Android Recovery模式

LinuxSmartphone

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

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  command == 'boot-recovery' → 启动recovery.img。recovery模式
  
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  command == 'update-radio/hboot' → 更新firmware（bootloader)
  
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  其他 → 启动boot.img
  

Recovery涉及到的其他系统及文件

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  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：
  
  
  
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    --send_intent=anystring - write the text out to recovery.intent
    
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    --update_package=root:path - verify install an OTA package file
    
  • 
    --wipe_data - erase user data (and cache), then reboot
    
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    --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
  


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  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

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  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

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

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  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

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  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]
    
  
  
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  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]
    
  
  
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  Parser argv[] filled above
  
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  register_update_commands():commands.c [ register all commands with name and hook function ]
  
  
  
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    registerCommand():commands.c
    
    
    
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      Register command with name, hook, type, cookie.
      
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      Commands, e.g: assert, delete, copy_dir, symlink, write_raw_image.
      
    
    
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    registerFunction():commands.c
    
    
    
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      Register function with name, hook, cookie.
      
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      Function, e.g: get_mark, matches, getprop, file_contains
      
  
  
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  install_package():
  
  
  
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    translate_root_path():roots.c [ "SYSTEM:lib" and turns it into a string like "/system/lib", translate the updater.zip path ]
    
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    mzOpenZipArchive():zip.c [ open updater.zip file (uncompass) ]
    
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    handle_update_package():install.c
    
    
    
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      verify_jar_signature():verifier.c [ verify signature with keys.inc key; verify manifest and zip package archive ]
      
      
      
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        verifySignature() [ verify the signature file: CERT.sf/rsa. ]
        
        
        
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          digestEntry():verifier.c [ get SHA-1 digest of CERT.sf file ]
          
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          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 ]
        
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        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 ]
      
      
      
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        parseAmendScript():amend.c [ call yyparse() to parse to command ]
        
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        exeCommandList():install.c
        
        
        
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          exeCommand():execute.c [ call command hook function ]
          
  
  
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  erase DATA/CACHE partition
  
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  prompt_and_wait():recovery.c [ wait for user input: 1) reboot 2) update.zip 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:update.zip')
    
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    3) erase_root() → format_root_device() DATA/CACHE
    
  
  
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  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 ]
    
  
  
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  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. ]
  
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  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。





本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u2/66024/showart_2178242.html