seaweedfs/weed/storage/disk_location.go

package storage

import (
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"slices"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/google/uuid"
	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/stats"
	"github.com/seaweedfs/seaweedfs/weed/storage/erasure_coding"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/storage/volume_info"
	"github.com/seaweedfs/seaweedfs/weed/util"
)

const (
	UUIDFileName = "vol_dir.uuid"
	UUIDFileMod  = 0644
)

type DiskLocation struct {
	Directory              string
	DirectoryUuid          string
	IdxDirectory           string
	DiskType               types.DiskType
	Tags                   []string
	MaxVolumeCount         int32
	OriginalMaxVolumeCount int32
	MinFreeSpace           util.MinFreeSpace
	AvailableSpace         atomic.Uint64
	// Headroom promised to in-flight copies that statfs cannot see yet.
	// Probes keep it out of AvailableSpace so they cannot re-spend it; a
	// copy that lands ends its charge, one that fails removes only its own.
	ReservedSpace atomic.Uint64
	// Physical filesystem capacity from the latest CheckDiskSpace probe, reported
	// to the master so balancing can see real disk fullness, not just slot counts.
	diskTotalBytes atomic.Uint64
	diskFreeBytes  atomic.Uint64
	volumes        map[needle.VolumeId]*Volume
	volumesLock    sync.RWMutex

	// erasure coding
	ecVolumes     map[needle.VolumeId]*erasure_coding.EcVolume
	ecVolumesLock sync.RWMutex
	// vids whose EcVolume was removed from ecVolumes but is still being
	// destroyed off-lock; the channel closes when Destroy returns. A remount
	// of the vid must wait for it, or the dying volume could unlink files
	// the new one just opened.
	ecVolumesDestroying map[needle.VolumeId]chan struct{}

	ecShardNotifyHandler func(collection string, vid needle.VolumeId, shardId erasure_coding.ShardId, ecVolume *erasure_coding.EcVolume)

	isDiskSpaceLow    atomic.Bool
	isDiskUnavailable atomic.Bool
	syncBatch         SyncBatchOption
	closeCh           chan struct{}
}

func GenerateDirUuid(dir string) (dirUuidString string, err error) {
	glog.V(1).Infof("Getting uuid of volume directory:%s", dir)
	fileName := filepath.Join(dir, UUIDFileName)
	if !util.FileExists(fileName) {
		dirUuidString, err = writeNewUuid(fileName)
	} else {
		uuidData, readErr := os.ReadFile(fileName)
		if readErr != nil {
			return "", fmt.Errorf("failed to read uuid from %s : %v", fileName, readErr)
		}
		if len(uuidData) > 0 {
			dirUuidString = string(uuidData)
		} else {
			dirUuidString, err = writeNewUuid(fileName)
		}
	}
	return dirUuidString, err
}

func writeNewUuid(fileName string) (string, error) {
	dirUuid, _ := uuid.NewRandom()
	dirUuidString := dirUuid.String()
	if err := util.WriteFile(fileName, []byte(dirUuidString), UUIDFileMod); err != nil {
		return "", fmt.Errorf("failed to write uuid to %s : %v", fileName, err)
	}
	return dirUuidString, nil
}

