stdopen: copy from last use in coreutils

* lib/stdopen.c, lib/stdopen.h, m4/stdopen.m4:
New files, taken from their last commit in coreutils
2007-07-23T12:35:58Z!jim@meyering.net
71aa3ea88084d17bcb4fc1031ad7b66f8647115e.

2 files changed, 90 insertions, 0 deletions

diff --git a/lib/stdopen.c b/lib/stdopen.c
new file mode 100644
index 0000000000..e9b554485d
--- /dev/null
+++ b/lib/stdopen.c
@@ -0,0 +1,74 @@
+/* stdopen.c - ensure that the three standard file descriptors are in use
+
+   Copyright (C) 2005, 2006 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert and Jim Meyering.  */
+
+#include <config.h>
+
+#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;
+}
diff --git a/lib/stdopen.h b/lib/stdopen.h
new file mode 100644
index 0000000000..d54e5f1350
--- /dev/null
+++ b/lib/stdopen.h
@@ -0,0 +1,16 @@
+#ifndef STDOPEN_H
+# define STDOPEN_H 1
+
+# include <stdbool.h>
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+bool stdopen (void);
+
+# ifdef __cplusplus
+}
+# endif
+
+#endif