Cygwin: open(2): Change comment in disabled O_TMPFILE POSIX unlink code

- Turns out, the definition of POSIX unlink semantics is half-hearted
  so far: It's not possible to link an open file HANDLE if it has
  been deleted with POSIX semantics, nor is it possible to remove
  the delete disposition.  This breaks linkat on an O_TMPFILE.

  Tested with W10 1809.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
index c1a3ed4180e21819a2d64bed52a1d03232d3172d..0d4809037be874f60b4066513df9935d49a8ecbb 100644 (file)
--- a/winsup/cygwin/syscalls.cc
+++ b/winsup/cygwin/syscalls.cc
@@ -1468,13 +1468,20 @@ open (const char *unix_path, int flags, ...)
          || !fh->open_with_arch (flags, mode & 07777))
        __leave;                /* errno already set */
 #if 0
-      /* W10 1709 POSIX unlink semantics:
+      /* Don't use W10 1709 POSIX unlink semantics here.
 
-         TODO: Works nicely for O_TEMPFILE but using linkat requires that
-        we first fix /proc/self/fd handling to allow opening by handle
-        rather than by symlinked filename only. */
+        Including W10 1809, NtSetInformationFile(FileLinkInformation) on a
+        HANDLE to a file unlinked with POSIX semantics fails with
+        STATUS_ACCESS_DENIED.  Trying to remove the delete disposition on
+        the file prior to calling link fails with STATUS_FILE_DELETED.
+        This breaks
+
+          fd = open(O_TMPFILE);
+          linkat("/proc/self/fd/<fd>);
+
+         semantics. */
       if ((flags & O_TMPFILE) && wincap.has_posix_file_info ()
-         && fh->pc.fs_is_ntfs ())
+         && !fh->pc.isremote () && fh->pc.fs_is_ntfs ())
        {
          HANDLE del_h;
          OBJECT_ATTRIBUTES attr;