Shows how to manipulate a plug qdisc manually using pyroute2

manipulate_qdisc.py

import pyroute2
from pyroute2 import IPRoute
from pyroute2.iproute import transform_handle
from pyroute2.netlink import NLM_F_ACK
from pyroute2.netlink import NLM_F_REQUEST
from pyroute2.netlink.rtnl.tcmsg import tcmsg
 
PLUG_CLASS = '1:4'
PLUG_QDISC = '40:'
 
def manage_plug_via_netlink(interface_name, action='unplug'):
    """ Manipulates a plug qdisc via netlink"""
    ip = IPRoute()
    index = ip.link_lookup(ifname=interface_name)[0]
    # See the linux source at include/uapi/linux/pkt_sched.h
    # #define TCQ_PLUG_BUFFER                0
    # #define TCQ_PLUG_RELEASE_ONE           1
    # #define TCQ_PLUG_RELEASE_INDEFINITE    2
    # #define TCQ_PLUG_LIMIT                 3
    action = {'unplug': 2, 'plug': 0}[action]
    limit = 10000
    handle = transform_handle(PLUG_QDISC)
    parent = transform_handle(PLUG_CLASS)
    # This is a bit of magic sauce, inspired by xen's remus project
    flags = NLM_F_REQUEST | NLM_F_ACK
    command = pyroute2.netlink.rtnl.RTM_NEWQDISC
    opts = struct.pack('iI', action, limit)
 
    msg = tcmsg()
    msg['index'] = index
    msg['handle'] = handle
    msg['parent'] = parent
    msg['attrs'] = [['TCA_KIND', 'plug']]
    msg['attrs'].append(['TCA_OPTIONS', opts])
    try:
        nlm_response = ip.nlm_request(msg, msg_type=command, msg_flags=flags)
    except pyroute2.netlink.NetlinkError as nle:
        if nle.code == 22:
            # This is an old kernel and we're talking to a qfifo, chill
            print('Detected a non plug qdisc, likely due to an old kernel.\n'
                  'If you wish to have zero downtime haproxy restarts, '
                  'upgrade your kernel.\n'
                  'Doing nothing to the SYN traffic lane...')
            return
        else:
            raise
    # As per the netlink manpage (man 7 netlink), we expect an
    # acknowledgment as a NLMSG_ERROR packet with the error field being 0,
    # which it looks like pyroute2 treats as None. Really we want it to be
    # non negative.
    if not(len(nlm_response) > 0 and
           nlm_response[0]['event'] == 'NLMSG_ERROR' and
           nlm_response[0]['header']['error'] is None):
        raise RuntimeError(
            'Had an error while communicating with netlink: {0}'.format(
                nlm_response))