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81 lines
2.2 KiB
81 lines
2.2 KiB
package storage
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import (
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"fmt"
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"os"
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"github.com/chrislusf/seaweedfs/weed/glog"
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"github.com/chrislusf/seaweedfs/weed/util"
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)
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const (
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SuperBlockSize = 8
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)
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/*
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* Super block currently has 8 bytes allocated for each volume.
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* Byte 0: version, 1 or 2
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* Byte 1: Replica Placement strategy, 000, 001, 002, 010, etc
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* Byte 2 and byte 3: Time to live. See TTL for definition
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* Byte 4 and byte 5: The number of times the volume has been compacted.
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* Rest bytes: Reserved
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*/
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type SuperBlock struct {
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version Version
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ReplicaPlacement *ReplicaPlacement
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Ttl *TTL
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CompactRevision uint16
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}
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func (s *SuperBlock) Version() Version {
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return s.version
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}
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func (s *SuperBlock) Bytes() []byte {
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header := make([]byte, SuperBlockSize)
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header[0] = byte(s.version)
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header[1] = s.ReplicaPlacement.Byte()
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s.Ttl.ToBytes(header[2:4])
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util.Uint16toBytes(header[4:6], s.CompactRevision)
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return header
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}
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func (v *Volume) maybeWriteSuperBlock() error {
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stat, e := v.dataFile.Stat()
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if e != nil {
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glog.V(0).Infof("failed to stat datafile %s: %v", v.dataFile, e)
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return e
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}
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if stat.Size() == 0 {
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v.SuperBlock.version = CurrentVersion
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_, e = v.dataFile.Write(v.SuperBlock.Bytes())
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if e != nil && os.IsPermission(e) {
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//read-only, but zero length - recreate it!
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if v.dataFile, e = os.Create(v.dataFile.Name()); e == nil {
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if _, e = v.dataFile.Write(v.SuperBlock.Bytes()); e == nil {
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v.readOnly = false
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}
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}
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}
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}
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return e
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}
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func (v *Volume) readSuperBlock() (err error) {
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if _, err = v.dataFile.Seek(0, 0); err != nil {
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return fmt.Errorf("cannot seek to the beginning of %s: %v", v.dataFile.Name(), err)
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}
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header := make([]byte, SuperBlockSize)
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if _, e := v.dataFile.Read(header); e != nil {
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return fmt.Errorf("cannot read volume %d super block: %v", v.Id, e)
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}
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v.SuperBlock, err = ParseSuperBlock(header)
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return err
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}
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func ParseSuperBlock(header []byte) (superBlock SuperBlock, err error) {
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superBlock.version = Version(header[0])
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if superBlock.ReplicaPlacement, err = NewReplicaPlacementFromByte(header[1]); err != nil {
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err = fmt.Errorf("cannot read replica type: %s", err.Error())
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}
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superBlock.Ttl = LoadTTLFromBytes(header[2:4])
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superBlock.CompactRevision = util.BytesToUint16(header[4:6])
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return
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}
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