replication & pruning: ditch replicated-property, use bookmark as cursor instead

A bookmark with a well-known name is used to track which version was
last successfully received by the receiver.
The createtxg that can be retrieved from the bookmark using `zfs get` is
used to set the Replicated attribute of each snap on the sender:
If the snap's CreateTXG > the cursor's, it is not yet replicated,
otherwise it has been.

There is an optional config option to change the behvior to
`CreateTXG >= the cursor's`, and the implementation defaults to that.

The reason: While things work just fine with `CreateTXG > the cursor's`,
ZFS does not provide size estimates in a `zfs send` dry run
(see acd2418).
However, to enable the use case of keeping the snapshot only around for
the replication, the config flag exists.

config/config.go

@@ -205,6 +205,7 @@ type PruningEnum struct {
 
 type PruneKeepNotReplicated struct {
 	Type string `yaml:"type"`
+	KeepSnapshotAtCursor bool `yaml:"keep_snapshot_at_cursor,optional,default=true"`
 }
 
 type PruneKeepLastN struct {

daemon/pruner/pruner.go

@@ -9,13 +9,14 @@ import (
 	"github.com/zrepl/zrepl/pruning"
 	"github.com/zrepl/zrepl/replication/pdu"
 	"net"
+	"sort"
 	"sync"
 	"time"
 )
 
 // Try to keep it compatible with gitub.com/zrepl/zrepl/replication.Endpoint
 type History interface {
-	SnapshotReplicationStatus(ctx context.Context, req *pdu.SnapshotReplicationStatusReq) (*pdu.SnapshotReplicationStatusRes, error)
+	ReplicationCursor(ctx context.Context, req *pdu.ReplicationCursorReq) (*pdu.ReplicationCursorRes, error)
 }
 
 type Target interface {
@@ -47,6 +48,7 @@ type args struct {
 	receiver                       History
 	rules                          []pruning.KeepRule
 	retryWait                      time.Duration
+	considerSnapAtCursorReplicated bool
 }
 
 type Pruner struct {
@@ -69,6 +71,7 @@ type PrunerFactory struct {
 	senderRules                    []pruning.KeepRule
 	receiverRules                  []pruning.KeepRule
 	retryWait                      time.Duration
+	considerSnapAtCursorReplicated bool
 }
 
 func checkContainsKeep1(rules []pruning.KeepRule) error {
@@ -95,14 +98,19 @@ func NewPrunerFactory(in config.PruningSenderReceiver) (*PrunerFactory, error) {
 		return nil, errors.Wrap(err, "cannot build sender pruning rules")
 	}
 
-	if err := checkContainsKeep1(keepRulesSender); err != nil {
-		return nil, err
+	considerSnapAtCursorReplicated := false
+	for _, r := range in.KeepSender {
+		knr, ok := r.Ret.(*config.PruneKeepNotReplicated)
+		if !ok {
+			continue
+		}
+		considerSnapAtCursorReplicated = considerSnapAtCursorReplicated || !knr.KeepSnapshotAtCursor
 	}
-
 	f := &PrunerFactory{
 		keepRulesSender,
 		keepRulesReceiver,
 		10 * time.Second, //FIXME constant
+		considerSnapAtCursorReplicated,
 	}
 	return f, nil
 }
@@ -115,6 +123,7 @@ func (f *PrunerFactory) BuildSenderPruner(ctx context.Context, target Target, re
 			receiver,
 			f.senderRules,
 			f.retryWait,
+			f.considerSnapAtCursorReplicated,
 		},
 		state: Plan,
 	}
@@ -129,6 +138,7 @@ func (f *PrunerFactory) BuildReceiverPruner(ctx context.Context, target Target,
 			receiver,
 			f.receiverRules,
 			f.retryWait,
+			false, // senseless here anyways
 		},
 		state: Plan,
 	}
@@ -254,56 +264,66 @@ func statePlan(a *args, u updater) state {
 	}
 
 	pfss := make([]*fs, len(tfss))
+fsloop:
 	for i, tfs := range tfss {
+
+		l := GetLogger(ctx).WithField("fs", tfs.Path)
+		l.Debug("plan filesystem")
+
 		tfsvs, err := target.ListFilesystemVersions(ctx, tfs.Path)
 		if err != nil {
+			l.WithError(err).Error("cannot list filesystem versions")
 			return onErr(u, err)
 		}
 
+		rcReq := &pdu.ReplicationCursorReq{
+			Filesystem: tfs.Path,
+			Op:         &pdu.ReplicationCursorReq_Get{},
+		}
+		rc, err := receiver.ReplicationCursor(ctx, rcReq)
+		if err != nil {
+			l.WithError(err).Error("cannot get replication cursor")
+			return onErr(u, err)
+		}
+		if rc.GetError() != "" {
+			l.WithField("reqErr", rc.GetError()).Error("cannot get replication cursor")
+			return onErr(u, fmt.Errorf("%s", rc.GetError()))
+		}
+
 		pfs := &fs{
 			path:  tfs.Path,
 			snaps: make([]pruning.Snapshot, 0, len(tfsvs)),
 		}
+		pfss[i] = pfs
 
+		// scan from older to newer, all snapshots older than cursor are interpreted as replicated
+		sort.Slice(tfsvs, func(i, j int) bool {
+			return tfsvs[i].CreateTXG < tfsvs[j].CreateTXG
+		})
+		preCursor := true
 		for _, tfsv := range tfsvs {
 			if tfsv.Type != pdu.FilesystemVersion_Snapshot {
 				continue
 			}
 			creation, err := tfsv.CreationAsTime()
 			if err != nil {
-				return onErr(u, fmt.Errorf("%s%s has invalid creation date: %s", tfs, tfsv.RelName(), err))
-			}
-			req := pdu.SnapshotReplicationStatusReq{
-				Filesystem: tfs.Path,
-				Snapshot:   tfsv.Name,
-				Op:         pdu.SnapshotReplicationStatusReq_Get,
-			}
-			res, err := receiver.SnapshotReplicationStatus(ctx, &req)
-			if err != nil {
-				GetLogger(ctx).
-					WithField("req", req.String()).
-					WithError(err).Error("cannot get snapshot replication status")
-			}
-			if err != nil && shouldRetry(err) {
-				return onErr(u, err)
-			} else if err != nil {
-				pfs.err = err
-				pfs.snaps = nil
-				break
-			}
-			if res.Status == pdu.SnapshotReplicationStatusRes_Nonexistent {
-				GetLogger(ctx).
-					Debug("snapshot does not exist in history, assuming was replicated")
+				pfs.err = fmt.Errorf("%s%s has invalid creation date: %s", tfs, tfsv.RelName(), err)
+				l.WithError(pfs.err).Error("")
+				continue fsloop
 			}
+			atCursor := tfsv.Guid == rc.GetGuid()
+			preCursor = preCursor && !atCursor
 			pfs.snaps = append(pfs.snaps, snapshot{
-				replicated: !(res.Status != pdu.SnapshotReplicationStatusRes_Replicated),
+				replicated: preCursor || (a.considerSnapAtCursorReplicated && atCursor),
 				date:       creation,
 				fsv:        tfsv,
 			})
-
 		}
-
-		pfss[i] = pfs
+		if preCursor {
+			pfs.err = fmt.Errorf("replication cursor not found in prune target filesystem versions")
+			l.WithError(pfs.err).Error("")
+			continue fsloop
+		}
 
