Android系統Recovery工作原理之使用update.zip升級過程分析（一）---update.zip包的製作

          Android系統Recovery工作原理之使用update.zip升級過程分析（一）---update.zip包的製作

轉自：http://blog.csdn.net/mu0206mu/article/details/7399822

         這篇及以後的篇幅將通過分析update.zip包在具體Android系統升級的過程，來理解Android系統中Recovery模式服務的工作原理。我們先從update.zip包的製作開始，然後是Android系統的啓動模式分析，Recovery工作原理，如何從我們上層開始選擇system update到重啓到Recovery服務，以及在Recovery服務中具體怎樣處理update.zip包升級的，我們的安裝腳本updater-script怎樣被解析並執行的等一系列問題。分析過程中所用的Android源碼是gingerbread0919（tcc88xx開發板標配的），測試開發板是tcc88xx。這是在工作中總結的文檔，當然在網上參考了不少內容，如有雷同純屬巧合吧，在分析過程中也存在很多未解決的問題，也希望大家不吝指教。

一、 update.zip包的目錄結構
          |----boot.img
          |----system/
          |----recovery/
                `|----recovery-from-boot.p
                `|----etc/
                        `|----install-recovery.sh
          |---META-INF/
              `|CERT.RSA
              `|CERT.SF
              `|MANIFEST.MF
              `|----com/
                     `|----google/
                             `|----android/
                                    `|----update-binary
                                    `|----updater-script
                             `|----android/
                                    `|----metadata
二、 update.zip包目錄結構詳解
         以上是我們用命令make otapackage 製作的update.zip包的標準目錄結構。
         1、boot.img是更新boot分區所需要的文件。這個boot.img主要包括kernel+ramdisk。

         2、system/目錄的內容在升級後會放在系統的system分區。主要用來更新系統的一些應用或則應用會用到的一些庫等等。可以將Android源碼編譯out/target/product/tcc8800/system/中的所有文件拷貝到這個目錄來代替。

         3、recovery/目錄中的recovery-from-boot.p是boot.img和recovery.img的補丁(patch),主要用來更新recovery分區，其中etc/目錄下的install-recovery.sh是更新腳本。
         4、update-binary是一個二進制文件，相當於一個腳本解釋器，能夠識別updater-script中描述的操作。該文件在Android源碼編譯後out/target/product/tcc8800/system bin/updater生成，可將updater重命名爲update-binary得到。
               該文件在具體的更新包中的名字由源碼中bootable/recovery/install.c中的宏ASSUMED_UPDATE_BINARY_NAME的值而定。
         5、updater-script：此文件是一個腳本文件，具體描述了更新過程。我們可以根據具體情況編寫該腳本來適應我們的具體需求。該文件的命名由源碼中bootable/recovery/updater/updater.c文件中的宏SCRIPT_NAME的值而定。
         6、 metadata文件是描述設備信息及環境變量的元數據。主要包括一些編譯選項，簽名公鑰，時間戳以及設備型號等。
         7、我們還可以在包中添加userdata目錄，來更新系統中的用戶數據部分。這部分內容在更新後會存放在系統的/data目錄下。

         8、update.zip包的簽名：update.zip更新包在製作完成後需要對其簽名，否則在升級時會出現認證失敗的錯誤提示。而且簽名要使用和目標板一致的加密公鑰。加密公鑰及加密需要的三個文件在Android源碼編譯後生成的具體路徑爲：

               out/host/linux-x86/framework/signapk.jar 

               build/target/product/security/testkey.x509.pem         

               build/target/product/security/testkey.pk8 。

              我們用命令make otapackage製作生成的update.zip包是已簽過名的，如果自己做update.zip包時必須手動對其簽名。

              具體的加密方法：$ java –jar gingerbread/out/host/linux/framework/signapk.jar –w gingerbread/build/target/product/security/testkey.x509.pem                                      gingerbread/build/target/product/security/testkey.pk8 update.zip update_signed.zip
              以上命令在update.zip包所在的路徑下執行，其中signapk.jar testkey.x509.pem以及testkey.pk8文件的引用使用絕對路徑。update.zip 是我們已經打好的包，update_signed.zip包是命令執行完生成的已經簽過名的包。
         9、MANIFEST.MF：這個manifest文件定義了與包的組成結構相關的數據。類似Android應用的mainfest.xml文件。
        10、CERT.RSA：與簽名文件相關聯的簽名程序塊文件，它存儲了用於簽名JAR文件的公共簽名。
        11、CERT.SF：這是JAR文件的簽名文件，其中前綴CERT代表簽名者。
        另外，在具體升級時，對update.zip包檢查時大致會分三步：①檢驗SF文件與RSA文件是否匹配。②檢驗MANIFEST.MF與簽名文件中的digest是否一致。③檢驗包中的文件與MANIFEST中所描述的是否一致。
三、 Android升級包update.zip的生成過程分析

         1) 對於update.zip包的製作有兩種方式，即手動製作和命令生成。

          第一種手動製作：即按照update.zip的目錄結構手動創建我們需要的目錄。然後將對應的文件拷貝到相應的目錄下，比如我們向系統中新加一個應用程序。可以將新增的應用拷貝到我們新建的update/system/app/下（system目錄是事先拷貝編譯源碼後生成的system目錄），打包並簽名後，拷貝到SD卡就可以使用了。這種方式在實際的tcc8800開發板中未測試成功。簽名部分未通過，可能與具體的開發板相關。

          第二種製作方式：命令製作。Android源碼系統中爲我們提供了製作update.zip刷機包的命令，即make otapackage。該命令在編譯源碼完成後並在源碼根目錄下執行。 具體操作方式：在源碼根目錄下執行

                ①$ . build/envsetup.sh。 

                ②$ lunch 然後選擇你需要的配置(如17)。

                ③$ make otapackage。

          在編譯完源碼後最好再執行一遍上面的①、②步防止執行③時出現未找到對應規則的錯誤提示。命令執行完成後生成的升級包所在位置在out/target/product/full_tcc8800_evm_target_files-eng.mumu.20120309.111059.zip將這個包重新命名爲update.zip，並拷貝到SD卡中即可使用。

