diff --git a/include/utils/ByteOrder.h b/include/utils/ByteOrder.h
index 4c06067..baa3a83 100644
--- a/include/utils/ByteOrder.h
+++ b/include/utils/ByteOrder.h
@@ -38,6 +38,16 @@
  * intent is to allow us to avoid byte swapping on the device.
  */
 
+static inline uint32_t android_swap_long(uint32_t v)
+{
+    return (v<<24) | ((v<<8)&0x00FF0000) | ((v>>8)&0x0000FF00) | (v>>24);
+}
+
+static inline uint16_t android_swap_short(uint16_t v)
+{
+    return (v<<8) | (v>>8);
+}
+
 #define DEVICE_BYTE_ORDER LITTLE_ENDIAN
 
 #if BYTE_ORDER == DEVICE_BYTE_ORDER
@@ -49,16 +59,6 @@
 
 #else
 
-static inline uint32_t android_swap_long(uint32_t v)
-{
-    return (v<<24) | ((v<<8)&0x00FF0000) | ((v>>8)&0x0000FF00) | (v>>24);
-}
-
-static inline uint16_t android_swap_short(uint16_t v)
-{
-    return (v<<8) | (v>>8);
-}
-
 #define	dtohl(x)	(android_swap_long(x))
 #define	dtohs(x)	(android_swap_short(x))
 #define	htodl(x)	(android_swap_long(x))
@@ -66,4 +66,16 @@
 
 #endif
 
+#if BYTE_ORDER == LITTLE_ENDIAN
+#define fromlel(x) (x)
+#define fromles(x) (x)
+#define tolel(x) (x)
+#define toles(x) (x)
+#else
+#define fromlel(x) (android_swap_long(x))
+#define fromles(x) (android_swap_short(x))
+#define tolel(x) (android_swap_long(x))
+#define toles(x) (android_swap_short(x))
+#endif
+
 #endif // _LIBS_UTILS_BYTE_ORDER_H
diff --git a/include/utils/backup_helpers.h b/include/utils/backup_helpers.h
index 137c5f1..73b9989 100644
--- a/include/utils/backup_helpers.h
+++ b/include/utils/backup_helpers.h
@@ -1,15 +1,69 @@
+/*
+ * 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.
+ */
+
 #ifndef _UTILS_BACKUP_HELPERS_H
 #define _UTILS_BACKUP_HELPERS_H
 
+#include <utils/Errors.h>
+#include <utils/String8.h>
+
+namespace android {
+
 int back_up_files(int oldSnapshotFD, int oldDataStream, int newSnapshotFD,
         char const* fileBase, char const* const* files, int fileCount);
 
+/**
+ * Reads the data.
+ *
+ * If an error occurs, it poisons this object and all write calls will fail
+ * with the error that occurred.
+ */
+class BackupDataWriter
+{
+public:
+    BackupDataWriter(int fd);
+    // does not close fd
+    ~BackupDataWriter();
+
+    status_t WriteAppHeader(const String8& packageName);
+
+    status_t WriteEntityHeader(const String8& key, size_t dataSize);
+    status_t WriteEntityData(const void* data, size_t size);
+
+    status_t WriteAppFooter();
+
+private:
+    explicit BackupDataWriter();
+    status_t write_padding_for(int n);
+    
+    int m_fd;
+    status_t m_status;
+    ssize_t m_pos;
+    int m_entityCount;
+};
+
 #define TEST_BACKUP_HELPERS 0
 
 #if TEST_BACKUP_HELPERS
 int backup_helper_test_empty();
 int backup_helper_test_four();
 int backup_helper_test_files();
+int backup_helper_test_data_writer();
 #endif
 
