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>Hello World (part 2)</H1
><A
NAME="AEN238"
></A
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></A
><P
>As of Linux 2.4, you can rename the init and cleanup functions of your modules; they no longer have to be called
<TT
CLASS="FUNCTION"
>init_module()</TT
> and <TT
CLASS="FUNCTION"
>cleanup_module()</TT
> respectively. This is done with the
<TT
CLASS="FUNCTION"
>module_init()</TT
> and <TT
CLASS="FUNCTION"
>module_exit()</TT
> macros. These macros are defined in <TT
CLASS="FILENAME"
>linux/init.h</TT
>. The only caveat is that your init and cleanup functions must be defined before calling
the macros, otherwise you'll get compilation errors. Here's an example of this technique:</P
><A
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></A
><DIV
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><A
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></A
><P
><B
>Example 2-3. hello-2.c</B
></P
><PRE
CLASS="PROGRAMLISTING"
>/*
* hello-2.c - Demonstrating the module_init() and module_exit() macros.
* This is preferred over using init_module() and cleanup_module().
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_ALERT */
#include <linux/init.h> /* Needed for the macros */
static int __init hello_2_init(void)
{
printk(KERN_ALERT "Hello, world 2\n");
return 0;
}
static void __exit hello_2_exit(void)
{
printk(KERN_ALERT "Goodbye, world 2\n");
}
module_init(hello_2_init);
module_exit(hello_2_exit);</PRE
></DIV
><P
>So now we have two real kernel modules under our belt. Adding another module is as simple as this: </P
><DIV
CLASS="EXAMPLE"
><A
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></A
><P
><B
>Example 2-4. Makefile for both our modules</B
></P
><PRE
CLASS="PROGRAMLISTING"
>obj-m += hello-1.o
obj-m += hello-2.o</PRE
></DIV
><P
>Now have a look at <TT
CLASS="FILENAME"
>linux/drivers/char/Makefile</TT
> for a real world example. As you can see, some things
get hardwired into the kernel (obj-y) but where are all those obj-m gone? Those familiar with shell scripts will easily be
able to spot them. For those not, the obj-$(CONFIG_FOO) entries you see everywhere expand into obj-y or obj-m, depending on
whether the CONFIG_FOO variable has been set to y or m. While we are at it, those were exactly the kind of variables
that you have set in the <TT
CLASS="FILENAME"
>linux/.config</TT
> file, the last time when you said <B
CLASS="COMMAND"
>make menuconfig</B
>
or something like that.
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>Hello World (part 3): The <TT
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> and <TT
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>__exit</TT
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