sysdeps/posix/dup2.c

   1 /* Copyright (C) 1991-2024 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <fcntl.h>
  20 #include <limits.h>
  21 #include <unistd.h>
  22
  23 /* Duplicate FD to FD2, closing the old FD2 and making FD2 be
  24    open the same file as FD is.  Return FD2 or -1.  */
  25 int
  26 __dup2 (int fd, int fd2)
  27 {
  28   int save;
  29
  30   if (fd2 < 0
  31 #ifdef OPEN_MAX
  32       || fd2 >= OPEN_MAX
  33 #endif
  34 )
  35     {
  36       __set_errno (EBADF);
  37       return -1;
  38     }
  39
  40   /* Check if FD is kosher.  */
  41   if (fcntl (fd, F_GETFL) < 0)
  42     return -1;
  43
  44   if (fd == fd2)
  45     return fd2;
  46
  47   /* This is not atomic.  */
  48
  49   save = errno;
  50   (void) close (fd2);
  51   __set_errno (save);
  52
  53   return fcntl (fd, F_DUPFD, fd2);
  54 }
  55 libc_hidden_def (__dup2)
  56 weak_alias (__dup2, dup2)