package storage import ( "encoding/binary" "fmt" "os" "github.com/chrislusf/seaweedfs/go/glog" ) 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 Version ReplicaPlacement *ReplicaPlacement Ttl *TTL CompactRevision uint16 } func (s *SuperBlock) Version() Version { return s.version } 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]) binary.BigEndian.PutUint16(header[4:6], s.CompactRevision) return header } func (v *Volume) maybeWriteSuperBlock() error { stat, e := v.dataFile.Stat() if e != nil { glog.V(0).Infof("failed to stat datafile %s: %v", v.dataFile, e) 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: %v", v.dataFile.Name(), err) } header := make([]byte, SuperBlockSize) if _, e := v.dataFile.Read(header); e != nil { return fmt.Errorf("cannot read volume %d super block: %v", v.Id, e) } 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()) } superBlock.Ttl = LoadTTLFromBytes(header[2:4]) superBlock.CompactRevision = binary.BigEndian.Uint16(header[4:6]) return }