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
public static void verifyPackage(File packageFile,
ProgressListener listener,
File deviceCertsZipFile)
throws IOException, 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，
public static void installPackage(Context context, File packageFile)
throws IOException {
String filename = packageFile.getCanonicalPath();
Log.w(TAG, "!!! REBOOTING TO INSTALL " + filename + " !!!");
final String filenameArg = "--update_package=" + filename;
final String localeArg = "--locale=" + Locale.getDefault().toString();
bootCommand(context, filenameArg, localeArg);
}
这里定义了两个参数，我们接着看，
private static void bootCommand(Context context, String... args) throws IOException {
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，
int arg;
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') {
char buffer[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，
static const struct option OPTIONS[] = {
{ "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 on the 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 or userdebug build, then automatically
// turn the text display on if the script fails so the error
// message is visible.
char buffer[PROPERTY_VALUE_MAX+1];
property_get("ro.build.fingerprint", buffer, "");
if (strstr(buffer, ":userdebug/") || strstr(buffer, ":eng/")) {
ui->ShowText(true);
}
}
} else if (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");
} else if (wipe_cache) {
if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
if (status != INSTALL_SUCCESS) ui->Print("Cache wipe failed.\n");
} else if (!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，
int
install_package(const char* path, int* wipe_cache, const char* install_file,
bool needs_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));
}
int result;
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);
}
return result;
}
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 int
really_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 package into 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");
return INSTALL_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");
return INSTALL_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);
return INSTALL_CORRUPT;
}
/* Try to open the 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);
return INSTALL_CORRUPT;
}
/* Verify and install 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);
return result;
}
该方法主要做了三件事
1、验证签名
int numKeys;
Certificate* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);
if (loadedKeys == NULL) {
LOGE("Failed to load keys\n");
return INSTALL_CORRUPT;
}
装载签名文件，如果为空 ，终止升级；
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);
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
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);
return INSTALL_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
int result = 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 package contains an update binary, extract it and run it.
static int
try_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);
return INSTALL_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);
return INSTALL_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);
return INSTALL_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 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.
//
const char** args = (const char**)malloc(sizeof(char*) * 5);
args[0] = binary;
args[1] = EXPAND(RECOVERY_API_VERSION); // defined in Android.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
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->ShowProgress(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->SetProgress(fraction);
} else if (strcmp(command, "ui_print") == 0) {
char* str = strtok(NULL, "\n");
if (str) {
ui->Print("%s", str);
} else {
ui->Print("\n");
}
fflush(stdout);
} else if (strcmp(command, "wipe_cache") == 0) {
*wipe_cache = 1;
} else if (strcmp(command, "clear_display") == 0) {
ui->SetBackground(RecoveryUI::NONE);
} else if (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。
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，
int chosen_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，
case Device::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");
} else if (!ui->IsTextVisible()) {
return Device::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。
int status = install_package(FUSE_SIDELOAD_HOST_PATHNAME, &wipe_cache,
TEMPORARY_INSTALL_FILE, false);