diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index d8a397d..1fe6c2c 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -304,6 +304,30 @@
     lint: { strict_updatability_linting: true },
 }
 
+java_library {
+    name: "net-utils-device-common-async",
+    srcs: [
+        "device/com/android/net/module/util/async/*.java",
+    ],
+    sdk_version: "module_current",
+    min_sdk_version: "29",
+    visibility: [
+        "//frameworks/libs/net/common/tests:__subpackages__",
+        "//frameworks/libs/net/common/testutils:__subpackages__",
+        "//packages/modules/Connectivity:__subpackages__",
+    ],
+    libs: [
+        "framework-annotations-lib",
+    ],
+    static_libs: [
+    ],
+    apex_available: [
+        "com.android.tethering",
+        "//apex_available:platform",
+    ],
+    lint: { strict_updatability_linting: true },
+}
+
 // Use a filegroup and not a library for telephony sources, as framework-annotations cannot be
 // included either (some annotations would be duplicated on the bootclasspath).
 filegroup {
diff --git a/staticlibs/device/com/android/net/module/util/async/Assertions.java b/staticlibs/device/com/android/net/module/util/async/Assertions.java
new file mode 100644
index 0000000..ce701d0
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/Assertions.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import android.os.Build;
+
+/**
+ * Implements basic assert functions for runtime error-checking.
+ *
+ * @hide
+ */
+public final class Assertions {
+    public static final boolean IS_USER_BUILD = "user".equals(Build.TYPE);
+
+    public static void throwsIfOutOfBounds(int totalLength, int pos, int len) {
+        if (!IS_USER_BUILD && ((totalLength | pos | len) < 0 || pos > totalLength - len)) {
+            throw new ArrayIndexOutOfBoundsException(
+                "length=" + totalLength + "; regionStart=" + pos + "; regionLength=" + len);
+        }
+    }
+
+    public static void throwsIfOutOfBounds(byte[] buffer, int pos, int len) {
+        throwsIfOutOfBounds(buffer != null ? buffer.length : 0, pos, len);
+    }
+
+    private Assertions() {}
+}
diff --git a/staticlibs/device/com/android/net/module/util/async/AsyncFile.java b/staticlibs/device/com/android/net/module/util/async/AsyncFile.java
new file mode 100644
index 0000000..2a3231b
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/AsyncFile.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import java.io.IOException;
+
+/**
+ * Represents an EventManager-managed file with Async IO semantics.
+ *
+ * Implements level-based Asyn IO semantics. This means that:
+ *   - onReadReady() callback would keep happening as long as there's any remaining
+ *     data to read, or the user calls enableReadEvents(false)
+ *   - onWriteReady() callback would keep happening as long as there's remaining space
+ *     to write to, or the user calls enableWriteEvents(false)
+ *
+ * All operations except close() must be called on the EventManager thread.
+ *
+ * @hide
+ */
+public interface AsyncFile {
+    /**
+     * Receives notifications when file readability or writeability changes.
+     * @hide
+     */
+    public interface Listener {
+        /** Invoked after the underlying file has been closed. */
+        void onClosed(AsyncFile file);
+
+        /** Invoked while the file has readable data and read notifications are enabled. */
+        void onReadReady(AsyncFile file);
+
+        /** Invoked while the file has writeable space and write notifications are enabled. */
+        void onWriteReady(AsyncFile file);
+    }
+
+    /** Requests this file to be closed. */
+    void close();
+
+    /** Enables or disables onReadReady() events. */
+    void enableReadEvents(boolean enable);
+
+    /** Enables or disables onWriteReady() events. */
+    void enableWriteEvents(boolean enable);
+
+    /** Returns true if the input stream has reached its end, or has been closed. */
+    boolean reachedEndOfFile();
+
+    /**
+     * Reads available data from the given non-blocking file descriptor.
+     *
+     * Returns zero if there's no data to read at this moment.
+     * Returns -1 if the file has reached its end or the input stream has been closed.
+     * Otherwise returns the number of bytes read.
+     */
+    int read(byte[] buffer, int pos, int len) throws IOException;
+
+    /**
+     * Writes data into the given non-blocking file descriptor.
+     *
+     * Returns zero if there's no buffer space to write to at this moment.
+     * Otherwise returns the number of bytes written.
+     */
+    int write(byte[] buffer, int pos, int len) throws IOException;
+}
diff --git a/staticlibs/device/com/android/net/module/util/async/CircularByteBuffer.java b/staticlibs/device/com/android/net/module/util/async/CircularByteBuffer.java
new file mode 100644
index 0000000..92daa08
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/CircularByteBuffer.java
@@ -0,0 +1,210 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import java.util.Arrays;
+
+/**
+ * Implements a circular read-write byte buffer.
+ *
+ * @hide
+ */
+public final class CircularByteBuffer implements ReadableByteBuffer {
+    private final byte[] mBuffer;
+    private final int mCapacity;
+    private int mReadPos;
+    private int mWritePos;
+    private int mSize;
+
+    public CircularByteBuffer(int capacity) {
+        mCapacity = capacity;
+        mBuffer = new byte[mCapacity];
+    }
+
+    @Override
+    public void clear() {
+        mReadPos = 0;
+        mWritePos = 0;
+        mSize = 0;
