Android Framework学习(一)之init进程解析

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);
    }

    // Clear the umask.
    umask(0);

    add_environment("PATH", _PATH_DEFPATH);

    bool is_first_stage = (argc == 1) || (strcmp(argv[1], "--second-stage") != 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.
    //1.创建一些文件夹，并挂载设备，这些都是与Linux相关
    if (is_first_stage) {
        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));
        mount("sysfs", "/sys", "sysfs", 0, NULL);
    }

    // We must have some place other than / to create the device nodes for
    // kmsg and null, otherwise we won't be able to remount / read-only
    // later on. Now that tmpfs is mounted on /dev, we can actually talk
    // to the outside world.
    //2.重定向标准输入，输出，错误输出到/dev/_null_
    open_devnull_stdio();
    3.初始化内核log系统 
    klog_init();
    klog_set_level(KLOG_NOTICE_LEVEL);

    NOTICE("init %s started!\n", is_first_stage ? "first stage" : "second stage");

    if (!is_first_stage) {
        // Indicate that booting is in progress to background fw loaders, etc.
        close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
        //4.初始化和属性相关资源
        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();
    }

    // Set up SELinux, including loading the SELinux policy if we're in the kernel domain.
    5.完成SELinux相关工作
    selinux_initialize(is_first_stage);

    // If we're in the kernel domain, re-exec init to transition to the init domain now
    // that the SELinux policy has been loaded.
    if (is_first_stage) {
        6.重新设置属性
        if (restorecon("/init") == -1) {
            ERROR("restorecon failed: %s\n", strerror(errno));
            security_failure();
        }
        char* path = argv[0];
        char* args[] = { path, const_cast<char*>("--second-stage"), nullptr };
        if (execv(path, args) == -1) {
            ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
            security_failure();
        }
    }

    // These directories were necessarily created before initial policy load
    // and therefore need their security context restored to the proper value.
    // This must happen before /dev is populated by ueventd.
    NOTICE("Running restorecon...\n");
    restorecon("/dev");
    restorecon("/dev/socket");
    restorecon("/dev/__properties__");
    restorecon("/property_contexts");
    restorecon_recursive("/sys");
    7.创建epoll句柄 
    epoll_fd = epoll_create1(EPOLL_CLOEXEC);
    if (epoll_fd == -1) {
        ERROR("epoll_create1 failed: %s\n", strerror(errno));
        exit(1);
    }
    8.装载子进程信号处理器
    signal_handler_init();

    property_load_boot_defaults();
    export_oem_lock_status();
    //9.启动属性服务
    start_property_service();

    const BuiltinFunctionMap function_map;
    Action::set_function_map(&function_map);

    Parser& parser = Parser::GetInstance();
    parser.AddSectionParser("service",std::make_unique<ServiceParser>());
    parser.AddSectionParser("on", std::make_unique<ActionParser>());
    parser.AddSectionParser("import", std::make_unique<ImportParser>());
    //10.解析init.rc配置文件
    parser.ParseConfig("/init.rc");

    ActionManager& am = ActionManager::GetInstance();

    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(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 = property_get("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");

    while (true) {
        if (!waiting_for_exec) {
            am.ExecuteOneCommand();
            restart_processes();
        }

        int timeout = -1;
        if (process_needs_restart) {
            timeout = (process_needs_restart - gettime()) * 1000;
            if (timeout < 0)
                timeout = 0;
        }

        if (am.HasMoreCommands()) {
            timeout = 0;
        }

        bootchart_sample(&timeout);

        epoll_event ev;
        int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, timeout));
        if (nr == -1) {
            ERROR("epoll_wait failed: %s\n", strerror(errno));
        } else if (nr == 1) {
            ((void (*)()) ev.data.ptr)();
        }
    }

    return 0;
}

//清除屏蔽字(file mode creation mask)，保证新建的目录的访问权限不受屏蔽字影响。
umask(0);

add_environment("PATH", _PATH_DEFPATH);

bool is_first_stage = (argc == 1) || (strcmp(argv[1], "--second-stage") != 0);

