diff --git a/vendor/go.etcd.io/etcd/pkg/flags/selective_string.go b/vendor/go.etcd.io/etcd/pkg/flags/selective_string.go
new file mode 100644
index 0000000..4b90fbf
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/pkg/flags/selective_string.go
@@ -0,0 +1,114 @@
+// Copyright 2018 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 flags
+
+import (
+	"errors"
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// SelectiveStringValue implements the flag.Value interface.
+type SelectiveStringValue struct {
+	v      string
+	valids map[string]struct{}
+}
+
+// Set verifies the argument to be a valid member of the allowed values
+// before setting the underlying flag value.
+func (ss *SelectiveStringValue) Set(s string) error {
+	if _, ok := ss.valids[s]; ok {
+		ss.v = s
+		return nil
+	}
+	return errors.New("invalid value")
+}
+
+// String returns the set value (if any) of the SelectiveStringValue
+func (ss *SelectiveStringValue) String() string {
+	return ss.v
+}
+
+// Valids returns the list of valid strings.
+func (ss *SelectiveStringValue) Valids() []string {
+	s := make([]string, 0, len(ss.valids))
+	for k := range ss.valids {
+		s = append(s, k)
+	}
+	sort.Strings(s)
+	return s
+}
+
+// NewSelectiveStringValue creates a new string flag
+// for which any one of the given strings is a valid value,
+// and any other value is an error.
+//
+// valids[0] will be default value. Caller must be sure
+// len(valids) != 0 or it will panic.
+func NewSelectiveStringValue(valids ...string) *SelectiveStringValue {
+	vm := make(map[string]struct{})
+	for _, v := range valids {
+		vm[v] = struct{}{}
+	}
+	return &SelectiveStringValue{valids: vm, v: valids[0]}
+}
+
+// SelectiveStringsValue implements the flag.Value interface.
+type SelectiveStringsValue struct {
+	vs     []string
+	valids map[string]struct{}
+}
+
+// Set verifies the argument to be a valid member of the allowed values
+// before setting the underlying flag value.
+func (ss *SelectiveStringsValue) Set(s string) error {
+	vs := strings.Split(s, ",")
+	for i := range vs {
+		if _, ok := ss.valids[vs[i]]; ok {
+			ss.vs = append(ss.vs, vs[i])
+		} else {
+			return fmt.Errorf("invalid value %q", vs[i])
+		}
+	}
+	sort.Strings(ss.vs)
+	return nil
+}
+
+// String returns the set value (if any) of the SelectiveStringsValue.
+func (ss *SelectiveStringsValue) String() string {
+	return strings.Join(ss.vs, ",")
+}
+
+// Valids returns the list of valid strings.
+func (ss *SelectiveStringsValue) Valids() []string {
+	s := make([]string, 0, len(ss.valids))
+	for k := range ss.valids {
+		s = append(s, k)
+	}
+	sort.Strings(s)
+	return s
+}
+
+// NewSelectiveStringsValue creates a new string slice flag
+// for which any one of the given strings is a valid value,
+// and any other value is an error.
+func NewSelectiveStringsValue(valids ...string) *SelectiveStringsValue {
+	vm := make(map[string]struct{})
+	for _, v := range valids {
+		vm[v] = struct{}{}
+	}
+	return &SelectiveStringsValue{valids: vm, vs: []string{}}
+}