summaryrefslogtreecommitdiffstats
path: root/tools/net/ynl/lib/ynl.py
blob: 13c4b019a881f3b822a8161103f2b192abc8f909 (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
# SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause

from collections import namedtuple
import functools
import os
import random
import socket
import struct
from struct import Struct
import yaml
import ipaddress
import uuid

from .nlspec import SpecFamily

#
# Generic Netlink code which should really be in some library, but I can't quickly find one.
#


class Netlink:
    # Netlink socket
    SOL_NETLINK = 270

    NETLINK_ADD_MEMBERSHIP = 1
    NETLINK_CAP_ACK = 10
    NETLINK_EXT_ACK = 11
    NETLINK_GET_STRICT_CHK = 12

    # Netlink message
    NLMSG_ERROR = 2
    NLMSG_DONE = 3

    NLM_F_REQUEST = 1
    NLM_F_ACK = 4
    NLM_F_ROOT = 0x100
    NLM_F_MATCH = 0x200

    NLM_F_REPLACE = 0x100
    NLM_F_EXCL = 0x200
    NLM_F_CREATE = 0x400
    NLM_F_APPEND = 0x800

    NLM_F_CAPPED = 0x100
    NLM_F_ACK_TLVS = 0x200

    NLM_F_DUMP = NLM_F_ROOT | NLM_F_MATCH

    NLA_F_NESTED = 0x8000
    NLA_F_NET_BYTEORDER = 0x4000

    NLA_TYPE_MASK = NLA_F_NESTED | NLA_F_NET_BYTEORDER

    # Genetlink defines
    NETLINK_GENERIC = 16

    GENL_ID_CTRL = 0x10

    # nlctrl
    CTRL_CMD_GETFAMILY = 3

    CTRL_ATTR_FAMILY_ID = 1
    CTRL_ATTR_FAMILY_NAME = 2
    CTRL_ATTR_MAXATTR = 5
    CTRL_ATTR_MCAST_GROUPS = 7

    CTRL_ATTR_MCAST_GRP_NAME = 1
    CTRL_ATTR_MCAST_GRP_ID = 2

    # Extack types
    NLMSGERR_ATTR_MSG = 1
    NLMSGERR_ATTR_OFFS = 2
    NLMSGERR_ATTR_COOKIE = 3
    NLMSGERR_ATTR_POLICY = 4
    NLMSGERR_ATTR_MISS_TYPE = 5
    NLMSGERR_ATTR_MISS_NEST = 6


class NlError(Exception):
  def __init__(self, nl_msg):
    self.nl_msg = nl_msg

  def __str__(self):
    return f"Netlink error: {os.strerror(-self.nl_msg.error)}\n{self.nl_msg}"


class NlAttr:
    ScalarFormat = namedtuple('ScalarFormat', ['native', 'big', 'little'])
    type_formats = {
        'u8' : ScalarFormat(Struct('B'), Struct("B"),  Struct("B")),
        's8' : ScalarFormat(Struct('b'), Struct("b"),  Struct("b")),
        'u16': ScalarFormat(Struct('H'), Struct(">H"), Struct("<H")),
        's16': ScalarFormat(Struct('h'), Struct(">h"), Struct("<h")),
        'u32': ScalarFormat(Struct('I'), Struct(">I"), Struct("<I")),
        's32': ScalarFormat(Struct('i'), Struct(">i"), Struct("<i")),
        'u64': ScalarFormat(Struct('Q'), Struct(">Q"), Struct("<Q")),
        's64': ScalarFormat(Struct('q'), Struct(">q"), Struct("<q"))
    }

    def __init__(self, raw, offset):
        self._len, self._type = struct.unpack("HH", raw[offset:offset + 4])
        self.type = self._type & ~Netlink.NLA_TYPE_MASK
        self.payload_len = self._len
        self.full_len = (self.payload_len + 3) & ~3
        self.raw = raw[offset + 4:offset + self.payload_len]

    @classmethod
    def get_format(cls, attr_type, byte_order=None):
        format = cls.type_formats[attr_type]
        if byte_order:
            return format.big if byte_order == "big-endian" \
                else format.little
        return format.native