+        Arrays.fill(mBuffer, (byte) 0);
+    }
+
+    @Override
+    public int capacity() {
+        return mCapacity;
+    }
+
+    @Override
+    public int size() {
+        return mSize;
+    }
+
+    /** Returns the amount of remaining writeable space in this buffer. */
+    public int freeSize() {
+        return mCapacity - mSize;
+    }
+
+    @Override
+    public byte peek(int offset) {
+        if (offset < 0 || offset >= size()) {
+            throw new IllegalArgumentException("Invalid offset=" + offset + ", size=" + size());
+        }
+
+        return mBuffer[(mReadPos + offset) % mCapacity];
+    }
+
+    @Override
+    public void readBytes(byte[] dst, int dstPos, int dstLen) {
+        if (dst != null) {
+            Assertions.throwsIfOutOfBounds(dst, dstPos, dstLen);
+        }
+        if (dstLen > size()) {
+            throw new IllegalArgumentException("Invalid len=" + dstLen + ", size=" + size());
+        }
+
+        while (dstLen > 0) {
+            final int copyLen = getCopyLen(mReadPos, mWritePos, dstLen);
+            if (dst != null) {
+                System.arraycopy(mBuffer, mReadPos, dst, dstPos, copyLen);
+            }
+            dstPos += copyLen;
+            dstLen -= copyLen;
+            mSize -= copyLen;
+            mReadPos = (mReadPos + copyLen) % mCapacity;
+        }
+
+        if (mSize == 0) {
+            // Reset to the beginning for better contiguous access.
+            mReadPos = 0;
+            mWritePos = 0;
+        }
+    }
+
+    @Override
+    public void peekBytes(int offset, byte[] dst, int dstPos, int dstLen) {
+        Assertions.throwsIfOutOfBounds(dst, dstPos, dstLen);
+        if (offset + dstLen > size()) {
+            throw new IllegalArgumentException("Invalid len=" + dstLen
+                    + ", offset=" + offset + ", size=" + size());
+        }
+
+        int tmpReadPos = (mReadPos + offset) % mCapacity;
+        while (dstLen > 0) {
+            final int copyLen = getCopyLen(tmpReadPos, mWritePos, dstLen);
+            System.arraycopy(mBuffer, tmpReadPos, dst, dstPos, copyLen);
+            dstPos += copyLen;
+            dstLen -= copyLen;
+            tmpReadPos = (tmpReadPos + copyLen) % mCapacity;
+        }
+    }
+
+    @Override
+    public int getDirectReadSize() {
+        if (size() == 0) {
+            return 0;
+        }
+        return (mReadPos < mWritePos ? (mWritePos - mReadPos) : (mCapacity - mReadPos));
+    }
+
+    @Override
+    public int getDirectReadPos() {
+        return mReadPos;
+    }
+
+    @Override
+    public byte[] getDirectReadBuffer() {
+        return mBuffer;
+    }
+
+    @Override
+    public void accountForDirectRead(int len) {
+        if (len < 0 || len > size()) {
+            throw new IllegalArgumentException("Invalid len=" + len + ", size=" + size());
+        }
+
+        mSize -= len;
+        mReadPos = (mReadPos + len) % mCapacity;
+    }
+
+    /** Copies given data to the end of the buffer. */
+    public void writeBytes(byte[] buffer, int pos, int len) {
+        Assertions.throwsIfOutOfBounds(buffer, pos, len);
+        if (len > freeSize()) {
+            throw new IllegalArgumentException("Invalid len=" + len + ", size=" + freeSize());
+        }
+
+        while (len > 0) {
+            final int copyLen = getCopyLen(mWritePos, mReadPos,len);
+            System.arraycopy(buffer, pos, mBuffer, mWritePos, copyLen);
+            pos += copyLen;
+            len -= copyLen;
+            mSize += copyLen;
+            mWritePos = (mWritePos + copyLen) % mCapacity;
+        }
+    }
+
+    private int getCopyLen(int startPos, int endPos, int len) {
+        if (startPos < endPos) {
+            return Math.min(len, endPos - startPos);
+        } else {
+            return Math.min(len, mCapacity - startPos);
+        }
+    }
+
+    /** Returns the amount of contiguous writeable space. */
+    public int getDirectWriteSize() {
+        if (freeSize() == 0) {
+            return 0;  // Return zero in case buffer is full.
+        }
+        return (mWritePos < mReadPos ? (mReadPos - mWritePos) : (mCapacity - mWritePos));
+    }
+
+    /** Returns the position of contiguous writeable space. */
+    public int getDirectWritePos() {
+        return mWritePos;
+    }
+
+    /** Returns the buffer reference for direct write operation. */
+    public byte[] getDirectWriteBuffer() {
+        return mBuffer;
+    }
+
+    /** Must be called after performing a direct write using getDirectWriteBuffer(). */
+    public void accountForDirectWrite(int len) {
+        if (len < 0 || len > freeSize()) {
+            throw new IllegalArgumentException("Invalid len=" + len + ", size=" + freeSize());
+        }
+
+        mSize += len;
+        mWritePos = (mWritePos + len) % mCapacity;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        sb.append("CircularByteBuffer{c=");
+        sb.append(mCapacity);
+        sb.append(",s=");
+        sb.append(mSize);
+        sb.append(",r=");
+        sb.append(mReadPos);
+        sb.append(",w=");
+        sb.append(mWritePos);
+        sb.append('}');
+        return sb.toString();
+    }
+}
diff --git a/staticlibs/device/com/android/net/module/util/async/EventManager.java b/staticlibs/device/com/android/net/module/util/async/EventManager.java
new file mode 100644
index 0000000..4ed4a70
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/EventManager.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import java.io.IOException;
+import java.util.concurrent.Executor;
+
+/**
