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2.6. Passing Command Line Arguments to a Module
Modules can take command line arguments, but not with the argc/argv you might be
used to.
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, (defined in linux/moduleparam.h) to set the mechanism up. At runtime, insmod will fill the variables with any
command line arguments that are given, like ./insmod mymodule.ko myvariable=5. The variable
declarations and macros should be placed at the beginning of the module for clarity. The example code should clear up my
admittedly lousy explanation.
module_param() macro takes 3 arguments: the name of the variable, its type and
permissions for the corresponding file in sysfs. Integer types can be signed as usual or unsigned.
If you'd like to use arrays of integers or strings see module_param_array() and
module_param_string().
int myint = 3; module_param(myint, int, 0); |
Arrays are supported too, but things are a bit different now than they were in the 2.4. days. To keep track of the number of parameters you need to pass a pointer to a count variable as third parameter. At your option, you could also ignore the count and pass NULL instead. We show both possibilities here:
int myintarray[2]; module_param_array(myintarray, int, NULL, 0); /* not interested in count */ int myshortarray[4]; int count; module_parm_array(myshortarray, short, , 0); /* put count into "count" variable */ |
A good use for this is to have the module variable's default values set, like an port or IO address. If the variables contain the default values, then perform autodetection (explained elsewhere). Otherwise, keep the current value. This will be made clear later on.
Lastly, there's a macro function, MODULE_PARM_DESC(), that is used to document arguments that the
module can take. It takes two parameters: a variable name and a free form string describing that variable.
Example 2-7. hello-5.c
/*
* hello-5.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");
MODULE_AUTHOR("Peter Jay Salzman");
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");
static int __init hello_5_init(void)
{
int i;
printk(KERN_INFO "Hello, world 5\n=============\n");
printk(KERN_INFO "myshort is a short integer: %hd\n", myshort);
printk(KERN_INFO "myint is an integer: %d\n", myint);
printk(KERN_INFO "mylong is a long integer: %ld\n", mylong);
printk(KERN_INFO "mystring is a string: %s\n", mystring);
for (i = 0; i < (sizeof myintArray / sizeof (int)); i++)
{
printk(KERN_INFO "myintArray[%d] = %d\n", i, myintArray[i]);
}
printk(KERN_INFO "got %d arguments for myintArray.\n", arr_argc);
return 0;
}
static void __exit hello_5_exit(void)
{
printk(KERN_INFO "Goodbye, world 5\n");
}
module_init(hello_5_init);
module_exit(hello_5_exit); |
I would recommend playing around with this code:
satan# insmod hello-5.ko mystring="bebop" mybyte=255 myintArray=-1 mybyte is an 8 bit integer: 255 myshort is a short integer: 1 myint is an integer: 20 mylong is a long integer: 9999 mystring is a string: bebop myintArray is -1 and 420 satan# rmmod hello-5 Goodbye, world 5 satan# insmod hello-5.ko mystring="supercalifragilisticexpialidocious" \ > mybyte=256 myintArray=-1,-1 mybyte is an 8 bit integer: 0 myshort is a short integer: 1 myint is an integer: 20 mylong is a long integer: 9999 mystring is a string: supercalifragilisticexpialidocious myintArray is -1 and -1 satan# rmmod hello-5 Goodbye, world 5 satan# insmod hello-5.ko mylong=hello hello-5.o: invalid argument syntax for mylong: 'h' |
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