           這種方式(即完全升級)在tcc8800開發板中已測試成功。

       2) 使用make otapackage命令生成update.zip的過程分析。
            在源碼根目錄下執行make otapackage命令生成update.zip包主要分爲兩步，第一步是根據Makefile執行編譯生成一個update原包（zip格式）。第二步是運行一個python腳本，並以上一步準備的zip包作爲輸入，最終生成我們需要的升級包。下面進一步分析這兩個過程。

            第一步：編譯Makefile。對應的Makefile文件所在位置：build/core/Makefile。從該文件的884行（tcc8800,gingerbread0919）開始會生成一個zip包，這個包最後會用來製作OTA package 或者filesystem image。先將這部分的對應的Makefile貼出來如下：

          

# -----------------------------------------------------------------
# A zip of the directories that map to the target filesystem.
# This zip can be used to create an OTA package or filesystem image
# as a post-build step.
#
name := $(TARGET_PRODUCT)
ifeq ($(TARGET_BUILD_TYPE),debug)
  name := $(name)_debug
endif
name := $(name)-target_files-$(FILE_NAME_TAG)

intermediates := $(call intermediates-dir-for,PACKAGING,target_files)
BUILT_TARGET_FILES_PACKAGE := $(intermediates)/$(name).zip
$(BUILT_TARGET_FILES_PACKAGE): intermediates := $(intermediates)
$(BUILT_TARGET_FILES_PACKAGE): \
        zip_root := $(intermediates)/$(name)

# $(1): Directory to copy
# $(2): Location to copy it to
# The "ls -A" is to prevent "acp s/* d" from failing if s is empty.
define package_files-copy-root
  if [ -d "$(strip $(1))" -a "$$(ls -A $(1))" ]; then \
    mkdir -p $(2) && \
    $(ACP) -rd $(strip $(1))/* $(2); \
  fi
endef

built_ota_tools := \
    $(call intermediates-dir-for,EXECUTABLES,applypatch)/applypatch \
    $(call intermediates-dir-for,EXECUTABLES,applypatch_static)/applypatch_static \
    $(call intermediates-dir-for,EXECUTABLES,check_prereq)/check_prereq \
    $(call intermediates-dir-for,EXECUTABLES,updater)/updater
$(BUILT_TARGET_FILES_PACKAGE): PRIVATE_OTA_TOOLS := $(built_ota_tools)

$(BUILT_TARGET_FILES_PACKAGE): PRIVATE_RECOVERY_API_VERSION := $(RECOVERY_API_VERSION)

ifeq ($(TARGET_RELEASETOOLS_EXTENSIONS),)
# default to common dir for device vendor
$(BUILT_TARGET_FILES_PACKAGE): tool_extensions := $(TARGET_DEVICE_DIR)/../common
else
$(BUILT_TARGET_FILES_PACKAGE): tool_extensions := $(TARGET_RELEASETOOLS_EXTENSIONS)
endif

# Depending on the various images guarantees that the underlying
# directories are up-to-date.
$(BUILT_TARGET_FILES_PACKAGE): \
        $(INSTALLED_BOOTIMAGE_TARGET) \
        $(INSTALLED_RADIOIMAGE_TARGET) \
        $(INSTALLED_RECOVERYIMAGE_TARGET) \
        $(INSTALLED_SYSTEMIMAGE) \
        $(INSTALLED_USERDATAIMAGE_TARGET) \
        $(INSTALLED_ANDROID_INFO_TXT_TARGET) \
        $(built_ota_tools) \
        $(APKCERTS_FILE) \
        $(HOST_OUT_EXECUTABLES)/fs_config \
        | $(ACP)
    @echo "Package target files: $@"
    $(hide) rm -rf $@ $(zip_root)
    $(hide) mkdir -p $(dir $@) $(zip_root)
    @# Components of the recovery image
    $(hide) mkdir -p $(zip_root)/RECOVERY
    $(hide) $(call package_files-copy-root, \
        $(TARGET_RECOVERY_ROOT_OUT),$(zip_root)/RECOVERY/RAMDISK)
ifdef INSTALLED_KERNEL_TARGET
    $(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/RECOVERY/kernel
endif
ifdef INSTALLED_2NDBOOTLOADER_TARGET
    $(hide) $(ACP) \
        $(INSTALLED_2NDBOOTLOADER_TARGET) $(zip_root)/RECOVERY/second
endif
ifdef BOARD_KERNEL_CMDLINE
    $(hide) echo "$(BOARD_KERNEL_CMDLINE)" > $(zip_root)/RECOVERY/cmdline
endif
ifdef BOARD_KERNEL_BASE
    $(hide) echo "$(BOARD_KERNEL_BASE)" > $(zip_root)/RECOVERY/base
endif
ifdef BOARD_KERNEL_PAGESIZE
    $(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/RECOVERY/pagesize
endif
    @# Components of the boot image
    $(hide) mkdir -p $(zip_root)/BOOT
    $(hide) $(call package_files-copy-root, \
        $(TARGET_ROOT_OUT),$(zip_root)/BOOT/RAMDISK)
ifdef INSTALLED_KERNEL_TARGET
    $(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/BOOT/kernel
endif
ifdef INSTALLED_2NDBOOTLOADER_TARGET
    $(hide) $(ACP) \
        $(INSTALLED_2NDBOOTLOADER_TARGET) $(zip_root)/BOOT/second
endif
ifdef BOARD_KERNEL_CMDLINE
    $(hide) echo "$(BOARD_KERNEL_CMDLINE)" > $(zip_root)/BOOT/cmdline
endif
ifdef BOARD_KERNEL_BASE
    $(hide) echo "$(BOARD_KERNEL_BASE)" > $(zip_root)/BOOT/base
endif
ifdef BOARD_KERNEL_PAGESIZE
    $(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/BOOT/pagesize
endif
    $(hide) $(foreach t,$(INSTALLED_RADIOIMAGE_TARGET),\
                mkdir -p $(zip_root)/RADIO; \
                $(ACP) $(t) $(zip_root)/RADIO/$(notdir $(t));)
    @# Contents of the system image
    $(hide) $(call package_files-copy-root, \
        $(SYSTEMIMAGE_SOURCE_DIR),$(zip_root)/SYSTEM)
    @# Contents of the data image
    $(hide) $(call package_files-copy-root, \
        $(TARGET_OUT_DATA),$(zip_root)/DATA)
    @# Extra contents of the OTA package
    $(hide) mkdir -p $(zip_root)/OTA/bin
    $(hide) $(ACP) $(INSTALLED_ANDROID_INFO_TXT_TARGET) $(zip_root)/OTA/
    $(hide) $(ACP) $(PRIVATE_OTA_TOOLS) $(zip_root)/OTA/bin/
    @# Files that do not end up in any images, but are necessary to
    @# build them.
    $(hide) mkdir -p $(zip_root)/META
    $(hide) $(ACP) $(APKCERTS_FILE) $(zip_root)/META/apkcerts.txt
    $(hide) echo "$(PRODUCT_OTA_PUBLIC_KEYS)" > $(zip_root)/META/otakeys.txt
    $(hide) echo "recovery_api_version=$(PRIVATE_RECOVERY_API_VERSION)" > $(zip_root)/META/misc_info.txt
ifdef BOARD_FLASH_BLOCK_SIZE
    $(hide) echo "blocksize=$(BOARD_FLASH_BLOCK_SIZE)" >> $(zip_root)/META/misc_info.txt
endif
ifdef BOARD_BOOTIMAGE_PARTITION_SIZE
    $(hide) echo "boot_size=$(BOARD_BOOTIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
endif
ifdef BOARD_RECOVERYIMAGE_PARTITION_SIZE
    $(hide) echo "recovery_size=$(BOARD_RECOVERYIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
endif
ifdef BOARD_SYSTEMIMAGE_PARTITION_SIZE
    $(hide) echo "system_size=$(BOARD_SYSTEMIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
endif
ifdef BOARD_USERDATAIMAGE_PARTITION_SIZE
    $(hide) echo "userdata_size=$(BOARD_USERDATAIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
endif
    $(hide) echo "tool_extensions=$(tool_extensions)" >> $(zip_root)/META/misc_info.txt
ifdef mkyaffs2_extra_flags
    $(hide) echo "mkyaffs2_extra_flags=$(mkyaffs2_extra_flags)" >> $(zip_root)/META/misc_info.txt
endif
    @# Zip everything up, preserving symlinks
    $(hide) (cd $(zip_root) && zip -qry ../$(notdir $@) .)
    @# Run fs_config on all the system files in the zip, and save the output
    $(hide) zipinfo -1 $@ | awk -F/ 'BEGIN { OFS="/" } /^SYSTEM\// {$$1 = "system"; print}' | $(HOST_OUT_EXECUTABLES)/fs_config > $(zip_root)/META/filesystem_config.txt
    $(hide) (cd $(zip_root) && zip -q ../$(notdir $@) META/filesystem_config.txt)