+ * Manages Async IO files and scheduled alarms, and executes all related callbacks
+ * in its own thread.
+ *
+ * All callbacks of AsyncFile, Alarm and EventManager will execute on EventManager's thread.
+ *
+ * Methods of this interface can be called from any thread.
+ *
+ * @hide
+ */
+public interface EventManager extends Executor {
+    /**
+     * Represents a scheduled alarm, allowing caller to attempt to cancel that alarm
+     * before it executes.
+     *
+     * @hide
+     */
+    public interface Alarm {
+        /** @hide */
+        public interface Listener {
+            void onAlarm(Alarm alarm, long elapsedTimeMs);
+            void onAlarmCancelled(Alarm alarm);
+        }
+
+        /**
+         * Attempts to cancel this alarm. Note that this request is inherently
+         * racy if executed close to the alarm's expiration time.
+         */
+        void cancel();
+    }
+
+    /**
+     * Requests EventManager to manage the given file.
+     *
+     * The file descriptors are not cloned, and EventManager takes ownership of all files passed.
+     *
+     * No event callbacks are enabled by this method.
+     */
+    AsyncFile registerFile(FileHandle fileHandle, AsyncFile.Listener listener) throws IOException;
+
+    /**
+     * Schedules Alarm with the given timeout.
+     *
+     * Timeout of zero can be used for immediate execution.
+     */
+    Alarm scheduleAlarm(long timeout, Alarm.Listener callback);
+
+    /** Schedules Runnable for immediate execution. */
+    @Override
+    void execute(Runnable callback);
+
+    /** Throws a runtime exception if the caller is not executing on this EventManager's thread. */
+    void assertInThread();
+}
diff --git a/staticlibs/device/com/android/net/module/util/async/FileHandle.java b/staticlibs/device/com/android/net/module/util/async/FileHandle.java
new file mode 100644
index 0000000..9f7942d
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/FileHandle.java
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import android.os.ParcelFileDescriptor;
+
+import java.io.Closeable;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * Represents an file descriptor or another way to access a file.
+ *
+ * @hide
+ */
+public final class FileHandle {
+    private final ParcelFileDescriptor mFd;
+    private final Closeable mCloseable;
+    private final InputStream mInputStream;
+    private final OutputStream mOutputStream;
+
+    public static FileHandle fromFileDescriptor(ParcelFileDescriptor fd) {
+        if (fd == null) {
+            throw new NullPointerException();
+        }
+        return new FileHandle(fd, null, null, null);
+    }
+
+    public static FileHandle fromBlockingStream(
+            Closeable closeable, InputStream is, OutputStream os) {
+        if (closeable == null || is == null || os == null) {
+            throw new NullPointerException();
+        }
+        return new FileHandle(null, closeable, is, os);
+    }
+
+    private FileHandle(ParcelFileDescriptor fd, Closeable closeable,
+            InputStream is, OutputStream os) {
+        mFd = fd;
+        mCloseable = closeable;
+        mInputStream = is;
+        mOutputStream = os;
+    }
+
+    ParcelFileDescriptor getFileDescriptor() {
+        return mFd;
+    }
+
+    Closeable getCloseable() {
+        return mCloseable;
+    }
+
+    InputStream getInputStream() {
+        return mInputStream;
+    }
+
+    OutputStream getOutputStream() {
+        return mOutputStream;
+    }
+}
diff --git a/staticlibs/device/com/android/net/module/util/async/ReadableByteBuffer.java b/staticlibs/device/com/android/net/module/util/async/ReadableByteBuffer.java
new file mode 100644
index 0000000..7f82404
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/async/ReadableByteBuffer.java
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+/**
+ * Allows reading from a buffer of bytes. The data can be read and thus removed,
+ * or peeked at without disturbing the buffer state.
+ *
+ * @hide
+ */
+public interface ReadableByteBuffer {
+    /** Returns the size of the buffered data. */
+    int size();
+
+    /**
+     * Returns the maximum amount of the buffered data.
+     *
+     * The caller may use this method in combination with peekBytes()
+     * to estimate when the buffer needs to be emptied using readData().
+     */
+    int capacity();
+
+    /** Clears all buffered data. */
+    void clear();
+
+    /** Returns a single byte at the given offset. */
+    byte peek(int offset);
+
+    /** Copies an array of bytes from the given offset to "dst". */
+    void peekBytes(int offset, byte[] dst, int dstPos, int dstLen);
+
+    /** Reads and removes an array of bytes from the head of the buffer. */
+    void readBytes(byte[] dst, int dstPos, int dstLen);
+
+    /** Returns the amount of contiguous readable data. */
+    int getDirectReadSize();
+
+    /** Returns the position of contiguous readable data. */
+    int getDirectReadPos();
+
+    /** Returns the buffer reference for direct read operation. */
+    byte[] getDirectReadBuffer();
+
+    /** Must be called after performing a direct read using getDirectReadBuffer(). */
+    void accountForDirectRead(int len);
+}
diff --git a/staticlibs/framework/com/android/net/module/util/ConnectivitySettingsUtils.java b/staticlibs/framework/com/android/net/module/util/ConnectivitySettingsUtils.java
index b7eb70b..f4856b3 100644
--- a/staticlibs/framework/com/android/net/module/util/ConnectivitySettingsUtils.java
+++ b/staticlibs/framework/com/android/net/module/util/ConnectivitySettingsUtils.java
@@ -60,6 +60,10 @@
     }
 
