emacs/lib/cloexec.c

/* cloexec.c - set or clear the close-on-exec descriptor flag

   Copyright (C) 1991, 2004-2006, 2009-2020 Free Software Foundation,
   Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.

   The code is taken from glibc/manual/llio.texi  */

#include <config.h>

#include "cloexec.h"

#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

/* Set the 'FD_CLOEXEC' flag of DESC if VALUE is true,
   or clear the flag if VALUE is false.
   Return 0 on success, or -1 on error with 'errno' set.

   Note that on MingW, this function does NOT protect DESC from being
   inherited into spawned children.  Instead, either use dup_cloexec
   followed by closing the original DESC, or use interfaces such as
   open or pipe2 that accept flags like O_CLOEXEC to create DESC
   non-inheritable in the first place.  */

int
set_cloexec_flag (int desc, bool value)
{
#ifdef F_SETFD

  int flags = fcntl (desc, F_GETFD, 0);

  if (0 <= flags)
    {
      int newflags = (value ? flags | FD_CLOEXEC : flags & ~FD_CLOEXEC);

      if (flags == newflags
          || fcntl (desc, F_SETFD, newflags) != -1)
        return 0;
    }

  return -1;

#else /* !F_SETFD */

  /* Use dup2 to reject invalid file descriptors; the cloexec flag
     will be unaffected.  */
  if (desc < 0)
    {
      errno = EBADF;
      return -1;
    }
  if (dup2 (desc, desc) < 0)
    /* errno is EBADF here.  */
    return -1;

  /* There is nothing we can do on this kind of platform.  Punt.  */
  return 0;
#endif /* !F_SETFD */
}


/* Duplicates a file handle FD, while marking the copy to be closed
   prior to exec or spawn.  Returns -1 and sets errno if FD could not
   be duplicated.  */

int
dup_cloexec (int fd)
{
  return fcntl (fd, F_DUPFD_CLOEXEC, 0);
}