前言：從之前WiFi的連線流程可以知道WiFi最後一步會和服務端進行dhcp以獲取ip地址，那麼WiFi熱點開啟的時候應該也要配置相關dhcp屬性，以供後續WiFi連線的時候ip分配，根據這塊流程繼續梳理。

1. log

01-01 08:01:26.451   840   862 D Tethering: interfaceStatusChanged wlan0, true
01-01 08:01:26.545   840   985 D SoftApManager: startMonitoring
01-01 08:01:26.545   840   985 D SoftApManager: mConnectedToHostapd true
01-01 08:01:26.546   840   985 D WifiStateMachine: setWifiApState: enabled
01-01 08:01:26.548   840   986 D WifiStateMachine:  SoftApState !CMD_GET_SUPPORTED_FEATURES uid=1000 rt=87950/87950 0 0
01-01 08:01:26.548   840   986 E WifiStateMachine: Error! unhandled message{ when=-2ms what=131133 target=com.android.internal.util.StateMachine$SmHandler }
01-01 08:01:26.548   840   986 D WifiStateMachine:  DefaultState !CMD_GET_SUPPORTED_FEATURES uid=1000 rt=87951/87951 0 0
01-01 08:01:26.552   840   863 D Tethering: Tethering wlan0
01-01 08:01:26.583   840   863 D Tethering: sendTetherStateChangedBroadcast avail=[] local_only=[] tether=[wlan0] error=[]
01-01 08:01:26.590   840   986 D WifiStateMachine:  SoftApState !CMD_AP_GET_CONNECTED_STATION_DETAIL uid=1000 rt=87992/87992 0 0
01-01 08:01:26.593   840   986 D WifiStateMachine:  SoftApState !CMD_AP_GET_BLOCK_STATION_DETAIL uid=1000 rt=87995/87995 0 0
01-01 08:01:26.593   840   986 D SoftApManager: Get Soft AP Blocked Station
01-01 08:01:26.601   840   863 D Tethering: Tether Mode requested by name=wlan0 state=TetheredState
01-01 08:01:26.616   639   713 D TetherController: Starting tethering services
01-01 08:01:26.625   639   713 D TetherController: Tethering services running
 

2.流程梳理

先看這一句log

01-01 08:01:26.451   840   862 D Tethering: interfaceStatusChanged wlan0, true

tether百度翻譯是用繩子拴住（牲畜）( tether的過去式和過去分詞 )

這句log雖然有點沒頭沒尾，主要由於對supplicant的hostapd初始化沒有系統學習和梳理，先看framework吧。

2.1 Tethering

    @Override
    public void interfaceStatusChanged(String iface, boolean up) {
        // Never called directly: only called from interfaceLinkStateChanged.
        // See NetlinkHandler.cpp:71.
        if (VDBG) Log.d(TAG, "interfaceStatusChanged " + iface + ", " + up);
        synchronized (mPublicSync) {
            if (up) {
                maybeTrackNewInterfaceLocked(iface);
            } else {
                if (ifaceNameToType(iface) == TETHERING_BLUETOOTH) {
                    stopTrackingInterfaceLocked(iface);
                } else {
                    // Ignore usb0 down after enabling RNDIS.
                    // We will handle disconnect in interfaceRemoved.
                    // Similarly, ignore interface down for WiFi.  We monitor WiFi AP status
                    // through the WifiManager.WIFI_AP_STATE_CHANGED_ACTION intent.
                    if (VDBG) Log.d(TAG, "ignore interface down for " + iface);
                }
            }
        }
    }
 

看下注釋，解釋了這個方法是被NetlinkHandler.cpp進行回撥的，這邊後續梳理，待續。

[email protected]:~/expand/aosp/aosp/system$ vim +71 ./netd/server/NetlinkHandler.cpp

void NetlinkHandler::onEvent(NetlinkEvent *evt) {

接著往下看up為true，呼叫maybeTrackNewInterfaceLocked

    private void maybeTrackNewInterfaceLocked(final String iface) {
        // If we don't care about this type of interface, ignore.
        final int interfaceType = ifaceNameToType(iface);
        if (interfaceType == TETHERING_INVALID) {
            mLog.log(iface + " is not a tetherable iface, ignoring");
            return;
        }
        maybeTrackNewInterfaceLocked(iface, interfaceType);
    }

    private void maybeTrackNewInterfaceLocked(final String iface, int interfaceType) {
        // If we have already started a TISM for this interface, skip.
        if (mTetherStates.containsKey(iface)) {
            mLog.log("active iface (" + iface + ") reported as added, ignoring");
            return;
        }

        mLog.log("adding TetheringInterfaceStateMachine for: " + iface);
        final TetherState tetherState = new TetherState(
                new TetherInterfaceStateMachine(
                    iface, mLooper, interfaceType, mLog, mNMService, mStatsService,
                    makeControlCallback(iface), mDeps));
        mTetherStates.put(iface, tetherState);
        tetherState.stateMachine.start();
    }
 

