new features: {resumable,encrypted,hold-protected} send-recv, last-received-hold

- **Resumable Send & Recv Support**
  No knobs required, automatically used where supported.
- **Hold-Protected Send & Recv**
  Automatic ZFS holds to ensure that we can always resume a replication step.
- **Encrypted Send & Recv Support** for OpenZFS native encryption.
  Configurable at the job level, i.e., for all filesystems a job is responsible for.
- **Receive-side hold on last received dataset**
  The counterpart to the replication cursor bookmark on the send-side.
  Ensures that incremental replication will always be possible between a sender and receiver.

Design Doc
----------

`replication/design.md` doc describes how we use ZFS holds and bookmarks to ensure that a single replication step is always resumable.

The replication algorithm described in the design doc introduces the notion of job IDs (please read the details on this design doc).
We reuse the job names for job IDs and use `JobID` type to ensure that a job name can be embedded into hold tags, bookmark names, etc.
This might BREAK CONFIG on upgrade.

Protocol Version Bump
---------------------

This commit makes backwards-incompatible changes to the replication/pdu protobufs.
Thus, bump the version number used in the protocol handshake.

Replication Cursor Format Change
--------------------------------

The new replication cursor bookmark format is: `#zrepl_CURSOR_G_${this.GUID}_J_${jobid}`
Including the GUID enables transaction-safe moving-forward of the cursor.
Including the job id enables that multiple sending jobs can send the same filesystem without interfering.
The `zrepl migrate replication-cursor:v1-v2` subcommand can be used to safely destroy old-format cursors once zrepl has created new-format cursors.

Changes in This Commit
----------------------

- package zfs
  - infrastructure for holds
  - infrastructure for resume token decoding
  - implement a variant of OpenZFS's `entity_namecheck` and use it for validation in new code
  - ZFSSendArgs to specify a ZFS send operation
    - validation code protects against malicious resume tokens by checking that the token encodes the same send parameters that the send-side would use if no resume token were available (i.e. same filesystem, `fromguid`, `toguid`)
  - RecvOptions support for `recv -s` flag
  - convert a bunch of ZFS operations to be idempotent
    - achieved through more differentiated error message scraping / additional pre-/post-checks

- package replication/pdu
  - add field for encryption to send request messages
  - add fields for resume handling to send & recv request messages
  - receive requests now contain `FilesystemVersion To` in addition to the filesystem into which the stream should be `recv`d into
    - can use `zfs recv $root_fs/$client_id/path/to/dataset@${To.Name}`, which enables additional validation after recv (i.e. whether `To.Guid` matched what we received in the stream)
    - used to set `last-received-hold`
- package replication/logic
  - introduce `PlannerPolicy` struct, currently only used to configure whether encrypted sends should be requested from the sender
  - integrate encryption and resume token support into `Step` struct

- package endpoint
  - move the concepts that endpoint builds on top of ZFS to a single file `endpoint/endpoint_zfs.go`
    - step-holds + step-bookmarks
    - last-received-hold
    - new replication cursor + old replication cursor compat code
  - adjust `endpoint/endpoint.go` handlers for
    - encryption
    - resumability
    - new replication cursor
    - last-received-hold

- client subcommand `zrepl holds list`: list all holds and hold-like bookmarks that zrepl thinks belong to it
- client subcommand `zrepl migrate replication-cursor:v1-v2`

daemon/job/active.go

@@ -2,6 +2,7 @@ package job
 
 import (
 	"context"
+	"fmt"
 	"sync"
 	"time"
 
@@ -28,7 +29,7 @@ import (
 
 type ActiveSide struct {
 	mode      activeMode
-	name      string
+	name      endpoint.JobID
 	connecter transport.Connecter
 
 	prunerFactory *pruner.PrunerFactory
@@ -82,17 +83,19 @@ type activeMode interface {
 	DisconnectEndpoints()
 	SenderReceiver() (logic.Sender, logic.Receiver)
 	Type() Type
+	PlannerPolicy() logic.PlannerPolicy
 	RunPeriodic(ctx context.Context, wakeUpCommon chan<- struct{})
 	SnapperReport() *snapper.Report
 	ResetConnectBackoff()
 }
 
 type modePush struct {
-	setupMtx sync.Mutex
-	sender   *endpoint.Sender
-	receiver *rpc.Client
-	fsfilter endpoint.FSFilter
-	snapper  *snapper.PeriodicOrManual
+	setupMtx      sync.Mutex
+	sender        *endpoint.Sender
+	receiver      *rpc.Client
+	senderConfig  *endpoint.SenderConfig
+	plannerPolicy *logic.PlannerPolicy
+	snapper       *snapper.PeriodicOrManual
 }
 
 func (m *modePush) ConnectEndpoints(loggers rpc.Loggers, connecter transport.Connecter) {
@@ -101,7 +104,7 @@ func (m *modePush) ConnectEndpoints(loggers rpc.Loggers, connecter transport.Con
 	if m.receiver != nil || m.sender != nil {
 		panic("inconsistent use of ConnectEndpoints and DisconnectEndpoints")
 	}
-	m.sender = endpoint.NewSender(m.fsfilter)
+	m.sender = endpoint.NewSender(*m.senderConfig)
 	m.receiver = rpc.NewClient(connecter, loggers)
 }
 
