seaweedfs/weed/storage/erasure_coding/ec_volume.go

package erasure_coding

import (
	"errors"
	"fmt"
	"os"
	"slices"
	"sync"
	"time"

	"github.com/seaweedfs/seaweedfs/weed/glog"
	"github.com/seaweedfs/seaweedfs/weed/pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
	"github.com/seaweedfs/seaweedfs/weed/pb/volume_server_pb"
	"github.com/seaweedfs/seaweedfs/weed/storage/idx"
	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
	"github.com/seaweedfs/seaweedfs/weed/storage/types"
	"github.com/seaweedfs/seaweedfs/weed/storage/volume_info"
)

var (
	NotFoundError             = errors.New("needle not found")
	destroyDelaySeconds int64 = 0
)

type EcVolume struct {
	VolumeId                  needle.VolumeId
	Collection                string
	dir                       string
	dirIdx                    string
	ecxActualDir              string // directory where .ecx/.ecj were actually found (may differ from dirIdx after fallback)
	ecxFile                   *os.File
	ecxFileSize               int64
	ecxCreatedAt              time.Time
	Shards                    []*EcVolumeShard
	ShardLocations            map[ShardId][]pb.ServerAddress
	ShardLocationsRefreshTime time.Time
	// ShardLocationsStale marks the map for a prompt re-check: a read that failed
	// against a cached location has disproved what the map claims, and the normal
	// freshness window is far too long to serve from a map known to be wrong.
	ShardLocationsStale bool
	ShardLocationsLock  sync.RWMutex
	Version             needle.Version
	ecjFile             *os.File
	ecjFileAccessLock   sync.Mutex
	diskType            types.DiskType
	datFileSize         int64
	ExpireAtSec         uint64     //ec volume destroy time, calculated from the ec volume was created
	ECContext           *ECContext // EC encoding parameters

	// EncodeTsNs is the encode time (unix nanos) loaded from .vif; reads carry it
	// so a shard from a different encode run is rejected. 0 for pre-upgrade volumes.
	EncodeTsNs int64

	// ecjFileSize mirrors the on-disk size of the .ecj deletion journal and
	// is maintained under ecjFileAccessLock. It is only used by IO helpers
	// (seek/truncate) — the authoritative runtime delete count comes from
	// deletedNeedles.
	ecjFileSize int64

	// deletedNeedles is the in-memory set of needle ids that have been
	// deleted since the volume was encoded. .ecx is immutable at runtime —
	// it only stores the sorted (id, offset, size) index written at encode
	// time — and runtime deletes are journaled to .ecj + tracked here.
	// Reads consult this set to mask out deleted needles on top of the
	// sealed .ecx lookup. Heartbeat delete_count is derived from len(set).
	// Seeded from .ecj in NewEcVolume and updated under deletedNeedlesLock.
	deletedNeedlesLock sync.RWMutex
	deletedNeedles     map[types.NeedleId]struct{}

	// Bitrot checksum sidecar for the active generation (optional). bitrot is
	// nil unless bitrotStatus == BitrotOn, and is loaded at mount. Guarded by
	// bitrotLock.
	bitrotLock   sync.RWMutex
	bitrot       *volume_server_pb.EcBitrotProtection
	bitrotStatus BitrotStatus
}

// statEcxSize returns the size of an .ecx file, os.ErrNotExist when it is absent
// (or a directory), so the resolver can prefer a non-empty copy.
func statEcxSize(path string) (int64, error) {
	info, statErr := os.Stat(path)
	if statErr != nil {
		return 0, statErr
	}
	if info.IsDir() {
		return 0, os.ErrNotExist
	}
	return info.Size(), nil
}

func NewEcVolume(diskType types.DiskType, dir string, dirIdx string, collection string, vid needle.VolumeId) (ev *EcVolume, err error) {
	ev = &EcVolume{dir: dir, dirIdx: dirIdx, Collection: collection, VolumeId: vid, diskType: diskType}

	dataBaseFileName := EcShardFileName(collection, dir, int(vid))
	indexBaseFileName := EcShardFileName(collection, dirIdx, int(vid))

