qemu: handle multicast overflow on macvtap NIC_RX_FILTER_CHANGED

Guest network devices can set 'overflow' when there are a number of multicast
ips configured. For virtio_net, the limit is only 64. In this case, the list
of mac addresses is empty and the 'overflow' condition is set. Thus, the guest
will currently receive no multicast traffic in this state.

When 'overflow' is set in the guest, let's turn this into ALLMULTI on the host.
Signed-off-by: NJason Baron <jbaron@akamai.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Acked-by: NMichal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_driver.c

@@ -4443,11 +4443,12 @@ static void
 syncNicRxFilterMultiMode(char *ifname, virNetDevRxFilterPtr guestFilter,
                          virNetDevRxFilterPtr hostFilter)
 {
-    if (hostFilter->multicast.mode != guestFilter->multicast.mode) {
+    if (hostFilter->multicast.mode != guestFilter->multicast.mode ||
+        (guestFilter->multicast.overflow &&
+        guestFilter->multicast.mode == VIR_NETDEV_RX_FILTER_MODE_NORMAL)) {
         switch (guestFilter->multicast.mode) {
             case VIR_NETDEV_RX_FILTER_MODE_ALL:
                 if (virNetDevSetRcvAllMulti(ifname, true)) {
-
                     VIR_WARN("Couldn't set allmulticast flag to 'on' for "
                              "device %s while responding to "
                              "NIC_RX_FILTER_CHANGED", ifname);
@@ -4455,17 +4456,24 @@ syncNicRxFilterMultiMode(char *ifname, virNetDevRxFilterPtr guestFilter,
                 break;
 
             case VIR_NETDEV_RX_FILTER_MODE_NORMAL:
-                if (virNetDevSetRcvMulti(ifname, true)) {
+                if (guestFilter->multicast.overflow &&
+                    (hostFilter->multicast.mode == VIR_NETDEV_RX_FILTER_MODE_ALL)) {
+                    break;
+                }
 
+                if (virNetDevSetRcvMulti(ifname, true)) {
                     VIR_WARN("Couldn't set multicast flag to 'on' for "
                              "device %s while responding to "
                              "NIC_RX_FILTER_CHANGED", ifname);
                 }
 
-                if (virNetDevSetRcvAllMulti(ifname, false)) {
-                    VIR_WARN("Couldn't set allmulticast flag to 'off' for "
-                             "device %s while responding to "
-                             "NIC_RX_FILTER_CHANGED", ifname);
+                if (virNetDevSetRcvAllMulti(ifname,
+                                            guestFilter->multicast.overflow) < 0) {
+                     VIR_WARN("Couldn't set allmulticast flag to '%s' for "
+                              "device %s while responding to "
+                              "NIC_RX_FILTER_CHANGED",
+                              virTristateSwitchTypeToString(virTristateSwitchFromBool(guestFilter->multicast.overflow)),
+                              ifname);
                 }
                 break;