4 files changed, 125 insertions, 2 deletions
diff --git a/weed/storage/backend/backend.go b/weed/storage/backend/backend.go
new file mode 100644
index 000000000..ae0f84216
--- /dev/null
+++ b/weed/storage/backend/backend.go
@@ -0,0 +1,15 @@
+package backend
+
+import (
+	"io"
+	"time"
+)
+
+type DataStorageBackend interface {
+	io.ReaderAt
+	io.WriterAt
+	Truncate(off int64) error
+	io.Closer
+	GetStat() (datSize int64, modTime time.Time, err error)
+	String() string
+}
diff --git a/weed/storage/backend/disk_file.go b/weed/storage/backend/disk_file.go
new file mode 100644
index 000000000..7f2b39d15
--- /dev/null
+++ b/weed/storage/backend/disk_file.go
@@ -0,0 +1,50 @@
+package backend
+
+import (
+	"os"
+	"time"
+)
+
+var (
+	_ DataStorageBackend = &DiskFile{}
+)
+
+type DiskFile struct {
+	File         *os.File
+	fullFilePath string
+}
+
+func NewDiskFile(f *os.File) *DiskFile {
+	return &DiskFile{
+		fullFilePath: f.Name(),
+		File:         f,
+	}
+}
+
+func (df *DiskFile) ReadAt(p []byte, off int64) (n int, err error) {
+	return df.File.ReadAt(p, off)
+}
+
+func (df *DiskFile) WriteAt(p []byte, off int64) (n int, err error) {
+	return df.File.WriteAt(p, off)
+}
+
+func (df *DiskFile) Truncate(off int64) error {
+	return df.File.Truncate(off)
+}
+
+func (df *DiskFile) Close() error {
+	return df.File.Close()
+}
+
+func (df *DiskFile) GetStat() (datSize int64, modTime time.Time, err error) {
+	stat, e := df.File.Stat()
+	if e == nil {
+		return stat.Size(), stat.ModTime(), nil
+	}
+	return 0, time.Time{}, err
+}
+
+func (df *DiskFile) String() string {
+	return df.fullFilePath
+}
diff --git a/weed/storage/backend/memory_map/memory_map.go b/weed/storage/backend/memory_map/memory_map.go
index e940fcc0e..5dc7ba33d 100644
--- a/weed/storage/backend/memory_map/memory_map.go
+++ b/weed/storage/backend/memory_map/memory_map.go
@@ -21,8 +21,6 @@ type MemoryMap struct {
 	End_of_file            int64
 }
 
-var FileMemoryMap = make(map[string]*MemoryMap)
-
 func ReadMemoryMapMaxSizeMb(memoryMapMaxSizeMbString string) (uint32, error) {
 	if memoryMapMaxSizeMbString == "" {
 		return 0, nil
diff --git a/weed/storage/backend/memory_map/memory_map_backend.go b/weed/storage/backend/memory_map/memory_map_backend.go
new file mode 100644
index 000000000..d999b917e
--- /dev/null
+++ b/weed/storage/backend/memory_map/memory_map_backend.go
@@ -0,0 +1,60 @@
+package memory_map
+
+import (
+	"os"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/storage/backend"
+)
+
+var (
+	_ backend.DataStorageBackend = &MemoryMappedFile{}
+)
+
+type MemoryMappedFile struct {
+	mm *MemoryMap
+}
+
+func NewMemoryMappedFile(f *os.File, memoryMapSizeMB uint32) *MemoryMappedFile {
+	mmf := &MemoryMappedFile{
+		mm : new(MemoryMap),
+	}
+	mmf.mm.CreateMemoryMap(f, 1024*1024*uint64(memoryMapSizeMB))
+	return mmf
+}
+
+func (mmf *MemoryMappedFile) ReadAt(p []byte, off int64) (n int, err error) {
+	readBytes, e :=  mmf.mm.ReadMemory(uint64(off), uint64(len(p)))
+	if e != nil {
+		return 0, e
+	}
+	// TODO avoid the extra copy
+	copy(p, readBytes)
+	return len(readBytes), nil
+}
+
+func (mmf *MemoryMappedFile) WriteAt(p []byte, off int64) (n int, err error) {
+	mmf.mm.WriteMemory(uint64(off), uint64(len(p)), p)
+	return len(p), nil
+}
+
+func (mmf *MemoryMappedFile) Truncate(off int64) error {
+	return nil
+}
+
+func (mmf *MemoryMappedFile) Close() error {
+	mmf.mm.DeleteFileAndMemoryMap()
+	return nil
+}
+
+func (mmf *MemoryMappedFile) GetStat() (datSize int64, modTime time.Time, err error) {
+	stat, e := mmf.mm.File.Stat()
+	if e == nil {
+		return stat.Size(), stat.ModTime(), nil
+	}
+	return 0, time.Time{}, err
+}
+
+func (mmf *MemoryMappedFile) String() string {
+	return mmf.mm.File.Name()
+}