bootconfig: Add Extra Boot Config support

Extra Boot Config (XBC) allows admin to pass a tree-structured
boot configuration file when boot up the kernel. This extends
the kernel command line in an efficient way.

Boot config will contain some key-value commands, e.g.

key.word = value1
another.key.word = value2

It can fold same keys with braces, also you can write array
data. For example,

key {
   word1 {
      setting1 = data
      setting2
   }
   word2.array = "val1", "val2"
}

User can access these key-value pair and tree structure via
SKC APIs.

Link: http://lkml.kernel.org/r/157867221257.17873.1775090991929862549.stgit@devnote2Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

MAINTAINERS

@@ -15770,6 +15770,12 @@ W:	http://www.stlinux.com
 S:	Supported
 F:	drivers/net/ethernet/stmicro/stmmac/
 
+EXTRA BOOT CONFIG
+M:	Masami Hiramatsu <mhiramat@kernel.org>
+S:	Maintained
+F:	lib/bootconfig.c
+F:	include/linux/bootconfig.h
+
 SUN3/3X
 M:	Sam Creasey <sammy@sammy.net>
 W:	http://sammy.net/sun3/

include/linux/bootconfig.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_XBC_H
+#define _LINUX_XBC_H
+/*
+ * Extra Boot Config
+ * Copyright (C) 2019 Linaro Ltd.
+ * Author: Masami Hiramatsu <mhiramat@kernel.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+
+/* XBC tree node */
+struct xbc_node {
+	u16 next;
+	u16 child;
+	u16 parent;
+	u16 data;
+} __attribute__ ((__packed__));
+
+#define XBC_KEY		0
+#define XBC_VALUE	(1 << 15)
+/* Maximum size of boot config is 32KB - 1 */
+#define XBC_DATA_MAX	(XBC_VALUE - 1)
+
+#define XBC_NODE_MAX	1024
+#define XBC_KEYLEN_MAX	256
+#define XBC_DEPTH_MAX	16
+
+/* Node tree access raw APIs */
+struct xbc_node * __init xbc_root_node(void);
+int __init xbc_node_index(struct xbc_node *node);
+struct xbc_node * __init xbc_node_get_parent(struct xbc_node *node);
+struct xbc_node * __init xbc_node_get_child(struct xbc_node *node);
+struct xbc_node * __init xbc_node_get_next(struct xbc_node *node);
+const char * __init xbc_node_get_data(struct xbc_node *node);
+
+/**
+ * xbc_node_is_value() - Test the node is a value node
+ * @node: An XBC node.
+ *
+ * Test the @node is a value node and return true if a value node, false if not.
+ */
+static inline __init bool xbc_node_is_value(struct xbc_node *node)
+{
+	return node->data & XBC_VALUE;
+}
+
+/**
+ * xbc_node_is_key() - Test the node is a key node
+ * @node: An XBC node.
+ *
+ * Test the @node is a key node and return true if a key node, false if not.
+ */
+static inline __init bool xbc_node_is_key(struct xbc_node *node)
+{
+	return !xbc_node_is_value(node);
+}
+
+/**
+ * xbc_node_is_array() - Test the node is an arraied value node
+ * @node: An XBC node.
+ *
+ * Test the @node is an arraied value node.
+ */
+static inline __init bool xbc_node_is_array(struct xbc_node *node)
+{
+	return xbc_node_is_value(node) && node->next != 0;
+}
+
+/**
+ * xbc_node_is_leaf() - Test the node is a leaf key node
+ * @node: An XBC 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.
+ */
+static inline __init bool xbc_node_is_leaf(struct xbc_node *node)
+{
+	return xbc_node_is_key(node) &&
+		(!node->child || xbc_node_is_value(xbc_node_get_child(node)));
+}
+
+/* Tree-based key-value access APIs */
+struct xbc_node * __init xbc_node_find_child(struct xbc_node *parent,
+					     const char *key);
+
+const char * __init xbc_node_find_value(struct xbc_node *parent,
+					const char *key,
+					struct xbc_node **vnode);
+
+struct xbc_node * __init xbc_node_find_next_leaf(struct xbc_node *root,
+						 struct xbc_node *leaf);
+
+const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
+						 struct xbc_node **leaf);
+
+/**
+ * xbc_find_value() - Find a value which matches the key
+ * @key: Search key
+ * @vnode: A container pointer of XBC value node.
+ *
+ * Search a value whose key matches @key from whole of XBC tree and return
+ * the value if found. Found value node is stored in *@vnode.
+ * Note that this can return 0-length string and store NULL in *@vnode for
+ * key-only (non-value) entry.
+ */
+static inline const char * __init
+xbc_find_value(const char *key, struct xbc_node **vnode)
+{
+	return xbc_node_find_value(NULL, key, vnode);
+}
+
+/**
+ * xbc_find_node() - Find a node which matches the key
+ * @key: Search key
+ *
+ * Search a (key) node whose key matches @key from whole of XBC tree and
+ * return the node if found. If not found, returns NULL.
+ */
+static inline struct xbc_node * __init xbc_find_node(const char *key)
+{
+	return xbc_node_find_child(NULL, key);
+}
+
+/**
+ * xbc_array_for_each_value() - Iterate value nodes on an array
+ * @anode: An XBC arraied value node
+ * @value: A value
+ *
+ * Iterate array value nodes and values starts from @anode. This is expected to
+ * be used with xbc_find_value() and xbc_node_find_value(), so that user can
+ * process each array entry node.
+ */
+#define xbc_array_for_each_value(anode, value)				\
+	for (value = xbc_node_get_data(anode); anode != NULL ;		\
+	     anode = xbc_node_get_next(anode),				\
+	     value = anode ? xbc_node_get_data(anode) : NULL)
+
+/**
+ * xbc_node_for_each_child() - Iterate child nodes
+ * @parent: An XBC node.
+ * @child: Iterated XBC node.
+ *
+ * Iterate child nodes of @parent. Each child nodes are stored to @child.
+ */
+#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_array_value() - Iterate array entries of geven key
+ * @node: An XBC node.
+ * @key: A key string searched under @node
+ * @anode: Iterated XBC node of array entry.
+ * @value: Iterated value of array entry.
+ *
+ * Iterate array entries of given @key under @node. Each array entry node
+ * is stroed to @anode and @value. If the @node doesn't have @key node,
+ * it does nothing.
+ * Note that even if the found key node has only one value (not array)
+ * this executes block once. Hoever, if the found key node has no value
+ * (key-only node), this does nothing. So don't use this for testing the
+ * key-value pair existence.
+ */
+#define xbc_node_for_each_array_value(node, key, anode, value)		\
+	for (value = xbc_node_find_value(node, key, &anode); value != NULL; \
+	     anode = xbc_node_get_next(anode),				\
+	     value = anode ? xbc_node_get_data(anode) : NULL)
+
+/**
+ * xbc_node_for_each_key_value() - Iterate key-value pairs under a node
+ * @node: An XBC node.
+ * @knode: Iterated key node
+ * @value: Iterated value string
+ *
+ * Iterate key-value pairs under @node. Each key node and value string are
+ * stored in @knode and @value respectively.
+ */
+#define xbc_node_for_each_key_value(node, knode, value)			\
+	for (knode = NULL, value = xbc_node_find_next_key_value(node, &knode);\
+	     knode != NULL; value = xbc_node_find_next_key_value(node, &knode))
+
+/**
+ * xbc_for_each_key_value() - Iterate key-value pairs
+ * @knode: Iterated key node
+ * @value: Iterated value string
+ *
+ * Iterate key-value pairs in whole XBC tree. Each key node and value string
+ * are stored in @knode and @value respectively.
+ */
+#define xbc_for_each_key_value(knode, value)				\
+	xbc_node_for_each_key_value(NULL, knode, value)
+
+/* Compose partial key */
+int __init xbc_node_compose_key_after(struct xbc_node *root,
+			struct xbc_node *node, char *buf, size_t size);
+
+/**
+ * xbc_node_compose_key() - Compose full key string of the XBC node
+ * @node: An XBC node.
+ * @buf: A buffer to store the key.
+ * @size: The size of the @buf.
+ *
+ * Compose the full-length key of the @node into @buf. Returns the total
+ * length of the key stored in @buf. Or returns -EINVAL if @node is NULL,
+ * and -ERANGE if the key depth is deeper than max depth.
+ */
+static inline int __init xbc_node_compose_key(struct xbc_node *node,
+					      char *buf, size_t size)
+{
+	return xbc_node_compose_key_after(NULL, node, buf, size);
+}
+
+/* XBC node initializer */
+int __init xbc_init(char *buf);
+
+/* XBC cleanup data structures */
+void __init xbc_destroy_all(void);
+
+/* Debug dump functions */
+void __init xbc_debug_dump(void);
+
+#endif

