Android -- Analysis of NUD detection mechanism of WiFi
During this period, I encountered the problem of sudden disconnection after several WiFi connections. Finally, it was found that it was caused by Android's NUD detection mechanism. The underlying implementation of NUD(Neighbor Unreachable Detection) still relies on the kernel. The Android layer has services to establish communication. When the kernel detects that the current network is unreachable to the surrounding neighbor, it will send a message to the upper layer. The upper layer will process msg, and finally WiFi will transfer to Disconnect STATE, resulting in the disconnection of the network itself, which will affect the user experience, Let users have trouble.
Here we mainly introduce the process of NUD in Android FWK to deepen our understanding of this process, which can facilitate us to solve relevant problems or add some small customization.
When the user clicks the WiFi switch and turns on WiFi, the WiFi Statemachine will enter the ConnectMode to prepare to process the user's connection request:
class ConnectModeState extends State {
@Override
public void enter() {
Log.d(TAG, "entering ConnectModeState: ifaceName = " + mInterfaceName);
mOperationalMode = CONNECT_MODE;
setupClientMode();
if (!mWifiNative.removeAllNetworks(mInterfaceName)) {
loge("Failed to remove networks on entering connect mode");
}
mScanRequestProxy.enableScanningForHiddenNetworks(true);
mWifiInfo.reset();
mWifiInfo.setSupplicantState(SupplicantState.DISCONNECTED);
mWifiInjector.getWakeupController().reset();
mNetworkInfo.setIsAvailable(true);
if (mNetworkAgent != null) mNetworkAgent.sendNetworkInfo(mNetworkInfo);
// initialize network state
setNetworkDetailedState(DetailedState.DISCONNECTED);
// Inform WifiConnectivityManager that Wifi is enabled
mWifiConnectivityManager.setWifiEnabled(true);
// Inform metrics that Wifi is Enabled (but not yet connected)
mWifiMetrics.setWifiState(WifiMetricsProto.WifiLog.WIFI_DISCONNECTED);
// Inform p2p service that wifi is up and ready when applicable
p2pSendMessage(WifiStateMachine.CMD_ENABLE_P2P);
// Inform sar manager that wifi is Enabled
mSarManager.setClientWifiState(WifiManager.WIFI_STATE_ENABLED);
}
......
}ClientMode is the Station mode. setupClientMode() will make some preparations for subsequent network connections:
/**
* Helper method to start other services and get state ready for client mode
*/
private void setupClientMode() {
Log.d(TAG, "setupClientMode() ifacename = " + mInterfaceName);
mWifiStateTracker.updateState(WifiStateTracker.INVALID);
if (mWifiConnectivityManager == null) {
synchronized (mWifiReqCountLock) {
mWifiConnectivityManager =
mWifiInjector.makeWifiConnectivityManager(mWifiInfo,
hasConnectionRequests());
mWifiConnectivityManager.setUntrustedConnectionAllowed(mUntrustedReqCount > 0);
mWifiConnectivityManager.handleScreenStateChanged(mScreenOn);
}
}
mIpClient = mFacade.makeIpClient(mContext, mInterfaceName, new IpClientCallback());
mIpClient.setMulticastFilter(true);
registerForWifiMonitorEvents();
mWifiInjector.getWifiLastResortWatchdog().clearAllFailureCounts();
setSupplicantLogLevel();
// reset state related to supplicant starting
mSupplicantStateTracker.sendMessage(CMD_RESET_SUPPLICANT_STATE);
// Initialize data structures
mLastBssid = null;
mLastNetworkId = WifiConfiguration.INVALID_NETWORK_ID;
mLastSignalLevel = -1;
mWifiInfo.setMacAddress(mWifiNative.getMacAddress(mInterfaceName));
// Attempt to migrate data out of legacy store.
if (!mWifiConfigManager.migrateFromLegacyStore()) {
Log.e(TAG, "Failed to migrate from legacy config store");
}
// TODO: b/79504296 This broadcast has been deprecated and should be removed
sendSupplicantConnectionChangedBroadcast(true);
mWifiNative.setExternalSim(mInterfaceName, true);
setRandomMacOui();
mCountryCode.setReadyForChange(true);
mWifiDiagnostics.startLogging(mVerboseLoggingEnabled);
mIsRunning = true;
updateBatteryWorkSource(null);
/**
* Enable bluetooth coexistence scan mode when bluetooth connection is active.
* When this mode is on, some of the low-level scan parameters used by the
* driver are changed to reduce interference with bluetooth
*/
mWifiNative.setBluetoothCoexistenceScanMode(mInterfaceName, mBluetoothConnectionActive);
// initialize network state
setNetworkDetailedState(DetailedState.DISCONNECTED);
// Disable legacy multicast filtering, which on some chipsets defaults to enabled.
