loopback: Utimens: deduplicate and fix time conversion code

1) Fix the "a" instead of "m" typo in loopbackFile.Utimens.
   Besides the incorrect behavoir, this causes a crash if "a"
   is nil.
   Obsoletes hanwen#100 .

2) Enable nanosecond resolution for dates after 1970.
   syscall.NsecToTimespec is broken for dates before 1970 but
   works fine otherwise, so let's keep the nanoseconds there.

3) Deduplicate the time conversion code in nodefs and paths into
   the new function fuse.UtimeToTimespec.

4) Add a test case.

fuse/misc.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"reflect"
 	"syscall"
+	"time"
 	"unsafe"
 )
 
@@ -86,3 +87,21 @@ func init() {
 		log.Panicf("page size incorrect: %d", p)
 	}
 }
+
+const _UTIME_OMIT = ((1 << 30) - 2)
+
+// UtimeToTimespec converts a "Time" pointer as passed to Utimens to a
+// "Timespec" that can be passed to the utimensat syscall.
+// A nil pointer is converted to the special UTIME_OMIT value.
+func UtimeToTimespec(t *time.Time) (ts syscall.Timespec) {
+	if t == nil {
+		ts.Nsec = _UTIME_OMIT
+	} else {
+		ts = syscall.NsecToTimespec(t.UnixNano())
+		// Go bug https://github.com/golang/go/issues/12777
+		if ts.Nsec < 0 {
+			ts.Nsec = 0
+		}
+	}
+	return ts
+}

fuse/nodefs/files_darwin.go

@@ -65,7 +65,6 @@ func (f *loopbackFile) Allocate(off uint64, sz uint64, mode uint32) fuse.Status
 	return fuse.OK
 }
 
-const _UTIME_NOW = ((1 << 30) - 1)
 const _UTIME_OMIT = ((1 << 30) - 2)
 
 // timeToTimeval - Convert time.Time to syscall.Timeval

fuse/nodefs/files_linux.go

@@ -21,27 +21,11 @@ func (f *loopbackFile) Allocate(off uint64, sz uint64, mode uint32) fuse.Status
 	return fuse.OK
 }
 
-const _UTIME_NOW = ((1 << 30) - 1)
-const _UTIME_OMIT = ((1 << 30) - 2)
-
 // Utimens - file handle based version of loopbackFileSystem.Utimens()
 func (f *loopbackFile) Utimens(a *time.Time, m *time.Time) fuse.Status {
 	var ts [2]syscall.Timespec
-
-	if a == nil {
-		ts[0].Nsec = _UTIME_OMIT
-	} else {
-		ts[0] = syscall.NsecToTimespec(a.UnixNano())
-		ts[0].Nsec = 0
-	}
-
-	if m == nil {
-		ts[1].Nsec = _UTIME_OMIT
-	} else {
-		ts[1] = syscall.NsecToTimespec(a.UnixNano())
-		ts[1].Nsec = 0
-	}
-
+	ts[0] = fuse.UtimeToTimespec(a)
+	ts[1] = fuse.UtimeToTimespec(m)
 	f.lock.Lock()
 	err := futimens(int(f.File.Fd()), &ts)
 	f.lock.Unlock()

fuse/pathfs/loopback_linux.go

@@ -39,27 +39,11 @@ func (fs *loopbackFileSystem) SetXAttr(name string, attr string, data []byte, fl
 	return fuse.ToStatus(err)
 }
 
-const _UTIME_NOW = ((1 << 30) - 1)
-const _UTIME_OMIT = ((1 << 30) - 2)
-
 // Utimens - path based version of loopbackFile.Utimens()
 func (fs *loopbackFileSystem) Utimens(path string, a *time.Time, m *time.Time, context *fuse.Context) (code fuse.Status) {
 	var ts [2]syscall.Timespec
-
-	if a == nil {
-		ts[0].Nsec = _UTIME_OMIT
-	} else {
-		ts[0] = syscall.NsecToTimespec(a.UnixNano())
-		ts[0].Nsec = 0
-	}
-
-	if m == nil {
-		ts[1].Nsec = _UTIME_OMIT
-	} else {
-		ts[1] = syscall.NsecToTimespec(m.UnixNano())
-		ts[1].Nsec = 0
-	}
-
+	ts[0] = fuse.UtimeToTimespec(a)
+	ts[1] = fuse.UtimeToTimespec(m)
 	err := sysUtimensat(0, fs.GetPath(path), &ts, _AT_SYMLINK_NOFOLLOW)
 	return fuse.ToStatus(err)
 }

fuse/test/loopback_linux_test.go

@@ -70,6 +70,41 @@ func TestNegativeTime(t *testing.T) {
 	}
 }
 
+// Setting nanoseconds should work for dates after 1970
+func TestUtimesNano(t *testing.T) {
+	tc := NewTestCase(t)
+	defer tc.Cleanup()
+
+	path := tc.mountFile
+	err := ioutil.WriteFile(path, []byte("xyz"), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ts := make([]syscall.Timespec, 2)
+	// atime
+	ts[0].Sec = 1
+	ts[0].Nsec = 2
+	// mtime
+	ts[1].Sec = 3
+	ts[1].Nsec = 4
+	err = syscall.UtimesNano(path, ts)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var st syscall.Stat_t
+	err = syscall.Stat(path, &st)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if st.Atim != ts[0] {
+		t.Errorf("Wrong atime: %v, want: %v", st.Atim, ts[0])
+	}
+	if st.Mtim != ts[1] {
+		t.Errorf("Wrong mtime: %v, want: %v", st.Mtim, ts[1])
+	}
+}
+
 func clearStatfs(s *syscall.Statfs_t) {
 	empty := syscall.Statfs_t{}
 	s.Type = 0