diff --git a/fs_mgr/libfiemap_writer/.clang-format b/fs_mgr/libfiemap_writer/.clang-format
new file mode 120000
index 0000000..8b770a1
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/.clang-format
@@ -0,0 +1 @@
+../../.clang-format-4
\ No newline at end of file
diff --git a/fs_mgr/libfiemap_writer/Android.bp b/fs_mgr/libfiemap_writer/Android.bp
new file mode 100644
index 0000000..ed209aa
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/Android.bp
@@ -0,0 +1,64 @@
+//
+// Copyright (C) 2018 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.
+//
+
+cc_library_static {
+    name: "libfiemap_writer",
+    defaults: ["fs_mgr_defaults"],
+    recovery_available: true,
+    export_include_dirs: ["include"],
+    cflags: [
+        "-D_FILE_OFFSET_BITS=64",
+    ],
+
+    srcs: [
+        "fiemap_writer.cpp",
+        "split_fiemap_writer.cpp",
+        "utility.cpp",
+    ],
+
+    static_libs: [
+        "libdm",
+        "libext4_utils",
+    ],
+
+    header_libs: [
+        "libbase_headers",
+        "liblog_headers",
+    ],
+}
+
+cc_test {
+    name: "fiemap_writer_test",
+    cflags: [
+        "-D_FILE_OFFSET_BITS=64",
+    ],
+    static_libs: [
+        "libbase",
+        "libdm",
+        "libfiemap_writer",
+        "liblog",
+    ],
+
+    data: [
+        "testdata/unaligned_file",
+        "testdata/file_4k",
+        "testdata/file_32k",
+    ],
+
+    srcs: [
+        "fiemap_writer_test.cpp",
+    ],
+}
diff --git a/fs_mgr/libfiemap_writer/Android.mk b/fs_mgr/libfiemap_writer/Android.mk
new file mode 100644
index 0000000..3c07b8e
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/Android.mk
@@ -0,0 +1,22 @@
+#
+# Copyright (C) 2019 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.
+#
+
+LOCAL_PATH := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := VtsFiemapWriterTest
+-include test/vts/tools/build/Android.host_config.mk
diff --git a/fs_mgr/libfiemap_writer/AndroidTest.xml b/fs_mgr/libfiemap_writer/AndroidTest.xml
new file mode 100644
index 0000000..08cff0e
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/AndroidTest.xml
@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2019 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.
+-->
+<configuration description="Config for VTS VtsFiemapWriterTest">
+    <option name="config-descriptor:metadata" key="plan" value="vts-kernel" />
+    <target_preparer class="com.android.compatibility.common.tradefed.targetprep.VtsFilePusher">
+        <option name="abort-on-push-failure" value="false"/>
+        <option name="push-group" value="HostDrivenTest.push"/>
+    </target_preparer>
+    <test class="com.android.tradefed.testtype.VtsMultiDeviceTest">
+      <option name="test-module-name" value="VtsFiemapWriterTest"/>
+        <option name="binary-test-source" value="_32bit::DATA/nativetest/fiemap_writer_test/fiemap_writer_test" />
+        <option name="binary-test-source" value="_64bit::DATA/nativetest64/fiemap_writer_test/fiemap_writer_test" />
+        <option name="binary-test-type" value="gtest"/>
+        <option name="test-timeout" value="1m"/>
+    </test>
+</configuration>
diff --git a/fs_mgr/libfiemap_writer/fiemap_writer.cpp b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
new file mode 100644
index 0000000..0a3ba6c
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
@@ -0,0 +1,745 @@
+/*
+ * Copyright (C) 2018 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 <libfiemap_writer/fiemap_writer.h>
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include <limits>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+#include <libdm/dm.h>
+
+namespace android {
+namespace fiemap_writer {
+
+using namespace android::dm;
+
+// We are expecting no more than 512 extents in a fiemap of the file we create.
+// If we find more, then it is treated as error for now.
+static constexpr const uint32_t kMaxExtents = 512;
+
+// TODO: Fallback to using fibmap if FIEMAP_EXTENT_MERGED is set.
+static constexpr const uint32_t kUnsupportedExtentFlags =
+        FIEMAP_EXTENT_UNKNOWN | FIEMAP_EXTENT_UNWRITTEN | FIEMAP_EXTENT_DELALLOC |
+        FIEMAP_EXTENT_NOT_ALIGNED | FIEMAP_EXTENT_DATA_INLINE | FIEMAP_EXTENT_DATA_TAIL |
+        FIEMAP_EXTENT_UNWRITTEN | FIEMAP_EXTENT_SHARED | FIEMAP_EXTENT_MERGED;
+
+// Large file support must be enabled.
+static_assert(sizeof(off_t) == sizeof(uint64_t));
+
+static inline void cleanup(const std::string& file_path, bool created) {
+    if (created) {
+        unlink(file_path.c_str());
+    }
+}
+
+static bool BlockDeviceToName(uint32_t major, uint32_t minor, std::string* bdev_name) {
+    // The symlinks in /sys/dev/block point to the block device node under /sys/device/..
+    // The directory name in the target corresponds to the name of the block device. We use
+    // that to extract the block device name.
+    // e.g for block device name 'ram0', there exists a symlink named '1:0' in /sys/dev/block as
+    // follows.
+    //    1:0 -> ../../devices/virtual/block/ram0
+    std::string sysfs_path = ::android::base::StringPrintf("/sys/dev/block/%u:%u", major, minor);
+    std::string sysfs_bdev;
+
+    if (!::android::base::Readlink(sysfs_path, &sysfs_bdev)) {
+        PLOG(ERROR) << "Failed to read link at: " << sysfs_path;
+        return false;
+    }
+
+    *bdev_name = ::android::base::Basename(sysfs_bdev);
+    // Paranoid sanity check to make sure we just didn't get the
+    // input in return as-is.
+    if (sysfs_bdev == *bdev_name) {
+        LOG(ERROR) << "Malformed symlink for block device: " << sysfs_bdev;
+        return false;
+    }
+
+    return true;
+}
+
+static bool ValidateDmTarget(const DeviceMapper::TargetInfo& target) {
+    const auto& entry = target.spec;
+    if (entry.sector_start != 0) {
+        LOG(INFO) << "Stopping at target with non-zero starting sector";
+        return false;
+    }
+
+    auto target_type = DeviceMapper::GetTargetType(entry);
+    if (target_type == "bow" || target_type == "default-key" || target_type == "crypt") {
+        return true;
+    }
+    if (target_type == "linear") {
+        auto pieces = android::base::Split(target.data, " ");
+        if (pieces[1] != "0") {
+            LOG(INFO) << "Stopping at complex linear target with non-zero starting sector: "
+                      << pieces[1];
+            return false;
+        }
+        return true;
+    }
+
+    LOG(INFO) << "Stopping at complex target type " << target_type;
+    return false;
+}
+
+static bool DeviceMapperStackPop(const std::string& bdev, std::string* bdev_raw) {
+    *bdev_raw = bdev;
+
+    if (!::android::base::StartsWith(bdev, "dm-")) {
+        // We are at the bottom of the device mapper stack.
+        return true;
+    }
+
+    // Get the device name.
+    auto dm_name_file = "/sys/block/" + bdev + "/dm/name";
+    std::string dm_name;
+    if (!android::base::ReadFileToString(dm_name_file, &dm_name)) {
+        PLOG(ERROR) << "Could not read file: " << dm_name_file;
+        return false;
+    }
+    dm_name = android::base::Trim(dm_name);
+
+    auto& dm = DeviceMapper::Instance();
+    std::vector<DeviceMapper::TargetInfo> table;
+    if (!dm.GetTableInfo(dm_name, &table)) {
+        LOG(ERROR) << "Could not read device-mapper table for " << dm_name << " at " << bdev;
+        return false;
+    }
+
+    // The purpose of libfiemap_writer is to provide an extent-based view into
+    // a file. This is difficult if devices are not layered in a 1:1 manner;
+    // we would have to translate and break up extents based on the actual
+    // block mapping. Since this is too complex, we simply stop processing
+    // the device-mapper stack if we encounter a complex case.
+    //
+    // It is up to the caller to decide whether stopping at a virtual block
+    // device is allowable. In most cases it is not, because we want either
+    // "userdata" or an external volume. It is useful for tests however.
+    // Callers can check by comparing the device number to that of userdata,
+    // or by checking whether is a device-mapper node.
