Merge "Support NetworkStatsEventLogger" into main

service-t/src/com/android/server/net/NetworkStatsEventLogger.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.net;
+
+import static com.android.internal.annotations.VisibleForTesting.Visibility.PRIVATE;
+
+import android.annotation.IntDef;
+import android.annotation.NonNull;
+import android.util.IndentingPrintWriter;
+import android.util.LocalLog;
+
+import com.android.internal.annotations.VisibleForTesting;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Helper class for NetworkStatsService to log events.
+ *
+ * @hide
+ */
+public class NetworkStatsEventLogger {
+    static final int POLL_REASON_DUMPSYS = 0;
+    static final int POLL_REASON_FORCE_UPDATE = 1;
+    static final int POLL_REASON_GLOBAL_ALERT = 2;
+    static final int POLL_REASON_NETWORK_STATUS_CHANGED = 3;
+    static final int POLL_REASON_OPEN_SESSION = 4;
+    static final int POLL_REASON_PERIODIC = 5;
+    static final int POLL_REASON_RAT_CHANGED = 6;
+    static final int POLL_REASON_REG_CALLBACK = 7;
+    static final int POLL_REASON_REMOVE_UIDS = 8;
+    static final int POLL_REASON_UPSTREAM_CHANGED = 9;
+
+    @Retention(RetentionPolicy.SOURCE)
+    @IntDef(prefix = { "POLL_REASON_" }, value = {
+            POLL_REASON_DUMPSYS,
+            POLL_REASON_FORCE_UPDATE,
+            POLL_REASON_GLOBAL_ALERT,
+            POLL_REASON_NETWORK_STATUS_CHANGED,
+            POLL_REASON_OPEN_SESSION,
+            POLL_REASON_PERIODIC,
+            POLL_REASON_RAT_CHANGED,
+            POLL_REASON_REMOVE_UIDS,
+            POLL_REASON_REG_CALLBACK,
+            POLL_REASON_UPSTREAM_CHANGED
+    })
+    public @interface PollReason {
+    }
+    static final int MAX_POLL_REASON = POLL_REASON_UPSTREAM_CHANGED;
+
+    @VisibleForTesting(visibility = PRIVATE)
+    public static final int MAX_EVENTS_LOGS = 50;
+    private final LocalLog mEventChanges = new LocalLog(MAX_EVENTS_LOGS);
+    private final int[] mPollEventCounts = new int[MAX_POLL_REASON + 1];
+
+    /**
+     * Log a poll event.
+     *
+     * @param flags Flags used when polling. See NetworkStatsService#FLAG_PERSIST_*.
+     * @param event The event of polling to be logged.
+     */
+    public void logPollEvent(int flags, @NonNull PollEvent event) {
+        mEventChanges.log("Poll(flags=" + flags + ", " + event + ")");
+        mPollEventCounts[event.reason]++;
+    }
+
+    /**
+     * Print poll counts per reason into the given stream.
+     */
+    @VisibleForTesting(visibility = PRIVATE)
+    public void dumpPollCountsPerReason(@NonNull IndentingPrintWriter pw) {
+        pw.println("Poll counts per reason:");
+        pw.increaseIndent();
+        for (int i = 0; i <= MAX_POLL_REASON; i++) {
+            pw.println(PollEvent.pollReasonNameOf(i) + ": " + mPollEventCounts[i]);
+        }
+        pw.decreaseIndent();
+        pw.println();
+    }
+
+    /**
+     * Print recent poll events into the given stream.
+     */
+    @VisibleForTesting(visibility = PRIVATE)
+    public void dumpRecentPollEvents(@NonNull IndentingPrintWriter pw) {
+        pw.println("Recent poll events:");
+        pw.increaseIndent();
+        mEventChanges.reverseDump(pw);
+        pw.decreaseIndent();
+        pw.println();
+    }
+
+    /**
+     * Print the object's state into the given stream.
+     */
+    public void dump(@NonNull IndentingPrintWriter pw) {
+        dumpPollCountsPerReason(pw);
+        dumpRecentPollEvents(pw);
+    }
+
+    public static class PollEvent {
+        public final int reason;
+
+        public PollEvent(@PollReason int reason) {
+            if (reason < 0 || reason > MAX_POLL_REASON) {
+                throw new IllegalArgumentException("Unsupported poll reason: " + reason);
+            }
+            this.reason = reason;
+        }
+
+        @Override
+        public String toString() {
+            return "PollEvent{" + "reason=" + pollReasonNameOf(reason) + "}";
+        }
+
+        /**
+         * Get the name of the given reason.
+         *
+         * If the reason does not have a String representation, returns its integer representation.
+         */
+        @NonNull
+        public static String pollReasonNameOf(@PollReason int reason) {
+            switch (reason) {
+                case POLL_REASON_DUMPSYS:                   return "DUMPSYS";
+                case POLL_REASON_FORCE_UPDATE:              return "FORCE_UPDATE";
+                case POLL_REASON_GLOBAL_ALERT:              return "GLOBAL_ALERT";
+                case POLL_REASON_NETWORK_STATUS_CHANGED:    return "NETWORK_STATUS_CHANGED";
+                case POLL_REASON_OPEN_SESSION:              return "OPEN_SESSION";
+                case POLL_REASON_PERIODIC:                  return "PERIODIC";
+                case POLL_REASON_RAT_CHANGED:               return "RAT_CHANGED";
+                case POLL_REASON_REMOVE_UIDS:               return "REMOVE_UIDS";
+                case POLL_REASON_REG_CALLBACK:              return "REG_CALLBACK";
+                case POLL_REASON_UPSTREAM_CHANGED:          return "UPSTREAM_CHANGED";
+                default:                                    return Integer.toString(reason);
+            }
+        }
+    }
+}

