Restripe BTRFS: add or remove devices from the particular mounted filesystem.

def _restripe(mountpoint, direction, *devices, **kwargs):
    '''
    Restripe BTRFS: add or remove devices from the particular mounted filesystem.
    '''
    fs_log = []

    if salt.utils.fsutils._is_device(mountpoint):
        raise CommandExecutionError(
            "Mountpount expected, while device \"{0}\" specified".format(mountpoint))

    mounted = False
    for device, mntpoints in six.iteritems(salt.utils.fsutils._get_mounts("btrfs")):
        for mntdata in mntpoints:
            if mntdata['mount_point'] == mountpoint:
                mounted = True
                break

    if not mounted:
        raise CommandExecutionError(
            "No BTRFS device mounted on \"{0}\" mountpoint".format(mountpoint))

    if not devices:
        raise CommandExecutionError("No devices specified.")

    available_devices = __salt__['btrfs.devices']()
    for device in devices:
        if device not in six.iterkeys(available_devices):
            raise CommandExecutionError("Device \"{0}\" is not recognized".format(device))

    cmd = ['btrfs device {0}'.format(direction)]
    for device in devices:
        cmd.append(device)

    if direction == 'add':
        if kwargs.get("nodiscard"):
            cmd.append("-K")
        if kwargs.get("force"):
            cmd.append("-f")

    cmd.append(mountpoint)

    out = __salt__['cmd.run_all'](' '.join(cmd))
    salt.utils.fsutils._verify_run(out)
    if out['stdout']:
        fs_log.append(out['stdout'])

    if direction == 'add':
        out = None
        data_conversion = kwargs.get("dc")
        meta_conversion = kwargs.get("mc")
        if data_conversion and meta_conversion:
            out = __salt__['cmd.run_all'](
                "btrfs balance start -dconvert={0} -mconvert={1} {2}".format(
                    data_conversion, meta_conversion, mountpoint))
        else:
            out = __salt__['cmd.run_all']("btrfs filesystem balance {0}".format(mountpoint))
        salt.utils.fsutils._verify_run(out)
        if out['stdout']:
            fs_log.append(out['stdout'])

    # Summarize the result
    ret = {}
    if fs_log:
        ret.update({'log': '\n'.join(fs_log)})
    ret.update(__salt__['btrfs.info'](mountpoint))

    return ret