make otapackage是Android Build系统支持的命令，用来生成Recovery系统能够进行升级的zip包。因此，想要了解Android的OTA升级机制，我们首先需要学习make otapackage命令的执行过程。
为了防止泄密，以下源码内容都是基于Android4.4.2_r1分支进行分析。
make otapackage是一个.PHONY伪目标。make系统中，伪目标并不是一个文件，只是一个标签，由于伪目标不是文件，所以make无法生成它的依赖关系和决定它是否要执行。我们只能通过显示的指明这个“目标”才能让其生效。需要注意的是，伪目标的取名不能和文件名重名，不然就失去伪目标的意义了。
了解了.PHONY之后，我们来看一下make otapackage的make源码：
.PHONY: otapackage
otapackage: $(INTERNAL_OTA_PACKAGE_TARGET)通过make代码，我们看到otapackage这个伪目标是依赖于$(INTERNAL_OTA_PACKAGE_TARGET)的，接下来，我会分析一下依赖文件的生成源码:
INTERNAL_OTA_PACKAGE_TARGET := $(PRODUCT_OUT)/$(name).zip
$(INTERNAL_OTA_PACKAGE_TARGET): KEY_CERT_PAIR := $(DEFAULT_KEY_CERT_PAIR)
$(INTERNAL_OTA_PACKAGE_TARGET): $(BUILT_TARGET_FILES_PACKAGE) $(DISTTOOLS)
@echo "Package OTA: $@"
$(hide) ./build/tools/releasetools/ota_from_target_files -v -p $(HOST_OUT) -k $(KEY_CERT_PAIR) $(BUILT_TARGET_FILES_PACKAGE) $@可以看到，$(INTERNAL_OTA_PACKAGE_TARGET)依赖于$(KEY_CERT_PAIR),$(HOST_OUT),$(BUILT_TARGET_FILES_PACKAGE)这三个文件和$(DISTTOOLS)所代表的jar包。
而这些所依赖的文件，最后都会作为参数传递给ota_from_target_files这个python脚本，这个python脚本会进一步生成最终的recovery升级包。示例参数如下：
[‘-v‘, ‘-p‘, ‘out/host/linux-x86‘, ‘-k‘, ‘build/target/product/security/testkey‘, ‘out/target/product/xxx/obj/PACKAGING/target_files_intermediates/product-target_files-wangzhengyi.zip‘, ‘out/target/product/xxx/product_20150724.1246-ota.zip‘]从参数中可以看出，out/target/product/xxx/product_20150724.1246-ota.zip是最终的recovery升级包，而out/target/product/xxx/obj/PACKAGING/target_files_intermediates/product-target_files-wangzhengyi.zip是中间的临时zip包，它其实就是$(BUILT_TARGET_FILES_PACKAGE)，接下来我们看一下$(BUILT_TARGET_FILES_PACKAGE)的生成代码。
BUILT_TARGET_FILES_PACKAGE的make源码如下：
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
endif
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,sqlite3)/sqlite3 $(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)
$(BUILT_TARGET_FILES_PACKAGE): PRIVATE_RECOVERY_FSTAB_VERSION := $(RECOVERY_FSTAB_VERSION)
# 开始构建中间zip包
$(BUILT_TARGET_FILES_PACKAGE): $(INSTALLED_BOOTIMAGE_TARGET) $(INSTALLED_RADIOIMAGE_TARGET) $(INSTALLED_RECOVERYIMAGE_TARGET) $(INSTALLED_SYSTEMIMAGE) $(INSTALLED_USERDATAIMAGE_TARGET) $(INSTALLED_CACHEIMAGE_TARGET) $(INSTALLED_VENDORIMAGE_TARGET) $(INSTALLED_ANDROID_INFO_TXT_TARGET) $(SELINUX_FC) $(built_ota_tools) $(APKCERTS_FILE) $(HOST_OUT_EXECUTABLES)/fs_config | $(ACP)
@echo "Package target files: $@"
# 删除之前的zip文件
$(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) $(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_PAGESIZE
$(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/RECOVERY/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)
ifdef BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE
@# Contents of the vendor image
$(hide) $(call package_files-copy-root, $(TARGET_OUT_VENDOR), $(zip_root)/VENDOR)
endif
@# 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
# 向otakeys.txt文件中写入各种信息
$(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
$(hide) echo "fstab_version=$(PRIVATE_RECOVERY_FSTAB_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
$(hide) echo "tool_extensions=$(tool_extensions)" >> $(zip_root)/META/misc_info.txt
$(hide) echo "default_system_dev_certificate=$(DEFAULT_SYSTEM_DEV_CERTIFICATE)" >> $(zip_root)/META/misc_info.txt
ifdef PRODUCT_EXTRA_RECOVERY_KEYS
$(hide) echo "extra_recovery_keys=$(PRODUCT_EXTRA_RECOVERY_KEYS)" >> $(zip_root)/META/misc_info.txt
endif
$(hide) echo "mkbootimg_args=$(BOARD_MKBOOTIMG_ARGS)" >> $(zip_root)/META/misc_info.txt
$(hide) echo "use_set_metadata=1" >> $(zip_root)/META/misc_info.txt
$(hide) echo "update_rename_support=1" >> $(zip_root)/META/misc_info.txt
$(call generate-userimage-prop-dictionary, $(zip_root)/META/misc_info.txt)
# 打包zip包
$(hide) (cd $(zip_root) && zip -qry ../$(notdir $@) .)