    @classmethod
    def formatted_string(cls, raw, display_hint):
        if display_hint == 'mac':
            formatted = ':'.join('%02x' % b for b in raw)
        elif display_hint == 'hex':
            formatted = bytes.hex(raw, ' ')
        elif display_hint in [ 'ipv4', 'ipv6' ]:
            formatted = format(ipaddress.ip_address(raw))
        elif display_hint == 'uuid':
            formatted = str(uuid.UUID(bytes=raw))
        else:
            formatted = raw
        return formatted

    def as_scalar(self, attr_type, byte_order=None):
        format = self.get_format(attr_type, byte_order)
        return format.unpack(self.raw)[0]

    def as_strz(self):
        return self.raw.decode('ascii')[:-1]

    def as_bin(self):
        return self.raw

    def as_c_array(self, type):
        format = self.get_format(type)
        return [ x[0] for x in format.iter_unpack(self.raw) ]

    def as_struct(self, members):
        value = dict()
        offset = 0
        for m in members:
            # TODO: handle non-scalar members
            if m.type == 'binary':
                decoded = self.raw[offset:offset+m['len']]
                offset += m['len']
            elif m.type in NlAttr.type_formats:
                format = self.get_format(m.type, m.byte_order)
                [ decoded ] = format.unpack_from(self.raw, offset)
                offset += format.size
            if m.display_hint:
                decoded = self.formatted_string(decoded, m.display_hint)
            value[m.name] = decoded
        return value

    def __repr__(self):
        return f"[type:{self.type} len:{self._len}] {self.raw}"


class NlAttrs:
    def __init__(self, msg):
        self.attrs = []

        offset = 0
        while offset < len(msg):
            attr = NlAttr(msg, offset)
            offset += attr.full_len
            self.attrs.append(attr)

    def __iter__(self):
        yield from self.attrs

    def __repr__(self):
        msg = ''
        for a in self.attrs:
            if msg:
                msg += '\n'
            msg += repr(a)
        return msg


class NlMsg:
    def __init__(self, msg, offset, attr_space=None):
        self.hdr = msg[offset:offset + 16]

        self.nl_len, self.nl_type, self.nl_flags, self.nl_seq, self.nl_portid = \
            struct.unpack("IHHII", self.hdr)

        self.raw = msg[offset + 16:offset + self.nl_len]

        self.error = 0
        self.done = 0

        extack_off = None
        if self.nl_type == Netlink.NLMSG_ERROR:
            self.error = struct.unpack("i", self.raw[0:4])[0]
            self.done = 1
            extack_off = 20
        elif self.nl_type == Netlink.NLMSG_DONE:
            self.done = 1
            extack_off = 4

        self.extack = None
        if self.nl_flags & Netlink.NLM_F_ACK_TLVS and extack_off:
            self.extack = dict()
            extack_attrs = NlAttrs(self.raw[extack_off:])
            for extack in extack_attrs:
                if extack.type == Netlink.NLMSGERR_ATTR_MSG:
                    self.extack['msg'] = extack.as_strz()
                elif extack.type == Netlink.NLMSGERR_ATTR_MISS_TYPE:
                    self.extack['miss-type'] = extack.as_scalar('u32')
                elif extack.type == Netlink.NLMSGERR_ATTR_MISS_NEST:
                    self.extack['miss-nest'] = extack.as_scalar('u32')
                elif extack.type == Netlink.NLMSGERR_ATTR_OFFS:
                    self.extack['bad-attr-offs'] = extack.as_scalar('u32')
                else:
                    if 'unknown' not in self.extack:
                        self.extack['unknown'] = []
                    self.extack['unknown'].append(extack)

            if attr_space:
                # We don't have the ability to parse nests yet, so only do global
                if 'miss-type' in self.extack and 'miss-nest' not in self.extack:
                    miss_type = self.extack['miss-type']
                    if miss_type in attr_space.attrs_by_val:
                        spec = attr_space.attrs_by_val[miss_type]
                        desc = spec['name']
                        if 'doc' in spec:
                            desc += f" ({spec['doc']})"
                        self.extack['miss-type'] = desc

    def cmd(self):
        return self.nl_type

    def __repr__(self):
        msg = f"nl_len = {self.nl_len} ({len(self.raw)}) nl_flags = 0x{self.nl_flags:x} nl_type = {self.nl_type}\n"
        if self.error:
            msg += '\terror: ' + str(self.error)
        if self.extack:
            msg += '\textack: ' + repr(self.extack)
        return msg