這邊新起了一個狀態機，應該是用來管理wlan0 各個狀態的變化。

2.2 TetherInterfaceStateMachine

看一下這個狀態機方法，可以看到一系列和網路配置相關的介面。

構造方法如下

    public TetherInterfaceStateMachine(
            String ifaceName, Looper looper, int interfaceType, SharedLog log,
            INetworkManagementService nMService, INetworkStatsService statsService,
            IControlsTethering tetherController,
            TetheringDependencies deps) {
        super(ifaceName, looper);
        mLog = log.forSubComponent(ifaceName);
        mNMService = nMService;
        mNetd = deps.getNetdService();
        mStatsService = statsService;
        mTetherController = tetherController;
        mInterfaceCtrl = new InterfaceController(ifaceName, nMService, mNetd, mLog);
        mIfaceName = ifaceName;
        mInterfaceType = interfaceType;
        mLinkProperties = new LinkProperties();
        mDeps = deps;
        resetLinkProperties();
        mLastError = ConnectivityManager.TETHER_ERROR_NO_ERROR;
        mServingMode = IControlsTethering.STATE_AVAILABLE;

        mInitialState = new InitialState();
        mLocalHotspotState = new LocalHotspotState();
        mTetheredState = new TetheredState();
        mUnavailableState = new UnavailableState();
        addState(mInitialState);
        addState(mLocalHotspotState);
        addState(mTetheredState);
        addState(mUnavailableState);

        setInitialState(mInitialState);
    }

有四個狀態，分別是

• InitialState
• LocalHotspotState
• TetheredState
• UnavailableState

其中InitialState為初始狀態，看下InitialState狀態：

    class InitialState extends State {
        @Override
        public void enter() {
            sendInterfaceState(IControlsTethering.STATE_AVAILABLE);
        }

        @Override
        public boolean processMessage(Message message) {
            logMessage(this, message.what);
            switch (message.what) {
                case CMD_TETHER_REQUESTED:
                    mLastError = ConnectivityManager.TETHER_ERROR_NO_ERROR;
                    switch (message.arg1) {
                        case IControlsTethering.STATE_LOCAL_ONLY:
                            transitionTo(mLocalHotspotState);
                            break;
                        case IControlsTethering.STATE_TETHERED:
                            transitionTo(mTetheredState);
                            break;
                        default:
                            mLog.e("Invalid tethering interface serving state specified.");
                    }
                    break;
                case CMD_INTERFACE_DOWN:
                    transitionTo(mUnavailableState);
                    break;
                case CMD_IPV6_TETHER_UPDATE:
                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
                    break;
                default:
                    return NOT_HANDLED;
            }
            return HANDLED;
        }
    }

看下sendInterfaceState

    private void sendInterfaceState(int newInterfaceState) {
        mServingMode = newInterfaceState;
        mTetherController.updateInterfaceState(
                TetherInterfaceStateMachine.this, newInterfaceState, mLastError);
        sendLinkProperties();
    }

    private void sendLinkProperties() {
        mTetherController.updateLinkProperties(
                TetherInterfaceStateMachine.this, new LinkProperties(mLinkProperties));
    }

其中mTetherController對應於Tethering傳遞進來的如下物件

    private IControlsTethering makeControlCallback(String ifname) {
        return new IControlsTethering() {
            @Override
            public void updateInterfaceState(
                    TetherInterfaceStateMachine who, int state, int lastError) {
                notifyInterfaceStateChange(ifname, who, state, lastError);
            }

            @Override
            public void updateLinkProperties(
                    TetherInterfaceStateMachine who, LinkProperties newLp) {
                notifyLinkPropertiesChanged(ifname, who, newLp);
            }
        };
    }

繼而呼叫

    // TODO: Move into TetherMasterSM.
    private void notifyInterfaceStateChange(
            String iface, TetherInterfaceStateMachine who, int state, int error) {
        synchronized (mPublicSync) {
            final TetherState tetherState = mTetherStates.get(iface);
            if (tetherState != null && tetherState.stateMachine.equals(who)) {
                tetherState.lastState = state;
                tetherState.lastError = error;
            } else {
                if (DBG) Log.d(TAG, "got notification from stale iface " + iface);
            }
        }

        mLog.log(String.format("OBSERVED iface=%s state=%s error=%s", iface, state, error));

        try {
            // Notify that we're tethering (or not) this interface.
            // This is how data saver for instance knows if the user explicitly
            // turned on tethering (thus keeping us from being in data saver mode).
            mPolicyManager.onTetheringChanged(iface, state == IControlsTethering.STATE_TETHERED);
        } catch (RemoteException e) {
            // Not really very much we can do here.
        }

        // If TetherMasterSM is in ErrorState, TetherMasterSM stays there.
        // Thus we give a chance for TetherMasterSM to recover to InitialState
        // by sending CMD_CLEAR_ERROR
        if (error == TETHER_ERROR_MASTER_ERROR) {
            mTetherMasterSM.sendMessage(TetherMasterSM.CMD_CLEAR_ERROR, who);
        }
        int which;
        switch (state) {
            case IControlsTethering.STATE_UNAVAILABLE:
            case IControlsTethering.STATE_AVAILABLE:
                which = TetherMasterSM.EVENT_IFACE_SERVING_STATE_INACTIVE;
                break;
            case IControlsTethering.STATE_TETHERED:
            case IControlsTethering.STATE_LOCAL_ONLY:
                which = TetherMasterSM.EVENT_IFACE_SERVING_STATE_ACTIVE;
                break;
            default:
                Log.wtf(TAG, "Unknown interface state: " + state);
                return;
        }
        mTetherMasterSM.sendMessage(which, state, 0, who);
        sendTetherStateChangedBroadcast();
    }