$(hide) zipinfo -1 $@ | awk ‘BEGIN { FS="SYSTEM/" } /^SYSTEM\// {print "system/" $$2}‘ | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/filesystem_config.txt
$(hide) zipinfo -1 $@ | awk ‘BEGIN { FS="BOOT/RAMDISK/" } /^BOOT\/RAMDISK\// {print $$2}‘ | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/boot_filesystem_config.txt
$(hide) zipinfo -1 $@ | awk ‘BEGIN { FS="RECOVERY/RAMDISK/" } /^RECOVERY\/RAMDISK\// {print $$2}‘ | $(HOST_OUT_EXECUTABLES)/fs_config -C -S $(SELINUX_FC) > $(zip_root)/META/recovery_filesystem_config.txt
$(hide) (cd $(zip_root) && zip -q ../$(notdir $@) META/*filesystem_config.txt)
.PHONY: target-files-package
target-files-package: $(BUILT_TARGET_FILES_PACKAGE)不知道大家第一次看到这段代码，第一感觉如何，会不会觉得很难理解？
反正，我学习Android Build系统的makefile源码时候，都感觉很晕、很绕、很难入手，毕竟我之前是写解释型语言的。这里给大家介绍两个经验：
接下来，我进一步解释一下上面这块目标(target-files-package)主要实现了哪些功能：
上面的make系统只是生成了target-files-package这个临时目标文件，而最终Recovery系统能使用的zip包还需要经过ota_from_target_files脚本处理。
ota_from_target_files脚本还是很强大的，可以生成：
这里我们只介绍OTA全量包的生成过程。
在最初的otapackage的make源码中，我们已经看到，最终是会调用ota_from_target_files脚本的，并且还有必要的参数传递，这里给出示例的参数如下：
[‘-v‘, ‘-p‘, ‘out/host/linux-x86‘, ‘-k‘, ‘build/target/product/security/testkey‘, ‘out/target/product/xxx/obj/PACKAGING/target_files_intermediates/product-target_files-wangzhengyi.zip‘, ‘out/target/product/xxx/product_20150724.1246-ota.zip‘]参数作用：
跟OTA增量升级相关的源码如下(为了理清逻辑关系，我的代码顺序和声明顺序正好是反过来的)：
if __name__ == ‘__main__‘:
try:
main(sys.argv[1:])
except common.ExternalError, e:
print
print " ERROR: %s" % (e,)
print
sys.exit(1)
def main(argv):
# 调用getprop.getprop处理我们传入的参数，这里省略处理参数代码
# 处理参数主要是为了给OPTIONS对象赋值
# 以上面的传入参数为例，处理之后，OPTIONS对象的成员属性赋值如下：
# OPTIONS.package_key = build/target/product/security/testkey
# OPTIONS.verbose = True
# OPTIONS.search_path = out/host/linux-x86
if len(args) != 2:
# args是getprop.getprop无法处理的参数
# 这里的args是[‘target-files-package‘, ‘final ota zip name‘]组成的list
sys.exit(1)
print "unzipping target target-files..."
