zfs: helper for ZFSGet guid and createtxg

zfs/replication_history.go

@@ -2,7 +2,6 @@ package zfs
 
 import (
 	"fmt"
-	"strconv"
 
 	"github.com/pkg/errors"
 )
@@ -26,30 +25,18 @@ func ZFSGetReplicationCursor(fs *DatasetPath) (*FilesystemVersion, error) {
 func ZFSSetReplicationCursor(fs *DatasetPath, snapname string) (guid uint64, err error) {
 	snapPath := fmt.Sprintf("%s@%s", fs.ToString(), snapname)
 	debug("replication cursor: snap path %q", snapPath)
-	propsSnap, err := zfsGet(snapPath, []string{"createtxg", "guid"}, sourceAny)
+	snapProps, err := ZFSGetCreateTXGAndGuid(snapPath)
 	if err != nil {
-		return 0, errors.Wrap(err, "zfs: replication cursor: get snapshot createtxg")
+		return 0, errors.Wrapf(err, "get properties of %q", snapPath)
-	}
-	snapGuid, err := strconv.ParseUint(propsSnap.Get("guid"), 10, 64)
-	if err != nil {
-		return 0, errors.Wrap(err, "zfs: replication cursor: parse snapshot guid")
 	}
 	bookmarkPath := fmt.Sprintf("%s#%s", fs.ToString(), ReplicationCursorBookmarkName)
-	propsBookmark, err := zfsGet(bookmarkPath, []string{"createtxg"}, sourceAny)
+	propsBookmark, err := ZFSGetCreateTXGAndGuid(bookmarkPath)
 	_, bookmarkNotExistErr := err.(*DatasetDoesNotExist)
 	if err != nil && !bookmarkNotExistErr {
 		return 0, errors.Wrap(err, "zfs: replication cursor: get bookmark txg")
 	}
 	if err == nil {
-		bookmarkTxg, err := strconv.ParseUint(propsBookmark.Get("createtxg"), 10, 64)
+		if snapProps.CreateTXG < propsBookmark.CreateTXG {
-		if err != nil {
-			return 0, errors.Wrap(err, "zfs: replication cursor: parse bookmark createtxg")
-		}
-		snapTxg, err := strconv.ParseUint(propsSnap.Get("createtxg"), 10, 64)
-		if err != nil {
-			return 0, errors.Wrap(err, "zfs: replication cursor: parse snapshot createtxg")
-		}
-		if snapTxg < bookmarkTxg {
 			return 0, errors.New("zfs: 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
@@ -59,5 +46,5 @@ func ZFSSetReplicationCursor(fs *DatasetPath, snapname string) (guid uint64, err
 	if err := ZFSBookmark(fs, snapname, ReplicationCursorBookmarkName); err != nil {
 		return 0, errors.Wrapf(err, "zfs: replication cursor: create bookmark")
 	}
-	return snapGuid, nil
+	return snapProps.Guid, nil
 }

zfs/zfs.go

@@ -4,7 +4,6 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -20,6 +19,7 @@ import (
 
 	"github.com/prometheus/client_golang/prometheus"
 
+	"github.com/pkg/errors"
 	"github.com/zrepl/zrepl/util/envconst"
 )
 
@@ -1024,6 +1024,41 @@ func zfsGet(path string, props []string, allowedSources zfsPropertySource) (*ZFS
 	return res, nil
 }
 
+type ZFSPropCreateTxgAndGuidProps struct {
+	CreateTXG, Guid uint64
+}
+
+func ZFSGetCreateTXGAndGuid(ds string) (ZFSPropCreateTxgAndGuidProps, error) {
+	props, err := zfsGetNumberProps(ds, []string{"createtxg", "guid"}, sourceAny)
+	if err != nil {
+		return ZFSPropCreateTxgAndGuidProps{}, err
+	}
+	return ZFSPropCreateTxgAndGuidProps{
+		CreateTXG: props["createtxg"],
+		Guid:      props["guid"],
+	}, nil
+}
+
+// returns *DatasetDoesNotExist if the dataset does not exist
+func zfsGetNumberProps(ds string, props []string, src zfsPropertySource) (map[string]uint64, error) {
+	sps, err := zfsGet(ds, props, sourceAny)
+	if err != nil {
+		if _, ok := err.(*DatasetDoesNotExist); ok {
+			return nil, err // pass through as is
+		}
+		return nil, errors.Wrap(err, "zfs: set replication cursor: get snapshot createtxg")
+	}
+	r := make(map[string]uint64, len(props))
+	for _, p := range props {
+		v, err := strconv.ParseUint(sps.Get(p), 10, 64)
+		if err != nil {
+			return nil, errors.Wrapf(err, "zfs get: parse number property %q", p)
+		}
+		r[p] = v
+	}
+	return r, nil
+}
+
 type DestroySnapshotsError struct {
 	RawLines      []string
 	Filesystem    string