port是neutron的核心资源之一，port的主要目的是承载Mac地址和ip地址。

有了Mac和ip地址虚拟机才能够实现彼此之间的通信。当然port不一定是

仅仅给虚拟机使用，也可能将port绑定在路由器上。一个port一定是属于一个

networks的，但是一个port有可能属于多个subnets，属于多个subnets意味着

一个网卡可以有多个ip地址，在创建虚拟机绑定网络的时候可以指定挂载的网卡

和对应的fixed_ip。

 

网卡创建的代码依然是放在了plugin.py这个文件里

/neutron/plugins/ml2/plugin.py

@utils.transaction_guard@db_api.retry_if_session_inactive()def create_port(self, context, port):    result, mech_context = self._create_port_db(context, port)    # notify any plugin that is interested in port create events    kwargs = {
    'context': context, 'port': result}    registry.notify(resources.PORT, events.AFTER_CREATE, self, **kwargs)    try:        self.mechanism_manager.create_port_postcommit(mech_context)    except ml2_exc.MechanismDriverError:        with excutils.save_and_reraise_exception():            LOG.error(_LE("mechanism_manager.create_port_postcommit "                          "failed, deleting port '%s'"), result['id'])            self.delete_port(context, result['id'], l3_port_check=False)    self.notify_security_groups_member_updated(context, result)    try:        bound_context = self._bind_port_if_needed(mech_context)    except os_db_exception.DBDeadlock:        # bind port can deadlock in normal operation so we just cleanup        # the port and let the API retry        with excutils.save_and_reraise_exception():            LOG.debug("_bind_port_if_needed deadlock, deleting port %s",                      result['id'])            self.delete_port(context, result['id'])    except ml2_exc.MechanismDriverError:        with excutils.save_and_reraise_exception():            LOG.error(_LE("_bind_port_if_needed "                          "failed, deleting port '%s'"), result['id'])            self.delete_port(context, result['id'], l3_port_check=False)    return bound_context.current

其中最重要的是上面四个步骤，最最重要的是_create_port_db这个函数。

def _create_port_db(self, context, port):    attrs = port[attributes.PORT]    if not attrs.get('status'):        attrs['status'] = const.PORT_STATUS_DOWN    session = context.session    with session.begin(subtransactions=True):        dhcp_opts = attrs.get(edo_ext.EXTRADHCPOPTS, [])        port_db = self.create_port_db(context, port)        result = self._make_port_dict(port_db, process_extensions=False)        self.extension_manager.process_create_port(context, attrs, result)        self._portsec_ext_port_create_processing(context, result, port)        # sgids must be got after portsec checked with security group        sgids = self._get_security_groups_on_port(context, port)        self._process_port_create_security_group(context, result, sgids)        network = self.get_network(context, result['network_id'])        binding = db.add_port_binding(session, result['id'])        mech_context = driver_context.PortContext(self, context, result,                                                  network, binding, None)        self._process_port_binding(mech_context, attrs)        result[addr_pair.ADDRESS_PAIRS] = (            self._process_create_allowed_address_pairs(                context, result,                attrs.get(addr_pair.ADDRESS_PAIRS)))        self._process_port_create_extra_dhcp_opts(context, result,                                                  dhcp_opts)        self.mechanism_manager.create_port_precommit(mech_context)        self._setup_dhcp_agent_provisioning_component(context, result)    self._apply_dict_extend_functions('ports', result, port_db)    return result, mech_context

如上图所示_create_port_db做了很多和安全组以及port_binding相关的工作：主要是将port，security_group, port_binding等相关数据存入数据库，从中可以总结出ml2关于数据库

操作的逻辑，涉及数据存储到数据库的工作都会放在_create_xxx_db（xxx代表subnet, port, network等）函数内部进行操作。比如这里的创建_create_port_db。

db.add_port_binding(session, result['id']) 这句话处理port_binding相关的入库工作。具体代码如下所示：

def add_port_binding(session, port_id):    with session.begin(subtransactions=True):        record = models.PortBinding(            port_id=port_id,            vif_type=portbindings.VIF_TYPE_UNBOUND)        session.add(record)        return record

 

create_port_db则处理的是port本身的入库逻辑。port的创建有一个比较重要的逻辑就是分配ip地址，ip地址和mac地址是port这个资源模型所要承载的最终要的两个数据。

 下面看一下分配ip地址的代码：

def allocate_ips_for_port_and_store(self, context, port, port_id):    # Make a copy of port dict to prevent changing    # incoming dict by adding 'id' to it.    # Deepcopy doesn't work correctly in this case, because copy of    # ATTR_NOT_SPECIFIED object happens. Address of copied object doesn't    # match original object, so 'is' check fails    port_copy = {
     'port': port['port'].copy()}    port_copy['port']['id'] = port_id    network_id = port_copy['port']['network_id']    ips = []    try:        ips = self._allocate_ips_for_port(context, port_copy)        for ip in ips:            ip_address = ip['ip_address']            subnet_id = ip['subnet_id']            IpamPluggableBackend._store_ip_allocation(                context, ip_address, network_id,                subnet_id, port_id)        return ips    except Exception:        with excutils.save_and_reraise_exception():            if ips:                ipam_driver = driver.Pool.get_instance(None, context)                if not ipam_driver.needs_rollback():                    return                LOG.debug("An exception occurred during port creation. "                          "Reverting IP allocation")                self._safe_rollback(self._ipam_deallocate_ips, context,                                    ipam_driver, port_copy['port'], ips,                                    revert_on_fail=False)