# Copyright 2014 Red Hat, Inc.
# All Rights Reserved.
#
#    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.

"""
Various utilities related to disk handling.

Imported from ironic-lib's disk_utils as of the following commit:
https://opendev.org/openstack/ironic-lib/commit/42fa5d63861ba0f04b9a4f67212173d7013a1332
"""

import logging
import os
import re
import stat
import time

from oslo_concurrency import processutils
from oslo_config import cfg
from oslo_utils import excutils
from oslo_utils.imageutils import format_inspector
import tenacity

from ironic_python_agent import disk_partitioner
from ironic_python_agent import errors
from ironic_python_agent import qemu_img
from ironic_python_agent import utils

CONF = cfg.CONF

LOG = logging.getLogger(__name__)

_PARTED_PRINT_RE = re.compile(r"^(\d+):([\d\.]+)MiB:"
                              r"([\d\.]+)MiB:([\d\.]+)MiB:(\w*):(.*):(.*);")
_PARTED_TABLE_TYPE_RE = re.compile(r'^.*partition\s+table\s*:\s*(gpt|msdos)',
                                   re.IGNORECASE | re.MULTILINE)

CONFIGDRIVE_LABEL = "config-2"
MAX_CONFIG_DRIVE_SIZE_MB = 64

# Maximum disk size supported by MBR is 2TB (2 * 1024 * 1024 MB)
MAX_DISK_SIZE_MB_SUPPORTED_BY_MBR = 2097152

# NOTE(JayF): Image types we write bit-perfect to disk, no conversion
RAW_LIKE_IMAGETYPES = ['gpt', 'raw']


def list_partitions(device):
    """Get partitions information from given device.

    :param device: The device path.
    :returns: list of dictionaries (one per partition) with keys:
              number, start, end, size (in MiB), filesystem, partition_name,
              flags, path.
    """
    output = utils.execute(
        'parted', '-s', '-m', device, 'unit', 'MiB', 'print',
        use_standard_locale=True)[0]
    if isinstance(output, bytes):
        output = output.decode("utf-8")
    lines = [line for line in output.split('\n') if line.strip()][2:]
    # Example of line: 1:1.00MiB:501MiB:500MiB:ext4::boot
    fields = ('number', 'start', 'end', 'size', 'filesystem', 'partition_name',
              'flags')
    result = []
    for line in lines:
        match = _PARTED_PRINT_RE.match(line)
        if match is None:
            LOG.warning("Partition information from parted for device "
                        "%(device)s does not match "
                        "expected format: %(line)s",
                        dict(device=device, line=line))
            continue
        # Cast int fields to ints (some are floats and we round them down)
        groups = [int(float(x)) if i < 4 else x
                  for i, x in enumerate(match.groups())]
        item = dict(zip(fields, groups))
        item['path'] = partition_index_to_path(device, item['number'])
        result.append(item)
    return result


def count_mbr_partitions(device):
    """Count the number of primary and logical partitions on a MBR

    :param device: The device path.
    :returns: A tuple with the number of primary partitions and logical
              partitions.
    :raise: ValueError if the device does not have a valid MBR partition
            table.
    """
    # -d do not update the kernel table
    # -s print a summary of the partition table
    output, err = utils.execute('partprobe', '-d', '-s', device,
                                use_standard_locale=True)
    if 'msdos' not in output:
        raise ValueError('The device %s does not have a valid MBR '
                         'partition table' % device)
    # Sample output: /dev/vdb: msdos partitions 1 2 3 <5 6 7>
    # The partitions with number > 4 (and inside <>) are logical partitions
    output = output.replace('<', '').replace('>', '')
    partitions = [int(s) for s in output.split() if s.isdigit()]

    return (sum(i < 5 for i in partitions), sum(i > 4 for i in partitions))


def get_disk_identifier(dev):
    """Get the disk identifier from the disk being exposed by the ramdisk.

