[RFC,v4,01/22] bootconfig: Add Extra Boot Config support
diff mbox series

Message ID 157528160980.22451.2034344493364709160.stgit@devnote2
State New
Headers show
Series
  • tracing: bootconfig: Boot-time tracing and Extra boot config
Related show

Commit Message

Masami Hiramatsu Dec. 2, 2019, 10:13 a.m. UTC
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.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v4:
  - Rename suppremental kernel command line to extended boot.
    config so that easy to understand what it is.
  - Clean up given data if failed to parse it.
  - Add comment support (start with #)
  - Return -ENOENT if given data has no node.
  - Ensure the key max depth and keylen are under limitation.
  - Add single quotes support.
  - Allow newline and closing brace to terminate key-value.
  - Add xbc_node_compose_key_after().
  - Move kconfig to generic setup.
  - Expand the max number of node to 1024.
---
 MAINTAINERS                |    6 
 include/linux/bootconfig.h |  221 ++++++++++++
 init/Kconfig               |   11 +
 lib/Kconfig                |    3 
 lib/Makefile               |    2 
 lib/bootconfig.c           |  783 ++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 1026 insertions(+)
 create mode 100644 include/linux/bootconfig.h
 create mode 100644 lib/bootconfig.c

Comments

Randy Dunlap Dec. 8, 2019, 7:34 p.m. UTC | #1
Hi,

On 12/2/19 2:13 AM, Masami Hiramatsu wrote:
> diff --git a/init/Kconfig b/init/Kconfig
> index 67a602ee17f1..13bb3eac804c 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1235,6 +1235,17 @@ source "usr/Kconfig"
>  
>  endif
>  
> +config BOOT_CONFIG
> +	bool "Boot config support"
> +	select LIBXBC
> +	default y

questionable "default y".
That needs lots of justification.

> +	help
> +	 Extra boot config allows system admin to pass a config file as
> +	 complemental extension of kernel cmdline when boot.

	                                          when booting.

> +	 The boot config file is usually attached at the end of initramfs.

The 3 help text lines above should be indented with one tab + 2 spaces,
like the "If" line below.

> +
> +	  If unsure, say Y.
> +
>  choice
>  	prompt "Compiler optimization level"
>  	default CC_OPTIMIZE_FOR_PERFORMANCE
Masami Hiramatsu Dec. 9, 2019, 5:50 a.m. UTC | #2
Hi Randy,

Thank you for your review!

On Sun, 8 Dec 2019 11:34:32 -0800
Randy Dunlap <rdunlap@infradead.org> wrote:

> Hi,
> 
> On 12/2/19 2:13 AM, Masami Hiramatsu wrote:
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 67a602ee17f1..13bb3eac804c 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1235,6 +1235,17 @@ source "usr/Kconfig"
> >  
> >  endif
> >  
> > +config BOOT_CONFIG
> > +	bool "Boot config support"
> > +	select LIBXBC
> > +	default y
> 
> questionable "default y".
> That needs lots of justification.

OK, I can make it 'n' by default.

I thought that was OK because most of the memories for the
bootconfig support were released after initialization.
If user doesn't pass the bootconfig, only the code for
/proc/bootconfig remains on runtime memory.

> > +	help
> > +	 Extra boot config allows system admin to pass a config file as
> > +	 complemental extension of kernel cmdline when boot.
> 
> 	                                          when booting.

OK.

> 
> > +	 The boot config file is usually attached at the end of initramfs.
> 
> The 3 help text lines above should be indented with one tab + 2 spaces,
> like the "If" line below.

Ah, thanks for pointing it out!
I'll fix that.

