# Linux Kernel Module Cheat

#### 17.11.2. dummy-irq

The Linux kernel v4.16 mainline also has a `dummy-irq` module at `drivers/misc/dummy-irq.c` for monitoring a single IRQ.

We build it by default with:

    CONFIG_DUMMY_IRQ=m

And then you can do

    ./run --graphic

and in guest:

    modprobe dummy-irq irq=1

Outcome: when you click a key on the keyboard, dmesg shows:

    dummy-irq: interrupt occurred on IRQ 1

However, this module is intended to fire only once as can be seen from its source:

        static int count = 0;

        if (count == 0) {
            printk(KERN_INFO "dummy-irq: interrupt occurred on IRQ %d\n",
                irq);
            count++;
        }

and furthermore interrupt `1` and `12` happen immediately TODO why, were they somehow pending?