Android Recovery模式
AndroidRecovery模式
(muddogxp原创，转载请注明)
http://blogold.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:
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camera +power：bootloader模式，ADP里则可以使用fastboot模式
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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（BootloaderControl 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
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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
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--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recoverybootloader message。结构如下：
structbootloader_message {
charcommand[32];
charstatus[32]; //未知用途
charrecovery[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recoverymode
“update-hboot/radio”：指示bootloader更新firmware
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recovery内容
“recovery\n
<recoverycommand>\n
<recoverycommand>”
其中recoverycommand为CACHE:/recovery/command命令
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Recovery工具通过NANDcache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。
两种RecoveryCase
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FACTORYRESET（恢复出厂设置）
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用户选择“恢复出厂设置”
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设置系统将"--wipe_data"命令写入/cache/recovery/command
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系统重启，并进入recover模式（/sbin/recovery）
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get_args()将"boot-recovery"和"--wipe_data"写入BCB
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erase_root()格式化（擦除）DATA分区
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erase_root()格式化（擦除）CACHE分区
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finish_recovery()擦除BCB
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重启系统
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OTAINSTALL（OTA升级）
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升级系统下载OTA包到/cache/some-filename.zip
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升级系统写入recovery命令"--update_package=CACHE:some-filename.zip"
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重启，并进入recovery模式
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get_args()将"boot-recovery"和"--update_package=..."写入BCB
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install_package()作升级
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finish_recovery()擦除BCB
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**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
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main()调用maybe_install_firmware_update()
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如果包里有hboot/radio的firmware则继续，否则返回
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将"boot-recovery"和"--wipe_cache"写入BCB
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将firmware image写入cache分区
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将"update-radio/hboot"和"--wipe_cache"写入BCB
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重启系统
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bootloader自身更新firmware
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bootloader将"boot-recovery"写入BCB
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erase_root()擦除CACHE分区
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清除BCB
-
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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 graphicmode, 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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create2 threads: progress/input_thread [create progress show and inputevent 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 forcommandline]
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checkif nand misc partition has boot message. If yes, fill argc/argv.
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Ifno, 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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Parserargv[] 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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Registercommand 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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Registerfunction with name, hook, cookie.
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Function,e.g: get_mark, matches, getprop, file_contains
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-
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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 zippackage 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(publickey:keys.inc, signature:CERT.rsa, CERT.sf's digest):libc/rsa.c [ Verify a 2048 bit RSA PKCS1.5 signature against an expectedSHA-1 hash. Use public key to decrypt the CERT.rsa to getoriginal SHA digest, then compare to digest of CERT.sf ]
-
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verifyManifest() [ Get manifest SHA1-Digest from CERT.sf. Then do digest toMANIFEST.MF. Compare them ]
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verifyArchive() [ verify all the files in update.zip with digest listed inMANIFEST.MF ]
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find_update_script():install.c[ find META-INF/com/google/android/update-script updater script ]
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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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-
-
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eraseDATA/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_xxxget 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_imagecommand, it stores the bootloader image to CACHE partition, andwrite update-hboot/radio command to MISC partition for bootloadermessage 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 (hopefullyworking) system, copy our log file to cache as well (for the systemto read), and record any intent we were asked to communicate back tothe 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。
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