本文主要介绍init 过程， 下面三张图，基本覆盖了核心点
Init main 流程
SIGCHLD流程
options 执行流程
对system/core/init/init.cpp中的main 函数分成核心部分进行阐述
int main(int argc, char** argv) {
if (!strcmp(basename(argv[0]), "ueventd")) {
return ueventd_main(argc, argv);
}
if (!strcmp(basename(argv[0]), "watchdogd")) {
return watchdogd_main(argc, argv);
}
if (REBOOT_BOOTLOADER_ON_PANIC) {
InstallRebootSignalHandlers();
}
add_environment("PATH", _PATH_DEFPATH);
bool is_first_stage = (getenv("INIT_SECOND_STAGE") == nullptr);
if (is_first_stage) {
boot_clock::time_point start_time = boot_clock::now();
// Clear the umask.
umask(0);
// Get the basic filesystem setup we need put together in the initramdisk
// on / and then we'll let the rc file figure out the rest.
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
#define MAKE_STR(x) __STRING(x)
mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));
// Don't expose the raw commandline to unprivileged processes.
chmod("/proc/cmdline", 0440);
gid_t groups[] = { AID_READPROC };
setgroups(arraysize(groups), groups);
mount("sysfs", "/sys", "sysfs", 0, NULL);
mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));
mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));
mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));
// Now that tmpfs is mounted on /dev and we have /dev/kmsg, we can actually
// talk to the outside world...
InitKernelLogging(argv);
LOG(INFO) << "init first stage started!";
if (!DoFirstStageMount()) {
LOG(ERROR) << "Failed to mount required partitions early ...";
panic();
}
SetInitAvbVersionInRecovery();
// Set up SELinux, loading the SELinux policy.
selinux_initialize(true);
// We're in the kernel domain, so re-exec init to transition to the init domain now
// that the SELinux policy has been loaded.
if (selinux_android_restorecon("/init", 0) == -1) {
PLOG(ERROR) << "restorecon failed";
security_failure();
}
setenv("INIT_SECOND_STAGE", "true", 1);
static constexpr uint32_t kNanosecondsPerMillisecond = 1e6;
uint64_t start_ms = start_time.time_since_epoch().count() / kNanosecondsPerMillisecond;
setenv("INIT_STARTED_AT", std::to_string(start_ms).c_str(), 1);
char* path = argv[0];
char* args[] = { path, nullptr };
execv(path, args);
// execv() only returns if an error happened, in which case we
// panic and never fall through this conditional.
PLOG(ERROR) << "execv(\"" << path << "\") failed";
security_failure();
}
// At this point we're in the second stage of init
=============================================================================
第一个部分，在init 进程中启动kernel log
InitKernelLogging(argv);
LOG(INFO) << "init second stage started!";
// Set up a session keyring that all processes will have access to. It
// will hold things like FBE encryption keys. No process should override
// its session keyring.
keyctl_get_keyring_ID(KEY_SPEC_SESSION_KEYRING, 1);
// Indicate that booting is in progress to background fw loaders, etc.
close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
=============================================================================
第二个部分，property_init
property_init();
// If arguments are passed both on the command line and in DT,
// properties set in DT always have priority over the command-line ones.
process_kernel_dt();
process_kernel_cmdline();
// Propagate the kernel variables to internal variables
// used by init as well as the current required properties.
export_kernel_boot_props();
// Make the time that init started available for bootstat to log.
property_set("ro.boottime.init", getenv("INIT_STARTED_AT"));
property_set("ro.boottime.init.selinux", getenv("INIT_SELINUX_TOOK"));
// Set libavb version for Framework-only OTA match in Treble build.
const char* avb_version = getenv("INIT_AVB_VERSION");
if (avb_version) property_set("ro.boot.avb_version", avb_version);
// Set memcg property based on kernel cmdline argument
bool memcg_enabled = android::base::GetBoolProperty("ro.boot.memcg",false);
if (memcg_enabled) {
// root memory control cgroup
mkdir("/dev/memcg", 0700);
chown("/dev/memcg",AID_ROOT,AID_SYSTEM);
mount("none", "/dev/memcg", "cgroup", 0, "memory");
// app mem cgroups, used by activity manager, lmkd and zygote
mkdir("/dev/memcg/apps/",0755);
chown("/dev/memcg/apps/",AID_SYSTEM,AID_SYSTEM);
mkdir("/dev/memcg/system",0550);
chown("/dev/memcg/system",AID_SYSTEM,AID_SYSTEM);
}
// Clean up our environment.
