一、回顾
先回顾下上部分得分析，从最开始的PM.reboot()，经过层层调用，最终调用
SystemProperties.set(“sys.powerctl”, “reboot,” + reason);
二、重启流程
aosp/system/core/init/property_service.cpp
aosp/system/core/init/reboot.cpp
aosp/system/core/init/reboot_utils.cpp
aosp/system/core/init/init.cpp
PM.reboot最终也就是setprop sys.powerctl，那么谁来监听sys.powerctl 值呢，肯定是init了，接下来就也就引入本节得重点，
init监听 sys.powerctl 处理关机后半部流程
2.1 HandlePropertySet
[->property_service.cpp]
// This returns one of the enum of PROP_SUCCESS or PROP_ERROR*.
uint32_t HandlePropertySet(const std::string& name, const std::string& value,
const std::string& source_context, const ucred& cr, std::string* error) {
...
// sys.powerctl is a special property that is used to make the device reboot. We want to log
// any process that sets this property to be able to accurately blame the cause of a shutdown.
//此时会记录到logcat中，那个进程设置sys.powerctl得以及原因
if (name == "sys.powerctl") {
std::string cmdline_path = StringPrintf("proc/%d/cmdline", cr.pid);
std::string process_cmdline;
std::string process_log_string;
if (ReadFileToString(cmdline_path, &process_cmdline)) {
// Since cmdline is null deliminated, .c_str() conveniently gives us just the process
// path.
process_log_string = StringPrintf(" (%s)", process_cmdline.c_str());
}
LOG(INFO) << "Received sys.powerctl='" << value << "' from pid: " << cr.pid
<< process_log_string;
}
...
return PropertySet(name, value, error); //设置属性值
}
2.2 HandlePropertySet
[->property_service.cpp]
static uint32_t PropertySet(const std::string& name, const std::string& value, std::string* error) {
...
property_changed(name, value);// 会通知init property值改变
return PROP_SUCCESS;
}
2.3 property_changed
[->init.cpp]
void property_changed(const std::string& name, const std::string& value) {
// If the property is sys.powerctl, we bypass the event queue and immediately handle it.
// This is to ensure that init will always and immediately shutdown/reboot, regardless of
// if there are other pending events to process or if init is waiting on an exec service or
// waiting on a property.
// In non-thermal-shutdown case, 'shutdown' trigger will be fired to let device specific
// commands to be executed.
if (name == "sys.powerctl") { //当init检测到某个进程设置 sys.powerctl时，会把do_shutdown 置true，init主循环会执行关机动作 见2.3节
// Despite the above comment, we can't call HandlePowerctlMessage() in this function,
// because it modifies the contents of the action queue, which can cause the action queue
// to get into a bad state if this function is called from a command being executed by the
// action queue. Instead we set this flag and ensure that shutdown happens before the next
// command is run in the main init loop.
// TODO: once property service is removed from init, this will never happen from a builtin,
// but rather from a callback from the property service socket, in which case this hack can
// go away.
shutdown_command = value;
do_shutdown = true;
}
if (property_triggers_enabled) ActionManager::GetInstance().QueuePropertyChange(name, value);
if (waiting_for_prop) {
if (wait_prop_name == name && wait_prop_value == value) {
LOG(INFO) << "Wait for property took " << *waiting_for_prop;
ResetWaitForProp();
}
}
}
2.4 SecondStageMain
[->init.cpp]
int SecondStageMain(int argc, char** argv) {
...
while (true) {
// By default, sleep until something happens.
auto epoll_timeout = std::optional<:chrono::milliseconds>{};
if (do_shutdown && !shutting_down) {
do_shutdown = false;
if (HandlePowerctlMessage(shutdown_command)) { //执行关机重启流程
shutting_down = true;
}
}
if (!(waiting_for_prop || Service::is_exec_service_running())) {
am.ExecuteOneCommand();
}
if (!(waiting_for_prop || Service::is_exec_service_running())) {
if (!shutting_down) {
auto next_process_action_time = HandleProcessActions();
// If there's a process that needs restarting, wake up in time for that.