init/Kconfig

@@ -1215,6 +1215,17 @@ source "usr/Kconfig"
 
 endif
 
+config BOOT_CONFIG
+	bool "Boot config support"
+	select LIBXBC
+	default y
+	help
+	  Extra boot config allows system admin to pass a config file as
+	  complemental extension of kernel cmdline when booting.
+	  The boot config file is usually attached at the end of initramfs.
+
+	  If unsure, say Y.
+
 choice
 	prompt "Compiler optimization level"
 	default CC_OPTIMIZE_FOR_PERFORMANCE

lib/Kconfig

@@ -566,6 +566,9 @@ config DIMLIB
 config LIBFDT
 	bool
 
+config LIBXBC
+	bool
+
 config OID_REGISTRY
 	tristate
 	help

lib/Makefile

@@ -228,6 +228,8 @@ $(foreach file, $(libfdt_files), \
 	$(eval CFLAGS_$(file) = -I $(srctree)/scripts/dtc/libfdt))
 lib-$(CONFIG_LIBFDT) += $(libfdt_files)
 
+lib-$(CONFIG_LIBXBC) += bootconfig.o
+
 obj-$(CONFIG_RBTREE_TEST) += rbtree_test.o
 obj-$(CONFIG_INTERVAL_TREE_TEST) += interval_tree_test.o