Recovery 升级流程

Android8.0.0-r4的OTA升级流程

原网址：https://blog.csdn.net/dingfengnupt88/article/details/52875228

 Android系统进行升级的时候，有两种途径，一种是通过接口传递升级包路径自动升级（Android系统SD卡升级），升级完之后系统自动重启；另一种是手动进入recovery模式下，选择升级包进行升级，升级完成之后停留在recovery界面，需要手动选择重启。前者多用于手机厂商的客户端在线升级，后者多用于开发和测试人员。但不管哪种，原理都是一样的，都要在recovery模式下进行升级。

1、获取升级包，可以从服务端下载，也可以直接拷贝到SD卡中

2、获取升级包路径，验证签名，通过installPackage接口升级

3、系统重启进入Recovery模式

4、在install.cpp进行升级操作

5、try_update_binary执行升级脚本

6、finish_recovery，重启

一、获取升级包，可以从服务端下载，也可以直接拷贝到SD卡中

    假设SD卡中已有升级包update.zip

二、获取升级包路径，验证签名，通过installPackage接口升级

1、调用RecoverySystem类提供的verifyPackage方法进行签名验证

public static void verifyPackage(File packageFile,
                                 ProgressListener listener,
                                 File deviceCertsZipFile)
    throws IOException, GeneralSecurityException

    签名验证函数，实现过程就不贴出来了，参数，

        packageFile--升级文件

        listener--进度监督器

        deviceCertsZipFile--签名文件，如果为空，则使用系统默认的签名

    只有当签名验证正确才返回，否则将抛出异常。

    在Recovery模式下进行升级时候也是会进行签名验证的，如果这里先不进行验证也不会有什么问题。但是我们建议在重启前，先验证，以便及早发现问题。

    如果签名验证没有问题，就执行installPackage开始升级。

2、installPackage开始升级

    如果签名验证没有问题，就进行重启升级，

public static void installPackage(Context context, File packageFile)
    throws IOException {
    String filename = packageFile.getCanonicalPath();
    Log.w(TAG, "!!! REBOOTING TO INSTALL " + filename + " !!!");

    final String filenameArg = "--update_package=" + filename;
    final String localeArg = "--locale=" + Locale.getDefault().toString();
    bootCommand(context, filenameArg, localeArg);
}

    这里定义了两个参数，我们接着看，

private static void bootCommand(Context context, String... args) throws IOException {
    RECOVERY_DIR.mkdirs();  // In case we need it
    COMMAND_FILE.delete();  // In case it's not writable
    LOG_FILE.delete();

    FileWriter command = new FileWriter(COMMAND_FILE);
    try {
        for (String arg : args) {
            if (!TextUtils.isEmpty(arg)) {
                command.write(arg);
                command.write("\n");
            }
        }
    } finally {
        command.close();
    }

    // Having written the command file, go ahead and reboot
    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    pm.reboot(PowerManager.REBOOT_RECOVERY);

    throw new IOException("Reboot failed (no permissions?)");
}

    创建目录/cache/recovery/，command文件保存在该目录下；如果存在command文件，将其删除；然后将上面一步生成的两个参数写入到command文件。

    最后重启设备，重启过程就不再详述了。

三、系统重启进入Recovery模式

    系统重启时会判断/cache/recovery目录下是否有command文件，如果存在就进入recovery模式，否则就正常启动。

    进入到Recovery模式下，将执行recovery.cpp的main函数，下面贴出关键代码片段，

int arg;
while ((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) {
    switch (arg) {
    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': show_text = 1; 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;
    }
}

    这是一个While 循环，用来读取 recovery 的 command 参数， OPTIONS 的不同选项定义如下，

static const struct option OPTIONS[] = {
  { "send_intent", required_argument, NULL, 's' },
  { "update_package", required_argument, NULL, 'u' },
  { "wipe_data", no_argument, NULL, 'w' },
  { "wipe_cache", no_argument, NULL, 'c' },
  { "show_text", no_argument, NULL, 't' },
  { "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 },
};

    显然，根据第二步写入的命令文件内容，将为update_package 赋值。

    接着看，

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 = (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;
    }
}

    兼容性处理。

int status = INSTALL_SUCCESS;

if (update_package != NULL) {
    status = install_package(update_package, &wipe_cache, TEMPORARY_INSTALL_FILE, true);
    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");

        // If this is an eng or userdebug build, then automatically
        // turn the text display on if the script fails so the error
        // message is visible.
        char buffer[PROPERTY_VALUE_MAX+1];
        property_get("ro.build.fingerprint", buffer, "");
        if (strstr(buffer, ":userdebug/") || strstr(buffer, ":eng/")) {
            ui->ShowText(true);
        }
    }
} else if (wipe_data) {
    if (device->WipeData()) status = INSTALL_ERROR;
    if (erase_volume("/data")) status = INSTALL_ERROR;
    if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
    if (erase_persistent_partition() == -1 ) 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 if (!just_exit) {
    status = INSTALL_NONE;  // No command specified
    ui->SetBackground(RecoveryUI::NO_COMMAND);
}

    update_package不为空，执行install_package方法。

    我们也可以看到擦除数据、缓存的实现也是在这个里执行的，这里就不展开了。

四、在install.cpp进行升级操作

    具体的升级过程都是在install.cpp中执行的，先看install_package方法，

int
install_package(const char* path, int* wipe_cache, const char* install_file,
                bool needs_mount)
{
    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;
    if (setup_install_mounts() != 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);
    }
    if (install_log) {
        fputc(result == INSTALL_SUCCESS ? '1' : '0', install_log);
        fputc('\n', install_log);
        fclose(install_log);
    }
    return result;
}

    这个方法中首先创建了log文件，升级过程包括出错的信息都会写到这个文件中，便于后续的分析工作。继续跟进， really_install_package，

static int
really_install_package(const char *path, int* wipe_cache, bool needs_mount)
{
    ui->SetBackground(RecoveryUI::INSTALLING_UPDATE);
    ui->Print("Finding update package...\n");
    // Give verification half the progress bar...
    ui->SetProgressType(RecoveryUI::DETERMINATE);
    ui->ShowProgress(VERIFICATION_PROGRESS_FRACTION, VERIFICATION_PROGRESS_TIME);
    LOGI("Update location: %s\n", path);

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

    if (path && needs_mount) {
        if (path[0] == '@') {
            ensure_path_mounted(path+1);
        } else {
            ensure_path_mounted(path);
        }
    }

    MemMapping map;
    if (sysMapFile(path, &map) != 0) {
        LOGE("failed to map file\n");
        return INSTALL_CORRUPT;
    }

    // 装入签名文件
    int numKeys;
    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");

    // 验证签名
    int err;
    err = verify_file(map.addr, map.length, loadedKeys, numKeys);
    free(loadedKeys);
    LOGI("verify_file returned %d\n", err);
    // 签名失败的处理
    if (err != VERIFY_SUCCESS) {
        LOGE("signature verification failed\n");
        sysReleaseMap(&map);
        return INSTALL_CORRUPT;
    }

    /* Try to open the package.
     */
    // 打开升级包
    ZipArchive zip;
    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);
        return INSTALL_CORRUPT;
    }

    /* Verify and install the contents of the package.
     */
    ui->Print("Installing update...\n");
    ui->SetEnableReboot(false);
    // 执行升级脚本文件，开始升级
    int result = try_update_binary(path, &zip, wipe_cache);
    ui->SetEnableReboot(true);
    ui->Print("\n");

    sysReleaseMap(&map);

    return result;
}

    该方法主要做了三件事

1、验证签名

int numKeys;
Certificate* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);
if (loadedKeys == NULL) {
    LOGE("Failed to load keys\n");
    return INSTALL_CORRUPT;
}

    装载签名文件，如果为空 ，终止升级；

int err;
err = verify_file(map.addr, map.length, loadedKeys, numKeys);
free(loadedKeys);
LOGI("verify_file returned %d\n", err);
// 签名失败的处理
if (err != VERIFY_SUCCESS) {
    LOGE("signature verification failed\n");
    sysReleaseMap(&map);
    return INSTALL_CORRUPT;
}

    调用verify_file进行签名验证，这个方法定义在verifier.cpp文件中，此处不展开，如果验证失败立即终止升级。

2、读取升级包信息

ZipArchive zip;
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);
    return INSTALL_CORRUPT;
}

    执行mzOpenZipArchive方法，打开升级包并扫描，将包的内容拷贝到变量zip中，该变量将作为参数用来执行升级脚本。

3、执行升级脚本文件，开始升级

int result = try_update_binary(path, &zip, wipe_cache);

    try_update_binary方法用来处理升级包，执行制作升级包中的脚本文件 update_binary ，进行系统更新。

五、try_update_binary执行升级脚本

// 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) {
    // 检查update-binary是否存在
    const ZipEntry* binary_entry =
            mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);
    if (binary_entry == NULL) {
        mzCloseZipArchive(zip);
        return INSTALL_CORRUPT;
    }

    const 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;
    }
    // update-binary拷贝到"/tmp/update_binary"
    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;
    }

    // 创建管道，用于下面的子进程和父进程之间的通信
    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
    //            fill up the next  part of of the progress bar
    //            over  seconds.  If  is zero, use
    //            set_progress commands to manually control the
    //            progress of this segment of the bar
    //
    //        set_progress
    //             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">
    //            arrange to install the contents of  in the
    //            given partition on reboot.
    //
    //            (API v2:  may start with "PACKAGE:" to
    //            indicate taking a file from the OTA package.)
    //
    //            (API v3: this command no longer exists.)
    //
    //        ui_print
    //            display  on the screen.
    //
    //   - the name of the package zip file.
    //

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

    // 创建子进程。负责执行binary脚本
    pid_t pid = fork();
    if (pid == 0) {
        umask(022);
        close(pipefd[0]);
        execv(binary, (char* const*)args);// 执行binary脚本
        fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno));
        _exit(-1);
    }
    close(pipefd[1]);

    *wipe_cache = 0;

    // 父进程负责接受子进程发送的命令去更新ui显示
    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->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 = 1;
        } 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).