转载自：http://blog.chinaunix.net/uid-22028566-id-3533857.html
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。
上一篇：Android OTA升级原理和流程分析（七）---Recovery服务的核心install_package函数