// Legacy IPv6 multicast filtering blocks ICMPv6 router advertisements which breaks IPv6
// provisioning. Legacy IPv4 multicast filtering may be re-enabled later via
// IpClient.Callback.setFallbackMulticastFilter()
mWifiNative.stopFilteringMulticastV4Packets(mInterfaceName);
mWifiNative.stopFilteringMulticastV6Packets(mInterfaceName);
// Set the right suspend mode settings
mWifiNative.setSuspendOptimizations(mInterfaceName, mSuspendOptNeedsDisabled == 0
&& mUserWantsSuspendOpt.get());
mWifiNative.setPowerSave(mInterfaceName, true);
if (mP2pSupported) {
p2pSendMessage(WifiStateMachine.CMD_ENABLE_P2P);
}
// Disable wpa_supplicant from auto reconnecting.
mWifiNative.enableStaAutoReconnect(mInterfaceName, false);
// STA has higher priority over P2P
mWifiNative.setConcurrencyPriority(true);
}The setupClientMode() function contains many contents. Here we are more concerned about two points:
1. WiFi connectivity Manager: it mainly manages WiFi related scanning actions, such as scanning, obtaining scanning results, and autoconnect after scanning. The main logic is in it
2. FrameworkFacade::makeIpClient(): create IpClient through FrameworkFacade. We know that IpClient is related to triggering DHCP, and the registration of our NUD mechanism will be completed through IpClient. See the Callback implementation brought in by it:
class IpClientCallback extends IpClient.Callback {
@Override
public void onPreDhcpAction() {
sendMessage(DhcpClient.CMD_PRE_DHCP_ACTION);
}
@Override
public void onPostDhcpAction() {
sendMessage(DhcpClient.CMD_POST_DHCP_ACTION);
}
@Override
public void onNewDhcpResults(DhcpResults dhcpResults) {
if (dhcpResults != null) {
sendMessage(CMD_IPV4_PROVISIONING_SUCCESS, dhcpResults);
} else {
sendMessage(CMD_IPV4_PROVISIONING_FAILURE);
mWifiInjector.getWifiLastResortWatchdog().noteConnectionFailureAndTriggerIfNeeded(
getTargetSsid(), mTargetRoamBSSID,
WifiLastResortWatchdog.FAILURE_CODE_DHCP);
}
}
@Override
public void onProvisioningSuccess(LinkProperties newLp) {
mWifiMetrics.logStaEvent(StaEvent.TYPE_CMD_IP_CONFIGURATION_SUCCESSFUL);
sendMessage(CMD_UPDATE_LINKPROPERTIES, newLp);
sendMessage(CMD_IP_CONFIGURATION_SUCCESSFUL);
}
@Override
public void onProvisioningFailure(LinkProperties newLp) {
mWifiMetrics.logStaEvent(StaEvent.TYPE_CMD_IP_CONFIGURATION_LOST);
sendMessage(CMD_IP_CONFIGURATION_LOST);
}
@Override
public void onLinkPropertiesChange(LinkProperties newLp) {
sendMessage(CMD_UPDATE_LINKPROPERTIES, newLp);
}
@Override
public void onReachabilityLost(String logMsg) {
mWifiMetrics.logStaEvent(StaEvent.TYPE_CMD_IP_REACHABILITY_LOST);
sendMessage(CMD_IP_REACHABILITY_LOST, logMsg);
}
@Override
public void installPacketFilter(byte[] filter) {
sendMessage(CMD_INSTALL_PACKET_FILTER, filter);
}
@Override
public void startReadPacketFilter() {
sendMessage(CMD_READ_PACKET_FILTER);
}
@Override
public void setFallbackMulticastFilter(boolean enabled) {
sendMessage(CMD_SET_FALLBACK_PACKET_FILTERING, enabled);
}
@Override
public void setNeighborDiscoveryOffload(boolean enabled) {
sendMessage(CMD_CONFIG_ND_OFFLOAD, (enabled ? 1 : 0));
}
}The onReachabilityLost() callback will be called after receiving the kernel notification, and then send the CMD_IP_REACHABILITY_LOST msg to notify WiFi fwk to disconnect WiFi.
Continue to see the construction process of IpClient:
@VisibleForTesting
IpClient(Context context, String ifName, Callback callback, Dependencies deps) {
super(IpClient.class.getSimpleName() + "." + ifName);
Preconditions.checkNotNull(ifName);
Preconditions.checkNotNull(callback);
mTag = getName();
mContext = context;
mInterfaceName = ifName;
mClatInterfaceName = CLAT_PREFIX + ifName;
mCallback = new LoggingCallbackWrapper(callback);
mDependencies = deps;
mShutdownLatch = new CountDownLatch(1);
mNwService = deps.getNMS();
sSmLogs.putIfAbsent(mInterfaceName, new SharedLog(MAX_LOG_RECORDS, mTag));
mLog = sSmLogs.get(mInterfaceName);
sPktLogs.putIfAbsent(mInterfaceName, new LocalLog(MAX_PACKET_RECORDS));
mConnectivityPacketLog = sPktLogs.get(mInterfaceName);
mMsgStateLogger = new MessageHandlingLogger();
// TODO: Consider creating, constructing, and passing in some kind of
// InterfaceController.Dependencies class.
