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diff --git a/core/java/android/util/AtomicFile.java b/core/java/android/util/AtomicFile.java
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+++ b/core/java/android/util/AtomicFile.java
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+/*
+ * 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 android.util;
+
+import android.os.FileUtils;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/**
+ * Helper class for performing atomic operations on a file by creating a
+ * backup file until a write has successfully completed.  If you need this
+ * on older versions of the platform you can use
+ * {@link android.support.v4.util.AtomicFile} in the v4 support library.
+ * <p>
+ * Atomic file guarantees file integrity by ensuring that a file has
+ * been completely written and sync'd to disk before removing its backup.
+ * As long as the backup file exists, the original file is considered
+ * to be invalid (left over from a previous attempt to write the file).
+ * </p><p>
+ * Atomic file does not confer any file locking semantics.
+ * Do not use this class when the file may be accessed or modified concurrently
+ * by multiple threads or processes.  The caller is responsible for ensuring
+ * appropriate mutual exclusion invariants whenever it accesses the file.
+ * </p>
+ */
+public class AtomicFile {
+    private final File mBaseName;
+    private final File mBackupName;
+
+    /**
+     * Create a new AtomicFile for a file located at the given File path.
+     * The secondary backup file will be the same file path with ".bak" appended.
+     */
+    public AtomicFile(File baseName) {
+        mBaseName = baseName;
+        mBackupName = new File(baseName.getPath() + ".bak");
+    }
+
+    /**
+     * Return the path to the base file.  You should not generally use this,
+     * as the data at that path may not be valid.
+     */
+    public File getBaseFile() {
+        return mBaseName;
+    }
+
+    /**
+     * Delete the atomic file.  This deletes both the base and backup files.
+     */
+    public void delete() {
+        mBaseName.delete();
+        mBackupName.delete();
+    }
+
+    /**
+     * Start a new write operation on the file.  This returns a FileOutputStream
+     * to which you can write the new file data.  The existing file is replaced
+     * with the new data.  You <em>must not</em> directly close the given
+     * FileOutputStream; instead call either {@link #finishWrite(FileOutputStream)}
+     * or {@link #failWrite(FileOutputStream)}.
+     *
+     * <p>Note that if another thread is currently performing
+     * a write, this will simply replace whatever that thread is writing
+     * with the new file being written by this thread, and when the other
+     * thread finishes the write the new write operation will no longer be
+     * safe (or will be lost).  You must do your own threading protection for
+     * access to AtomicFile.
+     */
+    public FileOutputStream startWrite() throws IOException {
+        // Rename the current file so it may be used as a backup during the next read
+        if (mBaseName.exists()) {
+            if (!mBackupName.exists()) {
+                if (!mBaseName.renameTo(mBackupName)) {
+                    Log.w("AtomicFile", "Couldn't rename file " + mBaseName
+                            + " to backup file " + mBackupName);
+                }
+            } else {
+                mBaseName.delete();
+            }
+        }
+        FileOutputStream str = null;
+        try {
+            str = new FileOutputStream(mBaseName);
+        } catch (FileNotFoundException e) {
+            File parent = mBaseName.getParentFile();
+            if (!parent.mkdir()) {
+                throw new IOException("Couldn't create directory " + mBaseName);
+            }
+            FileUtils.setPermissions(
+                parent.getPath(),
+                FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,
+                -1, -1);
+            try {
+                str = new FileOutputStream(mBaseName);
+            } catch (FileNotFoundException e2) {
+                throw new IOException("Couldn't create " + mBaseName);
+            }
+        }
+        return str;
+    }
+
+    /**
+     * Call when you have successfully finished writing to the stream
+     * returned by {@link #startWrite()}.  This will close, sync, and
+     * commit the new data.  The next attempt to read the atomic file
+     * will return the new file stream.
+     */
+    public void finishWrite(FileOutputStream str) {
+        if (str != null) {
+            FileUtils.sync(str);
+            try {
+                str.close();
+                mBackupName.delete();
+            } catch (IOException e) {
+                Log.w("AtomicFile", "finishWrite: Got exception:", e);
+            }
+        }
+    }
+
+    /**
+     * Call when you have failed for some reason at writing to the stream
+     * returned by {@link #startWrite()}.  This will close the current
+     * write stream, and roll back to the previous state of the file.
+     */
+    public void failWrite(FileOutputStream str) {
+        if (str != null) {
+            FileUtils.sync(str);
+            try {
+                str.close();
+                mBaseName.delete();
+                mBackupName.renameTo(mBaseName);
+            } catch (IOException e) {
+                Log.w("AtomicFile", "failWrite: Got exception:", e);
+            }
+        }
+    }
+
+    /** @hide
+     * @deprecated This is not safe.
+     */
+    @Deprecated public void truncate() throws IOException {
+        try {
+            FileOutputStream fos = new FileOutputStream(mBaseName);
+            FileUtils.sync(fos);
+            fos.close();
+        } catch (FileNotFoundException e) {
+            throw new IOException("Couldn't append " + mBaseName);
+        } catch (IOException e) {
+        }
+    }
+
+    /** @hide
+     * @deprecated This is not safe.
+     */
+    @Deprecated public FileOutputStream openAppend() throws IOException {
+        try {
+            return new FileOutputStream(mBaseName, true);
+        } catch (FileNotFoundException e) {
+            throw new IOException("Couldn't append " + mBaseName);
+        }
+    }
+
+    /**
+     * Open the atomic file for reading.  If there previously was an
+     * incomplete write, this will roll back to the last good data before
+     * opening for read.  You should call close() on the FileInputStream when
+     * you are done reading from it.
+     *
+     * <p>Note that if another thread is currently performing
+     * a write, this will incorrectly consider it to be in the state of a bad
+     * write and roll back, causing the new data currently being written to
+     * be dropped.  You must do your own threading protection for access to
+     * AtomicFile.
+     */
+    public FileInputStream openRead() throws FileNotFoundException {
+        if (mBackupName.exists()) {
+            mBaseName.delete();
+            mBackupName.renameTo(mBaseName);
+        }
+        return new FileInputStream(mBaseName);
+    }
+
+    /**
+     * A convenience for {@link #openRead()} that also reads all of the
+     * file contents into a byte array which is returned.
+     */
+    public byte[] readFully() throws IOException {
+        FileInputStream stream = openRead();
+        try {
+            int pos = 0;
+            int avail = stream.available();
+            byte[] data = new byte[avail];
+            while (true) {
+                int amt = stream.read(data, pos, data.length-pos);
+                //Log.i("foo", "Read " + amt + " bytes at " + pos
+                //        + " of avail " + data.length);
+                if (amt <= 0) {
+                    //Log.i("foo", "**** FINISHED READING: pos=" + pos
+                    //        + " len=" + data.length);
+                    return data;
+                }
+                pos += amt;
+                avail = stream.available();
+                if (avail > data.length-pos) {
+                    byte[] newData = new byte[pos+avail];
+                    System.arraycopy(data, 0, newData, 0, pos);
+                    data = newData;
+                }
+            }
+        } finally {
+            stream.close();
+        }
+    }
+}