Android OTA 升级(四)：进入根文件系统

分类： Android OTA2012-10-25 17:59 1939人阅读 评论(0) 收藏 举报

一、简介

        从bootloader 进入Recovery 模式后，首先也是运行Linux内核，该内核跟普通模式没有区别(减轻了BSP开发者的任务)。区别从执行文件系统开始。 Recovery 模式的细节就隐藏在其根文件系统中。

下面，我们就看看进入Recovery 根文件系统都干些啥。

二、init.rc
       和正常启动一样，内核进入文件系统会执行/init, init 的配置文件就是 /init.rc, 前面文章讲过，这个文件来自：bootable/recovery/etc/init.rc，下面，我们看看它的内容。

on early-init
    start ueventd

on init
    export PATH /sbin
    export ANDROID_ROOT /system
    export ANDROID_DATA /data
    export EXTERNAL_STORAGE /sdcard

    symlink /system/etc /etc

    mkdir /sdcard
    mkdir /system
    mkdir /data
    mkdir /cache
    mount /tmp /tmp tmpfs

on boot
    ifup lo
    hostname localhost
    domainname localdomain

    class_start default

service ueventd /sbin/ueventd
    critical

service recovery /sbin/recovery

service adbd /sbin/adbd recovery
    disabled

# Always start adbd on userdebug and eng builds
on property:ro.debuggable=1
    write /sys/class/android_usb/android0/enable 0
    write /sys/class/android_usb/android0/idVendor 18D1
    write /sys/class/android_usb/android0/idProduct D001
    write /sys/class/android_usb/android0/functions adb
    write /sys/class/android_usb/android0/enable 1
    write /sys/class/android_usb/android0/iManufacturer $ro.product.manufacturer
    write /sys/class/android_usb/android0/iProduct $ro.product.model
    write /sys/class/android_usb/android0/iSerial $ro.serialno
    start adbd

# Restart adbd so it can run as root
on property:service.adb.root=1
    write /sys/class/android_usb/android0/enable 0
    restart adbd
    write /sys/class/android_usb/android0/enable 1

可以看到，它很非常简单：
1）   设置几个环境变量。备用。
2）   建立 etc 链接。
3）   造几个目录。备用。
4）   Mount /tmp 目录为内存文件系统 tmpfs，后面会用到。
5）   Trival 设置,不必关心。
6）   启动 recovery主程序。
7）   如果是eng模式（此时persist.service.adb.enable），启动adb
当然，init主程序还会装载属性配置文件 /default.prop, 它包含了很多系统属性设置，比如，ro.build.*， 等等。很明显，这里最重要的就是recovery主程序，下面，我们分析它。

 三、Recovery.c 分析

bootable/recovery/recovery.c

Recovery.c: main->

     install_package->
            really_install_package->
                    try_update_binary->

                        execv(META-INF/com/google/android/update-binary, args);

/*
* 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=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_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
*/

 代码及注释如下：

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

    // 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。后面还会看到，recovery模式运行完毕后，
    // 会将其拷贝到cache分区，以便后续分析。
    // 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);

    freopen("/dev/ttyS1", "a", stdout); setbuf(stdout, NULL);
    freopen("/dev/ttyS1", "a", stderr); setbuf(stderr, NULL);

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

    // Recovery 使用了一个简单的基于framebuffer的ui系统，叫miniui,这里，
    // 进行了简单的初始化（主要是图形部分以及事件部分），并启动了一个
    // event 线程用于响应用户按键。
    device_ui_init(&ui_parameters);
    ui_init();
    ui_set_background(BACKGROUND_ICON_INSTALLING);
    load_volume_table();
    SetSdcardRootPath();
    SureCacheMount();
    ui_print("Recovery system v4.00 \n\n");

    // 从misc 分区以及 CACHE:recovery/command 文件中读入参数，写入到argc, argv ,
    // 并且，如果有必要，回写入misc分区。这样，如果recovery没有操作成功
    // （比如，升级还没有结束，就拔电池），系统会一直进入recovery模式。
    // 提醒用户继续升级，直到成功。
    get_args(&argc, &argv);

