mipsnet: Flush queued packets when receiving is enabled

Drop .can_receive and move the semantics to mipsnet_receive, by
returning 0.

After 0 is returned, we must flush the queue explicitly to restart it:
Call qemu_flush_queued_packets when s->busy or s->rx_count is being
updated.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>
Message-id: 1436955553-22791-10-git-send-email-famz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/net/mipsnet.c

@@ -80,7 +80,7 @@ static ssize_t mipsnet_receive(NetClientState *nc, const uint8_t *buf, size_t si
 
     trace_mipsnet_receive(size);
     if (!mipsnet_can_receive(nc))
-        return -1;
+        return 0;
 
     s->busy = 1;
 
@@ -134,6 +134,9 @@ static uint64_t mipsnet_ioport_read(void *opaque, hwaddr addr,
         if (s->rx_count) {
             s->rx_count--;
             ret = s->rx_buffer[s->rx_read++];
+            if (mipsnet_can_receive(s->nic->ncs)) {
+                qemu_flush_queued_packets(qemu_get_queue(s->nic));
+            }
         }
         break;
     /* Reads as zero. */
@@ -170,6 +173,9 @@ static void mipsnet_ioport_write(void *opaque, hwaddr addr,
         }
         s->busy = !!s->intctl;
         mipsnet_update_irq(s);
+        if (mipsnet_can_receive(s->nic->ncs)) {
+            qemu_flush_queued_packets(qemu_get_queue(s->nic));
+        }
         break;
     case MIPSNET_TX_DATA_BUFFER:
         s->tx_buffer[s->tx_written++] = val;
@@ -214,7 +220,6 @@ static const VMStateDescription vmstate_mipsnet = {
 static NetClientInfo net_mipsnet_info = {
     .type = NET_CLIENT_OPTIONS_KIND_NIC,
     .size = sizeof(NICState),
-    .can_receive = mipsnet_can_receive,
     .receive = mipsnet_receive,
 };