Android系统Recovery工作原理1 升级包 的 制作

      我们先从update.zip包的制作开始，然后是Android系统的启动模式分析，Recovery工作原理，如何从我们上层开始选择system update到重启到Recovery服务，以及在Recovery服务中具体怎样处理update.zip包升级的，我们的安装脚本updater-script怎样被解析并执行的等一系列问题。

一、 update.zip包的目录结构
          |----boot.img

          |----bootloader.img //自己添加

          |----logo.img //自己添加

          |----xxx_logo.img //自己添加

          |----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包目录结构详解
         以上是我们用命令make otapackage 制作的update.zip包的标准目录结构。
         1、boot.img是更新boot分区所需要的文件。这个boot.img主要包括kernel+ramdisk。

         2、system/目录的内容在升级后会 放在 系统的system分区。主要用来 更新系统的一些应用 或者是 更新 应用 会用到的一些库 等等。可以将Android源码编译out/target/product/tcc8800/system/中的所有文件拷贝到这个目录来代替。

         3、recovery/目录中的recovery-from-boot.p是boot.img和recovery.img的补丁(patch),主要用来更新recovery分区，其中etc/目录下的install-recovery.sh是更新脚本。
         4、update-binary是一个二进制文件，相当于一个脚本解释器，能够识别updater-script中描述的操作。该文件在Android源码编译后out/target/product/tcc8800/system bin/updater生成，可将updater重命名为update-binary得到。
               该文件在具体的更新包中的名字由源码中bootable/recovery/install.c中的宏ASSUMED_UPDATE_BINARY_NAME的值而定。
         5、updater-script：此文件是一个脚本文件，具体描述了更新过程。我们可以根据具体情况编写该脚本来适应我们的具体需求。该文件的命名由源码中bootable/recovery/updater/updater.c文件中的宏SCRIPT_NAME的值而定。
         6、 metadata文件是描述 设备信息 及 环境变量 的元数据。主要包括一些 编译选项，签名公钥，时间戳 以及 设备型号等。
         7、我们还可以在包中添加userdata目录，来更新系统中的用户数据部分。这部分内容在更新后会存放在系统的/data目录下。

         8、update.zip包的签名：update.zip更新包在制作完成后需要对其 签名，否则在升级时会出现认证失败的错误提示。而且签名要使用和目标板一致的加密公钥。加密公钥 及 加密需要的三个文件 在Android源码编译后生成的具体路径为：

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

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

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

              我们用命令make otapackage制作生成的update.zip包是 已签过名的，如果自己做update.zip包时必须手动对其签名。

              具体的加密方法：$ 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包所在的路径下执行，其中signapk.jar testkey.x509.pem以及testkey.pk8文件的引用使用 绝对路径。update.zip 是我们已经打好的包，update_signed.zip包是命令执行完生成的已经签过名的包。
         9、MANIFEST.MF：这个manifest文件定义了与包的组成结构相关的数据。类似Android应用的mainfest.xml文件。
        10、CERT.RSA：与签名文件相关联的签名程序块文件，它存储了用于签名JAR文件的公共签名。
        11、CERT.SF：这是JAR文件的签名文件，其中前缀CERT代表签名者。
        另外，在具体升级时，对update.zip包检查时大致会分三步：①检验SF文件与RSA文件是否匹配。②检验MANIFEST.MF与签名文件中的digest是否一致。③检验包中的文件与MANIFEST中所描述的是否一致。

三、 Android升级包update.zip的生成过程分析

         1) 对于update.zip包的制作有两种方式，即 手动制作 和 命令生成。

          第一种手动制作：即按照update.zip的目录结构手动创建我们需要的目录。然后将对应的文件拷贝到相应的目录下，比如我们向系统中新加一个应用程序。可以将新增的应用拷贝到我们新建的update/system/app/下（system目录是事先拷贝编译源码后生成的system目录），打包并签名后，拷贝到SD卡就可以使用了。

          第二种制作方式：命令制作。Android源码系统中为我们提供了制作update.zip刷机包的命令，即make otapackage。该命令在编译源码完成后并在源码根目录下执行。具体操作方式：在源码根目录下执行

