virtio-serial: make flow control explicit in virtio-console

virtio-console.c used to return a value less than the number of bytes
asked to be written out to a chardev backend in case the backend is not
writable.  virtio-serial-bus.c then implicitly enabled flow control for
that port.

Make this explicit instead.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Message-id: f5ec50b068c25422256e499cf4adc06d353bf394.1362505276.git.amit.shah@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/hw/virtio-console.c b/hw/virtio-console.c
index b3ee074a87..194de6431e 100644
--- a/hw/virtio-console.c
+++ b/hw/virtio-console.c
@@ -47,20 +47,21 @@ static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
     ret = qemu_chr_fe_write(vcon->chr, buf, len);
     trace_virtio_console_flush_buf(port->id, len, ret);
 
-    if (ret < 0) {
+    if (ret <= 0) {
+        VirtIOSerialPortClass *k = VIRTIO_SERIAL_PORT_GET_CLASS(port);
+
         /*
          * Ideally we'd get a better error code than just -1, but
          * that's what the chardev interface gives us right now.  If
          * we had a finer-grained message, like -EPIPE, we could close
-         * this connection.  Absent such error messages, the most we
-         * can do is to return 0 here.
-         *
-         * This will prevent stray -1 values to go to
-         * virtio-serial-bus.c and cause abort()s in
-         * do_flush_queued_data().
+         * this connection.
          */
         ret = 0;
-        qemu_chr_fe_add_watch(vcon->chr, G_IO_OUT, chr_write_unblocked, vcon);
+        if (!k->is_console) {
+            virtio_serial_throttle_port(port, true);
+            qemu_chr_fe_add_watch(vcon->chr, G_IO_OUT, chr_write_unblocked,
+                                  vcon);
+        }
     }
     return ret;
 }