android recovery 主系統代碼分析

我們已經清楚瞭如何進入正常模式和Recovery模式已有深刻理解瞭,假設進入瞭Recovery模式,那麼其核心代碼是怎麼做的呢?

 

代碼路徑在 android 源碼的根路徑: bootable\recovery 其入口文件就是 recovery.c 中 main函數

 

下面就開始逐步瞭解其Recovery的設計思想:

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

 

註解裡面描述的相當清楚:

 * 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";

 

 

下面的描述針對寫入的 command 有大致的介紹:

 * 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

 

 

兩種升級模式步驟說明:

 * 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

從上面的幾段註解中,基本上就明白的 Recovery 是如何工作的啦。下面就從具體代碼開始一步步分析。

 

1、recovery main 函數

 
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));

將標準輸出和標準錯誤輸出重定位到"/tmp/recovery.log",如果是eng模式,就可以通過adb pull /tmp/recovery.log, 看到當前的log信息,這為我們提供瞭有效的調試手段。

ui_init();

一個簡單的基於framebuffer的ui系統,叫miniui 主要建立瞭圖像部分(gglInit、gr_init_font、framebuffer)及進度條和事件處理(input_callback)
load_volume_table();

根據 /etc/recovery.fstab 建立分區表

// 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);

從misc 分區以及 CACHE:recovery/command 文件中讀入參數,寫入到argc, argv (get_bootloader_message) 並有可能寫回 misc 分區(set_bootloader_message)

 

 

做完以上事情後就開始解析具體參數:

    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_text(1); break;
        case '?':
            LOGE("Invalid command argument\n");
            continue;
        }
    }

 

 

    printf("Command:");
    for (arg = 0; arg < argc; arg++) {
        printf(" \"%s\"", argv[arg]);
    }
    printf("\n");

以上僅僅是打印表明進入到哪一步,方便調試情況的掌握

 

下面的代碼就是具體幹的事情瞭:

    if (update_package != NULL) {
        status = install_package(update_package, &wipe_cache, TEMPORARY_INSTALL_FILE);
        if (status == INSTALL_SUCCESS && wipe_cache) {
            if (erase_volume("/cache")) {
                LOGE("Cache wipe (requested by package) failed.");
            }
        }
        if (status != INSTALL_SUCCESS) ui_print("Installation aborted.\n");
    } else if (wipe_data) {
        if (device_wipe_data()) status = INSTALL_ERROR;
        if (erase_volume("/data")) status = INSTALL_ERROR;
        if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
        if (status != INSTALL_SUCCESS) ui_print("Data wipe failed.\n");
        clear_sdcard_update_bootloader_message();
    } else if (wipe_cache) {
        if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
        if (status != INSTALL_SUCCESS) ui_print("Cache wipe failed.\n");
        clear_sdcard_update_bootloader_message();
    } else {
        status = update_by_key();  // No command specified
    }

 

 

根據用戶提供參數,調用各項功能,比如,安裝一個升級包,擦除cache分區, 擦除user data分區等等,後在會將繼續詳細分解。
if (status != INSTALL_SUCCESS) prompt_and_wait();如果前面做的操作成功則進入重啟流程,否則由用戶操作,可選操作為: reboot, 安裝update.zip,除cache分區, 擦除user data分區

    // Otherwise, get ready to boot the main system…
    finish_recovery(send_intent);

先看函數註解:

// 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.
// this function is idempotent: call it as many times as you like.

 

 

其實主要的就是如下函數操作:

    // Remove the command file, so recovery won't repeat indefinitely.
    if (ensure_path_mounted(COMMAND_FILE) != 0 ||
        (unlink(COMMAND_FILE) && errno != ENOENT)) {
        LOGW("Can't unlink %s\n", COMMAND_FILE);
    }
   

    將指定分區mounted 成功並 unlink 刪除一個文件的目錄項並減少它的鏈接數

    ensure_path_unmounted(CACHE_ROOT);

    將指定分區 unmounted
    sync();  // For good measure.

 

 

對於上面的代碼總結:

它的功能如下:1、將前面定義的intent字符串寫入(如果有的話):CACHE:recovery/command2、將 /tmp/recovery.log 復制到 "CACHE:recovery/log";3、清空 misc 分區,這樣重啟就不會進入recovery模式4、刪除command 文件:CACHE:recovery/command;

 

最後重啟機器

    ui_print("Rebooting…\n");
    android_reboot(ANDROID_RB_RESTART, 0, 0);

 

 

2、factory reset 核心代碼實現

 

按照前面所列的8條步驟,其中1-6及7-8都與 main 通用流程一樣,不再復述。

 * 5. erase_volume() reformats /data
 * 6. erase_volume() reformats /cache

這兩個操作是如何做到的呢?

if (erase_volume("/data")) status = INSTALL_ERROR;

if (erase_volume("/cache")) status = INSTALL_ERROR;

最後就是

clear_sdcard_update_bootloader_message();

 

 