if (next_process_action_time) {
epoll_timeout = std::chrono::ceil<:chrono::milliseconds>(
*next_process_action_time - boot_clock::now());
if (*epoll_timeout < 0ms) epoll_timeout = 0ms;
}
}
// If there's more work to do, wake up again immediately.
if (am.HasMoreCommands()) epoll_timeout = 0ms;
}
if (auto result = epoll.Wait(epoll_timeout); !result) {
LOG(ERROR) << result.error();
}
}
return 0;
}
2.5 HandlePowerctlMessage
[->reboot.cpp]
bool HandlePowerctlMessage(const std::string& command) {
unsigned int cmd = 0;
std::vector<:string> cmd_params = Split(command, ",");
std::string reboot_target = "";
bool run_fsck = false;
bool command_invalid = false;
if (cmd_params.size() > 3) {
command_invalid = true;
} else if (cmd_params[0] == "shutdown") {
cmd = ANDROID_RB_POWEROFF;
if (cmd_params.size() == 2) {
if (cmd_params[1] == "userrequested") {
// The shutdown reason is PowerManager.SHUTDOWN_USER_REQUESTED.
// Run fsck once the file system is remounted in read-only mode.
run_fsck = true;
} else if (cmd_params[1] == "thermal") {
// Turn off sources of heat immediately.
TurnOffBacklight();
// run_fsck is false to avoid delay
cmd = ANDROID_RB_THERMOFF;
}
}
} else if (cmd_params[0] == "reboot") {
cmd = ANDROID_RB_RESTART2;
if (cmd_params.size() >= 2) {
reboot_target = cmd_params[1];
// adb reboot fastboot should boot into bootloader for devices not
// supporting logical partitions.
if (reboot_target == "fastboot" &&
!android::base::GetBoolProperty("ro.boot.dynamic_partitions", false)) {
reboot_target = "bootloader";
}
// When rebooting to the bootloader notify the bootloader writing
// also the BCB.
if (reboot_target == "bootloader") {
std::string err;
if (!write_reboot_bootloader(&err)) {//会把bootloader写到kernel，重启使用
LOG(ERROR) << "reboot-bootloader: Error writing "
"bootloader_message: "
<< err;
}
} else if (reboot_target == "sideload" || reboot_target == "sideload-auto-reboot" ||
reboot_target == "fastboot") {
std::string arg = reboot_target == "sideload-auto-reboot" ? "sideload_auto_reboot"
: reboot_target;
const std::vector<:string> options = {
"--" + arg,
};
std::string err;
if (!write_bootloader_message(options, &err)) {//会把recovery写到kernel，重启使用
LOG(ERROR) << "Failed to set bootloader message: " << err;
return false;
}
reboot_target = "recovery";
}
// If there is an additional parameter, pass it along
if ((cmd_params.size() == 3) && cmd_params[2].size()) {
reboot_target += "," + cmd_params[2];
}
}
} else {
command_invalid = true;
}
if (command_invalid) {
LOG(ERROR) << "powerctl: unrecognized command '" << command << "'";
return false;
}
LOG(INFO) << "Clear action queue and start shutdown trigger";
ActionManager::GetInstance().ClearQueue();
// Queue shutdown trigger first
ActionManager::GetInstance().QueueEventTrigger("shutdown");//处理init.rc中shutdown部分，依次关闭各个模块
// Queue built-in shutdown_done
auto shutdown_handler = [cmd, command, reboot_target, run_fsck](const BuiltinArguments&) {
DoReboot(cmd, command, reboot_target, run_fsck); //reboot 流程核心，见下节
return Success();
};
ActionManager::GetInstance().QueueBuiltinAction(shutdown_handler, "shutdown_done");//设置中shutdown_done部分,shutdown执行完会执行DoReboot
// Skip wait for prop if it is in progress
ResetWaitForProp();
// Clear EXEC flag if there is one pending
for (const auto& s : ServiceList::GetInstance()) {
s->UnSetExec();
}
return true;
}
2.6 DoReboot
[->reboot.cpp]
//* Reboot / shutdown the system.