// Get the basic filesystem setup we need put together in the initramdisk
if (is_first_stage) {
    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));
    mount("sysfs", "/sys", "sysfs", 0, NULL);
}

open_devnull_stdio();

void open_devnull_stdio(void)
{
    // Try to avoid the mknod() call if we can. Since SELinux makes
    // a /dev/null replacement available for free, let's use it.
    int fd = open("/sys/fs/selinux/null", O_RDWR);
    if (fd == -1) {
        // OOPS, /sys/fs/selinux/null isn't available, likely because
        // /sys/fs/selinux isn't mounted. Fall back to mknod.
        static const char *name = "/dev/__null__";
        if (mknod(name, S_IFCHR | 0600, (1 << 8) | 3) == 0) {
            fd = open(name, O_RDWR);
            unlink(name);
        }
        if (fd == -1) {
            exit(1);
        }
    }

    dup2(fd, 0);
    dup2(fd, 1);
    dup2(fd, 2);
    if (fd > 2) {
        close(fd);
    }
}

if (!is_first_stage) {
    .......
    property_init();
    .......
}

void property_init() {
    if (__system_property_area_init()) {
        ERROR("Failed to initialize property area\n");
        exit(1);
    }
}

// Set up SELinux, including loading the SELinux policy if we're in the kernel domain.
selinux_initialize(is_first_stage);

static void selinux_initialize(bool in_kernel_domain) {
    Timer t;

    selinux_callback cb;
    //用于打印log的回调函数
    cb.func_log = selinux_klog_callback;
    selinux_set_callback(SELINUX_CB_LOG, cb);
    //用于检查权限的回调函数
    cb.func_audit = audit_callback;
    selinux_set_callback(SELINUX_CB_AUDIT, cb);

    if (in_kernel_domain) {
        //内核态处理流程
        INFO("Loading SELinux policy...\n");
        //用于加载sepolicy文件。该函数最终将sepolicy文件传递给kernel，这样kernel就有了安全策略配置文件，后续的MAC才能开展起来。
        if (selinux_android_load_policy() < 0) {
            ERROR("failed to load policy: %s\n", strerror(errno));
            security_failure();
        }
        //内核中读取的信息
        bool kernel_enforcing = (security_getenforce() == 1);
        //命令行中得到的数据
        bool is_enforcing = selinux_is_enforcing();
        if (kernel_enforcing != is_enforcing) {
            //用于设置selinux的工作模式。selinux有两种工作模式：
            //1、”permissive”，所有的操作都被允许（即没有MAC），但是如果违反权限的话，会记录日志
            //2、”enforcing”，所有操作都会进行权限检查。在一般的终端中，应该工作于enforing模式
            if(security_setenforce(is_enforcing)) {
                ........
                //将重启进入recovery mode
                security_failure();
            }
        }
        if (write_file("/sys/fs/selinux/checkreqprot", "0") == -1) {
            security_failure();
        }

        NOTICE("(Initializing SELinux %s took %.2fs.)\n",
               is_enforcing ? "enforcing" : "non-enforcing", t.duration());
    } else {
        selinux_init_all_handles();
    }
}

// If we're in the kernel domain, re-exec init to transition to the init domain now that the SELinux policy has been loaded.
if (is_first_stage) {
    //按selinux policy要求，重新设置init文件属性
    if (restorecon("/init") == -1) {
        ERROR("restorecon failed: %s\n", strerror(errno));
        security_failure();
    }
    char* path = argv[0];
    char* args[] = { path, const_cast<char*>("--second-stage"), nullptr };
    //这里就是前面所说的，启动用户态的init进程，即second-stage
    if (execv(path, args) == -1) {
        ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
        security_failure();
    }
}

