vdsm的network模块中的dhcp-monitor

dhcp_monitor 是 VDSM 的 network 模块中的一部分，这里单独记录下源码分析。

def initialize_monitor(cif):
    global _monitor_instance
    try:
        monitor = Monitor.instance()
        monitor.add_handler(lambda event: _dhcp_event_handler(cif, event))
        monitor.start()
    except Exception as e:
        _monitor_instance = None
        raise e
Monitor 的 add_handler 接收了一个 event 作为 handler，然后在 monitor 的 init 函数中会通过 serve_forever 去执行这个方法
    def handle_event(self, event):
        for handler in self._handlers:
            handler(event)

    def serve_forever(self):
        for event in self._nl_monitor:
            self.handle_event(event)

对应到前面，执行这个 _dhcp_event_handler，其中 address.address, address.prefixlen 对应 ip address 和 network mask。这里的 address 和 iface 是从 event 中读取的，EventField.IFACE 和 EventField.ADDRESS 是常量：

class EventField(object):
    class Scope(object):
        KEY = 'scope'
        GLOBAL = 'global'

    class Event(object):
        KEY = 'event'
        NEW_ADDR = 'new_addr'

    class Family(object):
        KEY = 'family'
        IPV4 = 'inet'
        IPV6 = 'inet6'

    ADDRESS = 'address'
    IFACE = 'label'

def _dhcp_event_handler(cif, event):
    if not _is_valid_event(event):
        return

    pool = MonitoredItemPool.instance()

    iface = event[EventField.IFACE]
    family = _get_event_family(event.get(EventField.Family.KEY))
    address = IPAddressData(event[EventField.ADDRESS], iface)
    item = (iface, family)

    if not pool.is_item_in_pool(item):
        logging.warning(
            'Nic %s is not configured for IPv%s monitoring.', iface, family
        )
        return

    if family == 4:
        add_dynamic_source_route_rules(
            iface, address.address, address.prefixlen
        )

    cif.notify('|net|host_conn|no_id')
    pool.remove(item)

然后 add_dynamic_source_route_rules -> _setup_desired_state -> setup -> state_apply， state_apply 是 libnmstate 的方法，也就是设置网络的期望状态（声明式网络管理器API），也就是说，这里提交了该物理机期望的网络状态，提交给 nmstate，由 nmstate 去设置。

def add_dynamic_source_route_rules(next_hop, ipaddr, mask):
    if not _should_add_source_route_rules(next_hop):
        return

    _setup_desired_state(
        generate_dynamic_source_route_rule_state(
            next_hop, ipaddr, mask
        ).state()
    )

generate_dynamic_source_route_rule_state 用于生成网络配置信息。

def generate_dynamic_source_route_rule_state(next_hop, ipaddr, mask):
    helper = SourceRouteHelper(next_hop, ipaddr, mask, None)
    return NetworkingState(route_rules_state=helper.rules_state())

查看helper ，目前只支持 IPv4 的 source routing

# FIXME: Currently we are supporting only IPv4 source routing
class SourceRouteHelper(object):
    def __init__(self, next_hop, ipaddr, mask, gateway):
        self._next_hop = next_hop
        self._ipaddr = ipaddr
        self._mask = mask
        self._gateway = gateway

        self._table_id = generate_table_id(next_hop) if next_hop else None
        self._network = self._parse_network()

    def _parse_network(self):
        if not self._ipaddr or not self._mask:
            return None

        return str(
            ipaddress.ip_interface(f'{self._ipaddr}/{self._mask}').network
        )

最后调用 NetworkingState 生成了一个 networkingstate 对象，里面设置了 ip，mask，gateway。
此时 NetworkingState 对象的其它方法就可以通过 network api 去调用，去修改 vdsm host 网络的信息。比如
lib/vdsm/network/nmstate/state.py 中的 update_mtu() 方法，在 lib/vdsm/network/nmstate/api.py 中的 generate_state 接口调用，而 generate_state 在 lib/vdsm/network/netswitch/configurator.py 的 _setup_nmstate 中调用，一直到最上层，就是 setupNetworks 接口。

Cif 的 notify 方法位置：
lib/vdsm/clientIF.py 中的 notify

def notify(self, event_id, params=None):
    """
    Send notification using provided subscription id as
    event_id and a dictionary as event body. Before sending
    there is notify_time added on top level to the dictionary.

    Please consult event-schema.yml in order to build an appropriate event.
    https://github.com/oVirt/vdsm/blob/master/lib/api/vdsm-events.yml

    Args:
        event_id (string): unique event name
        params (dict): event content
    """
    if not params:
        params = {}

    if not self.ready:
        self.log.warning('Not ready yet, ignoring event %r args=%r',
                         event_id, params)
        return

    json_binding = self.servers['jsonrpc']

    def _send_notification(message):
        json_binding.reactor.server.send(
            message, config.get('addresses', 'event_queue'))

    try:
        notification = Notification(event_id, _send_notification,
                                    json_binding.bridge.event_schema)
        notification.emit(params)
        self.log.debug("Sending notification %s with params %s ",
                       event_id, params)
    except KeyError:
        self.log.warning("Attempt to send an event when jsonrpc binding"
                         " not available")

跟网络相关的，很多地方使用 event.get() 获取的数据，_event 是从 _nl_monitor 中获取的

lib/vdsm/network/dhcp_monitor.py 
    def add_handler(self, handler):
        self._handlers.append(handler)

    def handle_event(self, event):
        for handler in self._handlers:
            handler(event)

    def serve_forever(self):
        for event in self._nl_monitor:
            self.handle_event(event)

nl_monitor 实际上是 lib/vdsm/network/netlink/monitor.py 中的 Monitor，而这个 Monitor 实际上是 netlink 的 monitor，跟 libnl.GROUPS 对应。netlink 参考 Netlink 和 libnl 基础