# SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
#
# pylint: disable=missing-class-docstring, missing-function-docstring
# pylint: disable=too-many-branches, too-many-locals, too-many-instance-attributes
# pylint: disable=too-many-lines

"""
YAML Netlink Library

An implementation of the genetlink and raw netlink protocols.
"""

from collections import namedtuple
from enum import Enum
import functools
import os
import random
import socket
import struct
from struct import Struct
import sys
import ipaddress
import uuid
import queue
import selectors
import time

from .nlspec import SpecFamily

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


class YnlException(Exception):
    pass


# pylint: disable=too-few-public-methods
class Netlink:
    # Netlink socket
    SOL_NETLINK = 270

    NETLINK_ADD_MEMBERSHIP = 1
    NETLINK_LISTEN_ALL_NSID = 8
    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_CMD_GETPOLICY = 10

    CTRL_ATTR_FAMILY_ID = 1
    CTRL_ATTR_FAMILY_NAME = 2
    CTRL_ATTR_MAXATTR = 5
    CTRL_ATTR_MCAST_GROUPS = 7
    CTRL_ATTR_POLICY = 8
    CTRL_ATTR_OP_POLICY = 9
    CTRL_ATTR_OP = 10

    CTRL_ATTR_MCAST_GRP_NAME = 1
    CTRL_ATTR_MCAST_GRP_ID = 2

    CTRL_ATTR_POLICY_DO = 1
    CTRL_ATTR_POLICY_DUMP = 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

    # Policy types
    NL_POLICY_TYPE_ATTR_TYPE = 1
    NL_POLICY_TYPE_ATTR_MIN_VALUE_S = 2
    NL_POLICY_TYPE_ATTR_MAX_VALUE_S = 3
    NL_POLICY_TYPE_ATTR_MIN_VALUE_U = 4
    NL_POLICY_TYPE_ATTR_MAX_VALUE_U = 5
    NL_POLICY_TYPE_ATTR_MIN_LENGTH = 6
    NL_POLICY_TYPE_ATTR_MAX_LENGTH = 7
    NL_POLICY_TYPE_ATTR_POLICY_IDX = 8
    NL_POLICY_TYPE_ATTR_POLICY_MAXTYPE = 9
    NL_POLICY_TYPE_ATTR_BITFIELD32_MASK = 10
    NL_POLICY_TYPE_ATTR_PAD = 11
    NL_POLICY_TYPE_ATTR_MASK = 12

    AttrType = Enum('AttrType', ['flag', 'u8', 'u16', 'u32', 'u64',
                                  's8', 's16', 's32', 's64',
                                  'binary', 'string', 'nul-string',
                                  'nested', 'nested-array',
                                  'bitfield32', 'sint', 'uint'])

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

    def __str__(self):
        msg = "Netlink error: "

        extack = self.nl_msg.extack.copy() if self.nl_msg.extack else {}
        if 'msg' in extack:
            msg += extack['msg'] + ': '
            del extack['msg']
        msg += os.strerror(self.error)
        if extack:
            msg += ' ' + str(extack)
        return msg


class ConfigError(Exception):
    pass


class NlPolicy:
    """Kernel policy for one mode (do or dump) of one operation.

    Returned by YnlFamily.get_policy(). Attributes of the policy
    are accessible as attributes of the object. Nested policies
    can be accessed indexing the object like a dictionary::

        pol = ynl.get_policy('page-pool-stats-get', 'do')
        pol['info'].type            # 'nested'
        pol['info']['id'].type      # 'uint'
        pol['info']['id'].min_value # 1

    Each policy entry always has a 'type' attribute (e.g. u32, string,
    nested). Optional attributes depending on the 'type': min-value,
    max-value, min-length, max-length, mask.

