fusefrontend: Rework the Utimens handling on macOS.

For Linux, everything effectively stays the same. For both path-based and
fd-based Utimens() calls, we use unix.UtimesNanoAt(). To avoid introducing
a separate syscall wrapper for futimens() (as done in go-fuse, for example),
we instead use the /proc/self/fd - trick.

On macOS, this changes quite a lot:

* Path-based Utimens() calls were previously completely broken, since
  unix.UtimensNanoAt() ignores the passed file descriptor. Note that this
  cannot be fixed easily since there IS no appropriate syscall available on
  macOS prior to High Sierra (10.13). We emulate this case by using
  Fchdir() + setattrlist().

* Fd-based Utimens() calls were previously translated to f.GetAttr() (to
  fill any empty parameters) and syscall.Futimes(), which does not does
  support nanosecond precision. Both issues can be fixed by switching to
  fsetattrlist().

Fixes https://github.com/rfjakob/gocryptfs/issues/350

1 files changed, 2 insertions, 4 deletions

diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index a0b82ba..531274a 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -44,8 +44,6 @@ type File struct {
 	qIno openfiletable.QIno
 	// Entry in the open file table
 	fileTableEntry *openfiletable.Entry
-	// go-fuse nodefs.loopbackFile
-	loopbackFile nodefs.File
 	// Store where the last byte was written
 	lastWrittenOffset int64
 	// The opCount is used to judge whether "lastWrittenOffset" is still
@@ -75,7 +73,6 @@ func NewFile(fd *os.File, fs *FS) (*File, fuse.Status) {
 		contentEnc:     fs.contentEnc,
 		qIno:           qi,
 		fileTableEntry: e,
-		loopbackFile:   nodefs.NewLoopbackFile(fd),
 		fs:             fs,
 		File:           nodefs.NewDefaultFile(),
 	}, fuse.OK
@@ -474,5 +471,6 @@ func (f *File) GetAttr(a *fuse.Attr) fuse.Status {
 func (f *File) Utimens(a *time.Time, m *time.Time) fuse.Status {
 	f.fdLock.RLock()
 	defer f.fdLock.RUnlock()
-	return f.loopbackFile.Utimens(a, m)
+	err := syscallcompat.FutimesNano(f.intFd(), a, m)
+	return fuse.ToStatus(err)
 }