Recovery啟動流程(3)--recovery.cpp分析

轉載請注明來源：cuixiaolei的技術博客

 

這篇文章主要通過分析高通recovery目錄下的recovery.cpp源碼，對recovery啟動流程有一個宏觀的了解。MTK和高通的recovery幾乎一樣，只是使用自己家的mt_xxx文件。

 

為什么要分析recovery.cpp這個文件？

我們知道，當我們通過按鍵或者應用進入recovery模式，實質是kernel后加載recovery.img,kernel起來后執行的第一個進程就 是init，此進程會讀入init.rc啟動相應的服務。在recovery模式中，啟動的服務是執行recovery可執行文件，此文件是

bootable/recovery/recovery.cpp文件生成，我們就從recovery.cpp文件開始分析。此出可參考我的另一篇文章android-ramdisk.img分析、recovery.img&boot.img執行過程

下面的代碼位於bootable/recovery/etc/init.rc，由此可知，進入recovery模式后會執行sbin /recovery，此文件是bootable/recovery/recovery.cpp生成（可查看對應目錄的Android.mk查看），所以recovery.cpp是recovery模式的入口。

service recovery /sbin/recovery
    seclabel u:r:recovery:s0

 

開始主題

bootable/recovery/recovery.cpp

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

    redirect_stdio(TEMPORARY_LOG_FILE);

    // If this binary is started with the single argument "--adbd",        如果二進制文件使用單個參數"--adbd"啟動
    // instead of being the normal recovery binary, it turns into kind     而不是正常的recovery啟動（不帶參數即為正常啟動）
    // of a stripped-down version of adbd that only supports the           它變成精簡版命令時只支持sideload命令。它必須是一個正確可用的參數
    // 'sideload' command.  Note this must be a real argument, not         不在/cache/recovery/command中，也不受B2B控制
    // anything in the command file or bootloader control block; the       
    // only way recovery should be run with this argument is when it       是apply_from_adb()的副本
    // starts a copy of itself from the apply_from_adb() function.
    if (argc == 2 && strcmp(argv[1], "--adbd") == 0) {
        adb_main(0, DEFAULT_ADB_PORT);
        return 0;
    }

    printf("Starting recovery (pid %d) on %s", getpid(), ctime(&start));

    load_volume_table();                //加載並建立分區表
    get_args(&argc, &argv);             //從傳入的參數或/cache/recovery/command文件中得到相應的命令

    const char *send_intent = NULL;
    const char *update_package = NULL;
    bool should_wipe_data = false;
    bool should_wipe_cache = false;
    bool show_text = false;
    bool sideload = false;
    bool sideload_auto_reboot = false;
    bool just_exit = false;
    bool shutdown_after = false;


    int arg;
    while ((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) {         //while循環解析command或者傳入的參數，並把對應的功能設置為true或給相應的變量賦值
        switch (arg) {
        case 'i': send_intent = optarg; break;
        case 'u': update_package = optarg; break;
        case 'w': should_wipe_data = true; break;
        case 'c': should_wipe_cache = true; break;
        case 't': show_text = true; break;
        case 's': sideload = true; break;
        case 'a': sideload = true; sideload_auto_reboot = true; break;
        case 'x': just_exit = true; break;
        case 'l': locale = optarg; break;
        case 'g': {
            if (stage == NULL || *stage == '\0') {
                char buffer[20] = "1/";
                strncat(buffer, optarg, sizeof(buffer)-3);
                stage = strdup(buffer);
            }
            break;
        }
        case 'p': shutdown_after = true; break;
        case 'r': reason = optarg; break;
        case '?':
            LOGE("Invalid command argument\n");
            continue;
        }
    }

    if (locale == NULL) {          //設置語言
        load_locale_from_cache();
    }
    printf("locale is [%s]\n", locale);
    printf("stage is [%s]\n", stage);
    printf("reason is [%s]\n", reason);

