etcdserver: Move Read/Update methods on Meta bucket to one place

There are still some left like compact keys, but they will require more
work to avoid circular dependency.

etcdutl/etcdutl/backup_command.go

@@ -31,7 +31,6 @@ import (
 	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v2store"
-	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
 	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 	"go.etcd.io/etcd/server/v3/verify"
@@ -326,8 +325,8 @@ func saveDB(lg *zap.Logger, destDB, srcDB string, idx uint64, term uint64, desir
 		tx := be.BatchTx()
 		tx.Lock()
 		defer tx.Unlock()
-		cindex.UnsafeCreateMetaBucket(tx)
+		buckets.UnsafeCreateMetaBucket(tx)
-		cindex.UnsafeUpdateConsistentIndex(tx, idx, term, false)
+		buckets.UnsafeUpdateConsistentIndex(tx, idx, term, false)
 	} else {
 		// Thanks to translateWAL not moving entries, but just replacing them with
 		// 'empty', there is no need to update the consistency index.

etcdutl/snapshot/v3_snapshot.go

@@ -40,7 +40,6 @@ import (
 	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v2store"
 	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
-	"go.etcd.io/etcd/server/v3/etcdserver/version"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
 	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 	"go.etcd.io/etcd/server/v3/verify"
@@ -137,7 +136,7 @@ func (s *v3Manager) Status(dbPath string) (ds Status, err error) {
 			return fmt.Errorf("snapshot file integrity check failed. %d errors found.\n"+strings.Join(dbErrStrings, "\n"), len(dbErrStrings))
 		}
 		ds.TotalSize = tx.Size()
-		v := version.ReadStorageVersionFromSnapshot(tx)
+		v := buckets.ReadStorageVersionFromSnapshot(tx)
 		if v != nil {
 			ds.Version = v.String()
 		}

server/etcdserver/api/v3rpc/maintenance.go

@@ -27,9 +27,9 @@ import (
 	"go.etcd.io/etcd/raft/v3"
 	"go.etcd.io/etcd/server/v3/auth"
 	"go.etcd.io/etcd/server/v3/etcdserver"
-	serverversion "go.etcd.io/etcd/server/v3/etcdserver/version"
 	"go.etcd.io/etcd/server/v3/mvcc"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
+	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 
 	"go.uber.org/zap"
 )
@@ -101,7 +101,7 @@ func (ms *maintenanceServer) Defragment(ctx context.Context, sr *pb.DefragmentRe
 const snapshotSendBufferSize = 32 * 1024
 
 func (ms *maintenanceServer) Snapshot(sr *pb.SnapshotRequest, srv pb.Maintenance_SnapshotServer) error {
-	ver := serverversion.ReadStorageVersion(ms.bg.Backend().ReadTx())
+	ver := buckets.ReadStorageVersion(ms.bg.Backend().ReadTx())
 	storageVersion := ""
 	if ver != nil {
 		storageVersion = ver.String()

server/etcdserver/backend.go

@@ -22,8 +22,8 @@ import (
 	"go.etcd.io/etcd/raft/v3/raftpb"
 	"go.etcd.io/etcd/server/v3/config"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
-	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
+	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 
 	"go.uber.org/zap"
 )
@@ -99,7 +99,7 @@ func openBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
 func recoverSnapshotBackend(cfg config.ServerConfig, oldbe backend.Backend, snapshot raftpb.Snapshot, beExist bool, hooks backend.Hooks) (backend.Backend, error) {
 	consistentIndex := uint64(0)
 	if beExist {
-		consistentIndex, _ = cindex.ReadConsistentIndex(oldbe.BatchTx())
+		consistentIndex, _ = buckets.ReadConsistentIndex(oldbe.BatchTx())
 	}
 	if snapshot.Metadata.Index <= consistentIndex {
 		return oldbe, nil

server/etcdserver/cindex/cindex.go

@@ -15,7 +15,6 @@
 package cindex
 
 import (
-	"encoding/binary"
 	"sync"
 	"sync/atomic"
 