Thank you,

> 
> > +
> > +	  If unsure, say Y.
> > +
> >  choice
> >  	prompt "Compiler optimization level"
> >  	default CC_OPTIMIZE_FOR_PERFORMANCE
> 
> 
> -- 
> ~Randy
>
Steven Rostedt Dec. 9, 2019, 3:54 p.m. UTC | #3
On Mon, 9 Dec 2019 14:50:09 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hi Randy,
> 
> Thank you for your review!
> 
> On Sun, 8 Dec 2019 11:34:32 -0800
> Randy Dunlap <rdunlap@infradead.org> wrote:
> 
> > Hi,
> > 
> > On 12/2/19 2:13 AM, Masami Hiramatsu wrote:  
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index 67a602ee17f1..13bb3eac804c 100644
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1235,6 +1235,17 @@ source "usr/Kconfig"
> > >  
> > >  endif
> > >  
> > > +config BOOT_CONFIG
> > > +	bool "Boot config support"
> > > +	select LIBXBC
> > > +	default y  
> > 
> > questionable "default y".
> > That needs lots of justification.  
> 
> OK, I can make it 'n' by default.
> 
> I thought that was OK because most of the memories for the
> bootconfig support were released after initialization.
> If user doesn't pass the bootconfig, only the code for
> /proc/bootconfig remains on runtime memory.

As 'n' is usually the default, I will argue this should be 'y'!

This is not some new fancy feature, or device that Linus
complains about "my X is important!". I will say this X *is* important!
This will (I hope) become standard in all kernel configs. One could even
argue that there shouldn't even be a config for this at all (forced
'y'). This would hurt more not to have than to have. I would hate to
try to load special options only to find out that the kernel was
compiled with default configs and this wasn't enabled.

This is extended boot config support that can be useful for most
developers. The only ones that should say 'n' are those that are
working to get a "tiny" kernel at boot up. As Masami said, the memory
is freed after init, thus this should not be an issue for 99.9% of
kernel users.

-- Steve


> 
> > > +	help
> > > +	 Extra boot config allows system admin to pass a config file as
> > > +	 complemental extension of kernel cmdline when boot.  
> > 
> > 	                                          when booting.  
>
Masami Hiramatsu Dec. 10, 2019, 2:15 p.m. UTC | #4
On Mon, 9 Dec 2019 10:54:03 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> > > > +config BOOT_CONFIG
> > > > +	bool "Boot config support"
> > > > +	select LIBXBC
> > > > +	default y  
> > > 
> > > questionable "default y".
> > > That needs lots of justification.  
> > 
> > OK, I can make it 'n' by default.
> > 
> > I thought that was OK because most of the memories for the
> > bootconfig support were released after initialization.
> > If user doesn't pass the bootconfig, only the code for
> > /proc/bootconfig remains on runtime memory.
> 
> As 'n' is usually the default, I will argue this should be 'y'!
> 
> This is not some new fancy feature, or device that Linus
> complains about "my X is important!". I will say this X *is* important!
> This will (I hope) become standard in all kernel configs. One could even
> argue that there shouldn't even be a config for this at all (forced
> 'y'). This would hurt more not to have than to have. I would hate to
> try to load special options only to find out that the kernel was
> compiled with default configs and this wasn't enabled.
> 
> This is extended boot config support that can be useful for most
> developers. The only ones that should say 'n' are those that are
> working to get a "tiny" kernel at boot up. As Masami said, the memory
> is freed after init, thus this should not be an issue for 99.9% of
> kernel users.

Thanks Steve!

Yes, for the users point of view, it is hard to notice that their kernel
can accept the boot config or not before boot.
To provide consistent system usability, I think it is better to be enabled
by default. Anyway, if there is no boot config, almost all buffers and
code are released after init (except for /proc/bootconfig entry point,
which will return an empty buffer).

It will increase the binary image size, but it must be small.
FYI, here is an example of vmlinux (non compressed image)

   text	   data	    bss	    dec	    hex	filename
16178353	5843418	13324364	35346135	21b56d7	vmlinux
16183993	5855858	13316172	35356023	21b7d77	vmlinux.xbc
16187248	5855870	13307980	35351098	21b6a3a	vmlinux.xbc.btt

So, for the extra boot config support, it will increase ~6KB code and
12KB data, the boot time tracing increase ~3KB code and 12bytes data
in binary file. 