     private static int getPrivateDnsModeAsInt(String mode) {
+        // If both PRIVATE_DNS_MODE and PRIVATE_DNS_DEFAULT_MODE are not set, choose
+        // PRIVATE_DNS_MODE_OPPORTUNISTIC as default mode.
+        if (TextUtils.isEmpty(mode))
+            return PRIVATE_DNS_MODE_OPPORTUNISTIC;
         switch (mode) {
             case "off":
                 return PRIVATE_DNS_MODE_OFF;
@@ -68,7 +72,10 @@
             case "opportunistic":
                 return PRIVATE_DNS_MODE_OPPORTUNISTIC;
             default:
-                throw new IllegalArgumentException("Invalid private dns mode: " + mode);
+                // b/260211513: adb shell settings put global private_dns_mode foo
+                // can result in arbitrary strings - treat any unknown value as empty string.
+                // throw new IllegalArgumentException("Invalid private dns mode: " + mode);
+                return PRIVATE_DNS_MODE_OPPORTUNISTIC;
         }
     }
 
@@ -82,9 +89,6 @@
         final ContentResolver cr = context.getContentResolver();
         String mode = Settings.Global.getString(cr, PRIVATE_DNS_MODE);
         if (TextUtils.isEmpty(mode)) mode = Settings.Global.getString(cr, PRIVATE_DNS_DEFAULT_MODE);
-        // If both PRIVATE_DNS_MODE and PRIVATE_DNS_DEFAULT_MODE are not set, choose
-        // PRIVATE_DNS_MODE_OPPORTUNISTIC as default mode.
-        if (TextUtils.isEmpty(mode)) return PRIVATE_DNS_MODE_OPPORTUNISTIC;
         return getPrivateDnsModeAsInt(mode);
     }
 
diff --git a/staticlibs/native/bpf_headers/include/bpf/KernelVersion.h b/staticlibs/native/bpf_headers/include/bpf/KernelVersion.h
index e0e53a9..29a36e6 100644
--- a/staticlibs/native/bpf_headers/include/bpf/KernelVersion.h
+++ b/staticlibs/native/bpf_headers/include/bpf/KernelVersion.h
@@ -16,8 +16,7 @@
 
 #pragma once
 
-#include <stdlib.h>
-#include <string.h>
+#include <stdio.h>
 #include <sys/utsname.h>
 