service-t/src/com/android/server/net/NetworkStatsService.java

@@ -66,6 +66,17 @@ import static android.text.format.DateUtils.SECOND_IN_MILLIS;
 import static com.android.internal.annotations.VisibleForTesting.Visibility.PRIVATE;
 import static com.android.net.module.util.NetworkCapabilitiesUtils.getDisplayTransport;
 import static com.android.net.module.util.NetworkStatsUtils.LIMIT_GLOBAL_ALERT;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_PERIODIC;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_DUMPSYS;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_FORCE_UPDATE;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_GLOBAL_ALERT;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_NETWORK_STATUS_CHANGED;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_OPEN_SESSION;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_RAT_CHANGED;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_REG_CALLBACK;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_REMOVE_UIDS;
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_UPSTREAM_CHANGED;
+import static com.android.server.net.NetworkStatsEventLogger.PollEvent;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
@@ -281,6 +292,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
     static final String NETSTATS_IMPORT_ATTEMPTS_COUNTER_NAME = "import.attempts";
     static final String NETSTATS_IMPORT_SUCCESSES_COUNTER_NAME = "import.successes";
     static final String NETSTATS_IMPORT_FALLBACKS_COUNTER_NAME = "import.fallbacks";
+    static final String CONFIG_ENABLE_NETWORK_STATS_EVENT_LOGGER =
+            "enable_network_stats_event_logger";
 
     private final Context mContext;
     private final NetworkStatsFactory mStatsFactory;
@@ -441,6 +454,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
      * Map from key {@code OpenSessionKey} to count of opened sessions. This is for recording
      * the caller of open session and it is only for debugging.
      */
+    // TODO: Move to NetworkStatsEventLogger to centralize event logging.
     @GuardedBy("mOpenSessionCallsLock")
     private final HashMap<OpenSessionKey, Integer> mOpenSessionCallsPerCaller = new HashMap<>();
 
@@ -513,20 +527,21 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         public void handleMessage(Message msg) {
             switch (msg.what) {
                 case MSG_PERFORM_POLL: {
-                    performPoll(FLAG_PERSIST_ALL);
+                    performPoll(FLAG_PERSIST_ALL, maybeCreatePollEvent((int) msg.obj));
                     break;
                 }
                 case MSG_NOTIFY_NETWORK_STATUS: {
                     synchronized (mStatsLock) {
                         // If no cached states, ignore.
                         if (mLastNetworkStateSnapshots == null) break;
-                        handleNotifyNetworkStatus(
+                        handleNotifyNetworkStatus(mDefaultNetworks, mLastNetworkStateSnapshots,
-                                mDefaultNetworks, mLastNetworkStateSnapshots, mActiveIface);
+                                mActiveIface, maybeCreatePollEvent((int) msg.obj));
                     }
                     break;
                 }
                 case MSG_PERFORM_POLL_REGISTER_ALERT: {
-                    performPoll(FLAG_PERSIST_NETWORK);
+                    performPoll(FLAG_PERSIST_NETWORK,
+                            maybeCreatePollEvent(POLL_REASON_GLOBAL_ALERT));
                     registerGlobalAlert();
                     break;
                 }
@@ -612,6 +627,13 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         mStatsMapB = mDeps.getStatsMapB();
         mAppUidStatsMap = mDeps.getAppUidStatsMap();
         mIfaceStatsMap = mDeps.getIfaceStatsMap();
+        // To prevent any possible races, the flag is not allowed to change until rebooting.
+        mSupportEventLogger = mDeps.supportEventLogger(mContext);
+        if (mSupportEventLogger) {
+            mEventLogger = new NetworkStatsEventLogger();
+        } else {
+            mEventLogger = null;
+        }
 
