summaryrefslogtreecommitdiff
path: root/cloudinit/config/cc_disk_setup.py
blob: 127b5879103b6fea23d5d944a0b091a8d13c2371 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
# vi: ts=4 expandtab
#
#    Copyright (C) 2009-2010 Canonical Ltd.
#    Copyright (C) 2012 Hewlett-Packard Development Company, L.P.
#
#    Author: Ben Howard <ben.howard@canonical.com>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License version 3, as
#    published by the Free Software Foundation.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
from cloudinit.settings import PER_INSTANCE
from cloudinit import util
import logging
import os
import shlex

frequency = PER_INSTANCE

# Define the commands to use
UDEVADM_CMD = util.which('udevadm')
SFDISK_CMD = util.which("sfdisk")
LSBLK_CMD = util.which("lsblk")
BLKID_CMD = util.which("blkid")
BLKDEV_CMD = util.which("blockdev")
WIPEFS_CMD = util.which("wipefs")

LOG = logging.getLogger(__name__)


def handle(_name, cfg, cloud, log, _args):
    """
    See doc/examples/cloud-config_disk-setup.txt for documentation on the
    format.
    """
    disk_setup = cfg.get("disk_setup")
    if isinstance(disk_setup, dict):
        update_disk_setup_devices(disk_setup, cloud.device_name_to_device)
        log.debug("Partitioning disks: %s", str(disk_setup))
        for disk, definition in disk_setup.items():
            if not isinstance(definition, dict):
                log.warn("Invalid disk definition for %s" % disk)
                continue

            try:
                log.debug("Creating new partition table/disk")
                util.log_time(logfunc=LOG.debug,
                              msg="Creating partition on %s" % disk,
                              func=mkpart, args=(disk, definition))
            except Exception as e:
                util.logexc(LOG, "Failed partitioning operation\n%s" % e)

    fs_setup = cfg.get("fs_setup")
    if isinstance(fs_setup, list):
        log.debug("setting up filesystems: %s", str(fs_setup))
        update_fs_setup_devices(fs_setup, cloud.device_name_to_device)
        for definition in fs_setup:
            if not isinstance(definition, dict):
                log.warn("Invalid file system definition: %s" % definition)
                continue

            try:
                log.debug("Creating new filesystem.")
                device = definition.get('device')
                util.log_time(logfunc=LOG.debug,
                              msg="Creating fs for %s" % device,
                              func=mkfs, args=(definition,))
            except Exception as e:
                util.logexc(LOG, "Failed during filesystem operation\n%s" % e)


def update_disk_setup_devices(disk_setup, tformer):
    # update 'disk_setup' dictionary anywhere were a device may occur
    # update it with the response from 'tformer'
    for origname in disk_setup.keys():
        transformed = tformer(origname)
        if transformed is None or transformed == origname:
            continue
        if transformed in disk_setup:
            LOG.info("Replacing %s in disk_setup for translation of %s",
                     origname, transformed)
            del disk_setup[transformed]

        disk_setup[transformed] = disk_setup[origname]
        disk_setup[transformed]['_origname'] = origname
        del disk_setup[origname]
        LOG.debug("updated disk_setup device entry '%s' to '%s'",
                  origname, transformed)


def update_fs_setup_devices(disk_setup, tformer):
    # update 'fs_setup' dictionary anywhere were a device may occur
    # update it with the response from 'tformer'
    for definition in disk_setup:
        if not isinstance(definition, dict):
            LOG.warn("entry in disk_setup not a dict: %s", definition)
            continue

        origname = definition.get('device')

        if origname is None:
            continue

        transformed = None
        if len(origname.split('.')) > 1:
            # this maps ephemeralX.Y to a proper disk name. For example,
            # if the origname is 'ephemeral0.1' and transformed is /dev/sdb
            # then the returned device will be /dev/sdb1 _if_ /dev/sdb1 exists
            # otherwise NONE
            base_name = origname.split('.')[0]
            tformed = tformer(base_name)
            LOG.info("base device for %s is %s" % (origname, tformed))

            transformed = util.map_device_alias(tformed, alias=origname)
            LOG.info("%s is mapped to %s" % (origname, transformed))

        else:
            transformed = tformer(origname)

        if transformed is None or transformed == origname:
            continue

        LOG.info("Mapped %s to physical device %s" % (origname, transformed))
        definition['_origname'] = origname
        definition['device'] = transformed


def value_splitter(values, start=None):
    """
    Returns the key/value pairs of output sent as string
    like:  FOO='BAR' HOME='127.0.0.1'
    """
    _values = shlex.split(values)
    if start:
        _values = _values[start:]

    for key, value in [x.split('=') for x in _values]:
        yield key, value


def enumerate_disk(device, nodeps=False):
    """
    Enumerate the elements of a child device.

