%Linux Hello World
%Thadeu Cascardo

# Module Tools

* lsmod
* insmod
* rmmod
* modprobe
* modinfo
* depmod

# Module Files

* /lib/modules/
* /proc/modules
* /sys/module/

# Module parameters

* modinfo output
* modprobe configuration files
* /sys/module/*/parameters/

# Headers

* include linux/module.h
* include linux/init.h

# Init and Exit Functions

We use *module\\_init* and *module\\_exit* to declare our init and exit
functions.

The *\\_\\_init* and *\\_\\_exit* marks allow the kernel to remove them when
they are not needed, reducing memory consumption.

# printk

*printk* is very similar to printf. The messages are usually preceded by a
string in the form \<n\>, where *n* is a priority. There are macros, like
*KERN\\_ALERT* and *KERN\\_DEBUG* to use for that.

# License and taint

*MODULE\\_LICENSE* is highly recommended. A free software license should be
used, otherwise the kernel is tainted. This indicates to developers that
something has gone wrong, and some bug reports are ignored some times.

# Building out-of-tree

Building an out-of-tree linux module is very simple.

Let's take a look at a simple command line and a simple Makefile.

# Module description definitios

* MODULE\\_AUTHOR
* MODULE\\_LICENSE
* MODULE\\_DESCRIPTION
* MODULE\\_INFO
* MODULE\\_ALIAS
* MODULE\\_VERSION

# Module parameters

Besides *MODULE\\_PARM\\_DESC* to inform user about the parameter, we must use
*module\\_param*.

module\\_param(name, type, perm);

# Memory allocation

* include linux/slab.h
* kmalloc
* kfree