    This disk identifier is appended to the pxe config which will then be
    used by chain.c32 to detect the correct disk to chainload. This is helpful
    in deployments to nodes with multiple disks.

    http://www.syslinux.org/wiki/index.php/Comboot/chain.c32#mbr:

    :param dev: Path for the already populated disk device.
    :raises OSError: When the hexdump binary is unavailable.
    :returns: The Disk Identifier.
    """
    disk_identifier = utils.execute('hexdump', '-s', '440', '-n', '4',
                                    '-e', '''\"0x%08x\"''',
                                    dev, attempts=5, delay_on_retry=True)
    return disk_identifier[0]


def get_partition_table_type(device):
    """Get partition table type, msdos or gpt.

    :param device: the name of the device
    :return: dos, gpt or None
    """
    out = utils.execute('parted', '--script', device, '--', 'print',
                        use_standard_locale=True)[0]
    m = _PARTED_TABLE_TYPE_RE.search(out)
    if m:
        return m.group(1)

    LOG.warning("Unable to get partition table type for device %s", device)
    return 'unknown'


def _lsblk(device, deps=True, fields=None):
    args = ['--pairs', '--bytes', '--ascii']
    if not deps:
        args.append('--nodeps')
    if fields:
        args.extend(['--output', ','.join(fields)])
    else:
        args.append('--output-all')

    output, err = utils.execute('lsblk', device, *args,
                                use_standard_locale=True)
    return output.strip()


def get_device_information(device, fields=None):
    """Get information about a device using blkid.

    Can be applied to all block devices: disks, RAID, partitions.

    :param device: Device name.
    :param fields: A list of fields to request (all by default).
    :return: A dictionary with requested fields as keys.
    :raises: ProcessExecutionError
    """
    output = _lsblk(device, fields=fields, deps=False)
    if output:
        return next(utils.parse_device_tags(output))
    else:
        return {}


def find_efi_partition(device):
    """Looks for the EFI partition on a given device.

    A boot partition on a GPT disk is assumed to be an EFI partition as well.

    :param device: the name of the device
    :return: the EFI partition record from `list_partitions` or None
    """
    is_gpt = get_partition_table_type(device) == 'gpt'
    for part in list_partitions(device):
        flags = {x.strip() for x in part['flags'].split(',')}
        if 'esp' in flags or ('boot' in flags and is_gpt):
            LOG.debug("Found EFI partition %s on device %s", part, device)
            return part
    else:
        LOG.debug("No efi partition found on device %s", device)


_ISCSI_PREFIX = "iqn.2008-10.org.openstack:"


def is_last_char_digit(dev):
    """check whether device name ends with a digit"""
    if len(dev) >= 1:
        return dev[-1].isdigit()
    return False


def partition_index_to_path(device, index):
    """Guess a partition path based on its device and index.

    :param device: Device path.
    :param index: Partition index.
    """
    # the actual device names in the baremetal are like /dev/sda, /dev/sdb etc.
    # While for the iSCSI device, the naming convention has a format which has
    # iqn also embedded in it.
    # When this function is called by ironic-conductor, the iSCSI device name
    # should be appended by "part%d". While on the baremetal, it should name
    # the device partitions as /dev/sda1 and not /dev/sda-part1.
    if _ISCSI_PREFIX in device:
        part_template = '%s-part%d'
    elif is_last_char_digit(device):
        part_template = '%sp%d'
    else:
        part_template = '%s%d'
    return part_template % (device, index)


def make_partitions(dev, root_mb, swap_mb, ephemeral_mb,
                    configdrive_mb, node_uuid, commit=True,
                    boot_option="netboot", boot_mode="bios",
                    disk_label=None, cpu_arch=""):
    """Partition the disk device.

    Create partitions for root, swap, ephemeral and configdrive on a
    disk device.

    :param dev: Path for the device to work on.
    :param root_mb: Size of the root partition in mebibytes (MiB).
    :param swap_mb: Size of the swap partition in mebibytes (MiB). If 0,
        no partition will be created.
    :param ephemeral_mb: Size of the ephemeral partition in mebibytes (MiB).
        If 0, no partition will be created.
    :param configdrive_mb: Size of the configdrive partition in
        mebibytes (MiB). If 0, no partition will be created.
    :param commit: True/False. Default for this setting is True. If False
        partitions will not be written to disk.
    :param boot_option: Can be "local" or "netboot". "netboot" by default.
    :param boot_mode: Can be "bios" or "uefi". "bios" by default.
    :param node_uuid: Node's uuid. Used for logging.
    :param disk_label: The disk label to be used when creating the
        partition table. Valid values are: "msdos", "gpt" or None; If None
        Ironic will figure it out according to the boot_mode parameter.
    :param cpu_arch: Architecture of the node the disk device belongs to.
        When using the default value of None, no architecture specific
        steps will be taken. This default should be used for x86_64. When
        set to ppc64*, architecture specific steps are taken for booting a
        partition image locally.
    :returns: A dictionary containing the partition type as Key and partition
        path as Value for the partitions created by this method.