	// open ecx file. Wrap errors with %w so callers walking up the stack
	// (notably Store.MountEcShards) can use errors.Is(err, os.ErrNotExist)
	// to decide whether to try the next local disk vs. bail. A 0-byte .ecx
	// is a legitimate index for a volume that had no live needles at encode
	// time (e.g. all needles deleted before WriteSortedFileFromIdx) and
	// must mount successfully here. A 0-byte stub left by a failed copy
	// stream is indistinguishable from that empty case by file size alone;
	// preventing such stubs is the receiver-side cleanup in writeToFile's
	// job, not this open path.
	// Resolve the .ecx, preferring the copy co-located with the shard data on
	// this disk — where a move or reconstruct leaves it — then the caller's
	// index directory. That directory is either the shared -dir.idx dir or a
	// sibling disk that owns the .ecx when this disk holds only a 0-byte stub
	// left by an interrupted copy (#9212). A 0-byte .ecx is a legitimate empty
	// index, so the local copy yields only to a *non-empty* copy elsewhere,
	// never to a mere absence: prefer a non-empty .ecx local-first, then fall
	// back to whichever exists at all.
	localBaseFileName := dataBaseFileName
	sharedBaseFileName := indexBaseFileName
	localSize, localErr := statEcxSize(localBaseFileName + ".ecx")
	sharedSize, sharedErr := int64(0), os.ErrNotExist
	if dirIdx != dir {
		sharedSize, sharedErr = statEcxSize(sharedBaseFileName + ".ecx")
	}
	switch {
	case localErr == nil && localSize > 0:
		indexBaseFileName, ev.ecxActualDir = localBaseFileName, dir
	case sharedErr == nil && sharedSize > 0:
		indexBaseFileName, ev.ecxActualDir = sharedBaseFileName, dirIdx
		glog.V(1).Infof("ecx not local at %s.ecx, using %s.ecx", localBaseFileName, sharedBaseFileName)
	case localErr == nil: // local exists but is a 0-byte empty index
		indexBaseFileName, ev.ecxActualDir = localBaseFileName, dir
	case sharedErr == nil: // only a 0-byte copy in the index dir
		indexBaseFileName, ev.ecxActualDir = sharedBaseFileName, dirIdx
	default:
		return nil, fmt.Errorf("cannot open ec volume index %s.ecx (or %s.ecx): %w", localBaseFileName, sharedBaseFileName, os.ErrNotExist)
	}
	if ev.ecxFile, err = os.OpenFile(indexBaseFileName+".ecx", os.O_RDWR, 0644); err != nil {
		return nil, fmt.Errorf("cannot open ec volume index %s.ecx: %w", indexBaseFileName, err)
	}
	ecxFi, statErr := ev.ecxFile.Stat()
	if statErr != nil {
		_ = ev.ecxFile.Close()
		return nil, fmt.Errorf("can not stat ec volume index %s.ecx: %w", indexBaseFileName, statErr)
	}
	ev.ecxFileSize = ecxFi.Size()
	ev.ecxCreatedAt = ecxFi.ModTime()

	// open ecj file and seed the in-memory deleted set from it.
	if ev.ecjFile, err = os.OpenFile(indexBaseFileName+".ecj", os.O_RDWR|os.O_CREATE, 0644); err != nil {
		return nil, fmt.Errorf("cannot open ec volume journal %s.ecj: %v", indexBaseFileName, err)
	}
	if ecjFi, statErr := ev.ecjFile.Stat(); statErr == nil {
		ev.ecjFileSize = ecjFi.Size()
	} else {
		glog.Warningf("stat ec volume journal %s.ecj: %v", indexBaseFileName, statErr)
	}
	ev.deletedNeedles = make(map[types.NeedleId]struct{})
	if loadErr := ev.loadDeletedNeedlesFromEcj(); loadErr != nil {
		glog.Warningf("ec volume %d: load deleted needles from .ecj: %v", vid, loadErr)
	}

	// read volume info. Prefer .vif at the data dir (where shards live), but
	// fall back to the index dir when the data dir does not have one — the
	// orphan-shard reconciliation in Store loads shards on a disk whose only
	// EC artefacts are .ec?? files, with .ecx / .ecj / .vif on a sibling disk
	// (issue #9212). Without this fallback we'd write a stub .vif on the
	// shard disk and lose the real EC config + datFileSize.
	vifFileName := dataBaseFileName + ".vif"
	if dirIdx != dir {
		if _, statErr := os.Stat(vifFileName); statErr != nil && os.IsNotExist(statErr) {
			altVif := EcShardFileName(collection, dirIdx, int(vid)) + ".vif"
			if _, altStatErr := os.Stat(altVif); altStatErr == nil {
				vifFileName = altVif
			}
		}
	}
	ev.Version = needle.Version3
	if volumeInfo, _, found, _ := volume_info.MaybeLoadVolumeInfo(vifFileName); found {
		ev.Version = needle.Version(volumeInfo.Version)
		ev.datFileSize = volumeInfo.DatFileSize
		ev.ExpireAtSec = volumeInfo.ExpireAtSec

