diff --git a/go.mod b/go.mod
index f53cc3fa8..89a0d4776 100644
--- a/go.mod
+++ b/go.mod
@@ -106,7 +106,7 @@ require (
 	github.com/smartystreets/assertions v0.0.0-20180927180507-b2de0cb4f26d // indirect
 	github.com/smartystreets/goconvey v0.0.0-20180222194500-ef6db91d284a // indirect
 	github.com/soheilhy/cmux v0.1.4 // indirect
-	github.com/spf13/afero v1.0.2
+	github.com/spf13/afero v1.2.1
 	github.com/terraform-providers/terraform-provider-openstack v1.15.0
 	github.com/tmc/grpc-websocket-proxy v0.0.0-20171017195756-830351dc03c6 // indirect
 	github.com/ugorji/go v0.0.0-20180813092308-00b869d2f4a5 // indirect
diff --git a/go.sum b/go.sum
index 0ce64b319..aa6bdc2f6 100644
--- a/go.sum
+++ b/go.sum
@@ -358,8 +358,8 @@ github.com/soheilhy/cmux v0.1.4 h1:0HKaf1o97UwFjHH9o5XsHUOF+tqmdA7KEzXLpiyaw0E=
 github.com/soheilhy/cmux v0.1.4/go.mod h1:IM3LyeVVIOuxMH7sFAkER9+bJ4dT7Ms6E4xg4kGIyLM=
 github.com/sourcegraph/annotate v0.0.0-20160123013949-f4cad6c6324d/go.mod h1:UdhH50NIW0fCiwBSr0co2m7BnFLdv4fQTgdqdJTHFeE=
 github.com/sourcegraph/syntaxhighlight v0.0.0-20170531221838-bd320f5d308e/go.mod h1:HuIsMU8RRBOtsCgI77wP899iHVBQpCmg4ErYMZB+2IA=
-github.com/spf13/afero v1.0.2 h1:5bRmqmInNmNFkI9NG9O0Xc/Lgl9wOWWUUA/O8XZqTCo=
-github.com/spf13/afero v1.0.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
+github.com/spf13/afero v1.2.1 h1:qgMbHoJbPbw579P+1zVY+6n4nIFuIchaIjzZ/I/Yq8M=
+github.com/spf13/afero v1.2.1/go.mod h1:9ZxEEn6pIJ8Rxe320qSDBk6AsU0r9pR7Q4OcevTdifk=
 github.com/spf13/pflag v1.0.2 h1:Fy0orTDgHdbnzHcsOgfCN4LtHf0ec3wwtiwJqwvf3Gc=
 github.com/spf13/pflag v1.0.2/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
diff --git a/vendor/github.com/spf13/afero/.travis.yml b/vendor/github.com/spf13/afero/.travis.yml
index 618159a4e..0637db726 100644
--- a/vendor/github.com/spf13/afero/.travis.yml
+++ b/vendor/github.com/spf13/afero/.travis.yml
@@ -2,8 +2,8 @@ sudo: false
 language: go
 
 go:
-  - 1.7.5
-  - 1.8
+  - 1.9
+  - "1.10"
   - tip
 
 os:
diff --git a/vendor/github.com/spf13/afero/basepath.go b/vendor/github.com/spf13/afero/basepath.go
index 5e4fc2ec0..616ff8ff7 100644
--- a/vendor/github.com/spf13/afero/basepath.go
+++ b/vendor/github.com/spf13/afero/basepath.go
@@ -1,7 +1,6 @@
 package afero
 
 import (
-	"errors"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -9,6 +8,8 @@ import (
 	"time"
 )
 
+var _ Lstater = (*BasePathFs)(nil)
+
 // The BasePathFs restricts all operations to a given path within an Fs.
 // The given file name to the operations on this Fs will be prepended with
 // the base path before calling the base Fs.
@@ -22,6 +23,16 @@ type BasePathFs struct {
 	path   string
 }
 