mInterfaceCtrl = new InterfaceController(mInterfaceName, mNwService, deps.getNetd(), mLog);
mNetlinkTracker = new NetlinkTracker(
mInterfaceName,
new NetlinkTracker.Callback() {
@Override
public void update() {
sendMessage(EVENT_NETLINK_LINKPROPERTIES_CHANGED);
}
}) {
@Override
public void interfaceAdded(String iface) {
super.interfaceAdded(iface);
if (mClatInterfaceName.equals(iface)) {
mCallback.setNeighborDiscoveryOffload(false);
} else if (!mInterfaceName.equals(iface)) {
return;
}
final String msg = "interfaceAdded(" + iface +")";
logMsg(msg);
}
@Override
public void interfaceRemoved(String iface) {
super.interfaceRemoved(iface);
// TODO: Also observe mInterfaceName going down and take some
// kind of appropriate action.
if (mClatInterfaceName.equals(iface)) {
// TODO: consider sending a message to the IpClient main
// StateMachine thread, in case "NDO enabled" state becomes
// tied to more things that 464xlat operation.
mCallback.setNeighborDiscoveryOffload(true);
} else if (!mInterfaceName.equals(iface)) {
return;
}
final String msg = "interfaceRemoved(" + iface +")";
logMsg(msg);
}
private void logMsg(String msg) {
Log.d(mTag, msg);
getHandler().post(() -> { mLog.log("OBSERVED " + msg); });
}
};
mLinkProperties = new LinkProperties();
mLinkProperties.setInterfaceName(mInterfaceName);
mProvisioningTimeoutAlarm = new WakeupMessage(mContext, getHandler(),
mTag + ".EVENT_PROVISIONING_TIMEOUT", EVENT_PROVISIONING_TIMEOUT);
mDhcpActionTimeoutAlarm = new WakeupMessage(mContext, getHandler(),
mTag + ".EVENT_DHCPACTION_TIMEOUT", EVENT_DHCPACTION_TIMEOUT);
// Anything the StateMachine may access must have been instantiated
// before this point.
configureAndStartStateMachine();
// Anything that may send messages to the StateMachine must only be
// configured to do so after the StateMachine has started (above).
startStateMachineUpdaters();
}
.......
// Use a wrapper class to log in order to ensure complete and detailed
// logging. This method is lighter weight than annotations/reflection
// and has the following benefits:
//
// - No invoked method can be forgotten.
// Any new method added to IpClient.Callback must be overridden
// here or it will never be called.
//
// - No invoking call site can be forgotten.
// Centralized logging in this way means call sites don't need to
// remember to log, and therefore no call site can be forgotten.
//
// - No variation in log format among call sites.
// Encourages logging of any available arguments, and all call sites
// are necessarily logged identically.
//
// TODO: Find an lighter weight approach.
private class LoggingCallbackWrapper extends Callback {
private static final String PREFIX = "INVOKE ";
private Callback mCallback;
public LoggingCallbackWrapper(Callback callback) {
mCallback = callback;
}
private void log(String msg) {
mLog.log(PREFIX + msg);
}
@Override
public void onPreDhcpAction() {
mCallback.onPreDhcpAction();
log("onPreDhcpAction()");
}
@Override
public void onPostDhcpAction() {
mCallback.onPostDhcpAction();
log("onPostDhcpAction()");
}
@Override
public void onNewDhcpResults(DhcpResults dhcpResults) {
mCallback.onNewDhcpResults(dhcpResults);
log("onNewDhcpResults({" + dhcpResults + "})");
}
@Override
public void onProvisioningSuccess(LinkProperties newLp) {
mCallback.onProvisioningSuccess(newLp);
log("onProvisioningSuccess({" + newLp + "})");
}
@Override
public void onProvisioningFailure(LinkProperties newLp) {
mCallback.onProvisioningFailure(newLp);
log("onProvisioningFailure({" + newLp + "})");
}
@Override
public void onLinkPropertiesChange(LinkProperties newLp) {
mCallback.onLinkPropertiesChange(newLp);
log("onLinkPropertiesChange({" + newLp + "})");
}
@Override
public void onReachabilityLost(String logMsg) {
mCallback.onReachabilityLost(logMsg);
log("onReachabilityLost(" + logMsg + ")");
}
@Override
public void onQuit() {
mCallback.onQuit();
log("onQuit()");
}
@Override
public void installPacketFilter(byte[] filter) {
mCallback.installPacketFilter(filter);
log("installPacketFilter(byte[" + filter.length + "])");
}
@Override
public void startReadPacketFilter() {
mCallback.startReadPacketFilter();
log("startReadPacketFilter()");
}
@Override
public void setFallbackMulticastFilter(boolean enabled) {
mCallback.setFallbackMulticastFilter(enabled);
log("setFallbackMulticastFilter(" + enabled + ")");
}
@Override
public void setNeighborDiscoveryOffload(boolean enable) {
mCallback.setNeighborDiscoveryOffload(enable);
log("setNeighborDiscoveryOffload(" + enable + ")");
}
}IpClient will encapsulate the Callback parameter passed in once, but it is just a simple wrapper, and so is the onReachabilityLost() Callback we are most concerned about.
