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|
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
}
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