基於P版本，對卷基於快照進行恢復的源碼分析
1、特性描述
在pike版本中，openstack官網增加了一個新特性，Cinder volume revert to snapshot，該特性支持將卷恢復到最近的快照。還原過程將覆蓋卷的當前狀態和數據。如果在快照之后對卷進行了擴展，那么請求將被拒絕。該特性的目的是讓用戶能夠更方便地恢復實例和卷，並減少停機時間。
2、api接口參數樣例
POST /v3/{project_id}/volumes/{volume_id}/action
恢復一個卷到它自己最新的快照，這個接口僅僅支持恢復卸載的卷，並且卷的狀態是有效的
Request Example
{
"revert": {
"snapshot_id": "5aa119a8-d25b-45a7-8d1b-88e127885635"
}
}
3、源碼跟蹤
cinder-api服務側的處理
api接口，對http請求的處理
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')-----------獲取用戶傳入的快照uuid
volume = self.volume_api.get_volume(context, id)-----------通過卷的id，獲取卷對象
try:
l_snap = volume.get_latest_snapshot()------讀取數據庫獲取卷最新的快照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:-------判斷用戶是否輸入快照及輸入的快照是否為最新的快照
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 調用恢復卷快照的接口
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模塊對請求的處理
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(-----------------更新卷的狀態由 available 變為 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(------------更新快照的狀態由available 變為 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調用cinder volume的rpc接口
調用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側接受到rpc請求，對rpc信息進行處理
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) 為了防止數據丟失創建一個快照的備份
2.1. use driver's specific logic to revert volume 調用驅動的revert_to_snapshot接口來恢復卷
2.2. try the generic way to revert volume if driver's method is missing 如果驅動的revert_to_snapshot 方法沒有，那么就使用一般的方式去恢復卷
3. delete the backup snapshot 刪除快照的備份
"""
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)---------創建卷的快照的備份
self._revert_to_snapshot(context, volume, snapshot)--------------s1 執行快照的恢復
except
...........
v_res = volume.update_single_status_where('available', 'reverting')-----------把卷的狀態由reverting更新為available
if not v_res:
msg_args = {"id": volume.id,
"status": 'available'}
msg = _("Revert finished, but failed to reset "----------底層恢復完了，但是狀態的狀態沒有設置成功，需要手動設置
"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(---------------把快照的狀態由reverting更新為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 "-----------底層恢復完成，但是快照的狀態沒有設置成功，需要手動設置
"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,----------------------刪除備份的快照
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)------調用相關驅動去恢復快照
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)----------沒有實現revert_to_snapshot功能，那么走一般路徑ceph調用的就是這個
self._notify_about_volume_usage(context, volume, "revert.end")
self._notify_about_snapshot_usage(context, snapshot, "revert.end")
基於lvm的驅動
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，那么不支持快照恢復
msg = _("Revert volume to snapshot not implemented for thin LVM.")
raise NotImplementedError(msg)
else:
self.vg.revert(self._escape_snapshot(snapshot.name))-----執行的是lvconvert --merge命令，合並快照到原始卷中，此時這個快照會被銷毀
self.vg.deactivate_lv(volume.name)------執行的是lvchange -a n命令，表示更改lv卷的狀態為無效，lvchange表示更改lv的活動狀態，y表示lv活動或有效，n表示lv不活動或無效
self.vg.activate_lv(volume.name)--------執行的是lvchange -a y --yes，表示更改lv卷的狀態為有效狀態，--yes表示不提示確認互動，直接認為是，
# Recreate the snapshot that was destroyed by the revert
self.create_snapshot(snapshot)-----------創建快照
由於ceph目前沒有實現revert_to_snapshot方法，因此調用_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-----從快照創建一個臨時的卷
2. mount two volumes to host--------------掛載兩個卷到主機上
3. copy data from temporary volume to original volume--------從臨時卷拷貝數據到原始卷中
4. detach and destroy temporary volume----------卸載並銷毀臨時卷
"""
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(--------通過快照創建臨時卷
ctxt, volume, snapshot, volume_options=v_options)
self._copy_volume_data(ctxt, temp_vol, volume)-------從臨時卷拷貝數據到原始卷，這個過程會分三個小步驟：掛載原始卷和臨時卷；從臨時卷拷貝數據到原始卷；
卸載臨時卷和原始卷
self.driver.delete_volume(temp_vol)-----刪除臨時卷
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()