[PATCH] build: fix build with older libxml2

[Eric Blake <eblake@xxxxxxxxxx>]

On RHEL 5, with libxml2-2.6.26, the build failed with:
virsh.c: In function 'vshNodeIsSuperset':
virsh.c:11951: warning: implicit declaration of function 'xmlChildElementCount'

(or if warnings aren't errors, a link failure later on).

* src/util/xml.h (virXMLChildElementCount): New prototype.
* src/util/xml.c (virXMLChildElementCount): New function.
* src/libvirt_private.syms (xml.h): Export it.
* tools/virsh.c (vshNodeIsSuperset): Use it.
---

I haven't decided yet whether this is trivial enough to push under
the build-breaker rule, but it did fix my build on RHEL 5.

 src/libvirt_private.syms |    1 +
 src/util/xml.c           |   20 ++++++++++++++++++++
 src/util/xml.h           |    1 +
 tools/virsh.c            |    9 +++++----
 4 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 99a1099..a81c230 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1400,6 +1400,7 @@ virTimeStringThenRaw;


 # xml.h
+virXMLChildElementCount;
 virXMLParseHelper;
 virXMLPropString;
 virXMLSaveFile;
diff --git a/src/util/xml.c b/src/util/xml.c
index 4e98b05..2909e85 100644
--- a/src/util/xml.c
+++ b/src/util/xml.c
@@ -833,3 +833,23 @@ virXMLSaveFile(const char *path,

     return virFileRewrite(path, S_IRUSR | S_IWUSR, virXMLRewriteFile, &data);
 }
+
+/* Returns the number of children of node, or -1 on error.  */
+long
+virXMLChildElementCount(xmlNodePtr node)
+{
+    long ret = 0;
+    xmlNodePtr cur = NULL;
+
+    /* xmlChildElementCount returns 0 on error, which isn't helpful;
+     * besides, it is not available in libxml2 2.6.  */
+    if (!node || node->type != XML_ELEMENT_NODE)
+        return -1;
+    cur = node->children;
+    while (cur) {
+        if (cur->type == XML_ELEMENT_NODE)
+            ret++;
+        cur = cur->next;
+    }
+    return ret;
+}
diff --git a/src/util/xml.h b/src/util/xml.h
index c492063..a3750fa 100644
--- a/src/util/xml.h
+++ b/src/util/xml.h
@@ -52,6 +52,7 @@ int              virXPathNodeSet(const char *xpath,
                                  xmlNodePtr **list);
 char *          virXMLPropString(xmlNodePtr node,
                                  const char *name);
+long     virXMLChildElementCount(xmlNodePtr node);

 /* Internal function; prefer the macros below.  */
 xmlDocPtr      virXMLParseHelper(int domcode,
diff --git a/tools/virsh.c b/tools/virsh.c
index d02be5c..a51478f 100644
--- a/tools/virsh.c
+++ b/tools/virsh.c
@@ -11919,7 +11919,7 @@ vshNodeIsSuperset(xmlNodePtr n1, xmlNodePtr n2)
     bool found;
     bool visited;
     bool ret = false;
-    unsigned long n1_child_size, n2_child_size, n1_iter;
+    long n1_child_size, n2_child_size, n1_iter;
     virBitmapPtr bitmap;

     if (!n1 && !n2)
@@ -11948,9 +11948,10 @@ vshNodeIsSuperset(xmlNodePtr n1, xmlNodePtr n2)
         attr = attr->next;
     }

-    n1_child_size = xmlChildElementCount(n1);
-    n2_child_size = xmlChildElementCount(n2);
-    if (n1_child_size < n2_child_size)
+    n1_child_size = virXMLChildElementCount(n1);
+    n2_child_size = virXMLChildElementCount(n2);
+    if (n1_child_size < 0 || n2_child_size < 0 ||
+        n1_child_size < n2_child_size)
         return false;

     if (n1_child_size == 0 && n2_child_size == 0)
-- 
1.7.7.3

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