		// Initialize EC context from .vif if present; fallback to defaults
		if volumeInfo.EcShardConfig != nil {
			ds := int(volumeInfo.EcShardConfig.DataShards)
			ps := int(volumeInfo.EcShardConfig.ParityShards)
			ev.EncodeTsNs = volumeInfo.EcShardConfig.GetEncodeTsNs()

			// Validate shard counts to prevent zero or invalid values
			if ds <= 0 || ps <= 0 || ds+ps > MaxShardCount {
				glog.Warningf("Invalid EC config in VolumeInfo for volume %d (data=%d, parity=%d), using defaults", vid, ds, ps)
				ev.ECContext = NewDefaultECContext(collection, vid)
			} else {
				ev.ECContext = &ECContext{
					Collection:   collection,
					VolumeId:     vid,
					DataShards:   ds,
					ParityShards: ps,
				}
				glog.V(1).Infof("Loaded EC config from VolumeInfo for volume %d: %s", vid, ev.ECContext.String())
			}
		} else {
			ev.ECContext = NewDefaultECContext(collection, vid)
		}
	} else {
		// Don't fabricate a stub .vif here: a version-only stub implies the
		// default 10+4 ratio with DatFileSize=0 and no encode identity, which
		// the custom-ratio resolver and the startup credibility checks must not
		// mistake for an authoritative config. Mount with in-memory defaults and
		// leave the real .vif to the encoder or a recovery tool (the Rust volume
		// server already behaves this way).
		glog.Warningf("vif file not found, using defaults, volumeId:%d, filename:%s", vid, vifFileName)
		ev.ECContext = NewDefaultECContext(collection, vid)
	}

	ev.ShardLocations = make(map[ShardId][]pb.ServerAddress)

	// Load the active-generation bitrot checksum sidecar (optional).
	ev.loadActiveBitrotSidecar()

	return
}

func (ev *EcVolume) AddEcVolumeShard(ecVolumeShard *EcVolumeShard) bool {
	for _, s := range ev.Shards {
		if s.ShardId == ecVolumeShard.ShardId {
			return false
		}
	}
	ev.Shards = append(ev.Shards, ecVolumeShard)
	slices.SortFunc(ev.Shards, func(a, b *EcVolumeShard) int {
		if a.VolumeId != b.VolumeId {
			return int(a.VolumeId - b.VolumeId)
		}
		return int(a.ShardId - b.ShardId)
	})
	return true
}

func (ev *EcVolume) DeleteEcVolumeShard(shardId ShardId) (ecVolumeShard *EcVolumeShard, deleted bool) {
	foundPosition := -1
	for i, s := range ev.Shards {
		if s.ShardId == shardId {
			foundPosition = i
		}
	}
	if foundPosition < 0 {
		return nil, false
	}

	ecVolumeShard = ev.Shards[foundPosition]
	ecVolumeShard.Unmount()
	ev.Shards = append(ev.Shards[:foundPosition], ev.Shards[foundPosition+1:]...)
	return ecVolumeShard, true
}

func (ev *EcVolume) FindEcVolumeShard(shardId ShardId) (ecVolumeShard *EcVolumeShard, found bool) {
	for _, s := range ev.Shards {
		if s.ShardId == shardId {
			return s, true
		}
	}
	return nil, false
}

func (ev *EcVolume) Close() {
	for _, s := range ev.Shards {
		s.Close()
	}
	ev.ecjFileAccessLock.Lock()
	if ev.ecjFile != nil {
		_ = ev.ecjFile.Close()
		ev.ecjFile = nil
	}
	ev.ecjFileAccessLock.Unlock()
	if ev.ecxFile != nil {
		_ = ev.ecxFile.Sync()
		// Do NOT nil ecxFile: LocateEcShardNeedle reads it without the
		// ecVolumesLock after the resolving lookup released it, so a concurrent
		// eviction that nils the field would race that read. A closed-but-set fd
		// yields a clean read error (recovered from parity) and no data race.
		_ = ev.ecxFile.Close()
	}
}