// These directories were necessarily created before initial policy load
// and therefore need their security context restored to the proper value.
// This must happen before /dev is populated by ueventd.
INFO("Running restorecon...\n");
restorecon("/dev");
restorecon("/dev/socket");
restorecon("/dev/__properties__");
restorecon_recursive("/sys");

start_property_service();

void start_property_service() {
    //创建了一个非阻塞socket
    property_set_fd = create_socket(PROP_SERVICE_NAME, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0666, 0, 0, NULL);
    if (property_set_fd == -1) {
        ERROR("start_property_service socket creation failed: %s\n", strerror(errno));
        exit(1);
    }
    //调用listen函数监听property_set_fd， 于是该socket变成一个server
    listen(property_set_fd, 8);
    //监听server socket上是否有数据到来
    register_epoll_handler(property_set_fd,  handle_property_set_fd);
}

static void handle_property_set_fd() {
    ..........
    if ((s = accept(property_set_fd, (struct sockaddr *) &addr, &addr_size)) < 0) {
        return;
    }
    ........
    r = TEMP_FAILURE_RETRY(recv(s, &msg, sizeof(msg), MSG_DONTWAIT));
    .........
    switch(msg.cmd) {
    .........
    }
    .........
}

on property:ro.debuggable=1
    # Give writes to anyone for the trace folder on debug builds.
    # The folder is used to store method traces.
    chmod 0773 /data/misc/trace
    start console

on early-init
    # Set init and its forked children's oom_adj.
    write /proc/1/oom_score_adj -1000
    .........
    start ueventd

service ueventd /sbin/ueventd
    class core
    critical
    seclabel u:r:ueventd:s0

bool Parser::ParseConfig(const std::string& path) {
    if (is_dir(path.c_str())) {
        //传入参数为目录地址
        return ParseConfigDir(path);
    }
    //传入参数为文件地址
    return ParseConfigFile(path);
}

bool Parser::ParseConfigDir(const std::string& path) {
    ...........
    std::unique_ptr<DIR, int(*)(DIR*)> config_dir(opendir(path.c_str()), closedir);
    ..........
    //看起来很复杂，其实就是递归目录
    while ((current_file = readdir(config_dir.get()))) {
        std::string current_path = android::base::StringPrintf("%s/%s", path.c_str(), current_file->d_name);
        if (current_file->d_type == DT_REG) {
            //最终还是靠ParseConfigFile来解析实际的文件
            if (!ParseConfigFile(current_path)) {
                .............
            }
        }
    }
}

bool Parser::ParseConfigFile(const std::string& path) {
    INFO("Parsing file %s...\n", path.c_str());
    Timer t;
    std::string data;
    //读取路径指定文件中的内容，保存为字符串形式
    if (!read_file(path.c_str(), &data)) {
        return false;
    }

    data.push_back('\n'); // TODO: fix parse_config.
    //解析获取的字符串
    ParseData(path, data);
    for (const auto& sp : section_parsers_) {
        sp.second->EndFile(path);
    }

    // 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();

    NOTICE("(Parsing %s took %.2fs.)\n", path.c_str(), t.duration());
    return true;
}

void Parser::ParseData(const std::string& filename, const std::string& data) {
    .......
    parse_state state;
    .......
    std::vector<std::string> args;

    for (;;) {
        //next_token以行为单位分割参数传递过来的字符串
        //最先走到T_TEXT分支
        switch (next_token(&state)) {
        case T_EOF:
            if (section_parser) {
                //EOF,解析结束
                section_parser->EndSection();
            }
            return;
        case T_NEWLINE:
            state.line++;
            if (args.empty()) {
                break;
            }
            //创建parser时，会为init.rc中以service，on，import开头的都定义了对应的解析parser 
            //这里就是根据第一个参数，判断是否有对应的parser
            if (section_parsers_.count(args[0])) {
                if (section_parser) {
                    //结束上一个parser的工作，将构造出的对象加入到对应的service_list与action_list中
                    section_parser->EndSection();
                }
                //获取参数对应的parser
                section_parser = section_parsers_[args[0]].get();
                std::string ret_err;
                //调用实际parser的ParseSection函数
                if (!section_parser->ParseSection(args, &ret_err)) {
                    parse_error(&state, "%s\n", ret_err.c_str());
                    section_parser = nullptr;
                }
            } else if (section_parser) {
                std::string ret_err;
                //如果第一个参数不是service，on，import
                //则调用前一个parser的ParseLineSection函数
                //这里相当于解析一个参数块的子项
                if (!section_parser->ParseLineSection(args, state.filename, state.line, &ret_err)) {
                    parse_error(&state, "%s\n", ret_err.c_str());
                }
            }
            //清空本次解析的数据
            args.clear();
            break;
        case T_TEXT:
            //将本次解析的内容写入到args中
            args.emplace_back(state.text);
            break;
        }
    }
}

