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..33c3cad
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/Android.bp
@@ -0,0 +1,56 @@
+//
+// 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: [
+        // TODO(b/121211685): Allows us to create a skeleton of required classes
+        "-Wno-unused-private-field",
+        "-Wno-unused-parameter",
+    ],
+
+    srcs: [
+        "fiemap_writer.cpp",
+    ],
+
+    header_libs: [
+        "libbase_headers",
+        "liblog_headers",
+    ],
+}
+
+cc_test {
+    name: "fiemap_writer_test",
+    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/fiemap_writer.cpp b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
new file mode 100644
index 0000000..097e07f
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/fiemap_writer.cpp
@@ -0,0 +1,637 @@
+/*
+ * 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 <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>
+
+namespace android {
+namespace fiemap_writer {
+
+// 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;
+
+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 DeviceMapperStackPop(const std::string& bdev, std::string* bdev_raw) {
+    // TODO: Stop popping the device mapper stack if dm-linear target is found
+    if (!::android::base::StartsWith(bdev, "dm-")) {
+        // We are at the bottom of the device mapper stack.
+        *bdev_raw = bdev;
+        return true;
+    }
+
+    std::string dm_leaf_dir = ::android::base::StringPrintf("/sys/block/%s/slaves", bdev.c_str());
+    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);
+}
+
+static bool FileToBlockDevicePath(const std::string& file_path, std::string* bdev_path) {
+    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;
+    }
+
+    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 GetBlockDeviceParams(int bdev_fd, const std::string& bdev_path, uint64_t* blocksz,
+                                 uint64_t* bdev_size) {
+    // TODO: For some reason, the block device ioctl require the argument to be initialized
+    // to zero even if its the out parameter for the given ioctl cmd.
+    uint64_t blksz = 0;
+    if (ioctl(bdev_fd, BLKBSZGET, &blksz)) {
+        PLOG(ERROR) << "Failed to get block size for: " << bdev_path;
+        return false;
+    }
+
+    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;
+    }
+
+    *blocksz = blksz;
+    *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) {
+    // Check if the size aligned to the block size of the block device.
+    // We need this to be true in order to be able to write the file using FIEMAP.
+    if (file_size % blocksz) {
+        LOG(ERROR) << "File size " << file_size << " is not aligned to block size " << blocksz
+                   << " for file " << file_path;
+        return false;
+    }
+
+    struct statfs64 sfs;
+    if (statfs64(file_path.c_str(), &sfs)) {
+        PLOG(ERROR) << "Failed to read file system status at: " << file_path;
+        return false;
+    }
+
+    // Check if the filesystem is of supported types.
+    // Only ext4 and f2fs are tested and supported.
+    if ((sfs.f_type != EXT4_SUPER_MAGIC) && (sfs.f_type != F2FS_SUPER_MAGIC)) {
+        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;
+    }
+
+    *fs_type = sfs.f_type;
+    return true;
+}
+
+static bool AllocateFile(int file_fd, const std::string& file_path, uint64_t blocksz,
+                         uint64_t file_size) {
+    // 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.