+type BasePathFile struct {
+	File
+	path string
+}
+
+func (f *BasePathFile) Name() string {
+	sourcename := f.File.Name()
+	return strings.TrimPrefix(sourcename, filepath.Clean(f.path))
+}
+
 func NewBasePathFs(source Fs, path string) Fs {
 	return &BasePathFs{source: source, path: path}
 }
@@ -30,7 +41,7 @@ func NewBasePathFs(source Fs, path string) Fs {
 // else the given file with the base path prepended
 func (b *BasePathFs) RealPath(name string) (path string, err error) {
 	if err := validateBasePathName(name); err != nil {
-		return "", err
+		return name, err
 	}
 
 	bpath := filepath.Clean(b.path)
@@ -52,7 +63,7 @@ func validateBasePathName(name string) error {
 	// On Windows a common mistake would be to provide an absolute OS path
 	// We could strip out the base part, but that would not be very portable.
 	if filepath.IsAbs(name) {
-		return &os.PathError{Op: "realPath", Path: name, Err: errors.New("got a real OS path instead of a virtual")}
+		return os.ErrNotExist
 	}
 
 	return nil
@@ -111,14 +122,22 @@ func (b *BasePathFs) OpenFile(name string, flag int, mode os.FileMode) (f File,
 	if name, err = b.RealPath(name); err != nil {
 		return nil, &os.PathError{Op: "openfile", Path: name, Err: err}
 	}
-	return b.source.OpenFile(name, flag, mode)
+	sourcef, err := b.source.OpenFile(name, flag, mode)
+	if err != nil {
+		return nil, err
+	}
+	return &BasePathFile{sourcef, b.path}, nil
 }
 
 func (b *BasePathFs) Open(name string) (f File, err error) {
 	if name, err = b.RealPath(name); err != nil {
 		return nil, &os.PathError{Op: "open", Path: name, Err: err}
 	}
-	return b.source.Open(name)
+	sourcef, err := b.source.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	return &BasePathFile{File: sourcef, path: b.path}, nil
 }
 
 func (b *BasePathFs) Mkdir(name string, mode os.FileMode) (err error) {
@@ -139,7 +158,23 @@ func (b *BasePathFs) Create(name string) (f File, err error) {
 	if name, err = b.RealPath(name); err != nil {
 		return nil, &os.PathError{Op: "create", Path: name, Err: err}
 	}
-	return b.source.Create(name)
+	sourcef, err := b.source.Create(name)
+	if err != nil {
+		return nil, err
+	}
+	return &BasePathFile{File: sourcef, path: b.path}, nil
+}
+
+func (b *BasePathFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
+	name, err := b.RealPath(name)
+	if err != nil {
+		return nil, false, &os.PathError{Op: "lstat", Path: name, Err: err}
+	}
+	if lstater, ok := b.source.(Lstater); ok {
+		return lstater.LstatIfPossible(name)
+	}
+	fi, err := b.source.Stat(name)
+	return fi, false, err
 }
 
 // vim: ts=4 sw=4 noexpandtab nolist syn=go
diff --git a/vendor/github.com/spf13/afero/cacheOnReadFs.go b/vendor/github.com/spf13/afero/cacheOnReadFs.go
index b026e0de8..29a26c67d 100644
--- a/vendor/github.com/spf13/afero/cacheOnReadFs.go
+++ b/vendor/github.com/spf13/afero/cacheOnReadFs.go
@@ -205,7 +205,7 @@ func (u *CacheOnReadFs) OpenFile(name string, flag int, perm os.FileMode) (File,
 			bfi.Close() // oops, what if O_TRUNC was set and file opening in the layer failed...?
 			return nil, err
 		}
-		return &UnionFile{base: bfi, layer: lfi}, nil
+		return &UnionFile{Base: bfi, Layer: lfi}, nil
 	}
 	return u.layer.OpenFile(name, flag, perm)
 }
@@ -251,7 +251,7 @@ func (u *CacheOnReadFs) Open(name string) (File, error) {
 	if err != nil && bfile == nil {
 		return nil, err
 	}
-	return &UnionFile{base: bfile, layer: lfile}, nil
+	return &UnionFile{Base: bfile, Layer: lfile}, nil
 }
 