看看 erase_volume() 函數先:

 static int 
erase_volume(const char *volume) { 
    ui_set_background(BACKGROUND_ICON_INSTALLING); 
    ui_show_indeterminate_progress(); 
    ui_print("Formatting %s...\n", volume); 
 
    ensure_path_unmounted(volume); 
 
    if (strcmp(volume, "/cache") == 0) { 
        // Any part of the log we'd copied to cache is now gone.  
        // Reset the pointer so we copy from the beginning of the temp  
        // log.  
        tmplog_offset = 0; 
    } 
 
    return format_volume(volume); 
} 

static int
erase_volume(const char *volume) {
    ui_set_background(BACKGROUND_ICON_INSTALLING);
    ui_show_indeterminate_progress();
    ui_print("Formatting %s...\n", volume);

    ensure_path_unmounted(volume);

    if (strcmp(volume, "/cache") == 0) {
        // Any part of the log we'd copied to cache is now gone.
        // Reset the pointer so we copy from the beginning of the temp
        // log.
        tmplog_offset = 0;
    }

    return format_volume(volume);
}

上面紅字標明的是重要函數調用

int ensure_path_unmounted(const char* path) {

Volume* v = volume_for_path(path);

 result = scan_mounted_volumes();

return unmount_mounted_volume(mv);

}

就是將指定的path中徑mount point進行卸載掉,而 format_volume的主要功能就是:

MtdWriteContext *write = mtd_write_partition(partition);

mtd_erase_blocks(write, -1);

mtd_write_close(write);

不要細說瞭吧,就是將整個分區數據全清掉。

最後一個函數:

void
clear_sdcard_update_bootloader_message() {
    struct bootloader_message boot;
    memset(&boot, 0, sizeof(boot));
    set_bootloader_message(&boot);
}

就是將misc分區數據重置清0

這樣子就完成的恢復出廠設置的情況瞭。將 data/cache分區erase擦掉就好瞭。

 

3、OTA 安裝 核心代碼實現

主要函數就是如何安裝 Package :

 * 5. install_package() attempts to install the update
 *    NOTE: the package install must itself be restartable from any point

 

 

int
install_package(const char* path, int* wipe_cache, const char* install_file)

–>

static int
really_install_package(const char *path, int* wipe_cache){

clear_sdcard_update_bootloader_message();

    ui_set_background(BACKGROUND_ICON_INSTALLING);
    ui_print("Finding update package…\n");
    ui_show_indeterminate_progress();
    LOGI("Update location: %s\n", path);

    更新 ui 顯示

 

    for(;((i < 5)&&(ensure_path_mounted(path) != 0));i++){
        LOGE("Can't mount %s\n",path);
        sleep(1);
    }
    if((i >= 5)&&(ensure_path_mounted(path) != 0)){
        return INSTALL_CORRUPT;
    }

   

  確保升級包所在分區已經mount,通常為 cache 分區或者 SD 分區   RSAPublicKey* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);// Look for an RSA signature embedded in the .ZIP file comment given
// the path to the zip.  Verify it matches one of the given public
// keys.
//
// Return VERIFY_SUCCESS, VERIFY_FAILURE (if any error is encountered
// or no key matches the signature).
  err = verify_file(path, loadedKeys, numKeys);  從/res/keys中裝載公鑰,並進行確認文件的合法性
    /* Try to open the package.
     */
    ZipArchive zip;
    err = mzOpenZipArchive(path, &zip);        打開升級包,將相關信息存到ZipArchive數據機構中,便於後面處理。
    /* Verify and install the contents of the package.
     */
    ui_print("Installing update…\n");
    return try_update_binary(path, &zip, wipe_cache);         進行最後的安裝包文件
}

 

// If the package contains an update binary, extract it and run it.
static int
try_update_binary(const char *path, ZipArchive *zip, int* wipe_cache) {
    const ZipEntry* binary_entry =
            mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);

 

 

    char* binary = "/tmp/update_binary";
    unlink(binary);
    int fd = creat(binary, 0755);

 

    bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);
    close(fd);
    mzCloseZipArchive(zip);

   

  將升級包內文件META-INF/com/google/android/update-binary 復制為/tmp/update_binary

 

    // When executing the update binary contained in the package, the
    // arguments passed are:
    //
    //   – the version number for this interface
    //
    //   – an fd to which the program can write in order to update the
    //     progress bar.  The program can write single-line commands:

    int pipefd[2];
    pipe(pipefd);

 

 

    char** args = malloc(sizeof(char*) * 5);

    args[0] = binary;
    args[1] = EXPAND(RECOVERY_API_VERSION);   // defined in Android.mk
    args[2] = malloc(10);
    sprintf(args[2], "%d", pipefd[1]);
    args[3] = (char*)path;
    args[4] = buf_uuid;
    args[5] = NULL;

    組裝新的進程參數   

    pid_t pid = fork();
    if (pid == 0) { // child process
        close(pipefd[0]);
        execv(binary, args);

    }

    // parent process
    close(pipefd[1]);

    ui_show_progress

    ui_set_progress

    ui_print

 

總結一下代碼主要行為功能:

1、將會創建新的進程,執行:/tmp/update_binary

2、同時,會給該進程傳入一些參數,其中最重要的就是一個管道fd,供新進程與原進程通信。

3、新進程誕生後,原進程就變成瞭一個服務進程,它提供若幹UI更新服務:

a)   progress

b)   set_progress

c)   ui_print

這樣,新進程就可以通過老進程的UI系統完成顯示任務。而其他功能就靠它自己瞭

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