+    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;
+    }
+
+    // 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;
+    }
+
+    for (; offset < file_size; offset += blocksz) {
+        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;
+        }
+    }
+
+    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;
+    }
+
+    return true;
+}
+
+static bool PinFile(int file_fd, const std::string& file_path, uint32_t fs_type) {
+    if (fs_type == EXT4_SUPER_MAGIC) {
+        // No pinning necessary for ext4. 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) {
+        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;
+}
+
+#if 0
+static bool PinFileStatus(int file_fd, const std::string& file_path, uint32_t fs_type) {
+    if (fs_type == EXT4_SUPER_MAGIC) {
+        // No pinning necessary for ext4. 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
+
+    uint32_t pin_status;
+    int error = ioctl(file_fd, F2FS_IOC_GET_PIN_FILE, &pin_status);
+    if (error) {
+        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;
+    }
+
+    return !!pin_status;
+}
+#endif
+
+static void LogExtent(uint32_t num, const struct fiemap_extent& ext) {
+    LOG(INFO) << "Extent #" << num;
+    LOG(INFO) << "  fe_logical:  " << ext.fe_logical;
+    LOG(INFO) << "  fe_physical: " << ext.fe_physical;
+    LOG(INFO) << "  fe_length:   " << ext.fe_length;
+    LOG(INFO) << "  fe_flags:    0x" << std::hex << ext.fe_flags;
+}
+
+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;
+}
+
+FiemapUniquePtr FiemapWriter::Open(const std::string& file_path, uint64_t file_size, bool create) {
+    // 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 (!FileToBlockDevicePath(abs_path, &bdev_path)) {
+        LOG(ERROR) << "Failed to get block dev path for file: " << file_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    ::android::base::unique_fd bdev_fd(
+            TEMP_FAILURE_RETRY(open(bdev_path.c_str(), O_RDWR | O_CLOEXEC)));
+    if (bdev_fd < 0) {
+        PLOG(ERROR) << "Failed to open block device: " << bdev_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    uint64_t blocksz, bdevsz;
+    if (!GetBlockDeviceParams(bdev_fd, bdev_path, &blocksz, &bdevsz)) {
+        LOG(ERROR) << "Failed to get block device params 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;
+        }
+    }
+
+    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(file_path, create);
+        return nullptr;
+    }
+
+    if (create) {
+        if (!AllocateFile(file_fd, abs_path, blocksz, file_size)) {
+            unlink(abs_path.c_str());
+            return nullptr;
+        }
+    }
+
+    // f2fs may move the file blocks around.
+    if (!PinFile(file_fd, file_path, fs_type)) {
+        cleanup(file_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());
+    if (!ReadFiemap(file_fd, abs_path, &fmap->extents_)) {
+        LOG(ERROR) << "Failed to read fiemap of file: " << abs_path;
+        cleanup(file_path, create);
+        return nullptr;
+    }
+
+    fmap->file_path_ = abs_path;
+    fmap->bdev_path_ = bdev_path;
+    fmap->file_fd_ = std::move(file_fd);
+    fmap->bdev_fd_ = std::move(bdev_fd);
+    fmap->file_size_ = file_size;
+    fmap->bdev_size_ = bdevsz;
+    fmap->fs_type_ = fs_type;
+    fmap->block_size_ = blocksz;
+
+    LOG(INFO) << "Successfully created FiemapWriter for file " << abs_path << " on block device "
+              << bdev_path;
+    return fmap;
+}
+
+bool FiemapWriter::Flush() const {
+    if (fsync(bdev_fd_)) {
+        PLOG(ERROR) << "Failed to flush " << bdev_path_ << " with fsync";
+        return false;
+    }
+    return true;
+}
+
+// TODO: Test with fs block_size > bdev block_size
+bool FiemapWriter::Write(off64_t off, uint8_t* buffer, uint64_t size) {
+    if (!size || size > file_size_) {
+        LOG(ERROR) << "Failed write: size " << size << " is invalid for file's size " << file_size_;
+        return false;
+    }
+
+    if (off + size > file_size_) {
+        LOG(ERROR) << "Failed write: Invalid offset " << off << " or size " << size
+                   << " for file size " << file_size_;
+        return false;
+    }
+
+    if ((off & (block_size_ - 1)) || (size & (block_size_ - 1))) {
+        LOG(ERROR) << "Failed write: Unaligned offset " << off << " or size " << size
+                   << " for block size " << block_size_;
+        return false;
+    }
+#if 0
+    // TODO(b/122138114): check why this fails.
+    if (!PinFileStatus(file_fd_, file_path_, fs_type_)) {
+        LOG(ERROR) << "Failed write: file " << file_path_ << " is not pinned";
+        return false;
+    }
+#endif
+    // find extents that must be written to and then write one at a time.
+    uint32_t num_extent = 1;
+    uint32_t buffer_offset = 0;
+    for (auto& extent : extents_) {
+        uint64_t e_start = extent.fe_logical;
+        uint64_t e_end = extent.fe_logical + extent.fe_length;
+        // Do we write in this extent ?
