diff --git a/libs/utils/BackupHelpers.cpp b/libs/utils/BackupHelpers.cpp
new file mode 100644
index 0000000..4ad9b51
--- /dev/null
+++ b/libs/utils/BackupHelpers.cpp
@@ -0,0 +1,1314 @@
+/*
+ * 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/BackupHelpers.h>
+
+#include <utils/KeyedVector.h>
+#include <utils/ByteOrder.h>
+#include <utils/String8.h>
+
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/stat.h>
+#include <sys/time.h>  // for utimes
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <utime.h>
+#include <fcntl.h>
+#include <zlib.h>
+
+#include <cutils/log.h>
+
+namespace android {
+
+#define MAGIC0 0x70616e53 // Snap
+#define MAGIC1 0x656c6946 // File
+
+/*
+ * File entity data format (v1):
+ *
+ *   - 4-byte version number of the metadata, little endian (0x00000001 for v1)
+ *   - 12 bytes of metadata
+ *   - the file data itself
+ *
+ * i.e. a 16-byte metadata header followed by the raw file data.  If the
+ * restore code does not recognize the metadata version, it can still
+ * interpret the file data itself correctly.
+ *
+ * file_metadata_v1:
+ *
+ *   - 4 byte version number === 0x00000001 (little endian)
+ *   - 4-byte access mode (little-endian)
+ *   - undefined (8 bytes)
+ */
+
+struct file_metadata_v1 {
+    int version;
+    int mode;
+    int undefined_1;
+    int undefined_2;
+};
+
+const static int CURRENT_METADATA_VERSION = 1;
+
+#if 1
+#define LOGP(f, x...)
+#else
+#if TEST_BACKUP_HELPERS
+#define LOGP(f, x...) printf(f "\n", x)
+#else
+#define LOGP(x...) LOGD(x)
+#endif
+#endif
+
+const static int ROUND_UP[4] = { 0, 3, 2, 1 };
+
+static inline int
+round_up(int n)
+{
+    return n + ROUND_UP[n % 4];
+}
+
+static int
+read_snapshot_file(int fd, KeyedVector<String8,FileState>* snapshot)
+{
+    int bytesRead = 0;
+    int amt;
+    SnapshotHeader header;
+
+    amt = read(fd, &header, sizeof(header));
+    if (amt != sizeof(header)) {
+        return errno;
+    }
+    bytesRead += amt;
+
+    if (header.magic0 != MAGIC0 || header.magic1 != MAGIC1) {
+        LOGW("read_snapshot_file header.magic0=0x%08x magic1=0x%08x", header.magic0, header.magic1);
+        return 1;
+    }
+
+    for (int i=0; i<header.fileCount; i++) {
+        FileState file;
+        char filenameBuf[128];
+
+        amt = read(fd, &file, sizeof(FileState));
+        if (amt != sizeof(FileState)) {
+            LOGW("read_snapshot_file FileState truncated/error with read at %d bytes\n", bytesRead);
+            return 1;
+        }
+        bytesRead += amt;
+
+        // filename is not NULL terminated, but it is padded
+        int nameBufSize = round_up(file.nameLen);
+        char* filename = nameBufSize <= (int)sizeof(filenameBuf)
+                ? filenameBuf
+                : (char*)malloc(nameBufSize);
+        amt = read(fd, filename, nameBufSize);
+        if (amt == nameBufSize) {
+            snapshot->add(String8(filename, file.nameLen), file);
+        }
+        bytesRead += amt;
+        if (filename != filenameBuf) {
+            free(filename);
+        }
+        if (amt != nameBufSize) {
+            LOGW("read_snapshot_file filename truncated/error with read at %d bytes\n", bytesRead);
+            return 1;
+        }
+    }
+
+    if (header.totalSize != bytesRead) {
+        LOGW("read_snapshot_file length mismatch: header.totalSize=%d bytesRead=%d\n",
+                header.totalSize, bytesRead);
+        return 1;
+    }
+
+    return 0;
+}
+
+static int
+write_snapshot_file(int fd, const KeyedVector<String8,FileRec>& snapshot)
+{
+    int fileCount = 0;
+    int bytesWritten = sizeof(SnapshotHeader);
+    // preflight size
+    const int N = snapshot.size();
+    for (int i=0; i<N; i++) {
+        const FileRec& g = snapshot.valueAt(i);
+        if (!g.deleted) {
+            const String8& name = snapshot.keyAt(i);
+            bytesWritten += sizeof(FileState) + round_up(name.length());
+            fileCount++;
+        }
+    }
+
+    LOGP("write_snapshot_file fd=%d\n", fd);
+
+    int amt;
+    SnapshotHeader header = { MAGIC0, fileCount, MAGIC1, bytesWritten };
+
+    amt = write(fd, &header, sizeof(header));
+    if (amt != sizeof(header)) {
+        LOGW("write_snapshot_file error writing header %s", strerror(errno));
+        return errno;
+    }
+
+    for (int i=0; i<N; i++) {
+        FileRec r = snapshot.valueAt(i);
+        if (!r.deleted) {
+            const String8& name = snapshot.keyAt(i);
+            int nameLen = r.s.nameLen = name.length();
+
+            amt = write(fd, &r.s, sizeof(FileState));
+            if (amt != sizeof(FileState)) {
+                LOGW("write_snapshot_file error writing header %s", strerror(errno));
