[android] init进程 .rc文件中service、action的parsing

init进程code位置：system/core/init

system/core/init/README.md，这个文件是描述rc文件语法的。

在.rc文件中，有3中类型：

1. service

2. on(action)

3. import

init.cpp

Parser CreateParser(ActionManager& action_manager, ServiceList& service_list) {
    Parser parser;

    parser.AddSectionParser("service", std::make_unique<ServiceParser>(&service_list, subcontexts));
    parser.AddSectionParser("on", std::make_unique<ActionParser>(&action_manager, subcontexts));
    parser.AddSectionParser("import", std::make_unique<ImportParser>(&parser));

    return parser;
}

　　

以service开头，表示是service；以on开头表示是Action。

对于service行或者on行，调用ParseSection()，在ParseSection中会创建Servcie或者Action对象。

然后处理service或者on行后的行（service或者action的子行）。对于每个子行，都会调用ParseLineSection()，在这个函数中，对于service，会执行对应的函数，比如对于writepid，会调用Servcie::ParseWritepid()；

对于action，会执行AddCommand()。

等这个service或者action的所有子行都parse完后，在parse下一个servcie或者action前(调用ParseSection之前)，会call endSection()，这个函数会call EndSection。在EndSection()中，对于service，会执行add service；对于action，会add action到action manager。

对于service，对应文件是service.cpp；对于action，对应文件是action_parser.cpp。

parse .rc文件的入口：init.cpp/LoadBootScripts()

Parser CreateParser(ActionManager& action_manager, ServiceList& service_list) {
    Parser parser;

    parser.AddSectionParser("service", std::make_unique<ServiceParser>(&service_list, subcontexts));
    parser.AddSectionParser("on", std::make_unique<ActionParser>(&action_manager, subcontexts));
    parser.AddSectionParser("import", std::make_unique<ImportParser>(&parser));

    return parser;
}

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()) {
        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);
    }
}

ParseData()函数中通过next_token(&state)将一行中的所有单词（以比如空格分隔）走T_TEXT case调用args.emplace_back(state.text)加到args中。当一行结束时( 符)，next_token()会返回T_NEWLINE，在T_NEWLINE case中处理这一行。处理完后，将args clear。

void Parser::ParseData(const std::string& filename, const std::string& data, size_t* parse_errors) {
    // TODO: Use a parser with const input and remove this copy
    std::vector<char> data_copy(data.begin(), data.end());
    data_copy.push_back('');

    parse_state state;
    state.line = 0;
    state.ptr = &data_copy[0];
    state.nexttoken = 0;

    SectionParser* section_parser = nullptr;
    int section_start_line = -1;
    std::vector<std::string> args;

    auto end_section = [&] {
        if (section_parser == nullptr) return;

        if (auto result = section_parser->EndSection(); !result) {
            (*parse_errors)++;
            LOG(ERROR) << filename << ": " << section_start_line << ": " << result.error();
        }

        section_parser = nullptr;
        section_start_line = -1;
    };

    for (;;) {
        switch (next_token(&state)) {
            case T_EOF:
                end_section();
                return;
            case T_NEWLINE:
                state.line++;
                if (args.empty()) break;
                // If we have a line matching a prefix we recognize, call its callback and unset any
                // current section parsers.  This is meant for /sys/ and /dev/ line entries for
                // uevent.
                for (const auto& [prefix, callback] : line_callbacks_) {
                    if (android::base::StartsWith(args[0], prefix)) {
                        end_section();

                        if (auto result = callback(std::move(args)); !result) {
                            (*parse_errors)++;
                            LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                        }
                        break;
                    }
                }
                if (section_parsers_.count(args[0])) {
                    end_section();
                    section_parser = section_parsers_[args[0]].get();
                    section_start_line = state.line;
                    if (auto result =
                            section_parser->ParseSection(std::move(args), filename, state.line);
                        !result) {
                        (*parse_errors)++;
                        LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                        section_parser = nullptr;
                    }
                } else if (section_parser) {
                    if (auto result = section_parser->ParseLineSection(std::move(args), state.line);
                        !result) {
                        (*parse_errors)++;
                        LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                    }
                }
                args.clear();
                break;
            case T_TEXT:
                args.emplace_back(state.text);
                break;
        }
    }
}

service class有一个Action的成员--onrestart_

在parse一个service时，例如下面的audioserver.rc，对于service里的onrestart行，就是对应一个command。这个command会被add到onrestart_ Action中，是通过如下的方法add的：

