2024年2月25日发(作者：)
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/?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/
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模式
command == 'update-radio/hboot' → 更新firmware（bootloader)
其他 → 启动
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。
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/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
--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
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/cache/recovery/log：recovery过程日志，由主系统读出
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/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];
};
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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
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recovery内容
“recoveryn
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/
2. 升级系统写入recovery命令"--update_package=CACHE:"
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 → → /sbin/recovery →
main():recovery.c
ui_init():ui.c ［UI initialize］
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gr_init():minui/graphics.c ［set tty0 to graphic mode, open fb0]
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ev_init():minui/events.c [open /dev/input/event*]
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res_create_surface:minui/resource.c [create surfaces for all bitmaps used later, include icons,
bmps]
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create 2 threads: progress/input_thread [create progress show and input event handler thread]
get_args():recovery.c
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get_bootloader_message():bootloader.c [read mtdblock0(misc partition) 2nd page for
commandline]
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check if nand misc partition has boot message. If yes, fill argc/argv.
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If no, get arguments from /cache/recovery/command, and fill argc/argv.
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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 ]
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registerCommand():commands.c
install_package():
Register command with name, hook, type, cookie.
Commands, e.g: assert, delete, copy_dir, symlink, write_raw_image.
Register function with name, hook, cookie.
Function, e.g: get_mark, matches, getprop, file_contains
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registerFunction():commands.c
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translate_root_path():roots.c [ "SYSTEM:lib" and turns it into a string like "/system/lib",
translate the path ]
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mzOpenZipArchive():zip.c [ open file (uncompass) ]
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handle_update_package():install.c
verify_jar_signature():verifier.c [ verify signature with key; verify manifest
and zip package archive ]
verifySignature() [ verify the signature file: /rsa. ]
digestEntry():verifier.c [ get SHA-1 digest of file ]
RSA_verify(public key:, signature:, '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
to get original SHA digest, then compare to digest of
]
verifyManifest() [ Get manifest SHA1-Digest from . Then do
digest to . Compare them ]
verifyArchive() [ verify all the files in with digest listed in
]
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
erase DATA/CACHE partition
exeCommand():execute.c [ call command hook function ]
prompt_and_wait():recovery.c [ wait for user input: 1) reboot 2) 3) wipe data ]
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ui_key_xxx get ALT+x keys
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1) do nothing
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2) install_package('SDCARD:')
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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 ]
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set_bootloader_message()
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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。
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