Here, the related initialization preparations are completed. NUD detection will be meaningful only after the user is connected to the network; After obtaining the IP, it will enter the IpClient::RunningState:
class RunningState extends State {
private ConnectivityPacketTracker mPacketTracker;
private boolean mDhcpActionInFlight;
@Override
public void enter() {
ApfFilter.ApfConfiguration apfConfig = new ApfFilter.ApfConfiguration();
apfConfig.apfCapabilities = mConfiguration.mApfCapabilities;
apfConfig.multicastFilter = mMulticastFiltering;
// Get the Configuration for ApfFilter from Context
apfConfig.ieee802_3Filter =
mContext.getResources().getBoolean(R.bool.config_apfDrop802_3Frames);
apfConfig.ethTypeBlackList =
mContext.getResources().getIntArray(R.array.config_apfEthTypeBlackList);
mApfFilter = ApfFilter.maybeCreate(mContext, apfConfig, mInterfaceParams, mCallback);
// TODO: investigate the effects of any multicast filtering racing/interfering with the
// rest of this IP configuration startup.
if (mApfFilter == null) {
mCallback.setFallbackMulticastFilter(mMulticastFiltering);
}
mPacketTracker = createPacketTracker();
if (mPacketTracker != null) mPacketTracker.start(mConfiguration.mDisplayName);
if (mConfiguration.mEnableIPv6 && !startIPv6()) {
doImmediateProvisioningFailure(IpManagerEvent.ERROR_STARTING_IPV6);
transitionTo(mStoppingState);
return;
}
if (mConfiguration.mEnableIPv4 && !startIPv4()) {
doImmediateProvisioningFailure(IpManagerEvent.ERROR_STARTING_IPV4);
transitionTo(mStoppingState);
return;
}
final InitialConfiguration config = mConfiguration.mInitialConfig;
if ((config != null) && !applyInitialConfig(config)) {
// TODO introduce a new IpManagerEvent constant to distinguish this error case.
doImmediateProvisioningFailure(IpManagerEvent.ERROR_INVALID_PROVISIONING);
transitionTo(mStoppingState);
return;
}
if (mConfiguration.mUsingMultinetworkPolicyTracker) {
mMultinetworkPolicyTracker = new MultinetworkPolicyTracker(
mContext, getHandler(),
() -> { mLog.log("OBSERVED AvoidBadWifi changed"); });
mMultinetworkPolicyTracker.start();
}
if (mConfiguration.mUsingIpReachabilityMonitor && !startIpReachabilityMonitor()) {
doImmediateProvisioningFailure(
IpManagerEvent.ERROR_STARTING_IPREACHABILITYMONITOR);
transitionTo(mStoppingState);
return;
}
}
......
}startIpReachabilityMonitor() will be called to create the IpReachabilityMonitor object, and NUD related operations will be assigned to it for processing:
private boolean startIpReachabilityMonitor() {
try {
mIpReachabilityMonitor = new IpReachabilityMonitor(
mContext,
mInterfaceParams,
getHandler(),
mLog,
new IpReachabilityMonitor.Callback() {
@Override
public void notifyLost(InetAddress ip, String logMsg) {
mCallback.onReachabilityLost(logMsg);
}
},
mMultinetworkPolicyTracker);
} catch (IllegalArgumentException iae) {
// Failed to start IpReachabilityMonitor. Log it and call
// onProvisioningFailure() immediately.
//
// See http://b/31038971.
logError("IpReachabilityMonitor failure: %s", iae);
mIpReachabilityMonitor = null;
}
return (mIpReachabilityMonitor != null);
}When constructing the IpReachabilityMonitor object, an IpReachabilityMonitor is implemented Callback() callback interface, which will call the Callback wrapper of IpClient to notify onReachabilityLost() event.
