1/* save-cwd.c -- Save and restore current working directory.
2
3   Copyright (C) 1995, 1997, 1998, 2003, 2004, 2005 Free Software
4   Foundation, Inc.
5
6   This program is free software; you can redistribute it and/or modify
7   it under the terms of the GNU General Public License as published by
8   the Free Software Foundation; either version 2, or (at your option)
9   any later version.
10
11   This program is distributed in the hope that it will be useful,
12   but WITHOUT ANY WARRANTY; without even the implied warranty of
13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   GNU General Public License for more details.
15
16   You should have received a copy of the GNU General Public License
17   along with this program; if not, write to the Free Software Foundation,
18   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
19
20/* Written by Jim Meyering.  */
21
22#ifdef HAVE_CONFIG_H
23# include <config.h>
24#endif
25
26#include "save-cwd.h"
27
28#include <stdbool.h>
29#include <stdio.h>
30#include <stdlib.h>
31
32#if HAVE_UNISTD_H
33# include <unistd.h>
34#endif
35
36#include <fcntl.h>
37
38#include <errno.h>
39
40#include "chdir-long.h"
41#include "unistd-safer.h"
42#include "xgetcwd.h"
43
44/* On systems without the fchdir function (WOE), pretend that open
45   always returns -1 so that save_cwd resorts to using xgetcwd.
46   Since chdir_long requires fchdir, use chdir instead.  */
47#if !HAVE_FCHDIR
48# undef open
49# define open(File, Flags) (-1)
50# undef fchdir
51# define fchdir(Fd) (abort (), -1)
52# undef chdir_long
53# define chdir_long(Dir) chdir (Dir)
54#endif
55
56/* Record the location of the current working directory in CWD so that
57   the program may change to other directories and later use restore_cwd
58   to return to the recorded location.  This function may allocate
59   space using malloc (via xgetcwd) or leave a file descriptor open;
60   use free_cwd to perform the necessary free or close.  Upon failure,
61   no memory is allocated, any locally opened file descriptors are
62   closed;  return non-zero -- in that case, free_cwd need not be
63   called, but doing so is ok.  Otherwise, return zero.
64
65   The `raison d'etre' for this interface is that the working directory
66   is sometimes inaccessible, and getcwd is not robust or as efficient.
67   So, we prefer to use the open/fchdir approach, but fall back on
68   getcwd if necessary.
69
70   Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
71   SCO Xenix.  Also, SunOS 4 and Irix 5.3 provide the function, yet it
72   doesn't work for partitions on which auditing is enabled.  If
73   you're still using an obsolete system with these problems, please
74   send email to the maintainer of this code.  */
75
76int
77save_cwd (struct saved_cwd *cwd)
78{
79  cwd->name = NULL;
80
81  cwd->desc = fd_safer (open (".", O_RDONLY));
82  if (cwd->desc < 0)
83    {
84      cwd->desc = fd_safer (open (".", O_WRONLY));
85      if (cwd->desc < 0)
86	{
87	  cwd->name = xgetcwd ();
88	  return cwd->name ? 0 : -1;
89	}
90    }
91
92  return 0;
93}
94
95/* Change to recorded location, CWD, in directory hierarchy.
96   Upon failure, return -1 (errno is set by chdir or fchdir).
97   Upon success, return zero.  */
98
99int
100restore_cwd (const struct saved_cwd *cwd)
101{
102  if (0 <= cwd->desc)
103    return fchdir (cwd->desc);
104  else
105    return chdir_long (cwd->name);
106}
107
108void
109free_cwd (struct saved_cwd *cwd)
110{
111  if (cwd->desc >= 0)
112    close (cwd->desc);
113  if (cwd->name)
114    free (cwd->name);
115}
116