 func (u *CacheOnReadFs) Mkdir(name string, perm os.FileMode) error {
@@ -286,5 +286,5 @@ func (u *CacheOnReadFs) Create(name string) (File, error) {
 		bfh.Close()
 		return nil, err
 	}
-	return &UnionFile{base: bfh, layer: lfh}, nil
+	return &UnionFile{Base: bfh, Layer: lfh}, nil
 }
diff --git a/vendor/github.com/spf13/afero/copyOnWriteFs.go b/vendor/github.com/spf13/afero/copyOnWriteFs.go
index f2ebcd226..e8108a851 100644
--- a/vendor/github.com/spf13/afero/copyOnWriteFs.go
+++ b/vendor/github.com/spf13/afero/copyOnWriteFs.go
@@ -8,6 +8,8 @@ import (
 	"time"
 )
 
+var _ Lstater = (*CopyOnWriteFs)(nil)
+
 // The CopyOnWriteFs is a union filesystem: a read only base file system with
 // a possibly writeable layer on top. Changes to the file system will only
 // be made in the overlay: Changing an existing file in the base layer which
@@ -76,18 +78,55 @@ func (u *CopyOnWriteFs) Chmod(name string, mode os.FileMode) error {
 func (u *CopyOnWriteFs) Stat(name string) (os.FileInfo, error) {
 	fi, err := u.layer.Stat(name)
 	if err != nil {
-		origErr := err
-		if e, ok := err.(*os.PathError); ok {
-			err = e.Err
-		}
-		if err == os.ErrNotExist || err == syscall.ENOENT || err == syscall.ENOTDIR {
+		isNotExist := u.isNotExist(err)
+		if isNotExist {
 			return u.base.Stat(name)
 		}
-		return nil, origErr
+		return nil, err
 	}
 	return fi, nil
 }
 
+func (u *CopyOnWriteFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
+	llayer, ok1 := u.layer.(Lstater)
+	lbase, ok2 := u.base.(Lstater)
+
+	if ok1 {
+		fi, b, err := llayer.LstatIfPossible(name)
+		if err == nil {
+			return fi, b, nil
+		}
+
+		if !u.isNotExist(err) {
+			return nil, b, err
+		}
+	}
+
+	if ok2 {
+		fi, b, err := lbase.LstatIfPossible(name)
+		if err == nil {
+			return fi, b, nil
+		}
+		if !u.isNotExist(err) {
+			return nil, b, err
+		}
+	}
+
+	fi, err := u.Stat(name)
+
+	return fi, false, err
+}
+
+func (u *CopyOnWriteFs) isNotExist(err error) bool {
+	if e, ok := err.(*os.PathError); ok {
+		err = e.Err
+	}
+	if err == os.ErrNotExist || err == syscall.ENOENT || err == syscall.ENOTDIR {
+		return true
+	}
+	return false
+}
+
 // Renaming files present only in the base layer is not permitted
 func (u *CopyOnWriteFs) Rename(oldname, newname string) error {
 	b, err := u.isBaseFile(oldname)
@@ -219,7 +258,7 @@ func (u *CopyOnWriteFs) Open(name string) (File, error) {
 		return nil, fmt.Errorf("BaseErr: %v\nOverlayErr: %v", bErr, lErr)
 	}
 
-	return &UnionFile{base: bfile, layer: lfile}, nil
+	return &UnionFile{Base: bfile, Layer: lfile}, nil
 }
 
