Add dumpimage, a tool to extract data from U-Boot images

Given a multi-file image created through the mkimage's -d option:

  $ mkimage -A x86 -O linux -T multi -n x86 -d vmlinuz:initrd.img:System.map \
  multi.img

  Image Name:   x86
  Created:      Thu Jul 25 10:29:13 2013
  Image Type:   Intel x86 Linux Multi-File Image (gzip compressed)
  Data Size:    13722956 Bytes = 13401.32 kB = 13.09 MB
  Load Address: 00000000
  Entry Point:  00000000
  Contents:
     Image 0: 4040128 Bytes = 3945.44 kB = 3.85 MB
     Image 1: 7991719 Bytes = 7804.41 kB = 7.62 MB
     Image 2: 1691092 Bytes = 1651.46 kB = 1.61 MB

It is possible to perform the innverse operation -- extracting any file from
the image -- by using the dumpimage's -i option:

  $ dumpimage -i multi.img -p 2 System.map

Although it's feasible to retrieve "data files" from image through scripting,
the requirement to embed tools such 'dd', 'awk' and 'sed' for this sole purpose
is cumbersome and unreliable -- once you must keep track of file sizes inside
the image. Furthermore, extracting data files using "dumpimage" tool is faster
than through scripting.

Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/imagetool.h b/tools/imagetool.h
index b8adb61..c2c9aea 100644
--- a/tools/imagetool.h
+++ b/tools/imagetool.h
@@ -34,7 +34,9 @@
 	int dflag;
 	int eflag;
 	int fflag;
+	int iflag;
 	int lflag;
+	int pflag;
 	int vflag;
 	int xflag;
 	int skipcpy;
@@ -50,6 +52,7 @@
 	char *datafile;
 	char *imagefile;
 	char *cmdname;
+	const char *outfile;	/* Output filename */
 	const char *keydir;	/* Directory holding private keys */
 	const char *keydest;	/* Destination .dtb for public key */
 	const char *comment;	/* Comment to add to signature node */
@@ -97,6 +100,15 @@
 	void (*set_header) (void *, struct stat *, int,
 					struct image_tool_params *);
 	/*
+	 * This function is used by the command to retrieve a data file from
+	 * the image (i.e. dumpimage -i <image> -p <position> <data_file>).
+	 * Thus the code to extract a file from an image must be put here.
+	 *
+	 * Returns 0 if the file was successfully retrieved from the image,
+	 * or a negative value on error.
+	 */
+	int (*extract_datafile) (void *, struct image_tool_params *);
+	/*
 	 * Some image generation support for ex (default image type) supports
 	 * more than one type_ids, this callback function is used to check
 	 * whether input (-T <image_type>) is supported by registered image