+        if (off >= e_start && off < e_end) {
+            uint64_t written = WriteExtent(extent, buffer + buffer_offset, off, size);
+            if (written == 0) {
+                return false;
+            }
+
+            buffer_offset += written;
+            off += written;
+            size -= written;
+
+            // Paranoid check to make sure we are done with this extent now
+            if (size && (off >= e_start && off < e_end)) {
+                LOG(ERROR) << "Failed to write extent fully";
+                LogExtent(num_extent, extent);
+                return false;
+            }
+
+            if (size == 0) {
+                // done
+                break;
+            }
+        }
+        num_extent++;
+    }
+
+    return true;
+}
+
+bool FiemapWriter::Read(off64_t off, uint8_t* buffer, uint64_t size) {
+    return false;
+}
+
+// private helpers
+
+// WriteExtent() Returns the total number of bytes written. It will always be multiple of
+// block_size_. 0 is returned in one of the two cases.
+//  1. Any write failed between logical_off & logical_off + length.
+//  2. The logical_offset + length doesn't overlap with the extent passed.
+// The function can either partially for fully write the extent depending on the
+// logical_off + length. It is expected that alignment checks for size and offset are
+// performed before calling into this function.
+uint64_t FiemapWriter::WriteExtent(const struct fiemap_extent& ext, uint8_t* buffer,
+                                   off64_t logical_off, uint64_t length) {
+    uint64_t e_start = ext.fe_logical;
+    uint64_t e_end = ext.fe_logical + ext.fe_length;
+    if (logical_off < e_start || logical_off >= e_end) {
+        LOG(ERROR) << "Failed write extent, invalid offset " << logical_off << " and size "
+                   << length;
+        LogExtent(0, ext);
+        return 0;
+    }
+
+    off64_t bdev_offset = ext.fe_physical + (logical_off - e_start);
+    if (bdev_offset >= bdev_size_) {
+        LOG(ERROR) << "Failed write extent, invalid block # " << bdev_offset << " for block device "
+                   << bdev_path_ << " of size " << bdev_size_ << " bytes";
+        return 0;
+    }
+    if (TEMP_FAILURE_RETRY(lseek64(bdev_fd_, bdev_offset, SEEK_SET)) == -1) {
+        PLOG(ERROR) << "Failed write extent, seek offset for " << bdev_path_ << " offset "
+                    << bdev_offset;
+        return 0;
+    }
+
+    // Determine how much we want to write at once.
+    uint64_t logical_end = logical_off + length;
+    uint64_t write_size = (e_end <= logical_end) ? (e_end - logical_off) : length;
+    if (!android::base::WriteFully(bdev_fd_, buffer, write_size)) {
+        PLOG(ERROR) << "Failed write extent, write " << bdev_path_ << " at " << bdev_offset
+                    << " size " << write_size;
+        return 0;
+    }
+
+    return write_size;
+}
+
+}  // 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..6653ada
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/fiemap_writer_test.cpp
@@ -0,0 +1,360 @@
+/*
+ * 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 <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>
+
+using namespace std;
+using namespace android::fiemap_writer;
+using unique_fd = android::base::unique_fd;
+using LoopDevice = android::dm::LoopDevice;
+
+std::string testfile = "";
+std::string testbdev = "";
+uint64_t testfile_size = 536870912;  // default of 512MiB
+
+TEST(FiemapWriter, 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(FiemapWriter, CreateUnalignedFile) {
+    // Try creating a file of size 4097 bytes which is guaranteed
+    // to be unaligned to all known block sizes. The creation must
+    // fail.
