From ffb0ccd04bc3505f20827a0bfcf7a7060dfd4d89 Mon Sep 17 00:00:00 2001
From: Lorenzo Colitti <lorenzo@google.com>
Date: Wed, 24 Feb 2021 12:15:50 +0900
Subject: [PATCH] Add a BpfMap#clear method.

A caller can mostly already do this via forEach(), but having a
specific method is faster (since the code does not need to read
the value) and easier to use.

The semantics of this method (e.g., ignore ENOENT while deleting
a key, but throw on any other error) match those of the native
BpfMap::clear method.

Test: new unit tests
Change-Id: I5cd32efd0f87c823cd2d0a2fa3a95a83093fb6f9
---
 .../networkstack/tethering/BpfMap.java        | 14 ++++++++++
 .../networkstack/tethering/BpfMapTest.java    | 26 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/Tethering/src/com/android/networkstack/tethering/BpfMap.java b/Tethering/src/com/android/networkstack/tethering/BpfMap.java
index 9a9376f0a7..e9b4ccf2f4 100644
--- a/Tethering/src/com/android/networkstack/tethering/BpfMap.java
+++ b/Tethering/src/com/android/networkstack/tethering/BpfMap.java
@@ -226,6 +226,20 @@ public class BpfMap<K extends Struct, V extends Struct> implements AutoCloseable
         closeMap(mMapFd);
     }
 
+    /**
+     * Clears the map. The map may already be empty.
+     *
+     * @throws ErrnoException if the map is already closed, if an error occurred during iteration,
+     *                        or if a non-ENOENT error occurred when deleting a key.
+     */
+    public void clear() throws ErrnoException {
+        K key = getFirstKey();
+        while (key != null) {
+            deleteEntry(key);  // ignores ENOENT.
+            key = getFirstKey();
+        }
+    }
+
     private static native int closeMap(int fd) throws ErrnoException;
 
     private native int bpfFdGet(String path, int mode) throws ErrnoException, NullPointerException;
diff --git a/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java b/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
index cceaa8c82e..62302c37c8 100644
--- a/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
+++ b/Tethering/tests/privileged/src/com/android/networkstack/tethering/BpfMapTest.java
@@ -311,6 +311,32 @@ public final class BpfMapTest {
         assertNull(mTestMap.getFirstKey());
     }
 
+    @Test
+    public void testClear() throws Exception {
+        // Clear an empty map.
+        assertTrue(mTestMap.isEmpty());
+        mTestMap.clear();
+
+        // Clear a map with some data in it.
+        final ArrayMap<TetherDownstream6Key, Tether6Value> resultMap =
+                new ArrayMap<>(mTestData);
+        for (int i = 0; i < resultMap.size(); i++) {
+            mTestMap.insertEntry(resultMap.keyAt(i), resultMap.valueAt(i));
+        }
+        assertFalse(mTestMap.isEmpty());
+        mTestMap.clear();
+        assertTrue(mTestMap.isEmpty());
+
+        // Clearing an already-closed map throws.
+        mTestMap.close();
+        try {
+            mTestMap.clear();
+            fail("clearing already-closed map should throw");
+        } catch (ErrnoException expected) {
+            assertEquals(OsConstants.EBADF, expected.errno);
+        }
+    }
+
     @Test
     public void testInsertOverflow() throws Exception {
         final ArrayMap<TetherDownstream6Key, Tether6Value> testData =