一、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。
二、G1中的三种启动模式
1、MAGIC KEY:
1）camera + power：bootloader模式，ADP里则可以使用fastboot模式
2）home + power：recovery模式
2、正常启动
Bootloader正常启动，又有三种方式，按照BCB（Bootloader Control Block）中的command
分类：
1）command == 'boot-recovery' → 启动recovery.img。recovery模式
2）command == 'update-radio/hboot' → 更新firmware（bootloader)
3）其他 → 启动system.img
三、Recovery涉及到的其他系统及文件
1、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。
1）/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
2）/cache/recovery/log：recovery过程日志，由主系统读出
3）/cache/recovery/intent：recovery输出的intent
2、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：
1）boot-recovery：标示recovery正在进行，或指示bootloader应该进入recovery mode
2）update-hboot/radio：指示bootloader更新firmware
recovery的值：
1）
其中recovery command为CACHE:/recovery/command命令。
四、两种操作分析
1、FACTORY RESET（恢复出厂设置）
1）用户选择“恢复出厂设置”
2）设置系统将"--wipe_data"命令写入/cache/recovery/command
3）系统重启，并进入recover模式（/sbin/recovery）
4）get_args() 将 "boot-recovery"和"--wipe_data"写入BCB
5）erase_root() 格式化（擦除）DATA分区
6）erase_root() 格式化（擦除）CACHE分区
7）finish_recovery() 擦除BCB
8）重启系统
2、OTA INSTALL（OTA升级）
1）升级系统下载 OTA包到/cache/some-filename.zip
2）升级系统写入recovery命令"--update_package=CACHE:some-filename.zip"
3）重启，并进入recovery模式
4）get_args() 将"boot-recovery" 和 "--update_package=..." 写入BCB
5）install_package() 作升级
6）finish_recovery() 擦除 BCB
7）** 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
8）main() 调用 maybe_install_firmware_update()
8.1) 如果包里有hboot/radio的firmware则继续，否则返回
8.2) 将 "boot-recovery" 和 "--wipe_cache" 写入BCB
8.3) 将 firmware image写入cache分区
8.4) 将 "update-radio/hboot" 和 "--wipe_cache" 写入BCB
8.5) 重启系统
8.6) bootloader自身更新firmware
8.7）bootloader 将 "boot-recovery" 写入BCB
8.8）erase_root() 擦除CACHE分区
8.9）清除 BCB
9）main() 调用 reboot() 重启系统
五、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()