+                return 1;
+            }
+
+            // filename is not NULL terminated, but it is padded
+            amt = write(fd, name.string(), nameLen);
+            if (amt != nameLen) {
+                LOGW("write_snapshot_file error writing filename %s", strerror(errno));
+                return 1;
+            }
+            int paddingLen = ROUND_UP[nameLen % 4];
+            if (paddingLen != 0) {
+                int padding = 0xabababab;
+                amt = write(fd, &padding, paddingLen);
+                if (amt != paddingLen) {
+                    LOGW("write_snapshot_file error writing %d bytes of filename padding %s",
+                            paddingLen, strerror(errno));
+                    return 1;
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+static int
+write_delete_file(BackupDataWriter* dataStream, const String8& key)
+{
+    LOGP("write_delete_file %s\n", key.string());
+    return dataStream->WriteEntityHeader(key, -1);
+}
+
+static int
+write_update_file(BackupDataWriter* dataStream, int fd, int mode, const String8& key,
+        char const* realFilename)
+{
+    LOGP("write_update_file %s (%s) : mode 0%o\n", realFilename, key.string(), mode);
+
+    const int bufsize = 4*1024;
+    int err;
+    int amt;
+    int fileSize;
+    int bytesLeft;
+    file_metadata_v1 metadata;
+
+    char* buf = (char*)malloc(bufsize);
+    int crc = crc32(0L, Z_NULL, 0);
+
+
+    fileSize = lseek(fd, 0, SEEK_END);
+    lseek(fd, 0, SEEK_SET);
+
+    if (sizeof(metadata) != 16) {
+        LOGE("ERROR: metadata block is the wrong size!");
+    }
+
+    bytesLeft = fileSize + sizeof(metadata);
+    err = dataStream->WriteEntityHeader(key, bytesLeft);
+    if (err != 0) {
+        free(buf);
+        return err;
+    }
+
+    // store the file metadata first
+    metadata.version = tolel(CURRENT_METADATA_VERSION);
+    metadata.mode = tolel(mode);
+    metadata.undefined_1 = metadata.undefined_2 = 0;
+    err = dataStream->WriteEntityData(&metadata, sizeof(metadata));
+    if (err != 0) {
+        free(buf);
+        return err;
+    }
+    bytesLeft -= sizeof(metadata); // bytesLeft should == fileSize now
+
+    // now store the file content
+    while ((amt = read(fd, buf, bufsize)) != 0 && bytesLeft > 0) {
+        bytesLeft -= amt;
+        if (bytesLeft < 0) {
+            amt += bytesLeft; // Plus a negative is minus.  Don't write more than we promised.
+        }
+        err = dataStream->WriteEntityData(buf, amt);
+        if (err != 0) {
+            free(buf);
+            return err;
+        }
+    }
+    if (bytesLeft != 0) {
+        if (bytesLeft > 0) {
+            // Pad out the space we promised in the buffer.  We can't corrupt the buffer,
+            // even though the data we're sending is probably bad.
+            memset(buf, 0, bufsize);
+            while (bytesLeft > 0) {
+                amt = bytesLeft < bufsize ? bytesLeft : bufsize;
+                bytesLeft -= amt;
+                err = dataStream->WriteEntityData(buf, amt);
+                if (err != 0) {
+                    free(buf);
+                    return err;
+                }
+            }
+        }
+        LOGE("write_update_file size mismatch for %s. expected=%d actual=%d."
+                " You aren't doing proper locking!", realFilename, fileSize, fileSize-bytesLeft);
+    }
+
+    free(buf);
+    return NO_ERROR;
+}
+
+static int
+write_update_file(BackupDataWriter* dataStream, const String8& key, char const* realFilename)
+{
+    int err;
+    struct stat st;
+
+    err = stat(realFilename, &st);
+    if (err < 0) {
+        return errno;
+    }
+
+    int fd = open(realFilename, O_RDONLY);
+    if (fd == -1) {
+        return errno;
+    }
+
+    err = write_update_file(dataStream, fd, st.st_mode, key, realFilename);
+    close(fd);
+    return err;
+}
+
+static int
+compute_crc32(int fd)
+{
+    const int bufsize = 4*1024;
+    int amt;
+
+    char* buf = (char*)malloc(bufsize);
+    int crc = crc32(0L, Z_NULL, 0);
+
+    lseek(fd, 0, SEEK_SET);
+
+    while ((amt = read(fd, buf, bufsize)) != 0) {
+        crc = crc32(crc, (Bytef*)buf, amt);
+    }
+
+    free(buf);
+    return crc;
+}
+
+int
+back_up_files(int oldSnapshotFD, BackupDataWriter* dataStream, int newSnapshotFD,
+        char const* const* files, char const* const* keys, int fileCount)
+{
+    int err;
+    KeyedVector<String8,FileState> oldSnapshot;
+    KeyedVector<String8,FileRec> newSnapshot;
+
+    if (oldSnapshotFD != -1) {
+        err = read_snapshot_file(oldSnapshotFD, &oldSnapshot);
+        if (err != 0) {
+            // On an error, treat this as a full backup.