　　/*初始化UI*/
    Device* device = make_device();
    ui = device->GetUI();
    gCurrentUI = ui;
    show_text = true;
    ui->SetLocale(locale);
    ui->Init();



    int st_cur, st_max;
    if (stage != NULL && sscanf(stage, "%d/%d", &st_cur, &st_max) == 2) {
        ui->SetStage(st_cur, st_max);
    }

    ui->SetBackground(RecoveryUI::NONE);           //設置recovery界面背景
    if (show_text) ui->ShowText(true);             //設置界面上是否能夠顯示字符，使能ui->print函數開關

    struct selinux_opt seopts[] = {                //設置selinux權限，以后會有專門的文章或專題講解selinux，這里不做講解    
      { SELABEL_OPT_PATH, "/file_contexts" }
    };

    sehandle = selabel_open(SELABEL_CTX_FILE, seopts, 1);

    if (!sehandle) {
        ui->Print("Warning: No file_contexts\n");
    }

    device->StartRecovery();       //此函數為空，沒做任何事情

    printf("Command:");                      //打印/cache/recovery/command的參數
    for (arg = 0; arg < argc; arg++) {
        printf(" \"%s\"", argv[arg]);
    }
    printf("\n");

    if (update_package) {                          //根據下面的注釋可知，對old "root" 路徑進行修改，把其放在/cache/文件中 。  當安裝包的路徑是以CACHE：開頭，把其改為/cache/開頭                               
        // For backwards compatibility on the cache partition only, if
        // we're given an old 'root' path "CACHE:foo", change it to
        // "/cache/foo".
        if (strncmp(update_package, "CACHE:", 6) == 0) {
            int len = strlen(update_package) + 10;
            char* modified_path = (char*)malloc(len);
            strlcpy(modified_path, "/cache/", len);
            strlcat(modified_path, update_package+6, len);
            printf("(replacing path \"%s\" with \"%s\")\n",
                   update_package, modified_path);
            update_package = modified_path;
        }
    }
    printf("\n");

    property_list(print_property, NULL);              //打印屬性列表，其實現沒有找到代碼在哪里，找到后會更新此文章
    printf("\n");

    ui->Print("Supported API: %d\n", RECOVERY_API_VERSION);

    int status = INSTALL_SUCCESS;    //設置標志位，默認為INSTALL_SUCCESS

    if (update_package != NULL) {     //install package情況
        status = install_package(update_package, &should_wipe_cache, TEMPORARY_INSTALL_FILE, true);     //安裝ota升級包
        if (status == INSTALL_SUCCESS && should_wipe_cache) {   //如果安裝前點擊了清楚緩存，執行下面的語句，安裝成功后清楚緩存
            wipe_cache(false, device);   
        }
        if (status != INSTALL_SUCCESS) {                  //安裝失敗，打印log，並根據is_ro_debuggable()決定是否打開ui->print信息（此信息顯示在屏幕上）
            ui->Print("Installation aborted.\n");
            if (is_ro_debuggable()) {
                ui->ShowText(true);
            }
        }
    } else if (should_wipe_data) {     //只清除用戶數據
        if (!wipe_data(false, device)) {
            status = INSTALL_ERROR;
        }
    } else if (should_wipe_cache) {    //只清除緩存
        if (!wipe_cache(false, device)) {
            status = INSTALL_ERROR;
        }
    } else if (sideload) {       //執行adb reboot sideload命令后會跑到這個代碼段
        // 'adb reboot sideload' acts the same as user presses key combinations
        // to enter the sideload mode. When 'sideload-auto-reboot' is used, text
        // display will NOT be turned on by default. And it will reboot after
        // sideload finishes even if there are errors. Unless one turns on the
        // text display during the installation. This is to enable automated
        // testing.
        if (!sideload_auto_reboot) {
            ui->ShowText(true);
        }
        status = apply_from_adb(ui, &should_wipe_cache, TEMPORARY_INSTALL_FILE);
        if (status == INSTALL_SUCCESS && should_wipe_cache) {
            if (!wipe_cache(false, device)) {
                status = INSTALL_ERROR;
            }
        }
        ui->Print("\nInstall from ADB complete (status: %d).\n", status);
        if (sideload_auto_reboot) {
            ui->Print("Rebooting automatically.\n");
        }
    } else if (!just_exit) {              //當command命令中有just_exit字段
        status = INSTALL_NONE;  // No command specified
        ui->SetBackground(RecoveryUI::NONE);

        if (is_ro_debuggable()) {

            ui->ShowText(true);
        }
    }

    if (!sideload_auto_reboot && (status == INSTALL_ERROR || status == INSTALL_CORRUPT)) {   //安裝失敗，復制log信息到/cache/recovery/。如果進行了wipe_data/wipe_cache/apply_from_sdcard（也就是修改了flash），
//直接return結束recovery，否則現實error背景圖片
        copy_logs();
        ui->SetBackground(RecoveryUI::ERROR);
    }