 	}
 
@@ -324,7 +344,13 @@ func stateExec(a *args, u updater) state {
 	var pfs *fs
 	state := u(func(pruner *Pruner) {
 		if len(pruner.prunePending) == 0 {
-			pruner.state = Done
+			nextState := Done
+			for _, pfs := range pruner.pruneCompleted {
+				if pfs.err != nil {
+					nextState = ErrPerm
+				}
+			}
+			pruner.state = nextState
 			return
 		}
 		pfs = pruner.prunePending[0]

endpoint/endpoint.go

@@ -109,10 +109,7 @@ func (p *Sender) DestroySnapshots(ctx context.Context, req *pdu.DestroySnapshots
 	return doDestroySnapshots(ctx, dp, req.Snapshots)
 }
 
-// Since replication always happens from sender to receiver, this method  is only ipmlemented for the sender.
-// If this method returns a *zfs.DatasetDoesNotExist as an error, it might be a good indicator
-// that something is wrong with the pruning logic, which is the only consumer of this method.
-func (p *Sender) SnapshotReplicationStatus(ctx context.Context, req *pdu.SnapshotReplicationStatusReq) (*pdu.SnapshotReplicationStatusRes, error) {
+func (p *Sender) ReplicationCursor(ctx context.Context, req *pdu.ReplicationCursorReq) (*pdu.ReplicationCursorRes, error) {
 	dp, err := zfs.NewDatasetPath(req.Filesystem)
 	if err != nil {
 		return nil, err
@@ -125,35 +122,25 @@ func (p *Sender) SnapshotReplicationStatus(ctx context.Context, req *pdu.Snapsho
 		return nil, replication.NewFilteredError(req.Filesystem)
 	}
 
-	version := zfs.FilesystemVersion{
-		Type: zfs.Snapshot,
-		Name: req.Snapshot, //FIXME validation
-	}
-
-	var status pdu.SnapshotReplicationStatusRes_Status
-	switch req.Op {
-	case pdu.SnapshotReplicationStatusReq_Get:
-		replicated, err := zfs.ZFSGetReplicatedProperty(dp, &version)
-		if _, ok := err.(*zfs.DatasetDoesNotExist); ok {
-			status = pdu.SnapshotReplicationStatusRes_Nonexistent
-		} else if err != nil {
-
-		}
-		if replicated {
-			status = pdu.SnapshotReplicationStatusRes_Replicated
-		} else {
-			status = pdu.SnapshotReplicationStatusRes_NotReplicated
-		}
-	case pdu.SnapshotReplicationStatusReq_SetReplicated:
-		err = zfs.ZFSSetReplicatedProperty(dp, &version, true)
+	switch op := req.Op.(type) {
+	case *pdu.ReplicationCursorReq_Get:
+		cursor, err := zfs.ZFSGetReplicationCursor(dp)
 		if err != nil {
 			return nil, err
 		}
-		status = pdu.SnapshotReplicationStatusRes_Replicated
-	default:
-		return nil, errors.Errorf("unknown opcode %v", req.Op)
+		if cursor == nil {
+			return &pdu.ReplicationCursorRes{Result: &pdu.ReplicationCursorRes_Error{Error: "cursor does not exist"}}, nil
+		}
+		return &pdu.ReplicationCursorRes{Result: &pdu.ReplicationCursorRes_Guid{cursor.Guid}}, nil
+	case *pdu.ReplicationCursorReq_Set:
+		guid, err := zfs.ZFSSetReplicationCursor(dp, op.Set.Snapshot)
+		if err != nil {
+			return nil, err
+		}
+		return &pdu.ReplicationCursorRes{Result: &pdu.ReplicationCursorRes_Guid{Guid: guid}}, nil
+	default:
+		return nil, errors.Errorf("unknown op %T", op)
 	}
-	return &pdu.SnapshotReplicationStatusRes{Status: status}, nil
 }
 
 type FSFilter interface {
@@ -352,7 +339,7 @@ const (
 	RPCReceive                = "Receive"
 	RPCSend                   = "Send"
 	RPCSDestroySnapshots      = "DestroySnapshots"
-	RPCSnapshotReplicationStatus = "SnapshotReplicationStatus"
+	RPCReplicationCursor      = "ReplicationCursor"
 )
 
 // Remote implements an endpoint stub that uses streamrpc as a transport.
@@ -578,18 +565,18 @@ func (a *Handler) Handle(ctx context.Context, endpoint string, reqStructured *by
 		}
 		return bytes.NewBuffer(b), nil, nil
 
-	case RPCSnapshotReplicationStatus:
+	case RPCReplicationCursor:
 
 		sender, ok := a.ep.(replication.Sender)
 		if !ok {
 			goto Err
 		}
 
-		var req pdu.SnapshotReplicationStatusReq
+		var req pdu.ReplicationCursorReq
 		if err := proto.Unmarshal(reqStructured.Bytes(), &req); err != nil {
 			return nil, nil, err
 		}
-		res, err := sender.SnapshotReplicationStatus(ctx, &req)
+		res, err := sender.ReplicationCursor(ctx, &req)
 		if err != nil {
 			return nil, nil, err
 		}

replication/fsrep/fsfsm.go

@@ -42,7 +42,7 @@ type Sender interface {
 	// any next call to the parent github.com/zrepl/zrepl/replication.Endpoint.
 	// If the send request is for dry run the io.ReadCloser will be nil
 	Send(ctx context.Context, r *pdu.SendReq) (*pdu.SendRes, io.ReadCloser, error)
-	SnapshotReplicationStatus(ctx context.Context, r *pdu.SnapshotReplicationStatusReq) (*pdu.SnapshotReplicationStatusRes, error)
+	ReplicationCursor(ctx context.Context, req *pdu.ReplicationCursorReq) (*pdu.ReplicationCursorRes, error)
 }
 
