Add support for clobbered blocks

In ext4 filesystems, some blocks might be changed even being mounted
R/O, such as the superblock (block 0). We need to exclude such blocks
from integrity verification. Plus such blocks should always be
written to the target by copying instead of patching.

Bug: http://b/20939131
Change-Id: I657025b7b1ad50d4365e7b18dc39308facfe864e
(cherry picked from commit ff7778166b)

tools/releasetools/ota_from_target_files.py

@@ -475,7 +475,13 @@ def GetImage(which, tmpdir, info_dict):
       path = add_img_to_target_files.BuildVendor(
           tmpdir, info_dict, block_list=mappath)
 
-  return sparse_img.SparseImage(path, mappath)
+  # Bug: http://b/20939131
+  # In ext4 filesystems, block 0 might be changed even being mounted
+  # R/O. We add it to clobbered_blocks so that it will be written to the
+  # target unconditionally. Note that they are still part of care_map.
+  clobbered_blocks = "0"
+
+  return sparse_img.SparseImage(path, mappath, clobbered_blocks)
 
 
 def WriteFullOTAPackage(input_zip, output_zip):
@@ -773,7 +779,6 @@ def WriteBlockIncrementalOTAPackage(target_zip, source_zip, output_zip):
         OPTIONS.info_dict.get("blockimgdiff_versions", "1").split(","))
 
   system_diff = common.BlockDifference("system", system_tgt, system_src,
-                                       check_first_block=True,
                                        version=blockimgdiff_version)
 
   if HasVendorPartition(target_zip):
@@ -784,7 +789,6 @@ def WriteBlockIncrementalOTAPackage(target_zip, source_zip, output_zip):
     vendor_tgt = GetImage("vendor", OPTIONS.target_tmp,
                           OPTIONS.target_info_dict)
     vendor_diff = common.BlockDifference("vendor", vendor_tgt, vendor_src,
-                                         check_first_block=True,
                                          version=blockimgdiff_version)
   else:
     vendor_diff = None