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 4097);
+    EXPECT_EQ(fptr, nullptr);
+    EXPECT_EQ(access(testfile.c_str(), F_OK), -1);
+    EXPECT_EQ(errno, ENOENT);
+}
+
+TEST(FiemapWriter, CheckFilePath) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 4096);
+    ASSERT_NE(fptr, nullptr);
+    EXPECT_EQ(fptr->size(), 4096);
+    EXPECT_EQ(fptr->file_path(), testfile);
+    EXPECT_EQ(access(testfile.c_str(), F_OK), 0);
+}
+
+TEST(FiemapWriter, CheckBlockDevicePath) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, 4096);
+    EXPECT_EQ(fptr->size(), 4096);
+    EXPECT_EQ(fptr->bdev_path(), testbdev);
+}
+
+TEST(FiemapWriter, 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(FiemapWriter, CheckFileSizeActual) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, testfile_size);
+    ASSERT_NE(fptr, nullptr);
+
+    struct stat sb;
+    ASSERT_EQ(stat(testfile.c_str(), &sb), 0);
+    EXPECT_EQ(sb.st_size, testfile_size);
+}
+
+TEST(FiemapWriter, CheckFileExtents) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, testfile_size);
+    ASSERT_NE(fptr, nullptr);
+    EXPECT_GT(fptr->extents().size(), 0);
+}
+
+TEST(FiemapWriter, CheckWriteError) {
+    FiemapUniquePtr fptr = FiemapWriter::Open(testfile, testfile_size);
+    ASSERT_NE(fptr, nullptr);
+
+    // prepare buffer for writing the pattern - 0xa0
+    uint64_t blocksize = fptr->block_size();
+    auto buffer = std::unique_ptr<void, decltype(&free)>(calloc(1, blocksize), free);
+    ASSERT_NE(buffer, nullptr);
+    memset(buffer.get(), 0xa0, blocksize);
+
+    uint8_t* p = static_cast<uint8_t*>(buffer.get());
+    for (off64_t off = 0; off < testfile_size; off += blocksize) {
+        ASSERT_TRUE(fptr->Write(off, p, blocksize));
+    }
+
+    EXPECT_TRUE(fptr->Flush());
+}
+
+class TestExistingFile : public ::testing::Test {
+  protected:
+    void SetUp() override {
+        std::string exec_dir = ::android::base::GetExecutableDirectory();
+        std::string unaligned_file = exec_dir + "/testdata/unaligned_file";
+        std::string file_4k = exec_dir + "/testdata/file_4k";
+        std::string file_32k = exec_dir + "/testdata/file_32k";
+        fptr_unaligned = FiemapWriter::Open(unaligned_file, 4097, false);
+        fptr_4k = FiemapWriter::Open(file_4k, 4096, false);
+        fptr_32k = FiemapWriter::Open(file_32k, 32768, false);
+    }
+
+    FiemapUniquePtr fptr_unaligned;
+    FiemapUniquePtr fptr_4k;
+    FiemapUniquePtr fptr_32k;
+};
+
+TEST_F(TestExistingFile, ErrorChecks) {
+    EXPECT_EQ(fptr_unaligned, nullptr);
+    EXPECT_NE(fptr_4k, nullptr);
+    EXPECT_NE(fptr_32k, nullptr);
+
+    EXPECT_EQ(fptr_4k->size(), 4096);
+    EXPECT_EQ(fptr_32k->size(), 32768);
+    EXPECT_GT(fptr_4k->extents().size(), 0);
+    EXPECT_GT(fptr_32k->extents().size(), 0);
+}
+
+TEST_F(TestExistingFile, CheckWriteError) {
+    ASSERT_NE(fptr_4k, nullptr);
+    // prepare buffer for writing the pattern - 0xa0
+    uint64_t blocksize = fptr_4k->block_size();
+    auto buff_4k = std::unique_ptr<void, decltype(&free)>(calloc(1, blocksize), free);
+    ASSERT_NE(buff_4k, nullptr);
+    memset(buff_4k.get(), 0xa0, blocksize);
+
+    uint8_t* p = static_cast<uint8_t*>(buff_4k.get());
+    for (off64_t off = 0; off < 4096; off += blocksize) {
+        ASSERT_TRUE(fptr_4k->Write(off, p, blocksize));
+    }
+    EXPECT_TRUE(fptr_4k->Flush());
+
+    ASSERT_NE(fptr_32k, nullptr);
+    // prepare buffer for writing the pattern - 0xa0
+    blocksize = fptr_32k->block_size();