TetherMastartSM進行處理EVENT_IFACE_SERVING_STATE_INACTIVE訊息

        class InitialState extends State {
            @Override
            public boolean processMessage(Message message) {
                logMessage(this, message.what);
                switch (message.what) {
                    case EVENT_IFACE_SERVING_STATE_ACTIVE:
                        TetherInterfaceStateMachine who = (TetherInterfaceStateMachine) message.obj;
                        if (VDBG) Log.d(TAG, "Tether Mode requested by " + who);
                        handleInterfaceServingStateActive(message.arg1, who);
                        transitionTo(mTetherModeAliveState);
                        break;
                    case EVENT_IFACE_SERVING_STATE_INACTIVE:
                        who = (TetherInterfaceStateMachine) message.obj;
                        if (VDBG) Log.d(TAG, "Tether Mode unrequested by " + who);
                        handleInterfaceServingStateInactive(who);
                        break;
                    case EVENT_IFACE_UPDATE_LINKPROPERTIES:
                        // Silently ignore these for now.
                        break;
                    default:
                        return NOT_HANDLED;
                }
                return HANDLED;
            }
        }

        private void handleInterfaceServingStateInactive(TetherInterfaceStateMachine who) {
            mNotifyList.remove(who);
            mIPv6TetheringCoordinator.removeActiveDownstream(who);
            mOffload.excludeDownstreamInterface(who.interfaceName());
            mForwardedDownstreams.remove(who);

            // If this is a Wi-Fi interface, tell WifiManager of any errors.
            if (who.interfaceType() == TETHERING_WIFI) {
                if (who.lastError() != TETHER_ERROR_NO_ERROR) {
                    getWifiManager().updateInterfaceIpState(
                            who.interfaceName(), IFACE_IP_MODE_CONFIGURATION_ERROR);
                }
            }
        }

這邊只是初始化的。

再看一下這句log:

01-01 08:01:26.546   840   985 D WifiStateMachine: setWifiApState: enabled
01-01 08:01:26.552   840   863 D Tethering: Tethering wlan0

Tethering接收到了wifiap開啟的訊息，進行後續處理。

    private class StateReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context content, Intent intent) {
            final String action = intent.getAction();
            if (action == null) return;

            if (action.equals(UsbManager.ACTION_USB_STATE)) {
                handleUsbAction(intent);
            } else if (action.equals(CONNECTIVITY_ACTION)) {
                handleConnectivityAction(intent);
            } else if (action.equals(WifiManager.WIFI_AP_STATE_CHANGED_ACTION)) {
                handleWifiApAction(intent);
            } else if (action.equals(Intent.ACTION_CONFIGURATION_CHANGED)) {
                mLog.log("OBSERVED configuration changed");
                updateConfiguration();
            }
        }


        private void handleWifiApAction(Intent intent) {
            final int curState = intent.getIntExtra(EXTRA_WIFI_AP_STATE, WIFI_AP_STATE_DISABLED);
            final String ifname = intent.getStringExtra(EXTRA_WIFI_AP_INTERFACE_NAME);
            final int ipmode = intent.getIntExtra(EXTRA_WIFI_AP_MODE, IFACE_IP_MODE_UNSPECIFIED);

            synchronized (Tethering.this.mPublicSync) {
                switch (curState) {
                    case WifiManager.WIFI_AP_STATE_ENABLING:
                        // We can see this state on the way to both enabled and failure states.
                        break;
                    case WifiManager.WIFI_AP_STATE_ENABLED:
                        enableWifiIpServingLocked(ifname, ipmode);
                        break;
                    case WifiManager.WIFI_AP_STATE_DISABLED:
                    case WifiManager.WIFI_AP_STATE_DISABLING:
                    case WifiManager.WIFI_AP_STATE_FAILED:
                    default:
                        disableWifiIpServingLocked(ifname, curState);
                        break;
                }
            }
        }
    }
    

private void enableWifiIpServingLocked(String ifname, int wifiIpMode) {
        // Map wifiIpMode values to IControlsTethering serving states, inferring
        // from mWifiTetherRequested as a final "best guess".
        final int ipServingMode;
        switch (wifiIpMode) {
            case IFACE_IP_MODE_TETHERED:
                ipServingMode = IControlsTethering.STATE_TETHERED;
                break;
            case IFACE_IP_MODE_LOCAL_ONLY:
                ipServingMode = IControlsTethering.STATE_LOCAL_ONLY;
                break;
            default:
                mLog.e("Cannot enable IP serving in unknown WiFi mode: " + wifiIpMode);
                return;
        }

        if (!TextUtils.isEmpty(ifname)) {
            maybeTrackNewInterfaceLocked(ifname, TETHERING_WIFI);
            changeInterfaceState(ifname, ipServingMode);
        } else {
            mLog.e(String.format(
                   "Cannot enable IP serving in mode %s on missing interface name",
                   ipServingMode));
        }
    }
    