unsetenv("INIT_SECOND_STAGE");
unsetenv("INIT_STARTED_AT");
unsetenv("INIT_SELINUX_TOOK");
unsetenv("INIT_AVB_VERSION");
// Now set up SELinux for second stage.
selinux_initialize(false);
selinux_restore_context();
=============================================================================
第三个部分 创建epoll_fd, 利用此fd监控属性，signal_handle ,handle_keychord
epoll_fd = epoll_create1(EPOLL_CLOEXEC);
if (epoll_fd == -1) {
PLOG(ERROR) << "epoll_create1 failed";
exit(1);
}
signal_handler_init();
property_load_boot_defaults();
export_oem_lock_status();
start_property_service();
set_usb_controller();
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
=============================================================================
第四个部分 am,sm 建立，parser init.rc**
ActionManager& am = ActionManager::GetInstance();
ServiceManager& sm = ServiceManager::GetInstance();
Parser& parser = Parser::GetInstance();
parser.AddSectionParser("service", std::make_unique(&sm));
parser.AddSectionParser("on", std::make_unique(&am));
parser.AddSectionParser("import", std::make_unique(&parser));
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
parser.ParseConfig("/init.rc");
parser.set_is_system_etc_init_loaded(
parser.ParseConfig("/system/etc/init"));
parser.set_is_vendor_etc_init_loaded(
parser.ParseConfig("/vendor/etc/init"));
parser.set_is_odm_etc_init_loaded(parser.ParseConfig("/odm/etc/init"));
} else {
parser.ParseConfig(bootscript);
parser.set_is_system_etc_init_loaded(true);
parser.set_is_vendor_etc_init_loaded(true);
parser.set_is_odm_etc_init_loaded(true);
}
// Turning this on and letting the INFO logging be discarded adds 0.2s to
// Nexus 9 boot time, so it's disabled by default.
if (false) DumpState();
am.QueueEventTrigger("early-init");
// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...
am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");
// ... so that we can start queuing up actions that require stuff from /dev.
am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
am.QueueBuiltinAction(set_mmap_rnd_bits_action, "set_mmap_rnd_bits");
am.QueueBuiltinAction(set_kptr_restrict_action, "set_kptr_restrict");
am.QueueBuiltinAction(keychord_init_action, "keychord_init");
am.QueueBuiltinAction(console_init_action, "console_init");
// Trigger all the boot actions to get us started.
am.QueueEventTrigger("init");
// Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
// wasn't ready immediately after wait_for_coldboot_done
am.QueueBuiltinAction(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
// Don't mount filesystems or start core system services in charger mode.
std::string bootmode = GetProperty("ro.bootmode", "");
if (bootmode == "charger") {
am.QueueEventTrigger("charger");
} else {
am.QueueEventTrigger("late-init");
}
// Run all property triggers based on current state of the properties.
am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");
=============================================================================
第五个部分 while ExecuteOneCommand restart_processes epoll_fd
while (true) {
// By default, sleep until something happens.
int epoll_timeout_ms = -1;
if (do_shutdown && !shutting_down) {
do_shutdown = false;
if (HandlePowerctlMessage(shutdown_command)) {
shutting_down = true;
}
}
if (!(waiting_for_prop || sm.IsWaitingForExec())) {
am.ExecuteOneCommand();--->执行action
}
if (!(waiting_for_prop || sm.IsWaitingForExec())) {
if (!shutting_down) restart_processes();------》 重启process ,根据sv flags 进行判断
// If there's a process that needs restarting, wake up in time for that.
if (process_needs_restart_at != 0) {
epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;
if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
}
// If there's more work to do, wake up again immediately.