+            oldSnapshot.clear();
+        }
+    }
+
+    for (int i=0; i<fileCount; i++) {
+        String8 key(keys[i]);
+        FileRec r;
+        char const* file = files[i];
+        r.file = file;
+        struct stat st;
+
+        err = stat(file, &st);
+        if (err != 0) {
+            r.deleted = true;
+        } else {
+            r.deleted = false;
+            r.s.modTime_sec = st.st_mtime;
+            r.s.modTime_nsec = 0; // workaround sim breakage
+            //r.s.modTime_nsec = st.st_mtime_nsec;
+            r.s.mode = st.st_mode;
+            r.s.size = st.st_size;
+            // we compute the crc32 later down below, when we already have the file open.
+
+            if (newSnapshot.indexOfKey(key) >= 0) {
+                LOGP("back_up_files key already in use '%s'", key.string());
+                return -1;
+            }
+        }
+        newSnapshot.add(key, r);
+    }
+
+    int n = 0;
+    int N = oldSnapshot.size();
+    int m = 0;
+
+    while (n<N && m<fileCount) {
+        const String8& p = oldSnapshot.keyAt(n);
+        const String8& q = newSnapshot.keyAt(m);
+        FileRec& g = newSnapshot.editValueAt(m);
+        int cmp = p.compare(q);
+        if (g.deleted || cmp < 0) {
+            // file removed
+            LOGP("file removed: %s", p.string());
+            g.deleted = true; // They didn't mention the file, but we noticed that it's gone.
+            dataStream->WriteEntityHeader(p, -1);
+            n++;
+        }
+        else if (cmp > 0) {
+            // file added
+            LOGP("file added: %s", g.file.string());
+            write_update_file(dataStream, q, g.file.string());
+            m++;
+        }
+        else {
+            // both files exist, check them
+            const FileState& f = oldSnapshot.valueAt(n);
+
+            int fd = open(g.file.string(), O_RDONLY);
+            if (fd < 0) {
+                // We can't open the file.  Don't report it as a delete either.  Let the
+                // server keep the old version.  Maybe they'll be able to deal with it
+                // on restore.
+                LOGP("Unable to open file %s - skipping", g.file.string());
+            } else {
+                g.s.crc32 = compute_crc32(fd);
+
+                LOGP("%s", q.string());
+                LOGP("  new: modTime=%d,%d mode=%04o size=%-3d crc32=0x%08x",
+                        f.modTime_sec, f.modTime_nsec, f.mode, f.size, f.crc32);
+                LOGP("  old: modTime=%d,%d mode=%04o size=%-3d crc32=0x%08x",
+                        g.s.modTime_sec, g.s.modTime_nsec, g.s.mode, g.s.size, g.s.crc32);
+                if (f.modTime_sec != g.s.modTime_sec || f.modTime_nsec != g.s.modTime_nsec
+                        || f.mode != g.s.mode || f.size != g.s.size || f.crc32 != g.s.crc32) {
+                    write_update_file(dataStream, fd, g.s.mode, p, g.file.string());
+                }
+
+                close(fd);
+            }
+            n++;
+            m++;
+        }
+    }
+
+    // these were deleted
+    while (n<N) {
+        dataStream->WriteEntityHeader(oldSnapshot.keyAt(n), -1);
+        n++;
+    }
+
+    // these were added
+    while (m<fileCount) {
+        const String8& q = newSnapshot.keyAt(m);
+        FileRec& g = newSnapshot.editValueAt(m);
+        write_update_file(dataStream, q, g.file.string());
+        m++;
+    }
+
+    err = write_snapshot_file(newSnapshotFD, newSnapshot);
+
+    return 0;
+}
+
+#define RESTORE_BUF_SIZE (8*1024)
+
+RestoreHelperBase::RestoreHelperBase()
+{
+    m_buf = malloc(RESTORE_BUF_SIZE);
+    m_loggedUnknownMetadata = false;
+}
+
+RestoreHelperBase::~RestoreHelperBase()
+{
+    free(m_buf);
+}
+
+status_t
+RestoreHelperBase::WriteFile(const String8& filename, BackupDataReader* in)
+{
+    ssize_t err;
+    size_t dataSize;
+    String8 key;
+    int fd;
+    void* buf = m_buf;
+    ssize_t amt;
+    int mode;
+    int crc;
+    struct stat st;
+    FileRec r;
+
+    err = in->ReadEntityHeader(&key, &dataSize);
+    if (err != NO_ERROR) {
+        return err;
+    }
+
+    // Get the metadata block off the head of the file entity and use that to
+    // set up the output file
+    file_metadata_v1 metadata;
+    amt = in->ReadEntityData(&metadata, sizeof(metadata));
+    if (amt != sizeof(metadata)) {
+        LOGW("Could not read metadata for %s -- %ld / %s", filename.string(),