target-files-package: $(BUILT_TARGET_FILES_PACKAGE)


ifneq ($(TARGET_SIMULATOR),true)
ifneq ($(TARGET_PRODUCT),sdk)
ifneq ($(TARGET_DEVICE),generic)
ifneq ($(TARGET_NO_KERNEL),true)
ifneq ($(recovery_fstab),)

            根據上面的Makefile可以分析這個包的生成過程：

            首先創建一個root_zip根目錄，並依次在此目錄下創建所需要的如下其他目錄

            ①創建RECOVERY目錄，並填充該目錄的內容，包括kernel的鏡像和recovery根文件系統的鏡像。此目錄最終用於生成recovery.img。

            ②創建並填充BOOT目錄。包含kernel和cmdline以及pagesize大小等，該目錄最終用來生成boot.img。
            ③向SYSTEM目錄填充system image。
            ④向DATA填充data image。
            ⑤用於生成OTA package包所需要的額外的內容。主要包括一些bin命令。
            ⑥創建META目錄並向該目錄下添加一些文本文件，如apkcerts.txt(描述apk文件用到的認證證書)，misc_info.txt(描述Flash內存的塊大小以及boot、recovery、system、userdata等分區的大小信息)。
            ⑦使用保留連接選項壓縮我們在上面獲得的root_zip目錄。
            ⑧使用fs_config(build/tools/fs_config)配置上面的zip包內所有的系統文件(system/下各目錄、文件)的權限屬主等信息。fs_config包含了一個頭文件#include“private/android_filesystem_config.h”。在這個頭文件中以硬編碼的方式設定了system目錄下各文件的權限、屬主。執行完配置後會將配置後的信息以文本方式輸出 到META/filesystem_config.txt中。並再一次zip壓縮成我們最終需要的原始包。

             第二步：上面的zip包只是一個編譯過程中生成的原始包。這個原始zip包在實際的編譯過程中有兩個作用，一是用來生成OTA update升級包，二是用來生成系統鏡像。在編譯過程中若生成OTA update升級包時會調用（具體位置在Makefile的1037行到1058行）一個名爲ota_from_target_files的python腳本，位置在/build/tools/releasetools/ota_from_target_files。這個腳本的作用是以第一步生成的zip原始包作爲輸入，最終生成可用的OTA升級zip包。

             下面我們分析使用這個腳本生成最終OTA升級包的過程。

                   ㈠ 首先看一下這個腳本開始部分的幫助文檔。代碼如下：

#!/usr/bin/env python
#
# Copyright (C) 2008 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""
Given a target-files zipfile, produces an OTA package that installs
that build.  An incremental OTA is produced if -i is given, otherwise
a full OTA is produced.

Usage:  ota_from_target_files [flags] input_target_files output_ota_package

  -b  (--board_config)  <file>
      Deprecated.

  -k  (--package_key)  <key>
      Key to use to sign the package (default is
      "build/target/product/security/testkey").

  -i  (--incremental_from)  <file>
      Generate an incremental OTA using the given target-files zip as
      the starting build.

  -w  (--wipe_user_data)
      Generate an OTA package that will wipe the user data partition
      when installed.

  -n  (--no_prereq)
      Omit the timestamp prereq check normally included at the top of
      the build scripts (used for developer OTA packages which
      legitimately need to go back and forth).

  -e  (--extra_script)  <file>
      Insert the contents of file at the end of the update script.