在service.cpp里有一个Service::OptionParserMap::map()函数，根据key onrestart找到其对应的函数：Service::ParseOnrestart()，然后执行这个函数。这个函数会调用Action.cpp中的addcommand函数。

frameworks/av/media/audioserver/audioserver.rc

service audioserver /system/bin/audioserver
    class core
    user audioserver
    # media gid needed for /dev/fm (radio) and for /data/misc/media (tee)
    group audio camera drmrpc inet media mediadrm net_bt net_bt_admin net_bw_acct
    ioprio rt 4
    writepid /dev/cpuset/foreground/tasks /dev/stune/foreground/tasks
    onrestart restart vendor.audio-hal-2-0
    # Keep the original service name for backward compatibility when upgrading
    # O-MR1 devices with framework-only.
    onrestart restart audio-hal-2-0
 
on property:vts.native_server.on=1
    stop audioserver
on property:vts.native_server.on=0
    start audioserver

　　

const Service::OptionParserMap::Map& Service::OptionParserMap::map() const {
    constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
    // clang-format off
    static const Map option_parsers = {
        {"capabilities",
                        {1,     kMax, &Service::ParseCapabilities}},
        {"class",       {1,     kMax, &Service::ParseClass}},
        {"console",     {0,     1,    &Service::ParseConsole}},
        {"critical",    {0,     0,    &Service::ParseCritical}},
        {"disabled",    {0,     0,    &Service::ParseDisabled}},
        {"enter_namespace",
                        {2,     2,    &Service::ParseEnterNamespace}},
        {"group",       {1,     NR_SVC_SUPP_GIDS + 1, &Service::ParseGroup}},
        {"interface",   {2,     2,    &Service::ParseInterface}},
        {"ioprio",      {2,     2,    &Service::ParseIoprio}},
        {"priority",    {1,     1,    &Service::ParsePriority}},
        {"keycodes",    {1,     kMax, &Service::ParseKeycodes}},
        {"oneshot",     {0,     0,    &Service::ParseOneshot}},
        {"onrestart",   {1,     kMax, &Service::ParseOnrestart}},
        {"override",    {0,     0,    &Service::ParseOverride}},
        {"oom_score_adjust",
                        {1,     1,    &Service::ParseOomScoreAdjust}},
        {"memcg.swappiness",
                        {1,     1,    &Service::ParseMemcgSwappiness}},
        {"memcg.soft_limit_in_bytes",
                        {1,     1,    &Service::ParseMemcgSoftLimitInBytes}},
        {"memcg.limit_in_bytes",
                        {1,     1,    &Service::ParseMemcgLimitInBytes}},
        {"namespace",   {1,     2,    &Service::ParseNamespace}},
        {"rlimit",      {3,     3,    &Service::ParseProcessRlimit}},
        {"seclabel",    {1,     1,    &Service::ParseSeclabel}},
        {"setenv",      {2,     2,    &Service::ParseSetenv}},
        {"shutdown",    {1,     1,    &Service::ParseShutdown}},
        {"socket",      {3,     6,    &Service::ParseSocket}},
        {"file",        {2,     2,    &Service::ParseFile}},
        {"user",        {1,     1,    &Service::ParseUser}},
        {"writepid",    {1,     kMax, &Service::ParseWritepid}},
    };
    // clang-format on
    return option_parsers;
}

Action.cpp中的addcommand函数会根据builtins.cpp中的Map builtin_fucnctions找到对应的函数，比如上面例子中的onrestart restart vendor.audio-hal-2-0，就是根据key restart找到对应的函数do_restart。

