fs: use SetAttrIn.GetFh() instead of SetAttrIn.Fh

On OSX, Fh apparently is non-zero sometimes, even with FATTR_FH unset.

Fixes #329

Change-Id: I4d9b6a83a3a8e8fa615dfbfa4d1b132b752528da

fs/bridge.go

@@ -431,11 +431,10 @@ func (b *rawBridge) getattr(ctx context.Context, n *Inode, f FileHandle, out *fu
 func (b *rawBridge) SetAttr(cancel <-chan struct{}, in *fuse.SetAttrIn, out *fuse.AttrOut) fuse.Status {
 	ctx := &fuse.Context{Caller: in.Caller, Cancel: cancel}
 
-	n, fEntry := b.inode(in.NodeId, in.Fh)
+	fh, _ := in.GetFh()
+
+	n, fEntry := b.inode(in.NodeId, fh)
 	f := fEntry.file
-	if in.Valid&fuse.FATTR_FH == 0 {
-		f = nil
-	}
 
 	var errno = syscall.ENOTSUP
 	if fops, ok := n.ops.(NodeSetattrer); ok {

fuse/types.go

@@ -159,6 +159,7 @@ type SetAttrInCommon struct {
 	Unused5 uint32
 }
 
+// GetFh returns the file handle if available, or 0 if undefined.
 func (s *SetAttrInCommon) GetFh() (uint64, bool) {
 	if s.Valid&FATTR_FH != 0 {
 		return s.Fh, true