+                (long)amt, strerror(errno));
+        return EIO;
+    }
+    metadata.version = fromlel(metadata.version);
+    metadata.mode = fromlel(metadata.mode);
+    if (metadata.version > CURRENT_METADATA_VERSION) {
+        if (!m_loggedUnknownMetadata) {
+            m_loggedUnknownMetadata = true;
+            LOGW("Restoring file with unsupported metadata version %d (currently %d)",
+                    metadata.version, CURRENT_METADATA_VERSION);
+        }
+    }
+    mode = metadata.mode;
+
+    // Write the file and compute the crc
+    crc = crc32(0L, Z_NULL, 0);
+    fd = open(filename.string(), O_CREAT|O_RDWR|O_TRUNC, mode);
+    if (fd == -1) {
+        LOGW("Could not open file %s -- %s", filename.string(), strerror(errno));
+        return errno;
+    }
+    
+    while ((amt = in->ReadEntityData(buf, RESTORE_BUF_SIZE)) > 0) {
+        err = write(fd, buf, amt);
+        if (err != amt) {
+            close(fd);
+            LOGW("Error '%s' writing '%s'", strerror(errno), filename.string());
+            return errno;
+        }
+        crc = crc32(crc, (Bytef*)buf, amt);
+    }
+
+    close(fd);
+
+    // Record for the snapshot
+    err = stat(filename.string(), &st);
+    if (err != 0) {
+        LOGW("Error stating file that we just created %s", filename.string());
+        return errno;
+    }
+
+    r.file = filename;
+    r.deleted = false;
+    r.s.modTime_sec = st.st_mtime;
+    r.s.modTime_nsec = 0; // workaround sim breakage
+    //r.s.modTime_nsec = st.st_mtime_nsec;
+    r.s.mode = st.st_mode;
+    r.s.size = st.st_size;
+    r.s.crc32 = crc;
+
+    m_files.add(key, r);
+
+    return NO_ERROR;
+}
+
+status_t
+RestoreHelperBase::WriteSnapshot(int fd)
+{
+    return write_snapshot_file(fd, m_files);;
+}
+
+#if TEST_BACKUP_HELPERS
+
+#define SCRATCH_DIR "/data/backup_helper_test/"
+
+static int
+write_text_file(const char* path, const char* data)
+{
+    int amt;
+    int fd;
+    int len;
+
+    fd = creat(path, 0666);
+    if (fd == -1) {
+        fprintf(stderr, "creat %s failed\n", path);
+        return errno;
+    }
+
+    len = strlen(data);
+    amt = write(fd, data, len);
+    if (amt != len) {
+        fprintf(stderr, "error (%s) writing to file %s\n", strerror(errno), path);
+        return errno;
+    }
+
+    close(fd);
+
+    return 0;
+}
+
+static int
+compare_file(const char* path, const unsigned char* data, int len)
+{
+    int fd;
+    int amt;
+
+    fd = open(path, O_RDONLY);
+    if (fd == -1) {
+        fprintf(stderr, "compare_file error (%s) opening %s\n", strerror(errno), path);
+        return errno;
+    }
+
+    unsigned char* contents = (unsigned char*)malloc(len);
+    if (contents == NULL) {
+        fprintf(stderr, "malloc(%d) failed\n", len);
+        return ENOMEM;
+    }
+
+    bool sizesMatch = true;
+    amt = lseek(fd, 0, SEEK_END);
+    if (amt != len) {
+        fprintf(stderr, "compare_file file length should be %d, was %d\n", len, amt);
+        sizesMatch = false;
+    }
+    lseek(fd, 0, SEEK_SET);
+
+    int readLen = amt < len ? amt : len;
+    amt = read(fd, contents, readLen);
+    if (amt != readLen) {
+        fprintf(stderr, "compare_file read expected %d bytes but got %d\n", len, amt);
+    }
+
+    bool contentsMatch = true;
+    for (int i=0; i<readLen; i++) {
+        if (data[i] != contents[i]) {
+            if (contentsMatch) {
+                fprintf(stderr, "compare_file contents are different: (index, expected, actual)\n");
+                contentsMatch = false;
+            }
+            fprintf(stderr, "  [%-2d] %02x %02x\n", i, data[i], contents[i]);
+        }
+    }
+
+    free(contents);
+    return contentsMatch && sizesMatch ? 0 : 1;
+}
+
+int
+backup_helper_test_empty()
+{
+    int err;
+    int fd;
+    KeyedVector<String8,FileRec> snapshot;
+    const char* filename = SCRATCH_DIR "backup_helper_test_empty.snap";
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+
+    // write
+    fd = creat(filename, 0666);
+    if (fd == -1) {
+        fprintf(stderr, "error creating %s\n", filename);
+        return 1;
+    }
+
+    err = write_snapshot_file(fd, snapshot);
+
+    close(fd);
+
+    if (err != 0) {
+        fprintf(stderr, "write_snapshot_file reported error %d (%s)\n", err, strerror(err));
+        return err;
+    }
+
+    static const unsigned char correct_data[] = {