        // 解析参数
    int previous_runs = 0;
    const char *send_intent = NULL;
    const char *update_package = NULL;
    const char *update_rkimage = NULL;
    int wipe_data = 0, wipe_cache = 0, wipe_all = 0;
    int factory_test_en = 0;
    char prop[64] = {0};
    int arg;
    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 'r':  update_rkimage = optarg; break;
        case 'w': wipe_data = wipe_cache = 1; break;
        case 'c': wipe_cache = 1; break;
        case 'f'+'t':{ factory_test_en = 1;ui_show_text(1);} break;
        case 't': ui_show_text(1); break;
        case 'w'+'a':{ wipe_all = wipe_data = wipe_cache = 1;ui_show_text(1);
} break;
        case '?':
            LOGE("Invalid command argument\n");
            continue;
        }
    }
    // 这个函数没干什么。看名字，它給设备制造商提供了一个调用机会，可写入设备相关初始化代码。
    device_recovery_start();

    // 打印出命令，比如，正常启动进入recovery模式，会打印：Command: "/sbin/recovery"
    printf("Command:");
    for (arg = 0; arg < argc; arg++) {
        printf(" \"%s\"", argv[arg]);
    }
    printf("\n");

    if (update_package) {
        // 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 = 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;
        }
                strcpy(updatepath,update_package);
    }
    printf("\n");

    if (update_rkimage) {
        // 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_rkimage, "CACHE:", 6) == 0) {
            int len = strlen(update_rkimage) + 10;
            char* modified_path = malloc(len);
            strlcpy(modified_path, "/cache/", len);
            strlcat(modified_path, update_rkimage+6, len);
            printf("(replacing path \"%s\" with \"%s\")\n",
                   update_rkimage, modified_path);
            update_rkimage = modified_path;
        }
        strcpy(updatepath,update_rkimage);
    }
    printf("\n");

    // 打印出所有的系统属性（from default.prop）到log文件。
    property_list(print_property, NULL);
    printf("\n");

    int status = INSTALL_SUCCESS;
    if(factory_test_en)
    {
        ui_print("\nwait factory test tool connect........\n");
        char factory_test_finish = 0;
        while(1)
        {
            property_get("FACTORY_TEST_FINISH", prop, "0");
            factory_test_finish = (unsigned long)strtoumax(prop, 0, 16);
            if(factory_test_finish != 0)break;
            sleep(1);
        }
        ui_print("\n factory test finish........\n");

    }

    // 根据用户提供参数，调用各项功能，比如，安装一个升级包，擦除cache分区,
    // 擦除user data分区，install_package比较复杂，后面专门分析，其它都很简单。忽略。
    if (update_package != NULL) {
        printf("update_package = %s", update_package);
        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
                    bAutoUpdateComplete=true;
    } else if (update_rkimage != NULL) {
        status = install_rkimage(update_rkimage);
        if (status != INSTALL_SUCCESS) ui_print("Installation aborted.\n");
        else
                    bAutoUpdateComplete=true;
    } 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 (wipe_all && erase_volume(IN_SDCARD_ROOT)) status = INSTALL_ERROR;
        if (status != INSTALL_SUCCESS) ui_print("Data wipe failed.\n");
    } else if (wipe_cache) {
        if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
        if (status != INSTALL_SUCCESS) ui_print("Cache wipe failed.\n");
    } else {
        status = INSTALL_ERROR;  // No command specified
    }

    //如果前面已经做了某项操作并且成功，则进入重启流程。否则，等待用户选择具体操作。
    // 而用户可选操作为： reboot, 安装update.zip，除cache分区, 擦除user data分区,
    // 如前所述，只有安装package 比较复杂，其它简单。
    if (status != INSTALL_SUCCESS) ui_set_background(BACKGROUND_ICON_ERROR);
    if (status != INSTALL_SUCCESS) {
        bClearbootmessage = false;
        prompt_and_wait();
    }


   // 1）将前面定义的intent字符串写入（如果有的话）：CACHE:recovery/command
   // 2）将 /tmp/recovery.log 复制到 "CACHE:recovery/log";
   // 3）清空 misc 分区，这样重启就不会进入recovery模式
   // 4)删除command 文件：CACHE:recovery/command;
    // Otherwise, get ready to boot the main system...
    finish_recovery(send_intent);
    ui_print("Rebooting...\n");
    android_reboot(ANDROID_RB_RESTART, 0, 0);
    return EXIT_SUCCESS;
}

