UML - clocksource support

Index: linux-2.6.20/arch/um/kernel/time.c
===================================================================
@@ -97,6 +97,21 @@ static irqreturn_t um_timer(int irq, voi
 	return IRQ_HANDLED;
 }
 
+static cycle_t itimer_read(void)
+{
+	return os_nsecs();
+}
+
+static struct clocksource itimer_clocksource = {
+	.name		= "itimer",
+	.rating		= 300,
+	.read		= itimer_read,
+	.mask		= CLOCKSOURCE_MASK(64),
+	.mult		= 1,
+	.shift		= 0,
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
 static void __init setup_itimer(void)
 {
 	int err;

@@ -106,6 +121,12 @@ static void __init setup_itimer(void)
 		printk(KERN_ERR "register_timer : request_irq failed - "
 		       "errno = %d\n", -err);
 
+	err = clocksource_register(&itimer_clocksource);
+	if (err) {
+		printk(KERN_ERR "clocksource_register returned %d\n", err);
+		return;
+	}
+
 	itimer_clockevent.mult = div_sc(HZ, NSEC_PER_SEC, 32);
 	itimer_clockevent.max_delta_ns =
 		clockevent_delta2ns(60 * HZ, &itimer_clockevent);