         // TODO: Remove bpfNetMaps creation and always start SkDestroyListener
         // Following code is for the experiment to verify the SkDestroyListener refactoring. Based
@@ -840,6 +862,14 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
                 IBpfMap<CookieTagMapKey, CookieTagMapValue> cookieTagMap, Handler handler) {
             return new SkDestroyListener(cookieTagMap, handler, new SharedLog(TAG));
         }
+
+        /**
+         * Get whether event logger feature is supported.
+         */
+        public boolean supportEventLogger(Context ctx) {
+            return DeviceConfigUtils.isTetheringFeatureNotChickenedOut(
+                    ctx, CONFIG_ENABLE_NETWORK_STATS_EVENT_LOGGER);
+        }
     }
 
     /**
@@ -1432,7 +1462,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
                 | NetworkStatsManager.FLAG_POLL_FORCE)) != 0) {
             final long ident = Binder.clearCallingIdentity();
             try {
-                performPoll(FLAG_PERSIST_ALL);
+                performPoll(FLAG_PERSIST_ALL, maybeCreatePollEvent(POLL_REASON_OPEN_SESSION));
             } finally {
                 Binder.restoreCallingIdentity(ident);
             }
@@ -1828,7 +1858,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
 
         final long token = Binder.clearCallingIdentity();
         try {
-            handleNotifyNetworkStatus(defaultNetworks, networkStates, activeIface);
+            handleNotifyNetworkStatus(defaultNetworks, networkStates, activeIface,
+                    maybeCreatePollEvent(POLL_REASON_NETWORK_STATUS_CHANGED));
         } finally {
             Binder.restoreCallingIdentity(token);
         }
@@ -1845,7 +1876,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
 
         final long token = Binder.clearCallingIdentity();
         try {
-            performPoll(FLAG_PERSIST_ALL);
+            // TODO: Log callstack for system server callers.
+            performPoll(FLAG_PERSIST_ALL, maybeCreatePollEvent(POLL_REASON_FORCE_UPDATE));
         } finally {
             Binder.restoreCallingIdentity(token);
         }
@@ -1902,7 +1934,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         }
 
         // Create baseline stats
-        mHandler.sendMessage(mHandler.obtainMessage(MSG_PERFORM_POLL));
+        mHandler.sendMessage(mHandler.obtainMessage(MSG_PERFORM_POLL,
+                POLL_REASON_REG_CALLBACK));
 
         return normalizedRequest;
    }
@@ -1999,7 +2032,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
             new TetheringManager.TetheringEventCallback() {
                 @Override
                 public void onUpstreamChanged(@Nullable Network network) {
-                    performPoll(FLAG_PERSIST_NETWORK);
+                    performPoll(FLAG_PERSIST_NETWORK,
+                            maybeCreatePollEvent(POLL_REASON_UPSTREAM_CHANGED));
                 }
             };
 
@@ -2008,7 +2042,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         public void onReceive(Context context, Intent intent) {
             // on background handler thread, and verified UPDATE_DEVICE_STATS
             // permission above.
-            performPoll(FLAG_PERSIST_ALL);
+            performPoll(FLAG_PERSIST_ALL, maybeCreatePollEvent(POLL_REASON_PERIODIC));
 
             // verify that we're watching global alert
             registerGlobalAlert();
@@ -2072,19 +2106,20 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
     public void handleOnCollapsedRatTypeChanged() {
         // Protect service from frequently updating. Remove pending messages if any.
         mHandler.removeMessages(MSG_NOTIFY_NETWORK_STATUS);
-        mHandler.sendMessageDelayed(
+        mHandler.sendMessageDelayed(mHandler.obtainMessage(MSG_NOTIFY_NETWORK_STATUS,
-                mHandler.obtainMessage(MSG_NOTIFY_NETWORK_STATUS), mSettings.getPollDelay());
+                        POLL_REASON_RAT_CHANGED), mSettings.getPollDelay());
     }
 