private void changeInterfaceState(String ifname, int requestedState) {
        final int result;
        switch (requestedState) {
            case IControlsTethering.STATE_UNAVAILABLE:
            case IControlsTethering.STATE_AVAILABLE:
                result = untether(ifname);
                break;
            case IControlsTethering.STATE_TETHERED:
            case IControlsTethering.STATE_LOCAL_ONLY:
                result = tether(ifname, requestedState);
                break;
            default:
                Log.wtf(TAG, "Unknown interface state: " + requestedState);
                return;
        }
        if (result != TETHER_ERROR_NO_ERROR) {
            Log.e(TAG, "unable start or stop tethering on iface " + ifname);
            return;
        }
    }

    private int tether(String iface, int requestedState) {
        if (DBG) Log.d(TAG, "Tethering " + iface);
        synchronized (mPublicSync) {
            TetherState tetherState = mTetherStates.get(iface);
            if (tetherState == null) {
                Log.e(TAG, "Tried to Tether an unknown iface: " + iface + ", ignoring");
                return TETHER_ERROR_UNKNOWN_IFACE;
            }
            // Ignore the error status of the interface.  If the interface is available,
            // the errors are referring to past tethering attempts anyway.
            if (tetherState.lastState != IControlsTethering.STATE_AVAILABLE) {
                Log.e(TAG, "Tried to Tether an unavailable iface: " + iface + ", ignoring");
                return TETHER_ERROR_UNAVAIL_IFACE;
            }
            // NOTE: If a CMD_TETHER_REQUESTED message is already in the TISM's
            // queue but not yet processed, this will be a no-op and it will not
            // return an error.
            //
            // TODO: reexamine the threading and messaging model.
            tetherState.stateMachine.sendMessage(
                    TetherInterfaceStateMachine.CMD_TETHER_REQUESTED, requestedState);
            return TETHER_ERROR_NO_ERROR;
        }
    }

向TetherInterfaceStateMachine發出訊息，InitialState進行處理

    class InitialState extends State {
        @Override
        public void enter() {
            sendInterfaceState(IControlsTethering.STATE_AVAILABLE);
        }

        @Override
        public boolean processMessage(Message message) {
            logMessage(this, message.what);
            switch (message.what) {
                case CMD_TETHER_REQUESTED:
                    mLastError = ConnectivityManager.TETHER_ERROR_NO_ERROR;
                    switch (message.arg1) {
                        case IControlsTethering.STATE_LOCAL_ONLY:
                            transitionTo(mLocalHotspotState);
                            break;
                        case IControlsTethering.STATE_TETHERED:
                            transitionTo(mTetheredState);
                            break;
                        default:
                            mLog.e("Invalid tethering interface serving state specified.");
                    }
                    break;
                case CMD_INTERFACE_DOWN:
                    transitionTo(mUnavailableState);
                    break;
                case CMD_IPV6_TETHER_UPDATE:
                    updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
                    break;
                default:
                    return NOT_HANDLED;
            }
            return HANDLED;
        }
    }

先假定mode為IControlsTethering.STATE_TETHERED，切換到TetheredState狀態

    // Handling errors in BaseServingState.enter() by transitioning is
    // problematic because transitioning during a multi-state jump yields
    // a Log.wtf(). Ultimately, there should be only one ServingState,
    // and forwarding and NAT rules should be handled by a coordinating
    // functional element outside of TetherInterfaceStateMachine.
    class TetheredState extends BaseServingState {
        @Override
        public void enter() {
            super.enter();
            if (mLastError != ConnectivityManager.TETHER_ERROR_NO_ERROR) {
                transitionTo(mInitialState);
            }

            if (DBG) Log.d(TAG, "Tethered " + mIfaceName);
            sendInterfaceState(IControlsTethering.STATE_TETHERED);
        }

        @Override
        public void exit() {
            cleanupUpstream();
            super.exit();
        }

        private void cleanupUpstream() {
            if (mUpstreamIfaceSet == null) return;

            for (String ifname : mUpstreamIfaceSet.ifnames) cleanupUpstreamInterface(ifname);
            mUpstreamIfaceSet = null;
        }

        private void cleanupUpstreamInterface(String upstreamIface) {
            // Note that we don't care about errors here.
            // Sometimes interfaces are gone before we get
            // to remove their rules, which generates errors.
            // Just do the best we can.
            try {
                // About to tear down NAT; gather remaining statistics.
                mStatsService.forceUpdate();
            } catch (Exception e) {
                if (VDBG) Log.e(TAG, "Exception in forceUpdate: " + e.toString());
            }
            try {
                mNMService.stopInterfaceForwarding(mIfaceName, upstreamIface);
            } catch (Exception e) {
                if (VDBG) Log.e(TAG, "Exception in removeInterfaceForward: " + e.toString());
            }
            try {
                mNMService.disableNat(mIfaceName, upstreamIface);
            } catch (Exception e) {
                if (VDBG) Log.e(TAG, "Exception in disableNat: " + e.toString());
            }
        }