+} // namespace android
+
 #endif // _UTILS_BACKUP_HELPERS_H
diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index f9fb780..5a1a89b 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -117,7 +117,8 @@
 	IPermissionController.cpp \
 	IServiceManager.cpp \
 	Unicode.cpp \
-	file_backup_helper.cpp
+    backup_data.cpp \
+	backup_helper_file.cpp
 
 ifeq ($(TARGET_SIMULATOR),true)
 LOCAL_SRC_FILES += $(hostSources)
diff --git a/libs/utils/backup_data.cpp b/libs/utils/backup_data.cpp
new file mode 100644
index 0000000..c7f1fdb
--- /dev/null
+++ b/libs/utils/backup_data.cpp
@@ -0,0 +1,236 @@
+/*
+ * 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.
+ */
+
+#include <utils/backup_helpers.h>
+#include <utils/ByteOrder.h>
+
+#include <stdio.h>
+#include <unistd.h>
+
+namespace android {
+
+/*
+ * File Format (v1):
+ *
+ * All ints are stored little-endian.
+ *
+ *  - An app_header_v1 struct.
+ *  - The name of the package, utf-8, null terminated, padded to 4-byte boundary.
+ *  - A sequence of zero or more key/value paires (entities), each with
+ *      - A entity_header_v1 struct
+ *      - The key, utf-8, null terminated, padded to 4-byte boundary.
+ *      - The value, padded to 4 byte boundary
+ */
+
+#define APP_MAGIC_V1 0x31707041 // App1 (little endian)
+#define ENTITY_MAGIC_V1 0x61746144 // Data (little endian)
+#define FOOTER_MAGIC_V1 0x746f6f46 // Foot (little endian)
+
+typedef struct {
+    int type; // == APP_MAGIC_V1
+    int packageLen; // length of the name of the package that follows, not including the null.
+} app_header_v1;
+
+typedef struct {
+    int type; // ENTITY_MAGIC_V1
+    int keyLen; // length of the key name, not including the null terminator
+    int dataSize; // size of the data, not including the padding
+} entity_header_v1;
+
+typedef struct {
+    int type; // FOOTER_MAGIC_V1
+    int entityCount; // the number of entities that were written
+} app_footer_v1;
+
+const static int ROUND_UP[4] = { 0, 3, 2, 1 };
+
+static inline size_t
+round_up(size_t n)
+{
+    return n + ROUND_UP[n % 4];
+}
+
+static inline size_t
+padding_extra(size_t n)
+{
+    return ROUND_UP[n % 4];
+}
+
+BackupDataWriter::BackupDataWriter(int fd)
+    :m_fd(fd),
+     m_status(NO_ERROR),
+     m_pos(0),
+     m_entityCount(0)
+{
+}
+
+BackupDataWriter::~BackupDataWriter()
+{
+}
+
+// Pad out anything they've previously written to the next 4 byte boundary.
+status_t
+BackupDataWriter::write_padding_for(int n)
+{
+    ssize_t amt;
+    ssize_t paddingSize;
+
+    paddingSize = padding_extra(n);
+    if (paddingSize > 0) {
+        uint32_t padding = 0xbcbcbcbc;
+        amt = write(m_fd, &padding, paddingSize);
+        if (amt != paddingSize) {
+            m_status = errno;
+            return m_status;
+        }
+        m_pos += amt;
+    }
+    return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteAppHeader(const String8& packageName)
+{
+    if (m_status != NO_ERROR) {
+        return m_status;
+    }
+
+    ssize_t amt;
+
+    amt = write_padding_for(m_pos);
+    if (amt != 0) {
+        return amt;
+    }
+
+    app_header_v1 header;
+    ssize_t nameLen;
+
+    nameLen = packageName.length();
+
+    header.type = tolel(APP_MAGIC_V1);
+    header.packageLen = tolel(nameLen);
+
+    amt = write(m_fd, &header, sizeof(app_header_v1));
+    if (amt != sizeof(app_header_v1)) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+
+    amt = write(m_fd, packageName.string(), nameLen+1);
+    if (amt != nameLen+1) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+
+    return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteEntityHeader(const String8& key, size_t dataSize)
+{
+    if (m_status != NO_ERROR) {
+        return m_status;
+    }
+
+    ssize_t amt;
+
+    amt = write_padding_for(m_pos);
+    if (amt != 0) {
+        return amt;
+    }
+
+    entity_header_v1 header;
+    ssize_t keyLen;
+
+    keyLen = key.length();
+
+    header.type = tolel(ENTITY_MAGIC_V1);
+    header.keyLen = tolel(keyLen);
+    header.dataSize = tolel(dataSize);
+
+    amt = write(m_fd, &header, sizeof(entity_header_v1));
+    if (amt != sizeof(entity_header_v1)) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+
+    amt = write(m_fd, key.string(), keyLen+1);
+    if (amt != keyLen+1) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+
+    amt = write_padding_for(keyLen+1);
+
+    m_entityCount++;
+
+    return amt;
+}
+
+status_t
+BackupDataWriter::WriteEntityData(const void* data, size_t size)
+{
+    if (m_status != NO_ERROR) {
+        return m_status;
+    }
+
+    // We don't write padding here, because they're allowed to call this several
+    // times with smaller buffers.  We write it at the end of WriteEntityHeader
+    // instead.
+    ssize_t amt = write(m_fd, data, size);
+    if (amt != (ssize_t)size) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+    return NO_ERROR;
+}
+
+status_t
+BackupDataWriter::WriteAppFooter()
+{
+    if (m_status != NO_ERROR) {
+        return m_status;
+    }
+
+    ssize_t amt;
+
+    amt = write_padding_for(m_pos);
+    if (amt != 0) {
+        return amt;
+    }
+
+    app_footer_v1 footer;
+    ssize_t nameLen;
+
+    footer.type = tolel(FOOTER_MAGIC_V1);
+    footer.entityCount = tolel(m_entityCount);
+
+    amt = write(m_fd, &footer, sizeof(app_footer_v1));
+    if (amt != sizeof(app_footer_v1)) {
+        m_status = errno;
+        return m_status;
+    }
+    m_pos += amt;
+
+    return NO_ERROR;
+}
+
+} // namespace android
diff --git a/libs/utils/file_backup_helper.cpp b/libs/utils/backup_helper_file.cpp
similarity index 79%
rename from libs/utils/file_backup_helper.cpp
rename to libs/utils/backup_helper_file.cpp
index 453084a..1fa6a0f 100644
--- a/libs/utils/file_backup_helper.cpp
+++ b/libs/utils/backup_helper_file.cpp
@@ -1,3 +1,19 @@
+/*
+ * 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.
+ */
+
 #define LOG_TAG "file_backup_helper"
 
