qemu: add a qemuInterfaceStopDevices(), called when guest CPUs stop

We now have a qemuInterfaceStartDevices() which does the final
activation needed for the host-side tap/macvtap devices that are used
for qemu network connections. It will soon make sense to have the
converse qemuInterfaceStopDevices() which will undo whatever was done
during qemuInterfaceStartDevices().

A function to "stop" a single device has also been added, and is
called from the appropriate place in qemuDomainDetachNetDevice(),
although this is currently unnecessary - the device is going to
immediately be deleted anyway, so any extra "deactivation" will be for
naught. The call is included for completeness, though, in anticipation
that in the future there may be some required action that *isn't*
nullified by deleting the device.

This patch is a part of a more complete fix for:

  https://bugzilla.redhat.com/show_bug.cgi?id=1081461

src/qemu/qemu_hotplug.c

@@ -3513,6 +3513,14 @@ qemuDomainDetachNetDevice(virQEMUDriverPtr driver,
         VIR_WARN("cannot clear bandwidth setting for device : %s",
                  detach->ifname);
 
+    /* deactivate the tap/macvtap device on the host (currently this
+     * isn't necessary, as everything done in
+     * qemuInterfaceStopDevice() is made meaningless when the device
+     * is deleted anyway, but in the future it may be important, and
+     * doesn't hurt anything for now)
+     */
+    ignore_value(qemuInterfaceStopDevice(detach));
+
     qemuDomainMarkDeviceForRemoval(vm, &detach->info);
 
     qemuDomainObjEnterMonitor(driver, vm);

src/qemu/qemu_interface.c

@@ -41,8 +41,9 @@ int
 qemuInterfaceStartDevice(virDomainNetDefPtr net)
 {
     int ret = -1;
+    virDomainNetType actualType = virDomainNetGetActualType(net);
 
-    switch (virDomainNetGetActualType(net)) {
+    switch (actualType) {
     case VIR_DOMAIN_NET_TYPE_BRIDGE:
     case VIR_DOMAIN_NET_TYPE_NETWORK:
         break;
@@ -98,3 +99,70 @@ qemuInterfaceStartDevices(virDomainDefPtr def)
     }
     return 0;
 }
+
+
+/**
+ * qemuInterfaceStopDevice:
+ * @net: net device to stop
+ *
+ * Based upon the type of device provided, perform the appropriate
+ * work to deactivate the device so that packets aren't forwarded to
+ * it from the rest of the network.
+ */
+int
+qemuInterfaceStopDevice(virDomainNetDefPtr net)
+{
+    int ret = -1;
+    virDomainNetType actualType = virDomainNetGetActualType(net);
+
+    switch (actualType) {
+    case VIR_DOMAIN_NET_TYPE_BRIDGE:
+    case VIR_DOMAIN_NET_TYPE_NETWORK:
+        break;
+
+    case VIR_DOMAIN_NET_TYPE_DIRECT:
+        /* macvtap interfaces need to be marked !IFF_UP (ie "down") to
+         * prevent any host-generated traffic sent from this interface
+         * from putting bad info into the arp caches of other machines
+         * on this network.
+         */
+        if (virNetDevSetOnline(net->ifname, false) < 0)
+            goto cleanup;
+        break;
+
+    case VIR_DOMAIN_NET_TYPE_USER:
+    case VIR_DOMAIN_NET_TYPE_ETHERNET:
+    case VIR_DOMAIN_NET_TYPE_VHOSTUSER:
+    case VIR_DOMAIN_NET_TYPE_SERVER:
+    case VIR_DOMAIN_NET_TYPE_CLIENT:
+    case VIR_DOMAIN_NET_TYPE_MCAST:
+    case VIR_DOMAIN_NET_TYPE_INTERNAL:
+    case VIR_DOMAIN_NET_TYPE_HOSTDEV:
+    case VIR_DOMAIN_NET_TYPE_LAST:
+        /* these types all require no action */
+        break;
+    }
+
+    ret = 0;
+ cleanup:
+    return ret;
+}
+
+/**
+ * qemuInterfaceStopDevices:
+ * @def: domain definition
+ *
+ * Make all interfaces associated with this domain inaccessible from
+ * the rest of the network.
+ */
+int
+qemuInterfaceStopDevices(virDomainDefPtr def)
+{
+    size_t i;
+
+    for (i = 0; i < def->nnets; i++) {
+        if (qemuInterfaceStopDevice(def->nets[i]) < 0)
+            return -1;
+    }
+    return 0;
+}

src/qemu/qemu_interface.h

@@ -28,5 +28,7 @@
 
 int qemuInterfaceStartDevice(virDomainNetDefPtr net);
 int qemuInterfaceStartDevices(virDomainDefPtr def);
+int qemuInterfaceStopDevice(virDomainNetDefPtr net);
+int qemuInterfaceStopDevices(virDomainDefPtr def);
 
 #endif /* __QEMU_INTERFACE_H__ */

src/qemu/qemu_process.c

@@ -3182,6 +3182,9 @@ int qemuProcessStopCPUs(virQEMUDriverPtr driver,
     if (ret < 0)
         goto cleanup;
 
+    /* de-activate netdevs after stopping CPUs */
+    ignore_value(qemuInterfaceStopDevices(vm->def));
+
     if (priv->job.current)
         ignore_value(virTimeMillisNow(&priv->job.current->stopped));