gl/lib/fd-reopen.c

   1 /* Invoke open, but return either a desired file descriptor or -1.
   2
   3    Copyright (C) 2005-2023 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation, either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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 General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 #include <config.h>
  21
  22 #include "fd-reopen.h"
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <unistd.h>
  27
  28 /* Open a file to a particular file descriptor.  This is like standard
  29    'open', except it always returns DESIRED_FD if successful.  */
  30
  31 int
  32 fd_reopen (int desired_fd, char const *file, int flags, mode_t mode)
  33 {
  34   int fd = open (file, flags, mode);
  35
  36   if (fd == desired_fd || fd < 0)
  37     return fd;
  38   else
  39     {
  40       int fd2 = dup2 (fd, desired_fd);
  41       int saved_errno = errno;
  42       close (fd);
  43       errno = saved_errno;
  44       return fd2;
  45     }
  46 }