Android Recovery
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AndroidRecovery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(BootloaderControl 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
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];
};
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
recovery内容
“recovery/n
<recoverycommand>/n
<recoverycommand>”
其中recoverycommand为CACHE:/recovery/command命令
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
FACTORYRESET(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
OTAINSTALL(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
ui_init():ui.c [UI initialize]
gr_init():minui/graphics.c [set tty0 to graphicmode, 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]
create2 threads: progress/input_thread [create progress show and inputevent handler thread]
get_args():recovery.c
get_bootloader_message():bootloader.c [read mtdblock0(misc partition) 2nd page forcommandline]
checkif nand misc partition has boot message. If yes, fill argc/argv.
Ifno, get arguments from /cache/recovery/command, and fill argc/argv.
set_bootloader_message():bootloader.c [set bootloader message back to mtdblock0]
Parserargv[] filled above
register_update_commands():commands.c[ register all commands with name and hook function ]
registerCommand():commands.c
Registercommand with name, hook, type, cookie.
Commands,e.g: assert, delete, copy_dir, symlink, write_raw_image.
registerFunction():commands.c
Registerfunction 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 zippackage archive ]
verifySignature() [ verify the signature file: CERT.sf/rsa. ]
digestEntry():verifier.c [ get SHA-1 digest of CERT.sf file ]
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 ]
verifyManifest() [ Get manifest SHA1-Digest from CERT.sf. Then do digest toMANIFEST.MF. Compare them ]
verifyArchive() [ verify all the files in update.zip with digest listed inMANIFEST.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 ]
eraseDATA/CACHE partition
prompt_and_wait():recovery.c [ wait for user input: 1) reboot 2) update.zip 3) wipe data ]
ui_key_xxxget 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_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 ]
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 (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. ]
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/u/14459/showart_1911144.html
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