#include <linux/module.h>
#include <linux/notifier.h>

#define USER_DEFINED_NOTIFIER_COMMAND 0x0001

/* PROVIDER */
static BLOCKING_NOTIFIER_HEAD(user_defined_chain);

/* CONSUMER */
int consumer_callback( struct notifier_block *self,
    unsigned long val, void *data)
{
    printk("consumer: val: %ld, data: %p\n",
        val, data);
    return NOTIFY_DONE;
}
static struct notifier_block user_defined_notifier = {
    .notifier_call = consumer_callback,
};

static int __init notifier_init(void)
{
    blocking_notifier_chain_register(
        &user_defined_chain,
        &user_defined_notifier);
    /* PROVIDER */
    blocking_notifier_call_chain(
        &user_defined_chain,
        USER_DEFINED_NOTIFIER_COMMAND,
        NULL);
    return 0;
}

static void __exit notifier_exit(void)
{
    blocking_notifier_chain_unregister(
        &user_defined_chain,
        &user_defined_notifier);
}

module_init(notifier_init);
module_exit(notifier_exit);
MODULE_LICENSE("GPL");