...........
Parser& parser = Parser::GetInstance();
parser.AddSectionParser("service",std::make_unique<ServiceParser>());
parser.AddSectionParser("on", std::make_unique<ActionParser>());
parser.AddSectionParser("import", std::make_unique<ImportParser>());
...........

class ServiceParser : public SectionParser {......}
class ActionParser : public SectionParser {......}
class ImportParser : public SectionParser {.......}

bool ServiceParser::ParseSection(.....) {
    .......
    const std::string& name = args[1];
    .......
    std::vector<std::string> str_args(args.begin() + 2, args.end());
    //主要根据参数，构造出一个service对象
    service_ = std::make_unique<Service>(name, "default", str_args);
    return true;
}

//注意这里已经在解析子项了
bool ServiceParser::ParseLineSection(......) const {
    //调用service对象的HandleLine
    return service_ ? service_->HandleLine(args, err) : false;
}

bool Service::HandleLine(.....) {
    ........
    //OptionHandlerMap继承自keywordMap<OptionHandler>
    static const OptionHandlerMap handler_map;
    //根据子项的内容，找到对应的handler函数
    //FindFunction定义于keyword模块中,FindFunction方法利用子类生成对应的map中，然后通过通用的查找方法，即比较键值找到对应的处理函数
    auto handler = handler_map.FindFunction(args[0], args.size() - 1, err);

    if (!handler) {
        return false;
    }
    //调用handler函数
    return (this->*handler)(args, err);
}

class Service::OptionHandlerMap : public KeywordMap<OptionHandler> {
    ...........
    Service::OptionHandlerMap::Map& Service::OptionHandlerMap::map() const {
    constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
    static const Map option_handlers = {
        {"class",       {1,     1,    &Service::HandleClass}},
        {"console",     {0,     0,    &Service::HandleConsole}},
        {"critical",    {0,     0,    &Service::HandleCritical}},
        {"disabled",    {0,     0,    &Service::HandleDisabled}},
        {"group",       {1,     NR_SVC_SUPP_GIDS + 1, &Service::HandleGroup}},
        {"ioprio",      {2,     2,    &Service::HandleIoprio}},
        {"keycodes",    {1,     kMax, &Service::HandleKeycodes}},
        {"oneshot",     {0,     0,    &Service::HandleOneshot}},
        {"onrestart",   {1,     kMax, &Service::HandleOnrestart}},
        {"seclabel",    {1,     1,    &Service::HandleSeclabel}},
        {"setenv",      {2,     2,    &Service::HandleSetenv}},
        {"socket",      {3,     6,    &Service::HandleSocket}},
        {"user",        {1,     1,    &Service::HandleUser}},
        {"writepid",    {1,     kMax, &Service::HandleWritepid}},
    };
    return option_handlers;
}

//以class对应的处理函数为例，可以看出其实就是填充service对象对应的域
bool Service::HandleClass(const std::vector<std::string>& args, std::string* err) {
    classname_ = args[1];
    return true;
}

//注意此时service对象已经处理完毕
void ServiceParser::EndSection() {
    if (service_) {
        ServiceManager::GetInstance().AddService(std::move(service_));
    }
}

void ServiceManager::AddService(std::unique_ptr<Service> service) {
    Service* old_service = FindServiceByName(service->name());
    if (old_service) {
        ERROR("ignored duplicate definition of service '%s'",
              service->name().c_str());
        return;
    }
    //将service对象加入到services_里
    //7.0里，services_已经是个vector了
    services_.emplace_back(std::move(service));
}

bool ActionParser::ParseSection(....) {
    ........
    //创建出新的action对象
    auto action = std::make_unique<Action>(false);
    //根据参数，填充action的trigger域，不详细分析了
    if (!action->InitTriggers(triggers, err)) {
        return false;
    }
    .........
}

bool ActionParser::ParseLineSection(.......) const {
    //构造Action对象的command域
    return action_ ? action_->AddCommand(args, filename, line, err) : false;
}