        @Override
        public boolean processMessage(Message message) {
            if (super.processMessage(message)) return true;

            logMessage(this, message.what);
            switch (message.what) {
                case CMD_TETHER_REQUESTED:
                    mLog.e("CMD_TETHER_REQUESTED while already tethering.");
                    break;
                case CMD_TETHER_CONNECTION_CHANGED:
                    final InterfaceSet newUpstreamIfaceSet = (InterfaceSet) message.obj;
                    if (noChangeInUpstreamIfaceSet(newUpstreamIfaceSet)) {
                        if (VDBG) Log.d(TAG, "Connection changed noop - dropping");
                        break;
                    }

                    if (newUpstreamIfaceSet == null) {
                        cleanupUpstream();
                        break;
                    }

                    for (String removed : upstreamInterfacesRemoved(newUpstreamIfaceSet)) {
                        cleanupUpstreamInterface(removed);
                    }

                    final Set<String> added = upstreamInterfacesAdd(newUpstreamIfaceSet);
                    // This makes the call to cleanupUpstream() in the error
                    // path for any interface neatly cleanup all the interfaces.
                    mUpstreamIfaceSet = newUpstreamIfaceSet;

                    for (String ifname : added) {
                        try {
                            mNMService.enableNat(mIfaceName, ifname);
                            mNMService.startInterfaceForwarding(mIfaceName, ifname);
                        } catch (Exception e) {
                            mLog.e("Exception enabling NAT: " + e);
                            cleanupUpstream();
                            mLastError = ConnectivityManager.TETHER_ERROR_ENABLE_NAT_ERROR;
                            transitionTo(mInitialState);
                            return true;
                        }
                    }
                    break;
                default:
                    return false;
            }
            return true;
        }

        private boolean noChangeInUpstreamIfaceSet(InterfaceSet newIfaces) {
            if (mUpstreamIfaceSet == null && newIfaces == null) return true;
            if (mUpstreamIfaceSet != null && newIfaces != null) {
                return mUpstreamIfaceSet.equals(newIfaces);
            }
            return false;
        }

        private Set<String> upstreamInterfacesRemoved(InterfaceSet newIfaces) {
            if (mUpstreamIfaceSet == null) return new HashSet<>();

            final HashSet<String> removed = new HashSet<>(mUpstreamIfaceSet.ifnames);
            removed.removeAll(newIfaces.ifnames);
            return removed;
        }

        private Set<String> upstreamInterfacesAdd(InterfaceSet newIfaces) {
            final HashSet<String> added = new HashSet<>(newIfaces.ifnames);
            if (mUpstreamIfaceSet != null) added.removeAll(mUpstreamIfaceSet.ifnames);
            return added;
        }
    }

先看下enter內，繼而回調Tethering的notifyInterfaceStateChange方法

            case IControlsTethering.STATE_TETHERED:
            case IControlsTethering.STATE_LOCAL_ONLY:
                which = TetherMasterSM.EVENT_IFACE_SERVING_STATE_ACTIVE;
                break;
            default:
                Log.wtf(TAG, "Unknown interface state: " + state);
                return;
        }
        mTetherMasterSM.sendMessage(which, state, 0, who);

傳送EVENT_IFACE_SERVING_STATE_ACTIVE訊息

        class InitialState extends State {
            @Override
            public boolean processMessage(Message message) {
                logMessage(this, message.what);
                switch (message.what) {
                    case EVENT_IFACE_SERVING_STATE_ACTIVE:
                        TetherInterfaceStateMachine who = (TetherInterfaceStateMachine) message.obj;
                        if (VDBG) Log.d(TAG, "Tether Mode requested by " + who);
                        handleInterfaceServingStateActive(message.arg1, who);
                        transitionTo(mTetherModeAliveState);
                        break;

先看下handleInterfaceServingStateActive方法

        private void handleInterfaceServingStateActive(int mode, TetherInterfaceStateMachine who) {
            if (mNotifyList.indexOf(who) < 0) {
                mNotifyList.add(who);
                mIPv6TetheringCoordinator.addActiveDownstream(who, mode);
            }

            if (mode == IControlsTethering.STATE_TETHERED) {
                // No need to notify OffloadController just yet as there are no
                // "offload-able" prefixes to pass along. This will handled
                // when the TISM informs Tethering of its LinkProperties.
                mForwardedDownstreams.add(who);
            } else {
                mOffload.excludeDownstreamInterface(who.interfaceName());
                mForwardedDownstreams.remove(who);
            }

            // If this is a Wi-Fi interface, notify WifiManager of the active serving state.
            if (who.interfaceType() == TETHERING_WIFI) {
                final WifiManager mgr = getWifiManager();
                final String iface = who.interfaceName();
                switch (mode) {
                    case IControlsTethering.STATE_TETHERED:
                        mgr.updateInterfaceIpState(iface, IFACE_IP_MODE_TETHERED);
                        break;
                    case IControlsTethering.STATE_LOCAL_ONLY:
                        mgr.updateInterfaceIpState(iface, IFACE_IP_MODE_LOCAL_ONLY);
                        break;
                    default:
                        Log.wtf(TAG, "Unknown active serving mode: " + mode);
                        break;
                }
            }
        }

