\label{sec:introduction}

The Linux Kernel Module Programming Guide is a free book; you may reproduce or modify it under the terms of the \href{https://opensource.org/licenses/OSL-3.0}{Open Software License}, version 3.0.

This book is distributed in the hope that it would be useful, but without any warranty, without even the implied warranty of merchantability or fitness for a particular purpose.

This book is distributed in the hope that it would be useful, but without any warranty,

without even the implied warranty of merchantability or fitness for a particular purpose.

The author encourages wide distribution of this book for personal or commercial use, provided the above copyright notice remains intact and the method adheres to the provisions of the \href{https://opensource.org/licenses/OSL-3.0}{Open Software License}.

In summary, you may copy and distribute this book free of charge or for a profit. No explicit permission is required from the author for reproduction of this book in any medium, physical or electronic.

The author encourages wide distribution of this book for personal or commercial use,

provided the above copyright notice remains intact and the method adheres to the provisions of the \href{https://opensource.org/licenses/OSL-3.0}{Open Software License}.

In summary, you may copy and distribute this book free of charge or for a profit.

No explicit permission is required from the author for reproduction of this book in any medium, physical or electronic.

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Please make revisions and updates available directly to the document maintainer, Jim Huang <jserv@ccns.ncku.edu.tw>.

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Contributing in this way shows your support for free software and the LDP. If you have questions or comments, please contact the address above.

If you publish or distribute this book commercially, donations, royalties,

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Contributing in this way shows your support for free software and the LDP.

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\subsection{Authorship}

\label{sec:authorship}

The example code should clear up my admittedly lousy explanation.

The \cpp|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 would like to use arrays of integers or strings, see \cpp|module_param_array()| and \cpp|module_param_string()|.

Integer types can be signed as usual or unsigned. If you would like to use arrays of integers or strings,

see \cpp|module_param_array()| and \cpp|module_param_string()|.

\begin{code}

int myint = 3;

Arrays are supported too, but things are a bit different now than they were in the olden days.

To keep track of the number of parameters, you need to pass a pointer to a count variable as the third parameter.

At your option, you could also ignore the count and pass \cpp|NULL| instead. We show both possibilities here:

At your option, you could also ignore the count and pass \cpp|NULL| instead.

We show both possibilities here:

\begin{code}

int myintarray[2];

\end{code}

A good use for this is to have the module variable's default values set, like a port or IO address.

If the variables contain the default values, then perform autodetection (explained elsewhere). Otherwise, keep the current value.

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 is a macro function, \cpp|MODULE_PARM_DESC()|, that is used to document arguments that the module can take.