conf: domain: support for virtio packed option

Expose the virtio parameter for packed virtqueues as an optional libvirt
XML attribute to virtio-backed devices, e.g.:

    <interface type='user'>
      <mac address='00:11:22:33:44:55'/>
      <model type='virtio'/>
      <driver packed='on'/>
    </interface>

If the attribute is omitted, the default value for this attribute is 'off' and
regular split virtqueues are used.
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.ibm.com>
Signed-off-by: NBjoern Walk <bwalk@linux.ibm.com>
Signed-off-by: NJán Tomko <jtomko@redhat.com>

docs/schemas/domaincommon.rng

@@ -5961,6 +5961,11 @@
         <ref name="virOnOff"/>
       </attribute>
     </optional>
+    <optional>
+      <attribute name="packed">
+        <ref name="virOnOff"/>
+      </attribute>
+    </optional>
   </define>
 
   <define name="usbmaster">

src/conf/domain_conf.c

@@ -1512,6 +1512,16 @@ virDomainVirtioOptionsParseXML(xmlNodePtr driver,
         }
         res->ats = val;
     }
+    VIR_FREE(str);
+
+    if ((str = virXMLPropString(driver, "packed"))) {
+        if ((val = virTristateSwitchTypeFromString(str)) <= 0) {
+            virReportError(VIR_ERR_XML_ERROR, "%s",
+                           _("invalid packed value"));
+            return -1;
+        }
+        res->packed = val;
+    }
 
     return 0;
 }
@@ -5091,6 +5101,12 @@ virDomainCheckVirtioOptions(virDomainVirtioOptionsPtr virtio)
                          "for virtio devices"));
         return -1;
     }
+    if (virtio->packed != VIR_TRISTATE_SWITCH_ABSENT) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("packed driver option is only supported "
+                         "for virtio devices"));
+        return -1;
+    }
     return 0;
 }
 
@@ -7377,6 +7393,10 @@ virDomainVirtioOptionsFormat(virBufferPtr buf,
         virBufferAsprintf(buf, " ats='%s'",
                           virTristateSwitchTypeToString(virtio->ats));
     }
+    if (virtio->packed != VIR_TRISTATE_SWITCH_ABSENT) {
+        virBufferAsprintf(buf, " packed='%s'",
+                          virTristateSwitchTypeToString(virtio->packed));
+    }
 }
 
 
@@ -22415,6 +22435,14 @@ virDomainVirtioOptionsCheckABIStability(virDomainVirtioOptionsPtr src,
                        virTristateSwitchTypeToString(src->ats));
         return false;
     }
+    if (src->packed != dst->packed) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target device packed option '%s' does not "
+                         "match source '%s'"),
+                       virTristateSwitchTypeToString(dst->packed),
+                       virTristateSwitchTypeToString(src->packed));
+        return false;
+    }
     return true;
 }
 

src/conf/domain_conf.h

@@ -2417,6 +2417,7 @@ struct _virDomainVsockDef {
 struct _virDomainVirtioOptions {
     virTristateSwitch iommu;
     virTristateSwitch ats;
+    virTristateSwitch packed;
 };
 
 /*