diff --git a/mem/dir.go b/mem/dir.go
new file mode 100644
index 0000000..02f632e
--- /dev/null
+++ b/mem/dir.go
@@ -0,0 +1,38 @@
+// Copyright © 2014 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 mem
+
+type Dir interface {
+	Len() int
+	Names() []string
+	Files() []File
+	Add(File)
+	Remove(File)
+}
+
+func RemoveFromMemDir(dir *File, f *File) {
+	dir.memDir.Remove(*f)
+}
+
+func AddToMemDir(dir *File, f *File) {
+	dir.memDir.Add(*f)
+}
+
+func InitializeDir(d *File) {
+	if d.memDir == nil {
+		d.dir = true
+		d.memDir = &DirMap{}
+	}
+
+}
diff --git a/mem/dirmap.go b/mem/dirmap.go
new file mode 100644
index 0000000..59c5d8d
--- /dev/null
+++ b/mem/dirmap.go
@@ -0,0 +1,43 @@
+// Copyright © 2015 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 mem
+
+import "sort"
+
+type DirMap map[string]File
+
+func (m DirMap) Len() int      { return len(m) }
+func (m DirMap) Add(f File)    { m[f.Name()] = f }
+func (m DirMap) Remove(f File) { delete(m, f.Name()) }
+func (m DirMap) Files() (files []File) {
+	for _, f := range m {
+		files = append(files, f)
+	}
+	sort.Sort(filesSorter(files))
+	return files
+}
+
+type filesSorter []File
+
+// implement sort.Interface for []File
+func (s filesSorter) Len() int           { return len(s) }
+func (s filesSorter) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s filesSorter) Less(i, j int) bool { return s[i].Name() < s[j].Name() }
+
+func (m DirMap) Names() (names []string) {
+	for x := range m {
+		names = append(names, x)
+	}
+	return names
+}
diff --git a/memfile.go b/mem/file.go
similarity index 61%
rename from memfile.go
rename to mem/file.go
index d3d8223..4a652cb 100644
--- a/memfile.go
+++ b/mem/file.go
@@ -1,4 +1,4 @@
-// Copyright © 2014 Steve Francia <spf@spf13.com>.
+// Copyright © 2015 Steve Francia <spf@spf13.com>.
 // Copyright 2013 tsuru authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
@@ -12,10 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package afero
+package mem
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -25,15 +26,9 @@
 
 import "time"
 
-type MemDir interface {
-	Len() int
-	Names() []string
-	Files() []File
-	Add(File)
-	Remove(File)
-}
+const FilePathSeparator = string(filepath.Separator)
 
-type InMemoryFile struct {
+type File struct {
 	// atomic requires 64-bit alignment for struct field access
 	at           int64
 	readDirCount int64
@@ -41,18 +36,38 @@
 	sync.Mutex
 	name    string
 	data    []byte
-	memDir  MemDir
+	memDir  Dir
 	dir     bool
 	closed  bool
 	mode    os.FileMode
 	modtime time.Time
 }
 
-func MemFileCreate(name string) *InMemoryFile {
-	return &InMemoryFile{name: name, mode: os.ModeTemporary, modtime: time.Now()}
+func CreateFile(name string) *File {
+	return &File{name: name, mode: os.ModeTemporary, modtime: time.Now()}
 }
 
-func (f *InMemoryFile) Open() error {
+func CreateDir(name string) *File {
+	return &File{name: FilePathSeparator, memDir: &DirMap{}, dir: true}
+}
+
+func ChangeFileName(f *File, newname string) {
+	f.name = newname
+}
+
+func SetMode(f *File, mode os.FileMode) {
+	f.mode = mode
+}
+
+func SetModTime(f *File, mtime time.Time) {
+	f.modtime = mtime
+}
+
+func GetFileInfo(f *File) *FileInfo {
+	return &FileInfo{file: f}
+}
+
+func (f *File) Open() error {
 	atomic.StoreInt64(&f.at, 0)
 	atomic.StoreInt64(&f.readDirCount, 0)
 	f.Lock()
@@ -61,26 +76,26 @@
 	return nil
 }
 
-func (f *InMemoryFile) Close() error {
+func (f *File) Close() error {
 	f.Lock()
 	f.closed = true
 	f.Unlock()
 	return nil
 }
 
-func (f *InMemoryFile) Name() string {
+func (f *File) Name() string {
 	return f.name
 }
 
-func (f *InMemoryFile) Stat() (os.FileInfo, error) {
-	return &InMemoryFileInfo{f}, nil
+func (f *File) Stat() (os.FileInfo, error) {
+	return &FileInfo{f}, nil
 }
 
-func (f *InMemoryFile) Sync() error {
+func (f *File) Sync() error {
 	return nil
 }
 
