Android ADB实现解析

ADB是Android系统提供的调试工具，整个ADB工具由三部分组成：adb client、adb service、adb daemon。

1、ADB client

提供HOST端运行的命令

2、ADB service

HOST端上的一个后台进程

3、ADB daemom

DEVICE端（真实的机器或者模拟器）的守护进程

ADB代码位于/system/core/adb目录下，通过查看Android.mk，可以知道，该目录下的代码生成了两个MODULE，分别是adb和adbd,  adb client和adb service都是由adb这个可执行文件实现， adb daemon由adbd实现。adb和adbd的一些源代码文件是用同一个的，编译时通过LOCAL_CFLAGS的参数ADB_HOST来区分，这种你中有我我中有你的关系，对于初次接触的朋友们，多少增加了些困扰。理清了ADB几部分的关系，以及源代码的结构，对ADB的认识已经有一个飞越了。

一、main函数

adb.c的main函数是adb client、adb service、adb daemon的共同入口，

int main(int argc, char **argv)
{
#if ADB_HOST
    adb_sysdeps_init();
    adb_trace_init();
    D("Handling commandline()\n");
    return adb_commandline(argc - 1, argv + 1);
#else
    /* If adbd runs inside the emulator this will enable adb tracing via
     * adb-debug qemud service in the emulator. */
    adb_qemu_trace_init();
    if((argc > 1) && (!strcmp(argv[1],"recovery"))) {
        adb_device_banner = "recovery";
        recovery_mode = 1;
    }

    start_device_log();
    D("Handling main()\n");
    return adb_main(0, DEFAULT_ADB_PORT);
#endif
}

根据Android.mk中传入的ADB_HOST确定编译的是adb client\adb service, 或者是adb daemon, ADB_HOST为1时编译adb client\adb service的代码， ADB_HOST为0时编译adb daemon的代码。

以上代码中，adb client\adb service端代码如下,

    adb_sysdeps_init();
    adb_trace_init();
    D("Handling commandline()\n");
    return adb_commandline(argc - 1, argv + 1);

1、adb_sysdeps_init():  adb client\adb service适用于linux和windows版本，所以代码中有平台相关的部分。

2、adb_trace_init():   初始化log输出配置，初始化后在HOST上设置ADB_TRACE这个环境变量，可以控制client\service端的log输出等级，

配置为1或者all的话，将输出所有 的log。

3、adb_commandline():  关键函数，代码如下。

int adb_commandline(int argc, char **argv)
{
    char buf[4096];
    int no_daemon = 0;
    int is_daemon = 0;
    int is_server = 0;
    int persist = 0;
    int r;
    int quote;
    transport_type ttype = kTransportAny;
    char* serial = NULL;
    char* server_port_str = NULL;

        /* If defined, this should be an absolute path to
         * the directory containing all of the various system images
         * for a particular product.  If not defined, and the adb
         * command requires this information, then the user must
         * specify the path using "-p".
         */
    gProductOutPath = getenv("ANDROID_PRODUCT_OUT");
    if (gProductOutPath == NULL || gProductOutPath[0] == '\0') {
        gProductOutPath = NULL;
    }
    // TODO: also try TARGET_PRODUCT/TARGET_DEVICE as a hint

    serial = getenv("ANDROID_SERIAL");

    /* Validate and assign the server port */
    server_port_str = getenv("ANDROID_ADB_SERVER_PORT");
    int server_port = DEFAULT_ADB_PORT;
    if (server_port_str && strlen(server_port_str) > 0) {
        server_port = (int) strtol(server_port_str, NULL, 0);
        if (server_port <= 0 || server_port > 65535) {
            fprintf(stderr,
                    "adb: Env var ANDROID_ADB_SERVER_PORT must be a positive number less than 65535. Got \"%s\"\n",
                    server_port_str);
            return usage();
        }
    }