    """
    LOG.debug("Starting to partition the disk device: %(dev)s "
              "for node %(node)s",
              {'dev': dev, 'node': node_uuid})
    part_dict = {}

    if disk_label is None:
        disk_label = 'gpt' if boot_mode == 'uefi' else 'msdos'

    dp = disk_partitioner.DiskPartitioner(dev, disk_label=disk_label)

    # For uefi localboot, switch partition table to gpt and create the efi
    # system partition as the first partition.
    if boot_mode == "uefi" and boot_option == "local":
        part_num = dp.add_partition(CONF.disk_utils.efi_system_partition_size,
                                    fs_type='fat32',
                                    boot_flag='boot')
        part_dict['efi system partition'] = partition_index_to_path(
            dev, part_num)

    if (boot_mode == "bios" and boot_option == "local" and disk_label == "gpt"
        and not cpu_arch.startswith('ppc64')):
        part_num = dp.add_partition(CONF.disk_utils.bios_boot_partition_size,
                                    boot_flag='bios_grub')
        part_dict['BIOS Boot partition'] = partition_index_to_path(
            dev, part_num)

    # NOTE(mjturek): With ppc64* nodes, partition images are expected to have
    # a PrEP partition at the start of the disk. This is an 8 MiB partition
    # with the boot and prep flags set. The bootloader should be installed
    # here.
    if (cpu_arch.startswith("ppc64") and boot_mode == "bios"
            and boot_option == "local"):
        LOG.debug("Add PReP boot partition (8 MB) to device: "
                  "%(dev)s for node %(node)s",
                  {'dev': dev, 'node': node_uuid})
        boot_flag = 'boot' if disk_label == 'msdos' else None
        part_num = dp.add_partition(8, part_type='primary',
                                    boot_flag=boot_flag, extra_flags=['prep'])
        part_dict['PReP Boot partition'] = partition_index_to_path(
            dev, part_num)
    if ephemeral_mb:
        LOG.debug("Add ephemeral partition (%(size)d MB) to device: %(dev)s "
                  "for node %(node)s",
                  {'dev': dev, 'size': ephemeral_mb, 'node': node_uuid})
        part_num = dp.add_partition(ephemeral_mb)
        part_dict['ephemeral'] = partition_index_to_path(dev, part_num)
    if swap_mb:
        LOG.debug("Add Swap partition (%(size)d MB) to device: %(dev)s "
                  "for node %(node)s",
                  {'dev': dev, 'size': swap_mb, 'node': node_uuid})
        part_num = dp.add_partition(swap_mb, fs_type='linux-swap')
        part_dict['swap'] = partition_index_to_path(dev, part_num)
    if configdrive_mb:
        LOG.debug("Add config drive partition (%(size)d MB) to device: "
                  "%(dev)s for node %(node)s",
                  {'dev': dev, 'size': configdrive_mb, 'node': node_uuid})
        part_num = dp.add_partition(configdrive_mb)
        part_dict['configdrive'] = partition_index_to_path(dev, part_num)

    # NOTE(lucasagomes): Make the root partition the last partition. This
    # enables tools like cloud-init's growroot utility to expand the root
    # partition until the end of the disk.
    LOG.debug("Add root partition (%(size)d MB) to device: %(dev)s "
              "for node %(node)s",
              {'dev': dev, 'size': root_mb, 'node': node_uuid})

    boot_val = 'boot' if (not cpu_arch.startswith("ppc64")
                          and boot_mode == "bios"
                          and boot_option == "local"
                          and disk_label == "msdos") else None

    part_num = dp.add_partition(root_mb, boot_flag=boot_val)

    part_dict['root'] = partition_index_to_path(dev, part_num)

