lib/dup3.c

   1 /* Copy a file descriptor, applying specific flags.
   2    Copyright (C) 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include <unistd.h>
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24 #include <limits.h>
  25
  26 #include "binary-io.h"
  27
  28 int
  29 dup3 (int oldfd, int newfd, int flags)
  30 {
  31 #if HAVE_DUP3
  32 # undef dup3
  33 # if HAVE_SETDTABLESIZE
  34   /* Avoid a cygwin crasher. */
  35   setdtablesize (newfd + 1);
  36 # endif
  37   /* Try the system call first, if it exists.  (We may be running with a glibc
  38      that has the function but with an older kernel that lacks it.)  */
  39   {
  40     /* Cache the information whether the system call really exists.  */
  41     static int have_dup3_really; /* 0 = unknown, 1 = yes, -1 = no */
  42     if (have_dup3_really >= 0)
  43       {
  44         int result = dup3 (oldfd, newfd, flags);
  45         if (!(result < 0 && errno == ENOSYS))
  46           {
  47             have_dup3_really = 1;
  48 # if REPLACE_FCHDIR
  49             if (0 <= result)
  50               result = _gl_register_dup (oldfd, newfd);
  51 # endif
  52             return result;
  53           }
  54         have_dup3_really = -1;
  55       }
  56   }
  57 #endif
  58
  59   if (newfd < 0 || newfd >= getdtablesize () || fcntl (oldfd, F_GETFD) == -1)
  60     {
  61       errno = EBADF;
  62       return -1;
  63     }
  64
  65   if (newfd == oldfd)
  66     {
  67       errno = EINVAL;
  68       return -1;
  69     }
  70
  71   /* Check the supported flags.
  72      Note that O_NONBLOCK is not supported, because setting it on newfd
  73      would implicitly also set it on oldfd.  */
  74   if ((flags & ~(O_CLOEXEC | O_BINARY | O_TEXT)) != 0)
  75     {
  76       errno = EINVAL;
  77       return -1;
  78     }
  79
  80   if (flags & O_CLOEXEC)
  81     {
  82       int result;
  83       close (newfd);
  84       result = fcntl (oldfd, F_DUPFD_CLOEXEC, newfd);
  85       if (newfd < result)
  86         {
  87           close (result);
  88           errno = EIO;
  89           result = -1;
  90         }
  91       if (result < 0)
  92         return -1;
  93     }
  94   else if (dup2 (oldfd, newfd) < 0)
  95     return -1;
  96
  97 #if O_BINARY
  98   if (flags & O_BINARY)
  99     set_binary_mode (newfd, O_BINARY);
 100   else if (flags & O_TEXT)
 101     set_binary_mode (newfd, O_TEXT);
 102 #endif
 103
 104   return newfd;
 105 }