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[libvirt] [PATCH] 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>
Cc: Laine Stump <laine laine org>
---
 docs/formatnetwork.html.in                                 | 12 +++++++++++-
 docs/schemas/network.rng                                   |  3 +++
 src/conf/network_conf.c                                    |  5 +++++
 src/conf/network_conf.h                                    |  1 +
 src/network/bridge_driver.c                                |  5 +++++
 .../networkxml2confdata/nat-network-dns-local-domain.conf  | 14 ++++++++++++++
 tests/networkxml2confdata/nat-network-dns-local-domain.xml |  9 +++++++++
 tests/networkxml2conftest.c                                |  1 +
 8 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 tests/networkxml2confdata/nat-network-dns-local-domain.conf
 create mode 100644 tests/networkxml2confdata/nat-network-dns-local-domain.xml

diff --git a/docs/formatnetwork.html.in b/docs/formatnetwork.html.in
index dc438aee8622..defcdba00930 100644
--- a/docs/formatnetwork.html.in
+++ b/docs/formatnetwork.html.in
@@ -82,7 +82,7 @@
     <pre>
         ...
         &lt;bridge name="virbr0" stp="on" delay="5"/&gt;
-        &lt;domain name="example.com"/&gt;
+        &lt;domain name="example.com" localOnly="no"/&gt;
         &lt;forward mode="nat" dev="eth0"/&gt;
         ...</pre>
 
@@ -113,6 +113,16 @@
         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 1.2.11</span>
+        </p>
       </dd>
       <dt><code>forward</code></dt>
       <dd>Inclusion of the <code>forward</code> element indicates that
diff --git a/docs/schemas/network.rng b/docs/schemas/network.rng
index 4546f8037580..a1da28092375 100644
--- a/docs/schemas/network.rng
+++ b/docs/schemas/network.rng
@@ -225,6 +225,9 @@
         <optional>
           <element name="domain">
             <attribute name="name"><ref name="dnsName"/></attribute>
+            <optional>
+              <attribute name="localOnly"><ref name="virYesNo"/></attribute>
+            </optional>
           </element>
         </optional>
 
diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c
index 067334e87cb0..61451c39805f 100644
--- a/src/conf/network_conf.c
+++ b/src/conf/network_conf.c
@@ -2083,6 +2083,11 @@ 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->domain_local = STRCASEEQ(tmp, "yes");
+        VIR_FREE(tmp);
+    }
 
     if ((bandwidthNode = virXPathNode("./bandwidth", ctxt)) != NULL &&
         (def->bandwidth = virNetDevBandwidthParse(bandwidthNode, -1)) == NULL)
diff --git a/src/conf/network_conf.h b/src/conf/network_conf.h
index 660cd2d10cd1..6308a7dcfbf7 100644
--- a/src/conf/network_conf.h
+++ b/src/conf/network_conf.h
@@ -232,6 +232,7 @@ struct _virNetworkDef {
 
     char *bridge;       /* Name of bridge device */
     char *domain;
+    bool domain_local; /* Choose not to forward dns for this domain */
     unsigned long delay;   /* Bridge forward delay (ms) */
     bool stp; /* Spanning tree protocol */
     virMacAddr mac; /* mac address of bridge device */
diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index 6cb421c52850..dfa375d3aa72 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -912,6 +912,11 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
     }
 
     if (network->def->domain) {
+        if (network->def->domain_local) {
+            virBufferAsprintf(&configbuf,
+                              "local=/%s/\n",
+                              network->def->domain);
+        }
         virBufferAsprintf(&configbuf,
                           "domain=%s\n"
                           "expand-hosts\n",
diff --git a/tests/networkxml2confdata/nat-network-dns-local-domain.conf b/tests/networkxml2confdata/nat-network-dns-local-domain.conf
new file mode 100644
index 000000000000..5f41b9186cbc
--- /dev/null
+++ b/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
diff --git a/tests/networkxml2confdata/nat-network-dns-local-domain.xml b/tests/networkxml2confdata/nat-network-dns-local-domain.xml
new file mode 100644
index 000000000000..a92d71f1f2f6
--- /dev/null
+++ b/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>
diff --git a/tests/networkxml2conftest.c b/tests/networkxml2conftest.c
index 4f1d9345ffe4..d2aa8c62cfcd 100644
--- a/tests/networkxml2conftest.c
+++ b/tests/networkxml2conftest.c
@@ -146,6 +146,7 @@ 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);
-- 
2.1.0


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