We can pass the arguments to any other functions in same program. But Is it possible to pass any arguments to any program? I think Probably yes. Right? Well, we can. In C Programming we can pass the arguments to the program. For that we need to add argc and argv in main function definition. I hope everyone knows that. Now come to our topic. Is it possible to pass the argument to the Device Driver.

Module Parameters Macros

module_param()// module_param(name, type, perm);

This macro used to initialize the arguments.module_param takes three parameters: the name of the variable, its type, and a permissions mask to be used for an accompanying sysfs entry.

module_param_array()//
module_param_array(name,type,num,perm);

Where,

name is the name of your array (and of the parameter),

type is the type of the array elements,

num is an integer variable (optional) otherwise NULL, and

perm is the usual permissions value.

This macro is used to send the array as a argument. Array parameters, where the values are supplied as a comma-separated list.

module_param_cb()

This macro used to register the callback whenever the argument (parameter) got changed.

There are several types of permissions:

S_IWUSR
S_IRUSR
S_IXUSR
S_IRGRP
S_IWGRP
S_IXGRP

In this S_I is common header.
R = read ,W =write ,X= Execute.
USR =user ,GRP =Group
Using OR ‘|’ (or operation) we can set multiple permissions at a time.

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

For Example,

I have created one parameter by using module_param().

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module_param(valueETX, int, S_IWUSR|S_IRUSR);

This will create the sysfs entry. (/sys/module/hello_world_module/parameters/valueETX)

You can change the value of valueETX from command line by

echo 1 > /sys/module/hello_world_module/parameters/valueETX

This will update the valueETX variable. But there is no way to notify your module that “valueETX” has changed.

By using this module_param_cb() macro, we can get notification.

If you want to get notification whenever value got change. we need to register our handler function to its file operation structure.

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struct kernel_param_ops {

        int (*set)(const char *val, const struct kernel_param *kp);

        int (*get)(char *buffer, const struct kernel_param *kp);

        void (*free)(void *arg);

};

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

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#include

#include

#include

#include

int valueETX, arr_valueETX[4];

char *nameETX;

int cb_valueETX = 0;

module_param(valueETX, int, S_IRUSR|S_IWUSR);                      //integer value

module_param(nameETX, charp, S_IRUSR|S_IWUSR);                     //String

module_param_array(arr_valueETX, int, NULL, S_IRUSR|S_IWUSR);      //Array of integers

/*----------------------Module_param_cb()--------------------------------*/

int notify_param(const char *val, const struct kernel_param *kp)

{

        int res = param_set_int(val, kp); // Use helper for write variable

        if(res==0) {

                printk(KERN_INFO "Call back function called...\n");

                printk(KERN_INFO "New value of cb_valueETX = %d\n", cb_valueETX);

                return 0;

        }

        return -1;

}

const struct kernel_param_ops my_param_ops = 

{

        .set = &notify_param, // Use our setter ...

        .get = &param_get_int, // .. and standard getter

};

module_param_cb(cb_valueETX, &my_param_ops, &cb_valueETX, S_IRUGO|S_IWUSR );

/*-------------------------------------------------------------------------*/

static int __init hello_world_init(void)

{

        int i;

        printk(KERN_INFO "ValueETX = %d  \n", valueETX);

        printk(KERN_INFO "cb_valueETX = %d  \n", cb_valueETX);

        printk(KERN_INFO "NameETX = %s \n", nameETX);

        for (i = 0; i < (sizeof arr_valueETX / sizeof (int)); i++) {

                printk(KERN_INFO "Arr_value[%d] = %d\n", i, arr_valueETX[i]);

        }

        printk(KERN_INFO "Kernel Module Inserted Successfully...\n");

 return 0;

}

void __exit hello_world_exit(void)

{

 printk(KERN_INFO "Kernel Module Removed Successfully...\n");

}

module_init(hello_world_init);

module_exit(hello_world_exit);

MODULE_LICENSE("GPL");

MODULE_AUTHOR("EmbeTronicX ");

MODULE_DESCRIPTION("A simple hello world driver");

MODULE_VERSION("1.0");

Compiling

This is the code of Makefile.

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obj-m += hello_world_module.o

KDIR = /lib/modules/$(shell uname -r)/build

all:

 make -C $(KDIR)  M=$(shell pwd) modules

clean:

 make -C $(KDIR)  M=$(shell pwd) clean