"""

                        下面簡單翻譯一下他們的使用方法以及選項的作用。

                        Usage: ota_from_target_files [flags] input_target_files output_ota_package
                        -b 過時的。
                        -k簽名所使用的密鑰
                        -i生成增量OTA包時使用此選項。後面我們會用到這個選項來生成OTA增量包。
                        -w是否清除userdata分區
                        -n在升級時是否不檢查時間戳，缺省要檢查，即缺省情況下只能基於舊版本升級。
                        -e是否有額外運行的腳本
                        -m執行過程中生成腳本(updater-script)所需要的格式,目前有兩種即amend和edify。對應上兩種版本升級時會採用不同的解釋器。缺省會同時生成兩種格式的腳 本。
                        -p定義腳本用到的一些可執行文件的路徑。
                        -s定義額外運行腳本的路徑。
                        -x定義額外運行的腳本可能用的鍵值對。
                        -v執行過程中打印出執行的命令。
                        -h命令幫助

                   ㈡ 下面我們分析ota_from_target_files這個python腳本是怎樣生成最終zip包的。先講這個腳本的代碼貼出來如下：

import sys

if sys.hexversion < 0x02040000:
  print >> sys.stderr, "Python 2.4 or newer is required."
  sys.exit(1)

import copy
import errno
import os
import re
import sha
import subprocess
import tempfile
import time
import zipfile

import common
import edify_generator

OPTIONS = common.OPTIONS
OPTIONS.package_key = "build/target/product/security/testkey"
OPTIONS.incremental_source = None
OPTIONS.require_verbatim = set()
OPTIONS.prohibit_verbatim = set(("system/build.prop",))
OPTIONS.patch_threshold = 0.95
OPTIONS.wipe_user_data = False
OPTIONS.omit_prereq = False
OPTIONS.extra_script = None
OPTIONS.worker_threads = 3

def MostPopularKey(d, default):
  """Given a dict, return the key corresponding to the largest
  value.  Returns 'default' if the dict is empty."""
  x = [(v, k) for (k, v) in d.iteritems()]
  if not x: return default
  x.sort()
  return x[-1][1]


def IsSymlink(info):
  """Return true if the zipfile.ZipInfo object passed in represents a
  symlink."""
  return (info.external_attr >> 16) == 0120777


class Item:
  """Items represent the metadata (user, group, mode) of files and
  directories in the system image."""
  ITEMS = {}
  def __init__(self, name, dir=False):
    self.name = name
    self.uid = None
    self.gid = None
    self.mode = None
    self.dir = dir

    if name:
      self.parent = Item.Get(os.path.dirname(name), dir=True)
      self.parent.children.append(self)
    else:
      self.parent = None
    if dir:
      self.children = []

  def Dump(self, indent=0):
    if self.uid is not None:
      print "%s%s %d %d %o" % ("  "*indent, self.name, self.uid, self.gid, self.mode)
    else:
      print "%s%s %s %s %s" % ("  "*indent, self.name, self.uid, self.gid, self.mode)
    if self.dir:
      print "%s%s" % ("  "*indent, self.descendants)
      print "%s%s" % ("  "*indent, self.best_subtree)
      for i in self.children:
        i.Dump(indent=indent+1)

  @classmethod
  def Get(cls, name, dir=False):
    if name not in cls.ITEMS:
      cls.ITEMS[name] = Item(name, dir=dir)
    return cls.ITEMS[name]

  @classmethod
  def GetMetadata(cls, input_zip):

    try:
      # See if the target_files contains a record of what the uid,
      # gid, and mode is supposed to be.
      output = input_zip.read("META/filesystem_config.txt")
    except KeyError:
      # Run the external 'fs_config' program to determine the desired
      # uid, gid, and mode for every Item object.  Note this uses the
      # one in the client now, which might not be the same as the one
      # used when this target_files was built.
      p = common.Run(["fs_config"], stdin=subprocess.PIPE,
                     stdout=subprocess.PIPE, stderr=subprocess.PIPE)
      suffix = { False: "", True: "/" }
      input = "".join(["%s%s\n" % (i.name, suffix[i.dir])
                       for i in cls.ITEMS.itervalues() if i.name])
      output, error = p.communicate(input)
      assert not error

    for line in output.split("\n"):
      if not line: continue
      name, uid, gid, mode = line.split()
      i = cls.ITEMS.get(name, None)
      if i is not None:
        i.uid = int(uid)
        i.gid = int(gid)
        i.mode = int(mode, 8)
        if i.dir:
          i.children.sort(key=lambda i: i.name)

    # set metadata for the files generated by this script.
    i = cls.ITEMS.get("system/recovery-from-boot.p", None)
    if i: i.uid, i.gid, i.mode = 0, 0, 0644
    i = cls.ITEMS.get("system/etc/install-recovery.sh", None)
    if i: i.uid, i.gid, i.mode = 0, 0, 0544

  def CountChildMetadata(self):
    """Count up the (uid, gid, mode) tuples for all children and
    determine the best strategy for using set_perm_recursive and
    set_perm to correctly chown/chmod all the files to their desired
    values.  Recursively calls itself for all descendants.

    Returns a dict of {(uid, gid, dmode, fmode): count} counting up
    all descendants of this node.  (dmode or fmode may be None.)  Also
    sets the best_subtree of each directory Item to the (uid, gid,
    dmode, fmode) tuple that will match the most descendants of that
    Item.
    """

    assert self.dir
    d = self.descendants = {(self.uid, self.gid, self.mode, None): 1}
    for i in self.children:
      if i.dir:
        for k, v in i.CountChildMetadata().iteritems():
          d[k] = d.get(k, 0) + v
      else:
        k = (i.uid, i.gid, None, i.mode)
        d[k] = d.get(k, 0) + 1

    # Find the (uid, gid, dmode, fmode) tuple that matches the most
    # descendants.

    # First, find the (uid, gid) pair that matches the most
    # descendants.
    ug = {}
    for (uid, gid, _, _), count in d.iteritems():
      ug[(uid, gid)] = ug.get((uid, gid), 0) + count
    ug = MostPopularKey(ug, (0, 0))

