Volume创建过程源码解读

完成volume创建的入口在VolumeManager类的create_volume()函数

#cinder/volume/manager.py
class VolumeManager(manager.SchedulerDependentManager):
    """Manages attachable block storage devices."""
    def create_volume(self, context, volume_id, request_spec=None,
                      filter_properties=None, allow_reschedule=True,
                      snapshot_id=None, image_id=None, source_volid=None,
                      source_replicaid=None, consistencygroup_id=None):
        try:
            # NOTE(flaper87): Driver initialization is
            # verified by the task itself.
            flow_engine = create_volume.get_flow(
                context,
                self.db,
                self.driver,
                self.scheduler_rpcapi,
                self.host,
                volume_id,
                snapshot_id=snapshot_id,
                image_id=image_id,
                source_volid=source_volid,
                source_replicaid=source_replicaid,
                consistencygroup_id=consistencygroup_id,
                allow_reschedule=allow_reschedule,
                reschedule_context=context_saved,
                request_spec=request_spec,
                filter_properties=filter_properties)

create_volume()函数主要工作就是利用TaskFlow库构建卷的flow并执行。

# cinder/volume/flows/manager/create_volume.py
def get_flow(context, db, driver, scheduler_rpcapi, host, volume_id,
             allow_reschedule, reschedule_context, request_spec,
             filter_properties, snapshot_id=None, image_id=None,
             source_volid=None, source_replicaid=None,
             consistencygroup_id=None):
    volume_flow.add(ExtractVolumeSpecTask(db),
                    NotifyVolumeActionTask(db, "create.start"),
                    CreateVolumeFromSpecTask(db, driver),
                    CreateVolumeOnFinishTask(db, "create.end"))
return taskflow.engines.load(volume_flow, store=create_what)

创建Volume的flow共添加了4个task：ExtractVolumeSpecTask、NotifyVolumeActionTask、CreateVolumeFromSpecTask、CreateVolumeOnFinishTask。

其中最重要的是CreateVolumeFromSpecTask，它根据要求实现卷的创建。

# cinder/volume/flows/manager/create_volume.py
class CreateVolumeFromSpecTask(flow_utils.CinderTask):
    """Creates a volume from a provided specification.
    def execute(self, context, volume_ref, volume_spec):
        if create_type == 'raw':
            model_update = self._create_raw_volume(context,
                                                   volume_ref=volume_ref,
                                                   **volume_spec)
        elif create_type == 'snap':
            model_update = self._create_from_snapshot(context,
                                                      volume_ref=volume_ref,
                                                      **volume_spec)
        elif create_type == 'source_vol':
            model_update = self._create_from_source_volume(
                context, volume_ref=volume_ref, **volume_spec)
        elif create_type == 'source_replica':
            model_update = self._create_from_source_replica(
                context, volume_ref=volume_ref, **volume_spec)
        elif create_type == 'image':
            model_update = self._create_from_image(context,
                                                   volume_ref=volume_ref,
                                                   **volume_spec)
            raise
        return volume_ref

CreateVolumeFromSpecTask区分了5种创建Volume的方式：建立raw格式的新卷，从快照建立新卷，从已有卷建立新卷，从副本建立新卷，从镜像建立新卷。

对于建立raw格式新卷的情况，将直接调用指定Driver的create_volume()函数进行创建。

    def _create_raw_volume(self, context, volume_ref, **kwargs):
        return self.driver.create_volume(volume_ref)

对于默认的LVMISCSIDriver，就是直接调用”lvcreate”命令创建Volume。

# cinder/volume/drivers/lvm.py
class LVMVolumeDriver(driver.VolumeDriver):
    def _create_volume(self, name, size, lvm_type, mirror_count, vg=None):
        vg_ref = self.vg
        if vg is not None:
            vg_ref = vg
        vg_ref.create_volume(name, size, lvm_type, mirror_count)
    def create_volume(self, volume):
        """Creates a logical volume."""
        mirror_count = 0
        if self.configuration.lvm_mirrors:
            mirror_count = self.configuration.lvm_mirrors
        self._create_volume(volume['name'],
                            self._sizestr(volume['size']),
                            self.configuration.lvm_type,
                            mirror_count)

到此，一个新的Volume被创建成功，此后，Nova会根据这个Volume的ID调用cinder.volume.manager.VolumeManager.initialize_conneion(),该函数会根据指定的方式（比如默认TGT）创建iSCSI Target，并返回Target的相关信息，比如iSCSI的iqn，之后Nova就可以通过该存储节点的IP地址和iqn来连接并且挂载这个Volume。