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# Author: Tamilmani Manoharan <tamanoha@microsoft.com>
#
# This file is part of cloud-init. See LICENSE file for license information.
import logging
import os
import select
import socket
import struct
from collections import namedtuple
from cloudinit import util
LOG = logging.getLogger(__name__)
# http://man7.org/linux/man-pages/man7/netlink.7.html
RTMGRP_LINK = 1
RTM_NEWLINK = 16
RTM_DELLINK = 17
RTM_GETLINK = 18
RTM_SETLINK = 19
MAX_SIZE = 65535
MSG_TYPE_OFFSET = 16
SELECT_TIMEOUT = 60
NLMSGHDR_FMT = "IHHII"
IFINFOMSG_FMT = "BHiII"
NLMSGHDR_SIZE = struct.calcsize(NLMSGHDR_FMT)
IFINFOMSG_SIZE = struct.calcsize(IFINFOMSG_FMT)
RTATTR_START_OFFSET = NLMSGHDR_SIZE + IFINFOMSG_SIZE
RTA_DATA_START_OFFSET = 4
PAD_ALIGNMENT = 4
IFLA_IFNAME = 3
IFLA_OPERSTATE = 16
# https://www.kernel.org/doc/Documentation/networking/operstates.txt
OPER_UNKNOWN = 0
OPER_NOTPRESENT = 1
OPER_DOWN = 2
OPER_LOWERLAYERDOWN = 3
OPER_TESTING = 4
OPER_DORMANT = 5
OPER_UP = 6
RTAAttr = namedtuple("RTAAttr", ["length", "rta_type", "data"])
InterfaceOperstate = namedtuple("InterfaceOperstate", ["ifname", "operstate"])
NetlinkHeader = namedtuple(
"NetlinkHeader", ["length", "type", "flags", "seq", "pid"]
)
class NetlinkCreateSocketError(RuntimeError):
"""Raised if netlink socket fails during create or bind."""
def create_bound_netlink_socket():
"""Creates netlink socket and bind on netlink group to catch interface
down/up events. The socket will bound only on RTMGRP_LINK (which only
includes RTM_NEWLINK/RTM_DELLINK/RTM_GETLINK events). The socket is set to
non-blocking mode since we're only receiving messages.
:returns: netlink socket in non-blocking mode
:raises: NetlinkCreateSocketError
"""
try:
netlink_socket = socket.socket(
socket.AF_NETLINK, socket.SOCK_RAW, socket.NETLINK_ROUTE
)
netlink_socket.bind((os.getpid(), RTMGRP_LINK))
netlink_socket.setblocking(0)
except socket.error as e:
msg = "Exception during netlink socket create: %s" % e
raise NetlinkCreateSocketError(msg) from e
LOG.debug("Created netlink socket")
return netlink_socket
def get_netlink_msg_header(data):
"""Gets netlink message type and length
:param: data read from netlink socket
:returns: netlink message type
:raises: AssertionError if data is None or data is not >= NLMSGHDR_SIZE
struct nlmsghdr {
__u32 nlmsg_len; /* Length of message including header */
__u16 nlmsg_type; /* Type of message content */
__u16 nlmsg_flags; /* Additional flags */
__u32 nlmsg_seq; /* Sequence number */
__u32 nlmsg_pid; /* Sender port ID */
};
"""
assert data is not None, "data is none"
assert (
len(data) >= NLMSGHDR_SIZE
), "data is smaller than netlink message header"
msg_len, msg_type, flags, seq, pid = struct.unpack(
NLMSGHDR_FMT, data[:MSG_TYPE_OFFSET]
)
LOG.debug("Got netlink msg of type %d", msg_type)
return NetlinkHeader(msg_len, msg_type, flags, seq, pid)
def read_netlink_socket(netlink_socket, timeout=None):
"""Select and read from the netlink socket if ready.
:param: netlink_socket: specify which socket object to read from
:param: timeout: specify a timeout value (integer) to wait while reading,
if none, it will block indefinitely until socket ready for read
:returns: string of data read (max length = <MAX_SIZE>) from socket,
if no data read, returns None
:raises: AssertionError if netlink_socket is None
"""
assert netlink_socket is not None, "netlink socket is none"
read_set, _, _ = select.select([netlink_socket], [], [], timeout)
# Incase of timeout,read_set doesn't contain netlink socket.
# just return from this function
if netlink_socket not in read_set:
return None
LOG.debug("netlink socket ready for read")
data = netlink_socket.recv(MAX_SIZE)
if data is None:
LOG.error("Reading from Netlink socket returned no data")
return data
def unpack_rta_attr(data, offset):
"""Unpack a single rta attribute.
:param: data: string of data read from netlink socket
:param: offset: starting offset of RTA Attribute
:return: RTAAttr object with length, type and data. On error, return None.
:raises: AssertionError if data is None or offset is not integer.
"""
assert data is not None, "data is none"
assert isinstance(offset, int), "offset is not integer"
assert (
offset >= RTATTR_START_OFFSET
), "rta offset is less than expected length"
length = rta_type = 0
attr_data = None
try:
length = struct.unpack_from("H", data, offset=offset)[0]
rta_type = struct.unpack_from("H", data, offset=offset + 2)[0]
except struct.error:
return None # Should mean our offset is >= remaining data
# Unpack just the attribute's data. Offset by 4 to skip length/type header
attr_data = data[offset + RTA_DATA_START_OFFSET : offset + length]
return RTAAttr(length, rta_type, attr_data)
def read_rta_oper_state(data):
"""Reads Interface name and operational state from RTA Data.
:param: data: string of data read from netlink socket
:returns: InterfaceOperstate object containing if_name and oper_state.
