conf: Format seclabels for <backingStore>

We parse the seclabels and use them internally so omitting them when
formatting would be misleading. Additionally our schema actually allows
them.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/conf/domain_conf.c

@@ -23876,8 +23876,7 @@ virDomainDiskBackingStoreFormat(virBufferPtr buf,
     virBufferAdjustIndent(buf, 2);
 
     virBufferAsprintf(buf, "<format type='%s'/>\n", format);
-    /* We currently don't output seclabels for backing chain element */
-    if (virDomainDiskSourceFormatInternal(buf, backingStore, 0, flags, false,
+    if (virDomainDiskSourceFormatInternal(buf, backingStore, 0, flags, true,
                                           false, xmlopt) < 0 ||
         virDomainDiskBackingStoreFormat(buf, backingStore->backingStore,
                                         xmlopt, flags) < 0)

tests/qemuxml2argvdata/disk-backing-chains.xml

@@ -38,7 +38,11 @@
           <source file='/tmp/image2.qcow'/>
           <backingStore type='file' index='3'>
             <format type='qcow2'/>
-            <source file='/tmp/image3.qcow'/>
+            <source file='/tmp/image3.qcow'>
+              <seclabel model='selinux' relabel='yes'>
+                <label>system_u:system_r:public_content_t:s0</label>
+              </seclabel>
+            </source>
             <backingStore type='file' index='4'>
               <format type='qcow2'/>
               <source file='/tmp/image4.qcow'/>

tests/qemuxml2xmloutdata/disk-backing-chains-active.xml

@@ -39,7 +39,11 @@
           <source file='/tmp/image2.qcow'/>
           <backingStore type='file' index='3'>
             <format type='qcow2'/>
-            <source file='/tmp/image3.qcow'/>
+            <source file='/tmp/image3.qcow'>
+              <seclabel model='selinux' relabel='yes'>
+                <label>system_u:system_r:public_content_t:s0</label>
+              </seclabel>
+            </source>
             <backingStore type='file' index='4'>
               <format type='qcow2'/>
               <source file='/tmp/image4.qcow'/>

tests/qemuxml2xmloutdata/disk-backing-chains-inactive.xml

@@ -39,7 +39,11 @@
           <source file='/tmp/image2.qcow'/>
           <backingStore type='file'>
             <format type='qcow2'/>
-            <source file='/tmp/image3.qcow'/>
+            <source file='/tmp/image3.qcow'>
+              <seclabel model='selinux' relabel='yes'>
+                <label>system_u:system_r:public_content_t:s0</label>
+              </seclabel>
+            </source>
             <backingStore type='file'>
               <format type='qcow2'/>
               <source file='/tmp/image4.qcow'/>