patch the /system/build.prop file last

Works around a problem observed on a retail device: incremental update
from build 1 to build 2 partially completed, leaving a mix of files
from the two builds.  (Why it booted into the regular system instead
of recovery to restart update installation is still a mystery.)
build.prop was one of the files updated, so the device reported itself
as having build 2.  The device hobbled along for months in this state,
until build 3 was released and the 2-to-3 incremental package
repeatedly failed (because some of the files it was trying to patch
were build 1).

This change makes updating build.prop the very last thing does by an
incremental update script, so if installation is aborted and the
regular system starts (and works at all), it will continue reporting
itself as build 1 and be sent the 1-to-2 OTA package again.

Change-Id: I1edc1dcef2bd2495b6fd96517c2f4c574b994f27
diff --git a/tools/releasetools/ota_from_target_files b/tools/releasetools/ota_from_target_files
index aead38f..4264efa 100755
--- a/tools/releasetools/ota_from_target_files
+++ b/tools/releasetools/ota_from_target_files
@@ -613,7 +613,12 @@
   so_far = 0
   script.Print("Patching system files...")
-  for fn, tf, sf, size, _ in patch_list:
+  deferred_patch_list = []
+  for item in patch_list:
+    fn, tf, sf, size, _ = item
+    if == "system/build.prop":
+      deferred_patch_list.append(item)
+      continue
     script.ApplyPatch("/"+fn, "-", tf.size, tf.sha1, sf.sha1, "patch/"+fn+".p")
     so_far += tf.size
     script.SetProgress(so_far / total_patch_size)
@@ -715,6 +720,15 @@
   if OPTIONS.extra_script is not None:
+  # Patch the build.prop file last, so if something fails but the
+  # device can still come up, it appears to be the old build and will
+  # get set the OTA package again to retry.
+  script.Print("Patching remaining system files...")
+  for item in deferred_patch_list:
+    fn, tf, sf, size, _ = item
+    script.ApplyPatch("/"+fn, "-", tf.size, tf.sha1, sf.sha1, "patch/"+fn+".p")
+  script.SetPermissions("/system/build.prop", 0, 0, 0644)
   script.AddToZip(target_zip, output_zip)
   WriteMetadata(metadata, output_zip)