+    if (table.size() > 1) {
+        LOG(INFO) << "Stopping at complex table for " << dm_name << " at " << bdev;
+        return true;
+    }
+    if (!ValidateDmTarget(table[0])) {
+        return true;
+    }
+
+    auto dm_leaf_dir = "/sys/block/" + bdev + "/slaves";
+    auto d = std::unique_ptr<DIR, decltype(&closedir)>(opendir(dm_leaf_dir.c_str()), closedir);
+    if (d == nullptr) {
+        PLOG(ERROR) << "Failed to open: " << dm_leaf_dir;
+        return false;
+    }
+
+    struct dirent* de;
+    uint32_t num_leaves = 0;
+    std::string bdev_next = "";
+    while ((de = readdir(d.get())) != nullptr) {
+        if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
+            continue;
+        }
+
+        // We set the first name we find here
+        if (bdev_next.empty()) {
+            bdev_next = de->d_name;
+        }
+        num_leaves++;
+    }
+
+    // if we have more than one leaves, we return immediately. We can't continue to create the
+    // file since we don't know how to write it out using fiemap, so it will be readable via the
+    // underlying block devices later. The reader will also have to construct the same device mapper
+    // target in order read the file out.
+    if (num_leaves > 1) {
+        LOG(ERROR) << "Found " << num_leaves << " leaf block devices under device mapper device "
+                   << bdev;
+        return false;
+    }
+
+    // recursively call with the block device we found in order to pop the device mapper stack.
+    return DeviceMapperStackPop(bdev_next, bdev_raw);
+}
+
+bool FiemapWriter::GetBlockDeviceForFile(const std::string& file_path, std::string* bdev_path,
+                                         bool* uses_dm) {
+    struct stat sb;
+    if (stat(file_path.c_str(), &sb)) {
+        PLOG(ERROR) << "Failed to get stat for: " << file_path;
+        return false;
+    }
+
+    std::string bdev;
+    if (!BlockDeviceToName(major(sb.st_dev), minor(sb.st_dev), &bdev)) {
+        LOG(ERROR) << "Failed to get block device name for " << major(sb.st_dev) << ":"
+                   << minor(sb.st_dev);
+        return false;
+    }
+
+    std::string bdev_raw;
+    if (!DeviceMapperStackPop(bdev, &bdev_raw)) {
+        LOG(ERROR) << "Failed to get the bottom of the device mapper stack for device: " << bdev;
+        return false;
+    }
+
+    if (uses_dm) {
+        *uses_dm = (bdev_raw != bdev);
+    }
+
+    LOG(DEBUG) << "Popped device (" << bdev_raw << ") from device mapper stack starting with ("
+               << bdev << ")";
+
+    *bdev_path = ::android::base::StringPrintf("/dev/block/%s", bdev_raw.c_str());
+
+    // Make sure we are talking to a block device before calling it a success.
+    if (stat(bdev_path->c_str(), &sb)) {
+        PLOG(ERROR) << "Failed to get stat for block device: " << *bdev_path;
+        return false;
+    }
+
+    if ((sb.st_mode & S_IFMT) != S_IFBLK) {
+        PLOG(ERROR) << "File: " << *bdev_path << " is not a block device";
+        return false;
+    }
+
+    return true;
+}
+
+static bool GetBlockDeviceSize(int bdev_fd, const std::string& bdev_path, uint64_t* bdev_size) {
+    uint64_t size_in_bytes = 0;
+    if (ioctl(bdev_fd, BLKGETSIZE64, &size_in_bytes)) {
+        PLOG(ERROR) << "Failed to get total size for: " << bdev_path;
+        return false;
+    }
+
+    *bdev_size = size_in_bytes;
+
+    return true;
+}
+
+static uint64_t GetFileSize(const std::string& file_path) {
+    struct stat sb;
+    if (stat(file_path.c_str(), &sb)) {
+        PLOG(ERROR) << "Failed to get size for file: " << file_path;
+        return 0;
+    }
+
+    return sb.st_size;
+}
+
+static bool PerformFileChecks(const std::string& file_path, uint64_t file_size, uint64_t* blocksz,
+                              uint32_t* fs_type) {
+    struct statfs64 sfs;
+    if (statfs64(file_path.c_str(), &sfs)) {
+        PLOG(ERROR) << "Failed to read file system status at: " << file_path;
+        return false;
+    }
+
+    if (!sfs.f_bsize) {
+        LOG(ERROR) << "Unsupported block size: " << sfs.f_bsize;
+        return false;
+    }
+
+    // Check if the filesystem is of supported types.
+    // Only ext4, f2fs, and vfat are tested and supported.
+    switch (sfs.f_type) {
+        case EXT4_SUPER_MAGIC:
+        case F2FS_SUPER_MAGIC:
+        case MSDOS_SUPER_MAGIC:
+            break;
+        default:
+            LOG(ERROR) << "Unsupported file system type: 0x" << std::hex << sfs.f_type;
+            return false;
+    }
+
+    uint64_t available_bytes = sfs.f_bsize * sfs.f_bavail;
+    if (available_bytes <= file_size) {
+        LOG(ERROR) << "Not enough free space in file system to create file of size : " << file_size;
+        return false;
+    }
+
+    *blocksz = sfs.f_bsize;
+    *fs_type = sfs.f_type;
+    return true;
+}
+
+static bool FallocateFallback(int file_fd, uint64_t block_size, uint64_t file_size,
+                              const std::string& file_path,
+                              const std::function<bool(uint64_t, uint64_t)>& on_progress) {
+    // Even though this is much faster than writing zeroes, it is still slow
+    // enough that we need to fire the progress callback periodically. To
+    // easily achieve this, we seek in chunks. We use 1000 chunks since
+    // normally we only fire the callback on 1/1000th increments.
+    uint64_t bytes_per_chunk = std::max(file_size / 1000, block_size);
+
+    // Seek just to the end of each chunk and write a single byte, causing
+    // the filesystem to allocate blocks.
+    off_t cursor = 0;
+    off_t end = static_cast<off_t>(file_size);
+    while (cursor < end) {
+        cursor = std::min(static_cast<off_t>(cursor + bytes_per_chunk), end);
+        auto rv = TEMP_FAILURE_RETRY(lseek(file_fd, cursor - 1, SEEK_SET));
+        if (rv < 0) {
+            PLOG(ERROR) << "Failed to lseek " << file_path;
+            return false;
+        }
+        if (rv != cursor - 1) {
+            LOG(ERROR) << "Seek returned wrong offset " << rv << " for file " << file_path;
+            return false;
+        }
+        char buffer[] = {0};
+        if (!android::base::WriteFully(file_fd, buffer, 1)) {
+            PLOG(ERROR) << "Write failed: " << file_path;
+            return false;
+        }
+        if (on_progress && !on_progress(cursor, file_size)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+static bool AllocateFile(int file_fd, const std::string& file_path, uint64_t blocksz,
+                         uint64_t file_size, unsigned int fs_type,
+                         std::function<bool(uint64_t, uint64_t)> on_progress) {
+    // Reserve space for the file on the file system and write it out to make sure the extents
+    // don't come back unwritten. Return from this function with the kernel file offset set to 0.
+    // If the filesystem is f2fs, then we also PIN the file on disk to make sure the blocks
+    // aren't moved around.
+    switch (fs_type) {
+        case EXT4_SUPER_MAGIC:
+        case F2FS_SUPER_MAGIC:
+            if (fallocate(file_fd, FALLOC_FL_ZERO_RANGE, 0, file_size)) {
+                PLOG(ERROR) << "Failed to allocate space for file: " << file_path
+                            << " size: " << file_size;
+                return false;
+            }
+            break;
+        case MSDOS_SUPER_MAGIC:
+            // fallocate() is not supported, and not needed, since VFAT does not support holes.
+            // Instead we can perform a much faster allocation.
+            return FallocateFallback(file_fd, blocksz, file_size, file_path, on_progress);
+        default:
+            LOG(ERROR) << "Missing fallocate() support for file system " << fs_type;
+            return false;
+    }
+
+    // write zeroes in 'blocksz' byte increments until we reach file_size to make sure the data
+    // blocks are actually written to by the file system and thus getting rid of the holes in the
+    // file.
+    auto buffer = std::unique_ptr<void, decltype(&free)>(calloc(1, blocksz), free);
+    if (buffer == nullptr) {
+        LOG(ERROR) << "failed to allocate memory for writing file";
+        return false;
+    }
+
+    off64_t offset = lseek64(file_fd, 0, SEEK_SET);
+    if (offset < 0) {
+        PLOG(ERROR) << "Failed to seek at the beginning of : " << file_path;
+        return false;
+    }
+
+    int permille = -1;
+    while (offset < file_size) {
+        if (!::android::base::WriteFully(file_fd, buffer.get(), blocksz)) {
+            PLOG(ERROR) << "Failed to write" << blocksz << " bytes at offset" << offset
+                        << " in file " << file_path;
+            return false;
+        }
+
+        offset += blocksz;
+
+        // Don't invoke the callback every iteration - wait until a significant
+        // chunk (here, 1/1000th) of the data has been processed.
