conf: introduce WithDefault function

This patch introduces a new set of functions to the ConfGetChildValue
family. They permit to look under a default node if looking under
base node as failed. This will be used to access to default parameters
for a data type (for instance, first usage will be interface).

src/conf.c

@@ -286,6 +286,17 @@ int ConfGetChildValue(ConfNode *base, char *name, char **vptr)
     }
 }
 
+
+int ConfGetChildValueWithDefault(ConfNode *base, ConfNode *dflt, char *name, char **vptr)
+{
+    int ret = ConfGetChildValue(base, name, vptr);
+    /* Get 'default' value */
+    if (ret == 0 && dflt) {
+        return ConfGetChildValue(dflt, name, vptr);
+    }
+    return ret;
+}
+
 /**
  * \brief Retrieve a configuration value as an integer.
  *
@@ -337,6 +348,15 @@ int ConfGetChildValueInt(ConfNode *base, char *name, intmax_t *val)
 
 }
 
+int ConfGetChildValueIntWithDefault(ConfNode *base, ConfNode *dflt, char *name, intmax_t *val)
+{
+    int ret = ConfGetChildValueInt(base, name, val);
+    /* Get 'default' value */
+    if (ret == 0 && dflt) {
+        return ConfGetChildValueInt(dflt, name, val);
+    }
+    return ret;
+}
 
 
 /**
@@ -376,6 +396,17 @@ int ConfGetChildValueBool(ConfNode *base, char *name, int *val)
     return 1;
 }
 
+int ConfGetChildValueBoolWithDefault(ConfNode *base, ConfNode *dflt, char *name, int *val)
+{
+    int ret = ConfGetChildValueBool(base, name, val);
+    /* Get 'default' value */
+    if (ret == 0 && dflt) {
+        return ConfGetChildValueBool(dflt, name, val);
+    }
+    return ret;
+}
+
+
 /**
  * \brief Check if a value is true.
  *

src/conf.h

@@ -80,6 +80,9 @@ ConfNode *ConfNodeLookupKeyValue(ConfNode *base, const char *key, const char *va
 int ConfGetChildValue(ConfNode *base, char *name, char **vptr);
 int ConfGetChildValueInt(ConfNode *base, char *name, intmax_t *val);
 int ConfGetChildValueBool(ConfNode *base, char *name, int *val);
+int ConfGetChildValueWithDefault(ConfNode *base, ConfNode *dflt, char *name, char **vptr);
+int ConfGetChildValueIntWithDefault(ConfNode *base, ConfNode *dflt, char *name, intmax_t *val);
+int ConfGetChildValueBoolWithDefault(ConfNode *base, ConfNode *dflt, char *name, int *val);
 char *ConfLoadCompleteIncludePath(char *);
 
 #endif /* ! __CONF_H__ */