Android OTA升级包制作脚本详解（二，解压缩）

第一步：解压缩（ota_from_target_files）

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

def UnzipTemp(filename, pattern=None):
  """Unzip the given archive into a temporary directory and return the name.

  If filename is of the form "foo.zip+bar.zip", unzip foo.zip into a
  temp dir, then unzip bar.zip into that_dir/BOOTABLE_IMAGES.

  Returns (tempdir, zipobj) where zipobj is a zipfile.ZipFile (of the
  main file), open for reading.
  """
  # 该函数用于创建一个临时文件夹,参数指的是临时文件夹的前缀，返回值tmp是临时文件夹的绝对路径，并赋给OPTIONS的tempfiles属性
  tmp = tempfile.mkdtemp(prefix="targetfiles-")
  OPTIONS.tempfiles.append(tmp)

  def unzip_to_dir(filename, dirname):
    #这里设置了一个变量名cmd的数组，里面存放的是需要执行的命令和参数，这个命令也就是“unzip -o -q filename -d dirname”
    cmd = ["unzip", "-o", "-q", filename, "-d", dirname]
    if pattern is not None:
      cmd.append(pattern)
	#这里调用了Run方法
    p = Run(cmd, stdout=subprocess.PIPE)
	"""Popen.communicate(input=None)与子进程进行交互。向stdin发送数据，或从stdout和stderr中读取数据。可选参数input指定发送到子进程的参数。Communicate()返回一个元组：(stdoutdata,stderrdata)。注意：如果希望通过进程的stdin向其发送数据，在创建Popen对象的时候，参数stdin必须被设置为PIPE。同样，如果希望从stdout和stderr获取数据，必须将stdout和stderr设置为PIPE。"""
    p.communicate()
    if p.returncode != 0:
      raise ExternalError("failed to unzip input target-files \"%s\"" %
                          (filename,))
  #match ：只从字符串的开始与正则表达式匹配，匹配成功返回所匹配的项，否则返回none；
  m = re.match(r"^(.*[.]zip)\+(.*[.]zip)$", filename, re.IGNORECASE)
  #如果这里加上并执行"""print m"""语句的话，结果为"""[target.zip]"""
  if m:
    unzip_to_dir(m.group(1), tmp)
    unzip_to_dir(m.group(2), os.path.join(tmp, "BOOTABLE_IMAGES"))
    filename = m.group(1)
  else:
    #这里执行解压操作，文件名的值为"target.zip",tem的值为"/tmp/targetfiles-fEX9aH"，并且调用upzip_to_dir方法来执行解压缩命令
    unzip_to_dir(filename, tmp)

  #这里返回临时路径和存储了zipfile内容的变量
  # 这里的第二个参数用r表示是读取zip文件，w是创建一个zip文件
  return tmp, zipfile.ZipFile(filename, "r")

def Run(args, **kwargs):
  """Create and return a subprocess.Popen object, printing the command
  line on the terminal if -v was specified."""
  if OPTIONS.verbose:
    print "  running: ", " ".join(args)
  """这里调用Popen模块开启新的进程用来执行系统命令,这种方式可运用对进程的控制，将返回结果复制给变量，更方便去处理。args的值实际上是一个list，用于指定进程的可执行文件及其参数。"""
  return subprocess.Popen(args, **kwargs)

  OPTIONS.target_tmp = OPTIONS.input_tmp
  OPTIONS.info_dict = common.LoadInfoDict(input_zip)

这是misc_info.txt中的内容：

recovery_api_version=3
fstab_version=2
tool_extensions=out/target/product/wt98360/obj/CUSTGEN/config/../common
default_system_dev_certificate=build/target/product/security/testkey
mkbootimg_args=
use_set_metadata=1
update_rename_support=1
fs_type=ext4
system_size=1363148800
userdata_size=1152385024
cache_size=132120576
extfs_sparse_flag=-s
mkyaffs2_extra_flags=-c 2048 -s 64   
selinux_fc=out/target/product/wt98360/root/file_contexts

具体代码如下：

def LoadInfoDict(zip):
  """Read and parse the META/misc_info.txt key/value pairs from the
  input target files and return a dict."""
  #定义一个字典变量用于存储处理后的信息
  d = {}
  try:
    #这里zip.read（）方法打开update.zip中的META/misc_info.txt，并按"\n"进行切片
    for line in zip.read("META/misc_info.txt").split("\n"):
      line = line.strip()#用于移除字符串头尾指定的字符（默认为空格）
      if not line or line.startswith("#"): continue#跳过注释信息
      k, v = line.split("=", 1)#这里按照第一个"="进行切片
      d[k] = v#封装成数据字典
  except KeyError:
    # ok if misc_info.txt doesn't exist
    pass