     private void handleNotifyNetworkStatus(
             Network[] defaultNetworks,
             NetworkStateSnapshot[] snapshots,
-            String activeIface) {
+            String activeIface,
+            @Nullable PollEvent event) {
         synchronized (mStatsLock) {
             mWakeLock.acquire();
             try {
                 mActiveIface = activeIface;
-                handleNotifyNetworkStatusLocked(defaultNetworks, snapshots);
+                handleNotifyNetworkStatusLocked(defaultNetworks, snapshots, event);
             } finally {
                 mWakeLock.release();
             }
@@ -2098,7 +2133,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
      */
     @GuardedBy("mStatsLock")
     private void handleNotifyNetworkStatusLocked(@NonNull Network[] defaultNetworks,
-            @NonNull NetworkStateSnapshot[] snapshots) {
+            @NonNull NetworkStateSnapshot[] snapshots, @Nullable PollEvent event) {
         if (!mSystemReady) return;
         if (LOGV) Log.v(TAG, "handleNotifyNetworkStatusLocked()");
 
@@ -2108,7 +2143,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
 
         // poll, but only persist network stats to keep codepath fast. UID stats
         // will be persisted during next alarm poll event.
-        performPollLocked(FLAG_PERSIST_NETWORK);
+        performPollLocked(FLAG_PERSIST_NETWORK, event);
 
         // Rebuild active interfaces based on connected networks
         mActiveIfaces.clear();
@@ -2325,12 +2360,12 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         }
     }
 
-    private void performPoll(int flags) {
+    private void performPoll(int flags, @Nullable PollEvent event) {
         synchronized (mStatsLock) {
             mWakeLock.acquire();
 
             try {
-                performPollLocked(flags);
+                performPollLocked(flags, event);
             } finally {
                 mWakeLock.release();
             }
@@ -2342,11 +2377,15 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
      * {@link NetworkStatsHistory}.
      */
     @GuardedBy("mStatsLock")
-    private void performPollLocked(int flags) {
+    private void performPollLocked(int flags, @Nullable PollEvent event) {
         if (!mSystemReady) return;
         if (LOGV) Log.v(TAG, "performPollLocked(flags=0x" + Integer.toHexString(flags) + ")");
         Trace.traceBegin(TRACE_TAG_NETWORK, "performPollLocked");
 
+        if (mSupportEventLogger) {
+            mEventLogger.logPollEvent(flags, event);
+        }
+
         final boolean persistNetwork = (flags & FLAG_PERSIST_NETWORK) != 0;
         final boolean persistUid = (flags & FLAG_PERSIST_UID) != 0;
         final boolean persistForce = (flags & FLAG_PERSIST_FORCE) != 0;
@@ -2546,7 +2585,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         if (LOGV) Log.v(TAG, "removeUidsLocked() for UIDs " + Arrays.toString(uids));
 
         // Perform one last poll before removing
-        performPollLocked(FLAG_PERSIST_ALL);
+        performPollLocked(FLAG_PERSIST_ALL, maybeCreatePollEvent(POLL_REASON_REMOVE_UIDS));
 
         mUidRecorder.removeUidsLocked(uids);
         mUidTagRecorder.removeUidsLocked(uids);
@@ -2629,7 +2668,8 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
             }
 
             if (poll) {
-                performPollLocked(FLAG_PERSIST_ALL | FLAG_PERSIST_FORCE);
+                performPollLocked(FLAG_PERSIST_ALL | FLAG_PERSIST_FORCE,
+                        maybeCreatePollEvent(POLL_REASON_DUMPSYS));
                 pw.println("Forced poll");
                 return;
             }
@@ -2689,6 +2729,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
                     pw.println("(failed to dump platform legacy stats import counters)");
                 }
             }
+            pw.println(CONFIG_ENABLE_NETWORK_STATS_EVENT_LOGGER + ": " + mSupportEventLogger);
 
             pw.decreaseIndent();
 
@@ -2746,6 +2787,10 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
             pw.decreaseIndent();
             pw.println();
 
+            if (mSupportEventLogger) {
+                mEventLogger.dump(pw);
+            }
+
             pw.println("Stats Providers:");
             pw.increaseIndent();
             invokeForAllStatsProviderCallbacks((cb) -> {
@@ -3215,6 +3260,22 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         }
     }
 
