android recovery mode

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
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 。
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
 
两种Recovery Case
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
 
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()
1.如果包里有 hboot/radio 的 firmware 则继续，否则返回
2.将 "boot-recovery" 和 "--wipe_cache" 写入 BCB
3.将 firmware image 写入 cache 分区
4.将 "update-radio/hboot" 和 "--wipe_cache" 写入 BCB
5.重启系统
6.bootloader 自身更新 firmware
7.bootloader 将 "boot-recovery" 写入 BCB
8.erase_root() 擦除 CACHE 分区
9.清除 BCB
9.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。