安卓系统怎么升级到最新版本（Android系统OTA升级流程）

Android系统进行升级的时候，有两种途径，一种是通过接口传递升级包路径自动升级（Android系统SD卡升级），升级完之后系统自动重启；另一种是手动进入recovery模式下，选择升级包进行升级，升级完成之后停留在recovery界面，需要手动选择重启。前者多用于手机厂商的客户端在线升级，后者多用于开发和测试人员。但不管哪种，原理都是一样的，都要在recovery模式下进行升级。

1、获取升级包，可以从服务端下载，也可以直接拷贝到SD卡中

2、获取升级包路径，验证签名，通过installPackage接口升级

3、系统重启进入Recovery模式

4、在install.cpp进行升级操作

5、try_update_binary执行升级脚本

6、finish_recovery，重启

一、获取升级包，可以从服务端下载，也可以直接拷贝到SD卡中

假设SD卡中已有升级包update.zip

二、获取升级包路径，验证签名，通过installPackage接口升级

1、调用RecoverySystem类提供的verifyPackage方法进行签名验证

publicstaticvoidverifyPackage(File packageFile, ProgressListener listener, File deviceCertsZipFile)throwsIOException, GeneralSecurityException

签名验证函数，实现过程就不贴出来了，参数，

packageFile–升级文件

listener–进度监督器

deviceCertsZipFile–签名文件，如果为空，则使用系统默认的签名

只有当签名验证正确才返回，否则将抛出异常。

在Recovery模式下进行升级时候也是会进行签名验证的，如果这里先不进行验证也不会有什么问题。但是我们建议在重启前，先验证，以便及早发现问题。

如果签名验证没有问题，就执行installPackage开始升级。

2、installPackage开始升级

如果签名验证没有问题，就进行重启升级，

publicstaticvoidinstallPackage(Context context, File packageFile)throwsIOException { String filename = packageFile.getCanonicalPath(); Log.w(TAG, "!!! REBOOTING TO INSTALL "+ filename + " !!!"); finalString filenameArg = "--update_package="+ filename; finalString localeArg = "--locale="+ Locale.getDefault().toString(); bootCommand(context, filenameArg, localeArg); }

这里定义了两个参数，我们接着看，

privatestaticvoidbootCommand(Context context, String... args)throwsIOException { RECOVERY_DIR.mkdirs(); // In case we need it COMMAND_FILE.delete(); // In case it's not writable LOG_FILE.delete(); FileWriter command = new FileWriter(COMMAND_FILE); try { for (String arg : args) { if (!TextUtils.isEmpty(arg)) { command.write(arg); command.write("\n"); } } } finally { command.close(); } // Having written the command file, go ahead and reboot PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE); pm.reboot(PowerManager.REBOOT_RECOVERY); throw new IOException("Reboot failed (no permissions?)"); }

创建目录/cache/recovery/，command文件保存在该目录下；如果存在command文件，将其删除；然后将上面一步生成的两个参数写入到command文件。

最后重启设备，重启过程就不再详述了。

三、系统重启进入Recovery模式

系统重启时会判断/cache/recovery目录下是否有command文件，如果存在就进入recovery模式，否则就正常启动。

进入到Recovery模式下，将执行recovery.cpp的main函数，下面贴出关键代码片段，

intarg; while((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) { switch(arg) { case's': send_intent = optarg; break; case'u': update_package = optarg; break; case'w': wipe_data = wipe_cache = 1; break; case'c': wipe_cache = 1; break; case't': show_text = 1; break; case'x': just_exit = true; break; case'l': locale = optarg; break; case'g': { if(stage == NULL|| *stage == '\0') { charbuffer[20] = "1/"; strncat(buffer, optarg, sizeof(buffer)-3); stage = strdup(buffer); } break; } case'p': shutdown_after = true; break; case'r': reason = optarg; break; case'?': LOGE("Invalid command argument\n"); continue; } }

这是一个While循环，用来读取 recovery的 command参数， OPTIONS的不同选项定义如下，

staticconststructoptionOPTIONS[] = {{ "send_intent", required_argument, NULL, 's'}, { "update_package", required_argument, NULL, 'u'}, { "wipe_data", no_argument, NULL, 'w'}, { "wipe_cache", no_argument, NULL, 'c'}, { "show_text", no_argument, NULL, 't'}, { "just_exit", no_argument, NULL, 'x'}, { "locale", required_argument, NULL, 'l'}, { "stages", required_argument, NULL, 'g'}, { "shutdown_after", no_argument, NULL, 'p'}, { "reason", required_argument, NULL, 'r'}, { NULL, 0, NULL, 0},};