    /* modifiers and flags */
    while(argc > 0) {
        if(!strcmp(argv[0],"server")) {
            is_server = 1;
        } else if(!strcmp(argv[0],"nodaemon")) {
            no_daemon = 1;
        } else if (!strcmp(argv[0], "fork-server")) {
            /* this is a special flag used only when the ADB client launches the ADB Server */
            is_daemon = 1;
        } else if(!strcmp(argv[0],"persist")) {
            persist = 1;
        } else if(!strncmp(argv[0], "-p", 2)) {
            const char *product = NULL;
            if (argv[0][2] == '\0') {
                if (argc < 2) return usage();
                product = argv[1];
                argc--;
                argv++;
            } else {
                product = argv[0] + 2;
            }
            gProductOutPath = find_product_out_path(product);
            if (gProductOutPath == NULL) {
                fprintf(stderr, "adb: could not resolve \"-p %s\"\n",
                        product);
                return usage();
            }
        } else if (argv[0][0]=='-' && argv[0][1]=='s') {
            if (isdigit(argv[0][2])) {
                serial = argv[0] + 2;
            } else {
                if(argc < 2 || argv[0][2] != '\0') return usage();
                serial = argv[1];
                argc--;
                argv++;
            }
        } else if (!strcmp(argv[0],"-d")) {
            ttype = kTransportUsb;
        } else if (!strcmp(argv[0],"-e")) {
            ttype = kTransportLocal;
        } else if (!strcmp(argv[0],"-a")) {
            gListenAll = 1;
        } else if(!strncmp(argv[0], "-H", 2)) {
            const char *hostname = NULL;
            if (argv[0][2] == '\0') {
                if (argc < 2) return usage();
                hostname = argv[1];
                argc--;
                argv++;
            } else {
                hostname = argv[0] + 2;
            }
            adb_set_tcp_name(hostname);

        } else if(!strncmp(argv[0], "-P", 2)) {
            if (argv[0][2] == '\0') {
                if (argc < 2) return usage();
                server_port_str = argv[1];
                argc--;
                argv++;
            } else {
                server_port_str = argv[0] + 2;
            }
            if (strlen(server_port_str) > 0) {
                server_port = (int) strtol(server_port_str, NULL, 0);
                if (server_port <= 0 || server_port > 65535) {
                    fprintf(stderr,
                            "adb: port number must be a positive number less than 65536. Got \"%s\"\n",
                            server_port_str);
                    return usage();
                }
            } else {
                fprintf(stderr,
                "adb: port number must be a positive number less than 65536. Got empty string.\n");
                return usage();
            }
        } else {
                /* out of recognized modifiers and flags */
            break;
        }
        argc--;
        argv++;
    }

    adb_set_transport(ttype, serial);
    adb_set_tcp_specifics(server_port);

    if (is_server) {
        if (no_daemon || is_daemon) {
            r = adb_main(is_daemon, server_port);
        } else {
            r = launch_server(server_port);
        }
        if(r) {
            fprintf(stderr,"* could not start server *\n");
        }
        return r;
    }

top:
    if(argc == 0) {
        return usage();
    }

    /* adb_connect() commands */

    if(!strcmp(argv[0], "devices")) {
        char *tmp;
        char *listopt;
        if (argc < 2)
            listopt = "";
        else if (argc == 2 && !strcmp(argv[1], "-l"))
            listopt = argv[1];
        else {
            fprintf(stderr, "Usage: adb devices [-l]\n");
            return 1;
        }
        snprintf(buf, sizeof buf, "host:%s%s", argv[0], listopt);
        tmp = adb_query(buf);
        if(tmp) {
            printf("List of devices attached \n");
            printf("%s\n", tmp);
            return 0;
        } else {
            return 1;
        }
    }

    if(!strcmp(argv[0], "connect")) {
        char *tmp;
        if (argc != 2) {
            fprintf(stderr, "Usage: adb connect <host>[:<port>]\n");
            return 1;
        }
        snprintf(buf, sizeof buf, "host:connect:%s", argv[1]);
        tmp = adb_query(buf);
        if(tmp) {
            printf("%s\n", tmp);
            return 0;
        } else {
            return 1;
        }
    }