+    auto buff_32k = std::unique_ptr<void, decltype(&free)>(calloc(1, blocksize), free);
+    ASSERT_NE(buff_32k, nullptr);
+    memset(buff_32k.get(), 0xa0, blocksize);
+    p = static_cast<uint8_t*>(buff_32k.get());
+    for (off64_t off = 0; off < 4096; off += blocksize) {
+        ASSERT_TRUE(fptr_32k->Write(off, p, blocksize));
+    }
+    EXPECT_TRUE(fptr_32k->Flush());
+}
+
+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;
+};
+
+TEST_F(VerifyBlockWritesExt4, CheckWrites) {
+    EXPECT_EQ(access(fs_path.c_str(), F_OK), 0);
+
+    std::string file_path = mntpoint + "/testfile";
+    uint64_t file_size = 100 * 1024 * 1024;
+    auto buffer = std::unique_ptr<void, decltype(&free)>(calloc(1, getpagesize()), free);
+    ASSERT_NE(buffer, nullptr);
+    memset(buffer.get(), 0xa0, getpagesize());
+    {
+        // scoped fiemap writer
+        FiemapUniquePtr fptr = FiemapWriter::Open(file_path, file_size);
+        ASSERT_NE(fptr, nullptr);
+        uint8_t* p = static_cast<uint8_t*>(buffer.get());
+        for (off64_t off = 0; off < file_size / getpagesize(); off += getpagesize()) {
+            ASSERT_TRUE(fptr->Write(off, p, getpagesize()));
+        }
+        EXPECT_TRUE(fptr->Flush());
+    }
+    // unmount file system here to make sure we invalidated all page cache and
+    // remount the filesystem again for verification
+    ASSERT_EQ(umount(mntpoint.c_str()), 0);
+
+    LoopDevice loop_dev(fs_path);
+    ASSERT_TRUE(loop_dev.valid());
+    ASSERT_EQ(mount(loop_dev.device().c_str(), mntpoint.c_str(), "ext4", 0, nullptr), 0)
+            << "failed to mount: " << loop_dev.device() << " on " << mntpoint << ": "
+            << strerror(errno);
+
+    ::android::base::unique_fd fd(open(file_path.c_str(), O_RDONLY | O_SYNC));
+    ASSERT_NE(fd, -1);
+    auto filebuf = std::unique_ptr<void, decltype(&free)>(calloc(1, getpagesize()), free);
+    ASSERT_NE(filebuf, nullptr);
+    for (off64_t off = 0; off < file_size / getpagesize(); off += getpagesize()) {
+        memset(filebuf.get(), 0x00, getpagesize());
+        ASSERT_EQ(pread64(fd, filebuf.get(), getpagesize(), off), getpagesize());
+        ASSERT_EQ(memcmp(filebuf.get(), buffer.get(), getpagesize()), 0)
+                << "Invalid pattern at offset: " << off << " size " << getpagesize();
+    }
+}
+
+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;
+};
+
+TEST_F(VerifyBlockWritesF2fs, CheckWrites) {
+    EXPECT_EQ(access(fs_path.c_str(), F_OK), 0);
+
+    std::string file_path = mntpoint + "/testfile";
+    uint64_t file_size = 100 * 1024 * 1024;
+    auto buffer = std::unique_ptr<void, decltype(&free)>(calloc(1, getpagesize()), free);
+    ASSERT_NE(buffer, nullptr);
+    memset(buffer.get(), 0xa0, getpagesize());
+    {
+        // scoped fiemap writer
+        FiemapUniquePtr fptr = FiemapWriter::Open(file_path, file_size);
+        ASSERT_NE(fptr, nullptr);
+        uint8_t* p = static_cast<uint8_t*>(buffer.get());
+        for (off64_t off = 0; off < file_size / getpagesize(); off += getpagesize()) {
+            ASSERT_TRUE(fptr->Write(off, p, getpagesize()));
+        }
+        EXPECT_TRUE(fptr->Flush());
+    }
+    // unmount file system here to make sure we invalidated all page cache and
+    // remount the filesystem again for verification
+    ASSERT_EQ(umount(mntpoint.c_str()), 0);
+
+    LoopDevice loop_dev(fs_path);
+    ASSERT_TRUE(loop_dev.valid());
+    ASSERT_EQ(mount(loop_dev.device().c_str(), mntpoint.c_str(), "f2fs", 0, nullptr), 0)
+            << "failed to mount: " << loop_dev.device() << " on " << mntpoint << ": "