显然，根据第二步写入的命令文件内容，将为update_package 赋值。

接着看，

if(update_package) { // For backwards compatibility onthe cache partition only, if // we're given an old 'root' path "CACHE:foo", change it to // "/cache/foo". if (strncmp(update_package, "CACHE:", 6) == 0) { int len = strlen(update_package) + 10; char* modified_path = (char*)malloc(len); strlcpy(modified_path, "/cache/", len); strlcat(modified_path, update_package+6, len); printf("(replacing path \"%s\" with \"%s\")\n", update_package, modified_path); update_package = modified_path; } }

兼容性处理。

int status= INSTALL_SUCCESS; if(update_package != NULL) { status= install_package(update_package, &wipe_cache, TEMPORARY_INSTALL_FILE, true); if(status== INSTALL_SUCCESS && wipe_cache) { if(erase_volume("/cache")) { LOGE("Cache wipe (requested by package) failed."); } } if(status!= INSTALL_SUCCESS) { ui->Print("Installation aborted.\n"); // If this is an eng oruserdebug build, thenautomatically // turn the text display on ifthe script fails so the error// message is visible. charbuffer[PROPERTY_VALUE_MAX+1]; property_get("ro.build.fingerprint", buffer, ""); if(strstr(buffer, ":userdebug/") || strstr(buffer, ":eng/")) { ui->ShowText(true); } } } elseif(wipe_data) { if(device->WipeData()) status= INSTALL_ERROR; if(erase_volume("/data")) status= INSTALL_ERROR; if(wipe_cache && erase_volume("/cache")) status= INSTALL_ERROR; if(erase_persistent_partition() == -1) status= INSTALL_ERROR; if(status!= INSTALL_SUCCESS) ui->Print("Data wipe failed.\n"); } elseif(wipe_cache) { if(wipe_cache && erase_volume("/cache")) status= INSTALL_ERROR; if(status!= INSTALL_SUCCESS) ui->Print("Cache wipe failed.\n"); } elseif(!just_exit) { status= INSTALL_NONE; // No command specified ui->SetBackground(RecoveryUI::NO_COMMAND); }

update_package不为空，执行install_package方法。

我们也可以看到擦除数据、缓存的实现也是在这个里执行的，这里就不展开了。

四、在install.cpp进行升级操作

具体的升级过程都是在install.cpp中执行的，先看install_package方法，

intinstall_package(constchar* path, int* wipe_cache, constchar* install_file, boolneeds_mount){ FILE* install_log = fopen_path(install_file, "w"); if(install_log) { fputs(path, install_log); fputc('\n', install_log); } else{ LOGE("failed to open last_install: %s\n", strerror(errno)); } intresult; if(setup_install_mounts() != 0) { LOGE("failed to set up expected mounts for install; aborting\n"); result = INSTALL_ERROR; } else{ result = really_install_package(path, wipe_cache, needs_mount); } if(install_log) { fputc(result == INSTALL_SUCCESS ? '1': '0', install_log); fputc('\n', install_log); fclose(install_log); } returnresult;}

这个方法中首先创建了log文件，升级过程包括出错的信息都会写到这个文件中，便于后续的分析工作。继续跟进， really_install_package，

static intreally_install_package(const char*path, int* wipe_cache, bool needs_mount){ ui->SetBackground(RecoveryUI::INSTALLING_UPDATE); ui->Print("Finding update package...\n"); // Give verification half the progress bar... ui->SetProgressType(RecoveryUI::DETERMINATE); ui->ShowProgress(VERIFICATION_PROGRESS_FRACTION, VERIFICATION_PROGRESS_TIME); LOGI("Update location: %s\n", path); // Map the update packageinto memory. ui->Print("Opening update package...\n"); if(path&& needs_mount) { if(path[0] == '@') { ensure_path_mounted(path+1); } else{ ensure_path_mounted(path); } } MemMapping map; if(sysMapFile(path, &map) != 0) { LOGE("failed to map file\n"); returnINSTALL_CORRUPT; } // 装入签名文件 int numKeys; Certificate* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys); if(loadedKeys == NULL) { LOGE("Failed to load keys\n"); returnINSTALL_CORRUPT; } LOGI("%d key(s) loaded from %s\n", numKeys, PUBLIC_KEYS_FILE); ui->Print("Verifying update package...\n"); // 验证签名 int err; err = verify_file(map.addr, map.length, loadedKeys, numKeys); free(loadedKeys); LOGI("verify_file returned %d\n", err); // 签名失败的处理 if(err != VERIFY_SUCCESS) { LOGE("signature verification failed\n"); sysReleaseMap(&map); returnINSTALL_CORRUPT; } /* Try to openthe package. */ // 打开升级包 ZipArchive zip; err = mzOpenZipArchive(map.addr, map.length, &zip); if(err != 0) { LOGE("Can't open %s\n(%s)\n", path, err != -1? strerror(err) : "bad"); sysReleaseMap(&map); returnINSTALL_CORRUPT; } /* Verify andinstall the contents of the package. */ ui->Print("Installing update...\n"); ui->SetEnableReboot(false); // 执行升级脚本文件，开始升级 int result = try_update_binary(path, &zip, wipe_cache); ui->SetEnableReboot(true); ui->Print("\n"); sysReleaseMap(&map); returnresult;}