NUD is to detect the accessibility of surrounding neighbor s, so it is normal to start triggering detection after a WiFi network connection is completed and the connection information is obtained. After WiFi connection, ConnectModeState receives WPA_ Connection completion event notified by supplicant:
case WifiMonitor.SUPPLICANT_STATE_CHANGE_EVENT:
SupplicantState state = handleSupplicantStateChange(message);
// Supplicant can fail to report a NETWORK_DISCONNECTION_EVENT
// when authentication times out after a successful connection,
// we can figure this from the supplicant state. If supplicant
// state is DISCONNECTED, but the mNetworkInfo says we are not
// disconnected, we need to handle a disconnection
if (state == SupplicantState.DISCONNECTED
&& mNetworkInfo.getState() != NetworkInfo.State.DISCONNECTED) {
if (mVerboseLoggingEnabled) {
log("Missed CTRL-EVENT-DISCONNECTED, disconnect");
}
handleNetworkDisconnect();
transitionTo(mDisconnectedState);
}
// If we have COMPLETED a connection to a BSSID, start doing
// DNAv4/DNAv6 -style probing for on-link neighbors of
// interest (e.g. routers); harmless if none are configured.
if (state == SupplicantState.COMPLETED) {
mIpClient.confirmConfiguration();
mWifiScoreReport.noteIpCheck();
}
break;It will call IpClient::confirmConfiguration() to confirm the network configuration, and then open the kernel probe of NUD:
IpClient:
public void IpClient::confirmConfiguration() {
sendMessage(CMD_CONFIRM);
}
IpClient::RunningState {
......
@Override
public boolean processMessage(Message msg) {
switch (msg.what) {
case CMD_STOP:
transitionTo(mStoppingState);
break;
case CMD_START:
logError("ALERT: START received in StartedState. Please fix caller.");
break;
case CMD_CONFIRM:
// TODO: Possibly introduce a second type of confirmation
// that both probes (a) on-link neighbors and (b) does
// a DHCPv4 RENEW. We used to do this on Wi-Fi framework
// roams.
if (mIpReachabilityMonitor != null) {
mIpReachabilityMonitor.probeAll();
}
break;
......
}
}It will be found that all operations are handled by IpReachabilityMonitor. Let's look back at its construction and Implementation:
@VisibleForTesting
IpReachabilityMonitor(InterfaceParams ifParams, Handler h, SharedLog log, Callback callback,
MultinetworkPolicyTracker tracker, Dependencies dependencies) {
if (ifParams == null) throw new IllegalArgumentException("null InterfaceParams");
mInterfaceParams = ifParams;
mLog = log.forSubComponent(TAG);
mCallback = callback;
mMultinetworkPolicyTracker = tracker;
mDependencies = dependencies;
mIpNeighborMonitor = new IpNeighborMonitor(h, mLog,
(NeighborEvent event) -> {
if (mInterfaceParams.index != event.ifindex) return;
if (!mNeighborWatchList.containsKey(event.ip)) return;
final NeighborEvent prev = mNeighborWatchList.put(event.ip, event);
// TODO: Consider what to do with other states that are not within
// NeighborEvent#isValid() (i.e. NUD_NONE, NUD_INCOMPLETE).
if (event.nudState == StructNdMsg.NUD_FAILED) {
mLog.w("ALERT neighbor went from: " + prev + " to: " + event);
handleNeighborLost(event);
}
});
mIpNeighborMonitor.start();
}mCallback stores the Callback object we passed in, which implements the notifyLost() function; IpNeighborMonitor will accept and parse the packet s from the kernel, including which IP S we need to monitor, and receive the result of NUD loss, and call handleneighborloss() to notify WiFi FWK NUD loss.
/**
* IpNeighborMonitor.
*
* Monitors the kernel rtnetlink neighbor notifications and presents to callers
* NeighborEvents describing each event. Callers can provide a consumer instance
* to both filter (e.g. by interface index and IP address) and handle the
* generated NeighborEvents.
*
* @hide
*/
public class IpNeighborMonitor extends PacketReader {
......
public static class NeighborEvent {
final long elapsedMs;
final short msgType;
final int ifindex;
final InetAddress ip;
final short nudState;
final MacAddress macAddr;
public NeighborEvent(long elapsedMs, short msgType, int ifindex, InetAddress ip,
short nudState, MacAddress macAddr) {
this.elapsedMs = elapsedMs;
this.msgType = msgType;
this.ifindex = ifindex;
this.ip = ip;
this.nudState = nudState;
this.macAddr = macAddr;
}
boolean isConnected() {
return (msgType != RTM_DELNEIGH) && StructNdMsg.isNudStateConnected(nudState);
}
boolean isValid() {
return (msgType != RTM_DELNEIGH) && StructNdMsg.isNudStateValid(nudState);
}
@Override
public String toString() {
final StringJoiner j = new StringJoiner(",", "NeighborEvent{", "}");
return j.add("@" + elapsedMs)
.add(stringForNlMsgType(msgType))
.add("if=" + ifindex)
.add(ip.getHostAddress())
.add(StructNdMsg.stringForNudState(nudState))
.add("[" + macAddr + "]")
.toString();
}
}
public interface NeighborEventConsumer {
// Every neighbor event received on the netlink socket is passed in
// here. Subclasses should filter for events of interest.
