monif.py

import os
import socket
import struct

# These constants map to constants in the Linux kernel. This is a crappy
# way to get at them, but it'll do for now.
RTMGRP_LINK = 1

NLMSG_NOOP = 1
NLMSG_ERROR = 2

RTM_NEWLINK = 16
RTM_DELLINK = 17

IFLA_IFNAME = 3

# Create the netlink socket and bind to RTMGRP_LINK,
s = socket.socket(socket.AF_NETLINK, socket.SOCK_RAW, socket.NETLINK_ROUTE)
s.bind((os.getpid(), RTMGRP_LINK))

while True:
    data = s.recv(65535)
    msg_len, msg_type, flags, seq, pid = struct.unpack("=LHHLL", data[:16])

    if msg_type == NLMSG_NOOP:
        print("SKIP: no-op")
        continue
    elif msg_type == NLMSG_ERROR:
        print("ERROR, exit")
        break

    # We fundamentally only care about NEWLINK messages in this version.
    if msg_type == RTM_NEWLINK:
        print("NEWLINK")
    elif msg_type == RTM_DELLINK:
        print("DELLINK")
    else:
        print("SKIP: msg-type " + hex(msg_type))
        continue

    data = data[16:]

    family, _, if_type, index, flags, change = struct.unpack("=BBHiII", data[:16])

    remaining = msg_len - 32
    data = data[16:]

    while remaining:
        rta_len, rta_type = struct.unpack("=HH", data[:4])

        # This check comes from RTA_OK, and terminates a string of routing
        # attributes.
        if rta_len < 4:
            break

        rta_data = data[4:rta_len]

        align = (rta_len + 4 - 1) & ~(4 - 1) # align to 4 byte
        data = data[align:]
        remaining -= align

        # Hoorah, a link is up!
        if rta_type == IFLA_IFNAME:
            print("IF %d: %s FLAG:%s" % (index, rta_data, hex(flags)))

host if의 change이벤트는 위와 같이 받을 수 있습니다.

다음과 같이 해서 foo device를 만들고 up하고 down하고 지우면

root@vagrant:/home/vagrant/work# ip link add name foo type dummy
root@vagrant:/home/vagrant/work# ip link set dev foo up
root@vagrant:/home/vagrant/work# ip link set dev foo down
root@vagrant:/home/vagrant/work# ip link del dev foo

아래와 같이 감지해요

vagrant@vagrant:~/work$ /usr/bin/python3 monif.py 
NEWLINK
IF 6: b'foo\x00' FLAG:0x82
NEWLINK
IF 6: b'foo\x00' FLAG:0x100c3
NEWLINK
IF 6: b'foo\x00' FLAG:0x82
DELLINK
IF 6: b'foo\x00' FLAG:0x82
11:44 AM

플래그는 net/if.h에 있습니다. up=0x1, run=0x40 등등