    if(!strcmp(argv[0], "disconnect")) {
        char *tmp;
        if (argc > 2) {
            fprintf(stderr, "Usage: adb disconnect [<host>[:<port>]]\n");
            return 1;
        }
        if (argc == 2) {
            snprintf(buf, sizeof buf, "host:disconnect:%s", argv[1]);
        } else {
            snprintf(buf, sizeof buf, "host:disconnect:");
        }
        tmp = adb_query(buf);
        if(tmp) {
            printf("%s\n", tmp);
            return 0;
        } else {
            return 1;
        }
    }

    if (!strcmp(argv[0], "emu")) {
        return adb_send_emulator_command(argc, argv);
    }

    if(!strcmp(argv[0], "shell") || !strcmp(argv[0], "hell")) {
        int r;
        int fd;

        char h = (argv[0][0] == 'h');

        if (h) {
            printf("\x1b[41;33m");
            fflush(stdout);
        }

        if(argc < 2) {
            D("starting interactive shell\n");
            r = interactive_shell();
            if (h) {
                printf("\x1b[0m");
                fflush(stdout);
            }
            return r;
        }

        snprintf(buf, sizeof buf, "shell:%s", argv[1]);
        argc -= 2;
        argv += 2;
        while(argc-- > 0) {
            strcat(buf, " ");

            /* quote empty strings and strings with spaces */
            quote = (**argv == 0 || strchr(*argv, ' '));
            if (quote)
                strcat(buf, "\"");
            strcat(buf, *argv++);
            if (quote)
                strcat(buf, "\"");
        }

        for(;;) {
            D("interactive shell loop. buff=%s\n", buf);
            fd = adb_connect(buf);
            if(fd >= 0) {
                D("about to read_and_dump(fd=%d)\n", fd);
                read_and_dump(fd);
                D("read_and_dump() done.\n");
                adb_close(fd);
                r = 0;
            } else {
                fprintf(stderr,"error: %s\n", adb_error());
                r = -1;
            }

            if(persist) {
                fprintf(stderr,"\n- waiting for device -\n");
                adb_sleep_ms(1000);
                do_cmd(ttype, serial, "wait-for-device", 0);
            } else {
                if (h) {
                    printf("\x1b[0m");
                    fflush(stdout);
                }
                D("interactive shell loop. return r=%d\n", r);
                return r;
            }
        }
    }

    if(!strcmp(argv[0], "kill-server")) {
        int fd;
        fd = _adb_connect("host:kill");
        if(fd == -1) {
            fprintf(stderr,"* server not running *\n");
            return 1;
        }
        return 0;
    }

    if(!strcmp(argv[0], "sideload")) {
        if(argc != 2) return usage();
        if(adb_download("sideload", argv[1], 1)) {
            return 1;
        } else {
            return 0;
        }
    }

    if(!strcmp(argv[0], "remount") || !strcmp(argv[0], "reboot")
            || !strcmp(argv[0], "reboot-bootloader")
            || !strcmp(argv[0], "tcpip") || !strcmp(argv[0], "usb")
            || !strcmp(argv[0], "root")) {
        char command[100];
        if (!strcmp(argv[0], "reboot-bootloader"))
            snprintf(command, sizeof(command), "reboot:bootloader");
        else if (argc > 1)
            snprintf(command, sizeof(command), "%s:%s", argv[0], argv[1]);
        else
            snprintf(command, sizeof(command), "%s:", argv[0]);
        int fd = adb_connect(command);
        if(fd >= 0) {
            read_and_dump(fd);
            adb_close(fd);
            return 0;
        }
        fprintf(stderr,"error: %s\n", adb_error());
        return 1;
    }

    if(!strcmp(argv[0], "bugreport")) {
        if (argc != 1) return usage();
        do_cmd(ttype, serial, "shell", "bugreport", 0);
        return 0;
    }