    # Now find the dmode and fmode that match the most descendants
    # with that (uid, gid), and choose those.
    best_dmode = (0, 0755)
    best_fmode = (0, 0644)
    for k, count in d.iteritems():
      if k[:2] != ug: continue
      if k[2] is not None and count >= best_dmode[0]: best_dmode = (count, k[2])
      if k[3] is not None and count >= best_fmode[0]: best_fmode = (count, k[3])
    self.best_subtree = ug + (best_dmode[1], best_fmode[1])

    return d

  def SetPermissions(self, script):
    """Append set_perm/set_perm_recursive commands to 'script' to
    set all permissions, users, and groups for the tree of files
    rooted at 'self'."""

    self.CountChildMetadata()

    def recurse(item, current):
      # current is the (uid, gid, dmode, fmode) tuple that the current
      # item (and all its children) have already been set to.  We only
      # need to issue set_perm/set_perm_recursive commands if we're
      # supposed to be something different.
      if item.dir:
        if current != item.best_subtree:
          script.SetPermissionsRecursive("/"+item.name, *item.best_subtree)
          current = item.best_subtree

        if item.uid != current[0] or item.gid != current[1] or \
           item.mode != current[2]:
          script.SetPermissions("/"+item.name, item.uid, item.gid, item.mode)

        for i in item.children:
          recurse(i, current)
      else:
        if item.uid != current[0] or item.gid != current[1] or \
               item.mode != current[3]:
          script.SetPermissions("/"+item.name, item.uid, item.gid, item.mode)

    recurse(self, (-1, -1, -1, -1))


def CopySystemFiles(input_zip, output_zip=None,
                    substitute=None):
  """Copies files underneath system/ in the input zip to the output
  zip.  Populates the Item class with their metadata, and returns a
  list of symlinks.  output_zip may be None, in which case the copy is
  skipped (but the other side effects still happen).  substitute is an
  optional dict of {output filename: contents} to be output instead of
  certain input files.
  """

  symlinks = []

  for info in input_zip.infolist():
    if info.filename.startswith("SYSTEM/"):
      basefilename = info.filename[7:]
      if IsSymlink(info):
        symlinks.append((input_zip.read(info.filename),
                         "/system/" + basefilename))
      else:
        info2 = copy.copy(info)
        fn = info2.filename = "system/" + basefilename
        if substitute and fn in substitute and substitute[fn] is None:
          continue
        if output_zip is not None:
          if substitute and fn in substitute:
            data = substitute[fn]
          else:
            data = input_zip.read(info.filename)
          output_zip.writestr(info2, data)
        if fn.endswith("/"):
          Item.Get(fn[:-1], dir=True)
        else:
          Item.Get(fn, dir=False)

  symlinks.sort()
  return symlinks


def SignOutput(temp_zip_name, output_zip_name):
  key_passwords = common.GetKeyPasswords([OPTIONS.package_key])
  pw = key_passwords[OPTIONS.package_key]

  common.SignFile(temp_zip_name, output_zip_name, OPTIONS.package_key, pw,
                  whole_file=True)


def AppendAssertions(script, input_zip):
  device = GetBuildProp("ro.product.device", input_zip)
  script.AssertDevice(device)


def MakeRecoveryPatch(output_zip, recovery_img, boot_img):
  """Generate a binary patch that creates the recovery image starting
  with the boot image.  (Most of the space in these images is just the
  kernel, which is identical for the two, so the resulting patch
  should be efficient.)  Add it to the output zip, along with a shell
  script that is run from init.rc on first boot to actually do the
  patching and install the new recovery image.

  recovery_img and boot_img should be File objects for the
  corresponding images.

  Returns an Item for the shell script, which must be made
  executable.
  """

  d = common.Difference(recovery_img, boot_img)
  _, _, patch = d.ComputePatch()
  common.ZipWriteStr(output_zip, "recovery/recovery-from-boot.p", patch)
  Item.Get("system/recovery-from-boot.p", dir=False)

  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 = sha.sha(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
  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
  log -t recovery "Recovery image already installed"
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,
        'boot_device': boot_device,
        'recovery_type': recovery_type,
        'recovery_device': recovery_device,
        }
  common.ZipWriteStr(output_zip, "recovery/etc/install-recovery.sh", sh)
  return Item.Get("system/etc/install-recovery.sh", dir=False)


def WriteFullOTAPackage(input_zip, output_zip):
  # TODO: how to determine this?  We don't know what version it will
  # be installed on top of.  For now, we expect the API just won't
  # change very often.
  script = edify_generator.EdifyGenerator(3, OPTIONS.info_dict)

  metadata = {"post-build": GetBuildProp("ro.build.fingerprint", input_zip),
              "pre-device": GetBuildProp("ro.product.device", input_zip),
              "post-timestamp": GetBuildProp("ro.build.date.utc", input_zip),
              }

  device_specific = common.DeviceSpecificParams(
      input_zip=input_zip,
      input_version=OPTIONS.info_dict["recovery_api_version"],
      output_zip=output_zip,
      script=script,
      input_tmp=OPTIONS.input_tmp,
      metadata=metadata,
      info_dict=OPTIONS.info_dict)

  if not OPTIONS.omit_prereq:
    ts = GetBuildProp("ro.build.date.utc", input_zip)
    script.AssertOlderBuild(ts)

  AppendAssertions(script, input_zip)
  device_specific.FullOTA_Assertions()

  script.ShowProgress(0.5, 0)

  if OPTIONS.wipe_user_data:
    script.FormatPartition("/data")

  script.FormatPartition("/system")
  script.Mount("/system")
  script.UnpackPackageDir("recovery", "/system")
  script.UnpackPackageDir("system", "/system")

  symlinks = CopySystemFiles(input_zip, output_zip)
  script.MakeSymlinks(symlinks)

  boot_img = common.File("boot.img", common.BuildBootableImage(
      os.path.join(OPTIONS.input_tmp, "BOOT")))
  recovery_img = common.File("recovery.img", common.BuildBootableImage(
      os.path.join(OPTIONS.input_tmp, "RECOVERY")))
  MakeRecoveryPatch(output_zip, recovery_img, boot_img)

