virtio-serial-bus: let chardev know the exact number of bytes requested

Using the virtqueue_avail_bytes() function had an unnecessarily
crippling effect on the number of bytes needed by the guest as reported
to the chardev layer in the can_read() callback.

Using the new virtqueue_get_avail_bytes() function will let us advertise
the exact number of bytes we can send to the guest.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 3 insertions, 8 deletions

diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index 82073f5dc2..d20bd8bf75 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -287,6 +287,7 @@ ssize_t virtio_serial_write(VirtIOSerialPort *port, const uint8_t *buf,
 size_t virtio_serial_guest_ready(VirtIOSerialPort *port)
 {
     VirtQueue *vq = port->ivq;
+    unsigned int bytes;
 
     if (!virtio_queue_ready(vq) ||
         !(port->vser->vdev.status & VIRTIO_CONFIG_S_DRIVER_OK) ||
@@ -296,14 +297,8 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port)
     if (use_multiport(port->vser) && !port->guest_connected) {
         return 0;
     }
-
-    if (virtqueue_avail_bytes(vq, 4096, 0)) {
-        return 4096;
-    }
-    if (virtqueue_avail_bytes(vq, 1, 0)) {
-        return 1;
-    }
-    return 0;
+    virtqueue_get_avail_bytes(vq, &bytes, NULL);
+    return bytes;
 }
 
 static void flush_queued_data_bh(void *opaque)