compat.h

#include <linux/version.h>

/* arbitrary cut-off point. 3.19 is known to work, 3.13 is known broken. */
#if LINUX_VERSION_CODE < KERNEL_VERSION(3, 14, 0)

/*
 * Work around bug in older kernels that unsigned or out of tree
 * modules disable trace points. Thanks to Mathieu Desnoyers
 * and Ben Porter.
 */
static void fix_tracepoints(void)
{
	/*
	 * Force tracepoints to load by spoofing this module's taint
	 * and calling trace_module_notify and tracepoint_module_notify
	 * manually.
	 * Will duplicate calls to trace/tracepoint notify cause
	 * issues? perhaps detect if notify has already succeeded, and
	 * if so break before calling again.
	 */
	int (*tracepoint_module_notify_sym)(struct notifier_block *nb,
					unsigned long val, struct module *mod);
	int (*trace_module_notify_sym)(struct notifier_block * nb,
		    unsigned long val, struct module * mod);

	trace_module_notify_sym = (void*)__symbol_get("trace_module_notify");
	tracepoint_module_notify_sym = (void*)__symbol_get("tracepoint_module_notify");

	if (trace_module_notify_sym && tracepoint_module_notify_sym) {
		unsigned old_taint = THIS_MODULE->taints;
		THIS_MODULE->taints = 0;
		trace_module_notify_sym(NULL, MODULE_STATE_COMING, THIS_MODULE);
		tracepoint_module_notify_sym(NULL, MODULE_STATE_COMING, THIS_MODULE);
		THIS_MODULE->taints = old_taint;
	}
}

#else
static inline void fix_tracepoints(void) {}
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(4,8,0)
/*
 * Deal with the Gleixnerfication of CPU hotplug.
 * Only a single include instance supported for now.
 */

#define CPUHP_AP_ONLINE_DYN 0

static int (*do_startup)(unsigned int cpu);
static int (*do_teardown)(unsigned int cpu);

static int compat_cpu_notifier(struct notifier_block *nb, unsigned long action,
			       void *v)
{
	switch (action) {
	case CPU_STARTING:
		do_startup(smp_processor_id());
		break;
	case CPU_DYING:
		do_teardown(smp_processor_id());
		break;
	}
	return NOTIFY_OK;
}

static struct notifier_block cpu_notifier = {
	.notifier_call = compat_cpu_notifier,
};

static void call_startup(void *arg)
{
	int err = do_startup(smp_processor_id());
	if (err)
		*(int *)arg = err;
}

static void call_teardown(void *arg)
{
	do_teardown(smp_processor_id());
}


static inline int cpuhp_setup_state(int state, char *name,
			  int (*startup)(unsigned int cpu),
			  int (*teardown)(unsigned int cpu))
{
	int err = 0;

	get_online_cpus();
	do_startup = startup;
	do_teardown = teardown;
	on_each_cpu(call_startup, &err, 0);
	if (err)
		on_each_cpu(call_teardown, NULL, 0);
	else
		register_cpu_notifier(&cpu_notifier);
	put_online_cpus();
	return err;
}

static inline int cpuhp_remove_state(int state)
{
	get_online_cpus();
	on_each_cpu(call_teardown, NULL, 0);
	unregister_cpu_notifier(&cpu_notifier);
	put_online_cpus();
	return 0;
}

#endif