 // A Sender is usually part of a github.com/zrepl/zrepl/replication.Endpoint.
@@ -423,19 +423,22 @@ func (s *ReplicationStep) doMarkReplicated(ctx context.Context, sender Sender) S
 		return s.state
 	}
 
-	log.Debug("mark snapshot as replicated")
-	req := pdu.SnapshotReplicationStatusReq{
+	log.Debug("advance replication cursor")
+	req := &pdu.ReplicationCursorReq{
 		Filesystem: s.parent.fs,
+		Op: &pdu.ReplicationCursorReq_Set{
+			Set: &pdu.ReplicationCursorReq_SetOp{
 				Snapshot:   s.to.GetName(),
-		Op:         pdu.SnapshotReplicationStatusReq_SetReplicated,
+			},
+		},
 	}
-	res, err := sender.SnapshotReplicationStatus(ctx, &req)
+	res, err := sender.ReplicationCursor(ctx, req)
 	if err != nil {
-		log.WithError(err).Error("error marking snapshot as replicated")
+		log.WithError(err).Error("error advancing replication cursor")
 		return updateStateError(err)
 	}
-	if res.Status != pdu.SnapshotReplicationStatusRes_Replicated {
-		err := fmt.Errorf("sender did not report snapshot as replicated: %s", res.Status)
+	if res.GetError() != "" {
+		err := fmt.Errorf("cannot advance replication cursor: %s", res.GetError())
 		log.Error(err.Error())
 		return updateStateError(err)
 	}

replication/internal/diff/diff.go

@@ -59,10 +59,9 @@ func IncrementalPath(receiver, sender []*FilesystemVersion) (incPath []*Filesyst
 
 	for mrcaRcv >= 0 && mrcaSnd >= 0 {
 		if receiver[mrcaRcv].Guid == sender[mrcaSnd].Guid {
-			if mrcaSnd-1 >= 0 && sender[mrcaSnd-1].Guid == sender[mrcaSnd].Guid && sender[mrcaSnd-1].Type == FilesystemVersion_Bookmark {
-				// prefer bookmarks over snapshots as the snapshot might go away sooner
-				mrcaSnd -= 1
-			}
+			// Since we arrive from the end of the array, and because we defined bookmark < snapshot,
+			// this condition will match snapshot first, which is what we want because it gives us
+			// size estimation
 			break
 		}
 		receiverCreation, err := receiver[mrcaRcv].CreationAsTime()

replication/pdu/pdu.pb.go

@@ -38,56 +38,7 @@ func (x FilesystemVersion_VersionType) String() string {
 	return proto.EnumName(FilesystemVersion_VersionType_name, int32(x))
 }
 func (FilesystemVersion_VersionType) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{5, 0}
-}
-
-type SnapshotReplicationStatusReq_Op int32
-
-const (
-	SnapshotReplicationStatusReq_Get           SnapshotReplicationStatusReq_Op = 0
-	SnapshotReplicationStatusReq_SetReplicated SnapshotReplicationStatusReq_Op = 1
-)
-
-var SnapshotReplicationStatusReq_Op_name = map[int32]string{
-	0: "Get",
-	1: "SetReplicated",
-}
-var SnapshotReplicationStatusReq_Op_value = map[string]int32{
-	"Get":           0,
-	"SetReplicated": 1,
-}
-
-func (x SnapshotReplicationStatusReq_Op) String() string {
-	return proto.EnumName(SnapshotReplicationStatusReq_Op_name, int32(x))
-}
-func (SnapshotReplicationStatusReq_Op) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{14, 0}
-}
-
-type SnapshotReplicationStatusRes_Status int32
-
-const (
-	SnapshotReplicationStatusRes_Nonexistent   SnapshotReplicationStatusRes_Status = 0
-	SnapshotReplicationStatusRes_NotReplicated SnapshotReplicationStatusRes_Status = 1
-	SnapshotReplicationStatusRes_Replicated    SnapshotReplicationStatusRes_Status = 2
-)
-
-var SnapshotReplicationStatusRes_Status_name = map[int32]string{
-	0: "Nonexistent",
-	1: "NotReplicated",
-	2: "Replicated",
-}
-var SnapshotReplicationStatusRes_Status_value = map[string]int32{
-	"Nonexistent":   0,
-	"NotReplicated": 1,
-	"Replicated":    2,
-}
-
-func (x SnapshotReplicationStatusRes_Status) String() string {
-	return proto.EnumName(SnapshotReplicationStatusRes_Status_name, int32(x))
-}
-func (SnapshotReplicationStatusRes_Status) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{15, 0}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{5, 0}
 }
 
