Chapter 2. Hello World --- 内核模块证书和内核模块文档说明

Chapter 2. Hello World

内核模块证书和内核模块文档说明

如果你在使用2.4或更新的内核，当你加载你的模块时，你也许注意到了这些输出信息：

# insmod hello-3.o
Warning: loading hello-3.o will taint the kernel: no license
  See for information about tainted modules
Hello, world 3
Module hello-3 loaded, with warnings

  在2.4或更新的内核中，一种识别代码是否在GPL许可下发布的机制被引入，因此人们可以在使用非公开的源代码产品时得到警告。这通过在下一章展示的宏MODULE_LICENSE()当你设置在GPL证书下发布你的代码时，你可以取消这些警告。这种证书机制在头文件linux/module.h 实现，同时还有一些相关文档信息。

/*
 * The following license idents are currently accepted as indicating free
 * software modules
 *
 *    "GPL"                          [GNU Public License v2 or later]
 *    "GPL v2"                       [GNU Public License v2]
 *    "GPL and additional rights"    [GNU Public License v2 rights and more]
 *    "Dual BSD/GPL"                 [GNU Public License v2
 *                                            or BSD license choice]
 *    "Dual MPL/GPL"                 [GNU Public License v2
 *                                            or Mozilla license choice]
 *
 * The following other idents are available
 *
 *    "Proprietary"                   [Non free products]
 *
 * There are dual licensed components, but when running with Linux it is the
 * GPL that is relevant so this is a non issue. Similarly LGPL linked with GPL
 * is a GPL combined work.
 *
 * This exists for several reasons
 * 1.    So modinfo can show license info for users wanting to vet their setup
 *    is free
 * 2.    So the community can ignore bug reports including proprietary modules
 * 3.    So vendors can do likewise based on their own policies
 */

  类似的，宏MODULE_DESCRIPTION()用来描述模块的用途。 宏MODULE_AUTHOR()用来声明模块的作者。宏MODULE_SUPPORTED_DEVICE() 声明模块支持的设备。

  这些宏都在头文件linux/module.h定义， 并且内核本身并不使用这些宏。它们只是用来提供识别信息，可用工具程序像objdump查看。 作为一个练习，使用grep从目录linux/drivers看一看这些模块的作者是如何 为他们的模块提供识别信息和档案的。

Example 2-6. hello-4.c
/*  
 *  hello-4.c - Demonstrates module documentation.
 */
#include
#include
#include
#define DRIVER_AUTHOR "Peter Jay Salzman "
#define DRIVER_DESC   "A sample driver"

static int __init init_hello_4(void)
{
    printk(KERN_ALERT "Hello, world 4\n");
    return 0;
}

static void __exit cleanup_hello_4(void)
{
    printk(KERN_ALERT "Goodbye, world 4\n");
}

module_init(init_hello_4);
module_exit(cleanup_hello_4);

/*  
 *  You can use strings, like this:
 */

/*
 * Get rid of taint message by declaring code as GPL.
 */
MODULE_LICENSE("GPL");

/*
 * Or with defines, like this:
 */
MODULE_AUTHOR(DRIVER_AUTHOR);    /* Who wrote this module? */
MODULE_DESCRIPTION(DRIVER_DESC);    /* What does this module do */

/*  
 *  This module uses /dev/testdevice.  The MODULE_SUPPORTED_DEVICE macro might
 *  be used in the future to help automatic configuration of modules, but is
 *  currently unused other than for documentation purposes.
 */
MODULE_SUPPORTED_DEVICE("testdevice");