linux/tools/net/ynl/lib/ynl.py

# 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.is_nest = self._type & Netlink.NLA_F_NESTED
        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

    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_auto_scalar(self, attr_type, byte_order=None):
        if len(self.raw) != 4 and len(self.raw) != 8:
            raise Exception(f"Auto-scalar len payload be 4 or 8 bytes, got {len(self.raw)}")
        real_type = attr_type[0] + str(len(self.raw) * 8)
        format = self.get_format(real_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 __repr__(self):
        return f"[type:{self.type} len:{self._len}] {self.raw}"


class NlAttrs:
    def __init__(self, msg, offset=0):
        self.attrs = []

        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._struct_size(op.fixed_header)
        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]



class SpaceAttrs:
    SpecValuesPair = namedtuple('SpecValuesPair', ['spec', 'values'])

    def __init__(self, attr_space, attrs, outer = None):
        outer_scopes = outer.scopes if outer else []
        inner_scope = self.SpecValuesPair(attr_space, attrs)
        self.scopes = [inner_scope] + outer_scopes

    def lookup(self, name):
        for scope in self.scopes:
            if name in scope.spec:
                if name in scope.values:
                    return scope.values[name]
                spec_name = scope.spec.yaml['name']
                raise Exception(
                    f"No value for '{name}' in attribute space '{spec_name}'")
        raise Exception(f"Attribute '{name}' not defined in any attribute-set")


#
# YNL implementation details.
#


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

        self.include_raw = False
        self.process_unknown = process_unknown

        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 _encode_enum(self, attr_spec, value):
        enum = self.consts[attr_spec['enum']]
        if enum.type == 'flags' or attr_spec.get('enum-as-flags', False):
            scalar = 0
            if isinstance(value, str):
                value = [value]
            for single_value in value:
                scalar += enum.entries[single_value].user_value(as_flags = True)
            return scalar
        else:
            return enum.entries[value].user_value()

    def _get_scalar(self, attr_spec, value):
        try:
            return int(value)
        except (ValueError, TypeError) as e:
            if 'enum' not in attr_spec:
                raise e
        return self._encode_enum(attr_spec, value);

    def _add_attr(self, space, name, value, search_attrs):
        try:
            attr = self.attr_sets[space][name]
        except KeyError:
            raise Exception(f"Space '{space}' has no attribute '{name}'")
        nl_type = attr.value

        if attr.is_multi and isinstance(value, list):
            attr_payload = b''
            for subvalue in value:
                attr_payload += self._add_attr(space, name, subvalue, search_attrs)
            return attr_payload

        if attr["type"] == 'nest':
            nl_type |= Netlink.NLA_F_NESTED
            attr_payload = b''
            sub_attrs = SpaceAttrs(self.attr_sets[space], value, search_attrs)
            for subname, subvalue in value.items():
                attr_payload += self._add_attr(attr['nested-attributes'],
                                               subname, subvalue, sub_attrs)
        elif attr["type"] == 'flag':
            if not value:
                # If value is absent or false then skip attribute creation.
                return b''
            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)
            elif isinstance(value, dict) and attr.struct_name:
                attr_payload = self._encode_struct(attr.struct_name, value)
            else:
                raise Exception(f'Unknown type for binary attribute, value: {value}')
        elif attr['type'] in NlAttr.type_formats or attr.is_auto_scalar:
            scalar = self._get_scalar(attr, value)
            if attr.is_auto_scalar:
                attr_type = attr["type"][0] + ('32' if scalar.bit_length() <= 32 else '64')
            else:
                attr_type = attr["type"]
            format = NlAttr.get_format(attr_type, attr.byte_order)
            attr_payload = format.pack(scalar)
        elif attr['type'] in "bitfield32":
            scalar_value = self._get_scalar(attr, value["value"])
            scalar_selector = self._get_scalar(attr, value["selector"])
            attr_payload = struct.pack("II", scalar_value, scalar_selector)
        elif attr['type'] == 'sub-message':
            msg_format = self._resolve_selector(attr, search_attrs)
            attr_payload = b''
            if msg_format.fixed_header:
                attr_payload += self._encode_struct(msg_format.fixed_header, value)
            if msg_format.attr_set:
                if msg_format.attr_set in self.attr_sets:
                    nl_type |= Netlink.NLA_F_NESTED
                    sub_attrs = SpaceAttrs(msg_format.attr_set, value, search_attrs)
                    for subname, subvalue in value.items():
                        attr_payload += self._add_attr(msg_format.attr_set,
                                                       subname, subvalue, sub_attrs)
                else:
                    raise Exception(f"Unknown attribute-set '{msg_format.attr_set}'")
        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.type == 'flags' or attr_spec.get('enum-as-flags', False):
            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:
            decoded = self._decode_struct(attr.raw, attr_spec.struct_name)
        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 = self._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_unknown(self, attr):
        if attr.is_nest:
            return self._decode(NlAttrs(attr.raw), None)
        else:
            return attr.as_bin()

    def _rsp_add(self, rsp, name, is_multi, decoded):
        if is_multi == None:
            if name in rsp and type(rsp[name]) is not list:
                rsp[name] = [rsp[name]]
                is_multi = True
            else:
                is_multi = False