    Policies can form infinite nesting loops. These loops are trimmed
    when policy is converted to a dict with pol.to_dict().
    """
    def __init__(self, ynl, policy_idx, policy_table, attr_set, props=None):
        self._policy_idx = policy_idx
        self._policy_table = policy_table
        self._ynl = ynl
        self._props = props or {}
        self._entries = {}
        self._cache = {}
        if policy_idx is not None and policy_idx in policy_table:
            for attr_id, decoded in policy_table[policy_idx].items():
                if attr_set and attr_id in attr_set.attrs_by_val:
                    spec = attr_set.attrs_by_val[attr_id]
                    name = spec['name']
                else:
                    spec = None
                    name = f'attr-{attr_id}'
                self._entries[name] = (spec, decoded)

    def __getitem__(self, name):
        """Descend into a nested policy by attribute name."""
        if name not in self._cache:
            spec, decoded = self._entries[name]
            props = dict(decoded)
            child_idx = None
            child_set = None
            if 'policy-idx' in props:
                child_idx = props.pop('policy-idx')
                if spec and 'nested-attributes' in spec.yaml:
                    child_set = self._ynl.attr_sets[spec.yaml['nested-attributes']]
            self._cache[name] = NlPolicy(self._ynl, child_idx,
                                         self._policy_table,
                                         child_set, props)
        return self._cache[name]

    def __getattr__(self, name):
        """Access this policy entry's own properties (type, min-value, etc.).

        Underscores in the name are converted to dashes, so that
        pol.min_value looks up "min-value".
        """
        key = name.replace('_', '-')
        try:
            # Hack for level-0 which we still want to have .type but we don't
            # want type to pointlessly show up in the dict / JSON form.
            if not self._props and name == "type":
                return "nested"
            return self._props[key]
        except KeyError:
            raise AttributeError(name)

    def get(self, name, default=None):
        """Look up a child policy entry by attribute name, with a default."""
        try:
            return self[name]
        except KeyError:
            return default

    def __contains__(self, name):
        return name in self._entries

    def __len__(self):
        return len(self._entries)

    def __iter__(self):
        return iter(self._entries)

    def keys(self):
        """Return attribute names accepted by this policy."""
        return self._entries.keys()

    def to_dict(self, seen=None):
        """Convert to a plain dict, suitable for JSON serialization.

        Nested NlPolicy objects are expanded recursively. Cyclic
        references are trimmed (resolved to just {"type": "nested"}).
        """
        if seen is None:
            seen = set()
        result = dict(self._props)
        if self._policy_idx is not None:
            if self._policy_idx not in seen:
                seen = seen | {self._policy_idx}
                children = {}
                for name in self:
                    children[name] = self[name].to_dict(seen)
                if self._props:
                    result['policy'] = children
                else:
                    result = children
        return result

    def __repr__(self):
        return repr(self.to_dict())


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 YnlException(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, c_type):
        format_ = self.get_format(c_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.error = struct.unpack("i", self.raw[0:4])[0]
            self.done = 1
            extack_off = 4

        self.extack = None
        if self.nl_flags & Netlink.NLM_F_ACK_TLVS and extack_off:
            self.extack = {}
            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')
                elif extack.type == Netlink.NLMSGERR_ATTR_POLICY:
                    self.extack['policy'] = _genl_decode_policy(extack.raw)
                else:
                    if 'unknown' not in self.extack:
                        self.extack['unknown'] = []
                    self.extack['unknown'].append(extack)

            if attr_space:
                self.annotate_extack(attr_space)

    def annotate_extack(self, attr_space):
        """ Make extack more human friendly with attribute information """

        # 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]
                self.extack['miss-type'] = spec['name']
                if 'doc' in spec:
                    self.extack['miss-type-doc'] = spec['doc']

    def cmd(self):
        return self.nl_type

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


# pylint: disable=too-few-public-methods
class NlMsgs:
    def __init__(self, data):
        self.msgs = []

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

    def __iter__(self):
        yield from self.msgs


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_decode_policy(raw):
    policy = {}
    for attr in NlAttrs(raw):
        if attr.type == Netlink.NL_POLICY_TYPE_ATTR_TYPE:
            type_ = attr.as_scalar('u32')
            policy['type'] = Netlink.AttrType(type_).name
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MIN_VALUE_S:
            policy['min-value'] = attr.as_scalar('s64')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MAX_VALUE_S:
            policy['max-value'] = attr.as_scalar('s64')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MIN_VALUE_U:
            policy['min-value'] = attr.as_scalar('u64')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MAX_VALUE_U:
            policy['max-value'] = attr.as_scalar('u64')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MIN_LENGTH:
            policy['min-length'] = attr.as_scalar('u32')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MAX_LENGTH:
            policy['max-length'] = attr.as_scalar('u32')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_POLICY_IDX:
            policy['policy-idx'] = attr.as_scalar('u32')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_BITFIELD32_MASK:
            policy['bitfield32-mask'] = attr.as_scalar('u32')
        elif attr.type == Netlink.NL_POLICY_TYPE_ATTR_MASK:
            policy['mask'] = attr.as_scalar('u64')
    return policy