+    private final boolean mSupportEventLogger;
+    @GuardedBy("mStatsLock")
+    @Nullable
+    private final NetworkStatsEventLogger mEventLogger;
+
+    /**
+     * Create a PollEvent instance if the feature is enabled.
+     */
+    @Nullable
+    public PollEvent maybeCreatePollEvent(@NetworkStatsEventLogger.PollReason int reason) {
+        if (mSupportEventLogger) {
+            return new PollEvent(reason);
+        }
+        return null;
+    }
+
     private class DropBoxNonMonotonicObserver implements NonMonotonicObserver<String> {
         @Override
         public void foundNonMonotonic(NetworkStats left, int leftIndex, NetworkStats right,

tests/unit/java/com/android/server/net/NetworkStatsEventLoggerTest.kt

@@ -0,0 +1,173 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server.net
+
+import android.util.IndentingPrintWriter
+import com.android.server.net.NetworkStatsEventLogger.MAX_POLL_REASON
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_DUMPSYS
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_FORCE_UPDATE
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_GLOBAL_ALERT
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_NETWORK_STATUS_CHANGED
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_OPEN_SESSION
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_PERIODIC
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_RAT_CHANGED
+import com.android.server.net.NetworkStatsEventLogger.POLL_REASON_REG_CALLBACK
+import com.android.server.net.NetworkStatsEventLogger.PollEvent
+import com.android.server.net.NetworkStatsEventLogger.PollEvent.pollReasonNameOf
+import com.android.testutils.DevSdkIgnoreRunner
+import java.io.StringWriter
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+
+const val TEST_PERSIST_FLAG = 0x101
+
+@RunWith(DevSdkIgnoreRunner::class)
+class NetworkStatsEventLoggerTest {
+    val logger = NetworkStatsEventLogger()
+    val stringWriter = TestStringWriter()
+    val pw = IndentingPrintWriter(stringWriter)
+
+    @Test
+    fun testDump_invalid() {
+        // Verify it won't crash.
+        logger.dump(pw)
+        // Clear output buffer.
+        stringWriter.getOutputAndClear()
+
+        // Verify log invalid event throws. And nothing output in the dump.
+        val invalidReasons = listOf(-1, MAX_POLL_REASON + 1)
+        invalidReasons.forEach {
+            assertFailsWith<IllegalArgumentException> {
+                logger.logPollEvent(TEST_PERSIST_FLAG, PollEvent(it))
+            }
+            logger.dumpRecentPollEvents(pw)
+            val output = stringWriter.getOutputAndClear()
+            assertStringNotContains(output, pollReasonNameOf(it))
+        }
+    }
+
+    @Test
+    fun testDump_valid() {
+        // Choose arbitrary set of reasons for testing.
+        val loggedReasons = listOf(
+            POLL_REASON_GLOBAL_ALERT,
+            POLL_REASON_FORCE_UPDATE,
+            POLL_REASON_DUMPSYS,
+            POLL_REASON_PERIODIC,
+            POLL_REASON_RAT_CHANGED
+        )
+        val nonLoggedReasons = listOf(
+            POLL_REASON_NETWORK_STATUS_CHANGED,
+            POLL_REASON_OPEN_SESSION,
+            POLL_REASON_REG_CALLBACK)
+
+        // Add some valid records.
+        loggedReasons.forEach {
+            logger.logPollEvent(TEST_PERSIST_FLAG, PollEvent(it))
+        }
+
+        // Collect dumps.
+        logger.dumpRecentPollEvents(pw)
+        val outputRecentEvents = stringWriter.getOutputAndClear()
+        logger.dumpPollCountsPerReason(pw)
+        val outputCountsPerReason = stringWriter.getOutputAndClear()
+
+        // Verify the output contains at least necessary information.
+        loggedReasons.forEach {
+            // Verify all events are shown in the recent event dump.
+            val eventString = PollEvent(it).toString()
+            assertStringContains(outputRecentEvents, TEST_PERSIST_FLAG.toString())
+            assertStringContains(eventString, pollReasonNameOf(it))
+            assertStringContains(outputRecentEvents, eventString)
+            // Verify counts are 1 for each reason.
+            assertCountForReason(outputCountsPerReason, it, 1)
+        }
+
+        // Verify the output remains untouched for other reasons.
+        nonLoggedReasons.forEach {
+            assertStringNotContains(outputRecentEvents, PollEvent(it).toString())
+            assertCountForReason(outputCountsPerReason, it, 0)
+        }
+    }
+
+    @Test
+    fun testDump_maxEventLogs() {
+        // Choose arbitrary reason.
+        val reasonToBeTested = POLL_REASON_PERIODIC
+        val repeatCount = NetworkStatsEventLogger.MAX_EVENTS_LOGS * 2
+
+        // Collect baseline.
+        logger.dumpRecentPollEvents(pw)
+        val lineCountBaseLine = getLineCount(stringWriter.getOutputAndClear())
+
+        repeat(repeatCount) {
+            logger.logPollEvent(TEST_PERSIST_FLAG, PollEvent(reasonToBeTested))
+        }
+
+        // Collect dump.
+        logger.dumpRecentPollEvents(pw)
+        val lineCountAfterTest = getLineCount(stringWriter.getOutputAndClear())
+
+        // Verify line count increment is limited.
+        assertEquals(
+            NetworkStatsEventLogger.MAX_EVENTS_LOGS,
+            lineCountAfterTest - lineCountBaseLine
+        )
+
+        // Verify count per reason increased for the testing reason.
+        logger.dumpPollCountsPerReason(pw)
+        val outputCountsPerReason = stringWriter.getOutputAndClear()
+        for (reason in 0..MAX_POLL_REASON) {
+            assertCountForReason(
+                outputCountsPerReason,
+                reason,
+                if (reason == reasonToBeTested) repeatCount else 0
+            )
+        }
+    }
+
+    private fun getLineCount(multilineString: String) = multilineString.lines().size
+
+    private fun assertStringContains(got: String, want: String) {
+        assertTrue(got.contains(want), "Wanted: $want, but got: $got")
+    }
+
+    private fun assertStringNotContains(got: String, unwant: String) {
+        assertFalse(got.contains(unwant), "Unwanted: $unwant, but got: $got")
+    }
+
+    /**
+     * Assert the reason and the expected count are at the same line.
+     */
+    private fun assertCountForReason(dump: String, reason: Int, expectedCount: Int) {
+        // Matches strings like "GLOBAL_ALERT: 50" but not too strict since the format might change.
+        val regex = Regex(pollReasonNameOf(reason) + "[^0-9]+" + expectedCount)
+        assertEquals(
+            1,
+            regex.findAll(dump).count(),
+            "Unexpected output: $dump " + " for reason: " + pollReasonNameOf(reason)
+        )
+    }
+
+    class TestStringWriter : StringWriter() {
+        fun getOutputAndClear() = toString().also { buffer.setLength(0) }
+    }
+}