if (am.HasMoreCommands()) epoll_timeout_ms = 0;
}
epoll_event ev;
int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));-----》wait epoll_fd
if (nr == -1) {
PLOG(ERROR) << "epoll_wait failed";
} else if (nr == 1) {
((void (*)()) ev.data.ptr)();
}
}
return 0;
}
} // namespace init
} // namespace android
int main(int argc, char** argv) {
android::init::main(argc, argv);
}
第一个部分，在init 进程中启动kernel log
在一个部分之前，调用了 selinux_initialize(true); 这里决定selinux 是否开启
selinux 是否开启
InitKernelLogging：
---> InitKernelLogging(argv);
void InitKernelLogging(char* argv[]) {
// Make stdin/stdout/stderr all point to /dev/null.---> 使用了 dev/null , 只是初始化动作
int fd = open("/sys/fs/selinux/null", O_RDWR);
if (fd == -1) {
int saved_errno = errno;
android::base::InitLogging(argv, &android::base::KernelLogger);
errno = saved_errno;
PLOG(FATAL) << "Couldn't open /sys/fs/selinux/null";
}
dup2(fd, 0);
dup2(fd, 1);
dup2(fd, 2);
if (fd > 2) close(fd);
android::base::InitLogging(argv, &android::base::KernelLogger);---》 传递参数KernelLogger
}
InitLogging 声明：默认初值
void InitLogging(char* argv[],
LogFunction&& logger = INIT_LOGGING_DEFAULT_LOGGER,
AbortFunction&& aborter = DefaultAborter);
system/core/base/logging.cpp
InitLogging(char* argv[], LogFunction&& logger, AbortFunction&& aborter)
---> SetLogger(std::forward(logger));--->kernel log
---> SetAborter(std::forward(aborter));---->aborter log
---> static auto& logger = *new LogFunction(LogdLogger());
---> static auto& aborter = *new AbortFunction(DefaultAborter);
}
第二个部分，property_init
bionic/libc/bionic/system_properties.cpp
property_init
--->map_system_property_area, --》创建区域，property 存储的地方
第三个部分 创建epoll_fd, 利用此fd监控属性，signal_handle ,handle_keychord
主要是对epoll_fd 的利用在什么地方:
system/core/init/keychords.cpp
system/core/init/property_service.cpp
system/core/init/signal_handler.cpp
epoll_fd = epoll_create1(EPOLL_CLOEXEC);
(1)--->signal_handler_init--->register_epoll_handler---> 注册epoll_fd
(2)--->keychord_init--->register_epoll_handler---> 注册epoll_fd
(3)--->start_property_service--->register_epoll_handler---> 注册epoll_fd
图片.png
signal_handler_init:创建了socketpair，init 进程的子进程死亡时候，发送SIGCHLD， init 父进程监听子进程死亡，启动SIGCHLD_handler 函数，SIGCHLD_handler write signal_write_fd, 这是signal_read_fd 就会可以读， 出发epoll 事件----------> 在 第五个部分 while 循环中，while就不再阻塞，进行一轮处理，然后再次epoll_wait epoll_fd
system/core/init/signal_handler.cpp
void signal_handler_init() {
// Create a signalling mechanism for SIGCHLD.
int s[2];
if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0, s) == -1) {
PLOG(ERROR) << "socketpair failed";
exit(1);
}
signal_write_fd = s[0];
signal_read_fd = s[1];
// Write to signal_write_fd if we catch SIGCHLD.
struct sigaction act;
memset(&act, 0, sizeof(act));
act.sa_handler = SIGCHLD_handler;
act.sa_flags = SA_NOCLDSTOP;
sigaction(SIGCHLD, &act, 0);
ServiceManager::GetInstance().ReapAnyOutstandingChildren();
register_epoll_handler(signal_read_fd, handle_signal);
}
system/core/init/signal_handler.cpp
SIGCHLD_handler:
static void SIGCHLD_handler(int) {
if (TEMP_FAILURE_RETRY(write(signal_write_fd, "1", 1)) == -1) {
PLOG(ERROR) << "write(signal_write_fd) failed";
}
}
第四个部分 am,sm 建立，parser init.rc
system/core/init/init.cpp
......
ServiceManager& sm = ServiceManager::GetInstance();-------> static ServiceManager instance;
parser.AddSectionParser("service", std::make_unique(&sm));---->添加sm 到section_parsers_
parser.AddSectionParser("on", std::make_unique(&am));
parser.AddSectionParser("import", std::make_unique(&parser));
parser.ParseConfig("/init.rc");
......
system/core/init/init_parser.cpp
void Parser::AddSectionParser(const std::string& name,
std::unique_ptr parser) {
section_parsers_[name] = std::move(parser); ---》根据键值对，添加【name, parser】
}
system/core/init/init_parser.cpp
ParseConfig---》ParseConfigFile---->ParseData
---》ParseConfigDir
--------------------------------------------------------------------------------------------------------
ParseData：
void Parser::ParseData(const std::string& filename, const std::string& data) {
........