    if commit:
        # write to the disk
        dp.commit()
        trigger_device_rescan(dev)
    return part_dict


def is_block_device(dev):
    """Check whether a device is block or not."""
    attempts = CONF.disk_utils.partition_detection_attempts
    for attempt in range(attempts):
        try:
            s = os.stat(dev)
        except OSError as e:
            LOG.debug("Unable to stat device %(dev)s. Attempt %(attempt)d "
                      "out of %(total)d. Error: %(err)s",
                      {"dev": dev, "attempt": attempt + 1,
                       "total": attempts, "err": e})
            time.sleep(1)
        else:
            return stat.S_ISBLK(s.st_mode)
    msg = ("Unable to stat device %(dev)s after attempting to verify "
           "%(attempts)d times.") % {'dev': dev, 'attempts': attempts}
    LOG.error(msg)
    raise errors.DeploymentError(msg)


def dd(src, dst, conv_flags=None):
    """Execute dd from src to dst."""
    args = ['bs=%s' % CONF.disk_utils.dd_block_size, 'oflag=direct']
    if conv_flags:
        args.append('conv=%s' % conv_flags)

    utils.execute('dd', 'if=%s' % src, 'of=%s' % dst, *args,
                  use_standard_locale=True)


def _image_inspection(filename):
    try:
        inspector_cls = format_inspector.detect_file_format(filename)
        if not inspector_cls:
            msg = "Security: Unable to safety check image"
            LOG.error(msg)
            raise errors.InvalidImage(details=msg)
        inspector_cls.safety_check()

    except format_inspector.ImageFormatError:
        msg = "Security: Image matched multiple potential formats"
        LOG.exception(msg)
        raise errors.InvalidImage(details=msg)

    except format_inspector.SafetyCheckFailed:
        msg = "Security: Image failed safety check"
        LOG.exception(msg)
        raise errors.InvalidImage(details=msg)

    return inspector_cls


def get_and_validate_image_format(filename, ironic_disk_format):
    """Get the format of a given image file and ensure it's allowed.

    This method uses the format inspector originally written for glance to
    safely detect the image format. It also sanity checks to ensure any
    specified format matches the provided one and that the format is in the
    allowed list of formats.

    If the image format provided by Ironic is a type which doesn't need
    conversion, we avoid all introspection of the image and use of qemu-img.

    It also performs a basic safety check on the image.

    This entire process can be bypassed, and the older code path used,
    by setting CONF.disable_deep_image_inspection to True.

    See https://bugs.launchpad.net/ironic/+bug/2071740 for full details on
    why this must always happen.

    :param filename: The name of the image file to validate.
    :param ironic_disk_format: The ironic-provided expected format of the image
    :returns: tuple of validated img_format (str) and size (int)
    """
    if CONF.disable_deep_image_inspection:
        data = qemu_img.image_info(filename)
        img_format = data.file_format
        size = data.virtual_size
    else:
        if ironic_disk_format in RAW_LIKE_IMAGETYPES:
            # NOTE(JayF): IPA avoids converting images which claim to be a
            #             type that doesn't need conversion. This negates any
            #             security risk the image file could pose.
            img_format = ironic_disk_format
            size = os.path.getsize(filename)
        else:
            img_format_cls = _image_inspection(filename)
            img_format = str(img_format_cls)
            size = img_format_cls.virtual_size
            if img_format not in CONF.permitted_image_formats:
                msg = ("Security: Detected image format was %s, but only %s "
                       "are allowed")
                fmts = ', '.join(CONF.permitted_image_formats)
                LOG.error(msg, img_format, fmts)
                raise errors.InvalidImage(
                    details=msg % (img_format, fmts)
                )
            elif (ironic_disk_format
                  and ironic_disk_format != img_format
                  and ironic_disk_format != 'unknown'):
                msg = ("Security: Expected format was %s, but image was "
                       "actually %s" % (ironic_disk_format, img_format))
                LOG.error(msg)
                raise errors.InvalidImage(details=msg)

    return img_format, size


def populate_image(src, dst, conv_flags=None, source_format=None, is_raw=False,
                   sparse_size='0', out_format='raw', **convert_args):
    """Populate a provided destination device with the image