func NewDiskLocation(dir string, maxVolumeCount int32, minFreeSpace util.MinFreeSpace, idxDir string, diskType types.DiskType, tags []string, config stats.DiskIOProbeConfig) *DiskLocation {
	glog.V(4).Infof("Added new Disk %s: maxVolumes=%d", dir, maxVolumeCount)
	dir = util.ResolvePath(dir)
	if idxDir == "" {
		idxDir = dir
	} else {
		idxDir = util.ResolvePath(idxDir)
		if err := os.MkdirAll(idxDir, 0755); err != nil {
			glog.Fatalf("cannot create idx dir %s: %v", idxDir, err)
		}
	}
	dirUuid, err := GenerateDirUuid(dir)
	if err != nil {
		glog.Fatalf("cannot generate uuid of dir %s: %v", dir, err)
	}
	// Defensive copy of tags to prevent external mutation
	var copiedTags []string
	if len(tags) > 0 {
		copiedTags = make([]string, len(tags))
		copy(copiedTags, tags)
	}
	location := &DiskLocation{
		Directory:              dir,
		DirectoryUuid:          dirUuid,
		IdxDirectory:           idxDir,
		DiskType:               diskType,
		Tags:                   copiedTags,
		MaxVolumeCount:         maxVolumeCount,
		OriginalMaxVolumeCount: maxVolumeCount,
		MinFreeSpace:           minFreeSpace,
		syncBatch:              DefaultSyncBatchOption,
	}
	location.volumes = make(map[needle.VolumeId]*Volume)
	location.ecVolumes = make(map[needle.VolumeId]*erasure_coding.EcVolume)
	location.ecVolumesDestroying = make(map[needle.VolumeId]chan struct{})
	location.closeCh = make(chan struct{})
	go func() {
		location.CheckDiskSpace(config)
		for {
			select {
			case <-location.closeCh:
				return
			case <-time.After(time.Minute):
				location.CheckDiskSpace(config)
			}
		}
	}()
	return location
}

func volumeIdFromFileName(filename string) (needle.VolumeId, string, error) {
	if isValidVolume(filename) {
		base := filename[:len(filename)-4]
		collection, volumeId, err := parseCollectionVolumeId(base)
		return volumeId, collection, err
	}

	return 0, "", fmt.Errorf("file is not a volume: %s", filename)
}

func parseCollectionVolumeId(base string) (collection string, vid needle.VolumeId, err error) {
	i := strings.LastIndex(base, "_")
	if i > 0 {
		collection, base = base[0:i], base[i+1:]
	}
	vol, err := needle.NewVolumeId(base)
	return collection, vol, err
}

func isValidVolume(basename string) bool {
	return strings.HasSuffix(basename, ".idx") || strings.HasSuffix(basename, ".vif")
}

func getValidVolumeName(basename string) string {
	if isValidVolume(basename) {
		return basename[:len(basename)-4]
	}
	return ""
}

// hasEcxFile reports whether an .ecx for volumeName exists on this disk.
// Checks the local Directory first (where the index sits co-located with the
// shards during a move or reconstruct), then the shared IdxDirectory.
func (l *DiskLocation) hasEcxFile(volumeName string) bool {
	if util.FileExists(filepath.Join(l.Directory, volumeName+".ecx")) {
		return true
	}
	if l.IdxDirectory != l.Directory {
		return util.FileExists(filepath.Join(l.IdxDirectory, volumeName+".ecx"))
	}
	return false
}

// removeEmptyEcDatStub removes a leftover empty EC .dat stub and returns
// whether one was swept. A stub is an empty .dat (<= a superblock, i.e. zero
// needles) whose .vif records an EC shard config. An EC volume keeps no local
// .dat, so the stub holds no data -- its shards live on other servers. Such
// stubs (phantoms from the pre-fix loader) otherwise load as phantom empty
// volumes, and a same-vid stub on two disks can shadow a real replica. The
// .dat and its empty .idx are removed; non-EC empty .dat files are left alone.
// The .vif is looked up in both the data and idx directories (which differ
// only when -dir.idx is configured).
func (l *DiskLocation) removeEmptyEcDatStub(volumeName string, vid needle.VolumeId, collection string) bool {
	datPath := l.Directory + "/" + volumeName + ".dat"
	if fi, err := os.Stat(datPath); err != nil || fi.Size() > int64(super_block.SuperBlockSize) {
		return false
	}
	if !vifIsEcVolume(l.Directory+"/"+volumeName+".vif") &&
		!(l.IdxDirectory != l.Directory && vifIsEcVolume(l.IdxDirectory+"/"+volumeName+".vif")) {
		return false
	}
	glog.Warningf("removing leftover empty .dat stub for EC volume %d (collection=%q)", vid, collection)
	os.Remove(datPath)
	os.Remove(l.IdxDirectory + "/" + volumeName + ".idx")
	return true
}

