Android Recovery模式

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Android
Recovery模式
(muddogxp 原创，转载请注明)
Recovery简介
Android利用Recovery模式，进行恢复出厂设置，OTA升级，patch升级及firmware升级。
升级一般通过运行升级包中的META-INF/com/google/android/update-script脚本来执行自定义升级，脚本中是一组recovery系统能识别的UI控制，文件系统操作命令，例如write_raw_image（写FLASH分区），copy_dir（复制目录）。该包一般被下载至SDCARD和CACHE分区下。如果对该包内容感兴趣，可以从http://forum.xda-developers.com/showthread.php?t=442480下载JF升级包来看看。
升级中还涉及到包的数字签名，签名方式和普通JAR文件签名差不错。公钥会被硬编译入recovery，编译时生成在：out/target/product/XX/obj/PACKAGING/ota_keys_inc_intermediates/keys.inc
G1中的三种启动模式
MAGIC KEY:

camera +
power：bootloader模式，ADP里则可以使用fastboot模式
home + power：recovery模式
正常启动

Bootloader正常启动，又有三种方式，按照BCB（Bootloader
Control Block, 下节介绍）中的command分类：

command == 'boot-recovery'
→ 启动recovery.img。recovery模式
command ==
'update-radio/hboot' → 更新firmware（bootloader)
其他 → 启动boot.img

Recovery涉及到的其他系统及文件

CACHE分区文件

/cache/recovery/command：
recovery命令，由主系统写入。所有命令如下：
- --send_intent=anystring
  - write the text out to recovery.intent
- --update_package=root:path
  - verify install an OTA package file
- --wipe_data
  - erase user data (and cache), then reboot
- --wipe_cache
  - wipe cache (but not user data), then reboot
/cache/recovery/log：recovery过程日志，由主系统读出
/cache/recovery/intent：recovery输出的intent

MISC分区内容

Bootloader Control Block
(BCB) 存放recovery
bootloader message。结构如下：

struct
bootloader_message {
};
- command可以有以下两个值
  
  “boot-recovery”：标示recovery正在进行，或指示bootloader应该进入recovery
  mode
  
  “update-hboot/radio”：指示bootloader更新firmware
- recovery内容
  
  “recovery\n
  
  \n
  
  ”
  
  其中recovery
  command为CACHE:/recovery/command命令

两种Recovery
Case

FACTORY
RESET（恢复出厂设置）

用户选择“恢复出厂设置”

设置系统将"--wipe_data"命令写入/cache/recovery/command

系统重启，并进入recover模式（/sbin/recovery）

get_args()
将
"boot-recovery"和"--wipe_data"写入BCB

erase_root()
格式化（擦除）DATA分区

erase_root()
格式化（擦除）CACHE分区

finish_recovery()
擦除BCB

重启系统

OTA
INSTALL（OTA升级）

升级系统下载
OTA包到/cache/some-filename.zip

升级系统写入recovery命令"--update_package=CACHE:some-filename.zip"

重启，并进入recovery模式

get_args()
将"boot-recovery"
和
"--update_package=..."
写入BCB

install_package()
作升级

finish_recovery()
擦除 BCB

**
如果安装包失败 **
prompt_and_wait() 等待用户操作，选择ALT+S或ALT+W
升级或恢复出厂设置

main()
调用
maybe_install_firmware_update()

如果包里有hboot/radio的firmware则继续，否则返回

将
"boot-recovery"
和 "--wipe_cache"
写入BCB

将
firmware image写入cache分区

将
"update-radio/hboot"
和 "--wipe_cache"
写入BCB

重启系统

bootloader自身更新firmware

bootloader
将 "boot-recovery"
写入BCB

erase_root()
擦除CACHE分区

清除
BCB

main()
调用 reboot()
重启系统
Recovery模式流程
/init
→ init.rc →
/sbin/recovery →
main():recovery.c

ui_init():ui.c
［UI initialize］
- gr_init():minui/graphics.c
  ［set tty0 to graphic
  mode, open fb0]
- ev_init():minui/events.c
  [open /dev/input/event*]
- res_create_surface:minui/resource.c
  [create surfaces for all bitmaps used later, include icons, bmps]
- create
  2 threads: progress/input_thread [create progress show and input
  event handler thread]
get_args():recovery.c
- get_bootloader_message():bootloader.c
  [read mtdblock0(misc partition) 2nd page for
  commandline]
- check
  if nand misc partition has boot message. If yes, fill argc/argv.
- If
  no, get arguments from /cache/recovery/command, and fill argc/argv.
- set_bootloader_message():bootloader.c
  [set bootloader message back to mtdblock0]
Parser
argv[] filled above
register_update_commands():commands.c
[ register all commands with name and hook function ]
- registerCommand():commands.c
  - Register
    command with name, hook, type, cookie.
  - Commands,
    e.g: assert, delete, copy_dir, symlink, write_raw_image.
- registerFunction():commands.c
  - Register
    function with name, hook, cookie.
  - Function,
    e.g: get_mark, matches, getprop, file_contains
install_package():
- translate_root_path():roots.c
  [ "SYSTEM:lib" and turns it into a string like
  "/system/lib", translate the updater.zip path ]
- mzOpenZipArchive():zip.c
  [ open updater.zip file (uncompass) ]
- handle_update_package():install.c
  - verify_jar_signature():verifier.c
    [ verify signature with keys.inc key; verify manifest and zip
    package archive ]
    - verifySignature()
      [ verify the signature file: CERT.sf/rsa. ]
      - digestEntry():verifier.c
        [ get SHA-1 digest of CERT.sf file ]
      - RSA_verify(public
        key:keys.inc, signature:CERT.rsa, CERT.sf's digest):libc/rsa.c
        [ Verify a 2048 bit RSA PKCS1.5 signature against an expected
        SHA-1 hash. Use public key to decrypt the CERT.rsa to get
        original SHA digest, then compare to digest of CERT.sf ]
    - verifyManifest()
      [ Get manifest SHA1-Digest from CERT.sf. Then do digest to
      MANIFEST.MF. Compare them ]
    - verifyArchive()
      [ verify all the files in update.zip with digest listed in
      MANIFEST.MF ]
  - find_update_script():install.c
    [ find META-INF/com/google/android/update-script updater script ]
  - handle_update_script():install.c
    [ read cmds from script file, and do parser, exec ]
    - parseAmendScript():amend.c
      [ call yyparse() to parse to command ]
    - exeCommandList():install.c
      - exeCommand():execute.c
        [ call command hook function ]
erase
DATA/CACHE partition
prompt_and_wait():recovery.c
[ wait for user input: 1) reboot 2) update.zip 3) wipe data ]
- ui_key_xxx
  get ALT+x keys
- 1)
  do nothing
- 2)
  install_package('SDCARD:update.zip')
- 3)
  erase_root() →
  format_root_device() DATA/CACHE
may_install_firmware_update():firmware.c
[ remember_firmware_update() is called by write_hboot/radio_image
command, it stores the bootloader image to CACHE partition, and
write update-hboot/radio command to MISC partition for bootloader
message to let bootloader update itself after reboot ]
- set_bootloader_message()
- write_update_for_bootloader():bootloader.c
  [ write firmware image into CACHE partition with update_header,
  busyimage and failimage ]
finish_recovery():recovery.c
[ clear the recovery command and prepare to boot a (hopefully
working) system, copy our log file to cache as well (for the system
to read), and record any intent we were asked to communicate back to
the system. ]
reboot()

Recovery模式流程图
以下流程图绘制了系统从启动加载bootloader后的行为流程。