 func (u *CopyOnWriteFs) Mkdir(name string, perm os.FileMode) error {
@@ -228,7 +267,7 @@ func (u *CopyOnWriteFs) Mkdir(name string, perm os.FileMode) error {
 		return u.layer.MkdirAll(name, perm)
 	}
 	if dir {
-		return syscall.EEXIST
+		return ErrFileExists
 	}
 	return u.layer.MkdirAll(name, perm)
 }
@@ -243,7 +282,8 @@ func (u *CopyOnWriteFs) MkdirAll(name string, perm os.FileMode) error {
 		return u.layer.MkdirAll(name, perm)
 	}
 	if dir {
-		return syscall.EEXIST
+		// This is in line with how os.MkdirAll behaves.
+		return nil
 	}
 	return u.layer.MkdirAll(name, perm)
 }
diff --git a/vendor/github.com/spf13/afero/go.mod b/vendor/github.com/spf13/afero/go.mod
new file mode 100644
index 000000000..086855099
--- /dev/null
+++ b/vendor/github.com/spf13/afero/go.mod
@@ -0,0 +1,3 @@
+module github.com/spf13/afero
+
+require golang.org/x/text v0.3.0
diff --git a/vendor/github.com/spf13/afero/go.sum b/vendor/github.com/spf13/afero/go.sum
new file mode 100644
index 000000000..6bad37b2a
--- /dev/null
+++ b/vendor/github.com/spf13/afero/go.sum
@@ -0,0 +1,2 @@
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
diff --git a/vendor/github.com/spf13/afero/lstater.go b/vendor/github.com/spf13/afero/lstater.go
new file mode 100644
index 000000000..89c1bfc0a
--- /dev/null
+++ b/vendor/github.com/spf13/afero/lstater.go
@@ -0,0 +1,27 @@
+// Copyright © 2018 Steve Francia <spf@spf13.com>.
+//
+// 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 afero
+
+import (
+	"os"
+)
+
+// Lstater is an optional interface in Afero. It is only implemented by the
+// filesystems saying so.
+// It will call Lstat if the filesystem iself is, or it delegates to, the os filesystem.
+// Else it will call Stat.
+// In addtion to the FileInfo, it will return a boolean telling whether Lstat was called or not.
+type Lstater interface {
+	LstatIfPossible(name string) (os.FileInfo, bool, error)
+}
diff --git a/vendor/github.com/spf13/afero/match.go b/vendor/github.com/spf13/afero/match.go
index 08b3b7e01..c18a87fb7 100644
--- a/vendor/github.com/spf13/afero/match.go
+++ b/vendor/github.com/spf13/afero/match.go
@@ -33,8 +33,8 @@ import (
 // built-ins from that package.
 func Glob(fs Fs, pattern string) (matches []string, err error) {
 	if !hasMeta(pattern) {
-		// afero does not support Lstat directly.
-		if _, err = lstatIfOs(fs, pattern); err != nil {
+		// Lstat not supported by a ll filesystems.
+		if _, err = lstatIfPossible(fs, pattern); err != nil {
 			return nil, nil
 		}
 		return []string{pattern}, nil
diff --git a/vendor/github.com/spf13/afero/mem/file.go b/vendor/github.com/spf13/afero/mem/file.go
index 885e55429..7af2fb56f 100644
--- a/vendor/github.com/spf13/afero/mem/file.go
+++ b/vendor/github.com/spf13/afero/mem/file.go
@@ -131,6 +131,9 @@ func (f *File) Sync() error {
 }
 
 func (f *File) Readdir(count int) (res []os.FileInfo, err error) {
+	if !f.fileData.dir {
+		return nil, &os.PathError{Op: "readdir", Path: f.fileData.name, Err: errors.New("not a dir")}
+	}
 	var outLength int64
 
 	f.fileData.Lock()
diff --git a/vendor/github.com/spf13/afero/os.go b/vendor/github.com/spf13/afero/os.go
index 6b8bce1c5..13cc1b84c 100644
--- a/vendor/github.com/spf13/afero/os.go
+++ b/vendor/github.com/spf13/afero/os.go
@@ -19,6 +19,8 @@ import (
 	"time"
 )
 
+var _ Lstater = (*OsFs)(nil)
+
 // OsFs is a Fs implementation that uses functions provided by the os package.
 //
 // For details in any method, check the documentation of the os package
@@ -92,3 +94,8 @@ func (OsFs) Chmod(name string, mode os.FileMode) error {
 func (OsFs) Chtimes(name string, atime time.Time, mtime time.Time) error {
 	return os.Chtimes(name, atime, mtime)
 }
+
+func (OsFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
+	fi, err := os.Lstat(name)
+	return fi, true, err
+}
diff --git a/vendor/github.com/spf13/afero/path.go b/vendor/github.com/spf13/afero/path.go
index 1d90e46dd..18f60a0f6 100644
--- a/vendor/github.com/spf13/afero/path.go
+++ b/vendor/github.com/spf13/afero/path.go
@@ -60,7 +60,7 @@ func walk(fs Fs, path string, info os.FileInfo, walkFn filepath.WalkFunc) error
 
