Linux内核之module_param()函数使用说明

待我称王封你为后i 2023-02-12 14:22 17阅读 0赞

**Table of Contents**

1. 概述:

2. module\_param定义:

3. 完整测试例程如下:

--------------------

### 1. 概述: ###

主要区别就是用户可否在系统启动或模块装载时为参数指定相应值，在驱动程序里，参数的用法如同全局变量。

*  不使用module\_param

如只定一个全局变量:

#define MY_MAJOR 0x09
    static int global_val_test = MY_MAJOR;

那么编译模块后,insmod加载模块时不能传参数进去,如:

[root@bogon hello_world]# insmod first_hello.ko global_val_test=5
    insmod: ERROR: could not insert module first_hello.ko: Invalid parameters

同时,insmod模块后,对应module目录下的对应模块下不会生成parameter子目录,更不会生成参数文件.

[root@bogon hello_world]# cat /sys/module/first_hello/
    coresize     holders/     initsize     initstate    notes/       refcnt       rhelversion  sections/    srcversion   taint        uevent       version

*  使用module\_param后,参考如下:

#define MY_MAJOR 0x09
    static int global_val_test = MY_MAJOR;
    module_param(global_val_test, int, 0644);

再编译模块后,再insmod加载模块时就可以传参数进去了,如:

[root@bogon hello_world]# insmod first_hello.ko global_val_test=5
    [root@bogon hello_world]# tail /var/log/messages
    May 26 14:20:08 localhost kernel: [63460.994397] global_val_test = 5
    May 26 14:20:08 localhost kernel: [63460.994409] hello world enter
    May 26 14:20:08 localhost kernel: global_val_test = 5
    May 26 14:20:08 localhost kernel: hello world enter

同时,在模块目录下会生成parameter目录及参数文件,如下:

[root@bogon hello_world]# cat /sys/module/first_hello/
    coresize     holders/     initsize     initstate    notes/       parameters/  refcnt       rhelversion  sections/    srcversion   taint        uevent       version
    [root@bogon hello_world]# ls -alt /sys/module/first_hello/parameters/
    total 0
    -rw-r--r-- 1 root root 16384 May 26 14:54 global_val_test

###    2. module\_param定义: ###

函数原型:

/**
     * module_param - typesafe helper for a module/cmdline parameter
     * @name: the variable to alter, and exposed parameter name.
     * @type: the type of the parameter
     * @perm: visibility in sysfs.
     *
     * @name becomes the module parameter, or (prefixed by KBUILD_MODNAME and a
     * ".") the kernel commandline parameter.  Note that - is changed to _, so
     * the user can use "foo-bar=1" even for variable "foo_bar".
     *
     * @perm is 0 if the the variable is not to appear in sysfs, or 0444
     * for world-readable, 0644 for root-writable, etc.  Note that if it
     * is writable, you may need to use kernel_param_lock() around
     * accesses (esp. charp, which can be kfreed when it changes).
     *
     * The @type is simply pasted to refer to a param_ops_##type and a
     * param_check_##type: for convenience many standard types are provided but
     * you can create your own by defining those variables.
     *
     * Standard types are:
     *	byte, short, ushort, int, uint, long, ulong
     *	charp: a character pointer
     *	bool: a bool, values 0/1, y/n, Y/N.
     *	invbool: the above, only sense-reversed (N = true).
     */
    #define module_param(name, type, perm)				\
    	module_param_named(name, name, type, perm)

/**
     * module_param_named - typesafe helper for a renamed module/cmdline parameter
     * @name: a valid C identifier which is the parameter name.
     * @value: the actual lvalue to alter.
     * @type: the type of the parameter
     * @perm: visibility in sysfs.
     *
     * Usually it's a good idea to have variable names and user-exposed names the
     * same, but that's harder if the variable must be non-static or is inside a
     * structure.  This allows exposure under a different name.
     */
    #define module_param_named(name, value, type, perm)			   \
    	param_check_##type(name, &(value));				   \
    	module_param_cb(name, &param_ops_##type, &value, perm);		   \
    	__MODULE_PARM_TYPE(name, #type)

name既是用户看到的参数名，又是模块内接受参数的变量；

type指定参数类型.

perm指定了在sysfs中相应文件的访问权限。访问权限与linux文件爱你访问权限相同的方式管理，如0644，或使用stat.h中的宏如S\_IRUGO表示。

0表示完全关闭在sysfs中相对应的项。

### 3. 完整测试例程如下: ###

/*
     * a simple kernel module: hello
     *
     * Copyright (C) 2020 
     *
     * Licensed under GPLv2 or later
     */
    #include <linux/init.h>
    #include <linux/module.h>
    
    #define MY_MAJOR 0x09
    static int global_val_test = MY_MAJOR;
    module_param(global_val_test, int, 0644);
    static int __init hello_init(void)
    {
            printk(KERN_INFO "global_val_test = %d\n", global_val_test);
            if (global_val_test == 9)
                    printk(KERN_INFO "hello my world enter\n");
            else
                    printk(KERN_INFO "hello world enter\n");
            return 0;
    }
    
    module_init(hello_init);
    
    static void __exit hello_exit(void)
    {
            printk(KERN_INFO "hello World exit\n");
    }
    module_exit(hello_exit);
    
    MODULE_AUTHOR("xxxx <xxxx>");
    MODULE_LICENSE("GPS v2");         //模块许可证声明,一般用GPL v2
    MODULE_VERSION("1.0.0");
    MODULE_DESCRIPTION("A simple hello world module");
    MODULE_ALIAS("a simplest module"); //别名

Makefile如下:

KVERS = $(shell uname -r)
    
    obj-m := first_hello.o
    first_hello-objs := hello.o
    
    build: kernel_modules
    
    kernel_modules:
            make -C /lib/modules/$(KVERS)/build M=$(CURDIR) modules
    
    clean:
            make -C /lib/modules/$(KVERS)/build M=$(CURDIR) clean

编译方法:make

加载模块:insmod first\_hello.ko global\_val\_test=5

查看log方法:tail /var/log/messages

或者可以通过:cat /sys/module/first\_hello/parameters/global\_val\_test 查看参数的值.

完整源码见:

[https://download.csdn.net/download/sinat\_29891353/12461625][https_download.csdn.net_download_sinat_29891353_12461625]

[https_download.csdn.net_download_sinat_29891353_12461625]: https://download.csdn.net/download/sinat_29891353/12461625