network: eliminate lag in updating dnsmasq hosts files

This addresses https://bugzilla.redhat.com/show_bug.cgi?id=713728

When "defining" a new network (or one that exists but isn't currently
active) the new definition is stored in network->def, but for a
network that already exists and is active, the new definition is
stored in network->newDef, and then moved over to network->def as soon
as the network is destroyed.

However, the code that writes the dhcp and dns hosts files used by
dnsmasq was always using network->def for its information, even when
the new data was actually in network->newDef, so the hosts files
always lagged one edit behind the definition.

This patch changes the code to keep the pointer to the new definition
after it's been assigned into the network, and use it directly
(regardless of whether it's stored in network->newDef or network->def)
to construct the hosts files.

src/network/bridge_driver.c

@@ -2338,6 +2338,7 @@ static virNetworkPtr networkDefine(virConnectPtr conn, const char *xml) {
     struct network_driver *driver = conn->networkPrivateData;
     virNetworkIpDefPtr ipdef, ipv4def = NULL;
     virNetworkDefPtr def;
+    bool freeDef = true;
     virNetworkObjPtr network = NULL;
     virNetworkPtr ret = NULL;
     int ii;
@@ -2367,21 +2368,19 @@ static virNetworkPtr networkDefine(virConnectPtr conn, const char *xml) {
     if (!(network = virNetworkAssignDef(&driver->networks,
                                         def)))
         goto cleanup;
-    def = NULL;
+    freeDef = false;
 
     network->persistent = 1;
 
-    if (virNetworkSaveConfig(driver->networkConfigDir,
+    if (virNetworkSaveConfig(driver->networkConfigDir, def) < 0) {
-                             network->newDef ? network->newDef : network->def) < 0) {
+        virNetworkRemoveInactive(&driver->networks, network);
-        virNetworkRemoveInactive(&driver->networks,
-                                 network);
         network = NULL;
         goto cleanup;
     }
 
     /* We only support dhcp on one IPv4 address per defined network */
     for (ii = 0;
-         (ipdef = virNetworkDefGetIpByIndex(network->def, AF_UNSPEC, ii));
+         (ipdef = virNetworkDefGetIpByIndex(def, AF_UNSPEC, ii));
          ii++) {
         if (VIR_SOCKET_IS_FAMILY(&ipdef->address, AF_INET)) {
             if (ipdef->nranges || ipdef->nhosts) {
@@ -2396,18 +2395,19 @@ static virNetworkPtr networkDefine(virConnectPtr conn, const char *xml) {
         }
     }
     if (ipv4def) {
-        dctx = dnsmasqContextNew(network->def->name, DNSMASQ_STATE_DIR);
+        dctx = dnsmasqContextNew(def->name, DNSMASQ_STATE_DIR);
         if (dctx == NULL ||
-            networkBuildDnsmasqHostsfile(dctx, ipv4def, network->def->dns) < 0 ||
+            networkBuildDnsmasqHostsfile(dctx, ipv4def, def->dns) < 0 ||
             dnsmasqSave(dctx) < 0)
             goto cleanup;
     }
 
-    VIR_INFO("Defining network '%s'", network->def->name);
+    VIR_INFO("Defining network '%s'", def->name);
-    ret = virGetNetwork(conn, network->def->name, network->def->uuid);
+    ret = virGetNetwork(conn, def->name, def->uuid);
 
 cleanup:
-    virNetworkDefFree(def);
+    if (freeDef)
+       virNetworkDefFree(def);
     dnsmasqContextFree(dctx);
     if (network)
         virNetworkObjUnlock(network);