Android OTA 升级(五)：updater

分类： Android OTA2012-10-26 11:41 2696人阅读 评论(1) 收藏 举报

一、简介

      前面分析的OTA升级的各部分代码都是在搭一个舞台，而主角现在终于登场，它就是updater。Google的代码架构设计非常好，各部分尽量松耦合。前面介绍升级脚本时，可知有两种类型的脚本，amend & edify(Amend脚本<update-script>在Android 1.5中已经被废除，只保留了Edify脚本<updater-script>). 他们各自对应一个updater. 这里，我们主要关注新的edify的updater.

       Updater可以作为学习解释器/编译器的同学一个很好的实例，但是我们只关心产品化相关的内容，所以并不去深究lex/yacc相关的东西。

二、入口函数main

bootable/recovery/updater/updater.c

// 这里定义脚本的位置，注释说明本updater支持edify格式的脚本。
// Where in the package we expect to find the edify script to execute.
// (Note it's "updateR-script", not the older "update-script".)
#define SCRIPT_NAME "META-INF/com/google/android/updater-script"

int main(int argc, char** argv) {
    // Various things log information to stdout or stderr more or less
    // at random.  The log file makes more sense if buffering is
    // turned off so things appear in the right order.
    setbuf(stdout, NULL);
    setbuf(stderr, NULL);

    if (argc != 4) {
        fprintf(stderr, "unexpected number of arguments (%d)\n", argc);
        return 1;
    }
    // 获取 version 参数。
    char* version = argv[1];
    if ((version[0] != '1' && version[0] != '2' && version[0] != '3') ||
        version[1] != '\0') {
        // We support version 1, 2, or 3.
        fprintf(stderr, "wrong updater binary API; expected 1, 2, or 3; "
                        "got %s\n",
                argv[1]);
        return 2;
    }

    // 获取命令管道（用于图形显示等，见前篇）
    // Set up the pipe for sending commands back to the parent process.
    int fd = atoi(argv[2]);
    FILE* cmd_pipe = fdopen(fd, "wb");
    setlinebuf(cmd_pipe);

    // Extract the script from the package.

    char* package_data = argv[3];
    ZipArchive za;
    int err;
    err = mzOpenZipArchive(package_data, &za);
    if (err != 0) {
        fprintf(stderr, "failed to open package %s: %s\n",
                package_data, strerror(err));
        return 3;
    }

   // 读入脚本 META-INF/com/google/android/updater-script
    const ZipEntry* script_entry = mzFindZipEntry(&za, SCRIPT_NAME);
    if (script_entry == NULL) {
        fprintf(stderr, "failed to find %s in %s\n", SCRIPT_NAME, package_data);
        return 4;
    }

    char* script = malloc(script_entry->uncompLen+1);
    if (!mzReadZipEntry(&za, script_entry, script, script_entry->uncompLen)) {
        fprintf(stderr, "failed to read script from package\n");
        return 5;
    }
    script[script_entry->uncompLen] = '\0';

    // Configure edify's functions.
    // 注册语句处理函数
    RegisterBuiltins();
    RegisterInstallFunctions();
    RegisterDeviceExtensions();
    FinishRegistration();

    // Parse the script.
    // 调用yy* 库函数解析脚本。
    Expr* root;
    int error_count = 0;
    yy_scan_string(script);
    int error = yyparse(&root, &error_count);
    if (error != 0 || error_count > 0) {
        fprintf(stderr, "%d parse errors\n", error_count);
        return 6;
    }

    // Evaluate the parsed script.
    UpdaterInfo updater_info;
    updater_info.cmd_pipe = cmd_pipe;
    updater_info.package_zip = &za;
    updater_info.version = atoi(version);

    State state;
    state.cookie = &updater_info;
    state.script = script;
    state.errmsg = NULL;

    // 解释执行脚本。 核心函数是 Evaluate。它会调用其他callback函数，而这些callback函数
    // 又会调用Evaluate去解析不同的脚本片段。从而实现一个简单的解释器
    char* result = Evaluate(&state, root);
    if (result == NULL) {
        if (state.errmsg == NULL) {
            fprintf(stderr, "script aborted (no error message)\n");
            fprintf(cmd_pipe, "ui_print script aborted (no error message)\n");
        } else {
            fprintf(stderr, "script aborted: %s\n", state.errmsg);
            char* line = strtok(state.errmsg, "\n");
            while (line) {
                fprintf(cmd_pipe, "ui_print %s\n", line);
                line = strtok(NULL, "\n");
            }
            fprintf(cmd_pipe, "ui_print\n");
        }
        free(state.errmsg);
        return 7;
    } else {
        fprintf(stderr, "script result was [%s]\n", result);
        free(result);
    }

    if (updater_info.package_zip) {
        mzCloseZipArchive(updater_info.package_zip);
    }
    free(script);

    return 0;
}

还没开始，就结束了。代码非常简单，因为细节隐藏在那些callback函数里。我们看一下。
三、callback函数

1)  RegisterBuiltins

void RegisterBuiltins() {
    RegisterFunction("ifelse", IfElseFn);
    RegisterFunction("abort", AbortFn);
    RegisterFunction("assert", AssertFn);
    RegisterFunction("concat", ConcatFn);
    RegisterFunction("is_substring", SubstringFn);
    RegisterFunction("stdout", StdoutFn);
    RegisterFunction("sleep", SleepFn);

    RegisterFunction("less_than_int", LessThanIntFn);
    RegisterFunction("greater_than_int", GreaterThanIntFn);
}

这些语句控制执行流程。
2) RegisterInstallFunctions

void RegisterInstallFunctions() {
    RegisterFunction("mount", MountFn);
    RegisterFunction("is_mounted", IsMountedFn);
    RegisterFunction("unmount", UnmountFn);
    RegisterFunction("format", FormatFn);
    RegisterFunction("show_progress", ShowProgressFn);
    RegisterFunction("set_progress", SetProgressFn);
    RegisterFunction("delete", DeleteFn);
    RegisterFunction("delete_recursive", DeleteFn);
    RegisterFunction("package_extract_dir", PackageExtractDirFn);
    RegisterFunction("package_extract_file", PackageExtractFileFn);
    RegisterFunction("retouch_binaries", RetouchBinariesFn);
    RegisterFunction("undo_retouch_binaries", UndoRetouchBinariesFn);
    RegisterFunction("symlink", SymlinkFn);
    RegisterFunction("set_perm", SetPermFn);
    RegisterFunction("set_perm_recursive", SetPermFn);

    RegisterFunction("getprop", GetPropFn);
    RegisterFunction("file_getprop", FileGetPropFn);
    RegisterFunction("write_raw_image", WriteRawImageFn);
    RegisterFunction("write_raw_parameter_image", WriteRawParameterImageFn);
    RegisterFunction("clear_misc_command", ClearMiscCommandFn);

    RegisterFunction("apply_patch", ApplyPatchFn);
    RegisterFunction("apply_patch_check", ApplyPatchCheckFn);
    RegisterFunction("apply_patch_space", ApplyPatchSpaceFn);

    RegisterFunction("read_file", ReadFileFn);
    RegisterFunction("sha1_check", Sha1CheckFn);

    RegisterFunction("wipe_cache", WipeCacheFn);

    RegisterFunction("ui_print", UIPrintFn);

    RegisterFunction("run_program", RunProgramFn);
}

    这些语句执行各种功能。基本上，我们只需要知道用法就可以了。值得注意的是，run_program原语允许我们去执行自定义程序，这应该足够满足我们的个性化需求了。