@@ -74,7 +73,7 @@ func (ci *consistentIndex) ConsistentIndex() uint64 {
 	ci.mutex.Lock()
 	defer ci.mutex.Unlock()
 
-	v, term := ReadConsistentIndex(ci.be.BatchTx())
+	v, term := buckets.ReadConsistentIndex(ci.be.BatchTx())
 	ci.SetConsistentIndex(v, term)
 	return v
 }
@@ -87,7 +86,7 @@ func (ci *consistentIndex) SetConsistentIndex(v uint64, term uint64) {
 func (ci *consistentIndex) UnsafeSave(tx backend.BatchTx) {
 	index := atomic.LoadUint64(&ci.consistentIndex)
 	term := atomic.LoadUint64(&ci.term)
-	UnsafeUpdateConsistentIndex(tx, index, term, true)
+	buckets.UnsafeUpdateConsistentIndex(tx, index, term, true)
 }
 
 func (ci *consistentIndex) SetBackend(be Backend) {
@@ -117,73 +116,8 @@ func (f *fakeConsistentIndex) SetConsistentIndex(index uint64, term uint64) {
 func (f *fakeConsistentIndex) UnsafeSave(_ backend.BatchTx) {}
 func (f *fakeConsistentIndex) SetBackend(_ Backend)         {}
 
-// UnsafeCreateMetaBucket creates the `meta` bucket (if it does not exists yet).
-func UnsafeCreateMetaBucket(tx backend.BatchTx) {
-	tx.UnsafeCreateBucket(buckets.Meta)
-}
-
-// CreateMetaBucket creates the `meta` bucket (if it does not exists yet).
-func CreateMetaBucket(tx backend.BatchTx) {
-	tx.Lock()
-	defer tx.Unlock()
-	tx.UnsafeCreateBucket(buckets.Meta)
-}
-
-// unsafeGetConsistentIndex loads consistent index & term from given transaction.
-// returns 0,0 if the data are not found.
-// Term is persisted since v3.5.
-func unsafeReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
-	_, vs := tx.UnsafeRange(buckets.Meta, buckets.MetaConsistentIndexKeyName, nil, 0)
-	if len(vs) == 0 {
-		return 0, 0
-	}
-	v := binary.BigEndian.Uint64(vs[0])
-	_, ts := tx.UnsafeRange(buckets.Meta, buckets.MetaTermKeyName, nil, 0)
-	if len(ts) == 0 {
-		return v, 0
-	}
-	t := binary.BigEndian.Uint64(ts[0])
-	return v, t
-}
-
-// ReadConsistentIndex loads consistent index and term from given transaction.
-// returns 0 if the data are not found.
-func ReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
-	tx.Lock()
-	defer tx.Unlock()
-	return unsafeReadConsistentIndex(tx)
-}
-
-func UnsafeUpdateConsistentIndex(tx backend.BatchTx, index uint64, term uint64, onlyGrow bool) {
-	if index == 0 {
-		// Never save 0 as it means that we didn't loaded the real index yet.
-		return
-	}
-
-	if onlyGrow {
-		oldi, oldTerm := unsafeReadConsistentIndex(tx)
-		if term < oldTerm {
-			return
-		}
-		if term == oldTerm && index <= oldi {
-			return
-		}
-	}
-
-	bs1 := make([]byte, 8)
-	binary.BigEndian.PutUint64(bs1, index)
-	// put the index into the underlying backend
-	// tx has been locked in TxnBegin, so there is no need to lock it again
-	tx.UnsafePut(buckets.Meta, buckets.MetaConsistentIndexKeyName, bs1)
-	if term > 0 {
-		bs2 := make([]byte, 8)
-		binary.BigEndian.PutUint64(bs2, term)
-		tx.UnsafePut(buckets.Meta, buckets.MetaTermKeyName, bs2)
-	}
-}
-
 func UpdateConsistentIndex(tx backend.BatchTx, index uint64, term uint64, onlyGrow bool) {
 	tx.Lock()
 	defer tx.Unlock()
-	UnsafeUpdateConsistentIndex(tx, index, term, onlyGrow)
+	buckets.UnsafeUpdateConsistentIndex(tx, index, term, onlyGrow)
 }

server/etcdserver/cindex/cindex_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
 	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
+	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 )
 
