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<B> Next:</B> <A NAME="tex2html517"
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<H1><A NAME="SECTION00300000000000000000"> </A><A NAME="hello-world"> </A>
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Hello, world
</H1>
<P>
When the first caveman programmer chiseled the first program on the walls
of the first cave computer, it was a program to paint the string `Hello,
world' in Antelope pictures. Roman programming textbooks began with the
`Salut, Mundi' program. I don't know what happens to people who break with
this tradition, and I think it's safer not to find out.
<A NAME="109"> </A>
<A NAME="110"> </A>
<P>
A kernel module has to have at least two functions: <TT>init_module</TT> which
is called when the module is inserted into the kernel, and
<TT>cleanup_module</TT> which is called just before it is removed.
Typically, <TT>init_module</TT> either registers
a handler for something with the kernel, or it replaces one of the kernel
function with its own code (usually code to do something and then call
the original function). The <TT>cleanup_module</TT> function is supposed to undo
whatever <TT>init_module</TT> did, so the module can be unloaded safely.
<A NAME="116"> </A>
<A NAME="117"> </A>
<P>
ex
<FONT SIZE="+1"><B>hello.c</B></FONT>
<A NAME="122"> </A><A NAME="123"> </A>
<P>
<PRE>
/* hello.c
* Copyright (C) 1998 by Ori Pomerantz
*
* "Hello, world" - the kernel module version.
*/
/* The necessary header files */
/* Standard in kernel modules */
#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h> /* Specifically, a module */
/* Deal with CONFIG_MODVERSIONS */
#if CONFIG_MODVERSIONS==1
#define MODVERSIONS
#include <linux/modversions.h>
#endif
/* Initialize the module */
int init_module()
{
printk("Hello, world - this is the kernel speaking\n");
/* If we return a non zero value, it means that
* init_module failed and the kernel module
* can't be loaded */
return 0;
}
/* Cleanup - undid whatever init_module did */
void cleanup_module()
{
printk("Short is the life of a kernel module\n");
}
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<ADDRESS>
<I></I>
<BR><I>1999-05-19</I>
</ADDRESS>
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