然后会根据找到的这个函数和args等其它参数构造一个Command，然后将这个Command对象add到commands_中。

const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const {
    constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
    // clang-format off
    static const Map builtin_functions = {
        {"bootchart",               {1,     1,    {false,  do_bootchart}}},
        {"chmod",                   {2,     2,    {true,   do_chmod}}},
        {"chown",                   {2,     3,    {true,   do_chown}}},
        {"class_reset",             {1,     1,    {false,  do_class_reset}}},
        {"class_restart",           {1,     1,    {false,  do_class_restart}}},
        {"class_start",             {1,     1,    {false,  do_class_start}}},
        {"class_stop",              {1,     1,    {false,  do_class_stop}}},
        {"copy",                    {2,     2,    {true,   do_copy}}},
        {"domainname",              {1,     1,    {true,   do_domainname}}},
        {"enable",                  {1,     1,    {false,  do_enable}}},
        {"exec",                    {1,     kMax, {false,  do_exec}}},
        {"exec_background",         {1,     kMax, {false,  do_exec_background}}},
        {"exec_start",              {1,     1,    {false,  do_exec_start}}},
        {"export",                  {2,     2,    {false,  do_export}}},
        {"hostname",                {1,     1,    {true,   do_hostname}}},
        {"ifup",                    {1,     1,    {true,   do_ifup}}},
        {"init_user0",              {0,     0,    {false,  do_init_user0}}},
        {"insmod",                  {1,     kMax, {true,   do_insmod}}},
        {"installkey",              {1,     1,    {false,  do_installkey}}},
        {"load_persist_props",      {0,     0,    {false,  do_load_persist_props}}},
        {"load_system_props",       {0,     0,    {false,  do_load_system_props}}},
        {"loglevel",                {1,     1,    {false,  do_loglevel}}},
        {"mkdir",                   {1,     4,    {true,   do_mkdir}}},
        // TODO: Do mount operations in vendor_init.
        // mount_all is currently too complex to run in vendor_init as it queues action triggers,
        // imports rc scripts, etc.  It should be simplified and run in vendor_init context.
        // mount and umount are run in the same context as mount_all for symmetry.
        {"mount_all",               {1,     kMax, {false,  do_mount_all}}},
        {"mount",                   {3,     kMax, {false,  do_mount}}},
        {"umount",                  {1,     1,    {false,  do_umount}}},
        {"readahead",               {1,     2,    {true,   do_readahead}}},
        {"restart",                 {1,     1,    {false,  do_restart}}},
        {"restorecon",              {1,     kMax, {true,   do_restorecon}}},
        {"restorecon_recursive",    {1,     kMax, {true,   do_restorecon_recursive}}},
        {"rm",                      {1,     1,    {true,   do_rm}}},
        {"rmdir",                   {1,     1,    {true,   do_rmdir}}},
        {"setprop",                 {2,     2,    {true,   do_setprop}}},
        {"setrlimit",               {3,     3,    {false,  do_setrlimit}}},
        {"start",                   {1,     1,    {false,  do_start}}},
        {"stop",                    {1,     1,    {false,  do_stop}}},
        {"swapon_all",              {1,     1,    {false,  do_swapon_all}}},
        {"symlink",                 {2,     2,    {true,   do_symlink}}},
        {"sysclktz",                {1,     1,    {false,  do_sysclktz}}},
        {"trigger",                 {1,     1,    {false,  do_trigger}}},
        {"verity_load_state",       {0,     0,    {false,  do_verity_load_state}}},
        {"verity_update_state",     {0,     0,    {false,  do_verity_update_state}}},
        {"wait",                    {1,     2,    {true,   do_wait}}},
        {"wait_for_prop",           {2,     2,    {false,  do_wait_for_prop}}},
        {"write",                   {2,     2,    {true,   do_write}}},
    };
    // clang-format on
    return builtin_functions;
}

对于service来说，只有onrestart才有对应的command，像writepid、group等等其它都是没有对应的command的。 

对于service定义的command(onrestart)，什么时候执行这个command呢？

这个是在service.cpp中的onrestart_.ExecuteAllCommands()的时候去执行的。

这个onrestart_.ExecuteAllCommands()对于media进程来说，它没有添加command（如下面的mediaserver.rc），所以不会做什么事情。

frameworks/av/media/mediaserver/mediaserver.rc

service media /system/bin/mediaserver
    class main
    user media
    group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
    ioprio rt 4
    writepid /dev/cpuset/foreground/tasks /dev/stune/foreground/tasks