# OPTIONS.input_tmp保存解压目录名称
# input_zip为根据target-files-package生成的zipfile对象
OPTIONS.input_tmp, input_zip = common.UnzipTemp(args[0])
OPTIONS.target_tmp = OPTIONS.input_tmp
# 主要是解析如下三个文件，并将文件内容以(k,v)键值对形式保存到OPTIONS.info_dict中
# 三个文件分别是：
# 1. META/misc_info.txt
# 2. SYSTEM/build.prop
# 3. RECOVERY/RAMDISK/etc/recovery.fstab
OPTIONS.info_dict = common.LoadInfoDict(input_zip)
if "selinux_fc" in OPTIONS.info_dict:
OPTIONS.info_dict["selinux_fc"] = os.path.join(OPTIONS.input_tmp, "BOOT", "RAMDISK", "file_contexts")
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
temp_zip_file = tempfile.NamedTemporaryFile()
output_zip = zipfile.ZipFile(temp_zip_file, "w", compression=zipfile.ZIP_DEFLATED)
# 构造全量包时OPTIONS.incremental_source的值为None
if OPTIONS.incremental_source is None:
# 构造全量包的关键函数，稍微重点分析
WriteFullOTAPackage(input_zip, output_zip)
if OPTIONS.package_key is None:
OPTIONS.package_key = OPTIONS.info_dict.get(
"default_system_dev_certificate",
"build/target/product/security/testkey")
output_zip.close()
# 对全量包进行防篡改签名，并进行重命名，稍微重点分析
SignOutput(temp_zip_file.name, args[1])
temp_zip_file.close()
print "done."
# common类的UnzipTemp函数源码
def UnzipTemp(filename, pattern=None):
# 创建/tmp目录下临时文件，用于存储target-files-package解压的内容
tmp = tempfile.mkdtemp(prefix="targetfiles-")
OPTIONS.tempfiles.append(tmp)
def unzip_to_dir(filename, dirname):
cmd = ["unzip", "-o", "-q", filename, "-d", dirname]
p = subprocess.Popen(cmd, stdout = subprocess.PIPE)
p.communicate()
if p.returncode != 0:
raise ExternalError("failed to unzip input target-files")
unzip_to_dir(filename, tmp)
return tmp, zipfile.ZipFile(filename, "r")
# common类的LoadInfoDict函数
def LoadInfoDict(zip):
d = {}
try:
for line in zip.read("META/misc_info.txt").split("\n"):
line = line.strip()
if not line or line.startswith("#"): continue
k, v = line.split("=", 1)
d[k] = v
except KeyError:
pass
# 解析挂载信息，不上源码了
d["fstab"] = LoadRecoveryFSTab(zip, d["fstab_version"])
d["build.prop"] = LoadBuildProp(zip)
return d
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
ota_from_target_files生成全量包的代码如上所示，一些不必要看的代码我已经省略了。但是还有两处生成全量包的关键函数我这边需要重点分析。
这是根据target-files-package生成全量包的关键函数，我们来看一下它的具体实现，有一点需要解释一下，根据我们的示例参数，input_zip和output_zip分别是：
def WriteFullOTAPackage(input_zip, output_zip):
script = edify_generator.EdifyGenerator(3, OPTIONS.info_dict)
# 从build.prop文件内容中获取属性构建metadata字典
metadata = {"post-build": GetBuildProp("ro.build.fingerprint",
OPTIONS.info_dict),
"pre-device": GetBuildProp("ro.product.device",
OPTIONS.info_dict),
"post-timestamp": GetBuildProp("ro.build.data.utc",
OPTIONS.info_dict),
}
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)
# 在updater-script脚本增加时间判断,如果需要升级的版本晚于当前系统的时间，
# 则不进行更新
if not OPTIONS.omit_prereq:
ts = GetBuildProp("ro.build.date.utc", OPTIONS.info_dict)
ts_text = GetBuildProp("ro.build.date", OPTIONS.info_dict)
script.AssertOlderBuild(ts, ts_text)
# 在updater-script脚本中增加产品类型判断
AppendAssertions(script, OPTIONS.info_dict)
# 在updater-script增加进度显示
script.ShowProgress(0.5, 0)
# 安全相关，将BOOT/RAMDISK/file_contexts写入到output_zip中
if "selinux_fc" in OPTIONS.info_dict:
WritePolicyConfig(OPTIONS.info_dict["selinux_fc"], output_zip)
# 在updater-script脚本中:
# 1. 增加system分区格式化代码
# 2. 增加system分区挂载代码
# 3. 将recovery目录解压到system分区
# 4. 将system目录解压到system分区
script.FormatPartition("/system")