    Device::BuiltinAction after = shutdown_after ? Device::SHUTDOWN : Device::REBOOT; 
    if ((status != INSTALL_SUCCESS && !sideload_auto_reboot) || ui->IsTextVisible()) {       //status在just_exit中已經變為none，會執行此if語句
#ifdef SUPPORT_UTF8_MULTILINGUAL
        ml_select(device);
#endif
        Device::BuiltinAction temp = prompt_and_wait(device, status);       //prompt_and_wait()函數是個死循環 開始顯示recovery選項 並處理用戶通過按鍵或者觸摸屏的選項，如Reboot system等
        if (temp != Device::NO_ACTION) {
            after = temp;
        }
    }

    finish_recovery(send_intent);

    switch (after) {
        case Device::SHUTDOWN:
            ui->Print("Shutting down...\n");
            property_set(ANDROID_RB_PROPERTY, "shutdown,");
            break;

        case Device::REBOOT_BOOTLOADER:
            ui->Print("Rebooting to bootloader...\n");
            property_set(ANDROID_RB_PROPERTY, "reboot,bootloader");
            break;

        default:
            char reason[PROPERTY_VALUE_MAX];
            snprintf(reason, PROPERTY_VALUE_MAX, "reboot,%s", device->GetRebootReason());
            ui->Print("Rebooting...\n");
            property_set(ANDROID_RB_PROPERTY, reason);
            break;
    }
    sleep(5); 
    return EXIT_SUCCESS;
}

 

上面的代碼中已經把recovery啟動后的流程描述的差不多了，下面是一點細節性的描述

 

1.獲取command命令

get_args(&argc, &argv);

此函數沒有什么可說的，先判斷事都有參數傳進來，如果有解析傳入的命令，否走從/cache/recovery/command文件中解析命令

注意，此函數會先把struct bootloader_message boot寫入到misc分區，目的是防止斷電等原因導致關機，開機后lk會從misc分區中讀取相關信息，如果發現是"boot-recovery"會再次進入recovery模式，misc分區會在退出recovery時被清除，以至於可以正常開機，如果手機每次都是進入recovery而不能正常開機，可以分析是否沒有清楚misc分區。

struct bootloader_message {
    char command[32];
    char status[32];
    char recovery[768];

    // The 'recovery' field used to be 1024 bytes.  It has only ever
    // been used to store the recovery command line, so 768 bytes
    // should be plenty.  We carve off the last 256 bytes to store the
    // stage string (for multistage packages) and possible future
    // expansion.
    char stage[32];
    char reserved[224];
};

// 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)
static void
get_args(int *argc, char ***argv) {
    struct bootloader_message boot;
    memset(&boot, 0, sizeof(boot));
    get_bootloader_message(&boot);  // this may fail, leaving a zeroed structure
    stage = strndup(boot.stage, sizeof(boot.stage));

    if (boot.command[0] != 0 && boot.command[0] != 255) {
        LOGI("Boot command: %.*s\n", (int)sizeof(boot.command), boot.command);
    }

    if (boot.status[0] != 0 && boot.status[0] != 255) {
        LOGI("Boot status: %.*s\n", (int)sizeof(boot.status), boot.status);
    }

    // --- if arguments weren't supplied, look in the bootloader control block
    if (*argc <= 1) {
        boot.recovery[sizeof(boot.recovery) - 1] = '\0';  // Ensure termination
        const char *arg = strtok(boot.recovery, "\n");
        if (arg != NULL && !strcmp(arg, "recovery")) {
            *argv = (char **) malloc(sizeof(char *) * MAX_ARGS);
            (*argv)[0] = strdup(arg);
            for (*argc = 1; *argc < MAX_ARGS; ++*argc) {
                if ((arg = strtok(NULL, "\n")) == NULL) break;
                (*argv)[*argc] = strdup(arg);
            }
            LOGI("Got arguments from boot message\n");
        } else if (boot.recovery[0] != 0 && boot.recovery[0] != 255) {
            LOGE("Bad boot message\n\"%.20s\"\n", boot.recovery);
        }
    }

    // --- if that doesn't work, try the command file
    if (*argc <= 1) {
        FILE *fp = fopen_path(COMMAND_FILE, "r");
        if (fp != NULL) {
            char *token;
            char *argv0 = (*argv)[0];
            *argv = (char **) malloc(sizeof(char *) * MAX_ARGS);
            (*argv)[0] = argv0;  // use the same program name

            char buf[MAX_ARG_LENGTH];
            for (*argc = 1; *argc < MAX_ARGS; ++*argc) {
                if (!fgets(buf, sizeof(buf), fp)) break;
                token = strtok(buf, "\r\n");
                if (token != NULL) {
                    (*argv)[*argc] = strdup(token);  // Strip newline.
                } else {
                    --*argc;
                }
            }

            check_and_fclose(fp, COMMAND_FILE);
            LOGI("Got arguments from %s\n", COMMAND_FILE);
        }
    }