class NlMsgs:
    def __init__(self, data, attr_space=None):
        self.msgs = []

        offset = 0
        while offset < len(data):
            msg = NlMsg(data, offset, attr_space=attr_space)
            offset += msg.nl_len
            self.msgs.append(msg)

    def __iter__(self):
        yield from self.msgs


genl_family_name_to_id = None


def _genl_msg(nl_type, nl_flags, genl_cmd, genl_version, seq=None):
    # we prepend length in _genl_msg_finalize()
    if seq is None:
        seq = random.randint(1, 1024)
    nlmsg = struct.pack("HHII", nl_type, nl_flags, seq, 0)
    genlmsg = struct.pack("BBH", genl_cmd, genl_version, 0)
    return nlmsg + genlmsg


def _genl_msg_finalize(msg):
    return struct.pack("I", len(msg) + 4) + msg


def _genl_load_families():
    with socket.socket(socket.AF_NETLINK, socket.SOCK_RAW, Netlink.NETLINK_GENERIC) as sock:
        sock.setsockopt(Netlink.SOL_NETLINK, Netlink.NETLINK_CAP_ACK, 1)

        msg = _genl_msg(Netlink.GENL_ID_CTRL,
                        Netlink.NLM_F_REQUEST | Netlink.NLM_F_ACK | Netlink.NLM_F_DUMP,
                        Netlink.CTRL_CMD_GETFAMILY, 1)
        msg = _genl_msg_finalize(msg)

        sock.send(msg, 0)

        global genl_family_name_to_id
        genl_family_name_to_id = dict()

        while True:
            reply = sock.recv(128 * 1024)
            nms = NlMsgs(reply)
            for nl_msg in nms:
                if nl_msg.error:
                    print("Netlink error:", nl_msg.error)
                    return
                if nl_msg.done:
                    return

                gm = GenlMsg(nl_msg)
                fam = dict()
                for attr in NlAttrs(gm.raw):
                    if attr.type == Netlink.CTRL_ATTR_FAMILY_ID:
                        fam['id'] = attr.as_scalar('u16')
                    elif attr.type == Netlink.CTRL_ATTR_FAMILY_NAME:
                        fam['name'] = attr.as_strz()
                    elif attr.type == Netlink.CTRL_ATTR_MAXATTR:
                        fam['maxattr'] = attr.as_scalar('u32')
                    elif attr.type == Netlink.CTRL_ATTR_MCAST_GROUPS:
                        fam['mcast'] = dict()
                        for entry in NlAttrs(attr.raw):
                            mcast_name = None
                            mcast_id = None
                            for entry_attr in NlAttrs(entry.raw):
                                if entry_attr.type == Netlink.CTRL_ATTR_MCAST_GRP_NAME:
                                    mcast_name = entry_attr.as_strz()
                                elif entry_attr.type == Netlink.CTRL_ATTR_MCAST_GRP_ID:
                                    mcast_id = entry_attr.as_scalar('u32')
                            if mcast_name and mcast_id is not None:
                                fam['mcast'][mcast_name] = mcast_id
                if 'name' in fam and 'id' in fam:
                    genl_family_name_to_id[fam['name']] = fam


class GenlMsg:
    def __init__(self, nl_msg):
        self.nl = nl_msg
        self.genl_cmd, self.genl_version, _ = struct.unpack_from("BBH", nl_msg.raw, 0)
        self.raw = nl_msg.raw[4:]

    def cmd(self):
        return self.genl_cmd

    def __repr__(self):
        msg = repr(self.nl)
        msg += f"\tgenl_cmd = {self.genl_cmd} genl_ver = {self.genl_version}\n"
        for a in self.raw_attrs:
            msg += '\t\t' + repr(a) + '\n'
        return msg


class NetlinkProtocol:
    def __init__(self, family_name, proto_num):
        self.family_name = family_name
        self.proto_num = proto_num

    def _message(self, nl_type, nl_flags, seq=None):
        if seq is None:
            seq = random.randint(1, 1024)
        nlmsg = struct.pack("HHII", nl_type, nl_flags, seq, 0)
        return nlmsg

    def message(self, flags, command, version, seq=None):
        return self._message(command, flags, seq)

