conf: Add support for parsing and formatting max memory and slot count

Add a XML element that will allow to specify maximum supportable memory
and the count of memory slots to use with memory hotplug.

To avoid possible confusion and misuse of the new element this patch
also explicitly forbids the use of the maxMemory setting in individual
drivers's post parse callbacks. This limitation will be lifted when the
support is implemented.

docs/formatdomain.html.in

@@ -675,6 +675,7 @@
 <pre>
 &lt;domain&gt;
   ...
+  &lt;maxMemory slots='16' unit='KiB'&gt;1524288&lt;/maxMemory&gt;
   &lt;memory unit='KiB'&gt;524288&lt;/memory&gt;
   &lt;currentMemory unit='KiB'&gt;524288&lt;/currentMemory&gt;
   ...
@@ -708,6 +709,25 @@
         <span class='since'><code>unit</code> since 0.9.11</span>,
         <span class='since'><code>dumpCore</code> since 0.10.2
         (QEMU only)</span></dd>
+      <dt><code>maxMemory</code></dt>
+      <dd>The run time maximum memory allocation of the guest. The initial
+        memory specified by either the <code>&lt;memory&gt;</code> element or
+        the NUMA cell size configuration can be increased by hot-plugging of
+        memory to the limit specified by this element.
+
+        The <code>unit</code> attribute behaves the same as for
+        <code>&lt;memory&gt;</code>.
+
+        The <code>slots</code> attribute specifies the number of slots
+        available for adding memory to the guest. The bounds are hypervisor
+        specific.
+
+        Note that due to alignment of the memory chunks added via memory
+        hotplug the full size allocation specified by this element may be
+        impossible to achieve.
+        <span class='since'>Since 1.2.14</span>
+      </dd>
+
       <dt><code>currentMemory</code></dt>
       <dd>The actual allocation of memory for the guest. This value can
         be less than the maximum allocation, to allow for ballooning

docs/schemas/domaincommon.rng

@@ -592,6 +592,14 @@
           </optional>
         </element>
       </optional>
+      <optional>
+        <element name="maxMemory">
+          <ref name="scaledInteger"/>
+          <attribute name="slots">
+            <ref name="unsignedInt"/>
+          </attribute>
+        </element>
+      </optional>
       <optional>
         <element name="currentMemory">
           <ref name='scaledInteger'/>