Hello World : Module Parameter

  • In this program, you are going to learn

How to pass module parameters to Linux kernel module ?

Topics in this section,

  • To allow arguments to be passed to your module, declare the variables that will take the values of the command line arguments as global and then use the module_param() macro.

  • Define the module parameter for integer

module_param(myint, int, 0644);

MODULE_PARM_DESC(myint, "An integer");

  • Pass the module parameter during module load

$ sudo insmod ./prgm1.ko myint=56

  • See the full program below,

 1#include <linux/module.h>
 2#include <linux/moduleparam.h>
 3#include <linux/kernel.h>
 4#include <linux/init.h>
 5#include <linux/stat.h>
 6
 7MODULE_LICENSE("GPL");
 8MODULE_AUTHOR("Linux_usr");
 9
10static int myint = 400;
11
12module_param(myint, int, 0644);
13MODULE_PARM_DESC(myint, "An integer");
14
15static int __init hello_init(void)
16{
17	pr_info("Hello, world\n");
18	pr_info("myint is an integer: %d\n", myint);
19	return 0;
20}
21
22static void __exit hello_exit(void)
23{
24	pr_info("Goodbye, world\n");
25}
26
27module_init(hello_init);
28module_exit(hello_exit);

1obj-m += prgm1.o
2
3all:
4        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
5
6clean:
7        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

 1$ make all
 2
 3$ sudo insmod ./prgm1.ko myint=56
 4
 5$ dmesg
 6[495039.286549] Hello, world
 7[495039.286550] myint is an integer: 56
 8
 9$ sudo rmmod prgm1
10
11$ dmesg
12[495039.286549] Hello, world
13[495039.286550] myint is an integer: 56
14[495049.549716] Goodbye, world

  • Define the module parameter for short

module_param(myshort, short, 0660);

MODULE_PARM_DESC(myshort, "A short integer");

  • Pass the module parameter during module load

$ sudo insmod ./prgm2.ko myshort=10

  • See the full program below,

 1#include <linux/module.h>
 2#include <linux/moduleparam.h>
 3#include <linux/kernel.h>
 4#include <linux/init.h>
 5#include <linux/stat.h>
 6
 7MODULE_LICENSE("GPL");
 8MODULE_AUTHOR("Linux_usr");
 9
10static short int myshort = 1;
11
12module_param(myshort, short, 0660);
13MODULE_PARM_DESC(myshort, "A short integer");
14
15static int __init hello_init(void)
16{
17	pr_info("Hello, world\n");
18	pr_info("myshort is a short integer: %d\n", myshort);
19	
20	return 0;
21}
22
23static void __exit hello_exit(void)
24{
25	pr_info("Goodbye, world\n");
26}
27
28module_init(hello_init);
29module_exit(hello_exit);

1obj-m += prgm2.o
2
3all:
4        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
5
6clean:
7        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

 1$ make all
 2
 3$ sudo insmod ./prgm2.ko myshort=10
 4
 5$ dmesg
 6[495335.891744] Hello, world
 7[495335.891745] myshort is a short integer: 10
 8
 9$ sudo rmmod prgm2
10
11$ dmesg
12[495335.891744] Hello, world
13[495335.891745] myshort is a short integer: 10
14[495343.492308] Goodbye, world

  • Define the module parameter for long

module_param(mylong, long, 0400);

MODULE_PARM_DESC(mylong, "A long integer");

  • Pass the module parameter during module load

$ sudo insmod ./prgm3.ko mylong=500

  • See the full program below,

 1#include <linux/module.h>
 2#include <linux/moduleparam.h>
 3#include <linux/kernel.h>
 4#include <linux/init.h>
 5#include <linux/stat.h>
 6
 7MODULE_LICENSE("GPL");
 8MODULE_AUTHOR("Linux_usr");
 9
10static long mylong = 100;
11
12module_param(mylong, long, 0400);
13MODULE_PARM_DESC(mylong, "A long integer");
14
15static int __init hello_init(void)
16{
17	pr_info("Hello, world\n");
18	pr_info("mylong is a long integer: %ld\n", mylong);
19	return 0;
20}
21
22static void __exit hello_exit(void)
23{
24	pr_info("Goodbye, world\n");
25}
26
27module_init(hello_init);
28module_exit(hello_exit);

