Add compact revision in volume super block

go/storage/volume_super_block.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/chrislusf/seaweedfs/go/glog"
+	"github.com/chrislusf/seaweedfs/go/util"
 )
 
 const (
@@ -16,12 +17,14 @@ const (
 * Byte 0: version, 1 or 2
 * Byte 1: Replica Placement strategy, 000, 001, 002, 010, etc
 * Byte 2 and byte 3: Time to live. See TTL for definition
+* Byte 4 and byte 5: The number of times the volume has been compacted.
 * Rest bytes: Reserved
  */
 type SuperBlock struct {
 	version          Version
 	ReplicaPlacement *ReplicaPlacement
 	Ttl              *TTL
+	CompactRevision  uint16
 }
 
 func (s *SuperBlock) Version() Version {
@@ -32,6 +35,7 @@ func (s *SuperBlock) Bytes() []byte {
 	header[0] = byte(s.version)
 	header[1] = s.ReplicaPlacement.Byte()
 	s.Ttl.ToBytes(header[2:4])
+	util.Uint16toBytes(header[4:6], s.CompactRevision)
 	return header
 }
 
@@ -72,5 +76,6 @@ func ParseSuperBlock(header []byte) (superBlock SuperBlock, err error) {
 		err = fmt.Errorf("cannot read replica type: %s", err.Error())
 	}
 	superBlock.Ttl = LoadTTLFromBytes(header[2:4])
+	superBlock.CompactRevision = util.BytesToUint16(header[4:6])
 	return
 }