该方法主要做了三件事

1、验证签名

intnumKeys; Certificate* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys); if(loadedKeys == NULL) { LOGE("Failed to load keys\n"); returnINSTALL_CORRUPT; }

装载签名文件，如果为空 ，终止升级；

interr; err = verify_file(map.addr, map.length, loadedKeys, numKeys); free(loadedKeys); LOGI("verify_file returned %d\n", err); // 签名失败的处理 if (err != VERIFY_SUCCESS) { LOGE("signature verification failed\n"); sysReleaseMap(&map); return INSTALL_CORRUPT; }

调用verify_file进行签名验证，这个方法定义在verifier.cpp文件中，此处不展开，如果验证失败立即终止升级。

2、读取升级包信息

ZipArchivezip; err = mzOpenZipArchive(map.addr, map.length, &zip); if(err != 0) { LOGE("Can't open %s\n(%s)\n", path, err != -1? strerror(err) : "bad"); sysReleaseMap(&map); returnINSTALL_CORRUPT; }

执行mzOpenZipArchive方法，打开升级包并扫描，将包的内容拷贝到变量zip中，该变量将作为参数用来执行升级脚本。

3、执行升级脚本文件，开始升级

intresult = try_update_binary(path, &zip, wipe_cache);

try_update_binary方法用来处理升级包，执行制作升级包中的脚本文件 update_binary ，进行系统更新。

五、try_update_binary执行升级脚本

// If the packagecontains an update binary, extract it andrun it.static inttry_update_binary(const char*path, ZipArchive *zip, int* wipe_cache) { // 检查update-binary是否存在 const ZipEntry* binary_entry = mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME); if(binary_entry == NULL) { mzCloseZipArchive(zip); returnINSTALL_CORRUPT; } const char* binary = "/tmp/update_binary"; unlink(binary); int fd = creat(binary, 0755); if(fd < 0) { mzCloseZipArchive(zip); LOGE("Can't make %s\n", binary); returnINSTALL_ERROR; } // update-binary拷贝到"/tmp/update_binary"bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd); close(fd); mzCloseZipArchive(zip); if(!ok) { LOGE("Can't copy %s\n", ASSUMED_UPDATE_BINARY_NAME); returnINSTALL_ERROR; } // 创建管道，用于下面的子进程和父进程之间的通信 int pipefd[2]; pipe(pipefd); // When executing the update binary contained inthe package, the // arguments passed are: // // - the version number forthis interface // // - an fd to which the program can writeinorder to update the // progress bar. The program can writesingle-line commands: // // progress   // fill up the next part of of the progress bar // over  seconds. If  is zero, use // set_progress commands to manually control the // progress of this segment of the bar // // set_progress  //  should be between 0.0and1.0; sets the // progress bar within the segment defined by the most // recent progress command. // // firmware   // arrange to install the contents of  inthe // given partition on reboot. // // (API v2:  may start with "PACKAGE:"to // indicate taking a file from the OTA package.) // // (API v3: this command no longer exists.) // // ui_print  // display  on the screen. // // - the name of the packagezip file. // const char** args = (const char**)malloc(sizeof(char*) * 5); args[0] = binary; args[1] = EXPAND(RECOVERY_API_VERSION); // defined inAndroid.mk char* temp = (char*)malloc(10); sprintf(temp, "%d", pipefd[1]); args[2] = temp; args[3] = (char*)path; args[4] = NULL; // 创建子进程。负责执行binary脚本 pid_t pid = fork(); if(pid == 0) { umask(022); close(pipefd[0]); execv(binary, (char* const*)args);// 执行binary脚本 fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno)); _exit(-1); } close(pipefd[1]); *wipe_cache = 0; // 父进程负责接受子进程发送的命令去更新ui显示 charbuffer[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; } elseif(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->ShowProgress(fraction * (1-VERIFICATION_PROGRESS_FRACTION), seconds); } elseif(strcmp(command, "set_progress") == 0) { char* fraction_s = strtok(NULL, " \n"); float fraction = strtof(fraction_s, NULL); ui->SetProgress(fraction); } elseif(strcmp(command, "ui_print") == 0) { char* str = strtok(NULL, "\n"); if(str) { ui->Print("%s", str); } else{ ui->Print("\n"); } fflush(stdout); } elseif(strcmp(command, "wipe_cache") == 0) { *wipe_cache = 1; } elseif(strcmp(command, "clear_display") == 0) { ui->SetBackground(RecoveryUI::NONE); } elseif(strcmp(command, "enable_reboot") == 0) { // packages can explicitly request that they want the user // to be able to reboot during installation (useful for// debugging packages that don't exit). ui->SetEnableReboot(true); } 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;}