                ①$ . build/envsetup.sh。 

                ②$ lunch 然后选择你需要的配置(如17)。

                ③$ make otapackage。

          在编译完源码后最好再执行一遍上面的①、②步防止执行③时出现未找到对应规则的错误提示。命令执行完成后生成的升级包所在位置在out/target/product/full_tcc8800_evm_target_files-eng.mumu.20120309.111059.zip将这个包重新命名为update.zip，并拷贝到SD卡中即可使用。

       2) 使用make otapackage命令生成update.zip的过程分析。
            在源码根目录下执行make otapackage命令生成update.zip包主要分为 两步，第一步是根据Makefile执行编译生成一个update原包（zip格式）。第二步是运行一个python脚本，并以上一步准备的zip包作为输入，最终生成我们需要的升级包。下面进一步分析这两个过程。

            第一步：编译Makefile。对应的Makefile文件所在位置：build/core/Makefile。从该文件的884行（tcc8800,gingerbread0919）开始会生成一个zip包，这个包最后会用来制作OTA package 或者filesystem image。先将这部分的对应的Makefile贴出来如下：

# -----------------------------------------------------------------
# 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),)

            根据上面的Makefile可以分析这个包的生成过程：

            首先创建一个zip_root 根目录，并依次在此目录下创建所需要的 如下 其他目录

            ①创建RECOVERY目录，并填充该目录的内容，包括kernel的镜像和recovery根文件系统的镜像。此目录最终用于生成recovery.img。

            ②创建并填充BOOT目录。包含kernel和cmdline以及pagesize大小等，该目录最终用来生成boot.img。
            ③向SYSTEM目录填充system.image。
            ④向DATA填充data.image。
            ⑤用于生成OTA package包所需要的额外的内容。主要包括一些bin命令。
            ⑥创建META目录并向该目录下添加一些文本文件，如apkcerts.txt(描述apk文件用到的认证证书)，misc_info.txt(描述Flash内存的块大小以及boot、recovery、system、userdata等分区的大小信息)。
            ⑦使用保留连接选项压缩我们在上面获得的root_zip目录。
            ⑧使用fs_config(build/tools/fs_config)配置上面的zip包内所有的系统文件(system/下各目录、文件)的权限属主等信息。fs_config.c包含了一个头文件#include“private/android_filesystem_config.h”。在这个头文件中 以硬编码 的方式设定了system目录下各文件的权限、属主。执行完配置后会将配置后的信息以文本方式输出 到META/filesystem_config.txt中。并再一次zip压缩成我们最终需要的原始包。

             第二步：上面的zip包 只是一个 编译过程中 生成的 原始包。这个原始zip包在实际的编译过程中有 两个作用，一是用来生成OTA update升级包，二是用来生成系统镜像。在编译过程中 若生成OTA update升级包 时会调用（具体位置在Makefile的1037行到1058行）一个名为ota_from_target_files的python脚本，位置在/build/tools/releasetools/ota_from_target_files。这个脚本的作用是以第一步生成的zip原始包作为输入，最终生成可用的OTA升级zip包。

             下面我们分析使用这个脚本生成最终OTA升级包的过程。

                   ㈠ 首先看一下这个脚本开始部分的帮助文档。代码如下：

#!/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.

"""

                        下面简单翻译一下他们的使用方法以及选项的作用。

                        Usage: ota_from_target_files [flags] input_target_files output_ota_package
                        -b 过时的。
                        -k签名所使用的密钥
                        -i生成增量OTA包时使用此选项。后面我们会用到这个选项来生成OTA增量包。
                        -w是否清除userdata分区
                        -n在升级时是否不检查时间戳，缺省要检查，即缺省情况下只能基于旧版本升级。
                        -e是否有额外运行的脚本
                        -m执行过程中生成脚本(updater-script)所需要的格式,目前有两种即amend和edify。对应上两种版本升级时会采用不同的解释器。缺省会同时生成两种格式的脚 本。
                        -p定义脚本用到的一些可执行文件的路径。
                        -s定义额外运行脚本的路径。
                        -x定义额外运行的脚本可能用的键值对。
                        -v执行过程中打印出执行的命令。
                        -h命令帮助