for (;;) {
switch (next_token(&state)) {
case T_EOF: ----》解析结束
if (section_parser) {
section_parser->EndSection();
}
return;
case T_NEWLINE:-----》解析line
state.line++;
if (args.empty()) {
break;
}
............
if (section_parsers_.count(args[0])) {
if (section_parser) {
section_parser->EndSection();
}
section_parser = section_parsers_[args[0]].get();
std::string ret_err;
if (!section_parser->ParseSection(std::move(args), filename, state.line, &ret_err)) {------>根据 on、service或import解析section
LOG(ERROR) << filename << ": " << state.line << ": " << ret_err;
section_parser = nullptr;
}
} else if (section_parser) {
std::string ret_err;
if (!section_parser->ParseLineSection(std::move(args), state.line, &ret_err)) { ----->解析section中的line，其中option(例如oneshot,class等）,并将这些属性添加到Service对象中
LOG(ERROR) << filename << ": " << state.line << ": " << ret_err;
}
}
args.clear();
break;
case T_TEXT:
args.emplace_back(state.text);
break;
}
}
}
system/core/init/service.cpp
-------------------------------------------------------------------------------------------------------------
bool ServiceParser::ParseSection(std::vector&& args, const std::string& filename,
int line, std::string* err) {
if (args.size() < 3) {
*err = "services must have a name and a program";
return false;
}
const std::string& name = args[1];
if (!IsValidName(name)) {
*err = StringPrintf("invalid service name '%s'", name.c_str());
return false;
}
Service* old_service = service_manager_->FindServiceByName(name);
if (old_service) {
*err = "ignored duplicate definition of service '" + name + "'";
return false;
}
std::vector str_args(args.begin() + 2, args.end());
service_ = std::make_unique(name, str_args);------>创建了service_
return true;
}
-------------------------------------------------------------------------------------------------------------
void ServiceParser::EndSection() {
if (service_) {
service_manager_->AddService(std::move(service_));-----> 添加service_ 到serivce_manager
}
}
<--------------------AddService--------------------->
void ServiceManager::AddService(std::unique_ptr service) {
services_.emplace_back(std::move(service));--> 添加到service list services_中
}
-------------------------------------------------------------------------------------------------------------
bool ServiceParser::ParseLineSection(std::vector&& args, int line, std::string* err) {
return service_ ? service_->ParseLine(std::move(args), err) : false;----->解析service options
}
-------------------------------------------ParseLine-----------------------------------------------------
bool Service::ParseLine(const std::vector& args, std::string* err) {
static const OptionParserMap parser_map;
auto parser = parser_map.FindFunction(args, err);
if (!parser) {
return false;
}
return (this->*parser)(args, err); ----->执行相应属性parser_map中的函数，添加对应的属性到Service对象中
}
system/core/init/service.cpp
OptionParserMap :
static const Map option_parsers = {
{"class", {1, kMax, &Service::ParseClass}},
{"critical", {0, 0, &Service::ParseCritical}},
{"disabled", {0, 0, &Service::ParseDisabled}},
{"group", {1, NR_SVC_SUPP_GIDS + 1, &Service::ParseGroup}},
{"keycodes", {1, kMax, &Service::ParseKeycodes}},
{"oneshot", {0, 0, &Service::ParseOneshot}},
......