    Parameters:
        device: the kernel device name
        nodeps <BOOL>: don't enumerate children devices

    Return a dict describing the disk:
        type: the entry type, i.e disk or part
        fstype: the filesystem type, if it exists
        label: file system label, if it exists
        name: the device name, i.e. sda
    """

    lsblk_cmd = [LSBLK_CMD, '--pairs', '--out', 'NAME,TYPE,FSTYPE,LABEL',
                 device]

    if nodeps:
        lsblk_cmd.append('--nodeps')

    info = None
    try:
        info, _err = util.subp(lsblk_cmd)
    except Exception as e:
        raise Exception("Failed during disk check for %s\n%s" % (device, e))

    parts = [x for x in (info.strip()).splitlines() if len(x.split()) > 0]

    for part in parts:
        d = {'name': None,
             'type': None,
             'fstype': None,
             'label': None,
            }

        for key, value in value_splitter(part):
            d[key.lower()] = value

        yield d


def device_type(device):
    """
    Return the device type of the device by calling lsblk.
    """

    for d in enumerate_disk(device, nodeps=True):
        if "type" in d:
            return d["type"].lower()
    return None


def is_device_valid(name, partition=False):
    """
    Check if the device is a valid device.
    """
    d_type = ""
    try:
        d_type = device_type(name)
    except:
        LOG.warn("Query against device %s failed" % name)
        return False

    if partition and d_type == 'part':
        return True
    elif not partition and d_type == 'disk':
        return True
    return False


def check_fs(device):
    """
    Check if the device has a filesystem on it

    Output of blkid is generally something like:
    /dev/sda: LABEL="Backup500G" UUID="..." TYPE="ext4"

    Return values are device, label, type, uuid
    """
    out, label, fs_type, uuid = None, None, None, None

    blkid_cmd = [BLKID_CMD, '-c', '/dev/null', device]
    try:
        out, _err = util.subp(blkid_cmd, rcs=[0, 2])
    except Exception as e:
        raise Exception("Failed during disk check for %s\n%s" % (device, e))

    if out:
        if len(out.splitlines()) == 1:
            for key, value in value_splitter(out, start=1):
                if key.lower() == 'label':
                    label = value
                elif key.lower() == 'type':
                    fs_type = value
                elif key.lower() == 'uuid':
                    uuid = value

    return label, fs_type, uuid


def is_filesystem(device):
    """
    Returns true if the device has a file system.
    """
    _, fs_type, _ = check_fs(device)
    return fs_type


def find_device_node(device, fs_type=None, label=None, valid_targets=None,
                     label_match=True, replace_fs=None):
    """
    Find a device that is either matches the spec, or the first

    The return is value is (<device>, <bool>) where the device is the
    device to use and the bool is whether the device matches the
    fs_type and label.

    Note: This works with GPT partition tables!
    """
    # label of None is same as no label
    if label is None:
        label = ""

    if not valid_targets:
        valid_targets = ['disk', 'part']

    raw_device_used = False
    for d in enumerate_disk(device):

        if d['fstype'] == replace_fs and label_match is False:
            # We found a device where we want to replace the FS
            return ('/dev/%s' % d['name'], False)

        if (d['fstype'] == fs_type and
            ((label_match and d['label'] == label) or not label_match)):
            # If we find a matching device, we return that
            return ('/dev/%s' % d['name'], True)

        if d['type'] in valid_targets:

            if d['type'] != 'disk' or d['fstype']:
                raw_device_used = True

            if d['type'] == 'disk':
                # Skip the raw disk, its the default
                pass

            elif not d['fstype']:
                return ('/dev/%s' % d['name'], False)

    if not raw_device_used:
        return (device, False)

    LOG.warn("Failed to find device during available device search.")
    return (None, False)


def is_disk_used(device):
    """
    Check if the device is currently used. Returns true if the device
    has either a file system or a partition entry
    is no filesystem found on the disk.
    """

    # If the child count is higher 1, then there are child nodes
    # such as partition or device mapper nodes
    use_count = [x for x in enumerate_disk(device)]
    if len(use_count.splitlines()) > 1:
        return True

    # If we see a file system, then its used
    _, check_fstype, _ = check_fs(device)
    if check_fstype:
        return True

    return False


def get_hdd_size(device):
    """
    Returns the hard disk size.
    This works with any disk type, including GPT.
    """

    size_cmd = [SFDISK_CMD, '--show-size', device]
    size = None
    try:
        size, _err = util.subp(size_cmd)
    except Exception as e:
        raise Exception("Failed to get %s size\n%s" % (device, e))

    return int(size.strip())


def get_dyn_func(*args):
    """
    Call the appropriate function.

    The first value is the template for function name
    The second value is the template replacement
    The remain values are passed to the function

    For example: get_dyn_func("foo_%s", 'bar', 1, 2, 3,)
        would call "foo_bar" with args of 1, 2, 3
    """
    if len(args) < 2:
        raise Exception("Unable to determine dynamic funcation name")

    func_name = (args[0] % args[1])
    func_args = args[2:]

    try:
        if func_args:
            return globals()[func_name](*func_args)
        else:
            return globals()[func_name]

    except KeyError:
        raise Exception("No such function %s to call!" % func_name)


def check_partition_mbr_layout(device, layout):
    """
    Returns true if the partition layout matches the one on the disk

    Layout should be a list of values. At this time, this only
    verifies that the number of partitions and their labels is correct.
    """

    read_parttbl(device)
    prt_cmd = [SFDISK_CMD, "-l", device]
    try:
        out, _err = util.subp(prt_cmd, data="%s\n" % layout)
    except Exception as e:
        raise Exception("Error running partition command on %s\n%s" % (
                        device, e))

    found_layout = []
    for line in out.splitlines():
        _line = line.split()
        if len(_line) == 0:
            continue

        if device in _line[0]:
            # We don't understand extended partitions yet
            if _line[-1].lower() in ['extended', 'empty']:
                continue

            # Find the partition types
            type_label = None
            for x in sorted(range(1, len(_line)), reverse=True):
                if _line[x].isdigit() and _line[x] != '/':
                    type_label = _line[x]
                    break

            found_layout.append(type_label)

    if isinstance(layout, bool):
        # if we are using auto partitioning, or "True" be happy
        # if a single partition exists.
        if layout and len(found_layout) >= 1:
            return True
        return False

    else:
        if len(found_layout) != len(layout):
            return False
        else:
            # This just makes sure that the number of requested
            # partitions and the type labels are right
            for x in range(1, len(layout) + 1):
                if isinstance(layout[x - 1], tuple):
                    _, part_type = layout[x]
                    if int(found_layout[x]) != int(part_type):
                        return False
            return True

    return False


def check_partition_layout(table_type, device, layout):
    """
    See if the partition lay out matches.

    This is future a future proofing function. In order
    to add support for other disk layout schemes, add a
    function called check_partition_%s_layout
    """
    return get_dyn_func("check_partition_%s_layout", table_type, device,
                        layout)


def get_partition_mbr_layout(size, layout):
    """
    Calculate the layout of the partition table. Partition sizes
    are defined as percentage values or a tuple of percentage and
    partition type.

    For example:
        [ 33, [66: 82] ]

    Defines the first partition to be a size of 1/3 the disk,
    while the remaining 2/3's will be of type Linux Swap.
    """

    if not isinstance(layout, list) and isinstance(layout, bool):
        # Create a single partition
        return "0,"

    if ((len(layout) == 0 and isinstance(layout, list)) or
        not isinstance(layout, list)):
        raise Exception("Partition layout is invalid")

    last_part_num = len(layout)
    if last_part_num > 4:
        raise Exception("Only simply partitioning is allowed.")

    part_definition = []
    part_num = 0
    for part in layout:
        part_type = 83  # Default to Linux
        percent = part
        part_num += 1

        if isinstance(part, list):
            if len(part) != 2:
                raise Exception("Partition was incorrectly defined: %s" % part)
            percent, part_type = part

        part_size = int((float(size) * (float(percent) / 100)) / 1024)

        if part_num == last_part_num:
            part_definition.append(",,%s" % part_type)
        else:
            part_definition.append(",%s,%s" % (part_size, part_type))

    sfdisk_definition = "\n".join(part_definition)
    if len(part_definition) > 4:
        raise Exception("Calculated partition definition is too big\n%s" %
                        sfdisk_definition)

    return sfdisk_definition


def purge_disk_ptable(device):
    # wipe the first and last megabyte of a disk (or file)
    # gpt stores partition table both at front and at end.
    start_len = 1024 * 1024
    end_len = 1024 * 1024
    with open(device, "rb+") as fp:
        fp.write('\0' * (start_len))
        fp.seek(-end_len, os.SEEK_END)
        fp.write('\0' * end_len)
        fp.flush()

    read_parttbl(device)


def purge_disk(device):
    """
    Remove parition table entries
    """

    # wipe any file systems first
    for d in enumerate_disk(device):
        if d['type'] not in ["disk", "crypt"]:
            wipefs_cmd = [WIPEFS_CMD, "--all", "/dev/%s" % d['name']]
            try:
                LOG.info("Purging filesystem on /dev/%s" % d['name'])
                util.subp(wipefs_cmd)
            except Exception:
                raise Exception("Failed FS purge of /dev/%s" % d['name'])

    purge_disk_ptable(device)


def get_partition_layout(table_type, size, layout):
    """
    Call the appropriate function for creating the table
    definition. Returns the table definition

    This is a future proofing function. To add support for
    other layouts, simply add a "get_partition_%s_layout"
    function.
    """
    return get_dyn_func("get_partition_%s_layout", table_type, size, layout)


def read_parttbl(device):
    """
    Use partprobe instead of 'udevadm'. Partprobe is the only
    reliable way to probe the partition table.
    """
    blkdev_cmd = [BLKDEV_CMD, '--rereadpt', device]
    udev_cmd = [UDEVADM_CMD, 'settle']
    try:
        util.subp(udev_cmd)
        util.subp(blkdev_cmd)
        util.subp(udev_cmd)
    except Exception as e:
        util.logexc(LOG, "Failed reading the partition table %s" % e)


def exec_mkpart_mbr(device, layout):
    """
    Break out of mbr partition to allow for future partition
    types, i.e. gpt
    """
    # Create the partitions
    prt_cmd = [SFDISK_CMD, "--Linux", "-uM", device]
    try:
        util.subp(prt_cmd, data="%s\n" % layout)
    except Exception as e:
        raise Exception("Failed to partition device %s\n%s" % (device, e))

    read_parttbl(device)


def exec_mkpart(table_type, device, layout):
    """
    Fetches the function for creating the table type.
    This allows to dynamically find which function to call.

    Paramaters:
        table_type: type of partition table to use
        device: the device to work on
        layout: layout definition specific to partition table
    """
    return get_dyn_func("exec_mkpart_%s", table_type, device, layout)


def mkpart(device, definition):
    """
    Creates the partition table.

    Parameters:
        definition: dictionary describing how to create the partition.

            The following are supported values in the dict:
                overwrite: Should the partition table be created regardless
                            of any pre-exisiting data?
                layout: the layout of the partition table
                table_type: Which partition table to use, defaults to MBR
                device: the device to work on.
    """

    LOG.debug("Checking values for %s definition" % device)
    overwrite = definition.get('overwrite', False)
    layout = definition.get('layout', False)
    table_type = definition.get('table_type', 'mbr')

    # Check if the default device is a partition or not
    LOG.debug("Checking against default devices")

    if (isinstance(layout, bool) and not layout) or not layout:
        LOG.debug("Device is not to be partitioned, skipping")
        return  # Device is not to be partitioned

    # This prevents you from overwriting the device
    LOG.debug("Checking if device %s is a valid device", device)
    if not is_device_valid(device):
        raise Exception("Device %s is not a disk device!", device)

    # Remove the partition table entries
    if isinstance(layout, str) and layout.lower() == "remove":
        LOG.debug("Instructed to remove partition table entries")
        purge_disk(device)
        return

    LOG.debug("Checking if device layout matches")
    if check_partition_layout(table_type, device, layout):
        LOG.debug("Device partitioning layout matches")
        return True

    LOG.debug("Checking if device is safe to partition")
    if not overwrite and (is_disk_used(device) or is_filesystem(device)):
        LOG.debug("Skipping partitioning on configured device %s" % device)
        return

    LOG.debug("Checking for device size")
    device_size = get_hdd_size(device)

    LOG.debug("Calculating partition layout")
    part_definition = get_partition_layout(table_type, device_size, layout)
    LOG.debug("   Layout is: %s" % part_definition)

    LOG.debug("Creating partition table on %s", device)
    exec_mkpart(table_type, device, part_definition)

    LOG.debug("Partition table created for %s", device)


def lookup_force_flag(fs):
    """
    A force flag might be -F or -F, this look it up
    """
    flags = {'ext': '-F',
             'btrfs': '-f',
             'xfs': '-f',
             'reiserfs': '-f',
            }

    if 'ext' in fs.lower():
        fs = 'ext'

    if fs.lower() in flags:
        return flags[fs]

    LOG.warn("Force flag for %s is unknown." % fs)
    return ''


def mkfs(fs_cfg):
    """
    Create a file system on the device.

        label: defines the label to use on the device
        fs_cfg: defines how the filesystem is to look
            The following values are required generally:
                device: which device or cloud defined default_device
                filesystem: which file system type
                overwrite: indiscriminately create the file system
                partition: when device does not define a partition,
                            setting this to a number will mean
                            device + partition. When set to 'auto', the
                            first free device or the first device which
                            matches both label and type will be used.