+        0x53, 0x6e, 0x61, 0x70,  0x00, 0x00, 0x00, 0x00,
+        0x46, 0x69, 0x6c, 0x65,  0x10, 0x00, 0x00, 0x00
+    };
+
+    err = compare_file(filename, correct_data, sizeof(correct_data));
+    if (err != 0) {
+        return err;
+    }
+
+    // read
+    fd = open(filename, O_RDONLY);
+    if (fd == -1) {
+        fprintf(stderr, "error opening for read %s\n", filename);
+        return 1;
+    }
+
+    KeyedVector<String8,FileState> readSnapshot;
+    err = read_snapshot_file(fd, &readSnapshot);
+    if (err != 0) {
+        fprintf(stderr, "read_snapshot_file failed %d\n", err);
+        return err;
+    }
+
+    if (readSnapshot.size() != 0) {
+        fprintf(stderr, "readSnapshot should be length 0\n");
+        return 1;
+    }
+
+    return 0;
+}
+
+int
+backup_helper_test_four()
+{
+    int err;
+    int fd;
+    KeyedVector<String8,FileRec> snapshot;
+    const char* filename = SCRATCH_DIR "backup_helper_test_four.snap";
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+
+    // write
+    fd = creat(filename, 0666);
+    if (fd == -1) {
+        fprintf(stderr, "error opening %s\n", filename);
+        return 1;
+    }
+
+    String8 filenames[4];
+    FileState states[4];
+    FileRec r;
+    r.deleted = false;
+
+    states[0].modTime_sec = 0xfedcba98;
+    states[0].modTime_nsec = 0xdeadbeef;
+    states[0].mode = 0777; // decimal 511, hex 0x000001ff
+    states[0].size = 0xababbcbc;
+    states[0].crc32 = 0x12345678;
+    states[0].nameLen = -12;
+    r.s = states[0];
+    filenames[0] = String8("bytes_of_padding");
+    snapshot.add(filenames[0], r);
+
+    states[1].modTime_sec = 0x93400031;
+    states[1].modTime_nsec = 0xdeadbeef;
+    states[1].mode = 0666; // decimal 438, hex 0x000001b6
+    states[1].size = 0x88557766;
+    states[1].crc32 = 0x22334422;
+    states[1].nameLen = -1;
+    r.s = states[1];
+    filenames[1] = String8("bytes_of_padding3");
+    snapshot.add(filenames[1], r);
+
+    states[2].modTime_sec = 0x33221144;
+    states[2].modTime_nsec = 0xdeadbeef;
+    states[2].mode = 0744; // decimal 484, hex 0x000001e4
+    states[2].size = 0x11223344;
+    states[2].crc32 = 0x01122334;
+    states[2].nameLen = 0;
+    r.s = states[2];
+    filenames[2] = String8("bytes_of_padding_2");
+    snapshot.add(filenames[2], r);
+
+    states[3].modTime_sec = 0x33221144;
+    states[3].modTime_nsec = 0xdeadbeef;
+    states[3].mode = 0755; // decimal 493, hex 0x000001ed
+    states[3].size = 0x11223344;
+    states[3].crc32 = 0x01122334;
+    states[3].nameLen = 0;
+    r.s = states[3];
+    filenames[3] = String8("bytes_of_padding__1");
+    snapshot.add(filenames[3], r);
+
+    err = write_snapshot_file(fd, snapshot);
+
+    close(fd);
+
+    if (err != 0) {
+        fprintf(stderr, "write_snapshot_file reported error %d (%s)\n", err, strerror(err));
+        return err;
+    }
+
+    static const unsigned char correct_data[] = {
+        // header
+        0x53, 0x6e, 0x61, 0x70,  0x04, 0x00, 0x00, 0x00,
+        0x46, 0x69, 0x6c, 0x65,  0xbc, 0x00, 0x00, 0x00,
+
+        // bytes_of_padding
+        0x98, 0xba, 0xdc, 0xfe,  0xef, 0xbe, 0xad, 0xde,
+        0xff, 0x01, 0x00, 0x00,  0xbc, 0xbc, 0xab, 0xab,
+        0x78, 0x56, 0x34, 0x12,  0x10, 0x00, 0x00, 0x00,
+        0x62, 0x79, 0x74, 0x65,  0x73, 0x5f, 0x6f, 0x66,
+        0x5f, 0x70, 0x61, 0x64,  0x64, 0x69, 0x6e, 0x67,
+
+        // bytes_of_padding3
+        0x31, 0x00, 0x40, 0x93,  0xef, 0xbe, 0xad, 0xde,
+        0xb6, 0x01, 0x00, 0x00,  0x66, 0x77, 0x55, 0x88,
+        0x22, 0x44, 0x33, 0x22,  0x11, 0x00, 0x00, 0x00,
+        0x62, 0x79, 0x74, 0x65,  0x73, 0x5f, 0x6f, 0x66,
+        0x5f, 0x70, 0x61, 0x64,  0x64, 0x69, 0x6e, 0x67,
+        0x33, 0xab, 0xab, 0xab,
+
+        // bytes of padding2
+        0x44, 0x11, 0x22, 0x33,  0xef, 0xbe, 0xad, 0xde,
+        0xe4, 0x01, 0x00, 0x00,  0x44, 0x33, 0x22, 0x11,
+        0x34, 0x23, 0x12, 0x01,  0x12, 0x00, 0x00, 0x00,
+        0x62, 0x79, 0x74, 0x65,  0x73, 0x5f, 0x6f, 0x66,
+        0x5f, 0x70, 0x61, 0x64,  0x64, 0x69, 0x6e, 0x67,
+        0x5f, 0x32, 0xab, 0xab,
+
+        // bytes of padding3
+        0x44, 0x11, 0x22, 0x33,  0xef, 0xbe, 0xad, 0xde,
+        0xed, 0x01, 0x00, 0x00,  0x44, 0x33, 0x22, 0x11,
+        0x34, 0x23, 0x12, 0x01,  0x13, 0x00, 0x00, 0x00,
+        0x62, 0x79, 0x74, 0x65,  0x73, 0x5f, 0x6f, 0x66,
+        0x5f, 0x70, 0x61, 0x64,  0x64, 0x69, 0x6e, 0x67,
+        0x5f, 0x5f, 0x31, 0xab
