storage/sys_unix.go | 1 +

diff --git a/storage/sys_unix.go b/storage/sys_unix.go
index 625f420f10ee3e8314bb7ec273c1b87386d87191..f294598cabe0248c56a3e10eefbc8d46e5f798c1 100644
--- a/storage/sys_unix.go
+++ b/storage/sys_unix.go
@@ -12,6 +12,7 @@ )
 
 func seekData(f *os.File, offset int64) (ret int64, err error) {
 	ret, err = unix.Seek(int(f.Fd()), offset, unix.SEEK_DATA)
+	// TODO: Handle filesystems that don't support sparse files.
 	if err == unix.ENXIO {
 		// File has no more data. Treat as short write like io.CopyN.
 		err = io.EOF