conf: Prepare making memory device target node optional

Adjust the config code so that it does not enforce that target memory
node is specified. To avoid breakage, adjust the qemu memory hotplug
config checker to disallow such config for now.

docs/formatdomain.html.in

@@ -6300,8 +6300,9 @@ qemu-kvm -net nic,model=? /dev/null
           added memory as a scaled integer.
         </p>
         <p>
-          The mandatory <code>node</code> subelement configures the guest NUMA
-          node to attach the memory to.
+          The <code>node</code> subelement configures the guest NUMA node to
+          attach the memory to. The element shall be used only if the guest has
+          NUMA nodes configured.
         </p>
       </dd>
     </dl>

docs/schemas/domaincommon.rng

@@ -4532,9 +4532,11 @@
         <element name="size">
           <ref name="scaledInteger"/>
         </element>
+        <optional>
           <element name="node">
             <ref name="unsignedInt"/>
           </element>
+        </optional>
       </interleave>
     </element>
   </define>

src/conf/domain_conf.c

@@ -12544,10 +12544,15 @@ virDomainMemoryTargetDefParseXML(xmlNodePtr node,
     int ret = -1;
     xmlNodePtr save = ctxt->node;
     ctxt->node = node;
+    int rv;
 
-    if (virXPathUInt("string(./node)", ctxt, &def->targetNode) < 0) {
+    /* initialize to value which marks that the user didn't specify it */
+    def->targetNode = -1;
+
+    if ((rv = virXPathInt("string(./node)", ctxt, &def->targetNode)) == -2 ||
+        (rv == 0 && def->targetNode < 0)) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
-                       _("invalid or missing value of memory device node"));
+                       _("invalid value of memory device node"));
         goto cleanup;
     }
 
@@ -17711,8 +17716,8 @@ virDomainMemoryDefCheckABIStability(virDomainMemoryDefPtr src,
 
     if (src->targetNode != dst->targetNode) {
         virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
-                       _("Target memory device targetNode '%u' "
-                         "doesn't match source targetNode '%u'"),
+                       _("Target memory device targetNode '%d' "
+                         "doesn't match source targetNode '%d'"),
                        dst->targetNode, src->targetNode);
         return false;
     }
@@ -20802,7 +20807,8 @@ virDomainMemoryTargetDefFormat(virBufferPtr buf,
     virBufferAdjustIndent(buf, 2);
 
     virBufferAsprintf(buf, "<size unit='KiB'>%llu</size>\n", def->size);
-    virBufferAsprintf(buf, "<node>%u</node>\n", def->targetNode);
+    if (def->targetNode >= 0)
+        virBufferAsprintf(buf, "<node>%d</node>\n", def->targetNode);
 
     virBufferAdjustIndent(buf, -2);
     virBufferAddLit(buf, "</target>\n");

src/conf/domain_conf.h

@@ -2022,7 +2022,7 @@ struct _virDomainMemoryDef {
 
     /* target */
     int model; /* virDomainMemoryModel */
-    unsigned int targetNode;
+    int targetNode;
     unsigned long long size; /* kibibytes */
 
     virDomainDeviceInfo info;

src/qemu/qemu_domain.c

@@ -3597,6 +3597,13 @@ qemuDomainDefValidateMemoryHotplugDevice(const virDomainMemoryDef *mem,
             return -1;
         }
 
+        if (mem->targetNode == -1) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("target NUMA node needs to be specified for "
+                             "memory device"));
+            return -1;
+        }
+
         if (mem->info.type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_DIMM) {
             if (mem->info.addr.dimm.slot >= def->mem.memory_slots) {
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED,