android是什么系统怎么升级（Android系统OTA升级流程）

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，

intinstall_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 intreally_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 inttry_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 <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.    //     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).            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函数，是真正实现读取升级包中的脚本文件并执行相应的函数的地方。 在此函数中，通过调用fork函数创建出一个子进程，在子进程中开始读取并执行升级脚本文件。在此需要注意的是函数fork的用法，fork被调用一次，将做两次返回，在父进程中返回的是子进程的进程ID，为正数；而在子进程中，则返回0。子进程创建成功后，开始执行升级代码，并通过管道与父进程交互，父进程则通过读取子进程传递过来的信息更新UI。

六、finish_recovery，重启

上一步完成之后，回到main函数，

    // Save logs and clean up before rebooting or shutting down.    finish_recovery(send_intent);

保存升级过程中的log，清除临时文件，包括command文件（不清除的话，下次重启还会进入recovery模式），最后重启。

以上就是升级的一个流程。

补充：

手动升级的流程也基本差不多，通过power key + volume上键组合，进入recovery模式，进入prompt_and_wait函数等待用户按键事件。

recovery.cpp的main函数，

    Device::BuiltinAction after = shutdown_after ? Device::SHUTDOWN : Device::REBOOT;    if (status != INSTALL_SUCCESS || ui->IsTextVisible()) {        Device::BuiltinAction temp = prompt_and_wait(device, status);        if (temp != Device::NO_ACTION) after = temp;    }

根据用户选择进入到相应的分支进行处理，如下图，

        int chosen_item = get_menu_selection(headers, device->GetMenuItems(), 0, 0, device);         // device-specific code may take some action here.  It may        // return one of the core actions handled in the switch        // statement below.        Device::BuiltinAction chosen_action = device->InvokeMenuItem(chosen_item);

当我们选择从外置 sdcard 升级，进入如下分支中，

            case Device::APPLY_EXT: {                ensure_path_mounted(SDCARD_ROOT);                char* path = browse_directory(SDCARD_ROOT, device);                if (path == NULL) {                    ui->Print("\n-- No package file selected.\n", path);                    break;                }                 ui->Print("\n-- Install %s ...\n", path);                set_sdcard_update_bootloader_message();                void* token = start_sdcard_fuse(path);                 int status = install_package(FUSE_SIDELOAD_HOST_PATHNAME, &wipe_cache,                                             TEMPORARY_INSTALL_FILE, false);                 finish_sdcard_fuse(token);                ensure_path_unmounted(SDCARD_ROOT);                 if (status == INSTALL_SUCCESS && wipe_cache) {                    ui->Print("\n-- Wiping cache (at package request)...\n");                    if (erase_volume("/cache")) {                        ui->Print("Cache wipe failed.\n");                    } else {                        ui->Print("Cache wipe complete.\n");                    }                }                 if (status >= 0) {                    if (status != INSTALL_SUCCESS) {                        ui->SetBackground(RecoveryUI::ERROR);                        ui->Print("Installation aborted.\n");                    } else if (!ui->IsTextVisible()) {                        return Device::NO_ACTION;  // reboot if logs aren't visible                    } else {                        ui->Print("\nInstall from sdcard complete.\n");                    }                }                break;            }

char* path = browse_directory(SDCARD_ROOT, device); 这个函数浏览 SD card 下的文件 ， 并把路径记录下来 , 然后根据名称排序 ， 并处理用户按键。

·当用户选择第一个条目“../”,直接跳转到上级目录,并且继续浏览文件

·当用户选择的条目以“/”开头,直接进入子目录

·其它情况表明,该条目就是zip包.写入BCB,copy 更新包至临时目录，直接转入install_package

选择zip包后，同样也是执行install_package函数，后面与自动升级的流程是一样的。

    int status = install_package(FUSE_SIDELOAD_HOST_PATHNAME, &wipe_cache,                                             TEMPORARY_INSTALL_FILE, false);