基于P版本，对卷基于快照进行恢复的源码分析
1、特性描述
在pike版本中，openstack官网增加了一个新特性，Cinder volume revert to snapshot，该特性支持将卷恢复到最近的快照。还原过程将覆盖卷的当前状态和数据。如果在快照之后对卷进行了扩展，那么请求将被拒绝。该特性的目的是让用户能够更方便地恢复实例和卷，并减少停机时间。
2、api接口参数样例
POST /v3/{project_id}/volumes/{volume_id}/action
恢复一个卷到它自己最新的快照，这个接口仅仅支持恢复卸载的卷，并且卷的状态是有效的
Request Example
{
"revert": {
"snapshot_id": "5aa119a8-d25b-45a7-8d1b-88e127885635"
}
}
3、源码跟踪
cinder-api服务侧的处理
api接口，对http请求的处理
cinder/api/v3/volumes.py
@wsgi.response(http_client.ACCEPTED)
@wsgi.Controller.api_version('3.40')
@wsgi.action('revert')
def revert(self, req, id, body):
"""revert a volume to a snapshot"""
context = req.environ['cinder.context']
self.assert_valid_body(body, 'revert')
snapshot_id = body['revert'].get('snapshot_id')-----------获取用户传入的快照uuid
volume = self.volume_api.get_volume(context, id)-----------通过卷的id，获取卷对象
try:
l_snap = volume.get_latest_snapshot()------读取数据库获取卷最新的快照UUID
except exception.VolumeSnapshotNotFound:
msg = _("Volume %s doesn't have any snapshots.")
raise exc.HTTPBadRequest(explanation=msg % volume.id)
# Ensure volume and snapshot match.
if snapshot_id is None or snapshot_id != l_snap.id:-------判断用户是否输入快照及输入的快照是否为最新的快照
msg = _("Specified snapshot %(s_id)s is None or not "
"the latest one of volume %(v_id)s.")
raise exc.HTTPBadRequest(explanation=msg % {'s_id': snapshot_id,
'v_id': volume.id})
try:
msg = 'Reverting volume %(v_id)s to snapshot %(s_id)s.'
LOG.info(msg, {'v_id': volume.id,
's_id': l_snap.id})
self.volume_api.revert_to_snapshot(context, volume, l_snap)------s1 调用恢复卷快照的接口
except (exception.InvalidVolume, exception.InvalidSnapshot) as e:
raise exc.HTTPConflict(explanation=six.text_type(e))
except exception.VolumeSizeExceedsAvailableQuota as e:
raise exc.HTTPForbidden(explanation=six.text_type(e))
cinder volume模块对请求的处理
cinder/volume/api.py
@wrap_check_policy
def revert_to_snapshot(self, context, volume, snapshot):
"""revert a volume to a snapshot"""
v_res = volume.update_single_status_where(-----------------更新卷的状态由 available 变为 reverting，
'reverting', 'available')
if not v_res:
msg = _("Can't revert volume %s to its latest snapshot. "
"Volume's status must be 'available'.") % volume.id
raise exception.InvalidVolume(reason=msg)
s_res = snapshot.update_single_status_where(------------更新快照的状态由available 变为 restoring
fields.SnapshotStatus.RESTORING,
fields.SnapshotStatus.AVAILABLE)
if not s_res:
msg = _("Can't revert volume %s to its latest snapshot. "
"Snapshot's status must be 'available'.") % snapshot.id
raise exception.InvalidSnapshot(reason=msg)
self.volume_rpcapi.revert_to_snapshot(context, volume, snapshot)--------s2调用cinder volume的rpc接口
调用rpc接口
cinder/volume/rpcapi.py
@rpc.assert_min_rpc_version('3.15')
def revert_to_snapshot(self, ctxt, volume, snapshot):
version = self._compat_ver('3.15')
cctxt = self._get_cctxt(volume.host, version)
cctxt.cast(ctxt, 'revert_to_snapshot', volume=volume,snapshot=snapshot)
cinder-voume侧接受到rpc请求，对rpc信息进行处理
cinder/volume/manager.py
def revert_to_snapshot(self, context, volume, snapshot):
"""Revert a volume to a snapshot.
The process of reverting to snapshot consists of several steps:
1. create a snapshot for backup (in case of data loss) 为了防止数据丢失创建一个快照的备份
2.1. use driver's specific logic to revert volume 调用驱动的revert_to_snapshot接口来恢复卷
2.2. try the generic way to revert volume if driver's method is missing 如果驱动的revert_to_snapshot 方法没有，那么就使用一般的方式去恢复卷
3. delete the backup snapshot 删除快照的备份
"""
backup_snapshot = None
try:
LOG.info("Start to perform revert to snapshot process.")