 // TestConsistentIndex ensures that LoadConsistentIndex/Save/ConsistentIndex and backend.BatchTx can work well together.
@@ -36,7 +37,7 @@ func TestConsistentIndex(t *testing.T) {
 	}
 	tx.Lock()
 
-	UnsafeCreateMetaBucket(tx)
+	buckets.UnsafeCreateMetaBucket(tx)
 	tx.Unlock()
 	be.ForceCommit()
 	r := uint64(7890123)

server/etcdserver/server.go

@@ -386,7 +386,7 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 	beHooks := &backendHooks{lg: cfg.Logger, indexer: ci}
 	be := openBackend(cfg, beHooks)
 	ci.SetBackend(be)
-	cindex.CreateMetaBucket(be.BatchTx())
+	buckets.CreateMetaBucket(be.BatchTx())
 
 	if cfg.ExperimentalBootstrapDefragThresholdMegabytes != 0 {
 		err := maybeDefragBackend(cfg, be)

server/etcdserver/server_test.go

@@ -651,7 +651,7 @@ func TestApplyConfigChangeUpdatesConsistIndex(t *testing.T) {
 
 	be, _ := betesting.NewDefaultTmpBackend(t)
 	defer betesting.Close(t, be)
-	cindex.CreateMetaBucket(be.BatchTx())
+	buckets.CreateMetaBucket(be.BatchTx())
 
 	ci := cindex.NewConsistentIndex(be)
 	srv := &EtcdServer{
@@ -698,7 +698,7 @@ func TestApplyConfigChangeUpdatesConsistIndex(t *testing.T) {
 		srv.beHooks.OnPreCommitUnsafe(tx)
 		assert.Equal(t, raftpb.ConfState{Voters: []uint64{2}}, *buckets.UnsafeConfStateFromBackend(lg, tx))
 	})
-	rindex, rterm := cindex.ReadConsistentIndex(be.BatchTx())
+	rindex, rterm := buckets.ReadConsistentIndex(be.BatchTx())
 	assert.Equal(t, consistIndex, rindex)
 	assert.Equal(t, uint64(4), rterm)
 }

server/etcdserver/version/version.go

@@ -18,7 +18,6 @@ import (
 	"fmt"
 
 	"github.com/coreos/go-semver/semver"
-	"go.etcd.io/bbolt"
 	"go.uber.org/zap"
 
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
@@ -42,7 +41,7 @@ func UpdateStorageVersion(lg *zap.Logger, tx backend.BatchTx) error {
 	case V3_5:
 		lg.Warn("setting storage version", zap.String("storage-version", V3_6.String()))
 		// All meta keys introduced in v3.6 should be filled in here.
-		unsafeSetStorageVersion(tx, &V3_6)
+		buckets.UnsafeSetStorageVersion(tx, &V3_6)
 	case V3_6:
 	default:
 		lg.Warn("unknown storage version", zap.String("storage-version", v.String()))
@@ -51,58 +50,18 @@ func UpdateStorageVersion(lg *zap.Logger, tx backend.BatchTx) error {
 }
 