bool Action::AddCommand(.....) {
    ........
    //找出action对应的执行函数
    auto function = function_map_->FindFunction(args[0], args.size() - 1, err);
    ........
    //利用所有信息构造出command，加入到action对象中
    AddCommand(function, args, filename, line);
    return true;
}

void Action::AddCommand(......) {
    commands_.emplace_back(f, args, filename, line);
}

void ActionParser::EndSection() {
    if (action_ && action_->NumCommands() > 0) {
        ActionManager::GetInstance().AddAction(std::move(action_));
    }
}

void ActionManager::AddAction(.....) {
    ........
    auto old_action_it = std::find_if(actions_.begin(),
                     actions_.end(),
                     [&action] (std::unique_ptr<Action>& a) {
                         return action->TriggersEqual(*a);
                     });

    if (old_action_it != actions_.end()) {
        (*old_action_it)->CombineAction(*action);
    } else {
        //加入到action链表中，类型也是vector，其中装的是指针
        actions_.emplace_back(std::move(action));
    }
}

.......
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
.......

BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const {
    constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
    static const Map builtin_functions = {
        {"bootchart_init",          {0,     0,    do_bootchart_init}},
        {"chmod",                   {2,     2,    do_chmod}},
        {"chown",                   {2,     3,    do_chown}},
        {"class_reset",             {1,     1,    do_class_reset}},
        {"class_start",             {1,     1,    do_class_start}},
        {"class_stop",              {1,     1,    do_class_stop}},
        {"copy",                    {2,     2,    do_copy}},
        {"domainname",              {1,     1,    do_domainname}},
        {"enable",                  {1,     1,    do_enable}},
        {"exec",                    {1,     kMax, do_exec}},
        {"export",                  {2,     2,    do_export}},
        {"hostname",                {1,     1,    do_hostname}},
        {"ifup",                    {1,     1,    do_ifup}},
        {"init_user0",              {0,     0,    do_init_user0}},
        {"insmod",                  {1,     kMax, do_insmod}},
        {"installkey",              {1,     1,    do_installkey}},
        {"load_persist_props",      {0,     0,    do_load_persist_props}},
        {"load_system_props",       {0,     0,    do_load_system_props}},
        {"loglevel",                {1,     1,    do_loglevel}},
        {"mkdir",                   {1,     4,    do_mkdir}},
        {"mount_all",               {1,     kMax, do_mount_all}},
        {"mount",                   {3,     kMax, do_mount}},
        {"powerctl",                {1,     1,    do_powerctl}},
        {"restart",                 {1,     1,    do_restart}},
        {"restorecon",              {1,     kMax, do_restorecon}},
        {"restorecon_recursive",    {1,     kMax, do_restorecon_recursive}},
        {"rm",                      {1,     1,    do_rm}},
        {"rmdir",                   {1,     1,    do_rmdir}},
        {"setprop",                 {2,     2,    do_setprop}},
        {"setrlimit",               {3,     3,    do_setrlimit}},
        {"start",                   {1,     1,    do_start}},
        {"stop",                    {1,     1,    do_stop}},
        {"swapon_all",              {1,     1,    do_swapon_all}},
        {"symlink",                 {2,     2,    do_symlink}},
        {"sysclktz",                {1,     1,    do_sysclktz}},
        {"trigger",                 {1,     1,    do_trigger}},
        {"verity_load_state",       {0,     0,    do_verity_load_state}},
        {"verity_update_state",     {0,     0,    do_verity_update_state}},
        {"wait",                    {1,     2,    do_wait}},
        {"write",                   {2,     2,    do_write}},
    };
    return builtin_functions;
}

ActionManager& am = ActionManager::GetInstance();

am.QueueEventTrigger("early-init");

// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...
m.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(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 = property_get("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");

void ActionManager::QueueEventTrigger(const std::string& trigger) {
    trigger_queue_.push(std::make_unique<EventTrigger>(trigger));
}

void ActionManager::QueueBuiltinAction(BuiltinFunction func, const std::string& name) {
    //创建action
    auto action = std::make_unique<Action>(true);
    std::vector<std::string> name_vector{name};