Thank you,

Patch
diff mbox series

diff --git a/MAINTAINERS b/MAINTAINERS
index b16b72ae6cd6..1a813164ff3f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -15689,6 +15689,12 @@  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/
diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
new file mode 100644
index 000000000000..3eb904ccefe9
--- /dev/null
+++ b/include/linux/bootconfig.h
@@ -0,0 +1,221 @@ 
+/* 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 !(node->data & XBC_VALUE);
+}
+
+/**
+ * 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);
+
+/* Debug dump functions */
+void __init xbc_debug_dump(void);
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index 67a602ee17f1..13bb3eac804c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1235,6 +1235,17 @@  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 boot.
+	 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
diff --git a/lib/Kconfig b/lib/Kconfig
index 681b7e50490e..d3f81ad6131b 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -566,6 +566,9 @@  config DIMLIB
 config LIBFDT
 	bool
 
+config LIBXBC
+	bool
+
 config OID_REGISTRY
 	tristate
 	help
diff --git a/lib/Makefile b/lib/Makefile
index c2f0e2a4e4e8..4e489c9453b0 100644
--- a/lib/Makefile
+++ b/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
 
diff --git a/lib/bootconfig.c b/lib/bootconfig.c
new file mode 100644
index 000000000000..3f27db98a23b
--- /dev/null
+++ b/lib/bootconfig.c
@@ -0,0 +1,783 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Extra Boot Config
+ * Masami Hiramatsu <mhiramat@kernel.org>
+ */
+
+#define pr_fmt(fmt)    "bootconfig: " fmt
+
+#include <linux/bug.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/bootconfig.h>
+#include <linux/string.h>
+
+/*
+ * Extra Boot Config (XBC) is given as tree-structured ascii text of
+ * key-value pairs on memory.
+ * xbc_parse() parses the text to build a simple tree. Each tree node is
+ * simply a key word or a value. A key node may have a next key node or/and
+ * a child node (both key and value). A value node may have a next value
+ * node (for array).
+ */
+
+static struct xbc_node xbc_nodes[XBC_NODE_MAX] __initdata;
+static int xbc_node_num __initdata;
+static char *xbc_data __initdata;
+static size_t xbc_data_size __initdata;
+static struct xbc_node *last_parent __initdata;
+
+static int __init xbc_parse_error(const char *msg, const char *p)
+{
+	int pos = p - xbc_data;
+
+	pr_err("Parse error at pos %d: %s\n", pos, msg);
+	return -EINVAL;
+}
+
+/**
+ * xbc_root_node() - Get the root node of extended boot config
+ *
+ * Return the address of root node of extended boot config. If the
+ * extended boot config is not initiized, return NULL.
+ */
+struct xbc_node * __init xbc_root_node(void)
+{
+	if (unlikely(!xbc_data))
+		return NULL;
+
+	return xbc_nodes;
+}
+
+/**
+ * xbc_node_index() - Get the index of XBC node
+ * @node: A target node of getting index.
+ *
+ * Return the index number of @node in XBC node list.
+ */
+int __init xbc_node_index(struct xbc_node *node)
+{
+	return node - &xbc_nodes[0];
+}
+
+/**
+ * xbc_node_get_parent() - Get the parent XBC node
