Adding --v2-deprecation flag.

server/embed/config.go

@@ -400,6 +400,9 @@ type Config struct {
 
 	// ExperimentalTxnModeWriteWithSharedBuffer enables write transaction to use a shared buffer in its readonly check operations.
 	ExperimentalTxnModeWriteWithSharedBuffer bool `json:"experimental-txn-mode-write-with-shared-buffer"`
+
+	// V2Deprecation describes phase of API & Storage V2 support
+	V2Deprecation V2DeprecationEnum `json:"v2-deprecation"`
 }
 
 // configYAML holds the config suitable for yaml parsing
@@ -494,6 +497,8 @@ func NewConfig() *Config {
 		ExperimentalDowngradeCheckTime:           DefaultDowngradeCheckTime,
 		ExperimentalMemoryMlock:                  false,
 		ExperimentalTxnModeWriteWithSharedBuffer: true,
+
+		V2Deprecation: V2_DEPR_DEFAULT,
 	}
 	cfg.InitialCluster = cfg.InitialClusterFromName(cfg.Name)
 	return cfg
@@ -795,6 +800,14 @@ func (cfg Config) InitialClusterFromName(name string) (ret string) {
 func (cfg Config) IsNewCluster() bool { return cfg.ClusterState == ClusterStateFlagNew }
 func (cfg Config) ElectionTicks() int { return int(cfg.ElectionMs / cfg.TickMs) }
 
+func (cfg Config) V2DeprecationEffective() V2DeprecationEnum {
+	if cfg.V2Deprecation == "" {
+		return V2_DEPR_DEFAULT
+	} else {
+		return cfg.V2Deprecation
+	}
+}
+
 func (cfg Config) defaultPeerHost() bool {
 	return len(cfg.APUrls) == 1 && cfg.APUrls[0].String() == DefaultInitialAdvertisePeerURLs
 }

server/embed/v2_deprecation.go

@@ -0,0 +1,46 @@
+// 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 embed
+
+type V2DeprecationEnum string
+
+const (
+// Default in v3.5.  Issues a warning if v2store have meaningful content.
+V2_DEPR_0_NOT_YET = V2DeprecationEnum("not-yet")
+// Default in v3.6.  Meaningful v2 state is not allowed.
+// The V2 files are maintained for v3.5 rollback.
+V2_DEPR_1_WRITE_ONLY = V2DeprecationEnum("write-only")
+// V2store is WIPED if found !!!
+V2_DEPR_1_WRITE_ONLY_DROP = V2DeprecationEnum("write-only-drop-data")
+// V2store is neither written nor read. Usage of this configuration is blocking
+// ability to rollback to etcd v3.5.
+V2_DEPR_2_GONE = V2DeprecationEnum("gone")
+
+V2_DEPR_DEFAULT = V2_DEPR_0_NOT_YET
+)
+
+func (e V2DeprecationEnum) IsAtLeast(v2d V2DeprecationEnum) bool {
+ return e.level() >= v2d.level()
+}
+
+func (e V2DeprecationEnum) level() int {
+	switch e {
+	case V2_DEPR_0_NOT_YET: return 0
+	case V2_DEPR_1_WRITE_ONLY: return 1
+	case V2_DEPR_1_WRITE_ONLY_DROP: return 2
+	case V2_DEPR_2_GONE: return 3
+	}
+	panic("Unknown V2DeprecationEnum: " + e)
+}

server/embed/v2_deprecation_test.go

@@ -0,0 +1,41 @@
+// 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 embed
+
+import "testing"
+
+func TestV2DeprecationEnum_IsAtLeast(t *testing.T) {
+	tests := []struct {
+		e    V2DeprecationEnum
+		v2d  V2DeprecationEnum
+		want bool
+	}{
+		{V2_DEPR_0_NOT_YET, V2_DEPR_0_NOT_YET, true},
+		{V2_DEPR_0_NOT_YET, V2_DEPR_1_WRITE_ONLY_DROP, false},
+		{V2_DEPR_0_NOT_YET, V2_DEPR_2_GONE, false},
+		{V2_DEPR_2_GONE, V2_DEPR_1_WRITE_ONLY_DROP, true},
+		{V2_DEPR_2_GONE, V2_DEPR_0_NOT_YET, true},
+		{V2_DEPR_2_GONE, V2_DEPR_2_GONE, true},
+		{V2_DEPR_1_WRITE_ONLY, V2_DEPR_1_WRITE_ONLY_DROP, false},
+		{V2_DEPR_1_WRITE_ONLY_DROP, V2_DEPR_1_WRITE_ONLY, true},
+	}
+	for _, tt := range tests {
+		t.Run(string(tt.e) + " >= " + string(tt.v2d), func(t *testing.T) {
+			if got := tt.e.IsAtLeast(tt.v2d); got != tt.want {
+				t.Errorf("IsAtLeast() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}