 #include <utils/backup_helpers.h>
@@ -19,13 +35,16 @@
 
 #include <cutils/log.h>
 
-using namespace android;
+namespace android {
 
 #define MAGIC0 0x70616e53 // Snap
 #define MAGIC1 0x656c6946 // File
 
+#if TEST_BACKUP_HELPERS
+#define LOGP(x...) printf(x)
+#else
 #define LOGP(x...) LOGD(x)
-//#define LOGP(x...) printf(x)
+#endif
 
 struct SnapshotHeader {
     int magic0;
@@ -118,6 +137,8 @@
         bytesWritten += sizeof(FileState) + round_up(name.length());
     }
 
+    LOGP("write_snapshot_file fd=%d\n", fd);
+
     int amt;
     SnapshotHeader header = { MAGIC0, N, MAGIC1, bytesWritten };
 
@@ -248,11 +269,13 @@
             // file added
             String8 realFilename(base);
             realFilename.appendPath(q);
+            LOGP("file added: %s\n", realFilename.string());
             write_update_file(realFilename, q);
             m++;
         }
         else if (cmp < 0) {
             // file removed
+            LOGP("file removed: %s\n", p.string());
             write_delete_file(p);
             n++;
         }
@@ -573,6 +596,107 @@
     return matched ? 0 : 1;
 }
 