+        int new_permille = (static_cast<uint64_t>(offset) * 1000) / file_size;
+        if (new_permille != permille && static_cast<uint64_t>(offset) != file_size) {
+            if (on_progress && !on_progress(offset, file_size)) {
+                return false;
+            }
+            permille = new_permille;
+        }
+    }
+
+    if (lseek64(file_fd, 0, SEEK_SET) < 0) {
+        PLOG(ERROR) << "Failed to reset offset at the beginning of : " << file_path;
+        return false;
+    }
+
+    // flush all writes here ..
+    if (fsync(file_fd)) {
+        PLOG(ERROR) << "Failed to synchronize written file:" << file_path;
+        return false;
+    }
+
+    // Send one last progress notification.
+    if (on_progress && !on_progress(file_size, file_size)) {
+        return false;
+    }
+    return true;
+}
+
+static bool PinFile(int file_fd, const std::string& file_path, uint32_t fs_type) {
+    if (fs_type != F2FS_SUPER_MAGIC) {
+        // No pinning necessary for ext4/msdos. The blocks, once allocated, are
+        // expected to be fixed.
+        return true;
+    }
+
+// F2FS-specific ioctl
+// It requires the below kernel commit merged in v4.16-rc1.
+//   1ad71a27124c ("f2fs: add an ioctl to disable GC for specific file")
+// In android-4.4,
+//   56ee1e817908 ("f2fs: updates on v4.16-rc1")
+// In android-4.9,
+//   2f17e34672a8 ("f2fs: updates on v4.16-rc1")
+// In android-4.14,
+//   ce767d9a55bc ("f2fs: updates on v4.16-rc1")
+#ifndef F2FS_IOC_SET_PIN_FILE
+#ifndef F2FS_IOCTL_MAGIC
+#define F2FS_IOCTL_MAGIC 0xf5
+#endif
+#define F2FS_IOC_SET_PIN_FILE _IOW(F2FS_IOCTL_MAGIC, 13, __u32)
+#endif
+
+    uint32_t pin_status = 1;
+    int error = ioctl(file_fd, F2FS_IOC_SET_PIN_FILE, &pin_status);
+    if (error < 0) {
+        if ((errno == ENOTTY) || (errno == ENOTSUP)) {
+            PLOG(ERROR) << "Failed to pin file, not supported by kernel: " << file_path;
+        } else {
+            PLOG(ERROR) << "Failed to pin file: " << file_path;
+        }
+        return false;
+    }
+
+    return true;
+}
+
+static bool IsFilePinned(int file_fd, const std::string& file_path, uint32_t fs_type) {
+    if (fs_type != F2FS_SUPER_MAGIC) {
+        // No pinning necessary for ext4 or vfat. The blocks, once allocated,
+        // are expected to be fixed.
+        return true;
+    }
+
+// F2FS-specific ioctl
+// It requires the below kernel commit merged in v4.16-rc1.
+//   1ad71a27124c ("f2fs: add an ioctl to disable GC for specific file")
+// In android-4.4,
+//   56ee1e817908 ("f2fs: updates on v4.16-rc1")
+// In android-4.9,
+//   2f17e34672a8 ("f2fs: updates on v4.16-rc1")
+// In android-4.14,
+//   ce767d9a55bc ("f2fs: updates on v4.16-rc1")
+#ifndef F2FS_IOC_GET_PIN_FILE
+#ifndef F2FS_IOCTL_MAGIC
+#define F2FS_IOCTL_MAGIC 0xf5
+#endif
+#define F2FS_IOC_GET_PIN_FILE _IOR(F2FS_IOCTL_MAGIC, 14, __u32)
+#endif
+
+    // f2fs: export FS_NOCOW_FL flag to user
+    uint32_t flags;
+    int error = ioctl(file_fd, FS_IOC_GETFLAGS, &flags);
+    if (error < 0) {
+        if ((errno == ENOTTY) || (errno == ENOTSUP)) {
+            PLOG(ERROR) << "Failed to get flags, not supported by kernel: " << file_path;
+        } else {
+            PLOG(ERROR) << "Failed to get flags: " << file_path;
+        }
+        return false;
+    }
+    if (!(flags & FS_NOCOW_FL)) {
+        LOG(ERROR) << "It is not pinned: " << file_path;
+        return false;
+    }
+
+    // F2FS_IOC_GET_PIN_FILE returns the number of blocks moved.
+    uint32_t moved_blocks_nr;
+    error = ioctl(file_fd, F2FS_IOC_GET_PIN_FILE, &moved_blocks_nr);
+    if (error < 0) {
+        if ((errno == ENOTTY) || (errno == ENOTSUP)) {
+            PLOG(ERROR) << "Failed to get file pin status, not supported by kernel: " << file_path;
+        } else {
+            PLOG(ERROR) << "Failed to get file pin status: " << file_path;
+        }
+        return false;
+    }
+
+    if (moved_blocks_nr) {
+        LOG(ERROR) << moved_blocks_nr << " blocks moved in file " << file_path;
+    }
+    return moved_blocks_nr == 0;
+}
+
+bool FiemapWriter::HasPinnedExtents(const std::string& file_path) {
+    android::base::unique_fd fd(open(file_path.c_str(), O_NOFOLLOW | O_CLOEXEC | O_RDONLY));
+    if (fd < 0) {
+        PLOG(ERROR) << "open: " << file_path;
+        return false;
+    }
+
+    struct statfs64 sfs;
+    if (fstatfs64(fd, &sfs)) {
+        PLOG(ERROR) << "fstatfs64: " << file_path;
+        return false;
+    }
+    return IsFilePinned(fd, file_path, sfs.f_type);
+}
+
+static bool ReadFiemap(int file_fd, const std::string& file_path,
+                       std::vector<struct fiemap_extent>* extents) {
+    uint64_t fiemap_size =
+            sizeof(struct fiemap_extent) + kMaxExtents * sizeof(struct fiemap_extent);
+    auto buffer = std::unique_ptr<void, decltype(&free)>(calloc(1, fiemap_size), free);
+    if (buffer == nullptr) {
+        LOG(ERROR) << "Failed to allocate memory for fiemap";
+        return false;
+    }
+
+    struct fiemap* fiemap = reinterpret_cast<struct fiemap*>(buffer.get());
+    fiemap->fm_start = 0;
+    fiemap->fm_length = UINT64_MAX;
+    // make sure file is synced to disk before we read the fiemap
+    fiemap->fm_flags = FIEMAP_FLAG_SYNC;
+    fiemap->fm_extent_count = kMaxExtents;
+
+    if (ioctl(file_fd, FS_IOC_FIEMAP, fiemap)) {
+        PLOG(ERROR) << "Failed to get FIEMAP from the kernel for file: " << file_path;
+        return false;
+    }
+
+    if (fiemap->fm_mapped_extents == 0) {
+        LOG(ERROR) << "File " << file_path << " has zero extents";
+        return false;
+    }
+
+    // Iterate through each extent read and make sure its valid before adding it to the vector
+    bool last_extent_seen = false;
+    struct fiemap_extent* extent = &fiemap->fm_extents[0];
+    for (uint32_t i = 0; i < fiemap->fm_mapped_extents; i++, extent++) {
+        // LogExtent(i + 1, *extent);
+        if (extent->fe_flags & kUnsupportedExtentFlags) {
+            LOG(ERROR) << "Extent " << i + 1 << " of file " << file_path
+                       << " has unsupported flags";
+            extents->clear();
+            return false;
+        }
+
+        if (extent->fe_flags & FIEMAP_EXTENT_LAST) {
+            last_extent_seen = true;
+            if (i != (fiemap->fm_mapped_extents - 1)) {
+                LOG(WARNING) << "Extents are being received out-of-order";
+            }
+        }
+        extents->emplace_back(std::move(*extent));
+    }
+
+    if (!last_extent_seen) {
+        // The file is possibly too fragmented.
