diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index b6ed8a4..83425cc 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -41,6 +41,7 @@
 from hashlib import sha1, sha256
 
 import images
+import rangelib
 import sparse_img
 from blockimgdiff import BlockImageDiff
 
@@ -3759,3 +3760,124 @@
   except ExternalError as e:
     logger.warning('Unable to get boot image timestamp: %s', e)
     return None
+
+
+def GetCareMap(which, imgname):
+  """Returns the care_map string for the given partition.
+
+  Args:
+    which: The partition name, must be listed in PARTITIONS_WITH_CARE_MAP.
+    imgname: The filename of the image.
+
+  Returns:
+    (which, care_map_ranges): care_map_ranges is the raw string of the care_map
+    RangeSet; or None.
+  """
+  assert which in PARTITIONS_WITH_CARE_MAP
+
+  # which + "_image_size" contains the size that the actual filesystem image
+  # resides in, which is all that needs to be verified. The additional blocks in
+  # the image file contain verity metadata, by reading which would trigger
+  # invalid reads.
+  image_size = OPTIONS.info_dict.get(which + "_image_size")
+  if not image_size:
+    return None
+
+  image_blocks = int(image_size) // 4096 - 1
+  assert image_blocks > 0, "blocks for {} must be positive".format(which)
+
+  # For sparse images, we will only check the blocks that are listed in the care
+  # map, i.e. the ones with meaningful data.
+  if "extfs_sparse_flag" in OPTIONS.info_dict:
+    simg = sparse_img.SparseImage(imgname)
+    care_map_ranges = simg.care_map.intersect(
+        rangelib.RangeSet("0-{}".format(image_blocks)))
+
+  # Otherwise for non-sparse images, we read all the blocks in the filesystem
+  # image.
+  else:
+    care_map_ranges = rangelib.RangeSet("0-{}".format(image_blocks))
+
+  return [which, care_map_ranges.to_string_raw()]
+
+
+def AddCareMapForAbOta(output_file, ab_partitions, image_paths):
+  """Generates and adds care_map.pb for a/b partition that has care_map.
+
+  Args:
+    output_file: The output zip file (needs to be already open),
+        or file path to write care_map.pb.
+    ab_partitions: The list of A/B partitions.
+    image_paths: A map from the partition name to the image path.
+  """
+  if not output_file:
+    raise ExternalError('Expected output_file for AddCareMapForAbOta')
+
+  care_map_list = []
+  for partition in ab_partitions:
+    partition = partition.strip()
+    if partition not in PARTITIONS_WITH_CARE_MAP:
+      continue
+
+    verity_block_device = "{}_verity_block_device".format(partition)
+    avb_hashtree_enable = "avb_{}_hashtree_enable".format(partition)
+    if (verity_block_device in OPTIONS.info_dict or
+            OPTIONS.info_dict.get(avb_hashtree_enable) == "true"):
+      if partition not in image_paths:
+        logger.warning('Potential partition with care_map missing from images: %s',
+                       partition)
+        continue
+      image_path = image_paths[partition]
+      if not os.path.exists(image_path):
+        raise ExternalError('Expected image at path {}'.format(image_path))
+
+      care_map = GetCareMap(partition, image_path)
+      if not care_map:
+        continue
+      care_map_list += care_map
+
+      # adds fingerprint field to the care_map
+      # TODO(xunchang) revisit the fingerprint calculation for care_map.
+      partition_props = OPTIONS.info_dict.get(partition + ".build.prop")
+      prop_name_list = ["ro.{}.build.fingerprint".format(partition),
+                        "ro.{}.build.thumbprint".format(partition)]
+
+      present_props = [x for x in prop_name_list if
+                       partition_props and partition_props.GetProp(x)]
+      if not present_props:
+        logger.warning(
+            "fingerprint is not present for partition %s", partition)
+        property_id, fingerprint = "unknown", "unknown"
+      else:
+        property_id = present_props[0]
+        fingerprint = partition_props.GetProp(property_id)
+      care_map_list += [property_id, fingerprint]
+
+  if not care_map_list:
+    return
+
+  # Converts the list into proto buf message by calling care_map_generator; and
+  # writes the result to a temp file.
+  temp_care_map_text = MakeTempFile(prefix="caremap_text-",
+                                           suffix=".txt")
+  with open(temp_care_map_text, 'w') as text_file:
+    text_file.write('\n'.join(care_map_list))
+
+  temp_care_map = MakeTempFile(prefix="caremap-", suffix=".pb")
+  care_map_gen_cmd = ["care_map_generator", temp_care_map_text, temp_care_map]
+  RunAndCheckOutput(care_map_gen_cmd)
+
+  if not isinstance(output_file, zipfile.ZipFile):
+    shutil.copy(temp_care_map, output_file)
+    return
+  # output_file is a zip file
+  care_map_path = "META/care_map.pb"
+  if care_map_path in output_file.namelist():
+    # Copy the temp file into the OPTIONS.input_tmp dir and update the
+    # replace_updated_files_list used by add_img_to_target_files
+    if not OPTIONS.replace_updated_files_list:
+      OPTIONS.replace_updated_files_list = []
+    shutil.copy(temp_care_map, os.path.join(OPTIONS.input_tmp, care_map_path))
+    OPTIONS.replace_updated_files_list.append(care_map_path)
+  else:
+    ZipWrite(output_file, temp_care_map, arcname=care_map_path)