+ * @node: An XBC node.
+ *
+ * Return the parent node of @node. If the node is top node of the tree,
+ * return NULL.
+ */
+struct xbc_node * __init xbc_node_get_parent(struct xbc_node *node)
+{
+	return node->parent == XBC_NODE_MAX ? NULL : &xbc_nodes[node->parent];
+}
+
+/**
+ * xbc_node_get_child() - Get the child XBC node
+ * @node: An XBC node.
+ *
+ * Return the first child node of @node. If the node has no child, return
+ * NULL.
+ */
+struct xbc_node * __init xbc_node_get_child(struct xbc_node *node)
+{
+	return node->child ? &xbc_nodes[node->child] : NULL;
+}
+
+/**
+ * xbc_node_get_next() - Get the next sibling XBC node
+ * @node: An XBC node.
+ *
+ * Return the NEXT sibling node of @node. If the node has no next sibling,
+ * return NULL. Note that even if this returns NULL, it doesn't mean @node
+ * has no siblings. (You also has to check whether the parent's child node
+ * is @node or not.)
+ */
+struct xbc_node * __init xbc_node_get_next(struct xbc_node *node)
+{
+	return node->next ? &xbc_nodes[node->next] : NULL;
+}
+
+/**
+ * xbc_node_get_data() - Get the data of XBC node
+ * @node: An XBC node.
+ *
+ * Return the data (which is always a null terminated string) of @node.
+ * If the node has invalid data, warn and return NULL.
+ */
+const char * __init xbc_node_get_data(struct xbc_node *node)
+{
+	int offset = node->data & ~XBC_VALUE;
+
+	if (WARN_ON(offset >= xbc_data_size))
+		return NULL;
+
+	return xbc_data + offset;
+}
+
+static bool __init
+xbc_node_match_prefix(struct xbc_node *node, const char **prefix)
+{
+	const char *p = xbc_node_get_data(node);
+	int len = strlen(p);
+
+	if (strncmp(*prefix, p, len))
+		return false;
+
+	p = *prefix + len;
+	if (*p == '.')
+		p++;
+	else if (*p != '\0')
+		return false;
+	*prefix = p;
+
+	return true;
+}
+
+/**
+ * xbc_node_find_child() - Find a child node which matches given key
+ * @parent: An XBC node.
+ * @key: A key string.
+ *
+ * Search a node under @parent which matches @key. The @key can contain
+ * several words jointed with '.'. If @parent is NULL, this searches the
+ * node from whole tree. Return NULL if no node is matched.
+ */
+struct xbc_node * __init
+xbc_node_find_child(struct xbc_node *parent, const char *key)
+{
+	struct xbc_node *node;
+
+	if (parent)
+		node = xbc_node_get_child(parent);
+	else
+		node = xbc_root_node();
+
+	while (node && xbc_node_is_key(node)) {
+		if (!xbc_node_match_prefix(node, &key))
+			node = xbc_node_get_next(node);
+		else if (*key != '\0')
+			node = xbc_node_get_child(node);
+		else
+			break;
+	}
+
+	return node;
+}
+
+/**
+ * xbc_node_find_value() - Find a value node which matches given key
+ * @parent: An XBC node.
+ * @key: A key string.
+ * @vnode: A container pointer of found XBC node.
+ *
+ * Search a value node under @parent whose (parent) key node matches @key,
+ * store it in *@vnode, and returns the value string.
+ * The @key can contain several words jointed with '.'. If @parent is NULL,
+ * this searches the node from whole tree. Return the value string if a
+ * matched key found, return NULL if no node is matched.