+        if (fiemap->fm_mapped_extents == kMaxExtents) {
+            LOG(ERROR) << "File is too fragmented, needs more than " << kMaxExtents << " extents.";
+        }
+        extents->clear();
+    }
+
+    return last_extent_seen;
+}
+
+static bool ReadFibmap(int file_fd, const std::string& file_path,
+                       std::vector<struct fiemap_extent>* extents) {
+    struct stat s;
+    if (fstat(file_fd, &s)) {
+        PLOG(ERROR) << "Failed to stat " << file_path;
+        return false;
+    }
+
+    unsigned int blksize;
+    if (ioctl(file_fd, FIGETBSZ, &blksize) < 0) {
+        PLOG(ERROR) << "Failed to get FIGETBSZ for " << file_path;
+        return false;
+    }
+    if (!blksize) {
+        LOG(ERROR) << "Invalid filesystem block size: " << blksize;
+        return false;
+    }
+
+    uint64_t num_blocks = (s.st_size + blksize - 1) / blksize;
+    if (num_blocks > std::numeric_limits<uint32_t>::max()) {
+        LOG(ERROR) << "Too many blocks for FIBMAP (" << num_blocks << ")";
+        return false;
+    }
+
+    for (uint32_t last_block, block_number = 0; block_number < num_blocks; block_number++) {
+        uint32_t block = block_number;
+        if (ioctl(file_fd, FIBMAP, &block)) {
+            PLOG(ERROR) << "Failed to get FIBMAP for file " << file_path;
+            return false;
+        }
+        if (!block) {
+            LOG(ERROR) << "Logical block " << block_number << " is a hole, which is not supported";
+            return false;
+        }
+
+        if (!extents->empty() && block == last_block + 1) {
+            extents->back().fe_length += blksize;
+        } else {
+            extents->push_back(fiemap_extent{.fe_logical = block_number,
+                                             .fe_physical = static_cast<uint64_t>(block) * blksize,
+                                             .fe_length = static_cast<uint64_t>(blksize),
+                                             .fe_flags = 0});
+        }
+        last_block = block;
+    }
+    return true;
+}
+
+FiemapUniquePtr FiemapWriter::Open(const std::string& file_path, uint64_t file_size, bool create,
+                                   std::function<bool(uint64_t, uint64_t)> progress) {
+    // if 'create' is false, open an existing file and do not truncate.
+    int open_flags = O_RDWR | O_CLOEXEC;
+    if (create) {
+        if (access(file_path.c_str(), F_OK) == 0) {
+            LOG(WARNING) << "File " << file_path << " already exists, truncating";
+        }
+        open_flags |= O_CREAT | O_TRUNC;
+    }
+    ::android::base::unique_fd file_fd(
+            TEMP_FAILURE_RETRY(open(file_path.c_str(), open_flags, S_IRUSR | S_IWUSR)));
+    if (file_fd < 0) {
+        PLOG(ERROR) << "Failed to create file at: " << file_path;
+        return nullptr;
+    }
+
+    std::string abs_path;
+    if (!::android::base::Realpath(file_path, &abs_path)) {
+        PLOG(ERROR) << "Invalid file path: " << file_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    std::string bdev_path;
+    if (!GetBlockDeviceForFile(abs_path, &bdev_path)) {
+        LOG(ERROR) << "Failed to get block dev path for file: " << file_path;
+        cleanup(abs_path, create);
+        return nullptr;
+    }
+
+    ::android::base::unique_fd bdev_fd(
+            TEMP_FAILURE_RETRY(open(bdev_path.c_str(), O_RDONLY | O_CLOEXEC)));
+    if (bdev_fd < 0) {
+        PLOG(ERROR) << "Failed to open block device: " << bdev_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    uint64_t bdevsz;
+    if (!GetBlockDeviceSize(bdev_fd, bdev_path, &bdevsz)) {
+        LOG(ERROR) << "Failed to get block device size for : " << bdev_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    if (!create) {
+        file_size = GetFileSize(abs_path);
+        if (file_size == 0) {
+            LOG(ERROR) << "Invalid file size of zero bytes for file: " << abs_path;
+            return nullptr;
+        }
+    }
+
+    uint64_t blocksz;
+    uint32_t fs_type;
+    if (!PerformFileChecks(abs_path, file_size, &blocksz, &fs_type)) {
+        LOG(ERROR) << "Failed to validate file or file system for file:" << abs_path;
+        cleanup(abs_path, create);
+        return nullptr;
+    }
+
+    // Align up to the nearest block size.
+    if (file_size % blocksz) {
+        file_size += blocksz - (file_size % blocksz);
+    }
+
+    if (create) {
+        if (!AllocateFile(file_fd, abs_path, blocksz, file_size, fs_type, std::move(progress))) {
+            LOG(ERROR) << "Failed to allocate file: " << abs_path << " of size: " << file_size
+                       << " bytes";
+            cleanup(abs_path, create);
+            return nullptr;
+        }
+    }
+
+    // f2fs may move the file blocks around.
+    if (!PinFile(file_fd, abs_path, fs_type)) {
+        cleanup(abs_path, create);
+        LOG(ERROR) << "Failed to pin the file in storage";
+        return nullptr;
+    }
+
+    // now allocate the FiemapWriter and start setting it up
+    FiemapUniquePtr fmap(new FiemapWriter());
+    switch (fs_type) {
+        case EXT4_SUPER_MAGIC:
+        case F2FS_SUPER_MAGIC:
+            if (!ReadFiemap(file_fd, abs_path, &fmap->extents_)) {
+                LOG(ERROR) << "Failed to read fiemap of file: " << abs_path;
+                cleanup(abs_path, create);
+                return nullptr;
+            }
+            break;
+        case MSDOS_SUPER_MAGIC:
+            if (!ReadFibmap(file_fd, abs_path, &fmap->extents_)) {
+                LOG(ERROR) << "Failed to read fibmap of file: " << abs_path;
+                cleanup(abs_path, create);
+                return nullptr;
+            }
+            break;
+    }
+
+    fmap->file_path_ = abs_path;
+    fmap->bdev_path_ = bdev_path;
+    fmap->file_size_ = file_size;
+    fmap->bdev_size_ = bdevsz;
+    fmap->fs_type_ = fs_type;
+    fmap->block_size_ = blocksz;
+
+    LOG(VERBOSE) << "Successfully created FiemapWriter for file " << abs_path << " on block device "
+                 << bdev_path;
+    return fmap;
+}
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp b/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
new file mode 100644
index 0000000..dda7dfd
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
@@ -0,0 +1,541 @@
+/*
+ * Copyright (C) 2018 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 <fcntl.h>
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include <string>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+#include <android-base/unique_fd.h>
+#include <gtest/gtest.h>
+#include <libdm/loop_control.h>
+#include <libfiemap_writer/fiemap_writer.h>
+#include <libfiemap_writer/split_fiemap_writer.h>
+
+#include "utility.h"
+
+namespace android {
+namespace fiemap_writer {
+
+using namespace std;
+using namespace std::string_literals;
+using namespace android::fiemap_writer;
+using unique_fd = android::base::unique_fd;
+using LoopDevice = android::dm::LoopDevice;
+
+std::string gTestDir;
+uint64_t testfile_size = 536870912;  // default of 512MiB
+size_t gBlockSize = 0;
+
+class FiemapWriterTest : public ::testing::Test {
+  protected:
+    void SetUp() override {
+        const ::testing::TestInfo* tinfo = ::testing::UnitTest::GetInstance()->current_test_info();
+        testfile = gTestDir + "/"s + tinfo->name();
+    }
+
+    void TearDown() override { unlink(testfile.c_str()); }
+
+    // name of the file we use for testing
+    std::string testfile;
+};
+
+class SplitFiemapTest : public ::testing::Test {
+  protected:
+    void SetUp() override {
+        const ::testing::TestInfo* tinfo = ::testing::UnitTest::GetInstance()->current_test_info();
+        testfile = gTestDir + "/"s + tinfo->name();
+    }
+
+    void TearDown() override {
+        std::string message;
+        if (!SplitFiemap::RemoveSplitFiles(testfile, &message)) {
+            cerr << "Could not remove all split files: " << message;
+        }
+    }
+
+    // name of the file we use for testing
+    std::string testfile;
+};
+
+TEST_F(FiemapWriterTest, CreateImpossiblyLargeFile) {
+    // Try creating a file of size ~100TB but aligned to
+    // 512 byte to make sure block alignment tests don't
+    // fail.
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 1099511627997184);
+    EXPECT_EQ(fptr, nullptr);
+    EXPECT_EQ(access(testfile.c_str(), F_OK), -1);
+    EXPECT_EQ(errno, ENOENT);
+}
+
+TEST_F(FiemapWriterTest, CreateUnalignedFile) {
+    // Try creating a file of size 4097 bytes which is guaranteed
+    // to be unaligned to all known block sizes.
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, gBlockSize + 1);
+    ASSERT_NE(fptr, nullptr);
+    ASSERT_EQ(fptr->size(), gBlockSize * 2);
+}
+
+TEST_F(FiemapWriterTest, CheckFilePath) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, gBlockSize);
+    ASSERT_NE(fptr, nullptr);
+    EXPECT_EQ(fptr->size(), gBlockSize);
+    EXPECT_EQ(fptr->file_path(), testfile);
+    EXPECT_EQ(access(testfile.c_str(), F_OK), 0);
+}
+
+TEST_F(FiemapWriterTest, CheckFileSize) {
+    // Create a large-ish file and test that the expected size matches.
