@node fcntl
@subsection @code{fcntl}
@findex fcntl

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

LSB specification:@* @url{https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib-fcntl-3.html}

Gnulib module: fcntl
@mindex fcntl

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
mingw, MSVC 14.

@item
This function does not support @code{F_DUPFD_CLOEXEC} on some
platforms:
glibc with Linux kernels before 2.6.24,
Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 7.5, AIX 7.1, HP-UX 11,
Solaris 11 2010-11, Cygwin 1.7.1.
Note that the gnulib replacement code is functional but not atomic.

@item
The @code{F_DUPFD_CLOEXEC} action of this function does not set the
@code{FD_CLOEXEC} flag on some platforms:
NetBSD 10.0.

@item
The @code{F_DUPFD_CLOEXEC} action of this function sets the
@code{FD_CLOEXEC} flag on the wrong file descriptor on some platforms:
Haiku.

@item
The @code{F_DUPFD} action of this function does not reject
out-of-range targets properly on some platforms:
AIX 7.1, Cygwin 1.5.x, Haiku.

@item
The @code{F_DUPFD} action of this function mistakenly clears
@code{FD_CLOEXEC} on the source descriptor on some platforms:
Haiku.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
The replacement function does not support @code{F_SETFD},
@code{F_GETFL}, @code{F_SETFL}, @code{F_GETOWN}, @code{F_SETOWN},
@code{F_GETLK}, @code{F_SETLK}, and @code{F_SETLKW} on some platforms:
mingw, MSVC 14.

@item
When a file does not support locking (such as on an NFS file system
that does not support file locking), calls with @code{F_SETLK} and
@code{F_SETLKW} fail with @code{errno} set to different values on
different systems: @code{EINVAL} on OpenIndiana (as suggested by the
POSIX 1003.1-2017 @code{fcntl} specification), @code{ENOLCK} on
GNU/Linux, and @code{EOPNOTSUPP} on FreeBSD.
@end itemize
