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  }