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 1024 * 1024 * 16);
+    ASSERT_NE(fptr, nullptr);
+
+    struct stat s;
+    ASSERT_EQ(stat(testfile.c_str(), &s), 0);
+    EXPECT_EQ(static_cast<uint64_t>(s.st_size), fptr->size());
+}
+
+TEST_F(FiemapWriterTest, CheckProgress) {
+    std::vector<uint64_t> expected;
+    size_t invocations = 0;
+    auto callback = [&](uint64_t done, uint64_t total) -> bool {
+        if (invocations >= expected.size()) {
+            return false;
+        }
+        EXPECT_EQ(done, expected[invocations]);
+        EXPECT_EQ(total, gBlockSize);
+        invocations++;
+        return true;
+    };
+
+    expected.push_back(gBlockSize);
+
+    auto ptr = FiemapWriter::Open(testfile, gBlockSize, true, std::move(callback));
+    EXPECT_NE(ptr, nullptr);
+    EXPECT_EQ(invocations, expected.size());
+}
+
+TEST_F(FiemapWriterTest, CheckPinning) {
+    auto ptr = FiemapWriter::Open(testfile, 4096);
+    ASSERT_NE(ptr, nullptr);
+    EXPECT_TRUE(FiemapWriter::HasPinnedExtents(testfile));
+}
+
+TEST_F(FiemapWriterTest, CheckBlockDevicePath) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, gBlockSize);
+    EXPECT_EQ(fptr->size(), gBlockSize);
+    EXPECT_EQ(fptr->bdev_path().find("/dev/block/"), size_t(0));
+    EXPECT_EQ(fptr->bdev_path().find("/dev/block/dm-"), string::npos);
+}
+
+TEST_F(FiemapWriterTest, CheckFileCreated) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 32768);
+    ASSERT_NE(fptr, nullptr);
+    unique_fd fd(open(testfile.c_str(), O_RDONLY));
+    EXPECT_GT(fd, -1);
+}
+
+TEST_F(FiemapWriterTest, CheckFileSizeActual) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, testfile_size);
+    ASSERT_NE(fptr, nullptr);
+
+    struct stat sb;
+    ASSERT_EQ(stat(testfile.c_str(), &sb), 0);
+    EXPECT_GE(sb.st_size, testfile_size);
+}
+
+TEST_F(FiemapWriterTest, CheckFileExtents) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, testfile_size);
+    ASSERT_NE(fptr, nullptr);
+    EXPECT_GT(fptr->extents().size(), 0);
+}
+
+TEST_F(FiemapWriterTest, ExistingFile) {
+    // Create the file.
+    { ASSERT_NE(FiemapWriter::Open(testfile, gBlockSize), nullptr); }
+    // Test that we can still open it.
+    {
+        auto ptr = FiemapWriter::Open(testfile, 0, false);
+        ASSERT_NE(ptr, nullptr);
+        EXPECT_GT(ptr->extents().size(), 0);
+    }
+}
+
+TEST_F(FiemapWriterTest, FileDeletedOnError) {
+    auto callback = [](uint64_t, uint64_t) -> bool { return false; };
+    auto ptr = FiemapWriter::Open(testfile, gBlockSize, true, std::move(callback));
+    EXPECT_EQ(ptr, nullptr);
+    EXPECT_EQ(access(testfile.c_str(), F_OK), -1);
+    EXPECT_EQ(errno, ENOENT);
+}
+
+TEST_F(FiemapWriterTest, MaxBlockSize) {
+    ASSERT_GT(DetermineMaximumFileSize(testfile), 0);
+}
+
+TEST_F(FiemapWriterTest, FibmapBlockAddressing) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, gBlockSize);
+    ASSERT_NE(fptr, nullptr);
+
+    switch (fptr->fs_type()) {
+        case F2FS_SUPER_MAGIC:
+        case EXT4_SUPER_MAGIC:
+            // Skip the test for FIEMAP supported filesystems. This is really
+            // because f2fs/ext4 have caches that seem to defeat reading back
+            // directly from the block device, and writing directly is too
+            // dangerous.
+            std::cout << "Skipping test, filesystem does not use FIBMAP\n";
+            return;
+    }
+
+    bool uses_dm;
+    std::string bdev_path;
+    ASSERT_TRUE(FiemapWriter::GetBlockDeviceForFile(testfile, &bdev_path, &uses_dm));
+
+    if (uses_dm) {
+        // We could use a device-mapper wrapper here to bypass encryption, but
+        // really this test is for FIBMAP correctness on VFAT (where encryption
+        // is never used), so we don't bother.
+        std::cout << "Skipping test, block device is metadata encrypted\n";
+        return;
+    }
+
+    std::string data(fptr->size(), '\0');
+    for (size_t i = 0; i < data.size(); i++) {
+        data[i] = 'A' + static_cast<char>(data.size() % 26);
+    }
+
+    {
+        unique_fd fd(open(testfile.c_str(), O_WRONLY | O_CLOEXEC));
+        ASSERT_GE(fd, 0);
+        ASSERT_TRUE(android::base::WriteFully(fd, data.data(), data.size()));
+        ASSERT_EQ(fsync(fd), 0);
+    }
+
+    ASSERT_FALSE(fptr->extents().empty());
+    const auto& first_extent = fptr->extents()[0];
+
+    unique_fd bdev(open(fptr->bdev_path().c_str(), O_RDONLY | O_CLOEXEC));
+    ASSERT_GE(bdev, 0);
+
+    off_t where = first_extent.fe_physical;
+    ASSERT_EQ(lseek(bdev, where, SEEK_SET), where);
+
+    // Note: this will fail on encrypted folders.
+    std::string actual(data.size(), '\0');
+    ASSERT_GE(first_extent.fe_length, data.size());
+    ASSERT_TRUE(android::base::ReadFully(bdev, actual.data(), actual.size()));
+    EXPECT_EQ(memcmp(actual.data(), data.data(), data.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, Create) {
+    auto ptr = SplitFiemap::Create(testfile, 1024 * 768, 1024 * 32);
+    ASSERT_NE(ptr, nullptr);
+
+    auto extents = ptr->extents();
+
+    // Destroy the fiemap, closing file handles. This should not delete them.
+    ptr = nullptr;
+
+    std::vector<std::string> files;
+    ASSERT_TRUE(SplitFiemap::GetSplitFileList(testfile, &files));
+    for (const auto& path : files) {
+        EXPECT_EQ(access(path.c_str(), F_OK), 0);
+    }
+
+    ASSERT_GE(extents.size(), files.size());
+}
+
+TEST_F(SplitFiemapTest, Open) {
+    {
+        auto ptr = SplitFiemap::Create(testfile, 1024 * 768, 1024 * 32);
+        ASSERT_NE(ptr, nullptr);
+    }
+
+    auto ptr = SplitFiemap::Open(testfile);
+    ASSERT_NE(ptr, nullptr);
+
+    auto extents = ptr->extents();
+    ASSERT_GE(extents.size(), 24);
+}
+
+TEST_F(SplitFiemapTest, DeleteOnFail) {
+    auto ptr = SplitFiemap::Create(testfile, 1024 * 1024 * 100, 1);
+    ASSERT_EQ(ptr, nullptr);
+
+    std::string first_file = testfile + ".0001";
+    ASSERT_NE(access(first_file.c_str(), F_OK), 0);
+    ASSERT_EQ(errno, ENOENT);
+    ASSERT_NE(access(testfile.c_str(), F_OK), 0);
+    ASSERT_EQ(errno, ENOENT);
+}
+
+static string ReadSplitFiles(const std::string& base_path, size_t num_files) {
+    std::string result;
+    for (int i = 0; i < num_files; i++) {
+        std::string path = base_path + android::base::StringPrintf(".%04d", i);
+        std::string data;
+        if (!android::base::ReadFileToString(path, &data)) {
+            return {};
+        }
+        result += data;
+    }
+    return result;
+}
+
+TEST_F(SplitFiemapTest, WriteWholeFile) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+    ASSERT_TRUE(ptr->Write(buffer.get(), kSize));
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WriteFileInChunks1) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+
+    // Write in chunks of 1000 (so some writes straddle the boundary of two
+    // files).
+    size_t bytes_written = 0;
+    while (bytes_written < kSize) {
+        size_t to_write = std::min(kSize - bytes_written, (size_t)1000);
+        char* data = reinterpret_cast<char*>(buffer.get()) + bytes_written;
+        ASSERT_TRUE(ptr->Write(data, to_write));
+        bytes_written += to_write;
+    }
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WriteFileInChunks2) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+
+    // Write in chunks of 32KiB so every write is exactly at the end of the
+    // current file.
