一、简介
从bootloader 进入Recovery 模式后，首先也是运行Linux内核，该内核跟普通模式没有区别(减轻了BSP开发者的任务)。区别从执行文件系统开始。 Recovery 模式的细节就隐藏在其根文件系统中。
下面，我们就看看进入Recovery 根文件系统都干些啥。
二、init.rc
和正常启动一样，内核进入文件系统会执行/init, init 的配置文件就是 /init.rc, 前面文章讲过，这个文件来自：bootable/recovery/etc/init.rc，下面，我们看看它的内容。
- start ueventd
- on init
- export PATH /sbin
- export ANDROID_ROOT /system
- export ANDROID_DATA /data
- export EXTERNAL_STORAGE /sdcard
- symlink /system/etc /etc
- mkdir /sdcard
- mkdir /system
- mkdir /data
- mkdir /cache
- mount /tmp /tmp tmpfs
- on boot
- ifup lo
- hostname localhost
- domainname localdomain
- class_start default
- service ueventd /sbin/ueventd
- critical
- service recovery /sbin/recovery
- service adbd /sbin/adbd recovery
- disabled
- # Always start adbd on userdebug and eng builds
- on property:ro.debuggable=1
- write /sys/class/android_usb/android0/enable 0
- write /sys/class/android_usb/android0/idVendor 18D1
- write /sys/class/android_usb/android0/idProduct D001
- write /sys/class/android_usb/android0/functions adb
- write /sys/class/android_usb/android0/enable 1
- write /sys/class/android_usb/android0/iManufacturer $ro.product.manufacturer
- write /sys/class/android_usb/android0/iProduct $ro.product.model
- write /sys/class/android_usb/android0/iSerial $ro.serialno
- start adbd
- # Restart adbd so it can run as root
- on property:service.adb.root=1
- write /sys/class/android_usb/android0/enable 0
- restart adbd
- write /sys/class/android_usb/android0/enable 1
可以看到，它很非常简单：
1） 设置几个环境变量。备用。
2） 建立 etc 链接。
3） 造几个目录。备用。
4） Mount /tmp 目录为内存文件系统 tmpfs，后面会用到。
5） Trival 设置,不必关心。
6） 启动 recovery主程序。
7） 如果是eng模式（此时persist.service.adb.enable），启动adb
当然，init主程序还会装载属性配置文件 /default.prop, 它包含了很多系统属性设置，比如，ro.build.*， 等等。很明显，这里最重要的就是recovery主程序，下面，我们分析它。
三、Recovery.c 分析
bootable/recovery/recovery.c
Recovery.c: main->
install_package->
really_install_package->
try_update_binary->
execv(META-INF/com/google/android/update-binary, args);
/*
* The recovery tool communicates with the main system through /cache files.
* /cache/recovery/command - INPUT - command line for tool, one arg per line
* /cache/recovery/log - OUTPUT - combined log file from recovery run(s)
* /cache/recovery/intent - OUTPUT - intent that was passed in
*
* The arguments which may be supplied in the recovery.command file:
* --send_intent=anystring - write the text out to recovery.intent
* --update_package=path - verify install an OTA package file
* --wipe_data - erase user data (and cache), then reboot
* --wipe_cache - wipe cache (but not user data), then reboot
* --set_encrypted_filesystem=on|off - enables / diasables encrypted fs
*
* After completing, we remove /cache/recovery/command and reboot.
* Arguments may also be supplied in the bootloader control block (BCB).
* These important scenarios must be safely restartable at any point:
*
* FACTORY RESET
* 1. user selects "factory reset"
* 2. main system writes "--wipe_data" to /cache/recovery/command
* 3. main system reboots into recovery
* 4. get_args() writes BCB with "boot-recovery" and "--wipe_data"
* -- after this, rebooting will restart the erase --
* 5. erase_volume() reformats /data
* 6. erase_volume() reformats /cache
* 7. finish_recovery() erases BCB
* -- after this, rebooting will restart the main system --
* 8. main() calls reboot() to boot main system
*
* OTA INSTALL
* 1. main system downloads OTA package to /cache/some-filename.zip
* 2. main system writes "--update_package=/cache/some-filename.zip"
* 3. main system reboots into recovery
* 4. get_args() writes BCB with "boot-recovery" and "--update_package=..."
