file from the
27. compilation of bar.ko to the directory where foo.ko is
28. built. During the module build, kbuild will read the
29. Module.symvers file in the directory of the external
30. module, and when the build is finished, a new
31. Module.symvers file is created containing the sum of
32. all symbols defined and not part of the kernel.
33. Use "make" variable KBUILD_EXTRA_SYMBOLS
34. If it is impractical to copy Module.symvers from
35. another module, you can assign a space separated list
36. of files to KBUILD_EXTRA_SYMBOLS in your build file.
37. These files will be loaded by modpost during the
38. initialization of its symbol tables.