 	for _, name := range names {
 		filename := filepath.Join(path, name)
-		fileInfo, err := lstatIfOs(fs, filename)
+		fileInfo, err := lstatIfPossible(fs, filename)
 		if err != nil {
 			if err := walkFn(filename, fileInfo, err); err != nil && err != filepath.SkipDir {
 				return err
@@ -77,15 +77,13 @@ func walk(fs Fs, path string, info os.FileInfo, walkFn filepath.WalkFunc) error
 	return nil
 }
 
-// if the filesystem is OsFs use Lstat, else use fs.Stat
-func lstatIfOs(fs Fs, path string) (info os.FileInfo, err error) {
-	_, ok := fs.(*OsFs)
-	if ok {
-		info, err = os.Lstat(path)
-	} else {
-		info, err = fs.Stat(path)
+// if the filesystem supports it, use Lstat, else use fs.Stat
+func lstatIfPossible(fs Fs, path string) (os.FileInfo, error) {
+	if lfs, ok := fs.(Lstater); ok {
+		fi, _, err := lfs.LstatIfPossible(path)
+		return fi, err
 	}
-	return
+	return fs.Stat(path)
 }
 
 // Walk walks the file tree rooted at root, calling walkFn for each file or
@@ -100,7 +98,7 @@ func (a Afero) Walk(root string, walkFn filepath.WalkFunc) error {
 }
 
 func Walk(fs Fs, root string, walkFn filepath.WalkFunc) error {
-	info, err := lstatIfOs(fs, root)
+	info, err := lstatIfPossible(fs, root)
 	if err != nil {
 		return walkFn(root, nil, err)
 	}
diff --git a/vendor/github.com/spf13/afero/readonlyfs.go b/vendor/github.com/spf13/afero/readonlyfs.go
index f1fa55bcf..c6376ec37 100644
--- a/vendor/github.com/spf13/afero/readonlyfs.go
+++ b/vendor/github.com/spf13/afero/readonlyfs.go
@@ -6,6 +6,8 @@ import (
 	"time"
 )
 
+var _ Lstater = (*ReadOnlyFs)(nil)
+
 type ReadOnlyFs struct {
 	source Fs
 }
@@ -34,6 +36,14 @@ func (r *ReadOnlyFs) Stat(name string) (os.FileInfo, error) {
 	return r.source.Stat(name)
 }
 
+func (r *ReadOnlyFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
+	if lsf, ok := r.source.(Lstater); ok {
+		return lsf.LstatIfPossible(name)
+	}
+	fi, err := r.Stat(name)
+	return fi, false, err
+}
+
 func (r *ReadOnlyFs) Rename(o, n string) error {
 	return syscall.EPERM
 }
diff --git a/vendor/github.com/spf13/afero/unionFile.go b/vendor/github.com/spf13/afero/unionFile.go
index 99f9e5db2..abcf12d36 100644
--- a/vendor/github.com/spf13/afero/unionFile.go
+++ b/vendor/github.com/spf13/afero/unionFile.go
@@ -21,32 +21,33 @@ import (
 // successful read in the overlay will move the cursor position in the base layer
 // by the number of bytes read.
 type UnionFile struct {
-	base  File
-	layer File
-	off   int
-	files []os.FileInfo
+	Base   File
+	Layer  File
+	Merger DirsMerger
+	off    int
+	files  []os.FileInfo
 }
 
 func (f *UnionFile) Close() error {
 	// first close base, so we have a newer timestamp in the overlay. If we'd close
 	// the overlay first, we'd get a cacheStale the next time we access this file
 	// -> cache would be useless ;-)
-	if f.base != nil {
-		f.base.Close()
+	if f.Base != nil {
+		f.Base.Close()
 	}
-	if f.layer != nil {
-		return f.layer.Close()
+	if f.Layer != nil {
+		return f.Layer.Close()
 	}
 	return BADFD
 }
 
