lib/cloexec.c

   1 /* cloexec.c - set or clear the close-on-exec descriptor flag
   2
   3    Copyright (C) 1991, 2004-2006, 2009-2024 Free Software Foundation, Inc.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* The code is taken from glibc/manual/llio.texi  */
  19
  20 #include <config.h>
  21
  22 #include "cloexec.h"
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <unistd.h>
  27
  28 /* Set the 'FD_CLOEXEC' flag of DESC if VALUE is true,
  29    or clear the flag if VALUE is false.
  30    Return 0 on success, or -1 on error with 'errno' set.
  31
  32    Note that on MingW, this function does NOT protect DESC from being
  33    inherited into spawned children.  Instead, either use dup_cloexec
  34    followed by closing the original DESC, or use interfaces such as
  35    open or pipe2 that accept flags like O_CLOEXEC to create DESC
  36    non-inheritable in the first place.  */
  37
  38 int
  39 set_cloexec_flag (int desc, bool value)
  40 {
  41 #ifdef F_SETFD
  42
  43   int flags = fcntl (desc, F_GETFD, 0);
  44
  45   if (0 <= flags)
  46     {
  47       int newflags = (value ? flags | FD_CLOEXEC : flags & ~FD_CLOEXEC);
  48
  49       if (flags == newflags
  50           || fcntl (desc, F_SETFD, newflags) != -1)
  51         return 0;
  52     }
  53
  54   return -1;
  55
  56 #else /* !F_SETFD */
  57
  58   /* Use dup2 to reject invalid file descriptors; the cloexec flag
  59      will be unaffected.  */
  60   if (desc < 0)
  61     {
  62       errno = EBADF;
  63       return -1;
  64     }
  65   if (dup2 (desc, desc) < 0)
  66     /* errno is EBADF here.  */
  67     return -1;
  68
  69   /* There is nothing we can do on this kind of platform.  Punt.  */
  70   return 0;
  71 #endif /* !F_SETFD */
  72 }
  73
  74
  75 /* Duplicates a file handle FD, while marking the copy to be closed
  76    prior to exec or spawn.  Returns -1 and sets errno if FD could not
  77    be duplicated.  */
  78
  79 int
  80 dup_cloexec (int fd)
  81 {
  82   return fcntl (fd, F_DUPFD_CLOEXEC, 0);
  83 }