libfdt: Add helper function to create a trivial, empty tree

The libfdt read/write functions are now usable enough that it's become a
moderately common pattern to use them to build and manipulate a device
tree from scratch.  For example, we do so ourself in our rw_tree1 testcase,
and qemu is starting to use this model when building device trees for some
targets such as e500.

However, the read/write functions require some sort of valid tree to begin
with, so this necessitates either having a trivial canned dtb to begin with
or, more commonly, creating an empty tree using the serial-write functions
first.

This patch adds a helper function which uses the serial-write functions to
create a trivial, empty but complete and valid tree in a supplied buffer,
ready for manipulation with the read/write functions.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

From git://git.jdl.com/software/dtc.git patch hash be6026838 with
adaptations to include/libfdt.h and lib/libfdt/Makefile for the U-Boot
environment.

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>

include/libfdt.h

@@ -1014,6 +1014,7 @@ int fdt_finish(void *fdt);
 /* Read-write functions                                               */
 /**********************************************************************/
 
+int fdt_create_empty_tree(void *buf, int bufsize);
 int fdt_open_into(const void *fdt, void *buf, int bufsize);
 int fdt_pack(void *fdt);
 

lib/libfdt/Makefile

@@ -27,7 +27,7 @@ LIB	= $(obj)libfdt.o
 
 SOBJS	=
 
-COBJS-libfdt += fdt.o fdt_ro.o fdt_rw.o fdt_strerror.o fdt_sw.o fdt_wip.o
+COBJS-libfdt += fdt.o fdt_ro.o fdt_rw.o fdt_strerror.o fdt_sw.o fdt_wip.o fdt_empty_tree.o
 
 COBJS-$(CONFIG_OF_LIBFDT) += $(COBJS-libfdt)
 COBJS-$(CONFIG_FIT) += $(COBJS-libfdt)

lib/libfdt/fdt_empty_tree.c

@@ -0,0 +1,84 @@
+/*
+ * libfdt - Flat Device Tree manipulation
+ * Copyright (C) 2012 David Gibson, IBM Corporation.
+ *
+ * libfdt is dual licensed: you can use it either under the terms of
+ * the GPL, or the BSD license, at your option.
+ *
+ *  a) This library is free software; you can redistribute it and/or
+ *     modify it under the terms of the GNU General Public License as
+ *     published by the Free Software Foundation; either version 2 of the
+ *     License, or (at your option) any later version.
+ *
+ *     This library is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public
+ *     License along with this library; if not, write to the Free
+ *     Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
+ *     MA 02110-1301 USA
+ *
+ * Alternatively,
+ *
+ *  b) Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *     1. Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *     2. Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ *     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ *     CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ *     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ *     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ *     DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ *     CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ *     SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ *     NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ *     LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ *     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *     CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ *     OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ *     EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#include "libfdt_env.h"
+
+#include <fdt.h>
+#include <libfdt.h>
+
+#include "libfdt_internal.h"
+
+int fdt_create_empty_tree(void *buf, int bufsize)
+{
+	int err;
+
+	err = fdt_create(buf, bufsize);
+	if (err)
+		return err;
+
+	err = fdt_finish_reservemap(buf);
+	if (err)
+		return err;
+
+	err = fdt_begin_node(buf, "");
+	if (err)
+		return err;
+
+	err =  fdt_end_node(buf);
+	if (err)
+		return err;
+
+	err = fdt_finish(buf);
+	if (err)
+		return err;
+
+	return fdt_open_into(buf, buf, bufsize);
+}
+