feat(zfspv): adding snapshot and clone support for ZFSPV (#39)

This commits support snapshot and clone commands via CSI driver. User can create snap and clone using the following steps. 

Note:
- Snapshot is created via reconciliation CR
- Cloned volume will be on the same zpool where the snapshot is taken
- Cloned volume will have same properties as source volume. 

-----------------------------------
Create a Snapshotclass
```
kind: VolumeSnapshotClass
apiVersion: snapshot.storage.k8s.io/v1beta1
metadata:
  name: zfspv-snapclass
  annotations:
    snapshot.storage.kubernetes.io/is-default-class: "true"
driver: zfs.csi.openebs.io
deletionPolicy: Delete
```
Once snapshotclass is created, we can use this class to create a Snapshot 
```
apiVersion: snapshot.storage.k8s.io/v1beta1
kind: VolumeSnapshot
metadata:
  name: zfspv-snap
spec:
  volumeSnapshotClassName: zfspv-snapclass
  source:
    persistentVolumeClaimName: csi-zfspv
```
```
$ kubectl get volumesnapshot
NAME          AGE
zfspv-snap    7m52s
```
```
$ kubectl get volumesnapshot -o yaml
apiVersion: v1
items:
- apiVersion: snapshot.storage.k8s.io/v1beta1
  kind: VolumeSnapshot
  metadata:
    annotations:
      kubectl.kubernetes.io/last-applied-configuration: |
        {"apiVersion":"snapshot.storage.k8s.io/v1beta1","kind":"VolumeSnapshot","metadata":{"annotations":{},"name":"zfspv-snap","namespace":"default"},"spec":{"source":{"persistentVolumeClaimName":"csi-zfspv"},"volumeSnapshotClassName":"zfspv-snapclass"}}
    creationTimestamp: "2020-01-30T10:31:24Z"
    finalizers:
    - snapshot.storage.kubernetes.io/volumesnapshot-as-source-protection
    - snapshot.storage.kubernetes.io/volumesnapshot-bound-protection
    generation: 1
    name: zfspv-snap
    namespace: default
    resourceVersion: "30040"
    selfLink: /apis/snapshot.storage.k8s.io/v1beta1/namespaces/default/volumesnapshots/zfspv-snap
    uid: 1a5cf166-c599-4f58-9f3c-f1148be47fca
  spec:
    source:
      persistentVolumeClaimName: csi-zfspv
    volumeSnapshotClassName: zfspv-snapclass
  status:
    boundVolumeSnapshotContentName: snapcontent-1a5cf166-c599-4f58-9f3c-f1148be47fca
    creationTime: "2020-01-30T10:31:24Z"
    readyToUse: true
    restoreSize: "0"
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""
```


Openebs resource for the created snapshot 
```
$ kubectl get snap -n openebs -o yaml
apiVersion: v1
items:
- apiVersion: openebs.io/v1alpha1
  kind: ZFSSnapshot
  metadata:
    creationTimestamp: "2020-01-30T10:31:24Z"
    finalizers:
    - zfs.openebs.io/finalizer
    generation: 2
    labels:
      kubernetes.io/nodename: pawan-2
      openebs.io/persistent-volume: pvc-18cab7c3-ec5e-4264-8507-e6f7df4c789a
    name: snapshot-1a5cf166-c599-4f58-9f3c-f1148be47fca
    namespace: openebs
    resourceVersion: "30035"
    selfLink: /apis/openebs.io/v1alpha1/namespaces/openebs/zfssnapshots/snapshot-1a5cf166-c599-4f58-9f3c-f1148be47fca
    uid: e29d571c-42b5-4fb7-9110-e1cfc9b96641
  spec:
    capacity: "4294967296"
    fsType: zfs
    ownerNodeID: pawan-2
    poolName: zfspv-pool
    status: Ready
    volumeType: DATASET
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""
```

Create a clone volume
    
 We can provide a datasource as snapshot name to create a clone volume
    
```yaml
    kind: PersistentVolumeClaim
    apiVersion: v1
    metadata:
      name: zfspv-clone
    spec:
      storageClassName: openebs-zfspv
      dataSource:
        name: zfspv-snap
        kind: VolumeSnapshot
        apiGroup: snapshot.storage.k8s.io
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 4Gi
```
It will create a ZFS clone volume from the mentioned snapshot and create the PV on the same node where original volume is there.
    