    /* adb_command() wrapper commands */

    if(!strncmp(argv[0], "wait-for-", strlen("wait-for-"))) {
        char* service = argv[0];
        if (!strncmp(service, "wait-for-device", strlen("wait-for-device"))) {
            if (ttype == kTransportUsb) {
                service = "wait-for-usb";
            } else if (ttype == kTransportLocal) {
                service = "wait-for-local";
            } else {
                service = "wait-for-any";
            }
        }

        format_host_command(buf, sizeof buf, service, ttype, serial);

        if (adb_command(buf)) {
            D("failure: %s *\n",adb_error());
            fprintf(stderr,"error: %s\n", adb_error());
            return 1;
        }

        /* Allow a command to be run after wait-for-device,
            * e.g. 'adb wait-for-device shell'.
            */
        if(argc > 1) {
            argc--;
            argv++;
            goto top;
        }
        return 0;
    }

    if(!strcmp(argv[0], "forward")) {
        char host_prefix[64];
        char remove = 0;
        char remove_all = 0;
        char list = 0;
        char no_rebind = 0;

        // Parse options here.
        while (argc > 1 && argv[1][0] == '-') {
            if (!strcmp(argv[1], "--list"))
                list = 1;
            else if (!strcmp(argv[1], "--remove"))
                remove = 1;
            else if (!strcmp(argv[1], "--remove-all"))
                remove_all = 1;
            else if (!strcmp(argv[1], "--no-rebind"))
                no_rebind = 1;
            else {
                return usage();
            }
            argc--;
            argv++;
        }

        // Ensure we can only use one option at a time.
        if (list + remove + remove_all + no_rebind > 1) {
            return usage();
        }

        // Determine the <host-prefix> for this command.
        if (serial) {
            snprintf(host_prefix, sizeof host_prefix, "host-serial:%s",
                    serial);
        } else if (ttype == kTransportUsb) {
            snprintf(host_prefix, sizeof host_prefix, "host-usb");
        } else if (ttype == kTransportLocal) {
            snprintf(host_prefix, sizeof host_prefix, "host-local");
        } else {
            snprintf(host_prefix, sizeof host_prefix, "host");
        }

        // Implement forward --list
        if (list) {
            if (argc != 1)
                return usage();
            snprintf(buf, sizeof buf, "%s:list-forward", host_prefix);
            char* forwards = adb_query(buf);
            if (forwards == NULL) {
                fprintf(stderr, "error: %s\n", adb_error());
                return 1;
            }
            printf("%s", forwards);
            free(forwards);
            return 0;
        }

        // Implement forward --remove-all
        else if (remove_all) {
            if (argc != 1)
                return usage();
            snprintf(buf, sizeof buf, "%s:killforward-all", host_prefix);
        }

        // Implement forward --remove <local>
        else if (remove) {
            if (argc != 2)
                return usage();
            snprintf(buf, sizeof buf, "%s:killforward:%s", host_prefix, argv[1]);
        }
        // Or implement one of:
        //    forward <local> <remote>
        //    forward --no-rebind <local> <remote>
        else
        {
          if (argc != 3)
            return usage();
          const char* command = no_rebind ? "forward:norebind:" : "forward";
          snprintf(buf, sizeof buf, "%s:%s:%s;%s", host_prefix, command, argv[1], argv[2]);
        }

        if(adb_command(buf)) {
            fprintf(stderr,"error: %s\n", adb_error());
            return 1;
        }
        return 0;
    }

