Android OTA升级包制作脚本详解（五，升级脚本updater-script的执行<2>）

写在前面：

    从前面一篇博文我们知道recovery下安装更新的主要内容就是去执行更新脚本程序update-binary，而update-binary的主要任务就是去解析执行updater-script，那update-binary是如何去解释执行updater-script的呢。我们下面一起来学习一下。

  源码位于android目录下/bootable/recovery/updater/upadter.c,整个源文件只有一个main函数，下面我们对main函数进行一个初步的了解。

// Generated by the makefile, this function defines the// RegisterDeviceExtensions() function, which calls all the// registration functions for device-specific extensions.#include "register.inc"// 首先这里封装了updater-script的路径，updater-binary会找到这个路径下的updater-script文件进行解释执行。 #define SCRIPT_NAME "META-INF/com/google/android/updater-script"struct selabel_handle *sehandle;int main(int argc, char** argv) {    // Various things log information to stdout or stderr more or less    // at random (though we've tried to standardize on stdout).  The    // log file makes more sense if buffering is turned off so things    // appear in the right order.    setbuf(stdout, NULL);    setbuf(stderr, NULL);    /*传递进来的参数    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;     */    if (argc != 4) {        fprintf(stderr, "unexpected number of arguments (%d)\n", argc);        return 1;    }    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;    }    // 获得一个管道用来向父进程发送命令。    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;    }    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';#if 1 //wschen 2012-06-01    fprintf(stderr, "====== Updater-Script:\n");    fprintf(stderr, "%s\n\n", script);#endif    // 配置edify函数    RegisterBuiltins();//注册程序中控制流程的语句    RegisterInstallFunctions();//注册实际安装过程中安装所需的功能函数    RegisterDeviceExtensions();//注册与设备相关的扩展项    FinishRegistration();//完成注册    // 解析脚本，调用yy*库函数解析脚本，并将解析后的内容存放到一个Expr类型的python类中。主要函数是yy_scan_string()和yyparse()    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;    }    struct selinux_opt seopts[] = {      { SELABEL_OPT_PATH, "/file_contexts" }    };    sehandle = selabel_open(SELABEL_CTX_FILE, seopts, 1);    if (!sehandle) {        fprintf(stderr, "Warning:  No file_contexts\n");        fprintf(cmd_pipe, "ui_print Warning: No file_contexts\n");    }    // Evaluate（）会调用其他的callback函数，而这些callback函数又会去调用Evaluate去解析不同的脚本片段，从而实现一个简单的脚本解释器。    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;    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;}