// Sync flushes the .ecx and .ecj files to disk without closing them.
// This ensures that deletions made via DeleteNeedleFromEcx are visible
// to other processes/file handles that may read these files.
func (ev *EcVolume) Sync() {
	ev.ecjFileAccessLock.Lock()
	if ev.ecjFile != nil {
		if err := ev.ecjFile.Sync(); err != nil {
			glog.Warningf("failed to sync ecj file for volume %d: %v", ev.VolumeId, err)
		}
	}
	ev.ecjFileAccessLock.Unlock()
	if ev.ecxFile != nil {
		if err := ev.ecxFile.Sync(); err != nil {
			glog.Warningf("failed to sync ecx file for volume %d: %v", ev.VolumeId, err)
		}
	}
}

func (ev *EcVolume) Destroy() {
	ev.Close()

	for _, s := range ev.Shards {
		s.Destroy()
	}
	// Sweep the EC-only index files from BOTH the data directory and the shared
	// index directory. A move or reconstruct can leave a copy in whichever
	// directory is not ecxActualDir; removing only the active one leaves a stale
	// index that a later reload could pick up and re-mount as a phantom EC
	// volume. .ecx/.ecj are EC-specific, so removing both copies is safe.
	for _, base := range ev.ecIndexBaseNames() {
		os.Remove(base + ".ecx")
		os.Remove(base + ".ecj")
	}
	// The .vif is shared with a coexisting normal volume (e.g. mid-decode), so
	// only remove the active copy, not both.
	os.Remove(ev.FileName(".vif"))
	// Remove the bitrot checksum sidecar(s) so a later volume reuse cannot load
	// stale protection. Search both the data and index bases.
	RemoveBitrotSidecars(ev.DataBaseFileName())
	if ev.IndexBaseFileName() != ev.DataBaseFileName() {
		RemoveBitrotSidecars(ev.IndexBaseFileName())
	}
}

// ecIndexBaseNames returns the base paths for the volume's EC index files in
// both the data and index directories, deduplicated when they coincide.
func (ev *EcVolume) ecIndexBaseNames() []string {
	bases := []string{ev.DataBaseFileName()}
	if ev.IndexBaseFileName() != ev.DataBaseFileName() {
		bases = append(bases, ev.IndexBaseFileName())
	}
	return bases
}

// DiskType returns the disk type the EC volume currently reports under.
// Defaults to the physical location's disk type; orchestrators can override
// it via SetDiskType so the volume keeps reporting under the source
// volume's disk type after encoding (#9423).
func (ev *EcVolume) DiskType() types.DiskType {
	return ev.diskType
}

// SetDiskType overrides the EC volume's reported disk type and propagates
// to its mounted shards. Intended for the orchestrator-driven mount path
// (VolumeEcShardsMount); not persisted across restarts.
func (ev *EcVolume) SetDiskType(d types.DiskType) {
	ev.diskType = d
	for _, s := range ev.Shards {
		s.DiskType = d
	}
}

func (ev *EcVolume) FileName(ext string) string {
	switch ext {
	case ".ecx", ".ecj":
		return EcShardFileName(ev.Collection, ev.ecxActualDir, int(ev.VolumeId)) + ext
	}
	// .vif
	return ev.DataBaseFileName() + ext
}

func (ev *EcVolume) DataBaseFileName() string {
	return EcShardFileName(ev.Collection, ev.dir, int(ev.VolumeId))
}

func (ev *EcVolume) IndexBaseFileName() string {
	return EcShardFileName(ev.Collection, ev.dirIdx, int(ev.VolumeId))
}

func (ev *EcVolume) ShardSize() uint64 {
	if len(ev.Shards) > 0 {
		return uint64(ev.Shards[0].Size())
	}
	return 0
}