 type ListFilesystemReq struct {
@@ -100,7 +51,7 @@ func (m *ListFilesystemReq) Reset()         { *m = ListFilesystemReq{} }
 func (m *ListFilesystemReq) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemReq) ProtoMessage()    {}
 func (*ListFilesystemReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{0}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{0}
 }
 func (m *ListFilesystemReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemReq.Unmarshal(m, b)
@@ -131,7 +82,7 @@ func (m *ListFilesystemRes) Reset()         { *m = ListFilesystemRes{} }
 func (m *ListFilesystemRes) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemRes) ProtoMessage()    {}
 func (*ListFilesystemRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{1}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{1}
 }
 func (m *ListFilesystemRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemRes.Unmarshal(m, b)
@@ -170,7 +121,7 @@ func (m *Filesystem) Reset()         { *m = Filesystem{} }
 func (m *Filesystem) String() string { return proto.CompactTextString(m) }
 func (*Filesystem) ProtoMessage()    {}
 func (*Filesystem) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{2}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{2}
 }
 func (m *Filesystem) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Filesystem.Unmarshal(m, b)
@@ -215,7 +166,7 @@ func (m *ListFilesystemVersionsReq) Reset()         { *m = ListFilesystemVersion
 func (m *ListFilesystemVersionsReq) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemVersionsReq) ProtoMessage()    {}
 func (*ListFilesystemVersionsReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{3}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{3}
 }
 func (m *ListFilesystemVersionsReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemVersionsReq.Unmarshal(m, b)
@@ -253,7 +204,7 @@ func (m *ListFilesystemVersionsRes) Reset()         { *m = ListFilesystemVersion
 func (m *ListFilesystemVersionsRes) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemVersionsRes) ProtoMessage()    {}
 func (*ListFilesystemVersionsRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{4}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{4}
 }
 func (m *ListFilesystemVersionsRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemVersionsRes.Unmarshal(m, b)
@@ -295,7 +246,7 @@ func (m *FilesystemVersion) Reset()         { *m = FilesystemVersion{} }
 func (m *FilesystemVersion) String() string { return proto.CompactTextString(m) }
 func (*FilesystemVersion) ProtoMessage()    {}
 func (*FilesystemVersion) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{5}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{5}
 }
 func (m *FilesystemVersion) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_FilesystemVersion.Unmarshal(m, b)
@@ -375,7 +326,7 @@ func (m *SendReq) Reset()         { *m = SendReq{} }
 func (m *SendReq) String() string { return proto.CompactTextString(m) }
 func (*SendReq) ProtoMessage()    {}
 func (*SendReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{6}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{6}
 }
 func (m *SendReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SendReq.Unmarshal(m, b)
@@ -456,7 +407,7 @@ func (m *Property) Reset()         { *m = Property{} }
 func (m *Property) String() string { return proto.CompactTextString(m) }
 func (*Property) ProtoMessage()    {}
 func (*Property) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{7}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{7}
 }
 func (m *Property) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Property.Unmarshal(m, b)
@@ -506,7 +457,7 @@ func (m *SendRes) Reset()         { *m = SendRes{} }
 func (m *SendRes) String() string { return proto.CompactTextString(m) }
 func (*SendRes) ProtoMessage()    {}
 func (*SendRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{8}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{8}
 }
 func (m *SendRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SendRes.Unmarshal(m, b)
@@ -560,7 +511,7 @@ func (m *ReceiveReq) Reset()         { *m = ReceiveReq{} }
 func (m *ReceiveReq) String() string { return proto.CompactTextString(m) }
 func (*ReceiveReq) ProtoMessage()    {}
 func (*ReceiveReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{9}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{9}
 }
 func (m *ReceiveReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ReceiveReq.Unmarshal(m, b)
@@ -604,7 +555,7 @@ func (m *ReceiveRes) Reset()         { *m = ReceiveRes{} }
 func (m *ReceiveRes) String() string { return proto.CompactTextString(m) }
 func (*ReceiveRes) ProtoMessage()    {}
 func (*ReceiveRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{10}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{10}
 }
 func (m *ReceiveRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ReceiveRes.Unmarshal(m, b)
@@ -637,7 +588,7 @@ func (m *DestroySnapshotsReq) Reset()         { *m = DestroySnapshotsReq{} }
 func (m *DestroySnapshotsReq) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotsReq) ProtoMessage()    {}
 func (*DestroySnapshotsReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{11}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{11}
 }
 func (m *DestroySnapshotsReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotsReq.Unmarshal(m, b)
@@ -683,7 +634,7 @@ func (m *DestroySnapshotRes) Reset()         { *m = DestroySnapshotRes{} }
 func (m *DestroySnapshotRes) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotRes) ProtoMessage()    {}
 func (*DestroySnapshotRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{12}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{12}
 }
 func (m *DestroySnapshotRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotRes.Unmarshal(m, b)
@@ -728,7 +679,7 @@ func (m *DestroySnapshotsRes) Reset()         { *m = DestroySnapshotsRes{} }
 func (m *DestroySnapshotsRes) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotsRes) ProtoMessage()    {}
 func (*DestroySnapshotsRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{13}
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{13}
 }
 func (m *DestroySnapshotsRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotsRes.Unmarshal(m, b)
@@ -755,96 +706,361 @@ func (m *DestroySnapshotsRes) GetResults() []*DestroySnapshotRes {
 	return nil
 }
 
-type SnapshotReplicationStatusReq struct {
+type ReplicationCursorReq struct {
 	Filesystem string `protobuf:"bytes,1,opt,name=Filesystem,proto3" json:"Filesystem,omitempty"`
-	Snapshot             string                          `protobuf:"bytes,2,opt,name=Snapshot,proto3" json:"Snapshot,omitempty"`
-	Op                   SnapshotReplicationStatusReq_Op `protobuf:"varint,3,opt,name=op,proto3,enum=pdu.SnapshotReplicationStatusReq_Op" json:"op,omitempty"`
+	// Types that are valid to be assigned to Op:
+	//	*ReplicationCursorReq_Get
+	//	*ReplicationCursorReq_Set
+	Op                   isReplicationCursorReq_Op `protobuf_oneof:"op"`
 	XXX_NoUnkeyedLiteral struct{}                  `json:"-"`
 	XXX_unrecognized     []byte                    `json:"-"`
 	XXX_sizecache        int32                     `json:"-"`
 }
 
-func (m *SnapshotReplicationStatusReq) Reset()         { *m = SnapshotReplicationStatusReq{} }
-func (m *SnapshotReplicationStatusReq) String() string { return proto.CompactTextString(m) }
-func (*SnapshotReplicationStatusReq) ProtoMessage()    {}
-func (*SnapshotReplicationStatusReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{14}
+func (m *ReplicationCursorReq) Reset()         { *m = ReplicationCursorReq{} }
+func (m *ReplicationCursorReq) String() string { return proto.CompactTextString(m) }
+func (*ReplicationCursorReq) ProtoMessage()    {}
+func (*ReplicationCursorReq) Descriptor() ([]byte, []int) {
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{14}
 }
-func (m *SnapshotReplicationStatusReq) XXX_Unmarshal(b []byte) error {
-	return xxx_messageInfo_SnapshotReplicationStatusReq.Unmarshal(m, b)
+func (m *ReplicationCursorReq) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ReplicationCursorReq.Unmarshal(m, b)
 }
-func (m *SnapshotReplicationStatusReq) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
-	return xxx_messageInfo_SnapshotReplicationStatusReq.Marshal(b, m, deterministic)
+func (m *ReplicationCursorReq) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ReplicationCursorReq.Marshal(b, m, deterministic)
 }
-func (dst *SnapshotReplicationStatusReq) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_SnapshotReplicationStatusReq.Merge(dst, src)
+func (dst *ReplicationCursorReq) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ReplicationCursorReq.Merge(dst, src)
 }
-func (m *SnapshotReplicationStatusReq) XXX_Size() int {
-	return xxx_messageInfo_SnapshotReplicationStatusReq.Size(m)
+func (m *ReplicationCursorReq) XXX_Size() int {
+	return xxx_messageInfo_ReplicationCursorReq.Size(m)
 }
-func (m *SnapshotReplicationStatusReq) XXX_DiscardUnknown() {
-	xxx_messageInfo_SnapshotReplicationStatusReq.DiscardUnknown(m)
+func (m *ReplicationCursorReq) XXX_DiscardUnknown() {
+	xxx_messageInfo_ReplicationCursorReq.DiscardUnknown(m)
 }
 