+// hexdump -v -e '"    " 8/1 " 0x%02x," "\n"' data_writer.data
+const unsigned char DATA_GOLDEN_FILE[] = {
+     0x41, 0x70, 0x70, 0x31, 0x0b, 0x00, 0x00, 0x00,
+     0x6e, 0x6f, 0x5f, 0x70, 0x61, 0x64, 0x64, 0x69,
+     0x6e, 0x67, 0x5f, 0x00, 0x44, 0x61, 0x74, 0x61,
+     0x0b, 0x00, 0x00, 0x00, 0x0c, 0x00, 0x00, 0x00,
+     0x6e, 0x6f, 0x5f, 0x70, 0x61, 0x64, 0x64, 0x69,
+     0x6e, 0x67, 0x5f, 0x00, 0x6e, 0x6f, 0x5f, 0x70,
+     0x61, 0x64, 0x64, 0x69, 0x6e, 0x67, 0x5f, 0x00,
+     0x41, 0x70, 0x70, 0x31, 0x0c, 0x00, 0x00, 0x00,
+     0x70, 0x61, 0x64, 0x64, 0x65, 0x64, 0x5f, 0x74,
+     0x6f, 0x5f, 0x5f, 0x33, 0x00, 0xbc, 0xbc, 0xbc,
+     0x44, 0x61, 0x74, 0x61, 0x0c, 0x00, 0x00, 0x00,
+     0x0d, 0x00, 0x00, 0x00, 0x70, 0x61, 0x64, 0x64,
+     0x65, 0x64, 0x5f, 0x74, 0x6f, 0x5f, 0x5f, 0x33,
+     0x00, 0xbc, 0xbc, 0xbc, 0x70, 0x61, 0x64, 0x64,
+     0x65, 0x64, 0x5f, 0x74, 0x6f, 0x5f, 0x5f, 0x33,
+     0x00, 0xbc, 0xbc, 0xbc, 0x41, 0x70, 0x70, 0x31,
+     0x0d, 0x00, 0x00, 0x00, 0x70, 0x61, 0x64, 0x64,
+     0x65, 0x64, 0x5f, 0x74, 0x6f, 0x5f, 0x32, 0x5f,
+     0x5f, 0x00, 0xbc, 0xbc, 0x44, 0x61, 0x74, 0x61,
+     0x0d, 0x00, 0x00, 0x00, 0x0e, 0x00, 0x00, 0x00,
+     0x70, 0x61, 0x64, 0x64, 0x65, 0x64, 0x5f, 0x74,
+     0x6f, 0x5f, 0x32, 0x5f, 0x5f, 0x00, 0xbc, 0xbc,
+     0x70, 0x61, 0x64, 0x64, 0x65, 0x64, 0x5f, 0x74,
+     0x6f, 0x5f, 0x32, 0x5f, 0x5f, 0x00, 0xbc, 0xbc,
+     0x41, 0x70, 0x70, 0x31, 0x0a, 0x00, 0x00, 0x00,
+     0x70, 0x61, 0x64, 0x64, 0x65, 0x64, 0x5f, 0x74,
+     0x6f, 0x31, 0x00, 0xbc, 0x44, 0x61, 0x74, 0x61,
+     0x0a, 0x00, 0x00, 0x00, 0x0b, 0x00, 0x00, 0x00,
+     0x70, 0x61, 0x64, 0x64, 0x65, 0x64, 0x5f, 0x74,
+     0x6f, 0x31, 0x00, 0xbc, 0x70, 0x61, 0x64, 0x64,
+     0x65, 0x64, 0x5f, 0x74, 0x6f, 0x31, 0x00, 0xbc,
+     0x46, 0x6f, 0x6f, 0x74, 0x04, 0x00, 0x00, 0x00,
+};
+const int DATA_GOLDEN_FILE_SIZE = sizeof(DATA_GOLDEN_FILE);
+
+static int
+test_write_header_and_entity(BackupDataWriter& writer, const char* str)
+{
+    int err;
+    String8 text(str);
+
+    err = writer.WriteAppHeader(text);
+    if (err != 0) {
+        fprintf(stderr, "WriteAppHeader failed with %s\n", strerror(err));
+        return err;
+    }
+
+    err = writer.WriteEntityHeader(text, text.length()+1);
+    if (err != 0) {
+        fprintf(stderr, "WriteEntityHeader failed with %s\n", strerror(err));
+        return err;
+    }
+
+    err = writer.WriteEntityData(text.string(), text.length()+1);
+    if (err != 0) {
+        fprintf(stderr, "write failed for data '%s'\n", text.string());
+        return errno;
+    }
+
+    return err;
+}
+
+int
+backup_helper_test_data_writer()
+{
+    int err;
+    int fd;
+    const char* filename = SCRATCH_DIR "data_writer.data";
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+    mkdir(SCRATCH_DIR "data", 0777);
+    
+    fd = creat(filename, 0666);
+    if (fd == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
+    BackupDataWriter writer(fd);
+
+    err = 0;
+    err |= test_write_header_and_entity(writer, "no_padding_");
+    err |= test_write_header_and_entity(writer, "padded_to__3");
+    err |= test_write_header_and_entity(writer, "padded_to_2__");
+    err |= test_write_header_and_entity(writer, "padded_to1");
+
+    writer.WriteAppFooter();
+
+    close(fd);
+
+    err = compare_file(filename, DATA_GOLDEN_FILE, DATA_GOLDEN_FILE_SIZE);
+    if (err != 0) {
+        return err;
+    }
+
+    return err;
+}
+
 static int
 get_mod_time(const char* filename, struct timeval times[2])
 {
@@ -594,8 +718,9 @@
 backup_helper_test_files()
 {
     int err;
-    int newSnapshotFD;
     int oldSnapshotFD;
+    int dataStreamFD;
+    int newSnapshotFD;
 
