bootconfig: Support mixing a value and subkeys under a key

Support mixing a value and subkeys under a key. Since kernel cmdline
options will support "aaa.bbb=value1 aaa.bbb.ccc=value2", it is
better that the bootconfig supports such configuration too.

Note that this does not change syntax itself but just accepts
mixed value and subkeys e.g.

key = value1
key.subkey = value2

But this is not accepted;

key {
 value1
 subkey = value2
}

That will make value1 as a subkey.

Also, the order of the value node under a key is fixed. If there
are a value and subkeys, the value is always the first child node
of the key. Thus if user specifies subkeys first, e.g.

key.subkey = value1
key = value2

In the program (and /proc/bootconfig), it will be shown as below

key = value2
key.subkey = value1

Link: https://lkml.kernel.org/r/162262194685.264090.7738574774030567419.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/bootconfig.h

@@ -80,6 +80,8 @@ static inline __init bool xbc_node_is_array(struct xbc_node *node)
  *
  * Test the @node is a leaf key node which is a key node and has a value node
  * or no child. Returns true if it is a leaf node, or false if not.
+ * Note that the leaf node can have subkey nodes in addition to the
+ * value node.
  */
 static inline __init bool xbc_node_is_leaf(struct xbc_node *node)
 {
@@ -129,6 +131,23 @@ static inline struct xbc_node * __init xbc_find_node(const char *key)
 	return xbc_node_find_child(NULL, key);
 }
 
+/**
+ * xbc_node_get_subkey() - Return the first subkey node if exists
+ * @node: Parent node
+ *
+ * Return the first subkey node of the @node. If the @node has no child
+ * or only value node, this will return NULL.
+ */
+static inline struct xbc_node * __init xbc_node_get_subkey(struct xbc_node *node)
+{
+	struct xbc_node *child = xbc_node_get_child(node);
+
+	if (child && xbc_node_is_value(child))
+		return xbc_node_get_next(child);
+	else
+		return child;
+}
+
 /**
  * xbc_array_for_each_value() - Iterate value nodes on an array
  * @anode: An XBC arraied value node
@@ -149,11 +168,24 @@ static inline struct xbc_node * __init xbc_find_node(const char *key)
  * @child: Iterated XBC node.
  *
  * Iterate child nodes of @parent. Each child nodes are stored to @child.
+ * The @child can be mixture of a value node and subkey nodes.
  */
 #define xbc_node_for_each_child(parent, child)				\
 	for (child = xbc_node_get_child(parent); child != NULL ;	\
 	     child = xbc_node_get_next(child))
 
+/**
+ * xbc_node_for_each_subkey() - Iterate child subkey nodes
+ * @parent: An XBC node.
+ * @child: Iterated XBC node.
+ *
+ * Iterate subkey nodes of @parent. Each child nodes are stored to @child.
+ * The @child is only the subkey node.
+ */
+#define xbc_node_for_each_subkey(parent, child)				\
+	for (child = xbc_node_get_subkey(parent); child != NULL ;	\
+	     child = xbc_node_get_next(child))
+
 /**
  * xbc_node_for_each_array_value() - Iterate array entries of geven key
  * @node: An XBC node.