@@ -121,6 +124,8 @@ func (m *modePush) SenderReceiver() (logic.Sender, logic.Receiver) {
 
 func (m *modePush) Type() Type { return TypePush }
 
+func (m *modePush) PlannerPolicy() logic.PlannerPolicy { return *m.plannerPolicy }
+
 func (m *modePush) RunPeriodic(ctx context.Context, wakeUpCommon chan<- struct{}) {
 	m.snapper.Run(ctx, wakeUpCommon)
 }
@@ -137,13 +142,22 @@ func (m *modePush) ResetConnectBackoff() {
 	}
 }
 
-func modePushFromConfig(g *config.Global, in *config.PushJob) (*modePush, error) {
+func modePushFromConfig(g *config.Global, in *config.PushJob, jobID endpoint.JobID) (*modePush, error) {
 	m := &modePush{}
+
 	fsf, err := filters.DatasetMapFilterFromConfig(in.Filesystems)
 	if err != nil {
 		return nil, errors.Wrap(err, "cannnot build filesystem filter")
 	}
-	m.fsfilter = fsf
+
+	m.senderConfig = &endpoint.SenderConfig{
+		FSF:     fsf,
+		Encrypt: &zfs.NilBool{B: in.Send.Encrypted},
+		JobID:   jobID,
+	}
+	m.plannerPolicy = &logic.PlannerPolicy{
+		EncryptedSend: logic.TriFromBool(in.Send.Encrypted),
+	}
 
 	if m.snapper, err = snapper.FromConfig(g, fsf, in.Snapshotting); err != nil {
 		return nil, errors.Wrap(err, "cannot build snapper")
@@ -153,11 +167,13 @@ func modePushFromConfig(g *config.Global, in *config.PushJob) (*modePush, error)
 }
 
 type modePull struct {
-	setupMtx sync.Mutex
-	receiver *endpoint.Receiver
-	sender   *rpc.Client
-	rootFS   *zfs.DatasetPath
-	interval config.PositiveDurationOrManual
+	setupMtx       sync.Mutex
+	receiver       *endpoint.Receiver
+	receiverConfig endpoint.ReceiverConfig
+	sender         *rpc.Client
+	rootFS         *zfs.DatasetPath
+	plannerPolicy  *logic.PlannerPolicy
+	interval       config.PositiveDurationOrManual
 }
 
 func (m *modePull) ConnectEndpoints(loggers rpc.Loggers, connecter transport.Connecter) {
@@ -166,7 +182,7 @@ func (m *modePull) ConnectEndpoints(loggers rpc.Loggers, connecter transport.Con
 	if m.receiver != nil || m.sender != nil {
 		panic("inconsistent use of ConnectEndpoints and DisconnectEndpoints")
 	}
-	m.receiver = endpoint.NewReceiver(m.rootFS, false)
+	m.receiver = endpoint.NewReceiver(m.receiverConfig)
 	m.sender = rpc.NewClient(connecter, loggers)
 }
 
@@ -186,6 +202,8 @@ func (m *modePull) SenderReceiver() (logic.Sender, logic.Receiver) {
 
 func (*modePull) Type() Type { return TypePull }
 
+func (m *modePull) PlannerPolicy() logic.PlannerPolicy { return *m.plannerPolicy }
+
 func (m *modePull) RunPeriodic(ctx context.Context, wakeUpCommon chan<- struct{}) {
 	if m.interval.Manual {
 		GetLogger(ctx).Info("manual pull configured, periodic pull disabled")
@@ -223,7 +241,7 @@ func (m *modePull) ResetConnectBackoff() {
 	}
 }
 
-func modePullFromConfig(g *config.Global, in *config.PullJob) (m *modePull, err error) {
+func modePullFromConfig(g *config.Global, in *config.PullJob, jobID endpoint.JobID) (m *modePull, err error) {
 	m = &modePull{}
 	m.interval = in.Interval
 
@@ -235,26 +253,56 @@ func modePullFromConfig(g *config.Global, in *config.PullJob) (m *modePull, err
 		return nil, errors.New("RootFS must not be empty") // duplicates error check of receiver
 	}
 