繼而呼叫到WifiServiceImpl

    private void updateInterfaceIpStateInternal(String ifaceName, int mode) {
        // update interface IP state related to tethering and hotspot
        synchronized (mLocalOnlyHotspotRequests) {
            // update the mode tracker here - we clear out state below
            Integer previousMode = WifiManager.IFACE_IP_MODE_UNSPECIFIED;
            if (ifaceName != null) {
                previousMode = mIfaceIpModes.put(ifaceName, mode);
            }
            Slog.d(TAG, "updateInterfaceIpState: ifaceName=" + ifaceName + " mode=" + mode
                    + " previous mode= " + previousMode);

            switch (mode) {
                case WifiManager.IFACE_IP_MODE_LOCAL_ONLY:
                    // first make sure we have registered requests..  otherwise clean up
                    if (mLocalOnlyHotspotRequests.isEmpty()) {
                        // we don't have requests...  stop the hotspot
                        stopSoftAp();
                        updateInterfaceIpStateInternal(null, WifiManager.IFACE_IP_MODE_UNSPECIFIED);
                        return;
                    }
                    // LOHS is ready to go!  Call our registered requestors!
                    sendHotspotStartedMessageToAllLOHSRequestInfoEntriesLocked();
                    break;
                case WifiManager.IFACE_IP_MODE_TETHERED:
                    // we have tethered an interface. we don't really act on this now other than if
                    // we have LOHS requests, and this is an issue.  return incompatible mode for
                    // onFailed for the registered requestors since this can result from a race
                    // between a tether request and a hotspot request (tethering wins).
                    sendHotspotFailedMessageToAllLOHSRequestInfoEntriesLocked(
                            LocalOnlyHotspotCallback.ERROR_INCOMPATIBLE_MODE);
                    break;


    /**
     * Helper method to send a HOTSPOT_FAILED message to all registered LocalOnlyHotspotRequest
     * callers and clear the registrations.
     *
     * Callers should already hold the mLocalOnlyHotspotRequests lock.
     */
    private void sendHotspotFailedMessageToAllLOHSRequestInfoEntriesLocked(int arg1) {
        for (LocalOnlyHotspotRequestInfo requestor : mLocalOnlyHotspotRequests.values()) {
            try {
                requestor.sendHotspotFailedMessage(arg1);
                requestor.unlinkDeathRecipient();
            } catch (RemoteException e) {
                // This will be cleaned up by binder death handling
            }
        }

        // Since all callers were notified, now clear the registrations.
        mLocalOnlyHotspotRequests.clear();
    }

依據

01-01 08:01:26.607   840   985 D WifiService: updateInterfaceIpState: ifaceName=wlan0 mode=1 previous mode= null

可以判斷出mode確實為WifiManager.IFACE_IP_MODE_LOCAL_ONLY

之後Tethering切換到TetherModeAliveState

        class TetherModeAliveState extends State {
            boolean mUpstreamWanted = false;
            boolean mTryCell = true;

            @Override
            public void enter() {
                // If turning on master tether settings fails, we have already
                // transitioned to an error state; exit early.
                if (!turnOnMasterTetherSettings()) {
                    return;
                }

                mSimChange.startListening();
                mUpstreamNetworkMonitor.start(mDeps.getDefaultNetworkRequest());

                // TODO: De-duplicate with updateUpstreamWanted() below.
                if (upstreamWanted()) {
                    mUpstreamWanted = true;
                    mOffload.start();
                    chooseUpstreamType(true);
                    mTryCell = false;
                }
            }

先看下turnOnMasterTetherSettings

        protected boolean turnOnMasterTetherSettings() {
            final TetheringConfiguration cfg = mConfig;
            try {
                mNMService.setIpForwardingEnabled(true);
            } catch (Exception e) {
                mLog.e(e);
                transitionTo(mSetIpForwardingEnabledErrorState);
                return false;
            }
            // TODO: Randomize DHCPv4 ranges, especially in hotspot mode.
            try {
                // TODO: Find a more accurate method name (startDHCPv4()?).
                mNMService.startTethering(cfg.dhcpRanges);
            } catch (Exception e) {
                try {
                    mNMService.stopTethering();
                    mNMService.startTethering(cfg.dhcpRanges);
                } catch (Exception ee) {
                    mLog.e(ee);
                    transitionTo(mStartTetheringErrorState);
                    return false;
                }
            }
            mLog.log("SET master tether settings: ON");
            return true;
        }

其中有兩個比較關鍵的方法：

1. mNMService.setIpForwardingEnabled(true);
2. mNMService.startTethering(cfg.dhcpRanges);

其中dhcpRanges預設值為

    // USB is  192.168.42.1 and 255.255.255.0
    // Wifi is 192.168.43.1 and 255.255.255.0
    // BT is limited to max default of 5 connections. 192.168.44.1 to 192.168.48.1
    // with 255.255.255.0
    // P2P is 192.168.49.1 and 255.255.255.0
    private static final String[] DHCP_DEFAULT_RANGE = {
        "192.168.42.2", "192.168.42.254", "192.168.43.2", "192.168.43.254",
        "192.168.44.2", "192.168.44.254", "192.168.45.2", "192.168.45.254",
        "192.168.46.2", "192.168.46.254", "192.168.47.2", "192.168.47.254",
        "192.168.48.2", "192.168.48.254", "192.168.49.2", "192.168.49.254",
    };

呼叫到NetworkManagerService的如下方法：

mConnector.execute本質上是通過socket與netd進行通訊。

    @Override
    public void setIpForwardingEnabled(boolean enable) {
        mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
        try {
            mConnector.execute("ipfwd", enable ? "enable" : "disable", "tethering");
        } catch (NativeDaemonConnectorException e) {
            throw e.rethrowAsParcelableException();
        }
    }