+ * Note that this returns 0-length string and stores NULL in *@vnode if the
+ * key has no value. And also it will return the value of the first entry if
+ * the value is an array.
+ */
+const char * __init
+xbc_node_find_value(struct xbc_node *parent, const char *key,
+		    struct xbc_node **vnode)
+{
+	struct xbc_node *node = xbc_node_find_child(parent, key);
+
+	if (!node || !xbc_node_is_key(node))
+		return NULL;
+
+	node = xbc_node_get_child(node);
+	if (node && !xbc_node_is_value(node))
+		return NULL;
+
+	if (vnode)
+		*vnode = node;
+
+	return node ? xbc_node_get_data(node) : "";
+}
+
+/**
+ * xbc_node_compose_key_after() - Compose partial key string of the XBC node
+ * @root: Root XBC node
+ * @node: Target XBC node.
+ * @buf: A buffer to store the key.
+ * @size: The size of the @buf.
+ *
+ * Compose the partial key of the @node into @buf, which is starting right
+ * after @root (@root is not included.) If @root is NULL, this returns full
+ * key words of @node.
+ * Returns the total length of the key stored in @buf. Returns -EINVAL
+ * if @node is NULL or @root is not the ancestor of @node or @root is @node,
+ * or returns -ERANGE if the key depth is deeper than max depth.
+ * This is expected to be used with xbc_find_node() to list up all (child)
+ * keys under given key.
+ */
+int __init xbc_node_compose_key_after(struct xbc_node *root,
+				      struct xbc_node *node,
+				      char *buf, size_t size)
+{
+	u16 keys[XBC_DEPTH_MAX];
+	int depth = 0, ret = 0, total = 0;
+
+	if (!node || node == root)
+		return -EINVAL;
+
+	if (xbc_node_is_value(node))
+		node = xbc_node_get_parent(node);
+
+	while (node && node != root) {
+		keys[depth++] = xbc_node_index(node);
+		if (depth == XBC_DEPTH_MAX)
+			return -ERANGE;
+		node = xbc_node_get_parent(node);
+	}
+	if (!node && root)
+		return -EINVAL;
+
+	while (--depth >= 0) {
+		node = xbc_nodes + keys[depth];
+		ret = snprintf(buf, size, "%s%s", xbc_node_get_data(node),
+			       depth ? "." : "");
+		if (ret < 0)
+			return ret;
+		if (ret > size) {
+			size = 0;
+		} else {
+			size -= ret;
+			buf += ret;
+		}
+		total += ret;
+	}
+
+	return total;
+}
+
+/**
+ * xbc_node_find_next_leaf() - Find the next leaf node under given node
+ * @root: An XBC root node
+ * @node: An XBC node which starts from.
+ *
+ * Search the next leaf node (which means the terminal key node) of @node
+ * under @root node (including @root node itself).
+ * Return the next node or NULL if next leaf node is not found.
+ */
+struct xbc_node * __init xbc_node_find_next_leaf(struct xbc_node *root,
+						 struct xbc_node *node)
+{
+	if (unlikely(!xbc_data))
+		return NULL;
+
+	if (!node) {	/* First try */
+		node = root;
+		if (!node)
+			node = xbc_nodes;
+	} else {
+		if (node == root)	/* @root was a leaf, no child node. */
+			return NULL;
+
+		while (!node->next) {
+			node = xbc_node_get_parent(node);
+			if (node == root)
+				return NULL;
+			/* User passed a node which is not uder parent */
+			if (WARN_ON(!node))
+				return NULL;
+		}
+		node = xbc_node_get_next(node);
+	}
+
+	while (node && !xbc_node_is_leaf(node))
+		node = xbc_node_get_child(node);
+