+    size_t bytes_written = 0;
+    while (bytes_written < kSize) {
+        size_t to_write = std::min(kSize - bytes_written, kChunkSize);
+        char* data = reinterpret_cast<char*>(buffer.get()) + bytes_written;
+        ASSERT_TRUE(ptr->Write(data, to_write));
+        bytes_written += to_write;
+    }
+
+    std::string expected(reinterpret_cast<char*>(buffer.get()), kSize);
+    auto actual = ReadSplitFiles(testfile, 3);
+    ASSERT_EQ(expected.size(), actual.size());
+    EXPECT_EQ(memcmp(expected.data(), actual.data(), actual.size()), 0);
+}
+
+TEST_F(SplitFiemapTest, WritePastEnd) {
+    static constexpr size_t kChunkSize = 32768;
+    static constexpr size_t kSize = kChunkSize * 3;
+    auto ptr = SplitFiemap::Create(testfile, kSize, kChunkSize);
+    ASSERT_NE(ptr, nullptr);
+
+    auto buffer = std::make_unique<int[]>(kSize / sizeof(int));
+    for (size_t i = 0; i < kSize / sizeof(int); i++) {
+        buffer[i] = i;
+    }
+    ASSERT_TRUE(ptr->Write(buffer.get(), kSize));
+    ASSERT_FALSE(ptr->Write(buffer.get(), kSize));
+}
+
+class VerifyBlockWritesExt4 : public ::testing::Test {
+    // 2GB Filesystem and 4k block size by default
+    static constexpr uint64_t block_size = 4096;
+    static constexpr uint64_t fs_size = 2147483648;
+
+  protected:
+    void SetUp() override {
+        fs_path = std::string(getenv("TMPDIR")) + "/ext4_2G.img";
+        uint64_t count = fs_size / block_size;
+        std::string dd_cmd =
+                ::android::base::StringPrintf("/system/bin/dd if=/dev/zero of=%s bs=%" PRIu64
+                                              " count=%" PRIu64 " > /dev/null 2>&1",
+                                              fs_path.c_str(), block_size, count);
+        std::string mkfs_cmd =
+                ::android::base::StringPrintf("/system/bin/mkfs.ext4 -q %s", fs_path.c_str());
+        // create mount point
+        mntpoint = std::string(getenv("TMPDIR")) + "/fiemap_mnt";
+        ASSERT_EQ(mkdir(mntpoint.c_str(), S_IRWXU), 0);
+        // create file for the file system
+        int ret = system(dd_cmd.c_str());
+        ASSERT_EQ(ret, 0);
+        // Get and attach a loop device to the filesystem we created
+        LoopDevice loop_dev(fs_path);
+        ASSERT_TRUE(loop_dev.valid());
+        // create file system
+        ret = system(mkfs_cmd.c_str());
+        ASSERT_EQ(ret, 0);
+
+        // mount the file system
+        ASSERT_EQ(mount(loop_dev.device().c_str(), mntpoint.c_str(), "ext4", 0, nullptr), 0);
+    }
+
+    void TearDown() override {
+        umount(mntpoint.c_str());
+        rmdir(mntpoint.c_str());
+        unlink(fs_path.c_str());
+    }
+
+    std::string mntpoint;
+    std::string fs_path;
+};
+
+class VerifyBlockWritesF2fs : public ::testing::Test {
+    // 2GB Filesystem and 4k block size by default
+    static constexpr uint64_t block_size = 4096;
+    static constexpr uint64_t fs_size = 2147483648;
+
+  protected:
+    void SetUp() override {
+        fs_path = std::string(getenv("TMPDIR")) + "/f2fs_2G.img";
+        uint64_t count = fs_size / block_size;
+        std::string dd_cmd =
+                ::android::base::StringPrintf("/system/bin/dd if=/dev/zero of=%s bs=%" PRIu64
+                                              " count=%" PRIu64 " > /dev/null 2>&1",
+                                              fs_path.c_str(), block_size, count);
+        std::string mkfs_cmd =
+                ::android::base::StringPrintf("/system/bin/make_f2fs -q %s", fs_path.c_str());
+        // create mount point
+        mntpoint = std::string(getenv("TMPDIR")) + "/fiemap_mnt";
+        ASSERT_EQ(mkdir(mntpoint.c_str(), S_IRWXU), 0);
+        // create file for the file system
+        int ret = system(dd_cmd.c_str());
+        ASSERT_EQ(ret, 0);
+        // Get and attach a loop device to the filesystem we created
+        LoopDevice loop_dev(fs_path);
+        ASSERT_TRUE(loop_dev.valid());
+        // create file system
+        ret = system(mkfs_cmd.c_str());
+        ASSERT_EQ(ret, 0);
+
+        // mount the file system
+        ASSERT_EQ(mount(loop_dev.device().c_str(), mntpoint.c_str(), "f2fs", 0, nullptr), 0);
+    }
+
+    void TearDown() override {
+        umount(mntpoint.c_str());
+        rmdir(mntpoint.c_str());
+        unlink(fs_path.c_str());
+    }
+
+    std::string mntpoint;
+    std::string fs_path;
+};
+
+bool DetermineBlockSize() {
+    struct statfs s;
+    if (statfs(gTestDir.c_str(), &s)) {
+        std::cerr << "Could not call statfs: " << strerror(errno) << "\n";
+        return false;
+    }
+    if (!s.f_bsize) {
+        std::cerr << "Invalid block size: " << s.f_bsize << "\n";
+        return false;
+    }
+
+    gBlockSize = s.f_bsize;
+    return true;
+}
+
+}  // namespace fiemap_writer
+}  // namespace android
+
+using namespace android::fiemap_writer;
+
+int main(int argc, char** argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+    if (argc > 1 && argv[1] == "-h"s) {
+        cerr << "Usage: [test_dir] [file_size]\n";
+        cerr << "\n";
+        cerr << "Note: test_dir must be a writable, unencrypted directory.\n";
+        exit(EXIT_FAILURE);
+    }
+    ::android::base::InitLogging(argv, ::android::base::StderrLogger);
+
+    std::string root_dir = "/data/local/unencrypted";
+    if (access(root_dir.c_str(), F_OK)) {
+        root_dir = "/data";
+    }
+
+    std::string tempdir = root_dir + "/XXXXXX"s;
+    if (!mkdtemp(tempdir.data())) {
+        cerr << "unable to create tempdir on " << root_dir << "\n";
+        exit(EXIT_FAILURE);
+    }
+    if (!android::base::Realpath(tempdir, &gTestDir)) {
+        cerr << "unable to find realpath for " << tempdir;
+        exit(EXIT_FAILURE);
+    }
+
+    if (argc > 2) {
+        testfile_size = strtoull(argv[2], NULL, 0);
+        if (testfile_size == ULLONG_MAX) {
+            testfile_size = 512 * 1024 * 1024;
+        }
+    }
+
+    if (!DetermineBlockSize()) {
+        exit(EXIT_FAILURE);
+    }
+
+    auto result = RUN_ALL_TESTS();
+
+    std::string cmd = "rm -rf " + gTestDir;
+    system(cmd.c_str());
+
+    return result;
+}
diff --git a/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h b/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
new file mode 100644
index 0000000..ee79262
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2018 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.
+ */
+
+#pragma once
+
+#include <linux/fiemap.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <functional>
+#include <string>
+#include <vector>
+
+#include <android-base/unique_fd.h>
+
+namespace android {
+namespace fiemap_writer {
+
+class FiemapWriter;
+using FiemapUniquePtr = std::unique_ptr<FiemapWriter>;
+
+class FiemapWriter final {
+  public:
+    // Factory method for FiemapWriter.
+    // The method returns FiemapUniquePtr that contains all the data necessary to be able to write
+    // to the given file directly using raw block i/o. The optional progress callback will be
+    // invoked, if create is true, while the file is being initialized. It receives the bytes
+    // written and the number of total bytes. If the callback returns false, the operation will
+    // fail.
+    //
+    // Note: when create is true, the file size will be aligned up to the nearest file system
+    // block.
+    static FiemapUniquePtr Open(const std::string& file_path, uint64_t file_size,
+                                bool create = true,
+                                std::function<bool(uint64_t, uint64_t)> progress = {});
+
+    // Check that a file still has the same extents since it was last opened with FiemapWriter,
+    // assuming the file was not resized outside of FiemapWriter. Returns false either on error
+    // or if the file was not pinned.
+    //
+    // This will always return true on Ext4. On F2FS, it will return true if either of the
+    // following cases are true:
+    //   - The file was never pinned.
+    //   - The file is pinned and has not been moved by the GC.