# pylint: disable=too-many-nested-blocks
def _genl_load_families():
    genl_family_name_to_id = {}

    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)

        while True:
            reply = sock.recv(128 * 1024)
            nms = NlMsgs(reply)
            for nl_msg in nms:
                if nl_msg.error:
                    raise YnlException(f"Netlink error: {nl_msg.error}")
                if nl_msg.done:
                    return genl_family_name_to_id

                gm = GenlMsg(nl_msg)
                fam = {}
                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'] = {}
                        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


# pylint: disable=too-many-nested-blocks
def _genl_policy_dump(family_id, op):
    op_policy = {}
    policy_table = {}

    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_GETPOLICY, 1)
        msg += struct.pack('HHHxx', 6, Netlink.CTRL_ATTR_FAMILY_ID, family_id)
        msg += struct.pack('HHI', 8, Netlink.CTRL_ATTR_OP, op)
        msg = _genl_msg_finalize(msg)

        sock.send(msg, 0)

        while True:
            reply = sock.recv(128 * 1024)
            nms = NlMsgs(reply)
            for nl_msg in nms:
                if nl_msg.error:
                    raise YnlException(f"Netlink error: {nl_msg.error}")
                if nl_msg.done:
                    return op_policy, policy_table

                gm = GenlMsg(nl_msg)
                for attr in NlAttrs(gm.raw):
                    if attr.type == Netlink.CTRL_ATTR_OP_POLICY:
                        for op_attr in NlAttrs(attr.raw):
                            for method_attr in NlAttrs(op_attr.raw):
                                if method_attr.type == Netlink.CTRL_ATTR_POLICY_DO:
                                    op_policy['do'] = method_attr.as_scalar('u32')
                                elif method_attr.type == Netlink.CTRL_ATTR_POLICY_DUMP:
                                    op_policy['dump'] = method_attr.as_scalar('u32')
                    elif attr.type == Netlink.CTRL_ATTR_POLICY:
                        for pidx_attr in NlAttrs(attr.raw):
                            policy_idx = pidx_attr.type
                            for aid_attr in NlAttrs(pidx_attr.raw):
                                attr_id = aid_attr.type
                                decoded = _genl_decode_policy(aid_attr.raw)
                                if policy_idx not in policy_table:
                                    policy_table[policy_idx] = {}
                                policy_table[policy_idx][attr_id] = decoded


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:]
        self.raw_attrs = []

    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, op):
        msg = self._decode(nl_msg)
        if op is None:
            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 YnlException(f'Multicast group "{mcast_name}" not present in the spec')
        return mcast_groups[mcast_name].value

    def msghdr_size(self):
        return 16


class GenlProtocol(NetlinkProtocol):
    genl_family_name_to_id = {}

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

        if not GenlProtocol.genl_family_name_to_id:
            GenlProtocol.genl_family_name_to_id = _genl_load_families()

        self.genl_family = GenlProtocol.genl_family_name_to_id[family_name]
        self.family_id = GenlProtocol.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 YnlException(f'Multicast group "{mcast_name}" not present in the family')
        return self.genl_family['mcast'][mcast_name]

    def msghdr_size(self):
        return super().msghdr_size() + 4


# pylint: disable=too-few-public-methods
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 YnlException(
                    f"No value for '{name}' in attribute space '{spec_name}'")
        raise YnlException(f"Attribute '{name}' not defined in any attribute-set")


#
# YNL implementation details.
#


class YnlFamily(SpecFamily):
    """
    YNL family -- a Netlink interface built from a YAML spec.

    Primary use of the class is to execute Netlink commands:

      ynl.<op_name>(attrs, ...)

    By default this will execute the <op_name> as "do", pass dump=True
    to perform a dump operation.

    ynl.<op_name> is a shorthand / convenience wrapper for the following
    methods which take the op_name as a string:

      ynl.do(op_name, attrs, flags=None) -- execute a do operation
      ynl.dump(op_name, attrs)           -- execute a dump operation
      ynl.do_multi(ops)                  -- batch multiple do operations

    The flags argument in ynl.do() allows passing in extra NLM_F_* flags
    which may be necessary for old families.

