Make virtual network netmasks optional

When a netmask isn't specified for an IPv4 address, one can be implied
based on what network class range the address is in. The
virNetworkDefPrefix function does this for us, so netmask isn't
required.

src/conf/network_conf.c

@@ -470,19 +470,14 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt)
         def->delay = 0;
 
     ipAddress = virXPathString("string(./ip[1]/@address)", ctxt);
-    netmask = virXPathString("string(./ip[1]/@netmask)", ctxt);
-    if (ipAddress &&
-        netmask) {
+    if (ipAddress) {
         xmlNodePtr ip;
 
         if (virSocketParseAddr(ipAddress, &def->ipAddress, AF_UNSPEC) < 0)
             goto error;
-        if (virSocketParseAddr(netmask, &def->netmask, AF_UNSPEC) < 0)
-            goto error;
 
         /* XXX someday we want IPv6, so will need to relax this */
-        if (!VIR_SOCKET_IS_FAMILY(&def->ipAddress, AF_INET) ||
-            !VIR_SOCKET_IS_FAMILY(&def->netmask, AF_INET)) {
+        if (!VIR_SOCKET_IS_FAMILY(&def->ipAddress, AF_INET)) {
             virNetworkReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                                   "%s", _("Only IPv4 addresses are supported"));
             goto error;
@@ -493,18 +488,25 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt)
             goto error;
     }
     VIR_FREE(ipAddress);
-    VIR_FREE(netmask);
 
+    netmask = virXPathString("string(./ip[1]/@netmask)", ctxt);
+    if (netmask) {
 
-    /* IPv4 forwarding setup */
-    if (virXPathBoolean("count(./forward) > 0", ctxt)) {
-        if (def->ipAddress.data.sa.sa_family != AF_INET ||
-            def->netmask.data.sa.sa_family != AF_INET) {
-            virNetworkReportError(VIR_ERR_INTERNAL_ERROR,
-                                  "%s", _("Forwarding requested, but no IPv4 address/netmask provided"));
+        if (virSocketParseAddr(netmask, &def->netmask, AF_UNSPEC) < 0)
+            goto error;
+
+        /* XXX someday we want IPv6, so will need to relax this */
+        if (!VIR_SOCKET_IS_FAMILY(&def->netmask, AF_INET)) {
+            virNetworkReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                  "%s", _("Only IPv4 addresses are supported"));
             goto error;
         }
+    }
+    VIR_FREE(netmask);
+
 
+    /* IPv4 forwarding setup */
+    if (virXPathBoolean("count(./forward) > 0", ctxt)) {
         tmp = virXPathString("string(./forward[1]/@mode)", ctxt);
         if (tmp) {
             if ((def->forwardType = virNetworkForwardTypeFromString(tmp)) < 0) {