+    // Thus, this method should only be called for pinned files (such as those returned by
+    // FiemapWriter::Open).
+    static bool HasPinnedExtents(const std::string& file_path);
+
+    // Returns the underlying block device of a file. This will look past device-mapper layers
+    // as long as each layer would not change block mappings (i.e., dm-crypt, dm-bow, and dm-
+    // default-key tables are okay; dm-linear is not). If a mapping such as dm-linear is found,
+    // it will be returned in place of any physical block device.
+    //
+    // It is the caller's responsibility to check whether the returned block device is acceptable.
+    // Gsid, for example, will only accept /dev/block/by-name/userdata as the bottom device.
+    // Callers can check the device name (dm- or loop prefix), inspect sysfs, or compare the major
+    // number against a boot device.
+    //
+    // If device-mapper nodes were encountered, then |uses_dm| will be set to true.
+    static bool GetBlockDeviceForFile(const std::string& file_path, std::string* bdev_path,
+                                      bool* uses_dm = nullptr);
+
+    ~FiemapWriter() = default;
+
+    const std::string& file_path() const { return file_path_; };
+    uint64_t size() const { return file_size_; };
+    const std::string& bdev_path() const { return bdev_path_; };
+    uint64_t block_size() const { return block_size_; };
+    const std::vector<struct fiemap_extent>& extents() { return extents_; };
+    uint32_t fs_type() const { return fs_type_; }
+
+    // Non-copyable & Non-movable
+    FiemapWriter(const FiemapWriter&) = delete;
+    FiemapWriter& operator=(const FiemapWriter&) = delete;
+    FiemapWriter& operator=(FiemapWriter&&) = delete;
+    FiemapWriter(FiemapWriter&&) = delete;
+
+  private:
+    // Name of the file managed by this class.
+    std::string file_path_;
+    // Block device on which we have created the file.
+    std::string bdev_path_;
+
+    // Size in bytes of the file this class is writing
+    uint64_t file_size_;
+
+    // total size in bytes of the block device
+    uint64_t bdev_size_;
+
+    // Filesystem type where the file is being created.
+    // See: <uapi/linux/magic.h> for filesystem magic numbers
+    uint32_t fs_type_;
+
+    // block size as reported by the kernel of the underlying block device;
+    uint64_t block_size_;
+
+    // This file's fiemap
+    std::vector<struct fiemap_extent> extents_;
+
+    FiemapWriter() = default;
+};
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h b/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h
new file mode 100644
index 0000000..7b977e1
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/include/libfiemap_writer/split_fiemap_writer.h
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <android-base/unique_fd.h>
+
+#include "fiemap_writer.h"
+
+namespace android {
+namespace fiemap_writer {
+
+// Wrapper around FiemapWriter that is able to split images across files if
+// necessary.
+class SplitFiemap final {
+  public:
+    using ProgressCallback = std::function<bool(uint64_t, uint64_t)>;
+
+    // Create a new split fiemap file. If |max_piece_size| is 0, the number of
+    // pieces will be determined automatically by detecting the filesystem.
+    // Otherwise, the file will be split evenly (with the remainder in the
+    // final file).
+    static std::unique_ptr<SplitFiemap> Create(const std::string& file_path, uint64_t file_size,
+                                               uint64_t max_piece_size,
+                                               ProgressCallback progress = {});
+
+    // Open an existing split fiemap file.
+    static std::unique_ptr<SplitFiemap> Open(const std::string& file_path);
+
+    ~SplitFiemap();
+
+    // Return a list of all files created for a split file.
+    static bool GetSplitFileList(const std::string& file_path, std::vector<std::string>* list);
+
+    // Destroy all components of a split file. If the root file does not exist,
+    // this returns true and does not report an error.
+    static bool RemoveSplitFiles(const std::string& file_path, std::string* message = nullptr);
+
+    // Return whether all components of a split file still have pinned extents.
+    bool HasPinnedExtents() const;
+
+    // Helper method for writing data that spans files. Note there is no seek
+    // method (yet); this starts at 0 and increments the position by |bytes|.
+    bool Write(const void* data, uint64_t bytes);
+
+    // Flush all writes to all split files.
+    bool Flush();
+
+    const std::vector<struct fiemap_extent>& extents();
+    uint32_t block_size() const;
+    uint64_t size() const { return total_size_; }
+    const std::string& bdev_path() const;
+
+    // Non-copyable & Non-movable
+    SplitFiemap(const SplitFiemap&) = delete;
+    SplitFiemap& operator=(const SplitFiemap&) = delete;
+    SplitFiemap& operator=(SplitFiemap&&) = delete;
+    SplitFiemap(SplitFiemap&&) = delete;
+
+  private:
+    SplitFiemap() = default;
+    void AddFile(FiemapUniquePtr&& file);
+
+    bool creating_ = false;
+    std::string list_file_;
+    std::vector<FiemapUniquePtr> files_;
+    std::vector<struct fiemap_extent> extents_;
+    uint64_t total_size_ = 0;
+
+    // Most recently open file and position for Write().
+    size_t cursor_index_ = 0;
+    uint64_t cursor_file_pos_ = 0;
+    android::base::unique_fd cursor_fd_;
+};
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp b/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp
new file mode 100644
index 0000000..16a82d2
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/split_fiemap_writer.cpp
@@ -0,0 +1,298 @@
+/*
+ * Copyright (C) 2019 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 <libfiemap_writer/split_fiemap_writer.h>
+
+#include <fcntl.h>
+#include <stdint.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+
+#include "utility.h"
+
+namespace android {
+namespace fiemap_writer {
+
+using android::base::unique_fd;
+
+// We use a four-digit suffix at the end of filenames.
+static const size_t kMaxFilePieces = 500;
+
+std::unique_ptr<SplitFiemap> SplitFiemap::Create(const std::string& file_path, uint64_t file_size,
+                                                 uint64_t max_piece_size,
+                                                 ProgressCallback progress) {
+    if (!file_size) {
+        LOG(ERROR) << "Cannot create a fiemap for a 0-length file: " << file_path;
+        return nullptr;
+    }
+
+    if (!max_piece_size) {
+        max_piece_size = DetermineMaximumFileSize(file_path);
+        if (!max_piece_size) {
+            LOG(ERROR) << "Could not determine maximum file size for " << file_path;
+            return nullptr;
+        }
+    }
+
+    // Call |progress| only when the total percentage would significantly change.
+    int permille = -1;
+    uint64_t total_bytes_written = 0;
+    auto on_progress = [&](uint64_t written, uint64_t) -> bool {
+        uint64_t actual_written = total_bytes_written + written;
+        int new_permille = (actual_written * 1000) / file_size;
+        if (new_permille != permille && actual_written < file_size) {
+            if (progress && !progress(actual_written, file_size)) {
+                return false;
+            }
+            permille = new_permille;
+        }
+        return true;
+    };
+
+    std::unique_ptr<SplitFiemap> out(new SplitFiemap());
+    out->creating_ = true;
+    out->list_file_ = file_path;
+
+    // Create the split files.
+    uint64_t remaining_bytes = file_size;
+    while (remaining_bytes) {
+        if (out->files_.size() >= kMaxFilePieces) {
+            LOG(ERROR) << "Requested size " << file_size << " created too many split files";
+            return nullptr;
+        }
+        std::string chunk_path =
+                android::base::StringPrintf("%s.%04d", file_path.c_str(), (int)out->files_.size());
+        uint64_t chunk_size = std::min(max_piece_size, remaining_bytes);
+        auto writer = FiemapWriter::Open(chunk_path, chunk_size, true, on_progress);
+        if (!writer) {
+            return nullptr;
+        }
+
+        // To make sure the alignment doesn't create too much inconsistency, we
+        // account the *actual* size, not the requested size.
+        total_bytes_written += writer->size();
+        // writer->size() is block size aligned and could be bigger than remaining_bytes
+        // If remaining_bytes is bigger, set remaining_bytes to 0 to avoid underflow error.
+        remaining_bytes = remaining_bytes > writer->size() ? (remaining_bytes - writer->size()) : 0;
+        out->AddFile(std::move(writer));
+    }
+
+    // Create the split file list.
+    unique_fd fd(open(out->list_file_.c_str(), O_CREAT | O_WRONLY | O_CLOEXEC, 0660));
+    if (fd < 0) {
+        PLOG(ERROR) << "Failed to open " << file_path;
+        return nullptr;
+    }
+
+    for (const auto& writer : out->files_) {
+        std::string line = android::base::Basename(writer->file_path()) + "\n";
+        if (!android::base::WriteFully(fd, line.data(), line.size())) {
+            PLOG(ERROR) << "Write failed " << file_path;
+            return nullptr;
+        }
+    }
+
+    // Unset this bit, so we don't unlink on destruction.