* -- after this, rebooting will attempt to reinstall the update --
* 5. install_package() attempts to install the update
* NOTE: the package install must itself be restartable from any point
* 6. finish_recovery() erases BCB
* -- after this, rebooting will (try to) restart the main system --
* 7. ** if install failed **
* 7a. prompt_and_wait() shows an error icon and waits for the user
* 7b; the user reboots (pulling the battery, etc) into the main system
* 8. main() calls maybe_install_firmware_update()
* ** if the update contained radio/hboot firmware **:
* 8a. m_i_f_u() writes BCB with "boot-recovery" and "--wipe_cache"
* -- after this, rebooting will reformat cache & restart main system --
* 8b. m_i_f_u() writes firmware image into raw cache partition
* 8c. m_i_f_u() writes BCB with "update-radio/hboot" and "--wipe_cache"
* -- after this, rebooting will attempt to reinstall firmware --
* 8d. bootloader tries to flash firmware
* 8e. bootloader writes BCB with "boot-recovery" (keeping "--wipe_cache")
* -- after this, rebooting will reformat cache & restart main system --
* 8f. erase_volume() reformats /cache
* 8g. finish_recovery() erases BCB
* -- after this, rebooting will (try to) restart the main system --
* 9. main() calls reboot() to boot main system
*/
代码及注释如下：
四、install_package分析
bootable/recovery/install.c
int
main(int argc, char **argv) {
time_t start = time(NULL);
// 将标准输出和标准错误输出重定位到"/tmp/recovery.log",如果是eng模式，
// 就可以通过adb pull /tmp/recovery.log, 看到当前的log信息，这为我们
// 提供了有效的调试手段。后面还会看到，recovery模式运行完毕后，
// 会将其拷贝到cache分区，以便后续分析。
// If these fail, there's not really anywhere to complain...
freopen(TEMPORARY_LOG_FILE, "a", stdout); setbuf(stdout, NULL);
freopen(TEMPORARY_LOG_FILE, "a", stderr); setbuf(stderr, NULL);
freopen("/dev/ttyS1", "a", stdout); setbuf(stdout, NULL);
freopen("/dev/ttyS1", "a", stderr); setbuf(stderr, NULL);
printf("Starting recovery on %s", ctime(&start));
// Recovery 使用了一个简单的基于framebuffer的ui系统，叫miniui,这里，
// 进行了简单的初始化（主要是图形部分以及事件部分），并启动了一个
// event 线程用于响应用户按键。
device_ui_init(&ui_parameters);
ui_init();
ui_set_background(BACKGROUND_ICON_INSTALLING);
load_volume_table();
SetSdcardRootPath();
SureCacheMount();
ui_print("Recovery system v4.00 \n\n");
// 从misc 分区以及 CACHE:recovery/command 文件中读入参数，写入到argc, argv ,
// 并且，如果有必要，回写入misc分区。这样，如果recovery没有操作成功
// （比如，升级还没有结束，就拔电池），系统会一直进入recovery模式。
// 提醒用户继续升级，直到成功。
get_args(&argc, &argv);
// 解析参数
int previous_runs = 0;
const char *send_intent = NULL;
const char *update_package = NULL;
const char *update_rkimage = NULL;
int wipe_data = 0, wipe_cache = 0, wipe_all = 0;
int factory_test_en = 0;
char prop[64] = {0};
int arg;
while ((arg = getopt_long(argc, argv, "", OPTIONS, NULL)) != -1) {
switch (arg) {
case 'p': previous_runs = atoi(optarg); break;
case 's': send_intent = optarg; break;
case 'u': update_package = optarg; break;
case 'r': update_rkimage = optarg; break;
case 'w': wipe_data = wipe_cache = 1; break;
case 'c': wipe_cache = 1; break;
case 'f'+'t':{ factory_test_en = 1;ui_show_text(1);} break;
case 't': ui_show_text(1); break;
case 'w'+'a':{ wipe_all = wipe_data = wipe_cache = 1;ui_show_text(1);
} break;
case '?':
LOGE("Invalid command argument\n");
continue;
}
}
// 这个函数没干什么。看名字，它給设备制造商提供了一个调用机会，可写入设备相关初始化代码。
device_recovery_start();
// 打印出命令，比如，正常启动进入recovery模式，会打印：Command: "/sbin/recovery"
printf("Command:");
for (arg = 0; arg < argc; arg++) {
printf(" \"%s\"", argv[arg]);
}
printf("\n");
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 = 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;
}
strcpy(updatepath,update_package);
}
printf("\n");
if (update_rkimage) {
// 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_rkimage, "CACHE:", 6) == 0) {
int len = strlen(update_rkimage) + 10;
char* modified_path = malloc(len);
strlcpy(modified_path, "/cache/", len);
strlcat(modified_path, update_rkimage+6, len);
printf("(replacing path \"%s\" with \"%s\")\n",
update_rkimage, modified_path);
update_rkimage = modified_path;
}
strcpy(updatepath,update_rkimage);