    /* do_sync_*() commands */

    if(!strcmp(argv[0], "ls")) {
        if(argc != 2) return usage();
        return do_sync_ls(argv[1]);
    }

    if(!strcmp(argv[0], "push")) {
        if(argc != 3) return usage();
        return do_sync_push(argv[1], argv[2], 0 /* no verify APK */);
    }

    if(!strcmp(argv[0], "pull")) {
        if (argc == 2) {
            return do_sync_pull(argv[1], ".");
        } else if (argc == 3) {
            return do_sync_pull(argv[1], argv[2]);
        } else {
            return usage();
        }
    }

    if(!strcmp(argv[0], "install")) {
        if (argc < 2) return usage();
        return install_app(ttype, serial, argc, argv);
    }

    if(!strcmp(argv[0], "uninstall")) {
        if (argc < 2) return usage();
        return uninstall_app(ttype, serial, argc, argv);
    }

    if(!strcmp(argv[0], "sync")) {
        char *srcarg, *android_srcpath, *data_srcpath;
        int listonly = 0;

        int ret;
        if(argc < 2) {
            /* No local path was specified. */
            srcarg = NULL;
        } else if (argc >= 2 && strcmp(argv[1], "-l") == 0) {
            listonly = 1;
            if (argc == 3) {
                srcarg = argv[2];
            } else {
                srcarg = NULL;
            }
        } else if(argc == 2) {
            /* A local path or "android"/"data" arg was specified. */
            srcarg = argv[1];
        } else {
            return usage();
        }
        ret = find_sync_dirs(srcarg, &android_srcpath, &data_srcpath);
        if(ret != 0) return usage();

        if(android_srcpath != NULL)
            ret = do_sync_sync(android_srcpath, "/system", listonly);
        if(ret == 0 && data_srcpath != NULL)
            ret = do_sync_sync(data_srcpath, "/data", listonly);

        free(android_srcpath);
        free(data_srcpath);
        return ret;
    }

    /* passthrough commands */

    if(!strcmp(argv[0],"get-state") ||
        !strcmp(argv[0],"get-serialno") ||
        !strcmp(argv[0],"get-devpath"))
    {
        char *tmp;

        format_host_command(buf, sizeof buf, argv[0], ttype, serial);
        tmp = adb_query(buf);
        if(tmp) {
            printf("%s\n", tmp);
            return 0;
        } else {
            return 1;
        }
    }

    /* other commands */

    if(!strcmp(argv[0],"status-window")) {
        status_window(ttype, serial);
        return 0;
    }

    if(!strcmp(argv[0],"logcat") || !strcmp(argv[0],"lolcat") || !strcmp(argv[0],"longcat")) {
        return logcat(ttype, serial, argc, argv);
    }

    if(!strcmp(argv[0],"ppp")) {
        return ppp(argc, argv);
    }

    if (!strcmp(argv[0], "start-server")) {
        return adb_connect("host:start-server");
    }

    if (!strcmp(argv[0], "backup")) {
        return backup(argc, argv);
    }

    if (!strcmp(argv[0], "restore")) {
        return restore(argc, argv);
    }

    if (!strcmp(argv[0], "jdwp")) {
        int  fd = adb_connect("jdwp");
        if (fd >= 0) {
            read_and_dump(fd);
            adb_close(fd);
            return 0;
        } else {
            fprintf(stderr, "error: %s\n", adb_error());
            return -1;
        }
    }

    /* "adb /?" is a common idiom under Windows */
    if(!strcmp(argv[0], "help") || !strcmp(argv[0], "/?")) {
        help();
        return 0;
    }

    if(!strcmp(argv[0], "version")) {
        version(stdout);
        return 0;
    }

    usage();
    return 1;
}

adb_commandline解析adb命令，如adb devices,  关于某个命令具体执行过程，后面专门针对某个命令进行解析。

main()中， adbd端代码如下，

   /* If adbd runs inside the emulator this will enable adb tracing via
     * adb-debug qemud service in the emulator. */
    adb_qemu_trace_init();
    if((argc > 1) && (!strcmp(argv[1],"recovery"))) {
        adb_device_banner = "recovery";
        recovery_mode = 1;
    }

    start_device_log();
    D("Handling main()\n");
    return adb_main(0, DEFAULT_ADB_PORT);								

1、adb_qemu_trace_init()：  建立和模拟器中的adb-debug qemud service的连接。

2、if((argc > 1) && (!strcmp(argv[1],"recovery"))) {

adb_device_banner = "recovery";

recovery_mode = 1;