    Notification API:

      ynl.ntf_subscribe(mcast_name)      -- join a multicast group
      ynl.ntf_listen_all_nsid()          -- listen on all netns
      ynl.check_ntf()                    -- drain pending notifications
      ynl.poll_ntf(duration=None)        -- yield notifications

    Policy introspection allows querying validation criteria from the running
    kernel. Allows checking whether kernel supports a given attribute or value.

      ynl.get_policy(op_name, mode)      -- query kernel policy for an op
    """
    def __init__(self, def_path, schema=None, process_unknown=False,
                 recv_size=0):
        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 as err:
            raise YnlException(f"Family '{self.yaml['name']}' not supported by the kernel") from err

        self._recv_dbg = False
        # Note that netlink will use conservative (min) message size for
        # the first dump recv() on the socket, our setting will only matter
        # from the second recv() on.
        self._recv_size = recv_size if recv_size else 131072
        # Netlink will always allocate at least PAGE_SIZE - sizeof(skb_shinfo)
        # for a message, so smaller receive sizes will lead to truncation.
        # Note that the min size for other families may be larger than 4k!
        if self._recv_size < 4000:
            raise ConfigError()

        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 = queue.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 close(self):
        if self.sock is not None:
            self.sock.close()
            self.sock = None

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc, tb):
        self.close()

    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 ntf_listen_all_nsid(self):
        """Enable NETLINK_LISTEN_ALL_NSID to receive notifications from all
        namespaces that have an nsid mapped in the current one."""
        self.sock.setsockopt(Netlink.SOL_NETLINK,
                             Netlink.NETLINK_LISTEN_ALL_NSID, 1)

    @staticmethod
    def _decode_nsid(ancdata):
        for cmsg_level, cmsg_type, cmsg_data in ancdata:
            if (cmsg_level == Netlink.SOL_NETLINK and
                    cmsg_type == Netlink.NETLINK_LISTEN_ALL_NSID):
                nsid = struct.unpack('i', cmsg_data)[0]
                if nsid >= 0:
                    return nsid
                return None
        return None

    def set_recv_dbg(self, enabled):
        self._recv_dbg = enabled

    def _recv_dbg_print(self, reply, nl_msgs):
        if not self._recv_dbg:
            return
        print("Recv: read", len(reply), "bytes,",
              len(nl_msgs.msgs), "messages", file=sys.stderr)
        for nl_msg in nl_msgs:
            print("  ", nl_msg, file=sys.stderr)

    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
        return enum.entries[value].user_value()

    def _get_scalar(self, attr_spec, value):
        try:
            return int(value)
        except (ValueError, TypeError) as e:
            if 'enum' in attr_spec:
                return self._encode_enum(attr_spec, value)
            if attr_spec.display_hint:
                return self._from_string(value, attr_spec)
            raise e

    # pylint: disable=too-many-statements
    def _add_attr(self, space, name, value, search_attrs):
        try:
            attr = self.attr_sets[space][name]
        except KeyError as err:
            raise YnlException(f"Space '{space}' has no attribute '{name}'") from err
        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
            sub_space = attr['nested-attributes']
            attr_payload = self._add_nest_attrs(value, sub_space, search_attrs)
        elif attr['type'] == 'indexed-array' and attr['sub-type'] == 'nest':
            nl_type |= Netlink.NLA_F_NESTED
            sub_space = attr['nested-attributes']
            attr_payload = self._encode_indexed_array(value, sub_space,
                                                      search_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 value is None:
                attr_payload = b''
            elif isinstance(value, bytes):
                attr_payload = value
            elif isinstance(value, str):
                if attr.display_hint:
                    attr_payload = self._from_string(value, attr)
                else:
                    attr_payload = bytes.fromhex(value)
            elif isinstance(value, dict) and attr.struct_name:
                attr_payload = self._encode_struct(attr.struct_name, value)
            elif isinstance(value, list) and attr.sub_type in NlAttr.type_formats:
                format_ = NlAttr.get_format(attr.sub_type)
                attr_payload = b''.join([format_.pack(x) for x in value])
            else:
                raise YnlException(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 YnlException(f"Unknown attribute-set '{msg_format.attr_set}'")
        else:
            raise YnlException(f'Unknown type at {space} {name} {value} {attr["type"]}')

        return self._add_attr_raw(nl_type, attr_payload)