public void accept(NeighborEvent event);
}
private final SharedLog mLog;
private final NeighborEventConsumer mConsumer;
public IpNeighborMonitor(Handler h, SharedLog log, NeighborEventConsumer cb) {
super(h, NetlinkSocket.DEFAULT_RECV_BUFSIZE);
mLog = log.forSubComponent(TAG);
mConsumer = (cb != null) ? cb : (event) -> { /* discard */ };
}
@Override
protected FileDescriptor createFd() {
FileDescriptor fd = null;
try {
fd = NetlinkSocket.forProto(OsConstants.NETLINK_ROUTE);
Os.bind(fd, (SocketAddress)(new NetlinkSocketAddress(0, OsConstants.RTMGRP_NEIGH)));
Os.connect(fd, (SocketAddress)(new NetlinkSocketAddress(0, 0)));
if (VDBG) {
final NetlinkSocketAddress nlAddr = (NetlinkSocketAddress) Os.getsockname(fd);
Log.d(TAG, "bound to sockaddr_nl{"
+ BitUtils.uint32(nlAddr.getPortId()) + ", "
+ nlAddr.getGroupsMask()
+ "}");
}
} catch (ErrnoException|SocketException e) {
logError("Failed to create rtnetlink socket", e);
IoUtils.closeQuietly(fd);
return null;
}
return fd;
}
......
}IpNeighborMonitor receives the processing from IpReachabilityMonitor. When creating IpNeighborMonitor, a NeighborEventConsumer object created with lambda expression is passed in, which implements the accept function. The main processing is as follows:
1. Resolve the IP address set reported from the kernel that needs to be monitored and save it in the mNeighborWatchList set
2. Judge whether the current event notifies NUD_FAILED, if yes, call handleNeighborLost() to process:
IpNeighborMonitor.start() is mainly used to create a listening socket, wait for the packet to be received, and parse it:
/**
* This class encapsulates the mechanics of registering a file descriptor
* with a thread's Looper and handling read events (and errors).
*
* Subclasses MUST implement createFd() and SHOULD override handlePacket().
* Subclasses can expect a call life-cycle like the following:
*
* [1] start() calls createFd() and (if all goes well) onStart()
*
* [2] yield, waiting for read event or error notification:
*
* [a] readPacket() && handlePacket()
*
* [b] if (no error):
* goto 2
* else:
* goto 3
*
* [3] stop() calls onStop() if not previously stopped
*
* The packet receive buffer is recycled on every read call, so subclasses
* should make any copies they would like inside their handlePacket()
* implementation.
*
* All public methods MUST only be called from the same thread with which
* the Handler constructor argument is associated.
*
* TODO: rename this class to something more correctly descriptive (something
* like [or less horrible than] FdReadEventsHandler?).
*
* @hide
*/
public abstract class PacketReader {
......
public final void start() {
if (onCorrectThread()) {
createAndRegisterFd();
} else {
mHandler.post(() -> {
logError("start() called from off-thread", null);
createAndRegisterFd();
});
}
}
......
private void createAndRegisterFd() {
if (mFd != null) return;
try {
mFd = createFd();
if (mFd != null) {
// Force the socket to be non-blocking.
IoUtils.setBlocking(mFd, false);
}
} catch (Exception e) {
logError("Failed to create socket: ", e);
closeFd(mFd);
mFd = null;
return;
}
......
}
/**
* IpNeighborMonitor.
*
* Monitors the kernel rtnetlink neighbor notifications and presents to callers
* NeighborEvents describing each event. Callers can provide a consumer instance
* to both filter (e.g. by interface index and IP address) and handle the
* generated NeighborEvents.
*
* @hide
*/
public class IpNeighborMonitor extends PacketReader {
......
@Override
protected FileDescriptor createFd() {
FileDescriptor fd = null;
try {
fd = NetlinkSocket.forProto(OsConstants.NETLINK_ROUTE);
Os.bind(fd, (SocketAddress)(new NetlinkSocketAddress(0, OsConstants.RTMGRP_NEIGH)));
Os.connect(fd, (SocketAddress)(new NetlinkSocketAddress(0, 0)));
if (VDBG) {
final NetlinkSocketAddress nlAddr = (NetlinkSocketAddress) Os.getsockname(fd);
Log.d(TAG, "bound to sockaddr_nl{"
+ BitUtils.uint32(nlAddr.getPortId()) + ", "
+ nlAddr.getGroupsMask()
+ "}");
}
} catch (ErrnoException|SocketException e) {
logError("Failed to create rtnetlink socket", e);
IoUtils.closeQuietly(fd);
return null;
}
return fd;
}
......
}
/**
* NetlinkSocket
*
* A small static class to assist with AF_NETLINK socket operations.
