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78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
/* stdopen.c - ensure that the three standard file descriptors are in use
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Copyright (C) 2005 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software Foundation,
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Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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/* Written by Paul Eggert and Jim Meyering. */
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#ifdef HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include "stdopen.h"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <errno.h>
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/* Try to ensure that all of the standard file numbers (0, 1, 2)
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are in use. Without this, each application would have to guard
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every call to open, dup, fopen, etc. with tests to ensure they
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don't use one of the special file numbers when opening a file.
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Return false if at least one of the file descriptors is initially
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closed and an attempt to reopen it fails. Otherwise, return true. */
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bool
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stdopen (void)
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{
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int fd;
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bool ok = true;
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for (fd = 0; fd <= 2; fd++)
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{
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if (fcntl (fd, F_GETFD) < 0)
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{
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if (errno != EBADF)
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ok = false;
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else
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{
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static const int contrary_mode[]
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= { O_WRONLY, O_RDONLY, O_RDONLY };
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int mode = contrary_mode[fd];
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int new_fd;
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/* Open /dev/null with the contrary mode so that the typical
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read (stdin) or write (stdout, stderr) operation will fail.
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With descriptor 0, we can do even better on systems that
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have /dev/full, by opening that write-only instead of
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/dev/null. The only drawback is that a write-provoked
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failure comes with a misleading errno value, ENOSPC. */
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if (mode == O_RDONLY
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|| (new_fd = open ("/dev/full", mode) != fd))
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new_fd = open ("/dev/null", mode);
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if (new_fd != fd)
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{
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if (0 <= new_fd)
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close (new_fd);
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ok = false;
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}
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}
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}
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}
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return ok;
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}
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