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

    def _add_nest_attrs(self, value, sub_space, search_attrs):
        sub_attrs = SpaceAttrs(self.attr_sets[sub_space], value, search_attrs)
        attr_payload = b''
        for subname, subvalue in value.items():
            attr_payload += self._add_attr(sub_space, subname, subvalue,
                                           sub_attrs)
        return attr_payload

    def _encode_indexed_array(self, vals, sub_space, search_attrs):
        attr_payload = b''
        for i, val in enumerate(vals):
            idx = i | Netlink.NLA_F_NESTED
            val_payload = self._add_nest_attrs(val, sub_space, search_attrs)
            attr_payload += self._add_attr_raw(idx, val_payload)
        return attr_payload

    def _get_enum_or_unknown(self, enum, raw):
        try:
            name = enum.entries_by_val[raw].name
        except KeyError as error:
            if self.process_unknown:
                name = f"Unknown({raw})"
            else:
                raise error
        return name

    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(self._get_enum_or_unknown(enum, i))
                raw >>= 1
                i += 1
        else:
            value = self._get_enum_or_unknown(enum, raw)
        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)
            if 'enum' in attr_spec:
                decoded = [ self._decode_enum(x, attr_spec) for x in decoded ]
            elif attr_spec.display_hint:
                decoded = [ self._formatted_string(x, attr_spec.display_hint)
                            for x in decoded ]
        else:
            decoded = attr.as_bin()
            if attr_spec.display_hint:
                decoded = self._formatted_string(decoded, attr_spec.display_hint)
        return decoded

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

            if attr_spec["sub-type"] == 'nest':
                subattrs = self._decode(NlAttrs(item.raw), attr_spec['nested-attributes'])
                decoded.append({ item.type: subattrs })
            elif attr_spec["sub-type"] == 'binary':
                subattr = item.as_bin()
                if attr_spec.display_hint:
                    subattr = self._formatted_string(subattr, attr_spec.display_hint)
                decoded.append(subattr)
            elif attr_spec["sub-type"] in NlAttr.type_formats:
                subattr = item.as_scalar(attr_spec['sub-type'], attr_spec.byte_order)
                if 'enum' in attr_spec:
                    subattr = self._decode_enum(subattr, attr_spec)
                elif attr_spec.display_hint:
                    subattr = self._formatted_string(subattr, attr_spec.display_hint)
                decoded.append(subattr)
            else:
                raise YnlException(f'Unknown {attr_spec["sub-type"]} with name {attr_spec["name"]}')
        return decoded

    def _decode_nest_type_value(self, attr, attr_spec):
        decoded = {}
        value = attr
        for name in attr_spec['type-value']:
            value = NlAttr(value.raw, 0)
            decoded[name] = value.type
        subattrs = self._decode(NlAttrs(value.raw), attr_spec['nested-attributes'])
        decoded.update(subattrs)
        return decoded

    def _decode_unknown(self, attr):
        if attr.is_nest:
            return self._decode(NlAttrs(attr.raw), None)
        return attr.as_bin()

    def _rsp_add(self, rsp, name, is_multi, decoded):
        if is_multi is None:
            if name in rsp and not isinstance(rsp[name], 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 YnlException(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 YnlException(f"No message format for '{value}' in sub-message spec '{sub_msg}'")

        spec = sub_msg_spec.formats[value]
        return spec, value

    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 YnlException(f"Unknown attribute-set '{msg_format.attr_set}' "
                                   f"when decoding '{attr_spec.name}'")
        return decoded

    # pylint: disable=too-many-statements
    def _decode(self, attrs, space, outer_attrs = None):
        rsp = {}
        search_attrs = {}
        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) as err:
                if not self.process_unknown:
                    raise YnlException(f"Space '{space}' has no attribute "
                                       f"with value '{attr.type}'") from err
                attr_name = f"UnknownAttr({attr.type})"
                self._rsp_add(rsp, attr_name, None, self._decode_unknown(attr))
                continue

            try:
                if attr_spec["type"] == 'pad':
                    continue
                elif 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)
                    if 'enum' in attr_spec:
                        decoded = self._decode_enum(decoded, attr_spec)
                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.display_hint:
                        decoded = self._formatted_string(decoded, attr_spec.display_hint)
                elif attr_spec["type"] == 'indexed-array':
                    decoded = self._decode_array_attr(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)
                elif attr_spec["type"] == 'nest-type-value':
                    decoded = self._decode_nest_type_value(attr, attr_spec)
                else:
                    if not self.process_unknown:
                        raise YnlException(f'Unknown {attr_spec["type"]} '
                                           f'with name {attr_spec["name"]}')
                    decoded = self._decode_unknown(attr)

