android adb源码分析(1)

ADB是Android debug bridge的缩写，它使用PC机可以通过USB或网络与android设备通讯。

adb的源码位于system/core/adb目录下，先来看下编译脚本Android.mk：

# Copyright 2005 The Android Open Source Project
#
# Android.mk for adb
#
LOCAL_PATH:= $(call my-dir)
# adb host tool
# =========================================================
include $(CLEAR_VARS)
# Default to a virtual (sockets) usb interface
USB_SRCS :=
EXTRA_SRCS :=
ifeq ($(HOST_OS),linux)
  USB_SRCS := usb_linux.c
  EXTRA_SRCS := get_my_path_linux.c
  LOCAL_LDLIBS += -lrt -ldl -lpthread
  LOCAL_CFLAGS += -DWORKAROUND_BUG6558362
endif
ifeq ($(HOST_OS),darwin)
  USB_SRCS := usb_osx.c
  EXTRA_SRCS := get_my_path_darwin.c
  LOCAL_LDLIBS += -lpthread -framework CoreFoundation -framework IOKit -framework Carbon
endif
ifeq ($(HOST_OS),freebsd)
  USB_SRCS := usb_libusb.c
  EXTRA_SRCS := get_my_path_freebsd.c
  LOCAL_LDLIBS += -lpthread -lusb
endif
ifeq ($(HOST_OS),windows)
  USB_SRCS := usb_windows.c
  EXTRA_SRCS := get_my_path_windows.c ../libcutils/list.c
  EXTRA_STATIC_LIBS := AdbWinApi
  ifneq ($(strip $(USE_CYGWIN)),)
    # Pure cygwin case
    LOCAL_LDLIBS += -lpthread -lgdi32
    LOCAL_C_INCLUDES += /usr/include/w32api/ddk
  endif
  ifneq ($(strip $(USE_MINGW)),)
    # MinGW under Linux case
    LOCAL_LDLIBS += -lws2_32 -lgdi32
    USE_SYSDEPS_WIN32 := 1
    LOCAL_C_INCLUDES += /usr/i586-mingw32msvc/include/ddk
  endif
  LOCAL_C_INCLUDES += development/host/windows/usb/api/
endif
LOCAL_SRC_FILES := \
	adb.c \
	console.c \
	transport.c \
	transport_local.c \
	transport_usb.c \
	commandline.c \
	adb_client.c \
	adb_auth_host.c \
	sockets.c \
	services.c \
	file_sync_client.c \
	$(EXTRA_SRCS) \
	$(USB_SRCS) \
	usb_vendors.c
LOCAL_C_INCLUDES += external/openssl/include
ifneq ($(USE_SYSDEPS_WIN32),)
  LOCAL_SRC_FILES += sysdeps_win32.c
else
  LOCAL_SRC_FILES += fdevent.c
endif
LOCAL_CFLAGS += -O2 -g -DADB_HOST=1  -Wall -Wno-unused-parameter
LOCAL_CFLAGS += -D_XOPEN_SOURCE -D_GNU_SOURCE
LOCAL_MODULE := adb
LOCAL_MODULE_TAGS := debug
LOCAL_STATIC_LIBRARIES := libzipfile libunz libcrypto_static $(EXTRA_STATIC_LIBS)
ifeq ($(USE_SYSDEPS_WIN32),)
	LOCAL_STATIC_LIBRARIES += libcutils
endif
include $(BUILD_HOST_EXECUTABLE)
$(call dist-for-goals,dist_files sdk,$(LOCAL_BUILT_MODULE))
ifeq ($(HOST_OS),windows)
$(LOCAL_INSTALLED_MODULE): \
    $(HOST_OUT_EXECUTABLES)/AdbWinApi.dll \
    $(HOST_OUT_EXECUTABLES)/AdbWinUsbApi.dll
endif
# adbd device daemon
# =========================================================
include $(CLEAR_VARS)
LOCAL_SRC_FILES := \
	adb.c \
	backup_service.c \
	fdevent.c \
	transport.c \
	transport_local.c \
	transport_usb.c \
	adb_auth_client.c \
	sockets.c \
	services.c \
	file_sync_service.c \
	jdwp_service.c \
	framebuffer_service.c \
	remount_service.c \
	usb_linux_client.c \
	log_service.c
LOCAL_CFLAGS := -O2 -g -DADB_HOST=0 -Wall -Wno-unused-parameter
LOCAL_CFLAGS += -D_XOPEN_SOURCE -D_GNU_SOURCE
ifneq (,$(filter userdebug eng,$(TARGET_BUILD_VARIANT)))
LOCAL_CFLAGS += -DALLOW_ADBD_ROOT=1
endif
LOCAL_MODULE := adbd
LOCAL_FORCE_STATIC_EXECUTABLE := true
LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT_SBIN)
LOCAL_UNSTRIPPED_PATH := $(TARGET_ROOT_OUT_SBIN_UNSTRIPPED)
LOCAL_STATIC_LIBRARIES := liblog libcutils libc libmincrypt
include $(BUILD_EXECUTABLE)
# adb host tool for device-as-host
# =========================================================
ifneq ($(SDK_ONLY),true)
include $(CLEAR_VARS)
LOCAL_LDLIBS := -lrt -ldl -lpthread
LOCAL_SRC_FILES := \
	adb.c \
	console.c \
	transport.c \
	transport_local.c \
	transport_usb.c \
	commandline.c \
	adb_client.c \
	adb_auth_host.c \
	sockets.c \
	services.c \
	file_sync_client.c \
	get_my_path_linux.c \
	usb_linux.c \
	usb_vendors.c \
	fdevent.c
LOCAL_CFLAGS := \
	-O2 \
	-g \
	-DADB_HOST=1 \
	-DADB_HOST_ON_TARGET=1 \
	-Wall \
	-Wno-unused-parameter \
	-D_XOPEN_SOURCE \
	-D_GNU_SOURCE
LOCAL_C_INCLUDES += external/openssl/include
LOCAL_MODULE := adb
LOCAL_STATIC_LIBRARIES := libzipfile libunz libcutils
LOCAL_SHARED_LIBRARIES := libcrypto
include $(BUILD_EXECUTABLE)
endif

