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 http://www.tux.org/lkml/#export-tainted 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 <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#define DRIVER_AUTHOR "Peter Jay Salzman <p@dirac.org>"
#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");