mirror of
https://github.com/coreutils/coreutils.git
synced 2024-12-11 10:53:42 +08:00
78 lines
2.3 KiB
C
78 lines
2.3 KiB
C
/* stdopen.c - ensure that the three standard file descriptors are in use
|
|
|
|
Copyright (C) 2005 Free Software Foundation, Inc.
|
|
|
|
This program is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
This program is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program; if not, write to the Free Software Foundation,
|
|
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
|
|
|
|
/* Written by Paul Eggert and Jim Meyering. */
|
|
|
|
#ifdef HAVE_CONFIG_H
|
|
# include <config.h>
|
|
#endif
|
|
|
|
#include "stdopen.h"
|
|
|
|
#include <sys/types.h>
|
|
#include <sys/stat.h>
|
|
#include <fcntl.h>
|
|
#include <unistd.h>
|
|
#include <errno.h>
|
|
|
|
/* Try to ensure that all of the standard file numbers (0, 1, 2)
|
|
are in use. Without this, each application would have to guard
|
|
every call to open, dup, fopen, etc. with tests to ensure they
|
|
don't use one of the special file numbers when opening a file.
|
|
Return false if at least one of the file descriptors is initially
|
|
closed and an attempt to reopen it fails. Otherwise, return true. */
|
|
bool
|
|
stdopen (void)
|
|
{
|
|
int fd;
|
|
bool ok = true;
|
|
|
|
for (fd = 0; fd <= 2; fd++)
|
|
{
|
|
if (fcntl (fd, F_GETFD) < 0)
|
|
{
|
|
if (errno != EBADF)
|
|
ok = false;
|
|
else
|
|
{
|
|
static const int contrary_mode[]
|
|
= { O_WRONLY, O_RDONLY, O_RDONLY };
|
|
int mode = contrary_mode[fd];
|
|
int new_fd;
|
|
/* Open /dev/null with the contrary mode so that the typical
|
|
read (stdin) or write (stdout, stderr) operation will fail.
|
|
With descriptor 0, we can do even better on systems that
|
|
have /dev/full, by opening that write-only instead of
|
|
/dev/null. The only drawback is that a write-provoked
|
|
failure comes with a misleading errno value, ENOSPC. */
|
|
if (mode == O_RDONLY
|
|
|| (new_fd = open ("/dev/full", mode) != fd))
|
|
new_fd = open ("/dev/null", mode);
|
|
if (new_fd != fd)
|
|
{
|
|
if (0 <= new_fd)
|
|
close (new_fd);
|
|
ok = false;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return ok;
|
|
}
|