openstack-nova-虚机挂载云盘过程以及源码分析

本文基于openstack Stein 版本

nova 侧虚机需要挂载云盘，包括创建时挂载系统盘以及普通数据盘

代码在 nova\compute]manager.py, nova 获取volume信息，并发起attach请求，最终调用cinder api发起了attach请求。

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nova.compute.manager.ComputeManager._attach_volume:
    try:
            bdm.attach(context, instance, self.volume_api, self.driver,
                       do_driver_attach=True)
    ......................................
    
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nova.virt.block_device.DriverVolumeBlockDevice.attach
def attach(self, context, instance, volume_api, virt_driver,
               do_driver_attach=False, **kwargs):
     ...................................
            self._do_attach(context, instance, volume, volume_api,
                            virt_driver, do_driver_attach)
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nova.virt.block_device.DriverVolumeBlockDevice.attach_volume
def _do_attach(self, context, instance, volume, volume_api, virt_driver,
                   do_driver_attach):
      ...................
            self._legacy_volume_attach(context, volume, connector, instance,
      ..........................

这里没有attachment id调用了_legacy_volume_attach

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nova.virt.block_device.DriverVolumeBlockDevice._legacy_volume_attach
def _legacy_volume_attach(self, context, volume, connector, instance,
                              volume_api, virt_driver,
                              do_driver_attach=False):
        volume_id = volume['id']

        connection_info = volume_api.initialize_connection(context,
                                                           volume_id,
                                                           connector)  #调用cinder client初始化connection连接信息
       .....................................................................
            try:
                virt_driver.attach_volume(
                        context, connection_info, instance,
                        self['mount_device'], disk_bus=self['disk_bus'],
                        device_type=self['device_type'], encryption=encryption)  #调用libvirt 连接volume云盘
            except Exception:
                with excutils.save_and_reraise_exception():
                    LOG.exception("Driver failed to attach volume "
                                  "%(volume_id)s at %(mountpoint)s",
                                  {'volume_id': volume_id,
                                   'mountpoint': self['mount_device']},
                                  instance=instance)
                    volume_api.terminate_connection(context, volume_id,
                                                    connector)
        self['connection_info'] = connection_info
        if self.volume_size is None:
            self.volume_size = volume.get('size')

        mode = 'rw'
        if 'data' in connection_info:
            mode = connection_info['data'].get('access_mode', 'rw')
        if volume['attach_status'] == "detached":
            # NOTE(mriedem): save our current state so connection_info is in
            # the database before the volume status goes to 'in-use' because
            # after that we can detach and connection_info is required for
            # detach.
            self.save()
            try:
                volume_api.attach(context, volume_id, instance.uuid,
                                  self['mount_device'], mode=mode)    #挂载云盘
        ...................................
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nova.libvirt.driver.ComputeDriver.attach_volume
    def attach_volume(self, context, connection_info, instance, mountpoint,
                      disk_bus=None, device_type=None, encryption=None):
        guest = self._host.get_guest(instance)

        disk_dev = mountpoint.rpartition("/")[2]
        bdm = {
            'device_name': disk_dev,
            'disk_bus': disk_bus,
            'device_type': device_type}

        # Note(cfb): If the volume has a custom block size, check that
        #            that we are using QEMU/KVM and libvirt >= 0.10.2. The
        #            presence of a block size is considered mandatory by
        #            cinder so we fail if we can't honor the request.
        data = {}
        if ('data' in connection_info):
            data = connection_info['data']
        if ('logical_block_size' in data or 'physical_block_size' in data):
            if ((CONF.libvirt.virt_type != "kvm" and
                 CONF.libvirt.virt_type != "qemu")):
                msg = _("Volume sets block size, but the current "
                        "libvirt hypervisor '%s' does not support custom "
                        "block size") % CONF.libvirt.virt_type
                raise exception.InvalidHypervisorType(msg)

        self._connect_volume(context, connection_info, instance,
                             encryption=encryption)

上面从nova收到请求，到调用cinder client 挂载云盘，再到libvirt 连接volume，从而虚机可以识别到磁盘，至此完成！