# Create a snapshot which can be used to restore the volume
# data by hand if revert process failed.
backup_snapshot = self._create_backup_snapshot(context, volume)---------创建卷的快照的备份
self._revert_to_snapshot(context, volume, snapshot)--------------s1 执行快照的恢复
except
...........
v_res = volume.update_single_status_where('available', 'reverting')-----------把卷的状态由reverting更新为available
if not v_res:
msg_args = {"id": volume.id,
"status": 'available'}
msg = _("Revert finished, but failed to reset "----------底层恢复完了，但是状态的状态没有设置成功，需要手动设置
"volume %(id)s status to %(status)s, "
"please manually reset it.") % msg_args
raise exception.BadResetResourceStatus(message=msg)
s_res = snapshot.update_single_status_where(---------------把快照的状态由reverting更新为available
fields.SnapshotStatus.AVAILABLE,
fields.SnapshotStatus.RESTORING)
if not s_res:
msg_args = {"id": snapshot.id,
"status":
fields.SnapshotStatus.AVAILABLE}
msg = _("Revert finished, but failed to reset "-----------底层恢复完成，但是快照的状态没有设置成功，需要手动设置
"snapshot %(id)s status to %(status)s, "
"please manually reset it.") % msg_args
raise exception.BadResetResourceStatus(message=msg)
if backup_snapshot:
self.delete_snapshot(context,----------------------删除备份的快照
backup_snapshot, handle_quota=False)
msg = ('Volume %(v_id)s reverted to snapshot %(snap_id)s '
'successfully.')
msg_args = {'v_id': volume.id, 'snap_id': snapshot.id}
LOG.info(msg, msg_args)
cinder/volume/manager.py
def _revert_to_snapshot(self, context, volume, snapshot):
"""Use driver or generic method to rollback volume."""
self._notify_about_volume_usage(context, volume, "revert.start")
self._notify_about_snapshot_usage(context, snapshot, "revert.start")
try:
self.driver.revert_to_snapshot(context, volume, snapshot)------调用相关驱动去恢复快照
except (NotImplementedError, AttributeError):
LOG.info("Driver's 'revert_to_snapshot' is not found. "
"Try to use copy-snapshot-to-volume method.")
self._revert_to_snapshot_generic(context, volume, snapshot)----------没有实现revert_to_snapshot功能，那么走一般路径ceph调用的就是这个
self._notify_about_volume_usage(context, volume, "revert.end")
self._notify_about_snapshot_usage(context, snapshot, "revert.end")
基于lvm的驱动
cinder/volume/drivers/lvm.py
def revert_to_snapshot(self, context, volume, snapshot):
"""Revert a volume to a snapshot"""
# NOTE(tommylikehu): We still can revert the volume because Cinder
# will try the alternative approach if 'NotImplementedError'
# is raised here.
if self.configuration.lvm_type == 'thin':--------如果lvm配置成thin，那么不支持快照恢复
msg = _("Revert volume to snapshot not implemented for thin LVM.")
raise NotImplementedError(msg)
else:
self.vg.revert(self._escape_snapshot(snapshot.name))-----执行的是lvconvert --merge命令，合并快照到原始卷中，此时这个快照会被销毁
self.vg.deactivate_lv(volume.name)------执行的是lvchange -a n命令，表示更改lv卷的状态为无效，lvchange表示更改lv的活动状态，y表示lv活动或有效，n表示lv不活动或无效
self.vg.activate_lv(volume.name)--------执行的是lvchange -a y --yes，表示更改lv卷的状态为有效状态，--yes表示不提示确认互动，直接认为是，
# Recreate the snapshot that was destroyed by the revert
self.create_snapshot(snapshot)-----------创建快照
由于ceph目前没有实现revert_to_snapshot方法，因此调用_revert_to_snapshot_generic接口
cinder/volume/manager.py
def _revert_to_snapshot_generic(self, ctxt, volume, snapshot):
"""Generic way to revert volume to a snapshot.
the framework will use the generic way to implement the revert
to snapshot feature:
1. create a temporary volume from snapshot-----从快照创建一个临时的卷
2. mount two volumes to host--------------挂载两个卷到主机上
3. copy data from temporary volume to original volume--------从临时卷拷贝数据到原始卷中
4. detach and destroy temporary volume----------卸载并销毁临时卷
"""
temp_vol = None
try:
v_options = {'display_name': '[revert] temporary volume created '
'from snapshot %s' % snapshot.id}
ctxt = context.get_internal_tenant_context() or ctxt
temp_vol = self.driver._create_temp_volume_from_snapshot(--------通过快照创建临时卷
ctxt, volume, snapshot, volume_options=v_options)
self._copy_volume_data(ctxt, temp_vol, volume)-------从临时卷拷贝数据到原始卷，这个过程会分三个小步骤：挂载原始卷和临时卷；从临时卷拷贝数据到原始卷；
卸载临时卷和原始卷
self.driver.delete_volume(temp_vol)-----删除临时卷
temp_vol.destroy()
except Exception:
with excutils.save_and_reraise_exception():
LOG.exception(
"Failed to use snapshot %(snapshot)s to create "
"a temporary volume and copy data to volume "
" %(volume)s.",
{'snapshot': snapshot.id,
'volume': volume.id})
if temp_vol and temp_vol.status == 'available':
self.driver.delete_volume(temp_vol)
temp_vol.destroy()
