util: storage: split function for JSON backing volume parsing in two

Split virStorageSourceParseBackingJSON into two functions so that the
core can be reused by other functions. The new function called
virStorageSourceParseBackingJSONInternal accepts virJSONValuePtr.
Signed-off-by: NTomáš Golembiovský <tgolembi@redhat.com>

src/util/virstoragefile.c

@@ -3053,29 +3053,28 @@ virStorageSourceParseBackingJSONDeflatten(virJSONValuePtr json)
 
 
 static int
-virStorageSourceParseBackingJSON(virStorageSourcePtr src,
-                                 const char *json)
+virStorageSourceParseBackingJSONInternal(virStorageSourcePtr src,
+                                         virJSONValuePtr json)
 {
-    virJSONValuePtr root = NULL;
     virJSONValuePtr fixedroot = NULL;
     virJSONValuePtr file;
     const char *drvname;
+    char *str = NULL;
     size_t i;
     int ret = -1;
 
-    if (!(root = virJSONValueFromString(json)))
-        return -1;
-
-    if (!(file = virJSONValueObjectGetObject(root, "file"))) {
-        if (!(fixedroot = virStorageSourceParseBackingJSONDeflatten(root)))
+    if (!(file = virJSONValueObjectGetObject(json, "file"))) {
+        if (!(fixedroot = virStorageSourceParseBackingJSONDeflatten(json)))
             goto cleanup;
 
         file = fixedroot;
     }
 
     if (!(drvname = virJSONValueObjectGetString(file, "driver"))) {
-        virReportError(VIR_ERR_INVALID_ARG, _("JSON backing volume defintion "
-                                              "'%s' lacks driver name"), json);
+        str = virJSONValueToString(json, false);
+        virReportError(VIR_ERR_INVALID_ARG,
+                       _("JSON backing volume defintion '%s' lacks driver name"),
+                       NULLSTR(str));
         goto cleanup;
     }
 
@@ -3091,12 +3090,29 @@ virStorageSourceParseBackingJSON(virStorageSourcePtr src,
                      "driver '%s'"), drvname);
 
  cleanup:
-    virJSONValueFree(root);
+    VIR_FREE(str);
     virJSONValueFree(fixedroot);
     return ret;
 }
 
 
+static int
+virStorageSourceParseBackingJSON(virStorageSourcePtr src,
+                                 const char *json)
+{
+    virJSONValuePtr root = NULL;
+    int ret = -1;
+
+    if (!(root = virJSONValueFromString(json)))
+        return -1;
+
+    ret = virStorageSourceParseBackingJSONInternal(src, root);
+
+    virJSONValueFree(root);
+    return ret;
+}
+
+
 virStorageSourcePtr
 virStorageSourceNewFromBackingAbsolute(const char *path)
 {