    //保证唯一性
    if (!action->InitSingleTrigger(name)) {
        return;
    }

    //创建action的cmd，指定执行函数和参数
    action->AddCommand(func, name_vector);

    trigger_queue_.push(std::make_unique<BuiltinTrigger>(action.get()));
    actions_.emplace_back(std::move(action));
}

while (true) {
    //判断是否有事件需要处理
    if (!waiting_for_exec) {
        //依次执行每个action中携带command对应的执行函数
        am.ExecuteOneCommand();
        //重启一些挂掉的进程
        restart_processes();
    }

    //以下决定timeout的时间，将影响while循环的间隔
    int timeout = -1;
    //有进程需要重启时，等待该进程重启
    if (process_needs_restart) {
        timeout = (process_needs_restart - gettime()) * 1000;
        if (timeout < 0)
            timeout = 0;
    }

    //有action待处理，不等待
    if (am.HasMoreCommands()) {
        timeout = 0;
    }

    //bootchart_sample应该是进行性能数据采样
    bootchart_sample(&timeout);

    epoll_event ev;
    //没有事件到来的话，最多阻塞timeout时间
    int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, timeout));
    if (nr == -1) {
        ERROR("epoll_wait failed: %s\n", strerror(errno));
    } else if (nr == 1) {
        //有事件到来，执行对应处理函数
        //epoll句柄（即epoll_fd）主要监听子进程结束，及其它进程设置系统属性的请求。
        ((void (*)()) ev.data.ptr)();
    }
}

void ActionManager::ExecuteOneCommand() {
    // Loop through the trigger queue until we have an action to execute
    //当有可执行action或trigger queue为空时结束
    while (current_executing_actions_.empty() && !trigger_queue_.empty()) {
        //轮询actions链表
        for (const auto& action : actions_) {
            //依次查找trigger表
            if (trigger_queue_.front()->CheckTriggers(*action)) {
                //当action与trigger对应时，就可以执行当前action
                //一个trigger可以对应多个action，均加入current_executing_actions_
                current_executing_actions_.emplace(action.get());
            }
        }
        //trigger event出队
        trigger_queue_.pop();
    }

    if (current_executing_actions_.empty()) {
        return;
    }

    //每次只执行一个action，下次init进程while循环时，跳过上面的while循环，接着执行
    auto action = current_executing_actions_.front();

    if (current_command_ == 0) {
        std::string trigger_name = action->BuildTriggersString();
        INFO("processing action (%s)\n", trigger_name.c_str());
    }

    //实际的执行过程，此处仅处理当前action中的一个cmd
    action->ExecuteOneCommand(current_command_);

    //适当地清理工作，注意只有当前action中所有的command均执行完毕后，才会将该action从current_executing_actions_移除
    // 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_.
    ++current_command_;
    if (current_command_ == action->NumCommands()) {
        current_executing_actions_.pop();
        current_command_ = 0;
        if (action->oneshot()) {
            auto eraser = [&action] (std::unique_ptr<Action>& a) {
                return a.get() == action;
            };
            actions_.erase(std::remove_if(actions_.begin(), actions_.end(), eraser));
        }
    }
}

void Action::ExecuteCommand(const Command& command) const {
    Timer t;
    //执行该command对应的处理函数
    int result = command.InvokeFunc();
    ........
}

void Action::ExecuteCommand(const Command& command) const {
    Timer t;
    //执行该command对应的处理函数
    int result = command.InvokeFunc();
    ........
}

static void restart_processes() {
    process_needs_restart = 0;
    ServiceManager::GetInstance().ForEachServiceWithFlags(
        SVC_RESTARTING,
        [] (Service* s) {
            s->RestartIfNeeded(process_needs_restart);
        });
}

void Service::RestartIfNeeded(time_t& process_needs_restart)(struct service *svc)
{
    time_t next_start_time = svc->time_started + 5;

    //两次服务启动时间的间隔要大于5s
    if (next_start_time <= gettime()) {
        svc->flags &= (~SVC_RESTARTING);
        //满足时间间隔的要求后，重启服务
        //Start将会重新fork服务进程，并做相应的配置
        Start(svc, NULL);
        return;
    }

    //更新main函数中，while循环需要等待的时间
    if ((next_start_time < process_needs_restart) ||
        (process_needs_restart == 0)) {
        process_needs_restart = next_start_time;
    }
}