 namespace android {
diff --git a/staticlibs/native/tcutils/Android.bp b/staticlibs/native/tcutils/Android.bp
index 88a2683..84a32ed 100644
--- a/staticlibs/native/tcutils/Android.bp
+++ b/staticlibs/native/tcutils/Android.bp
@@ -20,7 +20,7 @@
     name: "libtcutils",
     srcs: ["tcutils.cpp"],
     export_include_dirs: ["include"],
-    header_libs: ["bpf_syscall_wrappers"],
+    header_libs: ["bpf_headers"],
     shared_libs: [
         "liblog",
     ],
@@ -53,7 +53,7 @@
         "-Werror",
         "-Wno-error=unused-variable",
     ],
-    header_libs: ["bpf_syscall_wrappers"],
+    header_libs: ["bpf_headers"],
     static_libs: [
         "libgmock",
         "libtcutils",
diff --git a/staticlibs/native/tcutils/kernelversion.h b/staticlibs/native/tcutils/kernelversion.h
deleted file mode 100644
index 9aab31d..0000000
--- a/staticlibs/native/tcutils/kernelversion.h
+++ /dev/null
@@ -1,56 +0,0 @@
-/*
- * Copyright (C) 2022 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.
- */
-
-// -----------------------------------------------------------------------------
-// TODO - This should be replaced with BpfUtils in bpf_headers.
-// Currently, bpf_headers contains a bunch requirements it doesn't actually provide, such as a
-// non-ndk liblog version, and some version of libbase. libtcutils does not have access to either of
-// these, so I think this will have to wait until we figure out a way around this.
-//
-// In the mean time copying verbatim from:
-//   frameworks/libs/net/common/native/bpf_headers
-
-#pragma once
-
-#include <stdio.h>
-#include <sys/utsname.h>
-
-#define KVER(a, b, c) (((a) << 24) + ((b) << 16) + (c))
-
-namespace android {
-
-static inline unsigned uncachedKernelVersion() {
-  struct utsname buf;
-  if (uname(&buf)) return 0;
-
-  unsigned kver_major = 0;
-  unsigned kver_minor = 0;
-  unsigned kver_sub = 0;
-  (void)sscanf(buf.release, "%u.%u.%u", &kver_major, &kver_minor, &kver_sub);
-  return KVER(kver_major, kver_minor, kver_sub);
-}
-
-static unsigned kernelVersion() {
-  static unsigned kver = uncachedKernelVersion();
-  return kver;
-}
-
-static inline bool isAtLeastKernelVersion(unsigned major, unsigned minor,
-                                          unsigned sub) {
-  return kernelVersion() >= KVER(major, minor, sub);
-}
-
-} // namespace android
diff --git a/staticlibs/native/tcutils/tcutils.cpp b/staticlibs/native/tcutils/tcutils.cpp
index 4101885..37a7ec8 100644
--- a/staticlibs/native/tcutils/tcutils.cpp
+++ b/staticlibs/native/tcutils/tcutils.cpp
@@ -19,7 +19,7 @@
 #include "tcutils/tcutils.h"
 
 #include "logging.h"
-#include "kernelversion.h"
+#include "bpf/KernelVersion.h"
 #include "scopeguard.h"
 
 #include <arpa/inet.h>
@@ -504,7 +504,7 @@
     // shipped with Android S, so (for safety) let's limit ourselves to
     // >5.10, ie. 5.11+ as a guarantee we're on Android T+ and thus no
     // longer need this non-upstream compatibility logic
-    static bool is_pre_5_11_kernel = !isAtLeastKernelVersion(5, 11, 0);
+    static bool is_pre_5_11_kernel = !bpf::isAtLeastKernelVersion(5, 11, 0);
     if (is_pre_5_11_kernel)
       return false;
   }
diff --git a/staticlibs/native/tcutils/tests/tcutils_test.cpp b/staticlibs/native/tcutils/tests/tcutils_test.cpp
index 3a89696..53835d7 100644
--- a/staticlibs/native/tcutils/tests/tcutils_test.cpp
+++ b/staticlibs/native/tcutils/tests/tcutils_test.cpp
@@ -18,7 +18,7 @@
 
 #include <gtest/gtest.h>
 
-#include "kernelversion.h"
+#include "bpf/KernelVersion.h"
 #include <tcutils/tcutils.h>
 
 #include <BpfSyscallWrappers.h>
@@ -82,7 +82,7 @@
   // TODO: this should likely be in the tethering module, where using netd.h would be ok
   static constexpr char bpfProgPath[] =
       "/sys/fs/bpf/tethering/prog_offload_schedcls_tether_downstream6_ether";
-  const int errNOENT = isAtLeastKernelVersion(4, 19, 0) ? ENOENT : EINVAL;
+  const int errNOENT = bpf::isAtLeastKernelVersion(4, 19, 0) ? ENOENT : EINVAL;
 
   // static test values
   static constexpr bool ingress = true;
@@ -118,7 +118,7 @@
   ASSERT_LE(3, fd);
   close(fd);
 
-  const int errNOENT = isAtLeastKernelVersion(4, 19, 0) ? ENOENT : EINVAL;
+  const int errNOENT = bpf::isAtLeastKernelVersion(4, 19, 0) ? ENOENT : EINVAL;
 