 func detectStorageVersion(lg *zap.Logger, tx backend.ReadTx) (*semver.Version, error) {
-	v := unsafeReadStorageVersion(tx)
+	v := buckets.UnsafeReadStorageVersion(tx)
 	if v != nil {
 		return v, nil
 	}
-	_, cfs := tx.UnsafeRange(buckets.Meta, buckets.MetaConfStateName, nil, 0)
+	confstate := buckets.UnsafeConfStateFromBackend(lg, tx)
-	if len(cfs) == 0 {
+	if confstate == nil {
 		return nil, fmt.Errorf("missing %q key", buckets.MetaConfStateName)
 	}
-	_, ts := tx.UnsafeRange(buckets.Meta, buckets.MetaTermKeyName, nil, 0)
+	_, term := buckets.UnsafeReadConsistentIndex(tx)
-	if len(ts) == 0 {
+	if term == 0 {
 		return nil, fmt.Errorf("missing %q key", buckets.MetaTermKeyName)
 	}
 	copied := V3_5
 	return &copied, nil
 }
-
-// ReadStorageVersion loads storage version from given backend transaction.
-// Populated since v3.6
-func ReadStorageVersion(tx backend.ReadTx) *semver.Version {
-	tx.Lock()
-	defer tx.Unlock()
-	return unsafeReadStorageVersion(tx)
-}
-
-// unsafeReadStorageVersion loads storage version from given backend transaction.
-// Populated since v3.6
-func unsafeReadStorageVersion(tx backend.ReadTx) *semver.Version {
-	_, vs := tx.UnsafeRange(buckets.Meta, buckets.MetaStorageVersionName, nil, 1)
-	if len(vs) == 0 {
-		return nil
-	}
-	v, err := semver.NewVersion(string(vs[0]))
-	if err != nil {
-		return nil
-	}
-	return v
-}
-
-// ReadStorageVersionFromSnapshot loads storage version from given bbolt transaction.
-// Populated since v3.6
-func ReadStorageVersionFromSnapshot(tx *bbolt.Tx) *semver.Version {
-	v := tx.Bucket(buckets.Meta.Name()).Get(buckets.MetaStorageVersionName)
-	version, err := semver.NewVersion(string(v))
-	if err != nil {
-		return nil
-	}
-	return version
-}
-
-// unsafeSetStorageVersion updates etcd storage version in backend.
-// Populated since v3.6
-func unsafeSetStorageVersion(tx backend.BatchTx, v *semver.Version) {
-	sv := semver.Version{Major: v.Major, Minor: v.Minor}
-	tx.UnsafePut(buckets.Meta, buckets.MetaStorageVersionName, []byte(sv.String()))
-}

server/etcdserver/version/version_test.go

@@ -20,13 +20,12 @@ import (
 
 	"github.com/coreos/go-semver/semver"
 	"github.com/stretchr/testify/assert"
-	bolt "go.etcd.io/bbolt"
-	"go.uber.org/zap"
-
 	"go.etcd.io/etcd/api/v3/version"
+	"go.etcd.io/etcd/raft/v3/raftpb"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
 	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
 	"go.etcd.io/etcd/server/v3/mvcc/buckets"
+	"go.uber.org/zap"
 )
 