// vifIsEcVolume reports whether the .vif at vifPath records an EC shard config.
func vifIsEcVolume(vifPath string) bool {
	vi, _, _, err := volume_info.MaybeLoadVolumeInfo(vifPath)
	return err == nil && vi.GetEcShardConfig() != nil
}

func (l *DiskLocation) loadExistingVolume(basename string, needleMapKind NeedleMapKind, skipIfEcVolumesExists bool, ldbTimeout int64, diskId uint32) bool {
	volumeName := getValidVolumeName(basename)
	if volumeName == "" {
		return false
	}

	// parse out collection, volume id (moved up to use in EC validation)
	vid, collection, err := volumeIdFromFileName(basename)
	if err != nil {
		glog.Warningf("get volume id failed, %s, err : %s", volumeName, err)
		return false
	}

	// Sweep a leftover empty .dat stub before any EC presence checks below.
	// It must go first: next to an .ecx it would otherwise make
	// validateEcVolume mistake a healthy distributed EC volume for an
	// interrupted local encode and delete its shards.
	if l.removeEmptyEcDatStub(volumeName, vid, collection) {
		return false
	}

	// A .vif next to an .ecx with no .idx beside it is EC shard metadata, not a
	// regular volume. Without this guard NewVolume below would create a phantom
	// empty .dat. Ask for the .idx rather than trust which of a volume's two
	// entries the scan handed over: an .idx next to the .ecx is an interrupted
	// encode, and validateEcVolume below is what decides that one.
	if strings.HasSuffix(basename, ".vif") && l.hasEcxFile(volumeName) &&
		!util.FileExists(l.Directory+"/"+volumeName+".idx") {
		glog.V(1).Infof("loadExistingVolume: skipping .vif-only entry for volume %d (collection=%q); .ecx present", vid, collection)
		return false
	}

	// skip if ec volumes exists, but validate EC files first
	if skipIfEcVolumesExists {
		if l.hasEcxFile(volumeName) {
			// Validate EC volume: shard count, size consistency, and expected size vs .dat file
			if !l.validateEcVolume(collection, vid) {
				glog.Warningf("EC volume %d validation failed, removing incomplete EC files to allow .dat file loading", vid)
				l.removeEcVolumeFiles(collection, vid)
				// Continue to load .dat file
			} else {
				// Valid EC volume exists, skip .dat file
				return false
			}
		}
	}

	// check for incomplete volume
	noteFile := l.Directory + "/" + volumeName + ".note"
	if util.FileExists(noteFile) {
		note, _ := os.ReadFile(noteFile)
		glog.Warningf("volume %s was not completed: %s", volumeName, string(note))
		// Keep the .vif when an .ecx for this vid coexists on the disk: the
		// regular and EC volumes share <base>.vif, so removing the incomplete
		// regular copy must not strip the EC volume's info file.
		keepVif := l.hasEcxFile(volumeName)
		removeVolumeFiles(l.Directory+"/"+volumeName, keepVif)
		removeVolumeFiles(l.IdxDirectory+"/"+volumeName, keepVif)
		return false
	}

	// avoid loading one volume more than once
	l.volumesLock.RLock()
	_, found := l.volumes[vid]
	l.volumesLock.RUnlock()
	if found {
		glog.V(1).Infof("loaded volume, %v", vid)
		return true
	}

	// Load existing data only; never let NewVolume create a phantom .dat. A
	// lone .vif/.idx (e.g. an EC sidecar whose .ecx is on a sibling disk,
	// which the same-disk hasEcxFile() guard misses) would otherwise get an
	// 8-byte stub that the sibling-.dat prune deletes real shards against.
	// Remote-tiered volumes also have no local .dat, but their .vif points at
	// remote files and must still load via the remote path.
	if !util.FileExists(l.Directory + "/" + volumeName + ".dat") {
		_, hasRemote, _, _ := volume_info.MaybeLoadVolumeInfo(l.Directory + "/" + volumeName + ".vif")
		if !hasRemote && l.IdxDirectory != l.Directory {
			_, hasRemote, _, _ = volume_info.MaybeLoadVolumeInfo(l.IdxDirectory + "/" + volumeName + ".vif")
		}
		if !hasRemote {
			glog.V(1).Infof("loadExistingVolume: skipping volume %d (collection=%q); no .dat and no remote file", vid, collection)
			return false
		}
	}

