/* * export.c -- export a symbol (maybe a versioned one) (v2.1) * * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet * Copyright (C) 2001 O'Reilly & Associates * * The source code in this file can be freely used, adapted, * and redistributed in source or binary form, so long as an * acknowledgment appears in derived source files.  The citation * should list that the code comes from the book "Linux Device * Drivers" by Alessandro Rubini and Jonathan Corbet, published * by O'Reilly & Associates.   No warranty is attached; * we cannot take responsibility for errors or fitness for use. * */#ifndef __KERNEL__#  define __KERNEL__#endif#ifndef MODULE#  define MODULE#endif/* This stuff might go in the Makefile, but I'd better put it here */#include <linux/config.h> /* retrieve the CONFIG_* macros */#if defined(CONFIG_MODVERSIONS) && !defined(MODVERSIONS)#   define MODVERSIONS#endif/* * Include the versioned definitions for both kernel symbols and our * symbol, *unless* we are generating checksums (__GENKSYMS__ * defined) */#if defined(MODVERSIONS) && !defined(__GENKSYMS__)#    include <linux/modversions.h>#    include "export.ver" /* redefine "export_function" to include CRC */#endif/* * Everything from now on is normal. The previous stuff can be replaced * by "$(CC) -D__KERNEL__ -DMODULE -DMODVERSIONS -DEXPORT_SYMTAB \ *         -include $(INCLUDEDIR)/linux/modversions.h" if versioning * is enabled, and the following (simpler) cmdline for genksyms: *    "$(CC) -E -DCONFIG_MODVERSIONS -DEXPORT_SYMTAB" */#ifndef EXPORT_SYMTAB#  define EXPORT_SYMTAB /* need this one 'cause we export symbols */#endif#include <linux/module.h>#include <linux/sched.h>#include <linux/kernel.h> /* printk() */#include "sysdep.h"/* our dumb function, with two dumb arguments */int export_function(int a, int b);#ifdef __USE_OLD_SYMTAB__    static struct symbol_table export_syms = {        #include <linux/symtab_begin.h>        X(export_function),        #include <linux/symtab_end.h>    };#else    EXPORT_SYMBOL(export_function);#endifint export_init(void){    REGISTER_SYMTAB(&export_syms);    return 0;}void export_cleanup(void){}int export_function(int a, int b){return a+b;}module_init(export_init);module_exit(export_cleanup);