 func TestUpdateStorageVersion(t *testing.T) {
@@ -37,7 +36,6 @@ func TestUpdateStorageVersion(t *testing.T) {
 		expectVersion    *semver.Version
 		expectError      bool
 		expectedErrorMsg string
-		expectedMetaKeys [][]byte
 	}{
 		{
 			name:             `Backend before 3.6 without "confState" should be rejected`,
@@ -53,51 +51,54 @@ func TestUpdateStorageVersion(t *testing.T) {
 			expectVersion:    nil,
 			expectError:      true,
 			expectedErrorMsg: `cannot determine storage version: missing "term" key`,
-			expectedMetaKeys: [][]byte{buckets.MetaConfStateName},
 		},
 		{
-			name:             "Backend with 3.5 with all metadata keys should be upgraded to v3.6",
+			name:          "Backend with 3.5 with all metadata keys should be upgraded to v3.6",
-			version:          "",
+			version:       "",
-			metaKeys:         [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName},
+			metaKeys:      [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName},
-			expectVersion:    &semver.Version{Major: 3, Minor: 6},
+			expectVersion: &semver.Version{Major: 3, Minor: 6},
-			expectedMetaKeys: [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
 		},
 		{
-			name:             "Backend in 3.6.0 should be skipped",
+			name:          "Backend in 3.6.0 should be skipped",
-			version:          "3.6.0",
+			version:       "3.6.0",
-			metaKeys:         [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
+			metaKeys:      [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
-			expectVersion:    &semver.Version{Major: 3, Minor: 6},
+			expectVersion: &semver.Version{Major: 3, Minor: 6},
-			expectedMetaKeys: [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
 		},
 		{
-			name:             "Backend with current version should be skipped",
+			name:          "Backend with current version should be skipped",
-			version:          version.Version,
+			version:       version.Version,
-			metaKeys:         [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
+			metaKeys:      [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
-			expectVersion:    &semver.Version{Major: 3, Minor: 6},
+			expectVersion: &semver.Version{Major: 3, Minor: 6},
-			expectedMetaKeys: [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName},
 		},
 		{
-			name:             "Backend in 3.7.0 should be skipped",
+			name:          "Backend in 3.7.0 should be skipped",
-			version:          "3.7.0",
+			version:       "3.7.0",
-			metaKeys:         [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName, []byte("future-key")},
+			metaKeys:      [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName, []byte("future-key")},
-			expectVersion:    &semver.Version{Major: 3, Minor: 7},
+			expectVersion: &semver.Version{Major: 3, Minor: 7},
-			expectedMetaKeys: [][]byte{buckets.MetaTermKeyName, buckets.MetaConfStateName, buckets.MetaStorageVersionName, []byte("future-key")},
 		},
 	}
 	for _, tc := range tcs {
 		t.Run(tc.name, func(t *testing.T) {
+			lg := zap.NewNop()
 			be, tmpPath := betesting.NewTmpBackend(t, time.Microsecond, 10)
 			tx := be.BatchTx()
 			if tx == nil {
 				t.Fatal("batch tx is nil")
 			}
 			tx.Lock()
-			tx.UnsafeCreateBucket(buckets.Meta)
+			buckets.UnsafeCreateMetaBucket(tx)
 			for _, k := range tc.metaKeys {
-				tx.UnsafePut(buckets.Meta, k, []byte{})
+				switch string(k) {
+				case string(buckets.MetaConfStateName):
+					buckets.MustUnsafeSaveConfStateToBackend(lg, tx, &raftpb.ConfState{})
+				case string(buckets.MetaTermKeyName):
+					buckets.UnsafeUpdateConsistentIndex(tx, 1, 1, false)
+				default:
+					tx.UnsafePut(buckets.Meta, k, []byte{})
+				}
 			}
 			if tc.version != "" {
-				unsafeSetStorageVersion(tx, semver.New(tc.version))
+				buckets.UnsafeSetStorageVersion(tx, semver.New(tc.version))
 			}
 			tx.Unlock()
 			be.ForceCommit()
@@ -105,123 +106,15 @@ func TestUpdateStorageVersion(t *testing.T) {
 