 func (f *UnionFile) Read(s []byte) (int, error) {
-	if f.layer != nil {
-		n, err := f.layer.Read(s)
-		if (err == nil || err == io.EOF) && f.base != nil {
+	if f.Layer != nil {
+		n, err := f.Layer.Read(s)
+		if (err == nil || err == io.EOF) && f.Base != nil {
 			// advance the file position also in the base file, the next
 			// call may be a write at this position (or a seek with SEEK_CUR)
-			if _, seekErr := f.base.Seek(int64(n), os.SEEK_CUR); seekErr != nil {
+			if _, seekErr := f.Base.Seek(int64(n), os.SEEK_CUR); seekErr != nil {
 				// only overwrite err in case the seek fails: we need to
 				// report an eventual io.EOF to the caller
 				err = seekErr
@@ -54,109 +55,150 @@ func (f *UnionFile) Read(s []byte) (int, error) {
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.Read(s)
+	if f.Base != nil {
+		return f.Base.Read(s)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) ReadAt(s []byte, o int64) (int, error) {
-	if f.layer != nil {
-		n, err := f.layer.ReadAt(s, o)
-		if (err == nil || err == io.EOF) && f.base != nil {
-			_, err = f.base.Seek(o+int64(n), os.SEEK_SET)
+	if f.Layer != nil {
+		n, err := f.Layer.ReadAt(s, o)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o+int64(n), os.SEEK_SET)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.ReadAt(s, o)
+	if f.Base != nil {
+		return f.Base.ReadAt(s, o)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Seek(o int64, w int) (pos int64, err error) {
-	if f.layer != nil {
-		pos, err = f.layer.Seek(o, w)
-		if (err == nil || err == io.EOF) && f.base != nil {
-			_, err = f.base.Seek(o, w)
+	if f.Layer != nil {
+		pos, err = f.Layer.Seek(o, w)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o, w)
 		}
 		return pos, err
 	}
-	if f.base != nil {
-		return f.base.Seek(o, w)
+	if f.Base != nil {
+		return f.Base.Seek(o, w)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Write(s []byte) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.Write(s)
-		if err == nil && f.base != nil { // hmm, do we have fixed size files where a write may hit the EOF mark?
-			_, err = f.base.Write(s)
+	if f.Layer != nil {
+		n, err = f.Layer.Write(s)
+		if err == nil && f.Base != nil { // hmm, do we have fixed size files where a write may hit the EOF mark?
+			_, err = f.Base.Write(s)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.Write(s)
+	if f.Base != nil {
+		return f.Base.Write(s)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) WriteAt(s []byte, o int64) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.WriteAt(s, o)
-		if err == nil && f.base != nil {
-			_, err = f.base.WriteAt(s, o)
+	if f.Layer != nil {
+		n, err = f.Layer.WriteAt(s, o)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteAt(s, o)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.WriteAt(s, o)
+	if f.Base != nil {
+		return f.Base.WriteAt(s, o)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Name() string {
-	if f.layer != nil {
-		return f.layer.Name()
+	if f.Layer != nil {
+		return f.Layer.Name()
 	}
-	return f.base.Name()
+	return f.Base.Name()
+}
+
+// DirsMerger is how UnionFile weaves two directories together.
+// It takes the FileInfo slices from the layer and the base and returns a
+// single view.
+type DirsMerger func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error)
+
+var defaultUnionMergeDirsFn = func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error) {
+	var files = make(map[string]os.FileInfo)
+
+	for _, fi := range lofi {
+		files[fi.Name()] = fi
+	}
+
+	for _, fi := range bofi {
+		if _, exists := files[fi.Name()]; !exists {
+			files[fi.Name()] = fi
+		}
+	}
+
+	rfi := make([]os.FileInfo, len(files))
+
+	i := 0
+	for _, fi := range files {
+		rfi[i] = fi
+		i++
+	}
+
+	return rfi, nil
+
 }
 