}

启动adbd的时候，可以加参数， 例如，在recovery模式中init.rc文件中的adbd service是带recovery参数的，如果带

recovery参数就设置这两个标志，但目前没有看到哪里用到了这两个标志。

3、start_device_log()： 配置adb daemon的log输出， 前面说了adb client和service端的log输出可以通过ADB_TRACE这个环境

变量来控制，adb daemon端的log可以通过persist.adb.trace_mask控制， start_device_log()中判persist.adb.trace_mask

的值，如果有值，就会将log输出到/data/adb/目录下。

4、adb_main()：如下

int adb_main(int is_daemon, int server_port)
{
#if !ADB_HOST
    int port;
    char value[PROPERTY_VALUE_MAX];

    umask(000);
#endif

    atexit(adb_cleanup);
#ifdef HAVE_WIN32_PROC
    SetConsoleCtrlHandler( ctrlc_handler, TRUE );
#elif defined(HAVE_FORKEXEC)
    // No SIGCHLD. Let the service subproc handle its children.
    signal(SIGPIPE, SIG_IGN);
#endif

    init_transport_registration();

#if ADB_HOST
    HOST = 1;

#ifdef WORKAROUND_BUG6558362
    if(is_daemon) adb_set_affinity();
#endif
    usb_vendors_init();
    usb_init();
    local_init(DEFAULT_ADB_LOCAL_TRANSPORT_PORT);
    adb_auth_init();

    char local_name[30];
    build_local_name(local_name, sizeof(local_name), server_port);
    if(install_listener(local_name, "*smartsocket*", NULL, 0)) {
        exit(1);
    }
#else
    property_get("ro.adb.secure", value, "0");
    auth_enabled = !strcmp(value, "1");
    if (auth_enabled)
        adb_auth_init();

    // Our external storage path may be different than apps, since
    // we aren't able to bind mount after dropping root.
    const char* adb_external_storage = getenv("ADB_EXTERNAL_STORAGE");
    if (NULL != adb_external_storage) {
        setenv("EXTERNAL_STORAGE", adb_external_storage, 1);
    } else {
        D("Warning: ADB_EXTERNAL_STORAGE is not set.  Leaving EXTERNAL_STORAGE"
          " unchanged.\n");
    }

    /* don't listen on a port (default 5037) if running in secure mode */
    /* don't run as root if we are running in secure mode */
    if (should_drop_privileges()) {
        drop_capabilities_bounding_set_if_needed();

        /* add extra groups:
        ** AID_ADB to access the USB driver
        ** AID_LOG to read system logs (adb logcat)
        ** AID_INPUT to diagnose input issues (getevent)
        ** AID_INET to diagnose network issues (netcfg, ping)
        ** AID_GRAPHICS to access the frame buffer
        ** AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
        ** AID_SDCARD_R to allow reading from the SD card
        ** AID_SDCARD_RW to allow writing to the SD card
        ** AID_MOUNT to allow unmounting the SD card before rebooting
        ** AID_NET_BW_STATS to read out qtaguid statistics
        */
        gid_t groups[] = { AID_ADB, AID_LOG, AID_INPUT, AID_INET, AID_GRAPHICS,
                           AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_R, AID_SDCARD_RW,
                           AID_MOUNT, AID_NET_BW_STATS };
        if (setgroups(sizeof(groups)/sizeof(groups[0]), groups) != 0) {
            exit(1);
        }

        /* then switch user and group to "shell" */
        if (setgid(AID_SHELL) != 0) {
            exit(1);
        }
        if (setuid(AID_SHELL) != 0) {
            exit(1);
        }

        D("Local port disabled\n");
    } else {
        char local_name[30];
        build_local_name(local_name, sizeof(local_name), server_port);
        if(install_listener(local_name, "*smartsocket*", NULL, 0)) {
            exit(1);
        }
    }

    int usb = 0;
    if (access(USB_ADB_PATH, F_OK) == 0 || access(USB_FFS_ADB_EP0, F_OK) == 0) {
        // listen on USB
        usb_init();
        usb = 1;
    }