 			b := backend.NewDefaultBackend(tmpPath)
 			defer b.Close()
-			err := UpdateStorageVersion(zap.NewNop(), b.BatchTx())
+			err := UpdateStorageVersion(lg, b.BatchTx())
 			if (err != nil) != tc.expectError {
 				t.Errorf("UpgradeStorage(...) = %+v, expected error: %v", err, tc.expectError)
 			}
 			if err != nil && err.Error() != tc.expectedErrorMsg {
 				t.Errorf("UpgradeStorage(...) = %q, expected error message: %q", err, tc.expectedErrorMsg)
 			}
-			v := unsafeReadStorageVersion(b.BatchTx())
+			v := buckets.UnsafeReadStorageVersion(b.BatchTx())
 			assert.Equal(t, tc.expectVersion, v)
-			keys, _ := b.BatchTx().UnsafeRange(buckets.Meta, []byte("a"), []byte("z"), 0)
-			assert.ElementsMatch(t, tc.expectedMetaKeys, keys)
-		})
-	}
-}
-
-// TestVersion ensures that unsafeSetStorageVersion/unsafeReadStorageVersion work well together.
-func TestVersion(t *testing.T) {
-	tcs := []struct {
-		version       string
-		expectVersion string
-	}{
-		{
-			version:       "3.5.0",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-alpha",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-beta.0",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-rc.1",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.1",
-			expectVersion: "3.5.0",
-		},
-	}
-	for _, tc := range tcs {
-		t.Run(tc.version, func(t *testing.T) {
-			be, tmpPath := betesting.NewTmpBackend(t, time.Microsecond, 10)
-			tx := be.BatchTx()
-			if tx == nil {
-				t.Fatal("batch tx is nil")
-			}
-			tx.Lock()
-			tx.UnsafeCreateBucket(buckets.Meta)
-			unsafeSetStorageVersion(tx, semver.New(tc.version))
-			tx.Unlock()
-			be.ForceCommit()
-			be.Close()
-
-			b := backend.NewDefaultBackend(tmpPath)
-			defer b.Close()
-			v := unsafeReadStorageVersion(b.BatchTx())
-
-			assert.Equal(t, tc.expectVersion, v.String())
-		})
-	}
-}
-
-// TestVersionSnapshot ensures that unsafeSetStorageVersion/unsafeReadStorageVersionFromSnapshot work well together.
-func TestVersionSnapshot(t *testing.T) {
-	tcs := []struct {
-		version       string
-		expectVersion string
-	}{
-		{
-			version:       "3.5.0",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-alpha",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-beta.0",
-			expectVersion: "3.5.0",
-		},
-		{
-			version:       "3.5.0-rc.1",
-			expectVersion: "3.5.0",
-		},
-	}
-	for _, tc := range tcs {
-		t.Run(tc.version, func(t *testing.T) {
-			be, tmpPath := betesting.NewTmpBackend(t, time.Microsecond, 10)
-			tx := be.BatchTx()
-			if tx == nil {
-				t.Fatal("batch tx is nil")
-			}
-			tx.Lock()
-			tx.UnsafeCreateBucket(buckets.Meta)
-			unsafeSetStorageVersion(tx, semver.New(tc.version))
-			tx.Unlock()
-			be.ForceCommit()
-			be.Close()
-			db, err := bolt.Open(tmpPath, 0400, &bolt.Options{ReadOnly: true})
-			if err != nil {
-				t.Fatal(err)
-			}
-			defer db.Close()
-
-			var ver *semver.Version
-			if err = db.View(func(tx *bolt.Tx) error {
-				ver = ReadStorageVersionFromSnapshot(tx)
-				return nil
-			}); err != nil {
-				t.Fatal(err)
-			}
-
-			assert.Equal(t, tc.expectVersion, ver.String())
-
 		})
 	}
 }

server/mvcc/buckets/cindex.go

@@ -0,0 +1,85 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buckets
+
+import (
+	"encoding/binary"
+	"go.etcd.io/etcd/server/v3/mvcc/backend"
+)
+
+// UnsafeCreateMetaBucket creates the `meta` bucket (if it does not exists yet).
+func UnsafeCreateMetaBucket(tx backend.BatchTx) {
+	tx.UnsafeCreateBucket(Meta)
+}
+
+// CreateMetaBucket creates the `meta` bucket (if it does not exists yet).
+func CreateMetaBucket(tx backend.BatchTx) {
+	tx.Lock()
+	defer tx.Unlock()
+	tx.UnsafeCreateBucket(Meta)
+}
+
+// UnsafeReadConsistentIndex loads consistent index & term from given transaction.
+// returns 0,0 if the data are not found.
+// Term is persisted since v3.5.
+func UnsafeReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
+	_, vs := tx.UnsafeRange(Meta, MetaConsistentIndexKeyName, nil, 0)
+	if len(vs) == 0 {
+		return 0, 0
+	}
+	v := binary.BigEndian.Uint64(vs[0])
+	_, ts := tx.UnsafeRange(Meta, MetaTermKeyName, nil, 0)
+	if len(ts) == 0 {
+		return v, 0
+	}
+	t := binary.BigEndian.Uint64(ts[0])
+	return v, t
+}
+
+// ReadConsistentIndex loads consistent index and term from given transaction.
+// returns 0 if the data are not found.
+func ReadConsistentIndex(tx backend.ReadTx) (uint64, uint64) {
+	tx.Lock()
+	defer tx.Unlock()
+	return UnsafeReadConsistentIndex(tx)
+}
+
+func UnsafeUpdateConsistentIndex(tx backend.BatchTx, index uint64, term uint64, onlyGrow bool) {
+	if index == 0 {
+		// Never save 0 as it means that we didn't loaded the real index yet.
+		return
+	}
+
+	if onlyGrow {
+		oldi, oldTerm := UnsafeReadConsistentIndex(tx)
+		if term < oldTerm {
+			return
+		}
+		if term == oldTerm && index <= oldi {
+			return
+		}
+	}
+
+	bs1 := make([]byte, 8)
+	binary.BigEndian.PutUint64(bs1, index)
+	// put the index into the underlying backend
+	// tx has been locked in TxnBegin, so there is no need to lock it again
+	tx.UnsafePut(Meta, MetaConsistentIndexKeyName, bs1)
+	if term > 0 {
+		bs2 := make([]byte, 8)
+		binary.BigEndian.PutUint64(bs2, term)
+		tx.UnsafePut(Meta, MetaTermKeyName, bs2)
+	}
+}

