module_param

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我是靠谱客的博主贤惠裙子，这篇文章主要介绍module_param，现在分享给大家，希望可以做个参考。

一般用户态传递参数是通过main函数，第一个参数表示args个数，即argc，第二个参数表示具体的参数

在kernel态，无法通过这样的方式传递参数，一般使用宏module_param的方式，步骤如下：

1.使用module_param指定模块的参数

2.加载driver时给模块传递参数

该宏的定义见/linux/moduleparam.h中

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/**
 * module_param - typesafe helper for a module/cmdline parameter
 * @value: the variable to alter, and exposed parameter name.
 * @type: the type of the parameter
 * @perm: visibility in sysfs.
 *
 * @value 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 kparam_block_sysfs_write() 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)

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/**
 * module_param - typesafe helper for a module/cmdline parameter
 * @value: the variable to alter, and exposed parameter name.
 * @type: the type of the parameter
 * @perm: visibility in sysfs.
 *
 * @value 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 kparam_block_sysfs_write() 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)

具体使用为：

适用于2.4与2.6内核的模块输入参数模板

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#include <linux/module.h>
#ifdef LINUX26
#include <linux/moduleparam.h>
#endif 
int debug = 0;
char *mode = "800x600";
int tuner[4] = {1, 1, 1, 1};
#ifdef LINUX26
int tuner_c = 1;  
#endif 
#ifdef LINUX26
MODULE_PARM(debug, "i");
MODULE_PARM(mode, "s");
MODULE_PARM(tuner,"1-4i");
#else
module_param(debug, int, 0644);
module_param(mode, charp, 0644);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 10)
module_param_array(tuner, int, &tuner_c, 0644);
#else
module_param_array(tuner, int, tuner_c, 0644);
#endif 
#endif

模块编译生成后，加载模块时可以输入：`modprobe my_module mode=1024x768 debug=1 tuner=22,33`。

还有一类，是函数回调 module_param_cb，类似于module_param_call

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/**
 * module_param_cb - general callback for a module/cmdline parameter
 * @name: a valid C identifier which is the parameter name.
 * @ops: the set & get operations for this parameter.
 * @perm: visibility in sysfs.
 *
 * The ops can have NULL set or get functions.
 */
#define module_param_cb(name, ops, arg, perm)				      
	__module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1, 0)

具体实例如下：

在codec驱动代码中添加对寄存器访问的控制方式。调试codec的时候，可以直接查看或修改寄存器，免去了编译内核或模块的工作，节省宝贵时间。

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static int nau8810_debug_reg_set(const char *buffer, struct kernel_param *kp)
{
    u16 reg, val;
    if(!buffer)
        return -EINVAL;
    if(sscanf(buffer, "%x,%x", (uint *)®, (uint *)&val) != 2) {
        printk(KERN_ERR "invalid val = %sn", buffer);
        return -EINVAL;
    }
    if(debug)
        printk(KERN_INFO"%s:R0x%x=0x%xn", __func__, reg, val);
    snd_soc_write(nau8810_codec, reg, val);
    return 0;
}

static int nau8810_debug_reg_get(char *buffer, struct kernel_param *kp)
{
    u16 reg, val;
    int len = 0;
    len = sprintf(buffer, "nau8810 DUMP registers:");
    for(reg = 0; reg < NAU8810_CACHEREGNUM; reg++) {
        val = snd_soc_read(nau8810_codec, reg);
        if(!(reg%8))
            len += sprintf(buffer+len,"n");
        len += sprintf(buffer+len, "R%02x:%03x ", reg, val);
    }
    return len;
}
static unsigned int dummy = 0;
module_param_call(regs, nau8810_debug_reg_set, nau8810_debug_reg_get, &dummy, 0644);