// DatFileSize returns the source .dat file size as recorded in .vif at
// EC encoding time. Zero for old EC volumes whose .vif predates the
// field, or for .vif files we failed to parse. Used by the Store-level
// prune in store_ec_reconcile.go to validate that a sibling-disk .dat
// is plausibly the encoding source before deleting the partial EC.
func (ev *EcVolume) DatFileSize() int64 {
	return ev.datFileSize
}

func (ev *EcVolume) Size() (size uint64) {
	for _, shard := range ev.Shards {
		if shardSize := shard.Size(); shardSize > 0 {
			size += uint64(shardSize)
		}
	}
	return
}

func (ev *EcVolume) CreatedAt() time.Time {
	return ev.ecxCreatedAt
}

func (ev *EcVolume) ShardIdList() (shardIds []ShardId) {
	for _, s := range ev.Shards {
		shardIds = append(shardIds, s.ShardId)
	}
	return
}

func (ev *EcVolume) ToVolumeEcShardInformationMessage(diskId uint32) (messages []*master_pb.VolumeEcShardInformationMessage) {
	ecInfoPerVolume := map[needle.VolumeId]*master_pb.VolumeEcShardInformationMessage{}

	fileCount, deleteCount := ev.FileAndDeleteCount()

	for _, s := range ev.Shards {
		m, ok := ecInfoPerVolume[s.VolumeId]
		if !ok {
			m = &master_pb.VolumeEcShardInformationMessage{
				Id:          uint32(s.VolumeId),
				Collection:  s.Collection,
				DiskType:    string(ev.diskType),
				ExpireAtSec: ev.ExpireAtSec,
				DiskId:      diskId,
				FileCount:   fileCount,
				DeleteCount: deleteCount,
				EncodeTsNs:  ev.EncodeTsNs,
			}
			ecInfoPerVolume[s.VolumeId] = m
		}

		// Update EC shard bits and sizes.
		si := ShardsInfoFromVolumeEcShardInformationMessage(m)
		si.Set(NewShardInfo(s.ShardId, ShardSize(s.Size())))
		m.EcIndexBits = uint32(si.Bitmap())
		m.ShardSizes = si.SizesInt64()
	}

	for _, m := range ecInfoPerVolume {
		messages = append(messages, m)
	}
	return
}

// FileAndDeleteCount returns the current (fileCount, deleteCount) for this
// EC volume.
//
//   - fileCount = .ecx size / NeedleMapEntrySize — the total number of
//     needles recorded in the sealed sorted index. Because .ecx is written
//     at encode time and only overwritten during decode/rebuild (which
//     preserves record count), this matches the "cumulative put count"
//     semantics of regular volume FileCount.
//
//   - deleteCount = len(deletedNeedles) — the number of unique runtime
//     deletes tracked in memory. The set is seeded from .ecj on load and
//     appended to on every successful DeleteNeedleFromEcx. Because a
//     needle delete is applied on exactly one shard holder, the admin
//     aggregation sums deleteCount across nodes to get the volume's true
//     delete total.
//
// Both values are O(1) — no index walking.
func (ev *EcVolume) FileAndDeleteCount() (fileCount, deleteCount uint64) {
	fileCount = uint64(ev.ecxFileSize) / uint64(types.NeedleMapEntrySize)
	ev.deletedNeedlesLock.RLock()
	deleteCount = uint64(len(ev.deletedNeedles))
	ev.deletedNeedlesLock.RUnlock()
	return
}

// IsNeedleDeleted reports whether the given needle id is in the in-memory
// deleted set. Callers that have already looked the needle up in .ecx
// should consult this to apply runtime deletion state on top of the
// sealed index.
func (ev *EcVolume) IsNeedleDeleted(needleId types.NeedleId) bool {
	ev.deletedNeedlesLock.RLock()
	_, ok := ev.deletedNeedles[needleId]
	ev.deletedNeedlesLock.RUnlock()
	return ok
}

// markNeedleDeletedInMemory inserts a needle id into the deleted set.
func (ev *EcVolume) markNeedleDeletedInMemory(needleId types.NeedleId) {
	ev.deletedNeedlesLock.Lock()
	ev.deletedNeedles[needleId] = struct{}{}
	ev.deletedNeedlesLock.Unlock()
}