Here, As resize is not supported yet, the clone PVC size should match the size of the snapshot.
Also, all the properties from the storageclass will not be considered for the clone case, it will take the properties from the snapshot and create the clone volume. One thing to note here is that, the storageclass in clone PVC should have the same poolname as that of the original volume as across the pool, clone is not supported.


Signed-off-by: Pawan <pawan@mayadata.io>

pkg/mgmt/volume/volume.go

@@ -0,0 +1,257 @@
+/*
+Copyright 2019 The OpenEBS Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package volume
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/Sirupsen/logrus"
+
+	apis "github.com/openebs/zfs-localpv/pkg/apis/openebs.io/core/v1alpha1"
+	zfs "github.com/openebs/zfs-localpv/pkg/zfs"
+	k8serror "k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/client-go/tools/cache"
+)
+
+// isDeletionCandidate checks if a zfs volume is a deletion candidate.
+func (c *ZVController) isDeletionCandidate(zv *apis.ZFSVolume) bool {
+	return zv.ObjectMeta.DeletionTimestamp != nil
+}
+
+// syncHandler compares the actual state with the desired, and attempts to
+// converge the two.
+func (c *ZVController) syncHandler(key string) error {
+	// Convert the namespace/name string into a distinct namespace and name
+	namespace, name, err := cache.SplitMetaNamespaceKey(key)
+	if err != nil {
+		runtime.HandleError(fmt.Errorf("invalid resource key: %s", key))
+		return nil
+	}
+
+	// Get the zv resource with this namespace/name
+	zv, err := c.zvLister.ZFSVolumes(namespace).Get(name)
+	if k8serror.IsNotFound(err) {
+		runtime.HandleError(fmt.Errorf("zfsvolume '%s' has been deleted", key))
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	zvCopy := zv.DeepCopy()
+	err = c.syncZV(zvCopy)
+	return err
+}
+
+// enqueueZV takes a ZFSVolume resource and converts it into a namespace/name
+// string which is then put onto the work queue. This method should *not* be
+// passed resources of any type other than ZFSVolume.
+func (c *ZVController) enqueueZV(obj interface{}) {
+	var key string
+	var err error
+	if key, err = cache.MetaNamespaceKeyFunc(obj); err != nil {
+		runtime.HandleError(err)
+		return
+	}
+	c.workqueue.Add(key)
+
+}
+
+// synZV is the function which tries to converge to a desired state for the
+// ZFSVolume
+func (c *ZVController) syncZV(zv *apis.ZFSVolume) error {
+	var err error
+	// ZFS Volume should be deleted. Check if deletion timestamp is set
+	if c.isDeletionCandidate(zv) {
+		err = zfs.DestroyVolume(zv)
+		if err == nil {
+			zfs.RemoveZvolFinalizer(zv)
+		}
+	} else {
+		// if finalizer is not set then it means we are creating
+		// the volume. And if it is set then volume has already been
+		// created and this event is for property change only.
+		if zv.Finalizers != nil {
+			err = zfs.SetVolumeProp(zv)
+		} else {
+			if len(zv.Spec.SnapName) > 0 {
+				err = zfs.CreateClone(zv)
+			} else {
+				err = zfs.CreateVolume(zv)
+			}
+			if err == nil {
+				err = zfs.UpdateZvolInfo(zv)
+			}
+		}
+	}
+	return err
+}
+
+// addZV is the add event handler for ZFSVolume
+func (c *ZVController) addZV(obj interface{}) {
+	zv, ok := obj.(*apis.ZFSVolume)
+	if !ok {
+		runtime.HandleError(fmt.Errorf("Couldn't get zv object %#v", obj))
+		return
+	}
+
+	if zfs.NodeID != zv.Spec.OwnerNodeID {
+		return
+	}
+	logrus.Infof("Got add event for ZV %s/%s", zv.Spec.PoolName, zv.Name)
+	c.enqueueZV(zv)
+}
+
+// updateZV is the update event handler for ZFSVolume
+func (c *ZVController) updateZV(oldObj, newObj interface{}) {
+
+	newZV, ok := newObj.(*apis.ZFSVolume)
+	if !ok {
+		runtime.HandleError(fmt.Errorf("Couldn't get zv object %#v", newZV))
+		return
+	}
+
+	if zfs.NodeID != newZV.Spec.OwnerNodeID {
+		return
+	}
+
+	oldZV, ok := oldObj.(*apis.ZFSVolume)
+	if zfs.PropertyChanged(oldZV, newZV) ||
+		c.isDeletionCandidate(newZV) {
+		logrus.Infof("Got update event for ZV %s/%s", newZV.Spec.PoolName, newZV.Name)
+		c.enqueueZV(newZV)
+	}
+}
+
+// deleteZV is the delete event handler for ZFSVolume