-var xxx_messageInfo_SnapshotReplicationStatusReq proto.InternalMessageInfo
+var xxx_messageInfo_ReplicationCursorReq proto.InternalMessageInfo
 
-func (m *SnapshotReplicationStatusReq) GetFilesystem() string {
+func (m *ReplicationCursorReq) GetFilesystem() string {
 	if m != nil {
 		return m.Filesystem
 	}
 	return ""
 }
 
-func (m *SnapshotReplicationStatusReq) GetSnapshot() string {
+type isReplicationCursorReq_Op interface {
+	isReplicationCursorReq_Op()
+}
+
+type ReplicationCursorReq_Get struct {
+	Get *ReplicationCursorReq_GetOp `protobuf:"bytes,2,opt,name=get,proto3,oneof"`
+}
+
+type ReplicationCursorReq_Set struct {
+	Set *ReplicationCursorReq_SetOp `protobuf:"bytes,3,opt,name=set,proto3,oneof"`
+}
+
+func (*ReplicationCursorReq_Get) isReplicationCursorReq_Op() {}
+
+func (*ReplicationCursorReq_Set) isReplicationCursorReq_Op() {}
+
+func (m *ReplicationCursorReq) GetOp() isReplicationCursorReq_Op {
+	if m != nil {
+		return m.Op
+	}
+	return nil
+}
+
+func (m *ReplicationCursorReq) GetGet() *ReplicationCursorReq_GetOp {
+	if x, ok := m.GetOp().(*ReplicationCursorReq_Get); ok {
+		return x.Get
+	}
+	return nil
+}
+
+func (m *ReplicationCursorReq) GetSet() *ReplicationCursorReq_SetOp {
+	if x, ok := m.GetOp().(*ReplicationCursorReq_Set); ok {
+		return x.Set
+	}
+	return nil
+}
+
+// XXX_OneofFuncs is for the internal use of the proto package.
+func (*ReplicationCursorReq) XXX_OneofFuncs() (func(msg proto.Message, b *proto.Buffer) error, func(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error), func(msg proto.Message) (n int), []interface{}) {
+	return _ReplicationCursorReq_OneofMarshaler, _ReplicationCursorReq_OneofUnmarshaler, _ReplicationCursorReq_OneofSizer, []interface{}{
+		(*ReplicationCursorReq_Get)(nil),
+		(*ReplicationCursorReq_Set)(nil),
+	}
+}
+
+func _ReplicationCursorReq_OneofMarshaler(msg proto.Message, b *proto.Buffer) error {
+	m := msg.(*ReplicationCursorReq)
+	// op
+	switch x := m.Op.(type) {
+	case *ReplicationCursorReq_Get:
+		b.EncodeVarint(2<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.Get); err != nil {
+			return err
+		}
+	case *ReplicationCursorReq_Set:
+		b.EncodeVarint(3<<3 | proto.WireBytes)
+		if err := b.EncodeMessage(x.Set); err != nil {
+			return err
+		}
+	case nil:
+	default:
+		return fmt.Errorf("ReplicationCursorReq.Op has unexpected type %T", x)
+	}
+	return nil
+}
+
+func _ReplicationCursorReq_OneofUnmarshaler(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error) {
+	m := msg.(*ReplicationCursorReq)
+	switch tag {
+	case 2: // op.get
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(ReplicationCursorReq_GetOp)
+		err := b.DecodeMessage(msg)
+		m.Op = &ReplicationCursorReq_Get{msg}
+		return true, err
+	case 3: // op.set
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		msg := new(ReplicationCursorReq_SetOp)
+		err := b.DecodeMessage(msg)
+		m.Op = &ReplicationCursorReq_Set{msg}
+		return true, err
+	default:
+		return false, nil
+	}
+}
+
+func _ReplicationCursorReq_OneofSizer(msg proto.Message) (n int) {
+	m := msg.(*ReplicationCursorReq)
+	// op
+	switch x := m.Op.(type) {
+	case *ReplicationCursorReq_Get:
+		s := proto.Size(x.Get)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case *ReplicationCursorReq_Set:
+		s := proto.Size(x.Set)
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(s))
+		n += s
+	case nil:
+	default:
+		panic(fmt.Sprintf("proto: unexpected type %T in oneof", x))
+	}
+	return n
+}
+
+type ReplicationCursorReq_GetOp struct {
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *ReplicationCursorReq_GetOp) Reset()         { *m = ReplicationCursorReq_GetOp{} }
+func (m *ReplicationCursorReq_GetOp) String() string { return proto.CompactTextString(m) }
+func (*ReplicationCursorReq_GetOp) ProtoMessage()    {}
+func (*ReplicationCursorReq_GetOp) Descriptor() ([]byte, []int) {
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{14, 0}
+}
+func (m *ReplicationCursorReq_GetOp) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ReplicationCursorReq_GetOp.Unmarshal(m, b)
+}
+func (m *ReplicationCursorReq_GetOp) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ReplicationCursorReq_GetOp.Marshal(b, m, deterministic)
+}
+func (dst *ReplicationCursorReq_GetOp) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ReplicationCursorReq_GetOp.Merge(dst, src)
+}
+func (m *ReplicationCursorReq_GetOp) XXX_Size() int {
+	return xxx_messageInfo_ReplicationCursorReq_GetOp.Size(m)
+}
+func (m *ReplicationCursorReq_GetOp) XXX_DiscardUnknown() {
+	xxx_messageInfo_ReplicationCursorReq_GetOp.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_ReplicationCursorReq_GetOp proto.InternalMessageInfo
+
+type ReplicationCursorReq_SetOp struct {
+	Snapshot             string   `protobuf:"bytes,2,opt,name=Snapshot,proto3" json:"Snapshot,omitempty"`
+	XXX_NoUnkeyedLiteral struct{} `json:"-"`
+	XXX_unrecognized     []byte   `json:"-"`
+	XXX_sizecache        int32    `json:"-"`
+}
+
+func (m *ReplicationCursorReq_SetOp) Reset()         { *m = ReplicationCursorReq_SetOp{} }
+func (m *ReplicationCursorReq_SetOp) String() string { return proto.CompactTextString(m) }
+func (*ReplicationCursorReq_SetOp) ProtoMessage()    {}
+func (*ReplicationCursorReq_SetOp) Descriptor() ([]byte, []int) {
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{14, 1}
+}
+func (m *ReplicationCursorReq_SetOp) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ReplicationCursorReq_SetOp.Unmarshal(m, b)
+}
+func (m *ReplicationCursorReq_SetOp) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ReplicationCursorReq_SetOp.Marshal(b, m, deterministic)
+}
+func (dst *ReplicationCursorReq_SetOp) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ReplicationCursorReq_SetOp.Merge(dst, src)
+}
+func (m *ReplicationCursorReq_SetOp) XXX_Size() int {
+	return xxx_messageInfo_ReplicationCursorReq_SetOp.Size(m)
+}
+func (m *ReplicationCursorReq_SetOp) XXX_DiscardUnknown() {
+	xxx_messageInfo_ReplicationCursorReq_SetOp.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_ReplicationCursorReq_SetOp proto.InternalMessageInfo
+
+func (m *ReplicationCursorReq_SetOp) GetSnapshot() string {
 	if m != nil {
 		return m.Snapshot
 	}
 	return ""
 }
 
