Please do not merge (already submitted downstream); check entire recovery partition on startup

Checksum the entire recovery partition at boot time to see if we need
to rewrite it, rather than just the first 2kb.

Bug: 5668350
Change-Id: I777754f92e8da630ae3c09bb0d4c41884ff62f39
diff --git a/tools/releasetools/ota_from_target_files b/tools/releasetools/ota_from_target_files
index 0a27a19..1514ea7 100755
--- a/tools/releasetools/ota_from_target_files
+++ b/tools/releasetools/ota_from_target_files
@@ -336,13 +336,8 @@
   boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)
   recovery_type, recovery_device = common.GetTypeAndDevice("/recovery", OPTIONS.info_dict)
 
-  # Images with different content will have a different first page, so
-  # we check to see if this recovery has already been installed by
-  # testing just the first 2k.
-  HEADER_SIZE = 2048
-  header_sha1 = common.sha1(recovery_img.data[:HEADER_SIZE]).hexdigest()
   sh = """#!/system/bin/sh
-if ! applypatch -c %(recovery_type)s:%(recovery_device)s:%(header_size)d:%(header_sha1)s; then
+if ! applypatch -c %(recovery_type)s:%(recovery_device)s:%(recovery_size)d:%(recovery_sha1)s; then
   log -t recovery "Installing new recovery image"
   applypatch %(boot_type)s:%(boot_device)s:%(boot_size)d:%(boot_sha1)s %(recovery_type)s:%(recovery_device)s %(recovery_sha1)s %(recovery_size)d %(boot_sha1)s:/system/recovery-from-boot.p
 else
@@ -350,8 +345,6 @@
 fi
 """ % { 'boot_size': boot_img.size,
         'boot_sha1': boot_img.sha1,
-        'header_size': HEADER_SIZE,
-        'header_sha1': header_sha1,
         'recovery_size': recovery_img.size,
         'recovery_sha1': recovery_img.sha1,
         'boot_type': boot_type,