conf: domaincaps: Add 'backup' feature flag

This flag will allow figuring out whether the hypervisor supports the
incremental backup and checkpoint features.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

docs/formatdomaincaps.html.in

@@ -517,6 +517,7 @@
     <vmcoreinfo supported='yes'/>
     <genid supported='yes'/>
     <backingStoreInput supported='yes'/>
+    <backup supported='yes'/>
     <sev>
       <cbitpos>47</cbitpos>
       <reduced-phys-bits>1</reduced-phys-bits>
@@ -560,6 +561,13 @@
     the disk to a running guest, or similar.
     </p>
 
+    <h4><a id="featureBackup">backup</a></h4>
+
+    <p>Reports whether the hypervisor supports the backup, checkpoint, and
+    related features. (<code>virDomainBackupBegin</code>,
+    <code>virDomainCheckpointCreateXML</code> etc).
+    </p>
+
     <h4><a id="elementsSEV">SEV capabilities</a></h4>
 
     <p>AMD Secure Encrypted Virtualization (SEV) capabilities are exposed under

docs/schemas/domaincaps.rng

@@ -210,6 +210,9 @@
       <optional>
         <ref name='backingStoreInput'/>
       </optional>
+      <optional>
+        <ref name='backup'/>
+      </optional>
       <optional>
         <ref name='sev'/>
       </optional>
@@ -241,6 +244,12 @@
     </element>
   </define>
 
+  <define name='backup'>
+    <element name='backup'>
+      <ref name='supported'/>
+    </element>
+  </define>
+
   <define name='sev'>
     <element name='sev'>
       <ref name='supported'/>

src/conf/domain_capabilities.c

@@ -41,6 +41,7 @@ VIR_ENUM_IMPL(virDomainCapsFeature,
               "vmcoreinfo",
               "genid",
               "backingStoreInput",
+              "backup",
 );
 
 static virClassPtr virDomainCapsClass;

src/conf/domain_capabilities.h

@@ -163,6 +163,7 @@ typedef enum {
     VIR_DOMAIN_CAPS_FEATURE_VMCOREINFO,
     VIR_DOMAIN_CAPS_FEATURE_GENID,
     VIR_DOMAIN_CAPS_FEATURE_BACKING_STORE_INPUT,
+    VIR_DOMAIN_CAPS_FEATURE_BACKUP,
 
     VIR_DOMAIN_CAPS_FEATURE_LAST
 } virDomainCapsFeature;