load entropy data at boot. Periodically write entropy data to disk.

services/java/com/android/server/RandomBlock.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright (C) 2009 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;
+
+import android.util.Log;
+
+import java.io.Closeable;
+import java.io.EOFException;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+/**
+ * A 4k block of random {@code byte}s.
+ */
+class RandomBlock {
+
+    private static final String TAG = "RandomBlock";
+    private static final int BLOCK_SIZE = 4096;
+    private byte[] block = new byte[BLOCK_SIZE];
+
+    private RandomBlock() { }
+
+    static RandomBlock fromFile(String filename) throws IOException {
+        Log.v(TAG, "reading from file " + filename);
+        InputStream stream = null;
+        try {
+            stream = new FileInputStream(filename);
+            return fromStream(stream);
+        } finally {
+            close(stream);
+        }
+    }
+
+    private static RandomBlock fromStream(InputStream in) throws IOException {
+        RandomBlock retval = new RandomBlock();
+        int total = 0;
+        while(total < BLOCK_SIZE) {
+            int result = in.read(retval.block, total, BLOCK_SIZE - total);
+            if (result == -1) {
+                throw new EOFException();
+            }
+            total += result;
+        }
+        return retval;
+    }
+
+    void toFile(String filename) throws IOException {
+        Log.v(TAG, "writing to file " + filename);
+        OutputStream out = null;
+        try {
+            // TODO: Investigate using RandomAccessFile
+            out = new FileOutputStream(filename);
+            toStream(out);
+        } finally {
+            close(out);
+        }
+    }
+
+    private void toStream(OutputStream out) throws IOException {
+        out.write(block);
+    }
+
+    private static void close(Closeable c) {
+        try {
+            if (c == null) {
+                return;
+            }
+            c.close();
+        } catch (IOException e) {
+            Log.w(TAG, "IOException thrown while closing Closeable", e);
+        }
+    }
+}