	// load the volume
	v, e := NewVolume(l.Directory, l.IdxDirectory, collection, vid, needleMapKind, nil, nil, 0, needle.GetCurrentVersion(), 0, ldbTimeout)
	if e != nil {
		glog.V(0).Infof("new volume %s error %s", volumeName, e)
		return false
	}

	v.diskId = diskId // Set the disk ID for existing volumes
	l.SetVolume(vid, v)

	size, _, _ := v.FileStat()
	glog.V(2).Infof("data file %s, replication=%s v=%d size=%d ttl=%s disk_id=%d",
		l.Directory+"/"+volumeName+".dat", v.ReplicaPlacement, v.Version(), size, v.Ttl.String(), diskId)
	return true
}

func (l *DiskLocation) concurrentLoadingVolumes(needleMapKind NeedleMapKind, concurrency int, ldbTimeout int64, diskId uint32) {

	// Read the directory to its end before the workers start writing into it:
	// loading a volume creates .sdx, .vif and .ldb files in the same directory,
	// and a stream left open across those writes is not guaranteed to hand back
	// every entry it has not reached yet. Only the names are kept, one per
	// volume, which is what the dedup here always held.
	foundVolumeNames := make(map[string]string)
	if err := eachDirEntry(l.Directory, func(entry os.DirEntry) bool {
		if entry.IsDir() {
			return true
		}
		volumeName := getValidVolumeName(entry.Name())
		if volumeName == "" {
			return true
		}
		if _, found := foundVolumeNames[volumeName]; !found {
			foundVolumeNames[volumeName] = entry.Name()
		}
		return true
	}); err != nil {
		glog.Warningf("scan volume directory %s: %v", l.Directory, err)
	}

	task_queue := make(chan string, 10*concurrency)
	go func() {
		for _, basename := range foundVolumeNames {
			task_queue <- basename
		}
		close(task_queue)
	}()

	var wg sync.WaitGroup
	for workerNum := 0; workerNum < concurrency; workerNum++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for basename := range task_queue {
				_ = l.loadExistingVolume(basename, needleMapKind, true, ldbTimeout, diskId)
			}
		}()
	}
	wg.Wait()

}

func (l *DiskLocation) loadExistingVolumes(needleMapKind NeedleMapKind, ldbTimeout int64) {
	l.loadExistingVolumesWithId(needleMapKind, ldbTimeout, 0) // Default disk ID for backward compatibility
}

func (l *DiskLocation) loadExistingVolumesWithId(needleMapKind NeedleMapKind, ldbTimeout int64, diskId uint32) {

	workerNum := runtime.NumCPU()
	val, ok := os.LookupEnv("GOMAXPROCS")
	if ok {
		num, err := strconv.Atoi(val)
		if err != nil || num < 1 {
			num = 10
			glog.Warningf("failed to set worker number from GOMAXPROCS , set to default:10")
		}
		workerNum = num
	} else {
		if workerNum <= 10 {
			workerNum = 10
		}
	}
	// Recover any interrupted compaction commit before the volume scan. This
	// must run here, not inside loadExistingVolume: that loop is keyed on
	// .idx/.vif entries and would miss the marker-only or already-renamed-.idx
	// states a mid-commit crash can leave behind.
	l.reconcileCompactStates()

	l.concurrentLoadingVolumes(needleMapKind, workerNum, ldbTimeout, diskId)
	glog.V(2).Infof("Store started on dir: %s with %d volumes max %d (disk ID: %d)", l.Directory, len(l.volumes), l.MaxVolumeCount, diskId)

	l.loadAllEcShards(l.ecShardNotifyHandler)
	glog.V(2).Infof("Store started on dir: %s with %d ec shards (disk ID: %d)", l.Directory, len(l.ecVolumes), diskId)