// cmd ANDROID_RB_* as defined in android_reboot.h
// reason Reason string like "reboot", "shutdown,userrequested"
// rebootTarget Reboot target string like "bootloader". Otherwise, it should be an
// empty string.
// runFsck Whether to run fsck after umount is done.
//
static void DoReboot(unsigned int cmd, const std::string& reason, const std::string& rebootTarget,
bool runFsck) {
Timer t;
LOG(INFO) << "Reboot start, reason: " << reason << ", rebootTarget: " << rebootTarget;
// Ensure last reboot reason is reduced to canonical
// alias reported in bootloader or system boot reason.
size_t skip = 0;
std::vector<:string> reasons = Split(reason, ",");
if (reasons.size() >= 2 && reasons[0] == "reboot" &&
(reasons[1] == "recovery" || reasons[1] == "bootloader" || reasons[1] == "cold" ||
reasons[1] == "hard" || reasons[1] == "warm")) {
skip = strlen("reboot,");
}
property_set(LAST_REBOOT_REASON_PROPERTY, reason.c_str() + skip);//设置reboot 重启原因到persist.sys.boot.reason，重启后可以查看
sync();
bool is_thermal_shutdown = cmd == ANDROID_RB_THERMOFF;
auto shutdown_timeout = 0ms;
if (!SHUTDOWN_ZERO_TIMEOUT) {
constexpr unsigned int shutdown_timeout_default = 6;
constexpr unsigned int max_thermal_shutdown_timeout = 3;
auto shutdown_timeout_final = android::base::GetUintProperty("ro.build.shutdown_timeout",
shutdown_timeout_default);
if (is_thermal_shutdown && shutdown_timeout_final > max_thermal_shutdown_timeout) {
shutdown_timeout_final = max_thermal_shutdown_timeout;
}
shutdown_timeout = std::chrono::seconds(shutdown_timeout_final);
}
LOG(INFO) << "Shutdown timeout: " << shutdown_timeout.count() << " ms";
// keep debugging tools until non critical ones are all gone.
const std::set<:string> kill_after_apps{"tombstoned", "logd", "adbd"};
// watchdogd is a vendor specific component but should be alive to complete shutdown safely.
const std::set<:string> to_starts{"watchdogd"};
for (const auto& s : ServiceList::GetInstance()) {
if (kill_after_apps.count(s->name())) {
s->SetShutdownCritical();
} else if (to_starts.count(s->name())) {
if (auto result = s->Start(); !result) {
LOG(ERROR) << "Could not start shutdown 'to_start' service '" << s->name()
<< "': " << result.error();
}
s->SetShutdownCritical();
} else if (s->IsShutdownCritical()) {
// Start shutdown critical service if not started.
if (auto result = s->Start(); !result) {
LOG(ERROR) << "Could not start shutdown critical service '" << s->name()
<< "': " << result.error();
}
}
}
// remaining operations (specifically fsck) may take a substantial duration
if (cmd == ANDROID_RB_POWEROFF || is_thermal_shutdown) {
TurnOffBacklight();
}
Service* bootAnim = ServiceList::GetInstance().FindService("bootanim");
Service* surfaceFlinger = ServiceList::GetInstance().FindService("surfaceflinger");
if (bootAnim != nullptr && surfaceFlinger != nullptr && surfaceFlinger->IsRunning()) {
// will not check animation class separately
for (const auto& service : ServiceList::GetInstance()) {
if (service->classnames().count("animation")) service->SetShutdownCritical();
}
}
// optional shutdown step
// 1. terminate all services except shutdown critical ones. wait for delay to finish
//终止除shutdown关键之外的所有服务。 等待完成
if (shutdown_timeout > 0ms) {
LOG(INFO) << "terminating init services";
// Ask all services to terminate except shutdown critical ones.