-func (f *InMemoryFile) Readdir(count int) (res []os.FileInfo, err error) {
+func (f *File) Readdir(count int) (res []os.FileInfo, err error) {
 	var outLength int64
 
 	f.Lock()
@@ -108,7 +123,7 @@
 	return res, err
 }
 
-func (f *InMemoryFile) Readdirnames(n int) (names []string, err error) {
+func (f *File) Readdirnames(n int) (names []string, err error) {
 	fi, err := f.Readdir(n)
 	names = make([]string, len(fi))
 	for i, f := range fi {
@@ -117,7 +132,7 @@
 	return names, err
 }
 
-func (f *InMemoryFile) Read(b []byte) (n int, err error) {
+func (f *File) Read(b []byte) (n int, err error) {
 	f.Lock()
 	defer f.Unlock()
 	if f.closed == true {
@@ -136,12 +151,12 @@
 	return
 }
 
-func (f *InMemoryFile) ReadAt(b []byte, off int64) (n int, err error) {
+func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
 	atomic.StoreInt64(&f.at, off)
 	return f.Read(b)
 }
 
-func (f *InMemoryFile) Truncate(size int64) error {
+func (f *File) Truncate(size int64) error {
 	if f.closed == true {
 		return ErrFileClosed
 	}
@@ -157,7 +172,7 @@
 	return nil
 }
 
-func (f *InMemoryFile) Seek(offset int64, whence int) (int64, error) {
+func (f *File) Seek(offset int64, whence int) (int64, error) {
 	if f.closed == true {
 		return 0, ErrFileClosed
 	}
@@ -172,7 +187,7 @@
 	return f.at, nil
 }
 
-func (f *InMemoryFile) Write(b []byte) (n int, err error) {
+func (f *File) Write(b []byte) (n int, err error) {
 	n = len(b)
 	cur := atomic.LoadInt64(&f.at)
 	f.Lock()
@@ -194,35 +209,44 @@
 	return
 }
 
-func (f *InMemoryFile) WriteAt(b []byte, off int64) (n int, err error) {
+func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
 	atomic.StoreInt64(&f.at, off)
 	return f.Write(b)
 }
 
-func (f *InMemoryFile) WriteString(s string) (ret int, err error) {
+func (f *File) WriteString(s string) (ret int, err error) {
 	return f.Write([]byte(s))
 }
 
-func (f *InMemoryFile) Info() *InMemoryFileInfo {
-	return &InMemoryFileInfo{file: f}
+func (f *File) Info() *FileInfo {
+	return &FileInfo{file: f}
 }
 
-type InMemoryFileInfo struct {
-	file *InMemoryFile
+type FileInfo struct {
+	file *File
 }
 
 // Implements os.FileInfo
-func (s *InMemoryFileInfo) Name() string {
+func (s *FileInfo) Name() string {
 	_, name := filepath.Split(s.file.Name())
 	return name
 }
-func (s *InMemoryFileInfo) Mode() os.FileMode  { return s.file.mode }
-func (s *InMemoryFileInfo) ModTime() time.Time { return s.file.modtime }
-func (s *InMemoryFileInfo) IsDir() bool        { return s.file.dir }
-func (s *InMemoryFileInfo) Sys() interface{}   { return nil }
-func (s *InMemoryFileInfo) Size() int64 {
+func (s *FileInfo) Mode() os.FileMode  { return s.file.mode }
+func (s *FileInfo) ModTime() time.Time { return s.file.modtime }
+func (s *FileInfo) IsDir() bool        { return s.file.dir }
+func (s *FileInfo) Sys() interface{}   { return nil }
+func (s *FileInfo) Size() int64 {
 	if s.IsDir() {
 		return int64(42)
 	}
 	return int64(len(s.file.data))
 }
+
+var (
+	ErrFileClosed        = errors.New("File is closed")
+	ErrOutOfRange        = errors.New("Out of range")
+	ErrTooLarge          = errors.New("Too large")
+	ErrFileNotFound      = os.ErrNotExist
+	ErrFileExists        = os.ErrExist
+	ErrDestinationExists = os.ErrExist
+)
diff --git a/memmap.go b/memmap.go
index 6ad32e6..0263953 100644
--- a/memmap.go
+++ b/memmap.go
@@ -19,10 +19,11 @@
 	"log"
 	"os"
 	"path/filepath"
-	"sort"
 	"strings"
 	"sync"
 	"time"
+
+	"github.com/spf13/afero/mem"
 )
 
 var mux = &sync.Mutex{}
@@ -47,7 +48,7 @@
 
 		// Root should always exist, right?
 		// TODO: what about windows?
-		m.data[FilePathSeparator] = &InMemoryFile{name: FilePathSeparator, memDir: &MemDirMap{}, dir: true}
+		m.data[FilePathSeparator] = mem.CreateDir(FilePathSeparator)
 	}
 	return m.data
 }
@@ -60,40 +61,12 @@
 	mux.Unlock()
 	return m.mutex
 }
-
-type MemDirMap map[string]File
-
-func (m MemDirMap) Len() int      { return len(m) }
-func (m MemDirMap) Add(f File)    { m[f.Name()] = f }
-func (m MemDirMap) Remove(f File) { delete(m, f.Name()) }
-func (m MemDirMap) Files() (files []File) {
-	for _, f := range m {
-		files = append(files, f)
-	}
-	sort.Sort(filesSorter(files))
-	return files
-}
-
-type filesSorter []File
-
-// implement sort.Interface for []File
-func (s filesSorter) Len() int           { return len(s) }
-func (s filesSorter) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
-func (s filesSorter) Less(i, j int) bool { return s[i].Name() < s[j].Name() }
-
-func (m MemDirMap) Names() (names []string) {
-	for x := range m {
-		names = append(names, x)
-	}
-	return names
-}
-
 func (MemMapFs) Name() string { return "MemMapFS" }
 