                self._rsp_add(rsp, attr_spec["name"], attr_spec.is_multi, decoded)
            except:
                print(f"Error decoding '{attr_spec.name}' from '{space}'")
                raise

        return rsp

    # pylint: disable=too-many-arguments, too-many-positional-arguments
    def _decode_extack_path(self, attrs, attr_set, offset, target, search_attrs):
        for attr in attrs:
            try:
                attr_spec = attr_set.attrs_by_val[attr.type]
            except KeyError as err:
                raise YnlException(
                    f"Space '{attr_set.name}' has no attribute with value '{attr.type}'") from err
            if offset > target:
                break
            if offset == target:
                return '.' + attr_spec.name

            if offset + attr.full_len <= target:
                offset += attr.full_len
                continue

            pathname = attr_spec.name
            if attr_spec['type'] == 'nest':
                sub_attrs = self.attr_sets[attr_spec['nested-attributes']]
                search_attrs = SpaceAttrs(sub_attrs, search_attrs.lookup(attr_spec['name']))
            elif attr_spec['type'] == 'sub-message':
                msg_format, value = self._resolve_selector(attr_spec, search_attrs)
                if msg_format is None:
                    raise YnlException(f"Can't resolve sub-message of "
                                       f"{attr_spec['name']} for extack")
                sub_attrs = self.attr_sets[msg_format.attr_set]
                pathname += f"({value})"
            else:
                raise YnlException(f"Can't dive into {attr.type} ({attr_spec['name']}) for extack")
            offset += 4
            subpath = self._decode_extack_path(NlAttrs(attr.raw), sub_attrs,
                                               offset, target, search_attrs)
            if subpath is None:
                return None
            return '.' + pathname + subpath

        return None

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

        msg = self.nlproto.decode(self, NlMsg(request, 0, op.attr_set), op)
        offset = self.nlproto.msghdr_size() + self.struct_size(op.fixed_header)
        search_attrs = SpaceAttrs(op.attr_set, vals)
        path = self._decode_extack_path(msg.raw_attrs, op.attr_set, offset,
                                        extack['bad-attr-offs'], search_attrs)
        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
        return 0

    def _decode_struct(self, data, name):
        members = self.consts[name].members
        attrs = {}
        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 = {}
                    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(f'{b:02x}' for b in raw)
        elif display_hint == 'hex':
            if isinstance(raw, int):
                formatted = hex(raw)
            else:
                formatted = bytes.hex(raw, ' ')
        elif display_hint in [ 'ipv4', 'ipv6', 'ipv4-or-v6' ]:
            formatted = format(ipaddress.ip_address(raw))
        elif display_hint == 'uuid':
            formatted = str(uuid.UUID(bytes=raw))
        else:
            formatted = raw
        return formatted

    def _from_string(self, string, attr_spec):
        if attr_spec.display_hint in ['ipv4', 'ipv6', 'ipv4-or-v6']:
            ip = ipaddress.ip_address(string)
            if attr_spec['type'] == 'binary':
                raw = ip.packed
            else:
                raw = int(ip)
        elif attr_spec.display_hint == 'hex':
            if attr_spec['type'] == 'binary':
                raw = bytes.fromhex(string)
            else:
                raw = int(string, 16)
        elif attr_spec.display_hint == 'mac':
            # Parse MAC address in format "00:11:22:33:44:55" or "001122334455"
            if ':' in string:
                mac_bytes = [int(x, 16) for x in string.split(':')]
            else:
                if len(string) % 2 != 0:
                    raise YnlException(f"Invalid MAC address format: {string}")
                mac_bytes = [int(string[i:i+2], 16) for i in range(0, len(string), 2)]
            raw = bytes(mac_bytes)
        else:
            raise YnlException(f"Display hint '{attr_spec.display_hint}' not implemented"
                            f" when parsing '{attr_spec['name']}'")
        return raw

    def handle_ntf(self, decoded, nsid=None):
        msg = {}
        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
        if nsid is not None:
            msg['nsid'] = nsid
        self.async_msg_queue.put(msg)

    def _recvmsg(self, flags=0):
        reply, ancdata, _, _ = self.sock.recvmsg(self._recv_size, 4096, flags)
        return reply, ancdata

