conf: Introduce @access to <memory/>

Now that NVDIMM has found its way into libvirt, users might want
to fine tune some settings for each module separately. One such
setting is 'share=on|off' for the memory-backend-file object.
This setting - just like its name suggest already - enables
sharing the nvdimm module with other applications. Under the hood
it controls whether qemu mmaps() the file as MAP_PRIVATE or
MAP_SHARED.

Yet again, we have such config knob in domain XML, but it's just
an attribute to numa <cell/>. This does not give fine enough
tuning on per-memdevice basis so we need to have the attribute
for each device too.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatdomain.html.in

@@ -1417,7 +1417,7 @@
       <span class='since'>Since 1.2.9</span> the optional attribute
       <code>memAccess</code> can control whether the memory is to be
       mapped as "shared" or "private".  This is valid only for
-      hugepages-backed memory.
+      hugepages-backed memory and nvdimm modules.
     </p>
 
     <p>
@@ -7100,7 +7100,7 @@ qemu-kvm -net nic,model=? /dev/null
 <pre>
 ...
 &lt;devices&gt;
-  &lt;memory model='dimm'&gt;
+  &lt;memory model='dimm' access='private'&gt;
     &lt;target&gt;
       &lt;size unit='KiB'&gt;524287&lt;/size&gt;
       &lt;node&gt;0&lt;/node&gt;
@@ -7139,6 +7139,18 @@ qemu-kvm -net nic,model=? /dev/null
         </p>
       </dd>
 
+      <dt><code>access</code></dt>
+      <dd>
+        <p>
+          An optional attribute <code>access</code>
+          (<span class="since">since 3.2.0</span>) that provides
+          capability to fine tune mapping of the memory on per
+          module basis. Values are the same as
+          <a href="#elementsMemoryBacking">Memory Backing</a>:
+          <code>shared</code> and <code>private</code>.
+        </p>
+      </dd>
+
       <dt><code>source</code></dt>
       <dd>
         <p>

docs/schemas/domaincommon.rng

@@ -4750,6 +4750,14 @@
           <value>nvdimm</value>
         </choice>
       </attribute>
+      <optional>
+        <attribute name="access">
+          <choice>
+            <value>shared</value>
+            <value>private</value>
+          </choice>
+        </attribute>
+      </optional>
       <interleave>
         <optional>
           <ref name="memorydev-source"/>