 func (m *MemMapFs) Create(name string) (File, error) {
 	name = normalizePath(name)
 	m.lock()
-	file := MemFileCreate(name)
+	file := mem.CreateFile(name)
 	m.getData()[name] = file
 	m.registerWithParent(file)
 	m.unlock()
@@ -112,8 +85,9 @@
 	if parent == nil {
 		log.Fatal("parent of ", f.Name(), " is nil")
 	}
-	pmem := parent.(*InMemoryFile)
-	pmem.memDir.Remove(f)
+	pmem := parent.(*mem.File)
+	fmem := f.(*mem.File)
+	mem.RemoveFromMemDir(pmem, fmem)
 }
 
 func (m *MemMapFs) findParent(f File) File {
@@ -144,18 +118,15 @@
 			return
 		}
 	}
-	pmem := parent.(*InMemoryFile)
+	pmem := parent.(*mem.File)
+	fmem := f.(*mem.File)
 
 	// TODO(mbertschler): memDir is only nil when it was not made with Mkdir
 	// or lockfreeMkdir. In this case the parent is also not a real directory.
 	// This currently only happens for the file ".".
 	// This is a quick hack to make the library usable with relative paths.
-	if pmem.memDir == nil {
-		pmem.dir = true
-		pmem.memDir = &MemDirMap{}
-	}
-
-	pmem.memDir.Add(f)
+	mem.InitializeDir(pmem)
+	mem.AddToMemDir(pmem, fmem)
 }
 
 func (m *MemMapFs) lockfreeMkdir(name string, perm os.FileMode) error {
@@ -171,7 +142,7 @@
 			return err
 		}
 	} else {
-		item := &InMemoryFile{name: name, memDir: &MemDirMap{}, dir: true}
+		item := mem.CreateDir(name)
 		m.getData()[name] = item
 		m.registerWithParent(item)
 	}
@@ -195,7 +166,7 @@
 		}
 	} else {
 		m.lock()
-		item := &InMemoryFile{name: name, memDir: &MemDirMap{}, dir: true}
+		item := mem.CreateDir(name)
 		m.getData()[name] = item
 		m.registerWithParent(item)
 		m.unlock()
@@ -226,7 +197,7 @@
 
 	m.rlock()
 	f, ok := m.getData()[name]
-	ff, ok := f.(*InMemoryFile)
+	ff, ok := f.(*mem.File)
 
 	if ok {
 		ff.Open()
@@ -243,7 +214,7 @@
 func (m *MemMapFs) lockfreeOpen(name string) (File, error) {
 	name = normalizePath(name)
 	f, ok := m.getData()[name]
-	ff, ok := f.(*InMemoryFile)
+	ff, ok := f.(*mem.File)
 	if ok {
 		ff.Open()
 	}
@@ -330,9 +301,9 @@
 			m.runlock()
 			m.lock()
 			m.unRegisterWithParent(oldname)
-			file := m.getData()[oldname].(*InMemoryFile)
+			file := m.getData()[oldname].(*mem.File)
 			delete(m.getData(), oldname)
-			file.name = newname
+			mem.ChangeFileName(file, newname)
 			m.getData()[newname] = file
 			m.registerWithParent(file)
 			m.unlock()
@@ -351,7 +322,8 @@
 	if err != nil {
 		return nil, err
 	}
-	return &InMemoryFileInfo{file: f.(*InMemoryFile)}, nil
+	fi := mem.GetFileInfo(f.(*mem.File))
+	return fi, nil
 }
 
 func (m *MemMapFs) Chmod(name string, mode os.FileMode) error {
@@ -361,10 +333,10 @@
 		return &os.PathError{"chmod", name, ErrFileNotFound}
 	}
 
-	ff, ok := f.(*InMemoryFile)
+	ff, ok := f.(*mem.File)
 	if ok {
 		m.lock()
-		ff.mode = mode
+		mem.SetMode(ff, mode)
 		m.unlock()
 	} else {
 		return errors.New("Unable to Chmod Memory File")
@@ -379,10 +351,10 @@
 		return &os.PathError{"chtimes", name, ErrFileNotFound}
 	}
 
-	ff, ok := f.(*InMemoryFile)
+	ff, ok := f.(*mem.File)
 	if ok {
 		m.lock()
-		ff.modtime = mtime
+		mem.SetModTime(ff, mtime)
 		m.unlock()
 	} else {
 		return errors.New("Unable to Chtime Memory File")