-func (m *SnapshotReplicationStatusReq) GetOp() SnapshotReplicationStatusReq_Op {
-	if m != nil {
-		return m.Op
-	}
-	return SnapshotReplicationStatusReq_Get
-}
-
-type SnapshotReplicationStatusRes struct {
-	Status               SnapshotReplicationStatusRes_Status `protobuf:"varint,1,opt,name=status,proto3,enum=pdu.SnapshotReplicationStatusRes_Status" json:"status,omitempty"`
+type ReplicationCursorRes struct {
+	// Types that are valid to be assigned to Result:
+	//	*ReplicationCursorRes_Guid
+	//	*ReplicationCursorRes_Error
+	Result               isReplicationCursorRes_Result `protobuf_oneof:"Result"`
 	XXX_NoUnkeyedLiteral struct{}                      `json:"-"`
 	XXX_unrecognized     []byte                        `json:"-"`
 	XXX_sizecache        int32                         `json:"-"`
 }
 
-func (m *SnapshotReplicationStatusRes) Reset()         { *m = SnapshotReplicationStatusRes{} }
-func (m *SnapshotReplicationStatusRes) String() string { return proto.CompactTextString(m) }
-func (*SnapshotReplicationStatusRes) ProtoMessage()    {}
-func (*SnapshotReplicationStatusRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_b3a98b3542e9fb4e, []int{15}
+func (m *ReplicationCursorRes) Reset()         { *m = ReplicationCursorRes{} }
+func (m *ReplicationCursorRes) String() string { return proto.CompactTextString(m) }
+func (*ReplicationCursorRes) ProtoMessage()    {}
+func (*ReplicationCursorRes) Descriptor() ([]byte, []int) {
+	return fileDescriptor_pdu_cbdc4740ab26577c, []int{15}
 }
-func (m *SnapshotReplicationStatusRes) XXX_Unmarshal(b []byte) error {
-	return xxx_messageInfo_SnapshotReplicationStatusRes.Unmarshal(m, b)
+func (m *ReplicationCursorRes) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_ReplicationCursorRes.Unmarshal(m, b)
 }
-func (m *SnapshotReplicationStatusRes) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
-	return xxx_messageInfo_SnapshotReplicationStatusRes.Marshal(b, m, deterministic)
+func (m *ReplicationCursorRes) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_ReplicationCursorRes.Marshal(b, m, deterministic)
 }
-func (dst *SnapshotReplicationStatusRes) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_SnapshotReplicationStatusRes.Merge(dst, src)
+func (dst *ReplicationCursorRes) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_ReplicationCursorRes.Merge(dst, src)
 }
-func (m *SnapshotReplicationStatusRes) XXX_Size() int {
-	return xxx_messageInfo_SnapshotReplicationStatusRes.Size(m)
+func (m *ReplicationCursorRes) XXX_Size() int {
+	return xxx_messageInfo_ReplicationCursorRes.Size(m)
 }
-func (m *SnapshotReplicationStatusRes) XXX_DiscardUnknown() {
-	xxx_messageInfo_SnapshotReplicationStatusRes.DiscardUnknown(m)
+func (m *ReplicationCursorRes) XXX_DiscardUnknown() {
+	xxx_messageInfo_ReplicationCursorRes.DiscardUnknown(m)
 }
 
-var xxx_messageInfo_SnapshotReplicationStatusRes proto.InternalMessageInfo
+var xxx_messageInfo_ReplicationCursorRes proto.InternalMessageInfo
 