server/mvcc/buckets/confstate_test.go

@@ -29,7 +29,7 @@ func TestConfStateFromBackendInOneTx(t *testing.T) {
 	defer betesting.Close(t, be)
 
 	tx := be.BatchTx()
-	tx.UnsafeCreateBucket(Meta)
+	CreateMetaBucket(tx)
 	tx.Lock()
 	defer tx.Unlock()
 	assert.Nil(t, UnsafeConfStateFromBackend(lg, tx))
@@ -47,7 +47,7 @@ func TestMustUnsafeSaveConfStateToBackend(t *testing.T) {
 
 	{
 		tx := be.BatchTx()
-		tx.UnsafeCreateBucket(Meta)
+		CreateMetaBucket(tx)
 		tx.Commit()
 	}
 

server/mvcc/buckets/version.go

@@ -0,0 +1,61 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buckets
+
+import (
+	"github.com/coreos/go-semver/semver"
+	"go.etcd.io/bbolt"
+	"go.etcd.io/etcd/server/v3/mvcc/backend"
+)
+
+// ReadStorageVersion loads storage version from given backend transaction.
+// Populated since v3.6
+func ReadStorageVersion(tx backend.ReadTx) *semver.Version {
+	tx.Lock()
+	defer tx.Unlock()
+	return UnsafeReadStorageVersion(tx)
+}
+
+// UnsafeReadStorageVersion loads storage version from given backend transaction.
+// Populated since v3.6
+func UnsafeReadStorageVersion(tx backend.ReadTx) *semver.Version {
+	_, vs := tx.UnsafeRange(Meta, MetaStorageVersionName, nil, 1)
+	if len(vs) == 0 {
+		return nil
+	}
+	v, err := semver.NewVersion(string(vs[0]))
+	if err != nil {
+		return nil
+	}
+	return v
+}
+
+// ReadStorageVersionFromSnapshot loads storage version from given bbolt transaction.
+// Populated since v3.6
+func ReadStorageVersionFromSnapshot(tx *bbolt.Tx) *semver.Version {
+	v := tx.Bucket(Meta.Name()).Get(MetaStorageVersionName)
+	version, err := semver.NewVersion(string(v))
+	if err != nil {
+		return nil
+	}
+	return version
+}
+
+// UnsafeSetStorageVersion updates etcd storage version in backend.
+// Populated since v3.6
+func UnsafeSetStorageVersion(tx backend.BatchTx, v *semver.Version) {
+	sv := semver.Version{Major: v.Major, Minor: v.Minor}
+	tx.UnsafePut(Meta, MetaStorageVersionName, []byte(sv.String()))
+}