    @Override
    public void startTethering(String[] dhcpRange) {
        mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
        // cmd is "tether start first_start first_stop second_start second_stop ..."
        // an odd number of addrs will fail

        final Command cmd = new Command("tether", "start");
        for (String d : dhcpRange) {
            cmd.appendArg(d);
        }

        try {
            mConnector.execute(cmd);
        } catch (NativeDaemonConnectorException e) {
            throw e.rethrowAsParcelableException();
        }
    }

命令會下發到netd由system/netd/server/CommandListener.cpp進行處理,其中tether命令處理如下。

CommandListener::TetherCmd::TetherCmd() :
                 NetdCommand("tether") {
}

int CommandListener::TetherCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    int rc = 0;

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing argument", false);
        return 0;
    }

    if (!strcmp(argv[1], "stop")) {
        rc = gCtls->tetherCtrl.stopTethering();
    } else if (!strcmp(argv[1], "status")) {
        char *tmp = NULL;

        asprintf(&tmp, "Tethering services %s",
                 (gCtls->tetherCtrl.isTetheringStarted() ? "started" : "stopped"));
        cli->sendMsg(ResponseCode::TetherStatusResult, tmp, false);
        free(tmp);
        return 0;
    } else if (argc == 3) {
        if (!strcmp(argv[1], "interface") && !strcmp(argv[2], "list")) {
            for (const auto &ifname : gCtls->tetherCtrl.getTetheredInterfaceList()) {
                cli->sendMsg(ResponseCode::TetherInterfaceListResult, ifname.c_str(), false);
            }
        } else if (!strcmp(argv[1], "dns") && !strcmp(argv[2], "list")) {
            char netIdStr[UINT32_STRLEN];
            snprintf(netIdStr, sizeof(netIdStr), "%u", gCtls->tetherCtrl.getDnsNetId());
            cli->sendMsg(ResponseCode::TetherDnsFwdNetIdResult, netIdStr, false);

            for (const auto &fwdr : gCtls->tetherCtrl.getDnsForwarders()) {
                cli->sendMsg(ResponseCode::TetherDnsFwdTgtListResult, fwdr.c_str(), false);
            }
        }
    } else {
        /*
         * These commands take a minimum of 4 arguments
         */
        if (argc < 4) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing argument", false);
            return 0;
        }

        if (!strcmp(argv[1], "start")) {
            if (argc % 2 == 1) {
                cli->sendMsg(ResponseCode::CommandSyntaxError, "Bad number of arguments", false);
                return 0;
            }

            const int num_addrs = argc - 2;
            // TODO: consider moving this validation into TetherController.
            struct in_addr tmp_addr;
            for (int arg_index = 2; arg_index < argc; arg_index++) {
                if (!inet_aton(argv[arg_index], &tmp_addr)) {
                    cli->sendMsg(ResponseCode::CommandParameterError, "Invalid address", false);
                    return 0;
                }
            }

            rc = gCtls->tetherCtrl.startTethering(num_addrs, &(argv[2]));
        } else if (!strcmp(argv[1], "interface")) {
            if (!strcmp(argv[2], "add")) {
                rc = gCtls->tetherCtrl.tetherInterface(argv[3]);
            } else if (!strcmp(argv[2], "remove")) {
                rc = gCtls->tetherCtrl.untetherInterface(argv[3]);
            /* else if (!strcmp(argv[2], "list")) handled above */
            } else {
                cli->sendMsg(ResponseCode::CommandParameterError,
                             "Unknown tether interface operation", false);
                return 0;
            }
        } else if (!strcmp(argv[1], "dns")) {
            if (!strcmp(argv[2], "set")) {
                if (argc < 5) {
                    cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing argument", false);
                    return 0;
                }
                unsigned netId = stringToNetId(argv[3]);
                rc = gCtls->tetherCtrl.setDnsForwarders(netId, &argv[4], argc - 4);
            /* else if (!strcmp(argv[2], "list")) handled above */
            } else {
                cli->sendMsg(ResponseCode::CommandParameterError,
                             "Unknown tether interface operation", false);
                return 0;
            }
        } else {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown tether cmd", false);
            return 0;
        }
    }

    if (!rc) {
        cli->sendMsg(ResponseCode::CommandOkay, "Tether operation succeeded", false);
    } else {
        cli->sendMsg(ResponseCode::OperationFailed, "Tether operation failed", true);
    }

    return 0;
}

這邊暫時不繼續追了，重新回到TetherModeAliveState的enter方法

        class TetherModeAliveState extends State {
            boolean mUpstreamWanted = false;
            boolean mTryCell = true;

            @Override
            public void enter() {
                // If turning on master tether settings fails, we have already
                // transitioned to an error state; exit early.
                if (!turnOnMasterTetherSettings()) {
                    return;
                }

                mSimChange.startListening();
                mUpstreamNetworkMonitor.start(mDeps.getDefaultNetworkRequest());

                // TODO: De-duplicate with updateUpstreamWanted() below.
                if (upstreamWanted()) {
                    mUpstreamWanted = true;
                    mOffload.start();
                    chooseUpstreamType(true);
                    mTryCell = false;
                }
            }