+	return node;
+}
+
+/**
+ * xbc_node_find_next_key_value() - Find the next key-value pair nodes
+ * @root: An XBC root node
+ * @leaf: A container pointer of XBC node which starts from.
+ *
+ * Search the next leaf node (which means the terminal key node) of *@leaf
+ * under @root node. Returns the value and update *@leaf if next leaf node
+ * is found, or NULL if no next leaf node is found.
+ * Note that this returns 0-length string if the key has no value, or
+ * the value of the first entry if the value is an array.
+ */
+const char * __init xbc_node_find_next_key_value(struct xbc_node *root,
+						 struct xbc_node **leaf)
+{
+	/* tip must be passed */
+	if (WARN_ON(!leaf))
+		return NULL;
+
+	*leaf = xbc_node_find_next_leaf(root, *leaf);
+	if (!*leaf)
+		return NULL;
+	if ((*leaf)->child)
+		return xbc_node_get_data(xbc_node_get_child(*leaf));
+	else
+		return "";	/* No value key */
+}
+
+/* XBC parse and tree build */
+
+static struct xbc_node * __init xbc_add_node(char *data, u32 flag)
+{
+	struct xbc_node *node;
+	unsigned long offset;
+
+	if (xbc_node_num == XBC_NODE_MAX)
+		return NULL;
+
+	node = &xbc_nodes[xbc_node_num++];
+	offset = data - xbc_data;
+	node->data = (u16)offset;
+	if (WARN_ON(offset >= XBC_DATA_MAX))
+		return NULL;
+	node->data |= flag;
+	node->child = 0;
+	node->next = 0;
+
+	return node;
+}
+
+static inline __init struct xbc_node *xbc_last_sibling(struct xbc_node *node)
+{
+	while (node->next)
+		node = xbc_node_get_next(node);
+
+	return node;
+}
+
+static struct xbc_node * __init xbc_add_sibling(char *data, u32 flag)
+{
+	struct xbc_node *sib, *node = xbc_add_node(data, flag);
+
+	if (node) {
+		if (!last_parent) {
+			node->parent = XBC_NODE_MAX;
+			sib = xbc_last_sibling(xbc_nodes);
+			sib->next = xbc_node_index(node);
+		} else {
+			node->parent = xbc_node_index(last_parent);
+			if (!last_parent->child) {
+				last_parent->child = xbc_node_index(node);
+			} else {
+				sib = xbc_node_get_child(last_parent);
+				sib = xbc_last_sibling(sib);
+				sib->next = xbc_node_index(node);
+			}
+		}
+	}
+
+	return node;
+}
+
+static inline __init struct xbc_node *xbc_add_child(char *data, u32 flag)
+{
+	struct xbc_node *node = xbc_add_sibling(data, flag);
+
+	if (node)
+		last_parent = node;
+
+	return node;
+}
+
+static inline __init bool xbc_valid_keyword(char *key)
+{
+	if (key[0] == '\0')
+		return false;
+
+	while (isalnum(*key) || *key == '-' || *key == '_')
+		key++;
+
+	return *key == '\0';
+}
+
+static inline __init char *find_ending_quotes(char *p, int quotes)
+{
+	do {
+		p = strchr(p + 1, quotes);
+		if (!p)
+			break;
+	} while (*(p - 1) == '\\');
+
+	return p;
+}
+
+static char *skip_comment(char *p)
+{
+	char *ret;
+
+	ret = strchr(p, '\n');
+	if (!ret)
+		ret = p + strlen(p);
+	else
+		ret++;
+
+	return ret;
+}
+
+static int __init __xbc_open_brace(void)
+{
+	/* Mark the last key as open brace */
+	last_parent->next = XBC_NODE_MAX;
+
+	return 0;
+}
+
+static int __init __xbc_close_brace(char *p)
+{
+	struct xbc_node *node;
+
+	if (!last_parent || last_parent->next != XBC_NODE_MAX)
+		return xbc_parse_error("Unexpected closing brace", p);