    // --> write the arguments we have back into the bootloader control block
    // always boot into recovery after this (until finish_recovery() is called)
    strlcpy(boot.command, "boot-recovery", sizeof(boot.command));  //***************************************************
    strlcpy(boot.recovery, "recovery\n", sizeof(boot.recovery));
    int i;
    for (i = 1; i < *argc; ++i) {
        strlcat(boot.recovery, (*argv)[i], sizeof(boot.recovery));
        strlcat(boot.recovery, "\n", sizeof(boot.recovery));
    }
    set_bootloader_message(&boot);
}

 

 

2.解析command命令

while ((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) {...}

可知從/cache/recovery/command文件中獲取並與OPTIONS列表參數進行比較，把相應的字符串賦值或者修改相應的變量

 //while循環解析command或者傳入的參數，並把對應的功能設置為true或給相應的變量賦值，下面是command中可能的命令及其value /*
static const struct option OPTIONS[] = {
  { "send_intent", required_argument, NULL, 'i' },
  { "update_package", required_argument, NULL, 'u' },
  { "wipe_data", no_argument, NULL, 'w' },
  { "wipe_cache", no_argument, NULL, 'c' },
  { "show_text", no_argument, NULL, 't' },
  { "sideload", no_argument, NULL, 's' },
  { "sideload_auto_reboot", no_argument, NULL, 'a' },
  { "just_exit", no_argument, NULL, 'x' },
  { "locale", required_argument, NULL, 'l' },
  { "stages", required_argument, NULL, 'g' },
  { "shutdown_after", no_argument, NULL, 'p' },
  { "reason", required_argument, NULL, 'r' },
  { NULL, 0, NULL, 0 },
};
*/

 

 

3.安裝升級包

status = install_package(update_package, &should_wipe_cache, TEMPORARY_INSTALL_FILE, true);

此函數安裝升級包，update_package是路徑，從/cache/recovery/command文件中解析

static const char *TEMPORARY_INSTALL_FILE = "/tmp/last_install";  TEMPORARY_INSTALL_FILE存放升級時的log信息，后面會把此文件復制到/cache/recovery/文件中

bootable/recovery/install.cpp

int
install_package(const char* path, bool* wipe_cache, const char* install_file,
                bool needs_mount)
{
    modified_flash = true; 

    FILE* install_log = fopen_path(install_file, "w");        //打開log文件
    if (install_log) {
        fputs(path, install_log);                             //向log文件中寫入安裝包路徑
        fputc('\n', install_log);
    } else {
        LOGE("failed to open last_install: %s\n", strerror(errno));
    }
    int result;
    if (setup_install_mounts() != 0) {                       //mount /tmp和/cache ，成功返回0
        LOGE("failed to set up expected mounts for install; aborting\n");
        result = INSTALL_ERROR;
    } else {
        result = really_install_package(path, wipe_cache, needs_mount);       //執行安裝
    }
    if (install_log) {             //向log文件寫入安裝結果，成功寫入1，失敗寫入0
        fputc(result == INSTALL_SUCCESS ? '1' : '0', install_log);
        fputc('\n', install_log);
        fclose(install_log);
    }
    return result;
}

int setup_install_mounts() {                         //掛在/cache   /tmp分區
    if (fstab == NULL) {
        LOGE("can't set up install mounts: no fstab loaded\n");
        return -1;
    }
    for (int i = 0; i < fstab->num_entries; ++i) {
        Volume* v = fstab->recs + i;

        if (strcmp(v->mount_point, "/tmp") == 0 ||
            strcmp(v->mount_point, "/cache") == 0) {
            if (ensure_path_mounted(v->mount_point) != 0) {
                LOGE("failed to mount %s\n", v->mount_point);
                return -1;
            }

        } else {
            if (ensure_path_unmounted(v->mount_point) != 0) {
                LOGE("failed to unmount %s\n", v->mount_point);
                return -1;
            }
        }
    }
    return 0;
}

static int
really_install_package(const char *path, bool* wipe_cache, bool needs_mount)
{
    ui->SetBackground(RecoveryUI::INSTALLING_UPDATE);                   //設置背景為安裝背景，就是小機器人
    ui->Print("Finding update package...\n");             
    // Give verification half the progress bar...
    ui->SetProgressType(RecoveryUI::DETERMINATE);                            //初始化升級時進度條       
    ui->ShowProgress(VERIFICATION_PROGRESS_FRACTION, VERIFICATION_PROGRESS_TIME);        //設置進度條時間
    LOGI("Update location: %s\n", path);