    def _decode(self, nl_msg):
        return nl_msg

    def decode(self, ynl, nl_msg):
        msg = self._decode(nl_msg)
        fixed_header_size = 0
        if ynl:
            op = ynl.rsp_by_value[msg.cmd()]
            fixed_header_size = ynl._fixed_header_size(op)
        msg.raw_attrs = NlAttrs(msg.raw[fixed_header_size:])
        return msg

    def get_mcast_id(self, mcast_name, mcast_groups):
        if mcast_name not in mcast_groups:
            raise Exception(f'Multicast group "{mcast_name}" not present in the spec')
        return mcast_groups[mcast_name].value


class GenlProtocol(NetlinkProtocol):
    def __init__(self, family_name):
        super().__init__(family_name, Netlink.NETLINK_GENERIC)

        global genl_family_name_to_id
        if genl_family_name_to_id is None:
            _genl_load_families()

        self.genl_family = genl_family_name_to_id[family_name]
        self.family_id = genl_family_name_to_id[family_name]['id']

    def message(self, flags, command, version, seq=None):
        nlmsg = self._message(self.family_id, flags, seq)
        genlmsg = struct.pack("BBH", command, version, 0)
        return nlmsg + genlmsg

    def _decode(self, nl_msg):
        return GenlMsg(nl_msg)

    def get_mcast_id(self, mcast_name, mcast_groups):
        if mcast_name not in self.genl_family['mcast']:
            raise Exception(f'Multicast group "{mcast_name}" not present in the family')
        return self.genl_family['mcast'][mcast_name]


#
# YNL implementation details.
#


class YnlFamily(SpecFamily):
    def __init__(self, def_path, schema=None):
        super().__init__(def_path, schema)

        self.include_raw = False

        try:
            if self.proto == "netlink-raw":
                self.nlproto = NetlinkProtocol(self.yaml['name'],
                                               self.yaml['protonum'])
            else:
                self.nlproto = GenlProtocol(self.yaml['name'])
        except KeyError:
            raise Exception(f"Family '{self.yaml['name']}' not supported by the kernel")

        self.sock = socket.socket(socket.AF_NETLINK, socket.SOCK_RAW, self.nlproto.proto_num)
        self.sock.setsockopt(Netlink.SOL_NETLINK, Netlink.NETLINK_CAP_ACK, 1)
        self.sock.setsockopt(Netlink.SOL_NETLINK, Netlink.NETLINK_EXT_ACK, 1)
        self.sock.setsockopt(Netlink.SOL_NETLINK, Netlink.NETLINK_GET_STRICT_CHK, 1)

        self.async_msg_ids = set()
        self.async_msg_queue = []

        for msg in self.msgs.values():
            if msg.is_async:
                self.async_msg_ids.add(msg.rsp_value)

        for op_name, op in self.ops.items():
            bound_f = functools.partial(self._op, op_name)
            setattr(self, op.ident_name, bound_f)


    def ntf_subscribe(self, mcast_name):
        mcast_id = self.nlproto.get_mcast_id(mcast_name, self.mcast_groups)
        self.sock.bind((0, 0))
        self.sock.setsockopt(Netlink.SOL_NETLINK, Netlink.NETLINK_ADD_MEMBERSHIP,
                             mcast_id)

    def _add_attr(self, space, name, value):
        try:
            attr = self.attr_sets[space][name]
        except KeyError:
            raise Exception(f"Space '{space}' has no attribute '{name}'")
        nl_type = attr.value
        if attr["type"] == 'nest':
            nl_type |= Netlink.NLA_F_NESTED
            attr_payload = b''
            for subname, subvalue in value.items():
                attr_payload += self._add_attr(attr['nested-attributes'], subname, subvalue)
        elif attr["type"] == 'flag':
            attr_payload = b''
        elif attr["type"] == 'string':
            attr_payload = str(value).encode('ascii') + b'\x00'
        elif attr["type"] == 'binary':
            if isinstance(value, bytes):
                attr_payload = value
            elif isinstance(value, str):
                attr_payload = bytes.fromhex(value)
            else:
                raise Exception(f'Unknown type for binary attribute, value: {value}')
        elif attr['type'] in NlAttr.type_formats:
            format = NlAttr.get_format(attr['type'], attr.byte_order)
            attr_payload = format.pack(int(value))
        else:
            raise Exception(f'Unknown type at {space} {name} {value} {attr["type"]}')

