Android 系统 基于9.0.0 启动-init
以下所有学习资源来自于刘叔的,也可以直接略过我去读源文,我只是记录自己的学习过程.
传送门Android框架层
init相关源码位于: system/core/init
init之前:
- 开机执行引导程序Bootloader 拉起系统OS并运行
- 启动内核 开始设置系统设置 解析init配置文件
- 启动init进程 入口位于system/core/init/init.cpp的main函数
init职责:
- 创建zygote
- 初始化和启动属性服务
- 创建文件夹饼挂载设备
- 解析init.rc配置文件启动zygote进程
1. init入口main函数
int main(int argc, char** argv) {
...
//初始化属性资源
property_init();
...
sigchld_handler_init();
...
property_load_boot_defaults();
export_oem_lock_status();
//启动属性服务
start_property_service();
set_usb_controller();
...
ActionManager& am = ActionManager::GetInstance();
ServiceList& sm = ServiceList::GetInstance();
//加载启动的脚本 解析init.rc文件
LoadBootScripts(am, sm);
...
return 0;
}
main函数 主要步骤
- 初始化属性资源
- 启动属性服务
- 加载启动的脚本 解析init.rc文件
2. LoadBootScripts 函数
static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
Parser parser = CreateParser(action_manager, service_list);
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
//解析init.rc文件 位于system/core/rootdir/init.rc
//init.rc是一个配置文件，内部由Android初始化语言编写（Android Init Language）编写的脚本
parser.ParseConfig("/init.rc");
if (!parser.ParseConfig("/system/etc/init")) {
late_import_paths.emplace_back("/system/etc/init");
}
if (!parser.ParseConfig("/product/etc/init")) {
late_import_paths.emplace_back("/product/etc/init");
}
if (!parser.ParseConfig("/odm/etc/init")) {
late_import_paths.emplace_back("/odm/etc/init");
}
if (!parser.ParseConfig("/vendor/etc/init")) {
late_import_paths.emplace_back("/vendor/etc/init");
}
} else {
parser.ParseConfig(bootscript);
}
}
3. init.rc 文件
//位于system/core/rootdir/init.zygote64.rc
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
class main
priority -20
user root
group root readproc reserved_disk
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart audioserver
onrestart restart cameraserver
onrestart restart media
onrestart restart netd
onrestart restart wificond
writepid /dev/cpuset/foreground/tasks
4. 解析rc文件里的service
//位于 system/core/init/service.cpp
//1.解析init.rc文件内的service
Result<Success> ServiceParser::ParseSection(std::vector<std::string>&& args,
const std::string& filename, int line) {
if (args.size() < 3) {
return Error() << "services must have a name and a program";
}
const std::string& name = args[1];
if (!IsValidName(name)) {
return Error() << "invalid service name '" << name << "'";
}
Subcontext* restart_action_subcontext = nullptr;
if (subcontexts_) {
for (auto& subcontext : *subcontexts_) {
if (StartsWith(filename, subcontext.path_prefix())) {
restart_action_subcontext = &subcontext;
break;
}
}
}
std::vector<std::string> str_args(args.begin() + 2, args.end());
//根据参数 构造service对象
service_ = std::make_unique<Service>(name, restart_action_subcontext, str_args);
return Success();
}
Result<Success> ServiceParser::ParseLineSection(std::vector<std::string>&& args, int line) {
return service_ ? service_->ParseLine(std::move(args)) : Success();
}
//2.将service加入vector类型的services链表中
Result<Success> ServiceParser::EndSection() {
if (service_) {
Service* old_service = service_list_->FindService(service_->name());
if (old_service) {
if (!service_->is_override()) {
return Error() << "ignored duplicate definition of service '" << service_->name()
<< "'";
}
service_list_->RemoveService(*old_service);
old_service = nullptr;
}
//将service对象加入到services链表中
service_list_->AddService(std::move(service_));
}
return Success();
}
5. 开始启动zygote
位于 system/core/rootdir/init.rc
...
on nonencrypted
class_start main //main即zygote
class_start late_start
...
6. class_start对应的函数为do_class_start 位于system/core/init/builtins.cpp
static Result<Success> do_class_start(const BuiltinArguments& args) {
// Starting a class does not start services which are explicitly disabled.
// They must be started individually.
for (const auto& service : ServiceList::GetInstance()) {
if (service->classnames().count(args[1])) {
if (auto result = service->StartIfNotDisabled(); !result) {
LOG(ERROR) << "Could not start service '" << service->name()
<< "' as part of class '" << args[1] << "': " << result.error();
}
}
}
return Success();
}
...
7. StartIfNotDisabled() 位于 system/core/init/service.cpp
Result<Success> Service::StartIfNotDisabled() {
if (!(flags_ & SVC_DISABLED)) {
return Start();
} else {
flags_ |= SVC_DISABLED_START;
}
return Success();
}
8. Start() 函数
Result<Success> Service::Start() {
bool disabled = (flags_ & (SVC_DISABLED | SVC_RESET));
flags_ &= (~(SVC_DISABLED|SVC_RESTARTING|SVC_RESET|SVC_RESTART|SVC_DISABLED_START));
// 如果service 已经在运行 则返回成功
if (flags_ & SVC_RUNNING) {
if ((flags_ & SVC_ONESHOT) && disabled) {
flags_ |= SVC_RESTART;
}
// It is not an error to try to start a service that is already running.
return Success();
}
...
}
//判断需要启动的service对应的执行文件是否存在 不存在则返回错误信息
struct stat sb;
if (stat(args_[0].c_str(), &sb) == -1) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Cannot find '" << args_[0] << "'";
}
...
pid_t pid = -1;
if (namespace_flags_) {
pid = clone(nullptr, nullptr, namespace_flags_ | SIGCHLD, nullptr);
} else {
//复制作为子进程
pid = fork();
}
...
//通过execve执行程序
if (!ExpandArgsAndExecv(args_)) {
PLOG(ERROR) << "cannot execve('" << args_[0] << "')";
}
...
NotifyStateChange("running");
return Success();
}
9. ExpandArgsAndExecv()函数
static bool ExpandArgsAndExecv(const std::vector<std::string>& args) {
std::vector<std::string> expanded_args;
std::vector<char*> c_strings;
expanded_args.resize(args.size());
c_strings.push_back(const_cast<char*>(args[0].data()));
for (std::size_t i = 1; i < args.size(); ++i) {
if (!expand_props(args[i], &expanded_args[i])) {
LOG(FATAL) << args[0] << ": cannot expand '" << args[i] << "'";
}
c_strings.push_back(expanded_args[i].data());
}
c_strings.push_back(nullptr);
//执行system/bin/app_process
return execv(c_strings[0], c_strings.data()) == 0;
}
10. 进入app_process 的main函数,完成启动zygote
//位于framework/cmds/app_process/app_main.cpp
int main(int argc, char* const argv[])
{
...
//启动zygote
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
} else if (className) {
runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
} else {
fprintf(stderr, "Error: no class name or --zygote supplied.\n");
app_usage();
LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
}
}
流程图
