Android系统Recovery工作原理之使用update.zip升级过程分析（八）---升级程序update_binary的执行过程

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：

[cpp] view
plaincopy

/*

* 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。