看下chooseUpstreamType這個方法

        protected void chooseUpstreamType(boolean tryCell) {
            // We rebuild configuration on ACTION_CONFIGURATION_CHANGED, but we
            // do not currently know how to watch for changes in DUN settings.
            maybeUpdateConfiguration();

            final TetheringConfiguration config = mConfig;
            final NetworkState ns = (config.chooseUpstreamAutomatically)
                    ? mUpstreamNetworkMonitor.getCurrentPreferredUpstream()
                    : mUpstreamNetworkMonitor.selectPreferredUpstreamType(
                            config.preferredUpstreamIfaceTypes);
            if (ns == null) {
                if (tryCell) {
                    mUpstreamNetworkMonitor.registerMobileNetworkRequest();
                    // We think mobile should be coming up; don't set a retry.
                } else {
                    sendMessageDelayed(CMD_RETRY_UPSTREAM, UPSTREAM_SETTLE_TIME_MS);
                }
            }
            mUpstreamNetworkMonitor.setCurrentUpstream((ns != null) ? ns.network : null);
            setUpstreamNetwork(ns);
        }

        protected void setUpstreamNetwork(NetworkState ns) {
            InterfaceSet ifaces = null;
            if (ns != null) {
                // Find the interface with the default IPv4 route. It may be the
                // interface described by linkProperties, or one of the interfaces
                // stacked on top of it.
                mLog.i("Looking for default routes on: " + ns.linkProperties);
                ifaces = TetheringInterfaceUtils.getTetheringInterfaces(ns);
                mLog.i("Found upstream interface(s): " + ifaces);
            }

            if (ifaces != null) {
                setDnsForwarders(ns.network, ns.linkProperties);
            }
            notifyDownstreamsOfNewUpstreamIface(ifaces);
            if (ns != null && pertainsToCurrentUpstream(ns)) {
                // If we already have NetworkState for this network update it immediately.
                handleNewUpstreamNetworkState(ns);
            } else if (mCurrentUpstreamIfaceSet == null) {
                // There are no available upstream networks.
                handleNewUpstreamNetworkState(null);
            }
        }


        protected void setDnsForwarders(final Network network, final LinkProperties lp) {
            // TODO: Set v4 and/or v6 DNS per available connectivity.
            String[] dnsServers = mConfig.defaultIPv4DNS;
            final Collection<InetAddress> dnses = lp.getDnsServers();
            // TODO: Properly support the absence of DNS servers.
            if (dnses != null && !dnses.isEmpty()) {
                // TODO: remove this invocation of NetworkUtils.makeStrings().
                dnsServers = NetworkUtils.makeStrings(dnses);
            }
            try {
                mNMService.setDnsForwarders(network, dnsServers);
                mLog.log(String.format(
                        "SET DNS forwarders: network=%s dnsServers=%s",
                        network, Arrays.toString(dnsServers)));
            } catch (Exception e) {
                // TODO: Investigate how this can fail and what exactly
                // happens if/when such failures occur.
                mLog.e("setting DNS forwarders failed, " + e);
                transitionTo(mSetDnsForwardersErrorState);
            }
        }

設定dns，預設duns伺服器為 

 private final String[] DEFAULT_IPV4_DNS = {"8.8.4.4", "8.8.8.8"};

setDns完了之後會呼叫notifyDownstreamsOfNewUpstreamIface

        protected void notifyDownstreamsOfNewUpstreamIface(InterfaceSet ifaces) {
            mCurrentUpstreamIfaceSet = ifaces;
            for (TetherInterfaceStateMachine sm : mNotifyList) {
                sm.sendMessage(TetherInterfaceStateMachine.CMD_TETHER_CONNECTION_CHANGED, ifaces);
            }
        }

觸使TetherInterfaceStateMachine$TetheredState來處理

                case CMD_TETHER_CONNECTION_CHANGED:
                    final InterfaceSet newUpstreamIfaceSet = (InterfaceSet) message.obj;
                    if (noChangeInUpstreamIfaceSet(newUpstreamIfaceSet)) {
                        if (VDBG) Log.d(TAG, "Connection changed noop - dropping");
                        break;
                    }

                    if (newUpstreamIfaceSet == null) {
                        cleanupUpstream();
                        break;
                    }

                    for (String removed : upstreamInterfacesRemoved(newUpstreamIfaceSet)) {
                        cleanupUpstreamInterface(removed);
                    }

                    final Set<String> added = upstreamInterfacesAdd(newUpstreamIfaceSet);
                    // This makes the call to cleanupUpstream() in the error
                    // path for any interface neatly cleanup all the interfaces.
                    mUpstreamIfaceSet = newUpstreamIfaceSet;

                    for (String ifname : added) {
                        try {
                            mNMService.enableNat(mIfaceName, ifname);
                            mNMService.startInterfaceForwarding(mIfaceName, ifname);
                        } catch (Exception e) {
                            mLog.e("Exception enabling NAT: " + e);
                            cleanupUpstream();
                            mLastError = ConnectivityManager.TETHER_ERROR_ENABLE_NAT_ERROR;
                            transitionTo(mInitialState);
                            return true;
                        }
                    }
                    break;

繼續呼叫NMS的

                            mNMService.enableNat(mIfaceName, ifname);                             mNMService.startInterfaceForwarding(mIfaceName, ifname);

暫時不知道幹嘛的。。。

待續。。。