try_update_binary函数，是真正实现读取升级包中的脚本文件并执行相应的函数的地方。在此函数中，通过调用fork函数创建出一个子进程，在子进程中开始读取并执行升级脚本文件。在此需要注意的是函数fork的用法，fork被调用一次，将做两次返回，在父进程中返回的是子进程的进程ID，为正数；而在子进程中，则返回0。子进程创建成功后，开始执行升级代码，并通过管道与父进程交互，父进程则通过读取子进程传递过来的信息更新UI。

六、finish_recovery，重启

上一步完成之后，回到main函数，

// Save logs and clean up before rebooting or shutting down. finish_recovery(send_intent);

保存升级过程中的log，清除临时文件，包括command文件（不清除的话，下次重启还会进入recovery模式），最后重启。

以上就是升级的一个流程。

补充：

手动升级的流程也基本差不多，通过power key + volume上键组合，进入recovery模式，进入prompt_and_wait函数等待用户按键事件。

recovery.cpp的main函数，

Device::BuiltinAction after = shutdown_after ? Device::SHUTDOWN : Device::REBOOT; if(status != INSTALL_SUCCESS || ui->IsTextVisible()) { Device::BuiltinAction temp = prompt_and_wait(device, status); if(temp != Device::NO_ACTION) after = temp; }

根据用户选择进入到相应的分支进行处理，如下图，

intchosen_item = get_menu_selection(headers, device->GetMenuItems(), 0, 0, device); // device-specific code may take some action here. It may // return one of the core actions handled in the switch // statement below. Device::BuiltinAction chosen_action = device->InvokeMenuItem(chosen_item);

当我们选择从外置 sdcard升级，进入如下分支中，

caseDevice::APPLY_EXT: { ensure_path_mounted(SDCARD_ROOT); char* path = browse_directory(SDCARD_ROOT, device); if(path == NULL) { ui->Print("\n-- No package file selected.\n", path); break; } ui->Print("\n-- Install %s ...\n", path); set_sdcard_update_bootloader_message(); void* token = start_sdcard_fuse(path); int status = install_package(FUSE_SIDELOAD_HOST_PATHNAME, &wipe_cache, TEMPORARY_INSTALL_FILE, false); finish_sdcard_fuse(token); ensure_path_unmounted(SDCARD_ROOT); if(status == INSTALL_SUCCESS && wipe_cache) { ui->Print("\n-- Wiping cache (at package request)...\n"); if(erase_volume("/cache")) { ui->Print("Cache wipe failed.\n"); } else{ ui->Print("Cache wipe complete.\n"); } } if(status >= 0) { if(status != INSTALL_SUCCESS) { ui->SetBackground(RecoveryUI::ERROR); ui->Print("Installation aborted.\n"); } elseif(!ui->IsTextVisible()) { returnDevice::NO_ACTION; // reboot if logs aren't visible } else { ui->Print("\nInstall from sdcard complete.\n"); } } break; }

char* path = browse_directory(SDCARD_ROOT, device);这个函数浏览 SD card下的文件 ，并把路径记录下来 ,然后根据名称排序 ，并处理用户按键。

·当用户选择第一个条目“../”,直接跳转到上级目录,并且继续浏览文件

·当用户选择的条目以“/”开头,直接进入子目录

·其它情况表明,该条目就是zip包.写入BCB,copy 更新包至临时目录，直接转入install_package

选择zip包后，同样也是执行install_package函数，后面与自动升级的流程是一样的。

intstatus = install_package(FUSE_SIDELOAD_HOST_PATHNAME, &wipe_cache, TEMPORARY_INSTALL_FILE, false);