   // static test values
   static constexpr unsigned rateInBytesPerSec =
diff --git a/staticlibs/tests/unit/Android.bp b/staticlibs/tests/unit/Android.bp
index 21e8c64..6e223bd 100644
--- a/staticlibs/tests/unit/Android.bp
+++ b/staticlibs/tests/unit/Android.bp
@@ -12,14 +12,15 @@
     min_sdk_version: "29",
     defaults: ["framework-connectivity-test-defaults"],
     static_libs: [
-        "net-utils-framework-common",
-        "net-utils-device-common-ip",
         "androidx.test.rules",
         "mockito-target-extended-minus-junit4",
-        "net-utils-device-common",
-        "net-utils-device-common-bpf",
-        "net-tests-utils",
         "netd-client",
+        "net-tests-utils",
+        "net-utils-framework-common",
+        "net-utils-device-common",
+        "net-utils-device-common-async",
+        "net-utils-device-common-bpf",
+        "net-utils-device-common-ip",
     ],
     libs: [
         "android.test.runner",
diff --git a/staticlibs/tests/unit/src/com/android/net/module/util/async/CircularByteBufferTest.java b/staticlibs/tests/unit/src/com/android/net/module/util/async/CircularByteBufferTest.java
new file mode 100644
index 0000000..01abee2
--- /dev/null
+++ b/staticlibs/tests/unit/src/com/android/net/module/util/async/CircularByteBufferTest.java
@@ -0,0 +1,267 @@
+/*
+ * Copyright (C) 2022 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.net.module.util.async;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.fail;
+
+import androidx.test.filters.SmallTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidJUnit4.class)
+@SmallTest
+public class CircularByteBufferTest {
+    @Test
+    public void writeBytes() {
+        final int capacity = 23;
+        CircularByteBuffer buffer = new CircularByteBuffer(capacity);
+        assertEquals(0, buffer.size());
+        assertEquals(0, buffer.getDirectReadSize());
+        assertEquals(capacity, buffer.freeSize());
+        assertEquals(capacity, buffer.getDirectWriteSize());
+
+        final byte[] writeBuffer = new byte[15];
+        buffer.writeBytes(writeBuffer, 0, writeBuffer.length);
+
+        assertEquals(writeBuffer.length, buffer.size());
+        assertEquals(writeBuffer.length, buffer.getDirectReadSize());
+        assertEquals(capacity - writeBuffer.length, buffer.freeSize());
+        assertEquals(capacity - writeBuffer.length, buffer.getDirectWriteSize());
+
+        buffer.clear();
+        assertEquals(0, buffer.size());
+        assertEquals(0, buffer.getDirectReadSize());
+        assertEquals(capacity, buffer.freeSize());
+        assertEquals(capacity, buffer.getDirectWriteSize());
+    }
+
+    @Test
+    public void writeBytes_withRollover() {
+        doTestReadWriteWithRollover(new BufferAccessor(false, false));
+    }
+
+    @Test
+    public void writeBytes_withFullBuffer() {
+        doTestReadWriteWithFullBuffer(new BufferAccessor(false, false));
+    }
+
+    @Test
+    public void directWriteBytes_withRollover() {
+        doTestReadWriteWithRollover(new BufferAccessor(true, true));
+    }
+
+    @Test
+    public void directWriteBytes_withFullBuffer() {
+        doTestReadWriteWithFullBuffer(new BufferAccessor(true, true));
+    }
+
+    private void doTestReadWriteWithFullBuffer(BufferAccessor accessor) {
+        CircularByteBuffer buffer = doTestReadWrite(accessor, 20, 5, 4);
+
+        assertEquals(0, buffer.size());
+        assertEquals(20, buffer.freeSize());
+    }
+
+    private void doTestReadWriteWithRollover(BufferAccessor accessor) {
+        // All buffer sizes are prime numbers to ensure that some read or write
+        // operations will roll over the end of the internal buffer.
+        CircularByteBuffer buffer = doTestReadWrite(accessor, 31, 13, 7);
+
+        assertNotEquals(0, buffer.size());
+    }
+
+    private CircularByteBuffer doTestReadWrite(BufferAccessor accessor,
+            final int capacity, final int writeLen, final int readLen) {
+        CircularByteBuffer buffer = new CircularByteBuffer(capacity);
+
+        final byte[] writeBuffer = new byte[writeLen + 2];
+        final byte[] peekBuffer = new byte[readLen + 2];
+        final byte[] readBuffer = new byte[readLen + 2];
+
+        final int numIterations = 1011;
+        final int maxRemaining = readLen - 1;
+
+        int currentWriteSymbol = 0;
+        int expectedReadSymbol = 0;
+        int expectedSize = 0;
+        int totalWritten = 0;
+        int totalRead = 0;
+
+        for (int i = 0; i < numIterations; i++) {
+            // Fill in with write buffers as much as possible.
+            while (buffer.freeSize() >= writeLen) {
+                currentWriteSymbol = fillTestBytes(writeBuffer, 1, writeLen, currentWriteSymbol);
+                accessor.writeBytes(buffer, writeBuffer, 1, writeLen);
+
+                expectedSize += writeLen;
+                totalWritten += writeLen;
+                assertEquals(expectedSize, buffer.size());
+                assertEquals(capacity - expectedSize, buffer.freeSize());
+            }
+
