Add a SingleWriterBpfMap class that caches reads.
This should speed up BPF map reads by returning the cached value
without needing a system call.
Bug: 343166906
Test: added parameterization to BpfMapTest
Change-Id: Ifc0c5baa80f6d46356434c249749e87fe2f9ec6c
diff --git a/staticlibs/Android.bp b/staticlibs/Android.bp
index ede6d3f..e2834b0 100644
--- a/staticlibs/Android.bp
+++ b/staticlibs/Android.bp
@@ -135,6 +135,7 @@
"device/com/android/net/module/util/BpfUtils.java",
"device/com/android/net/module/util/IBpfMap.java",
"device/com/android/net/module/util/JniUtil.java",
+ "device/com/android/net/module/util/SingleWriterBpfMap.java",
"device/com/android/net/module/util/TcUtils.java",
],
sdk_version: "module_current",
diff --git a/staticlibs/device/com/android/net/module/util/SingleWriterBpfMap.java b/staticlibs/device/com/android/net/module/util/SingleWriterBpfMap.java
new file mode 100644
index 0000000..3eb59d8
--- /dev/null
+++ b/staticlibs/device/com/android/net/module/util/SingleWriterBpfMap.java
@@ -0,0 +1,129 @@
+/*
+ * Copyright (C) 2020 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;
+
+import android.os.Build;
+import android.system.ErrnoException;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.RequiresApi;
+
+import java.util.HashMap;
+import java.util.NoSuchElementException;
+
+/**
+ * Subclass of BpfMap for maps that are only ever written by one userspace writer.
+ *
+ * This class stores all map data in a userspace HashMap in addition to in the BPF map. This makes
+ * reads (but not iterations) much faster because they do not require a system call or converting
+ * the raw map read to the Value struct. See, e.g., b/343166906 .
+ *
+ * Users of this class must ensure that no BPF program ever writes to the map, and that all
+ * userspace writes to the map occur through this object. Other userspace code may still read from
+ * the map; only writes are required to go through this object.
+ *
+ * Reads and writes to this object are thread-safe and internally synchronized. The read and write
+ * methods are synchronized to ensure that current writers always result in a consistent internal
+ * state (without synchronization, two concurrent writes might update the underlying map and the
+ * cache in the opposite order, resulting in the cache being out of sync with the map).
+ *
+ * getNextKey and iteration over the map are not synchronized or cached and always access the
+ * isunderlying map. The values returned by these calls may be temporarily out of sync with the
+ * values read and written through this object.
+ *
+ * TODO: consider caching reads on iterations as well. This is not trivial because the semantics for
+ * iterating BPF maps require passing in the previously-returned key, and Java iterators only
+ * support iterating from the beginning. It could be done by implementing forEach and possibly by
+ * making getFirstKey and getNextKey private (if no callers are using them). Because HashMap is not
+ * thread-safe, implementing forEach would require either making that method synchronized (and
+ * block reads and updates from other threads until iteration is complete) or switching the
+ * internal HashMap to ConcurrentHashMap.
+ *
+ * @param <K> the key of the map.
+ * @param <V> the value of the map.
+ */
+@RequiresApi(Build.VERSION_CODES.S)
+public class SingleWriterBpfMap<K extends Struct, V extends Struct> extends BpfMap<K, V> {
+ // HashMap instead of ArrayMap because it performs better on larger maps, and many maps used in
+ // our code can contain hundreds of items.
+ private final HashMap<K, V> mCache = new HashMap<>();
+
+ protected SingleWriterBpfMap(@NonNull final String path, final int flag, final Class<K> key,
+ final Class<V> value) throws ErrnoException, NullPointerException {
+ super(path, flag, key, value);
+
+ if (flag != BPF_F_RDWR) {
+ throw new IllegalArgumentException(
+ "Using " + getClass().getName() + " for read-only maps does not make sense");
+ }
+
+ // Populate cache with the current map contents.
+ K currentKey = super.getFirstKey();
+ while (currentKey != null) {
+ mCache.put(currentKey, super.getValue(currentKey));
+ currentKey = super.getNextKey(currentKey);
+ }
+ }
+
+ public SingleWriterBpfMap(@NonNull final String path, final Class<K> key,
+ final Class<V> value) throws ErrnoException, NullPointerException {
+ this(path, BPF_F_RDWR, key, value);
+ }
+
+ @Override
+ public synchronized void updateEntry(K key, V value) throws ErrnoException {
+ super.updateEntry(key, value);
+ mCache.put(key, value);
+ }
+
+ @Override
+ public synchronized void insertEntry(K key, V value)
+ throws ErrnoException, IllegalStateException {
+ super.insertEntry(key, value);
+ mCache.put(key, value);
+ }
+
+ @Override
+ public synchronized void replaceEntry(K key, V value)
+ throws ErrnoException, NoSuchElementException {
+ super.replaceEntry(key, value);
+ mCache.put(key, value);
+ }
+
+ @Override
+ public synchronized boolean insertOrReplaceEntry(K key, V value) throws ErrnoException {
+ final boolean ret = super.insertOrReplaceEntry(key, value);
+ mCache.put(key, value);
+ return ret;
+ }
+
+ @Override
+ public synchronized boolean deleteEntry(K key) throws ErrnoException {
+ final boolean ret = super.deleteEntry(key);
+ mCache.remove(key);
+ return ret;
+ }
+
+ @Override
+ public synchronized boolean containsKey(@NonNull K key) throws ErrnoException {
+ return mCache.containsKey(key);
+ }
+
+ @Override
+ public synchronized V getValue(@NonNull K key) throws ErrnoException {
+ return mCache.get(key);
+ }
+}