Android系统Recovery工作原理之使用update.zip升级过程分析（八）---解...
一、update_binary的执行过程分析
上一篇幅中的子进程所执行的程序binary实际上就是update.zip包中的update-binary。我们在上文中也说过，Recovery服务在做这一部分工作的时候是先将包中update-binary拷贝到内存文件系统中的/tmp/update_binary，然后再执行的。update_binary程序的源码位于gingerbread0919/bootable/recovery/updater/updater.c，源码如下：
/* * Copyright (C) 2009 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include "edify/expr.h" #include "updater.h" #include "install.h" #include "minzip/Zip.h" // Generated by the makefile, this function defines the // RegisterDeviceExtensions() function, which calls all the // registration functions for device-specific extensions. #include "register.inc" // 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; } 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; } // 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; } 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. RegisterBuiltins(); RegisterInstallFunctions(); RegisterDeviceExtensions(); FinishRegistration(); // Parse the script. 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; 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; }
通过上面的源码来分析下这个程序的执行过程：
①函数参数以及版本的检查：当前updater binary API所支持的版本号有1，2，3这三个。
②获取管道并打开：在执行此程序的过程中向该管道写入命令，用于通知其父进程根据命令去更新UI显示。
③读取updater-script脚本：从update.zip包中将updater-script脚本读到一块动态内存中，供后面执行。
④Configure edify’s functions：注册脚本中的语句处理函数，即识别脚本中命令的函数。主要有以下几类
RegisterBuiltins()：注册程序中控制流程的语句，如ifelse、assert、abort、stdout等。
RegisterInstallFunctions()：实际安装过程中安装所需的功能函数，比如mount、format、set_progress、set_perm等等。
RegisterDeviceExtensions()：与设备相关的额外添加項，在源码中并没有任何实现。
FinishRegistration()：结束注册。
⑤Parsethe script：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()。
⑥执行脚本：核心函数是Evaluate（），它会调用其他的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。
⑦错误信息提示：最后就是根据Evaluate（）执行后的返回值，给出一些打印信息。
这一执行过程非常简单，最主要的函数就是Evaluate。它负责最终执行解析的脚本命令。而安装过程中的命令就是updater-script。
下一篇幅将介绍updater-script脚本中的语法以及这个脚本在具体升级中的执行流程。