}

// reconcileCompactStates is the directory pre-pass that recovers interrupted
// compaction commits. It collects every volume id that still has a .cpc commit
// marker or a leftover .cpd/.cpx temp file across the data and idx directories,
// then runs reconcileCompactState per volume to roll the swap forward (marker
// present) or back (marker absent).
func (l *DiskLocation) reconcileCompactStates() {
	type volKey struct {
		collection string
		vid        needle.VolumeId
	}
	pending := make(map[volKey]bool)
	collect := func(dir string) {
		if err := eachDirEntry(dir, func(entry os.DirEntry) bool {
			if entry.IsDir() {
				return true
			}
			name := entry.Name()
			if !strings.HasSuffix(name, ".cpc") && !strings.HasSuffix(name, ".cpd") && !strings.HasSuffix(name, ".cpx") {
				return true
			}
			collection, vid, err := parseCollectionVolumeId(name[:len(name)-4])
			if err != nil {
				return true
			}
			pending[volKey{collection, vid}] = true
			return true
		}); err != nil {
			glog.Warningf("scan %s for interrupted compactions: %v", dir, err)
		}
	}
	collect(l.Directory)
	if l.IdxDirectory != l.Directory {
		collect(l.IdxDirectory)
	}

	for k := range pending {
		// On a runtime reload (SIGHUP -> LoadNewVolumes), an already-loaded
		// volume may be mid-vacuum: its .cpd/.cpx are live, not crash
		// leftovers, and rolling them back would clobber the in-flight
		// compaction (and remove a live .ldb). Only reconcile vids that are
		// not currently loaded; genuine startup recovery runs before any
		// volume is loaded, so the map is empty then.
		l.volumesLock.RLock()
		_, loaded := l.volumes[k.vid]
		l.volumesLock.RUnlock()
		if loaded {
			continue
		}
		v := &Volume{dir: l.Directory, dirIdx: l.IdxDirectory, Collection: k.collection, Id: k.vid}
		if err := v.reconcileCompactState(); err != nil {
			glog.Errorf("volume %d: reconcile interrupted compaction failed: %v", k.vid, err)
		}
	}
}

// DeleteCollectionFromDiskLocation destroys the collection's volumes and ec
// shards, and returns the volumes it destroyed so the caller can tell the
// master they are gone.
func (l *DiskLocation) DeleteCollectionFromDiskLocation(collection string) (deleted []*Volume, e error) {

	l.volumesLock.Lock()
	delVolsMap := l.unmountVolumeByCollection(collection)
	l.volumesLock.Unlock()

	l.ecVolumesLock.Lock()
	delEcVolsMap := l.unmountEcVolumeByCollection(collection)
	l.ecVolumesLock.Unlock()

	errChain := make(chan error, 2)
	var wg sync.WaitGroup
	wg.Add(2)
	go func() {
		for k, v := range delVolsMap {
			if err := v.Destroy(false, false, false); err != nil {
				errChain <- err
			} else {
				l.volumesLock.Lock()
				delete(l.volumes, k)
				l.volumesLock.Unlock()
				deleted = append(deleted, v)
			}
		}
		wg.Done()
	}()

	go func() {
		for k, v := range delEcVolsMap {
			v.Destroy()
			l.ecVolumesLock.Lock()
			done := l.ecVolumesDestroying[k]
			l.ecVolumesLock.Unlock()
			close(done)
		}
		wg.Done()
	}()

	go func() {
		wg.Wait()
		close(errChain)
	}()

	errBuilder := strings.Builder{}
	for err := range errChain {
		errBuilder.WriteString(err.Error())
		errBuilder.WriteString("; ")
	}
	if errBuilder.Len() > 0 {
		e = fmt.Errorf("%s", errBuilder.String())
	}

	return
}

func (l *DiskLocation) deleteVolumeById(vid needle.VolumeId, onlyEmpty bool, onlyGarbage bool, keepRemoteData bool) (found bool, e error) {
	v, ok := l.volumes[vid]
	if !ok {
		return
	}
	e = v.Destroy(onlyEmpty, onlyGarbage, keepRemoteData)
	if e != nil {
		return
	}
	found = true
	delete(l.volumes, vid)
	return
}