-func (m *SnapshotReplicationStatusRes) GetStatus() SnapshotReplicationStatusRes_Status {
+type isReplicationCursorRes_Result interface {
+	isReplicationCursorRes_Result()
+}
+
+type ReplicationCursorRes_Guid struct {
+	Guid uint64 `protobuf:"varint,1,opt,name=Guid,proto3,oneof"`
+}
+
+type ReplicationCursorRes_Error struct {
+	Error string `protobuf:"bytes,2,opt,name=Error,proto3,oneof"`
+}
+
+func (*ReplicationCursorRes_Guid) isReplicationCursorRes_Result() {}
+
+func (*ReplicationCursorRes_Error) isReplicationCursorRes_Result() {}
+
+func (m *ReplicationCursorRes) GetResult() isReplicationCursorRes_Result {
 	if m != nil {
-		return m.Status
+		return m.Result
 	}
-	return SnapshotReplicationStatusRes_Nonexistent
+	return nil
+}
+
+func (m *ReplicationCursorRes) GetGuid() uint64 {
+	if x, ok := m.GetResult().(*ReplicationCursorRes_Guid); ok {
+		return x.Guid
+	}
+	return 0
+}
+
+func (m *ReplicationCursorRes) GetError() string {
+	if x, ok := m.GetResult().(*ReplicationCursorRes_Error); ok {
+		return x.Error
+	}
+	return ""
+}
+
+// XXX_OneofFuncs is for the internal use of the proto package.
+func (*ReplicationCursorRes) XXX_OneofFuncs() (func(msg proto.Message, b *proto.Buffer) error, func(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error), func(msg proto.Message) (n int), []interface{}) {
+	return _ReplicationCursorRes_OneofMarshaler, _ReplicationCursorRes_OneofUnmarshaler, _ReplicationCursorRes_OneofSizer, []interface{}{
+		(*ReplicationCursorRes_Guid)(nil),
+		(*ReplicationCursorRes_Error)(nil),
+	}
+}
+
+func _ReplicationCursorRes_OneofMarshaler(msg proto.Message, b *proto.Buffer) error {
+	m := msg.(*ReplicationCursorRes)
+	// Result
+	switch x := m.Result.(type) {
+	case *ReplicationCursorRes_Guid:
+		b.EncodeVarint(1<<3 | proto.WireVarint)
+		b.EncodeVarint(uint64(x.Guid))
+	case *ReplicationCursorRes_Error:
+		b.EncodeVarint(2<<3 | proto.WireBytes)
+		b.EncodeStringBytes(x.Error)
+	case nil:
+	default:
+		return fmt.Errorf("ReplicationCursorRes.Result has unexpected type %T", x)
+	}
+	return nil
+}
+
+func _ReplicationCursorRes_OneofUnmarshaler(msg proto.Message, tag, wire int, b *proto.Buffer) (bool, error) {
+	m := msg.(*ReplicationCursorRes)
+	switch tag {
+	case 1: // Result.Guid
+		if wire != proto.WireVarint {
+			return true, proto.ErrInternalBadWireType
+		}
+		x, err := b.DecodeVarint()
+		m.Result = &ReplicationCursorRes_Guid{x}
+		return true, err
+	case 2: // Result.Error
+		if wire != proto.WireBytes {
+			return true, proto.ErrInternalBadWireType
+		}
+		x, err := b.DecodeStringBytes()
+		m.Result = &ReplicationCursorRes_Error{x}
+		return true, err
+	default:
+		return false, nil
+	}
+}
+
+func _ReplicationCursorRes_OneofSizer(msg proto.Message) (n int) {
+	m := msg.(*ReplicationCursorRes)
+	// Result
+	switch x := m.Result.(type) {
+	case *ReplicationCursorRes_Guid:
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(x.Guid))
+	case *ReplicationCursorRes_Error:
+		n += 1 // tag and wire
+		n += proto.SizeVarint(uint64(len(x.Error)))
+		n += len(x.Error)
+	case nil:
+	default:
+		panic(fmt.Sprintf("proto: unexpected type %T in oneof", x))
+	}
+	return n
 }
 
 func init() {
@@ -862,57 +1078,57 @@ func init() {
 	proto.RegisterType((*DestroySnapshotsReq)(nil), "pdu.DestroySnapshotsReq")
 	proto.RegisterType((*DestroySnapshotRes)(nil), "pdu.DestroySnapshotRes")
 	proto.RegisterType((*DestroySnapshotsRes)(nil), "pdu.DestroySnapshotsRes")
-	proto.RegisterType((*SnapshotReplicationStatusReq)(nil), "pdu.SnapshotReplicationStatusReq")
-	proto.RegisterType((*SnapshotReplicationStatusRes)(nil), "pdu.SnapshotReplicationStatusRes")
+	proto.RegisterType((*ReplicationCursorReq)(nil), "pdu.ReplicationCursorReq")
+	proto.RegisterType((*ReplicationCursorReq_GetOp)(nil), "pdu.ReplicationCursorReq.GetOp")
+	proto.RegisterType((*ReplicationCursorReq_SetOp)(nil), "pdu.ReplicationCursorReq.SetOp")
+	proto.RegisterType((*ReplicationCursorRes)(nil), "pdu.ReplicationCursorRes")
 	proto.RegisterEnum("pdu.FilesystemVersion_VersionType", FilesystemVersion_VersionType_name, FilesystemVersion_VersionType_value)
-	proto.RegisterEnum("pdu.SnapshotReplicationStatusReq_Op", SnapshotReplicationStatusReq_Op_name, SnapshotReplicationStatusReq_Op_value)
-	proto.RegisterEnum("pdu.SnapshotReplicationStatusRes_Status", SnapshotReplicationStatusRes_Status_name, SnapshotReplicationStatusRes_Status_value)
 }
 
-func init() { proto.RegisterFile("pdu.proto", fileDescriptor_pdu_b3a98b3542e9fb4e) }
+func init() { proto.RegisterFile("pdu.proto", fileDescriptor_pdu_cbdc4740ab26577c) }
 
-var fileDescriptor_pdu_b3a98b3542e9fb4e = []byte{
-	// 666 bytes of a gzipped FileDescriptorProto
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-	0xff, 0xff, 0x3a, 0x00, 0x8b, 0x6e, 0x72, 0x06, 0x00, 0x00,
+var fileDescriptor_pdu_cbdc4740ab26577c = []byte{
+	// 657 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0x8c, 0x55, 0xcb, 0x6e, 0xdb, 0x3a,
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+	0xff, 0xd1, 0x45, 0x3f, 0xa7, 0xe0, 0x58, 0x92, 0x15, 0xdb, 0x0d, 0xbc, 0x32, 0xcf, 0xf0, 0x70,
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+	0xa3, 0x2f, 0xb8, 0x89, 0xf9, 0xaf, 0x60, 0xf7, 0x74, 0x8c, 0x81, 0x5a, 0x1e, 0x1c, 0x4f, 0xac,
+	0xc4, 0xf9, 0x56, 0x21, 0xb3, 0xe6, 0x23, 0xd8, 0x3f, 0x43, 0x6d, 0x94, 0x9c, 0x65, 0x5f, 0xc1,
+	0x26, 0x53, 0xc4, 0x4e, 0xa0, 0x91, 0xf3, 0xfd, 0xf2, 0xb3, 0x93, 0xb2, 0x20, 0xf2, 0x8f, 0xc0,
+	0x96, 0x8a, 0xa5, 0x43, 0x97, 0x41, 0xaa, 0xf4, 0xcc, 0xd0, 0x65, 0x3c, 0x7b, 0x7b, 0xe7, 0x4a,
+	0x49, 0x95, 0xdd, 0x1e, 0x01, 0xde, 0x5f, 0xd7, 0x8c, 0x7d, 0xa6, 0xea, 0xd6, 0x80, 0xb1, 0xc9,
+	0x86, 0xfa, 0x6f, 0xca, 0xbf, 0x2a, 0x45, 0x64, 0x3c, 0xfe, 0xd3, 0x81, 0x03, 0x81, 0xf1, 0x38,
+	0xba, 0xa7, 0xa1, 0x39, 0x4d, 0x94, 0x96, 0x6a, 0x13, 0x63, 0x8e, 0xa1, 0xf2, 0x19, 0x0d, 0xc9,
+	0x6a, 0x76, 0xff, 0xa7, 0x3a, 0xeb, 0xf2, 0x74, 0x2e, 0xd1, 0x5c, 0xc7, 0xfd, 0x92, 0xb0, 0x6c,
+	0x7b, 0x48, 0xa3, 0xa1, 0x41, 0x79, 0xf6, 0xd0, 0x20, 0x3b, 0xa4, 0xd1, 0x1c, 0xd5, 0xa1, 0x4a,
+	0x49, 0x8e, 0x5e, 0x40, 0x95, 0x36, 0xec, 0xf0, 0xe4, 0x46, 0xce, 0x7d, 0xc9, 0x71, 0xcf, 0x85,
+	0xb2, 0x8c, 0xf9, 0xd5, 0xda, 0xae, 0xec, 0x68, 0xcd, 0x5f, 0x18, 0xdb, 0x8f, 0xdb, 0x2f, 0xa5,
+	0x6f, 0xcc, 0xe1, 0x13, 0x93, 0xfb, 0xa5, 0xd4, 0xe6, 0x9e, 0x07, 0xb5, 0xb9, 0x4f, 0x9f, 0x6a,
+	0xf4, 0xb7, 0x71, 0xfc, 0x3b, 0x00, 0x00, 0xff, 0xff, 0x02, 0x35, 0xe7, 0x43, 0x43, 0x06, 0x00,
+	0x00,
 }