    // If one of these properties is set, also listen on that port
    // If one of the properties isn't set and we couldn't listen on usb,
    // listen on the default port.
    property_get("service.adb.tcp.port", value, "");
    if (!value[0]) {
        property_get("persist.adb.tcp.port", value, "");
    }
    if (sscanf(value, "%d", &port) == 1 && port > 0) {
        printf("using port=%d\n", port);
        // listen on TCP port specified by service.adb.tcp.port property
        local_init(port);
    } else if (!usb) {
        // listen on default port
        local_init(DEFAULT_ADB_LOCAL_TRANSPORT_PORT);
    }

    D("adb_main(): pre init_jdwp()\n");
    init_jdwp();
    D("adb_main(): post init_jdwp()\n");
#endif

    if (is_daemon)
    {
        // inform our parent that we are up and running.
#ifdef HAVE_WIN32_PROC
        DWORD  count;
        WriteFile( GetStdHandle( STD_OUTPUT_HANDLE ), "OK\n", 3, &count, NULL );
#elif defined(HAVE_FORKEXEC)
        fprintf(stderr, "OK\n");
#endif
        start_logging();
    }
    D("Event loop starting\n");

    fdevent_loop();

    usb_cleanup();

    return 0;
}

二、adb_main()函数

上一节中已经附上adb_main()函数代码， 其中，adb service端的代码如下,

    usb_vendors_init();
    usb_init();
    local_init(DEFAULT_ADB_LOCAL_TRANSPORT_PORT);
    adb_auth_init();

    char local_name[30];
    build_local_name(local_name, sizeof(local_name), server_port);
    if(install_listener(local_name, "*smartsocket*", NULL, 0)) {
        exit(1);
    }

     .........

        start_logging();
    }
    D("Event loop starting\n");

    fdevent_loop();

    usb_cleanup();

1、usb_vendors_init()： 每个设备产家都会定义一个vender id来标识自己的usb 设备，ADB service端只会连接已知的vender

id，这个函数的作用就是初始化一个vender id的数组，初始化后这个数组中将包含adb代码中内建的一些产家的id以及HOST

端的android配置文件中定义的id。

2、usb_init(): 创建一个线程，线程处理函数device_poll_thread, 进入一个循环，每隔1s执行一次find_usb_device和

kick_disconnected_devices,find_usb_device搜索所有的usb设备，判断vender id是否在上面初始化的列表中，如果是，则

将该usb设备注册到一个handle_list中。调用register_usb_transport基于这个fd 构造一个atransport类型的对象，再基于

这个atransport对象调用register_transport构造一个tmsg类型的对象。

最后，将这个tmsg对象写到transport_registration_send这个fd,
 将触发相应的socket监控。kick_disconnected_devices

判断adb设备是否还正常，不正常的话从handle_list中支掉。

3、local_init(): 创建一个线程，尝试连接HOST端5555-5585端口，如果连接成功，则返回一个fd, register_socket_transport

基于这个fd 构造一个atransport类型的对象，再基于这个atransport对象调用register_transport构造一个tmsg类型的

对象。最后，将这个tmsg对象写 transport_registration_send这个fd,  将触发相应的socket监控。

4、install_listener():  监听"tcp:5037" ,  adb client与adb service之间通讯用这个端口。

5、start_logging():  将stdin重写向到/dev/null, 将stdout、stderr重定向/tmp/adb.log, 然后输出"adb starting"到

stderr。

6、fdevent_loop():  前面通过fdinstall()注册了几个fde, 这里就通过一个无限循环epoll相应的fd,  有相应的事件则调用

fdinstall时注册的处理函数。

7、usb_cleanup()： usb相关的清理工作，对应linux平台的实现目前为空。

其中，adb daemon端代码如下，

    property_get("ro.adb.secure", value, "0");
    auth_enabled = !strcmp(value, "1");
    if (auth_enabled)
        adb_auth_init();