 四、install_package分析

bootable/recovery/install.c

 

int
install_package(const char* path, int* wipe_cache, const char* install_file)
{
    FILE* install_log = fopen_path(install_file, "w");
    if (install_log) {
        fputs(path, install_log);
        fputc('\n', install_log);
    } else {
        LOGE("failed to open last_install: %s\n", strerror(errno));
    }
    int result = really_install_package(path, wipe_cache);
    if (install_log) {
        fputc(result == INSTALL_SUCCESS ? '1' : '0', install_log);
        fputc('\n', install_log);
        fclose(install_log);
    }
    return result;
}

static int
really_install_package(const char *path, int* wipe_cache)
{
    // 更新 UI 显示
    ui_set_background(BACKGROUND_ICON_INSTALLING);
    ui_print("Finding update package...\n");
    ui_show_indeterminate_progress();
    LOGI("Update location: %s\n", path);

    //确保升级包所在分区已经mount,通常为 cache 分区或者 SD 分区
    if (ensure_path_mounted(path) != 0) {
        LOGE("Can't mount %s\n", path);
        return INSTALL_CORRUPT;
    }

    ui_print("Opening update package...\n");

    //从/res/keys中装载公钥。
    int numKeys;
    RSAPublicKey* 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);

    // Give verification half the progress bar...
    ui_print("Verifying update package...\n");
    ui_show_progress(
            VERIFICATION_PROGRESS_FRACTION,
            VERIFICATION_PROGRESS_TIME);

        // 根据公钥验证升级包verify_file
    int err;
    err = verify_file(path, loadedKeys, numKeys);
    free(loadedKeys);
    LOGI("verify_file returned %d\n", err);
    if (err != VERIFY_SUCCESS) {
        LOGE("signature verification failed\n");
        return INSTALL_CORRUPT;
    }

        // 打开升级包，将相关信息存到ZipArchive数据结构中，便于后面处理。
    /* Try to open the package.
     */
    ZipArchive zip;
    err = mzOpenZipArchive(path, &zip);
    if (err != 0) {
        LOGE("Can't open %s\n(%s)\n", path, err != -1 ? strerror(err) : "bad");
        return INSTALL_CORRUPT;
    }

    /* Verify and install the contents of the package.
     */
    ui_print("Installing update...\n");
    return try_update_binary(path, &zip, wipe_cache);
}

五、try_update_binary分析

bootable/recovery/install.c

 

// 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);
    if (binary_entry == NULL) {
        mzCloseZipArchive(zip);
        return INSTALL_CORRUPT;
    }

    // 将升级包内文件META-INF/com/google/android/update-binary
    // 复制为/tmp/update_binary
    char* binary = "/tmp/update_binary";
    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);
    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.
    //
    //   - the name of the package zip file.
    //

    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] = NULL;

        // 创建新的进程，执行：/tmp/update_binary
        // 同时，会给该进程传入一些参数，其中最重要的就是一个管道fd，供新进程与原进程通信。
        // 新进程诞生后，原进程就变成了一个服务进程，它提供若干UI更新服务
        // 新进程就可以通过老进程的UI系统完成显示任务。而其他功能就靠它自己了。
    pid_t pid = fork();
    if (pid == 0) {
        close(pipefd[0]);
        execv(binary, args);
        fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno));
        _exit(-1);
    }
    close(pipefd[1]);

    *wipe_cache = 0;

    // 更新UI
    char buffer[1024];
    FILE* from_child = fdopen(pipefd[0], "r");
    while (fgets(buffer, sizeof(buffer), from_child) != NULL) {
        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_show_progress(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_set_progress(fraction);
        } else if (strcmp(command, "ui_print") == 0) {
            char* str = strtok(NULL, "\n");
            if (str) {
                ui_print("%s", str);
            } else {
                ui_print("\n");
            }
        } else if (strcmp(command, "wipe_cache") == 0) {
            *wipe_cache = 1;
        } 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;
}

这样，我们又回到了升级包中的文件：META-INF/com/google/android/update-binary，下回继续研究。