[PATCH] Cygwin: fchmodat: add limited support for AT_SYMLINK_NOFOLLOW

[Corinna Vinschen]

On Jan 27 08:22, Ken Brown via Cygwin-patches wrote:
> On 1/27/2021 7:40 AM, Corinna Vinschen via Cygwin-patches wrote:
> > On Jan 26 16:30, Ken Brown via Cygwin-patches wrote:
> > > Allow fchmodat with the AT_SYMLINK_NOFOLLOW flag to succeed on
> > > non-symlinks.  Previously it always failed, as it does on Linux.  But
> > > POSIX permits it to succeed on non-symlinks even if it fails on
> > > symlinks.
> > > 
> > > The reason for following POSIX rather than Linux is to make gnulib
> > > report that fchmodat works on Cygwin.  This improves the efficiency of
> > > packages like GNU tar that use gnulib's fchmodat module.  Previously
> > > such packages would use a gnulib replacement for fchmodat on Cygwin.
> > 
> > Wait, what?  So if Cygwin behaves like Linux, gnulib treats fchmodat
> > as non-working?  So what does gnulib do on a Linux system?  Does it
> > use its own fchmodat there, too?
> 
> Apparently so.  Here's a comment from gnulib's test program for fchmodat:
> 
>               /* Test whether fchmodat+AT_SYMLINK_NOFOLLOW works on non-symlinks.
>                  This test fails on GNU/Linux with glibc 2.31 (but not on
>                  GNU/kFreeBSD nor GNU/Hurd) and Cygwin 2.9.  */
> 
> I agree that it's strange.

¯\_(ツ)_/¯


Corinna