Hello World (part 4): 内核模块证书和内核模块文档说明


# 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


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");


 *  You can use strings, like this:

 * Get rid of taint message by declaring code as 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.