+            // Keep reading into read buffers while there's still data.
+            while (buffer.size() >= readLen) {
+                peekBuffer[1] = 0;
+                peekBuffer[2] = 0;
+                buffer.peekBytes(2, peekBuffer, 3, readLen - 2);
+                assertEquals(0, peekBuffer[1]);
+                assertEquals(0, peekBuffer[2]);
+
+                peekBuffer[2] = buffer.peek(1);
+
+                accessor.readBytes(buffer, readBuffer, 1, readLen);
+                peekBuffer[1] = readBuffer[1];
+
+                expectedReadSymbol = checkTestBytes(
+                    readBuffer, 1, readLen, expectedReadSymbol, totalRead);
+
+                assertArrayEquals(peekBuffer, readBuffer);
+
+                expectedSize -= readLen;
+                totalRead += readLen;
+                assertEquals(expectedSize, buffer.size());
+                assertEquals(capacity - expectedSize, buffer.freeSize());
+            }
+
+            if (buffer.size() > maxRemaining) {
+                fail("Too much data remaining: " + buffer.size());
+            }
+        }
+
+        final int maxWritten = capacity * numIterations;
+        final int minWritten = maxWritten / 2;
+        if (totalWritten < minWritten || totalWritten > maxWritten
+                || (totalWritten - totalRead) > maxRemaining) {
+            fail("Unexpected counts: read=" + totalRead + ", written=" + totalWritten
+                    + ", minWritten=" + minWritten + ", maxWritten=" + maxWritten);
+        }
+
+        return buffer;
+    }
+
+    @Test
+    public void readBytes_overflow() {
+        CircularByteBuffer buffer = new CircularByteBuffer(23);
+
+        final byte[] dataBuffer = new byte[15];
+        buffer.writeBytes(dataBuffer, 0, dataBuffer.length - 2);
+
+        try {
+            buffer.readBytes(dataBuffer, 0, dataBuffer.length);
+            assertTrue(false);
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+
+        assertEquals(13, buffer.size());
+        assertEquals(10, buffer.freeSize());
+    }
+
+    @Test
+    public void writeBytes_overflow() {
+        CircularByteBuffer buffer = new CircularByteBuffer(23);
+
+        final byte[] dataBuffer = new byte[15];
+        buffer.writeBytes(dataBuffer, 0, dataBuffer.length);
+
+        try {
+            buffer.writeBytes(dataBuffer, 0, dataBuffer.length);
+            assertTrue(false);
+        } catch (IllegalArgumentException e) {
+            // expected
+        }
+
+        assertEquals(15, buffer.size());
+        assertEquals(8, buffer.freeSize());
+    }
+
+    private static int fillTestBytes(byte[] buffer, int pos, int len, int startValue) {
+        for (int i = 0; i < len; i++) {
+            buffer[pos + i] = (byte) (startValue & 0xFF);
+            startValue = (startValue + 1) % 256;
+        }
+        return startValue;
+    }
+
+    private static int checkTestBytes(
+            byte[] buffer, int pos, int len, int startValue, int totalRead) {
+        for (int i = 0; i < len; i++) {
+            byte expectedValue = (byte) (startValue & 0xFF);
+            if (expectedValue != buffer[pos + i]) {
+                fail("Unexpected byte=" + (((int) buffer[pos + i]) & 0xFF)
+                        + ", expected=" + (((int) expectedValue) & 0xFF)
+                        + ", pos=" + (totalRead + i));
+            }
+            startValue = (startValue + 1) % 256;
+        }
+        return startValue;
+    }
+
+    private static final class BufferAccessor {
+        private final boolean mDirectRead;
+        private final boolean mDirectWrite;
+
+        BufferAccessor(boolean directRead, boolean directWrite) {
+            mDirectRead = directRead;
+            mDirectWrite = directWrite;
+        }
+
+        void writeBytes(CircularByteBuffer buffer, byte[] src, int pos, int len) {
+            if (mDirectWrite) {
+                while (len > 0) {
+                    if (buffer.getDirectWriteSize() == 0) {
+                        fail("Direct write size is zero: free=" + buffer.freeSize()
+                                + ", size=" + buffer.size());
+                    }
+                    int copyLen = Math.min(len, buffer.getDirectWriteSize());
+                    System.arraycopy(src, pos, buffer.getDirectWriteBuffer(),
+                        buffer.getDirectWritePos(), copyLen);
+                    buffer.accountForDirectWrite(copyLen);
+                    len -= copyLen;
+                    pos += copyLen;
+                }
+            } else {
+                buffer.writeBytes(src, pos, len);
+            }
+        }
+
+        void readBytes(CircularByteBuffer buffer, byte[] dst, int pos, int len) {
+            if (mDirectRead) {
+                while (len > 0) {
+                    if (buffer.getDirectReadSize() == 0) {
+                        fail("Direct read size is zero: free=" + buffer.freeSize()
+                                + ", size=" + buffer.size());
+                    }
+                    int copyLen = Math.min(len, buffer.getDirectReadSize());
