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

[Peter Krempa]

On Tue, Feb 26, 2019 at 18:08:11 +0100, Peter Krempa wrote:
> 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}

Oops, forgot to commit some local changes:

diff --git a/src/util/virxml.h b/src/util/virxml.h
index 1bd2c0e518..72b9d749d0 100644
--- a/src/util/virxml.h
+++ b/src/util/virxml.h
@@ -239,6 +239,7 @@ VIR_DEFINE_AUTOCLEAN_FUNC(virXPathContextNodeSave, virXPathContextNodeRestore);
  * 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}
+    VIR_AUTOCLEAN(virXPathContextNodeSave) ctxt##CtxtSave = {ctxt, ctxt->node}; \
+    ignore_value(&ctxt##CtxtSave)

 #endif /* LIBVIRT_VIRXML_H */


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