virtio-serial: don't set MULTIPORT for 1 port dev

Since commit 98b19252cf1bd97c54bc4613f3537c5ec0aae263, all
serial devices declare MULTIPORT feature.
To allow 0.12 compatibility, we should clear this when
max_nr_ports is 1.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index ab456ea..d0e0219 100644 (file)
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -335,8 +335,10 @@ static void handle_input(VirtIODevice *vdev, VirtQueue *vq)
 
 static uint32_t get_features(VirtIODevice *vdev, uint32_t features)
 {
-    features |= (1 << VIRTIO_CONSOLE_F_MULTIPORT);
-
+    VirtIOSerial *vser = DO_UPCAST(VirtIOSerial, vdev, vdev);
+    if (vser->bus->max_nr_ports > 1) {
+        features |= (1 << VIRTIO_CONSOLE_F_MULTIPORT);
+    }
     return features;
 }