Linux Driver 入门

 Abstract

1.  What are Module parameters?
2. Ways to change these module parameters
3. module_param macro
4. Array module parameters
5. Source code in this blog: https://github.com/yubaoliu/Linux/tree/master/driver

Pass parameters to a module

There are two ways to pass these parameters.

1. While insmod or modprobe

Ex: $insmod <Module.ko> [Module_parameters-1 = value-1] [Module_parameters-2 = value-2]

2. Reading parameter assignment from the configuration file "/etc/modprobe.conf"

 module_param

/* 
 * module_param(foo, int, 0000)
 * The first param is the parameters name
 * The second param is it's data type
 * The final argument is the permissions bits, 
 * for exposing parameters in sysfs (if non-zero) at a later stage.
 */

module_param(myshort, short, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(myshort, "A short integer");
module_param(myint, int, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
MODULE_PARM_DESC(myint, "An integer");
module_param(mylong, long, S_IRUSR);
MODULE_PARM_DESC(mylong, "A long integer");
module_param(mystring, charp, 0000);
MODULE_PARM_DESC(mystring, "A character string");

S_IRUGO=(S_IRUSR|S_IRGRP|S_IROTH)

S_IRUSR：用户读  00400

S_IRGRP：用户组读 00040

S_IROTH: 其他读 00004

Example source code:

#include <linux/init.h>
#include <linux/module.h>

#include <linux/moduleparam.h>

int param_var=0;

module_param(param_var,int,S_IRUSR|S_IWUSR);

void display(void)
{
  printk(KERN_ALERT "TEST:param_var=%d 
", param_var);
}

static int hello_init(void)
{
  printk(KERN_ALERT "TEST: hello world, this is hello world module
");
  display();

  return 0;
}

static void hello_exit(void)
{
  printk(KERN_ALERT "TEST: Good bye, from hello world module
");
}

module_init(hello_init);
module_exit(hello_exit);

Run:

yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/HelloWorldParameter$ sudo insmod hello.ko p aram_var=100

Result: (dmesg)

[20811.755698] TEST: hello world, this is hello world module
[20811.755701] TEST:param_var=100

Possible Error:

If you use 

void display()

you tend to encounter this error:

warning: function declaration isn’t a prototype.

How to solve:

void display(void)

 

Pass array parameter

/*
 * module_param_array(name, type, num, perm);
 * The first param is the parameter's (in this case the array's) name
 * The second param is the data type of the elements of the array
 * The third argument is a pointer to the variable that will store the number 
 * of elements of the array initialized by the user at module loading time
 * The fourth argument is the permission bits
 */
module_param_array(myintArray, int, &arr_argc, 0000);

Source:

#include <linux/init.h>
#include <linux/module.h>

#include <linux/moduleparam.h>

int param_var[3]={0,0,0};

module_param_array(param_var,int,NULL,S_IRUSR|S_IWUSR);

void display(void)
{
  printk(KERN_ALERT "TEST:param_var[0]=%d 
", param_var[0]);
  printk(KERN_ALERT "TEST:param_var[1]=%d 
", param_var[1]);
  printk(KERN_ALERT "TEST:param_var[2]=%d 
", param_var[2]);
}

static int hello_init(void)
{
  printk(KERN_ALERT "TEST: hello world, this is hello world module
");
  display();

  return 0;
}

static void hello_exit(void)
{
  printk(KERN_ALERT "TEST: Good bye, from hello world module
");
}

module_init(hello_init);
module_exit(hello_exit);

Run:

yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/HelloWorldParameter$ sudo insmod hello.ko p aram_var=10,25,111

Result:(dmesg)

[21586.818714] TEST: hello world, this is hello world module
[21586.818718] TEST:param_var[0]=10
[21586.818719] TEST:param_var[1]=25
[21586.818720] TEST:param_var[2]=111

Example:

/*
 *  moduleParameters.c - Demonstrates command line argument passing to a module.
 */
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/stat.h>

MODULE_LICENSE("GPL");

static short int myshort = 1;
static int myint = 420;
static long int mylong = 9999;
static char *mystring = "blah";
static int myintArray[2] = { -1, -1 };
static int arr_argc = 0;

/* 
 * module_param(foo, int, 0000)
 * The first param is the parameters name
 * The second param is it's data type
 * The final argument is the permissions bits, 
 * for exposing parameters in sysfs (if non-zero) at a later stage.
 */

module_param(myshort, short, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
MODULE_PARM_DESC(myshort, "A short integer");
module_param(myint, int, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
MODULE_PARM_DESC(myint, "An integer");
module_param(mylong, long, S_IRUSR);
MODULE_PARM_DESC(mylong, "A long integer");
module_param(mystring, charp, 0000);
MODULE_PARM_DESC(mystring, "A character string");

/*
 * module_param_array(name, type, num, perm);
 * The first param is the parameter's (in this case the array's) name
 * The second param is the data type of the elements of the array
 * The third argument is a pointer to the variable that will store the number 
 * of elements of the array initialized by the user at module loading time
 * The fourth argument is the permission bits
 */
module_param_array(myintArray, int, &arr_argc, 0000);
MODULE_PARM_DESC(myintArray, "An array of integers");

int init_module (void)
{
    int i;
    printk(KERN_INFO "Module Parameters:=============
");
    printk(KERN_INFO "myshort is a short integer: %hd
", myshort);
    printk(KERN_INFO "myint is an integer: %d
", myint);
    printk(KERN_INFO "mylong is a long integer: %ld
", mylong);
    printk(KERN_INFO "mystring is a string: %s
", mystring);
    for (i = 0; i < (sizeof myintArray / sizeof (int)); i++)
    {
        printk(KERN_INFO "myintArray[%d] = %d
", i, myintArray[i]);
    }
    printk(KERN_INFO "got %d arguments for myintArray.
", arr_argc);
    return 0;
}

void cleanup_module (void)
{
    printk(KERN_INFO "moduleParameters finished.
");
}

Result:

yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/parameters$ sudo dmesg -c
yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/parameters$ sudo insmod moduleParameters.ko myshort=3 myint=100 myintArray=25,67 mylong=888 mystring="yubao"
yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/parameters$ dmesg
[31153.421469] Module Parameters:=============
[31153.421475] myshort is a short integer: 3
[31153.421478] myint is an integer: 100
[31153.421481] mylong is a long integer: 888
[31153.421484] mystring is a string: yubao
[31153.421488] myintArray[0] = 25
[31153.421492] myintArray[1] = 67
[31153.421495] got 2 arguments for myintArray.
yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/parameters$ sudo rmmod moduleParameters
yubao@yubao-ThinkPad-E560:~/MyProjects/Linux/driver/parameters$ dmesg
[31153.421469] Module Parameters:=============
[31153.421475] myshort is a short integer: 3
[31153.421478] myint is an integer: 100
[31153.421481] mylong is a long integer: 888
[31153.421484] mystring is a string: yubao
[31153.421488] myintArray[0] = 25
[31153.421492] myintArray[1] = 67
[31153.421495] got 2 arguments for myintArray.
[31167.661870] moduleParameters finished.

References:

1. Passing Command Line Arguments to a Module, https://www.tldp.org/LDP/lkmpg/2.6/html/x323.html

2. Use of Module Parameters in Kernel Programming, http://linuxkernel51.blogspot.com/2011/03/use-of-module-parameters-in-kernel.html

3. moduleParameters, https://www.cs.bham.ac.uk/~exr/lectures/systems/09_10/examples/moduleParameters.c