contrib/cvs-1.12/lib/save-cwd.c

   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 "unistd-safer.h"
  41 #include "xgetcwd.h"
  42
  43 /* On systems without the fchdir function (WOE), pretend that open
  44    always returns -1 so that save_cwd resorts to using xgetcwd.
  45    Since chdir_long requires fchdir, use chdir instead.  */
  46 #if !HAVE_FCHDIR
  47 # undef open
  48 # define open(File, Flags) (-1)
  49 # undef fchdir
  50 # define fchdir(Fd) (abort (), -1)
  51 # undef chdir_long
  52 # define chdir_long(Dir) chdir (Dir)
  53 #endif
  54
  55 /* Record the location of the current working directory in CWD so that
  56    the program may change to other directories and later use restore_cwd
  57    to return to the recorded location.  This function may allocate
  58    space using malloc (via xgetcwd) or leave a file descriptor open;
  59    use free_cwd to perform the necessary free or close.  Upon failure,
  60    no memory is allocated, any locally opened file descriptors are
  61    closed;  return non-zero -- in that case, free_cwd need not be
  62    called, but doing so is ok.  Otherwise, return zero.
  63
  64    The `raison d'etre' for this interface is that the working directory
  65    is sometimes inaccessible, and getcwd is not robust or as efficient.
  66    So, we prefer to use the open/fchdir approach, but fall back on
  67    getcwd if necessary.
  68
  69    Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
  70    SCO Xenix.  Also, SunOS 4 and Irix 5.3 provide the function, yet it
  71    doesn't work for partitions on which auditing is enabled.  If
  72    you're still using an obsolete system with these problems, please
  73    send email to the maintainer of this code.  */
  74
  75 int
  76 save_cwd (struct saved_cwd *cwd)
  77 {
  78   cwd->name = NULL;
  79
  80   cwd->desc = fd_safer (open (".", O_RDONLY));
  81   if (cwd->desc < 0)
  82     {
  83       cwd->desc = fd_safer (open (".", O_WRONLY));
  84       if (cwd->desc < 0)
  85         {
  86           cwd->name = xgetcwd ();
  87           return cwd->name ? 0 : -1;
  88         }
  89     }
  90
  91   return 0;
  92 }
  93
  94 /* Change to recorded location, CWD, in directory hierarchy.
  95    Upon failure, return -1 (errno is set by chdir or fchdir).
  96    Upon success, return zero.  */
  97
  98 int
  99 restore_cwd (const struct saved_cwd *cwd)
 100 {
 101   if (0 <= cwd->desc)
 102     return fchdir (cwd->desc);
 103   else
 104     return -1;
 105 }
 106
 107 void
 108 free_cwd (struct saved_cwd *cwd)
 109 {
 110   if (cwd->desc >= 0)
 111     close (cwd->desc);
 112   if (cwd->name)
 113     free (cwd->name);
 114 }