+    };
+
+    err = compare_file(filename, correct_data, sizeof(correct_data));
+    if (err != 0) {
+        return err;
+    }
+
+    // read
+    fd = open(filename, O_RDONLY);
+    if (fd == -1) {
+        fprintf(stderr, "error opening for read %s\n", filename);
+        return 1;
+    }
+
+
+    KeyedVector<String8,FileState> readSnapshot;
+    err = read_snapshot_file(fd, &readSnapshot);
+    if (err != 0) {
+        fprintf(stderr, "read_snapshot_file failed %d\n", err);
+        return err;
+    }
+
+    if (readSnapshot.size() != 4) {
+        fprintf(stderr, "readSnapshot should be length 4 is %d\n", readSnapshot.size());
+        return 1;
+    }
+
+    bool matched = true;
+    for (size_t i=0; i<readSnapshot.size(); i++) {
+        const String8& name = readSnapshot.keyAt(i);
+        const FileState state = readSnapshot.valueAt(i);
+
+        if (name != filenames[i] || states[i].modTime_sec != state.modTime_sec
+                || states[i].modTime_nsec != state.modTime_nsec || states[i].mode != state.mode
+                || states[i].size != state.size || states[i].crc32 != states[i].crc32) {
+            fprintf(stderr, "state %d expected={%d/%d, 0x%08x, %04o, 0x%08x, %3d} '%s'\n"
+                            "          actual={%d/%d, 0x%08x, %04o, 0x%08x, %3d} '%s'\n", i,
+                    states[i].modTime_sec, states[i].modTime_nsec, states[i].mode, states[i].size,
+                    states[i].crc32, name.length(), filenames[i].string(),
+                    state.modTime_sec, state.modTime_nsec, state.mode, state.size, state.crc32,
+                    state.nameLen, name.string());
+            matched = false;
+        }
+    }
+
+    return matched ? 0 : 1;
+}
+
+// hexdump -v -e '"    " 8/1 " 0x%02x," "\n"' data_writer.data
+const unsigned char DATA_GOLDEN_FILE[] = {
+     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, 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,
+     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, 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
+
+};
+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.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");
+
+    close(fd);
+
+    err = compare_file(filename, DATA_GOLDEN_FILE, DATA_GOLDEN_FILE_SIZE);
+    if (err != 0) {
+        return err;
+    }
+
+    return err;
+}
+
+int
+test_read_header_and_entity(BackupDataReader& reader, const char* str)
+{
+    int err;
+    int bufSize = strlen(str)+1;
+    char* buf = (char*)malloc(bufSize);
+    String8 string;
+    int cookie = 0x11111111;
+    size_t actualSize;
+    bool done;
+    int type;
+    ssize_t nRead;
+
+    // printf("\n\n---------- test_read_header_and_entity -- %s\n\n", str);
+
+    err = reader.ReadNextHeader(&done, &type);
+    if (done) {
+        fprintf(stderr, "should not be done yet\n");
+        goto finished;
+    }
+    if (err != 0) {
+        fprintf(stderr, "ReadNextHeader (for app header) failed with %s\n", strerror(err));
+        goto finished;
+    }
+    if (type != BACKUP_HEADER_ENTITY_V1) {
+        err = EINVAL;
+        fprintf(stderr, "type=0x%08x expected 0x%08x\n", type, BACKUP_HEADER_ENTITY_V1);
+    }
+
+    err = reader.ReadEntityHeader(&string, &actualSize);
+    if (err != 0) {
+        fprintf(stderr, "ReadEntityHeader failed with %s\n", strerror(err));
+        goto finished;
+    }
+    if (string != str) {
+        fprintf(stderr, "ReadEntityHeader expected key '%s' got '%s'\n", str, string.string());
+        err = EINVAL;
+        goto finished;
+    }
+    if ((int)actualSize != bufSize) {
+        fprintf(stderr, "ReadEntityHeader expected dataSize 0x%08x got 0x%08x\n", bufSize,
+                actualSize);
+        err = EINVAL;
+        goto finished;
+    }
+
+    nRead = reader.ReadEntityData(buf, bufSize);
+    if (nRead < 0) {
+        err = reader.Status();
+        fprintf(stderr, "ReadEntityData failed with %s\n", strerror(err));
+        goto finished;
+    }
+
+    if (0 != memcmp(buf, str, bufSize)) {
+        fprintf(stderr, "ReadEntityData expected '%s' but got something starting with "
+                "%02x %02x %02x %02x  '%c%c%c%c'\n", str, buf[0], buf[1], buf[2], buf[3],
+                buf[0], buf[1], buf[2], buf[3]);
+        err = EINVAL;
+        goto finished;
+    }
+
+    // The next read will confirm whether it got the right amount of data.
