virtio: make VIRTIO_F_VERSION_1 a transport bit

Activate VIRTIO_F_VERSION_1 automatically unless legacy_only
is set.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio.c

@@ -197,7 +197,11 @@ static int virtio_dev_probe(struct device *_d)
 		driver_features_legacy = driver_features;
 	}
 
-	if (driver_features & device_features & (1ULL << VIRTIO_F_VERSION_1))
+	/* Detect legacy-only drivers and disable VIRTIO_F_VERSION_1. */
+	if (drv->legacy_only)
+		device_features &= ~(1ULL << VIRTIO_F_VERSION_1);
+
+	if (device_features & (1ULL << VIRTIO_F_VERSION_1))
 		dev->features = driver_features & device_features;
 	else
 		dev->features = driver_features_legacy & device_features;

drivers/virtio/virtio_ring.c

@@ -780,6 +780,8 @@ void vring_transport_features(struct virtio_device *vdev)
 			break;
 		case VIRTIO_RING_F_EVENT_IDX:
 			break;
+		case VIRTIO_F_VERSION_1:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);

include/uapi/linux/virtio_config.h

@@ -43,11 +43,11 @@
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED		0x80
 
-/* Some virtio feature bits (currently bits 28 through 31) are reserved for the
+/* Some virtio feature bits (currently bits 28 through 32) are reserved for the
  * transport being used (eg. virtio_ring), the rest are per-device feature
  * bits. */
 #define VIRTIO_TRANSPORT_F_START	28
-#define VIRTIO_TRANSPORT_F_END		32
+#define VIRTIO_TRANSPORT_F_END		33
 
 /* Do we get callbacks when the ring is completely used, even if we've
  * suppressed them? */