可以看到，最终会有3个执行文件被生成，adbd和两个adb程序。adbd是手机终的守护进程；adb一个是windows、linux、darwin或freebsd运行的程序，另一个是目标机上运行的程序。

宏ADB_HOST用于区分是PC端程序还是目标机端的程序。宏ADB_HOST_ON_TARGET用于区分adb程序是否是在目标机上运行。这3个程序使用的是同一份源码，在内部，使用这些宏来区别不同的程序。

程序的入口在adb.c的main()函数：

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
}

先来看adbd程序，此时宏的设置是ADB_HOST=0。上面代码中start_device_log()是log的初始化操作，可以重定向输出的log信息，接着进入adb_main()函数。先来看下它的参数DEFAULT_ADB_PORT：

#if ADB_HOST_ON_TARGET
/* adb and adbd are coexisting on the target, so use 5038 for adb
 * to avoid conflicting with adbd's usage of 5037
 */
#  define DEFAULT_ADB_PORT 5038
#else
#  define DEFAULT_ADB_PORT 5037
#endif

如果是目标机程序，它的值是5038，否则它的值是5037。这里没有定义ADB_HOST_ON_TARGET，所以它是5037。

adb_main()的源代码如下：

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;
    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)) {
        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()) {
        struct __user_cap_header_struct header;
        struct __user_cap_data_struct cap;
        if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) != 0) {
            exit(1);
        }
        /* 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);
        }
        /* set CAP_SYS_BOOT capability, so "adb reboot" will succeed */
        header.version = _LINUX_CAPABILITY_VERSION;
        header.pid = 0;
        cap.effective = cap.permitted = (1 << CAP_SYS_BOOT);
        cap.inheritable = 0;
        capset(&header, &cap);
        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)) {
            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;
}

(1) init_transport_registration()初始化fevent transport_registration_fde；

(2) 判断系统属性ro.adb.secure，目标板没有设置这个宏；

(3) 没有定义环境变量adb_external_storage；

(4) should_drop_privileges()根据android编译环境should_drop_privileges返回不同的值，如果它的值是userdebug或eng，宏ALLOW_ADBD_ROOT的值被定义为1，执行install_listener()，否则不会定义，这种情况下，由于adbd运行在root下，为保证它的安全性，它需要降级运行；

(5) 判断是否存在设备文件USB_ADB_PATH或USB_FFS_ADB_EP0，存在则执行usb_init()；

(6) 读取属性service.adb.tcp.port或persist.adb.tcp.port（目标板均未定义），执行local_init()，它内部会创建adb thread；

(7) 执行init_jdwp()，jdwp是java调试体系中的一种，具体可百度；

(8) 调用fdevent_loop()监听fdevent并处理；

(9) 程序结束。

再来看adb程序的执行：

在main()中调用return adb_commandline(argc - 1, argv + 1)：

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) {
            fprintf(stderr,
                    "adb: Env var ANDROID_ADB_SERVER_PORT must be a positive number. 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 {
                /* 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")) {
        if(argc != 3) return usage();
        if (serial) {
            snprintf(buf, sizeof buf, "host-serial:%s:forward:%s;%s",serial, argv[1], argv[2]);
        } else if (ttype == kTransportUsb) {
            snprintf(buf, sizeof buf, "host-usb:forward:%s;%s", argv[1], argv[2]);
        } else if (ttype == kTransportLocal) {
            snprintf(buf, sizeof buf, "host-local:forward:%s;%s", argv[1], argv[2]);
        } else {
            snprintf(buf, sizeof buf, "host:forward:%s;%s", 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;
}

它的代码有点长，但可以很容易看明白它根据命令的参数执行不同的功能。adb程序可能以服务的方式或命令行客户端的方式运行。

－－－－－－－－－－

以上就是main()函数的执行过程，后续将分析其中的细节内容。

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