*
* @hide
*/
public class NetlinkSocket {
......
public static FileDescriptor forProto(int nlProto) throws ErrnoException {
final FileDescriptor fd = Os.socket(AF_NETLINK, SOCK_DGRAM, nlProto);
Os.setsockoptInt(fd, SOL_SOCKET, SO_RCVBUF, SOCKET_RECV_BUFSIZE);
return fd;
}
......
}The specific process of parsing packets will not be seen here. If necessary, you can analyze the code of IpNeighborMonitor and the parent class PacketReader.
Take another look at the IpReachabilityMonitor::probeAll() call that has not been analyzed previously:
public void probeAll() {
final List<InetAddress> ipProbeList = new ArrayList<>(mNeighborWatchList.keySet());
if (!ipProbeList.isEmpty()) {
// Keep the CPU awake long enough to allow all ARP/ND
// probes a reasonable chance at success. See b/23197666.
//
// The wakelock we use is (by default) refcounted, and this version
// of acquire(timeout) queues a release message to keep acquisitions
// and releases balanced.
mDependencies.acquireWakeLock(getProbeWakeLockDuration());
}
for (InetAddress ip : ipProbeList) {
final int rval = IpNeighborMonitor.startKernelNeighborProbe(mInterfaceParams.index, ip);
mLog.log(String.format("put neighbor %s into NUD_PROBE state (rval=%d)",
ip.getHostAddress(), rval));
logEvent(IpReachabilityEvent.PROBE, rval);
}
mLastProbeTimeMs = SystemClock.elapsedRealtime();
}probeAll() will traverse the IP address of mNeighborWatchList and perform NUD detection on them respectively:
/**
* IpNeighborMonitor.
*
* Monitors the kernel rtnetlink neighbor notifications and presents to callers
* NeighborEvents describing each event. Callers can provide a consumer instance
* to both filter (e.g. by interface index and IP address) and handle the
* generated NeighborEvents.
*
* @hide
*/
public class IpNeighborMonitor extends PacketReader {
......
/**
* Make the kernel perform neighbor reachability detection (IPv4 ARP or IPv6 ND)
* for the given IP address on the specified interface index.
*
* @return 0 if the request was successfully passed to the kernel; otherwise return
* a non-zero error code.
*/
public static int startKernelNeighborProbe(int ifIndex, InetAddress ip) {
final String msgSnippet = "probing ip=" + ip.getHostAddress() + "%" + ifIndex;
if (DBG) { Log.d(TAG, msgSnippet); }
final byte[] msg = RtNetlinkNeighborMessage.newNewNeighborMessage(
1, ip, StructNdMsg.NUD_PROBE, ifIndex, null);
try {
NetlinkSocket.sendOneShotKernelMessage(OsConstants.NETLINK_ROUTE, msg);
} catch (ErrnoException e) {
Log.e(TAG, "Error " + msgSnippet + ": " + e);
return -e.errno;
}
return 0;
}
......
}After requesting the kernel to probe through the Netlink mechanism, all FWK can do is wait for the result; If the kernel detects a NUD failure, after the packet is parsed and encapsulated into an event, the information will be processed by IpNeighborMonitor::NeighborEventConsumer mConsumer:
/**
* IpNeighborMonitor.
*
* Monitors the kernel rtnetlink neighbor notifications and presents to callers
* NeighborEvents describing each event. Callers can provide a consumer instance
* to both filter (e.g. by interface index and IP address) and handle the
* generated NeighborEvents.
*
* @hide
*/
public class IpNeighborMonitor extends PacketReader {
......
private void evaluateRtNetlinkNeighborMessage(
RtNetlinkNeighborMessage neighMsg, long whenMs) {
final short msgType = neighMsg.getHeader().nlmsg_type;
final StructNdMsg ndMsg = neighMsg.getNdHeader();
if (ndMsg == null) {
mLog.e("RtNetlinkNeighborMessage without ND message header!");
return;
}
final int ifindex = ndMsg.ndm_ifindex;
final InetAddress destination = neighMsg.getDestination();
final short nudState =
(msgType == RTM_DELNEIGH)
? StructNdMsg.NUD_NONE
: ndMsg.ndm_state;
final NeighborEvent event = new NeighborEvent(
whenMs, msgType, ifindex, destination, nudState,
getMacAddress(neighMsg.getLinkLayerAddress()));
if (VDBG) {
Log.d(TAG, neighMsg.toString());
}
if (DBG) {
Log.d(TAG, event.toString());
}
mConsumer.accept(event);
}
......
