Android Recovery模式

(muddogxp原创，转载请注明)

http://blog.chinaunix.net/u/14459/showart_1911144.html

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

Recovery工具通过NAND cache分区上的三个文件和主系统打交道。主系统(包括恢 复出厂设置和OTA升级)可以写入recovery所需的命令，读出recovery过程中的LOG和intent。

/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 {

char command[32];

char status[32]; //未知用途

char recovery[1024];

};

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

(结合上面的内容就是说，执行这个类似“二次引导”的程序是/cache/recovery/command，执行这个命令可以带的参数在MISC里面，可以是“boot-recovery”或者“update-hboot/radio”，执行前一个参数时会去读取recovery.img这个镜像文件，执行后一个参数时会去cache分区里面读取待升级的固件；可以在下面Recovery Case看出，这个command使用这样"magic key"+"参数的运行模式"，这样就能够兼容手动和程序自动的进入factory reset或者ota)

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 (重启后就能进入recovery)

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。