[PATCH v2] qemu: handle multicast overflow on macvtap NIC_RX_FILTER_CHANGED

[Jason Baron <jbaron@xxxxxxxxxx>]

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: Jason Baron <jbaron@xxxxxxxxxx>
---
v1->v2:
 1. check for < 0 in virNetDevSetRcvAllMulti() (Michal Privoznik)
 2. restrict overflow check to VIR_NETDEV_RX_FILTER_MODE_NORMAL mode as to
    avoid unnecessarily calling rx filter updates for other modes 
 3. update virNetDevSetRcvAllMulti() call to use guestFilter->multicast.overflow
    directly (Michal Privoznik)

 src/qemu/qemu_driver.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 7fb9102..f4bbfea 100644
--- a/src/qemu/qemu_driver.c
+++ b/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;
 
-- 
2.7.4

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