func (l *DiskLocation) LoadVolume(diskId uint32, vid needle.VolumeId, needleMapKind NeedleMapKind, collection *string) bool {
	if collection != nil {
		for _, ext := range []string{".vif", ".idx"} {
			filename := VolumeFileName(l.Directory, *collection, int(vid)) + ext
			if fi, err := os.Stat(filename); err == nil && !fi.IsDir() {
				return l.loadExistingVolume(fi.Name(), needleMapKind, false, 0, diskId)
			}
		}
	}
	if fileInfo, found := l.LocateVolume(vid); found {
		return l.loadExistingVolume(fileInfo.Name(), needleMapKind, false, 0, diskId)
	}
	return false
}

var ErrVolumeNotFound = fmt.Errorf("volume not found")

func (l *DiskLocation) DeleteVolume(vid needle.VolumeId, onlyEmpty bool, onlyGarbage bool, keepRemoteData bool) error {
	l.volumesLock.Lock()
	defer l.volumesLock.Unlock()

	_, ok := l.volumes[vid]
	if !ok {
		return ErrVolumeNotFound
	}
	_, err := l.deleteVolumeById(vid, onlyEmpty, onlyGarbage, keepRemoteData)
	return err
}

func (l *DiskLocation) UnloadVolume(vid needle.VolumeId) error {
	l.volumesLock.Lock()
	defer l.volumesLock.Unlock()

	v, ok := l.volumes[vid]
	if !ok {
		return ErrVolumeNotFound
	}
	v.Close()
	delete(l.volumes, vid)
	return nil
}

func (l *DiskLocation) unmountVolumeByCollection(collectionName string) map[needle.VolumeId]*Volume {
	deltaVols := make(map[needle.VolumeId]*Volume, 0)
	for k, v := range l.volumes {
		if v.Collection == collectionName && !v.isCompactionInProgress.Load() {
			deltaVols[k] = v
		}
	}
	return deltaVols
}

func (l *DiskLocation) SetVolume(vid needle.VolumeId, volume *Volume) {
	l.volumesLock.Lock()
	defer l.volumesLock.Unlock()

	l.volumes[vid] = volume
	volume.location = l
}

func (l *DiskLocation) FindVolume(vid needle.VolumeId) (*Volume, bool) {
	l.volumesLock.RLock()
	defer l.volumesLock.RUnlock()

	v, ok := l.volumes[vid]
	return v, ok
}

// Returns all regular volume IDs stored at this location.
func (l *DiskLocation) VolumeIds() []needle.VolumeId {
	l.volumesLock.RLock()
	defer l.volumesLock.RUnlock()

	vids := make([]needle.VolumeId, len(l.volumes))
	i := 0
	for vid := range l.volumes {
		vids[i] = vid
		i++
	}

	slices.Sort(vids)
	return vids
}

// Returns all EC volume IDs stored at this location.
func (l *DiskLocation) EcVolumeIds() []needle.VolumeId {
	l.ecVolumesLock.RLock()
	defer l.ecVolumesLock.RUnlock()

	vids := make([]needle.VolumeId, len(l.ecVolumes))
	i := 0
	for vid := range l.ecVolumes {
		vids[i] = vid
		i++
	}

	slices.Sort(vids)
	return vids
}

func (l *DiskLocation) VolumesLen() int {
	l.volumesLock.RLock()
	defer l.volumesLock.RUnlock()

	return len(l.volumes)
}

func (l *DiskLocation) LocalVolumesLen() int {
	l.volumesLock.RLock()
	defer l.volumesLock.RUnlock()

	count := 0
	for _, v := range l.volumes {
		if !v.HasRemoteFile() {
			count++
		}
	}
	return count
}

func (l *DiskLocation) SetStopping() {
	l.volumesLock.Lock()
	for _, v := range l.volumes {
		v.SyncToDisk()
	}
	l.volumesLock.Unlock()

	return
}

func (l *DiskLocation) Close() {
	l.volumesLock.Lock()
	for _, v := range l.volumes {
		v.Close()
	}
	l.volumesLock.Unlock()

	l.ecVolumesLock.Lock()
	ecVolumes := make([]*erasure_coding.EcVolume, 0, len(l.ecVolumes))
	for vid, ecVolume := range l.ecVolumes {
		ecVolumes = append(ecVolumes, ecVolume)
		delete(l.ecVolumes, vid)
	}
	l.ecVolumesLock.Unlock()