                   ㈡ 下面我们分析ota_from_target_files这个python脚本是怎样生成最终zip包的。先讲这个脚本的代码贴出来如下：

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)

                       主函数main是python的入口函数，我们从main函数开始看，大概看一下main函数（脚本最后）里的流程就能知道脚本的执行过程了。

                       ① 在main函数的开头，首先将用户设定的option选项存入OPTIONS变量中，它是一个python中的类。紧接着判断有没有额外的脚本，如果有就读入到OPTIONS变量中。
                       ② 解压缩输入的zip包，即我们在上文生成的原始zip包。然后判断是否用到device-specific extensions（设备扩展）如果用到，随即读入到OPTIONS变量中。
                       ③ 判断是否签名，然后判断是否有新内容的增量源，有的话就解压该增量源包放入一个临时变量中（source_zip）。自此，所有的准备工作已完毕，随即会调用该 脚本中最主要的函数WriteFullOTAPackage(input_zip,output_zip)
                       ④ WriteFullOTAPackage函数的处理过程是先获得脚本的生成器。默认格式是edify。然后获得metadata元数据，此数据来至于Android的一些环境变量。然后获得设备配置参数比如api函数的版本。然后判断是否忽略时间戳。
                       ⑤ WriteFullOTAPackage函数做完准备工作后就开始生成升级用的脚本文件(updater-script)了。生成脚本文件后将上一步获得的metadata元数据写入到输出包out_zip。
                       ⑥至此一个完整的update.zip升级包就生成了。生成位置在：out/target/product/tcc8800/full_tcc8800_evm-ota-eng.mumu.20120315.155326.zip。将升级包拷贝到SD卡中就可以用来升级了。

四、 Android OTA增量包update.zip的生成

         在上面的过程中生成的update.zip升级包是全部系统的升级包。大小有95M多，在实际升级中，我们只希望能够升级我们改变的那部分内容。这就需要使用增量包来升级。生成增量包的过程也需要上文中提到的ota_from_target_files的参与。

         下面是制作update.zip增量包的过程。

          ① 在源码根目录下依次执行下列命令
           $ . build/envsetup.sh
           $ lunch 选择17
           $ make
           $ make otapackage
           执行上面的命令后会在out/target/product/tcc8800/下生成我们第一个系统升级包。我们先将其命名为A.zip
          ② 在源码中修改我们需要改变的部分，比如修改内核配置，增加新的驱动等等。修改后再一次执行上面的命令。就会生成第二个我们修改后生成的update.zip升级包。将  其命名为B.zip。

          ③ 在上文中我们看了ota_from_target_files.py脚本的使用帮助，其中选项-i就是用来生成差分增量包的。使用方法是以上面的A.zip 和B.zip包作为输入，以update.zip包作  为输出。生成的update.zip就是我们最后需要的增量包。

              具体使用方式是：将上述两个包拷贝到源码根目录下，然后执行下面的命令。

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

              在执行上述命令时会出现未找到recovery_api_version的错误。原因是在执行上面的脚本时如果使用选项i则会调用WriteIncrementalOTAPackage会从A包和B包中的META目录下搜索misc_info.txt来读取recovery_api_version的值。但是在执行make  otapackage命令时生成的update.zip包中没有这个目录更没有这个文档。

              此时我们就需要使用执行make otapackage生成的原始的zip包。这个包的位置在out/target/product/tcc8800/obj/PACKAGING/target_files_intermediates/目录下，它是在用命令make otapackage之后的中间生产物，是最原始的升级包。我们将两次编译的生成的原始包分别重命名为A.zip和B.zip，并拷贝到SD卡根目录下重复执行上面的命令：

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

              在上述命令即将执行完毕时，device/telechips/common/releasetools.py会调用IncrementalOTA_InstallEnd,在这个函数中 读取包中的RADIO/bootloader.img。

              而包中是没有这个目录和bootloader.img的。所以执行失败，未能生成对应的update.zip。可能与我们未修改bootloader（升级firmware）有关。此问题在下一篇博客已经解决。