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Date: Fri, 28 Mar 2025 13:02:30 +0100
To: Bruno Haible <bruno AT clisp DOT org>
Subject: Re: symbolic link curiousity in 3.6.0
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Hi Bruno,

I found the problem, it's in a gnulib header. See below.

On Mar 28 12:21, Corinna Vinschen via Cygwin wrote:
> On Mar 28 10:59, Corinna Vinschen via Cygwin wrote:
> > [Adding Bruno Haible]
> > 
> > Hi Bruno,
> > 
> > can you please take a look?  To reiterate, with coreutils 9.6:
> > 
> >   $ ln -s foo bar
> >   $ ls -l bar
> >   ls: bar: Not supported
> >   lrwxrwxrwx 1 corinna vinschen 3 Mar 27 10:20 bar -> foo
> > 
> > The introducing commit in coreutils is apparently commit
> > b58e321c8d5dd ("ls: suppress "Permission denied" errors on NFS")
> > 
> > The reason this works as expected on Linux but not on Cygwin is that the
> > underlying gnulib function file_has_aclinfo() differs between Linux and
> > Cygwin.  On Cygwin, it's basically just a call to acl_get_file() since
> > Cygwin has the POSIX.1e functions but none of the extensions of Linux
> > or FreeBSD/NetBSD.
> > 
> > As a result, when calling file_has_aclinfo("bar",...), the symlink
> > "bar" is always followed and file_has_aclinfo() returns with errno
> > set to ENOENT.
> > 
> > See below for the rest of the story.
> > 
> > Two questions:
> > 
> > - Would you place the problem inside gnulib:file_has_aclinfo() or
> >   coreutils:gobble_file()?
> > 
> >   Personally I think this is a coreutils problem rather than a
> >   gnulib problem in that it fails to take ENOENT on symlinks into
> >   account.
> > 
> > - Would it make sense to implement the FreeBSD/NetBSD functions
> >   acl_get_fd_np() and acl_get_link_np() in Cygwin?  Theoretically
> >   this should fix the problem without having to fix coreutils,
> >   but I think coreutils really should take systems into account
> >   which only have the documented POSIX.1e functions.
> > 
> > What do you think?
> 
> Ok, there's something fishy going on.
> 
> Cygwin has acl_extended_file/acl_extended_file_nofollow.
> 
> And after configure, gnulib's config.h contains this:
> 
>   #define USE_ACL 1
>   #define HAVE_ACL_GET_FILE 1
>   #define HAVE_ACL_EXTENDED_FILE 1
> 
> But for some reason I still have to figure out the coreutils 9.6 build
> doesn't use acl_extended_file/acl_extended_file_nofollow, but
> acl_get_file.
> 
> Hmm...

Gnulib's acl-internal.h contains this:

  /* Linux-specific */
  /* Cygwin >= 2.5 implements this function, but it returns 1 for all
     directories, thus is unusable.  */
   #  if !defined HAVE_ACL_EXTENDED_FILE || defined __CYGWIN__
   #   undef HAVE_ACL_EXTENDED_FILE
   #   define HAVE_ACL_EXTENDED_FILE false
   #   define acl_extended_file(name) (-1)
   #  endif

This is simply not true.  Cygwin's acl_extended_file only returns
1 on dirs, if they actually contain more than the 3 default entries
to emulate POSIX access.  I just tried it and it works exactly
as required.

Can this be fixed, please?


Thanks,
Corinna

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