fchmodat
========

POSIX specification:
 https://pubs.opengroup.org/onlinepubs/9699919799/functions/fchmodat.html

Gnulib module: fchmodat

Portability problems fixed by Gnulib:

  * This function is missing on some platforms: glibc 2.3.6, Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8, AIX 5.1, HP-UX 11, IRIX 6.5, Solaris 10, Cygwin 1.5.x, mingw, MSVC 14. But the replacement function is not safe to be used in libraries and is not multithread-safe.

  * This function does not fail when the file name argument ends in a slash and (without the slash) names a non-directory, on some platforms: AIX 7.2.

  * When given the AT_SYMLINK_NOFOLLOW flag, this function fails with errno set to ENOTSUP, even when the file is not a symbolic link: GNU/Linux with glibc 2.31, Cygwin 2.9.

Portability problems not fixed by Gnulib:

  * Some platforms do not allow changing the access bits on symbolic links.

  * If the AT_SYMLINK_NOFOLLOW flag is specified, this function can fail with errno set to EMFILE or ENFILE, and it fails with errno set to EOPNOTSUPP if the /proc file system is not mounted: GNU/Linux with glibc 2.34.