Android recovery 系統(tǒng)

2010.08.05

Android Recovery模式

(muddogxp 原創(chuàng)，轉(zhuǎn)載請注明)

Recovery簡介

Android利用Recovery模式，進行恢復(fù)出廠設(shè)置，OTA升級，patch升級及firmware升級。

升級一般通過運行升級包中的META-INF/com/google/android/update-script腳本來執(zhí)行自定義升級，腳本中是一組recovery系統(tǒng)能識別的UI控制，文件系統(tǒng)操作命令，例如write_raw_image（寫FLASH分區(qū)），copy_dir（復(fù)制目錄）。該包一般被下載至SDCARD和CACHE分區(qū)下。如果對該包內(nèi)容感興趣，可以從http://forum.xda-developers.com/showthread.php?t=442480下載JF升級包來看看。

升級中還涉及到包的數(shù)字簽名，簽名方式和普通JAR文件簽名差不錯。公鑰會被硬編譯入recovery，編譯時生成在：out/target/product/XX/obj/PACKAGING/ota_keys_inc_intermediates/keys.inc

G1中的三種啟動模式

MAGIC KEY:

camera + power：bootloader模式，ADP里則可以使用fastboot模式

home + power：recovery模式

正常啟動

Bootloader正常啟動，又有三種方式，按照BCB（Bootloader Control Block, 下節(jié)介紹）中的command分類：

command == 'boot-recovery' → 啟動recovery.img。recovery模式

command == 'update-radio/hboot' → 更新firmware（bootloader)

其他 → 啟動boot.img

Recovery涉及到的其他系統(tǒng)及文件

CACHE分區(qū)文件

Recovery 工具通過NAND cache分區(qū)上的三個文件和主系統(tǒng)打交道。主系統(tǒng)（包括恢復(fù)出廠設(shè)置和OTA升級）可以寫入recovery所需的命令，讀出recovery過程中的LOG和intent。

/cache/recovery/command： recovery命令，由主系統(tǒng)寫入。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過程日志，由主系統(tǒng)讀出

/cache/recovery/intent：recovery輸出的intent

MISC分區(qū)內(nèi)容

Bootloader Control Block (BCB) 存放recovery bootloader message。結(jié)構(gòu)如下：

struct bootloader_message {

char command[32];

char status[32]; // 未知用途

char recovery[1024];

};

command可以有以下兩個值

“boot-recovery”：標(biāo)示recovery正在進行，或指示bootloader應(yīng)該進入recovery mode

“update-hboot/radio”：指示bootloader更新firmware
recovery內(nèi)容

“recovery\n

<recovery command>\n

<recovery command>”

其中recovery command為CACHE:/recovery/command命令

兩種Recovery Case

FACTORY RESET（恢復(fù)出廠設(shè)置）

用戶選擇“恢復(fù)出廠設(shè)置”

設(shè)置系統(tǒng)將"--wipe_data"命令寫入/cache/recovery/command

系統(tǒng)重啟，并進入recover模式（/sbin/recovery）

get_args() 將 "boot-recovery"和"--wipe_data"寫入BCB

erase_root() 格式化（擦除）DATA分區(qū)

erase_root() 格式化（擦除）CACHE分區(qū)

finish_recovery() 擦除BCB

重啟系統(tǒng)

OTA INSTALL（OTA升級）

升級系統(tǒng)下載 OTA包到/cache/some-filename.zip

升級系統(tǒng)寫入recovery命令"--update_package=CACHE:some-filename.zip"

重啟，并進入recovery模式

get_args() 將"boot-recovery" 和 "--update_package=..." 寫入BCB

install_package() 作升級

finish_recovery() 擦除 BCB

** 如果安裝包失敗 ** prompt_and_wait() 等待用戶操作，選擇ALT+S或ALT+W 升級或恢復(fù)出廠設(shè)置

main() 調(diào)用 maybe_install_firmware_update()

如果包里有hboot/radio的firmware則繼續(xù)，否則返回
將 "boot-recovery" 和 "--wipe_cache" 寫入BCB
將 firmware image寫入cache分區(qū)
將 "update-radio/hboot" 和 "--wipe_cache" 寫入BCB
重啟系統(tǒng)
bootloader自身更新firmware
bootloader 將 "boot-recovery" 寫入BCB
erase_root() 擦除CACHE分區(qū)
清除 BCB

main() 調(diào)用 reboot() 重啟系統(tǒng)

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) 2^nd 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()