  Item.GetMetadata(input_zip)
  Item.Get("system").SetPermissions(script)

  common.CheckSize(boot_img.data, "boot.img", OPTIONS.info_dict)
  common.ZipWriteStr(output_zip, "boot.img", boot_img.data)
  script.ShowProgress(0.2, 0)

  script.ShowProgress(0.2, 10)
  script.WriteRawImage("/boot", "boot.img")

  script.ShowProgress(0.1, 0)
  device_specific.FullOTA_InstallEnd()

  if OPTIONS.extra_script is not None:
    script.AppendExtra(OPTIONS.extra_script)

  script.UnmountAll()
  script.AddToZip(input_zip, output_zip)
  WriteMetadata(metadata, output_zip)


def WriteMetadata(metadata, output_zip):
  common.ZipWriteStr(output_zip, "META-INF/com/android/metadata",
                     "".join(["%s=%s\n" % kv
                              for kv in sorted(metadata.iteritems())]))




def LoadSystemFiles(z):
  """Load all the files from SYSTEM/... in a given target-files
  ZipFile, and return a dict of {filename: File object}."""
  out = {}
  for info in z.infolist():
    if info.filename.startswith("SYSTEM/") and not IsSymlink(info):
      fn = "system/" + info.filename[7:]
      data = z.read(info.filename)
      out[fn] = common.File(fn, data)
  return out


def GetBuildProp(property, z):
  """Return the fingerprint of the build of a given target-files
  ZipFile object."""
  bp = z.read("SYSTEM/build.prop")
  if not property:
    return bp
  m = re.search(re.escape(property) + r"=(.*)\n", bp)
  if not m:
    raise common.ExternalError("couldn't find %s in build.prop" % (property,))
  return m.group(1).strip()


def WriteIncrementalOTAPackage(target_zip, source_zip, output_zip):
  source_version = OPTIONS.source_info_dict["recovery_api_version"]
  target_version = OPTIONS.target_info_dict["recovery_api_version"]

  if source_version == 0:
    print ("WARNING: generating edify script for a source that "
           "can't install it.")
  script = edify_generator.EdifyGenerator(source_version, OPTIONS.info_dict)

  metadata = {"pre-device": GetBuildProp("ro.product.device", source_zip),
              "post-timestamp": GetBuildProp("ro.build.date.utc", target_zip),
              }

  device_specific = common.DeviceSpecificParams(
      source_zip=source_zip,
      source_version=source_version,
      target_zip=target_zip,
      target_version=target_version,
      output_zip=output_zip,
      script=script,
      metadata=metadata,
      info_dict=OPTIONS.info_dict)

  print "Loading target..."
  target_data = LoadSystemFiles(target_zip)
  print "Loading source..."
  source_data = LoadSystemFiles(source_zip)

  verbatim_targets = []
  patch_list = []
  diffs = []
  largest_source_size = 0
  for fn in sorted(target_data.keys()):
    tf = target_data[fn]
    assert fn == tf.name
    sf = source_data.get(fn, None)

    if sf is None or fn in OPTIONS.require_verbatim:
      # This file should be included verbatim
      if fn in OPTIONS.prohibit_verbatim:
        raise common.ExternalError("\"%s\" must be sent verbatim" % (fn,))
      print "send", fn, "verbatim"
      tf.AddToZip(output_zip)
      verbatim_targets.append((fn, tf.size))
    elif tf.sha1 != sf.sha1:
      # File is different; consider sending as a patch
      diffs.append(common.Difference(tf, sf))
    else:
      # Target file identical to source.
      pass

  common.ComputeDifferences(diffs)

  for diff in diffs:
    tf, sf, d = diff.GetPatch()
    if d is None or len(d) > tf.size * OPTIONS.patch_threshold:
      # patch is almost as big as the file; don't bother patching
      tf.AddToZip(output_zip)
      verbatim_targets.append((tf.name, tf.size))
    else:
      common.ZipWriteStr(output_zip, "patch/" + tf.name + ".p", d)
      patch_list.append((tf.name, tf, sf, tf.size, sha.sha(d).hexdigest()))
      largest_source_size = max(largest_source_size, sf.size)

  source_fp = GetBuildProp("ro.build.fingerprint", source_zip)
  target_fp = GetBuildProp("ro.build.fingerprint", target_zip)
  metadata["pre-build"] = source_fp
  metadata["post-build"] = target_fp

  script.Mount("/system")
  script.AssertSomeFingerprint(source_fp, target_fp)

  source_boot = common.File("/tmp/boot.img",
                            common.BuildBootableImage(
                                os.path.join(OPTIONS.source_tmp, "BOOT")))
  target_boot = common.File("/tmp/boot.img",
                            common.BuildBootableImage(
                                os.path.join(OPTIONS.target_tmp, "BOOT")))
  updating_boot = (source_boot.data != target_boot.data)

  source_recovery = common.File("system/recovery.img",
                                common.BuildBootableImage(
                                    os.path.join(OPTIONS.source_tmp, "RECOVERY")))
  target_recovery = common.File("system/recovery.img",
                                common.BuildBootableImage(
                                    os.path.join(OPTIONS.target_tmp, "RECOVERY")))
  updating_recovery = (source_recovery.data != target_recovery.data)

  # Here's how we divide up the progress bar:
  #  0.1 for verifying the start state (PatchCheck calls)
  #  0.8 for applying patches (ApplyPatch calls)
  #  0.1 for unpacking verbatim files, symlinking, and doing the
  #      device-specific commands.

  AppendAssertions(script, target_zip)
  device_specific.IncrementalOTA_Assertions()

  script.Print("Verifying current system...")

  script.ShowProgress(0.1, 0)
  total_verify_size = float(sum([i[2].size for i in patch_list]) + 1)
  if updating_boot:
    total_verify_size += source_boot.size
  so_far = 0

  for fn, tf, sf, size, patch_sha in patch_list:
    script.PatchCheck("/"+fn, tf.sha1, sf.sha1)
    so_far += sf.size
    script.SetProgress(so_far / total_verify_size)

  if updating_boot:
    d = common.Difference(target_boot, source_boot)
    _, _, d = d.ComputePatch()
    print "boot      target: %d  source: %d  diff: %d" % (
        target_boot.size, source_boot.size, len(d))

    common.ZipWriteStr(output_zip, "patch/boot.img.p", d)

    boot_type, boot_device = common.GetTypeAndDevice("/boot", OPTIONS.info_dict)

    script.PatchCheck("%s:%s:%d:%s:%d:%s" %
                      (boot_type, boot_device,
                       source_boot.size, source_boot.sha1,
                       target_boot.size, target_boot.sha1))
    so_far += source_boot.size
    script.SetProgress(so_far / total_verify_size)

