Modules Spanning Multiple Files
Sometimes it makes sense to divide a kernel module between several source files. In this case, you need to:
In all the source files but one, add the line #define __NO_VERSION__. This is important
because module.h normally includes the definition of
kernel_version, a global variable with the kernel version the module is compiled for. If you need
version.h, you need to include it yourself, because module.h won't do it for you with __NO_VERSION__.
Compile all the source files as usual.
Combine all the object files into a single one. Under x86, use ld -m elf_i386 -r -o <module
name.o> <1st src file.o> <2nd src file.o>.
Here's an example of such a kernel module.
Example 2-8. start.c
/* start.c - Illustration of multi filed modules
*
* Copyright (C) 2001 by Peter Jay Salzman
*
* 08/02/2006 - Updated by Rodrigo Rubira Branco <rodrigo@kernelhacking.com>
*/
/* Kernel Programming */
#define MODULE
#define LINUX
#define __KERNEL__
#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h> /* Specifically, a module */
int init_module(void)
{
printk("Hello, world - this is the kernel speaking\n");
return 0;
}
MODULE_LICENSE("GPL");
The next file:
Example 2-9. stop.c
/* stop.c - Illustration of multi filed modules
*
* Copyright (C) 2001 by Peter Jay Salzman
*
* 08/02/2006 - Updated by Rodrigo Rubira Branco <rodrigo@kernelhacking.com>
*/
/* Kernel Programming */
#define MODULE
#define LINUX
#define __KERNEL__
#if defined(CONFIG_MODVERSIONS) && ! defined(MODVERSIONS)
#include <linux/modversions.h> /* Will be explained later */
#define MODVERSIONS
#endif
#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h> /* Specifically, a module */
#define __NO_VERSION__ /* It's not THE file of the kernel module */
#include <linux/version.h> /* Not included by module.h because of
__NO_VERSION__ */
void cleanup_module()
{
printk("<1>Short is the life of a kernel module\n");
} And finally, the makefile:
Example 2-10. Makefile for a multi-filed module
CC=gcc
MODCFLAGS := -O -Wall -DMODULE -D__KERNEL__
hello.o: hello2_start.o hello2_stop.o
ld -m elf_i386 -r -o hello2.o hello2_start.o hello2_stop.o
start.o: hello2_start.c
${CC} ${MODCFLAGS} -c hello2_start.c
stop.o: hello2_stop.c
${CC} ${MODCFLAGS} -c hello2_stop.c