读书笔记--Android系统启动

int main(int argc, char** argv) {
       
       ...省略
965    if (is_first_stage) {//1
966        boot_clock::time_point start_time = boot_clock::now();
967
968        // Clear the umask.
969        umask(0);
970    
971        // Get the basic filesystem setup we need put together in the initramdisk
972        // on / and then we'll let the rc file figure out the rest.
973        mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
974        mkdir("/dev/pts", 0755);
975        mkdir("/dev/socket", 0755);
976        mount("devpts", "/dev/pts", "devpts", 0, NULL);
977        #define MAKE_STR(x) __STRING(x)
978        mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));
979        // Don't expose the raw commandline to unprivileged processes.
980        chmod("/proc/cmdline", 0440);
981        gid_t groups[] = { AID_READPROC };
982        setgroups(arraysize(groups), groups);
983        mount("sysfs", "/sys", "sysfs", 0, NULL);
984        mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
985        mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));
986        mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));
987        mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));
988
           ...省略
1026    }

        //初始化属性服务
1040    property_init();//2

        ...省略
1068    //创建epoll句柄
1069    epoll_fd = epoll_create1(EPOLL_CLOEXEC);//3
1070    if (epoll_fd == -1) {
1071        PLOG(ERROR) << "epoll_create1 failed";
1072        exit(1);
1073    }
1074    //用于设置子进程信号处理函数
1075    signal_handler_init();//4
1076
        //启动属性服务
1079    start_property_service();//5
1080    set_usb_controller();
1081
1082    const BuiltinFunctionMap function_map;
1083    Action::set_function_map(&function_map);
1084
1085    Parser& parser = Parser::GetInstance();
1086    parser.AddSectionParser("service",std::make_unique<ServiceParser>());
1087    parser.AddSectionParser("on", std::make_unique<ActionParser>());
1088    parser.AddSectionParser("import", std::make_unique<ImportParser>());
1089    std::string bootscript = GetProperty("ro.boot.init_rc", "");
1090    if (bootscript.empty()) {
           //解析init.rc 文件
1091        parser.ParseConfig("/init.rc");//6
1092        parser.set_is_system_etc_init_loaded(
1093                parser.ParseConfig("/system/etc/init"));
1094        parser.set_is_vendor_etc_init_loaded(
1095                parser.ParseConfig("/vendor/etc/init"));
1096        parser.set_is_odm_etc_init_loaded(parser.ParseConfig("/odm/etc/init"));
1097    } else {
1098        parser.ParseConfig(bootscript);
1099        parser.set_is_system_etc_init_loaded(true);
1100        parser.set_is_vendor_etc_init_loaded(true);
1101        parser.set_is_odm_etc_init_loaded(true);
1102    }
1103
        ...省略
1138
1139    while (true) {
1140        // By default, sleep until something happens.
1141        int epoll_timeout_ms = -1;
1142
1143        if (!(waiting_for_prop || ServiceManager::GetInstance().IsWaitingForExec())) {
1144            am.ExecuteOneCommand();
1145        }
1146        if (!(waiting_for_prop || ServiceManager::GetInstance().IsWaitingForExec())) {
1147            restart_processes();//重启死去的进程
1148
1149            // If there's a process that needs restarting, wake up in time for that.
1150            if (process_needs_restart_at != 0) {
1151                epoll_timeout_ms = (process_needs_restart_at - time(nullptr)) * 1000;
1152                if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
1153            }
1154
1155            // If there's more work to do, wake up again immediately.
1156            if (am.HasMoreCommands()) epoll_timeout_ms = 0;
1157        }
1158
1159        epoll_event ev;
1160        int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));//7
1161        if (nr == -1) {
1162            PLOG(ERROR) << "epoll_wait failed";
1163        } else if (nr == 1) {
1164            ((void (*)()) ev.data.ptr)();
1165        }
1166    }
1167
1168    return 0;
1169}

68void property_init() {
69    if (__system_property_area_init()) { //1 
70        LOG(ERROR) << "Failed to initialize property area";
71        exit(1);
72    }
73}

