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/blockimgdiff.py

@@ -82,6 +82,7 @@ class EmptyImage(Image):
   """A zero-length image."""
   blocksize = 4096
   care_map = RangeSet()
+  clobbered_blocks = RangeSet()
   total_blocks = 0
   file_map = {}
   def ReadRangeSet(self, ranges):
@@ -114,6 +115,7 @@ class DataImage(Image):
 
     self.total_blocks = len(self.data) / self.blocksize
     self.care_map = RangeSet(data=(0, self.total_blocks))
+    self.clobbered_blocks = RangeSet()
 
     zero_blocks = []
     nonzero_blocks = []
@@ -135,6 +137,8 @@ class DataImage(Image):
     return [self.data[s*self.blocksize:e*self.blocksize] for (s, e) in ranges]
 
   def TotalSha1(self):
+    # DataImage always carries empty clobbered_blocks.
+    assert self.clobbered_blocks.size() == 0
     return sha1(self.data).hexdigest()
 
 
@@ -184,6 +188,10 @@ class Transfer(object):
 #      (Typically a domain is a file, and the key in file_map is the
 #      pathname.)
 #
+#    clobbered_blocks: a RangeSet containing which blocks contain data
+#      but may be altered by the FS. They need to be excluded when
+#      verifying the partition integrity.
+#
 #    ReadRangeSet(): a function that takes a RangeSet and returns the
 #      data contained in the image blocks of that RangeSet.  The data
 #      is returned as a list or tuple of strings; concatenating the
@@ -193,7 +201,7 @@ class Transfer(object):
 #
 #    TotalSha1(): a function that returns (as a hex string) the SHA-1
 #      hash of all the data in the image (ie, all the blocks in the
-#      care_map)
+#      care_map minus clobbered_blocks).
 #
 # When creating a BlockImageDiff, the src image may be None, in which
 # case the list of transfers produced will never read from the
@@ -844,6 +852,12 @@ class BlockImageDiff(object):
                  "zero", self.transfers)
         continue
 
+      elif tgt_fn == "__COPY":
+        # "__COPY" domain includes all the blocks not contained in any
+        # file and that need to be copied unconditionally to the target.
+        Transfer(tgt_fn, None, tgt_ranges, empty, "new", self.transfers)
+        continue
+
       elif tgt_fn in self.src.file_map:
         # Look for an exact pathname match in the source.
         Transfer(tgt_fn, tgt_fn, tgt_ranges, self.src.file_map[tgt_fn],