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (!s->IsShutdownCritical()) s->Terminate();
}
int service_count = 0;
// Only wait up to half of timeout here
auto termination_wait_timeout = shutdown_timeout / 2;
while (t.duration() < termination_wait_timeout) {
ReapAnyOutstandingChildren();
service_count = 0;
for (const auto& s : ServiceList::GetInstance()) {
// Count the number of services running except shutdown critical.
// Exclude the console as it will ignore the SIGTERM signal
// and not exit.
// Note: SVC_CONSOLE actually means "requires console" but
// it is only used by the shell.
if (!s->IsShutdownCritical() && s->pid() != 0 && (s->flags() & SVC_CONSOLE) == 0) {
service_count++;
}
}
if (service_count == 0) {
// All terminable services terminated. We can exit early.
break;
}
// Wait a bit before recounting the number or running services.
std::this_thread::sleep_for(50ms);
}
LOG(INFO) << "Terminating running services took " << t
<< " with remaining services:" << service_count;
}
// minimum safety steps before restarting
// 2. kill all services except ones that are necessary for the shutdown sequence.
//2. 关闭所有得服务
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (!s->IsShutdownCritical()) s->Stop();
}
SubcontextTerminate();
ReapAnyOutstandingChildren();
// 3. send volume shutdown to vold
// 3. 关闭vold
Service* voldService = ServiceList::GetInstance().FindService("vold");
if (voldService != nullptr && voldService->IsRunning()) {
ShutdownVold();
voldService->Stop();
} else {
LOG(INFO) << "vold not running, skipping vold shutdown";
}
// logcat stopped here
for (const auto& s : ServiceList::GetInstance().services_in_shutdown_order()) {
if (kill_after_apps.count(s->name())) s->Stop();
}
// 4. sync, try umount, and optionally run fsck for user shutdown
//4. 同步，卸载分区，
{
Timer sync_timer;
LOG(INFO) << "sync() before umount...";
sync();
LOG(INFO) << "sync() before umount took" << sync_timer;
}
UmountStat stat = TryUmountAndFsck(runFsck, shutdown_timeout - t.duration());
// Follow what linux shutdown is doing: one more sync with little bit delay
{
Timer sync_timer;
LOG(INFO) << "sync() after umount...";
sync();
LOG(INFO) << "sync() after umount took" << sync_timer;
}
if (!is_thermal_shutdown) std::this_thread::sleep_for(100ms);
LogShutdownTime(stat, &t);
// Reboot regardless of umount status. If umount fails, fsck after reboot will fix it.
RebootSystem(cmd, rebootTarget); //重启系统
abort();
}
2.7 RebootSystem
[->reboot_utils.cpp]
void __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string& rebootTarget) {
LOG(INFO) << "Reboot ending, jumping to kernel";
if (!IsRebootCapable()) {
// On systems where init does not have the capability of rebooting the
// device, just exit cleanly.
exit(0);
}
//下面就是reboot的system call进入内核空间了:
switch (cmd) {
case ANDROID_RB_POWEROFF:
reboot(RB_POWER_OFF); //调用reboot函数执行关机
break;
case ANDROID_RB_RESTART2:
syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_RESTART2, rebootTarget.c_str());//调用syscall函数执行重启
break;
case ANDROID_RB_THERMOFF:
reboot(RB_POWER_OFF);//调用reboot函数执行重启
break;
}
// In normal case, reboot should not return.
PLOG(ERROR) << "reboot call returned";
abort();
}
三、总结
一句话总结，从 设置属性sys.powerctrl，最终重启调用libc库得 reboot或syscall， 也就意味这reboot下一步流程到达内核空间，
内核空间部分留着下一节继续。
——含有重复字符的全排列)
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)
