network: Let domains be restricted to local DNS

This adds a new "localOnly" attribute on the domain element of the
network xml.  With this set to "yes", DNS requests under that domain
will only be resolved by libvirt's dnsmasq, never forwarded upstream.

This was how it worked before commit f69a6b987d616, and I found that
functionality useful.  For example, I have my host's NetworkManager
dnsmasq configured to forward that domain to libvirt's dnsmasq, so I can
easily resolve guest names from outside.  But if libvirt's dnsmasq
doesn't know a name and forwards it to the host, I'd get an endless
forwarding loop.  Now I can set localOnly="yes" to prevent the loop.

Signed-off-by: Josh Stone <jistone@redhat.com>

docs/formatnetwork.html.in

@@ -82,7 +82,7 @@
     <pre>
         ...
         &lt;bridge name="virbr0" stp="on" delay="5" macTableManager="libvirt"/&gt;
-        &lt;domain name="example.com"/&gt;
+        &lt;domain name="example.com" localOnly="no"/&gt;
         &lt;forward mode="nat" dev="eth0"/&gt;
         ...</pre>
 
@@ -151,6 +151,16 @@
         a <code>&lt;forward&gt;</code> mode of "nat" or "route" (or an
         isolated network with no <code>&lt;forward&gt;</code>
         element). <span class="since">Since 0.4.5</span>
+
+        <p>
+          If the optional <code>localOnly</code> attribute on the
+          <code>domain</code> element is "yes", then DNS requests under
+          this domain will only be resolved by the virtual network's own
+          DNS server - they will not be forwarded to the host's upstream
+          DNS server.  If <code>localOnly</code> is "no", and by
+          default, unresolved requests <b>will</b> be forwarded.
+          <span class="since">Since 1.2.12</span>
+        </p>
       </dd>
       <dt><code>forward</code></dt>
       <dd>Inclusion of the <code>forward</code> element indicates that

docs/schemas/network.rng

@@ -234,6 +234,9 @@
         <optional>
           <element name="domain">
             <attribute name="name"><ref name="dnsName"/></attribute>
+            <optional>
+              <attribute name="localOnly"><ref name="virYesNo"/></attribute>
+            </optional>
           </element>
         </optional>
 

src/conf/network_conf.c

@@ -1854,6 +1854,18 @@ virNetworkDefParseXML(xmlXPathContextPtr ctxt)
 
     /* Parse network domain information */
     def->domain = virXPathString("string(./domain[1]/@name)", ctxt);
+    tmp = virXPathString("string(./domain[1]/@localOnly)", ctxt);
+    if (tmp) {
+        def->domainLocalOnly = virTristateBoolTypeFromString(tmp);
+        if (def->domainLocalOnly <= 0) {
+            virReportError(VIR_ERR_XML_ERROR,
+                           _("Invalid domain localOnly setting '%s' "
+                             "in network '%s'"),
+                           tmp, def->name);
+            goto error;
+        }
+        VIR_FREE(tmp);
+    }
 
     if ((bandwidthNode = virXPathNode("./bandwidth", ctxt)) &&
         virNetDevBandwidthParse(&def->bandwidth, bandwidthNode, -1) < 0)
@@ -2560,8 +2572,24 @@ virNetworkDefFormatBuf(virBufferPtr buf,
         virBufferAsprintf(buf, "<mac address='%s'/>\n", macaddr);
     }
 
-    if (def->domain)
-        virBufferAsprintf(buf, "<domain name='%s'/>\n", def->domain);
+    if (def->domain) {
+        virBufferAsprintf(buf, "<domain name='%s'", def->domain);
+
+        /* default to "no", but don't format it in the XML */
+        if (def->domainLocalOnly) {
+            const char *local = virTristateBoolTypeToString(def->domainLocalOnly);
+
+            if (!local) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("Unknown localOnly type %d in network"),
+                               def->domainLocalOnly);
+                return -1;
+            }
+            virBufferAsprintf(buf, " localOnly='%s'", local);
+        }
+
+        virBufferAddLit(buf, "/>\n");
+    }
 
     if (virNetworkDNSDefFormat(buf, &def->dns) < 0)
         goto error;

src/conf/network_conf.h

@@ -225,6 +225,7 @@ struct _virNetworkDef {
     char *bridge;       /* Name of bridge device */
     int  macTableManager; /* enum virNetworkBridgeMACTableManager */
     char *domain;
+    int domainLocalOnly; /* enum virTristateBool: yes disables dns forwarding */
     unsigned long delay;   /* Bridge forward delay (ms) */
     bool stp; /* Spanning tree protocol */
     virMacAddr mac; /* mac address of bridge device */

src/network/bridge_driver.c

@@ -928,6 +928,11 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
     }
 
     if (network->def->domain) {
+        if (network->def->domainLocalOnly == VIR_TRISTATE_BOOL_YES) {
+            virBufferAsprintf(&configbuf,
+                              "local=/%s/\n",
+                              network->def->domain);
+        }
         virBufferAsprintf(&configbuf,
                           "domain=%s\n"
                           "expand-hosts\n",

tests/networkxml2confdata/nat-network-dns-local-domain.conf

@@ -0,0 +1,14 @@
+##WARNING:  THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
+##OVERWRITTEN AND LOST.  Changes to this configuration should be made using:
+##    virsh net-edit default
+## or other application using the libvirt API.
+##
+## dnsmasq conf file created by libvirt
+strict-order
+local=/example.com/
+domain=example.com
+expand-hosts
+except-interface=lo
+bind-dynamic
+interface=virbr0
+addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts

tests/networkxml2confdata/nat-network-dns-local-domain.xml

@@ -0,0 +1,9 @@
+<network>
+  <name>default</name>
+  <uuid>81ff0d90-c91e-6742-64da-4a736edb9a9c</uuid>
+  <forward dev='eth0' mode='nat'/>
+  <bridge name='virbr0' stp='on' delay='0' />
+  <domain name='example.com' localOnly='yes'/>
+  <ip address='192.168.122.1' netmask='255.255.255.0'>
+  </ip>
+</network>

tests/networkxml2conftest.c

@@ -134,6 +134,7 @@ mymain(void)
     DO_TEST("nat-network-dns-hosts", full);
     DO_TEST("nat-network-dns-forward-plain", full);
     DO_TEST("nat-network-dns-forwarders", full);
+    DO_TEST("nat-network-dns-local-domain", full);
     DO_TEST("dhcp6-network", dhcpv6);
     DO_TEST("dhcp6-nat-network", dhcpv6);
     DO_TEST("dhcp6host-routed-network", dhcpv6);