    :param src: An image already security checked in format disk_format
    :param dst: A location, usually a partition or block device,
                to write the image
    :param conv_flags: Conversion flags to pass to dd if provided
    :param is_raw: Ironic indicates image is raw; do not convert!
    :param sparse_size: Sparse size to pass to qemu_img
    :param source_format: format of the image
    :param out_format: Output format
    :param convert_args: Additional arguments to optionally pass to qemu_img
    """
    try:
        if is_raw:
            # NOTE(JayF): Since we do not safety check raw images, we must use
            #  dd to write them to ensure maximum security. This may cause
            #  failures in situations where images are configured as raw but
            #  are actually in need of conversion. Those cases can no longer
            #  be transparently handled safely.
            LOG.info('Writing raw image %s to device %s', src, dst)
            dd(src, dst, conv_flags=conv_flags)
        else:
            qemu_img.convert_image(src, dst,
                                   out_format=out_format,
                                   sparse_size=sparse_size,
                                   source_format=source_format,
                                   **convert_args)
    except processutils.ProcessExecutionError as e:
        raise errors.ImageWriteError(dst, e.exit_code, e.stdout, e.stderr)


def block_uuid(dev):
    """Get UUID of a block device.

    Try to fetch the UUID, if that fails, try to fetch the PARTUUID.
    """
    info = get_device_information(dev, fields=['UUID', 'PARTUUID'])
    if info.get('UUID'):
        return info['UUID']
    else:
        LOG.debug('Falling back to partition UUID as the block device UUID '
                  'was not found while examining %(device)s',
                  {'device': dev})
        return info.get('PARTUUID', '')


def get_dev_byte_size(dev):
    """Get the device size in bytes."""
    byte_sz, cmderr = utils.execute('blockdev', '--getsize64', dev)
    return int(byte_sz)


def get_dev_sector_size(dev):
    """Get the device logical sector size in bytes."""
    sect_sz, cmderr = utils.execute('blockdev', '--getss', dev)
    return int(sect_sz)


def destroy_disk_metadata(dev, node_uuid):
    """Destroy metadata structures on node's disk.

    Ensure that node's disk magic strings are wiped without zeroing the
    entire drive. To do this we use the wipefs tool from util-linux.

    :param dev: Path for the device to work on.
    :param node_uuid: Node's uuid. Used for logging.
    """
    # NOTE(NobodyCam): This is needed to work around bug:
    # https://bugs.launchpad.net/ironic/+bug/1317647
    LOG.debug("Start destroy disk metadata for node %(node)s.",
              {'node': node_uuid})
    try:
        utils.execute('wipefs', '--force', '--all', dev,
                      use_standard_locale=True)
    except processutils.ProcessExecutionError as e:
        with excutils.save_and_reraise_exception() as ctxt:
            # NOTE(zhenguo): Check if --force option is supported for wipefs,
            # if not, we should try without it.
            if '--force' in str(e):
                ctxt.reraise = False
                utils.execute('wipefs', '--all', dev,
                              use_standard_locale=True)
    # NOTE(TheJulia): sgdisk attempts to load and make sense of the
    # partition tables in advance of wiping the partition data.
    # This means when a CRC error is found, sgdisk fails before
    # erasing partition data.
    # This is the same bug as
    # https://bugs.launchpad.net/ironic-python-agent/+bug/1737556

    sector_size = get_dev_sector_size(dev)
    # https://uefi.org/specs/UEFI/2.10/05_GUID_Partition_Table_Format.html If
    # the block size is 512, the First Usable LBA must be greater than or equal
    # to 34 [...] if the logical block size is 4096, the First Usable LBA must
    # be greater than or equal to 6
    if sector_size == 512:
        gpt_sectors = 33
    elif sector_size == 4096:
        gpt_sectors = 5

    # Overwrite the Primary GPT, catch very small partitions (like EBRs)
    dd_bs = 'bs=%s' % sector_size
    dd_device = 'of=%s' % dev
    dd_count = 'count=%s' % gpt_sectors
    dev_size = get_dev_byte_size(dev)
    if dev_size < gpt_sectors * sector_size:
        dd_count = 'count=%s' % int(dev_size / sector_size)
    utils.execute('dd', dd_bs, 'if=/dev/zero', dd_device, dd_count,
                  'oflag=direct', use_standard_locale=True)

