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/common.py

@@ -1148,6 +1148,9 @@ class BlockDifference(object):
     self.partition = partition
     self.check_first_block = check_first_block
 
+    # Due to http://b/20939131, check_first_block is disabled temporarily.
+    assert not self.check_first_block
+
     if version is None:
       version = 1
       if OPTIONS.info_dict:
@@ -1181,18 +1184,18 @@ class BlockDifference(object):
     if not self.src:
       script.Print("Image %s will be patched unconditionally." % (partition,))
     else:
+      ranges = self.src.care_map.subtract(self.src.clobbered_blocks)
+      ranges_str = ranges.to_string_raw()
       if self.version >= 3:
         script.AppendExtra(('if (range_sha1("%s", "%s") == "%s" || '
                             'block_image_verify("%s", '
                             'package_extract_file("%s.transfer.list"), '
                             '"%s.new.dat", "%s.patch.dat")) then') % (
-                            self.device, self.src.care_map.to_string_raw(),
-                            self.src.TotalSha1(),
+                            self.device, ranges_str, self.src.TotalSha1(),
                             self.device, partition, partition, partition))
       else:
         script.AppendExtra('if range_sha1("%s", "%s") == "%s" then' % (
-            self.device, self.src.care_map.to_string_raw(),
-            self.src.TotalSha1()))
+                           self.device, ranges_str, self.src.TotalSha1()))
       script.Print('Verified %s image...' % (partition,))
       script.AppendExtra('else')
 
@@ -1240,6 +1243,9 @@ class BlockDifference(object):
 
     return ctx.hexdigest()
 
+  # TODO(tbao): Due to http://b/20939131, block 0 may be changed without
+  # remounting R/W. Will change the checking to a finer-grained way to
+  # mask off those bits.
   def _CheckFirstBlock(self, script):
     r = rangelib.RangeSet((0, 1))
     srchash = self._HashBlocks(self.src, r)