+
+	node = last_parent;
+	node->next = 0;
+	do {
+		node = xbc_node_get_parent(node);
+	} while (node && node->next != XBC_NODE_MAX);
+	last_parent = node;
+
+	return 0;
+}
+
+/* Return delimiter or error, no node added */
+static int __init __xbc_parse_value(char **__v, char **__n)
+{
+	char *p, *v = *__v;
+	int c;
+
+	v = skip_spaces(v);
+	while (*v == '#') {
+		v = skip_comment(v);
+		v = skip_spaces(v);
+	}
+	if (*v == '"' || *v == '\'') {
+		c = *v;
+		v++;
+		p = find_ending_quotes(v, c);
+		if (!p)
+			return xbc_parse_error("No closing quotes", v);
+		*p++ = '\0';
+		while (isspace(*p) && *p != '\n')
+			p++;
+		if (!strchr(",;\n#}", *p))
+			return xbc_parse_error("No delimiter for value", v);
+		c = *p;
+		*p++ = '\0';
+	} else {
+		p = strpbrk(v, ",;\n#}");
+		if (!p)
+			return xbc_parse_error("No delimiter for value", v);
+		c = *p;
+		*p++ = '\0';
+		v = strim(v);
+	}
+
+	if (c == '#') {
+		p = skip_comment(p);
+		c = *p;
+	}
+	*__n = p;
+	*__v = v;
+
+	return c;
+}
+
+static int __init xbc_parse_array(char **__v)
+{
+	struct xbc_node *node;
+	char *next;
+	int c = 0;
+
+	do {
+		c = __xbc_parse_value(__v, &next);
+		if (c < 0)
+			return c;
+
+		node = xbc_add_sibling(*__v, XBC_VALUE);
+		if (!node)
+			return -ENOMEM;
+		*__v = next;
+	} while (c == ',');
+	node->next = 0;
+
+	return c;
+}
+
+static inline __init
+struct xbc_node *find_match_node(struct xbc_node *node, char *k)
+{
+	while (node) {
+		if (!strcmp(xbc_node_get_data(node), k))
+			break;
+		node = xbc_node_get_next(node);
+	}
+	return node;
+}
+
+static int __init __xbc_add_key(char *k)
+{
+	struct xbc_node *node;
+
+	if (!xbc_valid_keyword(k))
+		return xbc_parse_error("Invalid keyword", k);
+
+	if (unlikely(xbc_node_num == 0))
+		goto add_node;
+
+	if (!last_parent)	/* the first level */
+		node = find_match_node(xbc_nodes, k);
+	else
+		node = find_match_node(xbc_node_get_child(last_parent), k);
+
+	if (node)
+		last_parent = node;
+	else {
+add_node:
+		node = xbc_add_child(k, XBC_KEY);
+		if (!node)
+			return -ENOMEM;
+	}
+	return 0;
+}
+
+static int __init __xbc_parse_keys(char *k)
+{
+	char *p;
+	int ret;
+
+	k = strim(k);
+	while ((p = strchr(k, '.'))) {
+		*p++ = '\0';
+		ret = __xbc_add_key(k);
+		if (ret)
+			return ret;
+		k = p;
+	}
+
+	return __xbc_add_key(k);
+}
+
+static int __init xbc_parse_kv(char **k, char *v)
+{
+	struct xbc_node *prev_parent = last_parent;
+	struct xbc_node *node;
+	char *next;
+	int c, ret;
+
+	ret = __xbc_parse_keys(*k);
+	if (ret)
+		return ret;
+
+	c = __xbc_parse_value(&v, &next);
+	if (c < 0)
+		return c;
+
+	node = xbc_add_sibling(v, XBC_VALUE);
+	if (!node)
+		return -ENOMEM;
+
+	if (c == ',') {	/* Array */
+		c = xbc_parse_array(&next);
+		if (c < 0)
+			return c;
+	}
+
+	last_parent = prev_parent;
+
+	if (c == '}') {
+		ret = __xbc_close_brace(next - 1);
+		if (ret < 0)
+			return ret;
+	}
+
+	*k = next;
+
+	return 0;
+}
+
+static int __init xbc_parse_key(char **k, char *n)
+{
+	struct xbc_node *prev_parent = last_parent;
+	int ret;
+
+	*k = strim(*k);
+	if (**k != '\0') {
+		ret = __xbc_parse_keys(*k);
+		if (ret)
+			return ret;
