@node faccessat
@subsection @code{faccessat}
@findex faccessat

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/faccessat.html}

Gnulib module: faccessat
@mindex faccessat

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
glibc 2.3.6, macOS 10.9, FreeBSD 7.4, NetBSD 6.1.5, OpenBSD 4.9, Minix 3.1.8, AIX 5.1, HP-UX 11, Solaris 10, Cygwin 1.5.x, mingw, MSVC 14, Android 4.0.4.
@item
On some platforms, @code{faccessat (dfd, "file/", amode, flag)}
succeeds instead of failing when @file{file} is not a directory.
macOS 14.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
The replacement does not always take ACLs into account.
@item
The replacement is not safe to be used in libraries.
@item
The replacement is not thread-safe.
@item
The replacement does not support the @code{AT_SYMLINK_NOFOLLOW} flag,
which is supported by GNU @code{faccessat}.
@item
On some platforms, @code{faccessat} can mishandle @code{AT_EACCESS}
after a process starts as root and then becomes non-root:
@c https://sourceware.org/PR18683
GNU/Linux with glibc 2.32.
@item
This function does not support @code{AT_EMPTY_PATH}:
Linux kernel 2.6.38.
@item
When @code{AT_EMPTY_PATH} is used,
this function does not allow the file name to be a null pointer:
glibc 2.41, Linux kernel 6.10, Cygwin 3.6, FreeBSD 15.1.
@end itemize

Other problems of this function:
@itemize
@item
There is an inherent race between calling this function and performing
some action based on the results; you should think twice before trusting
this function, especially in a set-uid or set-gid program.
@end itemize
