android recovery 主系统代码分析

我们已经清楚了如何进入正常模式和Recovery模式已有深刻理解了，假设进入了Recovery模式，那么其核心代码是怎么做的呢？

代码路径在 android 源码的根路径： bootable\recovery 其入口文件就是 recovery.c 中 main函数

下面就开始逐步了解其Recovery的设计思想：

static const char *COMMAND_FILE = "/cache/recovery/command";
static const char *INTENT_FILE = "/cache/recovery/intent";
static const char *LOG_FILE = "/cache/recovery/log";

注解里面描述的相当清楚：

* 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

static const char *LAST_LOG_FILE = "/cache/recovery/last_log";

static const char *LAST_INSTALL_FILE = "/cache/recovery/last_install";
static const char *CACHE_ROOT = "/cache";
static const char *SDCARD_ROOT = "/sdcard";

下面的描述针对写入的 command 有大致的介绍：

* The arguments which may be supplied in the recovery.command file:
*   --send_intent=anystring - write the text out to recovery.intent
*   --update_package=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

两种升级模式步骤说明：

* 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_volume() reformats /data
* 6. erase_volume() 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_volume() 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

从上面的几段注解中，基本上就明白的 Recovery 是如何工作的啦。下面就从具体代码开始一步步分析。

1、recovery main 函数

 
int 
main(int argc, char **argv) { 
    time_t start = time(NULL); 
 
    // If these fail, there's not really anywhere to complain...  
    freopen(TEMPORARY_LOG_FILE, "a", stdout); setbuf(stdout, NULL); 
    freopen(TEMPORARY_LOG_FILE, "a", stderr); setbuf(stderr, NULL); 
    printf("Starting recovery on %s", ctime(&start));

int
main(int argc, char **argv) {
time_t start = time(NULL);

    // If these fail, there's not really anywhere to complain...
    freopen(TEMPORARY_LOG_FILE, "a", stdout); setbuf(stdout, NULL);
    freopen(TEMPORARY_LOG_FILE, "a", stderr); setbuf(stderr, NULL);
    printf("Starting recovery on %s", ctime(&start));

将标准输出和标准错误输出重定位到"/tmp/recovery.log",如果是eng模式，就可以通过adb pull /tmp/recovery.log, 看到当前的log信息，这为我们提供了有效的调试手段。

ui_init();

一个简单的基于framebuffer的ui系统，叫miniui 主要建立了图像部分（gglInit、gr_init_font、framebuffer）及进度条和事件处理（input_callback）
load_volume_table();

根据 /etc/recovery.fstab 建立分区表

// command line args come from, in decreasing precedence:
//   - the actual command line
//   - the bootloader control block (one per line, after "recovery")
//   - the contents of COMMAND_FILE (one per line)

get_args(&argc, &argv);

从misc 分区以及 CACHE:recovery/command 文件中读入参数，写入到argc, argv （get_bootloader_message）并有可能写回 misc 分区（set_bootloader_message）

做完以上事情后就开始解析具体参数：

    while ((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) {
        switch (arg) {
        case 'p': previous_runs = atoi(optarg); break;
        case 's': send_intent = optarg; break;
        case 'u': update_package = optarg; break;
        case 'w': wipe_data = wipe_cache = 1; break;
        case 'c': wipe_cache = 1; break;
        case 't': ui_show_te

补充：移动开发 , Android ,