Detect underlying disk mount/unmount (#8408)

pkg/ioutil/ioutil.go

@@ -160,6 +160,23 @@ func NewSkipReader(r io.Reader, n int64) io.Reader {
 	return &SkipReader{r, n}
 }
 
+// SameFile returns if the files are same.
+func SameFile(fi1, fi2 os.FileInfo) bool {
+	if !os.SameFile(fi1, fi2) {
+		return false
+	}
+	if !fi1.ModTime().Equal(fi2.ModTime()) {
+		return false
+	}
+	if fi1.Mode() != fi2.Mode() {
+		return false
+	}
+	if fi1.Size() != fi2.Size() {
+		return false
+	}
+	return true
+}
+
 // DirectIO alignment needs to be 4K. Defined here as
 // directio.AlignSize is defined as 0 in MacOS causing divide by 0 error.
 const directioAlignSize = 4096

pkg/ioutil/ioutil_test.go

@@ -101,3 +101,34 @@ func TestSkipReader(t *testing.T) {
 		}
 	}
 }
+
+func TestSameFile(t *testing.T) {
+	f, err := goioutil.TempFile("", "")
+	if err != nil {
+		t.Errorf("Error creating tmp file: %v", err)
+	}
+	tmpFile := f.Name()
+	f.Close()
+	defer os.Remove(f.Name())
+	fi1, err := os.Stat(tmpFile)
+	if err != nil {
+		t.Fatalf("Error Stat(): %v", err)
+	}
+	fi2, err := os.Stat(tmpFile)
+	if err != nil {
+		t.Fatalf("Error Stat(): %v", err)
+	}
+	if !SameFile(fi1, fi2) {
+		t.Fatal("Expected the files to be same")
+	}
+	if err = goioutil.WriteFile(tmpFile, []byte("aaa"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	fi2, err = os.Stat(tmpFile)
+	if err != nil {
+		t.Fatalf("Error Stat(): %v", err)
+	}
+	if SameFile(fi1, fi2) {
+		t.Fatal("Expected the files not to be same")
+	}
+}