    def check_ntf(self):
        while True:
            try:
                reply, ancdata = self._recvmsg(socket.MSG_DONTWAIT)
            except BlockingIOError:
                return

            nsid = self._decode_nsid(ancdata)
            nms = NlMsgs(reply)
            self._recv_dbg_print(reply, nms)
            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, None)
                if decoded.cmd() not in self.async_msg_ids:
                    print("Unexpected msg id while checking for ntf", decoded)
                    continue

                self.handle_ntf(decoded, nsid)

    def poll_ntf(self, duration=None):
        start_time = time.time()
        selector = selectors.DefaultSelector()
        selector.register(self.sock, selectors.EVENT_READ)

        while True:
            try:
                yield self.async_msg_queue.get_nowait()
            except queue.Empty:
                if duration is not None:
                    timeout = start_time + duration - time.time()
                    if timeout <= 0:
                        return
                else:
                    timeout = None
                events = selector.select(timeout)
                if events:
                    self.check_ntf()

    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 _encode_message(self, op, vals, flags, req_seq):
        nl_flags = Netlink.NLM_F_REQUEST | Netlink.NLM_F_ACK
        for flag in flags or []:
            nl_flags |= flag

        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)
        return msg

    # pylint: disable=too-many-statements
    def _ops(self, ops):
        reqs_by_seq = {}
        req_seq = random.randint(1024, 65535)
        payload = b''
        for (method, vals, flags) in ops:
            op = self.ops[method]
            msg = self._encode_message(op, vals, flags, req_seq)
            reqs_by_seq[req_seq] = (op, vals, msg, flags)
            payload += msg
            req_seq += 1

        self.sock.send(payload, 0)

        done = False
        rsp = []
        op_rsp = []
        while not done:
            reply, ancdata = self._recvmsg()
            nsid = self._decode_nsid(ancdata)
            nms = NlMsgs(reply)
            self._recv_dbg_print(reply, nms)
            for nl_msg in nms:
                if nl_msg.nl_seq in reqs_by_seq:
                    (op, vals, req_msg, req_flags) = reqs_by_seq[nl_msg.nl_seq]
                    if nl_msg.extack:
                        nl_msg.annotate_extack(op.attr_set)
                        self._decode_extack(req_msg, op, nl_msg.extack, vals)
                else:
                    op = None
                    req_flags = []

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

                    if Netlink.NLM_F_DUMP in req_flags:
                        rsp.append(op_rsp)
                    elif not op_rsp:
                        rsp.append(None)
                    elif len(op_rsp) == 1:
                        rsp.append(op_rsp[0])
                    else:
                        rsp.append(op_rsp)
                    op_rsp = []

                    del reqs_by_seq[nl_msg.nl_seq]
                    done = len(reqs_by_seq) == 0
                    break

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

                # Check if this is a reply to our request
                if nl_msg.nl_seq not in reqs_by_seq or decoded.cmd() != op.rsp_value:
                    if decoded.cmd() in self.async_msg_ids:
                        self.handle_ntf(decoded, nsid)
                        continue
                    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))
                op_rsp.append(rsp_msg)

        return rsp

    def _op(self, method, vals, flags=None, dump=False):
        req_flags = flags or []
        if dump:
            req_flags.append(Netlink.NLM_F_DUMP)

        ops = [(method, vals, req_flags)]
        return self._ops(ops)[0]

    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)

    def do_multi(self, ops):
        return self._ops(ops)

    def get_policy(self, op_name, mode):
        """Query running kernel for the Netlink policy of an operation.

        Allows checking whether kernel supports a given attribute or value.
        This method consults the running kernel, not the YAML spec.

        Args:
            op_name: operation name as it appears in the YAML spec
            mode: 'do' or 'dump'

        Returns:
            NlPolicy acting as a read-only dict mapping attribute names
            to their policy properties (type, min/max, nested, etc.),
            or None if the operation has no policy for the given mode.
            Empty policy usually implies that the operation rejects
            all attributes.
        """
        op = self.ops[op_name]
        op_policy, policy_table = _genl_policy_dump(self.nlproto.family_id,
                                                    op.req_value)
        if mode not in op_policy:
            return None
        policy_idx = op_policy[mode]
        return NlPolicy(self, policy_idx, policy_table, op.attr_set)