  if patch_list or updating_recovery or updating_boot:
    script.CacheFreeSpaceCheck(largest_source_size)

  device_specific.IncrementalOTA_VerifyEnd()

  script.Comment("---- start making changes here ----")

  if OPTIONS.wipe_user_data:
    script.Print("Erasing user data...")
    script.FormatPartition("/data")

  script.Print("Removing unneeded files...")
  script.DeleteFiles(["/"+i[0] for i in verbatim_targets] +
                     ["/"+i for i in sorted(source_data)
                            if i not in target_data] +
                     ["/system/recovery.img"])

  script.ShowProgress(0.8, 0)
  total_patch_size = float(sum([i[1].size for i in patch_list]) + 1)
  if updating_boot:
    total_patch_size += target_boot.size
  so_far = 0

  script.Print("Patching system files...")
  for fn, tf, sf, size, _ in patch_list:
    script.ApplyPatch("/"+fn, "-", tf.size, tf.sha1, sf.sha1, "patch/"+fn+".p")
    so_far += tf.size
    script.SetProgress(so_far / total_patch_size)

  if updating_boot:
    # Produce the boot image by applying a patch to the current
    # contents of the boot partition, and write it back to the
    # partition.
    script.Print("Patching boot image...")
    script.ApplyPatch("%s:%s:%d:%s:%d:%s"
                      % (boot_type, boot_device,
                         source_boot.size, source_boot.sha1,
                         target_boot.size, target_boot.sha1),
                      "-",
                      target_boot.size, target_boot.sha1,
                      source_boot.sha1, "patch/boot.img.p")
    so_far += target_boot.size
    script.SetProgress(so_far / total_patch_size)
    print "boot image changed; including."
  else:
    print "boot image unchanged; skipping."

  if updating_recovery:
    # Is it better to generate recovery as a patch from the current
    # boot image, or from the previous recovery image?  For large
    # updates with significant kernel changes, probably the former.
    # For small updates where the kernel hasn't changed, almost
    # certainly the latter.  We pick the first option.  Future
    # complicated schemes may let us effectively use both.
    #
    # A wacky possibility: as long as there is room in the boot
    # partition, include the binaries and image files from recovery in
    # the boot image (though not in the ramdisk) so they can be used
    # as fodder for constructing the recovery image.
    MakeRecoveryPatch(output_zip, target_recovery, target_boot)
    script.DeleteFiles(["/system/recovery-from-boot.p",
                        "/system/etc/install-recovery.sh"])
    print "recovery image changed; including as patch from boot."
  else:
    print "recovery image unchanged; skipping."

  script.ShowProgress(0.1, 10)

  target_symlinks = CopySystemFiles(target_zip, None)

  target_symlinks_d = dict([(i[1], i[0]) for i in target_symlinks])
  temp_script = script.MakeTemporary()
  Item.GetMetadata(target_zip)
  Item.Get("system").SetPermissions(temp_script)

  # Note that this call will mess up the tree of Items, so make sure
  # we're done with it.
  source_symlinks = CopySystemFiles(source_zip, None)
  source_symlinks_d = dict([(i[1], i[0]) for i in source_symlinks])

  # Delete all the symlinks in source that aren't in target.  This
  # needs to happen before verbatim files are unpacked, in case a
  # symlink in the source is replaced by a real file in the target.
  to_delete = []
  for dest, link in source_symlinks:
    if link not in target_symlinks_d:
      to_delete.append(link)
  script.DeleteFiles(to_delete)

  if verbatim_targets:
    script.Print("Unpacking new files...")
    script.UnpackPackageDir("system", "/system")

  if updating_recovery:
    script.Print("Unpacking new recovery...")
    script.UnpackPackageDir("recovery", "/system")

  script.Print("Symlinks and permissions...")

  # Create all the symlinks that don't already exist, or point to
  # somewhere different than what we want.  Delete each symlink before
  # creating it, since the 'symlink' command won't overwrite.
  to_create = []
  for dest, link in target_symlinks:
    if link in source_symlinks_d:
      if dest != source_symlinks_d[link]:
        to_create.append((dest, link))
    else:
      to_create.append((dest, link))
  script.DeleteFiles([i[1] for i in to_create])
  script.MakeSymlinks(to_create)

  # Now that the symlinks are created, we can set all the
  # permissions.
  script.AppendScript(temp_script)

  # Do device-specific installation (eg, write radio image).
  device_specific.IncrementalOTA_InstallEnd()

  if OPTIONS.extra_script is not None:
    scirpt.AppendExtra(OPTIONS.extra_script)

  script.AddToZip(target_zip, output_zip)
  WriteMetadata(metadata, output_zip)


def main(argv):

  def option_handler(o, a):
    if o in ("-b", "--board_config"):
      pass   # deprecated
    elif o in ("-k", "--package_key"):
      OPTIONS.package_key = a
    elif o in ("-i", "--incremental_from"):
      OPTIONS.incremental_source = a
    elif o in ("-w", "--wipe_user_data"):
      OPTIONS.wipe_user_data = True
    elif o in ("-n", "--no_prereq"):
      OPTIONS.omit_prereq = True
    elif o in ("-e", "--extra_script"):
      OPTIONS.extra_script = a
    elif o in ("--worker_threads"):
      OPTIONS.worker_threads = int(a)
    else:
      return False
    return True

  args = common.ParseOptions(argv, __doc__,
                             extra_opts="b:k:i:d:wne:",
                             extra_long_opts=["board_config=",
                                              "package_key=",
                                              "incremental_from=",
                                              "wipe_user_data",
                                              "no_prereq",
                                              "extra_script=",
                                              "worker_threads="],
                             extra_option_handler=option_handler)

  if len(args) != 2:
    common.Usage(__doc__)
    sys.exit(1)

  if OPTIONS.extra_script is not None:
    OPTIONS.extra_script = open(OPTIONS.extra_script).read()

  print "unzipping target target-files..."
  OPTIONS.input_tmp = common.UnzipTemp(args[0])