script.Mount("/system")
script.UnpackPackageDir("recovery", "/system")
script.UnpackPackageDir("system", "/system")
# 将input_zip的system目录文件拷贝到output_zip中,并返回链接文件名称
symlinks = CopySystemFiles(input_zip, output_zip)
script.MakeSymlinks(symlinks)
# 调用mkbootfs、minigzip、mkbootimg构造boot.img和recovery.img
boot_img = common.GetBootableImage("boot.img", "boot.img", OPTIONS.input_tmp, "BOOT")
recovery_img = common.GetBootableImage("recovery.img", "recovery.img", OPTIONS.input_tmp, "RECOVERY")
MakeRecoveryPath(OPTIONS.input_tmp, output_zip, recovery_img, boot_img)
# 在updater-script中设置system文件权限
Item.Get("system").SetPermissions(script)
# 将boot.img放入output_zip中，并在updater-script中增加写入信息
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")
# updater-script中增加分区卸载信息
script.UmountAll()
# 将updater-script和update-binary写入到output_zip
script.AddToZip(input_zip, output_zip)
#将metadata信息写入到output_zip的META-INF/com/android/metadata文件中
WriteMetadata(metadata, output_zip)
def CopySystemFiles(input_zip, output_zip=None, substitute=None):
symlinks = []
for info in input_zip.infolist():
if info.filename.startswith("SYSTEM/"):
basefilename = info.filename[7:]
if IsSymlink(info):
#链接文件
symlinks.append((input_zip.read(info.filename), "/system/" + basefilename))
else:
info2 = copy.copy(info)
fn = info2.filename = "system/" + basefilename
if output_zip is not None:
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)i
symlinks.sort()
return symlinks
def AddToZip(self, input_zip, output_zip, input_path=None):
common.ZipWriteStr(output_zip, "META-INF/com/google/android/updater-script",
"\n".join(self.script) + "\n")
if input_path is None:
data = input_zip.read("OTA/bin/updater")
else:
data = open(os.path.join(input_path, "updater")).read()
common.ZipWriteStr(output_zip, "META-INF/com/google/android/update-binary",
data, perms=0755)代码里注释写的很清楚了，大家有一点python基础，应该很好理解。
需要注意的是：这里的output_zip是tmp目录下的临时zip文件，那么真正的OTA包是在哪里生成的呢？
这就需要去看一下SignOutput的源码了。
首先，我们先看一下main函数中对SignOutput的调用：
SignOutput(temp_zip_file.name, args[1])其中：
所以，我们很容易想到通过签名之后才形成的正式OTA zip包。
源码如下：
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_file, output_zip_name, OPTIONS.package_key, pw, whole_file=True)
def SignFile(input_name, output_name, key, password, align=None, whole_file=False):
sign_name = output_name
cmd = [OPTIONS.java_path, "-Xmx2048m", "-jar",
os.path.join(OPTIONS.search_path, OPTIONS.signapk_path)]
cmd.extend(OPTIONS.extra_signapk_args)
if whole_file:
cmd.append("-w")
cmd.extend([key + OPTIONS.public_key_suffix,
key + OPTIONS.private_key_suffix,
input_name, sign_name])
p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE)
if password is not None:
password += "\n"
p.communicate(password)真正的签名执行命令如下：
java -Xmx2048m -jar out/host/linux-x86/framework/signapk.jar -w build/target/product/security/testkey.xxx.pem build/target/product/security/testkey.xxx /tmp/tmpXZiMiN out/target/product/xxx/product_20150724.1246-ota.zip这篇博客主要是总结了执行make otapackage所需要了解的依赖关系和python生成OTA包的脚本原理。
接下来，我还会总结一篇文章，是从Recovery源码角度出发，看Recovery是如何解析OTA zip包，执行升级流程。
版权声明：本文为博主原创文章，未经博主允许不得转载。
Android Recovery OTA升级（一）—— make otapackage
原文地址：http://blog.csdn.net/wzy_1988/article/details/47056035