    // Map the update package into memory.
    ui->Print("Opening update package...\n");

    if (path && needs_mount) {                            //判斷升級包所在路徑是否被掛在
        ensure_path_mounted((path[0] == '@') ? path + 1 : path);
    }

    MemMapping map;                                 //把升級包路徑映射到內存中
    if (sysMapFile(path, &map) != 0) {
        LOGE("failed to map file\n");
        return INSTALL_CORRUPT;
    }

    int numKeys;                                   //加載密鑰
    Certificate* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);
    if (loadedKeys == NULL) {
        LOGE("Failed to load keys\n");
        return INSTALL_CORRUPT;
    }
    LOGI("%d key(s) loaded from %s\n", numKeys, PUBLIC_KEYS_FILE);

    ui->Print("Verifying update package...\n");

    int err;                                  //校驗升級包是否被修改，一般在調試ota升級時會把這段代碼進行屏蔽，使本地編譯的升級包可以正常升級
    err = verify_file(map.addr, map.length, loadedKeys, numKeys);
    free(loadedKeys);
    LOGI("verify_file returned %d\n", err);
    if (err != VERIFY_SUCCESS) {
        LOGE("signature verification failed\n");
        sysReleaseMap(&map);
        return INSTALL_CORRUPT;
    }

    /* Try to open the package.
     */
    ZipArchive zip;                 //打開升級包
    err = mzOpenZipArchive(map.addr, map.length, &zip);
    if (err != 0) {
        LOGE("Can't open %s\n(%s)\n", path, err != -1 ? strerror(err) : "bad");
        sysReleaseMap(&map);          //這行代碼很重要，只有失敗時才釋放map內存，結束安裝。提前釋放map內存會導致下面代碼無法正常進行，界面上會顯示失敗。
        return INSTALL_CORRUPT;
    }

    /* Verify and install the contents of the package.
     */
    ui->Print("Installing update...\n");
    ui->SetEnableReboot(false);
    int result = try_update_binary(path, &zip, wipe_cache);        //執行安裝包內的執行腳本
    ui->SetEnableReboot(true);
    ui->Print("\n");

    sysReleaseMap(&map);

#ifdef USE_MDTP
    /* If MDTP update failed, return an error such that recovery will not finish. */
    if (result == INSTALL_SUCCESS) {
        if (!mdtp_update()) {
            ui->Print("Unable to verify integrity of /system for MDTP, update aborted.\n");
            return INSTALL_ERROR;
        }
        ui->Print("Successfully verified integrity of /system for MDTP.\n");
    }
#endif /* USE_MDTP */

    return result;
}

 install_package流程：

1).設置ui界面，包括背景和進度條

2).檢查是否掛在tmp和cache，tmp存放升級log，cache存放升級包

3).加載密鑰並校驗升級包，防止升級包被用戶自己修改

4).打開升級包，並執行升級包內的安裝程序

 

 

4.執行升級包中的升級文件

try_update_binary()

try_update_binary(const char* path, ZipArchive* zip, bool* wipe_cache) {
    const ZipEntry* binary_entry =                                     //在升級包中查找是否存在META-INF/com/google/android/update-binary文件
            mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);
    if (binary_entry == NULL) {
        mzCloseZipArchive(zip);
        return INSTALL_CORRUPT;
    }

    const char* binary = "/tmp/update_binary";      //在tmp中創建臨時文件夾，權限755
    unlink(binary);
    int fd = creat(binary, 0755);
    if (fd < 0) {
        mzCloseZipArchive(zip);
        LOGE("Can't make %s\n", binary);
        return INSTALL_ERROR;
    }
    bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);     //把update.zip升級包解壓到/tmp/update_binary文件夾中
    sync();
    close(fd);
    mzCloseZipArchive(zip);

    if (!ok) {
        LOGE("Can't copy %s\n", ASSUMED_UPDATE_BINARY_NAME);
        return INSTALL_ERROR;
    }

    int pipefd[2];
    pipe(pipefd);

