1 files changed, 69 insertions, 0 deletions
diff --git a/weed/storage/super_block/super_block.go b/weed/storage/super_block/super_block.go
new file mode 100644
index 000000000..f48cd0bdc
--- /dev/null
+++ b/weed/storage/super_block/super_block.go
@@ -0,0 +1,69 @@
+package super_block
+
+import (
+	"github.com/golang/protobuf/proto"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+	"github.com/chrislusf/seaweedfs/weed/pb/master_pb"
+	"github.com/chrislusf/seaweedfs/weed/storage/needle"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+const (
+	SuperBlockSize = 8
+)
+
+/*
+* Super block currently has 8 bytes allocated for each volume.
+* 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            needle.Version
+	ReplicaPlacement   *ReplicaPlacement
+	Ttl                *needle.TTL
+	CompactionRevision uint16
+	Extra              *master_pb.SuperBlockExtra
+	ExtraSize          uint16
+}
+
+func (s *SuperBlock) BlockSize() int {
+	switch s.Version {
+	case needle.Version2, needle.Version3:
+		return SuperBlockSize + int(s.ExtraSize)
+	}
+	return SuperBlockSize
+}
+
+func (s *SuperBlock) Bytes() []byte {
+	header := make([]byte, SuperBlockSize)
+	header[0] = byte(s.Version)
+	header[1] = s.ReplicaPlacement.Byte()
+	s.Ttl.ToBytes(header[2:4])
+	util.Uint16toBytes(header[4:6], s.CompactionRevision)
+
+	if s.Extra != nil {
+		extraData, err := proto.Marshal(s.Extra)
+		if err != nil {
+			glog.Fatalf("cannot marshal super block extra %+v: %v", s.Extra, err)
+		}
+		extraSize := len(extraData)
+		if extraSize > 256*256-2 {
+			// reserve a couple of bits for future extension
+			glog.Fatalf("super block extra size is %d bigger than %d", extraSize, 256*256-2)
+		}
+		s.ExtraSize = uint16(extraSize)
+		util.Uint16toBytes(header[6:8], s.ExtraSize)
+
+		header = append(header, extraData...)
+	}
+
+	return header
+}
+
+func (s *SuperBlock) Initialized() bool {
+	return s.ReplicaPlacement != nil && s.Ttl != nil
+}