+	m.plannerPolicy = &logic.PlannerPolicy{
+		EncryptedSend: logic.DontCare,
+	}
+
+	m.receiverConfig = endpoint.ReceiverConfig{
+		JobID:                      jobID,
+		RootWithoutClientComponent: m.rootFS,
+		AppendClientIdentity:       false, // !
+		UpdateLastReceivedHold:     true,
+	}
+	if err := m.receiverConfig.Validate(); err != nil {
+		return nil, errors.Wrap(err, "cannot build receiver config")
+	}
+
 	return m, nil
 }
 
-func activeSide(g *config.Global, in *config.ActiveJob, mode activeMode) (j *ActiveSide, err error) {
+func activeSide(g *config.Global, in *config.ActiveJob, configJob interface{}) (j *ActiveSide, err error) {
+
+	j = &ActiveSide{}
+	j.name, err = endpoint.MakeJobID(in.Name)
+	if err != nil {
+		return nil, errors.Wrap(err, "invalid job name")
+	}
+
+	switch v := configJob.(type) {
+	case *config.PushJob:
+		j.mode, err = modePushFromConfig(g, v, j.name) // shadow
+	case *config.PullJob:
+		j.mode, err = modePullFromConfig(g, v, j.name) // shadow
+	default:
+		panic(fmt.Sprintf("implementation error: unknown job type %T", v))
+	}
+	if err != nil {
+		return nil, err // no wrapping required
+	}
 
-	j = &ActiveSide{mode: mode}
-	j.name = in.Name
 	j.promRepStateSecs = prometheus.NewHistogramVec(prometheus.HistogramOpts{
 		Namespace:   "zrepl",
 		Subsystem:   "replication",
 		Name:        "state_time",
 		Help:        "seconds spent during replication",
-		ConstLabels: prometheus.Labels{"zrepl_job": j.name},
+		ConstLabels: prometheus.Labels{"zrepl_job": j.name.String()},
 	}, []string{"state"})
 	j.promBytesReplicated = prometheus.NewCounterVec(prometheus.CounterOpts{
 		Namespace:   "zrepl",
 		Subsystem:   "replication",
 		Name:        "bytes_replicated",
 		Help:        "number of bytes replicated from sender to receiver per filesystem",
-		ConstLabels: prometheus.Labels{"zrepl_job": j.name},
+		ConstLabels: prometheus.Labels{"zrepl_job": j.name.String()},
 	}, []string{"filesystem"})
 
 	j.connecter, err = fromconfig.ConnecterFromConfig(g, in.Connect)
@@ -267,7 +315,7 @@ func activeSide(g *config.Global, in *config.ActiveJob, mode activeMode) (j *Act
 		Subsystem:   "pruning",
 		Name:        "time",
 		Help:        "seconds spent in pruner",
-		ConstLabels: prometheus.Labels{"zrepl_job": j.name},
+		ConstLabels: prometheus.Labels{"zrepl_job": j.name.String()},
 	}, []string{"prune_side"})
 	j.prunerFactory, err = pruner.NewPrunerFactory(in.Pruning, j.promPruneSecs)
 	if err != nil {
@@ -283,7 +331,7 @@ func (j *ActiveSide) RegisterMetrics(registerer prometheus.Registerer) {
 	registerer.MustRegister(j.promBytesReplicated)
 }
 
-func (j *ActiveSide) Name() string { return j.name }
+func (j *ActiveSide) Name() string { return j.name.String() }
 
 type ActiveSideStatus struct {
 	Replication                    *report.Report
@@ -318,6 +366,15 @@ func (j *ActiveSide) OwnedDatasetSubtreeRoot() (rfs *zfs.DatasetPath, ok bool) {
 	return pull.rootFS.Copy(), true
 }
 
+func (j *ActiveSide) SenderConfig() *endpoint.SenderConfig {
+	push, ok := j.mode.(*modePush)
+	if !ok {
+		_ = j.mode.(*modePull) // make sure we didn't introduce a new job type
+		return nil
+	}
+	return push.senderConfig
+}
+
 func (j *ActiveSide) Run(ctx context.Context) {
 	log := GetLogger(ctx)
 	ctx = logging.WithSubsystemLoggers(ctx, log)
@@ -383,7 +440,7 @@ func (j *ActiveSide) do(ctx context.Context) {
 			*tasks = activeSideTasks{}
 			tasks.replicationCancel = repCancel
 			tasks.replicationReport, repWait = replication.Do(
-				ctx, logic.NewPlanner(j.promRepStateSecs, j.promBytesReplicated, sender, receiver),
+				ctx, logic.NewPlanner(j.promRepStateSecs, j.promBytesReplicated, sender, receiver, j.mode.PlannerPolicy()),
 			)
 			tasks.state = ActiveSideReplicating
 		})