  # backwards compatibility: These values used to be in their own
  # files.  Look for them, in case we're processing an old
  # target_files zip.

  if "mkyaffs2_extra_flags" not in d:
    try:
      d["mkyaffs2_extra_flags"] = zip.read("META/mkyaffs2-extra-flags.txt").strip()
    except KeyError:
      # ok if flags don't exist
      pass

  if "recovery_api_version" not in d:
    try:
      d["recovery_api_version"] = zip.read("META/recovery-api-version.txt").strip()
    except KeyError:
      raise ValueError("can't find recovery API version in input target-files")

  if "tool_extensions" not in d:
    try:
      d["tool_extensions"] = zip.read("META/tool-extensions.txt").strip()
    except KeyError:
      # ok if extensions don't exist
      pass

  if "fstab_version" not in d:
    d["fstab_version"] = "1"

  try:
    data = zip.read("META/imagesizes.txt")
    for line in data.split("\n"):
      if not line: continue
      name, value = line.split(" ", 1)
      if not value: continue
      if name == "blocksize":
        d[name] = value
      else:
        d[name + "_size"] = value
  except KeyError:
    pass

  def makeint(key):
    if key in d:
      if d[key].endswith('M'):
        d[key] = d[key].split("M")[0]
        d[key] = int(d[key], 0) * 1024 * 1024
      else:
        d[key] = int(d[key], 0)

  makeint("recovery_api_version")
  makeint("blocksize")
  makeint("system_size")
  makeint("userdata_size")
  makeint("cache_size")
  makeint("recovery_size")
  makeint("boot_size")
  makeint("fstab_version")
  #wschen 2012-11-07 
  makeint("custom_size")


  d["fstab"] = LoadRecoveryFSTab(zip, d["fstab_version"])
  d["build.prop"] = LoadBuildProp(zip)
  return d

上面的代码中，在方法的末尾有分别去解析了分区表和Build属性，那么具体的操作流程，我们下面进行详细的分析

def LoadRecoveryFSTab(zip, fstab_version):
  class Partition(object):
    pass
  try:
    data = zip.read("RECOVERY/RAMDISK/etc/recovery.fstab")#当前target.zip中并没有这文件，因此这里暂不作详解
  except KeyError:
    print "Warning: could not find RECOVERY/RAMDISK/etc/recovery.fstab in %s." % zip
    data = ""
  if fstab_version == 1:
    d = {}
    for line in data.split("\n"):
      line = line.strip()
      if not line or line.startswith("#"): continue
      pieces = line.split()
      if not (3 <= len(pieces) <= 4):
        raise ValueError("malformed recovery.fstab line: \"%s\"" % (line,))
      p = Partition()
      p.mount_point = pieces[0]
      p.fs_type = pieces[1]
      p.device = pieces[2]
      p.length = 0
      options = None
      if len(pieces) >= 4:
        if pieces[3].startswith("/"):
          p.device2 = pieces[3]
          if len(pieces) >= 5:
            options = pieces[4]
        else:
          p.device2 = None
          options = pieces[3]
      else:
        p.device2 = None
      if options:
        options = options.split(",")
        for i in options:
          if i.startswith("length="):
            p.length = int(i[7:])
          else:
              print "%s: unknown option \"%s\"" % (p.mount_point, i)
      d[p.mount_point] = p

  elif fstab_version == 2:
    d = {}
    for line in data.split("\n"):
      line = line.strip()
      if not line or line.startswith("#"): continue
      pieces = line.split()
      if len(pieces) != 5:
        raise ValueError("malformed recovery.fstab line: \"%s\"" % (line,))
      # Ignore entries that are managed by vold
      options = pieces[4]
      if "voldmanaged=" in options: continue
      # It‘s a good line, parse it
      p = Partition()
      p.device = pieces[0]
      p.mount_point = pieces[1]
      p.fs_type = pieces[2]
      p.device2 = None
      p.length = 0
      options = options.split(",")
      for i in options:
        if i.startswith("length="):
          p.length = int(i[7:])
        else:
          # Ignore all unknown options in the unified fstab
          continue
      d[p.mount_point] = p
  else:
    raise ValueError("Unknown fstab_version: \"%d\"" % (fstab_version,))
  return d
第四步，解析SYSTEM/build.prop属性信息，将解析的属性信息保存为一个数据字典，并返回

def LoadBuildProp(zip):
  try:
    data = zip.read("SYSTEM/build.prop")
  except KeyError:
    print "Warning: could not find SYSTEM/build.prop in %s" % zip
    data = ""

  d = {}
  for line in data.split("\n"):
    line = line.strip()
    if not line or line.startswith("#"): continue
    name, value = line.split("=", 1)
    d[name] = value
  return d