1obj-m += prgm3.o
2
3all:
4        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
5
6clean:
7        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

 1$ make all
 2
 3$ sudo insmod ./prgm3.ko mylong=500
 4
 5$ dmesg
 6[495455.686602] Hello, world
 7[495455.686604] mylong is a long integer: 500
 8
 9$ sudo rmmod prgm3
10
11$ dmesg
12[495455.686602] Hello, world
13[495455.686604] mylong is a long integer: 500
14[495464.038982] Goodbye, world

  • Define the module parameter for string

module_param(mystring, charp, 0000);

MODULE_PARM_DESC(mystring, "A character string");

  • Pass the module parameter during module load

$ sudo insmod ./prgm4.ko mystring="linux"

  • See the full program below,

 1#include <linux/module.h>
 2#include <linux/moduleparam.h>
 3#include <linux/kernel.h>
 4#include <linux/init.h>
 5#include <linux/stat.h>
 6
 7MODULE_LICENSE("GPL");
 8MODULE_AUTHOR("Linux_usr");
 9
10static char *mystring = "blah";
11
12module_param(mystring, charp, 0000);
13MODULE_PARM_DESC(mystring, "A character string");
14
15static int __init hello_init(void)
16{
17	pr_info("Hello, world\n");
18
19	pr_info("mystring is a string: %s\n", mystring);
20	return 0;
21}
22
23static void __exit hello_exit(void)
24{
25	pr_info("Goodbye, world\n");
26}
27
28module_init(hello_init);
29module_exit(hello_exit);

1obj-m += prgm4.o
2
3all:
4        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
5
6clean:
7        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

 1$ make all
 2
 3$ sudo insmod ./prgm4.ko mystring="linux"
 4
 5$ dmesg
 6[495668.254605] Hello, world
 7[495668.254607] mystring is a string: linux
 8
 9$ sudo rmmod prgm4
10
11$ dmesg
12[495668.254605] Hello, world
13[495668.254607] mystring is a string: linux
14[495697.631035] Goodbye, world

  • Define the module parameter for integer array

module_param_array(myintArray, int, &arr_argc, 0000);

MODULE_PARM_DESC(myintArray, "An array of integers");

  • Pass the module parameter during module load

$ sudo insmod ./prgm5.ko myintArray=10,20,30

  • See the full program below,

 1#include <linux/module.h>
 2#include <linux/moduleparam.h>
 3#include <linux/kernel.h>
 4#include <linux/init.h>
 5#include <linux/stat.h>
 6
 7MODULE_LICENSE("GPL");
 8MODULE_AUTHOR("Linux_usr");
 9
10static int myintArray[3]= {5,3,1};
11static int arr_argc = 1;
12
13module_param_array(myintArray, int, &arr_argc, 0000);
14MODULE_PARM_DESC(myintArray, "An array of integers");
15
16static int __init hello_init(void)
17{
18	int i;
19	pr_info("Hello, world\n");
20	for (i = 0; i < (sizeof(myintArray) / sizeof(int)); i++)
21		pr_info("myintArray[%d] = %d\n", i, myintArray[i]);
22	pr_info("got %d arguments for myintArray.\n", arr_argc);
23	return 0;
24}
25
26static void __exit hello_exit(void)
27{
28	pr_info("Goodbye, world\n");
29}
30
31module_init(hello_init);
32module_exit(hello_exit);

1obj-m += prgm5.o
2
3all:
4        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
5
6clean:
7        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

 1$ make all
 2
 3$ sudo insmod ./prgm5.ko myintArray=10,20,30
 4
 5$ dmesg
 6[504234.493933] Hello, world
 7[504234.493935] myintArray[0] = 10
 8[504234.493935] myintArray[1] = 20
 9[504234.493936] myintArray[2] = 30
10[504234.493936] got 3 arguments for myintArray.
11
12
13$ sudo rmmod prgm5
14
15$ dmesg
16[504234.493933] Hello, world
17[504234.493935] myintArray[0] = 10
18[504234.493935] myintArray[1] = 20
19[504234.493936] myintArray[2] = 30
20[504234.493936] got 3 arguments for myintArray.
21[504240.118160] Goodbye, world

API

Learning

module_param

macro used to initialize the arguments

MODULE_PARM_DESC

used to document arguments that the module can take
See Also