        pad = b'\x00' * ((4 - len(attr_payload) % 4) % 4)
        return struct.pack('HH', len(attr_payload) + 4, nl_type) + attr_payload + pad

    def _decode_enum(self, raw, attr_spec):
        enum = self.consts[attr_spec['enum']]
        if 'enum-as-flags' in attr_spec and attr_spec['enum-as-flags']:
            i = 0
            value = set()
            while raw:
                if raw & 1:
                    value.add(enum.entries_by_val[i].name)
                raw >>= 1
                i += 1
        else:
            value = enum.entries_by_val[raw].name
        return value

    def _decode_binary(self, attr, attr_spec):
        if attr_spec.struct_name:
            members = self.consts[attr_spec.struct_name]
            decoded = attr.as_struct(members)
            for m in members:
                if m.enum:
                    decoded[m.name] = self._decode_enum(decoded[m.name], m)
        elif attr_spec.sub_type:
            decoded = attr.as_c_array(attr_spec.sub_type)
        else:
            decoded = attr.as_bin()
            if attr_spec.display_hint:
                decoded = NlAttr.formatted_string(decoded, attr_spec.display_hint)
        return decoded

    def _decode_array_nest(self, attr, attr_spec):
        decoded = []
        offset = 0
        while offset < len(attr.raw):
            item = NlAttr(attr.raw, offset)
            offset += item.full_len

            subattrs = self._decode(NlAttrs(item.raw), attr_spec['nested-attributes'])
            decoded.append({ item.type: subattrs })
        return decoded

    def _decode(self, attrs, space):
        attr_space = self.attr_sets[space]
        rsp = dict()
        for attr in attrs:
            try:
                attr_spec = attr_space.attrs_by_val[attr.type]
            except KeyError:
                raise Exception(f"Space '{space}' has no attribute with value '{attr.type}'")
            if attr_spec["type"] == 'nest':
                subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'])
                decoded = subdict
            elif attr_spec["type"] == 'string':
                decoded = attr.as_strz()
            elif attr_spec["type"] == 'binary':
                decoded = self._decode_binary(attr, attr_spec)
            elif attr_spec["type"] == 'flag':
                decoded = True
            elif attr_spec["type"] in NlAttr.type_formats:
                decoded = attr.as_scalar(attr_spec['type'], attr_spec.byte_order)
            elif attr_spec["type"] == 'array-nest':
                decoded = self._decode_array_nest(attr, attr_spec)
            else:
                raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')

            if 'enum' in attr_spec:
                decoded = self._decode_enum(decoded, attr_spec)

            if not attr_spec.is_multi:
                rsp[attr_spec['name']] = decoded
            elif attr_spec.name in rsp:
                rsp[attr_spec.name].append(decoded)
            else:
                rsp[attr_spec.name] = [decoded]

        return rsp

    def _decode_extack_path(self, attrs, attr_set, offset, target):
        for attr in attrs:
            try:
                attr_spec = attr_set.attrs_by_val[attr.type]
            except KeyError:
                raise Exception(f"Space '{attr_set.name}' has no attribute with value '{attr.type}'")
            if offset > target:
                break
            if offset == target:
                return '.' + attr_spec.name

            if offset + attr.full_len <= target:
                offset += attr.full_len
                continue
            if attr_spec['type'] != 'nest':
                raise Exception(f"Can't dive into {attr.type} ({attr_spec['name']}) for extack")
            offset += 4
            subpath = self._decode_extack_path(NlAttrs(attr.raw),
                                               self.attr_sets[attr_spec['nested-attributes']],
                                               offset, target)
            if subpath is None:
                return None
            return '.' + attr_spec.name + subpath

        return None

    def _decode_extack(self, request, op, extack):
        if 'bad-attr-offs' not in extack:
            return

        msg = self.nlproto.decode(self, NlMsg(request, 0, op.attr_set))
        offset = 20 + self._fixed_header_size(op)
        path = self._decode_extack_path(msg.raw_attrs, op.attr_set, offset,
                                        extack['bad-attr-offs'])
        if path:
            del extack['bad-attr-offs']
            extack['bad-attr'] = path

    def _fixed_header_size(self, op):
        if op.fixed_header:
            fixed_header_members = self.consts[op.fixed_header].members
            size = 0
            for m in fixed_header_members:
                format = NlAttr.get_format(m.type, m.byte_order)
                size += format.size
            return size
        else:
            return 0

