conf: Introduce 'readonly' element into xml for NVDIMM memory

The 'readonly' option allows users to mark vNVDIMM read-only:

<devices>
  ...
  <memory model='nvdimm' access='shared'>
      <source>
          <path>/dev/dax0.0</path>
      </source>
      <target>
          <size unit='MiB'>4094</size>
          <node>0</node>
          <label>
              <size unit='MiB'>2</size>
          </label>
          <readonly/>
      </target>
  </memory>
  ...
</devices>

Signed-off-by: Luyao Zhong <luyao.zhong@intel.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>

docs/formatdomain.html.in

@@ -8330,6 +8330,7 @@ qemu-kvm -net nic,model=? /dev/null
       <label>
         <size unit='KiB'>128</size>
       </label>
+      <readonly/>
     </target>
   </memory>
   <memory model='nvdimm'>
@@ -8464,6 +8465,13 @@ qemu-kvm -net nic,model=? /dev/null
           attach the memory to. The element shall be used only if the guest has
           NUMA nodes configured.
         </p>
+        <p>
+          The following optional elements may be used:
+        </p>
+
+        <dl>
+          <dt><code>label</code></dt>
+          <dd>
             <p>
               For NVDIMM type devices one can optionally use
               <code>label</code> and its subelement <code>size</code>
@@ -8475,10 +8483,23 @@ qemu-kvm -net nic,model=? /dev/null
             </p>
             <ol>
               <li>the minimum label size is 128KiB,</li>
-          <li>the remaining size (total-size - label-size) has to be aligned to
+              <li>the remaining size (total-size - label-size) will be aligned
-            4KiB</li>
+                to 4KiB as default.</li>
             </ol>
           </dd>
+
+          <dt><code>readonly</code></dt>
+          <dd>
+            <p>
+              The <code>readonly</code> element is used to mark the vNVDIMM
+              as read-only. Only the real NVDIMM device backend can guarantee
+              the guest write persistence, so other backend types should use
+              the <code>readonly</code> element.
+              <span class="since">Since 5.0.0</span>
+            </p>
+          </dd>
+        </dl>
+      </dd>
     </dl>
 
     <h4><a id="elementsIommu">IOMMU devices</a></h4>

docs/schemas/domaincommon.rng

@@ -5422,6 +5422,11 @@
             </element>
           </element>
         </optional>
+        <optional>
+          <element name="readonly">
+            <empty/>
+          </element>
+        </optional>
       </interleave>
     </element>
   </define>

src/conf/domain_conf.c

@@ -15844,6 +15844,9 @@ virDomainMemoryTargetDefParseXML(xmlNodePtr node,
                            _("label size must be smaller than NVDIMM size"));
             goto cleanup;
         }
+
+        if (virXPathBoolean("boolean(./readonly)", ctxt))
+            def->readonly = true;
     }
 
     ret = 0;
@@ -22766,6 +22769,13 @@ virDomainMemoryDefCheckABIStability(virDomainMemoryDefPtr src,
                              "source NVDIMM pmem flag"));
             return false;
         }
+
+        if (src->readonly != dst->readonly) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("Target NVDIMM readonly flag doesn't match "
+                             "source NVDIMM readonly flag"));
+            return false;
+        }
     }
 
     return virDomainDeviceInfoCheckABIStability(&src->info, &dst->info);
@@ -26344,6 +26354,8 @@ virDomainMemoryTargetDefFormat(virBufferPtr buf,
         virBufferAdjustIndent(buf, -2);
         virBufferAddLit(buf, "</label>\n");
     }
+    if (def->readonly)
+        virBufferAddLit(buf, "<readonly/>\n");
 
     virBufferAdjustIndent(buf, -2);
     virBufferAddLit(buf, "</target>\n");

src/conf/domain_conf.h

@@ -2155,6 +2155,7 @@ struct _virDomainMemoryDef {
     int targetNode;
     unsigned long long size; /* kibibytes */
     unsigned long long labelsize; /* kibibytes; valid only for NVDIMM */
+    bool readonly; /* valid only for NVDIMM */
 
     virDomainDeviceInfo info;
 };

tests/qemuxml2argvdata/memory-hotplug-nvdimm-readonly.xml

@@ -0,0 +1,58 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <maxMemory slots='16' unit='KiB'>1099511627776</maxMemory>
+  <memory unit='KiB'>1267710</memory>
+  <currentMemory unit='KiB'>1267710</currentMemory>
+  <vcpu placement='static' cpuset='0-1'>2</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <idmap>
+    <uid start='0' target='1000' count='10'/>
+    <gid start='0' target='1000' count='10'/>
+  </idmap>
+  <cpu>
+    <topology sockets='2' cores='1' threads='1'/>
+    <numa>
+      <cell id='0' cpus='0-1' memory='219136' unit='KiB'/>
+    </numa>
+  </cpu>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <disk type='block' device='disk'>
+      <driver name='qemu' type='raw'/>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </memballoon>
+    <memory model='nvdimm' access='private'>
+      <source>
+        <path>/tmp/nvdimm</path>
+      </source>
+      <target>
+        <size unit='KiB'>523264</size>
+        <node>0</node>
+        <readonly/>
+      </target>
+      <address type='dimm' slot='0'/>
+    </memory>
+  </devices>
+</domain>

tests/qemuxml2xmloutdata/memory-hotplug-nvdimm-readonly.xml

@@ -0,0 +1 @@
+../qemuxml2argvdata/memory-hotplug-nvdimm-readonly.xml

tests/qemuxml2xmltest.c

@@ -1118,6 +1118,7 @@ mymain(void)
     DO_TEST("memory-hotplug-nvdimm-label", NONE);
     DO_TEST("memory-hotplug-nvdimm-align", NONE);
     DO_TEST("memory-hotplug-nvdimm-pmem", NONE);
+    DO_TEST("memory-hotplug-nvdimm-readonly", NONE);
     DO_TEST("net-udp", NONE);
 
     DO_TEST("video-virtio-gpu-device", NONE);