	// Close outside the write lock: EcVolume.Close takes the deletion-journal
	// lock, which a running ec.decode can hold — closing under the map lock
	// would stall every EC lookup and invert the map->journal lock order.
	for _, ecVolume := range ecVolumes {
		ecVolume.Close()
	}

	close(l.closeCh)
	return
}

func (l *DiskLocation) LocateVolume(vid needle.VolumeId) (os.DirEntry, bool) {
	var found os.DirEntry
	if err := eachDirEntry(l.Directory, func(entry os.DirEntry) bool {
		if entry.IsDir() {
			return true
		}
		volId, _, err := volumeIdFromFileName(entry.Name())
		if vid == volId && err == nil {
			found = entry
			return false
		}
		return true
	}); err != nil {
		glog.Warningf("locate volume %d in %s: %v", vid, l.Directory, err)
	}
	return found, found != nil
}

func (l *DiskLocation) UnUsedSpace(volumeSizeLimit uint64) (unUsedSpace uint64) {
	l.volumesLock.RLock()
	defer l.volumesLock.RUnlock()

	for _, vol := range l.volumes {
		if vol.IsReadOnly() {
			continue
		}
		datSize, idxSize, _ := vol.FileStat()
		// A preallocated volume already holds its space on disk.
		datSize = max(datSize, vol.datAllocatedSize())
		unUsedSpaceVolume := int64(volumeSizeLimit) - int64(datSize+idxSize)
		glog.V(4).Infof("Volume stats for %d: volumeSizeLimit=%d, datSize=%d idxSize=%d unused=%d", vol.Id, volumeSizeLimit, datSize, idxSize, unUsedSpaceVolume)
		if unUsedSpaceVolume >= 0 {
			unUsedSpace += uint64(unUsedSpaceVolume)
		}
	}

	return
}

// newDiskStatus is a seam letting a test observe the config CheckDiskSpace probes with.
var newDiskStatus = stats.NewDiskStatusOnStart

func (l *DiskLocation) CheckDiskSpace(config stats.DiskIOProbeConfig) {
	config.SlowLatency = config.SlowLatencyFor(l.DiskType.ReadableString())
	if dir, e := filepath.Abs(l.Directory); e == nil {
		s := newDiskStatus(dir, config)
		if len(s.Error) != 0 {
			l.isDiskUnavailable.Store(true)
			stats.VolumeServerDiskErrorGauge.WithLabelValues(l.Directory, "error").Set(1)
			glog.V(1).Infof("disk %s is not healthy: %s", dir, s.Error)
		} else {
			l.isDiskUnavailable.Store(false)
			stats.VolumeServerDiskErrorGauge.WithLabelValues(l.Directory, "error").Set(0)
		}
		available := l.MinFreeSpace.AvailableSpace(s.Free, s.All)
		stats.VolumeServerResourceGauge.WithLabelValues(l.Directory, "all").Set(float64(s.All))
		stats.VolumeServerResourceGauge.WithLabelValues(l.Directory, "used").Set(float64(s.Used))
		stats.VolumeServerResourceGauge.WithLabelValues(l.Directory, "free").Set(float64(s.Free))
		stats.VolumeServerResourceGauge.WithLabelValues(l.Directory, "avail").Set(float64(available))
		if pending := l.ReservedSpace.Load(); pending < available {
			l.AvailableSpace.Store(available - pending)
		} else {
			l.AvailableSpace.Store(0)
		}
		l.diskTotalBytes.Store(s.All)
		l.diskFreeBytes.Store(s.Free)
		isLow, desc := l.MinFreeSpace.IsLow(s.Free, s.PercentFree)
		if isLow != l.isDiskSpaceLow.Load() {
			l.isDiskSpaceLow.Store(isLow)
		}

		logLevel := glog.Level(4)
		if l.isDiskSpaceLow.Load() {
			logLevel = glog.Level(0)
		}

		glog.V(logLevel).Infof("dir %s %s", dir, desc)
	}
}