[libvirt] [PATCH 4/5] util: XML: Introduce automatic reset of XPath's current node

[Peter Krempa]

Quite a few parts modify the XPath context current node to shif the
scope and allow easier queries. This also means that the node needs
to be restored afterwards.

Introduce a macro based on 'VIR_AUTOCLEAN' which adds a local structure
on the stack remembering the original node along with a function which
will make sure that the node is reset when the local structure leaves
scope.

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 src/libvirt_private.syms |  1 +
 src/util/virxml.c        | 10 ++++++++++
 src/util/virxml.h        | 22 ++++++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 038a744981..ee5d9957b0 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -3246,6 +3246,7 @@ virXMLValidatorFree;
 virXMLValidatorInit;
 virXMLValidatorValidate;
 virXPathBoolean;
+virXPathContextNodeRestore;
 virXPathInt;
 virXPathLong;
 virXPathLongHex;
diff --git a/src/util/virxml.c b/src/util/virxml.c
index 8eb201fddf..f55b9a362c 100644
--- a/src/util/virxml.c
+++ b/src/util/virxml.c
@@ -1398,3 +1398,13 @@ virXMLFormatElement(virBufferPtr buf,
     virBufferFreeAndReset(childBuf);
     return ret;
 }
+
+
+void
+virXPathContextNodeRestore(virXPathContextNodeSavePtr save)
+{
+    if (!save->ctxt)
+        return;
+
+    save->ctxt->node = save->node;
+}
diff --git a/src/util/virxml.h b/src/util/virxml.h
index 23a4da1b7e..1bd2c0e518 100644
--- a/src/util/virxml.h
+++ b/src/util/virxml.h
@@ -219,4 +219,26 @@ virXMLFormatElement(virBufferPtr buf,
                     virBufferPtr attrBuf,
                     virBufferPtr childBuf);

+struct _virXPathContextNodeSave {
+    xmlXPathContextPtr ctxt;
+    xmlNodePtr node;
+};
+typedef struct _virXPathContextNodeSave virXPathContextNodeSave;
+typedef virXPathContextNodeSave *virXPathContextNodeSavePtr;
+
+void
+virXPathContextNodeRestore(virXPathContextNodeSavePtr save);
+
+VIR_DEFINE_AUTOCLEAN_FUNC(virXPathContextNodeSave, virXPathContextNodeRestore);
+
+/**
+ * VIR_XPATH_NODE_AUTORESTORE:
+ * @ctxt: XML XPath context pointer
+ *
+ * This macro ensures that when the scope where it's used ends @ctxt's current
+ * node pointer is reset to the original value when this macro was used.
+ */
+# define VIR_XPATH_NODE_AUTORESTORE(ctxt) \
+    VIR_AUTOCLEAN(virXPathContextNodeSave) ctxt ## CtxtSave = {(ctxt), (ctxt)->node}
+
 #endif /* LIBVIRT_VIRXML_H */
-- 
2.20.1