+            << strerror(errno);
+
+    ::android::base::unique_fd fd(open(file_path.c_str(), O_RDONLY | O_SYNC));
+    ASSERT_NE(fd, -1);
+    auto filebuf = std::unique_ptr<void, decltype(&free)>(calloc(1, getpagesize()), free);
+    ASSERT_NE(filebuf, nullptr);
+    for (off64_t off = 0; off < file_size / getpagesize(); off += getpagesize()) {
+        memset(filebuf.get(), 0x00, getpagesize());
+        ASSERT_EQ(pread64(fd, filebuf.get(), getpagesize(), off), getpagesize());
+        ASSERT_EQ(memcmp(filebuf.get(), buffer.get(), getpagesize()), 0)
+                << "Invalid pattern at offset: " << off << " size " << getpagesize();
+    }
+}
+
+int main(int argc, char** argv) {
+    ::testing::InitGoogleTest(&argc, argv);
+    if (argc <= 2) {
+        cerr << "Filepath with its bdev path must be provided as follows:" << endl;
+        cerr << "  $ fiemap_writer_test <path to file> </dev/block/XXXX" << endl;
+        cerr << "  where, /dev/block/XXX is the block device where the file resides" << endl;
+        exit(EXIT_FAILURE);
+    }
+    ::android::base::InitLogging(argv, ::android::base::StderrLogger);
+
+    testfile = argv[1];
+    testbdev = argv[2];
+    if (argc > 3) {
+        testfile_size = strtoull(argv[3], NULL, 0);
+        if (testfile_size == ULLONG_MAX) {
+            testfile_size = 512 * 1024 * 1024;
+        }
+    }
+
+    return RUN_ALL_TESTS();
+}
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..ae61344
--- /dev/null
+++ b/fs_mgr/libfiemap_writer/include/libfiemap_writer/fiemap_writer.h
@@ -0,0 +1,104 @@
+/*
+ * 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 <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.
+    static FiemapUniquePtr Open(const std::string& file_path, uint64_t file_size,
+                                bool create = true);
+
+    // Syncs block device writes.
+    bool Flush() const;
+
+    // Writes the file by using its FIEMAP and performing i/o on the raw block device.
+    // The return value is success / failure. This will happen in particular if the
+    // kernel write returns errors, extents are not writeable or more importantly, if the 'size' is
+    // not aligned to the block device's block size.
+    bool Write(off64_t off, uint8_t* buffer, uint64_t size);
+
+    // The counter part of Write(). It is an error for the offset to be unaligned with
+    // the block device's block size.
+    // In case of error, the contents of buffer MUST be discarded.
+    bool Read(off64_t off, uint8_t* buffer, uint64_t size);
+
+    ~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_; };
+
+    // 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_;
+
+    // File descriptors for the file and block device
+    ::android::base::unique_fd file_fd_;
+    ::android::base::unique_fd bdev_fd_;
+
+    // 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;
+
+    uint64_t WriteExtent(const struct fiemap_extent& ext, uint8_t* buffer, off64_t logical_off,
+                         uint64_t length);
+};
+
+}  // namespace fiemap_writer
+}  // namespace android
diff --git a/fs_mgr/libfiemap_writer/testdata/file_32k b/fs_mgr/libfiemap_writer/testdata/file_32k
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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
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diff --git a/fs_mgr/libfiemap_writer/testdata/unaligned_file b/fs_mgr/libfiemap_writer/testdata/unaligned_file
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