 // Readdir will weave the two directories together and
 // return a single view of the overlayed directories
+// At the end of the directory view, the error is io.EOF.
 func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
+	var merge DirsMerger = f.Merger
+	if merge == nil {
+		merge = defaultUnionMergeDirsFn
+	}
+
 	if f.off == 0 {
-		var files = make(map[string]os.FileInfo)
-		var rfi []os.FileInfo
-		if f.layer != nil {
-			rfi, err = f.layer.Readdir(-1)
+		var lfi []os.FileInfo
+		if f.Layer != nil {
+			lfi, err = f.Layer.Readdir(-1)
 			if err != nil {
 				return nil, err
 			}
-			for _, fi := range rfi {
-				files[fi.Name()] = fi
-			}
 		}
 
-		if f.base != nil {
-			rfi, err = f.base.Readdir(-1)
+		var bfi []os.FileInfo
+		if f.Base != nil {
+			bfi, err = f.Base.Readdir(-1)
 			if err != nil {
 				return nil, err
 			}
-			for _, fi := range rfi {
-				if _, exists := files[fi.Name()]; !exists {
-					files[fi.Name()] = fi
-				}
-			}
+
 		}
-		for _, fi := range files {
-			f.files = append(f.files, fi)
+		merged, err := merge(lfi, bfi)
+		if err != nil {
+			return nil, err
 		}
+		f.files = append(f.files, merged...)
 	}
+
+	if f.off >= len(f.files) {
+		return nil, io.EOF
+	}
+
 	if c == -1 {
 		return f.files[f.off:], nil
 	}
+
+	if c > len(f.files) {
+		c = len(f.files)
+	}
+
 	defer func() { f.off += c }()
 	return f.files[f.off:c], nil
 }
@@ -174,53 +216,53 @@ func (f *UnionFile) Readdirnames(c int) ([]string, error) {
 }
 
 func (f *UnionFile) Stat() (os.FileInfo, error) {
-	if f.layer != nil {
-		return f.layer.Stat()
+	if f.Layer != nil {
+		return f.Layer.Stat()
 	}
-	if f.base != nil {
-		return f.base.Stat()
+	if f.Base != nil {
+		return f.Base.Stat()
 	}
 	return nil, BADFD
 }
 
 func (f *UnionFile) Sync() (err error) {
-	if f.layer != nil {
-		err = f.layer.Sync()
-		if err == nil && f.base != nil {
-			err = f.base.Sync()
+	if f.Layer != nil {
+		err = f.Layer.Sync()
+		if err == nil && f.Base != nil {
+			err = f.Base.Sync()
 		}
 		return err
 	}
-	if f.base != nil {
-		return f.base.Sync()
+	if f.Base != nil {
+		return f.Base.Sync()
 	}
 	return BADFD
 }
 
 func (f *UnionFile) Truncate(s int64) (err error) {
-	if f.layer != nil {
-		err = f.layer.Truncate(s)
-		if err == nil && f.base != nil {
-			err = f.base.Truncate(s)
+	if f.Layer != nil {
+		err = f.Layer.Truncate(s)
+		if err == nil && f.Base != nil {
+			err = f.Base.Truncate(s)
 		}
 		return err
 	}
-	if f.base != nil {
-		return f.base.Truncate(s)
+	if f.Base != nil {
+		return f.Base.Truncate(s)
 	}
 	return BADFD
 }
 
 func (f *UnionFile) WriteString(s string) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.WriteString(s)
-		if err == nil && f.base != nil {
-			_, err = f.base.WriteString(s)
+	if f.Layer != nil {
+		n, err = f.Layer.WriteString(s)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteString(s)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.WriteString(s)
+	if f.Base != nil {
+		return f.Base.WriteString(s)
 	}
 	return 0, BADFD
 }
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 2b005811b..5b1aeb238 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -413,7 +413,7 @@ github.com/posener/complete/cmd
 github.com/posener/complete/match
 # github.com/satori/go.uuid v0.0.0-20160927100844-b061729afc07
 github.com/satori/go.uuid
-# github.com/spf13/afero v1.0.2
+# github.com/spf13/afero v1.2.1
 github.com/spf13/afero
 github.com/spf13/afero/mem
 # github.com/svanharmelen/jsonapi v0.0.0-20180618144545-0c0828c3f16d