Document and parser support for the Virtio free page reporting feature.

This will add the proper documentation and parser support for the free page
reporting feature that is introduced in QEMU 5.1.

Signed-off-by: Nico Pache <npache@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatdomain.rst

@@ -6755,6 +6755,12 @@ Example: manually added device with static PCI slot 2 requested
    release some memory at the last moment before a guest's process get killed by
    Out of Memory killer. :since:`Since 1.3.1, QEMU and KVM only`
 
+``free-page-reporting``
+   The optional ``free-page-reporting`` attribute allows to enable/disable
+   ("on"/"off", respectively) the ability of the QEMU virtio memory balloon to
+   return unused pages back to the hypervisor to be used by other guests or
+   processes. :since:`Since 6.9.0, QEMU and KVM only`
+
 ``period``
    The optional ``period`` allows the QEMU virtio memory balloon driver to
    provide statistics through the ``virsh dommemstat           [domain]``

docs/schemas/domaincommon.rng

@@ -4539,6 +4539,11 @@
           <ref name="virOnOff"/>
         </attribute>
       </optional>
+      <optional>
+         <attribute name="free-page-reporting">
+           <ref name="virOnOff"/>
+         </attribute>
+       </optional>
       <interleave>
         <optional>
           <ref name="alias"/>

src/conf/domain_conf.c

@@ -15336,6 +15336,7 @@ virDomainMemballoonDefParseXML(virDomainXMLOptionPtr xmlopt,
     VIR_XPATH_NODE_AUTORESTORE(ctxt)
     unsigned int period = 0;
     g_autofree char *model = NULL;
+    g_autofree char *freepage_reporting = NULL;
     g_autofree char *deflate = NULL;
 
     def = g_new0(virDomainMemballoonDef, 1);
@@ -15360,6 +15361,13 @@ virDomainMemballoonDefParseXML(virDomainXMLOptionPtr xmlopt,
         goto error;
     }
 
+    if ((freepage_reporting = virXMLPropString(node, "free-page-reporting")) &&
+        (def->free_page_reporting = virTristateSwitchTypeFromString(freepage_reporting)) <= 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("invalid free-page-reporting attribute value '%s'"), freepage_reporting);
+        goto error;
+    }
+
     ctxt->node = node;
     if (virXPathUInt("string(./stats/@period)", ctxt, &period) < -1) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
@@ -23538,6 +23546,15 @@ virDomainMemballoonDefCheckABIStability(virDomainMemballoonDefPtr src,
         return false;
     }
 
+    if (src->free_page_reporting != dst->free_page_reporting) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target balloon free-page-reporting attribute value "
+                         "'%s' does not match source '%s'"),
+                       virTristateSwitchTypeToString(dst->free_page_reporting),
+                       virTristateSwitchTypeToString(src->free_page_reporting));
+        return false;
+    }
+
     if (src->virtio && dst->virtio &&
         !virDomainVirtioOptionsCheckABIStability(src->virtio, dst->virtio))
         return false;
@@ -27644,6 +27661,10 @@ virDomainMemballoonDefFormat(virBufferPtr buf,
         virBufferAsprintf(&attrBuf, " autodeflate='%s'",
                           virTristateSwitchTypeToString(def->autodeflate));
 
+    if (def->free_page_reporting != VIR_TRISTATE_SWITCH_ABSENT)
+        virBufferAsprintf(&attrBuf, " free-page-reporting='%s'",
+                          virTristateSwitchTypeToString(def->free_page_reporting));
+
     if (def->period)
         virBufferAsprintf(&childrenBuf, "<stats period='%i'/>\n", def->period);
 

src/conf/domain_conf.h

@@ -1790,6 +1790,7 @@ struct _virDomainMemballoonDef {
     virDomainDeviceInfo info;
     int period; /* seconds between collections */
     int autodeflate; /* enum virTristateSwitch */
+    int free_page_reporting; /* enum virTristateSwitch */
     virDomainVirtioOptionsPtr virtio;
 };