}mConsumer is the object created by lambda expression when IpReachabilityMonitor creates ipneighbor monitor:
mIpNeighborMonitor = new IpNeighborMonitor(h, mLog,
(NeighborEvent event) -> {
if (mInterfaceParams.index != event.ifindex) return;
if (!mNeighborWatchList.containsKey(event.ip)) return;
final NeighborEvent prev = mNeighborWatchList.put(event.ip, event);
// TODO: Consider what to do with other states that are not within
// NeighborEvent#isValid() (i.e. NUD_NONE, NUD_INCOMPLETE).
if (event.nudState == StructNdMsg.NUD_FAILED) {
mLog.w("ALERT neighbor went from: " + prev + " to: " + event);
handleNeighborLost(event);
}
});
mIpNeighborMonitor.start();If the msg of neighbor event is NUD_FAILED indicates that the NUD detection fails. This event needs to be notified to the upper layer:
public class IpReachabilityMonitor {
......
private void handleNeighborLost(NeighborEvent event) {
final LinkProperties whatIfLp = new LinkProperties(mLinkProperties);
InetAddress ip = null;
for (Map.Entry<InetAddress, NeighborEvent> entry : mNeighborWatchList.entrySet()) {
// TODO: Consider using NeighborEvent#isValid() here; it's more
// strict but may interact badly if other entries are somehow in
// NUD_INCOMPLETE (say, during network attach).
if (entry.getValue().nudState != StructNdMsg.NUD_FAILED) continue;
ip = entry.getKey();
for (RouteInfo route : mLinkProperties.getRoutes()) {
if (ip.equals(route.getGateway())) {
whatIfLp.removeRoute(route);
}
}
if (avoidingBadLinks() || !(ip instanceof Inet6Address)) {
// We should do this unconditionally, but alas we cannot: b/31827713.
whatIfLp.removeDnsServer(ip);
}
}
final ProvisioningChange delta = LinkProperties.compareProvisioning(
mLinkProperties, whatIfLp);
if (delta == ProvisioningChange.LOST_PROVISIONING) {
final String logMsg = "FAILURE: LOST_PROVISIONING, " + event;
Log.w(TAG, logMsg);
if (mCallback != null) {
// TODO: remove |ip| when the callback signature no longer has
// an InetAddress argument.
mCallback.notifyLost(ip, logMsg);
}
}
logNudFailed(delta);
}
......
}
Then it will pass linkproperties Compareprovisioning() compares the configuration information of the current two IP S to determine whether the connection is unreachable. If so, it will notify the upper layer through the Callback notifyLost() of the mCallback object. It can be seen from the above that this Callback object has been encapsulated several times. In order to save time, let's look directly at the most original Callback implementation in WiFi Statemachine:
WifiStateMachine:
class IpClientCallback extends IpClient.Callback {
@Override
public void onPreDhcpAction() {
sendMessage(DhcpClient.CMD_PRE_DHCP_ACTION);
}
......
@Override
public void onReachabilityLost(String logMsg) {
mWifiMetrics.logStaEvent(StaEvent.TYPE_CMD_IP_REACHABILITY_LOST);
sendMessage(CMD_IP_REACHABILITY_LOST, logMsg);
}
......
}IpClientCallback::onReachabilityLost() will be called and CMD will be sent_ IP_ REACHABILITY_ Lost MSG, see the processing process of this msg:
class L2ConnectedState extends State {
@Override
public boolean processMessage(Message message) {
......
case CMD_IP_REACHABILITY_LOST:
if (mVerboseLoggingEnabled && message.obj != null) log((String) message.obj);
if (mIpReachabilityDisconnectEnabled) {
handleIpReachabilityLost();
transitionTo(mDisconnectingState);
} else {
logd("CMD_IP_REACHABILITY_LOST but disconnect disabled -- ignore");
}
......
}
......
}L2ConnectedState handles CMD_IP_REACHABILITY_LOST msg, if the miprachabilitydisconnectenabled variable is true, it will actively disconnect WiFi and transfer the state to DisconnectingState to handle the WiFi disconnection process:
public class WifiStateMachine extends StateMachine {
......
private boolean mIpReachabilityDisconnectEnabled = true;
......
// TODO: De-duplicated this and handleIpConfigurationLost().
private void handleIpReachabilityLost() {
mWifiInfo.setInetAddress(null);
mWifiInfo.setMeteredHint(false);
// TODO: Determine whether to call some form of mWifiConfigManager.handleSSIDStateChange().
// Disconnect via supplicant, and let autojoin retry connecting to the network.
mWifiNative.disconnect(mInterfaceName);
}
......
}
After calling WiFi native:: disconnect(), WiFi triggers disconnection, and WiFi Statemachine listens for WPA_ Supply state, and finally transfer to disconnected state, and the whole process ends.
Above, we combed the process of automatic disconnection of WiFi caused by NUD detection. Here, we just need to
private boolean mIpReachabilityDisconnectEnabled = true;
Just change it to false. In this way, the detection results of NUD will be ignored and the WiFi connection will not be disconnected, so as to avoid disturbing users; Of course, you can also add some other processes for processing.