+func (c *ZVController) deleteZV(obj interface{}) {
+	zv, ok := obj.(*apis.ZFSVolume)
+	if !ok {
+		tombstone, ok := obj.(cache.DeletedFinalStateUnknown)
+		if !ok {
+			runtime.HandleError(fmt.Errorf("Couldn't get object from tombstone %#v", obj))
+			return
+		}
+		zv, ok = tombstone.Obj.(*apis.ZFSVolume)
+		if !ok {
+			runtime.HandleError(fmt.Errorf("Tombstone contained object that is not a zfsvolume %#v", obj))
+			return
+		}
+	}
+
+	if zfs.NodeID != zv.Spec.OwnerNodeID {
+		return
+	}
+
+	logrus.Infof("Got delete event for ZV %s/%s", zv.Spec.PoolName, zv.Name)
+	c.enqueueZV(zv)
+}
+
+// Run will set up the event handlers for types we are interested in, as well
+// as syncing informer caches and starting workers. It will block until stopCh
+// is closed, at which point it will shutdown the workqueue and wait for
+// workers to finish processing their current work items.
+func (c *ZVController) Run(threadiness int, stopCh <-chan struct{}) error {
+	defer runtime.HandleCrash()
+	defer c.workqueue.ShutDown()
+
+	// Start the informer factories to begin populating the informer caches
+	logrus.Info("Starting ZV controller")
+
+	// Wait for the k8s caches to be synced before starting workers
+	logrus.Info("Waiting for informer caches to sync")
+	if ok := cache.WaitForCacheSync(stopCh, c.zvSynced); !ok {
+		return fmt.Errorf("failed to wait for caches to sync")
+	}
+	logrus.Info("Starting ZV workers")
+	// Launch worker to process ZV resources
+	// Threadiness will decide the number of workers you want to launch to process work items from queue
+	for i := 0; i < threadiness; i++ {
+		go wait.Until(c.runWorker, time.Second, stopCh)
+	}
+
+	logrus.Info("Started ZV workers")
+	<-stopCh
+	logrus.Info("Shutting down ZV workers")
+
+	return nil
+}
+
+// runWorker is a long-running function that will continually call the
+// processNextWorkItem function in order to read and process a message on the
+// workqueue.
+func (c *ZVController) runWorker() {
+	for c.processNextWorkItem() {
+	}
+}
+
+// processNextWorkItem will read a single work item off the workqueue and
+// attempt to process it, by calling the syncHandler.
+func (c *ZVController) processNextWorkItem() bool {
+	obj, shutdown := c.workqueue.Get()
+
+	if shutdown {
+		return false
+	}
+
+	// We wrap this block in a func so we can defer c.workqueue.Done.
+	err := func(obj interface{}) error {
+		// We call Done here so the workqueue knows we have finished
+		// processing this item. We also must remember to call Forget if we
+		// do not want this work item being re-queued. For example, we do
+		// not call Forget if a transient error occurs, instead the item is
+		// put back on the workqueue and attempted again after a back-off
+		// period.
+		defer c.workqueue.Done(obj)
+		var key string
+		var ok bool
+		// We expect strings to come off the workqueue. These are of the
+		// form namespace/name. We do this as the delayed nature of the
+		// workqueue means the items in the informer cache may actually be
+		// more up to date that when the item was initially put onto the
+		// workqueue.
+		if key, ok = obj.(string); !ok {
+			// As the item in the workqueue is actually invalid, we call
+			// Forget here else we'd go into a loop of attempting to
+			// process a work item that is invalid.
+			c.workqueue.Forget(obj)
+			runtime.HandleError(fmt.Errorf("expected string in workqueue but got %#v", obj))
+			return nil
+		}
+		// Run the syncHandler, passing it the namespace/name string of the
+		// ZV resource to be synced.
+		if err := c.syncHandler(key); err != nil {
+			// Put the item back on the workqueue to handle any transient errors.
+			c.workqueue.AddRateLimited(key)
+			return fmt.Errorf("error syncing '%s': %s, requeuing", key, err.Error())
+		}
+		// Finally, if no error occurs we Forget this item so it does not
+		// get queued again until another change happens.
+		c.workqueue.Forget(obj)
+		logrus.Infof("Successfully synced '%s'", key)
+		return nil
+	}(obj)
+
+	if err != nil {
+		runtime.HandleError(err)
+		return true
+	}
+
+	return true
+}