util: buffer: Add init macro for automatically setting child XML indent

Add a new macro which initializes a virBuffer on the stack and also sets
the indent level to be used for child XML element formatting.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/util/virbuffer.h

@@ -35,6 +35,15 @@ typedef virBuffer *virBufferPtr;
 
 #define VIR_BUFFER_INITIALIZER { NULL, 0 }
 
+/**
+ * VIR_BUFFER_INIT_CHILD:
+ * @parentbuf: parent buffer for XML element formatting
+ *
+ * Intitialize a virBuffer structure and set up the indentation level for
+ * formatting XML subelements of @parentbuf.
+ */
+#define VIR_BUFFER_INIT_CHILD(parentbuf) { NULL, (parentbuf)->indent + 2 }
+
 struct _virBuffer {
     GString *str;
     int indent;