2.7. Modules Spanning Multiple Files

Sometimes it makes sense to divide a kernel module between several source files.

Here's an example of such a kernel module.

Example 2-8. start.c

/*
 *  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(KERN_INFO "Hello, world - this is the kernel speaking\n");
        return 0;
}

The next file:

Example 2-9. stop.c

/*
 *  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(KERN_INFO "Short is the life of a kernel module\n");
}

And finally, the makefile:

Example 2-10. 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

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

This is the complete makefile for all the examples we've seen so far. The first five lines are nothing special, but for the last example we'll need two lines. First we invent an object name for our combined module, second we tell make what object files are part of that module.