+
+finished:
+    if (err != NO_ERROR) {
+        fprintf(stderr, "test_read_header_and_entity failed with %s\n", strerror(err));
+    }
+    free(buf);
+    return err;
+}
+
+int
+backup_helper_test_data_reader()
+{
+    int err;
+    int fd;
+    const char* filename = SCRATCH_DIR "data_reader.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;
+    }
+
+    err = write(fd, DATA_GOLDEN_FILE, DATA_GOLDEN_FILE_SIZE);
+    if (err != DATA_GOLDEN_FILE_SIZE) {
+        fprintf(stderr, "Error \"%s\" writing golden file %s\n", strerror(errno), filename);
+        return errno;
+    }
+
+    close(fd);
+
+    fd = open(filename, O_RDONLY);
+    if (fd == -1) {
+        fprintf(stderr, "Error \"%s\" opening golden file %s for read\n", strerror(errno),
+                filename);
+        return errno;
+    }
+
+    {
+        BackupDataReader reader(fd);
+
+        err = 0;
+
+        if (err == NO_ERROR) {
+            err = test_read_header_and_entity(reader, "no_padding_");
+        }
+
+        if (err == NO_ERROR) {
+            err = test_read_header_and_entity(reader, "padded_to__3");
+        }
+
+        if (err == NO_ERROR) {
+            err = test_read_header_and_entity(reader, "padded_to_2__");
+        }
+
+        if (err == NO_ERROR) {
+            err = test_read_header_and_entity(reader, "padded_to1");
+        }
+    }
+
+    close(fd);
+
+    return err;
+}
+
+static int
+get_mod_time(const char* filename, struct timeval times[2])
+{
+    int err;
+    struct stat64 st;
+    err = stat64(filename, &st);
+    if (err != 0) {
+        fprintf(stderr, "stat '%s' failed: %s\n", filename, strerror(errno));
+        return errno;
+    }
+    times[0].tv_sec = st.st_atime;
+    times[1].tv_sec = st.st_mtime;
+
+    // If st_atime is a macro then struct stat64 uses struct timespec
+    // to store the access and modif time values and typically
+    // st_*time_nsec is not defined. In glibc, this is controlled by
+    // __USE_MISC.
+#ifdef __USE_MISC
+#if !defined(st_atime) || defined(st_atime_nsec)
+#error "Check if this __USE_MISC conditional is still needed."
+#endif
+    times[0].tv_usec = st.st_atim.tv_nsec / 1000;
+    times[1].tv_usec = st.st_mtim.tv_nsec / 1000;
+#else
+    times[0].tv_usec = st.st_atime_nsec / 1000;
+    times[1].tv_usec = st.st_mtime_nsec / 1000;
+#endif
+
+    return 0;
+}
+
+int
+backup_helper_test_files()
+{
+    int err;
+    int oldSnapshotFD;
+    int dataStreamFD;
+    int newSnapshotFD;
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+    mkdir(SCRATCH_DIR "data", 0777);
+
+    write_text_file(SCRATCH_DIR "data/b", "b\nbb\n");
+    write_text_file(SCRATCH_DIR "data/c", "c\ncc\n");
+    write_text_file(SCRATCH_DIR "data/d", "d\ndd\n");
+    write_text_file(SCRATCH_DIR "data/e", "e\nee\n");
+    write_text_file(SCRATCH_DIR "data/f", "f\nff\n");
+    write_text_file(SCRATCH_DIR "data/h", "h\nhh\n");
+
+    char const* files_before[] = {
+        SCRATCH_DIR "data/b",
+        SCRATCH_DIR "data/c",
+        SCRATCH_DIR "data/d",
+        SCRATCH_DIR "data/e",
+        SCRATCH_DIR "data/f"
+    };
+
+    char const* keys_before[] = {
+        "data/b",
+        "data/c",
+        "data/d",
+        "data/e",
+        "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;
+    }
+
+    {
+        BackupDataWriter dataStream(dataStreamFD);
+
+        err = back_up_files(-1, &dataStream, newSnapshotFD, files_before, keys_before, 5);
+        if (err != 0) {
+            return err;
+        }
+    }
+
+    close(dataStreamFD);
+    close(newSnapshotFD);
+
+    sleep(3);
+
+    struct timeval d_times[2];
+    struct timeval e_times[2];
+
+    err = get_mod_time(SCRATCH_DIR "data/d", d_times);
+    err |= get_mod_time(SCRATCH_DIR "data/e", e_times);
+    if (err != 0) {