};
system/core/init/service.cpp
ParseDisabled:
bool Service::ParseDisabled(const std::vector& args, std::string* err) {
flags_ |= SVC_DISABLED; ---->set svc flags---->service 决定service 启动方式， 是在 xxx.rc 中option 定义
flags_ |= SVC_RC_DISABLED;
return true;
}
图片.png
上面的分析可以看出ServiceParser的ParseLineSection是直接执行option对应函数，读者如果分析ActionParser是将对应函数保存到commands_数组中，当Action触发时，才会依次执行command函数。
第五个部分 while ExecuteOneCommand restart_processes epoll_fd
讲解第五部分之前，先看看QueueEventTrigger, QueueBuiltinAction
system/core/init/init.cpp
void ActionManager::QueueEventTrigger(const std::string& trigger) {
event_queue_.emplace(trigger);-------->on action
}
void ActionManager::QueueBuiltinAction(BuiltinFunction func, const std::string& name) {
auto action = std::make_unique(true, "", 0);
std::vector name_vector{name};
if (!action->InitSingleTrigger(name)) {
return;
}
action->AddCommand(func, name_vector, 0);----》 添加action command
event_queue_.emplace(action.get());
actions_.emplace_back(std::move(action));
}
android init 最后进入了 epoll_wait等待
while (true) {
am.ExecuteOneCommand();----》5.1 执行命令
restart_processes();----》5.2 restart process
epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms) -->待定fd 出发，监控 property , SIGCHLD,keychord
}
5.1 执行命令& service
system/core/init/action.cpp
void ActionManager::ExecuteOneCommand() {
// Loop through the event queue until we have an action to execute
while (current_executing_actions_.empty() && !event_queue_.empty()) {
for (const auto& action : actions_) {--->轮询actions_
if (std::visit([&action](const auto& event) { return action->CheckEvent(event); },
event_queue_.front())) {
current_executing_actions_.emplace(action.get()); -->添加到current_executing_actions_ 中
}
}
event_queue_.pop();
}
if (current_executing_actions_.empty()) {
return;
}
auto action = current_executing_actions_.front();
if (current_command_ == 0) {
std::string trigger_name = action->BuildTriggersString();
LOG(INFO) << "processing action (" << trigger_name << ") from (" << action->filename()
<< ":" << action->line() << ")";
}
action->ExecuteOneCommand(current_command_);----> 执行
// If this was the last command in the current action, then remove
// the action from the executing list.
// If this action was oneshot, then also remove it from actions_.
阅读上面的注释：就可以知道侦测命令的多少，是否最后一个
++current_command_;
if (current_command_ == action->NumCommands()) {
current_executing_actions_.pop();
current_command_ = 0;
if (action->oneshot()) {
auto eraser = [&action] (std::unique_ptr& a) {
return a.get() == action;
};
actions_.erase(std::remove_if(actions_.begin(), actions_.end(), eraser));
}
}
}
ExecuteOneCommand：
void Action::ExecuteOneCommand(std::size_t command) const {
// We need a copy here since some Command execution may result in
// changing commands_ vector by importing .rc files through parser
Command cmd = commands_[command];
ExecuteCommand(cmd);
}
----------------------------------------------------------------------------------------------
void Action::ExecuteCommand(const Command& command) const {
android::base::Timer t;
int result = command.InvokeFunc();---》 执行
auto duration = t.duration();
// Any action longer than 50ms will be warned to user as slow operation
if (duration > 50ms || android::base::GetMinimumLogSeverity() <= android::base::DEBUG) {
std::string trigger_name = BuildTriggersString();
std::string cmd_str = command.BuildCommandString();
LOG(INFO) << "Command '" << cmd_str << "' action=" << trigger_name << " (" << filename_
<< ":" << command.line() << ") returned " << result << " took "
<< duration.count() << "ms.";
}
}
5.2 restart process
system/core/init/init.cpp
static void restart_processes()
{
process_needs_restart_at = 0;
ServiceManager::GetInstance().ForEachServiceWithFlags(SVC_RESTARTING, [](Service* s) {--->根据SVC flags 决定是否重启
s->RestartIfNeeded(&process_needs_restart_at);
});
}
system/core/init/service.cpp
void Service::RestartIfNeeded(time_t* process_needs_restart_at) {
boot_clock::time_point now = boot_clock::now();
boot_clock::time_point next_start = time_started_ + 5s;
if (now > next_start) {
flags_ &= (~SVC_RESTARTING);
Start();----->重启service
return;
}
就是一些时间的设定，启动时间控制
time_t next_start_time_t = time(nullptr) +
time_t(std::chrono::duration_cast(next_start - now).count());
if (next_start_time_t < *process_needs_restart_at || *process_needs_restart_at == 0) {
*process_needs_restart_at = next_start_time_t;
}
}
service 启动调用逻辑：
(init.cpp)sm.IsWaitingForExec()---->
(init.cpp)restart_processes();---->
ServiceManager::ForEachServiceWithFlags---> (service.cpp)
Service::RestartIfNeeded---->
Service::Start()--->启动service
有上面的可以知道，init main 主要的工作:log ,文件挂载，异常处理，解析rc 文件，启动service,启动property， 最后进入了epoll fd 等待
REF:
https://android.googlesource.com/platform/system/core/+/master/init/README.md