[Qemu-devel] [PATCH v2] virtio-serial: Do not notify virtqueue if no element was pushed back.

[Gal Hammer <ghammer@redhat.com>]

The redundant notification caused the Windows' driver to duplicate the
pending write request's buffer. The driver was fixed, but I think this
change is still required.

Signed-off-by: Gal Hammer <ghammer@redhat.com>
---
 hw/char/virtio-serial-bus.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index da417c7..0d38b4b 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -105,6 +105,7 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
                                  VirtIODevice *vdev)
 {
     VirtIOSerialPortClass *vsc;
+    bool elem_pushed = false;
 
     assert(port);
     assert(virtio_queue_ready(vq));
@@ -145,9 +146,12 @@ static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
             break;
         }
         virtqueue_push(vq, &port->elem, 0);
+        elem_pushed = true;
         port->elem.out_num = 0;
     }
-    virtio_notify(vdev, vq);
+    if (elem_pushed) {
+        virtio_notify(vdev, vq);
+    }
 }
 
 static void flush_queued_data(VirtIOSerialPort *port)
-- 
1.8.1.4