    # Overwrite the Secondary GPT, do this only if there could be one
    if dev_size > gpt_sectors * sector_size:
        gpt_backup = int(dev_size / sector_size - gpt_sectors)
        dd_seek = 'seek=%i' % gpt_backup
        dd_count = 'count=%s' % gpt_sectors
        utils.execute('dd', dd_bs, 'if=/dev/zero', dd_device, dd_count,
                      'oflag=direct', dd_seek, use_standard_locale=True)

    # Go ahead and let sgdisk run as well.
    utils.execute('sgdisk', '-Z', dev, use_standard_locale=True)

    try:
        wait_for_disk_to_become_available(dev)
    except errors.RESTError as e:
        raise errors.DeploymentError(
            f'Destroying metadata failed on device {dev}s. Error: {e}')

    LOG.info("Disk metadata on %s successfully destroyed for node "
             "%s", dev, node_uuid)


def _fix_gpt_structs(device, node_uuid):
    """Checks backup GPT data structures and moves them to end of the device

    :param device: The device path.
    :param node_uuid: UUID of the Node. Used for logging.
    :raises: InstanceDeployFailure, if any disk partitioning related
        commands fail.
    """
    try:
        output, _err = utils.execute('sgdisk', '-v', device)

        search_str = "it doesn't reside\nat the end of the disk"
        if search_str in output:
            utils.execute('sgdisk', '-e', device)
    except (processutils.UnknownArgumentError,
            processutils.ProcessExecutionError, OSError) as e:
        msg = ('Failed to fix GPT data structures on disk %(disk)s '
               'for node %(node)s. Error: %(error)s' %
               {'disk': device, 'node': node_uuid, 'error': e})
        LOG.error(msg)
        raise errors.DeploymentError(msg)


def fix_gpt_partition(device, node_uuid):
    """Fix GPT partition

    Fix GPT table information when image is written to a disk which
    has a bigger extend (e.g. 30GB image written on a 60Gb physical disk).

    :param device: The device path.
    :param node_uuid: UUID of the Node.
    :raises: InstanceDeployFailure if exception is caught.
    """
    try:
        disk_is_gpt_partitioned = (get_partition_table_type(device) == 'gpt')
        if disk_is_gpt_partitioned:
            _fix_gpt_structs(device, node_uuid)
    except Exception as e:
        msg = ('Failed to fix GPT partition on disk %(disk)s '
               'for node %(node)s. Error: %(error)s' %
               {'disk': device, 'node': node_uuid, 'error': e})
        LOG.error(msg)
        raise errors.DeploymentError(msg)


def udev_settle():
    """Wait for the udev event queue to settle.

    Wait for the udev event queue to settle to make sure all devices
    are detected once the machine boots up.

    :return: True on success, False otherwise.
    """
    LOG.debug('Waiting until udev event queue is empty')
    try:
        utils.execute('udevadm', 'settle')
    except processutils.ProcessExecutionError as e:
        LOG.warning('Something went wrong when waiting for udev '
                    'to settle. Error: %s', e)
        return False
    else:
        return True


def partprobe(device, attempts=None):
    """Probe partitions on the given device.

    :param device: The block device containing partitions that is attempting
                   to be updated.
    :param attempts: Number of attempts to run partprobe, the default is read
                     from the configuration.
    :return: True on success, False otherwise.
    """
    if attempts is None:
        attempts = CONF.disk_utils.partprobe_attempts

    try:
        utils.execute('partprobe', device, attempts=attempts)
    except (processutils.UnknownArgumentError,
            processutils.ProcessExecutionError, OSError) as e:
        LOG.warning("Unable to probe for partitions on device %(device)s, "
                    "the partitioning table may be broken. Error: %(error)s",
                    {'device': device, 'error': e})
        return False
    else:
        return True


def trigger_device_rescan(device, attempts=None):
    """Sync and trigger device rescan.

    Disk partition performed via parted, when performed on a ramdisk
    do not have to honor the fsync mechanism. In essence, fsync is used
    on the file representing the block device, which falls to the kernel
    filesystem layer to trigger a sync event. On a ramdisk using ramfs,
    this is an explicit non-operation.

