2.7. Modules Spanning Multiple Files

Sometimes it makes sense to divide a kernel module between several source files. In this case, you need to:

1. 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__.

2. Compile all the source files as usual.

3. 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>.

The makefile will, once again, save us from having to get our hands dirty with compiling and linking the object files.

Here's an example of such a kernel module.

/*
 *  start.c - Illustration of multi filed modules
 */

#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;
}

The next file:

/*
 *  stop.c - Illustration of multi filed modules
 */

#include <linux/kernel.h>	/* We're doing kernel work */
#include <linux/module.h>	/* Specifically, a module  */

void cleanup_module()
{
	printk("<1>Short is the life of a kernel module\n");
}

And finally, the makefile:

obj-m += hello-1.o
obj-m += hello-2.o
obj-m += hello-3.o
obj-m += hello-4.o
obj-m += hello-5.o
obj-m += startstop.o
startstop-objs := start.o stop.o