openstack中dhcp_agent在何時創建的dnsmasq進程

查看 /neutron/agent/dhcp/agent.py
中 class DhcpAgent
找到
self.dhcp_driver_cls = importutils.import_class(self.conf.dhcp_driver）

self.dhcp_driver_cls是Dnsmasq的類實例。

self.dhcp_driver_cls=importutils.import_class(self.conf.dhcp_driver)中的dhcp_driver也爲/etc/neutron/dhcp_agent.ini配置文件中參數。

DhcpAgent類_init_函數如下（創建實例部分）

class DhcpAgent(manager.Manager):
    """DHCP agent service manager.

    Note that the public methods of this class are exposed as the server side
    of an rpc interface.  The neutron server uses
    neutron.api.rpc.agentnotifiers.dhcp_rpc_agent_api.DhcpAgentNotifyApi as the
    client side to execute the methods here.  For more information about
    changing rpc interfaces, see doc/source/devref/rpc_api.rst.
    """
    target = oslo_messaging.Target(version='1.0')

    def __init__(self, host=None, conf=None):
        super(DhcpAgent, self).__init__(host=host)
        self.needs_resync_reasons = collections.defaultdict(list)
        self.dhcp_ready_ports = set()
        self.conf = conf or cfg.CONF
        self.cache = NetworkCache()
        self.dhcp_driver_cls = importutils.import_class(self.conf.dhcp_driver)
        self.plugin_rpc = DhcpPluginApi(topics.PLUGIN, self.conf.host)
        # create dhcp dir to store dhcp info
        dhcp_dir: Union[bytes, str] = os.path.dirname("/%s/dhcp/" % self.conf.state_path)
        fileutils.ensure_tree(dhcp_dir, mode=0o755)
        self.dhcp_version = self.dhcp_driver_cls.check_version()
        self._populate_networks_cache()
        # keep track of mappings between networks and routers for
        # metadata processing
        self._metadata_routers = {}  # {network_id: router_id}
        self._process_monitor = external_process.ProcessMonitor(
            config=self.conf,
            resource_type='dhcp')

DhcpAgent通過self.dhcp_driver_cls = importutils.import_class(self.conf.dhcp_driver)註冊了Dnsmasq這個Driver，並在需要的時候調用driver的相應接口。注意這個時候只是註冊了一個調用Dnsmasq的driver並沒有啓動dnsmasq這個進程哦。

agent先同步網絡的狀態再決定是否創建dnsmasq進程，以下是同步狀態的函數（/dhcp/agent.py），

特別注意 for network in active_networks:這段代碼，openstack的操作是，有一個子網就起一個dnsmasq進程，
spawn(self.safe_configure_dhcp_for_network, network)就類似linux的fork起進程的操作。spawn走 safe_configure_dhcp_for_network 要看

    def sync_state(self, networks=None):
        """Sync the local DHCP state with Neutron. If no networks are passed,
        or 'None' is one of the networks, sync all of the networks.
        """
        only_nets = set([] if (not networks or None in networks) else networks)
        LOG.info('Synchronizing state')
        pool = eventlet.GreenPool(self.conf.num_sync_threads)
        known_network_ids = set(self.cache.get_network_ids())

        try:
            active_networks = self.plugin_rpc.get_active_networks_info()
            LOG.info('All active networks have been fetched through RPC.')
            active_network_ids = set(network.id for network in active_networks)
            for deleted_id in known_network_ids - active_network_ids:
                try:
                    self.disable_dhcp_helper(deleted_id)
                except Exception as e:
                    self.schedule_resync(e, deleted_id)
                    LOG.exception('Unable to sync network state on '
                                  'deleted network %s', deleted_id)

            for network in active_networks:
                if (not only_nets or  # specifically resync all
                        network.id not in known_network_ids or  # missing net
                        network.id in only_nets):  # specific network to sync
                    pool.spawn(self.safe_configure_dhcp_for_network, network)
            pool.waitall()
            # we notify all ports in case some were created while the agent
            # was down
            self.dhcp_ready_ports |= set(self.cache.get_port_ids(only_nets))
            LOG.info('Synchronizing state complete')

當創建網絡的時候，發現子網裏面需要開啓DHCP server,則調用self.call_driver(‘enable’, network)。剩下的就是驅動做的事情了我找不到了。

   def safe_configure_dhcp_for_network(self, network):
        try:
            network_id = network.get('id')
            LOG.info('Starting network %s dhcp configuration', network_id)
            self.configure_dhcp_for_network(network)
            LOG.info('Finished network %s dhcp configuration', network_id)
        except (exceptions.NetworkNotFound, RuntimeError):
            LOG.warning('Network %s may have been deleted and '
                        'its resources may have already been disposed.',
                        network.id)
 def configure_dhcp_for_network(self, network):
        if not network.admin_state_up:
            return

        for subnet in network.subnets:
            if subnet.enable_dhcp:
                if self.call_driver('enable', network):
                    self.update_isolated_metadata_proxy(network)
                    self.cache.put(network)
                    # After enabling dhcp for network, mark all existing
                    # ports as ready. So that the status of ports which are
                    # created before enabling dhcp can be updated.
                    self.dhcp_ready_ports |= {p.id for p in network.ports}
                break

    def call_driver(self, action, network, **action_kwargs):
        """Invoke an action on a DHCP driver instance."""
        LOG.debug('Calling driver for network: %(net)s action: %(action)s',
                  {'net': network.id, 'action': action})
        try:
            # the Driver expects something that is duck typed similar to
            # the base models.
            driver = self.dhcp_driver_cls(self.conf,
                                          network,
                                          self._process_monitor,
                                          self.dhcp_version,
                                          self.plugin_rpc)
            getattr(driver, action)(**action_kwargs)
            return True
        except exceptions.Conflict:
            # No need to resync here, the agent will receive the event related
            # to a status update for the network
            LOG.debug('Unable to %(action)s dhcp for %(net_id)s: there '
                      'is a conflict with its current state; please '
                      'check that the network and/or its subnet(s) '
                      'still exist.', {'net_id': network.id, 'action': action})
        except exceptions.SubnetMismatchForPort as e:
            # FIXME(kevinbenton): get rid of this once bug/1627480 is fixed
            LOG.debug("Error configuring DHCP port, scheduling resync: %s", e)
            self.schedule_resync(e, network.id)
        except Exception as e:
            if getattr(e, 'exc_type', '') != 'IpAddressGenerationFailure':
                # Don't resync if port could not be created because of an IP
                # allocation failure. When the subnet is updated with a new
                # allocation pool or a port is  deleted to free up an IP, this
                # will automatically be retried on the notification
                self.schedule_resync(e, network.id)
            if (isinstance(e, oslo_messaging.RemoteError)
                and e.exc_type == 'NetworkNotFound'
                or isinstance(e, exceptions.NetworkNotFound)):
                LOG.debug("Network %s has been deleted.", network.id)
            else:
                LOG.exception('Unable to %(action)s dhcp for %(net_id)s.',
                              {'net_id': network.id, 'action': action})

現在找到了self.call_driver根據網絡和端口的變化，會調用/neutron/linux/dhcp.py代碼

   def enable(self):
        """Enables DHCP for this network by spawning a local process."""
        if self.active:
            self.restart()
        elif self._enable_dhcp():
            fileutils.ensure_tree(self.network_conf_dir, mode=0o755)
            interface_name = self.device_manager.setup(self.network)
            self.interface_name = interface_name
            self.spawn_process()

具體的C 在這個函數 def _build_cmdline_callback 也是/neutron/linux/dhcp.py下