Android系统Recovery工作原理之使用update.zip升级过程分析（七）---Recovery服务的核心install_package函数
一、 Recovery服务的核心install_package（升级update.zip特有）
和Recovery服务中的wipe_data、wipe_cache不同，install_package()是升级update.zip特有的一部分，也是最核心的部分。在这一步才真正开始对我们的update.zip包进行处理。下面就开始分析这一部分。还是先看图例：
这一部分的源码文件位于：/gingerbread0919/bootable/recovery/install.c。这是一个没有main函数的源码文件，还是把源码先贴出来如下：
/* * Copyright (C) 2007 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 <ctype.h> #include <errno.h> #include <fcntl.h> #include <limits.h> #include <sys/stat.h> #include <sys/wait.h> #include <unistd.h> #include "common.h" #include "install.h" #include "mincrypt/rsa.h" #include "minui/minui.h" #include "minzip/SysUtil.h" #include "minzip/Zip.h" #include "mtdutils/mounts.h" #include "mtdutils/mtdutils.h" #include "roots.h" #include "verifier.h" #define ASSUMED_UPDATE_BINARY_NAME "META-INF/com/google/android/update-binary" #define PUBLIC_KEYS_FILE "/res/keys" // If the package contains an update binary, extract it and run it. static int try_update_binary(const char *path, ZipArchive *zip) { const ZipEntry* binary_entry = mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME); if (binary_entry == NULL) { mzCloseZipArchive(zip); return INSTALL_CORRUPT; } char* binary = "/tmp/update_binary"; unlink(binary); int fd = creat(binary, 0755); if (fd < 0) { mzCloseZipArchive(zip); LOGE("Can't make %s\n", binary); return 1; } bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd); close(fd); mzCloseZipArchive(zip); if (!ok) { LOGE("Can't copy %s\n", ASSUMED_UPDATE_BINARY_NAME); return 1; } int pipefd[2]; pipe(pipefd); // When executing the update binary contained in the package, the // arguments passed are: // // - the version number for this interface // // - an fd to which the program can write in order to update the // progress bar. The program can write single-line commands: // // progress <frac> <secs> // fill up the next <frac> part of of the progress bar // over <secs> seconds. If <secs> is zero, use // set_progress commands to manually control the // progress of this segment of the bar // // set_progress <frac> // <frac> should be between 0.0 and 1.0; sets the // progress bar within the segment defined by the most // recent progress command. // // firmware <"hboot"|"radio"> <filename> // arrange to install the contents of <filename> in the // given partition on reboot. // // (API v2: <filename> may start with "PACKAGE:" to // indicate taking a file from the OTA package.) // // (API v3: this command no longer exists.) // // ui_print <string> // display <string> on the screen. // // - the name of the package zip file. // char** args = malloc(sizeof(char*) * 5); args[0] = binary; args[1] = EXPAND(RECOVERY_API_VERSION); // defined in Android.mk args[2] = malloc(10); sprintf(args[2], "%d", pipefd[1]); args[3] = (char*)path; args[4] = NULL; pid_t pid = fork(); if (pid == 0) { close(pipefd[0]); execv(binary, args); fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno)); _exit(-1); } close(pipefd[1]); char buffer[1024]; FILE* from_child = fdopen(pipefd[0], "r"); while (fgets(buffer, sizeof(buffer), from_child) != NULL) { char* command = strtok(buffer, " \n"); if (command == NULL) { continue; } else if (strcmp(command, "progress") == 0) { char* fraction_s = strtok(NULL, " \n"); char* seconds_s = strtok(NULL, " \n"); float fraction = strtof(fraction_s, NULL); int seconds = strtol(seconds_s, NULL, 10); ui_show_progress(fraction * (1-VERIFICATION_PROGRESS_FRACTION), seconds); } else if (strcmp(command, "set_progress") == 0) { char* fraction_s = strtok(NULL, " \n"); float fraction = strtof(fraction_s, NULL); ui_set_progress(fraction); } else if (strcmp(command, "ui_print") == 0) { char* str = strtok(NULL, "\n"); if (str) { ui_print("%s", str); } else { ui_print("\n"); } } else { LOGE("unknown command [%s]\n", command); } } fclose(from_child); int status; waitpid(pid, &status, 0); if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) { LOGE("Error in %s\n(Status %d)\n", path, WEXITSTATUS(status)); return INSTALL_ERROR; } return