a bit refactoring to prepare for volume format change and backward

compatibility.

go/storage/volume.go

@@ -12,22 +12,6 @@ import (
 	"time"
 )
 
-const (
-	SuperBlockSize = 8
-)
-
-type SuperBlock struct {
-	Version          Version
-	ReplicaPlacement *ReplicaPlacement
-}
-
-func (s *SuperBlock) Bytes() []byte {
-	header := make([]byte, SuperBlockSize)
-	header[0] = byte(s.Version)
-	header[1] = s.ReplicaPlacement.Byte()
-	return header
-}
-
 type Volume struct {
 	Id         VolumeId
 	dir        string
@@ -122,7 +106,7 @@ func (v *Volume) load(alsoLoadIndex bool, createDatIfMissing bool) error {
 	return e
 }
 func (v *Volume) Version() Version {
-	return v.SuperBlock.Version
+	return v.SuperBlock.Version()
 }
 func (v *Volume) Size() int64 {
 	stat, e := v.dataFile.Stat()
@@ -138,44 +122,6 @@ func (v *Volume) Close() {
 	v.nm.Close()
 	_ = v.dataFile.Close()
 }
-func (v *Volume) maybeWriteSuperBlock() error {
-	stat, e := v.dataFile.Stat()
-	if e != nil {
-		glog.V(0).Infof("failed to stat datafile %s: %s", v.dataFile, e.Error())
-		return e
-	}
-	if stat.Size() == 0 {
-		v.SuperBlock.Version = CurrentVersion
-		_, e = v.dataFile.Write(v.SuperBlock.Bytes())
-		if e != nil && os.IsPermission(e) {
-			//read-only, but zero length - recreate it!
-			if v.dataFile, e = os.Create(v.dataFile.Name()); e == nil {
-				if _, e = v.dataFile.Write(v.SuperBlock.Bytes()); e == nil {
-					v.readOnly = false
-				}
-			}
-		}
-	}
-	return e
-}
-func (v *Volume) readSuperBlock() (err error) {
-	if _, err = v.dataFile.Seek(0, 0); err != nil {
-		return fmt.Errorf("cannot seek to the beginning of %s: %s", v.dataFile.Name(), err.Error())
-	}
-	header := make([]byte, SuperBlockSize)
-	if _, e := v.dataFile.Read(header); e != nil {
-		return fmt.Errorf("cannot read superblock: %s", e.Error())
-	}
-	v.SuperBlock, err = ParseSuperBlock(header)
-	return err
-}
-func ParseSuperBlock(header []byte) (superBlock SuperBlock, err error) {
-	superBlock.Version = Version(header[0])
-	if superBlock.ReplicaPlacement, err = NewReplicaPlacementFromByte(header[1]); err != nil {
-		err = fmt.Errorf("cannot read replica type: %s", err.Error())
-	}
-	return
-}
 func (v *Volume) NeedToReplicate() bool {
 	return v.ReplicaPlacement.GetCopyCount() > 1
 }