     system("rm -r " SCRATCH_DIR);
     mkdir(SCRATCH_DIR, 0777);
@@ -616,17 +741,24 @@
         "data/f"
     };
 
+    dataStreamFD = creat(SCRATCH_DIR "1.data", 0666);
+    if (dataStreamFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
     newSnapshotFD = creat(SCRATCH_DIR "before.snap", 0666);
     if (newSnapshotFD == -1) {
         fprintf(stderr, "error creating: %s\n", strerror(errno));
         return errno;
     }
-
-    err = back_up_files(-1, newSnapshotFD, 0, SCRATCH_DIR, files_before, 5);
+    
+    err = back_up_files(-1, dataStreamFD, newSnapshotFD, SCRATCH_DIR, files_before, 5);
     if (err != 0) {
         return err;
     }
 
+    close(dataStreamFD);
     close(newSnapshotFD);
 
     sleep(3);
@@ -665,21 +797,30 @@
         return errno;
     }
 
+    dataStreamFD = creat(SCRATCH_DIR "2.data", 0666);
+    if (dataStreamFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
     newSnapshotFD = creat(SCRATCH_DIR "after.snap", 0666);
     if (newSnapshotFD == -1) {
         fprintf(stderr, "error creating: %s\n", strerror(errno));
         return errno;
     }
 
-    err = back_up_files(oldSnapshotFD, newSnapshotFD, 0, SCRATCH_DIR, files_after, 6);
+    err = back_up_files(oldSnapshotFD, dataStreamFD, newSnapshotFD, SCRATCH_DIR, files_after, 6);
     if (err != 0) {
         return err;
     }
 
     close(oldSnapshotFD);
+    close(dataStreamFD);
     close(newSnapshotFD);
     
     return 0;
 }
 
 #endif // TEST_BACKUP_HELPERS
+
+}
diff --git a/tests/backup/backup_helper_test.cpp b/tests/backup/backup_helper_test.cpp
index 6da16b4..66240e3 100644
--- a/tests/backup/backup_helper_test.cpp
+++ b/tests/backup/backup_helper_test.cpp
@@ -3,6 +3,8 @@
 #include <stdio.h>
 #include <string.h>
 
+using namespace android;
+
 #if TEST_BACKUP_HELPERS
 
 // ============================================================
@@ -20,6 +22,7 @@
     { "backup_helper_test_empty", backup_helper_test_empty, 0, false },
     { "backup_helper_test_four", backup_helper_test_four, 0, false },
     { "backup_helper_test_files", backup_helper_test_files, 0, false },
+    { "backup_helper_test_data_writer", backup_helper_test_data_writer, 0, false },
     { 0, NULL, 0, false}
 };