    def _decode_fixed_header(self, msg, name):
        fixed_header_members = self.consts[name].members
        fixed_header_attrs = dict()
        offset = 0
        for m in fixed_header_members:
            format = NlAttr.get_format(m.type, m.byte_order)
            [ value ] = format.unpack_from(msg.raw, offset)
            offset += format.size
            if m.enum:
                value = self._decode_enum(value, m)
            fixed_header_attrs[m.name] = value
        return fixed_header_attrs

    def handle_ntf(self, decoded):
        msg = dict()
        if self.include_raw:
            msg['raw'] = decoded
        op = self.rsp_by_value[decoded.cmd()]
        attrs = self._decode(decoded.raw_attrs, op.attr_set.name)
        if op.fixed_header:
            attrs.update(self._decode_fixed_header(decoded, op.fixed_header))

        msg['name'] = op['name']
        msg['msg'] = attrs
        self.async_msg_queue.append(msg)

    def check_ntf(self):
        while True:
            try:
                reply = self.sock.recv(128 * 1024, socket.MSG_DONTWAIT)
            except BlockingIOError:
                return

            nms = NlMsgs(reply)
            for nl_msg in nms:
                if nl_msg.error:
                    print("Netlink error in ntf!?", os.strerror(-nl_msg.error))
                    print(nl_msg)
                    continue
                if nl_msg.done:
                    print("Netlink done while checking for ntf!?")
                    continue

                decoded = self.nlproto.decode(self, nl_msg)
                if decoded.cmd() not in self.async_msg_ids:
                    print("Unexpected msg id done while checking for ntf", decoded)
                    continue

                self.handle_ntf(decoded)

    def operation_do_attributes(self, name):
      """
      For a given operation name, find and return a supported
      set of attributes (as a dict).
      """
      op = self.find_operation(name)
      if not op:
        return None

      return op['do']['request']['attributes'].copy()

    def _op(self, method, vals, flags, dump=False):
        op = self.ops[method]

        nl_flags = Netlink.NLM_F_REQUEST | Netlink.NLM_F_ACK
        for flag in flags or []:
            nl_flags |= flag
        if dump:
            nl_flags |= Netlink.NLM_F_DUMP

        req_seq = random.randint(1024, 65535)
        msg = self.nlproto.message(nl_flags, op.req_value, 1, req_seq)
        fixed_header_members = []
        if op.fixed_header:
            fixed_header_members = self.consts[op.fixed_header].members
            for m in fixed_header_members:
                value = vals.pop(m.name) if m.name in vals else 0
                format = NlAttr.get_format(m.type, m.byte_order)
                msg += format.pack(value)
        for name, value in vals.items():
            msg += self._add_attr(op.attr_set.name, name, value)
        msg = _genl_msg_finalize(msg)

        self.sock.send(msg, 0)

        done = False
        rsp = []
        while not done:
            reply = self.sock.recv(128 * 1024)
            nms = NlMsgs(reply, attr_space=op.attr_set)
            for nl_msg in nms:
                if nl_msg.extack:
                    self._decode_extack(msg, op, nl_msg.extack)

                if nl_msg.error:
                    raise NlError(nl_msg)
                if nl_msg.done:
                    if nl_msg.extack:
                        print("Netlink warning:")
                        print(nl_msg)
                    done = True
                    break

                decoded = self.nlproto.decode(self, nl_msg)

                # Check if this is a reply to our request
                if nl_msg.nl_seq != req_seq or decoded.cmd() != op.rsp_value:
                    if decoded.cmd() in self.async_msg_ids:
                        self.handle_ntf(decoded)
                        continue
                    else:
                        print('Unexpected message: ' + repr(decoded))
                        continue

                rsp_msg = self._decode(decoded.raw_attrs, op.attr_set.name)
                if op.fixed_header:
                    rsp_msg.update(self._decode_fixed_header(decoded, op.fixed_header))
                rsp.append(rsp_msg)

        if not rsp:
            return None
        if not dump and len(rsp) == 1:
            return rsp[0]
        return rsp

    def do(self, method, vals, flags):
        return self._op(method, vals, flags)

    def dump(self, method, vals):
        return self._op(method, vals, [], dump=True)