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

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;
}