seaweedfs/weed/storage/volume_super_block.go

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package storage
import (
"fmt"
"os"
"github.com/chrislusf/seaweedfs/weed/glog"
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"github.com/chrislusf/seaweedfs/weed/pb/master_pb"
"github.com/chrislusf/seaweedfs/weed/util"
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"github.com/golang/protobuf/proto"
)
const (
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_SuperBlockSize = 8
)
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/*
* 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
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*/
type SuperBlock struct {
version Version
ReplicaPlacement *ReplicaPlacement
Ttl *TTL
CompactRevision uint16
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Extra *master_pb.SuperBlockExtra
extraSize uint16
}
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func (s *SuperBlock) BlockSize() int {
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switch s.version {
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case Version2, Version3:
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return _SuperBlockSize + int(s.extraSize)
}
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return _SuperBlockSize
}
func (s *SuperBlock) Version() Version {
return s.version
}
func (s *SuperBlock) Bytes() []byte {
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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.CompactRevision)
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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
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glog.Fatalf("super block extra size is %d bigger than %d", extraSize, 256*256-2)
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}
s.extraSize = uint16(extraSize)
util.Uint16toBytes(header[6:8], s.extraSize)
header = append(header, extraData...)
}
return header
}
func (v *Volume) maybeWriteSuperBlock() error {
stat, e := v.dataFile.Stat()
if e != nil {
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glog.V(0).Infof("failed to stat datafile %s: %v", v.dataFile.Name(), 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
}
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func (v *Volume) readSuperBlock() (err error) {
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v.SuperBlock, err = ReadSuperBlock(v.dataFile)
return err
}
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// ReadSuperBlock reads from data file and load it into volume's super block
func ReadSuperBlock(dataFile *os.File) (superBlock SuperBlock, err error) {
if _, err = dataFile.Seek(0, 0); err != nil {
err = fmt.Errorf("cannot seek to the beginning of %s: %v", dataFile.Name(), err)
return
}
header := make([]byte, _SuperBlockSize)
if _, e := dataFile.Read(header); e != nil {
err = fmt.Errorf("cannot read volume %s super block: %v", dataFile.Name(), e)
return
}
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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
}
superBlock.Ttl = LoadTTLFromBytes(header[2:4])
superBlock.CompactRevision = util.BytesToUint16(header[4:6])
superBlock.extraSize = util.BytesToUint16(header[6:8])
if superBlock.extraSize > 0 {
// read more
extraData := make([]byte, int(superBlock.extraSize))
superBlock.Extra = &master_pb.SuperBlockExtra{}
err = proto.Unmarshal(extraData, superBlock.Extra)
if err != nil {
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err = fmt.Errorf("cannot read volume %s super block extra: %v", dataFile.Name(), err)
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return
}
}
return
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}