Revert "avoid file.Stat()"

This reverts commit 98c93ca465.

weed/storage/backend/disk_file.go

@@ -1,7 +1,6 @@
 package backend
 
 import (
-	"github.com/chrislusf/seaweedfs/weed/glog"
 	"os"
 	"time"
 )
@@ -13,21 +12,12 @@ var (
 type DiskFile struct {
 	File         *os.File
 	fullFilePath string
-	fileSize     int64
-	modTime      time.Time
 }
 
 func NewDiskFile(f *os.File) *DiskFile {
-	stat, err := f.Stat()
-	if err != nil {
-		glog.Fatalf("stat file %s: %v", f.Name(), err)
-	}
-
 	return &DiskFile{
 		fullFilePath: f.Name(),
 		File:         f,
-		fileSize:     stat.Size(),
-		modTime:      stat.ModTime(),
 	}
 }
 
@@ -36,24 +26,11 @@ func (df *DiskFile) ReadAt(p []byte, off int64) (n int, err error) {
 }
 
 func (df *DiskFile) WriteAt(p []byte, off int64) (n int, err error) {
-	n, err = df.File.WriteAt(p, off)
-	if err == nil {
-		waterMark := off + int64(n)
-		if waterMark > df.fileSize {
-			df.fileSize = waterMark
-			df.modTime = time.Now()
-		}
-	}
-	return
+	return df.File.WriteAt(p, off)
 }
 
 func (df *DiskFile) Truncate(off int64) error {
-	err := df.File.Truncate(off)
-	if err == nil {
-		df.fileSize = off
-		df.modTime = time.Now()
-	}
-	return err
+	return df.File.Truncate(off)
 }
 
 func (df *DiskFile) Close() error {
@@ -61,7 +38,11 @@ func (df *DiskFile) Close() error {
 }
 
 func (df *DiskFile) GetStat() (datSize int64, modTime time.Time, err error) {
-	return df.fileSize, df.modTime, nil
+	stat, e := df.File.Stat()
+	if e == nil {
+		return stat.Size(), stat.ModTime(), nil
+	}
+	return 0, time.Time{}, err
 }
 
 func (df *DiskFile) Name() string {