    As a result of this, we need to trigger a system wide sync operation
    which will trigger cache to flush to disk, after which partition changes
    should be visible upon re-scan.

    When ramdisks are not in use, this also helps ensure that data has
    been safely flushed across the wire, such as on iscsi connections.

    :param device: The block device containing partitions that is attempting
                   to be updated.
    :param attempts: Number of attempts to run partprobe, the default is read
                     from the configuration.
    :return: True on success, False otherwise.
    """
    LOG.debug('Explicitly calling sync to force buffer/cache flush')
    utils.execute('sync')
    # Make sure any additions to the partitioning are reflected in the
    # kernel.
    udev_settle()
    partprobe(device, attempts=attempts)
    udev_settle()
    try:
        # Also verify that the partitioning is correct now.
        utils.execute('sgdisk', '-v', device)
    except processutils.ProcessExecutionError as exc:
        LOG.warning('Failed to verify partition tables on device %(dev)s: '
                    '%(err)s', {'dev': device, 'err': exc})
        return False
    else:
        return True


def wait_for_disk_to_become_available(device):
    """Wait for a disk device to become available.

    Waits for a disk device to become available for use by
    waiting until all process locks on the device have been
    released.

    Timeout and iteration settings come from the configuration
    options used by the in-library disk_partitioner:
    ``check_device_interval`` and ``check_device_max_retries``.

    :params device: The path to the device.
    :raises: IronicException If the disk fails to become
        available.
    """
    pids = ['']
    stderr = ['']
    interval = CONF.disk_partitioner.check_device_interval
    max_retries = CONF.disk_partitioner.check_device_max_retries

    def _wait_for_disk():
        # A regex is likely overkill here, but variations in fuser
        # means we should likely use it.
        fuser_pids_re = re.compile(r'\d+')

        # There are 'psmisc' and 'busybox' versions of the 'fuser' program. The
        # 'fuser' programs differ in how they output data to stderr.  The
        # busybox version does not output the filename to stderr, while the
        # standard 'psmisc' version does output the filename to stderr.  How
        # they output to stdout is almost identical in that only the PIDs are
        # output to stdout, with the 'psmisc' version adding a leading space
        # character to the list of PIDs.
        try:
            # NOTE(ifarkas): fuser returns a non-zero return code if none of
            #                the specified files is accessed.
            # NOTE(TheJulia): fuser does not report LVM devices as in use
            #                 unless the LVM device-mapper device is the
            #                 device that is directly polled.
            # NOTE(TheJulia): The -m flag allows fuser to reveal data about
            #                 mounted filesystems, which should be considered
            #                 busy/locked. That being said, it is not used
            #                 because busybox fuser has a different behavior.
            # NOTE(TheJuia): fuser outputs a list of found PIDs to stdout.
            #                All other text is returned via stderr, and the
            #                output to a terminal is merged as a result.
            out, err = utils.execute('fuser', device, check_exit_code=[0, 1])

            if not out and not err:
                return True

            stderr[0] = err
            # NOTE: findall() returns a list of matches, or an empty list if no
            # matches
            pids[0] = fuser_pids_re.findall(out)

        except processutils.ProcessExecutionError as exc:
            LOG.warning('Failed to check the device %(device)s with fuser:'
                        ' %(err)s', {'device': device, 'err': exc})
        return False

    retry = tenacity.retry(
        retry=tenacity.retry_if_result(lambda r: not r),
        stop=tenacity.stop_after_attempt(max_retries),
        wait=tenacity.wait_fixed(interval),
        reraise=True)
    try:
        retry(_wait_for_disk)()
    except tenacity.RetryError:
        if pids[0]:
            raise errors.DeviceNotFound(
                ('Processes with the following PIDs are holding '
                 'device %(device)s: %(pids)s. '
                 'Timed out waiting for completion.')
                % {'device': device, 'pids': ', '.join(pids[0])})
        else:
            raise errors.DeviceNotFound(
                ('Fuser exited with "%(fuser_err)s" while checking '
                 'locks for device %(device)s. Timed out waiting for '
                 'completion.') % {'device': device, 'fuser_err': stderr[0]})