replication/pdu/pdu.proto

@@ -98,21 +98,21 @@ message DestroySnapshotsRes {
     repeated DestroySnapshotRes Results = 1;
 }
 
-message SnapshotReplicationStatusReq {
+message ReplicationCursorReq {
     string Filesystem = 1;
+    message GetOp {}
+    message SetOp {
         string Snapshot = 2;
-    enum Op {
-        Get = 0;
-        SetReplicated = 1;
     }
-    Op op = 3;
+    oneof op {
+        GetOp get = 2;
+        SetOp set = 3;
+    }
 }
 
-message SnapshotReplicationStatusRes {
-    enum Status {
-        Nonexistent = 0;
-        NotReplicated = 1;
-        Replicated = 2;
+message ReplicationCursorRes {
+    oneof Result {
+        uint64 Guid = 1;
+        string Error = 2;
     }
-    Status status = 1;
 }

zfs/replication_history.go

@@ -1,25 +1,58 @@
 package zfs
 
-const ReplicatedProperty = "zrepl:replicated"
+import (
+	"fmt"
+	"github.com/pkg/errors"
+	"strconv"
+)
 
-// May return *DatasetDoesNotExist as an error
-func ZFSGetReplicatedProperty(fs *DatasetPath, v *FilesystemVersion) (replicated bool, err error) {
-	props, err := zfsGet(v.ToAbsPath(fs), []string{ReplicatedProperty})
+const ReplicationCursorBookmarkName = "zrepl_replication_cursor"
+
+// may return nil for both values, indicating there is no cursor
+func ZFSGetReplicationCursor(fs *DatasetPath) (*FilesystemVersion, error) {
+	versions, err := ZFSListFilesystemVersions(fs, nil)
 	if err != nil {
-		return false, err
+		return nil, err
 	}
-	if props.Get(ReplicatedProperty) == "yes" {
-		return true, nil
+	for _, v := range versions {
+		if v.Type == Bookmark && v.Name == ReplicationCursorBookmarkName {
+			return &v, nil
 		}
-	return false, nil
+	}
+	return nil, nil
 }
 
-func ZFSSetReplicatedProperty(fs *DatasetPath, v *FilesystemVersion, replicated bool) error {
-	val := "no"
-	if replicated {
-		val = "yes"
+func ZFSSetReplicationCursor(fs *DatasetPath, snapname string) (guid uint64, err error) {
+	snapPath := fmt.Sprintf("%s@%s", fs.ToString(), snapname)
+	propsSnap, err := zfsGet(snapPath, []string{"createtxg", "guid"})
+	if err != nil {
+		return 0, err
 	}
-	props := NewZFSProperties()
-	props.Set(ReplicatedProperty, val)
-	return zfsSet(v.ToAbsPath(fs), props)
+	snapGuid, err := strconv.ParseUint(propsSnap.Get("guid"), 10, 64)
+	bookmarkPath := fmt.Sprintf("%s#%s", fs.ToString(), ReplicationCursorBookmarkName)
+	propsBookmark, err := zfsGet(bookmarkPath, []string{"createtxg"})
+	_, bookmarkNotExistErr := err.(*DatasetDoesNotExist)
+	if err != nil && !bookmarkNotExistErr {
+		return 0, err
+	}
+	if err == nil {
+		bookmarkTxg, err := strconv.ParseUint(propsBookmark.Get("createtxg"), 10, 64)
+		if err != nil {
+			return 0, errors.Wrap(err, "cannot parse bookmark createtxg")
+		}
+		snapTxg, err := strconv.ParseUint(propsSnap.Get("createtxg"), 10, 64)
+		if err != nil {
+			return 0, errors.Wrap(err, "cannot parse snapshot createtxg")
+		}
+		if snapTxg < bookmarkTxg {
+			return 0, errors.New("replication cursor can only be advanced, not set back")
+		}
+		if err := ZFSDestroy(bookmarkPath); err != nil { // FIXME make safer by using new temporary bookmark, then rename, possible with channel programs
+			return 0, err
+		}
+	}
+	if err := ZFSBookmark(fs, snapname, ReplicationCursorBookmarkName); err != nil {
+		return 0, err
+	}
+	return snapGuid, nil
 }

zfs/zfs.go

@@ -490,7 +490,7 @@ func ZFSGet(fs *DatasetPath, props []string) (*ZFSProperties, error) {
 	return zfsGet(fs.ToString(), props)
 }
 
-var zfsGetDatasetDoesNotExistRegexp = regexp.MustCompile(`^cannot open '(\S+)': dataset does not exist`)
+var zfsGetDatasetDoesNotExistRegexp = regexp.MustCompile(`^cannot open '(\S+)': (dataset does not exist|no such pool or dataset)`)
 
 type DatasetDoesNotExist struct {
 	Path string