    // Our external storage path may be different than apps, since
    // we aren't able to bind mount after dropping root.
    const char* adb_external_storage = getenv("ADB_EXTERNAL_STORAGE");
    if (NULL != adb_external_storage) {
        setenv("EXTERNAL_STORAGE", adb_external_storage, 1);
    } else {
        D("Warning: ADB_EXTERNAL_STORAGE is not set.  Leaving EXTERNAL_STORAGE"
          " unchanged.\n");
    }

    /* don't listen on a port (default 5037) if running in secure mode */
    /* don't run as root if we are running in secure mode */
    if (should_drop_privileges()) {
        drop_capabilities_bounding_set_if_needed();

        /* add extra groups:
        ** AID_ADB to access the USB driver
        ** AID_LOG to read system logs (adb logcat)
        ** AID_INPUT to diagnose input issues (getevent)
        ** AID_INET to diagnose network issues (netcfg, ping)
        ** AID_GRAPHICS to access the frame buffer
        ** AID_NET_BT and AID_NET_BT_ADMIN to diagnose bluetooth (hcidump)
        ** AID_SDCARD_R to allow reading from the SD card
        ** AID_SDCARD_RW to allow writing to the SD card
        ** AID_MOUNT to allow unmounting the SD card before rebooting
        ** AID_NET_BW_STATS to read out qtaguid statistics
        */
        gid_t groups[] = { AID_ADB, AID_LOG, AID_INPUT, AID_INET, AID_GRAPHICS,
                           AID_NET_BT, AID_NET_BT_ADMIN, AID_SDCARD_R, AID_SDCARD_RW,
                           AID_MOUNT, AID_NET_BW_STATS };
        if (setgroups(sizeof(groups)/sizeof(groups[0]), groups) != 0) {
            exit(1);
        }

        /* then switch user and group to "shell" */
        if (setgid(AID_SHELL) != 0) {
            exit(1);
        }
        if (setuid(AID_SHELL) != 0) {
            exit(1);
        }

        D("Local port disabled\n");
    } else {
        char local_name[30];
        build_local_name(local_name, sizeof(local_name), server_port);
        if(install_listener(local_name, "*smartsocket*", NULL, 0)) {
            exit(1);
        }
    }

    int usb = 0;
    if (access(USB_ADB_PATH, F_OK) == 0 || access(USB_FFS_ADB_EP0, F_OK) == 0) {
        // listen on USB
        usb_init();
        usb = 1;
    }

    // If one of these properties is set, also listen on that port
    // If one of the properties isn't set and we couldn't listen on usb,
    // listen on the default port.
    property_get("service.adb.tcp.port", value, "");
    if (!value[0]) {
        property_get("persist.adb.tcp.port", value, "");
    }
    if (sscanf(value, "%d", &port) == 1 && port > 0) {
        printf("using port=%d\n", port);
        // listen on TCP port specified by service.adb.tcp.port property
        local_init(port);
    } else if (!usb) {
        // listen on default port
        local_init(DEFAULT_ADB_LOCAL_TRANSPORT_PORT);
    }

    D("adb_main(): pre init_jdwp()\n");
    init_jdwp();
    D("adb_main(): post init_jdwp()\n");

1、local_init():  adb daemon的这个函数与adb service端的有所不同，adb service端的local_init只在adb service初始化

的时候扫描一下5555-5585端口，而adb daemon端的local_init会在线程中运行一个无限循环，不停尝试连接5555端口或者由

service.adb.tcp.port\persist.adb.tcp.port设置的端口，因为作为daemon随时要准备为他人服务。

2、init_jdwp():  jdwp全称为java debug wire protocol, 每dalvik VM都会创建一个jdwp, 可以建立在adb或者tcp基础上，

与DDMS或debugger进行通信， 这个函数就是初始化了监听socket描述符"\0jdwp-control"动作。

adb daemon其它部分的代码与adb service都比较类似，可能参考adb service部分。