Add a --vblock option to firmware_utility to only output the verification block.

src/platform/vboot_reference/vfirmware/include/firmware_image.h

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  * API definitions for a verified boot firmware image.
  * (Userland Portion)
  */
 
 #ifndef VBOOT_REFERENCE_FIRMWARE_IMAGE_H_
 #define VBOOT_REFERENCE_FIRMWARE_IMAGE_H_
@@ skipping 38 matching lines @@
 
 /* Get a verified firmware binary blob from an [image] and fill its
  * length into blob_len.
  *
  * Caller owns the returned pointer and must Free() it.
  */
 uint8_t* GetFirmwareBlob(const FirmwareImage* image, uint64_t* blob_len);
 
 /* Write firmware data from [image] into a file named [input_file].
  *
+ * If [is_just_vblock] is 1, only the verification block (excluding the
+ * actual firmware_data) is written.
  * Return 1 on success, 0 on failure.
  */
 int WriteFirmwareImage(const char* input_file,
-                       const FirmwareImage* image);
+                       const FirmwareImage* image,
+                       int is_only_vblock);
 
 /* Pretty print the contents of [image]. Only headers and metadata information
  * is printed.
  */
 void PrintFirmwareImage(const FirmwareImage* image);
 
 /* Performs a chained verify of the firmware [image].
  *
  * Returns 0 on success, error code on failure.
  */
@@ skipping 11 matching lines @@
 int AddFirmwareKeySignature(FirmwareImage* image, const char* root_key_file);
 
 /* Add firmware and preamble signature to a firmware image [image]
  * using the private signing key in file [signing_key_file].
  *
  * Return 1 on success, 0 on failure.
  */
 int AddFirmwareSignature(FirmwareImage* image, const char* signing_key_file);
 
 #endif  /* VBOOT_REFERENCE_FIRMWARE_IMAGE_H_ */