tests/unit/java/com/android/server/net/NetworkStatsServiceTest.java

@@ -64,6 +64,8 @@ import static android.text.format.DateUtils.HOUR_IN_MILLIS;
 import static android.text.format.DateUtils.MINUTE_IN_MILLIS;
 import static android.text.format.DateUtils.WEEK_IN_MILLIS;
 
+import static com.android.server.net.NetworkStatsEventLogger.POLL_REASON_RAT_CHANGED;
+import static com.android.server.net.NetworkStatsEventLogger.PollEvent.pollReasonNameOf;
 import static com.android.server.net.NetworkStatsService.ACTION_NETWORK_STATS_POLL;
 import static com.android.server.net.NetworkStatsService.NETSTATS_IMPORT_ATTEMPTS_COUNTER_NAME;
 import static com.android.server.net.NetworkStatsService.NETSTATS_IMPORT_FALLBACKS_COUNTER_NAME;
@@ -525,6 +527,11 @@ public class NetworkStatsServiceTest extends NetworkStatsBaseTest {
                     IBpfMap<CookieTagMapKey, CookieTagMapValue> cookieTagMap, Handler handler) {
                 return mSkDestroyListener;
             }
+
+            @Override
+            public boolean supportEventLogger(@NonNull Context cts) {
+                return true;
+            }
         };
     }
 
@@ -2674,4 +2681,14 @@ public class NetworkStatsServiceTest extends NetworkStatsBaseTest {
         doReturn(null).when(mBpfInterfaceMapUpdater).getIfNameByIndex(10 /* index */);
         doTestDumpIfaceStatsMap("unknown");
     }
+
+    // Basic test to ensure event logger dump is called.
+    // Note that tests to ensure detailed correctness is done in the dedicated tests.
+    // See NetworkStatsEventLoggerTest.
+    @Test
+    public void testDumpEventLogger() {
+        setMobileRatTypeAndWaitForIdle(TelephonyManager.NETWORK_TYPE_UMTS);
+        final String dump = getDump();
+        assertDumpContains(dump, pollReasonNameOf(POLL_REASON_RAT_CHANGED));
+    }
 }