}
printf("\n");
// 打印出所有的系统属性（from default.prop）到log文件。
property_list(print_property, NULL);
printf("\n");
int status = INSTALL_SUCCESS;
if(factory_test_en)
{
ui_print("\nwait factory test tool connect........\n");
char factory_test_finish = 0;
while(1)
{
property_get("FACTORY_TEST_FINISH", prop, "0");
factory_test_finish = (unsigned long)strtoumax(prop, 0, 16);
if(factory_test_finish != 0)break;
sleep(1);
}
ui_print("\n factory test finish........\n");
}
// 根据用户提供参数，调用各项功能，比如，安装一个升级包，擦除cache分区,
// 擦除user data分区，install_package比较复杂，后面专门分析，其它都很简单。忽略。
if (update_package != NULL) {
printf("update_package = %s", update_package);
status = install_package(update_package, &wipe_cache,
TEMPORARY_INSTALL_FILE);
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");
else
bAutoUpdateComplete=true;
} else if (update_rkimage != NULL) {
status = install_rkimage(update_rkimage);
if (status != INSTALL_SUCCESS) ui_print("Installation aborted.\n");
else
bAutoUpdateComplete=true;
} else if (wipe_data) {
if (device_wipe_data()) status = INSTALL_ERROR;
if (erase_volume("/data")) status = INSTALL_ERROR;
if (wipe_cache && erase_volume("/cache")) status = INSTALL_ERROR;
if (wipe_all && erase_volume(IN_SDCARD_ROOT)) 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 {
status = INSTALL_ERROR; // No command specified
}
//如果前面已经做了某项操作并且成功，则进入重启流程。否则，等待用户选择具体操作。
// 而用户可选操作为： reboot, 安装update.zip，除cache分区, 擦除user data分区,
// 如前所述，只有安装package 比较复杂，其它简单。
if (status != INSTALL_SUCCESS) ui_set_background(BACKGROUND_ICON_ERROR);
if (status != INSTALL_SUCCESS) {
bClearbootmessage = false;
prompt_and_wait();
}
// 1）将前面定义的intent字符串写入（如果有的话）：CACHE:recovery/command
// 2）将 /tmp/recovery.log 复制到 "CACHE:recovery/log";
// 3）清空 misc 分区，这样重启就不会进入recovery模式
// 4)删除command 文件：CACHE:recovery/command;
// Otherwise, get ready to boot the main system...
finish_recovery(send_intent);
ui_print("Rebooting...\n");
android_reboot(ANDROID_RB_RESTART, 0, 0);
return EXIT_SUCCESS;
}
四、install_package分析
bootable/recovery/install.c
int
install_package(const char* path, int* wipe_cache, const char* install_file)
{
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 = really_install_package(path, wipe_cache);
if (install_log) {
fputc(result == INSTALL_SUCCESS ? '1' : '0', install_log);
fputc('\n', install_log);
fclose(install_log);
}
return result;
}
static int
really_install_package(const char *path, int* wipe_cache)
{
// 更新 UI 显示
ui_set_background(BACKGROUND_ICON_INSTALLING);
ui_print("Finding update package...\n");
ui_show_indeterminate_progress();
LOGI("Update location: %s\n", path);
//确保升级包所在分区已经mount,通常为 cache 分区或者 SD 分区
if (ensure_path_mounted(path) != 0) {
LOGE("Can't mount %s\n", path);
return INSTALL_CORRUPT;
}
ui_print("Opening update package...\n");
//从/res/keys中装载公钥。
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);
// 根据公钥验证升级包verify_file
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;
}
// 打开升级包，将相关信息存到ZipArchive数据结构中，便于后面处理。
/* 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, wipe_cache);
}
五、try_update_binary分析
bootable/recovery/install.c
// 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) {
const ZipEntry* binary_entry =
mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);
if (binary_entry == NULL) {
mzCloseZipArchive(zip);
return INSTALL_CORRUPT;
}
// 将升级包内文件META-INF/com/google/android/update-binary
// 复制为/tmp/update_binary
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;
}
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;
}
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;
// 创建新的进程，执行：/tmp/update_binary
// 同时，会给该进程传入一些参数，其中最重要的就是一个管道fd，供新进程与原进程通信。
// 新进程诞生后，原进程就变成了一个服务进程，它提供若干UI更新服务
// 新进程就可以通过老进程的UI系统完成显示任务。而其他功能就靠它自己了。
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]);
*wipe_cache = 0;
// 更新UI
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 if (strcmp(command, "wipe_cache") == 0) {
*wipe_cache = 1;
} 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;
}
这样，我们又回到了升级包中的文件：META-INF/com/google/android/update-binary，下回继续研究。