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

    def _resolve_selector(self, attr_spec, search_attrs):
        sub_msg = attr_spec.sub_message
        if sub_msg not in self.sub_msgs:
            raise Exception(f"No sub-message spec named {sub_msg} for {attr_spec.name}")
        sub_msg_spec = self.sub_msgs[sub_msg]

        selector = attr_spec.selector
        value = search_attrs.lookup(selector)
        if value not in sub_msg_spec.formats:
            raise Exception(f"No message format for '{value}' in sub-message spec '{sub_msg}'")

        spec = sub_msg_spec.formats[value]
        return spec

    def _decode_sub_msg(self, attr, attr_spec, search_attrs):
        msg_format = self._resolve_selector(attr_spec, search_attrs)
        decoded = {}
        offset = 0
        if msg_format.fixed_header:
            decoded.update(self._decode_struct(attr.raw, msg_format.fixed_header));
            offset = self._struct_size(msg_format.fixed_header)
        if msg_format.attr_set:
            if msg_format.attr_set in self.attr_sets:
                subdict = self._decode(NlAttrs(attr.raw, offset), msg_format.attr_set)
                decoded.update(subdict)
            else:
                raise Exception(f"Unknown attribute-set '{attr_space}' when decoding '{attr_spec.name}'")
        return decoded

    def _decode(self, attrs, space, outer_attrs = None):
        rsp = dict()
        if space:
            attr_space = self.attr_sets[space]
            search_attrs = SpaceAttrs(attr_space, rsp, outer_attrs)

        for attr in attrs:
            try:
                attr_spec = attr_space.attrs_by_val[attr.type]
            except (KeyError, UnboundLocalError):
                if not self.process_unknown:
                    raise Exception(f"Space '{space}' has no attribute with value '{attr.type}'")
                attr_name = f"UnknownAttr({attr.type})"
                self._rsp_add(rsp, attr_name, None, self._decode_unknown(attr))
                continue

            if attr_spec["type"] == 'nest':
                subdict = self._decode(NlAttrs(attr.raw), attr_spec['nested-attributes'], search_attrs)
                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.is_auto_scalar:
                decoded = attr.as_auto_scalar(attr_spec['type'], attr_spec.byte_order)
            elif attr_spec["type"] in NlAttr.type_formats:
                decoded = attr.as_scalar(attr_spec['type'], attr_spec.byte_order)
                if 'enum' in attr_spec:
                    decoded = self._decode_enum(decoded, attr_spec)
            elif attr_spec["type"] == 'array-nest':
                decoded = self._decode_array_nest(attr, attr_spec)
            elif attr_spec["type"] == 'bitfield32':
                value, selector = struct.unpack("II", attr.raw)
                if 'enum' in attr_spec:
                    value = self._decode_enum(value, attr_spec)
                    selector = self._decode_enum(selector, attr_spec)
                decoded = {"value": value, "selector": selector}
            elif attr_spec["type"] == 'sub-message':
                decoded = self._decode_sub_msg(attr, attr_spec, search_attrs)
            else:
                if not self.process_unknown:
                    raise Exception(f'Unknown {attr_spec["type"]} with name {attr_spec["name"]}')
                decoded = self._decode_unknown(attr)

            self._rsp_add(rsp, attr_spec["name"], attr_spec.is_multi, 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._struct_size(op.fixed_header)
        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 _struct_size(self, name):
        if name:
            members = self.consts[name].members
            size = 0
            for m in members:
                if m.type in ['pad', 'binary']:
                    if m.struct:
                        size += self._struct_size(m.struct)
                    else:
                        size += m.len
                else:
                    format = NlAttr.get_format(m.type, m.byte_order)
                    size += format.size
            return size
        else:
            return 0

    def _decode_struct(self, data, name):
        members = self.consts[name].members
        attrs = dict()
        offset = 0
        for m in members:
            value = None
            if m.type == 'pad':
                offset += m.len
            elif m.type == 'binary':
                if m.struct:
                    len = self._struct_size(m.struct)
                    value = self._decode_struct(data[offset : offset + len],
                                                m.struct)
                    offset += len
                else:
                    value = data[offset : offset + m.len]
                    offset += m.len
            else:
                format = NlAttr.get_format(m.type, m.byte_order)
                [ value ] = format.unpack_from(data, offset)
                offset += format.size
            if value is not None:
                if m.enum:
                    value = self._decode_enum(value, m)
                elif m.display_hint:
                    value = self._formatted_string(value, m.display_hint)
                attrs[m.name] = value
        return attrs

    def _encode_struct(self, name, vals):
        members = self.consts[name].members
        attr_payload = b''
        for m in members:
            value = vals.pop(m.name) if m.name in vals else None
            if m.type == 'pad':
                attr_payload += bytearray(m.len)
            elif m.type == 'binary':
                if m.struct:
                    if value is None:
                        value = dict()
                    attr_payload += self._encode_struct(m.struct, value)
                else:
                    if value is None:
                        attr_payload += bytearray(m.len)
                    else:
                        attr_payload += bytes.fromhex(value)
            else:
                if value is None:
                    value = 0
                format = NlAttr.get_format(m.type, m.byte_order)
                attr_payload += format.pack(value)
        return attr_payload

    def _formatted_string(self, 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 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_struct(decoded.raw, 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=None, 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)
        if op.fixed_header:
            msg += self._encode_struct(op.fixed_header, vals)
        search_attrs = SpaceAttrs(op.attr_set, vals)
        for name, value in vals.items():
            msg += self._add_attr(op.attr_set.name, name, value, search_attrs)
        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_struct(decoded.raw, 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=None):
        return self._op(method, vals, flags)

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