Android刷机原理之recovery内部工作原理

现在Android版本更新太快，2.1是最普遍的版本，不过马上都开始升级2.2版本了，目前网路上提供了很多自制作的andorid ROM，通过刷机工具进行刷机，最普遍的是利用android的recovery机制进行update，现将recovery的

内部工作原理摘录如下（摘自recovery源码注释，等有空时候我来翻译下）

 

/*
 * The recovery tool communicates with the main system through /cache files.
 *   /cache/recovery/command - INPUT - command line for tool, one arg per line
 *   /cache/recovery/log - OUTPUT - combined log file from recovery run(s)
 *   /cache/recovery/intent - OUTPUT - intent that was passed in
 *
 * The arguments which may be supplied in the recovery.command file:
 *   --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
 *   --set_encrypted_filesystem=on|off - enables / diasables encrypted fs
 *
 * After completing, we remove /cache/recovery/command and reboot.
 * Arguments may also be supplied in the bootloader control block (BCB).
 * These important scenarios must be safely restartable at any point:
 *
 * FACTORY RESET
 * 1. user selects "factory reset"
 * 2. main system writes "--wipe_data" to /cache/recovery/command
 * 3. main system reboots into recovery
 * 4. get_args() writes BCB with "boot-recovery" and "--wipe_data"
 *    -- after this, rebooting will restart the erase --
 * 5. erase_root() reformats /data
 * 6. erase_root() reformats /cache
 * 7. finish_recovery() erases BCB
 *    -- after this, rebooting will restart the main system --
 * 8. main() calls reboot() to boot main system
 *
 * OTA INSTALL
 * 1. main system downloads OTA package to /cache/some-filename.zip
 * 2. main system writes "--update_package=CACHE:some-filename.zip"
 * 3. main system reboots into recovery
 * 4. get_args() writes BCB with "boot-recovery" and "--update_package=..."
 *    -- after this, rebooting will attempt to reinstall the update --
 * 5. install_package() attempts to install the update
 *    NOTE: the package install must itself be restartable from any point
 * 6. finish_recovery() erases BCB
 *    -- after this, rebooting will (try to) restart the main system --
 * 7. ** if install failed **
 *    7a. prompt_and_wait() shows an error icon and waits for the user
 *    7b; the user reboots (pulling the battery, etc) into the main system
 * 8. main() calls maybe_install_firmware_update()
 *    ** if the update contained radio/hboot firmware **:
 *    8a. m_i_f_u() writes BCB with "boot-recovery" and "--wipe_cache"
 *        -- after this, rebooting will reformat cache & restart main system --
 *    8b. m_i_f_u() writes firmware image into raw cache partition
 *    8c. m_i_f_u() writes BCB with "update-radio/hboot" and "--wipe_cache"
 *        -- after this, rebooting will attempt to reinstall firmware --
 *    8d. bootloader tries to flash firmware
 *    8e. bootloader writes BCB with "boot-recovery" (keeping "--wipe_cache")
 *        -- after this, rebooting will reformat cache & restart main system --
 *    8f. erase_root() reformats /cache
 *    8g. finish_recovery() erases BCB
 *        -- after this, rebooting will (try to) restart the main system --
 * 9. main() calls reboot() to boot main system
 *
 * ENCRYPTED FILE SYSTEMS ENABLE/DISABLE
 * 1. user selects "enable encrypted file systems"
 * 2. main system writes "--set_encrypted_filesystem=on|off" to
 *    /cache/recovery/command
 * 3. main system reboots into recovery
 * 4. get_args() writes BCB with "boot-recovery" and
 *    "--set_encrypted_filesystems=on|off"
 *    -- after this, rebooting will restart the transition --
 * 5. read_encrypted_fs_info() retrieves encrypted file systems settings from /data
 *    Settings include: property to specify the Encrypted FS istatus and
 *    FS encryption key if enabled (not yet implemented)
 * 6. erase_root() reformats /data
 * 7. erase_root() reformats /cache
 * 8. restore_encrypted_fs_info() writes required encrypted file systems settings to /data
 *    Settings include: property to specify the Encrypted FS status and
 *    FS encryption key if enabled (not yet implemented)
 * 9. finish_recovery() erases BCB
 *    -- after this, rebooting will restart the main system --
 * 10. main() calls reboot() to boot main system
 */