None if data does not contain valid IFLA_OPERSTATE and
IFLA_IFNAME messages.
:raises: AssertionError if data is None or length of data is
smaller than RTATTR_START_OFFSET.
"""
assert data is not None, "data is none"
assert (
len(data) > RTATTR_START_OFFSET
), "length of data is smaller than RTATTR_START_OFFSET"
ifname = operstate = None
offset = RTATTR_START_OFFSET
while offset <= len(data):
attr = unpack_rta_attr(data, offset)
if not attr or attr.length == 0:
break
# Each attribute is 4-byte aligned. Determine pad length.
padlen = (
PAD_ALIGNMENT - (attr.length % PAD_ALIGNMENT)
) % PAD_ALIGNMENT
offset += attr.length + padlen
if attr.rta_type == IFLA_OPERSTATE:
operstate = ord(attr.data)
elif attr.rta_type == IFLA_IFNAME:
interface_name = util.decode_binary(attr.data, "utf-8")
ifname = interface_name.strip("\0")
if not ifname or operstate is None:
return None
LOG.debug("rta attrs: ifname %s operstate %d", ifname, operstate)
return InterfaceOperstate(ifname, operstate)
def wait_for_nic_attach_event(netlink_socket, existing_nics):
"""Block until a single nic is attached.
:param: netlink_socket: netlink_socket to receive events
:param: existing_nics: List of existing nics so that we can skip them.
:raises: AssertionError if netlink_socket is none.
"""
LOG.debug("Preparing to wait for nic attach.")
ifname = None
def should_continue_cb(iname, carrier, prevCarrier):
if iname in existing_nics:
return True
nonlocal ifname
ifname = iname
return False
# We can return even if the operational state of the new nic is DOWN
# because we set it to UP before doing dhcp.
read_netlink_messages(
netlink_socket,
None,
[RTM_NEWLINK],
[OPER_UP, OPER_DOWN],
should_continue_cb,
)
return ifname
def wait_for_nic_detach_event(netlink_socket):
"""Block until a single nic is detached and its operational state is down.
:param: netlink_socket: netlink_socket to receive events.
"""
LOG.debug("Preparing to wait for nic detach.")
ifname = None
def should_continue_cb(iname, carrier, prevCarrier):
nonlocal ifname
ifname = iname
return False
read_netlink_messages(
netlink_socket, None, [RTM_DELLINK], [OPER_DOWN], should_continue_cb
)
return ifname
def wait_for_media_disconnect_connect(netlink_socket, ifname):
"""Block until media disconnect and connect has happened on an interface.
Listens on netlink socket to receive netlink events and when the carrier
changes from 0 to 1, it considers event has happened and
return from this function
:param: netlink_socket: netlink_socket to receive events
:param: ifname: Interface name to lookout for netlink events
:raises: AssertionError if netlink_socket is None or ifname is None.
"""
assert netlink_socket is not None, "netlink socket is none"
assert ifname is not None, "interface name is none"
assert len(ifname) > 0, "interface name cannot be empty"
def should_continue_cb(iname, carrier, prevCarrier):
# check for carrier down, up sequence
isVnetSwitch = (prevCarrier == OPER_DOWN) and (carrier == OPER_UP)
if isVnetSwitch:
LOG.debug("Media switch happened on %s.", ifname)
return False
return True
LOG.debug("Wait for media disconnect and reconnect to happen")
read_netlink_messages(
netlink_socket,
ifname,
[RTM_NEWLINK, RTM_DELLINK],
[OPER_UP, OPER_DOWN],
should_continue_cb,
)
def read_netlink_messages(
netlink_socket,
ifname_filter,
rtm_types,
operstates,
should_continue_callback,
):
"""Reads from the netlink socket until the condition specified by
the continuation callback is met.
:param: netlink_socket: netlink_socket to receive events.
:param: ifname_filter: if not None, will only listen for this interface.
:param: rtm_types: Type of netlink events to listen for.
:param: operstates: Operational states to listen.
:param: should_continue_callback: Specifies when to stop listening.
"""
if netlink_socket is None:
raise RuntimeError("Netlink socket is none")
data = bytes()
carrier = OPER_UP
prevCarrier = OPER_UP
while True:
recv_data = read_netlink_socket(netlink_socket, SELECT_TIMEOUT)
if recv_data is None:
continue
LOG.debug("read %d bytes from socket", len(recv_data))
data += recv_data
LOG.debug("Length of data after concat %d", len(data))
offset = 0
datalen = len(data)
while offset < datalen:
nl_msg = data[offset:]
if len(nl_msg) < NLMSGHDR_SIZE:
LOG.debug("Data is smaller than netlink header")
break
nlheader = get_netlink_msg_header(nl_msg)
if len(nl_msg) < nlheader.length:
LOG.debug("Partial data. Smaller than netlink message")
break
padlen = (nlheader.length + PAD_ALIGNMENT - 1) & ~(
PAD_ALIGNMENT - 1
)
offset = offset + padlen
LOG.debug("offset to next netlink message: %d", offset)
# Continue if we are not interested in this message.
if nlheader.type not in rtm_types:
continue
interface_state = read_rta_oper_state(nl_msg)
if interface_state is None:
LOG.debug("Failed to read rta attributes: %s", interface_state)
continue
if (
ifname_filter is not None
and interface_state.ifname != ifname_filter
):
LOG.debug(
"Ignored netlink event on interface %s. Waiting for %s.",
interface_state.ifname,
ifname_filter,
)
continue
if interface_state.operstate not in operstates:
continue
prevCarrier = carrier
carrier = interface_state.operstate
if not should_continue_callback(
interface_state.ifname, carrier, prevCarrier
):
return
data = data[offset:]