                            'any' means the first filesystem that matches
                            on the device.

            When 'cmd' is provided then no other parameter is required.
    """
    label = fs_cfg.get('label')
    device = fs_cfg.get('device')
    partition = str(fs_cfg.get('partition', 'any'))
    fs_type = fs_cfg.get('filesystem')
    fs_cmd = fs_cfg.get('cmd', [])
    fs_opts = fs_cfg.get('extra_opts', [])
    fs_replace = fs_cfg.get('replace_fs', False)
    overwrite = fs_cfg.get('overwrite', False)

    # This allows you to define the default ephemeral or swap
    LOG.debug("Checking %s against default devices", device)

    if not partition or partition.isdigit():
        # Handle manual definition of partition
        if partition.isdigit():
            device = "%s%s" % (device, partition)
            LOG.debug("Manual request of partition %s for %s",
                      partition, device)

        # Check to see if the fs already exists
        LOG.debug("Checking device %s", device)
        check_label, check_fstype, _ = check_fs(device)
        LOG.debug("Device %s has %s %s", device, check_label, check_fstype)

        if check_label == label and check_fstype == fs_type:
            LOG.debug("Existing file system found at %s", device)

            if not overwrite:
                LOG.debug("Device %s has required file system", device)
                return
            else:
                LOG.warn("Destroying filesystem on %s", device)

        else:
            LOG.debug("Device %s is cleared for formating", device)

    elif partition and str(partition).lower() in ('auto', 'any'):
        # For auto devices, we match if the filesystem does exist
        odevice = device
        LOG.debug("Identifying device to create %s filesytem on", label)

        # any mean pick the first match on the device with matching fs_type
        label_match = True
        if partition.lower() == 'any':
            label_match = False

        device, reuse = find_device_node(device, fs_type=fs_type, label=label,
                                         label_match=label_match,
                                         replace_fs=fs_replace)
        LOG.debug("Automatic device for %s identified as %s", odevice, device)

        if reuse:
            LOG.debug("Found filesystem match, skipping formating.")
            return

        if not reuse and fs_replace and device:
            LOG.debug("Replacing file system on %s as instructed." % device)

        if not device:
            LOG.debug("No device aviable that matches request. "
                      "Skipping fs creation for %s", fs_cfg)
            return
    elif not partition or str(partition).lower() == 'none':
        LOG.debug("Using the raw device to place filesystem %s on" % label)

    else:
        LOG.debug("Error in device identification handling.")
        return

    LOG.debug("File system %s will be created on %s", label, device)

    # Make sure the device is defined
    if not device:
        LOG.warn("Device is not known: %s", device)
        return

    # Check that we can create the FS
    if not (fs_type or fs_cmd):
        raise Exception("No way to create filesystem '%s'. fs_type or fs_cmd "
                        "must be set.", label)

    # Create the commands
    if fs_cmd:
        fs_cmd = fs_cfg['cmd'] % {'label': label,
                                  'filesystem': fs_type,
                                  'device': device,
                                 }
    else:
        # Find the mkfs command
        mkfs_cmd = util.which("mkfs.%s" % fs_type)
        if not mkfs_cmd:
            mkfs_cmd = util.which("mk%s" % fs_type)

        if not mkfs_cmd:
            LOG.warn("Cannot create fstype '%s'.  No mkfs.%s command", fs_type,
                     fs_type)
            return

        fs_cmd = [mkfs_cmd, device]

        if label:
            fs_cmd.extend(["-L", label])

    # File systems that support the -F flag
    if not fs_cmd and (overwrite or device_type(device) == "disk"):
        fs_cmd.append(lookup_force_flag(fs_type))

    # Add the extends FS options
    if fs_opts:
        fs_cmd.extend(fs_opts)

    LOG.debug("Creating file system %s on %s", label, device)
    LOG.debug("     Using cmd: %s", " ".join(fs_cmd))
    try:
        util.subp(fs_cmd)
    except Exception as e:
        raise Exception("Failed to exec of '%s':\n%s" % (fs_cmd, e))