（4）理解 neutron ml2---port创建流程代码解析

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)