INSTALL_SUCCESS; } // Reads a file containing one or more public keys as produced by // DumpPublicKey: this is an RSAPublicKey struct as it would appear // as a C source literal, eg: // // "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}" // // (Note that the braces and commas in this example are actual // characters the parser expects to find in the file; the ellipses // indicate more numbers omitted from this example.) // // The file may contain multiple keys in this format, separated by // commas. The last key must not be followed by a comma. // // Returns NULL if the file failed to parse, or if it contain zero keys. static RSAPublicKey* load_keys(const char* filename, int* numKeys) { RSAPublicKey* out = NULL; *numKeys = 0; FILE* f = fopen(filename, "r"); if (f == NULL) { LOGE("opening %s: %s\n", filename, strerror(errno)); goto exit; } int i; bool done = false; while (!done) { ++*numKeys; out = realloc(out, *numKeys * sizeof(RSAPublicKey)); RSAPublicKey* key = out + (*numKeys - 1); if (fscanf(f, " { %i , 0x%x , { %u", &(key->len), &(key->n0inv), &(key->n[0])) != 3) { goto exit; } if (key->len != RSANUMWORDS) { LOGE("key length (%d) does not match expected size\n", key->len); goto exit; } for (i = 1; i < key->len; ++i) { if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit; } if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit; for (i = 1; i < key->len; ++i) { if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit; } fscanf(f, " } } "); // if the line ends in a comma, this file has more keys. switch (fgetc(f)) { case ',': // more keys to come. break; case EOF: done = true; break; default: LOGE("unexpected character between keys\n"); goto exit; } } fclose(f); return out; exit: if (f) fclose(f); free(out); *numKeys = 0; return NULL; } int install_package(const char *path) { ui_set_background(BACKGROUND_ICON_INSTALLING); ui_print("Finding update package...\n"); ui_show_indeterminate_progress(); LOGI("Update location: %s\n", path); if (ensure_path_mounted(path) != 0) { LOGE("Can't mount %s\n", path); return INSTALL_CORRUPT; } ui_print("Opening update package...\n"); int numKeys; RSAPublicKey* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys); if (loadedKeys == NULL) { LOGE("Failed to load keys\n"); return INSTALL_CORRUPT; } LOGI("%d key(s) loaded from %s\n", numKeys, PUBLIC_KEYS_FILE); // Give verification half the progress bar... ui_print("Verifying update package...\n"); ui_show_progress( VERIFICATION_PROGRESS_FRACTION, VERIFICATION_PROGRESS_TIME); int err; err = verify_file(path, loadedKeys, numKeys); free(loadedKeys); LOGI("verify_file returned %d\n", err); if (err != VERIFY_SUCCESS) { LOGE("signature verification failed\n"); return INSTALL_CORRUPT; } /* Try to open the package. */ ZipArchive zip; err = mzOpenZipArchive(path, &zip); if (err != 0) { LOGE("Can't open %s\n(%s)\n", path, err != -1 ? strerror(err) : "bad"); return INSTALL_CORRUPT; } /* Verify and install the contents of the package. */ ui_print("Installing update...\n"); return try_update_binary(path, &zip); }
下面顺着上面的流程图和源码来分析这一流程：
①ensure_path_mount()：先判断所传的update.zip包路径所在的分区是否已经挂载。如果没有则先挂载。
②load_keys()：加载公钥源文件，路径位于/res/keys。这个文件在Recovery镜像的根文件系统中。
③verify_file()：对升级包update.zip包进行签名验证。
④mzOpenZipArchive()：打开升级包，并将相关的信息拷贝到一个临时的ZipArchinve变量中。这一步并未对我们的update.zip包解压。
⑤try_update_binary()：在这个函数中才是对我们的update.zip升级的地方。这个函数一开始先根据我们上一步获得的zip包信息，以及升级包的绝对路径将update_binary文件拷贝到内存文件系统的/tmp/update_binary中。以便后面使用。
⑥pipe()：创建管道，用于下面的子进程和父进程之间的通信。
⑦fork()：创建子进程。其中的子进程主要负责执行binary（execv(binary,args)，即执行我们的安装命令脚本），父进程负责接受子进程发送的命令去更新ui显示（显示当前的进度）。子父进程间通信依靠管道。
⑧其中，在创建子进程后，父进程有两个作用。一是通过管道接受子进程发送的命令来更新UI显示。二是等待子进程退出并返回INSTALL SUCCESS。其中子进程在解析执行安装脚本的同时所发送的命令有以下几种：
progress <frac> <secs>：根据第二个参数secs（秒）来设置进度条。
set_progress <frac>：直接设置进度条，frac取值在0.0到0.1之间。
firmware <”hboot”|”radio”><filename>：升级firmware时使用，在API V3中不再使用。
ui_print <string>：在屏幕上显示字符串，即打印更新过程。
execv(binary,args)的作用就是去执行binary程序，这个程序的实质就是去解析update.zip包中的updater-script脚本中的命令并执行。由此，Recovery服务就进入了实际安装update.zip包的过程。
下一篇继续分析使用update-binary解析并执行updater-script的过程。