+		last_parent = prev_parent;
+	}
+	*k = n;
+
+	return 0;
+}
+
+static int __init xbc_open_brace(char **k, char *n)
+{
+	int ret;
+
+	ret = __xbc_parse_keys(*k);
+	if (ret)
+		return ret;
+	*k = n;
+
+	return __xbc_open_brace();
+}
+
+static int __init xbc_close_brace(char **k, char *n)
+{
+	int ret;
+
+	ret = xbc_parse_key(k, n);
+	if (ret)
+		return ret;
+	/* k is updated in xbc_parse_key() */
+
+	return __xbc_close_brace(n - 1);
+}
+
+static int __init xbc_verify_tree(void)
+{
+	int i, depth, len, wlen;
+	struct xbc_node *n, *m;
+
+	/* Empty tree */
+	if (xbc_node_num == 0)
+		return -ENOENT;
+
+	for (i = 0; i < xbc_node_num; i++) {
+		if (xbc_nodes[i].next > xbc_node_num) {
+			return xbc_parse_error("No closing brace",
+				xbc_node_get_data(xbc_nodes + i));
+		}
+	}
+
+	/* Key tree limitation check */
+	n = &xbc_nodes[0];
+	depth = 1;
+	len = 0;
+
+	while (n) {
+		wlen = strlen(xbc_node_get_data(n)) + 1;
+		len += wlen;
+		if (len > XBC_KEYLEN_MAX)
+			return xbc_parse_error("Too long key length",
+				xbc_node_get_data(n));
+
+		m = xbc_node_get_child(n);
+		if (m && xbc_node_is_key(m)) {
+			n = m;
+			depth++;
+			if (depth > XBC_DEPTH_MAX)
+				return xbc_parse_error("Too many key words",
+						xbc_node_get_data(n));
+			continue;
+		}
+		len -= wlen;
+		m = xbc_node_get_next(n);
+		while (!m) {
+			n = xbc_node_get_parent(n);
+			if (!n)
+				break;
+			len -= strlen(xbc_node_get_data(n)) + 1;
+			depth--;
+			m = xbc_node_get_next(n);
+		}
+		n = m;
+	}
+
+	return 0;
+}
+
+/**
+ * xbc_init() - Parse given XBC file and build XBC internal tree
+ * @buf: boot config text
+ *
+ * This parses the boot config text in @buf. @buf must be a
+ * null terminated string and smaller than XBC_DATA_MAX.
+ * Return 0 if succeeded, or -errno if there is any error.
+ */
+int __init xbc_init(char *buf)
+{
+	char *p, *q;
+	int ret, c;
+
+	if (xbc_data)
+		return -EBUSY;
+
+	ret = strlen(buf);
+	if (ret > XBC_DATA_MAX - 1 || ret == 0)
+		return -ERANGE;
+
+	xbc_data = buf;
+	xbc_data_size = ret + 1;
+
+	p = buf;
+	do {
+		q = strpbrk(p, "{}=;\n#");
+		if (!q) {
+			p = skip_spaces(p);
+			if (*p != '\0')
+				ret = xbc_parse_error("No delimiter", p);
+			break;
+		}
+
+		c = *q;
+		*q++ = '\0';
+		switch (c) {
+		case '=':
+			ret = xbc_parse_kv(&p, q);
+			break;
+		case '{':
+			ret = xbc_open_brace(&p, q);
+			break;
+		case '#':
+			q = skip_comment(q);
+			/* fall through */
+		case ';':
+		case '\n':
+			ret = xbc_parse_key(&p, q);
+			break;
+		case '}':
+			ret = xbc_close_brace(&p, q);
+			break;
+		}
+	} while (!ret);
+
+	if (!ret)
+		ret = xbc_verify_tree();
+
+	if (ret < 0) {
+		xbc_data = NULL;
+		xbc_data_size = 0;
+	}
+
+	return ret;
+}
+
+/**
+ * xbc_debug_dump() - Dump current XBC node list
+ *
+ * Dump the current XBC node list on printk buffer for debug.
+ */
+void __init xbc_debug_dump(void)
+{
+	int i;
+
+	for (i = 0; i < xbc_node_num; i++) {
+		pr_debug("[%d] %s (%s) .next=%d, .child=%d .parent=%d\n", i,
+			xbc_node_get_data(xbc_nodes + i),
+			xbc_node_is_value(xbc_nodes + i) ? "value" : "key",
+			xbc_nodes[i].next, xbc_nodes[i].child,
+			xbc_nodes[i].parent);
+	}
+}