    // 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:
    //
    //        progress <frac> <secs>
    //            fill up the next <frac> part of of the progress bar
    //            over <secs> seconds.  If <secs> is zero, use
    //            set_progress commands to manually control the
    //            progress of this segment of the bar.
    //
    //        set_progress <frac>
    //            <frac> should be between 0.0 and 1.0; sets the
    //            progress bar within the segment defined by the most
    //            recent progress command.
    //
    //        firmware <"hboot"|"radio"> <filename>
    //            arrange to install the contents of <filename> in the
    //            given partition on reboot.
    //
    //            (API v2: <filename> may start with "PACKAGE:" to
    //            indicate taking a file from the OTA package.)
    //
    //            (API v3: this command no longer exists.)
    //
    //        ui_print <string>
    //            display <string> on the screen.
    //
    //        wipe_cache
    //            a wipe of cache will be performed following a successful
    //            installation.
    //
    //        clear_display
    //            turn off the text display.
    //
    //        enable_reboot
    //            packages can explicitly request that they want the user
    //            to be able to reboot during installation (useful for
    //            debugging packages that don't exit).
    //
    //   - the name of the package zip file.
    //

    const char** args = (const char**)malloc(sizeof(char*) * 5);          //創建指針數組，並分配內存
    args[0] = binary;                                                     //[0]存放字符串 "/tmp/update_binary" ,也就是升級包解壓的目的地址
    args[1] = EXPAND(RECOVERY_API_VERSION);   // defined in Android.mk    //[1]存放RECOVERY_API_VERSION，在Android.mk中定義，我的值為3  RECOVERY_API_VERSION := 3
    char* temp = (char*)malloc(10);
    sprintf(temp, "%d", pipefd[1]);
    args[2] = temp;
    args[3] = (char*)path;                                                //[3]存放update.zip路徑
    args[4] = NULL;

    pid_t pid = fork();                                                   //創建一個新進程，為子進程
    if (pid == 0) {       //進程創建成功，執行META-INF/com/google/android/update-binary腳本，給腳本傳入參數args
        umask(022);
        close(pipefd[0]);
        execv(binary, (char* const*)args);
        fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno));
        _exit(-1);
    }
    close(pipefd[1]);

    *wipe_cache = false;

    char buffer[1024];
    FILE* from_child = fdopen(pipefd[0], "r");
    while (fgets(buffer, sizeof(buffer), from_child) != NULL) {                    //父進程通過管道pipe讀取子進程的值，使用strtok分割函數把子進程傳過來的參數進行解析，執行相應的ui修改
        char* command = strtok(buffer, " \n"); 
        if (command == NULL) {
            continue;
        } else if (strcmp(command, "progress") == 0) {
            char* fraction_s = strtok(NULL, " \n");
            char* seconds_s = strtok(NULL, " \n");

            float fraction = strtof(fraction_s, NULL);
            int seconds = strtol(seconds_s, NULL, 10);

            ui->ShowProgress(fraction * (1-VERIFICATION_PROGRESS_FRACTION), seconds);
        } else if (strcmp(command, "set_progress") == 0) {
            char* fraction_s = strtok(NULL, " \n");
            float fraction = strtof(fraction_s, NULL);
            ui->SetProgress(fraction);
        } else if (strcmp(command, "ui_print") == 0) {
            char* str = strtok(NULL, "\n");
            if (str) {
                ui->Print("%s", str);
            } else {
                ui->Print("\n");
            }
            fflush(stdout);
        } else if (strcmp(command, "wipe_cache") == 0) {
            *wipe_cache = true;
        } else if (strcmp(command, "clear_display") == 0) {
            ui->SetBackground(RecoveryUI::NONE);
        } else if (strcmp(command, "enable_reboot") == 0) {
            // packages can explicitly request that they want the user
            // to be able to reboot during installation (useful for
            // debugging packages that don't exit).
            ui->SetEnableReboot(true);
        } else {
            LOGE("unknown command [%s]\n", command);
        }
    }
    fclose(from_child);

    int status;
    waitpid(pid, &status, 0);
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        LOGE("Error in %s\n(Status %d)\n", path, WEXITSTATUS(status));
        return INSTALL_ERROR;
    }

    return INSTALL_SUCCESS;
}

try_update_binary流程：

1.查找META-INF/com/google/android/update-binary二進制腳本

2.解壓update.zip包到/tmp/update_binary

3.創建子進程，執行update-binary二進制安裝腳本，並通過管道與父進程通信，父進程更新ui界面。

 

到此，android 的 Recovery的流程已經分析完了，知道流程后再去分析Recovery的相關問題就比較容易了。