//定义两个文件描述符
34static int signal_write_fd = -1;
35static int signal_read_fd = -1;
36
37static void handle_signal() {
38    // Clear outstanding requests.
39    char buf[32];
40    read(signal_read_fd, buf, sizeof(buf));
41
42    ServiceManager::GetInstance().ReapAnyOutstandingChildren();
43}
44
45static void SIGCHLD_handler(int) {
46    if (TEMP_FAILURE_RETRY(write(signal_write_fd, "1", 1)) == -1) {
47        PLOG(ERROR) << "write(signal_write_fd) failed";
48    }
49}
50
51void signal_handler_init() {
52    // Create a signalling mechanism for SIGCHLD.
53    int s[2];
      //创建读写socket对
54    if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0, s) == -1) {
55        PLOG(ERROR) << "socketpair failed";
56        exit(1);
57    }
58
      //通过 读写 socket对赋值fd
59    signal_write_fd = s[0];
60    signal_read_fd = s[1];
61
62    // Write to signal_write_fd if we catch SIGCHLD.
      //sigaction 处理信号的结构体
63    struct sigaction act;
64    memset(&act, 0, sizeof(act));
65    act.sa_handler = SIGCHLD_handler;
66    act.sa_flags = SA_NOCLDSTOP;
      // 调用信号安装函数sigaction()，传递参数给sigaction结构体，便完成信号处理的过程。
67    sigaction(SIGCHLD, &act, 0);
68
69    ServiceManager::GetInstance().ReapAnyOutstandingChildren();
70    //添加到epoll
71    register_epoll_handler(signal_read_fd, handle_signal);
72}

666void start_property_service() {
667    property_set("ro.property_service.version", "2");
668     //SOCK_NONBLOCK 创建非阻塞Sokcet 返回fd文件描述符
669    property_set_fd = create_socket(PROP_SERVICE_NAME,  SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
670                                    0666, 0, 0, NULL);
671    if (property_set_fd == -1) {
672        PLOG(ERROR) << "start_property_service socket creation failed";
673        exit(1);
674    }
675    //对property_set_fd监听 8表示最多同时处理8个服务
676    listen(property_set_fd, 8);
677    //handle_property_set_fd 方法处理属性服务
678    register_epoll_handler(property_set_fd, handle_property_set_fd);
679}

877void ServiceManager::AddService(std::unique_ptr<Service> service) {
878    Service* old_service = FindServiceByName(service->name());
879    if (old_service) {
880        LOG(ERROR) << "ignored duplicate definition of service '" << service->name() << "'";
881        return;
882    }
883    services_.emplace_back(std::move(service));//加入链表
884}

622on nonencrypted
623    class_start main
624    class_start late_start

129static int do_class_start(const std::vector<std::string>& args) {
130        /* Starting a class does not start services
131         * which are explicitly disabled.  They must
132         * be started individually.
133         */
134    ServiceManager::GetInstance().
135        ForEachServiceInClass(args[1], [] (Service* s) { s->StartIfNotDisabled(); });
136    return 0;
137}

762bool Service::StartIfNotDisabled() {
763    if (!(flags_ & SVC_DISABLED)) {
764        return Start();
765    } else {
766        flags_ |= SVC_DISABLED_START;
767    }
768    return true;
769}

bool Service::Start() {

648
649    pid_t pid = -1;//定义pid
650    if (namespace_flags_) {是否没有启动 
651        pid = clone(nullptr, nullptr, namespace_flags_ | SIGCHLD, nullptr);
652    } else {
653        pid = fork();//创建子进程
654    }
655
656    if (pid == 0) {
657        umask(077);
658
        //通过execve函数，启动Service子进程
721        if (execve(strs[0], (char**) &strs[0], (char**) ENV) < 0) {
722            PLOG(ERROR) << "cannot execve('" << strs[0] << "')";
723        }
724
725        _exit(127);
726    }

757
758    NotifyStateChange("running");
759    return true;
760}
761

12 import /init.${ro.zygote}.rc

1 service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
2    class main
3    priority -20
4    user root

187int main(int argc, char* const argv[])
188{

342
343    if (zygote) {//如果是zygote进程，则启动zygote
344        runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
345    } else if (className) {
346        runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
347    } else {
348        fprintf(stderr, "Error: no class name or --zygote supplied.\n");
349        app_usage();
350        LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
351    }
352}