  OPTIONS.target_tmp = OPTIONS.input_tmp
  input_zip = zipfile.ZipFile(args[0], "r")
  OPTIONS.info_dict = common.LoadInfoDict(input_zip)
  if OPTIONS.verbose:
    print "--- target info ---"
    common.DumpInfoDict(OPTIONS.info_dict)

  if OPTIONS.device_specific is None:
    OPTIONS.device_specific = OPTIONS.info_dict.get("tool_extensions", None)
  if OPTIONS.device_specific is not None:
    OPTIONS.device_specific = os.path.normpath(OPTIONS.device_specific)
    print "using device-specific extensions in", OPTIONS.device_specific

  if OPTIONS.package_key:
    temp_zip_file = tempfile.NamedTemporaryFile()
    output_zip = zipfile.ZipFile(temp_zip_file, "w",
                                 compression=zipfile.ZIP_DEFLATED)
  else:
    output_zip = zipfile.ZipFile(args[1], "w",
                                 compression=zipfile.ZIP_DEFLATED)

  if OPTIONS.incremental_source is None:
    WriteFullOTAPackage(input_zip, output_zip)
  else:
    print "unzipping source target-files..."
    OPTIONS.source_tmp = common.UnzipTemp(OPTIONS.incremental_source)
    source_zip = zipfile.ZipFile(OPTIONS.incremental_source, "r")
    OPTIONS.target_info_dict = OPTIONS.info_dict
    OPTIONS.source_info_dict = common.LoadInfoDict(source_zip)
    if OPTIONS.verbose:
      print "--- source info ---"
      common.DumpInfoDict(OPTIONS.source_info_dict)
    WriteIncrementalOTAPackage(input_zip, source_zip, output_zip)

  output_zip.close()
  if OPTIONS.package_key:
    SignOutput(temp_zip_file.name, args[1])
    temp_zip_file.close()

  common.Cleanup()

  print "done."


if __name__ == '__main__':
  try:
    common.CloseInheritedPipes()
    main(sys.argv[1:])
  except common.ExternalError, e:
    print
    print "   ERROR: %s" % (e,)
    print
    sys.exit(1)

                       主函數main是python的入口函數，我們從main函數開始看，大概看一下main函數（腳本最後）裏的流程就能知道腳本的執行過程了。

                       ① 在main函數的開頭，首先將用戶設定的option選項存入OPTIONS變量中，它是一個python中的類。緊接着判斷有沒有額外的腳本，如果有就讀入到OPTIONS變量中。
                       ② 解壓縮輸入的zip包，即我們在上文生成的原始zip包。然後判斷是否用到device-specific extensions（設備擴展）如果用到，隨即讀入到OPTIONS變量中。
                       ③ 判斷是否簽名，然後判斷是否有新內容的增量源，有的話就解壓該增量源包放入一個臨時變量中（source_zip）。自此，所有的準備工作已完畢，隨即會調用該 腳本中最主要的函數WriteFullOTAPackage(input_zip,output_zip)
                       ④ WriteFullOTAPackage函數的處理過程是先獲得腳本的生成器。默認格式是edify。然後獲得metadata元數據，此數據來至於Android的一些環境變量。然後獲得設備配置參數比如api函數的版本。然後判斷是否忽略時間戳。
                       ⑤ WriteFullOTAPackage函數做完準備工作後就開始生成升級用的腳本文件(updater-script)了。生成腳本文件後將上一步獲得的metadata元數據寫入到輸出包out_zip。
                       ⑥至此一個完整的update.zip升級包就生成了。生成位置在：out/target/product/tcc8800/full_tcc8800_evm-ota-eng.mumu.20120315.155326.zip。將升級包拷貝到SD卡中就可以用來升級了。
四、 Android OTA增量包update.zip的生成

         在上面的過程中生成的update.zip升級包是全部系統的升級包。大小有80M多。這對手機用戶來說，用來升級的流量是很大的。而且在實際升級中，我們只希望能夠升級我們改變的那部分內容。這就需要使用增量包來升級。生成增量包的過程也需要上文中提到的ota_from_target_files.py的參與。

         下面是製作update.zip增量包的過程。

          ① 在源碼根目錄下依次執行下列命令
           $ . build/envsetup.sh
           $ lunch 選擇17
           $ make
           $ make otapackage
           執行上面的命令後會在out/target/product/tcc8800/下生成我們第一個系統升級包。我們先將其命名爲A.zip
          ② 在源碼中修改我們需要改變的部分，比如修改內核配置，增加新的驅動等等。修改後再一次執行上面的命令。就會生成第二個我們修改後生成的update.zip升級包。將  其命名爲B.zip。

          ③ 在上文中我們看了ota_from_target_files.py腳本的使用幫助，其中選項-i就是用來生成差分增量包的。使用方法是以上面的A.zip 和B.zip包作爲輸入，以update.zip包作  爲輸出。生成的update.zip就是我們最後需要的增量包。

              具體使用方式是：將上述兩個包拷貝到源碼根目錄下，然後執行下面的命令。

              $ ./build/tools/releasetools/ota_from_target_files -i A.zip B.zip update.zip。

              在執行上述命令時會出現未找到recovery_api_version的錯誤。原因是在執行上面的腳本時如果使用選項i則會調用WriteIncrementalOTAPackage會從A包和B包中的META目錄下搜索misc_info.txt來讀取recovery_api_version的值。但是在執行make  otapackage命令時生成的update.zip包中沒有這個目錄更沒有這個文檔。

              此時我們就需要使用執行make otapackage生成的原始的zip包。這個包的位置在out/target/product/tcc8800/obj/PACKAGING/target_files_intermediates/目錄下，它是在用命令make otapackage之後的中間生產物，是最原始的升級包。我們將兩次編譯的生成的包分別重命名爲A.zip和B.zip，並拷貝到SD卡根目錄下重複執行上面的命令：

               $ ./build/tools/releasetools/ota_form_target_files -i A.zip B.zip update.zip。

              在上述命令即將執行完畢時，在device/telechips/common/releasetools.py會調用IncrementalOTA_InstallEnd,在這個函數中讀取包中的RADIO/bootloader.img。

              而包中是沒有這個目錄和bootloader.img的。所以執行失敗，未能生成對應的update.zip。可能與我們未修改bootloader（升級firmware）有關。此問題在下一篇博客已經解決。

             在下一篇中講解制作增量包失敗的原因，以及解決方案。