lib: introduce the yang_dnode_iterate helper

Implement helper function that iterates over data nodes that satisfy
XPath query.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

lib/yang.c

@@ -448,6 +448,32 @@ bool yang_dnode_exists(const struct lyd_node *dnode, const char *xpath_fmt, ...)
 	return found;
 }
 
+void yang_dnode_iterate(yang_dnode_iter_cb cb, void *arg,
+			const struct lyd_node *dnode, const char *xpath_fmt,
+			...)
+{
+	va_list ap;
+	char xpath[XPATH_MAXLEN];
+	struct ly_set *set;
+
+	va_start(ap, xpath_fmt);
+	vsnprintf(xpath, sizeof(xpath), xpath_fmt, ap);
+	va_end(ap);
+
+	set = lyd_find_path(dnode, xpath);
+	assert(set);
+	for (unsigned int i = 0; i < set->number; i++) {
+		int ret;
+
+		dnode = set->set.d[i];
+		ret = (*cb)(dnode, arg);
+		if (ret == YANG_ITER_STOP)
+			return;
+	}
+
+	ly_set_free(set);
+}
+
 bool yang_dnode_is_default(const struct lyd_node *dnode, const char *xpath_fmt,
 			   ...)
 {

lib/yang.h

@@ -107,6 +107,9 @@ enum yang_iter_flags {
 /* Callback used by the yang_snodes_iterate_*() family of functions. */
 typedef int (*yang_iterate_cb)(const struct lys_node *snode, void *arg);
 
+/* Callback used by the yang_dnode_iterate() function. */
+typedef int (*yang_dnode_iter_cb)(const struct lyd_node *dnode, void *arg);
+
 /* Return values of the 'yang_iterate_cb' callback. */
 #define YANG_ITER_CONTINUE 0
 #define YANG_ITER_STOP -1
@@ -357,6 +360,25 @@ extern struct lyd_node *yang_dnode_get(const struct lyd_node *dnode,
 extern bool yang_dnode_exists(const struct lyd_node *dnode,
 			      const char *xpath_fmt, ...);
 
+/*
+ * Iterate over all libyang data nodes that satisfy an XPath query.
+ *
+ * cb
+ *    Function to call with each data node.
+ *
+ * arg
+ *    Arbitrary argument passed as the second parameter in each call to 'cb'.
+ *
+ * dnode
+ *    Base libyang data node to operate on.
+ *
+ * xpath_fmt
+ *    XPath expression (absolute or relative).
+ */
+void yang_dnode_iterate(yang_dnode_iter_cb cb, void *arg,
+			const struct lyd_node *dnode, const char *xpath_fmt,
+			...);
+
 /*
  * Check if the libyang data node contains a default value. Non-presence
  * containers are assumed to always contain a default value.