// loadDeletedNeedlesFromEcj walks the .ecj journal and populates the
// in-memory deleted set. Called once from NewEcVolume under the exclusive
// ownership of the just-constructed (and not yet shared) EcVolume.
func (ev *EcVolume) loadDeletedNeedlesFromEcj() error {
	if ev.ecjFile == nil || ev.ecjFileSize < int64(types.NeedleIdSize) {
		return nil
	}
	buf := make([]byte, types.NeedleIdSize)
	for off := int64(0); off+int64(types.NeedleIdSize) <= ev.ecjFileSize; off += int64(types.NeedleIdSize) {
		if _, err := ev.ecjFile.ReadAt(buf, off); err != nil {
			return fmt.Errorf("read ecj at %d: %w", off, err)
		}
		id := types.BytesToNeedleId(buf)
		ev.deletedNeedles[id] = struct{}{}
	}
	return nil
}

func (ev *EcVolume) LocateEcShardNeedle(needleId types.NeedleId, version needle.Version) (offset types.Offset, size types.Size, intervals []Interval, err error) {

	// find the needle from ecx file
	offset, size, err = ev.FindNeedleFromEcx(needleId)
	if err != nil {
		return types.Offset{}, 0, nil, fmt.Errorf("FindNeedleFromEcx: %w", err)
	}

	intervals = ev.LocateEcShardNeedleInterval(version, offset.ToActualOffset(), types.Size(needle.GetActualSize(size, version)))
	return
}

func (ev *EcVolume) LocateEcShardNeedleInterval(version needle.Version, offset int64, size types.Size) (intervals []Interval) {
	shard := ev.Shards[0]
	var shardSize int64
	if ev.datFileSize > 0 {
		// Use datFileSize to calculate the shardSize to match the EC encoding logic.
		// This is the authoritative value stored in .vif during EC encoding.
		shardSize = ev.datFileSize / int64(ev.ECContext.DataShards)
	} else {
		// Fallback for old EC volumes without datFileSize in .vif.
		// Subtract 1 to handle the ambiguous case where ecdFileSize is an exact
		// multiple of ErasureCodingLargeBlockSize but the data is actually in small
		// blocks (e.g., datFileSize was just under DataShards*ErasureCodingLargeBlockSize).
		shardSize = shard.ecdFileSize - 1
	}
	// calculate the locations in the ec shards
	intervals = LocateData(ErasureCodingLargeBlockSize, ErasureCodingSmallBlockSize, shardSize, offset, types.Size(needle.GetActualSize(size, version)))

	return
}

func (ev *EcVolume) FindNeedleFromEcx(needleId types.NeedleId) (offset types.Offset, size types.Size, err error) {
	offset, size, err = SearchNeedleFromSortedIndex(ev.ecxFile, ev.ecxFileSize, needleId, nil)
	if err != nil {
		return
	}
	// Apply runtime deletion state on top of the sealed .ecx lookup.
	if ev.IsNeedleDeleted(needleId) {
		size = types.TombstoneFileSize
	}
	return
}

func SearchNeedleFromSortedIndex(ecxFile *os.File, ecxFileSize int64, needleId types.NeedleId, processNeedleFn func(file *os.File, offset int64) error) (offset types.Offset, size types.Size, err error) {
	var key types.NeedleId
	buf := make([]byte, types.NeedleMapEntrySize)
	l, h := int64(0), ecxFileSize/types.NeedleMapEntrySize
	for l < h {
		m := (l + h) / 2
		if n, err := ecxFile.ReadAt(buf, m*types.NeedleMapEntrySize); err != nil {
			if n != types.NeedleMapEntrySize {
				return types.Offset{}, types.TombstoneFileSize, fmt.Errorf("ecx file %d read at %d: %v", ecxFileSize, m*types.NeedleMapEntrySize, err)
			}
		}
		key, offset, size = idx.IdxFileEntry(buf)
		if key == needleId {
			if processNeedleFn != nil {
				err = processNeedleFn(ecxFile, m*types.NeedleMapEntrySize)
			}
			return
		}
		if key < needleId {
			l = m + 1
		} else {
			h = m
		}
	}

	err = NotFoundError
	return
}

func (ev *EcVolume) IsTimeToDestroy() bool {
	return ev.ExpireAtSec > 0 && time.Now().Unix() > (int64(ev.ExpireAtSec)+destroyDelaySeconds)
}

func (ev *EcVolume) WalkIndex(processNeedleFn func(key types.NeedleId, offset types.Offset, size types.Size) error) error {
	if ev.ecxFile == nil {
		return fmt.Errorf("no ECX file associated with EC volume %v", ev.VolumeId)
	}
	return idx.WalkIndexFile(ev.ecxFile, 0, processNeedleFn)
}