KVM: make io_bus interface more robust

Today kvm_io_bus_regsiter_dev() returns void and will internally BUG_ON
if it fails.  We want to create dynamic MMIO/PIO entries driven from
userspace later in the series, so we need to enhance the code to be more
robust with the following changes:

   1) Add a return value to the registration function
   2) Fix up all the callsites to check the return code, handle any
      failures, and percolate the error up to the caller.
   3) Add an unregister function that collapses holes in the array

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/i8254.c

@@ -605,6 +605,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 {
 	struct kvm_pit *pit;
 	struct kvm_kpit_state *pit_state;
+	int ret;
 
 	pit = kzalloc(sizeof(struct kvm_pit), GFP_KERNEL);
 	if (!pit)
@@ -639,14 +640,29 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
 
 	kvm_iodevice_init(&pit->dev, &pit_dev_ops);
-	__kvm_io_bus_register_dev(&kvm->pio_bus, &pit->dev);
+	ret = __kvm_io_bus_register_dev(&kvm->pio_bus, &pit->dev);
+	if (ret < 0)
+		goto fail;
 
 	if (flags & KVM_PIT_SPEAKER_DUMMY) {
 		kvm_iodevice_init(&pit->speaker_dev, &speaker_dev_ops);
-		__kvm_io_bus_register_dev(&kvm->pio_bus, &pit->speaker_dev);
+		ret = __kvm_io_bus_register_dev(&kvm->pio_bus,
+						&pit->speaker_dev);
+		if (ret < 0)
+			goto fail_unregister;
 	}
 
 	return pit;
+
+fail_unregister:
+	__kvm_io_bus_unregister_dev(&kvm->pio_bus, &pit->dev);
+
+fail:
+	if (pit->irq_source_id >= 0)
+		kvm_free_irq_source_id(kvm, pit->irq_source_id);
+
+	kfree(pit);
+	return NULL;
 }
 
 void kvm_free_pit(struct kvm *kvm)

arch/x86/kvm/i8259.c

@@ -539,6 +539,8 @@ static const struct kvm_io_device_ops picdev_ops = {
 struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 {
 	struct kvm_pic *s;
+	int ret;
+
 	s = kzalloc(sizeof(struct kvm_pic), GFP_KERNEL);
 	if (!s)
 		return NULL;
@@ -555,6 +557,11 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm)
 	 * Initialize PIO device
 	 */
 	kvm_iodevice_init(&s->dev, &picdev_ops);
-	kvm_io_bus_register_dev(kvm, &kvm->pio_bus, &s->dev);
+	ret = kvm_io_bus_register_dev(kvm, &kvm->pio_bus, &s->dev);
+	if (ret < 0) {
+		kfree(s);
+		return NULL;
+	}
+
 	return s;
 }