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><H1
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><A
NAME="AEN333"
></A
>Passing Command Line Arguments to a Module</H1
><P
>Modules can take command line arguments, but not with the <TT
CLASS="VARNAME"
>argc</TT
>/<TT
CLASS="VARNAME"
>argv</TT
> you might be
	used to.</P
><P
>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 <TT
CLASS="FUNCTION"
>MODULE_PARM()</TT
> macro, (defined in <TT
CLASS="FILENAME"
>linux/module.h</TT
>) to set the mechanism up.  At runtime, insmod will fill the variables with any
	command line arguments that are given, like <B
CLASS="COMMAND"
>./insmod mymodule.o myvariable=5</B
>.  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.</P
><P
>The <TT
CLASS="FUNCTION"
>MODULE_PARM()</TT
> macro takes 2 arguments: the name of the variable and its type.  The supported
	variable types are "<TT
CLASS="LITERAL"
>b</TT
>": single byte, "<TT
CLASS="LITERAL"
>h</TT
>": short int, "<TT
CLASS="LITERAL"
>i</TT
>": integer,
	"<TT
CLASS="LITERAL"
>l</TT
>": long int and "<TT
CLASS="LITERAL"
>s</TT
>": string, and the integer types can be signed as usual or unsigned.
	Strings should be declared as "<SPAN
CLASS="TYPE"
>char *</SPAN
>" and insmod will allocate memory for them.  You should always try to give
	the variables an initial default value.  This is kernel code, and you should program defensively.  For example:</P
><PRE
CLASS="SCREEN"
>int myint = 3;
char *mystr;

MODULE_PARM(myint, "i");
MODULE_PARM(mystr, "s");
	</PRE
><P
>Arrays are supported too.  An integer value preceding the type in MODULE_PARM will indicate an array of some maximum
	length.  Two numbers separated by a '-' will give the minimum and maximum number of values.  For example, an array of shorts
	with at least 2 and no more than 4 values could be declared as:</P
><PRE
CLASS="SCREEN"
>int myshortArray[4];
MODULE_PARM (myintArray, "3-9i");
	</PRE
><P
>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.</P
><P
>Lastly, there's a macro function, <TT
CLASS="FUNCTION"
>MODULE_PARM_DESC()</TT
>, 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.</P
><A
NAME="AEN356"
></A
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN359"
></A
><P
><B
>Example 2-7. hello-5.c</B
></P
><PRE
CLASS="PROGRAMLISTING"
>/*
 *  hello-5.c - Demonstrates command line argument passing to a module.
 */
#include &#60;linux/module.h&#62;
#include &#60;linux/moduleparam.h&#62;
#include &#60;linux/kernel.h&#62;
#include &#60;linux/init.h&#62;
#include &#60;linux/stat.h&#62;

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";

/* 
 * 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");

static int __init hello_5_init(void)
{
	printk(KERN_ALERT "Hello, world 5\n=============\n");
	printk(KERN_ALERT "myshort is a short integer: %hd\n", myshort);
	printk(KERN_ALERT "myint is an integer: %d\n", myint);
	printk(KERN_ALERT "mylong is a long integer: %ld\n", mylong);
	printk(KERN_ALERT "mystring is a string: %s\n", mystring);
	return 0;
}

static void __exit hello_5_exit(void)
{
	printk(KERN_ALERT "Goodbye, world 5\n");
}

module_init(hello_5_init);
module_exit(hello_5_exit);</PRE
></DIV
><P
>I would recommend playing around with this code:</P
><PRE
CLASS="SCREEN"
>satan# insmod hello-5.o 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.o mystring="supercalifragilisticexpialidocious" \
&#62; 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.o mylong=hello
hello-5.o: invalid argument syntax for mylong: 'h'</PRE
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