+        return err;
+    }
+
+    write_text_file(SCRATCH_DIR "data/a", "a\naa\n");
+    unlink(SCRATCH_DIR "data/c");
+    write_text_file(SCRATCH_DIR "data/c", "c\ncc\n");
+    write_text_file(SCRATCH_DIR "data/d", "dd\ndd\n");
+    utimes(SCRATCH_DIR "data/d", d_times);
+    write_text_file(SCRATCH_DIR "data/e", "z\nzz\n");
+    utimes(SCRATCH_DIR "data/e", e_times);
+    write_text_file(SCRATCH_DIR "data/g", "g\ngg\n");
+    unlink(SCRATCH_DIR "data/f");
+
+    char const* files_after[] = {
+        SCRATCH_DIR "data/a", // added
+        SCRATCH_DIR "data/b", // same
+        SCRATCH_DIR "data/c", // different mod time
+        SCRATCH_DIR "data/d", // different size (same mod time)
+        SCRATCH_DIR "data/e", // different contents (same mod time, same size)
+        SCRATCH_DIR "data/g"  // added
+    };
+
+    char const* keys_after[] = {
+        "data/a", // added
+        "data/b", // same
+        "data/c", // different mod time
+        "data/d", // different size (same mod time)
+        "data/e", // different contents (same mod time, same size)
+        "data/g"  // added
+    };
+
+    oldSnapshotFD = open(SCRATCH_DIR "before.snap", O_RDONLY);
+    if (oldSnapshotFD == -1) {
+        fprintf(stderr, "error opening: %s\n", strerror(errno));
+        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;
+    }
+
+    {
+        BackupDataWriter dataStream(dataStreamFD);
+
+        err = back_up_files(oldSnapshotFD, &dataStream, newSnapshotFD, files_after, keys_after, 6);
+        if (err != 0) {
+            return err;
+        }
+}
+
+    close(oldSnapshotFD);
+    close(dataStreamFD);
+    close(newSnapshotFD);
+
+    return 0;
+}
+
+int
+backup_helper_test_null_base()
+{
+    int err;
+    int oldSnapshotFD;
+    int dataStreamFD;
+    int newSnapshotFD;
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+    mkdir(SCRATCH_DIR "data", 0777);
+
+    write_text_file(SCRATCH_DIR "data/a", "a\naa\n");
+
+    char const* files[] = {
+        SCRATCH_DIR "data/a",
+    };
+
+    char const* keys[] = {
+        "a",
+    };
+
+    dataStreamFD = creat(SCRATCH_DIR "null_base.data", 0666);
+    if (dataStreamFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
+    newSnapshotFD = creat(SCRATCH_DIR "null_base.snap", 0666);
+    if (newSnapshotFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
+    {
+        BackupDataWriter dataStream(dataStreamFD);
+
+        err = back_up_files(-1, &dataStream, newSnapshotFD, files, keys, 1);
+        if (err != 0) {
+            return err;
+        }
+    }
+
+    close(dataStreamFD);
+    close(newSnapshotFD);
+
+    return 0;
+}
+
+int
+backup_helper_test_missing_file()
+{
+    int err;
+    int oldSnapshotFD;
+    int dataStreamFD;
+    int newSnapshotFD;
+
+    system("rm -r " SCRATCH_DIR);
+    mkdir(SCRATCH_DIR, 0777);
+    mkdir(SCRATCH_DIR "data", 0777);
+
+    write_text_file(SCRATCH_DIR "data/b", "b\nbb\n");
+
+    char const* files[] = {
+        SCRATCH_DIR "data/a",
+        SCRATCH_DIR "data/b",
+        SCRATCH_DIR "data/c",
+    };
+
+    char const* keys[] = {
+        "a",
+        "b",
+        "c",
+    };
+
+    dataStreamFD = creat(SCRATCH_DIR "null_base.data", 0666);
+    if (dataStreamFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
+    newSnapshotFD = creat(SCRATCH_DIR "null_base.snap", 0666);
+    if (newSnapshotFD == -1) {
+        fprintf(stderr, "error creating: %s\n", strerror(errno));
+        return errno;
+    }
+
+    {
+        BackupDataWriter dataStream(dataStreamFD);
+
+        err = back_up_files(-1, &dataStream, newSnapshotFD, files, keys, 1);
+        if (err != 0) {
+            return err;
+        }
+    }
+
+    close(dataStreamFD);
+    close(newSnapshotFD);
+
+    return 0;
+}
+
+
+#endif // TEST_BACKUP_HELPERS
+
+}