Add a BpfMap#clear method. am: ffb0ccd04b am: 10be22076e

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/1604974

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I1e4d5e6005cdd006ddd814692714fb80a6c46936

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;

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 =