net: fix qemu_flush_queued_packets() in presence of a hub

When frontend and backend are connected through a hub as below
(showing only one direction), and the frontend (or in general, all
output ports of the hub) cannot accept more traffic, the backend
queues packets in queue-A.

When the frontend (or in general, one output port) becomes ready again,
quemu tries to flush packets from queue-B, which is unfortunately empty.

  e1000.0 <--[queue B]-- hub0port0(hub)hub0port1 <--[queue A]-- tap.0

To fix this i propose to introduce a new function net_hub_flush()
which is called when trying to flush a queue connected to a hub.

Signed-off-by: Luigi Rizzo <rizzo@iet.unipi.it>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/net/net.c b/net/net.c
index be03a8dd14..a66aa02472 100644
--- a/net/net.c
+++ b/net/net.c
@@ -441,6 +441,12 @@ void qemu_flush_queued_packets(NetClientState *nc)
 {
     nc->receive_disabled = 0;
 
+    if (nc->peer && nc->peer->info->type == NET_CLIENT_OPTIONS_KIND_HUBPORT) {
+        if (net_hub_flush(nc->peer)) {
+            qemu_notify_event();
+        }
+        return;
+    }
     if (qemu_net_queue_flush(nc->send_queue)) {
         /* We emptied the queue successfully, signal to the IO thread to repoll
          * the file descriptor (for tap, for example).