server/mvcc/buckets/version_test.go

@@ -0,0 +1,133 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buckets
+
+import (
+	"testing"
+	"time"
+
+	"github.com/coreos/go-semver/semver"
+	"github.com/stretchr/testify/assert"
+	"go.etcd.io/bbolt"
+
+	"go.etcd.io/etcd/server/v3/mvcc/backend"
+	"go.etcd.io/etcd/server/v3/mvcc/backend/testing"
+)
+
+// TestVersion ensures that UnsafeSetStorageVersion/UnsafeReadStorageVersion work well together.
+func TestVersion(t *testing.T) {
+	tcs := []struct {
+		version       string
+		expectVersion string
+	}{
+		{
+			version:       "3.5.0",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-alpha",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-beta.0",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-rc.1",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.1",
+			expectVersion: "3.5.0",
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.version, func(t *testing.T) {
+			be, tmpPath := betesting.NewTmpBackend(t, time.Microsecond, 10)
+			tx := be.BatchTx()
+			if tx == nil {
+				t.Fatal("batch tx is nil")
+			}
+			tx.Lock()
+			tx.UnsafeCreateBucket(Meta)
+			UnsafeSetStorageVersion(tx, semver.New(tc.version))
+			tx.Unlock()
+			be.ForceCommit()
+			be.Close()
+
+			b := backend.NewDefaultBackend(tmpPath)
+			defer b.Close()
+			v := UnsafeReadStorageVersion(b.BatchTx())
+
+			assert.Equal(t, tc.expectVersion, v.String())
+		})
+	}
+}
+
+// TestVersionSnapshot ensures that UnsafeSetStorageVersion/unsafeReadStorageVersionFromSnapshot work well together.
+func TestVersionSnapshot(t *testing.T) {
+	tcs := []struct {
+		version       string
+		expectVersion string
+	}{
+		{
+			version:       "3.5.0",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-alpha",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-beta.0",
+			expectVersion: "3.5.0",
+		},
+		{
+			version:       "3.5.0-rc.1",
+			expectVersion: "3.5.0",
+		},
+	}
+	for _, tc := range tcs {
+		t.Run(tc.version, func(t *testing.T) {
+			be, tmpPath := betesting.NewTmpBackend(t, time.Microsecond, 10)
+			tx := be.BatchTx()
+			if tx == nil {
+				t.Fatal("batch tx is nil")
+			}
+			tx.Lock()
+			tx.UnsafeCreateBucket(Meta)
+			UnsafeSetStorageVersion(tx, semver.New(tc.version))
+			tx.Unlock()
+			be.ForceCommit()
+			be.Close()
+			db, err := bbolt.Open(tmpPath, 0400, &bbolt.Options{ReadOnly: true})
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer db.Close()
+
+			var ver *semver.Version
+			if err = db.View(func(tx *bbolt.Tx) error {
+				ver = ReadStorageVersionFromSnapshot(tx)
+				return nil
+			}); err != nil {
+				t.Fatal(err)
+			}
+
+			assert.Equal(t, tc.expectVersion, ver.String())
+
+		})
+	}
+}

server/mvcc/kvstore_bench_test.go

@@ -23,6 +23,7 @@ import (
 	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
 	"go.etcd.io/etcd/server/v3/lease"
 	betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
+	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 
 	"go.uber.org/zap"
 )
@@ -83,7 +84,7 @@ func BenchmarkConsistentIndex(b *testing.B) {
 
 	tx := be.BatchTx()
 	tx.Lock()
-	cindex.UnsafeCreateMetaBucket(tx)
+	buckets.UnsafeCreateMetaBucket(tx)
 	ci.UnsafeSave(tx)
 	tx.Unlock()
 

server/verify/verify.go

@@ -20,8 +20,8 @@ import (
 
 	"go.etcd.io/etcd/raft/v3/raftpb"
 	"go.etcd.io/etcd/server/v3/datadir"
-	"go.etcd.io/etcd/server/v3/etcdserver/cindex"
 	"go.etcd.io/etcd/server/v3/mvcc/backend"
+	"go.etcd.io/etcd/server/v3/mvcc/buckets"
 	wal2 "go.etcd.io/etcd/server/v3/wal"
 	"go.etcd.io/etcd/server/v3/wal/walpb"
 	"go.uber.org/zap"
@@ -109,7 +109,7 @@ func MustVerifyIfEnabled(cfg Config) {
 
 func validateConsistentIndex(cfg Config, hardstate *raftpb.HardState, snapshot *walpb.Snapshot, be backend.Backend) error {
 	tx := be.BatchTx()
-	index, term := cindex.ReadConsistentIndex(tx)
+	index, term := buckets.ReadConsistentIndex(tx)
 	if cfg.ExactIndex && index != hardstate.Commit {
 		return fmt.Errorf("backend.ConsistentIndex (%v) expected == WAL.HardState.commit (%v)", index, hardstate.Commit)
 	}