+    out->creating_ = false;
+    return out;
+}
+
+std::unique_ptr<SplitFiemap> SplitFiemap::Open(const std::string& file_path) {
+    std::vector<std::string> files;
+    if (!GetSplitFileList(file_path, &files)) {
+        return nullptr;
+    }
+
+    std::unique_ptr<SplitFiemap> out(new SplitFiemap());
+    out->list_file_ = file_path;
+
+    for (const auto& file : files) {
+        auto writer = FiemapWriter::Open(file, 0, false);
+        if (!writer) {
+            // Error was logged in Open().
+            return nullptr;
+        }
+        out->AddFile(std::move(writer));
+    }
+    return out;
+}
+
+bool SplitFiemap::GetSplitFileList(const std::string& file_path, std::vector<std::string>* list) {
+    // This is not the most efficient thing, but it is simple and recovering
+    // the fiemap/fibmap is much more expensive.
+    std::string contents;
+    if (!android::base::ReadFileToString(file_path, &contents, true)) {
+        PLOG(ERROR) << "Error reading file: " << file_path;
+        return false;
+    }
+
+    std::vector<std::string> names = android::base::Split(contents, "\n");
+    std::string dir = android::base::Dirname(file_path);
+    for (const auto& name : names) {
+        if (!name.empty()) {
+            list->emplace_back(dir + "/" + name);
+        }
+    }
+    return true;
+}
+
+bool SplitFiemap::RemoveSplitFiles(const std::string& file_path, std::string* message) {
+    // Early exit if this does not exist, and do not report an error.
+    if (access(file_path.c_str(), F_OK) && errno == ENOENT) {
+        return true;
+    }
+
+    bool ok = true;
+    std::vector<std::string> files;
+    if (GetSplitFileList(file_path, &files)) {
+        for (const auto& file : files) {
+            ok &= android::base::RemoveFileIfExists(file, message);
+        }
+    }
+    ok &= android::base::RemoveFileIfExists(file_path, message);
+    return ok;
+}
+
+bool SplitFiemap::HasPinnedExtents() const {
+    for (const auto& file : files_) {
+        if (!FiemapWriter::HasPinnedExtents(file->file_path())) {
+            return false;
+        }
+    }
+    return true;
+}
+
+const std::vector<struct fiemap_extent>& SplitFiemap::extents() {
+    if (extents_.empty()) {
+        for (const auto& file : files_) {
+            const auto& extents = file->extents();
+            extents_.insert(extents_.end(), extents.begin(), extents.end());
+        }
+    }
+    return extents_;
+}
+
+bool SplitFiemap::Write(const void* data, uint64_t bytes) {
+    // Open the current file.
+    FiemapWriter* file = files_[cursor_index_].get();
+
+    const uint8_t* data_ptr = reinterpret_cast<const uint8_t*>(data);
+    uint64_t bytes_remaining = bytes;
+    while (bytes_remaining) {
+        // How many bytes can we write into the current file?
+        uint64_t file_bytes_left = file->size() - cursor_file_pos_;
+        if (!file_bytes_left) {
+            if (cursor_index_ == files_.size() - 1) {
+                LOG(ERROR) << "write past end of file requested";
+                return false;
+            }
+
+            // No space left in the current file, but we have more files to
+            // use, so prep the next one.
+            cursor_fd_ = {};
+            cursor_file_pos_ = 0;
+            file = files_[++cursor_index_].get();
+            file_bytes_left = file->size();
+        }
+
+        // Open the current file if it's not open.
+        if (cursor_fd_ < 0) {
+            cursor_fd_.reset(open(file->file_path().c_str(), O_CLOEXEC | O_WRONLY));
+            if (cursor_fd_ < 0) {
+                PLOG(ERROR) << "open failed: " << file->file_path();
+                return false;
+            }
+            CHECK(cursor_file_pos_ == 0);
+        }
+
+        if (!FiemapWriter::HasPinnedExtents(file->file_path())) {
+            LOG(ERROR) << "file is no longer pinned: " << file->file_path();
+            return false;
+        }
+
+        uint64_t bytes_to_write = std::min(file_bytes_left, bytes_remaining);
+        if (!android::base::WriteFully(cursor_fd_, data_ptr, bytes_to_write)) {
+            PLOG(ERROR) << "write failed: " << file->file_path();
+            return false;
+        }
+        data_ptr += bytes_to_write;
+        bytes_remaining -= bytes_to_write;
+        cursor_file_pos_ += bytes_to_write;
+    }
+
+    // If we've reached the end of the current file, close it for sanity.
+    if (cursor_file_pos_ == file->size()) {
+        cursor_fd_ = {};
+    }
+    return true;
+}
+
+bool SplitFiemap::Flush() {
+    for (const auto& file : files_) {
+        unique_fd fd(open(file->file_path().c_str(), O_RDONLY | O_CLOEXEC));
+        if (fd < 0) {
+            PLOG(ERROR) << "open failed: " << file->file_path();
+            return false;
+        }
+        if (fsync(fd)) {
+            PLOG(ERROR) << "fsync failed: " << file->file_path();
+            return false;
+        }
+    }
+    return true;
+}
+
+SplitFiemap::~SplitFiemap() {
+    if (!creating_) {
+        return;
+    }
+
+    // We failed to finish creating, so unlink everything.
+    unlink(list_file_.c_str());
+    for (auto&& file : files_) {
+        std::string path = file->file_path();
+        file = nullptr;
+
+        unlink(path.c_str());
+    }
+}
+
+void SplitFiemap::AddFile(FiemapUniquePtr&& file) {
+    total_size_ += file->size();
+    files_.emplace_back(std::move(file));
+}
+
+uint32_t SplitFiemap::block_size() const {
+    return files_[0]->block_size();
+}
+
+const std::string& SplitFiemap::bdev_path() const {
+    return files_[0]->bdev_path();
+}
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/testdata/file_32k b/fs_mgr/libfiemap_writer/testdata/file_32k
new file mode 100644
index 0000000..12f3be4
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/testdata/file_32k
Binary files differ
diff --git a/fs_mgr/libfiemap_writer/testdata/file_4k b/fs_mgr/libfiemap_writer/testdata/file_4k
new file mode 100644
index 0000000..08e7df1
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/testdata/file_4k
Binary files differ
diff --git a/fs_mgr/libfiemap_writer/testdata/unaligned_file b/fs_mgr/libfiemap_writer/testdata/unaligned_file
new file mode 100644
index 0000000..c107c26
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/testdata/unaligned_file
Binary files differ
diff --git a/fs_mgr/libfiemap_writer/utility.cpp b/fs_mgr/libfiemap_writer/utility.cpp
new file mode 100644
index 0000000..192ec16
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/utility.cpp
@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2019 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 "utility.h"
+
+#include <stdint.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include <android-base/logging.h>
+#include <libfiemap_writer/fiemap_writer.h>
+
+namespace android {
+namespace fiemap_writer {
+
+uint64_t DetermineMaximumFileSize(const std::string& file_path) {
+    // Create the smallest file possible (one block).
+    auto writer = FiemapWriter::Open(file_path, 1);
+    if (!writer) {
+        return 0;
+    }
+
+    uint64_t result = 0;
+    switch (writer->fs_type()) {
+        case EXT4_SUPER_MAGIC:
+            // The minimum is 16GiB, so just report that. If we wanted we could parse the
+            // superblock and figure out if 64-bit support is enabled.
+            result = 17179869184ULL;
+            break;
+        case F2FS_SUPER_MAGIC:
+            // Formula is from https://www.kernel.org/doc/Documentation/filesystems/f2fs.txt
+            // 4KB * (923 + 2 * 1018 + 2 * 1018 * 1018 + 1018 * 1018 * 1018) := 3.94TB.
+            result = 4329690886144ULL;
+            break;
+        case MSDOS_SUPER_MAGIC:
+            // 4GB-1, which we want aligned to the block size.
+            result = 4294967295;
+            result -= (result % writer->block_size());
+            break;
+        default:
+            LOG(ERROR) << "Unknown file system type: " << writer->fs_type();
+            break;
+    }
+
+    // Close and delete the temporary file.
+    writer = nullptr;
+    unlink(file_path.c_str());
+
+    return result;
+}
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/utility.h b/fs_mgr/libfiemap_writer/utility.h
new file mode 100644
index 0000000..2d418da
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/utility.h
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace android {
+namespace fiemap_writer {
+
+// Given a file that will be created, determine the maximum size its containing
+// filesystem allows. Note this is a theoretical maximum size; free space is
+// ignored entirely.
+uint64_t DetermineMaximumFileSize(const std::string& file_path);
+
+}  // namespace fiemap_writer
+}  // namespace android