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