+                    System.arraycopy(
+                        buffer.getDirectReadBuffer(), buffer.getDirectReadPos(), dst, pos, copyLen);
+                    buffer.accountForDirectRead(copyLen);
+                    len -= copyLen;
+                    pos += copyLen;
+                }
+            } else {
+                buffer.readBytes(dst, pos, len);
+            }
+        }
+    }
+}
diff --git a/staticlibs/tests/unit/src/com/android/testutils/HandlerUtilsTest.kt b/staticlibs/tests/unit/src/com/android/testutils/HandlerUtilsTest.kt
new file mode 100644
index 0000000..46a3588
--- /dev/null
+++ b/staticlibs/tests/unit/src/com/android/testutils/HandlerUtilsTest.kt
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2019 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.testutils
+
+import android.os.Handler
+import android.os.HandlerThread
+import kotlin.test.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+private const val ATTEMPTS = 50 // Causes testWaitForIdle to take about 150ms on aosp_crosshatch-eng
+private const val TIMEOUT_MS = 200
+
+@RunWith(JUnit4::class)
+class HandlerUtilsTest {
+    @Test
+    fun testWaitForIdle() {
+        val handlerThread = HandlerThread("testHandler").apply { start() }
+
+        // Tests that waitForIdle can be called many times without ill impact if the service is
+        // already idle.
+        repeat(ATTEMPTS) {
+            handlerThread.waitForIdle(TIMEOUT_MS)
+        }
+
+        // Tests that calling waitForIdle waits for messages to be processed. Use both an
+        // inline runnable that's instantiated at each loop run and a runnable that's instantiated
+        // once for all.
+        val tempRunnable = object : Runnable {
+            // Use StringBuilder preferentially to StringBuffer because StringBuilder is NOT
+            // thread-safe. It's part of the point that both runnables run on the same thread
+            // so if anything is wrong in that space it's better to opportunistically use a class
+            // where things might go wrong, even if there is no guarantee of failure.
+            var memory = StringBuilder()
+            override fun run() {
+                memory.append("b")
+            }
+        }
+        repeat(ATTEMPTS) { i ->
+            handlerThread.threadHandler.post { tempRunnable.memory.append("a"); }
+            handlerThread.threadHandler.post(tempRunnable)
+            handlerThread.waitForIdle(TIMEOUT_MS)
+            assertEquals(tempRunnable.memory.toString(), "ab".repeat(i + 1))
+        }
+    }
+
+    // Statistical test : even if visibleOnHandlerThread doesn't work this is likely to succeed,
+    // but it will be at least flaky.
+    @Test
+    fun testVisibleOnHandlerThread() {
+        val handlerThread = HandlerThread("testHandler").apply { start() }
+        val handler = Handler(handlerThread.looper)
+
+        repeat(ATTEMPTS) { attempt ->
+            var x = -10
+            visibleOnHandlerThread(handler) { x = attempt }
+            assertEquals(attempt, x)
+            handler.post { assertEquals(attempt, x) }
+        }
+    }
+}
diff --git a/staticlibs/testutils/devicetests/com/android/testutils/HandlerUtils.kt b/staticlibs/testutils/devicetests/com/android/testutils/HandlerUtils.kt
index 861f45e..6871349 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/HandlerUtils.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/HandlerUtils.kt
@@ -21,9 +21,14 @@
 import android.os.ConditionVariable
 import android.os.Handler
 import android.os.HandlerThread
+import android.util.Log
+import com.android.testutils.FunctionalUtils.ThrowingRunnable
+import java.lang.Exception
 import java.util.concurrent.Executor
 import kotlin.test.fail
 
+private const val TAG = "HandlerUtils"
+
 /**
  * Block until the specified Handler or HandlerThread becomes idle, or until timeoutMs has passed.
  */
@@ -48,3 +53,28 @@
         fail("Executor did not become idle after ${timeoutMs}ms")
     }
 }
+
+/**
+ * Executes a block of code, making its side effects visible on the caller and the handler thread
+ *
+ * After this function returns, the side effects of the passed block of code are guaranteed to be
+ * observed both on the thread running the handler and on the thread running this method.
+ * To achieve this, this method runs the passed block on the handler and blocks this thread
+ * until it's executed, so keep in mind this method will block, (including, if the handler isn't
+ * running, blocking forever).
+ */
+fun visibleOnHandlerThread(handler: Handler, r: ThrowingRunnable) {
+    val cv = ConditionVariable()
+    handler.post {
+        try {
+            r.run()
+        } catch (exception: Exception) {
+            Log.e(TAG, "visibleOnHandlerThread caught exception", exception)
+        }
+        cv.open()
+    }
+    // After block() returns, the handler thread has seen the change (since it ran it)
+    // and this thread also has seen the change (since cv.open() happens-before cv.block()
+    // returns).
+    cv.block()
+}