Add stdopen, imported from coreutils.

[chaz/tar] / lib / stdopen.c

diff --git a/lib/stdopen.c b/lib/stdopen.c
new file mode 100644 (file)
index 0000000..92825b5
--- /dev/null
+++ b/lib/stdopen.c
@@ -0,0 +1,77 @@
+/* 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;
+}